Digital control machine tools, referred to as CNC machine tools (NC, Numerical Control), are mechatronics products that have been comprehensively applied to mechanical, electrical, hydraulic, pneumatic, microelectronics and information technologies in the past 30 years. In the production of modern machine tools, multi-motor drag is generally used, and the spindle and each feed system are dragged by their own motors.Due to the wide processing range of machine tools, different workpieces, different processes, and different tools are used, which require different movement speeds of machine tool execution components. Therefore, the main movement of the machine tool should be able to be regulated. The spindle speed control system generally adopts an AC spindle system. With the development of frequency conversion and speed control technology, the AC drag of the spindle of CNC machine tools can also meet the needs well.The main drive motor drives the spindle to rotate through the belt drive, or drives the spindle to rotate through the belt drive and the reduction gear in the headstock (to obtain greater torque).Due to the wide speed regulation range of the spindle motor and stepless speed regulation, the structure of the headstock is greatly simplified.
Requirements of CNC machine tools for application technology
1.Motor requirements
It is usually required to use variable frequency motors, asynchronous induction servos or ordinary motors with fans to meet the heat dissipation requirements of the motors at low frequencies, and to require a wide range of motor speed regulation.
2. Technical requirements of inverter
1) Requires a large low-frequency torque
The vector inverter is selected, and 150% of the rated torque can be output at 0.5HZ at low frequencies.
2) Fast torque dynamic response speed and high stability accuracy
The selection of vector frequency converter can achieve a good dynamic response effect. According to the change of load, it can respond quickly through the change of output torque, so as to achieve the stability of the shaft speed.
3) Slow down and stop fast
Usually, the acceleration and deceleration time of CNC machine tools is relatively short. The acceleration time is guaranteed by the performance of the inverter, and the deceleration time depends on the external brake resistor or brake unit.
4) Self-learning of motor parameters
After choosing QMA Q9000 high-performance vector inverter, to achieve good control performance, it is usually necessary to self-learn the parameters of the motor. The purpose is to obtain accurate internal parameters of the motor for vector control calculations.The motor nameplate parameters required for parameter self-learning are: motor rated voltage, motor rated current, motor rated frequency, motor rated speed, and motor pole number.When performing parameter self-learning, it must be carried out when there is no load (the motor shaft is not connected to the load).Only when there is no load can the accuracy of the self-learned motor parameters be guaranteed.
If no-load operation is not possible under on-site conditions, you can consider using the motor parameters of the inverter factory for trial operation.
5) Frequency instructions and operation instructions
The frequency instructions and operating instructions of the frequency converters used in CNC machine tools are derived from the CNC controller. Generally, there are two types of channels given, one is given by analog quantity, the other is given by multi-stage speed, or both are given at the same time, with multi-stage speed taking priority.Analog quantities are mainly voltage-type analog quantities, but there are also current-type ones.The inverter can collect both types of analog quantities.
3. Anti-interference problem
QMA Q9000 series high-performance vector frequency converters have been tested for anti-interference when they leave the factory and have strong anti-interference capabilities, but the frequency converter is also a source of interference. It is difficult to avoid interference with other equipment in use. The most easily disturbed equipment on CNC machine tools is the CNC controller.Once the CNC controller is disturbed, the system will not work properly.In particular, the frequency instructions and operating instructions of the inverter may also be disturbed. If the interference is serious, the frequency instructions will be unstable and the inverter will malfunction.The solution to such problems is to add a magnetic ring to the output line of the inverter to reduce high-frequency radiation.
The following takes the application of QMA Q9000 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 composition
QMA Q9000-C-0544 series high-performance vector inverter brake resistance 75Ω/1000W 5.5KW motor CNC CNC system 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 indicators: (feed performance and speed)
1. Spindle speed: 200r/min (inverter operating frequency 9～10Hz)
2. Spindle speed: 450r/min (inverter operating frequency is about 22Hz)
Inverter wiring diagram
Function parameter setting
Parameter | Name | Factory settings | Set |
22-01 | Zero speed level | 0.5 | 0.1 |
22-04 | DC braking time when stopping | 0.50 | 1.5 |
31-01 | Acceleration time 1 | 10.0 | 6 |
31-02 | Deceleration time 2 | 10.0 | 6 |
31-07 | Acceleration time 4 | 10.0 | 6 |
31-08 | Deceleration time 4 | 10.0 | 1.5 |
31-11 | Switching frequency of acceleration and deceleration time | 0.0 | 20 |
51-04 | Maximum output frequency | 60.0 | 276 |
51-05 | Maximum voltage | 200.0 | 380 |
51-09 | Minimum output frequency | 0.5 | 0.3 |
52-01 | Motor rated current | 1.90 | 24 |
52-02 | Motor rated slip | 2.90 | 1.61 |
52-03 | Motor no-load current | 1.20 | 9.5 |
52-05 | Inter-line resistance of the motor | 9.842 | 0.995 |
52-07 | The core saturation coefficient of the motor 1 | 0.50 | 0.32 |
52-08 | The core saturation coefficient of the motor 2 | 0.75 | 0.57 |
T1-03 | Function selection of terminal MSI | 3 | 1 |
T3-01 | Signal level selection of terminal FIV | 0 | 1 |
T3-12 | Filter constant | 0.00 | 0.03 |
P3-04 | Selection of stall prevention function during deceleration | 1 | 0 |
Characteristics of QMA Q9000 series high-performance vector inverter
QMA Q9000 series high-performance vector inverter adopts current vector control, which controls the primary current and phase of the motor at the same time.The magnetic field current and torque current are independently controlled, so smooth operation at extremely low speeds and high torque and high precision speed and torque control are realized.The price is reasonable, the functions are complete, and it has the functions of transient power failure processing and speed tracking and restarting to ensure that the system realizes a continuous operation mechanism to ensure that the motor is running at the highest efficiency. Therefore, the use of cool Horse Q9000 series high-performance vector inverter instead of the spindle AC servo system is the best choice in the machine tool industry.Cool Horse Q9000 series high-performance vector inverter has the following characteristics
(1) Advanced current vector control is used to realize true vector control without speed sensor, which is better than transmission in terms of control performance.
The V/F control method of the system has been greatly improved.
(2) Large starting torque, 0.5Hz/150%,
(3) The carrier frequency range is 0～15kHz; it can be adaptively adjusted according to the characteristics of temperature and load.
(4) Provide a standard 0~10V, 4-20mA analog interface, which is compatible with most CNC system interfaces and has strong versatility.
(5) Strong overload capacity, 150% rated output current for one minute；
(6) Provide multi-function output terminal signals, such as fault output signals, in-operation signals, speed arrival and other output signals, which can well meet the system's monitoring of the spindle speed status.；
Debugging results
Facts have proved that the use of QMA Q9000 series high-performance vector inverter can fully meet the requirements of machine tool spindle control.The leading magnetic flux algorithm used by the Cool Horse Q9000 series high-performance vector inverter can smoothly output 150% of the torque even at low speed (low frequency) operation to meet the processing needs of different parts. It can completely replace the traditional rolling bearing spindle structure, and this spindle structure is simple, compact, and can achieve true stepless speed regulation.The speed of this spindle is controlled by an external analog signal. The output frequency is controlled by an external analog signal. Different speeds are required in different processing processes (such as roughing, finishing, etc.). At this time, different analog voltage signals can be output by the CNC system to the inverter to achieve different speeds. At the same time, the start and stop signals are also controlled by the CNC system, which improves the degree of automation and extends the service life of the tool.
Concluding remarks
QMA Q9000 series high-performance vector inverter with its unique performance (small starting current, smooth speed regulation, large speed regulation range, energy saving and environmental protection, stable operation, high accuracy, high low-frequency torque, complete protection function, high reliability, easy operation and maintenance, etc.) and superior price/performance ratio, it has risen rapidly in the application of CNC machine tools.
