A frequency tracking method for an ultrasonic transmitter

Abstract

This invention relates to a frequency tracking method for an ultrasonic transmitter, comprising the following steps: data acquisition, real-time synchronous acquisition of three signals: primary current, secondary current, and secondary voltage of a transformer; for each acquisition cycle, the acquired data is placed into the peripheral integrated control law accelerator coprocessor built into the main chip for Fourier transform, flipping the real and imaginary parts of the complex number, performing bit inversion, decompressing, and then performing Fast Fourier Transform (FFT) calculation to obtain the true Fourier series; the acquired waveform is reconstructed in the software to complete phase establishment; acquiring parameters such as amplitude, phase, phase difference between primary and secondary currents, phase difference between secondary voltage and current, phase difference between primary and secondary current and voltage, voltage, current, power, impedance, and frequency; frequency tracking is performed by sampling the target impedance; real-time sampling results in more timely signal feedback, improving the speed and accuracy of frequency tracking, ensuring operation within the working range, reducing the risk of oscillator damage, and lowering costs and risks.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic frequency tracking technology, and more particularly to a frequency tracking method for an ultrasonic transmitter. Background Technology

[0002] Existing ultrasonic welding machines consist of an ultrasonic generator, transducer, amplitude transformer, and welding head. The combination of the transducer, amplitude transformer, and welding head is called the "oscillator." During the welding process, due to factors such as welding load, oscillator temperature, energy loss, welding area, and welding head wear, the impedance characteristics of the entire oscillator will change with the operation, thereby altering the oscillator's natural operating frequency and operating frequency range.

[0003] If the frequency of the inverter trigger pulse in the generator does not follow the change, it will cause the oscillator to become detuned, reduce working efficiency, and aggravate transducer losses. Therefore, the generator must have a frequency tracking function and ensure that the frequency of the inverter trigger pulse in the ultrasonic generator is within the working frequency range of the oscillator. The working principle of the existing frequency tracking technology is as follows: the electrical signal passing through the primary and secondary windings of the transformer is sampled at regular intervals, and the current phase difference, current, voltage, current working frequency, and other information are calculated. The current frequency is compared with the target frequency to be tracked. If they are inconsistent, the inverter in the generator is controlled to change the frequency of the trigger pulse. The frequency tracking point types are tracking the resonant frequency, tracking the anti-resonant frequency, and tracking the specified phase difference frequency (maximum, minimum, 0 phase). Summary of the Invention

[0004] The purpose of this invention is to provide a frequency tracking method for ultrasonic transmitters, which enables real-time sampling, more timely signal feedback, improved frequency tracking speed and accuracy, and enhanced welding effect and speed. Moreover, the frequency tracking is performed by sampling the target impedance, ensuring that the transmitter always operates within the working range, reducing the risk of damaging the oscillator, lowering costs and risks, and providing strong compatibility with the oscillator, making it more compatible with the oscillator system and eliminating the need for specific transducers to operate.

[0005] To achieve the above objectives, the sampling technical solution of the present invention is: a frequency tracking method for an ultrasonic transmitter, comprising the following steps:

[0006] Step 1: Data Acquisition. Real-time synchronous acquisition of three signals: primary current, secondary current, and secondary voltage of the transformer.

[0007] Step 2: Phase establishment. For each acquisition cycle, the acquired data is placed into the main chip's built-in peripheral - the integrated control law accelerator coprocessor (CLA) - to perform Fourier transform, flip the real and imaginary parts of the complex number, perform bit inversion, decompress, and then perform Fast Fourier Transform (FFT) calculation to obtain the true Fourier series. The acquired waveform is then restored in the software to complete phase establishment.

[0008] Step 3: Obtain the parameters: ① Amplitude: Amplitude = 2 * sqrt((maximum value in the period^2) + (minimum value in the period^2)). Input the FFT calculation results of the primary current, secondary current, and secondary voltage signals to obtain the amplitude of the corresponding signals; ② Phase: atan2(maximum value in the period, minimum value in the period) * 180 / π; ③ Primary and secondary current phase difference: Primary current phase - Secondary current phase; ④ Secondary voltage and current phase difference: Secondary voltage phase - Secondary current phase; ⑤ Primary and secondary current and voltage phase difference: Secondary voltage phase - Primary current phase; ⑥ Voltage = Secondary voltage amplitude * Voltage correction coefficient; ⑦ Current = Secondary current amplitude * Current correction coefficient; ⑧ Power = Voltage * Current * Power correction coefficient * cos(secondary current and voltage phase difference * π / 180); ⑨ Impedance = Voltage / Current * Impedance correction coefficient; ⑩ Frequency = 1 / Time for the current to complete one cycle of transformation;

[0009] Step 4: Frequency tracking, which involves sampling to track the target impedance.

[0010] Preferably, the frequency tracking method in step four, which tracks the target impedance, falls into the following two cases: ① When the impedance is ≥ target impedance * 3, track the frequency when the phase difference between the secondary current and voltage is 0: obtain the current phase difference and current frequency in real time; if the phase difference is ≠ 0, decrease the frequency; ② When the phase difference between the secondary current and voltage is 0 or the impedance is < target impedance * 3, track the target impedance frequency; if the current impedance is < target impedance, increase the frequency; if the current impedance is > target impedance, decrease the frequency.

[0011] Preferably, the frequency change value for each frequency tracking step is: first, set the PID coefficient, and then obtain the change value according to the PID algorithm. The PID algorithm is a packaged function provided by the main chip for users to call directly.

[0012] Preferably, the main chip has a built-in peripheral analog-to-digital converter (ADC) that synchronously acquires three signals: primary current, secondary current, and secondary voltage of the transformer in real time.

[0013] Preferably, the minimum and maximum impedances under load are obtained using an impedance analyzer, and the target impedance is set between the minimum and maximum impedances.

[0014] Preferably, the voltage correction factor is 1.493, the current correction factor is 0.019, the power correction factor is 1, and the impedance correction factor is 1.

[0015] The beneficial effects of this invention are as follows:

[0016] 1. Advantages of synchronous sampling: The signal feedback is more timely, improving the speed and accuracy of frequency tracking, thus enhancing the welding effect and welding speed; the safety is higher, with faster detection and processing of abnormal signals, thereby better protecting the oscillator, generator and personnel.

[0017] 2. Advantages of Fourier phase-building: The analog signal is more accurate, improving the accuracy of frequency tracking. Combined with synchronous sampling, the frequency fluctuation range can be reduced to within 5Hz (around 20Hz for Hermann in Germany); it improves welding effect and welding speed. Even when the signal is partially distorted due to possible interference, it can still complete phase building normally and continue frequency tracking, making it more adaptable.

[0018] 3. Advantages of tracking target impedance:

[0019] The disadvantages of existing technologies for tracking other frequencies: Tracking the resonant point: The frequency during tracking will actually fluctuate within a small range around the target frequency. The impedance at the resonant point is low, and the current is large. If it fluctuates to the forbidden zone below the resonant point, it is easy to damage the oscillator. Tracking the anti-resonant point: The impedance is high and the voltage is large. The transducer is prone to overheating during operation and is easily damaged during continuous welding. The requirements for the transducer are even higher. Tracking the target phase point: It requires the transducer to work with the generator. The target phase must be present during operation. In fact, when testing the original generator from Hermann in Germany with the original transducer, alarms still frequently occurred during welding, and the target phase could not be found.

[0020] The target impedance always operates within the working range, reducing the risk of oscillator damage and lowering costs and risks. It has strong compatibility with oscillators, making it more compatible with oscillator systems and eliminating the need for specific transducers. Heat generation is improved, and continuous welding increases work efficiency. It is simple and easy to use; only one parameter, the target impedance, needs to be adjusted to achieve the best welding results. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating a frequency tracking method for an ultrasonic transmitter.

[0022] Figure 2 This is a schematic diagram of a frequency tracking circuit module used in a frequency tracking method for an ultrasonic transmitter.

[0023] Figure 3 This is a schematic diagram of the transducer drive circuit after being connected to the sampling circuit.

[0024] Figure 4 This is a schematic diagram of the transformer primary current sampling circuit.

[0025] Figure 5 This is a schematic diagram of a transformer voltage sampling circuit.

[0026] Figure 6 This is a schematic diagram of the sampling circuit feedback circuit.

[0027] Figure 7 The schematic diagram is for a single OPA2197IDR operational amplifier. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings. The description in this part is only exemplary and explanatory, and should not be used to limit the scope of protection of the present invention in any way.

[0029] like Figure 1 As shown, this application discloses a frequency tracking method for an ultrasonic transmitter, comprising the following steps:

[0030] Step 1: Data Acquisition. The main chip's built-in peripheral analog-to-digital converter (ADC) acquires the transformer's primary current, secondary current, and secondary voltage signals in real time.

[0031] Step 2: Phase establishment. For each acquisition cycle, the acquired data is placed into the main chip's built-in peripheral - the integrated control law accelerator coprocessor (CLA) - to perform Fourier transform, flip the real and imaginary parts of the complex number, perform bit inversion, decompress, and then perform Fast Fourier Transform (FFT) calculation to obtain the true Fourier series. The acquired waveform is then restored in the software to complete phase establishment.

[0032] Step 3: Obtain the parameters: ① Amplitude: Amplitude = 2 * sqrt((maximum value in the period^2) + (minimum value in the period^2)). Input the FFT calculation results of the primary current, secondary current, and secondary voltage signals to obtain the amplitude of each signal; ② Phase: atan2(maximum value in the period, minimum value in the period) * 180 / π; ③ Primary and secondary current phase difference: Primary current phase - Secondary current phase; ④ Secondary voltage and current phase difference: Secondary voltage phase. - Secondary current phase; ⑤ Primary and secondary current voltage phase difference: secondary voltage phase - primary current phase; ⑥ Voltage = secondary voltage amplitude * voltage correction coefficient (1.493); ⑦ Current = secondary current amplitude * current correction coefficient (0.019); ⑧ Power = voltage * current * power correction coefficient (1H * cos(secondary current voltage phase difference * π / 180); ⑨ Impedance = voltage / current * impedance correction coefficient (1); ⑩ Frequency = 1 / time for current to complete one cycle of transformation;

[0033] Step 4: Frequency Tracking. Frequency tracking is performed by sampling and tracking the target impedance. The lowest and highest impedances under load are obtained using an impedance analyzer. The target impedance is set between the lowest and highest impedances. Frequency tracking by tracking the target impedance has the following two cases: ① When the impedance is ≥ target impedance * 3, track the frequency when the secondary current-voltage phase difference = 0: obtain the current phase difference and current frequency in real time. If the phase difference ≠ 0, subtract the frequency; ② When the secondary current-voltage phase difference = 0 or the impedance is < target impedance * 3, track the target impedance frequency. If the current impedance is < target impedance, increase the frequency; if the current impedance is > target impedance, decrease the frequency. The frequency change value for each step of frequency tracking is: first set the PID coefficient, and then obtain the change value according to the PID algorithm. The PID algorithm is a packaged function provided in the main chip for users to call directly.

[0034] The frequency tracking method for an ultrasonic transmitter disclosed in this application employs a frequency tracking circuit module comprising a full-bridge inverter circuit and four driver chips for adjusting the pulse frequency of the full-bridge inverter circuit. The full-bridge inverter circuit is connected to a transformer via a DC blocking capacitor, an inductor, and a capacitor. The transformer drives a transducer via a matching inductor. The transformer is equipped with a primary current sampling circuit, a secondary circuit sampling circuit, and a voltage sampling circuit. The current and voltage information sampled by these circuits is fed back to the main chip (MUC). The main chip calculates the frequency tracking information based on the feedback current and voltage information and then transmits it via P... The WM drive signal circuit outputs four PWM signals to control four drive chips. It also includes a power supply circuit, which receives AC380V and AC220V input voltages. The AC380V voltage is filtered by the EMI circuit and rectified by the rectifier bridge to output DC580V, powering the full-bridge inverter circuit. The AC220V voltage is converted by an alternating current circuit to output DC 24V and ±DC 6.5V. The 24V DC voltage powers the four drive chips, and the ±DC 6.5V powers the MUC. The 24V DC voltage is converted into ±isolated power supplies to power the four drive chips, and the ±DC 6.5V voltage is converted by a frequency converter circuit to output 3V. The transformer primary current sampling circuit supplies power to the MUC. It includes a current transformer (CT) connected to the circuit and resistors R1, R3, and R5 connected in parallel to the two output terminals of the CT for current shunting. Resistor R1 has a resistance of 33 ohms, resistor R3 has a resistance of 390 ohms, and resistor R5 has a resistance of 1 kΩ. The tolerance of resistors R1, R3, and R5 is 1%. The transformer voltage sampling circuit includes sampling wires connected to the two output terminals of the transformer. Resistors for voltage division are connected in series on these sampling wires, and resistors for current shunting are connected in parallel. The voltage division resistors include resistors R7, R8, R9, R10, R11, R12, R13, R14, and R5 connected in series. R15 and R16 both have a resistance of 18 kΩ and a tolerance of 1%. The shunt resistors include parallel resistors R17, R18, and R19. R17 has a resistance of 1500 Ω, R18 has a resistance of 390 Ω, and R19 has a resistance of 33 Ω. The tolerance of R17, R18, and R19 is 1%. The current and voltage information sampled by the transformer primary current sampling circuit, the transformer secondary circuit sampling circuit, and the transformer voltage sampling circuit are fed back to the main chip MUC after passing through the sampling circuit feedback circuit. The sampling circuit feedback circuit consists of two OPA2197IDR operational amplifiers, with a capacitor placed between the two OPA2197IDR operational amplifiers.

[0035] In practice, the frequency tracking circuit module of this application consists of three circuit boards. The first board is the driver board, which includes a power supply circuit, a full-bridge inverter circuit, and a driver chip drive circuit. The second board is the core board, which includes a MUC and a PWM drive signal circuit. The third board is the power board, which includes a DC blocking capacitor, an inductor, a capacitor, a transformer, a matching inductor, a transducer, a primary current sampling circuit, a transformer secondary circuit sampling circuit, and a transformer voltage sampling circuit. All three circuit boards are interconnected through terminals.

[0036] The frequency tracking method combined with the frequency tracking circuit module is as follows: The AC380V input voltage of the power supply circuit is filtered by the EMI circuit and rectified by the rectifier bridge to output DC580V voltage to power the full-bridge inverter circuit. The full-bridge inverter circuit sends pulses that pass through the DC blocking capacitor, inductor, capacitor, transformer, and matching inductor to drive the transducer. This is the normal operation of the generator and transducer. During operation, the AC220V input voltage of the power supply circuit is converted into 24V DC voltage to form four isolated power supplies to power the four driver chips respectively. The AC220V input voltage of the power supply circuit is also converted into ±DC6.5V, and after passing through the frequency conversion circuit, it forms a 3V power supply to power the main chip MUC. The current and voltage information sampled by the transformer primary current sampling circuit, transformer secondary circuit sampling circuit, and transformer voltage sampling circuit are first amplified by two OPA2197IDR operational amplifiers before being transmitted to the main chip MUC. For each sampling cycle, the data is placed in the main chip's built-in peripheral - integrated control law accelerator coprocessor (Control Law). The Accelerator (CLA) performs a Fourier transform, flipping the real and imaginary parts of the complex number, then performing a bit inversion, decompressing it, and performing a Fast Fourier Transform (FFT) to obtain the true Fourier series. The acquired waveform is then reconstructed in software to complete phase reconstruction. The principle is based on the property of Fourier series: any periodic function can be represented by an infinite series of sine and cosine functions. The main chip encapsulates the FFT processing function for direct user access. Then, the following key parameter is calculated: ① Amplitude: Amplitude = 2 * sqrt((maximum value in the period^2) + (minimum value in the period^2)). By inputting the FFT calculation results of the primary current, secondary current, and secondary voltage signals, the amplitude of the corresponding signals can be obtained.

[0037] ② Phase: atan2(maximum value in the period, minimum value in the period)*180 / π.

[0038] ③ Primary and secondary current phase difference: primary current phase - secondary current phase.

[0039] ④ Secondary voltage and current phase difference: Secondary voltage phase - Secondary current phase.

[0040] ⑤ Phase difference between primary and secondary current and voltage: secondary voltage phase - primary current phase.

[0041] ⑥ Voltage = Secondary voltage amplitude * Voltage correction factor (1.493).

[0042] ⑦ Current = Secondary current amplitude * Current correction factor (0.019).

[0043] ⑧ Power = Voltage * Current * Power Correction Factor (1) * cos(Secondary Current-Voltage Phase Difference * π / 180)

[0044] ⑨ Impedance = Voltage / Current * Impedance Correction Factor (1)

[0045] ⑩ Frequency = 1 / Time for the current to complete one cycle

[0046] Note: The parameters above are calculated immediately after each data acquisition cycle, i.e., sampling, phase construction, and calculation are performed synchronously in real time.

[0047] After obtaining the above key parameters, frequency tracking can be performed, starting from the anti-resonance frequency and proceeding downwards. The entire process is divided into two parts:

[0048] ① When the impedance is greater than or equal to the target impedance * 3, track the frequency at which the phase difference between the secondary current and voltage is 0: obtain the current phase difference and current frequency in real time. If the phase difference is not equal to 0, subtract the frequency. This is determined by the oscillator characteristics, so first track the 0 phase to ensure that the frequency is tracked downwards, operating within the frequency range (i.e., the working bandwidth) between the resonant point and the anti-resonant point. Obtain the minimum and maximum impedance under load using an impedance analyzer. The target impedance is set between the minimum and maximum impedances. The specific value required for good soldering can be adjusted. The higher the setting, the closer to the anti-resonant point, and the lower the setting, the closer to the resonant point.

[0049] ② When the phase difference between the secondary current and voltage is 0 or the impedance is less than 3 times the target impedance, the frequency is tracked to the target impedance. When the current impedance is less than the target impedance, the frequency is increased; when the current impedance is greater than the target impedance, the frequency is decreased; until the welding is completed, the current impedance is always kept near the target impedance.

[0050] Frequency change value for each step: Set the PID coefficient and derive the change value based on the PID algorithm; the algorithm is a packaged function provided by the main chip for direct user call.

[0051] The phase that needs to be tracked is calculated, and then four PWM signals are emitted through the PWM drive signal circuit. The PWM signals are transmitted to four drive chips to control the four drive chips to adjust the pulse emission phase of the full-bridge inverter circuit, so as to achieve the effect of real-time frequency tracking and ensure that the input frequency of the transducer is always within the normal range.

[0052] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0053] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only for the purpose of helping to understand the method and core ideas of the present invention. The above descriptions are only preferred embodiments of the present invention. It should be noted that due to the limitations of textual expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of the present invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of the present invention.

Claims

1. A frequency tracking method for an ultrasonic transmitter, characterized in that, Includes the following steps: Step 1: Data Acquisition. Real-time synchronous acquisition of three signals: primary current, secondary current, and secondary voltage of the transformer. Step 2: Phase establishment. For each acquisition cycle, the acquired data is placed into the main chip's built-in peripheral - integrated control law accelerator coprocessor - for Fourier transform, flipping the real and imaginary parts of the complex number, then performing bit inversion, decompressing, and performing fast Fourier transform calculation to obtain the true Fourier series. The acquired waveform is then restored in the software to complete phase establishment. Step 3: Obtain the parameters: ① Amplitude: Amplitude = 2 * sqrt((maximum value in the period^2) + (minimum value in the period^2)). Input the FFT calculation results of the primary current, secondary current, and secondary voltage signals to obtain the amplitude of the corresponding signals; ② Phase: atan2(maximum value in the period, minimum value in the period) * 180 / π; ③ Primary-Secondary Current Phase Difference: Primary current phase - Secondary current phase; ④ Secondary Voltage-Current Phase Difference: Secondary voltage phase - Secondary current phase; ⑤ Primary-Secondary Current-Voltage Phase Difference: Secondary voltage phase - Primary current phase; ⑥ Voltage = Secondary voltage amplitude * Voltage correction coefficient; ⑦ Current = Secondary current amplitude * Current correction coefficient; ⑧ Power = Voltage * Current * Power correction coefficient * cos(Secondary current-voltage phase difference * π / 180); ⑨ Impedance = Voltage / Current * Impedance correction coefficient; ⑩ Frequency = 1 / Time for the current to complete one cycle of transformation; Step 4: Frequency tracking. Frequency tracking is performed using the target impedance method, which has the following two cases: ① When the impedance is ≥ target impedance * 3, track the frequency when the secondary current-voltage phase difference is 0: obtain the current phase difference and current frequency in real time. If the phase difference is ≠ 0, decrease the frequency; ② When the secondary current-voltage phase difference is 0 or the impedance is < target impedance * 3, track the target impedance frequency. If the current impedance is < target impedance, increase the frequency; if the current impedance is > target impedance, decrease the frequency.

2. The frequency tracking method for an ultrasonic transmitter according to claim 1, characterized in that, Frequency tracking value for each frequency change: First, set the PID coefficient, and then obtain the change value according to the PID algorithm. The PID algorithm is a packaged function provided by the main chip for users to call directly.

3. The frequency tracking method for an ultrasonic transmitter according to claim 1, characterized in that, The main chip's built-in peripheral analog-to-digital converter can synchronously acquire three signals in real time: primary current, secondary current, and secondary voltage of the transformer.

4. The frequency tracking method for an ultrasonic transmitter according to claim 1, characterized in that, The minimum and maximum impedances under load are obtained using an impedance analyzer, and the target impedance is set between the minimum and maximum impedances.

5. The frequency tracking method for an ultrasonic transmitter according to claim 1, characterized in that, The voltage correction factor is 1.493, the current correction factor is 0.019, the power correction factor is 1, and the impedance correction factor is 1.

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