Application research of dot matrix online laser coding technology

Dot-matrix online laser coding technology can achieve high-speed and high-precision online coding, which represents the latest development direction of current online coding technology and can provide enterprises with efficient and feasible product coding solutions. This paper mainly conducts an in-depth study on the application of dot-matrix online laser coding technology.

1 Introduction to the principle of dot matrix online laser coding technology

The dot matrix online laser coding technology adopts a galvanometer scanning strategy. As shown in Figure 1, the coding system controls the laser scanning path by the angle deflection of the X and Y galvanometers.

Figure 1 Galvanometer scanning strategy

Dot matrix online laser coding technology uses dot matrix characters for online coding. Dot matrix characters are composed of a series of dots. Figure 2 shows the situation when the 5×7 dot matrix characters "N" and "C" are marked. When the galvanometer scans to the red position, the laser emits light and the object is marked with a point by the laser. When the galvanometer scans to the white position, the laser is closed and the object will not be marked.

Figure 2 Laser marking of dot matrix characters

When the coded product moves on the production line, it has a speed error V in the opposite direction relative to the galvanometer scanning (as shown in Figure 3). The speed error V is equal to the speed of the production line. The dot matrix online laser coding technology obtains this speed error by monitoring the speed of the production line online, and can generate a compensation signal based on this speed error to drive the galvanometer, thereby offsetting this error.

2 Advantages of dot matrix online laser coding technology

Dot matrix online laser coding technology has many excellent features:

(1) The dot matrix online laser coding technology adopts a galvanometer scanning strategy. During the scanning process, the galvanometer is almost unaffected by external resistance. It has the characteristics of fast speed, stable and reliable movement process, and precise positioning.

(2) Compared with traditional inkjet coding technology, dot matrix online laser coding technology does not require consumables such as ink, is easy to maintain, saves costs, and is environmentally friendly.

(3) Dot matrix online laser coding technology uses a high energy density laser beam to act on the target, causing physical or chemical changes on the target surface, thereby obtaining high-quality, permanent marking.

(4) Dot matrix online laser coding technology can be easily combined with digital control technology to develop a variety of products.

The above advantages make dot matrix online laser coding technology have a wide range of application prospects. At present, this technology has been successfully applied in actual production abroad. Some companies have developed relatively mature products.

Figure 3: When the product moves on the production line, it will generate a reverse speed error V

3. Progress of dot matrix online laser coding technology at South China University of Technology

3.1 DSP online laser coding control system

Since 2007, South China University of Technology has started research on dot matrix online laser coding technology. At present, it has successfully developed a DSP online laser coding control system. As shown in Figure 4, the system consists of two parts: the main control unit and the remote operation unit.

Figure 4 Structure of DSP online laser coding control system

Figure 5 Hardware structure of the main control unit of the DSP online laser coding control system

The main control unit can control the light output of the laser, the angle deflection of the galvanometer, and can collect the speed of the production line in real time to generate a speed error compensation signal. Its hardware structure is shown in Figure 5.

The remote operation unit is responsible for the human-machine interaction between the system and the operator. Through the remote operation unit, the operator can compile custom codes, control the operation and stop of the system, and other operations. After receiving the relevant operations of the operator, the remote operation unit forwards them to the main control unit for execution. Its hardware structure is shown in Figure 6.

Figure 6 Hardware structure of the remote operation unit of the DSP online laser coding control system The features of this control system include:

(1) The main control unit adopts DSP control, which has fast computing speed, high precision and low power consumption.

(2) The remote control unit adopts an embedded solution, which has the advantages of small size, high reliability and low cost compared to traditional PC.

(3) The open control structure is flexible and can be easily applied to a variety of lasers to form different types of coding systems.

3.2 Application example of DSP online laser coding control system

The DSP online laser coding control system of South China University of Technology is becoming more and more mature. As of 2009, it has been successfully applied to Nd:YAG lasers in cooperation with Dongguan Trump Optoelectronics Technology Co., Ltd., and developed Nd:YAG online laser coding machines. Currently, South China University of Technology is using the DSP online laser coding control system to study CO2 laser coding machines and has successfully developed a prototype.

Figure 7 Nd:YAG online laser coding machine

3.2.1 Nd:YAG online laser marking machine

Nd:YAG coding machine can make characters, graphics, one-dimensional and two-dimensional barcodes and continuous variable serial number marks on various metal materials and some non-metal materials; it can also print codes on the fly after being equipped with a production line. Application areas include electronics, hardware tools, bathroom equipment, equipment signs, plastics and other industries.

Figure 7 is the appearance of the Nd:YAG online laser coding machine jointly developed by South China University of Technology and Dongguan Trump Optoelectronics Technology Co., Ltd.

3.2.2 CO2 online laser coding machine

CO2 laser coding machine can make characters, graphics, barcodes and continuous serial number marks on various non-metallic materials; it can be used for flying coding when equipped with a production line, and the production line speed is greater than 60 meters/minute. Application areas include leather, cosmetics, alcohol, tobacco, medicine, beverages and IT industries.

Figure 8 Overall view of CO2 online laser coding machine

Figure 8 shows the overall body of the prototype independently developed by South China University of Technology, which is 850mm long (with vibration lens), 200mm wide and 150mm high. It can be easily installed on the lifting platform. The vibration lens can rotate 360 ​​degrees with the length of the coding machine as the axis. It can code in different directions.

The prototype can code a combination of serial codes, custom production dates, custom expiration dates, custom character strings, etc. Figure 9 shows a drug package coded by the coder, and Figure 10 shows a beverage package coded by the coder. The prototype also has a red light preview function.

Figure 9 Coding on drug packaging

Figure 10 Coding on beverage packaging

4 Conclusion

The dot-matrix online laser coding technology meets the needs of online rapid coding of products and is a promising online coding technology. At present, this technology has made great progress abroad, but it is still in its infancy in my country. We believe that with the market demand for rapid product coding, the dot-matrix online laser coding technology will gradually replace traditional technology and become the mainstream.