JPS60260029A - Image forming device - Google Patents

Abstract

PURPOSE:To correct a light quantity by simple constitution, by constituting a titled device so that a bias exposure of a light quantity for compensating roughly an illuminance drop portion with respect to an image forming body surface part having a low image exposing illuminance generated by an influence of a cosine four power rule, etc. of an image forming optical system is given by a bias exposure light source, at the same time as an image exposure to the image forming body surface. CONSTITUTION:l is image exposing light which is made incident on a slit exposing part surface of a photosensitive drum 10 from an image forming optical system, and an exposure quantity distribution of its exposing light has an uneven distribution as shown by a curve (4) of a graph. l25 is bias exposing light which is made incident on the slit exposing part surface of the photosensitive drum by turning on miniature lamps 25, 25 being bias exposure light sources, and an exposure quantity distribution running along the longitudinal direction of the slit exposing part surface of the photosensitive drum of the bias exposing light concerned is formed so as to show a distribution like a curve (5) of the graph. In this state, when bias exposures l25, l25 by the miniature lamps 25, 25 are given at the same time as the image exposure l to the photosensitive drum 10, the halftone light quantity running along the longitudinal direction of the slit exposing part surface of the photosensitive drum is equalized roughly as to each part as shown by a straight line (6) of the graph, by those exposure lights l, l25 and l25.

Description

DETAILED DESCRIPTION OF THE INVENTION A. OBJECTS OF THE INVENTION [Industrial Field of Application] The present invention relates to an apparatus for forming an image by exposing a document image onto the surface of an image forming body using an imaging optical system.

[Conventional technology]

Various image forming apparatuses as described above are known.

FIG. 1 schematically shows an example of a microfilm league printer as a specific example of such an apparatus. This printer will be specifically explained below using this printer as an example.

In the apparatus shown in FIG. 1, A is a microfilm l reset/illumination section as an original, B is an optical scanning mechanism section, and C is a copying mechanism section.

Microfilm 1 (roll microfilm Φ microfiche film 0 microstrip film, etc.) is a microfilm 1 (roll microfilm Φ microfiche film 0 microstrip film, etc.) whose target frame image 1a among the many frame images photographed and recorded on the film surface is searched by an automatic search mechanism (not shown) or manually. It is searched by the lighting section and held still. The frame image la in the illumination section is illuminated from below by an illumination lamp 2 such as a spherical halogen lamp through a condenser lens 4, and the film-transmitted light of the illumination light enters a projection lens 5.

3 is a reflective shade for the illumination lamp 2.

In the optical scanning mechanism section B, 11 is a first and a second mirror (
This is an optical scanning unit in which plane mirrors 6 and 7 are mounted and supported on a common support member 11a so that their surfaces, including their reflective surfaces, intersect at right angles. The unit 11
is always on standby with the one-dot chain line water position as its home position, and is moved to the right by a drive mechanism (not shown) based on a scanning start command signal to increase the rotational circumferential speed V of the photosensitive drum 10 as an image forming body, which will be described later. It is driven forward at the station's speed, and when it reaches the end point of the forward movement indicated by the two-dot chain line, it is driven back and returned to its initial home position.

When the optical scanning unit 11 is waiting at the home position, the first mirror 6 is located outside the optical path of the projection lens 5, and the film frame image/projection light emitted from the projection lens 5 is not shown. The image of the film frame image 1a is enlarged and projected onto the screen surface facing toward the league screen section C (leader state).

On the other hand, an enlarged copy (print) of the film frame image 1a
When a print switch (not shown) is turned on, the copying mechanism C starts operating and the photosensitive drum 10
is rotationally driven in the direction of the arrow at a circumferential speed V. Further, as described above, the optical scanning unit 11 is driven forward from the home position at the circumferential speed V of the photosensitive drum 10.

During the forward driving process of the unit hll, the film frame image projection light from the projection lens 5 is sequentially scanned by the first mirror 6 and reflected by the second mirror 7, and from the second mirror 7 it is transmitted to the slit member 8. The light passes through the slit portion 9 in the drum generatrix direction and enters the exposure position a of the rotating photosensitive drum IO. That is, an enlarged projected image of the film frame image 1a is sequentially projected onto the circumferential surface of the rotating photosensitive drum io, with slit exposure by the slit member 8 in the direction of the drum generatrix as the main scanning, and movement of the drum surface as the drum rotates as the sub-scanning. slit exposure (image exposure).

The photosensitive drum 10 of this example device has a photosensitive member with a three-layer structure of a conductive layer Φ photoconductive layer and a surface insulating layer on the circumferential surface of a drum base, and the following processes are sequentially performed during its rotational drive process. In response to this, image formation is performed and an enlarged copy of the target film frame image is output.

a, Uniform positive or negative charging by the primary discharger 12;

b. The above-mentioned image slit exposure at exposure position a, and DC discharge or AC discharge by the secondary discharger 13 with a polarity opposite to that of the charging by the primary discharger 12.

Uniform light irradiation by the C1 entire surface exposure lamp 14. More than as
By the bac process, electrostatic latent images corresponding to the image exposure pattern are sequentially formed on the circumferential surface of the drum.

d. Toner development of the latent image by the developing device 15.

e, transfer material 1 of developed toner image by transfer charger 16;
Transcription to 7.

f. Separating the transfer material 17 from the photosensitive drum surface, introducing it into a fixing device (not shown), and ejecting it from the device (print output).

g. Cleaning and neutralizing the photosensitive drum surface after transfer using the cleaner 18 and the static eliminating discharger 19.

By the way, in an imaging optical system, there is a phenomenon in which the image plane illuminance (exposure amount) decreases at the periphery of the imaging screen due to the cosine fourth power of the lens. Therefore, in the apparatus of the above example, based on this phenomenon, the exposure position a of the surface of the photosensitive drum 10, which is the surface of the object to be projected, is
Longitudinal surface of slit exposed area (photosensitive drum generatrix direction)
The exposure amount along the slit surface gradually decreases from the longitudinal center toward both ends, resulting in uneven exposure distribution. The degree of unevenness in the exposure distribution varies depending on the lens magnification. Curves ■ and ■-■ in the graph of Figure 2 have lens magnifications of X 14.5 and X 48, respectively. This figure shows an example of the above-mentioned exposure amount distribution unevenness in each case of X24 (the film frame image that is the subject is assumed to be a blank image).

In addition to the above-mentioned unevenness in exposure distribution occurring due to the cosine-fourth power side of the lens, in the case of the above example, the illumination lamp 2 is a spherical lamp that emits light radially to illuminate the surface of the film frame image la, which is the subject. Strictly speaking, this is related to the fact that the illumination intensity on the image plane of the film frame is lower in the center than in the periphery of the image plane. Even when a straight tube fluorescent lamp or halogen lamp is used as an illumination lamp to illuminate the image plane, which is the subject, the light intensity distribution along the length of the straight tube lamp is generally more concentrated at the ends of the tube than at the center. This is also relevant since the amount of light has a small distribution unevenness.

If image formation is performed without correcting the exposure dose distribution unevenness as shown in the graph of FIG. 2, the resulting printed image will have image unevenness corresponding to the exposure dose distribution unevenness described above. In particular, unevenness occurs noticeably in halftone areas or thin line areas, resulting in poor image quality.

Therefore, in the past, in order to correct the above-mentioned exposure dose distribution unevenness,
Either insert an optical filter into the imaging optical system that increases the density/density at the longitudinal center in the opposite relationship to the exposure distribution unevenness curve, and decrease the density toward both ends, or In a reverse relationship, the slit hole of the slit part 9 is narrowed in the longitudinal center and widened toward both ends, thereby making the exposure dose distribution uniform along the longitudinal direction of the slit exposure area surface. ing.

[Problem that the invention seeks to solve]

However, since both the optical filter means and slit hole shape means described above are designed to adjust the exposure correction level to a low level of exposure distribution unevenness, there is a problem in that the light loss is large.

In the case of an image forming apparatus having a variable magnification function, a plurality of correction optical fino holes or slit members corresponding to various switching magnification ratios may be provided, or the shape of the slit hole of the slit member may be freely changed. Each time the magnification is changed, it is necessary to switch to an appropriate optical filter or slit member corresponding to the magnification, or to change the shape of the slit hole, resulting in a problem that the mechanism configuration becomes extremely complicated.

The present invention is devised so that the light amount can be corrected without the above-mentioned problems.

Summary: Structure of the Invention [Means for Solving Problems] The present invention provides an apparatus for forming an image by exposing an original image onto the surface of an image forming body using an imaging optical system. A bias exposure light source that provides bias exposure separately from image exposure is provided, and simultaneously image exposure to the image forming body surface is performed.
The bias exposure light source is configured to apply bias exposure with an amount of light that substantially compensates for the decrease in illuminance to the image forming body surface portion where the image exposure illuminance is low due to the influence of the cosine-squared side of the imaging optical system, etc. The gist of the present invention is an image forming apparatus characterized by the following.

[Function/Effect] As mentioned above, at the same time as image exposure on the image forming body surface,
By providing bias exposure with a light amount that approximately compensates for the decrease in illuminance to the image forming surface with low image exposure illuminance (image exposure amount) caused by the influence of the cosine squared side of the imaging optical system, etc., the bias can be reduced. During exposure, unevenness in image exposure on the surface of the image forming body is compensated and corrected, and the amount of halftone light on the surface of the image forming body is approximately equalized overall. As a result, noticeable image unevenness that tends to occur particularly in halftone areas and thin line areas can be suppressed, and it is possible to obtain a high-quality image with little or substantially no image unevenness overall.

In this case, since the unevenness in the exposure distribution on the image forming body surface is corrected by applying bias exposure to a region of the image forming body surface where the exposure amount is small (low image surface illuminance), the above-mentioned conventional optical filter means or There is no problem of light amount loss due to image exposure narrowing as in the slit hole shape means.

In addition, correction for changes in the exposure distribution unevenness as shown in Figure 2 due to the magnification conversion of the imaging optical system is performed by adjusting the exposure amount on the image forming body surface of bias exposure in response to the exposure distribution unevenness that has changed due to the magnification conversion. This can be easily handled by changing the exposure area, or both, and the correction adjustment means can be configured as a simple mechanism.

〔Example〕

FIG. 3 shows the first embodiment, in which a slit and a pump 25 as a bias exposure light source are installed at both ends of the slit exposure section at the exposure position a of the photosensitive drum 1O, which is an image forming member.
-25 is installed. fL is image exposure light that enters the exposed surface of the photosensitive drum 10 from the imaging optical system, and the exposure amount distribution of the exposure light along the length of the exposed surface of the photosensitive drum slit is determined by the cosine-quadratic agent of the lens, etc. by the fourth
It is assumed that there is an uneven distribution as shown by curve (■) in the graph. Reference numeral 25 indicates bias exposure light that is incident on the exposed surface of the photosensitive drum slit by lighting of small lamps 25, 25 serving as bias exposure light sources, and the exposure amount distribution of the bias exposure light along the length of the exposed surface of the photosensitive drum slit is as described above. The light emitting quantity position of the small lamps 25, 25 is set in advance so as to compensate for the lack of exposure on both ends of the image exposure distribution curve (■).
The graph in FIG. 4 shows a distribution like the curve (■).

Therefore, when bias exposure 125 and 25 from the small lamps 25-25 are applied simultaneously to the image exposure light to the photosensitive drum 10, the half along the length of the exposed surface of the photosensitive drum slit is generated by these exposure 25-125. The amount of tone light is approximately equalized in each part as shown by the straight line (2) in the graph of FIG.

This allows image formation with little or substantially no image unevenness.

In addition, the exposure amount distribution characteristic of the bias exposure light along the length of the exposed surface of the photosensitive drum slit (curve ■ in the graph in Figure 4) is the exposure amount or exposure area of the bias exposure light to the photosensitive drum;
Alternatively, various changes can be made by changing both of them. Specifically, a. The amount of light emitted from the miniature lamp 25-25, which is a bias fog light source, is electrically controlled to be strong or weak.

b. Small lamp 2 as a bias exposure light source as shown in the example in Fig. 5.
Near 5-25, movable light shielding plates 26, 26, which can be freely moved in position by, for example, a forward/reverse small motor and a threaded rod, are arranged.
The bias exposure area with respect to the photosensitive drum surface is changed by automatically or manually moving the light shielding plates 26, 26 relative to the miniature lamps 25, 25, respectively.

C. The bias exposure light source is composed of a plurality of miniature lamp groups 25a, 25b, and 25c as shown in the example in FIG. By turning on the light, the bias exposure amount and exposure area for the photosensitive drum surface are changed.

etc.

Therefore, in response to a change in the image exposure distribution due to the magnification conversion of the imaging optical system, the exposure distribution of the bias exposure light along the length of the photosensitive drum slit exposure distribution is adjusted by the above-mentioned means in conjunction with the magnification conversion. By changing the characteristic to an appropriate distribution characteristic in the direction of correcting the distribution unevenness regarding the image exposure amount distribution characteristic for each switching magnification, it is possible to easily and appropriately correct and deal with various aspects of image exposure amount distribution unevenness. be able to.

Also, due to reasons such as the optical axis center of the illumination lamp 2 in the illumination section A being misaligned from the optical axis of the optical system during assembly, the exposure amount peak portion of the image exposure amount distribution characteristic along the length of the exposed surface of the photosensitive drum slit. Even if it is shifted toward one end of the photoconductor drum slit mist surface from the center of the longitudinal direction as shown by the curve ■ in the graph of Fig. 7, the bias exposure light source at both ends will be adjusted accordingly. 25 (25a, 25b-25c) by controlling and adjusting the bias exposure amount and exposure area for the longitudinal direction of the exposed surface of each photosensitive drum slit to provide bias exposure with an exposure distribution characteristic as shown by curve (■).
Correction can be easily and appropriately carried out.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of an example of an image forming apparatus (a microfilm league printer), Fig. 2 is a graph of the relationship between lens magnification and image exposure distribution characteristics, and Fig. 3 is a schematic diagram of an image forming apparatus equipped with a bias exposure light source. FIG. 4 is a graph showing the relationship between image exposure distribution characteristics, bias exposure distribution characteristics, and correction light amount distribution. FIG. FIG. 6 is a schematic diagram of a third embodiment equipped with a plurality of bias exposure light sources,
FIG. 7 is a graph of the image frost light amount distribution characteristic in which the exposure amount peak position is shifted and the bias frost light amount distribution characteristic for correcting it. 25.25as25b*25c is bias exposure light source, 2
6 is a movable light shielding plate.

Claims (2)

[Claims] (1) In an apparatus that performs image formation by exposing a document image onto an image forming body surface using an imaging optical system, a bias exposure light source is provided that applies bias exposure to the image forming body surface separately from the image exposure; Simultaneously with the image exposure on the image forming body surface, bias exposure of a light amount that approximately compensates for the decrease in illuminance is applied to the image forming body surface portion where the image exposure illuminance is low due to the influence of the cosine quartic agent of the imaging optical system, etc. using the above bias. An image forming apparatus characterized in that the image forming apparatus is configured to provide exposure light with an exposure light source. (2) Adjust the exposure amount of bias exposure or the exposure area, or both, in response to changes in the area of the image forming body surface portion where the image exposure illuminance is low and the degree of illuminance reduction that occurs with the magnification conversion of the imaging optical system. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to change the image forming apparatus.