JP2000330045A - Multi-beam scanner and scanning length matching method for multi-beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a multi-beam scanner which does not require any expensive beam synthesizing optical system, uses scanning and image forming elements having high degrees of freedom for design, and can highly match the scanning lengths of a plurality of beams to each other. SOLUTION: This multi-beam scanner is provided with a plurality of light sources 11 and 12, a plurality of first optical systems 13 and 14 which couple the light sources 11 and 12 with each other, and a second optical system 15 which condenses the beams from the first optical systems 13 and 14 into a linear beam which is long in the main scanning direction. The scanner is also provided with a deflector 16 having a deflecting and reflecting surface 17 which is separated from its rotation axis AX by a prescribed distance, and a third optical system containing scanning and image forming elements 18 and 19 which scan a surface to be scanned at about equal speeds. The light sources 11 and 12 have a light emitting wavelength difference Δλ between them and the two beams made incident to the deflector 16 have an angle of opening α in a deflective rotation plane and are nonparallel beams having a nonparallelism of D in the main scanning direction. The third optical system has a chromatic aberration of Δf at its focal distance and the Δλ, α, D, and Δf are set so that the difference between the scanning lengths of the beams may become a prescribed amount or smaller at the same deflective rotational angle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam scanning device and a scanning length matching method in the multi-beam scanning device.

[0002]

2. Description of the Related Art A plurality of beams from a plurality of light sources are deflected by a common deflector and condensed on a surface to be scanned by a common scanning image forming element to form a plurality of spots separated in a sub-scanning direction. A multi-beam scanning device that scans a plurality of lines with these plurality of spots is being put into practical use,
Various types have been proposed. Japanese Patent Application Laid-Open No. 8-304722 discloses one such multi-beam scanning device.
In this publication, two light sources are arranged substantially in a plane of rotation of deflection, and the beams from each light source are collimated into parallel beams, respectively, toward each other toward the deflection reflecting surface of the deflector. Although it is designed to be incident while approaching, it is excellent in that an expensive beam combining optical system is not required. Even in a multi-beam scanning device, a scanning imaging element for condensing a deflected beam on a surface to be scanned is a very important element, and it is no exaggeration to say that the quality of multi-beam scanning is determined by the scanning imaging element. . A semiconductor laser is generally used as a light source in a multi-beam scanning device. Recently, light sources having various emission wavelengths have been commercially available. However, if there are two or more types of light sources having different emission wavelengths in the multi-beam scanning device, it is necessary to correct chromatic aberration in the scanning image forming element. JP-A-8-3047
In the multi-beam scanning device described in Japanese Patent Application Laid-Open No. 22, the beam from each light source is deflected in a state of being converted into a parallel beam and is incident on the scanning image forming element. Therefore, the scanning image forming element collects the parallel beam on the surface to be scanned. Although it is designed to make light, from the standpoint of designing a scanning imaging element, the beam incident on the scanning imaging element is not limited to a parallel beam, leaving room for a convergent beam or a divergent beam. This increases the degree of freedom of design and facilitates design. Further, for example, when a convergent beam is made incident on the scanning imaging element, the power of the scanning imaging element can be reduced as compared with the case where a parallel beam is incident, and the thickness of the lens included in the scanning imaging element can be reduced. The lens can be made thinner, and the difference between the center thickness and the peripheral thickness (thickness) when the lens is formed by resin molding can be reduced, so that there is an advantage that the cooling time can be shortened and "sink" can be reduced. However, in the multi-beam scanning apparatus disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 8-304722, when a "deflecting reflecting surface and its rotation axis are separated" such as a rotary polygon mirror is used as a deflector, When a plurality of beams incident on the beam are made non-parallel beams, as described later, the scanning length of each beam for the same deflection angle of the beam by the deflector does not become the same,
"Line in the sub-scanning direction (vertical line)" by multi-beam scanning
Is written, the vertical line fluctuates (especially remarkable at the end of the scanning area) in the recorded image, which causes deterioration in the image quality of the recorded image.

[0003]

SUMMARY OF THE INVENTION The present invention does not require an expensive beam synthesizing optical system, has a high degree of freedom in designing a scanning image forming element, and has a high degree of matching of the scanning length of a plurality of beams. It is an object to realize a scanning device. Another object of the present invention is to realize a scanning length matching method for matching the scanning lengths of a plurality of beams in the multi-beam scanning device.

[0004]

According to the present invention, there is provided a multi-beam scanning apparatus comprising: a plurality of light sources; a plurality of first optical systems;
It has an optical system, a deflector, and a third optical system. The “plurality of light sources” are arranged at predetermined intervals substantially in the plane of rotation of deflection. The “plurality of first optical systems” respectively couple the plurality of light sources. The "second optical system" condenses each beam from the plurality of first optical systems in a substantially linear shape long in the main scanning direction. The “deflector” has a deflecting / reflecting surface in the vicinity of the substantially linear condensing portion, deflects each beam from the second optical system side at a constant angular velocity, and the deflecting / reflecting surface and its rotation axis A predetermined distance away. The “third optical system” condenses each beam deflected by the deflector toward the surface to be scanned, forms a spot separated in the sub-scanning direction on the surface to be scanned, and has a substantially constant velocity of the surface to be scanned. Includes a “scanning imaging element” that performs effective scanning.
In the above, the “deflection rotation surface” is a surface orthogonal to the rotation axis of the deflector. Multiple light sources (preferably semiconductor lasers)
Are disposed substantially in the plane of deflection rotation, in which case
It is not necessary that all light sources be arranged "in the same plane of deflection rotation". For example, when four light sources are considered, two of them may be provided in the first deflection rotation surface, and the remaining two may be provided in the second deflection rotation surface. . The number of the first optical systems may be the same as the number of the light sources, and the light sources may be used in a one-to-one correspondence. However, it is also possible that one first optical system couples a plurality of light sources. The beam from each light source must form a "spot separated in the sub-scanning direction" on the surface to be scanned. For this purpose, each light source and a first coupling
What is necessary is just to adjust the positional relationship between the optical system and the optical axis. For example,
If there are two light sources and two first optical systems, two first
The optical axis of the optical system is located in the same deflection rotation plane,
The light emitting units of the light source corresponding to the optical system may be arranged so as to be shifted in the sub-scanning direction in opposite directions with respect to the optical axis. In this case, due to the shift in the sub-scanning direction, the light emitting portion of each light source is not strictly within the plane of rotation for deflection. In the above description, the expression that the plurality of light sources are “substantially” disposed in the deflection rotation plane includes the case where the light emitting unit of the light source is slightly shifted from the deflection rotation plane in the sub-scanning direction. . In the deflector, the deflecting reflection surface and its rotation axis are separated by a predetermined distance. As such a deflector, a rotating polygon mirror,
A rotating two-sided mirror, or a rotating single-sided mirror in which the rotation axis does not coincide with the deflecting reflection surface can be used. "Third optical system"
Has a function of condensing the deflected beam toward the surface to be scanned, but includes one or more lenses.
The scanning imaging element can also include a reflecting mirror (concave mirror / convex mirror) having an imaging function in addition to one or more lenses. The third optical system may include, in addition to the scanning image forming element,
A "folding mirror" for bending the optical path of the deflected beam can be appropriately included. The multi-beam scanning device according to the first aspect has the following features. That is, at least two of the plurality of light sources have an emission wavelength difference:
At least two light rays emitted from a plurality of light sources having Δλ and having an emission wavelength difference: Δλ and entering the deflector from the second optical system
The beam has an opening angle: α in the plane of deflection rotation. The at least two beams are non-parallel beams having non-parallelism: D in the main scanning direction, and the third optical system has chromatic aberration of focal length: Δf. Chromatic aberration at this focal length: Δf
Is for the above emission wavelength difference: Δλ. The emission wavelength difference: Δλ, the opening angle: α, the non-parallelism: D, and the chromatic aberration of the focal length of the at least two beams so that the difference in scanning length for the same deflection rotation angle is equal to or less than a predetermined amount. Δf is set. The “opening angle” is such that when the two beams are incident on the deflector, when the respective beams are viewed from the rotation axis direction of the deflector, the principal ray of the two beams opens “from the deflector side to the light source side”. Angle ".
The “deflection rotation angle” refers to the angle at which each beam rotates while being deflected by the deflector. The non-parallelism D is related to the main scanning direction, and is defined as the reciprocal of the distance (unit: m) from the starting point of deflection by the deflector to the natural focal point in the main scanning direction, as described later. You. Non-parallelism: D is "positive" for a convergent beam and "negative" for a divergent beam. The “scanning length” is synonymous with a so-called writing width, and is a moving length of a spot for writing.

In the multi-beam scanning device according to the first aspect, when each beam emitted from a plurality of light sources having an emission wavelength difference: Δλ is incident on the deflector, the non-parallelism in the main scanning direction: D A beam having a large specific incident angle to the deflector (an angle formed by a reference line to be described later and a principal ray of the incident beam) may be configured to have a shorter wavelength. ). In this case, the convergent beam in the main scanning direction may be a “weak convergence beam” or a “strong convergence beam”. By making the incident beam a convergent beam, the lens center thickness of the scanning image forming element can be reduced and the thickness deviation can be reduced, so that the working and forming can be facilitated and the scanning image forming element can be realized at low cost. The multi-beam scanning device according to claim 1 or 2,
The optical system is a cylinder lens and is shared by multiple beams. "
(Claim 3). In addition to the first optical system,
A concave cylinder mirror can also be used. Further, the second optical system may be separately provided for each beam. When the cylinder lens of the second optical system is shared by a plurality of beams as in the second aspect of the present invention, a configuration in which one cylinder lens is used despite the plurality of light sources is possible, and the cost of parts can be reduced. In the multi-beam scanning device according to the first, second or third aspect, the scanning image forming element of the third optical system can be constituted by "one or more lenses" (claim 4). Of course, the scanning imaging element can be constituted by a single lens, but when it is constituted by several sub-lenses, it is preferable that these lenses do not include a lens having negative power. ). Since the constituent lens has no negative power, it has chromatic aberration of the focal length irrespective of the material, so that setting of the chromatic aberration is easy. When the scanning image forming element is composed of several sub-lenses, they can be composed of the same material. When the scanning imaging element is made of the same material as described above, chromatic aberration of a necessary focal length can be maintained, and when a lens is formed by molding, material exchange is not required at the time of molding, and the efficiency of material management is high. In the multi-beam scanning device according to any one of claims 1 to 6, one or more lenses constituting the scanning image forming optical system can be formed by a "molding method using a plastic material". .
This makes it possible to mass-produce the scanning imaging element at low cost. The multi-beam scanning device according to any one of claims 1 to 7, wherein a wavelength difference is provided as necessary:
The scan start timing can be made different between the two beams having Δλ (claim 8). In this manner, the scanning start position and the scanning end position can be adjusted, and the slight difference in the "scan length" is distributed to the scanning start side and the scanning end side, thereby improving the image quality of the recorded image. It is possible to further increase. In the multi-beam scanning apparatus according to any one of the first to eighth aspects, the number of light sources arranged at predetermined intervals substantially in the plane of rotation of deflection can be two (claims). 9).

The "scanning length matching method in a multi-beam scanning apparatus" of the present invention is directed to a method of coupling a plurality of light sources arranged at predetermined intervals substantially in a plane of rotation of deflection and a plurality of light sources, respectively. A plurality of first optical systems,
A second optical system that converges the beams from the plurality of first optical systems in a substantially linear manner in the main scanning direction, and a deflecting / reflecting surface near the substantially linear converging unit; Each beam from the optical system is deflected at a constant angular velocity, and a deflector in which the deflecting reflection surface and its rotation axis are separated by a predetermined distance, and collects each beam deflected by the deflector toward the surface to be scanned. A third optical system including a scanning imaging element for emitting light, forming spots separated in the sub-scanning direction on the surface to be scanned, and performing substantially constant-speed scanning of the surface to be scanned; Two beams incident on the deflector from the system have an opening angle: α in the plane of rotation of deflection, and the two beams are non-parallel beams having a non-parallelism: D in the main scanning direction. Emission wavelength difference between: Δ
In a multi-beam scanning apparatus in which there is λ and the scanning imaging element of the third optical system has a chromatic aberration of the focal length: Δf, a method of matching the scanning lengths of the two beams for the same deflection angle with each other, The opening angle: α, the non-parallelism: D, the emission wavelength difference: Δλ, and the chromatic aberration: Δf are set so that the scanning lengths of the two beams for the same deflection rotation angle are substantially equal. (Claim 1
0). This method is a method for matching the scanning length between two beams. However, when the number of light sources is two or more, there is no limitation on the two beams for matching the scanning length. The above method can be applied to a desired combination of two beams. In various cases, the opening angle: α, the non-parallelism: D, the emission wavelength difference: Δλ, and the chromatic aberration: Δf are set so that the scanning lengths of the two beams for the same deflection rotation angle are substantially equal. It is possible. For example, an opening angle: α and a non-parallelism: D are set in advance as design conditions, and according to the conditions set in this way,
Emission wavelength difference: Δλ and chromatic aberration Δ so that scanning lengths match
f can be selected, and the aperture angle: α and the emission wavelength difference: Δλ are set in advance as design conditions. Under these conditions, the non-parallelism: D and the chromatic aberration Δ are adjusted so that the scanning length matches.
f can also be selected. Alternatively, it is also possible to set the opening angle: α, the emission wavelength difference: Δλ, and the non-parallelism: D as design conditions, and select the chromatic aberration Δf so that the scanning length matches under these conditions.

[0007]

FIG. 1 shows an embodiment of a multi-beam scanning apparatus according to the present invention. In the figure, reference numerals 11 and 12 indicate semiconductor lasers as “light sources”, and reference numeral 1
Reference numerals 3 and 14 denote coupling lenses as a “first optical system”, reference numeral 15 denotes a cylinder lens as a “second optical system”, reference numeral 16 denotes a rotating polygon mirror as a “deflector”, reference numeral 1
Reference numeral 7 denotes a deflecting / reflecting surface, reference numerals 18 and 19 denote lenses constituting a “scanning imaging element of the third optical system”, and reference numeral 20 denotes a “scanned surface”.
Are respectively shown. FIG. 1 shows the rotary polygon mirror as a deflector viewed from the direction of the rotation axis AX, and therefore, the drawing is parallel to the “deflection rotary surface”. The semiconductor lasers 11 and 12 as a plurality of light sources are substantially arranged at predetermined intervals in the plane of rotation of deflection. Each beam emitted from the semiconductor lasers 11 and 12 (semiconductor laser 1
The beam from 1 is referred to as a “first beam”, and the beam emitted from the semiconductor laser 12 is referred to as a “second beam”. The coupling lenses 13 and 14 couple the beams to subsequent optical systems, respectively. In the embodiment, each beam after the coupling lenses 13 and 14 is a “convergent beam”. Each beam from the coupling lenses 13 and 14 is incident on a cylinder lens 15 provided in common to the first and second beams, and
The light is converged in the sub-scanning direction (the direction orthogonal to the drawing) by the action of 5, and is condensed in a substantially linear shape in the main scanning direction near the deflecting reflection surface 17 of the rotary polygon mirror 16. Semiconductor laser 11, 1
2. The positional relationship between the coupling lenses 13 and 14 is determined so that the principal rays of the first and second beams incident on the deflector 16 form an opening angle α as shown in the figure. The opening angle α is, as described above, when the first and second beams are incident on the deflector and these two beams are viewed from the direction of the rotation axis AX of the rotary polygon mirror 16 (the direction perpendicular to the drawing). This is the “angle formed so that the two beams are opened from the rotating polygon mirror 16 toward the light sources 11 and 12”.
The first and second beams reflected by the deflecting / reflecting surface 17 of the rotary polygon mirror 16 sequentially pass through the lenses 18 and 19 while being deflected at a constant angular velocity with the rotation of the rotary polygon mirror 16 at a constant speed. , 19, the light is converged toward the surface to be scanned 20 to form a spot on the surface to be scanned 20.
These spots scan the scanned surface 20. The lenses 18 and 19 forming the scanning image forming element are set to have “constant velocity characteristics” such that the movement of each beam spot on the surface to be scanned is substantially constant velocity movement. In addition, the light emitting units of the semiconductor lasers 11 and 12 have optical axes of the corresponding coupling lenses 13 and 14 (both are in the deflection rotation plane) so that the two spots are separated in the sub-scanning direction on the surface 20 to be scanned. ), At least one is shifted by a small distance in the sub-scanning direction. The scanned surface is actually a “photosensitive surface of a photosensitive recording medium”, specifically, for example, a photosensitive surface of a photoconductive photosensitive member, a photosensitive surface of a photosensitive film for plate making, or the like. The embodiments described above are summarized as follows.

That is, the multi-beam scanning apparatus whose embodiment is shown in FIG. 1 comprises a plurality of light sources 11 and 12 and a plurality of light sources which are arranged at predetermined intervals substantially in a plane of rotation of deflection. And a second optical system 15 for condensing each beam from the plurality of first optical systems in a substantially linear shape in the main scanning direction.
And a deflecting / reflecting surface 17 in the vicinity of the substantially linear condensing portion, and deflects each beam from the second optical system side 15 at a constant angular velocity, so that the deflecting / reflecting surface 17 and its rotation axis AX are at predetermined positions. The deflector 16 separated by a distance and the beams deflected by the deflector are condensed toward the surface to be scanned 20 to form spots separated in the sub-scanning direction on the surface to be scanned. A third image including the scanning imaging elements 18 and 19 for performing scanning at substantially constant speed
An optical system and two beams incident on the deflector 16 from the second optical system 15 have an opening angle α in the deflection rotation plane, and these two beams are convergent non-parallel beams in the main scanning direction. It is. Now, as in the embodiment of FIG.
If the two beams incident on the rotary polygon mirror 16 have an opening angle: α and the two beams incident on the rotary polygon mirror 16 are non-parallel beams (convergent beams) in the main scanning direction, the rotary polygon mirror 16
The scanning lengths of the first and second beams for the same deflection angle of the beam due to the above are not the same. This will be described with reference to FIG. 2 (a) and 2 (b), reference numerals B1, B
Numeral 2 indicates the first and second beams, respectively, and reference numeral 18A indicates the “scanning imaging element as a single lens”. In FIG. 2A, the first beam B1 and the second beam B2 are non-parallel beams in the main scanning direction (a direction parallel to the drawing), and in FIG. 2B, both the first and second beams B1 and B2 are main beams. It is a parallel beam in the scanning direction. Since the first and second beams B1 and B2 incident on the deflector 16 have an opening angle: α, the first beam B1 and the second beam B2 reflected by the deflecting reflection surface 17 of the deflector 16 are: Angle to each other: α
And enters the scanning imaging element 18A while spreading. Here, consider a state where each beam is directed to the outermost peripheral portion of the scanning area on the surface to be scanned 20. First, FIG.
In (b), a state in which the first beam B1 and the second beam B2 are directed to the position on the surface to be scanned indicated by the symbol A is considered. Assuming that the rotating direction of the rotary polygon mirror 16 is clockwise as shown by an arrow in the figure, the second beam B2 reflected by the deflecting / reflecting surface 17 is first reflected in the direction toward the point A, and the scanning image forming element 18A The light is focused toward point A by the action,
A spot is formed at point A. From this state, the rotating polygon mirror 1
6 rotates clockwise by an angle: α / 2, then the first
The beam B1 is reflected in the direction toward the point A. However, in the rotary polygon mirror 16, which is a deflector, the deflection reflecting surface 17 and its rotation axis AX are separated by a predetermined distance. Therefore, when the second beam B2 is reflected toward the point A and when the first beam B1 is reflected toward the point A, the reflection point on the deflecting / reflection surface 17 (the starting point of the reflected beam). Position) is different. For this reason, the principal ray of the first beam B1 reflected toward the point A does not coincide with the principal ray of the second beam B2 reflected toward the point A, as shown in the figure, and both principal rays are “each other”. parallel"
To separate. In FIG. 2B, the first beam B1,
Since both of the second beams B2 are “parallel beams in the main scanning direction”, the scanning imaging element 18A outputs the first beam B1, the second beam
Both beams B2 are focused on point A on the surface to be scanned. In FIG. 2B, the first and second beams deflected over the scanning area are shown.
The focal points of the beams B1 and B2 coincide with each other for the same deflection angle. Therefore, the “deflection rotation angle” of the first and second beams
Are θ1 and θ2 as shown in the drawing, if θ1 = θ2, the “scanning lengths” of the first and second beams B1 and B2 match each other. On the other hand, if the first beam B1 and the second beam B2 are "non-parallel beams in the main scanning direction" as in the case shown in FIG. The main beam of the second beam B2 reflected as shown in the drawing is converged toward the point A2 on the surface to be scanned by the operation of the scanning imaging element 18A, and a spot is formed at the point A2. From this state, the rotating polygon mirror 16 becomes
When rotated by α / 2, the principal ray of the first beam B1 is reflected in a direction parallel to the second beam B2 as shown in the figure, but the origin of the reflection at this time is “the second beam B2 is shifted to the point A2. From the point of reflection when condensing. Since both the first beam B1 and the second beam B2 are non-parallel to the main scanning direction, even if the principal rays of these two beams are parallel, the object points of these beams with respect to the scanning imaging element 18A are shifted in the main scanning direction. Therefore, the first beam B1 is
A spot is formed at point A1 on 0. That is, there is a difference “Δ” in the spot formation position between the first beam B1 and the second beam B2. Since the same occurs at the opposite end of the scanning area, if the deflection rotation angle: θ1 of the first beam B1 and the deflection rotation angle: θ2 of the second beam B2 are equal to each other (θ1 = θ2), the second beam The scanning length of B2 is the first
It is longer than the scanning length of the beam.

In the embodiment shown in FIG. 1, such a "difference in scanning length" is eliminated, and the scanning lengths of the first beam B1 and the second beam B2 are adjusted for the same deflection rotation angle. To match, do the following: That is, the semiconductor lasers 11 and 12 are provided with an emission wavelength difference: Δλ. And
The scanning imaging element has a chromatic aberration of the focal length: Δf with respect to the wavelength difference: Δλ. FIG. 2A is referred to again. The scanning imaging element 18A converges the “beam that is not parallel to the main scanning direction” incident thereon onto the surface to be scanned 20 and keeps the moving speed of each beam spot on the surface to be scanned constant. Assuming that the deflection angle of the beam is θ and the distance on the optical axis from the rear main surface of the scanning image forming element 18A to the surface to be scanned 20 is L, the moving speed of the beam spot is L · θ. The emission wavelength of the semiconductor laser 11 (the light source of the first beam B1) is “λ”, the emission wavelength of the semiconductor laser 12 (the light source of the second beam B2) is “λ + Δλ”, and the focal length of the scanning imaging element 18A is the wavelength. : F is “f” for λ and “f + Δf” for wavelength: λ + Δλ, this Δf is “chromatic aberration of focal length”. At this time, the first beam B1 is applied from the rear main surface of the scanning image forming element 18A.
If the distance to the imaging point is measured in the optical axis direction and is set to “L”, the same distance to the second beam B2 becomes “L + ΔL” due to the influence of chromatic aberration. ΔL is determined by the chromatic aberration: Δf and the non-parallelism of the beam: D. First and second beams B
If the deflection rotation angles of B1 and B2 are θ1 and θ2, respectively,
The scanning length for these deflection rotation angles is the first beam B
1 is “L · θ1” and the second beam B2 is “(L + ΔL) · θ2”. Same deflection rotation angle: θ
If 1 = θ2 = K, the scanning lengths are “L · K” and “(L + ΔL) · K”. Accordingly, as shown in FIG. 2A, the scanning length of the first beam B1 is
2 is shorter than the scanning length, the scanning imaging element 1
By giving the chromatic aberration of the focal length: Δλ such that “ΔL” becomes negative to 8A, and conversely, when the scanning length of the first beam B1 is longer than the scanning length of the second beam B2. For example, by giving the chromatic aberration of the focal length: Δλ such that the above “ΔL” is positive to the scanning imaging element 18A, the difference between the scanning lengths of the two beams can be reduced. That is, with respect to the first and second beams B1 and B2, the opening angle: α and the non-parallelism: D are set so that the difference in scanning length with respect to the same deflection rotation angle (θ1 = θ2) is equal to or smaller than a predetermined amount. Accordingly, the emission wavelength difference: Δλ and the chromatic aberration of the focal length: Δf can be set (claims 1 and 10).

In the embodiment shown in FIG. 1, as described above, when each beam emitted from the semiconductor lasers 11 and 12 enters the rotary polygon mirror 16, the degree of non-parallelism in the main scanning direction: D Is a positive convergent beam, the beam having a large natural rotation angle to the rotary polygon mirror 16 (the angle between the reference line in FIG. 1 and the principal ray of the angle incident beam, the first beam, the angle: β in FIG. 1) ( It is preferable that the second beam B2) has a shorter wavelength (Δλ <0) (claim 2). In the multi-beam scanning apparatus according to the embodiment shown in FIG. 1, the second optical system is a cylinder lens 15, which is shared by a plurality of beams (claim 3), and the third optical system has one scanning image forming element. It is composed of the above lenses 18 and 19 (claim 4). It is easy to impart chromatic aberration to the scanning imaging element. For example, if the scanning imaging element is constituted by a single lens, the single lens cannot correct the chromatic aberration, so that the chromatic aberration inevitably occurs. In this case, a desired “chromatic aberration of the focal length” can be realized by appropriately selecting the dispersion of the lens material. Further, when the scanning image forming element is composed of several sub-lenses, it may be configured so as to "do not include a lens having negative power in the main scanning direction" (claim 5), or The lens is made of the same material "
By doing so (claim 6), chromatic aberration of the focal length can be realized. With the above-described configuration, in the embodiment of FIG. 1, the difference between the scanning length and the same deflection rotation angle for the first and second beams is equal to or less than a predetermined amount (vertical line fluctuation is not visually recognized. ), And the scanning length can be matched. However, when the scanning lengths are adjusted in this manner, the scanning start point and the scanning end point by the second beam may be shifted in the same direction with respect to the scanning start point and the scanning end point by the first beam. In such a case, the scanning start positions of the first and second beams are made different from each other, whereby the scanning start positions of the respective beams can be aligned. In the multi-beam scanning apparatus according to the embodiment shown in FIG. 1, the number of light sources arranged at predetermined intervals substantially in the plane of rotation of deflection is two (claim 9).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Two specific embodiments will be described below. Examples 1 and 2 are specific examples of the embodiment shown in FIG. Embodiment 1 In the configuration shown in FIG. 1, after the first beam is reflected by the deflecting / reflecting surface 17, the reflected principal ray when the principal ray is orthogonal to the surface to be scanned 20 in the plane of the drawing is shown. "Reference line". The angle formed by the principal rays of the first and second beams incident on the rotary polygon mirror 16 with respect to this reference line is the “specific incident angle”, and the specific incident angle of the first beam (the angle β in FIG. 1).
Is 60 degrees and the specific incident angle of the second beam is 63.4 degrees. Therefore, at this time, the opening angle of the first and second beams: α =
3.4 degrees. The “reference wavelength” as a design standard of the optical system is 650 nm. Both the first and second beams are “convergent in the main scanning direction”. If these beams are left only to the convergence, the starting point of deflection by the rotary polygon mirror (when reflected in parallel with the reference direction) Converges in the main scanning direction at a position 847 mm from the lens (this convergence point is referred to as a “natural light converging point”). From this, the non-parallelism of the first and second beams in the main scanning direction: D is 1.18 (= 1 / 0.84).
7). The rotating polygon mirror 16 has six deflection reflection surfaces, and the distance (inscribed circle radius) from the rotation center AX to the deflection reflection surface 17 is 18 mm. When the first and second beams are reflected by the deflecting / reflecting surface 17 in the reference line direction, the angles of incidence of the first and second beams on the deflecting / reflecting surface are の of the specific incident angle.
Therefore, the first beam is 30 degrees and the second beam is 31 degrees.
7 degrees. Both beams cross in the main scanning direction substantially at the position of the deflecting reflection surface. Cylinder lens 1 forming second optical system
5 is shared by the first and second beams and is specified by the following data. Radius of curvature of the first surface (incident side surface) in the sub-scanning direction: R (cylinder surface) = 24 mm Second surface: flat Center thickness: 3 mm Refractive index at reference wavelength: 1.51452 Scanning imager of third optical system The child lenses 18, 19 are
Both surfaces of each lens have a non-arc shape in the main scanning direction and the sub-scanning direction. The non-arc shape in the main scanning direction is
The coordinates in the optical axis direction are X, the coordinates in the main scanning direction are Y, the paraxial radius of curvature is R _0m , the conic constant is K, and the higher order coefficients are M ₄ , M ₆ , M ₈ ,.
Can be expressed by the following well-known formula. X = Y ² / [R _0m + R _0m・ √ ｛1- (1 + K) Y ² / R _0m ² } + M ₄・ Y ⁴ + M ₆・ Y ⁶ + M ₈・ Y ⁸ + M ₁₀・Y ¹⁰ (1) The non-circular shape of the lenses 18 and 19 in the sub-scanning direction is
Coordinate: radius of curvature at Y: R _s (Y) is R _s (Y) = R _0s + S ₂ .Y ² + S ₃ .Y ³ + S ₄ .Y ⁴ +... + S ₁₂ .Y ¹² ( 2) A shape represented by (R _0s is a radius of curvature at Y = 0).

[0012] The center thickness of the lens 18: 15 mm The center thickness of the lens 19: 4.6 mm Both the lenses 18 and 19 are made of a polyolefin-based resin, and Nd = 1.53046, νd = 55.5.
N650 (wavelength: refractive index for light of 650 nm) =
1.52787. The lenses 18 and 19 are also provided with parallel movement eccentricity and rotational eccentricity with respect to the reference line. Distance from the reference line to the vertex of the incident side of the lens 18 (parallel movement eccentricity): 1.4 mm Distance from the reference line to the vertex of the incident side of the lens 19 (parallel motion eccentricity): -0.4 mm Rotational eccentricity of the lens 18: -11 'Rotational eccentricity of lens 19: 4' (clockwise rotation is plus in the figure) In the above data, for example, "E-04" is "10"
~ ⁴ ", and this numerical value is related to the immediately preceding numerical value. The same applies hereinafter. In the above arrangement, the emission wavelength of both the semiconductor lasers 11 and 12 is set to the reference wavelength: 650 nm, and the rotation angle (degree) of the rotary polygon mirror 16 and the beam spot condensing are set to 0 degree when the reference line and the deflecting surface are orthogonal to each other. The height (image height) is as follows. 1st beam 2nd beam Rotation angle Focus height Rotation angle Focus height -49.103 108.99648 -50.803 109.01930 -10.890 -106.84466 -12.590 -106.89264 Rotation angle width Focus height width Rotation angle width Focus height 38.213 215.84114 38.213 215.91194 The “rotation angle width” is “deflection rotation angle for each beam”, and the “condensing height width” is “scanning length”. As can be seen from the above results, when the emission wavelengths of the semiconductor lasers 11 and 12 are both set to the reference wavelength of 650 nm, the scanning length is 215.8 for the first beam for the same deflection rotation angle.
4114 mm, 215.991194 for the second beam
mm, 0.0708 mm = 70.8 μm (215.9
1194-215.84114) occurs in the scan length. Thus, the semiconductor laser 12 has an emission wavelength of 638.2 nm.
Use For the light of this wavelength, the lenses 18 and 1
The refractive index of 9 (consisting of the same material) is N638.2 =
1.52829, and the chromatic aberration of the scanning imaging element acts on the second beam. The rotation angle (degree) of the rotary polygon mirror 16 with respect to the second beam and the condensing height (image height) of the beam spot are as follows. Rotation angle Focusing height -50.803 108.98005 -12.590 -106.86131 Rotation angle width Focusing height width 38.213 215.84136 Therefore, the emission wavelength of the semiconductor laser 12 is 638.2.
nm, the difference between the scanning lengths of the first beam and the second beam is 0.24 μm, and the difference between the scanning lengths is about ３ as compared with the case where a semiconductor laser having both reference wavelengths is used.
It can be reduced to 20 and the vertical line fluctuation is almost invisible to the naked eye.

However, for the first beam, the second beam is:
The writing start position (scanning start position) is -16.43 µm, and the writing end position (scanning end position) is -16.65 µm, which is displaced in the same direction. Fine-tune. At this time, it is possible to set the synchronization timing so that the difference of the scanning length: 0.24 μm is distributed to the scanning start side and the scanning end side by 0.12 μm each. The image quality can be further improved.
In the above example, the emission wavelength of the semiconductor laser 12 was selected with reference to the semiconductor laser 11.
The emission wavelength of the semiconductor laser may be made different by using the emission wavelength of the semiconductor laser as a reference wavelength. Emission wavelength of the semiconductor laser 12: 65
0 nm, and the emission wavelength of the semiconductor laser 11 is 66
When 2.7 nm is selected, the refractive indices of the lenses 18 and 19 become N662.7 = 1.527 for this wavelength: 662.7 nm.
45, at this time, the rotating polygon mirror 1 for the first beam
Rotation angle (degree) of 6 and beam spot height (image height)
Is as follows. Rotation angle Focusing height -49.103 109.03179 -10.890 -106.88017 Rotation angle width Focusing height width 38.123 215.91196 That is, the difference in the scanning length of the first beam with respect to the second beam is 0.02 μm, which is sufficiently high performance. Multi-beam scanning is possible.

Embodiment 2 Angle between the principal ray of the first beam from the semiconductor laser 11 and the reference line: 60 degrees Angle between the principal ray of the second beam from the semiconductor laser 12 and the reference line: 64 degrees , The opening angle of the second beam: α = 4 degrees.
The “reference wavelength” as a design standard of the optical system is 650 nm. Both the first and second beams are “convergent in the main scanning direction”, and the natural focal point of these beams is 4860 mm from the starting point of deflection by the rotating polygon mirror. That is, the convergence is weaker than the first and second beams in the first embodiment. Non-parallelism of the first and second beams: D is 0.206 (= 1 /
4.860). The rotating polygon mirror 16 is the same as that in the first embodiment (the number of deflecting and reflecting surfaces: 6, the radius of the inscribed circle: 1).
8 mm). The specific incident angles of the first and second beams are 30 degrees for the first beam and 32 degrees for the second beam. Both beams cross in the main scanning direction substantially at the position of the deflecting reflection surface.
Both surfaces of the lenses 18 and 19 forming the scanning image forming element have a non-circular shape in both the main and sub-scanning directions, and their surface shapes are specified by the above-described equations (1) and (2). Center thickness of the first lens: 18 mm Center thickness of the second lens: 4.5 mm Distance from the reference line to the vertex of the incident side of the lens 18 (parallel movement eccentricity): 1.4 mm Distance from the reference line to the vertex of the incident side of the lens 19 (Parallel displacement eccentricity): 0.01 mm Rotational eccentricity of scanning lens 1: 0.8 'Rotational eccentricity of scanning lens 2: -13' In the above arrangement, when the emission wavelength of both semiconductor lasers 11 and 12 is set to the reference wavelength: 650 nm. , Rotating polygon mirror 1
Rotation angle (degree) of 6 and beam spot height (image height)
Is as follows. First beam Second beam Rotation angle Focus height Rotation angle Focus height -49.563 109.37417 -51.563 109.38121 -10.429 -106.88435 -12.429 -106.51706 Rotation angle width Focus height width Rotation angle width Focus height 39.134 215.88435 39.134 215.89827 As can be seen, the scan length is 0.013 for the same deflection rotation angle of the first and second beams: 39.134 degrees.
There is a difference of 92 mm = 13.92 μm. Therefore,
Assuming that the emission wavelength of the semiconductor laser 11 is maintained at the reference wavelength: 650 nm and the emission wavelength of the semiconductor laser 12 is 648 nm, the refractive index of the lenses 18 and 19 with respect to light of this wavelength is N648 = 1.52794, and the rotation with respect to the second beam. The rotation angle of the polygon mirror 16 and the condensing height of the beam spot are as follows. Rotation angle Focusing height -51.563 109.37428 -12.429 -106.51004 Rotation angle width Focusing height width 39.134 215.88432 The difference between the scanning length of the first beam and the second beam is 0.0.
3 μm, and the difference in scanning length is sufficiently reduced.
Also in this case, by finely adjusting the synchronization timing and distributing the difference in scanning length: 0.03 μm by 0.015 μm to the scanning start side and the scanning end side, multi-beam scanning leading to high image quality is realized. it can.

FIG. 3A shows the field curvature (left diagram), the constant velocity characteristic (linearity), and the fθ characteristic for the first beam (650 nm) in the first embodiment. FIG. 3 (b)
Shows the field curvature (left figure), constant velocity characteristics (linearity), and fθ characteristics for the second beam (638.2 nm) in the first embodiment. All show very good characteristics. Since the convergent beam is incident on the scanning image forming lens, the fθ characteristic is not a strict fθ characteristic, but is calculated by an equation of the fθ characteristic. Although an aberration diagram and constant velocity characteristics are not shown, extremely excellent performance equivalent to that of the first embodiment is also realized in the second embodiment. When the first embodiment and the second embodiment are compared, a great difference between the first embodiment and the second embodiment lies in a difference in non-parallelism (convergence) of the first and second beams incident on the deflector in the main scanning direction. In the first embodiment, a large convergence is positively employed in the non-parallelism. Since the convergence of the first beam and the second beam in the main scanning direction is increased in this manner, the positive power in the main scanning direction of the lenses 18 and 19 constituting the scanning image forming element can be effectively reduced, and the same specifications can be implemented. As compared with the case of Example 2, the center thickness of the lens 18 was successfully reduced by 3 mm. Since the thickness of the lens 18 is reduced by reducing the thickness of the lens 18, the lens 18 is manufactured by a plastic molding method (claim 7), which is advantageous in terms of cooling time and sink mark characteristics. In addition, by having a degree of freedom that a convergent beam and a divergent beam can be appropriately used as the form of the incident beam in the main scanning direction as a parameter of the optical system design, the overall performance balance can be brought to a high level. Embodiment 2 is an example in which the first and second beams are weakly converged to obtain high performance. When a little is captured, in the above-described embodiment, the scanning image forming element of the third optical system is constituted by the two lenses 18 and 19.
A configuration of three or more pieces may be used. If the scanning imaging element is constituted by a single lens, chromatic aberration cannot be corrected, which is generally disadvantageous. However, in the present invention, since chromatic aberration is effectively used, the existence of chromatic aberration is rather convenient. In the embodiment, each beam coupled by the first optical system is a strong convergent beam (embodiment 1) and a weak convergent beam (embodiment 2). However, each beam after coupling may be used as a divergent light beam. good. Further, in the multi-beam scanning, it is effective to separate two beams in the main scanning direction on the surface to be scanned in order to separate the synchronous detection of each beam. However, the present invention can be applied to this case.

[0016]

As described above, according to the present invention, a novel multi-beam scanning device and a scanning length matching method in the multi-beam scanning device can be realized. The multi-beam scanning device of the present invention does not require an expensive beam combining optical system, has a large degree of freedom in designing the optical system, and can realize good multi-beam scanning by effectively matching the scanning length of each beam. . The scanning length matching method of the present invention can effectively reduce the difference in scanning length between beams in a multi-beam scanning device. Further, when manufacturing a multi-beam scanning device, if magnification error detection is performed on beams from at least two light sources of a plurality of light sources, “variation in magnification error” until the scanning device is completed can be absorbed. Further, in any one of the processes up to the completion of the multi-beam scanning device, if a process of detecting a wavelength difference is provided for beams from at least two light sources of a plurality of light sources, the “wavelength until the multi-beam scanning device is completed” Variation in difference "can be absorbed.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of a multi-beam scanning device according to the present invention.

FIG. 2 is a diagram for explaining a mechanism that causes a difference in scanning length.

FIG. 3 is a diagram illustrating field curvature and constant velocity characteristics of a first beam and a second beam according to the first embodiment.

[Explanation of symbols]

11, 12 Semiconductor laser 13, 14 Coupling lens as a first optical system 15 Cylinder lens as a second optical system 16 Rotating polygon mirror as a deflector 17 Deflective reflecting surface 18, 19 Scanning imaging element of the third optical system Lens 20 to be scanned α opening angle

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Taku Amada 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (reference) 2H045 AA01 BA22 CA62 CA98

Claims (10)

[Claims] 1. A plurality of light sources substantially arranged at predetermined intervals in a deflection rotation plane, a plurality of first optical systems respectively coupling the plurality of light sources, and a plurality of first optical systems A second optical system that condenses each beam from the system in a substantially linear shape in the main scanning direction, and a deflecting / reflecting surface in the vicinity of the substantially linear condensing portion; Each beam is deflected at a uniform angular velocity, a deflector having the deflecting reflection surface and its rotation axis separated by a predetermined distance, and condensing each beam deflected by the deflector toward a surface to be scanned. A third optical system including a scanning imaging element that forms spots separated in the sub-scanning direction on the surface to be scanned and performs substantially constant-speed scanning of the surface to be scanned; At least two light emission wavelength differences:
Δλ, emitted from a plurality of light sources having the emission wavelength difference: Δλ,
At least two beams incident on the deflector from the second optical system have an opening angle: α in the deflection rotation plane, and the at least two beams are non-parallel beams having a non-parallelism: D in the main scanning direction. The third optical system has a chromatic aberration of the focal length: Δf, and the emission wavelength difference: Δλ, and the aperture of the at least two beams so that the difference in scanning length for the same deflection rotation angle is equal to or less than a predetermined amount. An angle: α, non-parallelism: D, and chromatic aberration of focal length: Δf are set. 2. The multi-beam scanning device according to claim 1, wherein each beam emitted from a plurality of light sources having an emission wavelength difference: Δλ has a non-parallelism in the main scanning direction: D at the time of entering the deflector. Is a positive convergent beam, and a beam having a large specific incident angle to the deflector has a shorter wavelength. 3. The multi-beam scanning device according to claim 1, wherein the second optical system is a cylinder lens and is shared by a plurality of beams. 4. The multi-beam scanning device according to claim 1, wherein the scanning image forming element of the third optical system comprises one or more lenses. 5. The multi-beam scanning device according to claim 4, wherein the scanning image forming element is constituted by a plurality of lenses, and does not include a lens having a negative power in the main scanning direction. apparatus. 6. A multi-beam scanning apparatus according to claim 4, wherein said scanning image forming element is composed of sub-several lenses made of the same material. 7. A multi-beam scanning apparatus according to claim 1, wherein at least one lens constituting a scanning image forming optical system is formed by a molding method using a plastic material. Multi-beam scanning device. 8. The multi-beam scanning apparatus according to claim 1, wherein the timing of starting scanning is made different between two beams having a wavelength difference of Δλ. . 9. The multi-beam scanning apparatus according to claim 1, wherein the number of light sources arranged at predetermined intervals substantially in the plane of rotation of deflection is two. Characteristic multi-beam scanning device. 10. A plurality of light sources arranged substantially at predetermined intervals in a deflection rotation plane, a plurality of first optical systems respectively coupling the plurality of light sources, and a plurality of first optical systems. A second optical system that condenses each beam from the system in a substantially linear shape in the main scanning direction, and a deflecting / reflecting surface in the vicinity of the substantially linear condensing portion; Each beam is deflected at a uniform angular velocity, a deflector having the deflecting reflection surface and its rotation axis separated by a predetermined distance, and condensing each beam deflected by the deflector toward a surface to be scanned. A third optical system including a scanning imaging element for forming spots separated in the sub-scanning direction on the scanned surface and performing substantially constant-speed scanning of the scanned surface; The two beams incident on the deflector have an opening angle: α in the plane of rotation of the deflection, and the two beams A non-parallel beam having a non-parallelism: D in the main scanning direction, and a light emission wavelength difference between the light sources emitting the two beams:
In a multi-beam scanning apparatus in which there is Δλ and the scanning imaging element of the third optical system has chromatic aberration of focal length: Δf, the scanning lengths of the two beams for the same deflection rotation angle are substantially equal. Opening angle: α, non-parallelism:
D, a method of adjusting a scanning length in a multi-beam scanning apparatus, wherein a difference in emission wavelength: Δλ and a chromatic aberration: Δf are set.