COSA-UDA finger: A novel coupled and self-adaptive under-actuated finger with upside-down actuator

Hands are important parts for humanoid robots, whose structure requires both flexibility and small size. Dexterous hands and under-actuated (UA) hands are designed in two different types, and the coupled and self-adaptive under-actuated (COSA) grasping mode combines the advantages of both the types, which includes the first coupled stage and the second self-adaptive stage. In order to realize the COSA grasping mode, a novel COSA finger with upside-down actuator (COSA-UDA) is proposed in this paper. The COSA-UDA finger utilizes traditional COSA grasping mode, but embeds the actuator into the proximal phalanx in an upside-down way. In this method, the COSA-UDA finger is able to achieve COSA grasping mode easily using a simplified structure, and the finger makes full use of the rest place of phalanx and remains enough space of palm for complicated instruments to be set. In this paper, several traditional fingers designed in COSA mode are compared and analyzed. The design for the structure of COSA-UDA is provided, and a typical COSA-UDA finger is designed in the following discussion. The mechanics module of the finger is established and discussed, and several rules are proposed in order to optimize the size and grasping force of the system. Analyzing results show that the COSA-UDA finger is a feasible optimal design for COSA grasping mode.