JP2006058677A - Scanning exposure apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the color blotting of a recorded image due to the difference in modulation systems of laser light. <P>SOLUTION: Green (G) laser light beam is modulated in intensity by an acousto-optic modulator (AOM) and red (R) and blue (B) laser light beams are directly modulated by a driving current control. The projection direction in which the propagation direction of an ultrasonic wave of AOM is virtually projected on a photoreceptor is the same as the scanning direction with respective laser light beams by a polygon mirror. The spot diameters of the R and G laser light beams are made larger than the spot diameter of the G laser light beam on the photoreceptor by the direct modulation. Alternatively, the spot diameters of the respective laser light beams on the photoreceptor are made equal and the image signal pulse duty of the R and B laser light beams is made larger than the image signal pulse duty of the G laser light beam. The integrated light intensity distribution for one pixel of the R and B laser beams is expanded to match the expanded width of the integrated light intensity distribution for one pixel of the G laser light beam with which the photoreceptor is scanned and exposed, and the color blotting of the recorded picture is reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a scanning exposure apparatus that scans and exposes a photosensitive member with laser light modulated in accordance with image density.

  Laser printers that use laser light are known as photographic printers that record image data. In a laser printer, a sheet-shaped photosensitive member is conveyed in the sub-scanning direction, and laser light is scanned and exposed in a main scanning direction perpendicular thereto. For example, a silver salt sensitive material is used for the photoreceptor, and an image is recorded as a latent image on the photoreceptor subjected to scanning exposure, and the image becomes apparent when developed.

  The scanning exposure apparatus used in such a laser printer includes a light source that generates laser light of each color of red, green, and blue, and modulates the laser light for each color based on color image data. Laser light is deflected in the main scanning direction by a polygon mirror to perform scanning exposure, and the photosensitive member is conveyed in the sub-scanning direction.

  In such a scanning exposure apparatus, for example, a semiconductor laser is used as a light source for red laser light and blue laser light, and a secondary high-frequency generation (SHG: SHG) is used as a light source for green laser light. A SHG laser using a combination of (Second Harmonic Generation) elements is used. In the semiconductor laser, modulation according to the image density is possible by controlling the current (intensity modulation) or controlling the duty (pulse width modulation), but in the SHG laser, the modulation according to the image density is possible. For this purpose, an external modulator such as an acousto-optic modulator (AOM) is used (see, for example, Patent Document 1). The AOM is an optical modulator that uses acousto-optic diffraction, and modulates the intensity of diffracted light by propagating ultrasonic waves in a direction perpendicular to laser light and controlling the intensity of the ultrasonic waves.

JP 2001-281777 A

  However, in the above scanning exposure apparatus, direct modulation is used for the red laser beam and the blue laser beam, and external modulation by AOM is used for the green laser beam. Even if the beam diameters of the laser beams are the same, the distribution of the amount of light applied to the photoconductor varies depending on the modulation method, resulting in a difference between colors and a color blur in the recorded image.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a scanning exposure apparatus that can reduce color bleeding of a recorded image due to a difference in a modulation method of laser light.

  The scanning exposure apparatus of the present invention includes a first light source that emits a first laser beam, a second light source that emits a second laser beam having a wavelength different from that of the first laser beam, and the first light source that emits the first laser beam. An acousto-optic modulator that modulates the intensity of the first laser beam by passing an ultrasonic wave in a direction that satisfies the Bragg condition and the propagation direction of the first laser beam, and the first laser emitted from the acousto-optic modulator And a deflector that deflects the light and the second laser light emitted from the second light source and scans in a predetermined direction on the surface to be scanned, and is virtually projected onto the surface to be scanned. The propagation direction of the ultrasonic wave is the same as the scanning direction of each laser beam by the deflector, and the spot diameter of the second laser beam on the surface to be scanned is defined as the spot of the first laser beam. Larger than the diameter The features.

  In the scanning exposure apparatus of the present invention, the first light source that emits the first laser light, the second light source that emits the second laser light having a wavelength different from that of the first laser light, and the first light source are emitted. An acoustooptic modulator that modulates the intensity of the first laser beam by passing an ultrasonic wave in a direction that satisfies the Bragg condition and the propagation direction of the first laser beam, and the first beam emitted from the acoustooptic modulator. A scanning exposure apparatus comprising a deflector that deflects one laser beam and the second laser beam emitted from the second light source to scan in a predetermined direction on the surface to be scanned, virtually onto the surface to be scanned The propagation direction of the projected ultrasonic wave is the same as the scanning direction of each laser beam by the deflector, and the spot diameters of the first laser beam and the second laser beam on the surface to be scanned are set. Approximately equal and The duty of the image signal pulses for modulating the laser beam, characterized by being larger than the duty of the image signal pulses for modulating the first laser beam.

  As the first light source, a light source including a semiconductor laser excitation type solid-state laser and a wavelength conversion element for wavelength-converting laser light emitted from the solid-state laser is used. The second light source is preferably a semiconductor laser.

  In the scanning exposure apparatus of the present invention, the propagation direction of the ultrasonic wave virtually projected onto the surface to be scanned is the same as the scanning direction of each laser beam by the deflector, and the second direction on the surface to be scanned is the second. Since the spot diameter of the laser light is made larger than the spot diameter of the first laser light, the second laser is adjusted so as to match the widening of the integrated light amount distribution for one pixel of the first laser light that is scanned and exposed on the surface to be scanned. The integrated light quantity distribution for one pixel of light spreads, and the color blur of the recorded image can be reduced.

  In the scanning exposure apparatus of the present invention, the propagation direction of the ultrasonic wave virtually projected onto the surface to be scanned is the same as the scanning direction of each laser beam by the deflector, and the first direction on the surface to be scanned is Since the spot diameters of the first laser beam and the second laser beam are made substantially equal and the duty of the image signal pulse for modulating the second laser beam is made larger than the duty of the image signal pulse for modulating the first laser beam, the surface to be scanned The integrated light amount distribution for one pixel of the second laser light is widened so as to match the widening of the integrated light amount distribution for one pixel of the first laser light that is scanned and exposed above, and the color blur of the recorded image is reduced. Can do.

  FIG. 1 is a schematic diagram showing a laser printer 2. The laser printer 2 includes an image processing unit 3 that performs various image processing, a scanning exposure device 4, a conveyance roller 6 that conveys a sheet-like photoconductor 5, and a conveyance roller 6. The motor 7 etc. which drive The image processing unit 3 receives image data obtained by reading a film image of a photographic film with a CCD scanner and image data obtained by photographing with a digital camera. The image processing unit 3 performs various image processing such as correction on the input image data, and outputs the image data to the scanning exposure apparatus 4 as recording image data.

  As will be described in detail later, the scanning exposure apparatus 4 includes a plurality of laser light sources that oscillate laser beams 8 a to 8 c corresponding to the respective colors of red, green, and blue, and a recording image input from the image processing unit 3. The photosensitive member 5 is irradiated with laser light modulated according to data, and scanning exposure is performed in the main scanning direction X (see FIG. 2). The photoconductor 5 is in the form of a sheet and is sensitive to a red photosensitive layer 5a that is sensitive to red (R) laser light 8a, a green photosensitive layer 5b that is sensitive to green (G) laser light 8b, and a blue (B) laser light 8c. A blue photosensitive layer 5c is sequentially laminated on the support 5d.

  The transport roller 6 is driven by a motor 7 and transports the photosensitive member 5 at a constant speed in the sub-scanning direction Y orthogonal to the main scanning direction X. As described above, the photosensitive member 5 is irradiated with the laser beams 8a to 8c swayed in the main scanning direction X by the scanning exposure device 4 while being conveyed in the sub-scanning direction Y (see FIG. 2). Done. The photosensitive member 5 is scanned and exposed by the laser printer 2, and an image is recorded on each of the photosensitive layers 5a to 5c as a latent image, and then developed, whereby the image becomes visible.

  FIG. 3 shows the configuration of the scanning exposure apparatus 4. The scanning exposure apparatus 4 includes laser light sources 11 to 13. The laser light source 11 includes, for example, an R semiconductor laser 14 that emits an R laser beam 8a having a wavelength of 680 nm, and a condenser lens 15 disposed on the emission side. Similarly, the laser light source 13 includes, for example, a B semiconductor laser 16 that emits B laser light 8c having a wavelength of 410 nm, and a condenser lens 17 disposed on the emission side. By directly turning on / off the oscillation of the R semiconductor laser 14 and the B semiconductor laser 16 and controlling the drive current, the R laser beam 8a and the B laser beam 8c are modulated, respectively.

  The laser light source 12 includes a semiconductor laser 18, a semiconductor laser excitation type solid-state laser 21 including a condensing lens 19 disposed on the emission side, and a laser crystal (laser active medium) 20, and an emission side thereof. The SHG laser is a combination of a secondary high frequency generation (SHG) element 22 as a wavelength conversion element. The semiconductor laser excitation type solid-state laser 21 emits laser light having a wavelength of 1064 nm, for example. The SHG element 22 converts the laser beam into a half wavelength when it is incident from the semiconductor laser excitation type solid-state laser 21, and emits a G laser beam 8b having a wavelength of 532 nm.

  On the emission side of the laser light source 12, a condenser lens 23 and an acousto-optic modulation element (AOM) 24 as an external modulator, which will be described in detail later, are sequentially arranged. When the G laser light 8b emitted from the laser light source 12 enters the AOM 24 via the condenser lens 23, the acoustooptic effect acts to cause diffraction, and the intensity is modulated and emitted as diffracted light. A shielding plate 25 that shields diffracted light other than the first-order diffracted light out of the diffracted light emitted from the AOM 24 is provided. Only the first-order diffracted light is selectively emitted from the AOM 24 by the shielding plate 25.

  On the emission side of the laser light sources 11 and 13 and the AOM 24, a plane mirror 26 is arranged, and R and B laser light 8 a and 8 c emitted from the laser light sources 11 and 13 and G emitted as the first-order diffracted light of the AOM 24. The laser beam 8b is reflected by the plane mirror 26. A collimator lens 27, a cylindrical lens 28, and a polygon mirror (deflector) 29 are sequentially arranged on the emission side of the plane mirror 26.

  The laser beams 8a to 8c reflected by the plane mirror 26 are irradiated and reflected at substantially the same position on the reflection surface of the polygon mirror 29 via the collimator lens 27 and the cylindrical lens 28. The polygon mirror 29 rotates at a substantially constant angular velocity in the C direction (clockwise direction) in the figure, deflects the laser beams 8a to 8c, and scans the photosensitive member 5 in the main scanning direction X described above. . On the exit side of the polygon mirror 29, there is an fθ lens 30 that corrects the scanning speed on the exposure surface (scanned surface) of the photoconductor 5, and a lens power in the sub-scanning direction Y (perpendicular to the paper surface in FIG. 3). A cylindrical lens 31 for surface tilt correction is disposed.

  As shown in FIG. 4, the AOM 24 includes a rectangular crystal body 24a that is an acousto-optic medium, and a transducer 24b disposed on the upper surface of the crystal body 24a. The AOM 24 is arranged in the scanning exposure apparatus 4 so that the G laser light 8b is incident as incident light from one surface of the crystal body 24a and transmitted to the other surface. An AOM driver 32 is connected to the transducer 24b, and the AOM driver 32 inputs a high frequency signal to the transducer 24b. The transducer 24b generates an ultrasonic wave having a frequency (several hundred MHz) according to the input high-frequency signal, and propagates the ultrasonic wave as a sound wave packet 33 into the crystal body 24a. The propagation direction P of the acoustic wave packet 33 is the direction indicated by the arrow P in the crystal body 24a, and intersects the incident direction of the G laser light 8b at an angle that satisfies the Bragg condition.

  In the portion where the acoustic wave packet 33 is generated in the crystal body 24a, the refractive index periodically changes along the propagation direction P thereof. When the G laser beam 8b that has entered the crystal body 24a crosses the acoustic wave packet 33, the acoustooptic effect acts to cause diffraction, and is emitted from the crystal body 24a as diffracted light having an intensity corresponding to the amplitude of the high-frequency signal. The As described above, of the emitted diffracted light, only the first-order diffracted light passes through the shielding plate 25 and travels toward the plane mirror 26. Therefore, the G laser beam 8b is emitted to the plane mirror 26 as the first-order diffracted light only when crossing the acoustic wave packet 33 in the crystal body 24a.

  FIG. 5 is a diagram simply showing the relationship between the propagation direction P of the acoustic wave packet 33 of the AOM 24 and the main scanning direction X of the G laser light 8 b on the photosensitive member 5. The propagation direction P of the acoustic wave packet 33, the rotation direction C of the polygon mirror 29, and the main scanning direction X are in a relationship as shown in FIG. An arrow P ′ in the figure indicates the direction in which the propagation direction P is virtually reflected by the plane mirror 26, and an arrow P ″ in the figure virtually reflects the direction P ′ by the polygon mirror 29. The direction virtually projected onto the photosensitive member 5 is shown below, and the relationship between the propagation direction P and the main scanning direction X is represented by the relationship between the projection direction P ″ and the main scanning direction X. In the present embodiment, the projection direction P ″ in the propagation direction P onto the photoconductor 5 is the same as the main scanning direction X.

  FIG. 6 is a diagram showing a state in which the acoustic wave packet 33 passes through the G laser light 8b in the crystal body 24a of the AOM 24, and shows a temporal change in a cross section perpendicular to the propagation direction of the G laser light 8b. In the G laser beam 8b incident on the crystal body 24a, only the portion overlapping the acoustic wave packet 33 is modulated and emitted as first-order diffracted light. The time τ required for the modulation start (t0 to t3) from when the G laser light 8b starts to be partially modulated until the whole is modulated is V, and the propagation speed of the acoustic wave packet 33 is V and the beam of the G laser light 8b. When the diameter is D, the relationship of τ = D / V is satisfied. Similarly, the time period τ is required for the period at the end of modulation (t4 to t7).

Note that when the beam intensity of the G laser beam 8b has a Gaussian distribution as shown in FIG. 7, the beam diameter D is, for example, a spread of the distribution when the relative intensity is 1 / e ² (e: base of natural logarithm) ( A displacement corresponding to four times the standard deviation σ).

The beam intensity of the G laser beam 8b that is modulated by one acoustic wave packet 33 in the crystal body 24a of the AOM 24 and is emitted as the first-order diffracted light changes with time as shown in FIG. The elapsed time from t0 to t7 corresponds to the exposure time per pixel (about 10 ⁻⁷ to 10 ⁻⁸ sec), and this exposure time is determined by the image signal pulse width. The smaller the beam diameter D, the shorter the response time τ when the beam intensity rises and falls, and the sharpness of the beam projected onto the photoconductor 5 improves.

  Since the exposure surface of the photoconductor 5 is disposed at a position optically conjugate with the position (diffraction point) of the AOM 24, the G laser light 8b modulated by the AOM 24 has the same beam shape and the exposure surface as it is. The spot diameter on the exposure surface is approximately equal to the beam diameter D. As shown in FIG. 9, the G laser beam 8b for one pixel is projected onto the exposure surface of the photoreceptor 5 while being scanned in the main scanning direction X. As shown in FIG. 5, since the propagation direction P (projection direction P ″) of the acoustic wave packet 33 and the main scanning direction X are the same, one pixel of the G laser light 8b projected on the exposure surface. 9 has a large spread in the main scanning direction X. This is because the G laser beam 8b starts to be partially modulated at the start of modulation (t0 to t3). At the same time, the modulation portion is projected to the rear side in the main scanning direction X, and the modulation portion is projected to the front side in the main scanning direction X at the end of the modulation (t4 to t7).

  FIG. 10 shows the beam intensity distribution of the G laser beam 8b obtained every specific time under a specific condition, with one pixel overlapped. FIG. 11 shows an integrated light amount distribution for one pixel obtained by superimposing the beam intensity distributions for each time, and the photosensitive member 5 is exposed based on the integrated light amount distribution. As described above, the G laser light 8 b for one pixel emitted from the laser light source 12 is expanded in the main scanning direction X due to the above-described modulation in the AOM 24.

  The R laser beam 8a and the B laser beam 8c are directly turned on / off the oscillation of the R semiconductor laser 14 and the B semiconductor laser 16, respectively, and modulated (directly modulated) by controlling the drive current. Projected onto a surface. When the spot diameters of the laser beams 8a to 8c on the exposure surface are made equal, the integrated light amount distribution of the G laser beam 8b is widened in the main scanning direction X, whereas the R laser beam 8a and the B laser beam 8c are Since the exposure time is controlled by turning on / off the R semiconductor laser 14 and the B semiconductor laser 16 based on the image signal pulse width, the integrated light quantity distribution of R and B is narrow, as in the G laser light 8b. There is no widening.

  If the integrated light quantity distribution is different depending on R, G, and B in this way, when the color image pattern is exposed on the photoconductor 5, the difference in the integrated light quantity distribution between G, R, and B results in the post-development. The color is blurred. In order to prevent this, the scanning exposure apparatus 4 performs either intensity modulation or pulse width modulation on the laser light sources 11 and 13 to correct the R and B integrated light quantity distributions. As a result, the difference between colors is reduced and the color blur is eliminated from the recorded image.

  In the case of intensity modulation, as shown in FIG. 12, the R laser light 8a and the B laser light that are directly modulated while keeping the duty of the image signal pulse equal in each color of R, G, and B (T1 = T2). The beam diameter D2 of 8c is set to an appropriate value larger than the beam diameter D1 of the G laser light 8b to be acousto-optic modulated. Thereby, the G integrated light quantity distribution width w1 in the main scanning direction X and the R, B integrated light quantity distribution width w2 are corrected so as to be substantially equal.

  In the case of pulse width modulation, as shown in FIG. 13, the R laser beam 8a and the B laser beam 8c that are directly modulated are maintained with the beam diameters being equal in each of R, G, and B colors (D1 = D2). The duty T2 of the image signal pulse is set to an appropriate value larger than the duty T1 of the image signal pulse of the G laser light 8b to be acousto-optic modulated. Here, the frequencies of the image signal pulses of the laser beams 8a to 8c are substantially equal. Thereby, the G integrated light quantity distribution width w1 in the main scanning direction X and the R, B integrated light quantity distribution width w2 are corrected so as to be substantially equal.

  In the above embodiment, the G laser beam 8b is subjected to acousto-optic modulation by the AOM 24 as an external modulator, and the R laser beam 8a and the B laser beam 8c are directly modulated. However, the present invention is not limited to this. Alternatively, any of the laser beams 8a to 8c may be optically modulated by the AOM 24.

  In the above embodiment, the laser light source 12 for the G laser light 8b is an SHG laser obtained by combining a semiconductor laser excitation type solid-state laser and an SHG element, and the laser light sources 11 and 13 for the R laser light 8a and the B laser light 8c are used. Although configured as a semiconductor laser, the present invention is not limited to this, and various laser light sources such as a semiconductor laser, a solid-state laser, and a gas laser can be used as the laser light sources of the laser beams 8a to 8c.

  Further, in the above embodiment, three types of laser light sources 11 to 13 relating to R, G, and B are used. However, the present invention is not limited to this, and the number of laser light sources, the wavelength of each laser beam, and acoustics You may change suitably the laser light source etc. which carry out an optical modulation.

It is the schematic which shows the structure of a laser printer. It is the schematic which shows the main scanning direction and subscanning direction of a laser beam. It is a top view which shows the structure of a scanning exposure apparatus. It is the schematic which shows the structure of an acousto-optic modulation element. It is a top view which shows simply the relationship between the propagation direction of a sound wave packet, and the main scanning direction of a laser beam. It is a figure explaining a mode that G laser light is modulated by the sound wave packet of an acousto-optic modulation element. It is an intensity distribution figure explaining the definition of a beam diameter. It is a figure which shows the time change of the beam intensity of the G laser beam for 1 pixel. It is a projection figure on the exposure surface of G laser light for 1 pixel. It is the figure which piled up and showed the beam intensity distribution of G laser light obtained for every specific time. It is a distribution map which shows the integral light quantity distribution of G laser beam for 1 pixel. It is a figure explaining intensity modulation of R and B laser light. It is a figure explaining the pulse modulation of R and B laser light.

Explanation of symbols

2 Laser printer 3 Image processing unit 4 Scanning exposure device 5 Photoconductor 8a Red laser beam (second laser beam)
8b Green laser beam (first laser beam)
8c Blue laser light (second laser light)
11 Laser light source (second light source)
12 Laser light source (first light source)
13 Laser light source (second light source)
DESCRIPTION OF SYMBOLS 14 Red semiconductor laser 16 Blue semiconductor laser 21 Semiconductor laser excitation type solid-state laser 22 Secondary high frequency generating element (wavelength conversion element)
24 acoustooptic modulator 24a crystal 24b transducer 29 polygon mirror (deflector)
33 Sound wave packet

Claims (4)

A first light source that emits first laser light; a second light source that emits second laser light having a wavelength different from that of the first laser light; and a propagation direction of the first laser light emitted from the first light source; An acousto-optic modulator that modulates the intensity of the first laser beam by passing an ultrasonic wave in a direction that satisfies the Bragg condition, and the first laser beam and the second light source that are emitted from the acousto-optic modulator. A scanning exposure apparatus comprising: a deflector that deflects the second laser beam and scans in a predetermined direction on the surface to be scanned;
The propagation direction of the ultrasonic wave virtually projected onto the surface to be scanned is the same as the scanning direction of each laser beam by the deflector, and the second laser beam on the surface to be scanned is A scanning exposure apparatus characterized in that a spot diameter is larger than a spot diameter of the first laser beam. A first light source that emits first laser light; a second light source that emits second laser light having a wavelength different from that of the first laser light; and a propagation direction of the first laser light emitted from the first light source; An acousto-optic modulator that modulates the intensity of the first laser beam by passing an ultrasonic wave in a direction that satisfies the Bragg condition, and the first laser beam and the second light source that are emitted from the acousto-optic modulator. A scanning exposure apparatus comprising: a deflector that deflects the second laser beam and scans in a predetermined direction on the surface to be scanned;
The propagation direction of the ultrasonic wave virtually projected onto the surface to be scanned is the same as the scanning direction of each laser beam by the deflector, and the first laser beam on the surface to be scanned and The scanning is characterized in that the spot diameters of the second laser light are made substantially equal, and the duty of the image signal pulse for modulating the second laser light is made larger than the duty of the image signal pulse for modulating the first laser light. Exposure device.   3. The scanning exposure apparatus according to claim 1, wherein the first light source comprises a semiconductor laser excitation type solid-state laser and a wavelength conversion element for wavelength-converting laser light emitted from the solid-state laser. The scanning exposure apparatus according to claim 1, wherein the second light source is a semiconductor laser.

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