Active and passive control algorithm for an exoskeleton with bowden cable transmission for hand rehabilitation

This paper investigates the control algorithm of an exoskeleton for hand rehabilitation, which accomplishes both active and passive rehabilitation training. In the passive mode control the PID control algorithm is executed in the velocity mode of the driver. In the active mode control, control architecture is proposed to deal with in both free space and constraint space. A resistance compensation control method is proposed to reduce the resistance in free space which is caused by the friction of the Bowden cable as well as the moment of inertial. To realize the compensation, force sensors are used to measure the force exerted by the human fingertip. A commercial driver, which could switch between the two control modes by a programmable digital switch rather than changing the physical connection manually, guarantees the realization of the required functions. The experiments are conducted to verify the proposed method, and the results show that in the active control mode, the maximum finger-exerted force with compensation is about two fifths of the force without compensation which means the resistance is greatly reduced. And in the passive mode, the maximum joint position error is about 1.2 degree, which satisfies the requirement in hand rehabilitation application. The experimental results demonstrate the validity of the proposed method.