JPH1078557A - Scanning optical device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive scanning optical device capable of writing an electrostatic latent image corresponding to an AIDC mark with which image density is precisely detected by an AIDC sensor on a photoreceptor even in the case of adopting a small-diameter light beam as a light beam for forming a highdefinition image, and an electrophotographic image forming device capable of forming the excellent image in terms of the image density where the scanning optical device is mounted. SOLUTION: This scanning optical device LB writing the electrostatic latent image on the photoreceptor 10 with the light beam (laser beam) is equipped with an optical means (lens 7 and reflecting mirror 8) arranged in the middle of an optical path for forming the electrostatic latent image so as to form the electrostatic latent image E corresponding to a test toner image (AIDC mark) ET for detecting the image density. The optical means makes the laser beam passing through the optical means have smaller beam peak intensity on the image surface of the photoreceptor 10 and larger beam spot diameter than the laser beam passing through the optical path for forming the electrostatic latent image corresponding to the image to be printed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to an electrophotographic image forming apparatus such as a printer or a digital copier equipped with a scanning optical device for writing an electrostatic latent image on a photoreceptor by a light beam such as a laser beam. For, in particular, with respect to the scanning optical device, more particularly on the photoreceptor by the scanning optical device,
It relates to writing of an electrostatic latent image corresponding to an AIDC mark (a test toner image for automatic image density control).

[0002]

2. Description of the Related Art In an image forming apparatus such as a printer or a digital copying machine of an electrophotographic system using a conventional scanning optical device such as a laser scanning device, an electrostatic latent image corresponding to an AIDC mark is written on a photosensitive member. In general, writing is performed using light rays for forming an electrostatic latent image corresponding to a desired print image as it is.

In the case where one laser beam is used as image writing light, the number of dots per inch (dpi) is switched using this single laser beam, and a high definition image is obtained by increasing the dpi. In a printer or the like that can form a low-definition image by reducing the beam diameter, the beam diameter is generally set to a small diameter so that a high-definition image can be favorably formed.

In such a case, when forming a low-definition image by reducing the dpi, the formed AIDC mark is
As shown in FIG. 6A, the AIDC pattern may be interrupted in the sub-scanning direction due to a large dot interval in the sub-scanning direction, while the AIDC mark is usually transferred to a transfer material and fixed. Rather, the AIDC sensor (for automatic image density control) remains in a state where it is formed on the photoreceptor, and in a state where the break in the sub-scanning direction is not crushed and filled by the fixing process. The image density is read by a sensor that reads the image density of the AIDC mark, which is a test toner image.

Accordingly, in the case where a break occurs in the image in the sub-scanning direction, even when the AIDC mark is to be formed as a black solid image, the stripe pattern is formed as shown in FIG. (So-called zebra pattern). As a result, the image density cannot be detected by the AIDC sensor, or the output of the AIDC sensor is not stabilized as shown in FIG. In addition, since the beam diameter is set to a small diameter so that high-definition image formation can be performed satisfactorily, when an AIDC mark is formed in high-definition image formation, as shown in FIGS. The black solid density of the mark becomes too high, and the output of the AIDC sensor is saturated as shown in FIG.

The problem that the black solid image density of the AIDC mark becomes too high and the output of the AIDC sensor is saturated and the detection accuracy decreases is that switching of dpi is not performed. This also occurs in an image forming apparatus in which the diameter is set to a small diameter. Therefore, a test toner image A for automatic image density control is used.
In a binary image forming apparatus, as a method for improving the detection accuracy by the AIDC sensor for detecting the density of the IDC mark, FIG.
As shown in (A), the AI is formed by a two-dot zigzag halftone dot pattern.
When writing an electrostatic latent image corresponding to a DC mark, or writing an electrostatic latent image corresponding to an AIDC mark, the laser power is intensity-modulated and written in a halftone shape, whereby the AIDC
A mark is used as a halftone image to prevent saturation of the sensor output.

[0007]

However, when a binary halftone pattern is formed as an AIDC mark, FIG.
As shown in (B), a waveform fluctuation of the detection signal output from the AIDC sensor occurs, and an integration circuit for correcting the fluctuation is required, and various controls and processes involved in image density detection are troublesome and costly.

[0008] Also, when forming an AIDC mark in a halftone shape by intensity-modulating the laser power, a modulation driver is required, which raises a problem that the cost is increased. Therefore, the present invention relates to a scanning optical device for writing an electrostatic latent image on a photoreceptor by using a light beam, and even when a small-diameter light beam is employed as a light beam for forming a high-definition image, the image density detection by the AIDC sensor is performed. It is an object of the present invention to provide a scanning optical device that can write an electrostatic latent image corresponding to an AIDC mark that can be accurately performed on a photoconductor, and that can be manufactured at a low cost.

Another object of the present invention is to provide an electrophotographic image forming apparatus which can form an image with good image density by mounting such a scanning optical device.

[0010]

According to the present invention, there is provided a scanning optical apparatus for writing an electrostatic latent image on a photoreceptor by using a light beam, which corresponds to a test toner image for detecting image density. An optical unit disposed in an optical path for forming the electrostatic latent image to form an electrostatic latent image,
The optical means reduces the light beam peak intensity at the image plane on the photoconductor relative to the light beam passing through the optical path for forming an electrostatic latent image corresponding to the image to be printed. Further, the present invention provides a scanning optical device which is configured to increase a beam spot diameter.

Further, the present invention has been made in order to solve the above-mentioned problems.
An image forming apparatus for forming an electrostatic latent image on a photoconductor by a scanning optical device, developing the latent image into a toner image, transferring the toner image to a transfer material, and fixing the toner image, wherein the scanning optical device Comprises optical means arranged in an optical path for forming the electrostatic latent image to form an electrostatic latent image corresponding to the test toner image for image density detection, the optical means comprising:
The light passing therethrough has a smaller light beam peak intensity on the image plane on the photoconductor than the light passing through an optical path for forming an electrostatic latent image corresponding to the image to be printed, and a light spot diameter. , And A for detecting the image density of the test toner image.
An image forming apparatus provided with an IDC sensor is provided.

In the scanning optical device and the image forming apparatus according to the present invention, the light beam passes through the optical means provided for forming an electrostatic latent image corresponding to the AIDC mark which is a test toner image. The light beam has a smaller light beam peak intensity on the image surface on the photoreceptor and a larger light beam spot diameter than a light beam for forming an electrostatic latent image corresponding to a printed image. Can be formed on the photoreceptor.

At this time, even in a mode in which a low definition image is formed by lowering the dpi, the light diameter is increased on the image surface on the photoreceptor, so that the AI is formed in a solid shape and a halftone shape.
An electrostatic latent image corresponding to a DC mark can be formed, and thus an AIDC mark of a halftone solid image can be obtained without generating a conventional zebra pattern.

In a mode for forming a high-definition image with a large dpi, an electrostatic latent image corresponding to the AIDC mark can be formed in a solid shape and a halftone shape by appropriately thinning out dots in the sub-scanning direction. An AIDC mark of a halftone solid image can be obtained. Since a halftone solid image can be obtained as an AIDC mark in this manner, the output of the AIDC sensor does not saturate in image density detection by the AIDC sensor based on this mark.

With these, the AIDC mark and the AID mark
The image density detection accuracy by the C sensor is increased, and a good image can be formed accordingly. As the optical means, for example, a light diffusing plate or a Fresnel lens or a light diameter expanding slit or a lens including a lens or the like that makes the light emitting point of the light source of the light and the image plane on the photoreceptor non-conjugated. Can be mentioned.

Further, the optical means for forming an electrostatic latent image corresponding to the test toner image may include a mirror which folds a light beam to an image-formable area on the photosensitive member.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic perspective view showing a scanning optical device according to the present invention together with a photoconductor. FIG. 2 shows FIG.
FIG. 2 is a diagram showing a schematic configuration of a printer equipped with the scanning optical device shown in FIG. The scanning optical device LB shown in FIG. 1 uses a laser beam and can be applied to an electrophotographic image forming apparatus such as a printer or a digital copying machine. Here, as shown in FIG. doing.

The illustrated scanning optical device LB includes a semiconductor laser light source 1 as a laser beam irradiation source, a collimator lens 2,
A cylindrical lens 3, a polygon mirror 4 rotationally driven by a driving device (not shown), a scanning lens group 5, a folding mirror 6, a lens 7 for writing an electrostatic latent image corresponding to the AIDC mark, and a laser beam passing through the lens 7 Of the photoconductor 10 toward the image forming area of the photoconductor 10 is provided. These components are mounted on the case 9. The case 9 is provided with a window 91 for irradiating the photoconductor 10 with a laser beam. The lens 7 is provided at one end of the window 91. The folding mirror 8 is also supported by the case 9 via a support member (not shown).

The lens 7 includes an image surface on the photoconductor and the laser light source 1.
Is a lens that makes the light emitting point non-conjugate with the laser beam passing therethrough. The laser beam passing through the optical path for forming an electrostatic latent image corresponding to the image to be printed is formed on the photosensitive member 10 by the laser beam. This is to reduce the beam peak intensity on the surface and increase the beam spot diameter.
The laser beam L emitted from the light source 1 passes through the collimator lens 2 and the cylindrical lens 3 sequentially, is reflected by the polygon mirror 4 that is driven to rotate, passes through the scanning lens group 5, is turned back by the turning mirror 6, and is provided in the case 9. The light passes through the window 91 or the lens 7 provided in the window, and is irradiated on the photoconductor 10.

The laser beam finally irradiated on the photoreceptor 10 scans the surface of the photoreceptor 10 in the main scanning direction (the direction of the rotation axis of the photoreceptor) by the rotation of the polygon mirror 4.
The photoconductor 10 is rotated in a sub-scanning direction (circumferential direction of the photoconductor) by being rotationally driven by a driving unit (not shown). As shown in FIG. 2, the surface of the photoconductor 10 is charged in advance by a charging device CH, and the light source 1 blinks according to an image to be printed or an AIDC mark according to an instruction from the laser scanning optical device control unit CONT1. The scanning of the charged area on the photoconductor with the blinking laser beam forms an electrostatic latent image corresponding to a print image and an electrostatic latent image E corresponding to an AIDC mark (see FIG. 1). .

The electrostatic latent image corresponding to the print image is developed by the developing device D to become a visible toner image. The toner image is transferred by a transfer device T onto a transfer material S such as transfer paper sent from a transfer material supply unit (not shown), and is subsequently fixed onto the transfer material by a fixing device F. In preparation for the next image formation, the toner remaining on the photoreceptor 10 is removed and cleaned by the cleaning device C, and the residual charge is erased by the eraser IR.

The electrostatic latent image corresponding to the AIDC mark is also developed by the developing device to form a test toner image (AIDC mark) ET (see FIGS. 1 and 2).
The C mark is formed in an area such as between images to be printed on the photoconductor 10, and the mark ET is provided by an AIDC sensor 11 provided in advance corresponding to the movement path of the AIDC mark.
Are detected. The AIDC mark ET after the image density detection is removed and cleaned by the cleaning device C without being transferred to the transfer material.

The result of detection by the AIDC sensor 11 is input to a part CONT2 which controls the developing device D. Based on this input, the control part CONT2 controls the developing device D so as to make the image density appropriate. The supply amount of toner from the apparatus to the electrostatic latent image is adjusted. Thus, an image having an appropriate density is formed. The AIDC mark ET will be further described. When the laser beam passes through the lens 7 to form an electrostatic latent image corresponding to the mark, FIG.
As shown in (A), the beam is focused on the photoreceptor 10
The photosensitive member 1 compared to a laser beam (see FIG. 3D) for forming an electrostatic latent image corresponding to the print image.
The laser beam has a small beam peak intensity on the image plane above zero and a large beam spot diameter, and an electrostatic latent image corresponding to the AIDC mark can be formed on the photosensitive member by the laser beam.

At this time, even in a mode in which a low definition image is formed by lowering the dpi, as shown in FIG. 4A, the dots are formed in the sub-scanning direction without any gap which should be regarded as a problem. As a result, the electrostatic latent image E corresponding to the halftone AIDC mark can be formed, and thus the AIDC mark ET of the halftone solid image can be formed as shown in FIG. Obtainable.

In a mode for forming a high-definition image with a large dpi, as shown in FIG. 5A, by appropriately thinning out the dots in the sub-scanning direction, the AIDC mark corresponding to a solid shape and a halftone shape can be handled. Can form an electrostatic latent image E of
From this, an AIDC mark ET of a halftone solid image can be obtained as shown in FIG. The beam spot diameter on the image plane is desirably about 3/2 times the laser beam spot diameter for forming an electrostatic latent image corresponding to a print image. The thinning may be determined based on the beam spot diameter on the image plane and the resolution.
As shown in FIG. 5, when forming an electrostatic latent image corresponding to a print image, every other line a to be scanned by a beam for that purpose is thinned out.

As described above, a halftone solid image can be obtained as the AIDC mark ET.
As shown in FIG. 5C and FIG. 5C, the AIDC sensor 11 based on this mark detects
The output of the DC sensor does not saturate and is stable. By these, AIDC mark ET and AID
The image density detection accuracy of the C sensor 11 is increased, and a good image can be formed accordingly.

In the scanning optical device LB described above, the lens 7 and the folding mirror 8 are employed as optical means for forming an electrostatic latent image corresponding to the AIDC mark for detecting image density. 3 instead of lens 7
The slit 12 shown in FIG. 3B and the diffusion plate 1 shown in FIG.
3 (here, ground glass) or the like may be employed. In FIG. 3A, a Fresnel lens may be used instead of the lens 7.

In FIG. 3, the folding mirrors 6 and 8 are not shown. The folding mirror 8 need not be provided when an electrostatic latent image can be formed at a predetermined position without the mirror. Further, instead of the window 91 of the case 9 in the scanning optical device described above, a lens unit, a mirror unit, and the like in the scanning optical device may be used as a laser beam irradiation window.

[0029]

As described above, according to the present invention,
A scanning optical device that writes an electrostatic latent image on a photoreceptor by using light beams, and even when a small-diameter light beam is employed as a light beam for forming a high-definition image, an AIDC sensor can accurately detect image density. An electrostatic latent image corresponding to the possible AIDC mark can be written on the photosensitive member, and a scanning optical device which is inexpensive can be provided.

Further, according to the present invention, it is possible to provide an electrophotographic image forming apparatus which can form a good image in terms of image density by mounting such a scanning optical device.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an example of a scanning optical device according to the present invention together with a photoconductor.

FIG. 2 is a diagram showing a schematic configuration of a printer equipped with the scanning optical device of FIG. 1;

FIG. 3A is a view showing a beam spot diameter and a beam peak intensity of a laser beam having passed through a lens 7 on an image surface on a photosensitive member, and FIG. FIG. 4C is a diagram showing a beam spot diameter and a beam peak intensity of the laser beam on the image surface on the photoconductor, and FIG. FIG. 4D is a diagram showing a beam spot diameter and a beam peak intensity of a laser beam for forming a print image on an image surface on a photoreceptor.

4A shows an electrostatic latent image corresponding to an AIDC mark formed in the low-definition image forming mode by the scanning optical device shown in FIG. 1, and FIG. 4B shows the latent image in FIG. Shows an AIDC mark developed from the mark, and FIG. (C) shows an output waveform of an AIDC sensor for detecting an image density from the mark in FIG. (B).

5A shows an electrostatic latent image corresponding to an AIDC mark formed in a high-definition image forming mode by the scanning optical device shown in FIG. 1, and FIG. 5B shows the latent image shown in FIG. Shows an AIDC mark developed from the mark, and FIG. (C) shows an output waveform of an AIDC sensor for detecting an image density from the mark in FIG. (B).

FIG. 6A shows a conventional laser scanning optical device.
FIG. 4B shows an electrostatic latent image corresponding to the AIDC mark formed in the low-definition image forming mode, FIG. 4B shows an AIDC mark of a zebra pattern obtained by developing the latent image in FIG. 4A, and FIG. AI for detecting image density from mark B)
It is a figure showing an output waveform of a DC sensor.

FIG. 7A shows a conventional laser scanning optical device.
FIG. 4B shows an electrostatic latent image corresponding to the AIDC mark formed in the high-definition image forming mode, FIG. 4B shows a high-density AIDC mark obtained by developing the latent image shown in FIG. 4A, and FIG. FIG. 7 is a diagram showing an output waveform of an AIDC sensor for detecting an image density from a mark of ()).

FIG. 8A shows an electrostatic latent image of a two-dot staggered halftone dot pattern, and FIG. 8B shows an AIDC obtained by developing the latent image.
FIG. 4 is a diagram illustrating an output waveform of an AIDC sensor that detects a mark.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Collimator lens 3 Cylindrical lens 4 Polygon motor 5 Scanning lens group 6 Folding mirror 7 Beam diameter enlargement lens 8 Folding mirror 9 Scanning optical device case 91 Window 10 Photoconductor 11 AIDC sensor E AIDC mark compatible electrostatic latent Image ET AIDC mark (test toner image) 12 Beam diameter expansion slit 13 Beam diameter expansion ground glass CH charging device D Developing device T Transfer device F Fixing device C Cleaning device IR eraser

Claims (4)

[Claims] 1. A scanning optical device for writing an electrostatic latent image on a photoreceptor by a light beam, said electrostatic latent image being formed to form an electrostatic latent image corresponding to a test toner image for detecting image density. Optical means arranged in the light path for forming, the light means passing through the light path for forming an electrostatic latent image corresponding to the image to be printed, for the light rays passing therethrough A scanning optical apparatus characterized in that the light beam peak intensity on the image surface on the photoreceptor is further reduced and the light spot diameter is increased. 2. The optical device according to claim 1, wherein the optical unit includes a light diffusing plate, a Fresnel lens, a slit for expanding a light beam diameter, or a lens that makes a light emitting point of a light source of the light beam non-conjugate with an image plane on the photoconductor. Item 2. The scanning optical device according to Item 1. 3. The scanning optical device according to claim 1, wherein the optical unit for forming an electrostatic latent image corresponding to the test toner image includes a mirror that deflects a light beam to an image-formable area on the photoconductor. 4. An image forming apparatus which forms an electrostatic latent image on a photoreceptor by a scanning optical device, develops the latent image into a toner image, transfers the toner image to a transfer material, and fixes the toner image. The scanning optical device includes an optical unit disposed in an optical path for forming the electrostatic latent image to form an electrostatic latent image corresponding to a test toner image for detecting image density. The optical means reduces a light beam peak intensity on an image plane on the photoconductor, for a light beam passing therethrough, than a light beam passing an optical path for forming an electrostatic latent image corresponding to an image to be printed, and An image forming apparatus configured to increase a beam spot diameter, and further provided with an AIDC sensor for detecting an image density of the test toner image.