Abstract: This paper focuses on the application of variable frequency servo technology in the saw blade punching process. The proposed solution replaces the original worm gear system's traction component with automated electromechanical control technology. Tooth pitch control is entirely achieved by the servo motor tracking the variable frequency position in real time; changes to the tooth pitch only require modification of the servo parameters.
Keywords: servo system, tracking error, feedforward gain, PLC
1 Introduction
The carding machine is a front-end process equipment in textile engineering. The carding saw blade is a key component of the carding machine (Figure 1). The punching tooth is the main processing technology of the carding saw blade. In the traditional punching tooth process, the punching tooth and traction are completed by a mechanical mechanism integrating a turbine and worm gear. Different tooth pitches require different turbine reduction ratios. Behind the cumbersome mechanical installation and debugging, the processing accuracy also has a certain degree of random fluctuation. However, the newly designed servo system replaces the traction part of the original turbine and worm gear system. The punching tooth is completed by frequency conversion alone, and the tooth pitch control is completely completed by the servo tracking the frequency conversion position in real time. Changing the tooth pitch only requires modifying the servo parameters. Not only is the efficiency high, but the consistency of the processed tooth pitch is also very good. This servo system has completely brought about a new concept and a qualitative leap to the industry (Figure 2).
Figure 1. Carding saw blade
Figure 2. Saw blade punching tooth servo system
2. Principle Design
Figure 3 Mechanical Equivalent Architecture
2.1 System Process and Control Analysis
The mechanical equivalent architecture is shown in Figure 3. When the tension of the production line changes, the frequency converter adjusts its PI control based on the tension feedback. Since the tension control process is not demanding, it is easy to control. However, when the speed of the frequency converter changes, the cutting speed of the file on the roller changes accordingly. To ensure a constant punch pitch, the downstream servo system needs to accurately track the speed of the frequency converter in real time. Based on the ratio of frequency converter speed to tooth pitch, the system aims to ensure both a pulse equivalent accuracy of less than one-tenth and a feedback encoder frequency of less than 500kHz at the motor's maximum speed. Therefore, a resolution of 1000PPR is selected for the feedback encoder of the tracked motor. The tooth pitch can be changed directly by modifying the electronic gear ratio of the servo via the PLC-servo RS-485 communication function.
2.2 Saw Blade Control Scheme
Saw blade machine control system solution. The entire automation system is implemented using Delta Electronics Automation products, including a Delta DVP14ES00T programmable controller and a Guangzhou Bowei Servo Technology BWS-BB-R40H21B 400W servo system (servo motor drive reduction ratio: 10:1). The encoder requires differential output/AB phase/1000PPR/DC5V.
3. Core technologies of the control system:
Ultimately, stable control of tooth pitch boils down to how the servo system accurately tracks the encoder. To overcome the dynamic/static friction inherent in this mechanical system, increasing the servo's rigidity is a prerequisite for stable pulse tracking. Simply increasing rigidity (increasing bandwidth/FW), even at 120Hz, significantly reduces the pulse tracking error to around 4. However, due to the slip rate of the tracked asynchronous motor and other discrete errors, the encoder's pulse source exhibits random fluctuations. Furthermore, an excessively large ratio makes deviation control prone to "output overshoot and oscillation," and the combined effect of the speed integral stage on phase shift causes significant fluctuations in the tracking error, with approximately 1/6 of the tooth pitch exceeding the allowable error range. Therefore, the key control objective of this servo system is to stabilize the tracking error rather than reduce it. Based on the above analysis, appropriately adjusting the servo system bandwidth to 80Hz, setting the speed ratio to around 2700, reducing the position feedforward gain to around 1500, and significantly reducing the speed integral to around 35 significantly improves accuracy, with most tooth pitches even reaching the user's "zero error standard."
4. Conclusion
The servo control system for carding saw blade punching, based on AC servo technology from Guangzhou Bowei Servo Technology, has been successfully put into operation. Project practice has proven that the solution not only fully achieves the expected design results but also provides a good economic solution for other similar industries. In similar servo synchronous control applications, such as winding pitch control in the wrapping machine industry and petal width control in the glass grinding machine industry, the above control model is ultimately adopted, demonstrating the system design approach's significant reference value and potential for expansion.
