KR100259883B1 - Control device of spot welding system and method of the same - Google Patents

Abstract

PURPOSE: A controller of a spot welding drive system and its method are provided to obtain the fine welding quality by exactly discriminating the welding quality and controlling a welding operation. CONSTITUTION: A controller(200) checks a starting of a welding. In starting the welding, the controller(200) stores welding voltage and welding current from a voltage measuring unit(100) and a current measuring unit(110) in an internal memory. The controller(200) checks a finishing of one spot welding. In finishing the spot welding, the controller(200) reads the voltage and the current values to be fed to welding electrodes(10a,10b) from the memory. The controller(200) converts the voltage and the current values to a resistance value by an operation algorithm. The controller(200) converts the resistance value to a size of a nugget. A finishing of the welding is checked when the size of the nugget is over a predetermined value. Otherwise, the controller(200) outputs a pulse into a switching unit(5) for increasing the welding current into the electrodes(10a,10b).

Description

Control device and method of spot welding drive system

The present invention relates to a control apparatus and a method of a spot welding drive system for estimating the quality of a weld and controlling the welding operation in the spot welding system.

In general, spot welding is the contact part of the base material by Joule heat using contact and compression resistance generated between welding base metals by supplying a constant current (about 5000 ~ 30000A) in a state in which two or more thin sheets are closely contacted with air pressure between electrodes. It is a welding method that can obtain a simple and clean joint to melt / bond.

In addition, the three basic elements of spot welding are pressing force, energization time, and current supply amount, and the spot welding control device sequentially performs operations such as pressurized cylinder operation, initial pressurization, energization, maintenance, and cylinder depressurization for the welding start request. It must be done.

In addition, the welding quality in spot welding is represented by the weld traces left on the surface, the size of the weld, the welding strength, the internal defects, and the flare of the metal surface as the welding base material. Appearance quality, weld strength and internal defects are items that are directly related to the quality of the actual welded structure.

The welding quality is generally referred to as the weld strength rather than the externally revealed quality, and the evaluation method is determined by the shear strength or the size of the sheet, that is, the melt portion called NUGGET generated between the welded structures. This is because there is a proportional relationship between the size of the nugget and the shear strength.

In general, since it is impossible to measure the shear strength by cutting at each welding site, the welding quality is judged by the size of the nugget generated after welding.

However, since the inspection method is a sampling of the inspection object, there is a limit to the inspection. Therefore, it is common to grasp the welding state by examining the welding parameters that qualitatively indicate the formation process of the weld.

As a method of judging welding quality using such welding variables, a method using a copper resistance characteristic during welding is conceived.

That is, in spot welding, as the welding proceeds, the resistance of the welding material changes with time, and the change state of the resistance is well reflected in the formation of the molten portion.

Therefore, by measuring the dynamic resistance, it is possible to detect the size of the melted part (nugget) and the like which can exhibit the welding quality.

If welding is performed continuously, wear of the electrode tip and coating components on the surface of the plate stick together, thereby increasing the cross-sectional area of the tip. Accordingly, the amount of heat required for melting is reduced because the current density flowing between the real plate is reduced. As a result, the size of the nugget is reduced.

That is, when the size of the nugget is reduced, it means a decrease in welding strength by that amount, resulting in poor welding quality.

Therefore, in order to maintain the original intended nugget size, appropriate compensation should be taken as the tip cross-sectional area increases.

One conventional method for this is to use the function of a stepper (STEPPER) to preset the welding score, and to raise or lower a certain amount of current when the set score is reached.

In another method, learning using an artificial neural network that inputs dynamic resistance or various welding variables and estimation of nugget size are attempted.

By the way, the conventional first method as described above can not guarantee accurate quality, the second method is very sensitive to the influence of the welding environment, the effect is reduced. In particular, since the number of inputs is fixed in the case of the artificial neural network that measures and uses only a simple change in resistance, it cannot actively cope with the increase or decrease in the number of inputs of dynamic resistance due to the change in the energization time under welding conditions.

In addition, there is a problem that it is impossible to trace back the estimation result.

Accordingly, the present invention has been made to solve the conventional problems as described above, the object of the present invention for this purpose is to accurately determine the welding quality to control the welding operation to obtain a good welding quality control device of a spot welding drive system And a method thereof.

1 is a control block diagram of a control device of a spot welding drive system according to an embodiment of the present invention.

2 is a flowchart showing a method of controlling a spot welding drive system according to an embodiment of the present invention.

<Explanation of symbols for main parts of drawing>

5 switch 10a, 10b electrode

100: voltage measuring unit 110: current measuring unit

200: control means

The control device of the spot welding drive system of the present invention for achieving the above object is to contact the two welding base metal to apply a welding current, and to apply a AC power to convert a constant voltage applied to the two electrodes A spot welding drive system comprising a drive transformer and a switching unit connected to an input terminal of the drive transformer to regulate an output of the drive transformer, the spot welding drive system comprising: a voltage measuring unit configured to measure voltages on both sides of an output terminal of the drive transformer; A current measuring unit for measuring the current on one side of the output transformer of the driving transformer, the voltage measuring unit and the current measuring unit is applied to the voltage and current measurement signal and calculated by the built-in algorithm to determine the welding quality, the corresponding control signal Control means for controlling the strength of the welding current applied to the welding base material by outputting the signal to an input terminal of the switching unit. Characterized in that consisting of.

In addition, the control method according to the control apparatus of the spot welding drive system as described above comprises a first step of determining whether or not welding is started, and if the welding is started in the first step, the voltage, the current measuring unit, the voltage, A second step of receiving and storing a current measurement signal, a third step of determining whether or not welding of one point is completed, and proceeding to the second step if welding of one point is not completed in the third step, A fourth step of converting the dynamic resistance value into a size of a nugget by calling the voltage and current values stored in the second step and converting the dynamic resistance value into a parameter of a hidden Markov model when the welding of one point is completed; A fifth step of determining whether the size of the nugget is greater than or equal to a set value; and a sixth step of determining whether welding is completed if the size of the nugget is greater than or equal to the set value in the fifth step; If the welding is not completed in the sixth step, the process proceeds to the first step, while the welding is completed.

Hereinafter, a control apparatus and a method of a spot welding drive system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a control block diagram of a control device of a spot welding drive system according to an embodiment of the present invention, the spot welding drive system applied to the present invention is the two electrodes (10a, 10b) and the drive transformer (T1) And the switching section 5.

The two electrodes 10a and 10b are in electrical contact with the two welding base materials 1 to receive welding current from the output terminal of the driving transformer T1 and to apply the welding current to the two welding base materials 1. The driving transformer T1 receives the AC input power V _IN and converts the voltage into a constant voltage required for welding, and applies it to the two electrodes 10a and 10b, respectively. The dies SCR1 and SCR2 are connected in anti-parallel so as to be connected to one side of the input terminal of the driving transformer T1 to interrupt the output of the driving transformer T1.

The control device for controlling the spot welding drive system having the above configuration is composed of a voltage measuring unit 100, a current measuring unit 110, and the control means 200.

The voltage measuring unit 100 measures the voltage on both sides of the output terminal of the driving transformer T1 and serves to apply the measured value to the control means 200.

The control means 200 receives the voltage and current measurement values from the voltage measuring unit 100 and the current measuring unit 110 and calculates the welding quality by calculating them by an embedded algorithm. To the input terminal of the switching unit 5 to control the strength of the welding current applied to the welding base material (1) as an internal input and output device, a memory means consisting of ROM and RAM, and a CPU have.

The ROM has built-in parameters and algorithms of hidden Markov models.

The operation by the control device of the spot welding drive system consisting of the above components will be described with reference to the following drawings.

2 is a flowchart illustrating a method of controlling a spot welding drive system according to an exemplary embodiment of the present invention, where S denotes a step.

First, in step S1, the control means 200 determines whether welding is started.

If welding is not started at the step S1 (NO), step S1 is repeatedly performed in a standby state, while if welding is started (YES), the control proceeds to step S2 and the control means 200 The welding voltage and the welding current values measured by the voltage measuring unit 100 and the current measuring unit 110 are received and stored in the internal memory, and the flow proceeds to step S3.

In step S3, if the control means 200 determines whether or not welding of one point is completed (NO), the process proceeds to the step S2, while if welding of one point is completed ( YES), the process proceeds to step S4, and the control means 200 calls up the voltage and current values applied to the welding electrodes 10a and 10b stored in the memory, and proceeds to step S5.

In step S5, the control means 200 converts the voltage and current values in step S4 into dynamic resistance values by means of a built-in calculation algorithm, and in step S6, the control means 200 converts the dynamic resistance. Convert the value to the size of the nugget by the parameters of the built-in hidden Markov model.

In step S7, the control means 200 determines whether the size of the nugget is different from the value set therein. If the value of the nugget is set to be higher (YES), the control proceeds to step S8, where welding is performed. Determine whether it is complete.

If the welding is not completed in the step S8 (NO), the process proceeds to the step S1, while the welding ends when the welding is completed.

On the other hand, if the size of the nugget is less than the set value (NO) in step S7, the process proceeds to step S9 so that the control means 200 sets the welding current applied to the electrodes 10a and 10b to a predetermined value. In order to increase, a pulse of a certain period is output to the switching unit 5, and the flow proceeds to the step S2.

As described above, according to the control device and method of the spot welding drive system according to the present invention, the welding current and the welding voltage are sensed as the welding starts, and the values are stored, and the welding current and the welding stored after the completion of the welding of one point are completed. The voltage is converted into a dynamic resistance value, and this resistance value is converted to the size of the nugget by the parameters of the hidden Markov model to determine the welding quality, thereby controlling the welding current applied to the electrode, thereby increasing the stability of the welding. It also has a big effect on quality control.

In addition, by using hidden Markov model, which is a probabilistic model with its own modeling ability and learning ability as a welding quality estimation algorithm, it completely compensates for the weaknesses of the conventional simple stepper and the neural network. Efficiency, as well as the best estimation path and the reason for it, is excellent for analysis and prediction.

Claims (3)

Two electrodes (10a, 10b) in contact with the two welding material (1) to apply a welding current, a drive transformer (T1) to be applied to the two electrodes by applying an alternating current power to a predetermined voltage, and the drive In the spot welding drive system comprising a switching unit 5 connected to an input terminal of the transformer T1 and intermittently outputting the output of the driver transformer T1, the voltage of both sides of the output terminal of the driver transformer T1 is measured. Voltage and current measurement signal from the voltage measuring unit 100, the current measuring unit 110 for measuring the current on one side of the output terminal of the driving transformer T1, and the voltage measuring unit 100 and the current measuring unit 110 Is applied to convert the voltage and current values into dynamic resistance values, and converts the converted dynamic resistance values into the size of the nugget by the parameters of the hidden Markov model and compares the size of the nugget with the set value to determine the welding current. Built-in algorithms to control It is composed of a control means 100 for controlling the strength of the welding current applied to the welding base material 1 by outputting a control signal to determine the welding quality and the corresponding control signal to the input terminal of the switching unit (5). Control device for a spot welding drive system characterized in that. The first step (S1) to determine whether the welding is started, and when the welding is started in the first step (S1), the voltage measuring unit 100 and the current measuring unit 110 applies a voltage, current measurement signal A second step (S2) of receiving and storing, a third step (S3) of determining whether or not welding of one point is completed, and the second step if the welding of one point is not completed in the third step (S3). In step S2, when the welding of one point is completed, the voltage and current values stored in the second step S2 are called and converted into dynamic resistance values, and the dynamic resistance values are converted into parameters of the hidden Markov model. In the fourth step (S4, S5, S6) of converting to the size of the nugget by, the fifth step (S7) of determining whether the size of the nugget is greater than or equal to the set value, and in the fifth step (S7) If the size of the nugget is greater than or equal to the set value, the sixth step (S8) and the sixth step (S8) to determine whether the welding is complete; If the welding is not completed in the first step (S1) proceeds, while the welding is completed, the control method of the spot welding drive system, characterized in that the seventh step is completed. According to claim 2, If the size of the nugget in the fifth step (S7) is less than the set value increases the welding current applied to the welding base material (1) to a predetermined value, and proceeds to the second step (S2) The control method of the spot welding drive system characterized by the above-mentioned.

Images