Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
  • H04N1/06—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using cylindrical picture-bearing surfaces, i.e. scanning a main-scanning line substantially perpendicular to the axis and lying in a curved cylindrical surface
  • H04N1/0607—Scanning a concave surface, e.g. with internal drum type scanners
  • H04N1/0621—Scanning a concave surface, e.g. with internal drum type scanners using a picture-bearing surface stationary in the main-scanning direction
  • H04N1/0635—Scanning a concave surface, e.g. with internal drum type scanners using a picture-bearing surface stationary in the main-scanning direction using oscillating or rotating mirrors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/435—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material
  • B41J2/47—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using the combination of scanning and modulation of light
  • B41J2/471—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of radiation to a printing material or impression-transfer material using the combination of scanning and modulation of light using dot sequential main scanning by means of a light deflector, e.g. a rotating polygonal mirror
• • 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
  • G02B26/12—Scanning systems using multifaceted mirrors
  • G02B26/123—Multibeam scanners, e.g. using multiple light sources or beam splitters
• • 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
  • G02B26/12—Scanning systems using multifaceted mirrors
  • G02B26/125—Details of the optical system between the polygonal mirror and the image plane
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
  • H04N1/047—Detection, control or error compensation of scanning velocity or position
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
  • H04N1/06—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using cylindrical picture-bearing surfaces, i.e. scanning a main-scanning line substantially perpendicular to the axis and lying in a curved cylindrical surface
  • H04N1/0607—Scanning a concave surface, e.g. with internal drum type scanners
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
  • H04N1/113—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using oscillating or rotating mirrors
  • H04N1/1135—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using oscillating or rotating mirrors for the main-scan only
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
  • H04N1/19—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using multi-element arrays
  • H04N1/191—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using multi-element arrays the array comprising a one-dimensional array, or a combination of one-dimensional arrays, or a substantially one-dimensional array, e.g. an array of staggered elements
  • H04N1/1911—Simultaneously or substantially simultaneously scanning picture elements on more than one main scanning line, e.g. scanning in swaths
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
  • H04N2201/04—Scanning arrangements
  • H04N2201/047—Detection, control or error compensation of scanning velocity or position
  • H04N2201/04753—Control or error compensation of scanning position or velocity
  • H04N2201/04755—Control or error compensation of scanning position or velocity by controlling the position or movement of a scanning element or carriage, e.g. of a polygonal mirror, of a drive motor

Definitions

• the present invention relates to imaging, and more specifically the present invention relates to high speed imaging as applied to photosensitive materials such as film, printed circuit laminates and printing plates, both for creating images and for reading images.
• Imaging is a marriage of the laser source with the plate.
• Printing Plates and other photosensitive materials are sensitive to certain wavelengths and require a specific amount of energy per cm square, i.e. the energy density.
• the energy density is measured in joules/cm/cm.
• Typical values for different plates are: Conventional analog plates 400 mJ/cm/cm
• Silver violet plates 5 ⁇ J/cm/cm Energy is the product of power (P) and time (t). Energy (E) is measured in J/cm/cm, power in watts/cm/cm, and time in seconds. Therefore to expose a plate in an imaging system the dot time and the power density are inversely related, and as the object is to get the smallest imaging time for the complete plate, the power has to be the highest. This puts pressure on the design of the laser source and the laser control.
• Imaging requires a specific amount of energy be incident on the surface, measured as joules per square centimeter.
• E P*t
• power and time being reciprocal the designer has a choice in finding the appropriate mix of the two variables. There is limit imposed by breakdown of reciprocity, thus P and t cannot be infinitely small or large.
• P i.e. power then becomes very large.
• the constraint on power is the availability of a light source with a wavelength similar to the wavelength the material is sensitive to.
• the light sources are limited in choice.
• Imaging on plates can be accomplished through three different strategies: external drum, internal drum, flat bed. Every so often, non-traditional methods have been tried but none have succeeded commercially. The only nominal success may be granted to Baysys Print, although the imaging time is 30 minutes and the quality is not good enough for commercial printing.
• the plate is wrapped around a metal cylinder and rotated about the axis of the cylinder.
• a laser beam, or a number of laser beams are focused on the rotating cylinder in an orthogonal manner such that as the laser beams, mounted on a carriage, moves parallel to the axis of the cylinder, they trace a set of helical lines.
• imaging time length of plate the laser moves across*dpi / (RPS of cylinder * number of beams)
• the internal surface of a cylinder is used to position the plate; there is no motion.
• the XY scan is accomplished by the use of a rotating mirror traveling along the axis of the cylinder with a laser beam focused on the mirror.
• the mirror being a truncated cylinder, the focus point of the laser beam is rotated through 360 degrees with every rotation of the mirror.
• This system does not require complex plate holding mechanisms and the moving parts are limited to two simple components. This lowers the cost dramatically, resulting in very cost effective designs that are equal or better than the quality produced by external drum designs. Throughput is equal or better due to a small rotating mass of the mirror.
• imaging time length of plate mirror moves over*dpi / RPS of rotating mirror
• RPS 400 revolutions per second (24,000 RPM)
• This design uses a multiple facet rotating mirror, reflecting a number of focused laser beams the focal points of which describe a complex surface.
• the complex surface is a concavely curved surface that is part of the surface of a cylinder.
• a flat field lens is used convert this complex surface to a flat surface with some remaining artifacts.
• the plate is placed on a flat bed and moved orthogonal to the rotating beams.
• This design has the advantage of being able to provide very high throughput of imaging due to multiple facets and multiple beams.
• the disadvantage is the flat field lens is difficult to fabricate for large scan width and high quality imaging, thus increasing the cost.
• imaging time length of plate moved across the scan over*dpi / RPS of rotating mirror*facets*number of beams
• US patent 4,814,606 describes a scanner in which an X-ray or radiograph is placed in a circular cross-section support and scanned using a scan beam directed via a rotating multifaceted mirror.
• the light transmitted through the radiograph is detected by a curved detector arranged on an opposite side of the support.
• the optical arrangement ensures that the beam shape impinging on the radiograph is not distorted. It is disclosed in the reference that the laser scanning apparatus provides constant pathlength to the radiograph, constant velocity of the spot of interrogating radiation across the radiograph, constant incidence angle of the beam onto the radiograph and, as a consequence of the latter, constant • pathlength through the radiograph.
• the combination of the rotating mirror, along with the short response, time of the photodetector provides a scanning apparatus with, increased scanning speed.
• a small variation in scan speed of, for example, a radiograph will result in a small variation in the acquired image in a predictable manner.
• the reference teaches providing the mentioned properties, the object is to reduce artefacts due to the combination . of all of the mentioned properties.
• a circular cross-section in combination with a flat multifaceted mirror does not provide a constant velocity of the scanning spot.
• the artefact resulting from this imprecision alone may not be important in the case of scanning an X-ray image, or can still be corrected in the scanned image.
• no such correction is possible, and, as mentioned above, it is essential to ensure a constant power delivery to the recording surface. .
• the proposed method and apparatus eliminates the obstacles to high speed imaging by combining a number of known technologies with a novel light source.
• the novel approach described below rests on two fundamental advances, one through advances in light sources and the other in the use of a multiple facet mirror using a complex surface to eliminate the need for a flat field lens.
• the means for generating the light are improved, and the use of large number of independent light sources in an internal drum imaging geometry, when combined together provide a very cost effective solution to improve imaging times by a factor of ten or more.
• the first advance is to replace the violet laser by LEDs of the same wavelength. Advances in LED technology have made it possible to obtain high power and high coupling efficiency from blue LEDs. The disadvantage remains that the switching time is not fast enough to replace laser diodes. In this novel approach the switching time is not a problem.
• n LEDs are placed with an accurate pitch of Xp
• the resulting light is composed of n light beams increasing uniformly in diameter.
• An optical system placed at a distance f-j from the light source will then focus these beams at a focal length of F forming a matrix or line of spots of diameter d 0 at a pitch Xj.
• the array of LEDs is controlled by switched current sources connected to the output of a computing device such that any of the n LEDs forming the n beams can be switched in or off as a function of the digital data available to the computer.
• the electronics and software will then take care of the relative positing of the dots from each so as to form an integrated image.
• the power of each such beam must meet the requirements of the material to be imaged.
• the power is reciprocal to the time. If time is large, power required is low.
• the number n, the number of beams, can be increased to overcome the increase in imaging time due to slower t,
• a motor with a polygon prism is mounted on a rotor of the motor.
• the faces of the polygon are polished to form a flat mirror and the faces of the polygon are parallel to the axis of the motor.
• the n light beams focused at distance F are made to be incident on one of the facets of the polygon mirror, the n beams are now reflected and focused at distance F, being the sum of F1 , the distance from the lens of the light source to the facet of the polygon mirror, and F2, the distance from the facet of the polygon mirror to the focal point.
• F1 the distance from the lens of the light source to the facet of the polygon mirror
• F2 the distance from the facet of the polygon mirror to the focal point.
• each rotation of the motor causes m scans of the surface by n beams.
• n*m*s the speed of the motor expressed as revolutions per second.
• a motor rotating at 10 RPS (s) with a polygon mirror of 8 facets (m) and number of beams being 32 (n), the number of can lines being beams 32*8*10 2560 scan lines per second.
• the above assembly is then mounted on a linear motion system such that as the assembly moves the scan lines are orthogonal to the travel of the linear motion system.
• the travel is equal to dj*n*m per rotation of the polygon mirror motor.
• any material placed on this surface will then be exposed to the energy of the n beams, m times per revolution.
• a complete imaging system can be formed.
• an apparatus for high speed scanning of a printing plate for image capture or creation comprises a printing plate support having a lengthwise axis and adapted to support a printing plate, at least one optoelectronic device for providing one of an image recording light source and an image light detector, a light beam optical relay system optically coupling the at least one optoelectronic device with a scanning imaging point on the printing plate.
• the relay system includes a rotating mirror for reflecting a beam of light to scan across the printing plate in a transverse direction, and a gantry for moving the beam in the lengthwise direction across the printing plate.
• At least one of the printing plate support and the rotating mirror is adapted to provide a substantially linear transverse direction scan speed on the printing plate as the mirror rotates substantially at a constant rotational speed, the relay system comprising essentially reflective optics between the gantry and the printing plate.
• the apparatus operates without the use of a flat field or f- ⁇ lens.
• the rotating mirror is flat
• the printing plate support is a cylinder including a concavely curved surface.
• the printing plate support may be flat, and the mirror may have a complex surface.
• a combination of complex surfaces may be used, although it is preferred for simplicity to maintain either the mirror surface or the plate support surface flat.
• the rotating mirror is multi-faceted, and the scanning imaging point performs a helical scan.
• Figure 1 is an- optical diagram of the scanning system of the preferred embodiment
• Figure 2 is a detailed illustration of a support having a complex surface according to the preferred embodiment
• Figure 3 is a construction diagram illustrating the formula describing the complex shape of the support in the case of a flat polygonal rotating mirror according to the preferred embodiment.
• an array of LEDs is formed on a ceramic substrate bonded with the 32 drivers and a connector to receive the digital signal to control the 32 LEDs is the light source.
• a lens that focuses the light beams at a distance of 350 mm forms the optics.
• the scanner is an eight faceted polygon mirror mounted on a static air bearing spindle with an encoder. The light source and the scanner are mounted in one assembly and aligned prior to mounting in the imaging engine.
• the imaging engine comprises of a complex surface of length 1000 mm is formed by pouring a slurry composed of granite and quartz mixed with resins such that when poured over a form, will acquire the shape of the form to within the tolerances of the imaging system design.
• the width of this surface is 800 mm.
• the surface is computed for F to be 350 mm. and D to be 150 mm.
• a linear motion system is mounted over this surface such that the travel is parallel to the surface and orthogonal to the complex form.
• the surface can hold material to be imaged on of a size 1000 x 800 mm. Thus the scan length will be 1000 mm and the linear motion will travel 800 mm.
• the cylindrical system is,
• N (a, (x 2 + y 2 ) 1/2 ) '

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Manufacture Or Reproduction Of Printing Formes (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 2004
  • 2004-03-12 EP EP04760758A patent/EP1609018A1/de not_active Withdrawn
  • 2004-03-12 WO PCT/CA2004/000364 patent/WO2004102255A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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