JP2010169855A - Scanning optical apparatus and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the illuminance distribution of an image face on a face to be scanned due to the variation in a luminous flux speed on the face to be scanned and the incident angle dependence of the reflectivity on a deflection face. <P>SOLUTION: The scanning optical apparatus includes: a deflection element which deflects and scans a luminous flux emitted from a light emitting point of a light source means; and an imaging optical system which images the luminous flux deflected and scanned onto a face to be scanned, wherein the deflection element is a resonance type deflection element in which a single defection face reciprocally moves around a rotary axis, the luminous flux from the light emitting point is made incident to a deflection face from a face including the rotary axis of the deflection element and the optical axis of the imaging optical system, when the illuminance distribution Ssp of the image face due to the deflection angle dependence of the scanning speed of the luminous flux on the face to be scanned becomes Ssp<1.05, by setting the polarization direction of the luminous flux emitted from the light emitting point and made incident to the deflection face so as to have P-polarization at the polarization point of the outermost off-axis luminous flux on the deflection face, the illuminance distribution of the image face due to the image angle dependence of the optical efficiency of the imaging optical system and the illuminance distribution of the image face due to the incident angle dependence of the reflectance of the deflection face are compensated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a scanning optical apparatus and an image forming apparatus using the same, and particularly 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). It is.

  Conventionally, in a scanning optical device such as a laser beam printer (LBP), a light beam emitted from a light source means is optically modulated in accordance with an image signal. Then, the light-modulated light beam is periodically deflected by an optical deflector composed of, for example, a polygon mirror, focused on a photosensitive recording medium surface by an imaging optical system having fθ characteristics, and optically scanned to record an image. It is carried out.

  FIG. 17 is a schematic view of the main part of a conventional scanning optical apparatus.

  In the figure, the divergent light beam emitted from the light source means 1 becomes a light beam close to a parallel light beam by the collimator lens 2, and the light beam is restricted by the aperture stop 3 and enters the cylindrical lens 4. Of the parallel luminous flux incident on the cylindrical lens 4, it exits as it is in the main scanning plane. In the sub-scanning plane, the light is focused and formed as a line image on a deflection surface (reflection surface) 95a of a deflection means (deflection element) 95 comprising a polygon mirror.

  The light beam deflected and scanned by the deflecting surface of the deflecting means 95 is guided to the scanned surface 8 through the imaging optical element (imaging optical system) 6 having the fθ characteristic. Then, the scanning unit 8 is scanned in the direction of arrow B (main scanning direction) by rotating the deflecting means 95 in the direction of arrow A.

  In recent years, these scanning optical devices are required to have a compact and high-definition optical system as the image forming apparatus main body becomes smaller and more accurate. In particular, there is a strong demand for miniaturization of the polygon mirror, which is a deflecting means, and a drive motor that rotationally drives the mirror. In order to satisfy these demands, studies have been made on a resonance type deflection element in which a deflection surface reciprocates around an axis.

  Various scanning optical devices using this resonance type deflection element have been proposed (see Patent Documents 1 and 2).

  FIG. 18 shows a schematic diagram of a main part of a typical resonance type deflection element.

  In the figure, a deflector 57 of a resonance type deflection element 56 is located in a frame body 58 and is held by two torsion bars 59 extending in the sub-scanning direction perpendicular to the main scanning surface (deflection scanning surface). Yes. A pulling force such as an electrostatic force, a magnetic force, and a Lorentz force acts between the deflecting surface 57a and the frame body 58 so that the deflecting surface reciprocates. A light beam from a light source means (not shown) is incident on the deflecting surface 57 a of the deflector 57, and the light beam is deflected and scanned by the reciprocating motion of the deflector 57.

  This reciprocating motion can be increased in speed by using it in a resonance state by sinusoidal vibration, and in recent years, the speed has been increased to a level that cannot be realized by a rotary deflecting means using a polygon mirror.

  On the other hand, miniaturization has been promoted by a micromachining technology based on a semiconductor process, and power consumption, noise, and the like have surpassed that of a rotating deflection means.

  One of the problems in using this resonance type deflection element is non-uniformity in the scanning speed of the surface to be scanned.

  In the case of a polygon mirror, the constant velocity of the spot on the surface to be scanned can be easily secured by combining with an fθ lens for scanning at an equal angular velocity.

  On the other hand, since the resonance type deflection element is sinusoidal vibration, it is necessary to combine it with an arc sin θ lens in order to correct the constant velocity on the scanned surface.

  However, with such a combination, even if the constant velocity can be corrected, the spot diameter is enlarged outside the optical axis.

  Patent Document 1 discloses an example in which a resonance type deflection element is combined with an fθ lens to reduce spot diameter enlargement.

  Patent Document 2 discloses an example in which a deflector sine-oscillated with a double wave is superimposed on a vibrator that sine-oscillates with a fundamental wave to cause the deflector to move at a constant speed in a certain region. .

  The second problem is the reflectance of the deflecting surface of the deflecting element and its incident angle characteristics.

  In order to avoid image deterioration due to non-uniformity of the scanning line interval in the sub-scanning direction, the resonance type deflection element is generally not used in both main scanning and sub-scanning directions, but is used in one-way scanning. Compared with the low light utilization efficiency, a highly reflective deflecting surface is required. Further, in order to make the image plane illuminance distribution uniform on the surface to be scanned, it is required that the reflectance changes little over the entire use angle of incidence of the deflection surface.

  In order to achieve both the high reflectivity and the low angle dependency of the reflectivity, there is an example in which gold or copper is vapor-deposited on a silicon substrate serving as a base of a deflection surface of the deflection means. However, it is difficult to deposit such a material on a silicon substrate. Therefore, the use with a protective film such as aluminum is desired.

  Due to the problems inherent to these two resonance type deflection elements, the scanning optical device using the deflection element causes a problem in the image surface illuminance distribution on the surface to be scanned, compared with the one using a polygon mirror as the deflection means. Cheap. In addition, the use of plastic imaging optical elements, dust-proof glass, etc. without the deposition film, and the deterioration of the image plane illuminance distribution due to the dependency of the reflection optical elements on the angle of view of the reflectance make this problem even more serious. It has become.

  Various scanning optical devices for correcting such an image surface illuminance distribution on the surface to be scanned have been proposed (see Patent Documents 3, 4, and 5).

  Patent Document 3 discloses an example in which an image plane illuminance distribution generated due to a factor due to a scanning speed is electrically corrected by the light emission power of a light source means.

  Patent Document 4 discloses an example in which the image plane illuminance distribution generated in the imaging optical element is corrected using the polarization dependence of the reflectance of the optical deflector.

Patent Document 5 discloses an example in which the image surface illuminance distribution is corrected by the beam deflection caused by the rotation of the optical deflector unique to the overfilled scanning system using the reflectance angle dependency of the optical deflector.
JP 2002-258204 A JP 2008-3530 A Japanese Patent Publication No.8-5210 JP-A-1-140116 JP 2001-183597 A

  In the scanning optical device in Patent Document 1, it is difficult to correct the constant velocity on the surface to be scanned, and the scanning speed off-axis with respect to the optical axis decreases, that is, the off-axis exposure amount increases with respect to the optical axis. There is a problem of becoming.

  The scanning optical device in Patent Document 2 does not completely move in a sine motion due to the superposition of sine waves, but has a problem that a certain amount of exposure change occurs on the surface to be scanned.

  The scanning optical device in Patent Document 3 has a problem that the whole device becomes complicated due to the addition of a correction circuit for electrical correction. There is also a problem that the correction accuracy is low.

  The scanning optical devices in Patent Documents 4 and 5 do not disclose an example of optically correcting an image plane illuminance distribution caused by a change in scanning speed generated by a resonance type deflection element.

  The present invention relates to a scanning optical device capable of improving the image surface illuminance distribution on the scanned surface resulting from the change in the velocity of the light beam on the scanned surface and the incident angle dependence of the reflectance of the deflecting surface, and an image using the same. An object is to provide a forming apparatus.

A scanning optical device according to a first aspect of the present invention comprises:
A light source unit; a deflection element that deflects and scans a light beam emitted from a light emitting point of the light source unit; and an imaging optical system that forms an image on the surface to be scanned that is deflected and scanned by the deflection surface of the deflection element. In a scanning optical device,
The deflection element is a resonance type deflection element in which a single deflection surface reciprocates around a rotation axis,
The light beam emitted from the light emitting point is incident on the deflection surface from the plane including the rotation axis of the deflection element and the optical axis of the imaging optical system,
When the image plane illuminance distribution due to the deflection angle dependence of the scanning speed of the light beam on the scanned surface by the deflection element is denoted by Ssp,
Ssp <1.05
However, when Ssp = exposure amount of off-axis light beam incident outside the most axis of the scanned surface / exposure amount of axial light beam incident on the optical axis of the scanned surface, the light beam emitted from the light emitting point Is set to be incident on the deflecting surface as P-polarized light at the deflection point of the most off-axis light beam on the deflecting surface,
Thereby, the image plane illuminance distribution caused by the field angle dependency of the optical efficiency of the imaging optical system and the image plane illuminance distribution due to the incident angle dependence of the reflectance of the deflection surface are compensated.

A scanning optical device according to a second aspect of the present invention comprises:
A light source unit; a deflection element that deflects and scans a light beam emitted from a light emitting point of the light source unit; and an imaging optical system that forms an image on the surface to be scanned that is deflected and scanned by the deflection surface of the deflection element. In a scanning optical device,
The deflection element is a resonance type deflection element in which a single deflection surface reciprocates around a rotation axis,
The light beam emitted from the light emitting point is incident on the deflection surface from the plane including the rotation axis of the deflection element and the optical axis of the imaging optical system,
When the image plane illuminance distribution due to the deflection angle dependence of the scanning speed of the light beam on the scanned surface by the deflection element is denoted by Ssp,
Ssp ≧ 1.05
However, when Ssp = exposure amount of off-axis light beam incident outside the most axis of the scanned surface / exposure amount of axial light beam incident on the optical axis of the scanned surface, the light beam emitted from the light emitting point Is set to be incident on the deflection surface as S-polarized light at the deflection point of the most off-axis light beam on the deflection surface,
Thereby, the image plane illuminance distribution caused by the field angle dependency of the optical efficiency of the imaging optical system and the image plane illuminance distribution due to the incident angle dependence of the reflectance of the deflection surface are compensated.

The invention of claim 3 is the invention of claim 1 or 2, wherein
The illuminance distribution on the image plane depending on the angle of view of the optical efficiency of the imaging optical system is represented by Ssl,
When the image plane illuminance distribution due to the incident angle dependence of the reflectance of the deflection surface is Sde,
0.90 / Ssl × Ssp ≦ Sde ≦ 1.10 / Ssl × Ssp
It is characterized by satisfying.

The invention of claim 4 is the invention of claim 1, 2 or 3,
The deflecting surface of the deflecting element is formed by depositing aluminum on a silicon substrate.

The invention of claim 5 is the invention of any one of claims 1 to 4,
The light incident / exit surface of the imaging optical system is not provided with an antireflection coating.

The invention of claim 6 is the invention of any one of claims 1 to 5,
The imaging optical system is housed and disposed in a housing, and a flat glass is provided between the imaging optical system and the surface to be scanned to prevent dust from entering the housing. The light incident / exit surface of the flat glass is not provided with an antireflection coating.

The image forming apparatus of the invention of claim 7
The scanning optical device according to any one of claims 1 to 6, 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 scanning optical 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. It is said.

An image forming apparatus according to an eighth aspect of the present invention provides:
The scanning optical apparatus 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 scanning optical apparatus. It is said.

  According to the present invention, a scanning optical apparatus capable of improving the image plane illuminance distribution on the scanned surface resulting from the change in the speed of the light beam on the scanned surface and the incident angle dependence of the reflectivity of the deflecting surface, and the same are used. Image forming apparatus can be achieved.

  The scanning optical device of the present invention includes a light source unit, a deflection element that deflects and scans a light beam emitted from a light emitting point of the light source unit, and a light beam that is deflected and scanned by the deflection surface of the deflection element. And an image optical system.

  The deflection element is a resonance type deflection element in which a single deflection surface reciprocates around a rotation axis, and the light beam emitted from the light emitting point is a surface including the rotation axis of the deflection element and the optical axis of the imaging optical system. It is incident on the deflecting surface from the inside.

  Let Ssp be the image plane illuminance distribution due to the deflection angle dependence of the scanning speed of the light beam on the surface to be scanned by the deflection element. At this time, the value of the image plane illuminance distribution Ssp is set so that the polarization direction of the light beam emitted from the light emitting point is incident on the deflection surface at an appropriate polarization direction at the deflection point of the most off-axis light beam on the deflection surface. . This compensates for the image plane illuminance distribution caused by the field angle dependence of the optical efficiency of the imaging optical system and the image plane illuminance distribution due to the incident angle dependence of the reflectivity of the deflecting surface.

  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. FIG. 2 is a sectional view (sub scanning sectional view) of the main part in the sub scanning direction according to the first embodiment of the present invention. is there.

  In the following description, the sub-scanning direction (Z direction) is a direction parallel to the rotation axis of the deflection means (deflection element). The main scanning section is a section whose normal is the sub-scanning direction (direction parallel to the rotation axis of the deflecting means). The main scanning direction (Y direction) is the direction in which the light beam deflected and scanned by the deflecting means is projected onto the main scanning section. The sub-scanning cross section is a cross section whose normal is the main scanning direction.

  In FIG. 1, reference numeral 1 denotes a light source means, for example, a semiconductor laser. Reference numeral 2 denotes a collimator lens as a light beam conversion means, which converts the state of the light beam emitted from the light emitting point (light emitting portion) of the light source means 1 into another state. In this embodiment, the divergent light beam emitted from the light emitting point of the light source means 1 is converted into a convergent light beam.

  A cylindrical lens 4 has 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 resonance type deflecting element 5 as a deflecting means to be described later in the sub-scan section in the sub-scan section. The cylindrical lens 4 is formed integrally with an imaging lens 6a described later, but the present embodiment is not limited to this.

  Each element of the collimator lens 2 and the cylindrical lens 4 constitutes one element of the incident optical system LA.

  Denoted at 5 is a deflecting means, which is composed of a resonant deflecting element in which a single deflecting surface 5a reciprocates around a rotation axis.

  An image forming optical system 6 includes an image forming lens (fθ lens, toric lens) 6a as a single image forming optical element made of a plastic material having different powers in the main scanning direction and the sub scanning direction. The housing is disposed in the housing. The imaging optical system 6 forms an image of a light beam based on image information deflected and scanned by the resonance type deflection element 5 on the photosensitive drum surface 8 as a scanned surface in the main scanning section, and resonates in the sub-scanning section. Surface tilt correction of the deflection surface 5a of the mold deflection element 5 is performed.

  In this embodiment, the imaging optical system 6 is composed of a single imaging optical element 6a, but it may be composed of two or more imaging optical elements.

  Reference numeral 8 denotes a photosensitive drum surface as a surface to be scanned.

  In this embodiment, a divergent light beam that is light-modulated and emitted from the light source means 1 according to image information is converted into a convergent light beam by the collimator lens 2 and enters the cylindrical lens 4. Of the convergent light beam incident on the cylindrical lens 4, the light enters the deflection surface 5 a (front incidence) from the center of the vibration angle (deflection angle) of the resonance type deflection element 5 in the main scanning section. In the sub-scan section, the light beam is incident (obliquely incident) on the deflection surface 5a from the plane including the rotation axis of the deflecting element 5 and the optical axis of the imaging lens 6a, and forms a line image on the deflection surface 5a. (Oblique incidence optical system).

The light beam deflected and scanned in the main scanning direction by the reciprocating motion of the deflecting surface 5a of the resonance-type deflecting element 5 is guided onto the photosensitive drum surface 8 through the imaging lens 6a. By reciprocating the deflection surface 5a of the resonance type deflection element 5, the photosensitive drum surface 8 is optically scanned in the main scanning direction. Thereby, an image is recorded on the photosensitive drum surface 8 as a recording medium.
<Resonant deflection element>
3 and 4 are explanatory views showing the resonance type deflection element 5 according to the first embodiment of the present invention. 3 is a front view of the resonance type deflection element 5, and FIG. 4 is a cross-sectional view taken along line AA of FIG.

  In the resonance type deflection element 5, first on the device side, a deflector 51 having a deflection surface 5 a, a driver 52, a torsion bar 53 and a frame for fixing them are integrally formed on a silicon substrate. A magnetized magnet 56 is attached.

  On the other hand, an actuator has a coil 55 wound around a core 54, and generates a magnetic field by electromagnetic induction by applying an AC voltage thereto. At this time, by bringing the AC frequency close to the natural frequency of the torsional mode of the device, the device will resonate.

The device has a two-stage structure of the driver 52 and the deflector 51 because the deflector 51 that sine-oscillates with the second harmonic is superimposed on the driver 52 that sine-oscillates with the fundamental wave. This is to cause the child 51 to move at a pseudo constant speed in a certain region.
<Deflection angle dependence of beam scanning speed>
As described above, the present embodiment is a two-stage resonance type deflection element in which a sinusoidally oscillating deflector is superimposed on a sinusoidally oscillating driver. I am exercising.

  FIG. 5 is an explanatory diagram showing the angular velocity of the deflection element in the present embodiment. In FIG. 5, the horizontal axis is the deflection angle θ, and the vertical axis is the angular velocity dθ / dt (the graph is normalized by the value on the optical axis).

  In this embodiment, this deflection element is combined with an fθ lens (imaging lens) as an imaging optical element. Since the fθ lens has dY / dθ = constant, the scanning speed dY / dt on the surface to be scanned is proportional to the angular speed dθ / dt of the deflection surface as shown by the following equation (1).

dY / dt = dθ / dt × dY / dθ∝dθ / dt (1)
Here, the relationship between the scanning speed and the exposure amount is in an inversely proportional relationship, that is, the exposure amount increases as the scanning speed becomes slower, so the reciprocal of dY / dt is proportional to the exposure amount. An image plane illuminance distribution (dotted line shown in FIG. 9) is obtained by connecting the exposure amounts at all angles of view.

In this embodiment, the discussion has been made with a perfect fθ lens. However, when the imaging optical element has other characteristics, the scanning speed dY / dt is calculated and normalized by applying the equation (1). If the reciprocal is taken, the exposure amount can be calculated.
<Dependence of the reflectance of the deflecting element on the incident angle>
In order to drive the deflection surface of the resonance type deflection element of this embodiment efficiently with a small amount of power, silicon is used as a semiconductor material. The deflection surface has a low reflectivity if it is a silicon material, so aluminum, SiO2, a protective film, etc. are deposited on the silicon substrate and subjected to a simple increased reflection process.

  FIG. 6 is an explanatory view showing the reflectance angle dependency at this time. In FIG. 6, the solid line is data when incident with P-polarized light and the dotted line with S-polarized light.

  As shown in FIG. 6, in the case of P-polarized light, the reflectance decreases as the incident angle increases. Conversely, in the case of S-polarized light, the reflectance increases as the incident angle increases. It can be read that it is possible to compensate. This reflectance dependency can be changed within a certain range by changing the material, film thickness, and number of layers of the vapor deposition substance, and can be used for fine correction of the image plane illuminance distribution.

In order to use the incident angle dependence of the reflectance of the polarizing element for image plane illuminance distribution compensation, the luminous flux is in the plane defined by the rotation axis of the deflecting element and the optical axis of the imaging optical system (imaging optical element). It is necessary to make it enter from the position which is symmetrical with respect to the deflection surface in the main scanning direction. This is because, as can be seen from FIG. 6, when the incident angle on the deflection surface becomes asymmetric in the main scanning direction, the image plane illuminance distribution also becomes asymmetric, which is difficult to compensate.
<Depending on angle of view of optical efficiency of imaging optical element (imaging optical system)>
The imaging optical element in this example is a plastic single toric lens as described above, and the light incident / exit surface (optical surface) is not provided with an antireflection coating.

  FIG. 7 is an explanatory diagram showing optical efficiency (transmittance in the case of a lens, diffraction efficiency in the case of a diffractive element) with respect to the incident angle of the imaging optical element in the present embodiment. In FIG. 7, the horizontal axis represents the angle of view, and the vertical axis represents the optical efficiency (transmittance).

In this embodiment, since the light is incident as P-polarized light off-axis, the optical efficiency improves as the field angle increases, that is, the image plane illuminance distribution increases off-axis.
<Image surface illumination distribution compensation>
Up to this point, compensation has been made for the image plane illuminance distribution due to the deflection angle dependency of the scanning speed of the light beam on the surface to be scanned, the incident angle dependency of the reflectivity of the deflecting means, and the field angle dependency of the optical efficiency of the imaging optical element. In order to establish the relationship, it is necessary to appropriately set the polarization direction of the light flux from the light source means.

  Here, the shape of the imaging optical element cannot be easily changed in consideration of aberration correction. Furthermore, the range in which the incident angle dependence of the reflectivity of the deflection surface of the resonance type deflection element can be changed is limited. Therefore, when the scanning speed of the light beam on the surface to be scanned is determined, an appropriate polarization direction for compensating the image plane illuminance distribution is limited.

More specifically, the image plane illuminance distribution due to the deflection angle dependence of the scanning speed of the light beam on the surface to be scanned by the deflection element 5 is set to Ssp. At this time,
Ssp <1.05 (2)
However, when Ssp = exposure amount of the off-axis light beam incident off the most axis of the scanned surface / exposure amount of the on-axis light beam incident on the optical axis of the scanned surface, the light beam emitted from the light emitting point The polarization direction is set so as to be incident on the deflection surface 5a as P-polarized light at the deflection point of the most off-axis light beam on the deflection surface 5a.

  P-polarized light indicates that the component ratio of the P-polarized light is 90% or more. The reason why the S-polarized light, which is a slightly opposite deflection component, remains at the deflection point of the most off-axis light beam is that the rotation axis and the imaging optical system (concatenation) of this embodiment with respect to the deflection surface of the resonance type deflection element. This is because the light is incident obliquely in the sub-scanning direction from the plane including the optical axis of the image optical element).

In this embodiment, the image plane illuminance distribution Ssp is
Ssp ≧ 1.05 (3)
In this case, the polarization direction of the light beam emitted from the light emitting point is set to be incident on the deflection surface 5a as S-polarized light at the deflection point of the most off-axis light beam on the deflection surface 5a.

  The S-polarized light means that the component ratio of the S-polarized light is 90% or more. The reason why P-polarized light, which is a slightly opposite deflection component, remains at the deflection point of the most off-axis light beam is that the present embodiment uses the rotation axis and the light of the imaging optical system with respect to the deflection surface of the resonance type deflection element. This is because the light is obliquely incident in the sub-scanning direction from the plane including the axis.

  Here, the image plane illuminance distribution Ssp based on the deflection angle dependence of the scanning speed of the light beam on the surface to be scanned by the deflection element is expressed as follows.

Where Ssp = exposure amount of the off-axis light beam incident off the most axis of the scanned surface / exposure amount of the on-axis light beam incident on the optical axis of the scanned surface
= Scanning speed of the light beam on the optical axis / Scanning speed of the most off-axis light beam FIG. 8 is an explanatory diagram showing the incident angle on the deflection surface and the component ratio of each polarized light beam in this embodiment. In FIG. 8, the solid line indicates P-polarized light and the dotted line indicates S-polarized light.

  Although the component ratio of S-polarized light increases near the on-axis deflection point due to the sub-scanning oblique incidence, the deflection angle in the main scanning direction becomes larger and the P-polarized component becomes dominant toward the off-axis, and the S-polarized component becomes The level can be safely ignored. Here, the P-polarized light has been described as an example, but the same applies to the S-polarized light.

  Table 1 shows the image plane illuminance distribution according to the generation factors in this embodiment.

From Table 1, the image plane illuminance distribution Ssp in this embodiment is
Ssp = 1.01
It is. Therefore, in order to correct the image plane illuminance distribution, it is necessary to set the polarization of the light beam so as to be incident on the deflecting surface as P-polarized light at the deflection point of the most off-axis light beam of the deflecting element from the above equation (2). .

  Therefore, in this embodiment, the polarization direction of the light beam emitted from the light emitting point is set to be incident on the deflection surface 5a as P-polarized light at the deflection point of the most off-axis light beam on the deflection surface 5a. This compensates for the image plane illuminance distribution caused by the field angle dependence of the optical efficiency of the imaging lens 6a and the image plane illuminance distribution caused by the incident angle dependence of the reflectance of the deflecting surface 5a.

  Further, in this embodiment, in order to further compensate for the image plane illuminance distribution within an effective range, the image plane illuminance distribution due to the angle of view of the optical efficiency of the imaging lens 6a is set to Ssl, and the deflection surface 5a. Let Sde be the image plane illuminance distribution due to the incident angle dependence of the reflectance.

  At that time, the image plane illuminance distribution Sde may be set so as to satisfy the following expression (4).

0.90 / Ssl × Ssp ≦ Sde ≦ 1.10 / Ssl × Ssp (4)
Here, the image plane illuminance distribution Sde due to the incident angle dependence of the reflectance of the deflecting surface 5a and the image plane illuminance distribution Ssl due to the field angle dependence of the optical efficiency of the imaging lens 6a are expressed as follows.

Sde = reflectance of off-axis light beam / reflectance of light beam on optical axis Ssl = optical efficiency of off-axis light beam / optical efficiency of light beam on optical axis Exceeding upper limit or lower limit value of conditional expression (4) However, the image surface illuminance distribution deteriorates, and image deterioration such as density unevenness occurs.

More desirably, in a scanning optical device for color and a scanning optical device for the purpose of high-definition printing,
0.95 / Ssl × Ssp ≦ Sde ≦ 1.05 / Ssl × Ssp (5)
It is preferable to set the image plane illuminance distribution Sde so as to satisfy the above.

In this example, from Table 1,
0.85 ≦ Sde ≦ 1.04
Preferably
0.90 ≦ Sde ≦ 0.99
The image plane illuminance distribution Sde should be set so that Sde = 0.98 from Table 1 in this embodiment.
The image plane illuminance distribution is corrected as follows.

  FIG. 9 is an explanatory diagram showing an image plane illuminance distribution in this embodiment. In FIG. 9, the horizontal axis is the image height (field angle), the vertical axis is the image plane illuminance distribution, and all data are normalized by the data on the optical axis.

  In FIG. 9, the solid line (thin line) is a factor due to the scanning speed, the alternate long and short dash line is a factor due to the incident angle dependence of the reflectivity of the deflecting surface, the dotted line is a factor due to the angle of view dependence of the optical efficiency of the imaging optical element, and a thick line Indicates a total image surface illuminance distribution obtained by multiplying the three. From the figure, it can be seen that the image plane illuminance distribution in the present embodiment is well corrected.

  As described above, in this embodiment, by appropriately setting the polarization direction of the light beam from the light emitting point according to the value of the image plane illuminance distribution Ssp, the image plane illuminance distribution caused by the view angle dependency of the optical efficiency of the imaging lens. And the image plane illuminance distribution due to the incident angle dependence of the reflectance of the deflecting surface is compensated.

  As a result, the scanning optical apparatus total can be easily configured with an easy configuration without individually improving the factors related to the deterioration of the image plane illuminance distribution such as the reflectance of the deflection surface of the resonance type deflection element and the scanning speed on the scanned surface. It is possible to improve the image plane illuminance distribution. A small-sized scanning optical device suitable for high-speed and high-definition printing can be realized.

  FIG. 10 is a sectional view (main scanning sectional view) of the main part in the main scanning direction according to the second embodiment of the present invention. FIG. 11 is a sectional view (sub scanning sectional view) of the main part in the sub scanning direction according to the second embodiment of the present invention. is there. 10 and 11, the same elements as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.

  This embodiment differs from the first embodiment described above in that the sinusoidal vibration type deflection element 15 shown in FIG. 18 is used as a resonance type deflection element, and the imaging optical element 6a and the scanned surface 8 The dustproof glass 7 is disposed between the two. Further, in accordance with these, the polarization direction of the light beam from the light emitting point of the light source means 1 is changed to S-polarized light. Other configurations and optical functions are the same as those in the first embodiment, and the same effects are obtained.

  That is, in FIGS. 10 and 11, reference numeral 15 denotes a deflecting means, which is a resonance type (sinusoidal vibration type) deflecting element in which a single deflecting surface 15a (reference numeral 57a in FIG. 18) reciprocates around a rotation axis. It is made up.

  A flat glass 7 is provided between the imaging lens 6 and the surface to be scanned 8 to prevent dust from entering the housing. The light incident / exit surface of the flat glass 7 is not provided with an antireflection coating.

  In this embodiment, a divergent light beam that is light-modulated and emitted from the light source means 1 according to image information is converted into a convergent light beam by the collimator lens 2 and enters the cylindrical lens 4. Of the convergent light beam incident on the cylindrical lens 4, the light enters the deflection surface 15 a (front incidence) from the center of the vibration angle (deflection angle) of the resonance type deflection element 15 in the main scanning section. In the sub-scan section, the light beam is incident (obliquely incident) on the deflecting surface 15a from the plane including the rotation axis of the deflecting element 15 and the optical axis of the imaging lens 6a, and forms a line image on the deflecting surface 15a. (Oblique incidence optical system).

  The light beam deflected and scanned in the main scanning direction by the reciprocating motion of the deflection surface 15a of the resonance type deflection element 15 is guided onto the photosensitive drum surface 8 through the imaging lens 6a. Then, the deflection surface 15a of the resonance type deflection element 15 is reciprocated to optically scan the photosensitive drum surface 8 in the main scanning direction. Thereby, an image is recorded on the photosensitive drum surface 8 as a recording medium.

  FIG. 12 is an explanatory diagram showing the angular velocity of the deflection element in the present embodiment. In FIG. 12, the horizontal axis represents the deflection angle θ, and the vertical axis represents the angular velocity dθ / dt (the graph is normalized by the value on the optical axis).

  As described above, in this embodiment, since a general sine vibration type deflection element is used, the angular velocity of the deflection element is reduced off-axis, and when combined with an imaging optical element having fθ characteristics, The scanning speed of the light beam on the surface to be scanned also decreases. As mentioned in the first embodiment, since the scanning speed and the exposure amount are in an inversely proportional relationship, the exposure amount increases off-axis with respect to the optical axis.

  The configuration of the reflecting film on the deflection surface of the deflecting element in this embodiment is the same as that in the first embodiment. However, unlike the first embodiment, in this embodiment, since it is made incident on the deflecting surface as S-polarized light, the angle dependency of the reflectance is reflected as the incident angle increases as shown by the dotted line in FIG. Becomes an increasing characteristic.

  FIG. 13 is an explanatory diagram showing the optical efficiency with respect to the incident angle of the imaging optical element and the dust-proof flat glass in this example. In FIG. 13, the horizontal axis represents the angle of view, and the vertical axis represents the optical efficiency (transmittance).

  In this embodiment, since the light is incident as S-polarized light off-axis, the optical efficiency is deteriorated as the angle of view increases, that is, the image surface illuminance distribution becomes low off-axis.

  In addition, in this embodiment, since the surface has the flat glass 7 on which no antireflection coating is applied, the decrease in the image plane illuminance distribution off the axis is particularly large.

  Table 2 shows the image plane illuminance distribution according to the generation factors in this embodiment.

From Table 2, the image plane illuminance distribution Ssp in this example is
Ssp = 1.08
It is. Therefore, in order to correct the image plane illuminance distribution, it is necessary to set the polarization of the light beam so as to be incident on the deflecting surface as S-polarized light at the deflection point of the most off-axis light beam of the deflecting element from the above equation (3). .

  Therefore, in this embodiment, the polarization direction of the light beam emitted from the light emitting point is set so as to be incident on the deflection surface 15a as S-polarized light at the deflection point of the most off-axis light beam on the deflection surface 15a. This compensates for the image plane illuminance distribution caused by the field angle dependence of the optical efficiency of the imaging lens 6a and the image plane illuminance distribution caused by the incident angle dependence of the reflectance of the deflecting surface 15a.

  Furthermore, in order to compensate the image plane illuminance distribution within an effective range, it is necessary to satisfy the above formula (4), and more desirably, the above image plane illuminance distribution to satisfy the above formula (5). Sde should be set.

In this example, from Table 2,
0.93 ≦ Sde ≦ 1.13,
Preferably
0.97 ≦ Sde ≦ 1.08
The image plane illuminance distribution Sde should be set so as to be as follows. In this embodiment, Sde = 1.02 from Table 2.
The image plane illuminance distribution is corrected as follows.

  FIG. 14 is an explanatory diagram showing the image plane illuminance distribution in this embodiment. In FIG. 14, the horizontal axis is the image height (field angle), the vertical axis is the image plane illuminance distribution, and all data are normalized by the data on the optical axis.

  Here, in FIG. 14, the solid line (thin line) is a factor due to the scanning speed, the alternate long and short dash line is a factor due to the incident angle dependence of the reflectivity of the deflecting surface, the dotted line is a factor due to the angle of view dependence of the optical efficiency of the imaging optical element, Indicates a total image surface illuminance distribution obtained by multiplying the three. From the figure, it can be seen that the image plane illuminance distribution in the present embodiment is well corrected.

  As described above, in this embodiment, by appropriately setting the polarization direction of the light beam from the light emitting point according to the value of the image plane illuminance distribution Ssp, the image plane illuminance distribution caused by the view angle dependency of the optical efficiency of the imaging lens. And the image plane illuminance distribution due to the incident angle dependence of the reflectance of the deflecting surface is compensated.

  As a result, even in a scanning optical device having a large image plane illuminance distribution generated by factors such as the optical efficiency of the imaging optical element and the scanning speed on the surface to be scanned, these factors can be easily configured without improving each factor individually. It is possible to improve the image plane illuminance distribution of the scanning optical device as a whole. A small scanning optical device suitable for high-speed printing with high speed can be realized.

[Image forming apparatus]
FIG. 15 is a cross-sectional view of the main part in the sub-scanning direction showing the 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 scanning optical device 100 having the configuration shown in the embodiment. The scanning optical device 100 emits a light beam 103 modulated in accordance with the image data Di, and the light beam 103 scans the photosensitive surface of the photosensitive drum 101 in the main scanning direction.

  The photosensitive drum 101 serving as an electrostatic latent image carrier (photoconductor) is rotated clockwise by a motor 115. With this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beam 103. 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 the light beam 103 scanned by the scanning optical device 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 abut on 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. Although the paper 112 is stored in the paper cassette 109 in front of the photosensitive drum 101, paper 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 a fixing device behind the photosensitive drum 101 (left side in FIG. 15). 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. 15, the print controller 111 not only converts the explanation data, but also controls each part in the image forming apparatus including the motor 115 and a polygon motor in the scanning optical apparatus.

  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 configurations of the first and second embodiments of the present invention are more effective in an image forming apparatus of 1200 dpi or more.

[Color image forming apparatus]
FIG. 16 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 (optical 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. 16, 60 is a color image forming apparatus, and 61, 62, 63, and 64 are scanning optical apparatuses each having one of the configurations shown in the first and second embodiments. Reference numerals 71, 72, 73, and 74 denote photosensitive drums as image carriers, reference numerals 31, 32, 33, and 34 denote developing units, and reference numeral 81 denotes a conveyance belt. In FIG. 16, 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. 16, the color image forming apparatus 60 receives R (red), G (green), and B (blue) color signals from an external device 82 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 83 in the apparatus. These image data are input to the scanning optical devices 61, 62, 63 and 64, respectively. These scanning optical devices emit light beams 41, 42, 43, and 44 that are modulated according to each image data, and the photosensitive surfaces of the photosensitive drums 71, 72, 73, and 74 are emitted by these light beams. Scanned in the main scanning direction.

  The color image forming apparatus in this embodiment has four scanning optical devices (61, 62, 63, 64) arranged in each of C (cyan), M (magenta), Y (yellow), and B (black). It corresponds. In parallel, image signals (image information) are recorded on the surfaces of the photosensitive drums 71, 72, 73, and 74, and color images are printed at high speed.

  As described above, the color image forming apparatus according to the present embodiment uses the four scanning optical devices 61, 62, 63, and 64 and the corresponding photosensitive drums 71 and 72 respectively corresponding to the latent images of the respective colors by using the light beams based on the respective image data. , 73, 74 on the surface. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 82, for example, a color image reading device 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. 2 is a main scanning sectional view of the scanning optical apparatus according to the first embodiment of the present invention. FIG. 3 is a sub-scan sectional view of the scanning optical apparatus according to the first embodiment of the present invention. 1 is a front view of a resonance type deflection element of a scanning optical device according to a first embodiment of the present invention. FIG. AA sectional view of the resonant deflection element in FIG. The figure which shows the deflection angle dependence of the angular velocity of the deflection | deviation means of Example 1 of this invention. The figure which shows the incident angle dependence of the reflectance of the deflection | deviation means of Example 1 of this invention. The figure which shows the view angle dependence of the optical efficiency of the imaging optical element of Example 1 of this invention The figure which shows the incident angle to the deflection surface in Example 1 of this invention, and the component ratio of each polarization | polarized-light beam. The figure which shows the image surface illumination intensity distribution in the scanning optical apparatus of Example 1 of this invention. FIG. 6 is a main scanning sectional view of the scanning optical apparatus according to the second embodiment of the present invention. FIG. 5 is a sub-scan sectional view of the scanning optical apparatus according to the second embodiment of the present invention. The figure which shows the deflection angle dependence of the angular velocity of the deflection | deviation means of Example 2 of this invention. The figure which shows the view angle dependence of the optical efficiency of the imaging optical element of Example 2 of this invention The figure which shows the image surface illumination intensity distribution in the scanning optical apparatus of Example 2 of this invention. FIG. 3 is a sub-scan sectional view showing an embodiment of the image forming apparatus of the present invention. 1 is a schematic view of a main part of a color image forming apparatus according to an embodiment of the present invention. Main part perspective view of scanning optical apparatus in conventional example Conceptual diagram of resonant deflection element

1 Light source means (semiconductor laser)
2 Light flux conversion means (collimator lens)
4 Cylindrical lens 5, 15 Deflection means (resonance type deflection element)
5a, 15a Deflection surface LA Incident optical system 6 Imaging optical system 6a Imaging optical element (imaging lens)
8 Scanned surface (photosensitive drum surface)
DESCRIPTION OF SYMBOLS 51 Deflector 52 Driver 53 Torsion bar 54 Core 55 Coil 56 Magnet 91A, 91B, 91C Detection means 94 Half mirror 92, 96 Arithmetic device 93, 97 Moving mechanism 61, 62, 63, 64 Scanning optical device 71, 72, 73 74 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 81 Conveying belt 82 External device 83 Printer controller 60 Color image forming device 100 Scanning optical device 101 Photosensitive drum 102 Charging roller 103 Light beam 104 Image forming device 107 Developing 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 (8)

A light source unit; a deflection element that deflects and scans a light beam emitted from a light emitting point of the light source unit; and an imaging optical system that forms an image on the surface to be scanned that is deflected and scanned by the deflection surface of the deflection element. In a scanning optical device,
The deflection element is a resonance type deflection element in which a single deflection surface reciprocates around a rotation axis,
The light beam emitted from the light emitting point is incident on the deflection surface from the plane including the rotation axis of the deflection element and the optical axis of the imaging optical system,
When the image plane illuminance distribution due to the deflection angle dependence of the scanning speed of the light beam on the scanned surface by the deflection element is denoted by Ssp,
Ssp <1.05
However, when Ssp = exposure amount of off-axis light beam incident outside the most axis of the scanned surface / exposure amount of axial light beam incident on the optical axis of the scanned surface, the light beam emitted from the light emitting point Is set to be incident on the deflecting surface as P-polarized light at the deflection point of the most off-axis light beam on the deflecting surface,
This compensates for the image plane illuminance distribution caused by the viewing angle dependence of the optical efficiency of the imaging optical system and the image plane illuminance distribution caused by the incident angle dependence of the reflectivity of the deflection surface. Optical device. A light source unit; a deflection element that deflects and scans a light beam emitted from a light emitting point of the light source unit; and an imaging optical system that forms an image on the surface to be scanned that is deflected and scanned by the deflection surface of the deflection element. In a scanning optical device,
The deflection element is a resonance type deflection element in which a single deflection surface reciprocates around a rotation axis,
The light beam emitted from the light emitting point is incident on the deflection surface from the plane including the rotation axis of the deflection element and the optical axis of the imaging optical system,
When the image plane illuminance distribution due to the deflection angle dependence of the scanning speed of the light beam on the scanned surface by the deflection element is denoted by Ssp,
Ssp ≧ 1.05
However, when Ssp = exposure amount of off-axis light beam incident outside the most axis of the scanned surface / exposure amount of axial light beam incident on the optical axis of the scanned surface, the light beam emitted from the light emitting point Is set to be incident on the deflection surface as S-polarized light at the deflection point of the most off-axis light beam on the deflection surface,
This compensates for the image plane illuminance distribution caused by the viewing angle dependence of the optical efficiency of the imaging optical system and the image plane illuminance distribution caused by the incident angle dependence of the reflectivity of the deflection surface. Optical device. The illuminance distribution on the image plane depending on the angle of view of the optical efficiency of the imaging optical system is represented by Ssl,
When the image plane illuminance distribution due to the incident angle dependence of the reflectance of the deflection surface is Sde,
0.90 / Ssl × Ssp ≦ Sde ≦ 1.10 / Ssl × Ssp
The scanning optical apparatus according to claim 1, wherein:   4. The scanning optical apparatus according to claim 1, wherein the deflecting surface of the deflecting element is formed by depositing aluminum on a silicon substrate.   5. The scanning optical apparatus according to claim 1, wherein the light incident / exit surface of the imaging optical system is not provided with an antireflection coating. 6.   The imaging optical system is housed and disposed in a housing, and a flat glass is provided between the imaging optical system and the surface to be scanned to prevent dust from entering the housing. 6. The scanning optical apparatus according to claim 1, wherein the light incident / exiting surface of the flat glass is not provided with an antireflection coating.   The scanning optical device according to any one of claims 1 to 6, 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 scanning optical 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. An image forming apparatus.   The scanning optical apparatus 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 scanning optical apparatus. An image forming apparatus.