U.S. patent application number 12/737393 was filed with the patent office on 2011-05-05 for tool for polishing conventional and free-form optical surfaces.
Invention is credited to Francisco Gonsalez Alcantara, Juan Carlos Dursteler Lopez, Leonardo De Jesus Valencia Merizalde.
Application Number | 20110104998 12/737393 |
Document ID | / |
Family ID | 39876258 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110104998 |
Kind Code |
A1 |
Valencia Merizalde; Leonardo De
Jesus ; et al. |
May 5, 2011 |
TOOL FOR POLISHING CONVENTIONAL AND FREE-FORM OPTICAL SURFACES
Abstract
A tool for polishing optical surfaces including a rigid base
having a spherical surface which carries a resilient cushion with a
polishing face. The diameter of the rigid base is between 50 and 65
mm, the radius of curvature of the spherical surface is between 54
and 60 mm, the thickness of the resilient cushion is between 13 and
16 mm and the resistance to compression of the resilient cushion is
substantially between 0.08 and 0.15 bar at 10% compression and
substantially between 0.55 and 0.8 bar at 70% compression. The tool
can be used for polishing an optical surface, particularly an
ophthalmic lens, and more particularly a free-form lens.
Inventors: |
Valencia Merizalde; Leonardo De
Jesus; (Barcelona, ES) ; Alcantara; Francisco
Gonsalez; (Barcelona, ES) ; Lopez; Juan Carlos
Dursteler; (Barcelona, ES) |
Family ID: |
39876258 |
Appl. No.: |
12/737393 |
Filed: |
July 7, 2009 |
PCT Filed: |
July 7, 2009 |
PCT NO: |
PCT/ES2009/000355 |
371 Date: |
January 7, 2011 |
Current U.S.
Class: |
451/526 |
Current CPC
Class: |
B24B 13/02 20130101;
B24D 13/147 20130101 |
Class at
Publication: |
451/526 |
International
Class: |
B24D 11/00 20060101
B24D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2008 |
EP |
EP08382026.6 |
Claims
1-10. (canceled)
11. A tool for polishing optical surfaces comprising: a rigid base
which has a spherical surface which carries a resilient cushion
which has a polishing face, wherein: the diameter of the rigid base
is between 50 and 65 mm, the radius of curvature of the spherical
surface is between 54 and 60 mm, the thickness of the resilient
cushion is between 13 and 16 mm, and the resistance to compression
of the resilient cushion (12) is substantially between 0.08 and
0.15 bar at 10% compression and substantially between 0.55 and 0.8
bar at 70% compression.
12. The tool according to claim 11, wherein the resistance to
compression of the resilient cushion is substantially between 0.10
and 0.16 bar at 15% compression and between 0.20 and 0.30 bar at
50% compression.
13. The tool according to claim 11, wherein the thickness of the
resilient cushion is between 14 and 15 mm.
14. The tool according to claim 11, wherein the radius of curvature
of the spherical surface of the rigid base is between 54 and 56
mm.
15. The tool according to claim 11, wherein the diameter of the
rigid base is between 55 and 65 mm.
16. The tool according to claim 11, wherein the resilient cushion
is Eurocell 130.TM..
17. The tool according to claim 11, wherein the polishing face of
the resilient cushion is a separate polishing pad attached to said
resilient cushion.
18. The tool according to claim 17, wherein the polishing pad
includes a top layer and a bottom layer, the top layer being a nap
layer adapted to carry an abrasive slurry.
19. The tool according to claim 18, wherein the bottom layer of the
polishing pad is a polyurethane impregnated non-woven fabric.
20. The use of the tool according to claim 11 for polishing an
optical surface.
21. The use of the tool according to claim 11 for polishing an
ophthalmic lens.
22. The use of the tool according to claim 11 for polishing a
free-form lens.
Description
[0001] The present invention relates to a tool for polishing
optical surfaces and to the use of such a tool when polishing
optical surfaces. More specifically it relates to a tool for
polishing optical surfaces comprising a rigid body carrying a
resilient cushion which has a polishing face and to the use of such
a tool for polishing optical surfaces.
[0002] In the manufacture of optical lenses, it is known to polish
a previously machined lens surface by means of a polishing tool. A
conventional type of polishing tool comprises a support which to a
certain extent has a similar surface as the lens to be polished and
on which a polishing pad is mounted. The tool is brought into
contact with the lens, and the lens surface is polished by the
combined effect of a pressure between the tool and the lens and a
relative angular velocity between them and with the aid of abrasive
slurry. The goal of the polishing process is reduce the roughness
of the lens to under 10 nanometres.
[0003] Lenses of largely varying surfaces are known. Firstly, the
surface of a lens may be spherical, aspherical, toric or atoric.
Additionally, lenses with more irregular surfaces have been
developed, so called free-forms. Free-form lenses can have largely
varying surfaces containing local curvatures from 13 dioptres to 0
dioptres (a locally flat surface). When polishing these free-form
lenses, the goal is not to reduce the thickness of the lens by more
than 20 micrometers and at the same time obtain a surface roughness
under 10 nanometers.
[0004] Traditionally, a manufacturer has a large number of
different polishing tools at his disposal, which can all be mounted
in the same polishing machine. Each of these tools is more or less
adapted to the surface of the lens that is to be polished.
[0005] EP 1 655 102 describes using polishing tools with a rigid
surface upon which an elastic body is mounted. The diameter of the
elastic body is between 20 and 60 mm. It is described to prepare
five to ten types of elastic bodies with a radius of curvature
ranging between 5 and 50 mm and several elastic bodies with a
radius of curvature between 100 and 200 mm to be able to polish
lenses of most lens prescriptions.
[0006] US 2008/0047301 describes using polishing tools which also
comprise a rigid body carrying a resilient pad which has a
polishing face. It also describes using 108 different devices to be
able to polish a variety free-form lenses.
[0007] A variety of different polishing tools is needed to be able
to polish the lenses of different prescriptions. So, to polish one
lens after another, the polishing tool needs to be changed. This is
cumbersome and slows down the polishing process. Additionally, it
is expensive to have a high number of different tools.
[0008] The present invention therefore aims at establishing a
single polishing tool which can be used to polish a large variety
of all lenses. Specifically, the invention aims at providing a
single polishing tool that can be used for polishing conventional
and free-form surfaces, which are made from any of the organic
materials normally used in opthalmological lenses and with
curvatures within the following curvature ranges: between 0 and -11
dioptres sphere, between 0 and -4 dioptres cylinder and additions
up to 3.5 dioptres, with a maximum allowable (combined) local
concave curvature along the surface of -11 dioptres. When they are
being polished, the lenses have a round or elliptical shape. The
diameter of the lenses is between 50 and 70 mm. The maximum
difference between the diameters of the elliptical lenses is 15
mm.
[0009] This goal is achieved with a polishing tool according to
claim 1. Namely, with a tool for polishing optical surfaces
comprising a rigid base which has a spherical surface which carries
a resilient cushion which has a polishing face, characterised in
that the diameter of the rigid base is between 50 and 65 mm, the
radius of curvature of the spherical surface is between 54 and 60
mm, the thickness of the resilient cushion is between 13 and 16 mm
and the resistance to compression of the resilient cushion is
substantially between 0.08 and 0.15 bar at 10% compression and
substantially between 0.55 and 0.8 bar at 70% compression.
[0010] The tool for polishing is mounted in a polishing machine and
the lens is polished through a combined effect of a pressure
between the tool and the lens and a relative angular velocity
between them and with the aid of abrasive slurry. For each lens,
the polishing machine may be programmed differently, i.e. the force
between lens and polisher, the speed of rotation, translation etc.
may be varied. With the described tool, a large variety of lenses
may be polished with the same tool. The polishing machine may be
pre-programmed to automatically change the values of the polishing
parameters (velocities, pressure etc.) depending on the curvature
of the surface to be polished.
[0011] Preferably, the resistance to compression of the resilient
cushion is substantially between 0.10 and 0.16 bar at 15%
compression and between 0.20 and 0.30 bar at 50% compression.
During polishing, the resilient cushion deforms to redistribute the
pressure and forces on the lens surface. The resistance to
compression is the parameter that describes how much the cushion
deforms under pressure and thus to what extent the cushion can
redistribute forces and pressures. The resistance to compression is
particularly relevant in the range of 15-50% compression, since
this is a compression that the resilient cushion experiences mostly
during polishing. A small increase in the pressure should lead to a
relatively large increase in deformation (or percentage of
compression). This ensures a good redistribution of forces over the
lens surface.
[0012] Preferably, the thickness of the resilient cushion is
between 14 and 15 mm. The resilient cushion, which deforms slightly
during polishing redistributes the pressure and forces on the lens
surface. For this, it needs to have a certain thickness. On the
other hand, if the resilient cushion is too thick, it is more
likely to bend and break during polishing. With a thickness between
14 and 15 mm, a good balance of redistribution of forces and
probability of breaking is achieved.
[0013] Preferably, the radius of curvature of the spherical surface
of the rigid base is between 54 and 56 mm. During polishing, the
resilient cushion deforms to redistribute pressure and forces on
the lens surface. This way, the polishing is more equal over the
entire lens surface and one can ensure that the required surface
roughness has been achieved while at the same time the stock
removal is uniformly distributed over the surface of the lens. The
resilient cushion can partly redistribute forces and pressure, but
this effect naturally is limited. If the curvature of the rigid
base corresponds more closely to the curvature of the lens surface
that is to be polished, the forces do not need to be redistributed
as much. But a large variety of lenses with varying radius of
curvature needs to be polished with this single tool and it has
been found, that the optimum form for the polishing tool is
obtained with a radius of curvature of the spherical surface of the
rigid body between 54 and 56 mm.
[0014] Preferably, the diameter of the rigid base is between 55 and
65 mm. The larger the diameter of the tool, the higher the velocity
at its extremity in rotation and this leads to more material
removed in the polishing process. On the other hand, with a larger
diameter, the necessary linear movement of the tool in polishing is
reduced, since with a small movement it already covers the entire
surface of the lens. This reduces polishing time. With a diameter
between 50 and 65 mm, satisfactory results are achieved, but
improved results are achieved with diameters between 55 and 65
mm.
[0015] Preferably, the resilient cushion is a sponge, commercially
available as Eurocell 130.TM. from Recticel. This sponge is made
from polyether, has the required resistance to compression and a
specific density between 110 kg/m.sup.3 and 130 kg/m.sup.3.
[0016] Preferably, the polishing face of the resilient cushion is
formed by a separate polishing pad which can be attached to the
resilient cushion. The separate polishing pad may be attached to
the resilient cushion using an adhesive. The polishing pads and
resilient cushions can thus be manufactured separately which is
easier.
[0017] Preferably, the polishing pad comprises a top layer and a
bottom layer, the top layer being a nap layer adapted to carry an
abrasive slurry. More preferably, the bottom layer of the polishing
pad is of a polyurethane impregnated non-woven fabric. The function
of the polishing pad is to hold the abrasive slurry and bring it
into contact with the lens. The pad with these characteristics has
been shown to function properly and also to last long. With other
polishing pads, the pad needs to be changed more frequently, which
is costly and slows down the polishing process.
[0018] A number of commercially available polishing pads have the
desired characteristics. For example, suitable pads are: Bellatrix
Polishing PAD K0034.TM. commercially available from Filwel Co.,
Ltd. and Politex.TM. Supreme finishing pad, commercially available
from EMINESS technologies Inc. The abrasive slurry used may be an
aluminium oxide water solution.
[0019] Particular embodiments of the present invention will be
described in the following, only by way of non-limiting example,
with reference to the appended drawings, in which:
[0020] FIG. 1 is a cross section showing a polishing tool according
to a preferred embodiment of the present invention, with its
components shown separately;
[0021] FIG. 2 is a cross section showing a polishing tool according
to a preferred embodiment of the present invention in use;
[0022] FIG. 3 is a perspective view of a polishing pad which might
be used in the invention;
[0023] FIG. 4a shows a graph of the resistance to compression of a
resilient cushion which may be used in the present invention;
[0024] FIG. 4b shows a detail of the graph shown in FIG. 4a.
[0025] In FIG. 1, it is shown how a polishing tool according to a
preferred embodiment of the present invention is built up from its
separate components. A first component is the rigid body (11).
Rigid body (11) comprises a surface (14), upon which resilient
cushion (12) is to be mounted. In this preferred embodiment, the
polishing face of the resilient cushion is formed by a polishing
pad (13). Reference sign (15) is used to indicate the side of the
rigid body (11) which is to be mounted in the polishing
machine.
[0026] According to the invention, the surface (14) is spherical
and has a radius of curvature between 54 and 60 mm. The diameter of
the tool is between 50 and 65 mm, and the thickness of resilient
cushion (12) is between 13 and 16 mm. The resilient cushion has a
resistance to compression between 0.14 and 0.4 bar when compressed
between 15% and 60%.
[0027] FIG. 2 shows a schematic cross section of polishing tool
(10) completely assembled with rigid body (11), resilient cushion
(12) and polishing pad (13). The top surface (16) of the polishing
pad is used to polish the surface (21) of a lens (20) and can be
regarded as the polishing face of the tool.
[0028] The lens surface that is to be polished (21) does not
exactly correspond to the surface (16) of the polishing tool. In
fact, it can be quite different, since a wide range of lenses
(between 0 and -11 dioptres sphere, between 0 and -4 dioptres
cylinder and additions up to 3.5 dioptres, but with a maximum
allowable combined local concave curvature along the surface of -11
dioptres) is polished with the same tool. The resilient cushion
(12) deforms when in contact with the lens. This ensures a
redistribution of forces over the surface (16) of the lens. This
ensures that the desired roughness and an even stock removal can be
obtained over then entire surface.
[0029] The tool is the same for the whole range of lenses, but the
program that the polishing machine performs can vary. Some
parameters of the polishing program may be e.g. rotational velocity
(.omega.1) of the tool, rotational velocity (.omega.2) of the lens,
lateral displacement and velocity (v) of the tool, inclination
between the axis of the tool and the axis of the lens, force
between lens and polisher and polishing time.
[0030] FIG. 3 shows a perspective view of a polishing pad (13)
which might form the polishing surface (16) of a tool according to
the invention. The bottom surface (19) may carry an adhesive to
easily attach it to the resilient cushion. The polishing pad shown
has two layers. A top layer (17) is designed to hold an abrasive
slurry. For this purpose, it preferably has vertical pores. The
abrasive slurry used may be an aluminium oxide water suspension.
The bottom layer (18) is preferably of a non-woven fabric.
[0031] FIG. 4a shows a graph of the resistance to compression of a
resilient cushion which may be used in the present invention. The
graph shows the resistance to compression of the cushion Eurocell
130.TM. commercially available from Recticel. The resistance to
compression is particularly relevant in the range of 15-50%
compression, since this is a compression that the resilient cushion
might ordinarily experience during polishing. As can be seen in the
graph, in this range, a small increase in the pressure leads to a
relatively large increase in deformation (or percentage of
compression). This ensures a good redistribution of forces over the
lens surface. FIG. 4b shows a more detailed view of the lower range
of compression.
* * * * *