Abrading – Precision device or process - or with condition responsive... – Computer controlled
Patent
1996-11-19
1999-08-10
Scherbel, David A.
Abrading
Precision device or process - or with condition responsive...
Computer controlled
451 41, B24B 4900, B24B 5100
Patent
active
059349727
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for NC-controlled grinding of the circumferential edge and top facet of an ophthalmic lens in accordance with the shape of a selected lens mount and the personal optometric data of the lens wearer.
For aesthetic reasons, the top facet on the circumferential edge of a finished ophthalmic lens should have the same distance from the leading edge of the lens all around the circumference of the lens, even if the ophthalmic lens has a shape that differs sharply from the circular.
If the front of the ophthalmic lens is purely spherical, a top facet made with a constant distance from the leading edge of the ophthalmic lens also lies on a spherical surface with the same midpoint as the spherical surface of the front surface of the ophthalmic lens. If an ophthalmic lens is produced by copy grinding according to a pattern disk corresponding to the lens mount, a constant distance of the top facet from the front surface of the ophthalmic lens can be achieved either by resting a feeler on the front surface of the lens mount and controlling the relative displacement of a grinding wheel relative to the ophthalmic lens in the axial direction, or by producing the axial displacement by means of a so-called Panhard rod, whose length corresponds to the radius of the spherical front surface of the ophthalmic lens less the distance of the top facet from the leading edge of the ophthalmic lens.
In NC-controlled grinding of the circumferential edge and top facet of an ophthalmic lens, the shape of the ophthalmic lens and the personal optometric data of the ophthalmic lens wearer are available in the form of a volume of data by which the ophthalmic lens edge grinding machine can be controlled in such fashion that an ophthalmic lens blank is ground in accordance with the shape of the selected lens mount and the top facet is placed on the circumferential edge of the ground ophthalmic lens in such fashion that it extends around the entire circumference at the circumferential edge and/or maintains a certain distance from the leading edge of the ground ophthalmic lens.
In order to acquire the data relating to the shape of the lens mount, it is known that the lens mount can be placed in a device for scanning the facet groove and recording the data in three-dimensional form. It should be noted in this regard that the facet groove in a lens mount, as a result of manufacturing tolerances or deviations in shape, need not necessarily lie on a spherical surface.
A device for three-dimensional scanning of lens mounts is described in German Utility Model G8608291.4 of the Applicant.
In German Offenlegungsschrift 3410040 an NC-controlled ophthalmic lens edge grinding machine is also described. The outer and inner surfaces of an ophthalmic lens blank which is clamped in the ophthalmic lens edge grinding machine are scanned on a curve that matches the shape of the ophthalmic lens. Two spring-mounted rod-shaped feelers constantly rest directly on the glass and their axial position is fed to potentiometers the values and data collected by these potentiometers are transmitted to a computer or a data storage device that uses them to calculate the spatial pattern of the leading and trailing edges of the ophthalmic lens as well as the respective thickness of the glass. From a stored volume of data on different top facets, the computer selects the top facet that can be provided on the circumferential edge of the finished ophthalmic lens without leaving the circumferential edge at any point.
When an ophthalmic lens is measured using this method or a method described in German Patent 3842601 of the Applicant, in which the leading and trailing edges of a pre-ground ophthalmic lens are measured by a scanning head, deviations of the ophthalmic lens from the spherical shape enter into the measurement. Such deviations can result from prismatic or cylindrical grinding superimposed on spherical grinding and also from the location of a near portion. In addition, the decentration of the optical axis of t
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JP,A,05 212661 (Nidek Co Ltd) Aug. 24, 1993 siehe Zusammenfassung.
Banks Derris Holt
Scherbel David A.
Wernicke & Co. GmbH
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