JPH085944A - Multibeam optical device - Google Patents

Abstract

PURPOSE:To obtain a multibeam optical device capable of excellently performing color mixture all over the area from a central part to an end on the surface of a photoreceptor drum as a surface to be scanned in the case of obtaining a multicolor image by superimposing plural color images by using plural light beams. CONSTITUTION:Plural light beams projected from plural light sources 1 and 2 and having different wavelength are synthesized by a beam synthesis means 3, condensed by an image formation means 5 through a deflecting means 4 deflecting and reflecting the synthesized light beam, and separated to plural light beams by a beam separation means 6, then guided to plural different areas on the surface to be scanned 9, so that the surface to be scanned is optically scanned with the plural light beams. In such a case, a correction means 8 correcting the state of a scanning line so that the states of the scanning lines of the plural light beams optically scanning on the surface to be scanned may nearly agree with each other is provided in at least one optical path of the optical paths of the plural light beams separated by the beam separation means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam optical device, and in particular, a plurality of light beams having different wavelengths are used to guide light onto a surface of a recording medium (for example, a photosensitive drum) as a surface to be scanned for optical scanning. The present invention relates to a multi-beam optical device suitable for an image forming apparatus such as a digital copying machine or a digital laser printer that records an image.

[0002]

2. Description of the Related Art Conventionally, an optical system of a multi-beam optical device used for a so-called two-color laser printer or the like, which records an image by using light beams of two wavelengths, is shown in FIG.
It consists of the configuration shown in.

In the figure, reference numerals 31 and 32 denote semiconductor lasers as light sources, which emit a light beam (laser light) optically modulated based on an image signal. The wavelengths of the light beams emitted from the semiconductor lasers 31 and 32 are different from each other. For example, the wavelength λ ₁ of the light beam emitted from the semiconductor laser 31 is 780 nm, and the wavelength λ ₂ of the light beam emitted from the semiconductor laser 32 is 670 nm. Is.

Reference numeral 33 is a synthetic dichroic mirror,
A wavelength of 67 nm emitted from the semiconductor laser 32 is transmitted through the light beam having a wavelength of 780 nm emitted from the semiconductor laser 31.
The 0 nm light beam is reflected and combined into one light beam.

Reference numeral 34 is an optical deflector, which is composed of a rotating polygon mirror, and is rotated at a predetermined speed in the direction of arrow A in the figure by a driving means (not shown).

Reference numeral 35 denotes an image forming lens, which collects a plurality of light beams deflected and reflected by the light deflector 34, and separates two exposure positions P1 on the surface of the photosensitive drum 39 via a separation dichroic mirror 36 described later. , P2 are imaged (focused) respectively.

The separation dichroic mirror 36 has optical characteristics equivalent to those of the composite dichroic mirror 33 described above, and transmits the light beam having a wavelength of 780 nm emitted from the semiconductor laser 31 and transmits the light having a wavelength of 670 nm emitted from the semiconductor laser 32. It is split into two light beams by reflecting the beam.

Reference numerals 37a and 37b denote folding mirrors, each of which has a wavelength of 78 which is transmitted through the separation dichroic mirror 36.
A 0 nm light beam is guided to the first exposure position P1 on the surface of the photosensitive drum 39. 37c is also a folding mirror, which guides the light beam having a wavelength of 670 nm reflected by the separation dichroic mirror 36 to a second exposure position P2 on the surface of the photosensitive drum 39. The photoconductor drum 39 rotates in the direction of arrow B in the figure at a predetermined speed.

In the figure, a plurality of semiconductor lasers 31,
A plurality of light beams having different wavelengths, which are optically modulated based on the image signal from 32, are combined into one light beam by the combining dichroic mirror 33, and are condensed by the image forming lens 35 via the optical deflector 34 and separated dichroic mirror. After being separated into a plurality of light beams by 36, they are imaged (focused) on a plurality of different regions (exposure positions) P1 and P2 on the surface of the same photosensitive drum 39 through a folding mirror provided in each optical path. ing.

By rotating the optical deflector 34 in the direction of arrow A, the optical scanning is performed in the direction (main scanning direction) perpendicular to the paper surface at the exposure positions P1 and P2. Then, along with the exposure in the main scanning direction, the photosensitive drum 39 is sequentially exposed at the exposure positions P1 and P2 as the photosensitive drum 39 rotates in the direction of the arrow B (sub scanning direction), and corresponding developing devices (not shown) Thus, the electrostatic latent image is developed on the surface of the photosensitive drum 39.

[0011]

Generally, when a thick separation dichroic mirror 36 is arranged at an angle (for example, 45 degrees) with respect to the optical axis of the imaging lens 35 as shown in FIG. 3, the separation dichroic mirror is arranged. The light beam transmitted through 36 loses the linearity of the scanning line on the surface of the photoconductor drum 39 depending on the angle of incidence on the separation dichroic mirror 36 and the thickness of the mirror substrate of the separation dichroic mirror 36, causing a curve. There is a problem that it ends up.

In this state, the folding mirror 37a,
When light scanning is performed on the surface of the photosensitive drum 39 after passing through 37b, the transmitted light beam has a one-line scanning line drawing an arc on the surface of the photosensitive drum 39 as shown by a solid line 40 in FIG. It will be in a state (curved state).

On the other hand, the light beam reflected by the separation dichroic mirror 36 does not have the curvature generated when it is reflected by the separation dichroic mirror 36. Therefore, one scanning line for optically scanning the surface of the photosensitive drum 39 is maintained in a straight line state as shown by a dotted line 41 in FIG.

Therefore, when such a multi-beam optical device is used for superimposing two-color images of black and other colors, for example, although the color is well mixed at the center of the photosensitive drum surface, There has been a problem that color mixing cannot be performed well toward the end of the surface of the photosensitive drum. As a result, there is a problem that a good mixed color image (for example, an image formed by superposing two color images of black and other color) is not obtained.

According to the present invention, when a plurality of light beams separated by a separation dichroic mirror as a beam separating means are used to optically scan different areas on a surface to be scanned (photosensitive drum surface), the light is separated by the separation dichroic mirror. By providing correction means for correcting the scanning line states of the plurality of light beams in the optical path of the at least one light beam so that the scanning line states of the plurality of light beams substantially coincide with each other, for example, images of two colors are superimposed. An object of the present invention is to provide a multi-beam optical device capable of favorably performing color mixing from the central portion to the entire end portion of the surface of the photosensitive drum even when used for matching purposes.

[0016]

A multi-beam optical device according to the present invention is (1-1) combining a plurality of light beams having different wavelengths emitted from a plurality of light sources by a beam combining means, and combining the combined light beams. After being condensed by the image forming means through the deflecting means for deflecting and reflecting, and separated into a plurality of light beams by the beam separating means, the light beams are guided to a plurality of different areas on the surface to be scanned, and the plurality of light beams When optically scanning the surface to be scanned, scanning of the plurality of light beams optically scanning the surface to be scanned in at least one of the optical paths of the plurality of light beams after being separated by the beam separating means. It is characterized in that a correction means for correcting the states of the scanning lines is provided so that the states of the lines substantially match each other.

Particularly, it is preferable that the correction means is made of a transparent flat plate member, and that the beam separation means separates the light beam in a specific wavelength region into a plurality of light beams by reflecting and transmitting the light beam. The beam separating means is composed of a dichroic mirror, and the correcting means is provided in an optical path of a transmitted light beam among a plurality of light beams separated by the beam separating means, and a scanning line of the light beam. Of the plurality of light beams separated by the beam separation means is provided in the optical path of the reflected light beam to bend the state of the scanning line of the light beam. In addition, the correction means is composed of a transparent parallel plate having a thickness substantially equal to that of the beam separation means.

(1-2) A plurality of light beams having different wavelengths emitted from a light source in which a plurality of light emitting portions are arranged side by side in an array are guided to a deflecting means, deflected and reflected by the deflecting means, and condensed by an image forming means. After that, after being separated into a plurality of light beams by the beam separating means, each is guided to a plurality of different regions on the surface to be scanned, when optically scanning the surface to be scanned with the plurality of light beams,
In such a manner that the states of the scanning lines of the plurality of light beams that optically scan the surface to be scanned substantially match in at least one of the optical paths of the plurality of light beams after being separated by the beam separating means. It is characterized in that a correction means for correcting the state of the scanning line is provided.

In particular, it is preferable that the correction means is made of a transparent flat plate member, and the beam separation means separates a light beam in a specific wavelength region into a plurality of light beams by reflecting and transmitting the light beam. The beam separating means is composed of a dichroic mirror, and the correcting means is provided in an optical path of a transmitted light beam among a plurality of light beams separated by the beam separating means, and a scanning line of the light beam. Of the plurality of light beams separated by the beam separation means is provided in the optical path of the reflected light beam to bend the state of the scanning line of the light beam. In addition, the correction means is composed of a transparent parallel plate having a thickness substantially equal to that of the beam separation means.

[0020]

Embodiment 1 FIG. 1 is a schematic view (side view of an essential portion) of an essential portion of Embodiment 1 of the present invention.

In the figure, reference numerals 1 and 2 denote semiconductor lasers as light sources, which emit a light beam (laser light) optically modulated based on an image signal. In the present embodiment, the wavelengths of the light beams emitted from the respective semiconductor lasers 1 and 2 are different, for example, the wavelength λ ₁ of the light beam emitted from the semiconductor laser ₁ is 780 nm, and the wavelength λ _{2 of the} light beam emitted from the semiconductor laser _2. Is 670 nm.

Reference numeral 3 denotes a beam synthesizing means, which comprises a dichroic mirror (synthetic dichroic mirror), which transmits a light beam having a wavelength of 780 nm emitted from the semiconductor laser 1 and transmits a wavelength 67 emitted from the semiconductor laser 2.
A 0 nm light beam is reflected and combined into one optical path.

Reference numeral 4 denotes an optical deflector as a deflecting means, which is composed of a rotating polygon mirror, and is rotated at a predetermined speed in the direction of arrow A by a driving means (not shown).

Reference numeral 5 denotes an image forming lens as an image forming means,
A plurality of different light beams deflected and reflected by the light deflector 4 are condensed and passed through a dichroic mirror (separation dichroic mirror) 6 as a beam separating means described later, and two different light beams on the surface of the photosensitive drum 9 as a surface to be scanned. Exposure position P1, P
2 are focused (focused) respectively.

The separating dichroic mirror 6 transmits the light beam having a wavelength of 780 nm among the incident light beams and reflects the light beam having a wavelength of 670 nm to form two light beams in the same manner as the above-mentioned optical characteristic of the composite dichroic mirror 3. Separated.

Further, the material of the mirror substrate of the separation dichroic mirror 6 in this embodiment is a glass material, and the image forming lens 5 is formed so that the incident angle of the light beam on the optical axis of the image forming lens 5 is approximately 45 degrees. The optical axis of the optical axis 5 is inclined in a predetermined direction.

7a and 7b are folding mirrors,
Wavelength 780 nm transmitted through the separation dichroic mirror 6
Light beam is guided to a first exposure position P1 on the surface of the photosensitive drum 9 through a correcting means 8 composed of a flat plate member (flat glass) described later. 7c is also a folding mirror, which has a wavelength of 67 reflected by the separation dichroic mirror 6.
The 0 nm light beam is guided to the second exposure position P2 on the surface of the photosensitive drum 9.

The flat plate member as the correction means 8 is made of transparent flat glass, and is made of an optical member having the same material (glass material) and the same thickness as the mirror substrate of the separation dichroic mirror 6, and the flat glass is used. The incident angle of the light beam entering 8 is set to be the same as the incident angle when entering the separation dichroic mirror 6 and has the opposite sign. That is, in the present embodiment, as will be described later, the amount of bending generated when passing through the flat glass 8 is substantially the same as the amount of bending generated when passing through the separation dichroic mirror 6, and only the bending direction is different. are doing. Thus, the states of the scanning lines of the plurality of light beams that optically scan the surface of the photosensitive drum 9 are corrected so as to be substantially coincident with each other (linear state).

The photosensitive drum 9 rotates in the direction of arrow B in the figure at a predetermined speed.

In the present embodiment, with such a structure, the light beams having a wavelength of 780 nm and the light beams having a wavelength of 670 nm emitted from each of the semiconductor lasers 1 and 2 after being optically modulated by an image signal are combined into one optical path by the dichroic mirror 3. Are combined, are deflected and reflected by the deflecting surface 4a of the optical deflector 4, are then condensed by the imaging lens 5, and are incident on the separation dichroic mirror 6.

The light beam having a wavelength of 780 nm passes through the separation dichroic mirror 6 and the two folding mirrors 7
After passing through the flat glass (correction glass) 8 via a and 7b to correct the curvature of the scanning line, the image is formed (focused) on the surface of the photosensitive drum 9 at the first exposure position.

On the other hand, the light beam having a wavelength of 670 nm is reflected by the separation dichroic mirror 6 and is turned over by the folding mirror 7.
An image is formed (focused) on the second exposure position on the surface of the photosensitive drum 9 via c.

By rotating the light deflector 4 in the direction of arrow A, light scanning is performed in the direction (main scanning direction) perpendicular to the paper surface at the exposure positions P1 and P2. Then, along with the exposure in the main scanning direction, the photosensitive drum 9 is sequentially exposed at the exposure positions P1 and P2 along with the rotation of the photosensitive drum 9 in the direction of the arrow B (sub scanning direction), and a developing device (not shown) corresponding to each is provided. Thus, the electrostatic latent image is developed on the surface of the photosensitive drum 9.

Next, a method for correcting the scanning state of each light beam separated by the separation dichroic mirror 6 as the beam separation means and the curvature of the scanning line will be described.

First, the light beam having a wavelength of 780 nm that has passed through the separation dichroic mirror 6 will be described. As described above, the light beam that has passed through the separation dichroic mirror 6 loses the linearity of the scanning line depending on the incident angle to the separation dichroic mirror 6 and the thickness of the mirror substrate of the separation dichroic mirror 6, and causes a curve. There is a point.

For example, a glass material having a thickness of 5 mm is used as the mirror substrate of the separation dichroic mirror 6, and the incident angle of the light beam on the optical axis with respect to the separation dichroic mirror 6 is 45 degrees and the scanning angle is 13 degrees. In that case, the amount of curvature of the scanning line is about 58 μm. This is a problem because the amount of curvature is close to one pixel when a 400 DPI printer is considered.

Therefore, in this embodiment, a flat glass 8 as a correcting means is provided in the optical path of the light beam having a wavelength of 780 nm separated by the separation dichroic mirror 6 as described above, and the flat glass 8 of the separation dichroic mirror 6 is provided. The mirror substrate is made of the same material (glass material) and has the same thickness, and the incident angle of the light beam on the flat glass 8 is the same as the incident angle of the light beam incident on the separation dichroic mirror 6 but opposite. It is set to be the sign.

That is, in the present embodiment, the amount of bending generated when passing through the flat glass 8 is approximately the same as the amount of bending generated when passing through the separation dichroic mirror 6, and only the direction of bending is different. It is corrected so that the state of the scanning line of the light beam after passing through the flat glass 8 is the state before entering the separation dichroic mirror 6 (linear state).

As a result, the state of one scanning line for optically scanning the surface of the photosensitive drum 9 is the same as the scanning line (dotted line 11) of the light beam having a wavelength of 670 nm (straight line state) as shown by the solid line 10 in FIG. I have to.

On the other hand, the light beam having a wavelength of 670 nm reflected by the separation dichroic mirror 6 does not cause the curvature generated when the light beam is reflected by the separation dichroic mirror 6. Therefore, the state of the scanning line of one line for optically scanning the surface of the photosensitive drum 9 is maintained in a linear state as in the state before entering the separation dichroic mirror 9 as indicated by the dotted line 11 in FIG. .

Therefore, when this multi-beam optical device is used for superimposing, for example, two-color images of black and other colors as described above, the states of the respective scanning lines are substantially the same as described above. Good color mixing can be performed over the entire area from the center to the end of the surface of the photosensitive drum 9. As a result, a good color mixture image is obtained.

In this embodiment, one of the plurality of light beams has a wavelength of 780 nm and the other light beam has a wavelength of 670 nm. However, the wavelengths of these light beams are the beam combining means or the beam separating means. The wavelength is not particularly limited as long as it can be synthesized or separated by means.

Next, a second embodiment of the present invention will be described.
The present embodiment differs from the above-described first embodiment in that the flat plate member serving as the correction means is made of a plastic material instead of the glass material to reduce the cost. Other configurations and optical functions are substantially the same as those in the first embodiment.

That is, although the thickness of the mirror substrate of the separation dichroic mirror is set to 5 mm in the above-described first embodiment in which the flat plate member is made of a glass material, in this embodiment, the flat plate member is made of a plastic material. By changing the thickness of the mirror substrate of the separation dichroic mirror to 5.07 mm, the amount of curvature generated when passing through the separation dichroic mirror 6 and the flat plate member made of a plastic material are passed as in the first embodiment. The amount of bending that occurs at this time is substantially the same, and only the bending direction can be different. As a result, the same effect as that of the above-described first embodiment is obtained.

As described above, in this embodiment, as long as it is an optical member capable of changing only the bending direction by the same amount as the bending amount generated when transmitting through the separation dichroic mirror, this optical member (correction means). There is no particular limitation on the material and thickness of the.

Next, a third embodiment of the present invention will be described.

The point of difference of this embodiment from the first embodiment is that a flat glass as a correcting means is provided in the optical path of the light beam of wavelength 670 nm reflected by the separation dichroic mirror. Other configurations and optical functions are substantially the same as those of the first embodiment, and the same effect is obtained.

In the first embodiment, the wavelength is 780 nm.
The flat glass is provided in the optical path of the light beam of, and the curvature of the scanning line of the light beam generated when the light passes through the separation dichroic mirror is corrected.In this embodiment, the flat glass is reflected by the separation dichroic mirror. Wavelength 670n
By providing it in the optical path of the light beam of m, it is configured so that the same amount of bending of the light beam transmitted through the separation dichroic mirror and in the same direction are generated.

That is, the flat glass so that the state of the scanning line of the light beam having a wavelength of 670 nm is substantially the same as the state (curved state) of the scanning line of the light beam having a wavelength of 780 nm as shown by the solid line 40 in FIG. Causes the bending. As a result, as described above, when the image is used for superimposing images of two colors of black and other colors, the states of the scanning lines are substantially the same as described above, so Good color mixing can be performed over the entire edge portion.

In this embodiment, since the deviation of the relative amount of curvature between the two light beams is also corrected by configuring the optical system in this way, the problem to be solved by the present invention is applied. It can have a different configuration.

In each of the above embodiments, two light beams having different wavelengths are used to obtain, for example, a color-mixed image. However, the present invention is not limited to this. For example, three light beams having different wavelengths may be used. The present invention can be applied in the same manner as in the above-described embodiments to an optical device that obtains a mixed color image using the above light beams.

Further, although two separate semiconductor lasers are used as the light source in each embodiment, a monolithic multi-laser array for emitting a plurality of light beams having different wavelengths (a light source in which a plurality of light emitting portions are arranged side by side in an array) The present invention can be applied in the same manner as in the above-mentioned embodiment by using. As a result, the optical system can be configured without using the synthetic dichroic mirror, and the overall size of the device can be reduced. The present invention is not limited to the digital copying machine and may be applied to, for example, an analog copying machine.

[0053]

According to the present invention, the states of the scanning lines of the plurality of light beams coincide with each other in at least one of the light paths of the plurality of light beams after being separated by the beam separating means as described above. By providing a correction means for correcting the state of the scanning line, even when the image is used for superimposing two-color images, for example, over the entire area from the center to the end of the surface of the photosensitive drum as the surface to be scanned. It is possible to achieve a multi-beam optical device that can perform good color mixing.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state of scanning lines on the surface of the photosensitive drum according to the first embodiment of the present invention.

FIG. 3 is a schematic view of a main part of a conventional multi-beam optical device.

FIG. 4 is an explanatory view showing a state of scanning lines on a surface of a photosensitive drum of a conventional multi-beam optical device.

[Explanation of symbols]

 1, 2 Light source (semiconductor laser) 3 Beam combining means 4 Deflection means 5 Imaging means 6 Beam separation means 7a, 7b, 7c Folding mirror 8 Correction means 9 Scanned surface (photosensitive drum) 10, 11 Scanning line

Claims (8)

[Claims] 1. A plurality of light beams emitted from a plurality of light sources having different wavelengths are combined by a beam combining means, and the combined light beams are condensed by an image forming means through a deflecting means for deflecting and reflecting the combined light beams. After being separated into a plurality of light beams by, the light is guided to a plurality of different regions on the surface to be scanned, and when the plurality of light beams are optically scanned on the surface to be scanned, after being separated by the beam separating means. Of the plurality of light beams, the state of the scanning lines is corrected so that the states of the scanning lines of the plurality of light beams that optically scan the surface to be scanned substantially match in at least one optical path. A multi-beam optical device comprising a correction means. 2. A plurality of light beams having different wavelengths emitted from light sources in which a plurality of light emitting portions are arranged side by side in an array are guided to a deflecting means, deflected and reflected by the deflecting means, and condensed by an image forming means, After being separated into a plurality of light beams by the beam separating means, each is guided to a plurality of different areas on the surface to be scanned, and when the light scanning is performed on the surface to be scanned with the plurality of light beams, the beam separating means Among the optical paths of the plurality of light beams after being separated by, in at least one optical path, the scanning lines of the plurality of light beams that optically scan the surface to be scanned are substantially aligned with each other. A multi-beam optical device comprising a correction means for correcting the state. 3. The multi-beam optical device according to claim 1, wherein the correction means is made of a transparent flat plate member. 4. The multi-beam optical device according to claim 1, wherein the beam separating means separates a light beam in a specific wavelength region into a plurality of light beams by reflecting and transmitting the light beam. 5. The multi-beam optical apparatus according to claim 4, wherein the beam separating means is a dichroic mirror. 6. The correction means is provided in an optical path of a light beam that has been transmitted among a plurality of light beams separated by the beam separation means, and corrects a curve of a scanning line of the light beam. The multi-beam optical device according to claim 3. 7. The correction means is provided in an optical path of a reflected light beam among a plurality of light beams separated by the beam separation means, and a state of a scanning line of the light beam is curved. The multi-beam optical device according to claim 3. 8. The multi-beam optical apparatus according to claim 1, wherein the correction means is composed of a transparent parallel plate having a thickness that is substantially equal to that of the beam separation means.