JP4354340B2 - Image forming apparatus and abnormality detection method - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image by an electrophotographic method. More specifically, the present invention relates to an electrostatic latent image carrier by applying a voltage to a charging member that applies a charge to the surface of the electrostatic latent image carrier. The present invention relates to an image forming apparatus and an abnormality detection method for detecting an abnormality by detecting a current applied to a charging member in a charging step for uniformly charging the surface of the image forming apparatus.

  Conventionally, in an image forming apparatus using an electrophotographic method such as a digital copying machine, a laser printer, a facsimile, etc., there is a merit that the amount of ozone generated at the time of discharge is smaller than that when a corona charger is used. Or a transfer roller is used.

  In an image forming apparatus using such a charging roller, if printing continues while a leak occurs on the photosensitive drum, which is an electrostatic latent image carrier, the leak of the photosensitive drum gradually increases, and only at the leak portion. A large amount of current will continue to flow. As a result, the pressure resistance of the charging roller as the charging member cannot be endured, and the charging roller is damaged, and not only the photosensitive drum but also the charging roller needs to be replaced, resulting in increased damage. That is, if the charging roller is damaged by leakage, the withstand voltage of the portion becomes very low, and a large amount of current flows out from the charging roller. An abnormal image will occur.

  In addition, if foreign matter adheres, it can be dealt with by simply removing the foreign matter at that time, but if printing continues with the foreign matter attached, the contamination on the circumference of the charging roller becomes severe and the charging roller becomes dirty. Will transfer to the photosensitive drum, increasing the damage. Therefore, if a leak or foreign matter adhesion can be detected at an early stage, damage can be minimized.

  Thus, various methods for quickly detecting the occurrence of such a leak have been proposed (see, for example, Patent Document 1).

In Patent Document 1, the average value (VppAve) of the voltage Vpp of the AC component applied to the charging roller is obtained and compared with the value of Vpp sampled successively. When VppAve is sufficiently large with respect to Vpp, leakage occurs. It has come to be judged that it has occurred.
JP-A-8-146718

  However, although it is possible to estimate whether or not a leak has occurred in the above-mentioned Patent Document 1, it is determined whether or not a foreign substance (insulator) is attached to the charging roller or the photosensitive drum. There was a problem that I could not do it.

  Moreover, in the thing of the said patent document 1, the bias voltage which superimposed the alternating voltage on the direct current voltage is applied to the charging roller. By superimposing the alternating current component on the direct current component in this manner, static elimination / discharge is repeated between the surface potential of the photosensitive drum and the alternating current component, and the surface potential approaches the direct current component. In this case, since the thing of patent document 1 is detecting the peak-to-peak voltage of the alternating current component currently applied to the charging roller, the influence with respect to an image quality is only estimated. The technique of Patent Document 1 is effective for a type in which a bias voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging roller, but in an image forming apparatus of a type in which only the DC voltage is applied to the charging roller. There was a problem that could not be applied.

  The present invention has been developed to solve such problems, and an object of the present invention is to detect a fluctuation range with respect to an average value of a current flowing through a charging roller in an image forming apparatus of a type in which only a DC voltage is applied to the charging roller. Accordingly, an object of the present invention is to provide an image forming apparatus and an abnormality detection method capable of determining whether or not a leak current is generated and whether or not a foreign matter is attached to a charging roller or a photosensitive drum.

In order to solve the above problems, an image forming apparatus of the present invention includes an electrostatic latent image carrier, a charging member that applies a charge to the surface of the electrostatic latent image carrier and uniformly charges the electrostatic latent image carrier, in the image forming apparatus and a power source for applying a voltage, a current detector for detecting a current while applying a predetermined constant voltage to the charging member during image forming operation, electrostatic sensed by the current sensing unit An average value calculation unit for calculating an average value in a predetermined measurement range of the flow in a time longer than a time for which the charging member makes one rotation, and in a predetermined measurement range when the current detected by the current detection unit decreases . a first peak value detector that detect the minimum current value, is predetermined as the difference between the average value of the minimum current value detected by the first peak value detector and the obtained by the average calculator current Compare with the first threshold value A first comparing section, and the second peak value detector for detecting a maximum current value in the predetermined measurement range when the current detected by the detection unit current increases, detected by said second peak value detector A second comparison unit that compares a difference between a maximum current value and an average value of currents obtained by the average value calculation unit and a predetermined second threshold; and a comparison result of the first comparison unit or the first comparison value And a determination unit that determines an abnormality of the charging member or the electrostatic latent image carrier based on a comparison result of the two comparison units .

According to the present invention having such a feature, the difference between the average value of the current applied to the charging member and the minimum current value when the current applied to the charging member decreases is obtained, and the difference is determined in advance. It compares with the set 1st threshold value, and when the difference is over the 1st threshold value, it determines with the foreign material adhering. As a result, it is possible to detect adhesion of foreign matters at an early stage, so that damage can be minimized. Further, according to the present invention, the difference between the average value of the current applied to the charging member and the maximum current value when the current applied to the charging member increases is obtained, and the difference is set in advance. Compared with the second threshold value, if the difference exceeds the second threshold value, it is determined that a leak has occurred. Thereby, since a leak can be discovered at an early stage, damage can be minimized.

  According to the present invention, the current detection unit is controlled to detect a current with a predetermined time delay when the power is turned on. By such control, noise (influence of inrush current) generated when the power is turned on can be removed, and detection malfunctions are reduced.

Further, according to the present invention, the determination unit obtains the period of minimum current detected by said first peak value detector, the determined result of said charging member and the latent electrostatic image bearing member on the basis of It is characterized by determining which abnormality has occurred. In Rukoto thus determined the period of minimum current, abnormality it is possible to determine whether the occurring anywhere in the charging member or latent electrostatic image bearing member, it is possible to easily identify the abnormal location.

  According to the present invention, a plurality of values are set as the first threshold value. By setting a plurality of values in this way, the size of the foreign matter can be specified to some extent, and the foreign matter can be easily removed.

  According to the present invention, a plurality of values are set as the second threshold value. For example, by setting a threshold value for determining when a leak occurs and a threshold value for determining immediately before an excessive current value flows, it is possible to determine an abnormality when a leak occurs and to check the abnormal location. However, if an excessive current value flows and damages the entire machine, it can be forcibly stopped to minimize damage.

The abnormality detection method of the present invention includes a step of uniformly charging the surface of the electrostatic latent image carrier by applying a voltage to a charging member that applies a charge to the surface of the electrostatic latent image carrier. An abnormality detection method for detecting an abnormality by detecting a current applied to a charging member, and detecting a current when a predetermined constant voltage is applied to the charging member during an image forming operation; An average value calculating procedure for calculating an average value in a predetermined measurement range of the current detected in the current detecting procedure in a time longer than a time for which the charging member makes one rotation; and a current detected in the current detecting procedure detect the maximum current value in the predetermined measurement range when the first peak value detection procedure you detect the minimum current value in the predetermined measurement range when decreasing said sensed by the current sensing procedure current increases Second peak value detector When the procedure is compared with the first threshold value is predetermined and the difference between the average value of the current obtained by the minimum current value and the average value calculation procedure which is detected by the first peak value detection procedure or the first, Based on a procedure for comparing a difference between the maximum current value detected by the two-peak value detection procedure and the average value of the currents obtained by the average value calculation procedure with a predetermined second threshold, the charging member or characterized by comprising the determination procedure to determine an abnormality of the electrostatic latent image bearing member.

According to the present invention having such a feature, the difference between the average value of the current applied to the charging member and the minimum current value when the current applied to the charging member decreases is obtained, and the difference is determined in advance. It compares with the set 1st threshold value, and when the difference is over the 1st threshold value, it determines with the foreign material adhering. As a result, it is possible to detect adhesion of foreign matters at an early stage, so that damage can be minimized. Further, according to the present invention, a difference between the average value of the current applied to the charging member and the maximum current value when the current applied to the charging member increases is obtained, and the difference is set in advance. When the difference exceeds the second threshold value, it is determined that a leak has occurred. Thereby, since a leak can be discovered at an early stage, damage can be minimized.

According to the present invention, the difference between the average value of the current applied to the charging member and the minimum current value when the current applied to the charging member decreases is obtained, and the difference is set to a first threshold value set in advance. If the difference exceeds the first threshold value, it is possible to detect the attachment of foreign matter at an early stage by determining that the foreign matter is attached, so that damage can be minimized. it can. Further, the difference between the average value of the current applied to the charging member and the maximum current value when the current applied to the charging member increases is obtained, and the difference is compared with a preset second threshold value. When the difference exceeds the second threshold value, it is possible to detect the leak at an early stage by determining that the leak has occurred, so that damage can be minimized.

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present embodiment, a case where the image forming apparatus of the present invention is applied to a multifunction machine will be described.

-Description of overall configuration of MFP-
FIG. 1 schematically shows an internal configuration of a multifunction machine 1 as an image forming apparatus according to the present embodiment. The multifunction device 1 has a copier mode, a printer mode, and a FAX mode as image forming modes for forming an image on recording paper (including recording media such as OHP), and each mode is selected by a user.

  The multifunction machine 1 includes a scanner unit 2 as an original reading unit, an image forming unit 3, and an automatic document feeder 4. Hereinafter, each part will be described.

<Description of Scanner Unit 2>
The scanner unit 2 reads image of a document placed on a document table 41 made of transparent glass or the like, or a document image fed one by one by the document automatic sheet feeding unit 4 to generate image data. It is. The scanner unit 2 includes an exposure light source 21, a plurality of reflecting mirrors 22, 23, 24, an imaging lens 25, and a photoelectric conversion device (CCD: Charge Coupled Device) 26.

  The exposure light source 21 emits light to a document placed on the document table 41 of the automatic document feeder 4 or a document conveyed through the automatic document feeder 4. Each reflecting mirror 22, 23, 24 reflects the reflected light from the document once in the left direction in the drawing, as shown by an alternate long and short dash line A in FIG. Reflected in the right direction in the figure so as to go to 25.

  As a document image reading operation, when a document is placed on the document table 41 (when used as a “sheet fixing method”), the exposure light source 21 and the reflecting mirrors 22, 23, 24 are connected to the document table 41. The image of the entire document is read by scanning in the horizontal direction. On the other hand, when reading a document conveyed by the automatic document feeder 4 (when used as a “sheet moving method”), the exposure light source 21 and the reflecting mirrors 22, 23, 24 are fixed at the positions shown in FIG. Then, the image is read when the document passes through a document reading unit 42 of the automatic document feeder 4 described later.

  The light reflected by the reflecting mirrors 22, 23, 24 and passing through the imaging lens 25 is guided to the photoelectric conversion element 26, and the reflected light is converted into an electric signal (original image data) by the photoelectric conversion element 26. It is like that.

<Description of Image Forming Unit 3>
The image forming unit 3 includes an image forming system 31 and a paper transport system 32.

  The image forming system 31 includes a laser scanning unit 31a and a photosensitive drum 31b as a drum-type image carrier. The laser scanning unit 31a irradiates the surface of the photosensitive drum 31b with laser light based on the document image data converted by the photoelectric conversion element 26. The photosensitive drum 31b rotates in a direction indicated by an arrow in FIG. 1, and an electrostatic latent image is formed on the surface of the photosensitive drum 31b by being irradiated with laser light from the laser scanning unit 31a.

  In addition to the laser scanning unit 31a, there are a developing device (developing mechanism) 31c, a transfer unit (transfer mechanism) (not shown) having a transfer roller 31d, and a cleaning device (cleaning mechanism) 31e around the outer periphery of the photosensitive drum 31b. A static eliminator (not shown) and a charging unit (not shown) having a charging roller 31f are sequentially arranged in the circumferential direction. The developing device 31c develops the electrostatic latent image formed on the surface of the photosensitive drum 31b into a visible image with toner (visualizing substance). The transfer roller 31d transfers a toner image formed on the surface of the photosensitive drum 31b onto a recording sheet as a recording medium. The cleaning device 31e removes the toner remaining on the surface of the photosensitive drum 31b after the toner transfer. The static eliminator removes residual charges on the surface of the photosensitive drum 31b. The charging roller 31f charges the surface of the photosensitive drum 31b before the electrostatic latent image is formed to a predetermined potential.

  For this reason, when an image is formed on a recording sheet, the surface of the photosensitive drum 31b is charged to a predetermined potential by the charging roller 31f, and the laser scanning unit 31a emits laser light based on the original image data to the photosensitive drum 31b. Irradiate the surface. Thereafter, the developing device 31c develops a visible image with toner on the surface of the photosensitive drum 31b, and the toner image is transferred onto the recording paper by the transfer roller 31d. Further, after that, the toner remaining on the surface of the photosensitive drum 31b is removed by the cleaning device 31e, and the residual charge on the surface of the photosensitive drum 31b is removed by the static eliminator. This completes one cycle of the image forming operation (printing operation) on the recording paper. By repeating this cycle, it is possible to continuously form images on a plurality of recording sheets.

  On the other hand, the paper transport system 32 transports recording paper stored in a paper cassette 33 serving as a paper storage section or recording paper placed on the manual feed tray 34 one by one to form an image by the image forming system 31. In addition, the recording paper on which the image is formed is discharged to a paper discharge tray 35 as a paper discharge portion.

  The paper transport system 32 includes a main transport path 36 and a reverse transport path 37. One end side of the main conveyance path 36 is branched into two, one branch end faces the discharge side of the paper cassette 33 and the other branch end faces the discharge side of the manual feed tray 34. Yes. The other end of the main transport path 36 faces the paper discharge tray 35. One end of the reverse conveyance path 37 is connected to the main conveyance path 36 on the upstream side (lower side in the figure) of the transfer roller 31d, and the other end is downstream of the transfer roller 31d. (Upper side in the figure) is connected to the main transport path 36.

  A pickup roller 36a having a semicircular cross section is disposed at one branch end of the main conveyance path 36 (a portion facing the discharge side of the paper cassette 33). By the rotation of the pickup roller 36a, the recording sheets stored in the sheet cassette 33 can be intermittently fed to the main transport path 36 one by one. Similarly, a pickup roller 36b having a semicircular cross section is disposed at the other branch end of the main conveyance path 36 (a portion facing the discharge side of the manual feed tray 34). By the rotation of the pickup roller 36b, the recording paper placed on the manual feed cassette 34 can be intermittently fed to the main transport path 36 one by one.

  A registration roller 36d is disposed upstream of the position where the transfer roller 31d is disposed in the main conveyance path 36. The registration roller 36d conveys the recording paper while aligning the toner image on the surface of the photosensitive drum 31b with the recording paper.

  Further, a paper detector 36c for detecting the end of the recording paper being conveyed is disposed further upstream than the position where the registration roller 36d is disposed and downstream of the branch portion of the main conveyance path 36. Has been. The paper detector 36c serves as a double feed detection unit that detects double feed of recording paper, which will be described later, and serves as a rear end detection unit that detects the rear end of the recording paper.

  A fixing device 39 including a pair of fixing rollers 39a and 39b for fixing the toner image transferred onto the recording sheet by heating is disposed downstream of the position where the transfer roller 31d is disposed in the main conveyance path 36. Has been. Further, a discharge roller 36 e for discharging the recording paper to the paper discharge tray 35 is disposed at the downstream end of the main transport path 36.

  A branching claw 38 is disposed at a connection position at the upstream end of the reverse conveyance path 37 with respect to the main conveyance path 36. The branch claw 38 is rotated about the horizontal axis between the first position indicated by the solid line in FIG. 1 and the second position that rotates counterclockwise from the first position to open the reverse conveyance path 37. It is free to rotate. When the branch claw 38 is at the first position, the recording paper is conveyed toward the paper discharge tray 35, and when it is at the second position, the recording paper can be supplied to the reverse conveyance path 37. A conveyance roller 37a is disposed in the reverse conveyance path 37, and when the recording paper is supplied to the reverse conveyance path 37 (when the recording paper is supplied to the reverse conveyance path 37 by so-called switchback conveyance), The recording sheet is conveyed by the conveying roller 37a, and the recording sheet is reversed upstream of the registration roller 36d and is conveyed again through the main conveying path 36 toward the transfer roller 31d. That is, an image can be formed on the back surface of the recording paper.

  In the image forming unit 3 having the above configuration, the sheet cassette 33, the manual feed tray 34, the pickup rollers 36a and 36b, the sheet detector 36c, and the registration roller 36d are also referred to as a recording sheet feeding unit hereinafter.

<Description of Automatic Document Feeder 4>
Next, the automatic document feeder 4 will be described. The automatic document feeder 4 is configured as a so-called automatic duplex document feeder. The automatic document feeder 4 can be used as a sheet moving type, and includes a document tray 43 as an original placement unit, an intermediate tray 44, a document discharge tray 45 as a document discharge unit, and trays 43, 44, A document transport system 46 is provided for transporting a document between 45.

  The document transport system 46 includes a main transport path 47 for transporting a document placed on the document tray 43 to the intermediate tray 44 or the document discharge tray 45 via the document reading unit 42, and the document on the intermediate tray 44. And a sub-transport path 48 for supplying the main transport path 47 to the main transport path 47.

  A document pick-up roller 47a and a separating roller 47b are disposed at the upstream end of the main conveyance path 47 (a portion facing the discharge side of the document tray 43). A separation plate 47c is disposed below the separation roller 47b, and one of the documents on the document tray 43 is placed between the separation roller 47b and the separation plate 47c as the document pickup roller 47a rotates. Is fed to the main transport path 47. PS rollers 47e and 47e are disposed on the downstream side of the joining portion (B portion in the figure) of the main transport path 47 and the sub transport path 48. The PS rollers 47 e and 47 e adjust the leading edge of the document and the image reading timing of the scanner unit 2 and supply the document to the document reading unit 42. That is, the PS rollers 47e and 47e temporarily stop the conveyance of the document while the document is supplied, and adjust the timing to supply the document to the document reading unit 42.

  The document reading unit 42 includes a platen glass 42a and a document pressing plate 42b. When the document supplied from the PS rollers 47e and 47e passes between the platen glass 42a and the document pressing plate 42b, the exposure light source 21 is provided. Is irradiated to the original through the platen glass 42a. At this time, the document image data is acquired by the scanner unit 2. A biasing force by a coil spring (not shown) is applied to the back surface (upper surface) of the document pressing plate 42b. Thereby, the document pressing plate 42b is in contact with the platen glass 42a with a predetermined pressing force, and prevents the document from floating from the platen glass 42a when passing the document reading unit 42.

  On the downstream side of the platen glass 42a, a conveyance roller 47f and a document discharge roller 47g are provided. The document that has passed over the platen glass 42a is discharged to the intermediate tray 44 or the document discharge tray 45 through the transport roller 47f and the document discharge roller 47g.

  An intermediate tray swinging plate 44 a is disposed between the document discharge roller 47 g and the intermediate tray 44. The intermediate tray swinging plate 44a swings between a position 1 indicated by a solid line in the figure and a position 2 that is flipped upward from the position 1 with the end on the intermediate tray 44 side being the center of swinging. It is possible. When the intermediate tray swinging plate 44 a is at position 2, the document discharged from the document discharge roller 47 g is collected to the document discharge tray 45. On the other hand, when the intermediate tray swinging plate 44a is at the position 1, the document discharged from the document discharge roller 47g is discharged to the intermediate tray 44. When the sheet is discharged onto the intermediate tray 44, the edge of the document is sandwiched between the document discharge rollers 47g and 47g. It is supplied to the transport path 48 and is sent again to the main transport path 47 via the sub-transport path 48. The reverse rotation operation of the document discharge roller 47g is performed by adjusting the document delivery to the main conveyance path 47 and the image reading timing. Thus, the image on the back side of the document is read by the document reading unit 42.

-Basic operation of MFP-
As an operation of the multi-function device 1 configured as described above, first, when the multi-function device 1 functions as a printer (printer mode), print data (image data or text) transmitted from a host device such as a personal computer is used. Data), and the received print data (print data) is temporarily stored in a buffer (memory) (not shown). Along with storing the print data in the buffer, the print data is sequentially read from the buffer, and based on the read print data, an image is formed on the recording paper by the image forming operation of the image forming unit 3 described above.

  When the multifunction machine 1 functions as a scanner (FAX mode), the scanned image data of the document read by the scanner unit 2 is temporarily stored in a buffer. Along with storing the scan image data in the buffer, the scan image data is sequentially transmitted from the buffer to the host device, and the image is displayed on the display or the like of the host device.

  Further, when the multifunction machine 1 functions as a copier (copier mode), an image is formed on a recording sheet by an image forming operation of the image forming unit 3 based on document image data read by the scanner function. Become.

-Description of control system block configuration-
FIG. 2 is a functional block diagram showing the basic configuration of the control system of the multifunction machine 1.

  The multifunction machine 1 is provided with a main CPU 101 for comprehensively controlling each of the devices (the scanner unit 2, the image forming unit 3, and the automatic document feeder 4). A document feeding control unit 102 that controls automatic feeding of documents, a charging control unit 103 that controls each part of the image forming unit 3, a development control unit 104, a transfer control unit 105, a fixing control unit 106, and a sheet detector 36c. The provided sheet conveyance control units 107 are connected in both directions. The main CPU 101 also has an operation control unit 108 that outputs a signal from an operation panel unit (not shown) where an operator performs an input operation or performs a display operation on the operation panel unit in accordance with a signal from the main CPU 101. It is connected.

-Explanation of block configuration for detecting abnormalities in the charging process-
FIG. 3 is a functional block diagram of an abnormality detection process that detects the current applied to the charging roller 31f and detects the occurrence of leakage or the attachment of foreign matter.

  That is, a constant voltage power source 51 that applies a predetermined voltage is connected to the charging roller 31f that uniformly charges the surface of the photosensitive drum 31b, and a current applied to the charging roller 31f is connected to the constant voltage power source 51. Is connected to a current detection unit 52 for detecting. The output of the current detection unit 52 is connected to a determination unit 53 that determines abnormality, and the output of the determination unit 53 is connected to the multifunction device 1 or a display unit (for example, a liquid crystal display) 54 of a printer (not shown). ing. However, the display unit 54 may be a display of a host computer when the multifunction device 1 is connected to a network.

  In order to avoid the influence of the inrush current, the current detector 52 detects the current with a predetermined time delay when the power is turned on. Such a predetermined time delay is controlled by the charging control unit 103.

The charging roller 31f covers, for example, an outer periphery of a core metal (for example, stainless steel (SUS304)) 31f1 that is a conductive rotating shaft of φ8 mm, and a conductive rubber (for example, epichlorohydrin rubber) 31f2 that is a semiconductor layer of φ14 mm, A surface layer (for example, urethane) 31f3 having a thickness of 10 μm is formed on the outer periphery of the conductive rubber 31f2. However, the charging roller 31f may have a blade shape as well as such a roller shape. The photosensitive drum 31b has a structure in which an OPC (Organic Photoconductor) 31b2 using an organic photoconductor as a photosensitive layer is laminated on an aluminum base 31b1. A charging roller 31f is brought into pressure contact with the photosensitive drum 31b, and the charging roller 31f is driven to rotate following the photosensitive drum 31b. A constant voltage (-1200 to 1400V) is applied to the charging roller 31f from the constant voltage power supply 51, whereby the photosensitive drum 31b is charged to about 600V. In the present invention, the current value when the constant voltage is applied is detected by the current detector 52.

<Description of Current Detection Unit 52>
FIG. 4 is a functional block diagram showing a circuit configuration of the current detection unit 52.

  The current detection unit 52 includes a first current detection unit 52a that detects a current that decreases with respect to the average current value (current fluctuation range due to adhesion of foreign matter: expressed as a minus side in the drawing), and an average current. And a second current detector 52b that detects a current that increases with respect to the value (fluctuation width of the leak current: indicated as a plus side in the drawing).

<Description of First Current Detection Unit 52a>
The first current detector 52a includes an average value calculator 52a1 that calculates an average value of currents, a first peak value detector 52a2 that includes a peak hold circuit that detects a peak value (minimum value) of a decreasing current, and a first peak. The output of the first differential amplifier 52a3 and the output of the first differential amplifier 52a3 connected to the plus input terminal and the output of the average value calculating unit 52a1 connected to the minus input terminal are connected to one input terminal. The other input terminal is composed of a first comparator 52a4 to which a preset first threshold is given, and the output of the first comparator 52a4 is inputted to the determination unit 53.

  The average value calculator 52a1 calculates an average value of current. The average value is calculated over a time longer than at least the time during which the charging roller 31f rotates once. For example, when the diameter of the charging roller 31f is φ14 mm and the process speed is 140 mm / sec, the time for which the charging roller 31f makes one rotation is about 314 ms, so the calculation time is set to 350 ms, for example.

The first differential amplifier 52a3 calculates a peak (minimum) current value-an average current value, and calculates a fluctuation range of the negative current.

  The first comparator 52a4 compares the fluctuation range of the negative current with the first threshold value. In the present embodiment, a plurality of threshold values (here, two threshold values 1A and 1B) are set as the first threshold value. Specifically, the threshold value 1A is set to a level for displaying an alarm (for example, −3 μA), and the threshold value 1B is set to, for example, a set current value (for example, −100 μA) × 0.8.

  In this embodiment, in this state, a constant voltage of -1340 V is actually applied to the charging roller 31f, and the current value is monitored. At that time, the current value limiter was set to 50 μA, and the current was set not to flow any more.

As a result, as shown in FIG. 5, the average was 29 μA on average and the minimum was 27 μA (see FIG. 5A), and the peak current value (27 μA) −average current value (29 μA) = − 2 μA. On the other hand, when an insulating foreign matter adheres to the charging roller 31f, the average is 29.5 μA and the minimum is 26 μA (see FIG. 5B), and the peak current value ( 26 μA) −average current value (29.5 μA) = -3.5 μA. Further, from FIG. 5B, the cycle of the peak current value is approximately every 300 ms which is substantially the same as the cycle of the charging roller 31f (314 ms).

<Description of Second Current Detection Unit 52b>
The second current detection unit 52b is configured such that the outputs of the second peak value detection unit 52b2 and the second peak value detection unit 52b2 each including a peak hold circuit that detects the peak value (maximum value) of the increasing current are connected to the positive input terminal. The outputs of the second differential amplifier 52b3 and the second differential amplifier 52b3, in which the output of the average value calculation unit 52a1 is connected to the negative input terminal, are connected to one input terminal, and the other input terminal is preset. The second comparator 52b4 is provided with a second threshold value, and the output of the second comparator 52b is input to the determination unit 53.

The second differential amplifier 52b3 calculates the peak (maximum) current value-average current value, and calculates the fluctuation range of the positive current.

  The second comparator 52b4 compares the fluctuation range of the positive current with the second threshold value. In the present embodiment, a plurality of threshold values (here, two threshold values 2A and 2B) are set as the second threshold value. Specifically, the threshold 2A is set to a level for displaying an alarm (for example, 15 μA), and the threshold 2B is set to, for example, a limit current value (for example, 100 μA) × 0.8.

  In this embodiment, in this state, a constant voltage of −1240 V is actually applied to the charging roller 31 f and the current value is monitored. At that time, the current value limiter was set to 50 μA, and the current was set not to flow any more.

As a result, as shown in FIG. 6, the average was 30 μA on average and 33 μA at maximum (see FIG. 6A), and the peak current value (33 μA) −average current value (30 μA) = 3 μA. On the other hand, when leakage occurred, the average was 32 μA and the maximum was 47 μA (see FIG. 5B), and the peak current value (47 μA) −average current value (32 μA) = 15 μA. Further, from FIG. 5B, the period of the peak current value immediately before the occurrence of the leak is every 700 ms which is almost the same as the period of the photosensitive drum 31b (670 ms).

<Description after determination unit 53>
Based on the information input from the first comparator 52a4, the determination unit 53 has a foreign matter (insulator) on the charging roller 31f or the photosensitive drum 31b when the fluctuation range of the negative current> the first threshold (especially the threshold 1A). Is determined to be attached. Further, when the fluctuation range of the positive current> the second threshold (especially the threshold 2A), it is determined that a leak current is generated.

  Further, the main CPU 101 that controls the charging control unit 103 executes an optimum process based on the above determination result, which will be described in detail with reference to the last FIG.

  FIG. 7 is a functional block diagram showing another embodiment of the determination unit 53. The current detection unit 52 has the same configuration as the current detection unit 52 shown in FIG. Are given the same reference numerals. In this embodiment, the period analysis unit 53a is added to the determination unit 53.

  The period analysis unit 53a obtains the peak generation period from the time when the peak value of the negative current is observed, and determines whether foreign matter is attached to the charging roller 31f or the photosensitive drum 31b based on the period. is there. Specifically, when the outer peripheral diameter of the charging roller 31f is φ14 mm, the outer peripheral diameter of the photosensitive drum 31b is φ30 mm, and the process speed is 140 mm / s, when the foreign matter adheres to the charging roller 31f, the peak When the generation cycle is about 300 ms and foreign matter is attached to the photosensitive drum 31b, the peak generation cycle is about 700 ms. Therefore, by determining the peak generation period, it is possible to determine which of the charging roller 31f or the photosensitive drum 31b has foreign matter attached thereto.

  Finally, with reference to the flowchart shown in FIG. 8, the entire abnormality detection processing procedure according to the present invention will be described.

  When the multifunction device 1 is operated and any mode (printer mode, FAX mode, copier mode) is executed, the current detection unit 52 starts detecting the current applied to the charging roller 31f, and first, the average value calculation unit The average value A is calculated from 52a1 (step S1). At the same time, the first peak value detector 52a2 detects the negative peak current value C (step S2), and the second peak value detector 52b2 detects the positive peak current value B (step S12).

  The first differential amplifier 52a3 calculates a difference (C−A) between the average value A obtained in step S1 and the negative peak current value C obtained in step S2 (step S3), and the calculation result is calculated as 1 is input to the comparator 52a4.

  The first comparator 52a4 compares the difference value (C−A) input from the first differential amplifier 52a3 with the threshold value 1B (−80 μA) of two preset first threshold values. (Step S4). As a result, when the difference value (C−A) is larger than the threshold value 1B (−80 μA) (when determined to be Yes), it is difficult for current to flow, that is, a predetermined surface potential cannot be obtained and fogging occurs. Since there is a possibility, the operation of the multifunction device 1 is stopped (step S10). On the other hand, if the difference value (C-A) is smaller than the threshold value 1B (−80 μA) (if No is determined in step S4), then the difference value (C-A) and the first threshold value are the threshold values. 1A (−3 μA) is compared (step S5). As a result, when the difference value (C−A) is larger than the threshold value 1A (−3 μA) (when it is determined Yes in step S5), foreign matter adheres to either the charging roller 31f or the photosensitive drum 31b. (Step S6), and then the peak generation period is analyzed (step S7). As a result, when the peak generation period is about 700 ms, it is determined that foreign matter is attached to the photosensitive drum 31b (step S8). On the other hand, when the peak generation period is about 300 ms, it is determined that foreign matter is attached to the charging roller 31f (step S9). In step S5, when the difference value (C-A) is smaller than the threshold value 1B (−80 μA) (when No is determined), it is determined that there is no problem in operation (step S11).

  On the other hand, the second differential amplifier 52b3 calculates the difference (C−B) between the average value A obtained in step S1 and the positive-side peak current value B obtained in step S12 (step S13), and the calculation result Is input to the second comparator 52b4.

  The second comparator 52b4 compares the difference value (C−B) input from the second differential amplifier 52b3 with the threshold value 2B (80 μA) among the two preset second threshold values ( Step S14). As a result, when the difference value (C−B) is larger than the threshold value 2B (80 μA) (when determined to be Yes), the leakage current is large and the image quality deteriorates (for example, the direction orthogonal to the paper transport direction). Therefore, the operation of the multifunction device 1 is stopped (step S10). On the other hand, when the difference value (C−B) is smaller than the threshold value 2B (80 μA) (when it is determined No in step S14), the threshold value 2A of the difference value (C−B) and the second threshold value is next. (15 μA) is compared (step S15). As a result, when the difference value (C−B) is larger than the threshold value 2A (15 μA) (when it is determined Yes in step S15), it is determined that a leak has occurred (step S16). On the other hand, when the difference value (C−B) is smaller than the threshold value 2B (15 μA) in Step S15 (when No is determined), it is determined that there is no problem in the operation (Step S11).

1 is a schematic configuration diagram of an internal configuration of a multifunction peripheral as an image forming apparatus according to the present invention. 2 is a functional block diagram illustrating a basic configuration of a control system of the multifunction machine. FIG. FIG. 4 is a functional block diagram of an abnormality detection system that detects a current applied to a charging roller and detects occurrence of a leak or adhesion of foreign matter. It is a functional block diagram which shows the circuit structure of an electric current detection part. It is a graph which shows the change of the detection electric current value before a foreign material adheres (normal time) and when a foreign material adheres. It is a graph which shows the change of the detection electric current value before a leak generate | occur | produces (normal time) and at the time of a leak generate | occur | produce. It is a functional block diagram which shows other embodiment of the determination part. It is a flowchart which shows the process sequence of the abnormality detection concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multifunctional device 2 Scanner part 3 Image forming part 4 Automatic document feeder 31 Image forming system 31a Laser scanning unit 31b Photosensitive drum 31c Developing device (developing mechanism)
31d Transfer roller 31e Cleaning device (cleaning mechanism)
31f Charging roller 51 Constant voltage power supply 52 Current detection unit 52a First current detection unit 52a1 Average value calculation unit 52a2 First peak value detection unit 52a3 First differential amplifier 52a4 First comparator 52b Second current detection unit 52b2 Second peak Value detection unit 52b3 Second differential amplifier 52b4 Second comparator 53 Determination unit 54 Display unit

Claims (6)

In an image forming apparatus comprising: an electrostatic latent image carrier; a charging member that applies a charge to the surface of the electrostatic latent image carrier and uniformly charges the surface; and a power source that applies a voltage to the charging member.
A current detection unit for detecting a current when a predetermined constant voltage is applied to the charging member during an image forming operation ;
An average value calculation unit for calculating an average value in the charging member is longer than the time for one rotation in a predetermined measurement range of the detected current by the current detection unit,
A first peak value detector that detect the minimum current value in the predetermined measurement range when the detected by the current detector current decreases,
A first comparison unit that compares a difference between a minimum current value detected by the first peak value detection unit and an average value of currents obtained by the average value calculation unit and a predetermined first threshold;
A second peak value detection unit for detecting a maximum current value in a predetermined measurement range when the current detected by the current detection unit increases;
A second comparison unit that compares a difference between a maximum current value detected by the second peak value detection unit and an average value of currents obtained by the average value calculation unit and a predetermined second threshold;
An image forming apparatus comprising: a determination unit that determines an abnormality of the charging member or the electrostatic latent image carrier based on a comparison result of the first comparison unit or a comparison result of the second comparison unit. apparatus. The image forming apparatus according to claim 1, wherein the current detection unit is controlled to detect a current with a predetermined time delay when the power is turned on . The determination unit obtains the period of the peak current detected by the first peak value detection unit, and determines whether the charging member or the electrostatic latent image carrier is abnormal based on the obtained result. determination to the image forming apparatus according to claim 1 or claim 2, characterized in Rukoto. The image forming apparatus according to any one of claims 1 to 3, characterized that you have multiple values is set as the first threshold value. The image forming apparatus according to any one of claims 1 to 4, wherein a plurality of values are set as the second threshold value. In the step of uniformly charging the surface of the electrostatic latent image carrier by applying a voltage to the charging member that applies a charge to the surface of the electrostatic latent image carrier, the current applied to the charging member is detected. An anomaly detection method for determining an anomaly,
A current detection procedure for detecting a current when a predetermined constant voltage is applied to the charging member during an image forming operation;
An average value calculation procedure for calculating an average value in a predetermined measurement range of the current detected in the current detection procedure in a time longer than a time in which the charging member makes one rotation;
A first peak value detection procedure for detecting a minimum current value in a predetermined measurement range when the current detected by the current detection procedure decreases;
A second peak value detection procedure for detecting a maximum current value in a predetermined measurement range when the current detected in the current detection procedure increases;
A procedure for comparing a difference between a minimum current value detected by the first peak value detection procedure and an average value of currents obtained by the average value calculation procedure with a predetermined first threshold, or the second peak Based on the procedure of comparing the difference between the maximum current value detected by the value detection procedure and the average value of the current obtained by the average value calculation procedure with a predetermined second threshold value, the charging member or the static member And a determination procedure for determining an abnormality of the electrostatic latent image carrier.

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