Optics: measuring and testing – By polarized light examination – With light attenuation
Reexamination Certificate
1999-08-26
2001-11-06
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
By polarized light examination
With light attenuation
C356S370000
Reexamination Certificate
active
06313915
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a displacement measuring method and apparatus, particularly, to a displacement measuring method for performing non-contact measurement of surface positions and surface displacements of measurement objects.
2. Description of the Related Art
FIG. 1
shows a configuration of a conventional displacement measuring apparatus
1
. The displacement measuring apparatus
1
uses a confocal optical system in which optical beams emitted from a light source
2
, such as a laser diode, are passed through a collimating lens
3
, are converted to parallel optical beams, and are passed through a beam-splitter cube
4
. After passing through the beam-splitter cube
4
, the optical beams are converged by an objective lens
5
, and the converged optical beams are incident on a surface of a measurement object
6
. The optical beams, having been reflected off the surface of the measurement object
6
, are passed through the objective lens
5
again, are incident on the beam-splitter cube
4
, and are reflected by 90 degrees therethrough. The optical beams having been reflected by 90 degrees through the beam-well-balanced stable optical-intensity curve, as shown in FIG.
2
. This allows the position to be measured with high precision.
When the surface of the measurement object
6
has irregularities, however, optical-intensity curves shown in
FIGS. 3 and 4
are produced. Determination of the point z
0
which is equivalent to the optical-intensity maximum (the position of the objective lens
5
at the optical intensity maximum value) is difficult, preventing the position and variations to be measured with high precision.
Also, with a method that detects the position of a surface of a measurement object according to the maximum value of an optical-intensity curve, when a high optical intensity is suddenly detected because of noise and the like (as shown in FIG.
10
), erroneous measurement results are produced. This causes measurement operation to be inconsistent.
Referring back to the above, the lens surface is a surface whose roughness Ra is at most 0.01 &mgr;m. A surface having irregularities means a surface whose roughness ranges from 0.1 &mgr;m to 1 &mgr;m.
SUMMARY OF THE INVENTION
In view of the problems described above, an object of the present invention is to provide a displacement measuring splitter cube
4
are converged through a converging lens
7
. The converged optical beams are passed through a pinhole arranged at the focal point of the converging lens
7
, and only optical beams passing through the pinhole
8
are incident on an optical detector
9
so as to be measured.
In the displacement measuring apparatus
1
, the objective lens
5
can be shifted and adjusted in the optical-axis direction (vertical direction in FIG.
1
). While shifting the objective lens
5
in the optical-intensity axis direction, the optical intensity to be measured by the optical detector
9
varies according to the position of the objective lens
5
. In this, when the distance between a surface of the measurement object
6
(optical-beam-target position) is equal to the effective focal length of the objective lens
5
, an optical intensity P of the optical detector
9
becomes a maximum value P
max
. Therefore, when a position z
0
of the objective lens
5
at which the optical intensity is maximum is defined according to the variations (optical-intensity curve), the position of the surface of the measurement object
6
a
can be detected by detecting a distance from position z
0
to the focal point of the objective lens
5
.
In the displacement measuring apparatus
1
as described above, when the surface of the measurement object
6
is close to the lens surface, the optical intensity P when the position of the objective lens
5
varies is represented by a method and a displacement measuring apparatus that can measure positions and displacements of measurement objects regardless of the condition of surfaces of the measurement objects.
To these ends, according to one aspect of the present invention, a displacement measuring method projects optical beams to a measurement object through an objective lens, receives optical beams reflected off the measurement object, and shifts the focal point of the objective lens in the optical-axis direction, thereby measuring variations in the optical intensity which are attributable to shifting of the focal point. A threshold is defined according to a curve representing the variations in the optical intensity and the center of gravity in a graph region surrounded by the curve and the threshold is defined, thereby measuring displacements of the measurement object according to the center-of-gravity position.
According to the above aspect of the present invention, a threshold is defined according to a curve representing variations in the optical intensity, the center of gravity in a graph region surrounded by the curve and the threshold is defined, and displacements of the measurement object are measured according to the center-of-gravity position. Therefore, positions and displacements of the measurement object can be measured with a precision range smaller than a sampling interval in the shift direction of the objective lens, and the measurement precision can be improved to be higher than conventional cases. Furthermore, the present invention defines a threshold and uses optical intensity data which is equal to or higher than the defined threshold. Therefore, noise components, which adversely affect measurement, can be eliminated, thereby improving the precision of measurements.
Also, the displacement measuring apparatus detects the position of a surface of the measurement object according to the center-of-gravity position of the optical-intensity curve. Therefore, even when unusually large values are detected because of factors such as noise, measurement is not affected thereby, and relatively stable measurement results can be produced.
According to another aspect of the present invention, a displacement measuring method projects optical beams to a measurement object through an objective lens, receives optical beams reflected off the measurement object, shifts the focal point of the objective lens in the optical-axis direction, thereby measuring variations in the optical intensity which are attributable to shifting of the focal point. A predetermined curve approximated from a curve representing the variations in the optical intensity and measuring displacements of the measurement object according to the approximate curve is defined. This allows the detection of displacements of the measurement object according to, for example, the center line, the center of gravity, or the maximum value of the approximate curve.
Also, the present invention may define a predetermined approximate curve according to a curve representing displacements of combined optical intensities, and displacements of the surface of the measurement object are measured according to the approximate curve. With this arrangement, the present invention can determine the focal point of the objective lens according to a substantially ideal curve to detect displacements of the measurement object.
Furthermore, according to another aspect of the present invention, a displacement measuring method projects optical beams to a measurement object through an objective lens, receives optical beams reflected off the measurement object, shifts the focal point of the objective lens in the optical-axis direction, thereby measuring variations in the optical intensity which are attributable to shifting of the focal point. Variations in the individual optical intensities measured at a plurality of measurement positions are combined and measuring displacements of the measurement object according to the combination result are measured.
The above method may be implemented by means of, for example, the following displacement measuring apparatus. The apparatus has a light emitter for emitting optical beams, an objective lens for projecting optical be
Ikeda Yoshinori
Koike Shintaro
Nishiki Ryo
Yanagisawa Kuniaki
Murata Manufacturing Co. Ltd.
Pham Hoa Q.
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