JP2008122706A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in a configuration that can eliminate the displacement of the scanning position of light beam due to the reflection point variations by preventing variation in the light incidence angle to the polygon mirror due to environmental changes. <P>SOLUTION: The optical scanner is composed of light sources 107-110, a deflector 106 to deflect the light flux from those light sources, and an imaging optical element to guide the light flux deflected by the above deflector to various surfaces to be scanned and to form spots. Each of the light flux led to various different surfaces to be scanned enters the deflector with a certain opening angle to the main scanning direction. At least one of the imaging optical elements leading to different surfaces to be scanned is disposed staggering in the direction perpendicularly crossing the optical axis in the main scanning direction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly to a configuration of a scanning optical system for forming a color image by superimposing a plurality of color toner images.

  In general, the light beam from the light source is deflected by the light deflecting means of the rotary polygon mirror, and the deflected light beam is condensed toward the scanned surface by using a scanning imaging optical system such as an fθ lens. 2. Description of the Related Art An optical scanning apparatus that forms a light spot on a surface and scans a surface to be scanned with the light spot is widely known in connection with image forming apparatuses such as an optical printer, an optical plotter, and a digital copying machine.

  In an image forming apparatus using an optical scanning device, an image writing step of writing an image by optical scanning is adopted as one step in the image forming process. It is affected by the quality of optical scanning. The quality of optical scanning depends on the scanning characteristics of the optical scanning device in the main scanning direction and the sub-scanning direction.

  On the other hand, the image formed by the image forming apparatus includes not only a monochrome image but also a color image obtained by superimposing a plurality of color toner images. The image is so-called monochrome and is written by a single optical scanning device. When formed, if the scanning line curve and imperfection of constant velocity (deviation from the ideal constant velocity scanning) are suppressed to some extent, “distorted enough to be visually recognized” occurs in the formed image. Nonetheless, such image distortion has never been less.

  In addition to the monochrome image, three colors of magenta, cyan, and yellow, or four colors with black added thereto, are formed as color component images, and these color component images are superimposed to form a color image An image forming apparatus is also widely known, and one of the methods for performing such color image formation is an image forming method called a tandem type in which an image for each color component is formed on a photoconductor for each color component.

In the tandem type image forming apparatus, as a configuration adopting a writing structure using an optical scanning device, a light beam from a light source corresponding to each color is scanned collectively with a single polygon mirror, and a scanning optical system corresponding to each And a configuration in which a plurality of folding mirrors for guiding to a photosensitive drum are integrally supported by a common optical housing, or a configuration in which an optical scanning device is individually arranged corresponding to each photosensitive drum is proposed. (For example, Patent Document 1).
In the configuration disclosed in Patent Document 1, a scanning lens used in the optical scanning device has a two-stage configuration, and a layout that guides a light beam toward each corresponding photosensitive drum is employed.

  On the other hand, in this type of multi-color image forming apparatus, the speed and density are increasing year by year. As a countermeasure, there is a method to increase the rotation speed of the polygon motor. However, since the bearing life is limited and heat and vibration cannot be suppressed, it is possible to scan multiple beams simultaneously at a lower rotation speed. A method using a multi-beam light source capable of realizing high speed and high density has been proposed.

  As a method for assembling a scanning lens layered vertically, methods have been proposed in which the lenses are integrated by bonding or fitting of concavo-convex portions (for example, Patent Documents 2 and 3).

JP 2002-148551 A JP 2000-75230 A JP 2003-5115 A

  However, in the case of the tandem type image forming method, if the imaging performance of the optical scanning devices with respect to the photosensitive member varies, a difference in image quality occurs for each color, and the desired color tone cannot be obtained. There is.

  In addition, if the scanning position varies, the scanning line is bent or tilted differently, an abnormal image called “color shift” appears in the formed color image, and the image quality of the color image is deteriorated.

On the other hand, the light source unit corresponding to each photoconductor is arranged close to each other, but the incident angle to the polygon mirror (the angle between the incident angle from the light source to the polygon mirror and the optical axis of the scanning lens) is If they are different, the amount of reflection point variation (sag) with respect to the scanning lens of the polygon mirror is different, and the field curvature is tilted (rotated), resulting in deterioration of imaging performance.
For this reason, conventionally, an incident mirror is arranged between the light source unit and the polygon mirror so that the light beams from the two light source units are incident on the polygon mirror in the main scanning direction.

  However, when the optical housing is deformed due to the temperature change caused by the heat generated by the polygon scanner or the fixing device, the arrangement positions of the scanning optical elements and mirrors, which are optical elements housed inside, change. In particular, in the case of a mirror, the double luminous flux with a change in tilt changes due to the reflection system.

  When transmitting like a lens, the power (refractive power) of the lens itself does not change so much, so the influence on the optical path change is relatively small. However, in the case of a mirror, the influence is great because the change in angle directly changes the optical path of the light beam. .

  On the other hand, the anamorphic lens (located closest to the scanned surface side) constituting the scanning optical element constitutes a surface tilt correction optical system in combination with a cylinder lens in front of the polygon mirror. Therefore, since the power (refractive power) in the sub-scanning direction is stronger than other lenses, the change in the light passing position in the sub-scanning direction of the anamorphic lens has a larger influence than other optical elements, and the scanning line is bent. Will be generated.

It is known from Patent Document 1 and the like described above that a mirror disposed in an optical housing is more greatly affected by a change in its posture as the mirror is more distant from the anamorphic lens.
In Patent Document 1, it is disclosed that the change in the attitude (tilt) of the incident mirror arranged between the light source unit and the polygon mirror has the greatest influence, and the amount of advantage is about 10 times larger than the mirror arranged after the polygon. Has been.

  Further, since the incident mirror is arranged in the vicinity of the polygon, it is at a position that is easily affected by the heat generated by the polygon, and the posture change is likely to increase.

  For example, when several tens of color images are continuously formed, the temperature inside the apparatus rises due to continuous operation of the image forming apparatus, and the optical housing is deformed by the accompanying temperature rise of the optical writing apparatus, and the beam position with respect to the optical element And the scanning position on the photoconductor shifts with time, such as a change in the position of the mirror and the setting angle of the folding mirror.

  In recent years, in order to improve scanning characteristics, it has become common to adopt special surfaces typified by aspherical surfaces in the imaging optical system of optical scanning devices, and such special surfaces can be easily formed. An imaging optical system made of a resin material that can be manufactured at a low cost is often used.

  The optical characteristic of the imaging optical system of resin material is likely to change due to the influence of temperature and humidity changes. When the temperature distribution in the lens becomes non-uniform due to the temperature change, the lens is warped and becomes a bow shape in the sub-scanning direction. Such warpage of the lens causes scanning line bending.

  Since the component parts are arranged so that the light beams traveling toward the photosensitive drums pass through different paths, the scanning position of each light beam easily varies depending on the environmental temperature where the multicolor image forming apparatus is installed. Invite.

  The object of the present invention is to prevent the change in the scanning position of the light beam caused by the variation in the reflection point by preventing the change in the incident angle to the polygon mirror due to environmental fluctuations, etc. An object of the present invention is to provide an optical scanning device and an image forming apparatus having a configuration capable of performing the above.

  In particular, the incident mirror arranged between the light source and the polygon mirror is eliminated, and the occurrence of scanning line bending due to environmental changes such as temperature changes is suppressed, and the light flux to different photoconductors has an opening angle and the polygon mirror An object of the present invention is to prevent the occurrence of a variation in the reflection point (zag) for a configuration that is incident on a deflector such as the above.

  Another object of the present invention is to facilitate the assembly of stacked lenses.

  Still another object of the present invention is to scan the surface to be scanned simultaneously with a plurality of light beams so that the rotational speed of the deflector can be lowered, thereby reducing the power consumption and the amount of heat generated by the deflector, thereby reducing the reflection point variation. It is to reduce the amount of heat generation that leads to environmental fluctuations, particularly temperature rise.

  It is still another object of the present invention to obtain a color image with high density and no color shift caused by a beam spot.

  In order to achieve this object, the present invention has the following configuration.

(1) a plurality of light sources;
A deflector for deflecting light beams from a plurality of light sources;
In an optical scanning device comprising an imaging optical element that guides a plurality of deflected light beams by the deflector onto different scanned surfaces and forms an image as a light spot,
A plurality of light beams guided to different scanned surfaces enter the deflector with an opening angle in the main scanning direction,
An optical scanning device characterized in that at least one of the imaging optical elements guided to different scanning surfaces is shifted from each other in a direction orthogonal to the optical axis in the main scanning direction.

  (2) The optical scanning device according to (1), wherein at least one of the imaging optical elements guided to different scanning surfaces is arranged so as to overlap in the sub-scanning direction.

  (3) The imaging optical elements to be arranged in an overlapping manner are formed by shifting the optical axis from the center of the outer shape in the main scanning direction, and are inverted by 180 ° with respect to the optical axis in relation to other imaging optical elements. The optical scanning device according to (2), characterized in that the optical scanning device is arranged.

  (4) The optical scanning device according to (2) or (3), wherein the imaging optical elements arranged in an overlapping manner have positioning references in the sub-scanning direction on both sides.

  (5) The optical scanning device according to any one of (2) to (4), wherein the imaging optical elements to be arranged in an overlapping manner are integrated by adhesion.

  (6) The scanning device according to any one of (2) to (4), wherein the imaging optical elements to be arranged in an overlapping manner are integrally formed of resin.

  (7) The optical scanning device according to (1), wherein each light source is a multi-beam optical scanning device that has a plurality of light emitting points and simultaneously scans the surface to be scanned with a plurality of light beams.

  (8) The optical scanning device according to (1) or (7), wherein the wavelength of the light source is 500 nm or less.

(9) The optical scanning device according to any one of (1) to (8) is mounted,
An image forming apparatus having a plurality of image bearing members, developing an electrostatic image formed on the image bearing member with each color toner, and superimposing them on a transfer member to form a color image, thereby forming a color image .

  (10) A scanning region outermost proximity color misregistration detection means in the image carrier is provided, and the color misregistration correction is performed by controlling the attitude of at least one imaging optical element based on the detection result ( The image forming apparatus according to 9).

  (11) The image forming apparatus according to (9) or 10), which has a network communication function.

  INDUSTRIAL APPLICABILITY According to the present invention, the present invention can be applied to a multi-beam image forming apparatus that optically scans a scanning medium with a plurality of light beams, and optical scanning is performed on the scanning medium with light beams from one light emitting point. Compared to the case, the rotational speed of the deflector can be lowered. In addition, the incident mirror for the deflector that has been used in the past is not equipped, and the influence of environmental fluctuations on the incident mirror causes variations in the incident angle due to the change in the incident angle. The situation can be resolved.

  Thereby, the power consumption by a deflector can be reduced and the emitted-heat amount can also be reduced. In addition, the motor constituting the deflector can be reduced, and the material cost can be reduced.

  Particularly in the first and second aspects of the invention, at least one of the imaging elements that guide the light beams toward different scanned surfaces is in a direction perpendicular to the optical axis in the main scanning direction. Since they are arranged so as to be shifted from each other in the sub-scanning direction, surface tilt in the sub-scanning direction can be corrected, so that the amount of scanning line bending at the time of temperature change can be reduced.

  According to the third and fourth aspects of the present invention, the scanning lenses arranged in an overlapping manner are arranged so that the optical axis is shifted from the center of the outer diameter shape in the main scanning direction and inverted by 180 ° with respect to the other imaging elements and the optical axis. Since the positioning reference in the sub-scanning direction at the time of reversal is provided on both sides, the position in the sub-scanning direction relative to the imaging element support at the time of reversal can be easily determined, and assembly errors can be reduced.

  In the inventions according to claims 5 and 6, since the imaging element is constituted by a multi-layer structure formed by bonding or resin molding, the structure can be simplified, and the positioning of the elements at the time of bonding is claimed. This can be done easily by using the invention described in the above.

  In the invention described in claim 7, by simultaneously scanning with a plurality of light sources, the number of rotations of the deflector can be reduced and the scanning time can be shortened, and the power consumption for driving the deflector and the amount of heat generated can be reduced.

  In the inventions according to claims 8 and 9, the use of the small-diameter spot can increase the density and prevent the occurrence of color misregistration when the spot is used.

  In the invention described in claim 10, the curvature of the scanning line is corrected by controlling the posture of the imaging element based on the detection result from the color misregistration detection means provided in the vicinity of the outermost measurement of the scanning region in the image carrier. As a result, it is possible to prevent the occurrence of color misregistration due to the misalignment of the scanning lines when forming a multicolor image.

  In the invention described in claim 11, by connecting a plurality of image forming apparatuses on the network, the status of each image forming apparatus (the degree of job congestion, whether the power is on, whether there is a failure or not) from each output request. And the like, and it is possible to select and output an image output device that is in the best condition (best suited to the user's wishes).

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram for explaining a main configuration of an optical scanning device according to the present invention, in which an optical scanning device that scans four stations is shown.
In FIG. 1, the optical scanning apparatus uses a counter scanning method in which two stations are divided into two, and beams are incident from opposite sides of a single polygon mirror to deflect and scan in opposite directions.
The four photosensitive drums 101, 102, 103, and 104 are arranged at equal intervals along the moving direction 105 of the transfer body, and sequentially transfer and superimpose different color toner images to form a color image.

  As shown in the figure, the optical scanning device that scans each photosensitive drum is integrally configured, and the polygon mirror 106 scans the light beam. Since the rotation direction of the polygon mirror is the same, the scanning direction is the opposite direction on the opposite side, and the image is written so that one writing position and the other writing end position coincide. In addition, each component which comprises an optical scanning device is mounted on the housing | casing (optical housing) not shown.

  In FIG. 1, a pair of semiconductor lasers are provided for each photoconductor, and scanning is performed by shifting one line pitch in the sub-scanning direction in accordance with the recording density so that two lines are scanned simultaneously.

  The beams 201, 202, 203, and 204 from each light source unit are portions whose emission positions differ in the sub-scanning direction for each light source unit, in the embodiment, the emission positions of the light source units 107, 108, 109, and 110 are a predetermined height, In the embodiment, the beams from the light source units 108 and 109 are arranged so as to be different by 6 mm, and the beams from the light source units 107 and 110 directly going to the polygon mirror 106 are incident on the polygon mirror 106 with the main scanning direction approaching. The

  The cylinder lenses 113, 114, 115, 116 are arranged such that one has a common curvature in the plane and the other has a common curvature in the sub-scanning direction, and the optical path lengths to the deflection reflection points of the polygon mirror 106 are equal. Each light beam is converged so as to be linear in the main scanning direction on the deflection surface, and the deflection reflection point and the surface of the photosensitive member are subordinated by a combination of an imaging optical system composed of a first scanning lens and an anamorphic lens described later. By adopting a conjugate relationship in the scanning direction, a surface tilt correction optical system is formed.

  The optical axis changing units 117, 118, and 119 are provided in stations (except for the beam from the light source unit 109 in the embodiment) except for the reference color, and stably hold (correct) the scanning position of each light beam.

  The polygon mirror 106 is a six-sided mirror, which is configured in two stages in the embodiment, and has a shape in which a groove is provided so that the intermediate portion not used for deflection is slightly smaller in diameter than the inscribed circle of the polygon mirror to reduce windage loss. Yes. The thickness of one layer is about 2 mm. Note that the phases of the upper and lower polygon mirrors are the same.

  Each of the first lenses 120 and 121 has a non-arc surface shape in which power is given so that the beam moves at a constant speed on the surface of the photosensitive member in accordance with the rotation of the polygon mirror in the main scanning direction. The anamorphic lenses 122, 123, 124, and 125 arranged in FIG. 4 form an imaging optical system, and each beam is imaged in a spot shape on the surface of the photosensitive member to record a latent image.

  In each color station, a plurality of sheets are used so that the optical path lengths from the polygon mirror to the surface of the photoconductor coincide with each other, and the incident positions and incident angles with respect to the photoconductor drums arranged at equal intervals are equal. Three folding mirrors are arranged per station.

  Explaining the optical path for each color station, the beam 201 from the light source unit 107 is deflected at the upper stage of the polygon mirror 106 via the optical axis changing means 117 and the cylinder lens 113, and then passes through the upper stage of the fθ lens 120. Then, the light is reflected by the folding mirror 126, passes through the anamorphic lens 122, is reflected by the folding mirrors 127 and 128, and is guided to the photosensitive drum 102 to form a magenta image as the second station.

  The beam 202 from the light source unit 108 is deflected at the lower stage of the polygon mirror 106 via the optical axis changing means 118 and the cylinder lens 114, passes through the lower stage of the first lens 120, and is reflected by the folding mirror 129. The light passes through the anamorphic lens 123, is reflected by the folding mirrors 130 and 131, is guided to the photosensitive drum 101, and forms a yellow image as a first station.

  The same applies to the opposing stations arranged symmetrically with the polygon mirror. The beam 203 from the light source unit 109 is deflected at the lower stage of the polygon mirror 106 and reflected by the folding mirrors 132, 133, and 134 to the photosensitive drum 104. The black image is guided as the fourth station, and the beam 204 from the light source unit 110 is deflected at the upper stage of the polygon mirror 106, reflected by the folding mirrors 135, 136, and 137 and guided to the photosensitive drum 103. A cyan image is formed as a third station.

FIG. 2 schematically shows a state in which the main scanning direction of the scanning optical system is viewed.
The light beam emitted from the semiconductor laser 1 is condensed by the coupling lens 2, shaped by the aperture stop 3, and then a line image that forms a long line image in the main scanning direction in the vicinity of the deflection reflection surface 9 </ b> A of the polygon mirror 9. The light is guided to a cylindrical lens 4 that is an optical element. The light beam deflected to the polygon mirror is condensed as a light spot on the photoconductor 12A that is the surface to be scanned by the lenses 10A and 11A that are scanning optical systems, and scans the photoconductor 12A as the polygon mirror rotates.

  Similarly, the light beam emitted from the semiconductor laser 5 is guided to the polygon mirror 9 via the coupling lens 6, the aperture stop 7, and the cylindrical lens 8, and is superimposed on the lenses 10 </ b> A and 11 </ b> A that are scanning optical systems. 10B and 11B perform deflection scanning on different photoconductors 12B as light spots (lenses 10A and 11A and 10B and 11B are arranged in the sub-scanning direction, that is, in a direction orthogonal to the drawing).

  The light beam emitted from the semiconductor laser 1 as the light source and the light beam emitted from the semiconductor laser 5 have an opening angle as shown in the figure in the main scanning direction, so that independent optical paths to different photoconductors are formed. The angles θ1 and θ2 with respect to the optical axes of the scanning lenses 10 and 11 (perpendicular to the photoconductor 12) have different values. That is, the light beams guided to the different photoconductors (surfaces to be scanned) are incident on the polygon mirror, which is a deflector, with an opening angle in the main scanning direction.

Hereafter, the result by an Example is shown.
The introduction of the scanning optical system is as shown in Table 1, and the lenses 10A and 10B and 11A and 11B are the same.

  Rx is a radius of curvature in the main scanning direction, and Ry is a radius of curvature in the sub-scanning direction.

  D is the distance between the lenses, and D0 is the distance between the deflecting / reflecting surface 9A and the lens 10.

  N is the refractive index and the wavelength is λ = 780 nm. The first surface of the lens 10 is a spherical surface, the second surface is a cylinder surface having a curvature only in the main scanning direction, the first surface of the lens 11 is a cylinder surface having a curvature only in the sub-scanning direction, and the second surface is a main scanning. The toroidal surface has different curvatures in the direction and the sub-scanning direction.

  FIG. 3 shows the field curvature when θ = 50 ° (plotted with ●) and when θ = 70 ° (plotted with ▲). The dotted line is the main scanning direction, and the solid line is the sub-scanning direction. When θ = 50 °, light is condensed in a well-balanced manner within an image height of ± 150 mm in both the main scanning direction and the sub-scanning direction. When θ = 70 °, the imaging performance is substantially the same in the main scanning direction, but the image plane is tilted (rotated) in the sub-scanning direction, and the imaging performance is deteriorated. This is because the reflection point variation (sag) of the polygon mirror is corrected satisfactorily when θ = 50 °, but cannot be corrected when θ = 70 °.

  On the other hand, it is possible to correct by shifting the scanning optical system in a direction orthogonal to the lens optical axis in the main scanning direction, for example, according to Japanese Patent No. 2994799 which is a prior application of the present applicant. It has been clarified that if both of the stacked lenses are shifted, θ = 70 ° is corrected, but θ = 50 ° conversely causes the image plane to tilt in the sub-scanning direction. As a result, the imaging performance deteriorates.

Therefore, the present invention proposes to shift only θ = 70 °.
In the embodiment, the field curvature when θ = 70 ° is shifted by S = + 2.56 mm is plotted in FIG.
When only θ = 70 ° is shifted, both θ = 50 ° (plotted with ●) and θ = 70 ° (plotted with ■) can obtain good performance. This is a feature of the invention described in claim 1.

  In addition, although it described as the arrangement | positioning overlapped above, in the case of a layout as shown in FIG. 1, the lens 10 will be arrange | positioned in the subscanning direction. This is a feature of the invention described in claim 2.

FIG. 4 schematically shows a state in which the lenses are arranged in the sub-scanning direction.
4A is a diagram viewed from the main scanning direction, and FIG. 4B is a diagram viewed from the sub-scanning direction.

  The upper lens optical axis (a) and the lower lens optical axis (b) are shifted as shown in the figure because the lens is shifted in a direction perpendicular to the lens optical axis. Therefore, the length d in the longitudinal direction is longer than the length of the single lens.

Therefore, in the present invention, as shown in FIG. 5, the upper lens unnecessary portion is cut to have an asymmetric shape with respect to the lens optical axis.
Since the introduction of the lower lens is the same as the introduction of the upper lens, as shown in FIG. 5B, the lens is arranged upside down with the lens optical axis as the center of rotation.

FIG. 6 shows a state in which the lower lens is arranged based on the principle described above.
Since unnecessary portions are cut in both the upper and lower stages, the length d ′ in the longitudinal direction can be shorter than d, and the size can be reduced. This is a feature of the invention described in claim 3.

  In order to arrange the lens upside down, if both side surfaces (c) and (c ′) of the lens shown in FIG. 5B have a positioning reference, the lens support when the lens is inverted and assembled. The position in the sub-scanning direction with respect to the part can be determined, and the assembly error can be reduced. This is a feature of the invention described in claim 4.

FIG. 7 shows a method of holding the lenses arranged in the upper and lower stages in the present invention.
FIG. 7A is an example in which an upper lens is disposed and fixed on a support portion (e) such as a sheet metal.
In this case, the lower lens may be fixed to the support part (e), or may be fixed on a support member that supports the lower surface of the lens (not shown), but the upper and lower lenses are supported on the support part (e). Is supported, the lens assembly tolerance between the upper and lower stages is only the processing error of the support portion (e), and the relative positional relationship is easy to control.

  FIG. 7B is an example in which the upper and lower lenses are bonded and fixed with an adhesive layer (f) with an adhesive. In this case, the support portion is the lower surface of the lower lens, but the upper and lower lens positions are highly accurate by configuring the both side surfaces (c) and (c ′) of the upper and lower lenses to have a positioning reference. Therefore, it is possible to prevent problems caused by adhesion. This is a feature of the invention described in claim 5.

  FIG. 7 (3) shows an example in which the upper and lower lenses are integrally formed using resin as a material. By integrally molding the upper and lower lenses, the lens placement error can be reduced to the processing level of the mold. In addition, the upper and lower stages can be assembled integrally, and the structure can be simplified. This is a feature of the invention described in claim 6.

FIG. 8 shows the configuration of the support housing of the anamorphic lens.
The anamorphic lens 305 is made of resin and has a rib portion 306 so as to surround the lens portion, and a positioning projection 307 is formed at the center portion.

The support plate 301 is formed of a sheet metal in a U-shape, and the projection 307 of the anamorphic lens 305 is engaged with the notch 311 formed in the vertical bending portion, and the lower surface of the rib is abutted against the vertical bending portion 310 and positioned. The pair of leaf springs 303 are biased from the upper surface of the rib to hold both ends.
The leaf spring 303 is fitted from the outside in a state where the anamorphic lens 305 is superimposed on the support plate 301, and one end is taken out from the opening 313 to be inserted into the opening 314 and fixed.

  At the center, an adjustment screw 08 is screwed into the screw hole 312, the leaf spring 302 is similarly fitted from the outside, and 317 and 318 are hooked on the inside of the lower rib and fixed in the same manner. Is urged so as to come into contact with each other (refer to FIG. 9 and a sectional view AA cut along AA in FIG. 9).

  With such a configuration, the pressing force applied to the anamorphic lens 305 by the adjustment screw 308 and the elastic force applied to the leaf spring 302 work in opposite directions to enable delicate adjustment.

  A leaf spring hole 319 is a hole penetrating the adjustment screw 308. In the embodiment, the adjustment screw 308 is similarly provided between the center portion and the lens end portion, but only the center portion may be provided.

FIG. 9 shows a state in which the anamorphic lens is mounted as viewed from the optical axis direction.
The anamorphic lens 305 is supported at both ends by the edge of the vertical bending portion 310 and at the center by the adjustment screw 308. When the protruding amount of the adjustment screw 308 is insufficient for the vertical bending portion 310, the anamorphic lens generatrix 312 is on the lower side. Warps to be convex. On the contrary, if the protruding amount exceeds, it will warp upward.
Therefore, by adjusting the adjustment screw, the attitude of the anamorphic lens is adjusted, the focal line is curved in the sub-scanning direction, and the bending of the scanning line can be corrected.

  In general, the bending of the scanning line is caused by an arrangement error of an optical element constituting the optical system, a warp at the time of molding, etc., and by correcting the linearity by curving the anamorphic lens 305 in a direction to cancel this, that is, The direction and amount of bending between the scanning lines can be made uniform.

By the way, when the temperature inside the image forming apparatus changes, the anamorphic lens 305 expands or contracts.
At this time, both ends of the anamorphic lens 305 are fixed by the spring force of the leaf spring 303, so that free expansion or expansion / contraction is hindered. As a result, tensile stress or compression stress is generated.
In the absence of the leaf spring 302, the anamorphic lens 305 is warped upward or downward by the generation of this stress, and the scanning line is bent in a quadratic curve.

Such a phenomenon is dealt with by a force acting between the leaf spring 302 and the adjusting screw 308.
The pressing force acting on the anamorphic lens 305 by the adjusting screw 308 and the elastic force acting on the leaf spring 302 make the leaf spring 303 strong enough to counteract the occurrence of warpage due to the tensile stress or compression stress (overcome the spring force of the leaf spring 303). By overcoming the frictional force generated in the above and assisting the expansion or expansion / contraction of the anamorphic lens 305, it is possible to suppress the occurrence of the above-mentioned quadratic scanning line bending.

As another solution, the frictional force may be reduced by making the portion of the anamorphic lens 305 in contact with the leaf spring 303 easy to slide to reduce the tensile stress or the compressive stress.
As the method, it is possible to increase the surface accuracy of the contact portion of the anamorphic lens 305, increase the hardness, apply a lubricant, insert a smooth member in the contact portion, etc. is there.

  Note that the above-mentioned adjusting screw can be corrected to a scanning curve with a quadratic curve if it is basically disposed at one central portion, but it is disposed at a plurality of locations along the main scanning direction. When it is deployed at a total of three locations in between 310 and M-type or W-type bending occurs due to the pressing force and elastic force at the center and the tensile or compressive stress due to the frictional force at both ends Can be corrected.

In FIG. 8, the support plate on which the anamorphic lens is mounted is positioned by fitting the projection 318 formed at the end into the 327 between the positioning guides 324 provided on the optical housing side, and is biased downward in the figure. The leaf springs 326 attached to the support portions 328 provided on the optical housings at both ends are bridged and supported.
The end portions 320 and 323 of the support plate 301 and the positioning guides 324 and 325 have a shape along an arc centered on “O”, and are supported by plate springs 326 so that corresponding portions are in contact with each other. Is done.

  The stepping motor 315 is fixed to the optical housing, a feed screw formed at the tip of the shaft is screwed into the screw hole of the movable cylinder 316, and the notch 321 formed at one end of the support plate and the concave portion of the movable cylinder 316 are fitted. As a result, the sub-scanning direction (the height direction of the anamorphic lens) can be displaced by the rotation of the stepping motor 315.

  As a result, the anamorphic lens 305 can follow the forward / reverse rotation of the stepping motor 315 to adjust the rotation γ with “O” (see FIG. 9) as the rotation center in the plane orthogonal to the optical axis, and accordingly, in the sub-scanning direction. The generatrix of the anamorphic lens is tilted, and the scanning line as the imaging position after passing through the anamorphic lens is tilted.

  In the embodiment, the adjustment screw 308 is provided in all anamorphic lenses including the fourth station serving as a reference, and the scanning of other stations is aligned so that the direction and amount of the reference scan line bend during manufacture are aligned. The lines are aligned, and the tilt adjustment described above can be performed while maintaining this state.

  In FIG. 1, substrates 138, 139 and 140, 141 on which photosensors are mounted are arranged on the scanning start side and the scanning end side of the image recording area, and the scanned beams are detected at each station.

  In the embodiment, the substrates 138 and 140 are used as synchronization detection sensors, and are shared so that the timing of starting writing is measured based on the detection signal.

  On the other hand, the substrates 139 and 141 serve as end detection sensors, and a change in scanning speed is detected by measuring a time difference between detection signals from the synchronous detection sensor. Each semiconductor laser is detected in response to the detected change in scanning speed. By resetting the reference frequency of the pixel clock to be modulated by inversely multiplying it, the full width magnification on the transfer belt of the image recorded by each station can be stably maintained.

  Further, as shown in FIG. 10, a time difference Δt from the photodiode 152 to the photodiode 153 is measured by configuring one of the sensors by a photodiode 152 perpendicular to the main scanning direction and a non-parallel photodiode 153. Thus, the sub-scanning position shift Δy of the light beam can be detected.

The shift Δy in the sub-scanning position is calculated by using the inclination angle γ of the photodiode 153 and the scanning speed V of the light beam. Δy = (V / tan γ) · Δt
In the embodiment, the irradiation position can be controlled so that the sub-scanning resist of each color image does not shift by holding using an optical axis changing unit described later so that Δt is always constant.

  Furthermore, if the sensor is arranged on both the scanning start side and the scanning end side, the difference in sub-scanning position deviation between the ends, that is, the inclination of the scanning line can be detected, and control is performed based on the detection result. be able to. This is a feature of the invention described in claim 10.

  In other words, the above-described inclination of the scanning line is an element that causes color misregistration. In this embodiment, as shown in FIG. 1, the main scanning magnification, the detection pattern of the toner image formed on the transfer belt 105 is used. Deviations from the reference station are discriminated for the sub-scanning resist and the inclination of the scanning line, respectively, thereby preventing the occurrence of color misregistration. The occurrence of color misregistration is prevented by correcting the posture of the lens based on the detection result of the detection target.

  The optical axis correction control described above is performed at the timing of starting up the apparatus or between jobs, for example, and when the number of prints of one job increases, in order to suppress the deviation due to temperature change during the process, Correction can be applied by interruption.

  In FIG. 1, the color misregistration detection means includes an illumination LED element 154, a photosensor 155 that receives reflected light, and a pair of condenser lenses 156. In this example, the color misregistration detection means is provided at two left and right ends. , Cyan, magenta, and yellow toner images are inclined by about 45 ° from the main scanning direction to form a line pattern group 1410 called a chevron patch arranged in parallel at a predetermined pitch, and is a reference color according to the movement of the transfer belt 105 Read the difference in detection time from black. The inclination deviation of the scanning line is obtained from the sub-scanning resist difference between both ends, and is corrected by driving the above-described inclination adjusting means of the scanning line (anamorphic lens).

  Incidentally, in recent years, in order to achieve high density, the oscillation wavelength of a semiconductor laser (LD) has been shortened (because the beam spot diameter on the surface to be scanned is proportional to the wavelength of the light source).

  Conventionally, an LD having a wavelength of 780 nm has been widely used, but an LD having a wavelength of 500 nm or less has begun to be used for the above purpose. For example, 405 nm / 780 nm = 0.55, and the diameter can be reduced to about ½. This is a feature of the invention described in claim 8.

  The above-mentioned LD having a wavelength of 500 nm or less has a different constituent material from the LD having a wavelength of 780 nm, and the constituent material of the LD having a wavelength of 780 nm is generally composed of an AlGaAs system, but the LD having a wavelength of 500 nm or less is composed of a GaN system or the like. For this reason, the amount of heat generation is larger than that of an LD having a wavelength of 780 nm, and the droop characteristic is likely to be deteriorated. Therefore, in order to put an LD with a short wavelength (500 nm or less) into practical use, it is necessary to reduce the amount of heat generated by the LD.

  In order to reduce the amount of heat generated by the LD, the oscillation output of the LD may be reduced. To that end, a multi-beam light source unit combining a plurality of LDs may be configured. In the case of this embodiment, since the photosensitive drum is scanned with two light beams by combining two semiconductor lasers as light sources, the output can be half that of one case.

  As a multi-beam light source unit, a light source unit is constituted by a plurality of light sources (LD), and a plurality of light source units are combined, whereby the number of light beams scanned on the photosensitive member can be further increased (for example, four). This is a feature of the invention described in claim 7.

  Thereby, the output speed of the image forming apparatus can be improved. On the other hand, if the output speed is not changed, the rotation speed of the deflector can be reduced, and a writing optical system considering the environment, such as reduction of power consumption and heat generation, can be configured. It becomes possible.

In the above embodiments, the semiconductor laser (LD) is used as the light source. However, by using a “semiconductor laser array in which a plurality of light emitting points are monolithically arrayed” (LDA) as the light source, an equivalent effect can be obtained. it can. A divergent light beam emitted from a plurality of light emitting points may be coupled by a common coupling lens, and a plurality of combinations may be combined to form a light source unit.
Further, a multi-beam light source unit may be configured using a “surface emitting laser array in which a plurality of light emitting points are two-dimensionally arrayed” as a light source.

By installing the multi-beam light source unit as described above, a multi-beam optical scanning device can be configured.
FIG. 11 shows an image forming apparatus equipped with the optical scanning device, that is, an embodiment according to the invention of claim 9.
Around the photosensitive drum 901, a charging charger 902 that charges the photosensitive member to a high voltage, a developing roller 903 that attaches a charged toner to an electrostatic latent image recorded by the optical scanning device 900, and visualizes it, and a developing roller A toner cartridge 904 for replenishing toner and a cleaning case 905 for scraping and storing toner remaining on the drum are disposed. As described above, a plurality of lines are recorded on the photosensitive drum by scanning each surface of the polygon mirror, and two lines in the example of FIG. 1 are simultaneously recorded.

  The image forming stations are arranged in parallel in the moving direction of the transfer belt 906, and yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt at the same timing, and are superimposed to form a color image. Each image forming unit has basically the same configuration except that the toner color is different.

On the other hand, the recording paper is supplied from the paper supply tray 907 by the paper supply roller 908, and is sent out by the registration roller pair 909 in accordance with the recording start timing in the sub-scanning direction. The color image is transferred from the transfer belt, and the fixing roller The image is fixed at 910 and discharged to a paper discharge tray 911 by a paper discharge roller 912.
In the above embodiment, the optical scanning device is configured integrally, but the optical scanning device may be configured as a separate body corresponding to each color, or the optical scanning device may be configured as two bodies.

  With such a configuration, an image is formed at a speed four times that of an image forming apparatus of a type having only one photoconductor, that is, an image forming apparatus that requires four writing operations corresponding to four colors. Can be formed.

  Further, the image forming apparatus of the present invention is connected to an electronic arithmetic unit (computer or the like), an image information communication system (facsimile or the like), etc. via a network, so that a single image forming apparatus can output from a plurality of devices. An information processing system that can be processed can be formed. In addition, if multiple image forming devices are connected to the network, the status of each image forming device (the degree of job congestion, whether the power is on, whether it is broken, etc.) can be known from each output request. Thus, it is possible to select and output an image output device that is in the best condition (best suited to the user's wishes). This is a feature of the invention described in claim 11.

It is a figure for demonstrating the principal part structure of the optical scanning device by this invention. It is the figure which showed typically the state which looked at the main scanning direction of the scanning optical system in the optical scanning device by this invention. In order to explain the principle of the optical scanning device according to the present invention, it is a diagram showing the relationship between the amount of deviation of the incident beam and the scanning position (image height). It is a figure which shows typically the state by which the lens used for the optical scanning device by this invention is piled up in the subscanning direction. FIG. 5 is a diagram schematically illustrating an asymmetric shape and a lower state with respect to a lens optical axis by cutting an upper lens unnecessary portion of the lens illustrated in FIG. 4. It is a figure which shows typically the state arrange | positioned upside down with respect to the lens of a lower stage among the lenses piled up for using for the optical scanning device by this invention centering on the lens optical axis. It is a figure which shows typically the method of hold | maintaining in the state which has arrange | positioned the lens used for the optical scanning device by this invention in the upper and lower stages. It is a perspective view for demonstrating the structure of the support housing | casing of the anamorphic lens used for the optical scanning device by this invention. It is the fragmentary sectional view of the support housing | casing which looked at the mounting state of the anamorphic lens from the optical axis direction, and sectional drawing of an AA arrow direction. It is a figure explaining the detection principle of the sensor which detects the shift | offset | difference of the sub-scanning position of a light beam. 1 is an overall schematic configuration diagram of a color image forming apparatus equipped with an optical scanning device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical housing | casing 101,102,103,104 Photosensitive drum 105 Transfer belt 106 Polygon mirror 107,108,109,110 Light source unit 113,114,115,116 Cylinder lens 117,118,119 Optical axis change means 120,121 fθ lenses 122, 123, 124, 125 Anamorphic lenses 126-128 Reflection mirrors 138-141 Substrate 150 forming a synchronous sensor Liquid crystal deflecting optical element 154 LED element 155 Photo sensor 156 Condensing lens 215 Deflector 501, 502 Semiconductor laser (LD)

Claims (11)

Multiple light sources;
A deflector for deflecting light beams from a plurality of light sources;
In an optical scanning device comprising an imaging optical element that guides a plurality of deflected light beams by the deflector onto different scanned surfaces and forms an image as a light spot,
A plurality of light beams guided to different scanned surfaces enter the deflector with an opening angle in the main scanning direction,
An optical scanning device characterized in that at least one of the imaging optical elements guided to different scanning surfaces is shifted from each other in a direction orthogonal to the optical axis in the main scanning direction.   The optical scanning device according to claim 1, wherein at least one of the imaging optical elements guided to different scanning surfaces is arranged so as to overlap in the sub-scanning direction.   The imaging optical elements to be arranged in an overlapping manner are formed by shifting the optical axis from the center of the outer shape in the main scanning direction, and are arranged so as to be reversed 180 ° with respect to the optical axis in relation to other imaging optical elements. The optical scanning device according to claim 2, wherein:   The optical scanning device according to claim 2 or 3, wherein the imaging optical elements arranged in an overlapping manner have positioning references in the sub-scanning direction on both sides.   5. The optical scanning device according to claim 2, wherein the imaging optical elements arranged in an overlapping manner are integrated by adhesion.   5. The scanning apparatus according to claim 2, wherein the imaging optical elements to be arranged in an overlapping manner are integrally formed of resin.   2. The optical scanning device according to claim 1, wherein each light source is a multi-beam optical scanning device having a plurality of light emitting points and simultaneously scanning a surface to be scanned with a plurality of light beams.   8. The optical scanning device according to claim 1, wherein the wavelength of the light source is 500 nm or less. The optical scanning device according to claim 1 is mounted,
An image forming apparatus having a plurality of image bearing members, developing an electrostatic image formed on the image bearing member with each color toner, and superimposing them on a transfer member to form a color image, thereby forming a color image .   10. The color shift correction unit according to claim 9, further comprising a color shift detection means for detecting a color shift near the outermost scanning area of the image carrier, and controlling the attitude of at least one imaging optical element based on the detection result. The image forming apparatus described.   The image forming apparatus according to claim 9, further comprising a network communication function.

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