Title: Cam Jump Phenomena
Print document In order to print this document from Scribd, you'll first need to download it. Cancel
ACCORDING TO FOLLOWER MOTION
A)DWELL-RISE-DWELL B)DWELL-RISE-RETURNDWELL C)RISE-RETURN-RISE
TYPES OF CAM
Download And Print
ACCORDING TO CONSTRAINT MOTION
ACCORDING TO SHAPE
A)PRELOADED SPRING
A)FLAT/WEDGE
B)POSITIVE DRIVE
B)RADIAL
C)GRAVITY CAM
C)DISC
Print document
In order to print this document from Scribd, you'll first need to download it. Cancel
Download And Print
Aim:-To study various types of cams and follower systems and verification of cam jump phenomena. Theory:Cam follower systems are frequently used in all kinds of machines, especially in automatic machines like machine tools, printing presses, IC engines, mechanical devices, etc. A cam is a mechanical member for transmitting desired motion to a follower by direct contact. Driver is called as cam and driven member is known as follower. The cam may remain stationery or translate, oscillate or rotate whereas follower may translate or oscillate. Because of the various cam geometries and large number of cam and followers combinations, the cam is a very versatile mechanical element. Although cam and follower maybe designed for motions, path or function generation, majority of applications utilize cam and follower for function generation. The rotary motion of cam is imparted to roller follower which is oscillating. The direct contact between cam and follower is maintained due to self-weight of follower and the spring force. In most of the cases the cam is connected with the frame to form a sliding pair. The cam and follower form a three link mechanism of the higher pair type. The three links of higher pair mechanisms are:-
Print document
In order to print this document from Scribd, you'll
Cam which is the driving link and has a straight or curved contact surface. first need to download it. The follower is the driven link and it gets motion by contact with surface of the cam. The frame which is used to support the cam and guide follower when cams are Cancelscale, milling Download And Print required to produce on a large methods are used.
Types of cams:Cams may be basically classified in three ways: According to follower motion. According to shape. According to the manner of constraint of follower. According to follower motion:There are three basic types of cams classified in terms of type of follower motion. A dwell is a zero displacement of the follower during rotation of the cam. Dwell-rise-dwell-cam(DRDC):The dwelling of the cam is followed by rise and dwell period. This type of cam is widely used in machinery. This type of cam is as shown in figure (2). Dwell-rise-return-dwell-cam(DRRDC):This type has the rise and return preceded and followed by a dwell. This type of cam is shown in figure it has applications in machinery. Rise-return-rise-cam(RRRC):This type has only the rise and return contour and has no dwell. This type of cam is as shown figure (1.4).it has a limited use in industry.
Print document
In order to print this document from Scribd, you'll first need to download it. Cancel
Download And Print
According to shape:Following are the three most common cam types according to cam shapes. Wedge cam or flat cam:Wedge cam has a wedge, which in general has translation motion. The follower may either translate or oscillate. Follower is held in contact by a spring. Instead of using this shape, flat plate with a groove can be used and hence also called flat cam. The follower is held in contact by a positive drive groove and a roller. Radial or disc cam:In this type, position of follower is determined by cam axis. The follower reciprocates or oscillates in a plane at right angles to the cam. Cylindrical or barrel cam:In cylindrical cam,a cylinder which has a circumferential contour cut into a surface of rotation. The follower reciprocates or oscillates in a plane parallel to axis of cam.in cylindrical cam,followers are usually used. Cam is of positive drive type. According to the manner of constraint of follower:-
Print document
In order to print this document from Scribd, you'll
For proper performance of cam follower system, followers must be constrained to maintain first need to download it. the contact with the cam at all speeds and for all types. This is by either a preloaded compression spring or a positive drive conductor or by gravity. Preloaded spring cam:- Cancel Download And Print This type of spring cam is used for the purpose of keeping contact between cam and follower. Positive drive cam:A cylindrical cam as shown in figure and a wedge cam as shown don’t need any external force to maintain contact between follower and cam profile. Figures show yoke cam and conjugated cam which are also positive drive cams. Gravity cam:In this type, the cam rise is achieved by rising surface of the cam and return due to force of gravity or due to weight of the follower.
Types of followers:As discussed earlier, followers either reciprocate of oscillate. They may be further divided into subgroups according to: Shape of the follower. Movement of follower. Location of line movement. According to shape of the follower: Knife edge:It is simplest in construction, but very little practical use due to the fact that extreme wear of cam surface and contact surface will take place. Roller follower:The rolling motion takes place between contact surfaces and hence the rate of wear is greatly reduced. The roller action at low speed is pure rolling but as speed increases fluctuation occurs.it is widely used in cam follower system. The roller follower jams the cam in case of steep rise. Flat face mushroom follower:Here the contacting end of the follower is a perfectly flat face. The relative motion between the contact surface is largely of sliding nature.
Print document
In order to print this document from Scribd, you'll first need to download it. Cancel
Download And Print
According to movement of the follower: Reciprocating follower:In this type, the cam rotates and the follower reciprocates or translates in the guides. Oscillating follower:In this type, cam rotates and the follower rotates about the pivot. According to location of line movement: Radial follower (inline):Radial follower is also known as inline follower in which the line of action of movement of follower passes through the centre of rotation of cam. Cam jump phenomena:Theory:The jump phenomena of eccentric cam and follower in a cam and follower system, the contact between cam surface and follower are maintained by means of retaining spring. Beyond a particular speed of cam rotation, follower may lose contact with the cam because of inertia force acting on the follower. This phenomenon is known as jump phenomena. When the follower re-establishes contact with the cam, it may do so with several impact loads that can damage the surface of cam and hammering noise can be heard at this jump speed. During follower jump, transient vibrations are setup in the follower and this occurs only at high speed, highly flexible cam and follower system with jump, the cam and follower separate owing to excessively unbalanced forces exceeding. The spring force is period of negative acceleration. This is undesirable as fundamental function of cam follower system, the constraint and control of follower motion are not maintained. Also life of cam flank surface is reduced due to hammering action of follower on cam and noise is generated, which results in system vibrations. The jump phenomena cam be avoided by limiting speed of the cam. Eccentric cam follower system which is anal ysed for the jump phenomena;
Lift of follower is; y=OC-CR
Print document =e-OPcosθ =e-ecosθ……….(1)
In order to print this document from Scribd, you'll first need to download it.
Differentiating eqn 1.wrt time(t) velocity Cancel of follower Downloadis;And Print
Differentiating again;
Now consider arrangement as shown in figure. Let, m: mass of follower e: eccentricity k: spring stiffness F: contact force between cam and follower Fs: total spring force P: preload in spring ω:angular speed of cam Then from FBD, we have; Inertia force=my” (downwards) Total spring force Fs=ky(downwards) Preload in spring=P (downwards) Contact force between cam and follower=F (upwards) Thus equilibrium becomes;
Description of setup:The machine is a motorised unit consisting of cam shaft driven by a d.c. motor. The shaft runs in a double ball bearing.at the end of the camshaft, a cam can be easily mounted. The follower is properly guided in gun metal bushes, which can be suited to the cam under test. A graduated circular protractor is fitted coaxially with the shaft and a dial gauge is fitted to note the follower displacement for the angle of cam rotations. A spring is used to provide the controlling force to the system. Weights on the follower rod can be adjusted according to the requirements.an arrangement is provided to vary the speed of the camshaft. The machine is very useful for cam performance.
Print document
In order to print this document from Scribd, you'll
The machine clearly shows the effect of change of inertia state on the jump of the cam first need to download it. follower system throughout the experiment.it is used for testing various cam follower pairs like; Circular arc cam with mushroom Cancel follower. Download And Print Tangent cam with roller follower. Eccentric cam with knife edge follower.
Experiment accessories:Setup of cam and follower, dimmer stat, dial gauge and tachometer. Procedure: Select a suitable cam and follower combination. Fix the cam on the driving shaft and follower on push rod and properly tighten the check nut. Give required initial compression to the spring in order that initial compression is not lost during compression. The check nut is to be tightened against the spring seat. Choose suitable amount of weight to be added to the follower. Weights in the central hole can be inserted from the top end to push rod. A test plate for weights should be first screwed and tightened against lowermost motion. Then add weights and tighten the upper end nut. See that the knob of dimmerstat is at zero position. Now switch on the supply and increase the motor speed gradually with dimmerstat.do not operates the knob vigorously. For different weights note the speed at which jump occurs. When the jump occurs, the follower bounces on the cam surface giving audible thumping sound. Plot the graph of speed versus the weights added.
Result table:-
Sr.NO.
Weight added(kg)
N (theoretical) rpm
N (experimental) rpm
01. 02. 03. 04. 05.
Conclusion:Hence we have studied various types of cams and followers and also studied the cam jump phenomena. It was found that speed of cam jump calculated theoretically is approximately equal to experimental speed.
Print document In order to print this document from Scribd, you'll first need to download it. Cancel
Download And Print
Observations table:-
Sr.No.
Weight added (kg)
01. 02. 03. 04. 05.
Calculations:-
Stiffness of spring (k) = Eccentricity (e) = Mass of follower = For 1kg weight;
N (experimental) rpm
