JPH04101112A - Multi-beam scanning optical system - Google Patents

Abstract

PURPOSE:To easily adjust scanning intervals of scanning lines on a scanned surface to a desired value and to form an image of high picture quality by providing an adjusting member which can adjust the scanning intervals of the scanning lines on the scanned surface in the path between a light source means and the scanned surface. CONSTITUTION:Plural light beams emitted by the light source means 1 are collimated by an optical means 2 which provides collimating operation into pieces of parallel luminous flux, which are made incident on the reflecting surface of an optical deflector 3. Then the respective light beams which are reflected by the reflecting surface of the optical deflector 3 form beam spots on the scanned surface 5 through an image formation optical system 4 for scanning to form (write) image information on the scanned surface 5 in order. In this case, an adjustment member 2 varies the focal length by varying the interval between two lens groups which are a front group 2a and a rear group 2b to vary the image formation magnification, thereby adjusting the scanning intervals of the scanning lines on the scanned surface (photosensitive medium surface) 5 to the desired value. Consequently, an image of improved picture quality can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a multi-beam scanning optical system, and more particularly, to a multi-beam scanning optical system that rotates a plurality of light beams emitted from the light source means using a light source means having a plurality of light emitting parts. The light is guided onto the surface of the photosensitive medium, which is the surface to be scanned, through an optical deflector such as a polygon mirror, and a plurality of light beams are
The present invention relates to a multi-beam scanning optical system suitable for a device such as a laser beam printer (LBP) that simultaneously performs optical scanning with a multi-beam beam to form image information, for example.

(Prior Art) Various so-called multi-beam scanning optical systems have heretofore been proposed in which the surface of a photosensitive medium, which is a surface to be scanned, is scanned all at once with a plurality of optical beams that can be optically modulated independently.

Generally, when forming an image by scanning a surface to be scanned with a light beam, it is necessary to reduce the diameter of the light beam spot on the surface to be scanned in order to obtain high resolution and good image quality. Therefore, when optically scanning a surface to be scanned using multiple light beams, it is necessary to form a dense spot of the light beam on the surface to be scanned in a direction perpendicular to the scanning direction, that is, in the sub-scanning direction. .

In a multi-beam scanning optical system, a light source means in which multiple semiconductor lasers or the like are arranged in one direction is often used.
A plurality of light beams emitted from the light source means are simultaneously guided onto the surface to be scanned for optical scanning.

When performing optical scanning using multiple semiconductor lasers as light source means, the method of arranging the light emitting parts (semiconductor lasers) is to arrange adjacent light emitting parts so that the interval (spot interval) between the beam spots on the scanned surface is smaller. Is there a way to arrange them so that the spacing is narrower?

However, it is very difficult to arrange adjacent light emitting parts with narrower intervals due to manufacturing limitations.

Therefore, conventional multi-beam scanning optical systems have been developed to compensate for the above-mentioned manufacturing defects of semiconductor lasers and scan the surface to be scanned simultaneously with a plurality of light beams.
Various proposals have been made in Publication No. 3019 and Japanese Patent Publication No. 1-45065.

(Problems to be Solved by the Invention) FIG. 4 is an explanatory diagram of a scanning surface when optically scanning a scanning surface in a conventional multi-beam scanning optical system.

In the figure, a light source array (light source means having a plurality of light emitting parts arranged in a row) at a slight angle θ with respect to the scanning direction AA' by a light beam from a light deflector such as a rotating polygon mirror (not shown) is shown.
The SA arrangement direction is tilted. This allows the pitch (interval) of scanning lines in the main scanning direction and sub-scanning direction on the scanning surface.
By changing P, a plurality of beam spots are densely imaged on the surface to be scanned.

In this case, there is a problem in that it is very difficult to adjust the angle .theta. at which the light source array is tilted in order to maintain a good degree of accuracy on the surface to be scanned. That is, in the figure, the angle between the scanning direction AA' and the arrangement direction BB' of the light source array SA is θ, and the interval between the light emitting parts of the light source array is P. shall be. Also, when M is the imaging magnification in the sub-scanning direction on the surface to be scanned by the optical member disposed in the optical path from the light source array to the surface to be scanned, the scanning interval P of the scanning lines on the surface to be scanned is p= It is given by 1Ml-Po sinθ ----- (1).

In equation (1) above, the angle θ is, for example, a minute angle Δ during manufacturing.
If an error of θ occurs, the interval error ΔP of the scanning interval P of the scanning line is ΔP= l M l − Pa s in Δθ −−
--(2).

Here, to give a specific numerical example, let's say the interval P between the light emitting parts of a 4f light source array. The value of is 0.05 mm, and the imaging magnification M is 12
．． 7 times, and the scanning line spacing error ΔP is intended to be within the permissible range for image formation, for example, 0.005 mm or less. At this time, according to the above equation (2), it is necessary to suppress the angular error Δθ to about 27 minutes or less, and as a result, it becomes extremely difficult to adjust the installation of the light source array.

In addition, there are multiple light beams emitted from the light source array (light source means) in a direction parallel to the deflection reflection surface of the optical deflector, and each principal ray emitted from the light source array passes through the collimator lens. Since the light is diverging, the deflection and reflection surface must be made large, which makes the optical deflector large, making it difficult to downsize the entire device.

5 and 6 are a schematic diagram of the main part of the scanning optical system proposed in Japanese Patent Publication No. 1-45065, and an explanatory diagram showing how a surface to be scanned is optically scanned.

In the figure, reference numeral 51 denotes a light source means, which has two light emitting sources (for example, semiconductor lasers) 51a and 51b. 52
53 is an objective lens (collimator lens), 53 is a light deflector such as a rotating polygon mirror, 54 is a scanning lens having f-θ characteristics, and 55 is a rotating cylinder having a photosensitive medium surface which is a surface to be scanned and rotates at a constant speed. It is the body.

1, fi2 are scanning lines along which the light beams emitted from the light emitting parts 51a and 51b optically scan the surface to be scanned 55a.

Now, the interval between the light emitting parts in the sub-scanning direction of the light beams from the light emitting parts 51a and 51b is P. , objective lens 52 and scanning lens 5
4, the imaging magnification in the sub-scanning direction by the synthesis system, M, the scanning interval of adjacent scanning lines on the scanned surface, P, and the light beam from the same light emitting unit on the scanned surface performs optical scanning. When Δ is the scanning interval of the scanning line, Δ=NP-P ・・・・・・・・・・・・・・・
...(3) p= l M l ・Pa / (nN+
1)・------(4). However, N is the number of light emitting parts, and n is an integer of 1 or more, so that multiple scanning lines do not overlap each other (overlap) and adjacent scanning lines (IL+, jQz
) are arranged at equal intervals.

FIG. 6 shows the state of the scanning line of optical scanning on the surface to be scanned when the above-mentioned formulas (3) and (4) are satisfied.

In the conventional scanning optical system shown in FIG. 5, as mentioned above, the light source array has manufacturing problems that cause errors in the pitch of the light emitting parts of the light source array, and the collimator lens that constitutes the scanning optical system. The focal length of the scanning lens may deviate from the set value due to errors in manufacturing. Then, for example, the scanning lines (beam spot imaging points) la'-1 and 1b' on the scanned surface shown in FIG.
1, an error occurs in the scanning interval P, making it impossible to obtain a uniform scanning interval, resulting in the problem of unevenness of the image.

For example, in the numerical example mentioned above, the interval P between the light emitting parts of the light source array. is 0.05 mm, the imaging magnification M is 12.7 times,
In order to reduce the interval error ΔP between the scanning line 1a-1 and the scanning line lb'-1 to 0.005 mm or less, which is the permissible range for image formation, the error in the interval between the light emitting parts of the light source array must be 0.4 mm.
It is necessary to keep it below μm.

Furthermore, it is necessary to suppress the error in the imaging magnification to 0.8% or less, which poses the problem that it becomes extremely difficult to perform optical scanning at even scanning intervals.

In order to solve the conventional problems, the present invention includes an adjustment member in the optical path between the light source means and the surface to be scanned, which can adjust the scanning interval (spot interval) of the scanning lines on the surface to be scanned. By making the imaging magnification, especially the imaging magnification in the sub-scanning direction, variable using the adjustment member, the scanning interval of the scanning lines on the surface to be scanned can be easily adjusted to a desired value, and the The purpose of this invention is to provide a multi-beam scanning optical system that enables high-quality image formation.

(Means for Solving the Problems) The multi-beam scanning optical system of the present invention uses optical means to deflect a plurality of light beams emitted from a light source means having a plurality of light emitting parts capable of independently modulating light. A multi-beam in which a light beam deflected by the optical deflector is guided onto the surface to be scanned by an imaging optical system, and the plurality of beams simultaneously scan the surface to be scanned. In the scanning optical system, the plurality of light emitting parts are arranged in a direction perpendicular to the scanning direction of the light beam on the surface to be scanned, and the optical means or the imaging optical system is arranged in a direction perpendicular to the scanning direction of the light beam on the surface to be scanned. It is characterized by having an adjustment member that adjusts the scanning interval of the scanning lines on the surface.

(Embodiment) FIG. 1 is a schematic diagram of the main parts of an optical system according to a first embodiment of the present invention.

In the figure, 1 is a light source means, which includes a plurality of light emitting parts 1a,
lb (two in this embodiment), and is made up of, for example, a plurality of semiconductor lasers. In this embodiment, each of the light emitting parts 1a and 1b is arranged in a direction perpendicular to the scanning direction of the light beam,
That is, they are arranged in rows in the sub-scanning direction.

2 is an optical means, which includes a light source means 1 and a light deflector 3 to be described later.
It is provided in the optical path between the light source means 1 and introduces the light beam from the light source means 1 into the optical deflector 3, which will be described later. In this embodiment, the optical means 2 also serves as an adjustment member. (Hereinafter, optical means 2
is also referred to as "adjustment member 2." ) The adjustment member 2 consists of two lens groups, a front group 2a and a rear group 2b, and the light source means 1
It has the function of a collimator lens that converts a plurality of light beams emitted from the lens into parallel light beams.

Further, the adjustment member 2 makes the focal length variable and the imaging magnification variable by relatively changing the distance between the two lens groups, the front group 2a and the rear group 2b, and the adjustment member 2 makes the focal length variable and the imaging magnification variable. The scanning interval of the scanning lines can be adjusted to a desired value.

Reference numeral 3 denotes an optical deflector made of a rotating polygon mirror or the like, which rotates at a constant speed in the direction of arrow a. Reference numeral 4 denotes a scanning imaging optical system having f-θ characteristics, and includes an anamorphic lens (anamorphic optical system) in part. Reference numeral 5 denotes a photosensitive medium surface which is a surface to be scanned, and is moving at a constant speed in the direction of the arrow.

1□ and IL2 are scanning lines in which the light beams emitted from the light emitting units 1a and lb scan the scanned surface 5, respectively, and P
are the scanning lines ILI and I! at this time. , 2 scanning intervals (spot intervals) are shown.

In this embodiment, a plurality of light beams emitted from a light source means 1 are each converted into parallel beams by an optical means 2 which acts as a collimator, and are incident on a reflecting surface of a light deflector 3. Each of the light beams reflected by the reflective surface of the optical deflector 3 forms a beam spot diameter on the scanned surface 5 by the scanning imaging optical system 4, thereby forming an image on the scanned surface 5. Information is formed (written) sequentially.

In this embodiment, when the surface to be scanned 5, which moves at a constant speed in the direction indicated by the arrow, is simultaneously scanned by a plurality of light beams, the beam spots do not scan adjacent scanning lines, but are separated by a predetermined distance. The scanning line is optically scanned, and the beam spot is configured not to scan the same scanning line more than once.

Next, the features of each element of this embodiment will be explained using specific numerical examples.

Now, the pixel density on the scanned surface is 400 d p i (do
To form an image with a resolution of t/1 nch), the scanning interval P of 1°12 scanning lines, which corresponds to the resolving power, must be an integral multiple of 63.5 μm (25.4 mm/400). Is there a need to configure each optical element? For example, as a reference value, the light emitting parts 1a, lb of the light source array 1
The interval P. 0.05 mm, the setting value of the focal length of the adjustment member 2 is 10 mm, and the setting value of the focal length of the imaging optical system 4 is 1.
The length shall be 27 mm. Then, the imaging magnification M in the sub-scanning direction becomes 12.7 times, so the scanning interval P between the scanning line f and the scanning line I12 on the scanned surface is 0.0.
It becomes 635mm (635μm).

This is an integral multiple (10
times).

However, at this time, due to manufacturing errors of the light source array 1, the interval between each light emitting part of the light source array 1 is, for example, 0.052 m.
m, the scanning interval P of scanning lines x, , n2 is P = 0.6604 mm with the setting values of each optical element as they are.
(660.4 μm), which is a 25.4 μm deviation from an integral multiple of the scanning interval of 63.5 μm, which corresponds to the resolution of an image with a pixel density of 400 dpi, resulting in image unevenness.

Therefore, in this embodiment, in order to correct the above-mentioned deviation in the scanning interval P, the front group 2a and the rear group 2b that constitute the adjustment member 2 are moved relatively on the optical axis, that is, the interval between the lens groups is changed as appropriate. , the focal length of the adjustment member 2 is changed.

As a result, the set value of the focal length of the adjustment member 2 is set to 10.4 m.
By changing to m, the imaging magnification M is set to 12.21 times. As a result, the scanning interval P is P=1Ml・P, so P
ro, 635 mm (635 μm). In this way, an integral multiple of the scanning interval of 63.5 μm, which corresponds to the above-mentioned resolution, is maintained.

Furthermore, when the focal length of the scanning imaging optical system 4 changes by, for example, 1% due to manufacturing errors, the distance between the front group 2a and the rear group 2b that constitute the adjustment member 2 changes as described above. By relatively changing the focal length of the adjustment member 2, the focal length of the adjustment member 2 is changed by about 1% from the set value. This maintains the same imaging magnification at all times.

In this way, in this embodiment, the scanning interval P of the scanning lines on the surface to be scanned is always kept constant by the adjusting member even if each optical element changes due to manufacturing errors as described above (in this embodiment, Scanning interval 63 corresponding to the set resolution
．． The diameter is adjusted to be an integral multiple of 5 μm). This makes it possible to form scanning lines on the surface to be scanned at equal pitches in the feeding direction as shown by the arrows in the figure, thereby preventing unevenness in the width of the scanning lines, that is, unevenness in the image.

FIG. 2 is a perspective view of essential parts of a second embodiment of the present invention. This figure shows the case where the present invention is applied to a surface tilt correction optical system (a system in which the deflection reflection surface and the surface to be scanned are in a conjugate relationship in the sub-scanning section). In this figure, the same elements as those shown in FIG. 1 are given the same reference numerals.

22 is a collimator lens with a fixed focal length. 27
is an adjustment member, which is made up of a line image forming element.

In this embodiment, the adjustment member 27 is composed of two cylindrical lenses, a negative lens 27a and a positive lens 27b, and the cylindrical lens has refractive power only in the sub-scanning direction. A line image is formed from the light beam.

The adjusting member 27 moves the negative lens 27a and the positive lens 27b relative to each other on the optical axis to appropriately change the lens interval, and also moves each lens as a whole on the optical axis to change the focal length in the sub-scanning direction. Thereby, a linear image based on the light beam from the light source array 1 is always formed near the deflection surface 3a of the optical deflector 3.

20 is an imaging optical system for scanning, and has an anamorphic optical system. That is, the imaging optical system 20 includes a spherical lens 20
a and a toric lens 20b, which have different focal lengths in the main scanning plane and in the sub-scanning plane, and satisfy the f-θ characteristic in the main scanning plane, and the deflection surface 3a and the toric lens 20b in the sub-scanning plane. It is arranged to have a conjugate relationship with the scanning plane 5a.

In this embodiment, the light source means! The plurality of light beams emitted from the collimator lens 22 are made into parallel light beams and are incident on an adjusting member 27 for forming a line image. Adjustment member 27
The two cylindrical lenses, the negative lens 27a and the positive lens 27b, which make up the main scanning section do not have refractive power in the main scanning cross section, so the optical dome remains parallel within the main scanning cross section of the incident parallel light beam. Proceed in a state of luminous flux.

On the other hand, since the adjusting member 27 has a refractive power in the sub-scanning section, the incident parallel light beam is focused in the sub-scanning section and is imaged on the deflection reflection surface 3a of the optical deflector 3 as a substantially line image. Ru.

Each light beam reflected by the deflection reflecting surface 3a of the optical deflector 3 is directed to the scanned surface 5 by the imaging optical system 2o.
A beam spot is formed on each surface 5 to be scanned.
Image information is sequentially formed (written) on a.

In this embodiment, the negative lens 2 constituting the adjustment member 27 is
By relatively changing the lens distance between 7a and the positive lens 27b, the focal length of the adjustment member 27 is changed,
The imaging magnification in the sub-scanning direction is variable.

As a result, as in the first embodiment described above, the pitch (interval) between the light emitting parts 1a and 1b of the light source array 1 may change due to manufacturing errors, or the collimator lens 22 or the scanning imaging optical system 20 may change. Even if the focal length changes due to manufacturing errors, by appropriately changing the focal length of the adjustment member 27, the scanning interval of the scanning lines I1, , 12 can be adjusted by an integral multiple of the value corresponding to the preset resolution on the scanned surface. It is adjusted so that

FIG. 3 is a perspective view of a main part of a third embodiment of the present invention, and shows the case where it is applied to a surface tilt correction optical system like the second embodiment shown in FIG. 2 described above. 1st and 2nd on the right in the same figure
Elements that are the same as those shown in the figures are given the same reference numerals.

In this embodiment, 37 is a line image forming element, which is composed of a fixed focal length lens. An adapter lens 31 is added as an adjustment member in the optical path between the collimator lens 22 and the line image forming element 37.

This point is different from the second embodiment shown in FIG. 2, and the other configurations are substantially the same.

In this embodiment, as described above, when an error occurs in the scanning line 42 or the second scanning interval on the scanned surface due to manufacturing problems of each optical element, the adapter lens 31 is adjusted appropriately on the optical axis. By moving it, the imaging magnification in the sub-scanning direction is changed, and the scanning intervals of the scanning lines f, . . . A2 are adjusted to be always at equal intervals. That is, the plurality of beam spots are always maintained at an integral multiple of the scanning interval corresponding to a preset resolution on the surface to be scanned.

In this embodiment, when the adapter lens 31 is used to vary the imaging magnification in the sub-scanning direction, the imaging position in the main-scanning direction moves slightly.

However, since the imaging optical system 2o for scanning generally has a deep focal depth in the main scanning direction, the adapter lens can be moved along the optical axis within the range of the focal depth.

In each of the above embodiments, the adjustment member was provided in the optical path between the light source means and the optical deflector, but the adjustment member was provided in the optical path between the surface to be scanned and the optical deflector to perform sub-scanning. Even if the imaging magnification in the direction is variable, the present invention can be applied in the same manner as in the above-described embodiments.

(Effects of the Invention) According to the present invention, as described above, an adjustment member for adjusting the scanning interval of the scanning lines on the surface to be scanned is provided in the optical path between the light source means and the surface to be scanned, and the adjustment member By making the imaging magnification, especially the imaging magnification in the sub-scanning direction, variable, multiple beam spots or integral multiples of the scanning interval corresponding to the preset resolution are always kept on the scanned surface. A multi-beam scanning optical system capable of forming images with improved image quality can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the main parts of the first embodiment of the present invention, and FIG. Third
The figures each show the second example when the present invention is applied to a surface tilt correction optical system. A perspective view of the main parts of the third embodiment, FIG. 4 is an explanatory diagram of the scanning surface when the surface to be scanned is optically scanned in a conventional multi-beam scanning optical system, and FIG. 5 is a main part of the conventional scanning optical system. The schematic diagram, FIG. 6, is an explanatory diagram showing how the surface to be scanned is optically scanned in the scanning optical system of FIG. 5. In the figure, 1 is a light source means, la and lb are light emitting parts, 2.27.
31 is an adjustment member, 3 is an optical deflector, 4 is an imaging optical system, 20
5 is an analog optical system, 5 is a scanned surface, 22 is a collimator lens, 37 is a line image forming element, 20a is a spherical lens, 20b is a toric lens, and 12 is a scanning line. Figure Figure d Figure 16'-6

Claims (3)

[Claims] (1) A plurality of light beams emitted from a light source means having a plurality of light emitting parts capable of independently modulating light is guided to an optical deflector by an optical means, and the light beams deflected by the optical deflector are combined. In a multi-beam scanning optical system in which light is guided onto a surface to be scanned by an imaging optical system and the surface to be scanned is simultaneously scanned with the plurality of light beams, the plurality of light emitting parts are configured to guide the light beams on the surface to be scanned. are arranged in a direction perpendicular to the scanning direction, and the optical means or imaging optical system has an adjusting member that adjusts the scanning interval of the scanning lines on the surface to be scanned by the plurality of light beams. A multi-beam scanning optical system characterized by: (2) The optical means has an adjustment member, the adjustment member has a line image forming element having refractive power only in a direction perpendicular to the scanning direction of the light beam, and the imaging optical system The multi-beam scanning optical system according to claim 1, characterized in that it has an anamorphic optical system. (3) The optical means has an adjustment member, the adjustment member is made of a collimator lens with a variable focal length, and the optical means has refractive power only in a direction perpendicular to the scanning direction of the light beam. 2. The multi-beam scanning optical system according to claim 1, further comprising a line image forming element having a linear image forming element, and wherein said imaging optical system has an anamorphic optical system.