The present invention relates to an arbor for lathe cutting lenses, especially contact lenses, from a blank or button, and a method and apparatus for making the arbor.
A conventional method of manufacturing lenses, especially contact lenses, involves lathing the lens from a cylindrical blank of polymerized lens material (such cylindrical blanks commonly referred to as a xe2x80x9cbuttonxe2x80x9d). The buttons may be cut initially from rod stock or sheets, or individually cast in cups using a curable liquid monomeric composition. Additionally, lenses may be lathe cut from a semi-finished lens blank, i.e., a blank having one molded-in lens surface, where the opposite lens surface is lathed to obtain a second desired lens surface and an article with a final contact lens shape.
While it is possible in some cases to insert the lens blank directly into the lathe collet, it is more typical to first attach the button to a separate pin or xe2x80x9cblockxe2x80x9d with an adhesive, the opposite end of the block being configured for removable insertion into the collet of the lathe. While the block and button are turned, the desired concave or convex curve is lathed into the exposed end of the blank. Eventually, the lathed article must be separated from the block (a process often referred to as xe2x80x9cdeblockingxe2x80x9d). However, a drawback of such lathe cutting operations is that the blocking and deblocking steps may consume a significant amount of time and are prone to error, especially when it is necessary to maintain axial alignment between the block and the article being lathe cut.
U.S. Pat. No. 4,921,205 discloses a process where a semi-finished blank is cast between a plastic mold cup and a radial die, for example, the radial die may form a finished concave lens surface. The radial die is removed, with the cast blank remaining adhered to the mold cup. The mold cup and blank assembly may be shipped to a lab for manufacture of a contact lens, by first machining the mold cup off the blank, then machining away the extraneous portion of the blank to form the second, opposite lens surface. Presumably, the cast surface of the blank would be adhered to a block for these machining operations, similar to other conventional methods for lathe cutting a lens surface from a semi-finished blank.
U.S. Pat. No. 5,110,278 discloses a process for producing toric contact lenses. A semi-finished blank is cast in an arbor having a cup-shaped top portion. The arbor also includes a hollow bottom portion integrally formed as a one-piece molding with the top portion. This hollow bottom portion is mounted on a lathe spud, for lathe cutting the exposed front surface of the semi-finished blank retained in the cup-shaped top portion. Each arbor is injection molded, and the arbors are not reusable since the lathing operation involves simultaneous cutting of the lens blank and sidewalls of the casting cup top portion.
The present invention provides an arbor for lathe cutting lenses, especially contact lenses, from a blank or button, and a method and apparatus for making the arbor. The arbor is designed for the mounting of a lens mold with a cast lens blank therein during lathing of the lens blank, and the arbor is made in a manner to ensure the lens mold is axially aligned with the arbor. The arbor can be reused for lathe cutting of multiple lens blanks retained in their respective lens molds.
According to a first embodiment, this invention provides a method for making an arbor comprising: providing a lens mold that includes a lens-forming molding surface and an opposed non-molding surface, and placing a hardenable material (for example, liquid or pliable solid material) between the opposed surface of the lens mold and an end of an arbor; moving the lens mold and the arbor towards one another while maintaining axial alignment therebetween, whereby the hardenable material is pressed between and contacts a surface of the lens mold and a surface of the arbor end and conforms to said surfaces; hardening the material to form a hardened replica of the lens mold surface contacted by said material; and separating the arbor with the hardened material attached thereto from the lens mold. The arbor may be placed on a lathe collet, a second contact lens mold including a lens blank cast therein may be secured to the hardened material of the arbor, and a desired lens surface may be lathe cut in the lens blank. This same hardened material of the arbor may be used repeatedly to lathe cut a desired lens surface in multiple lens blanks retained in their respective lens molds.
According to preferred embodiments, the central axis of the lens mold is congruent with the central axis of the arbor when said material conforms to the lens mold and arbor end surfaces. Also, the lens mold may be secured in a first fixture to inhibit axial movement thereof, and the arbor may be secured in a second fixture to inhibit axial movement thereof. These first and second fixtures may include complementary tapered surfaces for maintaining axial alignment of the lens mold and arbor secured thereon. The first and second fixtures may include a bore for securing the lens mold and arbor, respectively.
According to other preferred embodiments, the lens mold includes a sidewall depending from the opposed, non-molding surface, such that the hardenable material contacts and conforms to an inner surface of the sidewall, and wherein the arbor end is received in a space surrounded by the sidewall. At least a portion of the sidewall inner surface is preferably noncylindrical.
According to a second embodiment, this invention provides a method comprising: casting a lens blank in a lens mold; securing the lens mold with the blank on an arbor end, the arbor end including a replica of an inner surface of the lens mold; and lathe cutting a lens surface in the blank.
According to other embodiments, the invention provides an arbor comprising a first end for mounting on a lathe collet and an opposed second end, and a hardened material surrounding and adhered to the second arbor end, the hardened material having an outer surface that is a replica of an inner surface of a contact lens mold.