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

TECHNICAL FIELD

The present invention relates in general to a method of machining optical workpieces. In particular, the invention relates to a method of machining spectacle lenses of plastic, for example polycarbonate, CR39 or so-called “High Index” materials, such as is practiced on a very large scale in so-called “RX workshops”, i.e. production facilities for manufacture of individual spectacle lenses according to prescription.

PRIOR ART

Currently, the following process steps are usually performed in RX workshops within the scope of industrial production of spectacle lenses (in that regard see also FIG. 16 of the prior art): Initially a suitable righthand and/or lefthand spectacle lens blank (also called “blank”) is or are removed from a semi-finished product store or the like; semi-finished product insofar as the spectacle lens blanks, which as seen in plan view are usually round or oval and are not yet edged, already have their final geometry at one of their two respective optically effective surfaces. The spectacle lens blanks are then prepared for the blocking process, namely by application of a suitable protective film or a suitable protective lacquer for protection of the optically effective surface-which is already processed to finished state and produced by injection molding or molded in some other way-with its final geometry.

So-called “blocking” of the spectacle lens blanks is next carried out in accordance with FIG. 16. In that case, the spectacle lens blank is connected with a suitable so-called “block piece”, for example a block piece in accordance with German Standard DIN 58766. For the blocking, firstly position and optionally shape of the spectacle lens blank are determined by measurement before the spectacle lens blank is then positioned in six degrees of freedom relative to the block piece so that the block piece adopts a predetermined position relative to the protected surface, which is already processed to finished state, of the spectacle lens blank.

Fixing of this set position takes place subsequently. In that case the space between block piece and spectacle lens blank is filled with a molten material, for example “alloy”, i.e. a metallic alloy, which is usually based on bismuth, or wax (see, for example, document EP 1 593 458 A2). After hardening of the filler material the block piece represents a mount for processing of the spectacle lens blank or forms a machine interface which subsequently remains at the spectacle lens for several processing procedures in different machines and in that case has to reliably hold the spectacle lens in a defined position. As an alternative to the afore-mentioned hardenable blocking materials it has also already been proposed (cf., for example, documents DE 10 2007 007 161 A1 and EP 2 011 604 A1) to use a special curable—optionally under ultraviolet light—adhesive so as to connect block piece and spectacle lens blank with the adhesive as a layer therebetween. The process step of blocking can in that regard also be carried out entirely automatically (see, for example, document WO 2009/135689 A1).

Only then can the spectacle lens blanks in the next process step according to FIG. 16, the so-called “generation”, undergo preliminary machining to form a semi-finished product. This preliminary processing is carried out as a function of the material—in the case of plastic by geometrically defined cutting, i.e. regular milling and/or turning—in a special processing machine (see, in that regard, for example, documents EP 1 719 585 A2 and EP 2 011 603 A1), also termed “generator”, in which the blocked spectacle lens blank is held by the block piece at or in a mount of a rotationally driven workpiece spindle. In that case, the previously still-unprocessed optically effective surface of the respective spectacle lens blank gains its macrogeometry (optically active shape) in accordance with prescription.

According to FIG. 16 the generation in that case usually comprises two sub-steps (see in that respect also document EP 1 203 626 B1,FIG. 1), namely preliminary edge processing (also called preliminary edging or “cribbing”), in which the edge of the spectacle lens blank is processed from the so-called “raw diameter” to the so-called “finished diameter”, and a surface processing subsequent thereto. This routinely takes place in the case of plastics material lenses initially by milling by, for example, a high-speed rotationally driven plate mill TF which is shown in principle in FIG. 17 as prior art.

As described in, for example, document EP 0 758 571 B1 the milling can then be carried out in such a way that the plate mill TF—the tool center-point track of which is indicated in FIG. 17 by a thick line—coming from the edge RA quasi rotationally “rolls in” over the transition between edge RA and surface into the surface on the rear side RS of the spectacle lens blank RL, which in that case is rotationally driven about its center axis MA. A precondition for this milling is that the block piece BS temporarily mounted on the front side FS of the spectacle lens blank RL has a maximum diameter smaller than the finished diameter of the workpiece, since otherwise a collision between milling tool TF and block piece BS would occur. During this milling the connection between workpiece RL and block piece BS additionally has to withstand substantial forces and moments, also caused by lever action due to the—by comparison—still large spacing between the machining engagement of tool TF and workpiece RL at the workpiece edge RA and the connecting point of workpiece RL and block piece BS. At the end of this milling the main quantity of the blank material to be removed has already been taken off.

Routinely following as a further sub-step of surface processing with geometrically defined cutting on the rear side RS of the workpiece is turning machining with the help of a so-called “fast-tool” arrangement (see, in that regard, for example document EP 1 779 967 A2) serving the purpose of reciprocatingly moving a turning tool with a turning edge so as to (also) work non-rotationally symmetrical surface sections (for example freeform areas in varifocal lenses) at the rotating surface, which is to be processed, of the workpiece in a so-called “single-point cutting” process. At the end of this turning, in which the turning edge can also be guided in several cycles from radially outward to radially inward (or conversely) over the rotating workpiece, preliminary processing tracks such as milling lines or the like at the produced semi-finished product are eliminated and the workpiece has the macrogeometry according to prescription at its processed surface on the rear side RS.

Fine processing by (micro) cutting, which is broadly termed “polishing” in FIG. 16, of the spectacle lenses is then carried out, in which the pre-processed optically effective surface of the respective semi-finished product gains the desired microgeometry (surface quality), in particular by geometrically undefined cutting. For that purpose the blocked semi-finished product, which has been pre-processed by cutting, is removed from the generator and further processed in a fine-processing or polishing machine. In that case, positioning and fixing of the semi-finished product in the polishing machine also take place by the block piece.

Depending on, inter alia, the material of the spectacle lenses the fine-processing is usually divided into a fine grinding process and a polishing process subsequent thereto (see, in that regard, for example, documents EP 1 473 116 A1 and EP 1 698 432 A2) or includes merely a polishing process in the polishing machine (see in that regard, for example, document EP 2 308 644 A2) if in the pre-processing a surface capable of polishing was already produced, which will usually be case with plastics material lenses processed by turning. In the polishing treatment there is movement-with addition of a liquid polishing agent provided with abrasive particles—by a flexible polishing tool or polishing plate, such as disclosed in, for example, document WO 2016/058661 A1, in defined tracks over the pre-processed surface so as to reduce the surface roughness.

Marking of the semi-finished product takes place in accordance with FIG. 16 as a next, optional process step. In that case, for example, two small circles are generated on the rear surface of the semi-finished product by, for example, a laser beam or mechanically by an engraving graver. This is necessary for, for example, freeform surfaces so as to reliably find, by way of the applied markings, the position of the semi-finished product in later processing steps. Since a high degree of accuracy in positioning is required here, positioning and fixing during marking also take place by way of the block piece. In that regard, marking can already be undertaken in the generator (see, for example, document EP 1 916 060 B1) or a machine separate therefrom.

Only after this processing the semi-finished product is separated from the block piece (so-called “deblocking” in FIG. 16). This takes place, for example, in the case of the afore-mentioned adhesive connection by a high-pressure water jet which is delivered by a nozzle and which impinges on an edge location between block piece and semi-finished product in order to detach the semi-finished product from the block piece by application of hydraulic forces (see, for example, document WO 2011/042091 A1 or WO 2011/107227 A1). As a consequence, the processed semi-finished product is now present at a single item and the separated block piece is cleaned and returned to the process step of blocking.

In further processing the semi-finished product after cleaning in accordance with FIG. 16 is optionally coated at its front side and/or rear side in order to achieve additional effects (increase in scratch resistance by hard-coating, anti-reflection properties, coloration, metallization, hydrophobic properties, etc.).

In conclusion, according to FIG. 16 so-called “edging” is performed as a final process step in which the semi-finished product is processed again at the edge for fitting into a desired spectacles frame, so that it receives the shape of the respective spectacles rim. Since the semi-finished product is now no longer fixed on the block piece, the position has to be re-established here (for example by way of the afore-mentioned markings) before the semi-finished product can be suitably fixed and finally processed in a so-called “edger” as an edge processing device (see in that regard, for example, document EP 1 243 380 A2) with respect to its edge shape and fastening in the spectacles frame.

The process chain, which is described in that regard on the basis of FIG. 16, from the prior art includes in the steps “blocking” and “deblocking” two sequences which represent necessary auxiliary processes, but do not themselves increase the value of the produced spectacle lens. A process chain managing without these auxiliary processes would thus be desirable. In particular, in order to increase efficiency and also for ecological considerations it has already been proposed in the prior art to operate “blocklessly” in the production of optically effective surfaces of spectacle lenses (see, for example, documents WO 2015/059007 A1, U.S. Pat. No. 9,969,051 B2 and DE 10 2016 112 999 A1).

In this connection, for example, document WO 2015/059007 A1 discloses a method for block-free surface processing of spectacle lenses which in that case are held (inter alia) by vacuum. In this prior art a feature is that the lens during surface processing is held in “two stages”: If the cutting tool in the form of a turning tool or mill has surface-processing engagement in the region of the lens edge with a large lever action, holding of the lens is carried out at the front surface by application of a vacuum at a suction chamber, which is sealed relative to the front surface of the lens by an encircling seal, and a central counter-holder in the form of a rotating die at the rear surface, thus from both sides. When the surface processing then progresses and, with lower processing forces, approaches the lens center the central counter-holder is retracted and the lens is held solely by the vacuum. No kind of (preliminary) edge processing of the lens is addressed in this prior art. The lens edge is mentioned merely as a possible (alternative) holding surface for the surface processing.

A problem with this prior art is to be seen in the fact that, in particular, the lens is placed in “hollow” manner on the seal surrounding the central suction chamber. In the case of comparatively thin lenses there is thus specifically the risk of the lens experiencing elastic deformation or deflection as a consequence of the holding forces applied by the central counter-holder or the centrally acting processing forces. This can lead during processing to unacceptable differences between the actual geometry produced at the rear surface and the target geometry desired thereat, which become noticeable when the lens after processing “relaxes” again. Such lens deformations detracting from processing quality and caused by the holding system are particularly critical when comparatively complex surface geometries (i.e. other than purely spherical or toroidal surfaces) are to be produced. Indeed, in document WO 2015/059007 A1 there is also shown and described an embodiment (FIG. 3) which in the suction chamber has a plurality of concentrically arranged, individually axially movable rings, which are resiliently biased in the direction of the lens to be held, for support. However, if the lens to be held has a non-rotationally symmetrical geometry at its receiving surface, local cavities together with the above-discussed risk of undesired deformation of the lens under the acting processing forces in these unsupported cavities arise between the lens and the rings anyway.

In order to remedy this a specially constructed mount or holder for pneumatic blocking or holding of optical lenses at a surface processing machine has been proposed in the prior art in accordance with document U.S. Pat. No. 9,969,051 B2. The holder disclosed therein generally comprises a clamping part in order to secure the holder to an associated component of the surface processing machine, and a subassembly for blocking the lens, the subassembly comprising a base body from which project abutments intended to offer the lens a firm seat, as well as a seal with which the lens can be brought into contact so as to bound a vacuum chamber together with the base body. The abutments comprise a plurality of first rods which are mounted to be displaceable with respect to the base body so as to be supported at the lens by their free ends and three second rods fixedly connected with the base body. In addition, restoring elements in the form of springs are provided at the first rods so as to reset, i.e. lay, the first rods against the lens.

In this prior art the rods provided in the region of the vacuum chamber thus also produce—radially within the seal—axial support at the front surface of the optical lens, which is sucked against the mount, when processing forces act on the rear surface of the lens during machining of the lens. However, here as well comparatively large cavities, which are elastically bridged over by the lens, are present between the individual rods. Moreover, the resilient biasing of the rods reduces the retaining force generated by the effective suction area of the mount, so that there is a risk of the lens detaching from the mount in the case of high processing forces, particularly as a consequence of lever action at the lens edge.

In addition, document DE 10 2016 112 999 A1 is concerned with the design of a workpiece mount for holding optical lenses in lens processing machines, which is to enable block-free clamping of the lens during surface processing. The workpiece mount disclosed therein is also constructed for different “clamping technologies”: On the one hand, for suction of the lens against a mount surface of an insert formed from a porous material a sub-atmospheric pressure can be applied by way of an air channel, whereupon the lens can be (finely) processed with moderate forces (turning, grinding, polishing). On the other hand, the lens can be clamped at its round circumferential edge and, in particular, by mechanical clamping fast by clamping regions provided at a clamping chuck, which shall make “more forceful” (preliminary) processing (milling, turning) possible.

However, in this prior art there is also the risk of deformations of the lens detracting from processing quality when the lens is mechanically clamped at the circumferential edge by radially acting clamping forces. Moreover, mechanical clamping of the lens at the circumferential edge hampers or prevents preliminary processing in the edge region of the lens by machining, as described in the introduction.

Finally, document EP 1 037 727 B1 discloses an edger, i.e. a spectacle lens edge processing machine, with a spectacle lens holder, which has suckers, for a raw lens held at least at one side, and with a small-format processing device, which has only an end mill driven at high speed or a grinding pencil or laser jet as sole processing tool, for complete shape-working of the raw lens by a separating cut, for application of a roof bevel or a circumferential groove or of grooves for fastening of a spectacles frame by clamps or bores. However, this prior art does not impart anything with regard to processing of optically effective surfaces of the spectacle lens.

Object

By comparison with the prior art described so far the invention has the object of providing a simplest possible method for machining optical workpieces, particularly spectacle lenses of plastic, which addresses the above-described problems, in particular enables workpiece processing with process reliability and without workpiece deformations detracting from processing quality and ideally can be performed in block-free manner.

Illustration of the Invention

This object is fulfilled by a method with the method steps according to claim 1. Advantageous or expedient embodiments and developments of the invention are the subject of the dependent claims.

According to the invention a method for machining optical workpieces, particularly spectacle lenses of plastic, in which starting from the blank a semi-finished product with predetermined surface geometries at a front side and a rear side remote therefrom and with a contoured edge of predetermined edge thickness between the front side and the rear side is formed, comprises the following principal steps elapsing in the stated sequence: i) providing the blank, which has a blank thickness and can already have the predetermined surface geometry at the front side and which is to be processed at least at the rear side and the edge; ii) block-free picking up of the blank at the rear side for supported holding of the workpiece; iii) processing the blank at the front side by a first tool for formation of an encircling groove or step with a depth greater than or equal to the edge thickness of the semi-finished product to be formed and smaller than the blank thickness or an encircling cut having at least in part a depth equal to the blank thickness so that a circumferential surface defining the contoured edge of the semi-finished product to be formed remains at the tool; iv) picking up the workpiece at the front side for supported holding of the workpiece; 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.

Due to the fact that in the principal step iii) the groove, the step or the cut is formed on the front side of the blank in encircling manner with in each case a depth greater than or equal to the edge thickness of the semi-finished product to be formed, there is complete separation of the semi-finished product from the excess radially outer material of the blank in—at the latest—the principal step v) when the predetermined surface geometry of the semi-finished product is generated by machining at the rear side; “at the latest” in connection with the principal step v) inasmuch as the encircling cut—depending on the radial dimensions of the rear-side retainer, which is not to collide with the first tool—can have entirely and not merely partly a depth equal to the blank thickness so that a deeper cut of that kind in principal step iii) in the sense of a circumferential “penetration” already leads to separation of excess radially outer material of the blank. As a consequence of the depth dimension of the groove, the step or the cut in thickness direction of the workpiece, a circumferential surface of the workpiece, which according to the invention defines the contoured edge of the semi-finished product to be formed, then remains already in the principal step iii).

In connection with the claimed geometric shapes of groove, step and cut, which are produced at the front side of the blank in the principal step iii), the conjunction “or” which is used shall in general be understood to be non-exclusive. Accordingly, apart from grooves, steps or cuts encircling the whole circumference, mixed forms of these geometries are also conceivable here and therefore are not to be excluded. An example of such a mixed shape would be, for example, an encircling groove which in sub-regions “departs from” the blank material in radial direction to form a step and/or in axial direction to form a cut. This can result from, for example, the predetermined surface geometry at the front side of the blank and/or the desired edge contour of the semi-finished product.

In other words, according to the invention in the principal step iii) of the method the processing of the contoured edge of the semi-finished product to be formed—whether in the sense of preliminary edging or finish-edging of the workpiece—is advanced or brought forward in time and, in particular, starting from the front side of the blank, which in that case is held without blocking at the rear side in accordance with the principal step ii), before the workpiece after picking up at its front side in the principal step iv) is surface-processed at its rear side in accordance with the principal step v). In any case, according to the principal step v) the generated semi-finished product is then completely separated from excess radially outer blank material which drops off as an annular piece or in ring segments as is explained in the following.

This basically two-stage procedure—initially workpiece holding at the rear side and processing at the front side of the workpiece near the blank edge, thereafter holding at the front side and processing at the rear side of the workpiece, as well as in the center—together with the claimed sequence of the individual method steps offers a number of advantages in the machining of, in particular, spectacle lenses of plastic. These advantages primarily concern (1st) holding, which is important for process reliability, of the workpiece during the actual (preliminary) edge processing and (2nd) propping up or supporting of the workpiece, which is relevant for processing quality, during the actual surface processing.

As far as firstly (1st) holding of the workpiece is concerned, the need in the above-described prior art to mount or block the blank at its front side so that it radially projects by its edge region beyond the mount or the block piece in order to allow preliminary edging of the workpiece without collision of the workpiece with the mount or block piece is eliminated. In conjunction with that it is possible to avoid the processing forces (see in that regard FIG. 17) which in the prior art during preliminary edge processing act on the blank edge, i.e. maximally radially outward, and are directed from the front side towards the rear side and which endeavor to “lever off” the blank from its mount or the block piece. In particular, in order to solve the problem it is not necessary to dispense with preliminary edge processing, which in the case of spectacle lenses would cause other problems, namely in the entire calculation of the surface geometry to be produced at the rear side of the lens, because the calculated rear surface of a spectacle lens to be processed in many cases could not be extrapolated by way of the calculated finished diameter of the lens.

Rather, according to the invention a complete—i.e. not fundamentally limited in its processing depth and processing width—(preliminary) edge processing of the workpiece is possible, particularly in accordance with the predetermined edge thickness and edge contour of the semi-finished product to be formed. This is because the blank neither has to be clamped at the edge nor held at its front side for that purpose, but according to the principal step ii) and in distinction from the prior art discussed in the introduction is held at its rear side, whilst according to the principal step iii) the edge geometry or the contoured edge of the semi-finished product to be formed is produced without constraint by processing from the front side of the blank.

In that regard, the processing forces are more moderate by comparison with the prior art outlined above, since in the principal step iii) only a groove or a step or a cut is produced, for which purpose merely a small tool is required, and the entire excess blank material does not have to be machined. This advantageously allows appropriately smaller holding forces through the retainer and moreover leads to a swarf volume for disposal which is reduced by comparison, this also being of advantage. Moreover, the processing forces in the principal step iii) are primarily directed radially and also from the front side towards the held rear side, which is a positive for process-secure holding of the blank, and not mainly in reverse sense away from the holding at the rear side, which weakens the holding of the workpiece as in the prior art (see FIG. 17). Overall, the requirements, which are “reduced” by comparison with the previously known preliminary edging, of the principal step iii) according to the invention also advantageously enable uncomplicated “block-free” picking up of the blank in the principal step ii), for example by the technological operating principle of vacuum by a vacuum sucker, thus without a block piece at the blank, as described in the introduction with respect to conventional procedure.

With respect to (2nd) the propping-up or support, which is important for the requisite surface accuracy, of the workpiece during actual surface processing it is to be said with respect to the invention that the stepped procedure, which is proposed here, according to the principal steps iii) and v) of the processing—in brief: edge from front side before surface on rear side—with elimination of the need for an edge of the blank radially projecting beyond the retainer in accordance with the previously known concepts opens up the possibility of supporting the workpiece during surface processing not only centrally, but also in the edge region. This can take place with the help of, for example, suitable closely spaced pins or rods similar to the concept disclosed in document U.S. Pat. No. 9,969,051 B2 for a lens mount.

Ideally, the workpiece in the principal step iv) is even retained at the front side in such a way that the workpiece is held at the front side with support over the whole area-i.e. not merely at multiple locations—which is accordingly preferred. If, for example, in current production of spectacle lenses to prescription the finished diameter of the lenses is in a range between 50 millimeters and 80 millimeters a retainer with a diameter of at least 80 millimeters can be used for the principal steps iv) and v) according to the invention, which enables support at the entire front side.

Moreover, by comparison with the prior art discussed in the introduction with a projecting workpiece edge (cf. again FIG. 17), advantageously the entire surface on the front side of the workpiece is available in order to hold the workpiece during surface processing of the rear side. This also opens up the possibility of use—which is reliable in terms of process—of alternative holding concepts during the surface processing, in which holding by way of, for example, generation of a vacuum between workpiece and retaining system takes place. It is then also preferred if the workpiece in the principal step iv) is also held in block-free manner at the front side, because the method then can be carried out entirely without blocking and deblocking and the (extra) effort connected therewith. However, it also conceivable, although less preferred for reasons of efficiency, to hold the workpiece in the principal step iv)—as far as possible over the whole area—at the front side with use of a block piece as is known in principle from the prior art.

The actual surface processing at the rear side of the workpiece can then be carried out as known from the prior art, for example in the sequence (preliminary) milling, coarse turning, fine turning or only by processing of the rear side through turning. The force components in processing are in that case again primarily directed radially and advantageously axially towards the retainer at the front side of the workpiece.

As a result, the method according to the invention enables, in particular, machining of lens blanks to form semi-finished products for spectacle lenses even when the retaining system by which they are supported and held during processing of the rear side does not allow processing of the edge geometry. It thus also represents a significant component of a novel, simplified process chain for production of spectacle lenses from plastic, which, in particular, manages without needing to use of the previously known block pieces.

In a first alternative of the method it can be provided that in the principal step iii) for formation of the encircling groove or step or the encircling cut by the first tool there is produced at the semi-finished product an edge contour which has a slight oversize in relation to an edge contour of the workpiece processed to finished state, wherein the edge contour of the workpiece processed to finished state is produced only after the principal step v) for processing the rear side of the workpiece, for example in the way known from the prior art outlined in the introduction, i.e. with the assistance of an edger, optionally after undertaking usual coating steps. In other words, in this alternative of the method merely “cribbing” or preliminary edging of the workpiece is carried out from the front side of the workpiece in the principal step iii).

On the other hand, in a second alternative of the method provision can be made for production at the semi-finished product in the principal step iii) at the time of or after formation of the encircling groove or step or the encircling cut by the first tool or another tool of an edge contour which already corresponds with an edge contour of the workpiece processed to finished state. In this alternative of the method the workpiece thus already receives its final edge contour from its front side, which advantageously renders later edging for production of the macrogeometry required for fitting in a spectacles frame redundant. Depending on the shape of the rim, only polishing of the edge after the principal step iii) may be necessary at the edge of the workpiece before the spectacle lens—after performing the rest of the process steps such as, if required, coating—is inserted into the spectacles frame. This alternative does, of course, presuppose that the final edge shape of the spectacle lens is already known at the time of surface processing of the lens blank.

In both above-mentioned alternatives of the method it is possible in the principal step iii) to already apply a chamfer to the transition between the edge and the rear side of the semi-finished product to be formed and/or to apply a chamfer to the transition between the edge and the front side of the semi-finished product to be formed. Formation of such a chamfer as a protective bevel is recommended particularly when the workpiece (also) has to be manually moved or transported in further process steps, so as to prevent injuries at a sharp-edged workpiece edge. In the case of spectacle lenses, such a chamfer of the lens has to be present at the rear side in any case at the latest after the edging so as to avoid injury to the wearer of the spectacles.

In a preferred embodiment of the aforesaid development of the method it can additionally be provided that in the principal step iii) the chamfer or chamfers is or are applied by the first tool at the same time as the encircling groove or step or the encircling cut. A suitably equipped combination tool with appropriately formed cutting edges can be used for that purpose. This is conducive to rapid and efficient guidance of the method. However, it is also possible in the principal step iii) to initially form the main geometry (groove, step or cut with circumferential surface of the semi-finished product to be produced) by the first tool in a sub-step and thereafter to apply the chamfer or chamfers by a further tool—or again by the first tool in a different setting with respect to the workpiece if this is possible with the existing machine kinematics—in a succeeding sub-step, or with inverse time sequence.

In the case of the afore-described second alternative of the method (finish edging) it is in addition preferred if in the principal step iii) a fastening geometry for the workpiece processed to finished state is produced at the same time at the edge and/or at the front side of the semi-finished product to be produced. In particular, in the principal step iii) the fastening geometry for the workpiece processed to finished state can be formed by the first tool at the same time as the encircling groove or step or the encircling cut, which is equally conducive to rapid and efficient guidance of the method.

In that case, the fastening geometry produced in the principal step iii) for the workpiece processed to finished state can be a pointed or roof-shaped bevel or an encircling channel or groove at the edge of the semi-finished product to be formed, depending on the fastening requirements of the respective rim for the workpiece. For that purpose, the first tool can again be constructed as a combination tool with suitably shaped cutting edges. Alternatively or in addition thereto, the fastening geometry produced in the principal step iii) for the workpiece processed to finished state can have one or more bores or notches at the front side and/or the edge, again depending on the fastening requirements of the respective rim for the workpiece, for which purpose use may be made of a further tool if the afore-mentioned combination tool is not appropriately equipped.

Moreover, in concrete management of the method it is preferred if at the start of the principal step iii) the first tool and/or the workpiece are so moved relative to one another that the first tool for formation of the encircling groove or step or the encircling cut starting from the front side of the workpiece enters the workpiece at a frontal entry point. This assists holding of the workpiece at its rear-side retainer because a resultant force component is in any case directed towards the retainer.

Alternatively, at the start of the principal step iii) the first tool and/or workpiece can also be so moved relative to one another that the first tool for formation of the encircling groove or step or the encircling cut enters the workpiece starting from the edge of the workpiece at an edge entry point. As a result, a first separating point is advantageously already produced at the radially outer remnant which later drops off in the principal step v), of the blank material.

Moreover, in the principal step iii) after entry of the first tool into the workpiece the first tool and/or the workpiece can preferably be so moved relative to one another that the first tool produces the groove or step or the cut in at least one revolution (i.e., optionally also several revolutions) at the workpiece, wherein the first tool leaves the workpiece at an edge exit point, which is remote from the frontal or edge entry point, at the edge of the workpiece. This also leads to a separating point at the radially outer remnant, which later drops off in the principal step v), of the blank material.

During one or more revolutions at the workpiece it is also possible for the tool in the principal step iii) to be moved several times radially out of the workpiece and moved back in, so that a plurality of separating points arises in the blank material, which has the consequence that thereafter in the principal step v) the radially outer remnant, which is to be removed, of the blank material falls off in several ring segments from the produced semi-finished product. For example, two or three or even more ring segments can thus fall off as waste. A number of four to eight separating points leads, for example, to a corresponding number of consequently smaller-scale ring segments as waste in the principal step v), which, for example, can facilitate conducting away and preparation of a liquid cooling lubricant optionally used in the machining.

Finally, as far as the first tool used in the principal step iii) for processing the blank at the front side is concerned, in that regard this can preferably be a rotationally driven end mill. Such an end mill provided with a high-speed drive is not only able to form a high-quality circumferential surface at the semi-finished product, which is to be produced, with comparatively low processing forces, but also is, for example, well-suited to forming the afore-mentioned separating points in the remnant, which is to be removed, of the blank material by machining when a groove or a cut is to be formed in the principal step iii).

However, use of other tools is also possible, for example, if production of the above separating points does not matter and/or if more complex circumferential contours, particularly contours departing from a circular or elliptical shape, at the semi-finished product do not have to be formed by machining. Thus, for example, use can be made of a plate mill for forming the step in the principal step iii). In addition, use of a narrow turning tool held in rotationally secure manner is basically possible for formation of the groove, the step or the cut in the principal step iii) if the machine kinematics of the processing device used for this purpose provide it, i.e. the cutting speeds required for correct machining can be produced by, in particular, a suitable rotary drive of the workpiece.

In fact, in the case of use of the last-mentioned examples of tools the possibility of forming a wide range of edge geometries at the semi-finished product is limited. For that purpose, however, such a tool can also be used for surface processing of the rear side of the workpiece in the principal step v). Equally, with respect to greatest possible flexibility in the selection of possible geometries at the edge and surface of the workpiece it is preferred if the first tool used in the principal step iii) for processing the blank at the front side is different from the at least one second tool used in the principal step v) for processing the workpiece at the rear side.

Further features, characteristics and advantages of the method according to the invention are evident to the person skilled in the art from the following description of preferred examples.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

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;

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;

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;

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;

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;

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;

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;

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;

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;

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;

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;

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;

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;

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;

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;

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

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

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.

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.

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. 3—quasi as a “substitute”—illustrates only that material part of the blank RL from which the semi-finished product HZ is produced in the course of the method.

In general the method “block-free generation” of FIG. 1 comprises—obviously after the start

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

- still the following four principal steps ii) to v) taking place in the indicated sequence:
- 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”.
- 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 that—termed “preliminary edge processing” in FIG. 1—a 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 ST—in a given case also in a combination—an 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.
- 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.
- 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.

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.

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.

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 tool—during surface processing of the rear side RS—processing the workpiece up to the geometry (groove NU, step ST or cut) formed on the front side FS thereof.

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.

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 inversion—i.e. the tool is moved, whilst the workpiece is arranged at a fixed location—as 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.

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.

In the illustrated embodiment the end mill, which is used as the first tool WZ1, is provided around the circumference—considered in a projection as shown—with 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.

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.

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°.

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.

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.

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).

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.

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 as—in this embodiment or example of use of the method—to 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.

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.

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.

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.

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, the—in the illustrated embodiment—two (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.

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).

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.

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.

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.

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.

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.

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).

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 also—but does not have to—be formed therewith, as illustrated in FIG. 15 of the left.

In the case of the method embodiment illustrated in FIG. 15 on the right, even a fastening geometry for the workpiece processed to finished state—here, by way of example, shown at the transition from edge RA and front side FS of the semi-finished product HZ to be formed—is 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.

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.

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.

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

- AS exit point
- BS block piece
- D1 blank thickness
- D2 edge thickness
- ES entry point
- FA1 chamfer
- FS front side
- HZ semi-finished product
- MA center axis
- NU groove
- RA edge
- RG ring segments
- RK1 edge contour of the semi-finished product
- RK2 edge contour of the workpiece processed to finished state
- RL blank
- RS rear side
- SF pointed bevel
- SN suction cup
- SS support pin
- ST step
- TF plate mill
- TI depth
- UF circumferential surface
- VS vacuum sucker
- WA workpiece holding device
- WZ1 first tool
- WZ2 second tool

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

Information

Publication Number

Date Filed

Date Published

Inventors

Original Assignees

CPC

International Classifications

Abstract

Description

Claims

Priority Claims (1)

PCT Information