JP2000158148A - Inverter type resistance welding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a proper welding quality by welding a welding object based on a noise portion eliminated electric voltage between the welding electrodes. SOLUTION: In an inverter type resistance welding device 1, when a voltage between welding electrodes 9, 10 is detected by a voltage detection means, a high frequency portion of this voltage is cut off by an analog filter 15, and a ripple portion of said voltage is cut off by a digital filter 16. Thereby, an inverter control circuit 5 controls a transistor bridge circuit 4 based on a noise portion eliminated electric voltage between the welding electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter type resistance welding apparatus for welding an object to be welded with a welding current obtained by rectifying a current having a frequency higher than a power supply frequency.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing an overall configuration of a conventional inverter type resistance welding apparatus. The conventional inverter-type resistance welding apparatus 51 has a frequency of 50 Hz or 6 Hz.
A three-phase AC power supply voltage of, for example, 200 volts or 400 volts of 0 Hertz is rectified by a full-wave rectifier 52, and a DC voltage smoothed by a capacitor 53 is converted by a transistor bridge circuit 54 and an inverter control circuit 55 to, for example, 500 to 1200 Hertz. An inverter 56 for converting into a range of high-frequency voltages is provided.

An inverter transformer 57 is connected to the transistor bridge circuit 54. When the transistors Tr1 and Tr4 of the transistor bridge circuit 54 are turned on by the inverter control circuit 55, the DC current from the full-wave rectifier 52 is reduced. , Transistor T
r1, the primary winding of the inverter transformer 57, the transistor Tr4, and the flow returns to the full-wave rectifier 52. Next, the transistors Tr1 and Tr4 are controlled by the inverter control circuit 55.
Are switched off, and the transistors Tr2 and Tr
3 is switched on, the DC current from the full-wave rectifier 52 flows through the transistor Tr2, the primary winding of the inverter transformer 57, and the transistor Tr3, and returns to the full-wave rectifier 52.

As described above, when the group of the transistors Tr1 and Tr4 and the group of the transistors Tr2 and Tr3 are alternately turned on by the inverter control circuit 55, the DC current from the full-wave rectifier 52 is switched during this switching cycle. For example from 500 Hz to 1
It is converted into a high-frequency current in the frequency range of 200 Hz and flows through the primary winding of the inverter transformer 57. When the high-frequency current flows through the primary winding of the inverter transformer 57, the secondary current of the inverter transformer 57 is supplied to the rectifier 5
8, 59, and the current is passed between the welding electrodes (welding guns) 62, 63 via the welding current conductors 60, 61. Is applied, and the workpiece W is welded. If a high-frequency welding current is applied to the workpiece W sandwiched by the welding electrodes 62 and 63 under pressure without rectifying the secondary current of the inverter transformer 57, the secondary side of the inverter transformer 57 There is a problem that the application of the welding current is limited by the inductive impedance of the welding current application circuit composed of the welding current conductors 60 and 61, the welding electrodes 62 and 63, and the workpiece W. Therefore, the secondary current (high-frequency current) of the inverter transformer 57 is converted into direct current by the rectifiers 58 and 59, thereby reducing the influence of the inductive impedance of the welding current conduction circuit.

[0005] As shown in FIG.
7 is provided with a current detector 64 which detects a current flowing through the primary winding of the first circuit 7 and feeds it back to the inverter control circuit 55. The inverter control circuit 55 includes the current detector 6
By feeding back the current detected by 4, the transistor bridge circuit 54 is controlled so that the current flowing through the primary winding of the inverter transformer 57 has a current value programmed in advance. In this case, the inverter control circuit 55 includes the group of the transistors Tr1 and Tr4 of the transistor bridge circuit 54 and the transistor T
By performing frequency variable control for changing the on / off cycle of the group of r2 and Tr3, or PWM (pulse wide modulation) control, the inverter transformer 57 is controlled.
The current flowing through the primary winding is controlled to a pre-programmed current value.

[0006]

The above-described conventional inverter-type resistance welding apparatus 51 detects a current flowing through a primary winding of an inverter transformer 57 and outputs the detected current to the inverter transformer 57.
The current flowing through the primary winding is controlled to a pre-programmed current value. However, when the workpiece W cannot be properly welded due to, for example, wear of the welding electrodes 62 and 63, the There is no means to directly detect. Therefore, as shown by the two-dot chain line in FIG.
Means for directly detecting the voltage between the electrodes by the inter-electrode voltage detection lines 65 and 66 and feeding back the voltage to the inverter control circuit 55, and appropriately welding the workpiece W based on this voltage have been studied.

However, the inter-electrode voltage detection lines 65, 6
It has been confirmed that the voltage between the welding electrodes fed back to the inverter control circuit 55 via the line 6 has a complicated waveform as shown in FIG. The reason for this is that it is inevitable that the inter-electrode voltage detection lines 65 and 66 are laid in parallel with the welding current conductors 60 and 61, and the high frequency components (including harmonics) passing through the inverter transformer 57 cause the welding current to flow. This is presumably because the conductors 60 and 61 lead the voltage detection lines 65 and 66 between the electrodes.
Therefore, even if the voltage having such a waveform is fed back to the inverter control circuit 55, the inverter control circuit 5
In No. 5, it was confirmed that welding control of the workpiece W could not be properly performed.

Accordingly, an object of the present invention is to provide an inverter-type resistance welding apparatus for appropriately welding an object to be welded based on a voltage between welding electrodes excluding noise components.

[0009]

Means for solving the problem is to form an inverter type resistance welding apparatus as shown in claim 1, and according to the inverter type resistance welding apparatus having this configuration, When the voltage between the welding electrodes is detected by the detecting means, the high frequency component of the voltage is cut off by the first filter, and the ripple component is cut off by the second filter. The welding means can be controlled based on the applied welding electrode voltage.

[0010]

Next, an embodiment of the present invention will be described. FIG. 1 is a block diagram showing an overall configuration of the inverter-type resistance welding apparatus 1. The inverter type resistance welding apparatus 1 includes a full-wave rectifier 2 for full-wave rectifying a 50-Hz or 60-Hz three-phase AC power supply voltage of, for example, 200 V or 400 V, and a capacitor for smoothing the voltage rectified by the full-wave rectifier 2. 3, a transistor bridge circuit 4 for converting a DC voltage rectified by the full-wave rectifier 2 and smoothed by the capacitor 3 into a high-frequency voltage in a range of, for example, 500 Hz to 1200 Hz, and an inverter control circuit for controlling the transistor bridge circuit 4 5, an inverter transformer 6 that inputs a high-frequency voltage output from the transistor bridge circuit 4 and outputs a low voltage, rectifiers 7 and 8 that rectify a high-frequency current from the secondary side of the inverter transformer 6, and rectifiers 7 and 8. The welding current rectified by the welding object 8 is applied to the workpiece W through welding electrodes (welding guns) 9 and 10. And a welding current conduction 11 and 12 to be energized. The terminals of the inter-electrode voltage detection lines 13 and 14 are connected to portions of the welding current conductors 11 and 12 close to the welding electrodes 9 and 10, and the inter-electrode voltage detection lines 13 and 14 are connected to the inverter control circuit 5. A voltage detection circuit is provided that connects the voltage between the welding electrodes 9 and 10 (the voltage between the welding electrodes) to the inverter control circuit 5 by feedback.

The welding means described in claim 1 is a general term for the full-wave rectifier 2, the capacitor 3, the transistor bridge circuit 4, the inverter transformer 6, the rectifiers 7, 8, the welding current conductors 11, 12, and the like. The voltage detection means described in claim 1 corresponds to a voltage detection circuit that feeds back the voltage between the welding electrodes 9 and 10 to the inverter control circuit 5 via the inter-electrode voltage detection lines 13 and 14. The control means described in the item 1 corresponds to the inverter control circuit 5. The first filter and the second filter described in claim 1 correspond to an analog filter 15 and a digital filter 16 described later.

The transistor bridge circuit 4 is composed of transistors Tr1, Tr2, Tr3 and Tr4.
The group of transistors Tr1 and Tr4 and the group of transistors Tr2 and Tr3 are alternately turned on. Further, a current detector 17 for detecting a current flowing through the primary winding of the inverter transformer 6 and feeding it back to the inverter control circuit 5 is provided.

FIG. 2 is a side view showing a state in which inter-electrode voltage detection lines 13 and 14 connected to welding current conductors 11 and 12 are laid. As shown in FIG.
Since the terminals 3 and 14 are connected to portions of the welding current conductors 11 and 12 that are very close to the welding electrodes 9 and 10, the voltage between the welding electrodes is substantially changed via the electrode voltage detection lines 13 and 14. Is fed back to the inverter control circuit 5. The electrode voltage detection lines 13 and 14 are welding current conductors 11 and 12
And a welding current conductor 11, 1
It is unavoidable to lay in parallel with 2. for that reason,
A large high-frequency current (for example, 1
0000 to 15000 amps) flows through the welding current conductors 11 and 12,
2, a high-frequency voltage is induced to the inter-electrode voltage detection lines 13 and 14. Therefore, the voltage between the welding electrodes fed back to the inverter control circuit 5 has a complicated waveform as shown in FIG. The analog filter 15 and the digital filter 16 are connected to the inter-electrode voltage detection line 1 as described later.
It is provided to cut off unnecessary portions of the welding electrode voltage fed back to the inverter control circuit 5 by the switches 3 and 14.

As shown in FIG. 2, the upper welding electrode 9
The welding electrode 9 is lowered when the air cylinder 20 is pressurized by a pressure control circuit (not shown), and the upper welding electrode 9 and the lower welding electrode are provided. The workpiece W is pressed and held between the workpiece 10 and the workpiece 10. The pressure applied to the workpiece W sandwiched between the welding electrodes 9 and 10 is determined based on the air pressure supplied to the air cylinder 20.

FIG. 3 is a block diagram showing the configuration of the analog filter 15. The analog filter 15 is provided in the inverter control circuit 5 and includes a first-stage filter 21 and a second-stage filter 22. Although not shown, an insulation circuit is provided for preventing a welding current from flowing into the analog filter 15. The voltage between the welding electrodes fed back to the inverter control circuit 5 is:
1.3 kHz at the filter 21 before the analog filter 15
The frequency components exceeding z are cut off, and the post-filter 22 cuts off the frequency components exceeding 1.6 kHz that were not sufficiently cut off by the pre-filter 21. When the waveform of the voltage between the welding electrodes that passed through the analog filter 15 as described above was observed with a waveform observer, the waveform contained ripples as shown in FIG. 4B.
Note that the cutoff frequency of each of the first-stage filter 21 and the second-stage filter 22 of the analog filter 15 is a frequency at which the original fluctuation of the welding electrode voltage does not disappear, and is determined by experiments. In the present embodiment, the analog filter is configured in two stages, but may be configured in one stage as long as high-frequency components can be cut off sufficiently.

As described above, the voltage between the welding electrodes having a waveform including a ripple as shown in FIG. 4B passing through the analog filter 15 is sent to the digital filter 16.
The digital filter 16 processes the voltage between the welding electrodes having a waveform as shown in FIG. 4 (b) by software of a computer of the inverter control circuit 5 to make a waveform as shown in FIG. 4 (c). is there. Specifically, the computer of the inverter control circuit 5 includes an analog filter 15
The voltage between the welding electrodes that passed through the
The sampling is performed every s, and each time one sampling is performed, a moving average of the latest sampling data and, for example, seven sampling data before that is calculated. By calculating the moving average of eight pieces of sampling data every 1 ms, the voltage between the welding electrodes is changed to a waveform as shown in FIG. Although the digital filter 16 has been described as an example operated by software, a hardware having a hardware configuration may be used.

Next, the operation of the inverter type resistance welding apparatus 1 will be described. In a state where the three-phase AC power supply voltage is full-wave rectified by the full-wave rectifier 2 and the DC voltage smoothed by the capacitor 3 is supplied to the transistor bridge circuit 4, the inverter control circuit 5 operates the transistor Tr 1 of the transistor bridge circuit 4. , Tr4 are switched on, the DC current from the full-wave rectifier 2 is
1. The primary winding of the inverter transformer 6 flows through the transistor Tr4 and returns to the full-wave rectifier 2. Next, when the transistors Tr1 and Tr4 of the transistor bridge circuit 4 are turned off by the inverter control circuit 5 and the transistors Tr2 and Tr3 are turned on, the DC current from the full-wave rectifier 2
2. The primary winding of the inverter transformer 6 flows through the transistor Tr3 and returns to the full-wave rectifier 2.

As described above, when the group of the transistors Tr1 and Tr4 and the group of the transistors Tr2 and Tr3 are alternately turned on by the inverter control circuit 5, the DC current from the full-wave rectifier 2 is switched during this switching cycle. For example, from 500 Hz to 120
It is converted into a high-frequency current in a frequency range of 0 Hertz and flows through the primary winding of the inverter transformer 6. Further, the current from the secondary side of the inverter transformer 6 is rectified by the rectifiers 7 and 8 and supplied to the welding electrodes (welding guns) 9 and 10 via the welding current conductors 11 and 12, so that the welding electrodes 9 and
A direct current welding current is applied to the workpiece W pressed and clamped at 10.

When the welding electrode voltage is fed back to the inverter control circuit 5 via the electrode voltage detection lines 13 and 14 in a state where a DC welding current is applied to the workpiece W, the inverter control is performed. 1.3 kHz by the filter 21 before the analog filter 15 provided in the circuit 5
Is cut off, and the subsequent filter 2
In 2, frequency components exceeding 1.6 kHz are cut off. The voltage between the welding electrodes that has passed through the analog filter 15 is sent to the digital filter 16 in a waveform as shown in FIG.

The digital filter 16 is operated by software of the computer of the inverter control circuit 5 as described above. The digital filter 16 samples the voltage between the welding electrodes passing through the analog filter 15 every 1 ms, for example, and samples one. By calculating a moving average of the latest sampled data and the previous sampled data of, for example, seven samples each time, the voltage between the welding electrodes is made into a ripple-free waveform as shown in FIG. . The number of sampling data for which the moving average is calculated is not limited to eight.

The inverter control circuit 5 is based on the welding electrode voltage processed by the digital filter 16 and the secondary side current value of the inverter transformer 6 converted from the current value detected by the current detector 17. Workpiece W
Is calculated. In addition, the inverter control circuit 5
The amount of heat Jv per unit volume of the workpiece W is calculated by the following equation. Jv = I2 · R · t / S · L In the above equation, I is the welding current, R is the resistance value of the work W, t is the conduction time, S is the tip area of the welding electrode, and L is the work area of the work W. It is the total thickness. However, since the tip area S of the welding electrode cannot be known from the above equation, the inverter control circuit 5 calculates R = ρ · L / S (ρ is the specific resistance of the workpiece W).
The tip area S of the welding electrode is obtained from S = ρ · L / R derived from the above.

As described above, the inverter control circuit 5 calculates the amount of heat Jv per unit volume of the workpiece W by calculating the resistance value R of the workpiece W in advance, so that the amount of heat is constant. The welding current I is controlled. With this control, it is possible to prevent incomplete welding due to insufficient heat and spatter due to excessive heat.

As described above, the resistance value R of the work W is calculated by detecting the voltage between the welding electrodes, and the heat amount Jv per unit volume of the work W is calculated. The control of the welding current I as described above is an example, and a pressurization control circuit for controlling an air cylinder 20 for raising and lowering the upper welding electrode 9 based on the voltage between the welding electrodes is applied to the workpiece W. Pressure can also be controlled.
Alternatively, the welding current conduction time can be controlled. The embodiment described above is an example and does not limit the present invention.

[0024]

According to the first aspect of the present invention, the workpiece can be properly welded based on the voltage between the welding electrodes excluding the noise component.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an inverter type resistance welding apparatus.

FIG. 2 is a side view showing a laying state in a welding electrode portion.

FIG. 3 is a block diagram illustrating a configuration of an analog filter.

FIG. 4 is a waveform diagram of a voltage between welding electrodes.

FIG. 5 is a block diagram showing a configuration of a conventional inverter type resistance welding apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter type resistance welding apparatus 2 Full-wave rectifier 3 Capacitor 4 Transistor bridge circuit 5 Inverter control circuit 6 Inverter transformer 7,8 Rectifier 9,10 Welding electrode 11,12 Welding current conductor 13,14 Electrode voltage detection line 15 Analog filter 16 Digital filter W Workpiece

Claims (1)

[Claims] A welding means for welding an object to be welded pressed between welding electrodes by applying a welding current obtained by rectifying a current having a frequency higher than a power supply frequency, and a voltage detector for detecting a voltage between the welding electrodes. Means, a first filter for cutting off a high-frequency component of the voltage detected by the voltage detection means, a second filter for cutting off a ripple component of the voltage via the first filter, An inverter-type resistance welding apparatus comprising: a control unit that controls the welding unit based on the voltage passed through a first filter and a second filter.