EP2384854A2 - Polishing tool for machining optical surfaces, in particular free form surfaces - Google Patents

Abstract

The tool (22) has a flexible layer (26) arranged between a polishing sheet (28) and a carrier body (24), where an edge region of the polishing sheet is limited by a base circle (46) in radial direction (40). Edge elements (48) outwardly approximately extend about 4 mm from the base circle in the radial direction and are formed as teeth, where contour of each edge element ends in an end point (54). An active surface (29) of the polishing sheet outwardly and continuously decreases up to zero in the edge region of the sheet in the radial direction.

Description

The present invention relates to a polishing tool for processing an optical surface of a spectacle lens, comprising a carrier body and a polishing foil, wherein an elastic layer is arranged between the polishing foil and the carrier body.

Furthermore, the present invention relates to a device for processing optical surfaces with such a polishing tool.

Such polishing tools and devices are for example from the document WO 2005/068133 A1 known.

Spectacle lenses are conventionally produced from a semi-finished product by machining or abrasive processing of the so-called prescription surface or surfaces. This is the optically relevant design of the lens fixed. Finally, the lens is still polished, but by polishing no change in the optical properties of the lens may be effected.

For polishing a surface of a spectacle lens, a polishing head is usually used which has a polishing tool whose polishing surface is at least approximately adapted to a shape of the surface of the spectacle lens to be polished. The polishing tool and / or the spectacle gas are articulated, in particular with a ball joint, mounted, and are guided relative to one another with a predetermined sequence of movements, usually with the aid of CNC-controlled systems.

When polishing spherical or toric spectacle lenses, it is less problematic due to the relatively simple shape of the surface to be polished to find a suitable, complementary formed polishing tool that can be performed with simple movements over the surface and does not cause undue deformation. Due to the large number of possible spherical or toric spectacle lenses, it is only necessary to have a corresponding multiplicity of polishing tools available.

Such polishing tools are for example from the publications DE 101 00 860 A1 . EP 0 567 894 B1 . DE 44 42 181 A1 . DE 102 42 422 or DE 101 06 007 A1 known.

Common to these polishing tools is that a compressive rigidity running in a radial direction of the polishing tool is either constant from the inside to the outside or slightly decreases. The bending rigidity of the polishing tool thus decreases from the inside to the outside in a direction in which a force is applied to the spectacle lens by the polishing tool or is constant.

For spherical and toric, ie simply shaped, surfaces this is sufficient. When polishing so-called free-form surfaces or aspherical or point-symmetrical, arbitrarily shaped surfaces, such polishing tools, however, can not be used without problems.

Aspherical or point-symmetric surfaces and free-form surfaces have curvatures that change over the surface. In particular, such free-form surfaces are used in individual lenses adapted to a user. The polishing tool moves during the polishing processing of such free-form surfaces at least over a part of this irregularly curved surface. The polishing tool must therefore be able to adapt to the respective local curvature with its bending stiffness or elasticity, in such a way that the polishing pressure over the contact surface is as constant as possible. Only then is there a definable constant removal and the polished surface is evenly polished. If this is not guaranteed, the surface or the topography of the free-form surface will be deformed and its optical quality will be worsened.

For mass polishing of freeform surfaces and also of spherical or toric spectacle lenses made of plastic materials inexpensive and simply built polishing tools are used according to the currently known state of the art. The plastic materials of the spectacle lenses are, for example, a polycarbonate, such as CR 39, which is marketed by PPG Industries, Pittsburgh, USA. The polishing tools usually consist of an at least three-layered construction. The polishing tools have at least one of the tool spindle rotating the tool spindle facing solid base on which a foam layer or other elastic layer is glued or attached. In turn, a polishing foil facing the spectacle lens or workpiece is provided on this foam layer. Due to the elastic deformability of the foam layer, the polishing film can adapt to a certain degree of topography of the lens surface to be polished. To the adaptability of the polishing surface of the polishing tool to the surface of the spectacle lens To assist, the polishing tools are generally smaller than the lens. The polishing removal comes about with the aid of an abrasive polishing liquid by the relative movement of the pressurized polishing tool.

An example of such a polishing tool, which also allows the application of a polishing liquid, is in the document DE 10 2005 010 583 A1 specified.

For a high-quality polishing tool from an optical point of view, it is important that the polishing force applied by the tool to the glass decreases outwardly in the edge area of the polishing surface of the polishing tool, ideally to zero continuously. If this is not sufficiently ensured, visible on the polished glass, caused by the edge of the polishing tool spiral structures that deteriorate the quality of the lens surface and make it even unusable.

As a solution to this, it has been proposed in the prior art, for example, form foam layers with lower hardness in the edge region, such as by increasing the material thickness, and alternatively or cumulatively to let the polishing film over the edge of the foam layer. An example of such a solution can be found for example in the document EP 1 644 160 B1 ,

With this proposed solution, however, the objective of a strong decreasing polishing force in the edge region of the tool can not be sufficiently fulfilled. As a result, depending on the choice of polishing parameters, cosmetic defects still occur on the spectacle lens. Depending on a quality requirement for the spectacle lenses to be manufactured, these errors on the optical surface are tolerated or not. These problems are compounded by material fatigue with continued use of the polishing tool. Tires the material in the zone of greatest stress, in the solutions described above between Center and edge is increased, in turn, the polishing power in the edge zone and causes increased the undesirable effect.

Another observed effect is that after repeated use of the polishing tool, the polishing sheet curls and sets in the direction of the glass surface, which can cause polishing defects. This can be done by diffusing liquid polishing agent into the edge region of the polishing film and the resulting swelling of the porous material. Cosmetic defects can also be caused by peripherally embedded and firmly dried polishing agent.

As a further approach, it has been proposed to use a polishing film with a lower material thickness and resulting lower mechanical stability.

Ultimately, however, this solution only allows material thicknesses that preclude a requirement for high resistance and a long service life of the polishing film. For a high efficiency of the polishing process and a high resistance to mechanical wear sufficiently stable polishing films are needed.

Finally, polishing tools with different, pneumatically actuated pressure zones have also been proposed. Ultimately, however, these polishing tools require a structurally complex construction, which in turn is expensive and maintenance-prone. Furthermore, the pressure zones can not be arbitrarily finely resolved, so that, in particular, in critical marginal areas, despite everything, there is often insufficient control over the pressure conditions. An example of such an approach can be found in the document US 2006/0094341 A1 ,

It is therefore an object of the present invention to provide a polishing tool for the improved processing of optical surfaces, in particular free-form surfaces available.

Therefore, it is proposed to further develop the above-mentioned polishing tool in such a way that an area of the polishing foil which acts during the machining decreases in an edge region of the polishing foil in the radial direction towards the outside.

In this way it is possible to influence the force acting on the optical surface in the edge region. Although the pressure applied to the optical surface is also substantially constant in the edge region, the force acting toward the outside reduces the force acting toward the outside, too. Furthermore, the bending stiffness of the polishing film and thus of the polishing tool can be reduced to the outside by the decreasing acting surface. This effect can be implemented particularly effectively with a polishing film projecting beyond the elastic layer in the radial direction, since the bending stiffness of the polishing tool is then determined solely by the polishing film radially outward of the elastic layer.

In this way, the material removal generated under the polishing film can be selectively influenced in the edge region and reduced to nearly zero at the edge.

As will be explained below, such a design of the edge region also leads to a substantially increased circumferential length of a contour of the polishing tool. This allows a more intensive exchange of liquid polishing agent between the optical surface and the polishing film during the polishing process. As a result, an advantageous stabilization of the lubrication is achieved.

An "optical surface" is to be understood as meaning all optical surfaces of spectacle lenses, in particular aspheric surfaces or free-form surfaces. In principle, however, the optical surface may be spherical and toric surfaces, point-symmetrical aspheres or free-form surfaces. The optical surface can be curved both convexly and concavely. The polishing tool can also be used both for the processing of plastic spectacle lenses and mineral spectacle lenses.

The term "polishing film" is understood to mean the element of the polishing tool acting on the optical surface, i. That part or that element of the polishing tool which comes into contact with the optical surface, optionally with the aid of a liquid polishing agent. The term "polishing film" is in no way limiting, in particular with regard to the thickness or another embodiment of the polishing film or a polishing element to understand.

According to a further aspect, an apparatus for polishing optical surfaces with a polishing tool described above is proposed.

The device therefore has the same advantages as the polishing tool.

The object initially posed is thus completely solved.

In one embodiment, it can be provided that the surface of the polishing film which acts during the processing decreases steadily outward in the radial direction to the outside in the edge region of the polishing foil to zero.

In the context of this description, the term "edge region" is to be understood as meaning that region of the polishing tool in which the edge elements are provided, as will be explained in detail below. In the border area is the polishing tool is not formed over the entire surface, but has interruptions of the acting surface between the edge elements. In relative terms, the width of the edge region may be about 5% -20% of the outside diameter of the polishing tool. The dimensioning of the edge area will also be discussed in more detail below.

In this way, a uniform drop of the acting surface in the radial direction can be effected to the outside. Of course, it is not absolutely necessary that the acting surface decreases steadily towards the outside. It can also be provided areas in which the acting surface remains constant or decreases abruptly.

In particular, it should be provided that a continuous transition to zero is provided on an outer edge of the polishing tool, that is, no sudden drop of the acting surface is provided to zero.

It can be provided that the polishing tool is configured to apply a force to the optical surface to be processed in a certain direction, wherein a flexural rigidity of the polishing tool decreases in the specific direction in the radial direction towards the outside. The "certain direction" is normal to the acting surface of the polishing film.

In this way, the force distribution in the edge region can be further adjusted. In particular, it is thus possible to further decrease the force acting on the optical surface to the outside. However, it is not absolutely necessary that the flexural rigidity of the polishing tool decreases in the certain direction toward the outside. For example, it can merely be provided that a side of the polishing foil facing the optical surface is only partially reset.

In this way, although the acting area can be reduced because the recessed portion of the surface of the polishing sheet facing the optical surface does not contact the optical surface, the mechanical strength or bending rigidity can be substantially maintained. If complete openings of the polishing foil and also of the elastic layer and of the carrier body are provided, it is possible, for example, both to reduce the effective area and to reduce the bending stiffness.

In an embodiment it can be provided that the edge region is bounded in the radial direction on the inside by a base circle.

In this way, the basic form of the polishing tool is a circular shape. Inside the base circle, the polishing tool can be formed over its entire surface. Alternatively, however, there may also be recesses, in particular star-shaped slots pointing away from the center of the base circle, in order to increase the elasticity of the polishing tool towards the outside. For example, six slots each about 1.5 mm to 2.0 mm wide may be provided.

Furthermore, it can be provided that extends from the base circle a plurality of edge elements in the radial direction to the outside.

By means of the edge elements, it is possible in a simple manner to implement the demand for a decreasing in the radial direction outwardly acting surface of the polishing film. In particular, it is possible to form the edge elements by corresponding recesses from the polishing foil, the elastic layer and the carrier body, for example by machining.

In particular, it may be provided that a contour of each edge element ends radially outward in an end point.

In this way, it can be implemented particularly simply that the polishing foil steadily decreases to zero in the radial direction towards the outside.

This criterion is fulfilled for edge elements that terminate radially outward at an endpoint. Advantageously, it should not be provided that an edge element ends radially outwardly in more than one point, that is, for example, in a head line or the like. This reduces the advantageous effect achieved according to the invention.

Furthermore, it can be provided that the edge region is bounded in the radial direction on the outside by a tip circle, wherein the end point of at least one edge element lies on the tip circle.

In particular, it may be provided that the end point of each edge element lies on the top circle.

The edge elements can thus protrude equally far or differently far from the base circle radially outwards. This technically simplest solution results when the edge elements are formed such that their end points are all on the top circle.

It can of course also be provided that some shorter edge elements are provided between longer edge elements, so that the end points are not all located on the top circle, but also end points are arranged within the edge region, that is between the base circle and the top circle.

It can be provided in particular that the edge elements extend in the radial direction at least two millimeters, in particular about four millimeters.

This distance then corresponds to the difference between the radius of the top circle and the radius of the base circle. In relative terms, this difference of the radius of the top circle and base circle can correspond to about 5 to 20% of the radius of the top circle, in particular about 10 to 15%.

It can be provided that flanks of the edge elements are formed as teeth.

Furthermore, it can be provided that the edge elements are formed as involutes.

Thus arise for the edge elements shapes, which are known for example from the production of pinions. Accordingly, the production engineering measures known there can also be easily adapted. Furthermore, with regard to the meaning of the terms "tooth", "flank" and "involute" is based on the understanding of the average person skilled in the field of gears or pinions.

To produce the desired contours of the polishing film, for example, a conventional cutting device, such as a CNC-controlled water or laser beam cutting machines, or a corresponding punching device may be provided. Alternatively, abrasive production measures are conceivable.

It may be provided that an angle between mutually adjacent flanks of two adjacent edge elements between about 5 ° and 180 °, in particular 40 ° and 150 °, in particular 70 ° and 120 °, is, in particular, the angle 10 °, 15 °, 20 °, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170 and 175 degrees.

In the extreme case that the angle between adjacent flanks of two adjacent edge elements is 180 °, a square can accordingly result as a contour of the polishing tool. Correspondingly, the base circle forms an inner circle drawn in the square, the head circle forms an outer circle of the square drawn through the corners of the square. There are then four border areas.

Furthermore, it can be provided that a composite contour of the edge elements in the circumferential direction can be described as a sinusoidal function. Alternatively, of course, any other regularly or irregularly curved contour can be provided such that the surface acting during machining decreases in the radial direction to the outside.

It is therefore not absolutely necessary that the edge elements are formed, for example, as serrations or teeth and an angle is arranged between the flanks. It may also be that a sinusoidal function results for the contour in the circumferential direction, that is, the contour is wave-shaped. The amplitude and the frequency of the contour can be adjusted to achieve a corresponding distribution of the acting surface. For the amplitude, what has been said for the radial extent of the edge elements can be considered, i. a double amplitude may be about 5% to about 20% of the radius of the top circle. The frequency may be chosen such that the descriptive sine function over the circumference, more than two, in particular three to fifteen, in particular five to ten, in particular two, three, four, five, six, seven, eight, nine, ten, fifteen, performs twenty or more oscillations.

In particular, it can be provided that the polishing tool is designed to process freeform surfaces.

In the processing of free-form surfaces, the advantages according to the invention come into play in particular. One for the processing of freeform surfaces provided polishing tool is characterized by a sufficient adaptability to the lens. This is achieved on the one hand by an elastic construction and on the other hand by a diameter suitable for the spectacle lens and a curvature of the tool adapted to the polished surface.

In all of the above embodiments, an outer diameter of the polishing tool, i. a diameter of the top circle, about 40 mm to about 60mm, in particular about 45 mm to 50 mm. In this case, a diameter of the elastic layer may be formed smaller than a diameter of the polishing sheet, i. the polishing sheet protrudes outside over an edge of the elastic layer. For example, an outer diameter of the elastic layer may be 40 mm and an outer diameter of the polishing film 45 mm. The outer diameter of the polishing tool is usually selected such that a ratio of the outer diameter of the polishing tool to an outer diameter of the spectacle lens is about 0.5 to 1.0. However, the ratio may be greater than 1.0.

A thickness of the elastic layer in an axial direction may in all embodiments be about 6 mm to about 12 mm, in particular 8 mm. An axial thickness of the polishing sheet is from about 0.5 mm to about 2.0 mm, with prepreg polishing sheets being rather thin, i. about 0.5 to 0.8 mm, and polishing films for fine polishing are made rather thick, i. about 1.2 to 1.8 mm.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Figur 1

eine Ausführungsform einer Vorrichtung zum Polieren von optischen Flächen in einer schematischen Querschnittsansicht,

Figur 2

eine erste Ausführungsform eines Polierwerkzeugs,

Figur 3

eine zweite Ausführungsform eines Polierwerkzeugs, und

Figur 4

eine dritte Ausführungsform eines Polierwerkzeugs.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it:

FIG. 1

an embodiment of an apparatus for polishing optical surfaces in a schematic cross-sectional view,

FIG. 2

a first embodiment of a polishing tool,

FIG. 3

a second embodiment of a polishing tool, and

FIG. 4

a third embodiment of a polishing tool.

Fig. 1 shows a reference numeral 10 generally indicates a device for processing a spectacle lens 12. It is understood that the application of a spectacle lens is to be understood in the following only by way of example. Of course, the advantages of this device can also be used for polishing other optical components with spherical as well as aspheric or toric optical surfaces or free-form surfaces.

The spectacle lens 12 is held in a holder 14. The holder 14 may be arranged fixed in space about a first axis 15 around.

The spectacle lens 12 has a rear surface 16 and a front surface 18. In the present case, the rear surface 16 is designed as a prescription surface, that is to say as the surface which is optically processed in a predetermined manner and, in particular, is designed as a free-form surface. Of course, it may additionally be provided that in addition the front surface 18 is provided with an optical effect, for example with a predetermined addition.

It is a polishing head 20 is provided, which has a polishing tool 22 at its free end. The polishing tool 22 has a carrier body 24, an elastic layer 26 and a polishing foil 28. The elastic layer 26 is provided between the substantially rigid carrier body 24 and the polishing film 28. The elastic layer 26 may, for example, radially outwardly in increase in thickness to provide increasing elasticity at their outer ends.

In addition, openings (not shown) may be provided in the elastic layer 26 and the polishing sheet 28 to apply a polishing liquid or a polishing agent to the optical surface 16.

Accordingly, an operative surface 29 of the polishing film 28 is in sliding contact with the optical surface 16 of the spectacle lens 12.

The carrier body 24 has a ball socket 30, in which a ball head 32 of an actuator 34 is arranged. The actuator causes the polishing tool 22 to rotate about a second axis 36 and also to pivot about the ball head 32. A rotational speed about the second axis 36 is usually about 1200 to 1500 revolutions per minute, but in individual cases it can also be lower or higher. Instead of a ball joint may alternatively be provided a universal joint, possibly in combination with a surrounding bellows or a similar element. In addition to rotation about the second axis 36, movement about the first axis 15 is provided so that the optical surface 16 is completely swept and polished. An axial mobility of the polishing tool depends on a tool holder (not shown) and may, for example, be about 2 to about 5 mm in a tool holder with a bellows.

The elastic layer 26 is preferably made of rubber or rubber. But it can be made of a polyurethane material, such as polyurethane or polyetherurethane. Such materials are known and available, for example, under the trade names Sylomer, Sylodyn and Sylodamp. An elastic modulus of the elastic layer should be greater than 0.02 N / mm ² .

In addition to the illustrated central arrangement of the second axis 36 relative to the polishing tool 22 may also be an eccentric arrangement the second axis relative to the polishing tool 22 may be provided to cause an additional rotational movement of the polishing tool on the spectacle lens 12.

Possible embodiments of the polishing tool 22 will now be explained in detail with reference to the following figures.

Fig. 2 shows a first embodiment of a polishing tool 22. The polishing tool comprises in a conventional manner the carrier body 24, the elastic layer 26 and the polishing film 28, as already in Fig. 1 is shown.

In a schematic top view of the course of a contour 38 of the polishing tool 22 is shown. A radial direction is denoted by a reference numeral 40, a circumferential direction is denoted by a reference numeral 42.

In the illustrated embodiment, it is provided that the composite contour 38 in the circumferential direction 42 can be described as a sinusoidal function.

The contour 38 extends between a tip circle 44 and a base circle 46, which together define an edge region 47. The edge region 47 thus indicates the region of the polishing tool 22 in which the acting surface 29 of the polishing tool 22 decreases in the radial direction 40 to the outside.

In other words, the acting surface 29 is completely closed within the base circle 46 in the illustrated embodiment, that is, the acting surface 29 is provided over a complete arc angle of 360 °. If one moves from the base circle 46 in the radial direction 40 outwards to the tip circle 44 and determines the composite arc angle of the acting surface 29, the acting surface 29 or the composite arc angle increasingly decreases in the direction of the tip circle 44 and approaches zero.

The structural design of the acting surface 29 is realized by means of several edge elements 48. Due to the sinusoidal contour 38, the edge elements 48 correspondingly have a wave-shaped course. For the edge elements 48 thus results in a marked with the reference numeral 50 double amplitude and designated by the reference numeral 52 frequency.

The edge elements 48 are each only with an end point 54 on the top circle 44. This ensures that the acting surface 29 does not abruptly drops to zero on the top circle, but steadily strives towards zero.

Fig. 3 shows another possible embodiment of the polishing tool 22. In this embodiment, the edge elements 48 are formed as teeth, so that the polishing tool 22 results in a shape similar to a pinion.

Each edge element 48 or each point also has an end point 54, all of which lie on the top circle 44. Adjacent tooth flanks 56, 57 of two edge elements 48 enclose an angle 58. This angle can be between about 5 ° and 180 °, in the case shown it is about 80 °.

Except the in Fig. 3 Of course, all other forms of teeth, such as involute, are conceivable, as they are known from the production of pinions. However, it should be provided in particular that the selected shapes of the edge elements 48 end radially outward in an end point 54, but this is not mandatory. Preferably, the end points 54 all lie on the top circle 44.

Fig. 4 shows a further embodiment, which is a special case of in Fig. 3 shown embodiment. In the in Fig. 4 As shown, the angle 58 is exactly 180 °. For the contour 38 of the polishing tool 22 thus results in the present case a square shape. The base circle 46 in this case forms an inner circle of the square and the tip circle 44 through the corners of the square extending outer circle. The corners of the square then form the end points 54 which lie on the top circle 44. Already this contour 38 of the polishing tool 22 or the acting surface 29 of the polishing tool 22 can provide the advantages according to the invention and significantly improve the cosmetic quality of polished free-form surfaces.

Claims (13)

Polishing tool (22) for processing an optical surface (18) of a spectacle lens (12), comprising a carrier body (24) and a polishing foil (28), wherein between the polishing foil (28) and the carrier body (24) an elastic layer (26) is arranged, wherein an edge region (47) of the polishing film (28) in the radial direction (40) inside of a base circle (46) is limited, wherein from the base circle (46) has a plurality of edge elements (48) in the radial direction (40 ) extends to the outside, characterized in that a working during working surface (29) of the polishing film (28) in the edge region (47) of the polishing film (28) in the radial direction (40) decreases towards the outside, wherein during processing acting surface (29) of the polishing film (28) in the edge region (47) of the polishing film (28) in the radial direction (40) towards the outside steadily decreases to zero. A polishing tool according to claim 1, characterized in that the polishing tool (22) is provided to apply a force in a certain direction (36) to the optical surface (18) to be machined and a flexural rigidity of the polishing tool (22) in the specific direction (36) decreases in the radial direction (40) to the outside. Polishing tool according to claim 1 or 2, characterized in that a contour (38) of each edge element (48) ends radially outward in an end point (54). Polishing tool according to one of claims 1 to 3, characterized in that the edge region (47) in the radial direction (40) on the outside of a head circle (44) is limited, wherein the end point (54) of at least one edge element (48) on the top circle ( 44). Polishing tool according to claim 4, characterized in that the end point (54) of each edge element (48) lies on the top circle (44). Polishing tool according to one of claims 1 to 5, characterized in that the edge elements (48) extend in the radial direction at least 2 mm, in particular about 4 mm. Polishing tool according to one of claims 1 to 6, characterized in that the edge elements (48) are formed as teeth. Polishing tool according to one of claims 1 to 7, characterized in that flanks (56, 57) of the edge elements (48) are formed as involutes. Polishing tool according to one of claims 1 to 8, characterized in that one of adjacent flanks (56, 57) of two adjacent edge elements (48) included angle (58) is between about 5 ° and 180 °. Polishing tool according to one of claims 1 to 6, characterized in that a composite contour (38) of the edge elements (48) in the circumferential direction (42) can be described as a sinusoidal function. Polishing tool according to one of claims 1 to 10, characterized in that the polishing tool (22) is adapted to edit freeform surfaces. Polishing tool according to one of claims 4 to 11, characterized in that a difference between a radius of the top circle (44) and a radius of the base circle (46) corresponds to about 5 to 20% of the radius of the top circle (44). Device (10) for polishing an optical surface (18) of a spectacle lens (12) with a polishing tool (22) according to one of claims 1 to 12.

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