JPH0843757A - Scanning image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a scanning image forming apparatus capable of minimizing the occurrence of defocus and distortion of a copied image when a scan mirror is used. When a projected image F is formed on a light receiving medium D via a projection lens L and a scan mirror M, the projected image and the image formed on the light receiving medium are synchronized with each other. In a scanning type image forming apparatus that performs scanning exposure by rotating a scan mirror, the scan mirror is composed of a cylindrical back mirror having a plano-concave negative refractive power, and is generated by the rotation of the scan mirror. Corrected image distortion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning type image forming apparatus, and more particularly, to a reduced image such as a microphotograph which is enlarged and projected on a screen surface for observation, and the enlarged image is output as an enlarged copy. The present invention relates to a scanning image forming apparatus suitable for a device such as a micro reader printer.

[0002]

2. Description of the Related Art Conventionally, a scanning image forming apparatus such as a micro reader printer is an observation system (reader system) for enlarging and projecting image information (projected image) reduced and recorded on a microfilm onto a screen or the like by a projection lens. )When,
The image information is projected on a light receiving medium such as a photoconductor drum and output as an enlarged copy (printer system).

FIG. 5 is a schematic view showing the principle of a scanning system (scanning system) for forming a copy image in a scanning type image forming apparatus such as a micro reader printer of this type.
The principle will be described below with reference to FIG.

In the figure, F is a projected image, which is made of, for example, a microfilm, and has an illumination optical system (not shown).
It is illuminated by. Reference numeral L denotes a projection lens, which magnifies and projects the projected image F onto a photosensitive drum (or line sensor or the like) D as a light receiving medium or a screen (not shown). M is a rotatable scan mirror (rotating mirror)
It is fixedly arranged in the vicinity of the exit pupil of the projection lens L, and has a scanning function of the projected image F and a switching function of switching the light flux based on the image between the observation system and the copying system. S is a slit, which is arranged at a predetermined position in front of the photosensitive drum D.

In the figure, a projected image F illuminated by an illumination optical system (not shown) is magnified and projected by a projection lens L, reflected by a scan mirror M, passed through a slit S, and projected onto a surface of a photosensitive drum D. It Here, the photosensitive drum D is rotating in the direction of arrow B, and the scan mirror M
Rotates about its rotation axis O in the direction of arrow A in synchronization with the rotation of the photosensitive drum D.

In the figure, for example, it is assumed that the scan mirror M is located at the rotation position P1. At this time, the projected portion indicated by f1 on the surface of the microfilm F is imaged (projected) on the surface of the photosensitive drum D. Next, when the scan mirror M rotates in the direction of arrow A and is positioned at the rotation position P2, the projected portion indicated by f2 on the surface of the microfilm F is imaged on the surface of the photosensitive drum D. Similarly, when the scan mirror M further rotates in the direction of arrow A and is positioned at the rotation position P3, the projected portion indicated by f3 on the surface of the microfilm F is imaged on the surface of the photosensitive drum D.

In this way, the scan mirror M has a rotation range P.
By rotating in the direction of arrow A between 1 and P3 and changing its inclination angle, the projected range f on the surface of the microfilm F
All the images between 1 to f3 are scanned (scanned), and all the images are successively enlarged and projected on the surface of the photosensitive drum D rotating in the arrow B direction to form enlarged images.

[0008]

However, in the conventional scanning system shown in FIG. 5, since the rotation axis O of the scan mirror M is arranged at a fixed position, the scan mirror M is rotated at the rotation position P1 or When located at the rotation position P3, the respective equivalent projection points d of the projected portion f1 or the projected portion f3 on the surface of the microfilm F with respect to the surface of the photosensitive drum D.
1, d3 deviate toward the projection lens L side from the image plane (equivalent focal plane) I of the projection lens L, and the optical path lengths are Δd.
There was a problem that it was shortened by 1, Δd3.

For this reason, the scan mirror M is rotated to the rotational position P1.
Alternatively, there is a problem that the focus position is deviated when it is located at the rotation position P3, and defocus occurs in the copied image.

Further, there is a problem that a magnification error occurs due to the shortening of the optical path lengths by Δd1 and Δd3, respectively, and the magnification is reduced, so that barrel distortion aberration occurs in the copied image. .

In order to solve such a problem, for example, a method of setting the conjugate length of the projection lens L to be long and the rotation angle of the scan mirror M to be sufficiently small can be considered, but in this case, the entire apparatus is large. There was a problem that it became.

Therefore, a scanning type image forming apparatus for solving the above problems has been proposed in, for example, Japanese Patent Laid-Open No. 64-70735. In this publication, a rotation driving means for rotating the scan mirror to set the tilt angle and a shift driving means for shifting the scan mirror to correct the optical path length are provided on the supporting portion of the scan mirror, and the scan mirror is rotated. The optical path length is corrected by simultaneously performing the shift.

However, in the publication, there is a problem that the interlocking mechanism for accurately interlocking the rotational drive and the shift drive of the scan mirror becomes complicated, and the size of the entire apparatus becomes large. Further, the driving force is required to be larger than that of the conventional image forming apparatus, and further, there is a problem that vibration is increased and the image is adversely affected.

According to the present invention, when scanning exposure is performed using a scan mirror that is fixedly arranged as a projection scanning means of a copying system, the scan mirror is formed into a cylindrical lens shape having a negative refracting power within a planoconcave scanning plane. Scanning image capable of correcting the optical path length and obtaining a good copy image without distortion by using the flat mirror of the scan mirror and using the plane portion of the scan mirror as the back reflecting surface during printer (copying). An object is to provide a forming apparatus.

[0015]

The scanning type image forming apparatus of the present invention comprises: (1-a) When a projected image is formed on a light receiving medium via a projection lens and a scan mirror, the projected image is formed. In a scanning type image forming apparatus that performs scanning exposure by rotating the scan mirror in synchronization with the image formed on the light receiving medium, the scan mirror is provided with a cylindrical lens having a plano-concave negative refractive power. It is characterized in that it is composed of a rear mirror having a shape, and image distortion caused by the rotation of the scan mirror is corrected.

In particular, the back-side mirror has a negative refracting power in the scanning plane, and at the time of copying in which the projected image is formed on the light-receiving medium via the projection lens and the scan mirror, The flat portion of the scan mirror is used as a back reflection surface, and an optical element having a positive refractive power only in the scanning direction is arranged in the optical path between the projection lens and the scan mirror. .

(1-b) In a scanning type image forming apparatus using a rotatable scan mirror which is fixedly arranged as a projection scanning means of a copying system, the scan mirror is a cylindrical structure having a plano-concave negative refractive power. It is characterized in that it is composed of a rear mirror having a shape, and image distortion caused by the rotation of the scan mirror is corrected.

In particular, the back surface mirror has a negative refractive power in the scanning plane, the flat surface portion of the scan mirror is used as a back surface reflection surface at the time of copying, and the front optical path of the scan mirror is used. It is characterized in that an optical element having a positive refractive power is arranged only in the scanning direction.

[0019]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention. In the figure, in order to clarify the configuration of the scan system, a folding mirror of a reader system (observation system) for enlarging and projecting the projected image and a printer system for outputting the projected image as a magnified copy. The folding mirror and the like of (copy system) are omitted.

In the figure, F is an image to be projected, which is made of, for example, a microfilm and is illuminated by an illumination optical system (not shown). L is a projection lens,
The projected image F is enlarged and projected onto the surface of the photosensitive drum D (or line sensor) as a light receiving medium or the screen (not shown).

M is a rotatable scan mirror (cylindrical scan mirror) as a projection scanning means,
It is fixedly arranged near the exit pupil of the projection lens L, and has a scanning function for the projected image and a switching function for switching the light flux based on the image to the reader system and the printer system.

The scan mirror M in this embodiment is composed of a cylindrical rear surface mirror having a negative refracting power in a plane-concave scanning surface, and the scan mirror M is used when used as a printer system as described later. The flat surface (flat surface portion) m2 of the mirror M is used as a back surface reflection surface to correct image distortion caused by the rotation of the scan mirror M.
When used as a reader system, the plane m2 of the scan mirror M is rotated so as to face the projection lens L side, and the plane m2 is used as it is as a surface reflection surface as an ordinary reflection mirror.

S is a slit, which is arranged at a predetermined position in front of the photosensitive drum D. The photoconductor drum D rotates in the direction of arrow B in the figure at a predetermined speed. I is an image plane (equivalent focal plane) of the projection lens L.

In this embodiment, an illumination optical system (not shown)
The projected image F illuminated by the image is enlarged and projected by the projection lens L, is reflected by the scan mirror M during printing, passes through the slit S, and is projected (imaged) on the surface of the photosensitive drum D.

Here, the photosensitive drum D is rotating in the direction of arrow B in the figure, and the scan mirror M is rotating about its rotation axis O in the direction of arrow A in synchronization with the rotation of the photosensitive drum D. ing. Thereby, the copied image is obtained.

Next, a method of correcting the image distortion caused by the rotation of the scan mirror M will be described with reference to FIGS. 2A to 2C are enlarged explanatory views of the scan mirror M of this embodiment corresponding to the rotational positions P2, P1 and P3 of the scan mirror M in FIG. 5, respectively.

FIG. 3A shows f on the F surface of the microfilm.
The projected portion of 2 is reflected on the plane m2 side of the scan mirror M through a projection lens L (not shown) to form an image (projection) on the surface of the photosensitive drum D. Incidentally, in FIG. 3A, the back surface m is a plane from the cylindrical surface m1.
The distance to 2 is d2, and the distance from the back reflecting surface m2 to the cylindrical surface m1 is d2 '.

FIG. 3B shows f on the F surface of the microfilm.
The projected portion of No. 1 is back-reflected on the plane m2 side of the scan mirror M via a projection lens L (not shown) to form an image (projection) on the surface of the photosensitive drum D. Incidentally, in FIG. 2B, the back surface m is a plane from the cylindrical surface m1.
The distance to 2 is d1, and the distance from the back reflecting surface m2 to the cylindrical surface m1 is d1 '.

FIG. 3C shows f on the F surface of the microfilm.
The projected portion of 3 is reflected on the plane m2 side of the scan mirror M through the projection lens L (not shown) to form an image (projection) on the surface of the photosensitive drum D. In addition, in FIG. 6C, the back surface m is a plane from the cylindrical surface m1.
The distance to 2 is d3, and the distance from the back reflecting surface m2 to the cylindrical surface m1 is d3 '.

In the present embodiment, when the refractive index of the material of the scan mirror M is n, (n-1) / n. {(D1 + d1 ')-(d2 + d2')} ... (1) The following equation (1) coincides with the optical path length difference Δd1 shown in FIG. 5, and (n-1) / n. {(D3 + d3 ')-(d2 + d2')} ... (2) Similarly, the following equation (2) becomes the optical path length difference Δd shown in FIG.
The thickness of the scan mirror M and the curvature R of the cylindrical surface m1 are determined so as to coincide with No. 3. This prevents the defocusing of the copied image or the occurrence of barrel distortion due to the optical path length difference.

In the present embodiment, since the shape of the scan mirror M is a simple cylindrical shape, the above formulas (1) and (2) can be accurately expressed by the formula (1) due to the asymmetry of the light reflection point of the scan mirror M. n-1) / n ・ {(d1 + d1 ')-(d2 + d2')} = Δd1 ‥‥‥‥ (1) ', and (n-1) / n ・ {(d3 + d3')- (d2 + d2 ')} = Δd3 ‥‥‥‥ (2)' is difficult, d [| (n-1) / n ・ {(d1 + d1 ')-(d2 + d2')} -Δd1 | + | (n-1) / n ・ {(d3 + d3 ')-(d2 + d2')}-Δd3 |] / dR = 0 ... (3) Thickness of the scan mirror M d or the value of the curvature R of the cylindrical surface m1 is set, or

[0032]

[Equation 1] The value of the wall thickness d of the scan mirror M is set so that As a result, the defocus of the copied image or the occurrence of barrel distortion due to the difference in the optical path length is minimized.

Further, in the present embodiment, the scan mirror M is formed into a cylindrical shape having a plano-concave negative refractive power as described above, and the flat surface portion m2 of the scan mirror M is used as a back reflection surface at the time of printing. Therefore, the magnification changes only in the scanning direction during the printer. Therefore, in the present embodiment, the scanning speed is set to be higher than that in the case of scanning using the conventional scan mirror shown in FIG.

As described above, in the present embodiment, the shape of the scan mirror M is a cylindrical shape having a negative refracting power in the plane-concave scanning surface as described above, and the plane portion m2 of the scan mirror M is the back reflection surface. And the curvature R of the cylindrical surface m1 is set so as to satisfy the above formula (3) or formula (4). A good copy image is obtained with minimal distortion of the mold or defocus of the copy image without distortion.

Although the above description has been made for the printer, the flat portion m2 of the scan mirror M is rotated so as to face the projection lens L side when the reader is used, and the flat portion m2 is directly used as a surface reflection surface. It is used in the same way as the reflection mirror.

FIG. 3 is a schematic view of the essential portions of Embodiment 2 of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals. It should be noted that in the figure as well, scanning (scanning)
To clarify the configuration of the system, the folding mirror of the reader system (observation system) and the folding mirror of the printer system (copy system) are omitted.

This embodiment is different from the first embodiment described above in that a cylindrical lens (optical element) C having a positive refractive power only in the scanning direction is arranged in the optical path between the projection lens L and the scan mirror M. That is. Other configurations and optical functions are substantially the same as those in the first embodiment.

In the first embodiment described above, the curvature R of the scan mirror M causes a negative refracting power only in the scanning direction, so that there is a deviation between the image forming point between this scanning direction section and the section orthogonal to the scanning direction. Occurs.

That is, the image forming point of the cross section in the scan direction is displaced from the image forming point of the cross section orthogonal to the scan direction by Δdc in the direction away from the microfilm F. The value of the deviation amount Δdc is determined by the position where the scan mirror M is arranged, the refractive index n of the material of the scan mirror M, the curvature R of the scan mirror M, and the like.

For example, if the value of the deviation amount Δdc is smaller than the values of the deviation amounts Δd1 and Δd3 described above, there is no problem, but if the value is large, defocus occurs in the copied image.

Therefore, in this embodiment, the above-mentioned problem is solved by disposing the cylindrical lens C having a positive refractive power only in the scanning direction in the optical path between the projection lens L and the scan mirror M. .

That is, in the present embodiment, the cylindrical lens C having a positive refractive power only in the scanning direction is arranged on the scan mirror M side of the projection lens L, and the curvature R of the scan mirror M is caused by the refractive power of the cylindrical lens C. Deviation of the imaging point of the cross section in the scanning direction caused by
I am trying to cancel out c.

In this embodiment, by adopting such a constitution, the above-mentioned defocus of the copied image is further improved, and a good copied image without distortion is obtained.

FIG. 4 is a schematic view of the essential portions of Embodiment 3 of the present invention. In the figure, the same elements as those shown in FIG. 3 are designated by the same reference numerals. It should be noted that scanning is also performed in the same figure
To clarify the configuration of the system, the folding mirror of the reader system (observation system) and the folding mirror of the printer system (copy system) are omitted.

The present embodiment is different from the above-mentioned second embodiment in that instead of the cylindrical lens C provided in the optical path between the projection lens L and the scan mirror M, it has an optical function equivalent to that of the cylindrical lens C. That is, the cylindrical Fresnel lens CF is arranged. As a result, the same effect as that of the above-described second embodiment is obtained.

The optical element is not limited to the cylindrical lens as long as it is capable of canceling the deviation Δdc of the image forming point of the cross section in the scanning direction caused by the curvature R of the scan mirror M, and any optical element may be used. By using a cylindrical Fresnel lens having a positive refractive power only in the scanning direction as described above, the same effect as that of the above-described second embodiment can be obtained.

In the first embodiment described above, the flat surface of the scan mirror is used as the back reflection surface only when the printer is used. It is used as a back reflection surface.

Further, in this embodiment, the photosensitive drum is used as the light receiving medium of the printer system, but a line sensor (CCD) may be used instead of the photosensitive drum to read the projected image.

[0049]

According to the present invention, as described above, the scan mirror as the projection scanning means of the copying system is constituted by the cylindrical rear surface mirror having a negative refracting power in the plane-concave scanning surface, and at the time of printer. By using the flat portion of the scan mirror as the back reflecting surface, it is possible to minimize the occurrence of barrel distortion and defocus of the copied image, and thereby obtain a good copied image without distortion. Thus, it is possible to achieve a scanning type image forming apparatus having a simple structure capable of achieving the above.

[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 enlarged explanatory diagram of a scan mirror according to the first embodiment of the present invention.

FIG. 3 is a schematic view of the essential portions of Embodiment 2 of the present invention.

FIG. 4 is a schematic view of the essential portions of Embodiment 3 of the present invention.

FIG. 5 is a schematic view of a main part of a conventional scanning image forming apparatus.

[Explanation of symbols]

 F Projected image L Projection lens M Scan mirror S Slit D Photoreceptor drum C Cylindrical lens CF Cylindrical Fresnel lens

Claims (8)

[Claims] 1. When the projection image is formed on a light receiving medium via a projection lens and a scan mirror, the scan mirror is synchronized with the projection image and the image formed on the light receiving medium. In a scanning type image forming apparatus for performing scanning exposure by rotating a lens, the scan mirror is composed of a backside mirror having a plano-concave cylindrical shape with negative refracting power, and image distortion caused by the rotation of the scan mirror. A scanning image forming apparatus characterized in that 2. The scanning image forming apparatus according to claim 1, wherein the back surface mirror has a negative refractive power in a scanning plane. 3. The flat portion of the scan mirror is used as a back reflection surface when copying the projected image on the light receiving medium via the projection lens and the scan mirror. No. 1 scanning type image forming apparatus. 4. The scanning image forming apparatus according to claim 1, wherein an optical element having a positive refractive power only in the scanning direction is arranged in the optical path between the projection lens and the scan mirror. 5. A scanning type image forming apparatus using a rotatable scan mirror fixedly arranged as a projection scanning means of a copying system, wherein the scan mirror has a plano-concave cylindrical shape having a negative refracting power. A scanning image forming apparatus comprising a rear-view mirror and correcting image distortion caused by rotation of the scan mirror. 6. The scanning image forming apparatus according to claim 5, wherein the back surface mirror has a negative refractive power in a scanning plane. 7. The scanning image forming apparatus according to claim 5, wherein the flat portion of the scan mirror is used as a back reflection surface during the copying. 8. The scanning image forming apparatus according to claim 5, wherein an optical element having a positive refracting power only in the scanning direction is arranged in the front optical path of the scan mirror.