Turning – Radially moving rotating tool inside bore – Tool simultaneously moving axially
Reexamination Certificate
1998-12-30
2003-02-25
Tsai, Henry (Department: 3722)
Turning
Radially moving rotating tool inside bore
Tool simultaneously moving axially
C082S011300, C082S118000, C082S133000
Reexamination Certificate
active
06523443
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 invention relates to a method for producing optical surfaces, in particular ophthalmic lenses and shell moulds for producing ophthalmic lenses (in particular aspherical plastic lenses), and to a processing machine for carrying out the method.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98.
Optical surfaces and, in particular, ophthalmic lenses having a complicated geometry, for example continuous vision lenses, can presently be produced from silicate glass or from plastic. As silicate lenses, they are produced by grinding and subsequent polishing. Plastic lenses are produced by casting in a previously fabricated female mould. The female moulds, so-called shell moulds, are produced from silicate glass using the same method as in the fabrication of ophthalmic lenses, that is to say likewise by grinding and polishing.
It is a disadvantage of this mode of procedure that, particularly for the fabrication of ophthalmic lenses, all the required geometrical shapes must be kept in store.
It is also disadvantageous that in the case of multistage fabrication processes, the tolerances of the individual steps can unfavourably affect the end product. Correction strategies are very expensive and complicated. The situation becomes more complicated with each additional process step, since it is mostly possible to establish faults only at the conclusion of the process, and the cause can therefore possibly be located only with difficulty.
U.S. Pat. No. 5,320,006 has already disclosed the turning of the basic mould of plastic lenses on a suitable turning machine and subsequently processing them finally on a polishing machine, the curvature of the polishing tool being measured and used as control variable for the turning tool, in order to produce a blank which is matched as accurately as possible to the polishing tool, and thus to restrict polishing to a minimum. Leaving aside that an expensive polishing operation still remains, only spherical, possibly toroidally shaped spectacle lenses can be produced using this method. Continuous vision lenses have complicated aspherical shapes, and cannot be produced in this way.
It is the object of the invention to specify a method with which it is also possible to fabricate directly optical surfaces of geometrically complicated shape, and in particular ophthalmic lenses and shell moulds for producing ophthalmic lenses in accordance with individual data specification in a single process step, the aim being to necessitate no, or at least only a little, reworking to fabricate the optical surfaces and, in particular, the ophthalmic lenses and shell moulds for producing ophthalmic lenses.
According to the invention, this object is achieved by virtue of the fact that a blank for optical surface treatment or a blank of a shell mould is held on the workpiece support of a spindle axis (Z-axis) of a processing machine and is directly turned to its final shape by means of a turning tool which can execute a relative movement with respect to the blank (X-axis), it being the case that the turning tool can be moved transverse to the direction of tool movement and that during each spindle revolution the turning tool performs incremental infeeds in the direction of the blank or away from the latter in accordance with prescribed or online-calculated data of the surface.
Using the method according to the invention, a tool cutter can be moved so quickly that it is possible to machine out of a plastic blank the changes in height occurring in the circumferential direction, which are caused by the aspherical shape. The cutter can have a very small radius, as a result of which the engagement is virtually punctiform. However, the cutter can also have a radius of several millimeters. It can be fitted with a monocrystalline diamond.
The surface produced is generally already ready for use. Light reworking by polishing may still be required to produce the readiness for use. In this process, the shape is determined entirely by the turning process and is no longer changed by the polishing.
The surface can also be made ready for use by being dipped in lacquer, for example, as an alternative to polishing.
In addition to ophthalmic lenses, the method can also be used to produce shell moulds for producing ophthalmic lenses, for example of metal or ceramic. Here, as well, polishing is only necessary to a very slight extent. It is also possible to produce optical surfaces, for example other lenses or mirrors, having a complicated shape which is not rotationally symmetrical.
It is possible according to the invention advantageously to provide for the reaction force produced during the infeed to be balanced by static or dynamic counterbalancing.
For the purpose of fitting the lenses or mirrors, but in particular the spectacle lenses into the spectacle frame, marks must be provided on the surface which permit quick orientation. These marks, which it has so far been necessary to produce in addition using special diamond tools or with the aid of high-energy laser radiation, can now be directly coproduced during the processing operation, since it is possible to use a tool which works in a punctiform fashion. All the problems of reproducibility such as occur with each change of machine are thereby eliminated. Moreover, any symbols can be produced in a freely programmable fashion. Each lens can thereby be individually marked.
This relates in a similar way to the production of shell moulds, for example, for producing ophthalmic lenses. All the markings for later orientation of the lens and further symbols can be provided in the shell moulds, as well.
According to the invention, it is provided in an advantageous way that the turning tool executes a pivoting movement relative to the spindle. In this case, during turning the blank can additionally be pivoted about a centre point lying on the Z-axis. As an alternative to this, during turning the turning tool can also additionally be pivoted about a centre point lying on the Z-axis.
Since the sagging of the lens material (glass or plastic for lenses or mirrors) requires no quick tool movements, this movement can be replaced either by a slow Z-movement or by a pivoting movement which is superimposed on the quick Z-drive. The quick Z-movement must then have a travel of approximately 1 mm for the production of continuous vision lenses, for example. This mode of procedure has the particular advantage of reducing the region of the turning tool used for shaping. Irregular wear of the turning tool then has smaller effects.
A problem of every turning operation is the singularity in the middle of the workpiece. It can therefore be provided in a preferred way that the blank can be turned in two off-axis positions deviating slightly from the turning centre.
In this case, the blank is processed such that the respective turning centre is reached precisely only by the process in the respective other position. Thus, turning is not performed down to the spindle axis.
In the case of excessively large radial movements, the turning movement at the edge can run off the workpiece. This can be avoided according to the invention by varying the track spacings in the X-direction. This then also requires appropriate dynamics for this feed drive, which can be achieved, for example, by applying harmonic vibrations. Dynamic counterbalancing is also advantageous for this purpose. Dynamic counterbalancing requires that a second movement of a mass of the same size must be carried out with an opposite direction of movement. This colinear movement can be used for simultaneously processing the front and rear sides of, for example, a plastic lens or a second ophthalmic lens and/or a second shell mould for producing ophthalmic lenses. Depending on the surface design and the blank used, the counterbalancing of the two counterrotating quick tools, which is ef
Hof Albrecht
Mehlkopp Klaus
Carl-Zeiss-Stiftung Heidenheim/Brenz
Purdue David C.
Purdue John C.
Tsai Henry
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