Grasp synthesis for upper-extremity FNS. Part 1. Automated method for synthesising the stimulus map.

Functional neuromuscular stimulation (FNS) has been used in open-loop upper-extremity neuroprostheses to provide grasp and release for quadriplegic individuals. A principal issue in implementation of the open-loop neuroprosthesis is the synthesis of the grasp stimulus map, which is the relationship between the input control signal and the output stimulus applied to each electrode. The goal of this project was to develop a method of stimulus map synthesis which compensates for the influence of the electrode-position-dependent recruitment properties on the grasp output, and which can be performed using automated procedures. A method called the external moment grasp synthesis procedure (GSP) has been developed which meets these criteria. The GSP uses an external moment of model of the hand which describes the interaction between the active moments produced by electrical stimulation, the passive joint moments and the total joint moment and angle. The GSP was used to develop the stimulus map for three paralysed subjects, and in all cases the GSP-generated grasp patterns had lower errors than grasp patterns developed using the previously implemented rule-based method of stimulus map synthesis. The GSP was successfully implemented by computer and was able to compensate for the effects of the electrode recruitment properties on the grasp pinch force.