JPS63242471A - Method and device for controlling welding profile - Google Patents

Abstract

PURPOSE:To inexpensively control the welding profile with the high performance by detecting a weld zone of the tack welding based on detected signals of a means to detect an average electric current value and a means to calculate a power spectrum of a weaving frequency component. CONSTITUTION:An average current value detection circuit 13 calculates the average current value S13 for every weaving from a welding current signal S6 collected based on a weaving command signal S91 from a controller 9 of a robot main body. A power spectrum calculation circuit 14 calculates the power spectrum S14 of the weaving frequency component in the same way. A primary comparator 16 outputs a High signal S16 and a Low signal S16 to a decision circuit 19 of the weld zone of the tack welding in the case of the average current value S13<= a reference current value I0 and in the case of S13>I0 respectively. A secondary comparator 18 outputs a High signal S18 and a Low signal S18 in case the power spectrum S14 is in a reference spectrum area P0 and in case the power spectrum S14 is out of P0 respectively. The circuit 19 starts a torch position correction stop circuit 20 only when both S16 and S18 are High, namely, when the weld zone of the tack welding is detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method and apparatus for automatically copying welding by detecting a weld line while weaving a welding torch, and particularly relates to a method and apparatus for automatically copying welding by detecting a weld line while weaving a welding torch. The present invention relates to a suitable welding tracing control method and device for not being affected by welding line tracing performance even if

[Conventional technology]

In order to automate welding work, various sensors that imitate weld lines have been devised and put into practical use. In particular, arc sensors based on the welding arc phenomenon are the most commonly used because they are easy to use because there is no need to mount a detector around the torch, and are economical.

Generally, the objects to be welded are tack welded to position them, and then main welding is performed. This tack weld has a large effect on the followability of the arc sensor. Therefore, in order to perform proper copy welding, it is necessary to detect the tack weld and prevent copy malfunctions caused by this. This type of conventional device is equipped with a magnetic sensor in front of the welding torch, as described in Japanese Patent Laid-Open No. 61-14082, for example, and when a high voltage is output after passing through the tack welding part, the magnetic sensor is installed in front of the welding torch. There is a device that detects and stops the welding torch moving device to prevent malfunction of welding line copying, and as described in Japanese Patent Publication No. 51-7469, the tack welding area is detected based on the sum voltage of the output voltage of the E-type core. As another known example, as described in Japanese Patent Laid-Open No. 55-40019, copy welding is performed while a probe using a limit switch is brought into contact along the welding line, and the torch position is determined by this. There is a device that temporarily stops correcting the torch position when the amount of correction is larger than a predetermined reference amount.

[Problem that the invention seeks to solve]

The above-mentioned conventional technology has the advantage that it is possible to trace a weld line and detect and control a tack welded part using a single sensor. However, in practical use, it is necessary to protect the sensor from arc heat and spatter, so the sensor is often mounted at a sufficient distance from the welding torch. As a result, there was a problem in that the welding head became large and the device became expensive. Also, JP-A-6
The magnetic sensor described in Publication No. 1-14082 is suitable for butt joints, but there is no mention of fillet or lap joints, and even in other conventional technologies, when the target joints are restricted due to the principle of the sensor. There was also.

The present invention has been made in view of the above points, and its purpose is to provide a low-cost and highly practical welding tracing control method and device that includes a detection function for tack welding parts. Our goal is to provide the following.

[Means for solving problems]

The above object is to provide a method and apparatus for detecting a welding line from changes in electrical signals such as welding current when weaving a torch, and to provide a means for extracting the power spectrum of a specific frequency component in the welding current, and a means for extracting the power spectrum of a specific frequency component in the welding current. This is achieved by a means for calculating, and a determining means for determining the presence or absence of a tack welded portion from both the frequency power spectrum value and the average welding current value obtained thereby.

The present invention was born from the discovery of the phenomenon that a tack weld exists on the weld line when the average welding current value and the power spectrum of the weaving frequency component in the welding current simultaneously satisfy certain conditions. .

The first invention of the present application is a welding tracing control method for automatically making a welding torch follow a welding line while weaving a welding torch. Then, the average current value for each weaving cycle is determined, and the power spectrum of the weaving frequency component is calculated from the welding electric signal waveform. Based on the relationship between the two, the presence or absence of a tack weld is determined, and the section of the tack weld is determined. This method performs copy welding by temporarily stopping the correction of the torch position.

The second invention of the present application is an embodiment of the above-mentioned first invention of the present application into an apparatus.

That is, it is equipped with an average current value detection means for detecting the average current value for each weaving cycle and a power spectrum calculation means for extracting the power spectrum of the weaving frequency component from the welding electric signal waveform, and the signals output by these means are respectively , further comprising comparison means for comparing with a reference signal according to the comparison means, further comprising a tack weld determination means for determining the presence or absence of a tack weld based on the output signal from the comparison means, the tack weld determination means This welding tracing control device is equipped with a torch position corrective stop means for temporarily stopping the correction of the torch position in accordance with the output of the torch position.

The welding electric signal waveform means the fj contact current waveform or the welding voltage waveform. The former is effective in welding with constant voltage characteristics such as COx welding and MAG welding, and the latter is
It is effective in welding with constant current characteristics such as IG welding.

[Effect]

For example, in a fillet joint, if there is a tack weld part in the middle of the weld line, the welding arc length becomes shorter and the average current per weaving increases. However, since an increase in the average current is also seen due to a shift in the aiming position of the welding torch, it is impossible to judge whether there is a tack weld simply by the average current value. On the other hand, the inventor's experiments have revealed that the power spectrum of the weaving frequency component in the welding current when welding is performed along the weld line is almost constant regardless of the presence or absence of the tack weld. There is.

If the ridgeline of the tack weld is parallel to the weaving trajectory of the torch, there will be little change in the welding current, and as a result, the power spectrum of the weaving frequency will decrease. With the exception of cases where the weaving frequency component is not present, the tack welded part has an uneven shape and its cross section is small, so it is melted by the arc, so it is assumed that the change in the power spectrum of the weaving frequency component is small and almost constant.81g. On the other hand, it has been revealed that the power spectrum of the weaving frequency component increases as the torch is aimed at the welding line. Therefore, if the average current value increases and the change in the power spectrum of the weaving frequency is within a certain range, that is, if it is sufficiently smaller than the value that changes depending on the aim of the torch, it is determined to be a tack weld. can do.

In the present invention, means for detecting an average current value.

The present invention includes a means for obtaining a power spectrum of a weaving frequency component and a means for detecting a tack welded portion based on these detection signals.

In addition, in the present invention, it is of course possible to use a conventional positional deviation detection device (a device that detects the aimed positional deviation of the welding torch with respect to the welding line using electrical signals such as welding current or voltage during weaving). .

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a characteristic diagram illustrating the principle of detecting a tack weld in the present invention, and FIG. 2 is a perspective view of a lap fillet joint as an example. In the example shown in FIGS. 1 and 2, the welding line (
This is the case where tack welds 3 and 4 exist at When the tack weld is weaved as shown in Figure 1.

The average current value for each weaving cycle increases in the tack welding section, as shown by L1 and L2 in the figure. Further, the power spectrum of the weaving frequency in this section is almost the same as that in the area without the tack weld, as shown in the same figure. In addition, the average current value Ikl detected at the tack welding part 3 is measured at a place other than the tack welding part which is out of the weld line, for example at [Pl(
The same current value is also obtained at the coordinates yl, -zl). However, the power spectrum of the weaving frequency component at position P1 increases as shown at 81 in FIG. 1 as the position shifts. Therefore, in the present invention, firstly, the average current value per weaving cycle is determined, and the power spectrum of the weaving frequency component is also determined. It is checked whether the value of the power spectrum of the weaving frequency component is within the tack weld detection reference spectrum range PG, and if it is within Po, it is determined that a tack weld has appeared. Furthermore, the average current value also increases when the torch approaches the workpiece in the axial direction in areas other than the tack weld, but it has been revealed that in this case, the power spectrum of the weaving frequency component decreases extremely.
There is no misjudgment that it is a tack weld, and Pw in Fig. 1
is the value on the weld line other than the tack weld.

FIG. 3 is a schematic configuration diagram of a welding apparatus equipped with a welding profile control device according to an embodiment of the present invention. In Fig. 3, 5 is a welding machine, 6 is a welding current detection unit such as a shunt, and 7 is a torch drive unit that holds the welding torch 8 and performs weaving and driving the torch, and also includes the industrial robot body, etc. . 9 is, for example, a control device for the robot body, and t8
The position of the contact torch 8 is controlled, and the output (welding current and voltage) of the welding machine 5 is controlled via the welding machine interface 10. Reference numeral 11 designates a positional deviation detection device for detecting a target positional deviation of the welding torch 8 with respect to the welding line based on the output signal S6 from the welding current detection section 6, and 12 a tack welding portion detection device.

FIG. 4 is an internal configuration diagram of the tack weld detection device 12. In FIG. 4, the tack weld detection device 12 includes an average current value detection circuit 13 that detects the average current value for each cycle of weaving, a power spectrum calculation circuit 14 that extracts the power spectrum of the weaving frequency component, and a power spectrum calculation circuit 14 that extracts the power spectrum of the weaving frequency component. A primary comparison circuit 16 that compares the output value from the current value detection circuit 13 and the temporary welding total reference current value from the primary reference signal generation circuit 15; A second comparison circuit 18 that compares the output value with the tack weld detection reference spectral range PG from the second reference signal generation circuit 17, and the outputs of the second and second comparison circuits 16.18. Based on the output of the tack weld determination circuit 19, which determines the presence or absence of a tack weld, and the output of the tack weld determination circuit 19, the torch position correction signal detected by the positional deviation detection device 11 shown in FIG. The torch position correction and stop circuit 20 outputs suitable welding conditions (welding current or voltage or both) for stopping or tack welding. In FIG. 3, the positional deviation detection device 11 may detect the aim of the torch 8 based on the magnitude of the power spectrum of the weaving frequency component. In this case, the tack welding portion detection device 12 can also be used.

Next, the operation of the welding profile control device of the present invention will be explained using FIGS. 3 and 4.

In FIG. 4, the average current value detection circuit 13 calculates the average current value S13 for each weaving from the welding current signal S6 collected based on the weaving command S91 from the control device 9 of the robot body.

Similarly, the power spectrum calculation circuit 14 calculates the power spectrum S14 of the weaving frequency component for each weaving.
seek. The primary comparison circuit 16 uses the obtained average current value S
13 and the reference current value 0, and if S13≧0, outputs a high signal S16 to the tack welding part determination circuit 19, and if S13>Io, outputs a low signal S16.
A signal S16 is output to the tack welding portion determination circuit 19.

On the other hand, the second comparison circuit 18 determines whether the obtained power spectrum S14 is within the reference spectral range Po (see FIG. 1), and if it is within the reference spectral range Po,
Specifically, for example, Pw (Po/2)≦814≦Pw
+ (Pa/2), similarly to the operation of the primary comparison circuit 16, a High signal S18 is output to the tack welding portion determination circuit 19. Further, when the power spectrum S14 is outside the reference spectrum range PO, the signal 818 becomes Low.
It operates to output . The tack welding part determination circuit 19 is composed of, for example, an integration circuit, and starts the torch position correction stop circuit 20 only when the signals 816 and 818 are both high, that is, only when a tack welding part is detected. However, by outputting a signal 5120 for stopping the correction of the torch position to the positional deviation detection device 11, it is possible to prevent the influence of tracing errors caused by the tack welding portion. Furthermore, as shown in FIG. 4, the torch position v1 correction/stop circuit 20 is not necessarily limited to a circuit that stops correction of the torch position, and may be a circuit that outputs welding conditions suitable for the tack welding part. good.

Although the present invention has been implemented using a lap joint as an example, it can also be applied to a fillet joint. In the embodiment of the present invention, a tack weld is detected using the average welding current value obtained from the welding current and the power spectrum of the weaving frequency. Detection of tack welds can similarly be achieved by using the technique of the present invention based on the welding voltage, if effective and in other embodiments using a constant current characteristic power source.

〔Effect of the invention〕

As explained above, according to the present invention, a tack weld can be detected without requiring a special detector around the welding torch. Therefore, even if there is a tack welded portion, there will be no scanning malfunction, and extremely low-cost and high-performance welding scanning control can be realized.

[Brief explanation of drawings]

FIG. 3 is a schematic configuration diagram of a welding apparatus equipped with a welding tracing control device according to an embodiment of the present invention, and FIG. 4 is an internal configuration diagram of a tack weld detection device. 6... Welding current detection section, 8... Welding torch, 12.
...tentative Figure 1

Claims (1)

[Scope of Claims] 1. In a welding tracing control method for automatically following a welding line while weaving a welding torch, an average current value for each weaving cycle is detected; The power spectrum of the weaving frequency is extracted from the electrical signal waveform, and the relationship between the average current value and a pre-stored reference current value corresponding to the tack welding part and the value of the power spectrum and the predetermined reference power spectrum are determined. Detects the tack weld based on the relationship between
1. A welding tracing control method, characterized in that positional correction of the welding torch is stopped or welding conditions suitable for the tack welding part are output to perform tracing welding. 2. Average current value detection means for detecting the average current value for each weaving cycle; power spectrum calculation means for extracting the power spectrum of the weaving frequency component from the welding electric signal waveform of the welding torch performing the weaving operation; a first comparison means that compares the average current value with a predetermined reference current value; a second comparison means that compares the value of the power spectrum with a predetermined reference power spectrum; tack weld determination means that is electrically connected to the comparison means and the second comparison means and determines the presence or absence of a tack weld based on the results of both means; and the welding torch that is connected to the tack weld determination means. 1. A welding profiling control device comprising a torch position correction and stop means for stopping the position correction of the torch or outputting suitable welding conditions for the tack welding part.