JP2010025989A - Optical scanner and image forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner, expanding the incident system pitch without any increase in mirror, reducing the manufacturing cost, and deflecting and scanning a plurality of beams with good accuracy, and to provide an image forming apparatus including the same. <P>SOLUTION: The optical scanner includes: a semiconductor laser 41 emitting a beam; a light deflection unit 1 for deflecting a beam to the surface of a photoreceptor 32 provided corresponding to each beam; a lens 44 for imaging the beam deflected in the light deflection unit 1 on the surface of the photoreceptor 32. In the optical scanner, the light deflection unit 1 includes deflecting elements 3u, 3d, driving elements 4u, 4d, and a fixed part 12; the deflecting elements 3u, 3d, the driving elements 4u, 4d, and the fixed part 12 are connected to each other in a series by torsion springs 5u, 6u, 6d, 5d; the deflecting elements 3u, 3d rock with rocking of the driving elements 4u, 4d, and the deflecting elements 3u, 3d; and the driving elements 4u, 4d are arranged symmetrical about the fixed part 12 with the fixed part 12 interposed between them, and disposed so that the respective rocking axes are on a straight line. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus that performs optical writing using a laser beam in an image forming apparatus such as an LBP, a digital copying machine, or a digital FAX, and an image forming apparatus including the optical scanning apparatus.

  In recent years, colorization of image forming apparatuses has progressed, and so-called tandem image forming apparatuses that can perform high-speed printing at the same speed as monochrome are widely known. The tandem method is an image forming method in which an optical scanning system is provided for each toner color and a desired image is obtained by superimposing toner images formed in the respective optical scanning systems.

  Many types of image forming apparatuses having such a tandem method have been proposed which include a common rotary polygon mirror for a plurality of optical scanning systems.

  Among them, the one in which the rotating polygon mirror is replaced with one mirror that vibrates sinusoidally has been proposed (Patent Document 1 and Patent Document 2).

  Japanese Patent Application Laid-Open No. H10-260260 has a configuration in which a beam for four colors is deflected and scanned on one side of a single vibrating mirror, and the scanned beam is separated for each color and guided to the surface of each photoconductor. It is disclosed.

  In Patent Document 2, a beam is deflected and scanned using both surfaces of a vibrating double-sided mirror, and the beam subjected to the deflection scanning is separated for each color, and a photosensitive provided corresponding to each beam. A configuration for guiding light to the surface of the body is disclosed.

Furthermore, in Patent Document 2, not only the type using a double-sided mirror, but also mirrors with independent one-side mirror surfaces are supported by separate swinging shafts and arranged so that the opposite mirror surfaces face each other. A configuration for performing deflection scanning is also disclosed.
JP 2006-243034 A JP 2006-292891 A

  However, the conventional optical scanning device and the image forming apparatus including the same cause the following problems.

  In the above-described conventional optical scanning device, the mirror provided on the swing shaft is a single sheet (or a two-piece laminated mirror).

  Therefore, in order to make a beam accurately incident on a single mirror from a plurality of light sources, it is necessary to place incident members such as mirrors and lenses in a narrow space with high precision, which may increase manufacturing costs. There is sex.

  On the other hand, Patent Document 1 and Patent Document 2 disclose a configuration in which beams emitted from a plurality of light sources are combined using a half mirror or the like, and the combined beam is incident on one vibrating mirror. Has been.

However, in general, the half mirror is expensive, and the beam is tilted at an angle twice the mirror tilt angle caused by the assembly error of the half mirror. Therefore, the half mirror needs to be positioned with high accuracy on the optical path. is there. As a result, when a half mirror is used, the manufacturing cost increases.

  A configuration is also known in which the deflection points on one mirror surface that vibrates are aligned by inclining and arranging the members of the incident system. As the direction in which the incident system member is tilted, there are a case of tilting in the main scanning direction and a case of tilting in the sub-scanning direction.

  However, when the incident members are arranged side by side in the main scanning direction, the beams emitted from the plurality of light sources are all deflected in different directions when the oscillating mirror is stationary. The scanning center of each beam is different.

  Further, if the speed of the beam to be deflected and scanned is made constant on the photosensitive member by using a single sine-vibrating mirror, the scanning lens needs to have, for example, f · arcsin θ characteristics.

  However, since the phases of the sine waves of all four colors are different, it is difficult to make the beams of all four colors have the same speed on the photosensitive member.

  Further, when the beam is deflected and scanned by a single vibrating mirror, if the mirror size is not increased in the main scanning direction, the so-called vignetting that the light beam of the incident beam deviates from the mirror surface at the scanning end of the mirror. Occurs. When vignetting occurs, the spots on the photoreceptor are enlarged, and image defects may occur.

  On the other hand, when the incident members are arranged side by side in the sub-scanning direction, if the beam scanned by the mirror is directly guided onto the photoconductor, it is relative to a plane perpendicular to the oscillation axis of the vibrating mirror. A tilted beam will have a larger scan line bend.

  That is, a large scanning line bend is caused according to each color, and the printing position is different for each color on the image, so that color misregistration occurs.

  In order to prevent the occurrence of such color misregistration, there is a method of correcting the scanning line curve with the scanning lens. However, if the correction amount is too large, the imaging performance may be deteriorated and an image defect may occur.

  Further, when the beam is deflected and scanned using both sides of the scanning mirror as in Patent Document 2, the incident system beam deflected and scanned on one side of the scanning mirror is sufficient for two colors. Still, it doesn't mean that the effect is gone.

  Further, if the tilt angle in the sub-scanning direction is narrowed to reduce this influence, the pitch of the light source devices is narrowed and the beam pitch is narrowed, so that the beams may interfere with each other.

  On the other hand, if the tilt angle is too narrow, the beam pitch is too narrow and beam separation becomes difficult. In order to narrow the beam pitch of the incident system, there is a method using a semiconductor laser having a plurality of light emitting points, but the beam separation becomes more difficult.

  In addition, there is a method of widening the sub-scanning pitch of the incident system by shifting the mirror deflection point for each beam in the sub-scanning direction (the oscillating axis direction of the oscillating mirror). Will become bigger.

  Here, a problem that occurs when the mirror size increases will be described.

The resonance frequency of the mirror is expressed by the following equation.

  In the above equation, f is the resonance frequency, K is the spring constant of the beam (torsion spring) that supports the mirror, and I is the moment of inertia of the mirror. As the mirror size increases, the moment of inertia I increases, so the resonance frequency f decreases from the above equation.

  When the resonance frequency f is decreased, the writing speed of the image forming apparatus is decreased, the throughput is decreased, or the resolution is decreased and the desired specification is not satisfied. Therefore, in order to maintain the resonance frequency f at the original value, the spring constant It is necessary to raise K.

  In order to increase the spring constant K, it is only necessary to increase the cross-sectional area of the torsion spring that supports the scanning mirror. However, if the cross-sectional area of the torsion spring is increased, the stress applied to the spring at the maximum helix angle increases. May break.

  Therefore, in order to increase the spring constant without increasing the stress applied to the spring at the maximum torsion, it is conceivable to lengthen the torsion spring. However, if the torsion spring is lengthened, the optical scanning device becomes larger in the swing axis direction. This causes a problem.

  In view of this situation, the present invention is an optical scanning capable of widening the incident system pitch without increasing the mirror size, and capable of accurately deflecting and scanning a plurality of beams while reducing the manufacturing cost. It is an object to provide an apparatus and an image forming apparatus including the apparatus.

In order to achieve the above object, the present invention provides:
A plurality of light sources for emitting beams;
A light deflection unit that deflects the beams emitted from the plurality of light sources to the surface of the photoreceptor provided corresponding to each beam;
An imaging member for imaging the beam deflected in the light deflection unit on the surface of the photosensitive member;
In an optical scanning device comprising:
The light deflection unit is
A plate member for deflecting the beam;
A holding member for holding the plate member;
Have
The plate member is
A deflector formed with a deflection surface of the beam;
A driver that swings in response to a driving force;
A fixing portion for fixing the plate member to the holding member;
Have
The deflector, the driving element, and the fixed portion are connected in series by a torsion spring, and the deflecting element swings as the driving element swings by receiving a driving force,
The deflector and the driver are
It is characterized in that it is arranged on both sides of the fixed part so as to be symmetrical with respect to the fixed part, and the respective swing shafts are arranged in a straight line.

An image forming apparatus according to the present invention is
The above optical scanning device;
A photoreceptor on which a beam deflected from the optical scanning device is imaged;
Transfer means for transferring an image formed on the photoreceptor onto a sheet material;
It is characterized by providing.

  According to the present invention, an optical scanning device capable of accurately deflecting and scanning a plurality of beams while reducing the manufacturing cost with a configuration capable of widening the incident system pitch without increasing the mirror size, and the same It is possible to provide an image forming apparatus including the above.

  The best mode for carrying out the present invention will be exemplarily described in detail below based on the embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

[First Embodiment]
With reference to FIGS. 1 to 6, an optical scanning device and an image forming apparatus including the same according to a first embodiment of the present invention will be described.

(Overall configuration of image forming apparatus)
First, the overall configuration of the image forming apparatus according to the present embodiment will be described. FIG. 6 shows a schematic configuration of the image forming apparatus according to the present embodiment.

  When performing image formation, beams Lc, Lm, Ly, and Lk that are each light-modulated based on image information are emitted from the optical box 31, and the emitted beams are provided corresponding to the respective beams. Irradiation is performed on the surfaces of the drums (photoconductors) 32c, 32m, 32y, and 32k.

  The surface of each photosensitive drum is uniformly charged in advance by primary chargers 33c, 33m, 33y, and 33k, and each photosensitive drum is irradiated with beams Lc, Lm, Ly, and Lk. An electrostatic latent image is formed on the surface.

  Thereafter, cyan, magenta, yellow, and black toners are supplied from the developing units 34c, 34m, 34y, and 34k to the electrostatic latent images formed on the surfaces of the photosensitive drums 32c, 32m, 32y, and 32k, and the electrostatic latent images are formed. The image is visualized as a toner image.

  The toner image is conveyed to a position on the transfer belt 39 (transfer means) as the photosensitive drum 32 rotates. The transfer belt 39 conveys the sheet material 36 so that the toner image formed on the surface of each photosensitive drum 32 is transferred onto the sheet material 36 at a predetermined timing.

  By such an image forming process, cyan, magenta, yellow, and black toner images are sequentially superimposed and transferred onto the sheet material 36 to form a desired color image on the sheet material. Note that the drive roller 40 that drives the transfer belt 39 is connected to a drive motor (not shown) with small rotation unevenness in order to feed the transfer belt 39 with high accuracy.

  The sheet material 36 on which a desired color image is formed is passed through a fixing device 37, and the color image is heat-fixed on the sheet material 36 in the fixing device 37. Thereafter, the sheet material 36 on which the color image has been thermally fixed is conveyed by a discharge roller 38 and output to the outside of the image forming apparatus.

(Overall configuration of optical scanning device)
With reference to FIG. 5, the overall configuration of the optical scanning device according to the present embodiment will be described. FIG. 5 is a perspective view showing the overall configuration of the optical scanning device according to the present embodiment.

  As shown in FIG. 5, the optical scanning device according to the present embodiment includes a plurality of semiconductor lasers 41c, 41m, 41y, and 41k as light sources for emitting beams, and an optical deflection unit that deflects and scans the emitted beams. 1 is provided.

  Further, in addition to the above configuration, fθ lenses 44 cm and 44 yk through which the beam deflected and scanned in the optical deflection unit 1 is transmitted, and first to third reflection mirrors that reflect the beam are provided.

  The fθ lens and the first to third reflection mirrors are provided as image forming members for forming an image of the beam on the surface of the photosensitive drum 32. The imaging member and the light deflection unit 1 are integrally accommodated in an optical box (not shown).

  With the above configuration, when a beam is imaged on the surface of the photosensitive drums 32c, 32m, 32y, and 32k provided corresponding to each beam, first, the semiconductor lasers 41c, 41m, 41y, and 41k are based on the image information. The beam is emitted from.

  A total of four emitted beams are deflected and scanned by the optical deflection unit 1 in two different directions. The deflected and scanned beams pass through the fθ lenses 44 cm and 44 yk, respectively.

  For example, of the two beams transmitted through the fθ lens 44 cm, the beam emitted from the semiconductor laser 41 c is reflected by the first reflecting mirror 45 c and forms an image on the photosensitive drum 32 c as the beam Lc.

  On the other hand, the beam emitted from the semiconductor laser 41m is sequentially reflected by the second reflecting mirror 46m and the third reflecting mirror 47m, and forms an image on the photosensitive drum 32m as a beam Lm.

  Similarly, of the two beams transmitted through the fθ lens 44yk, the beam emitted from the semiconductor laser 41k is reflected by the first reflecting mirror 45k and forms an image on the photosensitive drum 32k as a beam Lk.

  The beam emitted from the semiconductor laser 41y is sequentially reflected by the second reflecting mirror 46y and the third reflecting mirror 47y, and forms an image on the photosensitive drum 32y as a beam Ly.

  The optical path will be described in more detail after these four beams are emitted from the semiconductor laser 41 until they are imaged on the corresponding photosensitive drums 32.

  Beams emitted from the semiconductor lasers 41c, 41m, 41y, and 41k are converted into parallel light (collimated light) by the collimator lenses 42c, 42m, 42y, and 42k. Thereafter, these collimated lights are compressed in the sub-scanning direction by the cylindrical lenses 43c, 43m, 43y, and 43k, and enter the light deflection unit 1.

  Although the detailed configuration of the optical deflection unit 1 will be described later, the optical deflection unit 1 in the present embodiment is provided with a plate member 2, and a beam deflection surface is formed on the plate member 2 and can be swung. The deflectors 3u and 3d configured in the above are provided one by one in the vertical direction.

When a beam is incident on the deflector, a beam compressed in the sub-scanning direction is formed on the deflecting surfaces formed on the deflectors 3u and 3d, and a line image is formed on the deflecting surface. In the deflectors 3u and 3d in the present embodiment, deflection surfaces are formed on both the front and back surfaces.

  The deflection surfaces on the front and back sides of these deflectors and the surfaces of the photosensitive drums 32c, 32m, 32y, and 32k provided corresponding to the respective deflection surfaces are configured so as to be conjugate with each other in the sub-scanning direction. Has been. Accordingly, it is possible to reduce the positional deviation of the beam in the sub-scanning direction on the surface of the photosensitive drum 32 due to the deflection surface tilt error, so-called surface tilt.

  Also, the four beams emitted from the semiconductor laser 41 are scanned as optimally narrowed beams on the corresponding photosensitive drums 32c, 32m, 32y, and 32k, respectively, so that the fθ lenses 44cm and 44yk are scanned. It is adjusted by.

  Furthermore, in the present embodiment, the beam deflected by the deflector 3u is detected by the two BD sensors 48m, and the beam deflected by the deflector 3d is detected by the two BD sensors 48k.

  According to this configuration, it is possible to synchronize the writing signals for the scanning times of the four beams and match the writing positions of the beams with reference to the output signals from the BD sensors 48m and 48k.

  It is also possible to control the scanning amplitude and scanning period of the deflectors 3u and 3d using output signals from the BD sensors 48m and 48k.

(Configuration of light deflection unit)
With reference to FIGS. 1-4, the structure of the optical deflection | deviation unit 1 with which the optical scanning device based on this Embodiment is equipped, and its effect | action are demonstrated.

  As shown in FIGS. 3 and 4, the optical deflection unit 1 has a plate member 2 for deflecting the beam, a single actuator 9 (driving means), and a holder 8 (holding member) for holding them. ing.

  Further, the plate member 2 includes deflectors 3u and 3d on which beam deflection surfaces are formed, driver elements 4u and 4d that receive a driving force, a fixing portion 12 that fixes the plate member 2 to the holder 8, and these. The torsion springs 5u, 6u, 6d, and 5d are connected in series (FIG. 1). The configuration of the plate member 2 will be described later.

  The optical deflection unit 1 having such a configuration is screw-fixed to the optical box 31 through a screw hole 13 formed in the holder 8.

  As the actuator 9, an iron core (core) 10 around a winding (coil) 11 is used. The actuator 9 applies driving force to the driver elements 4u and 4d provided on the plate member 2, and swings the driver elements 4u and 4d around the swing axis O.

  In addition, the actuator 9 is inserted into a notch 14 provided at a substantially central portion of the holder 8, and the tip of the iron core (core) 10 is press-fitted into the notch 14, so that the holder 9 is firmly attached to the holder 8. It is fixed to.

  That is, the actuator 9 is provided at a position facing the substantially central portion of the plate member 2 in the direction of the swing axis O. When the actuator 9 is inserted into the notch portion 14, the actuator 9 is inserted until the abutment surface 15 of the holder 8 contacts.

  After the actuator 9 is assembled to the holder 8 in this way, the plate member 2 is assembled to the holder 8 from the opposite side (front side) with respect to the actuator 9 with the holder 8 interposed therebetween. When the plate member 2 is assembled, the assembling operation is performed by bonding and fixing the fixing portion 12 of the plate member 2 to the fixing surface 14 provided on the holder 8.

(Configuration of plate member)
The configuration of the plate member 2 will be described with reference to FIG. FIG. 1 is a perspective view showing the overall configuration of the plate member 2 in the present embodiment.

  The plate member 2 (element) is manufactured by etching a Si single crystal wafer. As described above, the plate member 2 includes the deflectors 3u and 3d and the driver elements 4u and 4d, which are connected in series by the torsion springs 6u, 5u, 5d, and 6d. Further, a fixed portion 12 is provided at a substantially central portion of the plate member 2.

  In addition, rod-shaped permanent magnets (magnets) 7 are integrally fixed to the driver elements 4u and 4d, and aluminum or the like is vapor-deposited on both the front and back surfaces of the deflectors 3u and 3d. Thus, the surface on which the aluminum or the like is deposited on the surface of the deflector becomes a deflecting surface suitable for reflecting the beam.

  In addition, the present embodiment is characterized in that the deflectors 3u and 3d and the driver elements 4u and 4d are arranged on both sides of the fixed portion 12 so as to be symmetrical with respect to the fixed portion 12. .

  That is, on the upper side of the fixed part 12, the driver 4u and the deflector 3u are arranged in order from the side closer to the fixed part 12, and on the lower side of the fixed part 12, the driver elements 4d, The deflectors 3d are arranged.

  Further, the deflector 3u, the driver element 4u, the fixed portion 12, the driver element 4d, and the deflector element 3d are connected in series in this order by the torsion springs 5u, 6u, 6d, and 5d, and each torsion spring swings. The shaft is provided so as to be in a straight line.

  Thereby, the deflector and the driver provided above and below the fixed portion 12 exhibit the same behavior around the swing axis O. That is, when the actuators 4u and 4d are swung by the actuator 9, the upper and lower deflectors 3u and 3d can be swung similarly.

  A case where the beam is deflected and scanned by the plate member 2 having such a configuration will be described.

  As shown in FIG. 1, the beams L1u, L2u, L1d, and L2d from the light source are incident on the deflecting surfaces from the front and back sides of the plate member 2, respectively. The beams L1u and L2u are deflected by the deflector 3u, and the beams L1d and L2d are It is deflected by the deflector 3d.

  Further, the deflectors 3u and 3d are subjected to torsional vibration (oscillation) by the torsion springs 6u, 5u, 5d and 6d around the oscillation axis O when the driving elements 4u and 4d receive a driving force (Lorentz force) from the actuator 9. Is possible. As described above, the deflectors 3u and 3d swing around the swing axis O, whereby the beams L1u, L2u, L1d, and L2d can be deflected and scanned.

The drive elements 4u and 4d are configured to swing around the swing axis O in response to a driving force (Lorentz force) generated when a power source (not shown) energizes the winding (coil) 11 of the actuator 9. However, it is also possible to modulate the current supplied to the winding 11 in accordance with the vibration mode.

  As a result, the driver elements 4u, 4d and the deflectors 3u, 3d can be resonantly oscillated around the oscillation axis O of the torsion springs 5u, 6u, 5d, 6d, and the beam can be deflected and scanned with higher accuracy. Is possible.

  With reference to FIG. 2, the behavior of the deflectors 3u and 3d in the present embodiment will be described. FIG. 2 shows changes over time in the behavior of the deflectors 3u and 3d, where the vertical axis represents the amplitude angle θ of the deflector and the horizontal axis represents time t.

The optical deflection unit 1 is driven at a frequency obtained by superimposing a plurality of natural frequencies (a fundamental frequency ω and a frequency 2ω that is twice the fundamental frequency) of the plate member 2. That is, the behavior of the two deflectors 3u and 3d used for beam deflection is expressed by the following equation. In FIG. 2, φ = 0 and A ₃ = 0.

θ (t) = A ₁ sin (ωt) + A ₂ sin (2ωt + φ) + A ₃
A ₁ : Amplitude in fundamental frequency (fundamental wave) component A ₂ : Amplitude in frequency (double wave) component twice the fundamental frequency ω: Fundamental frequency φ: Phase difference between fundamental wave and harmonic wave A ₃ : Static angle Error, for example, error from design value due to initial assembly error

  According to the above equation and FIG. 2, the behavior of the deflectors 3u, 3d and the drivers 4u, 4d is a mode in which the fundamental frequency swings in the same phase and a mode in which the behavior swings in the opposite phase at twice the fundamental frequency. It shows that it can be obtained by superimposing.

  Further, by appropriately setting each parameter, it is possible to approximate θ (t) ≈kt + α (K, α: constant) in a specific range within each cycle.

  In this range, the deflectors 3u and 3d oscillate at a substantially constant angular velocity (dθ / dt = k), and the beams L1u, L1d, L2u, and L2d in FIG. 1 are deflected at a substantially constant angular velocity in a certain time range. Will be scanned.

(Operational effect of the present embodiment)
In the present embodiment, the deflector and the driver are provided on both sides of the fixed part 12 with the fixed part 12 interposed therebetween so as to be arranged symmetrically with respect to the fixed part 12. In addition, the respective oscillating shafts are provided so as to be aligned with the oscillating shaft O. According to this configuration, the following effects can be obtained.

  First, the deflectors 3u and 3d are in a state of being sufficiently separated with the fixed portion 12 interposed therebetween. Therefore, the deflection point of each beam can be shifted in the direction of the swing axis O without increasing the mirror surface size. Further, there is no possibility that the actuator 9 shields the beam deflected by the deflectors 3u and 3d.

  As a result, it is possible to dispose the incident system member by increasing the pitch in the sub-scanning direction of the incident system including the semiconductor laser 41, the collimator lens 42, and the cylindrical lens 43.

  Further, if the incident system is tilted in the sub-scanning direction, the pitch between the incident systems can be further increased, so that the size of the plate member 2 can be further reduced. At this time, according to the present embodiment, the tilt angle of the incident system in the sub-scanning direction can be kept to the minimum necessary, and the influence on the imaging performance can be kept to a minimum.

  Further, since the deflectors 3u and 3d are sufficiently separated on both sides with the fixed portion 12 in between, the lengths of the torsion springs 5u, 6u, 6d and 5d are also the minimum necessary length, and the entire optical scanning device can be obtained. It is possible to prevent an increase in size in the swing axis O direction, the so-called sub-scanning direction.

  In addition, since the plate member 2 is manufactured in a single piece from a single Si single crystal wafer, the upper and lower deflectors 3u and 3d and the driver elements 4u and 4d sandwiching the fixed portion 12 are manufactured by the same manufacturing process. be able to.

  Therefore, since there is no wafer lot difference due to manufacturing process variations, relative differences due to shape errors are unlikely to occur between the upper and lower deflectors and drivers. As a result, the natural frequencies on both sides of the fixed portion 12 are uniform, the mirror surface accuracy is uniform, and the scanning characteristics are uniform. Thereby, a difference in beam characteristics hardly occurs between beams subjected to deflection scanning, and good image quality can be realized.

  On the other hand, if the upper and lower deflectors 3u and 3d sandwiching the fixed portion 12 are separated, there may be a difference in scanning characteristics of each deflector due to assembly errors and semiconductor manufacturing variations. In the form, the deflectors 3u and 3d are integrated, so that a difference is hardly generated. Moreover, since it is an integral object, manufacturing cost can also be reduced.

  Further, since the swing axes of the upper and lower deflectors 3u and 3d and the driver elements 4u and 4d across the fixed portion 12 are on the same straight line (swing axis O), the upper and lower optical characteristics can be made uniform. It is possible.

  That is, if the respective swing axes are not on the same straight line, an unnecessary moment may be generated to induce an unnecessary vibration mode, or unnecessary stress may be generated in the fixed portion 12. According to this, these problems are reduced.

  Further, by arranging the plate member 2 in a vertically symmetrical arrangement with the fixing portion 12 in between, it is possible to fix the plate member 2 at one point in the substantially central portion in the swing axis O direction. In addition, the shape of the fixing | fixed part 12 is not restricted to the shape in this Embodiment.

  Further, since all the driver elements 4u, 4d provided on the plate member 2 are driven by a single actuator 9, and the actuator 9 is disposed at a substantially central portion in the swing axis O direction, the number of parts is reduced. In addition, the size of the light deflection unit 1 can be minimized.

  Further, since the fixed portion 12 is provided at the substantially central portion in the swing axis O direction, the size of the entire plate member 2 can be minimized.

  Further, since the holding portion of the plate member 2 also serves as the holding portion of the actuator 9 at the substantially central portion of the holder 8, the positioning accuracy between the plate member 2 and the actuator 9 can be improved.

  Further, since the deflectors 3u and 3d are driven at substantially equal angular speeds, it is possible to use almost the same optical system as that of a conventional optical scanning device using a rotating polygon mirror.

  Further, in the present embodiment, the deflector and the driver are arranged symmetrically up and down with the fixed portion 12 interposed therebetween, and the constant angular velocity drive is performed by superposing the fundamental wave and the harmonic wave. However, the sine wave drive may be used. In the case of sinusoidal driving, the plate member 2 is driven only with the fundamental wave.

In the case of sine wave drive, the scanning lens is not a conventional fθ lens but F · arc.
By using the sin θ lens, the beam can be scanned at a constant speed on the surface of the photosensitive drum 32.

  However, if the F. arcsin θ lens is used to make the speed constant, the beam spot diameter will be enlarged at the left and right scanning ends. As an alternative method, image writing can be performed according to changes in the scanning speed without using the F • arcsin θ lens. A method of smoothly changing the clock is also mentioned.

  Alternatively, it is also possible to adopt a combination means such that a lens close to F · arcsin θ is set to scan at approximately constant speed, and the amount by which the scanning speed slightly changes is corrected at the image writing timing.

  As described above, according to this embodiment, the mirror size is increased and the torsion spring is lengthened to prevent the optical scanning device from becoming thicker in the direction of the swing axis, while effectively increasing the incident pitch, and the optical component. Can be laid out. Also, it is possible to minimize the characteristic difference during operation between the scanning mirrors.

  Therefore, according to this embodiment, an optical system capable of accurately deflecting and scanning a plurality of beams while reducing the manufacturing cost with a configuration capable of widening the incident system pitch without increasing the mirror size. It becomes possible to provide a scanning device and an image forming apparatus including the same.

[Second Embodiment]
An optical scanning apparatus according to a second embodiment of the present invention and an image forming apparatus including the same will be described with reference to FIGS. FIG. 7 is a perspective view showing the overall configuration of the plate member in the present embodiment. FIG. 8 is a perspective view showing the overall configuration of the optical scanning device according to the present embodiment. Note that description of portions having the same configuration as in the first embodiment is omitted.

  As shown in FIG. 7, the present embodiment is characterized in that a deflecting surface is formed only on one surface of the deflector. Since each deflector has a deflecting surface formed only on one surface thereof, the plate member 2 is provided with four deflectors 3c, 3m, 3y, and 3k for deflecting and scanning four beams. Yes. Similarly to the first embodiment, two driver elements are provided, one on each side of the fixed portion 12.

  The deflectors 3c, 3m, 3y, and 3k and the drive elements 4u and 4d are arranged so as to be symmetrical with respect to the fixed portion 12 on both sides of the fixed portion 12, and the deflectors 3c, 3m, 3y, The beam is deflected and scanned by two-dot chain lines Lc, Lm, Ly, and Lk by 3k. Moreover, it is the same as that of the first embodiment in that each swing shaft is arranged so as to be on the same straight line.

  As shown in FIG. 8, the beams emitted from the semiconductor lasers 41c, 41m, 41y, and 41k are transmitted through the collimator lenses 42c, 42m, 42y, and 42k, and then sequentially to the cylindrical lenses 43c, 43m, 43y, and 43k. To Penetrate.

  Thereafter, unlike the first embodiment, each beam is incident on each deflection surface from one side of the plate member 2 and deflected and scanned by the deflectors 3c, 3m, 3y, and 3k. Thereafter, the beams deflected by the deflection surface pass through the scanning lenses 44 cm and 44 yk, and are sequentially folded by the first folding mirrors 45 c, 45 m, 45 y, and 45 k and the second folding mirrors 46 c, 46 m, 46 y, and 46 k.

Thereafter, beams Lc, Lm, Ly, and Lk are formed, and these beams are irradiated on the surfaces of the photosensitive drums 32c, 32m, 32y, and 32k. The beam emitted from the semiconductor laser 41c enters the BD sensor 48c outside the optical writing area, and the output signal synchronizes the writing signal and is used to detect the writing start timing. Moreover, you may use for the detection for control of the amplitude and a period of the deflectors 3c, 3m, 3y, and 3k.

  According to this embodiment, since the number of deflectors is four, the size of the optical scanning device in the direction of the swing axis O is larger than that of the first embodiment, but only one side of the deflector. Therefore, there is no possibility that the difference between the front and back surfaces of the deflection surface will affect the scanning characteristics.

  For example, the mirror surfaces of the deflectors 3c, 3m, 3y, and 3k are required to have very high precision flatness. However, if the material Si single crystal wafer is warped or warped or distorted by the subsequent semiconductor process, the spot shape may collapse on the surfaces of the photosensitive drums 32c, 32m, 32y, and 32k.

  Also, when deflecting scanning is performed using both the front and back sides of the deflector, the direction of warping is reversed between the front and back sides, so a relative difference occurs between the spot shape on the front surface and the spot shape on the back surface. May affect image quality.

  In contrast, in the present embodiment, since deflection scanning is performed only on one side of the deflector, the direction of warping of each deflection surface can be made uniform. Therefore, it is possible to take measures such as incorporating design corrections into the scanning lenses 44 cm and 44 yk.

  By aligning the warping directions of the deflection surfaces in this way, the imaging performance is uniform for each color, and the image quality can be improved. Further, since the surface processing (formation of a deflection film, etc.) on the deflection surface is completed on one side, the manufacturing cost can be reduced.

  As described above, according to the present embodiment, the mirror size is increased and the torsion spring is lengthened, and the optical scanning device is prevented from becoming thicker in the direction of the swing axis, and the optical pitch is efficiently increased while increasing the incident pitch. It becomes possible to lay out parts. Also, it is possible to minimize the characteristic difference during operation between the scanning mirrors.

  Therefore, according to this embodiment, an optical system capable of accurately deflecting and scanning a plurality of beams while reducing the manufacturing cost with a configuration capable of widening the incident system pitch without increasing the mirror size. It becomes possible to provide a scanning device and an image forming apparatus including the same.

The perspective view which shows the whole structure of the plate member in 1st Embodiment. The figure which shows the behavior of the deflector in 1st Embodiment. The perspective view which shows the whole structure of the light deflection | deviation unit in 1st Embodiment. The disassembled perspective view of the light deflection unit in the first embodiment The perspective view which shows the whole structure of the optical scanning device concerning 1st Embodiment. 1 is a schematic configuration diagram illustrating an overall configuration of an image forming apparatus according to a first embodiment. The perspective view which shows the whole structure of the plate member in 2nd Embodiment. The perspective view which shows the whole structure of the optical scanner which concerns on 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical deflection unit 2 Plate member 3 Deflector 4 Driver 5 Torsion spring 6 Torsion spring 7 Permanent magnet 8 Holder 9 Actuator 12 Fixed part O Oscillating shaft

Claims (4)

A plurality of light sources for emitting beams;
A light deflection unit that deflects the beams emitted from the plurality of light sources to the surface of the photoreceptor provided corresponding to each of the beams;
An imaging member for imaging the beam deflected in the light deflection unit on the surface of the photosensitive member;
In an optical scanning device comprising:
The light deflection unit is
A plate member for deflecting the beam;
A holding member for holding the plate member;
Have
The plate member is
A deflector formed with a deflection surface of the beam;
A driver that swings in response to a driving force;
A fixing portion for fixing the plate member to the holding member;
Have
The deflector, the driving element, and the fixed portion are connected in series by a torsion spring, and the deflecting element swings as the driving element swings by receiving a driving force,
The deflector and the driver are
An optical scanning device, characterized in that it is arranged on both sides of the fixed portion so as to be symmetric with respect to the fixed portion, and the respective swing axes are aligned. All the driving elements provided in the plate member are driven by a single driving means provided in the light deflection unit,
The driving means includes
The optical scanning device according to claim 1, wherein the optical scanning device is provided at a position facing a substantially central portion of the plate member in the swing axis direction. The driving means includes
The optical scanning device according to claim 1, wherein the optical scanning device is provided on an opposite side of the fixing portion with the holding member interposed therebetween. The optical scanning device according to any one of claims 1 to 3,
A photoreceptor on which a beam deflected from the optical scanning device is imaged;
Transfer means for transferring an image formed on the photoreceptor onto a sheet material;
An image forming apparatus comprising:

Images