JP2013195471A - Power supply unit, image forming apparatus, and output error detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply unit promptly detecting a short-circuit state without erroneously detecting an output of the power supply device as the short-circuit state, and an image forming apparatus.SOLUTION: A power supply unit 51 comprises: a power supply part 52 for supplying a current to a capacitive load 360; a voltage dividing resistor 54 series-connected to the capacitive load; an error detection part 53 for measuring a voltage between both ends of the voltage dividing resistor 54 when the power supply part 52 supplies to the capacitive load 360 a detection current for detecting an error of an output of the power supply part 52, and detecting the error of the output of the power supply part 52 according thereto; and a control part 190 for controlling the power supply part 52 so as to supply to the capacitive load 360 a current whose absolute value is larger than that of the detection current for a first period just before supplying the detection current to the capacitive load 360, and thereby to decrease the current to the detection current in the following second period.

Description

  The present invention relates to a power supply unit for checking an output abnormality, an image forming apparatus provided with the power supply unit, and an output abnormality detection method.

  In an electrophotographic color image forming apparatus, when a toner image formed on a photosensitive member is transferred to an intermediate transfer member, a high voltage is applied as a transfer voltage from a power supply device between the photosensitive member and the intermediate transfer member. Further, when the toner image transferred to the intermediate transfer member is transferred to a sheet, a transfer voltage is applied between the intermediate transfer member and the transfer roller.

  In the image forming apparatus, if the power supply device fails, the transfer voltage cannot be applied and the toner image cannot be transferred. Thus, some conventional image forming apparatuses detect an output abnormality of the power supply apparatus when the transfer voltage is output from the power supply apparatus to the load.

  For example, the image forming apparatus described in Patent Document 1 confirms a short circuit of the power output, and when the short circuit is detected, the abnormal operation is stopped by stopping the abnormal operation of the entire apparatus and ensuring the safety of the power apparatus. Immediately stop the drive of the high-voltage power supply to grasp the cause and remove the cause.

JP 2005-117769 A

  However, in the image forming apparatus, the load of the photosensitive member, the intermediate transfer member, the transfer roller, and the like to which the power supply device applies a high voltage is a capacitive load as is well known. As shown in FIG. 1, when a constant current is supplied from a power supply device with a normal output to a capacitive load, the transfer voltage applied between the intermediate transfer member and the transfer roller does not rise sharply, and the output of the power supply device. It takes time to reach a voltage value that can be determined to be normal.

  For this reason, in order to start image formation promptly, when a short-circuit of the output of the power supply device is confirmed immediately after starting the supply of current from the power supply device to the capacitive load, the low voltage state continues for a while, so that the short-circuit state is established. May be misdetected.

  SUMMARY An advantage of some aspects of the invention is that it provides a power supply unit, an image forming apparatus, and an output abnormality detection method that can quickly detect an output abnormality without erroneously detecting the output of the power supply device as a short-circuit state.

  The power supply unit of the present invention includes a power supply unit, a voltage dividing resistor, an abnormality detection unit, and a control unit. The power supply unit supplies current to the capacitive load. The voltage dividing resistor is connected in series with the capacitive load. The abnormality detection unit measures the voltage across the voltage dividing resistor when the power supply unit supplies the capacitive load with a detection current for detecting an abnormality in the output of the power supply unit, and based on the result. To detect abnormalities in the output of the power supply. The control unit supplies a current having a larger absolute value than the detection current for the first period immediately before supplying the detection current to the capacitive load, and reduces the current to the detection current in the subsequent second period. To control.

  In this configuration, the power supply unit supplies a current having an absolute value larger than the detected current for the first period immediately before supplying the detected current to the capacitive load, so that the capacitive load can be charged quickly. Thereby, the voltage between both ends of the capacitive load can be rapidly increased to the detection voltage for detecting an abnormality of the power supply unit, and the same state as the short state can be made in a shorter time than before. Accordingly, the output abnormality of the power supply apparatus is not erroneously detected as a short-circuit state, and the output abnormality can be detected promptly immediately after the supply of current having a larger absolute value than the detected current is started.

  Further, by connecting a voltage dividing resistor in series with the capacitive load, the voltage across the voltage dividing resistor becomes a voltage corresponding to the voltage across the capacitive load. Therefore, the abnormality of the power supply unit can be detected by measuring the voltage across the voltage dividing resistor. Also, by making the resistance value of the voltage dividing resistor connected in series with the capacitive load very small compared to the capacitive load, even if the voltage across the capacitive load is high, the voltage dividing resistor The voltage between both ends can be lowered, and the withstand voltage of the abnormality detection unit can be lowered. In addition, since a current having an absolute value larger than the detection current is supplied for the first period and then the current is reduced to the detection current in the subsequent second period, the voltage across the capacitive load is detected as an abnormality in the power supply unit. It is possible to prevent the detection voltage from fluctuating due to the inductor component included in the capacitive load after rapidly increasing to the detection voltage for use.

  The capacitive load includes not only a capacitor component but also an inductor component.

  In the above invention, the control unit controls the power supply unit so as to decrease the current continuously or stepwise in the second period.

  In this configuration, the current fluctuation amount per unit time is reduced by reducing the current continuously or stepwise in the second period, so that the detection voltage can be prevented from fluctuating.

  The image forming apparatus according to the present invention includes an image forming unit, a transfer unit, and a power supply unit. The image forming unit forms a toner image. The transfer unit is a capacitive load and transfers the toner image formed by the image forming unit to a recording medium. The power supply unit applies a voltage for transferring the toner image to the transfer unit.

  In this configuration, an output abnormality of the power supply unit that supplies current to the transfer unit can be detected immediately after the start of supplying a current having a larger absolute value than the detected current.

  In the above invention, the control unit detects an abnormality of the output of the power supply unit by the abnormality detection unit before the transfer unit transfers the toner image.

  In this configuration, it is possible to prevent the occurrence of a problem that the toner image cannot be normally transferred by detecting the output abnormality of the power supply unit before the toner image is transferred.

  According to the present invention, an output abnormality can be quickly confirmed without erroneously detecting the output of the power supply device as a short state.

It is a time chart which shows the change of the voltage and electric current which the conventional power supply device supplies to a capacitive load. 1 is a configuration diagram of an image forming apparatus. 1 is a block diagram of an image forming apparatus. (A) is a circuit diagram of a power supply unit having a voltage dividing resistor between the driving roller and the ground. FIG. 4B is a circuit diagram of a power supply unit having a voltage dividing resistance between the secondary transfer roller and the power supply unit. It is a time chart which shows the change of the voltage and electric current which a power supply unit supplies to a capacitive load. (A) shows a change in voltage between both ends of the transfer portion. (B) shows a change in current supplied by the power supply unit. It is a time chart which shows the change of a voltage and an electric current when the electric current which a power supply unit supplies to a capacitive load is reduced in steps. (A) shows a change in voltage between both ends of the transfer portion. (B) shows a change in current supplied by the power supply unit. It is a time chart which shows the change of a voltage and an electric current when the electric current which a power supply unit supplies to a capacitive load is decreased continuously. (A) shows a change in voltage between both ends of the transfer portion. (B) shows a change in current supplied by the power supply unit. It is a flowchart for demonstrating the detection process of the output abnormality of a power supply unit.

  A power supply unit according to an embodiment of the present invention and an image forming apparatus including the power supply unit will be described.

  As illustrated in FIG. 2, the image forming apparatus 100 includes a paper feeding unit 80, an image reading unit 90, and an image forming unit 110. In addition, the image forming apparatus 100 includes a panel unit 120 above the image reading unit 90. The panel unit 120 includes a display unit 130 and an operation unit 140 (not shown). The display unit 130 displays information notified to the user. The operation unit 140 receives user operations.

  The image forming apparatus 100 uses a plurality of electrophotographic methods on a sheet as a recording medium based on image data of a document read by the image reading unit 90 or image data input from an external device via a communication unit 180 described later. A color or single color image forming process is performed.

  The image forming unit 110 includes an exposure unit 9, image forming units 10 </ b> A to 10 </ b> D, an intermediate transfer unit 60 that is a transfer unit 360, a secondary transfer unit 30, a fixing unit 70, and a power supply unit 51 described later.

  The image forming unit 10A includes a developing device 2A, a photosensitive drum 3A, a cleaner unit 4A, and a charger 5A, and forms a black (hereinafter referred to as K) image. The charger 5A uniformly charges the surface of the photosensitive drum 3A to a predetermined potential. The developing device 2A visualizes the electrostatic latent image formed on the photosensitive drum 3A by exposure of the exposure unit 9 into a K toner image. The cleaner unit 4A collects the toner remaining on the peripheral surface of the photosensitive drum 3A. The image forming units 10B to 10D are configured in the same manner as the image forming unit 10A, and are respectively cyan (hereinafter referred to as C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y). The toner images are formed on the surfaces of the photosensitive drums 3B to 3D.

  The exposure unit 9 is a laser scanning unit including optical system components such as a semiconductor laser, a polygon mirror, an fθ lens, and a reflection mirror. The exposure unit 9 exposes and scans the surfaces of the photosensitive drums 3A to 3D of the image forming units 10A to 10D along the axial direction with the laser beams modulated by the image data of Y, M, C, and K, respectively. An electrostatic latent image is formed.

  The intermediate transfer unit 60 includes an intermediate transfer belt 61, a driving roller 62, a driven roller 63, primary transfer rollers 64A to 64D, a cleaning unit 65, a pre-transfer charger 67, and a counter roller 66. The intermediate transfer belt 61 is stretched around a driving roller 62, a driven roller 63, and a counter roller 66, and moves along a circulation path that passes through the image forming units 10D, 10C, 10B, and 10A in this order. Each of the primary transfer rollers 64A to 64D is disposed to face the photosensitive drums 3A to 3D with the intermediate transfer belt 61 interposed therebetween, and the toner images formed on the peripheral surfaces of the photosensitive drums 3A to 3D are intermediate transferred. Primary transfer is performed on the surface of the belt 61. When the toner image is transferred, a transfer voltage is applied between the photosensitive drums 3A to 3D and the opposing primary transfer rollers 64A to 64D.

  During the color image forming process, the Y, M, C, and K toner images are sequentially superimposed and transferred onto the surface of the intermediate transfer belt 61 while the intermediate transfer belt 61 moves along the circulation path. During the monochrome image forming process, only the K toner image is transferred to the surface of the intermediate transfer belt 61 while the intermediate transfer belt 61 moves along the circulation path.

  The pre-transfer charger 67 is a corona discharger, and applies a charge having the same polarity as the toner to the toner image on the intermediate transfer belt 61.

  The secondary transfer unit 30 includes a secondary transfer belt 31 and a secondary transfer roller 32. The secondary transfer belt 31 is stretched around a plurality of rollers and moves along a predetermined circulation path. The secondary transfer roller 32 is disposed to face the driving roller 62 with the secondary transfer belt 31 and the intermediate transfer belt 61 interposed therebetween. The secondary transfer unit 30 secondarily transfers the toner image on the surface of the intermediate transfer belt 61 to a sheet conveyed to a secondary transfer position between the intermediate transfer belt 61 and the secondary transfer belt 31. The toner image on the intermediate transfer belt 61 is transferred onto the sheet by electrostatic force at the secondary transfer position. The toner remaining on the surface of the intermediate transfer belt 61 after the secondary transfer is collected by the cleaning unit 65.

  The fixing unit 70 heats and pressurizes the sheet on which the toner image is transferred after passing through the secondary transfer position, and fixes the toner image on the surface of the sheet. The paper that has passed through the fixing unit 70 is discharged to the paper discharge tray 91.

  The paper feed unit 80 includes a paper feed cassette 81 and a manual feed tray 82. The paper feed cassette 81 stores a plurality of sheets used for image forming processing and is provided below the exposure unit 9. The manual feed tray 82 is provided on the side surface of the image forming apparatus 100. The paper feed unit 80 feeds paper one by one from the paper feed cassette 81 or the manual feed tray 82 to the paper transport path 40. The sheet conveyance path 40 is formed between the sheet feeding unit 80 and the intermediate transfer belt 61 and the secondary transfer unit 30 and the sheet discharge tray 91 via the fixing unit 70.

  Next, a control system of the image forming apparatus 100 will be described. As shown in FIG. 3, the control unit 190 of the image forming apparatus 100 includes a paper feeding unit 80, an image reading unit 90, an image forming unit 110, a display unit 130, an operation unit 140, a storage unit 160, an image processing unit 170, and Each communication unit 180 is controlled. The communication unit 180 receives image data output from an external device. In addition, the image forming unit 110 includes a power supply unit 51. The power supply unit 51 includes a power supply unit 52 and an abnormality detection unit 53, and the control unit 190 controls them.

  The power supply unit 51 includes a sub control unit, and the sub control unit can be configured to control the operation of the power supply unit 51.

  Next, the power supply unit will be described. As illustrated in FIG. 4A, the power supply unit 51 includes a power supply unit 52, an abnormality detection unit 53, and a resistor 54. The power supply unit 52 is a constant voltage source, one of the outputs is connected to the ground, and one of the outputs is connected to the secondary transfer roller 32. The secondary transfer roller 32 is electrically connected to the drive roller 62 via the secondary transfer belt 31 and the intermediate transfer belt 61. The drive roller 62 is connected to the ground via a resistor 54. The resistor 54 corresponds to a voltage dividing resistor and is installed to detect an output abnormality of the power supply unit 52.

  In the following description, the secondary transfer unit 30 (secondary transfer roller 32, secondary transfer belt 31 and the like), the intermediate transfer belt 61, and the driving roller 62 are referred to as a transfer unit 360.

  The secondary transfer roller 32, the secondary transfer belt 31, the intermediate transfer belt 61, and the drive roller 62 constituting the transfer unit 360 are usually made of synthetic rubber, synthetic resin, resin foam, or the like, and have an extremely high electric resistance value. The resistance value is, for example, 1 × 10E5Ω to 1 × 10E10Ω. The transfer unit 360 is a capacitive load as a whole, and an equivalent circuit thereof can be considered as a configuration in which a resistance component Rt and a capacitor component Ct are connected in parallel and an inductor component Lt is further included. When a high voltage is applied from the power supply unit 52 while the transfer unit 360 is in a pressure contact state, a transfer current of several μA to several tens of μA flows according to the applied voltage.

  When the operation unit 140 receives an image formation start operation or when the communication unit 180 receives print data, the control unit 190 controls the power supply unit 52 to output a predetermined voltage and current.

  The control unit 190 checks the output abnormality of the power supply unit 52 before executing the transfer of the toner image in order to prevent a problem from occurring when the toner image is transferred. Specifically, for example, 5 μA is supplied to the transfer unit 360 as the detection current I1 for detecting the output of the power supply unit 52 to the transfer unit 360 and the resistor 54 connected in series to the transfer unit 360. At this time, the voltage (detection voltage V1) between both ends of the resistor 54 is confirmed by the abnormality detection unit 53.

  When a voltage is applied from the power supply unit 52 to the transfer unit 360, the voltage across the transfer unit 360 becomes a high voltage, and in order to measure this voltage, it is necessary to take measures such as increasing the withstand voltage of the measurement circuit. Become. Therefore, in the present invention, a resistor 54 is connected in series as a voltage dividing resistor to the transfer unit 360, and the voltage across the resistor 54 is measured by the abnormality detection unit 53. Although the voltage between both ends of the resistor 54 is several V to several tens V depending on the resistance value, the withstand voltage of the abnormality detection unit 53 can be lowered.

  When the abnormality detection unit 53 detects that the voltage between both ends of the transfer unit 360, which is a capacitive load, is less than or equal to a preset first threshold value or more than the second threshold value based on the voltage across the resistor 54, Since an abnormality (short circuit state or open state) has occurred in the power supply unit 52, a signal is output to the control unit 190. When the signal is input from the abnormality detection unit 53, the control unit 190 stops the operation of the power supply unit 52.

  The power supply unit can also be configured as a power supply unit 51B shown in FIG. That is, the resistor 54 </ b> B may be provided between the secondary transfer roller 32 and the power supply unit 52 as a voltage dividing resistor for the abnormality detection unit 53 to detect an abnormality in the power supply unit 52. Even in this configuration, the voltage across the resistor 54B is a voltage corresponding to the voltage across the transfer unit 360. Therefore, the open state and the short state of the power supply unit 52 can be detected according to the measurement result between both ends of the transfer unit 360.

  Next, characteristic operations of the present invention will be described. As described above, the transfer unit 360 through which the power supply unit 51 passes current is a capacitive load as a whole. Therefore, when the output abnormality of the power supply unit 52 is confirmed, as described with reference to FIG. 1, a constant detection current (for example, 5 μA) is supplied from the power supply unit 52 to the capacitive load until the detection voltage is reached. Takes a long time, and there is a risk of erroneous detection of a short state.

  Therefore, in the present invention, in order to solve this problem, when confirming the presence or absence of abnormality of the power supply unit 52, as shown in FIG. 5, immediately before supplying the detection current to the transfer unit 360 which is a capacitive load, The power supply unit 52 is controlled so as to supply a current having a larger absolute value than the detection current (hereinafter referred to as a voltage adjustment current). The power supply unit 52 is a constant voltage source. For example, as shown in FIG. 5B, when the detection current is 5 μA, 25 μA is supplied as the voltage adjustment current for a certain period (first period) T1 (10 ms). When 10 ms elapses, the current value supplied from the power supply unit 52 is changed to the detection current (5 μA). Note that the voltage adjustment current and the period T1 during which this current flows are set to values that can sufficiently charge the capacitor component Ct of the capacitive load. That is, the voltage adjustment current may be set to a value of 25 μA to 40 μA, for example, depending on the ambient environment such as temperature and humidity and the capacitance of the capacitive component of the capacitive load. Further, the certain period (first period) T1 is set to, for example, 5 ms to 20 ms.

  When the voltage adjustment current is supplied before the detection current is supplied in this way, as shown in FIG. 5A, the capacitor component Ct is rapidly charged to reach a steady state, and the voltage across the transfer unit 360 is When the output of the power supply unit 52 is normal, the detection voltage (7 kV) is reached in a short time. When the output of the power supply unit 52 is abnormal, the voltage across the transfer unit 360 immediately becomes equal to or lower than the first threshold value (100 V) or equal to or higher than the second threshold value (8 kV). Therefore, the output abnormality of the power supply unit 52 can be confirmed immediately after the supply of the voltage adjustment current is started.

  If the current is rapidly decreased from the voltage adjustment current to the detection current immediately after the voltage adjustment current is supplied, depending on the surrounding environment (ambient temperature and humidity), an inductor component (not shown) included in the transfer unit 360 may be used. As shown in FIG. 5A due to the influence, the voltage (detection voltage) between both ends of the transfer unit 360 may temporarily fluctuate, and an output abnormality (for example, a short state) of the power supply unit 52 may be erroneously detected. There is. When the detection voltage fluctuates in this way, the detection voltage is usually stabilized after a time of about 10 ms to 30 ms has elapsed. Therefore, the control unit 190 checks the output of the abnormality detection unit 53 after the detection voltage is stabilized.

  When the detection voltage fluctuates as described above, the fluctuation in the detection voltage can be prevented by reducing the current supplied to the transfer unit 360 to a detection current at a predetermined rate after supplying the voltage adjustment current.

  For example, as shown in FIG. 6B, the current supplied to the transfer unit 360 is decreased stepwise from the voltage adjustment current to the detection current. That is, immediately before the detection current is supplied, the voltage adjustment current (25 μA) is supplied for a first period T1 (10 ms) from the state where no current is supplied. In the second period T2 (30 ms) following the first period T1, the current value is decreased stepwise by 5 μA every time 10 ms elapses, and is changed to the detected current (5 μA).

  Alternatively, as shown in FIG. 7B, the current supplied to the transfer unit 360 is continuously reduced from the voltage adjustment current to the detection current. That is, immediately before the detection current is supplied, the voltage adjustment current (25 μA) is supplied for a first period T1 (10 ms) from the state where no current is supplied. In the second period T2 (30 ms) following the first period T1, the current supplied to the transfer unit 360 is continuously reduced to the detection current (5 μA).

  By doing so, the applied voltage of the transfer unit 360 becomes the inspection voltage (7 kV) in a short time, and the influence of the inductor component can be suppressed, and the inspection voltage, which is the voltage across the transfer unit 360, varies. do not do. Along with this, the detection voltage, which is the voltage across the resistor 54, does not fluctuate and becomes stable. Therefore, the output abnormality of the power supply unit 52 can be confirmed immediately after the voltage adjustment current is supplied.

  The second period T2 during which the voltage adjustment current is reduced to the detection current is set according to the ambient environment such as the inductor component, capacitor component, temperature, and humidity of the transfer unit 360. For example, the second period T2 is set to 20 ms to 50 ms, for example.

  Next, output abnormality confirmation processing of the power supply unit 52 will be described based on the flowchart shown in FIG.

  The control unit 190 of the image forming apparatus 100 stands by until an image forming execution instruction is received (S1: N).

  When the operation unit 140 accepts an image formation execution instruction or the communication unit 180 accepts input of image data from an externally connected device (S1: Y), the control unit 190 before the transfer unit transfers the toner image. Then, an output command is output to the power supply unit 52 to control the voltage adjustment current (25 μA) to flow for 10 ms (during the first period T1) (S2).

  Subsequently, the control unit 190 outputs an output command to the power supply unit 52 to reduce the voltage adjustment current (25 μA) to the detection current (5 mA) (S3).

  The method of reducing the voltage adjustment current to the detection current is determined according to the ambient environment, the size of the capacitive load or inductive load of the transfer unit 360, and the like. That is, as shown in FIG. 5B, when the detection voltage hardly fluctuates even if the voltage adjustment current supplied to the transfer unit 360 is rapidly decreased from the voltage adjustment current to the detection current, the transfer unit is used as such. The current supplied to 360 is changed. On the other hand, when the detection voltage fluctuates when the voltage adjustment current supplied to the transfer unit 360 is rapidly decreased from the voltage adjustment current to the detection current, as shown in FIG. 6B or FIG. In two periods T2, the voltage adjustment current is decreased stepwise or continuously.

  The voltage across the transfer unit 360 is equal to or lower than the first threshold value (100 V) when the output of the power supply unit 52 is in a short state.

  The voltage across the transfer unit 360 is equal to or higher than the second threshold (8 kV) when the output of the power supply unit 52 is open.

  When the output of the power supply unit 52 is normal, the voltage across the transfer unit 360 is a value between the first threshold value (100 V) and the second threshold value (for example, 7 kV).

  The voltage between both ends of the resistor 54 is a voltage corresponding to the voltage between both ends of the transfer unit 360.

  The abnormality detection unit 53 measures the voltage across the resistor 54 and confirms the output abnormality of the power supply unit 52. That is, when the voltage between both ends of the resistor 54 is a voltage corresponding to a first threshold value (for example, 100 V) or less in the voltage between both ends of the transfer unit 360 (S4: Y), the abnormality detection unit 53 outputs the power. It is determined that there is an abnormality, that is, the output is in a short state, and a signal to that effect is output to the control unit 190. When the control unit 190 detects this signal, the control unit 190 stops the power supply unit 52. In addition, the control unit 190 causes the display unit 130 to display that the output of the power supply unit 52 is in a short state without performing the image forming operation (S5). Then, the process ends.

  On the other hand, when the voltage between both ends of the resistor 54 is equal to or higher than the second threshold (for example, 8 kV) in the voltage between both ends of the transfer unit 360 (S6: Y), the abnormality detection unit 53 It is determined that the output is abnormal, that is, the output is in an open state, and a signal to that effect is output to the control unit 190. When the control unit 190 detects this signal, the control unit 190 stops the power supply unit 52. Further, the control unit 190 causes the display unit 130 to display that the output of the power supply unit 52 is in an open state without performing an image forming operation (S7). Then, the process ends.

  In addition, the control unit 190 determines that the voltage V across the resistor 54 is a detection voltage, that is, a voltage corresponding to the first threshold value <V <the second threshold value (for example, 7 kV) in the voltage across the transfer unit 360. Sometimes (S6: N), since no abnormality has occurred in the output of the power supply unit 52, the abnormality detection process of the power supply unit 52 is terminated. Then, the control unit 190 forms an image. That is, the image forming unit forms an image, the secondary transfer unit transfers the toner image onto the sheet, the fixing unit fixes the toner image on the sheet, and the sheet is discharged.

  As described above, the power supply unit of the image forming apparatus supplies the voltage adjustment current that is larger than the detection current immediately before supplying the detection current, so that the capacitive load can be rapidly charged. Thus, immediately after the voltage adjustment current is supplied, the output state of the power supply unit 52 can be determined based on the voltage between both ends of the transfer unit 360, so there is no possibility of erroneously detecting a short state. If the output of the power supply unit 52 is normal as a result of the determination, image formation can be performed immediately.

  In the above description, the power supply unit that outputs a transfer voltage for secondary transfer of the toner image has been described. However, the present invention is not limited to this, and the toner image formed on the photosensitive drums 3A to 3D is transferred to the intermediate transfer belt 61. The present invention can also be applied to a power supply unit (not shown) that outputs a transfer voltage for transfer.

  Further, the present invention can be applied not only to a power supply unit that outputs a transfer voltage of an image forming apparatus, but also when detecting an output abnormality of a power supply that is generally used.

  In the above description, since negative polarity toner is used in the image forming apparatus, the polarity of the secondary transfer output voltage is assumed to be positive. However, the present invention is not limited to this, and when positive polarity toner is used. The polarity of the secondary transfer output voltage can be negative.

3A to 3D ... Photosensitive drums 10A to 10D ... Image forming unit 30 ... Secondary transfer unit 31 ... Secondary transfer belt 32 ... Secondary transfer roller 40 ... Paper transport path 51 ... Power supply unit 52 ... Power supply unit 53 ... Abnormality detection unit 54, 54B ... Resistance 60 ... Intermediate transfer unit 61 ... Intermediate transfer belt 62 ... Drive roller 63 ... Driven roller 80 ... Paper feed unit 100 ... Image forming unit 110 ... Image forming unit 120 ... Panel unit 130 ... Display unit 140 ... Operation unit 160: Storage unit 170 ... Image processing unit 180 ... Communication unit 190 ... Control unit 360 ... Transfer unit

Claims (5)

A power supply for supplying current to the capacitive load;
A voltage dividing resistor in series with a capacitive load;
When the power supply unit supplies the capacitive load with a detection current for detecting an abnormality in the output of the power supply unit, the voltage across the voltage dividing resistor is measured, and based on the result. An abnormality detection unit for detecting an abnormality in the output of the power supply unit;
Immediately before supplying the detection current to the capacitive load, a current having a larger absolute value than the detection current is supplied for the first period, and the current is reduced to the detection current in the subsequent second period. A control unit for controlling the unit,
Power supply unit with   2. The power supply unit according to claim 1, wherein the control unit controls the power supply unit so as to decrease the current continuously or stepwise in the second period. An image forming unit for forming a toner image;
A transfer unit serving as the capacitive load for transferring the toner image formed by the image forming unit to a recording medium;
The power supply unit according to claim 1, wherein a voltage for transferring a toner image is applied to the transfer unit.
An image forming apparatus.   The image forming apparatus according to claim 3, wherein the control unit detects an abnormality in the output of the power supply unit by the abnormality detection unit before the transfer unit transfers the toner image.   Measure the voltage across the voltage dividing resistor connected in series with the capacitive load by supplying a detection current to the power supply that supplies current to the capacitive load to detect abnormalities in the output of the power supply. Then, when detecting an output abnormality of the power supply unit based on the result, immediately before the power supply unit supplies the detection current, a current having a larger absolute value than the detection current is supplied for a first period, An output abnormality detection method for reducing the current to the detection current in a subsequent second period.

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