introduction
Digital control machine tool (NC, Numerical Control Machine) is a mechatronics product integrating mechanical, electrical, hydraulic, pneumatic, microelectronics and information technology in the past 30 years. Generally, multi-motor drag is used, and the spindle and each feed system are respectively dragged by respective motors. Due to the wide processing range of the machine tool, different workpieces, different processes, different tools, the machine tool execution parts have different motion speeds, so the main motion of the machine tool should be able to adjust the speed. The spindle speed control system generally adopts the AC spindle system. With the development of the frequency conversion speed regulation technology, the AC drag of the spindle of the CNC machine tool can also meet the needs well. The main drive motor drives the spindle to rotate through the belt drive, or the spindle rotates through the belt drive and the reduction gear in the headstock (for greater torque). Due to the wide speed range of the spindle motor and the stepless speed regulation, the structure of the spindle box is greatly simplified.
CNC machine tool requirements for application technology
1, motor requirements
It is usually required to use a variable frequency motor, or a common motor plus a fan to meet the heat dissipation requirements of the motor at low frequencies, and to require a wide range of motor speed regulation.
2, the technical requirements of the inverter
1) requires low frequency torque
The vector inverter is selected, and 150% rated torque can be obtained at low frequency (1~10Hz).
2) Torque dynamic response speed is fast, stable speed and high precision
The use of the vector inverter can achieve a very good dynamic response effect, and respond quickly according to the change of the load through the change of the output torque, thereby achieving the stability of the shaft speed.
3) Slow down speed
Generally, the acceleration and deceleration time of CNC machine tools is relatively short. The acceleration time is guaranteed by the performance of the inverter. The deceleration time depends on the external braking resistor or braking unit.
4) Perform motor parameter self-learning
After selecting the vector inverter, it is necessary to perform self-learning on the motor to achieve good control performance. The purpose is to obtain accurate internal parameters of the motor for vector control calculation. The motor nameplate parameters required for parameter self-learning are: motor rated power, motor rated frequency, motor rated speed, motor rated voltage, and motor rated current. Some variable frequency motors may not have a rated speed value on the nameplate. The rated speed can be estimated based on the empirical value. When performing parameter self-learning, be sure to do it at no load (no load on the motor shaft). The accuracy of the self-learned motor parameters is guaranteed only at no load.
If the field conditions are not available for no-load operation, consider using the motor parameters of the inverter to test run.
5) Frequency command and run command
The frequency command and running command of the frequency converter used on CNC machine tools are all from the CNC controller. Generally, there are two kinds of channels given, one is analog quantity given, the other is multi-speed speed given, or both At the same time given, multi-speed priority. The analog quantity is mainly based on the voltage type analog quantity, and also the current type. The frequency converter can collect both types of analog.
3, anti-interference problem
The inverter has a good anti-interference test when it leaves the factory, and it has strong anti-interference ability, but the inverter is also a source of interference. It is difficult to avoid interference with other equipment during use. It is the easiest on CNC machine tools. The interfered device is a CNC controller. Once the CNC controller is disturbed, the system will not work properly. In particular, the frequency command and operation command of the inverter may also be interfered. If the interference is serious, the frequency command may be unstable and the inverter may malfunction. The solution to this problem is to add a magnetic ring on the output line of the inverter to reduce high frequency radiation. Generally, the imported CNC has strong anti-interference ability.
The following is an example of the application of CHV100 series high performance vector frequency converter in a CNC machine tool factory in Shenyang, and introduces the frequency conversion speed control technology of CNC machine tools.
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