Definition of Pressure and Transmission Angles Applicable to Multi-Input Mechanisms

Abstract

Pressure angle is an important measure of the effectiveness with which a force is transmitted between a cam and follower. A pressure angle of zero degrees indicates that the force is transmitted with maximum effectiveness while a 90 deg pressure angle indicates that the force cannot make the desired contribution to the follower motion. There are a number of definitions available in the literature that can be used to determine pressure angle. These definitions are all consistent with the meaning of pressure angle described above when applied to followers driven by only a single cam. For followers driven by multiple inputs, however, we have found that none of these definitions provides a value of pressure angle that retains this same meaning. The purpose of this paper is to draw attention to this fact and to present a precise definition of pressure angle, as well as a discussion of its mathematical consequences, that property characterizes the performance of either single-input or multi-input cam-follower mechanisms. For single-input systems, this definition is shown to be equivalent to the definitions for pressure angle found in the literature. The applicability of this definition to the determination of transmission angle for linkages with multiple inputs is also discussed.