Soft Arm Weight Support Device for Reducing Shoulder Muscle Fatigue

Abstract

Arm movement are important not only for activities of daily livings, but also for works. Due to the repetitive use of the arm, unfortunately, the arm muscles are easily fatigued. This muscle fatigue often causes a variety of muscular disorders in the arm. Especially, in the shoulder, because of the arm weight, the muscle fatigue is cumulated rapidly when people sustain their arm raised for long time. The laparoscopic surgeon was selected as one of target subject to apply our device because they should sustain their arm raised for long surgery time. Although there are many kinds of the arm support devices to support the arm weight against gravity, they cannot use these devices because of the narrow and complex work environment. To satisfy these requirement, the soft weight support device was developed consisting of the soft material and the passive force profile generator based on the tendon-driven mechanism to generate the assistive force. Through these concepts, the device can be compact and simple. However, several challenges exist to support the arm weight successfully. First, to support the arm weight against the gravity, the force should be generated according to the vertical angle of the shoulder and the elbow angle. Also, the direction of the force should be applied to upward at various posture of the shoulder. Second, to transmit the assistive force efficiently and safely, the anchoring position should be carefully selected to prevent the damage on the body. Also, because the anchoring structure is passing through multi degree of freedom body joints such as spine, the anchoring structure can be easily loosened when the body is moved. If the anchoring structure is loosened, the force direction may be deformed and the efficiency may drop. In this thesis, to apply our device on actual worker, we targeted the laparoscopic surgeons who should often raise their arm raised for long time due to the surgery. The main contributions of this study are as follow. Through the passive force profile generator, the assistive force was generated according the vertical angle of the shoulder and the elbow angle by decoupling the effect of the horizontal arm movement to generate the assistive force. The looped tendon routing structure guided the direction of the assistive force to upward direction. At the various movements, the anchoring structure was kept tightened through the adjustable anchoring structure and the anchoring ability was improved. To validate the whole device, surface electromyography data and the sustaining time were measured during the subject sustained their arm raised. Based on the clinical trial, it was proven that the soft weight support device can reduce the muscle fatigue on the shoulder. Consequently, the soft weight support device is expected to reduce the shoulder disorder of the laparoscopic surgeon.