Optics: measuring and testing – Shape or surface configuration – Triangulation
Reexamination Certificate
2001-04-02
2003-01-21
Mack, Ricky (Department: 2873)
Optics: measuring and testing
Shape or surface configuration
Triangulation
C356S601000
Reexamination Certificate
active
06509973
ABSTRACT:
This application is based on Japanese Patent Application No. 2000-97241 filed on Mar. 31, 2000, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for measuring a three-dimensional shape of an object by irradiating light such as a slit light to the object, comprising obtaining both of measured data to be used for three-dimensional measurement of the object and two-dimensional image data of the object.
2. Description of the Prior Art
A non-contact type three-dimensional measuring apparatus is often utilized for inputting data to CG system or CAD system, anthropometry, visual recognition of robots and so on since the non-contact type three-dimensional measuring apparatus can conduct measurements more rapidly than a contact-type measuring apparatus does.
There is known, as the method of the non-contact measurement of an object, a method wherein an object is measured by projecting a specific detection light to an object and receiving reflected light based on the triangulation method. For example, a laser beam is projected on an object from a light source such as a semiconductor laser, and bright spot occurring thereby is captured by a camera from an angle different from that of the light source. Thus, a three-dimensional location is determined by connecting positions of the light source, camera and bright spot to form a triangle.
Spotlight projection method and slit light projection method are known as one of such methods. In the spotlight projection method, a spotlight is projected on an object and the projected spot light is optically and two-dimensionally scanned. In the slit light projection method, a slit light is projected on an object, and the projected slit light is optically and single-dimensionally scanned. The slit light projection method is called also as a light-section method. In the spotlight projection method, there is obtained a spot image whose sectional surface on a imaging surface is a punctiform image. In turn, in the slit light projection method, there is obtained a slit image whose sectional surface is linear is obtained. Three-dimensional image is obtained as a collection of pixels indicating three-dimensional positions of a plurality of parts on the object.
Turning to the drawings,
FIGS. 26A
to
26
D generally illustrate a scheme of the slit light projection method, and
FIGS. 27A and 27B
generally illustrate the principle of measurement which employs the slit light projection.
A measurement slit light U in the form of a strip having a thin sectional surface is irradiated on an object Q that is an object for measurement. Reflected light is then made incident to, for example, an imaging surface S of a two-dimensional light receiving element (FIG.
26
A). If the irradiated part of the object Q is flat, the obtained image (slit image) is linear (FIG.
26
B). If the irradiated part is rough, obtained image (slit image) is bent or step-wise (FIG.
26
C). Thus, distance between the measuring apparatus and the object Q influences a position of the incidence of the reflected light on the imaging surface S (FIG.
26
D). Sampling of three-dimensional position of an object is realized by deflecting the measurement slit light U in the widthwise direction and scanning part of a surface of the object which is visible from the light-receiving side. Number of sampling points depends on number of pixels of an image sensor.
In
FIGS. 27A and 27B
, a light projection system and a light receiving system are so arranged that a base line AS connecting a start point A of light projection with an imaging surface S of the light receiving system is perpendicular with respect to a light receiving axis. The light receiving axis is perpendicular to the imaging surface S, and an intersection S
0
of the light receiving axis and the imaging surface S is set as an original position of three-dimensional rectangular coordinate system. Z axis is the light receiving axis, Y axis is the baseline AS and X axis is the longitudinal direction of the slit light.
HH′ denotes distance between a front principal point H and a rear principal point H′ of a light receiving lens, and b denotes a distance between the point S
0
and the rear principal point H′.
The distance b is a so-called image distance. The image distance b is a distance from the rear principal point H′ of the lens to the imaging surface S when an image of an object at a finite position is formed on the imaging surface S. The image distance b depends on relationship between a focal length of the light receiving lens and a feed amount of the lens for focusing.
In the case of setting as projection angle &thgr;a the angle at which the light projection axis intersects a light projection reference surface (a light projection surface parallel to the light receiving axis) when a point (X, Y, Z) on the object is irradiated with the measurement slit light U, and setting as light receiving angle &thgr;p the angle at which a line connecting the point P with the front principal point H intersects a plane (light receiving axis surface) containing the light receiving axis, coordinate Z of the point P is represented by the following equation:
L
=
L1
+
L2
=
Z
tan
θ
a
+
(
Z
-
HH
′
-
b
)
tan
θ
p
.
∴
Z
=
(
L
+
(
HH
′
+
b
)
tan
θ
p
}
/
{
tan
θ
a
+
tan
θ
p
}
When setting the light receiving position of the point P as P′ (xp, yp,
0
) (see FIG.
27
A), and imaging magnification of the light receiving lens as coordinates of the point P are:
X=xp/&bgr;
Y=yp/&bgr;
In the above equations, the baseline L is determined by the locations of the light projection system and the light receiving system and, therefore, has a predetermined value. The light receiving angle &thgr;p can be calculated from the relationship of tan&thgr;p=b/yp. The imaging magnification of the light receiving lens is calculated from &bgr;=−b/(Z−HH′−b).
Thus, after obtaining the distance between the principal points HH′, the image distance b and the projection angle &thgr;a, it is possible to determine the three-dimensional position of the point P by measuring the position P′ (xp, yp) on the imaging surface S. The distance HH′ between the front principal point and the rear principal point and the image distance b are determined by relative positional relationship of the lenses comprised in the light receiving system.
In the three-dimensional measuring apparatus comprising a light receiving lens system having a fixed focal length and fixed focus, i.e., in the three-dimensional apparatus which can achieve measurement only when the light receiving lens and an object have a sole predetermined distance relationship, distances between the lenses and the imaging surface S are fixed. Fixed values of the distance HH′ and the image distance b can be input into such three-dimensional measuring apparatus in advance of the measurement.
On the other hand, in a three-dimensional measuring apparatus capable of changing distance relationship between a light receiving system and an object, it is necessary to move a part or whole part of lenses comprised in the light receiving system about its light receiving axis for focusing. Further, a three-dimensional measuring apparatus capable of varying an angle of view of a light receiving system typically has a zooming mechanism. According to such zooming mechanism, it is possible to change focal length of a lens by moving a part or whole part of the lenses about a light receiving axis.
In the above mentioned cases, it is possible to detect relative positions of lenses and to obtain the distance HH′ between the front principal point and the rear principal point and the image d
Kiyoi Kazuya
Tsurutani Katsutoshi
Mack Ricky
Minolta Co. , Ltd.
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