Research on signature detection system in collating machine
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One of the production processes of the printed matter is to bind and form a single-page printed sheet printed by the printing machine, and the key to success or failure is the matching process.
In order to avoid the phenomenon of manual matching such as reposting, less postings, messy postings, etc., two main solutions are currently adopted: one is to use the principle of photoelectric diffusion reflection, and the red LED is used as a light source to illuminate the signature according to the inspection area. The intensity of the reflected light is determined. The program is sensitive to ambient light and has a large dependence on the finish, reflective performance and printing density of the signature paper. Especially for the signatures with large color changes, the inspection accuracy is very low, and the ideal effect is not achieved. Optical image recognition technology for image recognition of some content in the signature. However, due to the placement offset, or the relative position shift or twist that occurs during the work, the signature discrimination rate is not high.
At present, bar code has been widely used as a timely, accurate, reliable and economical data input means. Therefore, the use of bar code recognition technology, applied to the printing product binding production site, is a simple and effective signature detection system, the starting point of this program design is based on this.
System structure and working principle
A signature detection system based on barcode recognition consists of: (1) items to be inspected with a barcode, (2) a bar code reader, (3) an embedded control system, and (4) a computer in an enterprise local area network.
First, the barcode is printed on the edge of the layout of the signature as the basis for the identification of the subsequent detection device of the system. Then, using the embedded control system with a barcode reader, the read barcode information is compared with the set reference barcode information, and the read barcode information is combined with the external electrical machinery according to the set control logic. The institution completes the operation of the signature.
The computer can communicate with the embedded control system through the communication interface, read the barcode content, thereby obtaining the signature information, and then writing the information into the database by counting and the like. The computer is in the company's local area network, and the computers in any other office area can also access the database in the computer in real time to understand the production process and production situation.
System design and implementation
In the specific system implementation, we use the existing bar code reader to form an embedded control unit with the MCU system, and write the control information of the control unit into the computer database through the RS485 serial communication port.
1 Bar code reader selection and transformation
CIPHER's 1000 handheld barcode reader was chosen here. The reader has the following advantages:
● A variety of common barcode systems can be identified.
● It has various digital interfaces such as keyboard (PS/2), RS232, and USB.
● Fast reading speed.
● A variety of reading methods and power saving methods.
We put the manual contact switch part on the reader for starting the reading bar code from manual start to automatic control by the embedded system, that is, the control of the human hand is controlled by the closure and release of the relay contacts controlled by the embedded system. .
2 embedded control system
● Hardware part design
The embedded control system section contains the digital interface circuit portion of the reader and a microcontroller system and its peripheral interface circuitry.
The reset and watchdog chips use the MAX813, which monitors the operation of the software to prevent program runaway or crashes. In order to control the communication rate more accurately, the 11.592MHz crystal oscillator is selected; the microcontroller uses the ATM89C51 from ATMEL.
● Embedded software part
The software is responsible for capturing the paper feed signal, then simulating the human hand button, starting the sensor work, reading the bar code information and then judging, according to the judgment result, performing different output, and simultaneously communicating with the upper computer.
In the software working process, in order to capture the input of the request signal in real time, the reading of the signal input is interrupted. After receiving the signal, the corresponding request event flag is set, and the processing of the request signal is performed outside the interrupt, so that the request input signal can be effectively captured, and the interrupt program can be prevented from occupying CPU resources for a long time.
After the main program is powered on, the event flags are viewed in turn. If the event request is found, the event is processed immediately, and the request flag is cleared after the processing is completed. The events to be processed include: capturing the paper feed beat, receiving the data sent by the computer, the comparison judgment after the barcode is read, and the processing after the judgment.
The paper feed beat is triggered by the external paper feed mechanism, and the software uses an external interrupt method. The communication event is triggered by the serial receive interrupt of the software, and the bar code processing event is triggered by the high priority interrupt that receives the digital bar code signal.
Set the CIPHER interface board to send the barcode content as a PS/2 keyboard.
The other two events, error signatures and white paper events are derived from the software's comparison of bar code information.
1 Processing the feed beat signal processing
After detecting the barcode read request-feed signal event, the barcode reader should be activated to read the barcode information. The original manual button on the reader is modified to simulate the electric shock by the relay, and the relay can be closed to completely open the reader.
2 Processing the event judged by the barcode
After the MCU receives the complete barcode information, the barcode is set to determine the event. When processing the judgment event, the read barcode and the set reference information are first compared. Since the bar code transmits data using the keyboard interface, the encoding rule for each number or character is "pass and break code", that is, each character to be transmitted includes three bytes: "encoding + 0x4F + encoding". Therefore, when performing the comparison, attention should be paid to the movement of the reference bar code pointer and the bar code pointer to be determined: the reference pointer moves by 1 byte each time, and the pointer to be judged is moved by 3 bytes.
In the wrong state of the signature, the MCU will output the alarm indication signal according to the set software, and output the drive control signal to the signature rejection device to eliminate the error signature; if only one signature rejection device is installed at the end of the pipeline, the single chip microcomputer The paper feed beat will be counted. When the error signature passes, the MCU sends a signal to the signature rejection device, and the rejection device rejects the signature set including the error signature.
3 computer communication part
In the collating machine assembly line, each reader station has a reader and an embedded control system installed, and all the signature detection devices can be connected to the computer through the bus to further complete the signature through the computer. Statistics, queries and other functions.
In the physical layer design, the mature RS485 serial communication bus is used to connect to different detection devices and computers; in the link layer design, in order to ensure reliable transmission and reception of data frames, in addition to the checksum, there are data frames. Special frame header bytes and end-of-frame bytes to avoid interference on the link.
4 Database section
The computer uses VC++6.0 to write a user-friendly interface, and uses ADO (ActiveX Data Object) to manage the database. The result record set to be obtained is obtained by executing the SQL command during operation.
The system can be used in any bar code inspection system. For different application requirements, as long as different electromechanical mechanisms are connected to the output terminals of the system according to the site conditions, the control logic can be performed according to the required control logic. automatic detection.