An encoder is an electronic sensor capable of measuring a position along a straight line. They are commonly used in robotics and automation systems. There are several different types of linear systems, each using a different detection method to determine encoder location.
All varieties of this instrument require both a scale and a sensor to use properly. The scale is a straight piece of material marked at regular intervals, similar to a common reference point.
A sensor within the linear encoder device can detect each of these measurement intervals is moving past the slide. Every time a marked interval is detected and counted by the sensor, the output of the linear encoder changes.
Optical linear encoders: Optical linear encoders are very common and use high-contrast visible markings on the scale. The sensor in this instrument generally emits infrared, visible, or laser light on the marks. Pulses of light reflected by the scale marks are detected and counted. An optical encoder can be very precise and is often capable of determining the linear position within a micrometre.
The encoder is a rotary transducer, which through an electrical signal, indicates the angular position of a shaft speed and acceleration of the rotor of a motor.
How does an encoder work?
An encoder consists of a disk connected to a rotating shaft. The disk is made of glass or plastic and is “coded” with transparent and opaque parts that block the passage of light emitted by the light source (typically infrared emitters). In most cases, these blocked (coded) areas are arranged in a radial pattern.
As the shaft rotates, the infrared emitter emits light received by the optical sensor (or photo-transistor), generating digital pulses as the light passes through the disk or is blocked at different disk sections. This produces a sequence that can control the radius of the turn, the direction of movement, and even the speed.
Not all linear encoder markings are visible to the human eye. Magnetic encoders use small magnetic areas embedded in the scale. Each area of magnetism is detected by the sensor and counted. These are generally not as accurate as of the optical variety but can be used in dirty or humid environments that prevent optical detection methods.
The third type of encoder uses eddy currents to determine position. The scale of an eddy current encoder is designed to have different levels of magnetic resistance. Areas of low and high magnetic resistance are detected by monitoring for eddy currents caused by induction. Linear encoder data is sometimes used for informational purposes in a readout or display. The data can also be used as part of a more sophisticated computer-controlled system. Encoders are often used to provide a computerised device, such as an industrial robot or automated machine, with feedback on moving parts’ location and travel distance