US2703470A - Lens grinding apparatus - Google Patents

Description

March 1955 H. M- FORTE-R ET AL LENS GRINDING APPARATUS s sheets-sheet 1 Filed Jan. 23, 1555 INVENTORS IamM/Mflwrkr March 8, 1955 H. M. PORTER ET AL 2,703,470

LENS GRINDING APPARATUS Y Filed Jan. 23, 1953 3 Sheets-Sheet 2 INVENTORS 8, 1955 M, PORTER r A 2,703,470

LENS GRINDING APPARATUS Filed Jan. 23, 1953 5 Sheets-Sheet '5 HIIHHI IN VENTORS LENS GRINDING APPARATUS I Harold M. Porter and Patrick H, Reardon, Hagerstown,

Md., assignors to The Mitchel-Tyler Company, Hagerstown, Md., a corporation of Maryland Application January 23, 1953, Serial No. 332,934

6 Claims. (CI. 51-60) This invention relates to lens grinding and more particula'rly to arrangements for continuously changing the position of a blocker so that the lens blanks mounted therein are uniformly subjected to action of the grinding head or cap.

In application Serial Number 230,883, filed June 11, 1951-, now Patent No. 2,686,391, by Harold M. Porter and Patrick H. Reardon, there is shown an arrangement whereby a plurality of blockers are simultaneously moved through various paths such that the abrading effect of the grinding composition is uniformly distributed over the surface of the several blockers. While that arrangeing head is of small radius and handles only a single blocker and in which the blocker is so moved as to pre sent every part of its surface for uniform grinding action. The present invention provides a long wearing highly accurate grinding system in which the blockers are maintained spherical through long repeated uses and in which the lenses .produced are of exceedingly high quality.

Other objectsand advantages of this invention will 'be apparent upon consideration of several embodiments thereof in conjunction with the annexed drawings where- Figure l is a perspective view of a preferred form of grinding apparatus according to the present invention;

, Figure 2 is a fragmentary end view of the apparatus of Figure 1 showing particularly the V-shaped channel for the reception and movement of the blocker;

, Figure 3 is, a view in side elevation of the apparatus of Figure 1 showing the blocker channel and the mechanism for moving the same;

Figure 4 is a top plan view of the mechanism illustrated in Figure 3;

Figure 5 is a top plan view of a modified type of grinding apparatus in which the blocker is caused to engage successive portions of a V-groove laid out in a square p Figure 6 is a view in section taken on the line 66 of Figure 5;

Figure 7 is a plan view taken on the line 77 of Figure 6; and

Figure 8 is a view of a blocker with the lens blanks therein as they appear after the grinding operation.

Referring now in detail to the form of the invention shown in Figures 1 to 4 inclusive, it will be noted that a spherical blocker 10 is engaged by a grinding head or cap 11 which is connected to a spindle 12 driven from the chuck of an ordinary drill press 13.

It is to be understood that the blocker 10 is a sphere normally made of hard bearing steel and provided with a number of symmetrically arranged, radially extendlng, cylindrical cavities. Short cylindrical lens blanks are cemented in these cavities with one end of the blank projecting from the spherical wall. This end of the blank is ground away and into conformity with the surface of the sphere. After grinding, the cement holdlng United States Patent 2,703,470 Patented- Mar. 8,.1

2 the lens blanks is dissolved and the Plano-convex" lenses which have been produced are removed;

In order that the blocker 10 will be moved continuously to present ever different surfaces tothe grinding cap 11 in order that the lens blanks within the blocker will be uniformly ground, the blocker is supported by a v-trough 14 having relatively movable walls. This trough and the associated apparatus is mounted" upon the work table of the drill press 13 by any con enient means, not shown.

The trough 14 is defined by supportingplates 1 5 and 16 which are connected at one edge to ro'ds 17and518 respectively. The rods 17 and 18fare mounted for reciprocation and to that end are, connected to crosshe'ads 21 and 22 at one end and are slotted at the otherj'endto coact with guide pins 23' and 24. The rod 17 is hired to crosshead 21 by screws 25 and the rod 18. is similarly fixed to the crosshead 22. The crosshead 21 lJJlPElISIhfi movement to rod 17 and, to this end,xit is mounted, to reciprocate on shafts 26 and 27. The crosshead 22 is slmilarly arranged to reciprocate on shafts 28" and 29. The shafts 26, 27, 28 and 29 are mounted in and'extend between blocks 30 and 31 and those blocks are supported from a plate 32 which is in turn supported from a plate 33 by short blocks 34. A plate 35 also rests on plates 33 and receives the threaded ends of the guide pins 23 and 24. The plate 35 has a generally V-shaped cut 'out {herein symmetrically arranged about its vertical center Keyed toshafts 36 and 37 which are journaled in the plates 32 and 33, are two sheaves 38 and 39. The upper end of shaft 36 has a pitman 40 extending therefrom and the upper end of shaft 37 has a like pitman 41. At the radially outer end of the pitman 40 there is a ve'rtically extending, pin 42 which engages in along slot-43 extending longitudinally across the entire lower surface of the crosshead 21. A similar arrangement exists between the pitman 41 and a like groove in the lower surface of the cross head 22.

An electric drive motor-gear box combination 44 is mounted on the plate 32 by bolts 45 and the drive shaft of this combination has attached thereto asheave 46 which is connected by a V-b'elt 47 to the sheaves'38 and :9, as can best be understood by reference to Figure It is now apparent that when the motor is operated the sheave 46, throughthe belt 47, will rotate sheaves 38.a-nd 39. Since sheaves 38 and 39 are keyed to the shaftslon which they are mounted and since the 'pitma'ns 40 -a'nd- 41 are also keyed to the respective shafts 36 and 37, it is apparent that thepitmans will rotate at a speeddetermined by the speed of the drive sheave 46- d the rela tion of its diameter to the diameter of the driven sheaves 38 and 39. In theform of the invention illustrated in the drawings sheave 38 is larger than sheave 46. Hence the shaft 36 will rotate at a lower speed than the shaft of the motor-gear box combination 44. On the other hand, sheave 39 is about the same diameter as sheave 46 so that shaft 37 will rotate at about the same. speed as the drive shaft. Since the pitmans 40 andv 41 are connected to the respective shafts 36 and 37, they will rotate at a speed equal to the speed of the shafts on which they are mounted. This rotating movement-is imparted to the crossheads 21 and 22, respectively, which receiprocate on the rods 26, 27, 28 and 29. Since the rods 17 and 18, which carry the components 15 and '16 of the blocker trough assembly, are connected to ;the crossh'eads, it will be seen that components 15 and16 are continuously reciprocating at different speeds. Sometimes they are moving in the samedirection and other times one is moving in a-direction opposite to the other. In anycase, however, their effect on the blocker 10.is to shift continuously its position to present all portions of-its surface uniformly to the grinding head 11.

Ordinary lens grinding compounds of the type described in application No. 230,883, now Patent No. 2,686,391,

It is to be understood that the drill press is modified by the removal of the spindle return spring so that the only weight is the ordinary spindle weight bearing on the blocker through the cap 11. In view of the presence ofrthe grinding composition and in view of the lining of the V-trough with rubber, the cap 11 does not drive the blocker but rotates relative to it to perform the grinding operation. The V-trough assembly, comprised of elements 15 and 16, is lined with a soft rubber liner 49, clearly indicated in Figures 2 and 4. This soft rubber liner, as mentioned above, prevents the rotation of blocker by action of the cap 11. On the other hand, the grinding compound and the rubber 49 cause a tight frictional engagement between the blocker 10 and the components of the V-groove so that the relative shifting of the elements and 16 continuously causes the presentation of a different surface of the blocker to the grinding cap 11. This results in the grinding of good planoconvex lenses, the blanks for which have the appearance illustrated in Figure 8 at the end of the grinding operation.

The end plate of the frame assembly is provided with a V-cutout so that a removable trough may be inserted under the moving components 15 and 16 to catch grinding compound that may fall down through the space between them.

It can be seen that the foregoing apparatus is designed primarily to secure uniform presentation of all parts of the surface of a blocker to the grinding head. The apparatus shown in Figures 5, 6 and 7 is also designed with that end in mind. Again, the blocker is ground by a cap connected to the spindle of the drill press and the illustrated apparatus is intended to be set or fastened to the drill press table in order to move the blocker at andom to distribute the grinding effect over its surace.

In the form of the invention shown in Figures 5, 6 and 7, a V-groove assembly in the form of a square path is located in a box 50. The V-grooves are defined by suitably supported soft rubber 51 and the box itself is provided with four corner legs 52 and a center leg 53. The corner legs rest upon a flat, square table 54 while the center leg is slightly short of the table surface and coacts with an operating arm 55 which extends out from a shaft 56 journaled in the table 54 and provided at its lower end (below the table) with a sheave 57 connected by a V-belt 58 to a sheave 59. The sheave 59 is connected to the drive shaft 60 of the gear box 61, which in turn is connected to a drive motor 62.

From the material just described it is apparent that operation of the motor will cause the arm 55 to rotate (anti-clockwise as viewed in Figure 7) and that such rotation will be imparted through the leg 53 to the box 50. The movement of the box 50 is not, however, a

random movement but a guided one and to this end the table 54 is provided with a marginal flange 63 and corner right angle members 64 defining between them spaces 65 substantially equal to the width of a box leg. The flange 63 and the right angle members 64 are of equal height and both are shorter than the legs 52.

It is now apparent that as the arm 55 rotates the box 50 is caused to move from the starting position of Figure 5 to the lower left corner of this figure. It then moves across to the lower right corner of that figure, then up to the upper right corner of that figure through the left corner and back to the starting position. These movements are controlled by the angle members 64, the length of which is so adjusted that the length of one of them, plus the distance between an adjacent pair of them, is less than the distance between two legs of the box by an amount equal to the width of a box leg. All of this is quite apparent from Figure 7 where the movements of the box 50 are depicted.

The driving arm 55 is notched at 66 to prevent a dead center condition when the box is in one of the corners of the square supporting table 54.

In view of the fact that the spindle of the drill press, and hence the blocker, is held bodily stationary, the movements of the box 50 impart to the blocker various rolling movements on continuously changing internal axes and these movements evenly distribute the abrading effeet of the grinding composition. The grinding composi tion is put by hand into the groove 51 and replenished as necessary.

Since even a small amount of movement of the grinding head when the blocker is not being rolled will cause perceptible uneven grinding, a solenoid brake is associated with the drill press spindle in such a way that when motors 44 or 62 are shut 01f the drill press spindle motor is also shut off and the brake is applied instantly to stop the drill press spindle. This arrangement is diagrammatically shown in Figure 1 at 67.

What is claimed is:

1. Lens grinding apparatus comprising a grinding cap having a cavity internally complementary to a portion of the surface of a sphere, a spherical blocker partially encased in said cavity and held bodily stationary thereby, sloping elements defining a V-groove positioned to act on the projecting remainder of said blocker, means to move said sloping elements past said blocker at different speeds to rotate the blocker on continuously shifting internal axes, and means to rotate said cap to bring about a grinding action.

2. Lens grinding apparatus comprising a grinding cap having a cavity internally complementary to a portion of the surface of a sphere, a spherical blocker partially encased in said cavity and held bodily stationary thereby, sloping elements defining a V-groove disposed in a square path intersecting the projecting remainder of said blocker, means to move said groove defining elements in a square path to bring successive portions of the groove into contact with the blocker, and means to rotate the cap to bring about a grinding action.

3. Lens grinding apparatus comprising a grinding cap having a cavity internally complementary to a portion of the surface of a sphere, a spherical blocker partially encased in said cavity and held bodily stationary thereby, sloping means defining a V-groove in contact with the projecting remainder of said blocker, means to move the sloping means defining said V-groove at mutually difierent speeds in a reciprocal path, and means to rotate said cap to bring about a grinding action.

4. Lens grinding apparatus comprising a grinding cap having a cavity facing downwardly and being complementary to a portion of the surface of a sphere, means to rotate said grinding cap about a vertical axis, a spherical blocker having its upper portion encased in said cavity and held bodily stationary thereby, means defining a supporting V-groove below said cap and in contact with the projecting remainder of said blocker, said V-groove defining means including two blocker contacting surfaces, means mounting said surfaces for independent reciprocation and common means to reciprocate the two surfaces at difierent speeds.

5. Lens grinding apparatus as claimed in claim 5 in which the means to reciprocate the said two surface mounting means at diiferent speeds comprises a pitman connected to each surface mounting means, each pitman being mounted on a rotatable shaft, a motor, and transmission means between said motor and said pitman shafts for driving said pitman shafts at different speeds from the said motor.

6. Lens grinding apparatus comprising a grinding cap having a cavity internally complementary to a portion of the surface of a sphere, means to rotate said cap, the cavity of said cap being adapted partially to encase and to hold bodily stationary a spherical blocker, means defining a V groove positioned to act on the projecting remainder of the blocker, and means to move said V groove defining means in a path including at least two opposite directions both in a plane normal to the axis of rotation of said cap.

References Cited in the file of this patent UNITED STATES PATENTS 537,971 Fuller Apr. 23, 1895 1,588,435 Adams June 15, 1926 FOREIGN PATENTS 612,828 Great Britain Nov. 18, 1948

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