Apparatus for edging ophthalmic lenses

An apparatus for simultaneously grinding a peripheral shape and edge surface upon a pair of ophthalmic lenses including an abrading wheel and first and second floating heads for rotatably supporting a pair of ophthalmic lenses on either side of the abrading wheel. The lenses are biased toward the wheel and are incrementally rotated about mutually parallel axes which lie parallel with a central longitudinal axis of the abrading wheel. An electronic control system is operably connected to each of the lenses and serves to control incremental rotation of each of the lenses as well as lateral engagement of the lenses with the central abrading wheel.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus for grinding an edge shape and 
peripheral surface configuration upon ophthalmic lenses. 
The art of preparing ophthalmic lenses from glass blanks entails two major 
processes. First, the circular lens blanks are surface ground with a 
prescriptive front and back curvature to provide a desired optic quality 
or characteristic and thus enhance the vision of an ultimate wearer. 
Secondly, the lenses are ground to a desired edge shape to fit a 
preselected frame. Additionally, the peripheral edge surface of the lens 
is typically beveled or finished to cooperate with a reciprocal bevel on 
an interior peripheral surface of a frame in order to hold the lenses 
within the frame. 
In the past at least one process of lens edging has been achieved by 
mounting a single lens upon a laterally fixed spindle or chucking 
mechanism and advancing an abrading wheel into lateral contact with the 
lens. The process is then repeated on an additional blank to produce a 
matching set or pair of lenses. 
In another previously known process a lens to be edge ground is 
horizontally mounted about a vertical axis. A pair of grinding wheels are 
vertically mounted for rotation on either side of the lens for selective 
advancement into grinding engagement with the central lens. Each of the 
grinding wheels is fashioned with an oppositely sloping peripheral 
surface. Accordingly, one wheel contacts a front peripheral portion of the 
lens and another wheel contacts a back peripheral portion of the lens. In 
combination the two grinding wheels form a beveled peripheral edge on the 
lens. Lateral control of the abrading wheels is achieved by a pair of 
conical cam followers which ride against a generally disc shaped cam. Once 
completed, the lens is removed and the process is repeated on a second 
lens blank to produce a pair. 
Although lens edging equipment of the foregoing and similar designs have 
received at least a degree of attention and acceptance in the art several 
significant difficulties exist. In this connection, edge grinding a pair 
of lenses on presently known machines is somewhat time consuming and 
requires a degree of operator attention and control. 
Additionally, these previously known edging devices are limited to grinding 
a single lens at one time and thus lack a certain degree of uniformity and 
symmetry desired of a pair of lenses. 
Further, the foregoing known machines do not provide a capability of edging 
a pair of lenses in a manner to sequentially remove glass and then fine 
grinding a desired edge configuration. 
Still further, the known prior art devices do not exhibit a capability for 
simultaneously grinding a pair of lenses and facilely and independently 
varying the lens size for a given lens shape. 
A significant advance was achieved in the art with the conception and 
reduction to practice of a dual headed edger such as disclosed in an 
application entitled METHOD AND APATUS FOR EDGING OPHTHALMIC LENSES by 
Messrs. Boyd Neisler and Joseph Stith commonly assigned with the subject 
application and filed on Jan. 24, 1978 as U.S. Ser. No. 871,871. 
Although a complete description of the above invention may be had by 
referring to said patent, in brief sum, this invention entails an abrading 
wheel and first and second floating heads for rotatably supporting a pair 
of ophthalmic lenses on either side of the abrading wheel. The lenses are 
biased toward the wheel and are incrementally rotated about mutually 
parallel axes which lie parallel with a central longitudinal axis of the 
abrading wheel. A cam control system is operably connected to the lenses 
and serves to control incremental rotation of each of the lenses as well 
as lateral engagement of the lenses with the central abrading wheel. The 
Neisler et al. method includes the steps of mounting a pair of ophthalmic 
lenses upon axes parallel with a central axis of an abrading wheel, 
biasing the lenses toward the abrading wheel and controlling rotation of 
the lenses to be edge ground with a cam control system to produce a 
desired lens peripheral shape and edge surface. 
Although introduction of the Neisler et al. system represented a singular 
advance in the art, room for further improvement remains. In this 
connection, the wide variety of glasses frames today requires a lens 
finisher to stock literally thousands of different mechanical cams (or 
patterns). It is estimated that an operator may use from time-to-time 
approximately 8,000 to 10,000 different patterns. This large variety of 
shapes requires a library file which is difficult and time consuming to 
maintain. Moreover, a complete library of accurately dimensioned patterns 
represents a significant initial capital investment. 
The difficulties suggested in the proceeding are not intended to be 
exhaustive, but rather are among many which may tend to reduce the 
effectiveness and user satisfaction of prior lens edging methods and 
apparatus. Other noteworthy problems may also exist; however, those 
presented above should be sufficient to demonstrate that ophthalmic lens 
edging machines and techniques appearing in the past will admit to 
worthwhile improvement. 
OBJECTS OF THE INVENTION 
It is therefore a general object of the invention to provide a novel 
apparatus for edging ophthalmic lenses which will obviate or minimize 
difficulties or the type previously described. 
It is a specific object of the invention to provide a novel apparatus for 
edging at least one ophthalmic lense which will significantly reduce the 
amount of time, expense and effort needed to maintain a pattern library. 
It is another object of the invention to provide a novel apparatus which 
will enable an operator to facilely call out a lens shape without 
locating, installing and setting up a lens pattern or cam. 
It is still another object of the invention to provide a novel apparatus 
for edging at least one ophthalmic lense wherein data storage facilities 
for lens shapes may be enhanced 
It is a further object of the invention to provide a novel apparatus for 
simultaneously edge grinding a pair of ophthalmic lenses wherein the 
finish shape or bevel may be accurately and reliably controlled with a 
minimum of operator attention and training. 
It is yet a further object of the invention to provide a novel apparatus 
for simultaneously edge grinding a pair of ophthalmic lenses which will 
exhibit the advantages of the previously described Neisler et al invention 
without requiring use of mechanical cams (or patterns) in the system.

DETAILED DESCRIPTION 
Referring now to the drawings and particularly to FIG. 1 thereof, there 
will be seen an axonometric representation of a dual head edge grinding 
unit 30 in accordance with a preferred embodiment of the invention. The 
dual grinding unit 30 includes a lens grinding chamber 32, a left floating 
head 34 and a right floating head 36. The floating heads are carried by a 
base member which in turn is supported upon a cabinet 38. The cabinet 38 
additionally serves to house a coolant tank and a system pump, not shown. 
A control panel 40 is mounted above the grinding chamber 32 and is fitted 
with an appropriate array of units to monitor and control an edge grinding 
operation. 
Before discussing in detail the structural features of the invention, it 
may be worthwhile to establish in functional terms the general operating 
concept of the dual edge grinding unit 30. In this regard, the reader's 
attention is invited in FIGS. 2 through 5, on sheets 1 and 2 of the 
drawings, where a grinding or abrading diamond wheel 42 is schematically 
disclosed upon a central longitudinal axis 44. On either side of the first 
axis 44 are second and third mutually parallel axes 46 and 48 
respectively, which in turn extend parallel with the grinding wheel axis 
44. A first 50 and second 52 ophthalmic lens to be edge ground is mounted 
transversely to the axes 46 and 48 respectively and in radial juxaposition 
to and upon opposite sides of the grinding wheel. 
The angular relationship of lenses 50 and 52 with respect to the abrading 
wheel 42 is controlled by drive units 54 and 56. The drive units are 
carried by the left and right floating heads 34 and 36. 
The drive units 54 and 56 are actuated to rotate the lenses 50 and 52 in 
response to the lateral position of contact pads 58 and 60 which are also 
carried by the floating heads 34 and 36. The contact pads extend adjacent 
contact paws 62 and 64 which are controlled by a microprocessor system in 
accordance with the invention. 
In brief operating sequence the lenses are hold in a rotationally 
stationary posture and biased against the abrading wheel until the 
contacts 58 and 60, which are mounted upon the floating heads, engage the 
processor positioned contact paws. At this point an electrical contact is 
made and the pattern and lenses are rotated to the next preselected 
angular position which is preferably less than one degree of angular 
movement. Contact of the excess glass portion of the lens to be ground 
away then pushes the floating heads away from the abrading wheel which in 
turn carries the contact pads 58 and 60 away from contact with paws 62 and 
64. When the pads 58 and 60 are withdrawn from the paws 62 and 64 
electrical contact is broken and rotation of the lenses ceases. As 
abrading progresses excess glass at the new angular position is ground 
away from the lenses 50 and 52 until the pads return to contact with the 
paws. Electrical contact will again be made and the lenses will be rotated 
to the next angular position and the sequence will be repeated. 
In the above regard, it will be seen, by reference to FIGS. 4 and 5 that 
the lenses have rotated approximately 270 degrees in the direction of 
arrows A and B. As the grinding operation progresses the lenses will be 
stepped about the second and third axes, a full 360 degrees of rotation. 
Returning to FIGS. 2 and 3, the abrading wheel 42 may consist of a 
plurality of individual wheels 66, 68 and 70 which comprise a coarse 
grinding wheel 66 to rapidly remove excess glass from the lens blank and 
selective finishing wheels 68 and 70 which simultaneously finalize the 
overall shape of the lenses and fashion a bevel edge around the periphery 
of the lenses so that the lenses may be retained within a glasses frame. 
Returning to the structural details of the dual edge grinding unit 30, FIG. 
6, note sheet 1, discloses an electric motor 72 which serves to operate a 
primary gear box 74 which in turn is connected to a microswitch gear box 
76, an encoder gear box 77, and left and right floating head gear boxes 78 
and 80 respectively. The encoder gear box 77 is directly coupled to a 
shaft encoder 81 which will be discussed more fully below. Another 
electric motor 82 is mounted within the base cabinet 38 and serves to 
drive a diamond wheel grinding spindle 84 by a flexible drive belt 86. Air 
limit valves 88 and 90 are positioned upon opposite sides of a cam control 
unit 92 which will be discussed more fully below. 
Referring now to FIG. 7, there will be seen a top view of the dual head 
edger 30. The left and right floating heads 34 and 36 are mounted for X--Y 
coordinate movement upon each side of the abrading wheel 42. 
The abrading wheel 42 is mounted upon a firxt axis 44 extending through a 
support quill 94. Ophthalmic lenses 50 and 52 to be edge ground and 
chucked and mounted transversely upon mutually parallel axes 46 and 48. 
Air cylinders 96 and 98 are mounted respectively upon rear stanchions 100 
and 102 which in turn are carried by the left and right floating heads 34 
and 36. Forward stanchions 104 and 106 are also carried by the floating 
heads and are positioned along axes 46 and 48 to carry the forward ends of 
lens shafts 108 and 110 respectively. The lenses 50 and 52 to be edge 
ground are held in place by felt pads 112 and 114 against chucks 116 and 
118 by pressurization of the air cylinders 96 and 98. 
A size control unit 124 is mounted upon the left floating head 34 and a 
similar size control unit 126 is mounted upon the right floating head 36. 
These size control units terminate at one end with plate holders 128 and 
130 designated to carry a plurality of contact plates 58 and 60 which will 
be discussed more fully below. 
Referring specifically to FIG. 8 there will be seen an expanded axonometric 
view of the floating heads 34 and 36 with respect to an underlying base 
132. As previously noted, the left floating head 34 includes a rear 
stanchion 100 and oppositely positioned forward stanchion 104 which serve 
to support a first lens to be edge ground. In a similar manner, the right 
hand floating head 36 includes a rear stanchion 102 and an oppositely 
positioned forward stanchion 106 which serve to support a second lens to 
be ground. 
The floating head 34 is mounted upon an X--Y coordinate way system carried 
by the base 132. The head is connected to parallel ways 134 and 136 for 
translation of the floating head 34 from the front to the rear in a "Y" 
direction. In a similar manner, ways 134 and 136 are mounted upon normally 
extending parallel ways 138 and 140 for translation of the floating head 
34 along an "X" axis directed laterally with respect to the base 132. 
The floating head 36 is also mounted upon an X--Y coordinate way system of 
ways including a first pair of parallel rods 142 and 144 which serve to 
permit movement of the floating head 36 in the "Y" direction with respect 
to the machine. The first pair of ways in turn are mounted upon a second 
set of ways 146 and 148 which are connected to the base 132 and permit the 
head 36 to be laterally translated in an "X" direction along the base as 
desired. 
FIG. 9, note sheet 4, discloses a plurality detailed bottom view of the 
base 132 and includes a system for driving the floating heads upon the 
above detailed ways in an X--Y rectilinear manner. Lateral or "X" movement 
of the left floating head 34 is achieved by controlled actuation of the 
first air motor 150 which is mounted at one end 152 upon the bottom 
surface of the base 132. A piston portion of the motor 150 extends 
outwardly from the free end thereof and is connected by a link 154, which 
extends through an elongated aperture 156, to the bottom surface of the 
floating head 34. 
In a similar manner, a second air motor 158 is mounted at one end 160 
directly to the base plate 132. A piston within the air motor 158 extends 
outwardly from the free end thereof and is connected by a link 162, which 
extends through an elongated aperture 164 in the base plate to the 
floating head 36. 
The air motors 150 and 158 can be actuated in either direction through air 
lines connected at the opposite ends thereof. Accordingly, lateral or "X" 
motion of the floating heads 34 and 36 with respect to the central axis 44 
of the cutting head may be controlled in either direction. Moreover, upon 
application of a predetermined amount of air pressure each of the floating 
heads may be biased by the motors toward the central axis 44 during a 
grinding operation. 
A third motor 166 is mounted within the base 132. One end of the motor 166 
is mounted against a downwardly extending wall of the base 132 as at 168. 
A piston rod within the motor 166 extends outwardly from the free end 
thereof and is affixed to a connecting column 170 which is mounted upon a 
lower slide block 172. 
The slide block 172 is free to move within a recess 174 cut into the base 
132. An upper slide block 176 is connected to the lower slide block 172 by 
a spacer column 178 which extends through an elongated aperture 180 in the 
base plate. Accordingly, the upper and lower slide blocks move in unison 
upon actuation of the motor 166. 
The upper slide block 176 is connected to one side to the floating head 34, 
note FIG. 10 on sheet 5, by a bevel positioning block 190. The bevel 
positioning block includes a cantilever arm 192 having downwardly 
extending roller 194 which projects into an arcuate raceway 196 of the 
block 180. Accordingly, translation of the upper slide block 176 will 
serve to concomitantly move the floating head 34 along the previously 
disclosed guide ways 134 and 136. In a similar manner another bevel 
position block 200 is connected to the right floating head 36, note FIG. 8 
on sheet 3, and includes a roller 202 which is operable to be received 
within an arcuate raceway 204 of the slide block 176. Translation of the 
slide block 176 will thus serve to move the floating head 36 along ways 
142 and 144. 
Referring again to FIG. 9, the base 132 overlays a further fluid motor 206. 
A piston rod 208 projects from a free end of the motor 206 and is coupled 
to a long bell crank arm 210. The short bell crank arm 212 is double ended 
and is provided at each end with a roller. The rollers are received within 
raceways on opposing faces of sliding contact paws 62 and 64. 
Turning now to FIG. 11, there will be seen a partial view of a grinding 
wheel in an expanded condition. More particularly, the base 132 serves to 
carry a quill 94 which receives a shaft 214 within bearings 216 in the 
direction of arrow 218. The shaft 214 is operable to vary a plurality of 
axially spaced grinding wheels 66, 68, and 70 as previously discussed. 
A second shaft 220 is journaled into the quill and carries a worm gear 224 
for rotation of the shaft, carrying a cam for cooperation with a 
microswitch as will be discussed in connection with FIGS. 20 and 21. 
In FIG. 12, note sheet 5, there will be seen a cam unit 92 connected to a 
shaft 226 which in turn is mounted upon the lower slide block 172, note 
FIG. 9. The actual connection of shaft 226 with the slide block 172, is 
not shown, but the coupling is a direct one with conventional fasteners. 
Accordingly, as the floating heads are traversed forward and backward in 
the "Y" direction the cam unit 92 will move forward and backward and 
upwardly extending peripheral band 228 of the cam 92 will come in contact 
with air pressure limit valves 230 and 232. The limit valves are connected 
to pressurized air conduits 234 and 236 respectively to limit forward and 
rearward actuation of the cylinder 166 and thus "Y" motion of the floating 
heads 34 and 36. 
Referring now to FIG. 13 there will be seen a rear view of a portion of the 
right floating head 36 and the rear stanchion 102 which serves to carry an 
air cylinder 98 for mounting a lens 52 to be ground. The right head gear 
box 80 is shown in an expanded posture and separated from a first chuck 
worm gear 240 of a gear train which ultimately connects to shaft 110, note 
FIG. 7 on sheet 1. Shaft 110 in turn is connected to the lens 52 to be 
edge ground. Rotation of the chuck worm gear 240 is initialed by a mating 
worm 242 which in turn is driven by a flexible connector 244 connected to 
gear box 74. A similar unit is provided on the left floating head 34 to 
rotate the lens 50. 
As previously discussed, a contact plate holder 130 is connected to a size 
control unit 126 mounted upon the floating head 36. Isometric views of 
this structure are depicted in FIGS. 15 and 16, note sheet 3. The contact 
plate holder 130 carries a contact plate 250 which in turn carries a 
plurality of contact pads 60. The contact plate 250 is pivoted to the 
holder 130 as at 252 and is biased outwardly from a holder 130 at the free 
end thereof by a spring 254. A dwell electrical contact bar 256 is carried 
by the holder 130 and is operable to make electrical contact with a 
corresponding contact plate 258 carried by the contact plate 250. 
Therefore when paw 64 contacts one of the pads 60 the contact plate will 
pivot, against the bias of spring 254, until electrical contact is 
established between bar 256 and silvered ball bearing contact 258. At this 
point in time the lenses will be rotated in a manner which will be 
discussed more fully below. 
Returning now to FIG. 14, note sheet 5, there will be seen a detailed plan 
view of the size control unit 126. As previously mentioned, this unit is 
mounted upon floating head 36 and serves to control the size of the lens 
to be ground for any given pattern shape. In this regard, the contact 
plate holder 130 is connected to a column 260 which in turn can be 
laterally adjusted with respect to the floating head 36. This adjustment 
is provided by rotating a shaft 262 which extends through a collar 264 
mounted upon the floating head. Rotation of the shaft is controlled 
through a set of bevel gears 266 upon rotation of a hand operated control 
knob 268. A zero position marker 270 is mounted upon thefloating head 36 
and serves to register with size control indicia carried by the shaft 260 
as at 272. Rotation of the hand control 268 will serve to rotate threaded 
shaft 262 and advance or retract the contact pads 60 in the directions of 
arrows 274 with respect to the paw 64. 
Turning now to FIGS. 17-19, note sheet 6, there will be seen a system for 
positioning paws 62 and 64 with respect to contact paws 58 and 60 as 
previously noted in connection with FIG. 9. 
More specifically, contact paw 62 is carried by a frame member 260 which is 
mounted for "X" reciprocation upon a pair of guide rails 262 and 264. In a 
similar manner contact paw 64 is carried by a frame member 261. The guide 
rails are connected at the left and right ends thereof to mounting blocks 
266 and 268 which in turn are mounted upon the base 132, note FIG. 19. 
A fluid motor 206 is pivotally mounted at one end to the base 132 or an 
internal wall surface 270 of the edger cabinet 38 as at 272. A piston rod 
208 extends from the other end of the motor 206 and is pivotally connected 
to the long arm 209 of a bell crank 210. A shaft 280 is journaled by 
sleeve bearings 282 through a wall portion of the base 132 and is fixedly 
connected at one end of the long arm 209 and at the other end to a mid 
portion of a double ended short arm 212 of the bell crank 210. 
The double ended short arm 212 of the bell crank 210 carries at one end a 
roller 284 and at the other end a similar roller 286. Rollers 284 and 286 
ride within raceways 288 and 300 of the left and right paw supports 260 
and 261 respectively. 
A rectilinear position potentiometer 303 is mounted at one end to support 
bracket 268 and the free end of a slide rod 305 is connected to the right 
support block 261. Accordingly the exact position of the paws 62 and 64 
may be monitored which will be discussed more fully below. 
In operation the motor serves to reciprocate piston rod 208 which in turn 
pivots the bell crank about its axis 304. The short bell crank arm 212 
then rotates about the axis 304 which pushes the left and right paw 
supports 260 and 261 away from the axis 304. A fully closed position of 
the paws is depicted in FIG. 17 and a fully open position is depicted in 
FIG. 18. 
The left 260 ane right 261 paw supports are biased against the rollers 284 
and 286 by left and right compression springs 310 and 312. Accordingly as 
piston rod 208 extends and the rollers are pivoted clockwise from a 
generally horizontal posture to a generally vertical position the left and 
right supports carrying paws 62 and 64 will slide together upon the 
support rails. 
Returning now to sheet 2 and FIGS. 20 and 21 there will be seen a 
microswitch unit 314 which functions to turn off the machine following a 
grinding operation. The microswitch unit 314 includes a conventional 
microswitch 316 with a cantilever cam follower 318 which rides upon a cam 
surface 320 mounted upon shaft 220 as previously mentioned in connection 
with FIG. 11. Rotation of the cam surface is controlled by a worm gear 224 
which in turn is rotated by a worm 322 connected to a drive cable 324 
(note FIG. 6). 
Regulation of the fluid motor 206 and thus in turn the position of contact 
paws 62 and 64 is controlled in the subject invention by an electronic 
computer system. A preferred embodiment of this system is depicted in FIG. 
22. 
More specifically a floppy disc memory 340 containing a bank of radial 
dimensional data for a wide variety of lens shapes is interfaced with a 
microprocessor 342 which feeds through an interface 344 to a plurality of 
digital memory chips U1-U8. 
The shaft encoder 81 reads angular position of the lenses 50 and 52. The 
encoder 81 continuously addresses the data stored within memory chips 
U1-U88. Data from the memory chips U1-U8 is input to a digital to analog 
converter 350. The analog output is fed to a summing amplifier 352 which 
drives a four-way servo valve 354. Pressurized fluid from lines 356 and 
358 is then applied to the motor 206 for positioning the paws 62 to 64 as 
previously discussed. Actual position of the piston rod 208, slide block 
261 and thus paw 64 is monitored by a rectilinear potentiometer 303 which 
is fed back into the summation amplifier 352 to complete a control loop. 
Having now described the major structural features of the subject dual head 
edger and computerized control system, an overall method of operation 
entails mounting a pair of lenses 50 and 52 to be edge ground upon shafts 
108 and 110 of the floating heads 34 and 36 with the base axes in a 
horizontal posture at a zero reference point. 
The encoder 81 is preferably selected to produce a natural binary output 
having a resolution of 2.sup.9 or 512 bytes or absolute positions. Each 
and every position will output a code relative to that position. That code 
will be the address in the memory chips U1-U8 for the data which will be 
the actual radial dimension of a lens, in thousandths of an inch 
increments, to be ground for that particular spindle shaft and lens 
angular position. 
At the zero reference point, with the lenses having their base axes in a 
horizontal position the encoder will address the zero location in memory 
U1-U8 which will input a digital radial lens dimension through buffer 360 
to the DAC 350. The analog output reading is amplified and the position 
servo actuates the motor 206 to drive contact paws 62 and 64 to a relative 
wide position such as approximately depicted in FIGS. 4 and 18. 
The lenses 50 and 52 start out in a circular shape (not shown). The 
peripheral edges of the lenses impinge upon the rough grinding wheel 66 
and because of the excess glass present the floating heads 34 and 36 are 
held in a posture away from the grinding wheel axis 44 in the "x 
direction" against the bias of air motors 150 and 158. Since the contact 
pads 58 and 60 are carried by the floating heads the paws will be 
initially spaced outwardly away from contact with paws 62 and 64 which, as 
previously mentioned, are positioned by the motor 206 to the final rough 
grind radial dimension at the zero angular position. Since the paws do not 
contact the pads, the spring 254 maintains the electrical contacts 256 and 
258 apart. As long as these contacts are separated an electronic (triac) 
switch is open and the circuit to the motor 82 which simultaneously 
rotates the lenses and encoder is broken. Accordingly, the lenses will 
dwell at the zero reference location against the rapidly rotating rough 
abrading wheel. 
As the lenses are ground away at the zero position the air cylinders 150 
and 158 continuously bias the floating heads together until the contact 
pads 58 and 60 are carried into engagement with the contact paws 62 and 
64. Upon engaging the contact paws the contact plates swing down until 
electrical contact is established with the contact bars. 
Current is then sent through electronic (triac) switches for the left and 
right floating heads to start the motor 82 and simultaneously rotate the 
left and right lenses 50 and 52 and the encoder shaft 220. This rotation 
will be brief but will continue until the excess glass on the lenses bears 
against the abrading wheel and pushes the floating heads and contact pads 
away from the contact paws. Once the pads disengage from the paws 
electrical contact will be broken and the drive motor 82 will stop. 
The encoder addresses the memory chips U1-U8 to the new angular position 
and a radial dimension will be imputed through the DAC 350 to the servo 
354 to reposition the contact paws 62 and 64. 
The lenses 50 and 52 will dwell at this new angular orientation until a 
sufficient amount of the lens is abraded away to enable the pads 58 and 60 
to reengage the paws 62 and 64 and the process will be repeated in a 
stepped sequence 360.degree. around the periphery of the lenses. 
At this point in time the cycle is repeated upon a substantially continuous 
basis wherein the contact pads 58 and 60 remain in continuous engagement 
with the paws 62 and 64. A timer unit, not shown, times a complete 
revolution of the encoder and lenses which in turn is synchronized with 
the microswitch 314. One cycle typically takes about seven seconds. Upon 
this complete revolution of the paws is continuous contact with the pads 
and simultaneous complete revolution of the microswitch cam 320 and air 
cylinders 150 and 158 will be extended to withdraw the lenses radially out 
of engagement with the coarse grinding wheel 66, note FIGS. 2 and 3 on 
sheet 1, and the lenses will be translated via cylinder 166 to a 
predetermined finishing wheel 68 and 70 designed to provide a finishing 
grind and bevel edge upon the lens. 
In this second axial position the process is again repeated in an angular 
incremental mode until the contact pads remain in engagement with the paws 
for two complete revolutions as timed by a timer, not shown. Upon two 
complete revolutions the timer is synchronized with the microswitch 316 to 
actuate the cylinders 150 and 158 to withdraw the lenses from contact with 
the abrading wheel and stop the machine. 
In a preferred embodiment, as previously noted, the encoder has a 
resolution of 512 bytes or absolute positions for 360 degrees. The hard 
memory chips U1-U8 are manufactured by Fairchild Industries, Inc. and are 
each one bit wide and can store 1024 bits of information. 
The lens shape library or radial dimensional data is originally stored in 
read only memory such as floppy disc 340. Although the encoder addresses 
512 absolute locations preferably only 128 bytes of dimensional 
information will be stored in ROM 340 for each lens shape. 
An address code from an operator is input to the microprocessor 342 by 
means of a decimal keyboard. This will cause a call routine to draw out of 
ROM 340 128 bytes of dimensional data for a selected lens shape. Upon 
issuing the call routine this data is placed into the upper 128 locations 
of the RAM U1-U8 (i.e. 896-1024). 
Immediately after the call routine, an interpolation routine is executed. 
This routine incrementally draws the first byte out of RAM and stores it 
into location H'00'. It then fetches the next byte, subtracts the first 
byte from it and divides the difference by four. Byte one plus the 
quotient is stored in H'01'. Byte one plus two times quotient is stored in 
H'02'. Byte one plus three times quotient is stored in H'03' and byte two 
is stored in H'04'. This interpolation routine goes through the entire 
process of calculation and relocating the data so that it finally occupies 
the lower 512 locations of the 1024.times.8 RAM U1-U8. 
As discussed previously the shaft encoder can then directly address any of 
the 512 dimensional data locations for use in generating the selected lens 
shape. 
Upon completion of the data transfer the floppy disc system 340 is left 
free end and will not normally be addressed again for approximately one 
minute. Therefore, it is entirely within reason that one floppy disc drive 
could be accessed by at least twelve to sixteen separate edging machines, 
allowing one library to be utilized most efficiently. 
In describing a method and apparatus for edge grinding opthalmic lenses in 
accordance with a preferred embodiment of the invention, those skilled in 
the art will recognize several advantages with singularly distinguish the 
invention from previously known methods and apparatus. 
A particular advantage of the invention is the provision of an electronic 
control system for an edger which enables ophthalmic lenses to be edge 
ground without requiring an extensive cam library. Additionally the 
subject invention eliminates maintenance, storage and retrieval time which 
is occasioned in utilizing present cam libraries. 
The subject invention further provides a shaft encoder utilizing a natural 
binary output of 512 bytes or absolute positions for each lens. This 
number of discrete dimensional addresses provides a high degree of 
accuracy in the resultant lens dimensions. 
Because a lens shape code may be input into the system by means of a 
decimal keyboard instead of setting up cam patterns an operator is easily 
trained to accurately and efficiently operate the subject equipment. In a 
similar vein change over time fron one lens shape to the next is 
significantly enhanced vis-a-vis cam pattern systems. 
Still further in a preferred embodiment time utilization of a ROM data 
library is enhanced by utilization of an interpolation subroutine which 
requires only 128 bytes of original dimension data. 
In describing the invention, reference has been made to a preferred 
embodiment. Those skilled in the art, however, and familiar with the 
disclosure of the subject invention, may recognize additions, deletions, 
modifications, substitutions and/or other changes which will fall within 
the purview of the subject invention.