EP0758571A1 - Process and tool for manufacturing a concave outer surface on a spectacle lens blank - Google Patents

Abstract

The appliance consists of a disc shaped grinding tool (2) with an annular grinding lip asymmetrically positioned and with its maximum radius leading into a circular cutting edge. The rear surface of the tool facing away from the grinding lip and opening into the cutting edge runs in relation to the tool's rotary axis (c) at an angle between the tool (b) and the rotary axis. The periphery has evenly distributed holder arms to whose outer ends cutter plates are fixed pointing radially to the grinder's rotary axis, and whose blades define an aspherical enveloping surface.

Description

The invention relates to a method for producing a concave surface from a lens blank, according to the preamble of claim 1, and also includes tools for performing the method on brittle and hard plastic lens blanks.

In a known method of the type specified at the beginning (DE 42 10 381 A1), the tool and the workpiece are controlled during the entire process sequence in such a way that the material is removed exclusively along a spiral path. In this way it is possible to achieve a shape of the concave surface which already largely corresponds to the finished lens surface, but this is done with a low cutting power. If larger material removals are to be carried out on the workpiece in this way, the workpiece and tool would have to be moved several times along a spiral path relative to one another, which leads to undesirably long processing times in the prescription production of spectacle lenses.

The invention has for its object to propose a method of the type specified in the preamble of claim 1, with which, at high cutting performance, both brittle hard materials and plastic materials for producing all the concave surface shapes customary in spectacle lens optics, with the result of a uniform surface quality and short machining times can be processed economically. The task of the invention also includes the provision of tools which are particularly suitable for carrying out the method. The object is achieved by the features of claim 1. Advantageous further developments of the method are specified in subclaims 2 to 5 and are also explained in more detail below. Tools which are particularly suitable for carrying out the process are specified in claims 6 and 7, of which claim 6 includes the tool design for brittle hard materials and claim 7 the tool design for plastic materials.

The step distribution of the method according to the invention into two work steps, namely a first plunge work step and a second work step with material removal along a spiral path, leads to very short processing times. Very high cutting or grinding capacities are possible during the plunge-cut operation, so that the majority of the blank material to be removed is quickly removed. The continuous piercing or immersion process saves the multiple cuts required in the known method in the case of thick spectacle lens blanks. Already during the plunge-in operation, a surface is achieved at least in the area of the outer edge which corresponds to the nominal outer contour of the optically effective inner surface of the spectacle lens.

The method according to the invention enables the generation of highly precise surfaces. It can be used to produce all the surface shapes that are customary in spectacle lens optics, namely toric, prismatic, decentered, multifocal or atoric surfaces on glasses and plastics.

An edge processing operation is preferably integrated in the method according to the invention, as a result of which not only can thin, comfortable spectacle lenses be produced, but also a reduction in working time with less tool wear on the side of the spectacle manufacturer for the later fitting of the spectacle lens. The advantage for the process user is that a smaller stock of semi-finished glasses with different diameters is made possible.

If the three operations edge machining, grooving and machining along the spiral path according to claim 3 are carried out in a continuous sequence, very short manufacturing times can be achieved. These operations can be carried out in a single clamping or blocking of the workpiece.

If the peripheral edge of the workpiece is to be provided with a facet, a faceting operation can also be switched on in the process sequence, so that when an edge processing operation is carried out, a total of four immediately successive operations are carried out on the workpiece with only one clamping or blocking.

A fixed angle between 90 ° and 120 ° is possible between the two rotational movement axes c and b. Preferably, this angle is set at 105 ° according to claim 5, i.e. with the workpiece axis b arranged vertically, the tool axis c is inclined to the horizontal at an angle of only 15 °. At this angle, there can be no collision between the tool spindle or the tool shaft and the rim of the lens while the grinding or milling process is being carried out, even with very strongly concave curved lens surfaces.

The grinding tool specified in claim 6 for performing the method on a brittle hard lens blank is very advantageous due to the special design of the grinding lip, because the cutting edge geometry remains constant even when worn. Only the diameter of the tool decreases due to wear, but this can easily be compensated for by measuring the thickness of the ground spectacle lens and subsequent calculation in the control program.

The milling tool according to claim 7 for performing the method on a plastic spectacle lens blank is disc-shaped in terms of its rotational shape, with individual milling cutting edges are distributed around the circumference. The cutting performance of this milling tool, in which the cutting edges define a shaping toric envelope, is high.

The service life of the milling cutters can advantageously be increased if the cutting plates of the milling tool having the cutting edges are rotatably fastened in accordance with claim 8. In this way, several areas of the cutting inserts can be screwed into a working position before the cutting inserts are replaced for reasons of wear or their outer diameter has to be reworked.

Fig. 1

eine teilweise geschnittene und abgebrochen dargestellte Seitenansicht einer Fräs- und Schleifmaschine für Brillengläser,

Fig. 2

die Vorderansicht der Maschine nach Fig. 1,

Fig. 3

eine Seitenansicht des Schleifwerkzeugs,

Fig. 4

die Seitenansicht gemäß Fig. 3, jedoch nach Benutzung und Verschleiß des Schleifwerkzeugs,

Fig. 5

eine Seitenansicht des Fräswerkzeugs,

Fig. 6

eine vergrößerte Einzelheit des Fräswerkzeugs gemäß Fig. 5, entsprechend dem Ausschnittskreis VI,

Fig. 7

die Vorderansicht des Fräswerkzeugs in Blickrichtung des Pfeils VII in Fig. 5,

Fig. 8

Werkzeug und Werkstück während des Randbearbeitungsvorgangs, in zwei Ansichten, nämlich mit einer Seitenansicht und der Vorderansicht des Werkzeugs,

Fig. 9

Werkzeug und Werkstück während des Facettierungs-Arbeitsgangs, in zwei Ansichten ähnlich Fig. 8,

Fig. 10

Werkzeug und Werkstück während des Einstech-Arbeitsgangs, in zwei Ansichten ähnlich Fig. 8 und 9,

Fig. 11

Werkzeug und Werkstück während des Arbeitsgangs mit Bearbeitung entlang des spiralförmigen Weges, in zwei Ansichten ähnlich Fig. 8,9 und 10,

Fig. 12

die Draufsicht auf das Werkstück nach dem Arbeitsgang mit Bearbeitung entlang des spiralförmigen Weges und

Fig. 13

den abgebrochenen und vergrößerten Schnitt durch das Werkstück gemäß der Linie XIII-XIII in Fig. 12.

The invention is explained in more detail below with reference to the drawings, which are carried out essentially schematically. It shows:

Fig. 1

a partially cut and broken side view of a milling and grinding machine for glasses,

Fig. 2

the front view of the machine of FIG. 1,

Fig. 3

a side view of the grinding tool,

Fig. 4

3, but after use and wear of the grinding tool,

Fig. 5

a side view of the milling tool,

Fig. 6

5 shows an enlarged detail of the milling tool according to FIG. 5, corresponding to the detail circle VI,

Fig. 7

the front view of the milling tool in the direction of arrow VII in Fig. 5,

Fig. 8

Tool and workpiece during the edge machining process, in two views, namely with a side view and the front view of the tool,

Fig. 9

Tool and workpiece during the faceting operation, in two views similar to FIG. 8,

Fig. 10

Tool and workpiece during the grooving operation, in two views similar to FIGS. 8 and 9,

Fig. 11

Tool and workpiece during machining with machining along the spiral path, in two views similar to FIGS. 8, 9 and 10,

Fig. 12

the top view of the workpiece after the operation with machining along the spiral path and

Fig. 13

the broken and enlarged section through the workpiece along the line XIII-XIII in Fig. 12th

Of the grinding or milling machine, only the parts 1 and 2 carrying or guiding and driving parts are shown in FIGS. 1 and 2 for simplification. The tool 2 is attached via a shaft 3 coaxially to a spindle 4, which is driven by an electric motor 5 so that it can be rotated and its speed can be regulated. The workpiece 1 is blocked on a workpiece holder 6, which is concentrically attached to a spindle 7. The spindle 7 is driven by a servo motor 8 in a numerically controlled manner.

Workpiece 1, tool holder 6, spindle 7 and motor 8 as well as all associated parts not specified in more detail are attached to a coordinate device of the machine and can therefore be moved together on mutually perpendicular linear movement axes x and y. The common central axis of the parts 1, 6, 7 and 8 coincides with the rotational movement axis b of the workpiece 1. The central axis common to the tool 2, the shank 3, the spindle 4 and the motor 5 coincides with the rotational movement axis c of the tool 2 and a tool setting axis z (FIG. 1). The linear movement axes x, y and the rotation movement axis b are CNC-controlled, while the rotation movement axis c can only be regulated by speed. The axis z is only used for the adjustment of the tool 2 on the rotational movement axis c. Since all CNC axes are combined in the workpiece spindle, simple loading results. The workpiece can be moved into a defined loading and unloading position, so that simple handling devices can also be used for automatic workpiece change.

In the example shown, the angle α defined by the machine construction between the two rotational movement axes b and c has the value of 105 °. The angle α is thus determined by the machine construction and cannot be changed.

The tool spindle 4 with the attached tool 2 and the associated electric motor 5 and all other associated unspecified parts can be adjusted while maintaining the design angle α for adjusting the tool 2 to the center of the workpiece 1 at right angles to the x-movement axis. For this purpose, the aforementioned adjustable parts are rigidly connected via a support arm 9 to a guide carriage 10 which is mounted on a guide bed 11 of the machine so as to be displaceable in the specified direction of adjustment. Between the guide carriage 10 and the guide bed 11, a threaded spindle 12 is effective for adjustment, which on the one hand is rotatable but axially immovable on the guide bed 11 is mounted and on the other hand engages in a corresponding thread of the guide carriage 10.

For a more detailed explanation of the tool 2 designed as a grinding tool, reference is now made to FIGS. 3 and 4. As can be seen from this, the grinding tool is disc-shaped with an annular grinding lip 13 located on its circumference. Starting from the end face of the asymmetrically designed grinding lip 13, its radius increases towards the spindle 4, its largest radius ending in a circular shaping cutting edge 14. To carry out the method, this shaping cutting edge must be set on the workpiece such that it is directed approximately radially to the center of the workpiece. The rear surface 15 of the grinding lip 13, which ends in the cutting edge 14 and is located on the spindle side, is designed taking into account the constructively defined angle α such that the rear surface to the tool rotation axis c runs at the angle α. A perpendicular through the lowest point 16 of the cutting edge 14 lies against the rear surface 15 in the manner of a radial surface line. The lowest point 16 is always in the plane of the two linear axes of movement x and y. This becomes clear when comparing FIGS. 3 and 4. The cutting edge 14 is always determined by the largest radius of the grinding lip and is always directed approximately radially to the center of the workpiece even as tool wear progresses. In addition to the wear contour shown in full lines, the new contour of the tool is also shown in dashed lines in FIG. 4. Due to this special tool geometry, the cutting edge always sharpens itself during the grinding process, so that the shape of the surface to be machined is not impaired. The reduction in the cutting edge radius due to wear can easily be taken into account in the computer program of the machine.

The grinding material of the grinding lip 13 consists of finely divided diamond particles. Here, the grinding lip 13 consists either of sintered material, in which the diamond particles are embedded in a finely divided form, or the finely divided diamond particles are applied to the annular grinding lip 13 in a galvanically bonded manner.

For the description of the milling tool 2 'provided for plastics processing, reference is now made to FIGS. 5 to 7. As can be seen from FIG. 5, the milling tool 2 'is disc-shaped with respect to its rotational shape. For this purpose, the milling tool 2 'is provided with a plurality, in the example shown with eight holding arms 17 which are evenly distributed on the circumference and which extend outwards from a central hub part 18. At the outer ends of the holding arms 17, matching cutting inserts 19 are attached. The annular cutting edges 20 of the cutting inserts 19 are aligned radially to the axis of rotation c of the milling tool 2 'and define a shaping toric envelope surface, which is indicated by broken lines in FIG. 5. The toric envelope surface is oriented approximately radially to the center of the workpiece with respect to its plane formed by its largest radius. The deepest point 16 'of the shaping toric envelope is always in the plane of the two linear axes of movement x and y.

In Fig. 6 it is shown that the cutting plates 19 are each fastened to the holding arms 17 by a central screw 21. With the help of the screw 21, the set rotational position of the cutting insert 19 is fixed on the holding arm 17. As indicated in Fig. 6 by the angle dimension β, only an angle of about 90 ° is used from the circular circumference of the ring cutting edge 20 for the milling process, i.e. only about a quarter of the circumference of the ring cutting edge is used for the milling process. This means that the cutting inserts 19 can be rotated three times into a new position after the first ring cutting sector has worn out.

For a more detailed explanation of the procedure, reference is now made to FIGS. 8 to 11 below. This process sequence covers all possible machining operations, namely the edge machining operation (FIG. 8), the faceting operation (FIG. 9), the plunge operation (FIG. 10) and the surface processing Final step in the context of the present method with machining along the spiral path (FIG. 11). 8, 9, 10 and 11, the relative movement of the tool center relative to the workpiece is indicated in dotted lines. In fact, it is not the tool that is moving relative to the workpiece, but the other way round, the workpiece is moving relative to the tool.

The process sequence is described using the example of machining an eyeglass lens blank 1 on a brittle hard material using a grinding tool 2. The machining of an eyeglass lens blank made of plastic using a milling tool is carried out accordingly. The procedural steps edge processing and faceting are optional, albeit preferably concurrent, processes. 8 to 11 show the sequence of the method steps used. The axes x, y, b and c indicated symbolically only in FIG. 8 apply to all of FIGS. 8 to 10.

The blocked workpiece 1 is first approximated to the tool 2 by lateral displacement on the x-axis, whereupon the workpiece 1 is displaced on the y-axis relative to the tool 2 which always remains stationary until the workpiece 1 is approximately at the same height as the tool axis is located and the workpiece edge tangent to the circular cutting edge 14. When the tool and workpiece rotate about the respective rotational movement axes c or b, material is removed from the workpiece edge. By further lateral movement of the workpiece 1 on the x-axis and continuous infeed on the y-axis, processing of the spectacle lens blank is now carried out to the circumferential contour predetermined by the shape of the spectacle frame. When the workpiece 1 is fed on the y-axis, the tool is attacked at the edge of the workpiece approximately in the manner of a helix.

After completion of the peripheral contour, the upper workpiece peripheral edge is faceted using the tool. This process takes place in a continuous sequence with the others Work steps with constant rotation of workpiece and tool. In this case, according to the extent and the direction of the desired faceting, the workpiece 1 is both approximated to the tool 2 on the x-axis and the workpiece is moved downward in a movement overlaid on the y-axis until the desired facet surface 22 is achieved .

In a further continuous process step sequence, the workpiece 1 is moved relative to the tool 2 during the plunge-in operation by means of coordinated, program-controlled movement on the x and y axes with constant rotation of the workpiece and tool about the associated rotation axes until the tool and workpiece are roughly the same as in FIG 10 take the relative position shown. At this point in the process, the bulk of the blank material to be removed is removed. This has resulted in an annular trough-shaped surface 23 which is adapted as far as possible to the surface to be produced. In addition, an outer edge 24 is achieved, which corresponds to the target outer contour of the optically effective inner lens surface. This completes the grooving process.

Now, in a continuous process step sequence, the last work step illustrated in FIG. 11 takes place, which serves to remove the remaining amount of the excess blank material until the surface is finally shaped. Here, a superimposed movement takes place between the workpiece 1 rotating about its axis b and the otherwise stationary tool 2 rotating about its axis c in the direction of the x and y axes with a spiral course of the machining path 25 shown in FIG. 12 on the machined surface . In this last work step, the annular trough-shaped surface resulting from the plunge-in work process disappears, ie the approximately conical central tip of this surface. Because of the large diameter of the shaping cutting edge 14 of the tool 2, only a very small groove formation occurs on the spiral machining path, ie a very small tip height above the groove base. With a diameter of the cutting edge 14 of 70 mm, for example, this is only 0.0642 mm with a tip spacing of 5 mm. These relationships are shown in FIG. 13. The result after the last process step, ie the working step with machining along the spiral path, is a machined surface which is already so precise that the fine grinding and polishing effort following the method according to the invention is low.

For simplification, the creation of a spherical-concave surface has been shown and described. Of course, other surface shapes mentioned at the outset can also be generated by corresponding program control of the x and y axes.

A method for producing a surface from an eyeglass lens blank is described which is suitable for brittle hard materials as well as for plastics. Here, a disk-shaped, rotationally symmetrical tool of relatively large diameter is used, with the aid of which the blank material to be removed is removed with a high grinding or milling capacity in at least two work steps, a plunge-cutting step and a shaping step with material removal along a spiral path. The last operation results in a machining path running spirally from the outside inwards with a low residual tip height and a relatively large tip spacing. The surface created requires only minor fine grinding and polishing post-processing. Optionally, both an edge machining process that adapts to the shape of the spectacle frame and a work step that facets the rim of the spectacle lens can be integrated into the method. Tools for carrying out the grinding or milling process are also proposed.

Claims (8)

Method for producing a concave surface on a lens blank (workpiece), which already largely corresponds to the finished lens inner surface, by means of a milling or grinding tool, in which the blocked workpiece and the tool in a CNC-controlled machining process with two linear movement axes (x and y-axis) and two rotational movement axes running at an angle (α) to one another, one of which is assigned to the workpiece (b-axis) and the other to the tool (c-axis), are guided so as to be movable relative to one another, with the shaping of the surface the material is removed along a spiral path on the surface by moving the tool and the workpiece in a controlled manner relative to one another along the x, y and b axes, and using a disk-shaped, rotationally symmetrical tool as the tool, which is arranged in such a way that the lowest point (16, 16 ') of the tool is in is in relation to the workpiece in a plane defined by the b- and x-axes , characterized in that the material removal along the spiral path is preceded by a plunge-cutting operation in which the workpiece rotates about its axis (b) and the tool at least is moved in the direction of the y-axis until an annular trough-shaped surface which is adapted to the concave surface to be produced is achieved at least in the region of the outer edge of the workpiece, so that the surface of the workpiece produced on the workpiece corresponds to the desired outer contour of the optically effective inner lens surface at least in the region of the outer edge. A method according to claim 1, characterized in that before the piercing operation, the edge of the spectacle lens is machined in an edge machining process to adapt to the contour of the spectacle frame, the tool and the workpiece first being machined lateral relative movement on the x-axis are approximated, whereupon the tool and workpiece are displaced relative to one another by relative movement on the y-axis until the workpiece is approximately at the same level as the tool axis and the edge of the workpiece touches the circular cutting edge of the tool, so that when the tool and workpiece rotate about the respective rotational movement axes (c- and b-axes), material is removed from the workpiece edge, with the relative movement on the x-axis and continuous infeed on the y-axis allowing the lens blank to be machined to match the shape of the frame predetermined circumferential contour is made. Method according to Claim 1 or 2, characterized in that the edge machining operation, the plunge-cutting operation and the machining along the spiral path are carried out in a continuous sequence in a single clamping of the workpiece. Method according to one of claims 1 to 3, characterized in that the upper workpiece circumferential edge is facetted by means of the tool before the plunge-cutting operation and possibly after the edge processing operation, the faceting operation being carried out in a continuous sequence with the other operations. Method according to one of claims 1 to 4, characterized in that the angle (α) between the workpiece axis (b) and the tool axis (c) is 105 ° during all operations. Disc-shaped grinding tool with an annular grinding lip for carrying out the method according to claims 1 to 5 for producing a concave surface from a brittle-hard spectacle lens blank, characterized in that the grinding lip (13) on the tool (2) is asymmetrical and with its largest radius in a circular shaping cutting edge (14), and that of the grinding lip (13) facing away, in the cutting edge (14) opening back surface (15) of the tool (2) to the tool rotation axis (c) at the angle (α) between the workpiece (b) and the tool rotation axis (c). Milling tool for carrying out the method according to claims 1 to 5 for producing a concave surface from a plastic spectacle lens blank, characterized in that it is disc-shaped in terms of its rotational shape and is provided with a plurality of holding arms (17) evenly distributed over the circumference the outer ends of which are attached cutting plates (19) which are aligned radially to the axis of rotation (c) of the milling tool (2 ') and whose cutting edges (20) define a shaping toric envelope surface. Milling tool according to claim 7, characterized in that the cutting plates (19) are rotatable about their circle center and can be fastened to the holding arms (17) in the respective rotational position.

Images