A Mechanism for Converting Revolute Motion into Harmonic Rotating Motion#

Abstract

In this paper, we describe the design and construction of a cam mechanism to convert a revolute motion into a symmetrical oscillating harmonic movement. The mechanism consists of a harmonic cam driven by a revolute electric motor joined to a follower by a desmodromic constraint. The linear reciprocating motion of the follower was then transmitted, by a rack-pinion mechanism, to a final device that oscillates symmetrically. The entire mechanism was designed to be used as the propeller of a boat model. The final device, indeed, will be connected to a tail that propels the boat. On account of the peculiar application for which the device is intended, the need for symmetrical motion of the tail—either in a cycle, from side to side and return, or in a semi-cycle, from side to side—becomes evident. The analysis of the kinematics and the analytic model of its dynamics are presented throughout the paper. A numerical model, able to capture the mechanism performance when the friction effects were taken into account and to predict its behavior when the motion conditions were varied, was developed as well. During construction of the mechanism, efforts were made to reduce friction, weight, and the overall dimensions. Several laboratory tests were carried out in order to clarify the mechanism's performance. Particular care was dedicated to measure the coefficient of friction between the materials of the desmodromic constraint and to the kinematics parameters for validating the design requirements. The dedicated test benches arranged and the data collected from the tests are presented in the paper.