GB2084493A

GB2084493A - Method and apparatus for blocking lenses during grinding and polishing operations

Info

Publication number: GB2084493A
Application number: GB8031919A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-10-03
Filing date: 1980-10-03
Publication date: 1982-04-15
Also published as: GB2084493B

Abstract

A method for the production of spectacle lenses from a lens blank, the method comprising the steps of cutting a detent or nick in the lens blank D at a defined location on the periphery and thereafter effecting subsequent grinding, lapping and polishing operations in apparatus incorporating a lens holder A with a projecting means C at a defined angular position which cooperates with the detent in the lens, the lens blank being removable from the lens holder in one apparatus during processing and subsequently replaced in the holder of the same or another apparatus for further processing, the projection and detent providing correct relative angular alignment in other lens holders during all processing operations. The method does not require conventional "blocking" and avoids transfer of the lens and holder from one work station to another. <IMAGE>

Description

SPECIFICATION Method and apparatus for blocking lenses during grinding and polishing operations This invention relates to a method and apparatus for mounting or blocking lenses during grinding and polishing operations and is mainly concerned with operations carried out on spectacle lenses during production.

In known methods it is necessary to mark off an axis or reference line on the lens blank and with bifocal lenses the axis has to be "layed-off" using a protractor. Careful visual alignment is then necessary each time the lens is remounted for subsequent operations during grinding.

Broadly according to this invention a method of blocking a lens comprises providing the edge of the lens blank with a cut-away 'nick' at a defined reference point, the nick cooperating with a peg or pin or the like positioned on a lens holder in a defined position whereby the lens may be seated in the holder with the nick and pin in engagement.

This invention also provides a processing method for carrying out operations on lenses, wherein each processing station includes a holding means for a lens with a pin or the like at a defined angular locating forming a reference point which engages a 'nick' in the lens also provided at a defined reference point, the lens being movable from one work station to another without requiring removal of the lens and lens holder assembly complete, the lens being removably secured in the holders, for example using vacuum enabling ready release to be effected.

With such an arrangement the lens may be removed from the holder at one processing station and relocated in a holder at another station with precise alignment. This avoids the necessity of having to remove the lens complete with holder for transfer to another operating station.

Further features of the invention are described in conjunction with the accompanying drawings showing examples and wherein: Figure 1 is a section through a lens and block for grinding, smoothing and polishing a spherical curve, Figures 2 and 2a show respectively section and plan of a block for operating on the back (concave) surface of the lens, Figure 3 shows a lens in plan with the locating or index nick, and Figures 4 and 4a show a section and plan respectively of a block for operations carried out on a toric generator.

In the system according to the invention the lens has a small 'nick' cut into the side as shown in Figure 3. With a single vision lens this cut-out can be placed anywhere, and after finishing the axis the cylindrical curve would be 900 to this cut-out.

In the case of a semi-finished bifocal lens it is necessary to "lay off" the lens, mark the axis position, then make a mark 900 off the axis. In the case of British semi-finished bifocal lenses the procedure is, however, as follows. With this lens it already has a cut-out at 900 off the segment and this can be used to make the nick. The lens is layed on a protractor table with a peg to engage in the nick which is then rotated to the axis required and allowing 50 for each 1 m/m of segment setting.

Then the lens, still held within this protractor table, is offered up to a cutting wheel which would cut a new nick at 900 from the new set position.

A small machine is used to make the cut with a stop screw to regulate depth and wear of the wheel.

For grinding, smoothing and polishing a spherical curve on the front surface (convex side) of a lens, the grinding is done on a spherical generator. To hold the lens in position block A of Figure 1 is fitted into the machine. This can be locked into the machine or just fitted in as required set by two pins engaging locating holes B on the base of the block.

The lens D fits into the block with the rim preventing the lens from slipping off and the pin C in the block fits the cut-out, preventing the lens from turning.

The grinding is from above so that the lens is well secured. After grinding the lens is removed from the block using compressed air injected at E.

For smoothing and polishing of the lens both operations are done on the same type of machines except that different pads and powder are used.

First the lens is fitted into the block A with a plastic button fitted in the recessed hole E. The machine has the correct curve tool (or lap) fitted, the lens is placed on this tool and held under pressure from above. The lens is quite secure although here it could be held under vacuum if required. After smoothing the lens is removed, washed and inspected. The same operation is effected for polishing.

At any stage the lens can be put back on the holder without the need to "re-block" in the conventional way.

For grinding, smoothing and polishing a spherical curve on the back surface (concave side) of a lens the procedure is as for working the front curve, except that block AA of Figure 2 and Figure 2a is used. As can be seen from the drawing the block is stepped down at BB to allow the lens DD to sit in the well resting on rubber'0' ring EE. The holder includes pin CC.

To remove the lens from the block an air gun may be used to "blow" the lens out if necessary.

For grinding, smoothing and polishing a lens with a cylindrical curve on the back surface (concave side) the lens will have this curve on the 1 800 line, as this-is iswhere it was "layed off".

The first stage is to grind the curves to reduce the lens thickness according to instructions set out. This is carried out on a toric generator and again the lens has to be held. For this block Al of Figure 4 and 4a is used, the lens is seated on the rubber'0' ring El and the lens and block are held in the end of the spindle by a vacuum.

The lens is now ground. After grinding the lens can be removed to check curves, edge and centre thickness and, if not correct, replaced and recut.

Location is effected by pin C1.

For smoothing and polishing the procedure is the same apart from powders used.

The lens is held in a block Al within a yoke using a vacuum. The yoke is held secured and the lens worked by the tool. Once again the lens is set in position in the block on pin Cl; the block is a permanent fitting within the yoke, set in correct position, and therefore the lens is worked on its correct axis so that there is no risk of operator error.

After these operations the lens can be returned if necessary.

With the described arrangements the marking of the lens has now a one only position and can at any time be re-worked on a correct alignment, and expensive metal is no longer required for the blocking of standard lenses and the time required for blocking is avoided.

At any stage the lens can be measured for centre and edge thickness without the encumbrance of a block fixed thereto.

In blocking plastic lenses the danger of marking the surface of the lens with hot metal is avoided.

Claims

1. A method for the production of spectacle lenses from a lens blank, the method comprising the steps of cutting a detent or nick in the lens blank at a defined location on the periphery and thereafter effecting subsequent grinding, lapping and polishing operations in apparatus incorporating a lens holder with a projecting means at a defined angular position which cooperates with the detent in the lens, the lens blank being removable from the lens holder in one apparatus during processing and subsequently replaced in the holder of the same or another apparatus for further processing, the projection and detent providing correct relative angular alignment in other lens holders during all processing operations.

2. A method according to Claim 1, wherein the lens holders at each processing station have an associated vacuum means, the lens being held in the holder during processing by vacuum, the lens holder including resilient sealing means engageable with the lens blank surface.

3. A method according to Claim 1 or 2, wherein each lens holder includes means for engaging with the processing apparatus at a defined angular position, the pin being positioned at a location defined relative to said means.

4. A method in accordance with any preceding Claim, wherein the detent in the lens blank is produced by positioning the lens blank on a graduated marking table and cutting the periphery of the lens using a grinding means associated with said table and at a defined position relative to an axis of the lens blank.