Chapter 8: Cam Design

 Chapter 8 - Cam Design

    Cams are frequently used in machines. They are easier to design to produce a function but are far more expensive than linkages. Cams perform the same functions as linkages, except the coupler link has been replaced by a half joint. The links constantly vary, which is the source of the large amount of functions that the cam can produce. The cam-follower system can be classified in the following ways:

            - Type of follower motion

            - Translation or rotation

            - Type of cam

            - Radial / cylindrical / 3D

            - Type of joint closure : force or form closed

            - Type of follower : curved, flat, or sliding

            - Type of motion constraints : Critical Extreme Position, Critical Path Motion

            - Type of motion program (RF, RFD, RDFD, etc.)

It is important to note that the fundamental law of cam design must be satisfied. This law states that the cam function must be continuous through the first and second derivatives of displacement across the entire interval and the jerk must be finite. This can be demonstrated by the graphs below for an unacceptable cam design.

This displacement graph seems okay - the rise is normal and continuous. The velocity and acceleration graphs are also usual. However, the jerk graph lets us know that the cam design violates the fundamental law.

The jerk is infinite at the beginning and end of the interval. This is because of the type of function used to plot position, which will not satisfy the fundamental law if a dwell is wanted in the cam.