Parallel coupled actuators for high performance force control: a micro-macro concept

Current force control capabilities are limited by actuator performance. Brush friction and actuator saturation lead to limit cycles and instability in many force control systems. The authors propose that actuators with the proper passive characteristics provide the best potential for fast, accurate force control. The authors report on a new actuator concept which combines two actuators to create a micro-macro actuator which has improved force resolution and bandwidth. Unlike previous micro-macro robots which used actuators coupled in series, the actuators in this system are coupled in parallel using a compliant transmission. Three specifications for force control performance are defined and a model is presented. A control law for the combined actuator is presented and a general analysis of the design is formulated. Finally, measurements of performance in a prototype device are presented. This system has achieved force resolution of 0.25% and force control bandwidth of 60 Hz.