The basic components of CNC wire-cutting machine tools include machining programs, high-frequency power supplies, drive systems, numerical control systems, and machine tool bodies. Machining programs can be written manually (such as the early 3B instructions), and are now mapped on computers (such as current CAXA, HL, HF, YH, etc. programming software), and then generate machining programs. The input of the program can be manually input by the panel (single board machine) of the CNC system, or it can be transmitted through the 232 serial port of the computer, or it can be transmitted by the computer USB interface. The following focuses on analysis from the numerical control system and the drive unit:
First, the choice of numerical control system
        The numerical control system is the "brain" of the numerical control machine tool, and operates and processes the machine tool control information. According to the principle of numerical control system can be divided into economical numerical control system and standard type numerical control system. First of all, economical numerical control system from the control method, generally refers to the open-loop numerical control system. The open-loop numerical control system is an exponential control system that does not have a position detection device. The numerical control system sends out a certain number and frequency of command pulses, and the drive unit performs machine positioning. In the case of an open-loop system under the influence of external factors, the machine tool does not act or move in place, but the system has reached the designated position when the machine tool reaches the specified position. At this time, the machining accuracy of the machine tool will be greatly reduced. However, due to its simple structure, rapid response, stable and reliable operation, convenient commissioning and maintenance, combined with very low prices, but by the stepper motor torque and frequency characteristics and accuracy, feed speed, torque constraints between the three, performance Increased restrictions. Therefore, the economical CNC system is currently used in CNC wire cutting and some economical wire-cutting wire-cutting machine tools with low speed and precision requirements. It has also been widely used in the numerical control transformation of ordinary wire walking machine tools.
       Secondly, precision CNC systems include semi-closed-loop numerical control systems and full-closed-loop numerical control systems. The semi-closed-loop numerical control system generally refers to the position signal of the servo motor of the machine tool (photoelectric encoder) feedback to the numerical control system. The system can automatically perform position detection and error comparison, and can compensate and control some of the errors, so its control accuracy is better than that of the open-loop numerical control system. To be high, but lower than the closed-loop numerical control system. In addition to the position feedback of the servo motor of the machine tool, the full-closed-loop numerical control system also feedbacks the position signal of the position detection device of the machine tool table (generally using a scale) to the system, thereby forming all position follow-up control, and the system is in process. Automatically detect and compensate for all position errors. The full-closed-loop numerical control system has the highest machining accuracy, but the commissioning and maintenance of such a system is extremely difficult, and the price of the system is very high. It is only applicable to medium-to-high-end CNC machine tools. Because the price of an open-loop control system is much lower than that of a closed-loop control system, when selecting a numerical control system, it is necessary to consider the numerical cost ratio of the numerical control system to the entire numerical control machine tool, and then according to the configuration of the machine tool and the requirements of the machine tool itself, The low-end machine tool adopts open-loop control system, while the medium- and high-grade machine tools use closed-loop control system.
Second, the matching of the drive unit
       Drive motors can be divided into three major categories: reactive stepper drive motors, hybrid (also known as permanent magnet reaction) stepper drive motors and servo drive motors. Reactive stepper drive motor rotor without windings, by the excitation of the stator windings generate reaction torque to achieve stepping operation. The permanent magnet for the rotor of the hybrid stepper motor is stepped by the electromagnetic torque generated by excitation and permanent magnets. The stepper motor is controlled by pulses. The direction of rotation of the motor can be changed by changing the order of energization. Changing the frequency of the pulse can change the rotation speed of the motor. The stepper motor has a certain step accuracy and there is no cumulative error. But the efficiency of the stepper motor is low, the ability to drag the load is not large, the pulse equivalent can not be too large, the speed range is not large. At present, the stepping motor can be divided into two phases, three phases, and five equal ones. The commonly used stepping motor is a five-phase stepping motor. For a long time in the past, stepper motors accounted for a large market, but are currently being replaced by servo motors.
       At present, the commonly used servo motor is an AC servo motor, and an optical encoder is installed at the shaft end of the motor, and the angle of the rotor is used for frequency conversion control. From the lowest speed to the highest speed, the servo motor can run smoothly and the torque ripple is small. The servo motor has a long overload capacity, a small moment of inertia and a large stall torque. The servo motor has a very small starting frequency and can quickly accelerate from the lowest speed to the rated speed.
      The AC servo motor is used as the driving device, which can be the same as a DC servo motor to form a high-precision, high-performance semi-closed-loop or closed-loop control system. Because the AC servo motor has a brushless structure, it needs little maintenance, and its volume is relatively small, which is beneficial to the increase of speed and power. At present, DC servo motors have been replaced in a wide range. After the emergence of a fully digital AC servo system using high-speed microprocessors and dedicated digital signal processors (DSPs), the original hardware servo control was changed to software servo control, and advanced algorithms in some modern control theories were realized, which greatly improved the Because of the performance of the servo system, the servo unit can greatly improve machining efficiency and machining accuracy, but the price of the servo drive unit is also high. With the gradual improvement of the servo control technology, the servo drive unit is gradually becoming the main force of the drive unit, and the price of the servo drive unit is also gradually reduced. There are two types of servo drives. An impulse control method is adopted. Such a driver and the motor are closed-loop, but they are not fed back to the numerical control system. Such a driver can be called open-loop servo control to some extent. Another kind adopts the voltage control way, carries on the electrical machinery rotational speed control through the high and low voltage, the electrical machinery feedback signal passes the driver feedback to the numerical control system to carry on the position control.
     When selecting the drive unit, the proportion of the drive unit's price in the entire CNC machine tool should also be considered. The lower price of the entire CNC machine tool generally chooses a stepping drive unit, while the higher-priced machine tool selects the servo drive unit. However, when selecting the drive unit, the matching between the drive unit and the numerical control system must also be considered. When selecting the closed-loop control system, the closed-loop servo drive unit must be selected. AC servo systems are superior to stepper motors in many performance aspects. However, stepper motors are often used to perform the motor in some less demanding applications. Therefore, in the design process of the control system, various factors such as control requirements and costs should be comprehensively considered, and appropriate control motors should be selected.