JP2024064281A - Image reading apparatus and image forming apparatus - Google Patents

Abstract

To solve the problem that, in a configuration in which an inclination angle is detected on the basis of a shadow generated by light emitted from a light source and irradiated on a document when the shadow generated is non-uniform in a main scanning direction, there is a possibility that the detected inclination angle and an actual inclination angle of the document are different and, in this case, when a rotational correction is performed on the basis of the detected angle, an inclination is generated in an image after correction.SOLUTION: A correction angle θ2 is calculated on the basis of a distribution of light emitted from a light guide 112A in a main scanning direction and a distribution of light emitted from a light guide 112B in the main scanning direction. A document information determining unit 207 corrects an angle θ1 on the basis of the correction angle θ2. A correction unit 208 performs rotation correction on the basis of an angle θ1' after correction. As a result, an inclination angle of a tip of a document with respect to the main scanning direction can be detected with higher accuracy.SELECTED DRAWING: Figure 8

Description

The present invention relates to a technique for correcting image data representing an image read by an image reading device.

Conventionally, image reading devices are known that read an image of a document transported in a transport direction. In the image reading device, light is irradiated onto the document from upstream and downstream of the document reading position in the transport direction, and the image of the document is read by detecting the light reflected from the document with a reading unit.

In an image reading device, variations in the nip pressure and rotation speed of the rollers that transport the document can cause the document to skew and the document's position in a direction perpendicular to the transport direction (hereinafter referred to as the main scanning direction). Patent document 1 describes a configuration in which the shadow of the leading edge of the document in the transport direction is detected from image data that represents the read result, and the image data is rotationally corrected based on the tilt angle of the detected shadow of the leading edge of the document with respect to the main scanning direction.

JP 2010-118911 A

10 is a diagram showing how a shadow corresponding to the leading edge of the document is generated. FIG. 10(a) is a diagram showing how the document 101 is irradiated from the LED 110A and the light guide 112A arranged upstream of the reading position in the transport direction. A shadow corresponding to the leading edge of the document is generated on the guide plate 116 by the light irradiated from the light guide 112A. FIG. 10(b) is a diagram showing how the document 101 is irradiated from the LED 110B and the light guide 112B arranged downstream of the reading position in the transport direction. The shadow generated by the light irradiated from the light guide 112A is canceled by the light irradiated from the light guide 112B to the document 101. Therefore, if the light amount distribution in the main scanning direction of the light emitted from the light guide 112B becomes non-uniform, the shadow will be non-uniform even if the light amount distribution in the main scanning direction of the light emitted from the light guide 112B is uniform.

In the configuration of Patent Document 1, the tilt angle is detected based on the shadow that is cast when the light emitted from the light source is irradiated onto the document. For example, if the cast shadow is non-uniform in the main scanning direction, the detected tilt angle may differ from the actual tilt angle of the document. In this case, if rotation correction is performed based on the detected angle, tilt will occur in the corrected image.

In view of the above problems, the present invention aims to detect the tilt angle of the leading edge of a document relative to the main scanning direction with higher accuracy.

In order to solve the above problems, an image reading device according to the present invention comprises:
a loading section on which documents are loaded;
a feeding section for feeding the originals loaded on the loading section;
a transport unit that transports the document fed by the feeding unit to a reading position;
a first illumination unit including a first light source that emits light and a first light guide that guides the light emitted from the first light source to a document passing through the reading position, the first illumination unit being provided at a position upstream of the reading position in a transport direction in which the document is transported;
a second illumination unit including a second light source that emits light and a second light guide that guides the light emitted from the second light source to a document passing through the reading position, the second illumination unit being provided at a position downstream of the reading position in a transport direction in which the document is transported;
a reading unit that reads an image of the document by receiving reflected light from the document passing through the reading position;
a guide member provided on an opposite side of the first illumination unit and the second illumination unit with respect to a transport path along which the document is transported;
a detection unit that detects a shadow generated on the facing member due to the light emitted from the first light source and the light emitted from the second light source based on image data representing an image of a document read by the reading unit;
a determining unit that determines an amount of inclination corresponding to an angle of inclination of a leading edge side of the document in a transport direction in which the document is transported with respect to a predetermined direction perpendicular to the transport direction, based on the shadow detected by the detecting unit;
a generating means for generating a correction angle based on a shadow detected by the detecting means in a state in which the document is illuminated by the light emitted from the first illumination unit and the second light source is not emitting light, a shadow detected by the detecting means in a state in which the document is illuminated by the light emitted from the second illumination unit and the first light source is not emitting light, and the amount of inclination determined by the determining means;
a correction means for performing rotation correction on the image data so that the correction angle generated by the generation means becomes smaller;
The present invention is characterized by having the following:

According to the present invention, the inclination angle of the leading edge of the document relative to the main scanning direction can be detected with higher accuracy.

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus. FIG. 2 is a control configuration diagram of the image reading apparatus. 5 is an explanatory diagram of acquisition timing of image data stored in an image memory. FIG. 5A to 5C are explanatory diagrams of processing in an edge detection unit according to the first embodiment. 1 is an image indicated by binarized data input to a document information determining unit. FIG. 13 is a diagram illustrating an image read out by a correction unit. 13A and 13B are diagrams showing the distribution of light emitted from a light guide provided on the upstream side and the distribution of light emitted from a light guide provided on the downstream side. FIG. 13 is a graph showing a regression line of light distribution. 4 is a flowchart of a document reading process. FIG. 13 is a diagram showing how a shadow corresponding to the leading edge side of a document appears.

The following describes a preferred embodiment of the present invention with reference to the drawings. However, the shapes of the components and their relative positions described in this embodiment may be modified as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and it is not intended that the scope of the present invention be limited to the following embodiment.

First Embodiment
[Image forming apparatus]
1 is a cross-sectional view showing the configuration of a monochrome electrophotographic copying machine (hereinafter referred to as an image forming apparatus) 100 used in this embodiment. Note that the image forming apparatus is not limited to a copying machine, and may be, for example, a facsimile machine, a printing machine, a printer, etc. Furthermore, the recording method is not limited to an electrophotographic method, and may be, for example, an inkjet method, etc. Furthermore, the type of the image forming apparatus may be either a monochrome type or a color type.

The configuration and functions of the image forming apparatus 100 will be described below with reference to FIG. 1. As shown in FIG. 1, the image forming apparatus 100 has an image reading device 200 including an original feeding device 201 and a reading device 202, and an image printing device 301. The original feeding device 201 is rotatable relative to the reading device 202.

<Image reading device>
Pickup roller 103 as a feeding section feeds originals 101 loaded on tray 102 as a loading section into the inside of original feeding device 201. Separation rollers 104 and 105 are provided to prevent pickup roller 103 from feeding a plurality of originals 101 at the same time. Originals 101 fed to the transport path are transported toward reading position A by transport roller 106 and lead roller 107. Separation rollers 104, 105, transport roller 106, and lead roller 107 are included in the transport section.

A transparent glass 108 is placed at reading position A, and a reading unit 109A is provided on the opposite side of the glass 108 from the transport path. The reading unit 109A has an LED 110, an image sensor 111, and a group of optical components 112. The image sensor 111 has multiple pixels that receive R (red), G (green), and B (blue) light in the main scanning direction.

The reading unit 109A reads an image of the surface (first surface) of the original 101 as follows. Specifically, the LED 110 as a light source irradiates (emits) light onto the surface of the original 101 through the glass 108. The optical component group 112 guides the reflected light from the original 101 received through the glass 108 to the image sensor 111. The image sensor 111 outputs analog image data based on the reflected light it receives. The image sensor 111 simultaneously reads one line of image across the main scanning direction. Therefore, by reading one line of image multiple times by the image sensor 111 while transporting the original 101, the image sensor 111 can output image data including the entire original 101. An A/D conversion unit (not shown) of the reading unit 109A converts the analog image data into digital image data and outputs it to the controller 200 (FIG. 2).

In the transport direction of the original 101, a detection sensor 113 that detects the original 101 is provided upstream of the reading position A. The controller 200 determines the timing at which the reading unit 109A of the original 101 starts reading based on the timing at which the detection sensor 113 detects the original 101.

Pressure rollers 114 and 115 press the original 101 against the glass 108. In addition, a white guide plate 116 is disposed as an opposing member between pressure rollers 114 and 115, directly opposite reading unit 109A, i.e., on the opposite side of the transport path along which the original is transported from reading unit 109A.

After passing through reading position A, the original 101 is transported by transport rollers 117 toward reading position B. A transparent glass 118 is arranged at reading position B, and a reading unit 109B is provided on the opposite side of the glass 118 from the transport path. Reading unit 109B has a similar configuration to reading unit 109A, and reads an image on the back side (second side) of the original 101. The timing at which reading unit 109B starts reading is also determined based on the timing at which the detection sensor 113 detects the original. A white guide plate 119 is arranged directly opposite reading unit 109B.

After passing through the reading position B, the document 101 is discharged to the discharge tray 121 by the discharge rollers 120.

A white reference plate 122, which serves as a reference reading member when acquiring shading data, is provided on the right side of the glass 108.

<Image Printing Device>
Inside the image printing device 301, sheet storage trays 302 and 304 are provided. Different types of recording media can be stored in the sheet storage trays 302 and 304. For example, A4-sized plain paper is stored in the sheet storage tray 302, and A4-sized thick paper is stored in the sheet storage tray 304. Note that the recording media refers to media on which an image is formed by the image forming device, and examples of the recording media include paper, resin sheets, cloth, overhead projector sheets, labels, etc.

The recording medium stored in the sheet storage tray 302 is fed by the pickup roller 303 and sent to the registration roller 308 by the transport roller 306. The recording medium stored in the sheet storage tray 304 is fed by the pickup roller 305 and sent to the registration roller 308 by the transport rollers 307 and 306.

The image data output from the image reading device 200 is input to an optical scanning device 311 including a semiconductor laser and a polygon mirror. The outer peripheral surface of the photosensitive drum 309 is charged by a charger 310. After the outer peripheral surface of the photosensitive drum 309 is charged, a laser beam corresponding to an image signal input from the document reading device 200 to the optical scanning device 311 is irradiated onto the outer peripheral surface of the photosensitive drum 309 from the optical scanning device 311 via the polygon mirror and mirrors 312 and 313. As a result, an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 309.

The electrostatic latent image is then developed by toner in a developing device 314, which serves as an image forming unit, and a toner image is formed on the outer peripheral surface of the photosensitive drum 309. The toner image formed on the photosensitive drum 309 is transferred to a recording medium by a transfer charger 315, which is provided at a position (transfer position) opposite the photosensitive drum 309. The registration rollers 308 feed the recording medium to the transfer position in accordance with the transfer timing at which the image is transferred to the recording medium by the transfer charger 315.

As described above, the recording medium onto which the toner image has been transferred is sent to the fixing device 318 by the conveyor belt 317, and the toner image is fixed to the recording medium by heating and pressurizing the recording medium by the fixing device 318. In this manner, an image is formed on the recording medium by the image forming device 100.

When an image is formed in single-sided printing mode, the recording medium that has passed through the fixing unit 318 is discharged to a discharge tray (not shown) by discharge rollers 319 and 324. When an image is formed in double-sided printing mode, the recording medium is conveyed to a reversal path 325 by discharge rollers 319, conveyance rollers 320, and reversal rollers 321 after a fixing process is performed on the first side of the recording medium by the fixing unit 318. The recording medium is then conveyed again to the registration rollers 308 by conveyance rollers 322 and 323, and an image is formed on the second side of the recording medium by the method described above. The recording medium is then discharged to a discharge tray (not shown) by discharge rollers 319 and 324.

When the recording medium with an image formed on its first side is discharged face down to the outside of the image forming apparatus 100, the recording medium that has passed through the fixing device 318 is conveyed through the discharge rollers 319 toward the conveying rollers 320. Then, just before the rear end of the recording medium passes through the nip of the conveying rollers 320, the rotation of the conveying rollers 320 is reversed, and the recording medium is discharged to the outside of the image forming apparatus 100 via the discharge rollers 324 with the first side of the recording medium facing downward.

This concludes the explanation of the configuration and functions of the image forming device 100.

<Control configuration>
2 is a block diagram showing an example of a control configuration of the image forming apparatus 100. First, the control configuration of the image printing apparatus 301 will be described.

As shown in FIG. 2, the system controller 151 includes a CPU 151a, a ROM 151b, and a RAM 151c. The system controller 151 is also connected to an analog-to-digital (A/D) converter 153, a high-voltage control unit 155, a motor control device 600, sensors 159, and an AC driver 160. The system controller 151 is capable of sending and receiving data and commands to and from each of the connected units.

The CPU 151a reads and executes various programs stored in the ROM 151b to execute various sequences related to a predetermined image formation sequence.

RAM 151c is a storage device. RAM 151c stores various data such as setting values for the high voltage control unit 155 and command values for the motor control device 600.

The system controller 151 receives signals from the sensors 159 and sets the setting value of the high voltage control unit 155 based on the received signals.

The high voltage control unit 155 supplies the necessary voltage to the high voltage unit 156 (charger 310, developer 314, transfer charger 315, etc.) according to the set value set by the system controller 151.

The motor control device 600 controls the motor 509 that drives the load provided in the image printing device 301 in response to commands output from the CPU 151a.

The A/D converter 153 receives a detection signal detected by a thermistor 154 for detecting the temperature of the fixing heater 161, converts the detection signal from an analog signal to a digital signal, and transmits it to the system controller 151. The system controller 151 controls the AC driver 160 based on the digital signal received from the A/D converter 153. The AC driver 160 controls the fixing heater 161 so that the temperature of the fixing heater 161 becomes a temperature required for performing the fixing process. The fixing heater 161 is a heater used in the fixing process, and is included in the fixing unit 318.

As described above, the system controller 151 controls the operation sequence of the image forming device 100.

Next, the control configuration of the image reading device 200 will be described. The CPU 203 controls the image reading device 100 by executing a program stored in the non-volatile memory 209.

The transport motor 201 is the drive source for each roller provided in the document feeder 201, and is driven to rotate under the control of the controller 200.

The operation unit 202 provides a user interface. The CPU 203 controls the operation unit 202 so that an operation screen for the user to set the type of recording medium to be used (hereinafter referred to as paper type) and the like is displayed on a display unit provided on the operation unit 202. The CPU 203 receives information set by the user from the operation unit 202 and outputs the information set by the user to the system controller 151.

The system controller 151 transmits information indicating the status of the image forming device to the operation unit 202. Note that information indicating the status of the image forming device is, for example, information regarding the number of images formed, the progress of the image forming operation, and information regarding sheet jams and multiple feeds in the image printing device 301 and the document feeding device 201. The operation unit 202 displays the information received from the system controller 151 on the display unit.

The reading units 109A and 109B output digital image data to the controller 200. The greater the intensity of the reflected light, the higher the numerical value of this image data. Hereinafter, this numerical level will be referred to as the brightness level. Hereinafter, the image data output by the reading unit 109A will be referred to as the front image data, and the image data output by the reading unit 109B will be referred to as the back image data.

The front image data output by the reading unit 109A is input to the shading circuit 204A, and the back image data output by the reading unit 109B is input to the shading circuit 204B. The shading circuits 204A and 204B perform addition/subtraction and multiplication/division on the image data to correct (shading correction) the effects of non-uniformity in the amount of light from the LED 110 and uneven sensitivity for each pixel of the image sensor 111, and generate image data that is uniform in the main scanning direction.

The front side image data after shading correction by the shading circuit 204A is stored in the image memory 205. On the other hand, the back side image data after shading correction by the shading circuit 204B is input to the image inversion circuit 210.

The image inversion circuit 210 inverts the main scanning direction of the back side image data. This is because, in this embodiment, the reading units 109A and 109B have the same configuration, and the image read by the reading unit 109B has an inverted main scanning direction compared to the image read by the reading unit 109A. The back side image data after processing by the image inversion circuit 210 is stored in the image memory 205. In other words, the image scale 205 functions as a first storage unit.

3 is an explanatory diagram of the timing of acquiring the front image data and the back image data stored in the image memory 205. After the transport of the original 101 is started at time t0, the detection sensor 113 detects the leading edge of the original 101 at time t1. The CPU 203 determines the time t2 before the original 101 reaches the reading position A based on the time t1, for example, based on the transport speed at which the original 101 is transported. Then, the CPU 203 stores the front image data output by the reading unit 109A in the image memory 205 for a predetermined period from the time t2. Note that the predetermined period is at least the period until the rear end of the original 101 leaves the reading position A. This predetermined period is determined based on the transport speed of the original 101. Similarly, the CPU 203 determines the time t3 before the original 101 reaches the reading position B based on the time t1. Then, the CPU 203 stores the back image data output by the reading unit 109B in the image memory 205 for a predetermined period from the time t3. CPU 203 may start reading by reading unit 109A at time t2 and store the front image data in image memory 205, or may store the front image data of reading unit 109A that has been reading since before time t2 in image memory 205. CPU 203 may start reading by reading unit 109B at time t3 and store the back image data of reading unit 109B that has been reading since before time t3 in image memory 205. In the following description, the image indicated by the front image data will also be referred to as the front image, and the image indicated by the back image data will also be referred to as the back image.

As shown in FIG. 2, the front image data output from the shading circuit 204A is also input to the edge detection unit 206. In addition, the back image data output from the image inversion circuit 210 is also input to the edge detection unit 206. Below, the correction of the front image data is explained, but the back image data is corrected in the same way.

Figure 4 is an explanatory diagram of the processing by the edge detection unit 206. Figure 4 shows an image in which pixel rows in the main scanning direction obtained by the reading unit 109A at predetermined times from time t2 are combined in the sub-scanning direction perpendicular to the main scanning direction. As described above, the surface image data input to the edge detection unit 206 is from time t2 before the leading edge of the original 101 in the transport direction reaches the reading position A. In other words, when the reading unit 109A starts reading an image, the guide plate 116 is read first. Then, as the original 101 is transported, the image of the original 101 is read. In other words, the surface image data input to the edge detection unit 206 includes image data representing the guide plate 116 and image data representing the leading edge side of the original 101.

The edge detection unit 206 performs binarization processing on the surface image data, with each block consisting of a total of nine pixels, three pixels in the main scanning direction and three pixels in the sub-scanning direction. In the following, the number of pixels in the main scanning direction of the reading units 109A and 109B is assumed to be 7488, and the reading units 109A and 109B perform reading 12000 times during the specified period. The pixel position in the main scanning direction is represented as n (0≦n≦7487), and the pixel position in the sub-scanning direction is represented as m (0≦m≦11999). The brightness values of the nine pixels in one block are represented as px (x=0 to 8), and the maximum and minimum values are represented as pmax and pmin.

At a location where all nine pixels are the guide plate 116 (white), such as point A in FIG. 4A, all nine pixels are white pixels, so the difference between pmax and pmin is small. On the other hand, at the boundary between the guide plate 116 (white) and the shadow (gray) of the leading edge of the document 101, such as point B in FIG. 4A, white and gray pixels are mixed among the nine pixels, so the difference between pmax and pmin is large. Therefore, if the difference between pmax and pmin is greater than a predetermined threshold pth, it can be determined that there is a pixel (hereinafter referred to as a candidate pixel) within the block that is a candidate for the shadow caused by the leading edge of the document 101. In this embodiment, if the difference between pmax and pmin within a block is greater than a predetermined threshold pth, the central pixel of the block (the pixel at coordinates (n, m)) is determined to be the candidate pixel. The edge detection unit 206 performs this determination process for each n and m except for n=0, n=7487, m=0, and m=11999. Note that in this embodiment, one scale mark on the x-axis and y-axis corresponds to the distance between the center positions of two adjacent pixels.

Figure 4(A) is an image represented by 8-bit (brightness level: 0-255) image data, and Figure 4(B) is an image represented by image data obtained by binarizing the image data of the image in Figure 4(A) using a threshold value pth = 14. The white color in Figure 4(B) indicates pixels that have been determined by the above process to be candidates for a shadow caused by the leading edge of the document 101. Of the multiple candidate pixels shown in Figure 4(B), the row of candidate pixels in the main scanning direction that is furthest to the leading edge in the sub-scanning direction (the row of pixels in the main scanning direction that are first determined to be candidate pixels in the sub-scanning direction) is determined to be a shadow caused by the leading edge of the document 101.

Figure 5 shows an image represented by the binarized data input to the document information determination unit 207. The image represented by the binarized data input to the document information determination unit 207 is an image of the range indicated by the dotted line in Figure 5, which includes the document 101. The range of this dotted line is n = 0 to 7487, m = 0 to 11999.

The manuscript information determination unit 207 determines the distance (width) W in the main scanning direction between the two corners on the leading edge side of the manuscript 101. Then, the manuscript information determination unit 207 outputs the front manuscript information and the width W to the CPU 203. Here, the front manuscript information is information including the position and angle of the manuscript in the front image. The position of the manuscript 101 is the position (x1, y1) in the front image of the first position of the manuscript 101. In this embodiment, this first position is one of the two corners on the leading edge side of the shadow generated by the manuscript 101 (left side in FIG. 5). In addition, the angle of the manuscript 101 is the angle of a predetermined side of the manuscript 101 in the front image with respect to the reference direction of the front image. In this embodiment, the predetermined side is the shadow generated by the side on the leading edge side of the manuscript 101, and the reference direction is the main scanning direction (predetermined direction). In other words, the angle of the manuscript 101 is θ1 in FIG. 5. In addition, if the shadow created by the edge on the leading edge of the document 101 in the transport direction is inclined upstream from the position (x1, y1), the angle θ1 takes a negative value, and if the shadow created by the edge on the leading edge of the document 101 is inclined downstream from the position (x1, y1), the angle θ1 takes a positive value.

The CPU 203 outputs the position (x1, y1) and the angle θ1 to the correction unit 208 as the front document information. The angle θ' will be described later.

Based on the position (x1, y1) and the angle θ1', the correction unit 208 reads the surface image data stored in the image memory and outputs it to the system controller 151. Specifically, the correction unit 208 reads the image data starting from the read start position (x1, y1) along a direction parallel to the shadow cast by the leading edge of the position original 101.

As described above, the correction unit 208 reads the front image data stored in the image memory up to the rear edge of the document. In other words, the correction unit 208 functions as a reading unit.

Figure 6 is a diagram showing an image read by the correction unit 208. As shown in Figure 6, the image data is read in an amount corresponding to the width W along a direction parallel to the shadow, so that the edge at the leading edge of the document becomes parallel to the main scanning direction. Note that the same process is also performed on the back side image data.

The system controller 151 cuts out the image area to be printed from the image data output from the correction unit 208. Specifically, for example, the system controller 151 cuts out the image data based on the position (0,0) of the image data shown in FIG. 6 output from the correction unit 208 according to the size of the recording medium set by the user using the operation unit 202. More specifically, for example, if the document shown in FIG. 6 is A4 size and the size of the recording medium set by the user using the operation unit 202 is A4 size, the system controller 151 can cut out the image of the document excluding the shadow on the right edge and the shadow on the rear edge of the document. The system controller 151 controls the image printing device 301 to print based on the cut-out image data. That is, the system controller 151 functions as an external device. Note that the external device includes not only the system controller 151 provided in the image forming device 100, but also a smartphone, a tablet, a PC, and the like.

<Light quantity distribution correction>
Next, the correction of the line distribution in this embodiment will be described. In this embodiment, the following configuration is used to detect the inclination angle of the leading edge of the document with respect to the main scanning direction with high accuracy.

Figure 7 shows the distribution of the amount of light in the main scanning direction of light emitted from light guide 112A provided upstream of the reading position in the transport direction, and the distribution of the amount of light in the main scanning direction of light emitted from light guide 112B provided downstream of the reading position in the transport direction. Figure 7(a) shows the distribution of the amount of light in the main scanning direction of light emitted from light guide 112A provided upstream of the reading position in the transport direction. Figure 7(b) shows the distribution of the amount of light in the main scanning direction of light emitted from light guide 112B provided downstream of the reading position in the transport direction.

As shown in Fig. 7(a) and (b), if the distribution of light emitted from the light guide 112A and the distribution of light emitted from the light guide 112B are uniform, the shadow generated at the tip of the document will have the same angle as the document 101, as shown in Fig. 7(c). However, if the distribution of light emitted from the light guide 112A has a tilt θA as shown in Fig. 7(d) and the distribution of light emitted from the light guide 112B has a tilt θB as shown in Fig. 7(e), the result will be as shown in Fig. 7(f). Specifically, a difference of θ2 occurs between the tilt of the shadow and the tilt of the actual document, and the detected tilt angle and the actual tilt angle of the document may differ. Therefore, in this embodiment, the registration calculation unit 207 calculates the correction angle θ2 from the difference between the angle θA of the distribution of light emitted from the light guide 112A with respect to the main scanning direction and the angle θB of the distribution of light emitted from the light guide 112B with respect to the main scanning direction. The registration calculation unit 207 adds the correction angle θ2 to the determined angle θ1, and performs rotation correction using the method described above based on the added angle θ1'.

Figure 8 shows the regression line of the light distribution in Figure 7 (d). Below, we will explain how to calculate the angle θA using Figure 8.

If the number of pixels in the main scanning direction is a, and the luminance value changed in the area of the number of pixels a is b, then θx is calculated by the following formula (1).
θx=tan−1(b/a) (1)
If the above calculated θx and a predetermined coefficient for adjusting the skew angle of the document are k, the angle θA can be calculated by the following equation (2).
θA=k*θx (2)
The angle θB is determined in the same manner as the angle θA.

Next, the correction angle θ2 is calculated by taking the difference between the angle θA and the angle θB.
θ2=θA-θB (3)
9 is a flowchart of an image reading process according to the present embodiment. The process of the flowchart shown in FIG.

When a sensor (not shown) detects the presence of a document on the tray 102 in S101, the controller 200 moves the reading unit 109A to the shading position in S102. Specifically, the controller 200 moves the reading unit 109A to below the white reference plate 122.

Then, in S103, the controller 200 turns on the LED 110A and causes the reading unit 109A to read the white reference plate 122 while the LED 110B is not turned on. Then, the document information determination unit 207 calculates the angle θA.

Next, in S104, the controller 200 turns on the LED 110B and causes the reading unit 109A to read the white reference plate 122 while the LED 110A is not turned on. Then, the document information determination unit 207 calculates the angle θB.

In S105, the manuscript information determination unit 207 calculates the correction angle θ2 based on the angle θA and the angle θ. Specifically, the manuscript information determination unit 207 calculates the correction angle θ2 by subtracting the angle θB from the angle θA.

When an instruction to start reading the document is input in S106, the controller 200 starts feeding and transporting the document 101 on the tray 102 in S107.

In S108, the controller 200 performs a detection process to read and detect the shadow caused by the leading edge of the document.

Next, in S109, the manuscript information determination unit 207 determines the front manuscript information.

In S110, the correction unit 208 starts reading the surface image data stored in the image memory 205 based on the detected tilt amount. As a result, rotation correction is performed.

When the correction unit 208 outputs the corrected image data in S110, the controller 200 determines in S111 whether the next document from which the image is to be read is present in the tray 102. If there is a next document, the controller 200 repeats the process from S10. On the other hand, if there is no next document, the controller 200 ends the process in FIG. 8.

As described above, in this embodiment, the correction angle θ2 is calculated based on the distribution in the main scanning direction of the light emitted from light guide 112A and the distribution in the main scanning direction of the light emitted from light guide 112B. The document information determination unit 207 corrects the angle θ1 based on the correction angle θ2. The correction unit 208 performs rotation correction based on the corrected angle θ1'. As a result, the tilt angle of the leading edge of the document with respect to the main scanning direction can be detected with higher accuracy.

The LED 110A and the light guide 112A correspond to the first lighting unit. The LED 110B and the light guide 112B correspond to the second lighting unit.

102 Tray 103 Pickup roller 104, 105 Separation roller 106 Conveyance roller 107 Read roller 110A, 110B LED
111 Image sensor 112A, 112B Light guide 200 Controller 203 CPU
206 Edge detection unit 207 Document information determination unit 208 Correction unit

Claims (3)

a loading section on which documents are loaded;
a feeding section for feeding the originals loaded on the loading section;
a transport unit that transports the document fed by the feeding unit to a reading position;
a first illumination unit including a first light source that emits light and a first light guide that guides the light emitted from the first light source to a document passing through the reading position, the first illumination unit being provided at a position upstream of the reading position in a transport direction in which the document is transported;
a second illumination unit including a second light source that emits light and a second light guide that guides the light emitted from the second light source to a document passing through the reading position, the second illumination unit being provided at a position downstream of the reading position in a transport direction in which the document is transported;
a reading unit that reads an image of the document by receiving reflected light from the document passing through the reading position;
an opposing member provided on an opposite side of the first illumination unit and the second illumination unit with respect to a transport path along which the document is transported;
a detection unit that detects a shadow generated on the facing member due to the light emitted from the first light source and the light emitted from the second light source based on image data representing an image of a document read by the reading unit;
a determining unit that determines an amount of inclination corresponding to an angle of inclination of a leading edge side of the document in a transport direction in which the document is transported with respect to a predetermined direction perpendicular to the transport direction, based on the shadow detected by the detecting unit;
a generating means for generating a correction angle based on a shadow detected by the detecting means in a state in which the document is illuminated by the light emitted from the first illumination unit and the second light source is not emitting light, a shadow detected by the detecting means in a state in which the document is illuminated by the light emitted from the second illumination unit and the first light source is not emitting light, and the amount of inclination determined by the determining means;
a correction means for performing rotation correction on the image data so that the correction angle generated by the generation means becomes smaller;
1. An image reading apparatus comprising: The image data includes a luminance value that represents an intensity of light received by the reading unit,
2. The image reading apparatus according to claim 1, wherein the detection means detects the shadow based on the luminance value. The image reading device according to claim 1, characterized in that the opposing member is white.

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