Keywords: servo drive technology, linear motor, programmable computer controller, motion control
1 Introduction
High-tech in the information age flows to traditional industries, causing profound changes in the latter. As one of the traditional industries, machinery industry has undergone qualitative changes in product structure and production system structure under the impact of this new technological revolution. With the rapid development of microelectronics and microcomputer technology, information and intelligence are combined with mechanical devices and power equipment, prompting the mechanical industry to start a large-scale electromechanical integration technology revolution.
With the development of computer technology, electronic power technology and sensor technology, electromechanical integration products in advanced countries emerge one after another. Machine tools, automobiles, meters, household appliances, light industrial machinery, textile machinery, packaging machinery, printing machinery, metallurgical machinery, chemical machinery, industrial robots, intelligent robots and many other products have made new progress every year. More and more attention has been paid to electromechanical integration technology, which plays a great role in improving people's lives, improving work efficiency, saving energy, reducing material consumption and enhancing the competitiveness of enterprises.
With the rapid development of mechatronics technology, the motion control technology, as its key component, has also made unprecedented development, and various manufacturers at home and abroad have successively introduced new technologies and new products of motion control. This paper mainly introduces several representative new technologies, such as fully enclosed AC servo drive technology, linear motor drive technology, programmable computer controller (PCC) and motion control card.
2 full closed-loop AC servo drive technology
In some mechatronics products that require high positioning accuracy or dynamic response, AC servo system is more and more widely used, among which digital AC servo system is more in line with the trend of digital control mode, and it is very simple to debug and use, so it is favored. The driver of the servo system adopts an advanced digital signal processor (DSP), which can sample the position of the photoelectric encoder at the rear end of the motor shaft, form a closed-loop control system of position and speed between the driver and the motor, give full play to the high-speed computing power of DSP, and automatically complete the gain adjustment of the whole servo system, even track the load change in real time and adjust the system gain. Some drivers also have the function of fast Fourier transform (FFT), which can calculate the mechanical vibration point of the equipment and eliminate the mechanical vibration through notch filtering.
Generally speaking, this digital AC servo system mostly works in semi-closed loop control mode, that is, the encoder feedback on the servo motor is both a speed loop and a position loop. This control method can not overcome or compensate the gap and error on the transmission chain. In order to obtain higher control accuracy, high-precision detection elements (such as grating ruler, photoelectric encoder, etc. ) should be installed in the final motion part, that is, full closed-loop control should be realized. The traditional full closed-loop control mode is that the servo system only accepts the speed command and completes the control of the speed loop, and the control of the position loop is completed by the upper controller (as is the case with most full closed-loop CNC machine tools). This greatly increases the difficulty of the upper controller and limits the promotion of the servo system. At present, a more perfect and high-precision closed-loop digital servo system has appeared abroad, which makes it easier to realize high-precision automation equipment. Its control principle is shown in figure 1.
The system overcomes the shortcomings of the above-mentioned semi-closed loop control system. Servo driver can directly sample position feedback elements (such as grating ruler, magnetic grating ruler, rotary encoder, etc.). ) is installed on the last mechanical moving part as the position loop, and the encoder feedback on the motor is only used as the speed loop at this time. In this way, the servo system can eliminate the gap (such as gear gap and spiral gap) in mechanical transmission, compensate the manufacturing error (such as pitch error) of mechanical transmission parts, realize the real full closed-loop position control function, and obtain high positioning accuracy. Moreover, this full closed-loop control is completed by the servo driver, which will not increase the burden of the upper controller, so more and more industries begin to adopt this servo system in the transformation and development of their automation equipment.
3 linear motor drive technology
The application of linear motor in machine tool feed servo system has been paid attention to in the world machine tool industry in recent years, which has set off a "linear motor fever" in industrialized areas of western Europe.
In the machine tool feed system, the biggest difference between the linear motor direct drive and the original rotary motor drive is that the mechanical transmission link from the motor to the workbench (carriage) is cancelled, and 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-drive" mode that it brings performance indicators and advantages that the original rotating motor drive mode cannot achieve.
1. High-speed response Because some mechanical transmission parts (such as lead screws) with large response time constants are directly cancelled 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.
2. The precision linear drive system eliminates the transmission gap and error caused by mechanical mechanisms such as lead screws, and reduces the tracking error caused by the lag of the transmission system during interpolation. Through the feedback control of linear position detection, the positioning accuracy of machine tools can be greatly improved.
3. High dynamic stiffness Due to the "direct drive", the motion lag caused by elastic deformation, friction and wear and reverse clearance in the process of starting, shifting and reversing of the intermediate transmission link is avoided, and its transmission stiffness is also improved.
4. Fast speed and short acceleration and deceleration process. Since linear motors were mainly used in maglev trains at the earliest (the speed can reach 500Km/h), it is certainly no problem to use them in the feed drive of machine tools to meet the maximum feed speed of ultra-high speed cutting (60 ~ 100 m/min or higher). Due to the high-speed responsiveness of the above "zero drive", the acceleration and deceleration process is greatly shortened. In order to realize the instantaneous high speed at the start, the instantaneous quasi-stop during the high-speed operation. Higher acceleration can be obtained, generally reaching 2 ~ 10g (g = 9.8m/S2), while the maximum acceleration of ball screw drive is generally only 0.1~ 0.5g.. ..
5. The stroke length is not limited. By connecting a linear motor in series on the guide rail, the stroke length can be extended indefinitely.
6. Quiet action and low noise. Because the mechanical friction of transmission screw and other parts is cancelled, the guide rail can be a rolling guide rail or a magnetic pad suspension guide rail (without mechanical contact), so the noise during movement will be greatly reduced.
7. High efficiency Because there is no intermediate transmission link, the energy loss caused by mechanical friction is eliminated, and the transmission efficiency is greatly improved.
The development of linear drive motor is getting faster and faster, and it has received extensive attention in the motion control industry. In foreign countries where industrial motion control is relatively developed, the corresponding products have been widely used. Among them, Kollmorgen's PLATINNM DDL series linear motor and SERVOSTAR CD series digital servo amplifier constitute a typical linear permanent magnet servo system, which can provide high dynamic response speed and acceleration, extremely high stiffness, high positioning accuracy and smooth and error-free motion. German Siemens, Japanese Mitsui Seiki Corporation and Taiwan Province Shangyin Technology Company have also started to apply linear motors in their products.
4 programmable computer controller technology
Since the advent of the first programmable logic controller (PLC) in the United States in the late 1960s, the PLC control technology has gone through 30 years of development, especially with the development of modern computer technology and microelectronics technology, the software and hardware technology has been far away from the initial "sequential control" embryonic stage. Programmable Computer Controller (PCC) is a new generation of programmable controller representing this development trend.
Compared with traditional PLC, PCC's biggest feature is the design of time-sharing multi-task operating system and diversified application software similar to large computers. Traditional PLC mostly uses single-task clock scanning or monitoring program to process the logic operation instructions of the program itself and the state acquisition and refresh of external I/O channels. This processing method directly leads to that the "control speed" of PLC depends on the size of the application program, which is undoubtedly contrary to the requirements of high real-time control in I/O channel. The system software of PCC solves this problem well. It uses time-sharing and multi-tasking mechanism to build the running platform of its application software, so that the running cycle of the application program has nothing to do with the length of the program, but is determined by the cycle cycle of the operating system. Thus, the scanning period and external control period of the application program are distinguished, and the requirements of real-time control are met. Of course, this control period can be arbitrarily modified according to the actual requirements of users on the premise that the computing power of CPU allows.
Based on this operating system, the application program of PCC is composed of multi-task modules, which brings great convenience to the development of engineering project application software. Because it is convenient to write control program modules (tasks) according to the different functional requirements of each part of the control project, such as motion control, data acquisition, alarm, PID adjustment operation, communication control and so on. These modules not only run independently, but also maintain a certain correlation between the data. After independent compilation and step-by-step debugging, these modules can be downloaded to the CPU of PCC, run in parallel under the scheduling management of multi-task operating system, and realize together.
The powerful functional advantages of PCC in industrial control reflect the development trend of the integration of programmable controller, industrial control computer and DCS (distributed industrial control system) technology. Although it is still a relatively young technology, it shows its development potential in more and more application fields.
5 motion control card
Motion control card is an upper control unit based on industrial PC, which is used in various motion control occasions (including displacement, speed, acceleration, etc. ). It appears mainly because: (1) In order to meet the requirements of standardization, flexibility and openness of new CNC systems; (2) Engaged in the development and transformation of automatic control systems of various industrial equipment (such as packaging machinery and printing machinery). ), national defense equipment (such as tracking and positioning system, etc. ), intelligent medical devices and other equipment urgently need a hardware platform of motion control module; (3) The wide application of pc in various industrial sites also urges the provision of corresponding control cards to give full play to the powerful functions of PC.
Motion control cards usually use professional motion control chips or high-speed DSP as the core of motion control, which are mostly used to control stepping motors or servo motors. General motion control card and PC constitute a master-slave control structure: PC is responsible for the management of human-computer interaction interface and real-time monitoring of control system (such as keyboard and mouse management, system state display, motion trajectory planning, control instruction sending, external signal monitoring, etc.). ); The control card completes all the details of motion control (including the output of pulse and direction signals, the processing of automatic acceleration and deceleration, the detection of signals such as origin and limit, etc.). ). The motion control card is equipped with an open function library for users to develop and build their own control system under DOS or Windows platform. Therefore, this open structure motion control card can be widely used in various fields of manufacturing equipment automation.
This motion control method is popular in the control system of foreign automation equipment, and the motion control card has also formed an independent specialized industry. Representative products include American PMAC, Parker and other motion control cards. Corresponding products have also appeared in China. For example, the DMC300 series cards of Chengdu Stepping Electromechanical Co., Ltd. have been successfully applied to automatic equipment such as CNC punch presses and auto parts performance test beds.
6 concluding remarks
With the rapid development of computer technology and microelectronics technology, industrial motion control technology has been continuously improved, and many advanced and practical technologies have emerged, such as fully closed-loop AC servo drive system, linear motor drive technology, programmable computer controller, motion control card, etc., which provide an efficient means for developing and manufacturing industrial automation equipment. This will also promote the continuous improvement of electromechanical integration technology in China.