JP2009031317A - Optical scanning device and image forming apparatus using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanning device for easily obtaining high quality images by achieving miniaturization of the whole device, and to provide an image forming apparatus using it. <P>SOLUTION: The optical scanning device has a light source, a deflection means for deflecting and scanning a light flux emitted from a light source means in a main scanning direction, and an imaging optical system for imaging a light flux deflected and scanned in a deflection face of the deflection means on a face to be scanned by being reciprocally moved. In a wavefront aberration of the imaging optical system, the sign of the wavefront aberration is reversed on the way from 0 to the maximum image height of image height which a light flux passing the imaging optical system reaches. The reversing image height is represented by Y1. The deflection face reciprocally moves, the sign of a deflection angle acceleration is reversed on the way which the image height arrived by the light flux deflected and scanned on the deflection face is from 0 to the maximum image height, and when the image height is Y2 at reversing of the sign, a condition being 0.8<Y1/Y2<1.2 (here, image height is at an imaging position of a main scanning direction of a light flux arriving on a face to be scanned) is satisfied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical scanning device and an image forming apparatus using the same, and is suitable for an image forming apparatus such as a laser beam printer (LBP) having an electrophotographic process, a digital copying machine, or a multifunction printer (multifunctional printer). is there.

  Conventionally, many optical scanning devices using an optical deflector (resonant optical deflector) that reciprocates as an optical deflector have been proposed (see Patent Document 1).

  Compared with an optical scanning device using a rotating polygon mirror such as a polygon mirror as an optical deflector, an optical scanning device using a resonant optical deflector has the following advantages.

    (1) The optical deflector itself can be greatly reduced in size.

    (2) Low power consumption.

    (3) A resonance type optical deflector made of a Si single crystal manufactured by a semiconductor process is theoretically free from metal fatigue and has excellent durability and high productivity.

  FIG. 12 is a schematic diagram of a main part of an optical scanning device using a conventional resonator type optical deflector.

  In the figure, a divergent light beam that is light-modulated and emitted from the light source means 1 according to image information is converted into a parallel light beam by a collimator lens 2, the light beam width and cross-sectional shape are adjusted by an aperture stop 3, and incident on a cylindrical lens 4. . Among the parallel light beams incident on the cylindrical lens 4, the light enters the deflection surface (deflection reflection surface) 5 a (front incidence) from the center of the vibration angle (deflection angle) of the optical deflector 5 in the main scanning section. In the sub-scanning section, the light is incident (obliquely incident) on the deflection surface 5a with a finite angle in the sub-scanning direction, and is formed as a line image on the deflection surface 5a.

Then, the light beam deflected and reflected in the main scanning direction by the reciprocating motion of the deflecting surface 5a of the optical deflector 5 is guided through the imaging optical system 6 onto the photosensitive drum surface 7 as the scanned surface. Then, by reciprocating the deflection surface 5a of the optical deflector 5, the photosensitive drum surface 7 is optically scanned in the main scanning direction. As a result, an image is recorded on the photosensitive drum surface 7 as a recording medium.
JP 2005-308863 A

  In order to reduce the size of the optical scanning device, it is effective to reduce the size of optical components and the number of lenses constituting the imaging optical system. However, when the number of lenses of the imaging optical system is reduced, various aberrations of the optical system cannot be sufficiently corrected, and the imaging performance deteriorates, and a good image cannot be obtained.

  An optical scanning device using a resonance type optical deflector is suitable for downsizing the device as compared with an optical scanning device using a rotary polygon mirror such as a polygon mirror as described above. However, the following problems exist.

  In general, in a resonant optical deflector that requires high-speed operation, the deflecting surface undergoes torsional vibration within a predetermined angle, and thus receives a large angular acceleration. Therefore, during driving, the deflection surface receives inertial force due to its own weight, and the deflection surface is greatly bent. Here, when the deflecting surface is deformed by dynamic deflection, the light beam deflected and reflected by the deflecting surface generates wavefront aberration (coma aberration) twice as much as the deformation amount. Adversely affects the imaging spot at.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning device capable of reducing the size of the entire apparatus and easily obtaining a high-quality image, and an image forming apparatus using the same.

The optical scanning device of the invention of claim 1
By reciprocating with the light source means, a deflection means for deflecting and scanning the light beam emitted from the light source means in the main scanning direction, and a light beam deflected and scanned by the deflection surface of the deflection means is formed on the surface to be scanned. In an optical scanning device having an image optical system,
The wavefront aberration of the imaging optical system is such that the sign of the wavefront aberration is reversed while the image height reached by the light beam that has passed through the imaging optical system is from 0 to the maximum image height, and the image height is reversed. Y1, the deflection angular acceleration when the deflection surface reciprocates, the sign is reversed while the image height reached by the light beam deflected and scanned on the deflection surface is from 0 to the maximum image height, and the sign is reversed. When the image height when doing is Y2,
0.8 <Y1 / Y2 <1.2
(However, the image height is the imaging position in the main scanning direction of the light beam reaching the scanned surface.)
It is characterized by satisfying the following conditions.

The invention of claim 2 is the invention of claim 1,
The imaging optical system includes a single imaging optical element or a plurality of imaging optical elements, the sum of refractive powers on the optical axis is positive, and the sum of refractive powers at 90% of the effective diameter. Is negative.

The invention of claim 3 is the invention of claim 1 or 2, wherein
The wavefront aberration of the imaging optical system is coma aberration in the meridional cross section, and Ymax is the maximum image height reached by the light beam that has passed through the imaging optical system, and passes through the imaging optical system in which coma aberration is reversed. When the image height at which the luminous flux reaches is Yc,
0.6 <Yc / Ymax <0.9
It is characterized by satisfying the following conditions.

The invention of claim 4 is the invention of claim 1, 2 or 3,
The deflection surface is driven so as to cancel the wavefront aberration of the imaging optical system.

The invention of claim 5 is the invention of any one of claims 1 to 4,
The reciprocating motion of the deflection surface is performed by resonance driving.

The invention of claim 6 is the invention of claim 5,
The reciprocating motion of the deflecting surface driven by resonance has a plurality of separated natural vibration modes, and among the separated natural vibration modes, a reference vibration mode which is a natural vibration mode of a reference frequency, and the reference There is an integer multiple vibration mode that is a natural vibration mode having a frequency that is an integral multiple of the frequency, and a region within ± 10% of the equiangular velocity is used in a partial region during the scanning.

The image forming apparatus of the invention of claim 7
7. The optical scanning device according to claim 1, a photosensitive member disposed on the surface to be scanned, and a static image formed on the photosensitive member by a light beam scanned by the optical scanning device. A developing device that develops an electrostatic latent image as a toner image, a transfer device that transfers the developed toner image onto a transfer material, and a fixing device that fixes the transferred toner image onto the transfer material. Yes.

An image forming apparatus according to an eighth aspect of the present invention provides:
The optical scanning device according to claim 1, and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device. It is said.

A color image forming apparatus according to a ninth aspect of the present invention provides:
A plurality of image carriers that are arranged on a surface to be scanned of the optical scanning device according to claim 1 and that form images of different colors.

The invention of claim 10 is the invention of claim 9,
It is characterized by having a printer controller that converts color signals input from an external device into image data of different colors and inputs them to each optical scanning device.

  According to the present invention, it is possible to reduce the size of the entire apparatus and to achieve an optical scanning apparatus that can easily obtain a high-quality image and an image forming apparatus using the same.

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

  FIG. 1 is a sectional view (main scanning sectional view) of the main part in the main scanning direction according to the first embodiment of the present invention. 2 is a cross-sectional view (sub-scanning cross-sectional view) of the main part in the sub-scanning direction of the optical scanning device shown in FIG.

  In the following description, the main scanning direction (Y direction) is a direction perpendicular to the oscillation axis of the deflecting means and the optical axis (X direction) of the imaging optical system (the light beam is deflected and reflected (deflected scanning) by the deflecting means). Direction). The sub-scanning direction (Z direction) is a direction parallel to the swing axis of the deflecting means. The main scanning section is a plane including the optical axis of the imaging optical system and the main scanning direction. The sub-scan section is a section that includes the optical axis of the imaging optical system and is perpendicular to the main scan section.

  In FIG. 1 and FIG. 2, reference numeral 1 denotes a light source means, for example, a semiconductor laser. Reference numeral 2 denotes a coupling lens (collimator lens) as a condensing optical system, which converts the luminous flux state of the luminous flux emitted from the light source means 1. In this embodiment, the divergent light beam is converted into a convergent light beam. Reference numeral 3 denotes an aperture stop, which shapes the beam shape by limiting the light beam that has been made a convergent light beam by the coupling lens 2. A cylindrical lens (cylinder lens) 4 has a predetermined power (refractive power) only in the sub-scan section (sub-scan direction). The cylindrical lens 4 forms a line image on the deflecting surface 5a of the optical deflector 5 as a deflecting means to be described later in the sub-scan section in the sub-scan section.

  Each element of the coupling lens 2 and the cylindrical lens 4 constitutes one element of the incident optical system LA. Further, the collimator lens 2 and the cylindrical lens 4 may be integrally configured as one optical element (anamorphic lens).

  Reference numeral 5 denotes a resonance type optical deflector serving as a deflecting means. The deflecting surface 5a reciprocates so that the scanned surface 7 is deflected and scanned in the main scanning direction by the light beam emitted from the condensing optical system 2. Yes. The reciprocating motion of the deflecting surface 5a in this embodiment is performed by resonance driving.

  Reference numeral 6 denotes an imaging optical system (fθ lens system) having an fθ characteristic, which has a single imaging optical element (imaging lens, toric lens) 6 a made of a plastic material, and is deflected by the optical deflector 5. The light beam deflected by the surface 5 a is imaged on the scanned surface 7. The imaging lens 6a in this embodiment has a shape in which the sum of refractive powers on the optical axis is positive and the sum of refractive powers at 90% of the effective diameter is negative.

  Reference numeral 7 denotes a photosensitive drum surface as a surface to be scanned.

  The imaging optical system 6 corrects the surface tilt of the deflection surface 5a of the resonance type optical deflector 5 in the sub-scan section. In general, in the case of a deflecting unit having a plurality of deflecting surfaces such as a polygon mirror, the tilting angle in the sub-scanning direction is different for each surface, so that a surface tilt correcting optical system is generally employed.

  In the case of the resonance type optical deflector 5, since there is only one deflection surface 5a, it is not necessary to consider the difference in the amount of tilt for each surface. However, due to the influence of a mounting accuracy error of the magnet 503 shown in FIG. Therefore, in order to make the beam spot position on the scanned surface constant from the start of scanning to the end of scanning, it is preferable that the deflection surface 5a and the scanned surface 7 are conjugated in the sub-scan section.

  In general, in the resonance type optical deflector 5, if the size of the deflection surface 5a is increased excessively, it becomes difficult to drive at high speed. When used in a laser beam printer or a digital copying machine, it is advantageous to reduce the size of the deflection surface 5a as much as possible.

  Therefore, in this embodiment, a light beam is incident from the front onto the deflecting surface 5a of the resonance type optical deflector 5 from the imaging lens 6a side in FIG. 1 (front incidence). By doing so, the width of the deflecting surface 5a of the resonance type optical deflector 5 in the main scanning direction can be minimized and can be easily swung at high speed.

  When the light is incident on the front as described above, the light beam incident on the deflection surface 5a of the resonance type optical deflector 5 interferes with the light beam deflected and reflected by the deflection surface 5a. For this reason, in this embodiment, as shown in FIG. 2, the light beam incident on the deflecting surface 5a is incident at a specific angle in the sub-scanning direction (oblique incidence).

  In FIG. 2, an oblique incident angle γ = 3 ° is given in the sub-scanning direction, and a light beam emitted from the light source means 1 is incident from an obliquely downward direction in the figure. Therefore, the light beam deflected and scanned by the deflecting surface 5a is also deflected and reflected upward in FIG. 2 at the same angle as the oblique incident angle γ ′ = 3 ° in the sub-scanning direction.

  The imaging lens 6a is arranged at a specific distance above the sub-scanning direction so that the deflected light beam deflected and reflected upward is incident, and the deflected light beam incident on the imaging lens 6a is placed on the surface 7 to be scanned. Is imaged in a spot shape.

  The resonance type optical deflector 5 of the present embodiment achieves deflection scanning with a wider equiangular velocity region than the sinusoidal vibration type by driving the second frequency wave superimposed on the fundamental frequency.

  When a resonance type optical deflector performing sinusoidal vibration is used, it is necessary to use an imaging optical system having an Arcsin characteristic in order to scan at a constant speed on the surface to be scanned. However, when an image is formed using an imaging optical system having an Arcsin characteristic, there is a problem in that the image end spot is enlarged with respect to the center of the image and the image quality is deteriorated.

  Therefore, in this embodiment, by using a two-degree-of-freedom resonance type optical deflector to widen the equiangular velocity region, the same fθ lens as when a conventional polygon mirror is used as an optical deflector is used. Making it possible.

As an example, the driving fundamental frequency is ω1 = 2π × 2000 (HZ),
ω2 = 2π × 4000 (HZ)
That is, ω2 = 2ω1. These vibration modes are hereinafter referred to as mode 1 and mode 2.

  FIG. 3 is a schematic diagram of a main part of the resonance type optical deflector according to the first embodiment of the present invention.

  In the resonance type optical deflector 5 of the present embodiment, a system comprising a plurality of movers (vibrators) 501 and 502 and a torsion spring 504 vibrate simultaneously at the fundamental frequency and a frequency that is an integer multiple thereof. The drive control unit 507 controls the drive unit 506. At this time, various driving can be performed by changing the amplitude and phase of the movable elements 501 and 502 driven at the fundamental frequency and a frequency that is an integral multiple of the fundamental frequency. In FIG. 3, 5a is a deflection surface, 503 is a magnet, and 505 is a support portion.

In this embodiment, the drive control means 507 is controlled so that the maximum vibration amplitude φ1 of the mover 501 in mode 1 is φ1 = 38.2279790 deg.
The angular frequency ω1,
ω1 = 2π × 2000 (HZ),
It is said. Further, the maximum vibration amplitude φ2 of the mover 502 in mode 2 is φ2 = 5.32752 (deg),
The angular frequency ω2,
ω2 = 2π × 4000 (HZ)
It is trying to become. The phases are set so as to differ by 180 degrees.

  The vibration angle (deflection angle) θ1 of the mover 501 at this time is

Given in.

Given in.

  In the present embodiment, the reciprocating motion of the deflecting surface 5a that is resonantly driven has a plurality of separated natural vibration modes. Among the plurality of separated natural vibration modes, there are a reference vibration mode that is a natural vibration mode of a reference frequency and an integer multiple vibration mode that is a natural vibration mode of an integer multiple of the reference frequency. An area within ± 10% with respect to the constant angular velocity is used in a part of the area during the scanning.

  4A and 4B show the deflection angle (reflection angle) of the scanning light beam by the movable element 501 of the resonance type optical deflector 5 in this embodiment. In FIGS. 2A and 2B, the horizontal axis represents the vibration period T (time), and the vertical axis represents the vibration angle (deflection angle) θ (unit deg).

  In the present embodiment, it can be seen that by resonating the mode 1 and the mode 2, there are many regions in which the vibration angle θ is proportional to time (equal angular velocity) as compared to normal sine vibration.

  FIGS. 5A and 5B are graphs showing the deflection angular velocity of the mover 501. FIG. 5B is an enlarged view of a part of FIG. In FIGS. 4A and 4B, the horizontal axis represents the vibration period T (time), and the vertical axis represents the deflection angular velocity dθ / dt.

  As shown in FIGS. 4A and 4B, it can be seen that the deflection angular velocity is constant (152 to 160 dθ / dt) at the time T of 0 to 0.16 T.

6A and 6B are graphs showing the deflection angular acceleration of the mover 501. FIG. FIG. 6B is an enlarged view of a part of FIG. In FIGS. 4A and 4B, the horizontal axis represents the vibration period T (time), and the vertical axis represents the deflection angular acceleration d ² θ / dt ² .

  The resonance type optical deflector 5 used in this embodiment has a thickness of 200 μm, a width in the main scanning direction (Y direction) of 3.2 mm, and a width of 1.1 mm in the sub scanning direction (Z direction). .

  When the thin movable element 501 is vibrated at a high speed, the deflecting surface 5a is torsionally vibrated within a predetermined angle, so that the deflecting surface 5a receives an inertial force due to its own weight and receives an inertial force due to its own weight. Surface deformation (dynamic deflection) occurs. The surface deformation changes in proportion to the angular acceleration of the mover 501.

  That is, the surface shape in the main scanning direction of the deflection surface 5a changes due to the reciprocating motion in the main scanning direction.

  FIG. 8 is a graph showing a result of calculating the surface deformation amount (dynamic deflection amount) of the deflecting surface 5a in a state where the image edge is scanned when the vibration described above is performed.

  In this graph, the surface deformation is obtained at a certain height of the deflecting surface 5a, and the inclination component at the center in the main scanning direction at each height is removed. From this graph, it can be seen that the amount of deformation varies greatly depending on the Z position in the sub-scanning direction (see FIG. 3).

  In the region where the deflecting surface 5a is supported by the torsion spring 504 (Z <0, lower side in FIG. 3), the amount of surface deformation is large, and in the region on the opposite side (Z> 0, upper side in FIG. 3) It can be seen that the amount of deformation is small. In general, it can be said that the supported side has a larger surface deformation and the unsupported side has a smaller surface deformation.

  Although the thickness of the movable element 501 of this embodiment is 200 μm, the thickness may be increased in order to suppress the dynamic bending caused by the angular acceleration. However, when the mover 501 is thickened, it is necessary to increase the length of the torsion spring 504 in order to cause resonance vibration at the same frequency. Therefore, the size of the resonance type optical deflector 5 itself is increased, which leads to an increase in the size of the optical scanning device.

  In addition, the number of resonance type optical deflectors 5 that can be taken out from one wafer is reduced, which is inefficient in manufacturing. If the thickness is reduced, the size of the resonance type optical deflector 5 itself is reduced. However, as described above, the amount of dynamic deflection increases, which affects the spot imaged on the scanned surface 7. Become. Therefore, the thickness of the mover 501 is desirably about 100 μm to 500 μm.

  FIG. 9 is a graph showing the wavefront aberration (coma aberration in the main scanning direction) at each scanning image height of the imaging optical system 6 of Example 1 of the present invention.

  In the figure, in the main scanning section, the wavefront aberration of the imaging optical system 6 becomes 0 at an image height (reversed image height Y1) of 80 mm on the scanned surface 7, and the sign is inverted before and after that. On the other hand, the angular acceleration (deflection angular acceleration) of the resonance type optical deflector 5 becomes 0 at 75 mm of the image height (reverse image height Y2), and the sign is inverted before and after that.

  As described above, since the surface deformation of the deflecting surface 5a is proportional to each acceleration of the movable element 501, the sign of wavefront aberration (coma aberration) generated by the surface deformation is reversed at the position where the angular acceleration becomes zero. Therefore, as shown in the graph of coma aberration in the main scanning direction after considering the surface deformation in FIG. 9, the coma aberration in the main scanning direction remaining in the design is corrected over the entire scanning region.

In this embodiment, in the main scanning section, the wavefront aberration of the imaging optical system 6 is reversed in the middle of the image height from 0 to the maximum image height as described above, and the reversed image height. Is Y1. Furthermore, the sign of the deflection angular acceleration when the deflecting surface 5a reciprocates is reversed in the middle of the image height from 0 to the maximum image height, and the image height when the sign is reversed is Y2. At this time,
0.8 <Y1 / Y2 <1.2 (1)
(However, the image height is the imaging position in the main scanning direction of the light beam reaching the scanned surface.)
Satisfy the following conditions.

  For example, the image height means the imaging position in the main scanning direction when the light beam that has passed through the imaging optical system 6 reaches the scanned surface 7.

  Further, for example, the image height means an imaging position in the main scanning direction when the light beam deflected and scanned by the deflecting surface 5a reaches the scanned surface 7.

  The same applies hereinafter.

  When the lower limit of conditional expression (1) is exceeded, the correction effect at the scanning end decreases, and when the upper limit of conditional expression (1) is exceeded, the correction effect at the intermediate image height decreases and overcorrection occurs at the end. There is a possibility of becoming.

In this example,
Y1 = 80 mm,
Y2 = 75mm
And
Y1 / Y2 = 1.07
It becomes. This satisfies the conditional expression (1).

  More preferably, the conditional expression (1) should be set as follows.

0.9 <Y1 / Y2 <1.1 (1a)
The wavefront aberration of the imaging optical system 6 is coma aberration in the meridional section (main scanning section) as described above. The maximum image height of the imaging optical system 6 is Ymax, and the image height at which coma aberration is inverted is Yc. And when
0.6 <Yc / Ymax <0.9 (2)
It is better to satisfy the following conditions.

  If the lower limit of conditional expression (2) is exceeded, the wavefront aberration (coma) near the maximum image height will increase, and if it is set to correct all the wavefront aberration, the deviation of the fθ characteristic may increase. There is sex. If the upper limit of conditional expression (2) is exceeded, the wavefront aberration (coma) at the intermediate image height may increase, and the amount of coma aberration correction at the intermediate image height is originally small, so the correction may be insufficient. There is.

  Tables 1-1 and 1-2 show various characteristics of the optical system of the optical scanning device in this example.

  The aspherical shape of the main scanning section of the imaging lens is based on the intersection of each lens surface and the optical axis as the origin, the optical axis direction is the X axis, and the axis orthogonal to the optical axis in the main scanning section is the Y axis. An axis orthogonal to the optical axis in the cross section is taken as the Z axis. At this time,

It is expressed by the following formula.

Here, R is a radius of curvature, k, and B _{4 to} B ₁₀ are aspherical coefficients.

  Further, the shape of the sub-scanning cross section is the radius of curvature r ′ where the lens surface coordinate in the main scanning direction is Y,

The shape is expressed by the following formula.

Note that r is a radius of curvature on the optical axis, and D _{2 to} D ₁₆ are coefficients.

  In this way, in this embodiment, as described above, the deflection surface 5a is driven so as to cancel the wavefront aberration (coma aberration in the main scanning direction) remaining in the imaging optical system 6, thereby obtaining a good spot in the entire scanning region. And a good image can be obtained.

  In this embodiment, the imaging optical system 6 is composed of a single imaging optical element (imaging lens). However, the effect of this embodiment is not limited thereto, and a plurality of imaging optical elements is used. It is also effective when configured with

  Further, the imaging optical system 6 may include a diffractive optical element.

[Image forming apparatus]
FIG. 10 is a cross-sectional view of the main part in the sub-scanning direction showing an embodiment of the image forming apparatus of the present invention. In the figure, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into image data (dot data) Di by a printer controller 111 in the apparatus. The image data Di is input to the optical scanning unit 100 having the configuration shown in the first embodiment. The light scanning unit 100 emits a light beam 103 modulated according to the image data Di, and the light beam 103 scans the surface of the photosensitive drum (photosensitive member) 101 in the main scanning direction. .

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

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

  The toner image developed by the developing unit 107 is transferred onto a sheet 112 as a transfer material by a transfer roller 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in the paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 10), but can be fed manually. A paper feed roller 110 is provided at the end of the paper cassette 109, and feeds the paper 112 in the paper cassette 109 into the transport path.

  As described above, the sheet 112 on which the unfixed toner image has been transferred is further conveyed to the fixing device behind the photosensitive drum 101 (left side in FIG. 10). The fixing device includes a fixing roller 113 having a fixing heater (not shown) therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113. Then, the sheet 112 conveyed from the transfer unit is heated while being pressed by the pressure contact portion between the fixing roller 113 and the pressure roller 114 to fix the unfixed toner image on the sheet 112. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and the fixed paper 112 is discharged out of the image forming apparatus.

  Although not shown in FIG. 10, the print controller 111 controls not only the data conversion described above but also each part in the image forming apparatus including the motor 115 and a motor in the optical scanning unit described later. Do.

  The recording density of the image forming apparatus used in the present invention is not particularly limited. However, considering that the higher the recording density is, the higher the image quality is required, the configuration of the first embodiment of the present invention is more effective in an image forming apparatus of 1200 dpi or more.

[Color image forming apparatus]
FIG. 11 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. This embodiment is a tandem type color image forming apparatus in which four scanning optical devices (scanning optical systems) are arranged in parallel and image information is recorded on the surface of a photosensitive drum as an image carrier. In FIG. 11, reference numeral 60 denotes a color image forming apparatus, and reference numerals 11, 12, 13, and 14 denote scanning optical apparatuses each having the configuration shown in the first embodiment. 21, 22, 23, and 24 are photosensitive drums as image carriers, 31, 32, 33, and 34 are developing units, and 71 is a conveyance belt. In FIG. 11, there are a transfer device (not shown) for transferring the toner image developed by the developing device to the transfer material, and a fixing device (not shown) for fixing the transferred toner image to the transfer material. is doing.

  In FIG. 11, R (red), G (green), and B (blue) color signals are input to the color image forming apparatus 60 from an external device 72 such as a personal computer. These color signals are converted into C (cyan), M (magenta), Y (yellow), and B (black) image data (dot data) by a printer controller 73 in the apparatus. These image data are input to the scanning optical devices 11, 12, 13, and 14, respectively. From these scanning optical devices, light beams 41, 42, 43, and 44 modulated in accordance with each image data are emitted, and the photoconductor surfaces of the photoconductor drums 21, 22, 23, and 24 are emitted by these light beams. Are scanned in the main scanning direction.

  The color image forming apparatus in this embodiment has four scanning optical devices (11, 12, 13, 14) arranged in each of C (cyan), M (magenta), Y (yellow), and B (black) colors. It corresponds. In parallel, image signals (image information) are recorded on the surfaces of the photosensitive drums 21, 22, 23, and 24, and color images are printed at high speed.

  As described above, the color image forming apparatus according to the present embodiment uses the light beams based on the respective image data by the four scanning optical devices 11, 12, 13, and 14, and the corresponding photosensitive drums 21, It is formed on the 22, 23, and 24 surfaces. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 53, for example, a color image reading apparatus including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.

FIG. 3 is a main scanning sectional view of the optical scanning device according to the first embodiment of the present invention. FIG. 3 is a sub-scan sectional view of the optical scanning device according to the first embodiment of the present invention. 1 is a schematic diagram of a resonant optical deflector according to a first embodiment of the present invention. Graph of deflection angle of resonance type optical deflector of embodiment 1 of the present invention Graph of deflection angular velocity of resonance type optical deflector of embodiment 1 of the present invention Graph of the deflection angular acceleration of the resonance type optical deflector according to the first embodiment of the present invention FIG. 3 is a diagram illustrating a surface deformation image of a deflection surface of the resonance type optical deflector according to the first embodiment of the present invention. Surface deformation simulation value of the deflection surface of the resonance type optical deflector according to the first embodiment of the present invention Wavefront Aberration (Main Scanning Frame) Considering Wavefront Aberration (Main Scanning Frame) and Deformation of Deflection Surface of Imaging Optical System of Example 1 of the Present Invention FIG. 3 is a sub-scan sectional view showing an embodiment of the image forming apparatus of the present invention. FIG. 3 is a sub-scan sectional view showing an embodiment of a color image forming apparatus according to the present invention. Main scanning sectional view of a conventional optical scanning device

Explanation of symbols

1 Light source means (semiconductor laser)
2 Condensing optical system 3 Aperture 4 Cylindrical lens 5 Deflection means (resonant optical deflector)
5a Deflection surface 6 Imaging optical system 7 Scanned surface (photosensitive drum surface)
11, 12, 13, 14 Optical scanning device 21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 51 Conveying belt 52 External device 53 Printer controller 60 Color image forming device 100 Optical scanning device 101 Photosensitive drum 102 Charging roller 103 Light beam 104 Image forming device 107 Development Device 108 Transfer roller 109 Paper cassette 110 Paper feed roller 111 Printer controller 112 Transfer material (paper)
113 Fixing Roller 114 Pressure Roller 115 Motor 116 Paper Discharge Roller 117 External Equipment

Claims (10)

By reciprocating with the light source means, the deflection means for deflecting and scanning the light beam emitted from the light source means in the main scanning direction, and the light beam deflected and scanned by the deflection surface of the deflection means is imaged on the surface to be scanned. In an optical scanning device having an image optical system,
The wavefront aberration of the imaging optical system is such that the sign of the wavefront aberration is reversed while the image height reached by the light beam that has passed through the imaging optical system is from 0 to the maximum image height, and the image height is reversed. Y1, the deflection angular acceleration when the deflection surface reciprocates, the sign is reversed while the image height reached by the light beam deflected and scanned on the deflection surface is from 0 to the maximum image height, and the sign is reversed. When the image height when doing is Y2,
0.8 <Y1 / Y2 <1.2
(However, the image height is the imaging position in the main scanning direction of the light beam reaching the scanned surface.)
An optical scanning device characterized by satisfying the following conditions.   The imaging optical system includes a single imaging optical element or a plurality of imaging optical elements, the sum of refractive powers on the optical axis is positive, and the sum of refractive powers at 90% of the effective diameter. The optical scanning device according to claim 1, wherein is negative. The wavefront aberration of the imaging optical system is coma aberration in the meridional cross section, and Ymax is the maximum image height reached by the light beam that has passed through the imaging optical system, and passes through the imaging optical system in which coma aberration is reversed. When the image height at which the luminous flux reaches is Yc,
0.6 <Yc / Ymax <0.9
The optical scanning device according to claim 1, wherein the following condition is satisfied.   4. The optical scanning device according to claim 1, wherein the deflecting surface is driven so as to cancel the wavefront aberration of the imaging optical system. 5.   5. The optical scanning device according to claim 1, wherein the reciprocating motion of the deflecting surface is performed by resonance driving.   The reciprocating motion of the deflecting surface driven by resonance has a plurality of separated natural vibration modes, and among the separated natural vibration modes, a reference vibration mode which is a natural vibration mode of a reference frequency, and the reference An integral multiple vibration mode that is a natural vibration mode having a frequency that is an integral multiple of the frequency exists, and a region within ± 10% of the equiangular velocity is used in a partial region during the scan. Item 6. The optical scanning device according to Item 5.   7. The optical scanning device according to claim 1, a photosensitive member disposed on the surface to be scanned, and a static image formed on the photosensitive member by a light beam scanned by the optical scanning device. A developing device that develops an electrostatic latent image as a toner image, a transfer device that transfers the developed toner image onto a transfer material, and a fixing device that fixes the transferred toner image onto the transfer material. Image forming apparatus.   The optical scanning device according to claim 1, and a printer controller that converts code data input from an external device into an image signal and inputs the image signal to the optical scanning device. An image forming apparatus.   7. A color image forming apparatus comprising: a plurality of image carriers that are arranged on a surface to be scanned of the optical scanning apparatus according to claim 1 and that form images of different colors. .   The color image forming apparatus according to claim 9, further comprising a printer controller that converts color signals input from an external device into image data of different colors and inputs the image data to each optical scanning device.