Machinery's Handbook, 31st Edition
CAMS AND CAM DESIGN
2363
CAMS AND CAM DESIGN Classes of Cams.— Cams may, in general, be divided into two classes: uniform motion cams and accelerated motion cams. The uniform motion cam moves the follower at the same rate of speed from the beginning to the end of the stroke; but as the movement is started from zero to the full speed of the uniform motion and stops in the same abrupt way, there is a distinct shock at the beginning and end of the stroke, if the movement is at all rapid. In machinery working at a high rate of speed, therefore, it is important that cams are so constructed that sudden shocks are avoided when starting the motion or when reversing the direction of motion of the follower. The uniformly accelerated motion cam is suitable for moderate speeds, but it has the disadvantage of sudden changes in acceleration at the beginning, middle and end of the stroke. A cycloidal motion curve cam produces no abrupt changes in acceleration and is often used in high-speed machinery because it results in low noise, vibration and wear. The cycloidal motion displacement curve is so called because it can be generated from a cycloid which is the locus of a point of a circle rolling on a straight line. * Cam Follower Systems.— The three most used cam and follower systems are radial and offset translating roller follower, Fig. 1a and Fig. 1b; and the swinging roller follower, Fig. 1c. When the cam rotates, it imparts a translating motion to the roller followers in Fig. 1a and Fig. 1b and a swinging motion to the roller follower in Fig. 1c. The motion of the follower is, of course, dependent on the shape of the cam; and the following section on displacement diagrams explains how a favorable motion is obtained so that the cam can rotate at high speed without shock.
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Fig. 1a. Radial Translating Roller Follower
Fig. 1b. Offset Translating Roller Follower
Fig. 1c. Swinging Roller Follower
Fig. 2a. Closed-Track Cam Fig. 2b. Closed-Track Cam With Two Rollers The arrangements in Fig. 1a, Fig. 1b, and Fig. 1c show open-track cams. In Fig. 2a and Fig. 2b the roller is forced to move in a closed track. Open-track cams build smaller than * Jensen, P. W., Cam Design and Manufacture, Industrial Press Inc.
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