JPH07108384A - Resistance welding equipment - Google Patents

Abstract

(57) [Summary] [Purpose] The piezoelectric actuator and welding gun are integrated into one structure to adjust the voltage supplied to the piezoelectric element to instantly make fine adjustments to the pressing force, and quickly without making holes on the surface to be welded. A resistance welding device for welding to. A piezoelectric element actuator 70 includes a pressure-applying piezoelectric element 74 that expands and contracts according to an input voltage, and a pressure-reaction-force-detecting piezoelectric element 72 that detects a pressure applied by the pressure-applying piezoelectric element 74. There is a welding tip 76 that directly pressurizes the surface to be welded 110. The pressurizing force is detected by the pressurizing reaction force detecting piezoelectric element 72 and the voltage supplied to the pressurizing piezoelectric element 74 is adjusted. Can be finely adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding device for welding by applying pressure by a piezoelectric element.

[0002]

2. Description of the Related Art Resistance welding carried out in a factory generates heat by applying pressure to the surface to be welded with an electrode tip and using the resistance peculiar to the material or the contact resistance between the materials to flow a welding current for welding. Let it weld. Therefore, resistance welding is widely used because it has less deformation of products due to the influence of heat than gas welding and has a good working environment because less fumes and gas are generated. Generally, the electrode tip presses the surface to be welded via a ball screw by a servo motor, but this servo motor uses a DC servo motor, an AC servo motor, etc. to adjust the applied pressure with high accuracy. ing.

[0003]

However, the adjustment of the pressing force by the servo motor and the ball screw as described above has a poor responsiveness and cannot cope with, for example, a subtle change in the melting on the surface to be welded during welding. As a result, there was a problem that welding failed, and as a result, holes could be made in the surface to be welded.

Therefore, an object of the present invention is to estimate the degree of metal melting on the surface to be welded from the welding current and pressurize it with a piezoelectric element actuator having a good responsiveness to instantaneously detect a slight change in the surface to be welded during melting. It is an object of the present invention to provide a resistance welding apparatus capable of coping with the above and reducing defects such as unnecessary holes on the surface to be welded due to welding failure.

[0005]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a piezoelectric element actuator that moves when a high voltage is applied, and a piezoelectric element actuator that is integral with the piezoelectric element actuator and that is welded to a surface to be welded. A resistance welding device comprising an electrode tip for supplying a welding current and a driving means for bringing the electrode tip into contact with or away from the surface to be welded, and increasing or decreasing the voltage applied to the piezoelectric element actuator according to the increase or decrease of the welding current. However, it is characterized by having a control means for performing optimum welding by increasing or decreasing the pressure applied to the surface to be welded.

[0006]

The resistance welding apparatus of the present invention estimates the molten metal state of the surface to be welded by the welding current flowing through the surface to be welded, and adjusts the voltage supplied to the piezoelectric element actuator according to the estimated molten metal state. As a result, the pressure applied by the piezoelectric element actuator can be instantly changed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A resistance welding apparatus according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram for explaining an electrical configuration. In the resistance welding apparatus of the present invention, a DC-DC booster unit 1 for supplying a high voltage to a piezoelectric element and a welding tip for welding. Power converter 1 for driving a hollow shaft servomotor 50, which is a drive means for bringing the surface into contact with or away from the surface to be welded.
0, and the control unit 20 which is a control means for controlling the DC-DC booster 1 and the power converter 10 described above.

The DC-DC booster 1 includes an AC three-phase power source 1
Diode bridge 3 connected to 00 and converting to direct current
, Reactance 5 forming an LC filter for reducing the ripple of DC converted by this diode bridge 3, capacitor 6 which is another element forming this LC filter, and push-pull operation, There are a transistor 8 for converting into alternating current and a transformer 9 for boosting the input alternating current.

The power conversion section 10 also includes a diode bridge 3, a reactance 5, a capacitor 6, and an inverter section 11 for converting DC into AC by three-phase PWM control.

The control unit 20 has an A / D converter 22 for converting an analog signal from the outside into a digital signal, and an operation based on the digital signal converted by the A / D converter 22 for DC-DC boosting. The MPU 24 that controls the unit 1 and the power conversion unit 10, the ROM 26 that stores the sine wave data for performing the PWM control, the D / A converter 28 that converts the digital signal from the MPU 24 into an analog signal, and the D / A A switching regulator IC 30 for directly controlling the push-pull operation of the transistor 8 attached to the DC-DC booster 1 according to a signal from the converter 28, a basic triangular wave for generating a PWM waveform, and a D / A converter 28 There is a comparator 32 that compares the sine waves.

Further, the signal digitally converted by the A / D converter 22 includes a welding current signal Ic detected by a current detector (not shown) and supplied from the welding tip 76 to the welded surface 110, and a pressure reaction force detection. Piezoelectric element 7
2. The pressing force signal .theta.A generated by the pressure-applying piezoelectric element 74 detected by 2 and the position signal .theta.S of the rotary shaft of the hollow shaft servomotor 50 detected by the rotary position sensor 60 such as an encoder or a resolver, and the current sensor 52 detected. There are a U-phase current signal IU and a W-phase current signal IW of a three-phase alternating current output from the inverter unit 13. These signals are digitally converted by the A / D converter 22 into welding current value Ic *, pressurization signal value θA *, position signal value θS *, U-phase current signal IU *, and W-phase current signal IW *, and input to the MPU 24. To be done.

The above-mentioned input signals are a boosted voltage reference signal VC * for instructing the boosting voltage to the switching regulator IC 30 by the MPU 24, and a sine wave signal SIN θG * for comparison with a reference triangular wave for PWM control. ,
Is output to the D / A converter 28. These signals are analog-converted by the D / A converter 28 into the boosted voltage reference signal VC and the sine wave signal SIN θG.
Then, this boosted voltage reference signal VC is processed inside the switching regulator IC 30 and is transmitted to the transistor 8 attached to the DC-DC booster 1 as a push-pull signal for obtaining a desired boosted voltage. On the other hand, the sine wave signal SIN θG is compared with the reference triangular wave by the comparator 32 to generate the switching signal GS, and this switching signal GS is connected to the inverter unit 13 attached to the power conversion unit 10 and the PWM of the hollow shaft servomotor 50 is generated. Take control.

FIG. 2 is a diagram for explaining the structure of the welding gun portion 80. In the welding gun portion 80, a hollow shaft servo in which the rotor has a hollow shaft structure controlled by the power conversion unit 10 described above. A piezoelectric element actuator 70 that expands and contracts according to the voltage supplied from the motor 50 and the DC-DC booster 1.
A dual welding tip 76 provided at the tip of the piezoelectric element actuator 70, and the piezoelectric element actuator 7
And a ball screw 82 that is connected to the central shaft portion of 0 and is movable in the hollow shaft of the hollow shaft servomotor 50 in a direction perpendicular to the surface 110 to be welded. Further, the welding gun portion 80 is freely movable by a robot 90 which is partially illustrated.

FIG. 3 shows the piezoelectric element actuator 7 described above.
In the piezoelectric element actuator 70, a pressing piezoelectric element 74 that expands and contracts according to an input voltage and a pressing force that is detected by the pressing piezoelectric element 74 are detected. Piezoelectric element 72 for detecting pressure reaction force
And a welding tip 76 for directly pressing the welded surface 110.
There is.

The resistance welding apparatus of one embodiment of the present invention constructed as above operates as follows.

For example, when welding is performed on the target surface 110 to be welded, first, the robot 90 moves the welding gun portion 80 to a desired position on the target surface 110.

At this time, a welding start signal (not shown) is input to the MPU 24, the signal for driving the hollow shaft servomotor 50 from the MPU 24 is calculated, and the switching signal G is sent to the inverter unit 13 through the above-described processing.
S is input to drive the hollow shaft servomotor 50. In this hollow shaft servomotor 50, the rotor shaft has a hollow structure, and the ball screw 82 is rotationally moved in the hollow rotor shaft so that the piezoelectric element actuator 70 connected to the ball screw 82 is attached to the welded surface 110. It can move vertically.

The piezoelectric element actuator 70, which is moved by the hollow shaft servomotor 50, contacts the surface 110 to be welded and pressurizes it. This pressing force is calculated from the U-phase current signal IU and the W-phase current signal IW detected by the current detector 52, and the position signal θS detected by the rotational position sensor 60. On the other hand, the MPU 24 activates the DC-DC booster 1 and applies a pressure force required for resistance welding by the piezoelectric element actuator 70. The applied pressure at this time is
According to the voltage generated by the DC-DC booster 1, the desired pressure is determined by feeding back the pressure detected by the pressing reaction force detecting piezoelectric element 72. Further, the degree of metal dissolution of the surface to be welded 110 to be resistance-welded can be estimated by the magnitude of the welding current IC actually detected by a current detector (not shown) because it suffices to detect a change in resistance value accompanying metal dissolution. can do.

This means that the welding time can be shortened by applying a high pressure at the initial stage of the process of resistance welding, and further, by suppressing the pressure at the time of melting the metal, the surface to be welded 110 can be reduced. Welding can be completed without making holes.

FIG. 4 is a flow chart of the resistance welding apparatus of the present invention.

First, the welding surface 1 is moved by the servomotor 50.
Pressurization of 10 is performed (S1). Then, the piezoelectric element actuator 70 applies the pressure required for resistance welding (S
2) If the welding current IC is reduced due to the melting of the metal (S3), the voltage supplied to the piezoelectric element actuator 70 is reduced to reduce the applied pressure (S4). Finally, when the preset welding work time is reached, the welding is finished (S5).

FIG. 5 shows another embodiment of the welding gun section.

In the welding gun portion 80A, a piezoelectric element actuator 70A having the same structure as the piezoelectric element actuator 70 described above, and a rack 84 for moving the piezoelectric element actuator 70A in a direction perpendicular to the surface 110 to be welded.
There is a pinion 86, a solenoid valve 88 for fixing the piezoelectric element actuator 70A when pressure is applied by the piezoelectric element actuator 70A, and a stopper 89. Since the piezoelectric element actuator 70A can be firmly held by the solenoid valve 88 and the stopper 89, for example, the structure for moving the piezoelectric element actuator 70A becomes easy and the motor may be small.

Further, the switching elements used in the DC-DC boosting section 1 and the power conversion section 10 may be high-speed switching elements such as IGBT and FET, and the DC-DC boosting section 1 is a half-bridge push-pull in this embodiment. However, a full bridge push-pull method or a chopper method may be used. Further, in this embodiment, both the power supply and the output to the motor are three-phase AC, but either one may be a single-phase AC system or both may be a single-phase AC system. The motor does not have to be a servo motor, but may be an induction machine or a stepping motor.

By configuring and operating as described above, the present invention detects the welding current supplied to the surface to be welded and the pressure applied to the surface to be welded to detect the voltage supplied to the piezoelectric element actuator. The pressure applied to the surface to be welded by the piezoelectric element actuator can be changed instantly by adjusting.

[0027]

As described above, according to the present invention, in the initial stage of welding, a high pressure is applied for prompt welding so that the metal dissolution on the surface to be welded is promoted and the welding current is further increased. By detecting it, the degree of melting can be estimated and the pressure applied by the piezoelectric element actuator can be instantly varied to perform optimum welding, so that it is possible to reduce problems such as unnecessary drilling on the surface to be welded.

[Brief description of drawings]

FIG. 1 is a drawing for explaining the configuration of a resistance welding apparatus that is an embodiment of the present invention.

FIG. 2 is a drawing for explaining the structure of the welding gun portion of the resistance welding apparatus which is an embodiment of the present invention.

FIG. 3 is a drawing for explaining the configuration of the piezoelectric element actuator of the resistance welding apparatus that is an embodiment of the present invention.

FIG. 4 is a flow chart of control of a resistance welding apparatus that is an embodiment of the present invention.

FIG. 5 is a drawing for explaining the structure of the welding gun portion of the resistance welding apparatus which is another embodiment of the present invention.

[Explanation of symbols]

1 ... DC-DC booster unit, 3 ... Diode bridge, 8 ... Transistor,
9 ... Transformer, 13 ... Inverter section,
20 ... control unit, 24 ... MPU,
50 ... Servo motor, 70 ... Piezoelectric element actuator, 72 ... Pressurizing reaction force detecting piezoelectric element, 74 ... Pressurizing piezoelectric element, 76 ...
Welding tip, 80 ... Welding gun,
82 ... Ball screw, 110 ... Surface to be welded.

Claims (1)

[Claims] 1. A piezoelectric element actuator which is movable when a high voltage is applied, an electrode tip which is integral with the piezoelectric element actuator and supplies a welding current for welding to a surface to be welded, and a surface to be welded to the electrode tip. In a resistance welding apparatus including a driving means for contacting or separating the welding means, by increasing or decreasing the voltage applied to the piezoelectric element actuator according to the increase or decrease of the welding current, the pressure applied to the surface to be welded is increased or decreased. A resistance welding apparatus having control means for performing optimum welding.