1. INTRODUCTION
The objective of this experiment is to investigate the kinematics motion of a Crank and Slotted Lever Quick Return mechanism. The investigation is to show that it is indeed a quick return mechanism and to evaluate the increase in efficiency that this would offer if applied to a machine tool. A mechanism is a simplified model, usually in the form of a line diagram, which is used to reproduce the motion occurring in a machine. The purpose of this reproduction is to enable the nature of the machine. The purpose of this reproduction is to enable the nature of the motion to be investigated without the encumbrance of the various solid bodies which form the machine elements the various parts of the mechanism are c alled links or elements. Where two links are in Contact and a relative motion is possible, then they are known as a pair. An arbitrary set of a links which form a closed chain that is capable of relative motion, and that can be made into a rigid structure by the addition of a single link, is known as a kinematics chain. To form a mechanism from a kinematics chain one of the links must be fixed. However as any of the links can be fixed, it follows that there are as many mechanism as there are links in the chain. The technique obtaining different mechanism by fixing the various links in turn is known as inversion.
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2.WORKING PRINCIPLE Kinematics Pairs
The relative motion between two links of a pair can take different form. Three types of a pairs are known as lower pairs and these are the frequently occurring ones: Sliding: such as occurs between a piston and a cylinder Turning : such as occurs with a wheel on an axle Screw motion : such as occurs between a nut and a bolt All other cases are considered to be combinations of sliding and rolling are called higher pairs. Strictly screw motion is a higher pair as it combines turning and sliding. Slider – Slider – Crank Crank Mechanism The slider- crank mechanism is well known as the basis of a reciprocating engine. As shown in the diagram below it consists of three turning pairs and one sliding pair
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3.C RANK AND SLOTTED LINK MECHANISM
It finds application in shaping machine, slotting machine, rotary internal combustion engine. In this mechanism link corresponding to the connecting rod (AC) is fixed. The crank CB (in the fig below) revolves about the fixed center C. A slider attached to the crank pin at B slides along the slotted lever AP. This makes the slotted lever oscillate about the pivoted point A A short link PQ transmits the motion from AP to the arm which reciprocates with the tool along the line of stroke.
We see that the angle β made by the forward or cutting stroke is greater than the angle α described by the return stroke. Hence the name quick return mechanism... Time of α Time of return stroke
cutting
stroke =
β
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In this mechanism the ram is actuated by gear drives associated with electric motor. First, the electric motor drives the pinion gear. Next, the pinion gear drives the bull gear which rotates in opposite direction due to external gear meshing. A radial slide is provided on the bull gear. A sliding block is assembled on this slide. The block can be positioned in radial direction by rotating the stroke adjustment screw.
The sliding block has a crank pin. A rocker arm is freely fitted to this crank pin. The rocker arm sliding block slides in the slot provided in the rocker arm called as slotted link. The upper end has fork which is connected to the ram block by a pin while the bottom end of the rocker arm is pivoted. When the pinion gear rotates along with the bull gear, the crank will also rotate. Due to this, the rocker arm sliding block also rotates in the same circle. Simultaneously, the sliding block slides up and down in the slot. This movement is transmitted to the ram which reciprocates. Hence, the rotary motion is converted in reciprocating motion.
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5.WITHWORTH QUICK RETURN MECHANISM
The shaft of an electric motor drives the pinion which rotates the bull gear. The bull gear has a crank pinion. A sliding block slides over this crank pin and slides inside the slot of a crank plate. A connecting rod connects the pin at one end and ram at the other end.
When the pinion rotates, the bull gear is also rotated along with the crank pin. At the same time, the sliding block slides on the slot provided on the crank plate. This makes the ram to move up and down by the connecting rod.
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The two important cases in this mechanism are 1. At an angle of the bull gear rotates in anti-clockwise direction and the ram moves in forward direction. 2. When the bull gear rotates further in the same direction at an angle of the return stroke will take place. Here the angle is lesser than angle . So, the time taken for the return stroke is reduced.
APPARATUS
PROCEDURES 1. Set the crank so that the pointer is at zero on the scale. Note the crosshead position, x. 2. Rotate the crank by 10° increments and for every increment, note the corresponding crosshead position, x.
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RESULTS 1. Find an expression for theoretical distance (x) in term of θ. 2. Plot a graph of experimental crosshead position, x, versus crank angle. 3. Plot on the same graph, a graph of theoretical crosshead position versus crank angle. 4. On both graphs, show the return and cutting stroke. 5. Plot a graph of crosshead velocity versus crank angle. On the graph, show the return and cutting stroke.
6. Pneumatic Actuator (Air Cylinder) Basics
There are thousands of industrial applications that require a linear motion during their operation sequence. One of the simplest and most cost effective ways to accomplish this is with a pneumatic actuator. Pneumatic actuators are also very clean operating because the operating fluid is a gas, which prevents leakage from dripping and contaminating the surroundings. This section will discuss the basic construction and function of a pneumatic actuator, the relationship with a fluid power system and the selection guidelines for pneumatic actuators or air cylinders. Basic Styles
Pneumatic actuators convert compressed air into rotary or linear motion. There are many styles of pneumatic actuators: diaphragm cylinders, rodless cylinders, telescoping cylinders and through-rod cylinders.
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he most popular style of pneumatic actuator consists of a piston and rod moving inside a closed cylinder. Even so, there is a large variety of construction techniques and materials to fit a wide range of applications and user preferences. Body materials can be aluminum, steel, stainless steel and even certain polymers. Construction can be either non-repairable or repairable. This actuator style can be sub-divided into two types based on the operating principle: single acting and double acting. Single-acting cylinders have a single port to allow compressed air to enter the cylinder to move the piston to the desired position. They use an internal spring or sometimes simply gravity to return the piston to the “home” position when the air pressure is removed. Single-acting cylinders are a good choice when work is done only in one direction such as lifting an object or pressing an object into another object. Double-acting cylinders have a port at each end and move the piston forward and back by alternating the port that receives the high pressure air. This uses about twice as much energy as a single-acting cylinder, but is necessary when a load must be moved in both directions such as opening and closing a gate.
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In a typical application, the actuator body is connected to a support frame and the end of the rod is connected to a machine element that is to be moved. A control valve is used to direct compressed air into the extend port while opening the retract port to atmosphere. The difference in pressure on the two sides of the piston results in a force equal to the pressure differential multiplied by the area of the piston. If the load connected to the rod is less than the resultant force, the piston and rod will extend and move the machine element. Changing the valve to direct compressed air to the retract port while opening the extend port to atmosphere will cause the cylinder assembly to retract back to the “home” position.
Pneumatic actuators are at the working end of a fluid power system. Upstream of these units, which produce the visible work of moving a load, there are compressors, filters, pressure regulators, lubricators, control valves and flow controls. Connecting all of these together is a network of piping or tubing (either rigid or flexible) and fittings.
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Pressure and flow requirements of the actuators in a system must be taken into account when selecting these upstream system components to ensure the desired performance. Undersized upstream components can cause a pneumatic actuator to perform poorly or even make it unable to move its load at all.
Force
The above Figure shows a basic system to power and control a pneumatic actuator. When selecting an actuator it is important to properly match the cylinder to the job.
A typical pneumatic system configuration is shown in Figure 4C. The theoretical force available in the actuator is the piston area multiplied by the supplied air pressure. Spring force must be subtracted from this value for single-acting cylinders. The actual force of the actuator will be 320 percent less due to pressure losses in the system. A good rule to use when sizing an actuator is to select an actuator that has about 25% more force available than needed for the job, and the following formula can help with determining size requirements. Take a look at our Interactive Cylinder Bore Calculator here.
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Speed
When the cylinder force (F) is known, the bore diameter(d) can be found by the above formula. F is the force required (lbs) and P is the supply pressure (psi). Stroke length is determined by the required travel of the machine element driven by the actuator. The speed at which the cylinder can move a load is directly related to the rate that the compressed air can flow through the pneumatic system to the piston to make it move. This can often be a little tricky to calculate, since as the flow rate increases, system resistance (basically friction of the air moving through pipes and components) will increase in a non-linear fashion. The result is a larger pressure drop from the supply (air compressor) to the cylinder. When the pressure drop is so large that the available pressure at the cylinder cannot move the load, the cylinder will stall. When speed is critical to a machine operation, it may require testing two or three combinations of valves, tubing and cylinders to get the desired performance. Let’s look at a practical example of how you would figure out your requirements. See our “Rules of Thumb” for fast cylinder action along with our Interactive Theoretical Speed Table here.
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For example:
It is desired to move a 200lb load 12 inches at a rate of 20 cycles per minute. Using a 2” bore cylinder, about 64 psi is required to move the load. Adding 25% gives an operating pressure of 80 psi. At the desired cycle rate and using 1/4” OD tubing (0.156” ID), pressure losses in the tubing a re about 1.5 psi per foot. It can be seen that the tubing run total (extend and retract lines) needs to be less than 10 feet or else the pressure losses due to friction will drop the available pressure at the cylinder below 64 psi and the cylinder will stall. Once the cylinder stops moving however, the friction losses go away and the pressure builds back up to 80 psi. This situation results in a jerky motion of the cylinder as it moves the load. Several factors could overcome this problem:
System pressure can be increased to overcome friction losses
Larger tubing can be used to reduce friction losses
Different size cylinder could be tried that will reduce the flow
Mounting
The final bit of basic selection criteria is the cylinder mounting arrangement. There are many different configurations available from various manufacturers. The more common ones include rigid nose or tail mount, trunnion mount, rear pivot mount and foot mount. A study of the machine motion required usually will show which mounting configuration is the best choice.
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Once the basic actuator size and configuration is known, other options such as end-of-stroke cushions, magnetic piston (for position detection switches) or special seals should be considered when making the final selection.
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How Pneumatic Cylinder Work
The pneumatic cylinder is a device that has been mechanically engineered to produce force (in linear motion) from compressed gas. They are also k nown as air cylinders.
The air cylinders come in various appearances and sizes and are meant to perform different functions depending on the rising needs of the market. Depending on your ready market, you can choose to go for Single-acting Cylinder
This type of air cylinder is quite small in size as compared to the other types. They create driving linear force (precisely &lout’) from the pressure imparted by the compressed air by the pist on which then springs back to the original position. This type of air cylinder will be best suitable for the customers who need little application since it has a limited extension due to the small space for compressed air.
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Double acting cylinders
With expanded application, a customer can consider buying this machine. It has two ports that enable it to perform both extend and retract strokes. Its stroke length is also not limited a fact that presents the double acting cylinder a better choice of pneumatic cylinder that should never miss in your hardware shop stock. 3) Multiple stage telescoping cylinder
As the name suggests, it is a combination of both sing-acting cylinder and the double acting cylinder in performance capability. With both piston rod nested with series of hollow stages in an increasing diameters; this machine allows notable longer strokes. lt is the best tool for customers who deal with applications that have minimal side loading.These are the main types of air cylinders that are well known and widely used whose demands suit the market. However, there are other types too.Why should you stock the pneumatic cylinders? The air cylinders work with the basic physics principles which state that force produced by the cylinder is directly proportional to the surface area of the piston acting on it with other factors like the friction and the turbulence kept constant. This theoretically implies that the machine performs reliably between 50% and 70%. Their extensive usage makes them more marketable since. Many engineers choose to use the pneumatic cylinder since they are cleaner, produce less noise,and they do not need large space for fluid storage.ii. In addition, pneumatic cylinders are also the most preferred in the market since their operating fluid is a gas; and by the fact that gases do not drip during leakages keeps the operating environment cleaner. The air cylinders are also worthy in the stock since their choice of use is wider depending on the job specification, the level of loads, temperature, and stroke length needed. Air cylinder installed with quick exhaust valves increases the air cylinder cycle. This makes your stock more marketable and allows quick replenishing of stock as these will be the most preferred machines. When going to shop for the pneumatic cylinders, the customer is often driven by the quality of the product. As an entrepreneur of air cylinders, you need to win the trust of your customer by stocking standard air cylinders that have a wide range of bone sizes of 16 and 18 inches of bore sizes and metric sizes respectively.
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The cylinders must also have many mounting configurations and standard switch capability that relies on the location of the application and mach-inability of the air cylinder. For the double-acting pneumatic cylinders with two pressure setup, you can consider stocking the types with air pressure and exhaust valve installed which during operation leads to a higher pressure production for the work force and low pressure for return force. This modification systematically reduces the operational cost; features that have made air cylinders more marketable as such are the machines that can be multipurpose. When operating with the pneumatic cylinder, customers are often pissed up by the noise it produces from the impacting air cylinder end caps. The noise is not only irritating to the user but also harmful to the machine itself and this could be a turnoff to the operators. Therefore to make small but significant changes to your models in stock will be to your business’ advantage. You can either add to your stock the internal cushions
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or customize your appliances by fixing the cushions that will add to the stroke time and reduce noise produced by the stocked air cylinders. Cushions are always adjustable hence are less expensive. This will significantly increase the demand from your customers as well as making the air cylinder more suitable for use even to customers in noise-restricted areas. In your stocking, you can also consider having a continuous feedback sensor and closed-loop valve controller incorporated air cylinders in stock thus making them both fully extended and fully retracted. These machines will effectively provide linear electric drives a quality looked for in the market. The features air cylinders definitely present uniqueness an increased demand for your stoked machines that will make them highly competitive in the market. Why the pneumatic cylinder suits a wider market
The varied sizes of the gadget with the ability to perform various jobs that vary from picking very small objects to larger ones make them more applicable for industrial use widely in different fields. You will never again suffer a dead-stock with these kinds of flexible air cylinders since they allow the operator to have full control over it as it follow a commanded motion or index to various adjustable locations of the operator’s choice.
ln addition to that, the design of air cylinder suits the vast needs of your customers in terms of configuration and scope of application. Therefore, your clients will comfortably offer to get the exact value for their money. The durability of a machine is also one of the key driving force to many customers and having air cylinder stock with command start and stop points of motion less than the full stroke of a cylinder makes the pneumatic cylinders more durable. With these features, modifications and broad application of pneumatic cylinder directly translate into their demand in the market with assured moving-stock.
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7. Working Principle Of Air Compressor
Air compressors have relatively simple design and can be sized all the way from the extremely powerful to ones that can just drive small tools. They have few parts and hence last for a long time with little maintenance. The factors make them drivers of choice from heavy equipment on manufacturing shop floors, to cleaning areas in gas stations and now, inside homes and small garages as parts of handy gadgets.
An air compressor works by transforming electrical energy in to kinetic energy in the form of air that is held in a highly compressed space before sudden release. The energy released when the compressed air is let out can be used for inflation, cleaning under pressure, turning, generating torque, driving or other similar movement by force.
The principle of an air compressor’s functioning is like that of an internal combustion unit. A crankshaft moves a piston through a connecting rod, in a linear fashion along the length of a cylinder in which it fits snugly. Air is drawn in through an open valve as the piston moves upwards, providing ample space for a high volume of air. The valve closes and the piston moves down, compressing the air. The latter has kinetic energy as it gains tremendous pressure because of the restricted space in to which it has been forced. The valve opens again to release the energy.
Cylinders may be placed in series, so that the compressed air is fed to an intake where it is compressed further. The pressure goes up further and hence the power is increased in proportion. All air compressors must have back up systems to release extra pressure in the event of a malfunction in the valve mechanism. This is required to prevent an accident such as in an explosion.
The efficiency of air compression depends on air temperature, atmospheric pressure and relative humidity. The rating of an air compressor therefore depends on ambient conditions. This aspect should be taken in to account if an air compressor is used in very cold weather, very wet weather or at an high altitude.
Oil is used to lubricate the piston as it moves inside the cylinder. Rings act as seals to reduce the amount of oil that can mix with the compressed air. Some oil contamination, especially in atomized form, will inevitably escape ring seals and hence a more secure oil containment design is required in case the compressed air energy source has to be completely free of oil. Painting and other functions related to finishing a surface have this kind of requirement as even a faint oil trace can affect appearance. 19
Air compressors have relatively few parts and hence require little maintenance. They last for years and are versatile and compact as well. This is why new uses for air compressors keep surfacing so many years after the first unit was built. Some models have a second cylinder and sizes can be adjusted at the design stage to increase the range of applications and uses.
Single and Dual Cylinder Versions
In general, compressors will have one or two-cylinder versions to ensure they meet tool requirements. For homeowners and independent contractors, 2 cylinder models operate very similarly to 1-cylinder version. The only difference is that there are 2 strokes per revolution. Compressors also use a pressure switch to make the motor stop when tank pressure goes to a certain limit, around 120 PSI for single stage units. The air line has a regulator which is set to be in accord with the PSI needs of whatever tool you want to use. Gauges on the tank will tell you how much pressure there is, and another gauge will motor air line pressure. Oil Lubrication
A lot of piston compressors have oil lubrication – essentially an oil bath that will lubricate the inner workings of the unit, including the cylinders and the bearings. Pistons have special rings, which contain the compressed air over the piston to keep the oil separate from the air.
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Compressor Power
Determining how much power the compressor has is done through motor horsepower. You also need to know the volume air that gets delivered in cubic feet per minute, known as the CFM. Atmospheric pressure determines just how fast the air will move into the cylinder, so CFM can change a bit. It is depending on the humidity of the air and what the current temperature is. So standard CFM will start at 68 degrees with 36 percent humidity, and as the pressure goes down, the SCFM goes up. Identifying Parts and Size
The pump is generally metal and has fins that come out on the side or the top. Smaller compressors also have pressure switches, which turn the unit on and off. If it goes below a certain level of air in the tank, it will come on and rebuild the pressure in the tank. There are basically three types of pressure delivering tanks: low pressure, which put out 150 PSI or lower, medium pressure, which put out anywhere between 151-100 PSI, and high pressure, which go over 1000 PSI. There are also rotary screw compressors and turbo compressors. Electric and Gas Compressors
You will generally find 2 different types of air compressors: electric versions or gas version. Gas and diesel powered unites will often be found in areas that can’t get easy access to electricity, and are louder, requiring exhaust gas ventilation. Electric versions are found often in production areas and garages, as well as auto shops and construction site. You will find pancake, hot dog, twin tank, and wheelbarrow style compressors. They all essentially function the same way, so as long as you know the basics, you’re all set.
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8.CONCLUSION
In this project, configuration of a modified design for the quick return mechanism is briefly introduced. This modified mechanism is a good alternative. When specially modified slotted bar is used, this mechanism gives the flexibility of variation of developed force F2 with the stroke length within certain limit. Using of class-1 lever in the mechanism is helpful to leverage the effort. Moreover proper construction would give the freedom for more than one motion simultaneously from the same mechanism which would increase productivity rat From the given dimensions of links of the quick return mechanism, time ratio has been calculated which is equal to 1.71 for constant stroke length of 520 mm. This approach will help designer to synthesize the quick return mechanism for desired stroke length. 9.REFERENCES
1. Harry H Cheng (2004), “Computer -Aided Mechanism Design”, Journal of Mechanical Engineering Science, Vol. 220, March 14. 2. Matt Campbell and Stephen S Nestinger (2004), ”Computer -Aided Design and Analysis of the Whitworth Quick Return Mechanism”, Department of Mechanical and Aeronautical Engineering, University of California Davis, CA. 3. Ron P Podhorodeski, Scott B Nokleby and Jonathan D Wittchen (2004), “Quick -Return Mechanism Design and Analysis Projects”, International Journal of Mechanical Engineering Education, Vol. 32, No. 2, pp. 100-114. 4. Wen-Hsiang Hsieh and Chia-Heng Tsai (2009), “A Study on a Novel Quick Return Mechanism”, CSME-13, E.I.C. Accession 3051, Vol. 08.
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