Bring it offset printing process of process control system (
Need to use multiple sensors to test the paper position, rotation Angle, the quantity of sensors to cause inconvenience, installation, debugging and use make the reliability of equipment is reduced, the cost of the electric control system.
Analysis, found that the function of the offset printing machine and mechanical transmission system of offset press pressure, code, dial the code, the spray powder and the function of rotary sequence control, can through the testing paper roll rotation Angle, implementation process control.
Considering the offset press oil, ink, water and dust fall pollution, and run continuously demanding application environment, the magnetic sensor is more suitable for sensitive type, but relatively little to control the location of offset press, selection of magnetic rotary encoder and look expensive.
As a result, the hall hall circuit design based on switch mode type offset press the rotary encoder system (
Hereinafter referred to as the hall rotary encoder)
, so that the sensor installation, commissioning and wiring to simplify, save the PLC controller input interface resources, its application in offset printing machine control system is a success.
1 rotary encoder principle block diagram hall hall rotary encoder is mainly composed of the rotating magnet assembly, sampling circuit and signal processing circuit and other parts, as shown in figure 1.
Among them, the combination of the rotating magnet installed on the offset printing paper roll, hall rotary encoder circuit part fixed on the body, sensitive face magnetic pole, the distance is less than 5 mm, the rotation Angle of paper roll sampling.
On the location of the magnetic pole is certain, the magnitude of the sampled signal is absolutely positioned.
If the sampling circuit with identification of printing process and the ability to position sequence control points, so the printing process will be able to pass a multipoint sampling sensors, implementation process control.
A3144 sampling is based on the basis of hall circuit, single chip hall can't realize clearly including the starting points and sequence of sampling, need to special design of sampling circuit, with the above requirements.
Sampling circuit to obtain the location of the signal to the signal processing circuit, the software
system to determine the signal, output encoding information after confirmation.
Double sampling system structure and principle of hall 1 according to the principle of switch type circuit hall, hall chip applies only to a direction of the magnetic field, which means that an induction hall chip surface for magnet s extremely sensitive, so the other side must be N is extremely sensitive, assuming that the two sides called s face and N, respectively.
The two type switch hall chip the same sensitive surface (A and B
N the surface, for example)
In the former, A, B in the stacked, composed of A pair of AB hall sampling circuit.
The output of A defined as Va, chip B output defined as Vb, apparently to come from the same direction of magnet, chip A to S is extremely sensitive, chip B is sensitive to the N pole, the S pole trigger double hall AB, the Va output, N trigger AB, the Vb output, as shown in figure 2.
This design make sampling chipset is sensitive to both magnetic field direction, because the chip independent output, have the ability to identify the poles.
As a result of the magnet group S, N pole position interval, so the Va, Vb signals don't overlap in time.
When S, N1, and N2 and N3 and N4 interchange once order triggered AB, A chip will output A pulse, referred to as the 'starting point' or zero signal;
Chip B four pulse output, called the 'order' signal.
Design sampling circuit based on this idea, implements the rotating magnet group each pole of the recognition, especially the key is to determine the starting point for the printing process.
used for offset printing machine combination of magnet consists of five pieces of magnets, one of the magnets, the S pole outwards and corresponding printing press 'close' position, the other four magnet n-pole outwards, corresponding to 'code', 'dial code', 'powder' and 'double rotary' process.
Because of the differences between the devices, 'code', 'dial code' position can be adjusted synchronization.
Magnet installed on offset printing paper roll, each completed a printing process, paper roll revolves, through testing the magnet position, realizes the program control of the offset printing process.
3 hall rotary encoder circuit design the core of the encoder circuit adopts Microchip Technology Inc, production PIC12C508A micro control unit.
It COMS based design, structure of RISC, on chip RAM memory EPROM and data storage program, integrates the electrical reset circuit (
, clock oscillator (
, the watchdog timer (
Functional units, such as with a miniaturized package (
, low power consumption,
Sampling rounds per rotation week, coding sequence of software system to complete a conversion.
Coded pulse width of low level is determined by the software, has nothing to do with rotation speed, and high level width is decided by the magnet n-pole interval.
Therefore a complete coding sequence contains a starting point, ordinal position interval and spin cycle three aspects of information.
4 software system design PIC12C508A micro control unit, using reduced instruction set system, in addition to the jump instruction cycle for the vast majority of instruction.
2 software system program listing software design including the initialization procedure, the main program and delay subroutine, refer to the program listing below.
Definition and register initialization program 5 knot language hall rotary encoder has the advantage that the switch type of hall sensor, which is based on the principle of simple and practical design, direct access to position signal, principle and structure on different sophisticated magnetic rotary encoder.
Application of this system on the offset press has achieved good effect, stable and reliable performance, excellent price performance ratio.
For position measurement, sampling points, the more the more obvious the superiority.
Although is designed according to the characteristics of the offset press, but its application is universal.
Magnets can design according to the need to be flexible, use for it to provide the convenience.
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