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Received May 20, 2017; Revised Oct 21, 2017; Accepted Nov 16, 2017
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1. Introduction
Transradial amputations refer to loss of both biological hand and wrist and are the most common form of upper extremity amputation according to statistics [1]. Traumatic accidents, vascular complications, and congenital deformity are notable causes leading to transradial amputation [1]. Transradial prosthesis is used as a wearable device by the transradial amputees. It consists of an artificial wrist and a terminal device which are either mechanically or electromechanically operated [2, 3]. Although there had been a marked improvement in functionality, performance, and appearance of subsequent generations of transradial prostheses, the robotic counterparts are still lacking in certain areas to restore or mimic the missing segments of the biological limb [3]. In particular, most transradial prostheses are designed to perform a few of the grasping tasks with limited degrees of freedom (DoF), in comparison to the biological wrist and hand that have 27 DoF [4].
In general, effectiveness of transradial prostheses has been determined based on power consumption, weight, mobility, appearance, and size of the device [5]. These also serve as benchmarks to compare and contrast different prosthetic developments. According to literature, three main categories of transradial prostheses can be identified based on method of powering: nonpowered, body-powered, and externally powered prostheses [3]. Nonpowered or cosmetic transradial prostheses are made considering anthropometry and appearance of hand and characteristically do not have any or limited functional capabilities [6]. At present, body-powered transradial prostheses are the most popular prostheses since they are lightweight, simple in operation, easily maintained, economical, and importantly capable of restoring certain functions of the biological hand [6]. Since they can only perform maximum two grasping actions from a single terminal device, different terminal devices are required to fulfill various activities of daily living (ADL) [7]. The externally powered transradial prostheses are mostly operated by means of electric and pneumatic actuators. These prostheses exhibit higher functional capabilities compared to other two categories. However, externally powered transradial prostheses are typically limited in operation due to high power consumption, complexity in operation, reliability, bulkiness,...