Paper 3: An Externally Powered Prosthesis for the Complete Arm

Abstract

The arm which is being developed at the Princess Margaret Rose Orthopaedic Hospital, Edinburgh, has voluntary control of four degrees of freedom of the hand (three positional and one rotational), prehension, automatic control of a further degree of freedom (rotational), and can provide an indication of ‘feel’. The control and use of a multimovement arm such as this would present an unacceptably severe task if it was attempted on a time/velocity basis. Over the last two and a half years we have been fitting a position-servo system to our present simple arm (two movements and prehension) and the children who use it have achieved a considerable degree of unconscious control and position awareness of the limb. The results that have been achieved with position-servo control of the present arm have depended on using the proprioceptive information which has been provided by the shoulder control sites as a reflection of the positional state of the limb, and they demonstrate the quality of the match of the characteristics of the arm to those of the user.