Moire apparatus having projection optical system and...

Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system

Reexamination Certificate

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C356S619000, C250S559220

Reexamination Certificate

active

06291817

ABSTRACT:

RELATED APPLICATIONS
This application claims the priorities of Japanese Patent Application No. 10-175718 filed on Jun. 23, 1998, Japanese Patent Application No. 10-208759 filed on Jul. 24, 1998, and Japanese Patent Application No. 10-208760 filed on Jul. 24, 1998, which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a so-called grating projection type moire apparatus; and, in particular, to a moire apparatus equipped with a fringe scanning function.
2. Description of the Prior Art
Moire apparatus have conventionally been known as an apparatus for easily capturing three-dimensional form information of an object to be measured in a short time. As the moire apparatus, those of a grating irradiation type and a grating projection type have been known, among which the degree of freedom in measurement of the object to be measured is higher in the latter since they do not need such a large reference grating as that of the former.
The grating projection type moire apparatus comprises a projection optical system and an observation optical system having their respective optical axes parallel to each other, and is configured such that an image of a projection grating is projected by the projection optical system onto an object to be measured, a deformed grating image formed on the object is focused by the observation optical system onto an observation reference grating, and the resulting moire fringe is observed. Here, if fringe scanning, by which the projection grating is moved in a direction orthogonal to the grating lines of both gratings within a plane orthogonal to both optical axes, is carried out, then whether the object is protruded or depressed can be determined, and phase connection can be made, whereby three-dimensional form information of the object can be obtained.
Since the moire fringe appearing on the monitor for observing the moire fringe is captured by way of the observation optical system, the actual depth of the moire fringe formed at a position on the object to be measured near the taking lens of the observation optical system differs from that of the moire fringe formed at a position far from the taking lens, even when they have the same grating line interval. Consequently, for obtaining correct three-dimensional form information of the object to be measured, it is necessary to correct the image magnification and sensitivity according to the position of each point on the object in the depth direction.
While it is necessary to carry out the image magnification correction and sensitivity correction according to the absolute distance between each point of the object to be measured and the taking lens of the observation optical system, the distance between the object and the taking lens must be measured separately from the moire fringe observation, since the three-dimensional data of the object computed from the moire fringe is inevitably relative positional data on the object.
This distance measurement is mainly carried out by a manual operation in which a measure is placed between a given point on the object and the taking lens, and its scale is read out. In such a measuring method, it is difficult to correctly measure the distance. As a consequence, it is problematic in that the image magnification correction cannot be carried out accurately.
Also, while the distance measurement is carried out by the above-mentioned manual operation with a measure or the like, or measurement using a measuring device or the like, the point subjected to the distance measurement on the object to be measured is also a reference point for the image magnification correction and sensitivity correction. Consequently, for accurately performing the image magnification correction and sensitivity correction, it is important to correctly grasp the position of this point within a plane orthogonal to the depth direction.
Further, while the above-mentioned fringe scanning is carried out by a driving means such as a pulse motor, the driving is effected in an open loop manner, whereby the reliability of fringe scanning accuracy is not always sufficient, which is desired to be improved.
SUMMARY OF THE INVENTION
In view of such circumstances, it is an object of the present invention to provide a grating projection type moire apparatus equipped with a fringe scanning function, which can improve the accuracy in image magnification correction and sensitivity correction necessary for obtaining correct three-dimensional form information of the object to be measured.
It is another object of the present invention to provide a grating projection type moire apparatus equipped with a fringe scanning function, which can improve the fringe scanning accuracy.
The moire apparatus in accordance with a first aspect of the present invention is configured such that a distance-measuring reference point on an object to be measured is automatically selected at the time of moire fringe observation, and the distance between the distance-measuring reference point and the taking lens is automatically measured, whereby the aimed objects are achieved.
Namely, the moire apparatus in accordance with the first aspect of the present invention is a moire apparatus comprising a projection optical system and an observation optical system which have optical axes parallel to each other, the apparatus being configured such that an image of a projection grating is projected by the projection optical system onto an object to be measured, a deformed grating image formed on the object is focused by the observation optical system onto an observation reference grating, and a moire fringe formed thereby is observed, the projection grating being movable in a direction orthogonal to grating lines of both of the gratings within a plane orthogonal to both of the optical axes;
wherein three-dimensional data of the object is computed from the moire fringe observed while the projection grating is moved, a distance-measuring reference point on the object is selected from the three-dimensional data, and a distance between the distance-measuring reference point and a taking lens of the observation optical system is automatically measured.
Though any point on the object to be measured can be employed as the distance-measuring reference point, the image magnification correction and the sensitivity correction can easily be carried out if an apex of the object is set as the reference point.
Thus, the distance-measuring reference point is preferably an apex of the object to be measured.
The automatic measurement may be performed such that the light quantity of reflected light from the object to be measured is detected, and a peak is detected according to thus detected light quantity.
The moire apparatus in accordance with a second aspect of the present invention is configured such that a distance-measuring reference point on an object to be measured is displayed with a flag on a monitor for observing a moire fringe, whereby the distance between the object and a taking lens of the observation optical system can be measured accurately.
Namely, the moire apparatus in accordance with the second aspect of the present invention is a moire apparatus comprising a projection optical system and an observation optical system which have optical axes parallel to each other, the apparatus being configured such that an image of a projection grating is projected by the projection optical system onto an object to be measured, a deformed grating image formed on the object is focused by the observation optical system onto an observation reference grating, and a moire fringe formed thereby is observed, the projection grating being movable in a direction orthogonal to grating lines of both of the gratings within a plane orthogonal to both of the optical axes;
wherein three-dimensional data of the object is computed from the moire fringe observed while the projection grating is moved, a distance-measuring reference point on the object is selected from the three-dimensional data, and the distance-measuring

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