Easy drive ED3300 series vector frequency in the application of CNC machine tool
, Is a comprehensive application set the machinery, Electric , Hydraulic, pneumatic, microelectronics and information technology as one of a number of mechanical and electrical integration products, in the modern machine tool production, the general multi- Motor Drag, the spindle and feed system by their own motor to drag. As the machining broader, different parts, different processes, use different tools require different machine implementation of the velocity components, so the machine should be able to carry out the main movement speed, spindle speed control system AC spindle system commonly used , with frequency conversion technology, the exchange of numerical control machine tool spindle drag, the same could very well meet the needs. Main drive motor driven by belt drive spindle rotation, or through the belt drive and shaft of reduction gear box (for more torque) drive spindle. As a wide range of spindle motor speed, but also variable speed, making the structure simplified spindle box. As Inverter Cost-effective, so use the converter in the car bed is very common.
In the current CNC lathe, the spindle control unit is usually used to control AC inverter AC spindle motor. CNC lathe to meet the requirements of the spindle drive, must have the following properties:
(1) wide speed range, stability and speed to high;
(2) in the intermittent load, the motor speed fluctuation to be small;
(3) deceleration time is short; (4) greater overload; (5) low noise, vibration, long life.
2, Spindle frequency of the system structure and operation mode
2.1 the basic principle of frequency control spindle
Theory known by the induction motor, spindle motor speed formula:
N = (60f / p) × (1-s) Which p? Motor pole pairs, s? Slip, f? Power Power supply Frequency, n? Motor speed. Can be seen from the above formula, the motor speed and frequency linearly proportional to the change in frequency that can be transferred smoothly Saving Rotational speed, and for transducer, its frequency adjustment range is very wide, can be 0 ~ 400hz (or even higher frequency) between the arbitrary regulation, so that the spindle motor speed can be adjusted in a wide range.
Course, the speed was raised, it should also take into account the impact of its bearings and windings, to prevent excessive wear and overheating motor, generally carried out by setting a maximum frequency limit.
Figure 1 bed converter application in NC
Figure 1 shows the frequency converter in the application of CNC lathes, CNC equipment including inverters and the links usually include
(1) CNC equipment to the inverter Reversible signal;
(2) numerical control device to the speed or frequency signal frequency converter;
(3) converter to the NC device failures and other state signal. Therefore all operations on the inverter and feedback can be programmed in the CNC panel and display.
2.2 spindle frequency control system structure
Not use inverter for variable speed drive lathe generally recognized using the time controller start the motor speed reaches the speed command feed, while the use of inverter, the machine can command signal feed, this way to enhance efficiency. If the workpiece shown in Figure 2 (a) shows the shape shown by the Figure 2 (1) shows that correspond to parts of the ab section, the spindle speed to maintain at 1000rpm, corresponds to the bc section of the motor shaft into a drag constant speed movement, but the speed of change is linked to high precision cutting.
Figure 2 indicate spindle inverter system structure
In this system, the speed of signal transmission device to the converter through numerical simulation for a given channel (voltage or current), through the inverter on the input signal and set the internal frequency of the input-output characteristic curve of the set, NC device can easily and freely control the spindle speed. The curve must cover the voltage / current signal, positive / reactive, single / Bipolar different configurations to meet the CNC lathe fast rotating, free speed, speed cutting requirements.
3, no speed Sensor Vector Control Inverter
3.1 Basic Selection spindle inverter
Present a relatively simple class inverter is v / f control, it is a voltage mode device occurred on FM during a given change in voltage regulation mode, common with the linear v / f control (for constant torque) and the square of v / f control (for fans of water Pump Variable torque). v / f control weakness is the low frequency torque is not enough (need torque increase), the speed stability of the bad (1:10 speed range), so the lathe spindle frequency during use be phased out, while the vector control inverter gradually to promote. The so-called vector control to make like a squirrel cage induction machine as a DC operational performance and high quality control performance, by controlling the size of inverter output current, frequency and phase, to maintain the motor flux is located within the value, generate the required torque.
Vector control compared with v / f control, its advantages are: (1) very good control characteristics, DC motor armature current can increase comparable to exciting current regulator; (2) to meet the required high-speed response of the occasion ; (3) Speed range (1:100); (4) can be torque control.
Course relative to the v / f control, the vector control complex, cumbersome calculations, and must be stored and frequent use of motor parameters. Sensorless vector control points and the speed sensor in two ways, except that the latter has a higher rate control accuracy (five ten thousandths), while the former is two hundred, but in the CNC lathe in the speed sensorless vector frequency device control performance control requirements have been met, so here recommended and introduced the speed sensorless vector inverter.
3.2 speed sensorless vector inverter
Speed sensorless vector inverter has the following characteristics: (1) motor parameters automatically and manually enter a combination of identification; (2) greater overload, such as 50% of the rated output current of 2min, 180% rated output current 10s ; (3) low frequency high output torque, such as the 150% rated torque / 1hz; (4) complete a variety of protection (simply, is not easy fried module).
Speed sensorless vector control inverter not only improved torque control characteristics, but also improves the changes for various loads generated by a particular environment is not controllable. Figure 3 shows, as easy to drive ED3300 Series Speed Sensor products in the low-frequency converter when the torque band and the normal test data (the motor is 5.5kw / 4 pole).
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