Data processing: measuring – calibrating – or testing – Measurement system – Dimensional determination
Reexamination Certificate
2002-05-31
2004-07-13
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Dimensional determination
C356S609000
Reexamination Certificate
active
06763319
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a profilometer and method for measuring, with high precision, the surface profile of an ultra-small area; for example, the surface profile of a pickup lens of an optical disk, that of a small-diameter lens to be used in optical communication, such as a fiber condenser lens, or that of a mold for the lens.
2. Description of the Related Art
Japanese Patent Application Laid-Open Nos. H04-299206, H10-170243, and Japanese Patent No. 2748702 describe an ultrahigh precision three-dimensional profilometer capable of measuring the surface profile of an aspheric lens or that of a mold for the lens. In the three-dimensional surface profiling method, there are some kinds of method; for example, a method to directly contact to an object by a probe, a measurement method using an optical probe and utilizing a behavior of an optical interference, or such. The Japanese Patent No. 2748702 discloses an error correction method by using a reference spherical reference ball in a profilometer including an optical probe.
FIG. 1
is a perspective view showing an example construction of the profilometer.
The profilometer is constructed such that a tip end of a stylus
5
attached to a moving element
3
is caused to follow a surface of measurement
2
a
(hereinafter called a “measurement surface”) of an object of measurement
2
(simply called an “object”), such as a lens, placed on a stone surface plate
1
, thereby measuring the surface profile of the object
2
. More specifically, an X reference mirror
6
, a Y reference mirror
7
, and a Z reference mirror
8
, which are intended for measuring the positional coordinates of the probe
5
by way of a support section, are placed on the stone surface plate
1
on which the object
2
is to be placed. The moving element
3
having the probe
5
attached thereto is equipped with an X stage
9
and a Y stage
10
. The moving element
3
and the probe
5
can be scanned in both the X-axis and Y-axis directions by means of following the surface profile of the measurement surface
2
a
of the object
2
. The moving element
3
is equipped with a laser length-measuring optical system
4
. By means of a known light interference method, the profilometer measures the X coordinate of the probe
5
with reference to the X reference mirror
6
; the Y coordinate of the probe
5
with reference to the Y reference mirror
7
; and the Z coordinate of the probe
5
with reference to the Z reference mirror
8
.
Measurement procedures for use in such a profilometer will now be described. First, design information, such as an equation representing the design profile of the measurement surface
2
a
of the object
2
, is input to the profilometer before measurement. Next, the probe
5
is caused to follow the measurement surface
2
a
of the object
2
at a constant measurement pressure. Centering of the object
2
is effected, by means of causing the probe
5
to perform axial scanning in the X and Y directions. Details on the centering operation are described in Japanese Patent Application Laid-Open No. 254307/1990. Subsequently, the probe
5
actually scans the measurement surface
2
a
of the object
2
in the X and Y directions, thereby measuring the profile of the surface.
FIG. 10
shows a view of how a stylus
31
provided at the extremity of the probe
5
of the profilometer follows the measurement surface
2
a
of the object
2
, when enlarged in the Z and X coordinates. Three-dimensional coordinates detected by the stylus
31
correspond to coordinates (X0, Y0, Z0) of the tip end T of the stylus
31
shown in FIG.
10
. However, as illustrated, a tip end section
32
of the stylus
31
has a curvature radius R. When the tip end section
32
is following the surface profile of the object
2
, a measurement error arises between three-dimensional coordinates (Xi, Yi, Zi) of an actual point of measurement P and the coordinates (X0, Y0, Z0) of the tip end T of the stylus
31
obtained as a result of scanning operation of the probe
5
.
If the inclination angle &thgr; of the measurement surface
2
a
at the actual position of point P of measurement is known, coordinates (Xi, Yi, Zi) of the actual point P of measurement can be computed from the coordinates (X0, Y0, Z0) of the tip end T of the stylus
31
. A measurement error derived from the curvature radius R of the tip end section
32
of the stylus
31
can be corrected by means of subtracting or adding the position of actual point P of measurement relative to the tip end T of the stylus
31
(i.e., a relative distance between two coordinates).
In connection with the Z-X coordinates, provided that coordinates of the tip end T of the stylus
31
belonging to the probe
5
assume (X0, Y0, Z0); that coordinates of an actual point P of measurement assume (Xi, Yi, Zi); and that the angle of inclination of the measurement surface
2
a
in the X direction assumes &thgr;x, then (Xi, Yi, Zi)=(X0−R·sin &thgr;x, Y0, Z0+R, (1−cos &thgr;x)) (where coordinate components Yi, Y0 in the Y direction in the Z-X coordinates are indefinite). Similarly, if the inclination angle &thgr; of the measurement surface
2
a
in the Y direction at the actual position of point P of measurement is known, the same correction can be made to the Z-Y coordinates. Correction of such a measurement error (i.e., an R error of the extremity of the probe) derived from the curvature radius R of the tip end section of the stylus belonging to the probe will hereinafter be called probe R correction. The inclination of angle &thgr; obtained at this time can be computed from previously-acquired or subsequently-acquired measurement data. Alternatively, the inclination of angle &thgr; can also be determined by means of the coordinates of the tip end T of the stylus
31
and the design equation of the object
2
.
Surface-profiled data pertaining to the object
2
detected by the stylus
21
include a placement error which has arisen at the time of placing of the object
2
(i.e., an alignment error). When occurrence of an error between the surface-profiled data and the input design formula has been determined, the coordinate system is transformed by means of three-dimensionally rotating and translating the data that have been subjected to probe R correction, thereby optimally superimposing the data onto the design equation. As a result, an alignment error is corrected. Subsequently, the probe R correction and the transformation of a coordinate system will be hereinafter collectively referred to as alignment processing.
After alignment processing, there is determined a profile error (deviation) in the Z direction between the input design equation and the measurement data pertaining to the object
2
, and deviation data are output. When a large profile error exists between the design equation and the actual object, the deviation data are fed back to a processing machine. Processing is repeated until the actual profile of the object
2
falls within a range of desired precision as compared with the design equation (e.g., a profile error falls within a range of ±0.1 &mgr;m in the case of an aspheric pickup lens for use with an optical disk), thereby manufacturing an aspheric lens or a mold thereof; that is, the object
2
, with high precision.
In the case of the ultrahigh precision three-dimensional profilometer capable of effecting measurement with high precision on the order of 50 nm or less, the tip end section
32
of the stylus
31
attached to the probe
5
which follows the surface profile of the object
2
is required to assume a high sphericity of 0.02 to 0.03 &mgr;m or less and excellent durability against repeated measurement. For this reason, there has widely been employed a ruby ball with an outer diameter of 1 mm or thereabouts which can achieve a high degree of sphericity through mechanical polishing and has superior machinability and hardness characteristics.
In recent years, in the field of optical communication, an optical fiber condense
Handa Koji
Kubo Keishi
Takeuchi Hiroyuki
Yoshizumi Keiichi
Barlow John
Matsushita Electric - Industrial Co., Ltd.
Pearne & Gordon LLP
Sun Xiuqin
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