JP2008015083A - Optical scanning device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner in which a precise printing quality is available without the deviation (jitter) of the printing position in a main scanning direction and to obtain an image forming apparatus using the optical scanner. <P>SOLUTION: The optical scanner has: a first optical system which focuses a luminous flux emitted from a light source means; a deflection means which deflects and scans the luminous flux; a second optical system which focuses the luminous flux onto a face to be scanned; a synchronization signal detection means which detects a portion of the luminous flux as a synchronization detection signal which decides the timing of the beginning position of scanning on the face to be scanned with the luminous flux; and a synchronization detection optical system which guides the portion of the luminous flux deflected and scanned on the deflection face of the deflection means onto the synchronization signal detection means, wherein the synchronization detection optical system has a luminous flux restriction means which restricts the width of the luminous flux in a subscanning direction which orthogonally intersects with a main scanning direction, refection mirrors are provided in the optical path from the light source means to the synchronization signal detection means, and the luminous flux restriction means is arranged in the optical path between the reflection mirror, which is closest to the synchronization signal detection means, and the synchronization signal detection means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  Optical scanning devices (scanning optical systems) are widely used as image forming apparatuses such as laser beam printers and digital copying machines having an electrophotographic process.

  The optical scanning device converts a light beam (light beam) emitted from a light source means such as a semiconductor laser into a parallel light beam by a collimator lens, and deflects a deflecting surface (deflection reflecting surface) of an optical deflector composed of a polygon mirror (rotating polygon mirror). Leading to. The light beam deflected and scanned by the optical deflector is scanned at a constant speed while spot-imaged on the surface to be scanned by using an imaging optical system (fθ lens system).

  In the sub-scanning direction (within the sub-scanning cross section) perpendicular to the deflection direction (main scanning direction), the parallel light beam emitted from the collimator lens is condensed on the deflection surface using a cylindrical lens, and then covered by the imaging optical system. A so-called surface tilt correction optical system that re-images on the scanning surface may be used.

  On the other hand, an underfilled scanning optical system (hereinafter referred to as “UFS”) in which the beam width of the parallel beam emitted from the collimator lens is made narrower than the deflection surface in the main scanning section and all the beams are deflected and scanned by the optical deflector. Has been used.

  While UFS can deflect and scan light energy without waste, it is necessary to enlarge the deflection surface to some extent, and the optical deflector tends to increase in size.

  In recent years, there has been a strong demand for improving the printing speed in laser beam printers and digital copying machines. To improve the printing speed, the optical deflector is rotated at a high speed or the number of deflection surfaces is increased. There is a need. In a UFS having a large optical deflector, problems such as heat generation, noise, and electric power of the optical deflector occur when the optical deflector is further rotated at a higher speed. Further, when the number of deflecting surfaces is increased, the size of the optical deflector is further increased, and similarly problems such as heat generation, noise, and electric power of the optical deflector arise.

  On the other hand, there is an overfilled scanning optical system (hereinafter referred to as “OFS”) in which the light beam emitted from the light source means is incident on the deflection surface of the optical deflector in a state wider than the width of the deflection surface in the main scanning direction. Has been used. (See Patent Documents 1 and 2).

  OFS is smaller in optical deflector than UFS, and can further rotate at a higher speed and increase the number of reflecting surfaces. However, OFS allows the light beam to be incident on the deflecting surface of the optical deflector in a state wider than the width of the deflecting surface in the main scanning direction, and a part of the light beam is cut off by the deflecting surface. There is a problem that the output power of the light source is lower than that of UFS. However, in recent years, high-power semiconductor lasers have appeared and this problem has been solved.

  In an optical scanning apparatus using either UFS or OFS, for the purpose of accurately controlling the image writing position, it detects the scanning light beam position immediately before writing the image signal and detects the timing of the scanning start position. It is common to provide signal detection means (synchronization detection sensor).

  Various optical scanning devices provided with this synchronization detection sensor have been proposed. (See Patent Documents 3, 4, and 5).

  FIG. 11 is a sectional view (main scanning sectional view) of the main part in the main scanning direction of a conventional optical scanning device provided with a synchronization detection sensor.

  In the figure, reference numeral 1 denotes a light source means, which is composed of, for example, a semiconductor laser. A condensing lens (collimator lens) 2 converts the light beam emitted from the light source means 1 into a parallel light beam. Reference numeral 3 denotes an aperture stop, which shapes the light beam emitted from the collimator lens 2 into a desired optimum beam shape. A cylindrical lens 41 has a finite refractive power only in the sub-scanning direction.

  Each element of the collimator lens 2, the aperture stop 3, and the cylindrical lens 41 constitutes one element of the incident optical system LA.

  Reference numeral 6 denotes an optical deflector as a deflecting means, which is composed of, for example, a rotating polygon mirror (polygon mirror) and is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor.

  Reference numeral 7 denotes an imaging optical system having fθ characteristics, which includes first and second imaging lenses 73 and 74, and the light beam deflected by the optical deflector 6 is a photosensitive drum surface (scanned surface) 8. A spot image is formed on the top. The imaging optical system 7 has a surface tilt correction function by providing a conjugate relationship between the deflection surface 62 of the optical deflector 6 and the photosensitive drum surface 8 in the sub-scan section.

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

  Reference numeral 63 denotes a synchronization detection lens for synchronization detection, and a light flux (synchronization detection) other than an effective image on the scanned surface 8 on a synchronization detection slit (synchronization detection edge) 11 for synchronization detection described later. Image light beam).

  Reference numeral 15 denotes a reflection mirror (hereinafter referred to as “synchronization detection mirror”), which reflects a synchronization detection light beam for adjusting the timing of the scanning start position on the photosensitive drum surface 8 toward the synchronization detection sensor 12 side. ing.

  Reference numeral 11 denotes a synchronization detection slit for synchronization detection, and the slit width is usually about 0.5 mm, and is constituted by two pairs of linear edges parallel to the direction perpendicular to the scanning direction (sub-scanning direction). . The synchronization detection slit 11 is not necessarily a slit, and is provided, for example, as a linear edge only upstream or downstream in the scanning direction.

  Reference numeral 16 denotes a correction lens for synchronization detection (hereinafter referred to as “correction lens for synchronization detection”), which is used to bring the synchronization detection mirror 15 and the synchronization detection sensor 12 into a conjugate relationship. The surface tilt of the detection mirror 15 is corrected. This is because the synchronization detection light beam reaches the synchronization detection sensor 12 even if the attitude accuracy of the synchronization detection mirror 15 is shifted due to assembly accuracy or vibration.

  Reference numeral 12 denotes an optical sensor (hereinafter referred to as a “synchronization detection sensor”) as a synchronization detection element, and in the figure, a synchronization signal (synchronization detection) obtained by detecting an output signal from the synchronization detection sensor 12. Signal) is used to adjust the timing of the scanning start position of image recording on the photosensitive drum surface 8.

  Each element such as the synchronization detection lens 63, the synchronization detection mirror 15, the synchronization detection slit 11, and the synchronization detection correction lens 16 constitutes one element of the synchronization detection optical system (synchronization detection optical system) LB. ing.

  The synchronization detection optical system has been known to have a problem that the detection accuracy of the synchronization detection sensor is lowered due to manufacturing parts and assembly accuracy, and a print position deviation (jitter) is likely to occur in the main scanning direction. ing.

  As variation in component accuracy, Patent Document 3 attempts to reduce jitter due to the effect of straightness error of the synchronization detection slit. Patent Document 3 proposes to provide a conjugate image of the synchronization detection slit by the synchronization detection lens between the optical deflector and the aperture stop in the sub-scan section in consideration of the variation in the light amount of the synchronization detection light beam. is doing. As a result, the degree of condensing of the light beam for synchronization detection in the sub-scanning section is relaxed on the synchronization detection slit so that it is less affected by the straightness error of the synchronization detection slit.

Patent Documents 4 and 5 propose countermeasures in the case where there is a difference in the light amount of the synchronous detection light beam between the deflecting surfaces due to variations in shape accuracy and reflectance of the deflecting surface of the optical deflector. As described in Patent Document 5, when there is a difference in the light amount of the synchronization detection light beam for each deflection surface, an error occurs in the writing timing due to the amount of light reaching the synchronization detection sensor. As a result, a deviation (jitter) occurs in the printing position accuracy in the main scanning direction. As a countermeasure against this, as disclosed in FIG. 1 of Patent Document 4 and FIG. 3 of Patent Document 5, a part of the light beam is placed in the main scanning direction between the optical deflector and the synchronization detection means (synchronization detection sensor). The limiting member which restrict | limits to is provided.
Japanese Patent No. 3104618 JP-A-8-171070 JP 2004-21171 A JP 2003-222811 A JP 2000-235154 A

  However, the synchronization detection optical system used in the above-described conventional optical scanning device has room for improvement on the following problems as countermeasures against a printing position shift (jitter) in the main scanning direction.

  If the position of the synchronization detection light beam that reaches the synchronization detection sensor is not stable, the synchronization detection light beam largely deviates from the light receiving portion of the synchronization detection sensor, or a part of the synchronization detection light beam is kicked and Variations occur in the amount of light obtained at the light receiving portion of the sensor. As a result, the detection accuracy of the synchronization detection sensor is lowered, and a printing position shift (jitter) occurs in the main scanning direction.

  Conventionally, in order to cope with this, even if the synchronization detection light flux is directed toward the synchronization detection sensor, particularly in the sub-scanning direction due to manufacturing parts and assembly accuracy, the light flux reaches the synchronization detection sensor. It is configured to do. In particular, when a transmission type optical element and a reflection type optical element are compared, in general, the reflection type optical element has a much larger fluctuation of the luminous flux due to the posture accuracy. For these reasons, attention has been paid to the variation in the posture of the reflective element in the design.

  For example, in FIG. 6 of Patent Document 3, the synchronization detection imaging lens (synchronization detection lens) forms an image of the synchronization detection light beam on the synchronization detection slit and conjugates the synchronization detection slit with the optical deflector. It has a fall compensation configuration. As a result, even if there is a difference in the tilting amount of each deflecting surface of the optical deflector, the synchronous detection light beam does not swing on the synchronous detection slit. A similar configuration is also shown in FIG.

  Further, in FIG. 6 of Patent Document 3, a conjugate lens for synchronization detection (a conjugate lens for synchronization detection) is provided, and the synchronization detection mirror and the synchronization detection element (synchronization detection sensor) are conjugated in the sub-scan section. A correction configuration is adopted. As a result, the synchronization detection light beam does not swing on the synchronization detection sensor even if the mirror is tilted in the sub-scan section of the synchronization detection mirror. A similar configuration is shown in FIG. 7 of Patent Document 4, FIG. 5 of Patent Document 5, and the like.

  As described above, conventionally, in order to reduce the influence of the fluctuation of the synchronization detection light beam when the reflection surface in the middle of the optical path falls in the sub-scanning cross section, each reflection surface, the synchronization detection sensor, and the synchronization detection sensor ) The synchronization detection slit is conjugated using a conjugate lens such as a synchronization detection lens or a synchronization detection conjugate lens. For this reason, the number of lenses constituting the synchronization detection optical system (synchronization detection optical system) increases, and the entire apparatus tends to be large.

  There is also a problem that the degree of freedom of arrangement of the optical system is lowered in order to achieve the conjugate relationship. Furthermore, there is a problem that it is difficult to achieve a conjugate relationship with respect to all the reflection surfaces when a large number of reflection mirrors are used to make the optical scanning device compact.

  In recent years, the number of cases using multi-beams is increasing due to the increase in the speed of image forming apparatuses. At that time, in the method for condensing the light flux on the synchronization detection sensor and the synchronization detection slit so as to satisfy the conjugate relationship with the reflection surface as described above, jitter is generated between the multiple beams due to the linearity error of the synchronization detection slit. It will occur.

  Further, the jitter is observed as a variation in printing position accuracy in a monotone image forming apparatus, but is observed as a registration shift between colors in a color image forming apparatus in which a plurality of colors are overlaid, which hinders high image quality. Yes.

  It is known that the OFS used for speeding up generally has a narrower scanning angle of view and a longer fθ coefficient than UFS in order to ensure the necessary print width. The optical path length of the entire imaging optical system is also increased. In addition, when the focal length of the synchronization detection optical system is significantly shortened relative to the imaging optical system, the synchronization detection optical system shortens the scanning distance for the same minute angle of view and decreases the detection accuracy for synchronization detection. The focal length of the optical system needs to be a focal length that is 1/3 or more of the fθ coefficient of the imaging optical system. As a result, the optical path length of the synchronization detection optical system tends to be longer in OFS. In the synchronization detection optical system having a long optical path length, the fluctuation of the light flux on the synchronization detection sensor increases due to the tilt of the reflecting surface on the optical path, leading to a decrease in the synchronization detection detection accuracy of the synchronization detection sensor.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning apparatus capable of obtaining high-precision printing quality free from a printing position shift (jitter) in the main scanning direction and an image forming apparatus using the same.

The optical scanning device of the invention of claim 1
A first optical system for imaging a light beam emitted from the light source means;
Deflecting means for deflecting and scanning the light beam from the first optical system;
A second optical system that forms an image of the light beam deflected and scanned by the deflecting means on the surface to be scanned;
Synchronization signal detection means for detecting a part of the light beam deflected and scanned on the deflection surface of the deflection means as a synchronization detection signal for determining the timing of the scanning start position of the light beam on the scanned surface;
A synchronization detection optical system for guiding a part of the light beam deflected and scanned by the deflection surface of the deflection means to the synchronization signal detection means,
The synchronization detection optical system includes a light beam limiting unit that limits a light beam width of a light beam in a sub-scanning direction orthogonal to the main scanning direction,
A reflection mirror is provided in the optical path from the light source means to the synchronization signal detection means, and the light flux limiting means is disposed in the optical path between the reflection mirror closest to the synchronization signal detection means and the synchronization signal detection means. It is characterized by having.

The invention of claim 2 is the invention of claim 1,
The synchronization detection optical system includes an independent synchronization detection imaging unit different from the second optical system in an optical path between the light beam limiting unit and the synchronization signal detection unit. .

The invention of claim 3 is the invention of claim 2,
The synchronization detection optical system includes an optical path separating / reflecting means for separating an optical path of a light beam that is deflected and scanned on the deflecting surface of the deflecting means and travels toward the synchronizing signal detecting means, between the deflecting means and the light beam limiting means. It is characterized by having in the optical path.

The invention of claim 4 is the invention of claim 2,
The synchronous detection imaging means has an anamorphic optical system having different powers in the main scanning direction and the sub-scanning direction, the focal length in the main scanning direction of the anamorphic optical system is F_am, and the focal length in the sub-scanning direction is F_as. When
F_am>F_as> 0
It is characterized by satisfying the following conditions.

The invention of claim 5 is the invention of claim 2,
The refractive power in the sub-scanning direction of the synchronization detection imaging means is the largest among the optical elements from the deflection means to the synchronization signal detection means.

The invention of claim 6 is the invention of claim 2,
The synchronization detection imaging means is arranged so that the light beam limiting means and the synchronization signal detection means are conjugate in the sub-scan section.

The invention of claim 7 is the invention of claim 2,
The number of reflection surfaces from the light source means to the synchronization signal detection means is N,
The distance along the optical path from the light beam limiting means to the synchronous detection imaging means is S1,
L, the distance along the optical path from the synchronization detection imaging means to the synchronization signal detection means,
The focal length in the sub-scanning direction of the synchronous detection imaging means is F_as,
When the width of the light receiving region in the sub-scanning direction of the synchronization signal detecting means is W,
| (S1 / F_as-1) × L-S1 | ≦ 250 × W / 3 / N
It is characterized by satisfying the following conditions.

The invention of claim 8 is the invention of claim 2,
The distance along the optical path from the deflecting means to the light flux limiting means is S0,
The distance along the optical path from the light beam limiting means to the synchronous detection imaging means is S1,
L, the distance along the optical path from the synchronization detection imaging means to the synchronization signal detection means,
The focal length in the sub-scanning direction of the synchronous detection imaging means is F_as,
The width of the light receiving area in the sub-scanning direction of the synchronization signal detecting means is W
When the width of the light beam limiting means in the sub-scanning direction is Wap,
Wap × [(L / F_as−1) × (S0 + S1) −L] / S0 ≦ W
It is characterized by satisfying the following conditions.

The invention of claim 9 is the invention of claim 1,
At least one of the synchronization signal detecting unit and the light beam limiting unit is inclined in the sub-scan section.

The invention of claim 10 is the invention of claim 1,
The first optical system is characterized in that, in the main scanning section, the light beam emitted from the light source means is converted into a parallel light beam having a light beam width wider than the width of the deflection surface of the deflection means.

The invention of claim 11 is the invention of any one of claims 1 to 10,
The light source means has a plurality of light emitting points, and at least two light fluxes of the plurality of light emitting points are guided to the synchronization signal detecting means and used for generating the synchronization detection signal. Yes.

The invention of claim 12 is the invention of any one of claims 1 to 11,
A plurality of the light source means, the light beam emitted from each light source means is guided to the deflection surface of the deflection means,
A plurality of light beams deflected and scanned by the deflecting means are imaged on a plurality of scanned surfaces provided for each light beam,
Among the plurality of light beams deflected and scanned by the deflecting means, at least one light beam is guided to the synchronization detection optical system.

The invention of claim 13 is the invention of claim 12,
The light beam from the light source unit corresponding to the optical path having the smallest number of reflection surfaces provided on the optical path from the plurality of light source units to the plurality of scanned surfaces is transmitted to the synchronization signal detection unit by the synchronization detection optical system. It is characterized by guiding.

An image forming apparatus according to a fourteenth aspect is provided.
The optical scanning device according to claim 1, a photosensitive drum disposed on the surface to be scanned, and a static beam formed on the photosensitive drum 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 a fifteenth 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.

The color image forming apparatus of the invention of claim 16
Each of the optical scanning devices according to any one of claims 1 to 13 is disposed on a surface to be scanned, and has a plurality of image carriers that form images of different colors.

The invention of claim 17 is the invention of claim 16,
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, a part of the light beam incident on the synchronization signal detection means (synchronization detection sensor) is appropriately limited by the light beam limiting means arranged on the light emission side of all the reflection surfaces, thereby allowing the main scanning direction. The printing position shift (jitter) can be reduced. As a result, it is possible to achieve an optical scanning device capable of obtaining high-precision printing quality 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 a main part in the main scanning direction of an optical scanning device according to a first embodiment of the present invention. 2 to 5 are cross-sectional views (sub-scanning cross-sectional views) in the sub-scanning direction of the optical scanning device shown in FIG. 2 is a sub-scan sectional view from the light source means to the reflecting mirror, FIG. 3 is a sub-scan sectional view from the reflecting mirror to the surface to be scanned, FIG. 4 is a sub-scan sectional view from the optical deflector to the synchronization detecting means, FIG. FIG. 4 is a sub-scan sectional view from a light beam limiting unit to a synchronization detection unit.

  In the following description, the main scanning direction is a direction perpendicular to the rotation axis of the rotating polygon mirror and the optical axis of the imaging optical system (the direction in which the light beam is deflected and scanned (deflected scanning) by the rotating polygon mirror). The sub-scanning direction is a direction parallel to the rotation axis of the rotary polygon mirror. The main scanning section is a plane including the main scanning direction and the optical axis of the imaging optical system. The sub-scanning section is a section perpendicular to the main scanning section.

  In the figure, reference numeral 1 denotes a light source means, for example, a semiconductor laser.

  A condensing lens (collimator lens) 2 converts the light beam emitted from the light source means 1 into a parallel light beam (or a divergent light beam or a convergent light beam).

  Reference numeral 3 denotes an aperture stop which shapes the light beam emitted from the condenser lens 2 into an optimum beam shape.

  A cylindrical lens (cylinder lens) 4 has a finite power (refractive power) only in the sub-scanning direction (within the sub-scanning section).

  Reference numeral 5 denotes an anamorphic lens (incident anamorphic lens), which has an incident surface composed of anamorphic aspheric surfaces having different powers in the main scanning direction (in the main scanning section) and in the sub-scanning direction. The anamorphic lens 5 is provided with a diffractive optical element on its exit surface.

  A reflection mirror 61 deflects the light beam that has passed through the anamorphic lens 5 with respect to the main scanning direction and guides it to an optical deflector 6 described later.

  Each element of the condenser lens 2, the aperture stop 3, the cylindrical lens 4, the anamorphic lens 5, and the first imaging lens 71 described later constitutes one element of the first optical system (incident optical system) LA. ing.

  An optical deflector 6 as a deflecting means is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor. The optical deflector 6 in this embodiment is composed of 10 polygon mirrors inscribed in φ23 (diameter 23 mm), and the width of the deflection surface 62 of the polygon mirror 6 in the main scanning direction is 7.11 mm. In the OFS, the width of the deflection surface 62 serves as a substantial stop in the main scanning direction.

  An imaging optical system 7 as a second optical system has first and second imaging lenses (anamorphic lenses) 71 and 72 having different powers in the main scanning section and the sub-scanning section. ing. The imaging optical system 7 forms an image of a light beam based on image information deflected and scanned by the optical deflector 6 onto a spot on a photosensitive drum surface 8 as a scanned surface in the main scanning section. In addition, surface tilt correction is performed by optically conjugating between the deflection surface 62 of the optical deflector 6 and the photosensitive drum surface 8 in the sub-scan section. The first imaging lens 71 also constitutes a part of the incident optical system LA.

  In this embodiment, the light beam (incident light beam) incident on the optical deflector 6 passes through the first imaging lens 71, and the light beam deflected by the optical deflector 6 (scanning light beam) again forms the first image. A double-pass configuration for entering the lens 71 is adopted.

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

  Reference numeral 63 denotes a reflecting mirror reflecting mirror (hereinafter referred to as “synchronous detection mirror”) as an optical path separating reflecting means, and a light beam (synchronous detecting light beam) directed to an image height other than the effective image area of the scanned surface 8. The optical path is separated, and is provided between the optical deflector 6 and a synchronous detection diaphragm 9 described later.

  The reflection mirror 63 reflects a synchronization detection light beam for generating a synchronization detection signal for determining the timing of the scanning start position on the photosensitive drum surface 8 toward the synchronization detection sensor 12 described later.

  Reference numeral 9 denotes a synchronization detection diaphragm (hereinafter referred to as “synchronization detection diaphragm”) as a light beam limiting means, which limits a light beam in the sub-scanning direction orthogonal to the main scanning direction. In this embodiment, the synchronization detection diaphragm 9 is arranged in the optical path between the reflection mirror closest to the synchronization detection sensor 12 among the reflection mirrors from the light source means 1 to the synchronization detection sensor 12 and the synchronization detection sensor 12. Has been.

  Reference numeral 10 denotes synchronization detection imaging means, which comprises a synchronization detection lens (hereinafter referred to as “synchronization detection lens”) as an anamorphic optical system having different powers in the main scanning direction and the sub-scanning direction. It is provided in the optical path on the light emitting side of the synchronous detection diaphragm 9 independently of the optical system 7.

  The synchronization detection lens 10 is used to make the synchronization detection mirror 63 and the synchronization detection sensor 12 have a conjugate relationship, and corrects the surface tilt of the synchronization detection mirror 63.

  Reference numeral 11 denotes an edge portion for synchronization detection (hereinafter referred to as “synchronization detection edge”), which is composed of linear edges and determines the image writing position.

  Reference numeral 12 denotes an optical sensor (hereinafter referred to as “synchronization detection sensor”) as a synchronization signal detection means. In this embodiment, a synchronization signal (a synchronization signal obtained by detecting an output signal from the synchronization detection sensor 12). The timing of the scanning start position of image recording on the photosensitive drum surface 8 is adjusted using a synchronization detection signal).

  Each element such as the synchronization detection mirror 63, the synchronization detection diaphragm 9, the synchronization detection lens 10, and the synchronization detection edge 11 constitutes one element of the synchronization detection optical system (synchronization detection optical system) LB. Yes.

  In the present embodiment, the divergent light beam that is light-modulated and emitted from the semiconductor laser 1 is converted into a parallel light beam by the condenser lens 2, and the diameter of the light beam is limited by the diaphragm 3. The limited light beam is once converted into a convergent light beam by the cylindrical lens 4 and is incident on the anamorphic lens 5. Of the light beams incident on the anamorphic lens 5, the light beams in the sub-scanning section converge and pass through the first imaging lens 71 (double path configuration) and enter the deflecting surface 62 of the optical deflector 6. An image 62 is formed as a line image (a line image elongated in the main scanning direction). At this time, the light beam incident on the deflecting surface 62 is projected from the sub-scan section including the rotation axis of the optical deflector 6 and the optical axis of the imaging optical system 7 to a plane perpendicular to the rotation axis of the optical deflector 6 (optical deflector). (6 rotation plane) with a finite angle (θ = + 1.5 degrees) from an oblique direction. Thereby, the incident light beam and the deflected light beam are separated (obliquely incident optical system).

  On the other hand, the light beam in the main scanning section diverges and is converted into a parallel light beam by passing through the first imaging lens 71, and is incident on the deflection surface 62 from the center of the deflection angle of the optical deflector 6 (front surface). incident).

  The beam width of the parallel beam at this time is set to be sufficiently larger than the facet width of the deflecting surface 62 of the optical deflector 6 in the main scanning direction (overfilled optical system).

  The light beam deflected and reflected by the deflecting surface 62 of the optical deflector 6 is guided to the photosensitive drum surface 8 through the first and second imaging lenses 71 and 72, and the optical deflector 6 is moved in the direction of arrow A. By rotating, the photosensitive drum surface 8 is scanned at a constant speed in the direction of arrow B (main scanning direction).

  Thereby, an image is recorded on the photosensitive drum surface 8 as a recording medium.

  At this time, in order to determine the timing of the scanning start position of the light beam on the photosensitive drum surface 8 before optical scanning on the photosensitive drum surface 8, a part of the light beam deflected and scanned by the optical deflector 6 is used for synchronous detection. The light is condensed on the surface of the synchronization detection edge 11 by the synchronization detection diaphragm 9 and the synchronization detection lens 10 via the mirror 63. Then, the light beam is condensed on the surface of the synchronization detection edge 11 and then guided to the synchronization detection sensor 12. The timing of the scanning start position of image recording on the photosensitive drum surface 8 is adjusted using a synchronization detection signal (synchronization detection signal) obtained by detecting the output signal from the synchronization detection sensor 12.

  Next, Table 1 shows the specifications of the optical system of the optical scanning device in Example 1. Table 2 shows the aspherical shape of each lens.

  However, the expression is defined as follows.

  ・ Lens surface shape (toric shape). . . An aspherical shape whose main scanning direction can be expressed by a function up to the 10th order, the intersection point with the optical axis as the origin, the optical axis direction as the x axis, the axis perpendicular to the optical axis in the main scanning plane, the y axis, and the sub scanning plane When the axis perpendicular to the optical axis is the z axis, the bus direction corresponding to the main scanning direction is

(Where R is the radius of curvature, and K, B ₄ , B ₆ , B ₈ , and B ₁₀ are aspheric coefficients)
The sub-scanning direction (the direction including the optical axis and orthogonal to the main scanning direction) and the sub-line direction are

Where r ′ = r ₀ (1 + D ₂ Y ² + D ₄ Y ⁴ + D ₆ Y ⁶ + D ₈ Y ⁸ + D ₁₀ Y ¹⁰ )
(Where r ₀ is the radius of curvature on the optical axis on the optical axis, and D ₂ , D ₄ , D ₆ , D ₈ and D ₁₀ are coefficients)
· Diffraction grating . . . Diffraction surface represented by a second-order phase function whose main scanning direction is up to the 10th order and whose sub-scanning direction varies depending on the position in the main scanning direction φ = mλ = b ₂ Y ² + b ₄ Y ⁴ + b ₆ Y ⁶ + b ₈ Y ⁸ + b ₁₀ Y ¹⁰
+ (D ₀ + d ₁ Y + d ₂ Y ² + d ₃ Y ³ + d ₄ Y ⁴ ) Z ²
(However, m is the diffraction order: + 1st order diffracted light is used.)
Next, the optical action of the first optical system LA will be described.

  The divergent light beam emitted from the light source means 1 is converted into a parallel light beam by the condenser lens 2 and then shaped by the diaphragm 3. The parallel light beam is subjected to the following optical action through the cylindrical lens 4, the anamorphic lens 5, and the first imaging lens 71. In the main scanning direction, the beam is expanded by passing through the cylindrical lens 4, the anamorphic lens 5, and the first imaging lens 71, and the beam width is wider than the width of one deflecting surface 62 of the optical deflector 6 in the main scanning direction. Is incident on the optical deflector 6.

  In the sub-scan section, the light passes through the cylindrical lens 4, the anamorphic lens 5, and the first imaging lens 71 to be converted into a convergent light beam and imaged on the deflecting surface 62. Therefore, the light beam forms a line image on the deflection surface 62. The reflecting mirror 61 in the middle of the optical path contributes to downsizing of the entire apparatus by bending the optical path.

  Next, the optical action of the optical deflector (polygon mirror) 6 will be described.

  In the optical deflector 6, a part of the incident light beam that has entered in a state wider than the width of the deflecting surface 62 in the main scanning direction is cut out by the deflecting surface 62 to guide the light beam to the imaging optical system 7. Therefore, different portions of the incident light beam to the optical deflector 6 are used according to the image height on the scanned surface 8. For example, the central part of the incident light beam to the optical deflector 6 is used for the light beam guided to the central part on the scanned surface 8, and the peripheral part of the incident light beam to the optical deflector 6 is used for the light beam guided to the peripheral part. It is.

  Next, the optical action of the imaging optical system 7 as the second optical system will be described.

  The light beam deflected and scanned by the optical deflector 5 is imaged on the scanned surface 8 to form a beam spot, and the scanned surface 8 is scanned at a constant speed. As shown in Table 1, the first imaging lens 71 having power mainly in the main scanning direction has an aspherical shape in which the lens surface shape is expressed by a function of the given equation. Non power in the sub-scanning direction.

  However, the present invention is not necessarily limited thereto, and for example, a cylinder shape in which both surfaces are flat in the sub-scanning direction may be used. For the incident light beam, image formation in the main scanning direction and constant speed scanning are mainly achieved. One second imaging lens 72 is an anamorphic lens having power mainly in the sub-scanning direction. This is also an aspherical lens, and the lens surface shape is an aspherical shape expressed by a function of the given equation. Non-power in the main scanning direction. He is mainly responsible for image formation in the sub-scanning direction and correction of slight distortion in the main scanning direction for the incident light flux. The imaging relationship in the sub-scanning direction by the imaging optical system 7 including the first and second imaging lenses 71 and 72 is a so-called tilt correction optical system in which the deflection surface 62 and the scanned surface 8 are in a conjugate relationship. Yes. The first and second imaging lenses 71 and 72 are both made of resin and can be manufactured by a known molding technique.

  The imaging optical system (fθ lens) 7 is not necessarily limited to the power arrangement, the number of used sheets, and the glass material characteristics as shown in Table 1. One or three or more lens configurations and other power arrangements are used. Alternatively, a known expression optical system such as a function expression or a glass material may be used.

  Next, the optical action of the anamorphic lens 5 constituting one element of the first optical system LA will be described.

  The anamorphic lens 5 cooperates with the cylindrical lens 4 and the first imaging lens 71 to convert the divergent light beam from the condenser lens 2 into a parallel light beam in the main scanning direction. At the same time, a first optical system LA is formed which is incident in a state wider than the width of one deflecting surface 62 of the optical deflector 6 in the main scanning direction. As described above, the anamorphic lens 5 is an anamorphic aspherical surface in which the incident surface has different powers in the main scanning direction and the sub-scanning direction. A diffractive optical element is provided on the exit surface. The diffractive surface has an effect of compensating for the deterioration of optical performance caused by the wavelength fluctuation of the light source means 1 or the refractive index fluctuation of the glass material when the operating temperature of the imaging optical system fluctuates.

  Next, the optical action of the synchronization detection optical system (synchronization detection optical system) LB will be described.

  The synchronization detection optical system LB reflects the light path of the image height (synchronization detection light beam) other than the effective image area on the scanned surface 8 by the synchronization detection mirror 63 to separate the optical path. The lens 10 and the synchronization detection edge 12 (slit) 11 lead to the synchronization detection sensor 12. At this time, the first imaging lens 71 and the synchronization detection lens 10 act on the imaging of the synchronization detection optical system LB, and the first imaging lens 71 also forms part of the synchronization detection optical system LB. is doing. A configuration in which an image is formed on the synchronization detection edge 11 in the main scanning direction is desirable.

  The synchronization detection edge 11 is provided upstream or downstream in the scanning direction, and is a straight edge in a direction perpendicular to the scanning direction (sub-scanning direction). Alternatively, it is a slit shape in which two pairs of linear edges parallel to the scanning direction (sub-scanning direction) are separated by a width of about 0.5 mm in the main scanning direction. When the shape of the light receiving portion of the synchronization detection sensor 12 is rectangular and the boundary area is sufficiently linear, the synchronization detection edge 11 may be omitted. In this case, the synchronization detection sensor 12 may be offset to the position of the synchronization detection edge 11.

  When the synchronization detection light beam reaches the synchronization detection sensor 12, an electrical signal is output. With respect to the rising waveform or falling waveform of the signal, the time for reaching the signal output at a specific slice level is defined as the detection time for synchronization detection. By measuring the time until the start of writing an image with the counter based on the detection time for synchronization detection, and driving the light source 1 with an image signal, the writing start position can always be kept constant. Such an electric driving method for detecting the synchronization signal is performed by a known method.

  Table 3 shows an optical arrangement from the deflection surface 62 of the optical deflector 6 to the synchronization detection sensor 12. Table 4 shows the shape of the synchronization detection lens 10.

  As is apparent from FIG. 1, there are three reflecting surfaces, that is, a reflecting mirror reflecting mirror 61, a deflecting surface 62, and a synchronizing detecting mirror 63 on the optical path from the light source means 1 to the synchronization detecting sensor 12 (synchronizing signal detecting means). To do. In this embodiment, the synchronization detecting diaphragm 9 is disposed in the optical path on the light reflecting side of the third reflecting surface 63. This synchronous detection diaphragm 9 has a slit shape for limiting the light beam in the sub-scanning direction.

  Further, as described above, an independent synchronization detection lens 10 different from the imaging optical system 7 is disposed behind the synchronization detection diaphragm 9. The synchronous detection lens 10 is composed of a spherical surface (R1 = 37.5) on the incident surface and an aspheric surface (R = -29.0) whose exit surface has a curvature only in the sub-scanning direction, and the refractive index n of the material is n = 1. It consists of 491.

In this embodiment, when the focal length in the main scanning direction of the synchronization detection lens 10 is F_am and the focal length in the sub-scanning direction is F_as,
F_am>F_as> 0 (1)
Satisfy the following conditions.

  Conditional expression (1) indicates that the synchronization detection imaging means 10 is an anamorphic lens, and the power in the sub-scanning direction is larger than the power in the main scanning direction.

In the present embodiment, the focal lengths F_am and F_as in the main scanning direction and the sub-scanning direction of the synchronization detection lens 10 are F_am = 76.389,
F_as = 33.646
It is. This satisfies the conditional expression (1).

  As can be seen from Table 1, the first imaging lens 71 has power mainly in the main scanning direction, and non-power in the sub-scanning direction. For this reason, the power in the sub-scanning direction of the synchronization detection lens 10 is the largest among the optical elements from the optical deflector 6 to the synchronization detection sensor 12.

  In this embodiment, as described above, in order to separate the optical path between the light beam (scanning light beam) traveling toward the scanning surface 8 and the synchronization detection light beam, the synchronization detection mirror 63 is provided between the optical deflector 6 and the synchronization detection diaphragm 9. It is provided in the optical path.

  In this embodiment, the number of reflecting surfaces from the light source means 1 to the synchronization detection sensor 12 is N.

  Further, the distance along the optical path from the synchronization detection diaphragm 9 to the synchronization detection lens 10 is S1, the distance along the optical path from the synchronization detection lens 10 to the synchronization detection sensor 12 is L, and the synchronization detection lens 10 The focal length in the sub-scanning direction is F_as, and the width of the light receiving region in the sub-scanning direction of the synchronization detection sensor 12 is W.

then,
| (S1 / F_as-1) × L-S1 | ≦ 250 × W / 3 / N (2)
Each element is set to satisfy the following conditions.

  Conditional expression (2) indicates that the sub-scanning aperture that determines the beam diameter in the sub-scanning direction is determined by the tilt error of the reflecting surface installed before the sub-scanning aperture that determines the beam diameter in the sub-scanning direction within the sub-scanning section. The light beam passing through causes an inclination.

  Defines the range in which the light beam on the synchronization detection means (synchronization detection sensor) can be swung by the refraction action of the synchronization detection imaging means after the sub-scanning diaphragm that determines the beam diameter in the sub-scanning direction when the tilt problem occurs. It is a thing. The case where the range in which the luminous flux swings is half the sensor width is shown.

In this embodiment, the number N of reflection surfaces from the light source means 1 to the synchronization detection sensor 12 is 3 from FIG. 1, FIG. 4, FIG. 5, Table 3, and Table 4.
A distance S1 = 69.5 along the optical path from the synchronization detection diaphragm 9 to the synchronization detection lens 10;
Distance L = 52.8 along the optical path from the synchronization detection lens 10 to the synchronization detection sensor 12
Focal length F_as = 33.645 in the sub-scanning direction of the synchronization detection lens 10
The width W of the light receiving region in the sub-scanning direction of the synchronization detection sensor 12 = 1.35,
It is said. As a result, the values on the left and right sides of the conditional expression (2) are
Left side = 13.23,
Right side = 37.5
This satisfies the conditional expression (2).

  More preferably, the conditional expression (2) should be set as follows.

| (S1 / F_as-1) × L-S1 | ≦ 100 × W / 3 / N (2a)
The values of the left side and right side of the conditional expression (2a) are
Left side = 13.23,
Right side = 15
This satisfies the conditional expression (2a).

It should be noted that the left side of the conditional expression (2) and the conditional expression (2a) is (S1 / F_as−1) × L−S1 = 0.
That is,
1 / F_as = 1 / S1 + 1 / L
Therefore, it can be understood that the synchronization detection diaphragm 9 and the synchronization detection sensor 12 are in a conjugate relationship by the synchronization detection lens 10.

Further, in this embodiment, the distance along the optical path from the optical deflector 6 to the synchronization detecting diaphragm 9 is S0,
When the width of the synchronization detection diaphragm 9 in the sub-scanning direction is Wap,
Wap × [(L / F_as−1) × (S0 + S1) −L] / S0 ≦ W (3)
Each element is set to satisfy the following conditions.

  Conditional expression (3) is an expression that prescribes the spread of the light beam on the synchronization detection means 12 (synchronization detection sensor), and expresses an imaging condition such that the light beam width is approximately equal to or smaller than the sensor width.

In this embodiment, from FIG. 4, FIG. 5, Table 3, and Table 4, the distance S0 = 200.19 along the optical path from the deflecting surface 62 to the stop 9 for detecting synchronization.
Width Wap = 0.96 in the sub-scanning direction of the synchronous detection diaphragm 9
It is said. As a result, the values on the left and right sides of conditional expression (3) are
Left side = 0.48,
Right side = 1.35
This satisfies the conditional expression (3).

  Since the synchronization detection sensor 12 is generally made of a semiconductor, the surface reflection is 20 to 40%. Therefore, the synchronization detection light beam incident on the synchronization detection sensor 12 may be reflected on the surface of the synchronization detection sensor 12 to form a flare. As a method for properly removing the flare light, it is preferable to tilt the synchronization detection sensor 12 in the sub-scan section and strike the surface reflected light against the back surface of the synchronization detection diaphragm 9. Further, when a part of the synchronization detection light beam is reflected on the surface of the synchronization detection diaphragm 9 and becomes flare, the synchronization detection diaphragm 9 is tilted in the sub-scanning section so that the surface reflected light escapes in the vertical direction. good.

  In this embodiment, OFS is employed as the optical system of the optical scanning device as described above. In this OFS, as described above, the problem that the detection accuracy for synchronization detection is lowered due to the attitude accuracy of the reflecting surface on the optical path as an adverse effect of the length of the optical path of the synchronization detection optical system is improved.

  In this embodiment, the number of light emitting points of the light source means 1 may be 1 or 2 or more. In particular, when there are a plurality of light emission points, two or more of the light beams may be guided to the synchronization detection sensor 12 by the above-described synchronization detection optical system to detect the synchronization signal.

  Next, optical performance obtained by the above-described configuration of the synchronization detection optical system LB will be described.

  As described above, in the optical path from the light source means 1 to the synchronization detection sensor 12, there are three reflection surfaces: the reflection mirror reflection mirror 61, the deflection surface 62, and the synchronization detection mirror 63. Table 5 shows the results of calculating the sensitivity of how much the light beam touches on the synchronization detection sensor 12 when the postures of these reflecting surfaces vary depending on the component accuracy and the mounting accuracy. For comparison, the sensitivity when the synchronous detection diaphragm 9 of this configuration is eliminated is also shown. Note that the deflection of the posture of each reflecting element is 10 minutes in the bow direction. In addition, the luminous flux width on the synchronization detection sensor 12 is also shown.

  As described above, with respect to the width W = 1.35 of the light receiving region in the sub-scanning direction of the synchronization detection sensor 12, by inserting the synchronization detection diaphragm 9, the fluctuation width of the light flux on the synchronization detection sensor 12 is It can be seen that it is sufficiently small relative to the width. It can also be seen that the beam width is within the sensor.

  As shown in Table 5, since the light beam spreads in the sub-scanning direction on the synchronization detection sensor 12, it is less affected by the straightness error as mentioned in the problem of Patent Document 3.

  In this embodiment, OFS is shown, but the present invention is not necessarily limited to this. For example, UFS using the same optical element can also be implemented. Specifically, the diameter of the optical deflector 6 is increased so that the deflecting surface 62 is widened and the number of surfaces is reduced, for example, a six-surface optical deflector of φ40, and the aperture stop 3 in the main scanning direction is changed. What is necessary is just to give it so that a width | variety may be narrowed and the light beam width in the optical deflector 6 may be set to 7.11 mm.

  In this embodiment, a polygon mirror is used as an optical deflector. However, the present invention is not limited to this, and a galvanometer mirror, for example, may be used.

  FIGS. 6 and 7 are sub-scan sectional views of Embodiment 2 of the present invention, FIG. 6 is a sub-scan sectional view from the light source means to the reflecting mirror reflecting mirror, and FIG. 7 is from the reflecting mirror reflecting mirror to the surface to be scanned. FIG.

  This embodiment differs from the first embodiment described above in that two optical systems (scanning optical systems) of the optical scanning apparatus shown in the first embodiment are coupled vertically (in the sub-scanning direction), and the optical path is reduced for compactness. It is constructed by bending. Therefore, the main scanning sectional view is the same as FIG. 1 shown in the first embodiment. Other configurations and optical actions are the same as those in the first embodiment, and the same effects are obtained.

  That is, the oblique incidence optical system of Example 1 described above has an oblique incidence angle in the sub-scan section of θ = + 1.5 °, but in this embodiment, the oblique incidence angle is configured as θ = ± 1.5 °. ing.

  In this embodiment, the optical system through which the light beam toward the photosensitive drum 81A as the first scanned surface passes is A station, and the optical system through which the light beam toward the photosensitive drum 81B as the second scanned surface passes is called B station. Call it. As apparent from FIGS. 6 and 7, in this embodiment, in the sub-scan section, the optical path of the A station and the B station crosses with the reflecting mirror reflecting mirror 61, and the upper and lower sides on the deflecting surface 62 of the optical deflector 6. It is configured to be separated by about 6 mm in the (sub-scanning direction).

  The A station and the B station have reflection mirrors 64, 65, and 66, respectively. The scanning light beams deflected and scanned by the deflecting surface 62 of the optical deflector 6 are respectively applied to the corresponding photosensitive drums 81A and 81B. Guided.

  Further, the reflecting mirror 61, the optical deflector 6, and the first imaging lens 71 are shared by each station. In the figure, the same optical elements as those in the first embodiment are used. The other optical elements arranged uniquely in each station are indicated by adding symbols A and B to the numbers in the first embodiment.

  In this embodiment, the first optical system from the light source means 1A, 1B to the optical deflector 6 and the imaging optical system 7 comprising the first imaging lens 71 and the second imaging lenses 72A, 72B are the first embodiment. The specifications are shown in Table 1 and Table 2.

  In this embodiment, synchronization signal detection (synchronization detection detection) is detected by the scanning light beam on the A station side. That is, in this embodiment, a light beam having an image height other than the effective image on the photosensitive drum 81A is reflected by the synchronization detection mirror 63 to separate the optical path, and the synchronization detection diaphragm 9, the synchronization detection lens 10, and the synchronization detection not shown. A synchronization detection optical system LB is configured to be guided to the synchronization detection sensor 12 through the edge (slit) 11. At this time, the first imaging lens 71 and the synchronization detection lens 10 act on the imaging of the synchronization detection optical system LB, and the first imaging lens 71 also has a part of the synchronization detection optical system LB. There is no. The optical arrangement from the optical deflector 6 to the synchronization detection sensor 12 is the same as that in the first embodiment, and its specifications are shown in Table 3 and have the same configuration as FIG.

  In the present embodiment, since the synchronization detection optical system LB is the same as that in the first embodiment, the reflection mirror reflection mirror 61, the deflection surface 62, and the synchronization detection are provided on the optical path from the light source means 1 to the synchronization detection sensor 12. There are three reflecting surfaces of the mirror 63 for use. The synchronization detection diaphragm 9 is disposed in the optical path on the light reflecting side of the third reflecting surface 63. The synchronous detection diaphragm 9 has a slit shape that restricts the light beam in the sub-scanning direction. Further, an independent synchronization detection lens 10 different from the imaging optical system 7 is disposed in the optical path on the light reflection side of the synchronization detection diaphragm 9.

  In this embodiment, the number N of reflection surfaces provided on the optical path from the light source means 1A to the photosensitive drum 81A is used as a parameter on the right side of the conditional expressions (2) and (3). The smaller the number N of reflecting surfaces, the larger the right sides of conditional expression (2) and conditional expression (3), and the margin for the left side increases. Therefore, it is more advantageous to detect the synchronization signal of the light beam of the light source unit corresponding to the optical path having the smallest number of reflecting surfaces provided on the optical path from the light source unit 1A or the light source unit 1B to the photosensitive drum 81.

  The number of reflecting surfaces provided on the optical path from each light source means 1 to each photosensitive drum 81 is three for A station and four for B station. On the other hand, the number of reflecting surfaces in the optical path from the light source means 1A to the synchronization detecting sensor 12 is 3, which is not more than the number of reflecting surfaces in each station.

  In this embodiment, since the number N of reflection surfaces of the synchronization detection optical system LB is made as small as possible, variations in the light flux on the synchronization detection sensor 12 can be reduced due to variations in assembly accuracy and component accuracy. Accuracy is improved.

  In this embodiment, the optical performance obtained when the synchronization detection optical system LB has the above-described configuration is the same as that of the first embodiment.

  FIG. 8 is a sectional view (main scanning sectional view) of the main part in the main scanning direction according to the third embodiment of the present invention. In the figure, the same elements as those shown in FIG.

  This embodiment differs from the first embodiment described above in that the first optical system LA is composed of an oblique incidence optical system even in the main scanning section, and the light beam deflected and scanned by the deflection surface 62 (synchronous detection light beam). Is guided to the synchronous detection sensor 12 without passing through the first imaging lens 71. Other configurations and optical actions are the same as those in the first embodiment, and the same effects are obtained.

  In this embodiment, the divergent light beam emitted from the light source means 1 is converted into a parallel light beam by the collimator lens 2, and the light beam is limited by the diaphragm 3 and enters the cylindrical lens 41 having a finite refractive power only in the sub-scanning direction. ing. Among the parallel light beams incident on the cylindrical lens 41, the parallel light beams are emitted as they are in the main scanning section. In the sub-scan section, the light beam is focused and formed as a line image on the deflecting surface 62 of the optical deflector 6 composed of a rotating polygon mirror.

  In this embodiment as well, OFS is used for the incident optical system as in the first embodiment.

  Then, the light beam deflected by the deflecting surface 62 of the optical deflector 6 is guided through the imaging optical system 7 onto the photosensitive drum surface 8 as the surface to be scanned. Then, by rotating the light deflector 6 in the direction of arrow A, the photosensitive drum surface 8 is scanned at a constant speed in the direction of arrow B to record image information.

  At this time, in order to adjust the timing of the scanning start position on the photosensitive drum surface 8 before optical scanning on the photosensitive drum surface 8, a part of the light beam deflected and scanned by the optical deflector 6 is synchronized with the synchronization detection mirror 63. The light is condensed on the surface of the synchronization detection edge 11 by the synchronization detection diaphragm 9 and the synchronization detection lens 10.

  Then, the light beam is condensed on the surface of the synchronization detection edge 11 and then guided to the synchronization detection sensor 12. The timing of the scanning start position of image recording on the photosensitive drum surface 8 is adjusted using a synchronization detection signal (synchronization detection signal) obtained by detecting the output signal from the synchronization detection sensor 12.

  The first and second imaging lenses 73 and 74 in this embodiment both have anamorphic power, and the surface shape is an aspherical shape expressed by a known function. The first and second imaging lenses 73 and 74 are made of resin and can be manufactured by a known molding technique.

  The imaging optical system 7 is not necessarily limited to the power arrangement, the number of used sheets, and the glass material characteristics as described above. One or three or more lens configurations, another power arrangement, a function expression, a glass material, etc. A configuration of a known imaging optical system may be used.

  Table 6 shows the optical arrangement from the deflection surface 62 to the synchronization detecting sensor 12 in this embodiment. Table 7 shows the shape of the synchronization detection lens 10.

  As shown in Tables 6 and 7, the synchronous detection lens 10 in this embodiment is formed of an aspherical surface (R = 19.61) whose entrance surface has a curvature only in the sub-scanning direction, and its exit surface is a spherical surface (R = -30.83). And the refractive index n of the material is n = 1.491.

In the present embodiment, the focal lengths F_am and F_as of the synchronization detection lens 10 in the main scanning direction and the sub-scanning direction are respectively F_am = 62.8,
F_as = 24.9
It is. This satisfies the conditional expression (1).

  Further, as can be seen from FIG. 8, the synchronization detection light beam is imaged on the synchronization detection sensor 12 only by the synchronization detection lens 10 without the first imaging lens 73 interposed. Therefore, among the optical elements from the optical deflector 6 to the synchronization detection sensor 12, the power in the sub-scanning direction of the synchronization detection lens 10 is maximum.

  Also in this embodiment, in order to separate the optical paths of the scanning light beam and the synchronization detection light beam traveling toward the scanning surface in the same manner as in the first embodiment, the synchronization detection mirror 63 is connected to the optical deflector 6 and the synchronization detection diaphragm 9. It is provided in the optical path between.

In this embodiment, from FIG. 8 and Table 6, the number N of reflection surfaces from the light source means 1 to the synchronization detecting sensor 12 is N = 2.
A distance S1 = 27.1 along the optical path from the synchronization detection diaphragm 9 to the synchronization detection lens 10;
Distance L = 62.8 along the optical path from the synchronization detection lens 10 to the synchronization detection sensor 12
Focal length F_as = 24.90 in the sub-scanning direction of the synchronization detection lens 10;
The width W of the light receiving region in the sub-scanning direction of the synchronization detection sensor 12 = 1.35,
It is said. Thereby, the values of the left side and the right side of the conditional expression (2) are
Left side = 21.55,
Right side = 56.25
This satisfies the conditional expression (2).

Furthermore, the values on the left side and right side of the conditional expression (2a) are:
Left side = 21.55,
Right side = 22.50
This satisfies the conditional expression (2a).

Note that the left side of conditional expression (2) and conditional expression (2a) is (S1 / F_as-1) × L-S1 = 0.
That is,
1 / F_as = 1 / S1 + 1 / L
Therefore, it can be understood that the synchronization detection diaphragm 9 and the synchronization detection sensor 12 are in a conjugate relationship by the synchronization detection lens 10.

Further, in this embodiment, from Table 6, the distance S0 = 98.0 along the optical path from the deflecting surface 62 to the synchronous detection diaphragm 9 is shown.
Width Wap = 0.90 in the sub-scanning direction of the synchronous detection diaphragm 9
It is said. Thereby, the values of the left side and the right side of the conditional expression (3) are
Left side = 1.17,
Right side = 1.35
This satisfies the conditional expression (3).

  Next, optical performance obtained by the above-described configuration of the synchronization detection optical system LB will be described.

  As described above, the light source means 1 to the synchronization detection sensor 12 have two reflection surfaces, the deflection surface 62 and the synchronization detection mirror 63. Table 8 shows the result of calculating the sensitivity of how much the light beam touches on the synchronization detection sensor 12 when the postures of these reflecting surfaces vary depending on the component accuracy and the mounting accuracy. For comparison, the sensitivity when the synchronization detection diaphragm of this configuration is eliminated is also shown. Note that the deflection of the posture of each reflecting element is 10 minutes in the bow direction. In addition, the luminous flux width on the synchronization detection sensor 12 is also shown.

  As described above, with respect to the width W = 1.35 of the synchronization detection sensor 12 by inserting the synchronization detection diaphragm 9, the fluctuation width of the light beam on the synchronization detection sensor 12 is larger than the sensor width. It is understood that it is small enough. It can also be seen that the beam width is within the sensor.

  As shown in Table 8, on the synchronization detection sensor 12, since the beam has a spread in the sub-scanning direction, it is difficult to be affected by the straightness error as mentioned in the problem of Patent Document 3.

[Image forming apparatus]
FIG. 9 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 any of the first and third embodiments. The light scanning unit 100 emits a light beam 103 modulated according to 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 as an electrostatic latent image carrier (photosensitive drum) 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 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. The electrostatic latent image is developed as a toner image by a developing unit 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. 9), 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 a fixing device behind the photosensitive drum 101 (left side in FIG. 9). 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. 9, the print controller 111 not only converts the data described above, but also controls 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 higher recording density requires higher image quality, the configurations of the first to third embodiments of the present invention are more effective in an image forming apparatus of 1200 dpi or more.

  Although the image forming apparatus of the present invention is of a type that prints in monotone, it goes without saying that the image forming apparatus can be diverted to a color image forming apparatus that has a plurality of photosensitive drums and performs scanning and drawing with a plurality of beams. For example, when the image forming apparatus has four photosensitive drums for superimposing four color images, the optical scanning apparatuses (scanning optical systems) of Embodiments 1 and 3 may be provided with four identical optical scanning apparatuses in parallel. In the optical scanning device according to the second embodiment, two identical optical scanning devices may be arranged in parallel.

[Color image forming apparatus]
FIG. 10 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 optical scanning devices (scanning optical systems) of Embodiments 1 and 3 are arranged in parallel and image information is recorded on a photosensitive drum surface as an image carrier. is there. In FIG. 10, 60 is a color image forming apparatus, 81, 82, 83, and 84 are optical scanning devices having any of the configurations shown in the first and third embodiments, and 21, 22, 23, and 24 are image carriers. The photosensitive drums 31, 32, 33 and 34 are developing units, and 51 is a conveyor belt. In FIG. 10, there are a transfer device (not shown) for transferring the toner image developed by the developing device to a transfer material, and a fixing device (not shown) for fixing the transferred toner image to the transfer material. is doing.

  In FIG. 10, R (red), G (green), and B (blue) color signals are input to the color image forming apparatus 60 from an external device 52 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 53 in the apparatus. These image data are input to the optical scanning devices 81, 82, 83, and 84, respectively. From these optical scanning devices, light beams 41, 42, 43, and 44 modulated according to each image data are emitted, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are caused by these light beams. Scanned in the main scanning direction.

  The color image forming apparatus in this embodiment has four optical scanning devices (81, 82, 83, 84) arranged in each color 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 21, 22, 23, and 24, and color images are printed at high speed.

  As described above, the color image forming apparatus according to this embodiment uses the light beams based on the respective image data by the four optical scanning devices 81, 82, 83, and 84, and the corresponding photosensitive drums 21 and 22 respectively corresponding to the latent images of the respective colors. , 23, 24 on the surface. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 52, 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.

Main scanning sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 1 of the present invention Sub-scan sectional view of Embodiment 2 of the present invention Main scanning sectional view of Embodiment 2 of the present invention Main scanning sectional view of Embodiment 3 of the present 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. Schematic diagram of main parts of a conventional optical scanning device

Explanation of symbols

1 Light source means (semiconductor laser)
2 Condensing lens 3 Aperture stop 4 Cylindrical lens 5 Anamorphic lens 61 Reflective mirror 6 Deflection means (polygon mirror)
7 imaging optical system 71, 72 imaging lens 73, 74 imaging lens 8 surface to be scanned 63 synchronization detection mirror 9 synchronization detection diaphragm 10 synchronization detection lens 11 synchronization detection edge 12 synchronization detection sensor LA first Optical system 81, 82, 83, 84 Optical scanning device 21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 51 Conveyor belt 52 External device 53 Printer controller 60 Color image forming apparatus 100 Optical scanning device 101 Photosensitive drum 102 Charging roller 103 Light beam 104 Image forming apparatus 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 (17)

A first optical system for imaging a light beam emitted from the light source means;
Deflecting means for deflecting and scanning the light beam from the first optical system;
A second optical system that forms an image of the light beam deflected and scanned by the deflecting means on the surface to be scanned;
Synchronization signal detection means for detecting a part of the light beam deflected and scanned on the deflection surface of the deflection means as a synchronization detection signal for determining the timing of the scanning start position of the light beam on the scanned surface;
A synchronization detection optical system for guiding a part of the light beam deflected and scanned by the deflection surface of the deflection means to the synchronization signal detection means,
The synchronization detection optical system includes a light beam limiting unit that limits a light beam width of a light beam in a sub-scanning direction orthogonal to the main scanning direction,
A reflection mirror is provided in the optical path from the light source means to the synchronization signal detection means, and the light flux limiting means is disposed in the optical path between the reflection mirror closest to the synchronization signal detection means and the synchronization signal detection means. An optical scanning device characterized by comprising:   The synchronization detection optical system includes at least an independent synchronization detection imaging unit different from the second optical system in an optical path between the light beam limiting unit and the synchronization signal detection unit. The optical scanning device according to claim 1.   The synchronization detection optical system includes an optical path separating / reflecting unit for separating an optical path of a light beam that is deflected and scanned on the deflecting surface of the deflecting unit and travels toward the synchronizing signal detecting unit. The optical scanning device according to claim 2, wherein the optical scanning device is provided in an optical path. The synchronous detection imaging means has an anamorphic optical system having different powers in the main scanning direction and the sub-scanning direction, the focal length in the main scanning direction of the anamorphic optical system is F_am, and the focal length in the sub-scanning direction is F_as. When
F_am>F_as> 0
The optical scanning device according to claim 2, wherein the following condition is satisfied.   3. The optical scanning device according to claim 2, wherein a refractive power in the sub-scanning direction of the synchronization detection imaging unit is a maximum among optical elements extending from the deflection unit to the synchronization signal detection unit.   3. The optical scanning apparatus according to claim 2, wherein the synchronization detection imaging unit is arranged so that the light beam limiting unit and the synchronization signal detection unit are conjugate in a sub-scan section. The number of reflection surfaces from the light source means to the synchronization signal detection means is N,
The distance along the optical path from the light beam limiting means to the synchronous detection imaging means is S1,
L, the distance along the optical path from the synchronization detection imaging means to the synchronization signal detection means,
The focal length in the sub-scanning direction of the synchronous detection imaging means is F_as,
When the width of the light receiving region in the sub-scanning direction of the synchronization signal detecting means is W,
| (S1 / F_as-1) × L-S1 | ≦ 250 × W / 3 / N
The optical scanning device according to claim 2, wherein the following condition is satisfied. The distance along the optical path from the deflecting means to the light flux limiting means is S0,
The distance along the optical path from the light beam limiting means to the synchronous detection imaging means is S1,
L, the distance along the optical path from the synchronization detection imaging means to the synchronization signal detection means,
The focal length in the sub-scanning direction of the synchronous detection imaging means is F_as,
The width of the light receiving area in the sub-scanning direction of the synchronization signal detecting means is W
When the width of the light beam limiting means in the sub-scanning direction is Wap,
Wap × [(L / F_as−1) × (S0 + S1) −L] / S0 ≦ W
The optical scanning device according to claim 2, wherein the following condition is satisfied.   The optical scanning device according to claim 1, wherein at least one of the synchronization signal detecting unit and the light beam limiting unit is inclined in a sub-scanning section.   The first optical system converts a light beam emitted from the light source means into a parallel light beam having a light beam width wider than a width of a deflection surface of the deflecting means in a main scanning section. 2. An optical scanning device according to 1.   The light source means has a plurality of light emitting points, and at least two light fluxes of the plurality of light emitting points are guided to the synchronization signal detecting means and used for generating the synchronization detection signal. The optical scanning device according to any one of claims 1 to 10. A plurality of the light source means, the light beam emitted from each light source means is guided to the deflection surface of the deflection means,
A plurality of light beams deflected and scanned by the deflecting means are imaged on a plurality of scanned surfaces provided for each light beam,
12. The optical scanning according to claim 1, wherein at least one of the plurality of light beams deflected and scanned by the deflecting unit is guided to the synchronization detection optical system. apparatus.   The light beam from the light source unit corresponding to the optical path having the smallest number of reflecting surfaces provided on the optical path from the plurality of light source units to the plurality of scanned surfaces is transmitted to the synchronization signal detection unit by the synchronization detection optical system. The optical scanning device according to claim 12, wherein the optical scanning device is guided.   The optical scanning device according to claim 1, a photosensitive drum disposed on the surface to be scanned, and a static beam formed on the photosensitive drum 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.   14. A color image comprising: a plurality of image carriers, each of which is disposed on a surface to be scanned of the optical scanning device according to claim 1 and forms images of different colors. Forming equipment.   17. The color image forming apparatus according to claim 16, 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.

Images