Development of an Anthropomorphic Prosthetic Hand with Underactuated Mechanism

An anthropomorphic prosthetic hand for wrist or forearm amputees is developed herein. The prosthetic hand was designed with an underactuated mechanism, which makes self-adaptive grasping possible, as well as natural motions such as flexion and extension. The finger and thumb modules were designed with four degrees of freedom by motions of the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints. In this research, we pursued several novel trials in prosthetic hand design. By using two four-bar linkages composed of a combination of linkages and gears for coupling joints at each finger, it was possible to make a compact design, and the linkage has advantages such as accurate positioning, uniform power transmission, and high payload. Also, by using constant-velocity joints, torque is transferred to finger modules regardless of adduction/abduction motions. In addition, adduction/abduction and self-adaptive grasping motions are passively realized using torsional springs. The developed prosthetic hand was fabricated with a weight of 475 g and a human hand size of 175 mm. Experiments with diverse objects showed its good functionality.

Development of Gripper to Achieve Envelope Grasping with Underactuated Mechanism Using Differential Gear

In a previous study, we developed a seven-axis multi-joint gripper (MJG) with a mechanism for varying the joint stiffness and showed that it was capable of dexterous grasping. In this research, we expand this design by introducing a hand with several multi-jointed fingers. The mechanism of grasping with this hand involves the use of serially connected differential gear systems (DGSs). The DGSs are controlled by only two actuators: one for driving the joints simultaneously and the other for adjusting the stiffness of all of the joints. The hand is shown to successfully grasp and envelope objects of some shapes without sensory feedback and handle objects by pinching them with the finger tips and subsequently transitioning to an envelope grasp. The mechanism that significantly contributes to this result is the tip roller attached to the fingertip. It is incorporated into the joint drive mechanism using a DGS. These functionalities are considerably advantageous in scenarios where information about the objects to be grasped, such as the shape and precise position, cannot be obtained.

HyPro: A Multi-DoF Hybrid-Powered Transradial Robotic Prosthesis

This paper proposes a multi-DoF hybrid-powered transradial robotic prosthesis, named HyPro. The HyPro consists of two prosthetic units: hand and wrist that can achieve five grasping patterns such as power grasp, tip grasp, lateral grasp, hook grasp, and index point. It is an underactuated device with 15 degrees of freedom. A hybrid powering concept is proposed and implemented on hand unit of HyPro where the key focus is on restoration of grasp functions of biological hand. A novel underactuated mechanism is introduced to achieve the required hand preshaping for a given grasping pattern using electric power in the pregrasp stage and body power is used in grasp stage to execute the final grasping action with the selected fingers. Unlike existing hybrid prostheses where each of the joints is separately controlled by either electric or body power, the proposed prosthesis is capable of delivering grasping power in combination. The wrist unit of HyPro is designed and developed to achieve flexion-extension and supination-pronation using electric power. Experiments were carried out to evaluate the functionality and performance of the proposed hybrid-powered robotic prosthesis. The results verified the potential of HyPro to perform intended grasping patterns effectively and efficiently.

Design, Modeling and Optimization of the Universal-Spatial Robotic Tail

This paper presents a novel robotic tail design that utilizes a serial chain of universal joints to generate spatial motion. In nature, animals utilize their tails to assist in maneuvering and stabilization while moving; this research aims to provide a robotic platform capable of extending these functionalities to a mobile robot. By utilizing a tail to assist in stabilization and maneuvering, the required functionality of other locomotion mechanisms in a mobile robot, such as legs, is reduced. The tail mechanism presented is actuated by sets of three cables routed along the robotic structure; quasi-independent segments within the tail are created by tying off a set of three cables to a link along the tail. Actuation is distributed within the underactuated mechanism by compression and extension springs mounted along the tail. Kinematic and dynamic analysis of the tail is performed to model the tail trajectory and predict the actuation requirements. Three methods of optimizing spring stiffnesses are provided that weigh different performance goals, and a methodology for using these results to select spring stiffnesses is provided. Results are generated to compare the kinematic, static and dynamic models to one another to analyze the impact the different loading effects have on the tail behavior.