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Optical Rotary Encoders - Incremental versus Absolute and Shafted versus Hollow Shaft Encoder Products

Optical Encoders

Encoder - Photo detector array - Code Disc - Spindle Assembly - Bearing Housing

There are two types of mechanical configurations for optical encoders: rotary encoders and linear encoders.

Optical rotary encoders are most commonly found in motion control systems while linear encoders are used more specifically for linear-positioning applications such as piston or actuator monitoring systems.

A rotary encoder using optical sensing technology relies on the rotation of an internal code disc that has opaque lines and patterns on it.

The disc is rotated (hence the name rotary encoder) in a beam of light such as an LED and the markings on the disc act as shutters blocking and unblocking the light.

An internal photodetector senses the alternating light beam and the encoder's electronics convert the pattern into an electrical signal that is then passed on to an external control system through the encoder's output


Rotary Encoders

Rotary encoders are also available in two formats: Incremental or absolute.
Rotary encoders can be built in two different body styles: shafted or hollow shaft.

Incremental versus Absolute Optical Encoders

Incremental vs. Absolute Optical Encoders
Incremental Encoders Absolute Encoders
Optical Rotary Encoder - incremental absolute hollow-shaft configurationsIncremental optical encoders are the simplest and most commonly used. The encoder provides information about the instantaneous position of a rotating shaft by producing one square wave cycle per increment of shaft movement. Referred to as the resolution of the encoder, this increment is built directly into the device's internal hardware.
Link to product pages: See BEI Optical Incremental Encoders or Magnetic Incremental Encoders.
Rotary Encoder - absolute - BEI Sensors Absolute optical encoders naturally have a more complicated signal structure. These encoders provide a "whole word" output with a unique code pattern that is derived from independent tracks on the encoder disc which correspond to individual photo-detectors and represents each position. The output from these detectors is HI or LO depending on the code disc pattern for that particular position.
Link to product pages: See BEI Optical Single-Turn Absolute Encoders, Optical Multi-Turn Absolute Encoders or Magnetic Single or Multi-Turn Absolute Encoders.

Shafted vs. Hollow Shaft Rotary Encoders.

Shafted vs. Hollow Shaft Rotary Encoders
Shafted Rotary Encoders Hollow Shaft Rotary Encoders
Optical Rotary Encoder - incremental BEI SensorsA shafted rotary encoder is built so that the rotor portion of the encoder is a short shaft that is usually attached through a flexible coupling to the shafts of various motion control equipment. The body of the shafted rotary encoder is commonly fixed by a rigid mounting bracket. See BEI shaft encoders as Optical or Magnetic. Encoder - HS35 - BEI SensorsA hollow shaft rotary encoder is composed in a way so that the rotor portion of the encoder is tubular, with the inner diameter of the rotor tube sized to accept and clamp to most standard shaft sizes. This style does not require the use of a coupling, however, the body of the rotary encoder must be constrained by a flexible tether arrangement. Hollow shaft encoders are available in two configurations: through-shaft and blind-shaft. See BEI hollow-shaft encoders as Optical Through/Blind Shaft or Magnetic Blind Shaft.