With the continuous development of ultrasonic technology, ultrasonic waves are widely used in detection, cleaning, welding, medical and other fields, even in textile and aerospace sectors. At present, ultrasound research and application can be divided into two major fields of power ultrasound and detect ultrasound, and ultrasound cleaning is one of the most widely used applications. It converts the acoustic energy of the power ultrasound into mechanical vibration through a transducer, while the strong ultrasonic wave generates "cavitation effect" when the liquid propagates. The impact wave emitted when the airborne bubbles suddenly closed, there is a thousand atmospheric pressure around it, and the direct repeated impact of the stained layer is destroyed from the surface of the dirt and the surface of the cleaning member, and the other hand can also cause a dirt layer. The destruction is detached from the surface of the cleaning member and disperses them into the cleaning liquid to remove impurities, dirt or greasy of the surface of the object. Compared with other cleaning, ultrasonic cleaning has a high efficiency, low energy consumption, clean and environmentally friendly, especially when cleaning complex parts, blind holes, and slit more, more highlights its advantages.
1 ultrasonic cleaning machine overall scheme design
The ultrasonic cleaning machine designed in the text is the control core, including rectifier filtering, inverting, IGBT driver, PWM occurrence and control, frequency scanning display, power adjustment, tuning matching, and impedance matching module, and related protection modules.
Figure 1 Bright block diagram of ultrasonic cleaning machine
In the ultrasonic cleaning machine, the 220 V50 Hz mains are divided into two roads, all the way to generate high-power ultrasonic waves, and the other is used to detect, control and display the power supply, as shown in Figure 1. Among them, the power of the cleaning machine can be controlled by two-way thyristor. The inverter module is a half-bridge inverter, and the DC voltage is inverted into a high frequency AC voltage, and then the tuning matching and the transformer of the impedance matching module, the inductance matching can be high efficient and maximum power to the piezoelectric transducer. . Finally, the piezoelectric transducer converts the electrical energy output from the ultrasonic power source into high frequency mechanical vibration.
2 Ultrasonic cleaning machine each module design principle
2.1 Rectifier Filtering and Power Adjustment Module
The 220 V50 Hz AC is rectified by the rectifier bridge B1 rectification and the electrolytic capacitor C12 filtering generates a DC output voltage. The two-way thyristor TR1 is used for power adjustment, and C11 is a conventional capacitor, R11 and C11 are mainly used to eliminate high frequency interference. The U1 is optically coupled, and the model can select the MOC3021, 1 pin and 3 foot connector module. The optocoupler U1 functions to isolate strong weak electricity, enhancing the reliability and safety of the circuit.
Figure 2 Rectifier filter module
During the operation of the ultrasonic power system, the rectifier filter module and the inverter module will heat it, and the two modules can be mounted on an aluminum tab, and the wind is cold. In this way, the system can work safer and reliably.
2.2 Inverter and Pulse Drive Module
Since the power devices used in the half-bridge inverter circuit are less cost, the ultrasonic cleaning machine designed in this paper is used in a half-bridge inverter circuit.
Figure 3 Half-bridge inverter module
In the half-bridge inverter circuit, the two full-control type switching devices are IGBT, ie Q1 and Q2 and diodes D11 and D12 constitute a half bridge inversion, a signal that is complementary on Q1 and Q2, O1 and Q2 two IGBT are turns Trigger, that is, each alternate is turned on. At the same time, the capacitors C1 and C2 on the DC side input should be large enough, and C1 = C2, the value value is optionally 2μF. Similarly, the resistor R14, R15 should also be large enough, and R14 = R15, the resistance is optionally 100 kΩ or more. The fuses F11 and F12 are used to protect the switches Q1 and Q2 to prevent the current from being too large.
Transformers T1 and resistors R16, R17, R18, R19 constitute a pulse drive module, providing complementary trigger signals for Q1 and Q2. Since the drive voltage of the IGBT should be less than 20 V, the input voltage between T12, T14 is about 12 V, so the transformer T1 is designed to be 1: 1.r18, R19 is used for limited flow, optional 20 Ω. Electrical resistance. In this ultrasonic cleaning machine, the upper and lower IGBT devices have a certain dead time to prevent both the two.
2.3 Transformer and linear regulation
The 220 V50 Hz AC is converted to 12 V by the transformer T4, and then the 12 V DC voltage is output, and the 12 V DC voltage is output, and the PWM is powered by the control module. At the same time, the DC 12 V is converted to 5 V by the U2 (L7805) twice, providing a power supply for the processor IAP15F2K61S2. LED1 light emitting diode, power source indication. In order to reduce the pulsation coefficient of the voltage, the capacitance C43 and C44 are added multiplexed.
Figure 4 Switch and linear regulation
2.4 PWM Action and Control Module and Drive Module
In the ultrasonic cleaning machine, the Ka3525A is used as the PWM and the control chip. As shown in FIG. 5, the KA3525A oscillation frequency sets the set range of 20 to 40 kHz, and one resistor Rd in series between the foot 5 and the foot 7 of the chip can be adjusted within a larger range. The oscillation frequency of Ka3525A can be expressed as:
Where: CT, RT is the capacitance and resistance of the oscillator connected to the foot 5, the foot 6; the RD is a discharge end resistor connected to the foot 7. Here: RD, CT, RT are R52, C5, (R51 + RP51) in the figure, respectively. Among them, RP51 is a precision adjustable resistor, that is, the PWM output frequency can be adjusted by R1 and R2. The pin 8 picks up a capacitor C51 to be soft start, reducing the power switch tube boot impact. 11 and 14 pin output two complementary PWM waves, the secondary power of the triodes Q1, Q2, Q3, Q4 amplified, and then drive two IGBTs by pulse driving transformer T1, control the inverter module to realize the half bridge inversion (as shown in Figure 3) Indicated). The high frequency transformer T1 is separated from the effect of strong and weak electricity, enhancing the reliability of driving capacity and power supply.
Figure 5 PWM occurrence and control module
2.5 Power Adjustment Module
The principle of power adjustment: The voltage size of the power resistor is detected by an AD port of the Iap15F2K61S2 single-chip microcomputer, and then the AD value is obtained by analog to digital conversion. According to this value, the two-way thyristor TR1 is controlled to control the output power by controlling the phase of the trigger pulse. Among them, Figure 6 is a schematic diagram of a zero-zero trigger, 12 V AC electrodes Diode D31, D32 rectification, and R31, R32, R33 current limiting voltage, and then detects zero points via the triode Q3. When the grid voltage is zero, P3.3 produces a negative pulse. In addition, the P3.3 port of the IAP15F2K61S2 single-chip microcomputer is an external interrupt opening by detecting a zero pulse to obtain an extension of the power frequency voltage.
Figure 6 Schematic diagram of the zero-zero trigation
2.6 Tuning matching and impedance matching module
The matching of ultrasonic power supply and transducer is mainly tuned matching and impedance matching. In the tuning match, in order to reduce the reactive loss generated by electrostatic resistance, the maximum power of the piezoelectric transducer is output, and the transducer is needed to approximate the pure resistance state, and the ultrasonic power supply output efficiency is improved. Further, when the tuning match is completed, ie the load is a pure resistance state, in order to make the power supply output maximum power, the optimum output impedance of the actual load and the power supply needs to be achieved: the transducer is achieved by the high frequency transformer The impedance transform is the optimal output impedance of the ultrasonic power supply, thereby outputting the maximum power of the piezoelectric transducer.
Figure 7 shows the ultrasonic cleaning machine tuning match match and impedance matching module. Wherein, an equivalent circuit diagram of a piezoelectric transducer is used in the dashed frame.
Figure 7 Tuning matching and impedance matching
Among them, CO is a static capacitor of the piezoelectric transducer, mainly by the capacitance generated by the clamping, which is a real electrical amount; RO is the dielectric loss resistance of the piezoelectric transducer, which is generally considered to be infinite, usually Ignore; LD, CD, and RD are dynamic inductors, dynamic capacitances and dynamic resistors of piezoelectric transducer, respectively. When the LD, the CD is in harmonics, the series branch is pure resistance. Under a series of electrosphorized tuning matches, the entire load of the ultrasonic power supply exhibits pure resistance. When the output voltage of the power supply is stable, the power obtained by the resistive load is only related to the resistance of the load, so the high-frequency transformer is required to perform impedance transformation, so that the ultrasonic power supply can be output in maximum power.
3 Conclusion
According to the actual demand, the SMS model IAP15F2K61S2 is used as a control core, and the overall design plan of the ultrasonic cleaning machine system is proposed. According to the design, software, hardware design and debugging, ensuring that its operating frequency is continuously adjustable within 20 to 50 kHz, and the dead time is stable, so that the ultrasonic power supply can produce large after matching the ultrasonic power supply and the piezoelectric transducer. Ultrasonic wave of power. Finally, an ultrasonic cleaning machine with transfer, FM, and timing functions is produced. Through the field test, the ultrasonic power system can operate stably for a long time.
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Source: Wiku Electronic Market Network
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