Development and Functional Evaluation of a Deformable Membrane Capsule for an Open Ball Glenohumeral Joint

Human has open ball joints in shoulder or hip joints, and can move such joints in wide range of motion without dislocation. One of the reason of it is that there is joint capsule in human joints. Joint capsule is a membrane structure which surrounds a joint and consists of two kinds of membrane, external one is fibrous membrane and internal one is synovial membrane. There is synovial fluid inside synovial membrane and plays a role of lubricant and cushioning material of the joint. However, there is no humanoid robots with joint capsule and human mimetic humanoids which have open ball joints sometimes dislocate their shoulders. In this paper, in reference to joint capsules, we developed an open ball joint which has membrane structure made of vulcanized natural rubber and moved the joint by tendon drive using motor modules which was disposed similar to human shoulder muscle arrangement. We also tested its function such as strength and range of motion for future use in glenohumeral joint of human mimetic musculoskeletal humanoids and showed that the joint becomes less likely to dislocate when there is membrane structure surrounding the joint.