Method and system for regulating and controlling welding current of inverter resistance welding machine in real time

Abstract

The invention provides a method and a system for regulating and controlling welding current of an inverter resistance welding machine in real time. The method comprises the following steps: welding and acquiring a primary side current signal of a transformer; carrying out segment processing on the current signal of the current cyclic wave; processing and calculating a fast rising section; judging a starting point of a slope section; calculating the target peak current of the slope section; calculating a current cyclic current statistical value; and adjusting the target peak current of the next cycle. Primary side current signals of the inverter type welding machine are collected in real time, segmentation processing and characteristic quantity extraction are conducted on the current signals, the starting point of the slope section is judged, and the target peak current of the slope section is calculated according to a current target value; when the current of the slope section reaches the target peak current, the welding current is cut off; calculating a current statistical value in the current cycle, comparing the current statistical value with a current target value, and adjusting the target peak current of the next cycle; and the steps are repeated until the welding power-on time reaches the preset value, and therefore real-time fine control over the welding current is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of real-time control of welding current of resistance spot welding, and specifically to a real-time control method and system for welding current of an inverter resistance welding machine, and in particular to a real-time control method for welding current of an inverter resistance welding machine based on primary current control. Background Art

[0002] In the process of resistance spot welding, the control of welding current plays a vital role in the welding quality. Traditional welding current control methods often rely on preset welding parameters and fixed control strategies. However, in practical applications, the actual value of welding current often deviates from the preset value, which can lead to unstable welding quality. In particular, due to the increase in the temperature of the workpiece during welding, its resistance value will change accordingly. When the load resistance changes, the control effect of welding current will be significantly affected. In addition, interference factors such as welding spatter and transformer magnetization may also occur during welding, making it impossible to achieve real-time and accurate control of welding current.

[0003] The present invention proposes a new real-time control method for welding current to improve the above technical problems. The method first collects the primary current signal and divides it into segments: a fast rising segment, a ramp segment and a current shut-off segment. The characteristic quantity of the current signal is then calculated to determine the starting point of the ramp segment. The target peak current of the next cycle is then continuously adjusted according to the current target value and the measured statistical value until the welding power-on time reaches the preset value, thereby achieving fine control of the welding current. Summary of the invention

[0004] In view of the defects in the prior art, the object of the present invention is to provide a method and system for real-time control of welding current of an inverter resistance welding machine.

[0005] According to a method for real-time control of welding current of an inverter resistance welding machine provided by the present invention, the method comprises the following steps:

[0006] Step a1: performing resistance spot welding, collecting primary current signals and obtaining a curve graph of current variation over time;

[0007] Step a2: Based on the curve diagram of current changing with time, the current signal is divided into different cycles according to the inversion period, and the current signal of each cycle is divided into a fast rising section T1, a ramp section T2 and a current closing section T3 according to the welding current being turned on and off;

[0008] Step a3: for the current signal of the current cycle, the fast rising section T1 is processed and calculated, and the characteristic quantity of the current signal is extracted by performing average value filtering on the primary current sampling value to obtain a characteristic quantity curve graph, and the fast rising section is determined according to the characteristic quantity curve graph;

[0009] Step a4: Determine the starting point of the slope segment T2, determine the starting point of the slope segment T2 according to the characteristic value curve, set the characteristic value threshold, including the high threshold D H , low threshold D L , where the feature value is higher than the high threshold D for the first time H And it is lower than the lower threshold D L When the current is lower than the low threshold, it is the starting point of the slope segment T2, which is recorded as the current value corresponding to the starting point of the slope segment T2 I V ;

[0010] Step a5: Calculate the target peak current of ramp section T2, based on the current target value I T and the current value I at the starting point of the ramp segment T2 V Calculate the target peak current I of ramp stage T2 P , that is, the current value at the time of on-off; when the current in the ramp section T2 reaches the target peak current I P The primary welding current is switched from on to off to adjust the welding current of the current cycle in real time;

[0011] Step a6: Calculate the current statistics of the current cycle, starting from the starting point of the ramp segment T2 to the current shut-off time, and perform point-by-point weighted accumulation calculation on the current sampling values ​​within the time range from the starting point of the ramp segment T2 to the current shut-off time to obtain the ramp segment T2 statistics I A ;

[0012] Step a7: According to I A and I T Adjust the target peak current I of the next cycle P The calculation formula of

[0013] Step a8: Repeat the above steps until the welding power-on time reaches a preset value.

[0014] Preferably, in the step a1: the primary current signal of the inverter resistance welding machine is collected in real time, and the primary current signal refers to the rated current of the winding on the high voltage side, ie, the power input side, of the transformer in the inverter welding machine.

[0015] Preferably, in step a2: the rapid rising section T1 refers to the stage in which the welding current conduction current value increases rapidly; the ramp section T2 refers to the stage in which the welding current is basically stable but increases slowly due to the change in workpiece resistance; the current closing section T3 refers to the stage from the welding current being shut off to being turned on again.

[0016] Preferably, in step a3: the characteristic quantity, namely the first-order difference of the current signal with respect to time, is used to obtain a first-order difference curve graph of the current signal with respect to time.

[0017] Preferably, in step a5: the target slope segment peak value I P The calculation formula is: Where: I T is the current target value, I V is the current value at the starting point of the ramp section, and α and β are both proportional parameters.

[0018] Preferably, the collected current value and characteristic quantity, i.e., the first-order differential data of the current value to time, are input into the calculation and analysis module, and the slope segment statistical value calculation formula is used to perform point-by-point weighted calculation, wherein the calculation and analysis module includes: a microprocessor, an industrial computer, a PLC, a monitoring instrument, a welding controller, a desktop computer, a laptop computer, a server or a workstation; the calculation formula of the point-by-point weighted cumulative calculation is: Among them I i is the sampling value of the i-th point, w i is the weight coefficient of the i-th point, n is the total number of sampling points, and m is the power weight coefficient.

[0019] Preferably, in step a7: according to I A and I T The difference adjusts the next cycle's proportion parameter β, that is, β←β+f(I A -I T ), where f is the specific adjustment method, and PID control method is adopted.

[0020] The present invention also provides a real-time control system for welding current of an inverter resistance welding machine, the system comprising the following modules:

[0021] Module m1: performs resistance spot welding, collects primary current signals and obtains a curve graph of current variation over time;

[0022] Module m2: Based on the curve of current changing with time, the current signal is divided into different cycles according to the inversion period. The current signal of each cycle is divided into a fast rising section T1, a ramp section T2 and a current closing section T3 according to the welding current on and off;

[0023] Module m3: for the current signal of the current cycle, the fast rising section T1 is processed and calculated, the characteristic quantity of the current signal is extracted by performing average value filtering on the primary current sampling value, a characteristic quantity curve is obtained, and the fast rising section is determined according to the characteristic quantity curve;

[0024] Module m4: Determine the starting point of the slope segment T2, determine the starting point of the slope segment T2 according to the characteristic curve, and set the characteristic threshold, including the high threshold D H , low threshold D L , where the feature value is higher than the high threshold D for the first time H And it is lower than the lower threshold D LWhen the current is lower than the low threshold, it is the starting point of the slope segment T2, which is recorded as the current value corresponding to the starting point of the slope segment T2 I V ;

[0025] Module m5: Calculate the target peak current of ramp section T2, according to the current target value I T and the current value I at the starting point of the ramp segment T2 V Calculate the target peak current I of ramp stage T2 P , that is, the current value at the time of on-off; when the current in the ramp section T2 reaches the target peak current I P The primary welding current is switched from on to off to adjust the welding current of the current cycle in real time;

[0026] Module m6: Calculate the current statistics of the current cycle, from the starting point of the ramp segment T2 to the current shut-off time, perform point-by-point weighted accumulation calculation on the current sampling values ​​within the time range from the starting point of the ramp segment T2 to the current shut-off time, and obtain the ramp segment T2 statistics I A ;

[0027] Module m7: According to I A and I T Adjust the target peak current I of the next cycle P The calculation formula of

[0028] Module m8: Repeat the above modules until the welding power-on time reaches the preset value.

[0029] Preferably, in the module m1: the primary current signal of the inverter resistance welding machine is collected in real time, wherein the primary current signal refers to the rated current of the winding on the high voltage side, i.e., the power input side, of the transformer in the inverter welding machine;

[0030] In the module m2: the rapid rise section T1 refers to the stage in which the welding current conduction current value increases rapidly; the ramp section T2 refers to the stage in which the welding current is basically stable but increases slowly due to the change of the workpiece resistance; the current closing section T3 refers to the stage from the welding current being turned off to being turned on again;

[0031] In the module m3: the characteristic quantity is the first-order difference of the current signal with respect to time, and a first-order difference curve graph of the current signal with respect to time is obtained.

[0032] Preferably, in the module m5: the target slope segment peak value I P The calculation formula is: Where: I T is the current target value, I V is the current value at the starting point of the ramp section, α and β are both proportional parameters;

[0033] The collected current value and characteristic quantity, i.e., the first-order differential data of the current value to time, are input into the calculation and analysis module, and the slope segment statistical value calculation formula is used to perform point-by-point weighted calculation, wherein the calculation and analysis module includes: a microprocessor, an industrial computer, a PLC, a monitoring instrument, a welding controller, a desktop computer, a laptop computer, a server or a workstation; the calculation formula of the point-by-point weighted accumulation calculation is: Among them I i is the sampling value of the i-th point, w i is the weight coefficient of the i-th point, n is the total number of sampling points, and m is the power weight coefficient;

[0034] In the module m7: according to I A and I T The difference adjusts the next cycle's proportion parameter β, that is, β←β+f(I A -I T ), where f is the specific adjustment method, and PID control method is adopted.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention collects the primary current signal of the inverter welding machine in real time, and processes it in sections, namely, a fast rising section, a ramp section and a current shut-off section; uses the characteristic quantity to determine the starting point of the ramp section, and calculates the target peak current of the ramp section according to the current target value; when the current of the ramp section reaches the target peak current, the welding current is shut off, thereby performing real-time regulation on the current cycle welding current; calculates the current statistical value of the current cycle and compares it with the current target value, and then adjusts the target peak current of the next cycle; repeats the above steps until the welding power-on time reaches the preset value, thereby achieving fine control of the welding current;

[0037] 2. The present invention effectively reduces welding current fluctuations caused by welding spatter, transformer magnetization, load changes, etc. by real-time monitoring and controlling welding current, improves the consistency of the welding process, ensures the strength and reliability of the joint, reduces the scrap rate in the welding process, and improves production efficiency;

[0038] 3. The present invention overcomes the drawbacks of the traditional method of only measuring the current frequency without adjusting it, realizes real-time control of the current frequency welding current, and improves the timeliness of control; by iteratively adjusting the target peak current of the next frequency, it realizes adaptation to different loads; it can be widely used in welding of plates of different materials and thicknesses, and improves the versatility and adaptability of current control. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0040] Figure 1 is a flow chart of the present invention;

[0041] Figure 2 It is a system schematic diagram of the present invention;

[0042] Figure 3 This is a schematic diagram of collecting primary current signals of the present invention;

[0043] Figure 4 It is a schematic diagram of the segmented processing of the current cycle current signal of the present invention;

[0044] Figure 5 This is a schematic diagram of determining the starting point of a slope section according to the present invention;

[0045] Among them, 1. electrode cap; 2. electrode rod; 3. workpiece to be measured; 4. current sensor; 5. current signal acquisition module; 6. calculation and analysis module; 7. current control module. DETAILED DESCRIPTION

[0046] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0047] Embodiment 1:

[0048] According to a method for real-time control of welding current of an inverter resistance welding machine provided by the present invention, the method comprises the following steps:

[0049] Step a1: Perform resistance spot welding, collect primary current signals and obtain a curve graph of current changes over time; collect the primary current signal of the inverter resistance welding machine in real time, wherein the primary current signal refers to the rated current of the winding on the high-voltage side, i.e., the power input side, of the transformer in the inverter welding machine.

[0050] Step a2: Based on the curve graph of current change over time, the current signal is divided into different cycles according to the inversion period, and the current signal of each cycle is divided into a fast rising section T1, a ramp section T2 and a current closing section T3 according to the welding current being turned on and off; the fast rising section T1 refers to the stage in which the welding current value increases rapidly after being turned on; the ramp section T2 refers to the stage in which the welding current is basically stable but increases slowly due to the change in workpiece resistance; the current closing section T3 refers to the stage from when the welding current is turned off to when it is turned on again.

[0051] Step a3: For the current signal of the current cycle, process and calculate the fast rising section T1, perform average value filtering on the primary current sampling value, extract the characteristic quantity of the current signal, obtain the characteristic quantity curve graph, and judge the fast rising section according to the characteristic quantity curve graph; the characteristic quantity is the first-order difference of the current signal with respect to time, and obtain the first-order difference curve graph of the current signal with respect to time.

[0052] Step a4: Determine the starting point of the slope segment T2, determine the starting point of the slope segment T2 according to the characteristic value curve, set the characteristic value threshold, including the high threshold D H , low threshold D L , where the feature value is higher than the high threshold D for the first time H And it is lower than the low threshold D L When the current is lower than the low threshold, it is the starting point of the slope segment T2, which is recorded as the current value corresponding to the starting point of the slope segment T2 I V ;

[0053] Step a5: Calculate the target peak current of ramp section T2, based on the current target value I T and the current value I at the starting point of the ramp segment T2 V Calculate the target peak current I of ramp stage T2 P , that is, the current value at the time of on-off; when the current in the ramp section T2 reaches the target peak current I P The original welding current is switched from on to off state, so as to adjust the welding current of the current cycle in real time; the target slope peak value I P The calculation formula is: Where: I T is the current target value, I V is the current value at the starting point of the ramp section, and α and β are both proportional parameters.

[0054] Step a6: Calculate the current statistics of the current cycle, starting from the starting point of the ramp segment T2 to the current shut-off time, and perform point-by-point weighted accumulation calculation on the current sampling values ​​within the time range from the starting point of the ramp segment T2 to the current shut-off time to obtain the ramp segment T2 statistics I A ; Input the collected current value and characteristic quantity, i.e., the first-order differential data of the current value to time, into the calculation and analysis module, and perform point-by-point weighted calculation using the slope segment statistical value calculation formula, wherein the calculation and analysis module includes: a microprocessor, an industrial computer, a PLC, a monitoring instrument, a welding controller, a desktop computer, a laptop computer, a server or a workstation; the calculation formula for the point-by-point weighted cumulative calculation is: Among them I i is the sampling value of the i-th point, w i is the weight coefficient of the i-th point, n is the total number of sampling points, and m is the power weight coefficient.

[0055] Step a7: According to I A and I T Adjust the target peak current I of the next cycle P The calculation formula is as follows: A and I T The difference adjusts the next cycle's proportion parameter β, that is, β←β+f(I A -I T ), where f is the specific adjustment method, and PID control method is adopted.

[0056] Step a8: Repeat the above steps until the welding power-on time reaches a preset value.

[0057] The present invention also provides a real-time control system for the welding current of an inverter resistance welding machine. The real-time control system for the welding current of an inverter resistance welding machine can be realized by executing the process steps of the real-time control method for the welding current of an inverter resistance welding machine, that is, those skilled in the art can understand the real-time control method for the welding current of an inverter resistance welding machine as a preferred implementation of the real-time control system for the welding current of an inverter resistance welding machine.

[0058] Embodiment 2:

[0059] The present invention also provides a real-time control system for welding current of an inverter resistance welding machine, the system comprising the following modules:

[0060] Module m1: Perform resistance spot welding, collect primary current signals and obtain a curve chart of current changes over time; collect primary current signals of the inverter resistance welding machine in real time, wherein the primary current signal refers to the rated current of the winding on the high-voltage side, i.e., the power input side, of the transformer in the inverter welding machine;

[0061] Module m2: Based on the curve of current changing with time, the current signal is divided into different cycles according to the inversion period. The current signal of each cycle is divided into a fast rising section T1, a ramp section T2 and a current closing section T3 according to the welding current being turned on and off; the fast rising section T1 refers to the stage in which the welding current value increases rapidly when the welding current is turned on; the ramp section T2 refers to the stage in which the welding current is basically stable but increases slowly due to the change of the workpiece resistance; the current closing section T3 refers to the stage from the welding current being turned off to being turned on again;

[0062] Module m3: For the current signal of the current cycle, the fast rising section T1 is processed and calculated. By performing average value filtering on the primary current sampling value, the characteristic quantity of the current signal is extracted to obtain a characteristic quantity curve graph, and the fast rising section is judged according to the characteristic quantity curve graph; the characteristic quantity is the first-order difference of the current signal with respect to time, and the first-order difference curve graph of the current signal with respect to time is obtained.

[0063] Module m4: Determine the starting point of the slope segment T2, determine the starting point of the slope segment T2 according to the characteristic curve, and set the characteristic threshold, including the high threshold D H , low threshold D L , where the feature value is higher than the high threshold D for the first time H And it is lower than the low threshold D L When the current is lower than the low threshold, it is the starting point of the slope segment T2, which is recorded as the current value corresponding to the starting point of the slope segment T2 I V ;

[0064] Module m5: Calculate the target peak current of ramp section T2, according to the current target value I T and the current value I at the starting point of the ramp segment T2 V Calculate the target peak current I of ramp stage T2 P , that is, the current value at the time of on-off; when the current in the ramp section T2 reaches the target peak current I P The original welding current is switched from on to off state, so as to adjust the welding current of the current cycle in real time; the target slope peak value I P The calculation formula is: Where: I T is the current target value, I V is the current value at the starting point of the ramp section, α and β are both proportional parameters;

[0065] Module m6: Calculate the current statistics of the current cycle, from the starting point of the ramp segment T2 to the current shut-off time, perform point-by-point weighted accumulation calculation on the current sampling values ​​within the time range from the starting point of the ramp segment T2 to the current shut-off time, and obtain the ramp segment T2 statistics I A ; Input the collected current value and characteristic quantity, i.e., the first-order differential data of the current value to time, into the calculation and analysis module, and perform point-by-point weighted calculation using the slope segment statistical value calculation formula, wherein the calculation and analysis module includes: a microprocessor, an industrial computer, a PLC, a monitoring instrument, a welding controller, a desktop computer, a laptop computer, a server or a workstation; the calculation formula for the point-by-point weighted cumulative calculation is: Among them I i is the sampling value of the i-th point, w i is the weight coefficient of the i-th point, n is the total number of sampling points, and m is the power weight coefficient;

[0066] Module m7: According to I A and I T Adjust the target peak current I of the next cycle P The calculation formula is as follows: A and I T The difference adjusts the next cycle's proportion parameter β, that is, β←β+f(I A -I T), where f is the specific adjustment method, and PID control method is adopted.

[0067] Module m8: Repeat the above modules until the welding power-on time reaches the preset value.

[0068] Embodiment 3:

[0069] like Figure 2 As shown, the workpieces to be welded in this embodiment are divided into three types of materials, namely no load, small load 0.8mm steel plate + 0.8mm steel plate and large load 1.6mm steel plate + 1.6mm steel plate. The inverter frequency is 1kHz, the transformer ratio is 40:1, and the current is set to 4-12kA. The welding current of the inverter resistance welding machine is controlled in real time through the following steps.

[0070] Step S1: Take a small load as an example to perform resistance spot welding, the welding current is selected as 8kA, so the target current I T = 200A, real-time acquisition and recording of current signals during resistance spot welding, and a curve graph of current changing with time is obtained, such as Figure 3 shown.

[0071] Step S2: Based on the curve graph of current variation over time, the current signal is divided into different cycles according to the inversion period. The current signal of each cycle is divided into a fast rising section T1, a ramp section T2 and a current closing section T3 according to the welding current on and off.

[0072] Step S3: For the current signal of the current cycle, process and calculate the fast rising section. By filtering the primary current sampling value by average value, extract the characteristic quantity of the current signal in the resistance spot welding process, and obtain the characteristic quantity curve diagram, such as Figure 5 As shown, the fast rising section is judged according to the characteristic quantity schematic diagram. At t1=0.65ms, the characteristic quantity changes from zero to greater than zero. Therefore, the moment t1 is the starting point of the fast rising section. In this example, the rising section time is 16.12μs.

[0073] Step S4: Determine the starting point of the slope segment according to the characteristic quantity diagram, such as Figure 5 As shown in Table 1, the feature threshold is set, where the high threshold D H 2×10 5 A.S. -1 , low threshold D L For 10 5 A.S. -1 At t2 = 0.66 ms, the feature value is higher than the high threshold D for the first time. H And it is lower than the low threshold D L The time t2 is the starting point of the slope segment. Figure 3 Find the current value I corresponding to time t2 V=125A.

[0074] Table 1 Recommended table for selecting high and low thresholds

[0075] <![CDATA[I T / A]]> <![CDATA[D H / A·S -1 ]]> <![CDATA[D L / A·S -1 ]]> 0-75 <![CDATA[3×10 4 ]]> <![CDATA[1×10 4 ]]> 75-150 <![CDATA[5×10 4 ]]> <![CDATA[2×10 4 ]]> 150-300 <![CDATA[1×10 5 ]]> <![CDATA[5×10 4 ]]> 300-600 <![CDATA[2×10 5 ]]> <![CDATA[1×10 5 ]]> 600-1200 <![CDATA[3×10 5 ]]> <![CDATA[2×10 5 ]]> 1200-2400 <![CDATA[3×10 5 ]]> <![CDATA[4×10 5 ]]>

[0076] Step S5: According to the current target value I T and the current value I at the starting point of the ramp segment V Calculate the target peak current I P , target peak current I P The calculation formula is: Among them I T is the current target value, I V is the current value at the starting point of the slope segment, α and β are both proportional parameters. In this example, α = 0.5, and the initial value of β is 1, that is, I P =2I T -I V , when the current target value I T =200A, the corresponding target peak current I can be obtained according to the formula P =275A, the corresponding moment t3=0.84ms is the current shut-off moment, and the welding current is turned off, thereby realizing real-time regulation of the welding current.

[0077] Step S6: From the start point of the ramp segment T2 to the current cut-off point, perform point-by-point weighted accumulation calculation on the current sampling values ​​within this time range to obtain the ramp segment T2 statistical value I A , Slope section statistics I A The calculation formula is: where w i is the weight coefficient of the i-th point. In this example I i is the sampling value of the i-th point, n is the total number of sampling points. In this embodiment, n=180, and the slope segment statistical value I is calculated. A =195A.

[0078] Step S7: According to I A and I T Adjust the proportion parameter β of the next cycle. This example uses proportional control, and the proportional coefficient is 0.01, that is, β←β+0.01(I A -I T ). After 5 cycles, the slope segment statistics value I A =198A, the error rate is 1.0%, achieving fine control of welding current.

[0079] It can be seen from Table 2 that when the current is set to 4-12 kA, the measured current also changes with the change of load size. Compared with the traditional method, the new method has smaller fluctuations under different loads, thereby verifying the effectiveness of the present invention.

[0080] Table 2 Comparison of the error between actual current and set current of different loads

[0081]

[0082] Example 4

[0083] Compared with Example 3, the workpiece to be welded in this embodiment is 2 mm aluminum plate + 2 mm aluminum plate, the welding current is 30 kA, the inverter frequency is 2 kHz, and the transformer ratio is 30:1, so the target current I T =1000A, and the welding current of the inverter resistance welding machine is controlled in real time using the same steps.

[0084] In this embodiment, the feature threshold is selected as a high threshold D H 3×10 5 A.S. -1 , low threshold D L 2×10 5 A.S. -1 .

[0085] In this embodiment, the starting point of the fast rising section is t1 = 0.56ms, and the rising section time is 60.36μs. According to the high threshold and the low threshold, the starting point of the ramp section is t2 = 0.62ms, and the starting point of the ramp section corresponds to the current value I V =923A.

[0086] The target peak current I P Using the current target value I A The current value I corresponding to the starting point of the slope segment V Calculated, in this example, α = 0.5, β initial value is 1, the calculation formula is: I P =2I T -I V , I T The target current value is equal to 1000A in this example, and the target peak current I is calculated. P =1079A, the welding current is turned off at the corresponding time t3=0.88ms.

[0087] In this embodiment, the slope section statistics value I A The calculation formula is: in I iis the sampling value of the i-th point, the total number of sampling points n = 260, and the slope segment statistical value I is calculated A =988.6A. According to I A and I T Adjust the proportion coefficient β of the next cycle. This example uses proportional integral control, the proportional coefficient is 0.01, and the integral time constant is 0.002. After 6 cycles, the current ramp segment statistical value I A =998.3A, the error rate is 0.17%, achieving fine control of welding current.

[0088] Those skilled in the art know that, in addition to realizing the system and its various devices, modules, and units provided by the present invention in a purely computer-readable program code, it is entirely possible to realize the same functions in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered as a hardware component, and the devices, modules, and units included therein for realizing various functions can also be regarded as structures within the hardware component; the devices, modules, and units for realizing various functions can also be regarded as both software modules for realizing the method and structures within the hardware component.

[0089] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A method for real-time control of welding current of an inverter resistance welding machine, characterized in that: The method comprises the following steps: Step a1: performing resistance spot welding, collecting primary current signals and obtaining a curve graph of current variation over time; Step a2: Based on the curve diagram of current changing with time, the current signal is divided into different cycles according to the inversion period, and the current signal of each cycle is divided into a fast rising section T1, a ramp section T2 and a current closing section T3 according to the welding current being turned on and off; Step a3: for the current signal of the current cycle, the fast rising section T1 is processed and calculated, and the characteristic quantity of the current signal is extracted by performing average value filtering on the primary current sampling value to obtain a characteristic quantity curve graph, and the fast rising section is determined according to the characteristic quantity curve graph; Step a4: Determine the starting point of the slope segment T2, determine the starting point of the slope segment T2 according to the characteristic value curve, set the characteristic value threshold, including the high threshold D H , low threshold D L , where the feature value is higher than the high threshold D for the first time H And it is lower than the lower threshold D L When the current is lower than the low threshold, it is the starting point of the slope segment T2, which is recorded as the current value corresponding to the starting point of the slope segment T2 I V ; Step a5: Calculate the target peak current of ramp section T2, based on the current target value I T and the current value I at the starting point of the ramp segment T2 V Calculate the target peak current I of ramp stage T2 P , that is, the current value at the time of on and off; When the current in ramp section T2 reaches the target peak current I P The primary welding current is switched from on to off to adjust the welding current of the current cycle in real time; Step a6: Calculate the current statistics of the current cycle, starting from the starting point of the ramp segment T2 to the current shut-off time, and perform point-by-point weighted accumulation calculation on the current sampling values ​​within the time range from the starting point of the ramp segment T2 to the current shut-off time to obtain the ramp segment T2 statistics I A ; Step a7: According to I A and I T Adjust the target peak current I of the next cycle P The calculation formula of Step a8: Repeat the above steps until the welding power-on time reaches a preset value.

2. The method for real-time control of welding current of an inverter resistance welding machine according to claim 1, characterized in that: In the step a1: the primary current signal of the inverter resistance welding machine is collected in real time, and the primary current signal refers to the rated current of the winding on the high-voltage side, i.e., the power input side, of the transformer in the inverter welding machine.

3. The method for real-time control of welding current of an inverter resistance welding machine according to claim 1, characterized in that: In step a2: the rapid rise section T1 refers to the stage when the welding current value increases rapidly; the ramp section T2 refers to the stage when the welding current is basically stable but increases slowly due to the change of workpiece resistance; the current closing section T3 refers to the stage from the welding current being turned off to being turned on again.

4. The method for real-time control of welding current of an inverter resistance welding machine according to claim 1, characterized in that: In the step a3: the characteristic quantity, namely the first-order difference of the current signal with respect to time, is used to obtain a first-order difference curve graph of the current signal with respect to time.

5. The method for real-time control of welding current of an inverter resistance welding machine according to claim 1, characterized in that: In step a5: target slope segment peak value I P The calculation formula is: Where: I T is the current target value, I V is the current value at the starting point of the ramp section, and α and β are both proportional parameters.

6. The method for real-time control of welding current of an inverter resistance welding machine according to claim 1, characterized in that: The collected current value and characteristic quantity, i.e., the first-order differential data of the current value to time, are input into the calculation and analysis module, and the slope segment statistical value calculation formula is used to perform point-by-point weighted calculation, wherein the calculation and analysis module includes: a microprocessor, an industrial computer, a PLC, a monitoring instrument, a welding controller, a desktop computer, a laptop computer, a server or a workstation; the calculation formula of the point-by-point weighted accumulation calculation is: Among them I i is the sampling value of the i-th point, w i is the weight coefficient of the i-th point, n is the total number of sampling points, and m is the power weight coefficient.

7. The method for real-time control of welding current of an inverter resistance welding machine according to claim 1, characterized in that: In step a7: according to I A and I T The difference adjusts the next cycle's proportion parameter β, that is, β←β+f(I A -I T ), where f is the specific adjustment method, and PID control method is adopted.

8. A real-time control system for welding current of an inverter resistance welding machine, characterized in that: The system includes the following modules: Module m1: performs resistance spot welding, collects primary current signals and obtains a curve graph of current variation over time; Module m2: Based on the curve of current changing with time, the current signal is divided into different cycles according to the inversion period. The current signal of each cycle is divided into a fast rising section T1, a ramp section T2 and a current closing section T3 according to the welding current on and off; Module m3: for the current signal of the current cycle, the fast rising section T1 is processed and calculated, the characteristic quantity of the current signal is extracted by performing average value filtering on the primary current sampling value, a characteristic quantity curve graph is obtained, and the fast rising section is determined according to the characteristic quantity curve graph; Module m4: Determine the starting point of the slope segment T2, determine the starting point of the slope segment T2 according to the characteristic curve, and set the characteristic threshold, including the high threshold D H , low threshold D L , where the feature value is higher than the high threshold D for the first time H And it is lower than the lower threshold D L When the current is lower than the low threshold, it is the starting point of the slope segment T2, which is recorded as the current value corresponding to the starting point of the slope segment T2 I V ; Module m5: Calculate the target peak current of ramp section T2, according to the current target value I T and the current value I at the starting point of the ramp segment T2 V Calculate the target peak current I of ramp stage T2 P , that is, the current value at the time of on and off; When the current in ramp section T2 reaches the target peak current I P The primary welding current is switched from on to off to adjust the welding current of the current cycle in real time; Module m6: Calculate the current statistics of the current cycle, from the starting point of the ramp segment T2 to the current shut-off time, perform point-by-point weighted accumulation calculation on the current sampling values ​​within the time range from the starting point of the ramp segment T2 to the current shut-off time, and obtain the ramp segment T2 statistics I A ; Module m7: According to I A and I T Adjust the target peak current I of the next cycle P The calculation formula of Module m8: Repeat the above modules until the welding power-on time reaches the preset value.

9. The real-time control system for welding current of an inverter resistance welding machine according to claim 8, characterized in that: In the module m1: real-time acquisition of the primary current signal of the inverter resistance welding machine, wherein the primary current signal refers to the rated current of the winding on the high-voltage side, i.e., the power input side, of the transformer in the inverter welding machine; In the module m2: the rapid rise section T1 refers to the stage in which the welding current conduction current value increases rapidly; the ramp section T2 refers to the stage in which the welding current is basically stable but increases slowly due to the change of the workpiece resistance; the current closing section T3 refers to the stage from the welding current being turned off to being turned on again; In the module m3: the characteristic quantity is the first-order difference of the current signal with respect to time, and a first-order difference curve graph of the current signal with respect to time is obtained.

10. The real-time control system for welding current of an inverter resistance welding machine according to claim 8, characterized in that: In the module m5: target slope segment peak value I P The calculation formula is: Where: I T is the current target value, I V is the current value at the starting point of the ramp section, α and β are both proportional parameters; The collected current value and characteristic quantity, i.e., the first-order differential data of the current value to time, are input into the calculation and analysis module, and the slope segment statistical value calculation formula is used to perform point-by-point weighted calculation, wherein the calculation and analysis module includes: a microprocessor, an industrial computer, a PLC, a monitoring instrument, a welding controller, a desktop computer, a laptop computer, a server or a workstation; the calculation formula of the point-by-point weighted accumulation calculation is: Among them I i is the sampling value of the i-th point, w i is the weight coefficient of the i-th point, n is the total number of sampling points, and m is the power weight coefficient; In the module m7: according to I A and I T The difference adjusts the next cycle's proportion parameter β, that is, β←β+f(I A -I T ), where f is the specific adjustment method, and PID control method is adopted.

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