JP2020182056A - Image reading device - Google Patents

Abstract

To improve the accuracy of detection of dirt at a reading position as compared to a case in which a constant value is used as a threshold value for detection when light reflected by a guide member to which a reflector is not attached is received and the dirt at the reading position is detected.SOLUTION: An image reading device includes storage control means that stores a value of the amount of light corresponding to each position in a direction intersecting a direction in which a document is conveyed as reference data when light reflected by the surface of a member that guides the document is received at a first time point in which the document does not pass through a scanning position of the image provided on a path for conveying the document, and detection means that detects dirt in the scanning position on the basis of a change in the value of the amount of light received by the surface of the member that guides the document for the reference data at a second point in which the document does not pass through the scanning position after the first point.SELECTED DRAWING: Figure 5

Description

The present invention relates to an image reader.

One of the methods for reading an image of a document is a method using an automatic document feeder. This method scans the image of the document while the document passes the scanning position. In this case, if the scanning position is dirty, a pattern that does not exist in the document will be superimposed on the scanned image. For example, black streaks appear. Therefore, during the period when the document does not exist at the scanning position, the image at the scanning position is acquired to detect the presence or absence of stains.

Japanese Unexamined Patent Publication No. 2005-59351

The dirt at the reading position is the image data in which the light emitted when the document does not pass through the scanning position receives the light reflected by the member that guides the document (hereinafter, also referred to as the "guidance member"). Detected by processing. Of the guiding members, a white reflector that facilitates detection of dirt such as dust is often attached as a separate member to the portion where light is incident. This type of reflector is processed so that the reflection characteristics in a direction intersecting the direction in which the document is conveyed (hereinafter referred to as "main scanning direction") become uniform. Therefore, when the reflector is attached to the guide member, it is possible to detect the presence or absence of dirt such as dust by comparing the amount of light reflected by the reflector with a constant value.

On the other hand, a guide member to which a reflector is not attached may be used. In this case, the color of the position where the light is incident depends on the material of the guiding member, and it is difficult to detect dirt such as dust. Further, the reflection characteristics of the guide member are different from the case of using the reflector, and the reflection characteristics in the main scanning direction are not stable for each position. That is, even if there is no dirt such as dust, the amount of light reflected by the guiding member differs depending on the position in the main scanning direction. Therefore, in the method of comparing with a constant value, the accuracy of dirt detection is lowered.

In the present invention, the reading position is compared with the case where a constant value is used as a threshold value for detection when the light reflected by the guiding member to which the reflector is not attached is received and the dirt on the reading position is detected. The purpose is to improve the accuracy of dirt detection.

The invention according to claim 1 receives light reflected on the surface of a member that guides a document at a first time point when the document does not pass through an image reading position provided on a path for transporting the document. In this case, a storage control means for storing the value of the amount of light corresponding to each position in the direction intersecting the direction in which the document is conveyed in the storage area as reference data, and the reading after the first time point. At the second time point when the document does not pass through the position, the dirt on the reading position is detected based on the change in the value of the amount of light received by the surface of the member guiding the document with respect to the reference data. It is an image reading device having a detecting means.
According to the second aspect of the present invention, the detection means sets a threshold value for detection for each of a plurality of values of the reference data, and the threshold value corresponding to each position of the value of the amount of light received at the second time point. The image reading device according to claim 1, wherein dirt is detected by comparison with the above.
The image reading according to claim 2, wherein the threshold value is a threshold value for detecting stains in which the value of the amount of light increases and a threshold value for detecting stains in which the value of the amount of light decreases. It is a device.
The invention according to claim 4 is the image reading device according to claim 1, wherein the initial value of the reference data is stored before the start of use.
The image according to claim 4, wherein when the detection means does not detect dirt, the reference data is updated with the value of the amount of light received at the second time point. It is a reading device.
According to the sixth aspect of the present invention, when dirt is detected by the detecting means, the detecting means changes the reading position to another position, and the value of the amount of light received for the other position after the change. The image reading device according to claim 4, which detects stains based on the above.
The invention according to claim 7 comprises a notification means for notifying the necessity of cleaning and a reception means for receiving update or non-update of the reference data when the other position where dirt is not detected remains. The image reading device according to claim 6, further comprising.
The invention according to claim 8 receives the reference data at the second time point when the detection means does not detect stains on all the reading position candidates when the update of the reference data is accepted. The image reading device according to claim 7, which is updated with the value of the amount of light.

According to the first aspect of the present invention, when a constant value is used as a detection threshold value when the light reflected by the guiding member to which the reflector is not attached is received and the dirt at the reading position is detected. In comparison, the accuracy of detecting dirt at the reading position can be improved.
According to the second aspect of the present invention, it is possible to speed up the detection of dirt as compared with the case of comparing each position.
According to the invention of claim 3, it is possible to distinguish between brightening stains and darkening stains.
According to the invention of claim 4, it is possible to guarantee a clean state.
According to the invention of claim 5, it is possible to cope with aging.
According to the invention of claim 6, since the reading position is changed to another clean position, the number of cleanings can be reduced.
According to the invention of claim 7, the user can select to update the reference data.
According to the invention of claim 8, it is possible to cope with aging.

It is a figure which shows the appearance example of the image forming apparatus provided with the mechanism which optically reads information from the document conveyed at a constant speed. It is a figure which shows the schematic structure of the document reading apparatus. It is a figure which enlarges and shows the vicinity of the reading window used when reading information from a document M conveyed at a constant speed. It is a block diagram which shows the structural example of the control system of an image forming apparatus. It is a block diagram which shows the structural example of an image reading control unit. It is a figure explaining the positional relationship between the candidate position of a reading position and dirt such as dust. It is a figure explaining the relationship between the detection example of dirt such as dust, and a reading position. (A) is an example of dirt adhering to the reading window, and (B) is an example of a detection signal of the dust detection unit. It is a figure which shows the change of the gradation value in the main scanning direction of the scanned image data output from the scanned image acquisition part when the surface of the reading window which is not attached with dirt Dc such as dust is imaged against the background of a scanning guide member. is there. It is a figure explaining an example of the threshold value generation method in this embodiment. It is a figure explaining the setting example of the range considered to be clean. It is a flowchart explaining an example of the reading operation executed at the time of the automatic transfer of a document M by an automatic document transfer unit. It is a figure explaining the dirt determination operation in this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Overall configuration>
FIG. 1 is a diagram showing an external example of an image forming apparatus 1 provided with a mechanism for optically reading information from a document conveyed at a constant speed.
The image forming apparatus 1 here is an example of an image reading apparatus.
The image forming apparatus 1 shown in FIG. 1 takes out a document reading device 10 for reading information on a document M, an image recording device 20 for recording an image on paper or other media, and supplies the media one by one to the image recording device 20. It has an accommodating device 30 including a mechanism for

In the case of the image forming apparatus 1 shown in FIG. 1, the document reading apparatus 10 is attached to the upper surface of the image recording apparatus 20, and the image recording apparatus 20 is attached to the upper surface of the accommodating apparatus 30. The image recording device 20 and the storage device 30 are connected by a path (not shown) in which a medium such as paper is conveyed.
The document reading device 10 shown in FIG. 1 includes a main body 11 having an optical system for reading information on the document M and a control unit for controlling the reading operation, and a document transporting device 12 for transporting the document M one by one at a constant speed. It is configured. The document transfer device 12 and the main body 11 are connected by a hinge provided on the back side. That is, the document transport device 12 is attached to the main body 11 so as to be openable and closable.

An operation reception unit 111 is arranged on the front surface of the main body 11. A touch panel 112 and a plurality of operation buttons 113 are arranged on the operation reception unit 111. The touch panel 112 is used not only for displaying operation menus and messages, but also for receiving user's instructions.
In the case of the present embodiment, the front surface of the main body 11 means a portion where the user approaches for the operation, and means the front side when viewed from the user during the operation. Further, the back surface of the main body 11 means a portion on the back side when viewed from the user.
On the upper surface of the main body 11, a platen 114 made of a material that allows light to pass through is provided. For example, colorless and transparent glass is used as the material of the platen 114. The platen 114 is used when reading information while the document M is stationary.

The document transport device 12 includes a document cover 121 that covers the entire upper surface of the main body 11 in a closed position, an automatic document transfer unit 122 that transports the document M to a scanning position (not shown) and ejects the scanned document M, and an automatic document. It has a document tray 123 in which the document M before transfer by the transfer unit 122 is stored.
The surface of the document cover 121 opposite to the document base 114 is used as a place for accommodating the scanned document M ejected from the automatic document transport unit 122.
The image recording device 20 has a built-in known mechanism for recording a toner image on the surface of a medium by, for example, an electrophotographic method. In the case of the present embodiment, the image recording device 20 can record in four colors of yellow, magenta, cyan, and black. The image data to be recorded is given from, for example, the document reading device 10. However, the recorded image data may be given via LAN (= Local Area Network) or USB (= Universal Serial Bus), or may be given from a semiconductor memory mounted in the insertion slot.

For example, when the document reading device 10 wants to read the information of the document M, the user can read the information of the document M placed on the document table 114 in that state and automatically convey the document M placed on the document tray 123. Select one of the reading methods while.
When the user instructs the start of scanning after placing the document M at any position, the scanning operation of the document M is started. That is, the information of the document M is read by the document reading device 10.
The read information is output from the document reading device 10 to the image recording device 20 through a signal line (not shown). The image recording device 20 records an image corresponding to the information received from the document reading device 10 on a medium such as paper and discharges it to an ejection tray.

<Configuration of document reader>
FIG. 2 is a diagram showing a schematic configuration of a document reading device 10.
The document reading device 10 supports two types of reading modes. One scanning mode is a mode for reading information from the document M conveyed by the automatic document conveying unit 122, and another scanning mode is a mode for reading information from the stationary document M placed on the platen 114. ..
Which reading mode to use depends on the user's choice.

A reading window dedicated to each reading mode is provided on the upper surface of the main body 11 of the document reading device 10.
One reading window is the document base 114 described above. The other reading window is a reading window 131 arranged at a position where the upper surface of the main body 11 and the path through which the document M is transported by the automatic document transport unit 122 overlap.
Here, the position where the reading window 131 is arranged is an example of the information reading position of the document M conveyed at a constant speed. In the case of this embodiment, a colorless and transparent glass plate is used for the reading window 131.
Inside the main body 11, a lighting unit 140 that irradiates the light that illuminates the document M and a light receiving unit 150 that receives the light reflected by the document M are provided.
In FIG. 2, a two-dot chain line shows the main path through which the light emitted from the illumination unit 140 travels.

The illumination unit 140 is also called a carriage, and inside the light source 141, a reflector 142 that reflects a part of the light emitted from the light source 141 (hereinafter, also referred to as “illumination light”) in the direction of the reading window. A reflector 143 is provided which bends the optical path of the light reflected by the document M or the like (hereinafter, also referred to as “reflected light”) and guides the light to the light receiving unit 150.
The movement of the lighting unit 140 is guided by a rail 144 mounted parallel to the X direction. In the case of the present embodiment, the lighting unit 140 is attached to the rail 144 so as to be reciprocating in the X direction.
In the case of FIG. 2, the X direction is a direction substantially parallel to the surface of the platen 114, and is a direction in which the document M transported by the automatic document transport unit 122 passes through the reading window 131. The X direction in the present embodiment corresponds to the reading direction or the sub-scanning direction. Incidentally, the Y direction orthogonal to the X direction is called the main scanning direction.

In the case of the present embodiment, the light source 141 is a line-type LED array in which a plurality of LED (= Light Emitting Diode) chips are linearly arranged on a substrate. The LED chips here are arranged parallel to the Y direction. Therefore, the light emitted from the illumination unit 140 becomes linear light that is substantially parallel to the main scanning direction. In other words, the light source 141 emits linear illumination light.
In the case of the present embodiment, a part of the linear illumination light is output in the direction of the reading position described later, and the other part is output in the direction of the reflector 142. The illumination light incident on the reflector 142 is reflected in the direction of the reading position.
The amount of light of the light source 141 in the present embodiment can be adjusted. For example, the amount of light can be adjusted by changing the ratio of the lighting time within the blinking cycle of the LED chip. The time when it is lit is also called the on time.

The position of the lighting unit 140 in the main body 11 is determined according to the reading mode.
For example, in the reading mode in which information is read from the document M being conveyed by the automatic document transfer unit 122, the lighting unit 140 is positioned below the reading window 131 provided at a position facing the lower surface of the automatic document transfer unit 122. The window. In this reading mode, the lighting unit 140 is kept stationary or stationary at a particular position throughout the reading. The reading window 131 has an elongated shape in the main scanning direction.
On the other hand, in the reading mode in which information is read from the document M arranged on the document table 114, the illumination unit 140 moves in the sub-scanning direction so that the illumination light emitted from the light source 141 scans the entire surface of the document M. Will be done. In this scanning mode, the document M is in a stationary state, and the lighting unit 140 moves relative to the document M.
In either reading mode, the movement of the lighting unit 140 is guided along the rail 144.

The light reflected by the reflector 143 of the lighting unit 140 is guided to the light receiving unit 150 through the reflection unit 160 composed of the reflectors 161 and 162. The reflection unit 160 serves to turn back the light incident from the reflection plate 143 in the opposite direction. When reading information from the document M arranged on the platen 114, the reflection unit 160 moves in the sub-scanning direction in conjunction with the illumination unit 140. However, the moving length of the reflection unit 160 is controlled so that the optical path length until the light reflected by the document M reaches the light receiving unit 150 is constant.

The light receiving unit 150 includes an image pickup element 151 that receives the reflected light from the document M or the like, and an imaging lens 152 that forms an image of the reflected light from the document M or the like and guides the image sensor 151. For the image sensor 151, for example, a charge coupling element sensor is used. In the charge coupling element sensor of the present embodiment, one-dimensional line sensors that output color signals corresponding to red, green, and blue from the received reflected light are arranged in a set of three rows. The image sensor 151 photoelectrically converts the received reflected light for each color and outputs it as a color signal corresponding to each color. These color signals are also referred to as image signals below.

Subsequently, the internal structure of the automatic document transport unit 122 will be described. The automatic document transport unit 122 has a path for transporting the documents M taken out one by one from the document tray 123 at a constant speed, that is, a document transport path 124.
The document transport path 124 defines a path for the document M drawn from the document tray 123 to be discharged to the document cover 121 after passing through the surface of the reading window 131.
In the document transport path 124, a plurality of transport rollers 125 for transporting the document M, a guide 126 for guiding the document M, and a reading guide member 127 for keeping the distance between the document M being transported and the reading window 131 constant. An ejection guide member 128 for guiding the document M passing through the reading window 131 in the ejection direction, a detection sensor Sn1 for detecting the presence or absence of the document M in the document tray 123, and a detection sensor Sn2 for detecting the passage of the document M. Have.

FIG. 3 is an enlarged view showing the vicinity of the reading window 131 used when reading information from the document M conveyed at a constant speed.
In the case of this embodiment, the position used for reading information from the document M being conveyed is called the reading position Pr. The reading position Pr is arranged on the surface side of the reading window 131, that is, in the document transport path 124. In the case of FIG. 3, the reading position Pr is determined to be substantially at the center of the width of the reading window 131 in the sub-scanning direction.
The reading guide member 127 is a component arranged above the reading position Pr for guiding the document M transported along the document transport path 124. In the case of the present embodiment, the portion of the surface of the reading guide member 127 facing the reading window 131 has a curved shape so as to project in the direction of the reading window 131. The reading guide member 127 is an example of a member that guides the document M.

The reading guide member 127 in the present embodiment is a component to which a dedicated background reflector prepared for detecting dirt such as dust is not attached. Therefore, the surface of the reading guide member 127 serves as a reflecting surface of the illumination light as it is. The reflection characteristics of the reading guide member 127 depend on the material, color, surface processing state, and the like of the reading guide member 127.
Needless to say, during the transportation of the document M, the illumination light emitted from the light source 141 (see FIG. 2) is reflected by the document M. Therefore, the illumination light is reflected on the surface of the reading guide member 127 when the illumination light from the light source 141 is incident on the surface of the reading guide member 127 while the document M does not pass through the reading position Pr. is there.

<Control system configuration>
FIG. 4 is a block diagram showing a configuration example of the control system of the image forming apparatus 1.
The control system of the image forming apparatus 1 is a main control device 201 that controls the operation of the entire device based on a user's instruction received through the operation receiving unit 111, and an image recording device 20 based on an instruction from the main control device 201. It has an image recording control unit 202 that controls the operation, and an image reading control unit 203 that controls the operation of the document reading device 10 based on an instruction from the main control device 201.
In the case of FIG. 4, the main control device 201 and the image recording control unit 202 are built in the image recording device 20, and the image reading control unit 203 is built in the document reading device 10. However, the main control device 201 may be built in the document reading device 10. Further, the main control device 201, the image recording control unit 202, and the image reading control unit 203 may be incorporated in either the document reading device 10 or the image recording device 20.

FIG. 5 is a block diagram showing a configuration example of the image reading control unit 203. The image reading control unit 203 in the present embodiment includes a reading image acquisition unit 231, a reading area detection unit 232, a dust detection unit 233, a reading position determination unit 234, a reading position control unit 235, and a document image output unit. It has 236.
The scanned image acquisition unit 231 in the present embodiment acquires an image signal from the image sensor 151 (see FIG. 2). The scanned image acquisition unit 231 executes processing such as gain adjustment, analog / digital conversion, shading correction, and gap correction on the acquired image signal, and outputs it as scanned image data.

The reading area detection unit 232 detects the reading area based on the scanned image data output from the scanned image acquisition unit 231. The reading area defines a range in which the reading position Pr is arranged.
The dust detection unit 233 detects the position of dirt such as dust existing on the surface of the reading window 131 by comparing the scanned image data included in the reading area detected by the reading area detection unit 232 with the threshold value for determination. The dust detection unit 233 in the present embodiment uses the gradation value of the read image data acquired in the absence of dirt Dc such as dust as a threshold value used for determining the presence or absence of dirt Dc such as dust.
Therefore, the dust detection unit 233 is provided with a reference data storage control unit 233A that stores the gradation value of the scanned image data output by the scanned image acquisition unit 231 in the storage area as reference data for giving a threshold value. The reference data storage control unit 233A is an example of the storage control means. For the storage area here, for example, a non-volatile semiconductor memory is used. The reason why the gradation value of the scanned image data output by the scanned image acquisition unit 231 is used as the reference data for giving the threshold value will be described later. The dust detection unit 233 is an example of the detection means.

The reading position determining unit 234 determines the reading position Pr based on the position of dirt such as dust detected by the dust detecting unit 233. The reading position Pr is determined by giving priority to a position that is not affected by dirt or a position that is less affected by dirt among a plurality of preset candidate positions.
The reading position control unit 235 adjusts the position of the lighting unit 140 according to the reading position Pr determined by the reading position determining unit 234. The adjustment of the position is realized by controlling the movement of the motor that moves the illumination unit 140 in the sub-scanning direction.
The original image output unit 236 outputs image data corresponding to the original M (hereinafter referred to as “original image data”) from the scanned image data. When outputting the original image data, the original image output unit 236 executes a process of detecting and correcting the inclination of the original image data included in the scanned image data, a process of cutting out the original image data from the corrected scanned image data, and the like. ..

<Determination of reading position Pr>
As described above, the reading position Pr is determined by the reading position determining unit 234 that inputs the detection signal of the dust detecting unit 233. The reading position Pr is determined by the reading position determining unit 234 in a state where the illumination light emitted from the light source 141 (see FIG. 2) is incident on the reading guide member 127 (see FIG. 3). For example, it is executed before shipping the product, when the main power is turned on, when all the documents M stored in the document tray 123 are read, and when the data for adjusting the candidate position is updated.

FIG. 6 is a diagram for explaining the positional relationship between the candidate positions P1, P2, P3, P4, P5 of the reading position Pr and the dirt Dc such as dust.
If dirt Dc such as dust is present at the scanning position Pr, streak-like noise that does not exist in the original M appears in the scanned image data acquired by the scanned image acquisition unit 231. This noise appears as a straight line extending in the sub-scanning direction. Therefore, when dirt Dc such as dust is detected in the reading window 131, it is necessary to determine that the reading position Pr of the document M and the dirt Dc such as dust do not overlap or the amount of overlap is small. is there.

Incidentally, the dirt Dc such as dust includes floating dust such as paper dust, as well as sticking dust due to correction fluid, glue, ink, etc. adhering to the surface of the original M. Even if the floating dust adheres to the reading window 131, it may be removed during the subsequent transportation of the original document M. On the other hand, when the fixed dust adheres to the reading window 131, it is unlikely that it will be removed by the subsequent transportation of the document M. Further, the fixed dust has a larger size than the floating dust. Therefore, the influence on the scanned image data is large.
The dirt Dc such as dust includes dark dirt and bright dirt. Dark stains are a type of stain that reduces the value of the amount of light received by the light receiving unit 150 (see FIG. 2), and bright stains increase the value of the amount of light received by the light receiving unit 150 (see FIG. 2). Kind of dirt.

In the case of FIG. 6, there are five candidate positions for the reading position Pr: P1, P2, P3, P4, and P5.
Candidate positions P1, P2, P3, P4, and P5 are stored as set values in a non-volatile semiconductor memory or the like. In the case of the present embodiment, the five candidate positions P1, P2, P3, P4, and P5 are arranged at intervals of 1 mm in the sub-scanning direction, for example.
In the example of FIG. 6, dirt Dc such as dust is attached to the candidate positions P3 and P5. When the positions of the candidate positions P3 and P5 are detected by the dust detection unit 233, the reading position determination unit 234 determines the reading position Pr to be one of the candidate positions P1, P2, and P4.

FIG. 7 is a diagram illustrating a relationship between a detection example of dirt Dc such as dust and a reading position Pr. (A) is an example of dirt Dc such as dust adhering to the reading window 131, and (B) is an example of a detection signal of the dust detection unit 233 (see FIG. 5).
In the case of (A), the vertical axis is the sub-scanning direction and the horizontal axis is the main scanning direction. Also in the case of (B), the horizontal axis is the main scanning direction.
In order to make the positional relationship easy to understand, the positions corresponding to the candidate positions P1, P2, P3, P4, and P5 are shown by broken lines in (A).
In each detection signal corresponding to the candidate positions P1, P2, P3, P4, and P5, a pulse waveform appears in a portion overlapping with dirt Dc such as dust.

The pulse waveform here is output when the gradation value of the scanned image does not fall within the threshold range for determination. In (B), since dark stains are assumed, the portion where the pulse waveform appears is “black” and the other portion is “white”. “White” means that it is determined that there is no dirt Dc such as dust. The gradation value here is an example of the value of the amount of light received by the image sensor 151.
The width of the pulse waveform corresponds to the width of the stain in the main scanning direction. The wider the width, the thicker the streaky noise superimposed on the scanned image data as noise, which means that the reading quality deteriorates. It also means that the larger the number of pulse waveforms, the larger the number of streaky noises.

The reading position determining unit 234 (see FIG. 5) determines the reading position Pr from the candidate positions P1, P2, P3, P4, and P5 where the pulse waveform does not appear in the detection signal.
When a pulse waveform appears in any of the detection signals, the reading position determination unit 234 determines a candidate position in which the total number of pixels corresponding to the pulse width is smaller than the others as the reading position Pr.
As described above, in determining the reading position Pr, it is important to detect the position of the dirt Dc such as dust in the dust detection unit 233.
Then, the dust detection unit 233 (see FIG. 5) detects dust by comparing the gradation value corresponding to each candidate position with the threshold value as described above.

By the way, in the case of the present embodiment, the scanned image data output from the scanned image acquisition unit 231 (see FIG. 5) in the absence of the document M is read against the background of the scanning guide member 127 to which the reflector is not attached. It is an image which imaged the surface of a window 131.
The reflector is processed so that the reflection characteristics on its surface are uniform. Therefore, the gradation value of the scanned image data obtained by imaging the reflector in the absence of dirt Dc such as dust is substantially constant not only in the main scanning direction but also in the sub-scanning direction.
On the other hand, when the reflector is not attached like the reading guide member 127 used in the present embodiment, there is no guarantee that the reflection characteristics on the surface of the reading guide member 127 will be uniform.

FIG. 8 shows the main reading image data output from the reading image acquisition unit 231 (see FIG. 5) when the surface of the reading window 131 to which dirt Dc such as dust is not attached is imaged against the background of the reading guide member 127. It is a figure which shows the change of the gradation value in the scanning direction.
In the case of FIG. 8, the vertical axis is the gradation value and the horizontal axis is the main scanning direction.
Each vertical bar in the figure corresponds to one pixel in the main scanning direction. Therefore, the height of the vertical bar represents the gradation value at each pixel position in the main scanning direction.
However, FIG. 8 shows only the gradation values corresponding to a part of the pixel strings arranged in the main scanning direction.

In the case of the present embodiment, the gradation value represented by the vertical bar uses the average value of the gradation values for 32 lines in the sub-scanning direction. The range of 32 lines does not include gradation values corresponding to adjacent candidate positions.
As shown in FIG. 8, in the case of the present embodiment, the gradation values appearing at each pixel position in the main scanning direction are irregular even when dirt Dc such as dust is not attached to the reading window 131. Take a value.
In the case of FIG. 8, the maximum gradation value is about 900 and the minimum is about 725. That is, there is a variation of about 175 in the gradation value only in the portion of FIG.
When a reflector is used, the gradation value in a state where dirt Dc such as dust is not attached to the reading window 131 is a theoretical value of 800 regardless of the pixel position in the main scanning direction. Therefore, the threshold value for determining the dirt Dc of dust or the like can be fixedly set to, for example, 850 in which 50 is added to the theoretical value and 750 in which 50 is subtracted from the theoretical value.

However, as shown in FIG. 8, when the gradation value is completely different depending on the pixel position, the threshold value cannot be fixedly set. Further, if it is set to be fixed, the width between the upper limit value and the lower limit value of the determination threshold value becomes too wide, and there is a possibility that even if there is dirt Dc such as dust, it cannot be detected.
Therefore, in the dust detection unit 233 (see FIG. 5) in the present embodiment, a reference for storing gradation values corresponding to each pixel position in the main scanning direction as reference data in a storage area such as a non-volatile semiconductor memory. A data storage control unit 233A (see FIG. 5) is provided. However, as will be described later, in the present embodiment, the average value of the gradation values corresponding to a plurality of pixels is used as the reference data instead of the gradation value of each pixel.
In the case of the present embodiment, the reference data is recorded for each pixel position in the main scanning direction corresponding to at least five candidate positions P1, P2, P3, P4, P5. If possible, the gradation value corresponding to each pixel position in the main scanning direction is recorded as reference data for the entire range set in the reading area.

FIG. 9 is a diagram illustrating an example of a threshold value generation method according to the present embodiment. FIG. 9 is shown with reference numerals corresponding to the portions corresponding to those in FIG.
In the case of the present embodiment, the main scanning direction is divided into a plurality of regions Area for each predetermined number of pixels. In FIG. 9, the range of pixel positions shown in FIG. 8 is divided into 11 regions Areas 1 to 11. Of course, the regions Areas 1 to 11 shown in FIG. 9 are a part of the region Areas that divide the pixel positions existing in the main scanning direction. The reference data storage control unit 233A also executes the division of this area.

FIG. 10 is a diagram illustrating a setting example of a range deemed to be clean. In FIG. 10, a reference numeral corresponding to a portion corresponding to that in FIG. 9 is added.
The vertical bar in FIG. 10 corresponds to a value obtained by averaging the gradation values of the pixels included in each area area in units of a predetermined number of pixels. In the example of FIG. 10, one region Area is divided into two subregions, and the average value is calculated for each.
In the present embodiment, the threshold value for giving the upper limit and the threshold value for giving the lower limit of the range considered to be clean are determined based on this average value. This process is also executed by the reference data storage control unit 233A.
The threshold value that gives the upper limit is an example of the threshold value for detecting dirt in which the value of the light amount increases, and the threshold value that gives the lower limit is an example of the threshold value for detecting dirt in which the value of the light amount decreases.

Here, the average value of the gradation values corresponding to a plurality of predetermined pixels is calculated and used as the reference data. If the threshold value is determined in units of one pixel, the reading position is deviated by only one pixel, and dust is generated. This is because there is a possibility of erroneously detecting dirt Dc such as.
In FIG. 10, the threshold value that gives the upper limit of the range considered to be clean is determined as a value obtained by adding 50 to the calculated average value. Further, the threshold value that gives the lower limit of the range considered to be clean is determined as a value obtained by subtracting 50 from the calculated average value.

In the present embodiment, the threshold value is determined by adding or subtracting the same value to the average value as the reference data regardless of the pixel position in the main scanning direction, but the threshold value is added to determine the threshold value that gives the upper limit. The value to be subtracted to determine the threshold that gives the lower bound may be different. For example, 40 may be used to calculate the threshold that gives the upper limit, and 50 may be used to calculate the threshold that gives the lower limit.
Further, the threshold value is determined by adding or subtracting the same value to the average value as the reference data regardless of the pixel position in the main scanning direction, but it is considered that there is less dirt near the center of the document M where dirt is easily noticeable. The threshold value that gives the upper limit and the threshold value that gives the lower limit may be determined so that the range is narrowed. For example, 30 is used as the value used for calculating the upper limit and the lower limit in the center of the main scanning direction of the document M, and 50 is used as the value used for calculating the upper limit and the lower limit near the edge of the document M in the main scanning direction. You may. Of course, the change in the range considered to be clean may be set more finely.

Further, the threshold value that gives the upper limit and the threshold value that gives the lower limit may be calculated by multiplying the reference data by a coefficient, instead of calculating based on the absolute value. In other words, the reference data having a large gradation value may be defined as having no stains, and the reference data having a small gradation value may be considered to have no stains.
In the case of the present embodiment, the threshold value for giving the upper limit and the lower limit of the range considered to be clean is set based on the reference data read from the corresponding device before the product is shipped. The time point before product shipment here is an example of the first time point. The value read before the product is shipped is the initial value of the reference data.

<Example of reading operation>
FIG. 11 is a flowchart illustrating an example of a reading operation executed during automatic transfer of the document M by the automatic document transfer unit 122. The symbol S shown in the figure means a step.
When a bundle of documents M is placed on the document tray 123 (see FIG. 1) and an instruction to execute scanning is instructed, the image reading control unit 203 (see FIG. 4) of the document reading device 10 (see FIG. 1) becomes a lighting unit. Move 140 to the correction position (step 101). The correction position here is a position different from reading the information.
When moving to the correction position, the image reading control unit 203 acquires correction data (hereinafter referred to as “correction data”) (step 102).

When the acquisition of the correction data is completed, the image reading control unit 203 moves the lighting unit 140 to the reading position Pr determined to be free of dirt by the dirt detection process executed last time (step 103). Immediately after the product is shipped, the lighting unit 140 is moved to, for example, the candidate position P3.
When the positioning to the reading position Pr is completed, the image reading control unit 203 reads information from the document M being conveyed (step 104).
After that, the image reading control unit 203 determines whether or not there is the next document M (step 105). While the negative result is obtained in step 105, the image reading control unit 203 returns to step 104 and continues reading information. For example, 10 originals M are arranged on the original tray 123 (see FIG. 1), and the number of originals M for which information has been read is 9 or less.

If an affirmative result is obtained in step 105, the image reading control unit 203 shifts to the process of detecting dirt Dc such as dust.
First, the image reading control unit 203 takes an image of the surface of the reading window 131 against the background of the reading guide member 127 while keeping the current reading position Pr, and acquires the line data of the reading guide member 127 (step 106). The time point of this step 106 is an example of the second time point. In other words, the time when the automatic transfer of the document M by the automatic document transfer unit 122 is completed is an example of the second time point.
Next, the image reading control unit 203 compares the acquired line data with the threshold value (step 107). As described above, the threshold value here is set based on the reference data actually read from the corresponding device before the product is shipped.
After that, the image reading control unit 203 determines whether or not the current reading position Pr is dirty (step 108).

FIG. 12 is a diagram illustrating a dirt determination operation in the present embodiment.
In FIG. 12, reference numerals are given corresponding to the portions corresponding to those in FIG. In the case of the present embodiment, as described above, a threshold value for giving an upper limit and a threshold value for giving a lower limit in a clean range are set for each plurality of pixels in the main scanning direction.
In the case of FIG. 12, the gradation value of the acquired line data is lower than the lower limit threshold value in the range from the latter half portion of the first region Area1 to the first half portion of the fourth region Area4. Therefore, it is determined that these areas have dark stains.
On the other hand, in the range from the first half portion of the sixth region Area 6 to the second half portion of the seventh region Area 7, the value of the acquired line data is higher than the upper limit threshold value. Therefore, it is determined that these areas have bright stains.

Returning to the description of FIG.
If there is no dirt, a positive result is obtained in step 108, and if there is dirt, a negative result is obtained in step 108.
If an affirmative result is obtained in step 108, the image reading control unit 203 sets the current candidate position to the next reading position Pr (step 109).
On the other hand, if a negative result is obtained in step 108, the image reading control unit 203 determines whether or not the number of loops during the previous execution of dirt detection is the upper limit (step 110). The number of loops here is the number of times the candidate position was moved during the previous execution of dirt detection. Incidentally, the number of loops means the number of times the reading position Pr is moved to the next candidate position. In the case of this embodiment, since there are five candidate positions, the upper limit of the number of loops is "4".

If a positive result is obtained in step 110, the image reading control unit 203 moves to step 109.
On the other hand, when a negative result is obtained in step 110, the image reading control unit 203 determines whether or not the number of loops this time has reached the upper limit (step 111). That is, it is determined whether or not the number of times the reading position Pr has been moved to another candidate position in the dirt detection this time has reached the upper limit.
If an affirmative result is obtained in step 111, the image reading control unit 203 sets the candidate position with the least amount of dirt to the next reading position Pr (step 112). In this case, it means that dirt was found at all five candidate positions. Therefore, the candidate position with the least dirt is set as the next reading position Pr.

On the other hand, when a negative result is obtained in step 111, the image reading control unit 203 adds 1 to the number of loops (step 113).
After that, the image reading control unit 203 moves the lighting unit 140 to the next candidate position (step 114). For example, when the current reading position Pr is the candidate position P1, the lighting unit 140 is moved to the adjacent candidate position P2. This movement is executed in order from the first reading position Pr of this job. If the current reading position Pr is the candidate position P5, the next reading position Pr is moved to the candidate position P1.
After the movement of the reading position Pr, the image reading control unit 203 shifts to step 106.
As described above, in the case of the present embodiment, even when the reflector is not attached to the reading guide member 127, dirt such as dust Dc is used by using the threshold value set according to each pixel in the main scanning direction. Is determined. As a result, even when the reading guide member 127 to which the reflector is not attached is used, it is possible to accurately determine the presence or absence of dirt Dc such as dust.

<Other embodiments>
Although the embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above-described embodiments. It is clear from the description of the scope of claims that the above-described embodiment with various modifications or improvements is also included in the technical scope of the present invention.

For example, in the above-described embodiment, the surface of the portion of the reading guide member 127 (see FIG. 3) facing the reading window 131 (see FIG. 3) is curved so as to project in the direction of the reading window 131. Although the case of having it has been described, the shape of the corresponding part may be arbitrary. For example, a part of the curved surface may be processed flat. This flat surface may be formed as the bottom of a recess recessed in a direction away from the reading window 131. Further, the flat surface may be formed so as to be inclined with respect to the reading window 131 so that the distance from the reading window 131 increases as the document M approaches the ejection side. If such an inclination is formed, the contact between the flat surface on which the illumination light from the light source 141 is incident and the document M being conveyed is suppressed. In other words, dirt on a flat surface is suppressed. Incidentally, it is desirable that the distance between the portion where the flat surface is most recessed and the reading window 131 is, for example, 1 mm to 5 mm.

In the above-described embodiment, each time the automatic document transfer unit 122 (see FIG. 1) finishes the automatic transfer of the document M, the operation of detecting the presence or absence of dirt Dc such as dust and the operation of adjusting the reading position Pr are performed. Although the case of execution has been described, these operations may be executed every time the main power is turned on or every time the data for adjusting the candidate position is updated.
That is, the time when the automatic document transfer by the automatic document transfer unit 122 (see FIG. 1) is completed, the time when the main power is turned on, and the time when the data for adjusting the candidate position is updated are all the second time points. This is an example.

When the data for adjusting the candidate position is updated, the reading guide is set when each candidate position P1 to P5 is set as the reading position Pr again on condition that the reading window 131 (see FIG. 2) is cleaned. The value of the amount of light actually reflected by the member 127 (see FIG. 2) may be measured, and the reference data giving a clean range may be updated. In this case, the update time of the reference data accompanying the update of the data for adjusting the candidate position is the first time.
Further, when dirt is not detected in the line data acquired after the user starts using the data, the reference data may be updated with the line data in which the dirt is not detected. In this case, even when the distribution of the amount of light in the main scanning direction acquired by the light receiving unit 150 (see FIG. 2) changes from the distribution at the time of product shipment due to the secular change of the reading guide member 127 and the reading window 131. , It is possible to maintain the accuracy of detecting dirt Dc such as dust.

Incidentally, in the above-described embodiment, when dirt is found at the reading position Pr in use, the candidate position with the least dirt is used for the next reading position Pr (step 112 in FIG. 11), but all the candidates. If dirt is detected at positions P1 to P5, in other words, if there are no candidate positions where dirt is not detected, a function may be provided to notify the user of the need for cleaning. This function is an example of a notification means. The notification may be made by voice or buzzer, a screen prompting cleaning may be displayed, or an e-mail prompting cleaning may be sent. The notification destination may be a service staff in charge of maintenance or the like, but may be a user or an administrator who uses the image forming apparatus 1 (see FIG. 1).
Further, after cleaning the reading window 131 (see FIG. 2) by the service staff or the like, a function of displaying a screen or the like for accepting whether to update the reference data or not and accepting the selection by the service staff or the like may be provided. .. This function is an example of reception means. If not updated is selected, the initial value is used as is. On the other hand, when update is selected, the presence or absence of dirt is detected in all the candidate positions P1 to P5, and when dirt is not detected in any of the candidate positions, the value of the amount of light received at the time corresponding to the second time point. May be set as the reference data. For example, an initial value is used as the reference data when detecting the presence or absence of dirt in the candidate positions P1 to P5.

Further, in the above-described embodiment, the case where five candidate positions are set has been described, but the number of candidate positions is arbitrary.
Further, in the above-described embodiment, the main scanning direction is divided into a plurality of regions Area as a predetermined plurality of pixel units, and it is considered that each of the first half portion and the second half portion in each region Area after the division is clean. Although the range is set, the range set in one area may be one or three or more.
In the above-described embodiment, the reference data is calculated as the average value of the light intensity values for 32 lines in the sub-scanning direction, but the number of lines used for calculating the average value is not limited to 32 lines.

In the above-described embodiment, the case where the candidate positions P1, P2, P3, P4, and P5 of the reading position Pr are arranged at 1 mm intervals has been described, but the arrangement intervals are not limited to 1 mm. As for the distance between the candidate positions, it is sufficient that dirt Dc such as dust can be avoided by changing the reading position Pr. Therefore, the distance between the candidate positions may be greater than or equal to the minimum dimension of dirt Dc such as dust. For example, when the minimum dimension of dirt Dc such as dust is assumed to be 0.2 mm, the distance between the candidate positions may be set to a value of 0.2 mm or more.

In the above-described embodiment, the image forming apparatus 1 having a device configuration in which the document reading device 10 and the image recording device 20 are connected has been described, but the document reading device 10 may be a single device. Further, in the above-described embodiment, the case where the image read by the document reading device 10 is recorded as it is on a medium such as paper by the image recording device 20 has been described, but the read image may be faxed. , It may be stored in an internal storage area or a storage area of an external device.

1 ... image forming device, 10 ... document reading device, 12 ... document transporting device, 20 ... image recording device, 30 ... accommodating device, 114 ... document stand, 121 ... document cover, 122 ... automatic document transport unit, 123 ... document tray , 124 ... Original transport path, 127 ... Reading guide member, 131 ... Reading window, 140 ... Lighting unit, 150 ... Light receiving unit, 160 ... Reflection unit, 201 ... Main control device, 202 ... Image recording control unit, 203 ... Image reading Control unit, 231 ... Scanned image acquisition unit, 232 ... Reading area detection unit, 233 ... Dust detection unit, 233A ... Reference data storage control unit, 234 ... Reading position determination unit, 235 ... Reading position control unit, 236 ... Original image output Department

Claims (8)

The original is conveyed when the light reflected by the surface of the member that guides the original is received at the first time point when the original does not pass through the reading position of the image provided on the path for conveying the original. A storage control means that stores the value of the amount of light corresponding to each position in the direction intersecting the direction as reference data in the storage area, and
Change in the value of the amount of light received by the surface of the member that guides the document at the second time point after the first time point when the document does not pass through the scanning position with respect to the reference data. An image reading device having a detecting means for detecting dirt at the reading position based on the above. The detection means sets a threshold value for detection for each of a plurality of values of the reference data, and detects dirt by comparing with the threshold value corresponding to each position of the value of the amount of light received at the second time point. The image reading device according to claim 1. The image reading device according to claim 2, wherein the threshold value is a threshold value for detecting stains in which the value of the amount of light increases and a threshold value for detecting stains in which the value of the amount of light decreases. The image reading device according to claim 1, wherein the initial value of the reference data is stored before the start of use. The image reading device according to claim 4, wherein when the detection means does not detect dirt, the reference data is updated with the value of the amount of light received at the second time point. When dirt is detected by the detection means, the detection means changes the reading position to another position and detects the dirt based on the value of the amount of light received for the other position after the change. Item 4. The image reading device according to item 4. If the other position where dirt is not detected does not remain, a notification means for notifying the need for cleaning and a notification means.
The image reading device according to claim 6, further comprising a receiving means for receiving update or non-update of the reference data. When the update of the reference data is accepted and the detection means does not detect dirt on all the reading position candidates, the reference data is updated with the value of the amount of light received at the second time point. The image reading device according to claim 7.