High-bandwidth active impedance control of the proprioceptive actuator design in dynamic compliant robotics

Abstract

Dynamic compliant robotics is a fast growing field because of its ability to widen the scope of robotics. The reason for this is that compliant mechanisms may ensure safe/compliant interactions between a robot and an external element-for instance, a human operator. Active impedance control may widen the scope even further in relation to passive elements, but it requires high-bandwidth robust torque and active impedance control which induces high-noise issues even if high-end sensors are used. To address these issues, a complete controller design scheme, including Field-Oriented Control (FOC) of a Brushless Direct Current (BLDC) motor, is proposed. In this paper, controller designs for controlling the virtual impedance, motor torque and field are proposed which enables high-bandwidth robust control. Additionally, a novel speed and angle observer is proposed that aims to reduce noise arising in the angle sensor (typically a 12-bit magnetic encoder) and a Kalman/Luenberger based torque observer is proposed that aims to reduce noise arising in the phase current sensors. Through experimental tests, the combination of the controller designs and observers facilitated a closed-loop torque bandwidth of 2.6 kHz and a noise reduction of 13.5 dB (in relation to no observers), at a sample rate and Pulse Width Modulation (PWM) frequency of 25 kHz. Additionally, experiments verified a precise and high performing controller scheme both during impacts and at a variety of different virtual compliance characteristics.