EP0685298B2 - Procedure of and device for fabricating aspheric lens surfaces - Google Patents

Abstract

The workpiece in its holder (H) is ground and/or polished by a tool (T) guided along a machining contour predetermined by the control unit. One rectilinear drive (I) is pivoted w.r.t. another (II) about a transverse axis (B), pref. by interpolative control of a third drive (III) to guide the tool from the edge to the centre of the workpiece and along a meridional line. An additional drive permits rotation of the holder about a central axis. The path of the tool is corrected by comparison of measurements at sample points with the predetermined contour. <IMAGE>

Description

The invention relates to a device for making aspherical lens surfaces.

First, the manufacture of optical lenses with spherical surfaces, which at Glass blanks conventionally using the Flächeri grinding process followed by a polishing process. By Surface contact between a polishing tool and the workpiece is polished. The disadvantage is that different for different ball radii Tools must be available from their Condition also the accuracy of the finished lens depends.

Another manufacturing process for spherical lenses processes the mostly preformed glass compacts with a diamond cup wheel Ball loops. The feed takes place either with the Tool spindle or with the workpiece spindle to which the diamond cup wheel at a defined angle stands. The radius of the sphere on the lens is determined by this Setting angle determined so that within certain Limit different spherical shapes with one and the same Tool can be produced. His sanding surface but changes due to wear during the grinding process the shape by adapting to itself changing spherical radii. If with the same pot tool changing ball radii can be machined should therefore be the grinding diameter to be generated not to be determined in advance. conditioned due to different radii and tool wear unforeseeable zones of intervention arise on the tool leading to unwanted macro shape changes on the workpiece surface. Such Machining errors must go through subsequent fine grinding processes be eliminated. For smaller series with frequently changing ball radii, the proportion of Tool costs on the total costs as well as the manufacturing effort very large when grinding. Furthermore is often in two stages with decreasing Diamond grit ground, so that the total Processing time for grinding considerably extended.

Provide optical lenses with aspherical surfaces a number of advantages. So is the mapping performance significantly increased compared to spherical lenses. Image errors are better corrected, and in optical ones Systems can be achieved through the use of aspherical lenses the number of lenses can be reduced. These advantages left have so far only been used to a very limited extent. The production engineering effort and thus associated high unit costs traditionally limited the use of aspherical, translucent Components on special and Special applications. Single and small series production were not or only for cost reasons Feasible to a limited extent.

For example, DE-A-2 441 976 describes a suction cup for lens blanks that have an aspherical Should get surface. The one sunk in the middle Negative contour is on top of one rigid glass blocks. This is centric pierced and clamped on a plate chuck, the rotatable via a hollow shaft with pump connection is driven. The sucked blank can after Machining its top turned and on one similarly shaped second glass block on its bottom to be edited. The process uses thin, bendable blanks ahead and exhibits the above Disadvantages.

EP-A2-0 453 094 describes a method and a Device for grinding toric lenses. On rotating diamond pot tool is selected with one Head angle in a swivel motion a linearly fed lens blank, wherein the swivel radius of the tool during a Swivel movement can be changed. The pot tool is on a swiveling cross slide arranged on a horizontal Axis pivotable and in and out in the radial direction extendable base slide is mounted. Around the corner of your head and thus along the vertical curvature of the lens of the changing circular path hold the tool with the help of the cross slide readjusted according to its position. For calculating the required alignment or readjustment both sledges along their path using a Microprocessor, the swivel angle of the base carriage during its movement from a sensor detected. After completing a swivel movement the lens blank is adjusted by means of a feed drive. This process is repeated until one desired lens thickness is reached.

Grinding aspherical glass lenses with high Precision requires a subsequent polishing process because of the non-spherical shape of the lens surface but not just in face-to-face contact can be done. Rather, they are flexible and very small Polishing tools necessary to get the most accurate Achieve illustration of the asphere. conventional there is the disadvantage that due to the mechanical Construction and flexibility of the tool Movements that match the aspherical geometry exactly correspond, are not easily executed can. The shape deviation increases with increasing polishing time and wear.

DE-A1-33 19 719 discloses a machine for machining curved workpiece surfaces, especially concave or convex rug areas, as well as non-spherical rotating body surfaces of workpieces material suitable for the planned use exist, by means of one material-lifting tool. In one Machine frame is a first turning tool support arranged, the turning tool being a cup-shaped grinding tool. That with the one to be processed curved surface of the in relation to the Machine frame fixed, rotating drivable work stitch during the editing process bringar is. The spindle of the tool is attached to a second support, the during the machining process using of a system with numerical control about one to the axis of rotation of the tool vertical axis of rotation is based on rotation, the second support from a third Support that is worn during the Machining process according to the numerical control according to the dwarf to each other and to the rotary eight perpendicular Axis is adjustable to this rotating eight of the second support according to vertical coordinates arranged to each other adjust and the curved surface to process the work hours, under simultaneous numerical control in two mutually perpendicular and / or Circular directions. The workpiece is made by a head of one Revolver type rotary supports worn and can be used to make a convex non-spherical surface be rotated around its optical axis.

The object of the invention is to overcome the disadvantages of the prior art the technology, the inexpensive manufacture of aspherical lenses significantly improve and accelerate. Furthermore, the processing time should be short high precision can be achieved without the need for post-processing. An important goal is to assess the impact of tool wear on the To minimize lens shape as far as possible.

The invention is set out in independent claim 1. refinements are the subject of dependent claims 2 to 3. Use of the device according to the invention is specified in claim 4.

This simple and compact, modular structure of a grinding machine according to claim 1 is clear, very precisely controllable and economical, especially since conventional linear drives are used can find. The integrated measuring and correction system ensures that precise and rational production of both extremely precise aspherical lens surfaces as well as so-called free-form surfaces, even in small series or Individual production. The main advantages of the invention are that contour-accurate, rotationally symmetrical lens surfaces independent of the central one Planning ahead and making bills with potting tools can be different Can have diamond grit, but do not require dressing which would affect the lens geometry. That by means of the feed axes to the The pan tool brought up to the workpiece comes due to its preselected inclination only with the corresponding pre-selected location on the workpiece to the system, i.e. the peripheral edge of the pot tool only touches the workpiece in one relatively narrow point of contact.

In the grinding machine according to claim 1 runs the rotating driven Workpiece holder opposite to the pot tool around; it is equipped with a further feed drive along a vertical axis moved into a machining position, the workpiece spindle of the workpiece holder can be converted into a controlled rotary axis by switching axes. About that In addition, according to the invention, the lead angle can always be in point contact Change the adjoining pot tool before starting the machining in such a way that a special desired grinding area diameter is set on the pot tool, at which the point of contact of the peripheral part always behind the piercing point of the Outer axis line is. - The grinding machine DE-A1-33 19 719 is missing an additional rotary actuator for one with respect to the workpiece holder coaxial axis, in particular in close proximity to the second Feed drive. Likewise there is a switchover device for the transition the holder operation from pure rotary motion to controlled rotary axis operation and vice versa not provided according to this prior art.

Preferably, the device according to claim 2 is designed so that the pot tool arranged at a fixed distance from the transverse axis and by means of a linear feed drive is pivotable. According to claim 3, this can be parallel to the feed direction of the first drive, which offers structural advantages, e.g. a simplified Frame and slide design.

a) das mit einem Drehantrieb rotierend angetriebene Topfwerkzeug wird mit einer über den Vorhaltewinkel wählbaren Anlagestelle an das um die erste Vorschubachse rotierende Werkstück heranbewegt,

b) das Topfwerkzeug wird mittels der Steuereinheit durch Interpolationssteuerung der Vorschubachsen sowie der Schwenkachse vom Rand des Werkstücks zu seiner Mitte und darüber hinaus entlang der Bearbeitungskontur geführt,

c) während oder nach der Bearbeitung des Werkstücks werden Abtastwerte seiner Oberfläche gewonnen und bei Folgebearbeitung durch geänderte Bahnführung des Topfwerkzeugs in der Steuereinheit berücksichtigt.

The use of a device of the type defined above for producing aspherical surfaces on lens blanks by grinding and / or polishing with point contact of the pot tool with a selectable constant lead angle along the machining contour, the pot tool being guided in this way on the lens blank along the machining contour specified via the control unit That the selectable lead angle (head angle) is kept constant between the longitudinal axis of the pot tool and the tangent at its point of contact on the workpiece is characterized according to claim 4 by the following features:

a) the pot tool, which is driven in rotation with a rotary drive, is moved towards the workpiece rotating about the first feed axis with a contact point which can be selected via the lead angle,

b) the pot tool is guided by the control unit by interpolation control of the feed axes and the swivel axis from the edge of the workpiece to its center and beyond along the machining contour,

c) during or after machining of the workpiece, samples of its surface are obtained and taken into account in the control unit during subsequent machining by changing the path of the pot tool.

The aforementioned optimization of grinding processing by selecting the lead angle beforehand such that a specifically desired grinding area diameter on the pot tool is set and / or the material is removed in the most favorable manner especially for targeted aspherical machining with the pot tool from great importance.

Especially for soft contact lenses with a spherical back, an in EP-A2-0 304 106 outlined method of a flat control surface, with selectable Axis offset is tangent to the rotating workpiece and together with a Tool is pivotable on a circular path about a common axis of rotation. The extent of the axis offset determines the asphericity during machining, that happens in the dewatered state of the lens blank on a lathe. It however, every setting must be specified and not during the cutting process changeable so that precise individual adjustments are not possible.

Significant advantages of the invention are based on the fact that contour-accurate rotationally symmetrical Lens surfaces independent of central planning and calculation with pot tools that can produce different diamond grits can own, but do not require dressing processes that the lens geometry would affect.

Fig. 1

eine schematische Seitenansicht einer Bearbeitungsgeometrie mit unterschiedlich geneigtem Topfwerkzeug,

Fig. 1a

eine vergrößerte Seitenansicht der Werkzeugstellung bei Arbeitsbeginn,

Fig. 1b

eine vergrößerte Seitenansicht der Werkzeugstellung bei Arbeitsende,

Fig. 2

eine schematische Seitenansicht eines Topfwerkzeuges bei sphärischer Linsenbearbeitung,

Fig. 3

eine schmematisierte Schrägansicht einer CNC-Werkzeugmaschine mit vier Achsen,

Fig. 4

ein Flußdiagramm eines Arbeitsablaufs und

Fig. 5

ein Grundschema einer CNC-Werkzeugmaschnine.

Further details and advantages of the invention emerge from the wording of the claims and from the following description of exemplary embodiments with reference to the drawings. In it show:

Fig. 1

1 shows a schematic side view of a machining geometry with a differently inclined pot tool,

Fig. 1a

an enlarged side view of the tool position at the start of work,

Fig. 1b

an enlarged side view of the tool position at the end of work,

Fig. 2

1 shows a schematic side view of a potting tool for spherical lens processing,

Fig. 3

a schematized oblique view of a CNC machine tool with four axes,

Fig. 4

a flow chart of a workflow and

Fig. 5

a basic scheme of a CNC machine tool.

In the schematic representations of FIG. 1, 1a, 1b, 2 a workpiece W is shown, which is in shape of a lens blank L from a pot tool T with inclined axis A along a machining contour K is processed. A peripheral part U sits on the edge of the Workpiece W and touches it at point P, the Outer axis line A 'a constant lead angle β to the tangent F includes. The workpiece W is rotating driven and runs counter to the pot tool um, from the edge of the workpiece W over the middle of which is led out. The lead angle remains β, which is also between the outer axis line A ' and the normal N to the tangent F is recognizable (Fig. 1), the same throughout. He can start work 0 °, but if necessary also set differently become. It can be seen that in the course of processing the tangent angle τ to the surface O is getting smaller becomes. The point of contact P is always behind Piercing point of the outer axis line A ', and the contact line or - annular surface of the peripheral part U guaranteed an even and gentle Material removal. Depending on the effective diameter D of the peripheral part U can tilt the pan tool T and the lead angle β for the respective Grinding or polishing task can be optimally set. Is a preprocessing with a spherical surface O to be carried out with an adjustment angle (Fig. 2) a constant inclination of the pot tool T to Axis Z of the value spindle S is specified.

The structural design is illustrated in Fig. 3. The CNC machine tool labeled 10 in total has a frame 12 with a table 14, on which a horizontal frame 16 is arranged. Thereon a carriage 18 with a housing 20 is displaceable arranged. With the housing 20 is a head 22 connected, which contains a reversing gear 24 and a rotatably driven tool spindle V holds. A carriage 28 is on a vertical frame 26 a rotary drive 30 for a rotary spindle S, which carries a holder H for the workpiece W.

The carriage 18 is by means of a second feed drive I movable in the direction of an axis X. For the A first feed drive II is provided for the carriage 28, which is a movement in the direction of an axis Z allows. The head 22 is about a transverse axis B. swiveling, for which a third feed drive III is used, which is arranged parallel to the X axis. One recognises, that only through the interaction of two linear drives in the direction of the X and Z axes and by a Swiveling movement around the transverse axis B the pot tool T with its circumferential part U compared to (in Fig. 3 omitted) workpiece on the holder H is controllable. In addition is a further feed drive IV available, which in relation is centered on the axis Z and after Switchover from the rotary drive of the workpiece spindle S their control by means of an additional rotary axis C enables.

A general flow chart of the workflow can be seen from Fig. 4. First you choose the Processing type depending on whether an aspherical or spherical machining contour K (Fig. 1) specified becomes. Then the geometry type is selected, the can be convex, concave or flat. The associated Geometry parameters such as radius of curvature, outer diameter, Center thickness of the lens etc. and the tool or processing parameters as more effective Diameter of the peripheral part U, its lip radius, Lead angle b, feed speed and speed of the pot tool are then entered. This becomes the in the control unit Tool path calculated, whereupon the machining of the Lens is made along the machining contour K. in the Connection to this step of grinding and / or polishing, the surface O is scanned, what is used to obtain correction data, to correct the tool path for a Subsequent processing can be used.

The basic structure of a suitable device is shown schematically in Fig. 5. The CNC machine tool 10 has a control panel 40, preferably with Screen, and an input / output part 50 which can be designed as a keyboard. Both units stand in connection with a microprocessor computer R, the measuring systems M1 to M4 are assigned. The latter are connected to a control unit E, which the feed drives I to III directly influenced. On Switching device or switch 60 is used, optionally only the rotary drive 30 for the workpiece spindle S or the fourth feed drive IV for the axis C to control.

The machine 10 has a modular structure and with (not shown) highly dynamic Servomotors. Interpolators, not shown ensure that the tool guide after Specification of the machining contour K in very fine steps - i.e. quasi-continuously - can be controlled and thus the manufacture of usable aspherical surfaces guaranteed. This can be compensatory movements are taken into account as well as possible Polishing allowances provided for an extremely aspherical contour can be a non-linear material removal to compensate.

It can be seen that according to the invention Method and with the CNC machine tool according to the invention the universal lens processing with aspherical, but also spherical surfaces advantageous is feasible. The arrangement is particularly suitable also for small series or Individual production.

The additional C-axis for the workpiece spindle S also allows free-form surface processing following basically the same procedure. Also here is a servo drive and a rotation measuring system provided for the controlled rotary axis, so that after Axis switching may require off-center surface machining can be executed. Are these not required, the switch 60 goes to clean Rotary drive 30 for the workpiece spindle S over.

The invention is not based on the illustrated embodiments limited; rather there are numerous Modifications possible. However, it can be seen that at a method of manufacturing aspherical Surfaces on lens blanks L, especially made of glass according to the invention preferably a CNC machine tool with a rotating pot tool T for grinding and / or polishing a workpiece W in a bracket H is used. The pot tool T is specified along a control unit E. Machining contour K performed such that between the longitudinal axis A of the pot tool T and the tangent F in its contact point P on the workpiece W an optional lead angle β of e.g. 0 ° kept constant becomes. At least one feed drive (e.g. I) with respect to another (e.g. II) about a transverse axis B pivoted, preferably under interpolation control another drive III to the Pot tool T from the edge of the workpiece W to its Center and above along a meridian line to lead. An additional feed drive IV enables the control of the workpiece holder H by a central Axis C. Each axis X, Z, B, C is a measuring system M1, M2, M3, M4 assigned, their measured values as well Sampling values of the processed surface in the control unit E feedable and in a microprocessor computer R by comparing the actual surface profile with the machining contour K for recalculating the Tool path can be evaluated. The surface of the Lentil blank L can be pre-machined to a spherical shape, that of the given machining contour K is largely approximated.

Reference numeral list

α

Setting angle

β

lead angle

τ

tangent angle

I, II, III, IV

feed drives

A

Axis (from T)

A '

Außenachslinie

B

transverse axis

C

central axis

D

diameter (from U)

e

control unit

F

tangent

H

bracket

K

machining contour

L

lens blank

M1, M2, M3, M4

Measuring Systems

N

Normal (to F)

O

surface (from W)

P

point of contact (T on W)

R

Microprocessor computer

S

(Rotary) spindle

T

cup-shaped tool

U

peripheral part

V

tool spindle

W

workpiece

X

axis

Z

axis

10

CNC machine tool

12

frame

14

table

16

Horizonalrahmen

18

carriage

20

casing

22

head

24

deflecting

26

vertical frame

28

carriage

30

Rotary drive (for A / W)

40

control panel

50

Input / output unit

60

Switchover device / switch

Claims (4)

1. Device for fabricating aspheric surfaces on lens blanks (L), particularly of glass, comprising a CNC machine tool having a control unit (E) and an advanceable cup-shaped tool (T) driven for rotation around an axis (A) for grinding and/or polishing the lens blank (L), further having a holder (H) for receiving the lens blank (L), which holder (H) is movable into a processing position along a first feeding axis (Z) by means of a first feeding drive (II), the cup-shaped tool (T) being pivotable around a pivot axis (B) at a right angle to the first feeding axis (Z) and being linearly advanceable, by means of a second feeding drive (I), along a second feeding axis (X) at right angles to the pivot axis (B) and to the first feeding axis (Z), measuring systems (M1, M2, M3, M4) assigned to each of the axes (B, X, Z) providing measurement values which together with surface tracing values are supplied to the control unit (E) and are evaluated in a microprocessor computer (R) for correcting the tool trajectory by comparison of the worked surface with the processing contour (K), wherein the cup-shaped tool (T) is advanceable to the holder (H) which rotates around the first feeding axis (Z) by means of a rotary drive (30), with a point of contact (P) being adjustable via an angle of lead (β), and which holder (H) is guidable from the edge of the workpiece (W) to its center and beyond with point contact to the lens blank (L) along the processing contour (K) by means of the control unit (E) through interpolation control of the feeding axes (X, Z) and of the pivot axis (B), wherein with the rotary drive (30) being active, the workpiece holder (H) rotates in opposite sense to the cup-shaped tool (T) and is advanceable into a working position by means of the first feeding drive (II) along the vertical first feeding axis (Z), wherein for rotation of the workpiece holder (H) around an additional axis (C) that is coaxial to the vertical first feeding axis (Z), an additional drive module (IV) serving for controlled rotary arbor operation is provided, in particular in the vicinity of the first feeding drive (II), and wherein a switch-over device (60) is provided for transition from the mere rotary motion of the holder (H) effected by means of the first rotary drive (30) to the controlled rotary arbor operation effected by means of the additional drive module (IV), and vice-versa.
2. Device according to claim 1, wherein the cup-shaped tool (T) is arranged at a fixed distance to the transverse axis (B) and is pivotable by means of a linear third feeding drive (III).
3. Device according to claim 2, wherein the third feeding drive (III) is arranged parallel to the feeding direcion of the second drive (I).
4. Use of the device according to any one of claims 1 to 3 for fabricating aspheric surfaces on lens blanks (L) by grinding and/or polishing with point contact (P) of the cup-shaped tool (T) under a selectable constant lead angle (β) along the processing contour (K), the cup-shaped tool (T) being guided on the lens blank (L) along the processing contour (K) determined by the control unit (E) in such manner that the selectable lead angle (head angle β) between the longitudinal axis (A) of the cup-shaped tool (T) and the tangent (F) at the contact point (P) to the workpiece (W) is held constant, wherein

   (a) the cup-shaped tool (T) rotated by an a rotary drive is advanced, with a contact point (P) selectable via the lead angle (β), toward the workpiece (W) that is rotated around the first feeding axis (Z),

   (b) the cup-shaped tool (T) is guided by means of the control unit (E) through interpolation control of the feeding axes (X and Z) and of the pivot axis (B) along the processing contour (K) from the edge of the workpiece (W) to its center and beyond,

   (c) tracing values of the surface of the workpiece (W) are obtained during or after its processing and are utilized in the control unit (E) for subsequent processing by way of modified trajectories of the cup-shaped tool (T).

Images