Design of A Compliant Dexterous Robot Hand Using Flexible Joint

Abstract

This thesis presents designing a compliant dexterous robot hand using a flexible joint. The mechanism was constructed using two kinds of joints, hinge joint and rolling-contact joint, for accurate position control. All joints are driven using tendons and Because tendondriven can control one joint with two tendons, the extension motion was implemented using elastic wire to control one joint with one tendon. Also, If there is no limiter mechanically, the over-extension of the finger cannot be prevented, so the shape of the joint was designed to limit the angle of the extension, thus limiting the over-extension to more than 180 degrees mechanically. The change of tendon length and the angle of the joint were mapped according to the movement of the joint and each joint of the finger was controlled using PD position control. The proposed robot hand system consists of 11 miniature geared motors, 6 drv8835 motor drivers from Pololu and 2 Arduino Megas. The motor is located inside each of the four CMC phalanges and one motor is located in the palm so the total number of motors is 11. Two motors in the CMC phalange of the other fourfingers except the thumb drive the MCP joint and the PIP joint, and two motors in the CMC phalnages of the thumb drive the flexion/extension of MCP joint and abduction/adduction of the CMC joint. If there is a change in the tendon length of the other phalanges when driving one phalanges by tendon driven, each phalanges is unable to make independent movements. therefore, when tendon routing was done at each joint, fixing the tendon at each joint for not changing the length of the tendon so that each joint could move independently. PIP joint and DIP joint are coupled to the limit of the number of motors, and the angle of movement is limited by adjusting the routing radius of each joint to enable natural motion. In order to implement biomimetic MCP joints, the robot hand’s CMC and MCP connected flexible joints made using task 13 materials to make passively moving 3DoF joints, which implemented various advantages and functions. First, to Describing biomimetic movements, rolling-contact joint with different radius in two directions were designed to produce biomimetic joints similar to the actual motion of the human hand, and experimentally confirmed the behavior similar to the human hand. Second, The MCP joint was designed using flexible materials and returned to its original state with joint self-resilience for abduction/adduction and inner-rotation, and the angle of finger is changed to suit the object as adaptive grasping is possible when grasping the object. The location of the thumb was determined by considering the length of phalanges and angle of the thumb in order to make the dexterous robot hand, and the experiment confirmed that the thumb and the other four fingers could be all opposition motions. In addition, almost all actions such as power grasping, span grasping, key pinch, chunk grasping, and precision pinch can be performed and confirmed by experiment. Finally, to check compliance, the two robot hands of the lab, iLimb robot hand and proposed robot hand, were compared by impacting the rubber hammer, the proposed hand returned to its original position with compliant characteristics. Commercial robot hands have the disadvantages of being heavy, expensive, and uncompliance. The purpose of thesis is to design cheap, compliant and light multi DoF robot hands by replacing commercial robot hands, and to produce end-effector similar to human hands by using biomimatic MCP joint. The proposed robot hand system, excluding power system, weights 495g, and has active 11DoFs passive 14DoFs and designed a robot hand with a total of 25DoFs. The production cost of the robot hand is about $800.