Technology Innovation on AC Servo System for 5-Axes Simultaneous Movements of CNC Machine

Technology innovation on AC servo system for 5-axes simultaneous movements of CNC machine

1 ?Introduction?

Summary: The article will introduce the technology innovation of ESTUN ProNet series digital AC servo system for the high speed and high precision request of 5-axes simultaneous movements of CNC machine.

Key words: AC servo system, 5-axes simultaneous movements, technology and innovation, high speed and high precision.

Equipment manufacturing is the foundation of National industry. It provides important methods to the development of new technology, products and modern industry production. It is a significant strategic industry and is valued even by developed industry countries. Mass high level CNC machines have been needed urgently in recent years along with the rapid development of National Economy and request of National defense. Machine tool is the symbol of National manufacture level, and 5-axes simultaneous movements CNC machine is the highest representative of machine tool manufacturing industry. 5-axes simultaneous movements CNC machine significantly effects a country's aviation, space flight, military, science research, precise equipment, and precise medical equipment and so on. It is generally believed that 5-axes simultaneous movements CNC machine is the only method to solve the processing problem of impeller, blade, marine screw, heavy generator rotor, steam turbine rotor, giant diesel engine crank shaft and so on.

As one of the key technology of 5-axes simultaneous movements CNC machine, servo drive technology is still at its primary stage in our country. At present, the Chinese self-own IPR servo products can only be used for regular CNC machine. The positioning precision is about several microns normally. Neither performance nor reliability can match the request of 5-axes simultaneous movements CNC machine.

As a professional AC servo system R&D unit and manufacturer, Estun obtained the key research project of " High Level CNC system, High Speed And Precision Servo System Technology Research" from National Science Department . Estun carried out deep research to the high speed high precision request of AC servo system for 5-axes simultaneous movements CNC machine in the project. Now, Estun new AC digital servo system-ProNet series is launched with a power range from 1kw to 15kw, which covers various automatic machine control application fields including CNC machine.

2 ?Technology innovation of AC servo system?

Estun ProNet series digital AC servo system select many new technologies and arts, mainly including:

(1) ProNet series select the newest DSP, its capacity of data processing is raised from 16 bits to 32 bits, basic frequency is raised above 100MB. Current forward feedback control is added in digital current loop. The running time of current loop is largely shorted to only tens microns by the high speed calculate capacity of 32 bits DSP. It can completely compare with the method of fixing the control calculate method to special hardware loop to realize current loop control of foreign products. The current loop torque control precision is further raised by raising the current inspection precision to 16 bits. It realizes keeping good performance at steady and momentary state. ProNet driver shorts the adjustment time to 1/5 of our previous products with the best control by the whole new software and hardware platform designed specially for the request of high speed and high precision control, so that the outstanding responsiveness is realized.

(2) The new motor series select new high resolution serial encoder. The encoder cores are decreased to 5, support both incremental and absolute types. Communication rate is 5M. The longest communication circle is 16us, encoder sense is 17bits/rev, means 131072 pulses are created by one rotation, it can be raised to 22bits/rev, means 4194304 pulses are created by one rotation, so that the nanometer level positioning control foundation is established. The mass programmable units in servo drive integrate the self-owned IPR serial encoder data decode function and speed real-time inspection function. Motor's low speed performance is further raised , the volatility of speed and torque are reduced to the less; on the other hand, the positioning precision is raised, new control calculate method shorts the positioning control setting time to 1/5 of previous one.

(3) In order to make the clients use servo system flexibly, ProNet lead off adding expansible and flexibility, open design. By optional modules, many communication interface and feedback interface can be expanded.

a. Profibus-DP bus module
It is corresponding to Profibus-DP net. Servo information(such as position, speed, torque, input and output, alarm)'s read and change of various instruction can be realized by real time control. A hose can realize at most 31 sites' multiple axes movement control.

b. Full closed loop optional module ( under development)
Servo control normally feedback by gathering the signals from shaft end of motor, means half closed loop control method; There are no signals feedback from machine part controlled. ProNet can offer full closed loop control function by full closed loop optional module, and adjust the effects by mechanic processing offset, gear seam, structure weighted elasticity distortion as so on through PC in servo drive.

(4) ProNet realizes software servo control in the all digital environment. It uses multiple calculate methods. The main calculate method includes current forward feedback control, speed forward feedback control, position forward feedback control, change gain control, active disturbance rejection control, mode tracing control, forced vibration control, on line inertia auto-identify control as so on. By these calculate methods, the responsiveness, stability, precision, operability is raised to very high level. The suppression to overshoot and vibration are enhanced. The positioning setting time of low rigidity can be shorted to 1/3 of our previous products. By the expansion of new calculation methods.

(5) ProNet completely achieved the simplicity of use. It can measure mechanic characters and set the needed servo gain, realizes "on line auto-adjustment function", automatically adjusts the servo system corresponding to the mechanic characters. It short the test time, make the operation easier, it can be set to the best even in first application.

(6) ProNet use the structure of electric isolation between main loop and control loop, which makes operation and inspection more convenient and safer. The power is expanded from 5kw to 15kw. Among them, 0.5kw to 5kw uses3 phase 200V power supply, 7.5W to 15KW uses 3 phases 400V power supply.

(7) Along with the constantly completion of permanent magnetism arts, Estun new servo motor uses newest Nd2Fe14B1(Neodymium Magnet) material. Its remagnet flux density, coercive force, BHmax are better than others'. Plus the reasonable design of magnetic energy, magnetic circuit and motor structure, the motor's performance is largely enhanced. Meanwhile, the motor size is shorted. Servo motor power is from 0.5kw to 15kw, the electric power voltage is from 200v to 400v.

3. ?Vision?

The applications of all digital AC servo system is getting wider and wider. The user's request to servo system technology is higher and higher. Therefore, AC servo system technology must be further developed. The future direction will be introduced as below:

(1) High performance:
The performance of servo system will be improved from mainly two parts in future. First the servo motor's performance should be raised, uses new arts and structure, enlarges output torque while shorts the volume, optimizes the output power. The second, the drive's performance should be improved. Use the hardware such as high speed DSP, ASIC, IPM intelligent power components. Use new control theory software, raise the calculate speed and current control precision. The resolution, multiple function will be largely enhanced in inspection part. In the near future, smaller and multiple function position inspection component will be used.

(2) Downsizing
High performance permanent magnetic material will be used in servo motor in order to improve magnetic field configuration, optimize winding technology, cooling technology.

(3) Software oriented
Use super mass integrated circuit in servo drive, make more hardware structure software-oriented.

(4) Networking
The networking technology will connect drive part, motion control, host control and CPU with net, create a integrated system solution. Realize centralized management through net high speed data transition. Make mechanic adjustment, error examination more simple and reliable. Even manage, control and maintain in different place through internet.

(5) Environment suitability
The servo system will improve the characters of anti-disturbance, low noise. So that the request to environment could be weakened and disturbance of environment will be decreased.

In one word: Estun servo technology will be developed to the drive control of higher performance, faster speed and more powerful all digitizing.

The Author: Wang Fan, Vice Technical General Manager of Estun Automation.
Research direction: AC servo system, DSP Technology, Electronic Reliability, Bus