Design and Hybrid Impedance Control of a Compliant and Balanced Wrist Rehabilitation Device

Wrist rehabilitation robotic devices have delivered the repetitive and gradual training necessary to rehabilitate individuals with wrist impairments properly. Generally, there are two approaches for the design of the wrist rehabilitation devices. In one approach, the motors are placed on the forearm with complex transmission mechanisms to reduce the weight and inertia. In the other approach, rotary motors are placed close to the wrist joints with simple design, and this leads to high weight and inertia. In this paper, a simple design of two-degrees of freedom compliant and balanced wrist rehabilitation device is proposed. It can provide the radial-ulnar deviation and flexion-extension rehabilitation motions. In the proposed design, the servomotors that are placed close to the wrist joints are counterweight balanced to reduce the inertia and the required torques. The balancing is carried out by optimizing the center of mass of the device in the SolidWorks model. A custom design series elastic unit is proposed to be coupled to the servomotor to achieve the compliance for safe human-robot interaction. Based on the device dynamics modeled by ADAMS software, hybrid position and force tracking impedance control is developed for position and force tracking through the different therapeutic exercises. The device is shown to be capable of achieving the different therapeutic exercises compliantly such as the passive, active-assisted and isometric exercises.