Process to Edge and Polish Polycarbonate and CR 39 Lenses With Diamond Wheels

The present invention relates to a process and apparatus for edging and polishing of an ophthalmic lens and, more specifically, a process and apparatus for edging and polishing a surface of an ophthalmic lens comprising polycarbonate, CR 39 or glass, wherein the step of edging and polishing may be performed with a single machine and the step of polishing may be performed with a single polishing wheel.

In the lens grinding industry a great number of ophthalmic labs have sprung up with the advent of modern bevel edger machines. These machines are capable of taking a lens blank and grinding a final shape of a lens for fitting of the lens in a particular frame. Thus, a lens blank of the proper prescription is rough cut to the rough shape of the frame and thereafter a bevel edge is ground on the lens such that the lens will properly fit in the glasses frame. Such procedures are known in the art and explained in the owner's manual of AIT and WECO bevel edger machines which are incorporated herein by reference. A final step of polishing the bevel edge is also employed to provide a lens edge with a high luster finish.

Typically, the steps of rough-cutting the lens, bevel edging and polishing are performed with different machines as required for various lens materials, i.e., polycarbonate, CR 39 or glass. The step of finishing also utilizes different grinding wheels depending on the lens material. This typically requires the lens grinding labs either to have separate machines with various grinding wheels or to send out work which cannot be done on a single existing machine commonly found in ophthalmic labs of today. The requirement of different machines is in part due to lenses made of polycarbonate require special wheels for grinding and typically utilize no coolant; whereas CR 39 plastic lenses require different wheel coolant or a lubricant (generally water) when grinding. This is because of the thermoplastic nature of the polycarbonate, which will flare in its thickness at the grinding edge if coolant or a lubricant is utilized during removal of material. Polycarbonates are therefore usually dry ground and thereafter polished at their edges on a separate machine. A further problem of combining the polycarbonate and CR 39 edging and polishing process is that a finishing wheel that is fine enough to polish CR 39 is too fine to grind polycarbonate lenses. The hardness of polycarbonate materials is also problematic because it causes excessive wear of polishing wheels commonly used for polishing of other materials.

Typically, the finishing and polishing steps are accomplished via two separate abrasive wheels with the "roughing" of the lens accomplished via a separate machine or a separate abrasive wheel in the same machine. In recent years, the market for ophthalmic lenses has become increasingly interested in achieving a polish on the edge of the lens which is equal in finish to the optical surfaces of the lens. In the past, this was accomplished by time consuming polishing with hand tools or the like. While there are a few mechanical polishing systems, they typically do not provide hand polished results and are exclusively used for a single type of lens material.

Thus, there remains a need in the art to provide a system for providing an optical quality polish on all common lens blank materials including polycarbonate, CR 39 plastic and glass on a single machine and polishing all common types of lens blank materials with a single polishing wheel system.

In accordance with the present invention, there is provided a process and apparatus for edging and polishing an ophthalmic lens comprising polycarbonate, utilizing a single finishing machine which is capable of polishing other materials, and utilizing a single polishing wheel system, wherein the final optical lens product has an edge surface polished to a substantially optical quality finish. The process of the present invention comprises the steps of first grinding a rough lens and thereafter polishing the first periphery of the lens with a dry cycle, and thereafter wet finishing the peripheral surface around the lens whereby an optical quality polished lens edge is the result.

It is, therefore, an object of the present invention to provide a process and apparatus for providing an optical lens having an edge surface polished to a substantially optical quality finish. It is also an object of the present invention to provide a process and apparatus for bevel edging all common lens blank materials including polycarbonate, CR 39 and glass on a single finishing machine. It is a further object of the present invention to provide a process and apparatus for forming ophthalmic lenses whereby a finished lens may be provided wherein the beveled edge is polished without an external polishing device.

Further objects and advantages of the present invention will be realized by review of the intended specification including the description of the drawings, the description of the preferred embodiments and the claims appended hereto.

FIG. 1 is a perspective view a of bevel edger machine utilizing the process of the invention.

FIG. 2 is a detailed view of the polishing process of the present invention .

Referring now to the drawings, there is shown a typical lens bevel edger machine utilized in ophthalmic labs today. Such bevel edgers include a rough grind wheel 14 and bevel edger wheel 16 (best shown in FIG. 2) which are situated in the lens edging portion of the machine generally indicated at 18. Referring now to FIG. 1, bevel edger machines typically include a lens holding system generally indicated at 20 and a lens edge forming assembly generally indicated at 22. The lens holding assembly typically includes lens drive spindles 24 and 26 which grip a lens by way of lens blocks 28 and 32. Typically, blocking pads, as are known in the art, grip lens 34 for holding a lens during rough grinding and bevel edging of the wheel.

The lens former assembly 22 typically includes a lens shape template 36 which is a specific shape for a particular frame. The template 36 is rotationally coupled with shaft 24 such that as the template member turns, the lens 34 also turns. The lens grinding assembly is pivotable along an axis generally indicated at 38 such that as the lens rotates while it is engaging the grinding wheel 14, the lens former member actuates the lens up and down by interaction between the template 36 and the former member upon which it rests. Such former members are referred to by various names in the art, such as former wheel, copy wheel, wear plates former shoes or former plates.

In accordance with the process of the present invention, a single lens edger machine typical in the art can edge an optical lens comprising all common optical lens materials including polycarbonate, CR 39 and glass. Furthermore, the beveled edge of the lens may be polished with a single polishing wheel, without an external polishing device. In particular, normal wet polishing of CR 39 and glass may be accomplished using conventional techniques. Thus, the polishing wheels as disclosed herein may be used on plastic and glass lenses, other than polycarbonates using conventional wet grinding techniques. However, utilizing the process of the present invention also allows polishing of polycarbonate lenses on the same machine using the same wheels used for the other materials.

In accordance with the present invention, there is provided a process for polishing of a polycarbonate lens on the same machine and using the same wheel as used with a glass or methyl methacrylate lens. In accordance with the process aspects of the present invention, an optical lens blank made of a polycarbonate material is provided in a roughed condition. In this condition, the polycarbonate lens includes a finished optical surface and the roughed lens edge. A finishing apparatus is provided which is used for polishing at least a portion of the edge surface of the lens to contact the finishing apparatus for one cycle without the use of any coolant or lubricant, and one cycle with the use of a coolant or lubricant. Thus, the process of the present invention comprises the steps of edging a lens either without coolant or with a substantially diminished coolant flow, i.e. less than about 8 ounces per minute, wherein the preferred coolant is water. The rough-edged lens is then polished with a finishing apparatus, such as a polishing wheel of the present invention, by first passing the polishing wheel over the surface of the lens for at least one full revolution of the lens ("cycle") substantially without the use of coolant ("dry"), and then passing the polishing wheel over the surface of the lens for at least one full revolution of the lens with the use of coolant ("wet"). In a preferred process of the present invention, at least one dry polishing cycle is made before the wet polishing cycle is begun, and thereafter three to four wet polishing cycles are used to achieve the final polish of the lens edge. Utilizing the process of the present invention results in a polished lens edge which is substantially the same as the quality of finish of the optical surface of the lens. While the use of a wheel type finishing apparatus is preferred for use in the present invention, other types of polishing devices can be used to achieve the optical quality polish by using the method of the present invention without deviating from the scope of the present invention. The process of the present invention may be used to polish any "roughed" lens. By the terms "roughed", "rough ground", "rough edge surface" or the like, it is meant that a lens which has been shaped to the shape required for attachment or insertion into an eyeglass frame. Typically, such lenses have an abraded edge surface which requires further finishing and polishing of the surface to obtain an acceptable lens edge finish. Thus, a typical roughed lens would include a bevel for insertion into a lens frame which is fabricated on the roughing cycle of the bevel edger machine. However, in certain eyeglass frames, the edge of the lens may be roughed in a flat edge or other shape which is thereafter polished via the process of the present invention.

The polishing wheel of the present invention may be used to polish all common optical lens materials including polycarbonate, CR 39 and glass. The polishing wheel of the present invention is impregnated with diamond grit particles in concentrations of generally from about 10 to about 200 concentration, typically from about 35 to about 150 concentration, and preferably from about 75 to about 125 concentration, (where 4.4 carats/cubic centimeter is equal to 100 concentration). A preferred abrasive grit of the present invention is diamond particles. The abrasive grit material used generally ranges from about 2 to about 60 microns, and typically from about 7 to about 30 microns. In some circumstances, 15 to about 20 micron particle sizes will work, while in other cases 8 to about 12 micron particles are preferred. The final particle size is somewhat dependant on the particular machine on which the wheel is used and the polish desired. Other diamond-like hardness materials would also be useful such as cubic boron nitride, corundum, polycrystalline diamond, silica carbide and tungsten carbides.

The polishing wheel of the present invention may be either a sintered wheel, a resin bonded wheel or the like, provided it contains abrasive particles in the size and quantities specified above which are critical for polishing of both polycarbonates and other materials. A metal matrix of a specific gravity of not less than 3.50 g/cc, and not more than 10.6 g/cc, is preferred. Preferably, a sintered metal bond is utilized which contains from about 400 to about 600 grams copper, from about 20 to about 100 grams tin, and from about 2 to about 15 grams of graphite as a sintering binder for the abrasive grit.

In accordance with the present invention, a cut-off switch 100 or the like is wired to the coolant pump (generally indicated at 102) of the bevel edger machine or the pump is otherwise disengaged from operation. Thereafter, the polishing wheel of the present invention is mounted on the bevel edger, and a polycarbonate lens blank is rough ground and bevel edged without coolant or lubricant. After the bevel edge is complete, the coolant flow is resumed and the machine is allowed to cycle for one pass over the portion of the lens edge to be polished. Thus, if the entire edge of the lens is to be polished, one full revolution is utilized. However, if only a portion of the lens is desired to be polished, then only that portion of the lens which needs polishing is contacted. This final step accomplishes a final polishing of the lens edge which is as good or better than that achieved on a separate polishing machine.

A foot switch is preferred for the pump power cut-off. Since the coolant pump of a bevel edger machine is typically connected separately to the wall socket, an in-line cut-off switch, wherein the plug of the pump may be connected to the switching plug of the foot switch, is utilized. This is then connected to a suitable outlet. Thus, an operator can step on the foot switch to cut coolant flow when grinding the polycarbonate lens, and release the foot switch for allowing coolant flow for final polishing of the lens.

In a second embodiment, the bevel edger apparatus could be programmed to provide the process set forth above automatically. Thus, an integrated circuit chip or the like with the proper programming, to allow automatic processing of a lens under the process steps of the present invention, could be utilized to vary the processing when polishing of a polycarbonate lens. This would be accomplished by programming the bevel edger to interrupt coolant flow for at least one cycle when finishing of a polycarbonate lens and rough edging the polycarbonate lens without the use of coolant. Also, many of the machines now available are operator programmable which would allow programmable control of the process. Thus, a machine could be provided for automatically carrying out the process, with the only necessary input from the operator being selection of the type of lens blank to be edged.

A metal bond mixture was formulated using 545 grams of copper powder, 61 grams of tin powder and 9 grams of graphite. One hundred and forty-seven (147) carats of 10/15 micron diamonds were mixed with 270 grams of the above mentioned metal bond mixture. The diamond metal bond mixture was then placed in a mold with a cavity for forming a bevel polish wheel and sintered at a temperature of 1300.degree. F. by hot-pressing.

The polish wheel is then fitted to a Gerber "ELITE". A polycarbonate lens blank was first rough edged without coolant flow. The lens is then bevel edged without coolant flow to the lens. The lens is then polished one revolution without coolant. Thereafter, four cycles are used with coolant to provide the final polish to the edge of the lens. The resulting polished lens edge is of an extremely high luster (i.e. optical quality resulting in a very pleasing aesthetic appearance).

A polishing wheel was formulated using a resinous binder as follows. A binder mixture is formulated from a mixture of 600 grams phenolic resin, 100 grams copper powder, 60 grams silica carbide #1000, 60 grams aluminum oxide, and 5.8 grams of graphite. Forty-five (45) grams of this bond mixture was then mixed with 50 carats of 10/20 micron diamond. A rough form of a bevel polish wheel was prepared by compression molding the bond/diamond mixture at a temperature of 325.degree. F. This rough blank is then further fabricated into a bevel polish wheel for a WECO Model 440 edger.

The resulting wheel was installed on a WECO Model 440 edger. A polycarbonate blank was "roughed out" using a conventional wheel in the edger without the use of coolant. Thereafter, the lens was polished using the wheel prepared as above. The cycle used was one dry revolution of the lens against the rotating polish wheel, with four final revolutions of the lens against the polishing wheel, with coolant flow to the wheel. The resulting lens had edges of extremely high luster approaching optical quality of the lens.

Using the bond material of Example I, several polishing wheels are made in the following diamond concentrations: 10, 50, 75, 125, 180 and 200. In each of these concentrations, wheels are made using 2 micron, 10 micron, 30 micron and 60 micron sizes of diamond.

Each of the above wheels is used to polish edges of a polycarbonate lens on various lens machines, such as Gerber, Coburn, WECO, BRIDT, AIT National Optronics, Essilor and Opti-vue. The cycle provides at least one dry revolution during polishing and one revolution with coolant flow to the wheel. The resulting lens has a high luster edge approaching optical quality.

While the above description constitutes the preferred embodiments of the present invention, it is to be appreciated that the invention can be practiced in ways other than that specifically disclosed without deviating from the scope or the fair meaning of the present invention as set forth in the accompanying claims.