Parallel-Coupled Micro-Macro Actuators

Abstract

This paper presents a new actuator system consisting of a micro- actuator and a macro-actuator coupled in parallel via a compliant transmission. The system is called the parallel-coupled micro-macro actuator, or PaCMMA. In this system, the micro-actuator is capable of high-bandwidth force control owing to its low mass and direct-drive connection to the output shaft. The compliant transmission of the macro-actuator reduces the impedance (stiffness) at the output shaft, and increases the dynamic range of force. Performance improvement over single- actuator systems was expected in force control, impedance control, force distortion, and transient impact force reduction. Several theoretical performance limits are derived from the sat uration limits of the system. A control law is presented. A prototype test bed was built and an experimental comparison was performed between this actuator concept and two single-actuator systems. A set of quantitative measures is proposed and the actuator system is evaluated against them with the following results: force bandwidth of 56 Hz, torque dynamic range of 800: 1, peak torque of 1,040 mNm, and minimum torque of 1.3 mNm. Peak impactforce, fonce distortion, and back-driven impedance of the PaCMMA system are shown to be better than either of the single-actuator configurations considered.