US2939252A

US2939252A - Ultrasonic lens generators

Info

Publication number: US2939252A
Application number: US638116A
Authority: US
Inventors: Cooke Frank
Original assignee: American Optical Corp
Current assignee: American Optical Corp
Priority date: 1957-02-04
Filing date: 1957-02-04
Publication date: 1960-06-07
Anticipated expiration: 1977-06-07

Description

June 7, 1960 F. COOKE 2,939,252

ULTRASONIC LENS GENERATORS Filed Feb. 4, 1957 2 Sheets-Sheet 1 INVENTOR FRA NK coo/ 5 ATTORNEY June 60 F. COOKE 2,939,252

ULTRASONIC LENS GENERATORS Filed Feb. 4, 195? 2 Sheets-Sheet 2 v 104 INVENTOR 77 FRANK cop/ 5 ATTO ULTRASONIC LENS GENERATORS Frank Cooke, North Broolrfield, Mass, assignor to American Optical Company, Southbridge, Mass, a voluntary association of Massachusetts Filed Feb. 4, 1957, Ser. No. 638,116 2 Claims. ((1151-67) This invention relates to improvements in lens generating machines and has particular reference to an improved high speed means and method of surfacing lens blanks or the like.

One of the principal objects of this invention is to provide a high speed, precise means and method of surfacing lens blanks or the like by the use of an ultrasonically vibrating tool.

. Another object is to provide a means of abrading the surface of a lens blank or the like comprising a lens supporting mechanism which is adapted to cause a lens blank or the like to be orbited about an axis with which a ringlike tool is aligned, further means within said supporting mechanism for simultaneously rotating said lens blank about its central axis, means for positioning said ringlike tool adjacent the surface of said lens blank, an abrasive feed system for causing abrasive material to be distributed over the surface of said lens blank between said ringlike tool and the surface of said lens blank to be abraded and means for causing said ringlike tool to be ultrasonically vibrated in a direction along the longitudinal axis of said ringlike tool to cause an abrading action upon the surface of said lens blank surface.

Another object is to provide a device of the above character wherein the surface of a lens blank being abraded by said device is moved about the abrading edge of a rin'glike tool portion in a manner such that the abrading action, caused by the abrasive material applied between said tool and said lens surface, is evenly distributed over the entire abrading surface of said tool portion so as to cause the wear upon said tool to be uniform.

Another object is to provide a high speed generating device of the above character which incorporates the use of loose abrasives with a simple, inexpensive and easily replaceable tool portion.

Another object is to provide a means and method of abrading the surfaces of lens blanks or the like by the use of an ultrasonically vibrating tool and loose abrasives wherein the finished surfaces of said lens blanks will be formed to accurate predetermined curvatures regardless of the wear encountered in said tool during the abrading process.

, Another object is to provide a high speed lens abrading device which is adapted to provide a lens blank or the like with a'finished surface thereon which is free of the objectionable, minute glass fractures caused by high Fatented June 7, 1960 tially at a position indicated by line 5-5 of Fig. 4 and looking in the direction of the arrows;

Fig. 6 is afragmentary sectional view of the lens holding mechanism taken at a position indicated by line 6-6 of Fig. 4 and looking in the direction of the arrows;

Fig. 7 is a sectional view taken on line 7 7 of Fig. 4; and

Fig. 8 is a fragmentary sectional view of a modified abrading tool which is adapted to be used in conjunction with the above device.

Referring more particularly to the drawings in which like characters of reference designate like parts throughout the several views, the device embodying the invention comprises a stand 10 having a base 11 and a vertically extending supporting post 12 secured within said base 11 upon which is mounted a tool supporting means hereinafter referred to as head 13, a lens supporting and actuating mechanism 14 and a drive means 15 for operation of said lens supporting and actuating mechanism 14.

The head 13 (Figs. 1, 2 and 3) comprises a bracket 16 which is fitted upon the upper end of the supporting post 12 by means of a longitudinal bore 17 provided within one end thereof and is retained in its desired vertical position upon said supporting post 12 by means of a stop ring 18 which is clamped to said supporting post 12 by set screws or the like 19.

The opposed end of said bracket 16 is provided with a similar longitudinal bore 20 (Fig. 3) into which is slidably fitted a tool carrying spindle 21 having a rack 22 attached to the rear portion thereof, by means of studs or the like 23 (Figs.- 2 and 3), which is adapted to be engaged by a pinion 24 positioned within a slotted opening 25 provided in the bracket 16. Said pinion 24 is in turn keyed to a shaft 26 which is rotatably fitted within a transverse bore 27 provided in the bracket 16. Rotation of shaft 26 by means of a handle 28, which is pinned or otherwise attached thereto, would then cause spindle 21 to be moved in a vertical direction within bore 20 due to the engagement of said pinion 24 with the attached rack 22.

A locking mechanism 29 (Figs. 1 and 3) is provided to secure the spindle 21 in any desired vertical position within bore 20. Rotation of handle 30 in the proper direction will cause the threaded end portion 39a to en-- gage shoe 31 and force the face 31a of said shoe 31 against the spindle 21 to prevent vertical movement of said spindle. Rotation of handle 36 in the opposite direction, however, will release shoe 31 from spindle 21 and allow said spindle to be moved vertically by means of handle 28.

The lower end of spindle 21 is provided with a vertically operated, water cooled magneto-striction transducer 32 (Figs. 1, 2 and 4), which is operated by a high frequency power supply unit 33 (Fig. 1) and is electrically connected thereto by means of a suitable cable or the like 34. Hoses 35 are provided to supply the cooling system of said transducer 32 with circulating cold water.

The vibrating shaft 36 (Fig. 4) of said transducer 32 is provided with a conically shaped tool holder 37 which is secured to shaft 36 by means of set screws or the like 33 and a tubular or ring shaped tool 39 is brazed, soldered or otherwise secured to a reduced shouldered portion 40 of the tool holder 37 in the manner illustrated best in Fig. 4.

When in operation, the transducer 32 will cause the vibrating shaft 36, tool holder 37 and tool 39 to vibrate or. move up and down in a vertical direction along the longitudinal axis of said transducer at ultrasonic speeds such as, for example, 22,000 times per second. The excompared to that of handle 28, it is evident'th'at'when the lockingmechanism 219 is released the .above. mentioned weight would cause a downward force upon a lens blank or the like being abraded by said' tool '39 and in order to control the amount of force or downward-pres- Isure exerted by said combined weight, an adjustable spring type counterbalance .mechanism 41 (Figs. 31, and 3) is provided upon the shaft 26'and bracket '16;

Said counterbalance mechanism comprises a spring housing; 42 having a reduced shouldered portion 43 thereon which is adapted tofit within a recessed area 44 in the bracket 16. Said reduced shouldered portion 43 is further provided with notches 45 which are adapted to be engaged by a spring loaded pawl 46 so that housing 4Z may be rotated in one direction while being restricted from rotation in the opposite direction by saidpawl 46. A spirally wound fiat spring 47 is positioned within housing 42having one end 47:: thereof attached to the end of shaft 26 which protrudes into said housing. 42

(Fig. 3) and its opposed end 47b anchored to the inner v wall ofsaid housing 42; With shaft 26 held stationary by means of locking mechanism 29', it can then be seen that rotation of housing 42 in the proper direction will cause'spring 47 to becomewound up andupon release of locking mechanism 29 the tension inspring 47 will tend to partially counteract the downward force due to the weight of spindle 21 and parts connected therewith. Variable tensions may be applied to spring 47 depending upon the extent to which housing 42. is rotated. The tension on spring 47 may also be entirely released by withdrawing pawl 46 from notches 45. I

Since the movement of tool 39 is restricted to an up and down or vertical motion it is evident that the lens blank, to be abraided, must then be actuated about the abraiding surface of said tool 39 so as to provide said lens blank with a predetermined curved surface upon one side thereof. In order to equally abrade all points upon thesurface of said lens, and to assure a uniform wearing effect upon the abraiding edge of tool 39 during the abrading operation, a lens supporting and "actuating mechanism 14 is provided.

Said mechanism 14 is constructed so as 'to have its axis of rotation AA (Fig. 4) aligned with the longitudinal axis of tool 39, and the lens blank B to be abraded is mounted upon the mechanism 14 so as to have its center C offset from said axis AA an amount equal to the radius of the ringlike tool 39 minus /2 the thickness of said tool 39. Rotation of mechanism 14 about axis AA would then cause the surface of lens blank B to be presented to all parts of the abrading surface of tool 39 and in order to assure that all parts of the surface of lens blank B will be equally abraded, means for independently rotating the lens blank B about its centrabaxis EE 530 (Fig. 5) are provided to retain guideway 53 upon said carrier 51. A slide 56, having an upstanding bifurcated cradle 57 integrally'formed thereon, is slidably positioned upon the upper surface of said guideway 53.

The undersideof said slide56 is provided with a pair of keyways 58 (Figs. 4 and 5) which are adapted to be engaged by keys 54 to guide said s1ide'56 when said slide 56 is adjusted relative to said guideway 53. In order to secure slide 56 in its desired adjusted position relative to guideway 53, a pair of slotted openings 59 (Fig. 5) are provided in said slide 56 and locking studs 59a are positioned so as to extend through the slotted openings 59 and threadedly engage guid'eway53. It is to be noted that point C is the center of lens blank B as described above and is located at a distance from axis AA equal to the radius of tool 39 minus /2 the thickness of said tool. The distance from axis AA to point C, however, would be directly related to the size of tool used and point C is positioned with respect to axis AA by adjusting slide 56 upon guideway 53.

The upper surfaces of the bifurcated upstanding cradle 57 of slide 56 are provided with radial guideways 60 having a center of curvature originating along an axis extending through point C (Fig. 4) and an adjustable lens supporting carriage 61' is mounted upon said radial guideways 60 by means of slides 61a integrally formed upon the lower sides of said carriage 61 (Figs. 4,5 and6).

Carriage 61 is provided with a longitudinal bore 62 in which an adjustable spindle housing 63 is fitted and said spindle housing 63 is adapted to be longitudinally adjusted within said bore 62'by 'means of a ring 64 which threadedly engages three outwardlyextending threaded lugs 65 integrally formed upon said spindle housing 63 (Figs. 4 and 6). Said threaded lugs 65 arefitted within three recessed areas 66 formed upon the upperportion of carriage 61 in a manner such as to restrict said spindle housing 63 from any rotational movement while allowing a longitudinal movement thereof by operation of ring 64 as follows:

Ring 64 is of a diameter suflicient to overlie the upper portion of carriage 61 at each side thereof as shown in Fig. 6 and is retained in said overlying relation therewith by means of a cover member 67 (Fig. 4) which is secured to the upper ends 61b of the carriage 61 by means of studs or the like 68. Rotation of ring 64 will then cause the spindle housing, having lugs 65 threadedly engaged therewith, to be slidably adjusted withinbore 62 of carriage 61.

A work carrying spindle 69 is rotatably mounted within the spindle housing 63 by means 'of suitable hearings or the like 70 and is provided with a tapered end portion 71 upon which is mounted a lens block 72 having a tapered opening 73 therein which is adapted to fit upon said end portion 71 of spindle 69. Removal of block 72 may be accomplished by causing athreaded screw 74 (Fig. 4) to be advanced into said block 72 so as to engage the tapered end 71 of said spindle and force the block outwardly thereof.

A lens blank B to be abraded is secured to surface of block 72 by any suitable means such as, for example, wax, pitch or vacuum.

From the above description, it can be seen that by sliding carriage 61 along the radial guideways' 60 of' cradle 57 that axis E-E may be angled with respect to axis AA and that lens blank B will be pivoted about point C and angled with respect to the abrading-edge-of tool 39 in such a manner as to control the'curvature of the surface to be abraded upon lens blank B.

in order to retain the carriage 61 in its desired adjusted position along the radial guideways 62, each,of said guideways 62 is provided with an adjustable gib 75 which. is adapted to be clamped against the slides 61a of said carriage by means of studs or the like 76.

After having properly angled the lens blank B as described above, the lens blank supporting mechanism 14 is rotated about axis AA by drive means 15 which comprises a supporting plate 77 secured to a bracket 78 by studs or the like 79 (Figs. 1 and 5). Said bracket 78 is in turn clamped to the supporting post 12' in a the upper manner'identical to clamping bracket 48. A motor 80, which is secured to plate 77 is connected by a belt and pulley arrangement 81 to a gear reduction means 82, also carried by said plate 77, which in turn is connected by a second belt and pulley arrangement 83 to the lower end of a shaft 84 of the lens blank supporting mechanism 14. Said shaft 84 is pinned or otherwise secured within a mounting plate 85 which is attached by studs 86 to a disklike cover 87 carried by the underside of the rotatable carrier 51.

Operation of motor 80 would then cause shaft 84 to be rotated by means of the above described belt and pulley arrangement 81, gear reduction means 82 and belt and pulley arrangement 83. By said rotation of shaft 84 the lens blank supporting mechanism would be rotated about axis AA and due to the above described positional relationship of the center C of lens blank B with respect to axis AA, said lens blank B would be rotated about the abrading edge of tool 39.

In order to'present all portions of the surface of said lens blank B to said abrading edge of tool 39 during said rotational movement thereof, a motor 88 is attached to the underside of carriage 61 by a mounting bracket 89. Said motor is provided with a gear 90 attached to its drive spindle which is adapted to engage a second gear 91 secured to the lower end of the work carrying spindle 69 (Fig. 4).

Operation of motor 83 would then cause lens blank B to be independently rotated about axis EE while being carried about a circular path around axis AA.

Since motor 88 is carried by the lens blank supporting mechanism 14 it can be seen that said motor 88 will rotate therewith during the lens blank abrading operation and in order to provide a means of electrically connecting said motor 88 to a source of current, which will not cause the necessary electrical conductors to become entangled during an abrading operation, a pair of slip rings 92a and 9212 (Fig. 4) are positioned upon shaft 84 so as to rotate therewith and a pair of electrical brushes 93a and 93b are mounted within an insulating portion 94 of a supporting member 95, which is in turn secured by studs or the like to the stationary supporting ring 50. Brush 93a is positioned so as to contact the uppermost slip ring 92a and the other of said brushes 93b is positioned to contact the lower slip ring 92b, so as to permit a source of electrical current to enter conductor 96a and pass through brush 93a, slip ring 92a, conductor 97a, motor 88 and return through conductor 97b, slip ring 9212, brush 93b and conductor 96!).

In order to abrade the surface of lens blank B by means of the vibrating action of tool 39 and the actuation of said lens blank B about the edge of tool 39 as described heretofore, an abrasive grit such as powdered emery or the like is suspended in a liquid vehicle such as for example Diglycol Stearate and is applied to the surface of said lens blank by means of a circulating system comprising a tank 98 (Fig. 1) in which a supply of said suspended grit hereinafter referred to as a slurry, is contained. A pump 99 is provided within tank 98 to cause said slurry to be forced through a hose or tube 100 and tubes 100a to the tool holder 37. Tool holder 37 is provided with a transverse bore 101 (Fig.

4) therethrough having tubes 100a attached at each end thereof and a centrally aligned longitudinal bore 102 extending from said bore 101 downwardly through the lower end of said tool holder. The slurry will then pass from tubes 100a through bore 101 and bore 102 to the surface of lens blank B and be returned to tank 98 for recirculation by means of drains 103 and tubes 104 which are provided upon the lower portion of a circular splash pan 105 mounted upon the stationary supporting ring 50. A flexible apron 106 which is attached to cradle 61 (Fig. 4) is provided to prevent said slurry from contacting the working parts of the lens supporting and actuating mechanism.

The abrading action upon the surface of lens blank B is accomplished by the speed and force exerted by the ultrasonic vibrations of tool 39 during the actuation of said lens blank thereabout, which causes the particles of abrasive caught between said tool and lens surface to be forced against the surface of said lens blank to abrade said lens blank. A slight abrading or wearing effect will also take place upon the abrading surface of the tool 39 during the above action but said wearing effect will be uniformly presented to all portions of said surface of tool 39 in the manner described previously so as to cause said tool 39 to retain its original contour shape regardless of said wear and provide the lens blank with an accurately curved abraded surface.

It is to be pointed out that the size of the particles of abrasive grit used in the slurry will determine the final texture of the finished surface of the lens blank being abraded and in order to control the time necessary for abrading a lens surface and the quality of said finished surface, it is necessary to control the speed atwhich tool 39 vibrates as well as to select an abrasive grit of the proper coarseness.

It is also to be noted that during the abrading operation, the tool 39 does not actually touch the surface of lens blank B but is spaced a distance away therefrom substantially equal to the size of the abrasive grit used.

In the surfacing of ophthalmic lenses it is essential in many instances to control the final thickness of the finished lens blank. In the device embodying the invention this may be accomplished by first measuring the center thickness of the unabraded lens blank and determining the depth of cut necessary to provide the final desired thickness when said lens blank is positioned upon block 72.

In order to provide an accurate curved surface upon a lens blank B such as shown in Fig. 4 it is necessary to abrade the surface to a depth at which point C is located precisely upon the finished surface of said lens blank since, as described above, the carriage 61 is pivoted about an axis, which extends through point C.

The adjustment provided by rotation of ring 64 described above is used to adjust the lens blank relative to point C along axis E-E so that said lens blank may be finished to various desired thicknesses. If, however, the range of said adjustment is not sufiicient to provide a lens blank of the desired thickness, block 72 may be replaced by a thicker or thinner lens block of the same type.

After having determined the depth of cut necessary to cause lens blank B to 'be abraded such that point C will be coincident with the finished surface thereof the counterbalance mechanism 41 is adjusted to provide the proper pressure upon lens blank B by tool 39 as described above and locking means 29 is released to allow the tool 39 to be lowered so as to engage the lens surface whereupon a zero reading is set upon an indicator 106 (Figs. 1 and 2) which is adjustably secured to bracket 16 of head 13 by means of a support 107. Said indicator 106 may be zeroized by moving it along support 107 or by adjusting the L-shaped contacting means 108 relative to the plunger 109 of said indicator 106. Adjustment of said L-shaped contacting means 108, which is carried by spindle 21, is accomplished by moving the ring-like supporting bracket 110 (Fig. 2) along spindle 21 and clamping said supporting bracket 110 in its adjusted position by means of a locking screw 11 1.

After having adjusted the indicator 106 as described above, the motors and 88 are energized to actuate the lens blank B, motor 99a is energized to operate pump 99 and circulate the slurry and the magneto-strictive transducer 32 is energized to cause tool 39 to vibrate. The abrading action produced thereby is allowed to continue until the depth of cut desired is registered upon the indicator whereupon tool 39 is removed from the work by handle 28 and the motors are de-energized to 7 permit the finished lens blank to be removed from block 72. g a

The depth of cut may also be controlled by calculating the time required for said device to remove the desired amount of glass and causing the motors 81), 88, 99a and transducer 32 to be manually or automatically deenergized at the end of said'time period.

Fig. 8 illustrates an alternative abrading tool 112 which may be used in conjunction with the above device. Said tool 112 is provided with a predetermined derside thereof and is sweat soldered, brazed or otherwise secured to a tool holder 114, which is identicalin construction to that of tool holder 37 described above.

Inloperation, the lens blank B would be angled by means of cradle 61 an amount sufficient to provide the desirede'radius of curvature upon the finished surface thereof as described previously, which'radius of curvature V would'be equal tothe curvatureof surface 113 of tool 112. 'Tool 112 is then caused to vibrate by means of transducer 32 and lens blank B is actuated about surface 113 of tool 112 as described above and the abrasive slurry is fed through tool 112 by means of openings 115.

it is to be noted that due to the actuation of lens blank simple, efiicient and economical means have been provided for accomplishing all the objects and advantages of the invention. However, it will be understood that various omissions, substitutions and changes in the forms and details of the embodiment illustratedmay be made by those skilled in the art without departing from the spirit of the invention.

Having described my invention I claim.:

1. A surface generating machine for forming curved surfaces on lens blanks comprising a work-supporting member rotatable about its axis and having a lens blank holder mounted thereon which is titltably adjust-able and independently rotatable relative to said work-supporting member, means for rotating said Work-supporting member and means for independently simultaneously rotating said work holder, an abrading tool adapted to be positioned in abrading relationship with the surface of a lens blank when said lens blank is mounted on said holder, means for vibrating said 'tool at ultrasonic frequencies in a direction substantially in line with said axis ofsaid work-supporting member, means to bring said tool into cylindrically curved abrading surface 113 upon the unsaid abrading relationship with said lens blank and means for continuously supplying a loose abrasive material to said lens blank between said tool and'the'adjacentsurface of said lens blank.

2. 'A lens surfacing machine for generatinga spherically curved surface on lens blanks comprising a worksupporting member rotatable about its axis and having a lens blank holder mounted thereon which is tiltable and independently rotatable relative to said work-supporting member, an abrading tool adapted to be vibrated at ultrasonic frequencies in a direction substantially in line With the axis of rotation of said work-supporting means, means to bring said abrading tool into abrading relationship with a lens blank when placed upon said holder, aligning means for tilting said lens blank holder a predetermined amount with respect to the abrading surface of said abrading tool in accordance with the finished radius of curvature desired upon said lens blank, means to adjust said lens blank holder laterally relative to-the axis of rotation of said rotatable work-supporting member so as to cause the center of said lens blank to be'positioned at a predetermined radial distance from the axisof rotation of said rotatable work supporting member in accordance with the size of said abrading tool, drive means for rotating said Work-supporting member to cause the center of said lens blank to 'be orbited concentrically about the axis of rotation of said rotatable work supporting member, further drive means for independently simultaneously revolving said lens blank holder and lens blank substantially about said center of said lens' blank, means for causing said abrading tool to be ultrasonically vibrated in a direction along the longitudinal axis thereof and an abrasive feed system for depositing loose abrasive material between the surface of said lens blank and said abrading tool to cause said abrasive material to be forced upon the surface of said lens blank by the vibration of said annular abrading element.

References Cited in the file of this patent UNITED STATES PATENTS 2,774,193 Thatcher et a]. Dec. 18,