A wire cutting pulse power supply circuit

Abstract

The present invention discloses a wire cutting pulse power supply circuit, which includes a working voltage input terminal, a host computer, a single-chip microcomputer, a tool, a workpiece, a switching circuit, and an overcurrent protection circuit. The switching circuit includes a VMOS transistor and a MOSFET driver; the single-chip microcomputer is connected to the host computer, and the PWM signal terminal of the single-chip microcomputer is connected to the MOSFET driver; one path of the working voltage input terminal is connected to the VMOS transistor, and the other path is connected to the workpiece electrode; the MOSFET driver is connected to the VMOS transistor, and the VMOS transistor is connected to the tool electrode; the input terminal of the overcurrent protection circuit is connected to the VMOS transistor, and the output terminal is connected to the MOSFET driver. By using a VMOS transistor as the power switching transistor, a MOSFET driver to replace the push-pull circuit, and the overcurrent protection circuit directly feedback to the MOSFET driver to achieve hardware locking, the circuit is simplified while the working efficiency is improved.

Description

Technical Field

[0001] The present invention relates to a wire-cutting pulse power supply circuit, belonging to the technical field of power supply circuits. Background Art

[0002] Wire-cutting machining is a processing method that directly utilizes electrical energy and thermal energy. Currently, it has been widely applied in many industries such as mechanical manufacturing, aerospace, and electronic equipment. Among them, the electro-discharge wire-cutting machining method can almost machine any hard conductive metal material, and during the machining process, it is not affected by macroscopic forces, which can ensure better machining accuracy and surface quality.

[0003] The pulse power supply circuit is a crucial component in an electro-discharge machining machine tool. Its voltage and current output characteristics directly determine technical and economic indicators such as the productivity, surface quality, machining speed, stability of the machining process, and tool electrode loss in electro-discharge machining, occupying an extremely important position in the electro-discharge machining machine tool.

[0004] Currently, most pulse power supply circuits in electro-discharge machining machine tools adopt a complementary push-pull circuit to achieve the rapid on-off of current. However, for complementary push-pull output, the on-off of two transistors is realized alternately. The circuit structure in the inductive mode is relatively complex, which also reduces the transmission efficiency and accuracy, and cannot accurately control high-frequency pulses. At the same time, when this circuit receives feedback current, once a short-circuit phenomenon occurs, the circuit current surges, and a hardware locking method must be adopted to reduce the reaction time of the system to ensure that the circuit is not damaged. However, the current circuit is not easy to control and lock, and a CD4081 AND gate control must be added in front of the circuit, which leads to the complication of the circuit structure.

[0005] The information disclosed in this background art section is only intended to enhance the overall understanding of the present invention and should not be regarded as an admission or any form of implication that this information constitutes prior art already known to those of ordinary skill in the art. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a wire-cutting pulse power supply circuit. By using VMOS transistors as power switching transistors and MOSFET drivers to replace the push-pull circuit, and directly feeding the overcurrent protection circuit back to the MOSFET driver to achieve hardware locking, the circuit is simplified while the working efficiency is improved.

[0007] To achieve the above object, the present invention is implemented by the following technical solutions:

[0008] The present invention discloses a wire cutting pulse power supply circuit, which includes a working voltage input terminal, a host computer, a single-chip microcomputer, a tool, a workpiece, a switching circuit, and an overcurrent protection circuit. The switching circuit includes a VMOS transistor and a MOSFET driver.

[0009] The single-chip microcomputer is connected to the host computer, and the PWM signal terminal of the single-chip microcomputer is connected to the MOSFET driver.

[0010] One path of the working voltage input terminal is connected to the VMOS transistor, and the other path is connected to the workpiece electrode.

[0011] The MOSFET driver is connected to the VMOS transistor, and the VMOS transistor is connected to the tool electrode.

[0012] The input terminal of the overcurrent protection circuit is connected to the VMOS transistor, and the output terminal is connected to the MOSFET driver.

[0013] Further, the overcurrent protection circuit includes a voltage dividing circuit and a voltage comparator. The VMOS transistor includes a first VMOS transistor and a second VMOS transistor.

[0014] The gate terminal of the first VMOS transistor and / or the second VMOS transistor is connected to a signal output terminal of the MOSFET driver. The source terminals are respectively connected in parallel to the working voltage input terminal and a diode, and the drain terminal is connected to the tool electrode.

[0015] Among them, a voltage dividing circuit is led out from the circuit where the drain terminal of the second VMOS transistor is connected to the tool electrode and connected to an input terminal of the voltage comparator. The single-chip microcomputer is connected to the other input terminal of the voltage comparator. The output terminal of the voltage comparator is connected to the MOSFET driver.

[0016] Further, the working power of the second VMOS transistor is less than or equal to the working power of the first VMOS transistor.

[0017] Further, two resistors are also connected in parallel to the circuit between the source terminal of the first VMOS transistor and / or the second VMOS transistor and the working voltage input terminal. Among them, one resistor is a heat dissipation resistor, and the other resistor is a current limiting resistor.

[0018] Further, a gap voltage detection circuit is also included.

[0019] The gap voltage detection circuit is used to detect the gap voltage between the tool and the workpiece and feedback it to the single-chip microcomputer.

[0020] The single-chip microcomputer judges the gap state according to the gap voltage and feedbacks it to the host computer.

[0021] The host computer outputs a control signal to adjust the gap voltage according to the gap state.

[0022] Further, the gap voltage detection circuit includes a synchronous voltage frequency converter. The input end of the synchronous voltage frequency converter is connected to the tool electrode through a voltage stabilizing circuit, and the output end is connected to the single-chip microcomputer.

[0023] Further, an LED display lamp for displaying the adjustment of the gap state is also provided on the single-chip microcomputer.

[0024] Further, the single-chip microcomputer is connected to the upper computer through an optocoupler.

[0025] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0026] In the wire cutting pulse power supply circuit of the present invention, a VMOS tube is used as the power switching tube, which has the advantages of high-speed on-off, large instantaneous current and small power consumption; the adopted MOSFET driver not only has the traditional push-pull circuit output mode, but also reduces the energy consumption, and can receive the over-current signal of the over-current protection circuit to achieve hardware locking to protect the circuit, further simplifies the circuit and improves the working efficiency.

[0027] The feedback loop of the present invention includes an over-current protection circuit and a gap voltage detection circuit, and adopts a current-voltage double feedback mode. Among them, the current protection can achieve stepless control, increase the control accuracy and the circuit's response ability; the voltage adjustment is captured by the PWM input method, and continuous voltage change can be obtained.

[0028] The present invention basically realizes the stability and high efficiency of the wire cutting pulse power supply processing process, and at the same time improves the control ability of the pulse power supply. Description of the Drawings

[0029] Figure 1 is the overall structure diagram of a wire cutting pulse power supply circuit;

[0030] Figure 2 is the switch circuit diagram;

[0031] Figure 3 is the voltage dividing circuit diagram;

[0032] Figure 4 is the input-output diagram of the voltage comparator;

[0033] Figure 5 is the gap voltage detection circuit diagram. Specific Embodiments

[0034] The present invention will be further described below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0035] Embodiment

[0036] This embodiment provides a wire-cut pulse power supply circuit, as Figure 1 and Figure 2 shown, which includes a working voltage input terminal, a host computer, a single-chip microcomputer, a tool, a workpiece, a switching circuit, and an overcurrent protection circuit. The switching circuit includes a VMOS transistor and a MOSFET driver;

[0037] The single-chip microcomputer is connected to the host computer, and the PWM signal terminal of the single-chip microcomputer is connected to the MOSFET driver;

[0038] One path of the working voltage input terminal is connected to the VMOS transistor, and the other path is connected to the workpiece electrode;

[0039] The MOSFET driver is connected to the VMOS transistor, and the VMOS transistor is connected to the tool electrode;

[0040] The input terminal of the overcurrent protection circuit is connected to the VMOS transistor, and the output terminal is connected to the MOSFET driver.

[0041] Specifically, the switching circuit of this embodiment is provided with 10 paths of VMOS transistors and their corresponding MOSFET drivers. Among them, 8 paths of VMOS transistors are the first VMOS transistors, with the model IRFP250N; 2 paths of VMOS transistors are the second VMOS transistors, with the model IRF640. As the processing accuracy and processing efficiency of the pulse power supply are adjusted, through this scheme, we can obtain 9*3 - 1 (that is, 8 paths of IRFP250N can be enabled in 9 states from 0 to 8 paths, 2 paths of IRF640 can be enabled in 3 states from 0 to 2 paths, and the first and second VMOS transistors cannot be all 0) for a total of 26 combination methods. With the modulation processing of the PWM pulse width and pulse interval, most of the processing under the condition of non-high-precision processing can already be completed.

[0042] The MOSFET driver uses a MOSFET gate driver of model UCC37322. As an integrated circuit, this model chip not only integrates a push-pull circuit output mode but also reduces power consumption. In particular, its ENBL interface has a unique locking function, which can accept overcurrent signals and achieve rapid locking in hardware to protect the circuit.

[0043] As Figure 2 shown, one path of the switching circuit includes a MOSFET driver U1 and a VMOS transistor Q1. Specifically, the IN interface of the MOSFET driver U1 accesses the PWM signal of the single-chip microcomputer, the ENBL interface accesses the overcurrent signal LM393_OUT of the overcurrent protection circuit, and the OUT interface is connected to the gate of the VMOS transistor Q1.

[0044] The source electrode of the VMOS transistor Q1 is connected to the 120V operating voltage through two parallel resistors. Among them, one resistor is the ceramic cement resistor R12 with a power of 5W2KJ. The ceramic cement resistor has good heat dissipation performance and is suitable for this kind of occasion where large current may cause serious heating. The other resistor is external to the circuit board and is not shown in the figure. Its resistance value is generally small, and different resistors can be connected according to the estimated value of the required current to control the overall resistance value, thus playing a role in current limiting.

[0045] It should be emphasized that a fast recovery diode Z1 is connected to the source electrodes of every two VMOS transistors. Its model is MUR3060, which adopts a dual-tube package, with a rated current of 30A and a rated operating voltage of 600V. Its reverse recovery time is only 65ns. Obviously, its working ability can meet the requirements of the technical indicators (15A, below 150V, us-level control). When a VMOS transistor changes from conduction to cutoff, the original forward voltage applied to the transistor quickly reverses to a reverse voltage, and the forward current rapidly decreases within a very short time, finally becoming a reverse current and gradually reaching the reverse peak, and then gradually cycling. The fast recovery diode is applied in high-frequency switching power supplies and plays a role in high-frequency rectification, which can greatly improve the instantaneous change rate of the current.

[0046] In the figure, the drain electrode of the VMOS transistor shows a direct grounding method. However, in the actual working process, this ground wire is both the ground terminal and the negative terminal of the tool electrode. Correspondingly, the positive pole of a 120V DC power supply is connected to the positive pole of the workpiece electrode. By controlling the number of conducting VMOS transistors and the magnitude of the output current, the real-time processing state is determined. This part requires both two-way feedback of voltage and current for real-time adjustment (this part will be described in detail in the subsequent overcurrent protection circuit), and also requires obtaining some corresponding processing conditions under conventional process processing conditions through a series of tests, including the adjustment of the number of conducting transistors and the pulse width and pulse interval of the PWM circuit to ensure reducing errors and adjustment time.

[0047] The overcurrent protection circuit design uses a method of measuring a single-channel current and selecting a voltage-dividing circuit to convert the single-channel current into a voltage value, and uses a voltage comparator to compare the real-time converted voltage with the reliable voltage value under the current working state respectively, and outputs the comparison value to judge and determine whether the system is in a normal working state.

[0048] The difference between the second VMOS transistor and the first VMOS transistor is that the working power of the second VMOS transistor is less than or equal to the power of the first VMOS transistor. Therefore, a second VMOS transistor is selected as a normally open transistor to detect the current at any time. Figure 3As shown, at the drain terminal of the second VMOS transistor Q9, different from the conventional way of directly grounding the VMOS transistor, a 2K ceramic cement resistor R7 is used to ground, and a voltage dividing circuit is derived between the two. In this voltage dividing circuit, an external 15V power supply is used, and the voltage is kept constant through the double voltage stabilization of capacitor C5 and 4.7V diode D1.

[0049] The model of the voltage comparator is LM393. It has a small input voltage offset, which plays an important role in precise control. At the same time, it has a small current consumption. As a normally open component, it has a good energy-saving effect.

[0050] As Figure 4 shown, the IN-_1 interface of the voltage comparator U3 is connected to Figure 3 the output voltage OUT from the voltage dividing circuit in . The ideal output voltage OUT is 0.83V. However, affected by the working current, in different working states, the actual output voltage will change even in the normal working state. Therefore, the input voltage of the voltage comparator also changes with the change of the working state.

[0051] In the current conventional circuit design, the IN+_1 interface of the voltage comparator U3 is generally connected in a way of five parallel resistors with different resistance values. By controlling whether different resistors are connected to the circuit, 2^5 = 32 different states can be obtained. This circuit design can control and solve most overcurrent problems to a certain extent, but there are still loopholes in improving the processing accuracy. In some cases, it is necessary to wait for the judgment of the gap voltage detection circuit to implement software locking, which increases the response time and the danger caused by overcurrent.

[0052] It should be emphasized that the IN+_1 interface of the voltage comparator U3 in this embodiment is connected to the PWM signal of the single-chip microcomputer. Among them, a voltage stabilizing and filtering circuit composed of resistor R8, resistor R9, resistor R10, capacitor C6, capacitor C7, and capacitor C8 is also set between the IN+_1 interface of the voltage comparator U3 and the PWM signal of the single-chip microcomputer to ensure a stable voltage value for the IN+_1 interface. Since this voltage value is generated by the PWM signal sent by the single-chip microcomputer, the waveform of this PWM pulse can be accurately adjusted according to the current processing pulse width, pulse interval, number of VMOS connections, etc. In theory, any voltage within the adjustable voltage range can be obtained, thus realizing the extension of voltage comparison from stepwise comparison to stepless comparison.

[0053] Combined with Figure 2 and Figure 4As shown in the figure, the overcurrent signal LM393_OUT output by the overcurrent protection circuit is connected to the ENBL interface of the MOSFET driver for efficient hardware locking. When the voltage at the IN+_1 interface of the voltage comparator U3 is greater than that at the IN-_1 interface, the output is high level, indicating that the circuit is working normally and ENBL is not locked. When the system is overcurrent, the voltage at the IN+_1 interface of the voltage comparator U3 is less than or equal to that at the IN-_1 interface. At this time, the output of the voltage comparator is low level, and ENBL is locked with low level being effective. All PWM signal inputs are locked and cannot be transmitted to the VMOS tube. Except for the switching circuit of one second VMOS tube in the normally open state, the switching circuits of the remaining VMOS tubes are all turned off, and the circuit stops working quickly, fully playing the role of circuit protection.

[0054] This power supply circuit also includes a gap voltage detection circuit. The gap voltage detection circuit is used to detect the gap voltage between the tool and the workpiece and feedback it to the single-chip microcomputer. The single-chip microcomputer judges the gap state according to the gap voltage and feedbacks it to the host computer. The host computer outputs a control signal according to the gap state to adjust the gap voltage.

[0055] In this embodiment, the core measurement feedback device of the gap voltage detection circuit of the synchronous voltage frequency converter is adopted. The synchronous voltage frequency converter can convert the analog voltage quantity into a pulse frequency, and the generated pulse frequency is proportional to the input voltage value. The synchronous voltage frequency converter in this embodiment adopts the AD7740 analog-to-digital converter.

[0056] As Figure 5 shown in the figure, the VIN interface of the synchronous voltage frequency converter U5 is connected to the tool electrode through the voltage division of the carbon film resistor R17 and the voltage stabilization of the Schottky diode D7, capacitor C25 and resistor R20. The workpiece electrode is connected to a fixed 120V, so no measurement needs to be connected.

[0057] The CLKIN clock signal of the synchronous voltage frequency converter U5 is provided by an external crystal oscillator circuit including the crystal oscillator X1 and two load capacitors C28 and C29. The output end FOUT changes the output voltage through the optocoupler U6 to transmit the GAPCLK signal to the single-chip microcomputer. Under the control of the input signal CLKIN clock, the voltage value transmitted by the GAP CLK signal forms a PWM signal and is fed back to the STM32 single-chip microcomputer. After receiving the PWM signal, the single-chip microcomputer identifies the voltage value and judges the current gap state. When the gap state is abnormal, the corresponding information is transmitted to the host computer to control the stepping motor to adjust the gap size. When the gap voltage is too small, it means partial short circuit and the gap needs to be increased. When the gap voltage is too large, it means partial open circuit and the stepping motor needs to be controlled to reduce the gap.

[0058] As the application part of the pulse power supply circuit, the multiplexed PWM pulse generation and the coordination function between multiple timers in the timer module of the STM32 single-chip microcomputer, the information interaction function with the host computer, the key interrupt scanning function, and the digital tube and LED display function are mainly applied in this design.

[0059] In this embodiment, 7 groups of 14 keys are set on the control board of the single-chip microcomputer. Their main functions are all for adjusting the digital size. Each group of keys is divided into an upper key and a lower key. Correspondingly, there are 12 one-digit 8-segment digital tubes for controlling digital display. At the same time, in order to realize the information interaction between the STM32 single-chip microcomputer and the host computer, multiple groups of optocouplers are adopted, and their model is selected as PC817, which realizes the signal conversion and transmission when the power supply voltages at both ends of the PC and the STM32 single-chip microcomputer are different. At the same time, multiple LED indicators for displaying the gap state adjustment are designed on the single-chip microcomputer board, which are mainly used to show the current working state and express the instructions of the host computer, and can also be used for manual operation when a work failure is found.

[0060] To sum up, one end of the 120V working voltage is connected to multiple VMOS tubes. Multiple VMOS tubes are used as switching tubes to control the on and off of multiple paths. The output currents of multiple VMOS tubes are gathered together and connected to the tool electrode as the negative electrode, so as to control the different currents flowing into the tool. The other end of the 120V working voltage is connected to the workpiece electrode as the positive electrode. As the number of controlled conduction of the VMOS tubes changes, the output current also changes, so as to realize different processing efficiencies and the control of roughing and finishing. The on and off of the VMOS tubes are controlled by the PWM pulse signal generated by the STM32 single-chip microcomputer. When the PWM pulse signal output is at a high level, the VMOS is turned on. When there is no PWM pulse or the pulse output is at a low level in this path, there is no current in this circuit. At the same time, a gap voltage detection circuit and an overcurrent protection circuit are provided in the circuit to ensure the high efficiency of processing. The overcurrent protection circuit focuses on protecting the circuit and adopts the method of hardware locking; the gap voltage detection circuit focuses on the adjustment of the gap to ensure that the processing has a stable and reliable working efficiency. At the same time, it has the function of assisting in locking and unlocking the hardware. The STM32 single-chip microcomputer module also realizes the functions of the control part such as reading data by keys, status display, and information interaction with the PC.

[0061] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0062] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected", "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0063] The above is only the preferred embodiment of the present invention. It should be pointed out that for those of ordinary skill in the art of this technology, without departing from the technical principle of the present invention, several improvements and modifications can still be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A wire cutting pulse power supply circuit, characterized in that It includes a working voltage input terminal, a host computer, a single-chip microcomputer, a tool, a workpiece, a switching circuit, and an overcurrent protection circuit. The switching circuit includes a VMOS transistor and a MOSFET driver; The single-chip microcomputer is connected to the host computer, and the PWM signal terminal of the single-chip microcomputer is connected to the MOSFET driver; One path of the working voltage input terminal is connected to the VMOS transistor, and the other path is connected to the workpiece electrode; The MOSFET driver is connected to the VMOS transistor, and the VMOS transistor is connected to the tool electrode; The input terminal of the overcurrent protection circuit is connected to the VMOS transistor, and the output terminal is connected to the MOSFET driver; The overcurrent protection circuit includes a voltage dividing circuit and a voltage comparator. The VMOS transistor includes a first VMOS transistor and a second VMOS transistor; The gate terminals of the first VMOS transistor and / or the second VMOS transistor are connected to a signal output terminal of the MOSFET driver. The source terminals are respectively connected in parallel to the working voltage input terminal and a diode, and the drain terminals are connected to the tool electrode; Among them, a voltage dividing circuit is led out from the circuit where the drain terminal of the second VMOS transistor is connected to the tool electrode and connected to an input terminal of the voltage comparator. The single-chip microcomputer is connected to the other input terminal of the voltage comparator; the output terminal of the voltage comparator is connected to the MOSFET driver.

2. The wire cutting pulse power supply circuit according to claim 1, characterized in that, The working power of the second VMOS transistor is less than or equal to the working power of the first VMOS transistor.

3. The wire cutting pulse power supply circuit according to claim 1, characterized in that, Two resistors are also connected in parallel to the circuit between the source terminals of the first VMOS transistor and / or the second VMOS transistor and the working voltage input terminal. Among them, one resistor is a heat dissipation resistor, and the other resistor is a current limiting resistor.

4. The wire cutting pulse power supply circuit according to claim 1, characterized in that, It also includes a gap voltage detection circuit, The gap voltage detection circuit is used to detect the gap voltage between the tool and the workpiece and feedback it to the single-chip microcomputer; The single-chip microcomputer judges the gap state according to the gap voltage and feedbacks it to the host computer; The host computer outputs a control signal to adjust the gap voltage according to the gap state.

5. The wire cutting pulse power supply circuit according to claim 4, characterized in that, The gap voltage detection circuit includes a synchronous voltage frequency converter. The input terminal of the synchronous voltage frequency converter is connected to the tool electrode through a voltage stabilizing circuit, and the output terminal is connected to the single-chip microcomputer.

6. The wire cutting pulse power supply circuit according to claim 4, characterized in that, An LED display lamp for displaying the adjustment of the gap state is also provided on the single-chip microcomputer.

7. The wire cutting pulse power supply circuit according to claim 1, characterized in that The single-chip microcomputer is connected to the host computer through an optocoupler.

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