WO2001018494A1 - Systeme d'imagerie numerique utilisant la lumiere modulee a bande large - Google Patents

Systeme d'imagerie numerique utilisant la lumiere modulee a bande large Download PDF

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Publication number
WO2001018494A1
WO2001018494A1 PCT/US2000/024192 US0024192W WO0118494A1 WO 2001018494 A1 WO2001018494 A1 WO 2001018494A1 US 0024192 W US0024192 W US 0024192W WO 0118494 A1 WO0118494 A1 WO 0118494A1
Authority
WO
WIPO (PCT)
Prior art keywords
light
modulators
array
imaging system
refractive optical
Prior art date
Application number
PCT/US2000/024192
Other languages
English (en)
Inventor
Frank A. Hull
Original Assignee
Cortron Corporation
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 Cortron Corporation filed Critical Cortron Corporation
Publication of WO2001018494A1 publication Critical patent/WO2001018494A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/04—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings formed by bundles of fibres
    • G02B6/06—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings formed by bundles of fibres the relative position of the fibres being the same at both ends, e.g. for transporting images
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
    • G02B26/10—Scanning systems

Definitions

  • the present invention relates to a high resolution digital imaging device employing modulated broadband light to create the individual pixels of the image to be recorded.
  • the invention is particularly useful in the graphic arts industry for exposing a variety of light-sensitizable media such as printing plates, proofing materials, relief plates and the like.
  • high resolution images are formed by exposing a light-sensitizable medium such as a printing plate with an appropriate light pattern.
  • the printing plates were covered with a patterned film and exposed by broadband light to create the desired image on the plate.
  • the broadband light was utilized at low energy levels, such that the film intermediary was required to properly expose the plate. More recently, methods that do not utilize film intermediaries have been developed, utilizing digital laser imaging at much higher levels of energy.
  • the present invention is a digital imaging system for exposing a light-sensitizable material utilizing broadband, non-coherent light at least partially in the ultraviolet spectrum.
  • the non-coherent light is directed into a modulator assembly that includes a plurality or array of individually controllable refractive optical modulators.
  • the refractive optical modulators are individually controlled to either pass the light therethrough and thereby transmit a light beam on to the light- sensitizable material and create a "light" pixel, or to refract the light for subsequent absorption and/or dissipation of the light so as to create a "dark" pixel on the light-sensitizable material.
  • a selected output light pattern is therefore created by the arrangement of "light” and “dark” pixels.
  • a fiber assembly is coupled to the optical modulator array for transmitting the light passed through the refractive optical modulators to the light-sensitizable medium and for absorbing and dissipating the light refracted by the optical modulators.
  • a lens is provided to focus the selected output light pattern onto the light-sensitizable material.
  • FIG. 1 is a block diagram of a typical digital imaging system for utilizing an imager according to an embodiment of the present invention.
  • FIG. 2 is a diagram of the imager head optics utilized with a digital imaging system according to an embodiment of the present invention.
  • FIG. 3 is a diagram illustrating the operation of the modulator employed by an embodiment of the present invention in more detail.
  • FIG. 1 is a block diagram showing the components of a typical high resolution broadband light digital imaging system 10 for utilizing an imager according to the present invention.
  • Digital imaging system 10 operates in a manner known in the art to form high resolution images by exposing a light-sensitizable medium such as a printing plate with an appropriate light pattern.
  • Rotating drum 12 is driven by drum drive 14, imager assembly 16 includes imager 18 focusing light 20 onto drum 12 in a controlled pattern, and computer 22 controls operations of imager assembly 16 and drum drive 14.
  • imager 18 shown in FIG. 1 employs a novel broadband light modulating system that improves the overall performance of the digital imaging system, with the details of imager 18 being shown in more detail in FIG. 2.
  • FIG. 2 is a diagram of imager 18 of the high resolution digital imaging system of the present invention.
  • Broadband noncoherent light source 30 such as an ultraviolet plasma capillary tube, is seated in ellipsoid cylindrical section reflector 32 or a similar apparatus for focusing non-coherent light in a selected direction.
  • the light is focused onto cylindrical reflector 34, which is coated to reflect light only in the wavelengths of interest, such as in the 360-400 nanometer (nm) range.
  • Light reflected by cylindrical reflector 34 is convergent in two planes, and is directed through polarizer 36, which passes only light waves that are aligned with the polarization angle of polarizer 36.
  • aperture 38 which serves to trim the polarized light to match the input dimensions of modulator array 40, with the non-coherent light preferably being shaped to slightly over-flood the aperture.
  • polarized light passes through aperture 38 as a beam having a width equal to the length of modulator array 40 and having a height equal to the total height of the modulators in modulator array 40, and the divergence of the light is low, preferably less than about 1.5 degrees.
  • the light is thereby apportioned into the plurality of individually controllable modulators contained in modulator array 40.
  • Digital information 41 in the form of a binary image file is utilized by modulator driving circuit 42 to control modulator array 40 and thereby create a selected output light pattern for imaging.
  • the position of drum 12 is provided to modulator driving circuit 42 by encoder 44 in order to synchronize the release of data to modulator array 40 with the position of drum 12, so that the modulation pattern is correlated to the imaging row on light-sensitive medium 46 mounted to drum 12.
  • Output fiber assembly 48 is connected to receive and further transmit the light output from modulator array 40.
  • Each modulator in modulator array 40 refracts or bends the light according to the control signal applied thereto by modulator driving circuit 42.
  • the light is refracted by an individual modulator at such an angle that the light is not transmitted through fiber assembly 48, but instead passes through the fiber wall and is absorbed and dissipated by the cladding and/or jacket of the fiber therein.
  • the light is merely passed through the individual modulator, with no more than negligible refraction, and is emitted from an end of fiber assembly 48.
  • fiber assembly 48 may be omitted and a stop plate employed instead, with each modulator being configured so that light is either passed from the modulator or refracted to impinge upon the stop plate.
  • the optical fibers of fiber assembly 48 taper from a 0.5 millimeter (mm) square area input aperture adjacent each modulator of modulator array 40 to a 0.020 mm square area output aperture (corresponding to the pixel resolution of the imaging system) to be focused onto light-sensitizable medium 46 mounted on recording drum 12 by focusing lens 50.
  • Focusing lens 50 may be of the relay type, the telecentric type, or the anamorphic type, depending on the imaging requirements as is known in the art.
  • the horizontal advancement of modulator array 40 can be controlled such that there is partial overlap between horizontal positions, so that the intensity of the output from modulator array 40 can be reduced while still achieving full exposure of medium 46.
  • the optical switches provided in modulator array 40 utilized by the present invention are illustrated in more detail in FIG. 3.
  • Light 60 enters each modulator 62 after passing through adjustable aperture 38.
  • Aperture 38 serves the purpose of limiting the light to only the active area inside modulator 62 and allows over-flooding of the light, thus preventing pointing and falloff errors inherent when trying to fill the input with a matched beam size.
  • Light 60 is slightly divergent at approximately a 1.5 degree half-angle entering modulator62.
  • Modulator 62 is a refractive electro-optic modulator constructed of a high index material lowering the divergence to 0.68 degrees whilst in modulator 62.
  • Active area 64 of modulator 62 is constructed such that all light passing through the input will remain within its active area 64.
  • modulator 62 is a broad cell electro-optic refractive modulator manufactured by Applied Electro-Optics Corporation of Pittsburgh, PA. Coupled to the modulator is tapered optical fiber 68 of the same size as active area 64 of the modulator 62. Light passing through modulator 62 in its normal state (no more than negligible refraction) is coupled to fiber 68 and exits at the opposite end reduced in size by the taper of fiber 68.
  • the fiber taper has two functions: first; it reduces the size of the output beam in accord with the taper, and second, it reduces the fiber's input Numerical Aperture (NA) by the ratio of the taper.
  • the fiber is configured with a 12-to-1 taper having an input NA of 0.018 and an output NA of 0.22, which causes the fiber not to transmit light entering beyond a 1.0 degree divergence angle.
  • Other taper arrangements may be employed with similar effects on the NA of the fiber to obtain desired transmittance characteristics of the fiber for acceptable divergence angles of light.
  • Fiber 68 Light that is refracted by modulator 62 in its active (refractive) state exceeds the critical angle that fiber 68 will transmit (i.e. reflect off of the fiber wall within the fiber), such as the 1.0 degree angle of the exemplary embodiment having a 12-to-1 taper, and therefore is not passed to the fiber output, as dictated by the Total Internal Reflectance (TIR) function of fiber 68. Instead, the refracted light strikes the wall of the fiber at an angle greater than the critical angle so that the light passes through the wall and is absorbed and dissipated by the cladding and/or outer jacket of the fiber. Tapered fiber 68 produces an output whose optical nature is achromatic, i.e. the light does not induce any focal displacement that is dependent upon wavelength of light.
  • TIR Total Internal Reflectance
  • a lens-based optical reduction system at the output of modulator 62 would be cost prohibitive to make achromatic at the high demagnification ratios employed with the present invention.
  • the divergence angle of light output from the fibers will not exceed the intrinsic NA capability of the fiber. This results in control of beam spread even though the system is operating at high demagnification.
  • modulator 62 is an optical switch realized by a prism-type refractive structure, in which prism-shaped regions with different indices of refraction are created with an applied voltage via the electro-optic effect, such as a lithium nobate glass structure operating by inversion of ferroelectric domains and serving as an optical grating.
  • a gradient-type refractive device may be utilized, where a nonuniform electric field distribution is created in the modulator crystal and induces a similar index distribution which bends the light as it propagates through the modulator.
  • the optical switch causes light to bend as it passes therethrough, with the bending being predictable based only on the voltage applied to the glass and the length of the glass.
  • the refractive optical switches are broad cell devices, operable to refract the entire light input received by the switch.
  • an optical switch in the manner of the present invention rather than a mechanically vibrating device such as an acousto-optic modulator having a piezoelectric vibrator, for example, the imaging system is essentially power-unlimited.
  • beams with high enough power to effectively expose the printing plate mounted on the recording drum typically plates require at least approximately 0.18 Watts per beam, based on a specification of 0.3 Joules per square centimeter at an exposing rate of 30 square centimeters per second) can be achieved without concern for the capacity of the optical switching components in the modulator.
  • a line of 96 pixels may be exposed at a sufficient power level by utilizing a relatively inexpensive broadband light source, such as a 5000 Watt plasma capillary light source having a 500 Watt ultraviolet output, although it should be understood that light sources with higher output power may also be used with the present invention due to the power-unlimited nature of the modulator switches.
  • a relatively inexpensive broadband light source such as a 5000 Watt plasma capillary light source having a 500 Watt ultraviolet output, although it should be understood that light sources with higher output power may also be used with the present invention due to the power-unlimited nature of the modulator switches.
  • the present invention therefore is a high resolution digital imaging system utilizing non-coherent light to expose a pre-sensitized medium such as a printing plate, particularly for use in the graphic arts industry, and provides several advantages over prior art systems such as lower cost, higher speed, and improved durability and reliability.
  • the system is capable of operating with conventional printing plates, which is advantageous because of the lower cost associated therewith and the acceptance in the industry of such printing plates as compared to thermal printing plates for use with laser imaging systems.
  • the system is able to achieve high resolution with outstanding beam quality and clarity, while utilizing a broadband non-coherent light source and a modulator assembly, output fiber assembly and focusing lens for defining individual pixels of the digital image and focusing the beams on the printing plate mounted on a recording drum.
  • the modulator assembly utilizes a plurality of optical switches that are power-unlimited, enabling a high powered broadband light source to be used and sufficient power to be contained in each output beam to properly expose the printing plate with the desired pattern, controlled by appropriate control signals applied to the modulator to operate the optical switches according to a predetermined graphical image stored in a computer.
  • the optical switches employ refractive optical modulators having no moving parts, they are able to withstand the relatively high levels of ultraviolet light delivered by the system.
  • the coupling optics have a fill factor of approximately 100%, such that in an exemplary embodiment a 5000 Watt plasma capillary light source providing 500 Watts of ultraviolet power is able to achieve about 20 Watts of power at the output of the system, or about 0.2 Watts per beam, which is sufficient to successfully expose the printing plate mounted on the recording drum. It should be understood that higher- powered light sources may also be used to increase the output power of the system, since the modulators are essentially power-unlimited devices at all spectra.
  • the present invention also exposes the printing plate with square pixels, which is advantageous due to the uniformity of power achievable with such a pixel shape. In an exemplary application, the present invention utilizing an inexpensive 5000 Watt plasma capillary light source is able to expose a conventional 30 inch by 40 inch printing plate in approximately 4.3 minutes, which is comparable performance to much more expensive laser imaging systems.

Abstract

L'invention concerne un système d'imagerie numérique destiné à exposer un matériau rendu sensible à la lumière (46) au moyen d'une source de lumière non cohérente (30). Un réseau de modulateurs optiques (40), optiquement couplé de manière à recevoir la lumière non cohérente depuis la source lumineuse (36), comprend plusieurs modulateurs optiques de réfraction (62). Un circuit de commande (42) est couplé de manière fonctionnelle au réseau de modulateurs optiques (40) de manière à commander chacun des modulateurs optiques de réfraction (62) pour créer un motif sélectionné de lumière émise. Une lentille (50) est couplée optiquement au réseau de modulateurs optiques (40) de manière à focaliser le motif sélectionné de lumière émise sur le matériau rendu sensible à la lumière (46).
PCT/US2000/024192 1999-09-03 2000-09-01 Systeme d'imagerie numerique utilisant la lumiere modulee a bande large WO2001018494A1 (fr)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
US15230299P 1999-09-03 1999-09-03
US60/152,302 1999-09-03
US48440500A 2000-01-14 2000-01-14
US09/484,405 2000-01-14
US50501700A 2000-02-16 2000-02-16
US09/505,017 2000-02-16

Publications (1)

Publication Number Publication Date
WO2001018494A1 true WO2001018494A1 (fr) 2001-03-15

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004025364A2 (fr) * 2002-09-11 2004-03-25 Day International, Inc. Procede d'impression numerique en quadrichromie et element d'image couleur faisant appel a des photopolymeres a sensibilite chromatique
US7305877B2 (en) 2003-07-14 2007-12-11 Robert Bosch Gmbh Device for determining at least one parameter of a medium flowing in a line having diversion surface

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4675702A (en) * 1986-03-14 1987-06-23 Gerber Scientific Inc. Photoplotter using a light valve device and process for exposing graphics
US5033814A (en) * 1989-04-10 1991-07-23 Nilford Laboratories, Inc. Line light source
US5317446A (en) * 1992-09-29 1994-05-31 Eastman Kodak Company Electrooptic device for scanning using domain reversed regions
US5517347A (en) * 1993-12-01 1996-05-14 Texas Instruments Incorporated Direct view deformable mirror device
US5844588A (en) * 1995-01-11 1998-12-01 Texas Instruments Incorporated DMD modulated continuous wave light source for xerographic printer
US5930027A (en) * 1998-02-12 1999-07-27 Mcdonnell Douglas Corporation Digitally controlled fiber optic light modulation system

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4675702A (en) * 1986-03-14 1987-06-23 Gerber Scientific Inc. Photoplotter using a light valve device and process for exposing graphics
US5033814A (en) * 1989-04-10 1991-07-23 Nilford Laboratories, Inc. Line light source
US5317446A (en) * 1992-09-29 1994-05-31 Eastman Kodak Company Electrooptic device for scanning using domain reversed regions
US5517347A (en) * 1993-12-01 1996-05-14 Texas Instruments Incorporated Direct view deformable mirror device
US5844588A (en) * 1995-01-11 1998-12-01 Texas Instruments Incorporated DMD modulated continuous wave light source for xerographic printer
US5930027A (en) * 1998-02-12 1999-07-27 Mcdonnell Douglas Corporation Digitally controlled fiber optic light modulation system

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2004025364A2 (fr) * 2002-09-11 2004-03-25 Day International, Inc. Procede d'impression numerique en quadrichromie et element d'image couleur faisant appel a des photopolymeres a sensibilite chromatique
WO2004025364A3 (fr) * 2002-09-11 2005-01-27 Day Int Inc Procede d'impression numerique en quadrichromie et element d'image couleur faisant appel a des photopolymeres a sensibilite chromatique
US7305877B2 (en) 2003-07-14 2007-12-11 Robert Bosch Gmbh Device for determining at least one parameter of a medium flowing in a line having diversion surface

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