Virtual artificial sensor technique for functional electrical stimulation.

In the control of Functional Electrical Stimulation (FES) gait systems artificial sensors are used to provide the controller with feedback information. The sensors used range in complexity from simple heel or hand switches to tri-axial accelerometers. There are three basic problems connected with the selection of sensors: the type(s) of sensor(s) to be used, the number of sensors required and the optimum location of the sensor set. In general the choice of the sensor sets has been based on the availability of actual sensors and the experts understanding of where these sensors should be located. Using motion analysis data it is possible to construct an almost unlimited number of virtual sensors on any location of the body surface. Our aim was to develop this technique for construction of virtual sensors and compare these virtual sensors with their physical counterparts. Virtual goniometers, inclinometers, accelerometers and foot switches were constructed and compared with their physical counterparts. In addition visualisation tools were developed to aid in the choice of sensor location. There was a very good correlation between all the virtual and physical sensors. This technique gives flexibility to place virtual sensors almost anywhere on the body surface and also allows the construction of novel sensors.