A shaft encoder or rotary encoder is an electro-mechanical device that allows the speed or angular position of a rotating shaft to be measured or signaled to a control system. It generates an electrical signal, either analog or digital, according to the rotational movement.

Different types of Shaft Encoder

There are two main types of shaft encoders which are available for both linear and rotary axes:

1- Absolute Encoder

This type of encoder maintains position information when power is removed from the encoder. On applying power, the position of the encoder is immediately available.

a)- The Resolver.
b)- Gray-Code encoder.

2- Incremental Encoder

An incremental encoder will immediately report changes in position, be it clockwise or counterclockwise. It does not though report or keep track of absolute position; it only reports incremental changes in position. As a result, to determine the absolute position at any particular moment, it is necessary to send the encoder signals to an additional encoder interface, which in turn tracks and reports the encoders absolute position.
The rotary incremental encoder is the most widely used of all encoders due to its low cost and its ability to provide real-time position information. They include:

a)-  Shaft Counters
b)-  Servo/Synchro Encoder
c)-  Incremental Quadrature Encoder

shaft encoder

How does a Shaft Encoder Work?

The working principle of the encoder are:

The knob (which can be rotated both clockwise or counter-clockwise) is internally connected to a disk. The disk has evenly spaced contact zones that are connected to a common pin and two other separate contact pins. When the disk starts rotating, the two contact pins start making contact with the common pin and the result is that two square wave output signals are generated.

Any of the output signals can be used to determine the rotated position by counting the signal pulses. If one wants to determine the rotation direction as well, both signals are considered at the same time. The two output signals are displaced at 90 degrees out of phase from each other. This means that if the encoder is rotating clockwise one output will be ahead of the other. If it is rotating counterclockwise, the output signals have equal values.

The controller can be programmed to read the encoder position and rotation direction by considering or counting the steps each time the signal changes, from High to Low or from Low to High, one can notice the opposite values of the two output signals at that time.
Shaft encoders can be built into a motor, or attached with a coupling to a protruding shaft.

shaft encoder

Applications of Shaft Encoder

Different applications of Shaft Encoder are:

1- Rotary encoders are ideal solutions for applications requiring measurement of speed, length, travel, the direction of rotation and where a high degree of accuracy is needed to know the position of a rotating component thus are used in all areas of industry. A shaft encoder is mainly used in Industrial Automation.

2- They are robustly constructed to withstand the conditions encountered in the industries.

3- They are used in servo systems for example packaging equipment, robotics, milling machines, motors, computer devices such as optomechanical mice, trackballs and in industries such as Printing, Packaging, Metal Processing, Textile and Machine Tools.