APPARATUS FOR BLOCKING A LENS BLANK

Abstract: The apparatus includes a support (18) for a lens blank (21), a pin-carrying member (55) spaced, in use, from the lens blank for engagement with a mounting button (90) and a feed conduit (7) for feeding molten alloy into the space between the button and the lens blank. The member (55) is rotatable about an axis (A) to position a cylinder curve axis and is also tiltable about a prism axis (PA) to select prism. The angular position of the prism axis can be varied by an adjustment member (40).

Description: APPARATUS FOR BLOCKING ' ■ LENS BLANK The invention relates to apparatus for positioning a lens blank prior to πvachinery the blank to produce a lens. Such apparatus is commonly known in the art as "Lens blockers"or "Lens blocking machine ". A lens blank _ is commonly attached to a mounting after being suitably positioned and it is conventional in lens blocking machines to use low melting point alloy to attach the blank to the mounting (known as a "button"). The button normally has sockets in a rear face which locates on two diametrically opposed pins on the blocking machine and has a convex or concave front surface to which the lens is secured by the alloy. Spectacle lenses are fequently of the "toric" type for correction of astigmatism. A toric lens has a curvature in one meridian known as the "Base curve" and a different curvature in another meridian known as the " Cylinder- curve". The base curve is the curve of greatest radius providing a surface power smaller than that of the cylinder curve. The axes about which the curves are formed are at right angles to each other. Certain lenses need to be formed with "prism" i.e. formed so that the lens is thinner towards one edge than it is towards an opposite edge portion. To do that the lens is usually tipped about a prism axis relative to the button before introduction of the molten alloy. Such prism needs to beaccurately applied and a prescription for a given lens will include data from which the relative positioning of the cylinder curve axis and prism axis is determined. Figs. 1 and 2 illustrate di grammatical ly part of a known type of lens blocking machine, Fig.l being a front view and Fig.2 being a diagrammatic cross section on line El - IT in Fig.l . A lens support ring 1 has a knife edge 2 against which a lens blank 3 is placed for blocking. The support ring 1 is pivotally mounted on the machine by pins 4 and can be tipped by a suitable mechanism such as a cam (not shown) about a prism axis PA defined by the pins. The ring is formed with a cut-out 5 at the top A pin carrying member 6 is mounted for rotation on the machine, e.g. by a lever 6a or gear transmission from a rotary spindle,, the amount of rotation being indicated by a rotatable scale 8 marked in degrees e.g. from 0 - 180° in clockwise and anticlockwise directions from a common zero. To block a lens blank requiring prism on such a machine , a mounting button B is placed on the pin carrying member 6 in known manner. The lens blank 3 is then placed against the mounting ring 3. The scale 8 is moved from a zero position so that the prescribed prism axis angle is aligned with a fixed inde.x 6b. The p i n carrying member is then rotated until a pointer Cd thereon points to the prescribed angle for the cylinder curve axis CC in relation to the prism axis PA. The cylinder curve axis will normally be aligned with pins 6c on the pin carrying member and will be aligned with axis PA when the pointer 6d points towards the index 6b - SUBSTITUTE SHEi£T Molten alloy is then introduced through the cut-out 5 so as to fill the space between the lens blank 3 and the button B. After the alloy has set, the blocked . lens blank 3 (complete with button B) is removed. Whilst setting is reasonably straightforward with normal lenses, certain bifocal lenses (which are ^ ry commonly used) are formed from blanks which include a bifocal segment standing proud of the adjacent lens • surface. The prism axis for such a lens can be in any one of an infinite number of positions in relation to the segment. When prism setting is required, the prism axis is normally drawn on the lens blank and aligned with datum marks 9 on the machine which indicate that axis. However, if the segment happensto fall on the knife edge 2, the immediately adjacent surfaces of the lens will effectively be lifted and therefore spaced from the edge. Unless those spaces are filled, the molton alloy will leak through the spaces and, moreover, the lifting of the lens blank in that way induces unwanted prism . To overcome that problem it has been proposed to use a bed of mastic or modelling clay such as Plasticine on the mounting ring 1 to level the lens blank and fill the spaces. However such an arrangement can induce i nnaccuraci es and preparation of the mastic bed is time consuming. An object of the invention is to provide an improved apparatus for positioning a lens blank. According to one aspect of the invention there is provided apparatus for blocking a lens blank including a member spaced, in use, from a lens blank and which is rotatable about an axis, means for tilting said member about a second axis relative to the lens blank, and rotatable adjustment means for orientating the second axis about which the said member is tilted. The lens blank is subsequently blocked by introduction of blocking material between the member and the lens blank. According to another aspect of the invention there is provided apparatus for blocking a lens blank including a support for the lens blank, a member spaced, in use, from the lens blank and which is rotatable about an axis, and feed means for introducing blocking material between the lens blank and the member, characterised in that means is provided for tilting said member about a second axis and rotatable adjustment means is provided for varying the position of the second axis about which said member is tilted. This member is preferably a pin-carrying member which can locate a mounting, eg a button or mounting formed by the blocking material, for the lens blank. The member is preferably associated with a movable element movement which tilts the member. The element may have a screw threaded part which co-operates with a screw means for varying the angle of tilt. The screw threade SUBSTITUTE SHEET part of the element may be a nut rotatable within the el ement . The screw means may be mounted on the adjustment means. The screw means may be rotatable by means of a handle or may be driven by a suitable motor, eg a stepper motor. In the latter case the stepper motor may be controlled by a processing unit. The adjustment means may be rotatably mounted and suitable means such as a pointer, handle or stepper motor may be used to rotate the adjustment means. The adjustment means also may rotate about the first said axi s . Suitable indicator means such as scales or digitial indicators may be provided for indicating rotation of the member and adjustment means or the aforesaid tilt. Where digital indicators are used, rotation sensor means such as potentiometers may be used connected to suitable circuitry including said indicators. The member may include a spherical surface portion which locates in a stationary spherical socket portion. The centre of curvature of the spherical curve may lie at the point where the first and second axes intersect. The two spherical surfaces may be urged into engagement with each other by resilient means such as a coil spring. The lens support may have a surface which is substantially a continuation of the spherical surface of the socket po rt i on . SUBSTITUTE SHEET An ejector me ber, such as a pin, may be provided to enable the blocked lens blank to be ejected from the apparatus. The pin may be pneumatically operated and may be slidable within a bore within the member, eg a bore coaxial with said first axis. The bl ockingmateri al be stored in a reservoir which may include a heater for keeping the material in molten form, The reservoir may be provided with a pressure relief valve compri sing a member movable from arese.rvoir sealing position to a reservoir relief position, the member being held in said relief position by magnetic means until reset. The blocking material may be ejected from the reservoir by introducing fluid such as air or other gas under pressure into the reservoir so as to force molten material along the outlet conduct. The conduit may have its outlet above a cut¬ out in the lens support so that molten material can be introduced between the lens blank and the member. The fluid used to pressurise the reservoir may be fed through a pressure release valve so that on cessati on of fluid feed the valve will immediately release the pressure in the reservoi . SUBSTITUTE SHEET »» Apparatus in accordance with the invention for blocking lenses will now be described with reference to the accompanying drawing in which: Fig.3 is a front view of one form of apparatus on axis A in accordance with the invention having scale indicators. Fig.4 is a cross-section of the apparatus in Fig.3 on the line IV - IV in Fig .3, Fig 4a is a plan view of part of the apparatus. Fig.5 is a view of a lens blank having axes marked thereon; Fig.6 is a view to a larger scale of part of the apparatus in Fig.l with a lens in position on the apparatus; and Fig.7 is a view similar to Fig.6 showing a modifica¬ tion in which the scale indicators are omitted and digital indicators utilised, and, Fig.8 is a block diagram illustrating the various indicators provided for the apparatus. The blocking machine has a body 10 to which is rigidly attached a top plate 12 carrying a reservoir 13. The body has a front plate 14 formed with a bore 15 which spigotally locates an annular cup 16 having a spherical concave internal socket . portion 17. An annular lens support 18 is mounted coaxially on the cup 16 and is formed with a gallery 19 for cooling liquid (e.g. water) from a source (not shown) . The front surface of the lens support 18 includes a EET projecting edge 20 against which a lens 21 is placed as shown in Fig.6. The internal surface 23 of the support 18 is tapered and forms a continuation of the spherical surface 17. The front plate 14 also carries an annular plate 24 carrying four sets of scales S-, ,5 2 ,S 3 ,5 4 calibrated in degrees. Scales S ~ , S 2 are use when the lens surface to be worked is minus (concave) and S3,S -when plus( The body 10 includes an intermediate plate 25 which is parallel with the front plate 14. The inter¬ mediate plate has a boss 26 at its upper end formed with a bore 27 coaxial with the bore 15 in the front plate 14. The bore 27 rotatabTy supports a rearwardly extending spindle 28 which projects coaxially from a circular flange 29 having a coaxial forwardly extending locating pin 30. The spindle 28 passes through a bearing 35 in the bore 27 and the flange 29 is drawn frictionally against the boss 26 by Belleville washers 33 which act between a nut 34 screwed on to the spindle 28 and the flange of bearing 35 engaging the rear face of the boss 26. The pin 30 locates in a bore in an adjustment member 40 which is of U-shaped cross section and rotatably supports a screw threaded rod 42 in limbs 43,44. The rod 42 extends through bearings 45 and is rotatably fast with a handle 46. The rod 42 carries a gear which drives a potentiometer (not shown) to sense the rotation of the rod 42. The adjustment member 40 also carries a forwardly projecting pointer 48, the forward end of which lies adjacent the outer scales S3, 5 * on the plate 24. SUBSTITUTE SHEET The rod 42 carries an adjustment nut 50 rotatable within a block 52 having a finger 53 projecting therefrom. The finger 53 locates in a bore in a cylinder member 54. The latter has its front end counterbored to receive a pin carrying member 55 (two pins 51 being provided thereon as shown but the number can vary) and houses a piston 56 having an ejector rod 57 thereon which passes si i dab1 y through the member 55. The member 55 constitutes the aforesaid "member"and is coaxially and rotatably fast with the cylinder member 54. The piston 56 is biased normally into the position shown by a spring 58. The outer surface of the member 55 includes a convex spherical portion 59 which is complementary with and urged against the surface 17 by a spring 60 acting between cup 16 and a thrust bearing 61 on a shoulder portion 62 of the cylinder member 54. An outer ring 63 is secured to the portion 62 and has a pointer 64 projecting forwardly therefrom. The forward end of the pointer lies adjacent the radially inner scale on plate 24 and also serves as a handle to rotate the ring. Rotation of the ring 63 rotates the cyl i nder member 54 and the member 55 about pin 53 and axis A. Ring 63 and cylinder member 54 are formed with ducting 65 through which compressed air can be directed into the cylinder member 54 to urge the piston 56 and ejector rod 57 forwardly against the bias of spring 58. A conduit 70 leads from the reservoir 13 to a point above the lens support 18. In use the reservoir contains blocking material in the form of molten lew-melting point alloy 105 of known kind kept at temperature by a heater (not shown). The reservoir is placed under low pressure from a supply of compressed air to force alloy through the conduit. A pressure relief valve 72 is provided on a lid 71 of the reservoir and comprises a valve body 73 formed with an axial bore 74 and two horizontal vent bores 75. The lid closes an aperture 84 in the top plate 12 over the reservoir. A weight 76 is slidable in the body and a pin 77 thereon normally locates in the bore 74 and closes vents 75. The weight 76 is made of a magnetic material and a magnet 78 is provided on the body. If pressure rises beyond a predetermined level, the pin 77 is urged upwards under pressure so as to uncover the vents 75. The magnet 78 thereupon attracts the weight 76 so that the latter moves to the top»ofthe body leaving the vents 75 open. A plunger 80 on the weight 76 can be depressed to reset the valve in its normal position. The supply S is switched on and off by means of a solenoid valve 111 operated by a switch 100 on plate 25. Incoming air from the supply urges a ball 112 in a valve against a spring 114 so as to close an outlet 115 in the valve 110. As soon as the switch 100 is released, the valve 111 cuts off air from the supply and the ball 112 is moved clear of the outlet 115 by the spring 114 to release pressure in the reservoir. The lid 71 is held in place sealingly by a bar 120 which is screwed downwards by means of hand-screws 121 threadedly mounted on the top plate 12. The bar 120 is formed with a central bore 122 through which a bolt 122a of handle 123 passes. A suitable sealing gasket 124 is provided on the underside of - π - the lid 71 for sealing engagement with the top plate. Referring to Figs. 4,5 and 6 the lens blank 21 to be mounted on a button 90 by the blocking machine is shown as a bi-focal type which includes a segment 92 of material integral with the remainder of the blank. .Data supplied with the lens blank indicates the position of a cylinder curve axis CC relative to a datum D (passing through the centre of the segment 92 and marked on the lens blank) and the angular position of the axis PA about which any prism is to be formed. With that information, the operator sets up the machine as follows bearing in mind that the segment 92 will always be located precisely in the uppermost position shown. Thatis easily done by the operator by aligning datum D with datum marks 126 on the support 18. The edge 20 is recessed at 125 (Fig.l ) to receive a portion 92a of the segment 92 which stands p roud of the adjacent surface of the lens blank. 1. The button 90 may be formed with apertures 93 which locate on the pins 51 , the button being received within a counterbore 94 in the member 55. Other button constructions may be used in which a rear surface is dimpled to receive the pins 51. 2. The pointer 64 is then turned so as to rotate ring 63 and member 55 about axis A to the angular position indicated in the data, thus setting the angular position of cylinder curve axes CC relative to the vertical datum D. The cylinder curve axis CC wall normally lie across the pins 51 which are indicated in the selected position in broken lines in Fig.3. Axis A constitutes the aforesaid first axis. When the lens blank is placed on subsequent forming machinery, pins on the machinery will locate the lens blank in the position which will result in correct cylinder curve orientation. Friction between the cup 16 and member 55 maintains the desired position of the member 55. 3. The handle 46 is then rotated to set the required amount of prism. The potentiometer drive by gear 47 is associated with ele ctronic circuitry which determines the amount by whoch the rod 42 is rotated. The pitch of the screw thread in the rod 42 is known and by sensing the amount of rotation the distance moved by the nut 50 can be determine The member 55 can swivel against the spherical surface 17 of the cup 16 which has a centre of curvature on prism axis PA where PA and A intersect. Movement of the nut 50 will therefore tip the member 55 about axis PA until axis A takes up the position, e.g. A 1 in Fig.6. The angle of tip is determined by the sensor circuitry. The circuitry then converts the angle of tip to dioptres which are indicated to the operator, e.g. on a screen. The handle 46 rotates the rod 42 about an axis Z and, as viewed in Fig.3, the prism axis PA is at right angles to the axis Z. The axes A and PA constitute the aforesaid first and second axes. SUBSTITUTE SHEET 4. The pointer 48 is then rotated to turn the adjustment member 40 to the angu lar position indicated in the data relative to the datum D thus turning the axis PA about which prism is to be formed e.g. through an angle & (Fig..3) to the required position. 5. The lens blank 21 is then placed against the edge 22 with its centre (which is marked on the blank) on axis A as shown and the reservoir is put under pressure by operating a switch 100 so that molten alloy flows from the conduit 70, through a cut-out 20a in the lens support 18 and into a space between the button 90 and the lens. The operator maintains the flow of alloy until the space and the apertures 93 around the pins 51 are filled with alloy. The flow is then stopped by releasing switch 100 and the alloy allowed to set. Cessation of flow is virtually instantaneous due to the operation of valve 120. The lens blank and button are then ejected from the machine depressing a switch button 130 (Fig.3) which causes compressed air from the source 5 to pass through the ducting 65. The piston 56 is thereby urged forwardly so that the rod 57 pushes the button off the pins 51. Any alloy which drips from the conduit 70 is collected in a tray 102 on the bed of the machine. The engagement of spherical surfaces 17,59 prevents molten alloy leaking between the cup 16 and member 55. The pressure applied to the reservoir is up to \ bar only. SUBSTITUTE SHEET Fig.7 shows a modified version of the blocking apparatus. As will be seen, the basic construction of the machine is ^ery similar to that in Fig.6 and corresponding parts carry the same reference numeral . However in .Fig.7, the annular plate 24 bearing scales 52 to 54 is omitted along with the pointers 48,64. The angular movements of the adjustment member 40 and the ring 63 are sensed by using respective rotary potent¬ iometers 140,150. The potentiometer 140 is mounted on the intermediate plate 25 and has a gear wheel 142 rotatably fast with its shaft 143. The gear wheel 142 meshes with a gear wheel 144 rotatably fast with spindle 28. As the adjustment member 40 is roated manually, the gear wheel 144 rotates the gear wheel 142 and hence the shaft 143. The potentiometer 150 is mounted on a pivotal bracket 151 on a radial extension 152 on ring 63 and has a gear whee; 153 on its shaft 154. A toothed rack 155 of part circular form (substantially the same shape as the part annular ring 24 as viewed in Fig.3) meshes with the gear 153 and is mounted on an extension 156 of the front plate 14. The rack 155 is coaxial with axis A. The gear wheel 153 is biased towards the rack by a spring 149. The extension 156 also carries a drip try 157 which replaces drip tray. Rotation of ring 63, eg by using a radial handle 158, causes the gear wheel 153 to run around the rack 155 and rotate the shaft 154 Tipping of the adjustment member 40 by rotation of handle 46 will cause the gear wheel 153 to slide over the teeth of the rack; the bracket 151 turning about its pivot 150a. As before, rotation of the handle 46 rotates gear wheel 47 which operates another potentiometer not shown in Fig.7 but indicated at 160 in Fig.8 to which reference is made be! ow. To select the cylinder curve axis CC prism axis PA and the amount of prism with the apparatus of Fig.7, an electronic processing unit indicated at 170 in Fig.8 is first set in accordance with the prescription for the lens to be blocked. The prescription may prescribe angles in 0-180° notation or 0-360° notation as well known in the art. The processing unit is set using two switches 172, 173 to select the appropriate notation for cylinder curve axis CC and prism axis PA respectively. The refractive index of the lens blank material is set using a switch 174 having a number of settings corresponding to respective refractive indices. A similar selector switch is used with the apparatus in Figs.3 and 4 to 6 associated with the circuitry mentioned in connection therewith. The potentiometers 140,150 and 160 are wired to the processing unit 170 and the operation thereof causes the selected angles for prism axis and cylinder curve axis to be displayed digitally on respective screens 175 and 176, and the selected prism in d i optres to be displayed digitally on a screen 177. The screens may be located on the front of plate 14. The amount of tipping of axis A (through angle (9 in Figs. 6 and 7) to provide the required amount of prism will vary depending on the refractive index selected by switch 174. SUBSTITUTE SHEET A switch 178 is provided for the selection of plus or minus curves so that the processing unit will cause the screens to read appropriately for convex or concave lens surfaces respecti vely When a lens blank is blocked by the apparatus, the underside of the lens blank to be adhered to the button is normally in its finished form and is coated with a suitable protective laquer which also assists adhesion to the alloy. For optimum accuracy in prism setting, the underside surface of the lens should be as close as possible to the prism axis PA. The lens 21 is shown with for clarity its concave face adjacent the axis PA / The majority of lenses are blocked the other way so that the minus (or a concave) side is subsequently worked to the desired curvature. Instead of using a button 90, the button can be omitted and the lens mounting formed by alloy alone fed from the conduit 70. In such a case the alloy simply fills the entire space between the pin carrying member 55 and the lens blank 21 to form a mounting for theblank. With apparatus in accordance with the invention it is possible to block plain lens blanks as well as blanks for bi-focal lenses. In the latter case there is no need to make a mastic bed to prevent leakage of alloy as before, as the segment 92 always lies in the recess 125 unlike the apparatus of Figs.l and 2. As the alloy fills the space SUBSTITUTE SHEET behind the lens, it eventually fills the recess 25 so that the lens blank is fully blocked. It is envisaged that stepper motors may be used in place of the potentiometers 140,150 and 160. The stepper motors would be controlled from a central processing unit into which an operator would feed the cylinder curve axis CC, prism axis PA and prism data. The central processing unit would then transmit drive signals to the stepper motors to set the apparatus at the selected parameters. As shown in Fig.3, inlet and outlet pipes 200,201 are provided for co oling liquid for the lens support. SUBSTITUTE SHEET

Claims: -!«- CLAIMS 1. Apparatus for blocking a lens blank including a support (18) for the lens blank (21), a member (55) spaced, in use, from the lens blank and which is rotatable about an axis (A), and feed means (70) for introducing blocking material (105) between the lens blank and the member, characterised in that means (46) is provided for tilting said member (55) about a second axis (PA) and rotatable adjustment means (40) is provided for varying the position of the second axis (PA) about which said member (55) is tilted. 2. Apparatus according to Claim 1 characterised in that the member (55) is associated with a movable element (52) movement of which tilts the member. 3. Apparatus according to Claim 2 characterised in that the element (52) has a screw threaded part (50) which co¬ operates with screw means (42) for varying the angle of tilt (θ). 4. Apparatus according to Claim 3 characterised in that said screw means (42) is mounted on said adjustment means (40). SUBSTITUTE SHEET -ft - - 5. Apparatus according to any preceding claim character¬ ised in that the adjustment means (40) is a body rotatably mounted on the apparatus. 7. Apparatus according to any preceding claim characterised i • n t ._.h__a *t an i • ndi-ca xtor mea { n 5] s /is> pro ] vi -Ade Ad for i -n Adi"ca -t_-i • ng t ,-Vh,e rotation of the member (55) about the first axis (A). 8. Apparatus according to any preceding claim characterised (51-54;175) in that an indicator means/ is provided for indicating rotation of the rotatable adjustment means (40). 9. Apparatus according to any preceding claim characterised in that an indicator means /is provided for indicating tilt of said member (55) about the second axis ( ?f\). 10. Apparatus according to any of Claims 7 to 9 characterised in that any one of said indicator means comprises a digital indicator. 11. Apparatus according to any preceding claim characterised in that the member (55) includes a spherical surface portion (59) which locates in a spherical socket portion ( 17 ) of the apparatus. characterised 12. Apparatus according to any preceding claim/ in that a reservoir (13) is provided from which said blocking material (150) is fed, by applying pressure to said material in reservoir. SUBSTITUTE SHEET

Inventors: SOPER PETER HENRY HUNT, STEPHENS ROY, SOPER, PETER, HENRY, HUNT, STEPHENS, ROY
Applicants: AUTOFLOW ENG LTD, AUTOFLOW ENGINEERING LIMITED
Application year: 1987
Main classification: B24B13
IPC codes: B24B13