JPH0790386B2 - Pressure control method and device in resistance welding machine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure control method and device in a resistance welding machine including a pair of electrodes that are opened and closed by a pressure cylinder.

(Prior Art) Conventionally, when welding a work by a resistance welding machine, a pair of electrodes are closed by a pressure cylinder so as to sandwich the work, and the work is sandwiched between the electrodes to apply pressure after energizing the work. In this case, as seen in Japanese Utility Model Laid-Open No. 56-175182, the fluid pressure supplied to the pressure cylinder was lowered during the initial pressurization time, and then the fluid pressure was increased to the required pressure. Things are also known.

(Problems to be Solved by the Invention) Even if the fluid pressure supplied to the pressurizing cylinder is lowered during the initial pressurizing time as described above, the electrode closes in a no-load state until it comes into contact with the work. The closing speed of the electrode increases,
The electrode comes into contact with the work at a high speed, and the work is displaced by the impact force, and the electrode is worn.

An object of the present invention is to provide a pressurization control method that solves the above problems.

(Means for Solving Problems) According to the present invention, in order to achieve the above object, when the pair of electrodes is closed so as to sandwich the work, the distance between the electrodes is smaller than the thickness of the welded part of the work and is larger than a predetermined value. It is characterized in that the amount of fluid supplied to the pressurizing cylinder is reduced when the set value is reduced.

A second aspect of the present invention provides a pressurizing control device used for implementing the first aspect of the present invention, including a detection unit that detects an inter-electrode distance,
Discriminating means for discriminating whether or not the inter-electrode distance has decreased to a predetermined set value slightly larger than the thickness of the welding potential of the work in response to the signal from the detecting means, and the electrode for receiving the signal from the discriminating means And a control means for reducing the amount of fluid supplied to the pressurizing cylinder when the distance is reduced to the set value.

(Operation) When the amount of fluid supplied to the pressurizing cylinder is reduced, the closing speed of the electrode is correspondingly reduced.

Here, the fluid supply amount is reduced when the distance between the electrodes is reduced to a set value that is slightly larger than the thickness of the welded portion of the work, that is, before the electrode abuts the work, and therefore the electrode is moved at a low speed. It comes into contact with the work and the impact force is alleviated.
Further, unlike the case where the electrode is closed at a constant low speed from the open position, the time required for the electrode closing operation is shortened and the welding work efficiency is improved.

(Embodiment) With reference to FIG. 1, (1) shows an X-shaped welding gun which is a resistance welding machine having a pair of gun arms (3) and (3) opened and closed by a pressure cylinder (2), A robot (not shown) sequentially moves the welding gun (1) to a plurality of welding portions of the work W, closes both gun arms (3) and (3) at each welding portion, and attaches the work between the electrodes (4) and (4) at the tip thereof. Both electrodes (4) by welding transformer (5) by sandwiching and pressing W
(4) The spot welding of the work W was performed by energizing the space.

The pressurizing cylinder (2) is operated by a pneumatic servo circuit (8) including a servo valve (6) controlled by a servo amplifier (6a) and a regulator (7) controlled by a driver amplifier (7a). A double-acting air cylinder to be controlled. The pressure of the welding gun (1) is changed from the pressure in one of the air chambers of the pressure cylinder (2) supplied when the gun arm (3) (3) is closed. A pressure sensor (9) for detection is provided, and the other gun arm (3) that engages with the rack (10a) interlocking with one gun arm (3)
From the rotation angle of the upper pinion (10b), the electrode (4)
An opening sensor for detecting the distance between (4) (hereinafter referred to as the gun opening) is provided.

In the figure, (11) is a robot controller, (12) is a gun controller that stores the following welding condition data corresponding to each welding site, (13) is a CPU, and (14) is a program for controlling the opening and pressure. (15) shows the energization control circuit, which operates as follows.

That is, when the welding gun (1) reaches each welding site, the robot controller (11) inputs a welding site discrimination signal to the gun controller (12), and the gun controller (1)
The welding condition data corresponding to the welding site reached by the welding gun (1) is read from the storage unit of 2).

The welding condition data includes first and second opening data regarding welding current, energizing time, pressure, and gun opening. The first opening data is a value slightly smaller than the thickness of the work at the welding site. In addition, the second opening degree data is set to a value necessary to prevent interference with the work during the movement to the next welding site.

Then, first, the gun controller (12) transmits the first opening degree data and the pressure data to the CPU (13), and when doing so, pressurizes the servo amplifier (6a) via the D / A converter (6b). A command signal is input, and a driver pressure signal is input to the driver amplifier (7a) via the D / A converter (7b), and the pressure cylinder is input via the servo valve (6) and the regulator (7). Air is supplied to (2) and the closing operation of the gun arms (3) and (3), that is, the electrodes (4) and (4) is started.

Here, a detection signal of the gun opening is input to the CPU (13) from the opening sensor (10) through the A / D converter (10c), and the gun opening is first opened in the CPU (13). whether or not reduced to a small Huh higher value l ₁ than the thickness l ₀ of the work of setting value or the welding site is defined in degrees data discrimination is performed and cancer opening is reduced to set value l _1, CPU In response to a command signal from (13), the servo valve (6) supplies air to the pressurizing cylinder (1) via the servo amplifier (6a) in a short cycle between the air supply position and the neutral position where air supply is stopped. As a result, the amount of air supplied to the pressurizing cylinder (1) decreases, and the closing speed of the electrodes (4) (4) decreases accordingly, and the gun opening falls below the set value l ₁ . After that, it changes gently as shown in the second figure, and the electrodes (4) and (4) come into contact with the work W at a low speed to reduce the impact force.

When the electrodes (4) and (4) come into contact with the work W and the gun opening becomes equal to the work thickness l ₀ , the servo valve (6) is held in the air supply position by the signal from the CPU (13), and then the pressure is increased. When it is confirmed by the signal input from the sensor (9) to the CPU (13) via the A / D converter (9a) that the applied pressure has risen to the set pressure determined by the data, the CPU (13) From the gun controller (12) to the pressurization completion signal,
Welding current and energization time setting signals are input from the gun controller (12) to the energization control circuit (15), and the electrodes (4)
In (4), energization is performed for a predetermined time T ₁ with a predetermined current value.

Then, after a predetermined hold time T _{2 has} passed from the end of energization,
The second opening data is sent from the gun controller (12) to the CPU (13), the opening setting signal is input from the CUP (13) to the servo amplifier (6a), and the gun opening is determined by the second opening data. The servo valve (6) is operated to open the electrodes (4) and (4) so that the set value l ₂ is reached, and the gun opening becomes the set value l ₂ which is a signal from the opening sensor (10). When confirmed, a welding completion signal is sent from the CPU (13) to the robot controller (11) via the gun controller (12),
The robot operates to move the welding gun (1) to the next welding site.

(Effects of the Invention) As described above, according to the present invention, the electrode closing speed can be reduced before the electrode contacts the work, so that the electrode can contact the work at a low speed, and the impact force is mitigated. As a result, the work is prevented from being displaced due to the impact force, and the wear of the electrode is suppressed, so that the life of the electrode is extended.

[Brief description of drawings]

FIG. 1 is a diagram showing an apparatus used for carrying out the method of the present invention, and FIG. 2 is a diagram showing a change characteristic of a gun opening degree (distance between electrodes) during a welding operation according to the present invention. W …… Workpiece, (1) …… Welding gun (resistance welding machine) (2) …… Pressurizing cylinder, (4) …… Electrode (6) …… Servo valve (control means) (10) …… Opening degree Sensor (opening detection means) (13) …… CPU (discrimination means)

Claims (2)

[Claims] 1. A pressure control method in a resistance welding machine comprising a pair of electrodes which are opened and closed by a pressure cylinder.
When closing the pair of electrodes so as to sandwich the work, the amount of fluid supply to the pressurizing cylinder is reduced when the distance between the electrodes is reduced to a predetermined set value that is slightly larger than the thickness of the welded portion of the work. And a method for controlling pressure in a resistance welding machine. 2. A pressurizing control device in a resistance welding machine comprising a pair of electrodes which are opened and closed by a pressurizing cylinder, the detecting means detecting an inter-electrode distance, and a signal from the detecting means. Discriminating means for discriminating whether or not the inter-electrode distance has decreased to a predetermined set value slightly larger than the thickness at the welded portion of the workpiece, and the inter-electrode distance has decreased to the set value in response to a signal from the discriminating means. A pressure control device in a resistance welding machine, wherein the pressure control device receives control means for reducing a fluid supply amount to the pressure cylinder.