Development and testing of a magnetorheological actuator for an assistive knee brace

This paper proposes an assistive knee brace that is aimed to provide assistance to old or disabled people. A magnetorheological (MR) actuator is developed to be used in assistive knee braces to provide controllable torque. The MR actuator consists of a DC motor and an MR brake/clutch. When active torque is needed, the DC motor works and the MR actuator functions as a clutch to transfer the torque generated by the motor to the leg; when passive torque is desired, the DC motor is turned off and the MR actuator functions as a brake to provide controllable passive torque. The prototype of this MR actuator is fabricated and experiments are carried out to investigate the characteristics of the MR actuator. The results show that the MR actuator is able to provide sufficient torque needed for normal human activities. Adaptive control is proposed for controlling the MR actuator. Experiments of the MR actuator under control are performed to study the torque tracking ability of the system.