Image forming apparatus, detection method

Abstract

To provide an image forming apparatus and a detection method capable of detecting the operation of a protection circuit without complicating its configuration. [Solution] The image forming apparatus 100 includes a charging roller that charges the photoreceptor drum 31 in response to the application of a charging voltage, a protection circuit 50 that stops the operation of the voltage generation circuit 40 that generates the charging voltage when the current flowing through the charging roller exceeds a threshold, a sensor 61 used to detect the density of the toner image formed by the developing apparatus, and a second detection processing unit 74 that uses the sensor 61 to detect the operation of the protection circuit 50.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and a detection method.

Background Art

[0002] An image forming apparatus capable of forming an image on a sheet by an electrophotographic method includes a charging unit such as a charging roller that charges an image carrier such as a photoreceptor drum. The charging unit charges the image carrier in response to the application of a charging voltage generated by a voltage generation circuit (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the image forming apparatus, due to noise mixed in a control signal used for controlling the voltage generation circuit and a failure of the voltage generation circuit, an excessive charging voltage may be output from the voltage generation circuit.

[0005] In contrast, by providing a protection circuit that stops the operation of the voltage generation circuit when the current flowing through the charging unit exceeds a predetermined threshold value, it is possible to suppress the output of an excessive charging voltage from the voltage generation circuit. Further, by notifying the user to that effect when the protection circuit operates, it is possible to prompt the user to remove the cause of the abnormal operation of the voltage generation circuit.

[0006] Here, when providing a dedicated sensor or the like for detecting that the protection circuit has operated, the configuration of the image forming apparatus becomes more complicated by that much.

[0007] The object of the present invention is to provide an image forming apparatus and a detection method that can detect the operation of a protection circuit without complicating its configuration. [Means for solving the problem]

[0008] An image forming apparatus according to one aspect of the present invention comprises an image carrier, a charging unit, a developing unit, a voltage generation circuit, a protection circuit, a sensor, and a detection processing unit. The image carrier carries a toner image. The charging unit charges the image carrier to a corresponding potential in response to the application of a predetermined charging voltage. The developing unit deposits toner onto a region of the image carrier whose surface potential is lower than the corresponding potential. The voltage generation circuit generates the charging voltage. The protection circuit stops the operation of the voltage generation circuit when the current flowing through the charging unit exceeds a predetermined threshold. The sensor is used to detect the density of the toner image formed by the developing unit. The detection processing unit uses the sensor to detect the operation of the protection circuit.

[0009] A detection method according to another aspect of the present invention is performed using an image forming apparatus comprising: an image carrier that carries a toner image; a charging unit that charges the image carrier to a corresponding potential corresponding to the charging voltage in response to the application of a predetermined charging voltage; a developing unit that deposits toner on a region of the image carrier whose surface potential is lower than the corresponding potential; a voltage generation circuit that generates the charging voltage; a protection circuit that stops the operation of the voltage generation circuit when the current flowing through the charging unit exceeds a predetermined threshold; and a sensor used to detect the density of the toner image formed by the developing unit. In this detection method, the sensor is used to detect the operation of the protection circuit. [Effects of the Invention]

[0010] According to the present invention, the operation of a protection circuit can be detected without complicating the configuration. [Brief explanation of the drawing]

[0011] [Figure 1]Figure 1 is a cross-sectional view showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] Figure 2 is a block diagram showing the system configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 3] Figure 3 is a cross-sectional view showing the configuration of the image forming section of an image forming apparatus according to an embodiment of the present invention. [Figure 4] Figure 4 is a bottom view showing the configuration of the intermediate transfer belt in an image forming apparatus according to an embodiment of the present invention. [Figure 5] Figure 5 shows a specific toner image formed on the intermediate transfer belt of an image forming apparatus according to an embodiment of the present invention. [Figure 6] Figure 6 is a flowchart showing an example of an operation detection process performed in an image forming apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described below with reference to the attached drawings. Note that the following embodiments are merely examples of the present invention and do not limit the technical scope of the present invention.

[0013] [Configuration of the image forming apparatus 100] First, the configuration of the image forming apparatus 100 according to an embodiment of the present invention will be described with reference to Figures 1 and 2.

[0014] For the sake of explanation, the vertical direction is defined as the up-down direction D1 when the image forming apparatus 100 is in a usable installation state (as shown in Figure 1). The front-to-back direction D2 is defined with the left side of the image forming apparatus 100 shown in Figure 1 as the front. The left-to-right direction D3 is defined with the front of the image forming apparatus 100 in the aforementioned installation state as the reference point.

[0015] The image forming apparatus 100 is a multifunction device having a plurality of functions such as a fax function and a copy function, in addition to a scan function for reading an image of a document and a print function for forming an image based on image data. Note that the present invention may be applied to image forming apparatuses such as printers, fax machines, and copy machines that can form images by an electrophotographic method.

[0016] As shown in FIGS. 1 and 2, the image forming apparatus 100 includes an ADF (Auto Document Feeder) 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, an operation display unit 5, a storage unit 6, and a control unit 7.

[0017] The ADF 1 conveys the document to be read by the scan function. The ADF 1 includes a document set unit, a plurality of conveyance rollers, a document holder, and a paper discharge unit.

[0018] The image reading unit 2 realizes the scan function. The image reading unit 2 includes a document table, a light source, a plurality of mirrors, an optical lens, and a CCD (Charge Coupled Device).

[0019] The image forming unit 3 realizes the print function. Specifically, the image forming unit 3 forms a color or monochrome image on a sheet supplied from the paper feeding unit 4 according to the electrophotographic method.

[0020] The paper feeding unit 4 supplies a sheet to the image forming unit 3. The paper feeding unit 4 includes a paper feeding cassette, a manual feed tray, and a plurality of conveyance rollers.

[0021] The operation display unit 5 is a user interface of the image forming apparatus 100. The operation display unit 5 has a display unit such as a liquid crystal display that displays various information in response to a control instruction from the control unit 7, and an operation unit such as an operation key or a touch panel that inputs various information to the control unit 7 in response to a user's operation.

[0022] The storage unit 6 is a non-volatile storage device. For example, the storage unit 6 is a non-volatile memory such as flash memory. The storage unit 6 may also be an SSD (Solid State Drive) or an HDD (Hard Disk Drive).

[0023] The control unit 7 comprehensively controls the image forming apparatus 100. As shown in Figure 2, the control unit 7 comprises a CPU 11, a ROM 12, and a RAM 13. The CPU 11 is a processor that performs various arithmetic operations. The ROM 12 is a non-volatile memory device in which information such as control programs for causing the CPU 11 to perform various operations is pre-stored. The RAM 13 is a volatile or non-volatile memory device used as temporary storage memory (work area) for the various operations performed by the CPU 11. The CPU 11 comprehensively controls the image forming apparatus 100 by executing various control programs pre-stored in the ROM 12.

[0024] Furthermore, the control unit 7 may be a separate control unit from the main control unit that comprehensively controls the image forming apparatus 100. Also, the control unit 7 may be composed of electronic circuits such as an integrated circuit (ASIC).

[0025] [Configuration of the image forming unit 3] Next, the configuration of the image forming unit 3 will be described with reference to Figures 1 to 4. Here, Figure 3 is a cross-sectional view showing the configuration of multiple image forming units 20, an intermediate transfer belt 26, and a secondary transfer roller 27. Figure 4 is a bottom view showing the configuration of the photoreceptor drum 31, intermediate transfer belt 26, drive roller 26A, and secondary transfer roller 27 of the image forming unit 24.

[0026] As shown in Figure 1, the image forming unit 3 comprises four image forming units 20, an optical scanning device 25, an intermediate transfer belt 26, a secondary transfer roller 27, a fixing device 28, and a paper output tray 29. Furthermore, as shown in Figure 2, the image forming unit 3 comprises four voltage generation circuits 40, four protection circuits 50, and a sensor 61.

[0027] Of the four image forming units 20, image forming unit 21 (see Figure 3) forms a yellow (Y) toner image. Of the four image forming units 20, image forming unit 22 (see Figure 3) forms a cyan (C) toner image. Of the four image forming units 20, image forming unit 23 (see Figure 3) forms a magenta (M) toner image. Of the four image forming units 20, image forming unit 24 (see Figure 3) forms a black (K) toner image. As shown in Figures 1 and 3, the four image forming units 20 are arranged in the order of yellow, cyan, magenta, and black from the front side of the image forming apparatus 100 along the front-to-back direction D2.

[0028] As shown in Figure 3, each image forming unit 20 includes a photoreceptor drum 31, a charging roller 32, a developing device 33, a primary transfer roller 34, and a drum cleaning unit 35. Each image forming unit 20 also includes a toner container 36 as shown in Figure 1.

[0029] The photoreceptor drum 31 carries a toner image. For example, the photoreceptor drum 31 has a photosensitive layer formed of amorphous silicon. The photoreceptor drum 31 rotates in the drum rotation direction D4 shown in Figure 3, receiving rotational driving force supplied from a motor (not shown). The photoreceptor drum 31 is an example of an image carrier of the present invention.

[0030] The charging roller 32 charges the photoreceptor drum 31 to a corresponding potential in response to the application of a predetermined charging voltage. For example, the charging roller 32 charges the surface of the photoreceptor drum 31 with positive polarity. The surface of the photoreceptor drum 31, which has been charged by the charging roller 32, is irradiated with light based on image data emitted from the optical scanning device 25. As a result, an electrostatic latent image is formed on the surface of the photoreceptor drum 31. The charging roller 32 is an example of a charging unit of the present invention.

[0031] The developing device 33 develops the electrostatic latent image formed on the surface of the photoreceptor drum 31. Specifically, the developing device 33 deposits toner onto the uncharged region of the photoreceptor drum 31, where the surface potential is lower than the corresponding potential. The uncharged region includes the area of ​​the photoreceptor drum 31 that has been irradiated with light emitted from the light scanning device 25. The uncharged region also includes the area of ​​the photoreceptor drum 31 that has not been charged by the charging roller 32. The developing device 33 is an example of the developing unit of the present invention.

[0032] For example, the developing device 33 comprises a pair of stirring members, a magnetic roller, and a developing roller. The pair of stirring members stir the developer containing toner and carrier housed inside the developing device 33. For example, the toner contained in the developer becomes positively charged by friction with the carrier contained in the developer. The magnetic roller pumps up the developer stirred by the pair of stirring members and supplies the toner contained in the developer to the developing roller. The developing roller transports the toner supplied from the magnetic roller to a position opposite the photoreceptor drum 31. The developing roller also supplies the toner transported to the opposite position to the photoreceptor drum 31 in response to the application of a predetermined developing bias voltage. As a result, toner is selectively supplied to the uncharged region of the photoreceptor drum 31, and the electrostatic latent image formed on the surface of the photoreceptor drum 31 is developed. The developing device 33 is supplied with toner from a toner container 36.

[0033] The photoreceptor drum 31 transports the toner image formed by the developing device 33 to the transfer position on the intermediate transfer belt 26 by the primary transfer roller 34.

[0034] The primary transfer roller 34 transfers the toner image formed on the surface of the photoreceptor drum 31 to the outer surface of the intermediate transfer belt 26 in accordance with the supply of a predetermined primary transfer current. As shown in Figure 3, the primary transfer roller 34 is positioned opposite the photoreceptor drum 31, with the intermediate transfer belt 26 in between.

[0035] The drum cleaning unit 35 removes toner remaining on the surface of the photoreceptor drum 31 after the toner image has been transferred by the primary transfer roller 34.

[0036] The optical scanning device 25 emits light based on image data toward the surface of the photosensitive drum 31 of each image forming unit 20.

[0037] The intermediate transfer belt 26 is an endless belt member onto which the toner images formed in each of the image forming units 20 are transferred. The intermediate transfer belt 26 is stretched at a predetermined tension by a drive roller 26A (see Figure 3) and a tension roller 26B (see Figure 3). The intermediate transfer belt 26 rotates in the belt rotation direction D5 shown in Figure 3, as the drive roller 26A rotates in response to rotational driving force supplied from a motor (not shown). As a result, the intermediate transfer belt 26 transports the toner images formed by the developing device 33 of each of the image forming units 20 to the transfer position to the sheet (an example of the transfer member of the present invention) by the secondary transfer roller 27. After the toner image has been transferred by the secondary transfer roller 27, the outer surface of the intermediate transfer belt 26 is cleaned by the belt cleaning unit 26C (see Figure 3). The intermediate transfer belt 26 is an example of a transport member of the present invention.

[0038] The secondary transfer roller 27 transfers the toner image transferred to the outer surface of the intermediate transfer belt 26 to the sheet supplied from the paper feeding unit 4, in accordance with the supply of a predetermined secondary transfer current. As shown in Figure 3, the secondary transfer roller 27 is provided opposite the drive roller 26A, with the intermediate transfer belt 26 in between.

[0039] As shown in Figure 4, the axial size (left-right direction D3) of the secondary transfer roller 27 is smaller than the width (size in the left-right direction D3) of the intermediate transfer belt 26. Therefore, a non-contact area A3 (see Figure 4) is created on the outer surface of the intermediate transfer belt 26 that does not come into contact with the secondary transfer roller 27. The non-contact area A3 is the area outside the contact area A2 (see Figure 4) that comes into contact with the secondary transfer roller 27 on the outer surface of the intermediate transfer belt 26, and includes the end of the intermediate transfer belt 26 in the width direction.

[0040] The fixing device 28 fixes the toner image transferred to the sheet by the secondary transfer roller 27 to the sheet.

[0041] The output tray 29 receives a sheet on which the toner image has been fixed by the fuser unit 28.

[0042] Of the four voltage generation circuits 40, voltage generation circuit 41 (see Figure 2) generates the charging voltage applied to the charging roller 32 of the image forming unit 21 (see Figure 3). Of the four voltage generation circuits 40, voltage generation circuit 42 (see Figure 2) generates the charging voltage applied to the charging roller 32 of the image forming unit 22 (see Figure 3). Of the four voltage generation circuits 40, voltage generation circuit 43 (see Figure 2) generates the charging voltage applied to the charging roller 32 of the image forming unit 23 (see Figure 3). Of the four voltage generation circuits 40, voltage generation circuit 44 (see Figure 2) generates the charging voltage applied to the charging roller 32 of the image forming unit 24 (see Figure 3). The operation of each voltage generation circuit 40 is controlled by the control unit 7.

[0043] In the image forming apparatus 100, excessive charging voltage may be output from the voltage generation circuit 40 due to noise mixed into the control signal used to control the voltage generation circuit 40, or due to a malfunction of the voltage generation circuit 40. To address this, the image forming apparatus 100 is provided with four protection circuits 50 (see Figure 2) corresponding to the four voltage generation circuits 40.

[0044] Of the four protection circuits 50, protection circuit 51 (see Figure 2) stops the operation of the voltage generation circuit 41 when the current flowing through the charging roller 32 of the image forming unit 21 (see Figure 3) exceeds a predetermined threshold. Of the four protection circuits 50, protection circuit 52 (see Figure 2) stops the operation of the voltage generation circuit 42 when the current flowing through the charging roller 32 of the image forming unit 22 (see Figure 3) exceeds the threshold. Also, of the four protection circuits 50, protection circuit 53 (see Figure 2) stops the operation of the voltage generation circuit 43 when the current flowing through the charging roller 32 of the image forming unit 23 (see Figure 3) exceeds the threshold. Also, of the four protection circuits 50, protection circuit 54 (see Figure 2) stops the operation of the voltage generation circuit 44 when the current flowing through the charging roller 32 of the image forming unit 24 (see Figure 3) exceeds the threshold.

[0045] By providing four protection circuits 50, it is possible to suppress the output of excessive charging voltage from each of the voltage generation circuits 40.

[0046] Furthermore, each of the protection circuits 50 restarts the operation of the voltage generation circuit 40 when a predetermined specific time has elapsed since the voltage generation circuit 40 stopped operating.

[0047] For example, each of the protection circuits 50 includes a current detection unit, a power supply stop unit, and a power supply restart unit. The current detection unit detects the current flowing through the charging roller 32. The power supply stop unit cuts off the power supply path between the power supply (not shown) that supplies power to the voltage generation circuit 40 and the voltage generation circuit 40 when the current detected by the current detection unit exceeds the threshold. The power supply restart unit restores the power supply path when the specified time has elapsed since the power supply was stopped by the power supply stop unit.

[0048] Sensor 61 is used to detect the density of the toner image formed by the developing device 33 of each image forming unit 20. Specifically, sensor 61 detects the toner density outside of a specific region A1 (see Figure 4) on the intermediate transfer belt 26 where the toner image to be transferred to the sheet is formed. Specific region A1 is the region inside the contact region A2 (see Figure 4) on the outer surface of the intermediate transfer belt 26. For example, specific region A1 is the contact region on the outer surface of the intermediate transfer belt 26 with the sheet supplied from the paper feeding unit 4. More specifically, sensor 61 detects the toner density in the non-contact region A3 (see Figure 4) on the intermediate transfer belt 26.

[0049] For example, the sensor 61 is a reflective photosensor comprising a light-emitting unit that emits light toward the non-contact area A3 of the intermediate transfer belt 26, and a light-receiving unit that receives the light emitted from the light-emitting unit and reflected by the non-contact area A3 of the intermediate transfer belt 26. As shown in Figure 3, the sensor 61 is positioned downstream in the belt rotation direction D5 from the toner image transfer position by the secondary transfer roller 27, and upstream in the belt rotation direction D5 from the cleaning position of the outer circumferential surface of the intermediate transfer belt 26 by the belt cleaning unit 26C. The sensor 61 inputs an electrical signal to the control unit 7 according to the toner density on the surface of the intermediate transfer belt 26. The sensor 61 may also be a CIS (Contact Image Sensor).

[0050] In the image forming apparatus 100, a sensor 61 is used to adjust the image forming conditions of the image forming unit 3. For example, the image forming conditions include the amount of light emitted by the optical scanning device 25 and the development bias voltage.

[0051] [Configuration of Control Unit 7] Next, the configuration of the control unit 7 will be described with reference to Figure 2.

[0052] As shown in Figure 2, the control unit 7 includes a transfer processing unit 71, a first detection processing unit 72, an adjustment processing unit 73, a second detection processing unit 74, and a notification processing unit 75.

[0053] Specifically, the ROM 12 of the control unit 7 contains pre-stored operation control programs that enable the CPU 11 to function as each of the aforementioned processing units. The CPU 11 then functions as each of the aforementioned processing units by executing the operation control programs stored in the ROM 12.

[0054] The operation control program may be recorded on a computer-readable recording medium such as a CD, DVD, or flash memory, and may be read from the recording medium and stored in a storage device such as the storage unit 6. Furthermore, the operation control program may be a program that causes multiple processors to function as the respective processing units described above. Also, some or all of the transfer processing unit 71, the first detection processing unit 72, the adjustment processing unit 73, the second detection processing unit 74, and the notification processing unit 75 may be composed of electronic circuits such as integrated circuits (ASICs).

[0055] The transfer processing unit 71 transfers multiple detection toner images X10 (see Figure 4) corresponding to multiple image forming units 20 to the outside of a specific region A1 (see Figure 4) in the intermediate transfer belt 26. In Figure 4, each of the detection toner images X10 is hatched.

[0056] Specifically, the transfer processing unit 71 transfers multiple detection toner images X10 (see Figure 4) to the non-contact area A3 (see Figure 4) on the outer surface of the intermediate transfer belt 26.

[0057] Of the multiple detection toner images X10, the detection toner image X11 (see Figure 4) corresponding to the image forming unit 21 is a yellow (Y) toner image formed in the image forming unit 21 based on image data including a predetermined first detection image. The first detection image is a monochrome image of yellow (Y) with a predetermined density. For example, the first detection image is a rectangular image (see Figure 4).

[0058] Of the multiple detection toner images X10, the detection toner image X12 (see Figure 4) corresponding to the image forming unit 22 is a cyan (C) toner image formed in the image forming unit 22 based on image data including a predetermined second detection image. The second detection image is a monochromatic cyan (C) image with a predetermined density. For example, the second detection image is a rectangular image similar to the first detection image (see Figure 4).

[0059] Of the multiple detection toner images X10, the detection toner image X13 (see Figure 4) corresponding to the image forming unit 23 is a magenta (M) toner image formed in the image forming unit 23 based on image data including a predetermined third detection image. The third detection image is a monochromatic magenta (M) image with a predetermined density. For example, the third detection image is a rectangular image similar to the first detection image (see Figure 4).

[0060] Of the multiple detection toner images X10, the detection toner image X14 (see Figure 4) corresponding to the image forming unit 24 is a K (black) toner image formed in the image forming unit 24 based on image data including a predetermined fourth detection image. The fourth detection image is a monochrome K (black) image with a predetermined density. For example, the fourth detection image is a rectangular image similar to the first detection image (see Figure 4).

[0061] For example, the transfer processing unit 71 transfers multiple detection toner images X10 to the intermediate transfer belt 26 while performing a printing process that forms an image on a sheet.

[0062] The number of detection toner images X10 transferred to the intermediate transfer belt 26 by the transfer processing unit 71 may be any number. Furthermore, the transfer processing unit 71 may transfer multiple detection toner images X10 (see Figure 4) to both of the pair of non-contact areas A3 (see Figure 4). In this case, the sensor 61 may be provided corresponding to each of the non-contact areas A3.

[0063] The first detection processing unit 72 uses the sensor 61 to detect the density of each detection toner image X10 that has been transferred to the intermediate transfer belt 26 by the transfer processing unit 71.

[0064] The adjustment processing unit 73 adjusts the image formation conditions based on the detection results from the first detection processing unit 72.

[0065] For example, the adjustment processing unit 73 adjusts the amount of light emitted by the optical scanning device 25 toward the image forming unit 21, or the development bias voltage of the image forming unit 21, so that the density of the detection toner image X11 (see Figure 4) detected by the first detection processing unit 72 approaches the density of the first detection image.

[0066] Furthermore, the adjustment processing unit 73 adjusts the amount of light emitted by the optical scanning device 25 toward the image forming unit 22, or the development bias voltage of the image forming unit 22, so that the density of the detection toner image X12 (see Figure 4) detected by the first detection processing unit 72 approaches the density of the second detection image.

[0067] Furthermore, the adjustment processing unit 73 adjusts the amount of light emitted by the optical scanning device 25 toward the image forming unit 23, or the development bias voltage of the image forming unit 23, so that the density of the detection toner image X13 (see Figure 4) detected by the first detection processing unit 72 approaches the density of the third detection image.

[0068] Furthermore, the adjustment processing unit 73 adjusts the amount of light emitted by the optical scanning device 25 toward the image forming unit 24, or the development bias voltage of the image forming unit 24, so that the density of the detection toner image X14 (see Figure 4) detected by the first detection processing unit 72 approaches the density of the fourth detection image.

[0069] The image formation conditions are not limited to the amount of light emitted by the optical scanning device 25 and the development bias voltage. For example, the image formation conditions may include the charging voltage, the primary transfer current, and the secondary transfer current.

[0070] By the way, if the protection circuit 50 is activated, it is possible to notify the user of that fact and prompt them to eliminate the cause of the abnormal operation of the voltage generation circuit 40.

[0071] If a dedicated sensor or the like is provided to detect when the protection circuit 50 is activated, the configuration of the image forming apparatus 100 becomes more complex.

[0072] In contrast, the image forming apparatus 100 according to an embodiment of the present invention can detect the operation of the protection circuit 50 without complicating its configuration, as will be described below.

[0073] The second detection processing unit 74 uses the sensor 61 to detect the operation of the protection circuit 50. The second detection processing unit 74 is an example of a detection processing unit of the present invention.

[0074] Specifically, the second detection processing unit 74 determines that the protection circuit 50 has been activated when a specific toner image X20 (see Figure 5) formed by the developing device 33 of the image forming unit 20 is detected when the protection circuit 50 corresponding to any of the image forming units 20 is activated.

[0075] When the protection circuit 50 corresponding to any of the image forming units 20 is activated, the charging operation by the charging roller 32 of the image forming unit 20 is temporarily stopped. As a result, the non-charged area is formed over the entire axial direction (left-right direction D3) of the photoreceptor drum 31 of the image forming unit 20. Therefore, the developing device 33 of the image forming unit 20 forms a long, high-density, band-shaped specific toner image X20 (see Figure 5) in the left-right direction D3, and this specific toner image X20 is transferred to the intermediate transfer belt 26.

[0076] For example, the second detection processing unit 74 detects the activation of the protection circuit 50 based on the duration of the state in which the toner density detected by the sensor 61 exceeds a predetermined specific density. For example, the specific density can be set based on the detection results of the density of four intentionally formed specific toner images X20 (yellow, cyan, magenta, and black).

[0077] Specifically, the second detection processing unit 74 detects a specific toner image X20 (see Figure 5) when the difference between the duration and the specific time falls within a predetermined range. In other words, it determines that the protection circuit 50 has been activated. To put it another way, the second detection processing unit 74 determines that the protection circuit 50 has been activated when the duration and the specific time are approximately the same. This makes it possible to detect the activation of the protection circuit 50 even while the image formation condition adjustment process is being performed, compared to a configuration in which the activation of the protection circuit 50 is detected when the toner density detected by the sensor 61 exceeds the specific density when the image formation condition adjustment process by the transfer processing unit 71, the first detection processing unit 72, and the adjustment processing unit 73 is not being performed. Furthermore, compared to the above configuration, it is possible to avoid false detection of the activation of the protection circuit 50 when a high-density toner image is formed in the non-contact area A3 (see Figure 4) on the outer surface of the intermediate transfer belt 26 due to an abnormality in the circuit that generates the development bias voltage or the like.

[0078] Furthermore, when the second detection processing unit 74 detects the activation of a protection circuit 50, it may identify the activated protection circuit 50 from among the four protection circuits 50 based on the value detected by the sensor 61.

[0079] The notification processing unit 75 notifies the system when the operation of the protection circuit 50 is detected by the second detection processing unit 74.

[0080] For example, the notification processing unit 75 displays a message on the operation display unit 5 indicating that the operation of the protection circuit 50 has been detected. This makes it possible to prompt the user of the image forming apparatus 100 to eliminate the cause of the abnormal operation of the voltage generation circuit 40.

[0081] The notification processing unit 75 may also send an email containing a message indicating that the activation of the protection circuit 50 has been detected to a predetermined recipient, such as a worker performing maintenance on the image forming apparatus 100. Furthermore, if the activated protection circuit 50 is identified, the notification processing unit 75 may also notify the identified protection circuit 50.

[0082] [Operation detection process] The detection method of the present invention will be described below with reference to Figure 6, along with an example of the procedure for operation detection processing performed by the control unit 7 in the image forming apparatus 100. Here, steps S11, S12, etc. represent the processing procedure (step) numbers performed by the control unit 7. The control unit 7 is executed when the image forming unit 3 is driven.

[0083] <Step S11> First, in step S11, the control unit 7 determines whether or not the operation of the image forming unit 3 has finished.

[0084] At this point, if the control unit 7 determines that the operation of the image forming unit 3 has finished (Yes side of S11), it terminates the operation detection process. If the operation of the image forming unit 3 has not finished (No side of S11), the control unit 7 proceeds to step S12.

[0085] <Step S12> In step S12, the control unit 7 determines whether or not it has detected the activation of any of the protection circuits 50. The process in step S12 is performed by the second detection processing unit 74 of the control unit 7.

[0086] Specifically, the control unit 7 detects the operation of one of the protection circuits 50 when the difference between the duration and the specified time falls within the specified range.

[0087] If the control unit 7 determines that it has detected the activation of any of the protection circuits 50 (Yes in S12), it proceeds to step S13. If it has not detected the activation of any of the protection circuits 50 (No in S12), the control unit 7 proceeds to step S11.

[0088] <Step S13> In step S13, the control unit 7 stops the operation of the image forming unit 3.

[0089] <Step S14> In step S14, the control unit 7 notifies that it has detected the activation of the protection circuit 50. The processing in step S14 is performed by the notification processing unit 75 of the control unit 7.

[0090] Specifically, the control unit 7 displays a message on the operation display unit 5 indicating that the operation of the protection circuit 50 has been detected.

[0091] Thus, in the image forming apparatus 100, the sensor 61 used for adjusting the image forming conditions is used to detect the operation of the protection circuit 50. This makes it possible to detect the operation of the protection circuit 50 without complicating the configuration.

[0092] The sensor 61 may also be used for processes such as acquiring the amount of charge on the toner.

[0093] Furthermore, the sensor 61 may detect the toner density outside the region of the photoreceptor drum 31 where the toner image to be transferred to the sheet is formed (another example of a specific region in the present invention). In other words, the sensor 61 may be provided opposite the photoreceptor drum 31, rather than on the intermediate transfer belt 26. In this case, the photoreceptor drum 31 is another example of the transport member of the present invention. Also, the intermediate transfer belt 26 is another example of the member to be transferred in the present invention.

[0094] Alternatively, instead of the sensor 61, a line sensor that reads the image formed on the sheet by the image forming unit 3 may be provided in the sheet transport path. In this case, the second detection processing unit 74 only needs to detect the operation of the protection circuit 50 (detect the specific toner image X20) based on the reading result from the line sensor.

[0095] [Notes on the invention] The following is an overview of the invention extracted from the above-described embodiments. Note that each configuration and processing function described below can be selected and combined as desired.

[0096] <Note 1> An image forming apparatus comprising: an image carrier that carries a toner image; a charging unit that charges the image carrier to a corresponding potential corresponding to the charging voltage in response to the application of a predetermined charging voltage; a developing unit that deposits toner on a region of the image carrier whose surface potential is lower than the corresponding potential; a voltage generation circuit that generates the charging voltage; a protection circuit that stops the operation of the voltage generation circuit when the current flowing through the charging unit exceeds a predetermined threshold; a sensor used to detect the density of the toner image formed by the developing unit; and a detection processing unit that uses the sensor to detect the operation of the protection circuit.

[0097] <Note 2> The image forming apparatus according to Appendix 1, comprising a transport member for transporting the toner image formed by the developing unit to a transfer position on a transfer member, the protection circuit restarts the operation of the voltage generation circuit when a predetermined specific time has elapsed since the operation of the voltage generation circuit stopped, the sensor detects the toner concentration outside a specific region on the transport member where the toner image to be transferred to the transfer member is formed, and the detection processing unit detects the operation of the protection circuit based on the duration of the state in which the toner concentration detected by the sensor exceeds a predetermined specific concentration.

[0098] <Note 3> The image forming apparatus according to Appendix 1 or 2, further comprising a notification processing unit that notifies the user when the detection processing unit detects the operation of the protection circuit.

[0099] <Note 4> A detection method performed in an image forming apparatus comprising: an image carrier that carries a toner image; a charging unit that charges the image carrier to a corresponding potential corresponding to the charging voltage in response to the application of a predetermined charging voltage; a developing unit that deposits toner on a region of the image carrier whose surface potential is lower than the corresponding potential; a voltage generation circuit that generates the charging voltage; a protection circuit that stops the operation of the voltage generation circuit when the current flowing through the charging unit exceeds a predetermined threshold; and a sensor used to detect the density of the toner image formed by the developing unit, wherein the detection method uses the sensor to detect the operation of the protection circuit. [Explanation of Symbols]

[0100] 1 ADF 2 Image reading unit 3 Image forming unit 4 Paper feed section 5 Operation display section 6 Memory section 7 Control Unit 20 Image forming unit 25 Optical scanning device 26 Intermediate transfer belt 27 Secondary transfer roller 28 Fixing device 31 Photoconductor Drum 32 Electrostatic Rollers 33 Developing equipment 34 Primary Transfer Roller 35 Drum Cleaning Department 36 Toner Containers 40 Voltage generation circuit 50 Protection circuit 61 sensors 71 Transfer Processing Unit 72 First detection processing unit 73 Adjustment Processing Unit 74 Second Detection Processing Unit 75 Notification Processing Unit 100 Image forming apparatus

Claims

1. An image carrier that holds the toner image, A charging unit that charges the image carrier to a corresponding potential corresponding to the charging voltage in response to the application of a predetermined charging voltage, A developing unit that deposits toner on a region of the image carrier whose surface potential is lower than the corresponding potential, A voltage generation circuit that generates the aforementioned charging voltage, A protection circuit that stops the operation of the voltage generation circuit when the current flowing through the charged part exceeds a predetermined threshold, A sensor used to detect the density of the toner image formed by the developing unit, A detection processing unit that uses the aforementioned sensor to detect the operation of the protection circuit, An image forming apparatus equipped with the following features.

2. The system includes a transport member that transports the toner image formed by the developing unit to the transfer position on the transfer member, The protection circuit restarts the operation of the voltage generation circuit when a predetermined specific time has elapsed since the operation of the voltage generation circuit stopped. The sensor detects the toner concentration outside a specific region in the transport member where the toner image to be transferred to the member to be transferred is formed. The detection processing unit detects the activation of the protection circuit based on the duration of the state in which the toner concentration detected by the sensor exceeds a predetermined specific concentration. The image forming apparatus according to claim 1.

3. The system includes a notification processing unit that notifies the user when the detection processing unit detects that the protection circuit has been activated. The image forming apparatus according to claim 1 or 2.

4. A detection method performed in an image forming apparatus comprising: an image carrier that carries a toner image; a charging unit that charges the image carrier to a corresponding potential corresponding to the charging voltage in response to the application of a predetermined charging voltage; a developing unit that deposits toner on a region of the image carrier whose surface potential is lower than the corresponding potential; a voltage generation circuit that generates the charging voltage; a protection circuit that stops the operation of the voltage generation circuit when the current flowing through the charging unit exceeds a predetermined threshold; and a sensor used to detect the density of the toner image formed by the developing unit, wherein Using the aforementioned sensor, the operation of the protection circuit is detected. Detection method.

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