JP2010286787A - Power source control device, image forming apparatus and power source control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power source control device, an image forming apparatus and a power source control method, capable of suppressing an abnormal discharge history from remaining on a photoreceptor, and reducing power consumption. <P>SOLUTION: The power source control device 100, which generates an AC voltage to be applied to a charging member, includes: a reference voltage signal output means 81 which outputs the reference voltage signal of the AC voltage; a feedback means 85 which outputs a voltage signal corresponding to a difference between the reference voltage signal and a feedback voltage detected from the charging member; an amplifying means 86 which amplifies the voltage signal and generates the AC voltage when receiving power supply; a voltage applying means 87 which applies the voltage in which the AC voltage and the DC voltage are superposed, to the charging member; and power-off means 82 and 90 which turn off the power to be supplied to the AC voltage generating means 86, after the reference voltage signal output means 81 turns off the reference voltage signal, and also, after a lapse of time required to reduce the voltage of the charging member 30 lower than a discharge start voltage. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power source control device for power supplied to a charging member, and more particularly to a power source control device, an image forming device, and a power source control method for image formation employing an electrophotographic system.

  FIG. 16 is a schematic configuration diagram of an image forming unit according to a conventional electrophotographic method. The image forming unit includes a charging roller 202 that charges the peripheral surface of the photosensitive member 204 around a drum-shaped photosensitive member 204 that is an image carrier, and a photosensitive member 35 that uses a laser beam to form a latent image on the photosensitive member 204. An exposure device 206 that scans the laser beam, a mirror 203 that guides the laser beam, a developing device 205 that attaches toner to an image formed as a latent image and forms a toner image on the peripheral surface of the photoconductor, and the surface of the photoconductor 204 A cleaning device 201 for removing the toner remaining on the toner.

  As a form of the charging roller 202, a contact-type charging roller and a non-contact type charging roller are known. However, in recent years, a non-contact-type charging roller that charges the photosensitive member without bringing the charging surface into contact with the surface of the photosensitive member. (Hereinafter simply referred to as “charging roller”) is increasingly being used. In the non-contact type charging roller 202, the charging surface and the photosensitive member 204 do not come into contact with each other, so that the toner attached to the photosensitive member 204 is difficult to adhere to the charging roller 202. On the other hand, since a gap is formed between the charging roller 202 and the photosensitive member because of non-contact, the charging voltage may fluctuate and charging unevenness may occur. For this reason, in order to uniformly charge the photosensitive member 204, the charging device of the non-contact type charging roller 202 often adopts an AC + DC superimposing method (see, for example, Patent Document 1).

  FIG. 17A is an example of a diagram schematically showing an AC voltage applied to the charging roller 202. Thus, even if the photoreceptor 204 is charged by the non-contact charging roller by applying the AC voltage, the photoreceptor 204 can be uniformly charged.

By the way, after charging the photosensitive member 204, the charging device immediately stops the application of the AC voltage, but this may leave a residual voltage on the photosensitive member.
FIG. 17B is an example of a diagram schematically illustrating the AC voltage after application is stopped. For example, when the application is stopped at the peak of the AC voltage, an excessive residual voltage remains on the photoreceptor. If an excessive residual voltage is left on the photoconductor for a long time, a voltage history may remain on the photoconductor 204.

  Therefore, in order to turn off the AC voltage after reducing the residual voltage remaining on the photoconductor, a technique for turning off the clock signal after a predetermined time after stopping the output of the reference voltage defining the AC voltage has been proposed. (For example, refer to Patent Document 2).

  FIG. 17C is an example of a diagram schematically illustrating the AC voltage when the output of the reference voltage is stopped. It can be seen that the AC voltage gradually decreases according to a predetermined time constant. The charging device described in Patent Document 2 stops the clock signal after the time T2 determined by the time constant has elapsed after stopping the output of the reference voltage that defines the AC voltage. Since this clock signal defines the frequency of the AC voltage, by stopping the clock signal, the AC voltage decreases according to the time constant without showing a periodic change.

  However, since a general charging device amplifies the power supplied from the power source to the amplifier circuit and applies the AC + DC voltage to the photosensitive member 204, the power consumed by the charging device even when the clock signal is stopped. There is a problem that does not become zero. That is, since the AC voltage decreases as the time T2 elapses after the reference voltage is stopped, it is possible to prevent an excessive residual voltage from remaining on the photosensitive member, but the problem remains that power is still consumed. Remain.

  Therefore, it can be considered to turn off the power supplied to the amplifier circuit. FIG. 17D is an example of a diagram schematically illustrating an AC voltage when power supplied to the amplifier circuit is turned off. Unlike FIGS. 17 (b) and 17 (c), the AC voltage can be drastically decreased (instantaneously reduced to zero). However, if the AC voltage is instantaneously reduced to zero, an abnormal discharge history may remain on the photoreceptor 204.

  An abnormal discharge history means that a maximum or minimum discharge history remains in a certain part of the photosensitive member 204 in the rotation direction. For example, if the AC voltage is instantaneously reduced to zero at the positive peak of the AC voltage, a large positive voltage discharge history may remain in parallel with the rotation axis of the photoconductor 204. In this case, black streaks (color streaks) appear on the paper printed by the image forming apparatus. Conversely, if the AC voltage is instantaneously reduced to zero at the negative peak of the AC voltage, a large negative discharge history may remain in parallel with the rotation axis of the photoconductor 204. In this case, white streaks appear on the paper printed by the image forming apparatus.

  That is, in the conventional charging device as in the cited document 2, it is possible to prevent both abnormal discharge history from remaining on the photoconductor and zero power consumption during standby of the image forming apparatus. There is a problem that it cannot be realized.

  SUMMARY An advantage of some aspects of the invention is that it provides a power supply control device, an image forming apparatus, and a power supply control method capable of suppressing abnormal discharge history from remaining on a photoreceptor and reducing power consumption. .

    In order to solve the above problems, the present invention provides a power supply control device for generating an AC voltage for application to a charging member, the reference voltage signal output means for outputting a reference voltage signal of the AC voltage, and the reference voltage A feedback means for outputting a voltage signal in accordance with a difference between the signal and a feedback voltage detected from the charging member; an amplifying means for receiving the power supply and amplifying the voltage signal and generating the AC voltage; After the AC voltage and DC voltage are superimposed and applied to the charging member, and after the reference voltage signal output means turns off the reference voltage signal, at least the voltage of the charging member is less than the discharge start voltage. And a power-off means for turning off the power supplied to the amplifying means after a lapse of decreasing time.

1 is an example of a schematic configuration diagram of an image forming apparatus. It is an example of the figure which shows a charging control apparatus and a charging roller typically. It is an example of the schematic hardware block diagram of a control board. It is an example of the functional block diagram of a high voltage power supply device and a control board. It is a figure which shows an example of the output of a filter circuit. It is an example of the figure explaining a trigger circuit. FIG. 3 is an example of a diagram illustrating a distance between a photoconductor and a charging roller and Paschen's law. It is an example of the figure explaining time for AC voltage to fall below discharge start voltage. It is an example of the figure which shows the relationship between AC voltage and fall time t1. FIG. 3 is an example of a flowchart illustrating a procedure for controlling an AC voltage applied to a charging roller by a charging control device. It is an example of the functional block diagram of a high voltage power supply device and a control board (Example 2). It is an example of the functional block diagram of a high voltage power supply device and a control board (Example 3). FIG. 9 is an example of a flowchart illustrating a procedure for controlling an AC voltage applied to a charging roller by a charging control device (third embodiment). It is an example of the functional block diagram of a high voltage power supply device and a control board (Example 4). FIG. 10 is an example of a flowchart illustrating a procedure for controlling an AC voltage applied to a charging roller by a charging control device (Example 4). It is a schematic block diagram of the image forming unit by the conventional electrophotographic system. It is an example of the figure which shows typically the AC voltage which a charging device applies to a charging roller (conventional figure).

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  First, an image forming apparatus 200 to which the charging control apparatus 100 of this embodiment is applied will be described. The image forming apparatus 200 is, for example, a copier, a printer, a facsimile, or an MFP (Multifunction Peripheral) having one or more of these functions. Further, a scanner function may be provided. The charge control device 100 of this embodiment can be suitably applied to the electrophotographic image forming apparatus 200.

  FIG. 1 shows an example of a schematic configuration diagram of an image forming apparatus 200. The image forming apparatus 200 in FIG. 1 is called an MFP. The MFP includes an automatic document feeder (ADF) 1000, a scanner unit 2000, an image forming unit 3000, and a paper feed unit 4000. The scanner unit 2000 conveys documents placed on the ADF 1000 or the document feeder 11 onto the contact glass 21 one by one, reads the image data from the document, and then ejects the document onto the sheet discharge tray 18. Specifically, the document set on the document feeder 11 is aligned in the width direction of the sheet by a side fence (not shown), separated from the lowest document by the sheet feed roller 12, and fed. It is conveyed on the contact glass 21 by the conveyance belt 19. The feeding unit 15 is provided with a document width detection sensor 13 and a document length detection sensor 14, which can detect the size (B5, A4, B4, etc.) of the document conveyed from the ADF 1000. The original on the contact glass 21 is discharged onto the paper discharge tray 18 by the conveying belt 19 and the paper discharge roller 16 after the reading of the image data is completed, and a series of operations is completed.

  Further, at the time of double-sided copying, the original is fed by the paper feed roller 12, passes through the contact glass 21 by the conveying belt 19, is reversed by the reversing claw 17, and is then conveyed again onto the contact glass 21, so The back side is read. Next, the document is transported by the transport belt 19, reversed by the reversing claw 17, and then transported onto the contact glass 21 again to read the surface of the document. Then, the document on the contact glass 21 is discharged onto the paper discharge tray 18 by the transport belt 19 and the paper discharge roller 16.

  The scanner unit 2000 includes a contact glass 21 for placing a document and an optical scanning system 20. The optical scanning system 20 includes an exposure lamp 23, a first mirror 26, a second mirror 24, a third mirror 25, a lens 22, and a full color CCD 27. The exposure lamp 23 and the first mirror 12 are mounted on a first carriage (not shown), and the first carriage moves in the sub-scanning direction at a constant speed by a stepping motor when reading a document. The second mirror 24 and the third mirror 25 are mounted on a second carriage (not shown), and the second carriage moves at a speed approximately half that of the first carriage by a stepping motor when reading a document. As the first carriage and the second carriage move, the image surface of the document is optically scanned, and the read data is imaged on the light receiving surface of the full-color CCD 27 by the lens 22 and subjected to photoelectric conversion. Image data photoelectrically converted into red (R), green (G), and blue (B) colors by the full color CCD 27 is A / D converted and subjected to various image processing.

  Further, when copying, image data is copied onto the paper by the image forming unit 3000. The image forming unit 3000 includes a laser output unit 28, an fθ lens 27, and a mirror 29. The laser output unit 28 includes a laser diode (LD), a polygon mirror, and a polygon motor. Around the photoreceptor 35, a charging roller 30, a black developing device 31, an LED writing unit 33 for writing an image of a red signal, a red developing device 34, a transfer device and a separator (not shown) are arranged.

  The charging roller 30 is a non-contact type charging roller as will be described later. The charging roller 30 is applied with an AC + DC voltage by the charging control device 100 and charges the peripheral surface of the photoreceptor 35. The laser output unit 28 emits a black signal laser beam modulated in accordance with an image read by a scanner during copying. The laser beam is guided so as to scan the peripheral surface of the photosensitive member 35 charged by the mirror 29 in the main scanning direction. As a result, a latent image is formed on the photoreceptor 35.

  The black developing device 31 and the red developing device 34 form a toner image (image visualized with toner) on the peripheral surface of the photoreceptor 35 by attaching toner to the latent image formed image. As described below, the sheet is conveyed to the transfer device 40 at a predetermined timing, and the toner image is transferred to the sheet by the transfer device 40. The toner remaining on the surface of the photoconductor 35 is removed by a cleaning device including a blade that is in sliding contact with the peripheral surface of the photoconductor 35.

  The sheet is selected from any of the duplex unit 46 in the image forming apparatus 200, the first tray 57, the second tray 54 in the sheet feeding unit 4000, the third tray 55, and the fourth tray 56. The selected paper is fed by the feed roller 43 and the separation roller 47, the first paper feeding device 48, the second paper feeding device 49, the third paper feeding device 51, or the fourth paper feeding device 52.

  The paper fed from the duplex unit 46 and the first tray 57 is transported upward by the vertical transport unit 45, and the second paper feeder 49, the third paper feeder 51, or the fourth paper feeder 52. Is fed via the bank vertical conveyance unit 53 and the vertical conveyance unit 45. Then, when a predetermined time elapses after the leading edge of the sheet is detected by the registration sensor 42, the sheet is abutted against the registration roller 41 and stops once. Further, the sheet is conveyed by the rotation of the registration roller 41 in synchronization with the sub-scanning effective period signal (FGATE), and the toner image on the photoconductor 35 is transferred.

  Next, the sheet is separated from the photoreceptor 35 by a separator (not shown), and then conveyed to the fixing device 37 by the conveying device 36, and the toner image is fixed by heat and pressure by the fixing device 37. The sheet after fixing is discharged onto the paper discharge tray 58 by the switching claw 39 and the paper discharge roller 38 during single-sided printing and double-sided printing during double-sided printing.

  The charging control device 100 of this embodiment will be described. The charging control apparatus 100 according to the present embodiment can turn off the power supplied to the amplifier circuit 86. In addition, the charging control device 100 of this embodiment controls the voltage value (amplitude) of the AC voltage applied to the charging roller 30 by the PWM signal. In such a charging control apparatus 100, the charging control apparatus 100 according to the present embodiment supplies the amplifier circuit 86 with the AC voltage falling time t1 determined by the time constant of the filter circuit after turning off the PWM signal. Turn off the power to be used.

  By waiting for the fall time t1 from turning off the PWM signal to turning off the power supplied to the amplifier circuit 86, an abnormal discharge history can be prevented from remaining on the photoconductor. Further, by turning off the power supplied to the amplifier circuit 86, power consumption during standby (while no image is formed) can be reduced.

  FIG. 2 is an example of a diagram schematically showing the charging control device 100 and the charging roller 30. The charging control device 100 includes a control board 61 and a high voltage power supply device 62. The charging control device 100 and the high-voltage power supply device 62 are connected by three signal lines, and the high-voltage power supply and the charging roller 30 are connected by one signal line. This figure shows only signal lines useful for this embodiment, and other signal lines are omitted.

  The high-voltage power supply device 62 is a device that supplies a high-voltage charging voltage (AC + DC voltage) to the charging roller 30 of the image forming apparatus 200. Since the present embodiment is characterized by the control of the AC voltage of the charging voltage, the charging voltage is hereinafter simply referred to as the AC voltage. The magnitude and frequency of the AC voltage are controlled by the control board 61. The control board 61 outputs the following three signals to the high voltage power supply device 62. With the three signals, the high voltage power supply device 62 can control the voltage value (amplitude) of the AC voltage, the frequency, and ON / OFF of the power supplied to the amplifier circuit 86.

PWM signal (corresponding to “reference voltage signal” in claims): AC voltage voltage value TRG signal: ON / OFF of power supply of amplifier circuit 86
CLK signal: AC voltage frequency The control board 61 is a form of a microcomputer, and includes hardware of a microcomputer represented by the CPU 71.
FIG. 3 shows an example of a schematic hardware configuration diagram of the control board 61. This figure is a hardware configuration diagram when the charging control device 100 is mainly implemented by software. For example, an IC generated for a specific function such as an ASIC (Application Specific Integrated Circuit) may be used.

  The control board 61 includes a CPU 71, a memory 72, a hard disk 73, an input device 74, a memory mounting unit 75, a display unit 76, and a network device 77. The hard disk 73 stores a program 70 for controlling the charging control device 100.

  The CPU 71 reads out and executes the program 70 from the hard disk 73 and controls the entire charging control device 100 in an integrated manner. The memory 72 is a volatile memory such as a DRAM, and serves as a work area when the CPU 71 executes the program 70. The input device 74 is an operation unit of the image forming apparatus 200, for example, and includes a touch panel and hard keys. Like a general computer, a mouse and a keyboard may be mounted. The display unit 76 is, for example, an LCD (Liquid Crystal Display) integrated with the operation unit.

  A storage medium 78 is detachable from the memory mounting portion 75, and is used when reading data from the storage medium 78 and writing data to the recording medium. The memory mounting unit 75 is, for example, a USB interface. The program 70 is distributed in a state stored in the storage medium 78, and the program 70 read from the storage medium 78 by the memory mounting unit 75 is installed in the hard disk 73. The storage medium 78 may be a nonvolatile memory such as a USB memory, a DIMM (Dual Inline Memory Module), a CD-ROM / RW, a DVD-ROM / RAM / RW, a Blu-ray disc, an SD card, a Memory Stick (registered trademark), or the like. It is a portable storage medium.

  The network device 77 is an interface (for example, an Ethernet (registered trademark) card) for connecting to a network such as a LAN or the Internet. The network device 77 executes processing according to a protocol defined in the physical layer and data link layer of the OSI basic reference model, and enables communication with various servers connected to the network. The program 70 can be downloaded from a predetermined server connected via a network.

  FIG. 4 shows an example of a functional block diagram of the high-voltage power supply device 62 and the control board 61. The control board 61 includes a PWM signal output unit 81, a trigger signal output unit 82, and a clock signal output unit 83. Each of these functions is realized by the CPU 71 of the control board 61 executing the program 70. The PWM signal output unit 81 is connected to the filter circuit 84, and the trigger signal output unit 82 and the clock signal output unit 83 are connected to the amplifier circuit 86 via an input / output interface (not shown).

  In the high-voltage power supply 62, the filter circuit 84 is connected to the positive side of the input terminal of the differential amplifier 85, and the charging AC voltage FB circuit 89 is connected to the negative side of the input terminal of the working amplifier. The output of the differential amplifier 85 is connected to the amplifier circuit 86. The amplification circuit 86 is connected to a high voltage conversion circuit 87, and the high voltage conversion circuit 87 is connected to a charging AC voltage FB circuit 89 via a capacitor. The high voltage conversion circuit 87, the charging AC voltage FB circuit 89, and the differential amplifier 85 constitute a negative feedback loop. The charging AC voltage FB circuit 89 is, for example, a half-wave rectifier circuit or a full-wave rectifier circuit. Further, a charging DC output circuit 88 is connected to the high voltage conversion circuit 87.

  The PWM signal output unit 81 outputs a PWM signal to the filter circuit 84 when an AC voltage is output to the charging roller 30. That is, when the image forming apparatus 200 charges the photoconductor 35 to form a latent image, the PWM signal output unit 81 outputs a PWM signal. The PWM signal is integrated by the filter circuit 84.

FIG. 5 is a diagram illustrating an example of the output of the filter circuit 84. Since the filter circuit 84 has a resistor and a capacitor connected in series, the voltage value output from the filter circuit 84 gradually increases according to the time constant τ ₁ (= R1 · C1) determined by the resistance value R1 and the capacitance C1. The voltage value of “amplitude of PWM signal × duty ratio” is reached. On the other hand, since the period of the PWM signal is sufficiently shorter than the time constant τ ₁ , the pulse is completely eliminated by the filter, and the output of the filter circuit 84 has a shape in which the voltage gradually increases.

  The AC voltage is determined mainly by the amplitude of the PWM signal, but the AC voltage can be adjusted with high accuracy by the duty ratio of the PWM signal. Therefore, the amplitude and duty ratio of the PWM signal become the output reference value of the AC voltage.

  For example, when the image forming apparatus 200 is turned on for the first time on the day, the PWM signal output unit 81 outputs PWM having a predetermined initial duty ratio. Then, the control board 61 detects the actual AC voltage and feedback-controls the duty ratio so that an appropriate value is detected. Once the duty ratio is determined, the relationship between the duty ratio and the AC voltage does not change greatly. For example, the PWM signal output unit 81 outputs a PWM signal having the same duty ratio until a predetermined number of prints are made. The output reference value is not necessarily a PWM signal, and may be a constant voltage whose value can be adjusted.

  The differential amplifier 85 outputs a voltage corresponding to the potential difference between two input voltages (the output voltage of the filter circuit 84 and the output voltage of the charging AC voltage FB circuit 89). The amplifier circuit 86 shapes the voltage output from the differential amplifier 85 into a sine wave. The amplification circuit 86 generates, for example, a positive rectangular wave corresponding to ON of the CLK signal and a negative rectangular wave corresponding to OFF using the ON / OFF of the CLK signal from the voltage before or after amplification. To do. By passing the rectangular wave through a low-pass filter and removing harmonics, a sine wave can be obtained. Therefore, the frequency of the clock signal becomes the frequency of the AC voltage.

  When a sine wave is generated before amplification, the amplifier circuit 86 further amplifies the waveform of the sine wave and outputs it to the high voltage conversion circuit 87. That is, the amplifier circuit 86 is supplied with power from a power supply Vd described later, and generates an AC voltage having an amplitude proportional to the voltage output from the differential amplifier 85.

  The high voltage conversion circuit 87 is mainly composed of a transformer or the like, and boosts the output of the amplifier circuit 86 to a high voltage output. The high-voltage conversion circuit 87 boosts the sine wave of several tens volts input from the amplifier circuit 86 to a sine wave of several kilovolts level, for example, and superimposes it on the DC voltage output from the charging DC output circuit 88, A charging AC + DC output is applied to the charging roller 30. The DC voltage output from the charging DC output circuit 88 is approximately the same as the charging voltage of the photoconductor 35. As described above, the charged AC + DC output is referred to as an AC voltage.

  Since the negative feedback loop is established by the amplification circuit 86, the high voltage conversion circuit 87, the charging AC voltage FB circuit 89, and the differential amplifier 85, the AC voltage applied to the charging roller 30 is the filter circuit 84 and the charging AC voltage FB circuit 89. When the output of the two coincides, it becomes stable.

[TRG signal]
The TRG signal will be described with reference to FIG. As shown in the figure, the amplifier circuit 86 is connected to a power supply Vd and GND1. The amplifier circuit 86 amplifies the sine wave generated from the rectangular wave with the power supplied from the power source Vd.

  FIG. 6B is an example for explaining the action of the trigger circuit 90 on the amplifier circuit 86. The trigger circuit 90 has two switches A and B, and each is connected to the trigger signal output unit 82. The switches A and B are turned on when the TRG signal is turned on and turned off when the TRG signal is turned off.

  The trigger circuit 90 is connected to the power sources Vcc and GND. Vcc is not the power supply voltage (100V / 200V) of the image forming apparatus 200 but the power supply voltage (24V) of the high-voltage power supply substrate, that is, the voltage supplied from the power supply unit (PSU) to the high-voltage power supply. GND is a ground potential of the image forming apparatus 200. Therefore, there is a relationship of Vcc> Vd, GND1> GND.

  When the TRG signal is ON, the switch A is ON, so that Vd and Vcc are equipotential. Further, since the switch B is turned on when the TRG signal is on, GND1 and GND are equipotential. Therefore, a current flows from Vcc to GND, and the amplifier circuit 86 consumes power.

  On the other hand, when the TRG signal is OFF, since the switch A is OFF, Vd and Vcc are electrically disconnected, and the switch B is OFF, so that GND1 and GND are electrically disconnected. Therefore, no current flows from Vd to GND1, and the amplifier circuit 86 can be prevented from consuming power. Therefore, the trigger signal output unit 82 outputs the TRG signal that is OFF to the trigger circuit 90, so that the amplifier circuit 86 can be prevented from consuming power during standby.

  Further, when the TRG signal is turned OFF, no power is supplied from the amplifier circuit 86 to the charging roller 30 side, so that the AC voltage goes to, for example, the ground on the photoconductor 35 side and instantaneously becomes zero. That is, when the TRG signal is turned OFF, the AC voltage applied to the charging roller 30 instantaneously becomes zero at the same time.

  The charging control device 100 according to the present embodiment prevents the abnormal discharge history from remaining on the photosensitive member 35 by controlling the timing at which the TRG signal is turned off.

[Timing to turn off the TRG signal]
First, a description will be given discharge starting voltage _{V 1.} In the case of the non-contact type charging roller 30 that forms a gap between the photosensitive member 35 and the charging roller 30, the surface of the photosensitive member 35 is charged by discharging.
FIG. 7A is an example for explaining the distance between the photosensitive member 35 and the charging roller 30. The non-contact type charging roller 30 applies a high voltage AC + DC voltage to the charging roller 30 and discharges it to the photoreceptor 35. Here, it is known that the discharge start voltage V ₁ required for the charging roller 30 to start discharging follows the Paschen's law.

FIG. 7B is an example for explaining Paschen's law. When the gap of the charging roller 30 and the photosensitive member 35 is d, the discharge starting voltage V ₁ was obtained as a function of atmospheric pressure and distance d. That is, the discharge start voltage V ₁ to the photosensitive member 35 is determined by the interval d and the atmospheric pressure. If it is the atmospheric pressure constant, the discharge starting voltage V ₁ was determined by the substantially interval d. Therefore, discharge starting voltages V ₁ is substantially constant.

Since abnormal discharge is also a form of discharge, it can be assumed that abnormal discharge does not occur below the discharge start voltage V ₁ determined by Paschen's law. Therefore, when the AC voltage decreases to less than the discharge start voltage _{V 1,} it can be seen that may be a TRG signal to OFF.

Figure 8 is an example of a diagram that AC voltage is described fall time t1 falls below the discharge starting voltage V _1. In FIG. 8, the vertical axis represents AC voltage, and the horizontal axis represents time. In FIG. 8, the periodic fluctuation of the AC voltage is omitted.

The amplifier circuit 86 amplifies the potential difference between the two input voltages output from the differential amplifier 85, but the input voltage on the negative feedback loop side follows the input voltage from the filter circuit 84 in a very short time. When the PWM signal is turned OFF, the input voltage from the filter circuit 84 to the differential amplifier 85 is attenuated according to the time constant τ ₁ of the filter circuit 84. Therefore, the AC voltage applied to the charging roller 30 is attenuated according to the time constant τ ₁ of the filter circuit 84. This time constant τ ₁ is the same time constant as when the AC voltage rises. That is, the AC voltage decreases with time according to the following equation.
AC voltage = V ₀ × exp (-t / τ ₁ )
Here, V ₀ is an AC voltage at time t = 0. Since the AC voltage starts to decrease when the voltage of the filter circuit 84 starts to decrease, it is when the PWM signal is turned OFF. Therefore, V ₀ is an AC voltage when the PWM signal is turned off.

From the above, since the PWM signal is turned OFF, if elapsed fall time t1 below the discharge starting voltages V ₁ shown in FIG. 8, even if the TRG signal to OFF, it is possible to prevent the abnormal discharge occurs . The fall time t1 can be calculated by the following equation.

Fall time t1 = τ ₁ × ln (V ₁ / V ₀ ) = R 1 · C 1 × ln (V ₁ / V ₀ )
The trigger signal output unit 82 turns off the TRG signal after the falling time t1 has elapsed since the PWM signal was turned off.

FIG. 9 is an example of a diagram illustrating the relationship between the AC voltage and the fall time t1. AC voltage is PWM signal is turned OFF at the time of the _{V 0.} The AC voltage decreases in proportion to exp (−t / τ ₁ ), and eventually decreases to less than the discharge start voltage V ₁ . From the PWM signal is turned OFF, the time until the AC voltage is less than the discharge starting voltage V ₁ is, when a fall time t1 determined by constant tau _1.

[Determination method of fall time t1]
The fall time t1 can be determined in several ways. The fall time t1 may be determined in advance and stored in the hard disk 73, calculated every predetermined period (every month, every week, every day), or calculated every time a predetermined number of sheets are printed. It may be calculated every time the PWM signal is turned off. Such calculation is performed by the trigger signal output unit 82. When the calculation is performed every time a predetermined number of sheets are printed, the calculation can be performed at the same timing as the timing of adjusting the duty ratio of the PWM signal. Therefore, the fall time t1 can be calculated with respect to the amplitude of the AC voltage V ₀ that has been accurately calibrated. it can.

For example, after adjusting the duty ratio of the PWM signal, the trigger signal output unit detects the amplitude of the AC voltage. The fall time t1 can be calculated from t1 = τ ₁ × ln (V ₁ / V ₀ ) using this value as the AC voltage when the PWM signal is turned off.

Although τ ₁ is a fixed value, since V ₁ is a function of atmospheric pressure, the atmospheric pressure may be detected and the fall time t1 may be calculated.

The fall time t1 should be different depending on the AC voltage V ₀ when the PWM signal is turned off, but it is assumed that the AC voltage takes the maximum value when the PWM signal is turned off. In this way, a margin can be provided for the fall time t1.

  When calculating every time the PWM signal is turned OFF, the trigger signal output unit 82 can detect the AC voltage when the PWM signal is turned OFF and calculate the fall time t1. Therefore, the fall time t1 can be calculated according to the magnitude of the AC voltage when the PWM signal is turned off, and the fall time t1 can be minimized. Therefore, power consumption can be easily suppressed.

By the way, the falling time t1 is the earliest timing at which abnormal discharge can be prevented regardless of the AC voltage V ₀ when the PWM signal is turned off. However, the TRG signal may not be turned off. Since the possibility of abnormal discharge further decreases after the fall time t1, it is preferable that the fall time t1 is long. Therefore, for example, after the AC voltage becomes zero, the trigger signal output unit 82 can turn off the TRG signal. In FIG. 9, the time until the AC voltage becomes zero (may be substantially zero) is indicated by time t2.

  On the other hand, if the PWM signal is turned off until the TRG signal is turned off, the power consumption in the standby state increases. Therefore, the time from when the PWM signal is turned off to when the TRG signal is turned off can be appropriately set between “fall time t1 or more and time t2 or less”. For example, experimentally, it is possible to determine a time during which abnormal discharge can almost always be prevented.

[Operation procedure]
FIG. 10 is an example of a flowchart illustrating a procedure for controlling the AC voltage applied to the charging roller 30 by the charging control device 100. The flowchart of FIG. 10 starts when the control board 61 requests the PWM signal output unit 81 to turn off the AC voltage. This request is acquired from, for example, an image forming process.

  When the PWM signal output unit 81 obtains the AC voltage OFF request, the PWM signal output unit 81 turns off the PWM signal (S10). The PWM signal output unit 81 notifies the trigger signal output unit 82 that the PWM signal has been turned off.

  In response to this notification, the trigger signal output unit 82 starts measuring the predetermined fall time t1 and waits until the fall time t1 elapses (S20). The fall time t1 may be measured by counting the clock signal or by setting the fall time t1 in a timer and waiting for an interrupt.

When the fall time t1 has elapsed (Yes in S20), since the AC voltage is good as drops below the discharge starting voltage _{V 1,} the trigger signal output section 82, the TRG signal to OFF (S30). The trigger signal output unit 82 notifies the clock signal output unit 83 that the TRG signal has been turned off.

  When the TRG signal is turned off, the clock signal for generating the AC voltage becomes unnecessary, and the clock signal output unit 83 turns the clock signal off (S40). Steps S30 and S40 may be executed substantially simultaneously.

As described above, by waiting for the fall time t1 from when the PWM signal is turned off until the TRG signal is turned off, it is possible to prevent the abnormal discharge history from remaining on the photoconductor, and the TRG signal. By turning OFF, power consumption during standby can be reduced.
The

  In the present embodiment, a charging control device 100 that determines the falling time t1 in consideration of the time constant of the charging AC voltage FB circuit 89 will be described. When the charging AC voltage FB circuit 89 can cause a delay in the negative feedback loop, the fall time t1 can be accurately determined by considering the time constant of the charging AC voltage FB circuit 89.

  FIG. 11 shows an example of a functional block diagram of the high-voltage power supply device 62 and the control board 61 in the present embodiment. 11, the same parts as those in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted. The charging control device 100 of FIG. 11 includes an AC smoothing circuit 95 in the charging AC voltage FB circuit 89. In the AC smoothing circuit 95, a capacitor and a resistor are connected in series. The resistance value of the resistor 95a is R2, and the capacitance of the capacitor 95b is C2.

When the charging AC voltage FB circuit 89 includes the AC smoothing circuit 95 as shown in FIG. 11, the AC voltage input to the differential amplifier 85 is delayed by time factor τ ₂ (= R 2 · C 2). Further, the filter circuit 84 has the time constant τ ₁ as in the first embodiment. Therefore, when two input voltages of the differential amplifier 85 are input with delays of time constants τ ₁ and τ ₂ as shown in FIG. 11, the time constant of the fall of the AC voltage is expressed by the following equation. .
Falling time constant = τ ₁ + τ ₂ = R1 · C1 + R2 · C2
Therefore, the fall time t1 can be calculated by the following equation.
Fall time t1 = (τ ₁ + τ ₂ ) × ln (V ₁ / V ₀ )
The trigger signal output unit 82 may turn off the TRG signal after the falling time t1 has elapsed since the PWM signal was turned off.

  The AC smoothing circuit 95 in FIG. 11 can be regarded as an example or an equivalent circuit of the charging AC voltage FB circuit 89, but the differential amplifier 85 often has a delay due to the charging AC voltage FB circuit 89. Therefore, according to the charging control apparatus 100 of the present embodiment, the falling time t1 can be accurately determined according to the configuration of the charging AC voltage FB circuit 89. By waiting for the falling time t1 of the present embodiment after the PWM signal is turned off, it is possible to more reliably prevent abnormal discharge history from remaining on the photosensitive member.

In the first and second embodiments, the trigger signal output unit 82 outputs the TRG signal after the falling time t1 has elapsed after the PWM signal is turned off. Without using the fall time t1 in this embodiment, the AC voltage is monitored by the control board 61, AC voltage Once below the discharge starting voltage _{V 1,} is turned OFF TRG signal. By doing so, it is possible to prevent an abnormal discharge history from remaining without calculating or storing the fall time t1.

  FIG. 12 shows an example of a functional block diagram of the high-voltage power supply device 62 and the control board 61 in the present embodiment. 12, the same parts as those in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted. The charging control device 100 of FIG. 12 includes an AC voltage detection unit 91 on the control board 61. The AC voltage detection unit 91 is realized by the CPU 71 executing the program 70.

  The AC voltage detection unit 91 includes, for example, an envelope detection circuit 92. The envelope detection circuit 92 includes a diode 92a, a capacitor 92b and a resistor 92c in series with the diode 92a. The diode 92 a is connected to the charging AC voltage FB circuit 89. The envelope detection circuit 92 makes it possible to detect a voltage value of “AC voltage = V0 × exp (−t / τ)” indicated by a dotted line in FIG. The AC voltage detection unit 91 detects the value of the AC voltage input from the charging AC voltage FB circuit 89, for example, by A / D conversion. Note that the envelope detection circuit 92 may be included in the charging AC voltage FB circuit 89.

By detecting the voltage of the envelope of the AC voltage by the envelope detection circuit 92, even AC voltage falls below the temporary discharge starting voltages V ₁ fluctuates periodically, an AC voltage detection unit 91, AC voltage There can be prevented erroneously detected as lower than the discharge starting voltage V _1. AC voltage detection unit 91 detects that the envelope of the AC voltage falls below the discharge starting voltage V _1, and notifies the trigger signal output section 82. When the trigger signal output unit 82 acquires this notification, the trigger signal output unit 82 turns off the trigger signal. Therefore, ensure that the AC voltage is actually lower than the discharge starting voltage V _1, can trigger signal to OFF, can be reliably prevented from abnormal discharge history remains on the photosensitive member.

When the AC voltage V ₀ when the PWM signal is turned off is lower than the maximum value of the AC voltage, the trigger signal can be turned off earlier than waiting for the elapse of the fall time t1. For this reason, it becomes easier to save power consumption.

Further, instead of detecting the AC voltage every time the PWM signal is turned off, the time during which the AC voltage falls below the discharge start voltage V ₁ may be stored in advance. For example, at the first start-up when the image forming apparatus 100 is turned on at the beginning of the day (that is, in the initialization operation), the PWM signal output unit turns on the PWM signal and outputs the PWM signal when the AC voltage is stabilized. Turn off. The trigger signal output unit is notified that it has been turned off. Trigger signal output unit, the PWM signal is turned OFF, monitoring the AC voltage, to measure the discharge starting voltages V ₁ to become time below. Since this time is the fall time t1, it is stored in the hard disk. Trigger signal output unit at the time of image formation, PWM signal from being OFF, the AC voltage that is stored in the hard disk time below the discharge starting voltage V ₁ is passed, to turn OFF the TRG signal.

Moreover, the frequency of the AC voltage, AC voltage is some time less than the discharge starting voltage V ₁ is made variable. Therefore, when the amplification circuit 86 can change the frequency of the AC voltage, it is preferable that the time when AC voltage is below the discharge starting voltages V ₁ for each frequency is stored in the hard disk.

  FIG. 13 is an example of a flowchart illustrating a procedure for controlling the AC voltage applied to the charging roller 30 by the charging control device 100. In FIG. 13, the same steps as those in FIG. The flowchart of FIG. 13 starts when the control board 61 requests the PWM signal output unit 81 to turn off the AC voltage. This request is acquired from, for example, an image forming process.

  When the PWM signal output unit 81 obtains the AC voltage OFF request, the PWM signal output unit 81 turns off the PWM signal (S10).

  The AC voltage detection unit 91 may start monitoring the AC voltage upon receiving a notification from the PWM signal output unit 81 that the PWM signal has been turned OFF, or may always start regardless of whether the PWM signal is ON or OFF. The AC voltage may be monitored.

AC voltage detection unit 91 determines whether the AC voltage is below the discharge starting voltage _{V 1} (S21). AC voltage detection unit 91, AC voltage continues to monitor to below the discharge start voltage _{V 1.}

When AC voltage is below the discharge starting voltage _{V 1} (Yes in S21), AC voltage detection unit 91 notifies that the AC voltage to the trigger signal output section 82 is actually lower than the discharge starting voltage _{V 1.}

  When this notification is acquired, the trigger signal output unit 82 turns off the TRG signal (S30). The trigger signal output unit 82 notifies the clock signal output unit 83 that the TRG signal has been turned off.

  When the TRG signal is turned off, the clock signal for generating the AC voltage becomes unnecessary, and the clock signal output unit 83 turns the clock signal off (S40).

In this manner, the AC voltage is turned OFF TRG signal Once below the discharge starting voltage V _1, or to calculate the fall time t1, without storing, that abnormal discharge history remains on the photoreceptor Can be prevented.

Note that Example 1 or 2 may be combined with this example. In this case, the fall time t1 has elapsed, and, when the AC voltage is lower than the discharge starting voltage _{V 1,} the trigger signal output unit 82 turns OFF the TRG signal. In this way, it is possible to reliably prevent the history of abnormal discharge from remaining on the photoreceptor.

  In the third embodiment, the AC voltage is monitored. However, the current generated by the discharge may be monitored to determine whether or not there is a possibility of discharging.

  FIG. 14 shows an example of a functional block diagram of the high-voltage power supply device 62 and the control board 61 in the present embodiment. 14, the same parts as those in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted. 14 includes an AC current detector 94 on the control board 61 and a charging AC current FB circuit 93 on the high-voltage power supply device 62. The charging AC current FB circuit 93 is connected to the high voltage conversion circuit 87, and the charging AC current FB circuit 93 is connected to the AC current detection unit 94.

While the high-voltage conversion circuit 87 discharges the charging roller 30, an AC current flows from the high-voltage power supply device 62 to the charging roller 30. Accordingly, PWM signals are to OFF, the AC voltage is discharged below the discharge starting voltage _{V 1} is stopped, AC current is also stopped. That is, an AC current flows during discharge, and no AC current flows while discharge is stopped. Now, the AC current becomes zero, the AC voltage is below the discharge starting voltage V ₁ was found to have a synonymous meaning.

  The charging AC current FB circuit 93 includes, for example, a diode 93a and a capacitor 93b in series with the diode 93a. The AC current is half-wave rectified by the charging AC current FB circuit 93. The AC current detection unit 94 detects the value of the AC current after half-wave rectification input from the charging AC current FB circuit 93, for example, by A / D conversion.

  When the AC current detection unit 94 detects that the value of the AC current becomes zero, the AC current detection unit 94 notifies the trigger signal output unit 82. It may be detected that it becomes almost zero, not completely zero. Hereinafter, it is assumed that the AC current detection unit 94 detects that the value of the AC current becomes substantially zero. When the trigger signal output unit 82 acquires this notification, the trigger signal output unit 82 turns off the trigger signal. Therefore, after confirming that the AC current has become zero, the trigger signal can be set to OFF, and the abnormal discharge history can be reliably prevented from remaining on the photosensitive member.

If the AC voltage V ₀ when the PWM signal is turned off is lower than the maximum value of the AC voltage, the trigger signal can be turned off earlier than waiting for the elapse of the falling time t1. For this reason, it becomes easier to supply power consumption.

  Further, instead of detecting the AC current every time the PWM signal is turned off, the time until the AC current becomes substantially zero may be stored in the hard disk in advance. When the amplifier circuit 86 can change the frequency of the AC voltage, it is preferable to store the time in the hard disk until the AC current becomes substantially zero for each frequency.

  FIG. 15 is an example of a flowchart illustrating a procedure for controlling the AC voltage applied to the charging roller 30 by the charging control device 100. In FIG. 15, the same steps as those in FIG. The flowchart of FIG. 15 starts when the control board 61 requests the PWM signal output unit 81 to turn off the AC voltage. This request is acquired from, for example, an image forming process.

  When the PWM signal output unit 81 obtains the AC voltage OFF request, the PWM signal output unit 81 turns off the PWM signal (S10).

  The AC current detection unit 94 may start monitoring of the AC current upon receiving a notification from the PWM signal output unit 81 that the PWM signal has been turned OFF, or always, regardless of whether the PWM signal is ON or OFF. The AC current may be monitored.

  The AC current detection unit 94 determines whether or not the AC current has become substantially zero (S22). The AC current detection unit 94 continues monitoring until the AC current becomes substantially zero.

  When the AC current becomes substantially zero (Yes in S22), the AC current detection unit 94 notifies the trigger signal output unit 82 that the AC current has become substantially zero.

  When this notification is acquired, the trigger signal output unit 82 turns off the TRG signal (S30). The trigger signal output unit 82 notifies the clock signal output unit 83 that the TRG signal has been turned off.

  When the TRG signal is turned off, the clock signal for generating the AC voltage is also unnecessary, so that the clock signal output unit 83 turns off the clock signal (S40).

  In this way, by turning off the TRG signal when the AC current becomes substantially zero, it is possible to prevent the abnormal discharge history from remaining on the photosensitive member without calculating or storing the falling time t1.

  In addition, you may combine Example 1 or 2 and a present Example. In this case, when the fall time t1 elapses and the AC current becomes substantially zero, the trigger signal output unit 82 turns off the TRG signal. In this way, it is possible to reliably prevent the history of abnormal discharge from remaining on the photoreceptor.

Moreover, you may combine Example 1 or 2 and Example 3 and a present Example. In this case, it elapsed fall time t1 is lower than the AC voltage the discharge starting voltage _{V 1,} and, when AC current becomes substantially zero, a trigger signal output unit 82 turns OFF the TRG signal. In this way, it is possible to reliably prevent the history of abnormal discharge from remaining on the photoreceptor.

DESCRIPTION OF SYMBOLS 30 Charging roller 35 Photoconductor 61 Control board 62 High voltage power supply device 81 PWM signal output part 82 Trigger signal output part 83 Clock signal output part 84 Filter circuit 85 Differential amplifier 86 Amplification circuit 87 High voltage conversion circuit 88 Charging DC output circuit 89 Charging AC Voltage FB circuit 90 Trigger circuit
91 AC voltage detection unit 92 Envelope detection circuit 93 Charging AC current FB circuit 94 AC current detection unit 100 Charging control device 200 Image forming apparatus

JP 2007-65485 A JP 2001-117325 A

Claims (8)

A power supply control device that generates an AC voltage to be applied to a charging member,
A reference voltage signal output means for outputting a reference voltage signal of the AC voltage;
Feedback means for outputting a voltage signal according to the difference between the reference voltage signal and the feedback voltage detected from the charging member;
Amplifying means for receiving power and amplifying the voltage signal and generating the AC voltage;
Voltage application means for applying the AC voltage and the DC voltage to the charging member in a superimposed manner;
After the reference voltage signal output means turns off the reference voltage signal, the power supplied to the amplifying means is turned off at least after the time for the voltage of the charging member to fall below the discharge start voltage has elapsed. Power off means,
A power supply control device comprising: The reference voltage signal output means outputs the reference voltage signal through a filter having a predetermined time constant,
The power off means turns off the power supplied to the amplifying means after the time determined by the time constant has elapsed;
The power supply control device according to claim 1. The high voltage applying means and the feedback means are connected via a feedback voltage generation circuit that outputs the feedback voltage,
The power off means is determined based on the time constant and a second time constant of the feedback voltage generation circuit, and turns off the power supplied to the amplifying means after the time has elapsed.
The power supply control device according to claim 2. Voltage detecting means for detecting the voltage of the charging member;
The power off means turns off the power supplied to the amplifying means after detecting that the voltage of the charging member has dropped below the discharge start voltage;
The power supply control device according to claim 1, wherein the power supply control device is a power supply control device. Current detecting means for detecting a current flowing from the high voltage applying means to the charging member;
The power off means turns off the power supplied to the amplification means after detecting that the current detected by the current detection means has become substantially zero.
The power supply control device according to any one of claims 1 to 4, wherein The power off means turns off the power supplied to the amplifying means when the voltage of the charging member drops to substantially zero;
The power supply control device according to claim 1, wherein the power supply control device is a power supply control device. A power supply control device according to any one of claims 1 to 6,
The charging member;
A photoreceptor whose peripheral surface is charged by the charging member;
An exposure device that scans the photosensitive member with a laser beam to form a latent image on the photosensitive member;
A developing device that attaches toner to the latent image and forms a toner image on the peripheral surface of the photoreceptor;
A transfer device for transferring a toner image to recording paper;
A fixing device for fixing a toner image on recording paper with heat and pressure;
A cleaning device that removes toner remaining on the surface of the photoreceptor with a blade;
An image forming apparatus comprising: A power supply control method for a power supply control device that generates an AC voltage to be applied to a charging member,
A reference voltage signal output means for outputting a reference voltage signal of the AC voltage;
A feedback means for outputting a voltage signal corresponding to a difference between the reference voltage signal and a feedback voltage detected from the charging member;
Amplifying means receiving power supply, amplifying the voltage signal and generating the AC voltage;
A voltage applying means for applying the AC voltage and the DC voltage to the charging member in a superimposed manner;
After the reference voltage signal output means turns off the reference voltage signal, the power off means is supplied to the amplifying means after at least the time that the voltage of the charging member falls below the discharge start voltage has elapsed. Turning off the power;
A power supply control method characterized by comprising:

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