Implementation of natural sensory feedback in a portable control system for a hand grasp neuroprosthesis.

This paper presents the design and implementation of the first generation of a portable system for a hand grasp neuroprosthesis that is controlled by means of signals from natural sensors in the skin of the index finger. To reduce development time and costs, we based our design on readily available, standardised modules such as a 486DX100 compatible CPU, a data acquisition board, a flash disk storage unit, and a high-efficiency DC/DC switch-mode power supply. Additionally, we designed and built a telemeter to supply an implanted muscle stimulator with power and control data. The signal from the natural sensors was recorded with a cuff electrode implanted around the palmar digital nerve innervating the radial aspect of the index finger. For amplification of the recorded nerve signal, we added an external low-noise nerve signal amplifier. For pre-processing of the recorded nerve signal, an optimised band-pass filter was used. A data-recording unit allowed storage and off-line analysis of the stimulator command and the recorded nerve signal. The portable system was used by a tetraplegic volunteer to test the feasibility of including natural sensors in a hand grasp neuroprosthesis for activities of daily living. The flexibility of the presented system allows rapid prototyping of experimental FES hand grasp systems intended for portable use.