Leveraging Disturbance Observer Based Torque Control for Improved Impedance Rendering with Series Elastic Actuators.

摘要

The fidelity with which series elastic actuators (SEA's) render desired impedances is important. Numerous approaches to SEA impedance control have been developed under the premise that high-precision actuator torque control is a prerequisite. Indeed, the design of an inner torque compensator has a significant impact on actuator impedance rendering. The disturbance observer (DOB) based torque control implemented in NASA's Valkyrie robot is presented here and a mathematical model is constructed of the robot's full actuator impedance control architecture. It is demonstrated through simulation and a series of experimental tests that leveraging a DOB significantly improves an SEA's ability to accurately render desired dynamic behaviors. Actuator transparency at low impedances is improved, hysteresis is reduced, and the dynamic response to commands and interaction torques more faithfully matches that of the desired model. All of this is achieved by incorporating a DOB into the control system rather than increasing compensator gains. Thus, DOB based torque control serves to expand the range of scenarios in which impedance controlled series elastic actuators are effective.