IN SITU BASE CURVE VERTEX DETECTION AND EMPLOYMENT THEREOF IN CONTACT LENS MANUFACTURE

Abstract: An apparatus and method for in situ concave base curve detection which is especially useful in the lathe. The apparatus and method utilize a laser beam (33) and a photo-diode detector (46) to effect a precise detection of the vertex (14) of the concave base curve (15) defined on the rear face of lens blank (16), fixed to an arbor (21). Once a reference point corresponding to the vertex has been established, a shaping tool (54) cuts a curve of predetermined radius on the front face of the lens at a precise lens thickness to provide the desired contact lens.

Description: IN SITU BASE CURVE VERTEX DETECTION AND EMPLOYMENT THEREOF IN CONTACT LENS MANUFACTURE BACKGROUND OF THE INVENTION This invention concerns an apparatus and method for measuring the vertex of a concave surface and utilization of the same in the shaping of contact lenses. In a conventional method of manufacturing a contact lens by cutting employing a lathe, a lens blank, or "button", of predetermined thickness usually one of acrylic material such as polymethyl methacrylate, is provided with a base curve (or posterior) surface of specified radius to fit the cornea of the eye. The outer (or anterior) surface is then cut on a radius turning lathe to a specified depth and curvature to provide the necessary power (piano, positive or negative) for the required visual correction of the cornea to which the lens is applied. In carrying out the aforesaid conventional method in a fixture provided for that purpose, the depth of the base curve of the button at its center and because of a fixed known reference in the fixture, the button-center thickness is measured with a dial gauge. The button is then fixed to an arbor employing a suitable adhesive, e.g., a wax, as is known, and trimmed on a lathe to the required diameter. By referencing the lathe on which final cutting is to be carried out with a dial indicator carried on -, that lathe to the anterior face of the button, the final cut position will be determined. The assembly is then positioned such that a required finished lens center thickness will be achieved on the final cut. c The foregoing procedure is subject to a variety of operator errors any of which can result in rejection of the finished lens. Thus, any errors in (a) button-center thickness measurement, (b) button/arbor fixation (c) possible anterior surface -, Q lathe operator error in calculation and/or dial indicator setting and/or (d) initial setting of the dial indicator, can result in an unacceptable finished lens. SUMMARY OF THE INVENTION 15 The present invention provides method and apparatus for detecting the base curve vertex of a dished concave surface and the employment of- that detection in connection with the manufacture of 20 contact lenses to provide lenses with precise desired center thickness. In accordance with the invention a transparent article such as a lens blank and having a concave dished rear surface is held with the dished surface so positioned that the base curve thereof is 25 disposed substantially symmetrically of a fixed axis. A light beam is projected in a path perpendicular to the fixed axis. By effecting orthogonal relative movement between the held position of the lens and the 30 35 -, light beam path, e.g., and preferably by moving the held lens blank along the fixed axis, the light beam can be caused to move through the lens blank in a direction from front to rear of the blank. In passing c through the lens blank the light beam will follow its projected path unless and until it impinges on the vertex of the base curve at which occurrence the beam is caused to be deflected from its projected path to one of a certain angle of diffraction. A recorder is 0 positioned situate such as to be unaffected by light projecting in the light beam path but to be responsive to a deflected light beam, i.e., record presence of the deflected light beam impinging the base curve vertex. This recordation event can be employed for a useful control function. In the instance of shaping the 5 convex front surface of a contact lens, the occurrence of beam deflection signals fixing of the vertex or center of the lens posterior surface at a certain, distance from the locus of a shaping tool on the fixed axis at a known location. The shaping of the lens 0 front surface involves advancing the lens blank into engagement with the shaping tool. Since the desired lens center thickness is known, the lens blank can be advanced along the fixed axis following occurrence of beam deflection, a travel which is the differential 5 between the vertex to locus distance at deflection and the known lens center thickness with the result that the shaping engagement of the lens blank and shaping tool will be of a duration required to produce the intended shape and center thickness in the contact 0 lens. 5 The object vertex detection and the shaping of a lens blank to provide a contact lens can be carried out on a lathe of known type, e.g., an Automatic Lathe Type UM-2 as manufactured by 5 c Max Gfeller A.G. of Switzerland and on which the ' detection apparatus readily can be mounted. Other known shaping machines of the automatic lathe type also could be used. One skilled in the art will readily understand that by following the teaching of the Q invention as it relates to base curve vertex detection, and using that occurrence to ascertain required further lens blank movement in engagement with a shaping tool and employing a control signal produced by that occurrence to effect that movement other machines ,j- readily can be adapted for the intended purpose at hand. The lens blank is mounted on an arbor and the arbor in turn received in the movable headstock of the automatic lathe. This mounting is such that the lens 20 blank is held with the base curve of the lens rear surface disposed symmetrically of the fixed axis defined by the headstock - arbor axis, the blank front face being remote from the arbor. A light source such as a helium-neon laser is mounted on the lathe near the headstock and to the front side of the lathe, the laser 25 being mounted such to project a light beam in a beam path perpendicular to the fixed axis. A recorder such as a photo di-ode is disposed fixed at the rear side of the lathe, its sensing element facing front. The 30 normally projected light beam path does not strike the recorder sensing element. The set up is such that only a deflected light beam path will strike the recorder. To detect the base curve vertex, the headstock is slid by suitable power drive along the fixed axis toward the light beam so that it can pass through the lens blank, the lens front end first passing the light beam without effect thereon. With continued headstock travel, the lens blank will move along the fixed axis until the light beam impinges on the base curve vertex and the light beam will be deflected and the deflection recorded by the recorder. This recorded occurrence sets the reference of the vertex from the shaping tool locus spaced a distance therefrom on the fixed axis. The recorded signal is an electrical signal fed to a control unit which processes the signal to provide a controlling output for driving the -headstock driving means so that during the shaping operation the headstock will following beam deflection occurrence, slide the distance vertex from locus minus the lens center thickness. The cutting tool desirably is provided as a diamond cutting bit, the cutting tip of which defines the locus. This cutting bit is carried in a tool support which can be guidingly moved between two extremes one of which is remote from the fixed axis and the other being on the fixed axis, i.e., the locus so the cutting tip transcribes a cutting course in correspondence to the convex curvature of the lens front surface. The drive unit for the tool support also is controlled from the control unit. -6- ^ The apparatus and method of the invention when employed for the manufacture of a contact lens, avoids the disadvantages enumerated above in connection with conventional techniques of employing a dial gauge c - or similar depth measuring instrument. Thus, there is no requirement for initial lens blank center thicknessing and therefore no labor or equipment costs for such an operation. Since the present apparatus and method totally avoid contact of the base curve with a τ _0 physical measurement instrument, there is no possibility of damaging the posterior face of the article. The apparatus and method eliminate any need for the operator to set a button position since the dial indicator is dispensed with. This eliminates .. _ possible error or dial indicator-setting error. Another advantage lies in the much greater accuracy of detecting the vertex of the base curve compared to that possible with the known dial gauge procedure. This greater accuracy permits improved control over final 20 lens parameters and reduces-.production losses resulting from off-specification lenses. BRIEF DESCRIPTION OF THE DRAWINGS A fuller understanding of the nature and objects of the invention will be had from the following detailed description taken in conjunction with the 25 accompanying drawings in which: 30 1 Figs. 1A and IB are illustrative of a known method of detecting the vertex of the concave base curve of a contact lens blank as part of an overall procedure for machine-shaping the front face of the lens to a predetermined radius and thickness; Fig 2. is a schematic top plan view illustration of base curve vertex detection apparatus as embodied in a lens shaping machine in accordance with the present invention; 10 Fig. 3 is a schematic depiction of the control system employed for controlling, inter alia, headstock travel and tool support movement. Fig. 4 is a flow diagram related to the operation of the control system. , .. Throughout the following description, like reference numerals are used to denote like parts in the drawings. DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding and appreciation 20 of the improvement and advantages of the apparatus and method of this invention and as it involves in situ base curve vertex detection, reference will now be made to a known method of base curve vertex detection employing dial gauge measuration and as schematically illustrated 25 in Figs. 1A and IB. As shown in Fig. 1A, dial gauge 10 is positioned a fixed distance from surface 11 of, e.g., a fixture 12. This measurement is taken at a location 30 remote from the shaping machine. The center tip of the dial gauge rod 13 is carefully aligned to exactly coincide with the center, or vertex, 14 of concave base curve 15 defined upon the rear (posterior) face of lens r - blank 16 held in the fixture 12. A reading of the thickness of vertex 14 is thereby obtained as shown by indicator 18 on face 19 of dial gauge 10. As shown in Fig. IB, the blank is then fixed at its rear face in a known manner (e.g., with wax) to face 22 of arbor 21, - jQ trimmed to the desired diameter, the assembly being mounted in a collect chuck 23 which in turn is received in lathe headstock 25 to rotate with the spindle in the usual manner. The desired final thickness of the lens to be -, - shaped is registered by subtracting that thickness from the initial dial gauge reading and employing that known in conjunction with utilization of- a second dial gauge 6 on the shaping machine to set-up the depth of cut•to - be taken from the blank to produce the finished item. 20 With the lathe pre-set to cut a specific front surface radius, the blank/arbor assembly is positioned to provide a finished contact lens on the final cut, a convex curve indicated by long and short line 24. The disadvantages inherent in the foregoing procedure, commented upon previously, become quite 25 evident when it is considered how difficult and error-prone it can be in practice to align the vertex of the base curve and the tip of the dial gauge along the same axis. Even slight errors in detecting the _ π true vertex of the base curve and/or mounting the ■ j _ button upon the arbor for the front face shaping operation can result in an off-specification lens. Compounding the difficulties of this procedure is its liability to operator error in making the correct dial c readings, subtracting the desired thicknesses and/or setting the dial gauge 6 for the final desired cut. Moreover, contact of the tip of the dial gauge can mar the posterior surface of the lens adding yet another possible source of manufacturing defect to those 0 already mentioned. Referring now to Figure 2 and the apparatus depicted therein, the lens blank 16 is shown fixed to arbor 21 by means of adhesive wax layer 31. The mounting of a blank on the arbor is a preliminary -, r- operation carried out at a location away from the shaping machine and is effected in such way that the blank is held to the complementary- configured arbor end face in a position wherein the base curve of the concave dished rear face of the blank is substantially 20 symmetrical of the arbor axis and in turn the headstock axis which are coincident with fixed axis x-x. A light source 32, preferably a helium-neon laser is fixed at the front side of the shaping apparatus and so mounted to project a light beam rearwardly. It will be understood that in Figure 2, the disposition of the 25 apparatus is depicted in a horizontal layout thereof for convenience of depiction showing the light beam as projecting from front to rear of the apparatus. It can with equal facility be laid out in vertical „ 0 orientation, i.e., with the light beam projecting in 35 -> vertical course from bottom to top. The normal light beam path 33 projects perpendicular to the fixed axis x-x. Located toward the rear side of shaping apparatus is a microscope 34 of the conventional type having a t - tube body 36, an objective 38, an eyepiece 40, a mask 42 presenting a knife edge at the microscope axis, a disc 44 in the eyepiece and having a central narrow slit 47, e.g., 50 microns dimension. Mounted on the eyepiece 40 is a recorder 46 in represented from, same -. Q being a photo-diode. Arbor 21 is received in collet chuck 23 which in turn is received in the headstock 25 in known manner. Headstock 25 is mounted slidably on ways 48 to slide along axis x-x being driven, e.g., in .. j - conventional manner by a leadscrew 52 (Fig. 3). Remote from the light beam path 33 is a shaping tool 54, e.g., a diamond cutting bit having a cutting tip which defines a tool locus 58 on the fixed axis x-x. The tool can be fixed in post 60 which is part of tool 20 support or quadrant 62. As will readily be apprehended by those skilled in the art, the tool 54 is intended when it is in cutting engagement with the front face 64 of the blank 16, to move in the course 66 which extends a distance from the one extreme L laterally remote from axis x-x to the other extreme which is at the locus 58, 25 that course following in correspondence, the convex surface to be formed on the lens blank front side. One manner of moving the tool guidingly in that course is represented although it should be understood that other 30 ways of doing this are within the skill of the art. As represented, quadrant 62 can be guided on track 70 ^ therebelow, the quadrant, e.g., having a pair of guide pins 72 riding the sides of the track. Template guidance also can be employed, such being an expedient well known in the art. c In Figure 2, the blank 16 is shown in dashed lines in a pre-detection position. That shown blank position could be one consequent from movement of the headstock from a more leftward location thereof or if the headstock was stopped only slightly to the left of -,0 I s Figure 2 position, the arbor could have been mounted while the headstock was so positioned. It will be assumed for purposes of further description that arbor mounting occurred some distance leftwardly, and a suitable control operated to move the headstock , c - rightwardly thereby moving the lens blank front side 64 toward light beam path 33. As the front face 64 and following blank structure cross beam path 33, the light beam is unaffected and strikes mask 42 thus being blocked so it cannot enter objective 38 and tube 36. 20 Continued blank travel along axis x-x will bring the base curve vertex 14 to the beam path and upon impinging on the vertex, the light beam is deflected rightwardly to the deflected path 80. The deflected path it will be noted is clear of the edge of mask 42, enters objective 38 and projects through the microscope 25 to strike the recorder 46 as a narrow beam of light. Recorder 46 records this deflection occurrence which establishes as well that the lens blank vertex is at a known distance from locus 58. Since the cutting tool 54 cuts in a course that includes the locus 58, if the 35 -12- lens desired center thickness be subtracted from the vertex-locus distance on axis x-x, the result is the distance the headstock must be moved following beam deflection to accomplish the final shaping c: the lens front convex face 82. With reference to Figures 2 and 3, it will be seen that the beam deflection is recorded as an electrical signal and in turn that signal fed into control unit 86 which can e.g., be a microprocessor. The control unit is programmed to process the electrical signal and create an output that is fed to a stepper motor drive 90, which in turn operates stepper motor 92 having output to a gear train 94 operating the headstock lead screw 52. Advance of the headstock along axis x-x after bean deflection brings the lens blank into cutting engagement with tool 54. The duration of cutting engagement when-the rotating blank is engaging the tool, is of course a factor of the headstock advance distance. That distance may be traversed in a number of increments inasmuch as quadrant 62 will move from extreme position L to the other extreme position 58 during a particular cut. It will then be withdrawn back to the L extreme without cutting the blank until the headstock is advanced ' another increment along x-x, this procedure being followed until the final finish cut is made. Control of the requisite quadrant 62 movement can be effected with appropriate signal from the control unit 86 to a quadrant drive 96. With the finish cut, the contact lens of desired center thickness has been provided and _ arbor 21 can be removed from the shaping machine and the lens in turn removed from the arbor. Other post shaping lens treatment may of course be carried out thereafter. i- Figure 4 is a flow diagram showing how the detection and shaping operation can be effected with suitable programming of the control unit, the respective program commands reflecting how detection is effected and then headstock and quadrant movements are 0 carried out to produce a cut lens. While there is above disclosed only one embodiment of the method and apparatus of the invention, it will be understood that modifications will be apparent to those skilled in the art while said modifications will still be within the scope of the 5 inventive concept disclosed. 0 5 0 5

Claims: -L WHAT IS CLAIMED IS; 1. In a method for shaping the front end of a contact lens blank to provide it with a convex c - surface, the lens blank having a concave dished rear surface which includes engaging the lens blank front end with a shaping tool to remove material therefrom in a course following the intended convex surface when one is 0 rotated relative to the other, the steps of holding the lens blank with the dished surface thereof so positioned that the base curve thereof is disposed substantially symmetrically of a fixed axis. projecting a light beam in a path 5 perpendicular to said fixed axis, the lens blank being held so as to locate the front end-thereof adjacent said light beam, effecting orthogonal relative movement between the light beam path and the he!-, position of the 0 lens blank therewith to cause the light beam to pass through the lens blank until the light beam impinges on the vertex of the rear surface base curve and is deflected from the beam path, recording the occurrence of the light beam 5 deflection, and employing the recorded occurrence to control the duration of engagement of the lens blank with the shaping tool thereby to produce a contact lens of desired center thickness. 35 _ 2. The method of Claim 1 in which the relative orthogonal movement between the light beam and the held position of the lens blank is effected by maintaining the light beam stationary and moving the c lens blank along the fixed axis in the direction of the light beam. 3. The method of Claim 1 in which the light beam is a laser light beam. 4. The method of Claim 3 in which the laser 0 is a helium-neon laser. 5. The method of Claim 1 in which engagement of the lens blank front end with the shaping tool is effected by holding one and moving the other into contact therewith. 5 6. the method of Claim 1 in which the lens blank is moved into contact with the shaping tool. 7. The method of Claim-6 in which the lens blank movement into contact with the shaping tool is in straight line movement along said fixed axis. 0 8. The method of Claim 7 in which the occurrence of light beam deflection is recorded as an electrical signal. 9. The method of Claim 8 in which the electrical signal is processed in a control unit to provide an output to control the length of straight 5 line movement of the lens blank into contact with the shaping tool following light beam deflection and until the convex surface shaping is completed. 0 5 -, 10. The method of Claim 9 in which the shaping tool has a locus on said fixed axis and the control unit output effects lens blank straight line movement following light beam deflection of a length c - representing at such deflection the differential of the straight line axis distance of the base curve vertex from the shaping tool locus and the contact lens desired thickness. 11. A method for detecting the vertex of the -, Q base curve of a concave dished surface formed in a transparent article which comprises projecting a light beam along a beam path, holding the article in a position in which the concave surface thereof is disposed substantially -J C - symmetrically of an axis extending perpendicular to the beam path, effecting orthogonal relative movement between said beam path and the held position of said article so that the light beam passes through the 20 article- until it impinges on the vertex of said base curve and thereby is deflected from the beam path, and recording the occurrence of the light beam deflection. 12. A contact lens shaped in accordance with the method of Claim 1. 25 13. Apparatus for detecting the vertex of the base curve of a concave dished surface formed in a transparent article which comprises means for projecting a light beam along a beam path, -17- -, means for holding the article in a position in which the concave surface thereof is disposed substantially symmetrically of an axis extending perpendicular to the beam path, i- means for effecting orthogonal relative movement between said beam path and the held position of said article so that the light " beam can be passed through the article until it impinges on the vertex of said base curve and thereby is deflected from the beam , 0 path, and recorder means situate in the path of the deflected light beam to record such deflection occurrence. 14. The apparatus of Claim 13 in which the recorder means is operable to record the presence of 15 the deflected light beam as an electrical signal. 15. The apparatus of Claim 14 further comprising a control unit for receiving said electrical signal and modifying it to provide an output for a desired control function. 20 16. In apparatus for shaping the front end of a contact lens blank to provide it with a convex surface, the lens blank having a concave dished rear surface, the apparatus including a shaping tool with which the lens blank 25 front end can be engaged to remove material therefrom in a course following the intended convex surface when one is rotated relative to the other, 30 35 -18- , a holder for holding the lens blank with the dished surface thereof so positioned that the base curve thereof in disposed substantially symmetrically of a fixed axis, c a light source supported for projecting a light beam in a path extending perpendicular to the fixed axis, the holder holding the blank adjacent the light beam path, means for effecting orthogonal relative , 0 movement between the light beam path and the holder therewith to cause the light beam to pass through the lens blank until the light beam impinges on the vertex of the rear surface base curve and is deflected from the beam path, and ., [ - recorder means situate in the path of the deflected light beam to record such deflection occurrence and operable to generate a signal for controlling the duration of engagement of the-lens blank and shaping tool when the two are thereafter 20 brought into engagement to produce a contact lens of desired center thickness. 17. The apparatus of Claim 16 in which the orthogonal relative movement effecting means comprises a support slidable along said fixed axis, said holder being mounted on said support. 25 18. The apparatus of Claim 17 further comprising drive means for sliding said support along said fixed axis, and a control unit controlling said drive means. 30 35 19. The apparatus of Claim 18 in which the shaping tool has a locus on said fixed axis remote from said light beam path, said recorder means being operable to record the presence of the deflected light j- beam as an electrical signal, said control unit receiving said electrical signal and modifying it as a output for operating said drive means to slide said support following light beam deflection toward said shaping tool locus a length representing at such 0 deflection the differential of the straight line axis distance of the base curve vertex from said locus and the contact lens desired thickness. 20. The apparatus of Claim 19 in which the support comprises the headstock of a lathe, the holder comprising an arbor received in said headstock. 5 21. The apparatus of Claim 20 in which said arbor has an end face generally conformably shaped with the rear face surface of said lens blank, a layer of wax adhesive intervening said end face and said rear face surface. 0 22. The apparatus of Claim 21 in which the shaping tool is a cutting bit having a cutting tip, the apparatus further comprising a tool support in which said cutting bit is received, means for guiding said tool support in movement between two extremes one 5 extreme being laterally spaced from said fixed axis and the other being at said locus so that the cutting bit tip can transcribe a cutting course corresponding to the convex curvature of the contact lens front surface, the center of the front lens surface being at said 0 locus. 5 , 23. The apparatus of Claim 22 in which the tool support guiding means includes a drive unit for moving the tool support between said two extremes. 24. The apparatus of Claim 23 in which the c - drive unit is controlled by a signal from said control unit. 25. The apparatus of Claim 13 further comprising a microscope intervening said recorder means and the location of said held article, the deflected -. Q light beam entering said microscope. 26. The apparatus of Claim 25 in which the microscope includes an eyepiece, the recorder means being mounted on said eyepiece. 27. The apparatus of Claim 26 in which the microscope includes a slitted mask upstream of said 15 eyepiece, the deflected light beam passing through the mask slit to strike the recorder means in a narrow band light form. 28. The apparatus of Claim 13 in which the light beam projecting means comprises a laser. 20 29. The apparatus of Claim 28 in which the laser is a helium-neon laser. 30. The apparatus of Claim 14 in which the recorder means is a photo diode. 25 30 35

Inventors: HALLER MICHAEL W E, PAYNE KENNETH R, WEBB BRIAN L, HALLER, MICHAEL, W., E., PAYNE, KENNETH, R., WEBB, BRIAN, L.
Applicants: INT HYDRON CORP, INTERNATIONAL HYDRON CORPORATION
Application year: 1987
Main classification: B23B1
IPC codes: B23B1, B23Q17, B24B1, B24B13, B24B49, G01B11, G02C7, G02C13