JP2012228720A - Resistance welding controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistance welding controller capable of forming an adequate nugget.SOLUTION: In the resistance welding controller, a differential pressure calculation circuit EP calculates the difference between the pressure detection value Pd and the pressure set value Pr, and a current correction value calculation circuit GD calculates the current setting correction value Gi and the current conduction time setting correction value Gt. A current set value correction circuit IRR adds the correction value Gi to the current set value Ir, and a current conduction time set value correction circuit ITRR adds the correction value Gt to the current conduction time set value ITr. A current error amplification circuit EI calculates the error between the current detection value Id and the current correction set value Irr, and outputs the current error amplification value Ei. An inverter drive circuit DV inputs the current error amplification value Ei and the current conduction time correction set value ITrr to control an inverter circuit INV. As a result, an adequate nugget can be formed.

Description

  The present invention relates to an improved resistance welding control apparatus capable of obtaining an appropriate nugget.

  A resistance welding control apparatus that performs spot welding detects a secondary current (hereinafter referred to as a welding current) in which a current detector provided on a secondary side of a welding transformer energizes a base material, and the detected value is Control is performed so as to coincide with a predetermined set value of the welding current. (For example, refer to Patent Document 1). For example, the amount of air supplied to an air cylinder provided in the upper electrode may be insufficient, and the base material sandwiched between the upper electrode and the lower electrode may not be pressurized with a predetermined pressure. In this case, when the applied pressure is lowered, the contact resistance between the electrode and the base material and between the base material and the base material is increased, and the heat generation amount is increased. Therefore, conventionally, the pressure applied to the base material is detected by a pressure detector provided in the vicinity of the upper electrode or the lower electrode, and the detected value is insufficient than a predetermined applied pressure. Thus, the welding current has been reduced so as to obtain a desired calorific value. In many cases, the pressure applied to the electrode is deficient due to the above-described causes, rather than the case where it increases.

JP 2001-138061 A

As described above, the resistance welding control device of the prior art reduces only the set value of the welding current when the pressure of the electrode is insufficient. In this case, if only the set value of the welding current is decreased, the change in the resistance value of the base metal becomes large during spot welding, so the welding state changes greatly, and it takes time to form the nugget, which is desired. In some cases, the nugget diameter could not be obtained. Therefore, when the energization time of the welding current is increased in order to obtain a desired nugget diameter, there is a problem that the amount of generated heat is thermally diffused and the periphery of the nugget is softened to reduce the strength.

An object of this invention is to provide the resistance welding control apparatus which can form an appropriate nugget.

In order to solve the above-described problems, the invention of claim 1
An inverter circuit;
A welding transformer for stepping down the output of the inverter circuit;
A current setter for setting a welding current of the welding transformer and outputting a current set value;
A current detector that detects the welding current and outputs a current detection value;
A pressure setting device that sets the electrode pressure and outputs a pressure setting value;
A pressure detector that detects the pressure of the electrode and outputs a pressure detection value;
A current energizing time setting device for setting the energizing time of the welding current and outputting a current energizing time set value;
A pressure difference calculation circuit for calculating a difference value between the pressure detection value and the pressure setting value;
A current correction value calculation circuit that calculates a current setting correction value and a current energization time setting correction value based on the calculated value of the pressure difference calculation circuit;
A current set value correction circuit for adding the current set correction value to the current set value;
A current conduction time setting value correction circuit for adding the current conduction time setting correction value to the current conduction time setting value;
A current error amplification circuit for amplifying an error between the current detection value and the output value of the current set value correction circuit;
An inverter drive circuit that controls the inverter circuit based on an output value of the current error amplifier circuit and an output value of the current energization time setting value correction circuit;
A resistance welding control apparatus comprising:

The invention of claim 2
2. The resistance welding control device according to claim 1, wherein when the detected pressure value is smaller than the pressure setting value, the current setting value and the current conduction time setting value are decreased.

  The resistance welding control device of the present invention can form an appropriate nugget when the detected pressure value is less than the set pressure value, and ensures the same welding quality as when the applied pressure is appropriate. can do.

It is a block diagram of the resistance welding control apparatus of this invention. It is a figure which shows the function of applied pressure difference value Ep% (right vertical axis), electric current setting correction value Gi% (left vertical axis), and electric current energization time setting correction value Gt% (horizontal axis).

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on examples with reference to the drawings. FIG. 1 is a block diagram of a resistance welding control apparatus according to the present invention, which is a case of an inverter control system, in which a welding current is a direct current. In the figure, an inverter circuit INV of the resistance welding control device receives a commercial AC power supply as an input, performs inverter control according to a drive signal Dv described later, and outputs a high-frequency AC. Although not shown, this inverter circuit INV has a primary rectifier circuit that rectifies commercial AC power, a smoothing capacitor that smoothes the rectified direct current, and a bridge that includes a plurality of switching elements that convert the smoothed direct current into high-frequency alternating current. It consists of a circuit.

The welding transformer TR comprises a primary coil 7 and a secondary coil 8, and the primary coil 7 is connected to the output side of the inverter circuit INV. The output terminal of the secondary coil 8 is connected to the upper arm 3a via the first rectifier element DR1 and the second rectifier element DR2, respectively, and the center tap 10 of the secondary coil 8 is connected to the lower arm 3b. An upper electrode 1a and a lower electrode 1b are respectively attached to the tip portions of the upper arm 3a and the lower arm 3b.

After the plurality of base materials 2 are pressurized by the upper electrode 1a and the lower electrode 1b, the high-frequency AC power output from the inverter circuit INV is applied to the primary coil 7 of the welding transformer TR, and the secondary of the welding transformer TR The coil 8 generates a high-frequency high-frequency AC power whose voltage is stepped down. The high-frequency AC power generated in the secondary coil 8 is alternately rectified every half cycle by the first rectifying element DR1 and the second rectifying element DR2, and the welding current Iw is passed through the upper electrode 1a and the lower electrode 1b, A welding voltage Vw is applied. The weld is metallurgically joined by Joule heat.

The current setter IR outputs a current set value Ir that is a preset value of the welding current Iw. The pressure setting device PR outputs a pressure setting value Pr which is a pressure applied to the base material 2 by a predetermined upper electrode 1a and lower electrode 1b. An air cylinder AS is attached to the upper arm 3a. The air cylinder AS receives a pressure setting value Pr, is supplied with an air amount corresponding to the pressure setting value Pr, and pressurizes the base material 2. A pressure detector PD is attached to the lower arm 3b, and the pressure detector PD detects a pressure applied to the base material 2 and outputs a pressure detection value Pd. The pressure difference calculation circuit EP calculates a pressure difference value Ep that is a difference between the pressure detection value Pd and the pressure setting value Pr. The current energization time setting unit ITR outputs a current energization time setting value ITr that is a predetermined energization time of the welding current Iw per time.

The current correction value calculation circuit GD includes a current setting correction value Gi that is a correction value of the current setting value Ir with respect to the pressure difference value Ep, a current conduction time setting correction value Gt that is a correction value of the current conduction time setting value ITr, and A function indicating the relationship is stored. This function is based on a relational expression of calorific value = 0.24 × current square × resistance × energization time, and spot welding is performed by changing the pressure difference value Ep for various materials and plate thicknesses of the base material 2. The nugget diameter is actually measured, and the current setting correction value Gi and the current conduction time setting correction value Gt when the desired nugget diameter is obtained are obtained and determined. The pressing force difference value Ep, the current setting correction value Gi, and the current energization time setting correction value Gt may be obtained by an absolute amount that increases or decreases, or a correction rate.

When the welding pressure is detected without correcting the current setting value Ir when the pressure detection value Pd is less than the pressure setting value Pr, the amount of heat generation increases because the resistance value of the base material is large. Therefore, the nugget diameter becomes larger than the corona bond diameter, and it becomes impossible to contain the molten metal at the pressure contact portion of the corona bond, and the molten metal breaks the pressure contact portion and is released to the outside, resulting in a lot of dust. Occur. Therefore, if the current set value Ir is decreased in order to prevent the heat generation amount from becoming large, the change in the resistance value of the base metal becomes large during spot welding as described in the problem of the prior art. In this case, the nugget formation takes time and the desired nugget diameter may not be obtained. Therefore, in the present invention, instead of greatly reducing only the current set value Ir, the amount of decrease in the current set value Ir is decreased, and at the same time, the current energization time set value ITr is also reduced, so that the resistance value of the base metal during spot welding is reduced. By reducing the change in the thickness of the weld so that the welding state does not change significantly, an appropriate nugget is obtained.

The current set value correction circuit IRR adds the current set correction value Gi to the current set value Ir and outputs a current correction set value Irr. The current conduction time setting value correction circuit ITRR adds the current conduction time setting correction value Gt to the current conduction time setting value ITr and outputs a current conduction time correction setting value ITrr. The current detector ID detects the welding current Iw and outputs a current detection value Id. The current error amplification circuit EI amplifies an error between the current detection value Id and the current correction set value Irr and outputs a current error amplification value Ei.

The welding start circuit ST outputs a welding start signal St that becomes High level when starting welding. The activation circuit ON inputs the current energization time correction set value ITrr and the welding start signal St, and becomes the High level for a time determined by the current energization time correction set value ITrr from the time when the welding start signal St changes to the High level. An activation signal On is output. The inverter drive circuit DV receives the current error amplification value Ei and the activation signal On, and performs pulse width modulation control based on the current error amplification value Ei while the activation signal On is at a high level. A drive signal Dv for driving is output.

  The operation will be described below. For example, when two sheets of mild steel with a thickness of 1 mm are overlapped and spot welding is performed with a welding current setting value of 10,000 A, a welding current energization time setting value of 0.2 sec, and an electrode pressure setting value of 3 kN Will be explained. In this case, for example, the function shown in FIG. 2 is used from the functions stored in the current correction value calculation circuit GD. FIG. 2 is a diagram showing a function of the pressure difference value Ep% (right vertical axis), the current setting correction value Gi% (left vertical axis), and the current conduction time setting correction value Gt% (horizontal axis). . In the figure, for example, when the pressure difference Ep is reduced by 20%, the current setting correction value Gi is reduced by 4%, and the current energization time setting correction value Gt is reduced by 10, which is shown in FIG. In addition, a desired nugget diameter can be obtained by correction.

  First, a case where an appropriate pressure set by the pressure setting device PR is applied to the base material 2 will be described. In order to start spot welding, the base material 2 is placed on the lower electrode 1b. A high level welding start signal St is input from the welding start circuit ST to the air cylinder AS, the upper electrode 1a is lowered, the base material 2 is sandwiched between the upper electrode 1a and the lower electrode 1b, and the pressure setting device PR A pressure of 3 kN set by is applied to the base material 2. Thereafter, a current of 10,000 A set by the current setting device IR is supplied to the base material 2 for a period of 0.2 sec set by the current supply time setting device ITR, and spot welding is normally performed.

  Next, there is a problem with the compressor that supplies air to the air cylinder AS, the air supplied to the air cylinder AS is insufficient, and the pressure set by the pressure setting device PR is not applied to the base material 2 properly. explain. In order to start spot welding, the base material 2 is placed on the lower electrode 1b. A high level welding start signal St is input from the welding start circuit ST to the air cylinder AS, the upper electrode 1a is lowered, the base material 2 is sandwiched between the upper electrode 1a and the lower electrode 1b, and the base material 2 is pressurized. Is done. At this time, when the applied pressure set by the applied pressure setting device PR is 3 kN and the detected applied pressure value Pd is only 2.4 kN, the applied pressure difference value calculation circuit EP has the applied pressure difference value Ep. Calculate that it is 0.6 kN, that is, a 20% reduction.

The current correction value calculation circuit GD calculates the current when the pressure difference value Ep is reduced by 20% from the function of the pressure difference value Ep, the current setting correction value Gi, and the current conduction time setting correction value Gt shown in FIG. The setting correction value Gi is reduced by 4%, and the current conduction time setting correction value Gt is selected by 10% reduction. The current setting value correction circuit IRR adds a current setting correction value Gi of 4% to the current setting value Ir of 10,000 A, and outputs a current correction setting value Irr of 9,600 A. The current conduction time setting value correction circuit ITRR adds a current conduction time setting correction value Gt of 10% to the current conduction time setting value ITr of 0.2 sec, and outputs a current conduction time correction setting value ITrr of 0.18 sec. To do.

The current error amplification circuit EI amplifies an error between the current detection value Id and the current correction set value Irr, and outputs the current error amplification value Ei to the inverter drive circuit DV. The start-up signal On which becomes the high level only for the time determined by the current energization time correction set value ITrr from the time when the welding start signal St is changed to the high level after the current energization time correction set value ITrr is input to the start-up circuit ON. Output to DV. As a result, the current value of 9,600 A corrected by the current set value correction circuit IRR is energized for the energization time of 0.18 sec corrected by the current energization time set value correction circuit ITRR, and spot welding is performed.

  As a result, when the detected pressure value Pd is less than the set pressure value Pr, instead of greatly reducing only the set current value Ir, the amount of decrease in the set current value Ir is reduced and current is applied simultaneously. The time set value ITr can also be decreased to reduce the change in the resistance value of the base metal during spot welding so that the welding state does not change significantly. Therefore, an appropriate nugget can be formed, and the same welding quality as when the applied pressure is appropriate can be ensured.

The resistance welding control device of the present invention described above has been described for the case where feedback control is performed by detecting the secondary current of the welding transformer TR, but the operation and the case where feedback control is performed by detecting the primary current of the welding transformer TR Since the effect is the same, the description is omitted.

The above-described resistance welding control apparatus of the present invention has been described in the case of the inverter control method when the molten current is DC, but the description is omitted because the same applies when the welding current is a single-phase AC current.

DESCRIPTION OF SYMBOLS 1a Upper electrode 1b Lower electrode 2 Base material 3a Upper arm 3b Lower arm 7 Primary coil 8 Secondary coil 10 Center tap AS Air cylinder DR1 1st rectification element DR2 2nd rectification element DV Inverter drive circuit Dv Drive signal EI Current error amplification circuit Ei Current error amplification value Ep Pressure difference value EP Pressure difference value calculation circuit GD Current correction value calculation circuit Gi Current setting correction value Gt Current conduction time setting correction value ID Current detector Id Current detection value INV Inverter circuit IR Current setting device Ir current set value IRR current set value correction circuit Irr current correction set value ITr current energization time set value ITR current energization time setter ITr current energization time set value ITr current energization time set value ITRR current energization time set value correction circuit ITrr current Energizing time correction set value Iw Welding current ON Start circuit On Start No. PD pressure detector Pd pressure start detection value PR pressure setter Pr pressure setpoint ST welding start circuit St welding signal TR welding transformer Vw welding voltage

Claims (2)

An inverter circuit;
A welding transformer for stepping down the output of the inverter circuit;
A current setter for setting a welding current of the welding transformer and outputting a current set value;
A current detector that detects the welding current and outputs a current detection value;
A pressure setting device that sets the electrode pressure and outputs a pressure setting value;
A pressure detector that detects the pressure of the electrode and outputs a pressure detection value;
A current energizing time setting device for setting the energizing time of the welding current and outputting a current energizing time set value;
A pressure difference calculation circuit for calculating a difference value between the pressure detection value and the pressure setting value;
A current correction value calculation circuit that calculates a current setting correction value and a current energization time setting correction value based on the calculated value of the pressure difference calculation circuit;
A current set value correction circuit for adding the current set correction value to the current set value;
A current conduction time setting value correction circuit for adding the current conduction time setting correction value to the current conduction time setting value;
A current error amplification circuit for amplifying an error between the current detection value and the output value of the current set value correction circuit;
An inverter drive circuit that controls the inverter circuit based on an output value of the current error amplifier circuit and an output value of the current energization time setting value correction circuit;
A resistance welding control device comprising: The resistance welding control device according to claim 1, wherein when the detected pressure value is smaller than the pressure setting value, the current setting value and the current application time setting value are decreased.

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