Abstract:
A mechanism which has a continuously variable amount of convergence and inward movement over the entire range of pupillary distance (PD) settings is disclosed. The repositioning of a pair of straight tracks transfers a continuously variable amount of motion to a pair of respective levers that control the position of a pair of carriages relative to the PD control and the angular relationship of lens batteries relative to the respective carriages.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a binocular refractor and, more particularly, to a binocular refractor having an infinitely variable convergence mechanism over the entire range of PD settings from narrow to wide for proper alignment of test lenses on the vision axes of a patient&#39;s eyes for both near and distant testing. 
     PRIOR ART 
     U.S. Pat. No. 2,923,200 issued Feb. 2, 1960 describes a convergence mechanism for a binocular refractor. Each battery is connected to a cam and when the respective cam is actuated, the battery rotates a fixed amount and slides toward the other battery. Instruments of this type normally have the amount of rotation and inward movement selected to accomodate the majority of patients refracted. However, there is no charge in the amount of rotation or inward movement in such instruments permitting precise alignment of the test lenses with the visual axes during near testing for patients having either a greater or lesser PD than the &#34;normal&#34; PD. 
     U.S. Pat. No. 3,413,056 issued Nov. 26, 1968 describes a modification of the &#39;200 mechanism for rotating a lens battery and moving the same toward the other lens battery when a single control is actuated. 
     BRIEF DESCRIPTION OF THE PRESENT INVENTION AND DRAWINGS 
     The present invention utilizes three tracks. One track supports a carriage for each respective lens battery to align one or more of a plurality of lenses with a patient&#39;s eyes. The other two tracks are movable from a normal position. When located in the normal position, these tracks are parallel to the first track. Contacts that follow the other tracks control the angular position of the respective lens batteries as well as their spacing relative to the PD adjustment. A single control moves the other tracks from their normal position to an alternate position that is both displaced from the normal position and at an angle thereto. Because of the angular relationship, the contacts travel different distances when they are located at different positions along the tracks as the tracks change from the normal to the alternate position. The variation in contact travel is used to vary the amount of convergence and inward movement of the lens batteries thereby maintaining alignment of the visual axes of the patient with the respective lens optical axis irrespective of the patient&#39;s PD. 
    
    
     FIG. 1 is a top view of the PD control and convergence mechanism, 
     FIG. 2 is a top view of the convergence mechanism assembly, 
     FIG. 3 is a mechanical diagram of the PD control and convergence mechanism positioned for distant testing, 
     FIG. 4 is a mechanical diagram of the PD control and convergence mechanism positioned for near testing, 
     FIG. 5 is a side view of the convergence actuating mechanism positioned for distant testing, 
     FIG. 6 is a side view of the convergence actuating mechanism positioned for near testing, and 
     FIG. 7 is a side view of the convergence actuating mechanism positioned for intermediate testing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG.1, frame 1 supports a pair of lens batteries, for presenting one or more of a plurality of test lenses along the visual axis of a patient&#39;s eyes, and has track 2 extending therethrough. A pair of carriages 3 and 3a are carried by track 2. Shaft 4 threadably engages nut 5 and nut 5a. Nuts 5 and 5a have reverse threads, i.e. one has left-hand threads and one has right-hand threads, in order to move carriages 3 and 3a toward each other when knob 6 is turned in one direction and away from each other when knob 6 is turned in the other direction in order to adjust the spacing between the test lens to accomodate the PD of diverse individuals. Since the right-hand mechanism is a mirror image of the left-hand mechanism, only those elements on the left-hand side will be specifically identified hereinafter. Pin 7 extends up from nut 5. Also, by referring to FIG. 2, it can be seen that lever 8 is pivotably mounted to pin 7. Roller 9 is carried by lever 8 and engages surface 10 of arm 11. Arm 11 is pivotably mounted to frame 1 by pivot screw 12 and is positioned by set screw 13 bearing against face 14 of arm 11. 
     Battery support 15 is pivotably connected to carriage 3 by pivot 16. Shoulder screw 17, extending from battery support 15, and slot 18 in lever 8, combine to transfer sliding motion through lever 8 from nut 5 to carriage 3. Pivotable motion is transferred from lever 8 through recess 19, block 20 and pin 21 to battery support 15. Spring 22 urges carriages 3 and 3a toward a central position of convergence. 
     The operation of the infinitely variable convergence mechanism will be described by reference to FIGS. 3 and 4. Pressure from spring 22 on carriage 3 is transmitted through shoulder screw 17 and lever 8 to force roller 9 against surface 10, which acts as a track for roller 9. Pivotal motion of arm 11 is resisted by pressure of set screw 13 against face 14. In FIG. 3, representative test lens 23 is located on the visual axis of a patient&#39;s eye aligned to view an object at an infinite distance, usually twenty feet. To converge the lens batteries for viewing at a near distance, set screw 13 is moved from the position shown in FIG. 3 to the position shown in FIG. 4 by structure to be described hereinafter. Since the bias force transferred from spring 22 forces face 14 to follow set screw 13, arm 11 is pivoted about pivot screw 12 causing surface 10 to move toward and assume an angular relationship with respect to track 2. As roller 9 follows surface 10, lever 8 pivots about pin 7 allowing carriage 3 to slide inward along track 2 toward the center of frame 1. Simultaneously, battery support 15 is rotated about pivot 16 by movement of lever 8 transmitted to battery support through pin 21. 
     Returning to FIG. 3, it can be easily seen that if the pupillary distance is adjusted by rotation of knob 6 the parallel relationship between surface 10 and track 2 prevents pivotal movement at pin 7 as roller 9 tracks along surface 10. Therefore, test lens 23 is maintained in a position for viewing at an infinite distance and carriage 3 moves the same distance as nut 5. 
     The dotted line in FIG. 4 shows surface 10 in the position illustrated in FIG. 3. The continuously changing space between the dotted line and surface 10 shows that the amount of movement transferred through roller 9 to lever 8 is continuously varied as the location of roller 9 along surface 10 is changed. A patient having a narrow PD would cause a relocation of roller 9 to a position to the right of that illustrated in FIG. 4. This relocation would result in a smaller amount of sliding motion in carriage 3 and a lesser amount of rotation of lens 23 as set screw 13 moves from the position shown in FIG. 3 to the position shown in FIG. 4, since roller 9 moves a shorter distance in following surface 10. Conversely, a patient having a large PD would result in a relocation of roller 9 to the left of the position shown in FIG. 4 which would result in a greater amount of inward movement of carriage 3 and greater amount of rotation of test lens 23 as a result of the larger movement of roller 9 while following surface 10 as it moves from the dotted position to the position shown in FIG. 4. 
     Referring to FIG. 1, rod holder 24 is pivotably mounted on frame 1. Socket 25 is adapted to receive a rod (not shown) for supporting the near point reading chart. Referring now to FIG. 5, rod holder 24 and cam 26 are both pivotably mounted to frame 1 by sleeve 27. Sliding member 28 positions set screw 13 in alignment with face 14 and the other end of member 28 carries cam follower 29 which rides in recess 30 of cam 26. Spring 31 urges ball 32 into near detent 33 or alternatively intermediate detent 34 as shown in FIGS. 6 and 7 respectively. For near point examination, maximum convergence and inward movement of the batteries is provided by the movement of set screw 13 over the distance Tn as shown in FIG. 6 when both rod holder 24 and cam 26 are rotated the full distance. 
     FIG. 7 illustrates the location of ball 32 in detent 34 when rod holder 24 is rotated the full distance but cam 26 is only partially rotated. As shown in FIG. 7, intermediate distance Ti is less than the distance travelled by set screw 13 shown in FIG. 6. since set screw 13 moves a smaller distance when cam 26 is in the intermediate position, a correspondingly smaller movement of surface 10 is permitted. Therefore, the amount of inward movement and rotation is less in each of the lens batteries when the instrument is set for an intermediate distance.