Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B13/00—Machines or devices designed for grinding or polishing optical surfaces on lenses or surfaces of similar shape on other work; Accessories therefor
  • B24B13/06—Machines or devices designed for grinding or polishing optical surfaces on lenses or surfaces of similar shape on other work; Accessories therefor grinding of lenses, the tool or work being controlled by information-carrying means, e.g. patterns, punched tapes, magnetic tapes

Definitions

• the present invention relates generally to lens surfacing apparatuses and is particularly directed to a computer controlled lens surfacing apparatus and method for producing an optical lens from a lens blank.
• the invention will be specifically disclosed in connection with an apparatus which does not utilize linear way systems, but rather incorporates a system of rotational axes whose relative orientation are controlled by a computer so as to guide the surface generating tool along a predetermined path to generate the desired surface.
• An opthalmic lens is typically manufactured from a lens blank which has a previously formed spherical surface on a first side.
• An optic surface is formed on the second side of the lens blank by cutting or grinding the appropriate shape into the blank surface. The exact shape to be cut or ground is determined based on the curvature of the first surface in conjunction with the required prescription.
• the second surface is concaved and may be spherical or toric.
• a toric lens has two different radii of curvature in planes which are perpendicular to each other. The second radius of curvature in a toric lens is generally known as the cylinder correction.
• Opthalmic lenses are frequently manufactured from lens blanks made of glass, polycarbonate, or a material known as CR39*" available from PPG, Industries.
• C S ⁇ "* and polycarbonate lens blanks may be surfaced by milling or cutting the blank to remove material. Glass, however, may only be surfaced by grinding the blank, typically using a diamond grinding tool.
• the lens blank is "blocked", and mounted to a support.
• a cup-shaped tool typically having a diameter of 3 inches to 4 inches, is mounted to the grinding machine and rotated about its axis as the tool is swept past the stationary lens.
• The. cup-shaped tool may be tilted with respect to the lens so as to approximate the desired radius of the lens in the plane being cut.
• the tool is usually swept past the lens manually or by a hydraulic feed so as to generate the approximate curve on the lens surface.
• the cup-shaped tool may include cutting blades disposed about the lip of the cup so as to form the lens surface by cutting the material from the blank.
• a cup-shaped grinding tool is utilized having diamonds adhered to the lip of the cup.
• the typical lens surfacing machine which utilizes a cup-shaped tool incorporates various linear way systems, frequently in combination with rotational way systems.
• the combination of rotational way systems and linear way systems is used to tilt the cup-shaped tool out of plane with respect to the lens blank and to sweep the tool past the lens in a predetermined path to form the desired surface.
• lens surfacing machines are designed to utilize a limited number of different cup-shaped tools to approximate all of the different radii by tilting the cup-shaped tool out of plane with respect to the lens blank.
• linear way systems and rotational way systems are incorporated together in various geometries.
• a major problem with lens surfacing machines utilizing tilted cup-shaped tools to approximate the desired radii of the lens is that the desired radius is only approximated, and elliptical error is introduced into the surface.
• the elliptical error exists as excess material which must be removed in subsequent operations, such as lapping. Lapping requires additional equipment, tooling, time and labor.
• Another drawback to these lens surfacing machines is the time required for changeover, setup and alignment when switching between polycarbonate or CR39TM lens blanks and glass lens blanks.
• the difference between the cup-shaped cutting tool for the respective materials is that an additional setup procedure must be followed in order to calibrate the machine to the new tool.
• quick change systems are available, changeover still requires a significant amount of time and effort. Improper setup due to changeover results in errors in the generation of the lens surface.
• An alternative to the commonplace cup-shaped tool lens surfacing machines is one in which a spherical, ball nose mill is utilized in conjunction with two precision way systems and a rotating lens blank. In this system, the rotating spherical cutting tool is mounted at an angle on a precision linear way system which moves in a first direction.
• the lens blank is mounted and rotated about its axis, which is supported by a second linear way system that moves in a second direction which is perpendicular to the movement of the first precision linear way system.
• a computer controls the displacement of both linear way systems with respect to the rotating lens blank, so as to generate the surface on the lens blank.
• This system has all of the drawbacks present with linear way systems of the other lens surfacing systems. It includes the expensive precision slides, ballscrews and preloaded nuts. As mentioned previously, such linear way systems require significant maintenance and lubrication. Setup and alignment can also take significant amounts of time. Additionally, the way system cannot be easily protected against contaminates or the cutting fluid used in grinding glass lens blanks. Such a system can therefore not be easily used to generate surfaces on glass lens blanks.
• a lens surfacing apparatus and method which eliminates elliptical error to generate a precision surface which need only be polished to produce an optical finish.
• a system which avoids the drawbacks of precision slides and the associated cost of manufacture, and also avoids the difficulty in protecting such slides.
• the system needs to include the capability of cutting or grinding all suitable materials, including but not limited to polycarbonate, CR39TM and glass, while maintaining accuracy and incorporating easy maintenance.
• the system also needs to be capable of being quickly changed over to handle the various types of materials, such as glass and polycarbonate or CR39TM.
• the system should not require any particular skill to operate, and should minimize the cycle time necessary to form the lens surface.
• Another object of the present invention is to provide a lens generating apparatus which is capable of generating spherical surfaces, toric surfaces, aspherical surfaces or quadric surfaces.
• Another object of the present invention is to provide a lens generating apparatus which is controlled by a computer, and may be operated by an unskilled technician.
• Another object of the present invention is to provide a lens generating apparatus wherein the calibration of the system may be accomplished by a computer control. It is another object of the present invention to provide a lens generating apparatus which is inexpensive to manufacture and is relatively small in size.
• the lens generating apparatus includes a rotatable tool support spindle which rotates a spheric tool about a first axis.
• the tool spindle is directly carried by a high torque, low inertia, direct drive servo motor which rotates the first rotational axis of the spherical tool about a second rotational axis.
• a workpiece spindle holds the workpiece and rotates it about a third axis which generally lies in the same plane as the first axis.
• the workpiece spindle is rotatably supported by a second high torque, low inertia, direct drive servo motor which rotates the third rotational axis about a fourth axis.
• the orientation of the first and third rotational axes are controlled by a CNC computer which controls the rotation of the two direct drive servo motors in dependence upon the rotational orientation of the workpiece.
• the spherical tool is controlled so as to follow a predetermined three dimensional tool path relative to the lens blank.
• FIG. 1 is a diagrammatic perspective view of a lens generating apparatus constructed in accordance with the present invention.
• FIG. 2 is a side elevational view of a lens generating apparatus constructed according to the present invention, along line 2-2 of FIG. 3.
• FIG. 3 is a plan view of the lens generating apparatus of FIG. 2, with the tool and lens blank in contact with each other.
• FIG. 4 is a plan view of the lens generating apparatus of FIG. 2, with the tool spindle and the workpiece spindle in the initial position.
• FIG. 5 is a side elevational view of a spherical cutting tool.
• FIG. 6 is an end view of the lens blank showing the tool path according to the present invention.
• FIG. 7 is a side view of the lens blank taken along line 7-7 of FIG. 6.
• FIG. 8 is a graph showing the angular position of the B axis as a function of the rotation of the lens blank.
• FIG. 9 is a graph showing the angular position of the A axis as a function of the rotation of the lens blank.
• FIG. 10 is an enlarged fragmentary view of a cross-section taken along line 10-10 of FIG. 6 showing the peaks between the tool paths.
• FIG. 1 is a diagrammatic perspective view of lens generating apparatus generally indicated as 2, constructed in accordance with the present invention.
• Lens generating apparatus 2 includes tool spindle motor 4 which supports and rotates tool 6, which includes spherical cutting head 8. Tool 6 is rotated by motor 4 about tool rotational axis T which runs longitudinally through tool 6. Axis T is shown in FIG. 1 as being disposed generally horizontal.
• Tool spindle motor 4 is carried by tool spindle motor support 10.
• Motor support 10 is rotatably supported by tool axis direct drive motor 12 to rotate about tool spindle rotational axis B.
• axis B is disposed vertically, and intersects axis T perpendicularly.
• Lens generating apparatus 2 also includes workpiece spindle motor 14 which supports and rotates workpiece 16 about workpiece rotational axis C, which runs through workpiece 16.
• Axis C is shown as being generally horizontal.
• Motor 14 is carried by workpiece spindle motor support 18, which is rotatably carried directly by workpiece axis direct drive motor 20.
• Motor 20 rotates motor 14 and axis C about workpiece spindle rotational axis A.
• Axis A is shown in FIG. 1 as being parallel to axis B, and as intersecting axis C at a right angle.
• Tool spindle motor 4 is a high speed motor which rotates tool 6 at approximately 30,000 RPM.
• Workpiece spindle motor 14 is a servo motor which rotates workpiece 16 in one direction during generation of the surface. Both motor 12 and motor 20 are direct drive servo motors having high torque and low inertia.
• Lens generating apparatus 2 is controlled by a CNC type computer 66 (FIGS. 3 and 4).
• the computer 66 causes spherical cutting head 8 to contact workpiece 16 and follow a three dimensional tool path thereon by controlling the orientation of axis B and axis A with respect to each other, and with respect, to the orientation of axis C.
• any mathematically determinable surface such. as spherical, toric, aspherical, or quadric, may be generated by lens generating apparatus 2, subject to the constraints presented by the diameter of cutting head 8 and the relative orientations and locations of the axes of rotation.
• FIG. 2 is a side elevational view of lens generating apparatus 2 illustrated in detail.
• Motors 12 and 20 are mounted to base 22, through motor mounts 12a and 20a, respectively, such that axis A and axis B are parallel to each other and spaced apart approximately 9.5 inches. It is noted that axes A and B are non-coincident with each other.
• Axis A is shown as intersecting axis C perpendicularly.
• axis B is shown as intersecting axis T perpendicularly.
• Axes C and T are shown as lying in the same plane with each other.
• axis A and axis B may be skewed with respect to each other.
• Axis T may be non-perpendicular or skewed with respect to axis B.
• axis C may be non-perpendicular or skewed with respect to axis A.
• the underlying criteria and limitations on the orientation and location of these four axes is that they be rotatable in concert with each other so as to generate a desired surface on workpieces 16.
• the computer program which operates lens generating apparatus 2 may easily be adapted to accommodate other orientations of these axes. However, it is believed that the orientation and location of these axes as illustrated herein, particularly in Figs. 1 through 4, as the most advantageous system with respect to ease and cost of construction and assembly, as well as ease of programming.
• Tool spindle motor 4 includes tool spindle 24 which has longitudinal end portion 26.
• Tool support mounting 28 is connected to longitudinal end portion 26 and adapted to receive and retain tool 6.
• tool support mounting 28 includes a quick release mechanism which permits easy and fast changing of tool 6.
• the tool mounting system is designed to locate the center 30 of any spherical cutting head 8 at a fixed, predetermined distance from axis B. It should be noted that while this distance is preferred to be constant no matter what tool is being utilized, the computer program operating the system may easily be set up to accommodate different dimensions between tool center 30 and axis B.
• the speed of rotation of tool 6 is dictated by the type of material being cut, or in the case of glass, being ground. Although the description herein refers specifically to polycarbonate, CR39TM and glass, it is to be understood that the present invention is not limited to these specific materials, and any suitable material may be used.
• tool 6 is rotated at 30,000 rpm, with an accuracy of plus or minus 25%, i.e., 7,500 rpm.
• the direction of rotation of tool 6 is dictated, solely by the shape of the teeth, as is well known.
• the horsepower required for spindle motor 4 is dependent upon the cutting requirement of the system.
• workpiece rotational speed and material composition determine the tool rotational speed based on the desired chip load, i.e., the amount of material removed per tooth of tool 6, subject to the maximum allowable chip load.
• the designed chip load was selected to be .001 inches of material removed per tooth.
• a three horsepower tool spindle motor 4 is adequate for operation with tool 6 as described in detail below.
• Tool spindle motor 4 is carried by tool spindle support 10.
• motor support 10 is a planar type mount which bolts directly to rotatable motor flange 32.
• the distance between center 30 and axis B may be adjusted using track 33 (FIG. 1). It is noted that such adjustment is not necessary during operation of the invention. but merely allows some flexibility to vary the center distance and to accommodate manufacturing tolerances in apparatus 2.
• Motor flange 32 is directly driven by direct drive motor 12.
• Seal 34 is disposed about flange 32 to seal between flange 32 and sealing ring 36. As will be described later, seal 34 prevents debris, such as dust and chips, and cutting fluid from contaminating motor 12.
• Motor 20 is mounted to motor mount 20a which is secured to base 22. As previously mentioned, supports workpiece spindle motor 14.
• Work piece spindle motor 14 is a D001 Delco Fanuc AC servo motor, and includes workpiece support spindle 38. Longitudinal end portion 40 of workpiece support spindle 38 carries lens clamp, or workpiece mounting 42.
• Block 44 securely carries workpiece 16 by utilizing a low melting point alloy as is well known in the industry. Block 44 is connected to lens clamp 42, which preferably has a quick disconnect design to simplify assembly thereto.
• Work piece spindle motor 14 is connected to workpiece spindle motor support 18. Support 18 is secured to rotatable motor flange 46 which is connected directly to direct drive motor 20.
• the position of support 18 relative to Axis A may be adjusted using tacks 47 (FIG. 1). Such adjustment is not required during operation of apparatus 2, but merely provided to allow flexibility and to accommodate manufacturing tolerances in apparatus 2.
• Seal 48 seals between motor flange 46 and sealing ring 50, serving to prevent debris, such as chips and dust, and cutting fluid from contaminating motor 20.
• Both motor 12 and motor 20 are direct drive, high 1 , fi 6
• motors 12 and 20 are NSK BS0608FN001 servo motors, having parallel axes of rotation spaced 9.5 inches apart. These motors are high torque low, inertia motors, capable of generating torque in the range of
• Each motor has an inertia of approximately 10 2 lb-in , and are designed to operate with a load inertia to motor inertia in the range of 10:1 to 100:1.
• motors 12 and 20 are operated at a load inertia to motor inertia ratio
• Additional inertia weights 51 and 53 may be mounted to be rotated by motors 20 and 12 respectively, concomitantly with supports 18 and 10, respectively, if necessary to achieve the desired load inertia to motor inertia 50:1 ratio. Inertia weights 51 and 53 may be mounted in any convenient manner and location. It is noted that it is desirable for both motor 12 and motor 20 to have nearly the same response time and accuracy. In the event that motor 12 is not identical to motor 20, the load inertia to motor inertia for each motor can be adjusted to produce the desired response time and acceleration/deceleration capability.
• lens generating apparatus 2 includes seals 34 and 48 which protect motors 12 and 20 from contamination.
• the rotational motion utilized in generating apparatus 2 greatly simplifies the protection of the system, in contrast to apparatuses which utilize linear way systems.
• This improved sealing capability permits the grinding of glass workpieces, which requires a continuous flow of cutting fluid from feed tube 52 directly into cutting zone 54.
• Feed tube 52 is supported in any conventional manner by base 22 or other support, as is well known in the art.
• Base 22 includes recess 56 which retains cutting fluid and directs it toward drain 58 formed in base 22, underlying cutting zone 54. Drain 58 may also operate as a vacuum port to withdraw chips and dust from cutting zone 54 when polycarbonate or CR39 W workpieces are being cut without cutting fluid.
• Tube 60 can double as a drain tube and as a vacuum tube.
• a shroud (not shown) is preferably located over the entire assembly during cutting or grinding of workpiece 16, both for containment of chips, dust and/or liquid, as well as for general safety.
• the rotational position of workpiece 16 about axis C is the master parameter which dictates the corresponding angular position of axis T about axis B and the angular position of axis C about axis A.
• Workpiece spindle motor 14 controls the angular position and velocity of workpiece 16 about axis C.
• Motor 14 includes an optical encoder which generates 8000 counts per revolution. The positional accuracy of motor 14 is within one count. Motor 14 also includes one home pulse per revolution.
• Direct drive motors 12 and 20 each include a resolver .type positional indicator which generates 614,000 counts per revolution. The dynamic positional accuracy of motors 12 and 20 are within 20 counts, due to overshoot in the control loop. Motors 12 and 20 include 150 index pulses per revolution. Respective limit switches 62 and 64 are disposed to generate one reference pulse per rotation of flanges 32 and 46 respectively.
• spherical cutting head 8 is caused to follow a spiral tool path across workpiece 16 as workpiece rotates about axis C.
• the tool path of spherical cutting head 8 will follow a three dimensional spiral between the outer edge and the center of workpiece 16, as shown in Fig. 6.
• the path may begin at the outer edge or at the center of workpiece 16.
• Fig. 7 illustrates a side view of the actual three dimensional tool path which is followed when generating a toric surface.
• tool 6 rotates in a counterclockwise direction when viewed along axis T in the direction of arrow 65 (FIG. 4).
• the direction of rotation of tool 6 is dictated by the shape of the teeth on cutting head 8.
• Workpiece 16 is rotated clockwise when viewed along axis C in the direction of arrow 67 for workpieces made of CR39"" and glass, and counterclockwise for workpieces made of polycarbonate. The selection of the direction of rotation of workpiece 16 is. based on which direction yields the best results for the given direction of rotation of tool 6.
• a toric surface model provides the positioning coordinates for the lens surface. These position coordinates then are translated into position angles by using mathematical formulas for the intersection of two circular arcs. The three dimensional tool path is determined based on the mathematical model of the surface to be generated.
• axis T In order to follow the necessary tool path, axis T must be rotated by motor 12 about axis B while axis C is simultaneously rotated by motor 20 about axis A.
• the actual relative position between axis T and axis C is determined as a function of the angular position of workpiece 16 about axis C, for any toric surface. Because the radius of curvature for a toric surface changes four times for each revolution of workpiece 16, the orientation of axes T and C about axis B and A respectively are constantly changing as a function of the angular position of workpiece 16 about axis C.
• Figures 8 and 9 graphically illustrate a simple example of the angular perturbations of axes T and C.
• spherical cutting head 8 takes four revolutions of workpiece 16 about axis C to travel from the outer edge of a three inch, diameter lens blank to the center. The angles were measured from the 0° line shown in Figure 4, with the counter clockwise rotation being the positive angular direction.
• the key to accurate generation of a surface on workpiece 16 is the control of the velocity of the C, A and B axes.
• the C axis velocity is controlled directly within 1%, and the resulting angular positions of workpiece 16 about axis C are used to generate the required angular rotations of axes T and C about axes B and A respectively.
• a relational table is created setting forth the velocities and angular positions of axes A and B based on the angular position and velocity of axis C.
• the angular position of workpiece 16 about axis C is referred to the master, while the resulting angular positions of axes T and C about axes B and A are referred to as slaves.
• Rotation about axes A and B is bi-directional, and is controlled by a closed loop control algorithm which incorporates a position loop with a feed forward branch.
• R is the radius at which the spherical cutting head is contacting workpiece 16
• f is a multiplying factor which is selected to maintain a desired and constant chip load on cutting head 8.
• R is the radius at which the spherical cutting head is contacting workpiece 16
• f is a multiplying factor which is selected to maintain a desired and constant chip load on cutting head 8.
• R is the radius at which the spherical cutting head is contacting workpiece 16
• f is a multiplying factor which is selected to maintain a desired and constant chip load on cutting head 8.
• R is the radius at which the spherical cutting head is contacting workpiece 16
• f is a multiplying factor which is selected to maintain a desired and constant chip load on
• the rotational velocity of workpiece 16 about axis C ranges from 30 rpm at the outer edge of the 3 inch workpiece to 350 rpm at the center when generating a toric surface, and up to 600 rpm at the center when generating a spherical surface.
• the angular velocity of the workpiece about axis C when spherical cutting head 8 is at the outer edge still begins at 30 rpms, although it could be allowed to begin at a higher rpm.
• the value of f is set lower so that the rotations of axes T and C about axes B and A respectively may respond accurately. This is because the greater the difference between the two radii of curvature of a toric surface, the greater the acceleration and deceleration necessary for the angular perturbations about the A and B axes.
• the value of f may be calculated for various ranges of differences between the radii of curvature.
• a spherical lens is analogous to a toric lens with both radii being equal, and may be easily generated by apparatus 2.
• the value of f is also a function of response time for the direct drive motors in relation to the prescription being cut, i.e., the differences between the radii of curvature.
• a reference table is generated by the computer control 66 ( Figure 3).
• computer control 66 operates lens generating apparatus 2 in a manner well known for controlling CNC machinery.
• tool 6 includes spherical cutting head 8 which is connected to tool shaft 7.
• Shaft 7 includes a reference surface 9.
• reference surface 9 is a distance G from center 30 of head 8.
• G represents a gauge distance which may be set or controlled by the manufacturer of tool 6, or alternatively set or controlled at a central tool crib. Any other conventional means of establishing a gauge dimension between center 30 and a reference mounting surface of tool 6 may be used, such as tapering shaft 7.
• shoulder 9, or other appropriate reference mounting surface abutts a corresponding and complimentarily-shaped reference mounting surface of tool support mounting 28. This establishes an accurate and repeatable distance between axis B and center 30 of head 8.
• Spherical cutting head 8 includes a plurality of cutting teeth 11. (FIGS. 1, 3, 4) Head 8 contacts workpiece 30 within a cutting band 13, illustrated in FIG. 5 as extending approximately 30° either side of the equator of head 8 as defined by a plane perpendicular to shaft 7 and passing through center 30. It is well known in the industry that ball nose mills such as illustrated in FIG. 5 are most accurate at the equator and in adjacent areas. It is therefore desirable to contact workpiece 16 within a cutting band close to the equator. The cutting band should be wide enough so as not to produce premature wear of the tool. The exact location, with and distribution of cutting band 13 depends upon the specific geometry of lens generating apparatus 2.
• tool 6 is illustrated as a ball nose mill, such as model 43750020 available from M.A. Ford Manufacturing Company, Inc. of Davenport, Iowa
• a spherical grinding head of identical dimensions may be used to grind glass workpieces in the same fashion based on the same criteria as that used for cutting polycarbonate and CR39 1 " workpieces.
• several passes by tool 6 may be required.
• several rough cuts are made by sequential passes of tool 6 across workpiece 16. In the preferred embodiment, these initial rough cuts are made with a lead of .200 inches (i.e.
• tool 6 moves radially .200 inches for each rotation of workpiece 16), and are cut to a depth of .030 inches. It is noted that a cut deeper than .040 inches would require additional horsepower from tool spindle motor 4.
• the initial rough spiral cut on workpiece 16 begins at the outer circumference of workpiece 16 and spirals inwardly to the center. Once the center has. been reached, a subsequent rough cut is made starting at the center and spiraling radially outward. By starting the subsequent rough cut at the center, cycle time is reduced by eliminating any repositioning of tool 6 and workpiece 16 so as to again start at the outer perimeter of workpiece 16. 0
• a typical lens may undergo 3 to 7 rough cuts, depending upon the prescription being cut.
• tool 6 is located at the center of workpiece
• An intermediate cut is then made, spiraling outwardly with a lead of .100 inches, and a maximum depth no greater than .020 inches.
• a finish cut is made after the intermediate cut, beginning at the outer edge ⁇ and spiraling inwardly.
• the finished cut is made at a lead of .030 inches, and a maximum depth of .015 inches.
• the finish cut preferably begins at the outer edge and spirals inwardly because, based on the dynamics of the system, it is easier to exit from the 5 center than to enter at the center.
• FIG. 10 diagrammatically illustrates the affect of lead L on the height H of peaks 68 located between center 70 of the tool path.
• the circular dashed lines represent spherical cutting head 8 having radius R.
• the height H of peaks 68 is dependent upon lead L and radius R.
• height H is affected only by the lead.
• lead must be selected in view of the desired cycle time as well as to maintain a sufficient chip load on each tooth. Too small of a lead may reduced the chip load to the point at which head 8 may burn the surface.
• height H is .0003 inches, sufficiently small to be polished to an optically clear finish.
• Motors 4, 12, 14 and 20 are controlled by a computer controller 66 (FIGS. 3 and 4).
• computer 66 is a PMC model 400, manufactured by PMC of Cincinnati, Ohio.
• the system calibrates itself when first turned on by determining the home positions of motors 12, 14 and 20. Because the resolvers are incremental devices, once the home position of motors 12 and 20 have been determined, the resolvers are reset to zero by the computer.
• FIG. 4 illustrates the home positions of axes T and C as determined by switches 62 and 64, respectively.
• Switches 62 and 64 are fixed to base 22, and are tripped whenever trips 62a and 64a, which rotate with motor flanges 32 and 46, respectively, rotate past respective switches 62 and 64, so as to generate a home pulse for each respective motor. It is not, however, necessary that the actual home position of axes T and C be paralleled to each other as shown. The parallel orientation of axes T and C as illustrated in FIG. 4 was selected for ease of mounting tool 6 and workpiece 16 to their respective mounts. If the actual home positions are not as shown, computer 66 may be programmed to orient axes T and C in the parallel positions illustrated once the home positions have been determined.
• the appropriate lens blank is selected, blocked and mounted to workpiece mounting 42.
• the lens blank may include a bar code located about its circumferential surface, which may be scanned by bar code scanner 72 (FIG. 3) when axis C is oriented as shown in FIG. 4, to ensure that the user has mounted the proper lens blank.
• Computer control 66 then controls the axes of lens generating apparatus 2 in the manner described above to generate the desired surface on workpiece 16. When the surface is complete, axes T and C are returned to the positions shown in FIG. 4.
• the lens generating apparatus generates a precise surface without elliptical error.
• the apparatus can generate a wide range of various surfaces. Polycarbonate, CR39TM and glass lens blanks may be cut or ground on the apparatus.
• the apparatus achieves this without the use of expensive and sensitive linear way systems.
• the apparatus does not require adjustment or alignment for each surface generated, nor does it require extensive calibration.
• the apparatus may be operated without extensive training or skill.

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• Engineering & Computer Science (AREA)
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• 1991
  • 1991-07-12 EP EP19910914021 patent/EP0538391A1/en not_active Withdrawn
  • 1991-07-12 WO PCT/US1991/004918 patent/WO1992000832A1/en not_active Application Discontinuation
  • 1991-07-12 JP JP51333491A patent/JPH05508355A/ja active Pending

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