Note: Descriptions are shown in the official language in which they were submitted.
40(~
QUICK CHANGE LENS TOOL
The present invention relates generally to the
generating of opthalmic lenses from lens blanks made of
polymeric material or of glass. In particular, the present
5 invention is an improvement in the conventional technique in
which a lens blank is mounted in an appropriate means on a
machine, and a rapidly rotating lens grinding tool is applied
to the surface of the lens blank in a precisely determined
manner in order to generate on the lens blank the desired
10 surface.
ln conventional lens grinding machines, the lens
grinding tool co~prises a metallic cup-shaped object whose
rim is encrusted with hard abrasive material such as diamond
grit, carbide, or the like. The grinding tool is rotated
15 very rapidly by an electric motor, and is attached to the
motor by means of a conical region of the tool which extends
from the convex surface of the tool along the axis of the
tool, in a manner such that the region is widest where it is
attached to the convex surface of the tool and progressively
tapers to a narrower width with increasing distance from that
convex surface.
It will be appreciated that the generation of the
desired surface on a lens blank requires extremely close
tolerances and close control of the position of the grinding
tool with respect to the lens blank. As the grinding tool is
used it becomes progressively worn despite the extreme
hardness of the grindi.ng medium itself. Thus, it becomes
necessary periodically to replace grinding tools to ensure
that a fresh, sharp surface is used in generating the desired
lens surface. Since the dimensions of different tools can
differ slightly, and the relative position of the grinding
surface and the lens blank must be very carefully maintained,
130~(3~
1 industry prac~ice to date has required extensive
recalibration of the tool, or of the shaft and associated
machinery to which the tool is attached, each time a new
grinding tool is attached to the machine. This extensive
5 recalibration introduces uncertainty into the operation, and
consumes time and effort which shoulcl preferably be emploYed
in generating additional lenses.
In one aspect, the present invention comprises
apparatus for generating a surface on a lens blank,
10 comprising
(a) shaft means having a first end, a second end,
and an axis of rotation extending between said ends, said
shaft means being rotatable about said axis of rotation,
wherein said shaft means has a contact surface at said first
15 end and has a bore extending through said shaft along said
axis of rotation;
(b) tool means for grinding a lens, said tool
means having an axis of rotation, and having a cylindrical
shank extending from a surface thereof coaxially with said
20 axis of rotation, said shank having a shoulder defining a
contact surface perpendicular to said axis of rotation, and
further comprising a threaded bore extending into said shank
along said axis of rotation; and
(c) means for releasably securing said lens
25 grin~ing tool means to said shaft means, with the axis of
rotation of said lens yrinding tool coaxial w.ith that of said
shaft means, said securing means including bolt means adapted
to fit in said axial bore in said shaft means and having a
threaded first end adapted to mate with said threaded bore in
30 the shank of said lens grinding tool means.
Another aspect of the present invention comprises a
machine for generating a lens surface included the afore-
--3--
1 mentioned apparatus in combination with means For holdin~ alens blank, means for moving said lens blank and said le~s
~rinding tool rne~ns with respect to each other for lens
generating engagement, and mo~or means for rota~ing said
5 shaft means.
The present invention further comprises the afore-
mentioned apparatus in combin~tion with additional means,
mountable on ~he shank of the lens grinding tool means, for
respective engagement with the contact surfaces on said shank
10 and said shaft.
The preferred aspect of the present invention
comprises any of the aforementioned apparatus in combination
with shim means for precisely varying the location of the
lens grinding tool means with respect to the shaft means.
A detailed description of the invention will now be
described with reference to the accompanying drawings, of
which Figure 1 is a perspective view of a lens grinding
machine with which the present invention may be practiced, and
Figure 2 is a perspective view of a lens grinding tool useful
in the present invention. Figure 3 is a cross-sectional view
of an embodiment of the present invention and Figure 4 is a
cross-sectional view of another embodiment of the present
invention.
The present invention is adaptable with lens
25 grinding machines having the conventional stations for
mounting a lens blank and for mounting a lens grinding tool
which is secured to a shaft that can be rotated at high speed
by a suitable motor. One suitable example is shown in Figure
1, although other embodiments will readily come to mind.
Referxing to Fiqure 1, numeral 1 denotes generally
the grinding tool station. It includes cup-shaped grinding
tool 2 secured to shaft 3 at the first end of shaft 3, in a
1 manner which will be described in greater detail below.
Shaft 3 extends through housing 4 and ls supported for
rotation within housing ~ by appropriate bearings. Pulley 5
secured near the second end of shaft 3 is connected via ~elt
5 6 to pulley 7 which is secured to the rotor of motor 8.
Shaft 3 can alternatively itsel~ be the rotor of motor 8.
Housing 4 and motor 8 do not themselves rotate about the axis
of rotation of shaft 3, but can be moved in other planes. In
particular, the position of the unlt comprising housing 4,
10 motor 8 and shaft 3, can be pivoted about a vertical axis
perpendicular to the axis of rotation of shaft 3, and can be
moved toward and away from lens mounting station 11 in a
direction parallel to the axis of rotation of shaft 3. Such
movement can b~ carried out manually, by electro-mechanical
15 control, or by computer control. Such controls are
well-known in the art.
Still referring to Figure 1, reference numeral 11
denotes generally the lens mounting station. A lens blank 12
of glass or polymeric material (such as polymerized
20 diethylene glycol bis (allyl carbon~te)) is mounted on lens
block 13 by any known means, such as with a waxy adhesive, so
as to be immobile during the grinding operation but removable
subsequently. Lens block 13 is in turn attached, removably
but in a fixed position, to mandrel 14, for instance by
25 mechanical coupling. In operation, lens grinding tool 2 is
rotated about its axis by means of shaft 3 and motor 8, and
the grinding surfaces of tool 2 trace a carefully controlled
path across the surface of lens blank 12 to produce a surface
having the desired geometric configuration. The ground lens
30 blank can then be finely polished, to provide a finished
ophthalmic surface, and the same operations can be carried
out on the othe~r side of the blank to provide a finished
4()~:)
--5--
1 lens. Apparatus for moving the tool 2 across lens blank 12
so as to ~3enerate a desired ophthalmic surface on lens blank
12 is well known to those acyu~inted in this art; one example
is shown in U.S. Patent No. 2,806,327.
Figure 2 depicts a lens qrinding tool 2 useful in
the present invention. It has a cup-shaped configuration
including a cylindrical rim portion 16 having an arcuate end
surface 17. Tool 2 also comprises spaced notches 18.
Cylindrical shank 32 extends axially from the convex side of
10 tool 2. Shank 32 includes shoulder 34 which defines a planar
contact surface perpendicular to the axis of rotation of tool
2. Grit plating is conveniently provided on the inside and
outside of surface 16, and on surface 17. Such a tool can
readily he manufactured by any of several suppliers to firms
15 that make and use lens generating machines.
The present invention is shown in more detail in
cross-sectional Figures 3 and 4. Turning first to Figure 3,
lens grinding station 2 includes shàft 3 which is mounted for
rotation in housing 4 by appropriate bearing means 20
including races 21 and ball bearings 22. End caps 23
provided with suitable bushings 24 seal the ends of housing
24 through which the ends of shaft 3 extend. Shaft 3
terminates with a contact surface 26 at its first end. Shaft
3 includes an axial bore 28 therethrough.
Cutting tool 2 is provided with integral
cylindrical shank 32 which extends coaxially with respect to
the axes of rotation of tool 2 and of shaft 3. Shan~ 32 also
has shoulder 34 which lies in a plane perpendicular to the
axis of rotation of tool 2. Shank 32 preferably is
30 dimensioned so that an end portion thereof extends into the
axial bore 28.
o~)o
1 solt 38 in bore 28 is threaded at its first end 38
to mate with a corresp~nding axial threaded hole 40 in shank
32. Bolt 36 als~ has stop means for engaginq the second end
wheTI the tool 2 and bolt 36 are threaded together tightly so
5 as to secure tool 2 with respect to shaft 3 (by "secure" is
meant that tool 2 and shaft 3 necessarily rotate together and
tool 2 and bolt 36 cannot move axially with respect to the
housing 4). Stop means can comprise a head 39 on bolt 36
wider than the axial bore 28.
The depth of hole 40, the len~th of bolt 36 and the
extent o~ threading on first end 38 of bolt 36 are determined
so that tool 2 can be secured onto bolt 36 by threading the
two together as tightly as possible. ~hile the parts of the
invention have been illustrated in Figure 3 with contact
surface 35 of shoulder 34 spaced apart from parallel contact
surface 26 on shaft 3, in operation surfaces 34 and 26 would
be tightly drawn toward each other so that rotation of shaft
3 causes tool 2 to rotate.
In this arrangement, the position of tool 2 (or,
20 more practically, of grinding surface 17) with respect to the
shaft 3 can be fixed precisely with the aid of a set of
shims, which are preferably flat and circular having an
outside diameter approximately equal to that of shoulder 34
and having a central hole whose diameter is slightly greater
25 than that of shank 32. An appropriate set of shims would
have a variety of thicknesses, as follows: 0.002 inch; 0.004
inch; 0.008 inch; 0.010 inch; 0.020 inchi 0.040 inch; 0.080
inch; two of 0.100 inch each; and 0.200 inch. Other
combinations of thicknesses are of course possible. l'hose
shims are capable of adjusting the axial position of grinding
surface 17 with respect to housing 4 and shaft 3 by up to
0.500 inch, plus or minus 0.001 inch.
13~7~
--7--
l To repl~ce a worn grinding tool with a fresh one,
while taking advantage of the ability to adjust precisely the
position of the fresh tool, it is necessary first to know the
desired distance, preferably to the nearest thousandth of an
5 inch, from the end of the shaft (or other fixed reference
point on the machine) to the grinding surface 17.
Conveniently, ~he fi~ed refe~ence point would be corner A on
shaft 3. This distance is a function of the desired distance
between the shaft and a lens blank mounted as shown generally
lO in Figure 1. It may not be necessary to measure this
distance more than once on a given machine. Ne~t, the axial
distance, also preferably to the nearest thousandth of an
inch, is measured from the grinding surface 17 on the fresh
grinding tool to a reference point on the tool, which should
15 be point B on shoulder 34. This distance can be e~pected to
vary by some thousandths of an inch from one tool to the
next. The difference between the two distances thus measured
is made up by a shim or an appropriate combination of shims
which are placed on the shank 32. The fresh tool 2, with
shims as necessary to make up the desired distance
difference, is then secured to shaft 3 by inserting shank 32
into the first end of shaft 3, and tightening bolt 36 into
hold 40 until tool 2 is secured to shaft 3.
An alternative, preferred embodiment of the
inventio~ is shown in cross-section in Figure 4. Shaft 3 is
mounted in housing ~ as descri~ed above, and supported by
bearings 22. The second end of shaft 3, not shown in Figure
4, is the same as Figure 3. The first end of shaft 3, which
can include a vertical face as described above also comprises
30 an angled portion 42. Tapered shim collar 44 adapted to fit
around shank 32 has first face 45 which is parrallel to the
face of shoulder 34, and second face 46 which forms an angle
~307~
--8--
1 with ~espect to the axis of rotation o~ tool 2. A double-
tapered ring ~ is adapted to fit relatively tightly onto
shank 32. Ring 4~ has one tapered portion 49 whose angle
with respect to t~e axis of rotation matches that o~ angled
5 portion 42 in shaft 3~ Ring 48 has s~cond tapered portion 50
whose angle to the axis matches that of angles portion 46 on
shim collar 44. Ring 48 preferably has a longitudinal slit
extending the entire length thereof, so that when tool 2 is
tightened onto shaft 3 as described herein the action of
10 collar 44 forcing ring 48 against angled surface 42 forces
ring 48 to grip shank 32 ever more tightly. Thus, the
combination of collar 44 and ring 48 comprise a means for
enhancing the immobilization of tool 2 onto shaft 3.
A fresh grinding tool 2 is secured to the shaft 3
15 in essentially the same manner as described above. The
distances from grinding surface 17 to points A and s,
respectively, are determined, and the difference is
calculated. The shims necessary to make up that dif~erence,
taking into account the axial dimentions of shim collar 44
20 and ring 48, are placed over shank 32, followed by collar 44
and ring 48, and the shank is tightened onto bolt 36 as
described above.
It will be recognized that another aspect of this
invention comprises a kit useful in adapting lens grinding
25 machines already having a shaft with an axial bore and a
vertical or inwardly tapered contact surface. ~he kit
comprises the lens grinding tool described hereinabove,
provided with a c~lindrical shank (which is preferably
capable of fitting within the first end of the shaft), and
30 having a perpendicular radial shoulder as described herein,
in combination with the shims described hexein, and
preferably also with the shim collar and a double-tapered
- 9 -
l ring whose tapered surac~s match with the tapered surface of
the shim collar, and the tapered contact surface of the
shaft, respectively.
The present invention provides the advantage of
5 easy and rapid replacement of grinding tool 2. Replacement
requires on]y loosening and subsequent retightening of bolt
3~, without the need to deal with a bolt head or nut located
inside the concave portion of tool 2~ Also, as described
above, tAe position of a given grinding tool can be adjusted
lO very quicklyO ~he axial distance from grinding surface 17 to
point B can be measured at any time prior to actual
attachment of the tool to shaft 3, so that when the time
comes to replace a worn tool it is not necessary to consume
extra down-time measuring and calibrating the new tool. One
15 simply slips the necessary shims onto the shank of the tool
and attaches the tool to the shaft.
3o
