Optics: measuring and testing – Refraction testing – Prism engaging specimen
Reexamination Certificate
1999-10-27
2001-01-09
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Refraction testing
Prism engaging specimen
C356S137000
Reexamination Certificate
active
06172746
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to the field of refractometers for measuring the refractive index of a sample, and more particularly to an automated transmitted light refractometer that reduces operator influence on the measurement taken.
B. Description of the Prior Art
Abbe refractometers are widely used for measuring the refractive index of liquid samples. Prior art Abbe refractometers are known to comprise a mirror movable relative to a light-transmitting prism assembly on which a sample is placed, such that a critical angle dependent shadowline is viewable through an eyepiece by adjusting the orientation or position of the mirror redirecting the transmitted light. With such instruments, the operator must adjust an externally mounted illumination source relative to the prism assembly and visually align the shadowline with a crosshair or other reference marking by adjusting the mirror. A reading of refractive index is based on the mirror position as determined by a motorized gauge which runs each time a reading is taken. The step of visually aligning a crosshair to a reference introduces human error, particularly among different operators. Also, the use of a motorized gauge for determining mirror position causes a delay in reporting the reading.
U.S. Pat. No. 4,640,616 teaches an automatic reflected light refractometer in which the various optical elements defining the instrument's optical path are fixed relative to one another. The optical path leads to a linear scanned array, as opposed to an operator's eye, to detect the location of a shadowline for calculating refractive index. The instrument described in the patent measures a relatively small range of refractive indices as compared with refractometers having a movable mirror, and is without a manual mode.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved transmitted light refractometer that eliminates the need for an operator to manually adjust shadowline position until the shadowline is aligned with a reference marker as viewed by the operator during a sample reading.
It is another object of the present invention to provide an improved transmitted light refractometer that can instantaneously determine the position of a movable mirror of the refractometer.
It is a further object of the present invention to provide an improved transmitted light refractometer that incorporates an internal fixed illumination source to eliminate the need for adjustment.
It is a further object of the present invention to provide an improved transmitted light refractometer that can be adjusted to any of a very large number of viewable ranges.
It is a further object of the present invention to provide an improved transmitted light refractometer that can be easily upgraded from semi-automatic to fully automatic through its entire range if desired.
It is yet a further object of the present invention to provide an improved transmitted light refractometer that incorporates a second illumination source for reflected light refractometry in addition to transmitted light refractometry.
In view of these and other objects, a refractometer formed in accordance with the present invention includes an elevator assembly for adjustably supporting a movable optical element relative to a light-transmitting prism assembly on which the sample is placed. A beam splitter is located downstream from the movable optical element to divide light between a pair of detection paths, the first detection path leading to an eyepiece and the second leading to a light-sensitive shadowline detector, whereby the refractometer can function in automatic or manual modes. The elevator assembly includes a position light source traveling with the movable optical element and cooperating with a position detector for instantaneously providing signal information indicative of the position of the movable optical element. In a preferred embodiment, both the position detector and shadowline detector are identical linear scanned arrays. The output from both detectors is converted to digital form and processed using stored relationships between refractive index and detector cell numbers, as well as calibration offsets and magnification factors, to arrive at sample refractive index.
REFERENCES:
patent: 2966091 (1960-12-01), Goldberg
patent: 3625620 (1971-12-01), Goldberg
patent: 4188116 (1980-02-01), Rartfay-Szabo
patent: 4243321 (1981-01-01), Okuka et al.
patent: 4640616 (1987-02-01), Michalik
patent: 5969808 (1999-10-01), Cotton et al.
LEICA ABBE MARK II Refractometer, Model 10480/10481/10494/10495—Instruction Manual—Copyright 1997.
Atkinson Robert C.
Bleyle Kyle R.
Byrne Michael J.
Cash David J.
Ryan Thomas E.
Leica Microsystems Inc.
Pham Hoa Q.
Simpson, Simpson & Snyder, L.L.P.
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