JP2644232B2 - Exposure equipment for color copiers - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus for a color copying machine that sequentially projects and forms an image on an image forming surface such as a photoconductor through three different color separation filters.

Prior Art As shown in FIG. 4, as a full-color copying machine utilizing an electrostatographic process, three separation filters 3B, 3G, 3R of blue, green, and red are provided in the optical paths of the same imaging optical systems 1, 2. Is selectively inserted, and the color original placed on the contact glass is illuminated by the white light source 4, and the reflected light is sequentially passed through the color separation filters 3B, 3G, and 3R to the photosensitive member 7 at the same position. The three latent images obtained are projected and imaged, developed with yellow, magenta, and cyan toners, which are complementary colors of each color separation light, by developing devices 6Y, 6M, and 6C, respectively, and superimposed on one copy paper. 2. Description of the Related Art A color copying machine of a color separation image superimposing transfer system for transferring a color image is well known.

By the way, it is well known that even if the medium such as glass or water is the same, the refractive index differs depending on the wavelength of light.
As a result, when an image is formed by the lens, the image forming position differs depending on each color light, and chromatic aberration occurs. For photographic lenses,
In order to solve this problem, an achromatic lens such as an achromat having two colors in focus using various glasses and an apochromat lens having three colors have been used. The above achromatic lens is not used in the imaging lens described above because of cost. In particular, when a convergent light transmitter array (commonly referred to as a Selfox lens array: abbreviated as SLA), which has recently been used for the purpose of reducing the size of an apparatus, is used as an imaging element, achromatization is impossible. As an example, SL with a distance of 63.5 mm between the imaging surface and the document surface
The change in the conjugate length due to the wavelength of light of the optical system using A is the second
As shown in the figure. In this case, the contact glass is ignored. That is, at a wavelength of 400 nm, the conjugate length is 62 mm, and at a wavelength of 700 nm, the conjugate length is 66 mm.

Therefore, when blue, green, and red filters are selectively inserted into the exposure light path and the reflected light of the document at the same position is projected on the photoconductor at the same position, the focus is adjusted to a certain color. Is also out of focus in the other two colors,
When the image is developed with color toner and transferred by superposition, a difference in resolution depends on the color, and a good image cannot be obtained.

The present invention solves the above-mentioned problems of the conventional color separation image superimposing transfer type color copying machine exposure apparatus, and corrects a difference in optical path length caused by a difference in wavelength of each color light. The purpose of the present invention is to provide an apparatus.

Configuration In order to achieve the above object, the present invention provides an imaging optical system.
The wavelength of each color light so that the effective value of the image forming optical path length for each color separation light of blue, green and red of the image forming element such as SLA is equal to the distance between the original placing surface and the predetermined image forming surface. A transparent flat plate having a thickness for correcting a difference in optical path length caused by the difference is inserted into the imaging optical path in accordance with insertion of each color separation filter.

The correction of the optical path length can also be performed by inserting a transparent flat plate into the optical path and moving an imaging element such as a lens in the optical axis direction in accordance with the insertion of each color separation filter.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In the present invention, the effective value of the image forming optical path length is changed by inserting a transparent flat plate such as glass into the optical path, and a transparent parallel flat plate having a thickness t and a refractive index n with respect to air is perpendicular to the optical axis. It is known that when inserted into the optical path, the substantial optical path length becomes longer by t (1-1 / n). For example, when the transparent parallel plate is a glass plate having a refractive index of 1.5, the optical path length is set to t (1-1 /
1.5) = t / 3 longer.

Therefore, to shorten the effective value of the imaging optical path length,
It is sufficient to insert a glass having a thickness of t such that the value obtained from the above equation becomes a length to be shortened in the imaging optical path. In the case of the same-magnification imaging optical system, since the optical path length on both sides of the imaging element such as a lens, that is, the object distance and the image distance are equal, the glass having a thickness of half of t is used as the optical path on both sides of the imaging element. , Respectively.

FIG. 1 is a view showing an embodiment in which the present invention is applied to an equal-magnification optical apparatus of a color copying machine using a convergent light transmitting array as an image forming element, and an image having a width X on a document surface 21 is shown. The slit is
The SLA 22 forms a slit having a width X on the image plane 23 on the photoconductor. If the length Z ₀ of the SLA in the optical axis direction, the distance between the document surface 21 and the image surface 23, that is, the conjugate length is TC, the distance from the document surface 21 to the emission surface of the SLA 22 to the image surface 23 is Equal length l
_{Becomes 0} and its value is Becomes The image on the document, for example a circle of radius X ₀ is forms an image of a circle of radius X ₀ in the corresponding position on the image plane.

Parallel flat glass plates 24 and 25 each having a thickness of t / 2 are perpendicular to the optical axis in the optical path between the document surface 21 and the SLA 22 and the incident surface and in the optical path between the emission surface and the image surface 23 of the SLA 22. Has been inserted. 2
One of the glass plates 24, 25 also serves as a substrate for the color separation filter, and is manufactured by attaching an extremely thin film on the glass plate, coloring the glass, or vapor-depositing an interference film. ing. Of course, the color separation filter and the glass plate for correcting the optical path length may be provided separately, and the sum of the thicknesses may be equal to t / 2.

For example, it is assumed that the conjugate length of green light is about 1.3 mm longer than the conjugate length of blue light, and the conjugate length of red light is about 2 mm longer. In that case, when exposing by inserting the blue filter into the optical path, make the blue filter extremely thin.Do not insert the glass plate for correcting the optical path length. The plate is inserted into each optical path on each side of the SLA, and when a red filter is inserted for exposure, a glass plate having a thickness of 3 mm is inserted into the optical path on each side of the SLA. Also in the case of (1), the distance TC substantially coincides with the distance TC between the original surface 21 and the image forming surface 23, and any color light image is correctly formed on the image forming surface.

Next, an embodiment will be described in which the effective optical path length is corrected by providing a transparent glass plate on one of the optical paths on the entrance side or the exit side of the imaging element and moving the imaging element in the optical axis direction. .

The method of increasing the conjugate length by S in the unity-magnification imaging optical system is to move the image forming element along the optical axis by S / 2 to the photosensitive member side or the document side, and to set the image forming element between the image forming element and the photosensitive member. This is achieved by inserting a transparent glass having a thickness of S (1-1 / n) (where n is the refractive index of glass) in the optical path between the image element and the original.

Therefore, similarly to the above embodiment, in the exposure apparatus using the SLA as the imaging element, the conjugate length of the SLA for green light and red light is about 1.
When the length is 3 mm and 2 mm, as shown in FIG. 3A, the SLA 22 has the same distance between the entrance surface and the original 21 and the distance between the exit surface and the imaging surface 23 of the photoreceptor when exposed to blue light. An extremely thin blue filter 26B is provided between the light exit surface and the imaging surface 23 of the photoreceptor.

At the time of green light exposure, as shown in FIG. 3 (b), the SLA22 is 0.65 mm from the position at the time of blue light exposure (indicated by HP in the figure).
(= 1.3mm / 2) Moved to the photoconductor side, 4m green filter 26G
An object affixed to the transparent glass 27 of m (= 1.3 × (1-1 / 1.5)) is inserted between the SLA and the imaging surface 23 of the photoconductor.

At the time of red exposure, as shown in FIG. 3 (c), the SLA 22 is moved to the photosensitive member side by 1 mm (= 2 mm / 2) from the position at the time of blue light exposure, and the red filter 26R is moved to 6 mm (= 2 mm × (1-1 / 1). 1.5)) The thing attached to the glass 28 is inserted between the SLA and the photoconductor.

In the above embodiment, an example in which the SLA is used as the imaging element has been described. However, the imaging element is not limited to the SLA, and may be a normal lens or a roof mirror lens array. In addition to the photoreceptor, the image forming surface is also used as a reading optical system of a color copying machine of a type that converts the image into an electric signal, modulates the laser beam with this, and writes on the photoreceptor. The invention is applicable.

As described above, according to the present invention, each of the color-separated colors correctly focuses on the imaging surface irrespective of the difference in the wavelength of the color light, so that the color with no color shift excellent in resolution and sharpness is obtained. A copy is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment in which the present invention is applied to an imaging optical system using a convergent light transmitter array, and FIG. 2 is a graph showing a change in conjugate length with respect to the wavelength of light of the convergent light transmitter array. 3 (a), 3 (b) and 3 (c) show the positions of the imaging elements and the thickness of the transparent plate inserted into the optical path during blue, green and red exposure, respectively, according to the embodiment of the present invention. Schematic diagram showing the fourth
FIG. 1 is a side sectional view showing a schematic configuration of an example of a known color copying machine. 1 Lens (imaging element) 3B, 3G, 3R Blue / green / red color separation filter 21 Original surface 22 Convergent light transmitter array (imaging element) 23 Imaging surface 24 , 25 ... transparent plate

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-29274 (JP, A) JP-A-53-74319 (JP, A) JP-A-55-73064 (JP, A) 95266 (JP, A) JP-A-56-107259 (JP, A) JP-A-62-187871 (JP, A) JP-A-57-197958 (JP, A) JP-A-60-107048 (JP, A) JP-A-62-203171 (JP, A) JP-A-61-33037 (JP, U)

Claims (4)

(57) [Claims] 1. An image forming apparatus according to claim 1, wherein three different color filters are selectively inserted in the optical path of the same image forming optical system, and reflected light of the original placed on the original placing surface and illuminated with white light is used for each color separation. In an exposure apparatus of a color copying machine for sequentially forming an image on the same image forming plane through a filter, an effective value of an image forming optical path length of an image forming element of the image forming optical system with respect to each color separation light is equal to or smaller than that of the image forming optical system. A transparent flat plate having a thickness suitable for correcting the difference in the optical path length caused by the difference in the wavelength of each color light so as to be equal to the distance between the document surface and the imaging surface is inserted into each color separation filter. An exposure apparatus, wherein the exposure apparatus is also inserted into an image forming optical path. 2. An exposure apparatus according to claim 1, wherein said transparent flat plate also serves as a substrate for each color separation filter. 3. The exposure apparatus according to claim 1, wherein said transparent flat plate is provided separately from each color separation filter. 4. A filter for selectively separating three colors is provided in the optical path of the same image forming optical system so that reflected light of a document placed on a document placing surface and illuminated with white light is used for each color separation. In an exposure apparatus of a color copying machine for sequentially forming an image on the same image forming plane through a filter, an effective value of an image forming optical path length of an image forming element of the image forming optical system with respect to each color separation light is different from a wavelength of each color light. Regardless of the difference in optical path length caused by the above, while moving the imaging element in the optical axis direction so as to be equal to the distance between the original surface and the imaging surface of the imaging optical system, An exposure apparatus, wherein a transparent flat plate is inserted into one of the incident side and the outgoing side of the imaging element.