The development of motion control system has experienced from DC to AC, from open loop to closed loop, from analog to digital, to servo control network system based on PC and motion control based on network. From the perspective of the development of motion control devices, it has roughly gone through the following stages:
① Analog circuit. The early motion control system generally used operational amplifier and other vertical components, which were composed of analog circuit hardware connection. This kind of control system has the advantages of fast response, high precision and wide bandwidth. However, compared with the digital system, the aging and the change of the ambient temperature have great influence on the component parameters of the system; there are many components and the system is complex, which reduces the system reliability; using hard wiring makes it difficult to modify; restricted by the system scale, it is difficult to realize complex control algorithm with high precision and large amount of calculation.
② Microprocessor. The microprocessor integrates CPU, ram, ROM and so on. It has the advantages of fast operation, low power consumption, high integration and strong anti-interference. However, the overall integration is still low, it does not have the control algorithm needed for motion control, and the processing speed and ability are limited.
③ General purpose computer. It uses high level programming language and corresponding control software, with the computer communication interface and the circuit board driving the motor, it can independently form a motion control system. The complex control algorithm with high performance and high precision can be realized, and the program modification is convenient. However, due to the limitation of general-purpose computer, it is difficult to be used in industrial field due to its poor real-time performance and large volume.
④ Special motion control chip. The special motion control chip integrates all kinds of logic functions and motion control functions required for motion control into a special integrated circuit board, provides some special control instructions, and has some auxiliary functions, which can reduce the workload of user software design to a minimum. However, due to the solidification of software algorithm, it is difficult to implement complex control algorithm, and the program scalability and flexibility are poor.
⑤ Digital signal processor. Digital signal processor (DSP) is a special chip which integrates strong digital signal processing ability and peripheral equipment such as input, output, analog-to-digital conversion, event capture and so on. It is a microprocessor that processes signals in real time. It has the characteristics of small volume, low power consumption and fast operation speed. In recent years, VLIW ARCHITECTURE, superscalar architecture and DSP / MCU hybrid processor are the new trends in the development of DSP architecture.
⑥ Programmable controller. In the early stage, the PLC was mainly based on logic operation, without motion control algorithm. In recent years, PLCopen has issued motion control specification, which combines motion control, logic control and security in one platform to realize motion control.
Table 1-1 shows the development history of motion control system.
The development of motion control technology in China is relatively backward. General motion controller products have been adopted since 1980s. The application scale is small and the application range is narrow. In addition, the motion speed of the motion controller is slow and the precision is not high. With the implementation of the opening-up policy, some foreign sports control products have entered China, and some foreign investors and joint ventures have been established, which has promoted the development of motion control technology.
2、 Key technologies of motion control system
Motion control technology is a comprehensive technology including mechanical engineering, electronic engineering, control engineering, computer science and sensor detection technology.
① Precision machinery technology. Mechanical technology is the technical basis of motion control. In motion control, the mechanical structure is simpler and the function is stronger. Some new mechanisms, new principles, new materials and new processes are applied, which can meet the needs of various applications. It can not only improve the accuracy and stiffness, but also improve the performance, such as reducing the volume, reducing the weight, and improving the cost performance.
② Sensing detection technology. The motion control technology needs to detect the position, speed, acceleration, etc. to form a feedback loop to realize the servo control system. Therefore, higher requirements are put forward for the sensor detection technology, such as high-precision detection, fast detection and harsh environmental conditions detection.
③ Computer and information processing technology. Motion control involves a lot of motion information, therefore, in addition to the detection and transmission of these information, it also involves a lot of work of computer and information processing. For example, information interaction, calculation, judgment, decision-making, etc. Different from the distributed control system used in process control, it has higher requirements for information processing time, real-time information and interaction.
④ Automatic control technology. In process control, control theory is the foundation. Similarly, in motion control, control theory is also the basis. Because the controlled objects are different, and many motors of servo system are nonlinear controlled objects. Therefore, high-precision position control, trajectory control, synchronous control and so on need control theory for guidance.
⑤ Servo drive technology. Servo drive technology is to control the driving elements to move according to the command requirements under the output command of the controller. Therefore, it is necessary to meet the performance indicators such as dynamic response of the motion process. Because different servo drive modes have different dynamic performance, there are higher requirements for DC servo, AC servo, stepping motor and frequency conversion technology. The servo technology changes from DC servo to AC servo. Full closed loop AC servo drive technology and linear motor drive technology have shown their advantages.
⑥ The overall technology of the system. Motion control technology is the control of the whole motion system. Therefore, the motion control system should be decomposed into autonomous and interactive units, and the individual performance should be considered under the overall performance requirements. Only in this way can the designed motion control system have good cost performance and meet the application requirements.
3、 Requirements of motion control products and systems in Intelligent Manufacturing Market
The requirements of intelligent manufacturing market for motion control products and systems are as follows:
① Better performance. Performance: high energy efficiency, improved energy efficiency algorithm, low drive power consumption, high encoder resolution, high speed of motion control communication bus, small jitter, etc.
② Safer. Implement the international mechanical safety standard (ul-iso-iec), provide motion control and safety control integrated system, and use high insulation materials.
③ Smarter. Servo driver intelligent algorithm and motion control software platform are more targeted for different industries and equipment. It develops to absolute positioning drive feedback on the premise of low manufacturing cost, optimizes energy saving and reduces energy consumption.
④ Faster. In order to improve the shaft speed of servo motor, high voltage drive requires high-performance IGBT and FET devices to meet the requirements of high-speed output, low harmonic, and improve the feedback bandwidth of the device to more than 400kHz.
⑤ Less noise. The new motor design is used to reduce the vibration and inherent harmonic of the motor, control the harmonic of the motor power input, control the waveform of the motor input voltage and current to reduce the harmonic.
⑥ Smoother operation. Using the performance of DSP and FPGA to calculate and store voltage and current waveforms, eliminate harmonic and distortion, make the motion speed and acceleration more smooth, high-resolution feedback signal and better motion control bus performance are also conducive to smooth motion.
⑦ It's smaller. The installation space of motion control products is reduced, so that the overall product volume is reduced.
⑧ It's cheaper. The servo system made in China is at least 20% cheaper than that in the United States, and the proportion of software in motion control system is higher than that of hardware, which means that the overall price tends to decline; the price of digital drive is cheaper than that of analog drive, and the performance is stronger; as the motion control products are more and more widely used in all walks of life, the production volume is larger and larger, and its cost can be rapidly reduced; in addition, with the development of computer science and technology, the cost of motion control system can be reduced rapidly The mechanical system becomes simple, and the overall cost is significantly reduced.
4、 Problems in motion control system
① For a long time, users can choose the hardware to realize motion control in a wide range. However, each hardware requires independent and incompatible development software. Even if the required functions are identical, the software needs to be rewritten when replacing another hardware. The essence of this problem is how to realize the standardization of motion control software.
② In order to meet the needs of application, the development of integrated logic control, motion control and visual control development platform is efficient and rapid development of intelligent manufacturing production line and intelligence