JPS588953B2 - resistance welding machine - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a resistance welding machine, and in particular, it makes constant the set welding current, corrects the shunt current, and makes the effective welding current constant with respect to the setting, making it possible to always perform stable resistance welding. That is.

In this specification, a single-phase seam weld for a steel process line (hereinafter referred to as a seam weld), which is an embodiment of the present invention, will be described.

Conventionally, seam welding in this type of steel process line is performed by joining two strips 1a and 1b to a welding disk 2, as shown in FIG.
and the lower electrode 30, and apply pressure from the welding power source 6 to the primary side of the welding transformer 50 via the anti-parallel thyristor 4, and connect the disc 2 and the lower electrode 3 to the secondary side, and apply pressure. The seam welding between the strips 1a and Ib was performed by controlling the voltage and rotating the welding disk 2 while flowing the welding current 7.

However, in such welding, welding current control is so-called open-loop control, and fluctuations in the voltage of the power source 6,
Due to impedance fluctuations due to the position of the welding disk 2, disturbances such as the surface condition of the strip 1, the welding current 7 fluctuates, which adversely affects the welding phenomenon.

However, in contrast to such conventional methods, by performing constant current control as shown in FIG. 2, it is possible to eliminate welding current fluctuations due to disturbances.

Note that the same reference numerals are used for parts corresponding to FIG. 1 in FIG. 2 and subsequent drawings.

Constant current control refers to the voltage set by the setting device 8 as a positive reference input (if the welding current value has been converted to voltage), the voltage of the welding primary current (converted to voltage) is input by the current transformer 11 as a negative feedback input. The two human forces are added together and calculated by the operational amplifier 9, and this output is input to the gate pulse generator 10 to control the firing phase of the anti-parallel thyristor 40.

Thus, the welding transformer 50 to which the anti-parallel thyristor 4 is connected
The phase of the voltage applied to the primary side is controlled, and the second
The welding current 70 equivalent current that flows through the strip 1 that is pressed into contact between the rotating disk 2 and the lower electrode 3 connected to the next side is changed, but since the entire rotation is in a closed loop, the current that has been set once is changed. remains constant without being affected by external disturbances.

However, even with such a device, if we compare the start and progress of the welding current shown in enlarged views of the strips 1a and 1b as shown in FIGS. 3 and 4, we can see that the effective welding current increases as the seam weld progresses. This causes the welding to become unstable depending on the welding position.

In other words. At the start of welding in FIG. 3, the welding current and the effective welding current 11 are equal, but as the seam welding progresses as shown in FIG. The shunt current 12 that does not occur increases.

On the other hand, in the constant current control shown in FIG. 2 described above, in order to control the welding primary current, in other words, to keep the effective welding current 11 and current 12 constant, the effective welding current increases as the shunt current 12 increases. Current l1 will decrease.

In consideration of the above points, in this invention, the constant current control shown in FIG. 2 described above is performed, and the shunt current is also corrected,
The effective welding current is kept constant so as to keep the energy applied to the welding part constant, and the constant current control is used to control the function value determined by the welding conditions such as the plate width, plate thickness, material, and welding speed of the workpiece to be welded. This is corrected by calculating the set value.

This invention will be explained with reference to the distributed current component function shown in FIG. 5, the circuit configuration diagram of the embodiment shown in FIG. 6, and the characteristic diagrams of shunt current and set current shown in FIGS. 7 and 8.

As is clear from a comparison between FIG. 6 and FIG. 2, only the circuit for supplying the output of the function generator 12 to the operational amplifier 9 is added in FIG.

First, in Fig. 5, the shunt current 12 increases according to a constant function depending on the elapsed welding time or the position P, so a function simulating this function is generated by the generator 12 shown in Fig. 6 at the start of welding, and as a positive input. When applied to the operational amplifier 9 of the constant current control device and calculated, the welding current becomes the current i set by the setting device 8 in FIG.

and the current i to which the current i3 for shunt correction in the same figure is added.
4 (see FIG. 8), and since the shunt current 12, which increases as welding progresses, is compensated for by the shunt correction i4, the effective current flowing through the welding portion remains constant with respect to the settings.

In this way, by inducing a function for the shunt flow determined by the plate width, plate thickness, welding speed, material, etc. in advance and selecting it together with the set values at the time of welding, stable and reliable welding on the steel process line is always possible. .

As described above, stable welding is possible, but since the proportion of this shunt current is small compared to the welding current, it is usually a single function that can be corrected.

For this reason, in welding, a constant effective current can be easily obtained depending on the settings by varying only the setting device 8, and stable welding can be performed without complicating the damping circuit.

As mentioned above, the welder alone can have a great effect, but since the conditions are selected based on information such as sheet width, sheet thickness, material, welding speed, etc., stable and reliable welding can be easily achieved even during centralized computer control of steel process lines. is possible.

Finally, I would like to add an explanation about the shunt correction function generator: when it is corrected according to the elapsed welding time, and when it is corrected according to the welding position. You could think so.

To explain these more specifically, in the former case, if an integrator is used, the relational expression between the output voltage vQ and the input voltage Vi is VQ=KXvixt (1) (however, VQ
1 output voltage, v1 output voltage, K constant number, t=elapsed time).

Therefore, when this VQ is used as a function generator, a function curve Q1 is obtained when the output vQ is plotted on the vertical axis and the elapsed time is plotted on the horizontal axis as shown in FIG. 9a.

Furthermore, as can be seen from equation (1), the slope of this curve Q1 can be varied by making the human power voltage Vi variable.

If the above-mentioned function is used for diversion correction, it is possible to correct the diversion amount for the elapsed time t.

In the latter case, the main body (commonly known as a carriage) to which the rotating disk 2 is attached moves as welding progresses, so connect the brush side of the potentiometer to the moving body and turn the O at the welding start position.
If ViV is applied at the end position of V, the brush potential vQ will change as shown in Figure 9b, with the output VQ on the vertical axis and the position P on the horizontal axis.
If we take , we get a function curve like Q2.

If this function is used for shunt flow correction, it is possible to correct the shunt flow for the welding position.

[Brief explanation of the drawings] Figures 1 and 2 are simplified configuration diagrams of different welding circuits in a conventional steel process line, and Figures 3 and 4 are at the time of welding start and welding progress in Figure 2. FIG. 5 is an enlarged view of the strips 1a and lb for explaining the current distribution, FIG. 5 is a shunt current component characteristic diagram for this invention, and FIG. 7 and 8 are characteristic diagrams of the shunt current and set current for this invention. FIGS. 9a and 9b are characteristic curve diagrams for different cases of the shunt correction function generator. In the figure, la and lb are the strips to be welded, 2 is the rotating disk, and 3
is the lower electrode, 4 is the anti-parallel sirisk, 5 is the welding transformer,
8 is a setting device, 9 is an operational amplifier, 10 is a gate pulse generator, 11 is a current transformer, and 12 is a function generator.

Claims (1)

[Scope of Claims] 1. During resistance welding, welding current fluctuations due to disturbances are made to become -5i with respect to the set value by performing constant current control, and the welding current that cannot be corrected by the constant current control is The shunt current is corrected by calculating a function value predetermined in advance based on welding conditions such as the plate width, plate thickness, material, and welding speed of the workpiece to be welded, with respect to the preset value. A resistance welding machine that is characterized by a constant current. 2. A resistance welding machine comprising two electrodes that clamp and pressurize an object to be welded, a welding transformer having a secondary winding connected to the two electrodes, and a constant current control device connected to the primary winding of the welding transformer. In this method, a function generator is installed which simulates a constant function of the increase in shunt current with respect to the welding elapsed time or position, which is determined by the welding conditions such as the plate width, plate thickness, material, and welding speed of the object to be welded, and its output is A resistance welding machine characterized by applying a constant current to a control device. 3 The constant current control device includes a setting device for setting voltage as a positive reference input, a current transformer for creating a negative feedback input of the welding primary current, and an operation for adding the outputs of the setting device and the current transformer. 3. The resistance welding machine according to claim 2, further comprising an amplifier, a gate pulse generator to which the operational output of the operational amplifier is applied, and an anti-parallel thyristor to which the output of the gate pulse generator is applied. 4. A positive function output from the function generator is applied to the operational amplifier included in the constant current control device, and in synergy with the constant current control action, a shunt correction amount is provided for the shunt current that increases as welding progresses. A resistance welding machine according to the second or third scope.