What is an encoder?
During motor operation, real-time monitoring of parameters such as current, rotational speed, and relative position of the circumferential direction of the rotating shaft determines the status of the motor body and the equipment being towed, and furthermore, real-time control of the motor and the equipment's operating conditions, thus realizing many specific functions such as servoing, speed regulation, and so on.
Here, the application of encoder as the front-end measurement element not only greatly simplifies the measurement system, but also precise, reliable and powerful.
Encoder is a rotary sensor that converts the 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 physical quantities of position and displacement of linear moving parts.
Encoder Classification
Basic encoder classification
Encoder is a mechanical and electronic close combination of precision measuring devices, the signal or data will be encoded, conversion, used for communication, transmission and storage of signal data. Encoders are categorized according to different features as follows:
● Code discs and scales: Encoders that convert linear displacements into electrical signals are called code scales, and those that convert angular displacements into electrical signals are code discs.
● Incremental encoder: Provides information such as position, angle, and number of revolutions, and defines the respective rate in terms of the number of pulses per revolution.
● Absolute encoder: Provides information such as position, angle and number of revolutions in angular increments, and each angular increment is given a unique code.
● Hybrid absolute encoders: Hybrid absolute encoders output two sets of information: one set of information is used to detect the position of the magnetic poles with an absolute information function, and the other set of information is exactly the same as the output information of incremental encoders.
Commonly used encoders for motors
Incremental encoder
Directly utilizing the principle of photoelectric conversion, it outputs three sets of square wave pulses A, B and Z. The phase difference between the A and B pulses is 90o, which makes it easy to determine the direction of rotation; the Z-phase has one pulse for each revolution, which is used for positioning the reference point. Advantages: simple principle of construction, the average mechanical life of tens of thousands of hours or more, strong anti-interference ability, high reliability, suitable for long-distance transmission. Disadvantages: unable to output the absolute position information of shaft rotation.
Absolute encoders
Direct output of digital sensors, sensors on the circular code disk along the radial direction of a number of concentric code channels, each channel by the light-transparent and light-impermeable sectors between the composition of the number of adjacent code channel sectors is a double relationship between the number of code channels on the code disk is the number of binary digits of the number of code channels is the number of bits of its code disk is a source of light, the other side of the corresponding to each code channel there is a light-sensitive element; when the code disk is in a different location, the light-sensitive element according to the light or not to convert the corresponding level signal to form a binary number. When the code disk is in a different position, the photosensitive element according to the light or not converted to the corresponding level signal, the formation of binary numbers.
This encoder is characterized by not counter, in any position of the rotary axis can be read out a fixed position corresponding to the digital code. Obviously, the more the code channel, the higher the resolution, for an encoder with N-bit binary resolution, the code disk must have N barcode channel. At present, there are 16-bit absolute encoder products.
Encoder working principle
By a center of the shaft of the photoelectric code plate, which has a ring through the dark lines, there are photoelectric transmitter and receiver devices to read, to obtain four sets of sine wave signals combined into A, B, C, D, each sine wave phase difference of 90 degrees phase difference (with respect to a circumferential wave of 360 degrees), the C, D signals reversed, superimposed on the A, B two-phase, which can be enhanced to stabilize the signal; and the other every turn to output a Z-phase pulses on behalf of the zero position Reference position.
Encoder Structure
Because of the difference of 90 degrees between the two phases A and B, it can be compared whether phase A is in front or phase B is in front in order to discriminate the encoder's forward and reverse rotation, and through the zero pulse, it can get the encoder's zero reference position.
Encoder code plate materials are glass, metal, plastic, glass code plate is deposited on the glass very thin engraved lines, its thermal stability, high precision, metal code plate directly to the pass and do not pass the engraved lines, not fragile, but because of a certain thickness of the metal, the accuracy of the limitations of its thermal stability is worse than the glass by an order of magnitude, the plastic code plate is an economical, its cost is low, but the accuracy, thermal stability, life expectancy is worse! Plastic code disk is economical, its cost is low, but the accuracy, thermal stability, life are poorer.
Resolution - encoder to provide how many through or dark engraved lines per 360 degrees of rotation called resolution, also known as resolution index, or directly called how many lines, generally 5 ~ 10,000 lines per revolution index.
Position Measurement and Feedback Control Principles
Encoders occupy an extremely important position in elevators, machine tools, material processing, motor feedback systems, and measurement and control equipment. The encoder uses a grating and an infrared light source to convert the optical signal into a TTL (HTL) electrical signal through the receiver, and by analyzing the frequency of the TTL level and the number of high levels, the angle of rotation of the motor and the rotational position are reflected visually.
Since the angle and position can be measured accurately, it is possible to form a closed-loop control system with the encoder and the inverter to make the control more precise, which is why elevators, machine tools, etc. can be used so accurately.
Summarize
In summary, we understand that the encoder is divided into incremental and absolute according to the structure of the two, they are also other signals, such as optical signals, into electrical signals that can be analyzed and controlled.
And we live in the common elevator, machine tools are just based on the precise regulation of the motor, through the feedback of the electrical signal closed-loop control, encoder with frequency converter is also a matter of course to achieve precise control.