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The biggest feature of ultra-precision machining is the new achievements in the development of integrated application machinery, and the new technology of modern electronics, measurement, and computer is the crystallization of mechatronics. It has become one of the important directions in the development of machinery manufacturing. The development of ultra-precision machining relies on ultra-precision machine tools, so the key parts of ultra-precision machine tools, ultra-precision servo control and ultra-precision measurement systems, as well as processing and measurement integration, have received extensive attention and development. In recent years, the development of microelectronics technology and computer technology has become the technical basis for promoting the development of servo control technology to high performance.
With the development of large-scale integrated circuit technology, DSP chips have been rapidly developed, and are widely used in many fields such as signal processing, communication, radar, remote sensing, voice and image processing, electronic measurement, and automatic control.
In the servo control of ultra-precision machine tools, in order to achieve the sub-micron linear motion accuracy of the machine table, the introduction of modern control technology is extremely necessary.
The refined control unit and continuous feed with small blocks have become a prominent feature of ultra-precision CNC machining. The interpolation cycle of super-precision CNC machining has reached the millisecond level. Large data volume, high-precision interpolation operations and control require the computer system to react to the machining instructions at high speed, process and calculate the amount of movement of the servo motor at high speed, and then issue control commands. DSP's data throughput is up to tens of MIPS, and its instruction cycle is as short as tens of nanoseconds, making it ideal for high-speed data acquisition systems and real-time control systems with large data volumes. It is a good strategy to apply DSP to the development of high-performance ultra-precision CNC systems. In fact, DSP microprocessors have been successfully applied in ultra-precision servo control systems, tool detection compensation, fast servo devices, and machine tool protection.
Designed and developed and achieved success. The core of the ADSP2181 chip, the interpolation period reaches 5ms, the control period is 0.5ms, and the programming resolution is 2nm. It has the basic conditions for practical application.
2 Typical Performance of Digital Signal Processors The main application of digital signal processor devices is to implement various digital signal processing algorithms in real time and quickly. As a typical DSP device, the functional structure of the ADSP2181 is shown. It has the following typical performance: Piezoelectric ceramic servo device diamond tool error compensation table can complete one multiplication and one addition in one instruction cycle; program and data space are separated, and instructions and data can be accessed at the same time; on-chip has fast RAM, usually Simultaneous access in two blocks through a separate data bus; fast interrupt processing and hardware I/O support, multiple operations can be performed in parallel; pipeline operations are supported, allowing operations such as fetch, decode, and execute to be performed in an overlapping manner.
The ADSP2181 chip's MAC ("submultiply and add-on" time has reached 33ns. The number of pins in the chip has reached more than 200. The increase in the number of pins means an increase in structural flexibility, such as external memory expansion and interprocessor. Communication, etc. At the same time, the development of DSP chips has greatly reduced the cost, size, weight and power consumption of DSP systems.
“All have good and efficient development tools and assembly language support. Each of the ADSP2100 series provides tools for compiling and linking to generate executable files that can be written to the DSP program memory area. DSP also has simulation software, which can simulate program running, interrupt, timing, etc., which has great convenience and is very suitable for the needs of numerical control development.
3DSP application in ultra-precision CNC system CNC system can be divided into two types: single processor and multi-processor. The single-processor system uses a single CPU as the control core, and all functions are executed by one CPU in a time-sharing manner. The software programming is very complicated, and the feed rate of the machine tool is also affected. The typical multi-processor system is the master-slave processor structure, the main CPU completes the foreground control, that is, the human-machine interface management, information display and pre-processing, etc.; completes the background control, ie, the interpolation operation, the servo control and the feedback processing from the CPU. Responsible for frequent data operations and I/O operations.
The interpolation cycle of the ultra-precision CNC system is extremely short, the interpolation interval is small, and its control and interpolation operations are quite frequent. Therefore, the numerical control system is required to process the position signals fed back by each axis in a very short time. The current interpolation cycle has been It reaches the millisecond level. Single-processor CNC systems are difficult to achieve such fast data processing speeds, making the adoption of multi-processor systems inevitable. Due to its powerful data computing capability and extremely high computing speed, DSP devices are an excellent choice for the development of ultra-precision CNC systems, and provide the possibility for the adoption of advanced control algorithms in ultra-precision CNC systems.
In fact, DSP devices have extensive and effective applications in servo control, tool monitoring compensation and fast servo, advanced control algorithm adoption, and machine tool protection systems for ultra-precision CNC machining.
3.1 DSP-based servo control system High-speed DSP microprocessor can realize high-precision position servo control and contour machining control of super-precision machine tools, and provide thermal effects and geometric error compensation and control of machine tools and tools. For example, the Fanc15-BCNC system implements a high-speed CNC control system with 1nm MC68EC030 dual-CPU microprocessor with 33MHz main frequency double-precision 64-word length. In high-precision contour processing control, automatic feed rate control is realized to ensure processing. The trajectory is within the allowable error range of the specified trajectory.
The basic workflow of ADSP2181 is to read the command position, calculate and form new trajectory, query and process external events, and control the movement of the actuator.
The super-precision CNC architecture ADSP2181 with master-slave multiprocessor has a 16-bit word length and can execute any instruction in 33ns. Due to the extremely high computing speed, the interpolation period and sampling control period of the system reach 2ms and 0.5ms respectively, which greatly improves the agility and real-time of the system. Correspondingly, the control precision in the experimental processing has reached 0.m, and the comprehensive precision index is greatly improved compared with the processing precision of the conventional host control and interpolation control cycle.
3.2 Using DSP to improve control algorithms High-speed, high-performance microprocessors, especially digital signal processors (DSPs), enable many advanced control strategies and methods, such as adaptive control, learning control, friction control, etc. In the high-precision servo control system, the control precision and rapidity are greatly improved.
A. Abler proposed the "Direct Damping Control (DDC) algorithm and implemented it with TMS320C30. This algorithm effectively reduces the dynamic vibration noise of ultra-precision machine tools while making the machine positioning and tracking control accuracy sub-micron. The influence of positioning accuracy. H.Yonezawaetal uses TMS320C30 to realize PID+ friction compensation control algorithm, which makes the ultra-precision worktable achieve high-speed positioning accuracy of 0. YH-I ultra-precision CNC system realizes FuzzrPid composite control based on ADSP2181's powerful data processing capability. The sampling rate of the servo control system reaches 2KHz. In actual operation, the system divides each interpolation cycle into 10 control cycles for servo control, which constitutes more effective control of the interpolation process and makes the curve interpolation more The results show that the method greatly improves the accuracy and rapidity of the system's curve tracking. Compared with the conventional main processor directly doing PID servo control, the sinusoidal disturbance of the servo system is reduced by about 60%, and the control accuracy is There is a 70% improvement.
3.3 DSP in tool monitoring and servo application In order to compensate the system error in the tool feed motion, YH~I ultra-precision CNC system adopts self-developed piezoelectric ceramics, and the servo structure is formed by ADSP2181 microprocessor. The servo control of the ring has the principle structure: the principle structure diagram. Due to the fast calculation capability of the ADSP2181, the compensation data of each interpolation control cycle can be quickly and accurately calculated. The tool servo mechanism makes the positioning accuracy of the tool reach the micron level, and has a good and fast dynamic CNC machine tool spindle AC motor frequency conversion speed control system He Ping, He Gang 2 Xia Xiuhong 3 (1. Department of Computer Science, Xiangtan University, Hunan Xiangtan 411105 2. Technical Department of Yiyang Rubber Machinery Factory, Yiyang, Hunan 4130003. Internship Factory of Xiangtan University, Hunan Xiangtan 41105) Torque ripple and motor loss caused by sine wave distortion of AC output.
In the mechanical industry production, in order to process some mechanical parts with complex shapes and high precision requirements. Everyone is doing everything possible to carry out scientific and technological research and strive to improve the processing technology and processing equipment. In particular, in the improvement of the machining accuracy of the digital probe machine, a great deal of effort has been made, and a good effect is obtained. In order to further improve the machining accuracy, it is still an important way for the best effect of error avoidance and error compensation in the machine tool numerical control system. The numerical control system of the CNC machine tool spindle speed closed-loop control uses a sine wave pulse width modulation inverter, which can greatly reduce the torque ripple and motor heat loss of the CNC machine tool spindle, thus improving the machining accuracy of the CNC machine tool. .
1 The structure of the machine numerical control system and the spindle speed control As the numerical control machine tool control center CNC machine system, the industrial computer IPC, feed control, auxiliary control and spindle speed control four basic parts group Dornfeld established a neural network based Real-time system, monitoring and dynamic compensation of tool wear, in order to improve the real-time response of the system, the system uses high-speed digital signal processor DSP to complete the data processing and operation. The system monitors the correct rate of tool wear and is not sensitive to the change of cutting conditions. Within a wide range of conditions, the correct discrimination rate can reach 95%, and the dynamic compensation effect is good.
4 Conclusion DSP has achieved successful application in ultra-precision CNC system due to its powerful computing power, good I/O operation function and extremely high processing speed.
The ultra-precision CNC system on the DSP-based PC platform allows users to continuously upgrade software and hardware with little cost, and keep up with the development of CNC technology in a certain period of time, unlike closed systems that will soon lag behind and even Eliminated. The application of DSP provides a good development prospect for the servo control system of ultra-precision CNC. From a long-term perspective, to achieve high-speed, accurate, and easily improved tracking servo control, the development of ultra-precision CNC systems with DSP microprocessors is the best choice.
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