JP2011150130A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the height of toner on a photoreceptor surface and on transfer paper is reduced, and thus a defective image such as void in developing, scatter at transfer or tailing at fixing is prevented. <P>SOLUTION: In the image forming apparatus, an optically modulated laser beam from a light source 100 is guided to a polarization means with a light guide means, the laser beam polarized by the polarization means is guided to the face to be scanned on a photoreceptor drum 10 by an imaging means and an image is formed. The light guide means includes a mirror 103 having a variable center cone 103a having a cone-shaped reflection part and a mirror 103b having a reverse-cone-shaped reflection part, wherein the variable center cone 103a is disposed more inside side than the mirror 103b so that the cross section of the laser beam reflected on the mirror 103 takes a doughnut shape. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and in particular, an electrophotographic process for forming an image by optically scanning a scanned surface of an image bearing member such as a photosensitive member or an electrostatic recording medium with a light-modulated laser beam from a light source. The present invention relates to an image forming apparatus using the.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic process, a laser beam modulated by light from a light source is guided to a polarizing unit by a light guiding unit, and the laser beam polarized by the polarizing unit is formed by an imaging unit. Some light guides form a light on the surface to be scanned. In recent years, in order to make the dot diameter and line width the same as in the past and make the toner height substantially uniform in the spot diameter direction, the cross-sectional shape of the laser beam is made to be a donut shape or a combination of multiple circles. An image forming apparatus having an output unit has been proposed (see, for example, Patent Document 1).

  As shown in FIGS. 10A to 10C, the electrostatic latent image on the surface of the photoreceptor formed by the laser beam having a Gaussian distribution also has a Gaussian distribution, and is developed on the surface of the photoreceptor by the developing device. The developed toner image is also developed with a toner height having a Gaussian distribution. This toner height is defined as a toner loading amount or a toner powder image rising amount.

  Even on the transfer paper, the toner image on the surface of the photosensitive drum is crushed, but finally, the transfer image has a raised central portion. Ideally, as shown in FIGS. 11A to 11C, the intensity distribution of the laser light has a rectangular distribution so that the electrostatic latent image on the photosensitive member surface and the toner height are rectangular. The distribution is desirable for image formation.

JP-A-8-276619

  However, in a conventional image forming apparatus using laser light having a Gaussian distribution, the light intensity distribution of the laser light, the electrostatic latent image, and the toner height on the transfer paper each have a Gaussian distribution. Therefore, for example, if the necessary dot diameter and line width are ensured, the toner height on the photoreceptor surface and the transfer paper may become very high. As a result, it may lead to image defects such as white spots during development, scattering during transfer, and tailing during fixing.

  The present invention has been made in view of the above problems, and reduces the toner height on the surface of the photosensitive member and on the transfer paper so that images such as white spots during development, scattering during transfer, and tailing during fixing are obtained. An object of the present invention is to provide an image forming apparatus capable of preventing defects.

  In order to achieve the above object, an image forming apparatus of the present invention guides light modulated laser light from a light source to polarizing means by light guiding means, and images the laser light polarized by the polarizing means by imaging means. In the image forming apparatus for forming an image by guiding light onto the surface to be scanned of the carrier, the light guide means includes a first mirror having a conical reflecting portion and a second mirror having an inverted conical reflecting portion. And the first mirror is arranged on the inner side of the second mirror so that the cross-sectional shape of the laser light reflected by the reflecting means is annular. To do.

  According to the present invention, a laser beam formed so as to have an annular cross section using an optical system having a variable center on the optical path is used as exposure light on the surface to be scanned, thereby reducing toner consumption and transfer. Reduction of time scattering, improvement of fixability, and prevention of tailing can be realized.

1 is a diagram for explaining a schematic configuration of an exposure apparatus in an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the structure of the mirror which has a variable center cone in FIG. It is a figure which shows an example of the beam shape of a laser beam when the variable center cone which comprises a mirror is moved. It is a figure which shows the change of the spot cross-sectional shape accompanying control of a mirror. FIG. 2 is a view showing a schematic configuration around a photosensitive drum exposed by the exposure apparatus of FIG. 1. It is a figure which shows intensity distribution, potential distribution, and toner height distribution of a laser beam. It is a figure which shows an example of the result of a latent image simulation, (a) is the time of a donut shape, (b) shows the time of the laser spot shape of a Gaussian distribution. 6A and 6B are diagrams illustrating a toner height distribution evaluated by the image forming apparatus illustrated in FIG. 5, in which FIG. 5A is on the photosensitive drum and FIG. 5B is on the transfer paper. It is a figure for demonstrating the formation principle of a donut-shaped beam, (a) is a toric lens, (b) shows an example of a donut-type laser formation mechanism. It is a figure which shows (a) intensity distribution, (b) electric potential distribution, and (c) toner height distribution of the laser beam which has normal Gaussian distribution. It is a figure which shows (a) intensity distribution, (b) electric potential distribution, and (c) toner height distribution of the laser beam with an ideal distribution.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a view for explaining a schematic configuration of an exposure apparatus in an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing the structure of a mirror having a variable center cone in FIG.

  In FIG. 1, 100 is a semiconductor laser as a light source. Reference numeral 101 denotes a collimator lens that converts laser light emitted from the semiconductor laser 100 into parallel light fluxes. Reference numeral 102 denotes a cylindrical lens, which has a predetermined refractive power only in the sub-scanning direction with respect to the passing light beam diameter.

  The mirror 103 has a variable center cone. As shown in FIG. 2, the mirror 103 has a variable center cone 103a (first mirror) having a conical reflecting portion, and a ring shape having an inverted conical reflecting portion. And a mirror 103b (second mirror).

  The variable center cone 103a is configured to be variable with respect to the optical path direction of the laser light. That is, the variable center cone 103a is disposed inside the mirror 103b when viewed from the direction in which the beam is incident (or the direction in which the beam is reflected).

  The collimator lens 101, the cylindrical lens 102, and the mirror 103 constitute a light guiding unit.

  In the exposure apparatus according to this embodiment, the cross-sectional shape (spot shape) of laser light emitted from the two semiconductor lasers 100 is scanned when the surface to be scanned of the photosensitive drum is scanned by the laser light. (Annular). Therefore, the mirror 103 having the variable center cone 103a is disposed on the light beam so that the cross-sectional shape is a donut shape. By providing a configuration in which the variable center cone 103a is variably movable in the optical path direction, the spot shape can be formed into an arbitrary donut shape by controlling the distance between the two beams.

  Here, the principle of forming a donut-shaped beam in the optical resonator having the variable center cone 103a will be described. Various formation principles of the doughnut-shaped beam have been proposed, but in the present embodiment, an open paper “J. Phys. D: Appl. Phys. 34 (2001) 68-77” is described as a basic principle and published. The basic principle is explained with the configuration adopted in the paper.

  9A and 9B show an outline of a donut-type laser forming mechanism using an optical resonator having a cylindrical slab type structure using two toric lenses. When the usable effective width is a with respect to the diameter r0 of the toric lens shown in FIG. 9A, the generated electric field strength is expressed by the following equation.

  E0 is the electric field intensity, λ is the laser wavelength, Hn is the Hamiltonian polynomial, k is the wave number of the laser, and w0 is the beam loss. According to the given condition n, it has a spatial radiation direction in the azimuthal direction. In this embodiment, the mirror curvature can be controlled by using the mirror 103 shown in FIG. 2, and the radial direction can be controlled by changing the condition of the cone angle of the center mirror.

  Next, the polarization of the beam will be described. The polarization of the beam is not linearly polarized but phase-converted by S-polarized light and P-polarized light. The polarization conditions are shown below.

  On control, the fixed value equation is set as follows.

Including other conditions, propagation in the above configuration can be expressed by the following equation.

  δ is a δ function, and Lcc is a parameter of the mirror 103 shown in FIG.

  From the above equation, the spot shape of the beam itself can be formed into a donut shape by the oscillation of the laser by the optical resonator.

  However, in the above configuration, the apparatus is increased in size and cannot be applied in terms of cost and spot diameter. In the present embodiment, the triangular pyramid portion (variable center cone 103a) folded at the center of the mirror 103 is variably movable, and the mirror 103 of FIG. 2 is disposed on an optical system employing an electrophotographic system. Then, the cross-sectional shape of the beam is formed into a donut shape using optical interference.

  The mirror 103 is made of copper as a material by diamond turning processing or three-dimensional lithography processing, and is coated with gold from above to obtain a reflectance of 99.9%, a surface roughness of 5 nm, and a shape fidelity of 85 nm (RMS). . The reflecting mirror of the mirror 103 has a triangular pyramid shape.

  Two semiconductor lasers (He—Ne, λ = 630 nm, TEM00) are used as light sources, but the present invention is not limited to this. As will be described later, the laser beam with this configuration makes the toner height uniform in the spot diameter direction.

  In FIG. 1, reference numeral 104 denotes a polygon mirror as a polarizing means, which is rotated at a constant speed about a shaft (not shown) by a drive motor (not shown). Reference numeral 105 denotes an fθ lens group as image forming means having fθ characteristics, which passes through a surface tilt correction lens 106 that corrects the surface tilt of polarized laser light, and is exposed as a scanning surface through a folding mirror 107. An image is formed on the surface of the body drum 10. Around the photosensitive drum 10, for example, as shown in FIG. 5 described later, various components for forming an image are disposed.

  Reference numeral 108 denotes a synchronous mirror. Reference numeral 109 denotes a photodetector (BD sensor). Each element described above controls the timing of the scanning start position of the image information on the photosensitive drum.

  Note that the movable control of the variable center cone 103a is performed by driving and controlling a drive motor by a control circuit (not shown). Further, the variable center cone may be configured to be driven and controlled based on the detection result of the photodetector 109.

  In the exposure apparatus of FIG. 1, the laser light that is light-modulated and emitted from the semiconductor laser 100 based on the image information is converted into a parallel light beam by the collimator lens 101, and the main scanning cross section of the light beam incident on the cylindrical lens 102 remains as it is. Is emitted to the mirror 103. The light beam formed by the interference of the two light beams is converged in the sub-scan section by the polygon mirror 104 and the fθ lens group 105, and is formed as a substantially line image (line image elongated in the main scanning direction).

  The polarized laser light is guided to the photosensitive drum 10 through the correction lens 106 and the folding mirror 107, and a spot is formed. Then, image recording is performed by scanning the surface of the photosensitive drum 10 by rotating the polygon mirror 104.

  In the present embodiment, the beam cross-sectional shape (spot shape) of the laser light emitted from the two semiconductor lasers 100 is configured to be a donut shape as shown in FIG. Further, as shown in FIG. 4, the intensity distribution of the laser beam (the intensity distribution of the beam cross section) is configured such that the central portion of the spot diameter is at least lower than the peripheral portion. Since the distance between the two beams changes by moving the variable center cone 103a of the mirror 103, different donut shapes can be created.

  In this embodiment, an electrostatic latent image is formed on the surface of the photosensitive drum using laser light having a light intensity distribution as shown in FIG. 6A as exposure light on the surface of the photosensitive drum. Yes. At this time, the electrostatic latent image formed on the surface of the photosensitive drum has a potential distribution as shown in FIG. For this reason, for example, even if toner splatters during transfer, the toner height on the transfer paper should be smaller than the toner height when using a Gaussian laser beam as shown in FIG. Can do. As a result, the amount of applied toner image is reduced while maintaining the same level as that of the conventional image forming apparatus, and the image is uniformly applied, which leads to improvement of edge enhancement in solid lines.

  By using the mirror 103 having the above-described shape, it is possible to improve electrostatic offset and tailing in terms of toner height uniformity and fixability. Note that the toner height on the transfer paper in this embodiment is set to be a value within the allowable range of the present apparatus.

  FIG. 5 is a view showing a schematic configuration around the photosensitive drum exposed by the exposure apparatus of FIG.

  As shown in FIG. 5, the image forming apparatus forms an electrostatic image by optically writing on the surface of the photosensitive drum 10 rotating in the direction of the arrow in the drawing by the exposure apparatus shown in FIG. The developing device 16 develops the toner image by bringing toner, which is a developer, into contact with the photosensitive drum 10 and attracting it to the electrostatic image. The toner image carried on the photosensitive drum 10 is primarily transferred to the intermediate transfer belt 15 by the transfer roller 14. After the primary transfer, the primary transfer residual toner remaining on the surface of the photosensitive drum 10 without contributing to the primary transfer is removed by the cleaning device 12. The cleaning device 12 scrapes off the primary transfer residual toner with a cleaning blade 13 in contact with the photosensitive drum 10 and other fur brushes.

  The surface of the photosensitive drum 10 from which the primary transfer residual toner has been removed is uniformly exposed by the pre-exposure device 108 and discharged, and then charged to a uniform charged state by the primary charger 18. As shown in FIG. 5, an optical sensor 17 for controlling the developer concentration is disposed immediately below the post charger 11.

  The photosensitive drum 10 as an image carrier has a photosensitive layer formed of OPC (organic optical semiconductor) having a negative charging characteristic, and has a process speed (circumferential speed) of 285 mm / sec centering on a central support shaft (not shown). ) Is driven to rotate in the direction of the arrow. The primary charger 18 is composed of a corona charger as a charging means. The primary charger 18 has an external power supply connected to the charging line, and applies a bias to the charging line to generate corona discharge, thereby uniformly charging the surface of the photosensitive drum 10. The exposure device 111 forms an electrostatic latent image on the surface of the charged photosensitive drum 10 as information writing means.

  The exposure apparatus 111 is a laser beam scanning exposure apparatus using a semiconductor laser light source and a polygon mirror optical system as shown in FIG. The developing device 16 as developing means supplies developer (toner) to the electrostatic latent image on the photosensitive drum 10 and visualizes the electrostatic latent image as a toner image. The transfer roller 14 as a transfer means is pressed against the surface of the photosensitive drum 10 with a predetermined pressing force, and the press-contact nip portion serves as a transfer portion. The intermediate transfer belt 15 is nipped and conveyed between the photosensitive drum 10 and the transfer roller 14. The cleaning blade 13 as a cleaning means is made of an elastic body of urethane rubber, and is pressed against the surface of the photosensitive drum 10 with a predetermined pressing force, and removes transfer residual toner.

  According to the present embodiment, the amount of toner consumption is reduced by using, as exposure light on the surface to be scanned, laser light formed so that the cross-sectional shape is circular using an optical system whose center is variable on the optical path. It is possible to reduce scattering during transfer, improve fixability, and prevent tailing.

  As described above, the case where the present invention is applied to the image forming apparatus having the configuration shown in FIG. 5 has been described. However, the present invention is not limited to this, and the exposure apparatus shown in FIG. Even a device having a configuration is applicable.

  With the above configuration, the dark potential on the photosensitive drum is set to -650 V, the developing bias potential is set to -500 V, the maximum value of the bright potential is set to -200 V, the transfer current value is set to a constant current of 35 μA, and a latent image of one line and two spaces is formed. FIG. 7 shows the result of a latent image simulation performed using a solid image. In this case, in order to observe the uniformity of how the toner is placed, the height profile of the unfixed toner image distribution on the photosensitive drum and on the paper by an actual machine was analyzed with a VK8500 manufactured by KEYENCE. On the drum, in order to keep the curvature, the analysis including the curvature was performed.

  A pseudo donut shape and a Gaussian distribution laser spot shape were created, a latent image was formed based on the sensitivity data of the photosensitive drum used in the actual machine, and a pseudo toner was placed thereon. This is a result of an analysis including a random number coefficient in consideration of the particle size of the toner being 5 μ and taking scattering into consideration. The line in the figure is a development bias line, and the toner is placed on the darker part. As long as the comparison with the two patterns of laser spots is made, the donut-shaped spot forms a more uniform latent image and the scattering is suppressed than the Gaussian spot shape, so the effect of this embodiment can be confirmed. it can.

  FIG. 8 is a diagram illustrating an example of the analysis result.

  In both figures, the vertical axis is the relative value when the maximum toner height is 1, and the horizontal axis is defined as the half width when the height is 0.5. The toner distribution on the photosensitive drum is a shape satisfying the latent image spot shape, and a shape different from the distribution formed in the Gaussian distribution is formed. Further, the unfixed toner distribution on the transfer paper has a shape in which the distribution on the photosensitive drum is maintained although it is crushed by the pressure bonding. Also in the fixing property, phenomena such as electrostatic offset and tailing do not occur, and the effect of solving the problems in the present invention is obtained.

DESCRIPTION OF SYMBOLS 100 Semiconductor laser 101 Collimator 102 Cylindrical lens 103 Mirror 104 Polygon mirror 105 f (theta) lens group 106 Correction lens 107 Folding mirror 108 Synchronous mirror 109 Photodetector

Claims (3)

The light modulated laser light from the light source is guided to the polarizing means by the light guiding means, and the laser light polarized by the polarizing means is guided to the scanned surface of the image carrier by the imaging means to form an image. In the image forming apparatus,
The light guiding means includes a reflecting means having a first mirror having a conical reflecting portion and a second mirror having an inverted conical reflecting portion, and a cross section of the laser light reflected by the reflecting means. The image forming apparatus, wherein the first mirror is disposed inside the second mirror so as to have a ring shape.   The image forming apparatus according to claim 1, wherein the light guide unit is configured such that a light intensity distribution of the laser light is smaller in a central part than in a peripheral part.   The image forming apparatus according to claim 1, wherein the first mirror is configured to be variably movable with respect to an optical path direction of the laser light.