Optics: measuring and testing – Shape or surface configuration – Triangulation
Reexamination Certificate
2000-10-02
2003-03-04
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
Triangulation
C356S606000
Reexamination Certificate
active
06529280
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a three-dimensional measuring device and three-dimensional measuring method for non-contact measuring of an object shape by illuminating an object with light.
2. Description of the Related Art
Three-dimensional measuring devices of the non-contact type commonly referred to as rangefinders are used for data input to CG systems and CAD systems, somatometry, robot visual recognition and the like because it is possible to measure at high speed compared to contact type devices. The optical slit projection method (also referred to as the light section method) is known as suitable measuring method for rangefinders. This method produces a three-dimensional image (distance image) by optically scanning an object, and is one type of active measuring method for imaging an object illuminated by a specific light. The three-dimensional image is a collection of pixels representing the three-dimensional positions of a plurality of parts on an object. In the optical slit projection method the section of a linear slit light is used as the detection light.
FIGS. 46
a
,
46
b
,
46
c
, and
46
d
briefly show the optical slit projection method, and
FIGS. 47
a
,
47
b
, and
47
c
illustrate the principles of measurement via the optical slit projection method.
A section of object Q serving as a measurement subject is illuminated by a thin band-like slit light U, and, the light reflected from the object Q impinges, for example, the imaging surface S
2
of a two-dimensional image sensor (
FIG. 46
a
). If the illuminated portion of object Q is flat, the sensed image (slit image) is a straight line (
FIG. 46
b
). If the illuminated portion is uneven, the straight line becomes curved and step-like (
FIG. 46
c
). That is, the magnitude of the distance between the measuring device and the object Q is reflected at the incident position of the reflected light on imaging surface S
2
(
FIG. 46
d
). Three-dimensional position sampling can be accomplished by scanning the object surface on a range viewed from the light reception side by deflecting the slit light U perpendicular to the length direction. The number of points of this sampling is dependent on the number of pixels of the image sensor.
In
FIGS. 47
a
,
47
b
, and
47
c
, the light emitting system and light receiving system are positioned such that the base line AO connecting the origin A of the projection light and the principal point of the light reception lens is perpendicular to the optical axis of received light. The principal point of the lens is a point on the receiving optical; axis separated from the sensing surface S
2
only by the so-called image distance b when the image of an object at infinite distance is formed on imaging surface S
2
. The image distance b is the sum of the focal length f of the light receiving system and the amount of lens extension for focusing adjustment.
The principal point O is the origin of the three-dimensional orthogonal coordinates. The light reception axis is the Z axis, the base AO is the Y axis, and the slit light length direction is the X axis. When the slit light U illuminates point P (X,Y,Z) on the object, and the angle of the projection axis and projection reference plane (projection plane parallel to the light reception axis) is designated &thgr;a, and the light reception angle is designated &thgr;p, the coordinates Z of point P are expressed by the equation below.
Base line length
L=L
1+
L
2=
Z
tan &thgr;
a+Z
tan &thgr;
p
∴
Z=L
/(tan &thgr;
a
+tan &thgr;
p
)
The light receiving angle &thgr;p is the angle formed by a line connecting point P and principal point O, and the plane including the light reception axis (i.e., light reception axis plane).
Since the imaging magnification &bgr;=b/Z, when the distance between the center of imaging surface S
2
and the light reception pixels in the x direction is designated xp and the distance in the Y direction is designated yp (refer to
FIG. 47
a
), the coordinates X,Y of point P are expressed by the equations below.
X=xp/&bgr;
Y=yp/&bgr;
The angle &thgr;a is unconditionally determined by the angular speed of deflection of slight light U. The light reception angle &thgr;p is calculated from the relationship: tan &thgr;p=b/yp. That is, the three-dimensional position of point P can be determined based on the angle &thgr;a by measuring the position (xp,yp) on the imaging surface S
2
When the light reception system is provided with a zoom lens unit as shown in
FIG. 47
c
, the principal point O becomes the posterior side principal point H′. When the distance between the posterior side principal point H′ and the anterior side principal point H is designated M, the Z coordinate of point P is expressed by the equation below.
L=L
1+
L
2=Z
tan&thgr;
a
+(
Z−M
)tan&thgr;
p
∴
Z
=(
L+M
tan&thgr;
p
)/(tan&thgr;
a
+tan&thgr;
p
)
When an image sensing means is used which comprises an imaging surface S
2
having a finite number of pixels as in, for example, a CCD sensor, in the measurement performed via the previously described slit light projection method, the measurement resolving power is dependent on the pixel pitch of the image sensing means. That is, the resolving power can be increased by setting the slit light U so that the width of said slit light U in the Y direction (scanning direction) impinges a plurality f pixels on the imaging surface S
2
.
FIG. 48
illustrates the principles of this measurement method.
When the reflectivity of the illuminated portion of the object is assumed to be uniform, the intensity of the received light is a normal distribution expanding on the Y direction. If the effective intensity range of this normal distribution is a plurality of pixels, the maximum intensity position (i.e., barycenter) can be measured in units under the pixel pitch by interpolation of the amount of light received by each pixel g. This interpolation fits the normal distribution to the amount of light received by each pixel. The X, Y, and Z coordinates are determined based on the barycenter determined by the aforesaid calculation. If this method is used, the actual resolving power is ⅛ to {fraction (1/10)} pixels.
When measuring via the slit light projection method, the person doing the measurement determine the position and direction of the rangefinder, and sets the scanning range (image sensing range) of the object Q via a zoom operation as necessary. It is useful to display a monitor image of the sensed object Q at the same field angle as the scanning range to easily accomplish the aforesaid framing operation. In three-dimensional CG, for example, color information of the object Q as well as measurement data expressing the shape of the object Q are often required.
Conventional rangefinders have a spectral means (e.g., dichroic mirror) for separating the light transmitted through the light-receiving lens system into slit light and environmental light, and are constructed so as to produce a color monitor image at the same field angle as the distance information by directing the environmental light to a color image sensing means separate from the image sensing means used for measurement (refer to Japanese Unexamined Patent Application No. SHO 7-74536).
If a dichroic mirror is used as the aforesaid spectral means, the entering light can be separated by wavelength virtually without decreasing the amount of light.
In practice, however, there are no dichroic mirrors which have ideal wavelength selectivity for reflection or transmission of only the slit light. Therefore, conventionally a disadvantage exists insofar as the environmental light greatly affects measurements because light of a comparatively broad wavelength range including the slit light wavelength enters the image sensing means.
In order to increase the resolving power, the width (i.e., length in the scanning direction) of the slit light may be increased by stages of projectio
Fujii Eiro
Fukumoto Tadashi
Hirose Satoru
Joko Takuto
Miyazaki Makoto
Minolta Co. , Ltd.
Rosenberger Richard A.
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