This invention relates to the manufacture of ophthalmic lenses. Specifically this invention relates to a new system and method for surfacing, edging and finishing ophthalmic lenses.
In the art of ophthalmic lens manufacture, a finished ophthalmic lens is usually made from finished uncut lenses or from semi-finished lens blanks. Finished uncut lenses are lenses that are optically finished on both front and back surfaces and only need to be edged to the proper shape and edge contour to become finished lenses. Most optical laboratories keep an inventory of single vision finished uncut lenses in various powers, sizes, and materials to take care of most of the more common single vision ophthalmic lens prescriptions.
Semi-finished lens blanks have optically finished front surfaces; however, the back surfaces of these blanks need to be generated and fined and are then either polished or coated to produce finished uncut lenses. Finished uncut lenses are then edged to the proper frontal shape and edge contour to fit into spectacle/glasses frames or other mounting structures. Single vision lenses that are outside the normal range of inventoried finished uncut lenses and most multifocals are made from semi-finished lens blanks. Semi-finished lens blanks are made with various front surface curve radii, and have various topographies including spherical, aspheric, hyperbolic, irregular aspheric such as progressive add lenses, and polyspheric such as executive type segmented bifocals and trifocals.
To generate a desired prescription for a lens, calculations are required to determine the topography of the back surface of a lens. Such calculations typically involve variables that include the front surface radii of the semi-finished blank, the index of refraction of the lens blank material, prescription values of the desired lens, statutory values regarding minimum lens thickness, and the physical dimensions of the frame or mounting structure.
In the art, various means have been devised to accomplish the physical process of producing a back surface of optical quality. Most of these methods begin by generating a back surface that approximates the desired back surface topography and surface smoothness. This approximate surface is then fined to a more perfect approximation in both curvature and surface smoothness. After the appropriate accuracy and smoothness is achieved in the fining process, the surface is then polished or surface coated to produce a surface of optical quality. The optically finished lens blank is then edged to the proper shape and edge profile to fit into the frame for which it was made.
Many business entities that sell ophthalmic lenses do lens finishing as a profit center activity and as a way to expedite delivery of single vision lenses. Only a small percentage of these entities also do surfacing of ophthalmic lenses. The business volume of most of these entities cannot justify the costs of acquiring and operating a surfacing laboratory. Surfacing laboratory setup costs have heretofore been several times the cost of setting up a laboratory for edging only.
Hiring qualified technicians for ophthalmic lens finishing or training personnel to perform ophthalmic lens finishing is relatively easy. However, hiring and training optical technicians to operate a surfacing laboratory is not easy. In many communities it is very difficult to find personnel that are trained in surfacing. Technicians who are qualified to do surfacing are generally remunerated at higher pay scales than technicians skilled only in optical finishing.
In addition to the significantly higher equipment and personnel costs of a surfacing lab, there are also higher ongoing costs for the additional lab space required. At least several hundred square feet of operational space and storage space have heretofore been required for a full service surfacing and edging ophthalmic lens laboratory. Consequently there is a need for a system and method of ophthalmic lens manufacture that would significantly reduce the investment required to acquire a surfacing and edging laboratory. There is a further need for a system and method of ophthalmic lens manufacture that significantly reduces the costs associated with operating a surfacing and edging laboratory. Further, there is a need for a system and method of ophthalmic lens manufacture that is operative to perform surfacing and edging by an operator with little skill in the art.
In the prior art, the processes of surfacing and edging are done on at least two separate machines. In the prior art, blocking for surfacing and edging required two separate blocking devices. Also in the prior art, the individual processes of lap tool surfacing and lens cribbing and safety beveling and edge grooving and edge polishing and lens engraving each requires its own machine or device or machine augmentation. Each of these machines or devices or augmentations is to varying degrees expensive to acquire and each of the machines or devices requires laboratory space. Each of these operations, if done by hand, requires the necessary acquisition of skills and application of those skills in order to perform the various operations. Consequently, there is therefore a need for a system and method of ophthalmic lens manufacture that reduces the need to employ a plurality of expensive and complex machines to manufacture lenses.
In the prior art, after a semi-finished lens blank is generated and fined and polished it is de-blocked and inspected and then laid out and blocked again for edging. Blocking for surfacing and blocking for edging are two different procedures that differ in significant ways requiring two different sets of skills and requiring two separate and very different mechanical blocking systems. Repeating the blocking process is necessary in part because the metallic block used for surfacing could interfere with the edging process. This is because portions of the uncut lens that lie under the surfacing block frequently need to be removed during the edging process. If the standard surfacing block were also used during edging, this could result in the metal surfacing block coming into contact with the cutting or grinding surfaces of the edging machine thereby damaging the cutting or grinding surfaces of the edging machine and damaging or destroying the block in the process. Additionally, the need to block a lens twice multiplies the opportunities for error and spoilage and requires the expenditure of time. Consequently there is a need for a method of ophthalmic lens manufacture that eliminates the need to block a lens blank twice for those lenses that require both surfacing and edging.
The prior art describes several types of single point blocking systems. One type describes centering the block on the point of the lens that would occupy the geometric center of the frame when the lens is finished (frame geometric center blocking). Another describes centering the block on the point of the lens that would occupy the optical center of the finished lens (optical center blocking). A third describes centering the block in the geometric center of the semi-finished uncut lens (lens blank geometric center blocking). In prior art, all three of methods are optimized for surfacing by tilting the front surface by the proper amount and in the proper direction to move the optic axis into alignment with the generator feed axis. Only in the case of xe2x80x9cframe geometric center blockingxe2x80x9d is it possible to optimize for edging. This optimization for edging is accomplished by aligning the front surface normal at the geometric center with the feed axis of the generator.
The xe2x80x9coptical centerxe2x80x9d and xe2x80x9clens blank geometric centerxe2x80x9d blocking arrangements create relationships between a lens blank and the generator feed axis that are optimal for generating lens back surfaces because errors in thickness at any stage in the process of surface generation and fining will not affect a change in the position of the optical center of the lens. This is because the optic axis does not move as the thickness of the blank decreases. However, in neither of these two cases are the blocking arrangements optimal for edging a lens. In both instances the lens is frequently tilted too much to apply an edge parallel to the normal at the geometric center of the front surface of the finished lens. Applying an edge to a lens at any angle other than parallel to the front surface normal at the geometric center results in edges that are skewed and frequently thicker than necessary and with edge beads that have less than optimal orientations.
A blocking system optimized for edging, like xe2x80x9cframe geometric center blockingxe2x80x9d, wherein the lens blank is blocked on the geometric center of the finished lens and where the normal at the geometric center of the front surface of the finished lens is parallel to the axis of rotation of the edging tool or edge grinding wheel, is not optimal for surfacing. Except for the relatively rare case where there is positional coincidence between the optical center of the lens and the frame geometric center of the lens, the optical center of the lens is made to move or xe2x80x9ccreepxe2x80x9d as the lens is made to decrease in thickness during fining.
A method of lens blocking that is optimized for edging and that is also operative for surface generation would be of considerable utility. It would allow for a single blocking step for both the surface generation of a lens and for the edging of that lens without de-blocking and re-blocking between the steps of surface generation and edging. Therefore there is a need for a system and method of blocking a lens for both surfacing and edging that reduces the problems associated with optical center creep.
Prescription lenses for patients are often generated in pairs for a spectacle frame. Prior art systems typically generate each lens independently. Production cycle times for generating lenses may be reduced by employing multiple surfacing and edging machines in the laboratory to generate pairs of lenses simultaneously, however duplication of equipment doubles the acquisition and operational costs of the laboratory. Thus there exists a need for a system and method of ophthalmic lens manufacture that provides for reduced production cycle times for pairs of prescription lens without significantly increasing costs for the laboratory.
Heat transfer into the lens blank from the heated blocking medium during the blocking procedure is a frequent cause of so called xe2x80x9clens warpagexe2x80x9d. The greater the amount of heat transfer involved and the more uneven the distribution of that heat transfer is, the greater the chance of producing warpage and ruining the lens or producing a substandard lens. There is therefore a need for a method of ophthalmic lens manufacture that could minimize the transference of heat into the lens blank during blocking, and that could make the distribution of that heat transference uniform over the entire area of the finished lens. Further, there is a need for a system and method of ophthalmic lens manufacture that could eliminate problems associated with heat transfer into the lens during blocking.
The standard block used for lens surfacing is generally smaller than the size of the finished lens being fabricated. The portion of a lens that remains unsupported can undergo flexure when submitted to the forces involved in the generating, fining and polishing processes. This results in flaws or xe2x80x9cwavesxe2x80x9d in the optics of the lens in the areas that underwent the flexure and is a common source of spoilage or of substandard lenses. Consequently, there is a need for a technique that would eliminate these optical flaws caused by flexion of the lens blank during generating and fining and polishing of the lens.
For cosmetic effect, the edges of lenses are sometimes polished. In prior art, when the edge of the lens has a mounting bevel, the bevel on the edge of the lens is polished when the edge is polished. Polishing the mounting bevel reduces the holding friction of the bevel that aids in holding the lens in the frame, and that holding friction is also important in resisting rotation of the lens within the frame. For this reason, a lens that has a polished edge with a polished bevel is more difficult to keep securely mounted and properly oriented in its frame. There is therefore a need for a system and method of ophthalmic lens manufacture that is operative to polish the edge of a lens without polishing the mounting bevel on the edge of the lens.
Prior art systems for lens manufacture are inherently non-mobile, due to the large amounts of laboratory space required to store an inventory of lap tools and the many pieces of heavy laboratory equipment needed to generate and surface and finish lenses. Thus, prior art systems cannot be easily transported to locations such as factories to manufacture safety lenses on-site or military theaters to support the optical needs of military personnel. Consequently, there is a need for an ophthalmic lens manufacturing system that is portable.
It is an object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that significantly reduces the costs of acquiring and operating a full service surfacing and edging ophthalmic lens laboratory.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operable with little knowledge of the optical arts by the operator.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that requires little physical laboratory space.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to perform both lens surfacing and lens edging.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that requires only one lens blocking operation to perform both surfacing and edging.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to block a lens for both surfacing and edging that is optimized for both the minimization of edge thickness and the compensation of optical center xe2x80x9ccreep.xe2x80x9d
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that does not require complicated rotating or tilting of the semi-finished lens blank when blocking for surfacing.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to perform both lens surfacing and lens edging in one machine operation.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that utilizes a single tool with multiple cutting surfaces capable of both surface generation and edging of lenses.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that does not require a lap tool library.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that does not require a lap tool library but is capable of using a lap tool library.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that does edging and surfacing of lenses and lap tool surfacing on the same machine.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to generate the precise lap tool for each lens manufactured.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to generate the precise mounting blocks for each lens manufactured.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to generate the precise mounting blocks for each lens manufactured with scribe marks applied to the surface of the blocks to facilitate alignment for blocking.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to perform surfacing of both lenses of a pair of lenses at the same time.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to perform edging of both lenses of a pair of lenses at the same time.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to perform lap tool surfacing of two lap tools at the same time.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that minimizes the transference of heat into the lens blank during blocking and that makes the distribution of that heat transference uniform over the entire area of the finished lens.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that eliminates the transference of heat into the lens blank during blocking
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that eliminates fabrication flaws caused when unsupported portions of a lens blank flexes under the forces incurred during the generating, fining, and polishing processes.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that provides for easy visual verification of proper blank size.
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is operative to polish the edge of a lens without polishing the mounting bevel on the edge of the lens
It is a further object of the exemplary form of the present invention to provide a system and method for ophthalmic lens manufacture that is portable.
Further objects of the present invention will be made apparent in the following Best Modes for Carrying Out Invention and the appended claims.
The foregoing objects are accomplished in one exemplary embodiment of the invention by a system and method for ophthalmic lens manufacture that employs computer numerically controlled (CNC) machining techniques that are operative to generate and edge semi-finished lenses and to edge finished uncut lenses.
An exemplary embodiment of the present invention relies on the fact that the topographies of optical surfaces are very well defined. If the spatial coordinates (x,y,z) of any three points on a lens front surface are known within a coordinate system, then the spatial coordinates of all other points on the front surface can be derived within the coordinate system.
Further, if the center thickness and position of the optical center of a lens are known, then the spatial coordinates of any point on the back surface of that same lens can be derived. Further still, if a sufficient number of planar coordinates (x,y) representing the shape of the frame into which the lens will be mounted are known relative to the position that the lens geometric center will occupy within the frame and if the offset from the front surface of the mounting groove or bevel is known, then the finished shape and contour of the lens can be accurately derived including the position of the mounting bevel or groove.
The exemplary embodiment of the present invention includes a CNC machining platform that is operative to direct an appropriate tool to perform both surfacing and edging of a lens blank. The system includes a computer that is operative to retrieve frame coordinates of the lens receiving portion of a spectacle frame. In the exemplary embodiment the frame coordinates are stored in a data store in operative connection with the computer. In one exemplary embodiment of the present invention these frame coordinates are acquired by tracing the inner circumference of the frame apertures with a graphics tablet, or other scanning device in operative connection with the computer.
The computer is also in operative connection with an input device and a data store. A user of the system inputs with the input device prescription specifications for the desired lens. The data store includes a plurality of front surface data values that correspond to the front surface topography of the lens blank. The computer calculates tool paths for machining the lens blank with the tool responsive to the frame coordinates, the front surface data values, and the prescription specifications.
These tool paths are calculated with respect to the reference frame of the machining platform. The machining platform is operative to direct the tool to move with respect to the lens blank according to the calculated machining tool paths.
The system is further operative to generate an appropriate lap tool for finishing the generated lens. The machining platform is operative to machine the surface of the lap tool responsive to the front surface data values, the prescription specifications, and, in cases where front surface radii are shorter than back surface radii, the data representing the size and shape of the frame. The orientation of the lap tool axes may be machined to match the orientation of the axes in the final lens so there is no need to rotate the lens blank in the surface blocking process in order to align the lens axes with the lap tool axes. There is also no need for prism blocking or prism ring tilting of the blocked lens blank for back surface generation.
The system is further operative to machine an appropriate block for receiving the front surface of the lens responsive to the front surface data, frame data, and prescription specifications, which include the interpupillary distance (Pd). In the exemplary embodiment the block is machined to include scribe lines that are used by an operator to properly position and align the lens blank so that all points on the front surface of the lens blank can be determined relative the reference frame of the block and the machining platform.
Further objects of the present invention will be made apparent in the following Best Modes for Carrying Out Invention and the appended claims.