Currently, due to their high cost-effectiveness, frequency converters are widely used in the CNC retrofitting of economical CNC machine tools and ordinary machine tools. Their main advantages are:
First, it simplifies the control circuit. Frequency converters are extremely convenient to use, allowing for full-range control through just a few external terminals. They have comprehensive internal protection mechanisms, eliminating the need for various protection circuits in the external wiring. Since the forward and reverse operation of the frequency converter is achieved by changing the inverter's output phase through control terminals, two fewer large DC contactors are needed compared to the original DC speed control system. Using a sensorless vector control frequency converter also eliminates the need for the speed sensor used for speed feedback, greatly simplifying the control circuit; standard asynchronous motors can be used. Using a squirrel-cage asynchronous motor leverages its advantages of simple structure, robustness, reliable operation, convenient maintenance, and low cost, avoiding the problems of periodically replacing and maintaining brushes and commutators associated with DC motors.
Easy to debug. Various operating parameters of the frequency converter can be debugged via an intelligent keyboard and display, making settings convenient, changes flexible, and debugging time short. Traditional DC speed control system debugging involves comprehensive adjustment of multiple parameters, such as trigger pulse phase adjustment and speed negative feedback debugging, which is difficult, time-consuming, and makes it difficult to achieve optimal control.
In addition, using a frequency converter to change the cutting speed allows for the selection of the most economically efficient cutting speed. Once the speed is selected, changing the pulley diameter and/or replacing the motor further alters the cutting speed. This method is both economical and convenient, and is an effective way for the machining industry to improve machining quality and reduce machining costs.
Most economical CNC lathes do not have automatic speed change; when a speed change is needed, the machine must be stopped and the speed manually changed. Full-function CNC lathes, on the other hand, mostly use continuously variable transmissions (CVTs) in their main drive systems. Currently, there are two main types of CVT systems: frequency converter spindle systems and servo spindle systems, generally using DC or AC spindle motors. The spindle is driven by a belt drive, or by a belt drive and reduction gears within the spindle box (to obtain greater torque). Because the spindle motor has a wide speed range and can be steplessly adjusted, the structure of the spindle box is greatly simplified. Currently, frequency converters are very commonly used on lathes due to their high cost-effectiveness.
Frequency converters reduce the number of gear pairs in speed-changing transmissions, lower noise, and improve spindle precision. They are highly adaptable to the spindle speed requirements of various products and different materials. They facilitate CNC machining, and their cost is significantly lower than similar CNC systems composed of DC speed control.
