Three Dimensional Capacitive Force Sensor for Tactile Applications

Abstract

Sensors, Focus on Tactile, Force and Stress Sensors 144 application areas for tactile sensors such as food processing, bio-medical, entertainment, future domestic and service industries and robotics in medicine for minimally invasive and micro-surgeries. A major requirement of a tactile sensor is to have the ability of measuring the magnitude and location of an exerted force over the sensor. Further, well-designed tactile sensors must be thin and flexible, similarly to sensitive skin. Further, capacitive sensors are used in a wide variety of measurement and control systems, such as liquid-level gauges, pressure meters, accelerometers, precision positioners, and as described in this chapter, as force sensors. In these applications, the capacitances to be measured often range from tenths to tens of picofarads. In particular, there are a large variety of applications for capacitive sensors acting as three axis force sensors. This chapter is organized as follows: Section 2 describes different types of tactile sensors, giving examples of the ones using electromagnetic, piezoelectric, resistive and piezoresistive working principles. In section 3, a complete description of a three dimensional tactile sensor based on capacitive elements is performed. Section 4 describes some readout electronic techniques that could be applied to the sensor of section 3, namely switched-capacitor, capacitance to pulse-width, capacitance to duty-cycle and capacitance to frequency techniques. Section 5 is devoted to a complete description of a capacitance to voltage conversion technique that shows very good results when associated to the sensor of section 3. Finally, section 6 is dedicated to the conclusions.