The digital servo control technology and the invincible combination of high-repetition fiber lasers achieve high-quality marking.
Digital state space servo control and "low-order mode" high repetition rate pulsed fiber laser technology enable high-speed and accurate laser marking for production lines requiring automation control and monitoring, high throughput, and minimal laser maintenance. The significance of this laser technology is that it matches high-speed scanners for high-quality marking.
The digital servo controller includes a high speed digital signal processor (DSP) for all necessary calculations of the servo motor for digital control of torque, speed or position mode. The controller interface to control and feedback signals (eg, motor current and voltage, position encoder measurements) is provided by a high resolution analog to digital conversion (ADC) integrated circuit. Parameter tuning can be extracted from the auto-tuning process and stored digitally in hardware, eliminating manual potentiometer adjustments and problems caused by analog circuit drift and aging. In addition, advanced motor control algorithms such as model-based high-bandwidth performance predictive control can be implemented using high-performance DSP technology. The predictive model is derived from the state space equation of the laser scanner motor motion and the observed motor position, as well as other dynamic variables (such as simulated current and voltage). The servo mechanism predicts the movement of the laser scanner in advance and generates a motor voltage signal to ensure that the source signal is limited by the power system. Compared to analog servos, drivers that integrate state space models can greatly enhance bandwidth.
Compared to existing lasers (such as Nd:YAG, Nd:YVO4, and CO2 lasers), pulsed fiber lasers have many advantages, such as laser parameters M2.
test results
The digital laser marking system used for the test consisted of a Cambridge Technology company's DC2000 digital state space servo with a 6230 scanning galvanometer and a 10 mm mirror and a 20 watt fiber laser from SPI. The laser operates at a repetition rate of 125 KHz. Laser marking treatment was studied using stainless steel plates. The marking performance of this system is compared to the output of an optimized analog marking system driven by an optimized CTI 671 analog servo drive. For both laser marking systems, the optimum performance of the particular pattern is determined by the correct selection of a set of relevant parameters, such as laser power, marking speed, laser marking delay, skip delay, and the like.
Figures 1a and 1b show laser marking patterns for digital and analog systems, respectively. The marking pattern is sufficiently complicated to include features such as hatching, prongs, spirals, lines and curves of different lengths. Therefore, it is obvious that for this particular pattern, the overall performance of the laser marking system is a reliable indicator of the important functions of the system. According to the test results, the digital system can complete the marking process in 25.6 seconds, but the simulation system takes 52 seconds to complete the same operation. This is the best result for both systems, as any additional effort to reduce the processing time of both systems will degrade the quality of the markup. Therefore, we state that this digital system increases the marking speed by 200% for moderately complex patterns when compared to analog systems.
The high performance servo mechanism also has the feature that during rapid acceleration and deceleration, torque is generated to control the motor. 2a and 2b respectively show horizontal line marking patterns when the servo mechanism of the digital and analog system performs the same marking speed (10 Kmm/sec). Two areas of different point spaces can be seen in the two graphs. Area 1 is an area having a different point space, corresponding to the acceleration/deceleration phase of the scanner. Region 2 is an area with a constant point space corresponding to the stable scanning phase of the scanner. Since the length of region 1 (~310um) in Figure 2a is shorter than the length of region 1 in Figure 2b (~2600 um), we can derive from this phenomenon that the short-term burst performance of the digital servo processing torque pulse is more than the analog servo mechanism. good. This inference is also an argument for the previous marking results, reinforcing our statement that the performance of the digital state space system exceeds the simulation system in terms of speed.
In the third experiment, we also studied the difference between the input parameters of the scanning galvanometer angle response for the digital system and the analog system, indicating that the digital state space servo technology has been improved. As before, the two servos drive a CTI 6230 scanning galvanometer with a 10 mm mirror. In Figure 3, the black and red lines represent the angular path (depending on time) of the digital servo controller and the analog servo controller, respectively. The angle of the mirror rotation is plotted along the Y axis and is represented by any internal unit. The path of the digital servo is closely matched to the input command, and both tracks are unrecognizable. The red line is distorted because the analog PID servo cannot accurately track the input signal due to bandwidth limitations.
in conclusion
We compared the performance of a model-based digital state space servo-driven high repetition rate pulsed fiber laser marking system with an analog PID servo and found that digital systems can increase speed performance by 200%. Therefore, for manufacturers seeking new or alternative laser marking systems, this digital laser marking system can provide valuable economic advantages, low maintenance costs and high output.
