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Enabling New Challenges In Motion Control For Precision Laser Machining Applications


Laser precision machining and cutting have been applied to precision machining such as solar crystalline silicon cutting, mobile phone panel cutting, semiconductor wafer cutting, Laser CNC and so on. How to adjust the energy intensity to meet the cutting on different materials, and present a layered effect, these are the new challenges faced by high-end motion control products.

In this article, we will discuss how to overcome the new challenges encountered in precision laser machining, as well as solutions that are demonstrated by example.Laser manufacturing technology is a new technology that integrates science and technology such as optics, machinery, electronic motors, and computers.

Enabling New Challenges In Motion Control For Precision Laser Machining Applications

It has been widely used in today’s society. According to the statistics of the international laser industry authority “LASER FOCUS WORLD” and “Industrial Laser Solution” in early 2013, the global sales of laser products have returned to the level of 2008 and showed an increasing trend. In the field of global laser material processing, the output value of metal processing has accounted for the majority in recent years, and the application side is surface treatment such as laser marking and line drawing, accounting for up to 42%, and laser cutting and welding are the second. The second and the third together account for 34% of the overall material processing applications, which are used in metal sheet metal industries such as automobiles, aerospace, electronics, machinery, and steel. In the “Global and China Laser Equipment and Processing Industry Report, 2012-2014” report published by GI (Global Information) at the end of 2012, it is pointed out that the global laser equipment market is generally expected to grow from about US$7.4 billion in 2010 to 14% in 2011. % growth, and in 2012 it grew by about 2%.

As far as the Chinese market is concerned, the laser equipment market slightly exceeded the growth rate of the global market in 2011. From the perspective of macroeconomic impact, although China’s laser processing market for the machinery industry and heavy industry has shrunk, the small and medium-sized laser processing market is growing. As China plays a central role in the global manufacturing industry, its demand for laser machinery is also quite huge, especially the automotive, semiconductor, and electronics industries have great potential demand. In China’s processing industry, precision metal parts processing and laser drilling account for 60% of the overall processing services.

In terms of application, laser precision machining and cutting have been applied to precision machining such as solar crystalline silicon cutting, mobile phone panel cutting, semiconductor wafer cutting, Laser CNC and so on. For motion control products, how to overcome the precision and micron processing of traditional cutting; how to easily cut any graphics and achieve the smoothing effect of its precision; how to complete very small graphics without space constraints; how to The energy intensity can be adjusted to meet the cutting on different materials and present a layered effect. These are new challenges faced by high-end motion control products.

In this article, we will discuss how to overcome the new challenges encountered in precision laser processing, as well as solutions that have been proven.

Challenge 1: Poor laser cutting accuracy

The adjustment of laser power is mostly controlled by frequency + duty cycle, so real-time and precise transformation is required for displacement control. Different speeds require different powers, but different speeds will be generated when cutting graphics. When the speed drops sharply and the laser power is too late to change, it will lead to over-melting phenomenon. And because the laser control is mostly controlled by PWM, the PWM control is performed by changing the duty cycle, so it will be better for a fixed speed. However, if the speed is increased, the frequency of the laser will be too late to emit light, which will result in poor melting uniformity during cutting.

Challenge 2: The motion trajectory is not easy to achieve under high precision

The cutting system needs to pay attention to the accuracy of the path during the movement, so the motor control needs to be very good, so that the cutting graphics will not be deformed, as shown in Figure 3 and Figure 4; ) method, the following degree cannot be corrected in real time; if the requirement of high precision is to be achieved, the requirement can only be achieved by using closed-loop (speed, torque) control. However, the closed-loop control needs to be adjusted by PID to have a better follow-up effect. However, the tuning of PID usually takes a long time, which is quite time-consuming.

Challenge 3: The laser power is not easy to adjust

At present, most of the objects to be cut are multi-layer materials (solar panels, mobile phone screen touch films), which need to be cut with different powers; however, because there are only one set of laser adjustment (VAO Table) for laser-specific controllers on the market, in the The cutting power is not easy to switch and adjust, so at present, the cutting path can only be repeatedly cut according to the material layer to meet the required requirements. However, this will result in an inability to increase the production speed.

Challenge 4: Speed ​​planning is time-consuming

Due to the complexity of laser processing graphics, simple speed planning can no longer meet the processing and cutting results, such as mobile phone touch mold cutting, in most cases, using Spline curves, or long geometric lines and arcs, if the speed cannot be accurately controlled. It will lead to acceleration and deceleration vibration of the mechanism or severe deformation of the graphics (such as overcut and jitter), as shown in Figure 5. Because most of the machine designers only provide a graphic point table (position), and there is no data for speed planning, it is necessary to plan the speed by manual operation. It will also result in the inability to increase production capacity.

In view of the above bottlenecks encountered in laser processing, how does the new generation of motion control cards meet the challenges?

Real-time presentation of PWM control capability

The PWM control of traditional motion control cards adopts the single control method of Duty, and through software control, it will face the timing that cannot be controlled in real time and stably. In order to cope with different speeds and different graphics, the new generation of motion control cards adopts more control methods, including Frequency Modulation, Duty Modulation, and Blend Modulation, as shown in Figure 6 , This control method will be completed by hardware control, this PWM can show different energy performance under various cutting speeds, so it is necessary to establish a corresponding energy meter to prevent the occurrence of “over-melting phenomenon”, this energy control is called (VAO)

Multi-VAO facilitates dynamic switching

PWM adopts the Multi-VAO method to achieve the effect of deep and shallow cutting due to different cutting materials, so that the path cutting can be completed at one time, and there is no need to repeat the path to cut again, as shown in Figure 8; it greatly shortens the production time and also improves the production efficiency.

Accurate motion track following and easy PID tuning

In order to achieve better and more accurate cutting graphics, the new generation of high-end motion control cards adopts a full close loop (Full close loop) control, and achieves a smaller Error count error. The following ability errors are quite small, as shown in Figure 9. In order to achieve high-accuracy following ability, the PID control system needs to be used, but in order to shorten the PID tuning time, the user can call out the best PID parameter settings in a short time with the assistance of the Easy tuning program, as shown in Figure 10. Dramatically improve performance and simplify operation!

Automatic Speed ​​Planning and Graphical Path Planning

Through Softmotion’s algorithm, the new generation of motion control card can automatically plan the optimal graphic path planning according to the graphic data provided by the user, so as to shorten the unnecessary path and improve the cutting speed and smoothness. In this way, unnecessary duplication can be reduced and production capacity can be greatly improved. Using the LookAhead function in Softmotion, when the motion trajectory has a large turning point, Softmotion will automatically calculate and reduce the speed in advance, so that the mechanism can adapt to the smooth speed and smoothly complete the movement of the trajectory. To realize such a complex function, the user only needs to input 3 system parameters, namely “Max. Velocity”, “Max. Acceleration” and “Tolerance” (Figure 12). ). Through the internal planning of Softmotion, the trajectory motion of complex graphics can be achieved.

Empirical performance

Through the research and development of the above new functions and new technologies, it is proved that ADLINK’s new generation motion control card has a good performance in laser cutting effect. controlled within a very small range. Table 1 shows the actual test equipment specifications as follows. The mechanism part uses a Servo Motor and a Ball Screw, and the maximum movement speed is 800 (mm/s). After the debugging of ADLINK Easy-Tuning software, the optimized closed-loop PID parameters were obtained, so that the control performance of the overall machine was within ±2 error units (the physical quantity here is 5um).

Because the processing is a graph composed of 4,500 small line segments (as shown in Figure 13), and the error data of four curved corner segments and four long straight line segments are specially obtained (as shown in Table 2), and the curved corner trajectory of the overall laser processing The error is less than 2.2um, and the trajectory error of the long straight end is less than 0.5um. In the enlarged picture of the following area, it can be clearly seen that the laser energy is uniformly controlled within a certain range, and the actual processing track is smooth and jitter-free. This also proves that ADLINK’s new-generation motion control card can not only realize general multi-axis interpolation motion, but also realize complex graphics processing such as laser cutting. The real-time laser intensity and feedback speed tracking implemented on the board can effectively save system CPU resources and ensure its processing efficiency.

ADLINK’s high-end motion control card PCI-8254/8258, with high-performance motion control performance, adopts the latest DSP and FPGA technology, and can provide high-speed, high-performance mixed analog and pulse sequence motion commands. The closed-loop PID with feedforward gain control is realized by hardware, and the servo update rate can be as high as 20kHz. Through program download, up to eight independent tasks can be executed simultaneously in real time. ADLINK provides easy-to-use application tools for free, including rich motion control application functions, as well as user diagnostics and operation interfaces, enabling high-speed, high-precision motion control capabilities. With ADLINK Softmotion technology, users can greatly reduce the development time and provide excellent synchronous motion control performance, which can save up to 25% to 50% of the cost for machine equipment manufacturers and users.

Summarize

The laser cutting industry will be closer to people’s lives in the future, such as automotive sheet metal, mobile phone and TV panels and casings, and even medical-related denture molding and human-related medical laser applications. The high efficiency of laser processing can also better meet the requirements of energy saving and emission reduction. All countries have invested a lot of resources in order to have leading breakthroughs in related technologies. As far as Greater China is concerned, more than 200 different laser equipment manufacturers are also vying to grab the market pie. However, in the face of high-end equipment in Europe and the United States, the integration of software strength will affect the market position of these manufacturers and improve the processing quality. Higher gross margins on equipment. With more than 10 years of motion control technology and years of application cooperation experience with manufacturers, ADLINK successfully developed synchronous motion and laser control technology, which put complex speed planning and laser intensity calculation on the motion control card, allowing users to You can plan the path of CAM by yourself, but you don’t need to worry about complex mathematical calculations, in order to achieve the market value-added effect of seeking differences in the same. In the future, the processing path will also be upgraded from 2D to 3D manufacturing, which will perform processing applications such as the current CNC machine tools, and will have better processing surface technology.

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