Analysis And Usage Of Cams And Their Followers Engineering Essay

Analysis And Usage Of Cams And Their Followers Engineering EssayA cam helper, also known as a track ally,1 is a specialized type of curler or needle bearing designed to follow cams. Cam following come in a vast array of different configurations, however the most defining characteristic is how the cam companion mounts to its mating part stud air cam pursual use a stud while the yoke style has a hole through the middle.2The first cam participator was invented and patented in 1937 by Thomas L. Robinson of the McGill Manufacturing Company.3 It replaced using just a standard bearing and bolt. The new cam following were easier to use because the stud was already included and they could also handle higher(prenominal)(prenominal) loads./CAM AND MECHANISMSA cam mechanism consists of three elements the cam, the follower (or follower system), and the frame. The follower is in direct sense of touch with the cam. The cam whitethorn be of various shapes. The follower system includes each (prenominal) of the elements to which move is imparted by the cam. This may be connected at unity time to the follower, or connected through linkages and gearing. The frame of the machine supports the bearing surfaces for the cam and for the follower.A CAM changes the input motion, which is ordinarily rotary motion (a rotating motion), to a reciprocating motion of the follower. They be found in many machines and toysWHAT IS THE CONCEPT BEHIND CAM?A CAM is a rotating machine element which gives reciprocating or oscillating motion to another element known as follower. The cam and follower has a point or delimitate intimacy constitute a higher pair or you can say that it is the mechanicl component of a machine that is utilize to transmit the motion to the another component of the machine called the follower, through a prescribed program by direct contact.The contact between them is maintained by an external force which is generally provided by the spring or sometimes by the weig ht of the follower itself ,when it is sufficient. Cam is the driver member and the follower is the driven member. The follower is in direct contact with the cam.CAM MECHANISM CONSIST OF THREE MECHANISMSCAMIt may be of many shapesFOLLOWER It includes all the elements to which motion is imparted by the cam.This may be connected directly by the cam.This may be connected directly to the follower, or connected through linkages and gearing.FRAME The frame of the machine supports the bearing surfaces for the cam and for the follower.APPLICATIONS OF CAM AND FOLLOWERSCam and follower are widely use for operating inlet and take up valve of I C locomotive.These are used in wall clock.These are used in feed mechanism of automatic lathe Machine.These are used in paper cutting machine.Used in weaving textile machineries.The cam mechanism is a versatile one. It can be designed to produce almost unmeasured types of motioning the follower.It is used to transform a rotary motion into a translating or oscillating motion.On certain occasions, it is also used to transform one translating or oscillating motion into a different translating or oscillating motion.Cams are used in a wide variety of automatic machines and instruments.The certain usuages of cam and followers that includes textile machineries, computers, printing presses, food processing machines, internal combustion engines, and countless other automatic machines, control systems and devices. The cam mechanism is indeed a very eventful component in modern mechanization.CLASSIFICATION OF CAMSBased on the physical shapeDisk or plate camsWorking of the disk cam with reciprocating follower.Working of the disc cam with oscillating follower.Cylindrical camTranslating camCLASSIFICATION OF FOLLOWES(i) Based on surface in contact(a) Knife edge follower(b) Roller follower(c) Flat go about follower(d) Spherical follower(ii) Based on type of motionOscillating followeTranslating follower(iii) Based on line of actionRadial (in li ne) follower(b) Off-set followerCams can be conveniently classified into two main groupsGroup aCams that impart motion to the follower in a categorical in line with the axis of whirling of the cam (as does a cylindrical cam).Group bCams that impart motion to the follower in a plane at 90 degrees to the axis of rotation, as with face or edge cams.Most cams fall into this category.TYPES OF CAMSEccentric camA circular cam is often called an eccentric cam becausethe axis of rotation of the cam is scratch from thegeometric center of the circular disc.Concentric discA concentric disc attached to a rotating shaft wouldhave its axis of rotation coinciding with its geometriccenter.PROFILE SHAPES OF SOME CAMSPEAR-SHAPED CAMSThese type cams are often used for controlling valves. For example, they are used on motor car camshafts to die the engine valves. Afollower controlled by a pear-shaped cam remains motionless for about half a revolution of the cam. During the time that the follower iss tationary, the cam is in a dwell period. During the other half revolution of the cam, the follower rises and then falls. As the pearshaped cam is symmetrical, the rise motion is the same as the fall motion.Edge camsIt must be appreciated that this type of cam, where the follower is in contact with the edge of the cam disc, is only capable of imparting positive motion to its follower in one direction, that is, during the rise portion of the cam movement. During the fall portion of the cam movement the follower must be maintained in contact with the cam either by the mass of the follower and itsmechanism or, more usually, by a spring. Both methods have their advantages.Box camsA groove can be milled in the face of cam discs. As the cam rotates, a follower located in the groove has its motion guided by the groove. This type of cam is called a box cam.Cylindrical camsCylindrical cams are used when motion has to be transmitted parallel to the axis of rotation of the cam. The cylindrical or barrel cam consists of a rotating cylinder with a helical (screw shaped) groove in its curvedsurface. A follower with a tapered roller end is located in the groove. As the cylinder turns, the follower moves in a straight line parallel to the axis of the rotation barrel cam.This type of cam is often used to guide thread on sewing machines, looms and fabric making machines.CIRCULAR CAMSThese cams are sometimes called eccentric cams. The cam profile is a circle. The center of rotation of the cam is often from the geometric center of the circle. The circular cam produces a smooth form of motion called a simple harmonic motion. These cams are often used to produce motion in pumps. Circular cams are often used to operate steam engine valves. As the cam is symmetrical, the rise and fall motions are the same.HEART SHAPED CAMSThis cam causes the follower to move with a uniform velocity. Heart-shaped cams are essential when the follower motion needs to be uniform or steady as, for example , in the mechanism that winds thread evenly on the bobbin of a sewing machine. A heart-shaped cam can be used for winding wire evenly on the former of a solenoid.UNIFORM ACCELERATION AND RETARDATION CAMSA cam shaped as shown controls the motion of the follower so that it moves with uniform acceleration and retardation. The follower gains and looses velocity at a constant rate. Uniform acceleration and retardation cams are used to controls the motion of linkages in complex machinery.Types of Cam FollowersThere are three types of cam followers, and since the type of follower influences the profile of the cam it is worthwhile con steadring the advantages and disadvantages of each type. The three types are the knife-edge, the roller follower and the flatfoot or mushroom follower.The Knife Edge FollowerThis is the simplest type, is not often used receivable to the rapid rate of wear. When it is adopted, it is usually for reciprocating motion, running game in slides and there is conside rable side thrust, this being a component of the thrust from the cam.The Roller FollowerThis eliminates the problem of rapid wear since the sliding power is largely replaced by a roller action. Some sliding will still take place due to the varying peripheral speed of the cam profile, due to the changing radius of the point of contact. Note also that the radial-ply tire position of the contact between the cam and the roller, relative to the follower center, will change according to whether arise or fall motion is taken place this fact has to be considered when constructing the cam profile. Again,with the roller follower, considerable side thrusts are present, a disadvantage when transaction with reciprocating motions. This side thrust will be increased when using small rollers.The Flat Foot or Mushroom FollowerThis has the advantage that the only side thrust present is that due to the friction between the follower and the cam. The problem of wear is not so great as with the knife-e dge follower, since the point of contact between the cam and follower will move across the face of the follower according to the change of shape of the cam. A trick to lessen further the fix of wear is to design thefollower to be capable of axial rotation and arrange the axis of the follower to lie to one side of the cam. Thus the contact with the cam will tend to cause rotation of the follower. The cam profile, to work with a flatfoot follower, must be convex at all parts, in order to delay the corners of the follower digging into the cam profile. The minimum cam radius should be as small as possible to minimize sliding velocity and friction.All three types of cam followers can be mountedin the following ways1) In-line with the cam center line,2) Offset from the cam center line, or3) Mounted on a swinging radial arm.CAM-VALVECAM TERMINOLOGYTrace pointA theoretical point on the follower,corresponding to the point of a fictitious knife-edge follower.It is used to generate the flip over curve.In the case of a roller follower, the tracepoint is at the center of the roller.2.Pitch curveThe path generated by the trace point at the follower isrotated about a stationary cam.3. Working curveThe working surface of a cam in contact with the follower. Forthe knife-edge follower of the plate cam, the reel curve and the working curvescoincide. In a close or grooved cam there is an inner profile and an outerworking curve.4. Pitch circleA circle from the cam center through the pitch point. Thepitch circle radius is used to calculate a cam of minimum size for a given mash topple.5. Prime circle (reference circle)The smallest circle from the cam centerthrough the pitch curve.6. Base circleThe smallest circle from the cam center through the cam profilecurve.7. Stroke or cut downThe greatest distance or angle through which the followermoves or rotates.8. Follower displacementThe position of the follower from a specific zeroor rest position (usually its the position when th e follower contacts with thebase circle of the cam) in relation to time or the rotary angle of the cam.9. Pressure angleThe angle at any point between the normal to the pitchcurve and the instantaneous direction of the follower motion. This angle isimportant in cam design because it represents the suddenness of the camprofile.Some question arises regarding cam and followersWhen is a flat faced follower preferred as compared to roller followers andwhy?Flat faced followers are preferred to roller followers where space is limitedfor eg cams with flat followers are used to operate valves of an automobile engine but in case of stationary and oil engines, roller followers are preferred because more space is available.What data is plotted on displacement diagram of cam and follower motion?AnsPlot of linear displacement i.e. lift or stroke (s) of follower (on Y axisdirection) versus angular displacement () of the cam for one rotation (on Xaxis direction)