JPS58169141A - Image-forming optical system in electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To prevent the excessive increase in the uneven illuminance on the surface of a photoreceptor that arises in the stage of changing an image-forming magnification without using a movable shading device by determining the magnification so as to avoid an excessive increase in the deviation of the illuminance. CONSTITUTION:When the magnification is max. m1, the half field angle theta0 of a lens in the unmagnification stage and the half field angle theta1 at the m1 differs; as a result, the luminance S1 in the end part is lower than the luminance at the center in the luminance distribution L21 of a picture image on the surface of a photoreceptor. Conversely, when the magnification is min. m2, the luminance S2 in the end part of the image is higher than the luminance at the center in the luminance distribution L22 of the image on the photoreceptor. If the luminance on the surface 17a of the photoreceptor is set at Sm when the magnification is 1, the luminance at the center D of the image is Sm both when the magnification is m1 and when m2. The image-forming magnification (mb) is determined as mbnot equal to 1 so as to satisfy 0.8<r<1.2, more preferably r=1 if (Sm- S1¦/¦Sm-S2¦. The magnification is determined empirically or thermoretically with ease.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a light source that illuminates the surface of a document, and a lens that focuses reflected light from the surface of the document onto the surface of a photoreceptor to form an image of the document on the surface of the photoreceptor. The present invention relates to an imaging optical system in an electronic copying machine that is configured to be convertible.

Imaging optical systems of the type described above are well known in the art. .

When using this type of optical system to form an image (latent image) on the surface of the light body, the light from the light source illuminates the entire document surface with a uniform amount of light, and the illuminance distribution on the document surface is uniform. In other words, if it is made flat, the 4θ law, the 1 Tsunaguchi efficiency of the lens (this is 1
00%], the illuminance at the edges of the image on the photoreceptor is lower than the illuminance at the center, and if this is visualized, density unevenness will occur in the visible image. Not immune to shortcomings. From this point of view, conventionally, the illuminance distribution on the surface of the document has been adjusted so that the above-described unevenness does not occur in the illuminance distribution of the image formed on the surface of the photoreceptor.

This method intentionally makes the illuminance distribution on the document surface uneven, thereby increasing the aperture efficiency of the lens, CQ! This is intended to compensate for the influence of the l'θ law and thereby eliminate uneven illuminance distribution on the photoreceptor. In this case, if the original image is always formed on the photoconductor at the same magnification by the imaging optical system, the illuminance distribution on the document surface is uniformly determined so that the illuminance on the photoconductor is uniform. This is sufficient and does not cause any particular problem. If the optical system has a variable magnification function for magnification and reduction, even if the illuminance distribution on the document surface is set so that the illuminance distribution on the photoreceptor surface is flat at the same magnification, the imaging magnification If the image changes from the same magnification to enlargement or reduction, the angle of view of the lens also changes, and the value of μs4θ (θ is a half angle of view) changes, so the illuminance distribution on the photoreceptor will not be flat, and the illuminance will change. Unevenness is inevitable. There is no problem if this illuminance unevenness is slight, but in conventional imaging optical systems, there is a risk that this illuminance unevenness becomes so large that it cannot be ignored.

One way to eliminate the above disadvantage is to adjust the amount of light directed from the light source toward the document surface using a movable shading device according to the magnification, so that even if the magnification changes, illuminance unevenness will substantially occur on the surface of the photoreceptor. There are ways to prevent this from happening. However, if such a device is provided, the installation cost of the optical system increases and its weight inevitably increases.

An object of the present invention is to provide a structure in which the illuminance unevenness on the surface of a photoreceptor that occurs when converting the imaging magnification does not become extremely large as in the past, without using a movable shading device that causes an increase in cost. The object of the present invention is to provide an imaging optical system capable of

In the present invention, the illuminance distribution on the document surface is simply determined so that the illuminance distribution on the surface of the photoreceptor at the same magnification is uniform in the conventional imaging optical system. It is constructed based on the new recognition that irreversible unevenness in illumination occurs on the photoreceptor.

FIG. 1 is a partial view showing an example of a copying machine having an imaging optical system to which the present invention can be applied. In order to understand the present invention, first, the configuration shown in FIG. 1 and the outline of its operation will be briefly explained, and then the fact regarding the uneven illuminance distribution and the idea of the present invention regarding this will be explained in accordance with the illustrated configuration. , will be explained in more detail, and advantageous embodiments of the invention will also be explained in detail.

In FIG. 1, an optical unit 3 including a casing 1 and an imaging optical system 2 provided inside the casing 1 is provided at the top of the copying machine, and a contact glass 4 is fixedly installed at the top of the casing 1. ing.

The casing l of the optical unit 3 is fixedly supported by the main body frame 5 of the copying machine.

The imaging optical system 2 includes a lamp 6 as a light source and a movable mirror 7.
A first scanning device 8 carrying a Tough 1 mirror 9, a second scanning device IO carrying a Tough 1 mirror 9, and a bottom plate 11 of the casing 1,
A lens 12 supported movably in the optical axis direction and its support 13, and a fixed mirror 1 fixed on the bottom plate 11.
4.

First and second scanning devices8. The lO is drivingly connected to a drive motor (not shown) via transmission means (not shown).

During a copying operation, the first and second scanning devices 8 and 10 are driven in the directions of arrows A and B by the operation of the drive motor, and at this time, light from the lamp 6 illuminates the original 15 placed on the contact glass 4 The reflected light is reflected by a movable mirror 7 and a Tahama mirror 9, and then is passed through a still lens 1.
Pass through 2 and reflect at fixed Mi→-14, then the bottom plate 1
The light passes through a slit 16 formed in the main body frame 5 and is focused on the surface of a drum-shaped photoreceptor 17 supported by the main body frame 5, and an image of the original 15 is formed thereon. At this time, photoreceptor 1
7 has its surface charged by a charger (not shown) and rotates in the direction of arrow C. An electrostatic latent image is formed on the photoreceptor by the irradiation of the light, and this latent image is well known. A developing device (not shown) produces a visible image, and this visible image is transferred onto transfer paper by a transfer device, also not shown.

A normal copying operation is performed as described above, but when converting the imaging magnification, the lens 12 and mirror are operated as follows.

That is, assuming that the position of the lens 12 indicated by the solid line in FIG. The support 13 is moved to the right in the figure along the optical axis of the lens by a distance corresponding to its magnification ratio, thereby shortening the optical path length (coast point distance) between the lens 12 and the photoreceptor. (The dashed line indicates the position of the lens at the time of the test). Furthermore, at least one mirror existing in the optical path between the lens 12 and the document surface, such as the roof mirror 9, is moved to the left in the figure to change the object point distance and conjugate length (the position of the roof mirror at this time is also shown in Figure 1). (indicated by a dashed line). On the other hand, when increasing the imaging magnification, the lens 12 is moved to the left (this position is shown by a broken line), and the roof mirror 9, for example, is moved to the position shown by a broken line. This allows the object point distance and the conjugate length to be changed according to the imaging magnification, and the photoreceptor 17 can be adjusted at a predetermined magnification.
An image (latent image) can be formed thereon.

By the way, if the entire surface of the document to be illuminated is illuminated with a uniform amount of light, the illuminance distribution will be as shown schematically above the document 15 in FIG. As a result, the aperture efficiency of the lens 12 and the portion 4
Due to the influence of the θ law, the illuminance distribution L21 on the photoreceptor 17, as schematically shown in FIG. This results in the disadvantage that the
By appropriately setting the position of the light emitting part (for example, filament) of the lamp 6, or attaching a cover having a slit of a predetermined shape to the lamp, the illuminance distribution L1 on the document surface as shown in FIG. The illuminance is adjusted so that the illuminance at each end is high and the illuminance at the center is low, so that the α illuminance distribution L2 on the photoreceptor 17 is uniform, that is, flat. FIG. 3 is a schematic graph showing the illuminance on the photoconductor on the vertical axis and the axis X direction 1 (FIG. 2) of the photoconductor surface 17a on the horizontal axis. The distribution shown by is the illuminance distribution on the photoreceptor shown in FIG. 2(b) and described above. As can be seen, the illuminance is almost uniform at both the edges and the center of the image on the photoreceptor, and its distribution is flat. In this case, conventionally, when the imaging magnification is 1, the above-mentioned flat illuminance distribution L2 is formed on the photoreceptor.
Although the illuminance distribution on the document surface is determined so as to obtain the following, such a setting method may cause problems as described below.

First, to simplify the explanation, let ml be the maximum magnification when the original image is enlarged to the maximum extent and formed on the photoreceptor, and m2 be the magnification when the original image is reduced at the largest rate, that is, the minimum magnification. . Lens 1 when forming an image at the same magnification with an imaging magnification of 1
Assuming that the position No. 2 is the position of the solid line a predetermined distance away from the photoreceptor surface 17a, as schematically shown in the upper part of FIG. 3, when the magnification is m2, As explained above, the lens 12 approaches the photoconductor surface 17a and is at the position shown by the dashed line in FIG. occupies In this case, if the illuminance distribution on the document surface is determined so that the illuminance distribution on the surface of the photoconductor is flat when the magnification is l, then when the magnification is the maximum m, half the image of the lens at the same magnification is As a result of the difference between the angle θ0 and the half angle of view θl at m1, the illuminance distribution of the image on the photoreceptor surface is as follows.
The illuminance S at each end is as shown with reference numeral L21 in FIG.

is lower than the central illuminance. On the other hand, m with the minimum magnification
2, the illuminance distribution of the image on the photoreceptor is as shown in FIG. 3 with reference numeral Ii2□, and the illuminance S2 at the edge of the image is higher than the illuminance at the center. In this case, if the illuminance on the photoreceptor surface becomes flat, that is, in this case, the illuminance on the photoreceptor surface 17a when the magnification is 1 is 5IT1, both when the magnification is ml and - , the illuminance at the center of the image is Sm. This is because the center of the image is not affected by the 4θ rule. For example, even when the illuminance distribution on the surface of the photoreceptor is adjusted to be flat, depending on the type of illumination light source, irregularities, generally called ripples, can occur in the illuminance distribution, as shown in FIG.
In this specification, such unevenness is completely ignored.

Now, as mentioned above, conventionally, when the magnification is 1, the illuminance distribution on the surface of the photoreceptor is flat.
The illuminance distribution on the document surface was determined, but if this illuminance setting method is adopted, the maximum magnification is m* m, and the minimum magnification is m
Depending on how to set 2, the illuminance S at the edge of the image at ml or m2, S2 and the illuminance Sm at the center
18m-811 (this is set as δ1), l
There is a possibility that either one of 5m-821 (also referred to as δ2) may become extremely large. In this way, the illuminance S
If the deviation δ1 or δ2 in illuminance from m becomes extremely large, significant density unevenness will occur in the visible image obtained from the image due to this unevenness in illuminance. If the above-described movable shading device is used to eliminate this drawback, the above-described drawback of increasing the cost of the optical system cannot be avoided.

The present invention is based on the above-mentioned novel recognition, and is based on the conventional method in which the imaging magnification (this is referred to as mb) is uniformly set to the same magnification when making the illuminance distribution on the surface of the photoreceptor uniform or flat. The above idea of illuminance bias δ1 or δ
Preferably δ1-δ2 so that 2 does not become extremely large.
The configuration for determining the magnification mb is designed so that the above magnification mb is determined. That is, in the present invention, when the illuminance distribution on the photoreceptor surface is approximately flat, the illuminance of the image formed on the photoreceptor surface is set to Sm, and when the maximum magnification is m8, the Let the illumination intensity at the edge of the image formed on the body surface be Sl in this case as well, and the minimum magnification m
When the illuminance at the end of the image formed on the surface of the photoreceptor in 2B4 is similarly set to 82, the imaging magnification mb is preferably determined so as to satisfy the following.

If the magnification mb is set as described above, as can be seen from FIG. It is possible to completely eliminate the inconvenience of one of them becoming larger. In other words, in the present invention, the illuminance bias δ1. δ2
Although it does not occur that either δ1 or δ2 becomes particularly small, it is possible to eliminate the drawback that either δ1 or δ2 becomes extremely large, which results in an image with extremely large density unevenness. It is possible to eliminate fatal flaws in the machine's functionality. Thus, without the use of a movable ink device, the occurrence of extremely large illumination irregularities is prevented, and the reason for the visible image is that δ1 or δ2 is particularly undesirable if the value of the ratio is within this range. It has been confirmed through experiments that the value of mb\l does not become extremely large.
The purpose of this is to make it clear that conventional thinking has been abandoned. However, even if the above conditions are met, δ,
Alternatively, if δ2 itself becomes too large, it will cause uneven illuminance on the surface of the photoreceptor and therefore uneven density of the visible image, so this should be taken into consideration when actually configuring the imaging optical system. Of course. No significant density unevenness was observed in the visible images in the experiment.

According to the above-mentioned concept of the present invention, in order to actually determine the multiplication factor mb, kneading can be easily determined experimentally or theoretically. Therefore, in order to understand the present invention, an example of a method for theoretically determining the value of mb will be described below. As mentioned above, uneven illuminance at the edge of the image on the surface of the photoconductor occurs when the aperture efficiency of the lens is less than 100% and due to the influence of the 4θ law. Let us consider the case where the aperture efficiency is 100 cm, and consider the case where ma is determined.

As shown in FIG. 5, the lens 12 is positioned between the photoreceptor surface +7a, which is an image plane, and the document surface 15a, which is an object plane. The size of the document surface 15a is considered with its center D' as a reference, and X is taken in the direction of the edge of the document surface (hereinafter referred to as image height). Although the maximum size of the document surface in the X direction is constant, the maximum value xm' of the object surface, that is, the maximum image height, varies depending on the magnification. It is assumed that the optical axis of the lens 12 coincides with the principal ray, the tefocus is ignored, and the focal length of the lens is f.

Now, assuming that the half angle of view when forming an image at magnification m is generally θn1, the following equation can be obtained, as can be seen from FIG.

10”=1+m=(1+m) fHere, the magnification is m
Considering the illuminance distribution on the photoreceptor surface (image surface) 17a when
The illuminance at a point P on the surface of the photoreceptor, which corresponds to the point P' located at a distance of X at a, can be expressed by the following specific illuminance.

The zero value is the half angle of view when the magnification mb is to be determined, and the illuminance at the center D is 1, so 4θmb=1.

From equation (1), the illuminance RQ on the photoconductor surface corresponding to xm0 (center of the document surface) is 1, and IRq-t+ is maximum at the point on the photoconductor surface corresponding to the points X-x and TI. 1RQ-tl means the bias in illuminance when the magnification is m with respect to illuminance 1 = where, if m)mb, then RQ-1<Om
(If there is mb, RQ-1) 0th order, large amount magnification”
Let xm be the maximum X of m', 'M, and let Xm2 be the maximum X of the ratio m2@, and the illuminance at the point on the surface of the photoreceptor corresponding to each point xml, xm2 will be respectively. m, )m b )m2, so equation (2) is PA・RQ++RQ2-2 = 0
(31. Therefore, substituting equation (3) into equation (1) and rearranging, C4mb' + C3mb3-1-C, mb2
-1- C,mb + Cl1=OHere, the magnification mb can be easily obtained. When the aperture efficiency is less than 100%, mb can be obtained by taking this into consideration and using a method similar to the method described above.

As described above, according to the present invention, the intended purpose can be achieved with a simple configuration. It should be noted that FIG. 1 merely shows an example of a copying machine to which the present invention can be applied for the purpose of understanding the present invention, and the present invention can also be applied to various other types of copying machines. For example, when converting the magnification, the lens is not moved in the direction of its optical axis, but instead it is used in copying machines with an optical system that uses a separate lens, or in direct-copying machines that use a photoreceptor as the final copy. Widely applicable.

[Brief explanation of the drawing]

FIG. 1 is a partial diagram showing an example of a copying machine to which the invention can be applied; FIG. The figure shows the illuminance on the surface of the photoreceptor at the same magnification and at variable magnification, and is an explanatory diagram that clarifies the drawbacks of the conventional configuration and the configuration according to the present invention.
FIG. 4 schematically shows an example of a more practical illuminance distribution on the photoreceptor, and FIG. 5 is a schematic diagram illustrating the relationship between the photoreceptor, the drum, and the document surface. 2... Imaging optical system 12... Lens 15a
...Document surface 17a...Photoconductor surface E...
・End part 1i2...Illuminance distribution S, ,
S, , Sml...Illuminance Figure 2 (b) 1. 31st Deposit Figure 4 1 Good 1 5!・1 Procedural amendment (voluntary) June 12, 1980 Director General of the Japan Patent Office Shima 1) Haruki Tono1, Indication of the case 1982 Patent Application No. 0527152, Title of invention Bonded optical system in electronic copying machine 3. Relationship with the person making the amendment Patent applicant address 1-3-6 Nakamagome, Ota-ku, Tokyo Name (67)
4) Ricoh Co., Ltd. Representative Dog Breed Samurai 4, Agent 105 Address 1-9-9 Nishi-Shinbashi, Minato-ku, Tokyo Chugin No. 5 Hif
iv 3rd Floor Ta (501) No. 4887 (11 Column for detailed explanation of the invention in the specification (2) Column for brief explanation of the drawings in the specification (3) Drawing 6, contents of amendment (]) Specification No. 6 Correct “C direction” on page 14, line 14 to “direction”. (2) Correct “lens magnification” on page 7, line 3 to “lens position”. (3) Correct “lens position” on page 7, line 13. ``Dahemira'' is ``Dano''
Mirror,” he corrected. (4) "Document surface... fluctuates" on page 15, lines 7 to 9. In this case, the maximum size of the document itself in the X direction (this is referred to as X') is constant, or the size of the maximum value difference varies depending on the magnification.'' I am corrected. [1+(-22-1)! ]” (1+m)・f Correct. (8) On page 17, line 7 of the same page, change [(group ceremony to (]) ceremony” to “(1
) formula: ``The illuminance at the edge of the image formed on the surface of the photoconductor'' explained earlier with reference to FIGS. It goes without saying that you should consider the illuminance of the area. For example, the third
As shown in Fig. a (a), the effective image forming area W of the photoconductor is exactly set during the same-magnification image formation, and the area W1 and the original are set so that the original image of the maximum size X' in the X direction can be formed at the same time. If the maximum size of J5 is determined, at the maximum magnification, the 3rd a
(As shown by the broken line in the mouth IK) 2 itself has the ability to form an image with a larger width W2, but the photoreceptor 17
As shown by the two-dot chain line above, images with different widths are formed in the effective image forming area. Therefore, in such a case, the illuminance at the edge E of this image and its deviation from the center illuminance δ, should be considered as the illuminance at the edge of the image and its deviation as described above. For reference, if the length of the photoreceptor is set as shown in Figure 3a, at the minimum magnification, the lens 121H;
As shown by the dashed line in →, it has the ability to form an image Wsk of an object within a range of xm2' in the X direction, but since the maximum size of the document X' is smaller than 'xm2', in reality,
An f-elevation of W4, which is smaller in width than W3, is formed on the photoreceptor ]7. In this case as well, the illuminance at the end E of this image and its bias δ are considered as the illuminance and bias described above. In addition, when explaining the theoretical formula above, we did not take into account the large document size or the length of the photoreceptor, and clarified the theory that holds generally, but when actually determining mb,
xml ' xm2, taking into account the size of the above manuscript, etc.
It is necessary to think about this. For example, the maximum size of the original in the X direction
′ and the effective image forming area width W of the photoreceptor 17 are expressed as 3rd a.
When set as shown in the figure, at maximum magnification the lens]2
The maximum value in the X direction of the document that can be formed in the effective image forming area of the photoreceptor by the lens 2 is, as shown in FIG. also becomes smaller (Wt <
Wt), and even at the minimum magnification, as can be seen from Figure 3a (c), the maximum value xrT12 is m2 smaller than the maximum value at which the lens ]2 can image the original (W4<W3). For). ” (10) The expression “moteroshita” on page 19, line 5 was expressed once.”
I am corrected. (11) On page 19, line 8 of the same page, “Explanatory diagram, after j” “3a
Figures (A) to (C) are explanatory diagrams schematically showing an example of the relationship among the photoreceptor, lens, and document when the magnification is changed.・(]2) Add Figure 3a. Procedural amendment (method) August 24, 1980 was filed with Director-General Kazuo Wakasugi (1) Indication of Patent Application No. 52715 (1983) (2) Name of the invention (3) Imaging optical system in an electronic copying machine (3) Case of a person making corrections Relationship Patent applicant address 1-3-6 Nakamagome, Ota-ku, Tokyo Name (67
4) Ricoh Co., Ltd. 4th generation director 105 Address 3, Chugin 5th Building, 1-9-9 Nishi-Shinbashi, Minato-ku, Tokyo
Floor Tl (501) 4887 July 9, 1981 Drawing 7, Contents of amendment

Claims (1)

[Claims] (1) An electronic device that has a light source that illuminates the document surface and a lens that focuses reflected light from the document surface onto the photoconductor surface to form the document image on the photoconductor surface, and is configured to be able to convert the imaging magnification. In the imaging optical system of a copying machine, the imaging magnification when the illuminance distribution on the photoreceptor surface is almost flat is mb, and the illuminance of the image formed on the photoreceptor surface at this time is Sm5I! jL When the illuminance at the edge of the image formed on the photoconductor surface at high magnification is 81, and the illuminance at the edge of the image formed on the photoconductor surface at minimum magnification is 82, the above conclusion is set so that the following is satisfied. Image magnification mb was determined