KR20230065661A - Control method for maintaining welding degree by maintaining pressure in certain range by detecting in real time wear state of electrode cap provided in electrode arm in spot welding robot - Google Patents

Abstract

The present invention relates to a control method for maintaining a welding degree by maintaining a pressure within a certain range by detecting in real time a wear state of an electrode cap provided on an electrode arm in a spot welding robot.

Description

A control method for maintaining the welding degree by maintaining the pressure within a certain range by detecting in real time the abrasion state of the electrode cap provided on the electrode arm in the spot welding robot TIME WEAR STATE OF ELECTRODE CAP PROVIDED IN ELECTRODE ARM IN SPOT WELDING ROBOT}

The present invention relates to a control method for maintaining a welding degree by maintaining a pressure within a certain range by detecting in real time a wear state of an electrode cap provided on an electrode arm in a spot welding robot.

In general, spot welding refers to a method of interposing a metal panel to be welded between a pair of electrode arms and bonding the electrode arms to the surface of the panel. Such spot welding is resistance welding in which a welding cap provided at an end of an electrode arm applies pressure to both sides of a pair of panels and simultaneously concentrates current to combine them.

When spot welding is performed, the end of the welding cap provided at the end of the electrode arm gradually wears out as the number of times of welding increases, and eventually fails to apply the required pressure to the panel, resulting in welding defects.

The spot welding monitoring device as a technology for detecting such welding defects detects the pressure change that the electrode presses on the base material upon the start of spot welding, extracts a shock wave from the pressure change, and correlates the thickness of the base material with the resultant welding quality. and the quality of the welding result is judged.

The technology disclosed in the prior art document is a method of detecting a welding defect, which can identify the welding state during the process and replace the welding cap of the electrode arm when a defect is found, but whenever a defect is detected, the welding cap of the electrode arm When the replacement work is performed, the entire process must be stopped, which is very inefficient in terms of time or cost.

An object to be solved by the present invention is to provide a control method for maintaining a welding degree by maintaining a pressure within a certain range by detecting in real time the worn state of an electrode cap provided on an electrode arm in a spot welding robot.

The problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

The control method of the spot welding robot of the present invention for solving the above problems is a pressure control method of the spot welding robot, which includes the steps of receiving pressure from a load cell during welding, and the average pressure value from the pressure detected for a certain period of time during welding. Calculating the average pressure value, comparing the average pressure value with a preset threshold pressure value, and correcting the pressure applied to the second electrode arm by adjusting the pressure of the cylinder when the average pressure value is lower than the critical pressure value. And, the step of calculating the average pressure value may be characterized in that the average pressure value is calculated when the detected pressure value is the same as the previous average pressure value.

According to the present invention, a shaft hole is formed in the piston of the cylinder and the second electrode arm, and the pressure applied to the second electrode arm during welding can be directly detected by installing a load cell in the shaft hole.

In addition, it is possible to maintain a predetermined welding degree by having an initially designed pressure at each predetermined period, and welding can be performed in a pressure range between a critical pressure value and an initially designed pressure value.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

1 shows a spot welding robot according to the present invention.
Figure 2 shows the operating state of the spot welding robot according to the present invention.
3 shows a pressure regulating device installed in the spot welding robot according to the present invention.
Figure 4 shows the pressure applied to the welding cap for the gap between the welding cap over time.
5 is a block diagram showing that spot welding is performed according to an embodiment of the present invention.
6 is a flow chart showing that spot welding is performed according to the present invention.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, only these embodiments are intended to complete the disclosure of the present invention, and are common in the art to which the present invention belongs. It is provided to fully inform the person skilled in the art of the scope of the invention, and the invention is only defined by the scope of the claims.

Terminology used herein is for describing the embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms unless specifically stated otherwise in a phrase. As used herein, "comprises" and/or "comprising" does not exclude the presence or addition of one or more other elements other than the recited elements. Like reference numerals throughout the specification refer to like elements, and “and/or” includes each and every combination of one or more of the recited elements. Although "first", "second", etc. are used to describe various components, these components are not limited by these terms, of course. These terms are only used to distinguish one component from another. Accordingly, it goes without saying that the first element mentioned below may also be the second element within the technical spirit of the present invention.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used with meanings commonly understood by those skilled in the art to which the present invention belongs. In addition, terms defined in commonly used dictionaries are not interpreted ideally or excessively unless explicitly specifically defined.

1 shows a spot welding robot according to the present invention.

The spot welding robot according to an embodiment of the present invention is fixed to the base (B) and moves to a predetermined position to perform welding. The spot welding robot includes a support 100 that rotates in three axes from a base, a cylinder 200 fixed to one side of the support, and a pair of electrode arms 300a that perform resistance welding by applying current to a panel to be welded. , 300b) and a controller 400 that drives the cylinder.

The pair of electrode arms includes a first electrode arm 300a fixed to a support and a second electrode arm 300b coupled to the piston of the cylinder. Further, welding caps are coupled to ends of the first and second electrode arms, respectively. The welding cap is in direct contact with the object to be welded.

On the other hand, in the present invention, although the use of a hydraulic cylinder is an embodiment, configuration with a server motor is not excluded. When configured as a server motor, the end of the moving shaft of the server motor and the second electrode arm are axially coupled, and a load cell for detecting pressure may be fitted into the shaft hole.

Figure 2 shows the operating state of the spot welding robot according to the present invention.

FIG. 2(a) shows a state in which the first electrode arm and the second electrode arm are open, and FIG. 2(b) shows a state in which the first and second electrode arms are closed.

Referring to the drawing, the first electrode arm is fixed to the support, and the second electrode arm is coupled to the piston end of the cylinder. In addition, the first electrode arm and the second electrode arm are axially coupled at each intermediate portion (CC). Due to the axial coupling, the second electrode arm rotates to perform welding in close proximity to the first electrode arm.

When welding starts, a panel (not shown) as a welding object is interposed between the first and second electrode arms. Subsequently, the piston of the cylinder moves forward to push one end of the second electrode arm so that the other end of the second electrode arm approaches the end of the first electrode arm.

Meanwhile, the piston of the cylinder and the second electrode arm are shaft-coupled, and a load cell for detecting pressure is fitted into the shaft hole. The load cell detects the pressure applied to the second electrode arm when the cylinder is operated and welding is performed.

3 shows a pressure regulating device installed in the spot welding robot according to the present invention.

The pressure regulating device of the spot welding robot according to an embodiment of the present invention includes a cylinder 200 for driving the second electrode arm, a load cell (LDS) for detecting the pressure applied to the second electrode arm during spot welding, and the load cell Based on the pressure detected from the controller 400 for controlling the driving of the cylinder.

The cylinder 200 is provided with a piston that moves forward or backward by hydraulic pressure, and an end of the piston is axially coupled with one end of the second electrode arm. When the piston moves backward, the welding caps of the first and second electrode arms are opened, and when the piston moves forward, the welding caps of the first and second electrode arms come into close proximity.

In general, a shaft hole is formed at an end of a piston of a spot welding robot and at one end of the second electrode arm, and a shaft is coupled to the shaft hole to rotate the second electrode arm. The load cell according to the present invention replaces the function of the shaft and is formed in the same shape as the shaft.

When the welding cap contacts the panel, which is an object to be welded, the rod is caught on the second electrode arm. The load cell LDS detects the pressure applied to the second electrode arm. The pressure detected by the load cell is output to the controller.

The pressure detected by the load cell is output to the controller. The controller 400 detects the pressure of the piston applied to the second electrode arm during welding and determines the pressure of the cylinder based on this.

Figure 4 shows the pressure applied to the welding cap for the gap between the welding cap over time.

Looking at the change in pressure during welding, the first and second electrode arms come into close proximity and the welding cap comes into contact with the panel. Subsequently, pressurization is performed until a predetermined pressure is reached (region A), and after maintaining the predetermined pressure for a predetermined time (region B), welding is performed (region C). When welding is completed, the second electrode arm is separated from the first electrode arm after the duration (region D) while the pressure is maintained (region E).

By the way, as the number of welding increases, the first and second welding caps provided on the first and second electrode arms are separated from each other by abrasion due to contact with the object to be welded, mechanical fatigue of the connecting parts of other components, and the like. The gap is widened, and accordingly, the pressure applied to the object to be welded during welding is lowered, so that a desired degree of welding cannot be obtained.

Initially, the gap between the first welding cap and the second welding cap is preset to obtain an optimal welding degree. Here, the preset gap is set based on the thickness of the panel to be welded first, the welding position, and the welding degree.

During spot welding, the pressure applied to the object to be welded moves from P1 to P2 after a predetermined number of welding times, because the gap between the welding caps is gradually spaced apart as the number of welding times increases. The gap between the welding caps causes the welding degree to be lowered.

Returning to FIG. 3 again, the controller 400 of the pressure regulating device according to the embodiment of the present invention adjusts the gap, current and pressure between the first and second welding caps so as to have a degree of welding necessary for welding the panel, which is a welding object. It stores and drives the cylinder to perform repetitive welding work using the stored data.

Meanwhile, the degree of welding is determined by the pressure output from the cylinder, and the pressure is determined according to the output value of the controller. For example, if good welding can be obtained at the welding pressure applied to the welding cap of 500 to 600 kgf, the welding must be maintained within the corresponding pressure range.

Hereinafter, a process in which spot welding is performed according to an embodiment of the present invention will be described in detail.

5 is a block diagram showing that spot welding is performed according to an embodiment of the present invention, and FIG. 6 is a flow chart showing that spot welding is performed according to the present invention.

1. The first step of receiving pressure from the load cell during welding;

The controller receives the pressure applied to the welding cap during welding from the load cell. As the number of welding increases, the welding cap gradually wears out and the pressure applied to the object to be welded decreases. In this way, the controller receives the applied pressure whenever welding is performed.

2. A second step of calculating an average pressure value at predetermined intervals;

The controller calculates an average pressure value from pressure data changed during a predetermined number of times. For s period (c times to n times), if the pressure for n times is P(n), the average pressure value can be calculated as Pa(n)=(P(c)+ ?? +P(n))/s can However, when P (n) is higher than Pa (n-1), the average pressure value is calculated with P (n) as Pa (n-1). For example, the average pressure value of 1 to 50 times may be 520 kgf, the average pressure value of 2 to 51 times may be 515 kgf, and the average pressure value of 3 to 52 times may be 511 kgf. At this time, if the detected pressure value is lower than the previous average pressure value, it is calculated as the average pressure value. However, if the average pressure value up until now has been calculated as 511 kgf and the detected pressure value is 512 kgf, the average pressure value is calculated as 511 kgf. This is to prevent the average pressure value from increasing as the number of times increases. This is because the pressure cap gradually decreases according to the number of times of use.

The reason for detecting the average pressure value is that the pressure during previous welding may be higher or lower than the pressure during subsequent welding due to various reasons such as different welding positions and welding directions. An increase in the number of welds does not necessarily appear as a linear decrease in pressure. According to the present invention, errors in temporary pressure changes can be prevented by setting the range of the number of times of welding.

3. A third step of comparing the average pressure value with a preset threshold pressure value;

It is determined whether the average pressure value calculated in this way is compared with the critical pressure value. For example, if the preset critical pressure value is 510 kgf and the average pressure value calculated during welding n times is 509 kgf, the calculated average pressure value is lower than the critical pressure value. In this step, whether or not the detected average pressure value is lower than a preset threshold pressure value is compared.

4. A fourth step of correcting the pressure applied to the second electrode arm by adjusting the pressure of the cylinder;

If the average pressure value calculated in the third step exceeds the critical pressure value, the pressure applied to the second electrode arm is increased during subsequent n+1 welding times. At this time, the pressure applied to the second electrode arm is set according to a preset correction pressure value. At this time, the corrected pressure value is set to have an initially designed pressure value. For example, if the initially designed pressure value is 520kgf and the critical pressure value is set to 510kgf, if the average pressure value calculated from n welding times is 509kgf, a correction pressure value of 11kgf is added to reset to the initially designed pressure value of 520kgf.

In this way, it is possible to maintain a predetermined degree of welding by having an initially designed pressure for each predetermined period. Therefore, the robot for spot welding can perform welding in a pressure range between the critical pressure value and the initially designed pressure value.

The pressure control method of the pressure regulating device of the present invention can be applied to mechanical devices that need to repeatedly maintain a constant pressure.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art to which the present invention pertains can be implemented in other specific forms without changing the technical spirit or essential features of the present invention. you will be able to understand Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (1)

A pressure control method for a spot welding robot comprising the steps of receiving pressure from a load cell during welding, calculating an average pressure value from the pressure detected for a certain period of time during welding, and comparing the average pressure value with a preset threshold pressure value. and correcting the pressure applied to the second electrode arm by adjusting the pressure of the cylinder when the average pressure value is lower than the critical pressure value. Control method of the spot welding robot, characterized in that the average pressure value is calculated when it is equal to the average pressure value of.

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