U.S. patent application number 14/268151 was filed with the patent office on 2014-11-06 for multi part blocking piece.
The applicant listed for this patent is Satisloh AG. Invention is credited to Marc Savoie.
Application Number | 20140329443 14/268151 |
Document ID | / |
Family ID | 48672774 |
Filed Date | 2014-11-06 |
United States Patent
Application |
20140329443 |
Kind Code |
A1 |
Savoie; Marc |
November 6, 2014 |
Multi Part Blocking Piece
Abstract
The invention refers to a blocking piece, comprising at least
two parts, at least one part being designed for multiple use and at
least one part being designed for single use, wherein a surface for
supporting one face of an optical article to be blocked is
constituted at least in part by the reusable part and at least in
part by the single use part.
Inventors: |
Savoie; Marc; (Wetzlar,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Satisloh AG |
Baar |
|
CH |
|
|
Family ID: |
48672774 |
Appl. No.: |
14/268151 |
Filed: |
May 2, 2014 |
Current U.S.
Class: |
451/43 ; 451/390;
451/42 |
Current CPC
Class: |
B24B 13/005 20130101;
B29D 11/00942 20130101; B24B 9/146 20130101 |
Class at
Publication: |
451/43 ; 451/390;
451/42 |
International
Class: |
B24B 13/005 20060101
B24B013/005 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2013 |
LU |
92190 |
Claims
1. A blocking piece for blocking an optical article, comprising at
least two parts, at least one reusable part being designed for
multiple use and at least one single use part being designed for
single use, wherein a working surface for supporting one face of an
optical article to be blocked is constituted at least in part by
the reusable part and at least in part by the single use part,
wherein the reusable part has a reusable part top surface and the
single use part has a single use part top surface, wherein the
reusable part top surface and the single use part surface form the
working surface, and wherein the reusable part has a first annular
peripheral surface with a first annular diameter, the first annular
peripheral surface extending from the reusable part top surface
towards a bottom of the reusable part, and a second annular
peripheral surface with a second annular diameter, the second
annular surface extending from the first annular surface towards a
bottom of the reusable part, the second annular diameter being
larger than the first annular diameter, thereby forming an abutting
shoulder for the single use part.
2. The blocking piece according to claim 1, wherein the working
surface is a continuous and step free surface.
3. The blocking piece according to claim 1, wherein the reusable
part top surface and the single use part top surface have the same
curvature.
4. The blocking piece according to claim 1, wherein the reusable
part and the single use part are arranged concentrically with
respect to each other, in particular wherein the single use part is
a ring shaped outer part and the single use part is a central block
designed to be engaged with the ring shaped part.
5. The blocking piece according to claim 1, wherein the reusable
part is configured and arranged with a chucking engaging portion
for engagement with a chucking tool as used in a device for
generating, polishing, coating etc., wherein the chucking
engagement portion is located on an opposite side to the single use
part top surface
6. The blocking piece according to claim 1, wherein the reusable
part and the single use part comprise at least a mating surface
section, in particular the reusable part and the single use part
being designed to cooperate snugglingly, by a form fit and/or using
connecting means such as thread or clipping means.
7. The blocking piece according to claim 1, wherein the single use
part has a third peripheral annular surface extending from the
single use part top surface towards a bottom of the single user
part, and a fourth annular peripheral surface extending from the
third peripheral annular surface towards a bottom of the single use
part, wherein the third annular surface cooperates with the first
annular surface, and the fourth annular surface cooperates with the
second annular surface.
8. The blocking piece according to claim 1, wherein at least one of
the first, second, third and fourth peripheral annular surfaces is
provided with at least one of a surface characteristics for light
scattering or focusing, and of an alternating pattern of reflective
elements and non-reflective elements.
9. The blocking piece according to claim 1 wherein the reusable
part and the single use part have tolerance coping means, in
particular a gap design to be filled with a bonding material, in
particular the bonding material used during blocking of the optical
article.
10. The blocking piece according to claim 1 wherein the single use
part has axially extending reinforcing ribs.
11. The blocking piece according to claim 1 wherein the reusable
part is provided with a over-moulded glass insert for strengthening
the reusable part.
12. The blocking piece according to claim 1 wherein the reusable
part comprises and preferably is composed of translucent, in
particular transparent material, and wherein at least the single
use part is made of plastic material, being translucent and more
preferably transparent.
13. A set of blocking pieces, composed of respectively at least two
blocking pieces according to claim 1, wherein a first blocking
piece is comprised of a reusable part and a single use part, both
parts having corresponding surface characteristic with respect to
the surface portion intended to support the optical article to be
blocked whereas a second blocking piece of said set is composed as
a reusable part and a single use part, both having corresponding
surface characteristics, different from the optical characteristics
of the first blocking piece so as to be suitable for accommodating
and supporting optical articles of a family having different shape
and/or configuration.
14. The set of blocking pieces according to claim 13, wherein the
optical articles to be blocked are optical lenses and wherein the
reusable part and the single use part define a common base curve
adapted for at least some of the lenses of a lens family,
respectively.
15. The set of blocking pieces as defined in claim 13, wherein the
set is comprised of five to seven different blocking pieces and/or
of blocking pieces being different with respect to each other by at
least one dioptre.
16. The method for manufacturing spectacle lenses using a blocking
piece according to claim 1, comprising the steps of: i. blocking a
spectacle lens blank with its blocking face on the working surface
of the blocking piece using 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. releasing the
processed spectacle lens from the block piece, wherein the
spectacle lens blank remains on the proposed block piece throughout
the whole processing stage or step (ii).
17. The method for manufacturing spectacle lenses using a set of
blocking pieces according to claim 13, comprising the steps of: i.
blocking a spectacle lens blank with its blocking face on the
working surface of the blocking piece using 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. releasing the processed spectacle lens from the block piece,
wherein the spectacle lens blank remains on the proposed block
piece throughout the whole processing stage or step (ii).
Description
CROSS-REFERENCE TO PATENT APPLICATIONS
[0001] The present application is related to U.S. patent
application Ser. No. 14/281,141, entitled Multimaterial Block
Piece, and filed on May 2, 2014. The entire disclosure of the
foregoing application is incorporated herein by reference.
[0002] The entire content of the foregoing application is
incorporated herein by reference.
TECHNICAL FIELD OF THE INVENTION
[0003] The present invention generally relates to a workpiece
support block ("blocking piece") for supporting an optical
workpiece during the processing thereof. In particular, the
invention relates to a blocking 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 set of blocking pieces
and a method for manufacturing spectacle lenses according to a
prescription.
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. 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 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.
[0021] In this difficult framework of restricted available
materials and the need to balance supporting characteristics with
particular needs for such rigidity requirements for the various
machining processes it has now proven necessary to also cope with
environmental needs and increasing cost pressure.
SUMMARY OF THE INVENTION
[0022] The object of the present invention is to provide a blocking
piece for holding an optical workpiece, in particular a spectacle
lens, for processing thereof, which blocking 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 with smaller impact to the environment 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 set of blocking
pieces as well as of a method for manufacturing spectacle lenses
using such a blocking piece or set of blocking pieces. Obviously
the blocking piece should preferably be compatible with existing
machining equipment.
[0023] The above object is solved by a blocking piece comprised of
at least two parts, at least one part being designed for multiple
use and at least one part being designed for single use, wherein a
working surface for supporting one face of an optical article to be
blocked is constituted at least in part by the reusable part and at
least in part by the single use part. The reusable part has a
reusable part top surface and the single use part has a single use
part top surface, wherein the reusable part top surface and the
single use part surface form the working surface. The reusable part
has a first annular peripheral surface with a first annular
diameter, the first annular peripheral surface extending from the
reusable part top surface towards a bottom of the reusable part,
and a second annular peripheral surface with a second annular
diameter, the second annular surface extending from the first
annular surface towards a bottom of the reusable part, the second
annular diameter being larger than the first annular diameter,
thereby forming an abutting shoulder for the single use part.
[0024] 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 blocking piece of one single suitable material.
However, such a single throw away part cannot be recycled.
Alternatively the most usual concept of having a base portion made
of hard metal with a lens supporting part made of a specific low
temperature melting alloy is prone to environmental issues as well.
Surprisingly it was now found possible to use instead of a
continuous single piece and single material supporting surface a
blocking piece having the supporting surface composed of two parts,
thus increasing the freedom to design either part. In doing so the
center part of the blocking piece can be designed to be a reusable
part with most exact tolerances and with high rigidity so as to
allow proper chucking. The part supporting the optical object at
the place or in the vicinity of the intended machining however can
be designed as a single use part. In doing so it is possible to
provide this part at particularly low cost and having small impact
on the environment, e.g. in choosing a material that can be handled
after usage in the same way as chips of the optical article or by
using a material that can be easily separated therefrom. Most
astonishingly it was found that using a supporting surface composed
of different parts can have further unexpected advantages such as
improved thermal characteristics during machining, improved bonding
capacities and improved optical properties allowing for enhanced
inspection options and most adequate curing of bonding material,
e.g. photocurable adhesive.
[0025] Preferably the working surface formed by the re-usable part
and the single-use part defines a continuous, in particular a
continuous and step free surface designed to support the optical
article to be blocked. Such a configuration is helpful in providing
for a most uniform bonding material or adhesive layer and reduces
any risks of inducing unwanted stresses into the optical
article.
[0026] In a preferred configuration, the reusable part and the
single use part are arranged concentrically with respect to each
other. A concentrically arrangement allows to easily maintain a
more or less adequate rotational symmetry that is not needed in all
circumstances, but possibly beneficial for processes that require
high rotational speeds like in polishing and spin-coating.
Furthermore, the support of the optical article can be improved and
is usually most balanced. Finally, the bonding or curing of the
adhesive can advantageously fix the separate parts together,
wherein the parts can optionally be held together by adhesive in
any existing space between the parts and/or the bonding versus the
optical article. Hence the junction between the parts will be
simultaneously reached or bridged, such that e.g. a ring shaped
single use part will be affixed to the re-usable part over the
entire junction surface at one single and specific moment in time
so as to avoid any stresses that might be transmitted to the
optical article. Transmitted stresses are particularly detrimental
when the optical article is thin. Preferably the parts are unified
together with the optical article.
[0027] Preferably the reusable part is configured and arranged for
engagement with a chucking tool as used in a device for grinding,
polishing, depositing etc. For such a purpose the re-usable part
will usually be the centre part and could be comprised of a
strengthening structure such as an overmoulded glass ring, a metal
surrounding collar or could be made of a particularly well suited
material. In Practice it is beneficial if the re-usable part is at
least in part translucent or transparent but provides at the same
time for adequate stiffness and hardness for the chucking process.
The separation of the blocking piece into a re-usable part and a
single use part as above allows also to compensate for eventually
induced deformations in the chucking center portion that will not
be transposed towards the outer peripheral areas beyond the
junction between the at least two parts.
[0028] In a preferred embodiment at least the single use part is
made of plastic material, formed preferably by injection moulding,
in particular of a translucent and more preferably of a transparent
material. In fact both parts could be made from injection molded
plastic material, however the re-usable part of the blocking piece
will need to have better resistance as to deformation but as well
against abrasion, whereas the single-use part should be
particularly adapted to allow proper machining, the material should
allow to build up chips without being as such too prone to brittle.
Injection moulded plastic parts are particularly un-expensive and
allow for mass production, thus allowing to use a wide range of
geometries and materials available.
[0029] Preferably the re-usable part and the single-use part
comprise at least a mating surface section, in particular the
re-usable part and the single-use part being designed to cooperate
snuggly, by a form fit and/or using connecting means such as thread
or clipping means. The provision of mating forms allows to avoid
the creation of voids that would be detrimental for e.g. vacuum or
spin coating as voids tend to hold back moisture that might degas
or contaminate any formed layer on the optical article.
[0030] In a particularly preferred embodiment the re-usable part
and the single-use part exhibit tolerance coping means, in
particular a gap design to be filled with a bonding material, in
particular the bonding material used during blocking of the optical
article. Astonishingly it was found that it is possible to provide
the supporting surface for the optical article to be blocked by
several parts that interact with little play for compensating
tolerances, whereas the void areas are subsequently filled with
bonding material or adhesive.
[0031] In a preferred embodiment the re-usable part comprises and
preferably is composed of translucent, in particular transparent
material. The use of a translucent or transparent re-usable part is
advantageous in that aside of the option to use photocurable
adhesives and of optical inspection of the optical article during
machining it is also possible to check the integrity of re-usable
part efficiently using well known optical analysing tools once the
re-usable part has was unblocked and is intended for the next
use.
[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 single use
part providing for a section of the supporting surface and a
re-usable part or a basic body that has a further section of the
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 reusable
part of 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 due to the provision of a
single use part made preferably of an easy to work material such as
plastic, so as to avoid undue use of machining tool. The invention
provides for a blocking 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 surfacing/processing machine
including thin film coating processes.
[0033] The invention also provides for a set of blocking pieces,
composed of respectively a blocking piece as described above
wherein each blocking piece is comprised of a reusable part and a
single use part, both parts having corresponding surface
characteristic with respect to the surface portion intended to
support the optical article to be blocked whereas another blocking
piece of said set is composed as a re-usable part and a single use
part, both having corresponding surface characteristics, different
from the optical characteristics of the first blocking piece so as
to be suitable for accommodating and supporting optical articles of
a family having different shape and/or configuration.
[0034] A preferred set of blocking pieces is designed and
configured so as to be suitable for blocking optical lenses as
optical articles, wherein the reusable part and the single use part
define a common base curve adapted for at least some of the lenses
of a lens family, respectively. In the ophthalmological field is
usual to provide as a prescription basis a family of lenses or lens
blanks, such that the final machining is performed on a blank that
has been previously chosen to be a suitable approximation. All
members of a lens family show similar characteristics and
accordingly it is beneficial to have a corresponding "family" or
rather set of blocking pieces.
[0035] A preferred set of blocking pieces is comprised of five to
seven different blocking pieces and/or of blocking pieces being
different with respect to each other by at least one dioptre. It
has proven beneficial to have a sufficient but restricted number of
blocking pieces, e.g. each suitable for or having a particular base
curve. In the example of seven blocking pieces it would be
conceivable to have seven reusable parts each having as supporting
surface a curvature corresponding to a particular power, let's say
of 1, 2, 3, 4, 5, 6 and 7 diopter. The single use parts at a number
of seven as well would each have a matching curvature. It is to be
noted that it is also possible to provide the usually softer and
more easily deformable single use part with a slightly different
radius so as to provide a small preload or a bonding being stronger
or weaker as compared to the bonding versus the reusable part.
[0036] 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 provided commonly by a re-usable part and a
single-use part of a blocking 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).
[0037] Since the spectacle lens blank remains on the block piece,
at least on the re-usable part thereof 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 an 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.
[0038] 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 including
polishing; 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.
[0039] 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.
[0040] Although in one preferred embodiment the several parts are
made from the same material, e.g. injection moulded plastic
material it is also possible to use different materials having
different rigidity, stiffness and/or hardness. Preferably at least
one of the materials and even more preferred both materials and/or
parts 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.
[0041] Preferably both materials/parts 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.
[0042] Preferably both materials/parts are translucent and most
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.
[0043] Preferably one or both materials have similar optical
proprieties compared to the optical article or lens to be blocked.
In opting for similar optical proprieties light diffraction at the
adjoined surface between the blocking piece and the optical article
or 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 optical article or lens
bonded thereto to act as a well-defined optical system such that
the progress of the work can be followed easily 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
deflection of the obtained assembly is responsive to a temperature
or a temperature gradient a monitored deflection 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 or deflection might be used as well.
[0044] 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, in particular the re-usable part where high righty or
support is needed whereas in other location such as within the
single use part an easy workability could be provided for. One
example of such an embodiment could be to overmould a mineral glass
ring with polymeric material so as to build the base body of the
blocking piece, configured to be the re-usable part. 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.
[0045] According to the invention the blocking piece comprises at
least two elements. In a preferred configuration, these can be
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 as a single use
part, e.g. made of one particular material adjoining a central
portion of the blocking piece as a re-usable part, commonly
defining said adjoining annular surface. Such an embodiment is most
cost efficient as the disposable or impaired part (single use 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
optical article or lens blocked thereto.
[0046] In the embodiments as above or independently it is
preferable that one material is formed to have an annular shape at
least in part surrounding the other material. Such a configuration
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.
[0047] Preferably at least the outer perimeter of the blocking
piece, e.g. the reusable part 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.
[0048] 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.
[0049] Further effects and advantages of the proposed block
piece(s), the set of blocking pieces 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
[0050] 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:
[0051] 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 and the finished blocking
piece.
[0052] FIG. 2 shows a schematically sectional view of a second
preferred embodiment making use of identical materials for the two
parts making up the blocking piece.
[0053] FIG. 3 shows a third preferred embodiment in a sectional
view together with a detail thereof and in a bottom view.
[0054] FIG. 4 shows a fourth preferred embodiment being a slight
modification of the third preferred embodiment as illustrated in
FIG. 3.
[0055] FIG. 5 shows schematically two elements of a set of blocking
pieces according to the invention.
[0056] FIG. 6 shows a flow chart of a lens machining process
carried out using the blocking 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
[0057] 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 separately or in conjunction
with other features described herein, irrespective as to whether
such feature combination is explicitly mentioned or rather
obtainable by omitting one or more single/isolated feature(s) from
any of the described embodiments.
[0058] The first preferred embodiment as illustrated in FIG. 1 can
be assembled by juxtaposing a basically ring shaped element 30--the
single use part--with a basically disk or block shaped element
50--the reusable part. 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 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.
[0059] In the illustrated embodiment the re-usable part or element
50 is a glass block, e.g. made from mineral glass which is
sufficiently stiff, rigid and hard in order to allow for engagement
with a working machine such that the blocking piece complies with
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 single use 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, as
an example of fourth and third annular surfaces. 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.
[0060] 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 (a set of blocking pieces having preferably between
five and seven different 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 do commonly
provide for the supporting surface with one single and particularly
specified radius. One could also contemplate to use one glass block
(re-usable part) 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 single use
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.
[0061] It is therefore noted that the entire surface formed by the
reusable part top surface 51 and the single use top surface 31
forms a working surface 61 against which a lens blank is lying for
the process of manufacturing the lens blank, in particular the
treatment of the optical surfaces thereof. As a result the lens is
supported on its entire surface and can better withstand the
processing forces during the manufacturing process. The lens is
less deformed. This measure improves the surface accuracy of the
lens significantly.
[0062] Coming back to the illustrated preferred embodiment of FIG.
1 the ring shaped or annular element 30 is presently made from a
plastic material, in particular an injection moulded plastic
material part. The plastic material is preferably a plastic
material that has proven to be usable 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. Preferably the material
is either such that the chips obtained during machining can be
processed further together with chips resulting from the optical
article being machined or such that the respective materials can be
separated easily. The plastic material is preferably neither
harmful for the operator nor the environment, representing a huge
advantage over the previously used heavy metal alloys. 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
(cf. Embodiment of FIG. 2) 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.
[0063] 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 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. Hence, the reusable part
always remains intact and the single use part can be specifically
adapted towards workability as it is conceived to be used only
once.
[0064] 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.
[0065] 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.
[0066] A beneficial feature adding a further advantage to the
embodiment can be realised when analysing the embodiment of FIG. 1
and resides in 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 that the entire
surface composed of the surfaces 31 and 51 be properly irradiated
with UV-light for curing the adhesive.
[0067] The person skilled in the art will realize that either one
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. Similarly, the first annular surface 56
and the third annular surface of the protrusion 36 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 and unblocking but also for monitoring
or inspection purposes.
[0068] 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.
[0069] In FIG. 2 an alternative embodiment is shown. The second
preferred embodiment is also relying on the beneficial effect of
having two distinct parts, a reusable centre part and a single use
ring shaped outer part. In this embodiment both parts are made from
the same material and are obtained from injection moulding. Again
the two parts are 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 36 and 56 allows to
compensate for differences in mechanical behaviour of the two
parts, such as due to different thicknesses and 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.
Additionally the engagement between the two parts is secured using
threads as illustrated at reference signs 39 and 59. In the
illustrated embodiment the thread extends approximately over the
lower third of the annular junction area. 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.
[0070] 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.
[0071] In FIG. 3 a third preferred embodiment according to the
present invention is illustrated in a bottom view, a sectional view
and a detailed view. 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, made here from injection moulded
plastic material. The element is once again transparent or at least
translucent and is provided on the top with the supporting surface
21 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 glass insert overmoulded by an injection moulded
plastic material. Both components are translucent and in particular
transparent and the overmoulded glass insert 24 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.
Additionally or alternatively an annular strengthening element (not
illustrated) could be provided on the outer side of the reusable
part with a cone shaped or chamfered guiding surface and a tool
engaging surface. The use of the strengthening ring 24 can
successfully minimize any deformation in the plastic part and can
thus avoid any deformation of the surface 21 which would in
particular when thin lens blanks are worked also result in a
distortion of the lens being worked.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] In the preferred embodiment as illustrated in FIG. 3, 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. 3 it is interesting to note that the use of the
same or two different plastic materials together with an
overmoulded glass ring is possible thus allowing 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.
[0076] In FIG. 4 a further preferred embodiment is illustrated. In
light of the third embodiment being very similar to the fourth
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.
[0077] In FIG. 5 two elements of a set of blocking pieces are
illustrated. On the left handed side the blocking piece is having a
rather strong curvature whereas the blocking piece on the right
side is rather shallow. The blocking pieces as such can be
configured according to any of the previously explained
configuration and thus reference can be given to the above
description of the preferred embodiments of the various blocking
pieces.
[0078] Finally, FIG. 6 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.
[0079] 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 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.
[0080] As can further be seen from FIG. 6, 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.
[0081] A blocking piece for holding in particular a spectacle lens
blank, a set thereof 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 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. This piece is specifically designed to be
reusable. 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.
[0082] In summary, the invention can be said to provide for the
very first time a blocking piece made of two distinct parts, a
reusable part and a single use part, both contributing in the
provision of the supporting surface. The same, similar but also
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 can be used. The optional feature of
having an annular adjoining surface allows to even better 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. Decomposing the supporting
surface so as to be provided by different pre-fabricated parts has
not been considered ever hereinbefore. Apparently the before
described embodiments are for illustrative purpose only and this
scope of the protection should only be defined by the appended
claims.
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