JPH02237362A - image reading device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image reading device of a type in which an image reading element receives light irradiated onto a document surface.

[Prior Art] Conventionally, in this type of image reading apparatus, a fluorescent lamp, which is more efficient than a halogen lamp, is often used as a light source for illuminating a document. However, the amount of light emitted by a fluorescent lamp fluctuates when the ambient temperature changes, or when the wall temperature of the lamp tube or the mercury gas vapor inside the tube changes due to self-heating.

For this reason, the original image could not be read accurately and high-quality image information could not be obtained.

Conventionally, as a countermeasure against this problem, the temperature of the tube wall of the fluorescent lamp is detected by a temperature sensing element, and the temperature of the tube wall is kept constant using a heater or an air cooling fan attached to the tube wall.

There has also been a method in which fluctuations in the amount of light due to self-heating after the fluorescent lamp is turned on are measured in advance, and the read image information is corrected based on the measured data.

[Problems to be Solved by the Invention] However, the method described above has the following problems. First, the first method involves heating the tube wall of the fluorescent lamp.
A heater and a fan are required for cooling, and the space required for these hinders miniaturization of the entire device and increases power consumption.

Furthermore, the second method is not sufficient to obtain high-quality image information, considering changes in environmental temperature and changes in the light output of the fluorescent lamp itself over time.

The present invention has been made to solve these problems, and even if the light intensity of the document irradiation light source of the image reading device fluctuates due to changes in the tube wall temperature of the fluorescent lamp that is the light source,
The main purpose is to accurately read the image density of a document and obtain high-quality images.

Furthermore, it is an object of the present invention to achieve miniaturization and cost reduction of the device.

[Means for Solving the Problems] In order to achieve this object, the image reading device of the present invention has the following features:
In an image reading device having a light source that irradiates light onto a document surface and an image reading element that receives reflected or transmitted light from the light source, a light source light amount detection sensor that is disposed near the light source and detects the amount of light from the light source; , a variable light transmittance filter that is arranged in an optical path until the light from the light source is received by the image and whose light transmittance gradually changes; and transmitted light amount control means for controlling the light transmittance of the variable filter.

"Operation" In the present invention having the above configuration, when the light amount of the light source is detected by the light source light amount detection sensor, the detection signal is sent to the transmitted light amount control means of the variable light transmittance filter, and the light amount of the filter is Transmittance is suitably controlled. Therefore, even if the amount of light from the light source changes, the amount of light such as reflected light from the document surface that reaches the image reading light amount element is kept constant, making it possible to obtain high-quality image information.

[Example] First, the configuration of the entire apparatus will be explained with reference to FIGS. 1 to 3. A transparent document table 3 on which a document 5 is placed is provided on the upper surface of the main body 2, and a document presser 4 is placed on top of the transparent document table 3. It is provided so that it can be opened and closed using one side as a rotational support shaft. Inside the main body 2, the scanner unit section 1 is slidably supported on two guide shafts 6 and 7 fixed to the inner bottom of the main body 2. That is, the scanner unit section 1 is slidably supported on a guide shaft 6 via a pair of mounting plates 8 protruding from its lower surface, and further transmits force from a drive system (not shown). A part of the wire rope 9 guides the scanner unit section 1 onto the guide shaft 6.
It is fixed to the mounting plate 8 so that it can be towed along. On the other hand, the guide shaft 7 is guided by a mounting plate 18 which also projects from the bottom surface of the scanner unit section 1 .

Next, to explain the internal configuration of the scanner unit section 1, the reading system built into the scanner unit section 1 is as follows.
A pair of light sources 10 for illuminating the original 5 and the original 5
A CCD type reading element 11 that receives reflected light from the reading element 11, a slit 30 that makes the reflected light into a slit shape, and three mirrors 12, 13, . . . that are provided to guide the reflected light to the reading element 11. 14, a lens 15, a color separation filter support 16 that is rotatably supported to be placed when reading a color document, a filter switching motor 7 that rotates the color separation filter support 16, and a light source light amount detection sensor. an optical fiber 21 for guiding part of the light from the light source to the four diode 20; a variable light transmittance filter 22 provided in the optical path between the lens 15 and the reading element 11; It consists of a filter drive motor 23 for driving the filter 22. The variable light transmittance filter 22 is a so-called ND filter in which the transmittance changes smoothly from one end of the rectangular filter toward the other end due to gradual density changes, as shown in FIG. A rack 28 is formed on the side edge in the transmittance change direction, and a gear 29 is attached to the rack to the drive shaft of the filter drive motor 23.
are meshed with each other, and are configured to move in the direction of the arrow by the drive of the motor 23.

In FIG. 5, photodiode 20 outputs a current proportional to the light output of light source 10. In FIG. The operational amplifier 24 is
The A/D converter 25 converts the current output of the photodiode 20 into a voltage, and the A/D converter 25 converts this voltage value into a digital value and sends a signal to the CPU 26. A motor drive circuit 27 is for controlling the filter drive motor 23 based on a signal from the CPU 26.

Next, the operation will be explained. First, the color original 5 is placed on the original placing table 3, and the original presser 4 is closed. Then, when the controller (not shown) starts reading the document (number n is given, the scanner unit 1 is moved to the reading start position via the wire rope 9. At this time, the filter support 16 is rotated by the filter switching motor 17,
The red, green, and blue filters are sequentially placed in front of the lens 5. Then, a white level check and a black level check are performed, upper and lower voltage limits for colors are set, and reading is started. Reading is done line by line, 1
After the transfer of data for one line is completed, the scanner unit section 1 waits until a signal for reading the next line is given. In this way, when reading a document, movement and stopping are repeated. At this time, the wire rope 9
Since the guide shaft 6 and guide shaft 6 are provided at the lower part of the scanner unit section 1 near the center of gravity, the drive system can pull the entire scanner unit section in a well-balanced manner. Therefore, the scanner unit section 1 can stably move in parallel on the guide shaft 6, allowing good image reading.

Further, an auxiliary guide shaft 7 is provided at the bottom end of the scanner unit section 1, but since the guide shaft 6 is arranged at the center of gravity, the guide shaft 7 is mainly used for the scanner unit section 1. This function is to prevent the rotation of the scanner unit 1 around the guide shaft 6, and has almost no effect on the movement of the scanner unit section 1.

A portion of the light output of the light source 10 is guided by an optical fiber 21 to a photodiode 20, which is connected to the light source 1.
Outputs a current proportional to the optical output of 0. As shown in FIG. 5, operational amplifier 24 converts the current output of photodiode 20 into a voltage, and this voltage is input to A/D converter 25. As shown in FIG. The CPU 26 sends a signal to the motor drive circuit 27 based on the signal from the A/D converter 25. A motor drive circuit 27 controls a filter drive motor 23 for driving the ND filter 22 described above.

Now, if the amount of light from the light source 10 becomes small, both the output current of the photodiode τ gate 20 and the output voltage of the operational amplifier 24 become low. As a result, the output value of the A/D converter 25 also becomes smaller, and as a result, the CPU 26 sends a signal to the motor drive circuit 27, and the ND filter drive motor 2
3 rotates and the ND filter 22 moves in the direction of arrow A in FIG. 4, thereby increasing the transmittance of the ND filter 22 in the optical path and keeping the amount of light reaching the reading element 11 constant.

On the other hand, the ND filter 22 may be of a circular shape, as shown in FIG. 6, in which the transmittance changes smoothly in the circumferential direction and remains constant in the radial direction. in this case,
The ND filter 22 controls the amount of light reaching the reading element 11 by rotating about the center of a circle as a rotation axis.

Alternatively, as yet another embodiment, each of the R, G, and B filters of the color separation filter 16 may be configured such that the transmittance of each filter changes smoothly in the circumferential direction, as shown in FIG. These may also serve as the ND filter 22. Note that in place of the ND filter, it is also possible to use an optical shutter or the like whose light transmittance is changed by so-called voltage control. Further, the position of the ND filter 22 does not have to be as shown in FIG. 1, and may be, for example, between the lens 15 and the mirror 14. Further, in this embodiment, a color image reading apparatus that separates and reads a color original is described, but it goes without saying that the present invention may also be applied to a black and white image reading apparatus.

[Effects of the Invention] As is clear from the above detailed description, according to the present invention, fluctuations in the light intensity of the light source are detected by the light source light intensity detection sensor, and based on this information, the light intensity between the document and the reading element is detected. By appropriately controlling the transmittance of a variable light transmittance filter installed on the road, the amount of light reaching the reading element can be corrected to the image information in a constant light source state even when the light amount of a light source such as a fluorescent lamp fluctuates. can. Therefore, high quality image information can be obtained even when the temperature environment of the light source changes. Furthermore, since a heater or fan for controlling the amount of light from the light source is not required, a compact, power-saving, and inexpensive image reading device can be provided.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a scanner unit section 1 according to an embodiment of the present invention, FIG. 2 is a perspective view showing the external appearance of an image reading apparatus according to the present embodiment, and FIG. 2 is a partial cross-sectional view seen from the direction of arrow B in FIG. 2, FIG. 4 is a perspective view showing the configuration of the variable light transmittance filter 22, and FIG.
6 is a perspective view showing a modification of the variable light transmittance filter with a light output of 0; FIG. 7 is a control block diagram of a variable light transmittance filter with a light output of 0; FIG. This is an example. In the figure, 10 is a light source, 11 is an image reading element, 20 is a photodiode (light source light amount detection sensor), 21 is an optical fiber, 22 is an ND filter (light transmittance variable filter), 23
is the ND filter drive motor.

Claims (1)

[Scope of Claims] 1. An image reading device including a light source that irradiates light onto a document surface and an image reading element that receives reflected or transmitted light from the light source, the image reading device being disposed near the light source and controlling the amount of light of the light source. a light source light amount detection sensor that detects the light source; a light transmittance variable filter that is disposed in the optical path until the light from the light source is received by the image reading element and whose light transmittance gradually changes; and the light source light amount detection sensor. An image reading device comprising: transmitted light amount control means for controlling the light transmittance of the variable light transmittance filter based on a detection signal from a sensor.