JP6205815B2 - Power supply apparatus, image forming apparatus, and output control method - Google Patents

Description

  The present invention relates to a power supply device, an image forming apparatus, and an output control method.

  In an electrophotographic image forming apparatus, an electrostatic toner pattern is usually applied by applying a DC voltage to an electrostatic toner pattern when the electrostatic toner pattern created by an image forming mechanism is transferred from a transfer belt to a sheet. The developer such as toner constituting the toner is moved from the transfer belt to the paper, and the electrostatic toner pattern is transferred to the paper.

  By the way, in the case of a paper having a large surface irregularity and low surface smoothness such as Rezac paper or Japanese paper, since the developer is not easily transferred compared to the convex portion, printing on the concave portion becomes light. There is a problem.

  For this reason, a technique has been proposed in which an alternating voltage is superimposed on a direct current voltage for transfer and the developer is vibrated to improve the transfer rate of the developer to the recesses (see, for example, Patent Document 1).

  Also, in the electrophotographic image forming apparatus, in order to reduce the possibility that the toner remaining on the transfer belt adheres to the paper via the transfer roller and stains the paper, the period during which the paper is not transported to the transfer position (hereinafter referred to as “transfer”) In “Paper space”), a technique is known in which a DC voltage having a polarity opposite to that applied at the time of transfer is applied.

  In the prior art as described above, as a power source configuration, a first DC power source that outputs a first DC voltage having a predetermined polarity, a second DC power source that outputs a second DC voltage having a polarity opposite to the predetermined polarity, and an AC power source are connected in series. A configuration in which the AC power supply outputs one of the first DC voltage, the second DC voltage, and the superimposed voltage obtained by superimposing the second DC voltage and the AC voltage to the outside is conceivable.

  Further, in order to prevent the voltage output from the AC power source from being directly applied to the first DC power source or the second DC power source, the capacitor into which the current accompanying the output of the AC power source flows in the first power source configuration described above is provided. A configuration in which the DC power supply and the second DC power supply are arranged in parallel is further conceivable.

  However, when such a power supply configuration is adopted, a discharge of electric charge occurs due to switching of the output of the DC voltage, and a current flows into each power supply. For this reason, starting failure occurs in the DC power source that outputs the DC voltage after switching, and there is a possibility that the target voltage value cannot be output at the target timing.

  SUMMARY An advantage of some aspects of the invention is that it provides a power supply apparatus, an image forming apparatus, and an output control method capable of starting a DC power supply without causing a start failure.

In order to solve the above-described problems and achieve the object, a power supply device according to one aspect of the present invention is connected to a first DC power supply that outputs a first DC voltage having a predetermined polarity and the first DC power supply in series. A second DC power source that outputs a second DC voltage having a polarity opposite to the predetermined polarity, and the first DC power source and the second DC power source connected in series, and the first DC voltage and the second DC voltage. And an AC power source that outputs one of the superimposed voltages obtained by superimposing the second DC voltage and the AC voltage, and a current flows in accordance with the output of the AC power source, and the first DC power source and the second DC current comprising a capacitor connected in parallel to the power supply, a, of the first DC power source, the second front Symbol first DC voltage to a predetermined time before output is started the second DC voltage from the DC power supply It stops the output, the predetermined time, the first Shorter than the output time of the first DC voltage by the flow source, and a possible time discharge the stored charge in the capacitor, characterized in that.

  According to the present invention, there is an effect that it is possible to start a DC power supply without causing startup failure.

FIG. 1 is a schematic diagram showing an example of the overall configuration of the copying system of the present embodiment. FIG. 2 is a schematic diagram illustrating an example of a configuration related to image formation and transfer of the copying machine according to the present embodiment. FIG. 3 is a block diagram showing an example of the electrical configuration of the copying machine according to the present embodiment. FIG. 4 is a circuit diagram showing an example of the configuration of the secondary transfer power supply according to the present embodiment. FIG. 5 is an explanatory diagram showing an example of a discharge current path according to the present embodiment. FIG. 6 is a diagram illustrating a comparative example with the transfer bias and reverse bias switching timing of the present embodiment. FIG. 7 is a diagram showing a comparative example of the transfer bias and reverse bias switching timing of the present embodiment. FIG. 8 is a diagram illustrating an example of the switching timing of the transfer bias and the reverse bias according to the present embodiment. FIG. 9 is a circuit diagram used for an example of a simulation of a discharge current when switching between the transfer bias and the reverse bias according to the present embodiment. FIG. 10 is a diagram illustrating an example of a waveform change of the inflow current due to the load of the present embodiment. FIG. 11 is a diagram illustrating an example of a change in waveform of the inflow current due to the load of the present embodiment. FIG. 12 is a flowchart illustrating an example of control performed by the power supply control unit and the secondary transfer power supply of the present embodiment.

  Hereinafter, embodiments of a power supply device, an image forming apparatus, and an output control method according to the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, the case where the image forming apparatus of the present invention is applied to an electrophotographic monochrome copying machine will be described as an example. However, the present invention is not limited to this. The image forming apparatus of the present invention can be applied to both monochrome and color as long as it is an apparatus that forms an image by an electrophotographic method. For example, the image forming apparatus can be applied to an electrophotographic printing apparatus or a multifunction peripheral (MFP). 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.

  First, the configuration of the copying system of this embodiment will be described.

  FIG. 1 is a schematic diagram illustrating an example of the overall configuration of a copying system 1 according to the present embodiment. As shown in FIG. 1, the copying system 1 includes a copying machine 2, an ADF (Auto Document Feeder) 3, a finisher 4, a double-side reversing unit 5, an extended sheet feeding tray 6, and a large capacity sheet feeding tray 7. , An insert feeder 8 and a 1-bin paper discharge tray 9 are provided.

  The copying machine 2 corresponds to the main body of the copying system 1, and includes a scanner unit that electronically reads a document to generate image data, an image forming unit that forms an image based on the image data generated by the scanner unit, and paper And a transfer unit for transferring the image formed on the paper (not shown for the scanner unit and the paper supply unit, and not shown in FIG. 1 for the image formation unit and the transfer unit). . Hereinafter, the sheet on which the image is transferred may be referred to as a copy.

  The ADF 3 automatically sends a document to the copying machine 2 (specifically, the scanner unit of the copying machine 2).

  The finisher 4 is a so-called post-processing apparatus having a stapler, a shift tray, and the like, and performs post-processing such as stapling on a copy copied by the copying machine 2. The finisher 4 is not limited to this, and any finisher such as a staple process, a punch (punching) process, and a folding process may be used.

  The double-side reversing unit 5 reverses the paper having an image transferred on one side and returns it to the copying machine 2 (specifically, the transfer unit of the copying machine 2) when copying on both sides of the paper.

  The expansion paper feed tray 6 is an expansion paper feed tray, and sends the paper to the transfer unit of the copying machine 2.

  The large-capacity paper feed tray 7 is a paper feed tray that can store more paper than the paper feed unit of the copier 2 and the extended paper feed tray 6, and sends the paper to the transfer unit of the copier 2.

  The insert feeder 8 sends a sheet such as a cover or a slip sheet to the transfer unit of the copying machine 2.

  The 1-bin paper discharge tray 9 is a paper discharge tray having one bin as a paper discharge destination, and a copy copied by the copying machine 2 is discharged.

  FIG. 2 is a schematic diagram illustrating an example of a configuration related to image formation and transfer of the copying machine 2 of the present embodiment. As shown in FIG. 2, the copying machine 2 includes an image forming unit 20, driving rollers 21 and 22, an intermediate transfer belt 23, a repulsive roller 24, a secondary transfer roller 25, and a secondary transfer power source 100. Is provided.

  The image forming unit 20 includes a photosensitive drum 20a, a charging device, a developing device, a primary transfer roller 20b, a cleaning device, and the like (the charging device, the developing device, and the cleaning device are not shown).

  The image forming unit 20 and an irradiation device (not shown) perform an image forming process (charging process, irradiation process, developing process, transfer process, and cleaning process) on the photoconductive drum 20a, so that the static image is formed on the photoconductive drum 20a. An electric toner pattern is formed and transferred to the intermediate transfer belt 23.

  First, in the charging step, a charging device (not shown) charges the surface of the photosensitive drum 20a that is driven to rotate.

  Subsequently, in the irradiation step, an irradiation device (not shown) irradiates the charged surface of the photosensitive drum 20a with light-modulated laser light to form an electrostatic latent image on the surface of the photosensitive drum 20a.

  Subsequently, in the developing process, a developing device (not shown) develops the electrostatic latent image formed on the photosensitive drum 20a with toner. As a result, an electrostatic toner pattern, which is a toner image obtained by developing the electrostatic latent image with toner, is formed on the photosensitive drum 20a.

  Subsequently, in the transfer step, the primary transfer roller 20b transfers (primary transfer) the electrostatic toner pattern formed on the photosensitive drum 20a to the intermediate transfer belt 23. A small amount of untransferred toner remains on the photosensitive drum 20a even after the electrostatic toner pattern is transferred.

  Subsequently, in the cleaning process, a cleaning device (not shown) wipes off the untransferred toner remaining on the photosensitive drum 20a.

  In this embodiment, since the copying machine 2 is a copying machine that performs monochrome copying, the number of image forming units is one. However, if the copying machine 2 can perform color copying, the number of image forming units is plural. The number of image forming units corresponding to the number of colors of toner to be used is provided. In this case, each image forming unit has a different configuration and operation, although the color of the toner to be used is different.

  The intermediate transfer belt 23 is an endless belt that is wound around a plurality of rollers such as the driving rollers 21 and 22 and the repulsive roller 24, and moves endlessly when one of the driving rollers 21 and 22 is rotationally driven. .

  The intermediate transfer belt 23 has the electrostatic toner pattern transferred by the image forming unit 20 (primary transfer roller 20 b), and conveys the transferred electrostatic toner pattern between the repulsive roller 24 and the secondary transfer roller 25. At this time, the paper P is transported between the repulsive roller 24 and the secondary transfer roller 25 in accordance with the transport timing of the electrostatic toner pattern by a paper feeding unit (not shown). For this reason, the transfer positions of the electrostatic toner pattern and the paper P match.

  In this embodiment, the paper P is, for example, a resack paper with low surface smoothness (large surface unevenness) or plain paper with high surface smoothness (small surface unevenness). It is not limited.

  The repulsive roller 24 transfers (secondary transfer) the electrostatic toner pattern conveyed by the intermediate transfer belt 23 to the paper P at a secondary transfer nip (not shown) with the secondary transfer roller 25. The repulsive roller 24 is connected to a secondary transfer power source 100 that is a power source for transfer bias, and the secondary transfer roller 25 is grounded.

  The secondary transfer power supply 100 (an example of a power supply device) applies a high voltage to the repulsive roller 24. Here, in the copying machine 2, since the toner is negatively charged as in a general image forming apparatus, the secondary transfer power source 100 performs secondary transfer by the repulsive roller 24 and the secondary transfer roller 25. By applying a negative high voltage to the repulsive roller 24 at the timing, repulsive force is applied to the toner to perform transfer.

  As a result, a potential difference is generated between the repulsive roller 24 and the secondary transfer roller 25, and a voltage is generated in which the toner travels from the intermediate transfer belt 23 toward the paper P. Therefore, the electrostatic toner pattern can be transferred onto the paper P. .

  In the copying machine 2, as in a general image forming apparatus, during the printing operation, the intermediate transfer belt 23 is always rotating, and therefore there is no paper between the repulsive roller 24 and the secondary transfer roller 25 ( The toner adhering to the intermediate transfer belt 23 adheres to the secondary transfer roller 25 and stains the back side of the next paper to be printed. In particular, when performing double-sided printing, the image surface (printing surface) is soiled, leading to deterioration in image quality.

  For this reason, the secondary transfer power supply 100 applies a high voltage having a reverse polarity (positive polarity) to the repulsive roller 24 during sheet-to-sheet transfer so that the toner is attracted to the intermediate transfer belt 23 and the secondary transfer roller 25. Prevent dirt.

  When the electrostatic toner pattern is transferred onto the paper P and a printed matter is manufactured, the paper P is heated and pressurized by a fixing device (not shown), and the electrostatic toner pattern is fixed onto the paper P. Then, the sheet P on which the electrostatic toner pattern is fixed is discharged from the copying machine 2 to a 1-bin discharge tray 9 (see FIG. 1).

  FIG. 3 is a block diagram illustrating an example of an electrical configuration of the copying machine 2 according to the present embodiment. As shown in FIG. 3, the copying machine 2 includes a secondary transfer power supply 100 and a power supply control unit 200. The secondary transfer power source 100 includes a DC power source 110 (an example of a second DC power source) that is a negative power source for toner transfer, a DC output detection unit 114, an AC power source 140 for toner transfer, and a bypass capacitor 170 (capacitor). ), An output abnormality detector 171, a DC power source 180 (an example of a first DC power source) that is a positive power source for cleaning, and a DC output detector 184.

  As shown in FIG. 3, in the secondary transfer power supply 100, a DC power supply 110, an AC power supply 140, and a DC power supply 180 are connected in series on the output path.

  When the copying machine 2 performs secondary transfer, the DC power supply 110 outputs a DC voltage having a negative polarity (an example of a polarity opposite to the predetermined polarity) to the AC power supply 140, and the AC power supply 140 is output from the DC power supply 110. The superimposed voltage obtained by superimposing the AC voltage on the negative DC voltage and the negative DC voltage output from the DC power supply 110 are selectively output to the repulsive roller 24. Specifically, the secondary transfer power supply 100 (AC power supply 140) applies a superimposed voltage to the repulsive roller 24 or applies a negative DC voltage to the repulsive roller 24 according to user settings. In the present embodiment, when the paper P is a Lesac paper, the user setting applies the repulsive roller 24 with a superimposed voltage. When the paper P is a plain paper, the repulsive roller 24 is applied with a negative DC voltage. It is assumed that the user setting to be applied is performed in advance by the user.

  Also, between the papers, the DC power supply 180 outputs a positive DC voltage (an example of a predetermined polarity) to the AC power supply 140, and the AC power supply 140 converts the positive DC voltage output from the DC power supply 110 into a repulsive roller. 24.

  The DC power supply 110 includes a DC output control unit 111, a DC drive unit 112, and a DC power supply secondary circuit 113. The AC power supply 140 includes an AC output control unit 141, an AC drive unit 142, an AC voltage transformer 143, and an AC output detection unit 144. The DC power supply 180 includes a DC output control unit 181, a DC drive unit 182, and a DC power supply secondary circuit 183. The power supply control unit 200 controls the secondary transfer power supply 100 and can be realized by, for example, a control device having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like.

  The DC output control unit 111 receives a DC (−) _ PWM signal that controls the output level of the negative DC voltage from the power supply control unit 200, and also receives a DC output detection unit from the DC output detection unit 114. The output value of the DC voltage output from the DC power supply 110 detected by 114 is input. Then, the DC output control unit 111 determines that the output value of the DC power supply secondary circuit 113 is DC (−) _ PWM based on the duty ratio of the input DC (−) _ PWM signal and the output value of the DC voltage output by the DC power supply 110. The drive of the DC power supply secondary circuit 113 (specifically, a DC voltage transformer) is controlled via the DC drive unit 112 so that the output value indicated by the signal is obtained.

  The DC drive unit 112 drives the DC power supply secondary circuit 113 according to the control from the DC output control unit 111.

  The DC power supply secondary circuit 113 is driven by the DC drive unit 112 and outputs a negative DC high voltage.

  The DC output detection unit 114 detects the output value of the DC voltage output from the DC power supply 110 and outputs it to the DC output control unit 111. Further, the DC output detection unit 114 outputs the detected output value to the power supply control unit 200 as an FB_DC (−) signal (feedback signal). This is for causing the power supply control unit 200 to control the duty of the DC (−) _ PWM signal so that the transferability does not deteriorate due to the environment and load.

  In the present embodiment, the DC power source 110 performs constant current control. However, the present invention is not limited to this, and constant voltage control may be performed.

  The AC output control unit 141 includes an AC_PWM signal for controlling the output level of the AC voltage from the power supply control unit 200, and an AC voltage transformer 143 detected by the AC output detection unit 144 from the AC output detection unit 144. The output value is input. The AC output control unit 141 then sets the output value of the AC voltage transformer 143 to the output value specified by the AC_PWM signal based on the duty ratio of the input AC_PWM signal and the output value of the AC voltage transformer 143. The driving of the AC voltage transformer 143 is controlled via the AC driving unit 142.

  An AC_CLK signal that controls the output frequency of the AC voltage is input to the AC drive unit 142. The AC drive unit 142 drives the AC voltage transformer 143 based on the control from the AC output control unit 141 and the AC_CLK signal. The AC drive unit 142 drives the AC voltage transformer 143 based on the AC_CLK signal, so that the output waveform generated by the AC voltage transformer 143 can be controlled to an arbitrary frequency indicated by the AC_CLK signal.

  The AC voltage transformer 143 is driven by the AC drive unit 142 to generate an AC voltage, and generates a superimposed voltage by superimposing the generated AC voltage and a negative DC high voltage output from the DC power supply 110. The generated superimposed voltage is output (applied) to the repulsive roller 24. The AC voltage transformer 143 outputs (applies) a negative DC high voltage output from the DC power supply 110 to the repulsive roller 24 when no AC voltage is generated. The voltage (superimposed voltage or negative DC voltage) output to the repulsive roller 24 is then fed back into the DC power supply 180 via the secondary transfer roller 25.

  The AC output detection unit 144 detects the output value of the AC voltage of the AC voltage transformer 143 and outputs it to the AC output control unit 141. In addition, the AC output detection unit 144 outputs the detected output value to the power supply control unit 200 as an FB_AC signal (feedback signal). This is for causing the power supply control unit 200 to control the duty of the AC_PWM signal so that the transferability does not deteriorate due to the environment and load.

  In the present embodiment, the AC power supply 140 performs constant voltage control. However, the present invention is not limited to this, and constant current control may be performed.

  The AC voltage generated by the AC voltage transformer 143 (AC power supply 140) may be either a sine wave or a rectangular wave. In the first embodiment, the AC voltage is a short pulse rectangular wave. This is because the waveform of the alternating voltage can be contributed to the improvement of the image quality by making it a short pulse rectangular wave.

  The DC output control unit 181 receives a DC (+) _ PWM signal for controlling the output level of the positive DC voltage from the power supply control unit 200, and the DC output detection unit 184 receives the DC output detection unit. The output value of the DC voltage output by the DC power supply 180 detected by 184 is input. Note that the power supply control unit 200 stops outputting the DC (−) _ PWM signal to the DC output control unit 111 when outputting the DC (+) _ PWM signal (in the case of the interval between sheets). Then, the DC output control unit 181 indicates the output value of the DC power supply 180 with the DC (+) _ PWM signal based on the duty ratio of the input DC (+) _ PWM signal and the output value of the DC voltage output by the DC power supply 180. The driving of the DC power supply secondary circuit 183 is controlled through the DC drive unit 182 so that the output value is obtained. When toner transfer to a new sheet occurs, the power supply control unit 200 stops outputting the DC (+) _ PWM signal to the DC output control unit 181 and DC (−) _ PWM to the DC output control unit 111. Start signal output.

  The DC drive unit 182 drives the DC power supply secondary circuit 183 according to the control from the DC output control unit 181.

  The DC power supply secondary circuit 183 is driven by the DC drive unit 182 and outputs a positive DC high voltage. At this time, since the DC power supply 110 and the AC power supply 140 are not driven, the positive DC voltage for cleaning is applied to the repulsive roller 24 as it is.

  The DC output detection unit 184 detects the output value of the DC voltage output from the DC power supply 180 and outputs it to the DC output control unit 181.

  In the present embodiment, the DC power supply 180 performs constant voltage control. However, the present invention is not limited to this, and constant current control may be performed.

  The bypass capacitor 170 receives a current along with the output of the AC power supply 140 and is connected in parallel to the DC power supply 110 and the DC power supply 180. Specifically, the bypass capacitor 170 flows into the DC power supply 110 or the DC power supply 180 when the AC power supply 140 applies a voltage (a negative DC voltage, a superimposed voltage, or a positive DC voltage) to the repulsive roller 24 ( Bypass current). As a result, it is possible to prevent a current from flowing into the DC power supply 110 or the DC power supply 180 with the output of the AC power supply 140, suppress loss in the DC power supply 110 or the DC power supply 180, and stabilize the DC power supply 110 or the DC power supply 180. Can contribute to the driving.

  The output abnormality detection unit 171 is arranged on the output line of the secondary transfer power supply 100, and outputs an LK signal to the power supply control unit 200 when an output abnormality occurs due to a ground fault or the like of the electric wire. Thereby, control for stopping the high-voltage output from the secondary transfer power supply 100 by the power supply control unit 200 becomes possible.

  FIG. 4 is a circuit diagram showing an example of the configuration of the secondary transfer power supply 100 of the present embodiment.

  The DC power supply 110 receives the DC (−) _ PWM signal from the power supply control unit 200, and the input DC (−) _ PWM signal is integrated and input to the current control circuit 122 (comparator). The value of the integrated DC (−) _ PWM signal becomes a reference voltage in the current control circuit 122. The direct current detection circuit 128 detects the direct current output from the direct current power supply 110 on the output line of the secondary transfer power supply 100 via a voltage dividing resistor and the like, and outputs the detected direct current output value to the current control circuit 122. To enter. The current control circuit 122 actively drives the direct current (−) drive circuit 123 of the direct current high voltage transformer when the direct current is small with respect to the reference voltage, and the direct current high voltage transformer when the direct current is large with respect to the reference voltage. The direct current (−) drive 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 121 (comparator). When the output value of the DC voltage reaches the upper limit, the voltage control circuit 121 regulates the driving of the direct current (−) drive circuit 123 of the direct current high voltage transformer. 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 200 as an FB_DC (−) 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 a diode and a capacitor, 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 control unit 200 and is input to the voltage control circuit 151 (comparator). 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 100 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 an AC current on the low voltage side of the bypass capacitor 170 for AC bypass, which is an output line of the secondary transfer power supply 100, and outputs the detected AC current output value to the current control circuit 152 (comparator). ). When the output value of the alternating current reaches the upper limit, the current control circuit 152 regulates the driving of the alternating current drive circuit 153 of the alternating current high voltage transformer. Moreover, the alternating current detection circuit 161 feeds back the detected output value of the alternating current to the power supply control unit 200 as an FB_AC signal.

  The AC drive circuit 153 of the AC high voltage transformer is driven according to the AND logic of the AC_CLK signal input from the power supply control unit 200, the voltage control circuit 151, and the current control circuit 152, and generates an output having the same cycle as AC_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 repulsive roller 24. However, when the AC power supply 140 is not driven, the DC voltage applied to the secondary winding N2_AC 156 is directly output (applied) from the high voltage output unit 158 to the repulsive roller 24.

  In the DC power supply 180, a DC (+) _ PWM signal is input from the power supply control unit 200 to the voltage control circuit 191 (comparator). The value of the input DC (+) _ PWM signal becomes a reference voltage in the voltage control circuit 191. The DC voltage detection circuit 196 detects the DC voltage output from the DC power supply 180 via a voltage dividing resistor or the like on the output line of the secondary transfer power supply 100, and outputs the detected DC voltage output value to the voltage control circuit 191. To enter. The voltage control circuit 191 actively drives the direct current (+) drive circuit 193 of the direct current high voltage transformer when the direct current voltage is smaller than the reference voltage, and the direct current high voltage transformer when the direct current voltage is larger than the reference voltage. The direct current (+) drive circuit 193 is regulated. As a result, the DC power supply 180 ensures constant voltage.

  The direct current detection circuit 197 detects the direct current output from the direct current power supply 180, and inputs the output value of the detected direct current to the current control circuit 192 (comparator). When the output value of the direct current reaches the upper limit, the current control circuit 192 regulates the driving of the direct current (+) drive circuit 193 of the direct current high voltage transformer.

  By driving the direct current (+) drive circuit 193 according to the control of the current control circuit 192 and the voltage control circuit 191, the primary side winding N1_DC (+) 194 of the direct current high voltage transformer and the secondary side winding N2_DC of the direct current high voltage transformer. The output generated in (+) 195 is smoothed by a diode and a capacitor, 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. . However, since the DC power supply 110 and the AC power supply 140 are not driven between the sheets, the DC voltage applied to the secondary winding N2_AC156 is output (applied) from the high voltage output unit 158 to the repulsive roller 24 as it is. .

  The output abnormality detection unit 171 detects an output abnormality due to a ground fault or the like on the output line of the secondary transfer power supply 100 and outputs an LK signal to the power supply control unit 200.

  Here, since the DC power supply 110 has a negative output, the current that flows when the DC power supply 110 outputs a negative DC voltage passes through the secondary transfer roller 25 and the repulsive roller 24 from the GND to the secondary transfer. The power supply 100 is entered, and again passes through the secondary winding N2_AC156 of the AC power supply 140, the secondary winding N2_DC (−) 125 of the DC power supply 110, and the discharge resistance R (+) 198 of the DC power supply 180 to GND. Go back. Therefore, the input of the DC (−) _ PWM signal from the power supply control unit 200 to the DC power supply 110 is started, and the secondary transfer power supply 100 outputs the output of the secondary transfer bias (hereinafter referred to as “transfer bias”). When started, the power supply side electrode of the bypass capacitor 170 is charged with a negative (minus) charge, and the GND side electrode is charged with a positive (plus) charge. As a result, when the input of the DC (−) _ PWM signal from the power supply control unit 200 to the DC power supply 110 is finished and the secondary transfer power supply 100 finishes outputting the transfer bias, electric charge discharge occurs.

  Further, since the DC power supply 180 has a positive output, the current that flows when the DC power supply 180 outputs a positive DC voltage from GND is the secondary winding N2_DC (+) 195 of the DC power supply 180, the DC The secondary transfer power supply 100 exits through the discharge resistance R (−) 129 of the power supply 110 and the secondary winding N2_AC156 of the AC power supply 140, and returns to GND again through the repulsive roller 24 and the secondary transfer roller 25. To go. For this reason, the input of the DC (+) _ PWM signal from the power supply control unit 200 to the DC power supply 180 is started, and the secondary transfer power supply 100 starts to output a paper gap bias (hereinafter referred to as “reverse bias”). Then, a positive charge is charged in the power supply side electrode of the bypass capacitor 170, and a negative charge is charged in the GND side electrode. As a result, when the input of the DC (+) _ PWM signal from the power supply control unit 200 to the DC power supply 180 is finished and the secondary transfer power supply 100 finishes the output of the reverse bias, the electric charge is discharged.

  FIG. 5 is an explanatory diagram showing an example of a discharge current path according to the present embodiment.

  First, the inflow current generated when switching from the reverse bias output to the transfer bias output, that is, switching from the positive DC voltage output by the DC power supply 180 to the negative DC voltage output by the DC power supply 110 or the like. explain.

  As described above, when the secondary transfer power supply 100 applies a reverse bias to the repulsive roller 24, the power supply side electrode of the bypass capacitor 170 is charged with a positive charge, so that the secondary transfer power supply 100 outputs a reverse bias output. When the process is completed, the electric charge is rapidly discharged along the path indicated by the solid line in FIG.

  In this case, the discharge current flows into GND through the smoothing high-voltage diode of the DC power supply 110, the secondary winding N2_DC (−) 125 of the DC power supply 110, and the discharge resistor R (+) 198 of the DC power supply 180. However, since the rise of the discharge current is very steep, the magnetism is generated in the DC high voltage transformer of the DC power supply 110 or the counter electromotive voltage is generated in the primary winding N1_DC (−) 124. .

  For this reason, the starting failure of the DC high-voltage transformer occurs, and the rise of the output of the DC power supply 110 is delayed. As a result, when the printing paper enters the transfer position, the transfer current is insufficient at the leading edge of the paper, the toner transfer amount does not reach the target, and an image defect occurs.

  Further, the discharge current passes through not only the DC power source 110 (specifically, the substrate of the DC power source 110) but also the AC power source 140 (specifically, the substrate of the AC power source 140), and the repulsive roller 24 and the secondary roller. It also flows to the transfer roller 25.

  Here, since the internal resistance value of the repulsive roller 24 and the secondary transfer roller 25 varies greatly depending on the use environment of the machine and aging deterioration, the discharge current flowing in the DC power source 110 and the repulsive roller 24 and the secondary transfer roller 25 are reduced. The ratio with the discharge current flowing through is not constant. For this reason, the output delay time due to the start-up failure of the DC power supply 110 varies depending on the machine (each of the copying machine 2), and the rise of the transfer bias also varies depending on the machine. The rise of the transfer bias varies and the transfer current at the time of entry into the sheet varies, so the amount of toner transferred at the leading edge of the sheet varies and stable image formation becomes impossible.

  Next, the inflow current generated when switching from the output of the transfer bias to the output of the reverse bias, that is, when switching from the output of the negative polarity DC voltage by the DC power supply 110 to the output of the positive polarity DC voltage by the DC power supply 180 is performed. explain.

  As described above, when the secondary transfer power supply 100 applies a transfer bias to the repulsive roller 24, the power supply side electrode of the bypass capacitor 170 is charged with a negative charge, so that the secondary transfer power supply 100 outputs the transfer bias. When the process is completed, the electric charge is suddenly discharged along the path indicated by the dotted line in FIG.

  In this case, the discharge current flows from GND to the bypass capacitor 170 through the secondary winding N2_DC (+) 195 of the DC power supply 180, the smoothing high-voltage diode of the DC power supply 180, and the discharge resistor R (−) 129 of the DC power supply 110. And flow into.

  Also in this case, the discharge current passes through the AC power supply 140 (specifically, the substrate of the AC power supply 140) and flows to the repulsive roller 24 and the secondary transfer roller 25. For the same reason as described above, the rise of the reverse bias also varies depending on the machine.

  Between the papers, control is performed so that the toner and dust on the intermediate transfer belt 23 are not transferred to the secondary transfer roller 25 side by applying a voltage in the opposite direction to that during transfer. However, there is a delay in the rise of the reverse bias. If this occurs, there is an increased risk of toner and dust moving to the secondary transfer roller 25, so that a load is generated on the cleaning mechanism of the secondary transfer roller 25 depending on the configuration of the machine.

  As described above, different problems occur between the rising delay of the transfer bias and the rising delay of the reverse bias. However, since the rising delay of the transfer bias directly affects the image quality, it becomes a very important problem.

  Therefore, in this embodiment, the DC power source 110 is started without causing a start failure when switching from the reverse bias output to the transfer bias output, thereby preventing the transfer bias rising delay and affecting the image quality. Reduce.

  6 and 7 are diagrams showing a comparative example with the transfer bias and reverse bias switching timing of the present embodiment, and FIG. 6 shows a case where only a negative DC voltage is used as the transfer bias. 7 shows a case where a superimposed voltage is used as a transfer bias.

  As shown in FIGS. 6 and 7, the secondary transfer power supply 100 applies a transfer bias, which is a negative polarity bias, to the repulsive roller 24 in order to transfer the toner to the printing paper while the printing paper is at the transfer position. .

  Here, a rise time is required before the secondary transfer power supply 100 can output a transfer bias having a desired voltage value. For this reason, the power supply control unit 200 starts the DC (−) _ PWM signal (in the case of the example shown in FIG. 6) or DC (−) from several tens of ms before the printing paper enters the transfer position (for example, about 50 ms before). ) _PWM signal and AC_PWM signal (in the case of the example shown in FIG. 7) are input to the secondary transfer power supply 100, and when the printing paper enters the transfer position, the secondary transfer power supply 100 applies a transfer bias of a desired voltage value. Control to enable output.

  Further, the secondary transfer power source 100 is configured to reduce the contamination of the printing paper between the trailing edge of the printing paper and the leading edge of the next printing paper, that is, between the papers, as shown in FIGS. A reverse bias, which is a positive bias, is applied to the repulsive roller 24.

  However, when the reverse bias is output to the secondary transfer power supply 100, the power supply control unit 200 causes the DC (−) _ PWM signal (in the example shown in FIG. 6) to the secondary transfer power supply 100 or DC (−). The DC (+) _ PWM signal is input to the secondary transfer power supply 100 at the timing when the input of the _PWM signal and the AC_PWM signal (in the example shown in FIG. 7) is completed. Then, when about 10 ms before the next printing paper enters the transfer position, the power supply control unit 200 ends the input of the DC (+) _ PWM signal and the DC (−) _ PWM signal (in the example shown in FIG. 6). Or the DC (−) _ PWM signal and the AC_PWM signal (in the example shown in FIG. 7) are input to the secondary transfer power supply 100.

  However, as described above, when the output of the secondary transfer power supply 100 is switched from the reverse bias to the transfer bias, the discharge of electric charge occurs, causing the DC high-voltage transformer of the DC power supply 110 to fail to start, and the DC power supply 110. The rise of the output is delayed. Therefore, in practice, as shown in FIGS. 6 and 7, when the printing paper enters the transfer position, the secondary transfer power supply 100 may not be able to output a transfer bias having a desired voltage value.

  For this reason, in this embodiment, the power supply control part 200 advances the timing which complete | finishes the input of DC (+) _ PWM signal by predetermined time rather than the timing shown in FIG.6 and FIG.7.

  FIG. 8 is a diagram illustrating an example of the switching timing of the transfer bias and the reverse bias according to the present embodiment, and illustrates a case where only a negative DC voltage is used as the transfer bias.

  Also in the example shown in FIG. 8, the power supply control unit 200 inputs the DC (−) _ PWM signal to the secondary transfer power supply 100 about several tens of milliseconds before the printing paper enters the transfer position, and the printing paper enters the transfer position. At this time, the secondary transfer power supply 100 is controlled so as to output a transfer bias having a desired voltage value.

  Further, when the reverse bias is output to the secondary transfer power supply 100, the power supply control unit 200 outputs the DC (+) _ PWM signal at the timing when the input of the DC (−) _ PWM signal to the secondary transfer power supply 100 is completed. Input to the next transfer power source 100. Here, the power supply control unit 200 ends the input of the DC (+) _ PWM signal when several tens of ms before the next printing paper enters the transfer position + a predetermined time. Then, the power supply control unit 200 inputs a DC (−) _ PWM signal to the secondary transfer power supply 100 when several tens of ms before the next printing sheet enters the transfer position. That is, the DC power supply 180 stops the output of the positive DC voltage a predetermined time before the output of the negative DC voltage by the DC power supply 110 is started.

  As described above, in the present embodiment, a discharge time that is a predetermined time is ensured from the end of the input of the DC (+) _ PWM signal to the start of the input of the DC (−) _ PWM signal. Here, the predetermined time may be a time that is relatively short with respect to the output time of the positive DC voltage from the DC power supply 180 and can discharge the charge accumulated in the bypass capacitor 170. This is because the DC power supply 110 can be started without causing start-up failure while ensuring prevention of contamination of the secondary transfer roller 25 during paper separation. Details of the predetermined time will be described later.

  Therefore, in the present embodiment, the secondary transfer power supply 100 starts outputting the transfer bias after the discharge of the charge generated by the secondary transfer power supply 100 completing the reverse bias output is completed. As a result, since the DC power supply 110 can be started after the DC power supply 110 is in a state in which the startup failure does not occur, the rise delay of the output of the DC power supply 110 can be prevented.

  Although illustration and description when the superimposed voltage is used as the transfer bias are omitted, the example is the same as the example shown in FIG. 8 except that the output timing of the AC_PWM signal is matched with the output timing of the DC (−) _ PWM signal. is there.

  Below, the determination method of the discharge time which is predetermined time is demonstrated.

  FIG. 9 is a circuit diagram used for an example of a simulation of a discharge current when switching between the transfer bias and the reverse bias according to the present embodiment.

  In the circuit diagram shown in FIG. 9, circuit components related to charge / discharge are shown, and other circuit components are omitted. For example, for the DC power supply 110, the AC power supply 140, and the DC power supply 180, only the secondary side circuit configuration is shown, and the configuration of the primary side drive circuit, the output FB (feedback) circuit, etc. is not shown. ing. Further, the repulsive roller 24 and the secondary transfer roller 25 may be referred to as loads 24 and 25 in some cases.

  In the circuit diagram shown in FIG. 9, the AC voltage generated in the secondary winding L1 when a transfer bias is applied is quadruple rectified using the diodes D1 to D4 and the capacitors C1 to C4, and the resistor R4 and the AC power supply 140 The output current is fed back to the secondary transfer power source 100 via the discharge resistor R5 (R +).

  A capacitor C7 of the AC power supply 140 represents a bypass capacitor 170, and the capacitor C7 serves as a current source when switching between the transfer bias and the reverse bias.

  The impedance between the loads 24 and 25 can be simply expressed by a resistance component and a capacitive load component, and is expressed by a parallel connection of a capacitor C8 and a resistor R6 in the circuit shown in FIG. It is known that the resistance value of the resistance component R6 of the loads 24 and 25 changes depending on the temperature and deterioration with time.

  In the circuit diagram shown in FIG. 9, the AC voltage generated in the secondary winding L2 when reverse bias is applied is double-rectified by the diodes D7 and D8 and the capacitors C5 and C6, and the discharge resistor R1 (R− ) And the AC power supply 140 to the loads 24 and 25.

  Since the transfer bias generally requires a larger voltage than the reverse bias, in the example shown in FIG. 9, the DC power supply 180 is designed as a double voltage rectifier circuit, and the DC power supply 110 is set as a quadruple voltage rectifier circuit. Designed to.

  10 and 11 are diagrams illustrating an example of a change in the waveform of the inflow current due to the loads 24 and 25 according to the present embodiment. In the circuit diagram illustrated in FIG. 9, the output voltage and the direct current when the reverse bias output is turned off are illustrated. The simulation result of the inflow current in the power supply 110 is shown. Specifically, FIG. 10 and FIG. 11 show the time variations of the voltage on the high voltage side of the capacitor C8 and the resistor R6 and the current flowing into the diodes D1 and D3 and the secondary winding L1, and the reverse bias is turned off. The line indicating the output end timing of the DC (+) _ PWM signal, which is the timing to turn off, and 2 ms, 4 ms, and 10 ms after OFF is shown. 10 shows the case where the resistance component R8 of the loads 24 and 25 is 1 MΩ, and FIG. 11 shows the case where the resistance component R8 of the loads 24 and 25 is 50 MΩ.

  10 and 11 both simulate that the reverse bias is turned off from the stable state of 800 V and spontaneously discharge, but the diodes D1 and D3 and the secondary side are caused by the resistance component R6 of the loads 24 and 25. It can be seen that the maximum value, waveform, and timing of the current flowing into the winding L1 are different.

  Since the transfer bias becomes unstable when the flow-in current is large, the DC power supply 110 is started during the period of 0 to 4 ms after the reverse bias is turned off, and the transfer bias is turned on. Then, it is considered that the rising waveform of the transfer bias is very varied.

  In an actual machine, the timing of the control signal varies depending on the operating rate of the CPU that controls the signal. Therefore, the transfer is performed after a sufficient time has elapsed after the reverse bias is turned off in accordance with the variation of the inflow current described above. By assembling the sequence so that the bias is turned on, it is possible to suppress variations in rising of the transfer bias (toner transfer amount at the front end of the paper).

  Therefore, in this embodiment, a time of about 10 ms is ensured for discharging. In other words, in the example shown in FIG. 8, the power supply control unit 200 ends the input of the DC (+) _ PWM signal when the next print sheet enters the transfer position several tens of ms + 10 ms before the next print sheet is transferred to the transfer position. The DC (−) _ PWM signal is input to the secondary transfer power supply 100 at a time of several tens of ms before entering the secondary transfer power source.

  FIG. 12 is a flowchart illustrating an example of control performed by the power supply control unit 200 and the secondary transfer power supply 100 according to the present embodiment. In the example shown in FIG. 12, it is assumed that only a negative DC voltage is used as the transfer bias.

  First, the power supply control unit 200 refers to a print start reference signal indicating a print start reference, etc., and turns on the DC (−) _ PWM signal 10 ms before the printing paper enters the transfer position, and the secondary transfer power supply 100. (Step S101). As a result, the secondary transfer power supply 100 starts outputting the transfer bias.

  Subsequently, the power supply control unit 200 refers to the print start reference signal or the like, and turns off the DC (−) _ PWM signal at the timing when the transfer to the printing paper is finished, and inputs the input to the secondary transfer power supply 100. Upon completion (step S103), the DC (+) _ PWM signal is turned on and input to the secondary transfer power supply 100 (step S105). As a result, the secondary transfer power supply 100 ends the transfer bias output and starts the reverse bias output.

  Subsequently, the power supply control unit 200 refers to the print start reference signal or the like, and whether or not a predetermined time before turning on the DC (−) _ PWM signal (for example, 10 ms before turning on the DC (−) _ PWM signal) is reached. (No in step S107). When a predetermined time before turning on the DC (−) _ PWM signal (Yes in step S107), the power supply control unit 200 turns off the DC (+) _ PWM signal and ends the input to the secondary transfer power supply 100. (Step S109).

  Subsequently, the power supply control unit 200 confirms whether or not a predetermined time has elapsed (No in step S111). Then, when a predetermined time has elapsed and 10 ms before the printing paper enters the transfer position (Yes in step S111), the power supply control unit 200 turns on the DC (−) _ PWM signal and inputs it to the secondary transfer power supply 100. (Step S101). As a result, the secondary transfer power supply 100 starts outputting the transfer bias.

  As described above, in the present embodiment, a discharge time that is a predetermined time is secured from the end of the input of the DC (+) _ PWM signal to the start of the input of the DC (−) _ PWM signal. For this reason, in this embodiment, since the secondary transfer power supply 100 starts outputting the transfer bias after the discharge of the charge generated when the secondary transfer power supply 100 ends the reverse bias output, the DC power supply 110 is started. Thus, the DC power supply 110 can be started after the startup failure has not occurred, and the rise of the output of the DC power supply 110 can be prevented. As a result, while ensuring the productivity of the printed matter, it is possible to prevent the transfer current from being insufficient at the leading edge of the paper when the printing paper enters the transfer position, the toner transfer amount does not reach the target, and image defects can be prevented.

(Modification)
In addition, this invention is not limited to said each embodiment, A various deformation | transformation is possible.

(Modification 1)
In the above-described embodiment, since the toner is negatively charged, the secondary transfer power source applies a negative high voltage to the repulsive roller to apply the repulsive force to the toner to perform transfer. It is not limited to this. For example, the secondary transfer power supply may apply the attractive force to the toner by applying a positive high voltage to the secondary transfer roller to perform the transfer.

(Modification 2)
The above-described embodiments and modifications are examples, and it has been confirmed in other image forming apparatuses and various image forming environments that the present invention can be realized even if the configuration and process conditions are changed.

1 Copying System 2, 1002 Copying Machine 3 ADF
4 Finisher 5 Double-sided reversing unit 6 Extended paper feed tray 7 Large-capacity paper feed tray 8 Insert feeder 9 1-bin paper output tray 20 Image forming unit 20a Photosensitive drum 20b Primary transfer roller 21, 22 Driving roller 23 Intermediate transfer belt 24 Repulsive force Roller 25 Secondary transfer roller 100 Secondary transfer power supply 110 DC power supply 111 DC output control unit 112 DC drive unit 113 DC power supply secondary circuit 114 DC output detection unit 121 Voltage control circuit 122 Current control circuit 123 DC (-) drive circuit 124 Primary winding N1_DC (-)
125 Secondary winding N2_DC (-)
126 DC voltage detection circuit 127 DC voltage detection circuit 128 DC current detection circuit 129 Discharge resistance R (-)
140 AC Power Supply 141 AC Output Control Unit 142 AC Drive Unit 143 AC Voltage Transformer 144 AC Output Detection Unit 151 Voltage Control Circuit 152 Current Control Circuit 153 AC Drive Circuit 154 Primary Winding N1_AC
155 Primary winding N3_AC
156 Secondary winding N2_AC
157 AC power input unit 158 High voltage output unit 160 AC current detection circuit 161 AC current detection circuit 162 AC voltage detection circuit 170 Bypass capacitor 171 Output abnormality detection unit 180 DC power supply 181 DC output control unit 182 DC drive unit 183 DC power supply secondary circuit 184 DC output detection unit 191 Voltage control circuit 192 Current control circuit 193 DC (+) drive circuit 194 Primary winding N1_DC (+)
195 Secondary winding N2_DC (+)
196 DC voltage detection circuit 197 DC current detection circuit 198 Discharge resistance R (+)
200 Power supply control unit

JP 2012-42835 A

Claims (5)

A first DC power supply that outputs a first DC voltage having a predetermined polarity;
A second DC power source connected in series with the first DC power source and outputting a second DC voltage having a polarity opposite to the predetermined polarity;
The first DC power supply and the second DC power supply are connected in series and output one of the first DC voltage, the second DC voltage, and a superimposed voltage obtained by superimposing the second DC voltage and the AC voltage. AC power supply,
A current flows with the output of the AC power supply, and a capacitor connected in parallel to the first DC power supply and the second DC power supply,
The first DC power supply stops the output of the first DC voltage before a predetermined time before the output of the second DC voltage by the second DC power supply is started ,
The predetermined time is shorter than the output time of the first DC voltage by the first DC power source and is a time during which the charge accumulated in the capacitor can be discharged.
A power supply device characterized by that . It said first DC power source and the second DC power source, cormorants rows alternately output,
The power supply device according to claim 1.   An image forming apparatus comprising the power supply device according to claim 1. The first DC power supply is a positive power supply for cleaning,
The first DC voltage is a positive DC voltage,
The second DC power source is a negative power source for toner transfer,
The image forming apparatus according to claim 3, wherein the second DC voltage is a negative DC voltage. An output control method executed by a power supply device,
The power supply device
A first DC power supply that outputs a first DC voltage having a predetermined polarity;
A second DC power source connected in series with the first DC power source and outputting a second DC voltage having a polarity opposite to the predetermined polarity;
The first DC power supply and the second DC power supply are connected in series and output one of the first DC voltage, the second DC voltage, and a superimposed voltage obtained by superimposing the second DC voltage and the AC voltage. AC power supply,
A current flows with the output of the AC power supply, and a capacitor connected in parallel to the first DC power supply and the second DC power supply,
The first DC power supply is shorter than a first DC voltage output time by the first DC power supply, which is a predetermined time before the output of the second DC voltage by the second DC power supply is started , and An output control method including an output control step of stopping the output of the first DC voltage before a predetermined time, which is a time during which the charge accumulated in the capacitor can be discharged .

Images