On the Dynamic Response of Actuation Devices in Open and Closed-Loop Mechanisms With Nonlinear Dynamics

Abstract

This paper presents a study of the dynamic response of actuation devices used in mechanical systems with open and closed-loop linkage mechanisms and highly nonlinear dynamics such as robot manipulators. The study shows that the actuation forces/torques provided by actuation devices can be divided into two basic groups. The first group corresponds to the components of each actuator force/torque that is “actuator motion independent”. The dynamic response of this group is relatively high and limited only by the dynamic response limitations — for the case of electrically driven actuation systems — of the driving power amplifiers, electronics, computational and signal processing devices and components. The second group corresponds to those components of the actuator forces/torques that is “actuator motion dependent”. The dynamic response of this group is relatively low and dependent on the actuator effective inertial load and actuation speed. In all mechanical systems that are properly designed, the dynamic response of the first group is significantly higher than those of the second group. By separating the required actuating forces/torques into the above two groups, the dynamic response of such nonlinear dynamics systems may be determined for a given synthesized trajectory. The information can also be used to significantly increase the performance of mechanical systems. When a feed-forward control signal is used, the performance of the system is shown to be significantly improved by generating each one of the group of actuation components separately considering the dynamic response of the actuation system to each group of components. A method for separating the actuation forces/torques into the said “actuator motion independent” and “actuator motion dependent” groups for mechanical systems with open-loop and closed-loop linkage mechanisms is provided. Provided examples include an open-loop manipulators with feed-forward trajectory control and a closed-loop mechanism, both with highly nonlinear dynamics. Practical methods for implementing the proposed feed-forward control for nonlinear dynamics systems are discussed.