Most popular encoder FAQ

2022-09-27
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Common questions and answers of encoder

I. ask: what are the precautions for the selection of incremental rotary encoder

three parameters should be paid attention to:

1. Mechanical installation size, 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. whether the resolution, that is, the number of pulses output per cycle when the encoder works, meets the design accuracy requirements

3. electrical interface, encoder output modes commonly 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. Its output mode shall match the interface circuit of its control system

II. Ask: how to use the incremental encoder

1, the incremental rotary encoder has a difference in resolution, which is measured by the number of pulses generated per cycle, ranging from 6 to 5400 or higher. The more pulses, the higher the resolution; This is one of the important bases for model selection

2, the incremental encoder usually has three signal outputs (six differential signals): A, B and Z, which generally adopt TTL level. A pulse is in front and combined with the local market demand in China. B pulse is in the back, and the difference between a and B pulses is 90 degrees. Each circle sends out a Z pulse, which can be used as the reference mechanical zero position. Generally, we use a ahead of B or a ahead of B ultrasound to judge the direction. Our incremental encoder is defined as the clockwise rotation of the encoder at the shaft end is forward rotation, a ahead of B is 90 °, and conversely, counterclockwise rotation is reverse rotation, a before B ultrasound is 90 °. There are also differences, depending on the product description

3, PLC is used to collect data, and high-speed counting module can be selected; The industrial computer is used to collect data, and the high-speed counting board can be selected; It is suggested to use the input port with optocoupler to collect data with single chip microcomputer

4, it is suggested that the B pulse should be a forward (forward) pulse, the a pulse should be a reverse (backward) pulse, and the Z origin zero position pulse

5, set up a counting stack in the electronic device

III. about outdoor use or use in harsh environments

a friend came to email and asked that his equipment was used in the field, and the on-site environment was dirty, and he was afraid of damaging the encoder

our company has aluminum alloy (special requirements can be made of stainless steel) sealed protective shell, double bearing heavy-duty encoder, which is not afraid of dirt when placed outdoors, and can be used in steel plants and heavy equipment

however, if there is space for the installation part of the encoder, I still suggest adding a protective shell outside the encoder to strengthen its protection. Unexpectedly, the encoder is a precision component, and there is still a certain gap between the value of an encoder and a protective shell

IV. from proximity switch, photoelectric switch to rotary encoder:

positioning in industrial control, the application of proximity switch and photoelectric switch has been quite mature and easy to use. However, with the continuous development of industrial control, there are new requirements. In this way, the application advantages of using rotary encoder are highlighted:

Informatization: in addition to positioning, the control room can also know its specific location

flexibility: the positioning can be flexibly adjusted in the control room

convenience, safety and longevity of on-site installation: a fist sized rotary encoder can measure the distance from several to tens or hundreds of meters, and N stations. As long as the safety installation problem of a rotary encoder is solved, many problems such as the trouble of mechanical installation of proximity switches and photoelectric switches on site, easy to be damaged and troubled by high temperature and moisture can be avoided. As it is a photoelectric code disk, there is no mechanical loss. As long as the installation position is accurate, its service life is often very long

multifunction: in addition to positioning, it can also transmit the current position remotely and convert the movement speed, which is particularly important for the application of frequency converter, stepping motor, etc

Economy: for multiple control stations, the cost of only one rotary encoder, as well as the more important installation, maintenance and loss costs are reduced, and the service life is increased. Its economy is gradually highlighted

with the advantages mentioned above, rotary encoder has been more and more widely used in various industrial control occasions

v. about power supply and connection between encoder and PLC:

there are three kinds of working power supply for general encoder: 5VDC, VDC or VDC. If the encoder you buy uses VDC, you can use the 24V power supply of PLC. It should be noted that:

1. The current consumption of encoder is within the power range of PLC

2. If the encoder is output in parallel, connect the i/o point of PLC. It is necessary to know whether the signal level of the encoder is push-pull (or push-pull) output or open collector output. If it is open collector output, there are two types: n-type and p-type, which need to be the same as the i/o polarity of PLC. If it is a push-pull output, there is no problem with the connection

3. if the encoder is a driver output, the general signal level is 5V. Be careful when connecting. Do not damage the signal end of the encoder by letting the 24V power level string into the 5V signal wiring. (our company can also make wide voltage driver output (VDC), which should be noted when ordering)

VI. in many cases, the encoder is not broken, but just the cause of interference, resulting in bad wave shape and inaccurate counting. How to judge? Thank you

the encoder is a precision component, which is mainly due to the serious interference around the encoder, such as whether there is interference caused by the frequent starting of large motors and electric welding machines, whether it is transmitted in the same pipeline with the power line, etc

it is also important to choose what kind of output to resist interference. Generally, the anti-interference of output with reverse signal is better, that is, a+~a-, b+~b-, z+~z-, which is characterized by adding 8 lines of power supply instead of 5 lines (total zero). The transmission with reverse signal in the cable is symmetrical and subject to little interference. Judgment can also be added in the receiving equipment (for example, when the signal of the receiving equipment uses the 90 ° phase difference of a and B signals, and reads the four states of level 10, 11, 01 and 00, it is counted as an effective pulse. This scheme can effectively improve the anti-interference performance of the system (accurate counting))

even the encoder is good or bad. Its code disk electronic chip internal circuit signal output varies greatly. Otherwise, how can a 1000 line incremental encoder vary so much from more than 300 yuan to more than 3000 yuan

① eliminate (remove, close, isolate) interference sources, ② judge whether it is the cumulative error of mechanical clearance, ③ judge whether it is the mismatch between the circuit interface of the control system and the encoder (encoder selection error); ① ② ③ if the fault phenomenon is eliminated after the compensation test, it can be preliminarily judged. If it is not eliminated, it must be further analyzed

the simple method to judge whether it is the fault of the encoder itself is troubleshooting. Now our encoder has been produced on a large scale, the technology production has been mature, and the product failure rate is controlled at a few thousandths. The specific method of troubleshooting is: replace it with an encoder of the same model. If the fault phenomenon is the same, it can be basically eliminated that it is the encoder fault problem, because the small probability event of two encoders having faults at the same time may be very small, which can be regarded as 0. If you change an encoder of the same model and the fault is eliminated immediately, you can basically determine that it is the encoder fault

VII. What is long-term drive? Can the ordinary encoder transmit long distance

answer: long line drive is also called differential long line drive. The positive and negative waveforms of 5V and TTL are symmetrical. Because the positive and negative current directions are opposite, and the external electromagnetic field is offset, the anti-interference ability is strong. The transmission distance of ordinary encoder is generally 100 meters. If it is 24V HTL type and has symmetrical negative signal, the transmission distance is meters

VIII. Q: can you briefly introduce the method of detecting linear displacement by rotary encoder

answer: 1. Use "elastic coupling" to directly connect the rotary encoder with the main shaft of the power device driving linear displacement

2, use a small gear (straight tooth, bevel gear or worm gear) box to couple with the power unit

3, the gear rotating on the straight rack is used to transmit the linear displacement information

4, obtain linear displacement information on the sprocket of the transmission chain

5, obtain linear displacement information on the synchronous belt of the synchronous belt pulley

6, use the rotary encoder installed with magnetic rollers to obtain displacement information on the flat steel material surface with linear displacement (to avoid slip)

7, use the "retractable steel wire assembly" similar to the "steel tape" to connect the rotary encoder to detect the linear displacement information (the lamination winding error must be overcome in data processing)

8, similar to 7, use the "retractable steel wire assembly" with a small torque motor to connect the rotary encoder to detect the linear displacement information (at present, there are similar products in Germany, with complex structure and almost no lamination winding error)

IX. can the incremental grating Z signal be zero? How to choose a circular grating encoder

the Z signal of both linear grating and axis encoder can achieve the same accuracy as the ab signal, except that the axis encoder is one circle, while the linear grating is one at a certain distance. With this signal, high repetition accuracy can be achieved. You can use an ordinary proximity switch for initial positioning, and then find the closest Z signal (each time in the same direction). When installing, don't forget to adjust its phase to be consistent with the grating phase, otherwise it is not allowed

select according to your subdivision accuracy and resolution requirements. With high accuracy, it is natural to choose the one with high weekly lines. If the accuracy is not high, there is no need to choose the circular grating encoder with high line number

X. what is the difference between incremental encoder and absolute encoder? How to choose a servo system

incremental encoder is commonly used. If there are strict requirements for position and zero position, absolute encoder is used. The servo system should be analyzed in detail to see that the fracture of the applied sample will always be broken on both sides

the commonly used incremental encoder is used to measure the speed, which can be accumulated infinitely; Absolute encoder is used to measure the position. The uniqueness of the position (single circle or multiple circles) depends on the application and the purpose and requirements to be achieved

Xi. Precautions for the selection of absolute rotary encoder. The advantages of rotary encoder compared with proximity switch and photoelectric switch:

the single lap of absolute encoder ranges from 8-bit economical to 17 bit high-precision, and the price can range from several hundred yuan to more than 10000 yuan

most of the absolute encoders use 25 bits for multiple turns, and the outputs include SSI, bus PROFIBUS DP, can L2, INTERBUS, DeviceNet. The prices can also range from more than 3000 to more than 10000

rotary photoelectric encoder is a very mature technology for measuring angle and length. Nowadays, the absolute encoder with high precision and large range is used, which greatly improves the measurement accuracy and reliability, and is economical and practical. At present, it is still the most choice for measuring length

XII. From incremental encoder to absolute encoder

rotating incremental encoder outputs pulses when rotating, 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 the power failure, the encoder cannot move at all. When the power is on, the encoder cannot lose the pulse due to interference in the process of outputting the pulse. Otherwise, the zero point memorized by the counting device will shift, and the amount of this shift is unknown. It can only be known after the wrong production result appears

the solution is to add reference points,

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