How to solve the four major "difficult and complicated problems" of gravure printing machine color matching system? You'll understand after reading it!
Our company currently has a Zhongshan Songde SDP10820 ten color gravure printing machine production line, which has been in operation for 15 years. This equipment is equipped with the Japanese Taiyang DT-2000 color system and the Japanese Sumitomo drive device. Due to years of use, equipment downtime and poor print quality often occur due to abnormal color matching systems, which affect the production of orders. The author of this article will study the principle of the color matching system in gravure printing machines, analyze the causes of faults, and summarize relevant solutions.
Composition and principle of color matching system
The color registration system of SDP10820 gravure printer is mainly divided into two parts: color registration control unit and drive control unit (as shown in Figure 1). The two parts adopt a master-slave networked connection. When the color control unit detects real-time color deviation, it will exchange data with each driving control unit through the cc link network. Finally, the servo motor drives the printing plate roller to perform color error correction, achieving precise control of the plate roller rotation position.
Figure 1 Components of the Color System
The specific composition of the color matching system is divided into several parts, including photoelectric eye (Taiyang Ff) and encoder (Taiyang PG IV-1000-E6H), color matching control unit (Taiyang DT-2000 MM703990), servo controller (Sumitomo MMC-550MCU), servo driver (Sumitomo MMC-550PAU), and servo motor (Sumitomo HTK-BV). The functions of each part are as follows.
01
Optoelectronic eye and encoder
The color matching system uses dual photoelectric eyes, consisting of one light source, two lenses, and two photoelectric eye tubes (Figure 2). There are two focal points on the reflective surface, and two phototubes receive the reflected light from each focal point. When the color markers on the two focal surfaces pass through, the change in reflected light is represented on the photoelectric cell, which is converted into current and transmitted to the color control unit as a change in current, called a pulse.
Figure 2 Optical Eye Structure Diagram
02
Color control unit
The color matching control unit includes input circuit, operation circuit, output circuit, etc. It analyzes the sampled pulse signal to determine whether there is any deviation in color matching, the magnitude and direction of the deviation, and performs signal processing.
(1) The input circuit samples pulses, and if there is a delay/advance time (T) relative to the main pulse, the main circuit generates a rectangular pulse with a width of T, which is sent to the arithmetic circuit as a delay/advance color deviation signal.
(2) The arithmetic circuit is the heart of the color matching control unit. It calculates the correction amount that can accurately match the color deviation data sent by the input circuit based on the set circumference of the printing plate roller, the reference pulse generated by the encoder, and the distance between each printing plate roller.
(3) The output circuit outputs the calculation results to the human-machine interface for display, and also outputs the correction amount to the servo controller, instructing the servo driver to drive the servo motor for deviation correction work.
03
Servo controller, servo motor driver, servo motor
Servo controller, servo motor driver, and servo motor are the executing mechanisms for correcting color deviation. In the color matching unit of the color group, the servo motor is equipped with a rotary encoder that rotates together with the servo motor. Each revolution emits 4800 consecutive pulse signals. Combined with the color mark position measured by the photoelectric eye, the number of pulses is converted and used as the input signal for the color matching control unit, representing the position given signal. Based on the obtained color deviation, the control quantity is calculated, and then the servo controller outputs the control quantity to the servo motor driver to drive the servo motor for phase adjustment, that is, to adjust the relative position of the plate roller to compensate for the color deviation.
Common problems and solutions of color matching system
Problem 1: The color matching waveform is too small, resulting in deviation during color matching
Reason for malfunction:
(1) The electric eye adjustment is not in place; (2) Insufficient brightness of the light source; (3) Insufficient light transmission on the surface of the lens; (4) Signal amplification issue.
Handling method:
(1) Figure 3 is a schematic diagram of the installation of the photoelectric eye. During printing operations, adjust the focal length of the photoelectric eye cursor to the most appropriate position. Generally, adjusting the distance between the photoelectric eye and the printing material to 8mm and perpendicular to the printing material is the most suitable. At this time, the bright spot and shape of the cursor are optimal, which minimizes the amount of noise sampled and is beneficial for subsequent waveform comparison.
Figure 3 Schematic diagram of photoelectric eye installation
(2) The light source of the photoelectric eye is provided by a halogen lamp. As is well known, halogen lamps emit light by passing sufficient current to the tungsten filament, causing it to heat up to incandescent state. Therefore, the lifespan of halogen lamps is relatively short. Generally, after using for 2000-2500 hours, the light source will attenuate, causing the cursor signal of the photoelectric eye to weaken and affecting the color matching effect. At this time, a new halogen lamp should be replaced.
(3) During printing, some ink may adhere to the surface of the fiber optic eye lens before it dries, resulting in insufficient light output. So before starting up, it is necessary to check whether the surface of the electric eye lens is clean. If there is dirt sticking, pure cotton cloth or cotton dipped in alcohol with a concentration of over 90% can be used to wipe until the surface of the optical eye lens is clean
bright.
(4) If the color group with smaller waveform is printed in light color, the gain knob on the signal amplifier circuit board inside the relay box can be adjusted. Use a pen to slowly rotate the knob to the right until the waveform on the display is amplified to the normal working waveform. However, this method has limitations on the adjustment amplitude.
Problem 2: The color matching waveform is not displayed and appears as a straight line directly
Reason for malfunction:
(1) Abnormal pulse generator; (2) Communication between color groups is abnormal.
Handling method:
(1) The encoder tracks the real-time position of the printing plate roller. If the system cannot detect the encoder signal, the waveform will naturally not be displayed. The detection method is to stop the machine and set the waveform free color group to "single action" mode, then jog the equipment and check the overprint human-machine interface. Adjust the human-machine interface to the confirmation page (as shown in Figure 4). If there is no change in the value displayed in the PG column, it can be judged that the encoder of the printing plate roller for that color group is damaged. At this time, only the encoder needs to be replaced to eliminate the fault.
Figure 4 Color group human-machine interface
(2) After the presentation of the color group without waveform, there is no waveform in the front (for example, there is waveform in the 7-10 color group and cutting, and no waveform in the 1-6 color group). Because the communication of DT-2000 uses serial communication, this situation is generally caused by the disconnection of communication between the sixth color group and the seventh color group. The general solution is to unplug the communication cable or use a network cable detector to check the connection of the network cable and replace the network cable or crystal connector.
Question 3: The color matching waveform moves left and right inside the gate circuit
Reason for malfunction:
(1) The encoder signal of the printing plate roller is abnormal; (2) The connection between the plate roller and the plate roller plug is abnormal.
Handling method:
(1) Because the encoder is strictly synchronized with the printing plate roller, if the soft connection of the encoder becomes loose and slips, the relative position of the printing plate roller will deviate, causing the color matching waveform to run left/right. At this time, as long as the soft connection of the encoder is reinforced at both ends, the waveform will naturally stabilize.
(2) The left/right movement of the color matching waveform directly reflects the accuracy of the color mark position printed by the printing plate roller each time. The printing plate roller is fixed by the plugs at both ends of the color group. If the clearance between the key slot on the printing plate roller and the key on the plug is too large, it will cause some deviation every time the printing plate roller rotates. At this time, it is necessary to remove the printing plate roller, measure the size of the key slot and key, and replace the new key or plate roller.
Question 4: The color matching waveform runs heavily
Reason for malfunction:
(1) Printing plate rollers and embossing rollers are unqualified or not installed properly; (2) The quality of the embossing roller is not qualified.
Handling method:
(1) The quality of the printing plate roller directly affects the printing accuracy, but whether it is installed properly also affects the printing accuracy. Therefore, the concentricity of the printing plate roller must be ensured within the allowable tolerance range. Regarding this issue, when installing the printing plate roller and plug for the first time, it is necessary to use a dial gauge to measure and adjust the concentricity of the plug and printing plate roller to ensure that they meet the printing requirements.
(2) The printing plate roller can only transfer ink to the paper by pressing it together with the embossing roller, so the concentricity of the embossing roller must be ensured. Due to the influence of paper tension, the embossing roller will produce delamination after tens of thousands to hundreds of thousands of revolutions, which will seriously affect the color matching effect. At this point, the embossing roller must be removed and re polished to eliminate any delamination before printing can resume.
By studying the principle and composition of the color matching system of the SDP10820 gravure printer, analyzing the causes and handling methods of color matching failures, it is possible to reduce the production impact caused by equipment color matching problems, greatly improve equipment efficiency, and provide reference for peers of similar models to handle.