The present invention relates generally to a device for clamping an optical workpiece, which is blocked on a block piece, for processing and/or coating thereof, which device serves the purpose of mounting the blocked workpiece in the respective processing machine and/or coating facility.
In particular, the invention relates to a device for clamping blocked spectacle lenses, which are to be clamped en masse in so-termed ‘RX workshops’ in the respective processing machine or coating facility, before the respective blocked spectacle lens is processed at its rear or front surface with respect to its optical effect and/or at the edge for fitting in an associated spectacles frame by geometrically defined (milling/turning) or geometrically undefined (grinding/polishing) machining and/or is coated on its rear or front surface for achieving additional effects (increase in scratch resistance, anti-reflection characteristics, metallizing, hydrophobic characteristics, etc.).
Various clamping devices are currently in use in spectacle lens prescription production (‘RX workshops’), such as shown in, for example, German Standard DIN 58739-5 ‘Optical production—Clamping means for optics—Part 5: Clamping chucks for clamping block pieces in spectacle lens production’, which defines the category. A characterizing feature of the previously known clamping chucks is that they fix the block piece at a diameter, which is intended therefor, by forces acting in radial direction, i.e. in the direction of the center axis of the block piece. These forces are applied either by way of bending of a solid body joint—‘version B’ according to the Standard—or, however, in ‘classical’ manner with the help of two inclined surfaces—‘Version A’ according to the Standard: the clamping chuck is constructed as an internal cone which is slotted in the clamping region and which is supported at a closed, somewhat steeper outer cone of an annular clamping sleeve fixedly connected with the workpiece spindle—when the clamping chuck is drawn against a central clamping pin by a tension rod.
follows:
A problem with this prior art occurs in that, particularly when the block piece is made of a plastics material, it can be deformed as a consequence of the radially acting pressure forces applied by the clamping device, so that the block piece adopts a form differing from the form it normally has, i.e. without the action of such forces. This deformation of the block piece can be transmitted by way of the block material to the blocked spectacle lens blank so that, for example, the curve which is machined on the spectacle lens during surface processing can distort or twist when the block piece together with the spectacle lens is taken out of the clamping device and the spectacle lens is unblocked from the block piece, whereupon without external application of force it adopts its ‘natural’ form. This distortion/twisting of the machined, optically effective surface at the spectacle lens is regarded as critical particularly in the production of open-die surfaces, which demand very close tolerances. In addition, a very slight distortion/twisting of the curve after unblocking of the processed spectacle lens from the block piece can here remove the processed spectacle lens from the permissible tolerance range, so that it is unusable for the intended purpose, thus a reject.
In the earlier European Patent Application 08 003 335.0 of the present applicant a block piece is described which is constructed in special mode and manner in order to, inter alia, combat the above-mentioned problem. This block piece has a base body with a center axis, a workpiece fastening section at which the spectacle lens blank can be blocked by a block material, and a clamping section by way of which the block piece and thus the blocked spectacle lens blank can be held in a clamping device, wherein this block piece has the clamping section of the base body being adapted—for example by construction with three clamping projections extending in radial direction—to be clamped or held by clamping forces which are oriented substantially in a circumferential direction with respect to the center axis of the base body or substantially in a tangential direction at a spacing with respect to the center axis of the base body. As a result, clamping forces applied in circumferential direction or tangentially to the block piece cannot ‘migrate’ through the entire block piece, as in the conventional case in which the radial pressure forces are applied to the clamping section of the block piece, so that excessive deformations of the block piece are avoided, i.e. such deformations which are transmissible to the blocked spectacle lens blank and then could have the consequence of an undesired distortion/twisting of the finished workpiece geometry. A clamping device suitable for that purpose is not, however, described in the earlier European Patent Application 08 003 335.0.
What is desired is starting from the prior art as represented by, for example, German Standard DIN 58739-5, providing a device of simplest possible construction for clamping an optical workpiece, particularly spectacle lens, blocked on a block piece for processing and/or coating thereof, the device being constructed in such a manner that excessive deformation of the clamped workpiece and the accompanying above-mentioned problems are largely avoided.
According to one aspect of the invention, a device for clamping an optical workpiece, particularly spectacle lens, blocked on a block piece for the processing and/or coating thereof, includes a receiving space, with a center axis, for a clamping section of the block piece and a plurality of clamping surfaces, which are provided in an edge region of the receiving space and which can be brought selectably into engagement with the clamping section of the block piece in order to clamp the block piece, the clamping surfaces are disposed in pairs opposite one another at a radial spacing from the center axis and are movable by a clamping member selectably towards or away from one another so as to clamp the clamping section of the block piece by clamping forces, which are oriented substantially in a circumferential direction with respect to the center axis or substantially in a tangential direction at a radial spacing from the center axis, or to release the clamping section of the block piece.
Due to the fact that the clamping surfaces of the at least one clamping surface pair are juxtaposed at a radial spacing from the center axis, which has the consequence in the case of, for example, substantially planar clamping surfaces that the surface normals of the clamping surfaces lie on a line which does not run through the center axis of the receiving space or the clamping device—as in the case of the prior art defining the category—but at a significant lateral spacing therefrom, there is avoidance, when clamping the above-described, suitably constructed block piece according to the earlier European Patent Application 08 003 335.0, in a just as simple and reliable manner that the clamping forces ‘migrate’ through the entire block piece and bend or otherwise deform this together with the optical workpiece blocked thereon during the processing, so that the geometry (attributable) faults at the workpiece as described in the introduction cannot arise. Rather, the clamping forces applied by a clamping surface pair are (substantially) mutually canceling or eliminating at the clamping projection, which is clamped in place therebetween, of the block piece without excessive deformation of the block piece, particularly not at its workpiece fastening section. Since all clamping surfaces of the clamping device are (relatively) movable by a clamping member selectably towards or away from one another in order to clamp or release the block piece at its clamping section without transmission of external radial forces to the block piece and workpiece, the clamping device can, moreover, be constructed in simple manner for a remotely actuated clamping or release of the block pieces, i.e. an automated actuation.
Although, in principle, even only one pair or two pairs of clamping surfaces can be provided, it is preferred with respect to good (self-)centering of the block piece and high holding forces particularly in the case of use of the clamping device in machines carrying out processing by machining if three pairs of clamping surfaces distributed over the circumference of the receiving space for the clamping section of the block piece are provided.
In a preferred embodiment of the clamping device according to the invention the clamping surface pairs are non-uniformly distributed over the circumference of the receiving space, whereby a rotational angle orientation—needed for processing geometries without rotational symmetry—of the block piece and thus of the workpiece blocked thereon about the center axis can be carried out in simple manner.
In a further preferred embodiment of the clamping device according to the invention at least one clamping surface of each clamping surface pair is provided with a profiling, which is required for high security of retention of the clamping block piece.
In principle, the clamping member can, for producing the relative movement at the clamping surface pair or pairs, be rotatable about the center axis by a rotary drive. However, with respect to a problem-free exchangeability of conventional clamping devices, i.e. a simple conversion or retrofitting of the clamping device according to the invention at existing processing machines or coating facilities, it is preferred if the clamping member is axially movable in the direction of the center axis for producing the relative movement of the clamping surfaces of each clamping surface pair, since the previously known clamping devices of existing processing machines are as a rule remotely actuated by a tension rod which is integrated in the workpiece spindle and usually spring-actuated and which opens pneumatically, so that the clamping device according to the invention can replace a conventional clamping device without a great amount of effort for conversion.
In an advantageous embodiment of the clamping device according to the invention at least one clamping surface of each clamping surface pair can additionally be formed at a base, which is preferably stationary, for example with respect to a part of the workpiece spindle of a processing machine, of the clamping device.
In a first constructional variant of the clamping device according to the invention, which in a manner that is particularly more economic and less susceptible to fault manages with only very few individual parts, the base has a plurality of resilient clamping elements which in pairs and opposite one another are each provided at the free end with a clamping surface and are disposed in operative connection with the clamping member, so that the mutually opposite clamping surfaces of each clamping element pair are movable towards one another, under resilient deformation of the clamping element, by relative movement of the clamping member with respect to the base. For this purpose, the clamping member preferably has a substantially hollow-cylindrical section, which is provided with cut-outs for reception of a respective clamping element pair, wherein the clamping member has in the region of each cut-out mutually opposite inclined surfaces which co-operate with rear inclined surfaces, which are remote from the clamping surfaces, at the clamping elements so as to resiliently deform the latter in the manner of a solid body joint in the case of relative movement between clamping member and base. With respect to a material-preserving deformation, which is resilient for as long as possible, of the clamping elements of the base it is in this regard preferred if the substantially planar inclined surfaces extend more flatly at the clamping elements of the socket with respect to the center axis—at, for example, an angle of 10°—than the substantially planar inclined surfaces in the region of the cut-outs of the clamping member—which can include an angle of, for example, 12° with the center axis—so that the clamping forces can be reliably introduced into the clamping elements by way of the clamping member ‘from above or at the end’. Finally, the first constructional variant of the clamping device could, even if less preferred, in principle also be modified so that of the clamping elements of each clamping element pair at the base merely one clamping element is of resilient construction, whilst the other clamping element is fixed with respect to the base.
In a second, only slightly more complicated constructional variant of the clamping device according to the invention the base has a substantially hollow-cylindrical section which, for formation of several stationary clamping jaws each having a clamping surface, is provided, starting from an end face, with several cut-outs in which movable clamping jaws each with a respective clamping surface are received, so that—similarly to a claw clutch—each clamping surface pair has one clamping surface at a stationary clamping jaw and one clamping surface at a movable clamping jaw. In this connection, it is preferred if the movable clamping jaws are mounted in crown-like manner on an annular part, which is rotatable with respect to the base about the center axis, which in simple manner ensures a common, synchronous mobility of these clamping jaws. For simple generation of the rotational movement of the annular part the clamping member can be operatively connected with the annular part in such a manner that an axial movement of the clamping member in the direction of the center axis produces the rotational movement of the annular part about the center axis. In that case a form of operative connection is preferred in which the clamping member, which is held to be secure against rotation with respect to the base, has at least one control surface which is set at an inclination with respect to the center axis and at which a clamping pin connected with the annular part engages so as to produce the rotational movement of the annular part when the clamping member is axially moved. In order to additionally prevent, in simple manner, sluggishness or tipping of the clamping member and the annular part, control surfaces set at an inclination with respect to the center axis can be formed on sides of the clamping member which are diametrically opposite with respect to the center axis and can co-operate with associated clamping pins at the annular part. Finally, with respect to problem-free release or opening of this clamping device preferably each clamping surface pair can be urged apart by a compression spring arranged between the stationary and movable clamping jaws associated with the respective clamping surface pair.
An outer sleeve, which surrounds the clamping surface pair, can be provided particularly for protection of the mechanism of the clamping device according to the invention and also for pre-centering of the block piece in the clamping device. This outer sleeve preferably has at its free end at the inner circumferential side a substantially conically extending (pre) centering surface for the block piece. Similarly, the outer sleeve can, at its free end, have at the end face a planar annular surface for support of the block piece. Finally, provision can be made for at least one back-pressure channel, which ends by an opening at the (supporting) annular surface, to extend through the outer sleeve, so that particularly in the case of an automated processing machine the correct position of the block piece can be recognized in simple manner by way of a back-pressure sensor system.
The invention is explained in more detail in the following by way of preferred exemplifying embodiments with reference to the accompanying, partly schematic drawings, in which the same reference numerals denote the same or corresponding parts and in which:
From
According to
This block piece B has the clamping section 16 of the base body 12 being adapted to be clamped or held by clamping forces which are oriented substantially in a circumferential direction with respect to the center axis A of the base body 12 or substantially in a tangential direction at a spacing with respect to the center axis A of the base body 12. For this purpose the clamping section 16 has at least one clamping projection 26, in the illustrated exemplifying embodiment three clamping projections 26, which extend in radial direction and are non-uniformly distributed over the circumference and which starting from the back surface 20 of the base body 12 bridge over the annular gap between the radially outer annular section 22 and the radially inner annular section 24. Each clamping projection 26 has two mutually remote side surfaces 28, which respectively face in circumferential direction, for application of the above-mentioned clamping forces, which are schematically indicated in
As is further evident from
These clamping surfaces 36, 36′ are arranged and actuable in a particular mode and manner and, specifically, they stand/lie in pairs opposite one another at a radial spacing from the center axis M (as can be readily seen particularly in
In addition, in both exemplifying embodiments three pairs of clamping surfaces 36, 36′ are provided, which in correspondence with the arrangement of the clamping projections 26 at the block piece B (see, with respect thereto, particularly
In the case of the first exemplifying embodiment the metallic base 40 has, particularly according to
For this purpose, the clamping member 38 according to, in particular,
Connected with the hollow-cylindrical section 50 of the clamping member 38 is a pin-shaped projection 60, which is provided with a stepped passage bore 58 and tightly engages through the opening 46 in the flange section 44 of the base 40 according to
As can, moreover, be inferred particularly from
The metallic outer sleeve 42, which is shown in more detail in
At the free end of the of the sleeve section 88 the outer sleeve 44 has at the end face a planar annular surface 98 for support of the block piece B. As evident, particularly from
Finally, it is to be noted with respect to the outer sleeve 42 that at least one back-pressure channel—in the illustrated exemplifying embodiments two back-pressure channels (shown in the second exemplifying embodiment in
With respect to the actual clamping process it remains to be noted that the block piece B in the case of optional automated insertion into the clamping device 10 is initially pre-centered on the one hand by co-operation of the radially outer inclined surfaces 30 at the clamping projections 26 with the centering surface 100 at the outer sleeve 42 and on the other hand by co-operation of the roof-shaped end sections 32 of the clamping projections 26 with the terminating edges of the clamping surfaces 36 at the free ends of the clamping elements 48 before the final centering of the block piece B in the receiving space 34 by the clamping movement, which is produced by way of the axial displacement of the clamping member 38, of the clamping elements 48 takes place (in the direction of the arrow F in
The second exemplifying embodiment of the clamping device 10′ shall be described in the following with reference to
The second exemplifying embodiment differs from the first exemplifying embodiment principally in that the actual clamping mechanism for generating the relative movement, which is necessary for the circumferential or tangential clamping of the block piece B, of the clamping surfaces 36′ is formed in a different way. Thus, the base 40′ according to, in particular,
As is evident particularly from
In the case of the second exemplifying embodiment the clamping member 38′ is operatively connected with the annular part 116 in such a manner that an axial movement of the clamping member 38′ in the direction of the center axis M produces a rotational movement of the annular part 116 about the center axis M. For this purpose, the clamping member 38′ held to be secure against rotation relative to the base 40′—which is effected by balls 128 (see
A device for clamping, in particular, a spectacle lens, which is blocked on a block piece, for processing and/or coating thereof is disclosed, which device comprises a receiving space, which has a center axis, for a clamping section of the block piece and a plurality of clamping surfaces, which are provided in an edge region of the receiving space and which can be selectably brought into engagement with the clamping section of the block piece in order to clamp the block piece. In order to avoid excessive deformation of the clamped block piece the clamping surfaces are disposed in pairs opposite one another at a radial spacing from the center axis and are selectably movable towards or away from another by a clamping member in order to clamp the clamping section of the block piece by clamping forces, which are oriented substantially in a tangential direction at a radial spacing from the center axis, or in order to release the block piece.
Variations and modifications are possible without departing from the scope and spirit of the present invention as defined by the appended claims.
Number | Date | Country | Kind |
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10 2008 051 833 | Oct 2008 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2009/007332 | 10/13/2009 | WO | 00 | 5/25/2011 |
Publishing Document | Publishing Date | Country | Kind |
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WO2010/043365 | 4/22/2010 | WO | A |
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Entry |
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Entwurf—Optikfertigung—Spannmittel für die Optik—Teil 5: Spannzangen zur Spannung der Blockstücke in der Brillenglasfertigung, DIN 58739-5, Nov. 2007, 6 pages. |
Number | Date | Country | |
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20110220018 A1 | Sep 2011 | US |