JP2001133711A - Multibeam scanning optical system and recorder using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multibeam scanning optical system capable of reducing a main scanning jitter and having a returning light reducing effect. SOLUTION: The surface of a photoreceptor drum is nearly perpendicular to the symmetric axis of an fθ lens but a paraxial image surface is inclined. Light fluxes A and B at both ends in the main scanning direction are temporarily crossed on the paraxial image surface. The surface of the drum is irradiated with the light fluxes based on mutual positional relation in accordance with the positional relation of the drum and the paraxial image surface. The reaching positions of the respective light fluxes are replaced at both ends in the main scanning direction and the flux A is always positioned on the outside. The image surface is constituted to be inclined in such a way, and the off-axis aberration of the fθ lens is adjusted so as to always constitute a minimum spot on the surface of the drum separately from the paraxial image surface. Namely, a main light beam crosses and its position is changed on the paraxial image surface, and it is defocused from the surface of the drum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam laser scanning optical system which simultaneously scans a plurality of laser beams and writes image information of a document at high speed, and a recording apparatus using the same. The present invention relates to a multi-beam laser scanning optical system that obliquely enters a light beam into an image carrier such as the above.

[0002]

2. Description of the Related Art Conventionally, in a laser scanning optical system, when an incident angle of a light beam on a photosensitive drum as viewed by projecting onto a sub-scanning section is perpendicularly incident, the drum from the drum surface near the center of the main scanning range is generally used. Since the reflection component due to the surface reflection returns straight, this return light becomes a ghost,
In consideration of adverse effects, the angle of incidence of the light beam on the drum when projected onto the sub-scanning cross section is not normal incidence.

FIG. 6 is an optical path diagram in the case of non-perpendicular incidence on the photosensitive drum in the sub-scan section. The positional relationship between the polygon mirror and the photosensitive drum and the two light beams incident on the drum surface are schematically shown. As shown here, two light beams are obliquely incident on the drum surface at a distance of the sub-scanning pitch. When the state at that time is viewed in a main scanning cross section, the arrival positions of the light beams differ at both ends in the main scanning direction, and a shift (main scanning jitter) shown by Δ appears. The plane formed by the principal ray of the scanned light beam (main scanning plane)
Intersects the drum surface in a substantially straight line, which is naturally substantially parallel to the drum rotation axis, but the drum rotation axis is not on a plane extending from the main scanning plane. In order to obtain high-speed output, it is advantageous to use a multi-beam.However, in a scanning optical system using a multi-beam, the incident angle of the drum projected on the In the case of non-perpendicular incidence, a phenomenon occurs in which the reaching distance of each beam to the drum surface differs at both ends in the main scanning direction. As a result, a deviation (main scanning jitter) of the irradiation position of each laser spot in the main scanning direction occurs at both ends of the main scanning. Therefore, at both ends of the output image in the main scanning direction, there is a problem that the positions of the light beams are not aligned and unevenness occurs.

Therefore, for example, Japanese Patent Application Laid-Open No. 5-33328
The scanning optical system disclosed in Japanese Patent Laid-Open No. 1-2005-143 has a condition that the incident angle (deviation from vertical incidence) with respect to the photosensitive drum in the sub-scanning section should be limited to below. Here, it is obtained from the fact that the allowable value of the positional deviation in the main scanning direction is set to の of the sub-scanning line pitch. This condition is such that, at normal incidence, there is an effect of the return light, and when the incident angle is removed from the sub-scanning cross-section at that angle, no matter how far the angle is applied, the deviation between both ends of the main scanning becomes 1
/ 2 pitch.

In a scanning optical system disclosed in, for example, Japanese Patent Application Laid-Open No. 9-197308, two light beams incident on a pupil of an fθ lens are decentered in the sub-scanning direction by the fθ lens so that the two light beams are focused on the optical axis. The light is made to enter asymmetrically. As a result, an optical path difference occurs in the sub-scanning cross section between the light beam passing on the optical axis and the light beam passing through the optical path deviated from the optical axis in the pupil. The optical path difference between the two light beams generated at the time is canceled out.

[0006]

However, the above-mentioned Japanese Patent Application Laid-Open
In the scanning optical system disclosed in JP-A-333281, the angle of incidence in the sub-scanning section is limited under the condition that the main scanning jitter falls within the allowable value (1/2 of the sub-scanning pitch). However, the allowable value of 1/2 of the sub-scanning pitch is too large as an allowable value since it is 1/2 pixel in the case of a general main and sub pitch. There is a trade-off between the condition for avoiding the influence of the return light and the reduction of the main scanning jitter. If the main scanning jitter is further reduced, the return light reduction effect is reduced.

In the scanning optical system disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 9-197308, a sufficiently effective optical path difference cannot be provided unless the interval between the light beams in the sub-scanning direction is large to some extent. For example, when spots are arranged at one line pitch on the photosensitive drum, the interval in the sub-scanning direction does not become so large. Therefore, even if the light flux is arranged to be asymmetrically incident on the optical axis in the fθ lens pupil, the interval between the two light beams remains at a very small level, so that it is difficult to provide a sufficient optical path difference for correction. is there. In particular, when a monolithic laser array is used, the intervals between the light emitting points of the laser chips are separated to some extent due to the amount of heat generated. When the laser chips are arranged on the photoconductor drum surface on the assumption that the spot intervals in the sub-scanning direction are aligned with, for example, one scanning line pitch, the laser chips are arranged such that the light emitting point interval is one scanning line pitch in the sub-scanning direction. Since the rotation is adjusted around the optical axis and the light emitting point interval in the main scanning direction is completed, the spot interval in the main scanning direction has a predetermined width, so that the two light beams are mutually angled in the main scanning direction. And propagate. As a result, when exposing points at the same position in the main scanning direction on the drum, the rotational positions of the polygon mirrors are different from each other, and the exposure must be performed at different times with respective light beams. Therefore, the position passing through the fθ lens is also different in the main scanning direction, and the effect cannot be sufficiently exhibited due to the difference in the passing position in the main scanning direction in the fθ lens.

Accordingly, an object of the present invention is to provide a multi-beam scanning optical system that reduces the main scanning jitter and also has the effect of reducing return light.

[0009]

In the present invention for solving the above-mentioned problems, each light beam at both ends of the main scanning on the drum surface is defocused on the main scanning image plane position of the fθ lens. By adjusting the spot position and defocusing the image plane so as to offset the deviation of the irradiation position at both ends in the main scanning direction, the main scanning jitter is reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described for a case where a two-beam array laser is used.
That is, for example, the case where two light beams deviated in the sub-scanning direction are simultaneously irradiated onto the photosensitive drum and the output speed is increased by simultaneously recording two scanning lines at a time is also included.

When recording two adjacent scanning lines with two light beams, the two light beams should have an interval of one pitch of the scanning lines in the sub-scanning direction on the drum surface. is there. In the case where the main and sub devices have a resolution of 600 dpi, the interval d is 42.3 μm.

Assuming that the radius r of the photosensitive drum is 15 mm and the incident angle ξ on the drum surface is ゜ = 10 °, the return light beam at the center of the main scanning range forms an angle of 2 ° = 20 ° in the sub-scanning direction. When reflected from the drum and returned to the fθ lens, fθ
Assuming that the focal length of the lens is f = 200 mm, the ray height on the main plane on the lens exit side is f × Tan 20 ゜ = 73 mm.
In the case of the apparatus having the above specifications, it is considered that the effective diameter of the fθ lens in the sub-scanning direction is sufficiently larger than the general size, so that the polygon mirror as well as the effective diameter of the fθ lens does not return. In order to satisfy this condition, the distance of the main scanning plane from the rotation axis of the drum is rsinξ = 2.
It needs to be 6 mm. That is, it is necessary that the main scanning plane be offset by 2.6 mm in the sub-scanning direction from a plane passing through the center of rotation of the drum and being parallel to the main scanning plane.

Assuming that the A3 width can be output, the one-side scanning width needs to be approximately W = 110 mm. f = 200m
m, the maximum one-sided scanning angle η is η = tan
⁻¹ (W / 200) = 28.8 °. The two light beams to be scanned enter the drum almost in parallel in the sub-scanning cross section.

At the center of the main scanning range, the two light beams are divided into a light beam that arrives first and a light beam that arrives later because the drum arrival point is an inclined surface.
An optical path difference of tanξ = 7.5 μm occurs. At the center of the main scanning range, the two light beams enter the drum surface substantially perpendicularly when viewed in the main scanning section, so that the dots do not shift in the main scanning direction.

However, at both ends of the main scanning range, the angle of incidence of the drum on the main scanning plane is equal to the maximum scanning angle η = 28.8. As a result, a position difference occurs in the main scanning direction between the light beam reaching the drum first and the light beam reaching the drum with a delay. The quantity Δ is Δ = δtan η = 4.1 μ
m. This is a dot pitch d = 4 of 600 dpi.
This is about 10% for 2.3 μm, and cannot be ignored when a high-definition image is desired.

This displacement in the main scanning direction similarly occurs at both ends in the main scanning direction. That is, the light beam that reaches the drum first starts writing inside and ends writing inside the main scanning direction in the screen. A light beam that arrives at the drum with a delay starts writing from the outside in the main scanning direction and ends writing outside. Thus, the outer spot on one side is also outer on the opposite end. This is because the positional relationship of incidence on the inclined surface of the drum at the time of incidence on the drum does not change in the entire main scanning area.

On the other hand, by setting and designing the paraxial image plane of the fθ lens in advance by tilting, for example, the image plane near the optical axis can be configured to be tilted with respect to the drum surface.
That is, the image plane is made coincident with the drum surface on the optical axis and defocused at the end in the main scanning direction. The direction of defocus is set to be opposite at both ends. That is, the image plane is a straight line that intersects with the straight line indicating the main scanning direction on the drum surface on the optical axis and is inclined at a predetermined angle.

The image plane and the drum surface do not always have to intersect on the optical axis. This is because, if the optical axis is located at the center of the main scanning range, the approximate defocus amount becomes substantially the object at both ends in the main scanning direction when crossing on the optical axis. This does not matter even if it comes to a position shifted from the optical axis in accordance with the degree of jitter cancellation at both ends of the main scanning as long as it is within the main scanning range.

Next, a description will be given of the reason why the shift of the light beams at both ends in the main scanning direction (main scanning jitter) is reduced by adopting this configuration. In a two-beam monolithic array laser, which is the light source of such a device, two light emitting points are in the same plane in a direction perpendicular to the PN junction direction of the laser chip. On the other hand, they are separated by several tens of μm in a direction parallel to the bonding. Since the interval between the light emitting points is unique to the laser, it is irrelevant to whether the light beams can be conveniently arranged on the drum. Therefore, it is necessary to set the sub-scanning magnification so that the required interval in the sub-scanning direction becomes a predetermined value, or to control the interval between the light emitting points in the sub-scanning direction by rotating the laser by a small angle around the optical axis. become. As a result, the light emitting points in the main scanning direction are formed as compared with the interval in the sub-scanning direction, but generally have a larger interval as compared with the interval in the sub-scanning direction. Due to the spacing, the two beams in the main scanning section are substantially parallel to each other, but reach the drum at a small angle.

As a result, the spot positions on the drum in the main scanning direction at the same time are not the same. Therefore, the 2
When exposing one light beam at the same position in the main scanning direction (for example, a straight line parallel to the sub-scanning direction), the deflector operates after one (light beam A) is exposed, for example, the polygon mirror rotates. It is necessary to use a delay time process, such as performing exposure with the light beam B when the other light beam (light beam B) is at the same angle as when the previous light beam A is exposed. It is. When the light beam A and the light beam B perform exposure at the same position on the drum in the main scanning direction as described above,
Each light beam enters the fθ lens at the same angle of view but at a different height. Also, at this incident height,
When entering the fθ lens at one end in the main scanning direction,
When the light beam B is outside in the main scanning direction and the light beam A is inside, at the opposite end, the outside is the light beam A and the inside is the light beam B. That is, the positional relationship of the light beam AB in the main scanning direction does not always change. Two light beams AB incident at different heights form an image on the image plane in agreement. Therefore, the position of the light beam AB is shifted in the main scanning direction before and after the image plane, and the positional relationship of the light beam AB is also switched. Thus, as described above, it is assumed that the image surface is arranged to be inclined with respect to the drum surface so that the image surface is located closer to the drum surface at an end in the main scanning direction.
At this time, it is assumed that the light beams AB once intersect on the image plane, and as a result, for example, the light beam A is on the outside and the light beam B is on the inside in the main scanning direction. Since the drum surface is behind the image surface, the light beam A is located outside in the main scanning direction and the light beam B is located inside in the main scanning direction at this end on the drum surface. The surface becomes deeper than the drum surface, and the light flux A on the drum surface
Are outside and the light beam B is inside, and the light beam A is outside and B is inside at both ends in the main scanning direction.

On the other hand, due to non-perpendicular incidence on the drum in the sub-scanning sectional direction, two light beams A substantially parallel to the sub-scanning direction
As described above, B is always offset to the outside in the main scanning direction as described above.
As a result, a scanning system with less main scanning jitter can be realized.

For this purpose, it is sufficient to design the image plane of the fθ lens system to be inclined, and the amount of inclination varies depending on other constituent parameters, but is several mm or less in order.

For example, when the distance between two light beams on the polygon mirror is approximately 0.2 mm, the focal length of the fθ lens is 200 mm, and the distance between the two light beams at the end in the main scanning direction is 4 μm. It is sufficient that the defocus of the image plane is 4 mm.

Therefore, the image plane is set to ± 4 m at both ends in the main scanning direction.
m so that the width in the main scanning direction is 220 m
Assuming that m, the image plane may be inclined by 2 ° with respect to the main scanning line on the drum surface. At this time, the drum surface is defocused from the image plane, but it is preferable that the drum surface be within the depth of focus of the fθ lens. Within the depth of focus, the position of the spot can be corrected, and the image quality of the spot can be realized without loss.

Alternatively, even when the paraxial image plane is tilted, the position where the size of the image spot becomes smallest is always on the drum surface, or deliberately shifted from the paraxial image surface, or at a position closer to the drum surface. It is preferable to design such that the spherical aberration is appropriately left at both off-axis ends of the fθ lens so as to be located.

It is theoretically possible to make the main scanning jitter completely zero by the method according to the present invention. However, in some cases, it is only necessary to reduce the pixel pitch to a few percent or less of the pixel pitch. It is not always necessary to strictly cancel the jitter if it is substantially sufficient if the jitter is reduced to some extent.

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

[0028]

FIG. 1 is an optical path diagram of a two-beam scanning optical system according to a first embodiment. Light beams A and B emitted from a two-beam array laser (not shown) pass through a condenser lens, are deflected by a polygon mirror, and reach a drum surface through a lens (not shown) of fθ. As shown in the figure, the light beams A and B are not parallel to each other because they have an angle of view when entering the condenser lens. Therefore, in order to expose the same position in the main scanning direction with the A and B lasers, the polygon rotation positions are different (ie, not at the same time), but they are overlapped as if at the same time. Is expressed. Here, the paraxial image plane formed by the luminous flux at each angle of view is shown by a straight line in the figure, but is inclined with respect to the photosensitive drum surface in the figure.

In the first embodiment, the photosensitive drum surface is substantially perpendicular to the axis of symmetry of the fθ lens, but the paraxial image surface is inclined.

As shown in the figure, the light beams A and B at both ends in the main scanning direction once intersect on the paraxial image plane. The light is irradiated onto the drum surface in a mutual positional relationship according to the positional relationship between the drum and the paraxial image plane. The rays shown here are the principal rays of A and B, respectively, because they are paraxial image planes as shown in the figure.
Therefore, the arrival positions of the respective light beams are switched at both ends in the main scanning direction as shown in the figure, and the A light beam is always located outside.

Although the image plane is configured to be inclined in this manner, the depth of focus is designed to be wide so as to always include the position on the drum, or by adjusting the off-axis aberration Halo to always move the drum away from the paraxial image plane. What is necessary is just to design so that the minimum spot may be comprised on a surface.

Embodiment 1 employs the latter. That is, on the paraxial image plane, the principal rays intersect and the position changes, but this is defocused from the drum surface. The actual imaging spot must be narrowed down to a predetermined size on the drum surface. Therefore, the off-axis aberration Halo of the fθ lens is changed with respect to the angle of view so that the best image plane is always positioned on the drum surface that is inclined from the paraxial image plane. In this case, it is possible to realize a state in which the imaging spot performance is sufficiently narrowed down.

[Embodiment 2] FIG. 2 is an optical path diagram of a two-beam scanning optical system of Embodiment 2. Light beams A and B emitted from a two-beam array laser (not shown) pass through a condenser lens and are deflected by a polygon mirror to reach a photosensitive drum surface through a fθ lens (not shown). As shown in the figure, the light beams A and B are not parallel to each other because they have an angle of view when entering the condenser lens. Therefore, in order to expose the same position in the main scanning direction with the A and B lasers, the polygon rotation positions are different (ie, not at the same time), but they are overlapped as if at the same time. Is expressed. Here, the paraxial image plane formed by the luminous flux at each angle of view is shown by a straight line in the figure. On the other hand, the photosensitive drum surface in FIG.

In the second embodiment, the paraxial image plane is perpendicular to the symmetry axis of the fθ lens in the main scanning plane.
The photosensitive drum surface is inclined.

As shown in the figure, the light beams A and B at both ends in the main scanning direction once intersect on the paraxial image plane. The light is irradiated onto the photosensitive drum surface in a mutual positional relationship according to the positional relationship between the photosensitive drum and the paraxial image plane. The rays shown here are the principal rays of A and B, respectively. Therefore, the arrival positions of the respective light beams are switched at both ends in the main scanning direction as shown in the figure, and the A light beam is always located outside. The image plane is configured to be tilted in this way, but the depth of focus should always be designed to be wide enough to include on the drum, or by adjusting off-axis aberrations and always away from the paraxial image plane and always have a minimum depth on the drum surface. What is necessary is just to design so that a suitable spot may be comprised.

Embodiment 2 adopts the former. That is, design to widen the depth of focus,
That is, the amount of tilt of the photoconductor drum is set so that the surface of the photoconductor drum exists within the depth of focus even if the photoconductor drum is tilted.

Even when such an arrangement is adopted, it is possible to realize a state where the imaging spot performance is sufficiently narrowed down.

In FIG. 2, the image surface and the drum surface intersect within the main scanning range for outputting a document. More specifically, since the principal rays of the two scanning light beams intersect at approximately the center of the main scanning range, the principal rays are before and after the intersection at both ends in the main scanning direction on the inclined drum surface. As a result, the main scanning jitter can be reduced.

FIG. 3 is an optical path diagram when the image surface and the drum surface intersect outside the main scanning range. In the main scanning range, the image surface and the drum surface are always separated. If the principal rays of the two light beams do not intersect in the main scanning range, the positional relationship between the two light beams at both ends of the main scanning range will not be reversed. Therefore, by changing the writing timing of the two light beams, that is, changing the polarization angle of the light beam by a deflector such as a polygon mirror, the position where the principal light beams intersect can be set at an arbitrary position away from the image plane. That is, the timing at which the two light beams intersect at the center of the main scanning range on the drum surface is defined as the writing timing. Thereby, even if the image plane and the drum surface do not coincide / intersect in the main scanning range, the main rays can intersect in the main scanning range. The positional relationship of the light beam in the main scanning direction can be reversed.

As a result, the effect of reducing the main scanning jitter can be similarly obtained. In this case, care must be taken that the drum surface is within the depth of focus because the drum surface is farther away from the image surface than when the image surface and the drum surface intersect within the main scanning range. It is.

As described above, according to the present invention, the effect can be obtained irrespective of the position where the image plane and the scanned surface intersect. However, the distance from the image surface of the drum surface can be relatively small when crossing in the main scanning range, especially near the center thereof.

Third Embodiment FIG. 4 is an optical path diagram of a three-beam scanning optical system according to a third embodiment. Light beams A, B, and C emitted from a three-beam array laser (not shown) pass through a condenser lens, are deflected by a polygon mirror, and reach a drum surface through a fθ lens (not shown). In the three-beam array laser, three light-emitting points are arranged in one line, a central light-emitting point B passes on the axis of the condenser lens, and A and C propagate on both sides thereof in the same manner as in the case of the two-beam laser. As a result, on the photosensitive drum, A, B,
Spots arranged by three light beams of C are scanned side by side.

The light beams A, B, and C are not parallel to each other because they have an angle of view when entering the condenser lens. Therefore, in order to expose the same position in the main scanning direction with the A, B, and C lasers, the polygon rotation positions are different (ie, not at the same time). Is overlaid on the expression.

The problem here is the main scanning jitter generated between the light beams A, B, and C of the three-beam array laser.

Here, the image plane constituted by the luminous flux at each angle of view is shown by a straight line in the figure, but it is inclined with respect to the drum surface. Here, the drum surface is perpendicular to the symmetry axis of the fθ lens, but the image surface is inclined. As shown in the figure, the light beams A and C at both ends in the main scanning direction once intersect on the image plane. Then, the light is irradiated onto the drum surface in a mutual positional relationship according to the positional relationship between the drum and the image plane. The image plane here is a paraxial image plane, and the rays shown here are the principal rays of A and C, respectively. Therefore, the arrival positions of the respective light beams are switched at both ends in the main scanning direction as shown in the figure, and the A light beam is always located outside. The image plane is configured to be inclined in this manner, but the depth of focus is designed to be wide enough to always include the position on the drum, or the output of the off-axis Halo aberration is adjusted to always leave the drum surface away from the paraxial image plane. What is necessary is just to design so that the minimum spot may be formed on the upper part.

Even when such an arrangement is employed, it is possible to realize a state where the imaging spot performance is sufficiently narrowed down. The main scanning jitter caused by this arrangement and the main scanning jitter caused by the cause shown in FIG. 6 (with the light beam B in FIG. 6 replaced by the light beam C) are set so as to occur simultaneously in the opposite signs, thereby reducing the main scanning jitter. An offset effect is obtained.

[Embodiment 4] FIG.
FIG. 3 is an optical path diagram of a beam scanning optical system. Light beams A, B, C, and D emitted from a three-beam array laser (not shown) are deflected by a polygon mirror via a condenser lens and reach the photosensitive drum surface via an fθ lens (not shown). In the four-beam array laser, four light-emitting points are arranged in one line, and each light-emitting point has a symmetric axis centered on the optical axis of the condenser lens, A and D are outside, B and B are outside.
C propagates on one side in the same way as in the case of a two-beam laser. As a result, four of A, B, C and D on the photosensitive drum
The spots arranged with the light beam are scanned side by side.

The light beams A, B, C, and D are not parallel to each other because they have an angle of view when entering the condenser lens. Therefore, in order to expose the same position in the main scanning direction with the A, B, C, and D lasers, the polygon rotation positions are different (that is, not at the same time). It is expressed repeatedly like.

The problem here is the main scanning jitter generated between the light beams of the four-beam array lasers A, B, C and D.

Here, the image plane formed by the luminous flux at each angle of view is shown by a straight line in the figure, but it is inclined with respect to the drum surface in the figure. Here, the drum surface is perpendicular to the symmetry axis of the fθ lens, but the image surface is inclined. As shown in the figure, the light beams A and D at both ends in the main scanning direction once intersect on the image plane. Then, the light is irradiated onto the drum surface in a mutual positional relationship according to the positional relationship between the drum and the image plane. The image plane here is a paraxial image plane, and the rays shown here are the principal rays of A and D, respectively. Therefore, the arrival positions of the respective light beams are switched at both ends in the main scanning direction as shown in the figure, and the A light beam is always located outside. The image plane is configured to be inclined in this manner, but the depth of focus is designed to be wide enough to always include the position on the drum, or the output of the off-axis Halo aberration is adjusted to always leave the drum surface away from the paraxial image plane. What is necessary is just to design so that the minimum spot may be formed on the upper part.

Even when such an arrangement is adopted, it is possible to realize a state where the imaging spot performance is sufficiently narrowed down.

The main scanning jitter due to this arrangement and FIG.
The light beam AB is replaced with the light beam AD or the light beam BC), and the main scanning jitter caused by the cause shown in FIG.

[0053]

According to the present invention described above, it is possible to obtain a good image with little main-scanning jitter while taking an arrangement for preventing reflection coast from a drum in a multi-beam optical system.

[Brief description of the drawings]

FIG. 1 is an optical path diagram of a two-beam scanning optical system according to the present invention when the optical axis of an fθ lens is not perpendicular to a paraxial image plane.

FIG. 2 is an optical path diagram of the two-beam scanning optical system of the present invention when the optical axis of the fθ lens is not perpendicular to the drum surface.

FIG. 3 is an optical path diagram of a two-beam scanning optical system according to the present invention when a paraxial image plane and a drum surface intersect outside a scanning area.

FIG. 4 is an optical path diagram of a three-beam scanning optical system according to the present invention.

FIG. 5 is an optical path diagram of a four-beam scanning optical system according to the present invention.

FIG. 6 is an optical path diagram of a conventional multi-beam scanning optical system in which main scanning jitter occurs.

[Explanation of symbols]

A, B, C, D A ', B', C ', D' Laser beam Δ, Δ 'Main scanning jitter

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Claims (15)

[Claims] 1. A scanning optical system using light beams from at least two light sources, wherein an image plane in the main scanning direction of the scanning optical system has an optical axis with respect to a surface to be scanned in a cross section in the main scanning direction. A light beam incident on the surface to be scanned in a cross section in the sub-scanning direction of the light beam is other than vertical. 2. A recording apparatus using a scanning optical system that uses light beams from at least two light sources, wherein an image plane of the scanning optical system in a main scanning direction has an image carrier surface in a cross section in the main scanning direction. To the optical axis direction,
A recording apparatus using a scanning optical system, wherein an incident angle of the light beam on the image carrier surface in a section in the sub-scanning direction is other than perpendicular. 3. A scanning optical system using luminous fluxes from at least two light sources, wherein (1) an image plane of the scanning optical system in a main scanning direction has a cross section with respect to a surface to be scanned in a cross section in the main scanning direction. (2) the incident angle of the light beam from the at least two light sources on the cross-section in the sub-scanning direction when the light beam is incident on the surface to be scanned is other than perpendicular; 2. The scanning optical system according to claim 1, wherein the positional offset in the main scanning direction caused between the light beams at the main scanning end on the surface to be scanned is offset by each arrangement. 4. A recording apparatus using a scanning optical system using light beams from at least two light sources, wherein (1) an image plane of the scanning optical system in the main scanning direction is a cross section in the main scanning direction. (2) an incident angle of a light beam from the at least two light sources in a cross section in the sub-scanning direction when the light beam is incident on the image carrier surface is other than perpendicular; 3. The scanning optical system according to claim 2, wherein the positional deviation in the main scanning direction between the light beams at the main scanning end on the image carrier is offset by each of the arrangements (1) and (2). Recording device using. 5. When viewed in a projected component with respect to the cross section in the main scanning direction, the surface to be scanned or the surface of the image carrier and the image plane of the scanning optical system are inclined at both ends in the main scanning direction. 4. The apparatus according to claim 1, wherein the surface to be scanned or the surface of the image carrier is within a predetermined depth of focus with respect to the image plane within the main scanning range. A multi-beam scanning optical system according to any one of the above. 6. When viewed in a projected component with respect to the cross section in the main scanning direction, the surface to be scanned or the surface of the image carrier and the image plane of the scanning optical system are inclined at both ends in the main scanning direction. 5. The method according to claim 2, wherein the surface to be scanned or the surface of the image carrier is within a predetermined depth of focus with respect to the image plane within the main scanning range. A recording device described in any one of the above. 7. The apparatus according to claim 5, wherein the depth of focus of the image plane is defined on the condition that the size of an image forming spot of the light beam does not degrade recorded image quality below a predetermined condition. And a recording apparatus using the same. 8. The apparatus according to claim 6, wherein the depth of focus of the image plane is defined on the condition that the size of the image forming spot of the light beam is within a range that does not deteriorate the quality of a recorded image below a predetermined condition. The recording device as described in the above. 9. A multi-beam scanning optical system according to claim 6, wherein the depth of focus of said image plane is within a range that does not degrade the quality of a recorded image below a predetermined condition. The change in the size of the imaging spot is within 15% of the size of the imaging spot at the image plane position at a diameter of 1 / e ² of the peak intensity. 8. The multi-beam scanning optical system according to 7. 10. The depth of focus of the image plane within a range that does not degrade the quality of a recorded image below a predetermined condition depends on the change in the size of the image spot of the light beam at the position of the image spot at the image plane position. 9. The recording apparatus according to claim 8, wherein a diameter of 1 / e ² of the peak intensity is within 15% of the size. 11. A multi-beam scanning optical system according to claim 1, wherein the recording device uses the scanning surface or the image carrier when viewed in a projection component with respect to a cross section in the main scanning direction. The image plane of the scanning optical system is separated from each other as it goes to both ends in the main scanning direction because they are inclined with respect to each other, but the image spot quality at the image plane position within the main scanning range A multi-beam scanning optical system, wherein an off-axis Halo aberration characteristic of an fθ lens is set so that an image spot quality is optimal for image formation on the surface to be scanned or the surface of the image carrier. And a recording device using the same. 12. When viewed as a projected component with respect to a cross section in the main scanning direction, the surface to be scanned or the surface of the image carrier and the image surface of the scanning optical system are inclined at both ends in the main scanning direction because they are inclined with respect to each other. It moves away from each other as it travels, but not the quality of the imaging spot at the image plane position within the main scanning range,
The off-axis Ha of the fθ lens is adjusted so that the image spot quality is optimal for image formation on the surface to be scanned or the surface of the image carrier.
2. An aberration characteristic of lo is set.
3. The multi-beam scanning optical system according to any one of 3. 13. A projection component in the main scanning direction with reference to an optical axis of a light beam substantially reaching the center of the main scanning range, and a main scanning direction based on an optical axis of a light beam reaching substantially the center of the main scanning range. In the projection component, the image plane is designed to be non-perpendicular to the reference optical axis, while the surface to be scanned or the surface of the image carrier is made substantially perpendicular, so that the surface to be scanned or the image 5. The recording apparatus according to claim 2, wherein the carrier surface and the image surface are configured to be inclined with respect to each other in the main scanning direction. 14. An image plane is designed to be substantially perpendicular to the reference optical axis in a projection component in the main scanning direction with reference to an optical axis of a light beam reaching a substantially center of the main scanning range; On the other hand, the scanned surface or the image carrier surface is made non-perpendicular, and as a result, the scanned surface or the image carrier surface and the image surface are configured to be non-parallel to each other in the main scanning direction. 3
A multi-beam scanning optical system according to any one of the above. 15. An image plane is designed to be substantially perpendicular to the reference optical axis in a projected component in the main scanning direction with reference to an optical axis of a light beam reaching a substantially center of the main scanning range; On the other hand, the surface to be scanned or the surface of the image carrier is made non-perpendicular, and as a result, the surface to be scanned or the surface of the image carrier and the image surface are configured to be non-parallel to each other in the main scanning direction. 4
A recording device described in any one of the above.