How Do Encoders Work? | Introduction

Before discussing the operating principle of an encoder, it is important to understand what an encoder is and what it is used for.

What is an Encoder?

An encoder is a device that converts motion into an electrical signal. This signal can be read by a control device such as a pulse counter or a PLC controller. Control devices can use this signal to control a process whose occurrence is dependent on a condition being met, such as activating a printing head and printing on components in the correct location.

Encoders use several technologies to create the signal, such as magnetic, resistance. The most widely used encoders today are OPTICAL encoders. These can be classified as ABSOLUTE or INCREMENTAL.

Incremental Encoders provide a signal in the form of a pulse wave with a high or low state, which allows the direction of rotation to be determined. They are characterized by the inability to determine a specific position, it is only possible to examine the movement from one position to another.

Absolute Encoders on the other hand also send a unique signal for each possible position. In other words, they provide information about the change in position from one to another, as well as a unique "indicator" code for each position.

Each type of encoder has its advantages, but in this article we will focus on the most popular encoders - INCREMENTAL ENCODERS.

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The above encoders are available with two types of outputs: single channel or dual "square" channel. Single-channel devices, often called tachometers, are used in systems that rotate in one direction and provide simple information about the range of motion and speed.

Encoders with a double output have two channels (A and B) phase-shifted by 90 degrees. Thanks to the two channels, it is possible to detect the direction based on the detection of mutual relations between them. This type of encoder is used for high-speed systems that require accurate information about the direction and range of motion.

How is the signal generated in the encoder?

The light beam emitted by the LED passes through a transparent disk on which an opaque line is applied. The light signal is read by a photo sensor, which is a sensor that detects light. In response to the supplied light pulses, the photo sensor generates a square wave, i.e. pulses. The pulses then go to a counter or controller, which after counting a certain number of pulses can perform a programmed action. Incremental encoders can also generate a signal for a full rotation, often called "index", "marker" or reference signal. This signal is generated on a separate "Z" channel.

Fig. Encoder construction scheme.

The resolution of the encoder is a parameter that determines the number of pulses generated during one full rotation of the encoder. The higher this value is, the more accurate the positioning is. The number of encoder applications in industry is very large. Cutting to length, plotters, industrial robots, packing, conveyor transport, sorting, filling, these are all examples of problems using encoders.