US2723514A - Optical lens blocking device - Google Patents

Description

Nov. 15, 1955 B. F. LUCKER 2,723,514

OPTICAL LENS BLOCKING DEVICE Filed Nov. 10, 1952 2 Sheets-Sheet 1 INVENTOR BAS/L FREDERICK LUCKER BY Wail/Thu Ma AGENT Nov. 15, 1955 B. F. LUCKER 2,723,514

OPTICAL LENS BLOCKING DEVICE INVENTOR BASIL FEEDER/CK LUCKER BY $444M M AGE NTS United States atent Ofifice 2,723,514 Patented Nov. 15, 1955 OPTICAL LENS BLOCKING DEVICE Basil F. Lucker, Cape Town, Cape Province, Union of South Africa Application November 10, 1952, Serial No. 319,644

Claims priority, application Union of South Africa November 9, 1951 Claims. (Cl. 51-277) This invention relates to optical lens-grinding and more particularly to the manner of blocking the lens for grinding in machines of the kind known as diamond generators whereby a more effective use may be made of the potentialities of such machines for accuracy of grinding and the need of completing the grinding by hand methods may be entirely eliminated.

Hitherto, lenses in being blocked, i. e. fixed by pitch or the like setting medium to a metal blocker or mount, have been set in position with a degree of accuracy or symmetry which has depended wholly upon the skill and eye of the worker, so that when the blocker is chucked in the generally known way for movement of the lens in a predetermined arc transversely in relation to the cutting edge of the rapidly rotating grinding wheel of the machine, the squarehess of presentation of the lens to the wheel for the required curve which is essential to the accuracy of the grinding is directly dependent upon the skill of the worker as aforesaid; e. g. after one side of a lens has been ground, the reverse side can only be ground accurately if, in re attaching the lens to the blocker, the finished (or back) surface of the lens is seated perfectly correctly in relation to the blocker. In the result, although the grinding machines may be furnished with all the means for fine adjustment and rapid grinding they have in practice been hitherto useful only for roughing the lens, or removing only some of the waste material, leaving the finishing to be done by hand.

In addition to overcoming the foregoing practical restrictions in lens grinding with high class machines inherently capable of finish grinding to practically perfect accuracy, the present invention is further of advantage in the working of bi-focal lenses wherein the optical centre of the so-called distance portion of a lens is required to be offset from the geometric centre of the lens.

According to the invention a blocking device suitable for all types of lenses is provided in which the blocker may be held during attachment of the lens to it in the generally known way, which device comprises an arrangement of fixed upstanding pins or the like engageable about the blocker with the underside of the lens to provide coplanar stops or registering elements for establishing the required accuracy of position of the lens with respect to the blocker during attachment thereto.

The said' device presents also suitable axis markings across it in suitable relationship to the pins or the like aforesaid for assisting in correct application of the lens for obtaining the required positioning thereof.

More particularly the said device consists of a solid base with a central hole to admit a shaft or stem of a standard blocker to seat squarely and to be firmly clamped therein. Four ball-pointed vertical pins are set securely into the base exactly at the four corners of a square, the diagonals of which are slightly longer than the diameter of the face of the blocker head and intersect in the axis of the aforesaid hole. The pins are made of precisely equal height and stand with their points coplanar a little higher than the surface of the blocker when the latter is clamped in position (to allow for suitable thickness of pitch or the like employed for bedding the lens on the blocker). Axis markings at right angles to each other and running midway between the pins enable either spherical or cylindrical surfaces to be seated squarely on the ball-points of all four pins and thus correctly in relation to the blocker.

The invention also consists in a lens-blocking device constructed and arranged for use substantially as hereinafter set forth.

Referring now to the accompanying drawings:

Figures 1, 2 and 3 are respectively a plan, a side elevation and a cross-section of one form of the blocking device;

Figures 4, 5 and 6 are respectively a plan, a side vieW and an underside plan of a blocker on which a lens may be correctly fixed by the use of a device such as that shown in Figures 1 to 3;

Figures 7, 8 and 9 are respectively a side elevation, a plan and a sectional elevation of a form of blocking device which is generally preferable to that shown in Figures l to 3;

Figures 10, 11 and 12 are respectively a side elevation, a plan and an end view of a suitable holder for a blocker to which a lens has been fixed for grinding;

Figure 13 represents a semi-finished fused bi-focal lens blank.

Figure 14 represents the same lens marked for application to a blocking device of either of the constructions described;

Figures 15 shows the same lens blocked on the device; and

Figure 16 shows the lens in section mounted for grinding or as mounted after the grinding is complete.

In one convenient construction the device, according to Figures 1, 2 and 3 of the drawings, consists of a rectangular block 1 of hard material such as one of the plastics, formed with a cylindrical recess 2 and a concentric through hole 3, the former providing a space for accommodating a heavy metal clamp 4.

The clamp is a fiat-faced block of brass or the like formed with a through hole 5 in which the blocker stem, as 6 in Figures 4 and 5, is an easy fit, slotted at 7 from one'side of the hole 5 diametrically through the adjacent metal, provided with a weakening hole 8 on the opposite side of the first hole, and provided with a tangentially arranged screw 9 for contracting the width of the slot so as to clamp the blocker stern when it has been inserted into holes 3 and 5.

The brass or like clamping block 4 is retained in the recess 2 in the first mentioned block by screws 10 passside of the complete device.

The four pins 11 are of steel with hard ball points at 11' and are fixed tightly into the brass block 4 in pairs symmetrically arranged on opposite sides of the diameter containing the slot 7, and each pin equidistant from the blocker stem-receiving hole.

A pair of like semi-annular plates 12 of plastic or other such material is applied, each over a pair of the pins and on to the brass clamping block 4 in position in the plastic block 1, and fixed by screws as 13 to the brass block to embrace the blocker stern-receiving hole 5, their diameter of parting then coinciding with the aforesaid diameter of the slot 7 and providing one of the axis markings aforesaid. The other axis marking consists of a line as 14 scribed across the upper faces of the applied plates.

The machined under or back face 15' of the head 15' of the blocker, when inserted in the device, settles on a truly finished annular face 16 formed by raised portions of the assembled plates 12, which annular face is made dead square with the stern-receiving hole and dead parallel with the underside 1 of the first-mentioned or plastic block 1 in which the brass block 4 is assembled.

In the use of this form of the device the blocker, see Figures 4 to 6, is forced down into and clamped in position in the opening 5 of block 4, the blocker face 15" being covered with a layer of pitch. The lens is then pressed down on to the pitch until the under surface of the lens is seated squarely on the coplanar ball points 11' of all four pins 11; the desired optical centre of the lens being placed directly over the centre of the blocker. This is achieved simply by placing the lens in such a position tthat the cross lines customarily marked on the lens and which run through the desired optical centre coincide with the axes provided on the device as above described by the parting diameter of the plates 12 (coincident with 7) and the line 14.

For accurate results the machined back face of the blocker 15 and the shaft or stem 6 thereof must be clean; the blocker must seat squarely on the machined surface on the base of the blocking device; the lens must be seated squarely on all four pins; and the blocker holding the lens must not be removed from the blocking device until the pitch has cooled sufiiciently to prevent shifting.

In the alternative and preferrred construction of block ing device according to the invention, as shown in Figures 7 to 9, the pins 11 are secured in the equi-spaced arrangement with their ball points 11 arranged coplanar, in a substantial annular brass or like block 4' secured on a heavy base 1x. Passed freely through a hole in the base which is truly coaxial with that in the block 4' is a tubular split metal chuck 17 into the upper end of which the stem 6 of the blocker 15 may be fitted as shown for centralising within the pins 11. With the chuck merely dropped or pushed down into position its upper flat machined surface or end is arranged to occur just below the plane of the annular face 16 of the block 4' so that the back face 15 of the inserted blocker rests fairly and truly on the face 16', and the narrower or lower end of the conical tapers formed at 17 from the upper end of the chuck bears against the internal taper formed inside the upper part of the hole through the base. The lower end of the chuck is arranged to project through the base and is screw threaded at 18 to fit in a complementary screw thread in an externally knurled disc nut 19 engageable with the under surface 1x of the base through an accurately finished annular bearing surface 18'. By rotation of the nut the chuck may be both drawn downwardly and tightly contracted at its upper part to grip the blocker stem 6, thus also to press the faces 15' and 16 into close and true engagement, with the blocker accurately centralised with respect to the four pins 11. Axis markings are provided as in the first-described example across the block face 16' by scribed diametrical lines denoted by references 7' and 14.

The mode of attaching the several components of the preferred blocking device is apparent from Figures 8 and 9 of the drawings. It is, in practice, highly desirable to have in use a number of the blocking devices to avoid waste of time while the pitch is cooling. If, for instance, six of the devices are being used by one worker, by the time the sixth lens has been blocked, the first should have cooled sutficiently to be removed.

In the case of cylindrical lenses, the block, i. e. the blocker with its lens cemented to it, as described, with the aid of one or other of the blocking devices, may be transferred to a holder of a generally similar construction to the brass or like clamping block already described in the first example. The holder may be of the construction shown in Figures to 12, wherein reference 20 denotes the split body, provided in this case with a concealed clamping screw 21 and radiating rods 22 for engagement by the work support of the lens grinding machine.

In a preferred construction, the blocker itself, see Figures 4, 5 and 9, may comprise a co-axial conical countersink 6 in its stem or shaft 6 penetrating into a hardened steel central insert 6"; and the upper or front face 15 of the blocker head 15 may be formed obtusely convex or concave with one or more concentric annular grooves or ribs as 15 for improving the adhesion of the lens-fixing pitch thereto.

In general illustration of the benefits accruing from the use of the present invention, the following results are given:

(a) A lens having a power of plus 3 dioptres having plus 8 dioptre curve on the under surface and minus 5 dioptre curve on the upper surface, was blocked by an experienced operative by the old blocking method of endeavouring to judge by the naked eye that the lens was seated symmetrically in relation to the blocker. The result was inaccurate, the edge substance at four equidistant points around the lens varying thus: 1.35l.7l.4.95.

(b) A lens having the same curves as lens in (a) above was blocked by the same operative using the present invention. The accuracy of the result was apparent from the equality of the edge substance at all points:

(c) A toric lens having a plus 6 dioptre curve in one direction and a plus 8.25 dioptre curve in the other direction on the under surface and a minus 8 dioptre curve on the upper surface, was blocked according to the present invention and the accuracy of the result was apparent from the equal substance of the opposite edges:

For an explanation of an application of this invention in the working of bi-focal lenses, reference is made to the accompanying semi-diagrammatic Figures 13, l4, l5 and 16. In these drawings, the blank shown in Figure 13 has its geometric centre 101, the segment 102 having its top 103 below, e. g. assumed to be 4 mm. below, the centre of the distance portion 104; and the optical centre for distance is assumed to be required at 2 mm. above 103. Such blank is shown (viewed from the inside surface) in Figure 14 marked off by diametrically opposed arrows 105 through the desired position 106 for optical centre. Thus marked off, the blank or lens is shown in Figure 15 blocked on a device of the kind already described, and here generally referenced 107, the axis of the device being at 108, lines XX and YY being the two axis markings with XX of which arrows 105 are registered, and items 109 being the four pins on which the lens is caused to bear as the fixing pitch sets. It will be noted the lens position is decentred on the pins.

Referring now to Figure 16 in which the lens is seen mounted on the blocker 15 on some imaginary chuck facing the generator or grinder lap, with its optical centre 106 fixed coincident with the centre line 111 thereof, the eccentric disposition of the lens in relation to the blocker is apparent from this figure in which also, reference 112 (the shaded portion) denotes glass ground away, 113 the top edge substance reduced to knife edge, 114 the bottom edge substance 1.0 mm. (showing 1 of prism decentration 5.0 D. Power by 2 mm. as desired), 115 the outer curve +9.00 D, 116 the inner curve 6.00 D, and 117 curve worked -4.00 D in vertical meridian.

It will be appreciated that provided all the blocking devices in use with a particular generator are identical, then any required number of lenses of a particular kind can be ground without readjustment to the substance regulator on the generatorpan important consideration for manufacturers concerned with the mass production of lenses.

What I claim is:

1. A blocking device whereby a partially ground lens blank of any type and configuration may be presented accurately positioned in relation to the axis of a standard blocker during the cementing of the blank to the head of the blocker; said blocking device comprising clamp means adapted to coaxially receive the stem of the blocker means defining a true surface located in fixed relation to the clamp means in a plane of rotation generated around the axis of the blocker as held coaxially therein by the clamp means, said true surface being also located with respect to the clamp means so that the rear surface of the blocker head may be pressed into complementary contact With the true surface during clamping of the blocker stem, means defining four point stops rigidly fixed in mutually equispaced relationship along the circumference of a circle arranged coaxially with the clamped blocker and of a diameter larger than that of the blocker head, said circle lying in a fixed plane disposed parallel to said true surface and displaced therefrom axially by a distance substantially greater than the thickness of the blocker head, so that said point stops are disposed axially beyond the head of the blocker when the latter is clamped in contact with said true surface, and means defining axis lines extending radially with respect to the axis of the clamp means across said true surface midway between adjacent pairs of the point stops, said axis lines projecting radially beyond the circle of thepoint stops for exposure beyond the head of the blocker clamped in said clamp means.

2. The blocking device of claim 1; wherein said clamp the blocker head engages said true surface on said split clamping member, said split clamping member being arranged to preserve the exact coaxiality of the blocker stern clamped therein with respect to said circle along which the point stops are disposed.

4. The blocking device of claim 2; wherein said clamp means further includes a block having a central hole for receiving the blocker stem, said block being split radially at one side of said central hole and contractable across the latter, screw means for contracting said block, said means defining a true surface including semi-annular, complementary plate members attached to said block on opposite sides of the radial split of the latter, and said fixed pins defining the point stops being anchored in said block.

5. The blocking device of claim 2; wherein said clamp means further includes a tubular split chuck axially movable within a hole in said base and adapted to receive the blocker stern coaxially therein, means in said hole of the base for contracting said chuck on the blocker stern as said chuck is retracted into the base, said means defining the true surface including a metal annulus on said base coaxial with said hole in the latter to firmly engage the rear surface of the blocker head as the latter is drawn thereagainst by retraction of the chuck into the base with the blocker stem engaged in the chuck.

References Cited in the file of this patent UNITED STATES PATENTS 259,892 Metten June 20, 1882 1,727,889 McCabe Sept. 10, 1929 2,031,380 McCabe Feb. 18, 1936 2,434,600 Swenson Jan. 13, 1948 2,441,472 DAvaucourt May 11, 1948 2,573,668 Long et a1 Oct. 30, 1951 2,603,922 McCarthy et al July 22, 1952

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