Abstract:
A retainer for retaining an abrasive pad on a lens making machine and an abrasive pad adapted to such retention comprises a retainer nestable with a lap of a lens making machine wherein when such retainer is nested, a pad placed upon said lap before nesting will be trapped in the desired position. The pad of the invention includes radially outwardly extending members beyond the working area of the pad whose purpose is to be trapped by the retainer. The invention enables automatic loading and unloading of pads on the lens making machine.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to the field of eyeglass lens production. More particularly, the invention relates to a device for retaining an abrasive pad on a lap for fining and polishing of lenses.  
           [0003]    2. Prior Art  
           [0004]    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.  
           [0005]    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.  
           [0006]    During fining and polishing operations, it is often necessary to lift the lens blank off of the lap and rinse the abrasive pad to remove lens material in the form of particulate that has built-up during the fining and/or polishing operations. To conventionally prevent the abrasive pad from separating from the mandrel during rinsing, a releasable adhesive is used to bond the pad to the mandrel. A difficulty associated with adhesively attaching the abrasive pad to the mandrel is that after extended periods of use it is often necessary to change abrasive. The adhesive can make separating the abrasive pad from the mandrel difficult and time consuming. In high production situations where abrasive pads are regularly replaced, significant amounts of time can be lost separating the abrasive pad from the mandrel, thereby adding to the time and expense associated with preparing lenses. For these reasons, the art is in need of an alternate pad retaining system which avoids lost time in connection with changing pads while concurrently also rendering the changing operation significantly less difficult.  
         SUMMARY OF THE INVENTION  
         [0007]    The above-identified drawbacks of the prior art are overcome or alleviated by the pad retaining system of the invention.  
           [0008]    The invention introduces unconventional pad geometry and an unconventional lap support. The features of these two elements function together to provide quick, easy and reliable pad retention on the lap while eliminating the difficulty of removal of the pad experienced by the prior art. The invention further renders such removal and replacement a very time efficient operation.  
           [0009]    The pad of the invention is oversized relative to conventional designs to provide surface area upon which to clamp without reducing the working abrasive surface of the pad. Pads generally are defined within a circle having a diameter of about three inches. The pads of the invention are defined by a circle having a diameter of about four and one-half inches. This provides a three quarter inch annular section of pad upon which to clamp the same. Adhesive is not required.  
           [0010]    Complementary to the pad described, a lap support including an actuator and a retainer are provided. The retainer is moveable between two positions: the first in which it is in close proximity to the surface of the lap and the second in which it has been distanced from the surface of the lap. In the first position, a pad is compressively retained between the retainer and the lap with compression being placed upon the annular area of the pad described. In the second position the compressive force of the first position is absent and a pad may be either removed from the lap or placed thereon.  
           [0011]    The retainer is actuated to move to the first and second positions by solenoid which is/are connected thereto through connecting rods. The retainer can be operated manually or automatically in response to conditions of the system.  
           [0012]    A significant benefit of the retainer system is that it allows automation of pad placement and replacement. Since adhesive is not required to retain the pad on the lap, a vacuum cup on a pick and place machine is employed to place and replace pads on the lap for retention without human intervention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    Referring now to the drawings wherein like elements are numbered alike in the several Figures:  
         [0014]    [0014]FIG. 1 is a plan view of a pad in accordance with the present invention;  
         [0015]    [0015]FIG. 2 is a perspective view of a retaining device in accordance with the present invention, with the retaining device in a first (closed) position;  
         [0016]    [0016]FIG. 3 is a perspective view of the retaining device of FIG. 2 in a second (open) position;  
         [0017]    [0017]FIG. 4 is a side elevation view of the retaining device of FIG. 2 in the first (closed) position;  
         [0018]    [0018]FIG. 5 is a side elevation view of the retaining device of FIG. 3 in the second (open) position;  
         [0019]    [0019]FIG. 6 is a top plan view of the retaining device of FIG. 2; and  
         [0020]    [0020]FIG. 7 is a schematic perspective view of an automatic loading and unloading system in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    A pad  10  of the invention will be understood by reference to FIG. 1. In order to simplify the discussion of the shape of the pad it is noted that a circumscription line  12  is a defining line which can be used for purposes of this discussion to delineate between a working area of the pad (inside line  12 ) used for fining and polishing (collectively referred to as “conditioning” herein) of a lens blank and a hold-down area of the pad exterior to circumscription line  12  which is used to retain the pad on the lap during conditioning operations. The portion interior to line  12  includes, in one embodiment, a central section  14  and a plurality of petals  16  (illustrated as seven). This portion of the design is known to the art and is currently used with adhesive backing in the conventional manner. The arrangement of petals and the mode of operation of the particular dimensions are known to the art.  
         [0022]    Outwardly of line  12 , it will be appreciated by review of FIG. 1, each petal  16  includes radially outwardly extending members  18  which in a preferred embodiment are about three-quarters inch long. Preferably, two members  18  are provided on each petal  16  each being about one-third inch wide. The arrangement is preferred because it facilitates balanced retention of the pad by the retaining device discussed herein below. It will be understood however that a single member  18  could be used if desired bearing in mind that the width of the member is adjustable as desired. If members  18  are made wider, materials cost is increased; if they are made thinner, structural integrity will be diminished. Thus, the width of members  18  requires consideration to balance these issues.  
         [0023]    The particular configuration of the two members  18  in a preferred embodiment (shown) is that they are spaced from one another on each petal  16  by about a quarter inch and that they are radiused. The configuration is preferred because it reduces the amount of material necessary to provide good retention of pad  10  in the retaining device of the invention. It will be understood that one could simply extend the radial length of petals  16  and achieve the function of the invention. More material, however, would be used in this instance and material cost would be undesirably increased. Thus, the configuration shown is preferred. It is also contemplated that one of ordinary skill in the art following exposure to this disclosure will be capable of producing other designs which fall within the scope of the invention and maintain the benefits thereof.  
         [0024]    Referring to FIGS. 2 and 3, the retaining device of the invention is illustrated in the closed and open positions, respectively. It will be appreciated that the device as illustrated is combinable with any type of lens conditioning machine and would replace the lap and lap support of those machines.  
         [0025]    In a preferred configuration, a lap  20  is attached to a lap cradle  24 . Cradle  24  is attached to a pair of tubes  26  which are preferably received in recesses at a bottom surface  28  of cradle  24 . Tubes  26  are secured in this location by any number of known means. Cradle  24  further includes a mounting flange  28  with several bolt holes  30  for connection with the machine (not shown). The tubes  26  are supported at bottom ends  32  by an appropriate portion of the lens blank conditioning machine (not shown). Tubes  26  house connecting rods  34  (FIG. 3) which actuate a retainer  36 . Rods  34  are bushed in tubes  26  by bushings  38  which preferably are constructed of bronze. Connecting rods  34  are actuated preferably by solenoids mounted on the lens blank conditioning machine (not shown). A preferred throw of the solenoids is illustrated by the difference in position of retainer  36  relative to cradle  24  in FIGS. 2 and 3 or  4  and  5 . As will be appreciated, the space created enables easy and effective manipulation of a conditioning pad.  
         [0026]    Lap  20  itself is supported by a cylindrical tower (support)  40  mounted directly to cradle  24 . A frustoconical skirt  42  (a part of lap  20 ) is mounted atop tower  40 .  
         [0027]    Retainer  36  is fixedly attached to connecting rods  34  at connecting sites  44  and is maintained in the fixed condition therewith by threaded fasteners. Centrally to retainer  36  is a frustoconical protuberance  46  out of plane with the balance of retainer  36 , which protuberance  46  is at an angle to substantially nest with the frustoconical tower  40  and skirt  42  of lap  20 . It is the nestability of these compartments that provides the compression force on the members  18  of pad  10  when the retainer  36  is in the closed position. The protuberance  46  may be integral with retainer  36  but in a preferred embodiment is a separate structure which is attached to retainer  36  by threaded connection or other reliable fastening arrangement.  
         [0028]    In operation, which can be well understood by a review of FIG. 5 in connection with the discussion hereunder, the device is opened by solenoids (not shown) and a pad  10  is placed in a centered relationship over lap  20 . It should be recognized that no adhesive is employed in a preferred embodiment although one could employ adhesive if desired. Adhesive use would reduce the ease of removal of the pad from the lap  20 . Once the pad  10  is properly positioned atop lap  20 , retainer  36  is brought downwardly and into close proximity or contact with carrier  24 . This action allows an inside surface  48  (FIG. 3) of protuberance  46  to come into contact with members  18  of pad  10 . The contact causes members  18  to bend downwardly toward frustoconical tower  40  and skirt  42  and become trapped against those features by inside surface  48 . In this condition, pad  10  is reliably retained on lap  20  and is ready for use. To change pads, the retainer  36  is raised to the second position and the pad is easily removed and replaced with another.  
         [0029]    The device described above allows for fully automatic initial placement of a pad and the replacement thereof. A conventional pick and place machine  50  illustrated schematically in FIG. 7 is modified to support a vacuum cup  52  of the operational end thereof. Machine  50  preferably is attached to a vacuum source via a line  54  or may provide its own vacuum source as desired. Machine  50  is programmable to take certain actions based upon sensor stimuli or passage of time. In the automatic system of the invention the action of the pick and place machine  50  will be to retrieve a first pad using vacuum and place it on the lap while the retainer  36  is in the open position. In one embodiment, the vacuum cup  52  is of a diameter that allows it to pass through the opening of retainer  36  to properly position the pad  10  on lap  20 . Machine  50  then allows sufficient time for retainer  36  to trap pad  10  as hereinbefore described and then releases the vacuum on the pad. The machine is then moved clear of the lap and pad and the lens procedure may continue or begin.  
         [0030]    According to its programming, the pick and place machine  50  will return to lap  20  and by vacuum, attach itself to pad  10  when that pad is to be removed. Retainer  36  will release pad  10  and machine  50  will move to a discard area and release vacuum to deposit the spent pad in this area. Machine  50  will then retrieve a new pad and place it on the lap as described above. Preferably, and in order to streamline the automatic operation, the new pads will be stored in a cylindrical housing so that the pick and place machine will only need to move to one place to pick up a pad. This entire operation is performable without human intervention and speeds the lens making process.  
         [0031]    It should be noted that the particular embodiment of the automatically loadable system of the invention wherein the pad is deposited and removed from lap  20  from above the retainer  36  is but one preferred embodiment and that machine  50  would be configured to deposit and withdraw pads from a side of lap  20  as well, if desired.  
         [0032]    In one embodiment of the invention, a controller is electrically connected to the lap retainer and the pick and place machine to coordinate movements. Moreover, sensors may be employed in various locations and for various purposes within the invention. One such purpose is to monitor the condition of a pad retained on the lap to determine when the pad requires replacement. The sensor is connected to the controller and the controller acts on a previously provided program upon receiving a signal from the sensor.  
         [0033]    The invention dramatically reduces the prior art&#39;s lost time for changing pads by economically providing the alternative of the foregoing embodiment of the invention.  
         [0034]    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.