Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM AND METHOD FOR OPHTHALMIC LENS NIANUFACTURE
TECHNICAL FIELD
This invention relates to the manufacture of ophthalmic lenses.
Specifically this invention relates to a new system and method for surfacing,
edging and finishing ophthahnic lenses.
BACKGROUND ART
In the art of ophthalmic lens manufacture, a finished ophthalmic lens is
usually made from finished uncut lenses or from semi-finished lens blanks.
Finished uncut lenses are lenses that are optically finished on both front and
back surfaces and only need to be edged to the proper shape and edge contour
to become finished lenses. Most optical laboratories keep an inventory of
single vision finished uncut lenses in various powers, sizes, and materials to
talce care of most of the more common single vision ophthalinic lens
prescriptions.
Semi-finished lens blanks have optically finished front surfaces;
however, the back surfaces of these blanks need to be generated and fined and
are then either polished or coated to produce finished uncut lenses. Finished
uncut lenses are then edged to the proper frontal shape and edge contour to
fit
into spectacle/glasses frames or other mounting structures. Single vision
lenses that are outside the normal range of inventoried finished uncut lenses
and most multifocals are made from semi-finished lens blanks. Semi-finished
lens blanks are made with various front surface curve radii, and have various
topographies including spherical, aspheric, hyperbolic, irregular aspheric
such
as progressive add lenses, and polyspheric such as executive type segmented
bifocals and trifocals.
To generate a desired prescription for a lens, calculations are required
to determine the topography of the back surface of a lens. Such calculations
typically involve variables that include the front surface radii of the semi-
finished blank, the index of refraction of the lens blank material,
prescription
values of the desired lens, statutory values regarding minimum lens thickness,
and the physical dimensions of the frame or mounting structure.
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In the art, various means have been devised to accomplish the physical
process of producing a back surface of optical quality. Most of these methods
begin by generating a back surface that approximates the desired back surface
topography and surface smoothness. This approximate surface is then fined to
a more perfect approximation in both curvature and surface smoothness.
After the appropriate accuracy and smoothness is achieved in the fming
process, the surface is then polished or surface coated to produce a surface
of
optical quality. The optically finished lens blank is then edged to the proper
shape and edge profile to fit into the frame for which it was made.
Many business entities that sell ophthahnic lenses do lens finishing as
a profit center activity and as a way to expedite delivery of single vision
lenses. Only a small percentage of these entities also do surfacing of
ophthalmic lenses. The business volume of most of these entities cannot
justify the costs of acquiring and operating a surfacing laboratory. Surfacing
laboratory setup costs have heretofore been several times the cost of setting
up
a laboratory for edging only.
Hiring qualified technicians for ophthalmic lens finishing or training
personnel to perform ophthalmic lens finishing is relatively easy. However,
hiring and training optical technicians to operate a surfacing laboratory is
not
easy. In many communities it is very difficult to find personnel that are
trained in surfacing. Technicians who are qualified to do surfacing are
generally remunerated at higher pay scales than technicians skilled only in
optical finishing.
In addition to the significantly higher equipment and personnel costs of
a surfacing lab, there are also higher ongoing costs for the additional lab
space
required. At least several hundred square feet of operational space and
storage
space have heretofore been required for a full service surfacing and edging
ophthalmic lens laboratory. Consequently there is a need for a system and
metllod of ophthalmic lens manufacture that would significantly reduce the
investment required to acquire a surfacing and edging laboratory. There is a
further need for a system and method of ophthalmic lens manufacture that
significantly reduces the costs associated with operating a surfacing and
edging laboratory. Further, there is a need for a system and method of
ophthalmic lens manufacture that is operative to perform surfacing and edging
by an operator with little skill in the art.
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In the prior art, the processes of surfacing and edging are done on at
least two separate machines. In the prior art, blocking for surfacing and
edging required two separate blocking devices. Also in the prior art, the
individual processes of lap tool surfacing and lens cribbing and safety
beveling
and edge grooving and edge polishing and lens engraving each requires its
own machine or device or machine augmentation. Each of these machines or
devices or augmentations is to varying degrees expensive to acquire and each
of the machines or devices requires laboratory space. Each of these
operations, if done by hand, requires the necessary acquisition of skills and
application of those skills in order to perform the various operations.
Consequently, there is therefore a need for a system and method of ophthalmic
lens manufacture that reduces the need to employ a plurality of expensive and
complex machines to manufacture lenses.
In the prior art, after a semi-finished lens blank is generated and fined
and polished it is de-blocked and inspected and then laid out and blocked
again for edging. Blocking for surfacing and blocking for edging are two
different procedures that differ in significant ways requiring two different
sets
of skills and requiring two separate and very different mechanical blocking
systems. Repeating the blocking process is necessary in part because the
metallic block used for surfacing could interfere with the edging process.
This is because portions of the uncut lens that lie under the surfacing block
frequently need to be removed during the edging process. If the standard
surfacing block were also used during edging, this could result in the metal
surfacing block coming into contact'with the cutting or grinding surfaces of
the edging machine thereby damaging the cutting or grinding surfaces of the
edging machine and damaging or destroying the block in the process.
Additionally, the need to block a lens twice multiplies the opportunities for
error and spoilage and requires the expenditure of time. Consequently there is
a need for a method of ophthalmic lens manufacture that elirninates the need
to
block a lens blank twice for those lenses that require both surfacing and
edging.
The prior art describes several types of single point blocking systems.
One type describes centering the block on the point of the lens that would
occupy the geometric center of the frame when the lens is finished (frame
geometric center blocking). Another describes centering the block on the point
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of the lens that would occupy the optical center of the finished lens (optical
center blocking). A third describes centering the block in the geometric
center
of the semi-finished uncut lens (lens blank geometric center bloclcing). In
prior
art, all three of methods are optimized for surfacing by tilting the front
surface
by the proper amount and in the proper direction to move the optic axis into
alignment with the generator feed axis. Only in the case of "frame geometric
center blocking" is it possible to optimize for edging. This optimization for
edging is accomplished by aligning the front surface normal at the geometric
center with the feed axis of the generator.
The "optical center" and "lens blank geometric center" blocking
arrangements create relationships between a lens blank and the generator feed
axis that are optimal for generating lens back surfaces because errors in
thickness at any stage in the process of surface generation and fining will
not
affect a change in the position of the optical center of the lens. This is
because
the optic axis does not move as the thiclrness of the blank decreases.
However, in neither of these two cases are the blocking arrangements optimal
for edging a lens. In both instances the lens is frequently tilted too much to
apply an edge parallel to the normal at the geometric center of the front
surface
of the fmished lens. Applying an edge to a lens at any angle other than
parallel to the front surface normal at the geometric center results in edges
that
are skewed and frequently thicker than necessary and with edge beads that
have less than optimal orientations.
A blocking system optimized for edging, like "frame geometric center
blocking", wherein the lens blank is blocked on the geometric center of the
finished lens and where the normal at the geometric center of the front
surface
of the finished lens is parallel to the axis of rotation of the edging tool or
edge
grinding wheel, is not optimal for surfacing. Except for the relatively rare
case
where there is positional coincidence between the optical center of the lens
and the frame geometric center of the lens, the optical center of the lens is
made to move or "creep" as the lens is made to decrease in thiclcness during
fining.
A method of lens blocking that is optimized for edging and that is also
operative for surface generation would be of considerable utility. It would
allow for a single blocking step for both the surface generation of a lens and
for the edging of that lens without de-blocking and re-blocking between the
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steps of surface generation and edging. Therefore there is a need for a system
and method of blocking a lens for both surfacing and edging that reduces the
problems associated with optical center creep.
Prescription lenses for patients are often generated in pairs for a
5 spectacle frame. Prior art systems typically generate each lens
independently.
Production cycle times for generating lenses may be reduced by employing
multiple surfacing and edging machines in the laboratory to generate pairs of
lenses simultaneously, however duplication of equipment doubles the
acquisition and operational costs of the laboratory. Thus there exists a need
for
a system and method of ophthalmic lens manufacture that provides for reduced
production cycle times for pairs of prescription lens without significantly
increasing costs for the laboratory.
Heat transfer into the lens blank from the heated blocking medium
during the blocking procedure is a frequent cause of so called "lens warpage".
The greater the amount of heat transfer involved and the more uneven the
distribution of that heat transfer is, the greater the chance of producing
warpage and ruining the lens or producing a substandard lens. There is
therefore a need for a method of ophthalmic lens manufacture that could
minimize the transference of heat into the lens blank during blocking, and
that
could make the distribution of that heat transference unifonn over the entire
area of the finished lens. Further, there is a need for a system and method of
ophthalmic lens manufacture that could eliminate problems associated with
heat transfer into the lens during blocking.
The standard block used for lens surfacing is generally smaller than the
size of the finished lens being fabricated. The portion of a lens that remains
unsupported can undergo flexure when submitted to the forces involved in the
generating, fining and polishing processes. This results in flaws or "waves"
in
the optics of the lens in the areas that underwent the flexure and is a common
source of spoilage or of substandard lenses. Consequently, there is a need for
a technique that would eliminate these optical flaws caused by flexion of the
lens blank during generating and fining and polishing of the lens.
For cosmetic effect, the edges of lenses are sometimes polished. In
prior art, when the edge of the lens has a mounting bevel, the bevel on the
edge of the lens is polished when the edge is polished. Polishing the mounting
bevel reduces the holding friction of the bevel that aids in holding the lens
in
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the frame, and that holding friction is also important in resisting rotation
of the
lens within the frame. For this reason, a lens that has a polished edge with a
polished bevel is more difficult to keep securely mounted and properly
oriented in its frame. There is therefore a need for a system and method of
ophthalmic lens manufacture that is operative to polish the edge of a lens
without polishing the mounting bevel on the edge of the lens.
Prior art systems for lens manufacture are inherently non-mobile, due
to the large amounts of laboratory space required to store an inventory of lap
tools and the many pieces of heavy laboratory equipment needed to generate
and surface and finish lenses. Thus, prior art systems cannot be easily
transported to locations such as factories to manufacture safety lenses on-
site
or military theaters to support the optical needs of military personnel.
Consequently, there is a need for an ophthalmic lens manufacturing system
that is portable.
DISCLOSURE OF INVENTION
It is an object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that
significantly reduces the costs of acquiring and operating a full service
surfacing and edging ophthalmic lens laboratory.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operable
with little knowledge of the optical arts by the operator.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that requires
little physical laboratory space.
It is a further object of the exemplary form of the present invention to
provide a system and method for oplithalmic lens manufacture that is operative
to perform both lens surfacing and lens edging.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that requires
only one lens blocking operation to perform both surfacing and edging.
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It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operative
to block a lens for both surfacing and edging that is optimized for both the
minimization of edge thickness and the compensation of optical center
"creep."
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that does not
require complicated rotating or tilting of the semi-finished lens blank when
blocking for surfacing.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operative
to perfonn both lens surfacing and lens edging in one machine operation.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that utilizes a
single tool with multiple cutting surfaces capable of both surface generation
and edging of lenses.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that does not
require a lap tool library.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that does not
require a lap tool library but is capable of using a lap tool library.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that does
edging and surfacing of lenses and lap tool surfacing on the same machine.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operative
to generate the precise lap tool for each lens manufactured.
It is a f-urther object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operative
to generate the precise mounting blocks for each lens manufactured.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operative
to generate the precise mounting blocks for each lens manufactured with
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scribe marks applied to the surface of the blocks to facilitate alignment for
blocking.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operative
to perform surfacing of both lenses of a pair of lenses at the same time.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operative
to perform edging of both lenses of a pair of lenses at the same time.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operative
to perform lap tool surfacing of two lap tools at the same time.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that minimizes
the transference of heat into the lens blank during blocking and that malces
the
distribution of that heat transference uniform over the entire area of the
finished lens.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that eliminates
the transference of heat into the lens blank during blocking
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufactlire that eliminates
fabrication flaws caused when unsupported portions of a lens blank flexes
under the forces incurred during the generating, fining, and polishing
processes.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthahnic lens manufacture that provides
for easy visual verification of proper blank size.
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is operative
to polish the edge of a lens without polishing the mounting bevel on the edge
of the lens
It is a further object of the exemplary form of the present invention to
provide a system and method for ophthalmic lens manufacture that is portable.
Further objects of the present invention will be made apparent in the
following Best Modes for Carrying Out Invention and the appended claims.
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The foregoing objects are accomplished in one exemplary embodiment
of the invention by a system and method for ophthalmic lens manufacture that
employs computer numerically controlled (CNC) machining techniques that
are operative to generate and edge semi-fmished lenses and to edge finished
uncut lenses.
An exemplary embodiment of the present invention relies on the fact
that the topographies of optical surfaces are very well defmed. If the spatial
coordinates (x,y,z) of any three points on a lens front surface are known
within
a coordinate system, then the spatial coordinates of all other points on the
front
surface can be derived within the coordinate system.
Further, if the center thickness and position of the optical center of a
lens are known, then the spatial coordinates of any point on the back surface
of
that same lens can be derived. Further still, if a sufficient number of planar
coordinates (x,y) representing the shape of the frame into which the lens will
be mounted are known relative to the position that the lens geometric center
will occupy within the frame and if the offset from the front surface of the
mounting groove or bevel is known, then the finished shape and contour of the
lens can be accurately derived including the position of the mounting bevel or
groove.
The exemplary embodiment of the present invention includes a CNC
machining platform that is operative to direct an appropriate tool to perform
both surfacing and edging of a lens blank. The system includes a computer
that is operative to retrieve frame coordinates of the lens receiving portion
of a
spectacle frame. In the exemplary embodiment the frame coordinates are
stored in a data store in operative connection with the computer. In one
exemplary embodiment of the present invention these frame coordinates are
acquired by tracing the inner circumference of the frame apertures with a
graphics tablet, or other scanning device in operative connection with the
computer.
The computer is also in operative connection with an input device and
a data store. A user of the system inputs with the input device prescription
specifications for the desired lens. The data store includes a plurality of
front
surface data values that correspond to the front surface topography of the
lens
blank. The computer calculates tool paths for machining the lens blank with
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the tool responsive to the frame coordinates, the front surface data values,
and
the prescription specifications.
These tool paths are calculated with respect to the reference frame of
the machining platform. The machining platform is operative to direct the tool
5 to move with respect to the lens blank according to the calculated machining
tool paths.
The system is further operative to generate an appropriate lap tool for
finishing the generated lens. The machining platform is operative to machine
the surface of the lap tool responsive to the front surface data values, the
10 prescription specifications, and, in cases where front surface radii are
shorter
than back surface radii, the data representing the size and shape of the
frame.
The orientation of the lap tool axes may be machined to match the orientation
of the axes in the final lens so there is no need to rotate the lens blank in
the
surface blocking process in order to align the lens axes with the lap tool
axes.
There is also no need for prism blocking or prism ring tilting of the blocked
lens blank for back surface generation.
The system is further operative to machine an appropriate block for
receiving the front surface of the lens responsive to the front surface data,
frame data, and prescription specifications, which include the interpupillary
distance (Pd). In the exemplary embodiment the bloclc is machined to include
scribe lines that are used by an operator to properly position and align the
lens
blanlc so that all points on the front surface of the lens blank can be
determined
relative the reference frame of the block and the machining platform.
Further objects of the present invention will be made apparent in the
following Best Modes for Carrying Out Invention and the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
Figures 1-3.show exemplary method steps of the present invention for
generating an ophthalmic lens from a lens blank.
Figure 4 is a schematic view representative of an exempla.iy system of
the present invention for generating an ophthalmic lens from a lens blank.
Figure 5 shows exemplary machining tools that are operative to
perform both surfacing and edging.
Figures 6 and 7 show exemplary machining tools machining the edge
of a lens blank.
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Figure 8 show an exemplary machining tool machining the back
surface of a lens blank.
Figure 9 shows an exemplary machining tool machining the finishing
surface of a lap tool.
Figure 10 shows further exemplary machining tools of the present
invention.
Figure 11 shows an exemplary block for the present exemplary
invention
Figure 12 shows a lens blank mounted to the exemplary block of the
present invention
Figure 13 shows the relative locations of exemplary marlcings for
blocking a lens blank.
Figure 14 shows a side cross-sectional view of an exemplary block.
Figure 15 shows a side cross-sectional view of an exemplary block that
has been machined to receive a lens blank with the lens blank positioned on
the block.
Figure 16 shows a top plan view of a lens blank positioned on the
machined bloclc.
Figure 17 shows a top plan view of the lens block with scribe lines in
the shape of a bifocal segment.
Figure 18 shows a side cross-sectional view of a lens blank mounted
on an exemplary block.
Figure 19 shows an alternative exemplary system for blocking a lens
blanlc.
Figure 20 shows a perspective view representative of an exemplary
machining platform of the present invention.
Figure 21 shows a perspective view representative of an exemplary
machining platform of the present invention with the mounting stage rotated to
an upward position.
Figure 22 shows a top plan view of an alternative exemplary
machining platform of the present invention.
Figure 23 shows a front plan view of the alternative exemplary
machining platform.
Figure 24 shows a side plan view of the alternative exemplary
machining platform.
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Figure 25 is a schematic view representative of a further alternative
exemplary system for simultaneously generating both the right and left lenses
for spectacles frames.
- Figure 26 shows the relative orientation of the x ball slide, y ball slides,
and z ball slides for the further alternative exemplary machining platform.
Figure 27 shows two exemplary orientations of a mounted lens blank
with respect to the relative feed axis of a tool for edging the lens blank.
BEST MODES FOR CARRYING OUT INVENTION
Referring now to the drawings and particularly to Figures 1, there is
shown therein exemplary method steps of the present invention for generating
an ophthalmic lens. Here the exemplary method comprises the step 10 of
acquiring or collecting and temporarily or permanently storing data about the
size and shape of the lens receiving aperture of a spectacle frame or other
mounting structure, or alternately about the finished lens circumference and
frame shape. In the exemplary embodiment frame data is collected in the form
of a plurality of planar points (x,y) relative to a planar coordinate system.
The exemplary method further comprises the step 12 of acquiring or
collecting and temporarily or permanently storing prescription specifications
for the desired ophthalmic lens being generated from the lens blank. For the
present exeinplary invention, the prescription specifications includes
information which describes the optical characteristics for the finished
ophthalmic lens and physical characteristics of the finished ophthalmic lens
including the material of the lens, the minimum thickness of the lens, and the
contour of the lens edge (bevel or groove). Such information can be acquired
by a user inputting the desired prescription specifications for the lens. In
an
alternative embodiment, the prescription information can be acquired from a
data store.
In Step 14, the exemplary method includes 'selecting and acquiring the
appropriate lens blank responsive to the prescription specification and frame
data. In one embodiment of the present invention, a human machine interface
(HMI) is operative to identify which lens blanks are appropriate from a data
store of different types of lens blanks. This described embodiment may also
include an inventory system of lens blanks that are available from inventory
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for the laboratory. The operator may then select from inventory at least one
of
the lens blanks that have been identified by the HMI as being in stock.
The exemplary method further comprises the step 16 of acquiring or
collecting and temporarily or permanently storing data about the optical
properties of the lens blank. The optical properties include the front surface
topography of a lens blank and the index of refraction of the material
comprising the lens blank. This data acquisition and storage can be done at
any point in time prior to the actual manufacturing process. This lens front
surface data is stored in a form and format that is operative to return a "z"
value for any "x,y" coordinate query. In.the exemplary embodiment when the
prescription data values indicate that the front surface on the lens blank is
spherical, these spatial coordinates can be acquired by calculation. When the
prescription data values indicate that the front surface of the lens blank is
aspherical, the front surface coordinates can be acquired from a data store of
front surface topography information responsive to the type of aspheric lens
being machined. It should be noted that front surface coordinates for
spherical
lens blanks may also be acquired from surface data stored previously acquired
or calculated and stored in a data store. In an alternative embodiment the
front
surface topography information can be acquired directly with a scanning
device. Within the described exemplary embodiment of the invention, the data
stores that hold topographical information are also operative to return
information about the locations of lens blank front surface artifacts such as
factory markings or bifocal segment lines that may be used for lens blank
alignment during bloclcing.
This described exemplary embodiment of the invention may further
include steps for generating a lap tool that is operative for fining and
polishing
the machined back surface of the lens. In step 18 the present exemplary
method includes calculating machining tool paths for machining the lap tool
with an appropriate machining tool of the CNC machining platform. The
machining tool paths for the lap tool are calculated responsive to the front
surface data, prescription specifications of the machined lens that will be
fined
and polished with the finished lap tool, the frame data in some cases, and the
thicknesses of the fining and polishing pads. In step 20 the method includes
mounting the lap tool blank on the machining platform and in step 22 the
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method includes machining the lap tool surfaces responsive to the calculated
machining tool paths to produce the finished lap tool.
The exemplary method further comprises the step 24 of calculating a
machining tool path for an appropriate tool for machining the top surfaces of
a
block for receiving the front surface of the selected lens blanlc. The
machining
tool paths are also calculated for machining alignment scribe lines or other
alignment features onto an upper surface of the block, which are used by the
operator in properly aligning the selected lens blank on the block. These tool
paths are calculated responsive ta the type of lens blank selected, the
positions
of artifacts on the lens surface that may be used for lens blank alignment
purposes, the fraine size and shape data, the front lens surface topography
data,
and the prescription specifications. In addition, the machining tool paths are
calculated for machining the top surfaces of the block so as to support the
portion of the front surface of the lens blank that will become the finished
lens. A block macllined in this manner will have 1) a top surface that mates
with the front surface of the lens blank when the blank is properly aligned
and
2) surface aligiunent scribe lines to facilitate lens blank alignment, and 3)
the
shape of the finished lens outline sculpted into the face of the block.
In step 26 the exemplary method further comprises the step 26 of
mounting a block on the CNC machining platform and the step 28 of
machining the top surface of the block with the appropriate tool responsive to
the calculated tool paths. The machined block is operative to receive the
front
surfaces of the selected lens blank such that when the lens blank is aligned
according to the machined scribe lines, all points on the front surface, of
the
lens blank are known with respect to the reference frame of the CNC
machining platform.
In step 30, the method includes identifying landmarks on the lens such
as a bifocal segment or temporary marks on the lens blank that are used to
align the lens blank with the scribe lines on the block. This step may also
include marking up the lens blanlc if necessary with the temporary alignment
and positioning marks responsive to instructions from the HMI.
In step 32 the exemplary method includes bloclcing the lens. This
exemplary blocking step includes affixing a thin transparent plastic fihn,
with
adhesive on both sides, onto the surface of the lens blank, aligning the
appropriate landmarks on the lens blank with the scribe lines on the block,
and
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securely bonding the lens blank to the block by applying appropriate pressure
to the back of the lens blank.
By generating custom blocks for each lens blank, the procedures for
blocking the lens are greatly simplified. These machined scribe lines
5 significantly reduce the need for a laboratory technician to measure and
place
complex alignment and positioning markings on the surface of the lens blank.
The scribe lines are positioned to correspond to readily identifiable
landmarks
on the lens block such as a bifocal segment line. For lenses that do not have
readily identifiable landmarks, the scribe lines may be positioned to
10 correspond to markings on the lens blank that are relatively easy to make
by an
operator. For example reference marks could be placed on the optical center
of the lens blank and two other points or a line could be placed along some
readily identifiable axis of the lens blank. The custom machined block for
such a lens would include scribe lines, which correspond to the optical center
15 and axis markings. ' Additionally, since the shape of the final lens is
sculpted
into the face of the block, visual verification of the proper blank size is
readily
made.
Once a lens blank has been blocked in this manner, all of the spatial
coordinate points (x,y,z) on the front surface of the lens blank can be
determined with adequate certainty relative to the coordinate system of the
machining platform when the blocked lens is mounted on the machining
platform.
The exemplary method further comprises the step 34 of calculating a
machining tool path for an appropriate tool for machining the back surface and
edge of the lens blank. The tool paths are calculated responsive to the frame
data, front lens surface data and other physical properties of the lens blanlc
like
the index of refraction, and prescription specifications. In step 36 the
method
includes mounting the blocked lens on the machining platform. In step 38 the
method includes machining the lens blank responsive to the calculated tool
paths with an appropriate, tool in operative connection with the CNC
machining platform. The back surface of the lens blank is machined to
produce a lens blank that is ready for the fining and subsequent polishing or
coating processes that may be required to finish the back surface of the lens
blanlc into an optical lens surface. The edge of the lens blank is machined
for
insertion into the spectacle frame for which the lens blank is being fashioned
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to fit. Step 38 may also include edge polishing and safety beveling the lens
and
edge grooving and engraving of the lens.
Once the lens blank has been machined, the exemplary method further,
if required, comprises the step 40 of fining and polishing the unfinished
surfaces of the lens with the lap tool machined in step 22 to produce an
optical
lens surface. In step 42 the exemplary method includes de-blocking, cleaning,
and inspecting the finished and edged lens. In step 44 the exemplary method
includes inserting the lens into the spectacle frame and inspecting the lens
and
frame combination.
It is to be understood that the method steps described above are
exemplary only. In this and in alternative embodiments other methods steps
and/or a differing order of these method steps may be performed to carry out
the exemplary embodiments of the present invention. In addition the
exemplary method may be performed with a system that is operative to
generate one or more optical lenses simultaneously
Figure 4 shows a schematic view representative of an exemplary
system that is operative to generate ophthalmic lenses according to the
previously described method. Here the system 100 comprises a computer 102
and a CNC machining platform 104 in operative connection with the
computer. The CNC machining platform 104 includes a mounting stage 110,
a mounting block 106 in releasable coiuiection with the mounting stage, and a
tool 112. An exemplary lens blank 108 is shown mounted to the bloclc 106.
The computer is further in operative connection with an input device 114, a
display device 116, and a data store 118. Examples of operative input devices
for this exemplary embodiment include a keyboard, mouse, touch screen,
trackball, voice recognition system, or any other device that is operative to
input signals into the computer. Examples of operative display devices for
this
exemplary embodiment include a CRT monitor, LCD display, or any other
output device that is operative to display information concerning the
operation
of the system 100. Exaiuples of operative data stores 118 for the exemplary
embodiment, include relational databases, flat files, CD's, DVD's, memory
arrays or any other device or structure that is operative to temporarily or
permanently store information. The data store 118 may also encompass a
combination of these different types of devices or structures. The data store
118 is operative to store frame data values that correspond to the lens
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receiving apertures for a plurality of spectacle frames. The data store 118 is
further operative to store physical properties for a plurality of lens blanks.
Such physical properties for example include data which describes the front
surface topographies of the lens blanks and the index of refraction of the
lens
blanks. The physical properties data may further include the blank diameter,
the blank edge thickness, the blank center thickness, the locations of front
surface artifacts, and any other useful attribute of the lens blank. Exemplary
tools 112 of the present invention encompass machining tools that are
operative to remove material from a mounting block or lens, including a
grinding wheel, a lathing tool, or any other tool that is operative for
cutting,
grinding, drilling, scratching, and polishing structures mounted to the
mounting stage.
In an alternative exemplary embodiment of the present invention, the
system 100 further comprises a graphics tablet 119, optical scanner or other
device that employs spatial digitizing technology, in operative connection
with
the computer. The graphic tablet or other similar digitizing device is used to
acquire spatial coordinates for the aperture receiving portion of a lens by
enabling an operator to manually trace the inner circumference of the frame
aperture on the graphics tablet. These frame aperture coordinates are then
stored in the data store 118.
The computer includes an appropriate software application and/or
firmware that is operative to control the movement of the tool 112 with
respect
to the mounting stage 110. The software application is further operative to
have the computer output with the display device 116 information conceniing
the operation of the system 100. In addition the software application is
further
operative to prompt a user of the system to input prescription information for
a
desired lens being generated with the system.
In one exemplary embodiment the mounting stage 110 responsive to
the computer 102 is operative to move the mounting block 106 and lens 108
relative to the feed axis of the tool 112. As shown in Figure 27, the relative
feed axis 714, 716 of a tool 710, 712 corresponds to the vector along which
the tool 710, 712 moves toward or away from the lens blank 108 and mounting
block 106. In this exemplary embodiment, the lens blank 108 is mounted to
the block 106 such that the axis of rotation 704 of the block is coincident
with
the front surface normal 702 at the geometric center 708 of the portion 706 of
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the lens blank that will remain after edging the lens blank to fit within the
lens
receiving portion of the spectacle frame. Also in this exemplary embodiment
a tool 710, 712 is positioned for edging the lens blank 108 such that relative
feed axis 714, 716 of the tool is generally parallel to the front surface
normal
702 at the geometric center 708 of the portion 706 of the lens blank that will
remain after edging.
For alternative exemplary embodiments.of the present invention and
for exemplary embodiments of the present invention in which the mounting
stage does not rotate the block, the lens blank may be mounted such that the
front surface normal at the geometric center of the portion of the lens blank
that remains after it is edged to fit the receiving portion of the spectacle
frame,
is orientated generally parallel to the feed axis of the tool used for edging
the
lens blank.
To aid an operator with mounting a lens blank in this described
exemplary orientation, the exemplary embodiment of the present invention is
operative to machine the block to include alignment features in an upper
surface of the block which provide a visual and/or structural guide for
aligning
the lens properly. When the lens blank 108 is blocked in these described
exemplary orientations, the relative location for specific points on the lens
blank can be determined by the computer system 102 relative the coordinate
system of the mounting stage, block and/or tool. Further, the computer 102 is
operative to direct one or more tools to machine both the back surface and the
edge of the lens blank 108 responsive to the stored frame data values, the
stored physical properties for the lens (including front surface topography
data), and the inputted prescription information. In addition by blocking the
lens blanks in the described orientations, the lens blank does not need to be
re-
blocked between surfacing and edging operations. Also the exemplary
orientation of the lens blank relative the tool used for edging is operative
to
minimize edge thickness for the finished lens.
Figure 5 illustrates several possible profiles for rotary cutting tools
capable of performing both surfacing and edging. These exemplary tools have
radiused end cutting surfaces 130 and side cutting flutes 132. Cutting tool
120
includes a V-bevel 134 with flat edges 136. Cutting tool 122 includes a V-
beve1138 with tapered edges 140, Cutting tool 124 includes a modified Hide-
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A Bevel 142. Cutting too1126 includes a V-bevel 144 with groover 146 for
nylon chord mounted lenses.
Although these exemplary machining tools include end cutting surfaces
(Radiused ends) 130 and side cutting surfaces (side flutes) 132 that come
together at the junction of the two cutting edges, it is to be understood that
the
present invention also encompasses machining tools with machining end
surfaces and side machining surfaces that are not so adjoined.
In the exemplary embodiment, the side flutes 132 are used for edging
lenses. Figure 6 depicts an exemplary tapered V-bevel rotary cutting tool 122
that is edging a V-beveled lens 150. Figure 7 shows an exemplary flat edge
grooving rotary cutting tool 126 edging a grooved lens 152. Also in the
exemplary embodiment, the radiused ends 130 are used to generate lens
surfaces and for cutting lap tool surfaces and for surfacing lens mounting
bloclcs. Figure 8 shows the radiused end 130 of a flat edged tool 120 malcing
a
surfacing pass 156 over a pre-edged lens 154. Figure 9 shows the radiused
end of the tool 120 making a machining pass 158 for surfacing a lap tool 160.
Using tools fashioned in this or similar manner makes possible the use of a
single CNC platform to perform both the surfacing and edging of lenses and
also to perform the surfacing of lap tool blanks and lens mounting blocks.
Figure 10 shows additional exemplary tools 502, 505; and 508 of the
present invention. Tool 502 includes an angled V-bevel edging surface 503
which tapers to a relatively narrower radiused end 504. Tool 505 includes a
single point tool tip 511 that is operative for surfacing. Tool 506 includes a
foreshortened tip radius 509 which eliminates portions of a full radius of the
too1510 which is unneeded for surfacing. In addition the shorter tip radius
509 reduces the "draft" or depth below the edge bead of the lens being milled.
As a result a smaller thinner lens block may be used. Tool 507 includes a
replaceable end 508 that may accommodate a plurality of different machining
surfaces. For example, the exemplary tool 507 includes a removable grooving
portion 513. In one exemplary embodiment the replaceable end 508 may
include a threaded portion that is received by the body of the too1507.
The exemplary tool 507 further includes a polishing surface portion
514 that is operative for edge polishing. The exemplary polishing surface
portion 514 further includes a recessed portion 512 that may be placed
adjacent the beveled surfaces of a lens. The recessed portion 512 prevents the
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beveled edge from being polished by the tool 507 so that the lens is less
likely
to slip when mounted within a spectacle frame.
Further exemplary tools may include engraving tips that are operative
for engraving markings on a lens mounting block such as alignment features,
5 lens identification values, the patients name, cosmetic embellishments,
and/or
prescription information. Other exemplary tools may include features for
machining a safety bevel. .
In exemplary embodiment of the present invention non-rotating tools
may also be used to perform machining operations. For example a pointed
10 edge of a non rotating tool 505 may be used to scratch the surface of the
lens
blanlc to form alignment features or other markings. Further, in exemplary
embodiments where the mounting stage is operative to rotate the lens, an
exemplary lathing tool may be used to machine the lens.
Figure 11 is representative of an exemplary reusable or a disposable
15 custom mounting block 540 of the present invention. As discussed previously
the exemplary lens mounting block 540 is operative to be machined to receive
a specific lens blank by the exemplary machining platform of the present
invention. The block 540 includes a support portion 560 that is adapted for
mounting on the mounting stage. The block 540 further includes a
20 machineable layer 562 that is shaped by the machining platform to receive
the
particular type of lens blank that will be mounted to the block 540. In the
exemplary embodiment the machining layer 562 includes a low melting point
wax compound, however, in alternative embodiments the machineable layer
562 may be comprised of a thermoplastic material, a metallic alloy or any
other reusable or disposable material that may be machined by the machining
platform.
The machining platform of the present invention removes blocking
material 542 to form an upper surface 544 in the block 540 which is operative
to support generally all of the front surface of the lens blank that will
remain
after the lens blank is surfaced and edged by the exemplary machining
platform. The tool paths for machining the lens block are calculated
responsive to the frame data, the optical properties of the lens including
front
surface topography information, and the inputted prescription data for the
ophthalmic lens being generated.
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Also as discussed previously the exemplary embodiment the machining
platform is further operative to place scribe lines 546 or other alignment
features into the upper surface 544 of the bloclc. The scribe lines 546 are
used
by the operator of the machine to properly align the lens blank with the
block.
Figure 12 shows a lens blank 550 mounted to the block 540. In this exemplary
embodiment an adhesive layer 548 is placed between the lens and lens blank
to securely bond the lens blank to the block. In the exemplary embodiment the
adhesive layer 548 is'comprised of a transparent or semi-transparent double-
sided pressure sensitive adhesive film which is placed between the block and
the lens blank by an operator. By pressing the lens blank 550 against the
adllesive layer 548 an adhesive bond is formed between the lens blank 550 to
the block 540.
In alternative exemplary embodiments various other methods may be
used to affix the lens to the block. In one alternative exemplary embodiment,
the top surface of the block is exposed to a heat source for a short period of
time, melting a very thin layer of the block surface. The lens blank is then
aligned and placed onto the molten surface. Re-hardening of the substrate
accomplishes the bond. In this method, the application of a protective plastic
film, onto the lens surface, significantly enhances the bonding strength. In
another alternative embodiment, semitransparent plastic film is applied to the
lens blank surface. The lens blank is then placed upon the scribed block in
proper alignment. This loose assembly is exposed to a light source of
appropriate wavelength composition and intensity so that photonic radiation
passes through the lens blank and is absorbed at the lens-block interface. The
photonic absorption causes local heating and melting of the surface of the
block. The melting, surface wetting, and re-hardening that occurs at the
interface accomplishes the bond. To prevent the upper surface from warping
when heat is applied, cold zones may be created over sufficient portions of
block to maintain the overall structural configuration of the block. Placing
an
insulating material or reflecting material between selected portions of the
bloclc and the heat and/or light source may create such cold zones.
In addition to the described bonding mechanisms many other methods
of bonding the lens to the block could be employed including the use of auto-
polymerizing agents or the use of heat activated polymerizing agents or
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photonically activated polymerizing agents or the use of epoxy resin
compounds.
For this described exemplary blocking systems, the lens blank is
aligned with the block by placing the point on the lens blank that will occupy
the geometric center of the frame at a fixed location within the coordinate
system of the block and exemplary machining platform. This is accomplished
by marking some point on the lens with a known positional relationship to the
point on the lens that will occupy the geometric center of the frame when
finished. It is also necessary to have some axial reference mark on the lens
to
represent the 0-180 axis orientation of the lens. Figure 13 shows a spherical
front surface bifocal lens blank 250 so marked. In this example, the lens
blank
250 is marked at the center 252 of the bifocal segment line 254. This point is
then positioned at the proper location relative to scribe lines 256 or other
alignment features of the block. The segment line 254 also acts as the axial
orientation marker. When the lens blank is aligned with the scribe markings on
the block, the lens blank may be adhesively affixed to the block by one of the
exemplary blocking methods discussed previously. When the lens blank is
aligned by this exemplary method, the geometric center of the lens will be
known relative the coordinate system of the block and machining platform.
In further alternative exemplary embodiment, the block surface is
machined so that only the outer rim of the block surface contacts and supports
the lens block. A thin cavity is left between the lens front surface and the
lens
blank top surface. Molten blocking medium is introduced into the cavity to
affect the bond between the blank and the block. Figures 14-18 shows this
exemplary alternative embodiment.
Figure 14 shows an exemplary alternative reusable custom block 300.
The block 300 includes a support portion 302 that is adapted for mounting on
the mounting stage. The block 300 also includes a machineable layer 304 that
is shaped by the machining platform to receive the particular type of lens
blank
that will be mounted to the block 300. In the exemplary embodiment the
machining layer 304 includes a low melting point wax compound, however, as
discussed previously alternative embodiments of the exemplary blocks may
include a machineable layer 304 comprised of a thermoplastic material, a
metallic alloy or any other reusable or disposable material that may be
machined by the machining platform.
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As shown in Figure 15, after the block 300 has been machined, a rim
306 with the shape of the finished lens with a hollow interior 308 is formed
in
the machineable layer 304. This rim 306 is generated with a three dimensional
contouring that mirrors the front surface topography 312 of a lens blank that
is
properly mounted on the block 300. With the block 300 machined in this
manner, the front surface of the lens touches substantially the entire rim 306
of
the top of the block. In the exemplary embodiment the width of the rim 306 is
about 4 mm. This approximate rim width affords sufficient support for the
lens during the blocking procedure and is wide enough so that the rim will not
become deformed by heat when fresh molten blocking medium is introduced
into the hollow interior 308 during the blocking procedure.
In this described exemplary embodiment the rim 306 is also machined
to be equal to or slightly smaller than the size of the finished lens. This
provides working support to the entire surface of the lens blank that
corresponds to the finished lens. Unlike a preexisting block, no damage will
result to the tool or the block when edging the lens blank because no portion
of
the block extends beyond the portion of the lens blank that encompasses the
finished lens.
In the exemplary embodiment a lens is positioned upon the block 300
so that the front surface normal at the geometric center of the finished lens
is
coincident with the "z" axis of the block coordinate system thereby placing
the
lens front surface generally parallel to the reference plane of the blocking
system and perpendicular to a relative feed axis of a machining tool. In the
exemplary embodiment, alignment scribe, lines 316 are machined onto the top
surface 318 of the block 300. As discussed previously, the scribe lines 316
are
used to properly align the lens blank. When the lens blank 310 is placed on
the block 300, an operator can properly position the lens blank by aligning
landmarks of the lens such as bifocal segments and/or other markings on the
lens blank with the scribe lines 316.
In the exemplary embodiment, the scribe lines 316 are machined so
that the space between the scribe lines on the block and the marlcings or
features on the lens front surface are narrow. This close approximation
between the features or markings on the lens and the matching scribe lines on
the block ensure that no significant parallax error is introduced when
aligning
the lens on the block by sighting directly above the lens.
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Figure 16 shows a top plan view of the lens blank 310 properly
positioned on the block 300. Here the lens blank 310 includes a bifocal
segment 320. The block 300 has been machined to include three scribe lines: a
base line 322, and two perpendicular lines 324 and 326. To properly align the
bifocal segment 320, the straight portion of the bifocal segment 320 is
aligned
with the base line 322. The left and right boundary positions of the bifocal
segment are aligned between the two perpendicular lines 324 and 326.
It is to be understood that this described layout of the scribe lines is
exemplary only. The present invention includes any pattern of scribe lines
that
are useful for aligning the lens blank properly. For example Figure 17 shows
an alternative pattern 328 for the scribe lines that are machined to
correspond
to the actual shape of a bifocal segment. Consequently a lens blank can be
properly aligned by positioning the bifocal segment to directly overlie the
scribe line pattern 328. In the exemplary embodiment the scribe lines are
generally about 2.5 mm wide. This dimension enables an operator to align fine
lens markings in the middle of the scribe lines to within .25 mni of the
desired
position.
When the lens is properly positioned, it is then held firmly in place,
either manually or mechanically, and molten wax or other adhesive material is
introduced into the space between the lens front surface and the hollowed out
surface 308 on the block through a bore 301. Figure 18 shows the lens blank
310 mounted to the block 300 after wax has been ejected into the llollow
interior. After the wax cools, the securely blocked lens blank is mounted on
the machining platform for edging and baclc surface generation.
Figure 19 is a schematic representation of an alternative exemplary
blocking method and blocking system of the present invention. Here the
blocking system 230 comprises a block 229 that includes a semicircular
mounting ring or rim 232 that is a known height above the origin plane 234 of
the blocking system. The radius of the semicircular mounting rim 232 is
known and the top plane of the ring is parallel to the reference plane 234 of
the
blocking system.
When blocking either spherical or aspherical front surface lens blanks,
the point 238 on the lens blank 236 that will occupy the geometric center of
the frame when the lens is finished, is positioned directly over the origin
240
of the blocking system 230. The point 238 on the lens 236 so positioned
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during blocking will end up in the geometric center of the lens after edging.
In
addition the front surface 242 is orientated so that it is generally parallel
to the
reference plane 234 of the blocking system. When the lens blank 236 is
mounted or blocked in this manner, the computer 102 is operative to calculate
5 or extrapolate from a data store the coordinate (x,y,z) of any point on the
lens
surface relative to the origin of the lens blocking system 230. That is, the z-
value can be determined for any chosen x,y location relative to the origin 240
of the blocking system.
The exemplary blocking system as shown in Figure 19 is operative to
10 bond a lens blank 242 securely to the block 229 by injecting a wax or other
adhesive material into a cavity 244 of the block 229 that is located adjacent
the
front surface of the blocked lens blank 242. When the wax hardens the
resulting bond between the lens blank 242 and the block 229 is sufficient to
hold the lens blank in place during the edging and surfacing operations.
15 In one exeinplary embodiment of the present invention the block may
be selected from a library of several dozen shapes and sizes of blocks that
most closely resembles the finished lens in size and shape while still being
smaller than the finished lens. Selecting a block for the lens blank with
roughly the same size and shape but slightly smaller than the final lens gives
20 support to the entire lens surface to minimize the bending and flexing of
the
lens during the surfacing and fining and polishing processes, thereby
eliminating optical errors. In addition such a bloclc will not come into
contact
with a tool while edging since it is slightly smaller than the finished lens.
When a lens is blocked in the previously described methods, all spatial
25 coordinate points (x,y,z) of the lens blank's front surface are known
relative to
the coordinate system of the machining platform. With knowledge of the
position of every point on the lens front surface relative to the coordinate
system of the machining platform, it is possible to calculate tool paths to
perform both the edging and surfacing of the lens with a properly configured
tool.
Figure 20 shows an exemplary machining platform 600 that is
operative to concurrently surface and edge two ophthalmic lenses. The
exemplary machining platform 600 is further operative to machine both
custom blocks for blocking lens blanks and both surface lap tools for
polishing
and fining ophthalmic lenses generated by the machining platform..
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The exemplary machining platform 600 includes an articulation shaft
602 and a mounting stage 604 in operative connection with the articulation
shaft 602. In the exemplary embodiment a computer system of the present
invention is operative to selectively rotate the articulation shaft 602 to
raise or
lower the position of the mounting stage 604. The exemplary mounting stage
604 includes an arbor 606 which is selectively rotatable responsive to the
computer processor. The arbor 606 is operative to receive two mounting
blocks 608, 610 positioned at opposed ends of the arbor.
The machining platform 600 further comprises at least one ball slide
carriage 612, at least two machining tools 614, 616 and two spindle motors
618, 620. The spindle motors are in operative connection with the at least one
ball slide carriage 612 and are positioned adjacent the opposed ends of the
arbor 606. Each too1614, 616 is in releasable connection with a spindle motor
618, 620. The spindle motors are operative to rotate the tools and are
independently operative responsive to the computer processor to move toward
and away from the arbor ends along the ball slide carriage 612. In the
exemplary embodiment the articulation shaft is turned by a planetary gear
motor 622 mounted on the end of the articulation shaft 602. The arbor 606 is
turned by the right angle gear motor 624 responsive to the computer processor.
In the exemplary embodiment of the machining platform 600, the
computer processor is operative to selectively move the machining tools 614,
616 relative the ends of the arbor 606 through a plurality of tool paths for
machining custom blocks, surfacing and edging lens blanks, and surfacing lap
tools. In addition to machining two lens simultaneously, two lap tools
simultaneously, or two mounting blocks simultaneously, the exemplary
embodiment of the machining platform may further be used to simultaneously
machine both a block and a lap tool for a particular lens. In addition the
exemplary machine may be used to simultaneously machine a lens and a
corresponding lap tool for the lens.
Figure 21 shows the exemplary machining platform 600 in a
configuration that enables an operator to more easily mount and remove
blocks, lap tools and lenses from the machine platform. Here the articulation
shaft arbor 606 responsive to the computer processor has rotated the mounting
stage 604 upwardly to move the arbor 606 away from the machining tools 614,
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616. In this exemplary orientation, the tools 614, 616 may also be more easily
removed.
An alternative exemplary embodiment of a machining platform for the
present invention is shown in Figures 22-24. Figure 22 shows a top plan view
of the machining platform 400 and Figure 23 shows a front view of the
machining platform 400. The machining platform 400 includes an arbor 402
mounted on a mounting stage 404. The arbor 402 is rotated by a servo-motor
412 in operative connection with the arbor.
The arbor 402 is operative to receive two blocked lens blanks 406 and
408 on opposed ends of the arbor 402. By selectively rotating the arbor with
the servo motor 412, the angular orientation of the lenses can be changed.
The machining platforrn also includes two spindles 414 and 416, with
tools 418 and 419 that are positioned adjacent to each of the lens blanks 406
and 408. In this described exemplary embodiment the axis of rotation of the
tools 418 and 419 is orientated parallel to the axis of rotation of the arbor
shaft. However, in other alternative embodiments other angular relationships
between the spindles and arbor shaft may be used depending on the shape of
the machining tool and the type of machining operation being performed.
Each of the spindles 414 and 416 is operative to move independently
of each other toward and away from the lens blanks 406 and 408 respectively.
This enables the machining platform to machine the back surfaces of the lens
blanks simultaneously according to different prescription specifications for
each lens being generated.
Figure 24 shows a side view of macliining platform 400. As shown in
Figure 24 the machining platform is operative to selectively move the arbor in
a plane perpendicular to the axis of rotation of the arbor shaft. In this
described exemplary embodiment this is accomplished by having the
mounting stage pivot at pivot point 432 of a pivot support 428. The amount of
pivot angular rotation is selectively controlled by a stage-moving device 420.
In this described exemplary embodiment the stage moving device 420
includes a ball slide 422 in operative connection with an end portion 426 of
the mounting stage. The ball slide 422 is selectively driven along a ball
screw
423 with a servo motor 424 that is operatively configured to selectively
rotate
the ball screw 423. The end portion 426 of the mounting stage moves up or
down responsive to the movement of the ball slide 422. As a result the
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angular position of the mounting stage 404 can be selectively adjusted to move
the arbor 402 and the lens blanks 406 and 408 relative to the machining tools.
In this described exemplary embodiment the pivot point 432 is located
between the stage moving device 420 and the arbor 402. However, in
alternative embodiments the arbor 402 may be located between the pivot point
432 and the stage moving device 420 or the stage moving device 420 may be
located between the pivot point 432 and the arbor 402.
The mounting stage may also include an encoder 430 at the pivot point
432 that is operative to measure the amount of angular rotation of the
mounting stage relative the pivot support 428. Alternatively, a linear encoder
could be used to monitor the linear position of a portion of the mounting
stage.
The feedback output of the encoder is used by the machining platform to
control the operation of the servo motor of the stage moving device. This
enables the system to accurately place the arbor in the proper position for
machining the lens blanks according to the calculated tool paths.
Figure 25 shows a schematic view of a further alternative exemplary
embodiment of a machining platform of the present invention. Here the
machining platform 170 includes two mounting stages 172 and 174 upon
which blocked semi-finished lenses are mounted for back surface generating
and edging, and upon which reusable lap tools are mounted for surfacing.
With two mounting stages, both right and left lenses 176 and 178 are surfaced
and edged at the same time. Similarly both the right and left mounting blocks
and right and left lap tools for lenses 176 and 178 may also be surfaced
simultaneously with machining platform 170.
In this described embodiment the machining platform 170 includes an
x-axis ball slide 190 and two y-axis ball slides 192 and 194. The x-axis ball
slide comprises a servo or stepper motor 184, a right handed ball screw 182, a
flexible coupling 186, and a left handed ball screw 18. The mounting stage
174 for right lenses and right lap tools is driven by the left handed ball
screw
180 and the mounting stage 172 for left lenses and left lap tools is driven by
the right handed ball screw 182. The two stages 172 and 174 travel along the
x-axis in synchronized opposing motion. The two ball screws are in operative
connection with a flexible connector which couples the motion of the right-
handed ball screw that is in direct connection with the drive motor with the
motion of the left-handed ball screw. This arrangement enables the single
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motor 184 to drive both mounting stages 172 and 174 in coordinated opposing
motion.
As shown in Figure 26, the single x-axis ball slide 190 is mounted on
the two parallel y-axis ball slides 192 and 194 so both stages always move
together in the y-axis. The y-axis ball slides 192 and 194 are also driven by
a
single servo or stepper motor (not shown). With this exemplary configuration,
when one stage performs a circular motion in the x-y plane moving clockwise,
the other stage performs precisely the same circular motion but moving
counterclockwise.
In this described embodiment, the machining platfornl includes two
high speed spindles 208 and 210 with corresponding tools 200 and 202.
Spindle 208 for machining a left lens or left lap tool is in operative
connection
with a left z-axis ball slide 204. Spindle 210 for machining a right lens or
right
lap tool is in operative connections with a right z-axis ball slide 206. The
two
stages 172 and 174 move under the z-axis spindles 208 and 210 for
simultaneous edging of both right and left lenses and for simultaneous
surfacing of both right and left lenses. The two z-axis ball slides 204 and
206
are positioned generally perpendicular to the two y-axis ball slides 192 and
194. The z-axis position of each spindle tool is driven by its own servo motor
or stepping motor 212 and 214. The motion of one tool can be and usually is
independent of the other tool.
For all the described embodiments, the tools should rotate in opposite
directions for the best results. Consequently, the tools affixed to each
spindle
require right or left isometric edge configurations appropriate for its
spindle
rotational direction and normal tool path direction. This allows both tools to
cut uphill at the same time with conventional milling. Without opposing
rotation, one spindle would be performing conventional milling while the
other would be performing so called "climb" cutting. This opposing
rotational direction is necessary in order to get similar finishes on the
edges of
the lenses. As discussed previously exemplary embodiments of the present
invention are operative to block lens blanks on the geometric center of the
finished lens such that the normal of the front surface at the geometric
center
of the finished lens is parallel to the relative feed axis of the edging tool.
Such
a blocking system is optimized for the edging of the lens blank. However, as
discussed previously, geometric center blocking may result in an optical
center
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of the lens which moves or "creeps" as the lens is made to decrease in
thickness during fining. In order to use this mode of blocking for surface
generation as well as edging, the exemplary machining platform of the present
invention is operative to compensate for this optical center "creep" when
5 calculating surface generation tool paths. In the exemplary embodiment tool
paths are calculated which produce a back surface with an optical center
position and/or thickness that are offset in order to compensate for the
amount
of expected optical center creep produced during fining. As a result, when the
lens is fined, the optical center will "creep" onto the correct position at
the
10 completion of fining.
When calculating for edging tool paths for spherical front surface
blanlcs, the "sagittal depth formula" is used and a constant is added to
represent
how far the eyewire bevel (or groove) on the lens should be from the front
surface of the lens (bevel offset), a z-value is calculated for each x,y
15 coordinate in the array of points. From this operation a three dimensional
array of points representing the shape of the lens and the position of the
eyewire bevel or groove is produced. This set of x,y,z points is then used to
calculate a tool path encompassing all these points in succession. Standard
CNC machining techniques are applied to compensate for the radius of the
20 tool being used and to generate tool paths for roughing passes before the
final
cut is performed.
Aspheric front surface lenses like Progressive Add Lenses (PAL's) or
Executive type multifocals are treated differently than spherical front
surface
lenses when calculating tool paths for surfacing and edging. Instead of
25 calculating the z-value for each x,y point as described above using the
sagittal
depth formula, a z-value for any x,y position on the lens is accurately
extrapolated from a database or data file containing topographical information
about the lens front surface. Lens front surface topographical coordinates can
be gathered to produce these databases or data files using either non-
30 contacting techniques or by physical probing techniques.
Aspheric front surface lens blanks are blocked just as spherical front
surface lens blanks are blocked. The point on the lens that will occupy the
geometric center of the frame receiving aperture is positioned so as to
correspond to the origin of the blocking system. Rather than using the
sagittal
depth formula, the x-y-z coordinates of the back surface are calculated
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31
responsive to the stored topographical coordinates that correspond to the
front
surface. It should be noted that spherical front surface lenses may also be
treated in this same fashion rather than using sagittal depth calculations.
Current systems for acquiring front surface scans for aspherical front
surface lens blanks are prohibitively expensive for most surfacing
laboratories.
However, the present exemplary method and system for machining ophthalmic
lenses does not require that each aspherical front surface lens blank be
scanned
prior to machining. Instead each lens type needs only be scanned once and the
data stored in a database or on physical media such as CD's or DVD's. The
scanned data can be made available to many optical laboratories through
distribution of CD's or DVD's or made available via download from a web site
on the Internet, for example. These data stores are operative to return a set
of
relative "z" values for any set of "x,y" coordinate queries for any specific
lens
type. These data stores may also hold other information about the lens blank
including the location of factory markings or other lens landmarks, the index
of refraction of the lens material, the edge and center thicknesses of the
blank,
and the lens blank diameter.
Acquiring the data in the optical laboratory through distribution is at
present less costly and less complicated than acquiring and employing surface
scanners at the optical laboratory site. However, this may change if surface
scanning devices become more cost effective and easier to use. If this should
occur, an alternative embodiment of the invention could then employ such a
surface scanner to acquire the front surface topographical data of a lens
blank.
The scanning device could then capture an array of x,y,z points describing the
front surface topography relative to the blocking mechanism and therefore
relative to the machining platform coordinate system.
The back surfaces of ophthalmic lenses are either spherical or toric.
Spherical surfaces can be thought of as special cases of toric surfaces where
the radii of the major and minor meridians are equal. Therefore, all lens back
surfaces can be considered to be toric. The radii and axial positions of the
major and minor meridians of the back surface toric surface can be calculated
from prescription data according to the formulae well known in the art. Once
these radii are known, it is possible to calculate the z-value of any point on
the
back surface relative to the back surface apex (e.g. the forward most point on
the lens back surface).
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Surfacing of the back surfaces of the lens is done using the radiused
end of the rotary tools. The tool paths for these radiused end tools are
defined
by the motion made by the center of curvature of the radiused ends of the
tool.
The tool path taken for surfacing a toric surface lies entirely within another
toric surface. The radii of the major and minor meridians of the tool path
torus
differ from the radii of the major and minor meridians of the toric surface
respectively by the length of the radius of curvature of the tool end. For a
concave toric surface the radius of the major meridian of the tool path torus
is
equal to the radius of the major meridian of the surface minus the length of
the
radius of the tool. Likewise, the radius of the minor meridian of the tool
path
torus is equal to the radius on the minor meridian of the surface minus the
length of the radius of the tool. The tool path needs to pass through enough
of
the points of the tool path torus to generate a surface smooth enough for
fining
in a standard system.
Calculation of the tool path torus for cutting the convex toric surfaces
of lap tools is similar to the concave surface calculations except that the
major
and minor meridian radii of the tool path torus are longer than the major and
minor radii of the toric surface respectively by the tool radius minus the
thickness of the fining and polishing pads used in order to be properly
compensated for the thickness of the fining and polishing pads.
In the exemplary embodiment of this invention, the lap tool surfaces
and the machineable layer of the blocks are made from the same low melting
point wax that is used to block the lenses. Other low melting point substances
could be adapted to serve the same purpose such as a thermoplastic material, a
metallic alloy or any other material that may be machined by the machining
platform. A substrate of this low melting point wax or other material is
applied fairly thickly to the base of each lap tool and block. Alternately,
disposable machinable materials of various composition could be employed as
the lap tool or the mounting bloclc substrate. Unless a lap tool library is
employed, each lens that is surfaced requires the preparation of its own lap
tool (if fining and polishing are required) and mounting block.
Thus the system and method for ophthalmic lens manufacture achieves
the above stated objectives, eliminates difficulties encountered in the use of
prior devices and systems, solves problems and attains the desirable results
described herein.
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In the foregoing description certain terms have been used for brevity,
clarity and understanding, however no unnecessary limitations are to be
implied therefrom because such terms are used for descriptive purposes and
are intended to be broadly construed. Moreover, the descriptions and
illustrations herein are by way of examples and the invention is not limited
to
the exact details shown and described.
In the following claims any feature described as a means for
performing a function shall be construed as encompassing any means known
to those skilled in the art to be capable of performing the recited function,
and
shall not be limited to the structures shown herein or mere equivalents
thereof.
Having described the features, discoveries and principles of the
invention, the manner in which it is constructed and operated, and the
advantages and useful results attained; the new and useful structures,
devices,
elements, arrangements, parts, combinations, systems, equipment, operations,
methods and relationships are set forth in the appended claims.
