Dynapar 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 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.
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Understanding Motor Encoder
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 is 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.
Key factors impacting motor encoder selection
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: These 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 these motors, and often times need to have more robust IP, shock and vibration parameters.
- Servo/Permanent Magnet Motors: These motors 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 these motors can be modular, incremental or absolute depending on the level of resolution and accuracy required.
- Stepper Motor: These 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.
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.
- 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.
Motor Encoder Mounting Options
The third factor impacting motor encoder selection is the mounting option, and the most common options are:
- Shafted: 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: Direct mount to the motor shaft via a spring loaded tether. This method is easy to install and required no shaft alignment, but proper care must be taken to provide electrical isolation.
- Bearningless: Also known as Ring mount, this mounting option is comprised of a sensor assembly in the form of a ring that is mounted on the motor face, and a magnetic wheel which is mounted on the motor shaft. This type of motor encoder mounting configuration is mostly found in heavy duty applications like paper, steel and cranes.