JP2000301348A - Method for controlling current for resistance welding machine and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To have a means for detecting the generation of expulsion, to improve current control after the generation of the expulsion and to prevent an increase of a current by which the expulsion is easily generated. SOLUTION: In a method for controlling current wherein a welding current is feedback controlled so as to be constant by detecting a current value of a primary side (or secondary side) of a welding transformer varying every moment during the flow of the welding current and resistance between chips (or a voltage between chips) and by ignition controlling an electronic switch part 4, when expulsion is generated, a constant electric power control system wherein variations of the resistance between chips are feedback controlled to keep welding electric power constant is changed over to a constant current control system wherein variations of the primary side current value are feedback controlled to keep the welding current constant, and whereby excessive variations of the current during the flow of the welding current are controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a resistance welding machine, and more particularly, to switching from a constant power type power supply to a constant current type power supply when dispersion occurs as a current control method, to maintain an optimum welding current for preventing dispersion. And a current control method for controlling the current.

[0002]

2. Description of the Related Art FIG. 1 shows a principle diagram of a conventional resistance welding machine for performing constant power control. In the drawing, reference numeral 1 denotes a welding transformer for generating a necessary welding current between the upper and lower electrode tips 2 and 3 of the resistance welding machine after the work is sandwiched and pressed. The upper and lower electrode tips 2 and 3 are connected to the secondary side of the welding transformer 1. Reference numeral 4 denotes an electronic switch unit such as a thyristor for controlling a welding current. Reference numeral 5 denotes a current phase control unit that controls an electronic switch unit such as a thyristor.

[0006] Reference numeral 6 denotes a primary current detector for measuring the current on the primary side of the welding transformer 1; 7, a converter for converting the measured primary current to a value suitable for arithmetic processing; This is an inter-electrode resistance detecting unit for detecting the value of the inter-chip resistance of FIG.

Reference numeral 9 denotes a constant power calculation unit which uses the primary current value for each half cycle detected by the primary current detection unit 6 and the resistance value for each half cycle detected by the interelectrode resistance detection unit 8, and The power applied in the cycle is calculated, and the difference from the set reference power is calculated. Further, a current value in the next half cycle for correcting this difference is calculated, and the calculation result is instructed to the current phase control unit 5.

FIG. 2 is a change curve showing a change in resistance between chips during welding. Normally, the resistance of the weld increases rapidly at the beginning and then decreases gradually. The transition of the current value at this time is the transition of the current value during welding in FIG. In order to keep the power constant, the transition of the current value contradicts the transition of the resistance value, and initially decreases and then increases.

[0006] The resistance welding machine performs welding by using heat generated by a welding current flowing through a welding portion. Its quality mainly depends on the current value, the conduction time, and the pressing force applied to the weld. Among them, the factor that particularly affects the quality is the current value.

As a method of controlling the current value, there are a constant current control in which a constant current value is always supplied with respect to a change in the welded portion, and a current value in which the calorific value (power) is always kept constant with respect to the change in the welded portion. There is constant power control to control.

In the constant power control, the resistance value of the welded portion is detected, the amount of change in the resistance value is fed back to control the current, and the power consumption (square of current × resistance value) of the welded portion is kept constant. In resistance welding, when the heat capacity of the welded portion exceeds a certain condition, scattering occurs in which the molten material in the welded portion is scattered. At this time, the resistance value of the weld decreases rapidly.

[0009] In the case where the dispersion occurs in the constant power control, there is a problem that the current value is excessively increased due to a drastic decrease in the resistance value, thereby causing a further factor of the occurrence of the dispersion.

[0010]

When the scattering occurs as shown by the dotted line in FIG. 2, the value of the resistance between the chips sharply decreases. As described above, in the conventional method, since the change in the resistance value is fed back to the current value as it is, the current value sharply increases as shown by the dotted line in FIG. The state is further accelerated,
There is a problem that a state in which scattering easily occurs is maintained.

The occurrence of spatter has problems such as spatters adhering to the surface of the welding base material, deteriorating the appearance, and deteriorating the welding work environment, and the development of spatter prevention has been urgently required these days.

[0012]

The object of the present invention is to solve this problem.
The present invention has a means for detecting occurrence of scattering, improves current control after the occurrence of scattering, and prevents an increase in current in which scattering is likely to occur.

[0013]

The present invention employs the following technical means to achieve the above object. That is, by detecting the current value on the primary side (or the secondary side) of the welding transformer and the resistance between the chips (or the voltage between the chips), which change moment by moment during the energization of the welding, and controlling the ignition of the electronic switch section. In a current control method for performing feedback control so that a welding current becomes constant, a constant power control method for making a welding power constant by feedback-controlling a change in inter-chip resistance is provided. The main feature is to switch to a constant current control method in which the change in the value is feedback-controlled to make the welding current constant, thereby suppressing excessive current change during welding energization.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a method according to the present invention. FIG. 4 shows an embodiment of the present invention. The same components as those described in the conventional embodiment of FIG. 1 are denoted by the same reference numerals. In FIG. 4, a welding transformer 1 for generating a welding current in a resistance welding machine, a current detector 7 for detecting a current value during welding current application on a primary side (or a secondary side) of the welding transformer, A converting means for converting the detected current value into a value suitable for arithmetic processing; and a value of resistance between chips (or voltage between chips) of an electrode portion arranged on the secondary side of the welding transformer during welding welding. The power applied in the first half cycle is detected using the chip-to-chip resistance detection unit 8 that detects momentarily and the resistance value of each half cycle detected by the resistance detection unit. A calculation unit 12 for calculating a difference, calculating a current value of the next cycle for correcting the difference, and outputting the calculation result to the current phase control unit 5, and a welding unit based on an output signal from the current phase control unit. To apply welding current to An electronic switch section 4 such as a lister, a scattering occurrence detecting section that receives information signals from the inter-electrode resistance detecting section, detects the occurrence of scattering, and outputs the result to the arithmetic section 12, and performs the determination of the occurrence of scattering. In the current control device having a reference value setting unit 10 internally provided with a reference value, a means 11 for detecting occurrence of dispersion due to a change in the inter-chip resistance value is connected to the arithmetic unit 12, and In addition to the constant power control function that makes the welding power constant by performing feedback control of the change in current, when the dispersion occurs, the constant power control is switched to constant current control, and the change in the primary side current value is feedback controlled. And a control function to make the welding current constant.

That is, FIG. 4 differs from the conventional system of FIG. 1 in that information from the inter-electrode resistance detecting unit 8 is received, and the occurrence of the scattering is detected and notified to the constant power calculation unit 12 by the scattering generation detecting unit 11. And that a reference value setting unit 10 capable of setting a reference value for determining occurrence of scattering is added, and a constant current calculation function is added to the calculation unit 12 in addition to the calculation for constant power control. It is.

Further, the present invention can be realized even if the constant power / constant current calculation unit 12 is replaced with a constant power calculation unit having a plurality of power reference values for calculating a control current.

FIG. 5 shows an example for implementing the current control method according to the second aspect. Normally, the reference value selection unit 13 selects the power reference value 14 and notifies the constant power / constant current calculation unit 12 to perform constant power calculation using this. In this case, when the scattering occurs, the scattering occurrence detecting unit 11 notifies the reference value selecting unit 13 of the occurrence of dust. The reference value selection unit 13 selects the high power value 1 or the low power value 2 according to the welding condition, and notifies the constant power / constant current calculation unit.

FIG. 6 shows an embodiment in which the detection level of the occurrence of scattering is made variable for carrying out the current control method of claim 3. In this case, the scattering occurrence detection unit 11 compares the scattering occurrence threshold value (threshold) 16 with the decrease amount of the resistance value notified from the inter-electrode resistance detection unit 8 to detect the occurrence of the scattering. In this embodiment, the scattering occurrence threshold value 16 can be variably set by the scattering occurrence threshold value setting unit 17. This makes it possible to arbitrarily change the scattering detection level according to the welding conditions such as the work material and the plate thickness.

[0019]

The operation of the present invention will be described below with reference to FIG. 4. In the inter-electrode resistance detecting section 8 of FIG. 4, the resistance value is detected every half cycle. In the scattering occurrence detecting section 11, the current resistance value sent from the inter-electrode resistance detecting section 8
The resistance values detected in the first half cycle are compared, and when it is determined that the amount of decrease in the resistance value exceeds the value set in the reference value setting unit 10, the constant power / constant current calculation unit 12 is scattered. Notify.

The constant power / constant current calculation unit 12 that has received the notification of the occurrence of dispersion switches the calculation of the current value from constant power control to constant current control. In the constant current control, the resistance between the chips is not used for controlling the current value, but only the current value detected by the primary current detector 6 is used. A sharp increase can be prevented, thereby suppressing the occurrence of scattering and returning the molten state of the welded portion to a normal one.

When a constant power calculation unit having a plurality of power reference values for calculating a control current is used as the constant power / constant current calculation unit 12, the calculation unit 12 which is notified of the occurrence of dispersion is used.
Changes the power reference value to a low power reference value. Thus, similarly to the case where the control is switched to the constant current control, a sharp increase in the current value can be prevented, and the molten state of the welded portion can be returned to a normal state.

[0022]

The method according to the first aspect of the present invention has means for detecting the occurrence of spatter, improves the current control after the spatter occurs, and subsequently prevents the current from excessively changing during welding. Things. According to the above invention, it is possible to minimize the dispersion generated during the constant power control, and it is possible to improve the quality of the spot weld. As a result, contamination of the welding base material can be eliminated, and the welding environment and the like can be improved.

According to the second aspect of the present invention, it is possible to select the power reference value in consideration of the change in the resistance value according to the welding conditions according to the height, and the constant power calculation unit only includes the constant power calculation unit. Can be omitted, which is advantageous for cost reduction.

According to the third aspect of the present invention, the detection level of the occurrence of the spill can be variably set in accordance with the welding conditions. It is possible to supply a stable current for generating a nugget in a spot weld.

According to the device of the fourth aspect of the present invention, since only the function of detecting the occurrence of dispersion is added as compared with the conventional current control device for resistance welding, the structure can be made simple and inexpensive. And a current control device capable of suppressing an excessive current during welding conduction after the occurrence of scattering and stably ensuring the generation of a nugget at a spot weld.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing the principle of a conventional resistance welding machine that performs low power control.

FIG. 2 shows a change curve of resistance between chips at the time of welding and a change of a resistance value at the time of occurrence of scattering.

FIG. 3 shows a change curve of a primary current value at the time of welding and a transition of a primary current value at the time of occurrence of scattering.

FIG. 4 is a block circuit diagram showing a configuration example of an apparatus for performing the method of the present invention.

FIG. 5 is a block circuit diagram showing a configuration example for implementing the method of the present invention (claim 2).

FIG. 6 is a block circuit diagram showing a configuration example of a method (claim 3) of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Welding transformer 2 Electrode tip 3 Electrode tip 4 Electronic switch part 5 Current phase control part 6 Primary current detection part 7 Primary current conversion part 8 Interelectrode resistance detection part 9 Constant power calculation part 10 Reference value setting part 11 Scatter occurrence detection part 12 Power / current calculation section 13 Reference value selection section 17 Scatter occurrence threshold value setting section

Claims (4)

[Claims] An ignition switch for an electronic switch is detected by detecting a current value on a primary side (or a secondary side) and a chip-to-chip resistance (or a chip-to-chip voltage) of a welding transformer, which change momentarily during energization of welding. In the current control method of performing feedback control so that welding power becomes constant by performing the above, when the dispersion occurs, the constant power control method for controlling the change in resistance between the chips by feedback to keep the welding power constant is used. Current control for resistance welding machines characterized by switching to a constant current control method that makes the welding current constant by feedback-controlling the change in the side current value, thereby suppressing excessive current change during welding energization after spattering has occurred. Method. 2. The current control method for a resistance welding machine according to claim 1, wherein a power reference value used for constant power control is switched when said dispersion occurs. 3. The current control method according to claim 1, wherein the detection level can be varied when detecting the occurrence of the scattering. 4. A welding transformer for generating a welding current in a resistance welding machine, a current detector for detecting a current value during welding on a primary side (or a secondary side) of the welding transformer; A conversion means for converting the detected current value into a value suitable for arithmetic processing; and a resistance between chips (or a voltage between chips) of an electrode portion arranged on the secondary side of the welding transformer, which is constantly changed during welding welding. A chip-to-chip resistance detector for detecting
Using the resistance value for each half cycle detected by the resistance detection unit, the power applied in the first half cycle is detected, a difference from a preset reference power is calculated, and a next value for correcting this difference is calculated. An arithmetic unit for calculating a half-cycle current value and outputting the calculation result to a current phase control unit; an electronic switch unit such as a thyristor for supplying a welding current to the welding unit with an output signal from the current phase control unit; A scattering detection section for detecting the occurrence of scattering in response to an information signal from the interelectrode resistance detecting section and outputting the detection to the computing section; and a reference value setting for internally setting a reference value for determining the occurrence of the scattering. And a constant power control function for detecting the occurrence of dispersion based on the inter-chip resistance value and performing feedback control of the change in the inter-chip resistance to keep the welding power constant. The resistance welding machine is provided with a constant current control function that switches from the constant power function when the scatter occurs, and has a constant current control function to make the welding current constant by feedback-controlling a change in the primary side current value. Current control device.