Optics: measuring and testing – Shape or surface configuration – Triangulation
Reexamination Certificate
1999-09-10
2003-04-29
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
Triangulation
C356S623000, C702S150000, C702S152000, C702S159000
Reexamination Certificate
active
06556307
ABSTRACT:
This application is based on Japanese Patent Application No. 10-257869/1998 filed on Sep. 11, 1999, No. 10-257870/1998 filed on Sep. 11, 1999, and No. 10-257871/1998 filed on Sep. 11, 1999, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for inputting three-dimensional data that determines the shape of an object by irradiating a reference light beam toward the object so as to scan the object.
2. Description of the Prior Art
An apparatus for inputting three-dimensional data, which is a non-contact type and enables rapid measurement compared with a contact type, is used for data input into a CG system or a CAD system, physical measurement, visual sense of a robot or other applications.
A slit light projection method (also referred to as light cutting method) is known as a measurement method suitable for the three dimensional configuration measuring apparatus. By this method a distance image (three-dimensional image) can be obtained by scanning an object optically. The method is one of active measurement methods for taking an image of an object by irradiating a specific reference light beam. The distance image is a set of pixels that indicate three-dimensional positions of plural parts of the object. In the slit light projection method, a slit light beam having a slit-like section of the irradiated. light beam is used as the reference light beam. At a certain time point in the scanning, a part of the object is irradiated and an emission line that is curved corresponding to ups and downs of the irradiated part appears on the image sensing surface. Therefore, a group of three-dimensional data that determine the shape of the object can be obtained by periodically sampling intensity of each pixel of the image sensing surface in the scanning.
In the conventional method, the position of the object is calculated by triangulation from incident angle of the slit light beam reflected by the object and entering the image sensing surface, irradiation angle of the slit light beam, and length of the base line (distance between a starting point of the irradiation and a light receiving reference point), after determining the incident angle of the slit light beam in accordance with the position of the emission line in the image sensing surface. Namely, the position is calculated in accordance with the irradiation direction and the receiving direction of the reference light beam. The position of the object is calculated from the irradiation direction and the receiving direction also in the case where a spot light whose beam section is like spot is used as shown in Japanese Unexamined Patent Application No. 10-2722.
The three dimensional measuring apparatus can realize zooming for adjusting angle of view in taking picture. Another method is known in which one sampling is limited not to an entire image sensing surface but to a part region where the reference light beam will enter, and the region is shifted for every sampling. According to this method, time period necessary for one sampling can be shortened and the scanning speed can be increased. Thus, data quantity can be reduced and the load on a signal processing system can be reduced.
In the conventional method, accuracy of three-dimensional input data depends on accuracy of incident angle of the reference light beam that is determined in accordance with the image information. Therefore, it is difficult to get three-dimensional input data with sufficiently high accuracy. In addition, a complicated operation is required to ensure the sufficient accuracy. Fore example, when using a mirror to take image of an object indirectly, the accuracy of the incident angle is lowered compared with direct capture of image, due to influences of accuracy of the mirror surface and the attachment position thereof. In the case where zooming function or focusing function is added, slightly different correction of lens distortion should be performed for each stop position of the movable lens. In some cases, a process is necessary in which the zoom step is switched for setting adjustment contents or the adjustment contents of other zoom steps are speculated in accordance with the measurement result.
Another problem is that expensive components have to be used for ensuring sufficient accuracy. Still another problem is that the adjustment of the attachment position of the irradiation system requires much effort. It is difficult to ensure the accuracy because the irradiation system includes a moving mechanism for deflecting the reference light beam, and the operation of the moving mechanism can be easily affected by change in environmental condition such as temperature or humidity.
In a three-dimensional distance measuring apparatus that irradiates a patterned light beam, orientations of the object position viewed from plural view points are determined by matching of characteristics of plural images that are “epipola” restricted, and the object position is calculated in accordance with the orientations using the triangulation method. In this method for inputting three-dimensional data, accuracy of the three-dimensional input data depends on accuracy of the matching though it does not depend on accuracy of projection of the pattern light. Variation of sensitiveness of pixels of a light receiving device also affects the matching.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and an apparatus in which input of three-dimensional data is realized not depending on incident angle information of the reference light beam, so that the operation for getting the incident angle information is not required, and accuracy of the three-dimensional data is improved when accuracy of the incident angle information is low compared with the irradiation angle information. Another object of the present invention is to provide a method and an apparatus in which three-dimensional input data with high accuracy can be obtained not depending on accuracy of irradiation angle control.
A first aspect according to the present invention comprises the steps of irradiating a first reference light beam form a first starting point to a specific part of an object; irradiating a second reference light beam from a second starting point at a distance from the first starting point to the specific part; and calculating the position of the specific part in accordance with irradiation angles of the first and the second reference light beams, and in accordance with a distance between the first and the second starting points. Preferably, each of the first and the second reference light beams may have a slit-like section. The irradiation angle of the slit-like reference light beam may be changed to scan in the direction perpendicular to the longitudinal direction of the slit-like section. The slit-like reference light beam preferably scans in the longitudinal direction of the slit-like section.
The position of the specific part may include information of the position in the direction perpendicular to the depth direction of the object. The scanning can be performed by changing the irradiation angles of the first and the second reference light beams. Each of the first and the second reference light beams may have a spot-like section.
A second aspect according to the present invention comprises the steps of irradiating a reference light beam toward an imaginary plane so as to scan the imaginary plane; receiving the reference light beam reflected by an object, at first and second receiving positions apart from each other simultaneously; detecting each time point when the reference light beam passes each sampling section of the imaginary plane after reflected by an object; and calculating the position of the object for each sampling section in accordance with light reception angles of the reference light beam of the first and the second receiving positions at each detected time point, and in accordance with a distance between the first and the second receiving po
Ide Eiichi
Norita Toshio
Uchino Hiroshi
McDermott & Will & Emery
Minolta Co. , Ltd.
Mooney Michael P.
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