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What Are Rotary Encoders?

Posted by David Collica on Wed, Jun 04, 2014

I’ve never been in contact with one before!

Have you ever come across a rotary encoder? Do you know what it does? Rotary encoders are used in everyday machinery. The word rotary means rotational motion. This device operates by detecting the rotation of a disk turning around an axis. Here is some information I found that helped me gain knowledge that will also help you understand.

What are rotary encoders?There are two main types of rotary sensors

1. Magnetic rotary encoders can be used for speed and  position feedback. These sensors are more robust than other technologies and they are often used in harsh-duty applications. Some magnetic encoders can provide absolute position feedback storing the position information even after power is shut off and turned back on.

2. Optical rotary encoders advance the rotary world. If you were to disassemble one, you would find an LED light source, code disks, a light detector, and a signal processor. Optical rotary sensors are more technically advanced than magnetic rotary sensors. When the shaft spins, a disk within the encoder also spins. The disk has multiple slots corresponding to the resolution. These slots rotate,  interrupting the LED light beam. The light exposure to the light detector begins to pulse with the rotation and sends a signal to the processor. This signal is conditioned and then output to the system to indicate rotation.

Let's move on to a different sort of device signals. There are incremental and absolute rotary encoders.

Incremental rotary encoders are a simpler device to understand as they are more basic in operation. The rotation of the device creates a pulse of two square waves corresponding to the rotation. These pulses are out of phase to each other by 90 degrees, which allows for not only frequency pulse output signals, but also allows the interface devices to detect direction from the phase relationship of the two pulses.

Absolute rotary encoders have multiple detectors with an encoded disk that has multiple unique tracks. The output signal can consist of various types of outputs such as parallel coding, or serial interfaces like EtherNet/IP, PROFIBUS or PROFINET, J1939, as well as other output types. Optical absolute sensors have more than one gear. The gears allow the absolute encoder to track the rotational position over many rotations of the shaft, and the processing of the disk count allows the total number of shaft turns to be calculated and maintained. This gives you not only direction and position, but it also can be used in applications that require the distance or location to be monitored

Maybe you don't realize it, but you come in contact with rotary encoders daily. They monitor rotation and send an output of digital signals. Whether you ride an elevator, operate a conveyor, or want to observe the speed and position of robotic systems, wind turbines, or other machines, rotary encoders are at work.

Rotary encoders for conveyor applications
There is so much information about rotary encoders available. If you are looking for additional information and cannot find what you’re looking for, I strongly encourage you to check out the article 'Basics of rotary encoders: Overview and new technologies' in Machine Design online. It has wonderful information that will truly help you as it helped me!

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Topics: Rotary Encoders

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