Abstract: The high technologies of the information age have driven the rapid development of traditional industries, and some new motion control technologies have emerged in the automation of the machinery industry, such as fully closed-loop AC servo drive technology, linear motor drive technology, programmable computer controllers, and motion control cards. This paper mainly analyzes and reviews the basic principles, characteristics, and current applications of these new technologies.
1 Introduction
The influx of cutting-edge technologies in the information age into traditional industries has triggered profound transformations. As one of the traditional industries, the machinery industry has undergone a qualitative leap in both product and production system structures under the impact of this new technological revolution. The rapid development of microelectronics and microcomputer technologies has combined information and intelligence with mechanical devices and power equipment, prompting a large-scale mechatronics technology revolution in the machinery industry. With the development of computer technology, electronic power technology, and sensor technology, mechatronics products from advanced countries are emerging in large numbers. Many categories of products, including machine tools, automobiles, instruments, home appliances, light industrial machinery, textile machinery, packaging machinery, printing machinery, metallurgical machinery, chemical machinery, as well as industrial robots and intelligent robots, see new advancements every year. Mechatronics technology is receiving increasing attention from all sectors, playing a significant role in improving people's lives, increasing work efficiency, saving energy, reducing material consumption, and enhancing enterprise competitiveness.
With the rapid development of mechatronics technology, motion control technology, as a key component, has also experienced unprecedented growth, with various manufacturers both domestically and internationally launching new motion control technologies and products. This article mainly introduces several representative new technologies, including Full Closed AC Servo, Linear Motor Driving, Programmable Computer Controller (PCC), and Motion Controlling Board.
2. Fully Closed-Loop AC Servo Drive Technology
In mechatronic products requiring high positioning accuracy or dynamic response, AC servo systems are increasingly widely used. Among them, digital AC servo systems are more in line with the trend of digital control and are very easy to debug and use, thus gaining popularity. The drivers of these servo systems employ advanced digital signal processors (DSPs), which can sample the position of the photoelectric encoder at the rear end of the motor shaft, forming a closed-loop control system for position and speed between the driver and the motor. They fully utilize the high-speed computing power of the DSP to automatically adjust the gain of the entire servo system, and can even track load changes and adjust the system gain in real time. Some drivers also have Fast Fourier Transform (FFT) functionality to calculate the mechanical resonance point of the equipment and eliminate mechanical resonance through notch filtering.
Generally, most digital AC servo systems operate in a semi-closed-loop control mode, where the encoder feedback on the servo motor serves as both the speed and position loops. This control method cannot overcome or compensate for backlashes and errors in the transmission chain. To achieve higher control accuracy, high-precision sensing elements (such as linear encoders or photoelectric encoders) should be installed in the final moving parts, thus realizing full closed-loop control. A more traditional full closed-loop control method involves the servo system only receiving speed commands and completing the speed loop control, while the position loop control is handled by a higher-level controller (this is the case for most full closed-loop CNC machine tool systems). This significantly increases the complexity of the higher-level controller and limits the widespread adoption of servo systems. Currently, a more sophisticated full closed-loop digital servo system capable of achieving higher precision has emerged abroad, making the implementation of high-precision automated equipment much easier.
This system overcomes the shortcomings of the aforementioned semi-closed-loop control systems. The servo drive can directly sample the position feedback elements (such as optical scales, magnetic scales, rotary encoders, etc.) mounted on the last-stage mechanical moving parts as the position loop, while the encoder feedback on the motor serves only as the speed loop. In this way, the servo system can eliminate backlashes in mechanical transmissions (such as gear backlash, lead screw backlash, etc.) and compensate for manufacturing errors in mechanical transmission components (such as lead screw pitch errors), achieving true full closed-loop position control and obtaining high positioning accuracy. Moreover, this full closed-loop control is entirely performed by the servo drive, without increasing the burden on the upper-level controller. Therefore, more and more industries are beginning to adopt this servo system in the transformation and development of their automation equipment.
3. Linear Motor Drive Technology
The application of linear motors in machine tool feed servo systems has gained attention in the global machine tool industry in recent years, sparking a "linear motor craze" in industrialized regions of Western Europe. The biggest difference between direct linear motor drive and traditional rotary motor transmission in machine tool feed systems is the elimination of the mechanical transmission link between the motor and the worktable (slide), shortening the machine tool feed transmission chain to zero. This transmission method is therefore known as "zero-transmission." It is precisely this "zero-transmission" method that brings performance indicators and advantages that traditional rotary motor drives cannot achieve.
1. High-speed response
Because some mechanical transmission components with large response time constants (such as lead screws) are directly eliminated from the system, the dynamic response performance of the entire closed-loop control system is greatly improved, and the response is exceptionally sensitive and fast.
2. Accuracy
Linear drive systems eliminate transmission backlash and errors caused by mechanical mechanisms such as lead screws, and reduce tracking errors caused by transmission system lag during interpolation movements. By using linear position detection feedback control, the positioning accuracy of machine tools can be greatly improved.
3. High dynamic stiffness
Because of "direct drive", motion lag caused by elastic deformation, friction and wear and backlash in the intermediate transmission links is avoided during starting, speed change and reversing, and the transmission stiffness is also improved.
4. High speed and short acceleration/deceleration process
Since linear motors were initially used primarily in maglev trains (reaching speeds of up to 500 km/h), their application in machine tool feed drives to meet the maximum feed speed requirements for ultra-high-speed cutting (60–100 m/min or higher) is certainly not a problem. Due to the aforementioned "zero-transmission" high-speed response, the acceleration and deceleration processes are significantly shortened. This allows for instantaneous high-speed start-up and instantaneous precise stopping during high-speed operation. Higher acceleration can be achieved, typically 2–10g (g = 9.8 m/s²), while the maximum acceleration of ball screw drives is generally only 0.1–0.5g.
5. No limit on trip length.
By connecting linear motors in series on the guide rail, the stroke length can be extended indefinitely.
6. Quiet operation and low noise.
Because the mechanical friction of components such as the lead screw is eliminated, and the guide rail can be a rolling guide rail or a magnetic pad suspension guide rail (without mechanical contact), the noise during its movement will be greatly reduced.
7. High efficiency
Because there are no intermediate transmission links, energy loss due to mechanical friction is eliminated, greatly improving transmission efficiency. The development of linear drive motors is also accelerating, and they are receiving increasing attention in the motion control industry. In countries with relatively advanced industrial motion control, the use of corresponding products has begun. For example, Kollmorgen's PLATINNM DDL series linear motors and SERVOSTAR CD series digital servo amplifiers constitute a typical linear permanent magnet servo system, providing high dynamic response speed and acceleration, extremely high stiffness, high positioning accuracy, and smooth, error-free motion. Siemens (Germany), Mitsui Seiki (Japan), and HIWIN Technologies (Taiwan) have also begun to apply linear motors in their products.
4 Programmable Computer Controller Technology
Since the first Programmable Logical Controller (PLC) was introduced in the United States in the late 1960s, PLC control technology has undergone 30 years of development. Especially with the development of modern computer and microelectronics technologies, it has far surpassed the rudimentary stage of "sequential control" in terms of both hardware and software technology. Programmable Computer Controllers (PCCs) represent this new generation of programmable controllers.
Compared to traditional PLCs, the biggest feature of PCCs lies in their design, which resembles a time-sharing multitasking operating system similar to a mainframe computer and offers diverse application software. Traditional PLCs mostly use single-task clock scanning or monitoring programs to handle the program's own logic operations and the acquisition and refreshing of external I/O channel status. This approach directly results in the PLC's "control speed" depending on the size of the application program, a consequence that undoubtedly contradicts the high real-time control requirements of the I/O channels. PCC system software perfectly solves this problem. It employs a time-sharing multitasking mechanism to construct its application software's operating platform, thus making the application program's execution cycle independent of program length, but determined by the operating system's cycle time. Therefore, it distinguishes the application program's scanning cycle from the external control cycle, meeting the requirements of real-time control. Of course, this control cycle can be arbitrarily modified according to the user's actual requirements, provided the CPU's computing power allows.
Based on this operating system, PCC applications consist of multi-task modules, greatly facilitating the development of application software for engineering projects. This allows for the easy creation of separate 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 control calculation, and communication control. These modules operate independently while maintaining a certain degree of interrelationship between their data. After being independently developed and debugged step by step, these modules can be downloaded together to the PCC CPU and run in parallel under the scheduling and management of the multi-task operating system to jointly achieve the project's control requirements.
The powerful functional advantages of PCC in industrial control reflect the development trend of mutual integration between programmable controllers, industrial control computers and DCS (distributed industrial control systems) technologies. Although it is still a relatively young technology, it is showing its considerable development potential in an increasing number of application areas.
5. Motion control card
A motion control card is a host control unit based on an industrial PC, used for various motion control applications (including displacement, speed, acceleration, etc.). Its emergence is mainly due to: (1) meeting the requirements of standardization, flexibility, and openness of new CNC systems; (2) the urgent need for a hardware platform for motion control modules in the development and transformation of automated control systems for various industrial equipment (such as packaging machinery, printing machinery, etc.), national defense equipment (such as tracking and positioning systems, etc.), and intelligent medical devices; and (3) the widespread application of PCs in various industrial sites has also prompted the provision of corresponding control cards to fully utilize the powerful functions of PCs. Motion control cards usually use professional motion control chips or high-speed DSPs as the core of motion control, and are mostly used to control stepper motors or servo motors. Generally, the motion control card and the PC form a master-slave control structure: the PC is responsible for the management of the human-computer interaction interface and the real-time monitoring of the control system (such as the management of the keyboard and mouse, the display of system status, motion trajectory planning, the sending of control commands, the monitoring of external signals, 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.). Motion control cards are equipped with open function libraries, allowing users to develop and construct the control systems they need under DOS or Windows system platforms. Therefore, this open-architecture motion control card can be widely used in various fields of equipment automation in manufacturing.
This motion control mode is popular in the control systems of automated equipment abroad, and motion control cards have formed an independent specialized industry. Representative products include motion control cards from American companies such as PMAC and PARKER. Corresponding products have also emerged in China. For example, the DMC300 series cards from Chengdu Stepper Electromechanical Co., Ltd. have been successfully applied to various automated equipment such as CNC drilling machines and automotive component performance testing benches.
6. Conclusion
The rapid development of computer and microelectronics technologies has driven continuous progress in industrial motion control technology, leading to the emergence of many advanced and practical technologies such as fully closed-loop AC servo drive systems, linear motor drive technology, programmable computer controllers, and motion control cards. These technologies provide highly efficient means for developing and manufacturing industrial automation equipment. This will inevitably further enhance my country's mechatronics technology level.
Edited by: He Shiping
