JP3592046B2 - Image reading device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image reading device that converts image information into digital information. In particular, it relates to an automatic document size detection function using an image reading device. The image reading device is mounted on a digital copying machine, digital facsimile, image scanner, or the like.
[0002]
[Prior art]
FIG. 7 is a diagram showing a configuration example of a conventional digital copying machine, and FIG. 8 is a diagram showing an external configuration example of the copying machine. In FIG. 8, reference numeral 26 denotes a paper feed tray for automatically feeding a document, and reference numeral 26a denotes a document insertion slot. Reference numeral 1 denotes a platen cover for holding a document, which also serves as an automatic paper feed mechanism (ADF). Reference numeral 19 denotes an upper tray for holding copy paper, 19a denotes a middle tray for holding copy paper, and 20 denotes a lower tray for holding copy paper. Reference numerals 24 and 25 denote a large capacity paper feed tray (LCT-1500) and a large capacity paper feed tray (LCT-1000), respectively. Note that 1500 and 1000 indicate the number of sheets of copy paper accommodated.
[0003]
In FIG. 7, reference numeral 40 denotes an operation unit for setting the number of copies of a copy sheet, setting a magnification, setting a selected sheet, and the like. Reference numeral 17 denotes a manual feed tray for manually feeding copy paper (not shown in FIG. 8). Reference numeral 1 denotes a platen cover (ADF), 2 denotes an exposure lamp for irradiating a document, and 3 denotes an image reading unit that receives reflected light from the document and reads it as an image signal.
[0004]
Reference numeral 23 denotes an image processing unit which converts a document image read by the image reading unit 3 into digital data, and performs predetermined image processing, and 4 receives an image signal processed by the image processing unit 23 and places an image on the photosensitive drum 5. Is an image writing unit for writing. In the image writing section 4, a polygon mirror 7 scans the emitted beam in the main scanning direction.
[0005]
Next, the configuration near the photosensitive drum 5 will be described. Reference numeral 6 denotes a developing unit for attaching toner to the electrostatic latent image formed on the photosensitive drum 5, reference numeral 8 denotes a transfer pole for transferring the toner image formed on the photosensitive drum 5 to copy paper, and reference numeral 9 denotes transfer simultaneous exposure. Is a PSL for removing the charge of the toner. Reference numeral 10 denotes a separation pole for separating the copy sheet from the photosensitive drum 5, and reference numeral 12 denotes a transport unit that transports the separated copy sheet. A fixing unit 13 fixes the copy paper conveyed from the conveyance unit 12.
[0006]
Reference numeral 14 denotes a cleaning unit that removes toner and the like remaining on the photosensitive drum 5 even after the transfer, 15 denotes a PCL that removes the charge remaining on the surface of the photosensitive drum 5 before charging, and 16 denotes a photosensitive drum 5 Is a band electrode for uniformly charging the surface of the electrode.
[0007]
Reference numeral 19 denotes an upper tray for storing copy sheets, and reference numeral 20 denotes a lower tray for storing copy sheets. Reference numeral 18 denotes a paper feed unit for feeding copy paper from these trays, and reference numeral 11 denotes a second paper feed unit for feeding copy paper.
[0008]
Reference numeral 27 denotes a discharge tray for receiving copy paper on which an image has been transferred, reference numeral 21 denotes an ADU discharge / conveyance unit that conveys the copy paper in a double-sided copy, and reference numeral 22 denotes a copy paper conveyed from the ADU discharge / conveyance unit 21. This is an ADU sheet feeding / conveying unit that is turned upside down and returned to the photosensitive drum entrance. Reference numeral 24 denotes a first large-capacity paper tray (LCT-1500), and reference numeral 25 denotes a second large-capacity paper tray (LCT-1000).
[0009]
A control unit 30 controls the overall operation of the image forming apparatus. As the control unit 30, for example, a microprocessor is used. The operation unit notifies the control unit 30 of the number of copies, enlargement magnification, copy density, manual setting of paper type, and the like. Here, the operation unit is shown outside the apparatus for the sake of simplicity. Specifically, as shown in FIG. 8, on the mounting surface of the ADF 1, a copy number setting button, an enlargement magnification selection button, a paper selection button It is usually provided along with the like.
[0010]
As the operation unit 40, for example, a keyboard or a function key is used. The control unit 30 outputs a control signal for driving a motor for rotating the photosensitive drum 5, a control signal for driving a conveyance system to specify a conveyance speed, a control signal for specifying a fixing temperature of the fixing unit 13, and the like. Is done. The operation of the device configured as described above will be described below.
[0011]
The general copying operation will be described below.
A document is placed on the ADF 1, the document is exposed by the exposure lamp 2, and optical image information is read by the image reading unit 3. As the reading element, for example, a CCD is used. The detection signal of the CCD is sent to the image processing unit 23 and is converted into digital image data, and then the image processing unit 23 performs predetermined correction and image processing. The output of the image processing unit 23 is sent to the image writing unit 4 after being converted into an analog signal.
[0012]
The photoreceptor drum 5 is formed by applying an OPC photoreceptor on the drum, is grounded in terms of potential, and is driven and rotated clockwise by a motor (not shown). The band electrode 16 uniformly charges the peripheral surface of the photosensitive drum 5. Prior to this charging, exposure is performed by an exposure device (for example, PCL) 15 using a light emitting diode or the like, and static electricity on the peripheral surface of the photosensitive drum is removed.
[0013]
After the photosensitive drum 5 is uniformly charged, the image writing unit 4 performs image exposure based on the image signal from the image processing unit 23. The image writing section 4 uses a laser diode (not shown) as a light-emitting light source, scans the optical path through a rotating polygon mirror 7 and bends an optical path by a mirror, and rotates the photosensitive drum 5 (sub-scanning) to perform an electrostatic latent image. To form
[0014]
A developing section 6 containing a developer including black toner and a carrier is provided on the peripheral edge of the photosensitive drum 5, and is developed by a developing sleeve (not shown) which contains a magnet and rotates while holding the developer. Is performed. The developer is transported to the development area. A predetermined AC bias voltage and a predetermined DC voltage are superimposed and applied between the developing sleeve and the photosensitive drum 5 in the developing area. As a result, the toner that has been triggered to separate from the carrier adheres to a portion lower than the DC potential, and visualization is performed.
[0015]
On the other hand, copy paper conveyed from the upper tray 19, the lower tray 20, the manual feed tray 17, the first large capacity paper feed tray (LCT-1500) 24 or the second large capacity paper feed tray (LCT-1000) 25 Is supplied to the transfer area by the transport system when the transfer timing is adjusted. In the transfer area, an image is transferred by the transfer pole 8 while a copy sheet is held on the peripheral surface of the photosensitive drum 5 in synchronization with the transfer timing.
[0016]
Next, the electric charge of the photosensitive drum 5 is eliminated by the PSL 9, the copy paper is separated by the separation pole 10 and transported to the fixing unit 13 by the transport unit 12, and the toner is fused by heating and pressing the heat roller and the pressure roller. Thereafter, the paper is discharged via a paper discharge roller and accumulated in the paper discharge tray 27. If necessary, the transfer of the original image transferred to the front surface is returned to the entrance of the photosensitive drum 5 via the ADU paper discharge / conveyance unit 21 and conveyed, and the original image is also transferred to the back surface.
[0017]
On the other hand, the photoreceptor drum 5 from which the copy paper is separated is pressed against the blade of the cleaning unit 14 to remove and clean the residual toner, and is again discharged by the PCL 15 and charged by the band electrode 16 to perform the next image forming process. Prepare.
[0018]
In the above-mentioned digital copying machine, an automatic document size detection function is realized by using the image reading section 3. The outline of this function is as follows.
(1) The operator places the document on the platen glass and closes the platen cover, or when the operator places the document on the platen glass and performs a copying operation, the image reading unit 3 is used to read the document image. Several lines are read in the sub-scanning direction (vertical direction of the document).
[0019]
(2) If the background of the scanned original is white and the image is read without closing the platen cover, the other parts will be converted to sky shots (images outside the optical system imaging range). Therefore, the output signal for one line in the main scanning direction (horizontal direction of the document) output from the image reading unit 3 is as shown in FIG. In the figure, the horizontal axis is the main scanning direction, and the vertical axis is the detection signal (luminance). The output of the line sensor increases when the image is bright, and decreases when the image is dark.
[0020]
(3) By storing in advance the information on the usable original paper width (correspondence between the original paper width and the number of pixels), the output detected by a predetermined threshold value (original edge detection threshold) is stored in the apparatus. The width of the document most suitable for the width (number of pixels) of the signal change point (points A and B in FIG. 9) can be specified.
[0021]
{Circle around (4)} If such a method is developed in the vertical direction of a document, the length of the document can be specified, and the document size is determined. However, in this case, it is necessary to scan the image reading unit 3 by the length of the document, so that it takes time to specify the size of the document. Therefore, in order to shorten the detection time, an optical position detection sensor or the like may be separately used for detecting the document in the vertical direction (sub-scanning direction).
[0022]
[Problems to be solved by the invention]
In the above-mentioned specific operation of the document size, in the case of a document whose background is black, only a black signal is output from the image reading unit 3 as shown in FIG. 10, and the width of the document cannot be detected from this signal. Failure occurs. Further, in the above-described specific operation of the document size, the signal processing from the image reading unit 3 may be performed using information that has been subjected to so-called “thinning processing” in order to improve processing speed and reduce the amount of processing information. .
[0023]
For example, when the image reading unit 3 having a resolution of 400 dpi (dots / inch) performs a thinning process of capturing information of one pixel for every 16 pixels, an image having a width of about 63 μm is captured at an interval of about 1 mm. .
[0024]
When a document having lines arranged at regular intervals (e.g., 1 mm intervals) such as graph paper is read in such a setting, there is a possibility that the original may be determined to be white or black depending on the place where the document is placed. Trouble occurs when performing
[0025]
FIG. 11 is an explanatory diagram of occurrence of a defect. This is the case of reading with a sky shot. The vertical axis is the main scanning direction, and the horizontal axis is the detection signal. The circles in the figure are sampling points for thinning. If the sampling point happens to overlap the black portion of the graph paper, the output of the line sensor will be in a low state as shown in the figure, and it will be difficult to determine the width of the document.
[0026]
The present invention has been made in view of such a problem, and has as its object to provide an image reading apparatus capable of reliably determining the size of a document.
[0027]
[Means for Solving the Problems]
An image reading apparatus for reading image information recorded on an original includes a line sensor that receives optical information from the original and converts the optical information into an electric signal, and converts an output of the line sensor into digital data. An A / D converter for performing conversion, and a control unit for performing at least a control operation of an image reading process, performing a first scan of the document in the main scanning direction without closing a platen cover; With the cover closed, a second scan of the document in the main scanning direction is performed. The control unit detects a document edge candidate from each of the line sensor outputs obtained by these two scans, and detects the document edge. When determining the document size from the distance between the set candidates, a document edge candidate detected from the line sensor output obtained in the first scan and a line sensor output obtained in the second scan are used. And the original end candidates to be issued From within , The outermost Two points Adopt manuscript edge candidates, These two points Between document edge candidates Distance Is used to determine the document size.
[0028]
According to the configuration of the present invention, by performing the first scan with the platen cover closed and the second scan with the platen cover closed, it is possible to reliably determine the size of the document. it can.
[0029]
In this case, a detecting unit for detecting opening and closing of the platen cover is provided,
When the detection means detects that the platen cover is about to be closed, the first scanning is performed, and when it is detected that the platen cover is completely closed, the second scanning is performed. .
[0030]
According to the configuration of the present invention, the point at which the operator attempts to close the platen cover is detected, the sky shot scanning is performed, and then the scanning is performed with the platen cover closed, so that the size of the document is reliably determined. can do.
[0031]
Further, the control unit may control a white area of the original in the first scan. Original edge candidate Is detected, and the black area of the original is Of the document end Detecting.
[0033]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic circuit diagram showing an embodiment of the present invention, and mainly shows the configuration of an image reading unit. The same components as those in FIG. 7 are denoted by the same reference numerals. In the figure, reference numeral 30 denotes a control unit for controlling at least the image reading process, for example, a microprocessor. Reference numeral 37 denotes a memory provided in the control unit 30 for storing various information. The memory 37 can be provided outside the control unit 30 instead of inside as shown in the figure. The memory 37 stores length information (the number of pixels) in the width direction of the document size (for example, A3, A4, B3, B4, B5, etc.).
[0034]
Reference numeral 31 denotes a line sensor for converting optical original information into an electric signal, for example, a CCD. An A / D converter 32 converts the output of the CCD line sensor 31 into digital data, and an image processing circuit 33 receives the output of the A / D converter 32 and performs image processing. As the image processing circuit 33, for example, an LUT (Look Up Table) or the like in which a relation between an input and an output is stored is used.
[0035]
Numeral 34 denotes a pulse width modulation unit which receives the output of the image processing circuit 33 and performs pulse width modulation (PWM) according to the gradation, and numeral 35 denotes a laser drive unit which receives the output of the pulse width modulation unit 34 and drives the laser. It is. The laser driving unit is provided to the image writing unit 4 (see FIG. 7).
[0036]
Reference numeral 36 denotes an open / close detection sensor for detecting that the platen cover is closed. The open / close detection sensor 36 is configured by a microswitch or the like that is turned on in two stages. When the switch is turned on and completely closed, the second-stage switch is turned on. Further, apart from this configuration, two micro switches may be provided according to the number of stages.
[0037]
An operation unit 40 sets copy conditions such as the number of copies, copy density, and magnification. The open / close detection sensor 36 is provided, for example, near the open / close fulcrum of the platen cover as shown in FIG. The outputs of the open / close detection sensor 36 and the operation unit 40 are given to the control unit 30. The control unit 30 controls operations of the CCD line sensor 31, the A / D converter 32, the pulse width modulation unit 34, and the laser driving unit 35. The operation of the device configured as described above will be described below.
[0038]
First, the operator places the document 41 on the platen glass 42 as shown in FIG. Then, when the platen cover 1 is to be closed, the opening / closing detection sensor 36 detects that the platen cover 1 is about to be closed at a point in time when the platen cover 1 is closed to a certain extent, and notifies the control unit 30. The control unit 30 operates the image reading unit 3 in this state, and performs sky shot scanning with the platen cover 1 not closed (first scanning). This scanning is performed for several lines in the sub-scanning direction. Then, an average of the obtained image data of several lines is obtained.
[0039]
At this time, the reflection image of the document 41 is formed on the CCD line sensor 31 via the optical system, and the CCD line sensor 31 converts a light signal into an electric signal. The output of the CCD line sensor 31 is thinned out, enters the subsequent A / D converter 32, and is converted into digital image data. Here, the reason why the output of the CCD line sensor 31 is thinned out is not the mode for reading the document information but the mode for determining the size of the document. It suffices if there is data of the number of pixels required to determine the size of the document 41. Therefore, it is sufficient to provide a predetermined number of sampling points in the main scanning direction and read the image. The output of the A / D converter 32 is sent to the control unit 30 and stored in the memory 37.
[0040]
When the platen cover 1 is completely closed next after reading the document information by the first scanning, the control unit 30 detects the second-stage opening / closing detection sensor 36 and notifies the control unit 30 of the detection. 30 operates the image reading unit 3 to perform scanning (second scanning). This scanning is also performed for several lines in the sub-scanning direction. At this time, the image signal read by the CCD line sensor 31 is decimated and input to the A / D converter 32, which converts the image signal into digital image data. It is stored in the memory 37.
[0041]
Next, the control unit 30 uses a document edge detection threshold set in advance based on the image data obtained by the first scan and the image data obtained by the second scan, which are stored in the memory 37. The change point of the signal is detected, and the document size is determined based on the maximum width (the number of pixels) of the plurality of change points. There are various states of the document 41 as shown in FIG. 3A shows a state in which the background of the document at the position where the width of the document is detected is white, FIG. 3B shows a state in which a part of the document is black (area indicated by hatching), and FIG. This shows a state where the background of the document is black. In each case, the control unit 30 determines the document size by the following operation.
[0042]
(1) When the background of the document is white (corresponding to FIG. 3A)
In this case, the image detected by the CCD line sensor 31 is as shown in FIG. (A) shows a sky shot state (first scan), and (b) shows a state (second scan) where the platen cover 1 is closed.
[0043]
In the sky shot scanning shown in (a), the CCD output is high (high level) only in the document portion, and the portions other than the document are dark (low level). In the case of the second scanning shown in (b), by setting the color of the back surface of the platen cover 1 to white in the area other than the document, the CCD output becomes high and cannot be distinguished from the edge of the document (undetectable). ). However, in this case, the detection signal is compared with a predetermined threshold value (document edge detection threshold) by the sky shot scanning shown in FIG. ₁ Point and B ₁ Point) can be recognized, so A ₁ Point and B ₁ It can be recognized that the distance W between the points is the width of the document.
[0044]
Specifically, by referring to the relationship between the number of CCD elements of the CCD line sensor 31 and the type of the document and the width of the document stored in the memory 37 in advance, the width information of the document is obtained from the output of the CCD line sensor 31. Can be requested. The same applies to the case where pixels are read out with thinning. It suffices to determine in advance how much the distance between the thinned pixels corresponds to the document distance.
[0045]
{Circle over (2)} When a part of the background of the document is black (corresponding to FIG. 3B)
In this case, the image detected by the CCD line sensor 31 is as shown in FIG. (A) shows a sky shot state (first scan), and (b) shows a state (second scan) where the platen cover 1 is closed.
[0046]
In sky shot scanning, since the left end of the document is black, the CCD output is low, and the low level range is apparently widened as shown in FIG. That is, the range of the high level of the document is narrowed.
[0047]
On the other hand, in the second scan in which the platen cover 1 is closed, in the sky shot, the signal at the portion where the low-level area reads the back surface of the platen cover 1 becomes white, so that the characteristic shown in FIG. Accordingly, in this case, the left end of the document is at the point A detected in the first scan of FIG. ₁ , B ₁ And point A detected in the second scan of (b) ₂ , B ₂ Is detected. As described above, when more than two document edge candidates are detected, the outermost (widest candidate) candidate point is adopted. Therefore, the document size is point A ₂ From point B ₂ Can be obtained as the distance W to the distance.
[0048]
(3) When the background of the document is black (corresponding to (c) in FIG. 3)
In this case, the image detected by the CCD line sensor 31 is as shown in FIG. (A) shows a sky shot state (first scan), and (b) shows a state (second scan) where the platen cover 1 is closed.
[0049]
In the sky shot scanning, the left and right ends of the document are dark, so that the CCD output is low, and apparently at a low level as shown in FIG. That is, the high-level range of the document cannot be detected.
[0050]
On the other hand, in the second scan in which the platen cover 1 is closed, a dark portion of the document is detected as shown in FIG. ₂ Point and B ₂ It can be recognized that the distance W between the points is the width of the document.
[0051]
When the width of the document is obtained in this way, the control unit 30 compares the width of the document with the data in the width direction of the document stored in the memory 37 and, if there is the same or almost the same width direction data, determines the width of the document. It can be determined that the document is of a specific size (for example, A4 or A3).
[0052]
Further, by combining the information with information of an optical sensor (not shown) for detecting the length of the document, the size of the document (for example, A4) can be specified.
In the above-described embodiment, by performing the first scan with the platen cover closed and the second scan with the platen cover closed, it is possible to reliably determine the width of the document. it can.
[0053]
Further, in this embodiment, the opening and closing detection sensor detects when the operator attempts to close the platen cover, performs a sky shot scan, and then performs scanning with the platen cover closed, thereby scanning the original. The width can be reliably determined.
[0054]
In this embodiment, the microprocessor of the control unit 30 processes the information stored in the memory 37 for realization. However, it may be realized by adding hardware for performing the same processing.
[0055]
Further, in the above-described embodiment, the case where the width of the document in the main scanning direction is obtained is taken as an example, but the present invention can be similarly applied to the document in the sub-scanning direction. In this case, since the width information and the length information of the document are added, the size of the document can be reliably determined without installing an optical sensor or the like. However, since it is necessary to perform the scanning after the document is placed and before the platen cover closes, it is necessary to take measures such as increasing the scanning speed.
[0056]
Further, in the above-described embodiment, the case of forming an image with a single color toner is taken as an example. However, the present invention is not limited to this. The same can be applied. In the case of forming a color image, yellow (Y), magenta (M), cyan (C), and black (K) toners are used.
[0057]
If a copy start is instructed while the platen cover is open, the second scan (the state where the platen cover is closed) cannot be detected. Therefore, the original is detected only by the detection result of the first scan. The width may be detected. Similarly, when the operator places the original on the platen glass and turns on the power while the platen cover is closed to perform the copy operation, the first scan cannot be detected. The width of the document may be detected only from the result.
[0058]
Further, in the above-described embodiment, the case where the present invention is applied to a copying machine is taken as an example. However, the present invention is not limited to this, and other types of a method of holding a document with a platen cover shape are used. The present invention can be similarly applied to an image reading apparatus such as a facsimile apparatus and an image scanner for reading image information such as a personal computer.
[0059]
Further, the line sensor to be used is not limited to the CCD sensor, but may be any photoelectric conversion element.
[0060]
【The invention's effect】
As described above in detail, according to the present invention, in an image reading device that reads image information recorded on a document, a line sensor that receives light information from the document and converts it into an electric signal, An A / D converter for converting an output into digital data, and a control unit for controlling at least image reading processing are provided, and the first scanning of the document in the main scanning direction is performed without closing the platen cover. Then, a second scan of the document in the main scanning direction is performed with the platen cover closed, and the control unit determines the document size based on the line sensor output obtained by these two scans. By
It is possible to reliably determine the size of a document without installing a special document size detection device.
[0061]
In this case, detecting means for detecting the opening and closing of the platen cover is provided. When the detecting means detects that the platen cover is about to be closed, the first scanning is performed, and then the platen cover is completely closed. By detecting the fact that the second scanning is performed,
The time when the operator attempts to close the platen cover is detected, the sky shot scan is performed, and then the scan is performed with the platen cover closed, so that the size of the document can be reliably determined.
[0062]
Further, the control unit receives one of the output of the line sensor by the first scan and the output of the line sensor by the second scan to determine the document size,
When the operator performs an original reading operation with the platen cover opened, or when the operator performs an original reading operation with the platen cover closed, the information of the first scan only or the second information is read. The original size can be determined from the information of only the scan.
[0063]
As described above, according to the present invention, it is possible to provide an image reading apparatus capable of reliably determining the size of a document.
[Brief description of the drawings]
FIG. 1 is a schematic circuit diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing an open / closed state of a platen cover.
FIG. 3 is a diagram illustrating a state of a document.
FIG. 4 is an explanatory diagram (1) of document width detection.
FIG. 5 is an explanatory diagram (2) of document width detection.
FIG. 6 is an explanatory diagram (3) of document width detection.
FIG. 7 is a diagram illustrating a configuration example of a copying machine.
FIG. 8 is a diagram illustrating an example of an external configuration of a copying machine.
FIG. 9 is a diagram illustrating an output signal waveform of an image reading unit.
FIG. 10 is an explanatory diagram (1) of occurrence of a defect.
FIG. 11 is an explanatory diagram (2) of the occurrence of a defect.
[Explanation of symbols]
31 CCD line sensor
32 A / D converter
33 Image processing circuit
34 pulse width modulator
35 Laser drive unit
36 Open / close detection sensor
40 Operation unit

Claims (3)

A line sensor that receives light information from a document and converts it into an electric signal in an image reading device that reads image information recorded on the document, an A / D converter that converts the output of the line sensor into digital data, A control unit for performing a control operation of the reading process,
Performing a first scan of the document in the main scanning direction with the platen cover not closed;
Next, a second scan of the document in the main scanning direction is performed with the platen cover closed,
The control unit detects a document edge candidate from each of the line sensor outputs obtained by these two scans, and determines a document size from a distance between the document edge candidates in the first scan. Adopt two outermost document edge candidates from among the document edge candidates detected from the obtained line sensor output and the document edge candidates detected from the line sensor output obtained in the second scan. An image reading apparatus for determining a document size from a distance between these two document edge candidates. Detecting means for detecting opening and closing of the platen cover is provided. When the detecting means detects that the platen cover is about to be closed, the first scanning is performed, and then, it is detected that the platen cover is completely closed. 2. The image reading device according to claim 1, wherein the second scanning is performed when the image is read. The control unit detects a document edge candidate in a white region of the document in the first scan, and detects a document edge candidate in a black region of the document in the second scan.
The image reading device according to claim 1, wherein:

Images