GB2050884A

GB2050884A - Lens polishing head

Info

Publication number: GB2050884A
Application number: GB8018073A
Authority: GB
Original assignee: American Optical Corp
Current assignee: American Optical Corp
Priority date: 1979-06-06
Filing date: 1980-06-03
Publication date: 1981-01-14
Also published as: JPS55164462A; BR8003488A; GB2050884B; DE3021244A1; CH639582A5; FR2458357A1; FR2458357B1

Abstract

A lens polishing head comprising: a rigid main body member 12; a machine adaptor 14 depending from one side of said main body member; an elastomeric lap 16 affixed to the opposite side of said main body member, said lap having a curved lens working surface and hollow interior 34; and means for affording adjustment of resilience of said working surface. The lap is secured in fluid-tight manner to the body member and the adjustment means includes a fluid passage having an air check valve 32, the air pressure in the interior 34 determining the resilience of the working surface and the curvature thereof so that the head may be used to polish lenses L in a range of curvatures. <IMAGE>

Description

SPECIFICATION Lens polishing head This invention relates to polishing apparatus for use in Ophthalmic lens surfacing.

In the ophthalmic lens surfacing art, lens blanks ground to prescription curvatures are finally polished with soft pads and polishing compounds. The pads, with applied polishing compounds, are pressed against the lens surfaces and caused to rub vigorously thereover until optical finish is obtained.

In order to avoid distorting the particular surface shape of a lens being so worked and to fully engage all portions of the surface with similar pressure and rubbing action, rigid pad supporting laps having working surface curvature corresponding to those of the ground lenses were heretofore required. These laps, as polishing pad backings, are required in numbers corresponding to the numbers of individual prescription surface curvatures encountered, i.e., one lap for each surface curvature and preferably duplicates or triplicates of the more popular sizes for maintaining normal production standards. For example, considering a range of lens surface curvatures of from 8 Diopters to 4 Diopters in increments of 1/8 Diopter steps, 32 laps would be required. Adding cylinder curves out to 2 Diopters in 1/8 Diopter steps, an additional 512 laps or total of 544 laps would be required.To the foregoing, it should be realized that a lens making facility would ordinarily be prepared to surface curvatures from 3 Diopters to 19 Diopters in 1/8 Diopter steps with and without cylinder correction. Accordingly, the required very large inventory of laps represents not only a major capital equipment investment but high storage and maintenance costs, not to mention job handling problems.

With consideration of the foregoing and related drawbacks of prior art lens surface finishing operations, it is an object of this invention to provide improved tooling therewith a wide range of lens surface curvatures and combinations of curvatures may be polished with a single polishing head.

According to the present invention we provide a lens polishing head comprising: a rigid main body member; a machine adaptor depending from one side of said main body member; an elastomeric lap affixed to the opposite side of said main body member, said lap having a curved lens working surface and hollow interior; and means for affording adjustment of resilience of said working surface.

Preferably, said lap is secured in fluid-tight fashion to said main body member and said means for adjusting resilience of said working surface includes fluid passage means into said hollow interior for use in pressurizing said lap.

With a thin polishing pad placed over the elastomeric lap and use of a suitable polishing compound, a ground lens surface pressed against the pad with a force causing conformance of the lap surface to the ground lens curvature and vigorous movement of the lens and lap, one relative to the other, final lens polishing without alteration of lens shape may be accomplished.

The foregoing provides space saving low tool inventory, easy and economical lap surface replacement, minimum tool handling and machine downtime and other shop conveniences.

Reference is now made to the accompanying drawings, in which :- Figure 1 is an illustration in vertical cross section, of a preferred embodiment of the invention; and Figure 2 is a fragmentary illustration in cross section of a modification of the lens polishing head of Figure 1.

In the drawings, polishing head 10 is illustrated as comprising rigid main body member 12 having depending machine adaptor 14 and hollow elastomeric lap 16.

Adaptor 14 is provided with internal taper 18 which is contoured to fit drive spindle 20 of a suitable lens polishing machine. This form of adaptation of tools to surfacing machinery is illustrated in U.S. Patents 2,916,857; 3,093,939 and 3,916,574. It should be understood, however, that adaptor 14 may be internally or externally threaded or otherwise rendered compatible with tool supporting spindles of other machines such as the work spindle of U.S. Patent 4,098,028, for example.

Lap 16 which may be cast or moulded to the illustrated cupped configuration having mounting flange 22 is secured in air tight fashion to main body 12 with clamping ring 24 and fastening screws 26. A lap 16 of approximately 3 and 3/4 inches in diameter with a working surface 28 of approximately 6 Diopter curvature and wall thicknesses approximately proportional to that depicted in Figure 1 may be cast of a room temperature vulcanizable (RTV) silicone of approximately 60 Shore A Durometers. One such silicone known to the trade is "Silastic J", a product of Dow Corning Corporation, Midland, Michigan.

Working surface 28 is preferably provided with a curvature which is approximately midrange of a series of lens surface curvatures intended to be worked (e.g., 6 Diopters for a range of lens surfaces of from 8 Diopters to 4 Diopters) and is covered with a thin polishing pad 30. Air check valve 32, e.g., of the Schrader (Registered Trade Mark) type, permits inflation of cavity 34. This allows selective toning of the surface for proper resilience, i.e., to the extent of cushioning necessary for maintaining optimum conformance to a ground lens curvature to be finished and maintenance of surface conformance at all times during a polishing operation. It is to be understood that other media such as liquids, foams, sponges or other compliant fillers may be substituted for the aforesaid air inflation.

Successful polishing of an optically fine ground surface 36 of a blocked lens L (Figure 1) having, for example, a diameter of 66 mm and surface 36 curvature of 6 Diopters may be accomplished under the following conditions: (1) Pad 30 used- Non-woven felt (2) Polishing compound 37- Mixtures of equal parts aluminum oxide and tin oxide or aluminum oxide and zirconium oxide in sufficient water and/ or glycerin for free flowability.

(3) Lower machine spindle Approximately 30 RPM.

20 speed (4) Upper machine spindle Approximately 400 RPM.

38 speed (5) Cavity 34 pressure- 2to 10 PSI.

(6) Loading in direction 17-20 Lbs.

Of arrow 40 (7) Sweep in direction Approximately 3/8" arrow42- total.

(8) Polishing time- 8 to 6 minutes.

It should be apparent from Figure 1 that the arrangement of lens block and eccentric upper spindle 38 is typically that used for polishing spherical lens surfaces (See U.S. Patents Nos. 2,916,857; 3,916,574; 4,098,028 (for example). This allows free rotational floating of lens L over the padded working surface 28 of polishing head 10.

Unlike surfacing (polishing) with rigid laps, however, the present surface 28 has a compliancy to the particular curvature of lens surface 36. This not only provides for polishing without distortion of initial lens surface curvature but permits the polishing of torics, i.e., compound curvatures.

Working surface 28, however, may be moulded or cast to a compound curvature (torus) 28a (Figure 2) if desired so that the blocked lens L can be supported in a lens cylinder axis aligning fixture 44 according to the usual practice for maintaining parallelism of the cylinder axis of a lens with the tool cylinder axis at all times during polishing. Reference may be made to U.S. Patents Nos. 2,916,857; 3,093,939 and 3,916,574 for details of cylinder axis aligning fixtures and their use. In the present case, however, the compliancy of working surface 28a to a wide range of toric surface curvatures permits single tool inventory.

All reference made herein to "lenses" and "opthalmic lenses" is intended to include the various forms thereof, i.e., whether ground and/or polished on one or both sides and/or cut or uncut to special edge contour shapes and formed of glass or plastic.

Those skilled in the art will readily appreciate that there are various other forms and adaptations of the present invention which may be made to suit particular requirements.

For example, working surfaces 28 and 28a (Figures 1 and 2) may be formed to a concave configuration for use in polishing convex surfaces of ophthalmic lenses and the like. Futhermore, the hereinabove reference to the work pieces as being ophthalmic lenses is not intended to exclude other glass or plastic articles such as instrument lenses or mirrors needing to be similarly worked. Accordingly, the foregoing illustrations are not to be interpreted as restrictive of the invention beyond that necessitated by the following claims.

Claims

1. A lens polishing head comprising: rigid main body member; a machine adaptor depending from one side of said main body member; an elastomeric lap affixed to the opposite side of said main body member, said lap having a curved lens working surface and hollow interior; and means for affording adjustment of resilience of said working surface.

2. A lens polishing head according to Claim 1 wherein said lap is secured in fluid-tight fashion to said main body member and said means for adjusting resilience of said working surface includes fluid passage means into said hollow interior for use in pressurizing said lap.

3. A lens polishing head according to Claim 2 wherein said fluid passage means is an air check valve.

4. A lens polishing head according to any of Claims 1 to 3 wherein said curved working surface is outwardly convex.

5. A lens polishing head according to any of Claims 1 to 3 wherein said curved working surface is outwardly concave.

6. A lens polishing head according to Claim 4 wherein the curvature of said convex working surface is approximately midrange in Dioptric measurement of a series of lens surface curvatures to be worked.

7. A lens polishing head according to Claim 5 wherein the curvature of said convex working surface is approximately midrange in Dioptric measurement of a series of lens surface curvatures to be worked.

8. A lens polishing head according to any of Claims 1 to 7 further including a polishing pad extending over said working surface.

9. A lens polishing head according to Claim 8 wherein said polishing pad is formed of non-woven felt.

10. A polishing head according to any of Claims 1 to 9 wherein said lap is formed of an RTV silicone of approximately 60 Shore A Durometers.

11. A lens polishing head substantially as herein described with reference to and as shown in the accompanying drawings.