Method and apparatus for detection of undesirable surface deformities

• US 4,792,232 A
• Filed: 05/18/1987
• Issued: 12/20/1988
• Est. Priority Date: 05/18/1987
• Status: Expired due to Fees

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Lepley, Allen E., Jobe, John D.
• Primary Examiner(s): ROSENBERGER, RICHARD A
• Application Number:
  US07/050,435
• Time in Patent Office: 582 Days
• Field of Search: 356/376, 356/394, 356/237, 382/22
• US Class Current: 356/394
• CPC Class Codes: G01B 11/25 by projecting a pattern, e.g. one or more lines, moiré fringes on the object G01B11/255 takes precedence ; image analysis for depth or shape recovery G06T7/50
• CPC Class Codes: G06T 7/521 from laser ranging, e.g. using interferometry; from the projection of structured light

Abstract

A method and apparatus for the detection of undesirable surface deformities is disclosed wherein a known (linear) light pattern is reflected off a fabricated part having a nominally smooth surface, the reflected light pattern subsequently being analyzed for distortions from the expected light pattern. The extent of the detected distortions may be quantified by the use of a computer having appropriate software, in order to identify and quantify unacceptable surface deformities.

Claims

1. A method of detecting undesirable deformities in a surface, comprising the steps of:

projecting a light pattern having at least one edge onto said surface from a light pattern source;

receiving at a light pattern receiver a reflected light pattern from said surface;

converting said reflected light pattern into an array of pixels, each pixel havin a value representing the intensity of light received from a portion of the reflected light pattern;

evaluating the value of said pixels to define at least one edge of said reflected light pattern;

forming a fitted curve through said at least one edge of said reflected light pattern;

measuring the amount of deviation of said at least one edge from said fitted curve; and

quantifying the amount of deviation of said at least one edge from said fitted curve, to the amount of undesirable deformity in said surface.

2. The method of claim 1 wherein the step of forming a fitted curve through said at least one edge of said reflected light pattern further includes the step of:

dividing said at least one edge along the length of said edge thereof into separate discrete edges, and forming discrete curves through each of said separate discrete edges.

3. The method of claim 1 wherein the step of forming a fitted curve through said at least one edge further includes the step of:

finding coefficients a₀, a₁, a₂, . . . a_m, of the equation;

space="preserve" listing-type="equation">Y=a.sub.o +a.sub.1 X+ . . . +a.sub.m X.sup.m.

4. The method of claim 1 wherein the step of measuring the amount of deviation of said at least one edge from said fitted curve further includes the steps of:

finding coefficients a₀, a₁, a₂, . . . a_m, of the equation;

space="preserve" listing-type="equation">Y=a.sub.o +a.sub.1 X+ . . . +a.sub.m X.sup.m,

using the Normal Equations of the Least Squares method of curve formation; and

substituting said coefficients into the equation;

space="preserve" listing-type="equation">Σ

d.sub.i.sup.2A =Σ

Y.sub.i.sup.2 -(a.sub.o Σ

Y.sub.i +a.sub.1 Σ

X.sub.i Y.sub.i + . . . +a.sub.m Σ

X.sub.i.sup.m Y.sub.i),

wherein Σ

d_i² =the amount of deviation of the edge of the reflected light pattern from the fitted curve.

5. A method of detecting undesirable deformities in a surface, comprising the steps of:

projecting a light pattern having at least one edge onto said surface from a light pattern source;

receiving at a light pattern receiver a reflected light pattern from said surface;

converting said reflected light pattern into an array of pixels, each pixel having a value representing the intensity of light received from a portion of the reflected light pattern;

segregating pixels having a selected value and pixels having a value greater than said selected value into a first group;

segretating pixels having less than said selected value into a second group;

defining at least one edge of said reflected light pattern at the boundary of said first group of pixels and said second group of pixels;

forming a fitted curve through said at least one edge of said reflected light pattern by

finding coefficients a₀, a₁, a₂, . . . a_m, of the equation;

space="preserve" listing-type="equation">Y=a.sub.o +a.sub.1 X+ . . . +a.sub.m X.sup.m,

using the Normal Equations of the Least Squares method of curve formation;

measuring the amount of deviation of sid at least one edge from said fitted curve by

finding coefficients a₀, a₁, a₂, . . . a_m, of the equation;

space="preserve" listing-type="equation">Y=a.sub.o +a.sub.1 X+ . . . +a.sub.m X.sup.m,

using the Normal Equations of the Least Squares method of curve formation; and

substituting said coefficients into the equation;

space="preserve" listing-type="equation">Σ

d.sub.i.sup.2 =Σ

Y.sub.i.sup.2 -(a.sub.o Σ

Y.sub.i +a.sub.1 Σ

X.sub.i Y.sub.i + . . . +a.sub.m Σ

X.sub.i.sup.m Y.sub.i),

wherein Σ

d_i² =the amount of deviation of the edge of the reflected light pattern from the fitted curve; and

quantifying the amount of deviation of said at least one edge from said fitted curve, to the amount of undesirable deformity in said surface.

6. An apparatus for detecting undesirable deformities in a surface, said apparatus comprising:

a light pattern source having at least one flourescent light carried by a support frame, said light pattern source generating a light pattern directed at said surface;

at least one camera located in the path of reflection of said light pattern, said at least one camera located so as to receive said reflected light pattern;

at least one computer, and software compatible with said at least one computer, said software being capable of;

converting said reflected light pattern into an array of pixels;

evaluating the value of said pixels to define at least one edge of said reflected light pattern, by segregating pixels having a selected value and pixels having a value greater than said selected value into a first group;

segregating pixels having less than said selected value into a second group, and defining at least one edge of said reflected light pattern at the boundary of said first group of pixels and said second group of pixels;

analyzing said at least one edge of said reflected light pattern to detect sid undesirable surface deformities by forming a fitted curve through said at least one edge of said reflected light pattern;

measuring the amount of deviation of said at least one edge from said fitted curve; and

quantifying the amount of deviation of said at least one edge from said fitted curve, to the amount of undesirable deformity in said surface.

7. An apparatus for detecting undesirable deformities in a surface, said apparatus comprising:

means for projecting a light pattern onto said surface;

means for receiving a reflected light pattern from said surface;

means for generating data representative of the received reflected light pattern;

means for evaluating said reflected light pattern data in order to define at least one edge of said reflected light pattern;

means for forming a fitted curve through said at least one edge of said reflected light pattern;

means for measuring the amount of deviation of said at least one edge from said fitted curve; and

means for quantifying the amount of deviation of said at least one edge from said fitted curve, to the amount of undesirable deformity in said surface.