Abstract:
A subjective ophthalmic refractor comprises a cylinder power adjustment knob for simultaneously actuating a cylinder power scale and an indexable lens carrier drive assembly. The drive assembly includes a gear phasing hub designed to allow a scale marking to be centered in a display window of the refractor and components of the drive assembly to be set in proper rotational orientation as independent operations.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to ophthalmic instruments, and more particularly to subjective ophthalmic refractors for evaluating refractive characteristics of a patient&#39;s eye. 
     BACKGROUND OF THE INVENTION 
     A subjective ophthalmic refractor typically comprises left-eye and right-eye batteries each having a defined viewing path along which an operator may selectively introduce combinations of testing lenses having known refractive properties. During examination, the patient is positioned in a darkened room with his or her eyes aligned to view a projected target chart along the viewing paths defined by the left-eye and right-eye batteries. The operator then performs well-known refracting procedures, including refraction using astigmatic charts and the Jackson cross-cylinder test. A goal of the examination procedure is to determine the sphere power, cylinder power, and cylinder axis of each eye so that a suitable pair of corrective lenses may be prescribed. 
     U.S. Pat. No. 2,968,213 describes an ophthalmic refractor of the prior art. FIG. 5 of the &#39;213 patent is an exploded view illustrating the internal components of a left eye lens battery, and serves to illustrate a longstanding arrangement for mechanically coupling a pair of rotatable cylinder lens carriers  8  and  9  and an associated ring-shaped cylinder power scale  50  of the battery to an adjustment knob  20  used by the operator to set a chosen cylinder power in the viewing path of the battery. As can be seen at FIG. 1 of the &#39;213 patent, the indicia on scale  50  can be viewed by the operator through an display window or opening  52  in the battery housing. Typically, the indicia are numerical cylinder power values from 0 to 6.00 diopters in quarter-diopter increments, and are angularly spaced at regular angular increments about a central axis of the ring-shaped scale. The mechanical interconnections from knob  20 , through cylinder power scale  50 , to the lens carriers  8  and  9  are designed such that rotation of knob  20  positions two lenses (or a lens and an empty lens cell), one from lens carrier  8  and one from lens carrier  9 , in series in the viewing path to produce a resultant cylinder power. Lens carrier  8  is a “weak” cylinder lens carrier having, for example, a blank lens cell (zero power)and four cylinder lenses ranging in power from 0.25 diopters to 1.00 diopters at quarter diopter increments. Meanwhile, lens carrier  9  is a “strong” cylinder lens carrier having, for example, a blank lens cell (zero power) and four cylinder lenses ranging in power from 1.25 diopters to 5.00 diopters at 1.25-diopter increments. Consequently, by indexing the weak cylinder lens carrier  8  five times for every one index movement of strong cylinder lens carrier  9 , a cylinder power range of 0.00 diopters to 6.00 diopters at quarter-diopter increments is possible in agreement with the indicia on scale  50 . 
     With continued reference to U.S. Pat. No. 2,968,213, it will be seen that adjustment knob  20  drives a shaft  21  having at its opposite end a dual gear comprising a small front gear  23  and a larger rear gear  25 . Larger gear  25  meshes with a gear  31  which is fixedly and permanently attached to driver plate  27  in coaxial arrangement therewith, whereby rotation of knob  20  and larger gear  25  produces counter-rotation of driver plate  27 . As driver plate  27  rotates about its axis, four short pegs.  39   a - 39   d  on the driver plate successively engage weak cylinder lens carrier  8  to index only the weak lens carrier, and a fifth longer peg  40  engages both the weak and strong lens carriers  8  and  9  to index both carriers, in the manner of a Geneva mechanism. A spring-biased roller  48 ′ cooperates with five circumferential detents  53 ′ in driver plate  27  to allow the operator to feel each index position at adjustment knob  20 . A locking plate  37  having a recess  49  is fixedly mounted for rotation with driver plate  27  by a hub  33  and cooperates with a star wheel  47  on strong cylinder lens carrier  9  to prevent rotation of the strong cylinder lens carrier except when it is time for the strong cylinder lens carrier to index. 
     Meanwhile, small front gear  23  meshes with internal gear teeth on ring-shaped scale  50  to rotate the scale in coordination with the indexing of cylinder lens carriers  8  and  9 , whereby an appropriate cylinder power value marked on the scale appears through display window  52 . Scale  50  is constrained both radially and axially by three bearings  56  located at respective positions about the circumference of scale  50 . 
     During manufacturing assembly of an ophthalmic refractor formed in accordance with the &#39;213 patent, it is necessary to carefully align cylinder power scale  50  such that a correct cylinder power value is precisely centered in display window  52  while dependent rotational positions of driver plate  27  and locking plate  37  are also in proper alignment for functioning of the Geneva mechanism. However, because an exact locational relationship between the internal gear teeth and the markings on scale  50  is not specified and one scale differs slightly from another in this regard, the task of centering the scale markings in the display window and achieving proper rotational alignment among the interconnected parts has involved a process of trial and error. For example, different scales  50  and other component parts in the mechanical interconnection are tried from production batches of these parts until a suitable combination of parts produces acceptable rotational alignment and centering of the scale markings. 
     FIGS. 2 and 3 herein help illustrate assembly of an ophthalmic refractor eye battery  111 A according to the prior art. A cylinder power scale  118  is mounted in eye battery housing  112 A, and adjustment knob shaft  124  is inserted through a provided bearing opening in the housing such that scale drive gear  126  (see small front gear  23  of the &#39;213 patent) fixed to the shaft meshes with internal gear  130  of cylinder power scale  118 . A driver plate  127  having a gear  131  permanently fixed thereto and a locking plate  133  having a hub  135  permanently fixed thereto are fastened together in a predefined angular relationship such that an arcuate recess  159  of the locking plate is centered with respect to the longer peg  160  of the driver plate. More specifically, three angularly spaced fastener holes  145  are provided through hub  135  in set relation to recess  159  and three corresponding threaded holes  147  are provided through gear  131  in set relation to longer peg  160 , and the hub  135  is fastened to gear  131  by threaded fasteners  149  operable through access openings  151  to form a subassembly  153  comprising locking plate  133 , hub  135 , driver plate  127 , and gear  131 . This subassembly  153  is then mounted on hub stem  137  such that gear  131  meshes with a larger gear  128  (see larger rear gear  25  of the &#39;213 patent) fixed to adjustment knob shaft  124  adjacent scale drive gear  126 . A spring-biased roller (not shown in FIGS. 2 and 3 but equivalent to spring-biased roller  48 ′ shown in the &#39;213 patent) engages an appropriate detent  155  in driver plate  127  to set the relationship of subassembly  153  to a star wheel and lens carriers (not shown in FIGS. 2 and 3 but equivalent to star wheel  47  and lens carriers  8  and  9  of the &#39;213 patent). Consequently, in order for gear  131  of subassembly  153  to mesh with larger gear  128 , the adjustment knob shaft may have to rotate slightly, thereby rotating the scale drive gear  126  and scale  118  and producing an “uncentered” appearance of the corresponding scale marking in display window  122 . To correct this, different scales  118 , driver plates  127  with attached gear  131 , and locking plates  133  with attached hub  135  must be tried until a satisfactory centering is achieved. 
     Understandably, this assembly process is time consuming and requires skill and patience on the part of the assembly technician. The introduction of tighter tolerances for the component parts can alleviate the problem to some extent, however this introduces increased costs associated with manufacturing the component parts. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to increase efficiency in the assembly process for manufacturing subjective ophthalmic refractors. 
     It is another object of the present invention to improve the precision with which cylinder power scale markings are centered in a display window of a subjective ophthalmic refractor for higher quality from one refractor to the next. 
     It is another object of the present invention to diminish the level of skill and patience required of an assembly technician in assembling a subjective ophthalmic refractor. 
     It is a further object of the present invention to achieve the objects stated above without introducing more exacting tolerances with respect to component parts of the ophthalmic refractor. 
     In furtherance of these and other objects, an ophthalmic refractor of a type comprising a cylinder power adjustment knob operatively connected to a drive assembly for indexing at least one rotatable lens carrier and to a corresponding rotatable cylinder power scale is made easier to assemble at a higher level of quality with respect to centering of scale markings in a display window. More specifically, the drive assembly can be set in a required rotational orientation separately from and after the centering of an appropriate scale marking in a display widow of the eye battery housing without affecting the centered position of the scale marking. In accordance with a preferred embodiment, the cylinder power adjustment knob is coupled to a shaft that carries a pair of gears at its distal end for rotation with the adjustment knob, a first gear for transmitting torque to the cylinder power scale and a second gear for transferring torque to a Geneva mechanism drive assembly and the other gear. The second gear meshes with a third gear that is coaxial with a driver plate of the Geneva mechanism. A gear phasing hub is adjustable axially relative to the third gear to selectively clamp the driver plate to the third gear at any necessary rotational orientation. An end cap threadably received by the gear phasing hub secures a locking plate of the Geneva mechanism to the, gear phasing hub in a proper rotational orientation relative to the driver plate. Thus, both the driver plate and locking plate can be set without disturbing the centered condition of the cylinder power scale. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
     FIG. 1 is a front elevational view of an ophthalmic refractor formed in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is an exploded perspective view of an eye battery of an ophthalmic refractor illustrating a construction according to the prior art; 
     FIG. 3 is a cross-sectional view illustrating the assembly of a driver plate and a locking plate of the prior art eye battery shown in FIG. 2; 
     FIG. 4 is an exploded perspective view of an eye battery of the ophthalmic refractor shown in FIG.  1  and incorporating the present invention; 
     FIG. 5 is a cross-sectional view showing assembly of a driver plate and a locking plate of the eye battery shown,in FIG. 4 in accordance with the present invention; and 
     FIG. 6 is a plan view of a cylinder power scale of the eye battery shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a subjective ophthalmic refractor  10  formed in accordance with a preferred embodiment of the present invention. Ophthalmic refractor  10  is of a type well-known in the art of ophthalmic instruments in that it generally comprises a right eye battery  11 A and a left eye battery  11 B that are mirror images of each other. Eye batteries  11 A and  11 B comprise respective housings  12 A and  12 B and respective viewing paths  14 A and  14 B along which a patient facing a back side of the instrument gazes during examination. The construction and operation of ophthalmic refractor  10  are generally and substantially as taught in U.S. Pat. Nos. 2,968,213 and 2,995,065, both these patents being incorporated herein by reference. 
     The present invention relates to an improvement involving a cylinder power adjustment system found in each eye battery  11 A and  11 B. For sake of simplicity, the invention is described with respect to right eye battery  11 A only, it being understood that left eye battery  11 B is a mirror image of right eye battery  11 A. Battery  11 A comprises a cylinder power adjustment knob  16 , a cylinder power scale  18  having numerical markings  20  indicative of a cylinder power introduced in viewing path  14 A (see FIG.  6 ), and an opening or display window  22  in battery housing  12 A for allowing an appropriate power value on scale  18  to be viewed by an ophthalmic practitioner. 
     Referring also now to FIGS. 4 and 5 of the drawings, adjustment knob  16  is fixed on a shaft  24  having at its opposite end a dual gear comprising a small front gear  26  and a larger rear gear  28 . Larger gear  28  transmits torque to a Geneva mechanism for indexing a pair of cylinder lens carriers (not shown) as described in referenced U.S. Pat. No. 2,968,213. In the relevant portion shown in FIG. 4, the Geneva mechanism includes a gear  31 , a driver plate  27 , a gear phasing hub  36 , a locking plate  33 , and an end cap  35  aligned coaxially on an axle stem  37  fixed to eye battery housing  12 A. 
     Larger rear gear  28  on adjustment knob  24  meshes with gear  31 , which is rotatably mounted on an axle stem  37  and has a plurality of threaded fastener holes  32  spaced about its rotational axis. Gear  31  includes a radial step  34  defining a radially reduced portion received in close slidable fit within a circular opening  40  through driver plate  27  centered on a common rotational axis of gear  31  and the driver plate. Likewise, gear phasing hub  36  has a plurality of fastener holes  38  corresponding to threaded holes  32  in gear  31 , and includes a radial step  42  defining a radially reduced portion received in close slidable fit within circular opening  40 . Accordingly, as best seen in FIG. 5, a plurality of threaded fasteners  44  extend through fastener holes  38  in gear phasing hub  36  and mate with threaded holes  32  in gear  31 , whereby gear phasing hub  36  can be adjusted axially relative to gear  31 . When fasteners  44  are tightened, gear phasing hub  36  securely clamps driver plate  27  to gear  31 . However, when fasteners  44  are loosened, driver plate  27  can be rotated independently of gear  31  and vice versa. Consequently, an assembly technician can selectively secure driver plate  27  to gear  31  at any chosen angular orientation relative to gear  31 . 
     Gear phasing hub  36  is provided with a radially stepped axial opening  46  slidably fitting over axle stem  37  as shown in FIG.  5 . Axial opening  46  includes an internally threaded portion  47  into which a threaded shank  48  of end cap  35  is mated after the shank passes through a central aperture  51  in locking plate  33 . When end cap  35  is tightened, it serves to securely clamp locking plate  33  to gear phasing hub  36 . When end cap  35  is loosened, locking plate  33  and gear phasing hub  36  are rotationally independent of one another. Therefore, an assembly technician can selectively secure locking plate  33  to gear phasing hub  36  at any chosen angular orientation relative to gear phasing hub  36 . In the preferred embodiment shown herein, end cap  35  includes a pair of spaced holes  50  for receiving corresponding prongs of a specially made adjustment tool (not shown) for tightening and loosening the end cap. End cap  35  is further provided with a central axial passage  57  sized for slidable fit onto axle stem  37 . 
     Small gear  26  on adjustment knob shaft  24  meshes with an internal gear  30  of cylinder power scale  18  to rotate the cylinder power scale simultaneously and in concert with the rotational indexing of the cylinder lens carriers via the Geneva mechanism. Cylinder power scale  18  includes a frontward-facing first side  18 . 1  on which markings  20  are applied, and a rearward-facing second side  18 . 2 . 
     As will be understood from the foregoing description, it is now possible during assembly of eye battery  11 A to adjust scale  18  independently of driver plate  27  until an appropriate scale marking is centered with respect to display window  22 , and then subsequently secure the driver plate  27  to gear  31  by means of gear phasing hub  36  and fasteners  44  such that driver plate  27  is at its proper rotational orientation. Moreover, the rotational orientation of locking plate  33  relative to driver plate  27  can be selectively adjusted and set by means of end cap  35  such that an arcuate recess  59  of locking plate  33  is centered with respect to a long peg  60  of driver plate  27 . As a consequence of the present invention, scale markings  20  are centered to a high degree within display window  22  in a fraction of the assembly time required for ophthalmic refractors of the prior art.