JP2012008244A - Optical scanning device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact optical scanning device that takes advantage of a feature of an oscillation mirror to prevent image degradation, and to provide an image forming apparatus.SOLUTION: The optical scanning device includes a scanning unit U1 and a scanning unit U2 arranged adjacent to each other. The scanning unit U1 includes: a light source 10K, an oscillation mirror 11 for scanning a laser beam from the light source 10K in a polarized manner; and a scanning lens 14K that collects the laser beam scanned in a polarized manner by the oscillation mirror 11 toward a scanned surface. The scanning unit U2 includes: a light source 10M; a different oscillation mirror 11 for scanning a laser beam from the light source 10M in a polarized manner; and a scanning lens 14M that collects the laser beam scanned in a polarized manner by the oscillation mirror 11 toward a scanned surface. The optical scanning device further includes: beam detectors 21 and 22 to be shared by both scanning units U1 and U2 to detect passage of a predetermined laser beam scanned in a polarized manner in each of the scanning units U1 and U2; and a control means that controls drive of the oscillation mirrors 11 in the scanning units U1 and U2 on the basis of the detection result of the beam detectors 21 and 22.

Description

  The present invention relates to an optical scanning apparatus and a color image forming apparatus having a vibrating mirror used in a laser raster writing optical system.

  Conventionally, in order to realize high-speed printing and high image quality of a color machine, it has been necessary to rotate the polygon mirror at a high speed of 25000 rpm or more and with high accuracy. This high-speed rotation increases the power consumption of the polygon scanner, and the heat generation adversely affects an optical element such as a scanning lens. Specifically, the temperature rise of the scanning lens closest to the polygon scanner. That is, the heat generated from the polygon scanner transfers heat to the optical housing, or the temperature of the scanning lens rises due to radiation. Actually, the temperature of the scanning lens is not raised uniformly, but it has a temperature distribution especially in the main scanning direction, which is the longitudinal direction, due to the distance from the heat source (polygon scanner) or the influence of the heat transfer coefficient and airflow of each material. . If there is a temperature distribution in the main scanning direction, particularly the shape accuracy and refractive index of the scanning lens change, the spot position of the laser beam fluctuates, and the image quality deteriorates. This problem is particularly noticeable in the case of plastics having a large coefficient of thermal expansion.

  In the color machine, the laser beam corresponding to each color (yellow, magenta, cyan, black) is scanned, so that the temperature deviation of the optical element corresponding to each color becomes a problem in addition to the above problem. The temperature deviation causes a shift in the relative positional relationship between the beam spots corresponding to each color, resulting in an image color shift.

  In order to solve the above problems, a vibrating mirror using a resonance phenomenon is being studied instead of a polygon mirror deflector. This method has low power consumption and has the advantage of reducing temperature rise of the scanning lens used in the optical scanning device, temperature deviation of optical elements in the color machine, and vibration of the optical scanning device. Conventionally, an optical scanning device that scans a plurality of scanned surfaces with a single oscillating mirror has been studied (see Patent Documents 1 to 3), but a laser beam corresponding to a plurality of colors is incident on the oscillating mirror. Since it is necessary to enter the sub-scanning direction at an angle (so-called oblique incidence), there is a problem that the optical scanning device is enlarged (particularly, the height in the sub-scanning direction).

  Further, in an optical scanning device that scans a plurality of scanned surfaces using a plurality of vibrating mirror deflectors (see Patent Documents 1 to 4), scanning characteristics and scanning amplitudes differ depending on the scanning frequency and vibration amplitude of the vibrating mirror. In the case of color mixing as in a color image, there has been a problem of image deterioration due to color misregistration / color unevenness. Further, even when the vibration amplitude is controlled to be constant, there is a problem in that the color information cannot be strictly eliminated because the amplitude information is performed by different beam detectors for each vibration mirror.

  The present invention has been made in view of the above-described problems in the prior art, and while minimizing the size of an image while taking advantage of the features of a vibrating mirror such as reducing power consumption and vibration to ensure stability over time of an image, It is an object of the present invention to provide an optical scanning device that suppresses deterioration and an image forming apparatus using the optical scanning device.

The present invention provided to solve the above problems is as follows. In addition, the site | part and code | symbol etc. which respond | correspond in the form for implementing this invention in a parenthesis are shown.
[1] At least one light source (light sources 10K and 10M) that emits laser light, a vibrating mirror (vibrating mirror 11) that deflects and scans laser light from the light source, and laser light that is deflected and scanned by the vibrating mirror A plurality of oscillating mirror scanning units (scanning units U1, U2) including scanning imaging means (scanning lenses 14K, 14M) for condensing toward the surface to be scanned are arranged, and are common to the adjacent oscillating mirror scanning units. A beam detector (beam detectors 21 and 22) that detects the passage of a predetermined laser beam that is arranged and is deflected and scanned in each of the adjacent vibrating mirror scanning units, and based on the detection result of the beam detector And control means (FIG. 10) for controlling driving of the vibrating mirrors of the adjacent vibrating mirror scanning units. An optical scanning device (optical scanning device 5, FIG. 1, FIG. 2, FIG. 10).
[2] The oscillating mirror scanning unit is disposed on each of the oscillating mirror having reflecting surfaces (reflecting surfaces 441a and 441b) on the front and back surfaces, and on the front and back surfaces of the oscillating mirror, and emits laser light to oscillate the oscillating mirror. Two light sources (light sources 10K and 10M) that are incident on the corresponding reflecting surfaces of the mirror and two laser beams that are reflected and deflected and scanned in the opposite directions by the vibrating mirror toward the corresponding scanned surfaces, respectively. The optical scanning device according to [1] (optical scanning device 5, FIGS. 1 to 3), characterized by comprising condensing scanning image forming means (scanning lenses 14K and 14M).
[3] In each of the adjacent oscillating mirror scanning units, among the two laser beams that are deflected and scanned, a light source related to the laser beam that passes through the beam detector is defined as a laser beam incident angle to the reflecting surface of the oscillating mirror. 2. The optical scanning device according to [2] (FIG. 1), wherein the scanning positions on the surface to be scanned are arranged so as to have the same relationship.
[4] The laser light emitted from the two light sources is incident on the reflecting surface so that both the front and back surfaces of the vibrating mirror are orthogonal to the rotation axis of the vibrating mirror. 3].
[5] The circuit board (substrate 19) on which a plurality of the beam detectors are mounted is disposed between the adjacent vibrating mirror scanning units (scanning units U1, U2). 1] to [4]. The optical scanning device according to any one of FIGS.
[6] The beam detector includes a photodiode (light receiving unit PD1) in which one light receiving element is electrically divided to form the two light receiving surfaces (light receiving surfaces PD1M and PD1Y), and the adjacent vibrations. [1], wherein predetermined laser beams (scanning beams (M) and (Y)) deflected and scanned in the mirror scanning units (scanning units U1 and U2) pass through the two light receiving surfaces, respectively. To [5] (5).
[7] The two laser beams respectively passing through the two light receiving surfaces are reciprocally scanned in the light receiving surface with the incident angles and the light amounts corresponding to the light receiving surfaces being matched. Optical scanning device (FIG. 13).
[8] The beam detector includes an amplitude variation (amplitude amount, FIG. 7) with respect to a target amplitude of each oscillating mirror of each of the adjacent oscillating mirror scanning units, and a difference between the amplitude center of the oscillating mirror and the scanning center of the laser beam ( Any one of the above [1] to [7], which detects an offset amount, FIG. 8), and a phase fluctuation (phase difference, FIG. 9) from the reference phase clock of the amplitude waveform of the vibrating mirror. The optical scanning device according to 1.
[9] The control means oscillates all the oscillating mirrors of the plurality of oscillating mirror scanning units based on the same drive frequency (drive frequency fD), and based on the detection result of the beam detector, The optical scanning device according to any one of [1] to [8], wherein the optical scanning device is controlled so as to match the scanning characteristics (FIG. 10).
[10] The optical scanning according to any one of [1] to [9], wherein the plurality of oscillating mirror scanning units perform scanning of laser light in the same direction on all scanned surfaces. Device (Figure 1).
[11] An image forming apparatus (FIG. 16) comprising the optical scanning device (optical scanning device 5) according to any one of [1] to [10].

According to the optical scanning device of the present invention, the control means controls each oscillating mirror scanning unit adjacent to each other while sharing the drive frequency signal, the target amplitude amount, the allowable offset amount, and the reference phase clock, and the beam detector is adjacent. Since they are arranged in common with the oscillating mirror scanning unit, the adjacent oscillating mirror scanning units control each scanning beam so that the amplitude amount, the offset amount, and the phase difference match even with different oscillating mirrors. As a result, it is possible to match the scanning characteristics for all the scanned surfaces. In addition, it is possible to reduce the size of the entire optical scanning device while taking advantage of the features of the oscillating mirror, such as reducing power consumption and vibrations and ensuring the stability of images over time.
According to the image forming apparatus of the present invention, since the scanning characteristics of the scanning beam for all the photoconductors are matched by using the optical scanning apparatus of the present invention, it is possible to always form a good color image with little color shift. .

It is a main scanning sectional view showing the composition of the principal part of the optical scanning device concerning the present invention. It is a sub-scanning sectional view showing a configuration of a main part of the optical scanning device according to the present invention. It is detail drawing which shows the structure of a vibration mirror. It is a disassembled perspective view of a vibration mirror. It is a perspective view which shows the structure of the vibration mirror of the form mounted in an optical housing. It is a figure which shows the relationship between the drive voltage waveform of an oscillation mirror, an amplitude waveform, a drive reference signal, the output signal of a beam detector, and a reference phase clock in the optical scanning device of the present invention. It is a figure which shows the mode of the fluctuation | variation of the amplitude of the amplitude waveform of a vibration mirror. It is a figure which shows the mode of the fluctuation | variation of the offset of the amplitude waveform of a vibration mirror. It is a figure which shows the mode of a fluctuation | variation of the phase of the amplitude waveform of a vibration mirror. It is a block diagram which shows the structure of a vibration mirror control means. It is a figure which shows the relationship between a beam detector and the laser beam scanned. It is a figure which shows the relationship between the output waveform of a beam detector, and a threshold voltage. It is a figure which shows the incident state of the laser beam in the reflective surface of a vibration mirror when injecting into the light-receiving part of a beam detector. FIG. 5 is a diagram in which the main scanning beam diameter is plotted for each image height when the characteristics of the optical element are as designed in the optical scanning device of the present invention. It is a figure which shows the relationship between the drive frequency and amplitude of a vibration mirror. 1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus according to the present invention.

The configurations of the optical scanning device and the image forming apparatus according to the present invention will be described below.
FIG. 1 is a main scanning sectional view (viewed from above) showing the configuration of the main part of the optical scanning device according to the present invention, and FIG. 2 shows the configuration of the main part of the optical scanning device according to the present invention. It is subscanning sectional drawing (figure seen from the side). Here, the optical scanning device 5 appropriately uses four photosensitive members 3Y, 3M, 3C, and 3K (hereinafter referred to as subscripts Y, M, C, and K) in the image forming apparatus (FIG. 16, described later) of the present invention. And Y: yellow, M: magenta, C: cyan, and K: black.) Is an example of an apparatus arranged above the image forming units arranged in parallel. In order to facilitate understanding, only the main part is shown in a simplified manner.

  As shown in FIGS. 1 and 2, the optical scanning device 5 includes two vibrating mirror scanning units (hereinafter referred to as scanning units) U1 and U2. Here, the configurations of the scanning units U1, U2 are the same, and the scanning units U1, U2 are arranged symmetrically with respect to the apparatus center line C. Hereinafter, the scanning unit U1 will be described in detail by taking a representative example.

  The scanning unit U1 includes at least one light source that emits a laser beam (also referred to as laser light), a vibrating mirror (also referred to as a vibrating mirror deflector) that deflects and scans the laser beam from the light source, and deflection scanning using the vibrating mirror. Scanning imaging means for condensing the laser beam to be scanned toward the surface to be scanned, and more specifically, a vibrating mirror (vibrating mirror 11) having a reflecting surface on the front and back surfaces, and the front and back surfaces of the vibrating mirror Two light sources (light sources 10M and 10K) that are arranged on the respective sides and emit laser beams and enter the corresponding reflecting surfaces of the vibrating mirror, and are reflected in the opposite directions by the vibrating mirror and deflected and scanned. Scanning image forming means (scanning lenses 14M, 14K) for condensing the two laser beams to be scanned toward the corresponding scanned surfaces, respectively.

  Specifically, the scanning unit U1 includes two light sources 10M and 10K corresponding to each color (M, K), a vibrating mirror 11 that is a light deflecting unit that deflects and scans the laser beams from the light sources 10M and 10K, and Scanning lenses 14M and 14K, which are scanning imaging optical systems that guide the scanning surfaces of the two photosensitive drums 3M and 3K, are provided, and these components are housed in an optical housing.

  Here, the oscillating mirror 11 is disposed substantially at the center of the scanning unit U1, has reflection surfaces on both the front surface and the back surface, and deflects and scans each incident laser beam to the opposite side.

3 is a detailed view of a mirror substrate 440 that is a main part of the vibrating mirror 11, and FIG. 4 is an exploded perspective view thereof.
The mirror substrate 440 is composed of a movable part that forms reflection surfaces (mirror surfaces) on the front and back surfaces to form a vibrator, a torsion beam that supports the rotating part, and a frame that forms a support part. The Si substrate is etched by etching. Cut out to form.

  In this embodiment, the wafer is manufactured using a wafer in which two substrates of 60 μm and 140 μm called SOI (Silicon on Insulator) substrates are bonded in advance with an oxide film interposed therebetween. First, a torsion beam 442, a vibration plate 443 on which a planar coil is formed, and a reinforcing beam (not shown) forming a skeleton of a movable part by a dry process by plasma etching from the surface side of a 140 μm substrate (second substrate) 461, The remaining part of the frame 447 is penetrated to the oxide film, and then the movable mirror part 441 and the frame 447 are formed by anisotropic etching such as KOH from the surface side of the 60 μm substrate (first substrate) 462. The remaining part is left up to the oxide film, and finally, the oxide film around the movable part is removed and separated to form a vibrating mirror structure.

  Here, the torsion beam 442 and the reinforcing beam 444 had a width of 40 to 60 μm. It is desirable that the moment of inertia I of the vibrator is small in order to increase the deflection angle. On the other hand, the mirror surface is deformed by the inertial force. Therefore, in this embodiment, the movable portion is thinned.

  Further, an aluminum thin film is vapor-deposited on the surface side of the 60 μm substrate 462 to form a reflection surface 441a. On the surface side of the 140 μm substrate 461, a terminal 464 wired with a coil pattern 463 and a torsion beam is formed. Naturally, a configuration may be adopted in which a thin film permanent magnet is provided on the diaphragm 443 side and a planar coil is formed on the frame 447 side. Further, a reflection surface 441b is also formed on the opposite side of the reflection surface 441a. The reflective surface 441b is closely contacted and positioned with high precision on the movable portion by a method such as adhesion of a mirror portion formed separately from the processing process of the reflective surface 441a. Note that the optical characteristics (reflectance), physical characteristics (density, Young's modulus, thermal expansion coefficient), and shape characteristics (dimensions, thickness, flatness) of the reflective surface 441b are the same as those of 441a, and initial and temporal temperature fluctuations. The configuration is such that the scanning characteristics at the time do not differ.

  On the mounting substrate 448, a frame-shaped pedestal 466 for mounting the 140 μm substrate 461 and the 60 μm substrate 462 and a yoke 449 formed so as to surround the vibration mirror are provided, and the yoke 449 is opposed to the end of the movable mirror. A pair of permanent magnets 450 that generate a magnetic field in a direction orthogonal to the rotation axis are joined to each other with the S and N poles facing each other. The 140 μm substrate 461 and the 60 μm substrate 462 are mounted on a pedestal 466, and a Lorentz force is generated on each side parallel to the rotation axis of the coil pattern 463 by passing a current between the terminals 464, and the torsion beam 442 is twisted to move the movable mirror unit 441. Is generated, and when the current is turned off, it returns to the horizontal state by the return force of the torsion beam.

  Therefore, by alternately switching the direction of the current flowing through the coil pattern 463 (AC signal), the movable mirror unit 441 can be reciprocally oscillated. When the current switching period is brought close to the natural frequency of the primary vibration mode of the structure constituting the oscillating mirror 11 with the torsion beam as the rotation axis, the so-called resonance frequency f0, the amplitude is excited and a large deflection angle is obtained. Can be obtained.

  On the other hand, by passing a DC component current (applying a voltage) to the coil pattern 463, the movable mirror portion 441 can be changed statically (the amplitude center is changed). However, since the resonance phenomenon is used for the amplitude operation principle, the change according to the current is within ± 1 ° in angle. By superimposing the DC component on the AC signal, the amplitude center can be changed while the vibrating mirror 11 is amplituded (deflected).

  FIG. 5 shows details of the vibrating mirror 11 mounted on the optical housing. In addition to the mirror substrate 440, a bracket 471 for maintaining and fixing the mirror posture and making electrical connection (electrode part 473), and a substrate 472 (electrical) mounted on an optical housing (not shown), with the bracket 471 fixed. Connector 474). Note that the bracket 471 is provided with an opening 471a for entering and exiting the reflection surface 441b.

  The oscillating mirror 11 is much smaller in mass and inertia of the movable part than the conventional polygon mirror, so the drive part is also miniaturized, and the power consumption can be kept low due to the high efficiency of the magnetic circuit. 1/50 or less). As a result, heat generation is reduced, and the temperature rise of the optical element and housing of the writing optical system can be substantially eliminated. In particular, with a scanning lens made of resin, there is no local temperature distribution and color Variations in the scanning position of the laser beam during image formation can be suppressed, and occurrence of color misregistration can be suppressed. Furthermore, since the mass and inertia of the movable part are small, there is little vibration transmitted to the outside (vibration due to mass imbalance) even if it is resonant vibration (1/100 or less of the polygon mirror). The vibration transmitted to the element is substantially eliminated, and the banding (roughness variation in the sub-scanning direction) at the time of image formation due to the vibration of the folding mirror, which has been generated in the polygon mirror system, can be eliminated.

  In FIG. 1, the scanning position of the maximum deflection angle of the laser beam 60 deflected and scanned by the oscillating mirror 11 is 60a, and enters the light receiving portion (light receiving element) PD1 of the beam detector 21 arranged within the maximum deflection angle. The position where the laser beam is scanned at the timing when the output signal is output is 60b, and the position where the end of the image area on the photosensitive member 3M is scanned is 60c.

  Here, as shown in FIGS. 1 and 2, the optical scanning device 5 is between the adjacent scanning units U1 and U2, and is in the main scanning direction (the deflection scanning direction of the light beam by the vibrating mirror 11, shown in FIG. A substrate 19 is provided with beam detectors 21 and 22 for detecting the passage of the laser beam at both ends thereof. At this time, a part of the light beam for writing the magenta color component image is incident on the light receiving portions (light receiving elements) PD1 and PD2 of the beam detectors 21 and 22, and the yellow color component is incident on the scanning unit U2. A part of the light beam for writing the image is made incident.

  Further, in the scanning unit U1 of FIG. 1 (upper half in the drawing), the scanning position of the edge of the image area on the photosensitive member 3M of the laser beam 60 from the light source 10M deflected and scanned by the vibrating mirror 11 is determined from 60c. Also, the laser beam at the scanning position 60b which is outside and inside the scanning position 60a having the maximum deflection angle is incident on the light receiving part PD1 of the beam detector 21 by the folding mirror 18a. In the lower half of FIG. 1, the laser beam is similarly incident on the light receiving part PD2 of the beam detector 22 by the folding mirror 18b.

  The following control is indispensable in order to make the best use of the merits of the vibrating mirror system described above, and a preferred embodiment will be described. Although the vibrating mirror 11 of the scanning unit U1 will be described in detail, the same applies to the vibrating mirror of the scanning unit U2, and the description thereof will be omitted.

FIG. 6 is a diagram showing the relationship among the drive voltage waveform, amplitude waveform, drive reference signal, beam detector output signal, and reference phase clock of the vibrating mirror in the optical scanning device of the present invention.
FIG. 6B shows the vibration mirror amplitude with respect to time. Since the oscillating mirror 11 generates a large amplitude using a resonance phenomenon, the amplitude of the oscillating mirror 11 draws a sinusoidal locus with respect to time, and the scanning speed of the laser beam deflected and scanned is not constant, but depends on the scanning position. It will be different (when there is no scanning lens). The scanning lens 14 has f · arcsin characteristics so as to be constant on the surface to be scanned even at such a scanning speed.

  Here, even if the scanning lens 14 having the above characteristics is used, fluctuations in amplitude variation of the oscillating mirror 11 as shown in FIGS. 7 to 9 occur, and therefore control is performed to suppress the fluctuations. Even if the vibration (drive) frequency of the oscillating mirror 11 is constant, the phenomenon shown in FIGS. 7 to 9 occurs, and the ideal amplitude waveform (sine waveform shown in red) all changes in the scanning position of the laser beam, resulting in image degradation. Will be generated.

FIG. 7 shows the amplitude variation. When the amplitude is larger than the target (the same is true when the amplitude is smaller), the beam detection as shown in FIG. 6 is performed in order to obtain the amplitude shown in the arrow direction. The time interval A (A ₁ , A ₂ ,... A _{n in the} figure) of the output of the detector 21 (PD1 output) and the time interval B (B1,. ..Control is performed so that the calculated value of B _n ) is constant. Specifically, the control target value is uniquely determined from the resonance frequency by averaging a plurality of times with (A ₁ + B ₁ ) / 2, (A 2 + B 2) / 2,... (A _n + B _n ) / 2. Control is performed as follows.

FIG. 8 shows the positional relationship between the amplitude center of the oscillating mirror 11 and the scanning center, and there is an offset in the amplitude waveform with respect to the scanning center (difference between the amplitude center of the oscillating mirror and the optical scanning center). This is an example. FIG. 8A and FIG. 8B show the difference depending on the offset amount. FIG. 8A shows an example in which the offset amount is at an allowable level, and FIG. 8B exceeds the allowable offset. It is an example showing the state.
In the case of FIG. 8A, the offset amount of the amplitude waveform affects the linearity and beam diameter which are optical scanning characteristics, but the offset amount does not necessarily have to be zero in consideration of the influence on the image. Specifically, the linearity error is corrected by controlling the lighting timing of the laser beam based on the image information, thereby suppressing the influence and suppressing the influence on the beam diameter. By controlling the light amount (integrated light amount) so that the electrostatic latent images are equal, the influence of the offset is reduced.

  In the first place, it is possible not to perform the control as long as it is within the allowable offset. By setting the allowable offset amount so that the deviation from the design value of linearity is 1% or less and the deviation from the design value by beam diameter is 10% or less, the influence on the image is suppressed as much as possible and the image is not required. It turns out that this is not a problem.

  In the case of FIG. 8B, it is necessary to adjust (correct) within an allowable range as described above. The adjustment is performed by superimposing a DC component corresponding to the offset amount on the driving voltage (AC component) of the oscillating mirror 11 to change the posture in the main scanning direction and adjust the amplitude center to be within the allowable offset. . Further, as another embodiment, adjustment can be made by a drive mechanism that changes the posture of the vibrating mirror 11. For example, a stepping motor is disposed on the lower surface of the substrate 472 in FIG. 5 (not shown), and the drive mechanism is disposed such that the rotational axis of the motor and the vibration axis of the vibration mirror 11 coincide. At this time, the vibration mirror 11 is adjusted within the allowable offset by changing the posture (rotation) about the vibration axis. The rotation step resolution of the stepping motor must be at least equivalent to 1/2 or less of the allowable offset amount.

  Conventionally, offset adjustment is performed in order to ideally set the offset amount to zero, and it is peculiar to the present embodiment to provide a permissible range of permissible offset. Therefore, the DC component superimposing circuit conventionally required for offset adjustment must have the performance of having an output voltage that can adjust (set to zero) all the offset amounts in FIG. 8B. Since the size and heat generation amount increase, the temperature in the optical scanning device rises, degrading the optical scanning characteristics. In addition, this increases the cost associated with an increase in circuit size. Also, the current (voltage) that is driven during offset adjustment cannot be driven indefinitely in accordance with the offset amount from the upper limit of the current rating of the oscillating mirror 11 (because the element is destroyed if the current rating is exceeded). ).

In FIG. 8B, in order to adjust the offset to within the allowable offset (as shown in the arrow direction), the calculated values of the time interval A of PD1 output and the time interval B of PD2 output as shown in FIG. Control is performed to be constant. Specifically, A ₁ -B ₁ , A ₂ -B ₂ ,... A _n -B _n are averaged several times, and it is determined by the comparator 81a in FIG. If it is within the allowable range, the control is not performed, and the offset control is performed only when the allowable offset is exceeded.

FIG. 9 shows the phase variation of the amplitude waveform of the oscillating mirror 11, and even if the phase variation with the reference phase clock signal (the waveform is not shown) as shown in FIG. Therefore, the reference phase clock for generating a signal for driving the oscillating mirror 11 as shown in FIG. 6 and the PD1 output time interval C (C ₁ , C ₂ ,... C _{n in the} figure). Control is performed so that the phase of is constant. Specifically, averaging is performed a plurality of times with C ₁ , C ₂ ... C _n , and control is performed so that the target value becomes zero. The output of the beam detector 21 that counts the time interval C is preferably an output that is the timing immediately before the image forming area (the rear end side of A). The phase is adjusted because the accuracy is higher immediately before the image writing start side (the rear end side of A), and in the case of the front end side of A, the phase accuracy at the time of image formation decreases due to phase fluctuations within the time A. It is.

  As shown in the actual amplitude state (solid line) in FIGS. 7 and 8B, when the ideal amplitude or the allowable offset is exceeded, the phenomenon is different from the ideal scanning speed, and thus the scanning position shift in the main scanning direction. . For example, image deterioration such as jitter in the main scanning direction (vertical line fluctuation) and main scanning magnification error is caused, and this is a common problem not only in color images that are mixed colors but also in monochrome images of a single color.

  On the other hand, the phase fluctuation from the reference phase clock in FIG. 9 becomes a particular problem when forming a color image. As shown in FIG. 1, a single oscillating mirror 11 scans a laser beam emitted from a light source 10 of each color onto a photoconductor 3 for each color according to an image signal. Since the deflection scanning position of each color laser beam changes, the sub-scanning position fluctuates on the image (on the intermediate transfer belt), causing color misregistration and color unevenness.

  In FIG. 1, the light source 10 is a “light source device” composed of a semiconductor laser and a coupling lens, and each color for image formation (magenta (M), black (K), yellow (Y), cyan (C )). The light source 10 is a generic name for the light sources 10M, 10K, 10Y, and 10C of the respective colors (other parts are equivalent to this). In the scanning unit U1 of FIG. 1, the light sources 10M and 10K are disposed opposite to each of the front and back surfaces of the oscillating mirror 11 with the oscillating mirror 11 therebetween, and the two semiconductor lasers of the light sources 10M and 10K are respectively M ( Light beams for writing the respective color component images of magenta) and K (black) are radiated so as to be horizontally incident on the corresponding reflecting surface of the vibrating mirror 11. Next, the light beam emitted from each semiconductor laser is converted into a light beam form (parallel light beam or weakly divergent or converging light beam) suitable for the subsequent optical system by the coupling lens, and is sub-scanned by the cylindrical lenses 12M and 12K. The beam is focused in the direction and formed as a long line image in the main scanning direction in the vicinity of the deflecting reflecting surface (reflecting surfaces 441a and 441b) of the oscillating mirror 11 serving as a deflection scanning means.

  In the oscillating mirror 11, the light beams from the light sources 10M and 10K are reflected in opposite directions and deflected and scanned. For example, of the two color deflected light beams deflected and scanned to the opposite side by the vibration of the vibration mirror 11, the magenta light beam passes through the scanning lens 14M of the scanning imaging optical system. The light beam for writing the magenta component image is condensed as a light spot on the scanned surface on the drum-shaped photoconductive photosensitive member 3M that forms the actual state of the scanned surface via the mirror 16M, and the surface of the photosensitive member 3M is collected. Optical scanning is performed in the direction of the arrow. Further, the black-side light beam passes through the scanning lens 14K of the scanning imaging optical system. The light beam for writing the black component image is condensed as a light spot on the scanned surface on the drum-shaped photoconductive photosensitive member 3K that forms the actual state of the scanned surface via the mirror 16K, and the surface of the photosensitive member 3K is collected. Optical scanning is performed in the same direction (arrow direction) as the light flux on the magenta side.

  The materials of the scanning lenses 14M and 14K are made of a plastic material that has an aspherical shape easily and at low cost. Specifically, it is made of polycarbonate having a low water absorption, high transmittance, and excellent moldability, and a synthetic resin mainly composed of polycarbonate. Is preferred.

  In the scanning unit U2, the light beams for writing the respective color component images of yellow and cyan are also reflected and deflected and scanned by the vibrating mirror 11, transmitted through the lens, and imaged as a light spot on the photosensitive member. The light source modulation driving of the image data is controlled in accordance with the vibration direction of the vibrating mirror 11 that is reciprocally oscillating so that the scanning is performed in the same arrow direction. The optical elements corresponding to the respective colors of the scanning unit U2 are not numbered, but components with “M”, which is an abbreviation for magenta, and “K”, which is an abbreviation for black. Are arranged in the same optical position for both yellow and cyan.

  Incidentally, in addition to the present embodiment, an optical scanning device in which the scanning direction is reversed on each of the scanning surfaces facing each other with the optical deflector interposed therebetween has been realized. In particular, when the optical deflector uses a rotary motor such as a polygon mirror, it is inevitable that the scanning direction is reversed. When the scanning direction is opposite, the scanning line moves at a constant speed in the sub-scanning direction, so that a difference in inclination between the scanning lines facing each other with the optical deflector interposed is generated in principle. In this embodiment, since all the scanning surfaces are scanned in the same direction, even if there is a scanning line inclination on each scanning surface, all the scanning directions are in the same direction, no inclination difference occurs, and no color shift appears. It is an effect peculiar to the oscillating mirror system capable of reciprocating that all the corresponding scanned surfaces can be set in the same direction across the optical deflector.

  Note that the scanning line inclination generated in principle is determined by the pixel density in the sub-scanning direction and the effective scanning period rate of the main scanning. In this embodiment, the pixel density in the sub-scanning direction is 600 dpi (= 42.3 μm), the effective scanning period rate is 0.2, and the scanning line inclination amount is 42.3 × 0.2 = 8.5 μm. However, since all of them are inclined by 8.5 μm in the same direction, no color shift occurs. On the other hand, in the case of the polygon mirror method, the pixel density in the sub-scanning direction is 600 dpi (= 42.3 μm), the effective scanning period rate is 0.6, and the scanning line inclination amount is 42.3 × 0.6 = 25.4 μm. The tilt amount is opposite to the scan direction when the optical deflector as shown in FIG. 1 is sandwiched, so that the tilt directions are opposite, but the scanning centers coincide, but both ends are 25.4 × 2 = 50. The color shift is 8 μm. In order to prevent this color misregistration, conventionally, a mechanism for tilting the attitude of the optical element is provided to correct the inclination of the scanning line. In the present embodiment, a mechanism for correcting the inclination of the scanning line generated in principle is not mounted.

  In the image forming apparatus, an electrostatic latent image of a color component image corresponding to each photoconductor is formed by this optical scanning. These electrostatic latent images are visualized with a corresponding color toner by a developing device and transferred onto an intermediate transfer belt. At the time of transfer, the color toner images are superimposed on each other to form a color image. This color image is transferred and fixed on a sheet-like recording medium.

  As described above, the optical scanning device shown in FIG. 1 uses a plurality of oscillating mirrors that are deflection scanning means to convert each light beam emitted from a plurality of light sources 10 corresponding to four color component images constituting a color image. 11 is deflected and scanned in the same direction, and is condensed by the scanning imaging means toward the surface to be scanned corresponding to each color component image by the scanning lens 14 provided in each scanning imaging means.

  In the present embodiment, the laser beam emitted from the light source 10 is incident on the reflecting surface of the oscillating mirror 11 so that both the front and back surfaces are orthogonal to the rotation axis (parallel to the normal line of the reflecting surface). : So-called horizontal incidence optical system). In a conventional optical scanning device using a oscillating mirror, each color laser beam incident on the reflecting surface of the oscillating mirror has a desired angle with respect to the sub-scanning direction (so-called oblique incidence optical system). The scanning line is greatly bent on the scanning surface, and the laser beam diameter is different depending on the oblique incident angle which is different for each color, resulting in image deterioration and a complicated scanning line bending mechanism. In addition, the scanning beams for the four colors are all laid out on the same side (only one side of the reflecting surface because the reflecting surface is a single surface) with respect to the reflecting surface of the oscillating mirror. However, there is also a problem that the height of the entire optical scanning device is increased due to the concentrated layout on one side.

  In this embodiment, only one color of laser beam is incident on one reflecting surface (using two vibrating mirrors having reflecting surfaces on the front and back surfaces, one color laser beam on each of the four reflecting surfaces. Therefore, it is not necessary to make oblique incidence, avoiding the intensive layout of the optical elements, realizing downsizing, and suppressing occurrence of scanning line bending.

  In addition, the scanning optical system of the present embodiment is configured by one imaging element of the scanning lens 14 for each color, and by using a horizontal incident optical system to the oscillating mirror 11, it is essential for conventional oblique incidence. The singularization of the plurality of scanning lenses that have been made can be realized. By adopting horizontal incidence, it is not necessary to load the scanning lens bending correction function required in the oblique incidence optical system and the surface tilt correction function required in the polygon scanner system on the scanning lens of this embodiment, so the scanning lens is simplified. it can.

By the way, in this embodiment, at least one oscillating mirror 11 is used for each of the scanning units U1 and U2, and it is necessary to match the vibration frequency and the vibration amplitude of the oscillating mirror 11 between the scanning units U1 and U2. The present invention solves the problem by adopting the following configuration.
That is, the optical scanning device 5 of the present invention is arranged as a common device for the adjacent scanning units U1 and U2, and detects the passage of a predetermined laser beam deflected and scanned in each of the adjacent scanning units U1 and U2. And control means (vibrating mirror control means, FIG. 10) for controlling the driving of the vibrating mirrors 11 of the adjacent scanning units U1 and U2 based on the detection results of the beam detectors 21 and 22. It is characterized by comprising.

  Further, the vibration frequencies of the plurality of vibration mirrors 11 are input to the plurality of vibration mirror drive (sine wave) signal generation units 119 and 219 from the same signal source with the same drive frequency fD as shown in FIG. Even if the resonance frequency of each vibrating mirror is different, the vibration frequency can be made the same. In order to manufacture a vibrating mirror having a completely matched resonance frequency, the process control is very strict and the yield is poor and expensive, which is not practical. This embodiment can be realized at low cost by using a plurality of vibrating mirrors having different resonance frequencies. Here, the different frequency means ± 0.3 Hz or more (that is, ± 0.01%, corresponding to the rotational speed accuracy of the polygon scanner system) or more in the case of a resonance frequency of 3000 Hz.

  On the other hand, for matching of vibration amplitude, amplitude control of each vibration mirror 11 is performed by a control system as shown in FIG. 10 (details will be described later). However, in addition to the control system, a detection system that detects the amplitude is also important. In order to detect the same amplitude in different scanning optical systems, the arrangement of the light receiving portions (light receiving elements) PD1 and PD2 in the beam detectors 21 and 22 and the interval between the plurality of beam detectors are the same as shown in FIGS. (The details will be described later).

FIG. 11 shows the relationship between the beam detector in the present embodiment and the laser beam passing through the beam detector. Here, the beam detector 21 will be described as an example, but the same applies to the beam detector 22.
As shown in FIG. 11A, the beam detector 21 is composed of a light receiving part PD1 made of a PIN photodiode, a circuit part 402b, and an IC lead 402c. ing.

  The light receiving part PD1 has two upper and lower light receiving surfaces, PD1M and PD1Y, the M (magenta) scanning beam from the scanning unit U1 on the light receiving surface PD1M, and the Y from the scanning negative unit U2 on the light receiving surface PD1Y. (Yellow) scanning beams are arranged to be scanned. The light receiving unit PD2 is above and below the light receiving surface PD2M on which the M (magenta) scanning beam from the scanning unit U1 is scanned and the light receiving surface PD2Y on which the Y (yellow) scanning beam from the scanning unit U2 is scanned. It has two light receiving surfaces.

  The two light receiving surfaces PD1M and PD1Y, PD2M and PD2Y divide a single light receiving portion (using a semiconductor process, a non-light receiving portion having a minute width of 10 μm or less is formed at the upper and lower boundary portions, The edge of the light receiving portion in the main scanning direction coincides with the top and bottom (edge deviation 5 μm or less).

  Since the scanning ends coincide with each other, the arrangement accuracy of the beam detectors 21 and 22 installed in two scanning regions as shown in FIG. 1 can be matched with high accuracy for each scanning beam. By matching, the amplitude amount in the amplitude control can be detected with high accuracy, and the deflection scanning characteristics between the scanning units U1 and U2, that is, the respective colors can be matched with high accuracy. Note that even if the amplitude control is performed in a state where the detection of the amplitude amount used for the amplitude control is different for each color, the deflection scanning characteristics for each color will be different, resulting in a color shift when forming a color image.

  As in this embodiment, two beam detectors 21 and 22 are mounted on a single substrate 19, and the light receiving surfaces PD1M and PD1Y, PD2M and PD2Y are adjacent to each other with high accuracy in the package of the beam detectors 21 and 22, respectively. Therefore, even when the environmental temperature changes, the distance between the beam detectors 21 and 22 can be matched for each scanning beam. This means that the beam detectors 21 and 22 are arranged in common with the adjacent scanning units U1 and U2. Therefore, even if the oscillating mirror 11 is different, it is possible to perform constant control with exactly the same amplitude.

  Unlike the present embodiment in which a single light receiving section is divided, when two separate light receiving sections are disposed adjacent to each other, the placement accuracy is poor and variations in characteristics such as light receiving sensitivity are likely to occur (this embodiment If the single light receiving surface is divided as described above, since the same semiconductor process is performed, characteristic variations such as light receiving sensitivity do not occur in practice), and therefore, it is difficult to detect the amplitude amount with high accuracy.

  The circuit unit 402b includes an amplifier circuit that amplifies output signals from the light receiving surfaces PD1M and PD1Y and a comparator circuit that shapes the waveform. When the scanning beam passes through the light receiving unit, FIG. (Actually, there are two output terminals corresponding to the light receiving surfaces PD1M and PD1Y. The output signal is an example of the light receiving surface PD1M, and the example of the light receiving surface PD1Y is omitted).

  As shown in FIG. 1, it is preferable to arrange the light receiving portion PD1 at a position optically equivalent to the laser beam scanned on the surface of the photosensitive member (beam diameter and scanning speed) for improving detection accuracy. However, when used for synchronous detection in the main scanning direction, there is no practical problem in beam detection because the beam diameter is within the light receiving surface (within the area of PD1M or PD1Y). In the embodiment, the laser beam is scanned in the light receiving portions PD1 and PD2 via the folding mirrors 18a and 18b, and a thin layout of the optical housing is achieved.

  Further, the incident angles of the two scanning beams (both in the main scanning direction and the sub-scanning direction) and the amounts of light are made to coincide with each other with respect to the light receiving surfaces of the light receiving portions PD1 and PD2, and the light receiving surface is reciprocally scanned. And the optical positional relationship between the light receiving elements. If the incident angles do not match, the output timing of the beam detectors 21 and 22 is changed due to the generation of stray light and the influence of the incident angle sensitivity of the light receiving surface when passing through the resin of the package. ing.

  In FIG. 11A, the dotted line area of the scanning beam is such that the light source is turned off (or the flare light is dimmed to such an extent that it does not form a light quantity that forms a latent image on the surface of the photoreceptor in the light receiving element). I'm drawing. If the light source emits light in the region between the maximum deflection angle of the oscillating mirror 11 and the vicinity of the light receiving element, ghost light due to irregular reflection of the optical components arranged in the optical scanning device is generated, and optical noise is transmitted to the light receiving unit. As a result, the beam detection timing is disturbed, resulting in control malfunction and instability. In order not to cause this problem, it is set in advance so as to be extinguished at the above timing (or dimmed to such an extent that the ghost light does not become a light amount at a level for forming a latent image on the surface of the photoreceptor in the light receiving element). Turning off or dimming can also have the effect of extending the life of a light source made of a semiconductor laser and reducing the temperature rise of the light source. Note that the vicinity of the light receiving element means a scanning position at a light emission timing at which the output signals from the beam detectors 21 and 22 can be normally detected without affecting the comparator output.

  FIG. 12 shows the relationship between the output waveform of the light receiving element (light receiving surface) and the threshold voltage. Since the rise time to the threshold voltage that determines the comparator output becomes longer (the inclination becomes slower) when the light quantity decreases when the reflectance or transmittance of the optical element decreases (deterioration with time), erroneous detection is performed. (In the case of a normal light amount (solid line in FIG. 12), the output timing t is delayed to t ′ when the light amount is decreased (dotted line in FIG. 12)). Therefore, the above problem is solved by controlling the light source so that the light amount is always constant when scanning the light receiving surfaces (light receiving elements) PD1Y and PD1M.

  FIG. 13 is an enlarged view of a main part of the substrate 19 on which the beam detectors 21 and 22 of FIG. 1 are mounted. FIG. 13A shows the beam detector 21 side (beam scanning upstream side), and FIG. 13B shows the beam detector 22 side (beam scanning downstream side).

  The configurations of the scanning unit U1 and the scanning unit U2 are the same, but the units are arranged symmetrically with respect to the apparatus center line C (FIG. 1). The reason for arranging them symmetrically is that the optical characteristics (beam diameter, light amount) on the M (magenta) side and Y (yellow) side when scanning the light receiving parts PD1 and PD2 of the beam detectors 21 and 22 are initial and time-dependent. This is because it is the same even when the temperature changes. By arranging them symmetrically, the relationship between the incident angle on the reflecting surface of the vibrating mirror 11 and the main scanning position of the scanning beam can be made the same. For example, in FIG. 13A, the incident angle on the reflecting surface of the oscillating mirror 11 related to the incident beam on the light receiving unit PD1 is θ1 in both the scanning units U1 and U2, and in FIG. 13B, the incident angle on the light receiving unit PD2 The incident angle on the reflecting surface of the oscillating mirror 11 with respect to the incident beam is θ2 for both the scanning units U1 and U2.

  When the scanning unit U2 is arranged in a point (rotation) symmetry instead of line symmetry, the scanning beam characteristic of Y (yellow) is switched between the beam detector 21 side and the beam detector 22 side (in the drawing of FIG. Inverted), the characteristics of the beam diameter and the light amount are different, and the detection timing at the light receiving element (PD) is different, which affects the amplitude detection.

FIG. 14 shows a curve in which the main scanning beam diameter is plotted for each image height when the characteristics of the optical element in the optical scanning device 5 are as designed.
In FIG. 14, a curve 41 indicates the beam diameter when the oscillating mirror 11 is stationary at the image height (when the positive / negative direction of the image height here is positive in FIG. The upper side of the drawing and the negative side as the lower side). Optically the same M (magenta) and Y (yellow) have the same characteristic curve. The curve 41 at the image height 0 of the curve 41 is normalized and shown as 1. The expansion ratio of the beam diameter is 1.23 times at an image height of ± 110 mm (symmetrical with positive and negative image heights). The curve 41 in the initial state has a symmetric shape with positive and negative image heights, but the symmetry is lost due to a change with time and a change in temperature environment. In the figure, a curve 41a indicates the upper limit of change, 41b indicates the lower limit of change, and the beam diameter changes within the upper and lower limits.

  Here, even if the symmetry is lost, there is no problem if the scanning units U1 and U2 are arranged in line symmetry as in this embodiment, but the scanning unit U2 is point (rotation) symmetrical with respect to the scanning unit U1. When the beam detector 21 is disposed, the beam diameters of M (magenta) and Y (yellow) when the beam detector 21 is scanned are different when a change with time and a change in temperature environment occur. Furthermore, since the incident angle to the reflecting surface is different, a difference in reflectance also occurs (removing the reflectance from dependence on the incident angle is very difficult in practice and the wavelength is limited or expensive). . As a result, the detection timing varies depending on the beam diameter change and light quantity change when scanning the beam detector (see FIG. 11A). If the amplitude amount of each oscillating mirror 11 and the writing timing in the main scanning direction vary, there is a problem that color misregistration occurs between the scanning unit U1 and the scanning unit U2 during image formation.

FIG. 10 is a block diagram showing the configuration of the vibrating mirror control means.
Based on FIG. 10, the structure of the vibration mirror control means for realizing the amplitude, offset, and phase control of the vibration mirror 11 will be described in detail.
The oscillating mirror control means of the present embodiment is composed of a control system 100 (upper dotted frame) of the oscillating mirror 11 of the scanning unit U1 and a control system 200 (lower dotted frame) of the oscillating mirror 11 of the scanning unit U2. ing. Here, the control systems 100 and 200 share the drive frequency signal, the target amplitude amount, the allowable offset amount, and the reference phase clock. That is, the vibrating mirrors 11 of the scanning units U1 and U2 are driven at a common driving frequency fD.

Hereinafter, control of the oscillating mirror 11 of the scanning unit U1 by the control system 100 will be described. Note that the control of the oscillating mirror 11 of the scanning unit U2 by the control system 200 is similar to this, and the corresponding reference numerals are described in parentheses.
By driving the oscillating mirror 11 of the scanning unit U1, time intervals A and B are measured by counters 111 (211) and 112 (212), respectively, for signals output by the laser beams that scan the beam detectors 21 and 22. Next, the comparator 81a (81b) compares the average of (A + B) / 2 calculated by the calculator 113 (213) with the target amplitude, and similarly determines whether the average of the differences of AB is within the allowable offset. Compare. At this time, if the comparison result is within the allowable range, it is output without correction, and if the comparison result is out of the allowable range, correction control is performed so as to adjust the difference from the allowable range. Therefore, after the correction control, a residual of the allowable offset amount remains even if the offset amount is not zero and is maximum. The reason for taking the average of the differences is that averaging processing is performed in order to prevent control by incorrect information such as when sudden electrical noise is mixed. In addition, the frequency | count of averaging is performed in the range of 2-10 times. This is because if it is 10 times or more, the control correction timing is delayed and the control deviation is increased.

  The controller 114 (214) calculates amplitude and offset correction amounts according to the comparison result. Next, the calculator 120 (220) corrects the sine wave generated by the sine wave signal generator 119 (219) with the amplitude correction amount, and the calculator 121 (221) corrects with the offset correction amount. The corrected sinusoidal drive signal is amplified by the vibration mirror drive circuit (amplifier) 110 (210) to drive and control the vibration mirror 11. The control system loop is an amplitude and offset control loop. The offset control is performed in a state where the amplitude control is performed.

  In the phase control loop, the amplitude and offset control work normally, and the control phase is in a desired range with respect to the target value, so that the reference phase clock signal and the oscillation angle of the oscillating mirror 11 have a constant phase. Run the control loop. In other words, phase control is highly accurate control over amplitude and offset control, so if all controls are executed at the same time, they will interfere with each other and drive signal fluctuations will increase and all will converge within the control target value range. Takes time. Therefore, it is possible to shorten the time until convergence within the control range by preferentially performing amplitude control, then controlling offset control, and then performing phase control as fine adjustment.

  As the phase control, the phase deviation between the output signal from the beam detector 21 and the reference phase clock (time interval C in FIG. 6F) is detected by the phase comparator 115 (215), and the counter 116 (216) is used. measure. The measurement result is converted into a voltage corresponding to the phase deviation by an LPF (Low Pass Filter) 117 (217)) and an integrator 118 (218), and according to the voltage amount (reference phase clock and output signal of the light receiving unit PD1) Control to change the phase (so-called PLL (Phase Locked Loop) control) is performed so that the phase deviation (time interval C) becomes constant. Next, the sine wave signal generation unit 119 (219) generates a sine wave signal having an optimum phase according to the increment of the phase change amount (resolution) prepared in advance based on the drive frequency fD and the phase change (θa). Generated. As a result, control is performed so that the drive signal of the vibrating mirror 11 and the deflection angle of the vibrating mirror 11 have a constant phase.

The drive frequency fD of the oscillating mirror 11 will be described in detail with reference to FIG.
Driving frequency fD is the frequency for realizing the number of prints per minute, is preferred because it can make the amplitude amount Y ₁ required for optical scanning is possible to match the resonant frequency fr of the vibrating mirror 11 ( The solid line in FIG. 15 may not actually match due to resonance frequency fluctuations (including initial fluctuations) of the vibrating mirror 11. As in that case shown in FIG. 15, in order to amplitude amount Y ₁ required for optical scanning, the input energy (voltage, current) to the vibrating mirror 11 increases, only Y ₂ at a frequency of fD amplitude The amplitude control of the oscillating mirror 11 is performed such that the amplitude of the oscillating mirror that has not been increased is increased to Y ₁ (dotted line).

  Note that the generation resolution of the sine wave signal corresponding to the phase control needs to have a high accuracy within the allowable range of the control amount. However, the higher the accuracy, the higher the cost because a memory is required. Therefore, the generation resolution of the sine wave signal is set so as to be 50 μm or less which is visually recognized as a color shift in the sub-scanning direction.

  As described above, according to the optical scanning device of the present invention, the control systems 100 and 200 that control the scanning units U1 and U2 share the drive frequency signal, the target amplitude amount, the allowable offset amount, and the reference phase clock, respectively. Since the intervals between the light receiving surfaces PD1M and PD2M in the detectors 21 and 22 and the intervals between the light receiving surfaces PD1Y and PD2Y are always consistent (even at the initial time and time (temperature fluctuation)), the scanning unit is arranged. In U1 and U2, it is possible to control the scanning beams so that the amplitude amount, the offset amount, and the phase difference are matched even with different vibrating mirrors 11. As a result, it is possible to match the scanning characteristics for all scanned surfaces.

Next, the image forming apparatus according to the present invention will be described.
FIG. 16 shows an image forming apparatus according to the present invention, which is a color image forming apparatus using the optical scanning device 5 shown in FIG.
This is a tandem type color image forming apparatus in which a plurality of photoconductors 3C, 3Y, 3M, 3K are arranged in parallel. An optical scanning device 5, a developing device 6 (6C, 6Y, 6M, 6K), a photoreceptor 3 (3C, 3Y, 3M, 3K), an intermediate transfer belt 2, a fixing device 7, and a paper feed cassette 1 are laid out in order from the top of the apparatus. Has been.

  The intermediate transfer belt 2 is provided with photoreceptors 3C, 3Y, 3M, and 3K corresponding to the respective colors at equal intervals in parallel order. The photoreceptors 3C, 3Y, 3M, and 3K are formed to have the same diameter, and members are sequentially disposed around the photoreceptors according to an electrophotographic process.

  The photoconductor 3C will be described as an example. A charging charger (not shown), a laser beam L1 based on an image signal emitted from the optical scanning device 5, a developing device 6C, a transfer charger (not shown), a cleaning device (not shown), and the like. Are arranged in order. The same applies to the other photoconductors 3Y, 3M, and 3K. That is, in the present embodiment, the photoconductors 3C, 3Y, 3M, and 3K are to be scanned surfaces set for each color, and the laser beams L1, L2, L3,. L4 is provided to correspond to each.

  The photoconductor 3C uniformly charged by the charging charger rotates in the direction of arrow A, thereby sub-scanning the laser beam L1, and an electrostatic latent image is formed on the photoconductor 3C. Further, a developing device 6C that supplies toner to the photoconductor 3C is disposed downstream of the irradiation position of the laser beam L1 by the optical scanning device 5 in the rotation direction of the photoconductor 3C, and cyan toner is supplied. The toner supplied from the developing device 6C adheres to the portion where the electrostatic latent image is formed, and a toner image is formed. Similarly, Y, M, and K monochromatic toner images are formed on the photoreceptors 3Y, 3M, and 3K, respectively.

  The intermediate transfer belt 2 is disposed further downstream in the rotation direction than the position where the developing unit 6C of each photoconductor 3C is disposed. The intermediate transfer belt 2 is wound around a plurality of rollers 2a, 2b, and 2c, and is moved and conveyed in the direction of arrow B by driving a motor (not shown). By this conveyance, the intermediate transfer belt 2 is sequentially moved to the photoreceptors 3C, 3Y, 3M, and 3K. The intermediate transfer belt 2 sequentially superimposes and transfers the single color images developed by the photoreceptors 3C, 3Y, 3M, and 3K, thereby forming a color image on the intermediate transfer belt 2. Thereafter, the transfer paper is conveyed from the paper feed tray 1 in the direction of arrow C, and the color image is transferred. The transfer paper on which the color image is formed is discharged as a color image after being fixed by the fixing device 7.

  As described above, the image forming apparatus of the present invention includes the optical scanning device 5 of the present invention, and matches the scanning characteristics of the scanning beams for all the photoconductors 3C, 3Y, 3M, and 3K. A few good color images can be formed.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

DESCRIPTION OF SYMBOLS 1 Paper feed tray 2 Intermediate transfer belt 2a, 2b, 2c, 2d Roller 3, 3C, 3Y, 3M, 3K Photoreceptor 5 Optical scanning device 6Y, 6M, 6C, 6K Developing device 7 Fixing device 10, 10K, 10M Light source 11 Vibrating mirror 12K, 12M Cylindrical lens 14K, 14M Scan lens 16K, 16M Mirror 18a, 18b Folding mirror 19 Substrate 21, 22 Beam detector 41 Curve 60, L1, L2, L3, L4 Laser beam 60a, 60b, 60c Scan position 81a , 81b Comparator 100, 200 Control system 110, 210 Drive circuit 111, 112, 116, 211, 212, 216 Counter 113, 120, 121, 213, 220, 221 Calculator 114, 214 Controller 115, 215 Phase comparator 117 , 217 LPF
118, 218 Integrator 119, 219 Sinusoidal signal generation unit 402b Circuit unit 402c IC lead 440 Mirror substrate 441 Movable mirror unit 441a, 441b Reflecting surface 442 Torsion beam 443 Vibration plate 444 Reinforcement beam 447 Frame 448 Mounting substrate 449 Yoke 450 Permanent magnet 455 Electrode 461, 462 Substrate 463 Coil pattern 464 Terminal 466 Base 466a Opening 471 Bracket 471a Opening 472 Substrate 473 Electrode 474 Electrical connector PD1, PD2 Light receiving part PD1M, PD1Y Light receiving surface U1, U2 Scan unit

JP 2007-171854 A JP 2007-233235 A JP 2008-15219 A JP 2008-70798 A

Claims (11)

At least one light source that emits laser light; a vibrating mirror that deflects and scans the laser light from the light source; and a scanning image forming unit that condenses the laser light deflected and scanned by the vibrating mirror toward a surface to be scanned; A plurality of vibrating mirror scanning units consisting of
A beam detector that is disposed in common with the adjacent oscillating mirror scanning units and detects the passage of a predetermined laser beam deflected and scanned in each of the adjacent oscillating mirror scanning units;
Control means for controlling the driving of the vibrating mirror of each of the adjacent vibrating mirror scanning units based on the detection result of the beam detector;
An optical scanning device comprising:   The oscillating mirror scanning unit is disposed on each side of the oscillating mirror having a reflecting surface on the front and back surfaces and the front and back surfaces of the oscillating mirror, and emits laser light to enter the corresponding reflecting surface of the oscillating mirror Characterized in that it comprises two light sources and scanning imaging means for condensing the two laser beams reflected and deflected and scanned by the oscillating mirror toward the corresponding scanned surfaces, respectively. The optical scanning device according to claim 1.   In each of the adjacent oscillating mirror scanning units, among the two laser beams that are deflected and scanned, a light source related to the laser beam that passes through the beam detector is used as a laser beam incident angle on the reflecting surface of the oscillating mirror and the scanned object. The optical scanning device according to claim 2, wherein the optical scanning devices are arranged so that the scanning positions on the surface have the same relationship.   4. The light according to claim 2, wherein the laser beams emitted from the two light sources are incident on the reflecting surface so that both front and back surfaces of the vibrating mirror are orthogonal to a rotation axis of the vibrating mirror. 5. Scanning device.   5. The optical scanning device according to claim 1, wherein a single circuit board on which a plurality of the beam detectors are mounted is disposed between the adjacent vibrating mirror scanning units.   The beam detector includes a photodiode in which one light receiving element is electrically divided to form the two light receiving surfaces, and predetermined laser light deflected and scanned in each of the adjacent vibration mirror scanning units is the 2 The optical scanning device according to claim 1, wherein the optical scanning device passes through each of the two light receiving surfaces.   The optical scanning device according to claim 6, wherein the two laser beams respectively passing through the two light receiving surfaces are reciprocally scanned in the light receiving surface with the incident angles and light amounts of the two light receiving surfaces being matched.   The beam detector includes an amplitude variation with respect to a target amplitude of each oscillating mirror of each of the adjacent oscillating mirror scanning units, a difference between the amplitude center of the oscillating mirror and the scanning center of the laser beam, and a reference phase clock of the amplitude waveform of the oscillating mirror The optical scanning device according to claim 1, wherein a phase variation from the light source is detected.   The control means oscillates all the oscillating mirrors of each of the plurality of oscillating mirror scanning units based on the same drive frequency so that the scanning characteristics of all the oscillating mirrors match based on the detection result of the beam detector. The optical scanning device according to claim 1, wherein the optical scanning device is controlled.   The optical scanning device according to claim 1, wherein the plurality of vibrating mirror scanning units perform scanning of laser light in the same direction on all scanned surfaces.   An image forming apparatus comprising the optical scanning device according to claim 1.