US 3704558 A
A lens block for plastic lens having a circumferential lens blank supporting ledge which is provided with a pair of diametrically opposed vents or grooves. One of the grooves is of a size to permit the egress of air but not of the blocking material.
Description (OCR text may contain errors)
Umted States Patent 1 1 3,704,558 Sarofeen [451 Dec. 5, 1972 [$4] LENS BLOCK 3,140,568 7/1964 Beasley ..5l/277 X 3,355,342 11/1967 Lanham ..51/277 X  5'' Swim" 3,353,307 11/1967 Sarofeen ..s1/277 x Helghts, Va.
 Assignee: Coburn Manufacturing Co., Primary Exami" Dna}d Kelly Muskogee. ok|a Attamey-John J. Byrne  Filed: Feb. 24, 1971 21 App1.No.: 118,318 [571 ABSTRACT A lens block for plastic lens having a circumferential lens blank supporting ledge which is provided with a US. Cl. LP, 5 pair of diametrically pp ed vents or grooveso f  Int. Cl .3241: 41/06, B22d 17/24 the grooves is of a size to permit the egress f air but  Field of Search ..51/277, 229, 216 LP, 217 R, not f the blocking i l.
 References Chad 5 Claims, 3 Drawing Figures UNITED STATES PATENTS 3,383,808 5/1968 Deshayes .....$l/277 X P'A'TENTEDHH: 5 m2 3704.558
INVENTOR GEORGE M. J. SAROFEEW LENS BLOCK This invention relates to lens blocking and more particularly to a lens blocking device for use with plastic lens.
Lens blanks are blocked for purposes of providing a means by which the lens blank is chucked into a lens processing apparatus such as a lens grinding and polishing machine. A lens block generally includes a concave surface on one side for receiving the convex surface of the lens to be treated or processed, and a body portion on the other side including a chucking surface having recesses therein for purposes of centering the block and the attached lens in a processing apparatus. Conventional practices include molding or casting the lens block from a low-melting point alloy or the like directly onto the convex surface of the lens blank. The lens blank may or may not be provided with a suitable coating to facilitate the release of the block from the blank after the processing thereof is finished. Perhaps a more accepted practice involves the use of a preformed lens block of a suitable metal which is adhered to the lens blank by means of a low-melting point alloy which is injected into a cavity formed between the block and the lens blank. It is this type of lens block with which this invention is concerned.
The above-mentioned blocking devices and methods are quite acceptable when dealing with glass lens blanks, wherein, due to the hardness of the glass, the uneven shrinkage or expansion of the blocking agent during the cool-down phase has little if any effect on the glass. However, expansion and contraction do cause problems when working with a relatively soft or flexible plastic lens, which lenses are becoming increasingly more popular. Therefore, there is a need to provide a blocking device which will not deform or otherwise cause zonal aberrations in the surface of the more readily deformable lens blank.
it is an important object of this invention to provide a lens blocking device which will permit the lens blocking agent to freeze uniformly so that the heat and pressure from the blocking agent will not cause zonal aberrations in the plastic lens being blocked. Generally speaking, there are two types of alloys that can be used, one which shrinks and the other type that expands. This invention is directed particularly toward the expandable type and it is a particular object of this invention to control the pattern of pressure exerted on the plastic lens blank upon expansion of the blocking agent during freezing.
It is desirable to provide a greater supporting surface for a plastic lens blank than it has heretofore been provided for a glass lens blank. This problem has been pointed out in the prior art and is dealt with in U.S. Pat. No. 3,140,568 to Beasley dated July 14, 1964, entitled LENS BLOCKING DEVICE, which discloses a lens block which is substantially coextensive with the plastic lens which it supports. Beasley discusses to a limited extent the problem of distortion of the plastic lens due to uneven shrinkage of the blocking material during the freezing thereof. The particular blocking agent disclosed therein is pitch or blocking wax. Beasley attempts to solve the problem of uneven shrinkage by providing a uniform layer of blocking material, which layer is created by placing a surplus of pitch or other bonding material between the blank and blocking body and then pressing the lens blank against the blocking body. The surplus pitch is forced outwardly between a plurality of gaps around the periphery of the block, which gaps define spaced lens blank supporting ledges. This process is particularly messy and involves an uneconomical usage of blocking material. Further, by providing a plurality of gaps as does the Beasley patent, the total area of support for the lens blank is somewhat lessened. Further, in the Beasley patent, there is no systematic method of placing the pitch between the lens blank and the lens block such that the air pockets which create uneven pressure areas are eliminated.
it is an object of this invention to provide a blocking device and a method of blocking lens whereby the blocking material is injected into the cavity between the lens blank and the lens block in such a manner as to exhaust all air therefrom.
It is a further object of this invention to provide a lens block having an inlet hole therein for the blocking material which also serves as a pressure absorber for absorbing abnormal pressures exerted by the blocking material in the cavity.
These objects are obtained by providing a lens block having a front side and a rear side, with the front side being concave in configuration to receive the convex surface of a lens block to be processed. The rear side is provided with means for mounting the block onto a lens blank processing apparatus. The front side of the block is provided with a lens supporting ledge circumscribing a concave surface for supporting a lens blank in spaced relationship to the concave surface to define a uniform thickness, blocking-material receiving cavity between the lens blank and the lens block. A blocking material inlet extends axially of the lens block and communicates the cavity to a suitable blocking material reservoir and injection apparatus. The lens-supporting ledge is provided with a first groove or passageway therein and a second groove or passageway diametrically opposed to the first groove, with the second groove being of a substantially less cross-sectional diameter than the first groove. ln operation, the lens block is supported on the lens blocking apparatus in tilted position such that the smaller groove is on the lower portion of the lens block and the larger groove is on the upper portion of the lens block. The blocking material is injected into the cavity and flows downwardly toward the smaller groove forcing air from the cavity and out through the smaller aperture. However, the aperture is of a size which prohibits the passage of lens blocking material therethrough. The lens blocking material then freezes at the opening and fills upwardly toward the larger opening therefrom and extrudes through the opening to indicate that the cavity has been filled. To prevent the exertion of abnormal pressures against the lens blank, the inlet conduit or passageway serves as a shock or pressure absorbing column whereby the blocking material flows back toward the reservoir, relieving pressures in the cavity.
These and other objects of the invention will become more apparent to those skilled in the art by reference to the following detailed description when viewed in light of the accompanying drawings wherein:
FIG. 1 is a perspective view showing the lens block of this invention in position on a lens blocking apparatus,
FIG. 2 is a plan view of a lens block of this invention, and
FIG. 3 is a cross sectional view taken along lines 3-3 of FIG. 2 showing in phantom the positioning of a lens blank thereon.
Referring now to the drawings wherein like numerals indicate like parts, the numeral generally indicates the lens block of this invention. In FIG. I, the lens block is shown in position on a lens blocking apparatus 12 which is of a type disclosed in US. Pat. No. 3,468,366, dated Sept. 23, I969, to Jack M. Suddarth, entitled LENS BLOCKER. The lens blocking apparatus is provided interiorly with a reservoir of molten, low-melting point alloy which is injected by a suitable hand pump, not shown but disclosed in the abovementioned patent, into the uniform-thickness cavity 14 between the lens blank 16 and the lens block 12. It is to be noted that the lens block, and, therefore, the lens blank are supported in an inclined or angulated attitude.
The lens block includes a front side having a concave surface 18 and a lens-supporting ledge 20. The lenssupporting ledge is slanted to receive and conform to the convex surface of the lens blank 16 and is raised above the concave surface 18 such that the lens blank defines a cavity with the concave surface 18 when it is seated on the ledge 20. The rear side 22 of the lens block is provided with centering recesses 24 which serve to align the lens block in a lens processing apparatus when it is chucked therein.
A conduit 26 extends axially of the lens block and communicates the cavity 14 with the blocking material reservoir. It is through this passageway that the lens blocking material is injected into the cavity 14.
The ledge is provided with diametrically opposed grooves 28 and 30 which, along with the surface of the lens blank resting on the ledge, defines a passageway communicating the cavity with the atmosphere. The groove 28 is considerably smaller than the groove 30 in cross-section, with the size of the groove 28 being sufficient to permit the egress of air but not of the blocking material.
In operation, blocking material is injected through passageway 26 and into cavity 14, and, due to the inclined attitude of the block and the lens blank supported thereon, the material first flows downwardly toward the smaller groove 28 and pushes air from the cavity out through the groove 28. The groove, however, as mentioned above, is so small that the blocking material cannot pass therethrough. The low-melting point alloy then freezes and seals the opening 28. Continued injection of the blocking material into the cavity 14 causes the level of the material to rise toward the larger opening 30 pushing air outwardly through the opening 30 and eventually extruding through the opening 30 to indicate that the cavity is filled. The thickness of the cavity 14 is constant throughout and the lens block is of such dimensions that it supports substantially the entire area of the lens blank.
Any undue pressures, instead of being forced against the lens blank surface, will be absorbed by the material in the inlet passageway 26. In other words, the material in the cavity will flow back through the passageway 26. In this manner, the passageway 26 acts as a pressure absorber. It can be seen that by using the lens block of this invention in the manner described, a uniform layer of blocking material will be for ed wi out exerting undue pressures against the su ace of t e plastic lens blank. The probability of creating zonal aberrations in the lens blank will be minimized.
In a general manner, while there has been disclosed an effective and efficient embodiment of the invention, it should be well understood that the invention is not limited to such an embodiment as there might be changes made in the arrangement, disposition, and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.
1. A lens block for use in lens blank processing apparatus wherein said lens block is angularly disposed comprising front and rear sides, a concave surface on said front side and means on said rear side for mounting said block on lens blank processing apparatus, a lens supporting ledge circumscribing said concave surface for supporting a lens blank in spaced relationship to said concave surface to define a blocking material receiving cavity, conduit means communicating said front and rear sides and providing an inlet for blocking material to said cavity, a first passageway in said ledge leading from said chamber to the exterior of said block, and a second passageway of smaller cross-sectional dimensions than said first passageway in said ledge diametrically opposite said first passageway and leading from said chamber to the exterior of said block, said block when mounted on said apparatus is angularly positioned to define upper and lower portions with said second passageway being in said lower portion.
2. The lens block of claim 1 wherein said second passageway is of a size sufficient to permit the passage of air therethrough, but not the blocking material, and said first passageway is of a cross-sectional size sufficient for the passage of said blocking material.
3. The lens block of claim I wherein said ledge is sloped radially inwardly and said lens blank and said surface is of constant dimensions.
4. The block of claim 1 wherein said conduit means extends axially of said block and is disposed adjacent the center thereof.
5. The block of claim I wherein said cavity is of uniform thickness.
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