Design of a robust force controller for the new mini motion package using quantitative feedback theory

The use of hydraulic systems in industrial applications has become widespread due to their efficiency advantages. In recent years, hybrid actuation system, which combines electric and hydraulic technology in a compact unit, can be adapted to a wide variety of force, speed and torque requirements. Moreover, the hybrid actuation system has dealt with the energy consumption and noise problem existed in the conventional hydraulic system. Mini motion package (MMP) is one type of the new low cost hybrid actuator. This MMP is considered as a novel linear actuator with various applications such as robotics, automation, plastic injection-molding and metal forming technology. However, this efficiency gain is often accompanied by a degradation of system stability and control problems. In this paper, to maintain robust performance requirement, tracking performance specification, and disturbance attenuation requirement, the design of a robust force controller for the new hybrid actuator using quantitative feedback theory (QFT) is presented. A family of plants model for MMP is obtained from experimental frequency responses of the system in the presence of significant uncertainty. Experimental results show that highly robust force tracking by the MMP actuator could be achieved even if the stiffness of environment and set-point force change. In addition, it is understood that the new system has energy-saving effect even though it has almost the same response as that of valve controlled system.