Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2002-05-07
2004-04-20
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
Reexamination Certificate
active
06724488
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical measurement devices and particular, to interferometers.
2. Related Arts
U.S. Pat. No. 4,509,858 to Smythe et al, dated Apr. 9, 1985 and entitled “Compact, Linear Measurement Interferometer With Zero Abbe Error”, comprises a light source
11
, a detector
12
and a beam splitter
13
. The beam splitter divides a beam of light from the source into a test beam and a reference beam. There is a retroreflector in the path of the reference beam and a separate retroreflector in the path of the test beam. The second retroreflector is mounted on a probe
15
which passes through the beam splitter and which can rest on a work piece
17
that is mounted on a table
16
. The source
11
, detector
12
, beam splitter
13
and retroreflector
14
are all mounted on a base that is sturdily positioned over measuring table
16
(see column
3
, lines
22
-
24
). The mounting table
16
is usually made of granite or ceramic or the like so that the force of the measurement probe does not deflect the workpiece and the reference holder down-wardly when the measurement probe makes contact with the workpiece Any such downward deflection will cause a significant measurement error. The Smyfte et al Patent also requires a central aperture
20
in the beam splitter
13
through which probe
15
can move (see column
2
, line
66
to column
3
, line
7
).
U.S. Pat.4,924,477 to Gilmore et a
1
, dated May 8, 1990 and entitled “Assembly And Method For Determining the Coefficient Of Thermal Expansion Of A Workpiece”, discloses an apparatus for measuring the coefficient of thermal expansion (CTE) of a workpiece of known length (see column
5
, line
50
through column
6
, line
36
). Th apparatus requires a dual channel light Source and reflectors situated at both ends of the workpiece. The two light signals are directed towards the first reflector, which reflects one signal but passes the other to the second reflector, from which it is reflected. A temperature control system is used to vary the temperature of the workpiece to cause thermal expansion and the CTE is determined by changes in measured light frequencies caused by relative doppler frequency shifts of the reflectors as the workpiece changes in length (see column
6
, lines
1
-
36
). As described at column
4
, lines
31
-
36
, the assembly has a flexure system so that a workpiece undergoing expansions and contractions during testing can flex causing the image devices (
36
and
38
in
FIG. 3
) to move. This assembly is used to measure the expansion and contraction of a workpiece with a flexure system, so that the coefficient of expansion of the workpiece can be determined. The flexure system only allows for a small amount of movement and is not suitable for measurement of relatively long workpieces. This assembly additionally has laser beam around the sides of the workpiece with imaging devices on both sides of the workpiece. This arrangement leads to a small amount of Abbe error since the measurement path is not directly in line with the gauging points.
SUMMARY OF THE INVENTION
The present invention provides a measurement interferometer comprising a frame structure on which is mounted a laser source that emits a source beam, a detector, a beam splitter, a reference retroreflector, a test retroreflector and a reference holder. The invention is characterized in that the beam splitter and the reference holder are interconnected in fixed mutual relation by a connector to constitute a splitter-holder assembly, the beam splitter is positioned to receive a light beam from the laser source and emit a test bean and a reference beam split from the source beam, the reference retroreflector is positioned at a fixed distance from the beam splitter to receive the reference beam from the beam splitter, and in that the test retroreflector is positioned to receive the test beam from the beam splitter and is movable on the frame structure relative to the splitter-holder assembly.
According to another aspect of the invention, the beam splitter is connected to the reference holder by a composite rod. Optionally, the test retroreflector may carry a probe comprising a carbon composite rod as well.
According to yet another aspect of the invention, the reference retroreflector may be in with the beam splitter.
Still another aspect of this invention provides that there may be vibration-dampering member between the splitter-holder assembly and the frame structure.
REFERENCES:
patent: 3582211 (1971-06-01), McClure et al.
patent: 4153370 (1979-05-01), Corey, III
patent: 4509858 (1985-04-01), Smythe et al.
patent: 4583856 (1986-04-01), Moore
patent: 4924477 (1990-05-01), Gilmore et al.
patent: 4950079 (1990-08-01), McMurtry et al.
patent: 5428446 (1995-06-01), Ziegert et al.
Renishaw® Product Data Sheet for HS10 Laser Head, Part No. L-8003-2415, 2 pages.
R. Smythe et al, “Instantaneous phase measuring interferometry”,Optical Engineering, Jul./Aug. 1984, vol. 23, No. 4, pp. 361-364.
ACC, Korea Aerospace Industry, Ltd., Carbon/Carbon Composite, Internet website http://www.koreaaero.com/acc/product_c_c_composite.htm, dated Feb. 3, 2002, pp. 1 and 2.
Clinton Chapman, 1995, Material World, An overview of Carbon/Carbon Composites, Internet website http://home.freeuk.com/dseymour/mw/mwccc.htm, dated Jan. 27, 2002, pp. 1 and 2. Chapter 40, 40-8, Michelson's Interferometer, p. 913.
Industrial Application of Lasers, Chapter 9, “Principles Used in Measurement”, pp. 247-250, and Chapter 10, “Distance Measurement and Dimensional Control”, pp. 256-263.
C.W. Ohlhorst et al, NASA Technical Memorandum 4787, “Thermal Conductivity Database of Various Structural Carbon-Carbon Composite Materials”, Nov. 1997, cover page and pp. lil, v and 1-3.
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