Servo Feedback Devices

feedback devices
This is a brief overview of the different types of Feedback Devices used to relay rotary position data to a controller :
  • Resolver – Rotating transformer where the magnitude of the energy through the resolver windings vary as the shaft rotates. Many are physically located on the motor shaft. Most do not have bearings because they use the motor shaft bearings, and they are very very rugged. They run even if they’re in an oily, dirty environment. There are resolvers with their own individual bearings but most don’t have any.
  • Incremental Encoder – Most commonly used and the simplest. The encoder provides information about the instantaneous position of a rotating shaft by producing one square wave of cycle per increment of shaft movement. This  Increment, which is referred to as the resolution, is built directly into the devices internal hardware.  An Incremental encoder has a glass lens with multiple lines around the outside, it counts the lines and signals with light when there isn’t a line, when it hits the Z-pulse it starts over again. Take great care when handling them.
  • Absolute Encoder – More complicated signal structure. They 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 represent each position. The output from these detectors is HI or LO depending on the code disc pattern for that particular position. The Absolute Encoder has a glass lens, multiple lines used for commutation, which reads a system of coded tracks to establish position information, no two positions are alike
  • Serial Encoder –  Has a glass lens and multiple lines used for commutation. It’s used for feedback where the encoder talks. Micro-processors are built onto the encoder itself and talks to the drive.
  • Hall Sensors – Activated by an external magnetic field. Located on the motor and are similar to a nut runner, basically a magnetic switch.
  • Tach Generator – Is an instrument that measures the rotational rate of the shaft using an internally generated electrical signal. They are not used very often in servo motors, because of the speed of the feedback we use with it.

At RepairZone, we see feedback devices all of the time when repairing Servo Motors.  The feedback device communicates with a Servo Amplifier or controller.  If this communication breaks down, an error message will occur on the controller and the motor will stop.

View our video on feedback devices or other tips and information here

If you have any questions or need assistance, please call 989-922-0043.

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  1. Dear sir,

    How to set encoder in new servo motor ?

    Jay desai

    • I can”t really answer that question without more information about the motor and encoder type. Depending on the type of servo motor if you don”t have the correct alignment data from the manufacturer (which is rare), a previous repair, the original motor or access to another motor that has the correct alignment you may not be able to get the alignment back into spec without MUCH trial and error and could damage the motor or new encoder in the process. Next, depending on the manufacturer and the type of encoder (incremental, absolute, serial….) will determine what kind of equipment you will need or can use to set the correct alignment. Please provide more information if you would like to discuss further. Thank you for your question.

      Jade York

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