USRE37376E1 - Method for rapid imaging of thermographic materials by extending exposure time in a single beam laser scanner - Google Patents
Method for rapid imaging of thermographic materials by extending exposure time in a single beam laser scanner Download PDFInfo
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- USRE37376E1 USRE37376E1 US09/618,750 US61875000A USRE37376E US RE37376 E1 USRE37376 E1 US RE37376E1 US 61875000 A US61875000 A US 61875000A US RE37376 E USRE37376 E US RE37376E
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- 239000000463 material Substances 0.000 title claims abstract description 39
- 238000000034 method Methods 0.000 title claims abstract description 26
- 238000003384 imaging method Methods 0.000 title claims abstract description 10
- 230000001360 synchronised effect Effects 0.000 claims description 2
- 230000000694 effects Effects 0.000 abstract description 5
- 230000010354 integration Effects 0.000 abstract description 3
- 238000007651 thermal printing Methods 0.000 abstract description 2
- 230000008901 benefit Effects 0.000 description 6
- 229920000642 polymer Polymers 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 238000001931 thermography Methods 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
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- 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
- B41J2/475—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 for heating selectively by radiation or ultrasonic waves
- B41J2/4753—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 for heating selectively by radiation or ultrasonic waves using thermosensitive substrates, e.g. paper
Definitions
- the invention relates to laser scanning and in particular, to scanning of thermal materials, also known as thermographic materials, with high power lasers.
- the common solution is to use a multibeam system, as the exposure time of each spot goes up in proportion to the number of beams for a given data rate.
- Multibeam systems increase the cost of a laser scanner, therefore it is desirable to increase the exposure time of a single beam system. Increasing the exposure time by simply increasing the spot size is not practical due to loss of resolution.
- Another object of the invention is to achieve higher utilization of the laser.
- Thermal imaging systems use high power and expensive IR lasers, typically multiwatt diode-pumped YAG lasers.
- the present invention enables the use of lasers which are allowed to have poor beam quality in one of the spot dimensions, such as wide area laser diode emitters, which are significantly cheaper than YAG lasers.
- no intensity matching between the sources is required. This is an advantage over systems using multiple spots in parallel, where intensity match is critical.
- the invention uses a scanning beam imaging a linear array of light sources to form each spot on the material being exposed.
- the data is shifted serially through this linear array while the array is imaged onto the material in a mode known as Time Domain Integration (TDI).
- TDI Time Domain Integration
- the total exposure time of each spot on the material is multiplied by the number of light sources (e.g. if the internal drum scanner used in the previous example had ten light sources, the exposure time will go from 10 nS to 100 nS while the system will stay a single beam system).
- the rate of shifting the data serially through the array of light spots needs to be matched to the scanning velocity in order to achieve a stationary image of the shifting data on the material being exposed.
- the TDI mode of imaging is well known in imaging sensors, such as Charge Coupled Devices (CCD), where it is used to increase sensitivity by integrating the light into a longer exposure without the loss of resolution.
- CCD Charge Coupled Devices
- the same light integrating property of TDI scanning is used by the present invention, in a single scan line configuration, to increase the exposure time without loss of resolution.
- FIG. 1 shows schematically a prior art laser scanner of the internal drum type.
- FIG. 2 shows schematically a prior art laser scanner of the multibeam external drum type.
- FIG. 3 shows schematically the invention implemented on an external drum scanner.
- FIG. 4 shows schematically the invention implemented on an internal drum scanner.
- FIG. 5 shows the cross section of the internal drum scanner of FIG. 4 .
- FIG. 6 shows schematically the invention implemented using an Acousto-Optical Modulator.
- FIG. 7a to FIG. 7d shows the use of the invention with uneven laser sources to produce even exposure.
- FIG. 8 shows schematically the invention implemented using an electro-optical modulator.
- a flat field scanner was used to illustrate the invention.
- Prior art high speed scanners are either of the internal drum type, as shown in FIG. 1, or the multichannel (also Known as multibeam or multispot) external drum type.
- the internal drum type a light beam 8 is focussed onto material 1 , loaded inside cylindrical surface 2 , by the action of lens 5 .
- the focussed light spot is scanned across material 1 by a scanning mirror 3 driven by motor 4 .
- the complete scanning assembly 6 is moved along material 1 by a linear positioner 7 .
- this type of scanner causes the rotation of the optical image carried by beam 8 , as shown by rotation of arrow 9 which is the image of arrow 10 .
- beam 8 has to be a round beam, insensitive to rotation.
- FIG. 2 Another common type of prior art is a multispot external drum recorder shown in FIG. 2 .
- Multiple lasers 11 are imaged by lens 5 to form multiple spots 12 on material 1 , which is mounted on cylinder 2 .
- FIG. 3 shows how the present invention allows one to convert the laser scanning system of FIG. 2 to have the advantages of a single spot system but retain the longer exposure times of a multispot system.
- the invention is more important for internal drum scanners, however it is explained first on an external drum system for conceptual simplicity.
- thermographic material 1 is mounted on drum 2 .
- An array of laser sources 11 is imaged onto material 1 using lens 5 .
- Spots 12 are imaged along a single line thus each one of scanning spots 12 will overlap with the previously imaged spot, forming a single line on material 1 .
- the data to be recorded is fed to laser sources 11 via shift register 15 , clocked by a clock generator 14 synchronized to the position of cylinder 2 via a shaft encoder 13 .
- the reason for not driving shift register 15 with output of shaft encoder 13 is that the writing clock, also known as pixel clock, is normally of higher resolution than the shaft encoder output.
- the writing clock can be an integer or non-integer multiple of shaft encoder output.
- Clock generator 14 can be of the phase lock loop type, synthesizer type or any one of the many well known clock generation methods.
- the period of the clock is set that shift register 15 moves the data one bit in the interval the surface of media 1 travels the distance between two adjacent spots. This distance is shown as “X” in FIG. 3 .
- Clocking the data in this fashion causes the image of a given data bit to be stationary relative to media 1 while it is being exposed, in sequence, by all laser sources 11 .
- This mode of imaging is well known by the name Time Domain Integration (TDI) and is normally used to increase exposure.
- TDI Time Domain Integration
- U.S. Pat. Nos. 5,049,091 and 5,132,723 co-owned with this application use TDI to increase exposure energy.
- TDI is used to increase the exposure time to allow the use of certain thermal materials without increasing the energy.
- FIG. 4 An array of laser sources 11 is imaged as spots 12 along a single line. A mirror 3 is rotated by motor 4 to scan spots 12 across thermographic material 1 . The scanning assembly 6 is moved along material 1 by a linear positioner 7 . The scanning arrangement is different from what is shown in FIG. I in order to avoid the problem of image rotation explained earlier. The details of shifting the data serially through lasers 11 is identical to FIG. 3 . These details are omitted from FIG. 4 for sake of clarity. More details about scanning configurations for internal drum recorders not causing rotation of image are disclosed in U.S. Pat. Nos. 4,206,482 and 4,595,957.
- FIG. 5 shows a cross section of FIG. 4, with the data from shaft encoder (not shown) coupled to motor 4 , synchronizing the shifting of the data through laser sources 11 , to match the scanning velocity of spots 12 .
- the synchronization is done via clock generator 14 and shift register 15 .
- discrete light sources can be:
- Laser diodes in combination with beam shaping optics
- Fiber optics coupled to laser diodes
- a single light source such as a high powered laser diode or a YAG type laser can be broken up into discrete sources using the following methods:
- AOM Acousto-Optical Modulator
- EOM Electro-Optical Modulators
- TDI TDI
- Scophony Imaging is used mainly with continuously moving data patterns, such as used in AOMs.
- Scophony/TDI techniques can be found in U.S. Pat. Nos. 4,357,627 and 4,639,037. Both these patents use the Scophony/TDI effect in order to increase the resolution of the scanner and not in order to increase the exposure time, which is the essence of the present invention.
- both patents do not take advantage of the possibility of using laser with non-uniform beams.
- the application of Scophony/TDI according to the present invention with non-uniform beams is shown in FIG. 6 and FIG. 7a to 7 d.
- the Scophony/TDI effect used by the present invention generates uniform and even spots, with long exposure times on the recorded material.
- a high power laser diode source 16 is partially collimated by lens 21 and illuminates an AOM 17 .
- the data fed into AOM 17 via AOM driver 18 travels down the AOM at a velocity which depends on the type of AOM used, typically about 4 km/sec. As AOMs are well known devices no further details on their operation is given here.
- the active aperture of AOM 17 is imaged onto material 1 by lens 5 . Either the zero order beam 19 or the diffracted beam 20 can be used (obviously the data needs to be inverted if the zero order beam 17 is used).
- the traveling acoustic wave inside AOM 17 is a replica of the serial data pattern and diffraction only occurs where the travelling wave, caused by the RF drive, is present.
- the exposure time of each bit will be A/ ⁇ .
- “A” can be easily made 10 mm, ⁇ ⁇ 4 mm/ ⁇ S, giving exposure time of 2.5 ⁇ S, which is sufficient for most thermal materials.
- FIG. 7-a to FIG. 7d shows how the present invention can be utilized to achieve uniform pixel to pixel exposure from non-uniform laser sources.
- FIG. 7a represents the radiation profile of laser diode 16 of FIG. 6 . As is the case with many wide emitter laser diodes, the profile is non-uniform with multiple “dark spots”.
- FIG. 7b is the acoustic wave travelling through the AOM of a given point in time.
- the exposure profile of the diffracted beam ( 20 in FIG. 6) of a given point in time is the product of FIG. 7 a and FIG. 7b, shown in FIG. 7 c.
- the profile is non-uniform, showing the same “dark spots” as the laser diode.
- each pixel on the material will be scanned by the complete profile of the laser diode captured by the active aperture “A” of the AOM, thus the total exposure of each bit will be the same, as shown in FIG. 7 d.
- FIG. 7d is the final exposure of the data pattern, after all pixels completed their scan.
- a highly uniform exposure is possible from a highly uneven source without the waste of laser power or special effort to balance the exposure.
- This feature of the present invention allows the utilization of lower cost lasers. It is obvious that the same method can be used not only with AOMs, but for any modulator or array of lasers.
- FIG. 8 shows the use of the invention with flat field scanning.
- an electro-optical modulator 17 was chosen to illustrate the invention, for example a modulator as disclosed in U.S. Pat. No. 4,639,073. While U.S. Pat. No. 4,639,073 uses the Scophony effect to increase resolution, the same layout can be used to increase exposure time for thermal materials and utilize low cost, low beam quality, laser sources.
- a polygon 3 is rotated by motor 4 .
- the beam from laser diode 16 is collected by lens 21 , passes modulator 17 reflected by polygon 3 and imaged by lens 5 onto material 1 .
- Scophony/TDI imaging conditions are met by synchronizing shift rate through shift register 15 using shaft encoder 13 and clock generator 14 .
- the invention is adaptable to any scanning system, laser source and modulator type.
- the three scanning systems shown were only by way of example.
Abstract
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Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US09/618,750 USRE37376E1 (en) | 1996-08-16 | 2000-07-14 | Method for rapid imaging of thermographic materials by extending exposure time in a single beam laser scanner |
Applications Claiming Priority (3)
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US69902596A | 1996-08-16 | 1996-08-16 | |
US08/861,065 US6072518A (en) | 1997-05-21 | 1997-05-21 | Method for rapid imaging of thermographic materials by extending exposure time in a single beam laser scanner |
US09/618,750 USRE37376E1 (en) | 1996-08-16 | 2000-07-14 | Method for rapid imaging of thermographic materials by extending exposure time in a single beam laser scanner |
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US08/861,065 Reissue US6072518A (en) | 1996-08-16 | 1997-05-21 | Method for rapid imaging of thermographic materials by extending exposure time in a single beam laser scanner |
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Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6541731B2 (en) * | 2000-01-25 | 2003-04-01 | Aculight Corporation | Use of multiple laser sources for rapid, flexible machining and production of vias in multi-layered substrates |
US6665048B2 (en) | 2002-01-22 | 2003-12-16 | Creo Inc. | Method for imaging a continuously moving object |
US9533514B2 (en) | 2012-10-31 | 2017-01-03 | Han's Laser Technology Industry Group Co., Ltd | Near-infrared laser focusing lens and laser printing device |
Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3750189A (en) * | 1971-10-18 | 1973-07-31 | Ibm | Light scanning and printing system |
US4206482A (en) * | 1977-09-09 | 1980-06-03 | Thomson-Csf | Electronoptical apparatus for analysing documents |
US4348593A (en) * | 1981-01-29 | 1982-09-07 | Xerox Corporation | Twisting geometry optical system utilizing imaging array with time delay segments |
US4357627A (en) * | 1980-04-28 | 1982-11-02 | Xerox Corporation | Method and apparatus for improving resolution of scophony scanning system utilizing carrier phase reversal |
US4595957A (en) * | 1983-05-19 | 1986-06-17 | Dr. Boger Photosatz Gmbh | Optical light bead scanning arrangement |
US4639073A (en) * | 1984-03-19 | 1987-01-27 | Xerox Corporation | Electro-optic pulse imaging raster output scanner |
US5049901A (en) * | 1990-07-02 | 1991-09-17 | Creo Products Inc. | Light modulator using large area light sources |
US5132723A (en) * | 1991-09-05 | 1992-07-21 | Creo Products, Inc. | Method and apparatus for exposure control in light valves |
US6025864A (en) * | 1995-12-14 | 2000-02-15 | Fuji Xerox Co., Ltd. | Optical scanning device and image forming apparatus |
-
2000
- 2000-07-14 US US09/618,750 patent/USRE37376E1/en not_active Expired - Lifetime
Patent Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3750189A (en) * | 1971-10-18 | 1973-07-31 | Ibm | Light scanning and printing system |
US4206482A (en) * | 1977-09-09 | 1980-06-03 | Thomson-Csf | Electronoptical apparatus for analysing documents |
US4357627A (en) * | 1980-04-28 | 1982-11-02 | Xerox Corporation | Method and apparatus for improving resolution of scophony scanning system utilizing carrier phase reversal |
US4348593A (en) * | 1981-01-29 | 1982-09-07 | Xerox Corporation | Twisting geometry optical system utilizing imaging array with time delay segments |
US4595957A (en) * | 1983-05-19 | 1986-06-17 | Dr. Boger Photosatz Gmbh | Optical light bead scanning arrangement |
US4639073A (en) * | 1984-03-19 | 1987-01-27 | Xerox Corporation | Electro-optic pulse imaging raster output scanner |
US5049901A (en) * | 1990-07-02 | 1991-09-17 | Creo Products Inc. | Light modulator using large area light sources |
US5132723A (en) * | 1991-09-05 | 1992-07-21 | Creo Products, Inc. | Method and apparatus for exposure control in light valves |
US6025864A (en) * | 1995-12-14 | 2000-02-15 | Fuji Xerox Co., Ltd. | Optical scanning device and image forming apparatus |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6541731B2 (en) * | 2000-01-25 | 2003-04-01 | Aculight Corporation | Use of multiple laser sources for rapid, flexible machining and production of vias in multi-layered substrates |
US6665048B2 (en) | 2002-01-22 | 2003-12-16 | Creo Inc. | Method for imaging a continuously moving object |
US9533514B2 (en) | 2012-10-31 | 2017-01-03 | Han's Laser Technology Industry Group Co., Ltd | Near-infrared laser focusing lens and laser printing device |
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