Development and evaluation of an inexpensive sensor system for use in measuring relative finger positions

An inexpensive sensor was developed using a carbon-based electrically conductive ink. A correlation of the actual flex angle to the measured flex angle of the sensors was obtained by experimentally determining a third-order polynomial that represented the response of the sensor and its hardware system (r = 0.999). The response time, when going from an angle of 0-90 degrees, was extremely good. The sensors exhibited an acceptable dynamic response with an error of less than 5% when flexed repeatedly to an angle of 90 degrees. A second-order polynomial was found to express the resistance as a function of angle (r = 0.999) for all of the sensors tested. Although these sensors are not as precise as the more expensive sensors that are available, it was estimated that the production cost of these sensors was less then US $0.50 a piece. In addition, there are many ways that the sensor production method might be improved to produce more accurate sensors using carbon-based electrically conductive ink. While much additional work is still necessary, the system presented in this paper could be incorporated into a complete device to monitor the rehabilitation of an impaired hand. Unlike other systems that are currently available commercially, this system is inexpensive, easily manufactured, accurate, and could be readily used in a variety of clinical settings.