JP5511276B2 - Arc start control method - Google Patents

Description

  The present invention relates to an improvement in an arc start control method in which a welding wire is once brought into contact with a base material and then separated to generate an arc.

  Robot welding is widely performed in which a welding voltage and a welding current are output from a welding power source to generate an arc between a welding wire and a base material, and welding is performed by moving a welding torch by a robot. Examples of consumable electrode arc welding methods used for robot welding include carbon dioxide arc welding, mag welding, MIG welding, and pulse arc welding. In this robot welding, when a welding start signal is input to the robot controller, the welding torch is moved to the welding start position taught in advance by moving the robot and stopped, and the wire feed motor is rotated forward. When the welding wire is fed forward to the base material, and subsequently it is determined that the welding wire is in contact with the base material, the wire feeding motor is reversely rotated to feed the welding wire backward, and at the same time a small current value (several tens of A) ), The welding wire is moved away from the base metal by reverse feeding, and after the initial arc is generated, the welding wire is fed forward again at the steady feeding speed and the steady welding current is turned on simultaneously. Conventionally, there has been an arc start control method for shifting a welding torch from a stationary state described above to a movement in a welding direction taught in advance to a steady arc generation state. Are (e.g., see Patent Document 1). Hereinafter, this arc start control method of the prior art will be described with reference to the drawings.

  FIG. 3 is a configuration diagram of a conventional robot welding apparatus. The welding start circuit ST outputs a welding start signal St. The welding start circuit ST corresponds to a push button, a programmable logic controller (PLC) that controls the welding line, or the like. When this welding start signal St is input, the robot control device RC outputs an operation control signal Mc for controlling the operation of the robot RM to the servo motor of the robot RM, as well as a voltage setting signal Vr, a steady feeding speed setting signal. A transmission / reception signal If including Fcr, start signal On, and start completion signal Wcr is transmitted to and received from the welding power source PS. The voltage setting signal Vr, the steady feeding speed setting signal Fcr and the start signal On are signals transmitted from the robot controller RC to the welding power source PS, and the start completion signal Wcr is transmitted from the welding power source PS to the robot controller RC. Signal. These signals will be described later.

  The robot RM is equipped with the wire feed motor WM and the welding torch 4 and moves the tip position (TCP) of the welding torch 4 along the motion locus taught in advance according to the operation control signal Mc. The welding wire 1 is fed through a coil liner 4a having a length of about 1.5 [m] connecting between the wire feeding motor WM and the main body of the welding torch 4. That is, the standard length of the welding torch 4 is about 1.5 m.

  The welding power source PS transmits / receives the transmission / reception signal If described above, supplies the welding wire 1 with the welding voltage Vw via the power supply tip attached to the tip of the welding torch 4, and supplies the welding current Iw with the welding wire 1. An arc 3 is generated between the base material 2. Further, the welding power source PS outputs a feed control signal Fc, controls the rotation direction and the rotation speed of the wire feed motor WM, and controls the feed speed Fw of the welding wire 1. In the following description, the feeding speed Fw represents the speed of the tip of the welding wire 1. Even if the wire feed motor WM is rotating, if the tip of the welding wire 1 is in contact with the base material, the feed speed Fw = 0. That is, there exists a state where the rotation of the wire feeding motor WM does not correspond to the feeding speed Fw. The distance between the tip of the welding wire 1 and the base material 2 is the wire tip / base material distance Lw [mm]. Therefore, the wire tip / base material distance Lw is substantially the same as the arc length during arc generation. The distance between the tip of the power feed tip and the base material 2 will be referred to as the torch height Lt (mm). When the welding torch 4 has an advancing angle or a receding angle, the distance between the feeding tip and the base material 2 in the feeding direction of the welding wire 1 is the torch height Lt.

  FIG. 4 is a timing chart of each signal in the welding apparatus of FIG. 3 showing a conventional arc start control method. (A) shows the time change of the welding start signal St, (B) shows the time change of the robot operation control signal Mc, (C) shows the time change of the torch height Lt, FIG. 4D shows the time change of the feed control signal Fc, FIG. 4E shows the time change of the feed speed Fw, and FIG. 4F shows the time change of the welding voltage Vw. (G) shows the time change of the welding current Iw, FIG. 11 (H) shows the time change of the start completion signal Wcr, and FIG. 11 (I) shows the time change of the wire tip / base material distance Lw. Here, the operation control signal Mc shown in FIG. 5B is a signal that is at a high level when the robot is moving and is at a low level when the robot is stopped. The feed control signal Fc shown in FIG. 6D and the feed speed Fw shown in FIG. 5E indicate forward feed when the value is positive, and reverse feed when the value is negative. Hereinafter, a description will be given with reference to FIG.

(1) Period before time t1 (standby period)
During the period before time t1, the welding start signal St is at the low level (welding stop) as shown in FIG. 9A, and therefore the operation control signal Mc is low as shown in FIG. Level and the robot remains stopped at the standby position. As shown in FIG. 5C, the torch height Lt is a large value because the robot is at the standby position. As shown in FIG. 4D, the feed control signal Fc remains 0, and the feed speed Fw is also 0 as shown in FIG. That is, the feeding of the welding wire is in a stopped state. During this period, since the welding power source has not been activated, the welding voltage Vw is not applied as shown in FIG. 5F and remains at 0 V. As shown in FIG. Since Iw is not energized, it remains at 0A. Further, as shown in FIG. 5I, the wire tip / base material distance Lw is a large value because the robot is at the standby position.

(2) Period of time t1 to t2 (movement period of robot to welding start position)
When the welding start signal St changes to the high level (welding start) at time t1, the robot RM moves from the standby position to the welding start position taught in advance by the robot controller RC, as shown in FIG. . For this reason, as shown in FIG. 5B, the operation control signal Mc becomes a high level indicating a moving state at time t1, and becomes a low level indicating a stopped state at time t2. As shown in FIG. 5C, the torch height Lt gradually decreases to the taught torch height Ls taught in advance at time t2. During this period, since the welding power source is not yet activated, the feed control signal Fc = 0 as shown in FIG. 4D, and the feed speed Fw = as shown in FIG. It remains 0. That is, feeding of the welding wire has not yet started. Similarly, as shown in FIG. 5F, the welding voltage Vw has not been applied yet and remains at 0V, and as shown in FIG. 5G, the welding current Iw has not yet been energized and is 0A. Remains. As shown in FIG. 3I, the wire tip / base material distance Lw gradually decreases.

(3) Period from time t2 to t3 (forward feed period)
When the robot RM reaches the welding start position and stops at time t2, a start signal On is output from the robot controller RC to the welding power source PS, although not shown. In response to this, the feed control signal Fc changes to a predetermined slow-down feed speed setting value having a small positive value, as shown in FIG. For this reason, as shown in FIG. 5E, the feeding speed Fw changes to a slow-down feeding speed having a small positive value. Therefore, during this period, the welding wire is fed forward toward the base material at a very slow slow-down feeding speed. Since the welding power source PS is activated by the activation signal On at time t2, the output of the welding voltage Vw is started as shown in FIG. However, since the tip of the welding wire has not yet reached the base material during this period, the welding voltage Vw becomes the maximum no-load voltage value. As shown in FIG. 5G, the welding current Iw is 0 A because it is not energized yet. Further, as shown in FIG. 1I, the wire tip / base material distance Lw is gradually shortened by forward feeding.

(4) Period from time t3 to t4 (reverse delay period Ta from forward feeding to backward feeding)
When the welding wire comes into contact with the base material at time t3, the wire tip / base material distance Lw becomes 0 mm as shown in FIG. At the same time, the welding voltage Vw changes from a no-load voltage value to a small short-circuit voltage value of about several volts as shown in FIG. Further, as shown in FIG. 5G, the welding current Iw is energized, and the value becomes an initial current value of about several tens of A. When the short-circuit state is determined by the decrease in the welding voltage, the feed control signal Fc changes to a predetermined reverse feed speed setting value having a negative value, as shown in FIG. However, the motor reversal delay time required for the wire feeding motor to switch the rotation direction and the play amount that is necessary to reverse the play portion of the welding wire being fed while meandering the coil liner of the welding torch. Due to the feeding delay time, the wire tip does not move until time t4. For this reason, the feeding speed Fw during this period remains 0 as shown in FIG. The period from time t3 to t4 is referred to as a reverse delay period Ta from forward feeding to backward feeding.

(5) Period from time t4 to t5 (arc length raising period Tu)
When the inversion delay period Ta ends at time t4, as shown in FIG. 5E, the feed speed Fw rises from 0 to a slope and changes to a reverse feed speed having a negative value. As a result, the tip of the wire moves backward and away from the base material, so that an initial arc is generated. When the initial arc is generated, the welding voltage Vw rapidly increases from the short-circuit voltage value to an arc voltage value of about several tens of volts as shown in FIG. During the period from when the occurrence of the initial arc is determined due to the rapid increase in the welding voltage Vw to when the predetermined arc length raising period Tu elapses, as shown in FIG. Since the reverse feed speed setting value remains unchanged, the feed speed Fw remains the reverse feed speed as shown in FIG. For this reason, the backward feeding is continued, and the length of the initial arc is gradually increased. As a result, as shown in FIG. 11I, the distance Lw between the wire tip and the base material increases from 0 mm in a slope shape. And as shown to the same figure (F), the welding voltage Vw also becomes large in a slope shape in proportion to arc length. As shown in FIG. 5G, the welding current Iw remains the initial current value.

(6) Period from time t5 to t7 (re-forward feed transient period Tb)
When the arc length raising period Tu set at time t5 ends, the feed control signal Fc changes to a positive steady feed speed set value as shown in FIG. This steady feed speed setting value is set by a steady feed speed setting signal Fcr transmitted from the robot controller RC to the welding power source PS as a transmission / reception signal If. However, as described above, during the reverse delay time of the wire feed motor WM and the play feed delay time (time t5 to t6), as shown in FIG. Decreases from a negative reverse feed speed to a curve and becomes 0 at time t6. During the period from time t6 to time t7, as shown in FIG. 5E, the feeding speed Fw increases from 0 to a curved line and converges to the steady feeding speed Fcw at time t7. The period from time t6 to time t7 is a feed rising period until the feed speed Fw converges from 0 to the steady feed speed Fcw. The period from the time t5 to the time t7 is the re-forward feed transient period Tb from when the setting is switched to the re-forward feed until it converges to the steady feed speed Fcw. At time t5, the external characteristic of the welding power source PS is switched from the constant current characteristic to the constant voltage characteristic. As a result, as shown in FIG. 11I, the wire tip-base material distance Lw greatly overshoots during this re-forward feed transient period Tb and converges to the steady arc length at time t7. The reason for overshooting is that the welding current value determined by the constant voltage characteristics and the arc load state is larger than the feeding speed Fw, so the melting speed becomes larger than the feeding speed and the wire tip burns up. is there. In other words, the feed speed Fw is slow because the feed speed Fw is in a transient state where it does not converge to the steady feed speed Fcw. Since the arc length overshoots, the welding voltage Vw also overshoots during this re-forward feed transient period and converges to a steady value at time t7 as shown in FIG. This steady value is set by the voltage setting signal Vr of the transmission / reception signal If. Further, as shown in FIG. 5G, the welding current Iw once rises to a value larger than the initial current value at time t5. Then, during the re-forward feed transient period Tb, it decreases once and then increases, and converges to a steady value at time t7. That is, the welding current Iw during this period changes in a convex shape. The steady value of the welding current Iw is a value determined by the steady feeding speed Fcw. At time t5, as shown in FIG. 5H, the start completion signal Wcr becomes High level and is transmitted from the welding power source PS to the robot controller RC as a transmission / reception signal If. Receiving this, the robot controller RC moves the robot RM along the taught motion trajectory, so that the motion control signal Mc changes to a high level indicating movement, as shown in FIG. As shown in FIG. 5C, the torch height Lt remains the teaching torch height Ls after time t2. This is because in normal welding, the torch height is maintained at a constant value. In the above, the case where the start completion signal Wcr shown in FIG. 5H changes to the High level at the time t5 when the command is switched to the re-forward feed is illustrated. In addition to this, the start completion signal Wcr is set to change to the high level at the time t3 when the initial current flows, and the start completion signal Wcr is changed to the high level at the time t4 when the initial arc occurs. May be set.

  The arc start control is completed by the above operation, and a steady arc generation state is obtained after time t7. In this arc start control method, after the welding wire is once brought into contact with the base material, the initial arc is surely generated by pulling it apart, and thereafter, the welding wire is re-advanced to make a transition to a steady arc. For this reason, even when using a small diameter steel wire, a soft aluminum wire, etc. which generally do not have good arc start properties, good arc start properties can be obtained. However, in this arc start control method, the arc length overshoot during the re-forward feed transient period Tb described above may adversely affect the welding quality. If the overshoot of the arc length increases, the effect appears on the bead appearance. This arc length overshoot increases when the transient characteristic of the wire feed motor WM is slow. When a servo motor is used as the wire feed motor WM, the overshoot does not become so large because the transient characteristics are good. In the case of a DC motor often used in a welding apparatus, the overshoot becomes large because the transient characteristics are slow. Servo motors are rarely used because they are more expensive than direct current motors. Further, when the length of the welding torch is a standard length of about 1.5 m as described above, the re-forward feed transient period Tb becomes long, and thus the overshoot becomes large. For this reason, the length of the welding torch may be shortened to about 20 cm by installing the wire feed motor WM on the wrist shaft near the tip of the robot RM. However, in order to install the motor on the wrist shaft, an expensive motor having a small size and a large output torque must be used. Furthermore, interference between the motor installed on the wrist shaft and the workpiece, jig, etc. also becomes a problem. Accordingly, it is desirable from the viewpoint of cost and workability to use a standard DC motor and to use a welding torch having a standard length. In this case, since the overshoot of the arc length becomes large, a countermeasure is required. An example of this countermeasure will be described below.

  In the invention of Patent Document 1, the value of the feed control signal Fc is set to a value larger than the steady feed speed set value Fcr during the period corresponding to the re-forward feed transient period Tb. As described above, the re-forward feed transient period Tb is a total value of the motor reverse delay period + the idle feed feed delay period + the feed rise period. By making it like patent document 1, a play part feeding delay period and a feed rising period can be shortened. Therefore, since the re-forward feed transient period Tb can be shortened, there is a certain cost for suppressing overshoot. However, when a DC motor is used, since the motor reversal delay period is long, the method of Patent Document 1 has a limited overshoot suppression effect.

    In the invention of Patent Document 2, the welding torch is moved forward by a robot instead of the forward feeding of the welding wire, and the welding torch is moved backward by the robot instead of the backward feeding. That is, with the welding wire feeding stopped, the welding torch is moved forward by the robot to bring the welding wire into contact with the base material. Thereafter, the welding torch is moved backward by the robot to pull the welding wire away from the base material to generate an initial arc. This backward movement is performed for a predetermined arc length raising period Tu from the initial arc generation. At this time, the state is the same as that at time t5 in FIG. In the method of Patent Document 2, the period corresponding to the re-forward feed transient period Tb is only the feed rise period. This is because the motor is not reversed, and there is no motor reversal delay period and idle feed delay period. Therefore, the arc length overshoot is suppressed. However, when the steady feed speed setting value Fcr is large, the feed rising period becomes long, so the overshoot suppressing effect is limited.

JP 2003-181641 A JP 2002-205169 A

  In the arc start control method of the prior art, when a DC motor that is frequently used as a wire feed motor is used, or when the length of the welding torch is a standard length of about 1.5 m, the above-described method is used. As described above, there is a problem that the overshoot of the arc length during the re-forward feed transient period becomes large. With respect to this problem, by implementing the invention of Patent Document 1 or 2, overshoot can be suppressed. However, this suppression effect is limited as described above.

  Therefore, in the present invention, even when a direct current motor is used as the wire feed motor, the length of the welding torch is about 1.5 m, and the steady feed speed is high, it is possible to restart the operation. An object of the present invention is to provide an arc start control method capable of suppressing an arc length overshoot during a forward feed transient period and obtaining a good welding quality.

In order to solve the above-described problems, the first invention is to feed a welding wire from a welding torch forward to a base material, and when the welding wire comes into contact with the base material, the welding wire is moved backward from the base material and a welding current is supplied. Arc start control to turn the welding wire from the initial arc generation state to the steady arc generation state after the welding wire is separated from the base metal by the backward feeding and the initial arc is generated by this backward feeding. In the method
Torch height control is performed in which the height of the welding torch is once lowered to a slope shape after the re-advance feeding start time and then returned to the original height by raising the slope shape .
An arc start control method characterized by the above.

The torch height control is a control that lowers the slope by a predetermined movement distance during a first predetermined period and returns it to the original height by increasing the slope during a second predetermined period. Is,
An arc start control method according to the first aspect of the invention.

In a third aspect of the invention, an inversion delay period at the time of switching from the forward feed to the reverse feed is detected, and the first period, the second period, and the moving distance are set based on the inversion delay period. ,
An arc start control method according to the second aspect of the invention.

  According to the first aspect of the present invention, when the re-forward feeding is started, the arc length overshoot is canceled by performing the torch height control in which the height of the welding torch is once lowered and then returned to the original height. can do. For this reason, even when a DC motor is used as the wire feeding motor, the welding torch is about 1.5 m in length, and the steady feeding speed is high, the re-advance feeding is performed. The overshoot of the arc length during feeding can be suppressed, and good welding quality can be obtained.

  According to the second invention, by setting the first period, the second period, and the movement distance so as to minimize the overshoot of the arc length, the consideration of the first invention can be maximized.

  According to the third aspect, in addition to the effect of the second aspect, the first period, the second period, and the movement distance are automatically set based on the reverse delay period when switching from forward feeding to backward feeding. Therefore, the setting efficiency of these parameters becomes unnecessary, so that the work efficiency is improved.

It is a timing chart which shows the arc start control method concerning an embodiment of the invention. It is an electric current / voltage waveform diagram in pulse arc welding for explaining an arc start control method concerning an embodiment of the invention. It is a block diagram of the conventional robot welding apparatus. It is a timing chart which shows the conventional arc start control method.

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

  FIG. 1 is a timing chart showing an arc start control method according to an embodiment of the present invention. (A) shows the time change of the welding start signal St, (B) shows the time change of the robot operation control signal Mc, (C) shows the time change of the torch height Lt, FIG. 4D shows the time change of the feed control signal Fc, FIG. 4E shows the time change of the feed speed Fw, and FIG. 4F shows the time change of the welding voltage Vw. (G) shows the time change of the welding current Iw, FIG. 11 (H) shows the time change of the start completion signal Wcr, and FIG. 11 (I) shows the time change of the wire tip / base material distance Lw. Here, the operation control signal Mc shown in FIG. 5B is a signal that is at a high level when the robot is moving and is at a low level when the robot is stopped. The feed control signal Fc shown in FIG. 6D and the feed speed Fw shown in FIG. 5E indicate forward feed when the value is positive, and reverse feed when the value is negative. About a welding apparatus, it is the same as FIG. 3 mentioned above. This figure corresponds to FIG. 4 described above, and the operation up to time t5 is the same, so the explanation is omitted. Hereinafter, the operation after time t5 will be described.

(6) Period from time t5 to t7 (re-forward feed transient period Tb)
When the arc length raising period Tu set at time t5 ends, the start completion signal Wcr changes to a high level as shown in FIG. 5H, and this signal is transmitted / received from the welding power source PS to the robot controller RC. Sent as If. Upon receiving this, the robot RM starts moving in the welding direction, and the torch height Lt is lowered by a predetermined moving distance ΔLt during a predetermined first period T1 from time t5 to t6. Moving. Therefore, as shown in FIG. 5B, the operation control signal Mc is at a high level (moving state) for a period after time t5. Further, as shown in FIG. 5C, the torch height Lt becomes the teaching torch height Ls until time t5, becomes shorter like a slope after time t5, and becomes Ls−ΔLt at time t6. The robot RM moves so as to increase the torch height by the movement distance ΔLt during a predetermined second period T2 from time t6 to t7, and returns to the teaching torch height Ls at time t7. Therefore, as shown in FIG. 3C, the torch height Lt increases in a slope shape from time t6, and returns to the teaching torch height Ls at time t7. The total value of the first period T1 and the second period T2 is set to substantially the same length as the re-forward feed transient period Tb in FIG. And what is necessary is just to set as T1 = T2. Further, the movement distance ΔLt is set to be substantially equal to the arc length overshoot amount shown in FIG. That is, the torch height Lt may be changed so as to cancel the overshoot of the arc length shown in FIG. In this way, the arc length quickly converges to a steady value from time t5 without overshooting.

  At time t5, as shown in FIG. 4D, the feed control signal Fc changes to a positive steady feed rate set value. This steady feed speed setting value is set by a steady feed speed setting signal Fcr transmitted from the robot controller RC to the welding power source PS as a transmission / reception signal If. However, as described above, during the reverse delay time of the wire feed motor WM and the play feed delay time (time t5 to t6), as shown in FIG. Decreases from a negative reverse feed speed to a curve and becomes 0 at time t6. During the period from time t6 to time t7, as shown in FIG. 5E, the feeding speed Fw increases from 0 to a curved line and converges to the steady feeding speed Fcw at time t7. The period from time t6 to time t7 is a feed rising period until the feed speed Fw converges from 0 to the steady feed speed Fcw. The period from the time t5 to the time t7 is the re-forward feed transient period Tb from when the setting is switched to the re-forward feed until it converges to the steady feed speed Fcw. At time t5, the external characteristic of the welding power source PS is switched from the constant current characteristic to the constant voltage characteristic. Here, during the period from the time t5 to the time t6, since the constant voltage characteristic is formed in a state where the feeding speed Fw does not reach the steady feeding speed Fcw, the arc length is overshooting, but as described above. In addition, the arc length quickly converges to a steady value by controlling the torch height. Therefore, as shown in FIG. 5I, the wire tip / base material distance Lw quickly converges to a steady value from time t5. Since the arc length does not overshoot, the welding voltage Vw quickly converges to a steady value from time t5 as shown in FIG. This steady value is set by the voltage setting signal Vr of the transmission / reception signal If. Further, as shown in FIG. 5G, the welding current Iw quickly converges from the initial current value at time t5 to the steady value. This steady value is a value determined by the steady feeding speed Fcw. After time t7, a steady arc is generated.

Regarding the above-described torch height control, there are various embodiments as follows.
The following is an explanation.
[First torch height control method]
(1a) When the robot control device RC receives the start completion signal Wcr, the robot control device RC moves the robot RM to once reduce the height of the welding torch, and then performs torch height control to return to the original height.
According to the first torch height control, since the arc length overshoot can be canceled, a DC motor is used for the wire feed motor WM, and the length of the welding torch is about 1.5 m. Even when the length is standard and the steady feeding speed is high, overshooting of the arc length at the time of re-forward feeding can be suppressed, and good welding quality can be obtained.

[Second Torch Height Control Method]
The second torch height control is as follows.
(2a) Upon receiving the start completion signal Wcr, the robot controller RC moves the robot RM to reduce the torch height by the movement distance ΔLt during the first period T1, and during the second period T2, the original teaching Return to torch height Ls.
According to the second torch height control, the first period T1, the second period T2, and the movement distance ΔLt are optimized according to the arc length overshoot, thereby suppressing the arc length overshoot to the maximum. be able to.

[Third Torch Height Control Method]
Further, the third torch height control is as follows.
(3a) The welding power source PS detects an inversion delay period Ta from forward feeding to backward feeding at time t3 to t4 in FIG. 1, and transmits the inversion delay period Ta to the robot controller RC as a transmission / reception signal If. To do.
(3b) The robot controller RC receives the reverse delay period Ta, and sets the first period T1, the second period T2, and the movement distance ΔLt based on this value.
(3c) Upon receiving the start completion signal Wcr, the robot controller RC moves the robot RM to reduce the torch height by the movement distance ΔLt during the first period T1, and during the second period T2, the original teaching Return to torch height Ls.
The total value of the first period T1 and the second period T2 is preferably set to be substantially equal to the re-forward feeding transient period Tb. Since the re-forward feed transient period Tb is also one of the reverse delay periods, the most forward feed transient period Tb can be estimated from the reverse delay period Ta. If the re-forward feed transient period Tb can be estimated, the moving distance ΔLt can also be estimated. Therefore, it is possible to estimate appropriate values of the first period T1, the second period T2, and the movement distance ΔLt from the inversion delay period Ta. For this reason, according to the third torch height control, in addition to the above-described effects, the first period T1, the second period T2, and the movement distance ΔLt can be automatically set, thereby improving work efficiency. To do.

[Fourth Torch Height Control Method]
Further, the fourth torch height control is as follows.
(4a) The robot controller RC detects the welding voltage Vw.
(4b) Upon receiving the start completion signal Wcr, the robot controller RC performs torch height control by moving the robot RM by feedback control so that the value of the welding voltage detection signal is equal to the value of the voltage setting signal Vr. .
Since the arc length and the welding voltage Vw are proportional, if the torch height is controlled so that the detected value of the welding voltage Vw is equal to the steady value (the value of the voltage setting signal Vr), the arc length overshoots. Can be compensated and maintained at a steady value. According to the fourth torch height control, since the torch height control can be automatically controlled in addition to the above-described effects, it is not necessary to set the first period T1, the second period T2, and the movement distance ΔLt. Work efficiency is improved.

[Fifth Torch Height Control Method]
Further, the fifth torch height control is a case where the above-described fourth torch height control is applied in pulse arc welding, and is as follows.
(5a) The robot controller RC detects the welding voltage Vw (peak voltage Vp) during the energization period (peak period Tp) of the peak current Ip described later in FIG.
(5b) Upon receiving the start completion signal Wcr, the robot controller RC moves the robot RM by feedback control so that the value of the welding voltage detection signal (peak voltage Vp) is equal to the value of the predetermined voltage setting signal. To control the torch height.

  FIG. 2 is a general current / voltage waveform diagram of consumable electrode pulse arc welding. FIG. 4A shows the welding current Iw for energizing the arc, and FIG. 4B shows the welding voltage Vw between the welding wire and the base material. Hereinafter, a description will be given with reference to FIG.

  During the peak period Tp from time t1 to t2, as shown in FIG. 4A, a peak current Ip greater than the critical current value is applied to transfer the droplets from the welding wire, and shown in FIG. Thus, the peak voltage Vp proportional to the arc length is applied between the welding wire and the base material.

  During the base period Tg from time t2 to t3, as shown in FIG. 5A, the base current Ib having a constant current value is applied to prevent the formation of droplets, as shown in FIG. In addition, a base voltage Vb is applied. The welding is performed by repeating the period from time t1 to t3 as the pulse period Tpb. The broken line shown in FIG. 5A shows the welding current average value Iav, and the broken line shown in FIG. 4B shows the welding voltage average value Vav. In FIG. 1 described above, when the welding method is the pulse arc welding method, a DC initial current is applied before time t5, and a pulsed current consisting of the peak current Ip and the base current Ib is applied after time t5. To do. Accordingly, the welding voltage Vw shown in FIG. 5F shows the welding voltage average value Vav after time t5, and the welding current Iw shown in FIG. 5G shows the welding current average value Iav after time t5. Here, the arc length of the pulse arc welding is proportional to the welding voltage average value Vav or the peak voltage Vp. Therefore, in pulse arc welding, the arc length can be detected by the welding voltage average value Vav or the peak voltage Vp. As the welding voltage average value Vav, a signal obtained by smoothing the welding voltage Vw, a signal obtained by removing a high frequency component from the welding voltage Vw by a low-pass filter, an average value of the welding voltage Vw for each pulse period Tpb, and the like are used. For this purpose, by controlling the torch height so that the welding voltage average value Vav or the peak voltage Vp is equal to a predetermined voltage setting value, the arc length overshoot can be compensated and maintained at a steady value. it can. According to the fifth torch height control, since the torch height control can be automatically controlled in the pulse arc welding in addition to the above-described effects, the first period T1, the second period T2, and the movement distance ΔLt. This eliminates the need for setting and improves work efficiency.

DESCRIPTION OF SYMBOLS 1 Welding wire 2 Base material 3 Arc 4 Welding torch 4a Coil liner Fc Feeding control signal Fcr Steady feeding speed setting signal Fcw Steady feeding speed Fw Feeding speed Iav Welding current average value Ib Base current If Transmission / reception signal Ip Peak current Iw Welding current Ls Teaching torch height Lt Torch height Lw Wire tip-base material distance Mc Operation control signal On Start signal PS Welding power supply RC Robot controller RM Robot ST Welding start circuit St Welding start signal T1 First period T2 Second Period Ta Reverse reversal period Tb from forward feed to reverse feed Tb Re-forward feed transient period Tg Base period Tp Peak period Tpb Pulse period Tu Arc length raising period Vav Welding voltage average value Vb Base voltage Vp Peak voltage Vr Voltage setting signal Vw Welding voltage Wcr Start completion signal WM Wire feed motor ΔLt Travel distance

Claims (3)

The welding wire is fed forward from the welding torch to the base metal, and when the welding wire comes into contact with the base metal, the welding wire is fed backward from the base metal and a welding current is energized. In an arc start control method in which a welding wire is re-forwarded after an initial arc is generated away from the initial arc, and a transition is made from the initial arc generation state to a steady arc generation state.
Torch height control is performed in which the height of the welding torch is once lowered to a slope shape after the re-advance feeding start time and then returned to the original height by raising the slope shape .
An arc start control method characterized by the above. The torch height control is a control that lowers the slope by a predetermined movement distance during a first predetermined period and returns it to the original height by increasing the slope during a second predetermined period. Is,
The arc start control method according to claim 1. Detecting a reverse delay period at the time of switching from the forward feed to the reverse feed, and setting the first period, the second period and the moving distance based on the reverse delay period;
The arc start control method according to claim 2, wherein:

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