JP2019095647A - Optical scanner and image forming apparatus including the same - Google Patents

Abstract

To achieve miniaturization and good imaging performance in an optical scanner and an image forming apparatus including the same.SOLUTION: An optical scanner 100 comprises: a deflector 4 that deflects a light beam from a light source 1 and scans a surface to be scanned 6 in a main scanning direction; and an imaging optical system 5 that includes a plurality of imaging optical elements 5a, 5b guiding the light beam deflected by the deflector 4 to the surface to be scanned 6. An on-axis image height and an off-axis image height on the surface to be scanned 6 are different from each other in light beam scanning speed, and the optical scanner satisfies the conditional expressions: 0.15≤T/Tc≤0.25, 83°≤α<90°, and 83°≤α<90°.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical scanning device, and is suitable, for example, for an image forming apparatus such as a laser beam printer (LBP), a digital copying machine, and a multifunction printer (multifunctional printer).

  In the past, there has been a demand for downsizing of an optical scanning device used in an image forming apparatus. In Patent Document 1, the entire apparatus can be downsized by appropriately setting the positions and shapes of a plurality of imaging optical elements constituting an imaging optical system for guiding a light flux from a deflector to a surface to be scanned. Describes an optical scanning device capable of correcting curvature of field while developing the image. Further, in Patent Document 2, while the imaging optical system is configured by a single imaging optical element, the configuration is such that the scanning surface is scanned at a non-uniform speed, thereby achieving downsizing of the entire apparatus. An optical scanning device is described.

JP, 2002-48993, A JP, 2015-31824, A

  However, in Patent Document 1, since each imaging optical element is disposed close to the deflector in order to miniaturize the entire apparatus, the optical system of each imaging optical element is required to correct the curvature of field favorably. It is necessary to sharply change the shape of the surface. In this case, since the thickness of each imaging optical element is increased, the size reduction of the entire apparatus is not sufficient.

  Further, in Patent Document 2, since the imaging optical system is configured of a single imaging optical element, when the imaging optical element is disposed close to the deflector for downsizing of the entire apparatus, image formation is performed. It is necessary to increase the sub-scanning magnification of the optical element. In this case, the irradiation position deviation in the sub-scanning direction on the surface to be scanned may occur due to a manufacturing error of the deflector or the like.

  An object of the present invention is to realize both downsizing and imaging performance in an optical scanning device and an image forming apparatus including the same.

In order to achieve the above object, an optical scanning device according to one aspect of the present invention includes a deflector which deflects a light flux from a light source to scan a surface to be scanned in a main scanning direction, and a light flux deflected by the deflector. An imaging optical system including a plurality of imaging optical elements for guiding light to the surface to be scanned, and the scanning speed of the light beam differs between the on-axis image height and the off-axis image height on the surface to be scanned; The distance from the on-axis deflection point of the deflector to the scan surface is Tc on the optical axis of the image optical system, and the distance from the on-axis deflection point to the exit surface of the imaging optical element closest to the scan surface The points of intersection of the light beam deflected at the maximum scanning angle by the deflector with the distance T by the deflector and the incident surface and the exit surface of the imaging optical element closest to the surface to be scanned are A and C, respectively. each alpha _in and alpha _ou the angle formed between the tangent line and the optical axis of the incident and exit surfaces When a, and satisfies the 0.15 ≦ T / Tc ≦ 0.25,83 ° ≦ α in <90 °, 83 ° ≦ α out <90 ° conditional expression.

  According to the present invention, in the optical scanning device and the image forming apparatus including the same, it is possible to realize both the miniaturization and the imaging performance.

BRIEF DESCRIPTION OF THE DRAWINGS The principal part schematic of the optical scanning device which concerns on Example 1 of this invention. FIG. 6 is a view for explaining the shape of the imaging optical element according to the first embodiment. FIG. 6 is a diagram showing an irradiation position shift in the light scanning device according to the first embodiment. The principal part schematic of the optical scanning device concerning Example 2 of this invention. FIG. 7 is a diagram showing an irradiation position shift in the light scanning device according to the second embodiment. FIG. 1 is a schematic view of an essential part of an image forming apparatus according to an embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Note that each drawing may be drawn at a scale different from the actual scale for convenience. Moreover, in each drawing, the same reference numeral is given to the same member, and the overlapping description is omitted.

  In the following description, the main scanning direction is the direction perpendicular to the rotation axis (or swinging axis) of the deflector and the optical axis direction of the imaging optical system (the surface to be scanned is optically scanned by the deflector) Direction), and the sub-scanning direction is a direction parallel to the rotation axis (or oscillation axis) of the deflector. The main scanning cross section is a cross section including the optical axis and parallel to the main scanning direction (cross section perpendicular to the sub scanning direction), and the sub scanning cross section is parallel to the optical axis of the imaging optical system and the sub scanning direction Cross section (cross section perpendicular to the main scanning direction).

  FIG. 1 is a schematic view of the main part of the optical scanning device 100 according to the embodiment of the present invention, FIG. 1 (a) shows a main scanning cross section (XY cross section), and FIG. 1 (b) is a sub scanning cross section (ZX cross section). ) Is shown. The optical scanning device 100 deflects a light flux from the light source 1 to scan the scanned surface 6 in the main scanning direction, and an imaging which guides the light flux deflected by the deflector 4 to the scanned surface 6 An imaging optical system 5 including optical elements 5a and 5b is provided. Further, the imaging optical system 5 according to the present embodiment is configured such that the light beam passing through it scans the surface 6 at a non-uniform speed. This will be described in detail.

  In general, the imaging optical system in the optical scanning device is an image in the main scanning direction on the surface to be scanned and the rotational angle (scanning angle) of the deflector so that the transmitted light beam scans the surface to be scanned at the same speed. The distortion aberration (fθ characteristic) has a substantially proportional relationship with the height. Further, in order to form a good image (spot) in the effective area (printed area) on the surface to be scanned, the imaging optical system needs to properly correct the curvature of field in the entire effective area.

  However, in order to ensure uniform velocity while properly correcting curvature of field, if the shape of each optical surface in the main scanning section of the imaging optical system is different between the on-axis image height and the off-axis image height. Need to Furthermore, when the imaging optical elements constituting the imaging optical system are disposed close to the deflector for downsizing the optical scanning device, the shapes of the optical surfaces become steep. In this case, coma aberration increases, and the thickness of each imaging optical element increases, which makes it difficult to miniaturize the entire apparatus.

  Therefore, the imaging optical system 5 according to the present embodiment is configured such that the transmitted light flux does not satisfy the constant velocity on the surface 6 to be scanned (scans at a non-uniform velocity). That is, in the light scanning device 100 according to the present embodiment, the scanning speed of the light flux is different between the on-axis image height and the off-axis image height. Thus, the imaging optical system 5 can be disposed closer to the deflector 4 while maintaining the imaging performance. Furthermore, since an increase in the thickness of each imaging optical element can be suppressed, it is possible to realize a further reduction in the diameter of the entire apparatus.

Here, on the optical axis of the imaging optical system 5, the distance from the on-axis deflection point of the deflector 4 to the scanned surface 6 is Tc, and the imaging optical element 5b closest to the scanned surface 6 from the on-axis deflection point. Let T be the distance to the exit surface of. Here, the on-axis deflection point is the intersection point of the chief ray of a light beam (on-axis light beam) emitted from the light source 1 and directed to the on-axis image height of the scanned surface 6 Point of intersection between the axis and the deflection surface. At this time, the optical scanning device 100 according to the present embodiment satisfies the following conditional expression (1).
0.15 ≦ T / Tc ≦ 0.25 (1)

  Conditional expression (1) indicates the condition of the arrangement of the imaging optical system 5 in the optical axis direction. By satisfying the conditional expression (1), each imaging optical element constituting the imaging optical system 5 can be disposed sufficiently close to the deflector 4. As a result, the optical scanning device 100 can be miniaturized in the optical axis direction and the main scanning direction.

  When the value exceeds the upper limit of the conditional expression (1), the optical surface closest to the scan surface 6 in the imaging optical system 5 is too far from the deflector 4, and the width of the optical surface in the main scanning direction is increased. Since it becomes necessary, it is difficult to miniaturize the entire device sufficiently. If the lower limit of conditional expression (1) is exceeded, each imaging optical element approaches the deflector 4 too much, and the optical path from the light source 1 to the deflector 4 and interference between other members and each imaging optical element It will be difficult to avoid. Alternatively, the subscanning magnification of the imaging optical system 5 becomes too large, and the irradiation position deviation (the printing position deviation) in the subscanning direction on the surface 6 to be scanned due to a manufacturing error (a surface deviation etc.) of the deflector 4 ) Will occur.

Also, when the scanning angle of the light beam deflected by the deflector 4 reaches the maximum value (θ _max ), that is, when the light beam is deflected at the maximum scanning angle and reaches the most off-axis image height, the light beam is most off-axis Let it be a ray. Furthermore, when the scanning angle of the light beam deflected by the deflector 4 is half the maximum value (θ _max / 2), ie, the light beam is deflected at a scanning angle of half the maximum scanning angle to reach the intermediate image height. , Let that ray be a middle ray.

Then, as shown in FIG. 2A, in the main scanning cross section, the intersections of the outermost off-axis ray with the incident surface and the exit surface of the imaging optical element 5b are respectively A and C, and the incident surface of the imaging optical element 5b. And the angles which the tangent of the intersections A and C of an output surface and the optical axis comprise in C are each set to (alpha) _in and (alpha) _out . However, each of the angles α _in and α _out indicates an acute angle side (smaller side) of the angle formed by each tangent and the optical axis. At this time, the optical scanning device 100 according to the present embodiment satisfies the following conditional expressions (2) and (3).
83 ° ≦ α _in <90 ° (2)
83 ° ≦ α _out <90 ° (3)

  The conditional expressions (2) and (3) indicate the shapes in the main scanning section of the end portion of the imaging optical element 5b closest to the surface 6 to be scanned. By satisfying the conditional expressions (2) and (3), the inclination (degree of bending) of each optical surface at the end of the imaging optical element 5b can be reduced, and the thickness of the imaging optical element 5b is reduced. It will be possible to

  If the upper limit of the conditional expressions (2) and (3) is exceeded, the power (refractive power) in the main scanning section of the end of the imaging optical element 5b will be substantially zero, so that good imaging performance can be obtained. It becomes difficult. If the lower limit of the conditional expressions (2) and (3) is not reached, the end of the imaging optical element 5b becomes sharp, and it becomes difficult to reduce the thickness of the imaging optical element 5b.

As described above, according to the optical scanning device 100 according to the present embodiment, it is possible to simultaneously satisfy the conditional expressions (1) to (3) while configuring the scanning surface 6 to scan at a nonuniform speed. Both size reduction and imaging performance can be realized. Furthermore, it is more preferable to satisfy the following conditional expressions (1a) to (3a).
0.17 ≦ T / Tc ≦ 0.23 (1a)
84.5 ° ≦ α _in <90 ° (2a)
84.5 ° ≦ α _out <90 ° (3a)

Here, as shown in FIG. 2A, in the main scanning cross section, the intersection of the optical axis and the incident surface of the imaging optical element 5b is A0, and the distance in the main scanning direction from the intersection A to the intersection A0 is two. Let A1 be an intersection of a straight line parallel to the divided optical axis and the incident surface. The intersection point between the optical axis and the exit surface of the imaging optical element 5b is C0, and the intersection point between a straight line parallel to the optical axis that bisects the distance in the main scanning direction from the intersection C to the intersection point C0 is C1. I assume. Then, as shown in FIG. 2B, the angle formed by the straight lines connecting the intersection A1 and each of the intersections A and A0 is β _in , the angle between the straight lines connecting the intersection C1 and each of the intersections C and C0 is mutually formed. _Let be β _out . However, each of the angles β _in and β _out indicates the obtuse angle side (larger one) of the angles formed by the respective straight lines. At this time, it is desirable to satisfy the following conditional expressions (4) and (5).
174 ° ≦ β _in <180 ° (4)
174 ° ≦ β _out <180 ° (5)

  The conditional expressions (4) and (5) indicate the shapes in the main scanning section of each optical surface of the imaging optical element 5b closest to the surface 6 to be scanned. By satisfying the conditional expressions (4) and (5), the inclination (degree of bending) of each optical surface of the imaging optical element 5b can be reduced in the entire main scanning direction, and the thickness of the imaging optical element 5b can be reduced. Can be reduced.

If the upper limits of the conditional expressions (4) and (5) are exceeded, the power will be substantially zero over the entire area in the main scanning section of the imaging optical element 5b, and it will be difficult to obtain good imaging performance. If the lower limits of the conditional expressions (4) and (5) are not reached, the inclination of each optical surface of the imaging optical element 5b increases over the entire area in the main scanning direction, and the thickness of the imaging optical element 5b increases. It becomes difficult to control Furthermore, it is more preferable to satisfy the following conditional expressions (4a) and (5a).
176 ° ≦ β _in <180 ° (4a)
176 ° ≦ β _out <180 ° (5a)

  Although the imaging optical system 5 according to the present embodiment is configured of two imaging optical elements 5a and 5b, it may be configured of three or more imaging optical elements as needed. Also in that case, when the imaging optical element closest to the surface 6 to be scanned satisfies the above-described conditional expressions, similar effects can be obtained.

Next, the scanning characteristics of the imaging optical system 5 according to the present embodiment will be described. The scanning characteristic of the imaging optical system 5 is the scanning angle of the deflector 4 θ (deg), the imaging coefficient at the on-axis image height K [mm], the image height in the main scanning direction on the surface 6 to be scanned When Y [mm], it is represented by the following equation (6).
Y = (K / B) × tan (B × θ) (6)

  Here, the imaging coefficient K is a coefficient corresponding to f at fθ characteristic which is a scanning characteristic when parallel light is incident on the imaging optical system 5: Y = f × θ It is a coefficient for expanding a light flux (convergent light or divergent light). That is, the imaging coefficient K is a coefficient for making the image height Y and the scanning angle θ in a proportional relationship regardless of the degree of convergence of the light beam incident on the imaging optical system 5.

  Further, B in the equation (6) is a coefficient (scanning characteristic coefficient) for determining the scanning characteristic of the imaging optical system 5. Equation (6) is Y = K × θ when B = 0 and corresponds to the fθ characteristic, but when B ≠ 0, the scanning characteristic is such that the image height Y and the scanning angle θ do not have a proportional relationship. For example, since equation (6) when B = 1 is Y = K tan θ, it corresponds to the projection characteristic Y = f tan θ of an optical system used in an imaging device such as a camera. That is, by setting the scanning characteristic coefficient B in the range of 0 <B <1 in Equation (6), the scanning characteristic between the projection characteristic Y = f tan θ and the fθ characteristic Y = fθ can be obtained.

Here, when the equation (6) is differentiated by the scanning angle θ, the scanning speed with respect to the scanning angle θ of the light beam on the surface to be scanned 6 is obtained as shown in the following equation (7).
dY / dθ = K / cos ² (B × θ) (7)

Further, when Expression (7) is divided by the velocity dY (0) / dθ = K at the axial image height, the following Expression (8) is obtained.
(DY / dθ) / K = 1 / cos ² (B × θ) (8)

  Equation (8) is the amount of deviation of the constant velocity at off-axis image height with respect to the on-axis image height, that is, the deviation amount of partial magnification at off-axis image height with respect to the partial magnification at axial image height (partial magnification deviation) Represents Since the optical scanning device 100 according to the present embodiment has a partial magnification, in the case of B ≠ 0, the scanning speed of the light flux is different between the on-axis image height and the off-axis image height. That is, since the scanning position (scanning distance per unit time) at the off-axis image height extends in accordance with the partial magnification shift, the scanned surface 6 is scanned without considering the partial magnification shift. Deterioration of the image formed on the scanning surface 6 (deterioration of printing performance) is caused.

  Therefore, in the present embodiment, deterioration of the printing performance is suppressed by controlling the light emission of the light source 1 by a control unit (not shown). Specifically, the scanning position and scanning time on the surface to be scanned 6 are electrically corrected by controlling the modulation timing (light emission timing) and modulation time (light emission time) of the light source 1 according to the partial magnification deviation. Can. As a result, it is possible to correct the partial magnification deviation and the image deterioration and to obtain good printing performance as in the case of satisfying the fθ characteristic. When the light source 1 is controlled by the control unit, it is desirable that the partial magnification shift of the imaging optical system 5 be within 2% of the total image height in order to ensure good printing performance.

At this time, it is preferable that the optical scanning device 100 according to the present embodiment satisfy the following conditional expression (9) at the outermost off-axis image height Y = ± h.
0.30 ≦ B ≦ 0.70 (9)

Below the lower limit value of the conditional expression (9), the partial magnification deviation becomes too small, which makes it difficult to achieve both the downsizing of the entire apparatus and the optical performance. When the value exceeds the upper limit value of the conditional expression (9), the partial magnification deviation becomes too large, which makes it difficult to correct the scanning position and the scanning time. Furthermore, it is more preferable to satisfy the following conditional expression (9a).
0.40 ≦ B ≦ 0.60 (9a)

Further, when the lateral magnification (sub scanning magnification) in the sub scanning cross section including the optical axis of the imaging optical system 5 is γ, it is preferable to satisfy the following conditional expression (10).
3.0 <| γ | <6.0 (10)

If the sub-scanning magnification of the imaging optical system 5 increases so as to exceed the upper limit of the conditional expression (10), the irradiation position deviation due to the manufacturing error, the arrangement error, etc. of each optical member becomes large. In addition, when the sub-scanning magnification of the imaging optical system 5 decreases so as to fall below the lower limit of the conditional expression (10), it becomes difficult to miniaturize each imaging optical element in the main scanning direction. Furthermore, it is more preferable to satisfy the following conditional expression (10a).
3.5 <| γ | <5.5 (10a)

Further, when the distance from the on-axis deflection point to the imaging optical element 5a closest to the deflector 4 on the optical axis of the imaging optical system 5 is T1, the following conditional expression (11) is satisfied: desirable.
0.20 ≦ T1 / T ≦ 0.50 (11)

If the upper limit of conditional expression (11) is exceeded, the imaging optical element 5a is too far from the deflector 4, and the imaging optical element 5a becomes large in the main scanning direction. When the value goes below the lower limit of the conditional expression (11), the imaging optical element 5a approaches the deflector 4 too much, which may cause interference between the optical path and other members and the imaging optical element 5a. Furthermore, it is more preferable to satisfy the following conditional expression (11a).
0.25 ≦ T1 / T ≦ 0.45 (11a)

When the distance from the imaging optical element 5a closest to the deflector 4 to the imaging optical element 5b closest to the scan surface 6 on the optical axis of the imaging optical system 5 is T2, the following conditional expression It is desirable to satisfy (12).
0.35 ≦ T2 / T ≦ 0.65 (12)

When the value exceeds the upper limit of the conditional expression (12), the distance from the imaging optical element 5a to the imaging optical element 5b becomes too large, which makes it difficult to miniaturize the entire apparatus. If the lower limit of the conditional expression (12) is not reached, the subscanning magnification of the imaging optical system 5 becomes too large, and print position deviation due to a manufacturing error of the deflector 4 tends to occur. Furthermore, it is more preferable to satisfy the following conditional expression (12a).
0.40 ≦ T2 / T ≦ 0.60 (12a)

  In the optical scanning device 100, it is necessary to give positive power to the entire system of the imaging optical system 5 in the main scanning cross section. Here, when the conditional expressions (2) and (3) and the conditional expressions (4) and (5) described above are satisfied, each optical surface of the imaging optical element 5b in the main scanning cross section has a shape close to a plane. It becomes difficult to give the imaging optical element 5b a sufficient positive power.

  Therefore, in the main scanning section, it is desirable that the imaging optical element 5a closest to the deflector 4 have a larger positive power than the imaging optical element 5b closest to the surface 6 to be scanned. On the other hand, in the sub-scanning cross section, it is desirable that the imaging optical element 5 b closest to the surface 6 to be scanned has a larger positive power than the imaging optical element 5 a closest to the deflector 4. Thus, good imaging performance can be obtained by appropriately setting the power in each cross section of each imaging optical element.

Specifically, assuming that the powers on the optical axis in the main scanning section of the imaging optical element 5a closest to the deflector 4 and the imaging optical element 5b closest to the scanned surface 6 are φ1m and φ2m, respectively. It is desirable to satisfy conditional expression (13) of
1.5 ≦ | φ1 m / φ2 m | ≦ 10 (13)

If the upper limit of the conditional expression (13) is exceeded, the power in the main scanning section of the imaging optical element 5a becomes too large, and it becomes difficult to correct various aberrations. When the value goes below the lower limit of the conditional expression (13), the power in the main scanning section of the imaging optical element 5a becomes too small, and it becomes difficult to sufficiently ensure the power of the entire imaging optical system 5. . Furthermore, it is more preferable to satisfy the following conditional expression (13a).
2.0 ≦ | φ 1 m / φ 2 m | ≦ 8.0 (13 a)

Further, when the powers on the optical axis in the sub-scanning cross section of the imaging optical element 5a closest to the deflector 4 and the imaging optical element 5b closest to the scanned surface 6 are φ1s and φ2s, respectively, the following conditional expressions It is desirable to satisfy (14).
5.0 ≦ | φ2s / φ1s | ≦ 30 (14)

When the value exceeds the upper limit of the conditional expression (14), the power in the sub-scanning cross section of the imaging optical element 5b becomes too large, and it becomes difficult to correct various aberrations. When the value goes below the lower limit of the conditional expression (14), the power in the sub-scanning cross section of the imaging optical element 5b becomes too small, and it becomes difficult to sufficiently secure the power of the entire system of the imaging optical system 5. . Furthermore, it is more preferable to satisfy the following conditional expression (14a).
10 ≦ | φ2s / φ1s | ≦ 25 (14a)

Further, in the main scanning section, the intersections of the entrance surface and exit surface of the imaging optical element 5a closest to the deflector 4 with the off-axis ray are respectively F and G, and the entrance surface and exit surface of the imaging optical element 5a. The angles formed by the tangents at the intersection points F and G and the optical axis are denoted by α1 _in and α1 _out , respectively. However, each of the angles α1 _in and α1 _out indicates an acute angle side (smaller side) of the angle formed by each tangent and the optical axis. At this time, it is desirable to satisfy the following conditional expressions (15) and (16).
35 ° ≦ α1 _in <60 ° (15)
25 ° ≦ α1 _out <50 ° (16)

If the upper limits of the conditional expressions (15) and (16) are exceeded, the inclination of the end of the imaging optical element 5a in the main scanning section becomes insufficient, and it becomes difficult to obtain good imaging performance. If the lower limit of the conditional expressions (15) and (16) is not reached, the inclination of the end of the imaging optical element 5a becomes too large, which makes it difficult to reduce the thickness of the imaging optical element 5a. Furthermore, it is more preferable to satisfy the following conditional expressions (15a) and (16a).
40 ° ≦ α1 _in <55 ° (15a)
30 ° ≦ α1 _out <45 ° (16a)

Example 1
Hereinafter, the optical scanning device 100 according to the first embodiment of the present invention will be described. The optical scanning device 100 according to the present embodiment has the same configuration as that of the optical scanning device 100 according to the above-described embodiment, and thus redundant description will be omitted. The optical scanning device 100 according to the present embodiment includes a light source 1, an aperture stop 2 that regulates a light flux from the light source 1, an incident optical system 3 that guides a light flux to a deflection surface of a deflector 4, and the deflector described above And an imaging optical system 5.

  In the light scanning device 100, the light beam emitted from the light source 1 passes through the aperture stop 2 provided with the aperture and is guided to the deflection surface of the deflector 4 by the incident optical system 3. For example, a semiconductor laser can be used as the light source 1, and the number of light emitting points may be one or more. In this embodiment, an elliptical stop provided with an elliptical opening is adopted as the aperture stop 2. However, the shape of the opening is not limited to this, and for example, a rectangular stop provided with a rectangular opening, etc. It may be adopted.

  The incident optical system 3 according to the present embodiment is composed of two incident optical elements of a collimator lens 3a and a cylindrical lens 3b. The collimator lens 3a is for converting the degree of convergence of the light beam emitted from the light source 1 in the main scanning section, and in this embodiment, converts the divergent light from the light source 1 into parallel light. However, parallel light here includes not only strictly parallel light but also substantially parallel light such as weakly convergent light and weak divergent light.

  The cylindrical lens 3b is a lens having power only in the sub-scanning cross section, condenses the light beam passing through the collimator lens 3a in the sub-scanning cross section, and the deflection surface of the deflector 4 or its vicinity in the main scanning direction Form a long line image. The collimator lens 3a and the cylindrical lens 3b may be integrated into one lens for further downsizing and cost reduction of the entire device.

  Furthermore, by providing a diffractive surface in the incident optical system 3, it is possible to compensate for focus variation when the oscillation wavelength of the light source 1 or the shape of each optical surface changes due to a change in environmental temperature. For example, when the ambient temperature rises with respect to the normal temperature, the power of the refracting surface becomes weak due to the long wavelength of the luminous flux and the elongation of the resin material, while the power of the diffractive surface becomes strong. Therefore, by providing the diffractive surface in the incident optical system 3, it is possible to mutually cancel the focus variation due to the refractive surface and the diffractive surface.

  The deflector 4 is rotated at a constant speed in the direction of the arrow in the figure by a drive unit (not shown) (such as a motor), and the light flux from the incident optical system 3 is deflected by the deflection surface to obtain an imaging optical system 5. The effective area on the surface 6 to be scanned is scanned in the main scanning direction via In this embodiment, a rotary polygon mirror (polygon mirror) having four deflection surfaces is employed as the deflector 4, but the number of deflection surfaces is not limited to this. Also, instead of the rotary polygon mirror, a swing mirror in which one or two deflection surfaces swing around a swing axis may be employed.

  The imaging optical elements 5a and 5b according to the present embodiment are toric lenses having different powers in the main scanning cross section and the sub scanning cross section. The imaging optical system 5 guides and condenses the light beam deflected by the deflector 4 onto the surface 6 to be scanned, and in or near the surface 6 in both the main scanning cross section and the sub scanning cross section. An image of the light source 1 is formed. Further, the imaging optical system 5 performs scanning on the scan surface 6 when the deflection surface is inclined by making the deflection surface or the vicinity thereof and the scan surface 6 or the vicinity thereof in a conjugate relationship in the sub-scanning cross section. Reduction of misregistration (tilt compensation) is performed.

  In addition, since each lens which comprises the incident optical system 3 which concerns on a present Example, and the imaging optical system 5 is a plastic molded lens formed by inject-molding a resin material, it compares with the case where a glass lens is employ | adopted And significant cost reduction is possible. In addition, by employing a plastic molded lens, molding of the diffractive surface or the aspheric surface becomes easy, and productivity and optical performance can be improved. However, if necessary, each lens constituting the incident optical system 3 and the imaging optical system 5 may be a glass lens.

  The shape (shape of the generatrix) in the main scanning section including the surface apex of each optical surface (lens surface) of the imaging optical system 5 according to the present embodiment is expressed by the following equation. Here, the intersection point of the surface apex of each optical surface and each optical axis is the origin, the axis in the optical axis direction is the X axis, and in the main scanning section, the axis orthogonal to the X axis is the Y axis, X axis and Y axis A local coordinate system is defined with the orthogonal axis as the Z axis.

Where R is the radius of curvature (radius of curvature of the main line) in the main scanning section on the optical axis, and k, B ₄ , B ₆ , B ₈ , B ₁₀ and B ₁₂ are the aspheric coefficients in the main scanning section It is. By making the values of the aspheric coefficients B _{4 to} B ₁₂ different from each other on both sides (plus side and minus side in the Y-axis direction) of each optical axis (X axis), the generatrix shape in the main scanning direction with respect to the optical axis It can be asymmetric.

Further, the radius of curvature r ′ (the radius of curvature of the sagittal line) in the sub-scanning section at each position (each image height) in the main scanning direction of each optical surface of the imaging optical system 5 according to the present embodiment is as follows. It is expressed by a formula. However, r is the radius of curvature in the sub-scanning section on the optical axis, E _i is the sagittal line variation coefficients. The sagittal shape can be reworded as a surface shape in a cross section perpendicular to the main scanning cross section including the surface normal on the generatrix at each position in the main scanning direction.

  The configuration of the optical scanning device 100 according to the present embodiment is shown in Table 1. Each distance shown in Table 1 indicates a value on the optical axis of the imaging optical system 5. The angle of the incident chief ray indicates the angle formed by the chief ray of the light beam exiting from the incident optical system 3 and entering the deflection surface and the optical axis of the imaging optical system 5. The rotation center coordinates of the deflector indicate the point of intersection of the deflector and the chief ray of the on-axis light beam as the origin. Further, the effective scanning width and the maximum scanning angle are symmetrical with respect to the optical axis of the imaging optical system 5, and the value on one side with respect to the optical axis is positive and the value on the other side is negative. .

Tables 2 and 3 show the shapes of the imaging optical elements 5a and 5b according to this example. In Tables 2 and 3, the radius of curvature and the aspheric coefficient of each optical surface are on the same side (plus side, Upper) as the light source 1 with respect to the optical axis and on the opposite side (minus side, Lower) to the light source 1 It shows separately. Also, “E ± N” means “× 10 ^{± N 2} ”.

  In FIG. 3, in the optical scanning device 100 according to the present embodiment, the irradiation position deviation in the sub-scanning direction on the surface to be scanned 6 when the deflection surface of the deflector 4 is inclined (tilted) by 2 with respect to the design value. Show. As can be seen from FIG. 3, the irradiation position deviation is suppressed to 5 μm or less over the entire area (full image height) in the main scanning direction.

Example 2
Hereinafter, an optical scanning device 200 according to a second embodiment of the present invention will be described. In the optical scanning device 200 according to the present embodiment, the description of the same configuration as that of the optical scanning device 100 according to the first embodiment described above will be omitted.

  FIG. 4 is a schematic view of a main part of the optical scanning device 200 according to the present embodiment, FIG. 4A shows a main scanning cross section, and FIG. 4B shows a sub scanning cross section. The configuration of the optical scanning device 200 according to the present embodiment is shown in Table 4, and the shapes of the imaging optical elements 5a and 5b according to the present embodiment are shown in Tables 5 and 6.

  FIG. 5 shows the irradiation position deviation in the sub-scanning direction on the surface to be scanned 6 in the case where the deflection surface of the deflector 4 is tilted by 2 with respect to the design value in the optical scanning device 200 according to this embodiment. As can be seen from FIG. 5, the irradiation position deviation is suppressed to 5 μm or less over the entire area in the main scanning direction.

  Table 7 shows the values of the middle sides of the conditional expressions (1) to (5) and (9) to (16) described above in Examples 1 and 2. As shown in Table 7, the optical scanning device according to any of the embodiments satisfies each conditional expression.

[Image forming apparatus]
FIG. 6 is a schematic view (sub-scan sectional view) of main parts of the image forming apparatus 104 according to the embodiment of the present invention. The image forming apparatus 104 includes the light scanning device (light scanning unit) 100 in the above-described embodiment.

  As shown in FIG. 6, code data Dc output from an external device 117 such as a personal computer is input to the image forming apparatus 104. The code data Dc is converted into an image signal (dot data) Di by a printer controller 111 in the apparatus, and is input to the light scanning unit 100. Then, a light beam 103 modulated according to the image signal Di is emitted from the light scanning unit 100, and the photosensitive surface (surface to be scanned) of the photosensitive drum 101 is scanned in the main scanning direction by the light beam 103. The printer controller 111 controls not only the data conversion described above, but also each unit in the image forming apparatus such as a motor 115 described later.

  The photosensitive drum 101 as an electrostatic latent image carrier (photosensitive member) is rotated clockwise by the driving force of the motor 115. Then, with this rotation, the photosensitive surface of the photosensitive drum 101 moves relative to the light beam 103 in the sub-scanning direction. Above the photosensitive drum 101, a charging roller 102 for charging the photosensitive surface uniformly is provided in contact with the photosensitive surface. The light beam 103 from the light scanning unit 100 is irradiated onto the photosensitive surface charged by the charging roller 102.

  As described above, the luminous flux 103 is modulated based on the image signal Di, and by irradiating the luminous flux 103, an electrostatic latent image is formed on the photosensitive surface. The electrostatic latent image is developed as a toner image by a developing device 107 disposed in contact with the photosensitive surface on the downstream side in the rotational direction of the photosensitive drum 101 further than the irradiation position of the light beam 103.

  The toner image developed by the developing device 107 is transferred onto a sheet 112 as a material to be transferred by a transfer roller (transfer device) 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. Ru. The sheet 112 is stored in the sheet cassette 109 in front of the photosensitive drum 101 (right side in FIG. 6), but can be fed manually. A sheet feeding roller 110 is disposed at an end of the sheet cassette 109, whereby the sheet 112 in the sheet cassette 109 is fed to the conveyance path.

  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. 6). 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. The fixing unit fixes the unfixed toner image on the sheet 112 by heating the sheet 112 conveyed from the transfer roller 108 while pressing the sheet 112 at the pressure contact portion between the fixing roller 113 and the pressure roller 114. Further, a sheet discharge roller 116 is disposed behind the fixing roller 113, and the sheet 112 on which the toner image is fixed is discharged out of the image forming apparatus 104.

  The image forming apparatus 104 may be a color image forming apparatus by providing a plurality of each of the light scanning unit 100, the photosensitive drum 101, and the developing device 107. Further, a color digital copying machine may be configured by connecting a color image reading apparatus provided with a line sensor such as a CCD sensor or a CMOS sensor to the image forming apparatus 104 as the external device 117.

[Modification]
Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the present invention.

  For example, in each of the above-described embodiments, one scanning surface is scanned by light flux from one light source. However, the present invention is not limited thereto. Light flux from a plurality of light sources is simultaneously deflected by one deflector. Alternatively, a configuration for scanning a plurality of scan surfaces may be employed.

DESCRIPTION OF SYMBOLS 1 light source 4 deflector 5 imaging optical system 5a, 5b imaging optical element 6 scanned surface 100 optical scanning device

Claims (15)

Imaging optics including a deflector for deflecting a light beam from a light source to scan a surface to be scanned in the main scanning direction, and a plurality of imaging optical elements for guiding the light beam deflected by the deflector to the surface to be scanned Equipped with
The scanning speed of the light beam differs between the on-axis image height and the off-axis image height on the surface to be scanned,
On the optical axis of the imaging optical system, the distance from the on-axis deflection point of the deflector to the scanned surface is Tc, and the exit surface of the imaging optical element closest to the scanned surface from the on-axis deflection point The distance between the light beam and the light incident surface and the light exit surface of the imaging optical element closest to the surface to be scanned is A and C, respectively. When angles formed by tangents of the incident surface and the exit surface at the intersection points A and C and the optical axis are respectively α _in and α _out :
0.15 ≦ T / Tc ≦ 0.25
83 ° ≦ α _in <90 °
83 ° ≦ α _out <90 °
An optical scanning device characterized by satisfying the following conditional expression. In the main scanning section, the light which bisects the distance in the main scanning direction from the intersection point A to the intersection point A0 as A0 and the intersection point between the optical axis and the incident surface of the imaging optical element closest to the scan surface. An angle formed by a straight line parallel to the axis and the point of intersection with the incident surface is A1, and a straight line connecting the point of intersection A1 and each of the points of intersection A and A0 is β _in, and is closest to the optical axis and the scanned surface The intersection point of the imaging optical element with the exit surface is C0, and the intersection point of the straight line parallel to the optical axis bisecting the distance in the main scanning direction from the intersection point C to the intersection point C0 is C1. When an angle formed by a straight line connecting the intersection point C1 and each of the intersection points C and C0 is β _out ,
174 ° ≦ β _in <180 °
174 ° ≦ β _out <180 °
The optical scanning device according to claim 1, wherein the following conditional expression is satisfied. Assuming that the imaging coefficient on the optical axis of the imaging optical system is K, and the light beam deflected at the scanning angle θ by the deflector is incident, the image height Y in the main scanning direction on the surface to be scanned is Y = ( K / B) × tan (B × θ)
In the image height Y when the scanning angle θ is maximized, 0.30 ≦ B ≦ 0.70.
The optical scanning device according to claim 1 or 2, wherein the following conditional expression is satisfied. Assuming that the lateral magnification in the sub-scanning cross section including the optical axis of the imaging optical system is γ,
3.0 <| γ | <6.0
The optical scanning device according to any one of claims 1 to 3, wherein the following conditional expression is satisfied. Assuming that the distance from the on-axis deflection point to the imaging optical element closest to the deflector on the optical axis of the imaging optical system is T1.
0.20 ≦ T1 / T ≦ 0.50
The optical scanning device according to any one of claims 1 to 4, wherein the following conditional expression is satisfied. When a distance from an imaging optical element closest to the deflector to an imaging optical element closest to the scan surface is T2 on the optical axis of the imaging optical system,
0.35 ≦ T2 / T ≦ 0.65
The optical scanning device according to any one of claims 1 to 5, wherein the following conditional expression is satisfied.   7. A control unit for controlling the light emission of the light source based on the deviation amount of the partial magnification at the off-axis image height with respect to the partial magnification at the on-axis image height of the imaging optical system. The optical scanning device according to any one of the above. Assuming that the imaging coefficient on the optical axis of the imaging optical system is K, and the light beam deflected at the scanning angle θ by the deflector is incident, the image height Y in the main scanning direction on the surface to be scanned is Y = ( K / B) × tan (B × θ)
The optical scanning device according to any one of claims 1 to 6, further comprising: a control unit that controls light emission of the light source according to 1 / cos ² (B × θ), . 0.17 ≦ T / Tc ≦ 0.23
The optical scanning device according to any one of claims 1 to 8, wherein the following conditional expression is satisfied. 84.5 ° ≦ α _in <90 °
84.5 ° ≦ α _out <90 °
The optical scanning device according to any one of claims 1 to 9, wherein the following conditional expression is satisfied. When the powers on the optical axis in the main scanning section of the imaging optical element closest to the deflector and the imaging optical element closest to the scan surface are φ1m and φ2m, respectively.
1.5 ≦ | φ1 m / φ2 m | ≦ 10
The optical scanning device according to any one of claims 1 to 10, wherein the following conditional expression is satisfied. When the power on the optical axis in the sub-scanning section of the imaging optical element closest to the deflector and the imaging optical element closest to the scan surface is φ1s and φ2s, respectively.
5.0 ≦ | φ2s / φ1s | ≦ 30
The optical scanning device according to any one of claims 1 to 11, wherein the following conditional expression is satisfied. In the main scanning section, the points of intersection of the light beam deflected at the maximum scanning angle by the deflector and the entrance surface and exit surface of the imaging optical element closest to the deflector are respectively F and G, and the intersections at the intersection points F and G When the angles formed by the tangents of the entrance surface and the exit surface and the optical axis are α1 _in and α1 _out , respectively
35 ° ≦ α1 _in <60 °
25 ° ≦ α1 _out <50 °
The optical scanning device according to any one of claims 1 to 12, wherein the following conditional expression is satisfied.   An optical scanning device according to any one of claims 1 to 13, a developing unit for developing an electrostatic latent image formed on the surface to be scanned by the optical scanning device as a toner image, and the developed toner An image forming apparatus comprising: a transfer unit configured to transfer an image to a transfer material; and a fixing unit configured to fix the transferred toner image to the transfer material.   An image comprising: the optical scanning device according to any one of claims 1 to 13; and a printer controller for converting data output from an external device into an image signal and inputting the signal to the optical scanning device. Forming device.

Images