Patent Description:
In related art, a known electrophotographic image forming apparatus has an alternating-current (AC) charging system in which a direct-current (DC) voltage and an AC voltage are superimposed on each other and applied to a charging member to charge an image bearer such as a photoconductor drum.

The known image forming apparatus of the AC charging system detects the output DC current of a power supply using a current detection circuit disposed in a charging power supply that applies a voltage to the charging member to obtain the surface potential of the image bearer that is charged by the charging member.

For example, as illustrated in <FIG>, <CIT> discloses that an AC voltage generator <NUM> serving as a high voltage section of a charging power supply <NUM> and including a current detector <NUM> performs current detection. Since the AC voltage is superimposed on the DC voltage, the current detector <NUM> extracts a DC current and then measures the DC current using a high withstand voltage element, extracts a current through insulation and measures the current, or drops a high potential to a low potential and measures a current. When the high voltage section detects the current, a detection path for detecting the current has a complicated circuit and is costly in any case.

In contrast, as illustrated in <FIG>, <CIT> discloses a configuration in which an AC voltage is superimposed on a DC voltage and a current detector <NUM> that detects an output DC current is provided at an output portion of a DC voltage generator <NUM> that is a low voltage section of a charging power supply <NUM>. With this configuration, since the current detector <NUM> is provided in the low voltage section, the current can be detected inexpensively and more easily.

However, <CIT> has not considered an inflow current of an AC voltage to the current detector <NUM>. Thus, an error may occur due to a ripple voltage caused by the AC current flowing into the current detector <NUM> depending on the number of samplings. Specifically, <FIG> illustrate waveforms presenting the reason why there is a difference in average value due to a difference in sampling rate when a voltage with an AC voltage flowing thereinto is detected. As illustrated in <FIG>, when the number of samplings is large at a sufficiently high sampling rate with respect to the ripple voltage frequency, the detected voltage on average is equivalent to an original average voltage. However, as illustrated in <FIG>, when a sufficient sampling rate is not obtained and the number of samplings is small, deviated points are detected and averaged, and hence a value deviated from the original average voltage is obtained. Thus, when a sufficient sampling rate is not obtained, the maximum error value is a difference Vpp between the maximum value and the minimum value of the ripple voltage.

In contrast, when a sufficient sampling rate is provided with respect to the ripple frequency to increase the number of samplings, the detection error generated due to the ripple voltage is suppressed. However, to implement sampling at a high frequency, the occupancy of the central processing unit (CPU) increases, and a high-performance CPU is desired.

Document <CIT> discloses an image forming apparatus including a printing engine including a charging member to charge a photoconductor, a power supply including a direct current (DC) power circuit to generate a DC power, an alternating current (AC) power circuit to generate an AC power and to superimpose the DC power on the generated AC power to provide the superimposed power to the charging member, and a sensing circuit to detect an output value of a comparator of the DC power circuit, and a processor to control the AC power circuit to vary a magnitude of the AC power and search for a current saturation point of the charging member based on the output value detected by the sensing circuit while varying the magnitude of the AC power.

A non-claimed example of the present disclosure includes a power supply device that applies a voltage in which a direct-current (DC) voltage and an alternating-current (AC) voltage are superimposed on each other to a charging member that charges an image bearer. The power supply device includes an AC voltage generator that generates the AC voltage; a DC voltage generator that generates the DC voltage; a DC current detector that is provided on an output terminal side of the DC voltage generator and that detects an output DC current flowing into the image bearer; and inflow reduction means that reduces an inflow of an AC current to the DC current detector.

Embodiments of the present disclosure include a power supply device that applies a voltage in which a DC voltage and an AC voltage are superimposed on each other to a charging member that charges an image bearer. The power supply device includes an AC voltage generator that generates the AC voltage; a DC voltage generator that generates the DC voltage; a DC current detector that is provided on an output terminal side of the DC voltage generator and that detects an output DC current flowing into the image bearer; and a reverse waveform applicator that applies a reverse phase waveform of a ripple voltage expected in the DC current detector to the DC current detector.

A non-claimed example of the present disclosure includes a power supply device that applies a voltage in which a DC voltage and an AC voltage are superimposed on each other to a charging member that charges an image bearer. The power supply device includes an AC voltage generator that generates the AC voltage; a DC voltage generator that generates the DC voltage; and a control device that is connected to an output terminal side of the DC voltage generator and that outputs a control signal for causing the AC voltage generator to generate a designated AC voltage and calculate an output DC current flowing into the image bearer. The control device includes an analog-to-digital (AD) converter that is connected to the output terminal side of the DC voltage generator and that detects a DC current; a ripple-voltage storage unit that stores in advance a ripple waveform to be generated per designated AC voltage of the control signal; and an arithmetic unit that expects a ripple waveform to be generated based on an ongoing control signal, calculates a reverse waveform of the expected ripple waveform, and sets a value obtained by adding the calculated reverse waveform to a DC current including a detected ripple as the output DC current.

Embodiments of the present disclosure include an image forming apparatus including the power supply device; an image bearer; a charging member that charges the image bearer; and a control device that calculates a surface potential of the image bearer based on the output DC current.

According to the embodiments, in the power supply device that detects the DC current at the position at which an inflow of the AC voltage occurs, a detection error can be reduced, while preventing the increase in cost.

A more complete appreciation of non-claimed examples as well as embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein:.

The accompanying drawings are intended to depict two non-claimed examples as well as embodiments of the present disclosure and should not be interpreted to limit the scope thereof.

In describing embodiments and a non-claimed examples illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected.

Referring now to the drawings, non-claimed examples and embodiments of the present disclosure are described below.

Non-claimed examples and embodiments of the present disclosure are described referring to the drawings. Like reference signs are applied to identical or corresponding components throughout the drawings and redundant description thereof may be omitted.

Hereinafter, an embodiment is described with reference to an example of an electrophotographic image forming apparatus including a secondary transfer mechanism having a tandem system. The image forming apparatus is a multifunction peripheral (MFP) printer product having a copy function, a print function, a facsimile function, and so forth, mounted in a housing.

<FIG> is a view illustrating a general arrangement example of an image forming apparatus <NUM>. The image forming apparatus <NUM> includes an intermediate transfer unit in a center portion thereof. The intermediate transfer unit includes an intermediate transfer belt <NUM> that is an endless belt. The intermediate transfer belt <NUM> extends around a first support roller <NUM>, a second support roller <NUM>, and a third support roller <NUM>, and is rotationally driven clockwise.

The image forming apparatus <NUM> further includes an intermediate transfer body cleaning unit <NUM> disposed rightward of the second support roller <NUM> to remove residual toner remaining on the intermediate transfer belt <NUM> after a toner image is transferred onto a recording medium P.

An image forming section <NUM> including a yellow (Y) image forming section, a magenta (M) image forming section, a cyan (C) image forming section, and a black (K) image forming section is provided to face the intermediate transfer belt <NUM> disposed between the first support roller <NUM> and the second support roller <NUM>. The image forming sections of the respective colors are arranged side by side in a travel direction of the intermediate transfer belt <NUM>.

The image forming sections of the respective colors have configurations similar to each other except that the colors of toner to be used are different from each other. Accordingly, in the description and drawings below, the suffixes "Y", "M", "C", and "K", each representing the color of toner, are omitted unless the color is discriminated. The image forming apparatus <NUM> may also include a white (W) image forming section on the upstream side of the yellow (Y) image forming section in the travel direction of the intermediate transfer belt <NUM>; however, the illustration is omitted in <FIG>.

The image forming section <NUM> includes, for each color, a photoconductor <NUM>, a charging roller <NUM> serving as an example of a charging member, a developing unit, and a cleaning unit, and is detachably attached to the image forming apparatus <NUM>. In this case, the photoconductor <NUM> is an example of an image bearer.

The image forming apparatus <NUM> also includes a light beam scanner <NUM> above the image forming section <NUM>. The light beam scanner <NUM> irradiates the photoconductors <NUM> of the respective colors with light beams (laser beams) for image formation to form electrostatic latent images (latent images) corresponding to image data on the photoconductors <NUM> of the respective colors.

The electrostatic latent images on the photoconductors <NUM> of the respective colors are developed by the developing units. The developed toner images of the respective colors are superimposed and primarily transferred onto the intermediate transfer belt <NUM>. Thus, a color toner image is formed on the intermediate transfer belt <NUM>. The toner image is borne by the intermediate transfer belt <NUM> and moved (conveyed) in the travel direction of the intermediate transfer belt <NUM>. The configuration of the image forming section <NUM> will be described later in detail referring to <FIG>.

The image forming apparatus <NUM> includes a secondary transfer unit <NUM> below the intermediate transfer belt <NUM>.

The secondary transfer unit <NUM> includes a secondary transfer belt <NUM> that is an endless belt, extending around two rollers <NUM>, and disposed to press up the intermediate transfer belt <NUM> against the third support roller <NUM>. The secondary transfer belt <NUM> can secondarily transfer the toner image formed on the intermediate transfer belt <NUM> onto a recording medium P.

The image forming apparatus <NUM> also includes a fixing unit <NUM> on a lateral side of the secondary transfer unit <NUM>. The fixing unit <NUM> fixes the toner image on the recording medium P, which has been conveyed in a state with the toner image secondarily transferred, to the recording medium P. The fixing unit <NUM> includes a fixing roller <NUM> that is an endless belt and a pressure roller <NUM>, and can fix the toner image transferred on the surface of the recording medium P to the recording medium P by the heat and pressure of the fixing roller <NUM> and the pressure roller <NUM>.

The image forming apparatus <NUM> further includes, below the secondary transfer unit <NUM> and the fixing unit <NUM>, a sheet inversion unit <NUM> that inverts the front and back sides of the recording medium P and sends the recording medium P to form an image also on the back side of the recording medium P immediately after the image is formed on the front side.

Next, a series of flows of forming an image on a recording medium P in the image forming apparatus <NUM> is described.

When a start button of "copy" in an operation unit (illustration being omitted) is pressed, in a case where a document is placed on a document feeding table <NUM> of an auto document feeder (ADF) <NUM> serving as an automatic document feeder, the image forming apparatus <NUM> causes the ADF <NUM> to convey the document onto a contact glass <NUM>. In contrast, in a case where a document is not placed on the document feeding table <NUM>, an image reading unit <NUM> including a first carriage <NUM> and a second carriage <NUM> is driven to read a document manually placed on the contact glass <NUM>.

In the image reading unit <NUM>, a light source included in the first carriage <NUM> irradiates the contact glass <NUM> with light. The reflected light from the document surface is reflected by a first mirror included in the first carriage <NUM> toward the second carriage <NUM>, and is reflected by a second mirror included in the second carriage <NUM>. The reflected light from the document surface forms an image on an imaging surface of a charge coupled device (CCD) <NUM> that is a reading sensor, by an imaging lens <NUM>. The CCD <NUM> captures an image of the document surface, and generates image data of each color of Y, M, C, and K based on an image signal of the image captured by the CCD <NUM>.

When a start button of "print" is pressed, when an instruction to form an image is provided from an external device such as a personal computer (PC), or when an instruction to output a facsimile (fax) is provided, the image forming apparatus <NUM> starts the rotational driving of the intermediate transfer belt <NUM>, and prepares for image formation of each unit of the image forming section <NUM>.

Then, the image forming apparatus <NUM> starts an image formation process for each color. The photoconductors <NUM> for the respective colors are irradiated with laser beams modulated based on image data of the respective colors to form electrostatic latent images. Then, the toner images of the respective colors obtained by developing the electrostatic latent images are superimposed on each other and formed as an image on the intermediate transfer belt <NUM>.

Then, a recording medium P is sent to the secondary transfer unit <NUM> at a certain timing so that the leading end of the recording medium P enters the secondary transfer unit <NUM> at a timing at which the leading end of the toner image on the intermediate transfer belt <NUM> enters the secondary transfer unit <NUM>. Then, the toner image on the intermediate transfer belt <NUM> is secondarily transferred onto the recording medium P by the secondary transfer unit <NUM>. The sheet with the toner image secondarily transferred thereon is sent to the fixing unit <NUM>, and the toner image is fixed to the recording medium P.

Sheet feeding of a recording medium P to the secondary transfer position is described. One of sheet feeding rollers <NUM> of a sheet feeding table <NUM> is rotationally driven to feed recording media P from one of sheet feeding trays <NUM> provided in multiple stages in a sheet feeding unit <NUM>. Then, one of the recording media P is separated by a separation roller <NUM>, enters a conveyance roller unit <NUM>, and is conveyed by a conveyance roller <NUM>. Then, the recording medium P is guided to a conveyance roller unit <NUM> in the image forming apparatus <NUM>, is abutted against a registration roller <NUM> of the conveyance roller unit <NUM> and is temporarily stopped. Then, the recording medium P is sent to the secondary transfer unit <NUM> in synchronization with the timing of the secondary transfer as described above.

Also, a user can insert a recording medium P into a manual sheet feeding tray <NUM> and feed the recording medium P. When the user inserts recording media P into the manual sheet feeding tray <NUM>, the image forming apparatus <NUM> rotationally drives a sheet feeding roller <NUM> to separate one of the recording media P on the manual sheet feeding tray <NUM> and to draw the separated recording medium P into a manual sheet feeding path <NUM>. Like the above-described configuration, the recording medium P is abutted against the registration roller <NUM> and temporarily stopped, and then is sent to the secondary transfer unit <NUM> in synchronization with the timing of the secondary transfer as described above.

The recording medium P fixed by the fixing unit <NUM> and ejected is guided to an ejection roller <NUM> by a switching claw <NUM>, is ejected by the ejection roller <NUM>, and is stacked on a sheet ejection tray <NUM>. Alternatively, the recording medium P is guided to the sheet inversion unit <NUM> by the switching claw <NUM>, inverted by the sheet inversion unit <NUM>, and guided to the secondary transfer position again. Then, an image is also formed on the back side of the recording medium P, and then the recording medium P is ejected onto the sheet ejection tray <NUM> by the ejection roller <NUM>.

Residual toner remaining on the intermediate transfer belt <NUM> after the image transfer is removed by the intermediate transfer body cleaning unit <NUM> to prepare for next image formation.

The image forming apparatus <NUM> can form a color image on a recording medium P in this way.

The image forming section <NUM> included in the image forming apparatus <NUM> is described next. <FIG> is a diagram illustrating a configuration example of the image forming section <NUM>. <FIG> illustrates a configuration example of the image forming section <NUM> for black. The image forming sections 20Y, <NUM>, and 20C of the other three colors have the same configuration as that of the image forming section <NUM> for black except that the colors of toner used in the image formation processes are different. Thus, illustration and description for the image forming sections 20Y, <NUM>, and 20C are omitted, and the image forming section <NUM> for black is described.

The image forming section <NUM> includes the photoconductor <NUM>, the charging roller <NUM>, a developing device <NUM>, a cleaning blade <NUM>, and a charge remover <NUM>.

The photoconductor (photoconductor drum) <NUM> is a drum-shaped organic photoconductor charged to a negative polarity. The photoconductor <NUM> includes a photoconductive layer overlaying a drum-shaped conductive support body. The photoconductor <NUM> includes multiple layers including the conductive support body that functions as a base layer, an undercoat layer that functions as an insulation layer, a charge generation layer and a charge transport layer that function as a photoconductive layer, and a surface layer (i.e., a protection layer). The undercoat layer is overlaid on the photoconductive support body, the charge generation layer and the charge transport layer are overlaid on the undercoat layer, and the surface layer is formed on top of the charge generation layer and the charge transport layer. The conductive support body of the photoconductor <NUM> may use a conductive material having a volume resistance of <NUM>Ωcm or less.

The charging roller <NUM> is a roller member including a conductive cored bar and an elastic layer of moderate resistivity covering an outer circumference of the conductive cored bar. A charging bias in which an AC voltage is superimposed on a DC voltage is applied from a charging high-voltage power supply <NUM> to the charging roller <NUM>, so that the surface of the photoconductor <NUM> facing the charging roller <NUM> is charged. A cleaning roller that removes dirt from the charging roller <NUM> may be provided in contact with the charging roller <NUM>.

The developing device <NUM> includes a developing roller 29a facing the photoconductor <NUM>. The developing roller 29a includes a magnet and a sleeve. The magnet includes a magnet roller or multiple magnets fixedly disposed inside the developing roller 29a and generates multiple magnetic poles around a circumferential surface of the developing roller 29a. The sleeve rotates about the magnet. The magnet forms multiple magnetic poles on (the sleeve of) the developing roller 29a, and a developer is borne on the developing roller 29a.

The cleaning blade <NUM> mechanically scrapes off extraneous matter, such as untransferred toner, adhering to the surface of the photoconductor <NUM>. The cleaning blade <NUM> is a blade-shaped member made of a rubber material such as urethane rubber and formed in a substantially plate shape, and is in contact with the surface of the photoconductor <NUM> at a predetermined angle and with a predetermined pressure.

The charge remover <NUM> removes the charge on the surface of the photoconductor <NUM> after the toner image is transferred.

The photoconductor <NUM> charged by the charging roller <NUM> is exposed to light by the light beam scanner <NUM> in accordance with image data. Thus, an electrostatic latent image is formed on the surface of the photoconductor <NUM>. The developing device <NUM> applies toner to the electrostatic latent image formed on the surface of the photoconductor <NUM>. Thus, a toner image is developed on the surface of the photoconductor <NUM>.

A voltage generated by a transfer high-voltage power supply <NUM> is applied to a primary transfer roller <NUM>, and hence the toner image on the surface of the photoconductor <NUM> is primarily transferred onto the intermediate transfer belt <NUM>. The toner image on the intermediate transfer belt <NUM> is transferred onto a recording medium P by the secondary transfer unit <NUM>, and is fixed to the recording medium P by the fixing unit <NUM>. Residual toner and so forth on the surface of the photoconductor <NUM> is removed by the cleaning blade <NUM>. The charge on the surface of the photoconductor <NUM> is removed by the charge remover <NUM>.

In the case of color printing, four similar configurations are provided for respective colors, toner images are transferred onto the intermediate transfer belt <NUM> on a per-color basis, and then a secondary transfer and a fixing process are executed.

According to the embodiment, the charging roller <NUM> is disposed close to the photoconductor <NUM> in a non-contact state with respect to the photoconductor <NUM>. The charging system in which a very small gap is set between the photoconductor <NUM> and the charging roller <NUM> is referred to as a non-contact charging system. According to this system, as compared to a contact charging system in which the photoconductor <NUM> and the charging roller <NUM> are used in contact with each other, a foreign substance such as toner or lubricant remaining on the photoconductor <NUM> is less likely to adhere to the charging roller <NUM>, thereby providing an advantageous effect of suppressing charging unevenness due to adhesion of a foreign substance. However, the charging system in the embodiment is not limited to the non-contact charging system, and may be a contact charging system.

A flow of power supply to the charging roller <NUM> is described next with reference to <FIG> is a diagram illustrating a section from control of a high-voltage power supply to a charging unit according to a first non-claimed example.

As illustrated in <FIG>, the charging roller <NUM> and a power supply control device <NUM> that is a host controller that controls a charging operation are connected to the charging high-voltage power supply <NUM>. The combination of the charging high-voltage power supply <NUM> and the power supply control device <NUM> is referred to as a power supply device α.

The charging high-voltage power supply <NUM> mainly includes an alternating-current (AC) generation circuit <NUM> and a direct-current (DC) generation circuit <NUM>. The DC voltage that is output from the charging high-voltage power supply <NUM> is from <NUM> V to <NUM> V, the AC voltage (AC_Vout) that is output from the charging high-voltage power supply <NUM> is from <NUM> Vpp to <NUM> Vpp, and a drive frequency (f) is from about <NUM> to <NUM>.

First, in response to an AC control signal and a DC control signal that are commands from a CPU <NUM> of the power supply control device <NUM>, the AC generation circuit <NUM> and the DC generation circuit <NUM> of the charging high-voltage power supply <NUM> operate to generate high voltages.

The charging high-voltage power supply <NUM> applies a voltage in which an AC voltage (alternating voltage) is superimposed on a DC voltage (direct voltage) to the charging roller <NUM>, so that the charging roller <NUM> charges the photoconductor <NUM> serving as an image bearer.

<FIG> is a diagram illustrating a configuration and a flow of current of the power supply device α according to the first non-claimed example. The power supply device α is described in detail referring to <FIG> and <FIG>.

The charging high-voltage power supply <NUM> includes a coupling capacitor <NUM>, a DC current detector <NUM>, and an AC current reducer <NUM> in addition to the above-described AC generation circuit <NUM> and DC generation circuit <NUM>.

The AC generation circuit <NUM> is an example of an AC voltage generator, and is an electric circuit that generates a designated AC voltage based on the AC control signal input from the power supply control device <NUM>. The AC generation circuit <NUM> includes a drive circuit <NUM>, a control circuit <NUM>, and an AC transformer <NUM>.

The drive circuit <NUM> is an electric circuit that drives the AC transformer <NUM>.

The AC transformer <NUM> is driven by the drive circuit <NUM> to generate an AC voltage.

The primary side of the AC transformer <NUM> includes a double-wound coil. One end of the secondary-side coil of the AC transformer <NUM> is connected to the charging roller <NUM> serving as a load, and the other end thereof is connected to each of the DC generation circuit <NUM> (one end of the secondary-side coil of a DC transformer <NUM>) and the coupling capacitor <NUM>.

The AC voltage generated by the AC transformer <NUM> is superimposed on the DC voltage generated by the DC generation circuit <NUM>, and the superimposed voltage is applied to the charging roller <NUM>.

The control circuit <NUM> supplies a drive-circuit control signal to the drive circuit <NUM> based on the amount of current generated in the double-wound coil of the AC transformer <NUM> to control the AC voltage generated by the AC transformer <NUM>. Thus, the AC voltage generated by the AC transformer <NUM> meets a target voltage indicated by the AC control signal input from the host power supply control device <NUM>.

The coupling capacitor <NUM> serving as an example of a coupling capacitor is provided between the AC generation circuit <NUM> and the DC generation circuit <NUM>. One end of the coupling capacitor <NUM> is connected to the other end of the secondary-side coil of the AC transformer <NUM>, and the other end of the coupling capacitor <NUM> is grounded.

Since the coupling capacitor <NUM> is arranged in this way, the AC current flowing between the AC generation circuit <NUM> and the charging roller <NUM> serving as the load mostly flows to the coupling capacitor <NUM>, and is prevented from flowing into the DC generation circuit <NUM>. As illustrated in <FIG>, an AC current Iac indicated by an arrow that flows outside the power supply to the load <NUM> also flows to the coupling capacitor <NUM>.

The coupling capacitor <NUM> also has a function of a bypass capacitor that allows just an AC current to flow therethrough.

The DC generation circuit <NUM> is an example of a DC voltage generator, and is an electric circuit that generates a designated DC voltage based on the DC control signal input from the power supply control device <NUM>. The DC generation circuit <NUM> includes a drive circuit <NUM>, a control circuit <NUM>, a DC transformer <NUM>, a diode <NUM>, a rectifier capacitor <NUM>, and a resistor <NUM>.

Among these components, the drive circuit <NUM> is an electric circuit that drives the DC transformer <NUM>. The DC transformer <NUM> is driven by the drive circuit <NUM> to generate a DC voltage that is higher than the input voltage from the input voltage.

The DC voltage generated by the DC transformer <NUM> is superimposed on the AC voltage generated by the AC generation circuit <NUM> and is applied to the load <NUM>.

One end of the secondary-side coil of the DC transformer <NUM> is connected to the AC generation circuit <NUM> (the other end of the secondary-side coil of the AC transformer <NUM>). The primary side of the DC transformer <NUM> includes a double-wound coil.

Both ends of the secondary-side coil of the DC transformer <NUM> are connected to the rectifier capacitor <NUM>. Thus, the DC current flowing to the secondary side is divided into a DC current flowing outside the charging high-voltage power supply <NUM> and a DC current flowing inside the charging high-voltage power supply <NUM>.

In <FIG>, an arrow Idc_o indicates the DC current flowing outside the charging high-voltage power supply <NUM>, and an arrow Idc_i indicates the DC current flowing inside the charging high-voltage power supply <NUM>.

The control circuit <NUM> supplies a drive-circuit control signal to the drive circuit <NUM> based on the amount of current generated in the double-wound coil of the DC transformer <NUM> to control the DC voltage generated by the DC transformer <NUM>.

For example, the control circuit <NUM> increases the control value of the drive circuit <NUM> when the amount of current generated in the double-wound coil of the DC transformer <NUM> is smaller than the amount of current corresponding to a target voltage indicated by the DC control signal input from the host power supply control device <NUM>. In contrast, the control circuit <NUM> decreases the control value of the drive circuit <NUM> when the amount of current generated in the double-wound coil of the DC transformer <NUM> is larger than the amount of current corresponding to the target voltage indicated by the DC control signal input from the host power supply control device <NUM>.

Accordingly, the control circuit <NUM> performs constant voltage control so that the output voltage of the DC generation circuit <NUM> meets the target voltage indicated by the DC control signal. The constant voltage control can be executed with a simple circuit configuration by using the amount of current generated in the double-wound coil of the DC transformer <NUM>.

The diode <NUM>, the rectifier capacitor <NUM>, and the resistor <NUM> define a half-wave rectifier circuit that rectifies and smooths a half cycle of an AC voltage to obtain a DC voltage. The ripple appearing in the output voltage is equal to the frequency of the AC power supply.

The current output terminal of the half-wave rectifier circuit is provided with the DC current detector <NUM> via the AC current reducer <NUM>. The AC current reducer <NUM> increases the impedance to reduce an AC component flowing toward the DC current detector <NUM> on the downstream side.

The DC current detector <NUM> is an output current detection circuit that is provided on the output terminal side (that is, downstream an output terminal) of the DC generation circuit <NUM> and that detects an output DC current, and includes a current detection element <NUM> and a detection analog-to-digital (AD) converter (hereinafter, referred to as detection ADC) <NUM>.

The current detection element <NUM> is connected between the DC generation circuit <NUM> and a reference potential portion and hence is grounded. The current detection element <NUM> functions as a resistor for detecting a current in the detection ADC <NUM>.

In the present example, the detection ADC <NUM>, which is a detection ADC circuit, detects the output DC current of the charging high-voltage power supply <NUM>, and outputs a current detection signal indicating the output DC current to a host control device <NUM>.

Potential information on the DC current detected by the detection ADC <NUM> of the DC current detector <NUM> is input to a CPU <NUM> (<FIG>) of the host control device <NUM>. The host control device <NUM> predicts a surface potential of the photoconductor <NUM> based on a measurement output DC current that is a charging DC current detected by the DC current detector <NUM>.

Described here is a calculation method of predicting the surface potential of the photoconductor <NUM> from the output DC current that is the charging DC current.

Since the photoconductor <NUM> is charged by accumulating a charge in the surface layer, charging the photoconductor <NUM> is considered equivalent to charging a capacitor. Thus, the following expression is established between a charge (Q) accumulated in the photoconductor <NUM> and a charging potential V In the following expression, C denotes an electrostatic capacity of the photoconductor <NUM>.

The charge Q accumulated in the photoconductor <NUM> is expressed by the following expression and can be converted. <MAT> <MAT>.

In this case, a pre-charging photoconductor surface potential (Vd<NUM>) and a charging application voltage (Vc) are constant. In charging with the AC voltage superimposed, an expression "charging application voltage Vc = ongoing photoconductor surface potential (Vd)" is established. Hence, the following expression (<NUM>) is established for the charging voltage V <MAT>.

The following expression is also established.

(In the expression, ε denotes a photoconductor-surface-layer dielectric constant, S denotes a photoconductor surface area contributing to charging, d denotes a photoconductor-surface-layer film thickness, L denotes a photoconductor length contributing to charging, and λ denotes a linear velocity. ) By transforming the relational expression (<NUM>), a DC component (Idc) of the charging current can derive the following expression using the photoconductor surface potential (Vd).

In this case, since it is found that the photoconductor film thickness d hardly changes over time in the non-contact charging system, the film thickness d is constant, the dielectric constant ε and the photoconductor length L are also constant, and hence the DC component Idc of the charging current is proportional to the photoconductor surface potential V (correctly, Vd - Vd<NUM>).

With such a calculation method, the host control device <NUM> can recognize the current flowing into the photoconductor <NUM>, calculate the surface potential of the photoconductor <NUM>, and perform image formation control or the like based on the measurement output DC current detected by the DC current detector <NUM>.

As described above, according to the present example, the AC current reducer <NUM> is provided upstream of the DC current detector <NUM>. The AC current reducer <NUM>, which may also be referred to as a reduction circuit, serves as inflow reduction means and is provided upstream of the DC current detector <NUM> to reduce a ripple voltage caused by the AC current flowing into the DC current detector <NUM>.

Specifically, although the coupling capacitor <NUM> originally serves as a bypass and prevents a large portion of the AC current from flowing to the DC current detector <NUM> side, the AC current may flow when the impedance of a first DC current detection line DL1 is low.

Thus, according to the present example, the AC current reducer <NUM> is provided immediately upstream of the DC current detector <NUM>. The AC current reducer <NUM> is, for example, a resistor. Providing a larger resistance value as the AC current reducer <NUM> can suppress the flow of the AC current.

In the DC current detector <NUM>, it is further desirable to increase the resistance value of the resistor included in the current detection element <NUM> used for current detection.

Specifically, in a case where the AC output has a frequency of <NUM>, a voltage of <NUM> Vpp, and a current of <NUM> mA, when the combination of the resistance values of the AC current reducer <NUM> and the current detection element <NUM> is <NUM> kQ, the ripple voltage detected by the detection ADC <NUM> is about <NUM> mVpp.

When the combination of the resistance values of the AC current reducer <NUM> and the current detection element <NUM> is <NUM> kQ, the ripple voltage detected by the detection ADC <NUM> is reduced to about <NUM> mVpp.

Thus, in the case where the resistance value is <NUM> kQ, the value detected is to be considered with regard to the variation of the detection value of ±<NUM> mV. In contrast, in the case of <NUM> kQ, it is sufficient to consider the tolerance of the detection value of ±<NUM> mV that is half or less compared to the case of <NUM> kQ.

<FIG> illustrates a ripple voltage flowing into the detection ADC <NUM>. <FIG> illustrates an example of a ripple voltage in the detection ADC <NUM> when reduction means, that is, the AC current reducer <NUM> is not provided, and <FIG> illustrates an example of a ripple voltage in the detection ADC <NUM> when reduction means, that is, the AC current reducer <NUM> is provided.

As illustrated in <FIG>, the AC current reducer <NUM> is added to suppress the inflow of the AC current and reduce (suppress) the ripple voltage of the potential of the detection ADC <NUM>. Since the ripple width decreases in this way, the detection ADC <NUM> can accurately detect the output DC current even though reading (sampling) at a high speed as illustrated in <FIG> is not performed.

Although adding the AC current reducer <NUM> like the first non-claimed example has a certain advantageous effect as illustrated in <FIG>, even with the addition of the AC current reducer <NUM>, it is difficult to make the impedance infinite, and hence the ripple voltage caused by the AC current flowing to the DC current detector <NUM> does not become zero. In addition, it may be difficult to mount the AC current reducer for various reasons.

Thus, another method of reducing the error due to the ripple voltage of the output DC current detected by the DC current detector <NUM> is described below.

<FIG> is a diagram illustrating a configuration and a flow of current of a power supply device β according to a first embodiment. <FIG> is a functional block diagram of a CPU 71A of a power supply control device 70A.

In the first embodiment, a reverse waveform applicator (reverse waveform applicator circuit) is provided as means for suppressing the ripple voltage in the output DC current detected by the DC current detector <NUM>. The reverse waveform applicator is implemented by the power supply control device 70A that is a host controller.

The reverse waveform applicator applies a reverse phase waveform (reverse waveform) of a ripple voltage expected in the DC current detector <NUM> to a second DC current detection line DL2 that connects the current detection element <NUM> to a detection ADC <NUM> of the power supply control device 70A.

In the present embodiment, the host control device <NUM> calculates a surface potential of the photoconductor <NUM> based on an output DC current (measurement output DC current) detected by the detection ADC <NUM> included in the power supply control device 70A, and performs image formation control or the like. The power supply control device 70A according to the present embodiment has a function of applying the reverse phase waveform of the expected ripple voltage to suppress the ripple voltage on the output DC current detected by the detection ADC <NUM>.

The power supply control device 70A includes the CPU 71A, a memory <NUM>, an AD converter <NUM> that is a detection ADC, and a digital-to-analog (DA) converter <NUM> that is an application DAC. Among these components, the CPU 71A, the memory <NUM>, and the application DAC <NUM> function as a reverse waveform applicator R.

The memory <NUM> stores the relationship between a control signal that is an AC output value and a ripple voltage. Specifically, the memory <NUM> stores a ripple waveform expected to be generated, that is, a ripple waveform caused by an AC output based on the voltage of a generated AC current. The ripple waveform to be stored is obtained by measuring in advance how much ripple is generated depending on the voltage and current to be used, for each situation, and is stored in the memory <NUM>.

The detection ADC <NUM> detects a DC current flowing to the second DC current detection line DL2. Since the detection ADC <NUM> is inside the power supply control device 70A and is connected to the output terminal side of the DC generation circuit <NUM>, the detection ADC <NUM> also functions as a DC current detector that detects an output DC current flowing from a charging high-voltage device 180A into the photoconductor <NUM>.

<FIG> illustrates functional blocks of the CPU 71A of the power supply control device 70A. Referring to <FIG>, the CPU 71A serving as an arithmetic unit includes a DC current calculation unit <NUM>, a control-signal command unit <NUM>, an ongoing-ripple calculation unit <NUM>, and a reverse-waveform calculation unit <NUM> in an executable manner.

The DC current calculation unit <NUM> calculates a DC current from a feedback voltage detected by the detection ADC <NUM>.

The control-signal command unit <NUM> commands control signals (DC control signal, AC control signal). Specifically, the control-signal command unit <NUM> commands a CLK signal corresponding to the frequency of the AC current flowing through the coupling capacitor <NUM>, that is, a high-low signal having the same frequency as the frequency of the AC current, and an output voltage signal of the AC current.

The ongoing-ripple calculation unit <NUM> expects a ripple voltage from the ongoing control signal (AC control signal) being commanded and information stored in the memory <NUM>. The expected ripple voltage is a switching ripple of AC, and a ripple of DC has a small influence and hence is ignored (see <FIG>).

The reverse-waveform calculation unit <NUM> calculates a reverse phase waveform (reverse waveform) of the expected ripple voltage, and commands the application DAC <NUM> to output the reverse phase waveform.

Then, the application DAC <NUM> generates a reverse phase waveform of the ripple waveform calculated by the CPU 71A and applies the reverse phase waveform to the second DC current detection line DL2.

As output means for applying a ripple reverse phase waveform, an operational amplifier may be further provided to amplify and output the ripple reverse phase waveform in situations such as when the application DAC <NUM> is sufficient in capacity, or impedance conversion is to be performed.

<FIG> provides diagrams illustrating a mechanism of cancelling a ripple voltage.

The reverse waveform applicator of the present embodiment applies a reverse phase waveform of a ripple voltage illustrated in <FIG>, which is calculated based on ongoing control information and stored memory information, to a current detection line in which a ripple voltage is generated as illustrated in <FIG>. Thus, the ripple voltage is cancelled, and an error due to the ripple voltage is reduced in the output DC current detected by the detection ADC <NUM> as illustrated in <FIG>.

<FIG> provides diagrams illustrating breakdown of a ripple voltage generated on the upstream side of the current detection element <NUM>.

A ripple voltage that is generated in the first DC current detection line DL1 located upstream of the current detection element <NUM> normally has a voltage waveform in which a DC switching ripple and an AC output ripple are combined.

<FIG> indicates a ripple that is generated when an AC current flows in, <FIG> indicates a ripple that is generated by switching of DC, and <FIG> indicates a ripple that appears in the DC current detector <NUM>. In this case, <FIG> illustrates a voltage waveform when the AC current reducer <NUM> is not provided for convenience of description.

For example, when the AC output frequency is <NUM> and the DC switching frequency is <NUM>, the ripple waveform appearing in the second DC current detection line DL2 is a waveform in which the waveform of <NUM> and the waveform of <NUM> are combined as illustrated in <FIG>.

In this case, since the inflow current flowing from the AC current does not change regardless of whether the output of the DC voltage is ON or OFF, a ripple voltage generated as a result of the inflow of the AC current when the DC output is OFF is measured in advance and is stored in the memory <NUM>.

The DC switching ripple is not eliminated; however, as found through comparison between <FIG>, the ripple voltage caused by the AC output is significantly larger than the DC switching ripple. Thus, by applying the reverse phase waveform of the ripple voltage caused by the AC output to cancel the ripple voltage caused by the AC output as described above, the ripple voltage caused by the output DC current detected by the detection ADC <NUM> decreases, and the detection error caused by the ripple voltage can be greatly reduced.

As described above, according to the present embodiment, the reverse phase waveform of the ripple caused by the AC output is generated and the reverse phase waveform of the ripple voltage is applied to the second DC current detection line DL2 immediately before the detection to cancel the ripple voltage and reduce the error due to the ripple. The detection ADC <NUM> can accurately detect the output DC current to output an accurate measurement output DC current.

A configuration in which control to apply the reverse phase waveform of the ripple voltage is performed in addition to the control performed by the AC current reducer <NUM> is described with reference to <FIG>, <FIG>, <FIG>, and <FIG> illustrating configurations of the first to third embodiment and the second non-claimed example (described later); however, the AC current reducer does not have to be provided in the configuration to apply the reverse phase waveform of the ripple voltage.

In the above-described first embodiment, to detect the voltage with the ripple component cancelled in the detection ADC <NUM>, the reverse phase waveform is output from the application DAC <NUM> of the power supply control device 70A and is applied to the second DC current detection line DL2. However, without providing the application DAC <NUM>, the power supply control device may detect an output DC current in which a ripple voltage is not cancelled, add a reverse waveform, and output a measurement output DC current.

<FIG> is a diagram illustrating a configuration and a flow of current of a power supply device γ according to a second non-claimed example.

In the present embodiment, a power supply control device 70B in a charging high-voltage power supply 180B inputs a current detected by a detection ADC 73B to a CPU 71B to correct the current, and then outputs the corrected current as a measurement output DC current. At this time, in the CPU 71B of the power supply control device 70B, calculation with a reverse phase waveform applied based on control information and memory information is performed on the current detected by the detection ADC 73B to calculate a detection current with a ripple cancelled, and the calculation result is used as a measurement output DC current. Thus, regarding the measurement output DC current output from the CPU 71B, the error due to the ripple is reduced from the detected current.

Specifically, the power supply control device 70B of the present embodiment creates a reverse phase waveform of a ripple voltage caused by an AC output as illustrated in <FIG> based on an AC control signal and a ripple voltage for each situation stored in the memory <NUM>. In the power supply control device 70B, the reverse phase waveform of the ripple voltage caused by the AC output generated through the calculation is added to an output DC current including a ripple voltage detected by the detection ADC 73B to calculate an output DC current with the ripple cancelled as illustrated in <FIG>, and the output DC current is output as a measurement output DC current. The host control device <NUM> can calculate the surface potential of the photoconductor <NUM> based on the calculated measurement output DC current, and perform image formation control or the like.

As described above, according to the present embodiment, in the power supply control device 70B, since the DC voltage is calculated while the ripple of the detected waveform including the ripple voltage detected by the detection ADC 73B is cancelled in the CPU 71B, the output DC current to be output (measurement output DC current) can be accurately calculated while the one DA converter (application DAC) in the power supply control device 70B is decreased as compared to the configuration in the first embodiment.

To cancel the reverse phase waveform of the ripple in accordance with the ripple voltage included in the detected output DC current, the phase of the reverse phase waveform is matched with the phase of the ripple voltage. Since the above-described power supply control device 70A (70B) outputs the DC control signal and the AC control signal to control the AC voltage and the DC voltage that are outputs, respectively, there is no problem as long as the phases can be matched based on the control signals.

However, in some cases, the phases of the detected ripple voltage and the generated ripple reverse phase waveform are not matched with each other depending on the circuit configuration after the control signals are applied. In this case, the phases are not matched based on the control signals, and hence a mechanism that detects a phase is to be used.

Thus, according to the present embodiment, a phase detection mechanism is provided in addition to the configuration of the first embodiment illustrated in <FIG>.

<FIG> is a diagram illustrating a configuration and a flow of current of a power supply device δ according to a second embodiment. In the present embodiment, a phase detection mechanism <NUM> is provided to connect the second DC current detection line DL2 to a power supply control device 70C in a charging high-voltage power supply 180C.

The phase detection mechanism <NUM>, which is an example of a phase detector (a phase detector circuit), detects the phase of the ripple voltage at a point A of the second DC current detection line DL2 immediately upstream of the DC current detector <NUM>. Consequently, the power supply control device 70C according to the present embodiment applies a reverse phase waveform to a point B on the downstream side with respect to the point A in accordance with the phase of the detected ripple voltage to cancel the ripple in the output DC current detected by the detection ADC <NUM>. In the power supply control device 70C according to the present embodiment, a CPU 71C, the memory <NUM>, and an application DAC 74C function as a reverse waveform applicator RC.

<FIG> is a diagram illustrating a first circuit example of the phase detection mechanism <NUM>. <FIG> provides diagrams illustrating a waveform at a point A in <FIG>, a generated rectangular wave, and a phase of an adjusted reverse phase waveform.

The phase detection mechanism <NUM> in <FIG> includes a capacitor <NUM> and a comparator <NUM> connected to the ground terminal.

With this configuration, the potential at the point A is coupled by the capacitor <NUM>, and is compared with the GND (<NUM> V) by the comparator <NUM> to create a rectangular wave in which a + portion is HIGH as illustrated in <FIG>. Then, by matching the start of the HIGH of the rectangular wave with the start of the generated reverse phase waveform of the ripple voltage, as illustrated in <FIG>, the reverse phase waveform of the ripple voltage matched with the phase of <FIG> can be created. As described above, the reverse phase waveform of the expected ripple created through the phase adjustment can perform cancelling in accordance with the phase of the ripple voltage.

When it is difficult to perform the coupling in the comparator <NUM>, a phase detection operation is performed to turn OFF the output of the DC voltage and turn ON the output of the AC voltage, and hence the DC component is reduced to as close as possible to <NUM> in the comparator <NUM>. Thus, the phase can be detected through comparison with a very small voltage (equal to or less than <NUM> peak of the ripple) at the terminal connected to the GND. Second Circuit Example of Phase Detector.

<FIG> is a diagram illustrating a second circuit example of a phase detection mechanism 860C. <FIG> provides diagrams illustrating a waveform at a point A in <FIG>, a rectangular wave generated in the circuit, and a phase of a reverse phase waveform.

The phase detection mechanism 860C in <FIG> includes a comparator <NUM> connected to a constant voltage source <NUM>.

In this configuration example, as illustrated in <FIG>, the waveform at the point A is at a position shifted to the + side while <NUM> does not serve as the center of the amplitude. In this case, the duty of the rectangular wave output from the comparator <NUM> of the phase detection mechanism 860C is not <NUM>% as illustrated in <FIG>.

In the CPU 71C of the power supply control device 70C, the rising edge and the falling edge of the rectangular wave in <FIG> are checked, and the timing at the center between the edges is determined as the timing of the vertex (the maximum value, the minimum value) of the detected ripple waveform. Thus, by controlling the phase such that the minimum value and the maximum value in the generated ripple reverse phase waveform respectively match the timings of the detected maximum value and minimum value of the ripple waveform, as illustrated in <FIG>, a reverse phase waveform of a ripple voltage can be created and output in accordance with the phase in <FIG>.

As described above, according to the present embodiment, when the ripple reverse phase waveform is generated, the power supply control device 70C calculates the voltage and phase of control, and generates a reverse phase waveform having a phase matched with the phase of the detected ripple voltage. Then, the ripple reverse phase waveform with the phase matched is applied to a point B that is closer to the detection ADC <NUM> than the point A (that is, on the downstream side with respect to the position of the second DC current detection line DL2 at which the phase detection mechanism <NUM> is connected). Thus, the ripple voltage generated due to the inflow of the AC current is cancelled, and the output DC current with the ripple suppressed can be detected by the detection ADC <NUM>.

Thus, according to the present embodiment, by calculating the phase of the ripple voltage, the ripple voltage can be cancelled with higher accuracy, and the output DC current can be detected with higher accuracy.

While the phase is calculated in the above-described second embodiment, it is further desirable to specify the timing of sampling for the output DC current including the ripple voltage.

<FIG> are diagrams illustrating waveforms of a normal sine wave and a distorted waveform when discharge occurs. <FIG> illustrates a normal sine wave and <FIG> illustrates a distorted waveform when discharge occurs.

In contact charging, as illustrated in <FIG>, distortion is hardly generated in the AC waveform. However, in non-contact charging, there is a gap (clearance) between the photoconductor <NUM> and the charging roller <NUM>, and when the voltage is equal to or higher than a certain value, discharge occurs from the charging roller <NUM> toward the photoconductor <NUM> to charge the photoconductor <NUM>. Since a current flows more than a normal situation during the discharge, the AC waveform may be distorted in non-contact charging as illustrated in <FIG>.

Moreover, in any one of the first non-claimed example, the first embodiment, and the second embodiment, even when the ripple voltage is generated due to the influence of the AC current by detection of the DC current flowing through a point C immediately upstream of the detection ADC <NUM>, the current can be detected without the influence of the ripple as long as sampling can be performed at a certain position of the ripple waveform and the degree of difference from the average voltage at the certain position can be predicted.

However, when the certain position of the waveform to be measured is near <NUM> V, a distortion may occur depending on the control circuit. Since the portion is most inclined, the error may be larger compared to the other portions, and hence the portion is desirably avoided.

The degree of distortion changes due to the influence of the gap or the load, and hence the measurement position is desirably a position before distortion. Moreover, distortion varies due to discharge of the charging roller <NUM> serving as the load, and hence measurement at a position after discharge is desirably avoided. Thus, measurement (sampling) at a certain position in a range from <NUM> V or higher to the start of discharge is desirable.

Thus, according to the present embodiment, the timing of measurement in the output DC current including the ripple voltage caused by the AC voltage is set to fall within a desirable measurement range in the waveform of the AC voltage.

<FIG> is a diagram illustrating a range of measurement in an AC waveform. The position to be measured is desirably a portion higher than <NUM> V and equal to or lower than a discharge portion indicated by a circle.

Thus, according to the present embodiment, similarly to the second embodiment, the phase detection mechanism <NUM> (860C) detects the phase of the ripple voltage at the point A of the second DC current detection line DL2. A power supply control device 70D (see <FIG>) derives a certain point of the waveform and obtains the timing of an average-value cross point (<NUM> sec) that is the center of the waveform.

In the present specification, the average-value cross point of <NUM> sec is a portion that rises to the plus side from the average point of the ripple waveform. For example, in the waveforms illustrated in <FIG> and <FIG>, since the waveform at the point A uniformly transitions with respect to the point <NUM>, the zero cross point that crosses the average value from the - side to the + side is the average-value cross point of <NUM> sec. In contrast, in the waveform illustrated in <FIG>, since the waveform at the point A uniformly transitions around the average value higher than the point <NUM>, the average-value cross point (<NUM> sec) is at a position indicated by an arrow that crosses the average value higher than <NUM> from the - side to the + side.

<FIG> provides diagrams illustrating a measurement range with respect to an average-value cross point (<NUM> sec) in an AC waveform. As described above, it is desired to determine, as the sampling timing in the output current waveform including the ripple voltage, when the measurement is performed counting from the average-value cross point of <NUM> sec.

For example, when the AC frequency is <NUM> (one cycle ≈ <NUM>), the gap between the charging roller <NUM> and the photoconductor <NUM> is <NUM>, and the discharge start is after <NUM> from <NUM> sec, it is assumed that <NUM> V is obtained.

When the ripple voltage is sampled, measurement is desirably performed at or before the start of discharge, and hence the measurement (sampling) is desirably performed within <NUM> from the average-value cross point of <NUM> sec.

Thus, how far from the average-value cross point of <NUM> sec the measurement is performed is stored in a memory in advance. At this time, when different frequencies or outputs are present, the time for reaching the discharge potential from <NUM> sec varies depending on the frequency, and hence the time is determined per frequency.

By performing measurement in the range of the waveform set as described above, a numerical value equal to or larger than the value at the average-value cross point (<NUM> sec) and at or before the start of discharge before the waveform is distorted can be measured as the output current including the ripple voltage.

<FIG> is a diagram illustrating a sampling timing corresponding to a sampling position in one cycle of an AC waveform. The result measurement can be performed at the same position of the waveform by measuring a portion at which the sampling has progressed by <NUM> from <NUM> sec at the latest.

In the present embodiment, without increasing the occupancy rate of the CPU by measuring all waveforms or increasing the number of samplings, as illustrated in <FIG>, one point is measured within a range allowed by a CPU 71D (see <FIG>) in one cycle with less distortion of waveform, thereby measuring a stable voltage.

<FIG> is a diagram illustrating a sampling position in an AC waveform. <FIG> is a diagram illustrating a measurement deviation of the average value of measurement from the average value of waveform.

In the present embodiment, as described above, since the sampling timing after an elapse of a predetermined interval from the average-value cross point is intentionally set, the average value of the measurement is detected while being deviated from the average value of the waveform as illustrated in <FIG>. Then, when the surface potential of the photoconductor <NUM> is calculated based on the sampled output DC current, the measurement deviation is to be corrected so that the average value of the waveform can be correctly used.

For a correction value for correcting the measurement deviation, a deviation is checked in advance to what extent the voltage at a point to be measured deviates from the average per AC voltage designated by the control signal, and the deviation is stored in a memory 72D (see <FIG>).

<FIG> provides diagrams illustrating an example of voltage values of an AC output and a ripple voltage on the downstream side.

When the maximum value of an AC voltage to be output is <NUM> V as illustrated in <FIG>, the voltage at a sampling timing after an elapse of a predetermined interval of <NUM> from the average-value cross point in the corresponding ripple voltage is <NUM> mV as illustrated in <FIG>.

<NUM> mV illustrated in <FIG> and <FIG> mV illustrated in <FIG> correspond to measurement deviations (amounts of deviation) of the average value of the measurement as illustrated in <FIG> from the average value of the waveform.

Since the measurement deviation is determined based on the amplitude of the AC voltage, the measurement deviation is stored per AC voltage. Alternatively, when the AC frequency is the same and measurement is performed at the same time, the amount of deviation is proportional to the voltage, and hence the amount of deviation may be measured at several points and converted into a table using the inclination thereof.

<FIG> presents an example of a correlation table that indicates correspondence among an AC drive frequency, an AC output value, a sampling timing (measurement point), and a measurement deviation.

As illustrated in the relationship in <FIG> and the correlation table in <FIG>, the measurement deviation (amount of deviation) at the sampling timing (measurement point) also changes in accordance with the AC voltage. Thus, the correlation of the measurement deviation per AC frequency is converted into a table or a graph and is saved in a memory per AC frequency.

At this time, setting is made such that the voltage at the measurement point in the output value of the frequency does not exceed the discharge start voltage. Thus, an expression "detected measurement value - average-value deviation amount = average value" is established.

After the measurement, the amount of deviation is added to (subtracted from) the averaged numerical value to eliminate an error in the expected ripple voltage and to generate a reverse phase waveform with the deviation adjusted, and the ripple in the output DC current is cancelled more precisely to obtain an accurate measurement value (measurement output DC current).

<FIG> is a diagram illustrating a configuration and a flow of current of a power supply device ε according to a third embodiment. The present embodiment differs from the second embodiment in that the power supply control device 70D inputs a current detected by a detection ADC 73D to the CPU 71D and then outputs a current as a measurement output DC current. In the power supply control device 70D according to the present embodiment, the CPU 71D, the memory 72D, and an application DAC 74D function as a reverse waveform applicator RD, and the CPU 71D and the memory 72D function as a measurement waveform selection corrector S.

<FIG> is a functional block diagram illustrating functional blocks in the memory 72D and the CPU 71D of the power supply control device 70D according to the third embodiment.

The memory 72D includes a ripple-voltage storage unit (memory) <NUM> and a deviation-amount storage unit (memory) <NUM>. The ripple-voltage storage unit <NUM> stores a ripple voltage per designated AC voltage in the control signal. The deviation-amount storage unit <NUM> stores the correlation of the measurement deviation per AC frequency converted into a table or a graph as illustrated in <FIG>.

The CPU 71D includes, in addition to the above-described DC current calculation unit <NUM>, control-signal command unit <NUM>, ongoing-ripple calculation unit <NUM>, and reverse-waveform calculation unit <NUM>, a ripple-phase confirmation unit <NUM>, an output-current average-value calculation unit <NUM>, a measurement-position determination unit <NUM>, a deviation-amount addition unit <NUM>, a voltage-value output unit <NUM>, and a reverse-waveform-phase adjustment unit <NUM> in an executable manner.

In the present embodiment, as preliminary preparation, the relationship among the AC frequency, the AC voltage, the time from the average-value cross point of <NUM> sec, and the amount of deviation from the average value is measured and stored in the deviation-amount storage unit <NUM> of the memory 72D in advance.

The ripple-phase confirmation unit <NUM> confirms the phase of a ripple waveform to be measured, and confirms the position of the average-value cross point of <NUM> sec.

The measurement-position determination unit <NUM> determines how far from the average-value cross point of <NUM> sec the measurement is performed, that is, determines a sampling timing (measurement point) in accordance with the AC frequency.

The DC current calculation unit <NUM> and the output-current average-value calculation unit <NUM> perform measurement and calculate an average.

The deviation-amount addition unit <NUM> adds (subtracts) a deviation voltage corresponding to the output voltage to (from) the average voltage.

That is, the average value of the measurement values is calculated by an expression "measurement value - average-value deviation amount = average value".

The voltage-value output unit <NUM> transmits the average value of the measurement values, which is obtained by subtracting an average-value deviation amount from a DC current value at a measurement point for the DC current detected by the detection ADC 73D, as a measurement output DC current to the host control device <NUM> for predicting the surface potential of the photoconductor <NUM>.

Like the second embodiment, the reverse-waveform-phase adjustment unit <NUM> creates a reverse phase waveform of a ripple voltage in accordance with the detected phase and outputs the reverse phase waveform.

Claim 1:
A power supply device that applies a voltage in which a DC voltage and an AC voltage are superimposed on each other to a charging member that charges an image bearer, comprising:
an AC voltage generator (<NUM>) configured to generate the AC voltage;
a DC voltage generator (<NUM>) configured to generate the DC voltage;
a DC current detector (<NUM>) provided on an output terminal side of the DC voltage generator (<NUM>) and configured to detect an output DC current flowing into the image bearer;
characterized in that the device further comprises:
a reverse waveform applicator (R, RC, RD) configured to apply a reverse phase waveform of a ripple voltage expected in the DC current detector (<NUM>) to the DC current detector (<NUM>).