Generalized discussion on design of force-sensor-less Power Assist Control

This paper generalizes the structure of Force-Sensor-less Power Assist Control (FSPAC) which is a essential technology to design a feedback controller in a human-friendly way. Based on the analysis of the control structure, this paper clarifies the functions of the generalized force-sensor-less power assist control; particularly the functions of two force observers in FSPAC are made clear. Since the FSPAC consists of a positive feedback control, the robustness of the FSPAC is much weaker than the other power assist control with force sensors. This paper clarifies the trade-off between assistance performance and weak robustness in the FSPAC. Comparing power assist control derived from model following design and the disturbance observer based design, the limitation of assistance performance and methods to adjust the gain are revealed. Finally methodology of design the feedback gain in the FSPAC is discussed.