Abstract:
Method for removing unwanted excess material from a mold section is particularly adapted for removing a monomer ring adhered within a reservoir of a female mold section used to mold a contact lens. The invention involves piercing the monomer ring and rotating the piercing members (e.g., annularly spaced pins) relative to the mold section whereby the monomer ring is sheared from the mold section to which it was adhered while the molded lens is left intact in the mold section.

Description:
This is a divisional of Application No. 09/628,517, filed Jul. 31, 2000, now U.S. Pat. No. 6,368,096. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to molding of articles of manufacture, and more particularly relates to methods and apparatus for separating excess, unwanted lens material from a mold surface. The present invention has particular application to the production of molded ophthalmic lenses such as contact lenses and intraocular lenses. 
     Static cast molding of contact lenses is known. See, for example, U.S. Pat. No. 5,466,147 issued to Bausch &amp; Lomb Incorporated, the entire reference of which is incorporated herein by reference. A single mold unit for making a single lens comprises a female mold section having a concave optical surface and a male mold section having a convex optical surface. The female and male mold sections are complimentary shaped and are brought together to form a lens-molding cavity between the facing concave and convex optical surfaces of the female and male mold sections, respectively. 
     Although less popular than full cast molding, forming lenses by spin-casting is also known where lens material is deposited into a female mold section and spun to form the anterior surface of the lens. The posterior surface is then formed by a lathe cutting operation. In this method of lens manufacture, excess material may also form on the female mold section with may require removal prior to lens release from the mold. 
     The basic process for cast molding a lens is as follows. A quantity of liquid lens material is dispensed into the concave optical surface of the female mold section and the male mold section is seated upon the female mold section with the concave and convex surfaces thereof facing one another to form a lens-shaped mold cavity. The joined female and male mold sections form a single mold unit which is subject to a curing cycle (e.g., by thermal or UV radiation) thereby causing polymerization of the lens material in the mold cavity. Once the lens material has cured, the male and female mold sections must be separated to retrieve the cured lens. 
     The opening or release of the mold sections must be carried out in a manner which will not harm the delicate lens. Once the lens has polymerized in the mold cavity, the lens and any excess lens material will have an adhesive bond to the opposite concave and convex mold surfaces. Thus, the release of the male mold section from the female mold section must be of a force strong enough to break the adhesive bond of the lens and excess lens material to the opposing mold surfaces, yet not so forceful or haphazard that the optical surfaces of the lens are harmed by the release process. Should the lens crack or be otherwise damaged during the mold release process, the lens must be scrapped, thereby lowering the output yield and increasing manufacturing costs. 
     Once the mold sections have been separated, the lens will adhere to one of the mold surfaces and must therefore be released from the mold section on which it is retained. Both wet and dry release methods of lens release have been proposed in the prior art. In wet lens release methods, an aqueous solution is used to wet the hydrophilic lens which absorbs water and swells, causing the lens to separate from the mold surface. In dry release methods, the lens is removed from the associated mold surface while still in the dry state. The adhesive bond between the lens and mold surface is broken, usually by application of a force to the mold body, for example by squeezing or pressing against the non-optical surface of the mold to move the mold surface relative to the rigid lens. Once the adhesive bond has been broken, the lens is retrieved, for example by a vacuum picking tool. 
     To ensure that the mold cavity is completely filled with the liquid lens material during the molding process described above, the quantity of liquid lens material dispensed in the female mold section is purposely greater than that needed to form the lens. When the male mold section is seated upon the female mold section, the excess liquid lens material is expelled from the mold cavity. This excess liquid is typically held in a reservoir, groove or flange surrounding the mold cavity and is cured along with the lens. The cured excess material is typically referred to as a “monomer ring” or “hema ring” in the contact lens art depending on the specific lens material used. The term “monomer ring” will be used herein for convenience, although it is understood this term is used broadly herein to cover any type of lens material employed. 
     During mold separation, the monomer ring will usually adhere to one of the mold sections with the monomer ring usually retained in the female mold section along with the lens. Should the lens be released and removed from the female mold surface without prior removal of the monomer ring from the reservoir, the lens edge will likely be damaged due to interference with the monomer ring. This problem is illustrated in prior art FIG. 5C herein. Presence of the monomer ring can also interfere with downstream processes and machinery. It is thus desirable to release and remove the monomer ring from the female mold section prior to release and removal of the lens therefrom. 
     Various monomer ring removal processes have been employed in the prior art, none of which has proven very satisfactory. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward a method and apparatus for removing a monomer ring from the mold section to which it is adhered following mold separation. The monomer ring may be located on a flange, groove, or reservoir surrounding the molding surface. 
     The present invention is particularly useful for removing cured excess material formed in contact lens or intraocular lens molds, although it is equally applicable to other molds requiring removal of excess material. Excess material in an ophthalmic mold, also known as a monomer ring, can cause damage to the molded lens if the monomer ring is not released and removed from the mold section prior to release and removal of the lens from the mold section. 
     In the preferred embodiment, following the curing stage, the mold is opened and the mold section to which the monomer ring and lens are adhered is presented for removal of the monomer ring while leaving the lens unharmed and intact. The monomer ring is removed by a plurality of members (e.g., pins or blades) which descend from a location directly above the mold section to pierce the monomer ring but not so deep as to penetrate the mold section. The pins then rotate which shears the monomer ring free of the mold section. The pins are then raised, carrying the monomer ring along with it for disposal. Thereafter, the now monomer ring-free mold section having the lens adhered thereto is transferred to a lens release station and further downline processing as desired. As used herein, the word “pierce” is broadly interpreted to mean any device or member capable of engaging and moving the monomer ring relative to the mold. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a prior art contact lens mold comprising a male mold section spaced above a lens and a female mold section; 
     FIG. 2 is an enlarged, cross-sectional view of the female mold section of FIG. 1; 
     FIG. 3 is an enlarged, fragmented, cross-sectional view of a prior art contact lens mold in the process of molding a contact lens therein; 
     FIG. 4 is the view of FIG. 3 showing the mold in the fully closed position; 
     FIGS. 5 a-c  are enlarged, detail views of the reservoir area of the mold of FIGS. 1-4 in sequential process steps of lens cure, mold separation and lens and monomer ring release, respectively; 
     FIG. 6 is a perspective view of an apparatus for carrying out the method of the present invention; 
     FIG. 7 is a top plan view of FIG. 6 with certain parts not shown for clarity; 
     FIG. 8 is a cross-sectional view of the apparatus as taken along the line  8 - 8  in FIG. 6; and 
     FIG. 9 is an enlarged, detail view of the part of the apparatus of the present invention which engages the female mold section in the intended manner. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1-5, a prior art mold  10  for cast molding an ophthalmic lens  12  is seen to comprise a female mold section  14  having a concave optical surface  14   a  and a male mold section  16  having a complimentary shaped convex mold surface  16   a.  In cast molding of an ophthalmic lens  12 , a liquid lens material  18  is dispensed into the concave surface  14   a  of the female mold section  14 . The male mold section  16  is seated upon the female mold section  14  until the mold surfaces  14   a,    16   a  thereof are closely adjacent as seen in FIG.  4 . As the mold surfaces move toward each other, excess liquid lens material is expelled into a reservoir  20  located peripherally of the mold surfaces  14   a,    16   a  (FIG.  4 ). U.S. Pat. No. 5,466,147 discloses such a mold for molding lenses, especially contact lenses. Upon polymerization, the lens material between the mold surfaces  14   a,    16   a  is cured to form a lens  12  (FIG.  1 ), together with the excess lens material  18 ′ located in reservoir  20  which, in the cured state, is referred to as a monomer ring denoted by reference numeral  18 ″ seen in FIGS. 5 a-c.    
     The &#39;147 patent recognized the problems associated with the attempted removal of the lens prior to removal of the monomer ring from a mold section which is illustrated herein in FIGS. 5 a-c.  FIG. 5 a  illustrates opening of the mold once the lens material has been cured where the male mold section  16  is lifted from the female mold section  14 . As is typically the case in this type of mold design, the lens  12  and monomer ring  18 ″ remain adhered to the female mold section  14 . In the mold design of the &#39;147 patent, the female mold section includes a knife edge  14   b  which interacts with an annulus  16   b  formed on the male mold section  16  to form the lens edge  12   a.  As seen in FIG. 5 c,  removal of lens  12  from the female mold section  14  without having first removed the monomer ring  18 ″ may result in accidental engagement between the lens edge  12   a  and the monomer ring  18 ″ which could irreversibly damage the lens edge  12   a.  This problem is exacerbated when a wet lens release method is employed which involves hydrating the lens which swells and releases from the female mold surface. Due to the swelling of the lens, the lens edge may push against the monomer ring and be damaged thereby. Although the problem is pronounced in the wet lens release method, there remains the chance of lens damage in a dry lens release method as well. 
     The &#39;147 patent describes a method of releasing the monomer ring with removal of the male mold section by incorporating a feature into the male mold section to which the monomer ring will attach upon cure (see feature 79 in FIGS. 18 and 19 therein). In the &#39;147 method, the monomer ring detaches from the female mold section upon lifting the male mold section therefrom. Since it is not always possible to incorporate this type of monomer ring removal mechanism in a particular mold design, the present invention offers a method of monomer ring removal from the female mold section which may be employed on molds having a variety of different mold designs. 
     FIG. 5 b  illustrates an enlarged cross-sectional area of the female mold section  14  where the lens edge  12   a  and monomer ring  18 ″ lie within the female mold section following removal of the male mold section  16  therefrom. The female mold section  14 , lens  12  and monomer ring  18 ″ is in this condition upon presentation to the apparatus and method of the present invention for removing the monomer ring  18 ″ therefrom, the preferred embodiment of which is illustrated in FIGS. 6-9. 
     A monomer ring removal mechanism is indicated generally by the reference numeral  30  which may be mounted upon a table  32  which is part of a contact lens production line. Upstream and downstream processing may vary according to need and is not critical to the operation of the invention described herein. Typical upstream processing would include mold production, monomer fill of the mold, mold clamping and curing, and opening of the mold. Once the mold has been opened, the male mold section  16  is set aside and the female mold section  14  is presented to the monomer ring removal mechanism  30 . Once the monomer ring has been removed by mechanism  30  in the manner to be described, the female mold section  14 , now having only a lens  12  adhered thereto, is transferred to subsequent processing stations such as lens release, with the lens further undergoing lens hydration and extraction, lens packaging and inspection as required for the particular production process employed. 
     As seen in FIGS. 6 and 7, the monomer ring removal mechanism  30  may be mounted upon a table  32  having a rotating carousel  34  for handling of the female mold sections  14  through this station, although other mold handling means may be employed as desired. In the embodiment of FIGS. 6 and 7, the female mold sections  14 , with respective lens  12  and monomer ring  18 ″ intact, are delivered onto table  32  at location  36  (e.g., by a conveyor  46 ). As a female mold section  14  is delivered onto table  32 , carousel  34  is indexed in the direction of arrow  35  whereupon female mold section  14  is captured by one of a plurality of peripheral recesses  34   a  in carousel  34  and move together with the next indexing movement of the carousel  34 . This is continued with each successive recess  34   a  engaging a respective female mold section  14  at input  36 . To ensure limited radial movement of the female mold section  14  within a respective recess  34   a,  a spool  38  may be fixed to carousel  34  adjacent each recess  34   a  which restrains the respective female mold section  14  as the carousel is indexed about table  32 . 
     Mechanism  30  is shown mounted to table  32  at a location approximately 180° from the mold section input  36 , although this spacing may vary as desired. The positioning of the mechanism  30  is such that each sequential recess  34   a  will come to rest directly beneath mechanism  30  upon each indexed movement of carousel  34 . As seen in FIG. 7, the location of mechanism  30  includes a second spool element in the form of a biasing pawl mechanism  40 ,  42  which act to bear against the female mold section to restrict substantially all rotational movement thereof within recess  34   a  during engagement of the female mold section  14  with mechanism  30 . Once mechanism  30  has removed the monomer ring  18 ″ from a respective female mold section  14  in the manner to be described, the carousel  34  is again indexed about arrow  35  whereupon the female mold section  14  is eventually output from table  32  at location  44  by a conveyor  46 , for example, which transports the female mold section  14  and adhered lens  12  to a lens release and removal station (not shown). It will be appreciated that once a female mold section  14  has been transported off table  32 , the recess  34   a  in which it was housed is now empty as it travels again toward input  36  to capture a new female mold section for processing by mechanism  30 . 
     Attention is now turned to the monomer ring removal apparatus and method of the invention and a preferred mechanism  30  by which this method may be carried out. As seen in FIGS. 8 and 9, a female mold section  14  having a lens  12  and monomer ring  18 ″ adhered thereto is presented beneath mechanism  30  by action of carousel  34  as discussed above. Mechanism  30  is mounted upon a linear slide  48  (FIG. 6) for reciprocating vertical movement of mechanism  30  with respect to table  32 . Once a female mold section  14  is in position beneath mechanism  30  as seen in FIG. 8, the linear slide  48  is activated which lowers mechanism  30  to remove monomer ring  18 ″ therefrom without harming the associated lens  12 . 
     More particularly, mechanism  30  includes a rotary actuator  49  coupled to a shaft  50  which carries a pin disk  51  having a plurality of annularly spaced pins  52  fixed thereto and extending downwardly therefrom. Pins  52  operate with mechanism  30  to pierce monomer ring  18 ″, loosen it from female mold section  14  upon rotation of shaft  50 , and then lift the ring  18 ″ free of the female mold section upon raising mechanism  30  and pins  52 . Any number of pins  52  may be used, however, three to four equally, annularly spaced pins  52  is most preferred. It is also envisioned that blades or other piercing shapes may be used in place of or in combination with pins  52 . 
     To ensure that pins  52  pierce only the monomer ring  18 ″ and not the female mold section  14  itself, a stop is incorporated in mechanism  30  in the form of a guide plate  54  which is fixed relative to pins  52 . As mechanism  30  is lowered, the lower surface  54 ′ of guide plate  54  engages mold shoulder  21  located outwardly adjacent the periphery of reservoir  20  (see also FIG.  2 ). Upon contact of guide plate  54  with female mold section  14 , slider  48  stops its downward travel. By fixing the position of guide plate  54  relative to the tips of pins  52 , and knowing the distance between the surfaces of shoulder  21  and reservoir  20 , mechanism  30  may be calibrated to ensure the tips of pins  52  penetrate only the monomer ring  18 ″ and do not penetrate the female mold section  14 . 
     A second shaft  56  telescopes within a longitudinal opening  50   a  in shaft  50  and is axially movable therein. A stripper plate  57  is provided at the lower end of shaft  56  and includes a plurality of annularly spaced openings  57   a  wherethrough pins  52  freely extend, respectively. A helical spring  58  is provided about shaft  56  between internal shoulder  50   b  of shaft  50  and stripper plate  57  whereby shaft  56  is biased by spring  58  in a downwardly extended position relative to shaft  50 . The downward travel of shaft  56  is limited by dowel  60  and in the full downward extension thereof, the free ends of pins  52  are concealed within the respective openings  57   a  of stripper plate  57 . 
     As slide  48  lowers mechanism  30  over a respective female mold section  14 , the lower surface  57   b  of stripper plate  57  engages the reservoir surface of mold section  14  which pushes shaft  56  in upwardly within shaft  50 . Shaft  50 , together with pins  52 , continues its downward travel until guide plate  54  engages mold surface  21  and stops further downward travel of slide  48  as explained above. It will be appreciated that due to the upward travel of shaft  56  within shaft  50  which carries pins  52 , the free ends of pins  52  extend and project through their respective openings  57   a  in stripper plate  57  and pierce the monomer ring  18 ″ located in mold reservoir  20 . Once this has happened, rotary actuator  49  is activated which rotates shaft  50  together with pins  52  which shears the monomer ring  18 ″ from its associated mold reservoir  20 . In a preferred embodiment, shaft  50  rotates about 180° with the monomer ring  18 ″ shearing from reservoir surface  20  at about 10° of rotation. Slide  48  then raises with shaft  50  together with pins  52  and monomer ring  18 ″. 
     Once the lower surface  57   b  of stripper plate  57  has lifted free of the reservoir surface  20 , spring  58  biases shaft  56  in a downward direction relative to shaft  50 , thereby retracting pins  52  within respective openings  57   a  which strips the monomer ring  18 ″ from the pins  52 . If desired, a source of compressed air (not shown) may also be delivered between shafts  50  and  56  to assist the biasing force of spring  58 . In order to prevent the monomer ring  18 ″ from free falling onto the surface of the female mold section  14  and lens  12 , one or more blowers are provided (not shown) which direct a stream of air between the stripper plate  57  and female mold section  14  which blows and directs the released monomer ring  18 ″ to a disposal chute (also not shown). Should the monomer ring  18 ″ fail to be lifted from the reservoir, one blower will still blow the monomer ring  18 ″ to the disposal chute. Also, a vacuum may be used instead of the blowers to remove the monomer ring  18 ″. 
     Once the monomer ring  18 ″ has been removed from the female mold section  14  as described above, carousel  34  is indexed to move the now monomer ring-free mold section  14  toward the exit location  44  where the mold section is now ready for lens release. At the same time, the next female mold section needing monomer ring removal is positioned beneath mechanism  30  for removal of its monomer ring  18 ″ in the manner described herein. 
     It will thus be appreciated that the present invention provides a novel method and apparatus for removing a monomer ring from a mold section which may be applied in an automated production line and which safely and quickly removes the undesired cured material from the mold reservoir without harming the delicate lens contained therein. Although the invention has been shown and described herein relative to preferred embodiments thereof, it will be appreciated to those skilled in the art that various modifications may be made to suit a particular production environment. The invention is thus not to be limited by the specific embodiments or molding applications shown and described herein, but rather should be interpreted in accordance with the spirit and scope of the claims which follow.