Automatic printing color control system based on DSP
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Aiming at the working characteristics of gravure printing machine, a novel control and implementation method of automatic color control system for gravure printing machine is proposed, and the control system is realized by connecting multiple DSP subsystems and one upper computer through CAN bus. The control system introduces the efficient and reliable DSP chip TMS320lf 2407 as a printing color control chip. Compared with the traditional single-chip control system, it has improved a big step in performance and reliability.
Therefore, the purpose of the control is to keep the distance between the two color scales at 20 mm. The control amount is the difference between the detected distance value and 20 mm.
1.1 Detection of overprint error
The detection of overprinting error is directly related to the precision of the color registration. In order to make the detected overprinting error as accurate as possible, this paper uses the photoelectric scanning head of the double photoelectric eye to perform error detection. The photoelectric scanning head has 2 photoelectric eyes, and the following is M1. M2, the distance between them is 20mm, the direction of the printing material is from bottom to top. After scanning the overprinting color code, each output two digital signals are amplified and shaped and then connected to the capture pin CAP1 of the EVA module of the TMS320lf2407 chip. CAP2; A photoelectric encoder is mounted on the spindle synchronized with the plate roller shaft. When the spindle motor rotates, a pulse signal is generated, and the frequency is proportional to the spindle speed. The signal is sent to the TCLKINA port of the EVA module as the clock of the general timer 1. source. When the overprint is accurate, the output signal of M1 should be 20mm ahead of the output signal of M2, that is, the second pulse signal output by M1 should arrive at the same time as the first pulse signal of M2.
1.2 Correction of overprint error
After the DSP obtains the overprint error e, according to the digital fuzzy algorithm PID control algorithm, the correction amount of the compensation motor is calculated to control the motor to perform corresponding action (the compensation motor here adopts the stepping motor). The entire automatic color registration system is basically a closed loop feedback system.
2 hardware system framework
The whole system (taking six sets of color printing machines as an example) consists of five DSP subsystems and an arm host computer with CAN interface to form a master-slave distribution system. The communication uses CAN bus interface, and each DSP subsystem can independently complete adjacent Two-color overprint. At the same time, the DSP keeps in contact with the host computer and transmits data and status to the host computer. The upper computer is connected to the display and the keyboard, and the data transmitted by the lower computer is used to display the position of each color mark, the overprinting error, the printing speed, the printing length, etc. in real time, so that the staff can know the operation of the system in time and perform corresponding operations. As shown in Figure 4, the host computer and DSP are driven by the uc5350 chip and transmit data using the CAN bus. After the plate rotates for one week, all the color code data is collected. The photoelectric encoder 0 bit signal will trigger an external interrupt. At this time, the program starts loading the data to be transmitted and prepares to communicate with the host computer.
3 system software design
The system software can be roughly divided into two parts: the color registration main program and the CAN transmission subprogram. The main contents of the color registration program are: initialization program, color code signal acquisition, query, calculation speed, error and correction amount, and start motor correction error.
CAN
The transmission subroutine mainly completes the data transmission from the lower computer to the upper computer and the upper computer data to the corresponding lower computer. Four CAN mailboxes will be used in each DSP subsystem, two of which send mailboxes txbox1 and txbox2, and two receive mailboxes rxbox1 and rxbox2. The main function of sending mailbox txbox1 is to send a specific set of data to other subsystems in advance when the subsystem is to send data to the host computer, prohibiting the subsystem from sending data to other subsystems in the transmitted data, so as to avoid receiving the host computer. Data is confusing. The way to achieve this is:
Set the mailbox identifier txbox1 of all subsystems to the mailbox identifier MSGID of the receiving mailbox rxbox1 (the receiving mailbox will only receive the data sent by the sending mailbox that is consistent with its own identifier); after the subsystem completes the loading of the transmitted data, Query the bus status bit stats (stats is the variable defined in the program, 0 means the CAN bus is idle, 1 means the CAN bus is busy), if it is 0, then a specific set of data is sent by tx-box1 (can be "1111") ), after receiving the data, the other subsystem sets its own bus status bit stats to 1, and then sends the data to be transmitted to the host computer one by one by txbox2, and then sends another set of specific data (such as "2222" by txbox1. ), after receiving other subsystems, set your own stats bit to 0. The subsystem first checks the stats bit before sending the data, only waiting for it to be. Only when the data is sent to the host computer, the program flow of the CAN data transmission is shown in Figure 6. The subsystems receive the data transmitted by the host computer is relatively simple. Each subsystem's txbox2 and rxbox2 have their own specific mailbox identifiers (the specific mailbox identifiers must be different for each subsystem in the whole large system), so that the upper level As long as the mailbox identifier of the target subsystem is written into its own sending mailbox identifier, the data can be accurately transmitted to the lower computer. When the host computer receives the data, it also determines which data is used by the mailbox identifier. Subsystem transmitted.
4 Conclusion
The designed printing color system introduces the efficient and reliable DSP chip TMS320lf2407 as the printing color control chip, and uses its integrated CAN module to communicate with the host computer. Compared with the traditional single-chip control system, both in performance and reliability. A big step forward. The number of nodes on CAN can reach 110, which provides great convenience for future system upgrades. If the system using RS232 communication has to expand the subsystem, the number of interfaces of the serial port card of the host computer must be extended on the hardware. The process is complicated; after adopting the CAN bus, the extension subsystem can allocate the extended subsystem to a new mailbox identifier on the software, and the whole system can operate normally. This automatic overprinting system has been tested and tested. The test shows that the system can be applied to any gravure printing machine that can be manually registered without adding any additional equipment. Even if the automatic control system is not used, the overprinting error can be maintained in the original labor. The best level of overprinting. The printing speed can be increased to the upper limit of the machine or the upper limit of the drying speed of the ink, so the system will have a good application prospect.