A linear motor application system is not only a linear motor with good performance, but also a control system that can achieve technical and economic requirements under safe and reliable conditions. With the development of automatic control technology and microcomputer technology, there are more and more control methods of linear motor. The research on linear motor control technology can be divided into three aspects: one is the traditional control technology, two is the modern control technology, three is the intelligent control technology.
Traditional control techniques such as PID feedback control and decoupling control have been widely used in AC servo system. PID control contains the past, present and future information in the process of dynamic control, and the configuration is almost optimal, has strong robustness, is the most basic control mode in AC servo motor drive system. In order to improve the control effect, decoupling control and vector control are often used.
Technology and application of linear motor drive control
Photo: Zhongweixing QXL direct drive products
The traditional control technology is simple and effective when the object model is fixed, unchanged and linear and the operating conditions and operating environment are fixed. But in high - precision micro - feed high - performance occasions, we must consider the change of object structure and parameters. All kinds of nonlinear influence, operating environment change and environmental interference and other time variation and uncertainty factor, in order to get satisfactory control effect. Therefore, modern control technology has attracted great attention in the research of linear servo motor control. Common control methods include adaptive control, sliding mode variable structure control, robust control and intelligent control.
In recent years, fuzzy logic control, neural network control and other intelligent control methods have been introduced into the control of linear motor drive system. At present, fuzzy logic, neural network, PID, H∞ control and other existing mature control methods are combined, learn from each other, in order to obtain better control performance.
The application of drive control technology of linear motor is as follows:
CNC system for piston turning
In the machine tool feed system, the biggest difference between the linear motor drive and the original rotary motor drive is to cancel the mechanical transmission link from the motor to the workbench (drag plate), the length of the machine tool feed transmission chain is shortened to zero, so this transmission mode is also called "zero transmission". It is precisely because of this "zero transmission" mode, brings the original rotary motor drive mode can not reach the performance index and advantages. First, high-speed response. Because some mechanical transmission parts with large response time constant (such as lead screw, etc.) are directly eliminated in the system, the dynamic response performance of the whole closed-loop control system is greatly improved, and the response is extremely sensitive and fast. Second, high precision. The linear drive system cancels the transmission gap and error caused by the mechanical mechanism such as the lead screw and reduces the tracking error caused by the delay of the transmission system during the interpolation movement. The positioning accuracy of machine tool can be greatly improved by linear position detection and feedback control. Linear motion mechanism using linear motor has been successfully applied in CNC turning and grinding of workpiece with special section because of its fast response and high precision. Aiming at the non-circular section parts with the largest output, the non-circular cutting Research Center of National University of Defense Technology developed a high frequency noise and large stroke NC feed unit based on linear motor. When used for CNC piston machine tools, the size of the table is 600 mm×320 mm, the stroke is 100 mm, the maximum thrust is 160 N, and the maximum acceleration can reach 13 g. Since the linear motor unit and the table have been fixed together, only closed-loop control can be adopted.
The control system diagram of this unit is shown in the figure.
This is a double closed loop system, with the inner loop being the velocity loop and the outer loop being the position loop. High precision grating ruler is used as position detection element. The positioning accuracy depends on the resolution of the grating, and the mechanical error of the system can be eliminated by the feedback to obtain higher accuracy.
Open CNC system with linear motor
The NC system is composed of PC and open programmable motion controller. The general microcomputer and Windows operating system are used as the platform. The motion controller in the form of standard plug-in on PC is used as the control core to realize the opening of NC system. The overall design scheme of the open CNC system based on linear motor is shown in Figure 3.
The system adopts the scheme of inserting PCI-8132 motion control card into the expansion slot of PC, which is composed of PC, motion control card, servo driver, linear motor, CNC workbench and so on. Among them, the CNC workbench is driven by a linear motor, servo control and machine logic control are completed by the motion controller, the motion controller is programmable, in the way of motion subroutine interpretation and execution of the CNC program (G code, etc., support user expansion). The PCI-8132 is a 2-axis motion control card with PCI interface. It can generate high frequency pulse to drive the stepper motor and servo motor, control the motor motion of two axes, and realize the linear and circular interpolation. In CNC machining, position feedback is provided. PCI bus gradually replaced ISA bus in today's industrial control technology, becoming the mainstream bus form, it has a lot of advantages, such as Plug and Play (Plug and Play), interrupt sharing, providing users with great convenience, is currently the most advanced, the most common bus on the PC.