Patent Application
20210018869
The present invention relates to image forming apparatuses such as multifunction machines and printers, and relates particularly to a technique for detecting an image failure.
US-2019-171153 discloses an image forming apparatus in which an image is formed on a sheet, the sheet is then conveyed to a circulative conveyance path, and an image failure is detected by reading a surface of the sheet in the circulative conveyance path. US-2009-003857 discloses an image forming apparatus that has a determination unit for determining the type of sheet.
In an image forming apparatus, an image failure called fog may occur. “Fog” refers to a phenomenon in which a substantially uniform concentration of toner is attached to an entire sheet. Fog may occur if development conditions are not appropriate during development using toner. To detect the occurrence of fog, the base color of a sheet before printing needs to be compared with the color in a non-image area (margin area) of this sheet after printing. Accordingly, to detect fog in the configuration described in US-2019-171153, it is necessary to convey a sheet to the circulative conveyance path and read the base color of the sheet before the sheet is printed, resulting in an increased print time.
According to an aspect of the present invention, an image forming apparatus includes: an image forming unit configured to form an image on a sheet; a detection unit configured to detect a characteristic value of the sheet; a reading unit configured to optically read the sheet; and a control unit configured to perform determination processing for determining whether or not an image failure has occurred, by comparing a determination value acquired by causing the reading unit to read a non-image area of the sheet after an image has been formed on the sheet, with a reference determination value that is based on the characteristic value detected by the detection unit.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but limitation is not made an invention that requires all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted.
A light source 221 of the photodetection unit 22 emits light toward the sheet. A rod lens 222 guides reflected light, i.e. light reflected off the sheet surface, toward a light receiving unit 223. The light receiving unit 223 outputs an electrical signal corresponding to the intensity (or amount) of the received reflected light to the control unit 90. The control unit 90 can acquire a characteristic value related to the brightness and the lightness of the sheet, as well as the roughness of the sheet surface, based on the average value and the amount of change in this electrical signal. Note that a glass plate 224 is provided to prevent the sheet from coming into contact with the light source 221 and the rod lens 222. A roller 225 is provided such that the sheet surface is not distant from the light source 221 and rod lens 222 by a predetermined distance or more. Note that a configuration may be employed in which a plurality of light receiving units 223 is provided in the sheet conveyance direction and a direction perpendicular to the conveyance direction. By arranging the light receiving units 223 in a two-dimensional plane, the control unit 90 can acquire a characteristic value related to two-dimensional roughness of the surface of the sheet.
The conversion table in
Note that, when either one of the photodetection unit 22 and the ultrasonic detection unit 21 is used, the conversion table is created in accordance with the characteristic value that can be obtained by the detection unit to be used. The characteristic values to be used are not limited to those shown in
After the reference determination value has been acquired in step S11, an image is formed on the sheet by the image forming unit 31, and the image is fixed to the sheet by the fixing unit 33. Upon the sheet reaching a position at which the reading unit 40 reads the sheet, the control unit 90 causes the reading unit 40 to read a non-image area of the sheet, i.e. an area (margin area) of the sheet to which toner has not been transferred. Then, in step S12, the control unit 90 acquires the result of reading the non-image area of the sheet from the reading unit 40. The reading result is image information regarding the non-image area. The control unit 90 obtains the whiteness of the non-image area based on the brightness indicated by the image information, and uses the obtained whiteness as a determination value. Note that the method of obtaining the whiteness based on the brightness is preset to the control unit 90. In step S13, the control unit 90 obtains a difference between the reference determination value and the determination value.
In step S14, the control unit 90 determines whether or not the difference is greater than a first threshold. If the difference is smaller than or equal to the first threshold, the non-image area of the printed sheet is close to the reference determination value, and it can be determined that no toner is attached to the non-image area, or the amount of attached toner is in a permissible range even if the toner is attached. Accordingly, if the difference is smaller than or equal to the first threshold, the control unit 90 ends processing in
The fault notification can be given by displaying the notification on a display unit (not shown) of the image forming apparatus 1, outputting a warning sound or voice from a speaker (not shown), or transmitting a message to a predetermined device via a network. The image forming apparatus 1 may also perform detailed fault diagnosis on the development unit along with or instead of giving the fault notification. Note that the content of the fault diagnosis is determined and set to the control unit 90 in advance. In
As described above, in this embodiment, a sheet does not need to be read by the reading unit 40 before printing, and the print time for the sheet can be restrained from lengthening for image failure detection.
Note that, in this embodiment, the determination unit 20 detects characteristic values of a sheet before an image is formed on the sheet. However, in the case of using ultrasound, a configuration may be employed in which a characteristic value of a sheet is detected after an image has been formed on the sheet. In step S14 in the flowchart in
Next, the second embodiment will be described, mainly regarding differences from the first embodiment.
The image forming apparatus 1 according to this embodiment has a circulative conveyance path 82 for forming an image on both faces of a sheet. In the case of forming an image on only one face of a sheet, after a toner image has been fixed, the sheet is discharged to the tray 52 by the discharge roller 51. Note that, at this time, a flapper 62 is set in a direction in which the flapper 62 guides the sheet toward the discharge roller 51. On the other hand, in the case of forming images on both faces of a sheet, after a toner image transferred to one face has been fixed, the sheet is conveyed toward an inverting roller 61. Note that, at this time, a flapper 62 is set in a direction in which the flapper 62 guides the sheet toward the inverting roller 61. Upon a trailing end of the sheet passing over a branch position toward the circulative conveyance path 82, the inverting roller 61 is rotated in a direction opposite to the direction in which the sheet has been conveyed thus far. Thus, the sheet is conveyed toward the circulative conveyance path 82. Note that, at this time, the flapper 62 is set in a direction in which the flapper 62 guides the sheet toward the circulative conveyance path 82. Then, the sheet is conveyed again to an image forming position, i.e., a position opposing the transfer roller 32 by the rollers 47, 71, and 13, and a toner image is transferred to the other face of the sheet. In this embodiment as well, sensors 81a, 81b, and 81c for detecting a sheet are provided along the conveyance path. In this embodiment, the reading unit 40 is provided in the circulative conveyance path 82. Note that the configuration for conveying a sheet toward the circulative conveyance path 82 is not limited to the configuration in
If the first difference is smaller than or equal to the third threshold, in step S23, the control unit 90 forms an image on the sheet. Then, the control unit 90 conveys the sheet to the circulative conveyance path 82. In step S24, the control unit 90 reads the non-image area of the sheet and acquires a determination value. In step S25, the control unit 90 obtains a second difference between a determination value and the reference determination value held by the control unit 90. Note that, in this embodiment, the determination value and the reference determination value are values that indicate the brightness of the base of the sheet. However, the determination value and the reference determination value may also indicate whiteness, similarly to the first embodiment. Furthermore, the determination value and the reference determination value may alternatively be color values of any color space, or may indicate brightness. Although the details will be described later, the reference determination value represents the lightness of the base of the sheet from which the reference characteristic value has been acquired. Accordingly, the reference determination value is updated when the reference characteristic value is updated. Note that, to determine a fog color, in step S24, the control unit 90 also reads a color value of the non-image area of the sheet, as will be described later. When updating the reference characteristic value, the control unit 90 stores, as a reference color value, a base color value of the sheet from which the reference characteristic value has been acquired.
In step S26, the control unit 90 determines whether or not the second difference is greater than the first threshold. If the second difference is smaller than or equal to the first threshold, the determination value of the non-image area of the printed sheet is close to the reference determination value, and it can be determined that no toner is attached to the non-image area, or the amount of attached toner is in a permissible range even if toner is attached thereto. Accordingly, if the second difference is smaller than or equal to the first threshold, the control unit 90 ends processing in
On the other hand, if, in step S22, the first difference is greater than the third threshold, in step S31, the control unit 90 performs processing to update the reference characteristic value, the reference determination value, and the reference color value. In this case, the control unit 90 sets the characteristic value detected in step S20 as the reference characteristic value. Also, the control unit 90 conveys the sheet toward the circulative conveyance path 82 without forming an image on the sheet. Note that, to prevent the toner from being attached to the sheet, the control unit 90 sets the developing roller 314 in the separate state. The reading unit 40 reads the lightness and the color value of the surface (base) of the sheet that is being conveyed through the circulative conveyance path 82. The control unit 90 then sets the read lightness of the sheet as the reference determination value. The control unit 90 also sets the read color value of the sheet as the reference color value. After performing the updating processing, the control unit 90 conveys the sheet again to the position opposing the determination unit 20 and performs determination processing. Note that when the sheet is conveyed again to the position opposing the determination unit 20 as a result of being conveyed through the circulative conveyance path 82, the face from which the determination unit 20 acquires the characteristic of the sheet is opposite to the face from which the determination unit 20 has first acquired the characteristic of the sheet. Accordingly, after the sheet has been read by the reading unit 40, the control unit 90 conveys the sheet again toward the circulative conveyance path 82 without forming an image on the sheet. Then, the control unit 90 repeats the processing from step S20. Note that a configuration may be employed in which, if there is a not significant difference in color and characteristics between the two sides of the sheets, processing in step S20 is started as-is after the base color of the sheet has been read by the reading unit 40.
The image forming apparatus 1 according to this embodiment has only one cassette 11 for storing sheets. However, image forming apparatuses 1 are commonly used that have a plurality of cassettes 11 and selectively feed sheets from the plurality of cassettes 11. Usually, different types of sheets are contained in respective cassettes 11. In this case, the control unit 90 manages the reference characteristic value, and the reference determination value and the reference color value that are associated with the reference characteristic value, for each of the cassettes 11. If the characteristic value of the sheet on which an image is to be formed significantly changes from the reference characteristic value of the cassette 11 in which the sheet has been stored by the third threshold or more, the control unit 90 updates the reference characteristic value, the reference determination value, and the reference color value of this cassette 11. Fog detection is also performed based on the reference determination value of the cassette 11 from which the sheet has been fed.
Note that a configuration may also be employed in which the reference characteristic value, the reference determination value, and the reference color value are updated not only when the first difference is greater than the third threshold, but also when any of the development units is replaced or fixed, or every time a predetermined number of sheets are printed.
As described above, in this embodiment, fog determination is performed while dynamically updating the reference determination value, and thus, fog detection accuracy can be increased. However, the reference determination value is acquired only when a predetermined condition is met, e.g. when the characteristic value has significantly changed by the third threshold or more. Therefore, the time required for printing can be prevented from lengthening as a whole.
Note that, although the above embodiment has given a description while taking fog detection as an example, the present invention is applicable to any image failure that can be detected by comparing the base color of a sheet before printing and the color of the non-image area of the printed sheet. In this embodiment, the reading unit 40 reads the surface of the sheet that is being conveyed through the conveyance path between the fixing unit 33 and the discharge port for discharging the sheet from the image forming apparatus. However, in the case of an image forming apparatus that has a circulative conveyance path 82, as in the case of the image forming apparatus in the second embodiment, the reading unit 40 in the first embodiment can also be provided in the circulative conveyance path 82.
A configuration can also be employed in which the user makes a setting as to whether or not to perform image failure determination processed (
Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2019-134014, filed on Jul. 19, 2019 and Japanese Patent Application No. 2019-226807, filed on Dec. 16, 2019, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-134014 | Jul 2019 | JP | national |
| 2019-226807 | Dec 2019 | JP | national |
