While many upper-extremity exoskeleton systems have been developed for rehabilitation, there are still challenges in designing an exoskeleton which has a back-drivable joint for assured safety and simultaneously can generate large assistive torque. This paper introduces a newly developed upper-extremity exoskeleton robot intended as a rehabilitation platform specialized for elevation of shoulder joint. By using a pneumatic cylinder, the shoulder joint can be back-drivable and can have hardware compliance while it fully actuates the entire arm, of both the exoskeleton and the user. In addition, our development is particularly featured in (a) the length-adjustable frame, (b) the high-resolution encoder built into a thrust bearing in a hollow compact joint, and (c) the physical slider implemented as an easy-to-use interface. We also developed a torque-based controller for the exoskeleton so that the therapist can teach the shoulder joint movement directly. In the experiment, we showed that we can program the exoskeleton robot movement by directly moving the exoskeleton with mannequin arm while the weights of the robot and the mannequin was supported using the gravity compensation control method.
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