Foreword
Wire-cutting technology (WEDM) plays an important role in many industrial production fields such as mold manufacturing, automobile manufacturing, and aerospace manufacturing. To make a prototype of a low-speed wire-cut EDM machine that omits its secondary structure and technical aspects, including two key technologies: 1. Digital unimpeded pulse power module, which can finish finishing and finishing; 2. Clearance The voltage detection module ensures efficient and smooth cutting process. The main reason for the domestic products that do not have independent intellectual property rights at present is that they do not have the key technologies of gap servo control system design and digital pulse power system design. The key technology for the design of digital pulse power system for precision CNC EDM machine is to provide necessary technical support for the development of precision CNC EDM machines with independent intellectual property rights. Through the research of it, coupled with the mechanical design to achieve the required technical indicators.
This paper proposes the idea of ​​using DSP as the core wire-cut pulse power supply. The author designed the pulse power module for wire cutting machine tool, and analyzed the output waveform to optimize the efficiency simulation experiment under various processing conditions. The experimental results verify that the pulse power supply of this design can meet the micro wire cutting process. Claim. With the powerful data processing capability, rich on-chip peripherals and high-speed real-time control capabilities of the TMS32OLF2812DSP controller chip, AC sampling, frequency measurement and PID control are realized. Accurately measure the stator voltage and current at the output end of the synchronous generator. Through the optimal control method, accurate PWM control signal output is obtained. A multi-control function of a DSP and a pulse power supply that generates PWM pulse waves. This prototype can reach the technical level of mid-range low-speed wire-cut EDM wire-cutting machine: with ns-level large peak current pulse power supply, the maximum processing efficiency is more than 200 mm2/min, the effective processing efficiency is 120-150mm2/min, and the surface roughness is less than 0.4. Μm (Ra≤0.4μm), the machining accuracy is about ±0.005mm.
Overall design of wire-cut pulse power supply
Figure 1 is a block diagram of the design of a wire-cut pulse power supply.
The wire cutting pulse power supply mainly includes: a rectifying and transforming and filtering circuit, a communication module with a PC, a pulse generating unit, a power driving amplifying module, and a discharge gap voltage state detecting circuit module. There are two main differences between the pulse power supply and the general line cutting processing pulse power supply: First, it has a gap discharge voltage comparison module more than the general pulse power supply. Through the module, the voltage between the electrode wire and the workpiece pole is compared with the set voltage in real time, and a signal for controlling whether the pulse generator is pulsed is generated, and the pulse can be cut off at the fastest response speed, and the electrode can be effectively monitored. The voltage between the wire and the workpiece, and the output pulse voltage is corrected in real time, which avoids the unevenness of the surface caused by the unevenness of the energy, thereby improving the surface quality of the microfabrication. Second, the maximum frequency of DSP2812 can reach 150MHz. The use of its high-speed pulse simplifies the conventional design circuit, with high efficiency, good waveform and real-time performance. The third is the use of DSP2812, its rich resources are easy to extend software and hardware.
Optocoupler circuit design
The photoelectric composite device of the design adopts a high-speed 6N135 chip, and is packaged with a high-infrared light-emitting tube and a phototransistor. The left side of Figure 2 shows the 6N135 pin and internal structure.
Figure 2 6N135 internal structure diagram and circuit diagram with DSP interface
The main feature of 6N135 is high speed, +=0.5 (RL=1.9k), so it can display and fully exert its high speed characteristics on the isolation of high-speed digital communication interface. The baud rate of data can reach more than 500k. . In contrast, the common photocoupler devices 4N25 and TIL117 can only achieve a baud rate of several thousand. The right side of Figure 2 shows the /6N136 schematic diagram of the connection circuit for the DSP output pulse and the main circuit. In many industrial-based measurement and control systems with main-slave structure, in order to prevent mutual interference between the upper and lower position machines, the use of opto-isolation devices is a simple and effective method. With 6N135, the subsystem can be realized without reducing the communication baud rate. The isolation between the two.
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