Perceptie van kabel bedieningskrachten en verplaatsingen tijdens de bediening van een lichaamsbekrachtigde prothese

Rationale: Nowadays 20 - 40 % of the arm amputees decide not to wear a prosthesis. Of those who wear a prosthesis 40 -60% do not to use the full functionality the prosthesis offers. Users of a shoulder controlled body powered prosthesis complain about the shoulder harness cutting into the arm pit and about the tiresome use of the prosthesis. Recent research showed that the operating forces of commercially available prostheses are (too) high. Therefore, operation forces need to be lowered. On the other hand, operation forces getting too low may result in a loss of perception and of control. This research will investigate which operating forces can be perceived and controlled best by the users. Additionally the influence of different cable displacements on the best operating force will be investigated. Furthermore, the maximum operating forces will be measured to indicate whether the user's physical capacities will influence the preference of operating forces. The results of this study will be used as requirements for a new physiological prosthesis control system which will be designed to match the capacities of the user to the demands the user puts on the prosthesis to enable execution of ADL (activities of daily living).

Objective: The main objective of this study is to find cable operation forces and displacements which can be perceived and controlled best by a prosthetic user. The secondary objective is to relate the physical capacities of the subjects/users to the outcome measures of the main objective. Furthermore the outcome measures of the main objective should be supported by subjective data from surveys.

The experiment of approximately 2 hours is conducted during one appointment with the subject.

Subjects: A total of 25 subjects with a trans-radial deficiency will participate in the experiment.

Intervention: This experiment is designed to give insight into the quality of control of a body powered prosthesis and, more specifically, to determine the cable force and displacement associated with an optimal level of control, which are expressed as the primary outcome measures force reproduction error and force variability.
The experiment consists of a force reproduction task using a prosthetic simulator consisting of a hard socket and a shoulder harness which are connected by a Bowden cable. The hard socket end of the Bowden cable is connected to a spring. The spring can be exchanged with other springs of different stiffness to investigate different force- displacement-configurations in different trials.

Reference force levels vary between 10 and 40 N and are each presented in combination with a cable displacements ranging between 0 and 80 mm. First, subjects’ maximum voluntary contraction level (MVC) will be determined. Next, the subjects performs a series of force reproduction trials. Each trial consists of (visually) matching a reference force shown on a laptop screen and repeating this without visual feedback. Between the trials, subject are requested to fill in a NASA TLX questionnaire and colour a body map at the places they might feel discomfort. Finally, another MVC measurement is taken.
Forces and displacement are measured at the control cable of the prosthesis simulator using a force and displacement sensors and provide the input for the primary outcome measures.

Duration of experiment: The experiment will last approximately 2 hours including breaks.