1， What is encoder
During the operation of a Worm gearbox N20 DC motor, parameters such as current, speed and relative position of the circumferential direction of the rotating shaft are monitored in real time to determine the state of the motor body and the equipment being towed, and furthermore to control the operating conditions of the motor and equipment in real time, thus realizing many specific functions such as servo and speed regulation. Here, the application of an encoder as a front-end measuring element not only greatly simplifies the measuring system, but is also precise, reliable and powerful. The encoder is a rotary sensor that converts the physical quantities of position and displacement of rotating parts into a series of digital pulse signals, which are collected and processed by the control system to issue a series of commands to adjust and change the operating status of the equipment. If the encoder is combined with a gear bar or screw screw, it can also be used to measure the position and displacement of linear moving parts.
2，the encoder classification
Encoder basic classification：
Encoder is a mechanical and electronic close combination of precision measurement device, the signal or data will be encoded, conversion, for communication, transmission and storage of signal data. According to different characteristics, encoders are classified as follows:
● Code disc and code scale. The encoder that converts linear displacement into electrical signal is called code scale, and the one that converts angular displacement into telecommunication is code disc.
● Incremental encoders. Provides information such as position, angle and number of turns, and defines the respective rate by the number of pulses per turn.
● Absolute encoder. Provides information such as position, angle, and number of turns in angular increments, and each angular increment is assigned a unique code.
● Hybrid absolute encoder. The hybrid absolute encoder outputs two sets of information: one set of information is used to detect the pole position with absolute information function, and the other set is exactly the same as the output information of the incremental encoder.
Encoders commonly used in motors：
●Incremental encoder
Directly using the photoelectric conversion principle to output three sets of square wave pulses A, B and Z. The phase difference between the two sets of pulses A and B is 90o, so that the direction of rotation can be easily judged; the Z phase is one pulse per revolution and is used for reference point positioning. Advantages: simple principle construction, average mechanical life can be over tens of thousands of hours, strong anti-interference ability, high reliability, and suitable for long distance transmission. Disadvantages: unable to output the absolute position information of shaft rotation.
● Absolute encoder
There are several concentric code channels along the radial direction on the circular code plate of the sensor, and each channel is composed of light-transmitting and non-light-transmitting sectors, and the number of sectors of adjacent code channels is double, and the number of code channels on the code plate is the number of binary digits. When the code plate is in different positions, each photosensitive element is converted to the corresponding level signal according to the light or not, forming the binary number.
This type of encoder is characterized by the fact that no counter is required and a fixed digital code corresponding to the position can be read at any position of the rotary axis. Obviously, the more code channels, the higher the resolution, and for an encoder with N-bit binary resolution, the code disk must have N code channels. At present, there are 16-bit absolute encoder products in China.
3, the working principle of encoder
By a photoelectric code disk with axis in the center, there are circular pass and dark inscription lines on it, and there are photoelectric transmitting and receiving devices to read it, and four groups of sine wave signals are combined into A, B, C and D. Each sine wave differs by 90 degrees phase difference (360 degrees relative to a circumferential wave), and C and D signals are reversed and superimposed on A and B phases, which can enhance the stable signal; and another Z phase pulse is output for each revolution to represent zero position reference position.
As the two phases A and B are different by 90 degrees, it can be compared whether phase A is in front or phase B is in front to discern the forward and reverse rotation of the encoder, and the zero reference bit of the encoder can be obtained through the zero pulse. Encoder code plate materials are glass, metal, plastic, glass code plate is deposited on the glass very thin engraved line, its thermal stability is good, high precision, metal code plate directly to pass and not engraved line, not fragile, but because the metal has a certain thickness, the accuracy is limited, its thermal stability is an order of magnitude worse than the glass, plastic code plate is economic, its cost is low, but the accuracy, thermal stability, life are poor Some.
Resolution - encoder to provide how many through or dark engraved lines per 360 degrees of rotation is called resolution, also known as resolution indexing, or directly how many lines, generally in 5 ~ 10000 lines per revolution indexing.
4， Position measurement and feedback control principle
Encoders occupy an extremely important position in elevators, machine tools, material processing, motor feedback systems, as well as in measuring and control equipment. The encoder uses a grating and an infrared light source to convert the optical signal into an electrical signal of TTL (HTL) through a receiver. By analyzing the frequency of the TTL level and the number of high levels, the rotational angle and the rotational position of the motor are visually reflected.
Since the angle and position can be accurately measured, the encoder and inverter can be formed into a closed-loop control system to make the control more accurate, which is why elevators, machine tools, etc. can be used so precisely.
5，Summary
In summary, we understand that encoders are divided into incremental and absolute according to their structure, and they both convert other signals, such as optical signals, into electrical signals that can be analyzed and controlled. The common elevators and machine tools in our life happen to be based on the precise adjustment of the motor, and through the feedback closed-loop control of the electrical signal, the encoder with the inverter is also a natural way to achieve precise control.
Post time: Jul-20-2023