Motor Encoder Overview

An encoder is an electromechanical device that provides an electrical signal that is used for speed and/or position control. Encoders turn mechanical motion into an electrical signal used by the control system to monitor specific parameters of the application and make necessary adjustments to maintain the machine operating as desired.

motor encoder mounted to vector motor

The type of application determines the parameters monitored and can include speed, distance, RPM, position among others. Applications that utilize encoders or other sensors to control specific parameters are often called closed-loop feedback or closed-loop control systems.

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What is A Motor Encoder?

Motor Encoders

A motor encoder is a rotary encoder mounted to an electric motor that provides closed-loop feedback signals by tracking a motor shaft's speed and/or position. Various motor encoder configurations are available such as incremental or absolute, optical or magnetic, and shafted or hub/hollow shaft, among others. The type of motor encoder used depends upon many factors, particularly motor type, the application requiring closed-loop feedback, and the mounting configuration required.

How to Specify A Motor Encoder

When selecting components for a closed-loop control system, the motor encoder choice is first determined by the type of motor chosen in the application. The most common motor types are:

AC Motors Encoders

AC induction motors are popular choices for general automation machine control systems as they are economical and rugged. Motor encoders are used for more precise speed control in applications using AC motors and often times need to have more robust IP, shock and vibration parameters.

Servo Motor Encoders 

Servo motors encoders (permanent magnet motor encoders) offer closed-loop feedback control systems to applications that require higher precision and accuracy and are less robust than AC induction motors. The motor encoder used on servo motors can be modular, incremental, or absolute, depending on the level of resolution and accuracy required.

Stepper Motor Encoders

Stepper motors are cost-effective, precise, and are typically used in open-loop systems. In systems using stepper motors where speed control is required, an incremental motor encoder is often mounted allowing the stepper motor system to achieve closed-loop feedback. Stepper motor encoders can also be used in some applications to allow for improved control of stepper motors by providing precision feedback of the location of the motor shaft in relation to the step angle. 

DC Motor Encoders 

DC motor encoders are used for speed control feedback in DC motors where an armature or rotor with wound wires rotates inside a magnetic field created by a stator. The DC motor encoder provides a mechanism to measure the speed of the rotor and provide closed-loop feedback to the drive for precise speed control.

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Motor Encoder Mounting Options

The next factor impacting motor encoder selection is the mounting option, and the most common options are:

  • Shafted Motor Encoders: Uses a coupling method to connect the motor encoder shaft to the motor shaft. The coupling provides mechanical and electrical isolation from the motor shaft but can add cost via the coupling and the longer shaft length required to mount the motor encoder.
  • Hub/Hollow shaft Motor Encoders: Hollow shaft encoders directly mount to the motor shaft via a spring-loaded tether. This method is easy to install and requires no shaft alignment, but proper care must be taken to provide electrical isolation.
  • Bearingless Motor Encoders: Also known as ring mount, this mounting option comprises a sensor assembly in the form of a ring mounted on the motor face and a magnetic wheel mounted on the motor shaft. This type of motor encoder mounting configuration is mostly found in heavy-duty applications like paper, steel, and cranes.

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Types of Encoder Technology

The application in which the motor encoder is being utilized will determine the motor encoder technology that needs to be used. The two broad types of motor encoder technologies available are:

  • Incremental Encoders: The output of an incremental motor encoder is used to control the speed of a motor shaft. Learn more about incremental encoder technology.
  • Absolute Encoders: The output of an absolute motor encoder indicates both the motion and the position of the motor shaft. Absolute motor encoders are most often used on Servo Motors in applications where position accuracy is required. Learn more about absolute encoder technology.
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Find The Right Feedback Solution for Your Application

Use our selection tool to narrow down your search

Step 1: Select Feedback Type (Learn How to Choose)

Absolute Encoders

Incremental Encoders