JP2006018237A - Multi-beam optical scanning apparatus and image forming apparatus using the multi-beam scanning apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-beam optical scanning apparatus, which is capable of reducing an inter-light-beam illuminance difference at the same image height on a surface to be scanned and forming a high-definition and high-quality image where no unevenness in density of image exists, and an image forming apparatus using the multi-beam optical scanning apparatus. <P>SOLUTION: In the multi-beam optical scanning apparatus that brings a plurality of light beams, emitted from a plurality of light-emitting portions into incident on the deflecting surface of a light deflector so as to exceed the width in the main scanning direction of the deflection plane, a control means independently controls the emitted light amounts of the plurality of light-emitting portions, and thereby reducing the inter-light-beam illuminance difference on the plane to be scanned. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multi-beam optical scanning device and an image forming apparatus using the same, and in particular, a plurality of light beams emitted from a light source unit having a plurality of light emitting portions are deflected by a rotating polygon mirror (polygon mirror) as an optical deflector. After that, for example, a laser beam printer or a digital copying machine having an electrophotographic process, in which image information is recorded by optically scanning the surface to be scanned through an imaging optical system (imaging optical system) having fθ characteristics. It is suitable for an image forming apparatus such as a multi-function printer.

  Conventionally, in an optical scanning device, a light beam (light beam) modulated and emitted from a light source means in accordance with an image signal is periodically deflected by, for example, an optical deflector composed of a rotating polygon mirror to form an image having fθ characteristics. An optical system collects light in a spot shape on the surface of a photosensitive recording medium and optically scans the surface to perform image recording.

  In recent years, with the increase in speed and size of devices such as laser beam printers, digital copiers, and multifunction printers, it has been desired that imaging optical systems used as optical systems be made faster and more compact. .

  For example, an overfilled optical system is used as a method for increasing the speed.

  In this overfilled optical system (hereinafter referred to as “OFS”), the deflecting surface (reflecting surface) of the rotary polygon mirror has a light beam width necessary for substantially deflecting and scanning out of a wide incident light beam. Therefore, the rotating polygonal mirror has a feature that it is possible to increase the number of surfaces with a small diameter and is suitable for speeding up.

  In OFS, the incident light beam to the rotating polygon mirror has a Gaussian distribution so that the light intensity is maximized in the vicinity of the optical axis of the condensing optical system. Therefore, the illuminance on the surface to be scanned tends to decrease as the image height increases.

  Furthermore, in OFS, the beam width in the main scanning direction of the reflected and deflected light beam becomes narrower as the angle of view increases, and the illuminance on the surface to be scanned becomes smaller as the image height increases. Yes. Illuminance distribution on the surface to be scanned at this time is shown in FIG. As can be seen from FIG. 12, in the imaging optical system using OFS, the illuminance on the surface to be scanned tends to decrease as the image height increases (hereinafter referred to as “light loss”).

  In addition, due to mounting errors of the light source means, the position where the light intensity of the incident light beam on the deflecting surface is maximized is shifted from the center of the effective light beam width in the main scanning direction of the deflecting surface to the effective light beam width end. Illuminance distribution on the scanning plane is shown in FIG. As can be seen from FIG. 13, in addition to the decrease in the amount of light, the illuminance on the surface to be scanned tends to increase and decrease from one image height to the other image height.

  As described above, nonuniformity occurs in the illuminance in one scanning line on the surface to be scanned, so that when OFS is used in the image forming apparatus, there is a problem that density unevenness occurs in the formed image.

  Furthermore, as a means to further speed up the OFS, in the case of the multi-beam OFS in which the light beams from a plurality of light emitting units are simultaneously scanned on the surface to be scanned in the direction perpendicular to the scanning direction, an image having the same pattern is formed. In this case, in addition to non-uniformity of illuminance in one scanning line on the scanning surface, an illuminance difference (hereinafter referred to as “illuminance difference between multiple beams”) occurs between a plurality of beams at the same image height. Therefore, there is a problem that density unevenness occurs in the formed image.

  Hereinafter, the principle that an illuminance difference occurs between two light beams at the same image height will be described.

  The multi-beam optical scanning device is a method for speeding up recording of image information by simultaneously scanning a plurality of light beams emitted from light source means having a plurality of light emitting units on a surface to be scanned. A multi-beam semiconductor laser will be described with reference to FIG. 14 as an example of light source means used at this time. FIG. 14 is a schematic view of the main part of a monolithic multi-beam semiconductor laser having two light emitting sections (lasers) 14a and 14b. The light emitting part 14a is also called A laser (or light emitting part A), and the light emitting part 14b is also called B laser (or light emitting part B).

  As shown in FIG. 14, the multi-beam semiconductor laser 1 has two light emitting portions 14a and 14b on one active layer 13, and emits divergent light beams from the two light emitting portions 14a and 14b, respectively. The intensity of the divergent light beam is Gaussian distributed so that the light intensity becomes maximum at the intensity center lines 14ap and 14bp. As shown in FIG. 14, in the actually manufactured multi-beam semiconductor laser 1, there are variations in the directions of the intensity center lines 14ap and 14bp of the light beams emitted from the two light emitting portions 14a and 14b. An angle difference RΔθ with respect to the main scanning direction is generated in the intensity center lines 14ap and 14bp of the light beam emitted between the light emitting units 14a and 14b.

  FIG. 15 is a cross-sectional view (main scanning cross-sectional view) of the main scanning direction of the multi OFS using the multi-beam semiconductor laser shown in FIG. 14 as light source means.

  In the figure, the incident optical system is represented as one condensing optical system 11. In the same figure, the angle difference between the intensity center lines 14ap and 14bp of the two light beams with respect to the main scanning direction is represented as RΔθ.

  In the figure, when these two light beams pass through the condensing optical system 11, the intensity center lines 14ap and 14bp of the two light beams having the angle difference RΔθ pass through different heights from the optical axis 12 of the condensing optical system 11. Therefore, in the vicinity of the deflection surface 7, an interval d1 ′ with respect to the main scanning direction is generated between the intensity center positions 14ap and 14bp of the two light beams.

  For this reason, the two light beams incident on the deflecting surface 7 have different intensity distributions in the main scanning direction, so that the illuminance distributions for the image heights of the two light beams on the scanned surface are also different. This is shown in FIG.

  FIG. 16 shows the two light emitting units 14a and 14b when the light emission amounts from the two light emitting units 14a and 14b are controlled to be equal and constant at the entire image height in order to form an image having the same pattern. It is a figure showing each illumination distribution 14ai and 14bi of the emitted light beam. The figure shows that in addition to the tendency that the illuminance on the surface to be scanned decreases as the image height increases, an illuminance difference occurs between two beam beams at the same image height.

  Various multi-beam optical scanning devices or optical scanning devices that solve this problem have been proposed. (See Patent Documents 1 and 2).

  In Patent Document 1, the opening shape of the opening plate disposed in the optical path between the light source means and the deflecting means is set so that the width in the sub-scanning direction is larger than the central portion in the main scanning direction. The illuminance in one scanning line on the surface to be scanned is made substantially uniform.

In Patent Document 2, a surface to be scanned is supplied by supplying a driving current of a semiconductor laser based on a correction coefficient in accordance with a position scanned so as to make the illuminance in one scanning line substantially uniform on the surface to be scanned. The illuminance in one scanning line is made substantially uniform.
Japanese Patent Laid-Open No. 11-218702 JP-A-9-197316

  However, in the multi-beam optical scanning devices proposed in these Patent Documents 1 and 2, it is difficult to reduce the illuminance difference between a plurality of light beams.

  For example, Patent Document 1 discloses a configuration for improving the non-uniformity of the light amount distribution by the aperture shape of the aperture plate for one light beam. However, if Patent Document 1 is shown in FIG. On the other hand, the illuminance distribution when the intensity center line of the two light beams is used for the multi OFS having the angle difference RΔθ is as shown in FIG. As can be seen from FIG. 17, when the two light beams pass through the aperture plate in which the width of the aperture shape in the sub-scanning direction is larger than the center portion in the main scanning direction, the light quantity drop of the two light beams is reduced. The light quantity difference between two light beams at the same image height cannot be improved.

   In the embodiment described in Patent Document 2, the illuminance distribution in one scanning line on the scanned surface of one laser is detected, and a correction coefficient for uniformly correcting the illuminance in one scanning line is calculated. Based on the correction coefficient, all laser drive currents are supplied. With respect to the multi OFS in which the intensity center lines 14ap and 14bp of the two light beams have an angle difference RΔθ with respect to the main scanning direction as shown in FIG. A correction coefficient for uniformly correcting the illuminance in one scanning line is detected by detecting the illuminance distribution in the line, and the illuminance distributions 14ai and 14bi when the A and B laser drive currents are supplied based on the correction coefficient are calculated. As shown in FIG. As can be seen from FIG. 18, since the same correction coefficient is used for a plurality of light beams, the light quantity distribution 14ai of the A laser can be corrected uniformly, but the light quantity distribution 14bi of the B laser (light emitting portion 14b) has a gradient, so The illuminance difference between the luminous fluxes cannot be improved.

  Such density unevenness due to the difference in illuminance between the plurality of light fluxes is more conspicuous than density unevenness due to a drop in the amount of light in which the density continuously changes in one scanning line because the density of adjacent dots is different. For this reason, if an illuminance difference between a plurality of light beams remains even if the light intensity drop is completely cancelled, a good image without density unevenness cannot be formed.

  The present invention reduces a difference in illuminance between a plurality of light beams at the same image height on a surface to be scanned, and can form a high-definition and high-quality image without density unevenness, and an image forming apparatus using the same The purpose is to provide.

The multi-beam optical scanning device of the invention of claim 1 comprises:
Light source means having a plurality of light emitting portions;
An optical deflector having a deflection surface;
An incident optical system that causes a plurality of light beams emitted from the plurality of light emitting units to enter the deflection surface of the optical deflector in a state wider than the width of the deflection surface in the main scanning direction;
An imaging optical system that forms an image on the scanned surface with a plurality of light beams reflected by the optical deflector;
A multi-beam optical scanning device having control means for independently controlling the amount of emitted light for the plurality of light emitting units,
The control means is characterized in that the illuminance difference between the plurality of beams on the surface to be scanned is reduced by independently controlling the amount of emitted light with respect to the plurality of light emitting units.

The multi-beam optical scanning device according to the invention of claim 2
Light source means having a plurality of light emitting portions;
An optical deflector having a deflection surface;
An incident optical system that causes a plurality of light beams emitted from the plurality of light emitting units to enter the deflection surface of the optical deflector in a state wider than the width of the deflection surface in the main scanning direction;
An imaging optical system that forms an image on the scanned surface with a plurality of light beams reflected by the optical deflector;
A multi-beam optical scanning device having control means for independently controlling the amount of emitted light for the plurality of light emitting units,
When controlling the amount of emitted light for each of the plurality of light emitting units so that the illuminance of the plurality of light beams is the same by the control means at the total image height on the scanned surface,
The control means is characterized in that the amount of light emitted between the plurality of light emitting portions at the maximum scanning angle is made different.

The multi-beam optical scanning device according to the invention of claim 3
Light source means having a plurality of light emitting portions;
An optical deflector having a deflection surface;
An incident optical system that causes a plurality of light beams emitted from the plurality of light emitting units to enter the deflection surface of the optical deflector in a state wider than the width of the deflection surface in the main scanning direction;
An imaging optical system that forms an image on the scanned surface with a plurality of light beams reflected by the optical deflector;
A multi-beam optical scanning device having control means for independently controlling the amount of emitted light for the plurality of light emitting units,
When controlling the amount of emitted light for each of the plurality of light emitting units so that the illuminance of the plurality of light beams is the same by the control means at the total image height on the scanned surface,
The control means is characterized in that the amount of emitted light between the plurality of light emitting portions at the same scanning angle is made different within a partial region of the entire scanning angle.

  According to the present invention, in a multi-beam optical scanning device using OFS, a laser output (amount of emitted light) is electrically controlled according to a scanning angle, so that a plurality of light beams at the same image height on the surface to be scanned can be obtained. It is possible to reduce a difference in illuminance, thereby achieving a multi-beam optical scanning device capable of obtaining a high-speed, high-definition and high-quality image and an image forming apparatus using the same.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 is a cross-sectional view of main parts in a main scanning direction (a main scanning cross-sectional view) of a multi-beam optical scanning apparatus using an OFS according to Embodiment 1 of the present invention, and FIG. 2 is a cross-sectional view of main parts in a sub-scanning direction of FIG. FIG.

  Here, the main scanning direction is a direction perpendicular to the rotation axis of the optical deflector and the optical axis of the scanning optical element (the direction in which the light beam is reflected and deflected (deflected and scanned) by the optical deflector), and the sub-scanning direction is The direction parallel to the rotation axis of the optical deflector is shown. The main scanning section indicates a plane parallel to the main scanning direction and including the optical axis of the imaging optical system. The sub-scanning cross section indicates a cross section perpendicular to the main scanning cross section.

  In this embodiment, the scanning angle can be defined as the angle formed by the principal ray of the light beam reflected by the optical axis of the imaging optical system and the deflecting surface of the optical deflector in the main scanning section.

  The maximum scanning angle can be defined as the angle formed by the principal ray of the light beam reaching the maximum image height (scanning end) of the scanning surface (photosensitive drum surface) and the optical axis of the imaging optical system in the main scanning section. .

  In the figure, reference numeral 1 denotes light source means, which is composed of, for example, a monolithic multi-beam semiconductor laser having two light emitting portions (lasers) 14a and 14b. Hereinafter, the light emitting unit 14a is also referred to as A laser (or light emitting unit A), and the light emitting unit 14b is also referred to as B laser (or light emitting unit B).

  In this embodiment, the two light emitting portions (lasers) 14a and 14b are separated from each other in the main scanning direction.

  When the light emitting part is separated in the main scanning direction as in this embodiment, the difference in illuminance between the two light fluxes is of a size that does not cause a problem when the light emitting part is separated only in the sub scanning direction. However, there is a problem that the image quality is increased to a level that causes deterioration of image quality to be formed.

  The reason is shown below.

  When the two light emitting portions (lasers) 14a and 14b are separated from each other in the main scanning direction, the A laser emitted from the two light emitting portions (lasers) 14a and 14b on the deflection surface of the rotary polygon mirror 6 in the main scanning section. Since the chief ray of 14a and the chief ray of B laser 14b are incident at different angles, the illuminance distribution of A laser 14a and B laser 14b on the deflection surface is different, and the illuminance difference between the two light beams on the scanned surface Cause.

  Further, the narrower the far field pattern in the main scanning direction, the larger the difference in illuminance distribution between the A laser 14a and the B laser 14b on the deflection surface, and the greater the illuminance difference between the two beams on the scanned surface. End up. In the multi-beam semiconductor laser, the direction in which the light emitting portions are separated from each other is the direction parallel to the active layer, so the far field pattern in the direction in which the light emitting portions are separated from the direction in which the light emitting portions are separated from each other. It tends to be narrower than the far field pattern in the vertical direction.

  That is, when the two light emitting units (lasers) are separated in the main scanning direction, the illuminance difference between the two light fluxes on the surface to be scanned becomes larger than when they are separated in the sub scanning direction.

  As described above, when the light emitting units are separated in the main scanning direction, the illuminance difference between the two light beams on the scanned surface is large. Therefore, in order to obtain a good image quality without density unevenness, 2 is actively used. It is necessary to reduce the illuminance difference between the two light beams.

  Reference numeral 71 denotes a control means (control system) that controls the amount of light emitted from one or more of the A and B lasers 14a and 14b (B laser 14b in this embodiment). In this embodiment, the amount of light emitted from the B laser 14b is controlled according to the scanning angle, thereby reducing the illuminance difference between the two light beams on the surface to be scanned (hereinafter also referred to as “illuminance difference between the two light beams”). ing.

  Reference numeral 2 denotes a collimator lens as a light beam conversion element, which converts two divergent light beams emitted from the light source means 1 into parallel light beams.

  Reference numeral 3 denotes an aperture (aperture stop) which forms a parallel light beam emitted from the collimator lens 2 into a desired optimum beam shape.

  Reference numeral 4 denotes an anamorphic lens (sub-scanning cylindrical lens) as an anamorphic optical element. The anamorphic lens (sub-scanning cylindrical lens) has a predetermined power (refractive power) mainly only in the sub-scanning direction. Thus, the image is formed as a longitudinal line image in the main scanning direction.

  Each element such as the collimator lens 2, the aperture 3 and the sub-scanning cylindrical lens 4 constitutes one element of the incident optical system 5.

  An optical deflector 6 is composed of, for example, a rotary polygon mirror (polygon mirror), and is rotated at a constant speed in the direction of arrow A in the figure by driving means (not shown) such as a motor.

  Reference numeral 8 denotes an imaging optical system having fθ characteristics, which includes an fθ lens 8a having a positive power only in the main scanning direction and a long toric lens 8b having a predetermined power only in the sub-scanning direction. Two light beams based on the image information reflected and deflected by the optical deflector 6 are imaged on the photosensitive drum surface 10 as the scanned surface in the main scanning section, and the deflecting surface of the optical deflector 6 in the sub-scanning section. 7 and the photosensitive drum surface 10 are optically conjugate to provide a tilt correction function.

  Reference numeral 9 denotes a folding mirror as a reflecting member. Reference numeral 10 denotes a photosensitive drum surface (recording medium surface) as a surface to be scanned.

  In this embodiment, two divergent light beams that are modulated and emitted from the monolithic multi-beam semiconductor laser 1 in accordance with image information are converted into parallel light beams by the collimator lens 2. The two light beams emitted from the collimator lens 2 pass through the aperture stop 3 (partially shielded) and enter the sub-scanning cylindrical lens 4. The two light beams that have passed through the sub-scanning cylindrical lens 4 are incident in a state wider than the width of the deflecting surface 7 of the optical deflector 6 in the main scanning direction (so-called overfilled optical system (OFS)). As a result, a long line image is formed in the main scanning direction.

  Further, the two light beams emitted from the sub-scanning cylindrical lens 4 are incident at a predetermined angle in the main scanning direction of the optical deflector 6 and at a predetermined angle in the sub-scanning section.

  The incident optical system 5 of the present embodiment is not limited to the configuration shown in FIG. 1. For example, two light beams emitted from the sub-scanning cylindrical lens 4 are front (light deflector 6) in the main scanning direction of the light deflector 6. In the main scanning direction, the light may be incident at a predetermined angle from the center of the scanning range along the front surface, that is, the center of the scanning range along the main scanning direction.

  Then, the light beam partially reflected and deflected by the deflecting surface 7 of the optical deflector 6 is guided on the photosensitive drum surface 10 by the imaging optical system 8, and the optical deflector 6 is rotated in the direction of arrow A, Image information is recorded by optically scanning the photosensitive drum surface 10 in the direction of arrow B (main scanning direction).

  In this embodiment, the light source means 1 comprises a monolithic multi-beam semiconductor laser having an angle difference RΔθ between the intensity center lines 14ap and 14bp of two light beams with respect to the main scanning direction as shown in FIG.

  FIG. 3 is a sectional view (main scanning sectional view) of the main part in the main scanning direction of the multi OFS of the present embodiment. In the figure, the same elements as those shown in FIG.

  In the figure, the incident optical system is represented as one condensing optical system 11. The intensity center lines 14ap and 14bp of the two light beams emitted from the A and B lasers (light emitting units) 14a and 14b are inclined with respect to the optical axis 12 of the condensing optical system 11.

Figure 4A illuminance on the surface to be scanned of the two light beams a drive current of the laser in the case of a multi-OFS emitted from a constant value A in the case of the I _0, B laser 14a, 14b in all the image height in FIG. 3 It is a figure showing distribution 14ai, 14bi. As can be seen from FIG. 4A, in addition to the tendency that the illuminance by both the A and B lasers decreases from the image height Y = 0 toward one of the maximum image heights ± Y ₀ , the A laser at the same image height, It can be seen that there is an illuminance difference between the two light beams of the B laser.

  Therefore, in this embodiment, the photodetector FD is arranged at the maximum image height position on the surface to be scanned as detection means for detecting the illuminance of the A laser and the B laser at the maximum image height in order to reduce the illuminance difference between the two light beams. Then, based on the illuminances A1, A2, B1, and B2 detected at the maximum image heights of the A and B lasers, the amount of light emitted by the B laser is varied according to the image height (scanning angle) by the control means 71.

  In this embodiment, control according to the image height of the light emission quantity of the B laser is performed by controlling the drive current amount of the B laser.

  The control means 71 varies the amount of emitted light between the two light emitting portions 14al and 14bl at the same scanning angle in a partial region of the entire scanning angle, and the A laser 14ai and B laser at the same image height on the scanned surface. The illuminance of 14bi is the same.

FIG. 5 is a graph showing the light emission amount of the laser with respect to the drive current amount of the laser in this example. As can be seen from FIG. 5, the amount of light emitted by the laser increases as the amount of drive current increases. As shown in FIG. 5, in order to reduce the illuminance difference between the two light beams, the laser drive current is increased or decreased from the drive current amount i ₀ when the light emission amount of the laser is I ₀ at an arbitrary image height. The amount of light emitted from the laser can be controlled to increase or decrease.

  FIG. 4B is a graph showing the light emission quantity of the laser controlled by changing the drive current according to the image height in order to reduce the illuminance difference between the two light fluxes of the illuminance distribution as shown in FIG. 4A.

As can be seen from FIG. 4B, the light emission amount 14aI of the A laser remains at a constant value I _{0 at} the entire image height, and the light emission of the B laser in order to reduce the illuminance difference between the A laser and the B laser at each image height. The drive current amount is controlled so that the amount of light 14bI decreases monotonously as it goes from the image height Y = −Y ₀ to the image height Y = + Y ₀ .

   For example, the light emission quantity IB of the B laser is linearly controlled so as to satisfy the following relational expression (1).

IB = a × Y + b (1)
a = I0 × {(B1−A1) / A1 − (B2−A2) / A2} / 2Y0
b = I0 x {2- (B1-A1) / A1-(B2-A2) / A2} / 2
Y: Arbitrary image height
IB: Amount of emitted light at an arbitrary image height of the B laser
A1: Illuminance of the A laser at an image height Y = −Y ₀ when the amount of emitted light is a constant value I ₀
A2: Illuminance of laser A at image height Y = -Y ₀ when the amount of emitted light is a constant value I ₀
B1: Illuminance of the B laser at an image height Y = + Y ₀ when the light emission quantity is a constant value I ₀
B2: Illuminance of the B laser at the image height Y = + Y ₀ when the amount of emitted light is a constant value I ₀
I0: A laser light intensity
Y0: Maximum image height However, the light emission quantity of the laser at an arbitrary image height Y does not satisfy the relational expression (1), but the illuminance of the maximum image height when the light emission quantity of the B laser is controlled is the following conditional expression If (1) ′ is satisfied, an effect sufficient for reducing the illuminance difference between the two light beams can be obtained.

0.9 ≦ | B1 ′ / A1 ′ | ≦ 1.1, 0.9 ≦ | B2 ′ / A2 ′ | ≦ 1.1 (1) ′
A1 ′: A laser illuminance at image height Y = −Y ₀ when light emission control is performed
A2 ′: Illuminance of the A laser at the image height Y = −Y ₀ when the emitted light quantity control is performed
B1 ′: Illuminance of the B laser at the image height Y = + Y ₀ when the amount of emitted light is controlled
B2 ′: Illuminance of the B laser at the image height Y = + Y ₀ when the emitted light amount control is performed FIG. 4C shows the case where the emitted light amount of each laser is controlled as shown in FIG. 4B in this embodiment. FIG. 3 is an illuminance distribution diagram on a scanned surface 10.

4C, at each maximum image height (Y = ± Y ₀ ) on the scanned surface, the illuminance on the scanned surface by the A laser 14a matches the illuminance on the scanned surface by the B laser 14b. In addition, the light emission amount IB of the B laser is controlled (A1 ′ = B1 ′, A2 ′ = B2 ′).

  That is, the control means 71 varies the emitted light amounts 14aI and 14bI between the two light emitting units at the maximum scanning angle.

  In this embodiment, as shown in FIG. 4C, the illuminance distributions 14ai and 14bi of the A laser and the B laser are corrected to be the same at the entire image height. If the multi OFS of this embodiment is used in, for example, an image forming apparatus, a good image in which density unevenness due to an illuminance difference between a plurality of light beams is reduced can be obtained.

  However, it can be seen from FIG. 4C that the illuminance distributions 14ai and 14bi by either laser tend to decrease as the image height increases, and that the gradient with respect to the illuminance with respect to the image height remains. These light intensity drop and density unevenness due to the gradient of illuminance are factors that degrade the image, but both are continuous density changes, so they are not noticeable when viewed with the naked eye. The density unevenness due to is easily noticeable because the density of adjacent dots changes significantly. For this reason, the effect of reducing the deterioration of the image can be expected only by reducing the density unevenness due to the illuminance difference between the plural light beams.

  In this embodiment, the amount of emitted light is controlled for each of the two light emitting units (lasers) 14a and 14b so that the illuminances of the two light beams are the same at the entire image height on the surface to be scanned (for example, FIG. 4B), the illuminance difference between the two light beams on the surface to be scanned is preferably 10% or less in the total image height.

  The difference in illuminance between the two light beams of 10% or less means the maximum value of the difference in illuminance between the two light beams 14a and 14b at the same image height over the entire image height on the surface to be scanned.

  That is, the illuminance difference between the two light beams on the surface to be scanned is preferably 10% or less at the total image height.

  If the difference in illuminance between the two light beams is 10% or less, density unevenness can be suppressed to a level that is not noticeable when viewed with the naked eye.

  Furthermore, recently, high-definition images are progressing, and density unevenness is more conspicuous. For this reason, more preferably, the illuminance difference between the two light beams on the surface to be scanned is preferably 1% or less in the total image height.

  That is, according to the present embodiment, the density unevenness of the image can be improved and a good image can be obtained only by controlling the light emission amount of the laser in the conventional multi OFS.

  In this embodiment, the light emission amount of the B laser is controlled by the control means, but the present invention is not limited to this, and the light emission amount of the A laser or both light emission amounts may be controlled.

  6 is a cross-sectional view of the main part in the main scanning direction (main scanning cross-sectional view) of the multi-beam optical scanning apparatus using the OFS according to the second embodiment of the present invention, and FIG. 7 is a cross-sectional view of the main part in the sub-scanning direction of FIG. FIG. 8 is a cross-sectional view of the main part in the optical axis direction of the aperture 3 ′ as the light amount correcting means. 6, 7, and 8, the same elements as those illustrated in FIGS. 1 and 2 are denoted by the same reference numerals.

The difference between the present embodiment and the first embodiment is that
(1) The use of an aperture (aperture stop) 3 'as an illuminance distribution compensation optical element (light loss compensation means) that compensates for light loss in one scanning line on the scanned surface;
(2) The distance between the position where the light intensity of each light beam emitted from the A and B lasers (light emitting portions) 14a and 14b is maximized on the deflection surface and the center position of the effective scanning area on the surface to be scanned. A point of providing an adjusting means for adjusting to be equal to each other,
(3) The control means controls the light emission amounts of both the A and B lasers so that they can be changed independently according to the image height (scanning angle).
It is. Other configurations and optical actions are the same as those of the first embodiment, and the same effects are obtained.

  In this embodiment, the two light emitting portions (lasers) 14a and 14b are separated from each other in the main scanning direction and the sub scanning direction.

That is, 3 'in the figure is an aperture (aperture stop) as an illuminance distribution compensating optical element, and the width in the sub-scanning direction of the aperture shape 3a of the aperture plate of the aperture 3' is set in the main scanning direction as shown in FIG. respect, formed to be larger toward the end portion from the central portion 3a ₀ of the main scanning direction, the end portion from the central portion 3a ₀ along the illumination of the scanning lines on the scan surface 10 in the scanning direction The illuminance is increased toward Thereby, in this embodiment, the light quantity drop in one scanning line on the surface to be scanned 10 is reduced.

  Reference numeral 72 denotes an adjusting means (adjusting mechanism), which rotates the multi-beam semiconductor laser 1 with respect to the main scanning direction. In the present embodiment, the adjustment means distributes the angular difference between the intensity center lines of the two light beams emitted from the multi-beam semiconductor laser 1 with respect to the main scanning direction equally to the left and right about the optical axis of the incident optical system. The light emission direction is adjusted.

  FIG. 9 is a sectional view (main scanning sectional view) of the main part in the main scanning direction of the multi OFS of this embodiment. In the figure, the same elements as those shown in FIG.

  In the figure, the incident optical system is represented as one condensing optical system 11. The intensity center lines 14ap and 14bp of the two light beams emitted from the A and B lasers (light emitting portions) 14a and 14b are inclined at the same angle RΔθ / 2 with respect to the optical axis 12 of the condensing optical system 11, respectively. In this figure, when these two light beams pass through the condensing optical system 11, the intensity center lines 14ap and 14bp of the two light beams each having an angle difference RΔθ / 2 with respect to the optical axis 12 are the light of the condensing optical system 11. Since the beam passes through a symmetrical position from the axis 12, the two light beams incident on the deflecting surface 7 have a symmetric intensity distribution centered on the center position of the effective light beam width with respect to the main scanning direction. At this time, the sum of the light amounts of the two light beams incident on one deflection surface is maximized. That is, since the utilization efficiency of the emitted light beam becomes the highest, the drive current can be minimized and the apparatus can be saved in power.

  FIG. 10A is a diagram showing the illuminance distributions 14ai and 14bi of the two light beams on the surface to be scanned when the amount of light emitted by the laser in the case of the multi OFS in FIG. 9 is constant at the total image height. As can be seen from FIG. 10A, the light quantity drop of the two light fluxes is corrected by making the aperture shape of the aperture plate of the aperture (aperture stop) 3 ′ larger in the sub-scanning direction than in the main scanning direction. You can see that.

  Further, by using the adjusting means, the angle difference RΔθ formed by the intensity center lines 14ap and 14bp of the two light beams with respect to the main scanning direction is distributed so as to be equal left and right with the optical axis of the incident optical system as the center. Although the illuminance distribution of the light beam is symmetric about the image height Y = 0, it can be seen that there is a difference in illuminance between the two light beams of the A laser and the B laser at the same image height.

  In this embodiment, as shown in FIG. 10A, in order to reduce the illuminance difference between two light beams on the surface to be scanned, the light emission amounts of the two lasers A and B are independently controlled by the control means. It is controlled so that it can be changed according to the scanning angle.

  FIG. 10B is a graph showing the amount of light emitted with respect to each image height of the two controlled lasers A and B.

  Unlike the first embodiment described above, the control means in this embodiment differs from the first embodiment described above in that the light emission amounts of both the A and B lasers are independent in order to reduce the illuminance difference between the two light beams on the scanned surface. Thus, control is performed so as to change according to the image height.

  That is, the control means 71 and 72 vary the emitted light amounts 14aI and 14bI between the two light emitting units at the maximum scanning angle.

As can be seen from FIG. 10B, in order to reduce the illuminance difference between the A laser and the B laser at each image height, the light emission amount 14aI of the A laser is moved from the image height Y = −Y ₀ to the image height Y = + Y _0. Accordingly, the amount of drive current of each laser is made different so that the amount of emitted light 14bI of the B laser monotonously decreases as the image height Y = −Y ₀ increases toward the image height Y = + Y ₀ . At this time, the straight lines representing the light emission amounts of the A laser and the B laser are symmetrical with respect to the image height Y = 0.

  For example, the light emission amounts IA and IB of the A laser and the B laser may be controlled independently and linearly so as to satisfy the following relational expression (2).

IA = I0 {(A1-B1) / 2 / B1 / Y0 * Y}
IB = I0 {(A2-B2) / 2 / A2 / Y0 * Y} (2)
Y: Arbitrary image height
IA: A laser emission quantity at any image height
IB: Light emission quantity of B laser at any image height
A1: Illuminance of the A laser at an image height Y = −Y ₀ when the amount of emitted light is a constant value I ₀
A2: Illuminance of laser A at image height Y = -Y ₀ when the amount of emitted light is a constant value I ₀
B1: Illuminance of the B laser at an image height Y = + Y ₀ when the light emission quantity is a constant value I ₀
B2: Illuminance of the B laser at the image height Y = + Y ₀ when the amount of emitted light is a constant value I ₀
I0: Light intensity when constant
Y0: Maximum image height However, even if the emitted light quantity does not satisfy the relational expression (2), if the illuminance of the maximum image height when the emitted light quantity of the B laser is controlled satisfies the following conditional expression (2) ′, A sufficient effect can be obtained in reducing the illuminance difference between the two light beams on the surface to be scanned.

0.9 ≦ | B1 ′ / A1 ′ | ≦ 1.1, 0.9 ≦ | B2 ′ / A2 ′ | ≦ 1.1 (2) ′
A1 ′: A laser illuminance at image height Y = −Y ₀ when light emission control is performed
A2 ′: Illuminance of the A laser at the image height Y = −Y ₀ when the emitted light quantity control is performed
B1 ′: Illuminance of the B laser at the image height Y = + Y ₀ when the amount of emitted light is controlled
B2 ′: Illuminance of the B laser at the image height Y = + Y ₀ when the emitted light amount control is performed. By satisfying the conditional expression (2) ′, each laser at each maximum image height (± Y ₀ ) Since the illuminances are A1 = B1 and A2 = B2 and RΔθ is equally distributed with respect to the optical axis of the incident optical system, the illuminance distributions 14ai and 14bi of the A laser and the B laser are always left-right symmetric. Since A1 = B2 and A2 = B1, the illuminance distributions 14ai and 14bi of the A laser and B laser are uniform at the entire image height, and the illuminance difference between the two light beams can be eliminated.

  The control means 71 and 72 vary the amount of emitted light between the two light emitting units 14al and 14bl at the same scanning angle in a partial region of the entire scanning angle, and the A laser 14ai at the same image height on the scanned surface. The illuminance of the B laser 14bi is the same.

  FIG. 10C is a diagram showing the illuminance distributions 14ai and 14bi on the surface to be scanned when the light emission amounts IA and IB of the respective lasers are controlled as shown in FIG. 10B. From FIG. 10C, it can be seen that the illuminance distributions 14ai and 14bi of the A laser and the B laser are uniform and corrected identically at the entire image height. The illuminance of each of the A laser and the B laser is A1 ′ = A2 ′ and B1 ′ = B2 ′.

  That is, according to the present embodiment, the conventional multi OFS uses the illuminance distribution compensating optical element and the control means for controlling the light emission quantity independently for the two lasers of A and B lasers. It is possible to simultaneously reduce the gradient of the illuminance distribution between the illuminance difference between the luminous fluxes and the drop in the amount of light, and in this embodiment, it is possible to compensate for a uniform illuminance distribution. Can be obtained.

  Next, a third embodiment of the present invention will be described. The main scanning sectional view and the sub-scanning sectional view of the present embodiment are the same as those in FIGS. 1 and 2 of the first embodiment.

The difference between the present embodiment and the first embodiment is that
(1) Of the A and B lasers (light emitting portions) on the deflection surface, the position where the light intensity of the light beam emitted from the A laser in the main scanning section becomes maximum and the surface to be scanned in the main scanning section A point provided with an adjusting means for adjusting so that the center positions of the effective scanning areas substantially coincide with each other.
(2) The amount of light emitted from both the A and B lasers is controlled by the control means so that it can be changed nonlinearly in accordance with the image height (scanning angle).
It is. Other configurations and optical actions are the same as those of the first embodiment, and the same effects are obtained.

  In this embodiment, the two light emitting portions (lasers) 14a and 14b are separated from each other in the main scanning direction and the sub scanning direction.

  That is, in the present embodiment, an intensity center line 14ap of one of the two light fluxes emitted from the lasers A and B is incident on the main scanning direction by an adjustment mechanism (not shown). The optical axis coincides with the optical axis 12 of the optical system.

  FIG. 11A is a sectional view (main scanning sectional view) of the main part in the main scanning direction of the multi OFS of this embodiment.

  In the figure, the incident optical system is represented as one condensing optical system 11. The intensity center line 14ap of the light beam emitted from the A laser (light emitting portion) 14a is adjusted by the adjusting means so as to coincide with the optical axis 12 of the condensing optical system 11, and is emitted from the B laser (light emitting portion) 14b. The intensity center line 14 bp of the luminous flux is inclined with an angle difference RΔθ with respect to the optical axis 12 of the condensing optical system 11.

  As can be seen from FIG. 11A, on the deflection surface 7, the intensity center line 14ap of the light beam is incident on the center position of the effective light beam width with respect to the main scanning direction, so that the intensity distribution is symmetric with respect to the center.

FIG. 11B is a diagram showing the illuminance distribution on the scanned surface of the two light beams when the light emission amount of the laser is set to a constant value I ₀ at the total image height in the multi OFS shown in FIG. 11A. From FIG. 11B, by adjusting the intensity center line 14ap of the light beam emitted from the A laser 14a using the adjusting means so as to coincide with the optical axis 12 of the condensing optical system 11, the illuminance distribution 14ai of the A laser is obtained. It can be seen that the image height is symmetric about Y = 0. Regarding the B laser, it can be seen that there is a difference in illuminance between the two beams of the A laser and the B laser at the same image height because the illuminance distribution 14bi has a gradient. In addition, it can be seen that a drop in the amount of light occurs in the illuminance distributions 14ai and 14bi of both the A laser and the B laser.

  FIG. 11C is a multi OFS having the illuminance distributions 14ai and 14bi as shown in FIG. 11B, and the light emission amounts of the respective lasers when the light emission amounts of the A laser and the B laser are independently controlled according to the image height. FIG.

  The dashed-dotted line 14aI and the alternate long and two short dashes line 14bI in FIG. 11C indicate the emitted light amount with respect to the image height when the emitted light amount of each laser is linearly changed according to the image height in order to reduce the illuminance difference between the two light beams. Represents.

As can be seen from the one-dot chain line 14aI and two-dot chain line 14bI in FIG. 11C, the light emission amount 14aI of the A laser remains at a constant value I _{0 at} the entire image height, and the illuminance difference between the A laser and the B laser at each image height In order to reduce the amount of light emitted, the amount of light emitted from each laser is controlled so that the amount of emitted light 14bI of the B laser monotonously decreases from the image height Y = −Y ₀ toward the image height Y = + Y ₀ .

  For example, the light emission amounts IA and IB of the A laser and the B laser are controlled to change linearly according to the image height so as to satisfy the following relational expression (3).

IA = I0
IB = a * Y + b (3)
a = I0 * {(B1-A1) / A1- (B2-A2) / A2} / 2Y0
b = I0 * {2- (B1-A1) / A1- (B2-A2) / A2} / 2
Y: Arbitrary image height
Y: Arbitrary image height
IA: Amount of light emitted at any image height of A laser
IB: Amount of emitted light at an arbitrary image height of the B laser
A1: Illuminance of the A laser at an image height Y = −Y ₀ when the amount of emitted light is a constant value I ₀
A2: Illuminance of laser A at image height Y = -Y ₀ when the amount of emitted light is a constant value I ₀
B1: Illuminance of the B laser at an image height Y = + Y ₀ when the light emission quantity is a constant value I ₀
B2: Illuminance of the B laser at the image height Y = + Y ₀ when the amount of emitted light is a constant value I ₀
I0: Constant value of emitted light
Y0: maximum image height Figure 11D is when the amount of emitted light to a constant value I ₀ at all image heights, illuminance distribution 14ai as shown in FIG. 11B, in a multi-OFS with 14Bi, A laser, any image of the B laser It is a figure showing illuminance distribution 14ai, 14bi on the to-be-scanned surface of A laser and B laser when it controls so that the emitted light quantity in high may become the dashed-dotted line 14aI and the dashed-two dotted line 14bI in FIG. 11C. .

  Although it can be seen from FIG. 11D that the illuminance difference between the two light beams of the A laser and the B laser is reduced, it can be seen that the light intensity drop has occurred in the illuminance distributions 14ai and 14bi of both the A laser and the B laser.

  Therefore, in this embodiment, in order to simultaneously reduce the illuminance difference between the two light beams and the light amount drop, the light emission amounts at arbitrary image heights of the A laser and B laser are represented by solid lines 14aI ′ and dotted lines 14bI ′ in FIG. 11C. It is controlled to become. In FIG. 11C, a solid line 14aI ′ and a dotted line 14bI ′ indicate image heights Y = Y for canceling the light amount drop in the amount of change in the light emission amount linear with respect to the image height for reducing the illuminance difference between the two light beams. It is obtained by adding a tendency to increase the amount of emitted light as the image height increases as the amount of emitted light is small at 0.

  For example, the amount of change in the amount of emitted light with respect to the image height to cancel out the light intensity is the ratio that the facet width decreases as the image height Y = 0 increases to the maximum image height, and the deflection as the image height Y = 0 increases to the maximum image height It can be approximated by the product of the Gaussian-distributed light intensity ratio on the surface. For this reason, the solid line 14aI 'and the dotted line 14bI' in FIG. For each [{(facet width at any image height) / (facet width at image height Y = 0)} * {(light intensity at the end of effective beam width) / (center of effective beam width) Light intensity at the part)}].

  In the first and second embodiments, the amount of emitted light is controlled so as to change linearly according to the image height, whereas in this embodiment, the amounts of emitted light of the A laser and the B laser are independently nonlinear. By performing control so as to change, it is possible to reduce the illuminance difference between the two light beams and at the same time to reduce the light amount without using an optical element (aperture 3 ') such as a light amount correction unit.

  FIG. 11E is a diagram showing the illuminance distributions 14ai and 14bi when the light emission amounts of the A laser and the B laser are independently controlled as shown in FIG. 11C in this embodiment.

  As can be seen from FIG. 11E, the illuminance distributions 14ai and 14bi of the A laser and the B laser are substantially the same and corrected uniformly at the total image height. In addition, density unevenness due to an illuminance difference between a plurality of light beams is reduced, and a good image can be obtained.

  In other words, according to the present embodiment, it is possible to improve the density unevenness of the image and obtain a good image by simply controlling the driving current and adjusting the emission direction of the light flux in the conventional multi OFS.

  In the present embodiment, the position where the light intensity of the light beam emitted from the A laser in the main scanning section is maximum and the center position of the effective scanning area in the main scanning section on the surface to be scanned are adjusted. In addition, the position where the light intensity of the light beam emitted from the B laser in the main scanning section becomes maximum may be adjusted so that the center position of the effective scanning area in the main scanning section on the surface to be scanned matches.

  In each of the first to third embodiments, the number of light emitting units (lasers) is two to simplify the description. However, the number of light emitting units (lasers) is three, for example. The above is also applicable.

  When controlling the amount of emitted light with respect to three or more light emitting units (lasers) so that the illuminance of three or more light beams is the same at the entire image height on the scanned surface, three on the scanned surface. The difference in illuminance between the above light beams is preferably 10% or less at the total image height.

  The difference in illuminance between three or more light beams is 10% or less when the total image height on the surface to be scanned is the light flux with the highest illuminance and the light flux with the lowest illuminance among the three or more light beams at the same image height. It means the maximum value of illuminance difference.

  If the difference in illuminance between the two light beams is 10% or less, density unevenness can be suppressed to a level that is not noticeable when viewed with the naked eye.

  Furthermore, recently, high-definition images are progressing, and density unevenness is more conspicuous. For this reason, more preferably, the illuminance difference between three or more light beams on the surface to be scanned is 1% or less in the total image height.

  In the first to third embodiments, the two light emitting units (lasers) 14a and 14b are separated from each other in the main scanning direction and the sub scanning direction, but the present invention is not limited thereto.

  In the case of the multi OFS, the present invention can also be applied to a form in which the two light emitting units (lasers) 14a and 14b are separated from each other only in the sub-scanning direction.

  Even when the two light emitting portions (lasers) 14a and 14b are separated from each other only in the sub-scanning direction, the problem shown in FIG. 14 occurs, and in a partial region of the entire scanning angle, which is the solution of the present invention, at the same scanning angle. By varying the amount of emitted light between the two light emitting portions 14al and 14bl, the illuminance variation of the A laser 14ai and the B laser 14bi at the same image height on the scanned surface can be reduced.

  The present invention can also be applied to a configuration in which three or more light emitting units are separated from each other only in the sub-scanning direction.

  In each of the first to third embodiments, the control means for controlling the amount of laser drive current is used to control the amount of emitted light. However, the present invention is not limited to this. For example, the control means for controlling the light emission time per dot. It may be configured.

  Further, in each of the first to third embodiments, the light source means having a plurality of light emitting portions is configured by a monolithic multi-beam semiconductor laser. However, the present invention is not limited to this, and for example, a plurality of light beams emitted from a plurality of light sources that are independent of each other. May be combined by a beam combining means such as a prism.

  In the second embodiment, the width of the aperture shape of the aperture plate in the sub-scanning direction as the illuminance distribution compensating optical element 3 ′ is larger at the end than at the center in the main scanning direction with respect to the main scanning direction. Although it is configured by an aperture, the present invention is not limited to this, for example, an absorbing material whose absorptance becomes smaller from the center in the main scanning direction toward the end with respect to the main scanning direction, or an image height from Y = 0 You may comprise by the folding | turning mirror which a reflectance becomes large as it goes to the maximum image height.

  In each of the second and third embodiments, a monolithic multi-beam semiconductor laser, which is a light source means, is used as an adjustment unit (adjustment mechanism) for adjusting the intensity center position of the laser on the deflection surface with respect to the main scanning direction. However, the present invention is not limited to this. For example, a part of the optical element of the incident optical system such as a collimator lens may be shifted or rotated in the main scanning direction.

  In each embodiment, the imaging optical system is composed of two lenses. However, the present invention is not limited to this. For example, the imaging optical system may be composed of a single lens or three or more lenses. Further, the imaging optical system may include a diffractive optical element and a curved mirror.

[Image forming apparatus]
FIG. 19 is a cross-sectional view of the main part in the sub-scanning direction showing an embodiment of the image forming apparatus of the present invention. In the figure, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into image data (dot data) Di by a printer controller 111 in the apparatus. The image data Di is input to the optical scanning unit 100 having the configuration shown in any one of the first to third embodiments. The light scanning unit 100 emits a light beam 103 modulated in accordance with the image data Di, and the light beam 103 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.

  The photosensitive drum 101 serving as an electrostatic latent image carrier (photoconductor) is rotated clockwise by a motor 115. With this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beam 103. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface. The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with the light beam 103 scanned by the optical scanning unit 100.

  As described above, the light beam 103 is modulated based on the image data Di, and by irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. The electrostatic latent image is developed as a toner image by a developing unit 107 disposed so as to contact the photosensitive drum 101 further downstream in the rotation direction of the photosensitive drum 101 than the irradiation position of the light beam 103.

  The toner image developed by the developing unit 107 is transferred onto a sheet 112 as a transfer material by a transfer roller 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in the paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 15), but can be fed manually. A paper feed roller 110 is provided at the end of the paper cassette 109, and feeds the paper 112 in the paper cassette 109 into the transport path.

  As described above, the sheet 112 on which the unfixed toner image has been transferred is further conveyed to the fixing device behind the photosensitive drum 101 (left side in FIG. 19). The fixing device includes a fixing roller 113 having a fixing heater (not shown) therein, and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113, and the sheet conveyed from the transfer unit. The unfixed toner image on the paper 112 is fixed by heating 112 while applying pressure at the pressure contact portion between the fixing roller 113 and the pressure roller 114. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and the fixed paper 112 is discharged out of the image forming apparatus.

  Although not shown in FIG. 19, the print controller 111 controls not only the data conversion described above, but also controls each part in the image forming apparatus including the motor 115 and a polygon motor in the optical scanning unit described later. I do.

  The recording density of the image forming apparatus used in the present invention is not particularly limited. However, considering that higher recording density requires higher image quality, the configurations of the first to third embodiments of the present invention are more effective in an image forming apparatus of 1200 dpi or more.

[Color image forming apparatus]
FIG. 20 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. This embodiment is a tandem type color image forming apparatus in which four optical scanning devices are arranged in parallel and image information is recorded on a photosensitive drum surface as an image carrier. In FIG. 20, 60 is a color image forming apparatus, 61, 62, 63, and 64 are optical scanning devices each having one of the configurations shown in Embodiments 1 to 3, and 21, 22, 23, and 24 are image carriers. The photosensitive drums 31, 32, 33 and 34 are developing units, and 51 is a conveyor belt.

  In FIG. 20, the color image forming apparatus 60 receives R (red), G (green), and B (blue) color signals from an external device 52 such as a personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 53 in the apparatus. These image data are input to the optical scanning devices 61, 62, 63 and 64, respectively. From these optical scanning devices, light beams 41, 42, 43, and 44 modulated according to each image data are emitted, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are caused by these light beams. Scanned in the main scanning direction.

  The color image forming apparatus according to the present embodiment has four optical scanning devices (61, 62, 63, 64) arranged in each color of C (cyan), M (magenta), Y (yellow), and B (black). Correspondingly, image signals (image information) are recorded on the photosensitive drums 21, 22, 23, and 24 in parallel, and a color image is printed at high speed.

  As described above, the color image forming apparatus in this embodiment uses the light beams based on the respective image data by the four optical scanning devices 61, 62, 63, and 64, and the corresponding photosensitive drums 21 and 22 respectively corresponding to the latent images of the respective colors. , 23, 24 on the surface. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 52, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.

Main scanning sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 1 of the present invention Explanatory drawing of deviation of intensity center position of two beams (main scanning sectional view) The figure which shows the illumination intensity distribution (constant light emission amount of a laser) of Example 1 of this invention. The figure which shows the emitted light quantity of the laser of Example 1 of this invention. The figure which shows the illuminance distribution (with laser light emission amount control) of Example 1 of this invention. The figure which shows the relationship between the drive current amount of the laser in Examples 1-3 of this invention, and emitted light quantity. Main scanning sectional view of Embodiment 2 of the present invention Sub-scan sectional view of Embodiment 2 of the present invention The figure which shows the light quantity correction means Main scanning sectional view of Embodiment 2 of the present invention The figure which shows the illumination intensity distribution (constant light emission amount of a laser) of Example 2 of this invention. The figure which shows the emitted light quantity of the laser of Example 2 of this invention The figure which shows the illuminance distribution (with the light emission light amount control of a laser) of Example 2, 3 of this invention. Main scanning sectional view of Embodiment 3 of the present invention The figure which shows the illumination intensity distribution (constant light emission amount of a laser) of Example 3 of this invention. The figure which shows the emitted light quantity of the laser of Example 3 of this invention The figure which shows the illumination intensity distribution (laser emission light amount linear control) of Example 3 of this invention. The figure which shows the illumination intensity distribution (laser emission light amount nonlinear control) of Example 3 of this invention. A diagram showing the illuminance distribution when there is a conventional light loss A diagram showing the illuminance distribution when there is a conventional drop in light intensity and gradient Overview of the main parts of a monolithic multi-beam laser Explanatory drawing of deviation of intensity center position of two beams (main scanning sectional view) Diagram showing conventional illuminance distribution (constant laser light emission) Figure showing conventional illuminance distribution Figure showing conventional illuminance distribution FIG. 3 is a sub-scan sectional view showing an embodiment of the image forming apparatus of the present invention. 1 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention.

Explanation of symbols

1 Light source means (monolithic multi-beam laser)
2 Imaging optical system (collimator lens)
3 Aperture (aperture stop)
4 Sub-scanning cylindrical lens 5 Incident optical system 6 Deflection means (polygon mirror)
7 Deflection Surface 8 Imaging Optical System 8a fθ Lens 8b Toric Lens 9 Folding Mirror 10 Scanned Surface (Photosensitive Drum Surface)
14a, 14b Light emitting unit 71 Control unit 72 Adjustment unit 3 'Light amount correction unit 61, 62, 63, 64 Optical scanning device 21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 51 Conveyor belt 52 External device 53 Printer controller 60 Color image forming apparatus 100 Optical scanning device 101 Photosensitive drum 102 Charging roller 103 Light beam 104 Image forming apparatus 107 Developing device 108 Transfer roller 109 Paper cassette 110 Paper feed roller 111 Printer controller 112 Transfer material (paper)
113 Fixing Roller 114 Pressure Roller 115 Motor 116 Paper Discharge Roller 117 External Equipment

Claims (14)

Light source means having a plurality of light emitting portions;
An optical deflector having a deflection surface;
An incident optical system that causes a plurality of light beams emitted from the plurality of light emitting units to enter the deflection surface of the optical deflector in a state wider than the width of the deflection surface in the main scanning direction;
An imaging optical system that forms an image on the scanned surface with a plurality of light beams reflected by the optical deflector;
A multi-beam optical scanning device having control means for independently controlling the amount of emitted light for the plurality of light emitting units,
The control means reduces the illuminance difference between the plurality of beams on the surface to be scanned by independently controlling the amount of emitted light with respect to the plurality of light emitting sections. . Light source means having a plurality of light emitting portions;
An optical deflector having a deflection surface;
An incident optical system that causes a plurality of light beams emitted from the plurality of light emitting units to enter the deflection surface of the optical deflector in a state wider than the width of the deflection surface in the main scanning direction;
An imaging optical system that forms an image on the scanned surface with a plurality of light beams reflected by the optical deflector;
A multi-beam optical scanning device having control means for independently controlling the amount of emitted light for the plurality of light emitting units,
When controlling the amount of emitted light for each of the plurality of light emitting units so that the illuminance of the plurality of light beams is the same by the control means at the total image height on the scanned surface,
The multi-beam optical scanning device characterized in that the control means varies the amount of emitted light between the plurality of light emitting sections at the maximum scanning angle. Light source means having a plurality of light emitting portions;
An optical deflector having a deflection surface;
An incident optical system that causes a plurality of light beams emitted from the plurality of light emitting units to enter the deflection surface of the optical deflector in a state wider than the width of the deflection surface in the main scanning direction;
An imaging optical system that forms an image on the scanned surface with a plurality of light beams reflected by the optical deflector;
A multi-beam optical scanning device having control means for independently controlling the amount of emitted light for the plurality of light emitting units,
When controlling the amount of emitted light for each of the plurality of light emitting units so that the illuminance of the plurality of light beams is the same by the control means at the total image height on the scanned surface,
The multi-beam optical scanning device according to claim 1, wherein the control means varies the amount of emitted light between the plurality of light emitting units at the same scanning angle within a partial region of the entire scanning angle.   The control means controls the amount of emitted light with respect to the plurality of light emitting sections so that the illuminance of the plurality of light beams on the scanned surface changes linearly according to the image height. The multi-beam optical scanning device according to any one of claims 1 to 3.   The control means controls the amount of emitted light with respect to the plurality of light emitting sections so that the illuminance of the plurality of light beams on the scanned surface changes nonlinearly according to the image height. The multi-beam optical scanning device according to any one of claims 1 to 3. An illuminance distribution compensating optical element for correcting the illuminance distribution in one scanning line on the scanned surface is provided in an optical path between the light source means and the scanned surface,
2. The illuminance distribution compensating optical element compensates so as to increase the illuminance of a scanning line on the surface to be scanned from the center to the end along the main scanning direction. 6. The multi-beam optical scanning device according to any one of items 1 to 5. Adjusting means for adjusting a position at which the light intensity of each light beam emitted from the plurality of light emitting units in the main scanning section is maximized on the deflection surface of the optical deflector;
By the adjusting means, the position where the light intensity of each light beam emitted from the plurality of light emitting sections in the main scanning section is maximized on the deflection surface and the effective scanning area in the main scanning section on the scanned surface. The multi-beam optical scanning device according to claim 1, wherein the multi-beam optical scanning device is adjusted so that intervals between the central positions are equal to each other. Adjusting means for adjusting a position at which the light intensity of each light beam emitted from the plurality of light emitting units in the main scanning section is maximized on the deflection surface of the optical deflector;
The adjustment means causes the main scanning section on the surface to be scanned and the position where the light intensity of the light beam emitted from one or more of the light emitting sections in the main scanning section is maximized on the deflection surface. 7. The multi-beam optical scanning device according to claim 1, wherein the center position of the effective scanning area is adjusted so as to coincide with each other.   The multi-beam optical scanning device according to claim 1, wherein the plurality of light emitting units are separated in a main scanning direction and a sub scanning direction.   The multi-beam optical scanning device according to claim 1, wherein the plurality of light emitting units are separated only in the sub-scanning direction.   The multi-beam optical scanning device according to claim 1, a photoconductor disposed on the scanned surface, and a light beam scanned by the multi-beam optical scanning device on the photoconductor. A developing unit that develops the formed electrostatic latent image as a toner image; a transfer unit that transfers the developed toner image to a transfer material; and a fixing unit that fixes the transferred toner image to the transfer material. An image forming apparatus.   11. The multi-beam optical scanning device according to claim 9 or 10, and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the multi-beam optical scanning device. Image forming apparatus.   A plurality of image carriers, each of which is arranged on a surface to be scanned of the multi-beam optical scanning device according to any one of claims 1 to 10 and forms images of different colors. Color image forming apparatus.   14. The color image forming apparatus according to claim 13, further comprising a printer controller that converts color signals input from an external device into image data of different colors and inputs the image data to each multi-beam optical scanning device.