A kind of pot processing line adaptive adjustment spot welding control system

Abstract

The present application relates to resistance welding control technical field, disclose a kind of pot processing production line adaptive adjustment spot welding control system, including servo module, inverter module, acquisition module and main control module.Main control module is analyzed dynamic inductance by injecting ripple detection pulse to welding secondary circuit, calculates topography correction coefficient to calibrate equivalent contact surface index;After locking servo motor main drive shaft, control piezoelectric ceramic micro-unit to exert step extrusion match multilayer composite bottom plastic softening critical contact force parameter;In main current output period, according to the parameter control micro-unit executes micro-displacement retreat along electrode unloading direction;Welding after combination characteristic deviation rate prolongs pressure maintaining time and exports attenuation tempering current.Through the above setting, the present system compensates the contact state recognition deviation caused by electrode wear, releases the transient internal pressure generated when the metal liquid phase expands, prevents internal splashing and tearing of the composite bottom, and slows down the thermal contraction stress in the cooling and solidification process.

Description

Technical Field

[0001] This invention relates to the field of resistance welding control technology, specifically to an adaptive spot welding control system for a cookware processing production line. Background Technology

[0002] Existing cookware processing production lines typically employ resistance spot welding technology for welding multi-layer composite bottoms. Spot welding equipment mainly consists of a servo pressurizing mechanism, an inverter power supply, and electrode welding clamps. In the conventional spot welding control process, the servo mechanism drives the electrodes to press the cookware workpiece firmly, and the inverter power supply outputs a set welding current to the welding circuit, causing resistance heat to be generated at the metal contact surface, melting and forming a weld nugget. Subsequently, under maintained mechanical pressure, cooling and crystallization occur, thereby completing the physical connection of the multi-layer structure.

[0003] In continuous batch processing of cookware, the electrode end faces undergo physical wear and deformation with each welding cycle. Existing control systems mostly rely on initially set static parameter models, failing to provide real-time feedback and compensation for contact area deviations caused by changes in electrode morphology, leading to errors in the assessment of the actual contact state. Simultaneously, during the thermal expansion phase of the main welding of the multi-layer composite bottom of the cookware, the internal metal melts, generating liquid phase expansion. Existing servo pressurizing mechanisms mostly maintain fixed positional constraints or set a single pressure output, failing to dynamically follow and release pressure according to the material's internal yield state while maintaining basic mechanical forging pressure. This rigid constraint prevents timely unloading of transient internal pressure in the molten core area, making the multi-layer composite bottom prone to spattering, delamination tearing, and thermal softening and crushing.

[0004] During the solidification and crystallization stage after the main current output ends, there are differences in the thermal shrinkage rates between the different material layers of the composite base. Existing technologies typically employ a fixed-duration mechanical pressure holding and direct current cut-off cooling logic, failing to incorporate the initial contact physical differences during a single workpiece clamping into subsequent compensation considerations. Using a fixed post-weld treatment method makes it difficult to dynamically adjust the pressure holding duration and heat input decay rate according to specific heat input and deformation states, easily leading to localized accumulation of thermal shrinkage stress during the cooling process of the bottom metal, affecting the overall structural stability. Therefore, this invention provides an adaptive adjustment spot welding control system for cookware processing production lines to address the shortcomings of existing technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an adaptive adjustment spot welding control system for cookware processing production lines. This system solves the problems of insufficient compensation for changes in contact state caused by electrode wear during spot welding of multi-layer composite bottoms of cookware, and difficulty in dynamically following the internal yield state of the material during the welding thermal expansion stage, which leads to problems such as spatter, delamination tearing, and thermal softening and crushing in the welding area.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides an adaptive adjustment spot welding control system for a cookware processing production line, comprising: The servo module includes a servo motor, an absolute encoder, a piezoelectric ceramic micro-motion unit, and a high-frequency pressure sensor; the absolute encoder acquires and feeds back the mechanical displacement of the welding gun; the piezoelectric ceramic micro-motion unit and the high-frequency pressure sensor are both located at the end of the welding gun's actuation mechanism; the high-frequency pressure sensor acquires the contact force signal of the contact area. The inverter module receives inverter control commands from the main control module and adjusts the output current of the welding secondary circuit. The acquisition module includes a face voltage sampling cable, a Rogowski coil, an integral conditioning circuit, and a contact force signal sampling channel. The face voltage sampling cable acquires the raw voltage signal. The Rogowski coil generates the raw loop current signal through the integral conditioning circuit. The contact force signal sampling channel receives the contact force signal. The acquisition module sends the raw voltage signal, the raw loop current signal, and the contact force signal to the main control module. The main control module is connected to the servo module, inverter module, and acquisition module respectively; the main control module has a built-in mechanical electromagnetic coupling dynamic analysis kernel; the main control module generates servo control commands and inverter control commands based on the original voltage signal, the original loop current signal, the mechanical displacement and the contact force signal.

[0007] Furthermore, after receiving the trigger signal, the main control module generates an initial digital motion command and sends it to the servo module; the servo motor drives the welding clamp to press down, and the absolute encoder collects the current mechanical displacement and feeds it back to the main control module; when the current mechanical displacement exceeds the entry boundary value close to the threshold range, the main control module sends a duty cycle control command to the inverter module, and the inverter module injects a unipolar ripple detection pulse into the welding secondary circuit; the unipolar ripple detection pulse is formed by the superposition of DC bias component and high-frequency alternating component; when the effective value of the original circuit current signal exceeds the safety monitoring lower limit and the contact force signal exceeds the initial contact pressure threshold, the main control module establishes an effective sampling window.

[0008] Furthermore, the main control module filters the original voltage signal and the original loop current signal within the effective sampling window to remove the DC bias component, obtaining the alternating voltage ripple component and the alternating current ripple component, respectively. The main control module tracks the phase angle of the alternating voltage ripple component through a phase-locked loop and calculates the total delay time by combining it with the delay constant. The main control module applies lead phase compensation to the alternating current ripple component according to the total delay time. The main control module performs Hilbert transform on the alternating voltage ripple component and the alternating current ripple component after lead phase compensation to reconstruct the transient complex impedance analytical model. The main control module separates the imaginary component of the dynamic inductive reactance through the transient complex impedance analytical model.

[0009] Furthermore, the main control module calculates the uncalibrated equivalent contact surface index based on the ratio of the amplitude of the alternating current ripple component to the amplitude of the alternating voltage ripple component; the main control module timestamps the dynamic reactance virtual component and the mechanical displacement, and matches the instantaneous decay rate of the dynamic reactance virtual component with the downward pressure micro-displacement increment of the mechanical displacement as a data pair according to the timestamp; the main control module calculates the morphology correction coefficient based on the instantaneous decay rate, the downward pressure micro-displacement increment, the reference profile constant, and the material yield sensitivity coefficient; the main control module uses the morphology correction coefficient to perform nonlinear weighted calibration on the uncalibrated equivalent contact surface index to generate the calibrated equivalent contact surface index.

[0010] Furthermore, when the displacement change fed back by the absolute encoder reaches a fixed physical step size, the main control module writes the mechanical displacement and the calibrated equivalent contact surface index as physical state data pairs into the internal buffer array. When the number of physical state data pairs in the internal buffer array reaches the set queue length, the main control module uses the least squares method to perform linear regression calculation on the physical state data pairs in the internal buffer array to obtain the slope of the area expansion trend. When the slope of the area expansion trend is less than the tolerance threshold for a continuous set number of calculation cycles, the main control module sends a position locking command to the servo module, and the main control module records the equivalent contact surface index of the current cycle as the initial feature value.

[0011] Furthermore, after receiving the position lock command, the servo motor enters a high-rigidity position holding state. In the high-rigidity position holding state, the main control module controls the servo motor to maintain the main drive shaft position lock and controls the piezoelectric ceramic micro-motion unit to generate superimposed step-type heavy-load extrusion. The main control module establishes a pre-sampling window before the superimposed step-type heavy-load extrusion occurs and establishes a post-sampling window after the step impulse of the superimposed step-type heavy-load extrusion reaches the absolute peak value. The main control module calculates the arithmetic mean of the calibrated equivalent contact surface index within the pre-sampling window, extracts the absolute peak value of the calibrated equivalent contact surface index within the post-sampling window, and calculates the yield evolution range by subtracting the absolute peak value from the arithmetic mean.

[0012] Furthermore, the main control module compares the yield evolution range with a preset comparison threshold. When the yield evolution range exceeds the preset comparison threshold, the main control module determines that the bottom metal has undergone microscopic plastic yielding. The main control module stores a multilayer composite material yield feature mapping table. The main control module inputs the yield evolution range into the multilayer composite material yield feature mapping table and obtains the critical contact force parameter for plastic softening of the multilayer composite bottom through linear interpolation matching.

[0013] Furthermore, the main control module calculates the difference between the initial characteristic value and the reference characteristic value. The main control module uses the ratio of the difference to the reference characteristic value as the deviation rate. The main control module extracts the absolute value of the deviation rate as the post-weld compensation strength parameter. The main control module generates welding pulse parameters including the peak value of the main welding current and the welding pulse rise time based on the deviation rate. The main control module controls the inverter module to output medium-frequency DC main current to the welding secondary circuit according to the welding pulse parameters.

[0014] Furthermore, during the output of the intermediate frequency DC main current by the inverter module, the servo motor maintains the main drive shaft position locked state; the main control module calculates the micro-displacement retraction amount based on the contact force signal fed back by the high-frequency pressure sensor, the critical contact force parameter of the multi-layer composite bottom plastic softening, and the micro-motion following gain constant; when the pressure value of the contact force signal exceeds the value of the critical contact force parameter of the multi-layer composite bottom plastic softening, the main control module controls the piezoelectric ceramic micro-motion unit to perform micro-displacement retraction along the electrode unloading direction according to the micro-displacement retraction amount.

[0015] Furthermore, after the intermediate frequency DC main current output is completed, the main control module calculates the compensated holding time based on the basic holding time, the holding compensation coefficient, and the post-weld compensation strength parameters. The main control module controls the servo motor to maintain the main drive shaft position lock state until the internal holding timer reaches the compensated holding time. The main control module calculates the attenuation time constant based on the reference attenuation time constant, the mapping gain coefficient, and the post-weld compensation strength parameters. Within the compensated holding time window, the main control module controls the inverter module to output a superimposed attenuated tempering current to the welding secondary circuit. The superimposed attenuated tempering current exhibits an exponential attenuation waveform according to the attenuation time constant.

[0016] A second aspect of this invention provides an adaptive adjustment spot welding control method for a cookware processing production line, applied to the aforementioned control system, comprising the following steps: Receive trigger signal and drive servo motor to press down welding clamp; when the displacement fed back by absolute encoder enters the threshold range, control inverter module to inject unipolar ripple detection pulse into welding secondary circuit; The original voltage signal and the original loop current signal are acquired synchronously and the alternating ripple component is extracted; the imaginary component of the dynamic reactance is separated by phase compensation and transient complex impedance analysis; the shape correction coefficient is calculated based on the instantaneous attenuation rate and mechanical displacement increment of the imaginary component of the dynamic reactance, and the uncalibrated equivalent contact surface index is calibrated using the shape correction coefficient; When the displacement change reaches a fixed physical step, the slope of the area expansion trend is fitted based on the mechanical displacement and the calibrated equivalent contact surface index; when the slope of the area expansion trend is continuously less than the tolerance threshold, the initial feature value is recorded and the position of the main drive shaft is locked; the piezoelectric ceramic micro-motion unit is controlled to generate superimposed step-type heavy-load extrusion, the yield evolution range before and after the state is extracted, and the critical contact force parameters of the multilayer composite bottom plastic softening are obtained by linear interpolation matching; By comparing the deviation rate between the initial characteristic value and the reference characteristic value, welding pulse parameters are generated, and the inverter module is controlled to output medium-frequency DC main current. During the output of medium-frequency DC main current, based on the pressure feedback value of the contact area and the critical contact force parameter of the multi-layer composite bottom plastic softening, the piezoelectric ceramic micro-motion unit is controlled to perform micro-displacement retreat along the electrode unloading direction. The micro-displacement retreat does not release the basic forging pressure of the welding clamp, and the retreat amount is limited by the maximum physical stroke and the minimum contact force threshold. After the intermediate frequency DC main current output is completed, the compensated holding time and decay time constant are calculated based on the absolute value of the deviation rate. Within the compensated holding time window, the main drive shaft is locked and the exponentially decaying tempering current is output.

[0017] This invention provides an adaptive adjustment spot welding control system for a cookware processing production line. It has the following beneficial effects: 1. This invention injects unipolar ripple detection pulses into the welding secondary circuit, combines this with mechanical displacement, and uses a transient complex impedance model to separate the imaginary component of the dynamic inductive reactance. Then, it calculates a morphology correction coefficient to perform nonlinear weighted calibration of the equivalent contact surface index. This method compensates for the deviation in contact area calculation caused by electrode wear and physical deformation during cookware mass production, enabling the system to issue subsequent inverter and servo control commands based on the corrected actual contact state.

[0018] 2. This invention controls the servo motor to lock the main drive shaft and controls the piezoelectric ceramic micro-motion unit to apply step-like heavy-duty extrusion to match the critical contact force parameter for plastic softening of the multilayer composite substrate. When outputting the intermediate-frequency DC main current, this parameter is used to control the piezoelectric ceramic micro-motion unit to perform micro-displacement retraction along the electrode unloading direction. This execution logic releases the transient internal pressure generated by the expansion of the liquid metal phase while maintaining the mechanical constraint of the welding clamp base, reducing the probability of spatter, delamination tearing, and thermal softening crushing inside the multilayer composite substrate.

[0019] 3. This invention calculates the deviation rate between the initial characteristic value and the reference characteristic value, and synchronously extends the mechanical holding time of the servo motor according to this deviation rate after the main welding stage, while controlling the inverter module to output an exponentially decaying tempering current. This adjustment process addresses the initial physical differences in each clamping contact state, altering the mechanical constraint duration and heat input decay rate during the weld crystallization stage, thus mitigating the accumulation of thermal shrinkage stress during the cooling and solidification process of the underlying metal. Attached Figure Description

[0020] Figure 1 This is a system framework diagram of the present invention; Figure 2 This is a flowchart of the method of the present invention; Figure 3 A timing diagram for the detection preparation and addressing control phases of this invention; Figure 4 This is a schematic diagram of the multidimensional signal decoupling and wear adaptive calibration stage of the present invention; Figure 5 This is a timing control diagram for the stiffness gradient detection and critical softening point identification stages of the present invention. Figure 6 This is a schematic diagram of the thermo-mechanical coupling macro-micro dual-drive flexible following control stage of the present invention; Figure 7 This is a timing-coordinated control diagram for the post-weld processing and automated closed-loop stage of the present invention. Figure 8 This is a thermal diagram showing the coupling evolution of the three-dimensional morphology and contact stress of the macro-micro dual-drive system according to the present invention. Figure 9 This is a radar topology diagram showing the combined distribution of shear strength and multidimensional micro-defects in the fusion joint of the present invention.

[0021] Among them, 10 is the servo module; 20 is the inverter module; 30 is the acquisition module; and 40 is the main control module. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] See attached document Figure 1 , Figure 1 This is a system architecture diagram of one embodiment of the present invention. The present invention provides an adaptive adjustment spot welding control system for a cookware processing production line, applicable to spot welding stations in a cookware processing production line, including a servo module 10, an inverter module 20, a data acquisition module 30, and a main control module 40.

[0024] The servo module 10 includes a servo motor, an absolute encoder, a piezoelectric ceramic micro-motion unit, and a high-frequency pressure sensor. The servo motor drives the welding clamp's movement according to digital motion commands issued by the main control module 40; the absolute encoder collects and feeds back the mechanical displacement of the welding clamp; the piezoelectric ceramic micro-motion unit is located at the end of the welding clamp's execution, providing micro-displacement compensation after the macroscopic pressing position of the welding clamp is determined; the high-frequency pressure sensor is located at the end of the welding clamp's execution, collecting the contact force signal between the electrode and the composite bottom of the cookware. The servo motor and the piezoelectric ceramic micro-motion unit together form a macro-micro dual-drive execution structure to balance the macroscopic feed of the welding clamp and rapid fine-tuning of the contact interface.

[0025] Inverter module 20 is connected to main control module 40 and is used to adjust the output current of welding secondary circuit according to the programmable duty cycle control command output by main control module 40. During the contact state detection stage, inverter module 20 outputs unipolar pulsating DC current; during the main welding stage, inverter module 20 outputs medium frequency DC main current.

[0026] The acquisition module 30 includes a face voltage sampling cable, a Rogowski coil, an integral conditioning circuit, and a contact force signal sampling channel. The face voltage sampling cable is used to acquire the voltage signal from the electrode face; the Rogowski coil is used to sense the current change signal in the welding secondary circuit, and the integral conditioning circuit generates the original loop current signal; the contact force signal sampling channel receives the contact force signal output by the high-frequency pressure sensor. The acquisition module 30 synchronously sends the original face voltage signal, the original loop current signal, and the contact force signal to the digital sampling interface of the main control module 40.

[0027] The main control module 40 is a spot welding station-level programmable digital controller, which communicates with the servo module 10, inverter module 20, and acquisition module 30. The main control module 40 has a built-in digital signal processor for inter-module communication synchronization, sampling timing control, and multi-source signal decoupling. The main control module 40 also constructs a mechanical-electromagnetic coupling dynamics analysis kernel, which includes a complex impedance analysis unit, a displacement synchronization unit, a morphology correction unit, an area expansion trend judgment unit, and a yield parameter identification unit. Based on synchronized data of end-face voltage, loop current, mechanical displacement, and contact pressure, the main control module 40 analyzes the changes in electrode end-face morphology and the yield state of the internal structure of the multi-layer composite bottom, and generates corresponding servo control commands and inverter control commands accordingly, enabling the spot welding station to complete adaptive closed-loop control according to a preset program.

[0028] The piezoelectric ceramic micro-motion unit is connected in series between the servo main drive shaft and the electrode holder. When the main drive shaft is kept in a locked position, the piezoelectric ceramic micro-motion unit can generate micron-level compensation displacement along the electrode pressure direction or load direction.

[0029] See attached document Figure 2, Figure 2 This is a flowchart of a control method according to an embodiment of the present invention. The present invention also provides an adaptive adjustment spot welding control method for a cookware processing production line, which is applied to the spot welding station in the cookware processing production line and includes the following steps.

[0030] S10, after receiving the programmable trigger signal from the spot welding station, the main control module 40 calls the preset control program to drive the servo module 10 to press down the welding clamp electrode; when the current displacement fed back by the servo module 10 enters the set near threshold range, the main control module 40 controls the inverter module 20 to inject unipolar ripple detection pulses into the welding secondary circuit according to the detection timing.

[0031] S20, the acquisition module 30 synchronously acquires the original voltage signal from the electrode end face and the original current signal from the welding secondary circuit. The main control module 40 extracts the alternating ripple component from these signals and performs feedforward correction on the phase shift between the voltage and current signals through a phase-locked loop and delay compensation. After phase correction, the main control module 40 analyzes the high-frequency fundamental characteristics and calculates the equivalent contact surface index. Simultaneously, the main control module 40 establishes a transient complex impedance analytical model based on the Hilbert transform, separating the imaginary component of the dynamic inductive reactance. The main control module 40 further pairs the instantaneous attenuation rate of the imaginary component of the dynamic inductive reactance with the downward pressure micro-displacement according to the timestamp, and inputs this pair into the morphology correction coefficient calculation model to obtain the morphology correction coefficient. Subsequently, the main control module 40 uses the morphology correction coefficient to perform nonlinear weighted calibration on the equivalent contact surface index, forming a digital characterization parameter for the spot welding station program control.

[0032] S30, during the continued downward pressure of the welding clamp, when the displacement change reaches the set physical step size, the main control module 40 writes the current displacement and the calibrated equivalent contact surface index into the internal buffer array, and fits the area expansion trend slope based on the data in the buffer array. When the area expansion trend slope is less than the tolerance threshold for multiple consecutive calculation cycles, the main control module 40 issues a position locking command to the servo module 10 and records the current equivalent contact surface index as the initial feature value. In the position locking state, the main control module 40 controls the servo module 10 to maintain the position lock of the main drive shaft, and drives the piezoelectric ceramic micro-motion unit at the execution end to generate superimposed step-type heavy-duty extrusion, thereby extracting the yield evolution range and identifying the critical contact force parameter for plastic softening of the multilayer composite bottom.

[0033] S40, the main control module 40 compares the pre-calibrated reference characteristic value with the initial characteristic value, reconstructs the digital welding parameters based on the comparison result, and controls the inverter module 20 to output the main welding current. When the main welding current causes the bottom metal to enter the fusion expansion cycle, the main control module 40 generates a flexible forging follow command in combination with the multi-layer composite bottom plastic softening critical contact force parameter: on the one hand, it controls the servo motor to maintain position lock and provide macro forging pressure for the welding area; on the other hand, it drives the piezoelectric ceramic micro-motion unit to perform micro-displacement retraction along the electrode unloading direction, and maintains the bottom contact stress based on the feedback of the high-frequency pressure sensor to release the transient high temperature internal pressure of the deep interface.

[0034] S50, after the main welding current output is completed, the main control module 40 calculates the extended holding time and superimposed attenuated tempering current parameters based on the deviation rate between the initial characteristic value and the reference characteristic value, as well as the post-weld compensation strength parameters. Subsequently, the main control module 40 controls the servo module 10 to perform the extended holding time and controls the inverter module 20 to output the superimposed attenuated tempering current. After the holding time and tempering are completed, the automated control cycle of the current spot welding station is completed.

[0035] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0036] See attached document Figure 3 , Figure 3 This is a timing diagram of the detection preparation and addressing control phase in one embodiment of the present invention. Step S10 is used to complete the welding clamp addressing, low-energy detection enabling, and effective sampling window establishment before the spot welding operation begins, and specifically includes the following processes.

[0037] S101, the main control module 40 receives the trigger signal from the spot welding station via the industrial communication bus. This trigger signal is issued by the production line's programmable logic controller or a host computer, carrying the model data of the workpiece to be welded and the theoretical contact surface coordinates. After parsing the trigger signal, the main control module 40 generates an initial digital motion command and sends it to the servo module 10. Upon receiving the command, the servo driver in the servo module 10 controls the servo motor to move the welding clamp electrode downwards along a preset motion axis.

[0038] During the downward pressing of the welding clamp, the absolute encoder collects the current mechanical displacement of the welding clamp according to the set communication synchronization cycle and feeds this current mechanical displacement back to the main control module 40. The main control module 40 compares the current mechanical displacement with the threshold range to determine whether the welding clamp electrode has entered the detection position near the workpiece surface.

[0039] The approach threshold range is a predetermined position range before the welding electrode contacts the workpiece surface. The entry boundary of this range can be determined as follows: obtain the theoretical total thickness of the multi-layer composite bottom of the target cookware and the absolute reference height of the positioning fixture; calculate the theoretical contact point displacement between the welding electrode and the workpiece surface; then subtract the safety detection margin from the theoretical contact point displacement to obtain the entry boundary value of the approach threshold range. The safety detection margin can be set from 1mm to 5mm.

[0040] If the current mechanical displacement does not exceed the entry boundary value of the near threshold range within the preset timeout period, the main control module 40 triggers an addressing anomaly alarm; if the current mechanical displacement exceeds the entry boundary value, the main control module 40 determines that the welding electrode has entered the near threshold range.

[0041] S102, when the welding electrode enters the near-threshold range, the main control module 40 sends a detection wake-up command to the inverter module 20. After receiving the detection wake-up command, the inverter module 20 starts the pulse width modulation controller and returns a ready feedback frame to the main control module 40. After receiving the ready feedback frame, the main control module 40 issues a duty cycle control command to the inverter module 20 according to the detection timing, causing the inverter module 20 to inject unipolar ripple detection pulses into the welding secondary circuit.

[0042] Within the threshold range, the unipolar ripple detection pulse is in a low-energy enabled state. The low-energy enabled state means that the peak current of the unipolar ripple detection pulse is limited to 1% to 5% of the peak value of the main welding current, and the inverter module 20 does not enter the main welding power output state. At this time, the main control module 40 does not directly use all sampled data for impedance calculation, but first performs effective contact determination. When the effective value of the loop current exceeds the preset safety monitoring lower limit, and the feedback value of the high-frequency pressure sensor exceeds the initial contact pressure threshold, the main control module 40 determines that the welding electrode and the workpiece surface have established initial electrical contact and establishes an effective sampling window. Subsequent complex impedance analysis uses the end-face voltage signal and loop current signal collected within this effective sampling window as the data source.

[0043] The unipolar ripple detection pulse is formed by the superposition of a DC bias component and a high-frequency alternating component, and its instantaneous voltage expression is: ; In the formula, The instantaneous voltage of the unipolar ripple probe pulse injected into the welding secondary circuit. This is the DC bias voltage. For the amplitude of the alternating component, This refers to the switching frequency of the pulse width modulation controller. This is a time variable. To ensure the probe pulse maintains unipolarity, the parameter calibration is performed using... Greater than Switching frequency It can be configured from 1kHz to 4kHz.

[0044] The use of unipolar ripple detection pulses aims to obtain the high-frequency response of the contact interface without entering the main welding discharge state. Pure DC excitation lacks frequency characteristics, making it difficult to form a frequency domain response suitable for inductive reactance analysis; standard AC excitation exhibits periodic reversal of current direction, which can easily increase the risk of micro-gap breakdown and electrical sparks before a stable contact pressure is established between the electrode and the workpiece. Unipolar ripple detection pulses provide the frequency information required for impedance analysis through high-frequency alternating components, while maintaining a single current direction with the help of DC bias, making them more suitable for the contact state detection stage.

[0045] For the full-bridge inverter circuit, pulse width modulation controller and duty cycle adjustment method in inverter module 20, those skilled in the art can select and configure them according to the welding power supply design requirements, and the specific circuit implementation will not be described in detail.

[0046] See attached document Figure 4 , Figure 4 This is a schematic diagram of the multi-dimensional signal decoupling and wear adaptive calibration stage in one embodiment of the present invention. Step S20 is used to extract contact state features from the end face voltage signal and the loop current signal, and to calibrate the measurement deviation caused by wear of the electrode end face in combination with the downward displacement of the welding clamp. Specifically, it includes the following process.

[0047] S201, during the process of the welding clamp electrode gradually pressing the workpiece, the acquisition module 30 synchronously acquires the original voltage signal of the electrode end face and the original current signal of the welding secondary circuit, and sends them to the digital sampling interface of the main control module 40. Among them, the Rogowski coil senses the current change signal in the welding secondary circuit, and the current change signal is processed by the integral conditioning circuit to form the original circuit current signal.

[0048] If the main control module 40 fails to acquire a valid voltage signal or a valid current signal within the preset sampling window, it will output a signal acquisition fault prompt and stop the subsequent calculation of the current cycle to avoid the algorithm entering an invalid running state in the absence of a data source.

[0049] The digital signal processor in the main control module 40 filters the original terminal voltage signal and the original loop current signal to remove the DC bias component, obtaining the alternating voltage ripple component and the alternating current ripple component, respectively. The filtering process can be implemented using an infinite impulse response high-pass filter. The cutoff frequency of the high-pass filter is lower than the switching frequency of the pulse width modulation controller, preferably configured as 500Hz to 800Hz.

[0050] Since the sampling conversion time of the analog-to-digital converter and the group delay of the digital filter introduce phase lag, the main control module 40 tracks the phase angle of the alternating voltage ripple component through a software phase-locked loop and calculates the total delay time in conjunction with a pre-calibrated hardware delay constant. The hardware delay constant can be determined based on the controller's internal clock period, the signal transmission link length, and the factory calibration results. The main control module 40 applies lead phase compensation to the alternating current ripple component according to this total delay time, ensuring that the voltage ripple component and the current ripple component are consistent in time reference.

[0051] When the phase-locked loop (PLL) loses lock due to electromagnetic interference, the main control module 40 sets the lockout reset flag and temporarily uses the phase compensation value from the previous cycle. Real-time phase compensation is restored after the PLL relocks. After phase alignment is completed, the main control module 40 analyzes the high-frequency fundamental amplitude of the alternating ripple component and calculates the uncalibrated equivalent contact surface index based on the ratio of the alternating current amplitude to the alternating voltage amplitude.

[0052] For the difference equation of the infinite impulse response high-pass filter, the discrete control algorithm of the software phase-locked loop, and the fundamental amplitude extraction method, those skilled in the art can perform conventional configuration and program implementation based on the hardware architecture of the digital signal processor, and will not be elaborated here.

[0053] S202, the main control module 40 performs Hilbert transform on the compensated alternating voltage ripple component and alternating current ripple component to obtain the corresponding quadrature components, and constructs an analytical signal from these components. Based on this analytical signal, the main control module 40 reconstructs the transient complex impedance analytical model of the welding secondary circuit. This model reflects both the dynamic contact resistance of the contact area and the change in inductive reactance formed by the high-frequency alternating current in the welding circuit.

[0054] The calculation expression for the transient complex impedance analytical model is as follows: ; In the formula, It is a transient complex impedance; This refers to the feedforward corrected alternating voltage ripple component. This is the feedforward corrected alternating current ripple component; For Hilbert transform operators; The imaginary unit; This represents the real part of the impedance, used to characterize dynamic contact resistance. This is the imaginary component of the dynamic reactance, used to characterize the high-frequency reactance of the circuit.

[0055] To ensure the stability of the calculation process, the main control module 40 sets threshold filtering conditions. When the effective value of the alternating current is lower than the safety monitoring lower limit, the main control module 40 skips the complex impedance calculation for the current cycle to avoid calculation overflow or result distortion due to excessively low current amplitude.

[0056] Using the transient complex impedance analytical model, the main control module 40 separates the imaginary component of the dynamic inductive reactance from the total impedance. During the process of extruding the composite bottom of the cookware by the welding electrode, the micro-curvature, local density, and contact microcavities of the composite bottom surface all change with pressure. As the microcavities are compressed, the local eddy current path and equivalent magnetic permeability of the high-frequency current change, which can be reflected as the imaginary component of the dynamic reactance. The attenuation characteristics.

[0057] S203, the main control module 40 uses the system main frequency clock as a unified time base to mark the timestamps of each set of dynamic reactance virtual component data and the downward pressure micro-displacement data fed back by the servo module 10. Subsequently, the main control module 40 forms a data pair with the instantaneous attenuation rate of the dynamic reactance virtual component and the downward pressure micro-displacement increment according to the same timestamp, and inputs the data pair into the morphology correction coefficient calculation model to obtain the morphology correction coefficient characterizing the wear state of the electrode end face.

[0058] The formula for calculating the morphology correction factor is as follows: ; In the formula, This is the morphology correction factor; The instantaneous decay rate of the imaginary component of the dynamic sensing over time; This represents the incremental pressure displacement within the corresponding sampling period; The baseline profile constant; This represents the material's yield sensitivity coefficient. and It can be obtained by fitting multiple sets of extrusion test data from standard dynamometer specimens during the initial calibration stage of the equipment.

[0059] To avoid instability in calculations due to excessively small displacement increments, the current pressure micro-displacement increment is used. When the physical resolution is less than the lower limit of the absolute encoder, the main control module 40 does not perform the division operation and adjusts the morphology correction coefficient. The value is set to 1 to maintain the basic measurement state in the current cycle.

[0060] After obtaining the morphology correction coefficients, the main control module 40 performs nonlinear weighted calibration on the uncalibrated equivalent contact surface index to obtain digital characterization parameters for subsequent program control. The calibration calculation logic is as follows: ; In the formula, This refers to the calibrated equivalent contact surface index, i.e., the digital characterization parameter. This refers to the uncalibrated equivalent contact surface index. This is a nonlinear weighted gain parameter, preferably with a value between 0.1 and 0.5, used to limit the calibration amplitude and avoid overshoot in the calibration results.

[0061] Under continuous high-intensity welding conditions, mushroom-shaped wear easily occurs on the electrode end face, causing a shift in the actual contact area corresponding to the same downward displacement. By jointly calibrating the dynamic impedance attenuation characteristics with the downward micro-displacement, the main control module 40 can compensate for the contact surface index measurement error caused by electrode wear, making the output digital characterization parameters closer to the actual contact state between the welding clamp electrode and the composite bottom of the cookware.

[0062] See attached document Figure 5 , Figure 5 This is a timing control diagram for the stiffness gradient detection and critical softening point identification stage in one embodiment of the present invention. Step S30 is used to determine the position locking point after the welding clamp electrode and the workpiece surface tend to be stably attached, and to identify the critical contact force parameter of the multilayer composite bottom for plastic softening by short-time step extrusion. Specifically, it includes the following process.

[0063] S301, the main control module 40 establishes a first-in-first-out queue internally as an internal buffer array for storing physical state data pairs. The system pre-sets a fixed physical step size, which can be configured from 0.05mm to 0.1mm. When the downward displacement change fed back by the servo module 10 reaches the fixed physical step size, the main control module 40 writes the current absolute displacement and the calibrated equivalent contact surface index obtained in step S20 as a data pair into the internal buffer array.

[0064] If the change in downward displacement does not reach the fixed physical step size within the set waiting time threshold, the main control module 40 determines that the mechanical feed is abnormal, triggers a feed abnormality alarm, and clears the internal buffer array to prevent invalid data from continuing to participate in subsequent fitting calculations. The waiting time threshold can be configured from 0.5 seconds to 2.0 seconds.

[0065] Once the number of data pairs in the internal buffer array reaches the set queue length, the main control module 40 uses the least squares method to perform linear regression on the data pairs in the queue to calculate the slope of the area expansion trend. The queue length can be set to 10 to 15 sets of data. The slope of the area expansion trend is used to characterize the degree of contact area growth corresponding to a unit downward displacement; as the slope gradually decreases, it indicates that the macroscopic adhesion process between the welding clamp electrode end face and the workpiece surface gradually approaches saturation.

[0066] The formula for calculating the slope of the area expansion trend is as follows: ; In the formula, The slope of the area expansion trend; This is the queue length of the internal buffer array; For the first in the internal buffer array Record the absolute displacement value; This is the arithmetic mean of the absolute displacements within the queue. For the first One calibrated equivalent contact surface index; This is the arithmetic mean of the equivalent contact surface indices within the queue. To avoid calculation anomalies caused by an excessively small denominator, when the denominator approaches zero within a calculation cycle, the main control module 40 discards the current fitting result and uses the slope value from the previous cycle.

[0067] The system presets a tolerance threshold, which can be determined as 5% to 10% of the maximum expansion rate of the full-load contact area under factory calibration. When the main control module 40 determines that the slope of the area expansion trend is less than the tolerance threshold for 3 to 5 consecutive calculation cycles, it considers that the macroscopic contact between the welding clamp electrode end face and the workpiece surface has entered the saturation stage. At this time, the main control module 40 issues a position locking command to the servo module 10.

[0068] After receiving the position lock command, the servo module 10 switches the underlying control state, clears the integral gain of the position loop proportional-integral-derivative controller to zero, increases the proportional gain to 3 to 5 times that of the normal down-press state, and disables the feedforward control channel, causing the servo motor to enter a high-rigidity position holding state. The main control module 40 records the equivalent contact surface index at this moment as the initial characteristic value used for subsequent welding parameter reconstruction.

[0069] The implementation of the least squares method and the configuration of the registers for the internal control parameters of the servo driver can be accomplished by those skilled in the art based on conventional control theory and servo driver interface specifications, and will not be elaborated here.

[0070] S302, in the high-rigidity position holding state, the main control module 40 controls the servo module 10 to maintain the position lock of the main drive shaft, while simultaneously driving the piezoelectric ceramic micro-motion unit located at the execution end to execute an additional displacement mutation command. This additional displacement mutation command serves as a small displacement offset superimposed on the position lock target value, used to generate a short-term step extrusion disturbance without releasing the main drive shaft lock; after the step ends, the piezoelectric ceramic micro-motion unit returns to the initial offset position.

[0071] The aforementioned position locking does not exclude the occurrence of minute displacements at the execution end, but rather maintains the main drive shaft with high rigidity, with the piezoelectric ceramic micro-motion unit completing the limited minute disturbances. The displacement amount corresponding to the additional displacement mutation command can be set from 0.01mm to 0.03mm, and the execution time can be limited to within 5 milliseconds to 10 milliseconds, thereby forming a superimposed step-type heavy-duty extrusion.

[0072] On the force-time response curve, the superimposed step-load extrusion manifests as a transient peak in contact pressure, followed by stress relaxation due to microscopic yielding of the material. To prevent damage to the equipment or workpiece, the main control module 40 simultaneously activates the pressure upper limit protection and the micro-motion drive limiting protection; when the feedback value of the high-frequency pressure sensor reaches the safety threshold, or the drive voltage of the piezoelectric ceramic micro-motion unit reaches the allowable upper limit, the main control module 40 terminates the step command. The safety threshold can be calibrated based on the minimum safety boundary among the servo motor's rated overload torque, the equipment's mechanical structure strength limit, and the maximum output force of the piezoelectric ceramic micro-motion unit.

[0073] To extract yield characteristics, the main control module 40 establishes a pre-sampling window with a time span of 2 milliseconds before the step command is issued, and a post-sampling window with the same time span after the step impulse reaches its peak. The main control module 40 calculates the arithmetic mean of the equivalent contact surface index within the pre-sampling window, extracts the absolute peak value of the equivalent contact surface index within the post-sampling window, and calculates the difference between the absolute peak value and the arithmetic mean to obtain the yield evolution range. The yield evolution range is used to characterize the microscopic contact incremental deformation capability of the multilayer composite substrate material under transient high-pressure impact.

[0074] S303, the multi-layer composite bottom of cookware is typically formed by pressing an outer stainless steel magnetic conductive layer and an inner aluminum heat-absorbing layer together. The hardness and yield strength of the different metal layers vary. The mechanical stress wave generated by the superimposed step-load heavy extrusion is transmitted from the surface stainless steel to the interface of the bottom layer; when the yield evolution difference increases significantly and exceeds the preset comparison threshold, the main control module 40 determines that the bottom aluminum layer has begun to undergo microscopic plastic yielding under local stress concentration.

[0075] The preset comparison threshold can be obtained through static compression tests. Specifically, the baseline range data of the base material in the elastic deformation stage is first obtained, and then the baseline range data is multiplied by an empirical coefficient of 1.5 to 2.0 to obtain the comparison threshold used to identify the plastic yield initiation state.

[0076] The main control module 40 internally stores a pre-constructed yield characteristic mapping table for multilayer composite materials. This mapping table uses the yield evolution range as the input parameter and the critical contact force parameter for plastic softening of the multilayer composite substrate as the output parameter. The mapping table can be established in a laboratory environment through standard tensile tests and high-frequency compression tests of the same batch of materials. During the test, discrete data points corresponding to different pressures and deformations are collected, and calibration is performed accordingly.

[0077] The main control module 40 inputs the currently calculated yield evolution range into the yield characteristic mapping table of multilayer composite materials, and matches the corresponding critical contact force parameter for plastic softening of the multilayer composite substrate through linear interpolation. This parameter is used to represent the critical stress boundary of the current workpiece in the actual assembly state and pressure coupling state, from the elastic deformation stage to the plastic flow stage, providing a mechanical benchmark for the flexible forging pressure control in the subsequent main welding stage.

[0078] See attached document Figure 6 Step S40 is used to reconstruct the main welding parameters based on the initial feature values ​​obtained from the previous detection, and during the main welding current output, the forging pressure in the welding area is controlled collaboratively by the servo spindle and the piezoelectric micro-motion unit, specifically including the following process.

[0079] S401, the main control module 40 reads the initial feature value recorded in step S30 and compares it with the reference feature value pre-stored in the non-volatile memory. The reference feature value can be obtained during the equipment factory calibration stage, specifically by performing multiple sets of trial welding on a multi-layer composite bottom workpiece of standard thickness, and taking the arithmetic mean of the equivalent contact surface index obtained during each set of trial welding.

[0080] The main control module 40 calculates the difference between the initial eigenvalue and the reference eigenvalue, and uses the ratio of this difference to the reference eigenvalue as the deviation rate; simultaneously, the main control module 40 takes the absolute value of the deviation rate as the post-weld compensation strength parameter. To avoid division errors caused by abnormal baseline data, when the read baseline feature value is lower than the preset effective lower limit, the main control module 40 terminates the current comparison process and outputs a baseline data abnormality prompt.

[0081] To prevent ineffective welding due to missing workpieces, misaligned assembly, or severely abnormal contact conditions, the system sets a safety tolerance range, with the upper limit of the absolute value of the deviation rate configurable from 15% to 20%. When the absolute value of the deviation rate exceeds this upper limit, the main control module 40 determines that the current assembly state is abnormal, blocks the trigger pulse of the inverter module 20, and outputs a shutdown alarm signal to prevent forced discharge from damaging the workpiece or electrodes.

[0082] When the absolute value of the deviation rate is within the safety tolerance range, the main control module 40 reconstructs the welding pulse parameters of the inverter module 20 based on the deviation rate. The welding pulse parameters include at least one of the main welding current peak value, welding pulse rise time, and welding pulse duration.

[0083] Specifically, when the initial characteristic value is less than the reference characteristic value, it indicates that the microscopic contact area of ​​the current workpiece surface is too small and the contact resistance is too large. At this time, the main control module 40 calls the built-in one-dimensional linear interpolation table, extends the compensation rise time of the welding pulse according to the absolute value of the deviation rate, and lowers the peak value setting of the constant welding current to reduce the risk of initial spatter caused by the local current density rising too quickly in the initial stage of power-on.

[0084] When the initial characteristic value is greater than the reference characteristic value, it indicates that the microscopic contact area of ​​the current workpiece surface is too large and the contact resistance is too small. At this time, the main control module 40 shortens the compensation rise time or maintains the basic rise time according to the absolute value of the deviation rate, and accordingly adjusts or maintains the peak value setting of the constant welding current. The compensation rise time and the peak value of the constant welding current are both constrained by the upper and lower limits of preset parameters. After the parameter reconstruction is completed, the main control module 40 controls the inverter module 20 to output the main welding current to the welding secondary circuit according to the reconstructed timing sequence.

[0085] In step S402, when the main welding current is injected into the composite bottom workpiece and the welding area enters the weld nugget expansion cycle, the servo motor in the servo module 10 maintains the high-rigidity position lock state established in step S30. This position lock state provides basic macroscopic forging pressure to the welding area and limits uncontrolled deformation of the workpiece on a macroscopic scale.

[0086] As welding heat continues to be input, the metal materials at the composite bottom interface undergo fusion and thermal expansion, leading to an increase in transient stress within the contact interface. To release the excessive internal pressure caused by thermal expansion, the main control module 40 drives the piezoelectric micro-motion unit located at the execution end of the servo module 10 to perform micro-displacement retraction along the electrode unloading direction. The calculation model for micro-displacement retraction along the electrode unloading direction is as follows: ; In the formula, For piezoelectric micro-motion units in The amount of minute displacement yield at any given moment; The real-time physical contact force feedback value synchronously acquired by the acquisition module 30; The critical contact force parameters for plastic softening of the multilayer composite bottom identified in step S30; This is the micro-motion follower gain constant, which is related to the inverse piezoelectric coefficient of the piezoelectric ceramic material and the transmission ratio of the mechanical amplification mechanism. It can be obtained through the mechanical calibration of the equipment foundation.

[0087] When the real-time physical contact force feedback value Less than or equal to the critical contact force parameter for plastic softening of multilayer composite bottoms At that time, the main control module 40 will adjust the micro-displacement yield amount. The value is set to zero to avoid unnecessary positive compensation actions by the piezoelectric micro-motion unit. When the calculated micro-displacement clearance exceeds the maximum physical stroke threshold of the piezoelectric micro-motion unit, the main control module 40 performs amplitude limiting to keep the piezoelectric micro-motion unit within the maximum allowable stroke range. The maximum physical stroke threshold can be determined based on the physical expansion limit of the piezoelectric ceramic stack and the structural constraints of the execution end.

[0088] S403, a high-frequency pressure sensor is installed at the execution end of the servo module 10 to collect the contact stress on the electrode end face at a set sampling rate. The acquisition module 30 receives the contact stress data through the contact force signal sampling channel and feeds it back to the main control module 40 via a high-speed serial bus. The sampling rate of the high-frequency pressure sensor can be configured from 5kHz to 10kHz.

[0089] The main control module 40 controls the piezoelectric micro-motion unit to form a closed-loop pressure maintenance based on real-time contact stress, the critical contact force parameter for plastic softening of the multilayer composite substrate, and the micro-displacement retraction calculation model along the electrode unloading direction. This closed-loop control enables the piezoelectric micro-motion unit to respond to pressure changes caused by the expansion of the weld nugget volume in less than milliseconds, and maintains the contact stress in the welding area near the critical contact force parameter for plastic softening of the multilayer composite substrate, thus forming a minimum contact stress.

[0090] When the weld metal is in a liquid or high-temperature plastic state, the metal vapor pressure and thermal expansion force inside the weld nugget tend to release outward. If the piezoelectric micro-motion unit retracts too quickly, and the external contact stress is lower than the critical contact force parameter for plastic softening of the multilayer composite bottom, the liquid metal may overflow along the interface gap between the inner heat-absorbing layer and the outer magnetic conductive layer, forming hidden spatter or delamination tearing; if the actuator does not retract at all, the continuously rising interface pressure may crush the bottom material in a thermally softened state.

[0091] By using the dynamic yielding of the piezoelectric micro-motion unit and maintaining the high-frequency pressure closed loop, the main control module 40 maintains the necessary forging pressure in the welding area while providing a controlled release space for the thermal expansion of the weld nugget, thereby reducing the probability of spatter, delamination tearing, and thermal softening crushing.

[0092] See attached document Figure 7 , Figure 7 This is a timing-coordinated control diagram for the post-weld processing and automated closed-loop stage in one embodiment of the present invention. Step S50 is used to extend the holding voltage and superimpose the attenuated tempering current according to the previous identification result after the main welding current ends, and at the same time reset the control state to prepare for the next weld point processing. Specifically, it includes the following process.

[0093] S501, After the main welding pulse output is completed, the main control module 40 calls the deviation rate and post-weld compensation strength parameters obtained in step S40. Calculate post-weld compensation parameters. For multi-layered composite bottom workpieces, the coefficients of thermal expansion and cooling contraction characteristics of different metal layers are different; if the weld cools too quickly, residual tensile stress is easily formed inside the weld nugget, inducing cold cracks. Therefore, extending the holding time in the early stage of weld cooling can offset some of the thermal contraction tensile stress through external mechanical constraints.

[0094] The main control module 40 calculates the post-weld compensation strength parameters. The formula for calculating the compensated holding time is as follows: ; In the formula, The pressure holding time after compensation; The basic holding time can be determined by the basic process parameter table pre-stored in the non-volatile memory of the main control module 40; The pressure-holding compensation coefficient can be configured to range from 0.5 to 1.5. This represents the absolute value of the deviation rate.

[0095] To avoid excessively long holding times affecting production line cycle time or causing high-temperature workpieces to stick to the electrodes, the main control module 40 sets a maximum heat dissipation time threshold. This maximum heat dissipation time threshold can be configured as the basic holding time. 1.5 to 2.0 times. When the calculated holding time... When the maximum heat dissipation time threshold is exceeded, the main control module 40 performs a limiting process, reducing the pressure holding time. It is limited to the maximum heat dissipation time threshold.

[0096] In addition to extending the holding time, the main control module 40 also generates control parameters for superimposed decaying temper current. The superimposed decaying temper current adopts an exponential decay waveform, and its mathematical expression is: ; In the formula, for The tempering current value at that moment; This represents the initial current amplitude during tempering. The decay time constant; This represents the duration after the temper pulse is triggered.

[0097] The main control module 40 sets the initial tempering current amplitude. Set the current to 30% to 50% of the peak value of the main welding current, and adjust the decay time constant. Post-weld compensation strength parameters The linear mapping is performed, and the calculation logic is as follows: ; In the formula, The reference decay time constant can be determined by the material heat treatment parameter table pre-stored in the non-volatile memory of the main control module 40; The mapping gain coefficient can be configured to range from 0.2 to 0.5. Through this parameter generation method, when the initial contact state of the workpiece is poor or the initial micro-deformation is large, the main control module 40 can provide relatively gentle heat compensation during the weld crystallization stage to reduce the temperature gradient in the weld joint area.

[0098] S502, the main control module 40 coordinates the operation of the servo module 10 and the inverter module 20 according to the joint finishing control timing. After the main welding current is turned off, the main control module 40 starts the internal pressure holding timer and controls the servo motor in the servo module 10 to continue to maintain the position lock state, so that the welding clamp electrode applies rigid pressure to the workpiece until the pressure holding timer reaches the compensated pressure holding time. .

[0099] Within this pressure holding time window, the main control module 40 synchronously controls the inverter module 20 to output a superimposed attenuated tempering current. By superimposing the tempering current under mechanical pressure holding conditions, the molten nucleus can release thermal stress more slowly under external constraints, reducing the risk of shrinkage defects caused by uncontrolled volume shrinkage during the solidification stage of liquid metal.

[0100] Once the holding timer reaches the set time and the superimposed decaying tempering current output is complete, the main control module 40 terminates the post-weld processing flow. To avoid logic delays caused by abnormal current output duration, the system configures the theoretical duration of the tempering current to be shorter than the compensated holding time. If the underlying timer detects a timeout in the backfire current output, the main control module 40 forcibly cuts off the pulse output of the inverter module 20.

[0101] Subsequently, the main control module 40 sends an electrode lift command to the servo module 10, and the servo drive shaft moves in the opposite direction, causing the welding clamp electrode to detach from the workpiece surface, and the current welding point processing is completed.

[0102] After the electrode is lifted, the main control module 40 executes the state machine reset logic: clears the internal buffer array established in step S30 and returns its read / write pointer to zero; clears the control output register of the piezoelectric micro-motion unit; restores the gain parameters of the position loop proportional-integral-derivative controller; resets the unlock reset flag and other operating variables. This reset logic reduces the impact of residual data and control bias from the previous solder joint on the calculation process of the next solder joint.

[0103] After the state machine is reset, the main control module 40 sends the current solder joint processing completion signal to the external production line programmable logic controller and waits for the next station movement signal or the next pressure start command, thus entering the next automated control cycle.

[0104] For the microcontroller's internal state machine reset procedure, timer configuration, and register clearing method, those skilled in the art can implement them in a conventional way according to the microcontroller architecture and controller interface specification, and will not be described in detail here.

[0105] The specific automated spot welding process is set as the machining of a multi-layer composite bottom for a cookware. The total thickness of the target workpiece is calibrated to 3.5mm, with the outer magnetic layer made of 0.5mm thick 304 stainless steel and the inner heat-absorbing layer made of 3.0mm thick 3003 aluminum alloy. The absolute reference height of the production line positioning fixture is set to 100.0mm. After the main control module 40 analyzes the machining instructions sent from the system communication bus, it calculates the theoretical contact point displacement to be 96.5mm, with a preset safety detection margin of 2.0mm. Thus, the entry boundary value of the approach threshold range is established to be 98.5mm. The servo module 10 drives the electrode to press down. When the absolute displacement reaches 98.5mm, the inverter module 20 injects a unipolar ripple detection pulse into the secondary circuit. The pulse switch switching frequency is configured to 2kHz, the DC bias voltage is set to 5.0V, and the alternating component amplitude is set to 2.0V.

[0106] During the low-pressure detection sequence, the acquisition module 30 extracts the high-frequency response signal. Within a certain sampling period, the servo module 10 reports a downward micro-displacement increment of 0.01 mm, and the main control module 40 calculates and extracts the instantaneous attenuation rate of the dynamic sensing imaginary component as 0.2 mΩ / ms. The system presets a reference profile constant of 1.0 and a material yield sensitivity coefficient of 0.01, which are then substituted into the morphology correction coefficient calculation model: ; The morphology correction coefficient was calculated. The value is 0.818. The uncalibrated equivalent contact surface index obtained in this sampling period is 100.0, the preset nonlinear weighted gain parameter is 0.2, and nonlinear weighted calibration is performed: ; The output digital calibration equivalent contact surface index is 100.66.

[0107] As displacement increases, the main control module 40 extracts the slope of the area expansion trend. When this slope is lower than the system tolerance threshold for four consecutive calculation cycles, a servo spindle position lock command is triggered, and the value of 100.66 at this time is recorded as the initial feature value. The main control module 40 then issues a micro-motion test command, and the piezoelectric micro-motion unit performs a 0.02mm step disturbance, acquiring the equivalent contact surface index peak value of 105.16. The difference between the two is used to extract the yield evolution range as 4.50. The yield feature mapping table of multilayer composite materials is called, and the interpolated output of the critical contact force parameter for plastic softening of the multilayer composite bottom of the target workpiece in the current state is 1500N.

[0108] The system retrieves the baseline characteristic value of 114.38 set in the non-volatile memory, compares it with the initial characteristic value to generate a deviation difference of -13.72, and calculates a deviation rate of -12%. The absolute value of this deviation rate, 0.12, is within the safety tolerance limit. Based on this data feedback, the initial assembly contact of the workpiece is in a state of high impedance underfitting. The main control module 40 reconstructs the welding sequence, extending the main current ramp-up time from the standard 20ms to 24ms. The main welding energy injection causes the metal sublayer to melt and expand, and the acquisition module 30 monitors a sudden increase in the real-time physical contact force feedback value to 1650N. The system presets the micro-motion following gain constant to 0.0001mm / N, and the main control module 40 calculates the reverse micro-displacement yield amount: ; A yield command of 0.015mm is generated and executed by the piezoelectric micro-motion unit to release the transient internal pressure and clamp the stress balance in the fusion zone.

[0109] Welding energy output shutdown triggers the termination control. The preset basic holding time is 200ms, and the holding time compensation coefficient is 1.0. The main control module 40 adaptively calculates and extends the holding time. ; The actual pressure holding time was determined to be 224ms, which meets the maximum heat dissipation time threshold constraint. The baseline decay time constant of 50ms and the mapping gain coefficient of 0.5 were extracted simultaneously to calculate the target decay constant. ; The output constant is 53ms. Based on this, inverter module 20 outputs an exponentially decaying waveform backfire current within a 224ms holding voltage window. After the timing ends, the underlying state machine is interrupted and reset, clearing the data pointer and entering the next cycle.

[0110] Continuous automated spot welding verification tests were conducted on the aforementioned equivalent hardware production line platform. 500 multi-layer composite bottom workpieces of the same specifications were selected and divided into two groups, each containing 250 test samples. The first group used traditional constant voltage and constant current hard specification welding, while the second group was connected to the macro-micro dual-drive adaptive flexible following control system described in this invention. Throughout the test, interface mechanical data were synchronously captured using an external high-frequency stress tester. After processing, joint fracture tests and metallographic defect detection were performed. Specific comparative data are shown in Table 1 below.

[0111] Table 1: Comparison of performance indicators between traditional control schemes and the scheme of the present invention

[0112] refer to Figures 8 to 9As shown in Table 1, the traditional rigid feed control mode lacks real-time response capability to the evolution of the interfacial thermophysical state when dealing with multilayer heterogeneous composite metals. During the main welding current injection, the underlying aluminum alloy and the surface stainless steel have different coefficients of thermal expansion, resulting in nonlinear volume expansion of the interfacial material during the thermal softening stage. The fixed macroscopic mechanical constraints cannot release the transient high pressure, leading to a sharp increase in the thermomechanical stress gradient at the interface. Combined with the analysis of the macro-micro dual-drive three-dimensional morphology and contact stress coupling evolution heat map data, it can be seen that the uncompensated rigid constraints force the local liquid material to break through the interfacial barrier to form extrusion splash, and induce deep microscopic delamination tearing along the phase interface.

[0113] This adaptive spot welding control scheme reconstructs the thermomechanical coupling release path through multi-dimensional signal decoupling and a macro-micro dual-drive architecture. During the displacement detection phase, the system removes the transient attenuation rate of the high-frequency dynamic impedance and generates online morphology correction coefficients to compensate for contact measurement offsets. Within the time window of volume expansion induced by the main current discharge, the main control module utilizes the critical barrier parameters output from the multilayer composite material yield characteristic mapping table to drive the piezoelectric micro-motion unit to perform closed-loop stress following and millisecond-level micro-displacement retraction. This spatiotemporal collaborative constraint mechanism, while maintaining the minimum forging pressure, provides a controlled expansion channel for the intense phase transformation of the deep liquid metal during the excited period, blocking the runaway overflow path of the molten alloy from its physical source.

[0114] The clustering characteristics of the radar topology map showing the combined distribution of shear strength and multidimensional micro-defects in the weld nugget joint verified the reliability of the aforementioned collaborative mechanism. The combined intervention of servo micro-motion retreat and post-weld superimposed attenuation tempering sequence resolved the structural thermal stress caused by the imbalance of cooling contraction during the solidification stage of the liquid metal. The range of spot weld shear strength converged significantly to 0.2 kN, and the overall mechanical property distribution exhibited highly dense and uniform characteristics. Experimental feedback indicators confirmed that core process defects such as contact state misjudgment, deep delamination tearing, and initial spatter were effectively suppressed. This digital closed-loop reconstruction algorithm significantly improved the joint forming quality and process consistency under continuous high-load spot welding conditions.

[0115] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A spot welding control system for adaptive adjustment in a cookware processing production line, characterized in that, include: The servo module includes a servo motor, an absolute encoder, a piezoelectric ceramic micro-motion unit, and a high-frequency pressure sensor; the absolute encoder acquires and feeds back the mechanical displacement of the welding gun; the piezoelectric ceramic micro-motion unit and the high-frequency pressure sensor are both located at the end of the welding gun's actuation mechanism; the high-frequency pressure sensor acquires the contact force signal of the contact area. The inverter module receives inverter control commands from the main control module and adjusts the output current of the welding secondary circuit. The acquisition module includes a face voltage sampling cable, a Rogowski coil, an integral conditioning circuit, and a contact force signal sampling channel. The face voltage sampling cable acquires the raw voltage signal. The Rogowski coil generates the raw loop current signal through the integral conditioning circuit. The contact force signal sampling channel receives the contact force signal. The acquisition module sends the raw voltage signal, the raw loop current signal, and the contact force signal to the main control module. The main control module is connected to the servo module, inverter module, and acquisition module respectively; the main control module has a built-in mechanical electromagnetic coupling dynamic analysis kernel; the main control module generates servo control commands and inverter control commands based on the original voltage signal, the original loop current signal, the mechanical displacement and the contact force signal.

2. The adaptive adjustment spot welding control system for cookware processing production line according to claim 1, characterized in that, After receiving the trigger signal, the main control module generates an initial digital motion command and sends it to the servo module. The servo motor drives the welding clamp to press down, and the absolute encoder collects the current mechanical displacement and feeds it back to the main control module. When the current mechanical displacement exceeds the entry boundary value close to the threshold range, the main control module sends a duty cycle control command to the inverter module, and the inverter module injects a unipolar ripple detection pulse into the welding secondary circuit. The unipolar ripple detection pulse is formed by the superposition of a DC bias component and a high-frequency alternating component. When the effective value of the original circuit current signal exceeds the safety monitoring lower limit and the contact force signal exceeds the initial contact pressure threshold, the main control module establishes an effective sampling window.

3. The adaptive adjustment spot welding control system for cookware processing production line according to claim 2, characterized in that, The main control module filters the original voltage signal and the original loop current signal within the effective sampling window to remove the DC bias component, and obtains the alternating voltage ripple component and the alternating current ripple component respectively. The main control module tracks the phase angle of the alternating voltage ripple component through a phase-locked loop and calculates the total delay time by combining the delay constant. The main control module applies lead phase compensation to the alternating current ripple component according to the total delay time. The main control module performs Hilbert transform on the alternating voltage ripple component and the alternating current ripple component after lead phase compensation to reconstruct the transient complex impedance analytical model. The main control module separates the imaginary component of the dynamic inductive reactance through the transient complex impedance analytical model.

4. The adaptive adjustment spot welding control system for cookware processing production line according to claim 3, characterized in that, The main control module calculates the uncalibrated equivalent contact surface index based on the ratio of the amplitude of the alternating current ripple component to the amplitude of the alternating voltage ripple component. The main control module timestamps the imaginary component of the dynamic reactance and the mechanical displacement, and matches the instantaneous decay rate of the imaginary component of the dynamic reactance with the incremental pressure displacement of the mechanical displacement as a data pair according to the timestamp. The main control module calculates the morphology correction coefficient based on the instantaneous decay rate, the incremental pressure displacement, the reference profile constant, and the material yield sensitivity coefficient. The main control module uses the morphology correction coefficient to perform nonlinear weighted calibration on the uncalibrated equivalent contact surface index to generate the calibrated equivalent contact surface index.

5. The adaptive adjustment spot welding control system for cookware processing production line according to claim 4, characterized in that, When the displacement change fed back by the absolute encoder reaches a fixed physical step, the main control module writes the mechanical displacement and the calibrated equivalent contact surface index as physical state data pairs into the internal buffer array. When the number of physical state data pairs in the internal buffer array reaches the set queue length, the main control module uses the least squares method to perform linear regression calculation on the physical state data pairs in the internal buffer array to obtain the slope of the area expansion trend. When the slope of the area expansion trend is less than the tolerance threshold for a continuous set number of calculation cycles, the main control module sends a position locking command to the servo module, and the main control module records the equivalent contact surface index of the current cycle as the initial feature value.

6. The adaptive adjustment spot welding control system for cookware processing production line according to claim 5, characterized in that, After receiving the position lock command, the servo module enters a high-rigidity position holding state. In this state, the main control module controls the servo motor to maintain the main drive shaft position lock and controls the piezoelectric ceramic micro-motion unit to generate superimposed step-load extrusion. The main control module establishes a pre-sampling window before the superimposed step-load extrusion occurs and establishes a post-sampling window after the step impulse of the superimposed step-load extrusion reaches its absolute peak value. The main control module calculates the arithmetic mean of the calibrated equivalent contact surface index within the pre-sampling window, extracts the absolute peak value of the calibrated equivalent contact surface index within the post-sampling window, and calculates the yield evolution range by subtracting the absolute peak value from the arithmetic mean.

7. The adaptive adjustment spot welding control system for cookware processing production line according to claim 6, characterized in that, The main control module compares the yield evolution range with a preset comparison threshold. When the yield evolution range exceeds the preset comparison threshold, the main control module determines that the bottom metal has undergone microscopic plastic yielding. The main control module stores a multilayer composite material yield feature mapping table. The main control module inputs the yield evolution range into the multilayer composite material yield feature mapping table and obtains the critical contact force parameter for plastic softening of the multilayer composite bottom through linear interpolation matching.

8. The adaptive adjustment spot welding control system for cookware processing production line according to claim 7, characterized in that, The main control module calculates the difference between the initial characteristic value and the reference characteristic value. The main control module uses the ratio of the difference to the reference characteristic value as the deviation rate. The main control module extracts the absolute value of the deviation rate as the post-weld compensation strength parameter. The main control module generates welding pulse parameters including the peak value of the main welding current and the welding pulse rise time based on the deviation rate. The main control module controls the inverter module to output medium-frequency DC main current to the welding secondary circuit according to the welding pulse parameters.

9. The adaptive adjustment spot welding control system for cookware processing production line according to claim 8, characterized in that, During the output of the intermediate frequency DC main current by the inverter module, the servo motor maintains the main drive shaft position locked state; the main control module calculates the micro-displacement yielding amount based on the contact force signal fed back by the high frequency pressure sensor, the critical contact force parameter of the multi-layer composite bottom plastic softening, and the micro-motion following gain constant; when the pressure value of the contact force signal exceeds the value of the critical contact force parameter of the multi-layer composite bottom plastic softening, the main control module controls the piezoelectric ceramic micro-motion unit to perform micro-displacement yielding along the electrode unloading direction according to the micro-displacement yielding amount.

10. The adaptive adjustment spot welding control system for cookware processing production line according to claim 9, characterized in that, After the medium-frequency DC main current output is completed, the main control module calculates the compensated holding time based on the basic holding time, the holding compensation coefficient, and the post-weld compensation strength parameters. The main control module controls the servo motor to maintain the main drive shaft position locked until the internal holding timer reaches the compensated holding time. The main control module calculates the attenuation time constant based on the reference attenuation time constant, the mapping gain coefficient, and the post-weld compensation strength parameters. Within the compensated holding time window, the main control module controls the inverter module to output a superimposed attenuated tempering current to the welding secondary circuit. The superimposed attenuated tempering current exhibits an exponential attenuation waveform according to the attenuation time constant.

Images