JP2010088157A - Power supply device and image forming apparatus including the power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for enhancing voltage control capability in proximity to zero volt in power supply control. <P>SOLUTION: A power supply device includes: a power circuit that outputs power of a voltage within a preset range including zero volt; a voltage measurement circuit that generates feedback voltage of single polarity according to output voltage as the voltage of power; and a control circuit that controls the power circuit so as to bring the output voltage close to a preset predetermined target voltage, according to the feedback voltage. The power supply device has a function of enhancing the accuracy of output voltage measurement within a predetermined range in proximity to zero volt. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power supply device.

  In order to form an image, the image forming apparatus uses high-voltage power in each process such as charging, photosensitivity, development, transfer, and fixing. On the other hand, an image forming apparatus may be required not only to form an image, but also to supply a wide range of power including zero volts, as well as high voltage power for maintenance and other uses.

However, regarding the power supply control method having a wide dynamic range from zero volts to a high voltage, the voltage accuracy particularly in the vicinity of zero volts has not been sufficiently studied. Furthermore, such a problem is not limited to the image forming apparatus, and is a problem common to power control having a wide dynamic range from zero volts to a high voltage.
JP 2003-209972 A

  The present invention has been completed to solve at least a part of the above-described problems, and provides a technique for improving the control performance of voltage control in the vicinity of zero volts in power supply control. Objective.

[Application Example 1]
A power supply unit,
A power circuit that outputs power of a voltage in a preset range including zero volts;
A voltage measuring circuit that generates a single polarity feedback voltage according to an output voltage that is a voltage of the power;
A control circuit for controlling the power circuit to bring the output voltage close to a predetermined target voltage set in advance according to the feedback voltage;
With
The power supply apparatus has a function of increasing the measurement accuracy of the output voltage in the vicinity of zero volts.

  Since the power supply device of the first application example has a function of increasing the voltage measurement accuracy in the vicinity of zero volts, the accuracy of the output voltage in the vicinity of zero volts can be improved regardless of the setting range of the output voltage. In the present specification, zero volt has a broad meaning including substantially zero volt, that is, substantially zero volt (for example, a low voltage such as 0.1 V or −1 V).

[Application Example 2]
A power supply device of Application Example 1,
The voltage measuring circuit includes a voltage gain changing circuit for increasing the measurement accuracy by increasing a voltage gain of the feedback voltage,
The control circuit controls the gain changing circuit to increase the voltage gain when the predetermined target voltage is within a predetermined range near the zero volt.

  In the power supply device of the second application example, the voltage gain of the feedback voltage can be increased when the target voltage is within a predetermined range in the vicinity of zero volts. Therefore, the output voltage can be measured with a high S / N ratio by increasing the signal component. it can.

[Application Example 3]
A power supply device according to application example 1 or 2,
The voltage measurement circuit measures an offset voltage that is the feedback voltage when the power circuit stops outputting,
The control circuit compensates for the offset voltage and controls the output voltage.

  In the power supply device of the third application example, one-point calibration is performed with reference to the feedback voltage when the output of the power circuit is stopped, that is, when the output voltage of the power circuit is zero volts (for example, before startup or control command value: 0V). Since the adjustment is performed, the error of the feedback voltage in the vicinity of approximately zero volts can be compensated for and the accuracy of the output voltage in the vicinity of approximately zero volts can be improved. Compensation can be realized as calibration or adjustment of the feedback voltage.

[Application Example 4]
The power supply device according to any one of Application Examples 1 to 3,
The power circuit includes a negative power circuit that generates negative power, and a positive power circuit that generates positive power,
The voltage measurement circuit is a power supply device that generates the single polarity feedback voltage according to output voltages of the negative power circuit and the positive power circuit.

  In the power supply device of the fourth application example, a single polarity feedback voltage is generated in accordance with the output voltages of the negative power circuit and the positive power circuit, so a simple control circuit (for example, a circuit using a single polarity AD converter). ), The output voltage of positive and negative two poles can be fed back and controlled.

[Application Example 5]
A power supply device according to Application Example 4,
The voltage measuring circuit generates a first reference potential, which is a reference potential when generating the feedback voltage according to the output voltage of the negative power circuit, and the feedback voltage according to the output voltage of the positive power circuit. A reference potential switching circuit that switches between a second reference potential that is a reference potential when
The control circuit monitors a feedback voltage after switching between the negative power circuit and the positive power circuit, and controls the reference potential switching circuit when the feedback voltage reaches a predetermined threshold to control the first reference A power supply device for switching between a potential and the second reference potential.

  In the power supply device of the fifth application example, when the feedback voltage after switching between the negative power circuit and the positive power circuit reaches a predetermined threshold, the first reference potential and the second reference potential are switched. Can be suppressed. The abnormality of the feedback voltage is caused by a mismatch between the polarity of the actual output potential and the first reference potential (negative output reference potential) and the second reference potential (positive output reference potential). It is.

  Such mismatch occurs when switching between the negative power circuit and the positive power circuit is delayed in switching the polarity of the actual output voltage due to the parasitic capacitance of the load, while the first reference potential is changed. This is because there is almost no delay in switching between the first reference potential and the second reference potential, and therefore there is a deviation in the switching timing of the polarity between the output system and the measurement system.

  The present invention can be realized in various forms other than those described above. For example, a power supply control device, a power supply device including the power supply control device, an image forming apparatus including the power supply device, a power supply control method, and the power supply control Can be realized in various forms such as a program or a program product for realizing the above.

  According to the present invention, in the power supply control, it is possible to improve the control performance of the voltage control in the vicinity of approximately zero volts.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Schematic configuration of an image forming apparatus in each embodiment of the present invention:
B. Configuration of the cleaning mechanism in each embodiment of the present invention:
C. Configuration and operation of the power supply device in the first embodiment:
D. Configuration and operation of the power supply device in the second embodiment and the comparative example:
E. Configuration and operation of the power supply device in the third embodiment:
F. Variation:

A. Schematic configuration of an image forming apparatus in each embodiment of the present invention:
FIG. 1 is a schematic cross-sectional view showing an internal configuration of a printer 1 (an example of an “image forming apparatus” recited in the claims) in each embodiment of the invention. In this embodiment, the printer 1 uses the light of a laser or a light emitting diode for photosensitivity, and forms an image with toners of C (cyan), M (magenta), Y (yellow), and K (black). Printer.

  The printer 1 includes a paper feeding unit 110, image forming devices 120 </ b> C, 120 </ b> M, 120 </ b> Y, and 120 </ b> K for each color, a conveyance mechanism 130, a fixing unit 140, a belt cleaning mechanism 150, and a high-voltage power supply device 200. The high-voltage power supply apparatus 200 supplies power of various voltages to the image forming devices 120C, 120M, 120Y, and 120K for each color and a plurality of components (described later) included in the transport mechanism 130. The internal configuration of the high-voltage power supply device 200 will be described later.

  The paper feeding unit 110 includes a tray 112 that stores sheet materials 111 such as printing paper and OHP sheets, a pickup roller 113 that takes out the sheet materials 111 one by one, and a paper feeding mechanism 114 that supplies the sheet material 111 to the transport mechanism 130. Is provided.

  The conveyance mechanism 130 is a mechanism that conveys the sheet material 111 in order to the image forming devices 120K, 120Y, 120M, and 120C of the respective colors. The conveyance mechanism 130 includes a driving roller 131 and a driven roller 132, and a belt 133 (an example of a “conveyance belt” described in claims) that is stretched between the driving roller 131 and the driven roller 132.

  FIG. 2 is an enlarged view showing the configuration of the image forming device 120K in each embodiment of the present invention. The image forming device 120K has almost the same configuration as the image forming devices 120C, 120M, and 120Y for each color except that a collecting roller 128 is additionally provided. The device 120K will be described as an example.

  The image forming device 120K includes a photoreceptor 121K (an example of an “image carrier” recited in the claims) for performing a charging process, and a charger 122K for performing a charging process on the photoreceptor 121K. An exposure device 123K for performing an exposure process on the photoconductor 121K, a developing roller 124K for executing a development process on the photoconductor 121K, a toner case 125K, and a transfer roller 126K. ing. With such a configuration, each process of the electrophotographic process is executed.

  When the transfer process is completed for the K (black) toner through these processes, the transfer is similarly performed for the Y (yellow), M (magenta), and C (cyan) toners to the sheet material 111. The process is executed. When the transfer process is completed for all the toners of K (black), Y (yellow), M (magenta), and C (cyan), the sheet material 111 is fixed to the fixing unit 140 (FIG. 1) to execute the fixing process. It is conveyed to.

  The fixing unit 140 thermally fixes the toner image on the sheet material 111 as a fixing process. In this way, when the heat fixing is completed, the sheet material 111 is discharged onto the upper surface of the printer 1 and the printing is completed.

  The image forming device 120K further includes, as a drum cleaning mechanism (an example of an “image carrier cleaner” recited in the claims), a drum cleaning roller 127K, a collection roller 128, It has.

B. Configuration of the cleaning mechanism in each embodiment of the present invention:
FIG. 3 is an enlarged view showing each configuration of the drum cleaning mechanism and the belt cleaning mechanism in each embodiment of the present invention. FIG. 3 shows a drum cleaning roller 127K and a collection roller 128 provided in the image forming device 120K. The other image forming devices 120M, 120C, and 120Y are equipped with three drum cleaning rollers 127M, 127C, and 127Y, respectively, but are not equipped with components corresponding to the collection roller 128.

  The drum cleaning roller 127K and the recovery roller 128 as the drum cleaning mechanism of each embodiment are cleaning mechanisms that suck and remove the deposits (toner and paper dust) on the photosensitive member 121K by electrostatic force. The drum cleaning roller 127K and the recovery roller 128 include a drum cleaning roller 127K, a recovery roller 128, and a storage box (not shown) for scraping and storing the recovered paper dust from the recovery roller 128.

  The drum cleaning roller 127K and the recovery roller 128 have two operation modes for removing toner having a positive polarity and paper dust having a negative polarity. The two operation modes are composed of a toner removal mode executed at the time of printing and a paper dust removal mode executed after the print job is completed or after printing a predetermined number of sheets.

  The toner removal mode is an operation mode for removing toner having positive polarity from the photoreceptor 121K. In this operation mode, in order to remove toner having positive polarity from the photosensitive member 121K, the drum cleaning roller 127K has a potential (negative polarity) opposite to the polarity (positive polarity) of the toner (for example, with respect to the reference potential). -400V) is applied.

  At this time, a potential having a lower absolute value than the potential applied to the drum cleaning roller 127K (for example, −300 V with respect to the reference potential) is applied to the collection roller 128. Therefore, the positive toner removed from the photosensitive member 121K by the drum cleaning roller 127K is not collected by the collection roller 128 but is held by the drum cleaning roller 127K.

  The paper dust removal mode is an operation mode for removing paper dust having negative polarity from the photoreceptor 121K. In this operation mode, a potential (for example, 600 V with respect to the reference potential) having a polarity (positive polarity) opposite to the polarity (negative polarity) of the paper dust is applied to the drum cleaning roller 127K. Since the potential (for example, 700 V with respect to the reference potential) having a larger potential difference from the paper dust than the drum cleaning roller 127K is applied to the collection roller 128, the adhering matter sucked by the drum cleaning roller 127K is collected. Can do.

  In the paper dust removal mode, the toner having positive polarity is returned to the photosensitive member 121K from the drum cleaning roller 127K charged to the positive electrode, and is passed through the belt 133 to the belt cleaning mechanism 150 (the “conveying belt cleaner described in the claims”). ")"). The belt cleaning mechanism 150 (FIGS. 1 and 2) has the same configuration as the drum cleaning mechanism.

  Thus, a positive potential is applied to the drum cleaning roller 127K and the collection roller 128 in the paper dust removal mode, while a negative potential is applied in the toner removal mode.

  Such a potential is generated by the control board 210 (an example of the “control circuit” recited in the claims) and the drum cleaning voltage generation circuit 220 (an example of the “power circuit” recited in the claims). Applied. The drum cleaning voltage generation circuit 220 applies an output potential to the drum cleaning roller 127K. The collection roller voltage generation circuit 230 applies an output potential to the collection roller 128.

  In the description of the first to third embodiments, which will be described later, the recovery roller voltage generation circuit 230 is omitted for ease of explanation, and only the configuration and operation of the drum cleaning voltage generation circuit 220 will be described. .

C. Configuration and operation of the power supply device in the first embodiment:
FIG. 4 is an explanatory diagram showing the configuration of the drum cleaning voltage generation circuit 220 of the first embodiment. The drum cleaning voltage generation circuit 220 includes a toner removal voltage generation circuit 221 that supplies toner removal power to the drum cleaning roller 127K (an example of the “negative power circuit” recited in the claims), and a paper dust removal mode. A paper dust removal voltage generation circuit 222 (an example of a “positive power circuit” described in claims) that supplies paper dust removal power to the recovery roller 128 and a feedback voltage generation circuit 250 (described in claims) An example of a “voltage measurement circuit”.

  The toner removal voltage generation circuit 221 includes a smoothing circuit SMC that demodulates the pulse width modulation signal PWM (−) input from the control board 210, a drive circuit DRC that drives the booster circuit PRC according to the demodulated signal, and a toner. And a booster circuit PRC that generates a high voltage as power for removal.

  The smoothing circuit SMC is configured as a low-pass filter having a transistor Tr1, a capacitor C1, and two resistors R1 and R2. The drive circuit DRC includes a transistor Tr2, a resistor R3, and a capacitor C2, and drives the boost transformer TRC of the boost circuit PRC in accordance with the smoothed pulse width modulation signal PWM (−). The step-up circuit PRC has a step-up transformer TRC, a diode D1, and a capacitor C3, and rectifies and smoothes AC power boosted by the step-up transformer TRC to generate high-voltage DC power.

  The paper dust removal voltage generation circuit 222 has the same configuration as the toner removal voltage generation circuit 221 except that the booster circuit PRC is changed to the booster circuit PRCa. The booster circuit PRCa is the same as the booster circuit PRC except that the diode D1 of the booster circuit PRC is changed to a diode D2 having a reverse polarity. In other words, the paper dust removal voltage generation circuit 222 is the same as the toner removal voltage generation circuit 221 except that the polarity of the output power is reversed.

  The feedback voltage generation circuit 250 includes two sense resistors Rs1 and Rs2 and a changeover switch Sw1 (an example of a “reference potential switching circuit” described in claims). The two sense resistors Rs1 and Rs2 have a fluctuation of ± 5 V in the output voltage range of the toner removal voltage generation circuit 221 and the paper dust removal voltage generation circuit 222 when the potential of the feedback voltage measurement point 251 as the connection point thereof is within the output voltage range. The resistance value is set to be in the range.

  The control board 210 switches the reference potential by operating the changeover switch Sw1 so that the polarity of the feedback voltage is always positive. Specifically, the changeover switch Sw1 is connected to the high potential side (+5 V side: “first reference potential” described in the claims) when the toner removal voltage generation circuit 221 generates a negative high voltage. When the paper dust removal voltage generation circuit 222 generates a positive high voltage, the low potential side (0 V side: an example of the “second reference potential” described in the claims) ).

  However, in the first embodiment, the following switching method is adopted in consideration of the transient response characteristics when switching the polarity of the output voltage. In this switching method, for example, when the output circuit is switched from the output of the negative toner removal voltage generation circuit 221 to the output of the positive paper dust removal voltage generation circuit 222, the feedback voltage in the transient state is changed by the control board 210. In addition to being monitored, a timing delay is included in the switching of the reference potential. The output circuit is switched, for example, by setting the duty of the pulse width modulation signal PWM (−) to zero and increasing the duty of the pulse width modulation signal PWM (+).

  The control board 210 monitors the feedback voltage in the transient state after switching of the output circuit, maintains the reference potential until the feedback voltage exceeds a predetermined threshold value set in advance, and when the feedback voltage exceeds the predetermined threshold value, the changeover switch Sw1. To switch the reference potential. In this embodiment, the comparison with the predetermined threshold value is performed by the control board 210, but may be configured by an electronic circuit using a comparator or the like.

  As described above, the control board 210 does not simultaneously perform the switching of the output circuits 221 and 222 and the switching of the reference potential because the feedback voltage generated due to the mismatch between the polarity of the actual output potential and the polarity of the reference potential. This is to suppress the abnormality.

  Such mismatching occurs because, in switching between the negative output circuit 221 and the positive output circuit 222, the switching of the actual voltage polarity of the load is delayed due to the parasitic capacitance of the load. This is because there is almost no delay in switching between the first reference potential and the second reference potential, and there is a difference in the polarity switching timing between the output system and the measurement system. Here, the load means a capacitance component or resistance component of the drum cleaning roller 127K or the like.

  In this way, the first embodiment can monitor the feedback voltage and suppress the abnormality of the feedback voltage by delaying the timing of polarity switching of the reference potential from the switching of the polarity of the output voltage.

  In particular, in the configuration for amplifying the feedback voltage (described later), for example, it is assumed that the feedback potential greatly exceeds the set input range of the analog-digital converter in the opposite polarity, so that a remarkable effect is achieved. Details will be described later.

D. Configuration and operation of the power supply device in the second embodiment and the comparative example:
FIG. 5 is an explanatory diagram showing a configuration of the drum cleaning voltage generation circuit 220com of the comparative example. This comparative example is shown as an example of a configuration for facilitating the explanation of the second embodiment. The drum cleaning voltage generation circuit 220com has the same configuration as the drum cleaning voltage generation circuit 220 of the first embodiment except that the feedback voltage generation circuit 250 is changed to a feedback voltage generation circuit 250a.

  The feedback voltage generation circuit 250a has three sense resistors Rs1a, Rs2a, and Rs3. The three sense resistors Rs1a, Rs2a, and Rs3 have a single output voltage range from a negative high voltage output from the toner removal voltage generation circuit 221 to a positive high voltage output from the paper dust removal voltage generation circuit 222. It is set to a resistance value that can be expressed by a polarity feedback voltage.

  In the feedback voltage generation circuit 250a, the feedback voltage measurement point 251 is connected to the high potential side (+ 5V) via the resistor Rs3 and grounded via the resistor Rs2a. In such connection, the potential when the output voltage of the drum cleaning voltage generation circuit 220com is zero volts is determined by the resistance ratio of the two resistors Rs2a and Rs3.

  FIG. 6 is a graph showing the relationship between the output voltage and the feedback voltage and the S / N ratio of the feedback voltage in the drum cleaning voltage generation circuit 220com of the comparative example. In this figure, the horizontal axis and the vertical axis indicate the output voltage and feedback voltage of the feedback voltage generation circuit 250a, respectively.

Specifically, for example, when the drum cleaning voltage generation circuit 220com does not generate an output voltage, that is, when the output voltage is zero volts, the feedback voltage is 2.5 volts. When such a relationship is expressed in an expression, it can be expressed as Expression 1.
Vfb = a × Vout + b Equation 1
Here, Vfb, a, Vout, and b are feedback voltage, proportionality constant, output voltage, and feedback voltage (intercept) when the output voltage is zero volts, respectively. In this example, the proportionality constant and intercept are 0.025 (dimensionless) and 2.5 volts, respectively.

  For example, when the toner removal voltage generation circuit 221 outputs a voltage of −400 volts, the feedback voltage is 1.5 volts. The difference (1 volt) from the intercept (2.5 volts) corresponds to the signal voltage Vs1 as a signal component generated due to the output voltage of the toner removal voltage generation circuit 221. When the paper dust removing voltage generation circuit 222 outputs a voltage of, for example, 600 volts, the feedback voltage is 4 volts. The difference from the intercept (1.5 volts) corresponds to the signal voltage Vs2 as a signal component generated due to the output voltage of the paper dust removal voltage generation circuit 222.

  The inventor of the present application has performed sensitivity analysis for each output voltage by paying attention to the ratio between the signal component of the feedback voltage and the noise component (for example, steady deviation). In this sensitivity analysis, in the configuration of the comparative example, a wide output voltage range from negative to positive is expressed by a feedback voltage range of 0 to 5 volts, and there are few signal components near zero volts. Therefore, it has been found that the S / N ratio is extremely lowered particularly in the vicinity of zero volts.

  FIG. 7 is an explanatory diagram showing the configuration of the drum cleaning voltage generation circuit 220a of the second embodiment. The drum cleaning voltage generation circuit 220a is different from the configuration of the drum cleaning voltage generation circuit 220com of the comparative example in that it includes a feedback voltage amplification circuit 260. On the other hand, the feedback voltage generation circuit 250a (an example of the “voltage measurement circuit” described in the claims) is the same as that of the comparative example.

The feedback voltage amplifier circuit 260 (an example of the “voltage gain changing circuit” described in the claims) is for switching the gain A between the operational amplifier 261, three resistors Rg1, Rg2, and Rg3 that operate the gain A. It is configured as a non-inverting amplifier circuit including a gain changeover switch Swg. The gain A of the feedback voltage amplifier circuit 260 is expressed by the following equation when the resistance values of the three resistors Rg1, Rg2, and Rg3 are R1, R2, and R3, respectively.
(1) Gain changeover switch Swg is off: Gain A = 1 + R2 / R1
(2) Gain changeover switch Swg is on: Gain A = 1 + R2 / RC
Here, RC is a combined resistance of two resistors Rg1 and Rg3. Since the two resistors Rg1 and Rg3 are connected in parallel, the combined resistance is smaller than the resistance value R1 of the resistor Rg1.

  Thus, it can be seen that the feedback voltage amplification circuit 260 can increase the gain A by turning on the gain changeover switch Swg.

  The gain changeover switch Swg is operated by a signal from a gain changeover signal port included in the control board 210. For example, the control board 210 turns on the gain changeover switch Swg when the target value (output voltage) is within a range of ± 100 volts, and turns off when the target value (output voltage) is outside the range of ± 100 volts. Can be set as follows. Such a setting can be appropriately determined based on the output range of the feedback voltage and the input voltage width of the analog-digital conversion port of the control board 210.

  FIG. 8 is a flowchart showing the contents of feedback value calibration processing in the second embodiment. In this calibration process, since a calibration value is obtained as a one-point calibration when the output is zero volts, the error near zero volts can be minimized.

  In step S110, the control board 210 executes a zero volt setting process. The zero volt setting process is a process for setting the output voltage of the drum cleaning voltage generation circuit 220a to zero volt. Specifically, a method of setting the control command values to the toner removal voltage generation circuit 221 and the paper dust removal voltage generation circuit 222 to zero (in this embodiment, the PWM duty is 0% or 100%), or toner This can be realized by maintaining the state before the activation of the removal voltage generation circuit 221 and the paper dust removal voltage generation circuit 222. Such processing is included in the “stop output” in the claims.

  In step S120, the control board 210 performs a sampling process. The sampling process is a process for obtaining a highly reliable feedback voltage. The content of the sampling process is, for example, after measuring the feedback voltage nine times at a sampling rate of 0.1 ms and removing the abnormal value of the measured value (removing the maximum value and the minimum value as abnormal values), This is done by calculating the average of the values.

  In step S130, the control board 210 executes a calibration value determination process. The calibration value determination process is a process for determining the calibration value Ca0. The calibration value Ca0 means the difference between the analog-digital conversion value of the feedback voltage of the drum cleaning voltage generation circuit 220a and the analog-digital conversion value as the nominal value in the zero volt setting process.

  The nominal value is a nominal value preset as an analog-digital conversion value of the feedback voltage of the drum cleaning voltage generation circuit 220 at the time of zero volt output. Specifically, it is an analog-digital conversion value of a feedback voltage as a nominal value at the time of zero volt output when multi-point calibration is performed between −500 volts and 700 volts, for example.

  In step S140, the control board 210 executes a calibration value storing process. The calibration value storing process is a process of storing the calibration value Ca0 in a memory (not shown) included in the control board 210.

  Such processing may be executed every time the drum cleaning voltage generation circuit 220 or the printer 1 is started, or periodically (every predetermined period, every predetermined number of starts, every predetermined number of jobs, or toner cartridge replacement). Every time).

  FIG. 9 is a flowchart showing the contents of the output voltage control process in the small output mode of the second embodiment. In this output voltage control process, the output voltage is controlled using the calibration value Ca0 as one-point calibration when the output is zero volts.

  In step S210, the control board 210 reads a feedback value (also expressed as an FB value). The feedback value is an analog-digital conversion value of the feedback voltage. The feedback value is acquired by using the same routine as the feedback value calibration process, and can be acquired in a time of less than 1 ms.

  In step S220, the control board 210 compares the feedback value with the corrected lower limit value. The corrected lower limit value is a value obtained by subtracting the calibration value Ca0 from the target lower limit value TL of the feedback value at the target value (for example, 50 volts). If the feedback value is below the corrected lower limit value, the process proceeds to step S230. The target lower limit value TL and the target upper limit value TH (described later) are threshold values set based on the nominal value.

  In step S230, the control board 210 executes an output potential increase process. The output potential increasing process is a process of increasing the output voltage of the drum cleaning voltage generation circuit 220 by increasing or decreasing the PWM duty, for example. On the other hand, if the feedback value exceeds the corrected lower limit value, the process proceeds to step S240.

  In step S240, the control board 210 compares the feedback value with the corrected upper limit value. The corrected upper limit value is a value obtained by subtracting the calibration value Ca0 from the target upper limit value TH of the feedback value at the target value (for example, 50 volts). If the feedback value exceeds the corrected upper limit value, the process proceeds to step S250.

  In step S250, the control board 210 executes an output potential lowering process. The output potential lowering process is a process for decreasing the output voltage of the drum cleaning voltage generation circuit 220 by increasing or decreasing the PWM duty, for example. On the other hand, if the feedback value falls below the corrected lower limit value, the process proceeds to step S260.

  In step S260, the control board 210 executes a hold process. The hold process is a process of holding the state for a certain time (1 ms in this embodiment). That is, during this holding time, the PWM duty is fixed at a constant value, and a new feedback value is acquired.

  Such processing is executed at an update rate of 1 ms until output is stopped (step S270).

  As described above, the second embodiment can accurately measure the output voltage near zero volt by compensation with the calibration value Ca0 near zero volt and amplification of the feedback voltage near zero volt. Thus, the accuracy of output voltage control can be improved.

  In particular, the amplification of the feedback voltage in the vicinity of zero volts effectively uses the input voltage width of the analog-to-digital conversion port, and the S / N ratio to noise mixed in the analog signal line between the control board 210 and the feedback voltage generation circuit 250. To increase the measurement accuracy of the output voltage.

  On the other hand, the acquisition of the calibration value in the vicinity of zero volt improves the accuracy by amplification of the feedback voltage in the vicinity of zero volt, so that both can remarkably improve the control performance in the vicinity of zero volt by synergistic effect. In the present embodiment, compensation by the calibration value Ca0 is executed using the target lower limit value TL and the target upper limit value TH set based on the nominal value, but the value measured by the feedback value calibration process. Based on the above, the target lower limit value TL and the target upper limit value TH may be readjusted.

  However, both can be carried out alone, and each effect can be achieved.

  The feedback voltage amplification circuit 260 can be added to the configuration of the first embodiment (FIG. 4). In such a combination, it is assumed that the feedback potential greatly exceeds the set input range of the analog-digital converter due to amplification, whereas the switching control of the first embodiment suppresses voltage fluctuation caused by polarity switching. Therefore, both have a remarkable synergistic effect.

  Specifically, when the target value of the output voltage is changed from a negative high voltage (−400V) to a positive low voltage (+50 V: within a range of ± 100 volts), the high voltage is reversed to the reverse polarity by switching. When a low voltage output is required, the configuration of the first embodiment and the configuration of the second embodiment can generate a synergistic effect.

E. Configuration and operation of the power supply device in the third embodiment:
FIG. 10 is an explanatory diagram showing the configuration of the drum cleaning voltage generation circuit 220b of the third embodiment. The drum cleaning voltage generation circuit 220b is different from the drum cleaning voltage generation circuit 220 of the second embodiment in that a feedback voltage adjustment circuit 270 is provided instead of the feedback voltage amplification circuit 260.

  The feedback voltage adjustment circuit 270 has a digital analog converter 271 that is connected to the high potential side (+5 V) as a reference potential and is grounded. The digital-analog converter 271 can generate a potential that can be varied as an analog output from the output terminal in accordance with a digital control signal input from the control board 210.

  The output terminal of the feedback voltage adjustment circuit 270 is connected to the high potential side of the feedback voltage generation circuit 250a via the resistor Rs3. This configuration is different from the configuration connected to the high potential side (+5 V) that generates the fixed potential in the second embodiment and the comparative example in that the potential on the high potential side can be changed.

  That is, in the second embodiment, the error of the feedback value at zero volts is compensated using the calibration value Ca0, whereas in the third embodiment, the feedback value is adjusted by adjusting the output potential of the feedback voltage adjusting circuit 270. Is different in that it is compensated (adjusted).

  FIG. 11 is a flowchart showing the content of the feedback value adjustment process in the third embodiment. The feedback value adjustment process is a process in which the configuration process in the third embodiment is replaced with feedback voltage adjustment.

  In step S310, the control board 210 executes a zero volt setting process. The zero volt setting process is the same as the zero volt setting process of the second embodiment.

  In step S320, the control board 210 executes an offset value measurement process. The offset value measurement process is a process that combines the sampling process (step S120) and the calibration value determination process (step S130) of the second embodiment. By such processing, the value determined as the calibration value Ca0 in the second embodiment is handled as the offset value Err in the third embodiment.

  In step S330, the control board 210 compares the absolute value of the offset value Err with a predetermined positive threshold Th. The threshold value Th is a value set in advance as an allowable error of the feedback voltage. If the absolute value of the offset value Err is larger than the threshold value Th, the process proceeds to step S340.

  In step S340, the control board 210 adjusts the digital-analog converter 271. Specifically, when the offset value Err is negative, the control board 210 increases the value of the digital control signal (DAC value) so that the potential of the output voltage of the digital-analog converter 271 increases, and the offset value Err is positive. Sometimes, the value of the digital control signal (DAC value) is reduced so that the potential of the output voltage of the digital-analog converter 271 is lowered.

  By repeating such adjustment, when the absolute value of the offset value Err becomes smaller than the threshold value Th, the process proceeds to step S350.

  In step S350, the control board 210 executes an offset value storage process. The offset value storing process is a process of storing the offset value Err in a memory (not shown) included in the control board 210.

  Similar to the second embodiment, such processing may be executed every time the drum cleaning voltage generation circuit 220b or the printer 1 is activated, or periodically (every predetermined period, every predetermined number of activations, a predetermined number of times). It may be executed every job count or every toner cartridge replacement.

  Thus, the third embodiment can accurately measure the output voltage in the vicinity of zero volts by reducing or eliminating the offset voltage in the vicinity of zero volts, so that the accuracy of the output voltage control can be improved using this measured value. Can be improved.

  This configuration may be combined with a configuration in which the feedback voltage is amplified near zero volts. Furthermore, the acquisition of the offset value Err in the vicinity of zero volts can improve the accuracy by amplifying the feedback voltage in the vicinity of zero volts, so that both can remarkably improve the control performance in the vicinity of zero volts. Is the same as in the second embodiment.

F. Variation:
As mentioned above, although several embodiment of this invention was described, this invention is not limited to such embodiment at all, and implementation in various aspects is possible within the range which does not deviate from the summary. is there. In particular, elements other than the elements described in the independent claims in the constituent elements in each of the embodiments described above can be omitted as appropriate because they are additional elements. Furthermore, elements described in the independent claims can be appropriately replaced with elements not described in the independent claims within the scope disclosed in the present specification.

  Furthermore, in the above-described embodiments, not all of the above-described advantages and effects lead to the essential constituent elements of the present invention, and the present invention has a degree of freedom in design that can easily realize each of the above-described advantages and effects. As long as it achieves at least one advantage or effect.

F-1. First Modification: In each of the above-described embodiments, a power circuit including a power circuit that supplies negative power and a power circuit that supplies positive power is used. You may make it use only the power circuit which supplies electric power. The power circuit that can be used in the present invention may be any circuit that outputs power in a voltage within a preset range including generally zero volts.

F-2. Second Modification: In each of the above-described embodiments and modifications, the feedback voltage generation circuit 250 generates a positive feedback voltage. For example, an analog-digital converter processes a negative voltage. Alternatively, a negative feedback voltage may be generated. The voltage measurement circuit that can be used in the present invention may be any circuit that generates a single polarity feedback voltage in accordance with the output voltage.

F-3. Third modified example: In each of the above-described embodiments and modified examples, the power source used for the drum cleaning mechanism of the image forming apparatus is disclosed. However, the power source is not limited to the drum cleaning mechanism. You may comprise as a power supply for devices used for other electrophotographic processes, such as a transfer roller. Furthermore, the present invention is not limited to the image forming apparatus, and can be used as a power supply apparatus for other purposes.

1 is a schematic cross-sectional view illustrating an internal configuration of a printer 1 in each embodiment of the present invention. FIG. 3 is an enlarged view showing a configuration of an image forming device 120K in each embodiment of the present invention. The enlarged view which shows each structure of the drum cleaning mechanism and belt cleaning mechanism in each Example of this invention. Explanatory drawing which shows the structure of the drum cleaning voltage generation circuit 220 of 1st Example. Explanatory drawing which shows the structure of the drum cleaning voltage generation circuit 220com of a comparative example. The graph which shows the relationship between the output voltage in the drum cleaning voltage generation circuit 220com of a comparative example, and a feedback voltage, and S / N ratio of a feedback voltage. Explanatory drawing which shows the structure of the drum cleaning voltage generation circuit 220a of 2nd Example. The flowchart which shows the content of the calibration process of the feedback value in 2nd Example. The flowchart which shows the content of the output voltage control process in the small output mode of 2nd Example. Explanatory drawing which shows the structure of the drum cleaning voltage generation circuit 220b of 3rd Example. The flowchart which shows the content of the feedback value adjustment process in 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Printer 110 ... Paper feed part 111 ... Sheet material 112 ... Tray 113 ... Pick-up roller 114 ... Paper feed mechanism 120C, 120K, 120M ... Image forming device 121K ... Photoconductor 122K ... Charger 123K ... Exposure device 124K ... Developing roller 125K ... toner case 126K ... transfer roller 127K, 127M ... drum cleaning roller 128 ... collection roller 130 ... conveying mechanism 131 ... driving roller 132 ... driven roller 133 ... belt 140 ... fixing unit 150 ... belt cleaning mechanism 200 ... high voltage power supply device 210 ... control Substrate 220com1, 220, 220a ... Drum cleaning voltage generation circuit 221 ... Toner removal voltage generation circuit 222com1, 222com2 ... Drum cleaning voltage generation circuit 221 ... Toner removal voltage generation Circuit 222 ... Paper dust removal voltage generation circuit 230 ... Recovery roller voltage generation circuit 250, 250com ... Feedback voltage generation circuit 251, 251com ... Feedback voltage measurement point 260 ... Feedback voltage amplification circuit 261 ... Operational amplifier 270 ... Feedback voltage adjustment circuit 271 ... Digital to analog converter

Claims (8)

A power supply unit,
A power circuit that outputs power of a voltage in a preset range including zero volts;
A voltage measuring circuit that generates a single polarity feedback voltage according to an output voltage that is a voltage of the power;
A control circuit for controlling the power circuit to bring the output voltage close to a predetermined target voltage set in advance according to the feedback voltage;
With
The power supply apparatus has a function of increasing the measurement accuracy of the output voltage in the vicinity of zero volts. The power supply device according to claim 1,
The voltage measuring circuit includes a voltage gain changing circuit for increasing the measurement accuracy by increasing a voltage gain of the feedback voltage,
The control circuit controls the gain changing circuit to increase the voltage gain when the predetermined target voltage is within a predetermined range near the zero volt. The power supply device according to claim 1 or 2,
The voltage measurement circuit measures an offset voltage that is the feedback voltage when the power circuit stops outputting,
The control circuit compensates for the offset voltage and controls the output voltage. The power supply device according to any one of claims 1 to 3,
The power circuit includes a negative power circuit that generates negative power, and a positive power circuit that generates positive power,
The voltage measurement circuit is a power supply device that generates the single polarity feedback voltage according to output voltages of the negative power circuit and the positive power circuit. The power supply device according to claim 4,
The voltage measuring circuit generates a first reference potential, which is a reference potential when generating the feedback voltage according to the output voltage of the negative power circuit, and the feedback voltage according to the output voltage of the positive power circuit. A reference potential switching circuit that switches between a second reference potential that is a reference potential when
The control circuit monitors a feedback voltage after switching between the negative power circuit and the positive power circuit, and controls the reference potential switching circuit when the feedback voltage reaches a predetermined threshold to control the first reference A power supply device for switching between a potential and the second reference potential. The power supply device according to claim 4 or 5,
The power supply device supplies power to an image forming unit that forms an image on a recording medium,
The image forming unit includes an image carrier, an image carrier cleaner for collecting deposits attached to the image carrier, a conveyor belt disposed opposite to the image carrier, and deposits attached to the conveyor belt. A conveyor belt cleaner for collecting
The power supply device generates a charging potential for collecting the deposit from the image carrier cleaner by the negative power circuit when the image is formed, and the conveyance belt when the image is not formed. The positive power circuit generates a charging potential for returning the collected deposits to the image carrier cleaner so as to be collected by the conveyor belt cleaner. An image forming apparatus,
An image forming unit that forms an image on a recording medium;
A power supply device according to any one of claims 1 to 6,
An image forming apparatus comprising: The image forming apparatus according to claim 7, wherein
The image forming unit includes an image carrier, an image carrier cleaner for collecting deposits attached to the image carrier, a conveyor belt disposed opposite to the image carrier, and deposits attached to the conveyor belt. A conveyor belt cleaner for collecting
The image forming apparatus according to claim 6, wherein the power supply apparatus is a power supply apparatus according to claim 6.

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