U.S. patent application number 14/268141 was filed with the patent office on 2014-11-06 for multimaterial block piece.
The applicant listed for this patent is Satisloh AG. Invention is credited to Marc Savoie.
Application Number | 20140329442 14/268141 |
Document ID | / |
Family ID | 48672775 |
Filed Date | 2014-11-06 |
United States Patent
Application |
20140329442 |
Kind Code |
A1 |
Savoie; Marc |
November 6, 2014 |
Multimaterial Block Piece
Abstract
The invention provides for a blocking piece comprised of at
least two materials having different rigidity/stiffness/hardness,
wherein at least one among the two materials is translucent and
defines an annular junction surface with respect to the other
material. The invention also provides for a process using such a
block piece.
Inventors: |
Savoie; Marc; (Wetzlar,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Satisloh AG |
Baar |
|
CH |
|
|
Family ID: |
48672775 |
Appl. No.: |
14/268141 |
Filed: |
May 2, 2014 |
Current U.S.
Class: |
451/42 ;
451/390 |
Current CPC
Class: |
B24B 13/005 20130101;
B29D 11/00884 20130101; B29D 11/00009 20130101; B29D 11/00942
20130101; B29D 11/00865 20130101; B24B 9/146 20130101 |
Class at
Publication: |
451/42 ;
451/390 |
International
Class: |
B24B 13/005 20060101
B24B013/005 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2013 |
LU |
92191 |
Claims
1. A blocking piece having a workpiece mounting face portion for
blocking a spectacle lens blank, the blocking piece comprising at
least two materials having different rigidity/stiffness/hardness,
characterized in that both materials are translucent and define an
annular junction surface for one material with respect to the other
material, wherein a first one of the at least two materials is
formed to have an annular shape at least in part surrounding the
second one of the at least two materials, so that the workpiece
mounting face portion comprises a first surface having the first
one of the at least two materials and a second surface having the
second one of the at least two materials and defines a
preconfigured un-deformable shape for receiving said spectacle lens
blank thereon.
2. The blocking piece according to claim 1, wherein both materials
have different optical properties.
3. The blocking piece according to claim 1 wherein at least one, in
particular both materials are transparent.
4. The blocking piece according to claim 1, wherein one or both
materials have similar optical properties compared to the lens to
be blocked.
5. The blocking piece according to claim 1, wherein one material is
fixedly attached, in particular embedded into the other
material.
6. The blocking piece according to claim 1, wherein the perimeter
of the blocking piece is made to conform in
rigidity/stiffness/hardness the lens to be blocked.
7. The blocking piece according to claim 1, comprising at least one
of an annular glass insert over moulded in the second material and
radial extending ribs extending in the first material.
8. A method for manufacturing spectacle lenses using a blocking
piece according to any one of the preceding claims, comprising the
steps of (i) blocking a spectacle lens blank with its blocking face
on the workpiece mounting face portion of the blocking piece with
the aid of a blocking material, (ii) processing the blocked
spectacle lens blank on the second face and optionally the edge to
obtain a processed spectacle lens, and (iii) deblocking the
processed spectacle lens from the block piece, with the
characterizing feature that the spectacle lens blank remains on and
lies against the workpiece mounting face portion throughout the
whole processing stage or step (ii).
9. The method according to claim 8, wherein the blocking material
used to block the spectacle lens blank is already present in the
blocking piece.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is related to U.S. patent
application Ser. No. ______ entitled Multi part blocking piece
(Attorney Docket No. 4091.22849) filed on May 2, 2014. The entire
disclosure of the foregoing application is incorporated herein by
reference.
[0002] The entire contents of the application are incorporated
herein by reference.
TECHNICAL FIELD OF THE INVENTION
[0003] The present invention generally relates to a workpiece
support block ("block piece") for supporting an optical workpiece
during the processing thereof. In particular, the invention relates
to a block piece for holding a spectacle lens for processing
thereof, as used in prescription workshops in masses, that is to
say production workshops for manufacturing individual spectacle
lenses from customary materials (mineral glass, polycarbonate,
PMMA, CR 39, HI index, etc.) according to a prescription. The
invention also concerns a method for manufacturing spectacle lenses
according to a prescription, as outlined in the preamble portion of
claim 20.
BACKGROUND OF THE INVENTION AND PRIOR ART
[0004] An ophthalmic lens blank generally has a first face with a
predetermined curvature and a second face, opposite the first face
on which a desired surface contour is generated by a machining
process. The overall process is generally referred to as "lens
surfacing" and the overall object is to yield a finished spectacle
lens so that the first and second face curvatures cooperate to
yield desired optical properties. In addition to this the first
and/or second faces of the lens are usually coated to provide the
finished spectacle lens with an enhanced ability to resist
scratching (by means of a "hard coating"), with a low residual
reflection and a desired color (by means of an "antireflection
coating"), and/or with certain surface properties such as
hydrophobic, oleophobic and dust repelling properties (by means of
a "top coating"). Usually also a further machining process takes
place (the so-called "edging"), the aim of which is to
finish-machine the edge of the spectacle lens in such a way that
the spectacle lens may be inserted into a spectacle frame. In all
these process steps the spectacle lens (blank) must somehow be held
in the machining machine(s) and coating apparatus respectively.
[0005] In more detail, hitherto the following main process steps
are usually carried out in prescription workshops: Firstly, a
suitable right and/or left ophthalmic lens blank is removed from a
semifinished product store. The term "semifinished" is used to mean
that the spectacle lens blanks, which are usually round or oval in
plan view and have not yet been edged, have already been molded,
machined or in another way contoured (surfaced) on one of their two
optically active faces only. The spectacle lens blanks are then
prepared for the blocking operation, namely by applying a suitable
protective film or a suitable protective lacquer to protect the
optically active face which has already been machined or contoured,
i.e. the first face or blocking face.
[0006] The so-called "blocking" of the ophthalmic lens blanks then
takes place. During this, the spectacle lens blank is joined to a
suitable block piece, for example a lens block according to German
standard DIN 58766 or document EP 1 593 458 A2 forming the preamble
portion of claim 1. To this end, the block piece is firstly brought
into a predefined position with respect to the protected first face
of the spectacle lens blank, and then in this position the space
between block piece and spectacle lens blank is filled with a
molten material (normally a metal alloy or wax) or an adhesive
composition that is curable, e.g., by UV or visible light, as
described in the earlier European patent application 07 013 158.6
by the same applicant for instance. Once this material has
solidified or cured, the block piece forms a holder or support for
machining the second face of the spectacle lens blank. The block
piece is grasped by a chuck or other suitable coupling means during
lens generation to provide in particular secure mounting to the
profiling machine while avoiding damage to the lens.
[0007] Lens surfacing is carried out then using profiling machines
which typically have a cutter of some type that is moved across the
second face of the ophthalmic lens blank to give the second face
its macrogeometry according to the prescription. The spectacle lens
blank may be stationary or rotating during the cutting operation,
depending on the particular profiling generator (which is) being
used. Typical machining processes for surfacing spectacle lenses
include single point diamond turning (as the presently preferred
fine cutting process for plastic materials and described in, e.g.,
document EP 1 719 585 A2 by the same applicant), diamond tool
fly-cutting, milling (as the presently preferred rough cutting
process for plastic materials and described in, e.g., document EP 0
758 571 A1 by the same applicant), and grinding processes, applied
depending on the lens material.
[0008] Usually fine machining of the ophthalmic lenses then takes
place, in which the pre-machined second face of the respective
spectacle lens blank is given the desired microgeometry, as
described, e.g., in documents EP 1 473 116 A1 and EP 1 698 432 A2
by the same applicant. Depending on inter alia the material of the
spectacle lenses, the fine machining process is divided into a fine
grinding operation and a subsequent polishing operation, or
includes only a polishing operation if a polishable second face has
already been produced during the pre-machining stage.
[0009] Only after the polishing operation is the ophthalmic lens
blank separated from the lens block ("deblocking") before cleaning
steps are carried out. Then the coating process(es) take(s) place
that, depending on among other things the material of the lens
blank, may include spin (or dip) coating of the deblocked spectacle
lens blank so as to provide at least the second face of the lens
blank with a hard coating or the like, as described, e.g., in the
earlier U.S. patent application Ser. No. 11/502,306, wherein the
spectacle lens blank is held in the spin coating apparatus by means
of a lens holder that has a suction cup for instance.
[0010] At any rate coating includes vacuum coating of the deblocked
spectacle lens blank so as to provide at least the second face of
the lens blank with an antireflection coating and optionally a top
coating serving the above mentioned purpose(s). In the vacuum
coating process the spectacle lens blank is clamped to a substrate
carrier of a rotary carrier device that is located in a vacuum
chamber in a vertically spaced relation with respect to an
evaporation source for emitting a vapor stream onto the lens blank
mounted on the substrate carrier, as described, e.g., in document
EP 0 806 492 A1.
[0011] After the coating step(s) the ophthalmic lens blank usually
is edged so that the spectacle lens can be inserted into a
spectacle frame. To this end, the coated spectacle lens blank is
blocked again, at this time however to a different, smaller block
piece by means of an adhesive film portion for instance, as
described, e.g., in document EP 1 243 381 A2 by the same applicant.
The edging process may also include the forming of bores, grooves,
channels and/or bevels corresponding to the respective mounting
requirements in the edge area of the spectacle lens, as described,
e.g., in document EP 1 243 380 A2 by the same applicant.
[0012] Finally, after edging and a further deblocking step the
spectacle lens is cleaned again and ready for inspection and
insertion into/mounting to the spectacle frame.
[0013] One disadvantage of the conventional overall process as
outlined above consists in the fact that the spectacle lens blank
needs to be deblocked after surfacing prior to coating, and then
again blocked after coating prior to edging, for this requiring
manual operations that are time-consuming, labor-intensive and add
the risk to damage the lens.
[0014] In this connection, documents U.S. Pat. No. 5,210,695 and
U.S. Pat. No. 5,341,604 disclose a system providing a lens blank
and block assembly capable of being mounted in any of a surface
generating machine, a finishing, i.e. lapping or polishing
apparatus and an edging machine without requiring re-blocking of
the lens in order to compensate for axis shifts, wherein the lens
block is formed from a plastic material capable of being readily
cut together with the lens blank in the edging machine. The
proposed lens block however is not intended or suitable to be used
in coating processes, in particular vacuum coating processes.
[0015] In this regard, document WO 2007/017385 A2 proposes a block
piece for holding an optical lens to be machined, with a coupling
part for holding in a workpiece chuck and with a holding part for
fastening the lens, the latter having a convex or concave holding
surface corresponding to a first side of the lens, wherein the
holding surface is, according to the shape of the lens to be held,
provided in the form of a negative aspherical, toric, progressive
or free-form surface, and the block piece is made from a plastic
material that can be machined. Although this document generally
mentions that the lens can remain on the block piece during a
coating process, it does not disclose or address how this could be
done in a vacuum coating process in which the lens is subjected to
a vacuum of, e.g., 5*10<-3> mbar. It can be expected that
liquids from the surfacing and cleaning processes will remain in
particular in the "equalizing and pressure medium channels"
provided in the proposed block piece, which liquids can excessively
prolong the time required to reach, if at all, the necessary vacuum
and in addition may lead to impure coating conditions resulting in
an imperfect coating.
[0016] Another problem with the conventional overall process as
outlined above is that, in particular if the block piece is made
from a plastic material, and the block piece is supported in the
surfacing machine(s) by means of a collet chuck or the like which
applies a radial compression force thereon, the block piece may
assume a shape other than that which it naturally assumes in the
absence of these forces. Any such deformation is transferred to the
spectacle lens blank blocked on the block piece so that the curve
which is cut into the surface of the lens blank may become
distorted when the block piece is removed from the chuck and the
lens blank is deblocked from the block piece and resumes its
natural shape. This problem becomes particularly acute in the
manufacture of free-form spectacle lenses requiring very precise
tolerances. Any slight distortion of the curve upon deblocking the
spectacle lens from the block piece may take it out of the
tolerance range of the particular prescription, thereby rendering
it useless for its desired purpose and resulting in substantial
waste. Finished ophthalmic lenses are generally very thin, flex
easily and are thus prone to such deformations.
[0017] Still another problem with the conventional process in
prescription workshops is associated with in particular the single
point diamond turning as the presently preferred fine cutting
process for spectacle lens blanks made from plastic materials. This
surfacing process as such is susceptible to small, but unacceptable
errors at the center of rotation of the lens blank that are
typically caused by errors of machine and tool calibration, as
explained in great detail in document EP 1 719 584 A1 by the same
applicant. This, coupled to certain limitations of the subsequent
(flexible) polishing process, where it can be difficult to totally
"clean up" or remove such center errors, have led to certain
limitations in the amount of prism (i.e. surface tilt or shift with
respect to the axis of rotation) permissible to cut and polish in
such combined surfacing process. Experiments have shown that it can
be relatively easy to cut and polish surfaces having 2 to 3 degrees
of prism at the center with accurate centers, however greater
amounts of prism at the center can pose problems.
[0018] A known method (see, e.g., document U.S. Pat. No. 6 913 356
B2) for fitting a block piece to a semifinished blank of an
ophthalmic lens intended to have a particular prism generally
consists of positioning the lens blank on a fixed base, in a
centered and angularly defined manner, so that the finished face of
the lens blank bears conjointly on a plurality of bearing points of
the base, defining an orientation of the block piece relative to
the lens blank, orienting the block piece in the defined manner,
and fixing the block piece to the finished face while maintaining
orientation, by means of a castable low melting point metal alloy
as the blocking material.
[0019] Once the lens blank is blocked on the block piece with the
predetermined amount of prism that the spectacle lens shall have
after surfacing, there is no need to generate, i.e. cut any prism
during the surfacing process. However, one disadvantage of this
known approach consists in the fact that, if the lens blank is
blocked with a greater amount of prism, say 7 or 8 degrees of
prism, the thickness of the wedge-shaped layer of blocking material
between lens blank and block piece strongly varies along the prism
axis. This gives rise to a different amount of shrinkage of the
blocking material in the thickness direction along the prism axis
when it solidifies (or cures if an adhesive composition would be
used), which shrinkage in turn may bend/distort (or even shift with
respect to the block piece) the blocked lens blank-as described in
the earlier European patent application 07 013 158.6 by the same
applicant-so that, again, the curve which is cut into the surface
of the lens blank may become distorted when the lens blank is
deblocked from the block piece and resumes its natural shape. For
this reason the amount of prism permissible to be blocked is also
limited in the known approach.
[0020] In an attempt to render the block piece more universally
usuable the applicant has previously suggested that the block piece
should comprise a basic body that has a workpiece mounting face
portion against which the workpiece can be blocked by means of a
blocking material, and a clamping portion via which the workpiece
blocked on the basic body can be fixed in a machine or apparatus
for processing of the workpiece; wherein the basic body consists of
mineral glass or a plastic material having particular degasing
properties (EP2093018). In this application it is indicated to be
favourable to have the block piece made of material transparent for
UV or VIS. It is however also indicated that using either plastic
material or mineral glass would have an inherent drawback,
respectively with respect to the workability or the capacities to
adequately support lenses to be worked.
SUMMARY OF THE INVENTION
[0021] The object of the present invention is to provide a block
piece for holding an optical workpiece, in particular a spectacle
lens, for processing thereof, which block piece serves to solve the
drawbacks previously cited of the techniques known in the art and
enables in particular spectacle lenses with high optical qualities
to be produced more quickly and at lower cost, without restrictions
as to the lens geometries usually processed in prescription
workshops while allowing a universal use during the entire process
that may include vacuum deposition, spin coating together with the
usual lathing, grinding or milling=generating and polishing steps.
The object of the invention further encompasses the provision of a
method for manufacturing spectacle lenses using such a block piece.
Obviously the block piece should preferably compatible with
existing machining equipment.
[0022] The above object is solved by a blocking piece having a
workpiece mounting face portion for blocking a spectacle lens
blank, the blocking piece comprising at least two materials having
different rigidity, stiffness and/or hardness, wherein both
materials are translucent and define an annular junction surface
for one material with respect to the other material, wherein a
first one of the at least two materials is formed to have an
annular shape at least in part surrounding the second one of the at
least two materials, so that the workpiece mounting face portion
comprises a first surface having the first one of the material and
a second surface having the second one of the material and defines
a preconfigured un-deformable shape for receiving said spectacle
lens blank thereon.
[0023] Heretofore it was found to be possible to cope with the need
in respect to the capability to provide for adequate support for
effective working conditions by using grinding and milling in
opting for a block piece of suitable material or in providing the
block piece of a diameter smaller than the final product.
Surprisingly it was now found possible to also do so by providing
at least two materials having different rigidity, stiffness and/or
hardness with at least one of the materials being translucent.
Indeed the person skilled in the art knew about blocking pieces
made of a rather hard clamping portion and a disc shaped lens
support made of a soft alloy. Further translucent single material
blocking pieces have been suggested as indicated above. With the
exception of accessory elements such as screws, springs and the
like heretofore a material mix using at least one translucent
material has not been contemplated. Indeed several particularities
rather hindered the person skilled in the art to do so. The
pressure in having inexpensive blocking piece and the requirements
in allowing the block piece to sustain the various mechanical
constraints both in fixing the block piece versus the tool as well
as during the different steps of lens processing were suggesting
such an approach to be difficult if not impossible. The variety in
lenses to be worked additionally requires particular attention,
such as having various base curve block pieces. All those
constraints could surprisingly been managed by providing an annular
adjoining surface. Indeed the annular adjoining surface allows to
have little negative impact upon rotation such as during spin
coating while being suitable for the mechanical properties as
required. Most astonishingly, it was found that the optical
characterises are improved as well. Both irradiation for curing the
adhesive as well as options to inspect/monitor the bonding and/or
the actually worked lens can be improved in that the annular
surface may optionally serve to focus and/or to scatter light.
Hence the use of two different materials on the one side and the
use of an annular adjoining surface on the other side result in a
surprising synergetic effect.
[0024] Such a configuration, wherein one material is formed to have
an annular shape at least in part surrounding the other material,
allows for instance to arrange for a metal ring around a portion
serving to be engaged by a collet chuck and or to have a ring
element with particularly well suited material regarding
workability at an outer edge. Of course a configuration of several
concentric and/or parallel annular elements is conceivable as
well.
[0025] Preferably both materials have different optical properties.
Having different optical properties allows for generating an
optical function at the adjoining surfaces without adding
additional optical active elements such as reflective coatings or
the like that would also be usable to enhance this kind of optical
effect for improving illumination uniformity or non-uniformity as
needed.
[0026] Preferably the blocking piece is void of non-translucent
elements. The use of as many translucent as possible and in
particular transparent elements--most preferably showing little
absorption--allows to avoid shading of material to be cured and
thus inappropriate blocking or local adhesion. This allows for most
uniform curing, but at the same time also for optical or visual
inspection of the bonding quality as well as with respect of the
lens actually worked.
[0027] Preferably one or both materials have similar optical
proprieties compared to the lens to be blocked. In opting for
similar optical proprieties light diffraction ad the adjoin surface
between the blocking piece and the lens to be worked, usually
comprised of a more or less uniform and more or less thick adhesive
layer can be set to particular needs or avoided. Indeed it might be
interesting to have the assembly of the blocking piece with the
lens bonded thereto to act as a well-defined optical system such
that the progress of the work can be followed easy using optical
inspection or analysis of light transmitted through such an
assembly. This can provide for an easy in-situ monitoring of the
process. Another example would be a temperature monitoring during
the process. Assuming that the resulting optical analysis such as
diffraction of the obtained assembly is responsive to a temperature
or a temperature gradient a monitored diffraction pattern could be
used to ascertain the avoidance of overheating the lens during
mechanical working thereof. Here any kind of optical analysis based
on interference of deflection might be used as well.
[0028] In a particularly preferred embodiment the one material is
fixedly attached, in particular embedded into the other material.
Such a configuration allows to locally strengthen the blocking
piece where high righty or support is needed whereas in other
location an easy workability could be provided for. One example of
such an embodiment could be to overmold a mineral glass ring with
polymeric material so as to build the base body of the blocking
piece. The connecting element might in such a configuration be an
integral part of the mineral glass or fixedly attached thereto.
Another example could consider an annular strengthening ring made
for instance of a preferably polished or reflective metal ring
surrounding e.g. an upper portion of the connecting portion or
chucking portion of the blocking piece.
[0029] Alternatively or additionally the block piece may preferably
comprise at least two elements loosely arranged before blocking.
Such a configuration could allow for more ease in handling
different base curves. A particularly preferred embodiment could
provide an external ring made of one particular material adjoining
a central portion of the blocking piece defining said adjoining
annular surface. Such an embodiment is most cost efficient as the
disposable or impaired part of the blocking piece during mechanical
working can be produced at little costs. The two separate elements
could be mutually engaged by a press fit or any kind of snap fit,
however it is also possible that the two elements are unified by
means of the adhesive and the lens blocked thereto.
[0030] Preferably at least the outer perimeter of the blocking
device is made to conform in rigidity/stiffness/hardness the lens
to be blocked. In using conforming materials the induced stresses
due to mechanical working and temperature changes can be
minimized.
[0031] A preferred blocking piece comprises radial extending zones
of physical particularity, such as ribs. Those radial extending
zones of physical particularity may serve various purposes such as
taking the function of a light guide, a light kollimator, a light
scattering element, a rigidifying rib and the like without
nevertheless impairing the capability to be rotated at high speeds
such as during a spin coating step.
[0032] In summary one aspect of the present invention is to provide
a block piece for holding an optical workpiece, in particular a
spectacle lens, for processing thereof, comprising a basic body
that has a workpiece mounting face portion against which the
workpiece can be blocked by means of a blocking material, and a
clamping portion via which the workpiece blocked on the basic body
can be fixed in a machine or apparatus for processing of the
workpiece. The block piece may be comprised of mineral glass or a
plastic material, while guaranteeing suitable optical and
mechanical supporting properties in spite of respecting existing
constraints in costs and workability so as to avoid undue use of
machining tool. The invention provides for a block piece being
adapted to be used as a universal holding element usable over the
entire process and also allowing to be used in any kind of thin
film coating processes.
[0033] The invention also provides for a method for manufacturing
spectacle lenses according to a prescription, comprising the steps
of: (i) blocking a lens blank with a blocking face on a workpiece
mounting face portion of a block piece with the aid of a blocking
material, the lens blank having a second face, opposite the
blocking face, and an edge between the blocking face and the second
face, (ii) processing the blocked lens blank on the second face
and, if required, the edge to obtain a processed lens, and (iii)
deblocking the processed lens from the block piece; wherein one and
the same block piece as described above is used on which the
blocked lens blank remains throughout step (ii).
[0034] Since the spectacle lens blank remains on the block piece
throughout the whole processing step the latter can be carried out
faster and more efficient with less handling effort as compared to
the conventional approach where the lens blank needs to be
deblocked and blocked again in the processing stage. This reduces
the manufacturing costs and even allows for more automation in the
prescription workshops. The approach according to the invention
also serves to ensure the production of spectacle lenses with high
optical qualities because one and the same geometrical relation
between lens blank and block piece is maintained throughout the
whole processing stage, thus any errors that are consequential on
the conventional re-blocking approach where the orientation of the
lens blank relative to the assigned different block pieces may
unintentionally change upon re-blocking are avoided. Further, as
the lens blank is always held on the block piece as standardized
interface and handling means during the processing stage the risk
that any operator unintentionally touches the lens blank--thereby
possibly causing problems in a coating substep--is reduced. A
further advantage consists in the fact that all production
information can be kept on the block piece, for instance by means
of a "transponder" integrated in or fixed to the block piece, as
proposed in the generic document EP 1 593 458 A2, which offers full
tracking possibility throughout the whole process.
[0035] Continuing the concept of the invention, the above
processing step (ii) may comprise the following substeps: machining
of the blocked lens blank to give the second face a macrogeometry
according to the prescription; fine machining of the blocked lens
blank to give the second face the required microgeometry; cleaning
the blocked lens blank that has been machined and fine machined; if
required, spin or dip coating of the blocked lens blank in order to
provide the second face with a hard coating, or a primer, or a
primer and a hard coating; vacuum coating of the blocked lens blank
to provide an antireflection coating and, if required, a top
coating such as hydrophobic and/or oleophobic and/or dust repelling
coating on the second face; and, if required, edging of the blocked
lens blank to give the edge the required geometry so that the
processed lens is ready for insertion into a spectacle frame or a
spectacle holder. Since there is no deblocking step inbetween the
aforementioned processing stages any more, some processing substeps
could even be carried out in a--as compared to the conventional
time sequence--different sequence where a certain fixed sequence is
not necessary from a product point of view, in particular all
machining operations including edging could be carried out prior to
the coating process(es) if desired or required.
[0036] Finally, it is preferred for the blocking face of the lens
blank to be fully finished prior to the above blocking step (i),
including hard coating, antireflection coating and, if required,
top coating such as hydrophobic and/or oleophobic and/or dust
repelling coating. In this instance the blocked spectacle lens
blank could advantageously be shipped from the lens manufacturer to
the prescription workshop where only the second face and, if
required, the edge of the lens blank would need to be processed to
obtain a spectacle lens ready for insertion into/mounting to the
spectacle frame, wherein the first face of the lens blank would be
protected by the block piece until the finished spectacle lens is
deblocked. This approach would also minimize the production efforts
in the prescription workshop.
[0037] Further effects and advantages of the proposed block
piece(s) and method for manufacturing spectacle lenses according to
a prescription will become apparent to the skilled person from the
following description of currently preferred examples of embodiment
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Herein below, the invention will be explained in more detail
on the basis of preferred examples of embodiment and with reference
to the appended, partially schematic drawings. In the drawings:
[0039] FIG. 1 shows schematically a first embodiment of the present
invention, wherein the blocking piece is made of two distinct
elements each comprised of a different material. The schematic
illustrations show the assembly step at the finish block piece.
[0040] FIG. 2 shows a schematically sectional view of a second
preferred embodiment making use of an insert using one material,
embedded into the other material.
[0041] FIG. 3 shows a third preferred embodiment in a bottom view,
a sectional view, a side view and a perspective view.
[0042] FIG. 4 shows various views of a ring shaped element that
could be integrated into the preferred embodiment as shown in FIG.
3.
[0043] FIG. 5 shows a fourth preferred embodiment in a sectional
view together with a detail thereof and in a bottom view.
[0044] FIG. 6 shows a fifth preferred embodiment being a slight
modification of the fourth preferred embodiment as illustrated in
FIG. 5.
[0045] FIG. 7 shows a flow chart of a lens machining process
carried out using the block piece of the invention engaged with a
standard interface of the machining tool as defined by German DIN
58766.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] The preferred embodiment of the present invention will now
be described in more detail, wherein it is to be noted that the
following description is given for illustrative purposes, only and
not with the intention to restrict the scope of protection to any
of the illustrated and discussed preferred embodiments. In
particular, the person skilled in the art will be well aware that
any single feature described in detail with respect to one
preferred embodiment could also be used separately from features
described in the same embodiment or in combination with features of
another embodiment. Furthermore, it should be understood that all
given indicia as to material choices, sizes, measures and the like
are as well to be considered as examples only, and if any of them
would prove to be an essential feature again such feature should be
considered as distinguishing if taken separetly or in conjunction
with other features described herein, irrespective as to whether
such feature combination is explicitely mentioned or rather
obtainable by omitting one or more single/isolated feature(s) from
any of the described embodiments.
[0047] The first preferred embodiment as illustrated in FIG. 1 can
be assembled by juxtaposing a basically ring shaped element 30 with
a basically disk or block shaped element 50. By juxtaposing the two
elements 30, 50 a blocking piece, basically in a shape as well
known is obtained, wherein the respective top surfaces 31 and 51 do
together provide for a workpiece mounting face portion 61 as the
surface allowing to block a spectacle lens blank that is intended
to be worked. The lower portion provides for a standard clamping
portion via which the spectacle lens blank blocked on the blocking
piece can be fixed in a machine or an apparatus for processing
(i.e. surfacing, coating, edging, tinting, cleaning, etc. as the
case may be) of the spectacle lens blank.
[0048] In the illustrated embodiment the element 50 is a glass
block, e.g. made from mineral glas which is sufficiently stiff,
rigid and hard in order to allow for engagement with a working
machine such that the blocking piece satisfies to German standard
DIN 58766. The glass block is showing comparatively little
deformation and comprises on its bottom the well-known
configuration with responding notches and cut-outs. In order to
allow easy insertion and correct clamping the glass block is
provided with a chamfer surface 52 and a cylindrical surface 54. In
the upper area of the glass block there is provided a first annular
surface 56 forming the edge with the concave or convex support
surface 51. A little bit further downward a second annular surface
58 with slightly larger diameter is provided. As the person skilled
in the art will appreciate the two annular surfaces 56 and 58 allow
proper engagement with a ring shape element 30. The ring shape or
annular element 30 is accordingly provided with a mating inner
annular surface portion 38 and an annular protrusion 36. With both
of said surfaces and the annular element 30 and the glass block 50
cooperating one can obtain a basically flush surface that could be
concave as in the illustrated embodiment, but as well convex in
case needed. It is to be noted that the two surfaces 31 and 51 are
comprised preferably of the same surface curvature. In other words
the blocking surface is preferably having a constant radius and for
practical reasons it has proven to be preferable of having several
blocking pieces available with different surface radii, so as to be
capable of supporting most intimately various lenses. The use of
different base curves is well known for monomaterial block pieces,
and hence this concept will not be detailed herein. Although in the
illustrated embodiment the supporting surface is structured such
that the surface 51 of the glass block and the surface 31 of the
ring shaped part to commonly provide for the supporting surface
with one single and particularly specified radius. One could also
contemplate to use one glass block with a fixed radius in the
medium range and to provide for the specific adaptation of the best
radius suitable to support the lens blank by using different ring
shaped elements 30, thus providing a block piece with adaptable
base curve. It should further be noted that although in the
illustrated embodiment only one single ring shaped or annular
element is used an assembly using a plurality of concentric ring
shaped elements is conceivable as well, the single elements could
have identical or variable surface curvatures, e.g. increasing
towards the perimeter of the block piece.
[0049] Coming back to the illustrated preferred embodiment of FIG.
1 the ring shaped or annular element 30 is presently made from a
plastic material. The plastic material is preferably a plastic
material that has proven to be useable in such processing, i.e.
having little outgassing, being resistant to usually encountered
processing temperatures, does not interfere with the material of
the lens blank and thus allowing secure blocking and unblocking
using the well-known bonding material etc. The engagement of the
annular or ring shaped plastic part with respect to the glass block
can be provided by a mating form configuration as illustrated, but
as well using a snap fit configuration (as will be discussed later)
or also by providing a threaded configuration or the like. It is to
be noted that it has been found to be preferable if the assembly
does not use any bonding material except for the one that is used
for adhering the lens blank to the upper surface.
[0050] The plastic ring shaped element can be produced at very low
cost by means of for example injection moulding and the hardness of
the annular plastic ring element allows for proper workability
without undue tooling fatigue. The rigidity and/or stiffness of the
annular part may be improved by using various ribs such as the ribs
34 illustrated in FIG. 1. The outer perimeter could comprise a rib
defining rim 32 it is however to be noted that for a later
processing of the lens blank it is most preferred that all rigidity
providing or enhancing components do extend in a radial direction,
only. In the specific case of the embodiment of FIG. 1 the outer
rim 32 will disappear during the first edging step since the
blocking piece is designed such that the lens blank to be worked
will rest on the surfaces 31 and 51 forming a workpiece mounting
face portion 61 in such a manner that the final lens would still be
slightly larger in the radial extension than the glass block. As
such the entire edging process can be performed such that the full
working area of the lens blank is always supported by the annular
element 30, without however performing the edging in such a way
that the cutting, grinding or milling tool would interfere with the
glass block.
[0051] As can be seen from the above the glass block, which of
course could also be made from any other rigid or stiff and hard
material can be reused and it is simply sufficient to replace the
annular plastic ring part for each new lens block to be worked. The
plastic annular or ring shaped element 30 presents a multitude of
advantages versus the previously commonly used alloy disk. In
particular there is among others no more need to thoroughly collect
the grinding or milling residues since the plastic material is less
harmful than the usually used alloy. The plastic material is also
more competitive cost wise and the material mix, i.e. using a
strong stiff and/or rigid center block part and an easily workable
annular part allows a most optimized adaptation towards the need of
tool engagement either with the machining chuck or with respect to
the working tool.
[0052] The embodiment as shown in FIG. 1 has proven to be most
suitable for blocking a lens blank using a photo curable bonding
material or adhesive and therefore both the block element 50 as
well as the annular element 30 are made of translucent material, in
the present case those materials are both transparent thus allowing
to transmit light trough the blocking piece and through the lens
blank. The fact that the blocking piece is allowing light
transmission, in particular for UV-light permits a most uniform
curing over the entire surface 31 and 51. The transparency, but
also translucent configuration allows for optical monitoring of the
quality of the bonding between the blocking piece and the lens
blank during the various processing steps. As an example the
blocking piece with the fixed lens blank could be optically
analysed by irradiating a particular pattern and monitoring said
pattern after transmission through the assembly of the block piece
and the lens blank.
[0053] An essential feature of the invention that can be well
understood when analysing the embodiment of FIG. 1 is the existence
of annular adjoining surfaces such as the surfaces 38 and 58,
mainly, but also 36 and 56. The surfaces 38 and 58 are adjoining
radial or ring shaped surfaces that allow proper alignment of the
two elements on the one hand and during blocking a little defined
play and/or stress compensation in the axial direction while
allowing at the same time a huge degree of design freedom as to the
optical characteristics. In particular the adjoining ring shaped
surfaces can be designed such the entire surface composed of the
surfaces 31 and 51 be properly irradiated with UV-light for curing
the adhesive. The person skilled in the art will realize that
either or both of the surfaces 38 and 58 could be provided with a
specific surface treatment or surface characteristic so as to allow
to scatter the light in case needed or to focus the light in
specifically desired areas. A further option could reside in the
possibility to initiate the curing process in the center area or
alternatively all to the contrary initiate the bonding process
between the lens blank and the block piece on the periphery or as a
further alternative to contemplate to have the bonding process to
begin close to the adjoining area that would otherwise most likely
considered to be shaded. The specific configuration according to
the invention using an annular ring shaped adjoining surface
configuration does indeed allow to take benefit both of the
respective mechanical properties of the two materials but as well
of the optical effect provided by the fact of using either
materials having closely matched optical characteristics or
alternatively different optical characteristics. In any case the
person skilled in the art is provided with a ring shape optical
element from which he can take benefit in conceiving the curing
during blocking an unblocking but also for monitoring or inspection
purposes.
[0054] Obviously the person skilled in the art can use most
versatile designs. For example he could provide an alternating
pattern of reflective element and non-reflective elements around
the surface 58 such that light transmission in the radial direction
is enhanced at location where the stiffening ribs 34 of the plastic
ring shaped elements are provided such that those reinforcing ribs
can provide for the double functionality to also act as a light
guide.
[0055] In FIG. 2 an alternative embodiment is shown. The second
preferred embodiment is also relying on the beneficial effect of
having two different materials provided in such a manner that they
show an annular interface or junction surface. The annular shape of
the junction as illustrated by reference signs 26 and 28 allows to
compensate for differences in mechanical behaviour of the two
materials, such as different thermal expansion or the like, can be
helpful in adsorbing vibrations during the machining process of the
lens blank and at the same time can provide an optical adaptive
system for improving the blocking process if based on photo curable
adhesives. As with the embodiment show in FIG. 1 the blocking piece
comprises on its upper surface a concave receiving surface for
accommodating a convex lens blank surface and on the opposite side
a chuck-engaging portion. The embodiment of FIG. 2 is basically
composed of an annular glass insert 24 overmoulded by an injection
moulded plastic material 22. Both components are translucent and in
particular transparent and the overmoulded glass insert is
positioned such that the surface 21 can maintain its configuration
irrespective of forces applied to the tool engagement portion
serving to fixedly hold ant to rotate or otherwise manipulate the
block piece.
[0056] Obviously the embodiment of FIG. 2 can serve again for
supporting a lens blank in all kinds of processing steps whether
those includes spin coating, edging, grinding or other working
steps and compared to the embodiment of FIG. 1 it appears possible
to have the blocking piece made as an integral one single piece
part made of two distinct materials. This configuration might be
beneficial in light of logistics, however the entire blocking piece
then becomes non-reusable. In light of the fact that the embodiment
as shown in FIG. 2 is however conceivable at very low cost it could
be contemplated to already fix the blocking piece to the lens blank
in the lens blank manufacturing facility.
[0057] Once again and similarly to the first illustrated embodiment
the person skilled in the art will realize that the junction
surfaces 26 and 28 can be configured specifically to improve
optical behaviour. It is to be noted that for ease of production it
would be best to provide the optical characteristics on the
overmoulded glass insert ring. It is clear that surfaces 26 and 28
can be provided with different optical characteristics as may be
needed for instance the inner annual surface 28 might be highly
polished for increasing the focusing capacity whereas the outer
surface 26 might be slightly roughened in order to allow a higher
portion of the light being scattered towards the peripheral
portions of the blocking piece.
[0058] It is to be noted that the location and size of the ring
material can be used to adjust the rigidity or stiffness of the
blocking piece. E.g. if the mineral glass ring is extending from
the area of the tool engagement up to the vicinity of the concave
surface the block piece will be more rigid and stiff as compared to
a block piece where a thick plastic layer exists between the lens
blank and the glass ring. The different thermal characteristics do
provide for another design feature. A glass ring close to the
supporting surface will obviously render a thermal dissipation of
heat within the blocked lens blank more effective.
[0059] In FIG. 3 a third preferred embodiment according to the
present invention is illustrated in a bottom view, a sectional
view, a side view and a perspective view form below. In the bottom
view one can realize the well-known standard configuration for
allowing to have the blocking piece engaged with a corresponding
apparatus or machine for working such as edging, polishing,
grinding, coating etc. As can best be seen in the sectional view
the here illustrated embodiment is comprised of a first element 40,
made here from injection moulded plastic material. The element 40
is once again transparent or at least translucent and is provided
on the top with the supporting surface 41 allowing to have a lens
blank blocked thereto, preferably using a photo curable adhesive.
In order to cope with the relatively high radial forces of the
chucking process this embodiment is provided with an annular
strengthening element 60 which is providing on its outer side with
a cone shaped or chamfered guiding surface 62 and the tool engaging
surface 64. The two elements made of different material do once
more provide for an annular adjoining surface illustrated with
reference signs 48 and 68. Once more the annular adjoining surfaces
are capable of providing both optical characteristics and
mechanical characteristics. The use of the strengthening ring 60
can successfully minimize any deformation in the plastic part and
can thus avoid any deformation of the surface 41 which would in
particular when thin lens blanks are worked also result in a
distortion of the lens being worked. The ring shaped element 60
thus compensates any clamping forces caused by the collet chuck of
the machine, which would otherwise distort the plastic block and
the attached lens.
[0060] It is to be noted that the embodiment shown in FIG. 3 is
illustrated to have a peripheral portion so as to accommodate
additionally a plastic annular element as illustrated in FIG.1,
however it is obvious to the person skilled in the art that the
peripheral portion made of transparent plastic material allows
directly for proper workability and therefore the shape of the
blocking piece could basically also correspond to the shape of FIG.
2 i.e. the lens blank supporting surface can be either composed by
a central blocking part and an annular surrounding ring or provided
as a one piece element made of injection moulding material,
possibly also including one or more embedded other material(s).
[0061] In FIG. 4 the ring shape reinforcing element is illustrated
in more detail and one can realize that the ring shaped
strengthening element 60 is preferably comprised of a torus
axis-orienting drive notch 63 and a register 65 for allowing proper
and easy engagement with the driving tool that is usually used such
as defined in the previously mentioned German DIN. In the
illustrated embodiment the strengthening ring 60 is made of a
non-transparent and non-translucent material, e.g. made from
aluminium or steel, it is however perfectly well conceivable to
provide the stiffening ring 60 also in translucent or transparent
material. Irrespective of the material chosen, it is possible to
adapt the surface 68 for forming part of the adjoining annular
surface with specific optical characteristics. E.g. if the
stiffening ring is made of a metallic material it might be
sufficient to polish the surface in order to attribute adequate
optical reflective characteristic if such optical effect is
desired. Obviously various other optical characteristics can be
provided such as depolishing in order to enhance scattering of
light etc.
[0062] In FIG. 5 a fourth preferred embodiment is illustrated,
basically combining the feature of the first preferred embodiment
as illustrated in FIG. 1 and the second preferred embodiment as
illustrated in FIG. 2. Obviously and as already mentioned the
various embodiments are combinable and even though the embodiment
shown in FIGS. 3 and 4 has not been illustrated in combination with
the features of the first two embodiments the person skilled in the
art should be aware that all three embodiments can be combined at
will, using one, two or three of the suggested solutions. The
embodiment in FIG. 5 is comprised of an over moulded glass ring 24
e. g. of mineral glass that is embedded into a transparent
injection moulding material forming a reusable center block part
provided on the top portion thereof with a concave surface 21
capable of supporting a lens blank that should be worked. Once
again the lens blank is preferably fixed thereto using photo
curable adhesive. Similarly as with the embodiment as shown in FIG.
1 a ring shaped peripheral portion is provided that during grinding
and edging will support the perimeter of lens blank and that will
be worked with the lens blank. The lens blank is at the same time
supported and blocked via the center blocking element composed of
the mineral glass ring 24 and the surrounding embedding material.
This part of the block piece is providing for a reusable element of
the blocking piece. As can thus be seen in the detail view the
outer plastic ring part is engaged with the center block part in a
manner to once again create an annular adjoining surface. The
annular adjoining surface is providing both for beneficial optical
characteristics and beneficial mechanical characteristics since the
material can be specifically adapted for the best result. In the
particular embodiment of FIG. 5 it is interesting to note that the
use of two different plastic materials together with an overmoulded
glass ring allows for a most advantageous thermal decoupling during
the edging process as the blocking piece itself does present little
thermal energy transmitting in a radial direction as prior art
blocking pieces would do.
[0063] Finally, in FIG. 6 a further preferred embodiment is
illustrated. In light of the sixth embodiment being very similar to
the fifth embodiment the elements and components similar will not
be described in detail again, it is however interesting to note on
the detailed view that in contrast to the previous embodiments the
outer plastic ring part is now snap fitted with the center element,
again composed of an overmoulded glass ring with plastic material.
However the person skilled in the art should realize that the
center element could also be a full material mineral glass block
such as in the first preferred embodiment. The snap engagement is
provided in that the lowest portion of the ring shaped element is
slightly protruding inwardly as illustrated at reference sign 39 in
order to cooperate with a corresponding chamfer 59 on the central
element.
[0064] Finally, FIG. 7 shows by means of a flow chart the main
process steps of a method for manufacturing spectacle lenses
according to a prescription with the aid of a block piece as
described above.
[0065] Basically, this method comprises the steps of: (i) blocking
a spectacle lens blank B with its blocking face cx on the workpiece
mounting face portion 61 of the block piece with the aid of a
blocking material, (ii) processing the blocked spectacle lens blank
on the second face and optionally the edge to obtain a processed
spectacle lens, and (iii) deblocking the processed spectacle lens
from the block piece, with the characterizing feature that the
spectacle lens blank B remains on the proposed block piece
throughout the whole processing stage or step (ii). According to
FIG. 7, the latter stage or step generally comprises the following
substeps: "Generating", i.e. machining of the blocked spectacle
lens blank to give the second face cc a macrogeometry according to
the prescription; "Polishing", i.e. fine machining of the blocked
spectacle lens blank to give the second face cc the required
microgeometry; cleaning the blocked spectacle lens blank that has
been machined and fine machined; (optionally) spin (or dip) coating
of the blocked spectacle lens blank in order to provide the second
face cc with a hard coating HC, or a primer, or a primer and a hard
coating; vacuum coating of the blocked spectacle lens blank B to
provide an antireflection coating AR (normally consisting of four
to seven layers made up of two to four materials with different
refractive indices) and (optionally) a top coating TC such as a
hydrophobic and/or oleophobic and/or dust repelling coating on the
second face cc; and (optionally) edging of the blocked spectacle
lens blank B to give the edge E the required geometry so that the
processed spectacle lens, after deblocking and final inspection, is
ready for insertion into a spectacle frame or a spectacle holder.
Since the single processing substeps and the equipment used in
those are well known to the person skilled in the art further
explanations in this respect are not required at this point.
[0066] As can further be seen from FIG. 7, for the reasons
indicated in the introductory portion of the description already,
it is preferred that the blocking face cx of the spectacle lens
blank B is fully finished prior to the above blocking step (i),
including hard coating HC, antireflection coating AR and optionally
top coating TC such as (super) hydrophobic and/or oleophobic and/or
dust repelling coating, i.e. the blocking face cx of the spectacle
lens blank B would carry the multilayer system prior to
blocking.
[0067] A block piece for holding in particular a spectacle lens
blank and its use are proposed, which comprises a basic body having
a workpiece mounting face portion against which the workpiece can
be blocked with a blocking material, and a clamping portion via
which the blocked workpiece can be fixed in a machine/apparatus for
processing it. The basic body consists of a material having a
defined low water absorption and/or is sealed to at least reduce
outgassing of water moisture under vacuum conditions, so that the
block piece is adapted to be used also in vacuum coating processes.
Alternatively or in addition, the clamping portion is adapted to be
clamped by forces directed essentially perpendicular to the radial
direction to cancel out each other and not deform the basic body,
and/or the workpiece mounting face portion is provided with a
predetermined amount of prism.
[0068] In summary, the invention can be said to provide for the
very first time a blocking piece made of two different materials
making up the body portion thereof (main body and supporting
portion) with one or both of them being translucent and in
particular transparent, wherein the concept of having an annular
adjoining surface allows to cope with all mechanical and cost
constraints while at the same time allowing an enhanced degree of
freedom to optically design the blocking piece. In particular it
has for a long time been believed to be rather impossible to have
different materials when wishing to use photo curable adhesive.
Shading problems and the like where considered to be predominant In
other words hereinbefore multimaterial blocking pieces where
exclusively opaque, whereas blocking pieces comprised of
translucent or transparent material were exclusively made from a
single material, exception made of course from elements as such not
constituting the blocking piece body, such as springs, stud screws
etc. Apparently the before described embodiments are for
illustrative purpose only and this scope of the protection should
only be defined by the appended claims.
* * * * *