JP2002176538A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader which can accurately measure the height of a document without blurring reference light projected on a document surface in spite of the rotation of a scanning mirror when the reference light is projected to detect the height of the document surface. SOLUTION: A conjugate length correction optical system 26 is arranged between a laser light projection device 25 which projects the reference light and the scanning mirror 21. In a preliminary scan, the document surface is vertically scanned by the rotation of the scanning mirror 21 and at this time, the conjugate length correction optical system 26 is so driven according to the rotational angle of the scanning mirror 21 that the reference light is always imaged on the document surface.

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 and, more particularly, to a distance measuring device for measuring the height of a book document surface placed on a document table for reading a book document having one end bound to a book or the like. The present invention relates to an image reading apparatus including means for adjusting the focus of a scanning optical system according to the height of a book document.

[0002]

2. Description of the Related Art As an image reading apparatus for reading a book manuscript such as a book, one end of which is bound, the apparatus is placed on a manuscript table with the manuscript surface to be read facing up, and a scanning optical system is adjusted to the height of the manuscript surface. 2. Description of the Related Art A device that reads an image while performing focus adjustment is known.

In this type of apparatus, the height of the original surface from the reference surface (for example, the original platen) is not constant. When the main scanning is performed, the focus of the scanning optical system needs to be adjusted based on the data indicating the measured document height.

For this reason, various methods have been proposed as a method for measuring the height of a document as follows. For example, a mirror for distance measurement is arranged inclining rearward of the document table, and the shape of the end face of the book document reflected on the distance measurement mirror is received by an image sensor such as a CCD, and a pixel indicating the contour shape of the end face is used. Calculating the document height based on the number (JP-A-7-79324), projecting light transmitted through a slit onto a book document, receiving the reflected light with an image sensor, There is one that calculates the document height based on the shape (Japanese Patent Laid-Open No. Hei 5-219323).

[0005] Further, a reflection type photosensor for measuring the height of a specific portion of a book document, or a device for measuring the height of a document using an ultrasonic sensor (Japanese Patent Laid-Open No. Hei 6-313314). An apparatus which measures the height of a document by projection and triangulation (JP-A-10-84461) has been proposed.

[0006]

As described above, there are various methods for measuring the document height of a book document.
In the method of measuring the document height from the shape of the end face of the book document reflected on the distance measuring mirror by arranging a mirror inclined rearward and rearward of the document table, the end face of the book document has a high density such as black. In this case, the distance measurement becomes impossible, and the area where the distance measuring mirror is disposed is read at the same time as the image area, so that the resolution of the read image is reduced.

In the case of projecting reference light onto a book original and measuring the height of the original by triangulation, the reference light is reflected by a scan mirror, and the reflected light is projected onto the original surface. The reference beam is moved in the sub-scanning direction on the original surface by rotating the scan mirror. In this projection optical system, the conjugate length (the distance between the beam light source and the original surface) is changed by the rotation angle of the scan mirror. Since the projected reference light moves in the sub-scanning direction due to the rotation of the scan mirror because the angle changes, the reference light projected on the document surface will not be spotted but will be blurred, and the accurate document height will be measured. There is a disadvantage that it cannot be done.

Although it is conceivable to project the reference light over the entire area of the book document in the sub-scanning direction, it is necessary to make the light brighter than the illumination light for reading the image, and use a high-output laser light projecting means. However, such a high output laser beam may harm the operator.

In the method of measuring the document height by triangulation by projecting the reference light, the first preliminary scan for detecting the document height, the background density of the document, the document size, and the document In order to erase the image of the finger to be held down, two preliminary scans are necessary, including a second preliminary scan for detecting the state of the document such as a finger image position, or a reference beam projected for distance measurement and image reading. The configuration is complicated, such as requiring an optical device for separating the illumination light for use by the wavelength difference. An object of the present invention is to solve the above problems.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and the invention of claim 1 scans a document surface in an image reading apparatus capable of reading a bound document such as a book. Mirror and projection lens and CC for
A scanning optical system composed of a D-line sensor, reference beam projection means for projecting a beam-like reference beam for detecting the height of the document surface onto the document surface via the scan mirror, and the reference light projection device and scan A conjugate length correction optical system disposed between the mirror and a mirror; and the control unit, when performing preliminary scanning, scans the document surface in the sub-scanning direction by rotating the scan mirror. The conjugate length correction optical system is driven and controlled in accordance with the rotation angle of the scan mirror so that the reference light always forms an image on the document surface.

In the prescanning, the control means detects the height of the document surface based on information on the position where the reflected light of the reference light is incident on the CCD line sensor.

In the main scanning, the control means scans the document surface in the sub-scanning direction by rotating the scan mirror so that the document image is always formed on the CCD line sensor. The drive of the projection lens is controlled in accordance with the rotation angle of the mirror and the detected height of the document surface.

It is preferable that the scan mirror and the conjugate length correction optical system have a common drive source, and the drive is controlled by the control means.

The reference light projected from the reference light projection means may be a beam light having a width in the sub-scanning direction larger than that in the main scanning direction.

Further, the image reading apparatus includes illumination light irradiating means for illuminating the surface of the document, and the control means turns on the illumination light and the reference light at the time of preliminary scanning, and turns off the reference light at the time of main scanning. The reference light projection unit and the illumination light irradiation unit may be controlled to turn on the illumination light.

[0016]

Embodiments of the present invention will be described below.

FIG. 1 is an external view showing the configuration of an image reading apparatus 10 according to an embodiment of the present invention. In FIG. 1, 1
A scanning unit 1 includes a scanning mirror, a projection lens, and a CCD line sensor. The configuration of the scanning optical system will be described later in detail. Reference numeral 12 denotes an exposure lamp unit.
A lamp for illuminating the original surface when reading the original is arranged. Further, a control panel 13 is arranged in the exposure lamp unit 12 to set various reading modes,
Performs device status, error display, and warning display.

Reference numeral 16 denotes a document table, and 17 denotes a movable recess at the center of the document table. By submerging from the surface, the spread pages of the book document can be made almost flat. Reference numeral 18 denotes a start key for instructing start of image reading, and 19 denotes a power switch.

In this embodiment, the main scanning direction is the direction in which the elements of the CCD line sensor are arranged.
In the illustrated image reading apparatus 10, the direction is from the back to the front, and the sub-scanning direction is a direction orthogonal to the arrangement direction of the elements of the CCD line sensor, and is the direction from right to left in the illustrated image reading apparatus.

FIG. 2 is a perspective view for explaining a state in which the book document is placed on the document table. When the book document 15 is placed on the document table 16 with the open side of the book document 15 facing upward, the opened page is opened. 3 shows a state in which an image is read by holding the blank portion with a finger so that the sheet does not move.

When the book document 15 is placed on the document table 16 with the open side up, the document surface is not flat, and the height in the front-back direction is substantially constant, but the height in the left-right direction is substantially The two ridges have a valley-shaped curve with a valley in the center where they are bound. Especially, the inclination of the valley in the center is a part where the image distortion that has been read suddenly becomes large. This is an area where highly accurate focus adjustment according to the height of the document 15 is required.

The height of the book original 15 in the front-rear direction when placed on the original table 16, ie, the height in the main scanning direction, is substantially constant. If the height is sequentially measured along the sub-scanning direction, the original height of the book original 15 at the measurement position can be obtained.

In FIG. 2, a line L is an image reading line in the main scanning direction read by the CCD line sensor, a point S is a document height measuring point, and a line R is the document height measuring point S in the sub-scanning direction. Show the trajectory.

Here, a method of measuring the document height of a book document will be briefly described. The method of detecting the document height of a book document is based on a known triangulation method, where the document height is defined as the height of the document surface to be read when the book document is opened and placed on the platen. Shall refer to height,
The reference surface is the surface of the document table. By knowing the document height, the focus of the scanning optical system can be adjusted so that the document surface is accurately imaged on the CCD line sensor.

FIG. 3 is a view for explaining a method of measuring the height of a document. In FIG. 3, a reference light is projected from a light source P onto a document surface at a predetermined projection angle θ, and the reflected light is transmitted to a CCD line sensor LS.
It is assumed that light is received. When the document surface is on the reference surface, that is, when the thickness of the book document is zero, the reference light is reflected at point A on the document surface (reference surface), and the reflected light is reflected by the projection lens L.
, And then enters the CCD line sensor LS, a signal having a peak value at point a is output from the sensor. In the case of a book original having a thickness H (original height H), a point B on the original surface
When the reflected light enters the CCD line sensor LS, a signal having a peak value at a point b is output from the sensor.

Here, when the width h of the peak value of the output signal, that is, the distance between the points a and b is obtained from the number of pixels of the CCD line sensor LS, the document height H can be obtained from the following equation. Where β is the magnification of the projection lens.

2Htan θ = βh FIG. 4 is a perspective view showing the configuration of the scanning optical system. In FIG. 4, reference numeral 21 denotes a scan mirror that rotates around a rotation axis N-N, reference numeral 22 denotes a reflection mirror, reference numeral 23 denotes a projection lens, and reference numeral 24 denotes a CCD line sensor. The reflected light from the book document 15 placed on the document table 16 is
The light enters a CCD line sensor 24 via a reflection mirror 22 and a projection lens 23.

The scanning of the document surface in the main scanning direction is performed by the CCD line sensor 24. The scanning of the document surface in the sub-scanning direction is performed by rotating the scan mirror 21 around the rotation axis N-N so that the document table 16 is moved from one end (for example, the lower right side in FIG. 4) to the other end (the upper left side in FIG. 4). Are scanned toward.

In addition, a laser beam projecting device 25 for projecting a reference beam for measuring the height of the document is provided.
The laser light projected from the laser light projecting device 25 is projected as a high-brightness light beam on the book document 15 on the document table 16 via the scan mirror 21.

A conjugate length correction optical system (not shown) is arranged on the projection optical path of the laser beam projection device 25. The conjugate length correction optical system will be described later in detail.

The projection lens 23 is provided with an automatic focus adjustment mechanism (AF mechanism) (not shown). The document height data at the document height measurement point S on the book document 15 and the scan mirror 21 are provided. The AF mechanism operates on the basis of the rotation angle of, and the focal position of the projection lens 23 is adjusted.

Next, the outline of the reading operation of the image reading apparatus will be described with reference to FIG. Book manuscript 1 on platen 16
When the start key 18 is turned on with the image reading surface 5 facing upward, the document surface is illuminated by the exposure lamp unit 12.

First, a preliminary scan is started. The reference light is transmitted from the laser beam projector 25 through the conjugate length correction optical system (not shown in FIG. 4) and the scan mirror 21 to the book document 1.
The light is projected onto the document height measurement point S on the reference numeral 5, and the reflected light is incident on the CCD line sensor 24 via the scan mirror 21, the reflection mirror 22, and the projection lens 23. Book manuscript 1
The projection position (the same position as the document height measurement point S) of the reference light on the reference numeral 5 moves in the sub-scanning direction along the line R by the rotation of the scan mirror 21 around the rotation axis N-N.

The output signal from the CCD line sensor 24 is processed by the CPU and output as data indicating the height of the book document 15 and is used for adjusting the focus of the projection lens 23 during the main scanning.

The exposure lamp unit 1 is also used for the preliminary scanning.
The surface of the original is illuminated by 2, information indicating the state of the original such as the original size, the original density, and the original background density is collected, and parameters necessary for image processing are calculated. These parameters are used for deleting the area outside the original at the time of the main scanning, automatically adjusting the density of the original, and the like.

When the preliminary scanning is completed, the main scanning is started using the data indicating the document height of the book document 15 obtained by the preliminary scanning. That is, the focus of the projection lens 23 is adjusted based on the document height data and the rotation angle of the scan mirror 21. The image of the book document 15 is read, and furthermore, deletion of the area outside the document, automatic adjustment of the document density, and the like are performed using parameters calculated based on information indicating the state of the document.

Here, the conjugate length correcting optical system arranged on the projection optical path of the laser beam projector 25 will be described.

FIG. 5 is a view for explaining the image forming position of the projection light when the laser light is projected from a laser light projection device having no conjugate length correction optical system onto a book document placed on a document table. The horizontal direction of the document table is the sub-scanning direction.

The projection optical system is connected so that the reference light, which is a high-brightness light beam projected from the laser beam projection device 25 via the scan mirror 21 onto the document table 16, is focused on the central portion P 1 of the document table 16. When the image position is adjusted, when the scan mirror 21 is rotated by the sub-scanning operation, the locus of the image forming position of the reference light moves as indicated by a line FL.

For this reason, when the reference light is projected on the right end (the same applies to the left end) P2 of the document table 16, the reference light focuses on a position P2 'remote from the document surface. The reference light projected toward the camera is out of focus,
The document height cannot be accurately detected.

Therefore, in the present invention, the conjugate length correction optical system 26 is arranged on the optical path between the laser beam projector 25 and the scan mirror 21 as shown in FIG. , At the left and right ends P2 and P3,
The reference light is accurately imaged on the document table 16.

Although the above description has been made on the assumption that the reference light forms an image on the document table 16, the reference light forms an image on the document table 16 in the initial setting of the conjugate length correction optical system. With this setting, the image forming position of the reference light projected on the document surface of the book document 15 is slightly shifted from the document surface.
There is no need to particularly adjust the conjugate length correction optical system, since it is within a range that does not hinder practical use in detecting.

However, especially when a thick book document is read, the conjugate length correction optical system is adjusted according to the thickness of the book document so that the image forming position of the reference light is set accurately. You can also

FIG. 7 is a view for explaining the configuration of the conjugate length correcting optical system 26. The laser beam projecting device 25 and the scan mirror 21 are shown in FIG.
And a collimator lens 26a and a cylindrical lens 26b are arranged between them. The reference light, which is the laser light projected from the laser light projection device 25, is adjusted to a parallel light by the collimator lens 26, enters the cylindrical lens 26b, and
The image is reflected on the platen 16 to form an image. Here, the axial position of the cylindrical lens 26b is adjusted according to the rotation angle of the scan mirror 21 to correct the conjugate length.

Here, it is assumed that a concave lens is used for the cylindrical lens 26b. As an initial setting, the projection optical system is set so that the projected reference light forms an image on the central portion P1 of the document table. As the projection position of the reference light moves to the right end P2 or the left end P3 of the document table due to the rotation of the scan mirror 21, the cylindrical lens 26b is moved in the direction approaching the laser light projection device 25 in accordance with the movement, and conjugated. The length is corrected so that the reference light always forms an image on the platen.

For the movement of the cylindrical lens 26b, for example, an actuator driven by a pulse motor may be used, and the pulse motor may be driven in accordance with the rotation angle of the scan mirror 21 detected by the encoder. it can. In addition, a configuration in which the rotation of the scan mirror is transmitted to a cylindrical lens by a belt transmission mechanism may be employed.

The reason why the cylindrical lens is used in the conjugate length correcting optical system is that the projected image of the reference light projected on the document table is longer in the sub-scanning direction than in the main scanning direction, and the projection of the reference light is performed. This is for facilitating the alignment adjustment between the position and the reading line of the CCD line sensor.

FIG. 8 is a block diagram showing a configuration of a control circuit of the image reading apparatus. The control circuit 30 is configured around the CPU 31. The input / output ports of the CPU 31 include a scan mechanism 41 that rotates the scan mirror 21 (see FIG. 4) around the rotation axis N-N to perform scanning in the sub-scanning direction. Automatic focusing mechanism (A) for adjusting the focal position of the projection lens 23
F mechanism) 42, an illumination light control circuit 43 for controlling the lamp of the exposure lamp unit 12, a laser light control circuit 44 for controlling the laser light projection device 25 (see FIG. 4) for projecting the reference light, and programs and the like are stored. ROM 45, a RAM 46 for temporarily storing data, a start key 18 (see FIG. 1), and the like.

Further, a first image processing circuit 33, a document height detecting circuit 34, and a second image processing circuit 35 are connected to the input / output port of the CPU 31.

In the preliminary scanning, the CPU 31 drives the illumination light control circuit 43 and the laser light control circuit 44 to control the illumination light to be turned on / off and the reference light to be turned on / off, and drives the scanning mechanism 41. To perform a preliminary scan.

An image signal output from the CCD line sensor 24 (see FIG. 4) is converted into digital data by an A / D converter 32, and a first image processing circuit 33 converts reflectance-density conversion, shading correction, and illuminance. Primary image processing such as correction is performed.

The image data subjected to the first image processing is subjected to detection of information indicating the state of the original such as the original height, the original size, the inclination of the original, etc. Predetermined parameters required for the processing are calculated.

In the main scanning, the illumination light control circuit 43 and the laser light control circuit 44 are driven to control the turning on / off of the illumination light and the turning off of the reference light, and the scanning mechanism 41 is driven to execute the main scanning. Is done. At this time, the automatic focus adjustment mechanism (AF mechanism) 42 is operated using the parameters calculated based on the document height detected in the preliminary scanning and the rotation angle of the scan mirror 21, and the projection lens 2
The focal position of No. 3 is automatically adjusted.

An image signal output from the CCD line sensor 24 (see FIG. 4) is converted into digital data by an A / D converter 32, and a first image processing circuit 33 converts reflectance-density conversion, shading correction, and illuminance. Primary image processing such as correction is performed.

The image data subjected to the first image processing is calculated by the second image processing circuit 35 based on information indicating the state of the original such as the original size, the inclination of the original detected in the preliminary scanning, and the like. Using the parameters, image processing such as enlargement / reduction of the image, inclination correction, binarization, deletion of the finger image, and the like are performed, and the processed image is output.

The outline of the control operation executed by the control circuit 30 will be described with reference to the flowchart of FIG.

The control operation is started by turning on the power switch 19 (see FIG. 2), and the illumination light of the exposure lamp unit 12 is turned on (step P1). Start key 18
Preliminary scanning is first started by the scanning (see FIG. 2) (step P2), and the reference light is turned on and the scan mirror 21 is turned on.
Is driven (step P3).

An image for one scanning line in the main scanning direction is read, and an operation of collecting information relating to the height of the original and information indicating the state of the original is performed (step P4).

It is determined whether the scanning in the sub-scanning direction is completed (step P5). If the scanning in the sub-scanning direction is not completed, the process returns to step P3. If it is determined in step P5 that the scanning in the sub-scanning direction has been completed, the end of the preliminary scanning is determined (step P6).

The reference light from the laser beam projecting device 25 is turned off (step P7), the height H of the document is calculated based on the information on the result of the distance measurement, and necessary for image processing based on the information indicating the state of the document. The parameters are calculated, and preparation for the main scan is made (step P8).

The main scanning starts (step P9). Parameters relating to the document height detected in the preliminary scanning,
Then, based on the rotation angle of the scan mirror 21, the automatic focus adjustment mechanism (AF mechanism) 42 is operated, the focal position of the projection lens 23 is automatically adjusted, and an image for one scanning line in the main scanning direction is read (step P10). .

It is determined whether the scanning in the sub-scanning direction is completed (step P11). If the scanning in the sub-scanning direction is not completed, the process returns to step P10. Further, if the scanning in the sub-scanning direction has been completed in the determination of step P11, the main scanning is completed,
The illumination light of the exposure lamp unit 12 is turned off (steps P12 and P13), and the process ends.

[0063]

As described above, the present invention is an image reading apparatus for reading a stitched original such as a book, and detects the height of the original by projecting a reference light onto the original at the time of preliminary scanning. When scanning the document surface in the sub-scanning direction by rotating the scan mirror, the conjugate length correction optical system is driven to correspond to the rotation angle of the scan mirror so that the reference light always forms an image near the document surface. Since the conjugate length between the reference light projecting means and the image forming position is corrected, even if the scan mirror is rotated, the reference light projected on the document surface is not blurred, and the document height is accurately detected. be able to.

Also, when a laser beam projecting device or the like is used as the reference beam projecting device, only the measurement point is illuminated with high accuracy, so that only one preliminary scan is required to detect the height of the document surface from the reference surface. And the information indicating the state of the document can be collected simultaneously, and not only can information required for image processing be obtained efficiently in a short time, but also because a high-power laser device is not particularly required, There is no danger of harm to the people.

[Brief description of the drawings]

FIG. 1 is an external view illustrating a configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a state in which a book document is placed on a document table.

FIG. 3 is a diagram illustrating a method of measuring the height of a book document.

FIG. 4 is a perspective view showing a configuration of a scanning optical system.

FIG. 5 is a view for explaining an image forming position of a reference beam when a conjugate length correction optical system is not provided.

FIG. 6 is a diagram illustrating an imaging position of reference light when a conjugate length is corrected according to rotation of a scan mirror, provided with a conjugate length correction optical system.

FIG. 7 is a diagram illustrating a configuration of a conjugate length correction optical system.

FIG. 8 is a block diagram illustrating a configuration of a control circuit of the image reading apparatus.

FIG. 9 is a flowchart illustrating an outline of a control operation performed by the control circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 Image reading device 11 Scanner unit 12 Exposure lamp unit 13 Control panel 15 Book document 16 Document table 17 Movable recess at the center of document table 18 Start key 19 Power switch 21 Scan mirror 22 Reflection mirror 23 Projection lens 24 CCD line sensor 25 Laser Light projection device 26 Conjugate length correction optical system 30 Control circuit 31 CPU 32 A / D converter 33 First image processing circuit 34 Document height etc. detection circuit 35 Second image processing circuit 41 Scanning mechanism 42 Automatic focus adjustment mechanism (AF mechanism) 43) Illumination light control circuit 44 Laser light control circuit 45 ROM 46 RAM

Claims (6)

[Claims] An image reading apparatus capable of reading a stitched original such as a book, a scanning optical system including a scan mirror for scanning the original surface, a projection lens, and a CCD line sensor; Reference beam projecting means for projecting a beam-like reference beam for detecting the beam through the scan mirror onto a document surface; a conjugate length correction optical system disposed between the reference beam projecting device and the scan mirror; Means for controlling the rotation of the scan mirror so that the reference light always forms an image on the document surface during the scanning of the document surface in the sub-scanning direction by the rotation of the scan mirror during the pre-scanning. An image reading device, wherein the conjugate length correction optical system is drive-controlled in accordance with an angle. 2. The apparatus according to claim 1, wherein said control means detects a document height based on information on a position where reflected light of said reference light is incident on said CCD line sensor during prescanning. Item 2. The image reading device according to Item 1. 3. The control means according to claim 1, wherein:
According to the rotation angle of the scan mirror and the detected document height, the projection is performed so that the document image is always formed on the CCD line sensor in the scanning of the document surface in the sub-scanning direction by the rotation of the scan mirror. 2. The image reading device according to claim 1, wherein the driving of the lens is controlled. 4. The image reading apparatus according to claim 1, wherein the scan mirror and the conjugate length correction optical system have a common drive source and are driven and controlled by the control unit. 5. The image reading apparatus according to claim 1, wherein the reference light projected from the reference light projection unit is a light beam having a width in the sub-scanning direction wider than that in the main scanning direction. 6. The image reading apparatus according to claim 1, further comprising: an illumination light illuminating unit that illuminates a document surface, wherein the control unit turns on the illumination light and the reference light during the pre-scan, and turns off the reference light during the main scan. 2. The image reading apparatus according to claim 1, wherein the reference light projection unit and the illumination light irradiation unit are controlled to turn on the illumination light.