JP2831785B2 - Control device of resistance welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a control device for a resistance welding machine.

(Prior Art) A control circuit of a conventional inverter type resistance welding machine is shown in FIG.

The DC voltage of the DC power supply 1 is converted into a high-frequency AC voltage by the inverter bridge 2, stepped down by the transformer 4, rectified by the rectifiers 5 a, 5 b, converted again to a DC voltage, and returned to the welding point via the welding electrode 6. It is supplied by DC power. The welding current flowing at the welding point is obtained as a signal I by detecting the current on the primary side of the transformer 4 by the current transformer 3 and performing peak rectification by the current detection circuit 8.

The welding current I is the current reference set by the current setting unit 7.
It is compared with I _R and the deviation value is determined by the amplifier 9 as a triangular wave oscillator.
And 12 a triangular wave signal and is compared by the comparison circuit 13 PWM (pulse width modulation) signal, a by turning on and off the transistors of the inverter bridge 2 via the drive circuit 14 PWM controlled welding current corresponding to the current reference I _R Control to a value.

(Problems to be Solved by the Invention) However, in the conventional method, the welding current is controlled to be constant, so that when the resistance at the welding point increases, the input power increases, and so-called “dust” in which the molten metal scatters around. There were inconveniences such as an increase in occurrence.

An object of the present invention is to provide a welding machine control device that can supply a predetermined power even if the resistance of a welding point changes and that can control a welding current according to a desired power setting curve. .

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a power conversion unit that is supplied with controlled AC power from a primary side of a transformer and converts AC power on a secondary side into DC power. In an apparatus for supplying this DC power to a welding point via a welding electrode, a power characteristic setting means for setting a plurality of control parameters, a DC voltage of the welding electrode is detected, and a target welding is performed using the control parameter. Providing welding current calculation means for determining the current,
A control device for a resistance welding machine configured to control the AC power based on the target welding current.

(Operation) P ₁ , I ₁ , α ₁ are set as control parameters by the power characteristic setting means, and based on the DC voltage V of the welding electrode, the welding current calculation means sets the target welding current I _R = (P ₁ + α ₁ I ₁ ) / (V +
By calculating α ₁ ) and supplying AC power based on the value of I _R , welding can be performed with a desired welding power (P ₁ ) even if the resistance at the welding point changes.

(Embodiment) An embodiment according to the present invention is shown in FIG. 6 are denoted by the same reference numerals and description thereof is omitted.

In FIG. 1, a power curve setting means 15 sets various control parameters P ₁ , I ₁ , and α ₁ described later. The voltage detection circuit 16 detects a voltage V between terminals of the welding electrode 6. The current reference calculating means 17 calculates a desired current reference in accordance with the terminal voltage V. Is calculated.

With the above configuration, a predetermined electric power can be supplied even when a change occurs in the resistance at the welding point. That is,
When the resistance at the welding point increases, the detection voltage V increases, and the current reference I _R decreases to act to suppress an increase in power.

What kind of control is most preferable for power control of resistance welding machines often depends on the know-how of the user,
It is desired that any characteristic can be set. FIG. 2 is a characteristic diagram of power control showing the relationship between welding current and power.

The power characteristic P (I) shown in FIG.
(1) is determined by the control parameter (1).

P (I) = P ₁ −α ₁ (I−I ₁ ) (1) where P ₁ is a target welding power at welding current I ₁ , α ₁
Is the droop coefficient of the welding power. On the other hand, the welding power P (I) is expressed as P (I) = VI (2). Thus, the welding current I at the detection voltage can be obtained. Current reference computation unit 17 performs the above-described effects by outputting the values obtained in the above (3) as a current reference I _R.

In the case where power is controlled by a complicated curve as shown in FIG. 3, the power curve setting means 15 also sets (P ₁ , α ₁ , I ₁ ).
(P ₂ , α ₂ , I ₂ ) By performing the above calculation, it is possible to easily perform complicated power control.

According to the present embodiment, since the control can be performed by simple calculations, the load on the CPU is light and the frequency of the inverter is 2 to 3 KH.
It can be controlled even if it rises to z.

Also, a complicated power curve can be easily performed by increasing the control parameters.

In the above embodiment, the voltage at both ends of the welding electrode is detected, but this voltage may be detected indirectly. For example, rectifiers 5a as shown in FIG. 4, detects the output voltage V ₁ of the 5b, may be V = V ₁ -IR _1. However, R ₁ is the resistance of the terminal from C, D A, until B. In this case, there is no practical problem even if approximate V ≒ V ₁ because computing time increases.
Power characteristics of this case the second view is a drooping curve like α is increased in accordance with the I increases practically the resistance component R ₁ is relatively small with no trouble.

Further, the voltage detection circuit 16 in FIG. 1 needs to insulate and detect the DC voltage, and an amplifier generally called an insulation amplifier is employed, but it is relatively expensive.

On the other hand, a tertiary winding 4b is provided in the transformer 4 and a diode is provided.
10a, rectified by 10b, and an insulating approximately equal DC voltage V ₁ by detecting the voltage through the filter 20, yet it is possible to economically detect.

Also, as shown in FIG. 5, the secondary winding of the transformer 4
Diode 10a is connected to a transformer 24, rectified at 10b, it is possible to obtain an output insulated as substitute for V ₁ through the filter 20.

Although the inverter type resistance welder has been described,
Exactly the same control is possible with a thyristor type.

〔The invention's effect〕

As described above, according to the present invention, the power control characteristics can be freely set and the welding machine DC output voltage can be detected to economically perform extremely high-speed power control according to the set power control characteristics. It is possible to provide a control device for a resistance welding machine that can be used.

[Brief description of the drawings]

FIG. 1 is a diagram of one embodiment of the present invention, FIG. 2 and FIG. 3 are power control characteristic diagrams for explaining the operation of the above embodiment, FIG.
FIG. 5 is a diagram showing another embodiment of the voltage detector of the present invention, and FIG. 6 is a block diagram showing an example of a conventional control device for a resistance welding machine. DESCRIPTION OF SYMBOLS 1 ... DC power supply 2 ... Inverter bridge 3 ... Current transformer 4 ... Transformer, 5a, 5b ... Rectifier 6 ... Welding electrode, 7 ... Current setting device 8 ... Current detection circuit, 9 ... ... Amplifier 12 ... Triangular wave generator, 13 ... Comparison circuit 14 ... Drive circuit 15 ... Power curve setting means, 16 ... Voltage detection circuit 17 ... Current reference calculation means 10a, 10b ... Diode 20 ... Filter , 24 ... Transformer

Claims (1)

(57) [Claims] 1. A power conversion means for supplying controlled AC power from a primary side of a transformer to convert AC power on a secondary side into DC power, and supplying the DC power to a welding point via a welding electrode. In the apparatus, there are provided power characteristic setting means for setting a plurality of control parameters, and welding current calculation means for detecting a DC voltage of the welding electrode and determining a target welding current using the control parameters. A control device for a resistance welding machine, wherein the control device controls the AC power based on a current.