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What is a rotary encoder? Structure - Principle of operation - Application

Are you new to the field of mechanical processing? Don't know what an Encoder is? How is it structured and how does it work? Which professions need to use this type of equipment? Then you've come to the right place. In this article, Amazen will provide you with the most general information about the Encoder, also known by another name, the rotary encoder. Come find out with me!

1. What is a rotary encoder?

Rotary encoder, also known as Encoder (Rotary Encoder), is a term used to refer to an electrical device that can change linear or circular motion into a digital signal or pulse. Thanks to the Encoder, the electric motor will be positioned accurately according to the control signals.

Encoder is mainly used to detect the position, direction of movement, speed... of the motor by counting the number of revolutions that the shaft rotates. Currently, Encoder is commonly used in automatic control systems. Because electronic systems in industrial machinery and equipment often operate at high speeds, they are combined with optical codes. As a result, system speed is precisely increased, cycle times are reduced, and efficient operation is increased.

2. General structure of the Rotary Encoder

The Encoder includes the following main parts:
- Body and shaft
- Light source: 1 LED light
- Code disk: has a small groove around the axis. When this disk rotates and shines an LED light on the surface of the disk, an interruption will occur. The grooves on the disc divide the circle 360o into equal angles. A disc can have many rows of grooves from the circular center.
- Photosensor: is a photoelectric eye that receives signals from the rotating disc.
- Electronic board: helps amplify the signal

3. Operating principle of Rotary Encoder

When the Encoder moves, the converter will process the movements and convert them into electrical signals. These signals will be transmitted to PLC control devices and processed to represent the values to be measured using a separate program. For signals with or without light shining through. People can still record whether the LED light shines through this hole or not. Furthermore, the number of pulses counted and increased is calculated by the number of times the light is cut off.

For example, on a disc there is a single hole, when each time the eye receives 1 LED signal, it means the disc has rotated 1 revolution. Therefore, this is the basic operating principle of the Encoder, but for many other types of Encoder, when the rotating disc has more holes, the received signal will be different. You can refer to the simulation video below to understand more about the operating principle of the encoder.

4. Classification of Rotary Encoders

Absolute rotary encoder
Absolute encoder's English name is Adsolute encoder. As the name suggests, this Encoder allows us to receive signals about their exact location without the user needing any additional processing steps.

The structure of Absolute Encoder includes:
- Light emitter (LED)
- Light receiver sensitive to emitted light (photosensor)
- The encoder disk contains a ribbon that carries the signal
Basic features of the encoder line include:
- Disk usage in binary or Gray code
- The encoder disk at Encoder is made from transparent material, the disk surface is divided into equal angles with concentric circles.
- Advantage: retains absolute value when Encoder loses power
- Disadvantages: high cost because of complex manufacturing, difficult to read signals
Relative rotary encoder

The relative encoder's English name is Incremental encoder. This type of device emits a gradually increasing or cyclical signal. With the following characteristics:
- The encoder disk consists of a series of pulse-generating tapes, usually divided into many equal and evenly spaced holes
- The material can be transparent to allow light to shine through
- An Encoder with only 1,2 or maximum 3 hole rings, and usually an additional positioning hole
- Advantages: low cost, simple manufacturing, easy processing of returned signals
- Disadvantage: susceptible to pulse errors when returned. Errors will accumulate during long-term operation
Classify encoders by technology
Besides the absolute and relative encoder types, we also have a number of other classifications such as:
- Magnetic encoder (magnetic field type)
- Encoder Mechanical (mechanical type)
- Resistive encoder (resistive type)
- Optical encoder (optical type)

5. Parameters to consider when choosing a Rotary Encoder

To choose the right Encoder for your needs, Amazen will tell you the following parameters that you need to pay attention to:
- Shaft diameter, shaft shape: Encoder has positive or negative shaft shape, shaft diameter from 5~50mm. Usually diameters larger than 6mm will be negative shaft type (concave shaft).
- Resolution: also known as number of pulses - corresponds to the number of encoder signals counted when rotating 1 revolution. The higher the number of pulses the encoder has, the higher the price. Elevators usually use 1024p/r pulse, machine manufacturing is around 360p/r, 1000p/r. There are also pulses up to 6000p/r or 6pr.
- Voltage: Encoder often burns out due to not paying attention to the power supply when installing. If the encoder has a voltage range of:5~24V, it is very easy. However, with some large shaft encoders: 30-40mm, the machine's encoder will often encounter a specified voltage: 5V, 12V or 15V. Therefore, you must read carefully before installing. Because the encoder is burned out, it is necessary to replace the whole unit, which is very expensive.
- Output: AB, ABZ, AB inverted, ABZ inverted. You can easily identify the output signal by looking at the wire number indicated on the label.

You can see very clearly that the encoder above has an inverted ABZ output pulse
- Output type: There are many output types, briefly listed: Open Collector, Voltage Output, Complemental, Totem Pole, Line Driver. Output type regulates power supply, information reader...
- Cable: the longer the cable, the more susceptible it is to interference. Standard wire from 1-3m. Sometimes up to 10m according to usage needs.
- Accessories: Included positive axis encoder is Coubling, negative axis encoder is Pass. Coubling helps connect the positive shaft encoder to the positive shaft motor, Pass helps attach the encoder to the machine. A negative axis encoder has 1-2 passes depending on the type.

6. Distinguish between absolute and relative rotary encoders

- Absolute encoder (Absolute): Corresponds to an 8-bit rotating disk or 8-track array, giving output in digital code (BCD), Binary (binary), Gray code.
- Incremental encoder (Relative): Corresponds to a 2-bit disk, giving AB phase square pulse output, or ABZ or inverted ABZ. The Encoder type with 2 pulse signals A and B is the most common. The Z slot signal is the signal to determine if the motor rotates one revolution.

Compare relative and absolute encoders
 

7. Application of Rotary Encoder (Encoder)

8. Which brand of Rotary Encoder should I buy?