Method and apparatus for measuring a three-dimensional curved surface shape

• US 5,102,223 A
• Filed: 02/07/1991
• Issued: 04/07/1992
• Est. Priority Date: 03/31/1988
• Status: Expired due to Fees

• Current Assignee: NKK Corporation (JFE Holdings Incorporated)
• Original Assignee: NKK Corporation (JFE Holdings Incorporated)
• Inventors: Komine, Isamu, Uesugi, Mitsuaki, Inomata, Masaichi
• Primary Examiner(s): Rosenberger, Richard A.
• Assistant Examiner(s): PHAM, HOA Q
• Application Number:
  US07/652,446
• Time in Patent Office: 425 Days
• Field of Search: 356/375, 356/376, 356/373, 356/380, 250/560, 250/561, 250/202
• US Class Current: 356/607
• CPC Class Codes: G01B 11/2522 the position of the object changing and being recorded

Abstract

A method and apparatus for measuring a three-dimensional curved surface shape based on a new measuring principle that a surface of an object to be measured is coded with information relating to a slit light which is used as a medium and moved or rotated at a constant speed. The manner in which a linear reflected pattern of the slit light is moved over the surface of the object to be measured is picked up by a television camera to form a composite image in which a value of each of picture elements in the image is represented by information relating to the slit light, e.g., a position, time or projection angle of the slit light at an instant that the slit light passes through one of positions on the object surface corresponding to that picture element. Then, a difference in value between each corresponding picture elements of the composite image and another composite image formed similarly with respect to a reference plane is determined to measure a three-dimensional curve surface shape of the object to be measured.

Claims

1. A method of measuring a three-dimensional curved surface shape, comprising the steps of:

causing a linear slit light to scan a surface of an object to be measured on a reference plane;

producing video signals by picking up the surface of said object using a television camera;

inputting said video signals corresponding to a plurality of picture elements into a memory means;

forming a composite image of the surface of said object by composing an image in which successive video signals of the same picture element are compared in magnitude to renew the same picture element in said memory means using as a value thereof information relating to scanning of said slit light at a time of application of the larger of said compared video signals and to thereby represent a value of each picture element in said memory means by information relating to scanning of said slit light at a time when said slit light passes respectively through a measuring point corresponding to each of said picture elements; and

measuring a three-dimensional curved surface shape of said object in accordance with said composite image.

2. A measuring method according to claim 1, wherein said television camera is aimed in a direction perpendicular to said reference plane.

3. A measuring method according to claim 2, wherein the step of measuring a three-dimensional curved surface shape of said object comprises measuring said three-dimensional curved surface in accordance with the difference between the values of the picture elements for said composite image of said object and the values of the corresponding picture elements for a preliminarily determined composite image of said reference plane.

4. A measuring method according to claim 3, wherein the step of causing a linear slit light to scan the surface of said object comprises causing said linear slit light to scan linearly the surface of said object, said linear slit light being projected from a direction which forms an angle θ

with said reference plane, wherein θ

is not equal to 90°

.

5. A measuring method according to claim 2, wherein the step of causing a linear light to scan the surface of said object comprises the steps of causing said linear slit light to scan the surface of said object by reflection from a rotatable mirror and

measuring angles of projection of said slit light,

whereby information relating to scanning of said slit light is represented by a slit light projection angle at an instant when said slit light passes through a measuring point corresponding to one of said picture element of by a value equivalent thereto.

6. An apparatus for measuring a three-dimensional curved surface shape comprising:

slit light projecting means for projecting a linear slit light onto a surface of an object to be measured on a first reference plane from a direction forming an angle θ

with said first reference plane which is not equal to 90°

;

slit light scanning means for causing said linear slit light to scan the surface of said object on said first reference plane;

a television camera for picking up the surface of said object from a direction different from the direction of projection of said slit light projecting means;

image composing means for composing a composite image of the surface of said object by composing an image in which successive video signals of the same picture element are applied from said television camera and compared in magnitude to renew said same picture element in a memory means by using as a value thereof information relating to scanning of said slit light at a time of application of the larger of said compared video signals, whereby a value of each of said picture elements in said memory means is represented by said respective information relating to scanning of said slit light at an instant when said slit light passes through a measuring point corresponding to said respective picture element; and

image processing means for measuring a three-dimensional curved surface shape in accordance with said composite image of said object.

7. A measuring apparatus according to claim 6, wherein said image composing means comprises:

maximum brightness memory means for storing a maximum level of said video signal for each of said picture elements during a predetermined period of time;

maximum brightness image procssing means for comparing said video signal and the signals stored in said maximum brightness memory means for each picture element thereof and writing a value of the greater one thereof in said maximum brightness memory means;

composite image memory means for storing a value of a synchronizing signal or external input signal at an instant when the magnitude said video signal is greatest for each of said picture elements during a predetermined time period; and

composite image processing means for storing in said composite image memory means an instantaneous synchronizing signal count value or external signal value for each picture signal count value or external signal value for each picture element for which said maximum brightness memory means determines that said video signal is greater than said signal stored in said maximum brightness memory means.

8. A measuring apparatus according to claim 6, wherein said slit light scanning means linearly scans said slit light all over the surface of said object and wherein said image processing means measures a three-dimensional curved surface shape of said object in accordance with the difference between the values of the picture elements of said composite image of said object and the values of the picture elements of a preliminarily determined composite image of said first reference plane.

9. A measuring apparatus according to claim 8, wherein said television camera is aimed in a direction perpendicular to said first reference plane.

10. A measuring apparatus according to claim 8, wherein said image processing means determines a three-dimensional shape f(x, y) of said object on the basis of a composite image u(x, y) of said object, a composite image u_o (x, y) of said first reference plane and a composite image u₁ (x, y) with respect to a second reference plane which is parallel to and separated by a distance d from said first reference plane in accordance with the equation. ##EQU10## where x and y are the positional coordinates of the picture elements.

11. A measuring apparatus according to claim 8, wherein said image processing means determines a three-dimensional shape f(x, y) of said object on the basis of a composite image u(x, y) of said object, a composite image u_o (x, y) of said first reference plane, a slit light projection angle θ

with respect to said first reference plane and a slit light scanning speed v in accordance with the equation;

space="preserve" listing-type="equation">f(x, y)={u.sub.o (x, y)-u(x, y)}v tan θ

,

where x and y are the positional coordinates of the picture elements.

12. A measuring apparatus according to claim 8, further comprising slit light angle measuring means for measuring a projection angle of said slit light, wherein said slit light scanning means rotates said slit light projecting means within a plane of said slit light beam about an axis of rotation consisting of a straight line parallel to said first reference plane to scan said slit light all over the surface of said object, and

said formation relating to scanning of said slit light is a slit light projection angle or a value equivalent thereto.

13. A measuring apparatus according to claim 12, wherein said image processing means determines a three-dimensional shape f(x, y) of said object according to two-dimensional coordinates x and y on the basis of a composite image θ

(x, y) of said object and a horizontal displacement x_o and vertical displacement z_o of said axis of rotation of said slit light relative to an origin of said first reference plane in accordance with the equation;

space="preserve" listing-type="equation">f(x, y)=z.sub.o -(x-x.sub.o) tan θ

(x, y)

14. A measuring apparatus according to claim 12, wherein said image processing means determines a three-dimensional shape f(x, y) of said object according to two-dimensional coordinates x and y at least on the basis of a composite image u(x, y) of said object surfaces and a preliminarily determined composite image θ

_o (x, y) of said first reference plane.

15. A measuring apparatus according to claim 12, wherein said large processing means determines a three-dimensional shape f(x, y) of said object according to two-dimensional coordinates x and y on the basis of a composite image θ

(x, y) of said object, a composite image θ

_o (x, y) of said first reference plane and a horizontal displacement x_o of said axis of rotation of said slit light relative to an orgin of said reference plane in accordance with the equation;

space="preserve" listing-type="equation">f(x, y)={tan θ

.sub.o (x, y)-tan θ

(x, y)}(x.sub.o -x)

16. A measuring apparatus according to claim 12, wherein said image processing means determines a three-dimensional shape f(x, y) of said object according to two-dimensional coordinates x and y on the basis of a composite image θ

(x, y) of said object, a composite image θ

_o (x, y) of said first reference plane and a vertical displacement z_o of said axis of rotation of said slit light relative to an origin of said reference plane in accordance with the equation;

##EQU11##

17. A measuring apparatus according to claim 12, wherein said image processing means determines a three-dimensional shape f(x, y) of said object according to two-dimensional coordinates x and y a composite image θ

₀ (x, y) of said first reference plane and a composite image θ

₁ (x, y) of a second reference plane which is parallel to and separated by a distane d from said first reference plane in accordance with the equation;

##EQU12##

18. An apparatus for measuring a three-dimensional curved surface shape comprising:

slit light projecting means for projecting a linear slit light onto a surface of an object to be measured on a first reference plane from a direction forming and angle θ

with said first reference plane which is not equal to 90°

;

slit light scanning means for causing said linear slit light to scan the surface of said object on said first reference plane;

a television camera for picking up the surface of said object from a direction different from the direction of projection of said slit light projecting means;

image composing means for composing a composite image of the surface of said object by composing an image in which video signals of the same picture element are successively applied from said television camera and successively compared in magnitude so as to renew said same picture element in a memory means by using a value thereof information relating to scanning of said slit light at a time of application of the greater one of said compared video signals, whereby a value of each of said picture elements in said memory means is represented by said respective information relating to scanning of said slit light at an instant when said slit light passes through a measuring point corresponding to said respective picture element;

image processing means for measuring a three-dimensional curved surface shape in accordance with said composite image of said object;

said slit light scanning means linearly scanning said slit light all over the surface of said object and said image processing means measures a three-dimensional curved surface shape of said object in accordance with the difference between the values of the picture elements of said composite image of said object and the values of the picture elements of a preliminarily determined composite image of said first reference plane;

and said image processing means determines a three-dimensional shape f(x, y) of said object on the basis of a composite image u(x, y) of said object, a composite image u_o (x, y) of said first reference plane and said slit light projection angle θ

with respect to said first reference plane in accordance with the equation;

space="preserve" listing-type="equation">f(x, y)=(u.sub.o (x, y)-u(x,y)) tan θ

where x and y are the positional coordinates of the picture elements.