WO1996016794A1 - Procede et appareil de fabrication de lentilles a diffraction en plastique - Google Patents

Procede et appareil de fabrication de lentilles a diffraction en plastique Download PDF

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Publication number
WO1996016794A1
WO1996016794A1 PCT/US1995/015168 US9515168W WO9616794A1 WO 1996016794 A1 WO1996016794 A1 WO 1996016794A1 US 9515168 W US9515168 W US 9515168W WO 9616794 A1 WO9616794 A1 WO 9616794A1
Authority
WO
WIPO (PCT)
Prior art keywords
lens
features
mold
diffractive features
plastic
Prior art date
Application number
PCT/US1995/015168
Other languages
English (en)
Inventor
Xiaohui Ning
Original Assignee
Aotec, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Aotec, Inc. filed Critical Aotec, Inc.
Priority to AU43680/96A priority Critical patent/AU4368096A/en
Publication of WO1996016794A1 publication Critical patent/WO1996016794A1/fr

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C33/00—Moulds or cores; Details thereof or accessories therefor
    • B29C33/30—Mounting, exchanging or centering
    • B29C33/303—Mounting, exchanging or centering centering mould parts or halves, e.g. during mounting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/17—Component parts, details or accessories; Auxiliary operations
    • B29C45/26—Moulds
    • B29C45/37—Mould cavity walls, i.e. the inner surface forming the mould cavity, e.g. linings
    • B29C45/372—Mould cavity walls, i.e. the inner surface forming the mould cavity, e.g. linings provided with means for marking or patterning, e.g. numbering articles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
    • B29D11/00—Producing optical elements, e.g. lenses or prisms
    • B29D11/00009—Production of simple or compound lenses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29L—INDEXING SCHEME ASSOCIATED WITH SUBCLASS B29C, RELATING TO PARTICULAR ARTICLES
    • B29L2011/00—Optical elements, e.g. lenses, prisms
    • B29L2011/0016—Lenses

Definitions

  • the present invention relates to lenses. More specifically, the present invention relates to a method and apparatus for making plastic lenses having diffractive features and the lenses made therefrom.
  • Optical systems employing diffractive features drastically simplify the system design, which reduces the number of components and/or improves the performance.
  • use of optical components having diffractive features in optical systems has not been widespread, primarily due to the cost of mass-producing the diffractive components.
  • the typical diffractive steps are on the order of 1 micron in height, and for a typical surface, there are up to several hundreds of these diffractive steps.
  • single-point diamond ⁇ ng has been the dominate method for accurately producing those features.
  • mass producing diffractive optics using single point diamond turning is too costly and not practical. Accordingly, a need exists to efficiently mass produce diffractive optical components for use in optical systems.
  • a mold has a plurality of "B" plates attached to a press platen which is driven by the ram of the press and a plurality of "A" plates attached to a fixed platen of the press.
  • the "A” plates include a mold plate having mold features at a surface of the plate.
  • the “B” plates also include a mold plate having mold features, which align with the mold features at the "A” mold plate when the press is closed. These mold features are defined by inserts which are disposed in openings in the plates and define the diffractive features at the surfaces of the lens.
  • a plurality of ejection pins are provided at the "B” plates and are used to eject the molded lens.
  • injection means is provided in at the "A” plates and comprises an injection port and cooperating channel. The press is then closed whereby the ram of the press is actuated causing the
  • FIGURE 1 is a side elevation view of the mold plates with the inserts for forming plastic lenses having diffractive features in accordance with the present invention, in a closed position;
  • FIGURE 2 is a view taken along the line 2-2 in FIGURE 1;
  • FIGURE 3 is a view taken along the line 3-3 in FIGURE 1;
  • FIGURE 4 is a view taken along the line 4-4 in FIGURE 2
  • FIGURE 5 is a view taken along the line 4-4 in FIGURE 2, in an open position and with a molded plastic lens having diffractive features being ejected;
  • FIGURE 6 is a cross sectional side elevation view of a plastic lens having diffractive features made in accordance with the method of the present invention.
  • FIGURE 7 is a front view of the plastic lens of FIGURE 6 prior to removal of the edge gate and runner;
  • FIGURE 8 are focus spot diagrams of one example of the lens of the present invention.
  • FIGURE 9 are field curvature/distortion plots of one example of the lens of the present invention.
  • mold plates for use in a hydraulic press (not shown), such as a Cincinnati two hundred ton press, is shown generally at 10 in a closed position.
  • Plates 12 comprise a mold plate 16 attached to plates 18 and 20 by a plurality of bolts 22.
  • a plate 24 is attached to plate 20 by a plurality of screws 26. It will be appreciated that the bolt and screw heads are disposed in corresponding recesses, as is shown in the FIGURES.
  • a pair of plates 28 and 30 connected by bolts 31 are disposed in an opening 32 of plate 20.
  • a plurality of ejection pins 34, 36 and 38 are attached to these plates 28, 30 and extend through corresponding openings in plates 16 and 18. Plates 28 and 30 are hydraulically driven through an opening 40 in plate 24, as is well known in the art. During ejection, pins 34, 36 and 38 are driven to eject a molded lens.
  • Plate 16 includes a rotatable member 52 disposed therein with an opening therethrough, through which pin 34 extends.
  • a surface of member 52 at the part line of the press has a cavity 54 which defines a portion of the runner of the lens being molded.
  • Member 52 is manually rotated by turning an Allen wrench which is inserted into a hexagonal opening 56 in member 52 to a selected position (i.e., one of four in the present example).
  • Member 52 is held in a selected position by a spring loaded pin 58 which engages a detent 60 in plate 18 at the selected position.
  • a surface of plate 16 at the part line of the press has a cavity 62 at each of the four selected positions which aligns with cavity 54 when that position is selected.
  • Cavity 62 also defines a portion of the runner of the lens being molded. Cavity 62 extends into a cavity 64 at the surface of plate 16 at the part line of the press and extends into the opening receiving pin 38. Cavity 64 defines the gate of the lens being molded.
  • Pin 38 comprises a threaded bolt 66 and an insert 68 rotatably attached at one end thereof to bolt 66.
  • End 70 of insert 68 includes features which define the shape and surface features of one surface of the lens being molded.
  • a gasket or seal 72 is disposed at the surface of plate 16 at the part line of the press to provide an air-tight seal when the press is closed and a vacuum is applied, as discussed below.
  • Plates 14 comprise a mold plate 74 attached to a plate 76 by a plurality of bolts 78. Plate 76 is attached to a plate 80 by a plurality of bolts 82. It will be appreciated that the bolt heads are disposed in corresponding recesses, as is shown in the FIGURES.
  • Plate 14 includes a rotatable member 84 disposed therein with an opening 86 therethrough for injection of plastic during molding. Opening 86 aligns and cooperates with an opening 87 through plate 67 which originates at an injection port 89.
  • a surface of member 84 at the part line of the press has a cavity 88 which defines a portion of the runner of the lens being molded.
  • Member 84 is manually rotated by turning an Allen wrench which is inserted into a hexagonal opening 90 in member 84 to a selected position (i.e., one of four in the present example). Member 84 is held in a selected position by a spring loaded pin 92 which engages a detent 94 in plate 76 at the selected position.
  • a surface of plate 74 at the part line of the press has a cavity 96, at each of the four selected positions, which aligns with cavity 88 when that position is selected. Cavity 88 also defines a portion of the runner of the lens being molded. It will be appreciated, and it is clearly shown in the FIGURES, that in a selected position cavity 54 aligns with cavity 88 and together they align with aligned cavities 62 and 96. Cavities 54, 88, 62 and 96 collectively define the runner of the lens being molded.
  • An insert 98 is mounted in an opening in plate 74 by a threaded bolt 100.
  • insert 102 of insert 98 includes features which define the shape and surface features of the other surface of the lens being molded. End 102 of insert 98 aligns and cooperates with end 70 of insert 68 to define the lens being molded. The positioning of inserts 68 and 98 are adjusted along corresponding bolts 38 and 100 to achieve a desired center thickness of the lenses.
  • Alignment of mold plates 16 and 74 is critical to the manufacture of a high performance plastic lens of the present invention.
  • a plurality of lead pins 104 (one of which 104' is offset) are secured to plate 74 and extend into openings in plates 16 and 18 to generally align the plates, as is shown in the FIGURES. More precise alignment is achieved with a precision machined, generally square and circular shaped interlocking block and cavity.
  • a square block 106 protrudes from the surface of plate 16 facing the part line of the press. Block 106 is received in a cavity 108 in the surface of plate 74 facing the part line of the press. Cavity 108 is generally circular with flat surfaces 110 extending inwardly for engaging the corresponding sides of the square block 106. The edges of block 106 and surfaces 110 are tapered (as is clearly shown in the FIGURES) to facilitate mating of cavity 108 and block 106 when the press is closed.
  • the press is closed, whereby the ram of the press is actuated causing plates 12 to move towards plates 14.
  • optical plastic melted plastic
  • a vacuum is applied at the mold prior to injection and is maintained during injection to assure the integrity of the molding process, as is known.
  • the vacuum is applied through an input port 101 in plate 74 and is communicated through a vacuum groove 103 and channels 105 with inserts 98.
  • the vacuum is also applied through an input port 107 in plate 16 and is communicated through channels 109 with inserts 68. While still in the closed position the plastic is at least partially cooled and allowed to harden.
  • the mold is cooled by fluid (e.g., water) circulated through channels 112 from input port 114 to output port 116, in each plate 16 and 74, as is well known in the art.
  • fluid e.g., water
  • the press is opened as shown in FIGURE 5.
  • plastic lenses having diffractive features have been formed as described above and are now ready to be stripped from the press. Plates 28 and 30 are urged toward plates 16 and 18, whereby ejector pins 34, 36 and 38 push the molded plastic lens assembly out of the mold and the plastic lens is removed from the press.
  • a stop 118 is mounted at plate 28 to limit the- travel of plates 28 and 30 in the direction of plates 18 and 16.
  • Plates 28 and 30 are then returned to their original positions, shown in FIGURES 1 - 4, whereby the position for molding of the next lens is selected and another lens can now be formed, as described above.
  • a stop 120 is mounted at plate 30 to limit the travel of plates 28 and 30 in the direction of plate 24.
  • Inserts 68 and 98 determine the surfaces of the injection molded plastic lens having diffractive features; in accordance with which, inserts 68 and 98 are made using precision single diamond turning.
  • the inserts are comprised of stainless steel coated with a thin layer of nickel (e.g., about 0.006") for ease of processing.
  • a precision diamond turning machine is programmed using equations generated by the design.
  • the diffractive features described herein are preferably blazed grating (or profiles), which by definition have continuous optical surfaces well suited for imaging.
  • Other types of diffraction features include, e.g., binary, which by definition have discontinuous optical surfaces not well suited for imaging (due to the discontinuities).
  • the flow characteristics of the optical plastic are an important feature, as such allows reliable replication of the diffractive features on the lenses.
  • acrylic has favorable flow characteristics, i.e., it has a melt flow index of about 20.
  • Acrylic has a low amount of internal birefringence and molded internal stress, both of which cause degradation to optical performance.
  • One such acrylic is ICI CP-51HF.
  • Suitable optical grade plastics include plyolefin, polystyrene, polycarbonate and SAN, however the present invention is not limited to such.
  • the inserts must limit sticking, excessive stress and birefringence.
  • the molding parameters are adjusted to have the mold fully "packed". The parameters that have most impact on the "packing" are: injection pressure, mold temperatures, injecting speed and cycle time. The method for determining these parameters is an iterative process. The parameters are experimentally adjusted until the molded lens replicates the inserts within the required tolerances. To achieve repeatable results, the critical molding parameters must be closely monitored and maintained.
  • Lens 122 comprises a first diffractive convex aspheric surface 124 and a second diffractive convex aspheric surface 126 having a center flange 128 therebetween (i.e., a bi-convex aspheric lens with diffraction).
  • the lens 122 having both refraction and diffraction was formed, as well as the inserts were machined in accordance with the following SAG height function for diffractive/aspheric surfaces:
  • r is the radial distance from the center of the lens (i.e., the optical axis of lens 122), R is the radius of the curvature at the center of the lens, K is the conic constant,
  • C] is the first diffractive coefficient
  • n is the index of refraction of the medium before surface 124
  • n 2 is the index of refraction of the medium after surface 126
  • ⁇ is the design wavelength
  • the "floor” is a discontinuous function which returns the integer value of the argument which is nearest to zero, whereby this part of the function adds or subtracts integer multiples of ⁇ /(n,-n 2 ) to form the diffractive grooves.
  • On-axis spot size (polychromatic using photopic response weighting) 9.0 microns microns
  • surface 124 has 96 steps, and surface 126 has 152 steps.
  • the spacing between these steps varies from 17 microns (at the edge of surface 126) to 515 microns (at the center of surface 124).
  • the step height is approximately 1 micron ( ⁇ /(n-l)).
  • Deliberate vignetting can be achieved by choosing an appropriate thickness for an aperture used with the lens. The lens is well-corrected for both lateral and longitudinal chromatic aberrations. This is readily appreciated with reference to the focus spot diagrams shown in FIGURE 8 and the field curvature/distortion plots shown in FIGURE 9.
  • the lens could be comprised of other designs that incorporate refraction and diffraction in a single lens on at least one surface thereof, as many are readily apparent to one of ordinary skill in the art.
  • lens 122 is shown with an edge gate 130 and a runner 132 extending therefrom, as are commonly used in plastic injection molding.
  • a large edge gate 130 is preferred as it eliminates imperfections in the lens near the edge gate.
  • the edge gate and runner are removed resulting in the lens shown in FIGURE 6.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Health & Medical Sciences (AREA)
  • Ophthalmology & Optometry (AREA)
  • Moulds For Moulding Plastics Or The Like (AREA)

Abstract

Procédé et appareil destinés à fabriquer des lentilles à diffraction en plastique, qui utilisent un moule doté d'une multitude de plaques 'B' (12) fixées à un plateau de serrage entraîné par un coulisseau de presse (10) et une multitude de plaques 'A' (14) jointes à un plateau fixe de la presse (10). Les plaques (12, 14) possèdent des caractéristiques de moulage définies par des pièces d'insertion situées à l'intérieur de plaques de moulage (16, 74). Lors de la fermeture de la presse, les pièces d'insertion définissent un volume de moulage et les caractéristiques de diffraction de la lentille en cours de moulage. A la fermeture de la presse, du plastique fondu est injecté à chaud et sous pression puis on fait refroidir le plastique jusqu'à ce qu'il se solidifie. Une fois la lentille de plastique formée, la presse est ouverte et la lentille en plastique éjectée.
PCT/US1995/015168 1994-11-28 1995-11-21 Procede et appareil de fabrication de lentilles a diffraction en plastique WO1996016794A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU43680/96A AU4368096A (en) 1994-11-28 1995-11-21 Method and apparatus for making plastic lenses having diffractive features

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US34552594A 1994-11-28 1994-11-28
US08/345,525 1994-11-28
US41603195A 1995-03-31 1995-03-31
US08/416,031 1995-03-31

Publications (1)

Publication Number Publication Date
WO1996016794A1 true WO1996016794A1 (fr) 1996-06-06

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PCT/US1995/015168 WO1996016794A1 (fr) 1994-11-28 1995-11-21 Procede et appareil de fabrication de lentilles a diffraction en plastique

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WO (1) WO1996016794A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015044314A1 (fr) * 2013-09-27 2015-04-02 Leonhard Kurz Stiftung & Co. Kg Procédé, insert de formage et moule d'injection pour la production d'une pièce moulée en matière plastique

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2227966A (en) * 1938-04-21 1941-01-07 Eastman Kodak Co Injection type mold
US4793953A (en) * 1987-10-16 1988-12-27 Galic/Maus Ventures Mold for optical thermoplastic high-pressure molding
US4936666A (en) * 1989-08-08 1990-06-26 Minnesota Mining And Manufacturing Company Diffractive lens
US5349471A (en) * 1993-02-16 1994-09-20 The University Of Rochester Hybrid refractive/diffractive achromatic lens for optical data storage systems

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2227966A (en) * 1938-04-21 1941-01-07 Eastman Kodak Co Injection type mold
US4793953A (en) * 1987-10-16 1988-12-27 Galic/Maus Ventures Mold for optical thermoplastic high-pressure molding
US4936666A (en) * 1989-08-08 1990-06-26 Minnesota Mining And Manufacturing Company Diffractive lens
US5349471A (en) * 1993-02-16 1994-09-20 The University Of Rochester Hybrid refractive/diffractive achromatic lens for optical data storage systems

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015044314A1 (fr) * 2013-09-27 2015-04-02 Leonhard Kurz Stiftung & Co. Kg Procédé, insert de formage et moule d'injection pour la production d'une pièce moulée en matière plastique
US10315370B2 (en) 2013-09-27 2019-06-11 Leonhard Kurz Stiftung & Co. Kg Method, mold insert and injection mold for producing a plastics molding

Also Published As

Publication number Publication date
AU4368096A (en) 1996-06-19

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