Analysis and design of motion control systems with positive force/torque feedback using robust control methods

Positive force/torque feedback (PFF) can compensate for the detrimental effects of load dynamics and exogenous force/torque disturbances on the tracking performance of motion control systems. With real world nonideal force/torque sensors/actuators, a PFF controller can be designed to accommodate the sensor\´s/actuator\´s dynamics and to minimize the impact of load dynamics or external force/torque disturbances upon the motion tracking loop. This brief shows that PFF is an effective method for many practical control problems. It is also shown that the analysis and design of motion control systems with PFF can be put into the μ framework and, thus, the tracking controller and the force/torque feedback controller can be synthesized simultaneously using commercially available μ tools. Some practical issues, which are independent of design methods, such as the robust stability (RS) of the PFF loop and the bandwidth requirements for the PFF controller, are also discussed. It is concluded that, outside the system\´s effective tracking bandwidth, it is not wise to use model-based "perfect" PFF for a "big" load due to the lack of robustness of the PFF loop against the actuator uncertainties. Experimental results with a UW hexapod strut show that the μ design method for PFF is promising.