An ultrasonic frequency tracking amplitude integrated control system with parameter acquisition

Abstract

The application discloses a kind of ultrasonic wave frequency tracking amplitude integrated control system with parameter acquisition, the system includes power drive module, frequency tracking module, amplitude control module, parameter acquisition module and main control module, frequency tracking module adopts two-stage mixed frequency tracking strategy of combination of sweep frequency coarse search and phase closed loop precision follow, and introduces adaptive bandwidth adjustment mechanism, frequency tracking speed and precision are considered, amplitude control module uses DC bus current as feedback, and closed loop control is formed by phase-shifted PWM and digital PID, realizes amplitude stable output, parameter acquisition module synchronously acquires voltage, current, frequency, temperature, pressure and other multi-path process parameters with not less than 200kHz sampling rate, records and stores not less than 100,000 records according to welding beat segmentation, supports data export and real-time upload, the present application solves the technical problems that frequency tracking speed and precision of existing ultrasonic control system are difficult to consider, amplitude lacks real closed loop control and welding process parameters cannot be traced back.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic welding technology, and in particular to an integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition. Background Technology

[0002] Ultrasonic metal welding technology has been widely used in recent years in fields such as welding of electrode tabs for new energy batteries, termination of automotive wiring harnesses, and connection of electronic and electrical contacts. Compared with traditional fusion welding and brazing processes, ultrasonic welding has significant advantages such as no need to add solder, small heat-affected zone, low welding resistance, and no spatter, and is especially suitable for joining highly conductive materials such as copper and aluminum.

[0003] In ultrasonic welding systems, the generator, as the core power unit, directly determines the stability and consistency of welding quality through its control performance. However, in practical applications, two long-standing technical challenges remain unresolved: frequency detuning and the loss of amplitude control and process parameter recording. The generator, as the welding head temperature rises, load changes, and tool head wears down during operation, causes its resonant frequency to drift. Once the driving frequency deviates from the transducer's mechanical resonant point, the output efficiency drops sharply, leading to insufficient welding strength or even damage to the transducer. Furthermore, the loss of amplitude control and process parameter recording means that welding quality depends not only on frequency matching but also directly on amplitude stability. Therefore, a high-precision, bidirectional power flow-adaptive method for calculating theoretical line loss in the welding area is urgently needed. Summary of the Invention

[0004] One objective of this invention is to provide an integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition, comprising a power drive module, a frequency tracking module, an amplitude control module, a parameter acquisition module, and a main control module. Power drive module: Composed of a rectifier and filter unit, a full-bridge inverter unit, and a high-frequency transformer, it is used to convert mains power into a high-frequency AC signal to drive the ultrasonic transducer. The full-bridge inverter unit uses MOSFETs or IGBTs as switching devices, and its control signal is provided by the PWM output channel of the main control module. The output terminal of the power drive module is connected in series with a high-frequency current transformer and a voltage divider sampling circuit, which are used to collect the transducer's operating current and voltage signals, respectively.

[0005] Frequency tracking module: This module is used to achieve real-time automatic tracking of the transducer's resonant frequency. Its core lies in a hybrid frequency tracking strategy: During startup, a frequency sweep method is used to determine the initial resonant point. A DDS generator outputs a drive signal within a certain frequency range in a step-by-step manner, while simultaneously monitoring the feedback current amplitude. The frequency corresponding to the maximum current is recorded as the initial resonant frequency and stored in non-volatile memory. After entering the steady-state operating phase, it switches to a phase-locked loop tracking mode. Based on the phase-locked loop principle, the phase difference between the drive voltage and the feedback current is compared. A PI regulator dynamically adjusts the drive frequency to bring the phase difference close to zero (i.e., voltage and current are in phase). At this point, the drive frequency is consistent with the transducer's mechanical resonant frequency. Unlike traditional PLL schemes, this invention introduces an adaptive bandwidth adjustment mechanism in the phase loop—when the detected frequency change rate exceeds a set threshold, the loop bandwidth is automatically increased to accelerate the tracking response; when the frequency stabilizes, the loop bandwidth is narrowed to improve steady-state accuracy and anti-interference capability.

[0006] Amplitude control module: This is used to achieve closed-loop stable control of the output amplitude of the welding head end face. The indirect feedback of the amplitude is taken from the DC bus current of the power drive module—the bus current and the mechanical amplitude output by the transducer have a monotonically positive correlation within a certain range. The amplitude control module compares the real-time collected bus current value with the preset target current value (corresponding to the target amplitude) in the process parameter table. The deviation is calculated by digital PID and outputs an adjustment amount, which controls the effective duty cycle of the full-bridge inverter through phase-shifted PWM, thereby adjusting the output power. When the load changes and causes the amplitude to decrease, the bus current decreases, and the PID regulator automatically increases the duty cycle to compensate for the power; conversely, the amplitude increases. In addition, the amplitude control module also has a segmented gain adjustment function—using a higher gain in the small deviation range for fast response, and appropriately reducing the gain in the large deviation range to prevent overshoot and oscillation.

[0007] Parameter acquisition module: One of the key improvements of this invention is that the module includes a multi-channel analog-to-digital conversion unit and a storage unit, which synchronously acquires the following process parameters at a sampling rate of not less than 200kHz: RMS value of driving voltage, RMS value of driving current, active power, frequency tracking value, amplitude control quantity (PWM duty cycle), DC bus voltage, transducer temperature (obtained via a patch thermocouple), and welding pressure (obtained via an external pressure sensor). These parameters are recorded in segments according to the welding cycle, indexed by timestamps—each time welding is initiated, the system automatically generates a record entry containing waveform data (sampling point sequence) and statistical characteristic values ​​(mean, peak, and final value) of the above parameters throughout the welding process. The storage unit employs a circular caching mechanism, capable of storing no fewer than 100,000 welding records, and supports export via RS485 or Ethernet interface.

[0008] Main control module: The core processor is an ARM Cortex-M series microcontroller, with an embedded real-time operating system (RTOS) to schedule the coordinated operation of the various modules. The main control module is also equipped with a human-machine interface, including a touch screen and external I / O ports. Users can set welding parameters (target frequency range, current value corresponding to target amplitude, welding time, etc.) through the human-machine interface, and can view real-time waveforms and call history.

[0009] Furthermore, the frequency tracking module also has a frequency lockout protection function—when the current feedback amplitude is continuously lower than the set threshold (i.e., the transducer is in a severely detuned state) and the frequency adjustment has exceeded the preset scanning range, the system automatically suspends power output and issues an alarm to prevent the transducer from being damaged due to abnormal operating conditions.

[0010] Furthermore, the data collected by the parameter acquisition module supports two export modes: real-time streaming mode, which pushes real-time data to an external MES system via an Ethernet interface using the Modbus TCP protocol; and batch export mode, which exports the stored historical records to an external storage device in CSV format via a USB interface.

[0011] Furthermore, the parameter acquisition module also includes an intelligent triggering function—users can set combinations of triggering conditions, such as "automatically start recording when welding pressure is below a certain threshold" or "trigger high-speed waveform recording when active power exceeds a certain threshold," to collect key data more effectively and avoid redundant information occupying storage space.

[0012] The beneficial effects of this invention are: The frequency tracking performance balances speed and accuracy, employing a two-stage frequency tracking strategy that combines coarse frequency sweeping with phase closed-loop fine tracking. Adaptive bandwidth adjustment is introduced in the closed-loop stage. Compared to a single step-sweep scheme or a fixed-parameter PLL scheme, this results in faster frequency tracking response, higher steady-state tracking accuracy, and adaptability to sudden load changes. Amplitude control achieves true closed-loop operation, using DC bus current as amplitude feedback. A closed-loop control loop is constructed using phase-shifted PWM and digital PID, significantly improving amplitude stability compared to open-loop constant power output or current threshold protection alone. It possesses complete process parameter acquisition and traceability capabilities, providing a complete data chain for the ultrasonic welding process through multi-channel synchronous sampling and segmented recording mechanisms. This provides quantitative data for product quality traceability, process parameter optimization, and predictive maintenance. It boasts strong compatibility and configurability; all parameters of the control system can be configured through a human-machine interface, adapting to different power levels, frequency ranges, and welding requirements for different materials. Attached Figure Description

[0013] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is an overall flowchart of an integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition proposed in this invention. Detailed Implementation

[0014] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0015] This embodiment provides an integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition. The specific steps are as follows: System Hardware Architecture The main control module uses an STM32F7 series ARM microcontroller with an embedded FreeRTOS real-time operating system, responsible for coordinating the collaborative work and task scheduling of various modules. The rectifier and filter unit of the power drive module converts 220V AC mains power into DC bus voltage. The full-bridge inverter unit uses four IGBTs to form an inverter bridge, and its switching control signal is provided by the PWM advanced timer channel of the main control module, driving the IGBTs after passing through an isolation drive circuit. The high-frequency AC signal after inversion is isolated and boosted by a high-frequency transformer before driving the ultrasonic transducer. The power drive module has a power rating of 3000W and an operating frequency range of 20kHz, suitable for medium-power metal welding scenarios.

[0016] At the output of the power drive module, a high-frequency current transformer is connected in series to collect the transducer operating current, and a voltage divider sampling circuit is connected in parallel to collect the drive voltage signal. The two analog signals are conditioned by operational amplifiers and then sent to the ADC channel of the main control module for analog-to-digital conversion. The DC bus current is collected by a Hall current sensor and also sent to the ADC channel.

[0017] The transducer temperature is obtained via a surface-mount thermocouple. The thermocouple signal is then fed into the ADC after cold junction compensation and amplification. The welding pressure is obtained via an external pressure sensor. The sensor outputs a standard 4-20mA current signal, which is sampled by a resistor and then fed into the ADC. All analog signal sampling is performed synchronously by multiple independent ADC channels of the main control module.

[0018] Specific implementation of frequency tracking After the system powers on, it first enters the frequency sweep phase of the frequency tracking module. The main control module scans the output PWM frequency from 15kHz to 40kHz in a step-by-step manner, while simultaneously acquiring the effective current value fed back from the high-frequency current transformer via an ADC. When the effective current value is detected to reach its peak value, this frequency point is recorded as the initial resonant frequency and stored in the non-volatile memory (EEPROM) as the initial frequency value for the next startup, avoiding repeated frequency sweeping with each power-on.

[0019] During steady-state operation, the system switches to phase closed-loop tracking mode. The main control module calculates the phase difference between the voltage and current by comparing the time difference between the zero-crossing points of the driving voltage and the feedback current. This phase difference is then fed into the PI regulator after being digitally low-pass filtered. The output of the PI regulator is superimposed on the current driving frequency, forming a closed-loop negative feedback. When the phase difference between the driving voltage and the feedback current approaches zero, the transducer operates in a resonant state, at which point the energy conversion efficiency is highest.

[0020] An adaptive bandwidth adjustment mechanism is introduced in the phase closed-loop tracking mode. The main control module calculates the frequency change rate in real time. When the frequency change rate exceeds a set threshold (e.g., 100Hz / s), it determines that the system is in a state of rapid load change, increases the proportional coefficient and integral coefficient of the PI regulator, and improves the loop response speed. When the frequency change rate is lower than the set threshold, it narrows the loop bandwidth to improve steady-state accuracy and avoid frequency jitter.

[0021] The frequency tracking module also includes a frequency unlock protection submodule. When the main control module detects that the current feedback amplitude is continuously lower than the set threshold (e.g., 30% of the normal value) and the frequency adjustment has exceeded the preset scanning range, it determines that the system frequency is unlocked. At this time, the main control module automatically pauses the PWM output, cuts off the power drive, and sends a fault alarm signal through the external I / O port, and displays the fault information on the touch screen.

[0022] Specific implementation of amplitude control The DC bus current and the transducer output amplitude exhibit a monotonically positive correlation, meaning the DC bus current indirectly characterizes the transducer's output amplitude. The process parameter table pre-stores target current values ​​for different welding conditions, determined in advance by calibration tests: under standard conditions, a laser vibration meter is used to calibrate the actual output amplitude of the transducer, while simultaneously recording the corresponding DC bus current value. An amplitude-current mapping table is then established and stored in non-volatile memory.

[0023] During the welding process, the amplitude control module reads the real-time DC bus current value at a period of 10ms, compares it with the preset target current value in the process parameter table, calculates the deviation value, and outputs an adjustment amount after the deviation is calculated by digital PID. This adjustment amount is used to adjust the duty cycle of the PWM drive signal, thereby changing the output power of the full-bridge inverter and making the actual amplitude approach the target value. The introduction of amplitude closed-loop control can stabilize the relative range of welding amplitude within 10%.

[0024] The amplitude control module also has a segmented gain adjustment function: the small deviation range is set as the range where the deviation value is less than 10% of the target value, and the large deviation range is the range where the deviation value is greater than 10% of the target value. In the small deviation range, the first gain coefficient Kp1 is used (2.0 in this embodiment), and in the large deviation range, the second gain coefficient Kp2 is used (0.8 in this embodiment). The first gain coefficient is greater than the second gain coefficient. This design provides a stronger adjustment effect to achieve fast convergence when the value is close to the target value, and avoids overshoot when the deviation is large, thus balancing response speed and stability.

[0025] Parameter acquisition and data management The multi-channel analog-to-digital converter of the parameter acquisition module synchronously acquires parameters such as the effective value of the driving voltage, the effective value of the driving current, the active power, the frequency tracking value, the amplitude control value, the DC bus voltage, the transducer temperature, and the welding pressure at a sampling rate of 100kHz. Recording is performed in segments according to the welding cycle: each time welding is initiated, the system automatically generates a record entry containing the waveform data sequence and statistical characteristic values ​​of the entire welding process.

[0026] The storage unit employs a circular cache mechanism, using NAND Flash as the storage medium to store the most recent 100,000 soldering records. When the storage capacity reaches its limit, new records automatically overwrite the oldest records. The storage unit supports export via a data interface and has two export modes: Real-time streaming mode: Pushes real-time data to external MES systems via Ethernet interface using Modbus TCP protocol, suitable for production process monitoring and quality traceability.

[0027] Batch export mode: Export the stored historical records to an external USB flash drive in CSV format via the USB interface for easy offline data analysis.

[0028] The parameter acquisition module also includes an intelligent triggering unit. Users can set combinations of triggering conditions via the touch screen. Triggering conditions include, but are not limited to: welding pressure below a set threshold (e.g., below 80% of the preset value), active power exceeding a set threshold (e.g., exceeding 120% of the rated power), and frequency deviation exceeding a set threshold. When any triggering condition or combination of conditions is met, the system automatically starts the high-speed waveform recording function, saving the high-speed waveform data 100ms before and after the trigger moment separately and marking them as "abnormal records" for subsequent analysis.

[0029] Human-computer interaction and system operation The main control module is equipped with a 7-inch touch screen for displaying real-time welding waveforms (voltage, current, and power curves), historical records, and process parameter settings. External I / O ports include start signal input (foot switch or PLC start command), welding completion signal output, and fault alarm signal output, facilitating integration with automated production lines.

[0030] After the system is powered on, the FreeRTOS real-time operating system starts multiple task threads: the frequency tracking task runs with a period of 100μs, the amplitude control task runs with a period of 10ms, the parameter acquisition task runs with a period of 1ms, and the human-computer interaction task runs with a period of 50ms. Each task is synchronized and exchanges data through message queues and semaphores to ensure the real-time performance and reliability of the system.

[0031] The system described in this embodiment has been verified on an ultrasonic metal welding equipment. Actual operation results show that the system achieves real-time automatic tracking of the transducer resonant frequency, with a tracking time of less than 120ms and a frequency tracking accuracy of up to 5Hz; amplitude closed-loop control significantly improves welding consistency; and parameter acquisition and data management functions provide complete data support for welding quality traceability.

[0032] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition, comprising a power drive module, a frequency tracking module, an amplitude control module, a parameter acquisition module, and a main control module, characterized in that, The power drive module consists of a rectifier and filter unit, a full-bridge inverter unit, and a high-frequency transformer. It is used to convert mains power into a high-frequency AC signal to drive the ultrasonic transducer. The control signal of the full-bridge inverter unit is provided by the PWM output channel of the main control module. The output of the power drive module is connected in series with a high-frequency current transformer and a voltage divider sampling circuit, which are used to collect the transducer's operating current and voltage signals, respectively. The frequency tracking module adopts a hybrid frequency tracking strategy to achieve real-time automatic tracking of the transducer resonant frequency. During the startup phase, the initial resonant point is determined by frequency sweeping and the frequency is stored in the non-volatile memory as the initial value. During the steady-state operation phase, it switches to the phase closed-loop tracking mode and dynamically adjusts the driving frequency through the PI regulator to make the phase difference between the driving voltage and the feedback current approach zero. The phase closed-loop tracking mode introduces an adaptive bandwidth adjustment mechanism. When the frequency change rate exceeds a set threshold, the loop bandwidth is increased to improve the response speed. When the frequency change rate is lower than the set threshold, the loop bandwidth is narrowed to improve the steady-state accuracy. The amplitude control module uses the DC bus current of the power drive module as an indirect feedback quantity for the output amplitude of the transducer. It compares the real-time collected bus current value with the preset target current value in the process parameter table. The deviation is calculated by digital PID and then the adjustment quantity is output. The amplitude control module also has a segmented gain adjustment function. A first gain coefficient is used in the small deviation range and a second gain coefficient is used in the large deviation range. The first gain coefficient is greater than the second gain coefficient. The parameter acquisition module includes a multi-channel analog-to-digital conversion unit and a storage unit. It synchronously acquires the effective values ​​of the driving voltage, driving current, active power, frequency tracking value, amplitude control quantity, DC bus voltage, transducer temperature, and welding pressure parameters. It records the data in segments according to the welding cycle, generating a record entry for each welding start, which includes the waveform data sequence and statistical feature values ​​of the entire welding process. The storage unit uses a circular caching mechanism to store no less than 100,000 welding records and supports exporting them through the data interface. The main control module uses an ARM microcontroller as its core processor, embeds a real-time operating system to schedule the collaborative work of the above modules, and is equipped with a human-machine interface, including a touch screen and external I / O ports.

2. The integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition according to claim 1, characterized in that, The frequency tracking module is also equipped with a frequency unlock protection submodule. When the current feedback amplitude is detected to be continuously lower than the set threshold and the frequency adjustment has exceeded the preset scanning range, the system automatically stops the power output and issues an alarm.

3. The integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition according to claim 1, characterized in that, The data interface of the parameter acquisition module supports two export modes: real-time stream mode, which pushes real-time data to an external MES system via Ethernet interface using Modbus TCP protocol; Batch export mode: Exports stored history records to external storage devices in CSV format via USB interface.

4. The integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition according to claim 1, characterized in that, The parameter acquisition module also includes an intelligent triggering unit, which allows users to set combinations of triggering conditions. When the triggering conditions are met, high-speed waveform recording is automatically started. The triggering conditions include any one or more combinations of welding pressure below a set threshold, active power exceeding a set threshold, and frequency deviation exceeding a set threshold.

5. The integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition according to claim 1, characterized in that, The transducer temperature is obtained through a patch thermocouple, and the welding pressure is obtained through an external pressure sensor.

6. The integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition according to claim 1, characterized in that, In the amplitude control module, the DC bus current and the transducer output amplitude are monotonically positively correlated. The target current value in the process parameter table is predetermined by calibration tests and stored in non-volatile memory.

7. The integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition according to claim 1, characterized in that, The main control module's touch screen is used to display real-time welding waveforms, query historical records, and set process parameters. The external I / O ports include start signal input, welding completion signal output, and fault alarm signal output.

8. The integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition according to claim 1, characterized in that, The power drive module has a power range of 500W to 18000W and a frequency range of 15kHz to 40kHz.

9. The integrated ultrasonic frequency tracking and amplitude control system with parameter acquisition according to claim 1, characterized in that, The waveform data sequence in the record entries of the above parameter acquisition module is a sampling point sequence, and the statistical feature values ​​include mean, peak value and final value.

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