Disturbance Compensation for Harmonic Drive Actuators With Accelerometers and Joint-Torque Sensors

This study aims to compensate for output torque ripple and load-side disturbance in a harmonic drive system. The control system is augmented with an accelerometer to reduce the adverse effects of load-side disturbance. Concerning the torque ripple compensation due to the harmonic drive gearing, this research presents a scheme called sliding adaptive feedforward cancellation (sliding AFC) that adapts Fourier coefficients and uses those coefficients to produce appropriate feedforward compensation. These two compensation methods are integrated into the so-called Sub-System Backstepping Design (SSBD) to reduce the output torque ripple and compensate for the load-side disturbance. The conventional AFC uses the tracking error to adapt a feedforward cancellation component. Hence, its convergence speed is limited, and the reference signal influences its performance. The proposed sliding AFC consists of an auxiliary process and an AFC resonator. The auxiliary process produces a switching signal equivalent to the error of disturbance compensation. The AFC resonator receives this switching signal to adapt its output, yielding fast convergence and diminishing the influence of the reference signal. Moreover, the sliding AFC can handle state-dependent disturbances. This research conducts experiments on a harmonic drive actuator with a joint-torque sensor. This sensor measures the actuator’s output torque, and the sliding AFC’s auxiliary process receives this torque signal to produce the switching signal that precisely reveals the compensation error and enables fast convergence. Experimental results are reported in this paper, and a comparative study is conducted to investigate the effectiveness of the proposed scheme.