JPH0655351B2 - Welding start point detection method in automatic welding equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a welding start point detecting method for performing overlap fillet welding by an automatic welding apparatus including an industrial robot.

[Conventional technology]

Conventionally, there is a wire earth method as a typical example of a welding start point detection method for an industrial robot. In this wire earth method, a voltage is applied between the wire electrode at the tip of the welding torch and the object to be welded, and the contact / non-contact state between the wire electrode and the object to be welded is detected by a voltage change, and a predetermined animal is detected. It is a method that tries to detect the starting point by performing it, and there is no need to install a special sensor around the welding torch, so there is no interference between the welding torch and the welding object or the jig holding the welding object. It has been considered relatively useful.

However, since the wire length after welding is variable, auxiliary operations such as an operation to adjust the wire length to a constant value, an operation to prevent the wire from retracting in the direction opposite to the wire bending or wire sticking out direction, The operation for detecting the starting point includes many operations that exclude the high-speed search operation. For this reason, it is a bottleneck in fields where productivity is important.

In the wire earth method, the detection accuracy is easily influenced by the surface condition of the work piece to be welded. In particular, the work piece to be welded, which is black or has an oxide film, or the insulating film formed on the tip of the wire after cratering is a big enemy. Therefore, special means for applying high frequency high voltage or high DC voltage must be provided between the wire electrode and the workpiece.

Further, if the searching operation is immediately performed in a state where the wire is heated by arc heat or Joule heat, the wire is particularly likely to bend, so that there is a drawback that a cooling time is required.

On the other hand, the method of detecting the starting point based on the characteristics of the arc current can overcome most of the above problems.

As such a method, there are methods disclosed in JP-A-58-77775 and JP-A-61-42488, but the former is a method of correcting a locus according to a characteristic value of a welding parameter while weaving. , It takes time to detect, and it cannot be applied to overlap fillet welding of thin plates.

Further, a method of detecting a welding current change occurring at the joint end face by welding in a direction intersecting with a welding line to be originally welded from the upper plate of lap fillet welding is sufficiently considered as an application of the arc sensor. In the idea of the arc sensor that detects the change in the protruding length of the, the current difference that occurs at the joint end face is too small, it is difficult to separate from the current change at the start of welding, the current change during welding,
There was a problem in practical application.

On the other hand, in the latter case, the arc current changes at the start point (S), the edge portion (N, C), and the end point (E). Although it is described as being constant, the current at the starting point (S) is actually very unstable, and the time at which the robot starts is also unstable, so Detecting is difficult due to the presence of current changes due to these disturbances.

[Problems to be Solved by the Invention]

Therefore, it is an object of the present invention to provide a method capable of detecting a welding start point with high accuracy and at high speed, without requiring any special means.

[Means for Solving the Problems]

INDUSTRIAL APPLICABILITY In the lap fillet welding, the present invention eliminates many problems that may occur when passing through the flank face by performing high-speed welding while shifting to short-circuit in the low current region of the welding current in the direction intersecting with the welding line to be originally welded. The welding start point is detected by detecting the welding current change separately from the current change at the start of welding and the current change during welding, and the welding start point detection that makes the control point of the tip of the welding torch reach this starting point The method has the advantages that it can be operated at high speed, and that it can not only ensure stable accuracy regardless of the surface condition of the workpiece, but that it can also be realized with an automatic welding device equipped with a normal arc sensor function. is there.

[Principle of Invention]

FIG. 1 is a view showing the principle of the present invention, and shows a case where a lap joint of an upper plate X and a lower plate Y is welded from the upper plate side to the lower plate side.

According to the present invention, regardless of CO ₂ gas welding or Ar-CO ₂ mixed gas welding, short-circuit transfer type welding is performed in a welding low current and low voltage region.

In welding, a large current flows when an arc is generated, a bead is formed to stabilize the arc, and then the torch is moved to continue welding. Since it is a short-circuit transfer, the wire droplets are short-circuited to the base metal side, but when the arc is generated, it is an unstable transfer, and then becomes a steady transfer form.

By the way, since the distance between the power feed tip and the base material in FIG. 1 is constant from the point A of the upper plate X to the upper plate edge point C (hereinafter, the joint end face is referred to as an edge), it is unstable when an arc occurs. After the transition, the steady transition form continues, but from point C, the distance between the power feed tip and the base material is increased by the thickness of the upper plate, that is, BC, so that the steady short-circuit transition cannot be performed.

If the welding speed is slow, the weld bead melts near the edge,
Although it tries to continue the steady short-circuit transition, the short-circuit transition can be forcibly cut off by increasing the welding speed.

As a result, after the point C is reached, until the wire extends by the distance between the base material and the chip, which has become longer, a short time elapses again after a time sufficiently longer than the normal arc section. As shown in FIG. 2, when the arc section is sufficiently long, the smoothing value of the welding current does not include the current at the time of the short circuit, and therefore decreases greatly compared with the normal smoothing current.

Then, a re-short circuit occurs and the smoothed value of the current starts to increase, so that there is a point (hereinafter referred to as the bottom) where the current changes from decreasing to increasing.

The point of interest of the present invention is to detect this characteristic welding current change and use it for starting point detection.

〔Example〕

FIG. 3 is a block diagram of hardware for realizing the present invention. The welding current detecting means 11 detects the welding current 20 ', and the smoothing means 12 alternates the short circuit and the arc as shown in FIG. A signal that repeatedly pulsates is smoothed.

An example of the smoothed current waveform is shown in FIG.

By performing the short-circuit transfer type welding at a high speed, in this experiment, the thin plate thickness of 1.6t was used, but 50% near the edge.
A large current difference of about A occurs.

This signal is converted from a physical continuous quantity into a digital quantity by the conversion means 13 and read by the sensor control means 14.

FIG. 5A shows a flow for detecting the bottom of the current generated near the edge.

First, in order to remove the unstable part of the current waveform generated at the start, set the timer at the time of arc generation (slightly longer than normal welding.) Next, to remove the unstable region at the beginning of movement Set the detection prohibition distance to. After that, detection is started. If the detected digital value is the threshold value or less and is the bottom after the number of consecutive reductions of N or more continues, it is determined that the bottom is near the edge and the edge is detected. The threshold value and the number of reductions of N times are values obtained by experiments.

This state is schematically shown in FIG.

Since the detected bottom position has a delay from the actual edge, this delay amount must be corrected. This operation flow is shown in FIG. Shown in b. When the bottom is detected, the position data is stored and the robot is stopped. next,
The robot is moved based on the correction amount defined in advance, and the control point at the tip of the torch is moved to the start point which is the edge portion.

The above is an example of means for realizing the present invention.

〔The invention's effect〕

The present invention is superior to the conventional wire earth method in stability of accuracy, high speed of exploration, and simplification of hardware, and is considered to be a major contribution to the industry in the future. . Further, the present invention is considered to be useful in a field where productivity and high stability are prioritized over bead appearance by exploration operation.

[Brief description of drawings]

FIG. 1 is a diagram explaining the principle of the present invention, FIG. 2 is a waveform diagram of welding current and welding voltage, FIG. 3 is a block diagram of an embodiment, and FIG. 4 is a smoothed welding current waveform diagram of the embodiment. FIG. 5-a is a bottom detection flow chart, FIG. 5-b is an operation flow chart after bottom detection, and FIG. 6 is a schematic view of bottom detection state. 11 ... Welding current detection means 12 ... Smoothing means 13 ... Conversion means 14 ... Sensor / control means 15 ... Robot controller 16 ... Robot 20 ... Welding voltage 20 '... Welding current 21 ... Smoothed Welding current

Claims (1)

[Claims] Claim: What is claimed is: 1. In lap fillet welding by an automatic welding device in which the relative position of the work piece and the welding torch is position controlled, short-circuit transfer type welding is performed from the upper plate to the lower plate in the direction intersecting the welding line. When performing at high speed, after reaching the preset detection inhibition distance from the arc generation position, the bottom value, which is the timing at which the current value decreases and starts to increase below the preset current value (threshold value), is set. A method for detecting a welding start point in an automatic welding device, characterized in that the position of the end face of the joint is detected by the detection, and the control point of the tip of the welding torch is reached at the welding start point.