What is a rotary encoder?

What is a rotary encoder?

A rotary encoder is an electromechanical device that reads the position of a rotating component, such as a motor shaft, and generates an electrical output signal related to that position.

• Magnetic rotary encoders use a magnetized wheel attached to the shaft. As the shaft turns, the position of this wheel is read by a magnetic sensor attached to the component’s housing.
• Transmissive optical rotary encoders work in much the same way, but use a patterned disc instead of a magnetic sensor. As the shaft and disc rotate, an LED light shines through the disc, and a photodetector records the results in counts per revolution (CPR).
• Reflective optical rotary encoders work much like transmissive encoders, but instead of light passing through the disc, the disc reflects the light toward a sensor on the same side of the encoder as the emitter. This allows for a more compact encoder.

How an optical rotary encoder works

What information does a rotary encoder transmit?

Rotary encoders can be configured to send a shaft’s position in one of two ways: as an incremental measure or as an absolute value. Each of these has its advantages and drawbacks.

• Incremental rotary encoders transmit a shaft’s rotational speed, position, or direction in terms of count per revolution. Most use a single output channel. Some add a second output channel via a sensor typically mounted 180 degrees from the first. Including an index channel allows incremental rotary encoders to relay a shaft’s total number of revolutions, or to help synchronize the components of a servo motor application.
• Absolute rotary encoders transmit a unique signal related to the shaft’s current position. This allows absolute encoders to record not only a shaft’s rotational speed and direction, but also its position at all times during its operation. Absolute rotary encoders must be configured to send position information using the same language as the system’s control infrastructure.

[Watch] Multi-turn absolute encoders explained

What can a rotary encoder do for your application?

Many applications require precise control over their moving components, and rotary encoders supply the information that enables that control. For example, rotary encoders supply feedback that allows systems to modulate the speed of electronic motors under a variety of loads: when the load increases, rotary encoders tell the system that the motor’s speed has decreased, signaling that more power should be sent to the motor to maintain consistent rotational speed.

Rotary encoders can also tell precision equipment about a shaft’s current position, making them essential components in applications like robotics and many factory automation settings where highly coordinated servo motors are required.

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