A new control strategy for DLR's multisensory articulated hand

Concerns a multisensory 12-DOF 4-finger hand in which all actuators are integrated in the palm or the fingers. It was necessary to use a specially designed miniaturized linear actuator. For telemanipulation our first approach was to make the hand follow the desired states commanded from higher levels, e.g., dataglove. This requires accurate tracking, compliance in the constrained environment, and smooth transition between these two modes. The tracking control problem is to design a control scheme which generates the appropriate control signal so as to ensure that the joint angle follows any specified reference trajectory as closely as possible. Compliance is needed for fine manipulation and also for the protection of the hand. Transition control is essentially the problem of making the energy conversion more effective and smooth. We propose a parallel torque/position control strategy for this task. The robust trajectory tracking in free space is implemented by sliding mode control; the compliant motion in the constrained environment is realized by using impedance control; and a parallel observer based on contact torques and system states has been built to determine the switch between these two kind of controllers for the transition control from or to contact motion.