A Development of Joint Mechanism of Robot Arm Based on Human Shoulder Morphology

The purpose of this study was to develop a new joint system based on human shoulder mechanism. The human shoulder joint has a ball joint mechanism that is surrounded by a number of muscles and is driven by the balance of those forces. The authors thought that the construction could realize 3 degrees of freedom with compact size and lightweight. An anatomical skeletal structure had been introduced to the mechanism, especially on the muscle arrangement. Muscles were replaced by wires and humeral head was altered by a ball joint. The movability of the mechanism was evaluated by the relative ratio of the moment arm to the ball radius produced from the wires that surround the ball joint. Several rearrangements in improvement processes enabled the joint to be driven by 6 wires. Inverse kinematics was solved by artificial neural network (NN) that learned the data sets of arm postures and wire displacements. Additional differential outputs were installed in the NN. The principle of virtual work was applied to drive the joint by a feedback control system in the range of 3 degrees of freedom. The movability and capability of the new joint system was satisfactorily demonstrated in this report