POLISHING DISC FOR A TOOL FOR FINE PROCESSING OF OPTICALLY EFFECTIVE SURFACES ON SPECTACLE LENSES

Abstract

The invention relates to a polishing disc for a tool for fine processing optically active surfaces on spectacle lenses, having a main body which has a central axis and to which an intermediate layer that is softer than the main body and is made of a resilient material is secured, a polishing medium carrier resting on the intermediate layer. The intermediate layer has at least two regions with different degrees of hardness, said regions being arranged one behind the other in the direction of the central axis of the main body. The intermediate layer region adjoining the main part is softer than the intermediate layer region on which the polishing medium carrier rests.

Claims

1. A polishing disc for a tool for fine processing of optically effective surfaces on spectacle lenses, comprising a base body which has a center axis and to which is secured an intermediate layer, on which a polishing medium carrier rests, of a resilient material, the intermediate layer being softer by comparison with the base body, characterized in that the intermediate layer has at least two regions of different hardness arranged in succession in the direction of the center axis, wherein the region of the intermediate layer adjoining the base body is softer than the region of the intermediate layer on which the polishing medium carrier rests.

2. A polishing disc according to claim 1, characterized in that the at least two regions of the intermediate layer are formed by mutually different foam material layers, namely at least one softer foam material layer on the base body and at least one harder foam material layer under the polishing medium carrier.

3. A polishing disc according to claim 2, characterized in that the mutually different foam material layers are glued together.

4. A polishing disc according to claim 3, characterized in that the ratio of the substantially constant thickness of the harder foam material layer to the substantially constant thickness of the softer foam material layer is between 1 to 2 and 1 to 4, the thicknesses being measured along or parallel to the center axis.

5. A polishing disc according to claim 2, characterized in that as determined for the case of whole-area compression the static modulus of elasticity of the harder foam material layer is between 0.40 and 1.50 N/mm.sup.2, whereas the static modulus of elasticity of the softer foam material layer is between 0.25 and 0.45 N/mm.sup.2.

6. A polishing disc according to claim 2, characterized in that the softer foam material layer is made from an at least partly open-pore polyetherurethane elastomer, whereas the harder foam material layer is made from of a closed-cell polyetherurethane elastomer.

7. A polishing disc according to claim 1, characterized in that the base body has a substantially spherical end surface which faces the intermediate layer and to which the intermediate layer is secured, in particular firmly glued, wherein the end surface has a radius of curvature (R.sub.G) of between 35 and 42 mm.

8. A polishing disc according to claim 7, characterized in that the base body has a diameter between 35 and 60 mm in the region of its end surface, wherein the substantially constant thickness of the intermediate layer is between 15 and 22 mm as measured along or parallel to the center axis.

9. A polishing disc according to claim 8, characterized in that the polishing medium carrier protrudes in radial direction with respect to the center axis (M) at all sides beyond the intermediate layer.

10. A tool for fine processing of optically effective surfaces at spectacle lenses, comprising a tool mounting head securable to a spindle shaft of a tool spindle to be capable of axial and rotational entrainment, characterized in that a polishing disc for a tool for fine processing of optically effective surfaces on spectacle lenses, said polishing disc comprising a base body which has a center axis and to which is secured an intermediate layer, on which a polishing medium carrier rests, of a resilient material, the intermediate layer being softer by comparison with the base body, wherein the intermediate layer has at least two regions of different hardness arranged in succession in the direction of the center axis, wherein the region of the intermediate layer adjoining the base body is softer than the region of the intermediate layer on which the polishing medium carrier rests is exchangeably mounted on the tool mounting head, wherein for mounting purposes the base body of the polishing disc and the tool mounting head are provided with complementary structures for axial detenting and rotational entrainment of the polishing disc with and by the tool mounting head.

11. A tool according to claim 10, characterized in that the tool mounting head has a ball joint with a ball head which is received in a ball socket and which is formed at a ball pin securable to the spindle shaft of the tool spindle, the ball socket being formed in a mounting plate with which the polishing disc is detentable.

12. A tool according to claim 11, characterized in that the ball head has a receiving bore for a transverse pin which extends through the ball head and engages on either side of the ball head in associated recesses in the ball socket so as to connect the mounting plate with the ball pin to be capable of rotational entrainment.

13. A tool according to claim 12, characterized in that the mounting plate is resiliently supported on a support flange at the ball-pin side by way of a resilient annular element so that the polishing disc detented with the mounting plate seeks to self-align by its center axis with the ball pin and thus the spindle shaft of the tool spindle.

14. A tool according to claim 13, characterized in that the base body of the polishing disc and the tool mounting head are each provided with a respective radially protruding collar, wherein the collars in the state in which the polishing disc is mounted on the tool mounting head are opposite one another and mechanically positively engaged over by a securing ring with a substantially U-shaped cross-section.

15. A tool according to claim 14, characterized in that the securing ring is formed by two half rings which are pivotably connected together on one side by use of a hinge and are releasably detentable together on the other side by way of a snap connection.

16. A tool according to claim 11, characterized in that the mounting plate is resiliently supported on a support flange at the ball-pin side by way of a resilient annular element so that the polishing disc detented with the mounting plate seeks to self-align by its center axis with the ball pin and thus the spindle shaft of the tool spindle.

17. A tool according to claim 10, characterized in that the base body of the polishing disc and the tool mounting head are each provided with a respective radially protruding collar, wherein the collars in the state in which the polishing disc is mounted on the tool mounting head are opposite one another and mechanically positively engaged over by a securing ring with a substantially U-shaped cross-section.

18. A polishing disc according to claim 4, characterized in that the ratio of the substantially constant thickness of the harder foam material layer to the substantially constant thickness of the softer foam material layer is approximately 1 to 3, the thicknesses being measured along or parallel to the center axis.

19. A polishing disc according to claim 5, characterized in that as determined for the case of whole-area compression the static modulus of elasticity of the harder foam material layer is between 0.80 and 1.00 N/mm.sup.2, whereas the static modulus of elasticity of the softer foam material layer is between 0.35 and 0.45 N/mm.sup.2.

20. A polishing disc according to claim 7, characterized in that the base body has a substantially spherical end surface which faces the intermediate layer and to which the intermediate layer is secured, in particular firmly glued, wherein the end surface has a radius of curvature of between 36 and 40 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention is explained in more detail in the following on the basis of a preferred embodiment with reference to the accompanying partly schematic drawings, which are not true to scale and in which:

[0028] FIG. 1 shows a longitudinal sectional view of a tool spindle, which is mounted in a pivot yoke—illustrated partly broken-away—of a polishing machine, with a tool according to the invention for fine processing of optically effective surfaces at spectacle lenses, on the tool mounting head of which is detachably mounted a polishing disc disposed in processing engagement with a surface to be processed, wherein the tool is in a lower setting moved out relative to the tool spindle;

[0029] FIG. 2 shows a half section of the tool spindle with tool according to FIG. 1 in the unmounted state and without a bellows between tool and tool spindle, the bellows having been omitted here to allow a better view, wherein the tool together with the polishing disc is disposed in an upper setting retracted relative to the tool spindle, in which the tool mounting head of the tool is detented with the tool spindle;

[0030] FIG. 3 shows a sectional view, which is broken away at the top, of the tool—which is mounted on the tool spindle—of FIG. 1 in correspondence with the section line III-III in FIG. 2;

[0031] FIG. 4 shows a sectional view of the tool, which is mounted on the tool spindle (here shown only partly), of FIG. 1 in the retracted upper setting according to FIG. 2, with the tool mounting head detented on the tool spindle and a polishing disc removed therefrom;

[0032] FIG. 5 shows a perspective exploded illustration of the tool, which is moved out relative to the tool spindle (here shown broken away), of FIG. 1 obliquely from below, with the tool mounting head, an opened securing ring and the polishing disc, for illustration of the interfaces between tool spindle, tool mounting head, securing ring and polishing disc;

[0033] FIG. 6 shows a perspective exploded illustration, which corresponds with respect to the illustrated parts of FIG. 5, of the tool, which is moved out relative to the tool spindle (again shown broken away), of FIG. 1 obliquely from above, with the tool mounting head, the securing ring in closed setting and the polishing disc, for further illustration of the interfaces between tool spindle, tool mounting head, securing ring and polishing disc; and

[0034] FIG. 7 shows a diagram of a spectacle lens and a polishing disc according to the invention for illustration of the significant geometrical data for the dimensioning of a universally usable polishing disc in dependence on spectacle lens curvatures and spectacle lens diameters.

DETAILED DESCRIPTION OF THE EMBODIMENT

[0035] According to, in particular, FIGS. 1 to 6 a polishing disc 10 for a tool 12 for fine processing of optically effective surfaces cc, cx at spectacle lenses L (cf. FIGS. 1 and 7) comprises a base body 14, which has a center axis M and on which is secured an intermediate layer 16 of a resilient material, the layer being softer by comparison with the base body 14, on which layer a polishing medium carrier 18 forming the actual, outer processing surface 19 of the polishing disc 10 rests. It is significant that the intermediate layer 16 has at least two regions of different hardness, which are arranged in succession in the direction of the center axis M, wherein the region of the intermediate layer 16 adjoining the base body 14 is softer than the region of the intermediate layer 16 on which the polishing medium carrier 18 rests, as will be explained in more detail in the following.

[0036] In the embodiment illustrated here, the two regions of the intermediate layer 16 are formed by mutually different foam material layers 20, 22 each of constant thickness as seen along the center axis M, namely a softer foam material layer 20 on the base body 14, more precisely the end surface 21 thereof, and a harder foam material layer 22 under the polishing medium carrier 18. In that case, the mutually different foam material layers 20 and 22 are adhered together at 23.

[0037] Equally, the polishing medium carrier 18 is adhered to the harder foam material layer 22 and the softer foam material layer 20 is adhered to the end surface 21 of the base body 14. In order to prevent the edge of the polishing disc 10 from being imaged on the processed surface cc of the spectacle lens L in the form of very fine scratch-like microstructures the polishing medium carrier 18 protrudes at all sides beyond the intermediate layer 16 in radial direction with respect to the center axis M.

[0038] The substantially rigid base body 14 on the one hand serves by its preshaped end surface 21 for shaping as well as supporting or bearing the afore-described resilient layer construction of the polishing disc 10 and on the other hand forms the connecting member for the rest of the tool 12, as will still be described in the following. In the illustrated embodiment the end surface 21 of the base body 14 is preshaped to be substantially spherical and quasi arches towards the intermediate layer 16. However, the end surface of the base body can also be differently preshaped, for example aspherically, according to the macrogeometry of the surfaces cc or cx to be processed.

[0039] As can be seen in FIGS. 1 to 6, the tool 12 has a tool mounting head 24 with a mounting plate 25, which is secured to a spindle shaft 26 of a tool spindle 28 to be capable of axial and rotational entrainment, but at the same time detachable. The polishing disc 10 is exchangeably mounted on the tool mounting head 24, for which purpose the base body 14 of the polishing disc 10 and the tool mounting head 24, more precisely the mounting plate 25 thereof, are provided with complementary structures 29 (see, in particular, FIGS. 5 and 6) for axial detenting and rotational entrainment of the polishing disc 10 by the tool mounting head 24.

[0040] The interface, which is formed by the complementary structures 29, between polishing disc 10 and tool mounting head 24 is the subject matter of document EP 2 464 493 B1, which was already mentioned in the introduction and to which, at the outset and for avoidance of repetition, express reference with respect to the construction and function of the interface may be made at this point. In short, as can be best seen in FIGS. 4 to 6, the base body 14 of the polishing disc 10 has at its inner side an inner space 32 which is bounded by a wall surface 30 and a base surface 31 and is provided for pushing the polishing disc 10 onto and detenting it to a mounting projection 33 of complementary form at the mounting plate 25 of the tool mounting head 24 and which has at its base surface 31 entrainer elements 34—which are associated with corresponding entrainer mating elements 35 at the mounting projection 33—for torque transmission. In addition, a resilient mounting ring 37 fixed in an annular groove 36 is provided between the wall surface 30 and the mounting projection 33 and provides detenting with a corresponding mating groove 38 and sealing of the inner space 32. In that case, the detenting arises during pushing-on of the polishing disc 10 before the entrainer elements 34 come into engagement with the entrainer mating elements 35, this being achievable only in the case of further pushing-on of the polishing disc 10 with formation of a seal between the wall surface 30 and the mounting projection 33.

[0041] On the side of the mounting plate 25 remote from the inner space 32 the tool mounting head 24 has a ball joint 40 with a ball head 44, which is received in a ball socket 42 and which is formed at a ball pin 46 securable to, more precisely able to be screwed into, the spindle shaft 26 of the tool spindle 28. On the other hand, the ball socket 42 is formed in the mounting plate 25 with which the polishing disc 10 is detentable. According to, in particular, FIGS. 3 and 4 the ball head 44 has a receiving bore 48 for a transverse pin 50. The transverse pin 50 extends through the ball head 44 by radiused ends and engages on either side of the ball head 44 in associated recesses 52 in the ball socket 42 so as to connect the mounting plate 35 with the ball pin 46, and thus with the spindle shaft 26 of the tool spindle 28, to be capable of rotational entrainment.

[0042] Moreover, as can be best seen in FIGS. 3 and 4, a circularly annular support flange 54 is inserted between the ball pin 46 and the free end of the spindle shaft 26 and is secured to the spindle shaft 26 by means of the ball pin 46. Resting on the support flange 54 is a resilient annular element 56 of, for example, a suitable foam material, by way of which the mounting plate 25 of the tool mounting head 24 can be resiliently supported on the support flange 54 at the ball-pin side in such a manner that the polishing disc 10 detented with the mounting plate 24 seeks to self-align by its center axis M with the ball pin 46 and thus the spindle shaft 26 of the tool spindle 28.

[0043] Finally, still to be mentioned is that according to, in particular, FIGS. 3, 5 and 6 each of the base body 14 of the polishing disc 10 and the tool mounting head 24 at the mounting plate 25 is provided with a radially protruding collar 58 or 59 for detachable connection of the polishing disc 10 and tool mounting head 24. In the state in which the polishing disc 10 is mounted on the tool mounting head 24 these collars 58, 59 are opposite one another and are mechanically positively engaged over by means of a securing ring 60 with a substantially U-shaped cross-section (see FIG. 3) so as to prevent unintended detaching of the polishing disc 10 from the tool mounting head 24. The securing ring 60, which advantageously consists of a suitable plastics material, is formed, as can be seen in FIGS. 3, 5 and 6, by two half rings 62, 63 which are pivotably connected together at one side by means of a hinge 64 and at the other side are releasably detentable together by way of a resilient snap connection 66, which is known per se, with undercuts.

[0044] In order to show the possibilities of movement of the tool 12 relative to the spectacle lens L to be polished, further details of the tool spindle 28 and the installation situation thereof in a polishing device are illustrated in, in particular, FIGS. 1 and 2. This tool spindle 28 as well as the polishing device preferred for use of the tool 12 described here are the subject of parallel, i.e. filed on the same application date, German Patent Application DE 10 2014 XXX XXX.X, express reference to which may be made at this point, for the avoidance of repetitions, with regard to the more precise construction and functioning of the tool spindle 28 and the polishing device.

[0045] With regard to the possibilities of movement of the spectacle lens L to be processed and of the tool 12 merely the following shall be mentioned here: Arranged opposite the tool spindle 28 in a work space is a workpiece spindle 68 which is indicated in FIG. 1 by dashed lines and by means of which the spectacle lens L to be polished can be driven by way of a block piece, which is mounted in a mount of the workpiece spindle 68, for rotation about a workpiece axis C of rotation. In addition, the spindle shaft 26 of the tool spindle 28 is drivable by way of an electric servomotor 70 by means of a belt drive 71 for rotation about a tool axis A of rotation. The tool spindle 28 additionally comprises a pneumatically actuable piston-cylinder arrangement 72, by means of which the tool 12 is axially adjustable by way of the spindle shaft 26 along an adjusting axis Z aligned with the tool axis A of rotation. In that case, the tool 12 can, in a setting near the tool spindle, be detented with the tool spindle 28 by means of a detent device 74 (cf. FIGS. 2 to 4).

[0046] The tool spindle 28 itself together with servomotor 70 and belt drive 71 is flange-mounted on a pivot yoke 76 pivotable in defined manner about a pivot setting axis B extending substantially perpendicularly to the workpiece axis C of rotation. In addition, the pivot yoke 76 together with tool spindle 28 and the drive thereof can be axially moved along a linear axis X which extends substantially perpendicularly to the plane of the drawing in FIG. 1 and which is oriented substantially perpendicularly not only to the pivot setting axis B, but also to the workpiece rotational axis C.

[0047] To that extent it is evident that the polishing disc 10 and the spectacle lens L can be rotationally driven in the same or opposite sense and at the same or different rotational speeds (rotational axes A, C). At the same time, the polishing disc 10 can be axially adjusted in the direction of the spectacle lens L (setting axis Z). Moreover, the rotational axes A, C can be preset or dynamically pivoted relative to one another in terms of angle (pivot setting axis B) as well as displaced transversely relative to one another (linear axis X). The different polishing processes performable with these kinematics are well-known to the expert and therefore shall not be described in more detail at this point.

[0048] In the following it shall be explained in more detail with reference to FIG. 7 how the above-described polishing disc 10 can be dimensioned.

[0049] In that case, initially there is to be predetermined the range of spectacle lens curvatures involved in polishing of the optically effective surface cc, with R.sub.Lmax as the maximum radius of curvature of the “flattest” spectacle lens L to be processed and R.sub.Lmin as the minimum radius of curvature of the most strongly “curved” spectacle lens L to be processed, as well as the diameter D.sub.L of the spectacle lenses L to be polished.

[0050] Based on the experience of the present inventors, the diameter D.sub.W of the polishing disc 10 should be selected to be somewhat smaller than the diameter D.sub.L of the spectacle lens L to be polished, but not too small. Advantageously, the diameter ratio D.sub.W/D.sub.L should lie in the following range:

[00001]$\frac{3}{5}\le \frac{D_W}{D_L}<1$

[0051] Thus, approximately 50 mm would be a standard diameter D.sub.W for the polishing disc 10. For very small spectacle lens diameters up to 40 mm and for very pronounced spectacle lens curvatures a diameter D.sub.W of the polishing disc 10 of approximately 35 mm would be suitable. On the other hand, for a basically equally possible processing of a spectacle lens at the convex side an even greater diameter D.sub.W of the polishing disc 10 of approximately 60 mm could be provided.

[0052] For the thus-selected diameter D.sub.W of the polishing disc 10 it is possible to calculate from the predetermined range of spectacle lens curvatures the (smallest) sagittal height P.sub.min of the “flattest” spectacle lens L and the (largest) sagittal height P.sub.min of the most strongly “curved” spectacle lens L from the following equations:

P.sub.min=R.sub.Lmax.Math.(1−cos φ.sub.min) and P.sub.max=R.sub.Lmin.Math.(1−cos φ.sub.max),

with the (smallest) opening angle φ.sub.min for the selected diameter D.sub.W of the polishing disc 10 at the “flattest” spectacle lens L and the (largest) opening angle φ.sub.max for the selected diameter D.sub.W of the polishing disc 10 at the most strongly “curved” spectacle lens L calculated from the following formulae:

[00002]${\varphi }_{\min }=\arcsin .Math.\frac{D_W}{2.Math.R_{\mathrm{Lmax}}}.Math..Math.\mathrm{and}.Math..Math.{\varphi }_{\min }=\arcsin .Math.\frac{D_W}{2.Math.R_{\mathrm{Lmin}}}.$

[0053] A mean sagittal height P.sub.m can be determined from the thus-obtained sagittal heights P.sub.min and P.sub.max:

[00003]$P_m=\frac{P_{\min }+P_{\max }}{2}$

and from that a mean radius of curvature R.sub.Lm of the spectacle lens L with which the radius of curvature R.sub.W of the polishing disc 10 is to correspond at its processing surface 19 at the polishing medium carrier 18:

[00004]$R_{\mathrm{LM}}=\frac{P_m^2+\frac{D_W^2}{4}}{2.Math.P_m}=R_W$

[0054] In principle, it would also be possible to additionally undertake weighting of the mean radius of curvature R.sub.Lm of the spectacle lens L and thus the radius of curvature R.sub.W Of the polishing disc 10 on the basis of statistical frequency of spectacle lens curvatures or to determine the radius of curvature of a universally usable polishing disc solely from a statistical distribution of spectacle lens curvatures, which depends on the respective mode. Thus, currently the maximum of a—regionally different—statistical distribution is approximately ±5 diopters. If, for example, the current trend to strongly curved sport glasses for prescription lenses continues, a “shift” towards more bowed curves, i.e. a reduction in the radius of curvature R.sub.W of the polishing disc 10, could be feasible.

[0055] Still to be calculated are the total thickness S.sub.S of the intermediate layer 16 and the individual thicknesses of the foam material layers 20, 22, with S.sub.W as the thickness of the softer foam material layer 20 and S.sub.H as the thickness of the harder foam material layer 22 each as seen along or parallel to the center axis M, as well as the radius of curvature R.sub.G of the end surface 21 of the base body 14, wherein the thickness S.sub.P of the proprietary polishing medium carrier 18 is known.

[0056] It is assumed for the thickness calculation that the polishing disc 10 during the polishing process has to be a position of bridging over the mean sagittal height P.sub.M under deformation of the intermediate layer 16. Investigations carried out by the inventors have yielded the result that for achieving reproducible polishing results this “bridging over” should occur in the purely elastic range of deformation of the foam material, in which connection the factor 4 has found to be a satisfactory value, i.e. the maximum deformation of the foam material should not be greater than 25% of the total thickness S.sub.S of the intermediate layer 16, thus:

S.sub.S=P.sub.M.Math.4=S.sub.H+S.sub.W

[0057] For determination of the individual thicknesses S.sub.H, S.sub.W of the foam material layers 20, 22 the inventors have carried out further tests so as to achieve a satisfactory compromise between capability of adaptation (predominantly macrogeometry) and polishing performance (microgeometry), the following range having been found for the thickness ratio S.sub.H/S.sub.W:

[00005]$\frac{1}{2}\ge \frac{S_H}{S_W}\ge \frac{1}{4},$

with a preferred thickness ratio being approximately 1 (S.sub.H) to 3 (S.sub.W).

[0058] Finally, it is left to calculate the radius of curvature R.sub.G of the end surface 21 of the base body 14 by way of the following simple subtraction:

R.sub.G=R.sub.W−S.sub.P−S.sub.S

[0059] Thus, radii of curvature R.sub.G of the end surface 21 between 35 and 42 mm, with a preferred range between 36 and 40 mm, were found for a typical geometry range, to be polished in spectacle lens production, of up to 14 diopters. In the case of tool diameters D.sub.W of 35 to 60 mm, layer thicknesses S.sub.S between 15 and 22 mm resulted.

[0060] In addition, different foam materials were tested in the experiments carried out by the inventors. In that regard, for the hardness or “softness” of the individual foam materials it has proved that, when determined for the case of whole-area compression (shape factor q=6), the static modulus of elasticity of the softer foam material layer 20 should lie between 0.25 and 0.45 N/mm.sup.2, preferably between 0.35 and 0.45 N/mm.sup.2, whereas the static modulus of elasticity of the harder foam material layer should be between 0.40 and 1.50 N/mm.sup.2, preferably between 0.80 and 1.00 N/mm.sup.2.

[0061] Moreover, in tests good results—including with regard to service lives—were achieved with foam materials of polyetherurethane elastomers, particularly with at least partly open-pore polyetherurethane elastomer foam material for the softer foam material layer 20, such as is commercially available from, for example, the company Getzner Werkstoffe GmbH, Burs, Austria, under the trade name “Sylomer [Registered Trade Mark] SR28” or “Sylomer [Registered Trade Mark] SR42”, and a closed-cell polyetherurethane elastomer foam material for the harder foam material layer 22 such as can be obtained from, for example, the company Getzner under the trade name “Sylodyn [Registered Trade Mark] NC”.

[0062] The polishing medium carrier 18 forming the tool component active in processing, also termed “polishing film” or “polishing pad”, can be a proprietary resilient and abrasion-resistant fine-grinding carrier or polishing-medium carrier such as, for example, a PUR (Eolyurethane) film having a thickness of 0.5 to 1.4 mm and a hardness of between 12 and 45 according to Shore D. In that regard, the polishing medium carrier 18 is formed to be thicker if preparatory polishing is to be carried out by means of the polishing disc 10, but thinner in the case of fine polishing. In addition, polishing felts or foam materials treated with heat and pressure can be used with or without carrier material as polishing medium carrier 18, such as available from, for example, the company Delamare, Mantes La Jolie, France. In this connection it may also be mentioned that the upper side, which faces the polishing medium carrier 18, of the harder foam material layer 22 can be provided with a closing “mold skin” resulting from production technology (separating layer from the mold; not illustrated)—although this is not essential—which gives the intermediate layer 16 at the outside an additional stiffness; in certain circumstances, such a “mold skin” can even itself form the polishing medium carrier 18.

[0063] The base body 14 of the polishing disc 10 is preferably injection-molded from a plastics material such as, for example, an ABS (Acrylnitrile-Butadiene-Styrene polymerisate), for example “Terluran [Registered Trade Mark] GP 35” of the company BASF SE, Ludwigshafen, Germany.

[0064] Finally, for example, a proprietary adhesive of the mark “Pattex [Registered Trade Mark]” of the company Henkel AG & Co. KGaA, Du sseldorf, Germany, is suitable for securing together the individual constituents of the polishing disc 10 (base body 14, softer foam material layer 20, harder foam material layer 22, polishing medium carrier 18). However, the polishing medium carrier 18 can, in particular, also be connected in a different way with the intermediate layer 16 with a greater or lesser degree of permanence, for example by vulcanization in place or by hook-and-burr fastening. In every instance, the connection between the individual components of the polishing disc 10 has to be sufficiently firm for mutual movement entrainment, particularly rotational entrainment, to be ensured at all times during processing.

[0065] A polishing disc for a tool for fine processing of optically effective surfaces at spectacle lenses comprises a base body, which has a center axis and to which is secured an intermediate layer, which is softer by comparison with the base body and on which a polishing medium carrier rests, of a resilient material. The intermediate layer has at least two regions of different hardness which are arranged in succession in the direction of the center axis of the base body. In that regard, the region of the intermediate layer adjoining the base body is softer than the region of the intermediate layer on which the polishing medium carrier rests. The polishing disc of simple construction can thus cover a large range of spectacle lens curvatures which, in particular, enables a high level of productivity in production according to prescription.

REFERENCE NUMERAL LIST

[0066] 10 polishing disc [0067] 12 tool [0068] 14 base body [0069] 16 intermediate layer [0070] 18 polishing medium carrier [0071] 19 processing surface [0072] 20 softer foam material layer [0073] 21 end surface [0074] 22 harder foam material layer [0075] 23 adhesive [0076] 24 tool mounting head [0077] 25 mounting plate [0078] 26 spindle shaft [0079] 28 tool spindle [0080] 29 complementary structures [0081] 30 wall surface [0082] 31 base surface [0083] 32 inner space [0084] 33 mounting projection [0085] 34 entrainer elements [0086] 35 entrainer mating elements [0087] 36 annular groove [0088] 37 mounting ring [0089] 38 mating groove [0090] 40 ball joint [0091] 42 ball socket [0092] 44 ball head [0093] 46 ball pin [0094] 48 receiving bore [0095] 50 transverse pin [0096] 52 recess [0097] 54 support flange [0098] 56 resilient annular element [0099] 58 collar [0100] 59 collar [0101] 60 securing ring [0102] 62 half ring [0103] 63 half ring [0104] 64 hinge [0105] 66 snap connection [0106] 68 workpiece spindle [0107] 69 block piece [0108] 70 servomotor [0109] 71 belt drive [0110] 72 piston-cylinder arrangement [0111] 74 detent device [0112] 76 pivot yoke [0113] A tool rotational axis [0114] B pivot setting axis [0115] C workpiece rotational axis [0116] cc second optically effective surface [0117] cx first optically effective surface [0118] D.sub.L diameter of the spectacle lens [0119] D.sub.W diameter of the polishing disc [0120] L spectacle lens [0121] M center axis of the base body [0122] P.sub.max maximum sagittal height [0123] P.sub.min mean sagittal height [0124] P.sub.min minimum sagittal height [0125] R.sub.G radius of curvature of the end surface of the base body [0126] R.sub.Lmax maximum radius of curvature of the spectacle lens [0127] R.sub.Lm mean radius of curvature of the spectacle lens [0128] R.sub.Lmin minimum radius of curvature of the spectacle lens [0129] R.sub.W radius of curvature of the polishing disc [0130] S.sub.H thickness of the harder foam material layer [0131] S.sub.P thickness of the polishing medium carrier [0132] S.sub.S total thickness of the intermediate layer [0133] S.sub.W thickness of the softer foam material layer [0134] X linear axis [0135] Z adjusting axis [0136] φ.sub.max maximum opening angle [0137] φ.sub.min minimum opening angle