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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 that is used by the control system to monitor specific parameters of the application and make adjustments if necessary to maintain the machine operating as desired.
The parameters monitored are determined by the type of application and can include speed, distance, RPM, position among others. Applications that utilize encoders or other sensors to control specific parameters are often referred to as closed-loop feedback or closed-loop control systems.
A motor encoder is a rotary encoder mounted to an electric motor that provides closed loop feedback signals by tracking the speed and/or position of a motor shaft. There are a wide variety of motor encoder configurations available such as incremental or absolute, optical or magnetic, shafted or hub/hollow shaft, among others. The type of motor encoder used is dependent upon a number of factors, particularly motor type, the application requiring closed-loop feedback, and the mounting configuration required.
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 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 motors encoders (permanent magnet motor encoders) offer closed loop feedback control systems to applications that require higher precision and accuracy, and are not as robust as 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 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 to this motor and will allow 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 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.
The next factor impacting motor encoder selection is the mounting option, and the most common options are:
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: