JP3243484B2 - Electric pressurization control method. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for performing spot welding by applying a pressure between an electrode tip and a workpiece to be welded by using a servomotor as a pressure driving source of the electrode tip. Spot welding machine to increase the electrode pressure during energization continuously or intermittently by using the characteristics of And an electric pressurization control method.

Conventionally, as a pressurizing source of a stationary spot welding machine,
As a pressurizing system using a servomotor, for example, an electric pressurizing device disclosed in Japanese Patent Publication No. 3-50631 is known. This apparatus can change the electrode pressing force by a simple operation, and can perform spot welding with good responsiveness corresponding to the energizing time.

[0003]

However, the above-described electric pressurizing device has the following performance problems. In other words, the stop position of the electrode tip and its pressing force can be set freely, but this is to pressurize at a fixed pressing force within the setting, and the pressing force can be set freely during energization (during nugget generation). Was difficult to change. Therefore, compressed air is used as the driving source for pressurizing the welding electrode of the conventional resistance spot welding machine, and the air cylinder adjusted with the regulator is supplied to the air cylinder having the electrode to pressurize the electrode. General.

[0004]

SUMMARY OF THE INVENTION Therefore, the claims of the present invention
1 is a method of performing spot welding by converting the rotation of a servo motor into a linear motion with a screw nut, ball screw, etc., and driving the electrode tip by applying pressure. Welding current (di) and electrode voltage (dv) every minute time during welding
Is measured and the inter-electrode resistance value of the welded portion is calculated from dv / di. When the resistance value falls below the reference resistance value, the pressing force F corresponding to the armature current of the servomotor detected every minute time is calculated.
And the set force Fo set to increase the electrode force every minute time, and the armature current of the servomotor is adjusted so as to follow the force Fo corresponding to the armature current of the servomotor. Perform feedback control. In this case, for example, energization is started from point A, and when the inter-electrode resistance value that changes every moment reaches the reference resistance value in b, the electrode pressure during energization is increased so that the electrode pressure during energization is increased. The feature is to control the pressure continuously or intermittently every minute time (Fig. 1).

Next, a second aspect of the present invention is to convert the rotation of a servomotor into a linear motion by a screw nut, a ball screw or the like, drive the electrode tip and drive the electrode tip under pressure, and apply an object to be welded between the electrode tips by a rotation torque. In the method of performing press spot welding, a very short time (d
t) The expansion pressure (df) of the weld after the welding is detected from the armature current of the servomotor, and the rate of increase df / dt of the pressure is determined to increase the armature current of the servomotor every minute time. Automatically adjusts to correspond to the power ratio. For example, the armature current corresponding to the electrode force is continuously increased according to the rising angle, or is increased intermittently to increase the electrode force during energization every minute. (Fig. 2).

According to the present invention, by taking the above technical measures, the armature current of the servomotor is detected moment by moment,
The detected value is compared with a preset set pressure value, and the result is reduced to an appropriate temperature by automatically increasing the electrode pressing force of the heating generator every minute time by the current feedback control loop. Scattering can be suppressed and the width of the welding current area can be expanded. In other words, the heat generation during welding can be controlled by arbitrarily and precisely controlling the change in the pressing force due to the heat expansion of the work piece during spot welding, and the maximum possible welding current range is expanded to ensure reliable resistance welding. It can be carried out.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a flowchart showing a control means for implementing the method of the present invention.

The rotation of the servomotor is controlled by a screw nut,
Ball screw, when small electrode tip by converted into a linear motion by a power transmission means such as a pressure-driven pressurized by rotation torque weld object, the pressure torque at the time of welding the welded object
The welding current (di) and the electrode voltage (dv) are measured
Dv / di to calculate the inter-electrode resistance value of the welded part.
When the value falls below the quasi-resistance value, it is detected from the armature current of the servo motor. If the change in the current value is within a certain reference range, and if a value other than a certain value (large or small abnormality) is observed, For example, if no work is supplied between the electrodes, if no current is applied, or if an accident such as an abnormal current value occurs, an energization stop signal is issued to the welding control unit and the energizing operation of the contactor is stopped. At the same time, a command to open the electrode is issued, and the state is set before starting the work.

On the other hand, when the detected value of the armature current of the servomotor is established within the reference value, an energization start signal is issued to the welding control device, and the welding current is applied between the electrodes via the contactor to start welding.

The restraining torque at the time of energization is detected every minute time from the armature current of the servomotor, and is compared with the detected pressure Fo corresponding to the detected armature current of the servomotor. As a result of the comparison, when the pressing force F corresponding to the armature current is lower or higher than the set value, the armature current of the servo motor is feedback-controlled by the feedback control loop so as to follow the set pressing force Fo. Substantially, the armature current is increased or decreased to change the electrode pressing force during energization every minute time.

[0011] By doing so, resistance welding is realized in which a pressurizing force during energization is feedback-controlled to the armature current of the servomotor and precisely and automatically controlled to generate a reliable nugget.

FIG. 4 shows a control method according to the present invention.
7 is a graph showing the electrode pressing force, the amount of electrode movement, and the welding current during welding when the embodiment of the pressing force control by the servomotor is compared with the air pressing force control.

[0013] The case where the pressing force of the servomotor is increased continuously and the degree of control of the air pressing force are determined by the displacement of the electrode pressing force, the amount of electrode movement, and the displacement of the electrode during welding under the same welding conditions.
It is a graph of the waveform of a welding current.

[0014] In the case of pressure control of the servo motor, the soluble
Expansion of the weld after a very short time (dt) from the start of the welding of the welded object
Pressing force (df) is detected from the armature current of the servo motor.
To determine the increase rate df / dt of the pressing force
The armature current of the servomotor is automatically adjusted to correspond to the rate of increase.
And adjust the armature current corresponding to the electrode pressure, for example.
By controlling in accordance with the rising angle, the heat generated by the welding material expands, but the change in the pressing force is arbitrarily controlled continuously to increase the heat generated during welding. In the case of the air pressurization control, it can be seen that the welding material expands due to the heat generated immediately after welding and the applied pressure increases to a steady state, so that the heat generated during welding cannot be controlled.

FIG. 5 shows a control method according to the present invention.
It is a comparison of current values from a generated current value of a nugget diameter four times the square root of a plate thickness at the time of welding to a scatter generation limit current value.

When the servo motor pressurization and the air cylinder pressurization are performed under the same welding conditions described in the drawing, the nugget diameter of the welded portion is scattered from the welding current value that is four times the square root of the plate thickness. The welding current range up to was compared. As shown in the figure, it can be seen that the pressurization of the electric motor doubles the weldable current range width more than the air pressurization.

As described above, claim 1 of the present invention
According to the control method described above, when welding the workpiece
The welding current (di) and the voltage between the electrodes (dv) are measured and dv
Calculate the resistance value between the electrodes of the welded part from / di and calculate the reference resistance
When the value falls below the value, the welding pressure during welding is
Armature current is detected and the detected armature current is
The pressure against the armature current of the motor
Follow the set force set in the direction to increase the force
Thus, the current feedback control can be performed, and the electrode pressing force during energization can be precisely and automatically controlled every minute time, so that reliable welding with a widened weldable current range can be performed.

Further , according to the control method of claim 2 of the present invention,
For example, welding a very short time (dt) after the start of welding the workpiece
The expansion pressure (df) of the part is calculated from the armature current of the servo motor.
And the pressure increase rate df / dt is determined
During energization corresponding to the armature current of the servo motor every time
By controlling the electrode pressure,
Arbitrarily precise control of pressure changes due to thermal expansion of the workpiece
You can control. Con heat generation during welding by Re This
Trolling can be performed to reduce the occurrence of splattering and increase the weldable current range.
It is possible to perform reliable resistance welding by expanding to the maximum.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a transition of a pressure increase according to claim 1 of the present invention.

FIG. 2 is a schematic diagram showing a change in pressure increase in pressure control according to claim 2 of the present invention.

FIG. 3 is a schematic diagram showing a transition of a pressure increase according to claim 1 of the present invention.

FIG. 4 is a schematic diagram showing a change in pressure increase in pressure control according to claim 2 of the present invention.

FIG. 5 is a diagram showing a comparison of a weldable current range width between the electric pressurization control system of the present invention and a conventional air pressurization control system.

Continuation of the front page (56) References JP-A-7-96376 (JP, A) JP-A-4-224,811 (JP, A) JP-A-63-199086 (JP, A) JP-A-5-24171 (JP, A) , U) JP-B-63-25876 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 11/24 B23K 11/11

Claims (2)

(57) [Claims] 1. A method of performing spot welding by converting the rotation of a servo motor into linear motion by a screw nut, a ball screw, or the like, driving an electrode tip, and pressurizing and driving a workpiece between the electrode tips by a rotational torque. When the welding current (di) and interelectrode voltage (dv) are measured at minute intervals during welding of the work to be welded, the interelectrode resistance of the welded portion is calculated from dv / di, and when the resistance is lower than the reference resistance, The force F corresponding to the armature current of the servomotor detected every minute time is compared with the set force Fo set to increase the electrode force every minute time, and the electric motor of the servomotor is compared. An electric pressurization control method in which an armature current of a servomotor is feedback-controlled so as to follow a pressurizing force Fo corresponding to a subordinate current, and the electrode pressing force during energization is continuously or intermittently increased. 2. A method for performing spot welding by converting the rotation of a servomotor into linear motion with a screw nut, a ball screw, or the like, driving an electrode tip, and pressurizing and driving a workpiece between the electrode tips by a rotational torque. The expansion pressure (df) of the welded portion after a very short time (dt) from the start of welding of the workpiece is detected from the armature current of the servo motor, and the rate of increase of the pressure df / dt is determined. An electric pressurization control method for controlling an electrode pressing force during energization according to an armature current of a servomotor.