Adaptive Delay Compensation for Admittance Control of Hydraulic Series Elastic Actuator

Abstract

Recently, series elastic actuators (SEAs) are considered to be promising devices for achieving safe human-robot interaction. Various Impedance/admittance control methods have been proposed to realize active compliance. Although lots of research have been conducted to improve the control accuracy, however, time-delay issue in SEA control is not well investigated. To resolve this problem, this paper proposes a novel parallel adaptive time delay (P-ATS) compensator for admittance control of a hydraulic SEA. An admittance controller is first developed and the P-ATS compensator is then adopted to reduce the time delay and tracking error. It is derived from the conventional adaptive time delay (ATS) compensator in which the coefficients are mechanically updated after sampling. This paper designs a special parallel mechanism that allows the coefficient determination procedure to be conducted independently. The whale swarm algorithm with iterative counter (WSA-IC) is adopted for coefficient determination. A criterion is also proposed to evaluate the quality of identified coefficients before updating. This unique mechanism can not only provide more computational resources on coefficient determination, but also increase the quality of the output coefficients. The simulation experiments confirm the superiorities of the P-ATS compensator over conventional methods. The results also verify that the P-ATS compensator can maintain a good performance with a lower sampling rate.