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Session: Poster session I
Session starts: Thursday 24 January, 15:00

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Mona Hichert (Delft University of Technology)
Dick Plettenburg (Delft University of Technology)

Abstract:
Introduction Body powered arm prostheses require too high operating forces. Prosthetic use is found tiresome or even painful. The required operating forces need to be lowered. The ideal prosthesis should be powered by cable operation forces and displacements which can be invariably perceived by the user and do not lead to pain or fatigue. Earlier research showed good perception in a force range between 20 and 30 N at fixed cable displacement. The question remains: With which cable force and displacement should a prosthesis be operated when also taking into account cable displacements? Method A prosthesis simulator was fitted to 30 subjects without arm defect. Instead of a prehensor an interchangeable spring was placed at the end of the control cable. The cable forces were measured with a force sensor located close to the shoulder harness. Cable displacement was calculated though the known spring constant and the measured cable forces close to the spring. Cable force and displacement were fed back to a laptop running a LABVIEW programme. The subject was requested to reproduce a given force and hold it constant for 2 seconds. Visual feedback was enabled every second repetition. Nine different combinations of forces and displacements were measured. Results The smallest replication error (reproduced minus reference force) was found between 24 and 33 N. For every spring an inverse relationship between cable displacement and replication error was found. Discussion & Conclusion The smaller the replication error the better the perception. Since in this experiment the smallest replication error (and therefore the preferred force level for prosthesis control) was found for cable forces between 24 and 33 N, the finding of the prior research seems to be confirmed. Perception of cable displacement seems to be dependent on spring constants and is better at larger spring deformations.