The study of tactile sensors has broad and narrow meanings. The generalized sense of touch includes touch, pressure, force, slip, cold and heat. The narrow sense of touch includes the sense of force on the interface between the robot and the object. From the perspective of function, tactile sensors can be roughly classified into contact sensors, force-torque sensors, pressure sensors, and sliding sensors.
In recent years, mainstream tactile sensors have been mainly classified into five categories according to their principle of action.
(1) Capacitive tactile array sensor. The principle is that the external force changes the relative displacement between the plates, so that the capacitance changes, and the haptic force is measured by detecting the amount of capacitance change.
(2) Inductive touch sensor. It uses the principle of electromagnetic induction to convert the pressure action into a change in the self-inductance coefficient and the mutual inductance of the coil, and then converts the circuit into a voltage or current change output.
(3) Photoelectric touch sensor. It is based on the principle of total internal reflection and is usually composed of a light source and a photodetector. When the pressure applied to the interface changes, the reflection intensity of the sensor's sensitive component and the source frequency change accordingly.
(4) Piezoresistive touch sensor. It is a device made according to the piezoresistive effect of semiconductor materials. The substrate can be directly used as a measuring sensor element, and the diffusion resistor is connected in the form of a bridge in the substrate. When the substrate is deformed by an external force, the resistance values will change, and the bridge will produce a corresponding unbalanced output.
(5) Piezoelectric touch sensor. Under the action of pressure, a potential difference occurs between the two end faces of the piezoelectric material; on the contrary, the applied voltage generates mechanical stress.