Application in Lathe Machines
Application of Inverters in Lathe Machines
Description
The technological advancement of CNC machines and the proportion of CNC machines in the total output and ownership of metal cutting machining machines are crucial indicators for assessing a country's overall economic development and industrial manufacturing capabilities. Among various types of CNC machines, CNC lathes hold a prominent position and have gained widespread recognition while experiencing rapid global development over several decades.
The spindle is a vital component of a lathe, playing a pivotal role in enhancing processing efficiency, expanding the range of materials processed, and improving processing quality. Economical CNC lathes generally lack automatic speed adjustment capabilities, requiring manual stopping and adjustment when speed changes are needed. In contrast, full-function CNC lathes typically feature a main transmission system with variable speed. Currently, there are two primary types of variable-speed systems: variable-frequency spindle systems and servo spindle systems. These systems commonly employ DC or AC spindle motors. The main spindle rotates through either a belt drive or a combination of belt drive and reduction gear (to achieve higher torque) within the spindle box. The wide speed adjustment range and continuous stepless adjustments provided by the spindle motor greatly simplify the structure of the spindle box. Due to its high cost-effectiveness, lathe-specific inverters are widely utilized in lathes. Wekont Electric's lathe inverter stands out for its unique performance and superior cost-effectiveness, quickly establishing itself as an influential player in the market for numerical control machine applications.
1. Introduction to the Special Inverter Performance of Car CNC Machine Tools.
The variable frequency drive of the CNC lathe is capable of meeting the variable-speed operation requirements of the main transmission system, employing a current vector control method. It particularly excels in fulfilling the low-speed torque demands of the lathe spindle. The starting torque at 0 Hz can exceed 150%. With a carrier frequency range from 0.5 to 15 kHz, it operates with minimal noise. Additionally, it offers a standard 0-10V analog interface that is compatible with most CNC systems, ensuring excellent versatility. Moreover, it possesses robust overload capacity, allowing for over one minute of operation at more than 150% rated output current. Furthermore, it provides multiple function output terminal signals including zero-speed signals, running signals, timing functions and fault indicators to meet monitoring requirements for spindle speed state within the system. It also features automatic torque compensation to satisfy machining needs at low speeds on the lathe spindle. Furthermore, it has an automatic motor nameplate parameter setting capability within a specified range which enables vector control operation from variable-frequency motor to general-purpose motor; thus enabling full functionality and guaranteeing stability and accuracy within the system.
2. The Principle of Lathe Spindle Control System.
The AI1/GND terminals of the spindle inverter receive a speed analog signal from the CNC system. AI1 is connected to the positive signal of the CNC system's analog interface, while GND is connected to the negative signal. This 0-10V analog voltage signal controls the spindle speed. DI1/DI2/COM are forward/reverse signal terminals of the inverter, typically driven by FWD or REV signals from the CNC system to operate relays. The normally open contacts of these relays are connected to DI1/COM or DI2/COM on the inverter, thereby controlling both forward and reverse rotation of the car lathe spindle.
a) The optimization of control system parameters:
During the process of parameter adjustment, it is important to take note of the following considerations:
- For the P00.03 parameter, select the main frequency instruction and set it to receive an analog signal input ranging from 0-10V (2).
- Set the P00.02 parameter for run instruction selection to terminal control (1).
- The P00.09 parameter corresponds to the maximum frequency selection and should be set at 105Hz considering that the speed is adjusted within a range of 0-3000rpm, taking into account mechanical gear ratio. This value represents the output frequency of the inverter when a 10V analog signal is input.
- According to customer requirements, set P00.14 as acceleration time 1 with a duration of 5 seconds and P00.15 as deceleration time 1 also with a duration of 5 seconds.
- Select vector control mode by setting P00.00 as 0.
It is crucial to emphasize that vector control necessitates the provision of motor parameters, specifically impedance. Therefore, it is imperative to provide comprehensive motor parameters (such as rated voltage, rated current, rated frequency, rated speed, number of poles) on the motor's nameplate and input them into the inverter via the keyboard's run key. During automatic operation, apart from calculating motor parameters accurately, standby current can also be detected. These parameters play a pivotal role in optimizing vector control and enabling the motor to achieve its utmost potential. It is essential to conduct parameter self-learning in an unloaded state (without any load on the motor shaft). Only under such circumstances can self-learned motor parameters be precise. The entire self-learning process typically takes approximately twelve seconds.
b) Testing and Operation: Within the constant torque output frequency range (0-50 Hz), the vector control exhibits an idle current that is approximately half of that observed in VF control, with a slightly smaller load current as well. Additionally, the VF control demonstrates a noticeable speed drop during the initial stage of cutting load, resulting in a significant difference between idle speed and load speed. In contrast, under vector control, the main spindle speed experiences a slight initial drop which is comparatively smaller and quickly recovers. Ultimately, there is not much discernible disparity between idle speed and load speed. Following these adjustments, performance has been significantly enhanced compared to VF control, particularly evident through improvements in both idle current and low-speed torque as well as changes in speed. The results are highly significant and fully meet the requirements of CNC machines. Upon implementation, satisfactory operational effects have been achieved, confirming the successful application of car bed-specific variable-frequency drive within the spindle control system.
