Abstract:
A quick change lap retaining device uses radially displaceable blades to engage a groove in the underside of a lap and thereby hold the lap in position. The device fails in the engaged position to prevent inadvertent movement of the lap. Removal of the lap occasioned by disengagement of the blades is preferentially by pneumatic drive but can also be manual.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the field of eyeglass lens production. More particularly, the invention relates to a device for retaining various laps for fining and polishing of lenses. 
     2. Prior Art 
     Ophthalmic and other types of lenses are typically produced from lens blanks of glass or plastic having two major surfaces, one of which is typically finished, and the other of which is unfinished. Cutting, fining, and polishing operations are performed on the unfinished surface of the lens blank by a machine responsive to data corresponding to a particular lens prescription. The cutting operations are usually accomplished by employing a ball mill for plastic lenses, or a grinder for glass lenses. These cutting operations generally create a lens surface closely approximating the shape of the finished lens. However, the cut surface of the lens blank is often rough and requires that subsequent fining and polishing operations be performed on the lens blank to achieve the requisite optical clarity. 
     The fining and polishing operations are ordinarily performed by engaging the cut surface of the lens blank with an abrasive surface having a shape that closely approximates the desired finished shape of the lens as defined by the lens prescription. This abrasive surface is referred to by those skilled in the pertinent art as a tool or “lap”. During operation, the device to which the lens blank is mounted, moves the blank over the abrasive surface of the lap along a conforming contoured semi-spherical path, thereby fining and/or polishing the lens surface. Laps generally consist of two main components, a mounting surface or mandrel, and a removable abrasive pad that mounts on the mandrel and against which the lens blank is moved during fining and polishing operations. The shape of the mandrel must conform as closely as possible to the prescribed shape of the lens, therefore, different lens prescriptions require different laps to be used. 
     One drawback of prior art apparatuses is due to the mounting system for the various laps. Conventionally, laps are secured to a support by clamping a flange extending from the bottom edge of the lap. Clamping devices used include hydraulic, pneumatic and mechanical fasteners. All of these require a significant amount of time to install and therefore leave the art in need of a more time efficient yet reliable means of securing laps to the lap tower. 
     SUMMARY OF THE INVENTION 
     The above-identified drawbacks of the prior art are overcome or alleviated by the lap retaining mechanism of the invention. 
     The invention provides for quick change of laps and reliable failsafe retention thereof. This is beneficial in that many different laps are needed for the many different possible prescriptions for lenses. 
     The invention comprises a base through which a pair of shafts extend. The shafts are keyed to a pair of blades, one on each shaft. The blades rotate with the shafts because of the keyed relationship. The blades when not actuated (the failsafe condition) are rotated such that an outer aspect of each blade extends radially outwardly so that such outer aspect is received in a recess in a lap disposed on the lap tower to prevent separation of the lap from the tower. Upon actuation of a pneumatic, hydraulic, mechanical or electromechanical driver, a biasing means is overcome and the blades are retracted. In this condition the lap may be removed and replaced. Advantageously, the system provides a means for manual operation to be employed in the event that the mechanized drive is lost. 
     With the system of the invention significant time savings is realized during lens manufacture due to speedy lap changes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
     FIG. 1 is a perspective view of a lapping device in accordance with the present invention; 
     FIG. 2 is a top plan view of the lapping device of FIG. 1; 
     FIG. 3 is a cross-section view of the invention taken along section line  3 — 3  in FIG. 2; 
     FIG. 4 is a top plan view of a lap tower or the lapping device of FIG. 1 with the lap removed; 
     FIG. 5 is a cross-section view of the invention taken along section line  5 — 5  in FIG. 3; 
     FIG. 6 is a schematic illustration of a single castellation on shafts of the lapping device as shown in FIG. 3; 
     FIG. 7 is a bottom perspective view of the lapping device of FIG. 1 illustrating an actuation linkage arrangement preferred for the invention; and 
     FIG. 8 is a bottom plan view of the lapping device of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, an exterior perspective view and top plan view of the retaining mechanism for a lapping device  10  are illustrated. It will be appreciated that a lap  12  externally exhibits no hold down features and is smooth. Lap  12  comprises a domed top portion  14  and an annular skirt  16  depending therefrom which together define a hollowed interior. The domed portion is preferably of constant thickness. The lap of the invention is securely, reliably, and in a failsafe manner, retained from the inside preferably, on a lap tower (support)  18 . Lap tower (support)  18  is supported by a carrier (support)  20  that is securable to a machine housing (not shown). Also partially visible in FIGS. 1 and 2 is an actuator  22  the balance of which is obscured under carrier  20  and which serves to actuate means for retaining lap  12  to the support, as described more fully hereinbelow. 
     Referring to FIG. 3 which is a cross section view of the invention taken along section line  3 — 3  in FIG. 2, FIG. 4 which is a schematic top view of lap tower  18  and FIG. 5 which is a cross-section view of FIG. 3 taken along section line  5 — 5  in FIG. 3, the operational components of the invention are addressed. Each lap  12  (the invention provides for a plurality of laps to be attached), individually, is secured to a lap tower  18  (preferably a plastic material) by a pair of blades  24   a  and  24   b.  It is important to note that in FIG. 4, blade  24   a  is illustrated in the retracted position while blade  24   b  is illustrated in the engaged position. The engaged position is the failsafe position and the one where lap  12  is secured to tower  18 . Blades  24   a  and  24   b,  when in the  24   a  position, are received in a groove  26  which is cut in the hollowed interior of lap  12 , radially in skirt  16 . Lap  12  then sits flush on top of tower  18 . Tower  18  in turn is received in a recess  28  of carrier  20  which then is fastened to a machine housing (not shown) by fasteners which pass through bolt holes  30  in a flange  32 . 
     Blades  24   a  and  24   b  are actuated by shafts  34  which extend though tower  18  and carrier  20 . Since tower  18  is in one embodiment (shown) plastic, bushings are not needed. In carrier  20  however it is preferable to apply a seal  36  in a seal bore  38  and a bushing (not shown) in a bushing bore  40 . Preferably the bushing material is bronze. The bushing and seal maintain an aligned position for shafts  34  in clearance bores  42  in carrier  20 . Shafts  34  extend below carrier  20  to be accessed by linkage to one of a number of actuators that are possible i.e. mechanical, hydraulic, electromechanical, electrical and pneumatic, with pneumatic being preferred. 
     Referring specifically to FIG. 4, blades  24   a  and  24   b  are attached fixedly at one end  44  thereof to an upper end  46  of shafts  34  by preferably a threaded fastener  48 . Threaded fasteners are preferred to allow for disassembly if necessary. At the upper end  46  of shafts  34  are a single castellation  50  illustrated in FIG. 6 schematically. As can be seen in FIG. 4, each blade  24  includes a keyhole  52  comprising a fastener bore  54  and a dependent slot  56 . Slot  56  is provided to receive castellation  50  and prevents turning of blades  24  relative to their respective shafts  34 , once each blade  24  is fastened thereto with appropriate fasteners  48 . In the fastened condition, rotary movement applied to shafts  34  causes a radially outward shift in position for blades  24 . The degree to which such shaft is desired and intended to rotate can be ascertained by comparing the position of blade  24   a  with that of blade  24   b  in FIG.  4 . It should also be appreciated that a curve  58  of fingers  24   a  and  24   b  is preferably matched to the curvature of groove  26  in lap  12  to ensure a solid engagement and reliable retention. 
     In order that shafts  34 , do not migrate upwardly through tower  18 , a cap ring  60  (annular) is positioned over the blades and is secured to the tower  18  with preferably threaded fasteners (not shown) which extend through openings  62 . It should be noted that an upper surface  64  of cap ring  60  is beveled inwardly. This helps to return water, used to heat or cool lap  12  from the interior thereof, to a central drain port  66 . 
     Turning now to the actuator  22  of blades  24   a  and  24   b,  rotational movement is imparted to shafts  34 , referring to FIGS. 3,  7  and  8 , by preferably a pneumatic drive  68  which is pivotally mounted through a bushing  70  to the housing (not shown) and a bushing  72  which rides in a frame section  74  that itself bolts to the housing. Frame section  74  bolts through openings  76 . The pneumatic drive includes a drive shaft  78  which at a distal end from the drive, includes a clevis  80 . Clevis  80  is connected via a clevis pin  82  to an actuator arm  84  which is fixedly connected by threaded a fastener  86  to one shaft  34 . Actuator arm  84  is further connected by a pivot pin  88  to a link  90  which connects via a pin  92  to a radius arm  94  which in turn is connected fixedly by a fastener  96  to the other shaft  34 . In order to prevent relative rotational movement between radius arm  94  and shaft  34 , and actuator arm  84  and shaft  34 , a single castellation is provided on each shaft. In FIG. 7, one of the castellations is visible and is identified as  98 . A spring is preferably placed in operable contact with the driver assembly to maintain the assembly in the position where the lap is locked onto tower  18 . The spring is not shown but could bear against any of the various linkage members or could be internal to the pneumatic drive so long as the bias tends to urge the drive in a direction opposite the actuation drive direction and into a position where blades  24   a  and  24   b  are engaged with groove  26 . Thus, when a lap  12  is to be removed, the actuator  22  is actuated overcoming the spring bias in the opposite direction and unlocks the blades  24  from the lap  12 . With the blades unlocked (disengaged from the lap groove  26 ) the lap easily is lifted off of tower  18 . Laps could be automatically removed and replaced using a pick and place machine with a vacuum cup at the working end thereof which has been created by Gerber Coburn. The cup being selectively energized and deenergized. 
     In the event that power to the drive  68  is lost, the device is in the failsafe or locked mode. The device can still be actuated manually by a user gripping actuation arm grips  100  and  102  and moving them to overcome the spring bias of the system. 
     Referring back to FIG. 5, another important feature of the invention is illustrated. It is desireable to provide pin  25  which extends radially outwardly from tower  18  to positively locate lap  12 . While blades  24 , secure lap  12  from moving in the z-axis i.e. prevent removal of lap  12  from tower  18 , they do not prevent rotation about the z-axis. For cylindrical laps, rotation about the z-axis causes significant axis problems in a lens produced thereby and that lens would necessarily be defective. Pin  25  prevents rotation about the z-axis and so produces accurate axis for cylindrical correction. Lap  12  is simply and easily engaged with pin  25  by notch  27 . Notch  27  is preferably machined into lap  12  from a bottom edge  29  thereof (see FIG. 5 for location). In one embodiment the notch  27  is flared at a bottom portion thereof to allow for some tolerance in aligning lap  12 . As lap  12  moves into full engagement with tower  18 , pin  25  moves into the indexed position of notch  27  and the lap  12  is aligned properly and prevented from rotational movement about the z-axis. 
     Finally, FIG. 7 provides a view of a seal groove  104  that receives a seal such as an o-ring to pressure tightly seal the junction between the carrier  20  and the housing (not show). This is advantageous for other aspects of the system of which the invention forms a part. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.