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Abstract-We measured the input-output properties of the hand grasps of 14 individuals with tetraplegia at the C5/C6 level who had received an implanted upper limb neuroprosthesis. The data provide a quantitative description of grasp-opening and grasp-- force control with neuroprosthetic hand grasp systems. Static properties were estimated by slowly ramping the command (input) from 0 to 100%. A hand-held sensor monitored the outputs: grasp force and grasp opening. Trials were performed at different wrist positions, with two different-sized objects being held, and with both grasp modes (lateral and palmar grasps). Larger forces were produced when grasping larger objects, and greater opening was achieved with the wrist in flexion. Although active grasp force increased with wrist extension, it was not significant statistically. Lateral grasp produced larger forces than the palmar grasp. The command range can be divided into a portion that controls grasp opening and a portion that controls grasp force. The portion controlling force increased with spacer size, but did not depend significantly on grasp mode or wrist position. The force-command relationships were more linear than the position-command relationships. Grasp opening decreased significantly over a one-year period, while no significant change in grasp force was observed. These quantitative descriptions of neuroprosthetic hand grasps under varying conditions provide useful information about output capabilities that can be used to gauge the effectiveness of different control schemes and to design future control systems.
Key words: FES, hand grasp, neuroprosthesis, tetraplegia.
INTRODUCTION
Individuals with C5/C6 level tetraplegia can have hand grasp and release restored by Functional Electrical Stimulation (FES) via an implanted neuroprosthesis (1). The device improves these individuals' functions in activities of daily living (2). Numerous factors affect the quality of the hand grasp of a neuroprosthesis user, including electrode placement, control method, physiological characteristics, and neuroprosthesis characteristics. To optimize the hand grasp patterns, it is necessary to quantitatively evaluate the outputs of the system (i.e., the force and opening of the hand) and determine their relationship to the input of the system (i.e., the command signal) from an external transducer (Figure 1). We developed a series of tests to quantify and evaluate these factors (3). These tests provide the foundation for the current study in a larger user population.
METHODS
Subjects
Experiments were performed on...