Kinematic-Dynamic Analysis of the Cam-Worm Mechanism for Humanoid Robots Shrug

Having in mind that humans use non-verbal communication extensively is very important to enable social robots with this capacity. There are two basic ways how it can be expressed. First one is by facial expressions by appropriate moving face parts, like eyebrows, eyeballs, eyelids, lips, either as manufactured real parts or by presenting them on screen—combining them is also possible. The second way of non-verbal communication is by gestures. This paper presents the kinematic-dynamic analysis of shrug mechanism for humanoid robots. Based on the set requirements, the cam-worm mechanism that has 1 DOF and enables the simultaneous shrug of both shoulders is proposed. It consists of a worm which is meshed with two worm gears whose directions of rotation are opposite and the two cam mechanisms whose input links—cams, are rigidly attached to the worm gears. Within the kinematic-dynamic analysis, the cam profile and the worm parameters are defined and the torque on the cam/worm gear and the driving torque of the complete cam-worm mechanism are determined. The cam mechanism has a high efficiency in all positions because the values of the pressure angle are within the prescribed ones during the entire movement. Worm mechanism enables a significant reduction of the driving torque and has acceptable efficiency. The rotation range of worm gear/cam is small and the movement of mechanism is very fast wherefore the shrug speed is large, which was one of the main requirement for realization.