Attaining impedance control objectives using Hinfinity design methods

A design methodology for manipulator impedance control is introduced based upon the successive application of H_infinity minimization techniques. A key component of this approach is the measurement of the distance between the desired and the achieved response through the use of H_infinity norm. The design process attempts to minimize this distance, subject to other constraints such as control authority limitations. This scheme allows for the independent design of mechanical admittance, sensitivity, and tracking bandwidth provided an output torque sensor is available on the actuator. In the absence of such a sensor, this methodology allows either the sensitivity requirements or the admittance requirements to be met, but generally not both. It is shown that both the torque-based and the position-based impedance control design approaches can be formulated within this three-part design methodology. The design methodology was demonstrated by applying it to a fourth-order harmonic drive actuator model with inner torque-loop control.