Frequency conversion subdivision circuit applied to CNC EDM wire cutting machine

EAâ–¡H repair and transformation bookmark0 Hunan University School of Electrical and Information Engineering Xu Zuhua frequency subdivision circuit applied to CNC EDM wire cutting machine The FPGA variable frequency pulse width subdivision drive circuit is not only suitable for stepping motor frequency conversion in wire cutting machine It can reduce the step angle, improve the running characteristics of the stepping motor, reduce the surface roughness of the machining, improve the machining accuracy and processing efficiency. The drive system also has the characteristics of simple structure, strong real-time performance and convenient adjustment.

The ggjp electric discharge wire cutting machine is a device for electro-erosion cutting of workpiece materials by spark discharge. Under the control of the program, the two stepping motors are stepped by the reduction gear and the stepping motor is operated by the pressure. A frequency conversion circuit is provided. Since the stepping angle of the stepping motor is 3°/1.5°, this restricts the application of the wire cutting machine in ultra-fine machining.

The block diagram of the stepping motor subdivision drive circuit of the digitally controlled electric discharge wire cutting machine with the FPGA as the core is shown in the figure. The voltage sampling and A/D conversion circuit reflects the analog voltage of the workpiece and the electrode wire. The sample is converted into a digital microcomputer. The interface circuit provides X, Y two stepping motors to start, stop, feed, retreat, and Subdivided multiples and other work command signals and parameters to ensure that the workbench moves according to the predetermined trajectory. The subdivided circuit includes IGBT and its driving circuit, stepping motor winding current sampling and conversion circuit.

The principle of subdivided pulse width modulation subdivision drive circuit is to reduce the step angle of the stepping motor to a few angular points, and subdivide the original step into several steps. The motion of the stepping motor is approximately uniform motion. The step winding is powered by a stepped current wave, and each circuit step causes the motor to rotate a part of the original step angle, and by dividing the step number of the current in the winding, the step angle can be divided into several small steps to complete. Thereby achieving the purpose of subdivision. The working frequency of the stepping motor in the numerical control electric discharge line cutting bed is only strictly proportional to the distance between the workpiece and the wire, so as to ensure the accuracy of the electric corrosion machining, otherwise the workpiece and the wire may be short-circuited, which may affect the cutting machine. normal work. Since the sampling voltage between the workpiece and the wire is not a constant, the working frequency of the stepping motor changes, in order to ensure the subdivision multiple, that is, the number of clock pulses for driving the IGBT in one step angle is constant, and The corresponding IGBT trigger pulse frequency changes, so the subdivision circuit uses the variable frequency pulse width modulation subdivision driving circuit.

The relationship between f and f/sampling is shown in Expressions (1) and (2).

Maintenance and modification of bookmark3 should be ascending segment, / corresponding to the constant velocity segment corresponding to the descending segment.

(1) Hardware circuit. The subdivided hardware circuit is taken as an example of the A-phase winding in the stepping motor X, XB and XC are extensions of the XA circuit, and the control circuit of the stepping motor Y is the same as the stepping motor X. Each stepper motor requires a Hall current sensing element and an A/D conversion.

(2) Work process. When the interval voltage sampling voltage f/sampling corresponds to the stepping motor operating frequency f, the frequency of the clock determines the working state of the IGBT in the FPGA program, and the IGBT (BUP304) is triggered by the EXB841. In each step angle range, the stepper motor undergoes acceleration, constant speed, deceleration, etc., and a reasonable selection of the value of /f can make the stepping motor run smoothly. If the subdivision circuit is not used, the IGBT is in a conducting state within one step angle. The following shows the operation of the subdivision circuit by taking the acceleration section winding current as an example. The time corresponding to the winding current acceleration is Ot., the subdivision multiple is A=3, /f=4, and the IGBT trigger pulse is 10 in each small step. In a step angle, the current value of each small step is shown in the attached table. On the rising edge of each trigger pulse, the values ​​of the winding current i and the current value I' are compared to determine the on and off of the IGBT.

Schedule One step angle current value Time current value i software program uses Xilinx EDA software ISE4.2i to complete the software development of the whole system. Using VHDU, I will design the digital logic circuit of the FPGA chip. VHDL is a high-speed integrated circuit hardware description language, which has the ability to describe the hardware functions of the system in multiple layers. It has become one of the standard hardware description languages ​​of IEEE. VHDL uses flexible and clear code description to design complex control logic, which is flexible and convenient. . The system composed of FPGA has the advantages of strong versatility and flexible upgrade, and can complete the upgrade and modification of the system without changing the hardware circuit. The process corresponding to the segmentation program is as shown. According to U sampling, f, f is constant within a step angle, and the time corresponding to the winding current of the stepping motor is calculated in the process of acceleration, constant speed, deceleration, etc. The program continuously determines the actual current of the winding during the subdivision process. The magnitude relationship of the given values ​​of each subdivision segment determines the turn-on and turn-off of the IGBT. The variable frequency pulse width adjustment subdivision driving circuit of the numerical control electric discharge wire cutting machine tool realized by FPGA ensures that the stepping motor runs smoothly, has simple structure, strong real-time performance, high precision and convenient adjustment, so that the numerical control electric discharge wire cutting machine tool is suitable for super Fine processing has broad market prospects. EA

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