JP5959857B2 - Power supply device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a power supply device for supplying a high-voltage power supply, and more particularly to an image forming apparatus to which a transfer bias or a charging bias is supplied by the power supply device.

  Generally, there are a copying machine and a laser beam printer as an image forming apparatus using an electrophotographic system. Here, a copying machine will be described as an example. An image on a document is read by a document reading unit and output as image data. The writing unit exposes the photoconductor according to the image data, and forms an electrostatic latent image on the photoconductor.

  The electrostatic latent image on the photoconductor is developed by a developing device to form a toner image. On the other hand, the paper (recording medium) stored in the paper feed tray 8 is conveyed to the transfer position in synchronization with the rotation of the photosensitive member. Then, at the transfer position, for example, the toner image on the photosensitive member is transferred onto the paper by a transfer roller. Thereafter, the toner image is fixed on the paper in the fixing unit, and the paper is discharged to a paper discharge tray.

  By the way, in the method of transferring a toner image onto a sheet by bringing the transfer roller into contact with the sheet, a transfer defect may occur due to a change in the resistance value of the transfer roller and the sheet. In order to prevent such a transfer failure, there is one in which the transfer bias is determined according to the resistance values of the transfer roller and the sheet (see Patent Document 1).

  In Patent Document 1, a transfer bias is applied to a transfer roller by a transfer bias power source while a sheet is nipped and conveyed by a transfer nip formed when the transfer roller is brought into contact with the surface of the photoconductor, and a toner on the photoconductor. Transfer the image to the paper. At this time, before the sheet passes through the transfer nip, ATVC (Active Transfer Voltage Control) is performed to detect an output voltage for constant current control. Note that ATVC may be used as an abbreviation for Automatic Transfer Voltage Control. When the paper is inserted into the transfer nip, a leakage current that leaks the paper from the transfer roller to the pre-transfer guide is detected. Then, according to the detection result, it is determined whether the transfer high-voltage output for low resistance paper or the normal transfer high-voltage output, and the transfer bias power source is controlled.

Japanese Patent Laid-Open No. 11-219042

  By the way, when detecting the output voltage used when calculating the resistance value of the transfer roller, a reference voltage is generally used. For example, an output voltage is obtained by using, as an output voltage detection signal, a voltage obtained by dividing the reference voltage and the transfer output voltage by a plurality of resistors connected in series between the reference voltage unit and the transfer output unit. Is divided by the output current to obtain the resistance value of the transfer roller.

  When the resistance value of the transfer roller is obtained as described above, the current detection circuit for performing the constant current control is provided with a function of generating a reference voltage, and the number of parts is inevitably increased. As a result, not only the circuit scale increases but also the cost increases.

  The above point can also be said for a power supply device that supplies power to the charging roller.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power supply device that prevents an increase in circuit scale and cost and does not cause transfer failure or charging failure, and an image forming apparatus using the power supply device.

In order to achieve the above object, a power supply device according to the present invention is a power supply device for supplying a high voltage to a load whose resistance value fluctuates, and the power supply device according to a level of a predetermined current value setting signal. Constant current control means for controlling a current value supplied to the load to a constant value, a transformer connected to the load on the secondary side and generating a high voltage to be supplied to the load, and a voltage value corresponding to the current flowing through the load Current detection means for generating a current value detection voltage indicating the current, a current supply path for supplying the current flowing through the load to the current detection means, and a voltage detection means for detecting the voltage value applied to the load as a detection voltage value; has a load resistance value calculating means for calculating a resistance value of said load, said current detector is connected to a predetermined reference power supply, current sensing current flowing through the load flows through the current supply path It has anti detects a voltage value corresponding to the voltage drop at the current sensing resistor as the current detection voltage, the constant current control means, the level and the current value detection voltage of the current setting signal An error amplifier that outputs a voltage corresponding to the deviation obtained as a result of the comparison; and a regulator that inputs a voltage corresponding to the output of the error amplifier to the primary side of the transformer; and the level of the current value setting signal Constant current control is performed so that the current value detection voltage is the same, and the voltage detection means includes a first resistor connected to a secondary side of the transformer, the first resistor, and the current. A second resistor connected in series with the detection resistor, and during the constant current control by the constant current control unit, the load resistance value calculating unit includes the first resistor and the second resistor. Connection with resistor Is provided as the detection voltage value, based on the applied detection voltage, the level of the current value setting signal, the resistance value of the first resistor, and the resistance value of the second resistor, The resistance value of the load is calculated .

An image forming apparatus according to the present invention includes the power supply device described above, and a transfer unit that is the load and transfers a toner image formed on a photoconductor to a recording medium.

The image forming apparatus according to the present invention, the above power supply device, a said load, characterized in that it has a charging unit for uniformly charging the surface of the photosensitive member when the image forming, a.

  According to the present invention, an increase in circuit scale and an increase in cost are prevented, and no transfer failure or charging occurs.

1 is a cross-sectional view schematically showing an image forming apparatus using a power supply device according to a first embodiment of the present invention. It is a figure for demonstrating the conventional transfer high voltage circuit. 3 is a flowchart for explaining control of the transfer high-voltage circuit shown in FIG. 2. It is a block diagram for demonstrating an example of the power supply device (transfer high voltage circuit) by the 1st Embodiment of this invention. 5 is a flowchart for explaining control of the transfer high-voltage circuit shown in FIG. It is a block diagram for demonstrating an example of the power supply device by the 2nd Embodiment of this invention. It is a flowchart for demonstrating control of the charging high voltage circuit shown in FIG.

  Hereinafter, an example of an image forming apparatus using a power supply device according to an embodiment of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a cross-sectional view schematically showing an image forming apparatus using a power supply device according to the first embodiment of the present invention.

  The illustrated image forming apparatus is a copying machine and includes an automatic document feeder 1. When a document or a bundle of documents is placed on a document table 2 provided in the automatic document feeder 1, the document is fed to a predetermined position on the contact glass 6 by a sheet feed roller 3 and a sheet feed belt 4. . Then, the image on the original fed to the contact glass 6 is read by the reading unit 50. The document that has been read is discharged to the outside by the paper feed belt 4 and the discharge roller 5. When the document set detection unit 7 detects that there is a next document on the document table 2, the document is similarly fed onto the contact glass 6.

  The reading unit 50 outputs image data corresponding to the read image, and this image data is given to the writing unit 57. The writing unit 57 outputs a laser beam modulated by the image data.

  The surface of the photoconductor 15 is uniformly charged by a charging roller 20 (charging means), and the photoconductor 15 is exposed by laser light, and an electrostatic latent image corresponding to image data is formed on the photoconductor 15. The electrostatic latent image on the photoreceptor 15 is developed by the developing device 27 to become a toner image.

  A plurality of recording media (paper sheets) are stacked on the paper feed tray 8, and the paper fed from the paper feed unit 8 is transported to the vicinity of the photoreceptor 15 by the paper transport unit 14. In synchronization with the rotation of the photoconductor 15, the sheet is conveyed to the transfer position by the conveyance belt 16.

  This transfer position is a transfer nip where the photoconductor 15 and the transfer roller 16 (transfer means) come into contact. When the transfer roller 16 is transported to the transfer position, the toner image on the photoconductor 15 is transferred to the paper by the transfer roller 16. Thereafter, the sheet is sent to the fixing unit 18 where the fixing process is performed. Then, the paper is discharged to the paper discharge tray 25 by the paper discharge unit 19.

  In the case of performing double-sided printing, the paper is conveyed to the double-sided paper conveyance path 21 after the fixing process. Then, the sheet is switched back and reversed by the reversing unit 22 and is once stored in the duplex conveying unit 23.

  Thereafter, the paper stocked in the duplex conveyance unit 23 is fed again from the duplex conveyance unit 23 to the vertical conveyance unit 14. Then, as described above, a toner image is formed on the back side of the sheet, and then the fixing process is performed.

  When the paper is reversed and discharged, the paper is reversely switched back by the reversing unit 22 and then sent to the reverse paper discharge conveyance path 24 where it is discharged to the paper discharge tray 25.

  Here, in the image forming apparatus shown in FIG. 1, a power supply apparatus (hereinafter also referred to as a transfer high voltage circuit) that applies a transfer bias (also referred to as a transfer high voltage) to the transfer roller 16 when a toner image is transferred onto a sheet will be described. Here, in order to facilitate understanding of the power supply device according to the first embodiment of the present invention, first, a conventional power supply device will be described.

  FIG. 2 is a diagram for explaining a conventional transfer high-voltage circuit.

  In FIG. 2, the transfer high-voltage circuit includes a constant current control unit 607, a high voltage generation unit 608, a current detection unit 610, and a voltage detection unit 609. The transfer high-voltage circuit is connected to the engine control circuit 600, and the transfer high-voltage circuit is controlled by the engine control circuit 600, as will be described later.

  The engine control circuit 600 is a circuit for controlling the image forming operation. Here, only the configuration relating to the operation of the transfer high-voltage circuit is shown. The engine control circuit 600 includes the image forming operation timing control unit 601, the transfer operation. An output control unit 602, an appropriate transfer current value calculation unit 603, and a transfer roller resistance value calculation unit 604 are provided. The engine control circuit 600 is connected with an environmental sensor 605 and a paper information detection sensor 606.

  The constant current control unit 607 is provided with an OP amplifier OP601. A control signal V_icont_tr is input from the transfer output control unit 602 to the non-inverting (+) input terminal of the OP amplifier OP601. A signal V_isns_tr described later is input to the inverting (−) input terminal of the OP amplifier OP601. The OP amplifier OP601 compares the voltage levels of the control signal V_icon_tr and the signal V_isns_tr, and outputs an output signal corresponding to the difference (deviation).

  An output signal of the OP amplifier OP601 is applied to the base of the transistor Q601. The transistor Q601 outputs a voltage corresponding to the output signal of the OP amplifier 601. As shown in the figure, the output of the OP amplifier 601 is fed back to the inverting input terminal via the capacitor C604. The emitter of the transistor Q601 is grounded via a capacitor C605, and 24 V, for example, is applied to its collector.

  In the high voltage generation unit 608, the voltage (DC voltage) output from the transistor Q601 is input to one end of the primary side winding of the high voltage transformer T601. The other end of the primary winding of the high voltage transformer T601 is connected to the drain of the FET Q602. The source of the FET Q602 is grounded, and the source and drain are connected.

  The drive pulse TR_CLK is input from the transfer output control unit 602 to the gate of the FET Q602, and the FET Q602 is switched (that is, turned on / off) at the frequency cycle of the drive pulse. As a result, the DC voltage applied to the high-voltage transformer T601 is boosted according to the winding ratio of the high-voltage transformer T601 and output as an AC voltage to the secondary winding. The AC voltage output to the secondary winding is rectified and smoothed by the rectifier diode D601 and the smoothing capacitor C602 to obtain a DC voltage. The DC voltage (Vout_tr) is applied to the transfer roller 16 (load) as a load.

  As illustrated, the voltage detection unit (voltage detection unit) 609 includes resistors R601 and R602, and the high voltage generation unit 608 includes a resistor R606 connected in parallel to the smoothing capacitor C602. The resistors R601 and R602 are connected in series, and a resistor R606 (current supply path) is connected in parallel to the series resistor. Further, the connection point between the resistors R601 and R602 is connected to the transfer roller resistance value calculation unit 604, and the resistors R602 and R606 are connected to the current detection unit 610.

  The current detection unit 610 detects a current value supplied to the transfer roller 16 that is a load. The current output from the secondary side of the high voltage generator 608 is divided into a current Ia indicated by a solid line and a current Ib indicated by a dotted line in FIG. Here, the current Ia is supplied to the transfer roller 16.

  The current detection unit 610 has an OP amplifier OP602, and resistors R602 and R & 06 are connected to the inverting input terminal of the OP amplifier OP602 as shown. The non-inverting input terminal of the OP amplifier OP602 is connected to the connection point between the resistors R604 and R605, and the resistor R605 is grounded. The resistors R602 and R606 are grounded via the capacitor C603, the output terminal of the OP amplifier OP602 and the inverting input terminal are connected by the resistor R603, and the output terminal of the OP amplifier OP602 is connected to the inverting input terminal of the OP amplifier OP601. ing.

  For example, a reference voltage generating voltage (for example, 12 V) is applied to the resistor R604. Resistors R604 and R605 are resistors for dividing the reference voltage generating voltage. The voltage Vref divided by the resistors R604 and R605 is input as a reference voltage to the non-inverting input terminal of the OP amplifier OP602.

  This reference voltage Vref is expressed by equation (1).

Vref = 12 × R605 / (R604 + R605) (1)
Here, R604 and R605 represent resistance values of the resistors R604 and R605, respectively.

  As a result, the OP amplifier OP602 outputs an output signal corresponding to the difference between the reference voltage Vref and the voltage applied to the inverting input terminal, and supplies this output signal as the signal V_isns_tr to the inverting input terminal of the OP amplifier OP601.

  Here, since the OP amplifier OP602 outputs an output signal corresponding to the difference between the reference voltage Vref and the voltage applied to the inverting input terminal, a current flows from the output terminal of the OP amplifier OP602 to the inverting input terminal via the resistor R603. . The value of this current is the same as the current Ia supplied to the transfer roller 16.

  Therefore, the current Ia can be expressed by the following formula (2).

Ia = (V_isns_tr−Vref) / R603 (2)
Here, R603 is the resistance value of the resistor R603.

  In the illustrated transfer high-voltage circuit, constant current control is performed so that the voltage level of the output signal V_isns_tr of the OP amplifier OP602 becomes the voltage level of the control signal V_icont_tr (this control is referred to as ATVC). That is, in the transfer high-voltage circuit, constant current control is performed so that the current flowing through the transfer roller 16 becomes the current Ia represented by the equation (2).

  Next, the control of the transfer high-voltage circuit shown in FIG. 2 will be described.

  FIG. 3 is a flowchart for explaining control of the transfer high-voltage circuit shown in FIG. The process according to the flowchart shown in the figure is executed by the engine control circuit 600.

  When the transfer high-voltage output operation is started, the transfer output control unit 602 determines whether an ATVC control request signal has been received from the image forming operation timing control unit 601 (S701). If the ATVC control request signal is not received (NO in S701), the transfer output control unit 602 stands by. On the other hand, when receiving the ATVC control request signal (YES in S701), the transfer output control unit 602 determines the value of the current to be applied to the transfer roller 16 during ATVC (ATVC control start: S702).

  When determining the value of this current, the transfer output control unit 602 is predetermined according to the detected temperature and detected humidity from the environmental sensor 605 and the paper information (for example, the type of paper) from the paper information detecting sensor 606. Select the current value. For example, the built-in memory of the transfer output control unit 602 stores a table (transfer current value table) in which the current value applied to the transfer roller 16 during transfer is defined according to the temperature, humidity, and paper type. ing. The transfer output control unit 602 determines a current value to be applied to the transfer roller 16 with reference to the transfer current value table according to the detected temperature, the detected humidity, and the paper information.

  Subsequently, the transfer output control unit 602 outputs a control signal V_icont_tr corresponding to the determined current value level to the non-inverting input terminal of the OP amplifier OP601. Further, the transfer output control unit 602 outputs a driving pulse TR_CLK to the FET Q602.

  As described above, in the transfer high voltage circuit, constant current control is performed so that the voltage levels of the output signal V_isns_tr of the OP amplifier OP602 and the control signal V_icont_tr are the same.

  Next, the transfer output control unit 602 sends a resistance value calculation command signal to the transfer roller resistance value calculation unit 604. In response to the command signal, the transfer roller resistance value calculation unit 604 calculates the resistance value of the transfer roller 16 from the voltage detection signal V_vsvs_tr according to a preset calculation formula (S703).

  As described with reference to FIG. 2, the voltage applied to the inverting input terminal of the OP amplifier OP602 is the reference voltage Vref and is a constant voltage. Since the voltage detection signal V_vsvs_tr is a voltage obtained by dividing the reference voltage Vref and the transfer output voltage Vout_tr by the resistors R601 / R602, Expression (3) is established.

V_vsvs_tr = (Vout_tr × R602 + Vref × R601) / (R601 + R602) (3)
When formula (3) is arranged with respect to the transfer output voltage Vout_tr, formula (4) is obtained.

Vout_tr = ((R601 + R602) × V_vsns_tr−R601 × Vref) / R602 (4)
By dividing the transfer output voltage shown in Expression (4) by the current Ia (Expression (2)), the resistance value R_tr of the transfer roller 16 is obtained. The resistance value R_tr is expressed by Expression (5).

R_tr = ((R601 + R602) × V_vsns_tr−R601 × Vref) / (R602 × Ia) (5)
In Expression (5), except for the voltage value of the voltage detection signal V_vsns_tr, other elements are constant. Therefore, Expression (5) may be set in the transfer roller resistance value calculation unit 604 as a setting arithmetic expression. The transfer roller resistance value calculation unit 604 calculates the resistance value of the transfer roller 16 by substituting V_vsns_tr, which is a variation parameter, into Equation (5). Then, the transfer roller resistance calculation unit 604 sends the resistance value of the transfer roller 16 to the appropriate transfer current value calculation unit 603.

  The appropriate transfer current value calculation unit 603 calculates an optimal transfer current value at the time of image formation based on the resistance value of the transfer roller 16, the detected temperature, the detected humidity, and the paper information (S704). For example, the built-in memory of the appropriate transfer current value calculation unit 603 stores a table (appropriate transfer current value table) in which an optimum transfer current value is defined in image formation according to temperature, humidity, and paper type. Has been. The appropriate transfer current value calculation unit 603 obtains an appropriate transfer current value by referring to the appropriate transfer current value table according to the detected temperature, the detected humidity, and the paper information. Then, the appropriate transfer current calculation unit 603 sends appropriate transfer current value data indicating an appropriate transfer current value to the transfer output current control unit 602.

  The transfer output control unit 602 sets the control signal V_icon_tr corresponding to the level of the appropriate transfer current value according to the appropriate transfer current value data, and prepares to output it to the non-inverting input terminal of the OP amplifier OP601. Then, the transfer output control unit 602 determines whether or not an ON signal indicating that the image forming operation is ON is sent from the image forming operation timing control unit 601 (S705).

  If the image forming operation ON signal is not sent (NO in S705), the transfer output control unit 602 stands by. On the other hand, when the image forming operation ON signal is sent (YES in S705), the transfer output control unit 602 outputs the control signal V_icon_tr to the non-inverting input terminal of the OP amplifier OP601.

  Accordingly, ATVC is performed as described with reference to FIG. 2 (transfer constant current control ON: S706). Subsequently, the transfer output control unit 602 determines whether an OFF signal indicating that the image forming operation is off has been sent from the image forming operation timing control unit 601 (S707). If the image forming operation OFF signal is not received (NO in S707), the transfer output control unit 602 stands by.

  When the image forming operation OFF signal is received (YES in S707), the transfer output control unit 602 switches the signal level of the control signal V_icont_tr from a proper transfer current value to a level corresponding to zero output current, and supplies a drive pulse to the FET Q602. Is stopped (transfer constant current control OFF: S708). Then, the transfer output control unit 602 returns to the process of step S701.

  As described above, in the transfer high-voltage circuit shown in FIG. 2, the current detection unit 610 needs to include at least the OP amplifier OP602 and the plurality of resistors R603, R604, and R605, and the circuit scale of the current detection unit 610 increases and the cost increases. It will be up.

  Therefore, in the first embodiment, the circuit scale of the current detection unit 610 is reduced, and the cost of the transfer high-voltage circuit is reduced.

  FIG. 4 is a block diagram for explaining an example of the power supply device (transfer high-voltage circuit) according to the first embodiment of the present invention. In FIG. 4, the same components as those in the transfer high-voltage circuit and the engine control circuit shown in FIG.

  In the transfer high-voltage circuit described with reference to FIG. 2, the current detection unit 610 includes an OP amplifier OP602 and a plurality of resistors R603, R604, R605, and the like. When the transfer output voltage value necessary for calculating the resistance value of the transfer roller 16 is obtained, the voltage value detection signal V_vsns_tr that is a variation parameter is used.

  On the other hand, in the transfer high-voltage circuit shown in FIG. 4, the current detection unit (current detection unit) 110 includes a resistor R103 (current detection resistor) and a capacitor C103. When the transfer output voltage value necessary for calculating the resistance value of the transfer roller 16 is obtained, the transfer roller resistance value calculation unit 104 provided in the engine control circuit 100 performs the voltage value detection signal V_vsns_tr and the control signal V_icont_tr. These two variation parameters are used.

  As described with reference to FIG. 2, a DC high voltage is applied from the high voltage generator 608 to the transfer roller 16. The current detection unit 110 detects the current supplied to the transfer roller 16.

  Since the current Ia flowing through the transfer roller 16 flows through the resistor R103 in the direction of the solid line arrow, the current Ia can be expressed by Expression (6).

Ia = (12−V_inss_tr) / R103 (6)
A predetermined voltage (for example, 12V) is applied to the resistor R103, and R103 represents the resistance value of the resistor R103.

  When Expression (6) is transformed with respect to V_isns_tr, Expression (7) is obtained.

V_isns_tr = 12−Ia × R103 (7)
As shown in the figure, one end of the resistor R103 (the end opposite to the 12V application end) is connected to the inverting input terminal of the OP amplifier OP601. The obtained voltage value is supplied to the inverting input terminal of the OP amplifier OP601 as the detection signal V_isns_tr. Since the level of this detection signal changes according to the current Ia, it is referred to herein as a current value detection signal (current value detection voltage).

  Accordingly, as described above, the transfer high-voltage circuit shown in FIG. 4 performs constant current control so that the level of the current value detection signal V_isns_tr and the level of the control signal V_icont_tr are the same. That is, the transfer high-voltage circuit shown in FIG. 4 performs constant current control so that the current Ia = (12−V_icon_tr) / R103 is supplied to the transfer roller 16.

  FIG. 5 is a flowchart for explaining the control of the transfer high-voltage circuit shown in FIG. Note that the processing according to the flowchart shown in the drawing is executed by the engine control circuit 100. Further, in FIG. 5, the same steps as those in the flowchart shown in FIG.

  In step S702, after starting the ATVC control, the transfer output control unit 602 instructs the transfer roller resistance value calculation unit 104 (load resistance value calculation unit) to check the level of the control signal V_icont_tr (S203). Subsequently, the transfer output control unit 602 instructs the transfer roller resistance value calculation unit 104 to calculate the resistance value of the transfer roller 16.

  Accordingly, the transfer roller resistance value calculation unit 104 calculates the resistance value of the transfer roller 16 by substituting the level of the voltage detection signal V_vsvs_tr and the level of the control signal V_icont_tr into a preset calculation formula (S204).

  As described above, in the transfer high voltage circuit, constant current control is performed so that the level of the current value detection signal V_isns_tr and the level of the control signal V_icon_tr are the same.

  The voltage detection signal V_vsvs_tr (detection voltage value) indicates a voltage value obtained by dividing the current value detection signal V_isns_tr and the transfer output voltage Vout_tr by the resistors R601 and R602. When the constant current control is performed, since the voltage value is the same as the voltage value obtained by dividing the control signal V_icont_tr and the transfer output voltage Vout_tr by the resistors R601 and R602, Expression (8) is established.

V_vsvs_tr = (Vout_tr × R602 + V_icont_tr × R601) / (R601 + R602) (8)
Resistors R601 and R602 are a first resistor and a second resistor, respectively.

  Rearranging equation (8) for Vout_tr yields equation (9).

Vout_tr = ((R601 + R602) × V_vsns_tr−R601 × V_icont_tr) / R602 (9)
Then, when the transfer output voltage Vout_tr is divided by the current Ia supplied to the transfer roller 16, the resistance value R_tr of the transfer roller 16 is obtained. This resistance value R_tr is shown by the equation (10).

R_tr = ((R601 + R602) × V_vsns_tr−R601 × V_icont_tr) / (R602 × Ia) (10)
In Expression (10), since elements other than V_vsns_tr and V_icont_tr are constant, the transfer roller resistance value calculation unit 104 receives the variation parameters V_vsns_tr and V_icont_tr as described above, and uses Expression (10). The resistance value of the transfer roller is calculated.

  In this way, the transfer roller resistance value calculation unit 104 calculates the resistance value of the transfer roller and sends it to the appropriate transfer current value calculation unit 103 as resistance value data. Thereafter, the processes in steps S704 to S708 are performed as described with reference to FIG.

  As described above, in the first embodiment of the present invention, it is not necessary to generate a reference voltage, and the current detection unit 110 for performing constant current control does not need to use an OP amplifier or the like. The circuit configuration can be simplified and the circuit scale can be reduced. As a result, cost reduction can be achieved.

  In the first embodiment, the resistance value of the transfer roller is obtained according to the transfer output voltage, but the constant current control may be performed by obtaining the appropriate current value directly from the transfer output voltage.

[Second Embodiment]
Next, an example of a power supply device (charging high voltage circuit) according to the second embodiment of the present invention will be described.

  In the image forming apparatus provided with the contact type charging roller 20 (load) shown in FIG. 1, a high voltage bias is applied to the charging roller 20 when paper is not passed to uniformly charge the surface of the photoconductor 15. . Also in this case, constant current control is performed to monitor the voltage value applied to the charging roller 20. Then, the resistance value of the charging roller 20 is obtained from the monitored voltage, and the charging current is controlled according to the resistance value of the charging roller 20. This control is also called APVC.

  FIG. 6 is a block diagram for explaining an example of a power supply device according to the second embodiment of the present invention. FIG. 6 shows a power supply device that supplies a high-voltage bias to the charging roller 20, but the configuration is almost the same as that of the transfer high-voltage circuit shown in FIG. 4. Here, for convenience of explanation, the transfer high-voltage shown in FIG. The same reference numerals are assigned to the same components as those of the circuit. Further, the power supply device shown in FIG. 6 is called a charging high voltage circuit.

  In FIG. 6, the high voltage generation unit 308 uses a diode D301 instead of the diode D601 shown in FIG. The forward direction of the diode D301 is connected to the secondary winding of the transformer T610 in the opposite direction to the diode D601.

  In FIG. 6, for convenience of explanation, currents are indicated by Ia and Ib as in FIG. The direction of the current Ia flowing through the charging roller 20 is opposite to the current Ia shown in FIG. Further, the direction of the current Ib is also opposite to that of the current Ib shown in FIG. The control signal, voltage detection signal, current value detection signal, drive pulse, and charging output voltage are indicated by V_icont_chg, V_vsns_chg, V_isns_chg, CHG_CLK, and Vout_chg, respectively. The operation of the charging high voltage circuit shown in FIG. 6 is the same as that of the transfer high voltage circuit shown in FIG.

  In FIG. 6, the current detection unit 310 includes a capacitor C103 and a resistor R303, and one end of the resistor R303 is grounded. The other end of the resistor R303 is connected to the resistors R602 and R606 and to the inverting input terminal of the OP amplifier OP601.

  As described with reference to FIG. 2, a DC high voltage is applied to the charging roller 20 from the high voltage generator 608. The current detection unit 310 detects the current supplied to the charging roller 20.

  Since the current Ia flowing through the charging roller 16 flows through the resistor R303 in the direction of the solid line arrow, the current Ia can be expressed by Expression (11).

Ia = V_isns_chg / R303 (11)
Rearranging equation (11) with respect to V_isns_chg, equation (12) is obtained.

V_isns_tr = Ia × R303 (12)
R303 is the resistance value of the resistor R303.

  Therefore, a voltage value corresponding to the voltage drop due to the resistor R303 is given as the detection signal V_isns_tr to the inverting input terminal of the OP amplifier OP601. Since the level of this detection signal changes according to the current Ia, it is referred to as a current value detection signal here.

  Accordingly, the charging high-voltage circuit shown in FIG. 6 performs constant current control so that the level of the current value detection signal V_isns_chg and the level of the control signal V_icont_chg are the same. That is, the charging high-voltage circuit shown in FIG. 6 performs constant current control so that the current Ia = V_isns_chg / R303 is supplied to the charging roller 20.

  As described with reference to FIG. 1, the engine control circuit 300 controls the image forming operation of the image forming apparatus. In the illustrated example, only the configuration related to the control of the charging high-voltage circuit is shown. The engine control circuit 300 includes an image forming operation timing control unit 601, a charging output control unit 302, an appropriate charging current value calculation unit 303, and A charging roller resistance value calculation unit 304 is included. The engine control circuit 600 is connected with an environmental sensor 605 and a paper information detection sensor 606.

  In the illustrated engine control circuit 300, the operations of the charging output control unit 302, the appropriate charging current value calculation unit 303, and the charging roller resistance value calculation unit 304 are the transfer output control unit 602 and the appropriate transfer current value calculation unit shown in FIG. 603 and the operation of the transfer roller resistance value calculation unit 104 are the same.

  Here, the built-in memory of the charging output control unit 302 stores a table (charging current value table) in which the current value applied to the charging roller 20 during charging is defined according to the temperature, humidity, and paper type. Has been. The charging output control unit 302 determines a current value to be applied to the charging roller 206 with reference to the charging current value table according to the detected temperature, detected humidity, and paper information.

  Further, the internal memory of the appropriate charging current value calculation unit 303 stores a table (appropriate charging current value table) in which an optimal charging current value is defined in image formation according to temperature, humidity, and paper type. Has been. The appropriate charging current value calculation unit 303 obtains an appropriate charging current value by referring to the appropriate charging current value table according to the detected temperature, detected humidity, and paper information. Then, the appropriate charging current calculation unit 303 sends appropriate charging current value data indicating the appropriate charging current value to the charging output current control unit 302.

  FIG. 7 is a flowchart for explaining control of the charging high-voltage circuit shown in FIG. Note that the processing according to the flowchart shown in the drawing is executed by the engine control circuit 300. In FIG. 7, the same steps as those in the flowchart shown in FIG.

  In step S701, upon receiving the ATVC control request signal, the charging output control unit 302 determines the value of the current applied to the transfer roller 20 during ATVC (ATVC control start: S402).

  After starting the ATVC, the charging output control unit 302 instructs the charging roller resistance value calculation unit 304 to check the level of the control signal V_icont_chg (S403). Subsequently, the charging output control unit 302 instructs the charging roller resistance value calculation unit 304 to calculate the resistance value of the charging roller 20.

  Accordingly, the charging roller resistance value calculation unit 304 calculates the resistance value of the charging roller 20 by substituting the level of the voltage detection signal V_vsvs_chg and the level of the control signal V_icont_chg into a preset calculation formula (S404).

  As described above, in the charging high-voltage circuit, constant current control is performed so that the level of the current value detection signal V_isns_chg and the level of the control signal V_icont_chg are the same.

  The voltage detection signal V_vsvs_chg indicates a voltage value obtained by dividing the current value detection signal V_isns_chg and the charging output voltage Vout_chg by the resistors R601 and R602. When the constant current control is performed, since the voltage value is the same as the voltage value obtained by dividing the control signal V_icont_chg and the charging output voltage Vout_chg by the resistors R601 and R602, the equation (13) is established.

V_vsvs_chg = (Vout_chg × R602 + V_icont_chg × R601) / (R601 + R602) (13)
Rearranging equation (13) for Vout_chg, equation (14) is obtained.

Vout_chg = ((R601 + R602) × V_vsns_chg−R601 × V_icont_chg) / R602 (14)
Then, when the charging output voltage Vout_chg is divided by the current Ia supplied to the charging roller 20, a resistance value R_chg of the charging roller 20 is obtained. This resistance value R_chg is expressed by equation (15).

R_chg = ((R601 + R602) × V_vsns_chg−R601 × V_icont_chg) / (R602 × Ia) (15)
In Expression (14), since elements other than V_vsns_chg and V_icont_chg are constant, the charging roller resistance value calculation unit 304 receives the fluctuation parameters V_vsns_chg and V_icont_chg, and uses Expression (15) to determine the resistance value of the charging roller 20. Is calculated.

  In this way, the charging roller resistance value calculation unit 304 calculates the resistance value of the transfer roller and sends it to the appropriate charging current value calculation unit 303 as resistance value data. The appropriate charging current value calculation unit 303 calculates an optimum charging current value at the time of image formation based on the resistance value of the charging roller 20, the detected temperature, the detected humidity, and the paper information (S405).

  Thereafter, the process of step S705 described with reference to FIG. 3 is performed, and subsequently, the charging output control unit 302 outputs the control signal V_icon_chg to the non-inverting input terminal of the OP amplifier OP601. Accordingly, ATVC is performed (charging constant current control ON: S407). Then, the process of step S707 described in FIG. 3 is performed.

  Subsequently, the charging output control unit 302 switches the signal level of the control signal V_icon_chg from a proper charging current value to a level corresponding to zero output current, and stops the supply of the drive pulse to the FET Q602 (charging constant current control OFF: S409). . Then, the charging output control unit 302 returns to the process of step S701.

  As described above, in the second embodiment of the present invention, the current detection unit 310 for performing constant current control does not need to use an OP amplifier or the like. Therefore, the circuit configuration in the charging high-voltage circuit is simplified to reduce the circuit scale. can do. As a result, cost reduction can be achieved.

  In the second embodiment, the resistance value of the charging roller is obtained according to the charging output voltage, but the constant current control may be performed by obtaining the appropriate current value directly from the charging output voltage.

  As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to these embodiment, Various forms of the range which does not deviate from the summary of this invention are also contained in this invention. .

104,604 Transfer roller resistance value calculation unit 302 Charging output control unit 303 Proper charging current value calculation unit 304 Charging roller resistance value calculation unit 602 Transfer output control unit 603 Proper transfer current value calculation unit 607 Constant current control unit 608 High voltage generation unit 609 Voltage detection unit 110, 310, 610 Current detection unit

Claims (4)

A power supply device for supplying high voltage to a load whose resistance value varies,
Constant current control means for controlling a current value supplied to the load to a constant value according to a level of a predetermined current value setting signal ;
A transformer connected to the secondary side for generating a high voltage to be supplied to the load;
Current detection means for generating a current value detection voltage indicating a voltage value corresponding to the current flowing through the load ;
A current supply path for supplying the current flowing through the load to the current detection means ;
Voltage detection means for detecting a voltage value applied to the load as a detection voltage value;
Load resistance value calculating means for calculating the resistance value of the load,
Said current sensing means is connected to a predetermined reference power supply has a current sensing resistor the current flowing in the load flows through the current supply path, wherein a voltage value corresponding to the voltage drop at the current sensing resistor Detect as current value detection voltage ,
The constant current control means outputs an error amplifier that outputs a voltage corresponding to a deviation obtained as a result of comparing the level of the current value setting signal and the current value detection voltage, and a voltage corresponding to the output of the error amplifier. A regulator that inputs to the primary side of the transformer, and performs constant current control so that the level of the current value setting signal and the current value detection voltage are the same,
The voltage detection means has a first resistor connected to the secondary side of the transformer, and a second resistor connected in series between the first resistor and the current detection resistor,
During constant current control by the constant current control means, the load resistance value calculation means is provided with a voltage value at a connection point between the first resistance and the second resistance as the detected voltage value. A power supply device that calculates a resistance value of the load based on the detection voltage, the level of the current value setting signal, the resistance value of the first resistor, and the resistance value of the second resistor . In response to the resistance value of the resulting said load by said load resistance value calculating means, to claim 1, characterized in that it comprises a voltage level control means for controlling the level of the current setting signal based on the resistance value The power supply described. The power supply device according to claim 1 or 2 ,
A said load, an image forming apparatus, characterized in that it comprises a transfer unit for transferring the toner image formed on the photosensitive member onto a recording medium. The power supply device according to claim 1 or 2 ,
An image forming apparatus comprising: a charging unit that is the load and uniformly charges the surface of the photosensitive member during image formation.

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