JPH0466428B2 - - Google Patents

Description

Detailed Description of the Invention - Field of Industrial Application - The present invention relates to an information reading device that reads character or graphic information on a document using an image sensor, and an information reading device that is capable of reading color information. This invention relates to means for correcting chromatic aberration.

-Summary of the Invention- This invention changes the thickness of a color filter inserted into the optical path from the original to the image sensor via the optical lens for each transmitted color, thereby adjusting the imaging position of each color due to the chromatic aberration of the optical lens. By correcting the fluctuations, the reading light of each color that has passed through the color filter is accurately focused on the light-receiving surface of the image sensor, avoiding blurring of the image due to chromatic aberration of the optical lens and reading color information clearly. It has been made possible to do so.

-Prior art- As shown in FIG. 5, a color information reading device uses an image sensor 32 in which color filters 31 _R , 31 _G , 31 _B of three primary colors are sequentially attached to light receiving cells 30...30. is known, but when such an image sensor is used,
The density of reading dots for each color is 1/ of that of a single color.
3, which has the disadvantage that precise reading cannot be performed.

Therefore, as shown in FIG. 4, the applicant of the present invention proposed that three
proposed a color information reading device that converts the color of reading light by inserting a disk 3 made up of a group of filters including fan-shaped color filters of primary colors and rotating the disk (Japanese Patent Laid-Open No. 60−
(See Publication No. 61863). In Fig. 4, 4 is the housing of the device;
Reference numeral 5 denotes a transparent document table provided on the top surface of the housing, 6 a guide rod mounted parallel to the document table 5, 7 a carrier for scanning the document 1 along the guide rod 6,
8 is a light source lamp for document illumination mounted on carrier 7; 9 is a second carrier that runs in the same direction as carrier 7 at 1/2 the speed; 10 is a reflector mounted on carrier 7; 11 and 12 are mirrors mounted on carrier 7; A reflecting mirror mounted on the second carrier 9, 13 an optical lens, A the optical path of the reading light, 14 an electric motor that rotates the disk 3,
15 is a belt transmission device that drives and connects the electric motor 14 and the disk 3.

-Problems to be Solved by the Invention- According to the color information reading device as shown in FIG. Because it can be read at a dot density of In the information reading device, an optical lens 13 is used to form an image of the information pattern of the document 1 on the light receiving surface of the image sensor 2. As is well known, the optical lens 13 has chromatic aberration, so when the read color is converted, A shift occurs in the image formation position of the information pattern on the original document 1, which places a limit on the resolution of the read color information.

For example, in the optical lenses commonly used in current information pattern reading devices, there is a deviation in the imaging position of about 0.34 mm between red light and blue light. Although it is of course possible to obtain a lens with less chromatic aberration using current technology, it is inevitable that the price of the lens will rise significantly. In addition, if a lens with a short focal length is used to miniaturize the device, chromatic aberration increases and the resolution of the read color information tends to decrease. It becomes a problem.

In view of the above-mentioned problems, the present invention provides an optical color information reading device that sequentially reads color information for each color by converting a color filter inserted in an optical path from a document 1 to an image sensor 2 as shown in FIG. The purpose of this invention is to provide a technical means for easily correcting the chromatic aberration of the lens 13, thereby making it possible to realize a color information reading device that is less expensive and has higher resolution.

- Means for Solving the Problems - The present invention provides thicknesses t _R , t G , t of the color filters 20 _R , 20 _G , 20 _B inserted in the optical path of the reading light from the original 1 to the image sensor ₂ . It is characterized in that _B is changed according to the chromatic aberration of the optical lens 13 with respect to the transmitted color of the filter, and the thickness difference Δt _RG and Δt _RB of the filters 20 _R , 20 _G , 20 _B for each color is changed. , which is characterized by correcting chromatic aberration of the optical lens 13.

In principle, each color filter 20 _R , 20 _G , 20 _B should be made thicker as it transmits light with a shorter wavelength, but in actual optical lenses, various chromatic aberrations are corrected. Since the change curve of refractive index with respect to wavelength is not uniform, it is necessary to determine the thicknesses t _R , t _G , and t _B of each color filter after measuring the actual imaging position of each color ray in the lens used. be.

-Operation- To simplify the explanation, an example will be described in which crown glass is used as an optical lens and a filter. The wavelength of visible light is approximately 3800Å (purple)
7800 Å (red), and the three primary colors of light, red light, green light, and blue light, are used as light for reading color information. The refractive index of crown glass is, for example, 1.5127 for red light with a wavelength of 6563 Å and 1.5214 for blue light with a wavelength of 4861 Å, and the shorter the wavelength, the higher the refractive index. Therefore, with a crown glass lens, the shorter the wavelength (on the violet side), the shorter the focal length.

On the other hand, when filters 20 _R and 20 _B with different thicknesses are inserted between the lens and its focal point as shown in Figure 3, the light that passes through the filter 20 _R whose thickness is t _{R is} It passes like this and gathers at the focal point P _R.
Furthermore, the light that has passed through the filter _20B having a thickness of _tB passes through like _AB and converges at the focal point _PB . That is,
When the filter thickness changes from t _R to t _B , the focus becomes
Move from P _R to P _B by ΔL.

That is, for example, if there is a focal length difference of ΔL between red light and blue light used as reading light in a certain optical lens 13, the thickness of the filter _20R that transmits the red light is determined as shown in FIG. t _R , the thickness of the filter 20 _B that transmits blue light as shown in Figure 3.
If we do this as t _B , the difference in their focal lengths will be cancelled, and the focal points of red and blue light will be the same.

The focal length of the red light in the lens 13 used now is L _R , the focal length of the blue light is L _B , the refractive index of the filter that transmits the red light is n _R , the thickness is t _R , and the focal length of the filter that transmits the blue light is If the refractive index is n _B and the thickness is t _B , the following equation holds true.

ΔL=L _R −L _B = (1−(1/n _B ))t _B −(1(1/n _R )
) t _R Now, approximately on the right side of the above equation, assuming n _B = n _R = 1.52, the difference in filter thickness when ΔL is 0.34 mm t _B −
If t _R =Δt is calculated, Δt≒1 mm. Therefore,
If the thickness of the red filter 20 _R is 1 mm, the thickness of the blue filter 20 _B should be 2 mm.
The thickness of the green filter _20G can also be determined by a similar calculation.

-Embodiment- Fig. 1 shows the main structure of an embodiment of the present invention. The overall configuration of the information reading device is the same as that shown in FIG. 4, and includes a fan-shaped red filter _20R ,
A rotating disk 3 is constructed using two green filters _20G and two blue filters _20B . Red filter 20 _R , green filter 20 _G and blue filter 20 _B
The thicknesses of t _R and t _G are shown in the developed diagram in Figure 2, respectively.
and _tB . The difference in thickness of these filters Δt _RG
and Δt _RB are each filter 20 _R of the optical lens 13,
The difference in focal length for the transmitted light of 20 _G and 20 _B is actually measured, and based on the difference, it is determined by the calculation formula explained in the section on the effect above.

Although the disk 3 is shown schematically in FIG. 1, the structure of the disk 3 is shown in more detail in FIG. 21 in Fig. 6 is a fan-shaped filter 20 _R , 20
_G , _20B , each filter is fitted and fixed in a fan-shaped opening 22...22 of the holding frame 21, and the holding frame 21 is continuous around its axis 25 in the direction of the arrow shown in the figure. It's rotating. Through-holes 23...23 and 24, 24 are provided on the outer periphery of the holding frame 21, and a light emitter and a light receiver (not shown) face each other across the through-holes. When the light that has reached the device is blocked again, a scanning command is given to the image sensor 2, and one scan is completed before the optical path A of the reading light is blocked by the rib 21a of the holding frame 21. do. That is, the structure is such that, in synchronization with the rotation of the disk 3, the color information of the document 1 is read by repeating reading for one scan using red light, green light, and blue light. Through holes 23 and 2
The reason why 4 is available in two different shapes is that
When the long through hole 23 passes, the light receiver is irradiated with light for a long time, and by detecting the time difference, the controller side can determine the start of the repeating cycle of red, green, and blue. This is to ensure that.

Since the disk 3 in the illustrated embodiment has six filters, it rotates once while the image sensor 2 scans the original 1 six times. The reason why the disc 3 is composed of two color filters 20 _R , 20 _G , and 20 _B is to make the rotation speed of the disc 3 as slow as possible and to avoid imbalance in the center of gravity of the disc 3. It's for a reason. Of course, if the reading speed is slow, the disk 3 can be constructed with three fan-shaped filters, one for each color, and the weight balance can be achieved by installing a balance weight on a rim (not shown) fitted around the outer periphery of the disk 3. Can be installed and fixed. Furthermore, if the number of colors of the reading light is four, the number of fan-shaped filters constituting the disk 3 may be a multiple of four.

- Effects of the Invention - As described above, according to the present invention, in a color information reading device that separates color information and sequentially reads it by converting a color filter inserted in an optical path from a document to an image sensor, an optical It is possible to easily correct the shift in the imaging position of the information pattern due to lens chromatic aberration and accurately focus the reading light beam of each color on the light receiving surface of the image sensor, improving the resolution in reading color information. be able to. Also,
Since the chromatic aberration of the optical lens is corrected by the thickness of the filter, it can be used even with lenses that have some chromatic aberration, and lenses with short focal lengths can also be easily manufactured, making it possible to read high-resolution color information. The device can be configured compactly and at the same time can be provided at low cost.

[Brief explanation of the drawing]

1 to 4 are diagrams showing an embodiment of the color information reading device of the present invention. FIG. 1 is a perspective view of the main part, and FIG. 2 shows the thickness of a filter group formed in a disk shape. FIG. 3 is an explanatory diagram showing the principle of correcting the imaging position depending on the thickness of the filter, and FIG. 4 is a sectional view showing the overall configuration of the apparatus. FIG. 5 is a partial plan view showing the structure of an image sensor used in a conventional color information reading device. FIG. 6 is a front view showing a specific example of a holding structure for a fan-shaped filter. In the figure, 1: original, 2: image sensor, 3: rotating disk, 13: optical lens, 20 _R , 20 _G , 20
_B : Color filter, _tR , _tG , _tB : Thickness of color filter, A: Optical path of reading light.

Claims (1)

[Claims] 1 Transmit text or image information from document 1 to optical lens 1.
3, the color filters 20R, 20G,
In a color information reading device that converts 20B and sequentially reads information for each color transmitted through the filter, color filters 20R, 2 whose focal lengths are shifted to the short side due to chromatic aberration of the optical lens 13 are used.
The thickness is increased to 0G and 20B, and the difference in focal length for each color of the optical lens 13 is adjusted using the color filter 2.
A color information reading device correcting chromatic aberration, characterized in that the reading light of each color is corrected by 0R, 20G, and 20B and is imaged at the same position.