Resistive Tactile Sensors

Friday, May 4th, 2018 - Force, Piezoelectric, Resistive Transducers

Resistive Tactile Sensors

Resistive devices are the most popular tactile sensors at present, because of their higher sensitivity and x-y resolution. They can be based on a variety of resistive compounds such as carbon fibres, conductive rubbers and various specially developed media impregnated with conductive dopants. Although they all exhibit the required property of a change in resistance in response to an applied pressure, the last category has achieved the highest popularity because of its lower hysteresis and larger dynamic range.

resistive tactile sensors,resistive tactile sensing,piezoresistive tactile sensor

Figure 1. Piezoresistive tactile sensor (after Robertson and Walkden, courtesy of SPIE, 1983)

There are two main ways to measure the resistance change-in line with the applied force vector, hence measuring vertical resistance changes, and perpendicular to the applied force vector, hence measuring horizontal resistance changes. An example of a tactile sensor which measures resistance change on a vertical plane is shown in Figure 1 (a).

The resistive mat used in this sensor is a piezoelectric material whose sensitivity curve is shown in Figure 2 which highlights the low hysteresis of this type of device.

Piezoresistive tactile sensor characteristic

Figure 2. Piezoresistive tactile sensor characteristic (after Robertson and Walkden, courtesy of SPIE,1983)

The advantage of such a construction is the higher x-y tactel resolution achieved by having the two electrode patterns on separate parallel planes. The consequent drawbacks are the higher crosstalk due to the capacitive effect, which can however be compensated for by the interfacing electronics as previously shown in Figure 1 (b), and the shorter life of the top electrode, which needs to be deformed mechanically by the applied force for each measurement. A typical output of the tactile sensor thus described is represented by Figure 3 which shows the pressure image of a rectangular object on an isometric display.

Typical tactile sensor output image

Figure 3. Typical tactile sensor output image (after Robertson and Walkden, courtesy SPIE,
1983)

An alternative approach to the construction of a resistive tactile sensor is to measure the resistance change horizontally, as shown in Figure 4, the main advantage being the absence of an electrode between the resistive material and the applied force which increases its operational life. However, accommodating both electrode patterns underneath the resistive medium necessarily increases the tactel size and therefore reduces the sensor x-y resolution.

Piezoresistive tactile sensor with horizontal electrodes geometry

Figure 4. Piezoresistive tactile sensor with horizontal electrodes geometry

I hope this information about “Resistive Tactile Sensors” is useful.