1.0 TITLE TRANSFER STATION (AUTOMATION LAB)
2.0 PROBLEM STATEMENT
Using a transfer station, blocks are to be transferred from a magazine to a processing station. The blocks are pushed out of the ma gazine by cylinder 1A and transferred to the processing station by cylinder 2A. The piston rod of cylinder 2A may only return when the piston rod of cylinder 1A has reached the retracted end position. The magazine is monitored by means of a limit switch. If there are no more blocks in the magazine, it is not possible to start the cycle. The control is to be operated continuously and can be stopped at any time. Include any other performance enhancement of the automation system.
Figure 2.1 : Positional sketch of the transfer station
3.0 OBJECTIVES
The objective of the experiment was listed below : i.
To design and realize coordinated sequential motion control with auxiliary conditions
ii.
To enhance the performance of the transfer station with student’s creativity
4.0 INTRODUCTION (BACKGROUND & THEORY)
On an automation system one can find three families of components, which are sensors valves and actuators. An adequate technique is needed to project the logic circuit to integrate all the necessary components and execute the sequence of movements properly. For a simple direct sequence of movement an intuitive method can be used, but for indirect or more complex sequence the intuition can generate a very complicated circuit and signal mistakes. It is necessary than to use another method that can save time of the project, make a clean circuit, can eliminate occasional signal overlapping and redundant circuits.
The electro-pneumatic system can be defined as a control system for pipe organs. The air pressure, controlled by an electric current and operated by the keys of an organ console, opens and closes valves within wind chests, allowing the pipes to speak. This system also allows the console to be physically detached from the organ itself. The only connection was via an electrical cable from the console to the relay, with some early organ consoles utilizing a separate wind supply to operate combination pistons.
An electric circuit is completed when the organ key is depressed, by means of a switch connected to that key. This causes a low-voltage current to flow through a cable to the windchest, upon which a rank or multiple ranks of pipes are set. Within the chest, a small electro-magnet associated with the key that is pressed becomes energized. This causes a very small valve to open.
This, in turn, allows wind pressure to activate a bellows or "pneumatic" which operates a larger valve. This valve causes a change of air pressure within a channel that leads to all pipes of that note. A separate "stop action" system is used to control the admittance of air or "wind" into the pipes of the rank or ranks selected by the organist's selection of stops, while other ranks are "stopped" from playing. The stop action can also be an electro-pneumatic action, or may be another type of action. One of the advantages of the electro-pneumatic system is the console of an organ which uses either type of electric action is connected to the other mechanisms by an electrical cable. This makes it possible for the console to be placed in any desirable location. It also permits the console to be movable, or to be installed on a "lift", as was the practice with theater organs. For the disadvantage, the electro-pneumatic system used the large quantities of thin perishable leather, usually lambskin and sometimes requires an extensive "releathering" of the windchests every twenty-five to forty years depending upon the quality of the material used, the atmospheric conditions and the use of the organ.
Figure 4.1: The example of electro-pneumatic system
5.0 METHOD OF APPROACH
1. The displacement-step diagram was design. 2. The pneumatic and electric circuit diagram was design 3. The pneumatic and electric circuit construction has been carry out 4. The sequential motion control system was implemented and realized 5. Check and trouble shoot the sequence of the circuit. 6. The report is prepared based on this case study.
6.0 APPARATUS
Component List Description
Quantity
Double Acting Cylinder
2
5/2-way double solenoid pilot valve
2
Limit Switch
4
24 DC power supply
1
7.0 EXPERIMENTAL PROCEDURE
1. The electro-pneumatic circuit was set up in the required sequence.
2. Once the circuit has been set up, the push button is pressed to turn on the system.
3. The first limit switch is pressed. The limit is used as a sensor to sense the block that needs to be moved.
4. Once the limit switch is pressed, the sequences of cylinders were observed.
Figure 7.1 : Cylinder 1A extends first
Figure 7.2 : Cylinder 2A extends after cylinder 1A is fully extended and cylinder 1A begin to retract once cylinder 2A is fully extended.
Figure 7.3 : Cylinder 2A starts to retract when cylinder 1A is fully retracted
5. The cycle repeats every time the sensor detects the block.
8.0 RESULT AND DATA ANALYSIS
9.0 DISCUSSION OF RESULTS
Check the Sequence of the Circuit As been mentioned before, the design displacement-step of the circuit is:-
Sense object
Extend 1A
Sense object
Extend 2A
Retract 1A
Retract 2A
Sequence of operation pneumatic circuit : 1. Cylinder A is extended (A+), while cylinder B is r etracted in position. 2. When cylinder A is fully extended, then the cylinder B is started to extend (B+). Note that the cylinder A is still in that position. 3. When the cylinder B is fully extend, then the cylinder A is starting retracted. It should note that the cylinder B is still in fully extending position. 4. When cylinder A is fully retracted the cylinder B then started to retract. This operation is continuous until the transfer block or component is completely, or stop button is pressed. 5. Therefore the sequence of this circuit is 1A+, 2A+, 1A-, 2B-.
An electro-pneumatics circuit above was design to operate the mechanism of two double acting cylinders where the operation is applied at the transfer station of the conveyer system where the double acting cylinder A is extended to push the magazines from the slot to the left. Then, the double acting cylinder B will extend and push the magazines into the box. The detail sequence as follow : 1. When main supply switched on, air is supplied to the directional control valve. If main supply switch is deactivated then the air supply to the system is switched off. 2. When limit switch (L1) is in detected by block of magazines it will activate the 5/2-way double solenoid pilot valve. 5/2- way double solenoid pilot valve is control the air for the cylinder A to extend. 3. After the cylinder A is fully extended, block of magazine will touch the limit switch (L2) and it will active the 5/2- way double solenoid pilot. The 5/2- way double solenoid pilot will control air at double acting cylinder B to extend fully. It should not that double acting cylinder A still extend fully. 4. Once the cylinder B is fully extended, block will touch the limit switch (L3) in which it will activate the 5/2- way double solenoid pilot and it will control the air for the cylinder A retracted. 5. When cylinder A fully retracted, it will touch the limit switch (L4). Then the cylinder B will retract fully in the transfer station.
Limit switch (L1) detect other block and the operation or cycle will be continuous until limit switch (L1) not detect any block
From the steps, it is related to the problem that has been given which blocks need to be transferred to one station to another station by using pneumatic system. The steps are needed to satisfy the given problem so that no problems occur during the system being operated. More creative design could be implemented in order to have different kind of sequence but still fulfill the objectives.
Trouble Shoot of the Circuit
The control of pneumatic cylinders could be affected by manual, mechanical, pneumatic and electrically actuated valves. Electrical energy has certain specific advantages over all other forms of control energy. However, electrical controls in pneumatic system should not be used where there exists the possibility of hazards due to fire-borne accidents which may be caused by electrical sparks. In comparison to other types of mechanical systems, pneumatic systems are found to be less problematic. However, industrial experience shows that even best of system sometimes fails and hence need to take necessary care in order to keep the system runs at the optimum efficiency. A systematic procedure for finding and eliminating faults reduces the downtime of pneumatic systems. Faults are generally occurs by external failures of machine components and internal failures within control system. Typical problems are seal wear, internal leakage and valve seal wear.
In order to have a good and efficient pneumatic s ystem, students should:
Understand the circuit function and component symbols of the total system including the construction
Understand the port-numbering system valves
Analysis the circuit problems
Troubleshoot from bottom to top of the circuit
Component with good and well planned preventive maintenance programmed, pneumatic components are expected to last quite a long period of time without any unexpected and untoward f ailure.
10.0
CONCLUSION
The electro pneumatic system is successfully designed and the coordinate sequential motion with auxiliary conditions is realized. A new idea for the performance of the transfer station is get from the understanding the basic pneumatic system and some basic about programming controller of the circuits.
The programming of the controller does not use PLC languages, but a configuration that is simple and intuitive. With electro-pneumatic system, the programming follows the same technique that was used before to design the system, but here the designer works directly with the states or steps of the system. With a very simple machine language the designer can define all the configuration of the step using four or five bytes. It depends only on his experience to use all the resources of the controller.
The controller task is not to work in the same way as a commercial PLC but the purpose of it is to be an example of a versatile controller that is design for an specific area. Because of that, it is not possible to say which one works better; the system made with microcontroller is an alternative that works in a simple way.
11.0 RECOMMENDATION
i.
Emergency stop button
Emergency stop (E-Stop) buttons are an important safety component of many electrical circuits, especially those that control hazardous equipment such as gas pumps, moving machinery, saws, mills, and cutting tools, conveyor belts, and many other types of equipment. They are designed to allow an operator or bystander to stop the equipment in a hurry should anything go wrong.
ii.
Relay
A relay is a simple electromechanical switch made up of an electromagnet and a set of contacts. Relays are found hidden in all sorts of devices. In fact, some of the first computers ever built used relays to implement Boolean gates. For example, in this case study, relay can be used to act as a switch to control the flow of blocks. When the sensor detected the block was empty, the relay will switch off the circuit to saving electricity.
iii.
Counter
In digital logic and computing, a counter is a device which stores (and sometimes displays) the number of times a particular event or process has occurred, often in relationship to a clock signal. In practice, there are two types of counters :
Up counters, which increase (increment) in value
Down counters, which decrease (decrement) in value
For example, in this case study, we recommend that the circuit used a counter in order to count the total number of blocks transfer or used in a cycle.
iv.
Buzzer
A buzzer or beeper is an audio signaling device, which may be mechanical, electro-mechanical, or electronic. Typical uses of buzzers and beepers include alarms, timers and confirmation of user input such as a mouse click or keystroke. For example, in this case study, we also recommended to use a buzzer in order to detect t he problem that occurs in the system/circuit.
v.
Timer
A timer is a specialized type of clock. A timer can be used to control the sequence of an event or process. Whereas a stopwatch counts upwards from zero for measuring elapsed time, a timer counts down from a specified time interval, like an hourglass. Timers can be mechanical, electromechanical, electronic (quartz), or even software as all modern include digital timers of one kind or another. When the set period expires some timers simply indicate so (e.g., by an audible signal), while others operate electrical switches.
12.0 REFERENCE
i. ii.
Amit M. Rampure, Pneumatic Training Report, Mumbai S. R. Majumdar, 1996, Pneumatic Systems: Principles and Maintenance, Tata McGraw-Hill
iii.
J. widera, G. Wszołeka, W. Carvalhob, Programmable controller designed for electro-pneumatic systems, Silesian University of Technology, Department of Mechanical Engineering, Ma y 2005
