JP2004037757A - Optical scanning device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively correct or reduce pitch irregularities due to low frequency components. <P>SOLUTION: In an optical scanning device for deflecting a light beam from a light source means by a deflecting means 100, image-forming the deflected light beam on a photosensitive drum 111 by image forming means 109 and 110 and optically scanning the photosensitive drum 111, an optical axis deflecting means 107 for finely vibrating the light beam in a sub scanning direction slowly compared to the cycle of optical scanning is provided in an optical path from the light source means to the deflecting means. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical scanning device and an image forming device.
[0002]
The optical scanning device of the present invention can be suitably implemented as a writing system of a digital copying machine, a laser printer, a laser plotter, a facsimile device, and the like. The present invention can be suitably implemented as a multicolor image forming apparatus for forming an image.
[0003]
[Prior art]
Generally, in an image forming apparatus using the Carlson process, latent image formation, development, and transfer are performed in accordance with the rotation of the photosensitive drum, but the latent image is formed by eccentricity of the photosensitive drum rotation shaft and rotation speed fluctuation of the “photosensitive drum drive motor”. The time from image formation to transfer fluctuates every moment, causing unevenness in the pitch, which is the “interval (scanning line pitch) between images written in each optical scan”, in the sub-scanning direction of the transferred image, resulting in uneven density. appear.
[0004]
In addition, a plurality of photosensitive drums are arranged in the moving direction of the transfer body, and “images having different colors” on each photosensitive drum are sequentially transferred onto the transfer body and superimposed to form a multicolor or color image. In a so-called tandem-type image forming apparatus to be obtained, a color shift or a color change occurs due to a positional shift between toner images superimposed on each other due to the pitch unevenness, thereby deteriorating image quality.
[0005]
Also, in the transfer section, pitch unevenness similarly occurs due to fluctuations in the moving speed of the transfer belt or the transport belt as the “transfer body”, which causes the above-mentioned uneven density, color shift, and color change. The pitch unevenness in this case is mainly caused by the eccentricity and the rotational speed fluctuation of the transport belt that transports the transfer paper and the drive roller that drives the transfer belt.
[0006]
Therefore, in order to eliminate the density unevenness, the color shift, and the color change, the eccentricity of the photosensitive drum rotating shaft, the rotational speed fluctuation of the photosensitive belt drive motor, the eccentricity and the rotational speed of the drive roller for driving the transfer belt and the conveyance belt, and the like. Although it is only necessary to eliminate the fluctuation, it is impossible to completely eliminate the processing limit and the load fluctuation in the power transmission system, and the eccentricity and the rotation speed fluctuation cannot be suppressed to zero.
[0007]
Further, in the case of the tandem type color image forming apparatus described above, even if the optical scanning devices that form a latent image on each photoreceptor drum, if the resists of the latent images of the respective colors are not accurately aligned, the "color shift and color change" may occur. And if the inclinations of the scanning lines written by the respective optical scanning devices are different from each other, or if the degrees of the bending of the scanning lines are different from each other, a color shift or a color change will also occur.
[0008]
As a method of removing the influence of the rotation unevenness of the photosensitive drum, the time from the formation of the latent image on the photosensitive drum to the transfer is set to “an integral multiple of the period of the rotation unevenness” so that the latent image that changes periodically is changed. There has been proposed a method of canceling the phase shift between the position shift amount during formation and the position shift amount during transfer (Japanese Patent Publication No. 8-14731).
[0009]
In addition, attention is paid to the fact that pitch unevenness occurs periodically, and a method of detecting the pitch unevenness, moving a correction mirror in accordance with the rotation of the photosensitive drum, and actively controlling the optical scanning position has been proposed. Japanese Unexamined Patent Publication No. 10-197810).
[0010]
Pitch unevenness on an image is composed of "low-frequency component" caused by uneven rotation of the photoconductor drum, transfer belt, and drive roller of the conveyor belt, and "high-frequency component" caused by gear meshing in the drive transmission system. However, due to the increasing demand for image quality, high-precision gears have been used, and photoconductor drums and transfer belts, which directly affect image degradation, have been driven directly to avoid "play" in the transmission system. Is coming. In addition, high-frequency components have been reduced by increasing the inertial force with a flywheel.
[0011]
However, the influence of low frequency components due to load fluctuations and the like due to “eccentricity and assembly variation due to part processing accuracy” is inevitable, and it is becoming important how to suppress this.
[0012]
In particular, in the "tandem type color image forming apparatus", the phase and amplitude of the pitch unevenness cycle in the sub-scanning direction due to the fluctuation of the toner image transfer timing are different for each image. I couldn't be sure.
[0013]
Conventionally, in order to match the registration of the latent images, the displacement of the registration is detected by an image recorded on a transfer body, and the sub-scanning position is adjusted by changing the writing start timing.
[0014]
For the "bending and tilting" of the scanning line, a correction method for bending a reflection mirror provided in the optical path or tilting the reflection mirror in a plane parallel to the transfer surface (Japanese Patent No. 3049606), an imaging optical system The height of the optical axis of some of the lenses constituting the optical system is changed (Japanese Patent Application Laid-Open No. H11-64758), the lens itself is forcibly curved (Japanese Patent Application Laid-Open No. 10-268217), and the imaging optical system is configured. There is known a correction method of rotating some of the lenses around the optical axis (Japanese Patent Application Laid-Open No. H11-153765).
[0015]
In recent years, a lens formed by resin molding has come to be mounted as a part of the image forming means of the optical scanning device. A lens formed by resin molding has the advantage of being able to freely form a complicated curved surface shape, and has the advantage of low cost.However, even if the inclination or bending of the scanning line is adjusted at the initial stage, deformation of the lens itself due to changes in environmental temperature etc. There is a problem that the scanning line is bent or tilted due to the cause.
[0016]
In particular, the resin lens disposed at a position distant from the deflecting unit is “long in the main scanning direction” and thus tends to have low rigidity, and holds the posture by abutting one surface in the sub-scanning direction. In such a conventional method, there is a problem in that the lens is held in a "stressed state such as warpage or torsion" due to a dimensional error of the lens mounting portion, and the lens itself is distorted.
[0017]
As described in Japanese Patent Application Laid-Open No. H10-268217, when a resin lens is "forcedly curved" to try to forcibly correct the bending of a scanning line, there is a problem that the curved surface shape of the lens surface is distorted due to stress concentration. As in the method described in Japanese Patent Application Laid-Open No. H11-64758, when the light beam is allowed to pass with a bias relative to the internal refractive index of the lens distributed around the optical axis in the sub-scanning direction, the beam spot diameter on the photosensitive drum surface is reduced. Causes problems such as non-uniformity.
[0018]
In addition, since the base holding the resin lens and the outside air have different heat conductivity, a temperature difference is generated between the mounting surface in the sub-scanning direction that is in contact with the base and the opposite surface that is exposed to the outside air. There is a problem that the lens itself is distorted and bent.
[0019]
[Problems to be solved by the invention]
In view of the above, it is an object of the present invention to effectively correct and reduce "pitch unevenness mainly caused by the low frequency component".
[0020]
Another object of the present invention is to provide a tandem-type color image forming apparatus that effectively corrects periodic pitch unevenness generated in each image forming station and realizes a good color image without color shift or color change. .
[0021]
It is still another object of the present invention to reduce bending and inclination of a scanning line caused by a resin-molded lens included in an imaging unit, and to realize a good color image without color shift or color change.
[0022]
[Means for Solving the Problems]
The light scanning device according to claim 1, wherein the light beam from the light source means is deflected by the deflecting means, the deflected light beam is imaged on the photosensitive drum by the image forming means, and the light beam is scanned on the photosensitive drum. Scanning device ", which is characterized by the following points.
[0023]
That is, an "optical axis deflecting means" is provided in the optical path from the light source means to the deflecting means, and the light beam is minutely vibrated slowly in the sub-scanning direction as compared with the period of the optical scanning.
[0024]
By deflecting the light beam by the optical axis deflecting means in this manner, the position of the scanning line by the optical scanning can be moved in the sub-scanning direction, and the above-described deflection is performed in accordance with the period of the rotation unevenness of the photosensitive drum. Thereby, the unevenness of the scanning line pitch can be effectively corrected and reduced.
[0025]
Further, since the deflection of the light beam by the optical axis deflecting means is slower than the period of the optical scanning, the deflection of the light beam does not "tilt or bend the scanning line".
[0026]
The optical axis deflecting means may be a "movable mirror having a vibration mode swinging in the sub-scanning direction" (claim 2), and the movable mirror may have "a plurality of vibration modes" (claim 3). ).
[0027]
The optical axis deflecting means used in the optical scanning device according to any one of claims 1 to 3 can include "phase variable means for adjusting the phase of vibration" (claim 4). The optical axis deflecting means used in the optical scanning device according to any one of the items (4) to (11) can include "amplitude variable means for adjusting the amplitude of vibration".
[0028]
The light source means in the optical scanning device according to any one of claims 1 to 5, further comprising: a light beam that has a plurality of light emitting sources and optically scans a first line in a sub-scanning direction to start image recording by optical scanning. And a selecting means for switching the light emitting source of the light emitting device. "
[0029]
The image forming apparatus according to claim 7, wherein "the light beam from the light source means is deflected by the deflecting means, the deflected light beam is imaged on the photosensitive drum by the imaging means, and the photosensitive drum is optically scanned. An image forming apparatus that forms a latent image and transfers an image obtained by developing the latent image from a photosensitive drum onto a transfer body, and has the following features.
[0030]
That is, the light source means has a plurality of light emitting sources, and according to the time during which the photosensitive drum rotates from the writing position on the photosensitive drum by optical scanning (by the multi-beam scanning method) to the transfer position on the transfer body, " A light beam for optically scanning the first line in the sub-scanning direction for starting image recording.
[0031]
The image forming apparatus according to claim 8, wherein "the light beam from the light source means is deflected by the deflecting means, the deflected light beam is imaged on the photosensitive drum by the imaging means, and the photosensitive drum is optically scanned. An image forming apparatus that forms a latent image and transfers an image obtained by developing the latent image from a photosensitive drum onto a transfer body, and has the following features.
[0032]
That is, the time required for the photosensitive drum to rotate from the writing position on the photosensitive drum by optical scanning to the transfer position on the transfer member is slightly changed within the same image recording process.
[0033]
In the image forming apparatus according to the seventh or eighth aspect, it is possible to "vibrate the writing position on the photosensitive drum by optical scanning in the sub-scanning direction at a frequency corresponding to the rotation cycle of the photosensitive drum". 9). This vibration can be performed by the optical axis deflecting means.
[0034]
In the image forming apparatus according to the ninth aspect, it is possible to "change the amplitude of the vibration of the writing position in the sub-scanning direction according to the amount of eccentricity between the center of the photosensitive drum and the rotation axis of the photosensitive drum". 10). Such variation of the amplitude can be performed using the amplitude varying means according to the fifth aspect.
[0035]
The image forming apparatus according to the ninth aspect further comprises a detecting means for detecting a reference position in the rotation direction of the photosensitive drum, and the phase of the vibration of the writing position in the sub-scanning direction is synchronized with the detection signal from the detecting means. Is controlled ”(claim 11). Such control of the phase can be performed by using the phase changing means according to the fourth aspect.
[0036]
In the image forming apparatus according to the seventh or eighth aspect, the writing position on the photosensitive drum by optical scanning can be vibrated in the sub-scanning direction at a frequency corresponding to the rotation cycle of the drive shaft for moving the transfer body. (Claim 12) This vibration can be performed by the optical axis deflecting means.
[0037]
The image forming apparatus according to claim 7 or 8 can further include "detecting means for detecting a pitch change in the sub-scanning direction which fluctuates in the same image based on the image transferred to the transfer body". The writing position on the body drum can be vibrated in the sub-scanning direction at a cycle corresponding to the pitch variation.
[0038]
The image forming apparatus according to the twelfth or thirteenth aspect may further include a detecting means for detecting a "reference position in the moving direction" of the transfer body. It is possible to control the phase of the vibration in the sub-scanning direction of the writing position on the body drum (claim 14).
[0039]
The optical scanning device according to claim 15, wherein "the light beams from the plurality of light source means are deflected by the deflecting means, and the deflected light beams are applied to the photosensitive drum corresponding to the respective light beams by the plurality of imaging means. An optical scanning device which forms an image and performs optical scanning on each photosensitive drum at the same time, has the following features.
[0040]
That is, the image forming device has a “substrate common to each image forming element” that holds an image forming element that constitutes a part of the image forming unit at “an arrangement position facing each photoconductor drum”, and the base is “each photoconductor”. A contact surface formed equidistant from the drum, and holds the attitude of the imaging element within the contact surface.
[0041]
In the optical scanning device according to the fifteenth aspect, the "imaging elements forming a part of the imaging means" are formed at both ends of the lens portion in the main scanning direction and contact the contact surface of the base. The lens unit may be provided with a flange portion that comes into contact with the lens unit, and the lens unit does not have a position regulating unit in the sub-scanning direction. In this case, it is preferable that “the cross-sectional area of the imaging element in the sub-scanning direction be the smallest at the flange portion”.
[0042]
It is preferable that the imaging element in the optical scanning device according to claim 15, 16, or 17 is “a resin lens (resin lens) formed by injection molding and arranged with the gate portions of the imaging elements aligned in the same direction”. (Claim 18).
[0043]
The optical scanning device according to any one of claims 15 to 18, further comprising "a positioning unit for abutting each imaging element in a sub-scanning direction within a contact surface, and a sub-scanning of each imaging element by the positioning unit." Direction can be aligned "(claim 19).
[0044]
The optical scanning device according to any one of claims 15 to 19, further comprising "positioning means for abutting each imaging element in the sub-scanning direction within the contact surface", and making the abutting portion variable. (Claim 20).
[0045]
An optical scanning device according to claim 21, wherein each of the light beams from the plurality of light source means is deflected by the deflecting means, and each of the deflected light beams is applied to the photosensitive drum corresponding to each of the light beams by the plurality of imaging means. An optical scanning device which forms an image and performs optical scanning on each photosensitive drum at the same time, has the following features.
[0046]
That is, an image forming element constituting a part of the image forming means is arranged to face each photosensitive drum, and at least one side of the image forming element in the sub-scanning direction has a tensile stress or a compressive stress in the main scanning direction. Is provided, and the amount of warpage of the imaging element in the sub-scanning direction can be adjusted.
[0047]
This "stress generating means" can be provided integrally with the imaging element (claim 22).
[0048]
An image forming apparatus according to claim 23, wherein "the light beams from the plurality of light source means are deflected by the deflecting means, and the deflected light beams are formed on the photosensitive drums corresponding to the respective light beams by the plurality of image forming means. The latent image is formed by simultaneously performing optical scanning on each photosensitive drum to form a latent image, and the image obtained by developing the latent image is sequentially transferred from each photosensitive drum to a common transfer body and transferred to the transfer body An image forming apparatus of a type in which a registration error of each image is detected by a detection unit on the basis of each of the obtained images is characterized by the following points.
[0049]
That is, an image forming element constituting a part of the image forming means is arranged to face each photosensitive drum, and the amount of tilt of the image forming element in the sub-scanning direction is determined based on the registration error detected by the detecting means. To adjust.
[0050]
An image forming apparatus according to claim 24, wherein "the light beams from the plurality of light source means are deflected by the deflecting means, and the deflected light beams are formed on the photosensitive drum corresponding to the respective light beams by the plurality of image forming means. The latent image is formed by simultaneously performing optical scanning on each photosensitive drum to form a latent image, and the image obtained by developing the latent image is sequentially transferred from each photosensitive drum to a common transfer body and transferred to the transfer body An image forming apparatus of a type in which a registration error of each image is detected by a detection unit on the basis of each of the obtained images is characterized by the following points.
[0051]
That is, an image forming element constituting a part of the image forming means is arranged to face each photosensitive drum, and the amount of warpage of the image forming element in the sub-scanning direction is determined based on the registration error detected by the detecting means. adjust.
[0052]
Needless to say, the optical scanning device described in any one of claims 15 to 22 can have the optical axis deflecting means in claim 1, and the optical axis deflecting means is described in claims 2 and 3. It may be a “movable mirror having a vibration mode that swings in the sub-scanning direction” or a “movable mirror having a plurality of vibration modes”. The optical axis deflecting means may include the "phase varying means for adjusting the phase of the vibration" according to claim 4 and may include the "variable amplitude means for adjusting the amplitude of the vibration".
[0053]
The light scanning device according to any one of claims 15 to 22 has a light source device similar to that in claim 6, wherein the light scanning device has a plurality of light emitting sources and starts image recording by optical scanning in the sub-scanning direction. And selecting means for switching the light source of the light beam for optically scanning the leading line. "
[0054]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments will be described.
FIG. 1 shows an embodiment of the optical scanning device. FIG. 1 shows a “part that optically scans one photosensitive drum” in a tandem-type color image forming apparatus that shows the “image forming part” in FIG. To avoid confusion, the reference numerals in FIG. 1 are different from those in FIG.
[0055]
The “image forming unit” of the tandem-type color image forming apparatus illustrated in FIG. 6 includes four photosensitive drums 601, 602, 603, and 604 arranged along a moving direction of a peripheral surface of a transfer belt 605 that is a transfer body. Then, the electrostatic latent images written and formed on the photosensitive drums 601 to 604 by optical scanning are visualized with toners of different colors, and the obtained toner images are sequentially transferred to a transfer belt 605 and superimposed to form a color image. Then, the color image is transferred and fixed on a sheet-shaped recording medium (not shown), for example, a recording sheet, to form a color image.
[0056]
In the optical scanning device that optically scans the photosensitive drums 601 to 605, a polygon mirror 606 serving as a “deflecting unit” is used in common, and the light beam deflected by the polygon mirror 606 is imaged on a corresponding photosensitive drum. A part of the lens forming the “means” is shared by a plurality of photosensitive drums.
[0057]
Each of the light source units 607 and 608 is housed in the same unit as a pair of “two semiconductor lasers that emit light beams deflected by the same deflecting and reflecting surface” of the polygon mirror 606. The embodiment of FIG. 6 will be described later in detail.
[0058]
Referring to FIG. 1, what is shown in FIG. 1 corresponds to, for example, a portion that optically scans the photosensitive drum 602 with a light beam from the light source unit 607 in the configuration of FIG.
[0059]
In FIG. 1, light beams emitted from a semiconductor laser 101 for optically scanning a photosensitive drum 111 and a “semiconductor laser 102 for exposing another photosensitive drum” are converted into parallel light beams by coupling lenses 103 and 104, respectively. And is incident from the same surface of the combining prism 105 in which the parallelogram prism and the trapezoidal prism are combined.
[0060]
The light beam from the semiconductor laser 101 is transmitted through (the trapezoidal prism of) the combining prism 105 as it is, and the light beam from the semiconductor laser 102 is sequentially reflected by a pair of parallel reflecting surfaces of the parallelogram prism. The beam "emits" at a predetermined interval in the sub-scanning direction, "approaching" the beam.
[0061]
Each light beam passes through the “position decentered in the sub-scanning direction from the central axis” of the cylinder lens 106, is refracted at the position of the deflecting and reflecting surface of the polygon mirror 100 so as to “intersect in the sub-scanning direction”, and the movable mirror 107. , 108 to form a “long line image in the main scanning direction” near the position of the deflecting reflection surface of the polygon mirror 100, and become a light beam deflected at a constant angular velocity by the constant rotation of the polygon mirror 100.
Hereinafter, only the light beam directed to the photosensitive drum 111 will be described.
[0062]
The light beam deflected by the polygon mirror 100 passes through the fθ lens 109 and the toroidal lens 110 as “imaging means”, and forms an image in the form of a spot on the photosensitive surface of the photosensitive drum 111 by the action of these lenses. The photosensitive surface is optically scanned.
[0063]
In this embodiment, the fθ lens 109 and the toroidal lens 110 are formed in “a narrow strip shape in the sub-scanning direction”.
[0064]
The movable mirror 107 has a function of deflecting a light beam for optically scanning the photosensitive drum 111 in the sub-scanning direction, and is an “optical axis deflecting unit” for the light beam.
The semiconductor lasers 101 and 102 are “a monolithically formed semiconductor laser array in which a plurality of light emitting sources are arranged in an array at a pitch of more than 10 μm”, and include a coupling lens 103, a cylinder lens 106, an fθ lens 109, and a toroidal lens. By designing the “composite imaging magnification in the sub-scanning direction: β” by 110 so that β = p / d with respect to the pitch of the light emitting source: d, the light beam from each light emitting source is The light spot formed on the drum has a pixel pitch: p corresponding to the recording density.
[0065]
The optical scanning is performed by a “multi-beam scanning method”, and an appropriate one of a plurality of light emitting sources can be selected for writing the first line.
[0066]
As described above, the light beams from the semiconductor lasers 101 and 102 intersect in the sub-scanning direction near the polygon mirror. By doing so, the light beam from each semiconductor laser deflected by the polygon mirror 100 can be separated in the sub-scanning direction and directed to a separate photosensitive drum. In FIG. 1, a light beam from a semiconductor laser 101 is guided to a photoreceptor drum 111 by two return mirrors 112 and 114 after being deflected by a polygon mirror.
[0067]
In FIG. 1, reference numeral 113 denotes a "synchronous detection sensor", which takes the timing of starting writing in the main scanning direction.
[0068]
In FIG. 1, the optical path of the light beam from the semiconductor laser 102 is omitted. In this embodiment, the movable mirrors 107 and 108 are a common “movable mirror module”, but each movable mirror may be separately provided for each light beam.
[0069]
FIG. 2 is an exploded perspective view of a “movable mirror module” as “optical axis deflecting means” using movable mirrors indicated by reference numerals 107 and 108 in FIG. 1 (indicated by reference numerals 201 and 202 in FIG. 2).
[0070]
The movable mirror module 200 has first and second movable mirrors 202 and 203 arranged in parallel in the sub-scanning direction supported by a support substrate 201 formed of a sintered metal or the like, and a cover 205 formed in a cap shape. And the light beam enters and exits through a glass window 204 provided at the opening of the cover 205. An “inert gas” is sealed in the sealed interior.
[0071]
The “movable mirror substrate” is configured by joining a Si substrate 206 and a Si support frame 207 via an insulating film. The Si substrate 206 is made of a Si substrate having a thickness of 60 μm, and the “peripheries of the first and second movable mirrors 202 and 203 and the torsion beams 208 and 209 supporting the movable mirrors” are cut off by etching. 202 and 203 are formed so as to be joined to the fixed frame 210 by torsion beams 208 and 209, respectively. The first and second torsion beams 208 and 209 are arranged parallel to each other in the main scanning direction.
[0072]
In the plane of the Si substrate 206, comb-shaped irregularities are formed at both end portions of the movable mirrors 202 and 203 and both end portions of the fixed frame 210 in a direction orthogonal to the torsion beams 208 and 209 so as to mesh with each other. ing. A “metal coating” of Au or the like is deposited on the surface of the movable mirrors 202 and 203 and the irregularities formed on the fixed frame 210, and the irregularities of the movable mirrors 202 and 203 are formed by the first and second movable electrodes, The concave and convex portions of the fixed frame are used as first and second fixed electrodes.
[0073]
When a voltage is applied to the first and second fixed electrodes, an electrostatic force is generated between the first and second fixed electrodes, and the movable mirrors 202 and 203 individually rotate by a small angle while twisting the torsion beams 208 and 209. By periodically applying a pulsed voltage to the fixed electrode, each of the movable mirrors 202 and 203 can be oscillated.
[0074]
At this time, if the width and length of the torsion beams 208 and 209 are set in accordance with the “resonance frequency inherent in the vibrating part”, the amplitude can be increased by resonance, and the applied current for driving can be reduced, thereby consuming less power. Although the power can be reduced, the resonance frequency is set to "a sufficiently high resonance frequency (200 Hz or more with respect to the vibration accompanying the rotation)" in order to prevent the resonance due to the vibration transmission accompanying the rotation of the photosensitive drum or the like. It is preferable to keep it.
[0075]
Conversely, the resonance frequency may be set so as to correct pitch fluctuation (banding) in the sub-scanning direction due to vibration transmission.
[0076]
As described above, by making the fixed and movable electrodes comb-shaped, it is possible to "increase the electrode length by making the outer peripheral length as long as possible" and obtain a larger electrostatic torque at a low voltage.
[0077]
The Si support frame 207 has an opening at the center of the Si substrate having a thickness of 200 μm and fixes the supporting portion of the Si substrate 206 so that the opening serves as a swing space for the movable mirrors 202 and 203. The lead terminal 212 is provided so as to penetrate the support substrate 201 via an insulating material, and each fixed electrode and a pad portion 213 wired on the substrate surface of the Si substrate 206 and an end protruding above the lead terminal 212. By connecting the parts to each other by wire bonding, sealed inner and outer electric wirings are formed.
[0078]
The cover 205 is fitted into a step provided on the outer periphery of the support substrate 201, and a glass window 204 is joined to the light beam emission opening from inside the cover.
[0079]
The dimensions of the “movable mirror” in the above are length: 2a, width: 2b, thickness: d, length of the torsion beam is L, width is c, density of Si: ρ, material constant: G, and the movable mirror Moment of inertia and torsion beam spring constant are
Moment of inertia: I = (4abρd / 3) · a²
Spring constant: K = (G / 2L) · ｛cd (c²+ D²) / 12｝
And the resonance frequency: f is
f = (1 / 2π) · (K / I)^1/2= (1 / 2π) · ｛Gcd (c²+ D²) / 24LI｝^1/2
It becomes. Since the length of the beam: L and the deflection angle: θ are in a proportional relationship, A is a constant
θ = (A / I) f²,
And the deflection angle θ is inversely proportional to the moment of inertia I.
[0080]
Therefore, when increasing the resonance frequency f, the deflection angle θ decreases unless the moment of inertia I is reduced. In the embodiment being described (FIG. 2), in the embodiment, the back sides of the movable mirrors 202 and 203 are "lightened" to reduce the weight and reduce the moment of inertia: I.
[0081]
Using the dielectric constant of air: ε, electrode length: H, applied voltage: V, distance between electrodes: δ, the electrostatic force between the fixed electrode and the movable electrode: F is
Electrostatic force between electrodes: F = εHV²/ 2δ
Where B is a constant and the deflection angle: θ = B · F / I
It can be expressed as.
[0082]
From this equation, it can be seen that the longer the electrode length H is, the larger the deflection angle θ becomes. In the embodiment described, the electrode length: H is increased by making the fixed electrode / movable electrode comb-shaped, so that a driving torque of 2n times the number of comb teeth: n can be obtained.
[0083]
Using the velocity of the movable mirror: υ, the area: E, the density of the gas around the movable mirror: η, the viscous resistance of the gas acting on the movable mirror: P is represented by
Viscous resistance: P = C · ηυ²・ E³,
It becomes.
[0084]
In the embodiment being described, as described above, the “movable mirror is kept in a sealed state”, and a reduced pressure inert gas is sealed therein to reduce the viscous resistance and to form the metal film formed on the movable mirror. Prevents alteration due to chemical change of
[0085]
FIG. 3A shows another example of the movable mirror. This movable mirror has "two vibration modes" (claim 3).
[0086]
The movable mirror shown in FIG. 3A is obtained by etching a Si substrate 306, a movable mirror 303, a first torsion beam 308 supporting the same, a movable frame 309 connected to the torsion beam 308, and a movable mirror 309. A second torsion beam 310 for connecting the frame 309 to the fixed frame 311 is formed separately from the fixed frame 311 as shown in the figure.
[0087]
Both ends of the movable mirror 303 and the movable frame 309 are formed with irregularities in a comb shape so as to sandwich the torsion beams 308 and 310, and irregularities are also formed on the movable frame and the fixed frame side facing the comb teeth so as to mesh with the comb teeth. ing. A metal film such as Au is vapor-deposited on the uneven portions formed on the movable mirror 303, the movable frame 309, and the fixed frame 311. The uneven portions on both ends of the movable mirror 303 are used as the first movable electrode and the corresponding uneven portions on the movable frame 309. The first fixed electrode and the uneven portion on both ends of the movable frame are defined as a second movable electrode, and the corresponding uneven portion of the fixed frame 311 is defined as a second fixed electrode.
[0088]
The movable mirror 303 and the movable frame 309 are individually rotated by a small angle by twisting the torsion beams 308 and 310 by an electrostatic force generated between the movable mirror 303 and the movable electrode facing each other by applying a voltage to the first and second fixed electrodes. Oscillates by applying a pulsed voltage periodically.
[0089]
At that time, since the torsion beams 308 and 310 are formed coaxially, if "voltages of different frequencies" are applied to the first and second fixed electrodes, "an amplitude in which two vibration modes overlap in the same direction" With this, the movable mirror 308 can be swung.
[0090]
The movable mirror shown in FIG. 3A is also provided on a Si support frame, sealed with a support substrate and a cover, and the inside is depressurized and sealed with an inert gas similarly to the one shown in FIG. . Electrical wiring and the like are performed in the same manner as in FIG.
[0091]
In each of the above examples, the oscillating mirror is driven by electrostatic force, but it is also possible to drive the oscillating mirror using a piezoelectric element or the like.
The optical axis deflecting means is not limited to the above-mentioned movable mirror, and any suitable means may be used as long as it can deflect the optical axis direction of the light beam. For example, as shown in FIG.₃A light beam can be made incident on an optical waveguide substrate 320 made of, for example, ZnO or the like, and the optical axis of the light beam can be deflected by a surface acoustic wave.
[0092]
By adjusting the frequency of the surface acoustic wave excited by the comb-shaped electrode (transducer) 321, the deflection angle of the light beam can be changed. Reference numerals 322 and 323 each denote a “diffraction grating for allowing a light beam to enter and exit the optical waveguide substrate 320”.
[0093]
Prior to proceeding with the description, the image formation by the image forming unit (of the tandem type color image forming apparatus) shown in FIG. 6 will be briefly described.
6, the light beams emitted from the light source units 607 and 608 pass through the cylinder lenses 609 and 610 and pass through the movable mirror modules 611 and 612 (the same as those described with reference to FIG. 2). Thus, the light is deflected by the polygon mirror 606 in the opposite direction.
[0094]
As described with reference to FIG. 1, the light beams from each light source unit are divided into upper and lower stages in the sub-scanning direction, and the two light beams are respectively symmetrically provided to cylinder lenses 609 and 610 symmetrically from the central axis. The incident light is decentered in the sub-scanning direction, intersects the sub-scanning direction in the vicinity of the deflecting reflection surface of the polygon mirror 606, and passes through the common fθ lenses 613 and 614 for the two light beams deflected in the same direction by the polygon mirror 606. The mirrors 615 and 636 are guided to the photosensitive drum 601 and the mirrors 616 and 617 are routed to the photosensitive drum 602, and the toroidal lenses 618 and 619 are individually provided.
[0095]
Similarly, the light is guided to the photosensitive drums 303 and 304 via two folding mirrors and a separate toroidal lens for each light beam. To avoid complication of the drawing, reference numerals are not given to the folding mirror and the toroidal lens for guiding the deflected light beam to the photosensitive drums 303 and 304.
[0096]
Each of the light source units 607 and 608 has a configuration in which a holder for holding the plurality of semiconductor lasers, the coupling lens, and the synthetic prism described above and a printed circuit board on which a drive circuit for the semiconductor laser is mounted are attached to the back surface. The light source unit is configured to be rotatable around a cylindrical portion that emits a light beam. By rotating and adjusting this portion, the writing phase of each of the upper and lower light beams is finely adjusted.
[0097]
The photoconductor drums 601, 602, 603, 604 are individually and directly connected to the motor shafts of the motors 621, 622, 623, 624, and the motors 621, 622, 623, 624 have a "common frequency", and Is rotated clockwise.
[0098]
The transfer belt 605 is driven to rotate counterclockwise by a motor 626 connected to a driving roller 625, and is held under a predetermined tension by driven rollers 627 and 628.
[0099]
In the example being described, the interval between the “transfer positions”, which are the contact positions between the respective photosensitive drums and the transfer belt 605, is set to an integral multiple of the circumference of the drive roller 625, and occurs due to the eccentricity of the drive roller 625 or the like. "The phases of the periodic speed fluctuations match each other". A “detector that reads a reference position of each image” formed on the transfer belt 605 is provided near the driving roller 625.
[0100]
The detector 629 includes a CCD area sensor 631 and an objective lens 630, and three sets (center and both ends) are provided in the main scanning direction, and a predetermined detection pattern formed by a reference color (black) toner image is enlarged. To read the “registration position of main scanning and sub-scanning”, and compare it with the multicolor (cyan, magenta, yellow) toner image to obtain the “registration shift amount” as the registration position in the main and sub-scanning directions. The “scanning line inclination” is detected based on the detection difference between the two positions on both ends in the main scanning direction, and the “scanning line bending” is detected based on the difference between the midpoint and the center of the two ends.
[0101]
In the case of detecting the pitch fluctuation, the “interval (time difference) of the caterpillar-shaped pattern (not shown)” formed at a constant period in the sub-scanning direction is read as “strip of the stripe” at a predetermined sampling time, and the frequency is analyzed. The phase and the amplitude of the movement speed fluctuation of the transfer belt 605 and the phase difference between the registration position and the transfer position are detected.
[0102]
FIG. 5 shows the relationship between the writing position WR on the photosensitive drum DR and the transfer position TR. Symbol O indicates the center of rotation of the photosensitive drum DR. The rotation center O is shifted from the center axis of the photosensitive drum DR. The writing position WR and the transfer position TR are set to form an angle α.
[0103]
Therefore, if the rotation center O of the photoconductor drum DR is not eccentric and each rotation speed is constant, the time t during which the photoconductor drum DR rotates from the writing position WR to the transfer position TR is constant.
[0104]
However, time “t” differs for each photoconductor drum due to “drum diameter variation” of the photoconductor drum DR and deviation of the writing position WR. When the rotation center O of the photoconductor drum DR is eccentric due to the processing accuracy, the time: t changes periodically for each photoconductor drum.
[0105]
In this embodiment, the time required for the photosensitive drum DR to rotate from the writing position WR to the transfer position TR: “drum diameter variation” or the time due to the deviation of the writing position WR among the variations and periodic changes in t: The change in t is corrected by selecting the optimum one from among the light emitting sources in the semiconductor laser array in the light source unit and writing the leading line (claims 6 and 7).
[0106]
FIG. 7 shows a case where the semiconductor laser array in the light source unit has “five light emitting sources”. Reference numerals LD-1 to LD-5 denote light spots formed by the light beams emitted from these five light emitting sources at the writing position WR on the photosensitive drum DR (FIG. 5). When scanning by the multi-beam scanning method is performed using such a semiconductor laser array, optical scanning of five scanning lines can be performed at one time.
[0107]
In FIG. 7, N denotes a deflecting / reflecting surface of a polygon mirror for simultaneously deflecting five light beams, and N + 1 denotes a deflecting / reflecting surface for performing the next deflection of the deflecting / reflecting surface. As shown in the figure, five scanning lines are optically scanned each time the deflecting reflection surface is switched.
[0108]
When writing is started on the photosensitive drum DR (FIG. 5) at the writing position WR, light spots LD-1, LD-2, LD-3, LD formed by a plurality of light beams deflected by the same deflecting and reflecting surface. -4 and LD-5, the light spot (the light spot in FIG. 7) that has the smallest difference from the “registration position of the reference color (right side in FIG. 7)” detected by the detector 629 (FIG. 6) described above. The spot LD-4) is selected as a “light spot for writing the first line”. In this case, in the deflection (writing start) by the deflecting / reflecting surface N, two scanning lines by the light spots LD-4 and LD-5 are written, and in the subsequent deflection by the deflecting / reflecting surface N + 1, five scanning lines are multi-beam scanned.
[0109]
FIG. 10 is a block diagram of a “circuit for selecting a light emitting source for writing the first line”. The same reference numerals as those of the light spots LD-1 to LD5 are used to represent the light emitting sources in the semiconductor laser array. As shown in FIG. 10, the image data is distributed to the buffer memories M1 to M5 every five lines and temporarily stored by the multiplexer MP1 in the preceding stage.
[0110]
In the multiplexer MP2 at the subsequent stage, the head line is selected based on the reference position data, the output semiconductor laser is switched, and the contents stored in the buffer memories M1 to M5 are read and written in synchronization with the synchronization signal for each polygon mirror. The light emitting sources LD-1 to LD-5 of the semiconductor laser array are driven via the control unit WCT. At this time, the image data not written by the deflection by the same deflection reflection surface is stored until the deflection by the next deflection reflection surface.
[0111]
As described above, by selecting the light spot that minimizes the difference from the resist position of the reference color as the light spot for writing the top line, the variation in the drum diameter of the photosensitive drum and the shift of the writing position cause It is possible to satisfactorily correct the “variation between the photosensitive drums” of the time: t.
[0112]
In that case, the timing in the main scanning direction until the image is written with the synchronization detection signal as a trigger is based on the above-described registration position detection result for each light scanning unit, so that the center position between the reference color and each image area matches. The image frequency for modulating the semiconductor laser is inversely multiplied by a change in the image width so that the image width (full-width magnification) is adjusted again by the writing control unit, and is determined stepwise by the frequency division ratio. By selecting the closest set value, each image area is made to overlap.
[0113]
The setting of the registration position in the sub-scanning direction and the main scanning direction is periodically performed so as to be suitable for the use environment of the image forming apparatus by using a preparation period before an image forming job or a waiting period between jobs. Is
[0114]
Hereinafter, the correction of the periodic change of the time t due to the eccentricity of the rotation center of the photosensitive drum or the transfer belt will be described.
[0115]
The angle γ in FIG. 5 is an angle between the writing position WR and the rotation center O as viewed from the center axis of the photosensitive drum DR, and is referred to as an eccentric angle γ. In order to correct the periodic change of the time: t due to the eccentricity of the rotation center of the photosensitive drum or the transfer belt, the movable mirror is set to the eccentric angle: γ in the “period of one rotation of the photosensitive drum DR”. Accordingly, the writing position is periodically changed so that the time: t is constant by micro-vibrating the amplitude and phase of the swing of the movable mirror in accordance with the amplitude and phase of the periodic change.
[0116]
When the center axis of the photosensitive drum is eccentric with respect to the rotation axis, the distance from the rotation axis to the photosensitive surface: r is the drum radius when there is no eccentricity: r₀Where eccentricity is Δr and r₀When focusing on an arbitrary position on the photosensitive drum, this portion has a specific peripheral speed when the photosensitive drum rotates at a constant speed. Therefore, when the peripheral speed is high, the light writing position by optical scanning is shifted to the side away from the transfer unit (upstream of the rotation of the photosensitive drum), and when the peripheral speed is low, the writing position is shifted to the side near the transfer unit. By shifting the position, the time: t during which the photosensitive drum rotates from the writing position to the transfer unit is made uniform (this means that, if the writing position is not changed, the time that fluctuates temporally: t (8).
[0117]
Since the peripheral speed of the photosensitive drum when passing through the writing position periodically changes with one rotation of the photosensitive drum as a cycle, the movable mirror shown in FIG. By deflecting in the scanning direction and changing the writing position in accordance with the change in the peripheral speed of the photosensitive drum, the time t can be kept constant. At this time, the fluctuation of the light beam in the sub-scanning direction due to the movable mirror is “slow enough compared to the period of the optical scanning”. Is extremely small and practically negligible.
[0118]
FIG. 8A shows an example of “recording pitch fluctuation in the sub-scanning direction on an image”. This fluctuation is a combination of "large undulation (2)" generated in one rotation cycle of the photosensitive drum and "small undulation (3)" generated in one rotation cycle of the drive roller of the transfer belt.
[0119]
What has been described above is a case where the above-mentioned "large waviness" is corrected by "periodic deflection of the light beam in the sub-scanning direction" by the movable mirror shown in FIG. 2, as shown in FIG. 8 (1). In the case where the recording pitch fluctuates due to "the two vibration modes overlap", the movable frame 309 is vibrated in accordance with the "large swell" by using the movable mirror shown in FIG. By vibrating the 303 according to the “small undulation”, the writing position can be reliably displaced in the sub-scanning direction according to the “swell” as shown in FIG. 8A. The time: t can be kept constant irrespective of the presence of the “swell” of 1).
[0120]
As described above, even when the movable mirror is vibrated in the cycle focusing on only the one having the larger amplitude (FIG. 8B) of the two “undulations” having different vibration modes, the pitch fluctuation at the transfer position is obtained. If the amplitude and the phase are made equal so that is canceled, the pitch unevenness due to the periodic fluctuation of the time: t can be effectively reduced.
[0121]
Since the above-described pitch fluctuation is a characteristic inherent to the image forming apparatus of the drive transmission system, it is effective to make the amplitude and phase uniform at the initial adjustment stage so that the pitch fluctuation at each transfer position is canceled. Can be reduced.
[0122]
FIG. 8 shows the case where “speed fluctuation occurs at a constant cycle”. However, even with respect to the speed fluctuation whose cycle changes spontaneously on the way due to a load fluctuation in the image forming process, the timing of occurrence is not limited to the timing. If the movable mirror is tilted in accordance with the above, the correction can be similarly performed.
[0123]
FIG. 9 is a block diagram illustrating a “movable mirror driving circuit”. The voltage supplied to each electrode 94 of the movable mirror shown in FIG. 2 generates a pulse train corresponding to the oscillation cycle of the movable mirror in the pulse width forming section 91 based on the reference clock.
[0124]
In the PLL circuit 92, the phase of the pulse train is matched with a reference position detection signal in the photoconductor drum rotation direction generated from the encoder of the photoconductor drum drive motor or the detection of a registration mark drawn on the transfer belt. (Claim 4). The gain adjuster 93 sets the amplitude of the swing of the movable mirror according to the speed fluctuation amount (the speed fluctuation amount in the writing unit on the peripheral surface of the photosensitive drum) and applies it to the electrode 94.
[0125]
The pulse width generation unit 91 can generate a pulse train having a constantly changing frequency or a single pulse, and can change the oscillation period of the movable mirror according to the correction data.
[0126]
Here, the description of the imaging means will be slightly supplemented with reference to FIG. 6. The fθ lenses 613 and 614 are “hybrid lenses in which aspherical components are bonded to a spherical lens formed by glass polishing by resin molding”, and a toroidal lens is used. 618 and 619 are formed by injection molding.
[0127]
The toroidal lenses provided corresponding to the respective photosensitive drums 601 to 604 are all the same as the toroidal lens 618. Therefore, taking the toroidal lens 618 as an example, the toroidal lens 618 will surround the lens section 632 and the lens section 632. And a flange 633 protruding from both ends in the main scanning direction (longitudinal direction) are integrally formed, and one end of the flange 633 is filled with a resin at the time of molding. Is provided.
[0128]
Since the toroidal lens is long, it has a "warp at the time of molding", for example, a uniform warpage due to a partial cooling time difference after injection molding. The four toroidal lenses 618, 619 and the like provided corresponding to the photoconductor drums 601 to 604 are arranged such that "the gate portions of the lenses are aligned in the same direction and the warpage of each toroidal lens is the same". (Claim 18). In this way, the direction of the scan line bending due to the warpage of the toroidal lens can be aligned with respect to each photosensitive drum.
[0129]
The flange portion 633 has a thin plate shape and has a lower sub-scanning section coefficient than the lens portion 632 reinforced by the rib portion 634, so that even if a torsional stress is applied, it is absorbed by this flange portion. . In this manner, the lens portion itself of the toroidal lens can be prevented from being greatly twisted by torsional stress.
[0130]
Hereinafter, “correction of the inclination of the scanning line” will be described with reference to FIG.
12, the toroidal lens denoted by reference numeral 618 in FIG.
For example, when the scanning line of the photosensitive drum 601 by the optical scanning has an “inclination”, this inclination is caused to rotate around the optical axis in a state where the toroidal lens 1201 “abuts in a plane perpendicular to the optical axis”. Correct by adjusting.
[0131]
As shown in FIG. 12, each of the toroidal lenses 1201 and the like face each of the photoconductor drums 601 to 604 and are provided on the housing bottom surface 1200 (which is a “base (claim 15)” common to the toroidal lenses) in the optical axis direction. The projections 1211 projecting toward the photosensitive drum at the center in the main scanning direction are engaged with the recesses 1213 on the housing bottom surface 1200 side, and are positioned in the main scanning direction (longitudinal direction). You.
[0132]
The toroidal lens 1201 and the like are pressed by the first leaf spring 1215 against the eccentric cams 1204 and 1205 provided so as to abut on the “one side surface” of the flange portion 1202 at both ends, and are positioned in the sub-scanning direction (claim). Item 19), the lower surface is pressed against the housing reference surface 1212 by the second leaf spring 1214 and positioned and held in the optical axis direction.
[0133]
One eccentric cam 1205 is screw-fixed in an adjusted state as a reference, and the other eccentric cam 1204 is for adjustment and is rotatable by a pulse motor 1207 via a pair of bevel gears 1206. Thus, the toroidal lens 1201 and the like are initialized with the eccentric cam 1205 for reference in the sub-scanning direction while the lower surface of the flange portion is in contact with the housing reference surface 1212, and are tilted. Is adjusted by an eccentric cam 1204 for adjustment (Claim 20), and a sub-scanning inclination due to a deviation between optical scanning units or an inclination of the axis of the photosensitive drum is detected from a recorded image on the transfer belt, and also over time. I am able to make corrections.
[0134]
In the example being described, in order to match multiple colors based on the black image, in the optical scanning device that writes the black image, all the eccentric cams that come into contact with the toroidal lens 1201 (corresponding to the photosensitive drum 601) are fixed by screws. And
[0135]
The reference eccentric cam 1205 can be used for correction of the above-mentioned "registration position in the sub-scanning direction" by providing a pulse motor in the same manner as the adjustment cam 1204 so as to be rotatable.
[0136]
With reference to FIG. 13, correction of “scanning line bending” will be described.
In the image forming apparatus shown in FIG. 6, as described above, the light beams that are incident on the same deflecting / reflecting surface and deflected so as to optically scan different photosensitive drums intersect at the deflecting / reflecting surface position in the sub-scanning direction. Therefore, they are inclined with respect to a plane orthogonal to the rotation axis of the polygon mirror, and therefore, the trajectory of the scanning line does not become a straight line but bends in the sub-scanning direction from the center to the periphery.
[0137]
The bending of the scanning line is also caused by an axis shift between the fθ lens and the toroidal lens which form the imaging means. In the example in the description, the curvature of the scanning line is corrected by “curving the toroidal lens 1201 and the like in a direction opposite to the curvature of the scanning line” so that the scanning line is straight on the photosensitive drum.
[0138]
The toroidal lens 1201 will be described as an example with reference to FIGS. As shown in FIG. 14A, the toroidal lens 1201 is supported on the housing reference surface 1212 by flange portions 1202 at both ends (the numbers in parentheses correspond to the reference numerals in FIG. 6), and the cross section in FIG. As shown in the figure, a "holding method in which the lens portion does not have any restricted portions in the sub-scanning direction" is adopted.
[0139]
As shown in FIG. 13, both ends of a shape memory metal plate 1208 curved in an arch shape are joined to one of the rib portions of the toroidal lens 1201.
As shown in FIG. 12, a thin film resistor 1209 is attached to the outer surface of the shape memory metal plate 1208, and the temperature of the shape memory metal plate 1208 can be changed by controlling the current flowing to the thin film resistor 1209. It has become. The shape memory metal plate 1208 can “change the curvature arbitrarily depending on the temperature”, and the amount of curvature of the toroidal lens 1201 can be adjusted by applying the stress of expansion and contraction due to the change in the curvature to the toroidal lens 1201 in the main scanning direction. .
[0140]
That is, when the shape memory metal plate 1208 is extended (shrinked), the toroidal lens 1201 warps so as to be convex (concave) toward the shape memory metal plate 1208. If the curvature of the shape memory metal plate 1208 is stored in advance so that a stress is applied in either direction at a low temperature, even if the temperature is lower than room temperature, the focal line in the sub-scanning direction will be bent in the scanning line on the photoconductor. Can be corrected by curving so as to cancel out.
[0141]
That is, the shape memory metal plate 1208 and the thin film resistor 1209 constitute "stress generating means (claim 21).
[0142]
If the direction in which the scanning line bends due to a change in the environmental temperature is uniform, the direction in which the toroidal lens 1201 and the like warp can be set in advance in accordance with the direction, so that the direction can be effectively set without using a thin film resistor. Bending caused by warpage can also be reduced.
[0143]
Further, it is also possible to provide a shape memory metal plate on both outer surfaces of the rib portion in the sub-scanning direction of the toroidal lens 1201 and the like, and cancel the bending of the scanning line by the balance between the shape memory metal plates.
[0144]
In the same configuration as described above, the curvature may be expanded and contracted by attaching a piezoelectric element to an arch-shaped plate material (in this case, it is not necessary to be a shape memory metal plate), and at least an arbitrary amount in the main scanning direction of the toroidal lens may be provided. If a tensile or compressive stress is applied between the two points, the effect of correcting the scanning line bending is the same as described above.
[0145]
FIG. 11 shows an example of an image forming apparatus equipped with the image forming unit described above. In this figure, the four photosensitive drums 601 to 604 in FIG.
[0146]
Taking the photoconductor drum 901 (photoconductor drum on which a black image is written) at the left end in FIG. 11 as an example, a charging charger 902 that charges the photoconductor drum 901 at high pressure and an optical scanning device 900 are provided around the photoconductor drum 901. A developing roller 903 for attaching a "charged toner" to the written electrostatic latent image to make it visible, a toner cartridge 904 for supplying toner to the developing roller 903, and scraping off toner remaining on the photosensitive drum after transfer A cleaning case 905 to be stored is arranged.
[0147]
As described above, a plurality of lines, that is, five lines in the example being described, are optically scanned by the multi-beam method on the photosensitive drum 901 by scanning per one deflecting reflection surface of the polygon mirror to write an image.
[0148]
The four photosensitive drums 901 and their peripheral devices are arranged in the moving direction of the transfer belt 906, and yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt 906 at the same timing, and are superimposed. Form a color image.
[0149]
The recording paper (recording medium on the sheet) on which the color image is transferred and fixed is fed from a paper feed tray 907 by a paper feed roller 908, sent out by a registration roller pair 909 at the timing of recording start, and transferred. The color image is transferred from the belt 906, the color image is fixed by the fixing roller 910, and is discharged onto the discharge tray 911 by the discharge roller 912.
[0150]
In the example described above, as shown in FIG. 6, a registration shift is detected from an image recorded on the transfer belt 605, and based on the detection result, a light emitting source that emits a light beam for writing a head line is selected. However, the present invention is not limited to this. For example, “the position of the light beam in the sub-scanning direction in the optical scanning device may be detected” and the light emitting source for the first line may be selected.
[0151]
A “sensor unit” for detecting the position of the light beam in the sub-scanning direction is indicated by reference numeral 400 in FIG. The sensor unit 400 is provided for each photoconductor drum, but has the same configuration. This sensor unit is shown in FIG.
[0152]
The sensor unit has two pin photodiodes 401 and 402 having “a linear light receiving surface that is long in one direction”. The pin photodiode 401 is provided with the longitudinal direction of the light receiving surface parallel to the sub-scanning direction, and the pin photodiode 402 is provided with the longitudinal direction of the light receiving surface inclined with respect to the sub-scanning direction. The sensor unit is provided for each photosensitive drum, is mounted on a common substrate 403 as shown in FIG. 12, and is provided “outside the writing area” in the optical path from the toroidal lens 1201 and the like to the photosensitive drum 601 and the like. . The substrate 403 is fixed to the lower side surface of the housing bottom 1200 on the reference side in the tilt adjustment of the toroidal lens 1201 and the like by screws 406.
[0153]
Returning to FIG. 4, the light spots LD-1, LD-2, LD-3, LD-4, and LD-5 are "scanned by a predetermined pitch" in the sub-scanning direction (the vertical direction in the figure). Therefore, the detection time differences t1 to t5 between the pin photodiodes 401 and 402 are different from each other, and when the sub-scanning position is shifted, this time uniformly expands and contracts.
[0154]
Therefore, a preset time difference: t₀By selecting a light-emitting source that emits a light beam that forms a light spot closest to the above, it is possible to minimize the displacement of the leading line and maintain the interval between the writing sections. The sensor units may be provided at both ends in the main scanning direction, and the inclination of the scanning line may be detected together with the detection of the displacement in the sub-scanning direction.
[0155]
By the way, the housing for holding the optical element of the optical scanning device is often made of “a material having a relatively large coefficient of thermal expansion” such as aluminum die-casting. As shown, the housing bottom surface 1200 is warped about the fastening portions 1218 at both ends as a fulcrum.
[0156]
When the housing bottom surface 1200 is warped in this manner, the columns 1216 and 1217, etc., which are implanted on the housing bottom surface 1200 and support the return mirrors 112 and 114 (615 and 636 in FIG. 6), also fall, and the reflection angle shifts. However, at this time, since the reflecting surfaces of the folding mirrors 112 and 114 are opposed to each other, even if the reflection angles are shifted as described above, the directions of the shifts are reversed by the turning mirrors 112 and 114 to cancel each other. Therefore, it is possible to effectively reduce the variation of the light beam arrival position due to the warpage of the housing bottom surface 1200.
[0157]
However, since the deviation of the arrival position of the light beam can be detected as the deviation of the scanning line in the sub-scanning direction, the folding mirror does not have to be configured as described above. The light may be guided to the toroidal lens by one folding mirror.
[0158]
Further, in the example described above, the convex surface of the toroidal lens is directed toward the photosensitive drum, but the concave surface may be directed toward the photosensitive drum.
[0159]
【The invention's effect】
As described above, according to the present invention, a novel optical scanning device and a new image forming apparatus can be realized. As described above, the optical scanning device of the present invention can effectively correct the periodic fluctuation of the scanning line pitch due to the low frequency component, the registration deviation when performing color image formation, or the bending or inclination of the scanning line, Image writing can be realized.
[0160]
Therefore, the image forming apparatus of the present invention using such an optical scanning device can effectively reduce unevenness in image density due to uneven scanning line pitch, color shift in color image formation, color change, etc. Can be formed.
[Brief description of the drawings]
FIG. 1 is a diagram showing one embodiment of an optical scanning device (showing a portion of one image forming unit shown in FIG. 6 that optically scans one photosensitive drum).
FIG. 2 is a diagram for explaining a possible mirror as an optical axis deflecting means.
FIG. 3 is a diagram showing another example of the optical axis deflecting means.
FIG. 4 is a diagram for explaining a sensor unit that detects a shift of a scanning line in a sub-scanning direction.
FIG. 5 is a diagram for explaining a relationship between a writing position and a transfer position with respect to a photosensitive drum.
FIG. 6 is a diagram illustrating an image forming unit according to an embodiment of the image forming apparatus.
FIG. 7 is a diagram for explaining the invention described in claim 7;
FIG. 8 is a diagram for explaining the invention described in claim 1;
FIG. 9 is a block diagram of a circuit for driving a movable mirror.
FIG. 10 is a block diagram of a circuit for selecting a light emitting source of the semiconductor laser array.
FIG. 11 is a diagram for describing an embodiment of an image forming apparatus.
FIG. 12 is a diagram for explaining correction of the inclination of a scanning line.
FIG. 13 is a diagram for explaining correction of scanning line bending.
FIG. 14 is a diagram for explaining a holding state of the toroidal lens in the imaging unit.
FIG. 15 is a diagram for explaining the warpage of the bottom surface of the housing in the optical scanning device and its influence.
[Explanation of symbols]
101 semiconductor laser array
106 cylinder lens
107, 108 optical axis deflecting means
100 polygon mirror
109 ° fθ lens
110 ° toroidal lens
112, 114 fold mirror

Claims (24)

An optical scanning device that deflects the light beam from the light source means by the deflecting means, forms the deflected light beam on the photosensitive drum by the imaging means, and optically scans the photosensitive drum;
An optical scanning device, comprising: an optical axis deflecting unit that slightly vibrates a light beam in a sub-scanning direction slowly in a sub-scanning direction in comparison with an optical scanning period in an optical path from a light source unit to a deflecting unit. The optical scanning device according to claim 1,
An optical scanning device, wherein the optical axis deflecting means is a movable mirror having a vibration mode that swings in the sub-scanning direction. The optical scanning device according to claim 2,
An optical scanning device, wherein a movable mirror serving as an optical axis deflecting unit has a plurality of vibration modes. The optical scanning device according to any one of claims 1 to 3,
An optical scanning device, wherein the optical axis deflecting means includes a phase varying means for adjusting a phase of the vibration. The optical scanning device according to any one of claims 1 to 4,
An optical scanning device, wherein the optical axis deflecting means includes amplitude varying means for adjusting the amplitude of vibration. The optical scanning device according to any one of claims 1 to 5,
An optical scanning device comprising: a light source unit having a plurality of light emitting sources; and a selecting unit that switches a light emitting source of a light beam that optically scans a first line in a sub-scanning direction in which image recording by optical scanning is started. The light beam from the light source means is deflected by the deflecting means, the deflected light beam is imaged on the photosensitive drum by the image forming means, and the photosensitive drum is optically scanned to form a latent image. In an image forming apparatus of a system for transferring an image obtained by developing
Sub-scanning in which the light source means has a plurality of light-emitting sources, and starts image recording by optical scanning according to the time during which the photosensitive drum rotates from a writing position on the photosensitive drum by optical scanning to a transfer position on a transfer body. An image forming apparatus comprising: a selection unit that switches a light source of a light beam that optically scans a leading line in a direction. The light beam from the light source means is deflected by the deflecting means, the deflected light beam is imaged on the photosensitive drum by the image forming means, and the photosensitive drum is optically scanned to form a latent image. In an image forming apparatus of a system for transferring an image obtained by developing
An image forming apparatus, wherein a time required for a photosensitive drum to rotate from a writing position on a photosensitive drum by optical scanning to a transfer position on a transfer body is minutely changed within the same image recording process. The image forming apparatus according to claim 7, wherein
An image forming apparatus, wherein a writing position on a photosensitive drum by optical scanning is vibrated in a sub-scanning direction at a frequency corresponding to a rotation cycle of the photosensitive drum. The image forming apparatus according to claim 9,
An image forming apparatus, wherein the amplitude of vibration of a writing position in the sub-scanning direction is adjusted according to the amount of eccentricity between the center of the photosensitive drum and the rotation axis of the photosensitive drum. The image forming apparatus according to claim 9,
An image forming apparatus comprising: detecting means for detecting a reference position in a rotation direction of a photosensitive drum, and controlling a phase of a vibration of a writing position in a sub-scanning direction in synchronization with a detection signal from the detecting means. The image forming apparatus according to claim 7, wherein
An image forming apparatus, wherein a writing position on a photosensitive drum by optical scanning is vibrated in a sub-scanning direction at a frequency corresponding to a rotation cycle of a drive shaft for moving a transfer body. The image forming apparatus according to claim 7, wherein
Detecting means for detecting a pitch fluctuation in the sub-scanning direction which fluctuates in the same image based on the image transferred to the transfer body; An image forming apparatus that vibrates in a scanning direction. The image forming apparatus according to claim 12, wherein
Detecting means for detecting a reference position of the transfer body in the moving direction, and controlling a phase of vibration in a sub-scanning direction of a writing position on the photosensitive drum by optical scanning in synchronization with a detection signal from the detecting means. An image forming apparatus comprising: Each light beam from a plurality of light source means is deflected by a deflecting means, and each deflected light beam is imaged on a photosensitive drum corresponding to each light beam by a plurality of image forming means, and is simultaneously formed on each photosensitive drum. In an optical scanning device that performs optical scanning,
An imaging element constituting a part of the imaging means is held at a position facing each photosensitive drum, and has a common base for each of the imaging elements,
An optical scanning device, wherein the base has an abutment surface formed at an equal distance from each of the photosensitive drums, and holds the attitude of the imaging element within the abutment surface. The optical scanning device according to claim 15,
An imaging element constituting a part of the imaging means includes a lens portion, and a flange portion formed at both ends of the lens portion in the main scanning direction and abutting against a contact surface of the base,
An optical scanning device, wherein the lens unit has no position regulating means in the sub-scanning direction. The optical scanning device according to claim 16,
An optical scanning device, wherein a sub-scanning cross-sectional area of an imaging element is minimized at a flange portion. The optical scanning device according to claim 15, 16 or 17,
An optical scanning device, wherein the imaging elements are resin lenses formed by injection molding, and the directions of gate portions of the respective imaging elements are aligned. The optical scanning device according to any one of claims 15 to 18,
An optical scanning device comprising positioning means for abutting each imaging element in a sub-scanning direction within a contact surface, wherein the abutting directions of the imaging elements in the sub-scanning direction by these positioning means are aligned. The optical scanning device according to any one of claims 15 to 19,
An optical scanning device comprising positioning means for abutting each imaging element in a sub-scanning direction within a contact surface, and having a variable abutting portion. Each light beam from a plurality of light source means is deflected by a deflecting means, and each deflected light beam is imaged on a photosensitive drum corresponding to each light beam by a plurality of image forming means, and is simultaneously formed on each photosensitive drum. In an optical scanning device that performs optical scanning,
An imaging element that constitutes a part of the imaging means is arranged to face each photosensitive drum,
A stress generating means for applying a tensile stress or a compressive stress in the main scanning direction is provided on at least one side in the sub-scanning direction of the imaging element, and the amount of warpage of the imaging element in the sub-scanning direction is made variable. Optical scanning device. The optical scanning device according to claim 21,
An optical scanning device, wherein the stress generating means is provided integrally with the imaging element. Each light beam from a plurality of light source means is deflected by a deflecting means, and each deflected light beam is imaged on a photosensitive drum corresponding to each light beam by a plurality of image forming means, and is simultaneously formed on each photosensitive drum. An optical scanning is performed to form a latent image, and an image obtained by developing the latent image is sequentially transferred from each photosensitive drum to a common transfer member. In the image forming apparatus of the system of detecting the registration deviation of the detection means,
Image forming elements constituting a part of the image forming means are arranged so as to face each of the photosensitive drums, and the amount of tilt of the image forming elements in the sub-scanning direction is determined based on the registration error detected by the detecting means. An image forming apparatus characterized by adjusting. Each light beam from a plurality of light source means is deflected by a deflecting means, and each deflected light beam is imaged on a photosensitive drum corresponding to each light beam by a plurality of image forming means, and is simultaneously formed on each photosensitive drum. An optical scanning is performed to form a latent image, and an image obtained by developing the latent image is sequentially transferred from each photosensitive drum to a common transfer member. In the image forming apparatus of the system of detecting the registration deviation of the detection means,
An image forming element constituting a part of the image forming means is arranged to face each photosensitive drum, and the amount of warping of the image forming element in the sub-scanning direction is adjusted based on the registration error detected by the detecting means. An image forming apparatus comprising:

Images