JP2018146897A - Power supply device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further reduce density unevenness or density dilution on a lead edge of a sheet.SOLUTION: The power supply device comprises: a DC power supply 110 for switching constant current control and constant voltage control to output a DC voltage; an AC power supply 140 for outputting either a superimposition voltage in which an AC voltage is superimposed on the DC voltage or the DC voltage; a bypass capacitor 159 for removing a voltage which has not been applied to an application object out of voltages output from the AC power supply 140; a discharge circuit 400 for discharging residual charge accumulated in the bypass capacitor 159; a switching circuit 180 for switching the DC power supply 110 from the constant voltage control to the constant current control; a power supply control part for, when a predetermined condition is established, switching the DC power supply 110 from the constant voltage control to the constant current control to gradually make an output value of DC currents approximate a value of target currents, and for causing the discharge circuit to discharge the residual charge accumulated in the bypass capacitor 159; and a current detection part 401 for detecting and outputting the DC currents based on the DC voltage to a power supply control part 300.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a power supply device and an image forming apparatus.

  In an electrophotographic image forming apparatus, an electrostatic latent image is formed on a uniformly charged image carrier, and the formed electrostatic latent image is developed with toner to form a toner image. The formed toner image Is transferred to a recording paper and fixed, thereby forming an image on the recording paper.

  By the way, recording paper usually has unevenness, and toner is not easily transferred to the concave portion compared to the convex portion. Therefore, when forming an image on recording paper having large unevenness, the toner is not transferred to the concave portion and the image is white. Density unevenness such as omission may occur.

  For this reason, the unevenness of the recording paper that has passed through the two metal roller pairs is identified from the difference between the current values flowing through the two metal roller pairs, and the toner adhesion amount is controlled so that the adhesion amount is suitable for the identified irregularities. The technology is already known.

  Further, for example, in Patent Document 1, a DC power source and an AC power source are connected in series, and a DC voltage is applied to a transfer portion in accordance with the size of the unevenness of the transfer object to transfer an image to the transfer object. Or a technique for switching by a relay whether to apply a superimposed voltage obtained by superimposing a DC voltage and an AC voltage to a transfer portion to transfer an image to a transfer target.

  However, in the conventional technology as described above, it takes more time for the DC voltage output from the DC power supply to rise than in the case of a DC power supply alone due to the configuration of the power supply.

  Therefore, Patent Document 2 discloses a technique for preventing the undershoot by gradually approaching the target current value when the voltage applied to the transfer portion is controlled at a constant current, thereby shortening the voltage rise time. .

  However, in the conventional technology as described above, when switching to the constant current control, it takes time for the electric charge stored in the capacitor to be discharged, so the rise time becomes long, and density unevenness or density at the leading edge of the paper. In some cases, diluting of the material may occur, causing a problem.

  The present invention has been made in view of the above, and an object thereof is to provide a power supply device and an image forming apparatus that can further reduce density unevenness and density dilution at the front end of a sheet.

  In order to solve the above-described problems and achieve the object, the present invention provides a DC power source that outputs a DC voltage by switching between constant current control and constant voltage control, and a superimposed voltage in which an AC voltage is superimposed on the DC voltage. And an AC power supply that outputs any one of the DC voltages, a bypass capacitor that removes a voltage that has not been applied to the application target from among the voltages that are output from the AC power supply, and discharges residual charges accumulated in the bypass capacitor. A discharge circuit for switching, a switching circuit for switching the DC power source from the constant voltage control to the constant current control, and when a predetermined condition is satisfied, a signal is sent to the switching circuit to switch the DC power source from the constant voltage control to the constant current Switch to control and gradually approach the target current value, and send a signal to the discharge circuit to discharge the residual charge stored in the bypass capacitor And a power control unit for, characterized in that it comprises a current detector which detects a DC current based on the DC voltage output to the power control unit.

  According to the present invention, it is possible to further reduce density unevenness and density dilution at the front end of a sheet.

FIG. 1 is a mechanical configuration diagram illustrating an example of a printing apparatus according to an embodiment. FIG. 2 is a mechanical configuration diagram illustrating an example of the image forming unit. FIG. 3 is a block diagram illustrating an example of an electrical configuration of the printing apparatus. FIG. 4 is a circuit diagram showing an example of the configuration of the secondary transfer power supply. FIG. 5 is a block diagram illustrating an example of the configuration of the power control unit. FIG. 6 is a flowchart illustrating an example of a transfer control process performed by the printing apparatus. FIG. 7 is a graph showing an example of control of the secondary transfer power supply by the power supply control unit.

  Hereinafter, embodiments of a power supply device and an image forming apparatus will be described in detail with reference to the accompanying drawings. In the following embodiments, the image forming apparatus of this embodiment is an electrophotographic color printing apparatus, specifically, four colors of yellow (Y), magenta (M), cyan (C), and black (K). However, the present invention is not limited to this example, but is applied to a printing apparatus that forms an image by superimposing these color component images on a recording medium.

  The image forming apparatus of the present embodiment can be applied to any color or monochrome image as long as it is an apparatus that forms an image by electrophotography. For example, the image forming apparatus can be applied to an electrophotographic copying machine or a multifunction peripheral (MFP). Is also applicable. Note that a multifunction peripheral is a device having at least two functions among a printing function, a copying function, a scanner function, and a facsimile function.

  FIG. 1 is a mechanical configuration diagram illustrating an example of a printing apparatus 1 according to an embodiment. As shown in FIG. 1, the printing apparatus 1 as an image forming apparatus includes an image forming unit 10Y, 10M, 10C, and 10K, an intermediate transfer belt 60, support rollers 61 and 62, and a secondary transfer unit facing roller ( Repulsive roller) 63 (an example of a load and transfer unit), a secondary transfer roller 64, a paper cassette 70, a paper feed roller 71, a conveying roller pair 72, a fixing device 90, and a secondary transfer power source 200 (power source). An example of an apparatus).

  As shown in FIG. 1, the image forming units 10Y, 10M, 10C, and 10K are arranged in the order of the image forming units 10Y, 10M, 10C, and 10K from the upstream side in the moving direction (arrow a direction) of the intermediate transfer belt 60. Arranged along the intermediate transfer belt 60.

  FIG. 2 is a mechanical configuration diagram illustrating an example of the image forming unit 10Y. As shown in FIG. 2, the image forming unit 10Y includes a photosensitive drum 11Y, a charging device 20Y, a developing device 30Y, a primary transfer roller 40Y, and a cleaning device 50Y. The image forming unit 10Y performs an image forming process (charging process, irradiation process, developing process, transfer process, and cleaning process) on the photoconductive drum 11Y, whereby a yellow toner image (color component) is formed on the photoconductive drum 11Y. Image) is formed and transferred to the intermediate transfer belt 60.

  The image forming units 10M, 10C, and 10K all have the same components as the image forming unit 10Y. The image forming unit 10M forms a magenta toner image by performing an image forming process. The image forming unit 10C forms a cyan toner image by performing an image forming process, and the image forming unit 10K forms a black toner image by performing an image forming process. Therefore, in the following, description will be made mainly on the components of the image forming unit 10Y, and the components of the image forming units 10M, 10C, and 10K will be denoted by Y attached to the reference numerals of the components of the image forming unit 10Y. Instead, M, C, and K are added (see FIG. 1), and description thereof is omitted.

  The photosensitive drum 11Y is an image carrier and is driven to rotate in the direction of arrow b. The photoreceptor drum 11Y is an organic photoreceptor having an outer diameter of 60 mm, for example. Similarly, the photosensitive drums 11M, 11C, and 11K are rotationally driven in the direction of the arrow b.

  The black photosensitive drum 11K and the color photosensitive drums 11Y, 11M, and 11C may be driven to rotate independently. Thus, when forming a monochrome image, only the black photosensitive drum 11K is rotationally driven, and when forming a color image, the photosensitive drums 11Y, 11M, 11C, and 11K are simultaneously rotationally driven. it can.

  First, in the charging step, the charging device 20Y charges the surface of the photosensitive drum 11Y that is being rotationally driven. Specifically, the charging device 20Y applies a voltage in which an AC voltage is superimposed on a DC voltage to a charging roller that is, for example, a roller-shaped conductive elastic body. As a result, the charging device 20Y directly discharges between the charging roller and the photosensitive drum 11Y, and charges the photosensitive drum 11Y to a predetermined polarity, for example, a negative polarity.

  Subsequently, in the irradiation step, the irradiation device irradiates the charged surface of the photosensitive drum 11Y with the light-modulated laser light L, thereby forming an electrostatic latent image on the surface of the photosensitive drum 11Y. As a result, the portion where the absolute value of the potential of the surface portion of the photosensitive drum 11Y is lowered by the irradiation with the laser beam L becomes an electrostatic latent image (image portion), and the absolute value of the potential is kept high without being irradiated with the laser beam L. The sagging part becomes the background part.

  Subsequently, in the developing process, the developing device 30Y develops the electrostatic latent image formed on the photoreceptor drum 11Y with yellow toner, and forms a yellow toner image on the photoreceptor drum 11Y.

  The developing device 30Y includes a storage container 31Y, a developing sleeve 32Y stored in the storage container 31Y, and a screw member 33Y stored in the storage container 31Y. The storage container 31Y stores a two-component developer having yellow toner and a carrier. The developing sleeve 32Y is a developer carrier, and is disposed so as to face the photosensitive drum 11Y through the opening of the storage container 31Y. The screw member 33Y is a stirring member that conveys the developer while stirring. The screw member 33Y is disposed on the developer supply side on the developing sleeve side and on the receiving side that is supplied from the toner replenishing device, and is rotatably supported by the receiving container 31Y by a bearing member.

  Subsequently, in the transfer process, the primary transfer roller 40Y transfers the yellow toner image formed on the photosensitive drum 11Y to the intermediate transfer belt 60. Note that a small amount of untransferred toner remains on the photosensitive drum 11Y even after the toner image is transferred.

  The primary transfer roller 40Y is an elastic roller having a conductive sponge layer, for example, and is disposed so as to be pressed against the photosensitive drum 11Y from the back surface of the intermediate transfer belt 60. The elastic roller is applied with a constant current controlled bias as a primary transfer bias. For example, the primary transfer roller 40Y has an outer shape of 16 mm, a mandrel diameter of 10 mm, and a sponge layer resistance R of about 3E7Ω. The resistance R of the sponge layer is determined from the current I flowing when a voltage V of 1000 V is applied to the mandrel of the primary transfer roller 40Y with a grounded metal roller having an outer diameter of 30 mm pressed by 10 N, from the current I. It is a value calculated using the law (R = V / I).

  Subsequently, in the cleaning process, the cleaning device 50Y wipes off the untransferred toner remaining on the photosensitive drum 11Y. The cleaning device 50Y includes a cleaning blade 51Y and a cleaning brush 52Y. The cleaning blade 51Y cleans the surface of the photoconductive drum 11Y while being in contact with the photoconductive drum 11Y from the counter direction with respect to the rotation direction of the photoconductive drum 11Y. The cleaning brush 52Y cleans the surface of the photosensitive drum 11Y while being in contact with the photosensitive drum 11Y while rotating in the direction opposite to the rotation direction of the photosensitive drum 11Y.

  Returning to FIG. 1, the intermediate transfer belt 60 is an endless belt wound around a plurality of rollers such as support rollers 61 and 62 and a secondary transfer unit facing roller 63, and one of the support rollers 61 and 62 is rotationally driven. As a result, it moves endlessly in the direction of arrow a. First, a yellow toner image is transferred to the intermediate transfer belt 60 by the image forming unit 10Y. Subsequently, the magenta toner image is transferred by the image forming unit 10M, the cyan toner image is transferred by the image forming unit 10C, and the image forming unit 10K is pressed. Black toner images are sequentially superimposed and transferred. As a result, a full-color toner image (full-color image) is formed on the intermediate transfer belt 60. The intermediate transfer belt 60 conveys the formed full-color toner image between the secondary transfer portion facing roller 63 and the secondary transfer roller 64.

  For example, the intermediate transfer belt 60 has a thickness of 20 to 200 μm (preferably about 60 μm) and a volume resistivity of 6.0 to 13.0 Log Ωcm (preferably 7.5 to 12.5 Log Ωcm, more preferably about 9 Log Ωcm) and an endless carbon-dispersed polyimide resin having a surface resistivity of 9.0 to 13.0 Log Ωcm (preferably 10.0 to 12.0 Log Ωcm). The volume resistivity is a resistance measurement value at Mitsubishi Chemical Hiresta UP MCP HT450 100V, 10 sec, and the surface resistivity is a resistance measurement value at Mitsubishi Chemical Hiresta HRS probe 500 V, 10 sec. The support roller 62 is grounded.

  In the paper cassette 70, a plurality of recording media P are accommodated in each tray. The recording medium is assumed to have a different paper type and size for each tray accommodated. In the present embodiment, the recording medium (an example of the transfer target) is, for example, plain paper or a highly rugged resack paper, but is not limited thereto, and may be an OHP sheet, a film, or the like. Good.

  The paper feed roller 71 is in contact with the recording medium P positioned at the top of the tray of the paper cassette 70 and feeds the recording medium P in contact therewith.

  The transport roller pair 72 transports the recording medium P fed by the paper feed roller 71 between the secondary transfer portion facing roller 63 and the secondary transfer roller 64 (in the direction of arrow c) at a predetermined timing.

  The secondary transfer unit facing roller 63 and the secondary transfer roller 64 are full-color toner images conveyed by the intermediate transfer belt 60 at the secondary transfer nip between the secondary transfer unit facing roller 63 and the secondary transfer roller 64. Are collectively transferred onto the recording medium P conveyed by the conveying roller pair 72.

  The secondary transfer portion facing roller 63 (an example of a transfer device) is, for example, a conductive NBR rubber layer having an outer shape of 24 mm and a mandrel diameter of 16 mm. In addition, the value of resistance R of the conductive NBR rubber layer is 6.0 to 12.0 LogΩ (or SUS), and preferably 4.0 LogΩ. The secondary transfer roller 64 is, for example, a conductive NBR rubber layer having an outer shape of 24 mm and a mandrel diameter of 14 mm. The value of resistance R of the conductive NBR rubber layer is about 1E6Ω or less by the same measurement method as that of the primary transfer roller 40Y. The volume resistance of the secondary transfer roller 64 is a resistance measurement value measured by rotation measurement. Weight: 5 N / one side, bias application: 1 KV applied to the transfer roller shaft, resistance of one roller rotation measured during 1 min measurement, average The value is a volume resistance.

  A secondary transfer power supply 200 for transfer bias is connected to the secondary transfer portion facing roller 63. The secondary transfer power supply 200 (an example of a power supply device) applies a voltage to the secondary transfer unit facing roller 63 in order to transfer a full-color toner image to the recording medium P at the secondary transfer nip. Specifically, the secondary transfer power supply 200 applies only a DC voltage (hereinafter sometimes referred to as “DC bias”) to the secondary transfer unit facing roller 63 according to a user setting, A superimposed voltage (hereinafter sometimes referred to as “superimposed bias”) superimposed with an AC voltage is applied to the secondary transfer unit facing roller 63. As a result, a potential difference is generated between the secondary transfer portion facing roller 63 and the secondary transfer roller 64, and a voltage is generated in which the toner travels from the intermediate transfer belt 60 to the recording medium P side. Can be transferred to. Here, the potential difference in the present embodiment is (potential of the secondary transfer portion facing roller 63) − (potential of the secondary transfer roller 64).

  The fixing device 90 fixes the full-color toner image on the recording medium P by heating and pressing the recording medium P on which the full-color toner image is transferred. Then, the recording medium P on which the full-color toner image is fixed is discharged outside the printing apparatus 1.

  FIG. 3 is a block diagram illustrating an example of an electrical configuration of the printing apparatus 1. As shown in FIG. 3, the printing apparatus 1 includes a secondary transfer power supply 200 and a power supply control unit 300. The secondary transfer power supply 200 includes a DC power supply 110 and an AC power supply 140. The DC power supply 110 and the AC power supply 140 are connected in series. The power supply controller 300 controls the secondary transfer power supply 200 and can be realized by, for example, a CPU (Central Processing Unit).

  As shown in FIG. 3, the AC power supply 140 includes an AC control unit 141, an AC drive unit 142, an AC high-voltage transformer 143, and an AC detection unit 144. The DC power supply 110 includes a DC control unit 111, a DC drive unit 112, a DC high-voltage transformer 113, and a DC detection unit 114. In the example shown in FIG. 3, the illustration of the power supply input used for the operation of the secondary transfer power supply 200 is omitted.

  The AC control unit 141 receives an AC_PWM signal (AC output control signal) for setting the AC high voltage output current or voltage of the AC high voltage transformer 143 from the power supply control unit 300, and the AC detection unit 144 supplies the AC detection unit. The output current value and output voltage value of the AC high-voltage output of the AC high-voltage transformer 143 detected by 144 are input. Then, the AC control unit 141 drives the AC high-voltage transformer 143 via the AC drive unit 142 so that the current or voltage indicated by the input AC_PWM signal and the input output current value become a predetermined value. To control.

  The AC drive unit 142 receives a CLK signal that sets the frequency of the AC voltage of the secondary transfer power supply 200 from the power supply control unit 300. The AC driving unit 142 drives the AC high-voltage transformer 143 in accordance with the input CLK signal and the control from the AC control unit 141. Instead of instructing the AC drive unit 142 to specify the frequency of the AC voltage of the secondary transfer power supply 200 by the CLK signal from the power supply control unit 300, the AC drive unit 142 may use a fixed frequency prepared in advance. Good.

  The AC high voltage transformer 143 is driven by the AC drive unit 142 and transforms an AC voltage from the secondary transfer power source 200 to generate an AC high voltage output. The AC high-voltage transformer 143 performs high-voltage output in which the DC high-voltage output from the DC high-voltage transformer 113 and the AC high-voltage output are superimposed.

  The AC detection unit 144 detects the output current value and output voltage value of the AC high-voltage output of the AC high-voltage transformer 143 and outputs the detected output current value and output voltage value to the AC control unit 141. In addition, the AC detection unit 144 outputs the detected output current value and output voltage value to the power supply control unit 300 as an AC_FB_I signal. This is because the power supply control unit 300 monitors the load state.

  Here, the AC detection unit 144 detects the output current value and the output voltage value in the AC control unit 141 in order to enable both constant current control and constant voltage control of the AC high voltage output of the AC high voltage transformer 143. doing. However, in the present embodiment, the AC control unit 141 gives priority to constant current control over constant voltage control, and normally performs constant current control using an output current value. In this embodiment, the output voltage value is used to suppress the upper limit voltage of the AC high voltage output of the AC high voltage transformer 143, and the AC control unit 141 uses the output voltage value to determine the maximum voltage in a no-load state or the like. Control.

  A DC_PWM signal (DC output control signal) for setting the current or voltage of the DC high-voltage output of the DC high-voltage transformer 113 is input from the power supply controller 300 to the DC controller 111, and the DC detector 114 receives the DC detector. The output current value and output voltage value of the DC high-voltage output of the DC high-voltage transformer 113 detected by 114 are input. Then, the direct current control unit 111 drives the direct current high voltage transformer 113 via the direct current drive unit 112 so that the current or voltage indicated by the input DC_PWM signal and the input output current value become a predetermined value. To control.

  The DC control unit 111 receives a switching signal for instructing switching between constant current control and constant voltage control from the power supply control unit 300, and the DC control unit 111 receives a constant current according to the input switching signal. Switch between control and constant voltage control. In this embodiment, the DC power source 110 mainly performs constant current control in order to keep the toner transfer rate constant, but may perform constant voltage control in order to shorten the rise time of the DC voltage. In the case of constant current control, the DC controller 111 controls the driving of the DC high voltage transformer 113 via the DC driver 112 so that the current value of the DC high voltage transformer 113 becomes the current value indicated by the DC_PWM signal. To do. In the case of constant voltage control, the DC controller 111 controls the driving of the DC high-voltage transformer 113 via the DC driver 112 so that the voltage value of the DC high-voltage transformer 113 becomes the voltage value indicated by the DC_PWM signal. To do.

  The DC drive unit 112 drives the DC high-voltage transformer 113 according to the control from the DC control unit 111.

  The direct current high voltage transformer 113 is driven by the direct current drive unit 112 and transforms the direct current voltage from the secondary transfer power source 200 to perform direct current high voltage output.

  The DC detection unit 114 detects the output current value and the output voltage value of the DC high-voltage output of the DC high-voltage transformer 113 and outputs them to the DC control unit 111. Further, the DC detection unit 114 outputs the detected output current value and output voltage value to the power supply control unit 300 as a DC_FB_I signal and a DC_FB_V signal. This is because the power supply control unit 300 monitors the load state.

  Here, the DC detection unit 114 detects an output current value and an output voltage value in the DC control unit 111 in order to enable both constant current control and constant voltage control of the DC high voltage output of the DC high voltage transformer 113. doing. However, in this embodiment, the DC control unit 111 prioritizes constant current control over constant voltage control, and normally performs constant current control using an output current value. In this embodiment, the output voltage value is used to suppress the upper limit voltage of the DC high voltage output of the DC high voltage transformer 113, and the DC control unit 111 uses the output voltage value to determine the maximum voltage in a no-load state or the like. Control.

  Here, an example has been described in which only the secondary transfer power supply 200 performs high-voltage output in which direct current and alternating current are superimposed. However, when the voltage level is high, it is difficult to create the power supply itself. You may make it perform the high voltage | pressure output which superimposed the direct current | flow and alternating current by the system switched by a relay.

  FIG. 4 is a circuit diagram showing an example of the configuration of the secondary transfer power supply 200.

  The DC (−) _ PWM signal and the switching signal are input to the DC power supply 110 from the power supply control unit 300 and input to the switching circuit 180. When the switching signal instructs switching to constant voltage control (CV) (in this embodiment, when the switching signal is High), the switching circuit 180 sends the DC (−) _ PWM signal to the current control circuit (comparator) 122. When the switching signal instructs switching to constant current control (CC) (in this embodiment, the switching signal is Low), the DC (−) _ PWM signal is output to the voltage control circuit (comparator) 121. .

  The DC (−) _ PWM signal output to the current control circuit (comparator) 122 is integrated and input to the current control circuit (comparator) 122. The value of the integrated DC (−) _ PWM signal becomes a reference voltage in the current control circuit 122. The direct current detection circuit 132 detects the direct current output from the direct current power supply 110 on the output line of the secondary transfer power supply 200, and inputs the detected output value of the direct current to the current control circuit 122. The current control circuit 122 actively drives the DC drive circuit 123 of the DC high-voltage transformer when the DC current is smaller than the reference voltage, and DC drive of the DC high-voltage transformer when the DC current is larger than the reference voltage. The drive of the circuit 123 is regulated. Thereby, the DC power supply 110 ensures constant current.

  The DC voltage detection circuit 126 detects the DC voltage output from the DC power supply 110 and inputs the output value of the detected DC voltage to the voltage control circuit (comparator) 121. When the output value of the DC voltage reaches the upper limit, the voltage control circuit 121 regulates driving of the DC drive circuit 123 of the DC high-voltage transformer. Further, the DC voltage detection circuit 127 feeds back the output value of the DC voltage detected by the DC voltage detection circuit 126 to the power supply control unit 300 as a DC_FB_V signal.

  By driving the direct current drive circuit 123 according to the control of the current control circuit 122 and the voltage control circuit 121, the primary side winding N1_DC (−) 124 of the direct current high voltage transformer and the secondary side winding N2_DC (−) of the direct current high voltage transformer. The output generated at 125 is smoothed by the diode 130 and the capacitor 131, and then input as a DC voltage from the AC power supply input unit 157 to the AC power supply 140, and applied to the secondary winding N2_AC156 of the AC high voltage transformer.

  The AC power supply 140 receives an AC_PWM signal from the power supply controller 300 and inputs it to the voltage control circuit (comparator) 151. The value of the input AC_PWM signal becomes a reference voltage in the voltage control circuit 151. The AC voltage detection circuit 162 predicts the output value of the AC voltage from the mutual induction voltage generated by the primary side winding N3_AC155 of the AC high-voltage transformer, and inputs the predicted output value of the AC voltage to the voltage control circuit 151. This is because it is difficult to detect only the output (AC voltage) of the AC power supply 140 itself on the output line of the secondary transfer power supply 200 because the AC voltage is superimposed on the DC voltage. The voltage control circuit 151 actively drives the AC drive circuit 153 of the AC high voltage transformer when the AC voltage is smaller than the reference voltage, and AC drive of the AC high voltage transformer when the AC voltage is larger than the reference voltage. The driving of the circuit 153 is restricted. Thereby, the AC power supply 140 ensures constant voltage.

  The AC current detection circuit 160 detects the current flowing through the AC bypass capacitor 159 on the low voltage side of the AC bypass capacitor (an example of a bypass capacitor) 159 that is an output line of the secondary transfer power supply 200, and detects the detected current. Are output to a current control circuit (comparator) 152. When the AC power supply 140 is driven, the current control circuit 152 regulates the driving of the AC drive circuit 153 of the AC high-voltage transformer when the output value of the input current reaches the upper limit. Further, the alternating current detection circuit 161 feeds back the output value of the current detected by the alternating current detection circuit 160 to the power supply control unit 300 as an AC_FB_I signal.

  The AC drive circuit 153 of the AC high-voltage transformer is driven according to the AND logic of the CLK signal input from the power supply control unit 300, the voltage control circuit 151, and the current control circuit 152, and generates an output having the same cycle as CLK.

  The AC voltage generated by the primary winding N1_AC154 of the AC high-voltage transformer by the driving of the AC driving circuit 153 is superimposed on the DC voltage applied to the secondary winding N2_AC156, and is output from the high-voltage output unit 158. The superimposed voltage is output (applied) to the secondary transfer unit facing roller (repulsive roller) 63. However, when the AC power supply 140 is not driven, the DC voltage applied to the secondary winding N2_AC156 is directly output (applied) from the high voltage output unit 158 to the secondary transfer unit opposing roller (repulsive roller) 63. The

  Generally, since the secondary winding of the step-up transformer is connected to the ground and the high voltage output terminal, it is not assumed that the low voltage side (input side) of the secondary winding becomes a high voltage. . However, in this embodiment, when the secondary transfer power supply 200 outputs a superimposed voltage, the DC high voltage generated by the DC power supply 110 is input to the low voltage side (input side) of the secondary winding N2_AC156 of the AC high voltage transformer. In addition, since the alternating voltage is further superimposed, the low voltage side (input side) of the secondary winding becomes higher than usual. As a result, when a general AC high voltage transformer is used, the secondary side winding cannot be insulated, and current leakage may occur inside the AC high voltage transformer.

  For this reason, not only the maximum output voltage of the secondary transfer power supply 200 (maximum value of the superimposed voltage), that is, the maximum output voltage of the AC power supply 140 but also the maximum output voltage of the AC power supply 140 and the DC power supply 110 with respect to the AC high-voltage transformer. The withstand voltage is improved so that it can withstand even when the maximum output voltage is applied. Specifically, the winding interval on the low-voltage side (input side) of the secondary winding N2_AC156 of the AC high-voltage transformer is made wider than that of a general AC high-voltage transformer to withstand the maximum output voltage of the secondary transfer power supply 200. I am trying to get it.

  More specifically, since the voltage of the step-up transformer is normally higher on the output side than on the input side, the spacing between the windings becomes wider toward the output side. Therefore, the winding interval on the low voltage side (input side) of the secondary winding N2_AC156 is set to an interval that can withstand the maximum output voltage of the DC power supply, and the high voltage side (output) of the secondary winding N2_AC156 of the AC high voltage transformer. The interval between the windings on the side) is an interval that can withstand the maximum output voltage (maximum value of the superimposed voltage) of the secondary transfer power supply 200.

  Note that the target value of direct current when the DC voltage is output alone (corresponding to the reference voltage in the current control circuit) is several times the target value of direct current when the AC voltage is superimposed on the DC voltage. The value increases by about 10%. Similarly, the value of the direct current voltage when the direct current output reaches the target value is larger when the direct current voltage is output alone than when the direct current voltage is superimposed on the direct current voltage. For this reason, at first glance, the maximum output voltage of the AC power supply 140 and the maximum output voltage of the DC power supply 110 are not simultaneously applied to the AC high voltage transformer. It seems that no withstand voltage is required to withstand even when a maximum output voltage of 110 is applied.

  However, even when an AC voltage is superimposed on a DC voltage and output, the maximum output voltage of the AC power supply 140 and the maximum output voltage of the DC power supply 110 are temporarily changed simultaneously to an AC high voltage depending on conditions such as the resistance of paper. May be applied to the transformer. For this reason, the pressure resistance is improved so that the AC high voltage transformer can withstand the maximum output voltage of the AC power supply 140 and the maximum output voltage of the DC power supply 110.

  In addition to the secondary winding N2_AC156 of the AC high-voltage transformer, the withstand voltage is improved not only for the peripheral circuit of the secondary winding N2_AC156, such as the AC drive circuit 153, the primary winding N1_AC154, and the primary winding N3_AC155. You may make it make it.

  Specifically, the peripheral circuit of the secondary winding N2_AC156 secures an insulation distance that can withstand even if the maximum output voltage of the secondary transfer power supply 200 is output to the secondary winding N2_AC156 of the AC high-voltage transformer. It is arranged. Here, since the AC high voltage transformer is constituted by the AC drive circuit 153, the primary side winding N1_AC154, the primary side winding N3_AC155, the secondary side winding N2_AC156, etc., sufficient insulation is provided in the AC high voltage transformer. It is arranged with a certain distance. The specific insulation distance includes the maximum output voltage of the secondary transfer power supply 200, the structure and material of the AC high voltage transformer, the number of turns of the secondary winding N2_AC 156, the thickness and material of the insulator in the AC high voltage transformer, and the like. Can be determined according to

  In addition, since both the DC voltage and the AC voltage are output through the AC high voltage transformer, the use of a winding having an appropriate thickness for the maximum output voltage of the secondary transfer power supply 200 allows 2 The resistance value of the secondary winding N2_AC156 is reduced and generation of large heat is also prevented.

  Here, the property of the AC bypass capacitor 159 in the secondary transfer power supply 200 will be described.

  The AC bypass capacitor 159 removes a voltage that is not output (applied) to the secondary transfer unit facing roller 63 (an example of an application target) from the voltage (DC voltage or superimposed voltage) output from the AC power supply 140. belongs to. As a result, it is possible to prevent the superimposed voltage that has not been output (applied) to the secondary transfer unit facing roller 63 from flowing into the DC power supply 110 and to suppress loss in the AC power supply 140.

  However, since the electric charge is not stored in the AC bypass capacitor 159 when the DC power supply 110 is started, the impedance of the AC bypass capacitor 159 is very low, and the DC voltage output from the DC power supply 110 is the AC voltage. It will flow into the bypass capacitor 159. For this reason, the DC power supply 110 cannot supply sufficient power to the secondary transfer portion facing roller 63 until the electric charge is accumulated in the AC bypass capacitor 159, and the rise time is delayed. There is a problem that density unevenness or density dilution may occur at the leading edge of the paper. Note that the term “rise” refers to a state in which there is a potential difference regardless of plus or minus from a state without potential difference (0 kV). Further, for reference, the falling means that a state having a potential difference regardless of plus or minus changes from a state having no potential difference (0 kV).

  For this reason, in this embodiment, as shown in FIG. 4, a discharge circuit 400 such as a transistor is inserted between the DC voltage detection circuit 126 and the voltage control circuit (comparator) 121. In the present embodiment, a direct current detection circuit 401 (an example of a current detection unit) that feeds back the output value of the direct current detected by the direct current detection circuit 132 to the power supply control unit 300 as a DC_FB_I signal is also provided.

  When the power supply control unit 300 outputs a switching signal to the switching circuit 180 to switch from constant voltage control to constant current control, the power supply control unit 300 outputs a discharge signal to the discharge circuit 400 and is stored in the AC bypass capacitor 159. The residual charge is discharged.

  Further, the direct current detection circuit 401 feeds back the output value of the direct current detected by the direct current detection circuit 132 (an example of a current detection unit) to the power supply control unit 300 as a DC_FB_I signal.

  When the output value of the direct current detected by the direct current detection circuit 132 reaches the target current value, the power supply control unit 300 instructs the end of discharge from the I / O control unit 310.

  As a result, when a DC voltage and an AC voltage are applied in accordance with a predetermined condition and switching from the rising constant voltage control to the constant current control, the residual charge of the AC bypass capacitor 159 is discharged to some extent and quickly reaches the target voltage. Thus, the rise time of the DC voltage by the DC power supply 110 is advanced. Therefore, according to the present embodiment, the toner is transferred to the concave and convex portions on the surface of the paper even at the front end of the paper, and a good image can be obtained even on paper with large unevenness. Can be further reduced.

  FIG. 5 is a block diagram illustrating an example of the configuration of the power control unit 300 included in the printing apparatus 1. As illustrated in FIG. 5, the power supply control unit 300 includes an I / O control unit 310, a RAM (Random Access Memory) 320, a ROM (Read Only Memory) 330, and a CPU 340.

  The I / O control unit 310 controls input / output of various signals, and controls input / output of signals exchanged with the secondary transfer power supply 200.

  The RAM 320 is a volatile storage device (memory), and is used as a work area for the CPU 340 and the like.

  The ROM 330 is a non-volatile storage device (memory) for reading, and stores various programs executed by power control, data used for various processes executed by power control, and the like. The ROM 330 may be realized by a flash memory or the like so that writing can be performed.

  For example, the ROM 330, as an example of the predetermined timing, has a constant voltage switching timing (first timing) for causing the DC power source 110 to switch to constant voltage control and a constant current switching timing for causing the DC power source 110 to switch to constant current control. Specific information for specifying (second timing) is stored. The identification information specifies, for example, a constant voltage switching timing and a constant current switching timing based on a printing start reference signal indicating a printing start reference.

  The CPU 340 accepts input of a print start reference signal or accepts user settings from an operation unit such as an operation panel. For example, when the recording paper is plain paper, the user inputs “high voltage output with only DC bias” as the user setting of the high voltage output from the operation unit, and when the recording paper is a lazac paper with large unevenness, Then, “High voltage output with superimposed bias” is input as the user setting of the high voltage output. Then, the CPU 340 causes the secondary transfer power source 200 to output a high voltage according to the user setting via the I / O control unit 310.

  The power supply control unit 300 controls the output of the DC voltage from the DC power supply 110 based on the specific information stored in the ROM 330 when the secondary transfer power supply 200 performs high voltage output (DC voltage output or superimposed voltage output). To do. Specifically, the power supply control unit 300 causes the DC power supply 110 to switch to constant voltage control and constant current control based on the specific information.

  Next, the operation of the printing apparatus 1 according to the embodiment will be described.

  FIG. 6 is a flowchart illustrating an example of a transfer control process performed by the printing apparatus 1 according to the embodiment. First, the power supply controller 300 determines the first time (the DC power supply 110 is switched to constant voltage control) from the elapsed time after the input of the print start reference signal is received and the specific information stored in the ROM 330. Voltage switching timing).

  As shown in FIG. 6, when the first timing comes (Yes in step S1), the power supply control unit 300 instructs the constant voltage control side from the I / O control unit 310 to the constant voltage control side (step S2). .

  Next, the power controller 300 determines the second timing (the DC power source 110 is switched to the constant current control based on the elapsed time since the input of the print start reference signal is received and the specific information stored in the ROM 330. Current switching timing).

  As shown in FIG. 6, when the second timing comes (Yes in Step S3), the power supply control unit 300 instructs the constant current control side from the I / O control unit 310 to a constant voltage constant current control signal (Step S4). .

  Subsequently, as shown in FIG. 6, the power supply controller 300 controls the discharge circuit 400 to discharge the residual charge accumulated in the AC bypass capacitor 159 (step S5).

  Next, the power supply control unit 300 identifies whether the current has reached the target value (step S6).

  When the power supply control unit 300 reaches the target current value (Yes in step S6), the power supply control unit 300 stops the discharge of the residual charges accumulated in the AC bypass capacitor 159 (step S7).

  FIG. 7 is a graph showing a control example of the secondary transfer power supply 200 by the power supply control unit 300. The dotted line in the graph indicates the voltage value, and the solid line indicates the current value.

  In the control example shown in FIG. 7, the voltage applied when the AC bypass capacitor 159 is sufficiently charged by the constant voltage control between the recording medium P and the recording medium P is switched to the constant current control to control the current. This shows the change.

  At the first timing, the power supply control unit 300 outputs a switching signal from the I / O control unit 310 to the secondary transfer reverse bias constant voltage control to the secondary transfer power supply 200 to instruct constant voltage output. The secondary transfer power supply 200 outputs a power supply controlled at a constant voltage.

  At the second timing, the power supply control unit 300 outputs a switching signal from the I / O control unit 310 to the secondary transfer reverse bias constant current control to the secondary transfer power supply 200 to instruct constant current output. The secondary transfer power source 200 outputs a power source controlled by constant current. At this time, the power supply control unit 300 outputs a discharge signal to the discharge circuit 400 to start discharging the residual charge accumulated in the AC bypass capacitor 159, and sets the target current value as shown in FIG. When it reaches, the discharge is terminated. The power supply control unit 300 can reach the target voltage earlier than before by this discharge control.

  As described above, the secondary transfer power source 200 includes the DC power source 110 and the AC power source 140 connected in series with the DC power source 110. The AC power supply 140 selectively outputs a superimposed voltage obtained by superimposing the AC voltage on the DC voltage output from the DC power supply 110 and the DC voltage output from the DC power supply 110. The printing apparatus 1 transfers the toner image to the recording medium P using the voltage output from the AC power supply 140.

  Therefore, when the recording medium P is a low-surface smoothness paper, the toner is transferred to the concave portion by transferring (vibrating) the toner in both directions (transfer direction and the opposite direction) with the superimposed voltage. The image transfer rate is improved and the occurrence of density unevenness can be prevented, so that the image quality can be improved. Also, when the recording medium P is plain paper with high surface smoothness, the toner is transferred in the transfer direction with a DC voltage, so that toner scattering can be suppressed and the occurrence of image blurring can be prevented. , Image quality can be improved.

  As described above, according to the present embodiment, when the DC voltage and the AC voltage are applied according to the predetermined condition and the control is switched from the constant voltage control of the rising to the constant current control, the residual accumulated in the AC bypass capacitor 159 is retained. The target voltage can be reached quickly by discharging the charge to some extent. As a result, even at the leading edge of the paper, the toner is transferred to the concave and convex portions on the surface of the paper, and a good image can be obtained even on the paper with large unevenness. Can be reduced.

63 Transfer Device 100 Image Forming Device 110 DC Power Supply 140 AC Power Supply 159 Bypass Capacitor 180 Switching Circuit 200 Power Supply Device 300 Power Supply Control Unit 400 Discharge Circuit 401 Current Detection Unit

JP 2012-042835 A JP2015-138493A

Claims (5)

A DC power source that switches between constant current control and constant voltage control to output a DC voltage;
A superimposed voltage obtained by superimposing an AC voltage on the DC voltage, and an AC power supply that outputs any one of the DC voltages;
A bypass capacitor that removes a voltage that is not applied to an application target from among the voltages output from the AC power supply;
A discharge circuit for discharging the residual charge stored in the bypass capacitor;
A switching circuit for switching the DC power source from the constant voltage control to the constant current control;
When a predetermined condition is established, a signal is sent to the switching circuit to switch the DC power supply from the constant voltage control to the constant current control, gradually approaching a target current value, and a signal is sent to the discharge circuit to send the bypass A power supply controller for discharging the residual charge accumulated in the capacitor;
A current detector that detects a direct current based on the direct current voltage and outputs the detected direct current to the power supply controller;
A power supply apparatus comprising: The current detection unit periodically detects a direct current and outputs it to the power supply control unit,
The power supply control unit causes the DC power supply to output the DC voltage so that an output value of the DC current detected next becomes a value of the target current.
The power supply device according to claim 1. The predetermined condition is an elapse of a predetermined timing after the start of the constant voltage control.
The power supply device according to claim 1, wherein the power supply device is a power supply device. The predetermined timing is a timing specified with reference to a print start reference signal.
The power supply device according to claim 3. The power supply device according to any one of claims 1 to 4,
A transfer device that transfers an image of toner to a recording medium by applying a voltage from the power supply device;
An image forming apparatus comprising:

Images