Method for Machining Optical Workpieces, in Particular Spectacle Lenses Made of Plastic

Abstract

A method for machining optical workpieces has the following steps: i) providing the blank that is to be machined at least on the rear side and edge; ii) receiving the blank without a block in order to retain it in a supported manner; iii) machining the blank on the front side by use of a first tool to form a peripheral geometric shape with a depth greater than or equal to the edge thickness of the semifinished product to be formed; iv) receiving the workpiece to retain it in a supported manner on the front side; and v) machining the workpiece on the rear side by use of a second tool to form the semifinished product with the predetermined surface geometry on the rear side.

Claims

1. A method of machining optical workpieces, in which a semi-finished product (HZ) with predetermined surface geometries at a front side (FS) and a rear side (RS) remote therefrom and with a contoured edge (RA) of predetermined edge thickness (D2) between the front side (FS) and the rear side (RS) is formed starting from a blank (RL), comprising the following principal steps executed in the stated sequence: i) providing the blank (RL), which has a blank thickness (D1) and can already have the predetermined surface geometry at the front side (FS) and which is to be processed at least at the rear side (RS) and the edge (RA); ii) block-free picking up of the blank (RL) at the rear side (RS) for supported holding of the workpiece; iii) processing of the blank (RL) at the front side (FS) by a first tool (WZ1) for formation of an encircling groove (NU) or step (ST) with a depth (TI) greater than or equal to the edge thickness (D2) of the semi-finished product (HZ) to be formed and smaller than the blank thickness (D1), or of an encircling cut having at least in part a depth equal to the blank thickness (D1) so that a circumferential surface (UF) defining the contoured edge (RA) of the semi-finished product (HZ) to be formed remains at the workpiece; iv) picking up the workpiece at the front side (FS) for supported holding of the workpiece; and v) processing the workpiece at the rear side (RS) by at least one second tool (WZ2) for formation of the semi-finished product (HZ) with the predetermined surface geometry at the rear side (RS).

2. A method according to claim 1, wherein, in the principal step iii), during formation of the encircling groove (NU) or step (ST) or of the encircling cut, an edge contour (RK1) is produced at the semi-finished product (HZ) by the first tool (WZ1), that has a slight oversize in relation to an edge contour (RK2) of the workpiece processed to finished state, and wherein the edge contour (RK2) of the workpiece processed to finished state is produced only after the principal step v) for processing the rear side (RS) of the workpiece.

3. A method according to claim 1, wherein, in the principal step iii), during or after formation of the encircling groove (NU) or step (ST) or of the encircling cut, an edge contour (RK2) is produced at the semi-finished product (HZ) by the first tool (WZ1) or a further tool, that already corresponds with an edge contour (RK2) of the workpiece processed to finished state.

4. A method according to claim 3, wherein, in the principal step iii), a chamfer (FA1) is applied to the transition between the edge (RA) and the rear side (RS) of the semi-finished product (HZ) to be formed and/or a chamfer is applied to the transition between the edge (RA) and the front side (FS) of the semi-finished product (HZ) to be formed.

5. A method according to claim 4, wherein, in the principal step iii), the chamfer or chamfers (FA1) is or are applied by the first tool (WZ1) at the same time as the encircling groove (NU) or step (ST) or the encircling cut.

6. A method according to claim 5, wherein, in the principal step iii), a fastening geometry for the workpiece processed to finished state is produced at the edge (RA) and/or at the front side (FS) of the semi-finished product (HZ) to be formed.

7. A method according to claim 6, wherein, in the principal step iii), the fastening geometry for the workpiece processed to finished state is formed by the first tool (WZ1) at the same time as the encircling groove (NU) or step (ST) or the encircling cut.

8. A method according to claim 7, wherein the fastening geometry produced in the principal step iii) for the workpiece processed to finished state is a pointed or roof bevel (SF) or an encircling channel or groove at the edge (RA) of the semi-finished product (HZ) to be formed and/or wherein the fastening geometry produced in the principal step iii) for the workpiece processed to finished state comprises one or more bores or notches at the front side (FS) and/or the edge (RA).

9. A method according to claim 8, wherein, at the start of the principal step iii), the first tool (WZ1) and/or the workpiece are so moved relative to one another that, for formation of the encircling groove (NU) or step (ST) or the encircling cut, the first tool (WZ1) enters the workpiece at a frontal entry point starting from the front side (FS) of the workpiece.

10. A method according to claim 8, wherein, at the start of the principal step iii), the first tool (WZ1) and/or the workpiece are so moved relative to one another that, for formation of the encircling groove (NU) or step (ST) or the encircling cut, the first tool (WZ1) enters the workpiece at an edge entry point(ES) starting from the edge (RA) of the workpiece.

11. A method according to claim 10, wherein, in the principal step iii) after entry of the first tool (WZ1) into the workpiece, the first tool (WZ1) and/or the workpiece are so moved relative to one another that the first tool (WZ1) produces the groove (NU) or step (ST) or cut in at least one revolution at the workpiece, and wherein the first tool (WZ1) leaves the workpiece at the edge (RA) of the workpiece at an edge exit point (AS) remote from the frontal or edge entry point(ES).

12. A method according to claim 11, wherein, in the principal step iii), a rotationally driven end mill is used as the first tool (WZ1) for processing the blank (RL) at the front side (FS).

13. A method according to claim 12, wherein the first tool (WZ1) used in the principal step iii) for processing the blank (RL) at the front side (FS) is different from the at least one second tool (WZ2) used in the principal step v) for processing the workpiece at the rear side (RS).

14. A method according to claim 13, wherein, in the principal step iv), the workpiece is picked up block-free at the front side (FS).

15. A method according to claim 14, wherein the workpiece in the principal step iv) is so picked up at the front side (FS) that the workpiece is held at the front side (FS) with support over the whole area.

16. A method according to claim 2, wherein, in the principal step iii), a chamfer (FA1) is applied to the transition between the edge (RA) and the rear side (RS) of the semi-finished product (HZ) to be formed and/or a chamfer is applied to the transition between the edge (RA) and the front side (FS) of the semi-finished product (HZ) to be formed.

17. A method according to claim 16, wherein, in the principal step iii), the chamfer or chamfers (FA1) is or are applied by the first tool (WZ1) at the same time as the encircling groove (NU) or step (ST) or the encircling cut.

18. A method according to claim 3, wherein, in the principal step iii), a fastening geometry for the workpiece processed to finished state is produced at the edge (RA) and/or at the front side (FS) of the semi-finished product (HZ) to be formed.

19. A method according to claim 18, wherein, in the principal step iii), the fastening geometry for the workpiece processed to finished state is formed by the first tool (WZ1) at the same time as the encircling groove (NU) or step (ST) or the encircling cut.

20. A method according to claim 6, wherein the fastening geometry produced in the principal step iii) for the workpiece processed to finished state is a pointed or roof bevel (SF) or an encircling channel or groove at the edge (RA) of the semi-finished product (HZ) to be formed and/or wherein the fastening geometry produced in the principal step iii) for the workpiece processed to finished state comprises one or more bores or notches at the front side (FS) and/or the edge (RA).

21. A method according to claim 1, wherein, at the start of the principal step iii), the first tool (WZ1) and/or the workpiece are so moved relative to one another that, for formation of the encircling groove (NU) or step (ST) or the encircling cut, the first tool (WZ1) enters the workpiece at a frontal entry point starting from the front side (FS) of the workpiece.

22. A method according to claim 1, wherein, at the start of the principal step iii), the first tool (WZ1) and/or the workpiece are so moved relative to one another that, for formation of the encircling groove (NU) or step (ST) or the encircling cut, the first tool (WZ1) enters the workpiece at an edge entry point(ES) starting from the edge (RA) of the workpiece.

23. A method according to claim 22, wherein, in the principal step iii) after entry of the first tool (WZ1) into the workpiece, the first tool (WZ1) and/or the workpiece are so moved relative to one another that the first tool (WZ1) produces the groove (NU) or step (ST) or cut in at least one revolution at the workpiece, and wherein the first tool (WZ1) leaves the workpiece at the edge (RA) of the workpiece at an edge exit point (AS) remote from the frontal or edge entry point(ES).

24. A method according to claim 1, wherein, in the principal step iii), a rotationally driven end mill is used as the first tool (WZ1) for processing the blank (RL) at the front side (FS).

25. A method according to claim 1, wherein the first tool (WZ1) used in the principal step iii) for processing the blank (RL) at the front side (FS) is different from the at least one second tool (WZ2) used in the principal step v) for processing the workpiece at the rear side (RS).

26. A method according to claim 1, wherein, in the principal step iv), the workpiece is picked up block-free at the front side (FS).

27. A method according to claim 1, wherein the workpiece in the principal step iv) is so picked up at the front side (FS) that the workpiece is held at the front side (FS) with support over the whole area.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The invention is explained in more detail in the following on the basis of preferred embodiments with reference to the accompanying schematic drawings, in which identical or corresponding parts or sections are provided with the same reference numerals. In the drawings:

[0053] FIG. 1 shows a flow chart of a process chain for production of spectacle lenses as an example of optical workpieces, wherein the process chain manages without the necessity of use of block pieces in manufacture and as an initiating process comprises a method, which is termed block-free generation for short, for the machining of spectacle lenses of plastic in accordance with a first embodiment of the invention;

[0054] FIG. 2 shows a perspective view of a retainer head of a processing device, at which for the principal step preliminary edge processing of the method block-free generation in the process chain according to FIG. 1 a spectacle lens blank is held at its rear side without blocking and with supported holding;

[0055] FIG. 3 shows a longitudinal sectional view of the retainer head according to FIG. 2 with the spectacle lens blank, which is held thereat without blocking, prior to the principal step preliminary edge processing in FIG. 1;

[0056] FIG. 4 shows a longitudinal sectional view of the retainer head according to FIG. 2 with the spectacle lens blank, which is held thereat without blocking, at the start of the principal step preliminary edge processing in FIG. 1, whilst a rotationally driven end mill as a first tool makes a machining entry into the workpiece from the edge of the workpiece at an edge entry point;

[0057] FIG. 5 shows a longitudinal sectional view of the retainer head, which by comparison with the illustration in FIGS. 3 and 4 is turned through 270? about its center axis, according to FIG. 2 with the workpiece, which is held thereat without blocking, during the principal step preliminary edge processing in FIG. 1, in which an encircling groove is formed in the front side of the workpiece by the rotationally driven end mill of FIG. 4;

[0058] FIG. 6 shows a perspective view of the workpiece, which for simplification of the illustration is shown separated from the retainer head according to FIG. 2, after the principal step preliminary edge processing in FIGS. 1, 4 and 5, with a view of the encircling groove which is formed in the front side of the workpiece as a result of this principal step and which already defines a contoured edge of the semi-finished product to be produced in the method according to the invention;

[0059] FIG. 7 shows a longitudinal section view of the retainer head according to FIG. 2 in correspondence with the manner of illustration in FIG. 5 with the workpiece, which is held thereat without blocking, in the processing state of FIG. 6, which in the principal step positioning and fixing of the method block-free generation in the process chain according to FIG. 1 is just positioned by its processed front side on a holding device, which is illustrated merely schematically, for supported holding;

[0060] FIG. 8 shows a schematic longitudinal sectional view of the retainer according to FIG. 7, at which the workpiece after the principal step positioning and fixing is held by its processed front side with area support for the principal step surface processing of the method block-free generation in the process chain according to FIG. 1;

[0061] FIG. 9 shows a schematic longitudinal sectional view of the retainer according to FIG. 7 with the workpiece, which is held thereat by way of its processed front side with area support and which in the principal step surface processing in FIG. 1 is undergoing processing by a second tool at its rear side so as to receive a predetermined surface geometry thereat;

[0062] FIG. 10 shows a perspective view of the semi-finished product which for simplification of the illustration is shown separated from the retainer according to FIG. 7 and has been generated in the principal step surface processing in FIG. 1 in correspondence with FIG. 9 and which is thereafter completely separated from excess radially outer blank material which drops off in the form of ring segments that are also depicted;

[0063] FIG. 11 shows a longitudinal sectional view of the retainer head according to FIG. 2 (here shown without support pins), which after the principal step surface processing in FIG. 1 picks up the generated semi-finished product from the retainer of FIG. 7 for subsequent processes in the process chain according to FIG. 1;

[0064] FIG. 12 shows a longitudinal sectional view of the retainer head according to FIG. 2 (illustrated here again without support pins) at which the semi-finished product generated as a result of the method block-free generation in the process chain according to FIG. 1 is held;

[0065] FIG. 13 shows a perspective view of a workpiece variant, which for simplification of the illustration is shown separated from the mounting head according to FIG. 2, after the principal step preliminary edge processing in FIG. 1 in the processing state of FIG. 6, in which as a result of this principal step an encircling step instead of the groove was formed at the front side, which also already defines a contoured edge of the semi-finished product to be produced in the method according to the invention;

[0066] FIG. 14 shows a flow chart of an alternative process chain for production of spectacle lenses as an example of optical workpieces, wherein the process chain again manages without the need to use block pieces in manufacture and as an initiating process comprises a method, which is again termed block-free generation for short, for machining of spectacle lenses of plastic according to a second embodiment of the invention, in which the workpiece prior to surface processing already undergoes final processing of its edge shape so that edging at the end of the process chain can be eliminated;

[0067] FIG. 15 shows a longitudinal section view of the retainer head according to FIG. 2 with a workpiece, which is held thereat without blocking, during the principal step final processing of edge shape of the method block-free generation in the processing chain according to FIG. 14 in a processing state corresponding with FIG. 5, wherein an encircling step at the front side of the workpiece is formed (shown on the left in FIG. 15) by a first tool, whereupon by a second tool an edge contour is produced at the workpiece (shown on the right in FIG. 15) which already corresponds with the edge contour of the workpiece processed to finished state;

[0068] FIG. 16 shows a flow chart of a conventional process chain for producing spectacle lenses in which, during production, block pieces are necessarily used and which accordingly comprises the auxiliary processes of blocking and deblocking, which do not increase the value of the produced spectacle lenses; and

[0069] FIG. 17 shows a basic illustration for the engagement situation of a plate mill as a tool with a blocked spectacle lens blank as workpiece during preliminary edge processing as a sub-process of the process generation in the previously known process chain according to FIG. 16.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0070] FIG. 1 shows a flow chart of a process chain for producing spectacle lenses of plastic as optical workpieces without the use of block pieces in manufacture, whereby at the outset the auxiliary processes of blocking and deblocking are eliminated by comparison with the prior art according to FIG. 16. As initial process the process chain comprises a method, which is termed block-free generation in FIG. 1, for machining of spectacle lenses of plastic according to a first embodiment, in which starting from a blank RL shown in FIG. 2 ultimately a semi-finished product HZ illustrated in FIG. 12 is formed. FIGS. 2 to 12 illustrate principal steps of this method.

[0071] The semi-finished product HZ produced as a result of this method (see FIG. 12) has predetermined surface geometries at a front side FS and at a rear side RS remote therefrom. Moreover, it is provided between the front side FS and the rear side RS with a contoured edge RA of predetermined edge thickness D2. As apparent from, for example, comparison of FIGS. 3, 7, 9 and 12, initially the contoured edge RA of the semi-finished product HZ and thereafter, in particular, the predetermined surface geometry at the rear side RS of the semi-finished product HZ arise in the course of the method.

[0072] For clarification, the final geometry of the semi-finished product HZ (see FIG. 12) is always indicated in the longitudinal sectional views according to FIGS. 3 to 5, 7 to 9, 11, 12 and 15 by a cross-hatching, although this geometry is, in fact, cut out of the blank material only at the end of the method. Accordingly, for example, the cross-hatching provided in the blank RL in accordance with FIG. 3quasi as a substituteillustrates only that material part of the blank RL from which the semi-finished product HZ is produced in the course of the method.

[0073] In general the method block-free generation of FIG. 1 comprisesobviously after the start

[0074] i) provision of the blank RL which has a blank thickness D1 (cf. FIGS. 2 and 3) and can already have at the front side the predetermined surface geometry, as shown here, and at which is to be processed at least at its rear side RS as well as its edge RA [0075] still the following four principal steps ii) to v) taking place in the indicated sequence: [0076] ii) Block-free picking up of the blank RL at the rear side RS for supported holding of the workpiece, as shown in FIGS. 2 and 3; included in FIG. 1 under fix position. [0077] iii) Processing the blank RL at the front side FS by a first tool WZ1 (see FIGS. 4 and 5) for formation of an encircling groove NU (cf., for example, FIG. 6) or step ST (see FIG. 13) with a depth TI which is greater than or equal to the edge thickness D2 of the semi-finished product HZ to be formed and smaller than the blank thickness D1, and in particular so thattermed preliminary edge processing in FIG. 1a circumferential surface UF which already defines the contoured edge RA of the semi-finished product HZ to be formed remains at the workpiece. As already explained further above, apart from the geometric (basic) shapes of groove NU and step STin a given case also in a combinationan encircling cut (not illustrated in the figures) which at least in part has a depth equal to the blank thickness D1 and thus at least locally penetrates the blank RL can be produced. [0078] iv) Picking up the workpiece at the front side FS for supported holding of the workpiece as shown in FIGS. 7 and 8; termed positioning and fixing in FIG. 1. [0079] v) Processing the workpiece at the rear side RS by at least one second tool WZ2 (see FIG. 9) for formation of the semi-finished product HZ (cf. FIGS. 10 to 12) with the predetermined surface geometry at the rear side RS; called surface processing for short in FIG. 1. As a consequence of this processing the semi-finished product HZ is necessarily also separated from the radially outer remnant of the blank material (marked in FIGS. 8, 9 and 11 by a smaller cross-hatching). The latter remnant drops off in the illustrated example as ring segments RG (cf. FIG. 10), as still to be explained in the following.

[0080] This separation of the semi-finished product HZ from the ring segments RG accordingly takes place inevitably, because the depth TI of the groove NU introduced or step ST worked (or cut, not shown) on the front side FS of the blank RL beforehand is greater than or equal to the edge thickness D2 of the produced semi-finished product HZ, which arises as a consequence of the surface processing of the workpiece from the rear side RS. In other words, the machining engagement of the second tool WZ2 in the production of geometry on the rear side RS of the workpiece cuts out the geometry (groove NU, step ST, cut) previously formed on the front side FS of the workpiece by the first tool WZ1 so that the excess blank material is entirely removed from the produced semi-finished product HZ.

[0081] In the case of the embodiment illustrated here, there is produced in the above principal step iii) when forming the encircling groove NU or step ST (or the encircling cut) by the first tool WZ1 according to FIGS. 6 and 10 an edge contour RK1, which has a slight oversize in relation to an edge contour RK2 (indicated in the mentioned figures by a dashed line) of the workpiece processed to finished state, at the semi-finished product HZ. The edge contour RK2 of the workpiece processed to finished state is then created only after the above principal step v) for processing the rear side RS of the workpiece and, in particular, in the concluding process of edging in the process chain according to FIG. 1.

[0082] In that regard it is apparent that the method block-free generation in FIG. 1 is in principle based on a two-stage procedure: In the first method step preliminary processing of the edge RA is carried out at the workpiece, which is held at its rear side RS, by processing the front side FS of the workpiece. In the second method step, surface processing takes place at the rear side RS of the workpiece, which is then held at its front side FS, wherein the final geometry at the edge and surfaces of the semi-finished product HZ produced at the end of this method is completed only through the toolduring surface processing of the rear side RSprocessing the workpiece up to the geometry (groove NU, step ST or cut) formed on the front side FS thereof.

[0083] In the illustrated embodiment the blank RL according to FIGS. 2 to 5 is held at the rear side RS by a vacuum sucker VS during processing of the front side FS. Due to the fact that only a comparatively small geometry (groove NU, step ST or cut) is worked onto the front side FS of the workpiece and the entire excess blank material does not have to be machined, there are only low forces on the holding mechanism. This makes it possible to use, for example, a conventional vacuum sucker VS which according to the earlier illustration in FIGS. 2 to 5 and 7 comprises in a manner known per se a central suction cup SN for holding the workpiece, which is surrounded by a plurality of support pins SS for supporting the held workpiece. Vacuum suckers of that kind from, for example, J. Schmalz GmbH, 72293 Glatten, Germany, are available on the market.

[0084] In order to generate the required relative movements between workpiece and tool, i.e. in order to position the blank RL in all six degrees of freedom, such a vacuum sucker VS can, for example, be moved by a six-axis kinematic system (not shown) which has three translational axes and three axes of rotation about the translational axes. As an alternative, the use of a six-axis articulated arm robot (also not illustrated), which carries such a vacuum sucker VS at its free end, is conceivable. In that case the tool can then be arranged at a fixed point, whilst the three-dimensional movement is executed on the workpiece side so as to generate the relative movement between tool and workpiece required for formation of the geometry. Movement mechanisms of that kind and also mechanisms which are possible in principle and which operate with a kinematic inversioni.e. the tool is moved, whilst the workpiece is arranged at a fixed locationas well as conceivable mixed forms of division of movement between tool and workpiece are sufficiently familiar to the person skilled in the art so that they do not need further explanation at this point.

[0085] As far as the tool WZ1 for processing the blank RL at the front side FS in the above principal step iii) is concerned, a rotationally driven end mill is shown in FIGS. 4, 5 and 15 by way of example. In the simplest form this can comprise, for example, milling cutters which are arranged at the end and circumferentially and which as a consequence of the tool rotation define a cylindrical envelope.

[0086] In the illustrated embodiment the end mill, which is used as the first tool WZ1, is provided around the circumferenceconsidered in a projection as shownwith angled milling cutters, for example as double or triple cutters. More precisely, each milling cutter of the illustrated end mill has a cutter section parallel with respect to the axis of rotation and a cutter section, which is angled radially outwardly through approximately 45? with respect to the axis of rotation, at the free end of the end mill. The result of this is a form of combination of T-grooving and tine cutter or dovetail mill.

[0087] It is possible with such a cutter construction at the first tool WZ1 to apply in the above principal step iii) in simple manner a chamfer FA1 (see FIGS. 4 and 5) at the transition between the edge RA and the rear side RS of the semi-finished product HZ to be formed and, in particular, at the same time as the encircling groove NU (or step or cut) as shown in the mentioned figures. This chamfer FA1 can then serve at the finished semi-finished product HZ (cf. FIG. 12) as a protective bevel as already mentioned further above.

[0088] However, it is also possible to work such geometries onto the workpiece, for example with use of a simple mill with a cylindrical envelope of the milling cutter or cutters in that such a tool in the principal step iii) is guided with two (or more) cuts around the semi-finished product HZ to be produced (or conversely the workpiece around such a tool or both around one another), wherein the then sequentially executed cuts take place at different angles of incidence of the tool axis with respect to the workpiece axis MA (for example, initially 0?, thereafter) 45?.

[0089] It is apparent to the person skilled in the art that in this mode and manner or with a different cutter configuration at the first tool WZ1 a chamfer can also be formed in the principal step iii) at the transition between the edge RA and the front side FS of the semi-finished product HZ to be formed (not shown in the figures). Moreover, although at this place an end mill is shown and described as the first tool WZ1 for the principal step iii) other types of tools are equally conceivable, such as already discussed in the introduction.

[0090] As far as the first cut of the blank RL at the start of the principal step iii) is concerned it is possible to move the first tool WZ1 and/or the workpiece relative to one another in such a way that the first tool WZ1 for formation of the encircling groove NU (or step or encircling cut) enters the workpiece starting from the front side FS of the blank RL at a frontal entry point. However, FIG. 4 illustrates a procedure in which at the start of the principal step iii) the first tool WZ1 and/or the workpiece are moved relative to one another in such a way that at the first tool WZ1 for formation of the encircling groove NU (or step or encircling cut) enters the workpiece starting from the edge RA of the blank RL at an edge entry point ES.

[0091] After entry of the first tool WZ1 into the workpiece the first tool WZ1 and/or the workpiece can then be moved relative to one another in such a way that the first tool WZ1 produces the groove NU (or step ST or cut) in the principal step iii) in at least one revolution at the workpiece, wherein the first tool WZ1 leaves the workpiece at an edge exit point AS, which is remote from the frontal or edge entry point ES, at the edge RA of the workpiece. The geometry thus produced at the workpiece is illustrated in FIG. 6 for the case that the first tool WZ1 enters the workpiece once (radial entry point ES) and leaves the workpiece once (radial exit point AS).

[0092] However, in one revolution the first tool WZ1 can also leave the workpiece multiple times at exit points AS angularly spaced around the center axis MA and re-enter the workpiece at entry points ES angularly spaced around the center axis MA. This leads to a subdivision of the material of the blank RL present radially outside the semi-finished product HZ to be produced. This excess blank material ultimately falls off the produced semi-finished product HZ as ring segments RG in correspondence with the number of tool entries and exits as a consequence of the principal step v), as already mentioned further above, thus advantageously does not have to be specially machined.

[0093] With respect to FIGS. 7 and 8 (as well as 9 and 11) it is at the outset to be noted that the workpiece in the above principal step iv) is also mounted at the front side FS in block-free manner so asin this embodiment or example of use of the methodto satisfy the main purpose of the block-free process chain illustrated in FIG. 1. In particular, in the illustrated embodiment the picking up of the workpiece at the front side FS is carried out in the principal step iv) so that the workpiece, more precisely the semi-finished product HZ to be produced, is held with support over the whole area at the front side FS, as can be best seen in FIG. 8.

[0094] Used for this purpose is a workpiece holding device WA which is illustrated merely schematically in FIGS. 7 to 9 and 11 and which can in principle function with the technological vacuum operating principle outlined in the introduction with respect to the prior art. However, other systems can also be used, such as are currently used in spectacle lens production.

[0095] Such a workpiece holding device WA can be mounted, for example, at the free end of a workpiece spindle of a generator, as is known from, for example, document EP 2 011 603 A1 already mentioned in the introduction, to which at this point express reference is made with respect to the construction and functioning of a suitable generator. The generator kinematics are also expressly described therein, i.e. how a workpiece rotatably held at the workpiece spindle can be moved relative to diverse tools.

[0096] In the second method step, i.e. the above principal step v), the rear side RS of the workpiece is then processed up to the pre-formed groove NU (or step ST or cut) in the course of surface processing in the generator. For that purpose, a plate mill as second tool WZ2 is indicated in the schematic FIG. 9. Thus, in this embodiment the first tool WZ1 used in the principal step iii) for processing the blank RL at the front side FS differs from the at least one second tool WZ2 used in the principal step v) for processing the workpiece at the rear side RS, which in principle can also be different.

[0097] The milling process as a first sub-step of the principal step v) of the surface processing at the rear side RS is carried out as described in the prior art and completely separates the resulting shape of the semi-finished product HZ from the surrounding blank material, as can be seen in FIG. 10. Due to the previously undertaken segmenting, thein the illustrated embodimenttwo (or more) ring segments RG drop from the semi-finished product HZ and can be conducted away and disposed of together with the inevitable swarf.

[0098] A turning process as a second sub-step of the principal step v) of the surface processing at the rear side RS can now be carried out in the same manner as in the prior art and, in particular, only at the rear-side geometry, which results from the preceding milling process, of the semi-finished product HZ to be produced. The thus-processed semi-finished product HZ can now be lifted off the workpiece holding device WA (see FIG. 11) and finally has (FIG. 12) the same geometric characteristics as would have resulted from processing by methods according to the prior art (see the introductory portion of the description).

[0099] In the following, the semi-finished product HZ removed from the generator can be polished (see the second process block-free polishing of the process chain according to FIG. 1). For that purpose, use can be made of basically the same polishing process as described in the prior art. Fixing of the semi-finished product HZ can in that regard be carried out with the planar holding system discussed above or, however, also with a vacuum sucker as already used for handling tasks at a different place.

[0100] The optional marking (process block-free marking in FIG. 1) of the polished semi-finished products HZ can now again be carried out by the same method as described in the prior art. Since in the process chain according to FIG. 1 the position of the semi-finished product HZ is not, however, fixed by way of a block piece, an additional measuring step is necessary by which location and position of the semi-finished product HZ are determined beforehand.

[0101] The polished and optionally marked semi-finished products HZ are then coated (process coating in FIG. 1) as known from the prior art before adaptation and fitting of the semi-finished product HZ to the rim shape can be started (process edging in FIG. 1), which equally takes place as known in the prior art. In that regard, the edge of the workpiece receives its final edge contour, as already indicated by the reference numeral RK2 in FIGS. 6 and 10. Moreover, in that case the fastening geometries, such as pointed and roof bevels, bores, etc., needed for fastening the spectacle lenses, which are produced as an end product, in the rim (spectacles frame) are formed.

[0102] The method variant, which is illustrated by FIG. 13 and in which no groove is milled, but the blank material in the principal step iii) is machined in correspondence with the depth of the calculated groove up to the edge of the semi-finished product HZ to be produced so that there is no step ST at the workpiece, was already discussed above. Such a step ST would also automatically arise in the principal step iii) if the finished diameter of the workpiece differs from the raw diameter of the blank RL by less than twice the mill diameter. However, such a processing is also possible in cases in which this diameter difference is greater.

[0103] FIG. 14 shows a flow chart of a process chain, which differs from the process chain according to FIG. 1, for producing spectacle lenses of plastic as optical workpieces without the use of block pieces in manufacture, whereby by comparison with the prior art according to FIG. 16 at the outset the auxiliary processes of blocking and deblocking are again eliminated. Moreover, in the process chain according to FIG. 14 the process edging as a final process of the process chain is also eliminated by comparison with the process chain according to FIG. 1. This is made possible by a different starting process, namely a method, which is again termed block-free generating in FIG. 14, for machining spectacle lenses of plastic in accordance with a second embodiment. This alternative method shall be described on the basis of FIG. 15 in the following only to the extent that it significantly differs from the above-described method according to the first embodiment.

[0104] It is obvious here from a comparison of FIGS. 1 and 14 that in place of the principal step preliminary edge processing in FIG. 1 is the principal step finally processed edge shape in FIG. 14, which ultimately makes the process edging of FIG. 1 redundant in the process chain according to FIG. 14. More precisely, in the method according to the second embodiment an edge contour RK2, which already corresponds with the edge contour RK2 of the workpiece processed to finished state, is generated in the principal step iii) at the semi-finished product HZ at the time of or after formation of the encircling groove NU or step ST (or encircling cut) by the first tool WZ1 or a further tool WZ1 (see FIG. 15).

[0105] For that purpose, in the case of the method embodiment illustrated on the left in FIG. 15 the afore-described end mill is used as the first tool WZ1 in the principal step iii) and produces at the workpiece a circumferential surface UF which already defines the edge contour RK2 of the workpiece processed to finished state. In that case, in correspondence with the mill shape, which is shown here by way of example, the afore-mentioned chamfer FA1 between edge RA and rear side RS of the semi-finished product HZ to be produced can alsobut does not have tobe formed therewith, as illustrated in FIG. 15 of the left.

[0106] In the case of the method embodiment illustrated in FIG. 15 on the right, even a fastening geometry for the workpiece processed to finished statehere, by way of example, shown at the transition from edge RA and front side FS of the semi-finished product HZ to be formedis produced in the principal step iii). In the illustrated embodiment the fastening geometry is a pointed bevel SF, which in the case of a spectacle lens usually co-operates with a complementary groove in a spectacles frame so as to fasten the spectacle lens in the spectacles frame. The formation of this fastening geometry for the workpiece processed to finished state takes place here in the principal step iii) by the tool WZ1, which is shown on the right in FIG. 15, at the same time as the encircling groove NU (or step ST or cut), for which purpose the tool WZ1 is provided with an appropriate shape of the cutter or cutters.

[0107] Finally, it is apparent to the person skilled in the art that through suitable tool selection other fastening geometries can be formed at the semi-finished product HZ in the principal step iii) instead of the pointed bevel SF illustrated on the right in FIG. 15. Thus, the fastening geometry, which is produced in the principal step iii), for the workpiece processed to finished state can be a roof bevel or an encircling channel or groove at the edge RA of the semi-finished product HZ to be formed (not shown here). Alternatively or in addition thereto the fastening geometry produced in the principal step iii) for the workpiece processed to finished state can also comprise one or more bores or notches at the front side FS and/or the edge RA, depending on the respective fastening requirements of the rim and in correspondence with the tool equipping of the processing machine used.

[0108] With respect to the remaining principal steps of the process block-free generation in FIG. 14 as well as the further processes of FIG. 14 reference may otherwise be made at this point to the above explanations with respect to FIGS. 1 to 13.

[0109] A method for machining optical workpieces in which a semi-finished product with predetermined surface geometries at front side and rear side and a contoured edge of predetermined edge thickness therebetween is formed from a blank, comprises the following principal steps: i) provision of the blank, which is to be processed at least at the rear side and edge, with a blank thickness; ii) block-free picking up of the blank for supported holding at the rear side; iii) processing of the blank at the front side by a first tool, for formation of an encircling geometric form with a depth greater than or equal to the edge thickness of the semi-finished product to be formed, wherein there is left at the workpiece a circumferential surface which defines the contoured edge of the semi-finished product to be formed; iv) picking up the workpiece for supported holding at the front side; and v) processing the workpiece at the rear side by at least one second tool for formation of the semi-finished product with the predetermined surface geometry at the rear side.

REFERENCE NUMERAL LIST

[0110] AS exit point [0111] BS block piece [0112] D1 blank thickness [0113] D2 edge thickness [0114] ES entry point [0115] FA1 chamfer [0116] FS front side [0117] HZ semi-finished product [0118] MA center axis [0119] NU groove [0120] RA edge [0121] RG ring segments [0122] RK1 edge contour of the semi-finished product [0123] RK2 edge contour of the workpiece processed to finished state [0124] RL blank [0125] RS rear side [0126] SF pointed bevel [0127] SN suction cup [0128] SS support pin [0129] ST step [0130] TF plate mill [0131] TI depth [0132] UF circumferential surface [0133] VS vacuum sucker [0134] WA workpiece holding device [0135] WZ1 first tool [0136] WZ2 second tool