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1、The properties and application of photoelectric encoder The working principle, photoelectric encoderPhotoelectric encoder, is a kind of photoelectric transformation through the machine will output shaft geometric displacement convert pulse or digital sensors. This is the most sensor, photoelectric e
2、ncoder and grating is by photoelectric detection device. Grating is in certain parts of the diameter of the circular plate to open several rectangle hole. Caused by the code, motor and motor coaxial rotates grating and motor rotate speed, with the light emitting diode and other electronic components
3、 testing unit output pulse signal with several, its principle diagram is shown in figure 1, Through the calculation of the output pulse of photoelectric encoder per number can reflect the current motor speed. In addition, the direction of rotation, the code for the judge may also provide phase diffe
4、rence dish of 90 two pulses.According to the measuring principle, encoder can be divided into optical and magnetic type, inductive and capacitor. According to the calibration method and the signal output form, can be divided into incremental, absolutely and hybrid three.Incremental encoderIncrementa
5、l encoder is directly for the use of photoelectric pulse output three square principle of A and B and Z, A and B group phase, pulse 90 can easily identify rotation direction, and for every turn A phase Z benchmark for positioning. Pulse, Its advantages are simple structure, mechanical principle, ave
6、rage life expectancy in tens of thousands of hours, strong anti-jamming capability, high reliability, suitable for long distance transmission. Its defect is not the absolute output shaft rotation location information.图1 光电编码器的远离示意图Absolute photoelectric encoderAbsolute encoder is direct digital outp
7、ut sensor, in its circular yards on several concentric yards along the radial direction of every faith, by pervious to light and not pervious to light, the sector and the adjacent code number of sectors, encoder is double the code number of bits of it in the code of digits, light source, the other s
8、ide is one word has a corresponding yard photosensitive components, When the code in different position, the dish by various photosensitive components according to the corresponding conversion or light signals, binary number level. This is not the encoder counter in the shaft can be read at any posi
9、tion of a fixed position corresponds with the digital code. Obviously, the word, the more the high resolution, for a N binary resolution coder code salver must have N barcode. Currently there are 16 bits of absolute encoder products.Single channel absolute photoelectric shaft encoder is using the na
10、tural binary or circular binary (Gregory yards) manner photoelectric conversion. Absolute photoelectric encoder and incremental encoder differs not pervious to light on the disk, the line, absolute encoders may have graphics, according to the number of code read code on coding, detection absolute po
11、sition. Code design can use binary code, circulation, binary complement, etc. Its features are:Can read Angle of absolute coordinates directly.No accumulative error. Power excision location information would be lost. But the resolution is determined by the binary digits, i.e., precision depends on t
12、he median 10, 14 etc. Hybrid absolute encoder.Hybrid absolute encoders, its output of two groups: a group of information, information for testing poles with absolute information function, Another group of incremental encoder is completely with the output information.Photoelectric encoder is an Angle
13、 (angular velocity) detection device, it will input shaft Angle for, using the principle of photoelectric convert electrical or digital accordingly, small size, high accuracy, high reliability, digital interface, etc. It is widely applied in nc machine tools, turning machine, servo drive, robots, ra
14、dar and military targets were needed in the Angle of device and equipment.Applied circuit of photoelectric encoderEPC - 755A application of photoelectric encoderEPC - 755A photoelectric encoder and the use of good performance in Angle measurement, displacement measurement, and has strong anti-jammin
15、g capability of the output pulse signal is stable and reliable, and the pulse signal can be obtained by counting were measured after the digital signal. Therefore, we in the car driving simulators, steering wheel rotation Angle measurement chooses EPC - 755A photoelectric encoder, the output circuit
16、 as sensors, choose open collector output resolution selection 360 pulse/circle, considering the steering wheel rotation is a two-way street, clockwise and counterclockwise, can also needs to the output signal phase coder to count. Figure 2 shows the actual use of photoelectric encoder and discrimin
17、ation, phase two-way counts circuit with a D flip-flop circuit and two cross-coupled nand gates, with 74LS193 3 counts circuit.图2 光电编码器鉴相计数电路When the photoelectric encoder clockwise, channel, A leading channel output waveform of output waveform B 90 , D flip-flop output waveform W1) for Q (high leve
18、l, Q (W2) for low-level waveform cross-coupled nand gates, open, counting pulse waveform W3) by (bidirectional, send to the 74LS193 counter CU input pulses, add count, At this time, below, its output cross-coupled nand gates close for high level (waveform W4). When the photoelectric encoder counter-
19、clockwise, channel A output waveform of output waveform delay than channel B 90 , D flip-flop output waveform W1) for Q (low level, Q (W2) for high level waveform, the output cross-coupled nand gates close, high level (waveform W3), Now, two cross-coupled nand gates open, counting under impulsive th
20、rough (waveform W4), send to two-way 74LS193 counter reduced input pulses, CD. Subtraction.Steering wheel clockwise and counter-clockwise, the maximum rotation Angle for two laps, choose resolution for 360 pulse/circle of the output pulse coder, its biggest for 900, Actual use three slices of counts
21、 circuit 74LS193 component in the system of initialization, the signal reset (CLR), the initial set for 800H, namely 2048 (LD); the signal, So, when the steering wheel clockwise, count the output circuit for 2048 2948, when steering counter-clockwise, count the output circuit for 2048-804, D0 output
22、 data counts circuit D11 to data processing circuit.In practice, the steering wheel frequently made clockwise and counterclockwise rotation, because existence, work longer quantization error after a period of time, the steering wheel when the output of a circuit to count, but may not 2048 several wo
23、rds deviation, To solve this problem, we added a steering wheel to detect circuits, systems, data processing circuit after work on the operation state in the simulator, system test in the back, if detection circuit in the back wheel, and counts circuit in the data output, but not to count 2048 reset
24、 circuit, and the initial reset.Photoelectric encoder gravity measurement instrument in the applicationThe rotary photoelectric encoder, the shaft and gravity measuring instrument for knob shaft. Gravity measurement of the angular displacement volume knob compensation for a signal is transformed, Ro
25、tary photoelectric encoder and absolute encoder two points and incremental encoder.Incremental encoder is the output pulse form, its code plate sensor than absolute encoder code easier to disk and higher resolution. Generally need only three barcode, heres code has not actually had word of absolute
26、encoder code, but produce counting pulse. Its code of WaiDao and middle way has the same number of uniform distribution of not pervious to light and sector (raster), but is two sector mutual stagger half area. When the code salver, turning the output signal is A difference for 90 with B in the pulse
27、 signal and only one third of the slit pervious word code generated by the pulse signal (it as the benchmark code salver position, to provide an initial counting system of zero signal). From A, B two output signal phase relationship (ahead or behind) can judge the direction of rotation. Graph 3 by (
28、a), when the code dish is a word, pulse than B ground PI / 2, and reverse, a word than B lagging ways pulses PI / 2. Figure 3. (b) is A practical circuit, use A word of plastic wave along the steady-state produces single trigger word and b are pulse wave phase and plastic disc, when the code is only
29、 positive mouth pulse output, whereas only reverse mouth pulse output. Therefore, the increment of the output pulse coder is according to the source and pulse count to determine the direction and the code salver. Relative angular Usually, if the encoder has N (yards), its output signal phase differe
30、nce of PI/N, may count for the number of times the grating 2N pulse, N = 2. Figure 3 circuit faults are sometimes mistake pulse, this error in a signal in a high or low , and level other signal is in high and low and change of state, though code salver, but will produce a shift in the output pulse.
31、For example, code salver or manual alignment occurs jitter position (below can see, in spring gravimeters measurement will have this kind of case).图3 增量光电编码器基本波形和电路图4 四倍计数方式的波形和电路Figure 4 is a can prevent error and can improve the resolution of the pulse frequency subdivision circuit four times. Her
32、e, the function of memory is D flip-flop and clock generator. Figure 4 shows, by every two D flip-flop, so take in the clock pulse, the interval of two Q end (such as the corresponding B 74LS175 2, 7 foot) maintain two clock period, if both input status, said the change in, Otherwise, can according
33、to the relationship between the changes from the party, which is to or backward output pulse. When a word because of high vibration in the , low , will change between reciprocating alternate positive and backward pulse, the two counter on the number and replace them when they can eliminate the shado
34、w ring (below instrument readings will involve this). Thus, the clock generator frequency of vibration frequency may be greater than the maximum. Can see from figure 4, a pulse signal of the cycle, four counts pulse. For example, the number of every lap pulse coder for 1000 produce four times the nu
35、mber of pulse frequency, and its resolution is 4000 for 0.09 degree. Actually, this kind of sensor products will enlarge the output signal of photosensitive components such as plastic circuit and sensor encapsulation testing components together, so just add subdivision and counts circuit can form a
36、angular measurement system (74159 is 4-16 decoder).Application problem analysis and improvement measuresApplication problem analysisPhotoelectric detection devices transmit and receive devices are installed in the production and use of exposed many defects, its internal factors have external factors
37、, which is mainly embodied in the following aspects:Devices or accept device for mechanical vibration, caused by the shift or offset, receiving devices not reliable to receive light signals, but cannot produce signals. For example, Photoelectric encoder used in steel rolling speed regulation systems
38、, because of photoelectric encoder is bolted directly in motor shell, photoelectric encoder shaft through hard shrapnal and motor rotor connections, because motor with load is a load of impact, while rolling steel rotor motor will have caused the shell and vibration. According to the mensuration, Af
39、ter steel time electricity encoder vibration velocity for 2.6 mm/s, this can damage the vibration velocity of photoelectric encoder internal functions. A pulse, thereby causing instability in control system, or misoperation cause accidents.Because of photoelectric detection device installed in produ
40、ction, production environment factors in photoelectric detection devices not reliable work. Such as the installation position of high temperature, humidity, photoelectric detection device to internal electronic components characteristics change or damage. For example in continuous caster send analyz
41、ed.essential tracking system, because of photoelectric detection equipment installation location near the slab, high temperature environment caused by photoelectric detection device signal or damage caused by accidents or production.Production site for all kinds of electromagnetic interference sourc
42、e photoelectric detection device, of interference, photoelectric detection device of output waveform distortion distortion occurs, the system maloperation accident or production. For example, Photoelectric detection device installed in the production equipment of the signal, the body to the control
43、system of the cable transmission distances in 20-100 meters, cable, although usually choose multiple shielded cable conductor, but due to cable capacitance between lines of resistance and impact plus and other cable laying together, vulnerable to all sorts of electromagnetic interference effect, thu
44、s causing waveform distortion, thus to drive system feedback signal and practical value deviation, and cause the system precision.Measures for improvementChange of photoelectric encoder installation. Photoelectric encoder is not installed in motor shell, but in the motor based on a fixed bracket to
45、independent installation photoelectric encoder, photoelectric encoder axis and motor shaft center must at the same level, two axis adopt soft rubber or nylon hose connection, to reduce the impact of photoelectric encoder motor load of mechanical shock. By this way after vibration testing, the vibrat
46、ion velocity to 1.2 mm/s.Reasonable choice of photoelectric detection device, the output signal transmission medium by twisted-pair cable instead of ordinary shield cable. Twisted-pair cable has two important characteristics of cable, one is by electromagnetic interference with strong protection abi
47、lity, because the space of electromagnetic interference current online can cancel each other out. Twisted-pair cable is another technical characteristics of two mutually twisted line spacing is small, after two lines of interference lines distance equal to two lines, basic capacitance of shielding n
48、etwork basic and same, it is to restrain common-mode interference effect more apparent.Using PLC software to monitor or interference. In the continuous process analyzed.essential photoelectric detection device has the timing signal, at the same time, the whole process of signal and corresponding dif
49、ferent stages. As shown in figure 5.图5 送引锭过程和光电信号关系 1 send analyzed.essential before starting the process, photoelectric signal 1 1. 2 after the start sending analyzed.essential process, in A stage, roller, start sending bar. When the lever block photoelectric device analyzed.essential emit light, the photoelectric signal for 0, When light guide bar through central 2 small round hole, photoelectric device sends a signal to 2 and 3, 1.