JPS5960418A - Optical image formation system - Google Patents

Abstract

PURPOSE:To form an image accurately on an image formation surface by putting a transparent plate member which compensates variation in optical path length in the optical path of luminous flux when a thick luminous flux splitting means is released. CONSTITUTION:A half-mirror for splitting exposure luminous flux is arranged in a dichromatic copying machine and two pictures in different color are formed on a photosensitive drum separately. For obtaining a normal black-and-white copy, the half-mirror is released and a colorless, transparent glass plate, interference filter, or color filter which has specific thickness and a specific refractive index is inserted as a means for compensating variation in optical path length due to the thickness of the half-mirror.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging optical system in which a beam splitting means, such as a half mirror, is inserted into and removed from an optical path behind a lens that forms an image of a beam emitted from an object.

When dividing four beams of exposure light for forming a latent image into a plurality of beams, or when using them without dividing them, a method is often used in which a no-f mirror is provided in the optical path so that it can be inserted and removed.

For example, one method of a two-color color copying machine uses two photoconductor drums with different photosensitive characteristics, and the exposure beam is divided by a half mirror, so that the two-color images on the original are transferred to separate photoconductors. There is a method in which a latent image is formed on a drum, each developed with a developer of a different color, and then transferred onto the same transfer paper to obtain a two-color copy. This type of copier has two colors (for example, red and black)
Not only can you make copies of images, but you can also make regular black and white copies. An example of a two-color copying machine of this type will be explained with reference to FIG. 1. An original placed on a contact glass L is illuminated by an exposure lamp 2, 5. It passes through the imaging lens 6 and reaches the half mirror 7. The luminous flux is divided by the half mirror 7 into a luminous flux that goes to the red photosensitive drum 11 and a luminous flux that goes to the black photosensitive drum 12. Since the sensitivity of the red photoreceptor is generally lower than the sensitivity of the black photoreceptor, the amount of light for red is set to be several times the amount of light for black. The red light beam divided by the half mirror 7 passes through the fourth mirror 8 and the fifth mirror 9 and reaches the red photosensitive drum 11. On the other hand, the black light beam is reflected by the sixth mirror IO and reaches the black photosensitive drum 12. Both optical path lengths are made to be completely the same, and images are accurately formed on the photosensitive drums 11 and 12.

Around both photosensitive drums 11 and 12, known copying process units for developing, cleaning, etc. are arranged, respectively. The principles and functions of these machines are not particularly different from ordinary black-and-white copying machines. The red and black toner images formed on both photosensitive drums 11 and 12 are transferred to the same transfer paper fed from a paper feeding section 13.

At this time, the latent image forming position, drum diameter, distance between drums, and transfer paper passage are set so that red and black color misregistration does not occur.

In the copying machine having the above configuration, a red light beam is not required when black and white copying is performed. Therefore, if the half mirror 7 is removed from the optical path, the total amount of light reaches the black photosensitive drum 12, so that the amount of light from the document exposure lamp can be reduced. Alternatively, the copy speed can be increased to increase the number of copies per unit time.

However, if the half mirror is temporarily removed from the light beam during black and white copying, as will be explained in detail later, the effective optical path length from the original to the black photoreceptor changes, causing the image to not be accurately formed on the photoreceptor and hidden. Problems arise in that the image is blurred and the resolution is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide an imaging optical system having a beam splitting means as in the above example, which is capable of accurately forming an image on an imaging plane even when the light beam splitting means is removed. shall be.

This object is achieved according to the invention by inserting a transparent plate member into the optical path of the utilized luminous flux as means for compensating for the change in optical path length when the luminous flux splitting means is released. The thickness h of this plate member is the luminous flux splitting means ()\
- If the thickness of the plate member is ζ, the refractive index is 02, and the refractive index of this plate member is 02, then

The theory and embodiments of the present invention will be described in detail below with reference to the drawings.

Before explaining the embodiments, a change in the optical path length when a transparent plate is inserted into the optical path will be explained.

As shown in FIG. 2, a light ray that is incident on a point A on the top surface of a glass plate 20 having a thickness t at an incident angle of 1 with respect to the normal line is refracted at the surface of the glass and travels inside the glass at a refraction angle r. In this case, there is a relationship between the angle of incidence i and the angle of refraction r: n=sin I/sin r, which is known as Snell's law. This n is called the refractive index. The ray of light that has traveled through the glass exits into the air again at point B on the bottom surface of the glass and travels parallel to the original direction of incidence. Therefore, the normal line is greater than the path of the ray of light (indicated by the broken line) if there was no glass. It will move downward by X in the direction.

In the figure, the intersection of the extension of the incident ray and the bottom surface of the glass is C
, If we draw the intersection of the perpendicular line drawn at point B and the line segment AC, and let E be the foot of the perpendicular line drawn from point A to the bottom surface of the glass, then EC=AC5iIl+ EB=A-C5ill r BC=EC-EB=AC(gfnj -5fnr)Δ
Since AEC and △DBC are similar, DB AE BCEC BC-AE, ", D13= □ BC DB = x, AE = t ECAC5ifff sin i sin 1=t(1
--) Therefore, by inserting a transparent plate having a thickness t1 and a refractive index n relative to air perpendicular to the optical axis, the effective conjugate length is lengthened by t(X--). For example, the refractive index of glass is 1.5
In this case, x=t(1--)=t--=-151,53.

As shown in FIG. 3, when the transparent mounting is inserted obliquely to the optical axis, the optical axis after passing through the transparent plate is shifted from the extension line of the original optical axis (indicated by a broken line), The imaging point P moves in the normal direction of the plate 2o by an amount of X according to the above equation.

In the two-color color copying apparatus shown in FIG. 1, the half mirror 7 is inserted obliquely to the optical path, so the effective optical path length changes and the optical axis is also slightly tilted compared to the case without the half mirror 7. That will happen.

Therefore, after removing the half mirror,
If a transparent plate is inserted into the optical path at the same angle as the change in optical path length equal to the amount of change in optical path length due to It is possible to form an image without any problems.

Now, if the refractive index of the half mirror is n□ and the thickness is tl, the moving distance X of the imaging point caused by removing it is x = tl (1-) 1 From the above theory, to compensate for this If the refractive index of the transparent plate to be inserted is n2, then the thickness t2 at which the imaging point movement distance becomes X can be obtained from the following equation.

"" tx (1-)=t2 (1-)nl
n2 If the refractive index n2 of the compensating transparent plate is equal to that of the half mirror, t1=t2.

The transparent plate for optical path length change compensation may be a colorless transparent glass plate or plastic plate if it is for black-and-white copying, but if the light flux is to be used for other purposes, such as correcting the spectral sensitivity of the photoreceptor, the purpose It is also possible to use interference filters and color filters that match.

The optical path length compensating member and the beam splitting member are integrally coupled, and when one is removed from the optical path, the other is inserted into the optical path, thereby simplifying the operation and preventing forgetting to insert the compensating member. I can do it.

As a means for combining the optical path length compensating member and the beam splitting member together and moving them at the same time, the optical path length compensating member and the beam splitting member are integrally provided in an axially symmetrical manner with respect to an axis provided at a position outside the range of the beam of light in the optical path. By rotating around the center, both can be replaced in the same position and posture.

Examples will be described below with reference to the drawings.

In the embodiment shown in FIG. 4, the half mirror 7 and the transparent plate 21, whose respective refractive indexes and thicknesses have the above-mentioned relationship, are arranged y11 from the optical axis outside the range of the light beam in the optical path after passing through the imaging lens 6.
An integral Ic connection is made on both sides of the axis 22 orthogonal at f'L. Therefore, if it rotates 180 degrees around the axis 23,
The half mirror 7 is retracted from the optical path, and the transparent plate 21 comes to that position with the same attitude.

In another embodiment shown in FIG. 5, the half mirror 7 and the transparent plate 21 are integrally connected adjacent to each other on the same plane, and a shaft 22 is provided at right angles to these planes at the center point of the connecting line. There is. This shaft 22 has a rotary linenoid 23, and when energized it has an angle of 8° compared to when it is not energized.

It is designed to rotate.

Still another embodiment shown in FIG. 6 is the same as the embodiment shown in FIG. 5 in that the half mirror 7 and the transparent plate 21 are adjacent to each other on the same plane and are integrally combined, but the replacement means In this case, the combination of the half mirror 7 and the transparent plate 21 is attached to a wire rope 27 which is passed between a drive pulley 25 rotated by a step motor 24 and a guide pulley 26, and which moves in a direction perpendicular to the optical path. Step motor 2
By rotating the mirror 4 by a predetermined step, the half mirror 7 and the transparent plate 21 are replaced.

The present invention has been described above with respect to an imaging optical device having a half mirror mainly used in a two-color color copying machine. However, the present invention is not limited thereto, and the present invention can be applied to a thick plate-shaped light beam splitting device such as a half mirror. It can be applied to various imaging optical systems in which the means can be inserted and removed. For example, in a printer that records by emitting light from a light-emitting element in response to an information signal and exposing the photoreceptor, a half mirror is installed in the optical path from the light-emitting element to the photoreceptor, and the light beam is divided and left behind at the same time as the hard copy is produced. A device has been proposed that performs monitoring by projecting one of the divided light beams onto a display using a phosphor with a long light time, but even with this device,
When inspecting information by projecting a luminous flux only onto the display prior to producing a hard copy, the no-f mirror may be canceled. In this case, by applying the present invention, the resolution of the image on the display can be improved.

Of course, in the optical system shown in FIG. 1, it is possible to correct the movement of the imaging point by canceling the No. 1 mirror by moving the sixth mirror 10, but as described above,
The amount of optical path length movement by the half mirror is about 1/3 of the thickness of the half mirror, and therefore it is not appropriate to provide a mirror moving device and link it with the release of the half mirror, as this would rather increase the cost.

As described above, according to the present invention, when making black and white copies using a two-color color copying machine, for example, the number of copies per unit time can be easily increased without reducing the resolution, and the optical path length correction member can also be used as an optical path length correction member. By using an interference filter or a colored glass filter instead of transparent glass, various effects can be obtained, such as being able to correct the spectral sensitivity of the photoreceptor.

Note that the present invention can also be applied to a case where two or more beam splitting means are provided in the imaging optical system.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an example of a two-color color copying machine having an imaging optical system equipped with a beam splitting means, and Figs. 2 and 3 show changes in the optical path length when a transparent plate is inserted in the optical path. Schematic diagrams for explanation; FIG. 4 is a sectional view showing essential parts of an embodiment in which the present invention is applied to the optical system in FIG. 1; FIGS. 5 and 6 show other embodiments of the present invention, respectively. FIG. 6...Imaging lens 7...Half mirror (light beam splitting means) 11.12...
・Photoreceptor drum (imaging surface) 21... Optical path length change compensation means (transparent plate) 22... Axis Figure 1 q. 2 1iC11 31st I

Claims (7)

[Claims] (1) A lens that forms an image of a light beam emitted from an object, a light beam splitting means having a thickness that is provided in an optical path behind the lens so as to be insertable/removable, and the light beams divided by the means are formed into images, respectively. and at least two or more imaging planes,
In an imaging optical system that utilizes only the light beam that travels along the optical path that would have passed if the light beam splitter had been inserted when the light beam splitter was released, if the light beam splitter was released, the 1. An imaging optical system characterized in that a transparent plate member is inserted into the optical path of a light beam as a means for compensating for a change in optical path length caused by release of a light beam splitting means. (2) The thickness of the above optical path length compensating transparent plate member is, if the thickness of the light beam splitting means described in 2 is tl, the refractive index is nl, and the refractive index of the optical path length compensating member is n2, then An imaging optical system according to claim 1, characterized in that the imaging optical system has the following characteristics. (3) The imaging optical system according to claim 1 or 2, wherein the optical path length compensating member is a filter. (4) The above-mentioned optical path length compensating means and light beam splitting means are integrally provided axially symmetrically to a shaft provided at a position outside the range of the light beam of the optical path, and by rotating around the axis, An imaging optical system according to any one of claims 1 to 3, characterized in that one part is inserted into the optical path and the other part is released. (5) The imaging optical system according to claim 4, wherein the axis is separated from the optical path and perpendicular thereto. (6) The imaging optical system according to claim 4, wherein the axis is perpendicular to the plane of the beam splitting means. (7) The above-mentioned optical path length compensating means and light beam splitting means are integrally provided adjacent to each other on the same plane, and by moving in a direction perpendicular to the optical axis, one of them is inserted into the optical path and the other is released. An imaging optical system according to any one of claims 1 to 3, characterized in that the imaging optical system is configured as follows.