An adjustable Scotch yoke mechanism for output torque regulation

Abstract

The robotic fish using servomotor was generally difficult to operate high frequency because the servo motor decreases the velocity to switch the direction of the tail fin. To solve this problem, various researchers have tried to use the Scotch yoke mechanism with DC motor for robotic fish. The Scotch yoke mechanism converts the rotating motion of motor into the reciprocating motion. However, in this mechanism, the torque of the motor with scotch yoke mechanism is changed in terms of the phase of the tail fin while the DC motor maintains the torque constantly. Thus, the objective of this paper is to regulate the motor output torque by using the adjustable Scotch yoke mechanism. This mechanism uses springs to store the motor torque and cam mechanism to release this torque at desired moment. We analyzed a kinematic model of the Scotch yoke mechanism to propose a method of designing the part of the adjustable Scotch yoke mechanism. In addition, we experiment to measure the thrust of tail fin while the equal input voltage of controller is supplied respectively and compare the conventional mechanism and adjustable Scotch yoke mechanism by considering the compliance of the fin. As a result, we conclude that the adjustable scotch yoke mechanism enables the propulsion system to improve the average thrust than conventional scotch yoke mechanism during the equivalent power consumption. Therefore, based on these result, the high speed robotic fish can be made by applying the adjustable Scotch yoke mechanism which regulated the output torque.