JPH06245027A - Color scanner - Google Patents

Abstract

PURPOSE:To provide a color scanner which can be prepared at low cost by simple constitution. CONSTITUTION:In the color scanner which radiates an original 1 with white light 2, converges its reflected scattered light by a lens 6, color-separats the converged light by a grating 12 and reads a picture element and color information on an optical detector 10, liquid crystal is used for the color-separating grating 12 to divide the line-shaped section 12a of liquid crystal, which is sectioned by the electrode into some groups (grating line), the refractive index of each section in each group is made to be the refractive index distribution of equal distribution and gradual values concerning any group, the refractive index distribution is quickly switched from one distribution to another one to change the phase of light transmitting each section to change a spatial frequency by a high diffraction efficiency and by adjusting the number of sections N in the group, a diffraction angle corresponding to a wave length is made almost equal and picture information is read in time-division manner by the same optical detector 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color scanner which is applied as an original image reading section for a digital color copying machine, a color plate making machine, a color fax machine or the like, or an image input apparatus for a computer or the like.

[0002]

2. Description of the Related Art Digital color copying machines, color plate making machines,
With the commercialization of color fax machines, color image information on the document surface is color-separated through an optical system, and the CCD (Charge Co
Various color scanners have been proposed in which an image is formed on the surface of a line sensor such as updled devices) and color image information is digitally read from an output signal from the line sensor (JP-A-3-289859). FIG. 5 shows a conventional example, which is an example of a digital color scanner of a color separation type using a stepwise binary hologram.
In the color scanner shown in FIG. 5, white light from the white light source 2 is applied to the original surface of the original 1, and the reflected light from the original surface guided through the slit 3, the moving mirror 4 and the filter 5 is telecentric. The condensing (imaging) lens 6 which is an fθ lens irradiates the reflection type binary hologram 7 so as to make the light incident on the reflection type binary hologram 7 substantially vertically, and the red, green and blue diffracted by the binary hologram 7 are the −1st order light and the 0th order. Light, 1
The next light is applied to a light detector 8 composed of three linear CCDs and the like, and color information of three colors of one line on the original is read at the same time.

The binary hologram 7 for color separation used in the color scanner shown in FIG. 5 is of a reflection type and has a high efficiency despite a low spatial frequency. Only the visible light is transmitted through the bandpass filter 5 in advance, and the transmitted light is color-separated by the binary hologram 7.
Blue is distributed into −1st order light, 0th order light and 1st order light. At that time, a telecentric optical system is used or aberrations are removed by making the grating intervals unequal to prevent color misregistration. Then, the red, green, and blue colors are read by a line sensor composed of a 3-line CCD or the like.
At this time, each wavelength does not form an image on the CCD continuously, but discretely and each color band forms an image. On the other hand, as a method often used, as shown in FIG. 6, the signal light 9 is color-separated using a color filter 11, and the light 9 ′ separated into each color is detected by a photodetector (1-line CCD or the like). There is a way to do it. In this case, since a method of reflecting light of a certain color and transmitting light of another color is used in the filter film portion of the color filter 11, two or more filters 11 are used to transmit the colored light in different directions. Reflected, separate 1 line C
It is detected by a CD or the like.

[0004]

By the way, in the color scanner shown in FIG. 5, unless the telecentric imaging lens (fθ lens or the like) is used for the imaging lens 6, the signal light carrying color information is linear. No image is formed on the line sensor. However, such a lens is large in size, difficult to manufacture, and expensive. Also, 3 lines of CC
D is required, which is also expensive. And, it requires a high degree of combination accuracy with each other. As described above, even though the performance is high, this method has a limit in terms of downsizing and cost reduction, because it requires advanced parts creation and advanced combination technology. Further, as shown in FIG. 6, there is a method of performing color separation using a color filter. In this method, a light of a certain color is reflected by a part of a filter film and a light of another color is transmitted. Since it is necessary to use two or more filters, and because it reflects or transmits colors in different directions, three CCDs are required, and highly accurate alignment of them is required. However, there is a problem that the cost is high and space is consumed.

The present invention has been made in view of the above circumstances, and is a color scanner which can be manufactured at a low cost without using a high-performance lens, with a simpler structure, and without requiring high accuracy. The purpose is to provide.

[0006]

In order to achieve the above object, a color scanner according to a first aspect of the invention illuminates an original with white light, collects the reflected and scattered light by a lens, and the condensed light is grating. In a color scanner that performs color separation by reading pixels and color information on a photodetector, a liquid crystal is used for the grating for color separation, and the line-shaped sections of the liquid crystal separated by the electrodes are divided into several groups. The refractive index of each section within each group is set to a graded index distribution with the same distribution for each group, and the refractive index distribution is switched from one distribution to another distribution at high speed and transmitted through each section. By changing the phase of light, the diffraction efficiency is high, and the number of sections in the group is adjusted to change the spatial frequency so that the diffraction angle by wavelength is almost the same and the image information is time-divided by the same photodetector. Characterized by reading There.

According to a second aspect of the present invention, in the color scanner of the above-described color scanner, the spatial frequency in the main scanning direction of the liquid crystal grating is varied depending on the location, so that the light is incident obliquely at the position on the liquid crystal grating and the diffraction angle is generated. Is corrected so that the signal light is imaged on a linear photodetector (line sensor). According to a third aspect of the present invention, there is provided a color scanner according to the second aspect, wherein the liquid crystal grating is configured to simultaneously diffract light of at least two colors of red, green, and blue, and a line sensor having a plurality of lines at the same time. The feature is that pixel information of two or more colors is read at the same time. A color scanner according to a fourth aspect is the color scanner according to the first aspect, wherein when the pixel information is read in a time division manner, the signal light is linearly imaged by a condensing lens, and the color which is not read at a certain point is read. Is adjusted so that the light is diffracted with high efficiency, the refractive index of each section in each group of liquid crystals is adjusted so that the transmitted light of the liquid crystal grating becomes the color at that time and forms an image on the line sensor. It has a feature.

[0008]

The structure, operation and operation of the present invention will be described in detail below. The original is illuminated with white light, the reflected and scattered light is condensed by a lens, and the condensed light is color-separated by a grating. In a color scanner that reads pixels and color information on a photodetector, the color is An element that can be disassembled is essential. Conventionally, the grating has a large dispersion depending on the wavelength and has been often used for spectroscopy. Further, compared to the case of using a color filter, there is an advantage that a single element can disperse into multiple colors and the number of parts can be reduced. Generally, light is continuously dispersed depending on the wavelength, but when the spatial frequency is low, the wavelength band with high diffraction efficiency becomes discrete, and a discrete dispersion phenomenon occurs. In the present invention, a grating using liquid crystal is used. This liquid crystal is divided into lines by electrodes.The liquid crystal divisions divided by the electrodes are divided into several groups, and the refractive index of each division within each group is graded so that each group has an equal distribution. The refractive index distribution is set to any value. Then, the refractive index distribution is switched from one distribution to another distribution at a high speed to change the phase of the light transmitted through each section to exchange wavelengths that diffract with high diffraction efficiency. In this case, since the diffraction angle changes depending on the wavelength, the number of sections in the group is changed so that light of each color is diffracted at substantially the same angle. That is,
To change the spatial frequency. When it is desired to separate light having a long wavelength, a lower spatial frequency is set, and when light having a shorter wavelength is desired to be separated, a slightly higher spatial frequency is set. By doing so, the diffraction angles due to the wavelengths can be made substantially the same, and the pixel information can be read by one photodetector. That is, the refractive index distribution of this liquid crystal is changed at high speed, and the diffracted light is red, green, blue, red, green, blue, red, green, blue, ...
Read color information by changing ... The reason why this is possible is as follows.

Conventionally, in a binary hologram, one grating line is divided into a plurality of stepped grating lines parallel to each other, and the phase of light transmitted therethrough is changed stepwise. By doing so, the optical power can be concentrated only on the diffracted light of a specific wavelength. A similar phenomenon occurs in media that can change phase significantly. The change in the refractive index of the liquid crystal is large and can be changed by up to 20%. Therefore, if a liquid crystal having an appropriate thickness is used, the phase of transmitted light can be set to any value.
In other words, a group of several liquid crystal partitions separated by electrodes is made into one grating line, and the phase of each partition can be adjusted appropriately so that the energy is concentrated in the desired diffraction direction. Is. This is the same as in the case of the binary hologram, but in the case of the binary hologram, the length of each step and the refractive index of the medium are fixed, and there is a drawback that there is no selectivity with respect to the wavelength or the order.

Here, at the wavelength λ, the phase delay of the transmitted light of the k-th section of each section when one grating line is generally divided into N is exp [-iψk
(λ)], the order of the diffracted light is q, and the normalized position of the k-th section of one grating line is ξ _k to ξ _{k + 1} , the power aq (λ) of the diffracted light is

[Equation 1] Calculated by At this time, as shown in FIG. 1B, each grating line of the liquid crystal (liquid crystal grating) 12 is divided into N sections 12a, for example, N =
In the case of 3, ξ ₀ = 0, ξ ₁ = 1/3, ξ ₂ = 2/3, ξ ₃ = 1.
The phase delay in this case can be appropriately adjusted by adjusting the refractive index of the liquid crystal, and the diffracted light 14 can be selected with high diffraction efficiency with respect to the incident light 13. That is, the phase delay of each section is 0,4
When π / 3, 8π / 3, the −1st order light has a phase delay of 0,2π
When it is set to / 3, 4π / 3, the primary light comes out strongly. actually,
In the former case, -4th order light, 2nd order light, 5th order light, 8th order light ...
In the latter case, the −2nd order light, the 4th order light, the 7th order light, etc. are generated, but the intensity of these can be lowered depending on the selection of the spatial frequency.

In this way, by adjusting the change in the refractive index of the liquid crystal so that the phase of the transmitted light in each section, which is one line of the liquid crystal, has a stepwise value, the red primary light is sometimes emitted. By diffracting the light, the green first-order light is diffracted at some times, and the blue first-order light is diffracted at other times, and color detection can be performed by time division. In addition, the −1st order light, the 0th order light, and the 1st order light can be substantially selected with high diffraction efficiency. Moreover, it can be set for each wavelength. That is, red has -1st order light, green has 0th order light, and blue has 1st order light.
It is also possible to detect each color simultaneously, such that the next light is strongly diffracted. As described above, in the present invention, by using the above liquid crystal grating as the color separation means, color separation can be performed with one liquid crystal grating and one (one) line sensor, and a color scanner can be realized with a compact configuration. it can.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a schematic configuration diagram of a color scanner showing an embodiment of the present invention. In FIG. 1, reference numeral 1 is a document, 2 is a white light source, 3 is a slit, 4 is a moving mirror,
Reference numeral 5 is a bandpass filter, and 6 is a condensing (imaging) lens, which are the same constituent elements as the color scanner shown in FIG. 5, but in the present invention, the liquid crystal grating 12 described above is used as the color separation means. As shown in FIG. 1B, the liquid crystal line-shaped sections 12a separated by the electrodes of the liquid crystal grating 12 are divided into N groups (grating lines), and each section in each group (grating line) is divided. The refractive index is set to a stepwise-valued refractive index distribution with the same distribution in all groups, and the refractive index distribution is switched from one distribution to another at high speed to change the phase of the light transmitted through each section. With high diffraction efficiency, the number of sections in the group is adjusted to change the spatial frequency, and the diffraction angles according to the wavelengths are set to almost the same angle.
Etc.) are read in a time-sharing manner (Claim 1). The configuration and operation of the liquid crystal grating 12 are as described above.

By the way, the configuration shown in FIG. 1A still requires a telecentric optical system. However, a telecentric optical system can be dispensed with as follows. That is, in the same color scanner as described above, the spatial frequency in the main scanning direction of the liquid crystal grating may be made different depending on the place. Here, FIG. 2 is a diagram showing a state in which light is incident on the liquid crystal grating 16 via the normal imaging lens 15 during main scanning, and the upper diagrams of (a), (b) and (c) are the paper surfaces. In the plan view with the direction parallel to the main scanning direction, light is incident on different places in the main scanning direction.The lower figure shows the plane when the direction perpendicular to the paper surface is the main scanning direction. It is a figure. As shown in FIG. 2, with the normal imaging lens 15,
When the light 9 is obliquely incident on the grating 16 (a) and (b) and when the light 9 is vertically incident (c), the effective diffraction angles are different even if diffracted by the grating having the same spatial frequency. There is a problem that the image forming points 9'are not aligned on a straight line. Therefore, in order to arrange the image forming points of the diffracted light 9'on a straight line, the spatial frequency of the liquid crystal grating is adjusted according to the angle at which the light is incident on the liquid crystal grating, and the diffracted light on the linear photodetector is adjusted. Should be imaged. In this case, an ordinary imaging lens can be used, and the degree of freedom in design is increased (claim 2). An example of the liquid crystal grating in this case is shown in FIG.

On the other hand, when reading only one color at a time by time division, speedup is somewhat difficult. Therefore, in a color scanner similar to the above, two line sensors are used, and at least two colors of red, green, and blue are simultaneously diffracted as diffracted light of different orders by a liquid crystal grating. It can be read at higher speed by reading two colors and sometimes one color. Alternatively, as already mentioned, red, green, and blue are −1st-order light, 0th-order light, 1
It is also possible to provide the next light and, as shown in FIG. 3, provide the sensor 8 of three lines corresponding to each diffracted light 9'of the liquid crystal grating 16 and read each color and pixel information at the same time (claim 3).

In the color scanner as described above, when the diffracted light is read by the line sensor using an ordinary imaging lens, the spatial frequency of the liquid crystal grating is changed to correct the diffracted light, but it is completely changed. To form an image on the line, as shown in FIG.
Liquid crystal grating with different intervals depending on the location 1
6 ″ is required, and fine spatial frequency modulation is required by a liquid crystal with a fine partition. However, if a liquid crystal having a rough section is used and a plurality of unread colors are prevented from entering the line sensor as diffracted light, only the desired color enters the line sensor in a completely linear form. Thus
By changing the read color that is diffracted at high speed by time division, it is possible to read the color information without variations due to the position in the main scanning direction (claim 4). In the above system, a bandpass filter may be placed in front of the sensor to transmit only visible light as in the conventional example, or infrared light and ultraviolet light can be adjusted by adjusting the refractive index distribution of the liquid crystal. Adjust the diffraction angle,
It may not be incident on the line sensor. Also,
The configuration of the optical system from the light source 2 to the imaging lens 6 of the color scanner is not limited to that shown in the drawing, and various configurations can be applied.

[0016]

As described above, in the color scanner of the first aspect, the liquid crystal grating is used as the color separation means, and the liquid crystal line-shaped divisions separated by the electrodes are divided into several groups. The refractive index of each section within each group is set to a graded index distribution with the same distribution for each group, and the refractive index distribution is switched from one distribution to another distribution at high speed and transmitted through each section. By changing the phase of light, the diffraction efficiency is high, and the number of sections in the group is adjusted to change the spatial frequency so that the diffraction angle by wavelength is almost the same and the image information is time-divided by the same photodetector. By reading
Color separation can be performed with one liquid crystal grating and one (one) line sensor, and each color and pixel information can be read, and a color scanner can be realized with a compact configuration.

In the color scanner according to the second aspect, the spatial frequency in the main scanning direction of the liquid crystal grating is varied depending on the location, so that the imaging lens is used.
Changes in the diffraction angle when light is obliquely incident on the grating can be corrected, and the image points of the diffracted light (signal light) can be arranged on a straight line, eliminating the need for a telecentric optical system and reducing costs. Can be created.

In a color scanner according to a third aspect of the present invention, light of at least two colors of red, green, and blue is simultaneously diffracted as diffracted light of different orders by a liquid crystal grating, and at some times, there are two colors. At the same time, three colors are read simultaneously, so high-speed image reading is possible.

In the color scanner of the fourth aspect, the liquid crystal grating has a function of simply removing an unnecessary color,
Since only the transmitted color of the liquid crystal grating is read, no aberration due to the grating is included, so you can use an ordinary cheap lens, and the sensor can be an ordinary line sensor, so you can create a color scanner with a simple structure at low cost. .

[Brief description of drawings]

FIG. 1A is a schematic configuration diagram of a color scanner showing an embodiment of the present invention, and FIG. 1B is an explanatory diagram of a liquid crystal grating used in the color scanner of the present invention.

FIG. 2 is a diagram showing a state in which light is incident on a liquid crystal grating via an imaging lens during main scanning of a color scanner, and the upper diagrams of (a), (b), and (c) are on the paper surface. In the plan view when the main scanning direction is the parallel direction, the state where light is incident on different places in the main scanning direction is shown, and the lower diagram is the plan view when the direction perpendicular to the paper surface is the main scanning direction. Is.

FIG. 3 is a configuration diagram of a main part of a color scanner showing an embodiment of claim 3;

FIG. 4 is a plan view showing an example of a liquid crystal grating used in the color scanner of claim 2.

FIG. 5 is a schematic configuration diagram of a color scanner showing an example of a conventional technique.

FIG. 6 is a schematic configuration diagram of a color scanner showing another example of the prior art.

[Explanation of symbols]

1 ... Original 2 ... White light source 3 ... Slit 4 ... Moving mirror 5 ... Bandpass filter 6 ... Telecentric imaging lens 7 ... Binary hologram 8 ... Light Detector (3-line sensor) 9,13 ... Incident light (signal light) to liquid crystal grating 9 ', 14 ... Diffracted light (signal light separated into each color) 10 ... Photodetector (1 line) Sensor) 11 ... Color filter 12, 16, 16 '' ... Liquid crystal grating 12a ... Each section of liquid crystal 15 ... Imaging lens 17 ... Grating line

Claims (4)

[Claims] 1. A color scanner in which a document is illuminated with white light, the reflected and scattered light is condensed by a lens, the condensed light is color-separated by a grating, and pixels and color information are read on a photodetector. , Liquid crystal is used for the color-separating grating, and the line-shaped sections of the liquid crystal separated by the electrodes are divided into several groups, and the refractive index of each section within each group is graded with an even distribution. The refractive index distribution is set to a different value, and the refractive index distribution is switched from one distribution to another at high speed to change the phase of the light transmitted through each section to achieve high diffraction efficiency and to increase the number of sections in the group. The color scanner is characterized by adjusting the spatial frequency to change the diffraction angle depending on the wavelength to almost the same angle and reading the image information by the same photodetector in time division. 2. The color scanner according to claim 1, wherein
By varying the spatial frequency in the main scanning direction of the liquid crystal grating depending on the location, the fluctuation of the diffraction angle caused by the oblique incidence of light at the position on the liquid crystal grating is corrected, and a linear photodetector (line sensor) A color scanner characterized in that signal light is focused on the image. 3. The color scanner according to claim 2, wherein
A liquid crystal grating is used to simultaneously diffract light of at least two colors of red, green, and blue, and a line sensor having a plurality of lines at the same time to read pixel information of two or more colors at the same time. Scanner. 4. The color scanner according to claim 1, wherein
When reading pixel information in a time-divisional manner, the signal light is focused in a straight line by the condenser lens, and the colors not read at a certain point are diffracted with high efficiency. A color scanner characterized in that the refractive index of each section is adjusted so that the transmitted light of the liquid crystal grating becomes the color at that point and forms an image on the line sensor.