The secondary tension control of the printing press plays a vital role in the printing process, which directly affects the accuracy of the overprint of the printed product, especially in the occasions where the requirement for overprinting is particularly important. Errors in the primary tension control system. Changes in machine speed and tension fluctuations caused by external objective factors require adjustment by a secondary tension control system to ensure tension balance in the printing unit. Without a good secondary tension control system, the overprint control system cannot completely eliminate errors caused by tension changes.
The KOCHS, EK seven-color gravure printing machine imported from Germany by our company adopts the reversible DC drive system of SIEMEMS company for its secondary tension control system. Device aging. Failures are frequent. Because it is difficult and expensive to obtain the original spare parts, there are many peripheral control devices, and the inherent maintenance difficulties of the DC motor itself can no longer meet the needs of production and technology. It is imperative to use existing mature control technology to transform the secondary tension control part of the machine to eliminate the impact of equipment failure on production.
Original machine secondary tension control system
1. The composition of the secondary tension control system of the original machine
(1) Tension detection and amplified tension detection are FAG company pressure sensors, model MGZ205, each sensor is composed of three precision resistances of 220n and a basic resistance of 220n pressure sensitive resistance, the power supply voltage is + 5VDC . The tension amplifier is composed of two FAG single amplifier boards MGZ110 and one two input average adder MGZ120 on the Infeed side. The Outfeed side is composed of a FAG double amplifier average amplifier board MGZ110B, and the input power voltage is 220VAC. The output voltage is 0-10VDC. The main functions of the amplifier board are: provide +5 for the pressure sensor. OVDC power supply. Provide + 2.7VDC reference power supply for calibration. Correction. Zero adjustment. Amplification adjustment, limiting and final power amplification output, fault detection and indication, etc.
(2) DC motor controller
SIEMEMS S ～ OREG M series reversible converter 6RA5021-3MA00 is adopted. The rated input voltage of the main circuit is three-phase 380VAC: -5%, + 10%, 50Hz; rated output voltage is 400VDC, current 35A, power 14kW. The rated input voltage of the excitation circuit is single-phase 380VAC, and the maximum output is 310VDC, 8A.
(3) DC motor components include the model 1GG511 2-OKDll-6JUl-Z motor, and its rated parameters are: armature voltage 60-400V, armature current 16.5A. Power 5.5kW, speed 50-2000 rpm. The excitation voltage is 180V, the excitation current is 1.20A; the model is TDP 0.09 S-3 speed measuring motor, and its parameter is 0.4W. 40VDC, 1000 rpm. Not marked in the figure are: electromagnetic brake with braking torque of 25Nm and parameters of three-phase 380V. 0.28A blower motor.
(4) Auxiliary circuit
In addition to providing power for each component, it mainly performs protection and control of the tension control system itself, and also completes chain protection and control with the host.
2. The control principle of the original secondary tension control system
The control signal of the original two-level tension control system. The work of the original system is described below.
(1) Tension detection and amplification. In order to eliminate the influence of various factors such as the deformation of the paper during the printing process and the paper is not completely in the middle, accurately detect the tension of the paper, install a pressure sensor at each end of the pressure detection roller, and input the detected signal into two channels Amplifier. After correction, zero adjustment and magnification adjustment, the weight of the tension roller itself and the inconsistency of the pressure detection amplification system itself are eliminated, and the weighted average is taken as the actual tension output.
(2) Tension control. The tension will be set. The difference between actual tension and tension offset, and according to the set tension. The size of the real-time difference of the actual tension is selected to be blocked by an external signal) or PID control mode and limited. According to the specific requirements of Infeed or Outfeed, the output is used as the auxiliary input of the speed loop. The setting range of the tension offset is 0-10% of the maximum tension value. Its purpose is to pre-tension the paper between the frames during the machine preparation stage to eliminate the possible paper break caused by the impact on the paper when the machine starts.
(3) Reversible converter. Normal speed current double closed-loop control mode. The output of the tension loop is attenuated to 20%. Together with the speed of the host (speed given) and the speed measuring motor signal, it forms a complete speed closed-loop feedback. The setting sequence is: after releasing the tension control signal and the speed loop ID parameter, and under no-load conditions, set the speed feedback component and proportional parameter, and then the ID parameter cross-approaching step by step, except for zero current detection, continuous current and interruption In addition to PID control of continuous current variable parameters, for four-quadrant reversible converter operation, it also involves zero setting, current commutation and dead zone control. The maximum conduction angle and the minimum inverter angle are set, so care should be taken when adjusting to prevent the converter from being subverted and damaged. Since the current loop is already set at the factory, there is basically no need for further adjustment.
(4) Auxiliary circuit. Provide power supplies that meet the conditions for each component, detect the working status of each component according to the timing requirements of the control, control the work of each component, and provide undercurrent and overcurrent. Undervoltage, overvoltage, overload protection. Chain protection and control with the host is reflected in: operation. Stop and acceleration and deceleration interlock, the host is accelerated to prevent protection when the tension is too small. [next]
Choice of transformation plan
1. Overall plan for transformation
The overall transformation plan has the following two types.
(1) Basically use the original mechanical structure, mainly to carry out new generation of electrical control system. The program has few changes to the machine, low cost, and short preparation time, but the online debugging takes a long time, and the recoverability of the original system is poor.
(2) Remake most of the mechanisms and all electrical control systems, and add the necessary mechanisms to the original machine to form two complete tension control systems. This solution has high cost, long preparation time, and limited installation space, but there are fewer changes to the machine. It can be debugged offline, and the time spent on online debugging is short. There is no restorative problem of the original system.
Because the company's production tasks are very heavy, in order to shorten the installation and commissioning time, as far as possible without affecting production, it is determined to use the second scheme.
2. Power amplification and choice of actuator
There are three main options for power amplification and actuators.
(1) DC reversible converter + DC motor. This solution has mature technology, good stability and controllability, can use existing motors, and has low cost, but the auxiliary control circuit is more complicated, and DC motor maintenance is more difficult.
(2) AC inverter + AC motor. This scheme has the lowest cost, the auxiliary control circuit is simple, and the motor maintenance is easy, but the technology used for four-quadrant operation is not comprehensive, and the low-speed stability and poor controllability are basically not used for a large range of requirements. High precision control occasions.
(3) Servo driver + servo motor. The technology is also mature, with good stability and controllability, simple auxiliary control circuit, and easy maintenance of the motor, but the highest cost.
In this transformation, the third solution of servo driver + servo motor is determined.
3. Determination of driver and motor
The original machine production speed is 100m / min, the maximum tension can be set F = 100kgf, and the instantaneous maximum speed is V = 140m / min. Synchronous belt transmission efficiency n = 0.93, the maximum speed of the drive motor N = 2000 rpm. If the diameter of the driving roller is D = 185mm, the average power P that the driving roller should provide is:
P1 = f * V = F * g * V
Among them, f is the tension, the unit is N; g is the acceleration of gravity, the unit is meter '/ second, then:
Pi = FxgxV two 100x 9.8x140 / 60 = 2286 (W) two 2.286 (kW)
Drive roller speed Nl = 1000xV ï¼ 3.14 ï¼ D = 1000x140 ï¼ 3.14 ï¼
185 = 241 (rev / min)
With two-stage synchronous belt drive for deceleration, the minimum power P output by the motor is:
P = P1 / n '2 2.286 / 0.93 / 0.93 = 2.643 (kW)
Considering the quick response to the requirements of acceleration and deceleration, the power is selected here according to the selection of the original drive system for the motor. OkW servo drive system.
4. Composition of secondary tension control system
With reference to the control method of the secondary tension of the original machine and various other gravure printing machines, considering the limitation of objective conditions and the degree of understanding and grasp of the tension control system by the author, I chose the floating roller tension sensor MCS-605E from WARNER ELECTRIC. Tension controller MCS2000-CTDA is used for Infeed tension detection and control, and Mitsubishi's dual pressure sensor LX-100TD and tension controller LE-40MTA-E are used for Outfeed tension detection and control. The execution components are all PANASONIC AC servo motor drivers. MHD503A1V. The motor MHM502A1, together with the corresponding mechanical components, form a complete secondary tension control system. [next]
Infeed secondary tension control system transformation plan
The electrical principle of the Infeed secondary tension control system is shown.
1. Due to the floating roller tension detection structure, the floating roller position setting point actually sets the position of the floating roller in the tension balance state, regardless of the tension setting value, and the tension setting generally adopts the following two forms.
(1) Counterweight. The early adopted form consisted of steel floating rollers. The counterweight brackets of the front and back of the floating roller are composed of corresponding counterweights. Adjustment is more difficult. Intuitive display is difficult to achieve; due to the presence of gravity acceleration, the counterweight itself will impact the tension when the floating roller floats, which greatly affects the accuracy of tension control.
(2) Pneumatic. The currently adopted form is composed of lightweight aluminum alloy floating rollers, precision pressure regulating valves or pressure-controlled proportional regulating valves. Slow; composed of medium gas tank and low-grind cylinder (preferably membrane cylinder). In this way, the influence of gravity acceleration on the tension control accuracy is minimized, adjustment and display are convenient, and even centralized control and display can be realized.
2. MCS2000-CTDA can realize three control modes: open-loop, closed-loop and open-closed loop. In open-loop control, the open-loop output and input Anl91 are in a linear relationship and can be set according to actual needs; closed-loop control uses the set point as a reference and adjusts the output according to sensor input and PID settings; hybrid control combines open-loop control output with closed-loop PID output Get up and make up its output. In actual use, open and closed loop mixed control mode is adopted. For the setting method of MCS2000-CTDA PID parameters, please refer to the article published in "Printing Technology", October 30, 2003 (Renovation of the Unwinding Tension Control System of Gravure Press)
3. Anlgl is taken from the speed measurement output of the host, and is set in proportion to the length of repeated printing as the reference, and limits its output voltage range from 0 to i4VDC, corresponding to the maximum speed of the host is 140 meters per minute. When setting open loop output, take Anlgl signal voltage as 3V. 11V and its corresponding servo motor speed are set points, which have good following ability in the normal working speed range, laying the foundation for the improvement of dynamic performance.
4. By using the digital I / O interface provided by MCS2000-CTDA and the driver MHD503A1V, it can conveniently carry out interlocking control with the host computer to realize the functions of emergency shutdown, shutdown and standby status of the original machine. [next]
Outfeed secondary tension control system transformation plan
1. Pressure sensor LX-100TD: Two 100kgf pressure sensors are installed on both ends of the tension detection roller. The sensor detects only the pressure or tension component parallel to the detection axis. No vertical component can be detected. Generally, the angle between the two paper surfaces of the detection roller is preferably within 90; the angle between the direction of the resultant force and the detection axis is within 30. Excessively large angles on the one hand reduce the sensitivity of the sensor, on the other hand it is easy to cause damage to the sensor. Reasonable use of this feature can appropriately increase the detection range of the same sensor.
2. Tension controller LE-40MTA-E: Tension controller produced by Mitsubishi Electric Company, its tension detection input can only use pressure sensor, and the output can be used to control a variety of actuators. The fully digital project setting interface and automatic detection function provide convenience for project application. In particular, it can directly control the voltage to 24VDC. Electromagnetic brake with current less than 4A. For the application of the unwinding mechanism, the circuit is simple and the control is convenient, which is unmatched by other types of tension controllers.
3. After completing the wiring according to the requirements of the tension controller and the control task, you can power on to initialize the settings, adjust the zero point and detection range of the pressure sensor, and use the factory settings. The system already has the basic conditions for operation. The next step is the setting of working parameters, namely P, parameters, dead zone and dead zone amplification factor. Only when the system is in working state (whether manual or automatic working state), the adjustment of working parameters can be carried out. First, perform automatic parameter adjustment: On the automatic working parameter setting screen, enter the largest possible step interference value, and press the "Enter" key, the adjustment process ends after about 10 seconds. According to the actual working conditions of the system, manual fine-tuning of working parameters should be carried out when necessary to improve the performance of the system. The principle of manual work parameter adjustment is: integration first and then proportion, first dead zone amplification factor and then dead zone.
Generally, the larger the integral coefficient, the better the steady-state performance of the system, but the slower the dynamic response. On the contrary, the controllability is better, but it is prone to oscillation. The larger the proportionality coefficient, the faster the reaction speed, but it is prone to oscillation, and its setting value is about 80% of the setting value when the system is just oscillating. Once the dead zone amplification factor is set, the system actually becomes variable proportional coefficient control, and its conversion threshold is the dead zone. When the deviation range exceeds the dead zone, the dead zone magnification factor and the scale factor work simultaneously, and the reverse does not work. Therefore, the adjustment should be considered at the same time as the scale factor adjustment; as the dead zone magnification factor is adjusted, the dead zone should be gradually reduced. Area.
Structural characteristics before and after the reconstruction of the secondary tension control system
It can be seen from the structure and paper feeding diagram of the secondary tension control system before and after transformation:
1. Two sets of tension control systems co-exist before and after the transformation, which can be interchanged at any time, so as to avoid the adverse impact on production due to mistakes in the transformation work;
2. The major changes to the original machine during the transformation process can be carried out offline, basically will not affect the production.
Conclusion
Due to the control and execution components used, the functions are cohesive, the reliability is improved, the peripheral components required are few, and the control structure is simple and clear. After the system transformation was completed, it was put into normal operation in May 2001. The operation situation in the past 3 years shows that the new system has realized the digitalization of control and setting, intuitive display, simple operation, and the chain control with the host, basically maintaining the original operating habits; stable operation. Reliable, eliminating the interference of human factors, basically no electrical and control failures occur again; with excellent dynamic response characteristics, tension control accuracy has been improved. Under the same production process conditions and normal operating conditions, based on the tension setting value, including biaxial switching, the tension control error is improved from the original soil 12% to soil 7%, and obvious economic benefits are obtained.
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