Force Control Strategy for a Hand Exoskeleton Based on Sliding Mode Position Control

This paper presents a force-based control mode for a hand exoskeleton. This device has been developed with focus on support of the rehabilitation process after hand injuries or strokes. As the device is designed for the later use on patients, which have limited hand mobility, fast undesired movements have to be averted. Safety precautions in the hardware and software design of the system must be taken to ensure this. The construction allows controlling motions of the finger joints. However, due to friction in gears and mechanical construction, it is not possible to move finger joints within the construction without help of actuators. Therefore force sensors are integrated into the construction to sense force exchanged between human and exoskeleton. These allow the human to control the movements of the hand exoskeleton, which is useful to teach new trajectories or can be used for diagnostic purposes. The force control scheme presented in this paper uses the force sensor values to generate a trajectory which is executed by a position control loop based on sliding mode control