Development of a passive shoulder joint tracking device for upper limb rehabilitation robots

This paper introduces a passive shoulder joint tracking device for upper limb rehabilitation robots and performance evaluation of the device. The Gleno-humeral (GH) joint of the shoulder translates in three-dimensional space as the arm moves. However, commercial rehabilitation robots for the upper limb lack in accommodating for the translation of the GH joint. The few robots which can support the translation were too heavy, expensive, and complex to use because of bulky mechanisms including additional actuators. The proposed three DOF passive shoulder joint tracking device consists of one DOF vertical tracking with gravity compensation and two DOFs for horizontal tracking. Because no actuators were used, the device is characterized by light weight and low cost. The passive shoulder joint tracking device can be utilized as an additional module to existing upper limb rehabilitation devices for enhanced performance. The tracking performance of the device was evaluated through motion capture experiments consisting of four different arm motions. Three different conditions were tested including free arm motions of a healthy subject and arm motions assisted by a commercial upper limb rehabilitation device with/without the proposed shoulder joint tracking mechanism. The shoulder joint tracking device allowed the commercial upper limb rehabilitation device to track the GH joint without delay allowing for greater amount of GH translation close to the free shoulder movement.