Chinese Name: Encoder mbth: Scope of application: Computer coding function: Main classification of converted signal forms, common faults, installation and use, wiring mode, working principle, main functions, signal output, selection precautions, advantages and disadvantages, main classification Encoders can be classified in the following ways. 1. Incremental type (1) is classified according to the punching mode of the code wheel: a pulse signal (sine and cosine signals are also sent once per unit angle, and then subdivided and chopped into pulses with higher frequency) is usually output by phase A, phase B and phase Z, and the delay between phase A and phase B is 1/4. Z-phase is a single-cycle pulse, that is, one pulse is emitted every cycle. Encoder (Figure 1) (2) Absolute value type: corresponding to a circle, each reference angle emits a unique binary value corresponding to the angle, and multiple positions can be recorded and measured by an external circular recording device. 2. According to the signal output type, it can be divided into voltage output, open collector output, push-pull complementary output and long-line drive output. 3. According to the mechanical installation form of encoder, there are shaft types (1): shaft types can be divided into clamping flange type, synchronous flange type and servo installation type. (2) Casing type: Casing type can be divided into half-empty type, full-empty type and large-caliber type. 4. According to the working principle of the encoder, it can be divided into photoelectric type, magnetoelectric type and touch brush type. Common failure 1, encoder failure: refers to the failure of the components of the encoder itself, which makes it impossible to generate and output correct waveforms. In this case, it is necessary to replace the encoder or repair its internal equipment. Encoder (fig. 2) 2. Cable failure of encoder connection: This kind of failure has the highest probability, which is often encountered in maintenance and should be a priority factor. Usually, the encoder cable is open circuit, short circuit or poor contact, so it is necessary to replace the cable or connector. Also pay special attention to whether the cable is loose due to poor fixation, resulting in open welding or open circuit. At this point, the cable should be clamped. 3. The encoder +5V power supply drops: It means that the +5V power supply is too low, usually not less than 4.75V The reason for the low power supply is power failure or the resistance value of the power transmission cable is too high, so it is necessary to repair the power supply or replace the cable. 4. Absolute encoder battery voltage drop: This kind of fault usually has a clear alarm, and the battery needs to be replaced. If the memory of the position of the reference point is lost, the operation of returning to the reference point must be performed. Encoder (fig. 3) 5. The forbidden line of the encoder cable is not connected or dropped: this will introduce interference signals, make the waveform unstable and affect the accuracy of communication. It is necessary to ensure the reliable welding and grounding of the forbidden wire. 6. Loose installation of encoder: This kind of fault will affect the position control accuracy, leading to the position deviation out of tolerance when stopping and moving, and even the servo system overload alarm will appear just after starting. Please pay special attention. 7. Grating pollution will reduce the signal output amplitude, so it is necessary to gently wipe off the oil stain with absorbent cotton dipped in anhydrous alcohol. Installation and use of mechanical installation of absolute rotary encoder: the mechanical installation of absolute rotary encoder has various forms, such as high-speed end installation, low-speed end installation and auxiliary mechanical device installation. The encoder (Figure 4) is installed at the high-speed end: at the rotating shaft end (or gear joint) of the power motor. This method has the advantage of high resolution. Because the multi-turn encoder has 4096 turns, the number of revolutions of the motor is within this range, so we can make full use of the full range to improve the resolution. The disadvantage is that there is a gear gap error when the moving object passes through the reduction gear, so it is generally used for unidirectional high-precision control and positioning, such as roll gap control of steel rolling. In addition, the encoder is directly installed at the high-speed end, so the motor jitter must be small, otherwise it is easy to damage the encoder. Low-speed end installation: installed behind the reduction gear, such as the shaft end of the winding wire rope drum or the end of the last reduction gear shaft. This method has no gear return clearance, and the measurement is more direct and accurate. This method generally measures long-distance positioning, such as the positioning of various lifting equipment and feeding trolley. Auxiliary machinery installation: commonly used are rack and pinion, chain belt, friction wheel, rope take-up machinery, etc. The connected rotary encoder is a photoelectric rotary measuring device, which directly converts the measured angular displacement into a digital signal (high-speed pulse signal).
Encoders can be divided into incremental encoders and absolute encoders according to the signal principle.
We usually use incremental encoder, which can directly input the output pulse signal of rotary encoder into PLC, and use the high-speed counter of PLC to count the pulse signal and get the measurement result. Different types of rotary encoders have different output pulse phases. Some rotary encoders output three-phase pulses of A, B and Z, some only have two phases of A and B, and the simplest one is only phase A. ..
The encoder has five leads, three of which are pulse output lines, 1 is the COM terminal line, and 1 is the power line (OC gate output type). The power supply of the encoder can be an external power supply, or it can directly use the DC24V power supply of PLC. The "-"terminal of the power supply should be connected to the COM terminal of the encoder, and the "+"terminal should be connected to the power supply terminal of the encoder. The COM end of the encoder is connected to the COM end of PLC input, and the output lines of A, B and Z are directly connected to the input end of PLC. A and B are pulses with a difference of 90 degrees. There is only one pulse in the Z-phase signal when the encoder rotates once, which is usually used as the basis of zero. Pay attention to the reverberation time of PLC input when connecting. The rotary encoder also has a forbidden line, so it should be grounded when it is used to improve the anti-interference performance.
Encoder -PLC
A - X0
B - X 1
Z - X2
+24V - +24V
The working principle of COM is composed of a photoelectric encoder with a shaft in the center, on which there are circular on-off and hidden lines. Four groups of sine wave signals are read by photoelectric transmitter and receiver, which are combined into A, B, C and D, and the difference between each group of sine waves is 90 degrees. In addition, a Z-phase pulse is output every revolution to represent the zero reference bit. Encoder (Figure 5) Because the difference between phase A and phase B is 90 degrees, the forward rotation and reverse rotation of the encoder can be judged by comparing whether phase A is in front or phase B is in front, and the zero reference bit of the encoder can be obtained by zero pulse. The materials of encoder dial are glass, metal and plastic. The glass encoder has fine lines deposited on the glass, which has good thermal stability and high precision. The metal code wheel can be directly crossed on and off, and it is not fragile. However, the thermal stability of metal is one order of magnitude worse than that of glass because of its certain thickness and limited precision. Plastic encoder is economical and low cost, but its accuracy, thermal stability and service life are poor. Resolution-The number of open or closed lines provided by the encoder every 360 degrees of rotation is called resolution, also called analysis scale, or simply more or less lines. Generally, it is 5~ 10000 lines per revolution. Its main function is to rotate the sensor and convert the rotational displacement into a series of digital pulse signals. These pulses can be used to control angular displacement. If the encoder is combined with a gear rod or a screw, it can also be used to measure linear displacement. Encoder (Figure 6) The electrical signal generated by the encoder is processed by CNC, PLC and control system. These sensors are mainly used in the following aspects: machine tools, material processing, motor feedback systems and measurement and control equipment. In ELTRA encoder, the conversion of angular displacement adopts photoelectric scanning principle. The reading system is based on the rotation of a radial indexing disk, which consists of alternating transparent windows and opaque windows. The system is vertically illuminated by an infrared light source, so that the light projects the image on the optical disc onto the surface of the receiver, which is covered with a grating called a collimator and has the same window as the optical disc. The receiver's job is to feel the light changes caused by the rotation of the optical disc, and then convert the light changes into corresponding electrical changes. Generally, the rotary encoder can also get a speed signal, which should be fed back to the inverter to adjust the output data of the inverter. Fault symptom: 1, when the rotary encoder is broken (no output), the inverter can't work normally, and the running speed becomes very slow. After a while, the inverter will be protected and display "PG OFF" ... and the joint action will take effect. In order to make the electrical signal rise to a higher level and generate square wave pulses without any interference, it must be processed by electronic circuits. The connection mode between the encoder pg and the parametric vector inverter and the encoder pg must correspond to the model of the encoder pg. Generally speaking, there are three types of encoder pg models: differential output, open collector output and push-pull output. The interface of pg card of frequency converter must be considered in signal transmission mode, so the appropriate pg card model should be selected or set reasonably. Encoders are generally divided into two types: incremental encoder and absolute encoder. The biggest difference between these two types is that the position of incremental encoder is determined by the number of pulses calculated by zero mark, while the position of absolute encoder is determined by the reading of output code. In a circle, the reading of the output code of each position is unique; Therefore, when the power supply is disconnected, the absolute encoder will not leave the actual position. If the power supply is turned on again, the position reading is still valid; Unlike incremental encoders, you have to look for zero marks. Encoder (Figure 7) The series of encoders produced by manufacturers are relatively complete, and they are generally dedicated, such as encoders for elevators, encoders for machine tools, encoders for servo motors, etc. And has various parallel interfaces to communicate with other devices. An encoder is a device that converts angular displacement or linear displacement into electrical signals. The former is called code wheel, and the latter is called code ruler. According to the reading mode, encoders can be divided into contact type and non-contact type. The contact type uses the brush output, and one brush contacts the conductive area or the insulating area, indicating whether the code state is "1" or "0". The non-contact receiving sensitive element is a photosensitive element or a magnetic sensitive element. When the photosensitive element is used, the light-transmitting area and the opaque area are used to indicate whether the encoding state is "1" or "0". According to the working principle, encoders can be divided into incremental and absolute types. Incremental encoder converts displacement into periodic electrical signal, and then converts this electrical signal into counting pulses, and the number of pulses indicates displacement. Each position of absolute encoder corresponds to a certain digital code, so its indication value is only related to the starting and ending positions of measurement, and has nothing to do with the intermediate process of measurement. The encoder (Figure 8) rotates the incremental encoder, outputs pulses when rotating, and its position is known by the counting device. When the encoder is stationary or powered off, the internal memory of the counting device will remember this position. In this way, the encoder can't move when the power is off, and the encoder can't lose the pulse due to interference when the incoming call works, otherwise the zero point of the memory of the counting device will shift, and the amount of this shift is unknown, only after the wrong production result appears. The solution is to increase the reference point, and every time the encoder passes the reference point, the reference position is corrected to the memory position of the counting device. Before the reference point, the accuracy of the position cannot be guaranteed. To this end, in industrial control, there are methods such as finding the reference point first and changing the zero point every time. Such an encoder is determined by the mechanical position of the code wheel and is not affected by power failure and interference. The uniqueness of each position of the absolute encoder is determined by the mechanical position. It doesn't need to remember, find a reference point, and it doesn't need to keep counting. Whenever it needs to know its location, it needs to read its location. This greatly improves the anti-interference characteristics and data reliability of the encoder. Because absolute encoder is obviously superior to incremental encoder in positioning, it has been used more and more in industrial positioning. Because of its high precision and many output bits, if parallel output is still used, the output signal of each bit must be connected well, and it must be isolated for more complicated working conditions, which brings a lot of inconvenience and reduces reliability. Therefore, in the multi-digit output type, absolute encoders generally choose serial output or bus output, and SSI (synchronous serial output) is the most commonly used serial output of absolute encoders produced in Germany. Encoder (Figure 9) Multi-turn absolute encoder. Encoder manufacturers use the principle of clock gear machinery. When the central code wheel rotates, the other set of code wheels (or multiple sets of gears and multiple sets of code wheels) is driven by gears, which increases the number of turns on the basis of single-turn coding and expands the measuring range of the encoder. This kind of absolute encoder is called multi-turn absolute encoder, which is also determined by the mechanical position. Each position code is unique and does not need to be memorized. Another advantage of multi-turn encoder is that it is often rich in practical use because of its large measurement range. When installing, you don't need to find the zero point, and a middle position can be used as the starting point, which greatly simplifies the difficulty of installation and debugging. Multi-turn absolute encoder has obvious advantages in length positioning, and it has been used more and more in industrial positioning. Signal output signal output includes sine wave (current or voltage), square wave (TTL, HTL), open collector (PNP, NPN) and push-pull type, in which TTL is long-line differential drive (symmetrical A, A-; B，B-； Z, Z-), HTL is also called push-pull and push-pull output, and the signal receiving device interface of the encoder should correspond to the encoder. Signal connection of the encoder (Figure 10)- The pulse signal of the encoder is generally connected to the counter, PLC and computer. The modules connected between PLC and computer are divided into low-speed module and high-speed module, and the switching frequency is low or high. Such as single-phase connection, for unidirectional counting and unidirectional speed measurement. A.B two-phase connection is used for forward and backward counting, forward and backward judgment and speed measurement. A, B and Z are connected in three phases for position measurement with reference position correction. A, A-, B-, B-, Z, Z- wires have symmetrical negative signals, and the electromagnetic field contributed by current to the cable is zero, with the smallest attenuation and the best anti-interference performance, and can transmit for a long distance. For TTL encoder with symmetrical negative signal output, the signal transmission distance can reach150m. For HTL encoder with symmetrical negative signal output, the signal transmission distance can reach 300 meters. Three parameters should be paid attention to in type selection: 1, and mechanical installation size: including positioning stop, shaft diameter and installation hole position; Cable output mode; Installation space volume; Whether the protection level of the working environment meets the requirements. 2. Resolution: that is, whether the number of pulses output per revolution of the encoder meets the design and use accuracy requirements. 3. Electrical interface: The common output modes of encoders are push-pull output (F-type HTL format), voltage output (E), open collector (C, common C is NPN tube output, C2 is PNP tube output) and long-line driver output. Its output mode should match the interface circuit of its control system. Advantages and disadvantages photoelectric encoder advantages: small size, high precision, high resolution, no contact and no wear; The same variety can detect both angular displacement and line displacement with the help of mechanical conversion device; Multi-turn photoelectric absolute encoder can detect a large range of linear displacement (such as 25-bit multi-turn). Long service life, no installation, rich interface forms and reasonable price. Mature technology has been widely used at home and abroad many years ago. Disadvantages: precision but high requirements for outdoor and harsh environment protection; The measurement of linear displacement depends on the conversion of mechanical devices, and it is necessary to eliminate the error caused by mechanical clearance; It is difficult to overcome slippage when detecting objects in orbit. Advantages of static magnetic grating absolute encoder: moderate volume, direct measurement of linear displacement, absolute digital coding, unlimited theoretical range; No contact, no wear and tear, resistant to harsh environment, and can be used in 1000 meters underwater; The interface forms are rich and the measurement methods are diverse; The price is acceptable. Disadvantages: 1mm resolution is not high; Different varieties should be used to measure straight lines and angles; It is not suitable for displacement detection in small places (greater than 260 mm).