Endoscopic optical system

Details Endoscopic optical system Endoscopic optical system

1999-08-10

2001-06-12

Ben, Loha (Department: 2873)

Optical waveguides

Optical fiber bundle

Imaging

C359S820000, C359S894000, C359S740000, C257S081000

Reexamination Certificate

active

06246823

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to an optical system of the type including a metal housing with an opening in which a substantially planar transparent window is received, the window having an outer edge surface which is metallized over at least part of its area and is opposed to the internal surface of the opening, an annular solder joint being provided in the gap between the opposed surfaces.
BACKGROUND OF THE INVENTION
Endoscopic optical systems have a metal housing which is generally constructed in the form of a tube in its distal region and with a broadened portion in its proximal end region. A window is provided at at least the distal end of the housing through which the optical device of the optical system can look outwardly with an objective. In endoscopes with an optical eyepiece, a window which enables one to look in is also provided at the proximal end. The windows are usually constructed as plane parallel plates of e.g. glass which are connected to the housing in a sealed manner at their edges.
The connection of the window to the housing is effected in optical systems of the type referred to above by soldering in a marginal gap between the cylindrical outer edge surface of the window and a cylindrical internal surface on the housing, as is illustrated in relation to the example of the distal window in DE 37 40 417 A1. As explained therein, the edge of the window is metallized in constructions of the type referred to above in order to render soldering possible, which can only be effected between metal surfaces.
The known construction referred to above requires very careful soldering of the entire window edge. It has, however, transpired that this is disadvantageous since soldering over the entire area of the edge or side surface of the window produces stresses in the glass which can lead to breakage. This occurs particularly as a result of current requirements on endoscopic optical systems as regards sterilizability which can only be fulfilled by frequent autoclaving, that is to say hot steam sterilization. The rapid changes in temperature associated therewith promote stress cracks in the glass.
An endoscopic optical system with a soldered window, which is not of the type referred to above, is disclosed in DE 196 44 729 A1. The cylindrical window is secured in a metal tube by introducing adhesive into the gap between the window and the housing. Corner soldering is provided on the internal surface of the window on an appropriately metallized annular portion of the internal surface of the window. This construction is, however, difficult to manufacture as a result of the soldering process within the tube and results in a reduction in the usable area of the window.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical system of the type referred to above in which soldering of the window does not result in breakage of the window, even when it is subjected to frequent, substantial changes in temperature.
In accordance with the present invention, in an endoscopic optical system of the type referred to above, the soldered joint has a dimension in the direction perpendicular to the window which is less than the thickness of the window. Thus, in the optical system in accordance with the invention, the outer edge surface of the window is soldered to the opposing surface of the metal housing only over a narrow annular region which extends over only a proportion of the thickness, i.e., less than the thickness of the window in the direction of the thickness of the window. In practice, the thickness of the annular soldered joint may be between one-quarter and three-quarters, preferably about one half, of the thickness of the window. It transpires that the stresses to which the window is subjected as a result of the soldering process are considerably reduced and thus that stress cracking of the window can be substantially eliminated. Optical systems in accordance with the invention can be autoclaved with rapid changes in temperature over a prolonged period of time without stress cracks occurring in the window.
In one embodiment of the invention, only that proportion of the edge surface of the window which is contacted by the solder is metallized. This permits solder to be applied to the entire edge surface of the window in a very simple manner. However, the solder adheres only to the metallized region of the window while the remaining portions of the gap automatically remain free of solder.
In one embodiment of the invention, the or each region of the gap which is not occupied by solder is occupied by a lost masking ring. The masking ring is “lost” in the sense that it is positioned around the window to shield part of the periphery thereof and then remains there as part of the endoscopic instrument. The masking ring or rings may be simply pushed onto the side surface of the window. Those portions of the gap which are occupied by a masking ring are automatically maintained free of solder during the subsequent soldering operation. Soldering thus occurs only in those regions of the gap in which no masking ring is located. This permits the window to be metallized over its entire peripheral edge surface which substantially simplifies the metalization process.
It is preferred that the soldered joint is positioned substantially centrally with respect to the height of the window in the direction of the length of the housing. This results in a particularly favorable distribution of stresses in the window and thus in a substantially reduced risk of breakage.
In one embodiment of the invention the window projects beyond the end of the metal housing, that is to say, it projects out of the opening in the housing, and the soldered joint is situated within the outer portion of the gap between the window and the housing. This is a simple way of maintaining the outer portion of the side surface of the window free of solder without the necessity of using any particular device, such as a masking ring, for this purpose. In one embodiment there is a masking ring disposed in the inner portion of the gap between the window and the housing. This inherently results in only the central portion of the side surface of the window being soldered to the housing. The solder joint is localized in the direction towards the exterior of the housing by the fact that the opposing surface of the housing is set back with respect to the side surface of the window and is localized towards the interior of the housing by the masking ring. The soldering can be effected very simply from the exterior of the housing and the window may be metallized over its entire side surface. This construction is very resistant to applied stresses and may be manufactured very economically.
In an alternative construction the window is partially cut away, on one side or on both sides, so as to reduce the height of the side surface. It is so cut away that proportion of the outer edge of the window which remains parallel and adjacent to the internal surface of the opening has a height which is only a proportion of the thickness of the window in the direction of the length of the housing.
In a further alternative, the opening in the housing is defined by an inwardly directed flange whose thickness is only a proportion of the thickness of the window in the direction of the length of the housing.
The invention also embraces an endoscope including an optical system of the type referred to above.


REFERENCES:
patent: 4723833 (1988-02-01), Yamada
patent: 5377669 (1995-01-01), Schulz
patent: 5504350 (1996-04-01), Ortyn
patent: 5691853 (1997-11-01), Miyano
patent: 5917651 (1999-06-01), Yahata

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