This invention relates generally to equipment used in making ophthalmic lenses and more particularly concerns equipment used for blocking and chucking lenses for lens generating, fining, polishing and edging.
In known lens making processes, after selection of an appropriate lens blank for a given prescription, the blank is marked for blocking and protective tape is applied to its entire front surface. A block also covering the entire surface is then applied to the tape. To the extent that the contour of the front face of the lens blank differs from that of the block, gaps or voids will occur between the tape and the block. To square up the lens blank face, an alloy is pumped in liquid state into the gaps or voids. When cooled and solidified, the alloy provides rigidity to the lens. The blocked lens blank is mounted in a lens generator to generate the desired lens and transferred to a finer/polisher for polishing the lens surface. The block is removed after polishing by shocking the block to break its bond to the tape. The alloy is reheated to a liquid state and reclaimed. The cleaned lens is inspected for power and quality, and, if satisfactory reblocked for the edging step of the lens making process using a much smaller diameter block. Blocking for edging is generally accomplished by inserting a double sided adhesive pad between the block and the lens. After the lens has been edged, the block is removed by twisting the block to break the adhesion.
The above lens making process is relatively expensive and inefficient. Twice blocking the lens is a time consuming and tedious operation. Alloy injection is costly and time consuming. It necessitates additional equipment for heating and injecting the alloy into the void. It causes a delay in the process until the alloy has sufficiently cooled and solidified. The alloy reclamation process is also costly and time consuming, requiring the alloy to be reheated to liquification for collection. Additional equipment is also required for its reclamation from the lens. Moreover, the use of alloys in the process will likely be discontinued since some of them contain cadmium and lead, materials which may be banned by governmental agencies due to health considerations.
While it is desirable to eliminate the need for multiple blocking steps and the use of an alloy which must be liquified for injection and again liquified for retrieval, the lens making process complicates possible solutions to these problems. The lens generating, fining and polishing steps result in the application of forces to the face of the lens which may cause the lens to flex and distort. Consequently, the block and chuck used in these steps must sufficiently complement and support the surface of the lens so as to prevent this deflection or distortion. On the other hand, the block used in the lens edging step of the process must be sufficiently small so that the edging equipment will not come into contact with the block. This is why presently known lens edging blocks are significantly smaller than presently known lens generating blocks.
It is, therefore, an object of this invention to provide a single lens block suitable not only for the lens generating, fining and polishing steps but also for the lens edging step of the lens making process. Another object of this invention is to provide a lens block chuck which provides support for the front face of a lens against cutting forces applied to the lens as it is being generated, fined and polished. Another object of this invention is to provide a lens block and lens block chuck which, when used in combination permit the chuck spindle shaft to contact the lens surface and thus serve as a reference for lens center thickness control. It is also an object of this invention to provide a lens block having a through hole permitting lens power and quality inspection without removal of the block from the polished lens. Yet another object of this invention is to provide a lens block which can be secured to the lens by use of a quick curing or instant adhesive. Another object of this invention is to provide a lens block which facilitates use of one or more preformed or molded wafers to build up the front surface of the lens blank to an apparently spherical contour to which the block can be securely applied. And it is an object of this invention to provide a lens block which, in combination with one or more wafers inserted between the block and the chuck, distributes torsional stress over a greater area of the lens surface than is possible with the block alone.