JP2009183976A - Welding control method and welding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that, when detecting variations in a welding current to perform copying control of the weld torch along a weld line in carrying out welding while making a weld torch weave, a phenomenon is generated in which a variation in a welding current is delayed behind the position of an actual weld torch according to components of a welding gas and to the material of a welding wire, and, if a welding current is sampled in synchronization with the position of the weld torch under the phenomenon, the sampling is performed at the position out of the peak of the variation in the welding current, so that copying motion is not accurately executed. <P>SOLUTION: A welding control device detects the peak value of variations in the welding current to determine the timing of sampling. Thereby, the device enables further accurate copying motion when converting the difference of variations in the welding current into a shift amount to an aimed position of the weld torch, even if a variation phase in the welding current is delayed behind a weaving phase. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a welding control method and a welding apparatus for detecting a change in a welding current and performing tracking control of a welding torch along a weld line when performing welding while weaving the welding torch.

  In a V-shaped groove or fillet weld in a welding member, a welding torch, that is, a weaving welding in which a welding wire that is a consumable electrode is swung in the horizontal direction with respect to the welding line is performed in order to increase the amount of metal deposition. Is called. As a mechanism for performing a weaving operation in which the welding torch is shaken in the left-right direction, a vertical articulated robot, an orthogonal robot composed of orthogonal slide axes, or the like is used.

  A current change during weaving welding will be described with reference to FIG. 71 is a welding wire, 72 is a welding torch for supplying power to the welding wire 71, and 73 is a welding member. In the weaving welding, the protruding length of the welding wire 71 from the tip of the power supply tip (not shown) provided on the welding torch 72 to the tip of the welding wire 71 is changed by the swinging operation of the welding torch 72. The welding current also changes. This is because the wire protruding portion of the welding wire 71 works as a resistance component in a constant voltage characteristic welding machine, and the wire protruding length increases, that is, when the resistance component increases, the current value decreases and the wire protruding length decreases. That is, the current value increases as the resistance component decreases. When the center of the weaving direction is the same as the center of the weld line of the V-shaped groove or fillet weld of the welding member, the current waveform having a cycle twice the weaving cycle is obtained. Observed.

  Next, a current change when the center of the weaving in the left-right swing direction deviates from the welding center will be described with reference to FIG. When the position of the welding torch 82 reaches the position A on the command locus, the protruding length of the welding wire 81 is shortened and the welding current is increased as in the C portion. On the other hand, also when the position of the welding torch 82 reaches the position B on the command trajectory, the protruding length of the welding wire 81 is shortened and the welding current is increased as in the D portion. However, in the protrusion length at the A position and the protrusion length at the B position, the protrusion length at the A position is shorter than the B position, so that the welding current has a higher current value in the C portion than in the D portion. Thus, when welding is performed in a state where the center of the weaving left and right swing direction deviates from the center of the weld line of the V-shaped groove or fillet weld of the welding member, the welding has a cycle twice the weaving cycle. A current waveform in which the same period component as the weaving period is superimposed on the current waveform is observed.

  As described above, when the center of the weaving left-right swing direction deviates from the welding center, for example, when the welding torch 82 is operating in the left direction of the weaving and in the case of operating in the right direction, for example, welding By comparing peak values such as the C part and D part of the current, the shift amount of the target position of the welding torch 82 is converted from the difference between the peak values, thereby shifting the welding torch 82 to the center of the weld line. The copying operation is realized. Alternatively, by comparing not only the peak value of the welding current but also the integrated value of the range E and the integrated value of the range F, the shift amount of the target position of the welding torch 82 is converted from the difference between the integrated values, thereby welding. The copying operation is realized by shifting the torch 82 around the center of the weld line.

  Here, both when the peak value of the welding current is detected and the difference is calculated, or when the difference of the integrated value from the peak of the welding current is calculated, the peak value of the welding current change is detected and sampled. It is a necessary condition for improving the scanning accuracy to be a trigger.

  The actually measured welding current has a complex waveform in which a short-circuit current component and a noise component when the welding wire 81 and the welding member 83 are in contact with each other and a pulse current component during pulse welding are superimposed. Therefore, in order to extract the necessary current waveform component, the copying operation is realized by measuring the current waveform from which the short-circuit component and noise component have been removed with an analog filter realized by an electric circuit or a digital filter realized by software processing. Is done.

  In the conventional welding line scanning control method, the fluctuation position of the detected welding current is extracted from the oscillation frequency component equal to the weaving cycle by using a Fourier function converter, and the center position of the weaving operation is reduced so as to reduce this frequency component. Some have been proposed to control. This is intended for welding line scanning control that is not affected by a short circuit component or the like by extracting only the frequency component even when the welding current changes in a complicated manner (see, for example, Patent Document 1).

The timing for sampling the change in the welding current is generally performed in synchronization with the position of the welding torch 82. When sampling the welding current in synchronization with the position of the welding torch 82, as shown in FIG. 8, when the welding torch 82 reaches the A position or the B position of the weaving end, Ideally, peak D occurs. However, in actuality, due to the delay in the response of the servo mechanism to the movement command of the welding torch 82, the actual servo track follows the command track with a delay. For this reason, if sampling is performed in synchronization with the position of the welding torch 82, sampling is performed at a position deviating from the peak of the welding current, and a precise copying operation cannot be realized. For the problem that the servo track follows the command track with a delay, the actual position of the welding torch is predicted from the position command value of the welding torch, and the data sampling timing is set based on the predicted actual position of the welding torch. A data sampling method to be determined has been proposed (see, for example, Patent Document 2).
JP-A-2-58031 JP-A-11-179542

  However, the conventional welding line tracking control method requires a mechanism such as a Fourier function converter in order to extract only the frequency component even when the welding current changes in a complicated manner. This requires a hardware such as a CPU (Central Processing Unit) and a memory for performing complicated calculations, and there is a problem that the price of the equipment becomes expensive.

  Moreover, the phenomenon that the change of the welding current is delayed with respect to the actual position of the welding torch also occurs depending on the welding gas component, the material of the welding wire, or the welding method such as pulse welding or short-circuit welding. This situation will be described with reference to FIG. When the position of the welding torch 92 is a servo locus, that is, when the actual position of the welding wire 91 reaches the position G in FIG. 9, the protruding length of the welding wire 91 is the shortest, and ideally the welding current value should be the highest. It is. However, the welding current is the highest with a delay like the I portion. For this reason, a time lag is generated as shown in the portion K, and when the weaving cycle operation of the welding torch 92 is considered as a phase, the current change phase is delayed with respect to the weaving phase.

  In this state, if the welding current is sampled in synchronism with the position of the welding torch, the sampling is performed at a position deviating from the peak of the welding current change, and a precise copying operation cannot be realized. In addition, when the weaving phase and the current change phase are greatly deviated, the peak position of the welding current change to be sampled is reversed from the original peak position, and is completely opposite to the direction in which the shift operation should be originally performed. A shift operation is performed.

  In this way, even if the welding torch actual position is predicted from the position command value of the welding torch and the data sampling timing is determined based on the predicted welding torch actual position, the actual torch position is detected instead of being predicted. Even if it is possible, there is a problem that the peak of the welding current change cannot be correctly sampled only by data sampling based on the welding torch position.

  In order to solve the above-mentioned problems, the welding control method of the present invention provides a weaving cycle when performing welding while weaving the welding torch in welding in which the distance between the welding wire and the workpiece is changed during the weaving operation. A welding control method that detects a change in the welding current by sampling the welding current synchronously and controls the welding torch along the welding line, and detects the peak value of the welding current from the change in the welding current. The welding current sampling timing is determined so as to coincide with or approach the welding current peak value detection timing.

  It is also possible to sample the peak of the welding current change, compare the welding current peak value, or compare the integrated value from peak to peak, and convert the shift amount of the target position of the welding wire from the difference It becomes possible to do.

  In addition to the above, the welding control method of the present invention detects the peak value of the welding current from the change in the welding current, and determines the welding current peak value detection timing and the welding current when determining the sampling timing of the welding current. The timing for sampling the welding current is determined so that the difference time with the sampling timing is gradually decreased and the two timings coincide or approach each other.

  The timing of sampling the welding current can be determined without giving a sudden change to the copying operation.

  In addition to the above, the welding control method of the present invention provides a welding current sampling timing so that the difference time between the welding current peak value detection timing and the welding current sampling timing is fed back for each weaving period to reduce the difference time. By determining the above, the difference time is gradually decreased for each weaving cycle.

  In addition to the above, the welding control method of the present invention detects the welding current when the change in the welding current changes from increase to decrease as the peak value on the upper limit side, and determines the welding current when the change from decrease to increase. It is detected as a peak value on the lower limit side.

  A welding apparatus according to the present invention includes a welding power supply apparatus, a robot that holds a welding torch fed from the welding power supply apparatus, and a robot control apparatus that controls the operation of the robot, and performs the welding control method. It is.

Sampling timing by detecting the peak value of the welding current change even if the welding current change phase is delayed with respect to the weaving phase without requiring hardware such as CPU or memory for high-speed calculation. When the shift amount of the target position of the welding torch is converted from the difference in the welding current change, it is possible to realize a copying operation with higher accuracy than before.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to FIGS.

(Embodiment 1)
In FIG. 1, 11 is a welding torch, 12 is a robot for holding / carrying the welding torch, 13 is a welding wire, 14 is a wire feeding device for feeding the welding wire 14, and 15 is a welding member. Reference numeral 16 denotes a welding control apparatus. As an internal configuration thereof, 17 is a robot control unit that controls the robot 12, 18 is a welding current detection unit that detects a welding current, and 19 is a welding control unit that performs welding waveform control. The robot control unit 17 and the welding control unit 19 include a CPU, a memory, and the like necessary for robot control or welding control.

  The operation during weaving welding will be described with reference to FIG. In the weaving welding, the robot control unit 17 gives a trajectory command to the robot 12, and the welding torch 11 performs the weaving welding while drawing a trajectory like the command trajectory of FIG. At this time, the robot control unit 17 generates a signal indicated by the weaving signal in FIG. 2 inside the CPU while performing the weaving swing motion. Based on the change timing of the weaving signal, a trigger signal for welding current sampling shown in the sampling trigger of FIG. 2 is generated in the CPU.

  Here, the robot controller 17 has a mechanism for delaying the sampling trigger in the CPU, and has a delay of T-delay time with respect to the change timing of the weaving signal as shown in the delayed sampling trigger of FIG. A sampling trigger can be generated. The mechanism for delaying the sampling trigger can be easily realized by using a timer function generally provided in the CPU, and does not require a high-performance CPU or memory.

  Next, the configuration of the welding current detection unit 18 in FIG. 1 will be described with reference to FIGS. 3 and 4. FIG. 3A is an example of a waveform in which the welding current detection unit 18 detects the welding current at a sampling period of 1 ms. This is a complex waveform in which a short-circuit current component and a noise component when the welding wire 13 and the welding member 15 are in contact with each other and a pulse current component and the like are superimposed during pulse welding. Therefore, in this state, it is impossible to detect a change in the welding current and control the copying of the welding torch 11 along the weld line. In addition, the peak of the welding current change cannot be detected. Therefore, a current waveform from which short-circuit components and noise components have been removed is measured by an analog filter realized as an electric circuit, a digital filter realized by software processing, and the like, and a copying operation and peak detection of current change are performed. An example of a welding current waveform subjected to this filter processing is shown in FIG. An example of a filter in an analog circuit is shown in FIG. At this time, the time constant T for the step input is determined by T = R × C.

  Next, the digital filter processing by software processing operating on the CPU is represented by Y [k] = (1-G) × X [k] + G × Y [k−1] shown in FIG. G = T / (T + t), T is a time constant, t is a sampling period, X [k] is a filter input at time k, and Y [k] is a filter output at time k.

  By these simple filter processes executed by the welding current detection unit 18, a welding current waveform in which only components relating to the weaving operation and the aim for the welding line are extracted is obtained, and the peak of the welding current change can be detected.

  Next, the peak detection method for the welding current change in the welding current detector 18 will be described. This peak detection method is not a special method, and can be performed by simple processing such as comparison of values before and after measurement data and comparison of waveform tangent slope before and after.

  Here, with reference to FIG. 5, a peak detection method in comparison between before and after the section average value will be described. Even if the measured welding current waveform is filtered, it is not a microscopically smooth curve like the waveform shown in FIG. Therefore, the average value of the welding current measurement values is calculated every certain time, and the peak detection is performed by comparing the average values before and after. In the flow 1 of the flow shown in FIG. 5B, the average value Ave [k] in the Ta [k] section is calculated. For example, assuming that the average value Ave [k−2] = 230 A in the Ta [k−2] section and the current time is [k−1], the average of the Ta [k−1] section in the flow 1 of FIG. The value Ave [k−1] = 240A is calculated. Next, in Flow 2, Ave [k-2] and Ave [k-1] are compared in magnitude. Since Ave [k-1] is larger than Ave [k-2], the determination result is NO. Determination is made, and the flow returns to the flow 1, and the average value Ave [k] = 242A in the Ta [k] section is calculated. Similarly, NO is determined in the flow 2, and the flow returns to the flow 1, and the average value Ave [k + 1] = 235A in the Ta [k + 1] section is calculated. At this time, in Flow 2, since Ave [k + 1] is smaller than Ave [k], it is determined as YES, and the upper limit peak value detection signal is generated in Flow 3 assuming that the upper limit peak of the welding current waveform has been reached. . This upper limit peak value detection signal is used as a sampling trigger. Regarding the lower limit side peak value detection, the current average values are compared in the flow 4, flow 5, and flow 6, and the lower limit side peak value detection signal is generated. This lower limit side peak value detection signal is used as a sampling trigger.

  By these processes, the peak value of the welding current can be sampled by detecting the peak value of the welding current from the actually detected change of the welding current and determining the sampling timing of the welding current. . Then, it is possible to compare the peak value of the welding current, or to compare the integrated value from the peak of the welding current to the peak, and to convert the shift amount of the target position of the welding wire from the difference. A good copying operation can be realized.

(Embodiment 2)
Embodiments of the present invention will be described below. In addition, the same code | symbol is attached | subjected to the location similar to Embodiment 1, and detailed description is abbreviate | omitted.

  Detect the peak value of the welding current waveform, compare the welding current peak value, or compare the integration value from the peak of the welding current to the peak, and convert the shift amount of the welding wire target position from the difference In the welding control apparatus, as shown in FIGS. 7 and 8, it is assumed that the change in the welding current is synchronized with the weaving cycle. However, in actual welding, a short-circuit current component and a noise component when the welding wire 13 and the welding member 15 are in contact with each other, and a complicated waveform in which a pulse current component is superimposed during pulse welding, for example, FIG. As shown in Fig. 1, there occurs a case where the change in the welding current is not synchronized with the weaving cycle. As a countermeasure, the sampling interval is set to a constant period synchronized with the weaving period, but the welding current change peak value is controlled by controlling the delay time T-delay time of the sampling trigger while referring to the welding current change peak value detection timing. It is effective to make the timing of and the timing of the sampling trigger coincide with each other. This method will be described with reference to FIG.

  As an example of controlling the T-delay time, PI control (control combining a proportional action and an integral action) which is a general feedback control method is performed. FIG. 6 shows a PI control block diagram of the digital processing system. Kp is a proportional gain, Ki is an integral gain, and 1 / Z is a signal delay for one sampling period. When the difference between the welding current change peak value detection timing and the timing synchronized with the weaving cycle is defined as a deviation e1 [k], control is performed so that the deviation e1 [k] becomes zero. Becomes 0. CS is a control target and corresponds to the robot 12. The input to the control target CS is T-delay [k] for setting the deviation, which is the difference between the welding current change peak value detection timing and the timing synchronized with the weaving cycle, to zero, and the output from the control target CS is Deviation e1 [k], which is the difference between the welding current change peak value detection timing at time [k] and the timing synchronized with the weaving cycle.

  Due to this feedback control mechanism, when there is a deviation between the weaving phase and the current change phase, the deviation e1 [k] becomes a value other than 0, and the operation input T− for making the deviation e1 [k] zero. The delay is determined. As described in the first embodiment, by generating the sampling trigger with the delay time T-delay with respect to the change timing of the weaving signal, it is possible to eliminate the deviation between the weaving phase and the current change phase. . It should be noted that feedback control is performed every weaving cycle and the difference time between the welding current peak value detection timing and the welding current sampling timing is gradually reduced, so that the welding current can be controlled without causing a sudden change in the copying operation. Sampling timing can be determined. A smooth bead can be formed by not giving a sudden change to the copying operation.

  The present invention detects a change in the welding current when performing welding while weaving the welding torch, and performs a tracking control of the welding torch along the weld line. By detecting the welding current and determining the sampling timing of the welding current, hardware such as a CPU and memory for performing high-speed calculation is not required, and the welding current change phase is delayed with respect to the weaving phase. Even when the welding current is detected, the peak value of the welding current change is detected and the sampling timing is determined. It is industrially useful as a welding control device that performs welding while weaving.

The figure which shows schematic structure of the apparatus which performs welding in Embodiment 1 of this invention. The figure which shows the weaving signal in Embodiment 1 of this invention (A) The figure which shows the example of a waveform before the filter process in Embodiment 1 of this invention (b) The figure which shows the example of the waveform after the filter process in Embodiment 1 of this invention (A) The figure which shows the example of the analog filter in Embodiment 1 of this invention (b) The figure which shows the example of the digital filter in Embodiment 1 of this invention The figure which shows the peak value detection method of the electric current change in Embodiment 1 of this invention. PI control block diagram in Embodiment 2 of the present invention Relationship diagram between weaving command locus and welding current change Diagram of welding current change when aim deviation occurs Diagram showing delay in welding current change

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Welding torch 12 Robot 13 Welding wire 14 Wire feeding apparatus 15 Welding member 16 Welding control apparatus 17 Robot control part 18 Welding current detection part 19 Welding control part

Claims (5)

In welding where the distance between the welding wire and the work piece is changed during the weaving operation, when welding is performed with the welding torch being weaved, a change in the welding current is detected by sampling the welding current in synchronization with the weaving cycle. A welding control method for controlling the copying of the welding torch along the welding line,
A welding control method for detecting a peak value of a welding current from a change in welding current and determining a sampling timing of the welding current so as to coincide with or approach the welding current peak value detection timing. When the peak value of the welding current is detected from the change in the welding current and the timing for sampling the welding current is determined, the difference time between the welding current peak value detection timing and the welding current sampling timing is gradually reduced, and the two The welding control method according to claim 1, wherein the sampling timing of the welding current is determined so that the timings match or approach each other. The difference time between the welding current peak value detection timing and the welding current sampling timing is fed back for each weaving cycle, and the welding current sampling timing is determined so as to reduce the difference time, thereby gradually increasing the difference time for each weaving cycle. The welding control method according to claim 2, which decreases to The welding current when the change in welding current changes from increase to decrease is detected as a peak value on the upper limit side, and the welding current when it changes from decrease to increase is detected as a peak value on the lower limit side. The welding control method according to claim 1. 5. The welding according to claim 1, comprising: a welding power supply device; a robot that holds a welding torch fed from the welding power supply device; and a robot control device that controls the operation of the robot. A welding apparatus that performs a control method.

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