JPH07162620A - Image reader - Google Patents

Abstract

(57) [Summary] [Purpose] Image reading with line image sensor
The change in the angle of view of the imaging lens during optical magnification
Combined optical shading correction and light source
Fluctuations in light intensity or when electrically reading the image sensor
The amount of light incident on the image sensor can be adjusted according to changes in
The purpose is to provide a means to do so. [Structure] For changing the angle of view of the imaging lens 19 during optical magnification change
Combined optical system COS ^Four Shade to correct the θ law
Optically by changing the shape of the swing correction plate 17.
Performs shading correction. Also, the fluctuation of the light amount of the light source 15
Or when the line image sensor 20 is electrically read
Change the shape of the shading correction plate 17 according to the change in
Incident on the line image sensor 20
Adjust the light intensity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus which can be used for a facsimile machine, a digital copying machine, a scanner and the like and can read image data of an original.

[0002]

2. Description of the Related Art In recent years, a one-dimensional self-scanning image sensor has been scanned in the sub-scanning direction as an image input means for a digital copying machine, a facsimile machine, an electronic filing machine, etc., and image data of a document is line by line. Image reading apparatuses capable of sequentially reading are becoming mainstream.

In such an image reading device, the illuminance distribution on the document surface is not uniform in the self-scanning direction of the image sensor due to the light distribution of the light source, and in the image reading device constituted by the reduction optical system, the optical system is used. At COS
^{4 Even} if a reflected image of a uniform-density original such as a white original is formed on the image sensor due to the influence of the θ law, etc.,
The illuminance distribution on the image sensor is not uniform. In general, the illuminance has a distribution that is brightest along the optical axis and darkens toward the periphery unless any measures are taken.

In order to make the illuminance distribution on the image sensor uniform, optical shading correction using a light shielding plate is generally performed. An image reading apparatus that performs conventional shading correction will be described below. Figure 11
11A is a side sectional view of a conventional image reading apparatus, FIG.
FIG. 12B is a horizontal sectional view of the same, and FIG. 12 is a schematic side sectional view of an optical system of an optical carriage of a conventional image reading apparatus. As shown in FIG. 11A, the image reading apparatus includes an original placing glass 2 on which an original 1 is placed, and an original placing glass 2
A document cover 3 that holds the document 1 in close contact with it, a white reference plate 4 that gives white reference data for shading correction to the image processing unit before the start of image reading, a document 1 is scanned, and the document 1 is sequentially read line by line. It has a carriage 5 for reading.

As shown in FIG. 11B, the carriage 5
Is supported by the support shafts 6a and 6b and the support rollers 7a and 7b, and its movement is restricted only in the sub-scanning direction. A pair of drive wires 8a and 8b are connected to the carriage 5, one drive wire 8a is banded to the drive pulley 9a and the driven pulley 10a, and the other drive wire 8b is banded to the drive pulley 9b and the driven pulley 10b. Has been done. The pair of drive pulleys 9a and 9b are connected by a drive shaft 11, and the other pair of driven pulleys 10a and 10b are connected by a driven shaft 12. A carriage drive motor 13 is connected to one end of the drive shaft 11, and a pair of tension generating members 14a and 14 such as springs that apply tension to the drive wires 8a and 8b are connected to both ends of the driven shaft 12.
b is connected.

In FIG. 12, a carriage 5 partially shields light incident on a light source 15 for illuminating the original 1, a reflection mirror 16 for reflecting a reflected image from the original 1, and an image forming lens 19 for optical shading. A shading correction plate 17 for correction, an imaging lens 19 for forming an image of the original 1 on the line image sensor 20, a line image sensor 20 for reading a reflected image from the original 1 and converting it into an electric signal,
An optical system magnification changing mechanism 21 for changing the magnification of the optical system is provided.

The operation of the conventional image reading apparatus configured as described above will be described below. First, when an external host issues an instruction to read the original 1, the CPU
(Not shown) rotates the carriage drive motor 13 to drive the carriage 5 connected by the drive pulleys 9a and 9b and the drive wires 8a and 8b to the shading correction position. When detecting that the position has been reached, the CPU stops the carriage 5, turns on the light source 15, outputs an operation command to the image sensor, and reads the white reference plate 4 arranged at that position by the line image sensor 20. The operation is started and electrical shading correction is performed.

After the shading correction is completed, the CPU
Stops driving the image sensor and drives the carriage 5 again at a constant speed. When the CPU detects that the carriage 5 has reached the reading start point of the document 1, it outputs an operation command to an image sensor drive circuit (not shown) to restart the image reading operation of the line image sensor 20. Then, the light flux from the light source 15 is applied to the reading portion of the original 1, and the reflected image of the reading portion of the original 1 enters the carriage 5. Further, the reflected image of the main scanning one line of the document 1 guided into the carriage 5 is reflected by the reflecting mirror 16 and the line image sensor 20 by the imaging lens 19.
An image is formed on and captured as reflectance data.

Thereafter, the image sensor output is converted into digital data by the image processing circuit. After that, a shading correction circuit (not shown) is used to correct variations in the illuminance of the light that illuminates the original surface that cannot be completely corrected by the optical shading correction, a decrease in the peripheral output due to the COS ⁴ θ rule of the lens, and sensor characteristic variations. ) To obtain the image data. The obtained image data is sequentially taken into a buffer memory (not shown) and is output by the CPU through the interface. This series of operations is performed by the CPU
This is performed every time the carriage drive motor 13 is driven to move the carriage 5 in the sub scanning direction by one line corresponding to the resolution. When the carriage 5 is moved to the reading end portion of the document 1, the reading is finished, the CPU turns off the light source 15, and the carriage drive motor 13 is driven to move the carriage 5 to the reading start portion of the document to complete the operation. . By the above operation, the image data of the two-dimensional original 1 can be read flatly.

Next, the variable magnification operation of the optical system will be described below with reference to FIG. FIG. 13 is a schematic diagram of an optical system variable magnification mechanism of a conventional image reading apparatus. When the image reading device receives a command to change the magnification from the outside, the CPU controls the optical system variable magnification mechanism drive circuit to rotate the drive motor 42 of the variable magnification mechanism, and the rotation thereof is the pinion gear 43 and the rack 4.
4 and the rotational driving force is converted into a linear driving force in the axial direction of the imaging lens 19. The linear driving force is transmitted to the imaging lens 19 and the line image sensor 20, both are driven to a predetermined position, and the zooming operation is completed. FIG. 14 is a view showing the change in the angle of view of the coupling lens when the magnification of the optical system of the conventional image reading apparatus is varied.

[0011]

However, in the above-mentioned conventional optical system configuration, when the angle of view θ of the imaging lens 19 changes from θ ′ to θ ′ during optical magnification change as shown in FIG. Since it is fixed at a predetermined position during assembly, the illuminance distribution on the line image sensor 20 changes according to the COS ⁴ θ law of the above optical system. When a uniform-density original such as the white reference plate 4 is read, even if the illuminance distribution on the line image sensor 20 is made uniform at a certain magnification, this uniformity is lost if the magnification is changed. was there.

This non-uniformity can be corrected by so-called electric shading correction, in which shading correction is performed after A / D conversion of an analog image electric signal obtained from the image sensor. However, in this case, when the white reference plate 4 is read by shading before the start of reading the original, the sensor output voltage also becomes maximum at the position where the illuminance on the image sensor becomes maximum, and this voltage becomes the A / D as a reference.
Since it is converted, not only the S / N ratio decreases at the position where the illuminance is low, that is, the position where the sensor output voltage is low, A /
The quantum ratio error accompanying D conversion becomes large, and as a result,
The dynamic range of image data is reduced. Also,
When the light source 15 is a fluorescent lamp, the light emission amount changes greatly immediately after lighting. At this time, the amount of light received by the image sensor also changes, the sensor output fluctuates, unevenness occurs in the read image, and the image accuracy deteriorates.

Even when the electrical reading time required for the image sensor to read the image data for one line of the original 1 is changed, for example, to change the reading time of the original 1, the analog output from the image sensor is output. In order to make the image signal constant, it is necessary to make the amount of light received by the sensor constant. However, if this light amount adjustment is performed by controlling the light amount of the light source 15 as in the conventional case, when the light source 15 is a fluorescent lamp or the like, its spectral characteristic changes. The image sensor output is obtained as a superposition of the spectral characteristics of the light source 15, the sensor, and other elements that make up the optical system. Therefore, if the spectral characteristics of the light source change, the sensor output will change even if the amount of light received by the sensor does not change. . In particular, in the case of a color original reading device, when the spectral characteristics of the light source are changed, the image data obtained even when the same original color is read, the two colors become different color data, and as a result, the color reproducibility deteriorates. There was a problem.

Therefore, according to the present invention, an optical shading correction is performed in accordance with a change in the angle of view of the imaging lens at the time of optical magnification change, and an image sensor is provided in accordance with a change in the light amount of the light source or a change in the electrical reading time of the image sensor. It is an object of the present invention to provide an image reading device capable of adjusting the amount of incident light.

[0015]

To this end, according to the present invention, the shape of the optical shading correction plate is changed so that the shading effect can be changed. The non-uniformity of the image sensor received light amount distribution caused by the change of the angle can be corrected.

[0016]

According to the above construction, the illuminance distribution incident on the image sensor can be made uniform when the density original is uniformly read when the magnification of the optical system is changed, such as when the optical system is enlarged or reduced. do not do. Further, it is possible to minimize the quantization error when A / D converting an analog image signal obtained by the image sensor, and it is possible to read an image with high gradation.
Further, even when the light amount of the light source fluctuates immediately after lighting, it is possible to read a stable image without unevenness by keeping the light receiving amount of the sensor constant. In addition, when the electrical reading time of the image sensor is changed, especially in the case of a color image reading apparatus, if the light amount of the light source is controlled, the spectral characteristics of the light source change and the color reproducibility deteriorates. By changing the shape of the plate and adjusting the amount of light received by the image sensor, it is possible to read an image without degrading color reproducibility.

[0017]

Embodiment 1 Next, an embodiment of the present invention will be described with reference to the drawings. 1A is a side sectional view of an image reading apparatus according to a first embodiment of the present invention, FIG. 1B is a horizontal sectional view thereof, and FIG. 2 is a schematic side sectional view of an optical system of the optical carriage. In each of the drawings described below, FIGS.
The same components as those of the conventional example shown in FIG. The image reading device shown in FIGS. 1A and 1B has the same configuration as the conventional image reading device shown in FIGS.

In FIG. 2, a shading correction plate drive unit 18 is provided between the reflection mirror 16 and the imaging lens 19, and the shading correction plate 17 is held on the back surface thereof, which is shown in FIG. It is different from the conventional optical system.

FIG. 3 is a block diagram of an electric system of the image reading apparatus according to the first embodiment of the present invention. The line image sensor 20 has an A / D converter 28,
The shading correction circuit 29, the buffer memory 30, and the interface 22 are connected. Reference numeral 23 is a CPU, which is an image sensor drive circuit 26 for driving the line image sensor 20 and a light source driver 2 for driving the light source 15.
5, a motor control circuit 24 for driving the carriage drive motor 13, a buffer memory 30, and an interface 22. Reference numeral 37 is a drive motor for the shading correction plate 17, 39 is a drive motor for driving an eccentric cam (described later) 38, which are respectively connected to the CPU 23 via a shading correction plate drive circuit 40, and further drive a scaling mechanism motor. The circuit 41 is also connected to the CPU 23.

Next, the operation of the image reading apparatus configured as described above will be described. First, when a document reading command is issued from the external host through the interface 22, the CPU 23 controls the motor control circuit 24 to rotate the carriage drive motor 13 to drive the drive pulleys 9a and 9a.
The carriage 5 connected by b and the drive wires 8a and 8b is driven to the shading correction position. When the CPU 23 detects that the position has been reached, the CPU 23 stops the carriage 5, lights the light source 15 by the light source driver 25, outputs an operation command to the image sensor drive circuit 26, and arranges the line image sensor 20 at that position. The reading operation of the white reference plate 4 is started, and the shading correction is executed.

After the shading correction is completed, the CPU
23 stops the image sensor drive circuit 26 and drives the carriage 5 again at a constant speed. When the CPU 23 detects that the carriage 5 has reached the reading start point of the document 1, it outputs an operation command to the image sensor drive circuit 26 and restarts the image reading operation of the line image sensor 20. Then, the light flux from the light source 15 is applied to the reading start portion of the original document 1, and a part of the diffuse reflection light of the reading portion of the original document 1 enters the carriage 5. Further, the diffused reflected light of one line of the main scanning of the document 1 guided into the carriage 5 is reflected by the reflection mirror 16 to form the imaging lens 19
Then, the image is formed on the line image sensor 20 and taken in as reflectance data.

Thereafter, in FIG. 3, the image sensor output is amplified by the amplifier 27 and converted into digital data by the A / D converter 28. After that, variations in illuminance of light irradiating the original surface that could not be completely corrected by the optical shading correction and a decrease in peripheral output due to the COS ⁴ θ rule of the lens,
Further, the shading correction circuit 29 normalizes and corrects variations in the characteristics of the sensor and the like to obtain image data. The obtained image data is sequentially fetched into the buffer memory 30, and the CPU 23 outputs the read image data of the original 1 to the interface 22 over a specified range.

In this series of operations, the CPU 23 controls the motor control circuit 24 to drive the carriage drive motor 13 to rotate the drive pulleys 9a and 9b, and the drive wire 8
This is performed every time the carriage 5 connected to a and 8b is moved by one line corresponding to the resolution in the sub-scanning direction. When the carriage 5 is moved to the reading end portion of the document 1, the reading is finished, and the CPU 23 issues a command to the light source driver 25 to turn off the light source 15, and the light source 15 is turned off. Next, the CPU 23 controls the motor control circuit 24
Command to drive the drive pulleys 9a and 9b by the carriage drive motor 13 to move the carriage 5 connected to the drive wires 8a and 8b to the reading start portion of the document 1 and complete the operation. By the above operation, the image data of the two-dimensional original 1 can be read flatly.

Next, the structure of the shading correction plate 17 whose shape can be changed and the mechanism for changing the shape will be described. FIG. 4A is a front view of a plate material that constitutes the shading correction plate 17 of the image reading apparatus of the first embodiment of the present invention, and FIGS. 4B and 5 and 6A are the combined state of the plate materials. 6B is a side view of the same. Figure 4
In FIG. 4A, reference numeral 31a denotes a fan-shaped plate material that constitutes the shading correction plate 17. As shown in FIG. 4B, four adjacent plate materials 31a, 31b, 31c and 31d are rotated by a pin 51. A long hole 52 that is movably coupled and that is further opened at the base end in the longitudinal direction is connected by a pin 32.
Is slidably coupled along. Therefore, the long hole 52
Plate material 31a, 31b, 31
By rotating c and 31d with the pin 51, the radius of the shading action curve (circular curve formed by the outer peripheral edges of the plate members 31a, 31b, 31c and 31d) 33 of the shading correction plate 17 as shown in FIGS. Can be changed.

Next, a mechanical portion for changing the shape of the shading correction plate 17 will be described. As shown in FIG. 6A, a steel wire ring 34 is engaged with a plate member 31a constituting the shading correction plate 17 by a pin 53, and the steel wire ring 34 is wound around a drive pulley 35 and a driven pulley 36. , The drive motor 37 on the drive pulley 35
Are connected. When the drive motor 37 is driven in the direction of the arrow in the figure, power is transmitted to the drive pulley 35 and the steel wire ring 34 is rotated. Therefore, the plate member 31a connected to the steel wire ring 34 is pulled in the direction of the arrow in the drawing by the pin 53, and the radius of the shading action curve 33 changes from the shape of FIG. 4B to the shape of FIG. Although the radius is maximum in FIG. 4B and minimum in FIG. 5, it can be set to any radius in between by adjusting the movement amount of the steel wire ring 34. Further, when the shading action curve 33 is deformed, the height of the shading correction plate 17 also changes. That is, in FIG. 6A, 38 is an eccentric cam for moving the shading correction plate 17 up and down, 39 is a drive motor for the eccentric cam 38, 54 and 55 are plate members 31a,
A frame for holding 31b, 31c, 31d, and the frames 54, 55 are grounded to the eccentric cam 38. Therefore, when the eccentric cam 38 is rotated by the drive motor 39, the plate members 31a, 3a forming the shading correction plate 17 are formed.
1b, 31c, 31d can be moved up and down.

The optical shading correction operation of the image reading apparatus configured as described above will be described below with reference to FIG.
-It demonstrates, referring FIG. 7A is an output diagram of the image sensor of the image reading apparatus according to the first embodiment of the present invention, and FIG. 7B is a change diagram of the shading action curve 33 of the shading correction plate 17 of the image reading apparatus. In FIG. 7B, reference numeral 46 is a lens entrance pupil.
When the optical magnification is changed, the angle of view of the imaging lens changes as described with reference to FIG. When the angle of view changes, the COS ⁴ θ law of the optical system changes the illuminance distribution on the image sensor. Therefore, by changing the radius and height of the shading correction plate 17, the distribution of the amount of light incident on the lens entrance pupil 46 is always distributed in the reciprocal of the COS ⁴ θ rule, and the illuminance distribution on the sensor is kept uniform. Specifically, the lens entrance pupil 46 at the optical shading correction plate position is considered, and the lens entrance pupil 46 and the shading correction plate 17 are in contact with each other at the end,
In the central part, the lens entrance pupil 46 and the shading correction plate 1
The radius of the shading correction plate 17 is set so that the ratio of the overlapping area of 7 (the shaded area in FIG. 7B) and the total area of the lens entrance pupil 46 is equal to the ratio of the amount of transmitted light in the central portion of the lens and the amount of transmitted light in the peripheral portion. And the height are determined and output to the shading correction plate drive circuit 40.

The shading correction plate drive circuit 40 drives the two drive motors 37 and 39 to change the shape of the shading correction plate 17 and change the shading action curve 33. Therefore, the distribution of the amount of light incident on the lens entrance pupil 46 can be distributed reciprocally according to the COS ⁴ θ rule, and the distribution of the amount of light incident on the lens entrance pupil 46 and the distribution of the amount of light transmitted through the lens cancel each other out, resulting in the image sensor The light distribution above is uniform. However, in this case, since it is determined under the two conditions of the end portion and the central portion, it is not strictly uniform at the intermediate position, but the error is within 5%, and there is no practical problem. Further, since the lens pupil diameter at the position of the shading correction plate 17 can be easily obtained, it can be treated as a known value if the angle of view is known at the time of shading correction.

Further, according to the above configuration, fine adjustment of shading correction can be optically performed, and the operation thereof will be described below. When the reading operation of the white reference plate 4 is started by the line image sensor 20, the digital data immediately after being A / D converted by the A / D converter 28 does not pass through another image processing unit and is directly buffered by the buffer memory 30.
Stored in. The CPU 23 reads the data, finds the distribution in the image sensor main scanning direction, and if the distribution is not uniform within the allowable range, calculates the deformation amount of the radius and height of the shading correction plate 17, and performs shading. Output to the correction plate drive circuit 40. The shading correction plate drive circuit 40 drives the two drive motors 37 and 39 of the correction plate drive mechanism to change the shape of the shading correction plate 17. The main scanning direction distribution of the image data is shown in FIG.
In this case, if the range indicated by the diagonal lines is within the allowable range of the image sensor output, the illuminance of the line image sensor 20 at both ends is too large, and the illuminance at the center is insufficient. Therefore, it is necessary to increase the illuminance at the center and decrease the illuminance at both ends. At this time, as shown in FIG. 7B, the shading action curve 33 of the shading correction plate 17 is transformed from the alternate long and short dash line to the solid line. After that, the white reference plate 4 is read again and the sensor output distribution is made uniform by repeating the above series of operations until the distribution of the obtained image data in the image sensor main scanning direction becomes uniform within the allowable range. You can

(Second Embodiment) Next, a color image reading apparatus according to a second embodiment of the present invention will be described. Second of the present invention
The configuration of the image reading apparatus in the embodiment is shown in FIG.
This is similar to the first embodiment shown in (b). 8 is a schematic side sectional view of an optical system of an optical carriage of an image reading apparatus according to a second embodiment of the present invention, FIG. 9 is a block diagram of an electric system of the image reading apparatus, and FIG. An output diagram of the image sensor of the reading device, and FIG. 10B is a change diagram of the shading action curve 33 of the shading correction plate 17 of the image reading device. The mechanism of the shading correction plate 17 is the same as that of the first embodiment shown in FIGS. In FIG. 8, the carriage 5 includes a light source 15 for irradiating the document 1, a light amount sensor 47 for monitoring a light amount variation of the light source 15, a reflection mirror 16 for reflecting a reflected image from the document 1, and a part of the light incident on the imaging lens 19. Shading correction plate 17, which shades light selectively, and shading correction plate 17
Shading correction plate drive unit 18 for changing the shape of the
Imaging lens 1 for imaging document 1 on an image sensor
9. A line image sensor 20 for reading a reflected image from the original 1 and converting it into an electric signal is provided. Further, in FIG. 9, the light amount sensor 47 is connected to the CPU 23.

The light amount control operation of the image reading apparatus configured as described above will be described below with reference to FIGS. 9 and 10. When the light source 15 is turned on and image reading is started, the light amount sensor 47 monitors the light amount variation of the light source 15. When the amount of light from the light source fluctuates, the amount of fluctuation is measured by the light amount sensor 47, and by varying the area and height of the shading correction plate 17, the amount of light incident on the lens entrance pupil 46 is inversely distributed with respect to the variation in the amount of light source. Adjust the illuminance distribution on the sensor to keep the sensor output constant.
Specifically, considering the lens entrance pupil 46 at the position of the optical shading correction plate, the overlapping area of the lens entrance pupil 46 and the shading correction plate 17, that is, the shading amount is changed so as to change in a constant ratio with respect to the light source light amount variation. The area and height of the correction plate 17 are determined and output to the shading correction plate drive circuit 40. The shading correction plate drive circuit 40 drives the two drive motors 37 and 39 to change the area and height of the shading correction plate 17. Then,
In FIG. 10B, the shading action curve 33 changes from a broken line to a solid line. Therefore, the lens entrance pupil 46
By varying the amount of light incident on the light source reciprocally with respect to the fluctuation of the light source light amount, the fluctuation of the light source light amount is canceled, the illuminance of the image sensor is made constant, and the output of the sensor is kept constant. In this case, since the lens pupil diameter at the position of the shading correction plate 17 can be easily obtained, it can be treated as a known value during the light amount control.

It should be noted that each of the above-described embodiments can be implemented by both monochrome and color image reading devices. Further, only the light source 15 and the reflection mirror 16 are mounted on the carriage 5, and the shading correction plate 17 and the imaging lens 1 are mounted.
9, the line image sensor 20, the optical system variable-magnification mechanism 21 are fixed to the image reading device main body, and the light source 15 and the reflection mirror 16 are also fixed to the image reading device main body to move the document 1. It can also be implemented in an image reading device that reads by reading.

[0032]

As described above, according to the present invention, the shape of the light-shielding plate is changed to change the optical shading effect. The COS ⁴ θ rule can be corrected to make the illuminance distribution incident on the image sensor uniform. Therefore, S /
It is possible to realize an image reading apparatus capable of reading a high gradation image in which the N ratio is not deteriorated and the quantization error when the analog image signal obtained by the image sensor is A / D converted is minimized.

When the light amount of the light source of the image reading device fluctuates, the shape of the light shielding plate is changed to change the optical shading effect and the light receiving amount of the image sensor is adjusted, so that the light receiving amount of the image sensor is constantly changed. It is possible to realize an image reading device capable of highly accurate image reading while keeping the amount constant.

[Brief description of drawings]

1A is a side sectional view of an image reading apparatus according to a first embodiment of the present invention, and FIG. 1B is a horizontal sectional view of an image reading apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic side sectional view of an optical system of an optical carriage of the image reading apparatus according to the first embodiment of the present invention.

FIG. 3 is a block diagram of an electric system of the image reading apparatus according to the first embodiment of the present invention.

FIG. 4A is a front view of a plate material forming a shading correction plate of the image reading apparatus of the first embodiment of the present invention, and FIG. 4B is a shading correction plate of the image reading apparatus of the first embodiment of the present invention. The front view which shows the combined state of the board material which comprises

FIG. 5 is a front view showing a combined state of plate materials constituting the shading correction plate of the image reading apparatus according to the first embodiment of the present invention.

FIG. 6 (a) is a front view showing a combined state of plate materials constituting the shading correction plate of the image reading apparatus of the first embodiment of the present invention. FIG. 6 (b) is an image reading apparatus of the first embodiment of the present invention. Side view showing the combined state of the plate material that constitutes the shading correction plate

7A is an output diagram of the image sensor of the image reading apparatus of the first embodiment of the present invention, and FIG. 7B is a shading action curve change diagram of the shading correction plate of the image reading apparatus of the first embodiment of the present invention.

FIG. 8 is a schematic side sectional view of an optical system of an optical carriage of the image reading apparatus according to the second embodiment of the present invention.

FIG. 9 is a block diagram of an electric system of the image reading apparatus according to the second embodiment of the present invention.

10A is an output diagram of the image sensor of the image reading apparatus according to the second embodiment of the present invention, and FIG. 10B is a shading action curve change diagram of the shading correction plate of the image reading apparatus according to the second embodiment of the present invention.

11A is a side sectional view of a conventional image reading apparatus, and FIG. 11B is a horizontal sectional view of a conventional image reading apparatus.

FIG. 12 is a schematic side sectional view of an optical system of an optical carriage of a conventional image reading device.

FIG. 13 is a schematic view of an optical system zooming mechanism of a conventional image reading device.

FIG. 14 is a view showing the change of the angle of view of the imaging lens when the magnification of the optical system of the conventional image reading apparatus is changed.

[Explanation of symbols]

 1 Document 5 Carriage 8a, 8b Drive Wire 9a, 9b Drive Pulley 10a, 10b Driven Pulley 13 Carriage Drive Motor 15 Light Source 16 Reflection Mirror 17 Shading Correction Plate 18 Shading Correction Plate Drive 19 Imaging Lens 20 Line Image Sensor 21 Optical System Change Double mechanism 31a, 31b, 31c, 31d Plate material 32 Pin 33 Shading action curve 34 Steel wire ring 35 Drive pulley 36 Driven pulley 37 Drive motor 38 Eccentric cam 39 Drive motor 47 Light intensity sensor 52 Oblong hole

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H04N 1/401 4226-5C H04N 1/40 101 A

Claims (6)

[Claims] 1. A light source for irradiating an original, an image sensor for converting a reflected image from the original into an electric signal, an image forming lens for connecting an image on the original onto the image sensor, and a space between the original and the image sensor. An image reading apparatus comprising: a light-shielding plate provided; and means for performing optical shading correction by changing the shape of the light-shielding plate. 2. A means for changing the area of the light shielding plate and a means for changing the height of the light shielding plate are provided as the means for changing the shape of the light shielding plate.
The image reading device described. 3. A means for changing the area of the light shielding plate, wherein shoulder portions of a plurality of fan-shaped plate members are rotatably connected,
Moreover, the light-shielding plate is constructed by providing a long hole in the longitudinal direction at the base end of each plate member and slidably connecting the long hole with one pin, and sliding each plate member along this pin. 3. The area of the light shielding plate is changed by changing the radius of the light shielding plate by moving the light shielding plate.
The image reading device described. 4. An actuator is provided in each of the means for changing the area of the light shielding plate and the means for changing the height, and the shape of the light shielding plate is changed by driving the actuator by a signal from the outside. The image reading device according to claim 2, wherein 5. An image reading apparatus according to claim 1, further comprising means for changing an object-to-image distance to perform optical scaling. 6. The image reading apparatus according to claim 1, further comprising means for detecting a variation in the light amount of the light source.