CA1167301A - Motorized refraction apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved refractor for use in the subjective examination of human eyes. Each half of the refractor in-cludes a plurality of lens supporting disks, a hub assembly for rotatably supporting the disks, and a comb assembly to space the disks along the optical axis. One of the disks supports at least one set of 4 cross cylinder lenses. Each disk is coupled to a stepping motor for selective rotation.
Each motor is, in turn, supported by a bracket which permits rotation equivalent to a partial motor step to insure align-ment of the optical elements supported on the disks with the optical axis. The cylinder lenses supported on the disks are also rotated by a stepping motor. The Risley prisms of each half of the refractor are always positioned on the optical axis and rotated by stepping motors. Finally, the refractor includes electronics, including a microprocessor, to control the rotation of the motors as required to move the various optical components as necessary to emulate the ophthalmic prescription of the person whose eyes are being examined.

Description

1 1~73~1 CROSS ~EFERENCE TO R~L~TED ~PPLICATIONS

This application is related to the following cofiled application Serial No. 388,898 of P. Augusto for Motor Control System for Motorized Ophthalmic Instrument.

1 ~ 6~

DESCRIPTION OF THE PRIOR ART

There are a wide variety of re~racting instruments u~ed in the clinical practice of ophthalmology and optometry, including: conventional re~ractors, automated monocular objective refracting devices and automated monocular and binocular subjecti~e refrac~ing devices.
A conventional refractor consists of a pair of housings in which are positioned corrective optics for emulating the ophthalmic prescription required to correct the vision o~ the patien~ whose eyes are being examined.
Typlcally, each housing contains sets o~ spherical and cylindrical lenses mounted in rotatable disks. The two housings are suspended from a stand or wall bracket for posi-tioning in ~ront of the patient's eyes. Further, in front of each refractor housing a number o~ accessories are mounted, typically on arm~, so that they ma~l be swung into place be-fore ~he patient'~ eyes. Typically, the~e accessories include a varlable power prism known as a Rlsley prism, Maddox rods, and a cross cylinder for perorming the J~ckson cross cylinder test.
In determining a patient's distance prescription, the patient views a variety o~ alpha numeric characters of different sizes throu~h various combinations of the spherical and/or cylindrical lenses supported in the refractor housings until the correct prescription is emulated. The characters, which are typically positioned 6 meters away, may be on a chart or may be projected on a screen by an acu~ty projector.

For near vision testing the same procedure is repeated, expect that the alpha numeric characters viewed by the ~atlent ~ ~ 67301 a~e positioned on a brac7;et 20 to 65 centimeters in front of the refractor housing.
The cross cylinder is used to refine the power and axis position of the cylindrical component of the patient's prescription. The cross cylinder is a lens con-sisting of equal power plus and minus cylinders with their axes 90 degrees apart. It is mounted in a loupe for rotation about a flip axis which is midway between the plus and minus axes. When the cross cylinder is flipped, the plus and minus axes change places.
In the Jackson cross cylinder test, the patient views a target through the spherical and/or cylindrical lenses of the refractor used to emulate the patient's prescrip-tion. The cross cylinder is used by lining up its flip axis with the previously determined astigmatism correcting cylinder axis. When the cross cylinder is flipped, i each of its po~ition~ produces an equal blur o th~ target, the astigmatism correcting cylinder axis is proper. If one position is clearer than the other, the astigmatism correctlng cylinder axis is rotated toward the cross cylinder axls which makes vision better. The process is continued until an equal blurring is achlev~d ~hen the cross cylinder is flipped. Then, to check cylinder power, the cros3 cylinder is rotated 4S degrees, thereby bringing one of its axes parallel with the correcting cylinder axis. The cross cylinder i9 aga$n ~llpped, and equal impairment of vision indicates the correct cylinder power.
When the astigmatism correcting cylinder is negative and if vision is better with the minus axis of the cross cylinder parallel to the correcting cylinder axis, the cylinder power should be increased, and vice versa. These steps are repeated until equal impairment is observed in each position.

ll~73~1 To insure that the flip a~is of the cross cylinder is aligned with the previously determined astigmatism coxrect-ing cylinder axis and thereafter to maintain the cross cyli~der ~lip axis in coincidence wi~h the cylinder axis S through the usual numerous corrections ta the cylinder axis, the cross cylinder mechanism is mechanically coupled to the cylinder lenses. u.s. Patent No. 3,498,699 discloses a cross-cylinder loupe assembly mechanically coupled to correcting cylinder lenses in order to maintain proper orientation o~

the cross cylinder assembly. U.S. Patent No. 3,860,330 also describes a mechanism for synchronizing the axial orientation o~ a cross cylinder lens assembly with the cylinder axis of a correcting cylinder lens.

In the above described mechanisms, the cross cylinder i~ placed in the optical path of the refractor only afte~ the pre~criptio~s has been initially dete~min~d. U.S.
Patent No. 4,185,896 discloses a refractor cross cylinder mechaniQm in which a pair of cylinder lenses are always in the optical path o~ each re~ractor half. Each pair of cylinder len~es has a combined power Q~ zero when their cylinder axes are parallel and a ~mall cross cylinder power when one lens is rotated until its axis is perpendlcular to the cylinder axis of the other lens.

A Risley prism is a "rotary prism" used for find-ing the necessary prismatic correction of a patient' 5 eye.
It consists of two ophthalmic prisms o~ equal power, one in front o~ the other, and mounted so that the prisms can be rotated about the optical axis of the refractor half. In the initial position the base of one prism corresponds ~ith the edge of the other, so that the t~o prisms are equivalent 1 3 ~;73nl to a glass plate with plane parallel faces. The maximum effect i5 obtained when the bases of ~he prisms correspond.
As those skilled in the art will appreciate, in order to proceed with the subjective determination of a patient's reractive error, it is necessary to have a start~
ing point. Typically, this is accomplished by an objective examination of a patient's eyes, through various combinations of the spherical and/or cylindrical lenses supported in the refractor housings, with a retinoscope. This procedure, particularly for a previously unrefracted patient, can be quite time consuming. To reduce the time required to make an objective measurement of a patient's refractive power, a number of objective automatic monocular objective refraction devices, also known as automatic infrared optometers, have been developed. Several of these devices are described in and compared with other refracting instruments in Clincial Ophthalmolog~, Volume 1, Chapter 67, "Automated Clinical Refraction", D. L. Guyton, Thomas D. Duane (Editor), Harper ~ Row, 1980.
A similar in~trument developed by Zeiss, and the sub~ect of U.S. Patent No. 3,791,719, inciudes a "refracto-metex attachment" in combination with a motorized reractor.
It is stated thak the lens disks are rotated by servomotors and that micro switches are used to accurately limit the rotary movement of these motors. In operation, the refracto-meter attachment delivers signals, corresponding to the state of refraction of the eye, to the servomotors to move one or more of the lenses supported on the lens disks into the optical path to achieve a rough refraction. The apparatus also ir-cludes a control unit f or manually actuating the servomotors G -1 1~7~,01 after switching off the automatically operatin~ refractometer.
The manually operated control unit is used to move selected corrective lenses in front of the patient's eyes for sub-jective refraction.
Automated subjective refracting devices include American Optical Corporation's SR III and SR IV subjective refraction systems, Humphrey Instruments' Vision Analyæer, and ~. Schwind's Refraktron. The SR III and IV, based on the subjective optometer disclosed in U.S. Patent No. 3,664,531, uses axially moveable lenses to achieve continuously variable spherocylindric power over a wide range. In operation, the patient looks into the instrument and focuses or aligns a programmed series of speclal line targets. Like the auto-matic infrared optometers, these instruments are intended to lS proYid~ a preliminary reraction that is usually subsequently refined by the practitioner.
The Rumphxey Instruments' Vision AnaLyzer, disclosed in U.S. Patent 3,874,774, is designed to perform the entire binocular reraction, both distance and near, and thus re-place the conventional refractor. The instxument includes a projection system in which pairs of variable lenses are incsrporated. Light from the targets is collimated, passed through the variable-power lenses, de~lected by mirrors designed for interpupillary distance ad~ustment, and finally collected by a concave vlewing mirror located approximately 3 meters away rom the patlent. The concave mirror reimages the variable-power optics directly in front of the patient's eyes. Because the optics are reimaged in front of the patient's eyes, the target appears to be located on the mirror. While intended to replace the conventional refractor, conventional ~1673~1 refraction cannot be performed with this instrument. Thus, ~he starting point for the subjective refraction must be obtained from the patiant's prior prescription or an objective refractor. Also, because of the optical design, conventional subjective refraction techniques cannot be used.
The Schwind eye testing instrument includes a refractor having conventional batteries of spherical and cylindrical lenses, an optical system for projecting a series of vision testing slides and a semi-reflective mirror.
In operation the patient whose eyes are to be examined is seated in front o~ the semi-reflective mirror. A blackboard or other similar surface may be placed on the opposite side to provide a non-dis~racting background. A target image is pro~cted, Via a suitable optics, through various combinations of the spherical and/or cylindrical lenses of the refractor halves for ~iewing by the patient. Though not apparent to the patient, the optical e~ect is as though the lenses o~
the re~ractor were in ~ront o~ the pat~.en~'s eyes. As with the Vision Analyzer, conventional objective refraction cannot be ~erformed with the instrument, but must be made with other instrumentation.
In the chapter on ~utomated Clincial Refraction, D. L. Guyton describes a computer actuated refractor ac follows: "Marg et al (24) have taken a more direct approach by developing a computerized system to perform subjective refractions u~ing conventional refractor optics and conventional refracting techniques. The most recent model, Refractor III
(Fig. 67-16), is a specially designed binocular refractor containing a full range of trial lenses and accessory optical devices for ~ach eye. The spherical and cylindric lenses, 1 1 673~ 1 cross cylinders, prisms, Maddox rods, filters, and pinhola apertures are arranged on four disks within each half of the refractor. The disks are driven by stepping motors in response to commands from the computer. The computer in-S structs the patient by means of tape-recorded of voice-synthesized messages and presents a variety of slides for visual acuity determination and refraction at both distance and near, using random-access slide projectors. The patient responds with a simple push-button box held in his lap as the computer follows a series of flow charts to arrive at the refractive correction and corrected visual acuity."

~ 1 673~ 1 SU~RY OF THE INVENTION
... . _ ..__ A refraction instru~ent including a base on which is supported a hub having several cylindrical bearing sur-faces. The instrument also includes a plurality of lens S supporting disks, each of which has a central bearing aperture, which apertures cooperate with the bearing surfaces to radially align the disks relative to the longltudinal axis of the hub.
~o position the disks along the optical axis of the instrument, a plurality of peripherial disk supports are provided. With the use of such peripheral supports and the positioning of one ~uch support adjacent the optical axis, the re~uired optical element air spacing between the optical elements sup-ported on the disks i5 maintained for those optical elements positioned on the optical axis, e~en if one or more of the lS di~ks 13 warped. Thus, in contrast to prior art disks which are machined, the disk~ utiLized in the present lnvention can be stamped ~rom sheet metal.
The di~ks have gear teeth formed on the periphery thereo~ and are drivon by stepping motors. The cylinder and cross aylinder lenses, supported on,the disks in rotatable mounts having g~ar teeth ~ormed on the periphery thereof, are likewise driven by a stepping motor. Finally, the Ri~ley pri~ms are always positioned on the optlcal axis and ro~ated by stepping motors. Since ~he stepping motors are programmed to index only in integral steps, the optical axLs of the lenses supported on the disks may, within the rotational increment of a disk produced by one step of its associated motor, be offset from the optical axis. To facilitate optical _ /0 ~ 1 B730 1 alignment, the motors which rotate the disks are supported by brackets which are connected to the base by apparatus which permits limited rotation of both the bracket and motor about an axis substantially coincident with the axis o~ the motor dxive shaft. The motor which drives the cylinder and cross cylinder lenses and the Risley prism motors are similarly sup-ported to permit adjustment of the angular orientation of these opt$cal elements. Apparatus is also pro~ided to remove back-lash and reduce noise. In the case of the disks, each pinion i9 coupled to its respective motor shaft by elastomeric material and each motor is coupled to its support by means which permit movement of the pinion towards and away from the hub axis to "spring load" the pinion into engagement with its associated disk.

_ //

I 1 673~) 1 BRIEF DESCRIPTION OF THE DRAWINGS
., . .. ,, _ . _ FIEURE 1 is a top ~iew of the one of refractor halves of the presen-t invention;
FIGURE 2 is an enlarged partial section of the _enter support for the lens disks taken along Section A-A
of FIGURE l;
FIGURE 3 is a side view of one of the perpherial supports for the lens disks taken along along Section B-B
of FIGURE l;
FIGURE 4 is a perspective view of another of the peripherial supportq for the lens supporting disks:
PIGURE S is a partial sectional view o~ one of the lens disk drive motors and its associated support;
FIGU~E 6 is a top view of the ~efractor half of FIGURE 1 with the len~ disks removed;
FIGURE 7 is a par~ial sectional vlew of the Risley prism mechanism taken alony Sectlon C-C of ~IGU~E 6;
FIGURE 8 is a ~chema~ic view of the auxiliary ~isk showing how ~he C~OS8 cylinders are mounted th~xeo~i and FIGURE 9 i~ a block dla~ram o~ the control, drive and dl~play electronlcs of the present invention.

3 V l DESCRIPTION OF THE PREFEARED EMBODIMENT

FIGURE 1 111ustrates, in top plane view, the right refractor half 11 with its cover ~not shown) removed.
~efractor half 11 is one of two ha}ves of a re~ractor, such as ~chematically ~llustrat~d in assignee's Canadian application Serial No. 383,266. Refractor half 11 includes a back plate 13 on wh$ch is supported rotatable disk assembly 15 and motor drive assemblies 17, 19, 21, 23 and 25. Back plate 13 includes a cutout 27 through which various wiring harnesses (not shown) pas~. Back plate 13 also includes a lip 29 against which the cover seats.
As best ~llustrated in FIGURE 2, rotatable disk as~embly 15 lncludes five lens ~upporting disks: strong ~phere lens disk 31; strong cylinder lens disk 33; weak sphere lens disk 35; weak cylinder len~ disk 37; and auxiliary disk 39. ~ens mount 41, disk 31, is one of a sorles of mounts ~or ~up~orting the seri~s of strong spherical lonJe~ 42-52, illustrated in FIGURE 1. Typiclly, these l~nse~ range in 4 diopter steps from -28.00D to +16.00D.
Similarly, rotatable lens mount 53, is one of a series of mounts in strong cylinder lens disk 33 for ~upporting a seri-s of strong cylinder lenses ~not shown). Depending ~pon the re~raction technique to be used, the cylinder lenses will range, typically, ~n 2 diopter Jteps from either -2.00D
to -6.00D or from +2.00D to +6.00D. ~ens mount 55, in diCk 35, ls for supporting one of a ~eries of weak spherical len~es (not shown), ranging in 1/4 diopter steps from O.OOD
to +3.75D. Rotatable lens mount 57 is for supporting one of a series of weak cylindrical lenses (not shown). Again, depending upon the re~raction technique to be used, these lenses will range, typically, in 1~4 diopter steps from either -.25D to -1.75D or from ~.25D to ~1.75D. Einally, rotatable lens mount 59, in auxiliary disk 39, is f~r sup-porting the cross cylinder lenses of the present invention as well as a series of well known auxiliary elements (also not shown) such as a pinhole, occluder, filters and Maddox rods. At least one aperture in each of disks 33-39 remains open. In normal operation, a plano lens 60 is in the "open"
aperture of disk 31 to provide additional glass thickness to optimize the optical path length when no strong sphere lens is required.
For the various lenses and auxiliary elements supported on dlsks 31-39 to be accurately positionable on and along optical axis 61 o~ refractor half 11, it is nece~ary that disk~ 31-39 be accurately posltioned relative to rotatlonal axls 63. In the present invention, this is accomplished by radially s~pporting disks 31-39 with hub assembly 65, as illustrated in FIGURE 2. The proper spacing of dis~s 31-39 along axis 63 i9 a~fected by comb assemblies 71, 73 and 75, as shown in FIGURES 1, 3 and 4.
Hub as~embly 65 includes a disk shaft 77, a drive tube 79 and spoolq 81, 83, 85, 87, 89 and 91. Disk shaft 77 includes an elongated cylindrical bearing surface 93, threads 95, a lip 97, and a screw slot 99. Threads 95 are received in the threaded opening 101 provided in boss 103 which is, preferably, formed as an interval part of back plate 13. 30ss 103 also includes a surface 105 and a tapped opening 107, as illustrated in FIGURE 2. Drive tube 79 includes / _ 1 ~67~'301 a bore 109 in which sur~ace 9~ of shaft 77 is received.
~ip 97 of shaft 77 is received within cutout lll and shaft 77 i~ tightened until rear surface 113 of drive tube 79 engages surface 105 of boss 103, and then backed off to allow drive tube 79 to rotate about shaft 77. A soft plastic ball 117 received within tapped opening 107 is forced against threads 95 by a set screw ll9 to prev~3nt further rotation of disk sha~t 77.
Supported on surface 121 o~ drive ~ube 79 and cap~ured between llp 12~ and bowed lock rlng 125 recelved ln groove 127 are spools 81-91. Spool 81 includes an internal cylindrical bore 131, which snuggl~ ~its o~er sur~a~ lZl, cyli~drical bearing sur~ace 133 and sur~ace 135. Identically, spool 83 includes bore 139 and sur~ace~ 141 and 143; spool 85, bore 145 and surfaces 147 and 149; spool 87, bore 151 and s~r~aces 153 and 155; spool 89, bore 157 and surfaces 159 and 161; and spool 91~ bo~e 163 and sur~aces 165 and 167.
Spools 81-91 ~re keyed to driv~ tube 79 50 a5 ~o prevent rQlatlve rotatlon.
As i~ also evident ~rom inspection of FIGURE 2 each o~ disk9 31-39 includes, ~espec~ively, bearing aperturss 171, 173, L75, 177 and 179. To radiall~ al~gn disks 31-~9 relatlve to ax~s 63, disk 31 ls ~itted over surface 133;
disk 33, over surface 141; disk 35, over surface 147i disk 37~ over surface 153; and di~k 39, over ~urface 159.
~he position~ng 0~ dlsks 31, 33, 35, 37 and ~9 along axis 61 ls accomplished by comb assemblies 71, ~3 and 75~ illustrated in FI~UR~S 1, 3 and ~. With re~erence to FIGURE 3, comb as~Tbly 71 comprises an upr~ght post 181 secured to boss 183 of back plate 13 by, preferably, a ~olt (not shown). Post 181 is provided with five grooves 185, 18?, 189, 191 and 193 which are spaced relative to each ~ S--I 1 673~ 1 other So as to hold lens disks 31-39 at those lntervals long optical axis 61 which will result in the required optical element air spacing between the lenses supported on lens disks 31-39. Each of grooves 185-193 is dimensioned 80 ag to provide a bearing fit for its respective disk.
Since, in the preferred embodiment disks 31-~9 are stamped out of 0.050 inch thick sheet metal and are ordinarily flat within 0.005 inches~ post 181 is positioned adjacent optical axis 61 to insure that the required optical air spacing iS maintained along axis 61.
As illustrated in FIGU~E 4, comb assembly 73 in-cludes an L-shaped support bracket 201~ the short leg 203 of which is secured, via bolts (no~ shown), to boss 205 provided on bac~ plate 13. Secured to upstanding leg 207 is fork member 209 which includes a base portion 211, an offset portion 213, and a pair of fork members 215 and 217.
Base portion 211 is secured to leg 207 ~ia screws 221 and 223 which pass ~hrough ~nlarged holes (not shown) in less 207 and 211 and are received ln a Tinnerman type nut plate (also not shown). The enl~rged h~les permit b~th height and angular adjustment. Fork memb~r 215, lik~ post 181 oE
comb assembly 71, is provided with five equally ~paced grooves, of whi~h 225 and 227 are illustrated in FIGUR~
4. These grooves, also dimensioned s~ as to provide a bear-ing fit, in association with grooves 185-193 of comb assembly 71 and an identical set of grooves (not shown) provided on comb assembly 75, position disk-~ 31-39 along optical axis 61.
For~ member 217 includes no grooves.
In order to selectively rotate dis~s 31-39 about axis 63, to align one or more lenses and/or auxiliary elements with optical axis 61, as required to emulate a patient's ophthalmic prescription, disks 31-39 are coupled to, respectively, 1 1 ~730 1 motor drive assemblies 17-25. With reference to FIGURES 1 and 5, assembly 17 includes motor support bracket 241, stepping motor 243 and pinion 245. Bracket 241 includes a base 247 and two upstanding legs 249 and 251. sase 247 includes a pin 253 and tapped holes 2S5 and 257. Legs 249 and 251 include, xespectively, tapped holes 259 and 261. Motor 243, preferably North American Phillips K82701-P2 or equivalen., includes an integral frame bracket 263 and a drive shaft 265. Pinion 245 includes a hollow hub 267 and gear teeth 269 which mesh with teeth 271 formed on the periphery of disk 31. In the preferred embodiment, the qear ratio between pinion 245 and~disk 31 is chosen such that for every 18 steps of motor 243, disk 31 is rotated from a position where one lens is aligned with axis 61 to a position where an immediately adjacent lens or opening is ali~ned with axis 61.
As assemblied, bracket 241 i5 secured to back plate 13 via screws 273 and 275 which pass through washers (not shown) and enlarged openings 277 and 279 in bosses 281 and 283 formed in back plate 13. Pin 253 is rotatably received ln opening 285 of boss 287, which is also integral with back plate 13. Enlarged openings 277 and 279 permit the position of bracket 241 to be angularly adjusted about ~he axis o pin 253. Motor frame bracket 263 ls secured to bracket 241 via motor attachment screws 291 and 293 which pass through washer~ and enlarged openings therein (not shown). Pinion 245 is secured to drive shaft by means of an elastomeric material 295 bonded to both members.
To remove the bac~lash between teeth 269 and teeth 271 and to reduce noise, pinion 245 is "spring loaded" into engagement with disk 31. With motor attachment screws 291 and 293 loosened, motor frame bracket 2~3 is mo~ed toward axis 1 1 673~ ~

63 until all backlash is removed from the gear mesh. Motor frame bracket 263 is then moved an additional incremental distance toward axis 63 and screws 291 and 293 tightened to thereby clamp motor frame ~racket 263 to bracket 241.
S This second predetermined movement displaces elastic material 295 to, in effect, "spring load" gear teeth 269 of pinion 245 into engagement with gear teetA 271 on disk 31.
Since the stepping motors are programmed to index only in integral steps, the optical axes of the strong sphere lenses supported on lens disk 31 may, within the rotational increment of disk 31 produced by one step of motor 243, be offset from optical axis 61. To insure optical alignment, it is necessary to provide for limited rotation of motor frame bracket 263. This angular rotation is permitted by the coupling between motor support bracket 241 and back plata 13. With bracket attachment screws 273 and 275 loosened, mot~r 243 is energized to hold it ln one of its magnetic detent pocitions. Motor 243 and bracket 241 are then rotated about the axis of pin 253 until the re~uired optical align-ment i~ achieved. In the preferred embodiment this is determined with a test fixture (not shown) referenced to an open aperture in disk 31. Since the gear ratio between pinion 245 and dlsk 31 is chosen so that for every 18 steps of motor 243 disk 31 is rotated rom a position where one lens or opening is aligned with axis 61 to a position where the immediately adjacent lens or opening is aligned witA
axis 61, alignment of an open aperture in disk 31 with o~tical axis 61 insures alignment of the o~tical axes of all the strong sphere lenses with axis 61. Once aligned, bracket attachment screws 273 and 275 are tightened. The gear mesh ~ ~7301 between teeth 269 and 271 is effectively unchanged since the displacement between the axis of drive shaft 265 and the axis of pin 253 is minimal.
With the exception of the height of the bosses on which they are mounted, motor drive assemblies 19-25 axe identical to motor drive assembly 17. Further, the structure and method o~ removing backlash and noise, and achieving optical alignment for the lenses and optical elements supported on disks 33-39 is the same as that used for disk 31.
As those skilled in the art will appreciate, the axes o~ the cylinder lenses supported on disks 33 and 37 must be rotatable about axis 61 in order to orientate the cylinder axes so as to neutralize a patient's cylinder refractlve error. The axes of the cross cylinder lenses supported on auxiliary disk 39 must al50 be rotatable about axis 61 and thls rotation synchronized with the rotation o~
the cylinder lenses. The structure for producing these requlred rotations is illustrated in FIGURES 2 and 6. ~ith reference to disk 33, this structure includes a plurality of rotatable lens mounts, such as mount 53, bull gear 301, spool 83, drive tube 79, spool 91, cylinder axis drive gear 303, gear cluster 305, pinion 307 and stepping motor 309.
Lens mount 53 includes aperture 310 having a lens supporting seat (not shown), bearing surface 311, shoulder 313, gear teeth (not shown) and three evenly spaced tabs, one sf which is illustrated at 315. As assembled, surface 311 bears against the surface of cylindrical opening 317 of disk 33, with tab 315 hooking disk face 319 to thereby hold shoulder 313 against disk face 321. Bull gear 301 1 ~67301 includes teeth (not shown), which mesh with the gear teeth ~also not shown) on lens mount 53, and a cylindrical aperture 323 in which is received surface 143 of spool 83.
Aperture 323 includes a key slot (not shown) which cooperates with a key ~also not show~) provided on spool 83 to preven~
relative rotation therebetween. To prevent relative movement along axis 63, bull gear 301 is cemented to spool 83~
Stepping motor 309, preferably a North American Phillips K82401-P2 or equivalent, includes an integral frame bracket 331 which is secured via screws, such as illustrated at 333, to motor support bracket 334 which, in turn, is secured to bosses, sUch as illustrated at 335 provided on back plate 13. Pinion 307, rigidly coupled to motor shaft 336, in~ludes teeth 337 whlch me~h ~ith teeth 339 on gear ~41 o~ gqar cluster 305. ~reeth 343 of pinion 345 mesh with teeth 347 o~ axis drive gear 303. As axis drive gear 303 is both keyed and cemented to spool 91 and as spools 91 and 83 are both keyed to drive tube 79, rotation of stepping motor 309 rctates bull gear 301 which, in turn, rotates lens mount 53 and the cylinder lens (not ~hown) support~d th~ein.
The rotatable lens mounts, such aq illus~rated at 57 and 59 of F~GU~E 2, provlded on disks 37 and 39 are coupled to drive tube 79 via, respectivel~, bull gears 349 and 351, which are keyed and cemented to, respectively, spools 87 and 89. With this arrangement, rotation of motor 309 produces simultaneous rotation of lens mounts S3, 57 and 59.
As those ~killed in the art will appreciate, in addition to being simultaneously rotatable, the cylinder and cross cylinder lenses supported on disks 33, 37 and 39 must be prealigned and synchronized. Synchronization is accomplished by the gearing. All the lens mounts, as ~- ~ ~~ ~ r~r 1 16~301 .2 1~~

exemplified by mounts 53, 57 and 59, have the same number of gear teeth. Further, each of bull gears 301, 349 and 351 have the same number of gear teeth. With reference to disk 33, the number of teeth on lens mount 53 and bull gear 301 is chosen such that each complete rotation of bull gear 301, about axis 63 relative to disk 33, produces a multiple o~ 180 degree rotations of lens mount 53. In the preferred embodiment, bull gear 301 is provided with 195 teeth and lens mount 53 with 39 teeth. With this arrangement, every complete rotation of bull gear 301 produces 5 complete rotations of lens mount 53.
With reference to strong cylinder lens disk 33, the first step in the alignment procedure is to assemble and cement bull gear 301 to spool 83. With all the necessary rotatable lens mounts, such as mount 53, assembled thereto, disk 33 is assembled to spool 83. Next, the alignment mark (not shown) provided on, for instance, mount 53 is aligned with the alignment mark (also not shown) provided on bull gear 301. This latter mark is aligned with the key slot provided in bull gear 301 to deine an axis which is perpen-dicular to axis 63. This procedure i8 repeated for all the lens mounts on disk 33. With the aid of a fixture, which includes a source o~ collimated light, the re~uired cylinder lens is inserted in mount 53, such that the cylinder axis is perpendicular ~o axis 63, and then cemented in place.
This process is repeated for the remaining strong cylinder lense~ .
With the weak cylinder lenses assembled to disk 37 and the cross cylinder assembled to disk 39 utilizing the procedure as set forth above, spools 83, 87 and 89 and the structure supported thereon are, together with spools 81, 85 and 91 and the structure supported thereon, assembled on drive tube 79, as illustrated in FIGURE 2.

~ 2 2 ~
Since stepping motor 309 is programmed to index only in integral steps, the axes of the cyllnder lenses sup-ported on disks 33 and 37 may, within the rotation increment of the lens mounts produced by one step of motor 309, not be cor-rect. To insure proper angular orientation, it is necessary to provide for limited rotation of motor frame bracket 331, via motor suppoxt bracket 334 which attaches to back plate 13 and fu~ctions in the same manner as motor support bracket 241.
In contrast to prior art refractors in which each Risley prism mechanism is movable into and out of the optical axis, in the present invention Risley prisms 353 and 355 are always positioned along axis 61. Accordingly, when not in use they must be orientated relative to each other so that they are essentially equivalent to a glass plate wlth parallel ~aces. Prisms 353 and 355 and the supportlng and rotating mechanisms, illustrated in FIGURES
6 and 7, includes support assembly 357, motor assemblies 359 and 361 and gear trains 363 and 365.
Support assembly 357 includes prism mounts 367 and 369, base plate 371 and cover plate 373. As illustrated in FIGURES 6 and 7, prism mount 367 is essentially a hollow cylindrical member having a lip 37S against which prism 353 is seated. Prism mount 367 also includes faces 377 and 379 and a shoulder 381 on which are provided gear teeth (not shown). Similarly, prism mount 369 includes lip 383, aces 385 and 387 and shoulder 389 having gear teeth thereon ~also not shown). Prism mount 3~9 is received within open-ing 391 provided in base plate 371 with shoulder 389 seating against shoulder 393. Prism mount 367 is received within opening 395 of and held in place by cover plate 373.
Internal shoulders provided or. cover plate 373 (not shown) position and hold ace 379 ir. bearing engagement with face 387. Cover plate 373 is secured to base plate 371 by screws 397, 399 and 401. In turn, base plate 371 is secured to 1 1 ~73(~1 bosses, such as illustrated at 403 and 405J provided on back plate 13, via screws 407,.409 and 411.
~otor assembly 359 includes stepping motor 413, integral frame bracket 415, drive shaft 417 and an alignment plate 419, which includes stepped opening 421. In the pre-ferred embodiment, motor 413 is a North American Phillips R82401-P2 or equivalent. Bracket 415 is secured to plate 419 via clips ~not shown), while plate 419 is secured to base plate 371 via screws tnot shown) which pass through enlarged open-ings therein ~also not shown). In a like manner, motor assembly 361 includes stepping motor 423, integral frame bracket 4Z5, drive shaft 427 and alignment bracket 429 having stepped op~ning 431.
Gear train 363 includes pinion 433, integrally ~ormed gears 435 and 437 and gear 439. Pinion 433, secured to drive sha~t 417, is received within stepped opening 421 and ope~ing 441 provided in base plate 371, a~ illustrated ln FIGURE 7. Gears 435 and 437 are secured to pla~e 371 via an eccsntric shoulder bolt 443. Gear 433, which is mounted o~ eccentric shoulder bolt 445, engage~ the gear teeth (not shown) provided on shoulder 381 of prism mount 367. As is evident from inspection of FIGURE 6, the teeth on ~houlder 381 are e~posed via cutout 446 ln cover plate 373. Similarly, gear train 36S includes pinion 447, integrally formed gears 449 and 451 and gear 453. Pinion 447, secured to drive sh~ft 427, is received within opening 455 provided in base plate 371 and stepped opening 431. Gears 449 and 451 are secured to plate 371 via eccentric shoulder bolt 457; gear 453, via eccentric shoulder bolt 453. The teeth ~not shown) provided on shoulder 389 of prism mount 369 are exposed by cutout 461.
In t~.9 preferred embodiment, prism mount 367 is provided with 63 gear teeth, gear 439 with 20 teeth, gear 437 with 21 teeth, gear 435 with 50 teeth and pinion 433 with 20 _ 2 3 _ 1 ~ 6730 1 teeth. This results in a motor pinion to prism mount gear reduction of 7.5 to 1. Thus, a single step of stepping motor 413, which produces a pinion rotation of 7.5 degrees, results in a one degree rotation of prism mount 367. The gear reduction between pinion 447 and prism mount 369 is also 7.5 to 1 so that each step o~ motor 423 produces a one degree rotation of prism mount 369. In assembly, the back-lash between gear 439 and prism mount 367 is adjusted by rotation of eccentric shoulder bolt 445. Similarly, the backlash between gear 439 and 437 is adjusted by rotation of shoulder bolt 443. With motor ~rame bracket 415 clamped to ad~usting plate 419 via clips (not shown), the screws ~not shown) which hold adjusting plate 419 to base plate 371 are loosened and adjusting plate 419 is moved toward the lS axis o~ gear 435 until the desired gear backlash adjustment between gear 435 and pinion 433 is obtained. The screws clamping ad~usting plate 419 to base plate 371 are then tightened. The same process, utiLiz:Lng ad~ustment plate 429, is used t~ adjust the gear back:Lash between pinion 447 and gear 449.
To orient prisms 353 And 355 so that when not in use they effectively optically nsutralize each other, it is neces~ary to step motor~ 413 and 423 until the optical bases o prisms 353 and 355 are 180 degrees apart. Since motors 413 a~d 423 are programmed to index only in integral steps, it may not be possible to orient pri~ms 353 and 355 accurately enough to neutralize each other completely without rota-ting at least one of motor frame brackets 415 and 425 to simulate a partial mo~or step. This is accomplished by energizing motor 413 to utilize its magnetic detent effect, unclamping 11~7~1 the clips ~not shown) which clamp motor frame bracket 415 to adjusting plate 419 and then rotating bracket 415 until the desired optical relationship is obtained between prisms 353 and 355. As motor shaft 417 is piloted in recess 421 of the adjusting plate 419, rotation of bracket 415 will not change the motor shaft center line location which, in turn, keeps the gear system backlash from changing. Alternately, this orientation of 2risms 353 and 355 can be accomplished by rotation of motor frame bracket 425 relative to adjusting plate 429.
Once the prisms 353 and 355 have been relatively located so as to completely neutralize each other, it is necessary to set the prism base direction accurately. First, prisms 353 and 355 are each counter-rotated 90 degrees so as to bring ~heir bases into an alignment which will result in the maximum additive prism power. The two prisms are then rotated together, by use of stepping motors 413 and 423, until the base direction of the prism pair is, or example, in the "base out" orientation. This measurement can be made with any of several appropriate optical methods, such as projecting a laser beam through prisms 353 and 355 and observiny the direction of the deflaction. If the exact "~ase out" direction cannot be obtained by identlcal integral steps of the motors 413 and 423, it will be necessary, with the motors energized, to rotate both motor frame brackets 415 and 425 in unison, utilizing the same procedure used to initially orientate prisms 353 and 355. The motor frame brackets 415 and 425 are then reclamped.
With the foregoing arrangement, Risley prisms 353 and 355 are controlled so that the full prism power -ange, in _ 2 5 _ .50D steps, i~ the base out, base in, base up or base down, configuration can be effectively introduced in optical path 61.
In contrast to prior art where the Jackson cross cylinder test is performed by flipping the cross cylinder about the flip axis, in the present invention the tes~ is per~ormed by utilizing one of two sets of 4 cross cylinders mounted on auxiliary disk 39. Each cross cylinder is mounted in a rotatable len~ mount, such as illustrated at 59 in FIGURE 2. As sùch mounts have the same number of gear ~eeth as mounts 53 and 57, as bull gear 351 is identical to bull gears 301 and 349, and because bull gears 301, 349 and 351 are keyed to drive tube 79, rotation of the cross cylinders i~ sy~ch~onized with rotation o~ the cylinde~ lenses. Furthe~, lS the cr~s~ ~ylinde~ lenses are prealign~d, with the same technlquo utillzed or allgnlng the cyl~ nder lenses With rel~erence to FIGURE 8, auxiliary distc 39 inc~ude~ set 46~ ~ .SOD c~oss cylind,e~ and a set 463 o~
.25D cro~s cyLinder lenses. Set 461 includes C~08~ cylind~r lenge5 465, 461, 469 and 471. ~he or~entatlon o~ the axes o~
the cylinder lens or len~es used to neutralize a patient'~
cylinder re~ract~ve error i~ represented by axls 473. As those skilLed in the ar~ will appreciate, the illustrated or~en~ation of axi~ 473 relatiYe to lens 465 and optical axis 61 i5 arb~trary. As those ~killed in the art will also appreciate, the illustrated orientation of axis 473 relative to lenses 467-471 is ~or convenience of explanation only. Be-cause lenses 467-471 are supported in rotatable mounts, which rotate relative to disk 39 as disk 39 is rotated about axis 63, the correct o~ientation is determined by the gear ratio 1 1~7301 between these rotatable lens mounts and bull gear 351. For refining axis, 47S represents the direction of the positive cylind_r axis of lens 465. It is orientated at 135 degrees relative to axis 473. Similarly, 477 represents the direction of the negative cylinder axis, orientated at 45 degrees relative to axis 473. With regard to lens 467, 479 represents the direction of the positive cylinder axis; 481, the direction cf the negative cylinder axis. Relative to axis 473, axis 479 is orientated at 45 degrees; axis 481, at 135 degrees.
For refining power, lenses 4Z9 and 471 are utilized. In this case 483, which represents the direction of the positive cylinder axis of lens 469, is perpendicular to axis 473;
485, the negative cylinder axis, is parallel to axis 473. For lens 471 the poRitive cylinder axis is 487; the negative, 489.
In operation, to refine cylinder axis, auxiliary disk 39 i9 rotated until lens 465 is aligned with optical axis 61. As they are prealigned and synchronized with the cylinder lenses, axis 475 is orientated at 135 degrees and axis 477 at 45 ~egrees relative to the axis of the cylinder lens or lenses which neutralize the patient's cylinder refractive error. To refine axis, stepping motor 491 of motor drivs assembly 25 is energized to rapidly rotate disk 39, via pi~ion 493, ~rom the position where lens 465 is aligned with axis 61 to the posltion where lens 467 is in alignment with axis 61. If each of lenses 465 and 467 produces an equal blur of the target being viewed, the orientation of the axis of the cylinder lens or lenses is proper. If one position is clearer than the other, the axis of the correcting cylinder lens or lenses is rotated toward, when the cylinder lens or lenses are positive, the one of cross c~linder axes 475 and 4~9 which produced better ~islon. Disk 39 is then again rotated to align the other of lenses 465 and 467 with axis 61 to a~ai~ detenmine i- both lenses 465 and 467 produc_ an equal blur. If not, the process is repeated until equal blur-ring is achieved.

To refine cylinder power, lenses 469 and 471 are utilized. As is evident from inspection o~ FIGU~E 8, negative cyllnaer axis 485 is parallel to the orlentatlon of the axis o~ the cylinaer lens or lenses which neutralize the patient~s re~ractive error, while ne~ative cylinder axis 489 is perpen-dicular thereto. I~ each o~ lenses 469 and 471 produc~s equal blurr~ng, the power is correct. When the correcting cylinder is negative and if vislon is ~etter with lens 469, when the minus axis 485 is parallel to the correcting cylinder axis, the powor should be increased and vice versa. This procedure ls repeated until equal impairmen~ of vision is obtained with both lenses 469 and 471.
Lens 3et 463 includes lenses 495, 497, 499 and 501. Expect ~or the ~act that they are all o~ . 25D power t they are ldentlcal in function and orientation with lenses 465-47l. Thus, lenses 495 and 497 have their axes orientated for refining cylinder axe~, and lens 499 and 501 have their axes orientated ~or refining power.
~ach of disks 3l-39 is dri~en by, respectively, the stepping motors of motor drive assemblies 17-25. Similarly, stepplng motor 309 drives the rotatable lens mounts exemplified by mounts 53, 57 and 59 illustrated in FIGURE 2, and stepping motors 413 and 423 rotate Risley prisms 353 and 355. In total, each refractor half includes 8 stepping motors, each of which must be dri~en by electrical pulses to incrementiall~

~l67~nl rotate disks 31-39, the rotatable lens mou~ts and Risley prisms 3s3 and 35s, as necessary to emulate the ophthalmic prescription required to correct the vision of the patient whose eyes are being examined. With re~erence o FIGURE 3, these pulses are supplied by motor driver board 511 which, in turn, is controlled by computer board 513. The elactronics also includes an encoder system 515, a display board 517, a key board 519, a prlnter control board 521, a printer driver board 523 and a thermal printer 525.
The heart o~ the electronics is computer board S13 which includes mirocprocessor chip 527, read only memory chip8 529 and lnterrupt decoder logic system 531. ~n the preferred embodiment, microprocessor 527 is an Intel 8048 or 8748 or e~uivalent, and memory chips 529 are Intel 8355 or 15 8755 ~ ~quivalent. As is eviden~ from inspection o~ FI~U~
9, microprOcescor 527 ~ends inormati~n to ~ED dicplay 53~ o d~splay board 517, via printer control board S21. If the re~ractor i~ in the reset mode, wherein all o~ disks 31-39, lenses and Riqley prisms 353 and 355 are in their re~et or zexo position, display 533 will indicate this. Further, as disks 31-39 and the other optical components are rotated, microprocessor 527 sends in~ormation to display 533 to tell the instrument operator which optical elementq ar~ positioned along optlcal axis 61 and, where appropriate, their orientation. Microprocessor 521 also periodically checks to see if new instructions are coming from key board 519.
~ey hoard 519 includes a se~ of OD refractor keys 535 and a set of OS refractor keys 537. In the preferred embodiment, the keys are dome or mem~rane switches. Set 535 includes plus and minus directional keys for each of the ~ 1673~1 - motors which drive disks 31-37, motor 309, and motors 413 and 423. In operation, when one of these keys is depressed, the associated motor is energized for the number of steps required to move the associated optical element from one operational position to the ad;acent operational position.
In ~ddition, the directional keys for motors 309, 413 and 423 are coupled to a high speed interlock key which, when depressed, provides for high speea rotation. Rotation of strong sphere disk 31 ~s normally coupled to the rotation of weak sphere disk 35. When the interlock key is depressed, the sphere directional keys move disk 31 while disk 35 remains stationary.
A duction key, for simultaneous rotation of the Risley prisms of both refractor halves, is also included. For the auxiliary elements supported on disk 39 individual operation keys are provided. Set 537 includes a ~ubstantially identical set of koy~. Key board 519 al~o includes a reset key and keys which control printer control board 521. ~n the event that micro-~roces~or 527 i8 used not only to control both refractor halves but al~o a compact re~ract$on instrument, such 25 disclosed ln assignee's copending appl~cation Serial No.383,266, key board 519 will also include a set of target and mode keys 539 and hddit$onal reset keys.
~n response to a key belng depressed, a circuit in key board 519 i8 closed and an electrical signal is sent to key ~oard decoder 541 whlch, via a demultiplexer that senses which circuit wa3 closed ~n ~ey board Sl9, sends a code to microprocessor 527. There i~ a dif~erent code ~or each key and for each code there is an instruction in memory 529, which instruction results in signals being sent to motor driver board 511 to rotate one or more motors a predetermined number B

~ 1 &730 1 of steps in a particular direction. ~icroprocessor 527 also outputs new data to display 533 to indicate that the instruction has been carried out.
In order to hold disks 31-39, rotatable lens mounts S such as illustrated at 53, and Risley prisms 353 and 355 in any given required position, all the motors are constantly energized at, approximately, 1/4 power in order to maintain the magnetic detent and, thus, keep the motors from rotating.
While the motors could be en~rgized at full power, the lower power is preferred in order to reduce the size of the power supply required and to reduce heat disipation. With this arrangement, motor driver board Sll incluaes, for each motor, a power up logic and a motor driver. With reference to FIGURE
9, theso are collectively designated 543 and 545.
In the preferred embodiment, the signals from microprocessor 527 to rotate, ~or instance, motor 243 a number of steps in a given direction are sent to both its motor driver and its power up logic. The motor driver ~eeps track of which two phases of motor 243 are on and which two phases are o~f. In response to the signals from microprocessor 527 to rotate shaft 265 of motor 243, the motor driyer sequentiall~ changes whlch phases are on and which are off until the desired rotation is ach~eved. The power up logic l~cludes the switching circuitry required to apply full power to, in this case, motor 243.
Printer control board 521, printer driver board 523 and thermal printer 525 are for providing a printout of:
(1) the retinoscopy finding; (2) the distance prescription;
(3) the near prescription; and (4~ the complete prescription of the patient whose eyes are being examined. For ~his purpose, printer control board 521 has its own microprocessor 547, 1 ~ 67~

preferably an Intel 8039, and its own read only memory 549, preferably an Intel 8355 or 8755. Microprocessor 547 monitors the information sent to LED display 533 to determine if one of the print keys has been depressed. If a print key has been depressed, microprocessor ;47 sends a signal to microprocessor 527 to send the requested refraction data to microprocessor 547 for printing. Printer control board 521 also includes an RS-232-C input/output port that can be used to input key codes from and output display data to a computer.
To rotate disk 31 from a position in which one stxong sphere lens or opening is aligned with optical axis 61 to an immediately adjacent position where another lens or opening is aligned with axis 61 requirss 18 steps of motor 243. As the gearing and motors are identical, 18 steps are al80 required to rotate each o~ disks 33-39 from one alignment position ~o an lmmediatsly adjacent alignment positiQn. Further, because of the gear reduction, each step of motor 309 produces a one degree rotation o~ lens mounts 53, 57 and 59. Finally, each step of motors 413 and 423 rotates, respectively, prisms ~0 353 and 355 one degree.
In order for microprocessor 527 to, ~or instance, rotate disk 31 from a position where one lens or opening is aligned with axis 61 to a position where another lens is aLigned with axis 61, it is necessary to provide disk 31 with a reset or zero position from which all steps o~ motor 243 are counted. This is accomplished by encoder system 515 and reflectiYe blocks. With reference to FIGURE 1, disk 31 is provided with a reflective block 551 which cooperates with encoder 553, preferably a Texas ~nstruments TIL-139 or equiYalent, positioned on comb assembly 73. Each of disks ~ 3 2 _ 7 3 ~) 1 ~3-39 is p~ovided w~th an ldentical re1ecti~e block (not shown~. Further, as is evident ~rom i~spection o~ ~IGURE 4, comb assemb}y 73 also includes optical encoders 5S5 and 557~
for monitoxing the positions of disks 35 and 39. For monitor-ing the posi~ions of disks 33 and 37, comb assembly 75 is pro~ided with two encoder-, one of which is illustrated at 559 i~ FIGURE 1.
Encoder 5~3, like all the encoders utilized, includes an LED and a ~hototransistor. E~ch phototransistor is coupled, and alway~ sending an analog signal, to a separate terminal in OD encoder board 561. Board 561 also includes decoder logic which transforms these analog signals to digital ~ignals, which are sent to interrupt decode logic system 531.
For each encoder there is a separate termin~l in logic S31. In lS operation, when the light emitted by the L~D of encoder 553 is xoflected ~ack t~ the photot~an8istor by th~ leading edge o~ block 551 as it moves past encoder 553, the analog signal 3ent ~y en~oder 553 changes. When the analog ~ignal sent to board 561 reaches a threshold value, the decoder logic changes the digital signal ~ent to logic 531. For each motor, lo~ic 531 includ~s a latch, preferably a ~K master slave fl~p-flop, which latches the ri~ing edge o~ the change in signal ~rom the decoder logic of bo~rd 561. In response to the latch being triggered, logic 531 sends an interrupt signal to microprocessor 527 that one of the latches has been triggered, and a signal to memory 529 which identifies which latch was triggered. If the rotatlon which triggered, for instance, encoder 553 was in response to a reset command ~rom key board Sl9, micro-processor 527 reads interrupt data latched on memor~ 529 to find out which motor is associated with the interrupt signai 3 3 _ 1 1 6'730 1 rec~ived, and stops sending electrical pulses to, in the case of disk 31, motor 243. If the encoder is triggered in response to an instruction other than a reset instruction, the signal transmitted from logic 531 to microprocessor 527 is ignored.
Since, for instance, stepping motor 243 is programmed to index only in in~egral steps, it may ~e necessary, with motor 243 energized to hold it in one of its magnetic de~ent positions, to rotate motor fiup~ort bracket 241 to insure proper alignment of the lenses supported on disk 31 with optical axis 61. To maintain this alignment, the electrical pulses which drive motor 243 must be interrupted so that motor 243 stops at that detent position where, in the case of dis~ 31, plano lens 60 is aligned with axis 61. Misalignment occurs if lS motor 243 stops rotating one step too soon or too late. This i8 true for disks 33-39. For the rotatable lens mounts and Risley prlsm 353 and 355, ~ailure of the associated motor to stop at the correct detent position r~qults in angular misorientation .
As those skllled in the art will appreciated, for motor 243 to stop at the correct detent position, encoder 553 must be trlggered prior to the correct detent position but 8ub~equent to the immediately preceeding detent po~ition.
Thus, the digital signal from encoder board 561 must be be-tween two magnetic detent positions of motor 243 in order for microprocessor 527 to qtop motor 243 at the step at which disk 31 is at its reset position. In view of manufacturing tolerances, it is necessary to be able to laterally adjust the position of each encoder to insure that the required signal is transmitted with the desired 1/2 step. With ref-erence to FIGURE 4, encoders 553, 555 and 557 are supported _ 3 L~_ I 167~1 between ~orks 215 and 217 of comb assembly 73 on encoder support brackets 565, 567 and 569. Brac~et 565 is secured to forks 215 and 217 via screws 571 and 573 which pass through slots 575 and 577 provided in tabs 579 and 581. Slots 575 and 577 permit the necessary lateral adjustment of encoder 553.
Brackets 567 and 569 are identical in construction to, and adjusted in the same manner as bracket 565.
For Risley prisms 353 and 355 and the rotatablP lens mounts, such as 53 and 57 which support the strong and weak cylinder lenses, pairs o~ encoders are required to insure that the associated motors stop precisely at the reset or starting position. With reference to the rotatable lens mounts, axis drive gear 303 is provided with 5 reflective blocks ~not shown) equally angularly spaced about its periphery.
lS Gear 341 is provlded with re1ective block 583. One encoder (not shown) is associated with gear 303; encoder 535, ~upported on po3t 587, with gear 341. With this arrangement, only when the phototransi3tors of both encoders are simultaneously above threshold and the resultant signals ANDed does encoder board 561 send the required digital signal to interrupt logic system 531. With the gear ratios and with 5 blocks on gear 303, this occurs for every 720 degree rotation of lens mounts 53, 57 and 59.
~he encoder system for Risley prisms 353 and 355, illustrated in FIGU~ES 6 and 7, includes reflective blocks 591, 593, 595 and 5g7 and 4 encoders, three of which are illustrated at 601, 603 and 605. Encoders 601 and 605 are supported on adjustable brackets 607 and 609. With reference to, for instance, Risley prism 353, because mount 367 rotates only one degree for each step of motor 413, block 593 and 3s--~ ~ ~7~n t encoder 603 ~annot be pos~tioned accurately enough to insure that encoder 603 will always be triggered prior to the cor~ect detent position but subse~uent to the i~unediately preceding detent position. In contrast to mount 367, gear 43S rotates three degrees for each step of motor 413 and, hen~e, block 591 and en~cder 601 can be po8itioned to o~taln the re~uired accuracy. ~owe~er, since gear 435 rotates 360 degrees or every 120 degree rotation o~ mount 367, encoder 691 cannot be usea alone, ~ut must be coupled with encodex 6~3. With thi~
a~angeJ:e~t~ o~ly w~e~ the phototransisto~ of both encoders are ~imultane~u~ly above threchold ar~d the resultant 91gnals ~NDed, does Qncoder ~oard 561 send the required digital signa~
to logic 531.
A8 i~ evide~t from inspection of FIGURE 9, encoder system 515 also ~ncludes 05 en~oder board 611. Where m~cro-proce8sor 527 ~s used not only to control both re~ractor h~l~es but the comp~ct ~efraction instrument dlsclosed in assignee's cope~ai~g ~pplication Serial No. 383,266 an additional en-coder board and ~et of encoders will be coupled to logic 531 and m~croprocessor 527.
WhereAs the drawings and accompanying description l~ave ~hown and described the pre~erred embodimen'c o~ the pre8~nt ~nventlon, lt should be apparent to those skilled in th~ ~rt that va~ious changes may be made in the form of the tnventlon without a~ecting the wope thereof.

Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an ophthalmic instrument including a base and one or more optical elements positionable along an optical axis:
(a) hub means supported by said base, said hub means having an axis and including at least one cylindrical bearing surface;
(b) a disk for supporting said optical elements, said disk including a central bearing aperture which cooperates with said cylin-drical bearing surface to radially align said disk relative to said hub axis; and (c) a plurality of peripheral disk support means supported by said base, each of said peripheral support means including a groove which receives the periphery of said disk to axially position said disk along said optical axis.

2. The instrument as set forth in claim 1, wherein said grooves are dimensioned so as to provide a bearing fit for said disk periphery.

3. The instrument as set forth in claim 1, wherein said optical elements are supported on a plurality of disks, wherein said hub means includes a like plurality of cylindrical bearing surfaces for radially aligning said disks, and wherein each of said peripheral support means includes a like plurality of grooves which are spaced relative to each other so as to position said disks at those intervals along said optical axis which will result in the required optical element air spacing between said optical elements supported on said disks.

4. The instrument as set forth in claim 3, wherein one of said support means is positioned adjacent said optical axis to thereby insure that said optical element air spacing between said optical elements supported on said disks is maintained for those optical elements positioned on said optical axis, even if one or more of said disks is warped.

5. The instrument as set forth in claim 1, wherein said disk periphery is in the form of gear teeth and further including a motor drive assembly, said assembly including a motor having a drive shaft, means for supporting said motor relative to said base and a pinion secured to said drive shaft and engaging said disk gear teeth.

6. The instrument as set forth in claim 5, wherein said pinion is secured to said drive shaft by elastomeric material and wherein said motor is connected to said motor support means by means which permit movement of said motor and said pinion towards and away from said disk, whereby said pinion can be spring loaded into engagement with said disk gear teeth.

7. The instrument as set forth in claim 5, where-in said motor is a stepping motor and said motor support means is connected to said base by means which permit limited rotation about an axis substantially coincident with the axis of said drive shaft, whereby said motor and said shaft can be rotated through an angle at least equal to the angular rotation of said shaft produced by one step, to insure align-ment of said optical elements with said optical axis.

8. The instrument as set forth in claim 7, wherein said motor support means is a U-shaped bracket having a base and two upstanding legs, said bracket base including a pin received in a bore provided in said base and two tapped holes which align with two openings in said base, said bracket being secured to said base by screws which pass through said openings and are received in said tapped open-ings, said openings being sufficiently larger than said screws to permit said rotation of said bracket about said pin.

9. The instrument as set forth in claim 1, wherein each of said optical elements is supported on a lens mount rotatably secured to said disk, wherein said hub means in-cludes a drive tube and means to rotatably secure said drive tube to said base, and further including means for rotating each of said lens mounts relative to said disk, said means including gear teeth formed on the periphery of each of said lens mounts, a gear having teeth which mesh with said lens mount gear teeth secured to said drive tube for rotation therewith, and means for rotating said drive tube relative to said base.

10. The instrument as set forth in claim 9, wherein said hub also includes a spool secured to said drive tube for rotation therein, said spool including said cylindrical bearing surface and a cylindrical surface for supporting said gear.

11. The instrument as set forth in claim 10, wherein said hub means includes a plurality of spools secured to said drive tube for rotation therewith, each spool including a cylindrical bearing surface and a cylindrical support sur-face, and wherein said means for rotating said lens mounts includes a drive gear supported by said cylindrical support surface of one of said spools.

12. The instrument as set forth in claim 9, wherein said means for rotating said lens mounts includes a motor having a drive shaft, means for supporting said motor relative to said base, a pinion secured to said drive shaft, and gear means coupling said pinion to said drive tube.

13. The instrument as set forth in claim 12, wherein said motor is a stepping motor and said motor support means is connected to said base by means which permit limited rotation of said motor support means about an axis substan-tially coincident with the axis of said drive shaft, whereby said motor and said drive shaft can be rotated through an angle at least equal to the angular rotation of said shaft produced by one step, to thereby adjust the angular orientation of said optical elements.

14. The instrument as set forth in claim 1, further including a pair of Risley prisms, means secured to said base for positioning said prisms on said optical axis, and means for rotating said prisms about said optical axis.

15. The instrument as set forth in claim 14, wherein said rotating means include, for each of said prisms, a rotatable lens mount having gear teeth formed thereon, a stepping motor having a drive shaft, means for supporting said motor relative to said positioning means, and a pinion secured to said drive shaft and coupled to said lens mount, said motor support means including means for removing back-lash and means which permit limited rotation of said motor about the axis of said drive shaft to thereby permit rotation of said lens mount at least equal to the amount of rotation produced by a step of said motor.

16. In an ophthalmic instrument including a base and a plurality of optical elements positionable along the optical axis thereof:

(a) hub means, including a drive tube having a longitudinal axis and means to rotatably secure said drive tube to said base for rotation about said drive tube axis, said hub means further including at least one cylindrical bearing surface;
(b) a disk for supporting at least some of said optical elements, said disk having a periphery in the form of gear teeth and a central bear-ing aperture which cooperates with said cylindrical bearing surface to radially algin align said disk relative to said drive tube axis;
(c) a plurality of peripheral disk support means supported by said base, each of said peripheral support means including a groove which receives said periphery of said disk to axially position said disk along said optical awxis;
(d) lens mounts rotatably supported on said disk for supporting at least some of said optical elements, said lens mounts having gear teeth formed in the periphery thereof;
(e) means for rotating said lens mounts, said means including a gear, having teeth which mesh with said lens mount gear teeth, secured to said drive tube for rotation therewith:
(f) motor drive means for rotating said disk, said means including a motor having a drive shaft, means for supporting said motor relative to said base and a pinion secured to said drive shaft and engaging said disk gear teeth; and (g) motor drive means for rotating said drive tube, said means including a motor having a drive shaft, means for supporting said motor relative to said base, a pinion secured to said drive shaft and gear means coupling said pinion to said drive tube.