EP0281480B1 - Ophthalmic glasses bevelling machines - Google Patents

Description

The present invention relates to automatic machines for grinding and beveling spectacle lenses.

Conventional machines for grinding and beveling ophthalmic lenses include a U-shaped carriage slidingly mounted and oscillating on a fixed horizontal shaft, a second horizontal shaft mounted to rotate perpendicularly between the branches of the U-shaped carriage, formed of two parts between which is clamped the glass to be worked, and a third rotary horizontal shaft carrying the various grinding wheels, to overflow and bevel.

When a blank of a thick rim optical lens has been cut to the shape of the frame, the edge of the lens has a cylindrical shape and a beveling operation must be carried out by guiding the lens to form a bevel of its edge. V-shaped section located between the edges of its periphery, this bevel being intended to be housed in the groove of the bezel of the frame.

The execution of such a bevel with manual control is extremely difficult; the "free bevel" system was used, according to which the edge of the blank is brought into a V-groove in a grinding wheel and the shaft carrying the free glass is allowed to move in translation during the operation of grinding.

However, this system does not provide a completely satisfactory result.

FR-A-2 456 304 describes a machine corresponding to the preamble of claim 1. This known machine comprises a device for measuring the distance between a determined point of the desired contour of an ophthalmic lens and the plane tangent to the pole of the convex surface of this glass.

This device comprises an assembly with two feelers cooperating one with the glass and the other with the template, mounted on the carriage and movable parallel to the axis of the template and the glass, one of the feelers being in contact with the glass surface.

As the glass rotates, the probe in contact with its surface provides an indication of moving an index in front of a graduated index.

In this device, the fact of only palpating a single point of the glass for a given angle thereof makes it necessary to carry out a correction calculation due to the fact that the grinding point moves differently according to the diameter of the grinding wheel and the non-circular shapes of the frames.

The invention therefore aims to achieve an automatic machine for grinding and beveling ophthalmic lenses, of the type comprising a sensor and in which this correction calculation is unnecessary.

The invention also aims to provide a device for making a bevel guided on the edge of an ophthalmic lens, automatically and with great precision.

The subject of the invention is to this end a machine for grinding and beveling ophthalmic lenses of the type comprising a carriage movable in translation and in oscillation parallel and perpendicular to a shaft carrying grinding wheels to be cut and beveled and a feeler in contact with the glass, characterized in that the surface of the probe is formed by the adjacent edges of several juxtaposed mobile or vibrating elements adapted to act on sensors sensitive to their movement when the probe comes into contact with the edge of a blank outline , perpendicular to this slice, to measure the distance L1 between the plane tangent to the pole of the convex face of the glass and the edge of the face, and to measure the value of L2 which corresponds to the thickness of the slice of the glass.

According to one embodiment of the invention, the feeler has a surface whose curvature is identical to that of the grinding wheel.

According to another embodiment, the feeler is arranged next to the grinding wheel, the curvature of its surface being concentric with that of the grinding wheel.

In a variant, the probe is mounted mobile above the grinding wheel, so that it can move perpendicular to the shaft of the grinding wheel between a position high, away from the blank, and a low position in which it is resiliently biased in contact with the edge of the blank.

Advantageously, the feeler consists of three juxtaposed mobile elements.

• La figure 1 est une vue schématique partielle d'une machine à meuler et à biseauter classique à laquelle est appliquée l'invention.
• La figure 2 en est une vue en élévation et en bout.
• La figure 3 est une vue schématique partielle à plus grande échelle montrant le positionnement de la tranche d'une ébauche sur le palpeur et l'agencement d'un mode de réalisation de celui-ci.
• La figure 4 est une vue partielle en élévation et en bout dans le sens de la flèche F de la figure 3.
• La figure 5 est une vue schématique partielle d'une variante dans laquelle le palpeur est monté sur le chariot de la machine.

The description which follows, with reference to the accompanying drawings by way of nonlimiting examples, will make it possible to understand clearly how the invention can be put into practice.

• Figure 1 is a partial schematic view of a conventional grinding and beveling machine to which the invention is applied.
• Figure 2 is an elevational and end view.
• Figure 3 is a partial schematic view on a larger scale showing the positioning of the edge of a blank on the probe and the arrangement of an embodiment thereof.
• FIG. 4 is a partial view in elevation and at the end in the direction of the arrow F in FIG. 3.
• Figure 5 is a partial schematic view of a variant in which the probe is mounted on the carriage of the machine.

Referring to the drawings and more particularly to Figures 1 and 2, a conventional grinding and beveling machine comprises a carriage 1 of U-shape mounted oscillating on a horizontal shaft (not shown) and between the branches of which is mounted a second horizontal shaft 2 in two parts between which is clamped a blank 3 of an ophthalmic lens which has been cut out on a grinding wheel 4 rotatably mounted on a third horizontal shaft 5.

As known per se, the machine comprises a sensor 6 of the angular position of the blank 3 in rotation, and another sensor (not shown) of the position of the carriage 1 in translation parallel to the shaft 2.

In operation, the carriage 1 is lowered to bring the blank 3 into contact with the grinding wheel 4.

According to the invention, the machine comprises a feeler, designated as a whole by the reference 7 having a surface having a curvature identical and concentric to that of the grinding wheel 4, and mounted adjacent to this on a suitable support 8.

The probe 7, the internal arrangement of which is not part of the invention and which can be mechanical, pneumatic, magnetic, electronic or other, has a curved surface formed by the edges of several plates or thin adjacent parallel movable blades 9 mounted in the field, vertically, acting independently on a device 10 sensitive to a pressure exerted on them to provide an electrical signal representative of the number of blades on which this pressure is exerted.

Knowing the thickness of the blades 9, the feeler 7 can therefore provide a measurement of the width of its surface on which the edge of a cut blank 3 brought into contact with it bears by means of a movement of the carriage 1.

If we bring the front edge of the blank 3 in coincidence with the edge of the probe 7 (L1 = 0) and then move it by bringing the plane corresponding to a flat glass to the edge of the probe 7, it provides the measurements of L1 and L2.

By rotating the blank 3 on the probe 7, a series of measurements of L1 and L2 is obtained over the entire periphery of the blank. The corresponding signals stored in a microprocessor then allow very precise control of the motor moving the carriage 1 in translation after having placed the edge of the blank on the beveling wheel 11.

FIGS. 3 and 4 show an embodiment of a feeler 17 comprising three blades 19 mounted to oscillate and acting on three sealed sensors 20. The total width of the feeler corresponds to the maximum total thickness of an ophthalmic lens, ie 20 mm.

The probe is limited by lateral stops 21 to detect the front and rear faces of the blank.

In this embodiment, part of the edge of the blank 3 is always in contact with the central blade 19. A measurement will be taken on the probe of the front face of the blank for a complete revolution thereof. , then we will proceed in the same way for the rear face. The measurements read on the probe will be memorized for each angle read by the angular position sensor 6 of the blank and then used by the microprocessor to control the movements of the carriage in translation for the execution of the bevel on the grinding wheel 11.

In the variant shown in Figure 5, the probe 27 can be mounted on the carriage 1. However, although providing the same result, this variant requires an additional mechanism on the carriage to raise and lower the probe in contact with the blank , making this solution more expensive without providing any particular advantage.

The operating cycle of the machine has been indicated by arrows in FIG. 3, from the end of the trimming of the blank (position A), translation on the probe B, C, D, lifting E, translation on the bevel wheel F and bevel G.

As will be understood by the technicians, it is of course provided for servo-control of the carriage drive in translation in order to position the blank on the probe.

It will also be noted that, since the radius of the probe is identical to that of the grinding wheel, the device takes account of the grinding point and makes it possible to read a theoretically unlimited quantity of measurements over the entire periphery of the glass, thus eliminating the correction calculation.

Finally, it should be emphasized that the invention makes it possible to suppress the production of a free bevel by passing directly from the trimming phase to that of the guided bevel while nevertheless leaving the possibility of producing a free bevel if desired.

Claims (6)

1. A machine for grinding and bevelling ophthalmic lenses, of the type comprising a carriage which can undergo movement of translation and oscillation parallel and perpendicularly to a shaft carrying grinding wheels for routing and bevelling, and a feeler in contact with the lens, characterised in that the surface of the feeler (7, 17) is formed by the adjacent edges of a plurality of juxtaposed movable or vibrating elements (9, 19) which are adapted to act on sensors (10, 20) responsive to their movement when the feeler (7, 17) comes into contact with the peripheral surface of a routed blank (3), perpendicularly to this peripheral surface, so as to measure the distance L1 between the plane tangential to the pole of the convex face of the lens (3) and the edge of the surface, and so as to measure the value of L2 which corresponds to the thickness of the peripheral surface of the lens.

2. A machine according to claim 1, characterised in that the surface of the feeler (7, 17) is of a curvature which is identical to that of the grinding wheel (4, 11).

3. A machine according to claim 2, characterised in that the feeler (7, 17) is disposed adjacent to the grinding wheel (4, 11), the curvature of the surface of the feeler being concentric to that of grinding wheel.

4. A machine according to claim 2, characterised in that the feeler (17) comprises three elements (19) each adapted to act on a sealed sensor (20).

5. A machine according to either of claims 2 or 4, in which the feeler is mounted movably on the carriage (1) of the machine, characterised in that the feeler (27) is able to move perpendicularly to the shaft (5) of the grinding wheel (4, 11) between an upper position, remote from the blank (3), and a lower position in which it is urged elastically into contact with the peripheral surface of the blank.

6. A machine according to any one of claims 1 to 5, characterised in that the sensors are mechanical, magnetic or electronic with variable resistivity.

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