A SIMPLIFIED CAD MODEL OF TRANS-RADIAL SOCKETS SUITABLE FOR SUBJECT ENERGY EXPENDITURE ASSESSMENT

Abstract

The measurement of the mechanical energy expenditure of a subject in accomplishing a given motor task has been reported as a valuable index to quantitatively assess his/her motor ability or pathology stage [1-3]. In order to compute this parameter applying inverse dynamics techniques [1], the subject’s joint kinematics during the motor task and the inertial parameters (i.e. the mass, centre of mass and inertia matrix) of his/her moving limbs must be known. While the joint kinematics can be measured in-vivo using a motion analysis system (e.g. an optoelectronic system), the inertial parameters of human limbs are usually retrieved from anthropometric tables [1]. When the subject acquired is an amputee fitted with an artificial limb the problem of determining the prosthesis inertial parameters therefore arises. Considering a trans-radial amputation levels, a prosthesis is composed by standardized parts (hand, battery, lamination ring and actuators), and the subject-specific inner and outer sockets: since the CAD models of these parts are usually unavailable their single and cumulative inertia parameters remain unknown. The aim of this work was therefore to propose two possible simplified CAD models for trans-radial prostheses and to identify among them which one leads to the best estimation of the mechanical energy expenditure during a flexion-extension of the elbow in the sagittal and horizontal plane and during a shoulder internal-external rotation. The models, of increasing complexity, take into account the sockets, battery and lamination ring.