US2179088A - Lens abrading machine - Google Patents

Description

Nov. 7, 1939. L. w. GODDU ET AL LENS ABRADING MACHINE Filed May 13, 1935 3 Sheets-Sheet l ODDL) ALDUJELL R Y m Nw R mos u Nmm .n ILR MA LA W Y B W NOV. 7, 1939. w GQDDU ETAL v 2.179.088

LENS ABRADING MACHINE Filed May 13, 1935 5 Sheets-Sheet 2 INVENTOR LLOYD LU. GODDU CHAR I BY I 1511 1 p LES H.CALDLUELL Nov. 7, 1939.

L. w. GODDU ET AL 2.179.088

LENS ABRADING MACHINE Filed May 15, 1935 3 Sheets-Sheet 3 INVENTOR LLOYD w. GODDU B CHARLES H. CALDUJELL Patented Nov. 7, 1939 l r I UNITED STATES PATENT OFFICE 2,179,088 LENS ABRADING MACHINE Lloyd W. Goddu and Charles H. Caldwell, Southbridge, Mass, assignors to American Optical Company, Southbridge, Mass, a voluntary association of Massachusetts Application May 13, 1935, Serial No. 21,212

Claims. (01. 51-59 This invention relates to an apparatus for tion to be expressed in the accompanying claims. grinding and polishing curved surfaces and is We, therefore, do not wish to be limited to the more particularly related to an apparatus for exact details shown and described as the pre grinding or polishing surfaces on ophthalmic ferred forms only have been shown by way of I lenses. illustration. 5

Prior to our invention apparatus used to grind Referring to the drawings: and polish the refracting surfaces of lenses in- Fig. I is a three-quarter partial elevational troduced a latent error into sphero cylindrical view. of the lens grinding apparatus embodying lenses which was not readily detected. The error the present invention; l' in these lenses was not very great and is of prac- Fig. II is a side elevational view of Fig. I showtically no consequence when the curves of the ing a preferred form of the invention; cylindrical surface of the lens are relatively weak, Fig. III is a partial detail plan view of Fig. I, but when the curves of the cylindrical surface are with parts removed for clarity; increased or relatively strong the error reaches Fig. IV is a partial plan view of Fig. I on lines ,e

such proportion that impairments of vision and IV-IV looking in the direction of the arrows 1'5:

eye strain in the wearer may result. Accordingly, and showing the break up motion actuating it is one of the major objects of this invention means;

to provide an apparatus which is capable of Fig. V is a partial elevational view of Fig. IV grinding and polishing toric or sphero cylindrical showing the means for supporting the lap; g L) lenses which will be substantially free from the Fig. VI is asectional view taken on line VI-VI latent errors set forth above. of Fig. II; I

Another object of this invention is to provid Fig. VII is a perspective view of a toric or an apparatus in which the lens block is guided sphero cylindrical lens showing the portion of the by mechanism which maintains theaxis of the surface into which an error is introduced by prior lens block parallel to the cylindrical axis of the art'machines; lens. In the prior devices, the guiding mecha- Fig. VIII is a perspective view of an element of nism allowed the lens block todepart from such the means for actuating the lens block; relation with the result that thesurface being Fig. IX is a plan view of a modification of generated was flattened on portions thereof and Fig. I, and 0 thereby departed from a true toric surface. Fig. X is an elevational view of Fig. IX. v Another object of this invention is to provide With reference to the drawings, an embodian apparatus of the type prescribed in which ment of the invention shown for illustration, the lens block carries oppositely disposed arms comprises a pedestal l0 which is carried on any which are adapted to engage a paralleling mechsuitable base (not shown). The pedestal IE! car- I r 5 anism which permits said arms to oscillate about ries upwardly extending columns or standards I I,

two axes at right angles to each other, while terminating in suitable slideways generally indimaintaining the lens block fixed about a third cated at l2, the upper ends of which are closed axis perpendicular to the first two axes. by means of plates 13 secured to the top of the Another object of the present invention is to columns in any suitable manner as by means of 0 provide a lens grinding apparatus in which there screws It. A slide l6, adapted to .slide in the is anovel break up motion imparted between the slideway I2, carries a tool. support H, which is lens block and lap whereby drag lines in the sursecured to the former by any suitable means, face of the lens will be positively eliminated. such as screws I8. The slideways. l2 are pro- Another object is to provide a break up motion vided with means for compensating for wear in .5 wherein a relative long movement is provided in the form of shims l9 which may be adjusted .45

the direction of the axis of the cylinder and a relative to the side of the slideways and against relative short movement is provided in a directhe slide by means of screws 2i. Means are tion transversely to said axis. provided for imparting oscillatory motions to the Other objects and advantages of the invention slide [6 in order to break up the motions of the I K will becomeapparent from the following descripgrinding action. To this end, a shaft 22 is jourtion taken in connection with the accompanying nalled in the base and carries an eccentric 23 drawings and it will be apparent that many which is adapted to engage an elongated slot 26 changes may be made in the details of construcin the enlarged central portion of the slide [6. tion, arrangement of parts shown and described The shaft 22 may be driven in any suitable man- 5 without departing from the spirit of the invenner as by means of gear 20. The pedestal I0 carries columns 27 to the upper ends of which are pivoted links 28 which carry a guide mechanism 4B, the exact purpose and structure of which will be described later.

Suitable actuating means are provided for moving a lens block 29 relative to a lap I5 carried on the support I! in order to get the proper abrading action. To this end, the apparatus is provided with a spindle 3! which may be journalled in any suitable manner in a frame carried by the base (not shown). Suitable driving means are provided for rotating the spindle 3| in the form of a pulley 32 fixed to the spindle, the pulley being driven by a suitable belt 33.

A driving connection is provided between a crank 34 carried by the lower end of the spindle 3| and the lens bearing block 29, for permitting a change in the path of the lens block 29 to assist in preventing drag lines being formed on the lens. This driving connection comprises a pin 3'! carried on the lower end of the crank 34 and is adapted to engage a hole in a cylindrical block carried in a bore 35 in the upper portion of the lens block 29. The hole 25 is eccentrically located in the block 30, which is adapted to fit loosely in the bore 35. As the crank and pin 3'! drive the lens block 29 in a circular path, the slide l6 carries the lap or abrading tool I 5 in an oscillatory path in the direction of the axis of the cylinder and provides a relatively long movement in said direction and transversely to the axis of the spindle 3|. Under the combined influence of these two movements the cylindrical block 351 will change its position relative to the bore 35, and thereby cause the efiective stroke of the eccentric driving connection for the lens block to be varied. Such a motion insures positive break up so that no drag lines will be formed in the lens surface being ground.

It is to be noted that the oscillatory movement is in the direction of the axis of the cylinder and that there is very little movement in a direction transversely to said axis. This thereby greatly reduces or substantially eliminates the error introduced by prior art devices of this nature, such error being primarily the departure of the generated surface from the toric curvature. The crank 34 is adjustable relative to the shaft 31 in order to regulate the eccentricity of the crank pin 31 and 'may be held in any adjusted position by means of a set screw 39.

The lens block holder has aligned, oppositely disposed, outwardly extending arms 36 which are adapted to engage the guiding means 46 which hold the lens block exactly on the cylindrical axis of the surface to be ground or'polished.

The means for maintaining the lens block in the proper relative position constitutes one of the. salient features of the present invention and will now be described.

The links 28 have pivotally connectedat their upper end a ring member or table All which carries substantially diametrically opposed spaced- -face being ground while allowing the block free up and down movement as well as transverse movement in a horizontal plane. The relative movement of the lens block 29 and the lap l5 will be understood from Fig. II, when it is ob- ;served' that since the table member 4| is; carried on the links 28 any oscillatory movement will cause the plane of the table member 4| to remain parallel to itself and thereby maintain the arms 42 in parallel planes. Looking at Fig. VII it will be seen that in toric lenses the axes A and B of the concave surface are of different curvature. In generating such surfaces the lens block 29 must be permitted to move freely about two axes at right angles to each other in order to follow the curve of a lens being abraded but must be held absolutely rigid and against rotationabout the third axis which is perpendicular to' the axes A and B. In other Words, the lens block must be permitted entirely free movement except that the axis of the block must be maintained in planes parallel to the toric axis of the generating surface of the tool. In the prior art devices the latter condition was not fulfilled and as a result the finished surface in the vicinity of the axis A represented as bounded by the dotted lines in Fig. VII departed from a true toric curve due to the twisting or departure of the lens blocks from the axis of the cylinder. This error was due to the fact that in theprior art devices the guide arms, corresponding to the arms 42 in Fig. I, were mounted for pivotal movement about a single pivot axis in the plane'of the cylindrical axis. From inspection of Fig. II it will be seen that if the surface of the lens being ground was sphero cylindrical, instead of cylindrical as shown, the lens blocks 29 would have to oscillate about the two major axes of the lens, tilting the guide arms 36 in a vertical plane so that one of the arms 36 would engage the arms 42 further from the pivotal point than would the other. If at the same time the actuating mechanism had moved the block to one side of the axis of the cylindrical curve, one side of the lens block will have been moved farther than the other, because one of the arms 36 will engage the arms 42 at a point further from the pivotal axis than the other arm and will therefore have to swing through a greater arc, resulting in a twisting of the lens block, 29 relative to the cylindrical axis of the lap. In lenses having a very weak cylindrical curve, departure from the correct curvature due to prior art grinding devices of the single pivot type is very small because the cylindrical curve does not very greatly depart from a plane surface, but when the desired surface does substantially depart from a plane the relative twisting flattens the curve on either side of the cylindrical axis and the error is greatest at the outer edges, diminishing-to zero at the intersection of the major axes of the curve.

Since the grinding and polishing operations on lenses are accomplished by using powdered abrasives, special construction of the link mechanism is necessary in order to prevent these abrasives from cutting away the bearings. As shown in Fig. I and II, the ring member or table 4| has lips 5| which completely overhang and protect the pivotal connection between the member 4| and the links 28. Likewise, the links 28 have outwardly extending bearing covers 52 which protect the pivotal connection 53 from the abrasives.

In Figs. IX and X is shown a modification of the mechanism for maintaining the aims of the lens block 29 on the axis of the grinding lap. To this end, a ring member or table 68 carrying the guide arms 42 is mounted for sliding movement relative to arms-6| which are secured in any suitable manner as by means of screws 62 to the top the opposed outer portions of the lens.

f standards 63 extending upwardly from the pedestal In. The table 60 is guided on the arms Bl through sliding. engagement with notches 64 in the ring member 60, the open ends of which are closed by means of plates 66 secured to the table 60 by means of screws 61. Suitable shields 68, shown only in Fig, X for purposes of clarity, are provided for preventing the abrasive from falling on the arms 6| during the grinding operations.

It is to be understood that the paralleling mechanism and associated parts may be provided as a separate attachment for lens abrading machines, it being understood that in such instances, the abrading machine and attachment would be provided with interfitting parts for connecting the attachment with the abrading machine and with its operating, mechanism.

The operation of the machine as shown in Figs.

, I to III, inclusive, is as follows:

A tool having the desired curve generating surface thereon is selected from a group of tools having dilferent surface curvatures. This tool is attached to the tool holder l1 and is adapted to 'be recipro'cated in a straight line movement in the lens is preferably mounted in a holder so that the plus side is up in order that the tool may more freely pass over the lens surface with equal abrading pressure over the entire area. It will readily appear from Fig II, that when the lens is mounted with the minus side up that there will be a binding action between the tool and the lens, especially on strong curves, when the tool reaches the outermost limits of its stroke in a direction transverse to the axis of the curve. It is to be understood that when mounting the lens with its positive or convex side up, the positions of the tool l5 and the lens holder block 29 would be reversed.

The lens to be abraded is mounted in the holder having the aligned arms 36 and the said holder is placed on the grinding attachment with the arms 36 between the upright arms 42 with the lens in engagement with the tool. The crank member 34 is then engaged with the holder and is adapted to move the lens in a circular-path over the face of the abrading tool. The interengaging arms 36 and 42 cooperate to hold the lens in positive axial relation withthe tool .during the abrading operation, that is, the lens, although moved in a circular path, is held against rotation about itself during said movement. The upright arms remain in a vertical position and thereby positively maintain the axial relation of the lens and eliminate the prior art error of the lens moving 01f axis and causing surface irregularities.

' The movement of the tool is in the direction of the axis of the cylinder and thereby greatly increases the abrading stroke in this direction. The movement of the lens in a direction normal to the cylindrical axis is relatively slight and thereby eliminates another prior art error which was introduced by prior art devices which had a relatively long stroke in this direction. This long stroke'caused the lens to be rocked over the opposed edges of the tool, which edges, due to the toric nature of the tool tendto flatten and depart from true toric curvature. This tends to cause the generated curve to be flattened along The.

short stroke of applicants device in this direc tion greatly reduces and substantially eliminates this error. the lens until it is reduced to the desired thickness. 1

From the foregoing description it will be readily apparent that by this invention we have provided a machine for grinding and'polishing toric lens surfaces in which means are provided for preventingthe lens from twisting on the grinding lap, thus permitting lenses of "the cylindrical type having strong curvatures to be made without the usual error attendantin lenses made on the prior art machines. Furthermore, by this invention means are provided-forproducing-a novel break up motion between the lens block and the lap thereby positively preventing the formation of drag lines on the lens being operated upon, and for producing truer toric surfaces.

Having described our invention, we claim:

1. For use with an abrading apparatus having a base, a lens bearing block for. holding a lens to be abraded, an abrading tool, means for imparting relative movement between said block and said tool, an attachment associated with said base and adapted to have an operative connection with said lens block' for maintaining the axis of the lens to be abraded and the axis of The abrading action is imparted to said tool in a common plane while permitting otherwise free movement of the lens and lens block, said attachment comprising a supporting member connected to the base by pivoted links causing it to move in transverse parallel motion and carrying spaced parallel upright elements which are maintained in said upright position during the transverse parallel motion.

2. For use with an abrading apparatus having a base,a lens bearingblock for holding a lens to be abraded, an abrading tool, means for imparting relative movement between said block and said tool, an attachment associated with said base and adapted to have an operative connection with said spaced parallel elements being each moved into successive positions which are parallel with each other in a single plane during the abrading.

3. In an apparatus of the type, described for grinding and polishing lenses having in combination an abrading member, a lens holding member, means for moving one of said members in a reciprocatory path and for moving the other 7 of said members in'a circular path and means for preventing relative twisting movements between said abrading member and said lens holding member during the relative movement of said members, the radius of,the circular path being small as compared to said rectilinear path, said means for preventing relative twisting move ments comprising a pair of spaced upright 'members each supported to move it spaced vertical planes substantially normal to the rectilinear movement whereby the said spaced upright members will move into successive positions which are parallel with each other in said planes.

4. An apparatus of the type described for abrading toric lenses by surface contact comprising a tool supporting member for supporting an abrading tool, a lens holding member for holding a lens blank in abrading contact with the tool, means for imparting a circular movement to one of said members, means for imparting a rectilinear movement to the other of said members, said rectilinear movement being only along a line parallel with the axis of strongest curvature of the tool and means associated with one of said members for maintaining it in constant axial relation with the other member during the abrading, said means comprising in part spaced arms each mounted to move in spaced planes extending substantially normal to the direction of the rectilinear movement whereby the said spaced arms will assume successive positions which are parallel with each other in said planes during the movement thereof.

5. An apparatus of the type described for abrading toric lenses by surface contact comprising a lens blank in abrading contact with the tool, means for imparting combined circular and rectilinear movement of said members relative to each other, said rectilinear movement being along a line substantially parallel with one of the major axes-of the abrading tool and means associated-withone of said members for maintaining it in constant axial relation with the other member during the abrading, said means comprising in part" supporting elements mounted to move in spaced planeslying in a direction substantially normal to the direction of the rectilinear movement whereby the said supporting elements will assume successive positions which are parallel with each other in said planes during the movementof one of said members relative to the other. i I

; LLOYD W. GODDU.

CHARLES H. CALDWELL.

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