| The fundamental requirement of a competent tactile sensor for manipulating an object is to determine the magnitude and the position of an applied force on it. In addition, it is important to determine orientation of the object in relation to the tactile sensor. In order to achieve these goals, most investigators have attempted to design a tactile sensor using an array of sensing elements arranged in matrix form. There are several problems associated with this type of tactile sensors. These problems include cross-talk between sensing elements, fragility, and complexity. This thesis reports on the design, modeling, fabrication and testing of a membrane tactile sensing system with only four sensing elements. By using membrane stress combined with triangulation approach, it is shown that it is possible to overcome the above problems. The prototype sensor consists of a single film of 25 micron thick Polyvinylidene Fluoride (PVDF) film, which is held between two 12 mm-thick flat Plexiglass plates, each with a 90 mm-diameter center hole. Four square sensing elements, each 3 min side, were fabricated around the center of the membrane. The fabrication of the sensing elements is performed using photolithographic and etching techniques. By applying force with a probe of various shapes and sizes at various points away from the sensing elements, and using a geometric mapping process, the sensor is calibrated. As the result of calibration various isocharge contours were drawn. Using both finite element and experimental analysis, it is shown that it is possible to determine the position, orientation and the magnitude of the applied load though various flat shaped probes, by using only four sensing elements. The experimental and the finite element results are compared. It is shown that there is a good correlation between the finite element predictions and experimental data. |
