What Is Absolute Encoder And How Does It Work

Introduction

Absolute encoders provide feedback on speed and position information by providing output in relation to the motion. The different types of absolute encoders, how they work, and their advantages are as follows:

Types of Absolute Encoders

Absolute encoders are classified into optical or magnetic encoders based on their sensing technology. Optical encoders have a code disc with markings. They also have a LED that shines through the code disc. Optical encoders can determine the changes in the position of the disc as it turns with the motor shaft. In the case of magnetic encoders, optical markings are replaced by magnetic poles. They contain a magnetic sensing array instead of an LED.

Absolute encoders determine the feedback based on the shaft rotation. However, the need to know the number of times the encoder makes a complete turn depends on the specific application.

How Absolute Encoders Work?

The key function of an absolute encoder is to determine the position of shaft rotation. It does so by using a static reference point. The method of determining the changes in position can differ depending upon whether an optical encoder or magnetic encoder is used. However, the working principle for both types of absolute encoders remains the same.

Absolute encoders have two discs with each disc having concentric rings with offset markings. One of these discs is fixed to the central shaft while the other can move freely. The markers along the track of absolute encoders change position as the disc rotates. Each of these configurations on an absolute encoder corresponds to a unique binary code. You can use these binary codes to determine the absolute position of the object.

Advantages of Using Absolute Encoders

Absolute encoders have some distinct advantages over incremental encoders. They can measure position accurately and very reliably by assigning unique binary codes to each configuration. This means that absolute encoders can measure changes in position even when the power is turned off. They also have higher resolutions compared to incremental encoders. They add additional tracks for achieving higher resolutions and do not provide output in terms of continuous pulses.

Many industries use absolute encoders on a large scale. They are used for determining multi-axis orientation for CNC machines and accurately positioning multiple stabilizers for large vehicles. Absolute encoders find use in applications for moving automatic doors and bays without a limiting switch, continuing robotic movement after a power failure, automatically determining the height of scissor beds in hospitals, etc.