JPS6218165A - Picture reader - Google Patents

Abstract

PURPOSE:To make the quantity of light stable at a visual light region by using an optical filter cutting off an infrared light having a wavelength of 690nm-1,100nm or below to the lighting light receiving system and the quantity of light detection feedback system so as to eliminate the effect of the infrared ray when a color separation signal is obtained. CONSTITUTION:The installing position of a photodetector 9 is made close to a luminous flux having a solid angle theta1 irradiated to an actual read position (a) of an original 2 from a fluorescent light 4(theta2=60 deg.). Thus, there is no tube wall temperature difference of the fluorescent light 4 and dimmer is applied. In the emission spectrum of the fluorescent light, the spectral distribution is moved from the emission spectrum of a rare gas lighted at a near infrared ray to the emission spectrum of mercury and fluorescent substance lighted as visual light. In order to eliminate the effect of the near infrared light having the emission spectrum of the rare gas, an optical filter 10 cutting off the infrared ray including light having a wavelength of >=690nm-<=1,100nm is used to the lighting system. Thus, the light received by a line sensor 13 is that having the spectrum of mercury and the activated fluorescent substance and the relative intensity of the spectral distribution from just after the lighting to the stable state is hardly fluctuated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image reading device that optically reads a color image, for example, and particularly to stabilization against fluctuations in the spectral distribution of a light source.

``Technical background of the invention and its problems Generally, in this type of image reading device, light from a light source is irradiated onto an object to be read (object) such as a document, and the reflected light is used as a photoelectric sensor such as a COD line sensor. The signal is photoelectrically converted by a converter, processed as an image signal, and then output.

By the way, in conventional image reading devices, a light source with good color rendering properties, such as a halogen lamp, has been used in order to obtain stable color separation characteristics. In the case of such a light source, if the applied voltage is kept constant, the spectral distribution will be constant;
Handling was relatively easy. However, such light sources are inefficient and generate a large amount of heat, so they cannot be used in small devices. Furthermore, when controlling the amount of light by changing the voltage applied to the light source, the spectral distribution also changes, making it difficult to adjust the amount of light.

Therefore, fluorescent lamps are being considered as an alternative to these light sources. When a fluorescent lamp is used as a light source, it has good luminous efficiency, and by appropriately combining a plurality of types of phosphors, a fairly free spectral distribution can be obtained. Therefore, by using such a fluorescent lamp, it is relatively easy to improve color separation characteristics in combination with a photoelectric converter.

However, immediately after lighting a fluorescent lamp, if the tube is cold,
Compared to the rated state (tube wall temperature of around 45°C), it has the characteristic that there is less visible light emission and more near-infrared light emission.

Additionally, the transmittance of color separation filters and the sensitivity of photoelectric converters (such as CCD line sensors) generally extend to the near-infrared region, so when the spectral distribution fluctuates as described above, The problem is that the color separation signal is different from the color separation signal at the rated time, and stable color separation characteristics cannot be obtained.

Incidentally, the above-mentioned problem is the same not only when obtaining a color signal but also when obtaining a monochrome binary code. For example, as described in Japanese Patent Application Laid-Open No. 60-57761, when an image contains red information such as a seal, and a large amount of near-infrared light is emitted, 2 If you perform digitization, the binarization will not be done correctly)
There was a problem. On the other hand, according to the above-mentioned publication, the above-mentioned problem is solved by varying the binarization level according to the amount of near-infrared light. However, when obtaining a multivalued color signal, it is impossible to eliminate the above-mentioned disadvantages using the method described in the above-mentioned publication.

Further, in the above-mentioned publication, a method of introducing an infrared light cut filter is studied in order to eliminate the above-mentioned disadvantages. According to this report, when an infrared light cut filter is used, not only the infrared wavelength region but also part of the red wavelength region is often cut off, which not only makes it impossible to read red information correctly, but also reduces the amount of light. This resulted in a reduction in resolution and aggravated temporal fluctuations in the light intensity distribution of fluorescent lamps, making it impractical for practical use. As described above, if an appropriate infrared cut filter is not used and an appropriate light source is not stabilized, the disadvantages pointed out in the above-mentioned publication will occur. In particular, when reading a color image, only a specific color is emphasized, resulting in an extremely unnatural color output signal.

In addition, in order to eliminate these problems, it is possible to control the tube wall temperature by turning on the light source for a certain period of time after the power is turned on, or by placing a heater around the fluorescent lamp to keep it warm. ing. However, when the light source is turned on and waited for a certain period of time, the time for the light source to stabilize is not constant depending on the environmental temperature, which poses a problem in stabilizing the light source. Furthermore, when controlling the temperature of the tube wall, the temperature of the portion emitting light is not necessarily controlled, which causes problems such as the light emission distribution being difficult to maintain constant. Note that a light source whose emission spectral distribution fluctuates is a phenomenon observed not only in fluorescent lamps but also in many light sources.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to eliminate the influence of infrared light output from a light source, and to reduce the amount of light emitted by the light source due to changes in environmental temperature, etc. An object of the present invention is to provide an image reading device that can always obtain stable color separation signals even if the amount of emitted light changes due to fluctuations or deterioration of a light source.

[Summary of the Invention] In order to achieve the above-mentioned object, the present invention provides a light beam of approximately 690 nm on the side of the illumination system including the light source or the side of the light receiving system including the photoelectric converter.
From the above, by using an optical filter that substantially cuts infrared light of 1100 nm or less or including infrared light, the influence of infrared light when obtaining color separation signals can be removed.
Furthermore, by using an optical filter similar to the above in the light intensity detection feedback system to stabilize the light source, we were able to stabilize the light intensity in the visible light region and obtain stable color separation signals. It is something.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In Figure 1, 1 is a fixed manuscript table (transparent glass)
Then, the original 2 as an object to be read is placed and set on top of it. Reference numeral 3 denotes a scanning photoelectric conversion section, which optically scans the image of the document 2 and photoelectrically converts it by moving along the lower surface of the document table 1 in the direction of the arrow shown in the figure. In the scanning photoelectric conversion unit 3, 4 is a fluorescent lamp as a light source,
The lighting is controlled by a lighting circuit 5 with a dimming function. Note that the lighting of the fluorescent lamp 4 is started by the CPU (Central Processing Unit), which controls the entire image reading device.
A lighting start signal is generated by the operation button 7 connected to the CPU 6, and the lighting circuit 5 is controlled by the CPU 6. When the fluorescent lamp 4 is turned on, the amount of light is reduced by an optical filter that cuts near-infrared light in the long wavelength range of about 690 nm to 1100 nm, for example, an optical filter having a spectral transmittance as shown in FIG. For example, it is detected by a light receiving element (for example, a silicon photodiode) 9 through a C-500) 8 made by Hoya Glass,
This detection signal is input to the input terminal of the feedback loop of the lighting circuit 5.

Here, FIG. 3 shows the spectral distribution immediately after the fluorescent lamp 4 is turned on without the above-mentioned feedback loop system, and FIG. 4 shows the spectral distribution until the lighting is restarted on time.

When the light from the fluorescent lamp 4 is detected by the optical filter 8 after removing the spectral component due to the rare gas (for example, argon gas) of the fluorescent lamp, the temporal change in the amount of light increases as shown in FIG. In other words, variations occur in the visible light region. Therefore, as shown in FIG. 5, the light with the infrared light cut is detected, and the detection signal is input to the lighting circuit 5 to stabilize the amount of light emitted by the fluorescent lamp 4 in the visible light region. That is, immediately after the fluorescent lamp 4 is turned on, as shown in FIG. 3, a lot of energy is attached to the emission of infrared light, and the amount of visible light emission is small. By detecting the infrared light at this time with the amount of light cut off by the optical filter 8, the amount of infrared light is reduced compared to when it is stable, as shown in FIG. Therefore, the lighting circuit 5
Then, a large amount of energy is supplied to the fluorescent lamp 4 so that the output signal of the light receiving element 9 is not constant. Then, much energy is supplied to the fluorescent lamp 4 until the amount of light becomes equal to the stable visible light amount. The emission spectrum of the fluorescent lamp 4 at this time is as shown in FIG. 6, and the emission spectrum in the visible light region is almost the same as the emission spectrum in the stable state shown in FIG.

When the light from the fluorescent lamp 4 stabilized in this way is transmitted through an optical filter 10 (an optical filter having the same characteristics as the optical filter 8) having a spectral transmittance as shown in FIG. As for the light amount fluctuation, there is no temporal fluctuation as shown in FIG.

At this time, the spectral distribution of the light transmitted through the optical filter 1o is only in the visible light region, as shown in FIG. 8, and there is no variation in the spectral distribution. This light (light transmitted through the optical filter 10) is irradiated onto the document 2 on the document table 1, and the reflected light is transmitted to the CCD line sensor 13 with the color separation filter 12 by the distributed refraction type rod lens array 11.
is imaged. This imaged light is photoelectrically converted by the intrusion sensor 13, and this photoelectrically converted signal is amplified by the amplifier 14, inputted to the A/D converter 15, and converted into a digital signal. In this way, the document 2 is illuminated with stabilized light, so that stable color separation signals can be obtained.

Incidentally, the light from the fluorescent lamp 4 is applied to the actual reading position a of the document 2 at a predetermined solid angle of 61 degrees. Also,
The amount of light emitted by the fluorescent lamp 4 is greatly affected by the temperature of the tube wall, so unless the installation position of the light receiving element 9 for detecting the amount of light is taken into account, there will be a considerable temperature difference from the actual light emitting surface, and as a result, the original original Do not perform dimming for the luminous flux. Therefore, in the present invention, as shown in FIG. = within 60 degrees>, there is no difference in the tube wall temperature of the fluorescent lamp 4, and dimming can be performed reliably.

As described above, the present invention is based on the fact that the fluctuation factor of the spectral distribution of a fluorescent lamp is caused by the emission spectrum of the rare gas sealed in the fluorescent lamp for starting discharge. That is, in a normal fluorescent lamp, argon gas is sealed in order to facilitate the start of discharge, and immediately after lighting, a large amount of the emission spectrum of argon gas (the wavelengths from 690 nm to 950 nm are the most common) is emitted. After lighting, the tube wall temperature rises due to discharge. As the mercury vapor pressure increases, the emission spectrum of mercury and the emission spectrum of the phosphor excited thereby increase, and after stabilization, the emission spectrum of argon gas almost disappears. That is, in the emission spectrum of a fluorescent lamp, the spectral distribution shifts from the emission spectrum of a rare gas that emits light in near-infrared light to the emission spectrum of mercury and phosphor that emits visible light.

On the other hand, many CCD line sensors generally have almost no sensitivity in a long wavelength band of 1100 nm or more.

Therefore, in order to eliminate the influence of near-infrared light, which is the emission spectrum of rare gases, the lighting system should be
By using an optical filter that cuts out infrared light, including light with a wavelength of m or less, the light received by the line sensor is limited to the emission spectrum of mercury and the emission spectrum of the phosphor excited by it. Therefore, the relative intensity of the spectral distribution hardly changes from immediately after lighting to when it is stable.

Furthermore, when the discharge energy of a fluorescent lamp is constant, the discharge energy is used to emit light from the rare gas immediately after lighting, and the amount of visible light emitted is small. Therefore, by detecting the light amount using the light that has passed through the optical filter that cuts the near-infrared light, and feeding back this light amount information to the fluorescent lamp lighting circuit, the amount of emitted light from the fluorescent lamp is kept constant. , it becomes possible to keep the spectral distribution in the visible light region constant, including light. By doing so, it becomes possible to read color images correctly, in particular, the amount of light does not decrease, there is no rough temporal variation, and it becomes possible to obtain stable color separation characteristics.

Furthermore, since the installation position of the light-receiving element that detects the amount of light from the fluorescent lamp is close to the light beam with a certain solid angle that is irradiated from the fluorescent lamp to the actual reading position of the document, for example within 60 degrees, the fluorescent lamp The rise in light intensity can be stabilized. That is, although the tube wall light amount distribution of the fluorescent lamp is caused by the tube wall temperature distribution of the fluorescent lamp, the above-mentioned installation position makes it possible to reliably control the light beam irradiating the original original.

In the above embodiment, the optical filter 10 is inserted on the illumination system side (that is, in the optical path between the fluorescent lamp 4 and the document 2). However, as shown in FIG. In other words, similar effects can be obtained even if the optical filter 10 is inserted in the optical path (between the original 2 and the line sensor 13).

Further, this optical filter 10 may also be used as a cover glass for a package of a line sensor 13 equipped with a color separation filter 12.

Furthermore, as shown in FIG. 10, for example, an optical filter 10 may be provided over the entire surface of the fluorescent lamp 4. In this case, the optical filter 8 disposed in front of the light receiving element 9 that detects the amount of light from the fluorescent lamp 4 becomes unnecessary. Further, by using the above-mentioned light-receiving element that is not sensitive to infrared light as the light-receiving element 9, the optical filter 8 can be omitted.

Furthermore, as shown in FIG. 11, the start-up characteristics of the fluorescent lamp 4 may be improved by installing a heat-retaining heater 21 around the fluorescent lamp 4.

In addition, 22 is a control circuit for the above-mentioned heat-retaining heater 21, and the heat-retaining heater 2 is controlled by a thermistor 23 as a temperature detection element.
1 and operates to maintain the temperature of the heat-retaining heater 21 at a constant level.

[Effects of the Invention] As detailed above, according to the present invention, the influence of infrared light output from a light source is removed, and the amount of light emitted by the light source fluctuates due to changes in environmental temperature, etc., or the light source deteriorates. It is possible to provide an image reading device that can always obtain stable color separation signals even if the amount of emitted light varies due to factors such as the following.

[Brief explanation of the drawing]

The figures are for explaining one embodiment of the present invention. Figure 1 is an overall configuration diagram, Figure 2 is a diagram showing the spectral transmittance of an optical filter that cuts infrared light, and Figure 3 is a diagram showing the spectral transmittance of an optical filter that cuts infrared light. Figure 4 is a diagram showing the emission spectrum of a fluorescent lamp at low temperatures. Figure 4 is a diagram showing the emission spectrum of a fluorescent lamp at stable conditions. Figure 5 is a diagram showing fluctuations in the amount of visible light when no stabilization is applied. The figure shows the emission spectrum of a fluorescent lamp immediately after lighting when the amount of visible light is stabilized, and Figure 7 shows the temporal fluctuation of the amount of light when the amount of visible light is stabilized. FIG. 8 is a diagram showing the spectral distribution of a fluorescent lamp transmitted through an optical filter that cuts infrared light, and FIGS. 9 to 11 are configuration diagrams of only the main parts showing other embodiments of the present invention. . 1...Document stand, 2...Document (object),
3... Scanning photoelectric conversion unit, 4... Fluorescent lamp (light source), 5... Lighting circuit, 8... Optical filter, 9... ... Light receiving element, 10...
・Optical filter, 11... Rod lens array, 12... Color separation filter, 13...
CCD line sensor (photoelectric converter), 15...
A/D converter.゛・へ １ − ・ Applicant's agent Patent attorney Takehiko Suzue @Bei゛Wat
Irregularity - μ The police life value soldier is a daughter - Ryo Farmer's mystery Ryoro'Ml 400 600 800 1α℃ liquid table (nm> Fig. 8 Fig. 9 Fig. s10 Fig. 11

Claims (7)

[Claims] (1) a light source that irradiates light onto an object having an image to be read;
A photoelectric converter that receives light from the object by light irradiation from this light source and converts it into an electrical signal;
an optical filter that substantially cuts infrared light of 0 nm or less or infrared light including it; a light amount detection means that is insensitive to the infrared light that detects the light amount of the light source and converts it into an electrical signal; and this light amount detection means. An image reading device comprising: control means for stabilizing and controlling the light amount of the light source according to an output signal of the image reading device. (2) The image reading device according to claim 1, wherein the optical filter is provided in an optical path between a light source and an object. (3) The image reading device according to claim 1, wherein the optical filter is provided in an optical path between an object and a photoelectric converter. (4) The light amount detecting means includes an optical filter that substantially cuts out the infrared light, and a light receiving element that converts the light transmitted through the optical filter into an electrical signal. The image reading device described in Section 1. (5) The image reading device according to claim 1, wherein the light amount detection means is a light receiving element that is not sensitive to the infrared light. (6) Claim 4 or 5, characterized in that the installation position of the light receiving element is close to a light beam having a certain solid angle that is irradiated from a light source to the actual reading position of the object. The image reading device described. (7) The image reading device according to claim 1, wherein the light source is a fluorescent lamp.