Introduction

In polydyne cams the cam profile is designed such that the follower lift curve matches a desired polynomial equation at the desired design speed given the cam-follower system dynamic characteristics. Automobile valve-gear linkages and textile machine members are prime examples of good polydyne applications. The polydyne method was originally presented by Dudley (1948) and elaborated by Stoddart (1953). This is the first method ever proposed that designs the cam shape to give the desired follower action. Polydyne s basic advantages are:

1. By direct means it can eliminate jump of the follower off the cam.

2. By direct calculation it provides control of the exact position of the follower end.

3. It limits vibrations to minimum amplitudes at the design speed.

Its primary shortcomings are:

1. High accuracy is needed to realize the advantage of the mathematically computed curve. Sometimes the cam calculated is impossible to cut; i.e. a dip in the cam is required.

2. The mathematical work is laborious and time-consuming.

3. The cam-follower system is valid at only one speed.

13.7.2 Fundamental Relationships

In the following sections a typical example indicating the method of attack establishes the basic equations for a high-speed cam-follower system.

First, the flexibility relationship of the linkage must be determined. Any cam-driven mechanism (assuming a single degree of freedom) may be divided into the usual dynamic equivalent system of four parts.

1. Compression spring to hold the follower on the cam. In positive-drive cams, this spring obviously does not exist.