AN ERGONOMIC TEST FOR A BENCH DRILL DESIGN IMPROVEMENT IN COMPLIANCE WITH THE HEHU HUM M A N- M A C HIN HINE E PERFO RM A NC E REQ UI UIR REM ENTS
0 4180 rpm 2030 rpm 990 rpm 480 rpm 230 rpm
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DANGEROUS DA NGEROUS AREA
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80 SAFETY AREA
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DANGEROUS AREA
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M ilti iltia a d is A . Bo Bo b o ulo s, Ph.D Ph.D.. Dip. Eng. Lazar Peshev
TABLE OF CONTENTS 1. THE HUMAN-MACHINE ENVIRONMENT_________________________________1 1.1 Basic terms terms _______________ ______________________ ______________ _______________ _______________ ______________ _______________ ______________ ______ 1 1.2 Working Environment Components_____________ Components_____________________________________________ ________________________________ 1 1.3 How does the the Human Factor Factor Relate Relate to the System ______________ _____________________ ______________ ____________ _____ 3
2. PRODUCT SELECTION PROCESS _______________________________ ________________________________________ _________5 5 2.1 Topic – Product Product Area _______________ _______________________ _______________ ______________ _______________ _______________ ____________ _____ 5 2.2 Describing the Product's Area_____________________________________ Area__ ________________________________________________ _____________ 6
3. AIM OF THE PROJECT__________________________________________________7 4. SHORT STUDY OF BENCH DRILLING MACHINE A15_____________________10 4.1 Study of similar products available in the market and characteristic ergonomic solutions solutions found in them. them. ______________ ______________________ _______________ ______________ _______________ _______________ __________ ___ 11 4.2 Analysis of the product from an ergonomic viewpoint. Identifying the ergonomic relations between the human and the machine. __________________________________ ___________________________________ _ 11 4.3 Analysis of other components of the working environment influencing influencing the human machine machine relation relationship ship _______________ ______________________ _______________ _______________ _______________ _______________ ___________ ____ 13
5. REVIEW OF RELEVANT INFORMATION _________________________ ________________________________ _______15 15 6. DEVELOPMENT OF TEST CRITERIA AND CONSIDERATION OF BOUNDARY CONDITIONS. ____________________________ _____________________________________________18 _________________18 7. DESIGN OF THE TEST AND SAMPLE POPULATION ______________________22 8. TESTING OF THE CURRENT VERSION OF A15___________________________28 8.1 Bench Bench drilling drilling machine machine assessment____________ assessment___________________ _______________ _______________ ______________ ___________ ____ 28 8.2 Consolidation of problem problem definition and idea generation generation ___________________________ 30
9. PURPOSE OF THE STUDY ________________________________ ______________________________________________38 ______________38 9.1 Main Tasks Tasks _______________ _______________________ _______________ _______________ _______________ _______________ _______________ ___________ ____ 38 Subject Subject of the Ergonom Ergonomic ic Developme Development nt ______________ _____________________ _______________ _______________ _____________ ______ 38 Working Working Environmen Environmentt _______________ ______________________ _______________ _______________ _______________ _______________ ___________ ____ 38 9.2 ANALYTICA ANALYTICAL L STUDY________________ STUDY________________________ _______________ _______________ _______________ _______________ ________ Short Short study of bench drilling machine machine A15 _______________ ______________________ ______________ ______________ ___________ ____ Analysis Analysis of the Product Product from from an Ergonomic Ergonomic Viewpoi Viewpoint nt ______________ _____________________ _______________ _________ _ Study Area Area with Main Problem Problemss _______________ ______________________ ______________ ______________ _______________ ____________ ____ Analysis Analysis of Problem Suitable Suitable for Test _______________ ______________________ ______________ _______________ _______________ _______
38 38 39 39 40
9.3 HYPOTHES HYPOTHESIS IS OF THE PROPOSED PROPOSED ERGONOMI ERGONOMIC C TEST ______________ _____________________ _________ __ 40 Test Criteria Criteria _______________ ______________________ ______________ _______________ _______________ _______________ _______________ ____________ _____ 40 Boundary Boundary Conditions Conditions _______________ ______________________ _______________ _______________ _______________ _______________ ____________ _____ 40 Design Design of Test and Method Method of Assessm Assessment ent _______________ ______________________ ______________ ______________ ___________ ____ 41 9.4 RESULTS RESULTS _______________ ______________________ _______________ _______________ _______________ _______________ _______________ _____________ _____ 42 Testing Testing of current machine machine version version ______________ ______________________ _______________ ______________ _______________ __________ __ 42 Design Design solutions___________ solutions___________________ _______________ _______________ _______________ ______________ _______________ _____________ _____ 43 9.5 TESTING TESTING THE THE NEW NEW MACHINE MACHINE VARIANT VARIANT ______________ _____________________ _______________ ______________ ______ 45 9.6 ANALYSIS ANALYSIS OF OF RESULTS RESULTS _______________ ______________________ ______________ _______________ _______________ ______________ _______ 46 9.7 CONCLUSI CONCLUSIONS___________ ONS___________________ _______________ _______________ _______________ _______________ _______________ ___________ ____ 48
REFERENCES____________________________________________________________49
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1.
THE HUMAN-MACHINE HUMAN-MACHINE ENVIRONMENT
New and complex types of labour activities are constantly emerging with modern development of technology. These usually demand fast and accurate visual, hearing and motive human reactions. Improvements in technological equipment result for machine design structure and other influencing factors of working environment, (lighting, noise, colours, etc.,) to be in agreement with the anatomic, physiological and psychological characteristics of humans. In other words, there is a need to adapt working environment to human requirements.
1.1 Basic terms In order to be able to achieve successfully individual unit aims it is necessary to clarify some basic terms used throughout the text to assist the developm еnt of human factor recuirements specification. Human-Machine System - is a term used in ergonomics to identify the combination of technical means, applicational methods and the people designated to operate these technical means. Working Place – is the area in the production premises equipped with all necessary means and designed for operations of the manufacturing process to be performed by several workers. Working Environment – this is the environment where all ergonomic relations between humans, machines and the working place are noticeable. Working Environment: Machine Tools; Metal Cutting machines For the purposes of the present project we selected the metal cutting machines as the field of studying the interrelations between the human factor and manufacturing environment.
The aim is to show the position of the human factor in this system. It will be achieved by determining the ergonomic relations between humans and environment. These raltions characterise specific locations and ways of interaction between the human factor and the components of the working environment. Therefore, we will adopt the term “identifying the ergonomic relations in the system”.
1.2 Working Environment Components First of all we will identify the working environment components. The basic ones include: Metal cutting machine. This can be of one of the following basic types: drilling, turning, milling, boring or grinding. A characteristic feature of all metal cutting machines is that the desired shape of the machined workpiece is usually achieved through the movement performed by the cutting tool relative to the workpiece resulting in removal of certain amount of material.
Additional units – compressors, cooling units, etc.
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Operational and measurement tools. These include cutting knives, drills, cutters, wrenches, screwdrivers and other specialized and measurement tooling.
Accessories and optional equipment. These include optional changing mechanisms and devices designed to facilitate the production process – vice, clamps, conductor attachments, etc.
Work tables. These include both assembly tables and benches. These are rather working furniture and they should not be confused with machine work tables included as assemblies in the machines themselves.
Sitting places. Chairs, seats, stools, etc.
Figure 1
Tool drawers. These are usually located within the working place area and are used to store operational and measurement tools and sometimes, operational documentation and some personal belongings.
Racks for storing semi-finished products and finished parts. These are located within the working place area, close to the basic operational equipment.
All-purpose transportation means. Mainly carriages, hoists and cranes.
Packing materials for semi-finished products and finished parts. These are usually delivered on the spot using the all-purpose transportation devices.
Working place. In this particular case the working place is used to designate the section within the production premises occupied by the metal cutting machine being considered and all the elements of working furnishings required to perform specific operations. An integrated ergonomic approach should also consider the ergonomic relations between different work places located within the same premises. For the purposes purposes of
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the present project we will limit our study in this particular case to just a single work place.
1.3 How does the Human Factor Relate Relate to the System We will describe this after we have considered the ergonomic relations within the sys-
tem – between humans and the components described above. Every relation that has been identified determines an ergonomic problem that requires optimisation. Basic ergonomic relations between humans and the metal cutting machine are (Fig.2): -
Operational relation with control devices – levers, buttons, handles, flywheels, pedals, etc.;
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Operational relation with the machine worktable (a machine assembly);
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Operational relation with machine spindle when tool change is required;
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Operational and protective relation with the protective schield of the machine;
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Visual relation with various machine indications, etc.
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Relation between machine noise and vibrations and the human perception of them.
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Agreement between the overall size of the machine and human anthropometric size. This should provide for optimum presence of operational and control devices within the operational area of the operator. The operational area is the area where working operations are performed. This is a significant component, which influences the rest of the constituent components in terms of both design and ergonomics. We can identify here the upper limb area and the lower limb area.
Figure 2. Relations between a human and a drilling machine
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Figure 3
In order for the work place to ensure optimum conditions for the functioning of the human-machine system, it should meet the following requirements: -
Provide sufficient space for the operator to be positioned there and to perform the required operational movements;
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Provide for suitable and correct position of the body;
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Agree with the technological sequence of performed operations;
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Provide for maximum protection of the operator against disturbances and harmful factors of the working environment;
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Provide for optimum micro-climate and optimum lighting of the operational surfaces;
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Provide for optimum conditions for the circulation of materials and information;
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Provide for optimum functional interconnection between individual work places in the overall operational flow;
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Provide opportunities for sufficient social contact between the operator and operators from neighbouring work places;
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Provide optimum access to the work place.
From all described above we are able to identify the working environment components for machine tools and the ergonomic relations within the system. These ergonomic relations illustrate how the human factor relates to the system aiming at providing operator
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safety, efficiency and reliability. So that his tasks are greatly aided and his sence of comfort and satisfaction is improved.
2.
PRODUCT SELECTION PROCESS
Having identified the working environment components – Machine Tools (Metal Cutting) and the ergonomic interrelations, we are able to formulate the basic principles featuring this environment:
Ergonomic relations between the human and the metal-cutting machine are the strongest compared to all other relations; Ergonomic relations between the human and all other components are stronger than the relations between components themselves; Ergonomic relations between the metal-cutting machine and all other components are stronger than the relations between components themselves;
2.1 Topic – Product Area The structural hierarchy of relations defined will assist in the idea generation and product selection process. It is now obvious that the basic structure-defining component of the working environment is the metal-cutting machine. We will therefore be concentrating on metal-cutting machines. Exerting influence on them will have the strongest effect on the working environment. This is the most serious ground for this particular selection. The most common and widely used type of metalcutting machines are the column drilling machines. They are used for drilling and machining finished holes and also, for cutting threads. They are a necessity requirement for any production or tool room. Column drilling machines are available in various sizes – from 6mm up to 60mm, depending on the maximum hole diameter they are capable of drilling. Moreover, a special class of drilling machines is available, the so-called bench drilling machines. By “special” we emphasize the following ergonomic features: since this is a metal-cutting machine, strong ergonomic relationship exists between the human and the metal cutting machine and between the metal-cutting machine and the work table or bench where the machine is usually positioned. The analysis thus drawn up gives sufficient grounds to Figure 4 The bench-drilling machoose the bench drilling machine as the product to be chine A15 from ALZMETALL described in the present project. Having made a short study of company literature and Internet web sites we found out a well-known manufacturer of metal-cutting machines and particularly bench drilling machines is the company
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ALZMETALL. They manufacture a single series achieving low cost and acceptable quality, making their machines widely used. Following the logical sequence of all we have carried out so far, we can specifically select product A15 model of the ALZMETALL - (Figure 4).
2.2 Describing the Product's Area We can now select some key words and phrases that will allow me to define the product and specifically those elements, which enter into an ergonomic relation with the human factor. Subsequently, this will greatly facilitate the process of identifying these relations and analyzing them. Column drilling machine – A15 is one of this particular type of metal-cutting machines featuring vertical column where all basic machine elements are mounted; Bench Drilling Machine (fig 5) – column drilling machines featuring shorter columns, suitable for mounting on top of work tables and benches; Machine size – used to classify drilling machines according to their maximum hole diameter drilling capacity. A15 is a 15 mm size machine; Main rotational movement – transmitted from the motor (9 - fig 6), via the belt drive (8 - fig 6) to the spindle (1 - fig 6) and the tool;
Figure 5
Feed – linear type of movement performed by the tailstock barrel with spindle and tool. Both these types of movement are ergonomically essential and 3 this will have to be considered in the course of the 4 ergonomic analysis of the product.
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Spindle (1 - fig 6) – used to hold the tool and transmit the rotational movement. This is actually 2 the link between the 5 Quill (2 - fig 6) – used to support the spindle and provide the linear feed movement.
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Drilling head (3 - fig 6) – this is the assembly com prising the motor, the gear box, which in turn com- 7 prises the main drive mechanism and the transmission; the spindle, etc.; Feed mechanism (4 - fig 6) – the set of levers used to feed the workpiece, the hub, the gear shaft and
Figure 6
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the return spring. Used to carry out the feeding operation from the operator to the tailstick barrel; Protective shield (5 - fig 6) – protects the operator from chipping metal. This is positioned in front of the machine operation area and is attached to the drilling head. Working table (6 - fig 6) – used to position and hold the workpiece. Capable of performing linear movement along the machine column by means of turning the operating handle. A worm gear moves the gear wheel, which moves the table up or down the gear rack fixed to the machine column. Base (7 - fig 6) – 6) – provides stable machine support on the bench. European legislation: reference for the product's health & safety issues The study carried out indicates that several European regulations are avialable and place certain safety requirements for column drilling machines. These include:
European Community Machine Tools Regulation 98/37/CEE;
BS EN 292 Industrial safety of machines & equipment;
Regulation for work with low voltage 73/23/CEE;
Electromagnetic compatibility 89/336/CEE.
3.
AIM OF THE PROJECT
The present project will describe elements of the manufacturing environment – Machine Tools (Metal Cutting). The objective is to identify and evaluate the role of the human factor in this particular environment. The result will be an improved level of compliance of this environment with human anthropometric and psycho-physiological characteristics and increased confidence and satisfaction.
The product to be described and improved in terms of ergonomic characteristics in the present project is a bench drilling machine A15, manufactured by the company ALZMETALL. This machine is available on the market of a 15mm size and is designed for drilling through and blind holes and machining holes made in forgings, castings, a nd semi finished products. Reasons for the Product Choice The choice for the A15 bench drilling machine as the selected product is based on logical sequence and the involvement of the following factors:
Ergonomic relations between the human and the metal-cutting machine are the strongest compared to all other relations existing in this particular manufacturing environment. They occupy the highest level of the hierarchy of relations and influencing them will have the strongest effect on the environment; Of all metal-cutting machines the most common and widest used ones are the column drilling machines. Of them, the bench drilling machines are the machines
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which feature not only strong ergonomic relations between the human and the metal-cutting machine but also a very strong ergonomic relation between the metalcutting machine and its location;
The A15 model of the company ALZMETALL is widely used and features reasonable price and good technical characteristics. The product also has the capacity to be used interactively.
Methods
The objectives of the present project can be achieved using the method of analysis and subsequent synthesis of analytical results. The method will aim at identifying the ergonomic relations in the Human-Machine-Environment system, making a comparative analysis and subsequent generation of ideas and possible solutions.
Planning events
Planning events will be necessary to be carried out before the ergonomic development of the Bench drilling machine A15 product can start and a breakdown of project activities will be made as a result of these planning events. Thus, individual stages in the course of work will be identified, as well as the milestones that have to be solved at each stage and their place in the time schedule.
Schedule of project activities
Code
STAGE / ACTIVITIES
A
B
C
Time
Study Stage
Short study of the product – the bench drilling machine A15: purpose, functions, structural arrangement. All this will be used in the subsequent identification of ergonomic relations in the HumanH umanMachine-Environment system.
25.02 - 26.02
Short study of existing similar products and characteristic ergonomic solutions adopted in them. This activity will be carried out in parallel with above and will assist us in searching for solutions in the right direction.
25.02 - 26.02
Short study of all those remaining environment com ponents that can influence the human – machine relations; in this particular case we will consider the work bench to be used for mounting the machine.
26.02 - 27.02
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Analysis Stage
D
Analysis of the bench drilling machine A15 from an ergonomic viewpoint.
27.02 - 28.02
E
Identifying the ergonomic relations between the human and the machine.
01.03 - 02.03
F
Analysis of other environment components influencing the human-machine relations.
03.03 – 04.03
G
Analysis of requirements of various rules and regulations relating to identified ergonomic relations.
02.03 – 03.03
H
Identification of the main problem area – this will only cover the ergonomic relations for which the comparison between currently available and required situation shows opportunities for intervention to im prove the existing relationship.
03.03 – 04.03
I
Research and identification of information sources of relevant information.
05.03 – 08.03
J
Analysis of problem suitable for test.
09.03 – 11.03
Synthesis Stage 12.03 – 18.03
K
Development of test criteria and consideration of boundary conditions.
L
Design of test and sample population.
19.03 – 23.03
M
Further development of product problem definition
23.03 – 25.03
N
Testing and consolidation of problem definition and generation of ideas for improvement of ergonomic relations included in the main problem area
26.03 – 01.04
O
Synthesis of design and test, and preparation of presentation. Final testing. Development of CAD drawings/models.
02.04 – 03.04
P
Preparing the final project Report
01.03 – 04.04
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We should keep in mind here that project activities in each individual stage are positioned in time under certain dependence between each other. Therefore, I shall use the Ghant Chart Method, a chronogram spread out in time giving corresponding designations of activities to be carried out.
4.
SHORT STUDY OF BENCH DRILLING MACHINE A15
The function of the bench drilling machine A15 is to drill and machine holes of 15 mm maximum diameter. The machine is capable of performing the following operations provided adequate tooling is available and the machine is fed manually by the operator:
Drilling blind and through holes of up to ∅15 mm in St60 steel and up to 80 mm deep; Machining holes made in castings, forgings and other semi-finished products; Drilling threaded holes and cutting threads of up to in ready-made holes;
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counter-sinking / facing; step drilling.
The operational movements, performed by the machine in the course of its functioning include (fig. 7):
Figure 7
main rotational movement of the spindle and tool performed around spindle axis;
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linear feed movement along the tool axis;
auxiliary linear movement of the work table along the column.
Structurally, the machine comprises the drill head and the bottom-back mounted motor, the column, the intermediate work table equipped with a lifting mechanism and the base.
4.1 Study of similar similar products available in in the market and characteristic ergonomic solutions found in them. Several different bench drilling machines were studied – KB16 (Knuth), 16B (Trapani), PN15 (Erlo), RAG16 (Serrmac), BT13 (Maxion). Relevant company Internet web sites and specialised company lit7 2 erature was used as sources of information. 1 The analysis of the ergonomic solutions found in these sample products leads to the following general summary: 3
Feed levers are positioned on the left of the machine, slightly slanted away from the drill head. The direction of rotation of the levers is towards the operator to move the spindle down. The number of levers varies from one to three; The handle on the lifting mechanism for the work table rotates in the direction towards the operator to move the table down and vice versa;
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The control panel in positioned in front of the drill head within the operational area; To comply with safety requirements warning plates are provided with Figure 8 The drill head of the machine signs for opening gear cover and changing belts, as well as using the guard shield; Correspondence and compliance with the anthropometric characteristics of the human factor has been achieved.
4.2 Analysis of the product from an ergonomic viewpoint. Identifying the ergonomic relations between the human and the machine. The analysis of ergonomic characteristics describes how the design of the bench drilling machine A15 is made in compliance c ompliance with the anatomic, physiological and psychological
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human characteristics. The basic size and proportions of the machine correspond to the anthropometric and physiologocal requirements of ergonomic indicators. The ergonomic relations thus identified between the human and the machine are as follows: 1. Handle (1 - Fig. 8) of the drill head cover. This is positioned on the left of the cover and serves to open the cover. The contact is established when the human operator takes the handle to open the cover. The size (18 mm diameter) is sufficient for this operation since the tactile contact is established between a section of the fingers and the ball provided on the handle, and the time required for this contact is short and the frequency of establishing it is rather low. We can not say that the handle is convenient and completely corresponds to its functional designation.
Figure 9
2. The cover (2 - Fig. 8) is made of plastic material and opens sideways requiring a minimum effort from the operator. A switch is installed on the drill head to automatically switch motor power off when the cover is opened. The transmission of movement is thus interrupted to prevent accidental operation of moving elements of the drive transmission. Thus human-operator safety is ensured during belt changing and tightening operations and other types of drive handling. 3. The control panel of the machine (3 - Fig. 8) is positioned in front of the drill head within the operational range of the human operator. No other interfering connections are avaible here to disturb its operation. The three-position switch (4 - Fig. 8) located in the control panel and used to change the direction of rotation, and the main circuit breaker (5 - Fig. 8), are positioned at a sufficient distance from each other. Corrsponding graphical indications of their functions assist the operator in distinguishing them correctly in terms of ergonomic characteristics. The power-on indicator light is also located on the control panel (6 - Fig. 8). It also provides a visual ergonomic relation with the human-operator ensuring the required degree of safety. 4. A transparent guard shield (7 - Fig. 8) is provided to protect the operator from accidental flying metal chips. This is installed on the righthand side of the casing and its vertical position is adjusted by the operator. 5. The handle levers (8 - Fig. 8) used to feed the machine are positioned on the lefthand side of the machine head convenient for the operator to operate them with his right hand. Two such levers are provided positioned at 180 ° from each other. The levers themselves are slanted outwards at 20 °, such that their round ends move away from the cover of the machine to ensure sufficient space is available between them and the machine for operator’s fingers to grip and move freely. An essential tactile contact is established here between the operator and the machine which also features high frequency of performance.
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6. Moving the quill downwards is an operational movement performed manually by the operator. This is achieved by rotating the handles in the “towards themselves” direction (Fig. 9) since this type of movement corresponds to the psycho-physical characteristics of the operator. Moreover, ergonomic studies show that the “towards onself” type of movement is usually performed easier than the “outwards from onself” movement and is therefore recommended for operational movements involving certain exercise of effort (the shear force directed up the tool axis). The biceps of the human hand thus contracts and this is the stronger type of movement performed. The movement of the quill back up is ensured by a retracting coil spring used to retract the spindle in its upper limit position and the operator is only required to exercise tactile control on the power and speed of the upward movement. 7. The work table moving handle (Fig. 10) is positioned laterally to the table bracket and slanted at 15 ° relative to the column cross axis, thus ensuring free movement of the handle past the table side edge protecting the hand of the operator from injuries. 8. The transmission of the movement via a worm gear, a gear and a gear rack allows for significant reduction in muscle power spent by the operator. Moreover, the directions of rotation of the handle which moves the work table up and down are similar to those for the up and down movement of the quill. I.e. Figure 10 Table with lifting mechanism the “towards oneself” direction of movement moves the table down and the “outwards from oneself” direction moves it up. 9. In order to increase safe operation of the machine warning plates are provided on the machine cover and guard shield (Fig. 8). Visual ergonomic contacts are thus established and these comply with the requirements of BS EN 292.
4.3 Analysis of other components of the working environment influinfluencing the human machine relationship 10. One such component in this case is the operational bench used to install the drilling machine A15. The essential parameter of the bench is the distance between the ground level and its working surface. This is related to the machine column and hence, to the position of the operational area of the machine, the control panel, the feed levers, the guard shield and the top surface of the work table. In our specific case of an A15 machine we can conclude that the overall size of the machine will ergonomically correspond to a work bench of a standard height for a standing work posture (between 850 and 950 mm). Identification of Main Problem Area
As a result of the ergonomic analysis thus carried out and the requirements provided in various regulations and documentation, I was able to identify the main problem area:
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The levers of the feed mechanism. The sharp edge (9 - Fig. 8) is disturbingly close to the area of travel of fingers while gripping on the handle. Another drawback of this system is the need for a second grip on the handle when deeper drilling sections are involved since only two levers are provided. The guard shield. A drawback here is the effort required to turn the shield and this is a problem when tool change handling operations are performed by the operator while the machine is in off position. Moreover, the gap between the bottom end of the drill head and the upper edge of the guard shield is too big to allow for a metal chip to fly out of the guarded area thus exposing the operator to danger. The colour selection for the machine drill head and cover does not comply with hygienic ergonomic requirements and do not meet to a sufficient extend the aesthetic requirements needed to ensure the degree of comfort during operation. Additionally, the position and shape of the cover handle can also be modified.
Study Area with Main Problems
As a result of the ergonomic analysis carried out for the bench drilling machine A15 and the requirements placed by various rules and regulations, the following area with main problems was identified as the subject of the current ergonomic study and further development:
Handle of the drill head cover. A better solution can be found for the position and shape of cover lifting handle. Cover. The colour solution adopted for the drill head and cover does not comply with hygiene ergonomic criteria and does not meet to a sufficient degree the aesthetic requirements needed to ensure a certain degree of comfort throughout the work process. Moreover, the shape of the cover can also be optimised from an ergonomic viewpoint. Handle levers and ball handles on them. A few doubts exist as of the need for having two levers when drilling depth is only 80mm. Preliminary studies indicated that machines of this size are available with only a single lever. In other words, we have to consider if we actually need to take hold of the workpiece during the drilling operation. Additionally, we could re-consider the shape and size of ball handles. Clash in between levers & the drilling head. A disturbing immediate proximity is present between the sharp edge (9 - Fig. 9) and the area where the fingers gripping on the handle are traveling. This may cause injuries and traumas for the operator. Transparent protective shield . One disadvantage here is the amount of effort required to move the shield, which is an inconvenience when tool change handling operations are performed by the operator when the machine is in its off position. Handle lever of the table lifting mechanism. This is the handle used to move the worktable . Subject to study for this element are the minimum distance between the handle and the worktable (when the handle is turned), the convenient design and the applied effort.
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5.
REVIEW OF RELEVANT INFORMATION
Having identified the main problem areas from an ergonomic viewpoint, we can now begin to study various sources of information that can help us solve these basic problems. These sources of information include specific sections of available regulations and standards dealing with these particular or similar problems and directly applicable to our specific case. The study will will also cover some novel sources of information, such as the Internet, books, guides, research studies, etc. relevant to the particular subject. The collected information is then referred to the corresponding fields of application in the problem areas during the subsequent stages of analysis and synthesis. Analysis of problem suitable for test
Handle of the drill head cover. cover. As we already mentioned above, the handle is positioned on the lefthand side of the cover and serves to establish a tactile link between the human operator and the machine when machine cover is opened. The frequency of establishing this link is rather low. The handle is quite suitable suitable to fulfil its functional purpose but can be further optimised since the round shape it currently features, its size (18 mm diameter) and position on the side in the center of the cover are not the best possible solution. First of all, the size of the ball handle is too small. Moreover, its position provides only insufficient lifting area for the lifting operation (its protrusion is only about 16 mm since it is tapered flat on the bottom). We are not discussing here the force required to lift the cover as this is of minimum amount (and the weight of the cover is low – it is made of plastic material). The combination between the small size and its position on the cover results in a psycho physiological problem. This is expressed in the fact that when one reaches instinctively for the handle, not looking straight at it, his hand might miss to grip it the first time. This implies for a new, larger size of the handle to be considered, along with re-designing its shape and position. Cover. We could say that the shape of the cover is not sufficiently convenient from an ergonomic viewpoint and a better result can be achieved through certain modifications. These modifications are required as a result of the changes involved in the optimisation of the handle, eliminating the dangerous proximity of the edge 9 and the feed levers 8 (Figure 9), and hence the modifications to the drill head. The colouration of the cover is not sufficiently ergonomically appropriate. The white colour merges with the colour of the drill head and does not provide for any functional distinction between them. Moreover, the white colour features high degree of reflection of light, which is not good for the operator. Additionally, this is not a very suitable colour from a practical viewpoint since any stains will be much more visi ble on a white background thus disturbing the aesthetics of perception and hence, the comfort throughout the work process. Handle levers and ball handles on them. There are two handle levers positioned on the lefthandside of the machine. The link with the operator is tactile and the frequency of establishing it is rather high. The operator grips on the ball of one of them (the one which is currently in its up position) and rotates it in the direction towards
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himself to move the quill and rotating spindle with tool downwards. The required number of levers will depend on the following factors: the depth of drilling and the diameter of the gear shaft used to move the quill. Maximum quill travel is l = 80 mm. d = 36mm is the step diameter of the gear shaft. Therefore, we can calculate the number of turns required to rotate the feed handles to achieve maximum drilling depth. We can calculate this using the formula: l π
* d
=
80 3.14 * 36
= 0.71 turns.
This means that a single lever option is rather unacceptable since this will have to be rotated at 0.71*360° = 256° - something very inconvenient to do with one hand (see fig. 11). We can even consider a three-lever option: an alternative much more convenient for the operator since for deeper drilling operations (60÷80mm) he can easily grip on the levers in alternating sequence with a single hand when three levers are provided. The amount of rotation exercised on the levers, and hence the number of levers, can be reduced, but this would imply an increase in the diameter of the gear shaft and Figure 11 Feed handles rotating angle - quill hence, the pitch size of the travel dependence transmission gear will have to be increased, all this resulting in significant and economically unjustified modifications in the overall design of the drilling head, quill and gear shaft. Of course, all these modifications could be built into a new type of machine during the design stage but in our case we have to consider improvements of the existing model. The shape of ball handles can be kept round but their diameter should be increased to fit the human grip thus bringing greater convenience throughout the operation.
Clash in between levers & the drilling head. It is necessary to increase the distance between them to help avoid the disturbing proximity of the sharp edge in the area of travel of human fingers gripping on the handle. Moreover, the sharp edge is better made slightly rounded. It should be kept in mind here that the edge fits into an area where the circuit breaker switch is positioned (when machine cover is opened). If we change the design position of this switch we could provide solution to three problems: the possible clash between levers and drilling head, the shape of the cover and optimisation of the shape of the drilling head.
17
Transarent protective . (fig. 12) To move shield the shield for tool change handling operations performed by the operator, it is necessary to untighten its handle before that and this is rather inconvenient. It is possible to avoid all this incorporating a change in the design that will simplify these operations meanwhile keeping the simple design of mechanisms at a reasonable level.
Figure 12 Protection of working area
Handle lever of the table lifting mechanism. It is believed that the adopted design solution for incorporating 15° slope to the side of the handle pivot would ensure both free movement of the handle past the side edge of the table and convenience for the operator (fig. 10). The ergonomic solution adopted for the entire assembly is very good and does not call for considering any further improvements.
18
6.
DEVELOPMENT OF TEST CRITERIA AND CONSIDERATION OF BOUNDARY CONDITIONS.
Having identified and analysed the main problem area from an ergonomic viewpoint, we can now proceed with the synthesis and generation of the criteria to be met by the subsequent ergonomic solutions. Handle of the drill head cover. The main currently available inconveniences here result from the size and shape of the handle (fig. 14). We found that the spherical handle features relatively small diameter, which in turn results in an insufficiently convenient grip of the fingers of the human hand when the cover needs to be lifted (fig. 14). a The diameter of the sphere is 18mm. Studies of available regulations and standards indicated an advisable diameter for the spherical handle entering in contact with the fingers of b the operator of a 12.5mm min. and 40mm max [3], [7], [9]. In other words, the current diameter of the handle is right at the Figure 14 Handle of the drill head cover lower limit. Actually, it is even lower since the sphere is flattened on the side of the cover and this means that if a = 18mm, then dimension b = 16mm. Figure 15 shows the inconvenience caused to the fingers of the operator when they grip on the small sphere. The situation is further aggravated when the cover is opened beyond an angle of 45 ° (Figure 15-B). The probability of mis-gripping the handle is higher (even slippage is possible when fingers try to grip on the smooth surface of the sphere). This can be avoided by means of introducing a suitable shape for the handle. The effort required to lift the cover should also be considered in as much as this relates to the convenience and stability of the handle. It is advisable that the amount of this effort is within 0,08 ÷ 50Nm to overcome the resistance of the cover when moved to open [15] .
A
B Figure 15
Therefore, the following test criteria and their corresponding boundary conditions could be used to deal with this problem: 1. Ergonomic dimensions – the diameter of the sphere. It is recommended that the diameter is within 12.5 to 40 mm. It should be kept in mind here that the grip on the handle is primarily by the fingers of the hand.
19
2. Ergonomic characteristics of the shape – a smooth and convenient to grip shape. Could be expressed as a percentage of the ideal shape, which is considered 100%. ). The maximum possible expert assessment score is 100 scores (i.e. the ideal situation). 3. Effort required to successfully establishing the functional relation – this is the effort required to open the cover. It is recommended that it be in the range of 0,08 to 12.5 Nm [4], [10]. 4. Functionality – degree of fulfilling its functions. This can be expressed as a percentage of the ideal functionality, which is considered to be 100%. 5. Frequency of establishing the functional relation – the frequency of the contact established between the operator and the cover handle.
Cover
We have already identified that the most significant problem of the cover from an ergonomic viewpoint is its colour. The white colour is currently coincident with the colour of the drill head and does not provide for distinguishing between the two functions – lack of contrast of colours. Another significant parameter here is the weight of the cover in as far as it defines the amount of effort required to lift it. Therefore, the following test criteria and their corresponding boundary conditions can be applied here: 1. Colour solution – it is necessary to avoid the white colour for the cover. It is recommended to have it painted in a contrast colour, preferably from the blue or green line of colours [2], [9]. 2. Weight of the cover – defines the resistance required to open the cover. It is advisable that the weight of the cover is within a range that would provide for a resistance force of between 0,08 and 50 Nm [10]. 3. Ergonomic characteristics of the shape – it is necessary that the shape of the cover is a visual continuation of the shape of the drilling head. This can be ex pressed as a percentage of the ideal shape, which is considered to be 100%. 4. Functionality – the degree of performing its intended function. The maximum possible expert assessment score is 100 scores. 5. Frequency of the functional relation – this is almost identical with the previously described problem area.
Handle levers and ball handles on them.
The main problem here is related to the diameter of the handle, the number of handle levers and the convenience of manual feeding operation when drilling depths of 60 to 80m. The handle is currently having a 25 mm diameter. The requirement applicable here as for the recommended diameter of the sphere is: min. 18mm and max. 50mm [3], [9]. Since the grip here is by the entire palm of the hand (see fig. 16), it is preferable to increase the size of the diameter to bring it closer to the upper limit of the range: 35 – 50mm. This will improve the stability and convenience of the grip. To improve the operating convenience we have to consider if two levers are sufficient to provide for this type of feeding operation (80mm) and its corresponding angle of rotation (256°) and we will therefore place its functionality as an evaluation criteria.
20
Additionally, we could consider here the effort required to rotate the levers and advance the tool during the drilling operation. The amount of the effort should be sufficient to overcome the resistance force of the return spring that retracts the quill and holds it in its upper position. The compression of the spring is adjustable and usually varies within 1,2 and 2,5Nm [4]. Additionally, we have to add here the momentum T = 43.2Nm, arising from the cutting force acting upwards along the tool axis. This is the maximum resistance force and this results from drilling the maximum possible diameter for the bench drilling machine A15 - ∅15mm, in steel workpieces. Based on the above considerations for the c problem being discussed we can formulate the following test criteria and their corresponding boundary conditions: 1. Ergonomic dimensions – the diameter of the sphere (dimension c – fig. 16). According to available standards, it is advisable to have this diameter in the range of 18 to 50 mm [4], [14]. It is also related to the anthropometric dimension “Size of grip of the hand”. 2. Ergonomic shape – it is necessary to have a soft and convenient to grip shape of the handles. The maximum Figure 16 possible expert assessment score is 100 scores. 3. Required effort to successfully establish the functional relation – this is the effort required to rotate the feed levers during the drilling operation. The amount of this effort should give consideration to the strength capabilities of the right hand of the operator. 4. Functionality – the degree of ergonomic compliance with the intended function. The maximum possible expert assessment score is 100 scores (i.e. the ideal situation). 5. Frequency of the functional relation – this is the frequency of the contact established by the operator and the handles. It is quite obvious that this is featured by high frequency of contact.
Clash in between levers & the drilling head.
Since this problem is present in close relation with the previous problem area (feed levers) the solutions to be provided are related as well. A significant parameter here is the distance between the feed handle and the cover (dimension d – fig. 17). This is related to the anthropometric dimension “Palm thickness”. It is necessary that the lower limit for the dimension d is equal to the thickness of the palm of the operator plus another 20 mm (for additional safety).
d
Therefore, we could apply the following test criteria and their corresponding boundary conditions: Figure 17
21
1. Ergonomic dimensions – the distance between the feed handle and cover (dimension d – fig. 17). This is related to the anthropometric dimension “Palm thickness” + 20mm [8], [6]. 2. Frequency of the functional relation – this is almost identical with the previously described problem area.
. Transparent protective shield
A brand new design solution has to be considered to solve the problem of the difficulty in rotating the guard shield. As far as the ergonomic dimensions of the shield are concerned, the width of the shield should be in compliance with the width of the drilling head (150mm), and the height shall be in compliance with the (1.5 ÷ 1.85)*maximum feed [13]. The following test criteria and their corresponding boundary conditions can be applied here: 1. Ergonomic dimensions – degree of compliance of guard shield dimensions with the operating area of the machine. Width (150 ÷ 170mm) and height (120 ÷ 150mm) of guard shield [2], . 2. Ergonomic considerations for rotating the shield – evaluate the degree of convenience and simplicity of rotating the shield when tool change or other maintenance operations are required. The maximum possible expert assessment score is 100 scores (i.e. the ideal situation). 3. Functionality – the degree of ergonomic compliance with the intended function. In this particular case, consideration should be given to operator safety and visibility in the operating area of the machine. 4. Frequency of the functional relation – the frequency of establishing the contact between the operator and the guard shield.
Handle lever of the table lifting mechanism.
The following test criteria and their corresponding boundary conditions can be applied here: 1. Ergonomic dimensions – Two dimensions are considered: the minimum distance between the handle and the bench (min 53 mm) [8]; and the handle diameter (25 ÷ 45mm) [14]. 2. Ergonomic characteristics of shape – smooth and convenient to grip shape of the handle is required. 3. Required effort – the effort to be applied to turn the handle and lift the worktable. This should be compatible with the lifting capabilities of the right hand of the operator. 4. Functionality. 5. Frequency of establishing the functional relation
22
7.
DESIGN OF THE TEST AND SAMPLE POPULATION
At this stage we will only develop the test to be used to evaluate the problem area. The aim is to develop the kind of an evaluation system that will eventually serve to make a comparative analysis of various options and ergonomic solutions allowing us to deliver the optimum solution. The test will be presented in the form of a table. It will be designed by following the order of individual elements of the identified problem area. This means that a separate ta ble will have to be made to evaluate the solution provided for each individual ergonomic problem. Thus, separate evaluation of each individual element of the pre-defined problem area can be made. Moreover, the final assessment for all individual problems can be added up to generate an overall ergonomic performance assessment of the identified problem area of the specified product. The first column of the table will contain the test criteria as defined in the previous stage of the present development. When more that one ergonomic dimensions are involved, these are arranged one under the other. The last test criterion to be included in all tables is the “Frequency of ergonomic relations ”. Its role is a special one and will be explained further. The second column of the table is reserved for recommended boundary conditions. Wherever possible, these are expressed by means of specific values and measurement units (such as for “Ergonomic dimensions” and “Required effort”) or by means of descriptions (such as for the colour selection when specific colours are recommended). For the rest of the criteria, the possible maximum expert assessment are 100 scores (i.e. the ideal situation) and this is also one boundary condition. In the third column, the current value for criteria is indicated, expressed in specific figures and measurement units, and those for which description of state is provided. In the fourth column an assessment is indicated expressed as percentage figures of the ideal situation (100%) This is an expert assessment and is related to the compliance and relation between columns 3 and 2. Since different criteria are ranked in different priority (or weighing) in the overall assessment of ergonomic performance (or human factor compliance), we will have to introduce another column – weighing of corresponding test criteria. Indicated in this column are coefficients applied to the corresponding assessments to produce the actual im pact of each criterion for the final assessment of each individual element. Corresponding weighings are determined by means of an expert evaluation based on statistics data and experience related to the impact of individual criteria. Weighing values vary within 0 and 1. Indicated in the last sixth column is the result of multiplying the assessment for each individual criterion and its corresponding weighing. The assessment for the ergonomic performance of each individual described element of the problem area is calculated by adding up in a vertical direction the criteria assessments provided in column 6. The sum is then entered into box 2 (fig. 18) against the “Frequency of ergonomic relation ” criterion.
23
Now is the time to clarify that the “Frequency of ergonomic relation ” criterion is included here only to provide for trustworthy calculation of the overall ergonomic performance assessment for the defined problem area. Therefore, columns “Current Condition” and “Assessment” and not filled in for this particular criterion and only the “Weighing ” column (1 - fig. 18) is filled in. In other words, this only serves to provide weighing to the final assessment for each individual element of the identified problem area when its final evaluation is made. The weighings of the “ Frequency of the ergonomic relation ” criterion also varies within 0 – 1. Hence, the final assessment of each element is calculated by multiplying the sum indicated in box 2 (fig. 18) by the weighing of the “Frequency of ergonomic relations ” criterion (1 - fig. 18) and entering this result in box 3 (fig. 18). Figure 18 is a visual indication of the process of drawing the final assessment for each individual element.
Crite Cr iteri rion on
Bound Bo undary ary Co Condi nditi tion onss
1
Curr Cu rrent ent Co Cond ndit ition ion As Asses sessm smen entt Weig eight ht As Asses sessm smen ent* t*
2
3
Criterion 1
......
......
Criterion 2
......
......
Criterion 3
......
......
Criterion 4
......
......
4
5
6 = 4*5
1 2
Figure 18 Design of Test Assessment.
3
Key: Red arrow arrow ...... ...... – multiply multiply Blue arrow arrow ...... – enter result result Yellow Yellow arrow arrow .. – sum of results results
The overall ergonomic performance assessment for the product is calculated as the sum of final assessments (3 - fig. 18) for each individual element of the problem area. At this stage we can design assessment tables for individual elements of the problem area. We can also design the sample population here. We found for the first element of the problem area that the recommended diameter for the spherical handle gripped by the fingers shall be in the upper part of the allowable range of 12.5 - 40mm. In other words, this range can be viewed as a normal distribution of values complying with the anthropometric characteristics. Anthropometric parameters are often expressed as so called percentiles. Percentiles are such values of the considered anthropometric parameter that divide its variation order into 100 identical sections, such that the number of cases which have their values for this parameter within two consecutive percentiles is 1% of the total number of cases considered. Therefore, the values of the range limited by percentiles P 50 and P95 – 35 – 40mm shall be entered into the column “Boundary Conditions”. Figures are rounded to the closest standard values for such handles (these products feature standard order of diameters).
24
We proceed in a similar way with the “Required effort” criterion but select the range between P5 and P50 or when rounded up (this is quite insignificant in this particular case), these are the values within 0.12 and 25 Nm.
Element 1: Handle of the drill head cover Test Crite Criteria ria
1
Boundary Boun dary Condi Condition tionss Curre Current nt Cond Condii- Assessme Assessment nt Weigh Weighing ing Assessmen Assessment* t* tion 2 3 4 5 6 =4*5
Ergonomic dimensions: - spherical handle dia Ergonomic characteristics of shape Required effort Functionality Frequency of establishing functional relation
35 – 40 mm
1.0
0 ÷ 100
0.5
0.12 – 25 Nm
0.7
0 ÷ 100 0÷1
0.5 0.75
Final Assessment =
For the second element for this criterion, the “ Weight of the cover ”, ”, we have the same range as for the previous element 0.12 to 12.5 Nm and the weight of the cover is converted into kilograms. This is done because the two criteria are directly linked with each other. We shall have to consider the size of the cover when defining the arm of the momentum and the resistance of the locking mechanism. An advisable range for the weight of the cover of 0, 65 - 69 N is thus obtained.
Element 2: Cover Test Crite Criteria ria
1
Boundary Boun dary Condi Condition tionss Curre Current nt Cond Condii- Assess Assessme ment nt Weighi Weighing ng Assessm Assessmen ent* t* tion 2 3 4 5 6 =4*5
Colour solution
Contrast of the cover
0.45
Weight of cover
0.65 – 69 N
1.0
Ergonomic characteristics of shape
0 ÷ 100
0.5
Functionality
0 ÷ 100
Frequency of establishing functional relation
0÷1
0.5 0.75
Final Assessment =
Some of the identified ergonomic problems are very closely related to each other. This is mostly true for the third and fourth elements – the feed levers and the clash in between levers & the drilling head. Moreover, the “ Frequency of establishing the ergonomic relation” test criterion is the same for both of them. Therefore, the two ergo-
25
nomic dimensions of the two elements will be arranged one under the other and assessed separately. The range of allowable values for the diameter of feed lever handles is defined similar to above, but it should be kept in mind here that the grip is made by the entire palm, not just the fingers. Therefore, the values of the range limited by percentiles P 50 and P95 – 35 ÷ 50 mm will be entered into the “Boundary Conditions” column.
The recommended distance between the feed handle and cover (dimension d – fig. 16) is equal at least to the anthropometric dimension “Palm thickness” + 20mm. For the anthropometric dimension “Palm thickness” we shall consider percentile P 95 for male individuals, the value of which is 33mm. We can also use here the anthropometric dimension “Finger thickness” but since its values for P 95 are lower, this was disregarded for the sake of safety.
The maximum required effort to rotate the levers to advance the tool is = 280N at P 5 for male individuals operating with their right hand. This effort is to overcome a resistance of 72Nm. The required effort will have to overcome the resistance of the return spring and the momentum T = 43.2Nm, caused by the maximum cutting speed (for tools of ∅15mm Dia).
The Functionality criterion will be assessed for the convenience of operation (the optimum number of levers for an 80mm feed and its corresponding angle of rotation).
Element 3&4: Handle levers and ball handles on them and Clash in between levers & the drilling head Test Crite Criteria ria
1
Boundary Boun dary Condi Condition tionss Curre Current nt Cond Condii- Assessme Assessment nt Weigh Weighing ing Assessmen Assessment* t* tion 2 3 4 5 6 =4*5
Ergonomic dimensions: - spherical handle dia
35 – 50 mm
1.0
- distance between feed handle and cover min. 53 mm (=33+20) Ergonomic characteristics of shape Required effort Functionality Frequency of establishing functional relation
1.0
0 ÷ 100
0.5
max. 72Nm
0.7
0 ÷ 100 0÷1
0.5 1.0
Final Assessment =
For the fifth element, the sum of weighings of the two ergonomic dimensions is equal to 1.0 and forms the overall weighing of the “Ergonomic dimensions” criterion.
26
Element 5: Transparent protective shield Test Crite Criteria ria
1
Boundary Boun dary Condi Condition tionss Current Current Con- Assessdition ment 2 3 4
Weighing
Assessment*
5
6 =4*5
Ergonomic dimensions: - width
150 – 180 mm
0.5
- height
120 – 150 mm mm
0.5
Ergonomic characteristics of rotation
0 ÷ 100
0.5
Functionality
0 ÷ 100
Frequency of establishing functional relation
0.85
0÷1
0.8
Final Assessment =
Issues for the sixth element are very similar to these adopted for element 3 ( Handle levers and ball handles on them ): Element 6: Handle lever of the table lifting mechanism Test Crite Criteria ria 1
Boundary Boun dary Condi Condition tionss Curre Current nt Condi Condition tion Asses Assessmen smentt Weigh Weightt Asses Assessmen sment* t* 2 3 4 5 6 =4*5
Ergonomic dimensions: - handle dia
25 – 45 mm
1.0
- distance between handle and table
min. 53 mm
1.0
Ergonomic characteristics of shape Required effort Functionality Frequency of establishing functional relation
0 ÷ 100
0.5
max. 90 Nm
0.7
0 ÷ 100 0÷1
0.5 0.75
Final Assessment =
Further development of product problem definition
From all read and analysed so far we can further develop some elements from the problem area. This will act as a link to generating design solutions that will optimise the ergonomic performance of the product. First of all, a solution can be adopted for the cover for an entirely new design of the handle used to open it. This will avoid the spherical shape of the handle and a few more components and will take us to the alternative of having a long plastic handle cast into the cover. For the purposes of the assessment, we will only have to replace the dimension in the “Boundary conditions” column with a smaller value.
27
Eventual modification to the shape of the drilling head will result in significant changes in the problem area: it will be possible to eliminate the hazardous edge, it will be possi ble to move the volume with the shut-down sensor, it will be automatically possible to change the shape of the cover to better match it with the shape of the drilling head thus providing better functionality. Since we are going to modify the drilling head, we will also be able to increase the diameter of the gear shaft, thus changing significantly the nature of the problem – the angle of rotation at maximum quill stroke will be reduced, which then allows us to consider the option of having a single feed lever. This will in turn eliminate the “Clash in between levers & the drilling head ” problem. ” problem. For the guard shield we can say there is no danger of a flying metal chips between the upper section of the shield and the bottom edge of the drilling head. This is due to the fact that metal chips and other particles coming off during the cutting operation are captured by the centrifugal forces acting on the spindle, thus flying out only in the horizontal plane within the safety range of the guard shield. Therefore, this problem is thus eliminated.
28
8.
TESTING OF THE CURRENT VERSION OF A15
8.1 Bench drilling machine assessment The test thus designed is used to make an assessment of the bench drilling machine A15 in its current design version. The objectve is to generate an estimate of the ergonomic characteristics of the pre-defined problem area. Separate assessment will be provided for each individual characteristic element. Finally, individual assessments of each parameter will be added up to provide the overall general ergonomic assessment for the pre-defined problem area of the product. All this will allow us to draw conclusions on the extent of compliance of individual ergonomically critical machine elements relative to the human factor. And most important – the extent of compliance will be quantifed. Then we will be able to consider where to introduce eventual alterations in structural elements and how to direct them (the Boundary conditions provided will serve as benchmark). We will be able to draw a comparative analysis with the altered version of the machine based not only on the overall general assessment but also on final assessments of individual elements.
Test Crite Criteria ria
1
Boundary Boun dary Condi Condition tionss Curre Current nt Condi Condition tion Asses Assessmen smentt Weigh Weightt Asses Assessmen sment* t*
2
3
4
5
6 =4*5
Element 1: Handle of the drill head cover Ergonomic dimensions: - spherical handle dia Ergonomic characteristics of shape Required effort Functionality Frequency of establishing functional relation
35 ÷ 40 mm
18 mm
0 ÷ 100 0.12 ÷ 25 Nm
0.24 Nm
0 ÷ 100
60
1.00
60.00
50
0.50
25.00
100
0.70
70.00
75
0.50
37.50
0.75
192.50
0÷1
Element 1: Final Assessment =
144.375
Element 2: Cover Colour solution
Blue and green line of colours
White colour
25
0.45
11.25
Weight of cover
0.65 ÷ 69 N
12 N
100
1.00
100.00
Ergonomic characteristics of shape
0 ÷ 100
60
0.50
30.00
Functionality
0 ÷ 100
75
0.50
37.50
0.75
178.75
Frequency of establishing functional relation
0÷1
Element 2: Final Assessment =
134.063
29
Element 3&4: Handle levers and ball handles on them and Clash in i n between levers & the drilling head Ergonomic dimensions: - spherical handle dia
35 – 50 mm
25
50
1.00
50.00
- distance between feed handle and cover
min. 53 mm (=33+20)
35
20
1.00
20.00
Ergonomic characteristics of shape
0 ÷ 100
90
0.50
45.00
70
0.70
49.00
60
0.50
30.00
1.00
194.00
Element 3&4: Final Assessment =
194.00
Required effort
max. 72Nm
Functionality
45.7Nm
0 ÷ 100
Frequency of establishing functional relation
0÷1
Element 5: Transparent protective shield Ergonomic dimensions: - width
150 ÷ 180 mm
150 mm
100
0.50
50.00
- height
120 ÷ 150 mm
120 mm
100
0.50
50.00
Ergonomic characteristics of rotation
0 ÷ 100
40
0.50
20.00
Functionality
0 ÷ 100
100
0.85
85.00
0.80
205.00
Frequency of establishing functional relation
0÷1
Element 5: Final Assessment =
164.00
Element 6: Handle lever of the table lifting lifti ng mechanism Ergonomic dimensions: - handle dia - distance between handle and table
25 – 45 mm
35
100
0.80
80.00
min. 53 mm (=33+20)
60
85
0.80
68.00
100
0.50
50.00
100
0.70
70.00
100
0.50
50.00
0.75
318
Ergonomic characteristics of shape
0 ÷ 100%
Required effort
max. 90Nm
Functionality Frequency of establishing functional relation
0 ÷ 100% 0÷1
9Nm
Element 6: Final Assessment = General assessment of the product =
Final Assessment 1 + 2 + 3&4 + 5+6 =
238.50 636.438
30
8.2 Consolidation of problem definition and idea generation For element 1 – the assessment for the ergonomic dimension of the spherical handle is 60 although the current diameter (18mm) is beyond the range defined by the boundary conditions calculated relative to percentiles P50 and P95 - 35 ÷ 40 mm (as we already discussed in the current logbook, weeks 5 and 6). However, we must keep in mind in this assessment that it occupies the lower section of the range recommended in existing standards – 12.5 ÷ 40 mm. Therefore, the final assessment is slightly above 50 scores as it still meets part of the compulsory requirements and ensures certain ergonomic compliance with the human factor. The ergonomic characteristics of shape is given lower score of assessment – 50 scores and this is exactly due to the problem of the flat bottom section of the spherical handle, which results in reduction of dimension b (see figure 14). Moreover, the spherical shape in this particular case is a possible solution but not the best alternative. The required effort is assessed at 100 scores since it entirely fits into the range calculated based on percentiles P 5 and P50 and occupies the optimum lower section of the range. The function of the handle is associated solely with the opening of the cover and is given a score of 75. This is influenced by some disadvantages in the ergonomic characteristics of shape and the location of the handle itself (in the middle of the cover, on the side) and this resulted in a 25 scores reduction of the final assessment. In other words, the assessment here is influenced by previous criteria in as far as any interference is available between some of the criteria. Idea generation: Analysis indicates that ergonomic characteristics can be further im proved by increasing the size of the handle and altering its shape. The risk of slippage of fingers when the cover is opened beyond and angle of 45 ° should be eliminated (figure 15-B). This can be achieved in the following two ways: either by incorporating certain cutout to increase surface roughness of the sphere, or by altering the shape of the handle. The fact that the grip here is by the fingers of the hand (and not by the palm or part of the palm) and the negative effect caused by the location of the handle, give us grounds to give preference to the second alternative. For element 2 – the assessment given to the colour solution adopted for the machine is very low, 25 scores, since using white colour as the basic colour for metal cutting machines is inappropriate. We must consider here the fact that the entire machine is painted in white and no contrast is provided. Thus, discomfort is brought to the operator resulting in subliminal sense of strain associated with the sterility of the white colour – one instinctively is avoiding to touch it fearing of “leaving stains” on the surface. Another disadvantage is that white coulour is very easy to become dirty and look unsightly as well as hard to keep clean. White colour features the lowest degree of “absorbing dirt” (disguise dirt to a certain extent), which practically makes it impossible to conceal dirt. Therefore, it is preferable to use other colours, such as some from the blue and green line of colours usually recommended for engineering equipment.
31
The ergonomic characteristics of shape are given low assessment, only 60 scores, due to the asymmetrical design and the influence of another element of the pre-defined problem area, element 4 (Clash in between levers& the drilling head). The logics in awarding the scores for cover weight (required effort) criterion and functionality criterion is similar to that adopted for element 1 above (certain interference between some of the criteria). Idea generation: Analysis indicates that ergonomic characteristics can be further im proved by: 1. Re-painting the colour and the entire machine in different colour. 2. Adding contrast between the colour of the cover and the colour of the drill head – this will rise the score for the assessment of the functionality criterion as a certain shade of contrast will give an indication of the type of function involved. 3. Alter the shape to achieve symmetry – this can be done only provided certain alterations in the shape of the drilling head are incorporated. For elements 3&4 – the assessment score for the ergonomic performance of the size of the spherical handle is 50 due to reasons similar to those given above for the assessment of the cover handle. Althouth the current diameter (25mm) is out of the range defined by the boundary conditions calculated based on percentiles P 50 and P95 - 35 ÷ 50 mm, it falls into the lower section of the range recommended by available industrial standards – 18 ÷ 50 mm. Therefore, it is given as as? sessment score of 50 since it still complies with part of the compulsory requirements but it should be kept in mind here that the grip is Figure 19 on the entire palm. The other ergonomically significant dimension, the distance between the machine feed handle and the cover, is given an especially low assessment score since it does not comply with the requirements for a minimum distance of 53mm. The ergonomic performance of shape has been given a high assessment score of 90 since it is very convenient for the grip of the human hand. 10 scores less than the maximum score is due to the insufficiently smooth transition between the spherical section and the elongation under the sphere (fig. 19), designed to give some support to the finger tips. The required effort has been given an assessment of 70 scores in view of the fact that a maximum score would be given to a machine of entirely different design solution (automatic feed or at least worm driven feed). However, the current effort is still within the normal range and is much lower when small diameter tools for drilling are employed (this reduces the cutting force and hence, the effort required to overcome it). As we already mentioned, when we consider functionality we assess the convenience associated with functioning, which in this particular case is directly related to the num ber of levers. In the case of the current handle, it is necessary to change hands on the handle lever when deeper drilling operations are involved and levers are rotated beyond 90°. Two is not the optimum number of levers for 80 mm feed distance and the relevant angle of rotation.
32
To improve operational convenience we will have to consider if two levers are sufficient for the specific feed distance of 80mm and its relevant angle of rotation (256°). Therefore, we will consider an assessment criterion for functionality, as well. Idea generation: increase the size of the handle and slightly alter the shape of the transition to the elongated section to im prove ergonomic performance. As of the “required effort” criterion – it is economically unjustified to make the design more complicated for this particular type of machine. Moreover, the current required effort level is very good. It would be preferable to have a singlelever feed with a maximum angle of rotation of 95 ÷ 100°. For this particular type and size of machine and the degree of precision involved, it is unjustified to have a larger number of handle levers, especially for a feed distance of 80mm.
Figure 20
For element 5 – the assessment score of ergonomic performance of the Transparent Protective Shield is 100 thanks to its complete compliance with the size of the operational area. The ergonomic performance of its rotation has been assessed much lower – 40 scores, which is due to the difficulty involved in turning it and the need to untighten and retighten the side screw. Functionality here is high, in as far as it concerns the degree of protection it provides for the operator. Idea generation: The only intervention here could be to incorporate a simple design solution to help avoid the need for performing several operations to turn the shield. For element 6 – 6 – the assessment score awarded to this element is rather high and no de-
sign or ergonomic modifications are considered here. Synthesis of the design and test. Development of drawings/models.
Having completed the analyses and idea generation we can now proceed with the synthesis of specific design solutions giving optimum consideration to the ergonomic requirements placed for individual elements. These solutions will observe individual elements and criteria and a single adopted solution might sometimes meet more than a single criterion due to their interrelation. This will be best illustrated by the fact that the design solution adopted for the handles
Figure 21
33
will at the same time result in some alterations in the shape of the drilling head and the cover. 1. We will have a single handle lever of different shape. To do this, the maximum angle of rotation of this handle should be 95 ÷ 100°. Therefore, we have to increase the pitch diameter of the gear shaft which transmits movement to the quill (fig. 20). If we 48 increase this to 100 mm then we will have: l π
* d
=
80 3.14 *100
25
= 0.25 turns.
This means the angle of rotation of the handle for maximum drilling depth (80mm) will be 0.25*360° = 90° (fig. 21). – this is very convenient to handle with just a single hand. The opening Sha rp So ft provided into the shaft will move back 22 mm. The length of the lever will have to be increased Wa s No w Figure 22 to compensate for this displacement and move this handle above the level of the cover handle. This, along with a slight bend incorporated into the shape of the lever (1 - fig. 23) will move the cover more than 53mm away (60mm - fig. 23). A longer lever will also reduce the required effort (the arm of the applied force is longer, hence the required momentum is reduced). The handle lever original position is vertical + 10° (fig. 21). This is much more convenient and in compliance with the psycho-motor reactions of the operator, since when he moves the lever the muscles of the biceps of his right hand contract and this is the strongest possible movement of the hand. Moreover, the upper position allows for some rest of the fingers and the palm using the vertical lever with handle as a kind of support, thus allowing the 60 3 hand to relax when no feed is 2 required. This is exactly why these + 10 ° are added – to change the direction of the load opposite to the applied load. 2. Alteration in the size and shape of the handle. The diameter of the handle will be increased to ∅48mm. The shape of the handle will be the same and only the smoothness of the transition between the spherical and conical/cylindrical section will be changed (fig. 22).
4
1
3. The cover will be located sym metrically when viewed from the Figure 23 face. Movement shut-down sensor for “cover open” position is moved back and into the drilling head to allow for some symmetry of the drilling head, and hence – the cover of the machine (2 - fig. 23).
34
4. Alteration of the overall concept for the opening handle. The cover opening handle will be machine-cast into the cover (the handle is part of the cover and hence, more rigid: 3 – fig. 23) and is rectangular in shape along the length of the cover. The crosssectional view shape of the handle features smooth rounded edges, which is sufficiently large (>20mm) and convenient to hold with the fingers of the hand. 5. Transparent protective shield is shield is of the same shape (2 - fig. 23).. Some design changes will be introduced on the sides where the clamp and height adjustment mechanism is located. The following alterations are implemented by means of introducing two additional grooves and a spring: -
When the shield is slightly lifted up (10 mm), it overcomes the pressure exerted by a small spring and falls into a groove where it can be rotated to provide access to the operational area of the machine. This is achieved with only a single slight movement of the hand.
-
A slight rotation into the opposite direction causes the spring to move the cover back into its original lower position
6. Change the colour of the exterior of the machine. The white colour is replaced by the more suitable and recommended for engineering equipment blue colour. The cover is painted in deeper shade of blue to provide for some contrast and indication of its functional purpose (fig. 23). Figure 23 illustrates the final appearance of the machine after introducing above alterations. This can now be subjected to the same test as the previous variant. The only difference will be observed in the name of the machine and the Boundary Conditions calculated for the first element, since now it features an entirely different shape: Test Crite Criteria ria
Boundary Boun dary Condi Condition tionss Curre Current nt Condi Condition tion Asses Assessmen smentt Weigh Weightt Asses Assessmen sment* t*
Element 1: Handle of the drill head cover Ergonomic dimensions: - depth of handle Ergonomic characteristics of shape Required effort Functionality Frequency of establishing functional relation
20 ÷ 30 mm
30 mm
0 ÷ 100% 0.12 ÷ 25 Nm
0.24 Nm
0 ÷ 100%
100
1.00
100.00
85
0.50
42.50
100
0.70
70.00
85
0.50
42.50
0.75
255.00
0÷1
Element 1: Final Assessment =
191.25
Element 2: Cover Colour solution
Blue and green line of colours
Blue
100
0.45
45.00
Weight of cover
0.65 ÷ 69 N
12 N
100
1.00
100.00
Ergonomic characteristics of shape
0 ÷ 100%
90
0.50
45.00
Functionality
0 ÷ 100%
90
0.50
45.00
35
Frequency of establishing functional relation
0.75
0÷1
Element 2: Final Assessment =
235.00
176.25
Element 3&4: Handle levers and ball handles on them and Clash in i n between levers & the drilling head Ergonomic dimensions: - spherical handle dia
35 – 50 mm
- distance between feed min. 53 mm (=33+20) handle and cover Ergonomic characteristics of shape
0 ÷ 100%
Required effort
max. 72Nm
Functionality
48
100
1.00
100.00
60
95
1.00
95.00
100
0.50
50.00
75
0.70
52.50
100
0.50
50.00
1.00
319.00
Element 3&4: Final Assessment =
347.50
39Nm
0 ÷ 100%
Frequency of establishing functional relation
0÷1
Element 5: Transparent protective shield Ergonomic dimensions: - width
150 ÷ 180 mm
150 mm
100
0.50
50.00
- height
120 ÷ 150 mm
120 mm
100
0.50
50.00
Ergonomic characteristics of rotation
0 ÷ 100%
100
0.50
50.00
Functionality
0 ÷ 100%
100
0.85
85.00
0.80
205.00
Frequency of establishing functional relation
0÷1
Element 5: Final Assessment =
164.00
Element 6: Handle lever of the table lifting lifti ng mechanism Ergonomic dimensions: - handle dia - distance between handle and table
25 – 45 mm
35
100
0.80
80.00
min. 53 mm (=33+20)
60
85
0.80
68.00
100
0.50
50.00
100
0.70
70.00
100
0.50
50.00
0.75
318
Ergonomic characteristics of shape
0 ÷ 100%
Required effort
max. 90Nm
Functionality Frequency of establishing functional relation
0 ÷ 100% 0÷1
General assessment of the product =
9Nm
Element 6: Final Assessment =
238.50
Final Assessment 1 + 2 + 3&4 + 5+6 =
1141.50
36
Comparative Analysis
Figure 24 illustrates the ergonomic changes introducing above alterations:
Figure 24
Based on the results thus obtained we can draw up a comparative analysis between the new version, the old version and an ideal variant (with all maximum assessment scores): Elements
New variant
Old variant
Improvement %
Ideal variant
% of the ideal variant
B
C
D = B/C*100%
E
F = B/E*100%
Element 1
191.25
144.375
132.4%
202.50
94.44 %
Element 2
176.25
134.063
131.4%
183.75
95.91 %
Elements 3&4
347.50
194.00
179.1%
370.00
93.91%
Element 5
188.00
164.00
114.6%
188.00
100 %
Element 6
238.50
238.50
0%
247.50
96.36%
General assessment
1141.50
874. 938
130.4%
1191.75
95.78 %
A
The table also shows the percentage improvement of the new version relative to the old one and the percentage achieved by the new version relative to the ideal variant. Values are exceptionally high - the overall improvement of ergonomic performance in the defined problem area of the product is increased by 30.4% relative to the old version and achieves 95.78% of the ideal assessment score, which is a very good result. Actually, most of the insufficient reminder score is due to the “required effort” criterion for element 3 & 4, where we already mentioned there are some objective causes (it is eco-
37
nomically unjustified to introduce automatic feed and the current solution provides for sufficiently acceptable characteristics for this particular type and size of machine). This is a very good result. However, the fact that the new version does not achieve 100% of the ideal level does not imply that the modified version is not sufficiently successful. We must remember here that the subject of the study here is the currently existing machine and this means that alterations are introduced observing a number of other requirements: technical, economic, etc. It is not a matter of designing a new product. Therefore, some of the decisions are made giving priority to the economic efficiency or observing available technical capabilities (and not necessarily achieving 100% ergonomic performance). For example, part of the insufficient percentage required to achieve the maximum value for elements 3 & 4 is due to the “required effort” criterion where automatic feeding is economically unjustified. However, the score of 93.91% achieved for for this particular element is rather sufficient and ensures excellent characteristics for this specific type and size of machine. The analysis thus drawn up allows us to consider the level of ergonomic performance of individual machine elements and adopt necessary decisions of introducing alterations in locations where intervention is most required as well as the scope of such intervention. The conclusion from all said so far is that the suggested new modified version of the machine can be assessed as very good from ergonomic performance viewpoint.
38
9.
PURPOSE OF THE STUDY
Critically develop a human factor requirements specification for design of existing bench drilling machine, develop a suitable ergonomic performance test for assessment of compliance with these requirements and apply ergonomic data to the design of the machine.
9.1 Main Tasks
Identify ergonomic relations in the human-machine system; Identify the problem area from an ergonomic viewpoint and analysis; Design an ergonomic test to provide quantitative assessment of the extent of compliance of the elements within the identified problem area with ergonomic performance requirements; Testing and consolidation of problem definition and idea generation; Synthesis of test results and design.
Improvements in technological equipment result for machine design structure and other influencing factors of working environment, (lighting, noise, colours, etc.,) to be in agreement with the anatomic, physiological and psychological characteristics of humans. In other words, there is a need to adapt working environment to human factor requirements.
Subject of the Ergonomic Development The product to be described and improved in terms of ergonomic characteristics in the present study is a benchdrilling machine A15 (Fig. 25), manufactured by the company ALZMETALL. This machine is available on the market for 15mm size models and is designed for drilling through holes and blind holes and machining holes made in forgings, castings, and semi finished products.
Working Environment
Figure 25 The bench drilling machine A15 machine A15
The subject of the present project, the bench-drilling machine A15, belongs to the type of working environment which is typical for the operation of Machine Tools (Metal Cutting). Its characteristic features involve the following components: metal-cutting machine, units, tooling, auxiliary attachments and equipment, working benches and furniture, production rooms, etc.
9.2 ANALYTICAL STUDY Short study of bench drilling machine A15 The subject of the study is the functional purpose of the machine, the operational movements involved in performing its functional purpose and the structural design of the machine. Additionally, some other similar machine types were studied to get a
39
general idea of the overall direction of implementation of ergonomic solutions and to develop a primary basic database for comparison. A study was carried out of currently available Euopean standards and regulations stipulating certain requirements for safety and reliability of column drilling machines.
Analysis of the Product from an Ergonomic Viewpoint The objective of this analysis was to identify the ergonomic relations between the human and the machine. The analysis of ergonomic characteristics describes how the design of the bench-drilling machine A15 is made in compliance with the anatomic, physiological and psychological human characteristics. The following ergo- 2 nomic relations between Man and the machine were identified and analysed:
Handle of the cover (1 - Fig. 26) - Human. Tactile 3 relation. Cover (2 - Fig. 26) – Human. Tactile relation. Control panel (3 - Fig. 26) – Human. Tactile and visual relation. Transparent protective shield (4 - Fig. 26) – Human. Tactile and visual relation. Handle levers (5 - Fig. 26) – Human. Tactile relation. Directions of movement – Human. Psycho- 4 physiological relation. Work table handle (Fig. 27) – Human. Tactile relation. Feed mechanism (6 - Fig. 26) 26) – Human. Tactile Figure 26 relation. Warning information (7 - Fig. 26 - nameplates) – Human. Visual relation.
Study Area with Main Problems As a result of the outcome from the ergonomic analysis and in compliance with the requirements placed by various regulations and standards, we were able to identify the Problem Area for the bench drilling machine A15. Its basic elements were defined as follows: Handle of the drill head cover; Cover; Handle levers and ball handles on them; Clash in between levers & the drilling head (8 Fig. 26); Figure 27 Transparent protective shield. Handle lever of the table lifting mechanism
These were subjected to further more detailed ergonomic study and development.
7 1
8
6
5
40
Analysis of Problem Suitable for Test The present analysis is directed at identifying the problems within the defined Problem Area which will eventually be used as the base for developing a system of criteria. Moreover, the aim was to use this as a base to develop a test to provide a quantitative assessment of ergonomic complinace of the studied product. Specific characteristics of ergonomic relations with the human factor were defned for each individual element in the Problem area, paying special attention to issues where the probability of interference of relations is the highest (when comparing currently existing parameters to required ones).
9.3 HYPOTHESIS OF THE PROPOSED ERGONOMIC TEST Test Criteria Certain basic criteria were synthesised based on the analysis and these were then used to assess the adopted ergonomic solutions. These constitute the first and most significant component of the test being developed [17]. Various elements of the pre-defined problem area feature the same criteria. For example: Ergonomic dimensions, Ergonomic characteristics of shape, Functionality, and the Frequency of establishing the functional relation [18]. It should be kept in mind that each individual criterion strongly and primarily depends on the specific element it is applied to. For example, the “ Ergonomic dimensions” criterion for Handle Handle of the drill head cover element refers to the size of a diameter, while for the Transparent protective shield element it refers to linear dimensions.
Boundary Conditions This is the second test component. Boundary conditions are directly related to corresponding criteria and the requirements placed by current regulations and standards. But before being incorporated into the test, boundary conditions are calculated relative to percentiles applicable to each individual element. For example, the values recommended for the “ Ergonomic dimensions” criterion for the first element, Handle of the drill head cover, are in the range of 12.5 ÷40mm but since there is a requirement for these values to fall within the range between percentiles* P50 and P95, then boundary conditions are re-calculated to arrive at 35÷40mm. Thus, exerpts from statistics of conducted anthropometric studies are considered. The decision as to which particular percentile is to be used is based on analytical methods (eg. for external dimensions small sizes are significant – percentile P 5, and for external dimensions – large sizes – perentiles P95). Boundary conditions are expressly defined where possible using specific values and measurement units (such as, for example, for “Ergonomic dimensions” and “Required effort”) or by means of describing the status status (for example, preferred colour for the
*
Anthropometric parameters are often expressed as so called percentiles. Percentiles are such values of the considered anthropometric parameter that divide its variation order into 100 identical sections, such that the number of cases which have their values for this parameter within two consecutive percentiles is 1% of the total number of cases considered.
41
adopted colour solution). The maximum possible expert assessment score for the rest of the criteria is 100 scores (i.e. the ideal situation).
Design of Test and Method of Assessment The test is illustrated in a table listing individual elements within the specified problem area. A corresponding section in the table provides the assessment of the solution adopted for each individual ergonomic problem (Figure 28). Each section ends with a final assessment for the individual element. Thus a separate assessment is provided for each element within the pre-defined problem area. Finally, assessment scores awarded to individual problem elements are added up to provide the general ergonomic performance assessment for the pre-defined problem area of the product. The first column of the table will contain the test criteria. When more that one ergonomic dimensions are involved, these are arranged one under the other. The last test criterion to be included in all tables is the “ Frequency of ergonomic relations ”. Its role is a special one and will be explained further. The second column of the table is reserved for calculated boundary conditions. In the third column, the current value for criteria is indicated, expressed in specific figures and measurement units, and those for which description of state is provided. The fourth column contains the assessment for the specific criterion. This can range between 0 and 100 scores (the ideal variant). The assessment is an expert type of assessment and depends on the correspondence and ratio between columns 3 and 2. Sometimes the assessment awarded to a particular criterion is affected by the non-fulfillment of some other criterion. This is due to the fact that there is a certain extent of interference between some of the criteria; these criteria form a system of interrelations for each individual element. Scores plus or minus are provided for the assessment of each of these interrelations. Since different criteria Criterio Crit erion n Boundar Boun dary y Con Conditio ditions ns Curr Current ent Con Conditi dition on Asse Assessme ssment nt Weigh eightt Asse Assessm ssment* ent* 1 2 3 4 5 6 = 4*5 are ranked in different ...... ...... priority (or weighing) in Criterion 1 ...... ...... the overall assessment of Criterion 2 ...... ...... ergonomic performance Criterion 3 1 ...... ...... (or human factor compli- Criterion 4 ance), we will have to in2 troduce another column – weighing of corre3 Figure 28 sponding test criteria. Key: Indicated in this column Red arrow .......– multiply are coefficients applied Blue arrow.......– enter result to the corresponding asYellow Yellow arrow arrow .. – sum of results results sessments to produce the actual impact of each criterion for the final assessment of each individual element. Corresponding weighings are determined by means of an expert evaluation based on statistics data and experience related to the impact of individual criteria. Weighing values vary within 0 and 1.
42
Indicated in the last sixth column is the result of multiplying the assessment for each individual criterion by its it s corresponding weighing. The assessment for the ergonomic performance of each individual described element of the problem area is calculated by adding up in a vertical direction the criteria assessments provided in column 6. The sum is then entered into box 2 (fig. 28) against the “Frequency of ergonomic relation ” criterion. The “Frequency of ergonomic relation ” criterion is included here only to provide for trustworthy calculation of the general ergonomic performance assessment for the defined problem area. Therefore, columns “Current Condition” and “Assessment” are not filled in for this particular criterion and only the “ Weighing ” column (1 - fig. 18) is filled in. In other words, this only serves to provide weighing to the final assessment for each individual element of the identified problem area when its general assessment (for the overall Problem Area) is made. The weighings of the “ Frequency of the ergonomic relation ” criterion also vary within 0 – 1. Hence, the final assessment of each element is calculated by multiplying the sum indicated in box 2 (fig. 28) by the weighing of the “Frequency of ergonomic relations ” criterion (1 - fig. 28) and entering this result in box 3 (fig. 28). Figure 28 is a visual indication of the process of drawing the final assessment for each individual element (i.e. for each separate section in the general table). The general assessment of ergonomic performance of the product is derived as the sum total of all final assessment scores (provided in box 3, Figure 28) for each individual element of the problem area.
9.4 RESULTS Testing of current machine version The test thus designed is used to assess the ergonomic performance characteristics of the bench drilling machine A15 in its current design version. The purpose is to generate an ergonomic performance assessment of the pre-defined problem area. Table 1 Test Crite Criteria ria
Boundary Boun dary Condi Conditions tions
Current Curre nt Cond Condition ition
Assessment Asses sment
Weight Weig ht
Assessmen Asses sment* t*
Element 1: Handle of the drill head cover
Ergonomic dimensions: - spherical handle dia Ergonomic Ergonomic characteristics of shape Required effort Functionality Frequency of establishing functional relation
35 ÷ 40 mm 0 ÷ 100 0.12 ÷ 25 Nm 0 ÷ 100
18 mm
1.00 0.50 0.70 0.50
60.00 25.00 70.00 37.50
0.75
192.50
Element 1: Final Assessment =
144.375
0.24 Nm
60 50 100 75
0÷1 Element 2: Cover
Colour solution Weight of cover Ergonomic Ergonomic characteristics of shape Functionality Frequency of establishing functional relation
blu-green 0.65 ÷ 69 N 0 ÷ 100 0 ÷ 100 0÷1
white 12 N
25 100 60 75
0.45 1.00 0.50 0.50
11.25 100.00 30.00 37.50
0.75
178.75
Element 2: Final Assessment =
134.063
43
Element 3&4: Handle levers and ball handles on them and Clash inbetween levers & the drilling head
Ergonomic dimensions: - spherical handle dia - distance between feed handle and cover Ergonomic Ergonomic characteristics of shape Required effort Functionality Frequency of establishing functional relation
35 – 50 mm min. 53 mm (=33+20) 0 ÷ 100% max. 72Nm 0 ÷ 100%
25 35
1.00 1.00 0.50 0.70 0.50
50.00 20.00 45.00 49.00 30.00
1.00
194.00
Element 3&4: Final Assessment =
194.00
45.7Nm
50 20 90 70 60
0÷1 Element 5: Transparent protective shield
Ergonomic dimensions: - width - height Ergonomic Ergonomic characteristics of rotation Functionality
150 ÷ 180 mm 120 ÷ 150 mm 0 ÷ 100% 0 ÷ 100%
Frequency of establishing functional relation
150 mm 120 mm
100 100 40 100
0.50 0.50 0.50 0.85
50.00 50.00 20.00 85.00
0.80
205.00
Element 5: Final Assessment =
164.00
0÷1
Element 6: Handle lever of the table lifting mechanism
Ergonomic dimensions: - handle dia - distance between handle and table Ergonomic Ergonomic characteristics of shape Required effort Functionality Frequency of establishing functional relation
25 – 45 mm min. 53 mm (=33+20) 0 ÷ 100% max. 90Nm 0 ÷ 100%
35 60
0.80 0.80 0.50 0.70 0.50
80.00 68.00 50.00 70.00 50.00
0.75
318
Element 6: Final Assessment =
238.50
Final Assessment 1 + 2 + 3&4 + 5 + 6 =
874.938
9Nm
100 85 100 100 100
0÷1
General assessment of the product =
The extent of compliance of individual machine elements which are of critical significance to the human factor was expressed in a quantified assessment of 874.938 scores (with a maximum possible score of 1122.438). The analysis of results compared to the maximum possible number of scores (the ideal variant) allowed us to identify the field and direction where design modifications are to be implemented in order to improve the ergonomic performance of individual elements and the machine as a whole. Consolidation of problem definition and idea generation was also carried out to improve overall ergonomic performance of the machine.
Design solutions Following the analyses carried out and the idea generation process we proceeded with the synthesis of specific design solutions observing to an optimum extent the ergonomic requirements for individual elements. 1. A single feed lever is now provided and its shape is altered, as well. The handle lever will have a maximum angle of rotation of 90° for a maximum drilling depth of 80mm (fig. 29). Its original position is vertical + 10°. This is much more convenient and in compliance with the psycho-motor reactions of the operator,
Figure 29
44
since when he moves the lever the muscles of the biceps of his right hand contract and this is the strongest possible movement of the hand. Moreover, the upper position allows for some rest of the fingers and the palm using the vertical lever with handle as a kind of support, thus allowing the hand to relax when no feed is required. This is exactly why these + 10 ° are added – to change the direction of the load opposite to the applied load [18]. The change in the shape of the lever (1 - fig. 31) results in moving the cover 60mm away and expanding the safety area for the hand. The longer lever also results in a reduction of the required effort. The design changes resulting from all these alterations are: increased pitch diameter of the gear shaft, which transmits movement to the quill; and move the shaft 22 mm back. These are technically feasible solutions with the current design of the drilling head. 2. Alterations in the size and shape of the feed lever handle. The diameter of the handle will be increased to ∅48mm. The shape is kept practically the same with the only alteration in the smoothness of transition between its spherical and conical/cylindrical section, as illustrated in fig. 30. As a result of this a larger contact area is ensured between the palm and the handle. The shape of elongation in the bottom section of the sphere follows the curve of the finger tips and improves the convenience and stability of the grip; fingers “fit into their position” [19].
48 25
Sha rp
So ft
Wa s
No w Figure 30
3. The cover looks symmetrical when viewed from the face. The movement shut-off sensor for “cover open” position is moved back and into the drilling head and this allows us to achieve 60 3 symmetry of the drilling 2 head and hence, the machine cover (2 - fig. 31). This alteration is also technically feasible. 4. Alteration in the overall concept for the handle used to open the cover. The handle is cast into the cover (3 – fig. 31). This improves rigidity. The area of contact is also increased several times. The risk of slippage is avoided when the cover is opened beyond 45 °. The handle is cast rectangular in shape and along the length of the cover. This results in
4
1
Figure 31
45
the following positive effects: - In a purely psycho-physiological aspect, it is not so hard for the operator to notice notice its location in his peripheral sight [20]. - In an aesthetic aspect aspect the new handle handle is a far better match of both the size and shape of the cover. When viewed crosswise, the shape of the handle features smooth rounded edges, sufficient size (>20mm) and convenient for the fingers of the hand. 5. New way of turning the Transparent protective shield. The shape of the shield is left unchanged and only the design solution which provides for its rotation is modified. This is technically simple and feasible. The following movements are required: - Slight lift of the shield (10 mm) and it can be rotated to provide access to the operational area of the machine. - Slight turn in the opposite direction and the spring retracts it into the previous lower position. 6. The colour of the machine is changed. White colour is replaced by the far more suitable and recommended blue colour. The cover is painted in darker shades of blue to achieve contrast and give an indication of its functional purpose – “colour distinction of functions” [21]. Thus, all drawbacks of the previously adopted colour solution are avoided. Figure 31 illustrates the final appearance appearance of the machine machine after all alterations are complete. Now it can be subjected to the same test which was applied to the old version.
9.5 TESTING THE NEW MACHINE VARIANT The altered design of the machine is assessed based on the same test. The only difference is the name of the first element and its boundary conditions, as now it features different shape. Table 2 Test Crite Criteria ria
Boundary Boun dary Condi Conditions tions
Current Curre nt Cond Condition ition
Assessment Asses sment
Weight Weig ht
Assessmen Asses sment* t*
Element 1: Handle of the drill head cover
Ergonomic dimensions: - spherical handle dia Ergonomic Ergonomic characteristics of shape Required effort Functionality Frequency of establishing functional relation
20 ÷ 30 mm 0 ÷ 100 0.12 ÷ 25 Nm 0 ÷ 100
30 mm
1.00 0.50 0.70 0.50
100.00 42.50 70.00 42.50
0.75
255.00
Element 1: Final Assessment =
191.25
0.24 Nm
100 85 100 85
0÷1 Element 2: Cover
Colour solution Weight of cover Ergonomic Ergonomic characteristics of shape Functionality Frequency of establishing functional relation
blu-green 0.65 ÷ 69 N 0 ÷ 100 0 ÷ 100 0÷1
blu 12 N
25 100 90 90
0.45 1.00 0.50 0.50
45.00 100.00 45.00 45.00
0.75
235.00
Element 2: Final Assessment =
176.25
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Element 3&4: Handle levers and ball handles on them and Clash in between levers & the drilling head
Ergonomic dimensions: - spherical handle dia - distance between feed handle and cover Ergonomic Ergonomic characteristics of shape Required effort Functionality
35 – 50 mm min. 53 mm (=33+20) 0 ÷ 100% max. 72Nm 0 ÷ 100%
Frequency of establishing functional relation
48 60
1.00 1.00 0.50 0.70 0.50
100.00 95.00 50.00 52.50 50.00
1.00
347.50
Element 3&4: Final Assessment =
347.50
39Nm
100 95 100 75 100
0÷1 Element 5: Transparent protective shield
Ergonomic dimensions: - width - height Ergonomic Ergonomic characteristics of rotation Functionality
150 ÷ 180 mm 120 ÷ 150 mm 0 ÷ 100% 0 ÷ 100%
Frequency of establishing functional relation
150 mm 120 mm
100 100 100 100
0.50 0.50 0.50 0.85
50.00 50.00 50.00 85.00
0.80
235.00
Element 5: Final Assessment =
188.00
0÷1
Element 6: Handle lever of the table lifting mechanism
Ergonomic dimensions: - handle dia - distance between handle and table Ergonomic Ergonomic characteristics of shape Required effort Functionality
25 – 45 mm min. 53 mm (=33+20) 0 ÷ 100% max. 90Nm 0 ÷ 100%
Frequency of establishing functional relation
35 60
0.80 0.80 0.50 0.70 0.50
80.00 68.00 50.00 70.00 50.00
0.75
318.00
Element 6: Final Assessment =
238.50
Final Assessment 1 + 2 + 3&4 + 5 + 6 =
1141.50
9Nm
100 85 100 100 100
0÷1
General assessment of the product =
9.6 ANALYSIS OF RESULTS The results from the test (table 1 and table 2) were used to draw a comparative analysis (table 3) between the new version, old version and the ideal variant (column E where all scores are maximum): Table 3
Elements
New variant
Old variant
Improvement %
Ideal variant
% of the ideal variant
B
C
D = B/C*100%
E
F = B/E*100%
Element 1
191.25
144.375
132.4%
202.50
94.44 %
Element 2
176.25
134.063
131.4%
183.75
95.91 %
Elements 3&4
347.50
194.00
179.1%
370.00
93.91%
Element 5
188.00
164.00
114.6%
188.00
100 %
Element 6
238.50
238.50
0%
247.50
96.36%
General assessment
1141.50
874. 938
130.4%
1191.75
95.78 %
A
The table also includes the coefficient of improvement of the new variant compared to the old one (column D = B/C*100%), as well as the percentage improvement of the new version relative to the ideal variant (column F = B/E*100%). Values are especially high – the overall improvement of ergonomic characteristics of the problem area of the
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product is improved by 30.4% relative to the old version and reaches up to 95.78% of the ideal assessment score. This is a very good result. However, the fact that the new version does not achieve 100% of the ideal level does not imply that the modified version is not sufficiently successful. We must remember here that the subject of the study here is the currently existing machine and this means that alterations are introduced observing a number of other requirements: technical, economic, etc. It is not a matter of designing a new product. Therefore, some of the decisions are made giving priority to the economic efficiency or observing available technical capabilities (and not necessarily achieving 100% ergonomic performance). For example, part of the insufficient percentage required to achieve the maximum value for elements 3 & 4 is due to the “required effort” criterion where automatic feeding is economically unjustified. However, the score of 93.91% achieved for for this particular element is rather sufficient and ensures excellent characteristics for this specific type and size of machine. Complete match, a 100% achievement of the ideal version, is observed for element 5. The next highest match percentage is for element 6 (96.36%) where no alterations are introduced since the result is originally high. High match rates are also observed for the rest of the elements within the problem area – above 90% as an average.
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9.7 CONCLUSIONS
The suggested modified version of the bench-drilling machine A15 features 30.4% higher general ergonomic performance compared to the old variant; The overall general ergonomic performance achieves an exceptionally high percentage of match with the ideal variant, 95.78%; Causes for failure to achieve a 100% match with the ideal variant in some of the elements are purely objective; they are of economic and technical nature; The highest improvement in ergonomic performance compared to the old version is achieved for element 3&4 – 79.1%; Improved are both ergonomic and aesthetic characteristics of the machine.
The final conclusion after all said so far is that the suggested new version can be assessed as very good from an ergonomic viewpoint. Figure 32 illustrates the final comparison between the old and the new machine:
Figure 32
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REFERENCES [1] Christ RE. 1995. Review and analysis of colour coding research for machine tools. Human Factors, 17:542-570. [2] Clarke TS, Corlett EN. 1984. The ergonomics of Workplaces and Machines: a Design Manal. Taylor and Francis, London: 57-63. [3] Warr P(ed.). 1997. Psychology at work, 6 th edition. Penguin Books, New York:260293. [4] Eklund JAE, Frievalds A. 1993. Machine Tools for the 1990s. Applied Ergonomics, 24:146-147. [5] Friedmann K. 1994. The effect of adding symbols to written warning labels on Machine Tools. Human Factors, 30:507-515. [6] Kline TJ, Ghali LM, Kline DW, Brown S. 2000. Visibility distance of Machine Tool signs among young, middle aged and older industrial workers: Icons are better than text. Human Factors, 30:609-619. [7] Khaleque A. 1981. Job Satisfaction, perceived effort and heart rate in light industrial work. Ergonomics, 24:735-742. [8] Marras WS, Kim JY. 1993. Anthropometry of industrial populations. Ergonomics, 36:371-378. [9] Norman DA. 1994. Stages and levels in human-machine interaction. International Journal of Man-Machine studies, 21:365-375. [10] Pheasant ST, O’Neill D. 1975. Performance in gripping and turning: A study in hand/handle effectiveness. Applied Ergonomics, 6:205-208. [11] Pope MH, Bevins T, David RPT, Wilder G, Frymower JW. 1995. The relationship between anthropometric, postural, muscular and mobility characteristics of males ages 18-55. Spine, 10:644-648. [12] Rys M, Konz S. 1998. Standing. Ergonomics, 37:677-687. [13] Singleton WT. 1992. Man-Machine Systems. Penguin, London. [14] Snook SH, Ciriello VM. 2001. The design of manual handling tasks: Revised ta bles of maximum acceptable weights and forces. Ergonomics, 34:1197-1213. [15] Wiker SF, Chaffin DB, Langolf GD. 1999. Shoulder posture and localized muscle fatique and discomfort. Ergonomics, 32:211-237. [16] H. Yoshikawa, T. Nakagawa, Y. Nakatani, T. Furuta, A. Hasegawa. Development of an analysis support system for man-machine system design information. Control Engineering Practice, Volume 5, Issue 3, March 1997, Pages 417-425. [17] C.B. Gibbs. Methodology of gain studies in man-machine systems Psychological Bulletin, Volume 60, Issue 2, March Marc h 1963, Pages 147-151. [18] Gunnar Johannsen, Alexander H. Levis, Henk G. Stassen. Theoretical problems in man-machine systems and their experimental validation. Automatica, Volume 30, Issue 2, February 1994, Pages 217-231.
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[19] William B. Rouse, William J. Cody. On the design of man-machine systems Principles, practices and prospects. Automatica, Volume 24, Issue 2, March 1988, Pages 227-238. [20] F. Margulies, H. Zemanek. Man's role in man-machine systems Automatica, Volume 19, Issue 6, November 1983, Pages 677-683. [21] V. Sree Krishna Chaitanya. Stability analysis of structurally unstable man–machine system involving time delays. Nonlinear Analysis: Real World Applications, Volume 6, Issue 5, December 2005, Pages 845-857.
E N I H N C A G I M S E N D A L L I M S R U T D H N E H E M C H T E N H R E T I B I U Q A W E E R R E O C F N C T A N S I L A E T P M M R C I O O M C F O N R E N I P O T G N E R M E E N V A O R P M I
The present book describes elements of the manufacturing environment, machine Tools -Metal Cutting. The objective is to identify and evaluate the role of the human factor in this particular environment. The result will be an improved level of compliance of this environment with human anthropometric and psychophysiological characteristics and increased confidence and satisfaction. The product to be described and improved in terms of ergonomic characteristics in the book is a bench drilling machine A15, by the Alzmetall Compa ny ny.. Available Available on the market mar ket of a 15m m size, the machine is designed des igned for drilling drilling through and an d blind holes and machining holes made in forgings, castings, and semi finished products. The objectives of the presented study have been achieved using analytical methods and subsequent results synthesis. The method will aim at identifying the ergonomic relations in the HumanMachine-Environment system, making a comparative analysis and subsequent generation and possible designn solutions. For the purposes of the present project we selected the metal cutting machines as the field of studying the interrelations between the human factor and manufacturing ma nufacturing environment. The aim of the book is to show the position of the human factor in this system and it will be achieved by determining the ergonomic relations between humans and environment. These relations characterise specific locations and ways of interaction between the human factor and the components of the working environment. Therefore, we will adopt the term “identifying the ergonomic relations in the system”.
Miltia d is A. Bo Bo b o ulo s, Ph.D Ph.D.. Dip. Eng. Lazar Peshev
