How can we measure the speed or direction of rotation of a motor?
Using a hall effect sensor and tachometer is a good option, but it has a drawback: it only measures the motor’s speed, not its direction of rotation.
Are there other methods for measuring both speed and direction of rotation?
As a professional optical rotary encoder supplier in China, Lorentzzi Electric recommends the AB dual-channel quadrature optical rotary encoder.
So, what exactly is an optical rotary encoder? How does it work?
In the following sections, we’ll explain them in detail, from the inside out.
What is an optical rotary encoder?
Simply put, an optical rotary encoder is a photoelectric type sensor that detects rotational motion by sensing light pulses generated by a code disk as it rotates between a light source and a detector.
It can measure the speed, direction, and angular position of a motor.
Optical rotary encoders are often installed in servo motors as feedback sensors for the control unit.
How does an optical rotary encoder work?
To understand how an optical rotary encoder works, we first need to understand its components and composition.
The figure below shows the structure of an optical rotary encoder.
As you can see from the above image, an optical rotary encoder consists of 7 main components: a light-emitting diode, a prism, a code disc, a photo-sensor, a power supply, a rotating shaft, and bearings.
The operating principle of an optical rotary encoder is as follows: When power is applied to the encoder, a light-emitting diode (LED) illuminates a fixed slit on a code disc through a prism. As the motor rotates the encoder, its transparent and opaque sections alternately transmit and block light. A photo-diode (or photo-transistor) behind the code disk converts the received light pulses into voltage pulses; when the opaque strip blocks the slit, no pulse is generated. By counting the number of pulses per unit time, the system can calculate the motor speed.
The above explanation applies to single-channel photoelectric encoders. However, the same principle also applies to dual-channel encoders.
In a dual-channel photoelectric encoder, two code tracks appear on the same code disk, 90 degrees apart.
These two code tracks are typically referred to as the A and B channels.
By measuring whether the A-phase pulse leads or lags the B-phase pulse, it is possible to determine whether the motor is rotating forward or reverse.
Types of optical rotary encoders
Now let’s take a look at how many types of optical rotary encoders there are.
The optical rotary encoders can be divided into two types: incremental optical rotary encoder and absolute optical rotary encoder.
Incremental encoders are the most popular optical encoders on the market. While they offer the advantage of being more affordable than absolute encoders, they also have the disadvantage of losing position signals if the power supply fails, requiring a new zero position.
Incremental optical rotary encoders offer two output formats: quadrature (digital square wave) and sinusoidal (analog sine/cosine),the latter has higher resolution and higher accuracy.
From other aspects, optical rotary encoders can be divided into solid shaft type and hollow shaft type.
Optical vs magnetic rotary encoders
There is another type of rotary encoder, a magnetic rotary encoder.
Unlike optical encoders, magnetic rotary encoders operate on the principle of magnetoelectric conversion.
They consist of a disk with a magnetic pattern mounted on a rotating shaft.
As the disk rotates, the surrounding magnetic field distribution changes. A magnetic sensor (such as a Hall element) senses these field changes and converts them into electrical signals.
The same processing circuitry then generates an output signal representing the rotation information.
Now let’s have a look at the two types rotary encoders differences:
| Item | Optical rotary encoder | Magnetic rotary encoder |
|---|---|---|
|
Working principle |
Using the principle of photoelectric conversion |
Utilizing the principle of magnetoelectric conversion |
|
Accuracy |
High |
Relatively low |
|
Anti-interference ability |
Relatively insensitive to electromagnetic interference |
Relatively weak resistance to strong magnetic field interference |
|
Code disc durability |
The code disc is easily damaged after being impacted, so do not knock the product during use. |
External shock will not damage the code disc, but it is susceptible to magnetic field interference |
|
Application scenario |
Position detection of CNC machine tools and robot joints, etc. |
Automobile engine speed detection, some rotating parts detection in industrial automation production lines. |
Conclusion
In summary, optical rotary encoders are sensors based on the photoelectric effect and are widely used in electric motors as feedback sensors for control units. They enable very precise control of speed, rotation angle, and direction.
Optical rotary encoders are becoming increasingly popular in automated control systems.
If you would like more information or would like to inquire about incremental optical rotary encoder pricing, please contact us or send an inquiry to shonxu@lorentzzi.com. Our sales staff will respond within 24 hours.
