JPH09150278A - Control method for resistance welding machine - Google Patents

Abstract

(57) [Abstract] [Purpose] In the resistance welding method that pressurizes the electrode by an electric servomotor, it automatically detects the wear amount of the electrode tip and outputs an electrode tip dress signal and an electrode tip replacement alarm. A control method for a resistance welding machine is provided. [Structure] In the resistance spot welding method in which the electrode pressurization operation is performed by an electric servomotor, when the electrode tip is replaced with a new one, a blank pressurization is performed without pinching the object to be welded, and it is built in the servomotor at that time. After reading the encoder value and setting the origin,
The wear of the electrode tip does not significantly progress, the blanking is periodically performed without pinching the work piece in the range of 10 to 100 dots, the encoder value at each time is detected, and the difference between this and the origin is calculated. The amount of wear of the electrode tip is calculated and the amount of wear is compared with a preset amount of wear or maximum amount of wear that requires dressing of the tip, and the amount of wear exceeds the standard value. In case of a contact, a dress signal or an electrode tip replacement alarm is output. In this way, the electrode stroke is always kept almost constant, so that extension of the cycle time can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding machine in which an electrode is pressed by an electric servomotor to automatically detect the wear amount of an electrode tip and output an electrode tip dress signal and a replacement alarm. The present invention relates to a control method for a resistance welding machine and a control method for a resistance welding machine, which corrects fluctuations in a pressing stroke due to wear of an electrode tip to prevent extension of cycle time.

[0002]

2. Description of the Related Art In resistance spot welding, the electrode tip gradually wears as the welding spot progresses, and this requires a prescribed dressing.
After reaching the limit of wear, it is necessary to wear a new dress or replace it with a new one. In the past, this time was judged by managing the number of RBIs based on experience values.

However, since this method does not directly detect the actual amount of wear of the electrode tip, it is not always possible to dress or replace the electrode tip at an optimum time, and usually the maximum wear should be taken with a margin. It was uneconomical to set the dress or the replacement period before reaching. Even if a separate sensor is installed to directly detect the actual wear amount, there are still problems such as cost, complexity of the device configuration, and mechanical interference.

Another problem is that when the electrode tip wears, the electrode opening amount equivalently increases, that is, the pressurizing stroke is extended, so that the moving time of the electrode pressurizing operation is extended and the cycle is increased. It means that the time will be long. In servo pressurization, generally, deceleration is performed from a few millimeters before the pressurization position in order to mitigate the impact of the electrode on the work to be welded, but this deceleration start point also recedes as the electrode wears. Therefore, there is a problem that the above problem has a greater effect on the cycle time.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems in a resistance spot welding machine in which an electrode pressurizing operation is performed by an electric servomotor. When the servomotor is applied to the pressurizing operation of the welding machine, its rotating operation is usually converted into a linear operation by a ball screw, etc., but at that time, the position and speed control of the movable electrode are generally controlled inside the servomotor. Is performed by detecting a signal from an encoder installed coaxially with the rotating shaft opposite to the movable electrode. In the present invention, the wear of the electrode tip is detected by the signal of the encoder in the servo motor instead of the position sensor near the electrode.

This encoder is physically shared with the servo control, but the calculation of the servo and the wear amount is performed independently. Since the encoder is installed away from the electrode part, there is no problem of damage due to scattering or mechanical interference, and the already installed encoder is shared for servo control, which is advantageous in terms of cost. Become.

[0007]

1 is a structural diagram of a servo pressurizing gun, which is an embodiment in which the present invention is applied to a dress signal of an electrode tip of a spot welding gun or a warning system for replacement.

When the electrode tip is first replaced with a new one, a blank pressure is applied without pinching the object to be welded, the encoder value built in the servo motor at that time is read, and the origin is set. During the work, the electrode tip wear is not significantly progressed, and the blank pressure is periodically applied without pinching the object to be welded in the range of 10 to 100 dots, and the encoder value at each time is detected. The wear amount of the electrode tip is calculated by calculating the difference from the origin, and the wear amount is compared with the wear amount that requires a preset dress and the reference value of the maximum wear amount that needs to be replaced. An electrode tip dress signal or a replacement alarm is output when the reference value is exceeded.

In this way, since the electrode tip replacement alarm is output in correspondence with the actual wear amount, the reference value can be set to the dress and the maximum wear limit value, so that there is no waste. Furthermore, since the encoder is installed away from the electrodes, there is no problem of damage or mechanical interference due to scattering, and the already installed encoder is shared for servo control, which is advantageous in terms of cost. Becomes

Next, FIG. 2 shows an embodiment of a pressurizing operation in the case where a pressurizing stroke correcting function is added to the servo pressurizing gun. Is the open state with a new electrode tip, is the pressurizing state, is the state where pressure is applied to the worn electrode tip without correcting the stroke, and is the open state where the stroke is corrected with the worn electrode tip The state is a state in which it is pressurized. Focusing on the pressurization stroke, when the pressure is applied to the worn electrode tip without correction of the pressurization stroke, the pressurization stroke is greater than the wear amount of the new electrode tip (e). ) You can see that it has been extended only.

However, if the pressure stroke is corrected, the pressure stroke from the open state to the pressure state even when the worn electrode tip is changed from the open state to the pressure state of the new electrode tip. It is the same as the pressure stroke.

In the servo pressure gun shown in FIG. 1, the number of servomotors is one and only the movable electrode is driven. On the other hand, the operation of FIG. 2 is designed so that the guns on both sides including the fixed side electrode move, but in actuality, the operation of the fixed side electrode is equalization such as floating the entire gun with a spring or the like. Depending on the function, it is done by shifting the entire gun. In this case, the operation of the movable-side electrode is twice the value of the moving stroke shown in FIG. Of course, the fixed side electrode may be moved by the equalizing function. Alternatively, the program may be performed by a robot that holds the gun, or a dedicated servo motor may be installed.

In this embodiment, when the electrode tip is first replaced with a new one, a blank pressure is applied without pinching the workpiece, the value of the encoder built in the servo motor at that time is read, and the origin is set. After that, in a series of welding operations, the pressure of the electrode tip was not significantly advanced, and the blanking of the workpiece to be welded was periodically performed within the range of 10 to 100 dots to detect the encoder value at each time. The difference between this and the origin is calculated to calculate the wear amount (e) of the electrode tip, and in the subsequent welding work, the position of the electrode tip is shifted by the shift amount (f) corresponding to the calculated wear amount. By performing the pressurization operation, the fluctuation of the pressurization stroke is corrected, and thereafter the welding amount is corrected by repeating the wear amount correction by periodical pressurization.

When the electrode tip wears, the electrode opening amount equivalently increases, that is, the pressing stroke is extended and the moving time of the electrode pressing operation is extended, and the cycle time becomes long. In servo pressurization, since the deceleration operation is generally performed several millimeters before the pressurization position in order to reduce the impact of pressurization of the electrode on the work to be welded, this problem is even more serious.

According to the embodiment, since the electrode stroke is always kept almost constant, it is possible to minimize the influence on the cycle time.

[0016]

As described above, according to the method of claim 1 of the present invention, the wear amount at the dressing timing of the tip of the electrode tip is detected from the value of the encoder incorporated in the servomotor, and the detection accuracy of the electrode tip dressing timing is detected. Since the electrode tip can be dressed in accordance with an appropriate wear amount, the tip of the electrode tip can be prevented from being over-cut, and the electrode life can be extended.

Further, according to the method of claim 2 of the present invention, since the electrode tip replacement alarm is output in accordance with the actual wear amount, the reference value can be set to the maximum wear limit value, which is wasteful. Absent.

Further, according to the method of claim 1 and the method of claim 2, since the encoder is installed at a place apart from the electrode portion, there is no problem of damage due to scattering or mechanical interference, and servo control. For this reason, the already installed encoder is shared, which is advantageous in terms of cost.

Further, according to the method of claim 3 of the present invention,
Periodically, air pressure is applied without pinching the work piece, the encoder value at each time is detected, and the difference between this and the origin is calculated to calculate the amount of wear of the electrode tip, and the subsequent welding The work is corrected by shifting the position of the electrode tip by the calculated wear amount and performing the pressurizing operation to correct the fluctuation of the pressurizing stroke, and then the wear amount is repeatedly corrected by periodical blank pressurization. Since this is done, the electrode stroke is always kept almost constant, and the effect on the cycle time can be minimized.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a C-type pressure gun using a servo motor for carrying out a control method of the present invention.

FIG. 2 shows a comparison operation between the pressurization / release state of a new electrode tip of a servo motor pressurizing gun and the pressurization / release state when a function of correcting a pressurization stroke to the wear of the electrode tip is added. It is a figure.

[Explanation of symbols]

1: fixed electrode, 2: movable electrode, 3: ball screw,
4: Servo motor, 5: Encoder, 6: Welding transformer: Open state with new electrode tip. : Pressed condition with a new electrode tip. : A state where pressure is applied without correcting the pressure stroke with the worn electrode tip. : Open state in which the pressure stroke is corrected by the worn electrode tip. : A state where pressure is applied by the corrected electrode tip.

Claims (3)

[Claims] 1. In a resistance spot welding method in which an electrode pressurizing operation is performed by an electric servomotor, when the electrode tip is replaced with a new one, a blank pressurization is performed without pinching a workpiece, and a servomotor at that time is applied. The value of the built-in encoder is read to set the origin, and the wear of the electrode tip does not significantly progress in the subsequent welding work.
The pressure of the electrode tip at each time point is detected by periodically performing a blank pressurization without pinching the workpiece in the range of 00 hit points, and the difference between this and the origin is calculated to calculate the wear amount of the electrode tip. The resistance welding machine is characterized in that the wear amount is compared with a preset wear amount reference value that requires dressing of the tip of the tip, and a dress signal is output when the wear amount exceeds the reference value. Control method. 2. In a resistance spot welding method in which an electrode pressurizing operation is performed by an electric servomotor, when the electrode tip is replaced with a new one, a blank pressurization is performed so as not to pinch a workpiece, and the servomotor at that time is applied. The value of the built-in encoder is read to set the origin, and the wear of the electrode tip does not significantly progress in the subsequent welding work.
The pressure of the electrode tip at each time point is detected by periodically performing a blank pressurization without pinching the workpiece in the range of 00 hit points, and the difference between this and the origin is calculated to calculate the wear amount of the electrode tip. A control method for a resistance welding machine, characterized in that the wear amount is compared with a preset maximum wear amount reference value and an electrode tip replacement alarm is output when the wear amount exceeds the reference value. 3. In a resistance spot welding method in which an electrode pressurizing operation is performed by an electric servomotor, when the electrode tip is replaced with a new one, an empty pressurization is performed so as not to pinch a workpiece, and the servomotor at that time is applied. The value of the built-in encoder is read to set the origin, and the wear of the electrode tip does not significantly progress in the subsequent welding work.
The pressure of the electrode tip at each time point is detected by periodically performing a blank pressurization without pinching the workpiece in the range of 00 hit points, and the difference between this and the origin is calculated to calculate the wear amount of the electrode tip. For the resistance welding machine, the subsequent welding work is characterized in that the welding work is performed while correcting the fluctuation of the pressing stroke by shifting the position of the electrode tip by the calculated wear amount and performing the pressing operation. Control method.