Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
2000-09-18
2001-07-24
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S368000, C359S382000, C200S047000
Reexamination Certificate
active
06266183
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related in general to the field of interferometry and, in particular, to a novel self-centering mechanism for crash protection of interference microscope objectives.
2. Description of the Related Art
Interferometers used in surface profilometry utilize a microscope objective facing a sample surface mounted on a stage. These microscope objectives typically produce magnifications in the 1.5× to 100× range. Earlier designs operated at finite conjugates, in which case a real image is formed at a known, typically constant, distance from the objective. Most current microscope objectives operate at infinite conjugates, in which case a tube lens with a specific reference focal length (for example, 200 mm for Nikon and Leica, 180 mm for Olympus, and 164.5 mm for Zeiss objectives) is used in conjunction with the objective to form a real image. Infinite conjugate objectives have a focal length that varies inversely with the magnification (power) according to the relation f
objective
=f
Reference
/power. For example, a 50× Nikon objective has a focal length of 4 mm; a 20× Nikon objective of 10 mm; and so on. Very high magnification objectives have correspondingly short focal lengths, as well as very short working distances. The working distance of a microscope objective (or other lens) is the distance from the objective to the mechanical surface closest to the objective. A typical working distance for a 100×-magnification achromatic objective is approximately 0.3 mm.
As a result of such short working distances, the process of focusing with high magnification objectives always carries the possibility that the objective may contact the sample (a very undesirable event referred to as “crashing” in the art). In order to protect the objective's optical components from damage when a crash occurs, manufacturers typically incorporate the objective with a spring-loaded mechanism that allows the axial motion of the objective away from the sample surface when upward pressure is applied upon contact. As illustrated in
FIGS. 1A and 1B
, the operational components of such conventional mechanisms consist of two cylindrical surfaces providing a telescopic coupling between the objective and its housing. The objective
10
includes a cylindrical inner sleeve
12
that is adapted for relative axial motion within the conforming inner surface of the housing
14
of the microscope (which thus functions as an outer sleeve for the inner sleeve
12
). The microscope objective
10
is urged forward by a spring
16
along the optical axis of the objective (i.e., its longitudinal axis). Thus, the objective is free to move inward when pushed as a result of an impact with a sample and is able to return to its original forward position upon release. A travel slot
18
and a pin
20
are used to prevent the objective
10
from rotating relative to the housing for the assembly.
The cylindrical connection between the inner sleeve and the housing of the crash protection mechanism necessarily includes a gap between the abutting surfaces of the two parts which may allow the position of the objective to shift in a radial direction. This gap, due in part to tolerances of manufacture and in part to the clearance necessary to permit the substantially frictionless axial translation of the objective, may produce misalignments whenever a crash occurs even though the objective is returned to its original axial position. Such radial shifts are often sufficient to cause measurement errors or require recalibration of other portions of the objective, especially in Linnik-interferometric applications.
Accordingly, there is still a need for a mechanism that protects a high-power interference objective from crash damage and that, in addition, prevents the radial shifting of the objective upon release from contact with the sample surface. This invention is directed at providing a novel approach to that end.
BRIEF SUMMARY OF THE INVENTION
The primary goal of this invention is a crash protection mechanism that prevents radial shifting of the interference objective after a crash with a sample surface.
Another objective of the invention is an approach that is particularly suitable for implementation in a Linnik interferometric arrangement.
Finally, a goal of the invention is a mechanism that is suitable for implementation with relatively minor modifications to existing interference microscope objectives and interferometric surface profilers.
Therefore, according to these and other objectives, the invention consists of a tapered, self-centering combination of sleeves interposed between the objective and its housing in an interferometric profiler. A three-lobed, tapered inner sleeve is affixed to the objective, while a matingly tapered outer sleeve is attached to the objective housing. A spring-loaded mechanism urges the objective outward toward the sample surface, so that it can move inward axially under crash conditions and then return to its original axial position. The mating tapered sleeves create an outward seated position that provides a high degree of repeatability when the objective is returned to its position after a crash.
Various other purposes and advantages of the invention will become clear from its description in the specification that follows and from the novel features particularly pointed out in the appended claims. Therefore, to the accomplishment of the objectives described above, this invention consists of the features hereinafter illustrated in the drawings, fully described in the detailed description of the preferred embodiment and particularly pointed out in the claims. However, such drawings and description disclose but one of the various ways in which the invention may be practiced.
REFERENCES:
patent: 87012 (1869-02-01), Thompson
patent: 3762881 (1973-10-01), Dunn
patent: 4364687 (1982-12-01), Adell
patent: 5108013 (1992-04-01), VanBrocklin
patent: 5315080 (1994-05-01), Kaczynski et al.
patent: 5764409 (1998-06-01), Colvin
patent: 34 02 583 (1985-01-01), None
Aziz David J.
Guenther Bryan W.
Durando Antonio R.
Nguyen Thong
Veeco Instruments Inc.
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