Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-10-07
2001-06-26
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S041000
Reexamination Certificate
active
06250993
ABSTRACT:
The invention concerns a method for finishing spectacle lenses after first cutting thereof, of the kind in which, for the purpose of a further passage of the spectacle lens through a grinding machine, a holding block is fitted to it for holding it in place on the grinding machine. A method of this kind is conventionally used by opticians for accurate fitting of a lens to a spectacle frame of their client. The invention also concerns the related device.
Spectacle lenses are made in the form of substantially circular blanks providing a particular optical correction. They are then cut by the manufacturer or the optician to the shape of the spectacle frames selected by the client. Clearly the cutting must be done allowing for the shape of the frame and for the position of the eyes of the user. The optical centre of the lens must be correctly placed in front of the eye for the required correction of vision to be obtained.
Usually, the first cut is made slightly outside the required final cut and the lens must then be finished to fit it perfectly to the frame, in particular in the case of metal frames.
The optician then has to perform the finishing cut on the lens subject to the same shape and optical centre constraints and within a time interval that is naturally limited by the desire of the client to collect their spectacles quickly.
In standard practice the lens is usually removed from its first cutting support for a trial fit of the lens to the frame and any defect is noted only at this time. Also, it is increasingly common for the optician not to cut the lens directly, but to transmit the measurements corresponding to a frame and a client to the lens manufacturer, who delivers the lens cut to size and bevelled and demounted from its cutting support, and in this case the lens may then require further finishing.
Two finishing methods are employed at present. The first consists in finishing trial and error by the optician, who recuts all or part of the contour of the lens, with the obvious drawbacks of lack of precision of the shape or partial offsetting of the optical centre relative to the eye of the user.
The second method uses an automated machine which requires of the optician precise orientation of the lens axes and positioning of the lens centre, followed by fitting the holding block to the lens at a precise point, allowing for the position of the eye of the user. The optician then uses a mechanical or digital contour reading device to read off the required final shape of the lens, corresponding to the client's frame. The contour reading device then controls the grinding of the lens to the required final shape when placed on the grinding machine with the holding block fitted to it. This method is complex and time consuming and any positioning error manifests itself in the final shape of the lens only after grinding.
The invention is directed to a spectacle lens finishing method that is quick to use and which finishes the lens precisely.
To this end the invention proposes a method of finishing a spectacle lens after first cutting thereof, of the kind in which, for a further passage of the spectacle lens through a grinding machine, a holding block is fitted to it for holding it in place on the grinding machine, characterized in that the block is fitted at any point of the spectacle lens, preferably close to its centre, the contour of the spectacle lens is read to provide a read shape for the spectacle lens, and the grinding machine is operated in accordance with the difference between the read shape and the required final shape.
In the above method, the read shape is preferably compared to the required final shape and a grinding function is established allowing for the difference between the read shape and the final shape and the grinding machine is controlled accordingly.
Clearly the above method can compensate an offset position of the block on the lens by the optician, thanks to reading the shape, which provides a reference for its own grinding, instead of using the centre of the lens as the reference as in the prior art, as this would then have to be determined precisely, as already pointed out.
The invention is also directed to a device for implementing a method as described above including means for comparing two shapes and means for establishing a grinding function allowing for the difference between the two shapes.
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Banks Derris H.
Essilor International (Compagnie Generale d'Optique)
Young & Thompson
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