Lens Polishing Pad and Apparatus

Embodiments of the disclosed technology relate generally to the fabrication of ophthalmic lenses. More particularly, embodiments of the disclosed technology relate to methods and apparatus for polishing ophthalmic lenses.

Freeform prescription lens surfacing technology has emerged toward the end of the last decade of the 20th century and currently has become the main stream technology for prescription ophthalmic lens processing globally. There have been a numerous developments and advancements not only in the equipment and the processing technology but also many improvements in the freeform lens design software. However, some aspects of the technology, for example, the freeform polishing pads or polishing buttons, have remained virtually the same for over 25 years.

The main technical features of the currently used pads globally:

When squeezed and released, the open cell foam is supposed to absorb the polish like a sponge. The small pinholes in the polyurethane pads are supposed to allow the polish through onto the lens surface when the open cell foam is compressed by pushing the button against the lens (typically with about one psi of pressure).

Based on years of hands-on experience in lab production and extensive testing, we have noticed the following current limitations of conventional polishing buttons:

The quality and the efficiency of the polishing process is significantly dependent on the amount of polish dragged across the lens surface.

The way that the open cell foam and pinholed polyurethane cover are supposed to work seems plausible, but, in practical use, the polishing buttons do not actually work that way. Even in maximum absorption followed by maximum squeeze only a few droplets actually appeared on the pad/lens during our numerous tests.

The solid polyurethane rubber pads mounted on substantially flat open cell foam base do not evenly adhere to the lens surfaces under the typical one psi polishing pressure. Rather, they polish with substantially the pad periphery. That causes an uneven lens surface material removal, compromises the lens intended optical integrity, and requires longer polishing cycles. That drawback can be alleviated by providing several various curvature shaped polishing pads.

The open cell foam bases currently used under the polyurethane pads not only fail to effectively “pump” the polish through the pinholes onto the lens surface but have two additional detrimental issues:

Once the polishing liquid gets absorbed into the pad the pad's elasticity deteriorates, its elasticity response time slows down.

When the spongy open cell foam pad gets saturated with the polish if left to dry up it becomes hard and loses its elasticity. To prevent that from happening the pads must be placed in a dish of water when not in use.

The solid polyurethane rubber pads suffer fatigue failure (cracking) due to cyclic strain when forced to adhere against various asymmetrical surfaces of lens during the polishing process.

Lens polishing generally removes 4-5 microns of lens material where the polishing pad touches the lens, in order to reduce surface roughness from around 0.3 micron RMS to around 10-15 Angstroms. Because conventional pads do not uniformly conform to the typically ageometrical lens surface, the material removal of freeform surfaces during polishing is not uniform. Conventional lens design processes do not account for uneven lens polishing material removal. Lens rejects due to over-polishing at the lens edge and under-polishing at the center can amount up to 20% of lenses.

The proposed technology is to improve upon the current state of the art in freeform lens polishing process by alleviating some or all of the following problems:

According to an aspect of the disclosure, the polishing pad or button attains a domed shape when pressed against a lens surface. The domed shape enhances conformance of the button to the curved surface that it will polish. According to some embodiments, the polishing pad includes a polyurethane or other substantially flexible and moderately compressible material cover on a base of closed cell foam or other substantially incompressible but moderately flexible material. Using closed cell foam can prevent the absorption of the polishing solution into the base body. That prevents the base from turning hard and not functional when not in use. Significantly, the closed cell foam elasticity response time will remain constant, as per its specification, thus it assures optimum and consistent polishing quality and performance.

According to an aspect of the disclosure, the closed cell foam conical base has an undercut around its periphery in order to relieve the polishing pressure in peripheral areas to facilitate conformance to higher curvature/shorter radii surfaces and to assure an even lens surface material removal that can enhance the optical integrity of the lens to the prescription. For example, the undercut may be in substantially the middle of the pad height.

Accordingly, instead of the pad base acting as a sponge to absorb and release the polishing emery fluid, the polyurethane cover holds the fluid. According to an aspect of the disclosure, the polishing pad has multiple channel cutouts going from the periphery of the pad towards the pad center, in order to better hold and distribute the polishing emery fluid throughout the entire polishing pad surface. According to some embodiments, the channel cutouts are shaped like water pump volutes or turbine impellers in order to increase the flow of the polishing solution on the polished surface. According to some embodiments, the polishing pad cutout pattern is eccentric from the center of the polishing pad, so that the substantially circular pattern center does not rotate concentrically on the closed cell foam base but rather moves around the center of the foam base in a circular motion to allow maximum amount of the polishing solution in the center of the polishing surface and to introduce another polishing pad motion pattern that improves the efficiency of polishing. According to some embodiments, the polishing pad cutout pattern includes dimples that relieve stress at the inner ends of the gyre cutouts. The dimples also accumulate polishing fluid.

According to an aspect of the disclosure, the sealed air bubbles inside the closed cell foam base provide for more rapid elastic response (as compared to conventional open cell foam bases) as the polishing button moves against the surface of the lens being polished.

These aspects of the disclosure, as discussed above, seem simple to the inventor but have not been considered or implemented by anyone in the field of ophthalmic lens processing during the preceding quarter century of work.

Some embodiments may not have these potential advantages and these potential advantages are not necessarily required of all embodiments. These and other features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.

The technology now will be described with reference to the attached drawing figures.

depicts a top view of an example of a polishing pad or button, according to aspects of the disclosure.depicts a side view of the polishing pad. The polishing pad has a polyurethane coverthat is attached to an upper surface of a closed cell foam base. The foam baseis mounted to a metal or organic (e.g., wood, plastic) chuck. The chuckis shaped to engage into a partof a polishing apparatus, an example of which is described with reference toand.

Materials other than those described may be used. Generally, the covershould be a flexible and elastic material whereas the baseshould be a substantially incompressible and rigid material. The material of the chuckshould be substantially stiff to solidly and matingly engage with the partof the apparatus.

When the polishing buttonis not in use it has a generally flat upper surface and the foam basehas an inverted frustoconical shape (narrower toward the chuck and wider toward the cover). When the polishing button is pressed against a lens, an undercutin the foam base permits the button to deform into a domed shape that better conforms to the lens surface. The undercut may be at substantially the middle of the height of the base. In certain embodiments of the technology, the undercut may be about 4 mm across and about 2 mm deep rounded groove. In other embodiments, it may be a V-shape groove or a square groove. Providing the undercut should enhance the elastic response at the edges of the polishing button so that the button adapts more quickly to variations in the surface of the lens as the lens and button rotate at up to or more than 200 rpm.

The polyurethane coveris not a continuous disc but rather includes cutoutsand dimplesthat are arranged in a gyre like blades of a fan or volutes of a pump. The cutoutsare about 6 mm wide at the periphery of the coverand narrow to points toward the middle of the cover. For example, there may be five cutouts. The dimplesare about 1 mm-2 mm in diameter. There may be the same number of dimples as cutouts or different numbers of each. Rotation of the buttoncauses the cutoutsto scoop polishing fluid from the peripheryof the button toward the dimples. This scooping action distributes the polishing fluid across the surface of the cover, which enhances polishing toward the center of the button as compared to prior art pads.

The cutoutsand dimplesare arranged in an eccentric manner, so that the cutouts and dimples converge toward a point that is not aligned with the button's geometric center. For example, the eccentric point may be 2 mm to 3 mm offset from the geometric center. This geometry causes a bubble or lump of polishing fluid to gyrate around the geometric center of the button as the button rotates against the surface of the lens. The gyrating lump of polishing fluid will enhance the efficiency of polishing.

Although the disclosed technology has been described by way of examples and with reference to illustrative drawings, the essential concepts of the technology as claimed should not be understood to extend merely to what is precisely described. Rather, the scope of the claims should be understood to encompass equivalents and alternatives that will be appreciated by the ordinary skilled worker in light of the present disclosure.

Although specific materials may be described as examples of the disclosed technology, the ordinary skilled worker will appreciate that materials with substantially similar properties may be substituted without departing from the scope of the claims, except where the claims are specifically limited to a given material.

Where a term such as “about” or “substantially” may be used, it should be understood to encompass not only the precisely disclosed amounts or measurements or relationships or properties but also approximations of the disclosure that are sufficiently similar so as to accomplish the same result in the same way.

Where terms such as “above” or “below” may be used, they should be understood to limit the spatial relationship of the components thus described only if the disclosure specifies that such limitation is an essential aspect of the technology. Otherwise it should be understood that spatial relationships between components may be arbitrary and that terms such as “above” or “below” are used only for convenience of reference to the illustrative drawings, rather than as essential relationships between components.

Where terms such as “first” or “second” may be used, they should be understood to be used only for convenience of description, not to limit the number or order of components.

The word “a” should be understood as “one or more” whereas the word “plurality” should be understood as “two or more”. Similarly, the word “the” should be understood to include “one or more” whereas “the plurality” should be understood to include “two or more”. Where “one” may be used, it should be understood as “only one”.