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Finger and Wrist Torque Measurement System for the evaluation of grasp performance with Neuroprosthesis


M. Lawrence, Gion-Pitschen Gross, T. Keller

International Workshop on Functional Electrical Stimulation, Krems, Austria, no. 9, pp. 87-90

New multi-channel neuroprotheses have been developed which can significantly improve grasping function by allowing selective stimulation of the finger and wrist flexors and extensors. A new isometric measurement system was therefore developed to enable assessment of finger forces and wrist torques generated using multi-channel techniques. Finger forces (from the middle phalanxes) were recorded using five load cells (range ±100N) mounted on a ‘grasp handle’ that can be arbitrarily positioned in space. The hand and the grasp handle were rigidly mounted to a six degree of freedom load cell (±1000N, ±100Nm), and the forces and torques about the wrist recorded. A vacuum cushion was used to comfortably fixate the forearm. The position and orientation of the forearm, wrist, fingers and handle were recorded using a new 3-dimensional position measurement system (accuracy <±1mm). A mathematical model was used to provide an estimate of the joint centres, enabling the finger and wrist torques to be calculated. Analysis of the model indicated that small movements of the hand (<2mm) would confine the measured force error to less than 5%. Actual measurements during maximum voluntary contractions indicated small drifts (±1N, ±0.1Nm), however, a good repeatability (error < ±1N) could still be achieved. The measurement system was integrated into a real-time multi-channel transcutaneous electrode environment which is able control multiple activation regions across both the flexors and extensors. Using the combined system it is possible to optimise configurations for selective activation of the finger and wrist flexors and extensors. The technology can be used to configure and assess new multi-channel neuroprostheses for grasping.

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% Autogenerated BibTeX entry
@InProceedings { LawGro:2007:IFA_2995,
    author={M. Lawrence and Gion-Pitschen Gross and T. Keller},
    title={{Finger and Wrist Torque Measurement System for the
	  evaluation of grasp performance with Neuroprosthesis}},
    booktitle={International Workshop on Functional Electrical Stimulation},
    address={Krems, Austria},
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