Tactile sensors are devices that are sensitive to touch, and they collect and document information when there is contact with objects in the environment. In general, tactile translates to “touch.” Hence a tactile sensor is also termed a touch sensor.

What are tactile sensors?

Tactile or touch sensors measure the intensity of touch with particular objects in the environment. They work when the sensor of a device comes close to a human or an object. They are designed to behave like switches when they are touched. Due to their inexpensive cost and simple design, mechanical switches often replace them.

There are three different types of touch sensors that are sensitive to contact, pressure, and force. They are:

  • Force sensor
  • Dynamic sensor
  • Thermal sensor

Operating principle of touch sensors

The operating principle of tactile sensors is similar to that of mechanical switches. When the sensors come close to force, touch, or temperature, they behave like closed switches, and when the pressure is released, they behave like open switches. Different types of tactile sensors mainly function on the following principles:

  • Piezoelectricity: When the magnitude of voltage generated during the deformation of crystal lattice changes, it changes the resistance in sensors.
  • Capacitance: The pressure applied on the two conductive plates changes, and the capacitance in the parallel plate capacitors changes directly.
  • Piezo- resistivity: The deformation of shape caused due to an applied force changes the resistance of a piezoresistivity sensor.

Working with a capacitive touch sensor

Capacitive tactile sensors are the simplest form of sensors. They consist of two metal plates that act as conductors and an insulator. The electrode at the end represents one of the conductor plates, and the second conductor plate is represented by the environment and a conductive object (human finger). Capacitance is directly proportional to surface area and inversely proportional to distance.

On one end, the sensor (electrode) is connected to a measuring device, and the capacitance is measured periodically. When an external object like a human finger approaches the sensor, the capacitance will increase, and the data is measured by a measuring device which converts it to a trigger signal.

touch sensor

Working with a resistive touch sensor

These sensors have a much longer duration than the capacitive sensors and work with non-conducting materials like plastic, stylus, etc. This sensor comprises two layers covered in the film, separated by spacer dots. The conductive layer is covered with a transparent metal layer and is subjected to voltage.

When an external pressure or force is applied on the other surface, the two layers come in contact and create a voltage drop, which is recorded in the measuring instrument. These types of sensors are used in harsh environments, and their response time is significantly greater. Hence they are being replaced by capacitive sensors.

Uses of tactile sensors

  • Everyday household items
  • Performance testing of various applications
  • Medical imaging
  • Robotics