Shape memory alloy actuators for upper limb prostheses

• Main Author: Soares, Alcimar Barbosa
• Published: University of Edinburgh 1997
• Subjects: 612
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.662230

Despite the technological advances of the twentieth century, we are not yet able to produce artificial limbs which "mimic" perfectly their natural counterparts. In general, artificial limbs are not as dextrous as human limbs, the control is unnatural and there is no proper feedback by which the user can assess the status of the prosthesis. In this thesis the problems related to upper-limb prostheses are considered. The use of a special material known as Shape Memory Alloy (SMA) is investigated towards producing improved joint actuators for small artificial prostheses such as those required by young children. SMA actuators can be very lightweight, their motion is silent and smooth and yet they are capable of delivering considerable power per unit of weight. The Shape Memory phenomenon and the many challenges involved in its application are discussed. The detailed design of an SMA joint actuator for a hand mechanism in an above-elbow prosthesis for young children is given. To assist the design and construction of both the artificial hand and the actuator, a mathematical model was developed and incorporated in a computer program simulating the forces and movements within the hand. The model was used to optimise the hand mechanism and specify the required joint actuator. Suitable SMA elements were identified through laboratory tests. The hand mechanism was constructed and the actuator, control systems and power source were attached to it. Tests were performed to investigate the characteristics of the complete device. The results show that, although SMA actuators must be designed and used with great care, they do offer a viable and more natural alternative to conventional actuators such as pneumatic devices and electric motors in certain applications.