The Development Trend of Laser Marking Machine and Its Control System Design

1. The creation and development of laser marking machines

In 1958, the birth of the laser was considered a great invention of the 20th century. Nowadays, laser technology has been developed even more rapidly, and its applications are extremely wide, including heavy industry, light industry, production manufacturing, mining, energy, aerospace and aviation, and medicine. According to theoretical research and specific applications, laser technology can be divided into 2 major categories, one is laser manufacturing technology, and the second is laser application technology. Laser marking (coding) technology belongs to a kind of laser application technology. The so-called marking (coding) means the production of signs on the product's surface, such as the manufacturer, manufacturing date, shelf life, contact number, etc... Before the emergence of laser marking technology, the common use of ink marking technology. Not only was it slow and inefficient, but there was also pollution, and the mark was not clear. After laser marking technology was created, it gradually replaced the traditional ink marking technology. Laser marking technology is fast and accurate and has the advantage of safety and non-pollution. As the application of laser marking technology becomes more and more widespread, the development of laser marking technology itself is also becoming more and more rapid. The trend is to combine it with automatic computer control, marking speed and accuracy can be better controlled.

We illustrate this with an example of an embedded laser marking machine control with the S7-200. This machine is the current hotspot and frontier of research in laser marking technology. The embedded laser marking machine combines a variety of the latest emerging technologies, of which there are three core technologies: laser technology, embedded technology, and EDA technology.
The embedded laser marking machine has portability advantages, fast marking speed, high integration, low price, and high marking quality.

2. Laser marking machine control system design

A machine should be designed according to the principle that the user determines the performance and the structure. A laser marking machine is no exception. According to the laser marking machine, work needs to determine the laser marking machine should have easy to carry, marking speed, high integration, low price, high marking quality performance. Generally speaking, the main structure of the laser marking machine consists of the laser system, power supply system, control system, scanning vibrating mirror system, and transmission mechanism. In the above structure, the control system is at the core. The control system design is good or bad to determine whether the embedded laser marking machine can meet the work performance.

We take the design of the laser marking machine control system as an example. The essence of the control system is information processing, embedded laser marking main machine processor using ARM microprocessor, auxiliary processor using field programmable gate array FPGA, the benefits of this choice is the main processor using ARM program as the main tool for information processing. Its main function is to edit the initial control signal, generate marking data. The main processor functions are controlling marking speed, reading and writing marking line objects, controlling marking position, and calculating compensation standard data. The ARM processor has powerful functions with various interfaces and strong information processing and data transmission capabilities during execution. Although its processing power is somewhat insufficient for high-speed data, other processors only have a limited number of I/O. Compared with them, the data processing speed of the FPGA is faster, positioning and timing capabilities are more accurate, and the interface is more versatile and scalable. The X and Y axis deflection mirrors are the main control objects in the embedded laser marking machine system. In addition, detecting the speed and position information of the marked object when the system is running is also very important. The whole system is mainly composed of the laser marking machine as the core control system, with the help of FPGA as the core control system, laser power generation and transmission system, high-speed scanning detector system, transmission device, and measurement system to complete the specific work procedures.
Embedded laser marking machine, while gathering the respective advantages of ARM and FPGA, ARM and FPGA parallel processing events, high-speed processing data, can achieve precise time control function, and the cost performance is also very high. Therefore, embedded laser marking machine has become the mainstream direction of marking machine development.

3. Composition of the control system of the embedded laser marking machine

The main equipment of the embedded laser marking machine control system is as follows.

(1) Processor: The processor of the embedded laser marking machine control system is divided into 2 major parts: the main processor and the assistance processor. ARM is the core component of the control system. Its most important function is responsible for marking data and generating initial control signals. In addition, the processor is also responsible for timely reading out the object of the marking line, controlling the marking speed and position information, timely calculation of compensation standard data, and other functions to achieve. Assist processor FPGA: FPGA as ARM's main processor on the system bus connected to the ARM external storage method is the control system of the auxiliary processor.
The FPGA receives and interprets through D/A conversion, generates control signals, and enhances the processing circuit through the driver while attaching some external interrupt request signals, which eventually form control commands to control the servo system driver and laser scanning vibrator laser marking. In addition, the auxiliary processor FPGA is also responsible for handling key events, reading the matrix keyboard key values, processing the photoelectric detection signals and emergency stop requests, and notifying the main processor.

(2) USB interface: USB is the storage device of the laser marking machine, which enables the copying, saving, and transferring functions of the marking files. Compared to the general laser marking machine, the USB interface of the embedded laser marking machine has better versatility and expansion performance, which can store multiple types of files and automatically identify the content of duplicate content, thus saving storage space.

(3) LCD and touch keyboard: LCD is the output device of the LCD to present various operation information of the system, embedded laser marking machine adopts touch keyboard, thus combining keyboard and display into one.

(4) Laser and Scanning Vibrating Mirror System: The laser's high energy can be concentrated in the marking area of the marking object, which requires deflected reflection by a vibrating mirror to cause physical and chemical changes in the marking area. And using the X and Y axes in the high-speed vibrating mirror optical scanning system, the vibrating mirror deflects the laser beam, enabling fast and precise positioning and rapid movement of the laser beam. 

(5) Transmission mechanism and speed measurement device: The operation of the marking production line requires a stable movement speed. The embedded laser marking machine can accurately measure the marking speed of the laser beam through a real-time speed measurement device and feedback to the controller, which then outputs this data after compensating for the marking position.

(6) Safety grading procedure: When designing a laser marking machine control system, safety performance is very important. In the event of misuse or virus invasion, the laser marking machine may not work, or the control system may collapse. In contrast, the embedded laser marking machine improves the security of the control system by setting up a system security detection program that can detect the system's security in real-time. The security of the control system of the embedded laser marking machine is divided into 3 levels. The first level is the security level, under which the control system can perform any operation without any restrictions. The second level is the protection level. The control system is in a safe and protected state, and only basic operations such as editing, saving, and copying can be performed. The third level is the emergency protection level. Under this level, the control system is installed with an emergency stop switch to perform an emergency shutdown operation while saving the current file to prevent the system from crashing.

4. Main processor circuit design

The main processor is the core part of the laser marking machine controller system. The main processor function is dependent on the circuit to complete. Therefore, the main processor circuit design is crucial for the laser marking machine control system. The laser marking machine control system's main processor circuit is divided into three types: storage, power, and reset.

(1) SDRAM memory circuit
Because SDRAM has high data transfer rate and high integration, it has become the most commonly used main memory for embedded systems. SDRAM is usually designed to select two HY57V561620 chips as the main memory of the system.
SDRAM memory circuit using a 3.3V power supply, 2 SDRAM and ARM for expansion mode connection was introduced to the LDATA000-LDATA031 full 32-bit data bus. Due to the SDRAM chip line and column address line of each part of the address pins ( A8 ~ A0 ) being multiplexed, the response to the location of the processing to the line address is 9, the column address is 13. Therefore The total number of bits of the address signal is 22, and the main memory capacity of the controller system is 4M x 16bit x 4 blocks x 2 pieces = 64Mb.

(2) NAND Flash memory circuit
In the embedded laser marking machine control system, a large amount of information is not allowed to be lost, so non-volatile memory needs to be used to store the information. At present, non-volatile storage devices, mainly NAND flash memory and NOR flash memory 2 kinds, because the NAND flash memory capacity, relatively low price, read and write speed, is the common non-volatile storage device solve the information. Therefore, the design of a NAND flash chip K9F1208UOM was chosen as a non-volatile memory with a capacity of 64 μm. The ARM processor K9F1208UOM chip uses a 3.3 V power supply, and the signal lines DATA7-DATA0 can be used both to transfer data and connect to the low 8-bit data bus and can be used to send address and control information. The symbols for the other chip functions are ready/output R/NB (O), control command latch CLE (I), with the input signal type in brackets, O for the output signal type, and I for the input signal type.

(3) Power supply circuit
The design of the controller system requires a variety of power supplies, including 12VDC, 5VDC, 3.3VDC, and 1.8VDC for the main processor circuit part. In addition to an emergency backup battery, the battery power is also sufficient to support the real-time clock operation when there is an unexpected power failure. 12VDC is required for the LCD backlight power supply, and +SVDC, +3.3VDC, and +1.8VDC for other circuit parts. And +1.8VDC. To avoid the hassle of multiple power inputs, the main processor circuitry has only ++12VDC and +SVDC as the only two power inputs, with the rest being obtained by stepping down the +SVDC. Most of the main processor circuit devices require 3.3VDC, which is supplied to the different module circuits by stepping down the +SVDC through several AMS1117-3.3 chips.

(4) Reset circuit
The reset circuit design is an important part of the ARM system circuit. Using the ARM system, often need to enter the reset state.
The RC reset circuit is the simplest ARM system reset circuit. After the system is powered on, the low-voltage capacitor is at both ends and reset low after 2 inverters. The capacitor is charged by 8304, and the voltage at both ends is gradually approached after the capacitor rises. The system is in the reset state when the inverter U302A input threshold voltage is not met. Reset is high when the voltage at both ends of the capacitor after the U302A threshold voltage is reached. Then the normal operation state of the system is entered.

5. Conclusion

In summary, the embedded laser marking machine is the product of the combination of laser technology and computer automation technology, is a new type of laser marking machine with embedded technology, laser technology, and EDA technology as the core technology. The embedded laser marking machine is mainly composed of a laser system, control system, power supply system, scanning mirror system, transmission mechanism, etc. This paper focuses on the overall design of the embedded laser marking machine controller and its component composition. Embedded laser marking machine has the advantages of fast marking speed, ease in carrying, high integration, low price, and high marking quality, so it has become the mainstream direction of marking machine technology development.