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Welding control using fuzzy logic analysis of video imaged puddle dimensions

a fuzzy logic and video image technology, applied in adaptive control, process and machine control, instruments, etc., can solve problems such as vexing problems, insufficient reliability, and insufficient accuracy of human knowledge base, and achieve unsatisfactory changes in weld strength

Inactive Publication Date: 2000-10-31
UNITED TECH CORP +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

The objects of the present invention include providing an improved GTAW welding system using fuzzy logic control with a reliable way to measure the puddle and a flexible way to apply the weld wire into the puddle.
Among the features of the present invention is that it provides an extremely precise and repeatable weld and minimizes excessive .[.energy.]. .Iadd.weld .Iaddend.input temperatures. Another feature is that the invention provides a versatile wire feed arrangement for robotic GTAW welders.

Problems solved by technology

Even small changes in the thickness can produce undesired changes in the weld strength, not to mention, that uneven heating can produce local variations in material qualities of the workpiece, because areas that are heated to a higher temperature may undergo slightly more removal of important material components.
The issue of uncertainty, which human knowledge intuitively always considers, is the essential issue in the design of fuzzy logic systems, and for a simple reason, much of the information in the knowledge base of a human is imprecise, incomplete or not entirely reliable--in other words, uncertain.
The harsh, small and unusual environment in which welding takes place presents vexing problems in effectively applying a fuzzy logic based process control approach.
For example, problems arise in sensing or detecting the characteristics of a molten metal puddle in the presence of an electric and an inert gas cloud.

Method used

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  • Welding control using fuzzy logic analysis of video imaged puddle dimensions
  • Welding control using fuzzy logic analysis of video imaged puddle dimensions
  • Welding control using fuzzy logic analysis of video imaged puddle dimensions

Examples

Experimental program
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Effect test

example 1

Using Only Width

Referring to FIG. 1, if the measured weld puddle width that is measured using the coaxial vision system is 0.355 wide, this measured puddle width value maps to two membership functions: P(positive) .[.an.]. .Iadd.and .Iaddend.BP(big positive). As shown the "P" and "BP" membership functions are defined as follows:

P=0.320 to 0.360

BP=0.340 to 1.00

Two membership functions are operated on in this example: the 0.355 .[.measure.]. .Iadd.measured .Iaddend.puddle width maps to the degree of membership of 0.4 for .[.BP.]. .Iadd.P .Iaddend.and 0.6 for .[.P.]. .Iadd.BP.Iaddend.. The 0.4 and 0.6 indicates the degree of membership for each fuzzy logic membership function that the 0.355 maps into. Therefore, the actual measured width belongs to two membership functions or membership sets.

When two membership functions are involved, the membership function uses an average, weighted by the respective degree of membership values to calculate the crisp or defuzzified output.

Following th...

example 2

Using Length and Width

The following example will demonstrate the use of these rules for 17-4 PH stainless .Iadd.steel .Iaddend.or any other material producing a puddle with observable length and width that are indicative of the weld quality in a real time mode.

Assume that the observed weld puddle length=0.310 and the measure weld puddle width=0.225. Using the membership functions in FIGS. 2 and 3, the 0.310 weld puddle length maps as follows: It has two fuzzy logic membership functions. Rule 1) the weld puddle length is in P with a membership of 0.6 and Rule 2) the weld puddle length is also in Z with a membership there of 0.5. For the weld puddle width of 0.225, the width maps to two fuzzy logic membership functions as well: Rule 3) in the function for Z, with a degree of membership there of 0.3 and Rule 4) in the function N, with a degree of membership of 0.8. In this case these four (4) out of the above twenty five (25) rules will fire: Rule 8, 9, 13, and 14. The computation for ...

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Abstract

A welding system includes an imaging system that takes frame by frame pictures of a weld puddle. The imaging system is located in the weld torch. From the images puddle length and width are determined. The length and width are applied against stored membership functions that cover a range of different weld current characteristics and the degree of membership of each dimension in those functions is determined, producing an alpha factor for each membership function. This provides a fuzzy current requirement. Stored values for moment and area for each membership function are multiplied by the alpha for the respective function. The total of the moments is divided by the total of the areas to produce a desired weld current. The weld head includes a weld wire feeder that is driven by a servo by which the wire can be feed along either side of the weld joint. The wire feeder is gear driven in such a way that it does not interfere with the optics in the weld torch. The optics include a strobe to illuminate the puddle. Signal processing includes a process for interpolating the puddle centerline from the range in puddle widths over successive strobed images of the puddle. The head is positioned automatically over the centerline.

Description

TECHNICAL FIELD OF THE INVENTIONThis invention relates to automated GTAW (gas tungsten arc welding) using computer based signal processing and programmed logic to control welding functions, in particular, welding control using fuzzy logic analysis of video imaged puddle dimensions.BACKGROUND OF THE INVENTIONGTAW is a widely used welding process in which an electric arc is formed by a welding torch, a shroud of inert gas, such as argon, is applied from the torch to the weld area and a weld material, such as titanium or 17-4 PH stainless .Iadd.steel.Iaddend., is supplied as a relatively thin wire. The weld and filler material forms a so-called "puddle" in the weld area, e.g., the space or joint between two pieces. The characteristics of the puddle are dependent on the type of wire, weld material, thickness and heat sink properties. Stainless steel is known to produce a weld bead that has waves or ripples to the eye. Titanium flows more easily, producing a generally smooth weld bead.Th...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): B23K9/10B23K9/095B23K9/23B23K9/127B25J9/18G05B13/02
CPCB23K9/1274B23K9/1062
Inventor AUSTIN, MARY A.DUNNE, KENNETH C.LINDLAND, DAGFREY, PHILLIP L.HYSTAD, DEAN G.NELSON, RICHARD E.WARNER, BRADLEY D.
Owner UNITED TECH CORP
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