JP2006195236A - Image forming apparatus and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus and a color image forming apparatus in which the bending amounts among a plurality of faces to be scanned are made coincident, a color slurring is reduced and the structure is made compact. <P>SOLUTION: The image forming apparatus has a plurality of optical scanners including a deflection means 5 which deflects a luminous flux emitted form a light source means 1, an focusing optical system 6 which focuses the luminous flux deflected with the deflection means on the face to be scanned. Every optical scanner has a reflection mirror which guides the luminous flux deflected with the deflection means onto the face to be scanned, and the condition L1<0.8L is satisfied, where L1 stands for the length in the longitudinal direction of the reflection mirror and L stands for the length from the deflection face of the deflection means to the face to be scanned. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and a color image forming apparatus, and more particularly, a light beam modulated and emitted from a light source means is reflected and deflected by an optical deflector (polygon mirror) as a deflecting means, and is scanned through an imaging optical system. It is suitable for an image forming apparatus such as a laser beam printer having an electrophotographic process, a digital copying machine, a multi-function printer (multi-function printer), etc., which records the image information by optically scanning the top.

  2. Description of the Related Art Conventionally, an optical scanning device used in an image forming apparatus such as a laser beam printer, a digital copying machine, or a multi-function printer uses an optical deflector (polygon mirror) as a deflecting means for deflecting a light beam emitted from a light source means by an incident optical system. ), And the light beam deflected by the optical deflector is imaged in a spot shape on the surface of the photosensitive drum, which is the surface to be scanned, by the imaging optical system. The light beam is optically scanned on the surface of the photosensitive drum. Yes.

  In such an optical scanning device, the light beam emitted from the light source means is converted into a substantially parallel light beam by a collimator lens or the like, and the light beam converted into a substantially parallel light beam to correct the tilt is deflected by the cylindrical lens by the optical deflector. A line image is formed near the surface. The light beam deflected by the deflecting surface of the optical deflector scans the surface of the photosensitive drum through the imaging lens at a substantially constant speed to form a spot.

  FIG. 12 is a schematic view of a main part of a conventional color image forming apparatus. In the figure, reference numerals 91a, 91b, 91c, and 91d denote light source means, for example, semiconductor lasers. Reference numeral 92 denotes an optical deflector as a deflecting means, which is composed of, for example, a rotating 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. An imaging optical system having an fθ characteristic (not shown) conjugates between the vicinity of the deflection surfaces 92a and 92b of the optical deflector 92 and the vicinity of the photosensitive drum surfaces 100a, 100b, 100c, and 100d as the scanned surfaces in the sub-scan section. By having a relationship, it has a tilt correction function. The latent images formed on the photosensitive drum surfaces 100a, 100b, 100c, and 100d become an image in which four colors are superimposed on the intermediate transfer belt 90, and transferred onto a transfer sheet (not shown).

  In addition, the color image forming apparatus in the figure is provided with a reflection mirror for folding the optical path in the optical path between the optical deflector 92 and the photosensitive drum surfaces 100a, 100b, 100c, and 100d in order to make the entire apparatus compact. As a result, downsizing has been achieved.

  In an optical scanning device used in this type of image forming apparatus, for example, when correcting a scanning line curve (scanning line bending) of a scanning line on a surface to be scanned, which is caused by a positional error of an optical element, etc. This is performed by tilting at least a part of the imaging lens constituting the optical system.

  Usually, in a color image forming apparatus having a scanned surface for a plurality of colors (for example, C (cyan), M (magenta), Y (yellow), B (black)), the amount of bending between the plurality of scanned surfaces is set. It is known to match and reduce color misregistration.

  However, in order to tilt the imaging lens as described above, there is a problem that the mechanical configuration becomes very complicated and it is very difficult to hold and fix the tilted state.

Therefore, in recent years, an optical scanning device that corrects scanning line bending in the sub-scanning direction by curving (deflecting) the shape of the reflecting mirror disposed in the optical path between the optical deflector and the surface to be scanned. Has been proposed (see Patent Document 1).
JP 2001-228427 A

  Usually, in order to correct the scanning line bending in the sub-scanning direction using a reflecting mirror, the deflection amount (adjustment amount) can be controlled with the following parameters.

(1) Reflection mirror deflection
(2) Incident angle of the light beam incident on the reflection mirror Conventionally, as disclosed in Patent Document 1, the adjustment sensitivity is optimized by controlling the incident angle of the light beam of the reflection mirror.

  However, the conventional optical scanning device described in Patent Document 1 has the following problems.

(1) Since a long reflecting mirror is used, it is difficult to reduce the size and price.
(2) The optical element closest to the surface to be scanned is a reflective member, so dust-proof glass is required separately.

  In this type of optical scanning device, in the so-called overfilled scanning system (OFS), the light beam width in the main scanning direction of the light beam incident on the deflecting surface of the optical deflector is wider than the width of the deflecting surface in the main scanning direction. Since a polygon mirror having a small diameter of 10 or more is used, wide-angle scanning becomes difficult, and the optical path length from the deflecting surface of the optical deflector to the photosensitive drum surface must be increased.

  In order to make such an optical scanning device compact, it is common to use a long reflecting mirror having a length in the longitudinal direction of 200 (mm) or more to fold the optical path.

  However, the optical scanning apparatus using a lot of long reflecting mirrors has a problem that the scanning line is likely to be bent. When a color image forming apparatus is configured using a plurality of such optical scanning devices, the amount of bending between the plurality of scanned surfaces does not match, and color misregistration occurs.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and a color image forming apparatus having a compact and simple configuration while matching the amount of bending between a plurality of scanned surfaces to reduce color misregistration.

The image forming apparatus of the invention of claim 1
In an image forming apparatus having a plurality of optical scanning devices including a deflection unit that deflects a light beam emitted from a light source unit, and an imaging optical system that forms an image on the surface to be scanned with the light beam deflected by the deflection unit.
Each optical scanning device has a reflection mirror for guiding the light beam deflected by the deflection means on the surface to be scanned, the length of the reflection mirror in the longitudinal direction is L1, and the deflection surface of the deflection means When the length to the surface to be scanned is L,
L1 <0.8L
It is characterized by satisfying the following conditions.

The invention of claim 2 is the invention of claim 1,
The reflection mirror is formed such that its reflection surface is bent in the longitudinal direction, the amount of deflection is Δ (mm), the incident angle of the axial light beam incident on the reflection mirror is α (deg), and When the resolution is D (dpi),
Δ ≧ 1 / (2 × sin α) × (25.4 / D)
It is characterized by being formed to satisfy the following conditions.

The invention of claim 3 is the invention of claim 1 or 2, wherein
The light beam from the light source means is incident on the deflection surface of the deflection means in a state wider than the width of the deflection surface in the main scanning direction.

The invention of claim 4 is the invention of claim 1, 2 or 3,
The light source means has a plurality of light emitting portions.

The image forming apparatus of the invention of claim 5
A photosensitive drum is arranged on each surface to be scanned of the optical scanning device according to any one of claims 1 to 4.

A color image forming apparatus according to a sixth aspect of the invention is the invention according to any one of the first to fourth aspects,
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, by setting each element so as to satisfy the conditional expression, the amount of bending between a plurality of scanned surfaces is matched, and color misregistration is reduced, and the image forming apparatus and color having a compact and simple configuration An image forming apparatus can be achieved.

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

  FIG. 1 is a cross-sectional view (sub-scanning cross-sectional view) of the main part in the sub-scanning direction of the image forming apparatus according to Embodiment 1 of the present invention.

  Here, the main scanning direction indicates a direction perpendicular to the rotation axis of the optical deflector and the optical axis of the imaging optical system (the direction in which the light beam is reflected and deflected (deflected and scanned) by the optical deflector). Indicates a direction parallel to the rotation axis of the optical deflector. The main scanning section indicates a plane parallel to the main scanning direction and including the optical axis of the imaging optical system. The sub-scanning cross section indicates a cross section perpendicular to the main scanning cross section.

  The image forming apparatus in this embodiment is composed of a single optical deflector 5 and four optical scanning devices (stations) S1, S2, S3, and S4 that use the optical deflector 5 in common. A single optical deflector 5 scans the photosensitive drum surfaces 8a, 8b, 8c, and 8d as different scanned surfaces, and forms a color image by multiple development.

  Although two optical deflectors 5 are shown in FIG. 1, the optical deflector 5 is configured as shown in FIG. 12, for example, and reflects and deflects two light beams respectively on different deflection surfaces of the optical deflector 5. is doing.

  In FIG. 1, reference numeral 5 denotes an optical deflector (polygon mirror) as a common deflecting means, which 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. 6a is a first imaging lens provided at each station, and 6b is a second imaging lens provided at each station. In the present embodiment, the first and second imaging lenses 6a and 6b constitute the imaging optical system of each of the stations S1, S2, S3 and S4.

  9a is a reflection mirror (folding mirror) disposed at station S1, 9b and 9c are each a reflection mirror (folding mirror) disposed at station S2, 9d is a reflection mirror (folding mirror) disposed at station S3, 9e, Reference numerals 9f are reflection mirrors (bending mirrors) disposed in the station S4, and these reflection mirrors 9a, 9b, 9c, 9d, 9e, and 9f are connected to the scanned surface 8 (8a, 8b, 8c, 8d) from the optical deflector 5. ) Is disposed closer to the optical deflector 5 than the second imaging lens 6b in the optical path.

  In this embodiment, the reflecting surfaces of the reflecting mirrors 9a, 9c, 9d, and 9f located closest to the surface to be scanned in each of the stations S1, S2, S3, and S4 are formed to bend in the longitudinal direction. Thus, in this embodiment, the curvature of the scanning line on the scanned surfaces 8a, 8b, 8c, and 8d in the sub-scanning direction (scanning line bending) is corrected. Hereinafter, the reflection mirror that corrects the scanning line bending is referred to as a “correction reflection mirror”.

  The correction reflection mirrors 9a and 9d have the same shape, and the correction reflection mirrors 9c and 9f have the same shape.

  Reference numerals 8a, 8d, 8c, and 8d denote photosensitive drum surfaces as scanned surfaces corresponding to the stations S1, S2, S3, and S4, respectively. Each station S1, S2, S3, S4 constitutes an element of the image forming apparatus.

  FIG. 2 is a sectional view (main scanning sectional view) of the main part in the main scanning direction of the station S1 shown in FIG. FIG. 3 is a sub-scan sectional view around the correction reflecting mirror 9a shown in FIG. The optical action of the other stations S2, S3, S4 is the same as that of the station S1.

  In FIG. 2, reference numeral 1 denotes light source means, which is made of, for example, a semiconductor laser.

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

  Reference numeral 3 denotes a first cylindrical lens having a predetermined power (refractive power) only in the sub-scan section (sub-scan direction), and a light beam that is made into a substantially parallel light beam by the collimator lens 2 in the sub-scan section. Is formed as a substantially line image on the deflection surface of an optical deflector described later.

  Reference numeral 4 denotes a second cylindrical lens, which has a predetermined power only in the main scanning section (main scanning direction), converts a parallel light beam that has passed through the collimator lens 2 into a divergent light beam, and corrects wavefront aberration. In addition, the spot shape on the scanned surface 8a is corrected well.

  A folding mirror 7 deflects the light beam that has passed through the second cylindrical lens 4 with respect to the main scanning direction and guides it to the optical deflector 5.

  Each element of the collimator lens 2, the first and second cylindrical lenses 3 and 4, and the first imaging lens 6a described later constitutes an element of the incident optical system LA.

  Reference numeral 5 denotes an optical deflector (polygon mirror) as a deflecting means having 10 deflecting surfaces, which 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.

  An imaging optical system 6 includes first and second imaging lenses (anamorphic lenses) 6a and 6b having different powers in the main scanning section and the sub-scanning section. The light beam based on the image information reflected and deflected by the light is imaged in a spot on the photosensitive drum surface 8a as the scanned surface in the main scanning section, and the deflection surface 5a of the optical deflector 5 and the photosensitive drum in the sub-scanning section. By having a substantially conjugate relationship with the surface 8a, a tilt correction function is provided. The first imaging lens 6a also constitutes a part of the incident optical system LA.

  In this embodiment, the light beam (incident light beam) incident on the optical deflector 5 passes through the first imaging lens 6a, and the light beam deflected by the optical deflector 5 (scanning light beam) again forms the first image. A double-pass configuration for entering the lens 6a is adopted.

  Reference numeral 9a denotes a correction reflecting mirror, which is disposed in the optical path between the optical deflector 5 and the surface to be scanned 8a, and curves the scanning line in the sub-scanning direction (scanning line bending) on the surface to be scanned 8a. Corrected (adjusted).

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

  In this embodiment, the light beam modulated and emitted from the semiconductor laser 1 is converted into a substantially parallel light beam by the collimator lens 2, converted into a substantially convergent light once by the first cylindrical lens 3, and incident on the second cylindrical lens 4. is doing. Of the light beams incident on the second cylindrical lens 4, the light beams in the sub-scanning cross section converge and pass through the first imaging lens 6 a (double path configuration) and enter the deflection surface 5 a of the optical deflector 5. An almost line image (line image elongated in the main scanning direction) is formed in the vicinity of the deflection surface 5a. At this time, the light beam incident on the deflecting surface 5a is projected from the sub-scanning section including the rotation axis of the optical deflector 5 and the optical axis of the imaging optical system 6 to a plane perpendicular to the rotation axis of the optical deflector 5 (optical deflector). The incident light beam and the deflected light beam are separated from each other (obliquely incident optical system).

  On the other hand, the light beam in the main scanning section diverges and is converted into a substantially parallel light beam by passing through the first imaging lens 6a, and is incident on the deflection surface 5a from approximately the center of the deflection angle of the optical deflector 5. (Front incidence). At this time, the light beam width of the substantially parallel light beam is set to be sufficiently wider than the facet width of the deflecting surface 5a of the optical deflector 5 in the main scanning direction (overfilled optical system).

  The light beam deflected and reflected by the deflecting surface 5a of the optical deflector 5 is guided to the photosensitive drum surface 8a through the first imaging lens 6a, the correction reflecting mirror 9a, and the second imaging lens 6b. By rotating the optical deflector 5 in the direction of arrow A, the photosensitive drum surface 8a is optically scanned in the direction of arrow B (main scanning direction). As a result, an image is recorded on the photosensitive drum surface 8a as a recording medium.

  In the present embodiment, the shapes of the first and second imaging lenses 6a and 6b are represented by the following mathematical expressions.

  The intersection of the imaging lens surface and the optical axis is the origin, and as shown in FIG. 2, the optical axis is the x axis on the scanning start side and the scanning end side with respect to the optical axis, and is orthogonal to the optical axis in the main scanning section. The y-axis is the direction to perform, and the z-axis is the direction orthogonal to the optical axis in the sub-scanning section, and can be expressed by the following continuous function.

  Scan start side

  End of scanning

R is a radius of curvature, and K, B ₄ , B ₆ , B _{8 and} B ₁₀ are aspherical coefficients.

  In this embodiment, the shape in the main scanning direction is symmetric with respect to the optical axis, that is, the aspheric coefficients on the scanning start side and the scanning end side are made to coincide.

  Further, the sub-scanning direction is the scanning start side and the scanning end side with respect to the optical axis, and the curvature in the sub-scanning cross section (surface including the optical axis and perpendicular to the main scanning cross section) of the second imaging lens 6b is set. The lens is continuously changed in the effective portion of the lens, and the shapes in the main scanning direction and the sub-scanning direction are symmetrical with respect to the optical axis.

  The shape in the sub-scanning direction is the scanning start side and the scanning end side with respect to the optical axis, the optical axis is the x axis, the direction orthogonal to the optical axis in the main scanning section is the y axis, and the optical axis is orthogonal to the sub scanning section The direction to be taken is the z-axis and can be expressed by the following continuous function

  Scan start side

  End of scanning

(r 'is the sub-scanning direction of curvature _{radius, D 2, D 4, D} 6, D 8, D 10 coefficients)
The coefficient suffix s represents the scanning start side, and e represents the scanning end side.

  Here, the radius of curvature in the sub-scanning direction is a radius of curvature in a cross section orthogonal to the shape (bus line) in the main scanning direction.

Table 1 shows various numerical values of the image forming apparatus of Example 1 of the present invention. Here, “E−x” indicates “10 ^−x ”.

  As shown in FIG. 1, the image forming apparatus according to the present embodiment is configured by using a plurality of stations (light scanning devices), and the light beam is separated in the sub-scanning direction on the facets of the polygon mirror, so that the first result is obtained. The light beam that has passed through the image lens 6a is easily separated and guided to different scanning surfaces. In addition, since the first imaging lens 6a is shared by the two stations S1, S2 (S3, S4), the number of lenses can be reduced, and the entire apparatus can be simplified.

In this embodiment, the length of the correction reflecting mirror 9 (9a, 9c, 9d, 9f) in the longitudinal direction is L1, and the surface to be scanned 8 (8a, 8b, 8c, 8d) from the deflection surface 5a of the optical deflector 5 is used. When the length up to L is
L1 <0.8L (1)
Each element is set to satisfy the following conditions.

  Conditional expression (1) defines the length L1 in the longitudinal direction of the correcting reflecting mirror 9 (9a, 9c, 9d, 9f). If the conditional expression (1) is deviated, the mirror will become larger, and the amount of deflection (adjustment amount) in the longitudinal direction of the mirror will increase, which will increase the pressing force on the mirror when adjusting the mirror. Absent. As the length of the mirror in the longitudinal direction is shorter, the scanning line is less likely to be bent.

Next, numerical examples of conditional expression (1) will be shown. In this example,
L1 = 200 (mm) L = 329 (mm)
It is. This satisfies the conditional expression (1).

  The mirror is up to Y = 100 (mm) (L1 = 200 (mm)), and a portion (holding portion) for holding the mirror is located at Y = 90 (mm). In this embodiment, the length L1 in the longitudinal direction of the correction reflecting mirror 9 (9a, 9c, 9d, 9f) is shorter than the length in the longitudinal direction of the second imaging lens 6b.

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

0.2L <L1 <0.65L (1a)
In the present embodiment, the correction reflecting mirror is formed such that its reflecting surface is bent in the longitudinal direction. As shown in FIG. 3, the amount of bending is Δ (mm), and the axis is incident on the correction reflecting mirror. When the incident angle of the light beam is α (deg) and the resolution of the image forming apparatus is D (dpi) (dots per inch is 1 / mm),
Δ ≧ 1 / (2 × sin α) × (25.4 / D) (2)
It is formed to satisfy the following conditions.

  Conditional expression (2) defines the amount of deflection Δ of the reflecting surface of the correcting reflecting mirror. If the conditional expression (2) is not satisfied, it is difficult to adjust the bending of one pixel or more.

Next, numerical examples of conditional expression (2) will be shown. In the present embodiment, the light beam incident angle α = 49.37 (deg) to the mirrors 9a and 9d,
Resolution D = 600 (dpi)
In this case, the deflection amount Δ is set to satisfy Δ ≧ 0.028. Also, the incident angle α of the light flux on the mirrors 9c and 9f is 42.75 (deg)
Resolution D = 600 (dpi)
In this case, the deflection amount Δ is set to satisfy Δ ≧ 0.031.

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

1 / (2 × sin α) × (25.4 × 10 / D) ≧ Δ ≧ 1 / (2 × sin α) × (25.4 / D) (2a)
The adjustment amount is not less than 1 pixel and not more than 10 pixels.

In this embodiment, from the deflecting surface 5a of the optical deflector 5 to the incident surface of the second imaging lens (light-transmitting optical element having the power closest to the scanned surface 8 (8a, 8b, 8c, 8d)) 6b. The distance from the deflecting surface 5a of the optical deflector 5 to the reflecting surface of the reflecting mirror 9 (9a, 9c, 9d, 9f) closest to the scanned surface 8 (8a, 8b, 8c, 8d). When S
0 <T / L <0.8 (3)
0 <S / L <0.7 (4)
Each element is set to satisfy the following conditions.

In this embodiment,
S / T <1
Is satisfied.

  Conditional expression (3) indicates that the distance T from the deflecting surface 5a of the optical deflector 5 to the incident surface of the second imaging lens 6b and the scanned surface 8 (8a, 8b, 8c,. 8d) is related to the ratio of the length L, and if the upper limit value of the conditional expression (3) is exceeded, the length in the longitudinal direction of the second imaging lens 6b becomes longer, which not only increases the cost. This is not good because the whole apparatus becomes large and it becomes difficult to arrange it in the image forming apparatus.

  Conditional expression (4) is the distance S from the deflecting surface 5a of the optical deflector 5 to the mirror surface of the reflecting mirror 9 (9a, 9c, 9d, 9f) closest to the scanned surface 8 (8a, 8b, 8c, 8d). And the ratio of the length L from the deflecting surface 5a of the optical deflector 5 to the scanned surface 8 (8a, 8b, 8c, 8d). If the upper limit of the conditional expression (4) is exceeded, the reflecting mirror 9 (9a , 9c, 9d, 9f) is not good because not only the length is increased and the cost is increased, but also the entire apparatus becomes large and difficult to arrange in the image forming apparatus.

Next, numerical examples of conditional expressions (3) and (4) will be shown. In this example,
L = 329 (mm) T = 173.5 (mm) S = 169 (mm)
Therefore, T / L = 173.5 / 329 = 0.53
S / L = 169/329 = 0.51
It is. This satisfies the conditional expressions (3) and (4).

  More preferably, conditional expressions (3) and (4) should be set as follows.

0.1 <T / L <0.65 (3a)
0.1 <S / L <0.6 (4a)
In the imaging optical system of the present embodiment, the optical element (second imaging lens 6b) closest to the surface to be scanned 8 is formed of a plastic lens having light transmitting power, and the optical box is sealed. This prevents toner and the like from entering the optical box. Note that the optical element having light-transmitting power may be made of glass, or may be an optical element having diffraction power.

  Next, how the scanning line curve changes when the correction reflecting mirror is bent will be described with reference to the schematic diagram of FIG.

  The schematic diagram of FIG. 4 shows only the correction reflecting mirror 450 and the photosensitive drum 460. Other optical elements are omitted for convenience of explanation.

  In the figure, a scanning light beam 401 indicates a light beam traveling toward the approximate center of the surface of the photosensitive drum 460, and scanning light beams 402 and 403 indicate a light beam traveling toward an end of the surface of the photosensitive drum 460. The correction reflecting mirror 450 is formed by a mechanical member (not shown) so that the reflecting surface (mirror surface) 450a is bent in the generatrix direction (longitudinal direction).

  The correction reflecting mirror 450 is held in a shape indicated by a solid line (the bus line is a substantially straight line), and scan line bending caused by a position error of the optical element is measured and corrected during initial adjustment. The shape of the correction reflecting mirror 450 at the time of correction is such that the bus is bent by a mechanical member (not shown) as indicated by a broken line, and the amount of bending (adjustment amount) is adjusted so that the amount of bending becomes a desired value.

  Next, the relationship between the amount of bending and the amount of bending in this embodiment is shown in FIGS. 5 shows a station on the side of one reflecting mirror, and FIG. 6 shows a station on the side of two reflecting mirrors.

  In the correction reflecting mirrors 9a, 9c, 9d, and 9f of the present embodiment, the incident angles of the light beams are set as described above. The correction reflecting mirrors 9a and 9d have the same configuration, the light beam folding angle is 101.5 (deg) (FIG. 5), the correction reflecting mirrors 9c and 9f have the same configuration, and the light beam folding angle. Is 89.5 (deg) (FIG. 6).

  In this embodiment, the optical element is arranged so that the incident angle α of the light beam incident on the correction reflecting mirror is 40 (deg) or more (the folding angle is 80 (deg) or more). If the incident angle α is 40 (deg) or less, the bending sensitivity decreases and the amount of deflection increases, which is not preferable.

  5 and 6, the horizontal axis indicates the amount of deflection (adjustment amount) (μm) of the mirror in the vicinity of the most off-axis light beam (Y = 90 mm), and the vertical axis indicates the amount of bending (mm) of the scanning line. Show.

  The amount of bending in this embodiment is defined by the difference in the arrival position of the most off-axis light beam and the on-axis light beam on the photosensitive drum surface in the sub-scanning direction (rotating direction of the photosensitive drum).

  The correction reflecting mirrors 9a and 9c have a distance S of 169.0 (mm) from the optical deflector 5 as described above, and the correcting reflecting mirror 9b is 117.5 (mm). Further, the correction reflecting mirrors 9a and 9c have the same distance from the optical deflector 5, but the incident angles to the correction reflecting mirrors 9a and 9c are different by 2 (deg). It can be seen that the adjustment sensitivity is different.

  For example, when the measured value of the bending at the time of initial adjustment is 0.03 (mm), in the station S1 including the correcting reflecting mirror 9a, the correcting reflecting mirror 9a is 33 (μm) at the position of Y = 90 (mm). It is possible to obtain a linear scanning line that is not curved in the sub-scanning direction by deflecting the bus bar in the normal direction of the mirror surface.

  Next, how the correction reflecting mirror of this embodiment is bent will be described.

  The correction reflecting mirror of this embodiment is configured to bend only to one of a concave surface and a convex surface. This is because the mechanical configuration can be simplified, but it is necessary to make the bending directions coincide in all four stations S1 to S4, so that the reflecting surfaces of the correction reflecting mirrors 9a and 9d are concave, and The reflecting surfaces of the correction reflecting mirrors 9c and 9f are configured to be convex.

  The procedure for adjusting the scanning line bending is as follows.

(1) Measure the scan line curvature of all stations S1 to S4 at the time of shipment using a CCD camera, etc.
(2) Calculate the bending amount of the other three stations so that the bending amount matches the bending amount of the largest station.
(3) The bending amount is converted into the correction amount of the correction reflecting mirror using the relationship shown in FIG. 5 and FIG.
(4) The mirror is bent using a mechanical member such as a screw.

  According to the above flow, the bending direction and the bending amount of all four stations coincide on the photosensitive drum surface, and the color misregistration can be reduced.

  In this embodiment, the correction reflecting mirror is bent only in one direction, ie, convex or concave, but the same correction reflecting mirror can be bent in two different directions. In this case, since both convex and concave surfaces can be formed, the scanning line can be made substantially linear, and there is no need to calculate a station with the largest bend, so that the adjustment tact can be shortened.

  In addition, the imaging optical system of the present embodiment is composed of a plastic lens in which the optical element closest to the scanning surface has light-transmitting power. By sealing the light emission direction, a sealing member such as dustproof glass is provided. It is possible to prevent toner and the like from entering the optical box without using it. The optical element having light-transmitting power may be made of glass, and may be an optical element having diffraction power.

  As described above, in this embodiment, by forming an image forming apparatus using a plurality of optical scanning devices (stations) having the above-described configuration, the bending direction and the bending amount of all four stations are matched on the photosensitive drum surface. As a result, color misregistration can be reduced. Furthermore, it is possible to achieve an image forming apparatus that can reduce the size of the entire apparatus.

  FIG. 7 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.

  The difference between the present embodiment and the first embodiment is that an image forming apparatus is configured using two optical deflectors. Other configurations and optical actions are substantially the same as those in the first embodiment, and the same effects are obtained.

  That is, the image forming apparatus in the present embodiment makes two light beams incident so as to scan oppositely the deflection surface of the optical deflector 501 (501a, 502b) as shown in FIG. The configuration of the incident optical system from the light source means to the optical deflector is the same as that in the first embodiment.

  In this embodiment, the light beams deflected by the optical deflector 501 (501a, 502b) are a first imaging lens 502, a correction reflecting mirror 510 (510a, 510b, 510c, 510d), and a second imaging lens 503. To form a color image by forming spots on the scanned surface 511 (511a, 511b, 511c, 511d) and scanning the scanned surface 511 (511a, 511b, 511c, 511d) at substantially the same speed. Yes.

  As shown in FIG. 7, the image forming apparatus in this embodiment has one correction reflecting mirror 510 (510a, 510b, 510c, 510d) in the optical path of each station S1, S2, S3, S4. Further, the bending of the scanning line in the sub-scanning direction on the scanned surface 511 (511a, 511b, 511c, 511d) is corrected. The correction method and effect are the same as those in the first embodiment.

  The correction reflecting mirrors 510a and 510c have the same shape, and the correction reflecting mirrors 510b and 510d have the same shape.

  In this embodiment, the length L1 in the longitudinal direction of the correction reflecting mirrors 510a, 510b, 510c, and 510d is defined so as to satisfy the conditional expression (1) as in the first embodiment. In this embodiment, L1 = 67 (mm) and the interval between the holding portions is 60 (mm). The correction reflecting mirrors 510a, 510b, 510c, and 510d are respectively arranged at a position of 26.6 (mm) from the deflection surface of the optical deflector 501 (501a, 502b).

Next, numerical examples of conditional expression (2) will be shown. In this embodiment, a light beam incident angle α = 41.0 (deg) to the mirrors 510a and 510c,
Resolution D = 1200 (dpi)
At this time, the deflection amount Δ is set to satisfy Δ ≧ 0.016. Also, the incident angle α = 49 (deg) of light flux on the mirrors 510b and 510d,
Resolution D = 1200 (dpi)
In this case, the deflection amount Δ is set to satisfy Δ ≧ 0.014. Therefore, as shown in FIG. 8 and FIG. 9, the optimum bending adjustment sensitivity can be obtained.

Next, numerical examples of conditional expressions (3) and (4) will be shown. In this example,
L = 168.8 (mm) T = 54.6 (mm) S = 26.6 (mm)
Therefore, T / L = 54.6 / 168.8 = 0.32.
S / L = 26.6 / 168.8 = 0.16
It is. This satisfies the conditional expressions (3) and (4).

  FIG. 8 and FIG. 9 are explanatory diagrams showing the bending adjustment sensitivity of the present embodiment. FIG. 8 shows the incident angle on the 41.0 (deg) side, and FIG. 9 shows the incident angle on the 49.0 (deg) side. It is a station. 8 and 9, the horizontal axis indicates the deflection amount (adjustment amount) (μm) of the reflecting surface of the mirror in the vicinity of the most off-axis light beam (Y = 30 mm) as in FIGS. The vertical axis shows the amount of bending (mm).

  As described above, the amount of bending in this embodiment is defined by the difference in the arrival position of the most off-axis light beam and the axial light beam on the surface of the photosensitive drum in the sub-scanning direction (rotating direction of the photosensitive drum). For example, when the measured value of the bending amount at the time of initial adjustment is 0.02 (mm), in the station S1 including the correcting reflection mirror 510a, the correcting reflecting mirror 510a is set to Y = 30 as shown in FIGS. It is possible to obtain a linear scanning line that is not curved in the sub-scanning direction by deflecting the bus bar in the surface normal direction of the mirror by 20 (μm) at the position (mm).

Table 2 shows various numerical values of the image forming apparatus of Example 2 of the present invention. Here, “E−x” indicates “10 ^−x ”. Note that the shapes of the first and second imaging lenses 502 and 503 are expressed by the above formulas (a) to (d).

  Next, a third embodiment of the present invention will be described. The difference between the present embodiment and the first embodiment is that the light source means is composed of a monolithic multi-beam laser having a plurality of light emitting portions. Other configurations and optical actions are substantially the same as those in the first embodiment, and the same effects are obtained.

  That is, in this embodiment, the light source means is constituted by a monolithic multi-beam laser that emits four light beams. As a result, the four light beams emitted from the light source means 1 are imaged on the same photosensitive drum surface so as to be separated by 21.2 (μm) in the sub-scanning direction, and image formation is performed at a resolution of 1200 (dpi). Can be done. Further, since the number of light beams emitted from the light source means is four times that of the first embodiment, the speed is increased four times, and a high-speed image forming apparatus can be provided. It is also possible to double the printing speed and set the resolution to 2400 (dpi). The number of light beams emitted from the light source means is not limited to four, and may be eight or sixteen or more, for example.

Next, a numerical example of conditional expression (2) when the resolution is set to 2400 (dpi) will be shown. In the present embodiment, the light beam incident angle α = 49.37 (deg) to the mirrors 9a and 9d,
Resolution D = 2400 (dpi)
In this case, the deflection amount Δ is set to satisfy Δ ≧ 0.007. Also, the incident angle α of the light flux on the mirrors 9c and 9f is 42.75 (deg),
Resolution D = 2400 (dpi)
In this case, the deflection amount Δ is set to satisfy Δ ≧ 0.008. As a result, the same effect as in the first embodiment is obtained.

As described above, in this embodiment, by increasing the number of light beams emitted from the light source means, it is possible to provide an image forming apparatus that is faster than the first embodiment.
[Color image forming device]
FIG. 10 is a sub-scan sectional view of the color image forming apparatus of the present invention.

  In the figure, 60 is a color image forming apparatus, 11 is an image forming apparatus having any of the configurations shown in the first to third embodiments, 21, 22, 23, and 24 are photosensitive drums as image carriers, Reference numerals 32, 33, and 34 denote developing devices, 51 denotes a conveyance belt, 52 denotes an external device such as a personal computer, 53 denotes a color signal input from the external device 52, and converts the color signal into image data of different colors to the image forming apparatus 11. This is the printer controller that lets you input.

  In the figure, the color image forming apparatus 60 receives R (red), G (green), and B (blue) color signals 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 image forming apparatus 11. The image forming apparatus 11 emits light beams (light beams) 41, 42, 43, and 44 that are modulated according to each image data, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are emitted by these light beams. Are scanned in the main scanning direction.

  In this embodiment, the color image forming apparatus emits light beams corresponding to C (cyan), M (magenta), Y (yellow), and B (black) from one image forming apparatus 11, and the photosensitive drums 21 and 22. , 23 and 24, image signals (image information) are recorded, and color images are printed at high speed.

  In the color image forming apparatus of this embodiment, as described above, the latent image of each color is formed on the corresponding photosensitive drums 21, 22, 23, and 24 using the light beams based on the respective image data by one image forming apparatus 11. Forming. After that, multiple transfer is performed on the recording material on the conveyance belt 51 to form one full-color image, and the full-color image is transferred to a sheet member (paper).

As the external device 52, for example, a color image reading device including a CCD (line 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.
[Color image forming device]
The color image forming apparatus of the present invention is not limited to the configuration shown in FIG. That is, in FIG. 11, four optical scanning devices (stations) 61, 62, 63, 64 are arranged side by side and correspond to each color light on the photosensitive drum surfaces 21, 22, 23, 24, which are image carriers. This is a tandem type color image forming apparatus for recording image information. In the figure, the same elements as those shown in FIG. 10 are denoted by the same reference numerals.

FIG. 3 is a sub-scan sectional view of the image forming apparatus according to the first exemplary embodiment of the present invention. Main scanning sectional view of the optical scanning device shown in FIG. Sub-scan sectional view around the reflection mirror shown in FIG. Schematic diagram of bending adjustment The figure which showed the bending adjustment sensitivity of Example 1 of this invention. The figure which showed the bending adjustment sensitivity of Example 1 of this invention. Sub-scan sectional view of the image forming apparatus according to the second embodiment of the present invention. The figure which showed the bending adjustment sensitivity of Example 2 of this invention. The figure which showed the bending adjustment sensitivity of Example 2 of this invention. Sectional drawing of the principal part of the color image forming apparatus of this invention Sectional drawing of the principal part of the color image forming apparatus of this invention Schematic diagram of main parts of a conventional color image forming apparatus

Explanation of symbols

1 Light source means (semiconductor laser)
2 Light flux conversion element (collimator lens)
3 First cylindrical lens 4 Second cylindrical lens 7 Folding mirror 5 Deflection means (polygon mirror)
5a Deflection surface 6 Imaging optical system 6a First imaging lens 6b Second imaging lens 8 (8a, 8b, 8c, 8d) Scanned surface (photosensitive drum)
9 (9a, 9b, 9c, 9d, 9e, 9f) Reflection mirror S1, S2, S3, S4 Station (optical scanning device)
11 Image forming apparatus 21, 22, 23, 24 Image carrier (photosensitive drum)
31, 32, 33, 34 Developer 41, 42, 43, 44 Light beam 51 Conveying belt 52 External device 53 Printer controller 60 Color image forming device 61, 62, 63, 64 Station (optical scanning device)

Claims (6)

In an image forming apparatus having a plurality of optical scanning devices including a deflection unit that deflects a light beam emitted from a light source unit, and an imaging optical system that forms an image on the surface to be scanned with the light beam deflected by the deflection unit.
Each optical scanning device has a reflection mirror for guiding the light beam deflected by the deflection means on the surface to be scanned, the length of the reflection mirror in the longitudinal direction is L1, and the deflection surface of the deflection means When the length to the surface to be scanned is L,
L1 <0.8L
An image forming apparatus satisfying the following conditions: The reflection mirror is formed such that its reflection surface is bent in the longitudinal direction, the amount of deflection is Δ (mm), the incident angle of the axial light beam incident on the reflection mirror is α (deg), and When the resolution is D (dpi),
Δ ≧ 1 / (2 × sin α) × (25.4 / D)
The image forming apparatus according to claim 1, wherein the image forming apparatus is formed so as to satisfy the following condition.   3. The image forming apparatus according to claim 1, wherein the light beam from the light source unit is incident on the deflection surface of the deflection unit in a state wider than the width of the deflection surface in the main scanning direction.   The image forming apparatus according to claim 1, wherein the light source unit includes a plurality of light emitting units.   An image forming apparatus, wherein a photosensitive drum is disposed on each surface to be scanned of the optical scanning device according to claim 1.   5. The printer controller according to claim 1, 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. Color image forming apparatus.