What is an encoder?

If you Google encoder, you’ll get a large and bewildering array of responses. For our goals, encoders are used in machinery for movement feedback and motion control. However, encoders are seen in machinery in all industries. You’ll notice encoders used in cut-to-length applications, packaging plotters, robotics, conveyors, automation, filling, sorting, imaging, and various other applications. Sometimes unnoticeable, but they are there. The below blog post will give you a basic introduction to the application of an encoder.

What is an encoder?

Plainly put, an encoder is a sensing device that produces feedback. Encoders change a movement to an electrical signal interpreted by some type of control equipment in a motion control system, like a PLC. The encoder transmits a feedback signal that can be utilised to determine position, count, direction or speed. A control device will use this information to convey a command for a precise function. For example:

  • Encoders with a measuring wheel indicate to the control device how much material has been fed in a cut-to-length application, knowing when to cut.
  • In an observatory, encoders tell actuators what position a mirror is by presenting position feedback.
  • Encoders provide precision-motion feedback on the railroad-car lifting jack, so the jacks lift in harmony.
  • In a precision servo label application, a PLC uses an encoder signal to manage the speed and timing of bottle rotation.
  • Feedback from the encoder will activate a printing head to create a mark at a precise location in a printing application.
  • An Encoder mounted to a motor shaft provides positioning feedback to a heavy-duty crane control system, so the crane knows when to release or pick up the load.
  • Where bottles or jars need to be filled, encoder signals indicate to the filling machines the location of the containers. 
  • In an elevator, encoders signal to the controller when the lift has reached the correct floor at the right time. In other words, encoder motion signals to the elevator’s control system ensure that elevator doors open level with the floor. If the encoders weren’t there, a person might find themselves climbing out of an elevator rather than simply walking out onto a building floor.
  • Many automated assembly lines, encoders give motion feedback to robots. This could mean ensuring the robotic welding arm has the correct information to weld in a suitable location on an automotive assembly line.

The process is similar in any application: the encoder generates a count or position. Then, it communicates with the controller, and the machine performs a function with the signal.

How do encoders work?

An Encoder will use different technologies to create a signal, including magnetic, mechanical, resistive, optical and resistive – optical is the most popular. In an optical instrument, the encoder provides feedback based on the obscuring of light.

A light beam from an LED passes through the Code Disk, patterned with solid lines (like the spokes on a bicycle wheel). As the encoder shaft rotates, the opaque lines interrupt the light beam that the LED produces on the marked Disk before the photodetector picks up the light. This is what we call a pulse signal: light – on; no light – off. Finally, the signal or pattern is sent to the counter or controller, sending the signal to produce the desired function.


What is the difference between an incremental and an absolute encoder?

Encoders will produce either absolute or incremental signals. The incremental signal does not indicate a specific position, only that the position has changed. On the other hand, absolute encoders use a different pattern for each position. This means an absolute encoder indicates that the position has changed and indicates the absolute position of the encoder.

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