Patent Application
20150055996
This application claims benefit of priority to Japanese Patent Application No. 2013-171992 filed Aug. 22, 2013, the content of which is incorporated herein by reference.
The present invention relates to an image forming apparatus capable of detecting the amount of possible curl of a sheet having a toner image formed thereon.
As an example of conventional image forming apparatuses of this type, an apparatus disclosed by Japanese Patent Laid-Open Publication No. 2005-008320 is known. In an image forming apparatus of this type, a two-dimensional area sensor (which will be hereinafter referred to simply as a sensor) is provided in the vicinity of a sheet path and downstream from a fixing device. This sensor obtains a thermal image of a sheet traveling from the fixing device downstream in the sheet path, and detects curl of the sheet based on the obtained thermal image.
In such a conventional image forming apparatus, it is necessary to provide a sensor to be used exclusively for detection of curl, which results in an increase in the cost of the image forming apparatus. Also, it is necessary to make a space for the sensor in the image forming apparatus, which results in an increase in the size of the image forming apparatus.
It is an object of the present invention to provide an image forming apparatus capable of detecting curl of a sheet at low cost without causing an increase in the size of the image forming apparatus.
According to an aspect of the present invention, an image forming apparatus comprises: an image forming section configured to form a toner image on a sheet; a fixing section configured to fix the toner image formed by the image forming section on the sheet and to feed the sheet out therefrom; and a sensor section configured to read the toner image on the sheet fed from the fixing section.
The sensor section includes: a sheet path configured to lead the sheet fed from the fixing section to pass in a predetermined sheet feeding direction; a light source unit configured to emit light toward an irradiation area preliminarily set in the sheet path, the light being elongated in a main-scanning direction different from the sheet feeding direction and having quantities of light varying according to positions in the main-scanning direction and according to positions in a height direction perpendicular to a sheet feed surface; and a light-receiving section configured to receive light diffused in a predetermined diffusing direction different from the sheet feeding direction and the main-scanning direction among the light emitted from the light source and then irradiated to the sheet passing in the sheet path, and to output information representing quantities of the received light.
The image forming apparatus further comprises: a control section configured to extract a predetermined parameter from the information output from the light-receiving section and to derive an amount of curl of the sheet passing in the sheet path.
An image forming apparatus according to an embodiment of the present invention will be hereinafter described with reference to the drawings.
First, the X-axis, Y-axis and Z-axis drawn in
Structure and Operation of the Image Forming Apparatus
In
The sheet feed section 2 picks up one sheet from a stack of sheets stored therein and feeds the sheet into a sheet path FP drawn by the broken line.
Image data representing an arbitrary image to be printed are sent to the image processing section 3 from a personal computer connected to the image forming apparatus 1. In the image data sent to the image processing section 3, each pixel value, for example, includes values of R (red), G (green) and B (blue). The image processing section 3 is, for example, a gate array, and the image processing section 3, for example, converts each pixel value into values of Y (yellow), M (magenta), C (cyan) and Bk (black) to be used by the image forming section 4. In this way, the image processing section 3 generates image data with respect to each of the colors of Y, M, C and Bk. The image processing section 3 sends the generated image data with respect to each of the colors to the image forming section 4. The image processing section 3 may carry out the above-described color conversion by using software.
The image forming section 4, as well known, comprises charging sections, photoreceptor drums and developing devices for the respective colors Y, M, C and Bk, and further comprises an exposure device, an intermediate belt and a secondary transfer area. In the image forming section 4, the charging sections uniformly charge the peripheral surfaces of the corresponding photoreceptor drums while the photoreceptor drums are rotating. On receiving image data of Y, M, C and Bk from the image processing section 3, the exposure device generates light beams for the respective colors based on the image data. The exposure device radiates the light beams for the respective colors to the peripheral surfaces of the corresponding photoreceptor drums, so that electrostatic latent images for the respective colors of the arbitrary image are formed on the peripheral surfaces of the corresponding photoreceptor drums.
The developing devices for the respective colors supply toner to the electrostatic latent images formed on the peripheral surfaces of the corresponding photoreceptor drums while the photoreceptor drums are rotating. Thereby, toner images in accordance with image data of the colors Y, M, C and Bk resolved from the arbitrary image are formed on the respective photoreceptor drums.
The toner images in the respective colors are transferred from the photoreceptor drums to the same area of the intermediate transfer belt while the intermediate transfer belt is rotating. Thereby, a composite toner image representing the arbitrary image in full color is formed on the intermediate transfer belt, and the composite toner image is carried to the secondary transfer area by the intermediate transfer belt.
Meanwhile, the sheet Sh fed from the sheet feed section 2 is conveyed in the sheet path FP to the secondary transfer area in the image forming section 4. In the secondary transfer area, the composite toner image is transferred from the intermediate transfer belt to the sheet Sh (secondary transfer). After the secondary transfer, the sheet Sh is fed toward the fixing section 5 as a sheet with an unfixed image.
The fixing section 5 comprises two rotating bodies forming a fixing nip portion. In the fixing section 5, the sheet Sh having an unfixed image is fed into the fixing nip portion, and heated and pressed by the two rotating bodies. Through this fixing step, the unfixed composite image on the sheet Sh is fixed to the sheet Sh. After the fixing step, the sheet Sh is fed as an ordinary sheet Sh with the arbitrary image printed thereon from the fixing section 5 to a curl correcting section 6 located downstream in the sheet path FP.
Any one of various conventional curl removing devices (which are also referred to as decurlers) can be used as the curl correcting section 6 as long as it is capable of correcting the curl or bend of the sheet Sh while the sheet Sh is being fed. In this embodiment, the curl correcting section 6, for example, comprises a first, a second and a third cylindrical roller. These rollers extend in a direction perpendicular to the sheet path FP. The first and the third rollers are located respectively the most upstream and the most downstream along the sheet path among the three rollers. The second roller is located between the first and third rollers and contacts with the first roller and the third roller to form two nip portions. The curl correcting section 6 nips the sheet Sh fed from the fixing section 5 in the two nip portions to correct the curl or bend of the sheet Sh, and feeds the curl/bend-corrected sheet Sh toward the sensor section 7 located downstream in the sheet path FP. Each of the first through third rollers has an elastic surface layer. The curl correcting section 6 adjusts the strength of the force to correct the curl by changing the position of the second roller relative to the first and third rollers.
The sensor section 7 is provided mainly to carry out an image quality test. The image quality test is carried out at a time when the above-described printing is not carried out. The image quality test is carried out, for example, in the following way. The image forming section 4 and the fixing device 5 form a predetermined test chart image (that is, a pattern image) on a sheet Sh to make a test sheet Sh. The sensor section 7 irradiates the test sheet Sh fed thereto with first light having substantially constant quantities of light regardless of positions in the main-scanning direction. The sensor section 7 further receives a part of light diffused from the test sheet Sh and performs photoelectric conversion to generate analog information (which will be hereinafter referred to as first analog information) representing the colors of the toner image on the sheet Sh with RGB values, density values, or the like. Then, the sensor section 7 outputs the first analog information to the signal processing circuit 8.
The sensor section 7 is also used for detection of curl during a printing operation. Thus, the sensor section 7 is a multipurpose section. During a printing operation, ordinary sheets Sh with toner images (arbitrary images) printed thereon are fed to the sensor section 7 sequentially. As will be described in more detail later, the sensor section 7 irradiates each of the ordinary sheets Sh fed thereto with second light having quantities of light varying according to positions in the main-scanning direction. The second light directed to the sheet Sh is reflected by the sheet Sh and diffused in various directions. The sensor section 7 receives a part of the light diffused from the sheet Sh and performs photoelectric conversion to generate analog information (which will be hereinafter referred to as second analog information) indicating the quantities of received light relevant to positions in the main-scanning direction. Then, the sensor section 7 outputs the second analog information to the signal processing circuit 8.
Thereafter, the sensor section 7 feeds the sheet Sh downstream in the sheet path FP. The sheet Sh is finally ejected on a printed-sheet tray (not drawn).
The signal processing circuit 8 is, for example, implemented by a gate array or a software. At the time of image quality test, the signal processing circuit 8 converts the first analog information sent from the sensor section 7 into first digital information and outputs the first digital information to the control circuit 9. During a printing operation, on the other hand, the signal processing circuit 8 operates for detection of the amount of curl, and specifically, the signal processing circuit 8 converts the second analog information sent from the sensor section 7 into second digital information and outputs the second digital information to the control circuit 9.
The control circuit 9 includes a microcomputer, a main memory, a non-volatile memory, etc. The control circuit 9 controls the above-described printing process by operating in accordance with a program stored in the non-volatile memory.
At the time of image quality test, the control circuit 9 carries out image quality stabilization control and the like based on the first digital information received from the signal processing circuit 8. During a printing operation, on the other hand, the control circuit 9 detects the amount of curl of the sheet Sh based on the second digital information sent from the signal processing circuit 8 and carries out feedback control of the curl correcting section 6 based on the detected amount of curl. The detection of the amount of curl and the feedback control will be described later.
Next, referring to
The guide 71 is a member to define a part of the sheet path FP downstream from the fixing section 5 and the curl correcting section 6. A sheet Sh is fed from the curl correcting section 6 to the guide 71 (see
In the part of the sheet path FP defined by the guide 71, an irradiation area P0 is preliminarily set. As understood from
Referring to
Referring to
In the light source unit 73, as drawn in
Again referring to
The light-receiving section 77 is an inline sensor having photoelectric conversion elements linearly arranged in the main-scanning direction, for example, a CCD (charge coupled device). Exemplary specifications of the light-receiving section 77 are as indicated in
Length in the main-scanning direction: 310 [mm]
Reading resolution: 600 [dpi]
Number of pixels: 1024 pixels per unit detection area
Unit detection width UW: approximately 43 [mm] in the main-scanning direction
The unit detection width UW means a width (size in the main-scanning direction) of a portion for which data, out of the data obtained by one-time scanning, is used for detection of curl. For example, for detection of curl in both end portions of a sheet, data for both end portions, each having the unit detection width UW (i.e., 1024 pixels), are used.
During the image quality test, at every scanning cycle, the light-receiving section 77 generates the first analog information representing the colors of a main-scanning line of the test sheet Sh passing through the guide 71 and outputs the first analog information to the signal processing circuit 8. During the detection of curl, at every scanning cycle, the light-receiving section 77 generates the second analog information representing quantities of received light for a main-scanning line of the sheet Sh passing through the guide 71 and outputs the second analog information to the signal processing circuit 8. The light-receiving section 77 may be a monochromatic sensor or alternatively a color sensor, for example, an RGB sensor. When an RGB color sensor is used as the light-receiving section 55, the density values with respect to the colors R, G and B may be converted into density values with respect to the colors Y, M C and Bk by the subsequent signal processing circuit 8 or the like.
Next, the principle of detection of curl is described. In the sensor section 7, the sheet Sh passes through the sheet feed surface of the guide 71 as drawn by
The light L2 passing through the slit board 75 is diffused at the irradiation area P0, and only the main diffused light L4 travels in the Z-direction. The light L4 enters the focusing optical system 76 and is focused on the light-receiving section 77. Then, as drawn in the middle section of
Next, a case where the sheet Sh passing through the sensor section 7 is curled is described. In this case, the curled portion of the sheet Sh is not parallel to the XY plane and passes above the irradiation area P0. As drawn by the uppermost section of
The light L2 passing through the slit board 75 is diffused at the curled portion and is focused on the light-receiving section 77 through the focusing optical system 76. The light-receiving section 77 carries out photoelectric conversion of the light L4 to generate analog information. In this moment, as drawn by the middle section of
When the amount of curl Ac is defined as a distance in the Z-direction between the irradiation area P0 and the sheet Sh, the amount of curl Ac is substantially proportional to the amount Δ. Accordingly, the amount of curl Ac is calculated as follows.
Ac=α×Δ (1)
In the expression (1), α is a proportional constant and is determined from the specifications of the sensor section 7. Accordingly, α is a known value, which is, for example, a value calculated before the shipment of the image forming apparatus 1 from the factory. The value Δ is a difference between the sections SS1 through SSi and the corresponding sections FS1 through FSi.
The positions in the main-scanning direction where peak quantity values of received light appear in the respective sections SS1 through SSi are referred to as YSS1 through YSSi respectively, and the positions in the main-scanning direction where peak quantity values of received light appear in the respective sections FS1 through FSi are referred to as YFS1 through YFSi respectively. Then, the value Δ is calculated by YSSj−YFSj (j is a natural number not less than one and not more than i). Accordingly, the expression above (1) can be rewritten as follows.
Ac=α×(YSSj−YFSj) (2)
The value YFSj is a value determined based on Z1, and accordingly, the value YFSj is a known value, which is, for example, a value calculated before the shipment of the image forming apparatus 1 from the factory. The YSSj is a value depending on the state of the sheet Sh, and accordingly, the YSSj is an unknown value. Thus, by detecting the position YSSj in the main-scanning direction with regard to the sheet Sh passing through the guide 71, the amount of curl Ac of the sheet Sh can be derived.
Next, referring to
While the sheet Sh is passing through the guide 71, at every scanning cycle, the light-receiving section 77 outputs the second analog information, and the signal processing circuit 8 converts the second analog information into second digital information and outputs the second digital information to the control circuit 9 (S02 in
On receiving the second digital information, the control circuit 9 carries out parameter extraction from the received-light quantity values with respect to a portion with the unit detection width UW (S03 in
In the following, the parameter extraction is described with reference to
In the graph in the upper left part of
The control circuit 9 carries out Fourier transform of the received-light quantity values for a portion with the unit detection width UW. The Fourier transform is, for example, FFT (fast Fourier transform). As a result of the Fourier transform, as represented by the graph in the upper middle part of
The graphs in the lower left part through the lower right part of
Next, the control circuit 9 substitutes the position YSSj extracted at step S03 in the expression (2) to derive the amount of curl Ac (S04 in
Next, the control circuit 9 determines whether or not the sheet Sh currently passing through the sensor section 7 is curled, based on the amount of curl Ac derived at step S04 (S05 in
On the other hand, if the control circuit 9 determines that curl occurs, the control circuit 9 sends the derived amount of curl Ac to the curl correcting section 6 and controls the curl correcting section 6 so as to perform curl correction on the sheet fed thereto (S06 in
As mentioned above, the image forming apparatus 1 carries out image quality stabilization control and the like at a time other than printing operation. For this purpose, the sensor section 7 is provided in the image forming apparatus 1, in the vicinity of the sheet path FP, downstream from the fixing section 5. Also, the image forming apparatus 1 derives an amount of curl of sheets during a printing operation by making efficient use of the sensor section 7 in the above-described way. Thus, in the image forming apparatus 1, the sensor section 7 is used for more than one purpose, namely, for image quality stabilization control and for derivation of curl of sheets. Accordingly, it is no longer necessary to provide a two-dimensional area sensor or the like in the image forming apparatus 1 only for the purpose of deriving an amount of curl of sheets. Thus, it is possible to derive an amount of curl of sheets at low cost without causing an increase in the size of the image forming apparatus 1.
In the embodiment above, the sensor section 7 includes a first light source 72 used for image quality tests, and a second light source 74 used for detection of curl. However, the first and second light sources 72 and 74 may be replaced with only one light source 72A. In this case, a part of light emitted from the light source 72A that passes through the slits SL is used for detection of curl, and a part of light emitted from the light source 72A that passes under the slit board 75 is used for image quality tests.
In the embodiment above, the light source unit 73 comprises the slit board 75. However, the light source unit 73 may comprise a slit board 75A according to a first modification instead of the slit board 75. In the following, the slit board 75A is described with reference to
When viewed from the sheet feeding direction, as drawn in the frame A of
With these slits SL1 through SLi, as drawn in
In this regard, before the shipment of the image forming apparatus 1 from the factory, the amounts of curl Ac relative to positions (more specifically, positions on the spatial frequency axis) of peak values VP are collected from an experiment or the like. Based on the collected data, a table representing the amounts of curl Ac relative to positions of peak values VP is prepared and stored in the control circuit 9. The control circuit 9 reads the amount of curl Ac matching the obtained position of the peak value VP from the table.
In the embodiment above, the light quantity values included in the analog information output from the sensor section 77 are also affected by the toner image formed on the sheet Sh and other factors. Therefore, the light quantity values do not always vary cyclically according to positions in the main-scanning direction and have high-frequency components (see, for example, the graphs in the upper left part and the upper middle part of
In the first modification, on the other hand, the amount of curl Ac is derived from the position of the peak value VP on the spatial frequency axis, and it is possible to significantly diminish the effect of the high-frequency components included in the analog information on the detection of curl.
Further, the light source unit 73 may comprise a slit board 75B according to a second modification instead of the slit board 75. In the following, the slit board 75B is described with reference to
When viewed from the sheet feeding direction, the lower side of the slit board 75B is saw-toothed, and specifically, notches N1 through Ni is an integer equal to or more than one) are arranged continuously in the main-scanning direction. In this modification, the width (size in the main-scanning direction) of each of the notches N1 through Ni decreases with progress in the positive diffusing direction. Each of the notches N1 through Ni has a symmetrical shape with respect to the center in the main-scanning direction.
The slit board 75B is positioned as drawn in
(1) A non-curled sheet Sh0 is irradiated at the irradiation area P0 with a part of the light L2 emitted from the light source 74 that passes under the slit board 75B (for example, passing through the position Z0 in the Z-direction).
(2) A slightly-curled sheet Sh1 is irradiated at a position above the irradiation area P0 with a part of the light L2 emitted from the light source 74 that passes through a relatively lower portion of the notches N1 through Ni (for example, passing through the position Z1 in the Z-direction).
(3) A greatly-curled sheet Sh2 is irradiated at a position above the irradiation area P0 with a part of the light L2 emitted from the light source 74 that passes through a relatively upper portion of the notches N1 through Ni (for example, passing through the position Z2 in the Z-direction).
Because of the slit board 75B positioned above, as drawn in the upper part of
The control circuit 9 carries out parameter extraction on the second analog information in the following manner. Specifically, the control circuit 9 carries out Fourier transform of the received-light quantity values with respect to a portion with the unit detection width UW, thereby obtaining power spectrum, as illustrated in
In the embodiment above, the image forming apparatus 1 comprises the light source unit 73. However, the image forming apparatus 1 may comprise a light source unit 73A according to a third modification instead of the light source unit 73. In the following, the light source unit 73A is described with reference to
As illustrated in
The second light source 74A is, for example, an LED array including LEDs linearly arranged in the main-scanning direction. Under the control of the control circuit 9, the second light source 74A, at the time of detection of curl, generates and emits a second linear beam of light L2 of which quantities of light on the irradiation area P0 vary cyclically according to positions in the main-scanning direction and of which quantities of light on different positions in the height direction (the Z-direction) are different. An exemplary way of generating the linear beam of light L2 is as follows. As illustrated in
The light source 74A can be used not only for detection of curl but also for image quality tests. For an image quality test, the control circuit 9 makes all of the LEDs to emit light so that the second light source 74A can emit light similar to the first linear beam of light L1. In this structure, it is possible to omit the first light source 72, and it becomes possible to further reduce the cost and the size of the image forming apparatus 1.
For an image quality test of a toner image formed on a sheet Sh by use of the sensor section 7, it is desired that the sheet Sh is positioned on the guide 71 as in parallel as possible to the XY plane. To this end, as illustrated in
By making the sheet Sh pass between the rollers 791 and the guide 71 and between the roller 792 and the guide 71, it is possible to position the sheet Sh substantially in parallel to the XY plane at least in the irradiation area P0, thereby allowing an accurate image quality test. In this regard, however, for accurate detection of sheet curl, one of the rollers 791 and 792 is retracted upward from the guide 71 during a printing operation.
For accurate detection of curl, it is preferred that the peak light quantity values included in the second analog information are large. An exemplary way of obtaining large peak light quantity values is setting the incident angle of the second linear beam of light L2 to the irradiation area P0 as close as possible to zero. Specifically, as illustrated in
Although the present invention has been described in connection with the preferred embodiments, it is to be noted that various changes and modifications are apparent to persons skilled in the art. Such changes and modifications are to be understood as being within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-171992 | Aug 2013 | JP | national |
