JPS6046886A - Control device for resistance welding machine - Google Patents

Abstract

PURPOSE:To improve working efficency together with welding quality by measuring the diameter of the electrode chip of a spot welding machine at every prescribed number of welding, calculating the set current value from the measured value thereof and desired current density and increasing automatically welding current. CONSTITUTION:A magnetic sensor 43 of which the top end is placed flush with d1 of a fitting part 42 which has the same taper as the tapered part of an electrode chip 12 and having lendth and the diameter of the upper and lower parts respectively of L, d2 and d1 is energized by terminals 44a, 44c to generate a magnetic flux phi. The voltage proportional to the distance (l) between the tips of the sensor 43 and the chip 12 when the chip 12 is fitted into the fitting part is inputted via a terminal 44d to a part 39 for measuring electrode diameter D, by which the diameter D is calculated. A part 40 for calculating current density determines the current I(=AXD) necessary for welding from the diameter D and the welding current density A set in a part 31 for setting welding conditions and outputs the same to a part 32 for setting a current value. The diameter D is determined at every set number N of welding and the set currentd value is likewise determined from the density A. The welding current is thus successively updated and increased.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a control device for a resistance welding machine, and particularly in a spot welding machine, the welding current density decreases due to wear of the tip of the electrode tip and the welding quality deteriorates. The present invention relates to a resistance welding device that prevents this from occurring.

[Technical background of the invention and its problems]

FIG. 1 shows the shape of an electrode tip used in a spot welder. Generally, in the spot welding machine ζ2, the electrode tip 12 attached to the tapered part in the tip holder 11 is attached to the workpiece 13a.

13b (= A large current is passed under high pressure, and welding is performed by the Joule heat generated in the pressurized area.The electrode tip 12 is welded ζ2 times, so wear progresses,
Its diameter increases. At this time, electrode tip 1
2 (=If the flowing current remains constant, the material to be welded 13
The current density of the current flowing through a and 13b is the electrode tip 1
Since it is inversely proportional to the diameter of No. 2, it decreases, causing welding defects.

Generally, after welding a certain number of times or for a certain period of time, the operator stops welding, dresses the tip of the electrode tip 12, and corrects it so that it is equal to the initial diameter. Furthermore, in order to reduce the number of work interruptions for dressing the electrode tip 12, a transformer 26 for detecting the number of welding operations is connected to the primary circuit of the welding transformer 21, as shown in Figure 2. Then, the one-stage counter 28 counts the pulses sent from the pulse generator 27, and the welding current is automatically increased every n times by the set value (2.
A signal is sent to the phase adjustment circuit 25 in order to control the firing phase angle of the anti-parallel connected thyristor 22 which opens and closes.

Also, the overflow pulse of the first stage counter 28 is sent to the m stage counter 29, and the thyristor 2 is sent every n times of welding.
A control device has been devised that sends a signal to advance the ignition phase angle of 2 to the phase adjustment circuit 25, and also sends a signal to the welding operation circuit 24 to stop welding when the m-stage counter 29 overflows. However, in this case, it is necessary to set a setting circuit in the counter 28 in order to increase the welding current value, but this setting value cannot be determined simply by the number of welding times, but the welding current value at that time, the welding material The degree of wear on the electrode tip varies depending on the material and other factors.

Therefore, in practice, an appropriate number of welding cycles is often set based on experience and intuition. However, in cases where the welding current setting range is narrow, such as with galvanized plated steel sheets that have been widely used recently, increasing the welding current too much may cause welding defects.

[Purpose of the invention]

The present invention was made based on the above reasons, and an object of the present invention is to provide a control device for a resistance welding machine that does not have the above-mentioned drawbacks and improves welding quality and work efficiency.

[A of the Invention (Requires 11L)] In order to achieve the above object, the present invention provides an electrode tip diameter measuring device, measures the tip diameter every fixed number of welding, and calculates the current setting value from the desired current density and the measured diameter. is calculated and automatically increases the welding current.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram showing one embodiment of the present invention.

That is, the thyristor 22 is connected in antiparallel to the AC power source 20 via the primary circuit of the welding transformer 21 . This one
A current transformer 37 is connected to the next circuit, and the welding current 11 flowing in the primary circuit is A/I) converted by the current detection section 38.
A current detection signal I is input to the current deviation detection section 33. 3
1 is a welding condition setting section which sets and stores welding information such as welding current density (A), number of energization cycles (N), and electrode tip tip diameter (temperature) prior to welding.

Reference numeral 32 denotes a current value setting section, which determines a welding current setting value I (I=AXD) from the welding current density (A) and the electrode tip tip diameter (D), and outputs a current setting signal Is to the current deviation detection section 33. 33 is a current deviation detection unit that compares the current detection signal ID and the current setting signal 8, and generates a current deviation signal △■ (△T=I.-
ID) is output to the firing angle setting section 34. Firing angle setting section 3
4) Set I to the current deviation signal and data table 35,
The firing angle (α) of the thyristor that makes the current deviation zero is determined from a data table (not shown) representing the relationship between the stored Δ■ and the phase firing angle of the thyristor.

That is, at the time of first welding, the sill risk firing angle (α0) of the first cycle is set in advance to 120°.

From the second cycle onwards, the cyrisk firing angle is determined for each cycle from the current deviation signal △■ and the data table 35,
A firing angle signal (α) that makes the actually applied welding current equal to the set current is output to the firing pulse generator 36. An ignition pulse signal P for igniting the thyristor is output to the thyristor 22 to supply welding current. Reference numeral 39 denotes an electrode diameter measuring section, which measures the number of welding times (rl) set in the welding condition setting section 31.
) Measure the diameter of the tip of the electrode tip.

FIG. 4 shows an embodiment of an electrode diameter measuring device, in which an electrode tip fitting part 42 having the same taper as the taper part of the upper electrode tip 12 has a length L, and the diameter d2 of the upper electrode is the diameter d2 of the lower electrode. It has a predetermined dimension of diameter d1.

The magnetic sensor 43 is installed with its tip portion aligned on the same plane as the surface d. This sensor has a connecting terminal 44a.
, 44c, an excitation power source is applied from the outside to generate magnetic flux φ. When the electromagnetic chip 12 is fitted,
The distance l(
The two proportional voltages are input to the electrode diameter measuring section 39 shown in FIG. 3 via the connecting terminal 44b, where the converter (
(not shown), the distance i is determined. The conditions are set in advance in the welding condition setting section 31. Dimensions of the electrode tip fitting part, dl.

Determine the diameter of the electrode tip using simple arithmetic calculations from d.

In FIG. 3, 40 is a current density calculating section, which calculates the current required for welding from the electrode tip D determined in (h) and the welding current density A set in the welding condition setting section 31 (=AxD).
This value is output to the current setting section 32 as the current setting value for the next welding.

In this way, the electrode tip diameter is measured every preset number of welding N, and the welding current is sequentially updated and increased by the set current value from the predetermined current density A that is also set. To fit the electrode tip and the electrode tip diameter sensor, if spot welding is performed using an industrial robot, the electrode tip diameter sensor is fixed, and the industrial robot itself moves the welding gun and inserts it into the electrode tip sensor fitting part. let In a regular fixed or dedicated spot welding machine, an electrode tip diameter sensor is attached to a material handler, and the material handle moves to fit the sensor to the electrode tip. The industrial robot or material handling device and the resistance welding machine control device can be easily linked by sending and receiving signals (not shown).

〔Effect of the invention〕

As explained above, according to the present invention, when the electrode tip is worn out, the electrode diameter is measured by the electrode diameter measuring device,
The welding current can be automatically increased so that the current density remains constant. Therefore, there is no need to rely on uncertain experience and intuition when setting welding conditions due to changes in the shape of the electrode tip. In addition, there is no need to interrupt work due to electrode tip dressing, which has the advantage of not only improving welding quality but also greatly improving welding efficiency.

In particular, it goes without saying that further effects can be obtained if the present invention is applied to automatic welding machines such as robots and multi-spot welding machines.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the shape of the electrode tip, Fig. 2 is a block diagram of a conventional welding control device, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a measurement of the tip diameter of the electrode tip. FIG. 2 is an explanatory diagram showing an example of an electrode diameter measuring device. 11...Tapered part of electrode tip, 12, 12a, 12b-electrode tip, 13g, 1
3b... Material to be welded, 2o... AC power supply, 21...
Welding transformer, 22... Thyristor, 23... Starting signal, 24... Welding operation circuit, 25... Phase adjustment circuit, 26... Transformer, 27... Pulse generator,
28...0 stage counter, 29...m stage counter,
31... Welding condition setting section, 32... Current value setting section, 33... Current deviation detection section, 34... Firing angle setting section, 35... Data table, 36... Firing Pulse generation section, 37... Current transformer, 38... Current detection section, 39.
... Electrode diameter measurement section, 40 ... Current density calculation section, 42
...Electrode chip fitting part, 43...Magnetic sensor, 44a, 44b, 44c - Connection terminal. (7317) Agent Patent Attorney Noriyuki Chika (and 1 others)
name) Figure 4-517-

Claims (1)

[Claims] It is equipped with a feedback circuit that compares the welding current value of the resistance welding machine with a current setting standard value, an electrode diameter measuring device, and a device that sets a current setting standard to maintain a constant welding current density from the measured electrode diameter. A control device for a resistance welding machine characterized by adjusting a current reference so that the welding current density is constant (=).