Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2000-10-12
2004-02-24
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
Reexamination Certificate
active
06697162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical interferometric measuring instrument, and more particularly to the ultra precision laser interferometric measuring instrument using laser light. Further, the present invention relates to a laser interference apparatus, and more particularly to the laser interference apparatus which processes an object disposed on a slider potion whose amount of movement is measured by a laser interferometric measuring instrument.
2. Related Art
In recent years, concerning the measurement of length, particular importance has come to be attached to the traceability of the length, and the presentation of the uncertainty of measurement accuracy has come to be required. In the present situation in which the laser wavelength serves as a standard of the length, a laser interferometric measuring system is widely used as a length measuring means in measuring instruments and apparatus, an ultra precision machining apparatus, and the like so as to facilitate the traceability of the standard of the length and simplify factors for the uncertainty of the measurement accuracy.
In the case where the laser interferometric measuring system is used as the means for measuring with high accuracy the displacement of a slider in the measuring instruments and apparatus, an ultra precision machining apparatus, and the like, variations of the laser wavelength ascribable to the change of the refractive index due to changes in the air temperature or pressure, humidity, and CO
2
concentration in the atmosphere hamper the high-precision length measurement, so that it has been proposed to evacuate the optical path of the laser.
FIG. 7
shows the configuration of a conventional optical interferometric measuring instrument. This optical interferometric measuring instrument is comprised of a body base
710
, a laser light source
712
, an interferometer portion
714
, a slider
716
, a slider driving mechanism
718
, a reflecting mirror
720
, and a bellows
722
.
The laser light source
712
is fixed on the body base
710
, and is adapted to emit laser light for length measurement toward the reflecting mirror
720
.
The interferometer portion
714
has a half mirror and the like, and is adapted to measure the distance to the reflecting mirror
720
, i.e., the distance to an end portion of the slider
716
, by detecting the phase difference between the direct light emitted from the laser light source
712
and the reflected light returned after being reflected by the reflecting mirror
720
after passing through the bellows
722
.
The slider
716
is disposed on the body base
710
, and is provided movably in the directions of arrows in the drawing by the slider driving mechanism
718
. In a case where the length of an object to be measured is measured, the slider
716
is moved so as to allow an end portion of the slider
716
to abut against the object to be measured.
The reflecting mirror
720
is disposed at the end portion of the slider
716
, and moves in the directions of arrows in the drawing in conjunction with the movement of the slider
716
. Then, reflecting mirror
720
reflects the light emitted from the laser light source
712
, and returns the laser light to the interferometer portion
714
.
The bellows
722
functions as a light guiding portion for guiding the laser light from the laser light source
712
to the reflecting mirror
720
, and one end thereof is connected to the interferometer portion
714
, while the other end thereof is connected to the reflecting mirror
720
. The bellows
722
is stretchable in the moving direction of the slider
716
, and if the slider
716
is moved to measure the length of the object to be measured, the bellows
722
is also extended or contracted in conjunction with the movement of the slider
716
. The interior of the bellows is exhausted of the air by a vacuum pump until it is set substantially in a vacuum state. Since the laser light from the laser light source
712
passes through the vacuum in the bellows
722
, the length-measuring optical path is constantly kept in a vacuum state. Accordingly, the variation of the laser wavelength ascribable to a change in the refractive index due to changes in the air temperature, atmospheric pressure, humidity, and the CO
2
concentration does not occur, so that high-accuracy measurement becomes possible.
However, there has been a problem in that the couple of forces consisting of the product of, on the one hand, an offset distance of an axis of a force combining a suction force of the bellows
722
attributable to the difference between the internal pressure (a vacuum state) of the vacuum bellows
722
and the atmospheric pressure and a spring force consisting of the product of a spring constant peculiar to the bellows
722
and its amount of extension and contraction and, on the other hand, an offset distance of a driving axis for moving the slider causes a change in the geometric attitude of the slider
716
and a change in its velocity during driving (these cause a positional change of the reflecting mirror
720
) as well as a strain in the interferometer portion
714
, thereby rendering the high-accuracy length measurement difficult.
FIG. 8
shows another configuration of the conventional optical interferometric measuring instrument. The difference with the optical interferometric measuring instrument shown in
FIG. 7
lies in that, instead of the bellows
722
, a bellows
824
having a double structure which is composed of an inner shell
824
a
and an outer shell
824
b
is provided as the light guiding portion. The inner side of the bellow
824
of the double structure (or an inside of the inner shell
824
a
) is exhausted of the air into a vacuum state by the vacuum pump in the same way as in
FIG. 7
, and the outer side (a space between the inner shell
824
a
and the outer shell
824
b
) is set to an appropriate pressure higher than the atmospheric pressure. Since the inner side of the bellows
824
is in a vacuum state, a suction force due to the difference with the atmospheric pressure occurs, but since the outer side of the bellows
824
is set to the pressure higher than the atmospheric pressure, an expanding force (force acting in an expanding direction) is conversely applied due to the difference with the atmospheric pressure. Accordingly, by using such a bellows
824
of the double structure, the suction force on the inner side which is in the vacuum state can be offset by the force consisting of the product of the appropriate pressure set on the outer side and the pressure receiving area in the extending and contracting direction.
It should be noted that the arrangements of the bellows
822
and
824
which are used in
FIGS. 7 and 8
are as shown in
FIGS. 9A-B
, for example. The bellows
722
and
824
are each formed by superposing a plurality of doughnut-shaped weldable metallic plates
925
(e.g., made of austenitic stainless steel) shown in FIG.
9
A and by welding them.
FIG. 9B
shows a vertical cross section of the bellows
722
and
824
, and by bending and mutually welding the doughnut-shaped weldable metallic plates
925
shown in
FIG. 9A
, it is possible to obtain a member which has a hollow portion in its interior and which is stretchable in the directions of arrows. It goes without saying that a metal formed bellows is also used in addition to the welded bellows.
However, also in the case of the optical interferometric measuring instrument using the bellows
824
having the double structure shown in
FIG. 8
, the bellows
824
extends or contracts in conjunction with the movement of the slider
816
, so that there has been a problem in that a change in the geometric attitude of the slider
816
and a change in its velocity during driving as well as a strain in the interferometer portion
814
still occur due to the force consisting of the product of the spring constant peculiar to the double-structure bellows
824
and the amount of its extension or contraction in the same case of
FIG. 7
, thereb
Kubo Tetsuhiko
Sakai Hisayoshi
Saruki Yoshio
Lyons Michael A.
Mitutoyo Corporation
Oliff & Berridg,e PLC
Turner Samuel A.
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