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Description  |
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FIELD OF THE INVENTION
The invention relates to improved lapping blocks for use in polishing glass
or plastic prescription lenses.
BACKGROUND OF THE INVENTION
In the optical lens making industry precision lenses, such as those used
for prescription eyeglasses, are conventionally produced by grinding the
lens to a rough finish using diamond grinders and thereafter polishing the
lens to prescribed dimensions and a fine finish. In the polishing of such
lenses conventionally a steel or hard plastic lapping block, which is
sized and configured for the particular desired prescription, is placed in
movable mating contact with the surface of the rough cut lens.
A grinding compound, which is mixed with water to form a slurry, is
introduced between the surfaces of the lapping block and the lens, while
one or both the block and the lens are moved in a figure eight motion.
Additionally, it is conventional to polish a lens in a coarse manner using
a relatively coarse grinding compound and thereafter producing a fine
polished surface through the use of a grinding compound containing
relatively fine particulate manner. During the polishing operation a
pressure of approximately 30 pounds per square inch is applied to the
lapping block. The above noted procedure is continued until the desired
results of a highly polished, uniformly finished lens surface are
obtained.
A disadvantage of the conventional lens polishing procedure is that there
are approximately 2,000 different prescriptions, each requiring a
different lapping block with each having a different radius of curvature.
Thus, approximately 2,000 different lapping blocks would be required in
order to obtain polishing of all the possible different prescriptions
which may be required in the finished lens.
SUMMARY OF THE INVENTION
I have discovered that through the use of a variable pitch lapping block
the number of different lapping blocks necessary for polishing
prescription lenses may be substantially reduced. In this regard, the
working surface of a conventional lapping block may be replaced with a
flexible and expandable surface, such as that of a rubber bladder
exhibiting a curved surface wherein the curvature of the surface may be
adjusted by varying the air pressure on the inner or non-working surface
of the bladder.
Thus, by varying the air pressure applied through a valve in the lapping
block to the flexible working surface, a variable pitch lapping block
exhibiting a range of radii of curvatures may be obtained wherein the
variation in air pressure may be used to conform the flexible surface to
the curvature of the unpolished rough cut lens surface. In this manner, a
single lapping block having a variable pitch surface controlled by
pneumatic or hydraulic pressure may be used to polish a wide range of
different prescriptions for glass or plastic lenses.
The objects and advantages of my invention will be more completely
understood and appreciated by the artisan carefully studying the following
description of the presently preferred exemplary embodiment taken in
conjunction with the accompanying drawings of which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a cross sectional view of a conventional lapping block
and lens as used in the prior art for polishing the lens;
FIGS. 2a, 2b and 2c are illustrative of the cross sections of conventional
convergent and divergent lens shapes;
FIG. 3 is a cross sectional view illustrative of my presently preferred
exemplary embodiment of a lapping block having variable pitch useful in
polishing lenses having a range of radii of curvature;
FIG. 4 is a top view of the exemplary embodiment of the lapping block of
FIG. 3; and
FIG. 5 is a cross sectional view of an alternative exemplary embodiment of
my variable pitch lapping block.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 is illustrative of a standard metal or hard plastic lapping block 1
as used in the optical industry for polishing a glass or plastic lens 2 so
that surface 2a results in a very smooth, highly polished surface having a
uniform radius of curvature across the surface. The raised portion 1a of
the lapping block is designed to be attached to an actuating mechanism of
a polishing machine. Moreover, surface 1b of the lapping block is
precisely formed with a radius of curvature for a particular lens
prescription. Clearly, the radius of curvature can vary over a range from
large to relatively small radii.
As may be seen from a consideration of FIGS. 2a to 2c, exemplary
conventional lens types of both divergent and convergent form are known
and are used, for example, in prescription eyeglasses. Such generalized
lens types, however, include a wide variety of radii of curvature in order
to comply with approximately 2,000 separate prescriptions.
A lens for a particular prescription, for example, is conventionally
initially formed or cut to prescription by a diamond grinder or cutting
device and thereafter polished through the use of a lapping block 1
configured for the particular prescription, thus requiring a large number
of separate lapping blocks. Once the appropriate lapping block has been
selected for the desired prescription, the lapping block and unpolished
lens are respectively attached and clamped in polishing machines in a
conventional manner. Thereafter, a slurry comprising water and a grinding
compound is pumped between the lapping block and lens as they are both
moved in a figure eight manner so as to polish the lens surface to a
uniform prescribed radius of curvature. As previously noted, it is
conventional to coarsely polish the lens surface and thereafter fine
polish the surface by means of slurries containing coarse and then fine
grinding compounds.
FIGS. 3 and 4 illustrate the presently preferred exemplary embodiment of my
variable pitch lapping block shown in cross section and top view,
respectively. The device includes a metal or hard plastic element 3 having
an upper portion 3a designed to be attached to lens polishing machines in
a conventional manner. Element 3, however, includes a hollow central
portion 3b, which together with portion 4b to be described below forms an
air or fluid chamber. Element 3 additionally includes a valve element 5
for the admission of air and/or other fluids so as to pressurize the
interior chamber to a desirable pressure.
Resilient element 4 made of rubber or the like is attached at 4a to the
metal or plastic element 3 by band clamps 6, adhesives, vulcanization
processes or other conventional fastening means so as to provide the lower
portion 4b of the fluid tight variable pressure interior chamber whereby
the radius of curvature of the exterior surface 4c may be modified to be
larger or smaller depending upon the pressure of the fluid introduced into
the chamber formed by portions 3b and 4b.
In a conventional lapping block of the nature illustrated in FIG. 1,
approximately 30 pounds per square inch of pressure is applied to the
lapping block during the lens polishing procedure. In the use of my
variable pitch lapping block shown in FIGS. 3 and 4, by varying the
pressure on the block, as well as the pressure within the chamber formed
by portions 3b and 4b, the exterior surface 4c of the elastically
resilient element 4 will conform to a range of curvatures exhibited by the
rough cut, unpolished lens 2 so as to produce uniform polished surfaces of
the desired radius of curvature. An exemplary elastically resilient
element 4 may be formed of rubber material (with or without fiber
reinforcement) of approximately one-eighth inch in thickness.
Additionally, as will be noted with respect to the embodiment of FIG. 5,
the resilient element 4 may be made so that different portions of the
element are made of rubber having different durometer hardnesses.
Moreover, it is contemplated that the use of a relatively small number of
such rubber bladder elements 4 having different radii of curvature in the
unpressurized condition will be adequate to cover the entire span of
approximately 2,000 different prescriptions, as opposed to the presently
used approximately 2,000 different lapping blocks, each dedicated to a
particular prescription.
In its simplest form, my variable pitch lapping block may comprise a
hollowed out conventional lapping block with the bottom portion including
surface 1b removed and with a valve 5 such as a conventional air valve
included so as to communicate with chamber portion 3b. Additionally
included is a rubber bladder element 4 which is configured to overlap the
sides of the lapping block portion 3 where it is clamped by a metal band
clamp 6 about the circumference of element 3 to form chamber portion 4b.
Alternatively, element 4 may be glued or vulcanized in place so that it
adheres to the sides of the block with or without the aid of the metal
band clamp. As will be appreciated, outer surface 4c of the bladder
element will exhibit a variable range of radii of curvature depending upon
the pressure of the interior air chamber.
FIG. 5 illustrates in cross section an alternative embodiment wherein a
conventional lapping block 53 with the bottom portion removed may be used
but without being hollowed out as in FIG. 3. However, conventional air
valve 55 and drilled airways 57 are included for communicating with and
pressurizing the chamber 58 formed by rubber bladder element 54.
The rubber element 54 may include a flat top portion 54(a) of hard rubber
attached to the lower surface of block 53 by adhesives or by vulcanizing
to the block. Element 54 may also include two or more sections (54b, 54c
and 54d, for example) made of rubber of different hardnesses. For example,
portion 54b may be made of relatively soft rubber and portion 54c of
rubber having medium hardness. In contrast portion 54d may be of
medium-hard rubber for increased wear resistance. This alternative
embodiment operates in a manner similar to that illustrated in FIG. 3 in
that it will exhibit a variable range of radii of curvature depending on
the pressure of the air chamber 58. Moreover, the rubber element 4 of FIG.
3 may also include one or more portions of rubber having different
hardnesses as in FIG. 5.
While the invention has been described in connection with what is presently
the most practical and preferred embodiments, variations will occur to
those skilled in the art. For example, element 4 may be formed of other
elastically resilient materials and/or be configured to include an upper
portion for added leak resistance which would conform to the inner walls
of chamber portion 3b, such portion being integrally molded with element
4, as presently illustrated. Additionally, although the chamber formed by
portions 3b and 4b is presently contemplated to form a pressurized air
chamber, it is clear that other fluids including liquids or combinations
of liquids and gases may be used. Thus, it is to be understood that the
invention is not to be limited to the disclosed embodiment but, on the
contrary, is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended claims.
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