Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2001-02-23
2003-04-08
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S043000, C451S256000, C451S384000
Reexamination Certificate
active
06544102
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to a device for centering clamping of workpieces in the field of high-precision optics, the watch and clock making industry and the semiconductor industry, where workpieces have initially to be clamped in a centred manner and subsequently machined at the edge and/or scanned. In particular, the invention relates to a device for centering clamping of optical lenses, by means of which it is possible to clamp a lens in centred manner for edge machining thereof by the so-called bell clamp method.
Lenses for objectives and the like are “centred” after machining of the optical surfaces, so that the optical axis, the position of which is distinguished by the straight line through the two centres of curvature, also passes through the geometric centre of the lens. To this end, the lens is initially aligned and clamped between two aligned centering spindles in such a way that the two centres of curvature of the lens coincide with the common axis of rotation of the centering spindles. The edge of the lens is then machined in a defined relationship to the optical axis of the lens, as is necessary later for mounting the lens in a holder. During this process, the edge, depending on the material of which the lens is made (glass or plastics), is provided with a defined geometry, both in plan view onto the lens (circumferential contour of the lens) and viewed in radial section (contour of the edge, for instance linear construction or construction with bevel(s)), by machining with geometrically non-specific or specific cutting edges. Thus, during so-called centering of optical lenses, it is necessary to distinguish between the actual aligning and clamping process, with which the present invention is primarily concerned, and the subsequent machining of the lens edge.
A general overview of current centering technology practice is provided in this context by the article “Was leisten moderne Zentriermaschinen?” by Dipl.-Ing. (FH) Michael Leitz, published in “Jahrbuch für Optik und Feinmechanik 1999” (Ed.: Dr.-Ing. Wolf-Dieter Prenzel; Fachverlag Schiele & Schön GmbH, Berlin; ISBN 3 7949 0634 9), pages 161 to 175.
The above-mentioned bell clamp process is understood to mean an aligning and clamping process, in which the lens and its optical axis are aligned and clamped automatically relative to the vertically extending axis of rotation of the centering spindles between cup-shaped bell clamps provided on the centering spindles. To this end, the lens is positioned on the bell clamp of the lower centering spindle and the bell clamp of the upper centering spindle is displaced in the axial direction relative to the lower bell clamp until the upper bell clamp also lies with slight pressure against the lens. The lens is then displaced automatically in the transverse direction, as a result of the curvature of its optical surfaces, optionally with the addition of a suitable lubricant and/or rotation of the centering spindles, wherein the bell clamps move closer together. The transverse movement of the lens relative to the bell clamps and the axial relative movement of the bell clamps ends when the lens has assumed a position between the bell clamps which allows the minimum spacing of the bell clamps under the given geometric conditions. The lens, which then has its optical axis aligned relative to the axis of rotation of the centering spindles, is then clamped firmly between the bell clamps by increasing the clamping force and may be machined at the edge. The above-described bell clamp method reaches its limits in the case of lenses with only slightly curved optical surfaces. Below a certain value of the angle, also designated as the centering angle, formed between a tangent to the edge of the one optical surface of the lens at the clamping point (= contact point of the bell clamp) and a tangent to the edge of the other optical surface at the clamping point when viewed in radial section, self-locking arises, which prevents transverse movement of the lens relative to the bell clamps.
A device for centering clamping of optical lenses for edge machining thereof, which is designed to operate according to the above-described bell clamp method, has, inter alia, to the fulfil the following requirements. On the one hand, the axial alignment of the two centering spindles may deviate from one another by at most a few thousandths of a millimeter and must also be maintained during the entire clamping movement, i.e. the relative axial movement of the centering spindles. On the other hand, the clamping movement has to proceed as smoothly or non-jerkily as possible. This applies in particular to the moment at which the lens is caught between the two bell clamps. At this point, jerky movements must be avoided, so that the lens may slip into its optical axis and undergo automatic alignment without the risk of mechanical damage.
DESCRIPTION OF THE PRIOR ART
The prior art is not short of proposals for constructing a device for centering clamping of optical lenses. Thus, a machine for centering edge grinding and bevelling of optical lenses is known from DE 37 44 115 C2, DE 37 44 116 C2 and DE 37 44 118 C2 held by the applicant as signee, which machine comprises in a machine frame two axially aligned centering spindles, which carry bell clamps at their mutually facing ends. The lens may be chucked between the bell clamps for machining purposes by means of a clamping device acting on the axially displaceably guided lower centering spindle. Each of the centering spindles is here arranged in a quill and supported therein by supporting bearings.
In this prior art, the quill of the lower centering spindle is guided in a plurality of air bearings, which are formed in a thin-walled guide sleeve held in the machine frame. The guide sleeve tightly surrounds the quill and is in turn surrounded by a cavity formed in the machine frame and pressurisable by a pressure medium. The quill air bearing system is designed to provide very small forces for aligning the lens, sensitive adjustability of these forces, jerk-free advance of the lower centering spindle and high axial alignment precision of the centering spindles, whereby damage of the optical surfaces of the lens during alignment thereof should be avoided. Once the lens has reached its precise alignment position, the cavity surrounding the guide sleeve is pressurised with high pressure, such that the quill of the lower centering spindle is clamped in its respective position and the disadvantage immanent in the air bearings during machining, namely their low rigidity, which is insufficient to produce a good working result, is countered. However, a disadvantage of this prior art is in particular that smooth-running but nonetheless centred guidance of the quill of the lower centering spindle during alignment of the lens is bought at great cost with regard to apparatus and control systems.
The same is true of the clamping apparatus which, according to this prior art, comprises a plate-like yoke arranged beneath the quill of the lower centering spindle, in which yoke a diaphragm piston/cylinder unit is arranged centrically relative to the lower centering spindle, which piston/cylinder unit acts on the lower end of the lower centering spindle, and to which yoke a double-acting pressure cylinder with a short-stroke and a long-stroke piston is attached on each side of the centering spindle axis.
While the pressure cylinders here generate the stroke, until the long-stroke piston lies against the short-stroke piston, which is required to bring the bell clamps close enough together to leave a slight gap between the upper bell clamp and the lens lying on the lower bell clamp, the diaphragm piston/cylinder unit serves as a precision stroke means for the lens alignment process, by means of which the required clamping force for aligning the lens may be sensitively established.
In addition, DE 31 39 873 A1 discloses a centering device for a machine for edge grinding and bevelling optical lenses, having two centering spindles
Schäfer Erhard
Schäfer Holger
Hail III Joseph J.
Loh Optikmaschinen AG
McAndrews Held & Malloy Ltd.
Thomas David B.
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