Great and sudden force applied to the joint by either a blow or fall, can cause the bones in joint to be displaced or dislocated from normal position, resulting in joint function loss at different degrees. Then joint closed reduction can be operated by trained medical professionals, and fragile joints are protected from impacting damage in this process. Inspired by such principle of dislocation and reduction of human joints, an overload protector applied protect key components from falling down in shoulder joint of humanoid robot is proposed to in this paper. The shoulder joint connects upper limb and shoulder through an overload protector. When a sudden external force applied in upper limb causes great impact on shoulder joint, the overload protector can disengage the connection between the shoulder and the upper limb temporarily, and the normal transmission can continue after closed reduction in a preset period. This process will cycle continuously until the impact force is reduced to the preset safety range. Thereby, it achieves protecting the key components of robot shoulder during falling down. In this paper, the working principle of overload protector is elaborated, its reliability is verified by a series of experiments. The experimental results show that the transmission of overload protector is reliable and stable as a rigid connecting mechanism under low external load, and it can protect the key components from damage by self-detaching when subjected to high external load or sudden impact.
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