Finger prostheses are devices developed to emulate the functionality of natural human fingers. On top of their aesthetic appearance in terms of shape, size and colour, such biomimetic devices require a high level of dexterity. They must be capable of gripping an object, and even manipulating it in the hand. This paper presents a biomimetic robotic finger actuated by a hybrid mechanism and integrated with a tactile sensor. The hybrid actuation mechanism comprises a DC micromotor and a Shape Memory Alloy (SMA) wire. A customized test rig has been developed to measure the force and stroke produced by the SMA wire. In parallel with the actuator development, experimental investigations have been conducted on Quantum Tunnelling Composite (QTC) and Pressure Conductive Rubber (PCR) towards the development of a tactile sensor for the finger. The viability of using these materials for tactile sensing has been determined. Such a hybrid actuation approach aided with tactile sensing capability enables a finger design as an integral part of a prosthetic hand for applications up to the transradial amputation level.
The aim of this work is to formulate a spasticity symptoms-oriented model, in terms of its capability to consistently emulate unidirectional and velocity-dependent spasticity symptoms, based on a Modified Tardieu Scale (MTS). Spasticity stiffness can be simulated using two dynamic equations expressing 1) muscle tone catch during passive stretching at different velocities and 2) resistance through Range Of Motion (ROM). Muscle tone is proportionate to velocity; where muscle resistance is constant until reaching a certain angular velocity. Following different Modified Ashworth Scale (MAS) levels, muscle resistance can occur at varying degrees through the ROM. The simulated spasticity of MAS 1+, based on the developed model, shows a strong positive linear correlation coefficient with average r = 0. 7414 for fast forearm extension. The derived model will be used to develop new principles of variable stiffness actuation in an upper limb part-task trainer that is able to emulate upper limb spasticity symptoms.
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