Principle of position sensors

Principle of position sensors

Position sensors are used to monitor the position of joints. Information about the position is fed back to the control systems that are used to determine the accuracy of positioning.

In most cases in robots, a primary interest is to control the position of the arm. There is a large variety of devices available for sensing position. However, the mostpopular angular-position sensors are the following devices:

Encoders

Synchros

Resolvers

Potentiometers

Types of Position Sensor:

Position sensors use different sensing principles to sense the displacement of a body. Depending upon the different sensing principles used for position sensors, they can be classified as follows:

1.         Resistance-based or Potentiometric Position sensors

2.         Capacitive position sensors

3.         Linear Voltage Differential Transformers

4.         Magnetostrictive Linear Position Sensor

5.         Eddy Current based position Sensor

6.         Hall Effect based Magnetic Position Sensors

7.         Fiber-Optic Position Sensor

8.         Optical Position Sensors

Potentiometric Position Sensors:

Potentiometric position sensor use resistive effect as the sensing principle. The sensing

element is simply a resistive (or conductive) track. A wiper is attached to the body or part of

the body whose displacement is to be measured. The wiper is in contact with the track. As the

wiper (with the body or its part) moves, the resistance between one end of the track and the

wiper changes. Thus, the resistance becomes a function of the wiper position. The change in

resistance per unit change in wiper position is linear.

Resistance, proportional to wiper position, is measured using voltage divider arrangement. A

constant voltage is applied across the ends of the track and the voltage across the resistance between the wiper and one end of the track is measured. Thus, voltage output across the wiper and one end of the track is proportional to the wiper position.

The conductive track can be made linear or angular depending upon the requirements.

The tracks are made from carbon, resistance wire or piezo resistive material.