Geometrical instruments – Gauge – Template
Reexamination Certificate
1999-10-19
2001-12-11
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Gauge
Template
C033S504000, C033S028000, C033S613000, C033S645000, C033S533000, C033S626000
Reexamination Certificate
active
06327790
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally concerned with the calibration that has to be carried out when starting up an ophthalmic lens grinding machine in order to determine with all the required accuracy, relative to its general reference system of axes, various parameters relating to the machining tools that can be used therein, and in particular the position of a machining tool in the reference system of axes, given that the calibration can, and even must, be repeated periodically, in particular when changing or sharpening the machining tool.
The present invention is more particularly directed to the situation in which the grinding machine to be calibrated includes a swing-arm which pivots on a frame, a lens-holder shaft which rotates on the swing-arm about a rotation axis parallel to the pivot axis of the swing-arm, and a tool-holder shaft which is carried by the frame at a distance from the pivot axis of the swing-arm and on which a machining tool can be mounted.
2. Description of the Prior Art
U.S. Pat. No. 5,806,198 proposes substituting a calibration template for a lens on the lens-holder shaft in order to carry out the required calibration, performing an approach phase during which the swing-arm, equipped in this way with a calibration template of this kind, is moved toward the tool-holder shaft, which is equipped with the machining tool whose co-ordinates are to be determined, and having interruption of the approach phase commanded by a sensor provided for this purpose and responsive to contact between the swing-arm and a component, usually referred to as the drive link, which during the machining of a lens drives the swing-arm in accordance with the machining to be effected, providing a support for the swing-arm when sufficient material has been removed.
The above arrangements have proved satisfactory and may continue to do so.
They nevertheless have the following drawbacks.
Firstly, detection occurs at a distance from the lens-holder shaft and from the tool-holder shaft with a lever arm that is less than that of the two shafts, which is detrimental to the accuracy of the results obtained.
Also, and most importantly, once detection has occurred the full weight of the swing-arm rests on the machining tool.
Although some machining tools are able to support a weight of this magnitude without deformation, and this is in fact the case for a grinding wheel, it is not necessarily the case for all possible machining tools.
To be more precise, it has now been proposed to use a relatively fragile machining tool on at least some grinding machines, namely a grooving tool to be used when it is necessary to machine a groove into the edge of a lens.
This is the case in particular with lenses to be mounted in spectacle frames, like those sold under the tradename “Nylor”, in which each circle or surround includes a rigid part and a filament which extends from one end of the rigid part to the other.
The grooving tool is usually on a secondary tool-holder shaft separate from and parallel to the main tool-holder shaft carrying one or more grinding wheels, the secondary tool-holder shaft being a simple spindle, for example, extending cantilever fashion from a retractable dedicated frame.
The grooving tool is usually a simple, relatively thin and narrow grinding wheel.
During the approach phase of the calibration process, the weight of the swing-arm resting on a grooving wheel of the above kind would inevitably cause unwanted and unacceptable deformation of the grooving wheel.
A general object of the present invention is an arrangement which avoids the above drawbacks and which in particular prevents deformation of a grooving wheel when calibrating it.
SUMMARY OF THE INVENTION
To be more precise, the present invention consists in a method of calibrating a grinding machine including a swing-arm mounted to pivot on a frame, a lens-holder shaft mounted to rotate on said swing-arm about a rotation axis parallel to the pivot axis of said swing-arm and on which a calibration template can be mounted, and a tool-holder shaft mounted to rotate on said frame at a distance from said pivot axis of said swing-arm and on which a machining tool can be mounted, the method including an approach phase during which said swing-arm, fitted with a calibration template, is moved toward said tool-holder shaft, which is equipped with a machining tool, and in which method said approach phase is interrupted as soon as contact is detected between said calibration template and said machining tool.
Thus, in accordance with the invention, contact is no longer detected between the swing-arm and the drive link driving it, but directly between the calibration template and the machining tool, without the intervention of any lever arm whatsoever, and therefore to the benefit of the accuracy of the results obtained.
In a preferred embodiment of the invention, at least the surface of said machining tool is electrically conductive and said calibration template has at least on its surface at least one electrically insulated conductive part which is electrically connected to an operating circuit, and interruption of said approach phase is conditional on detection by said operating circuit of a current flowing between said conductive part of said calibration template and said machining tool.
For example, the approach phase is preferably interrupted as soon as the current detected by the operating circuit reaches a particular threshold.
Be this as it may, the electrical detection approach has the advantage of avoiding excessive mechanical contact between the grooving tool and the calibration template likely to lead to deformation thereof.
The calibration template preferably used to implement the method of the invention includes at least one electrically insulated conductive part which can be electrically connected to an operating circuit of any kind.
A calibration template of the above kind and the corresponding calibration method can be suitable with equal advantage for calibrating a grinding wheel and for calibrating a grooving wheel.
When, as is usually the case, the axis of the tool-holder shaft on which the grooving wheel is mounted is inclined relative to the axis of the lens-holder shaft, the calibration template of the invention preferably has at least two conductive parts which are insulated from each other and each of which includes at least one contact face forming a dihedron with said contact face of the other one, and after contact has been detected between said contact face of one of said conductive parts of said calibration template and said machining tool, contact is equally caused to be established between said machining tool and the corresponding contact face of the other conductive part of said calibration template.
The calibration template of the invention therefore determines not only the position of the grooving wheel in the system of axes of the grinding machine but also the diameter of the grooving wheel even though, given the inclination of the grooving wheel, it physically senses only an elliptical contour of the grooving wheel.
To this end it exploits the geometrical relationship between the elliptical contour and the real circular contour of the grooving wheel.
The features and advantages of the invention will emerge from the following description which is given by way of example and with reference to the accompanying diagrammatic drawings.
REFERENCES:
patent: 4829715 (1989-05-01), Langlois et al.
patent: 5683288 (1997-11-01), Kujawa
patent: 5806198 (1998-09-01), Guillermin
patent: 6071176 (2000-06-01), Kruis
Essilor International (Compagnie Generale d'Optique)
Guadalupe Yaritza
Gutierrez Diego
Young & Thompson
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