Safe rendering of high impedance on a series-elastic actuator with disturbance observer-based torque control
This work addresses safety and performance in robotics for applications like human-robot interaction, but it is incremental as it builds on existing torque control methods.
The paper tackled the problem of safely rendering high impedance on series-elastic actuators by proposing passivity-based stability conditions for disturbance observer torque control, showing that it allows higher impedance than high-gain PD control and validating this experimentally with a dynamic feedforward compensator that increases maximum safe impedance.
An important performance metric for series-elastic actuators is the range of impedance which they can safely render. Advanced torque control, using techniques such as the disturbance observer, improve torque tracking bandwidth and accuracy, but their impact on safe impedance range is not established. However, to define a safe impedance range requires a practical coupled stability condition. Here, passivity-based conditions are proposed for two variants of DOB torque control, and validated experimentally in a high-stiffness environment. While high-gain PD torque control has been shown to reduce Z-width, it is here shown that a DOB reduces the need for high-gain PD feedback and allows a higher rendered impedance. A dynamic feedforward compensator is proposed which increases the maximum safe impedance of the DOB, validated in experimentally in collision with high-stiffness environments and manual excitation.