What is rotary encoder?

Have you ever come across Rotary encoder? Do you know what it does? Here is some information that help you to gain knowledge about it.

Rotary encoders are used in everyday machinery. The word rotary means rotational motion. A rotary encoder is a type of position sensor which is used for determining the angular position of a rotating shaft. It generates an electrical signal, either analog or digital, according to the rotational movement.

There are two main types of rotary encoders:

Magnetic rotary encoders:

It 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.

Optical rotary encoders:

This 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.

 Incremental rotary encoders:

This 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: 

It has 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

                                                         How Rotary Encoder Works?

Let’s take a closer look at the encoder and see its working principle. Here’s how the square wave pulses are generated: The encoder has a disk with evenly spaced contact zones that are connected to the common pin C and two other separate contact pins A and B, as illustrated below.

When the disk will start rotating step by step, the pins A and B will start making contact with the common pin and the two square wave output signals will be generated accordingly.

Any of the two outputs can be used for determining the rotated position if we just count the pulses of the signal. However, if we want to determine the rotation direction as well, we need to consider both signals at the same time.

We can notice that the two output signals are displaced at 90 degrees out of phase from each other. If the encoder is rotating clockwise the output A will be ahead of output B.

So if we count the steps each time the signal changes, from High to Low or from Low to High, we can notice at that time the two output signals have opposite values. Vice versa, if the encoder is rotating counter clockwise, the output signals have equal values. So considering this, we can easily program our controller to read the encoder position and the rotation direction.

                                                                    Uses of rotary encoder

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 are electromechanical devices used for sensing in myriad applications — on motors paired with drives and automated machinery for everything from consumer electronics, elevators, and conveyor speed monitoring to position control on automated industrial machines and robotics. Rotary encoders are used in a wide range of applications that require monitoring or control, or both, of mechanical systems, including industrial controls, robotics, photographic lenses, computer input devices such as optomechanical mice and trackballs, controlled stress rheometers, and rotating radar platforms.

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