JPS6049314A - Optical path dividing and color separating device for color image readout optical system - Google Patents

Abstract

PURPOSE:To reduce a decrease in the quantity of light by arranging a roof prism so that two pieces of luminous flux from a lens strike two roof surfaces respectively, and providing a means which separates luminous flux projected from the roof prism into color-separated light beams in different colors and photodetection sensors on which the color-separated pieces of luminous flux are incident. CONSTITUTION:Two reflected pieces of luminous flux projected from an original O in slightly different directions are incident on the lens 7 as optical-axis light and slanting light. The two projected pieces of luminous flux from the lens are incident on two roof surfaces of the roof prism 8. The roof surfaces 8A and 8B are dichroic reflecting surfaces which have different spectral reflection factors, and only light beams in their specific wavelength bands are reflected to form images on the 1st sensor 10 and the 3rd sensor 12 respectively. Luminous flux which is split by the roof surface 8B and projected from the 3rd surface 8C forms an image on the 2nd sensor 11. Consequently, there is no decrease in the quantity of light on the optical path before the light is projected from the lens 7, the quantity of incident light on the 1st sensor 10 is 100%, and the luminous flux is split into two by the roof surface as the dichroic surface, so the quantities of incident light on the 2nd sensor 11 and the 3rd sensor 12 are each 50%.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an optical path division and color separation device for a color image reading optical system that divides a color image into two or more color-separated light beams and reads them with a light receiving sensor such as a COD.

Conventional technology A device that uses one imaging lens to separate a color image into two or more colors and read them with a light receiving sensor such as a COD includes, for example, three devices each with a color filter such as a dichroic mirror on the contact surface. The light emitted from the lens is incident on one surface of the three-color separation optical system formed by bringing the prisms into surface contact with each other, and the result is the result of two light beams reflected at the contact surface between each prism and one light beam transmitted. A device is used in which a light receiving sensor is provided on each image plane.

However, in this configuration, two of the three light fluxes pass through the color filter twice, so the amount of light reaching the light receiving sensor for these light fluxes is reduced to 1/4, and there are three prisms behind the lens. Japanese Patent Laid-Open No. 154348/1983 features a special lens that has a long back focus and prevents image deterioration due to the prism, which improves the above drawbacks. In order to do this, a trapezoidal prism is installed in front of one lens, and color filters are installed on the three incident surfaces of the trapezoidal prism, and the three light beams emitted from the document are separated into three different colors, and then the three light beams are separated into three different colors and then passed through the lens at different incident angles. A device has been proposed in which the drive circuit is simplified by transmitting the light beam and forming images on three line sensors fabricated on the same substrate, but in this case, the three light beams are transmitted through one lens. Since the image is formed using a different part, the light intensity is reduced to approximately 1/3, and the Ic is the same as 4.
Plate [Since three line sensors are made, manufacturing is difficult, yield is low, and costs increase.

In addition, the inventor first slit-irradiated an original placed on a contact glass, and transmitted two light beams emitted in slightly different directions to a first mirror and a second mirror, which travel at a speed ratio of 2;l. A color image scanned by a group of mirrors, incident on a single imaging lens at different angles of incidence, followed by optical path splitting and color separation using a gicroic mirror, and read by three light receiving sensors. The optical system of the reader was proposed. This configuration reduces the amount of light by 1/2 and makes it possible to use a normal lens. However, recent sensors have a narrow bit interval (pitch), making it difficult to arrange three sensors. It turned out that it was cold.

Purpose: In view of the above-mentioned problems of conventionally used and proposed color image reading optical systems, the present invention has been made to reduce the decrease in light intensity, do not require a specially designed lens, and does not cause an increase in cost, and the pitch of the sensor. It is an object of the present invention to provide an optical path splitting and color separation device that facilitates the arrangement of sensors even when the size of the device is small and is useful for downsizing the device.

1-''L Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings.

FIG. 1 shows an embodiment in which the present invention is applied to a color image reading optical system having one lens and three CODs, in which the main scanning is performed by the self-scanning of the COD and the sub-scanning is performed by the scanning movement of a mirror. FIG.

The document 0 is placed on a contact glass l fixed to the top surface of the device casing, and is illuminated with a white lamp 2 such as a fluorescent light. A first traveling mirror 3 is carried by a first traveling body (not shown) integrally with the lamp 2, and scans and moves at a constant speed in the sub-scanning direction parallel to the document shown by the arrow in the figure. 4, 5.6 are carried by a second traveling body (not shown), and the first
It travels in synchronization with the traveling mirror 3 in the same direction at a speed of V/2 to perform sub-scanning of the document. Two reflected light beams emitted from the original 0 in slightly different directions are reflected by the first traveling mirror 3, and one light beam passes through the lens 56 and then enters the lens 7.
The other beam is reflected by the mirror 4 and enters the same lens 7 as an oblique ray. A roof prism 8 is provided on the exit side of the lens 7 so that the two output beams enter the two roof surfaces, respectively. As shown in an enlarged view in FIG. 2, the two roof surfaces 8A and 8B are dichroic reflecting surfaces with different spectral reflectances, and only light in a predetermined wavelength band is reflected, respectively. 3 images are formed on the sensor 12. It is divided by the dichroic reflection surface of the roof surface 8B and passes through the prism 8,
The light beam emitted from the third surface 8C is designed to form an image on the second sensor 11.

Since this optical system is configured as described above, the lens 7
There is no reduction in the amount of light on the optical path until it exits, and therefore the amount of light incident on the first sensor IO is 100%. Since the light beam is split into two on the dichroic surface of the roof surface 8B, the second sensor 11. The amount of light incident on the 37th sensor 12 is 50 inches each.

As described above, according to the configuration of this embodiment, the sensor IO,
, 11, 12 is 1/4 like the conventional device.
Moreover, there is no need to use a special lens as the lens 7, and a normal lens can be used.

In Figure 1, the angle θ formed by the two beams of light incident on the lens 7
is determined by the overall device design.

If the imaging points of the two beams without the roof prism 8 are Q and R, respectively, and the length between these two points is iL, m = bX - θ (1) However, b is It is the image distance.

When the width of the external dimension of the sensor is D, if L≧D, a sensor can also be provided at point R, but generally, as shown in the following example (L<D).

If the projection magnification m1 is the reading density d, the pitch of the sensor is P, and the focal length of the lenses is f, then m=dXp...(2) b2(1+m)f...(3) (2 ), by substituting equations (3) into equation (1), m= (1+d2X p) f Xtanθ−−(4)
is obtained.

As an illustration, d = 12dots/contact, p = 0.
014, f = 35 M, θ = lO°, (
4) From the formula, I, = (1-1-12X0.014)35
The width of the sensor varies depending on the manufacturer, but it is 1) = lO.

There are many things before and after. From the above, it becomes D)L, and two sensors cannot be placed on the same plane. Furthermore, in recent sensors, p is becoming smaller, and sensors with p of 0-007 ru are also manufactured, and L tends to become smaller according to equation (4).

However, according to the present invention, sensors io, ti.

12 are provided at positions facing the three surfaces of the roof prisms 80, so that even if the pitch of the sensors becomes finer, the sensors can be easily arranged.

Note that the roof surfaces 8A and 8B of the roof prism 8 are approximately perpendicular to each other,
The ridge line is arranged at right angles to the running direction of the mirror running body (ie parallel to the self-scanning direction of the sensor). Roof surface 8A, 8
Spectral reflectance (or transmittance) of the dichroic reflective surface of B
is determined according to the assigned wavelength band of each sensor.

Dichroic reflective surfaces are made of multiple layers of transparent non-metallic materials, such as magnesium fluoride, and utilize light interference.
It is a type of multilayer reflective surface that selectively reflects part of the visible light range and transmits the rest, and the wavelength band to be reflected can be arbitrarily determined by selecting the material and controlling the film thickness.

Note that the roof surface 8A of the roof mirror 8 does not necessarily have to be a dichroic reflective surface. Since this surface uses only reflected light, there is no need for wavelength division, and a single-layer reflective surface that reflects uniformly regardless of wavelength may be used. In this case, this is shown by the broken line in Figures 1 and 2. As shown, this surface and the first sensor lO
A color separation filter 9 is inserted in the optical path between the two. A single-layer reflective surface can be easily made by vapor deposition of aluminum, and even if a color separation filter 9 is included, it can be made cheaper than a dichroic reflective surface.

Effects As described above, according to the present invention, there is little reduction in the amount of light that reaches the sensor, there is no need for a specially designed lens, and even when the sensor pitch becomes small, the sensor arrangement is easy, and the device It is effective in downsizing and cost reduction.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, and FIG. 2 is an enlarged sectional view showing details of the vicinity of the roof prism. 0... Original document 1... Contact glass 2... White light source 3... First traveling mirror 4.5.6... Second traveling mirror group 7... Lens 8... Roof prism 8A, 8B・・・
・Dach surface 9...Color separation filter 10.11.12...
・Light receiving sensor

Claims (3)

[Claims] (1) A first traveling mirror that is movable at a constant speed and that 172 Optical path division and color separation of a color image reading optical system in which a group of second traveling mirrors movable synchronously in the same direction at speed are incident on a single lens at different angles of incidence through biases ζ. In the apparatus, a roof prism is arranged so that two beams of light emitted from the above lens are incident on two roof surfaces, respectively, and a beam of light reflected from the two roof surfaces of the roof prism and, if necessary, incident from one roof surface, is arranged so that the beams of light emitted from the above lens are incident on two roof surfaces, respectively. It is characterized by providing a means for converting the light beams emitted from the surface into color-separated lights of different colors, and a light-receiving sensor arranged so that the light beams separated into predetermined colors by the means are incident thereon. Optical path splitting and color separation device. (2) The means for color-separating each of the light beams into different colors is characterized in that the surfaces constituting the two roof surfaces of the roof prism are dichroic reflective surfaces having different spectral reflectances. Apparatus according to claim 1. (3) The means for color-separating each of the above luminous fluxes into mutually different colors uses at least one of the surfaces constituting the roof surface of the roof prism as a single-layer reflective surface, and connects this surface and the corresponding light receiving sensor. 2. The apparatus according to claim 1, further comprising a color separation filter provided between the apparatus.