Tactile Sensors

Introduction

Tactile sensing is the ability to detect an object and recognise its shape. For this, the sensor must have many sensing points. Tactile sensors are a type of external state sensor in Robotic Sensors.

• commercial tactile sensors are flat pads
• the sensor detects the force when an object is pushed against it
• it can recognise the shape of an object or find its orientation
• they are often installed on grippers or fingers

Photo detector tactile sensors

• a plastic pin is connected to an elastomeric (rubber like) pad
• the end of the pin blocks part of a light beam between a photo emitter and a photo detector
• when a force is applied, the pin moves in proportion to the force and blocks more of the light
• the sensor is a grid (array) of these cells, so it can sense the pressure at many points

VLSI tactile sensors

• the sensor is made from a VLSI wafer
• pressure sensitive conductive rubber is laid over an array of sensing electrodes

How it works:

• the rubber makes a resistive path between the electrodes in each cell of the array
• when pressure is applied, the rubber compresses and its resistance decreases, for example from 1000 $\Omega$ to 100 $\Omega$
• after a threshold pressure, current can flow between the electrodes and the rubber
• a voltage comparator changes the electrode voltage $V_m$ into digital pressure data