Design and control of a dual unidirectional brake hybrid actuation system for haptic devices

Hybrid actuators combining brakes and motors have emerged as an efficient solution to achieve high performance in haptic devices. In this paper, an actuation approach using two unidirectional brakes and a DC motor is proposed. The brakes are coupled to overrunning clutches and can apply a torque in only one rotational direction. The associated control laws, that are independent of the virtual environment model, calculate the control gains in real time in order limit the energy and the stiffness delivered by the motor to ensure stability. The reference torque is respected using the combination of the motor and the brake. Finally, an user experiment has been performed to evaluate the influence of passive and active torque differences in the perception of elasticity. The proposed actuator has a torque range of 0.03 Nm to 5.5 Nm with a 17.75 kNm (-2) torque density.