Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2001-12-19
2004-03-16
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S510000, C356S512000
Reexamination Certificate
active
06707559
ABSTRACT:
RELATED APPLICATIONS
This application claims the priorities of Japanese Patent Application No. 2000-397246 filed on Dec. 27, 2000 and Japanese Patent Application No. 2001-354545 filed on Nov. 20, 2001, which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of detecting a posture of an object by which an inclination of the object is detected, and an apparatus using the same. In particular, the present invention relates to a method of detecting a posture of an object by which the posture (inclination) of the object is automatically detected when the object (or a reference) is shifted by use of an actuator in an automatic stage or automatic measuring device such as an interferometer, and an apparatus using the same.
2. Description of the Prior Art
As an apparatus for detecting a posture (pitching, rolling, or the similar) of a moving object, an autocollimator such as the one shown in
FIG. 10
has conventionally been known. This autocollimator is one which irradiates an object
203
with a laser luminous flux by way of a PBS
201
and a quarter-wave plate
202
; illuminates a PSD (Position Sensitive Device)
205
, which is an analog position sensor, with the luminous flux reflected by the object
203
by way of the quarter-wave plate
202
, the PBS
201
, and a lens
204
; and determines the posture (inclination a) of the object
203
according to the distance d from the center axis of the PSD
205
to the position irradiated with the luminous flux. The inclination a in this case is determined by use of the expression of d=f·tan 2&agr; (where f is the focal length of the lens
204
).
Since the detection accuracy of the autocollimator is proportional to the focal length f of the lens
204
as can be seen from the above-mentioned expression, the focal length f increases when the detection accuracy is to be raised, whereby the apparatus becomes larger.
Therefore, in order to enable highly accurate detection while preventing the apparatus from becoming larger, a technique has been known in which, as shown in
FIG. 11
for example, two interference displacement meters
211
,
212
are installed in parallel in an object
210
, the difference between the respective distances d
1
, d
2
from the interference displacement meters
211
,
212
to a straightedge
214
arranged perpendicular to a reference table
213
is determined, and the posture (rolling angle) of the object
210
is calculated from this difference. Specifically, the rolling angle is expressed by:
&agr;=tan
−1
[(
d
1
−d
2
)/
D]
where D is the distance between the two interference displacement meters
211
,
212
.
In such a technique, however, it is necessary for the interference displacement meters
211
,
212
to be attached directly to the object. Since this technique fails to provide a so-called non-contact type, various problems occur, and it is also problematic in that the configuration of the apparatus becomes too complicated. In particular, at least three interference displacement meters are necessary in the two-dimensional posture detection, whereby their mutual alignment adjustment becomes complicated. Further, it is necessary to detect the above-mentioned distance D precisely, which makes the system hard to adjust.
SUMMARY OF THE INVENTION
In order to overcome the problems mentioned above, it is an objective of the present invention to provide a method of detecting a posture of an object by which the posture of the object, such as a two-dimensional posture in particular, can be obtained by a highly-accurate, high-speed, non-contact, and simple system configuration, and an apparatus using the same.
The present invention provides a method of detecting a posture of an object, by which a relative inclination of the object with respect to a reference is detected, the method comprising the steps of:
acquiring fringe image data carrying phase information of the object;
subjecting the whole or part of the fringe image data to arithmetic processing using Fourier transform so as to determine a tilt frequency of a fringe corresponding to an inclination of the object in the fringe image data; and
detecting the inclination of the object according to the tilt frequency.
The tilt frequency may be determined by defining positional coordinates of a predetermined peak in peaks on a frequency coordinate system obtained by the Fourier transform and carrying out an arithmetic operation for calculating the tilt frequency according to the positional coordinates.
The present invention provides an apparatus for detecting a posture of an object, which detects phase information from the object and a relative inclination of the object with respect to a reference, the apparatus comprising:
fringe image data acquiring means for acquiring fringe image data carrying the phase information from the object;
Fourier transform arithmetic means for subjecting the whole or part of the fringe image data to arithmetic processing using Fourier transform;
tilt frequency calculation means for determining a tilt frequency of a fringe corresponding to an inclination of the object in the fringe image data; and
object inclination detection means for detecting an inclination of the object according to the tilt frequency.
The present invention provides a method of detecting a posture of an object, by which a relative inclination of the object with respect to a reference is detected, the method comprising the steps of:
acquiring fringe image data carrying phase information of the object;
subjecting the whole or part of the fringe image data to arithmetic processing using Fourier transform so as to determine phase information including an inclination of the object; and
subjecting thus obtained phase information of the object to a predetermined arithmetic operation so as to detect the inclination of the object.
The phase information of the object may be determined by defining a predetermined spectrum distribution of a fringe corresponding to the inclination of the object in spectrum distributions on a frequency coordinate system obtained by the Fourier transform and carrying out an arithmetic operation for calculating the phase information according to the predetermined spectrum distribution.
Preferably, the predetermined arithmetic operation is an arithmetic operation for determining a least-square plane fitting the phase information of the object.
The present invention provides an apparatus for detecting a posture of an object, which detects phase information from the object and a relative inclination of the object with respect to a reference, the apparatus comprising:
fringe image data acquiring means for acquiring fringe image data carrying phase information from the object;
Fourier transform arithmetic means for subjecting the whole or part of the fringe image data to arithmetic processing using Fourier transform;
object phase information calculation means for determining phase information including an inclination of the object according to the fringe image data subjected to the Fourier transform; and
object inclination detection means for detecting the inclination of the object according to the phase information of the object.
The method and apparatus for detecting a posture of an object in accordance with the present invention are particularly effective when the object or a reference body providing a reference for the inclination of the object is a moving member movable by an actuator. The actuator may be a piezoelectric device.
The present invention provides a method of detecting a posture of an object, by which a change in inclination of the object between before and after a movement thereof is detected, the method comprising:
a first step of acquiring first fringe image data carrying phase information of the object before the movement,
subjecting the whole or part of the first fringe image data to arithmetic processing using Fourier transform so as to determine a tilt frequency of a fringe corresponding to an inclination of the object
Fuji Photo Optical Co., Ltd.
Snider Ronald R.
Snider & Associates
Turner Samuel A.
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