Design of Underactuated Tendon Driven Finger with Compliant Joint Mechanism

Abstract

This thesis proposes design of tendon routing for fingers which have compliant joints. There are two types of fingers in this thesis, and one called as single mode finger performs actively one motion (power grasping) with one actuator. The other called as double mode finger performs actively two motions (power grasping and pinch grasping) with two actuators. The movement of the joint is not only actively generated by the actuator, but also occurs passively by external force due to its compliance. All joints which are used in two types of fingers are based on tensegrity structure, and are compliant since they consist of only tensile parts and compressive parts. The proposed joints can be divided into two basic types, tensegrity universal joint and tensegrity revolute joint. In the case of the unmodified joint model, tensegrity universal joint allows rotational movement about two axes (flexion/extension and abduction/adduction), and tensegrity revolute joint allows rotational movement about one axis (flexion/extension), without deformation of structure. In addition, UR joint which is mixed properties of universal joint and revolute joint will is introduced. Two types of fingers have four phalanges and three joints. In the case of single mode finger, flexion/extension can be performed on all joints, and abduction/adduction can be performed when extension on proximal joint. One tendon is connected to one actuator, and makes the single mode finger to actively flex. Extension and abduction/adduction motions of single mode finger occur passively due to the structural features of joints. For the double mode finger, all joints are capable of flexion/extension and abduction/adduction motions. Two tendons are used to perform two motions. One tendon affects the proximal joint and middle joint, and performs an active flexion motion. The other tendon is connected antagonistically to the distal joint, which allows the distal joint to rotate independently. The tendons connected to the modified joints and the unmodified joints make angles of the joints by given force and position which are input values, respectively.