Design of a Musculoskeletal Upper Limb with Pseudo Ball Joint Modules for the Control of Redundant Nonlinear Elastic Elements

Abstract

The tendon-driven musculoskeletal humanoid imitates the joint and muscle structure of human beings, and has benefits of variable stiffness, redundant muscles, the flexible spine, ball joints, etc. However, this type of humanoid is not popular compared to the ordinary axis-driven humanoid. In this study, we assume that this is because its design is difficult due to the complex structures, its control system is complex due to the inability to directly measure joint angles by encoders, and it cannot realize intended joint angles due to the model error between the actual robot and its geometric model. Therefore, we developed a pseudo ball joint module that can directly measure joint angles. Also, we developed a musculoskeletal upper limb which is composed of joint modules, muscle modules, and a few attachments, and show that its design is effortless. To make use of the benefit which these joint modules can make the control and learning system simple and easy, this musculoskeletal upper limb includes redundant nonlinear elastic muscles.