Development of a Hand Exoskeleton System for Index Finger Rehabilitation

In order to overcome the drawbacks of traditional rehabilitation method, the robot-aided rehabilitation has been widely investigated for the recent years. And the hand rehabilitation robot, as one of the hot research fields, remains many challenging issues to be investigated. This paper presents a new hand exoskeleton system with some novel characteristics. Firstly, both active and passive rehabilitative motions are realized. Secondly, the device is elaborately designed and brings advantages in many aspects. For example, joint motion is accomplished by a parallelogram mechanism and high level motion control is therefore made very simple without the need of complicated kinematics. The adjustable joint limit design ensures that the actual joint angles don't exceed the joint range of motion (ROM) and thus the patient safety is guaranteed. This design can fit to the different patients with different joint ROM as well as to the dynamically changing ROM for individual patient. The device can also accommodate to some extent variety of hand sizes. Thirdly, the proposed control strategy simultaneously realizes the position control and force control with the motor driver which only works in force control mode. Meanwhile, the system resistance compensation is preliminary realized and the resisting force is effectively reduced. Some experiments were conducted to verify the proposed system. Experimentally collected data show that the achieved ROM is close to that of a healthy hand and the range of phalange length (ROPL) covers the size of a typical hand, satisfying the size need of regular hand rehabilitation. In order to evaluate the performance when it works as a haptic device in active mode, the equivalent moment of inertia (MOI) of the device was calculated. The results prove that the device has low inertia which is critical in order to obtain good backdrivability. The experiments also show that in the active mode the virtual interactive force is successfully feedback to the finger and the resistance is reduced by one-third; for the passive control mode, the desired trajectory is realized satisfactorily.