JPH0247313B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a rectifier type DC resistance welding machine that can adjust external characteristics determined by the relationship between the voltage between electrode tips and the welding current of each machine.

(b) Conventional technology A resistance welding machine has its own electrical external characteristics. For example, as shown in Fig. 6, when the object to be welded is inserted between the external characteristic line AB and the electrode tip, The welding current (I _M ) is applied at the intersection point M (operating point) with the load characteristic line X when the In this case, as the external characteristic line AB changes to A'B' due to fluctuations in the power supply voltage, the operating point changes to M', resulting in a large change in the welding current (I _M → I _M '). Welding results become unstable.

In particular, as shown in Figure 7, the external characteristics of rectifier DC resistance welding machines are closer to constant voltage characteristics (the slope is small). and,
This has the following problems. That is,
The welding current changes excessively in response to changes in load characteristics, which tends to cause dust during welding and poor nugget formation due to insufficient current.A large maximum current value (I _DS ) that is not used in actual welding can be applied. It is uneconomical to manufacture the equipment, etc.

Conventionally, in order to eliminate such adverse effects, the external characteristics are represented by the APQ diagram shown in Figure 6, and the welding current (I _N ) is
Types with so-called constant current control characteristics have been used, in which the current is determined and the current is set at a constant value.

However, in this constant current control, the current remains constant even when the slope of the load characteristic X fluctuates, and this may have a negative effect and cause welding to become unstable. That is, when the current carrying path area changes greatly during the welding energization process, such as in projection welding, the change in current density becomes large, resulting in a current shortage just before the welding ends, which may result in a welding failure.

(c) Problems to be Solved by the Invention The present invention solves the above-mentioned problems of the conventional art.Until the welding current reaches a certain control point, it is considered to be an external characteristic unique to the welding machine, and beyond the control point, it is determined to be an appropriate external characteristic. Welding stability can be achieved by keeping the fluctuations in welding current small in response to fluctuations in load characteristics, and by keeping the maximum current value small. By making it possible to manufacture the equipment economically, and by adjusting the welding current to vary appropriately in response to variations in load characteristics, for example, the disadvantages of constant current control such as in the case of projection welding mentioned above can be avoided. The purpose is to provide a welding machine that solves the problem.

(d) Means for solving the problems Means for achieving the above object will be explained based on FIGS. 1 to 4, which correspond to embodiments.

First of all, the first invention includes a rectifier 5 in the secondary circuit of the welding transformer shown in FIGS. In the rectifying type DC resistance welding machine, the control angle of the power control means 3, 3' is controlled by the control means 17, 17' based on the detected value. A means 11 for setting a specific control point P on an external characteristic line AB determined by the relationship between voltage and welding current and determining a corresponding welding current value, a detection value of the current detection means 8, and the welding current. means 14 for comparing with value setting means 11; and control point P on the external characteristic line AB.
Means 15 for setting drooping characteristics at an appropriate slope with
When the detected value by the comparison means 14 is larger than the set value, the control means 17, 1 of the power control means 3, 3' is adjusted based on the setting of the drooping characteristic setting means 15.
Means 16 serving to impart drooping characteristics to 7'
It is characterized by providing the following.

Further, the second invention includes a rectifier 5 in the secondary circuit of the welding transformer shown in FIG.
In a rectifying DC resistance welding machine that detects the current supplied to the welding machine and controls the control angle of the power control means 3 by the control means 17 based on this detected value, the relationship between the voltage between the electrode tips of the welding machine and the welding current A specific control point P is set on the external characteristic line AB determined by the means 11 for determining the corresponding welding current value, and the current between the detection value of the current detection means 8 and the control point setting means 11 means 14 for comparing the values; means 15 for setting the drooping characteristic at an appropriate slope with the control point on the external characteristic line as a boundary; and the drooping characteristic setting means when the detected value by the comparing means 14 is larger than the set value. Means 1 that operates to cause the control means 17 of the power control means 3 to have drooping characteristics based on the settings of 15;
6, means 30 for detecting the voltage of the primary circuit of the welding transformer, and the outputs of this voltage detecting means 20 and the means 16 for imparting the drooping characteristic are compared to compensate for fluctuations in the power supply voltage. The present invention is characterized in that means 32 for adjusting the control means of the power control means is provided.

(e) Effect In the welding machine of the first invention having the former configuration in item (d), the control point setting means 11 sets a specific control point P on the external characteristic line AB, and the current detection means 8 The current supplied to the welding transformer 4 detected at and the current corresponding to the control point P are compared. on the other hand,
Means 15 for setting drooping characteristics on external characteristic line AB
The drooping characteristic is set at an appropriate slope with the control point P as the boundary.

Then, in the comparison means 14, if the detected value by the current detection means 8 is smaller than the above set value, the power control means 3,
The control means 17, 1 so that 3' controls the power
7', and if the comparison means 14 determines that the detected value of the current detection means 8 is larger than the set value, the power control means 3,
3' is a means 16 for imparting a drooping characteristic to control the electric power and operates the control means 17, 17'.

In this way, in the present invention, the external characteristics unique to the welding machine are used until the welding current reaches a certain control point, and the external characteristics with an appropriate slope are obtained above the control point, so that fluctuations in the load characteristics can be avoided. On the other hand, it is possible to suppress fluctuations in the welding current to a small level and provide appropriate fluctuations.

Further, in the welding machine of the second invention having the latter configuration in item (d), in addition to the configuration of the welding machine of the first invention, means 30 for detecting the voltage of the primary circuit of the welding transformer 4, and this By providing the means 32 for comparing the outputs of the voltage detecting means 30 and the means 16 for imparting drooping characteristics and adjusting the control means 17 of the power control means 3 to compensate for fluctuations in the power supply voltage, the welding Even if there is a fluctuation in the power supply voltage of the machine, it can be compensated for, and the same effect as the first invention can be obtained without being affected by the fluctuation in the power supply voltage.

(f) Examples Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a block circuit diagram of an inverter-controlled rectifier type DC resistance welding machine according to an embodiment of the present invention.

In the figure, 1 is a rectifier circuit that rectifies a three-phase AC welding power source, 2 is a smoothing capacitor, 3 is an inverter device (power control means) that converts the DC power source into high-frequency AC power, 4 is a welding transformer, 5, 5 is a rectifier provided in the secondary circuit of the welding transformer 4, 6, 6 is an electrode chip, and 7, 7 is a workpiece.

Further, 8 is connected to a current transformer 9 coupled to the primary circuit of the welding transformer 4 and a current detection circuit 10 that outputs the primary current (I) detected by the current transformer 9 as a direct current voltage (E _I ) proportional to the primary current (I). current detection means, 11
is a means of setting a control point P on the external characteristic line AB of a welding machine, and as shown in Figure 2, a control point P is arbitrarily set on the external characteristic line AB unique to the welding machine. It is something. The control point setting means 11 outputs a welding current corresponding to the control point P and a corresponding DC voltage (E _P ) from the control point setting circuit 13 based on the reference power source 12 . This control point setting circuit 13 is provided with an adjustment mechanism so that the control point P can be arbitrarily determined on the external characteristic line AB.

Comparison means 14 compares the outputs of the current detection means 8 and the control point setting means 11, and outputs the result of subtraction of E _I -E _P.

Reference numeral 15 is a means for setting the drooping characteristic (drooping degree setting circuit), which sets the drooping characteristic at an appropriate slope (fo to fn) with the control point P on the external characteristic line AB as the boundary; This means operates to cause the control means 17 of the power control means 3 to impart a drooping characteristic based on the setting of the drooping characteristic setting means 15 when E _I is larger than E _P in the comparison means 14 . In the means 16 for imparting this drooping characteristic, if E _I is smaller than E _P ,
Without operating to adjust the degree of droop, a signal is sent to the pulse width modulation circuit 18 of the control means 17 so that the inverter device 3 operates at the maximum arc control angle, and the result in the comparison means 14 is such that E _I > E A command is issued to the pulse width modulation circuit 18 so that the inverter device 3 operates at the set degree of droop only in the case of _P.

That is, in the means 16 for imparting drooping characteristics,
The output E _I −E _P of the comparing means 14 is converted to α(E _I
-E _P ), but this amplification circuit does not operate when the input voltage is negative, and outputs only after receiving a positive input signal. In addition, when the next control circuit receives the output of the amplification circuit and the slope f based on the droop degree setting is fixed, the droop degree control circuit outputs the droop degree control voltage Ef corresponding to α(E _I − E _P ).
Output. Then, this output Ef is obtained by subtracting the set voltage E _C of the power supply voltage setting circuit by a subtraction circuit and giving E _C −
The Ef signal is input to the pulse width modulation circuit 18.
As a result, control APf shown in FIG. 2 is performed.

18 is a pulse width modulation circuit (PWM circuit) of the inverter device 3, 19 is a drive circuit that drives the semiconductor elements of the inverter device 3 based on the signal of the modulation circuit 18, and these are the power control means (inverter device 3). This is control means 17.

Although the embodiment described above is an invar-type resistance welding machine, the same applies to a single-phase rectifier type DC resistance welding machine in which a single-phase power supply is controlled by a power control means 3' (thyristor) as shown in Fig. 3. I can say that.

In addition, in the figure, 17' is a control means,
20 is a firing angle control circuit in the control means, and 21 is a firing circuit.

Next, what is shown in FIG. 4 is the above-mentioned invention with an added function to compensate for fluctuations in the power supply voltage. Specifically, the voltage of the primary circuit of the welding transformer 4 is adjusted. means 3 for adjusting the control means 17 of the power control means 3 so as to compensate for fluctuations in the power supply voltage by comparing the outputs of the means 30 for detecting the voltage and the means 16 for imparting drooping characteristics;
2.

That is, the transformer 31 detects the voltage of the primary circuit, and the voltage detection circuit 31' outputs a proportional DC voltage Vo, which is input to the subtraction circuit 32. The subtraction circuit 32 subtracts Vo from the input E _C -Ef from the droop characteristic imparting means 16 and outputs the result to the pulse width modulation circuit 18 . Pulse width modulation circuit 18
operates to increase the inverter output with a positive input, and decreases the inverter output with a negative input. In other words, this feedback circuit operates so that E _C -Ef-Vo=0.

FIG. 5 shows the relationship between the primary voltage and primary current of the welding transformer 4 when the device shown in FIG. 4 is operated. In this figure, while the primary current of the welding transformer 4 is between 0 and I _P , the welding transformer input voltage V _C is constant regardless of the current, and any fluctuations in the input power during this period are compensated for. value. In addition, in the current region above I _P , V _C is Pf due to the drooping degree setting f.
shows the voltage V on the line, and this voltage is always applied to the subtraction circuit 3
By being fed back to 2 as Vo,
The voltage on the Pf line will also be compensated for the power supply voltage.

Note that, in the same way as described in the first invention, this second invention can also be applied to a system in which a single-phase AC input power source is controlled by a thyristor.

(G) Effects of the Invention As described above, the resistance welding machine of the present invention can reduce fluctuations in welding current in response to fluctuations in load characteristics, thereby achieving welding stability and reducing the maximum current value. Since it can be made small, welding equipment can be manufactured economically.

In addition, by providing appropriate slope drooping characteristics,
Since the welding current has appropriate fluctuations in response to load fluctuations, the drawbacks of projection welding using constant current control are solved, and welding current is applied at an appropriate current density, eliminating the occurrence of welding defects. be able to.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram of a rectifying DC resistance welding machine according to an embodiment of the first invention, and Fig. 2 shows external characteristic lines determined by the relationship between electrode tip voltage and welding current, control points, and droop. An explanatory diagram of the characteristics, Figure 3 is the first
Figure 4 is a block circuit diagram of another embodiment of the invention, Figure 5 is the relationship between the input voltage and input current of the welding transformer in the device of Figure 4. 6 is an explanatory diagram of external characteristics, load characteristics, and constant current control, and FIG. 7 is an explanatory diagram of external characteristics of a single-phase AC resistance welding machine and a rectifying DC resistance welding machine. 3,3'~Power control means, 4~Welding transformer, 5
- Rectifier, 8 - Current detection means, 11 - Control point setting means, 14 - Comparison means, 15 - Drooping characteristic setting means, 16 - Means that acts to impart drooping characteristics to the control means, 17, 17' - Power control means control means,
30 - voltage detection means, 32 - means for adjusting control means, AB - external characteristic line, P - control point.

Claims (1)

[Scope of Claims] 1. A rectifier is provided in the secondary circuit of the welding transformer, a power control means is provided in the primary circuit, the current supplied to the welding transformer is detected by the current detection means, and the current is controlled based on this detected value. In a rectifying DC resistance welding machine in which the control angle of the power control means is controlled by means, a specific control point is set on an external characteristic line determined by the relationship between the voltage between the electrode tips of the welding machine and the welding current, and means for determining a corresponding welding current value; means for comparing the detected value of the current detection means with the current value of the control point setting means; and means for causing the control means of the power control means to apply a droop characteristic based on the setting of the droop characteristic setting means when the detected value by the comparison means is larger than the set value. Characteristic resistance welding machine. 2 The secondary circuit of the welding transformer is equipped with a rectifier, the primary circuit is equipped with a power control means, the current detection means detects the current supplied to the welding transformer, and the control means controls the power control means based on this detected value. In a rectifying DC resistance welding machine that controls the control angle, a specific control point is set on the external characteristic line determined by the relationship between the voltage between the electrode tips of the welding machine and the welding current, and the corresponding welding current value is set. means for comparing the detected value of the current detection means with the current value of the control point setting means; and means for setting the drooping characteristic at an appropriate slope with the control point on the external characteristic line as a boundary; means for causing the control means of the power control means to have a droop characteristic based on the setting of the droop characteristic setting means when the detected value by the comparison means is larger than a set value; and means for adjusting the control means of the power control means to compensate for fluctuations in power supply voltage by comparing outputs of the voltage detection means and the means for imparting drooping characteristics. A resistance welding machine featuring: