The encoder

                                                                       The encoder

Encoder is a device that compiles and converts signals (such as bit stream) or data into signals that can be used for communication, transmission and storage. The encoder converts angular displacement or linear displacement into electrical signals. The former is called code disk, and the latter is called code ruler. According to the reading mode, the encoder can be divided into contact type and non-contact type; 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 pulse. The number of pulses indicates the displacement. Each position of absolute encoder corresponds to a certain digital code, so its indication is only related to the starting and ending positions of measurement, and has nothing to do with the intermediate process of measurement.
Main classification
Encoders can be classified as follows.
1. Classification according to different hole cutting methods of code disk
(1) Incremental type: it means that a pulse signal (or sine and cosine signal) is sent every time the unit angle is turned,
Encoder (Figure 1) encoder (Figure 1) encoder (Figure 1)
Then it is subdivided, chopping out pulses with higher frequency), which are usually output by phase a, phase B and phase Z. phase A and phase B are pulse output with mutual delay of 1/4 cycle. According to the delay relationship, the forward and reverse can be distinguished, and the frequency can be doubled or quadrupled by taking the rising and falling edges of phase A and phase B; Phase Z is a single cycle pulse, i.e. one pulse per cycle.
(2) Absolute value type: it corresponds to a circle, and each reference angle sends out a unique binary value corresponding to the angle. Multiple positions can be recorded and measured through external circle recording devices.
2. According to the output type of signal, it is divided into voltage output, open collector output, push-pull complementary output and long line drive output.
3. Classified by encoder mechanical installation
(1) Shaft type: shaft type can be divided into clamping flange type, synchronous flange type and servo installation type.
(2) Shaft sleeve type: the shaft sleeve type can be divided into half empty type, full empty type and large diameter type.
4. According to the working principle of encoder, it can be divided into photoelectric type, magnetoelectric type and contact brush type.
Common faults
1. Encoder failure: refers to the failure of encoder components,
Encoder (Figure 2) encoder (Figure 2)
Encoder (Figure 2)
As a result, it cannot generate and output correct waveforms. In this case, it is necessary to replace the encoder or repair its internal components.
2. Encoder connecting cable fault: this kind of fault has the highest probability and is often encountered in maintenance. It should be a priority factor. Generally, the encoder cable is open circuit, short circuit or poor contact, and the cable or connector needs to be replaced. Special attention shall also be paid to whether the cable is loose due to loose fixation, which causes open welding or open circuit. At this time, the cable shall be clamped.
3. Decrease of encoder +5v power supply: it means that the +5v power supply is too low, usually not lower than 4.75V. The cause of the low power supply is the loss caused by power supply failure or too large resistance of power transmission cable. At this time, it is necessary to repair the power supply or replace the cable.
4. Battery voltage drop of absolute encoder: this fault usually has a clear alarm,
Encoder (Figure 3) encoder (Figure 3)
Encoder (Figure 3)
At this time, the battery needs to be replaced. If the reference point position memory is lost, the operation of returning to the reference point must also be performed.
5. The encoder cable shield wire is not connected or falls off: 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 shield wire.
6. Loose installation of encoder: this kind of fault will affect the position control accuracy, cause the position deviation in stopping and moving to be out of tolerance, and even generate the servo system overload alarm upon startup. Please pay special attention.
7. Grating pollution will reduce the signal output amplitude. You must use absorbent cotton dipped in absolute alcohol to gently wipe off the oil stain.
Installation and use
Mechanical installation and use of absolute rotary encoder:
The mechanical installation of absolute rotary encoder includes high-speed end installation, low-speed end installation
Encoder (Figure 4) encoder (Figure 4)
Encoder (Figure 4)
Auxiliary mechanical device installation and other forms.
High speed end installation: it is installed at the rotating shaft end (or gear connection) of the power motor. This method has the advantages of high resolution. Since the multi turn encoder has 4096 turns, and the number of motor turns is within this range, the resolution can be improved by making full use of the full range. The disadvantage is that after the moving object passes through the deceleration gear, there is gear clearance error in the return journey. It is generally used for one-way 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, and the motor jitter must be small, otherwise it is easy to damage the encoder.
Low speed end installation: it is installed behind the reduction gear, such as the shaft end of the winch wire rope drum or the shaft end of the last reduction gear. This method has no gear to return clearance, so it is more direct and has higher accuracy. This method generally measures long-distance positioning, such as the positioning of various lifting equipment and feeding trolley.
Auxiliary machinery installation:
Commonly used are gear rack, chain belt, friction runner, rope take-up machinery, etc.
working principle
It consists of a photoelectric code disc with a shaft in the center, on which there are circular through and dark scribed lines,
Encoder (Figure 5) encoder (Figure 5)
Encoder (Figure 5)
There are photoelectric transmitting and receiving devices to read. Four groups of sine wave signals are obtained and combined into a, B, C and D. each sine wave has a phase difference of 90 degrees (360 degrees relative to a cycle). The C and D signals are reversed and superimposed on the A and B phases to enhance the stable signal; In addition, one z-phase pulse is output per revolution to represent the zero reference position.
Since the difference between a and 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. The zero position reference position of the encoder can be obtained through the zero position pulse. The encoder code disc is made of glass, metal and plastic. The glass code disc is deposited with very thin lines on the glass, which has good thermal stability and high precision. The metal code disc is directly connected with and without lines, and is not fragile. However, due to the certain thickness of metal, the accuracy is limited, and its thermal stability is one order of magnitude worse than that of glass. The plastic code disc is economical, and its cost is low, but its accuracy, thermal stability and service life are worse.
Resolution - the resolution refers to the number of through or dark lines provided by the encoder per 360 degrees of rotation, which is also known as analytical division or direct division. Generally, it is 5~10000 lines per revolution.
Main functions of folding and editing this section
It is a rotary sensor that converts rotary displacement into a series of digital pulse signals,
Encoder (Figure 6) encoder (Figure 6)
Encoder (Figure 6)
These pulses can be used to control the angular displacement. If the encoder is combined with the gear strip or screw, it can also be used to measure the linear displacement.
After the encoder generates electrical signals, it is processed by CNC, PLC and control system. These sensors are mainly used in the following areas: machine tools, material processing, motor feedback systems, and measurement and control equipment. In the ELTRA encoder, the photoelectric scanning principle is used to convert the angular displacement. The reading system is based on the rotation of the radial dividing disc, which is composed of alternating light transmission windows and light tight windows. This system is all vertically illuminated by an infrared light source, so that the light will project the image on the plate onto the surface of the receiver. The receiver is covered with a layer of grating, called collimator, which has the same window as the optical disk. The work of the receiver is to feel the light changes caused by the rotation of the 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 frequency converter to adjust the output data of the frequency converter. Fault phenomenon: 1. When the rotary encoder is broken (no output), the frequency converter can not work normally, and the running speed becomes very slow. In addition, the frequency converter is protected for a while, and "PG off" is displayed Joint action can work. In order to make the electrical signal rise to a higher level and produce square wave pulse without any interference, it must be processed by electronic circuit. The connection mode between encoder PG wiring and parameter vector converter and encoder PG must correspond to the model of encoder PG. Generally speaking, there are three types of encoder PG: differential output, open collector output and push-pull output. The interface of frequency converter PG card must be considered in the signal transmission mode, so the appropriate PG card model or setting is reasonable
Encoder is generally divided into incremental type and absolute type, which have the biggest difference: in the case of incremental encoder,
Encoder (Figure 7) encoder (Figure 7)
Encoder (Figure 7)
The position is determined by the number of pulses calculated from the zero mark, while the position of the absolute encoder is determined by the reading of the output code. In a circle, the output code reading of each position is unique; Therefore, when the power supply is disconnected, the absolute encoder is not separated from the actual position. If the power is turned on again, the position reading is still current and valid; Unlike the incremental encoder, you have to look for the zero mark.
At present, the encoder manufacturers produce a wide range of series, which are generally dedicated, such as Elevator dedicated encoder, machine tool dedicated encoder, servo motor dedicated encoder, etc. in addition, the encoders are intelligent and have various parallel interfaces to communicate with other equipment.
Encoder is a device that converts angular displacement or linear displacement into electrical signal. The former becomes a code disk, and the latter is called a code ruler According to the reading mode, the encoder can be divided into contact type and non-contact type The contact type adopts brush output. One brush contacts the conductive area or insulation area to indicate whether the code status is "1" or "0"; The non-contact receiving sensitive element is a photosensitive element or a magnetic sensitive element. When a photosensitive element is used, the status of the code is "1" or "0" by light transmission area and light tight area.
According to the working principle, encoders can be divided into incremental and absolute types.
Encoder (Figure 8) encoder (Figure 8)
Encoder (Figure 8)
Incremental encoder converts displacement into periodic electrical signal, and then converts this electrical signal into counting pulse. The number of pulses indicates the displacement. Each position of absolute encoder corresponds to a certain digital code, so its indication is only related to the starting and ending positions of measurement, and has nothing to do with the intermediate process of measurement.
The rotary incremental encoder outputs pulses during rotation, and its position is known through the counting device. When the encoder does not move or power is cut off, the position is remembered by relying on the internal memory of the counting device. In this way, after power failure, the encoder can not move at all. When the power is on, the encoder can not lose pulses due to interference during the process of outputting pulses. Otherwise, the zero point memorized by the counting device will shift, and the amount of this shift can not be known until the wrong production results appear. The solution is to add a reference point, and the encoder will correct the reference position into the memory position of the counting device every time it passes through the reference point. Before the reference point, the accuracy of the position cannot be guaranteed. For this reason, in the industrial control, there are methods such as finding the reference point for each operation and starting the machine for change. Such an encoder is determined by the mechanical position of the code disk, and it is not affected by power failure and interference.
The absolute encoder determines the uniqueness of each position determined by the mechanical position. It does not need to memorize, find reference points, and count all the time. When it needs to know the position, it reads its position. In this way, the anti-interference characteristics and data reliability of the encoder are greatly improved.
Since absolute encoder is obviously superior to incremental encoder in positioning,
Encoder (Figure 9) encoder (Figure 9)
Encoder (Figure 9)
It has been more and more used in industrial control positioning. Because of its high precision and large number of output bits, if the absolute encoder is still used for parallel output, the output signal of each bit must be well connected. For more complex working conditions, it must be isolated, and the number of connecting cable cores is large, which brings a lot of inconvenience and reduces the reliability. Therefore, when the absolute encoder is used for multi bit output, it generally adopts serial output or bus output, SSI (synchronous serial output) is the most commonly used serial output of absolute encoder produced in Germany.
Multi turn absolute encoder. The encoder manufacturer uses the principle of clock gear machinery. When the central code plate rotates, another group of code plates (or multiple groups of gears and multiple groups of code plates) are driven by gears to increase the number of cycles on the basis of single cycle coding, so as to expand the measurement range of the encoder. Such an absolute encoder is called multi cycle absolute encoder. It is also determined by the mechanical position, and the coding of each position is unique and does not need to be memorized. Another advantage of multi turn encoder is that due to the large measurement range, it is often more abundant in actual use, so it is unnecessary to find the zero point during installation. It is OK to take a certain middle position as the starting point, which greatly simplifies the difficulty of installation and debugging. Multi turn absolute encoder has obvious advantages in length positioning, and has been more and more used in industrial control positioning.
signal output 
The signal output includes sine wave (current or voltage), square wave (TTL, HTL),
Encoder (Figure 10)
Collector open circuit (PNP, NPN), 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 equipment interface of the encoder shall correspond to the encoder.
Signal connection - 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 and high.
For example, single-phase connection is used for one-way counting and one-way speed measurement.
A. B two phase connection, used for forward and reverse counting, judging forward and reverse directions and speed measurement.
A. B, Z three-phase connection, used for position measurement with reference position correction.
A. A-, B, b-, Z, z- connection. Due to the connection with symmetrical negative signal, the electromagnetic field contributed by the current to the cable is 0, the attenuation is the smallest, the anti-interference is the best, and can be transmitted over a long distance.
For TTL encoder with symmetrical negative signal output, the signal transmission distance can reach 150m.
For HTL encoder with symmetrical negative signal output, the signal transmission distance can reach 300 meters.
Fold and edit this paragraph to develop the market
Encoder is widely used in OEM market, mainly in machine tool, elevator, servo motor, textile machinery, packaging machinery, printing machinery, hoisting machinery and other industries. In 2010, the rapid growth of China's OEM market drove the rapid growth of the encoder market. In 2010, the market scale of China's encoder market reached 1.3 billion yuan, a year-on-year increase of 42.9%.
In terms of industry, elevator, machine tool and servo motor are the key application fields of encoder, accounting for 53% of the overall application market. At present, the market share of textile machinery, packaging machinery and printing machinery is small. Generally, encoders do not directly enter these three industries. The competition of encoder manufacturers is mainly concentrated in the motor manufacturers that provide servo motors for these machinery industries. The current market share of hoisting machinery is also small, accounting for only 4%-5%. In the project-based industries such as metallurgy and electronics, the current application proportion of encoder is low, accounting for only 14% of the market share. In addition, the encoder is also used in medical machinery, wind power, automobile production lines, hybrid electric vehicles, water conservancy, rail transit and other fields, but the application proportion is low.
In 2010, the demand for automation products in the wind power industry increased by more than 50%, while the main application fields of encoders such as elevators, servo motors, textile machinery and machine tools also increased significantly, which is the main source of growth.
In terms of industry, elevator, machine tool and servo motor are the key application fields of encoder, accounting for 53% of the overall application market. At present, the market share of textile machinery, packaging machinery and printing machinery is small. Generally, encoders do not directly enter these three industries. The competition of encoder manufacturers is mainly concentrated in the motor manufacturers that provide servo motors for these machinery industries. The current market share of hoisting machinery is also small, accounting for only 4%-5%. In the project-based industries such as metallurgy and electronics, the current application proportion of encoder is low, accounting for only 14% of the market share. In addition, the encoder is also used in medical machinery, wind power, automobile production lines, hybrid electric vehicles, water conservancy, rail transit and other fields, but the application proportion is low.
In 2010, the demand for automation products in the wind power industry increased by more than 50%, while the main application fields of encoders such as elevators, servo motors, textile machinery and machine tools also increased significantly, which is the main source of growth.
From the perspective of manufacturers, at present, European and American brands occupy the high-end market, accounting for more than one third of the market share. Their product prices are high-end, and they have advantages in new energy fields such as heavy industry and wind power; Japanese and Korean brands mainly occupy the mid-range market, accounting for more than one-third of the market share. Their product prices are mid-range and are widely used in elevator, machine tool, servo motor and other industries; However, mainland enterprises mainly participate in the competition in the middle and low-end market, and their product prices are relatively low, accounting for nearly half of the market sales, and only 25% of the mainland market sales share.
Enterprises with high market share include Heidenhain, Tamagawa, NEMICON, Yuheng, Baumer, Rep, p+f, Danaher, Koyo, Omron, etc. Among them, the market share of the top three enterprises accounts for nearly 50% of the total market, with a high degree of market concentration. The application industries mainly targeted by enterprises are highly concentrated and have less industry competition. There is also a significant gap in the performance growth of mainstream manufacturers. The largest growth rate is 60%, and the smallest growth rate is less than 10%.
The encoder is divided into absolute value type and incremental type. At present, the price of absolute encoder is about 4 times higher than that of incremental encoder. 70% of the applications in the domestic market are incremental encoders with relatively low price. They are mainly used in machinery and equipment that only require speed measurement and do not require high absolute position measurement in industries such as packaging, textile, elevator, etc. However, in high-precision mechanical equipment or heavy industries such as steel, port and lifting, absolute value encoder will be used in more cases due to the relatively high requirements for measurement accuracy. In these heavy industrial applications, due to the poor working conditions, the encoder has high requirements for anti shock and vibration indicators.
With the improvement of the automation of mechanical equipment, the application fields of encoder products are becoming more and more extensive. Customers are no longer satisfied that the encoder can only convert physical rotation signals into electrical signals. They also require a higher degree of integration of the encoder and more durable products. They also hope that richer interface modes can appear in the absolute value encoder to make more equipment intelligent.
At present, more and more attention is paid to the production safety and communication safety in the whole industrial market. The national level has also begun to put forward requirements for the safety performance of products. There are corresponding specifications in terms of safety standards for encoders. However, due to the relatively low technical requirements for products in the domestic encoder market, customers prefer medium and low-end products.
Notes on model selection
Three parameters should be noted:
1. Mechanical installation dimension: including positioning seam, shaft diameter and installation hole position; Cable outgoing mode; Installation space volume; Whether the protection grade of working environment meets the requirements.
2. Resolution: that is, whether the number of pulses output per cycle when the encoder works meets the design accuracy requirements.
3. Electrical interface: common encoder output modes include 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. The output mode shall match the interface circuit of the control system.
Advantages and disadvantages
Photoelectric encoder
Advantages: small size, precision, high resolution, no contact and no wear; The same product can detect both angular displacement and linear displacement with the help of mechanical conversion device; The multi turn photoelectric absolute encoder can detect the linear displacement of a fairly long range (such as 25 bit multi turn). Long service life, random installation, rich interface forms and reasonable price. Mature technology has been widely used at home and abroad many years ago.
Disadvantages: precise, but it puts forward higher protection requirements for outdoor and harsh environment; The measurement of linear displacement depends on the conversion of mechanical devices, and the error caused by mechanical clearance should be eliminated; It is difficult to overcome the slip when detecting objects in orbit.
Magnetostatic grating absolute encoder
Advantages: moderate volume, direct measurement of linear displacement, absolute digital coding, and unlimited theoretical range; No contact and wear, resistant to harsh environment, and can be used under 1000 meters of water; Rich interface forms and various measurement methods; The price is acceptable.
Disadvantages: the resolution of 1mm is not high; Different varieties shall be used for measuring straight lines and angles; It is not suitable to carry out displacement detection (greater than 260 mm) at fine points.