This paper presents the mechanical design for a new, four-fingered robot hand. The hand was developed in the context of a service robot project that aims to produce a robot that can handle tableware of various shapes to set and clear a table. This project required the development of a new hand that has a small number of motors but still a high level of adaptability so that it can handle the various shapes of tableware found in a place setting. We therefore developed a four-fingered robot hand which consists of four finger mechanisms and a mechanism capable of changing its direction of movement. The movement orientation of the four fingers can change, in a synchronized state, from a posture in which they are directly opposed to one in which they are diagonally opposed. This state transformation can be achieved with only one motor. Also, four fingers can perform synchronous opening and closing motions, and these motions can be achieved by only one motor. Only two motors are needed to drive the robot hand, and both are installed in the base of the hand. Consequently, the hand is a simple but very effective mechanism for stably handling tableware. Tests have shown that it can successfully grasp various kinds of tableware, and that the new mechanism operates effectively.

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