Towards better perception

Abstract

The available shoulder harness controlled prostheses do no fulfill the requirements of the users. It is unknown for which operating forces and cable displacements the user can make good use of proprioceptive feedback without feeling pain, discomfort or fatigue. These operating forces and cable displacements can be related to grasping forces and opening widths for activities of daily living to result in force and displacement transmission ratios for improved prosthetic design. The purpose of this research was to find operating force and cable displacement combinations that could be produced best without visual feedback. The force-displacement combinations were realized by a force task and interchangeable spring in the experimental setup. Thirty participants without arm defect wore a prosthesis simulator. They were first asked to produce a reference force with direct visual feedback of their operating force, next they were asked to reproduce this reference force without visual feedback. The error between visual produced value and blind reproduced value was used to evaluate the results. Best reproduced operating forces were found between 24 and 32 N. Best reproduced cable displacements were dependent on the spring that was used; the larger the cable displacement was, the better the result. For larger forces it was more difficult to repeat the reference force-displacement. A perfect prosthesis should be operated by forces between 24 N and 32 N. It is important to take the amputee and their individual abilities into account as the results differ largely between participants.