JPH0363468B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a welding control device that performs welding control using a control signal obtained by weaving a welding arc in a direction perpendicular to the direction of welding progress, and particularly relates to a welding control device that automatically detects the welding end portion. Concerning improvements in means. [Prior art] Conventionally, automatic arc welding equipment or teach
In arc welding using a playback type arc welding robot, if welding is to be completed at the end of the welded part, or if welding is to be performed at the end of the welded part, welding must be carried out in advance. The position of the welding end portion is set by manual operation or teaching, and arc welding is performed based on this set value. [Problems to be Solved by the Invention] However, there is a risk that the position of the welding end portion may deviate from the set value due to installation errors, dimensional errors, or deformation during welding of the members to be welded.
In this case, the arc welding does not end at the welding end, making it impossible to obtain a correct welding result, which causes quality deterioration. Therefore, conventional methods have been to improve the mounting accuracy of the parts to be welded,
Measures have been taken to improve dimensional accuracy or to improve restraint accuracy to prevent welding deformation, but these have led to an increase in manufacturing costs due to increased processing man-hours in order to obtain more precision than necessary. There is also a method of redoing the position setting operation or reteaching every time the welding end position shifts, but this method not only increases the manufacturing cost due to the increase in the amount of work required for the position setting operation or reteaching, but also reduces the welding process. This has become an obstacle to automation and even unmanned work. On the other hand, in order to control the distance between the welding torch and the workpiece, conventional methods have been taken to use arc current or arc voltage as a control signal, but this method has low discrimination and causes noise interference. It is easily affected and the control accuracy is very poor. Therefore, the present invention is capable of automatically and highly accurately detecting the welding end even if there are installation errors, dimensional errors, or deformations during welding of welding parts, and it is possible to automate and even unmanned welding work, and to facilitate manufacturing. It is an object of the present invention to provide a welding control device that can reduce costs. [Means for Solving the Problems] The present invention is characterized by taking the following measures in order to solve the above problems and achieve the objectives. That is, the impedance of the welding arc is detected by an impedance detection means, and instantaneous values of the impedance of the welding arc at the left and right ends of the weaving are sampled and held from the detected impedance by first and second sampling and holding circuits. , a difference signal between the left end instantaneous impedance value and the right end impedance instantaneous value sampled and held in the second sampling and hold circuit is detected by the difference signal detection means, and the sign and magnitude of the detected difference signal are discriminated by the discrimination means. The present invention is characterized in that passage of the welding arc to the welding end portion is detected from a change in the discriminated difference signal. [Operation] By taking such measures, the welding end portion can be automatically detected from the arc impedance, which has a higher discrimination than the arc current or arc voltage. [Example] FIG. 1 is a diagram schematically showing an example of the present invention.
This figure shows the state of fillet welding by consumable electrode type gas-shielded arc welding. In the figure, 1 is a welding member, 2
is a welding torch, and a DC voltage is applied to these welding member 1 and welding roach 2 from a power source (not shown) connected to power supply terminals 3a and 3b. Therefore, by bringing the welding torch 2 into contact with the welding member 1 and then pulling it away, the arc 5 is removed from the welding rod 4.
occurs. In this state, move the welding torch 2 to Z
Fillet welding is performed by keeping the shaft height constant and moving in the Y-axis direction while weaving at a constant amplitude. Also, the arc voltage E at this time
The arc current I is constantly detected by a voltage detector 5 and a current detector 6, and is supplied to a control device, which will be described later, so that the position of the welding end portion can be automatically detected. FIG. 2 is a block diagram showing the configuration of the control device. In FIG. 2, reference numeral 11 denotes an impedance calculator, to which the arc voltage signal SE and arc current signal SI output from the voltage detector 5 and current detector 6 are supplied, and the arc impedance calculator
Za, that is, Za=E/I...(1) is to be calculated. The impedance signal SZa output from the impedance calculator 11 is passed through the low-pass filter 1
2 to first and second sampling and hold circuits (hereinafter abbreviated as S/H circuits) 13 and 14. The first S/H circuit 13 detects the instantaneous value of the impedance of the arc at the left end of the weaving of the welding torch 2 by the pulse signal P _L for detecting the left end of the weaving supplied from the input terminal 15.
This is to sample and hold Z _L , and the second
The S/H circuit 14 uses the weaving right edge detection pulse signal P _R supplied from the input terminal 16 to
The instantaneous value Z _R of the impedance Za at the right end of the weaving of the welding torch 2 is sampled and held. The left end impedance instantaneous value signal SZ _L and the right end impedance instantaneous value signal SZ _R output from both the S/H circuits 13 and 14 are supplied to the differential amplifier 17, and the difference between the above instantaneous impedance values Z _L and Z _R is supplied to the differential amplifier 17. Z _L −
Z _R is to be calculated. The difference signal SZD output from the differential amplifier 17 is supplied to a signal discriminator 18. The signal discriminator 18 discriminates the sign and magnitude of the difference signal SZ _D according to a threshold L preset by a threshold setter 19, and the discrimination result, that is, the signal discriminator 19 The output signal S ₀ is output from the output terminal 20,
The welding end portion is detected based on this output. FIGS. 3a, 3b, and 3c are circuit diagrams showing specific examples of the impedance calculator 11 in FIG. 2. FIG. 3a shows a divider 21 and operational amplifiers 22a, 22 based on arc voltage E and arc current I.
An example of a circuit configuration when calculating impedance Za using b is shown. Note that VR in the figure is a variable resistor, and COM indicates a common base line. The basic arithmetic function of the divider 21 is V ₀ ′=10(Z′/X′) (2). However, in the above equation, V ₀ ′ is the divider output (quotient), and Z′ is the quotient. The input to the divider (dividend) and X′ indicate the input to the divider (divisor). Therefore, using the above basic arithmetic function, input the E component to the divider input Z' and the I component to X', and set Za=E/ as the divider output V ₀ '.
The circuit is configured to calculate I. The operational amplifiers 22a and 22b function as linear amplifiers or sign inverters, and the variable resistor VR functions as a level adjuster for the I and E components. FIG. 3b shows an example of a circuit configuration in which impedance Za is calculated based on arc voltage E and arc current I using multiplier 23 and operational amplifiers 24a to 24c. Components that are the same as those in Figure a are given the same reference numerals. The basic calculation function of the multiplier 23 is V ₀ =(1/10)X·Y (3). However, in the above equation, V ₀ represents the multiplier output (product), X represents the multiplier input (multiplicand), and Y represents the multiplier input (multiplier). Here, by using the basic arithmetic function described above, the multiplier 23 is replaced by the operational amplifier 24c.
The circuit is configured to calculate Za=E/I by inserting it into a negative feedback circuit consisting of the following, and collectively forming a divider. Note that the operational amplifiers 24a to 24c act as linear amplifiers or sign inverters, and
acts as a level regulator for the I and E components. FIG. 3c shows transistors 25a to 25c and operational amplifier 2 based on arc voltage E and arc current I.
6a to 26f are used to calculate the impedance Za. In addition, the figure a,
Components that are the same as b are given the same reference numerals. In the same figure c, the transistors 25a to
The circuit is configured to calculate Za=E/I by using the logarithmic conversion/anti-logarithmic conversion functions of 25c and operational amplifiers 26a to 26f. That is, Za=E/I=e ^{(logeE-logeI)} ...(4) where e is the base of the natural logarithm. In this case, the operational amplifiers 26a to 26f are linear amplifiers, sign inverters, and even transistors 26a to 26f.
Together with 5a to 25c, it acts as a logarithm/antilogarithm converter, and VR acts as a level adjuster for the I component and the E component. FIGS. 4a and 4b are circuit diagrams showing specific examples of the first and second S/H circuits 13, 14 and the differential amplifier 17 in FIG. 2. FIG. 4a shows the arc impedance signal SZa supplied from the impedance calculator 11 via the low-pass filter 12, and the pulse signals P _L and P _R for detecting the left and right edges of weaving supplied from the input terminals 15 and 16. The operational amplifier 27a, 2
7b and FET28.
Circuit 13, operational amplifiers 29a, 29b, and FET
30, the instantaneous impedance values Z _L and Z _R at the left and right ends of weaving are sampled and held, and the difference between the sampled and held instantaneous values Z _L and Z _R is calculated. The circuit is constructed as required by a differential amplifier 17 composed of an amplifier 31. In addition, in the figure
_CH indicates a hold capacitor. FIG. 4b shows that in response to the same signal as in FIG. The instantaneous impedance values Z _L , Z _R at the left and right ends of weaving are
is sampled and held, and the difference between the sampled and held instantaneous values Z _L and Z _R is calculated by the operational amplifier 31.
The circuit is constructed as required using a differential amplifier 17 constructed as shown in FIG. Figures 5a and 5b show the signal discriminator 18 in Figure 2.
2 is a circuit diagram showing a specific configuration of a threshold value setter 19 and a threshold value setter 19. FIG. _{FIG . _}
Divided into cases where Z _L −Z _R < 0, variable resistor VR1,
The operational amplifiers 34a and 34b are controlled by the threshold L set by the threshold setter 19 consisting of VR2.
The _circuit is configured such that the _{signal discriminator} 18 configured as _shown in FIG. It is composed of Figure 5b shows the two independent output signals in figure a.
Synthesize at OR gate 35, Z _L −Z _R >0 or
The circuit is configured such that the output is output from the output terminal 20 even if Z _L -Z _R <0. Next, in this embodiment, [1] the function of the arc impedance Za as a control input, and [2] the function of detecting the welding end portion by discriminating the arc impedance Za will be explained. [1] Effect of arc impedance Za as a control input In this embodiment, impedance Za as a characteristic value of the arc is used as an input signal for controlling the distance h between the welding torch and the workpiece to be welded. In Fig. 6a, curves A1, A2, and A3 show voltage/current characteristic curves in general consumable electrode type gas-shielded arc welding, and curve B
shows the external characteristic curve of the welding power source. The voltage/current characteristic curve A1 has a distance h between the welding torch 2 and the workpiece 1 as shown in P in the figure b _.
The voltage/current characteristic curve A2 is the case where the distance h is h ₀ +△h as shown in Q in the figure b, and the voltage/current characteristic curve A3 is the case in which the distance h is R as shown in the figure b.
This is the case where the distance h is h ₀ +Δh as shown in FIG. As is clear from Fig. 6a, when the distance h between the welding torch and the workpiece to be welded changes up and down by △h around _h0 , the arc voltage/current characteristic curves A1 to A
3 moves with almost similar shapes. Furthermore, when an arc is generated by a welding power source with external characteristics close to constant voltage characteristics as shown in B, at distance h=h ₀ there is an intersection point P _N , and at distance h=h ₀ +△
At h, stable energization is performed at the intersection P _S , and a steady welding state is obtained. That is, the operating point moves from P _N , P _L , P _S , etc. in response to the change in the distance h, and
Along with this movement, arc current I and arc voltage E fluctuate. Specifically, when the distance changes from h=h ₀ to h=h ₀ +△h, the arc current I becomes I ₀
The arc voltage E changes from E ₀ to I ₀ −△I.
It fluctuates to E ₀ +△E. Also distance h=h ₀ to h=
When changing to h ₀ −△h, the arc current I changes from I ₀ to
₀ −△I, and the arc voltage E changes from E ₀ to E ₀ −
It changes to △E. Conventionally, therefore, the target value control of the distance h has been performed using fluctuations in the arc voltage E and arc current I. In particular, the current I
Since the amount of variation in is larger than the amount of variation in voltage E,
Many devices are used that utilize fluctuations in current I, and arc sensors are based on this principle. On the other hand, the curve C shown by the broken line in Fig. 6a
1, C2, and C3 are the voltage/current characteristic curve A
1, a2, and A3 are current/impedance characteristic curves. Then, the operating point P _N ′ at the distance h = h ₀ between the welding torch and the workpiece to be welded, the corresponding impedance Za is expressed as Za ₀ , and the operating point at the distance h = h ₀ +△h is expressed as P _L ′, this The impedance Za corresponding to this is expressed as Za ₀ +△Za, the operating point at the distance h=h ₀ +△h is P _S ′, and the corresponding impedance Za is expressed as
It is expressed as Za ₀ + △Za. The table below shows changes in arc current I, arc voltage E, and impedance Za as the distance h changes.

【table】

[Table] As is clear from the table above, the distance h is from h ₀ to h ₀
When the change is +△h or h ₀ -△h, the relationship between current change rate I/I ₀ , voltage change rate E/E ₀ , and impedance change rate Za/Za ₀ is E/E ₀ <I/I ₀ <Za/Za ₀ . This means that as a target value control signal for distance h, impedance is more important than voltage E or current I.
This indicates that using Za has a higher degree of discrimination. Therefore, by using impedance Za as a control signal as in this embodiment,
It is possible to stabilize control and improve accuracy. By the way, stabilization after droplets (spraying)
Therefore, a current obtained by superimposing a pulsed current I _P on a reference current I ₀ is sometimes used as the arc current I. As shown in Figure 7, the current I changes from I ₀ to I ₀ +I _P
, the voltage E changes from E ₀ to E ₀ +E _P and the operating point P ₀ moves to P _P . In this case, the pulse wave ratio included in the input signal differs depending on whether current I, voltage E, or impedance Za is used as the control signal. The table below shows changes in the arc voltage E and impedance Za, and the rate of change thereof, when the arc current I is configured by superimposing the reference current I ₀ and the pulse current _IP .

【table】

Claims (1)

[Claims] 1. In a welding control device that performs welding control using a control signal obtained by weaving a welding arc in a direction perpendicular to the direction of welding progress,
impedance detection means for detecting impedance of the welding arc; first and second impedance detection means for sampling and holding instantaneous impedance values of the welding arc at the left and right ends of the weaving from the impedance detected by the means;
a sampling and holding circuit, a difference signal detecting means for detecting a difference signal between the left end instantaneous impedance value and the right end impedance instantaneous value sampled and held in the first and second sampling and holding circuits, respectively; The present invention is characterized by comprising a discrimination means for discriminating the sign and magnitude of the difference signal, and an end detection means for detecting passage of the welding arc through the welding end from a change in the difference signal discriminated by the discrimination means. Welding control device.