JPS6257436B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides automatic control of the distance between the welding torch and the workpiece in a consumable electrode constant-rate feed type automatic arc welding device or a consumable electrode constant-rate feed type arc welding robot, and welding tracing detection for automatic tracking of the weld line. METHODS AND APPARATUS. When performing arc welding using an automatic arc welding device or a teaching/regeneration type arc welding robot, even if installation errors, dimensional errors, or deformation of the welded material occur during welding, the amount of variation can be detected. However, it is necessary to automatically correct it so that proper welding can be performed at all times. In the past, various methods have been proposed and put into practical use as methods for detecting the above-mentioned fluctuations associated with arc welding, but among them, there is a method that detects changes in the electrical characteristic values of the welding arc and uses them for the above-mentioned correction. A so-called "arc sensor" that is used as an input signal is also often used. Here, the operating principle of arc sensors that are currently mainly used will be explained with reference to FIGS. 1 and 2. FIG. 1 shows the current/voltage characteristics in general consumable electrode constant-speed gas-shielded arc welding and an example of the external characteristics of a general welding power source. As shown in the figure, as the distance h between the workpiece 1 and the welding torch 2 changes up and down by ±Δh around h _p , the characteristic curves move up and down while remaining substantially similar. On the other hand, when the arc is loaded by a welding power source with external characteristics (close to constant voltage characteristics) as shown in the figure, when h=h _p , P
_N , P L for h=h _p +Δh, P _L for h=h _p −Δh
Stable current is applied at each intersection of _S , and a steady welding state is obtained. That is, the material to be welded 1
The operating point of the welding power source changes to P _N , P _L , P _S etc. in response to a change in the distance h between the welding torch 2 and
This fluctuation causes the current and voltage to fluctuate. As is clear from the figure, when h=h _p changes to h=h _p +Δh, the current I changes from I _p to I _p -ΔI, the voltage E changes from E _p to E _p +ΔE, and h= h
If _p changes to h=h _p -hΔ, I=I _p +ΔI, E
It can be seen that the values change as follows: =E _p -ΔE. In this way, both I and E change due to a change in h, but as you can see from the figure, the change in I is much larger than the change in E, so in reality, the change in I is not used. Therefore, it becomes possible to control the target value of h, and a so-called arc sensor utilizes this phenomenon. FIG. 2 is an explanatory diagram of an example of a method for controlling the position of a welding torch by utilizing the phenomenon shown in FIG. FIG. 2a shows an example of automatic target value control of the distance h (ie, Z axis) between the workpiece 1 and the welding torch 2 during welding on a flat plate. In the same figure, b shows an example of automatic control of the target value of h during butt welding, and c shows an example of automatic control of the target value of h during fillet welding.
In Figures 2 a to c, t _i is an input terminal to which current I or arc voltage E is applied, LPF is a low-pass filter, and COM is a comparison between the output of the threshold setter SR and the output of the low-pass filter LPF. Discriminator, SA is servo amplifier, SM is servo motor,
DM is the drive mechanism of welding torch 2, and this drive mechanism
The DM drives the welding torch 2 in the Z-axis and Y-axis directions shown when the X-axis is perpendicular to the paper surface. In the case of Figure 2 a, only the Z axis is driven, but in the cases of b and c, h changes not only in response to changes in the Z axis but also in the Y axis, so it is used for automatic control related to both axes. I have made it possible. That is,
In FIGS. 2b and 2c, if the Y-axis is fixed, only the Z-axis can be controlled as in a. Next, if the Z-axis is fixed, h will change depending on the change in the Y-axis direction.
A discriminator detects a change in h due to a change in the Y-axis direction, and compares the detected value with the corresponding electrical threshold.
The weaving turning point is determined by comparison and discrimination using the COM, and by repeatedly advancing the weaving, an automatic tracking function for the welding line is provided.
Next, in Figure 2 b and c, if both the Z-axis and Y-axis are to be controlled, the Z-axis control is performed on h near the center of the Y-axis, and the Y-axis control is performed in the Y-axis direction as before. Both can be achieved by applying this to h of the weaving end. In this way, by skillfully utilizing the phenomenon shown in Fig. 1, it is possible to control the position of the welding torch while detecting changes in the current I as shown in Fig. 2. It has its drawbacks. (1) The change in I due to the change in h is much larger than the change in E, but when performing subtle control in the Z-axis direction or Y-axis direction, the input due to the change in I Stable comparative discrimination may be difficult for signals. (2) In order to make the droplet transfer into a stable spray transfer, a sharp pulsed current may be superimposed on the welding current, and in such a case, the control input signal based on I also has a sharp pulsed waveform. Because of this, the operation of the control circuit may become unstable. It is an object of the present invention to alleviate such drawbacks and to provide a high-accuracy, low-cost method and device for detecting welding traces that causes less noise interference and can reliably respond to minute changes. In order to achieve the above object, the present invention uses the arc conductance G obtained by dividing the welding current I by the voltage E as a control input signal for controlling the position of the welding torch, and has the following characteristics. I can do it. The magnitude of the change rate of the arc characteristic value due to the change in the distance h between the welding torch and the welded material is E<I<G
So, if G is used as a control input signal,
A larger rate of change can be obtained than in the case of using conventional I, which is effective in improving accuracy in comparison and discrimination and preventing malfunctions. When a pulsed current flows from the pulse generator built into the welding power source, the voltage changes along the arc load characteristic curve with the same sign as the current change, regardless of the external characteristics of the power source.
The conductance does not change much, so noise interference due to sharp pulsed currents is reduced accordingly, and control accuracy can be improved. Since the conductance G is obtained by dividing the current I by the voltage E, the circuit configuration is easy and can be realized at low cost. An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows an example of a block configuration for explaining the welding trace detection method according to the present invention, and FIG. 4 shows an example of a specific circuit configuration for detecting arc conductance. FIG. 3 is an example of a block configuration for detecting arc conductance and positioning a welding torch by detecting arc conductance in general consumable electrode constant-rate gas-shielded arc welding. Figure 3a shows an example of a configuration for welding on a flat plate, and a block configuration for automatically controlling the target value of the distance h between the welding torch and the workpiece in flat plate welding, and performing Z-axis control using arc conductance as an input signal. This is an example.
In the figure, 1 is the material to be welded, 2 is the welding torch, h is the distance between the material to be welded 1 and the welding torch 2, E is the arc voltage, I is the welding current, and is the polarity of the welding power source.
Z and Y indicate drive shafts that are subject to welding torch position control, respectively. Also, 3a is a current input signal, 3b
is an arc voltage input signal, 4 is a conductance calculation circuit, 5 is a conductance signal, 6 is a low-pass filter, 7 is a comparison/discrimination circuit, 8 is a comparison/discrimination threshold setting circuit, 9 is a servo amplifier, 10-Z is a Z
The axis servo motor and 11-Z each indicate an axis drive mechanism. Therefore, in the case of the configuration example shown in Fig. 3a, the arc conductance G is calculated from the welding current I and the arc voltage E to detect the position of the welding torch in the Z-axis direction, that is, the distance h between the welding torch and the workpiece to be welded. death,
It has a function of discriminating this using a threshold value and applying the result to the Z-axis servo amplifier to operate the Z-axis drive mechanism and automatically control h. Next, Fig. 3b shows an example of a configuration during butt welding, and target value control of the distance h between the welding torch and the workpiece in butt welding is performed by Z-axis control using the arc conductance as an input signal. This figure shows an example of a block configuration in the case where each component has the same function as those in FIG. 3a. Therefore, in the case of the configuration example shown in FIG. 3b,
As in FIG. 3a, the welding torch has a function of automatically controlling the position of the welding torch in the Z-axis direction, that is, h. Next, FIG. 3c shows an example of a configuration for fillet welding and an example of a block configuration when automatic follow-up control of the weld line in fillet welding is performed by Y-axis control using arc conductance as an input signal. 1,
2, h, E, I,, Z, Y and 3a, 3b,
......Each component of 9 is a component having the same function as those in a and b of the same figure, and 10-Y
is the Y-axis servo motor, 11-Y is the Y-axis drive mechanism,
Reference numeral 12 indicates a weaving mechanism of the welding torch in the Y-axis direction. Therefore, in the case of the configuration example shown in FIG. 3c, by moving the welding torch in the X-axis direction while vibrating (oscillating or weaving) in the Y-axis direction, the change in h due to the change in the Y-axis direction can be suppressed. By detecting the detected value, comparing and discriminating the detected value with the corresponding threshold value using a comparison discriminator to determine the weaving turning point, and repeating this process,
Equipped with automatic weld line tracking function. From the above explanation regarding the configuration examples in Figure 3a, b, and c, automatic control is limited to only the Z-axis direction in the case of Figure 3a, but automatic control is limited to the Z-axis direction and the Y-axis direction in the Figures b and c. Since h changes in response to changes in either axial direction, automatic control of the position related to both axes, i.e. automatic control of the distance between the welding torch and the workpiece, and automatic welding torch position for tracking the welding line. It turns out that it can be used for control. FIG. 4 shows a specific example of the arc conductance detection section and the arithmetic circuit 4, which are the basis of the present invention, among the functional components shown in FIG.
Figure 4a shows an example of a circuit configuration when calculating conductance from arc voltage and current using a divider and an operational amplifier. In the figure, 1 is the material to be welded, 2 is the welding torch, and 3a is the current input signal. , 3b is an arc voltage input signal, 4 is a conductance calculation circuit, 5 is a conductance signal, and SH is a current shunt.
The conductance calculation circuit 4 above is a variable resistor VR
-1, VR-2, operational amplifier OP-1, OP-2,
It is composed of a divider D, and the voltage input signal E is inputted to an input terminal t _iE and the current input signal I is inputted to an input terminal _tiI . and common terminal t
The common line COM is connected to _c . Figure 4b
shows an example of a circuit configuration when calculating conductance from arc voltage and current using a multiplier and an operational amplifier. VR-1 and VR-2 are variable resistors,
OP-1 to OP-3 are operational amplifiers, and M is a multiplier. Figure 4c shows an example of a circuit configuration when calculating conductance from arc voltage and current using an operational amplifier and a transistor.
-1, VR-2 are variable resistors, OP-1, OP-
2, OP-4 to OP-7 are operational amplifiers, TR-1 to
TR-3 is a transistor. Next, the operation of the welding trace detection device configured as described above will be described. First, the operation related to arc conductance detection will be explained. 1, 2, 3a, 3 in Figure 3 a, b, c
The conductance of the arc is detected as follows by each functional element in b, 4, 5, and a, b, c in FIG. The conductance G of the arc can be defined as in equation (1). G=I/E...(1) [G: Arc conductance (〓) I: Current (A) E: Arc voltage (V)] Therefore, in the arithmetic circuit shown in Figure 4a, division is The basic arithmetic function of device D is V _p ′=10・Z′/X′ ……(2) [V _p ′: Divider output (quotient) Z′: 〃 Input (dividend) X′: 〃 〃 ( The circuit is configured so that G can be calculated as V _p ' by inputting the I component to Z' and the E component to X' using the divisor). OP-1 and OP-2 in the figure is linear amplification or sign inversion, VR-1 and VR-2 are I component and E
Acts as a component level regulator. Therefore, in Fig. 4a, when arc voltage E and arc current I in welding are applied to the respective input terminals, the levels of arc voltage E and arc current I are adjusted by variable resistors VR-1 and VR-2. and is input to operational amplifiers OP-1 and OP-2. In the operational amplifiers OP-1 and OP-2, the arc voltage E and the arc current I are linearly amplified or sign-inverted and applied to the divider D, where the calculation of V ₀ ′=10・Z′/X′ is performed. The conductance G is output as V ₀ '. In addition, in the arithmetic circuit shown in Fig. 4b, the basic arithmetic function of the multiplier M is V _p =1/10X・Y ...(3) [V _p : Multiplier output (product) Y: 〃 〃 (multiplier)〕 is used, this is inserted into the negative feedback circuit of the operational amplifier, and the circuit is constructed so as to compose a divider as a whole and calculate G=I/E. In the figure, OP−
1 to OP-3 are linear amplification or sign inversion functions, VR-
1, VR-2 acts as a level adjuster for the I and E components. Therefore, when level-adjusted arc voltage E and arc current I are input to operational amplifiers OP-1 and OP-2 through signal paths similar to those shown in Figure 4a, these signals are linearly amplified or sign-inverted. The output of the operational amplifier OP-1 is applied to the input terminal X of the multiplier M, and the output of the operational amplifier OP-2 is applied to the input terminal Y of the multiplier M through the operational amplifier OP-3, where V ₀ = X・Y/10
The following calculations are performed. And operational amplifier OP−
By inputting the calculation result V ₀ through the negative feedback circuit of the operational amplifier OP-3 to which the output signal of No. 2 is input, division is performed comprehensively and the result is output as conductance G. Furthermore, the arithmetic circuit shown in FIG. 4c is configured to calculate G=I/E using logarithmic conversion and anti-logarithmic conversion functions using operational amplifiers and transistors. G=I/E=e (log e I-log e E) ...(4) [e: base of natural logarithm] In the figure, OP-1, OP-2, OP-4 to OP-7 are linear amplification , sign inversion or transistor TR-1~
Along with TR-3, logarithm/anti-logarithm conversion effect, VR-
1, VR-2 acts as a level adjuster for the I and E components. Therefore, as in FIG. 4a, the arc voltage E and arc current I linearly amplified or sign-inverted by the operational amplifiers OP-1 and OP-2 are applied to the operational amplifiers OP-4 and OP-5 and the transistors.
They are logarithmically converted and added by TR-1 and TR-2, respectively, and then only the negative signal is passed through to the operational amplifiers OP-6 and OP-7 and the transistor TR.
Dividing is performed comprehensively by performing anti-logarithmic transformation at -3, and the result is output as conductance G. Next, the operation when the conductance G as the characteristic value of the arc obtained by the arithmetic circuit in this manner is used as an input signal for controlling the distance h between the welding torch and the workpiece to be welded will be explained. FIG. 5 shows the current/voltage characteristics in general consumable electrode constant-speed gas-shielded arc welding and an example of the external characteristics of a general welding power source. As shown in the figure, as the distance h between the welding torch and the workpiece to be welded changes up and down by Δh around h _p , the arc voltage characteristic curve moves up and down while remaining substantially similar. On the other hand, when the arc is loaded with a welding power source having external characteristics (close to constant voltage characteristics) as shown in the figure, when h=h _p , P _N , h=h _p +Δ
Stable energization is performed at each intersection of P _L at h and P _S at h=h _p -Δh, and a steady welding state is obtained. That is, the material to be welded 1 and the welding torch 2
The operating point changes depending on the change in the distance h between P _N and
P _L , P _S etc. fluctuate, and this fluctuation causes current and voltage to fluctuate. As is clear from the figure, if h=h _p changes to h=h _p +Δh, the current I changes from I _p to I _p -ΔI, the voltage E changes from E _p to E _p +ΔE, and h= It can be seen that when changing from h _p to h _p -Δh, I changes to I _p +ΔI and E changes to E _p -ΔE. In this way, both I and E change due to a change in h, but as you can see from the figure, a change in E causes a much larger change in I, so the change in I can be used to set the target for h. Value control has conventionally been carried out, and so-called arc sensors are based on this principle. In contrast, in the present invention, the target value of h is controlled using changes in the conductance G of the arc. That is, in FIG. 5, the curve shown by the broken line is the current/conductance characteristic curve corresponding to the current/voltage characteristic curve shown by the solid line, and
The operating point at h=h _p (I=I _p , E=E _p ) is P _N ', and the corresponding conductance G is G=G.
_p , and h=h _p +Δh(I=I _p −ΔI, E=E _p
+ΔE) is the operating point P _L ′, and G is G _p −Δ
G, and h=h _p −Δh(I=I _p +ΔI, E=
E _p -ΔE) is expressed as P _S ′ and G=G _p +ΔG, respectively. Such a conductance G
The characteristics when using h as the control input signal will be explained with reference to Table 1.

[Table] Table 1 shows the results of comparing the changes in I, E, and G as h changes, and as can be seen from the table,
When h changes from h _p to h _p +Δh or h _p -Δh, the current change rate I/I _p or the voltage change rate E/
Conductance change rate G/G _p than either E _p
This means that as an input signal for h control, G has a higher discrimination degree than E and than I. In other words, by using G as an input signal, it is possible to stabilize the control and achieve high accuracy. It turns out that it is possible to achieve Next, in order to stabilize droplet transfer (spraying), a pulsed current may be applied to the welding current. In such a case, the pulse wave ratio included in the input signal differs depending on which of the current I, voltage E, and conductance G is used as the control signal.
The situation is shown in Figure 6. Figure 6 shows welding current I
shows a case where the reference current I _p and the pulse current I _p are superimposed (I=I _p +I _p ). In addition, the changes in the arc voltage E and conductance G at this time and their rate of change are
Shown in the table.

[Table] As can be seen from Table 2, the current I changes from I _p to I _p +I
_p , the operating point P _p moves to P _p and the voltage E
changes from E _p to E _p +E _p . Comparing the current change rate I/I _p , voltage change rate E/E _p and conductance change rate G/G _p in this case, G/G _p
It can be seen that is closest to 1. In other words, if G is used as a control input signal, even if a sharp pulse current is superimposed on the temporary current, the pulse ratio in the input signal will be smaller than when using other characteristic values, and control will be easier. Accuracy can be improved and stabilized. As is clear from the above-mentioned embodiments, in the present invention, Z regarding the distance h between the welding torch and the workpiece in welding robot or automatic arc welding is
Since the arc conductance G is used as the input signal for axis control and Y-axis control,
Compared to control using welding current I or arc voltage E, signal discrimination ability is large, and high control accuracy and stability can be obtained. By employing it as an input signal, the pulse wave ratio in the signal can be minimized, improving control stability. In addition, it can be installed on existing automatic arc welding equipment or welding robots with almost no modifications or modifications, and since the main parts are constructed from simple analog circuits, it can be realized at low cost. Furthermore, it not only provides a powerful clue to realizing labor savings through automation and robotization of welding-related equipment, but also strengthens market competitiveness by improving the functionality and reducing costs of welding robots or automatic welding equipment. As described above, according to the present invention, by using the arc conductance obtained by dividing the welding current by the arc voltage as a control input signal to control the position of the welding torch, noise interference is reduced and reliability is achieved even with minute changes. It is possible to provide a high-accuracy, low-cost welding trace detection method and device that can respond to the following.

[Brief explanation of the drawing]

Figure 1 shows an example of the current/voltage characteristics and the external characteristics of the welding power source in general consumable electrode constant-speed gas shielded arc welding, and Figure 2 shows the position of the welding torch using the characteristics in Figure 1. FIG. 3 is a block diagram showing an embodiment of the welding tracing detection method and device according to the present invention, and FIG. 4 is a diagram showing the detection of arc conductance in the same embodiment. Fig. 5 is a current/conductance characteristic curve diagram corresponding to the current/voltage characteristic curve to explain the operation of the same embodiment, and Fig. 6 is a circuit diagram showing a specific configuration example of the welding current. FIG. 1... Material to be welded, 2... Welding torch, 3a...
Current input signal, 3b...Arc voltage input signal, 4
... Conductance calculation circuit, 5 ... Conductance signal, 6 ... Low pass filter, 7 ... Comparison discrimination circuit, 8 ... Threshold setting circuit, 9 ... Servo amplifier, 10-Z, 10-Y ... Servo Motor, 11-Z, 11-Y... Drive mechanism.

Claims (1)

[Claims] 1. An arc conductance signal obtained by dividing a welding current signal by an arc voltage signal is used as a detection signal for the distance between a welding torch and a workpiece in an automatic arc welding device or an arc welding robot, and The welding torch and the welding material are controlled by applying the comparison discrimination signal, which has been compared and discriminated against a set threshold value, to the servo motor as an input signal for controlling the welding torch position of the distance between the welding torch and the material to be welded, and operating the shaft drive mechanism. A welding trace detection method characterized in that the distance between the welding material and the welding material is controlled to be constant. 2. A welding current signal and an arc voltage signal are input, the welding current signal is divided by the arc voltage signal to obtain an arc conductance signal, and this is used as a detection signal for the distance between the welding torch and the workpiece in the arc welding device or arc welding robot. A conductance arithmetic circuit that outputs a signal as a signal, a comparison discriminator that compares a detection signal output from the conductance arithmetic circuit with a threshold value set in a threshold value setter, and a signal that is compared and discriminated by the comparison discriminator. A servo motor is input as a welding torch position control signal for automatic control of the distance between the welding torch and the material to be welded, and the servo motor is driven to move the welding torch in the axial direction to adjust the distance between the materials to be welded. A welding tracing detection device characterized by comprising a shaft drive mechanism for controlling.