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introduction
Digital control machine tools, abbreviated as numerical control machine tools (NC, Numerical Control), are integrated electromechanical products integrating mechanical, electrical, hydraulic, pneumatic, microelectronics, and information technologies for more than 30 years, and are used in the production of modern machine tools. Generally, multi-motor drag is used, and the spindle and each feed system are respectively dragged by their own motors. Due to the wide range of machine tools, different workpieces, different processes, and different tools, the execution components of the machine tools are required to have different movement speeds. Therefore, the main movement of the machine tool should be able to adjust the speed. The spindle speed control system generally uses the AC spindle system. With the development of variable frequency speed control technology, the AC drive of the spindle of the CNC machine tool can meet the needs as well. The main drive motor drives the spindle to rotate through the belt drive, or through the belt drive and the reduction gear in the spindle box (to obtain more torque) to drive the spindle to rotate. Due to the wide speed range of the spindle motor and stepless speed regulation, the structure of the spindle box is greatly simplified.
Requirements of Application Technology for CNC Machine Tools
1, the motor requirements
Usually requires the use of variable frequency motor, or ordinary motor plus fan to meet the motor cooling requirements at low frequencies, and requires a wide range of motor speed.
2, the technical requirements of the inverter
1) It requires large low-frequency torque
The vector inverter is used to generate 150% rated torque at low frequency (1~10Hz).
2) The dynamic response of the torque is fast and the speed accuracy is high
The vector inverter is used to achieve a very good dynamic response. According to the change of the load, the response can be quickly responded by the change of the output torque so as to achieve the stability of the shaft speed.
3) Fast deceleration and parking speed
Generally, the accelerating and decelerating time of the CNC machine tool is relatively short. The accelerating time depends on the performance of the inverter and the decelerating time depends on the external braking resistor or the braking unit.
4) Conduct motor parameter self-learning
After selecting the vector inverter, to achieve good control performance, the parameters of the motor must be self-learned. The purpose is to obtain accurate motor internal parameters for vector control calculation. The motor nameplate parameters required for parameter self-learning are: motor rated power, motor rated frequency, motor rated speed, rated motor voltage, rated motor current. Some inverter motors may not have the rated speed value on the nameplate, and the rated speed can be estimated based on the empirical value. When performing parameter self-learning, be sure to do it when no load (load on the motor shaft is not connected). The accuracy of self-learned motor parameters can only be guaranteed when unloaded.
If the site conditions cannot be used for no-load operation, you can consider using the inverter's factory motor parameters for trial operation.
5) Frequency and operation instructions
The frequency inverter and the operation command of the inverter used on the CNC machine tool are all derived from the CNC controller. There are two channels that are generally given, one is the analog reference, the other is the multi-step speed reference, or both. At the same time given, multi-speed priority. The analog input is mainly voltage analog and current type. The frequency converter can collect these two types of analog quantities.
3, anti-jamming problem
When the inverter is shipped from the factory, it has a good anti-interference test, and it has a strong anti-interference ability, but the inverter is also a source of interference. It is very difficult to avoid interference with other equipment during use. It is easiest on CNC machine tools. The device that is disturbed is the CNC controller. Once the CNC controller is disturbed, the system will not work properly. In particular, the inverter frequency command and operation command may also be disturbed. Severe interference may cause frequency command instability and inverter malfunction. The solution to this problem is to add a magnetic ring on the output line of the inverter to reduce high-frequency radiation. The generally imported CNC has strong anti-interference ability.
Converter wiring schematic
The following takes the application of ECOM series high-performance vector inverter in a CNC machine tool factory in Shenyang as an example to describe the frequency conversion speed control technology of CNC machine tools.
System Components
EACON Inverter Braking Resistor 100Ω/520W 5.5KW Adjustable Speed ​​Motor CNC CNC System
Frequency converter and numerical control system parameters
The main parameters and performance indicators:
5.5kW CNC Lathe, Motor Parameters:
Rated power: 5.5kW, rated frequency: 50Hz,
Rated voltage: 380V, rated current: 11A,
Rated speed: 1440r/min Mechanical transmission ratio: 1:1.5
Processing material: 45# steel actual test performance index: (infeed performance and speed)
Spindle speed: 200r/min (frequency converter operating frequency 9 ~ 10Hz)
2. Spindle speed: 450r/min (frequency converter running frequency is around 22Hz)
Features of EC3000 Series Inverter
EC3000 series high-performance vector inverter adopts advanced magnetic flux control technology. The motor has large torque at low speed, high speed accuracy, reasonable price, complete functions, and has the functions of instantaneous power-off processing and speed tracking and restart to ensure that the system realizes continuous operation mechanism. In order to ensure that the motor operates at the highest efficiency, it is the best choice for the machine tool industry to use the EC3000 series high-performance vector inverter instead of the spindle AC servo system. EC3000 series inverter has the following features:
(1) The advanced flux control algorithm is used to realize true sensorless vector control, which greatly improves the control performance over the traditional V/F control method.
(2) Large starting torque, 0.5Hz/150%, 0Hz/180%
(3) Carrier frequency range 0 ~ 15KHz; adaptive adjustment based on temperature and load characteristics
(4) Provides a standard 0~10V analog interface that is compatible with most CNC system interfaces and has strong universality.
(5) Strong overload capacity, 150% of rated output current for one minute;
(6) Provide multi-functional output terminal signals, such as fault output signal, running signal, speed arrival and other output signals, which can well meet the system's monitoring of the spindle speed status;
Debug results
Facts have proved that the use of EC3000 series high-performance vector inverter can fully meet the requirements of the machine tool spindle control. The leading magnetic flux algorithm adopted by ECOM can smoothly output 150% of torque even under low-speed (low-frequency) operation to meet the machining requirements of different parts. It can completely replace the traditional spindle structure of the rolling bearing, and the spindle structure is simple. It is compact and can realize true stepless speed regulation. The speed of this spindle is controlled by an external analog signal to control the output frequency. Different machining processes (such as roughing, finishing, etc.) require different rotation speeds. At this time, the digital control system can output different analog voltage signals to the inverter. The realization of different speeds, at the same time the start-stop signal is also controlled by the numerical control system, which improves the degree of automation and prolongs the service life of the tools.
Conclusion
CNC machine tool spindle general AC servo system, imported brand vector control inverter and frequency conversion special motor, high purchase cost; EC3000 series inverter with its unique performance (small starting current, speed regulation, speed range, energy saving, The stable operation, high precision, low-frequency torque, complete protection functions, high reliability, easy operation and maintenance, etc., and superior cost-effectiveness have rapidly emerged in the application of CNC machine tools.
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