JP7114428B2 - Power supply and image forming apparatus - Google Patents

Description

The present invention relates to a power supply and an image forming apparatus equipped with the power supply.

An electrophotographic image forming apparatus is equipped with a high-voltage power supply that supplies various high voltages, and the high-voltage power supply is indispensable for the image forming process on recording materials. . As the high voltage power supply, there are various modularized power supplies such as a high voltage power supply for charging devices, a high voltage power supply for developing devices, and a high voltage power supply for transfer devices. These modularized high-voltage power supply devices have different specifications depending on the configuration of the image forming apparatus. For example, in the case of a high-voltage power supply for a transfer device, it is necessary to apply a voltage opposite in polarity to the voltage applied during normal transfer to remove toner adhering to the transfer roller during the cleaning operation of the image forming device. There is Generally, the toner itself has a negative polarity. Therefore, during image formation, toner (toner image) is transferred by applying a positive voltage from a high voltage power supply that outputs a positive high voltage (hereinafter referred to as a "positive power supply"). Specifically, by applying a positive voltage from a primary transfer positive power source to the primary transfer roller, the toner image formed on the photosensitive drum is transferred to the intermediate transfer belt. Further, by applying a positive voltage from the secondary transfer positive power source to the secondary transfer roller, the toner image on the intermediate transfer belt is transferred to the recording material. On the other hand, during the cleaning process, the secondary transfer roller and the intermediate transfer belt are cleaned by applying a negative voltage from a high voltage power supply that outputs a negative high voltage (hereinafter referred to as a "negative power supply"). That is, by applying a negative voltage to the secondary transfer roller from the secondary transfer negative power supply, residual toner that remains on the secondary transfer roller without being transferred to the recording material (residual toner) is transferred to the intermediate transfer belt. is exhaled. Further, by applying a negative voltage from a primary transfer negative power supply to the primary transfer roller, the toner on the intermediate transfer belt is transferred to the photosensitive drum, and then the toner on the photosensitive drum is collected in a waste toner container.

A high-voltage power supply used in an image forming apparatus has power supply units that generate high voltages of negative and positive polarities. has been conventionally performed (see, for example, Patent Document 1). FIG. 7 is a circuit diagram schematically showing a conventional secondary transfer power supply and intermediate transfer belt cleaning power supply in an image forming apparatus having an intermediate transfer belt. The secondary transfer power supply and the cleaning power supply are power supply units that supply positive and negative voltages to the secondary transfer roller P1 and the cleaning brush P2, respectively. The power supply device shown in FIG. 7 has a secondary transfer positive power supply V1 and a cleaning positive power supply V2 that supply a positive voltage. Further, the power supply device shown in FIG. 7 has a secondary transfer negative power supply and an ICL in which two negative power supplies, a secondary transfer negative power supply that supplies a negative voltage and a cleaning negative power supply that supplies a negative voltage, are shared. It has a negative power supply V3. A detailed description of FIG. 7 will be given later.

JP 2013-78252 A

In FIG. 7, the thick solid arrow indicates the secondary transfer negative voltage flowing to the secondary transfer roller P1 when the secondary transfer negative power supply and the ICL negative power supply V3 are turned on to apply a negative voltage to the secondary transfer roller P1. It shows the path of current. As shown in FIG. 7, part of the secondary transfer negative current flowing from the secondary transfer roller P1 to the power supply device flows through the path 1 to the current detection circuit IS1 that detects the secondary transfer current. Further, part of the secondary transfer negative current flows through the path 2 to the current detection circuit IS2 that detects the current flowing through the cleaning brush P2. Therefore, the current detection circuit IS1 and the current detection circuit IS2 cannot correctly detect the load current flowing through the secondary transfer roller P1 and the cleaning brush P2, respectively. As a result, there is a problem that the control for setting the voltage and current of the power supply unit of the power supply unit in which the power supply unit is shared to desired values cannot be performed.

SUMMARY OF THE INVENTION It is an object of the present invention to detect a load current correctly even when a common power supply unit is used.

In order to solve the above problems, the present invention has the following configuration.

(1) a first power supply section for outputting an AC voltage, connected to the first power supply section, rectifying the AC voltage output from the first power supply section, and outputting a DC voltage of a predetermined polarity; a first rectifying section and a second rectifying section that output a DC voltage having a polarity opposite to the predetermined polarity; and an output voltage of the first rectifying section. and the output voltage of the second power supply unit are superimposed on each other; a first current detection unit for detecting a current flowing through a first load; a second current detection unit for detecting a current flowing through a second load supplied with a voltage superimposed with the output voltage of the power supply unit 3; a current flowing through the first current detection unit; and a separation unit that separates the current flowing through the current detection unit from the current detection unit.

(2) An image forming section for forming an image; a first rectifying unit and a second rectifying unit connected to one power supply unit, rectifying the AC voltage output from the first power supply unit and outputting a DC voltage having a predetermined polarity; a second power supply section for outputting a DC voltage having a polarity opposite to the polarity; a third power supply section for outputting a DC voltage having a polarity opposite to the predetermined polarity; an output voltage from the first rectifying section; a first current detection unit for detecting a current flowing through a first load supplied with a voltage superimposed on the output voltage of the second power supply unit; a second current detection unit for detecting a current flowing through a second load supplied with a voltage superimposed on the output voltage of the power supply unit; a current flowing through the first current detection unit; and the second current. an image forming apparatus, comprising: a separation section that separates a current flowing through the detection section.

According to the present invention, the load current can be detected correctly even when the power supply unit is shared.

FIG. 2 is a circuit diagram showing configurations of a secondary transfer power supply and an ICL power supply in Embodiment 1; FIG. 10 is a diagram showing the relationship between the secondary transfer negative current and the detection voltage in the circuit diagrams of the first embodiment and the conventional example; FIG. 4 is a diagram showing current paths when voltages from power sources of both positive and negative polarities are superimposed according to the first embodiment; FIG. 4 is a diagram for explaining the load characteristics of the piezoelectric transformers of Examples 1 and 2; FIG. 4 is a circuit diagram showing configurations of a secondary transfer power supply and an ICL power supply in Embodiment 2; FIG. 11 shows an image forming apparatus according to the third embodiment; Circuit diagram showing configuration of conventional secondary transfer power supply and ICL power supply

BEST MODE FOR CARRYING OUT THE INVENTION Below, embodiments of the present invention will be described in detail with reference to the drawings.

[Overview of secondary transfer power supply and ITB cleaning power supply]
A conventional secondary transfer power supply and a cleaning power supply for an intermediate transfer belt will be described below for comparison with embodiments described later. FIG. 7 schematically shows a conventional secondary transfer power supply and an ITB cleaning (hereinafter referred to as "ICL") power supply of a power supply provided in an image forming apparatus having an intermediate transfer belt (hereinafter referred to as "ITB") P4. It is a circuit diagram. The secondary transfer power supply and the ICL power supply are power supplies that supply positive and negative DC high voltages to the secondary transfer roller P1 and the ICL brush P2, respectively. The power supply device shown in FIG. 1 has a secondary transfer positive power supply (second power supply section) V1 and an ICL positive power supply V2 (third power supply section) for supplying a positive DC voltage. Further, in the power supply device shown in FIG. 1, two negative power supplies, ie, a secondary transfer negative power supply that supplies negative DC voltage (predetermined polarity) and an ICL negative power supply that supplies negative DC voltage, are shared. It has a secondary transfer negative power supply and an ICL negative power supply V3.

(Power supply V1, V2, V3)
The secondary transfer positive power supply V1 and the ICL positive power supply V2 include a transformer drive circuit that drives the transformer according to a control signal from an ASIC IC1, which will be described later, a transformer that generates an output voltage, and a rectifier circuit that rectifies the output voltage of the transformer. I have it inside. The secondary transfer positive power supply V1 and the ICL positive power supply V2 apply positive voltages to the secondary transfer roller P1 and the ICL brush P2, respectively, according to control signals (analog signals) from the ASIC IC1. Resistors R1 and R12 connected in parallel to the secondary transfer positive power supply V1 and ICL positive power supply V2 are bleeder resistors. The bleeder resistors R1 and R12 serve as paths for load currents flowing through the secondary transfer roller P1 and the ICL brush P2, respectively, when a secondary transfer negative power supply and an ICL negative power supply V3, which will be described later, are turned on.

A secondary transfer negative power supply and an ICL negative power supply V3 (hereinafter referred to as "negative power supply V3") are composed of a voltage resonance circuit, a piezoelectric transformer T1, and rectifier circuits RE1 and RE2. The voltage resonance circuit is composed of a field effect transistor (hereinafter referred to as "FET") Q1, an inductor L1 and a capacitor C2. The voltage resonance circuit drives the piezoelectric transformer T1 at a frequency based on a control signal (frequency setting signal) input from the D/A port 3 of the ASIC IC1 to the gate terminal of the FET Q1 to output a predetermined voltage. The piezoelectric transformer T1 (first power supply unit) is an element that increases the voltage generated by the voltage resonance circuit. The piezoelectric transformer T1 is turned on by the control of the voltage resonance circuit and generates an AC voltage. The output terminal of the piezoelectric transformer T1 is connected to the input terminals of the rectifier circuits RE1 and RE2. The AC voltage generated by the piezoelectric transformer T1 is rectified into a DC voltage of negative polarity by a rectifying circuit RE1 (first rectifying section), supplied to the secondary transfer roller P1, and supplied to the secondary transfer roller P1. is rectified into a negative DC voltage and supplied to the ICL brush P2. The rectifier circuit RE1 is composed of diodes D1 and D2 and a capacitor C3, and the rectifier circuit RE2 is composed of diodes D4 and D5 and a capacitor C7. Output. A resistor R2 connected in parallel with the rectifier circuit RE1 and resistors R13 and R14 connected in parallel with the rectifier circuit RE2 are bleeder resistors. The bleeder resistor R2 serves as a path for the load current flowing through the secondary transfer roller P1 when the secondary transfer positive power supply V1 is turned on. becomes the route of

(ASIC)
The IC1 switches the secondary transfer positive power supply V1, the ICL positive power supply V2, and the negative power supply V3 based on the load current values flowing through the secondary transfer roller P1 and the ICL brush P2 detected by current detection circuits IS1 and IS2, which will be described later. It is an ASIC (Application Specific Integrated Circuit) that controls the output. ASIC IC1, which is a control unit, outputs control signals (analog signals) from D/A ports 1, 2, and 3, respectively, to control output voltages of secondary transfer positive power supply V1, ICL positive power supply V2, and negative power supply V3. Then, a positive voltage and a negative voltage are supplied to the secondary transfer roller P1 and the ICL brush P2.

The positive voltage supplied from the secondary transfer positive power supply V1 to the secondary transfer roller P1 is divided by the resistors R3 and R4, which are the second voltage detectors, and is input to the A/D port 1 of the ASIC IC1. . The ASIC IC1 performs constant voltage control of the secondary transfer positive power supply V1 based on the voltage input to the A/D port 1. FIG. When the negative power supply V3 is turned on, the input voltage to the A/D port 1 is set to 3.3 V through the diode D3 so that the A/D port 1 of the ASIC IC1 does not receive a negative voltage. Since it is pulled up by the voltage divided by the resistors R5 and R6, it is a positive voltage. Also, the positive voltage supplied from the ICL positive power supply V2 to the ICL brush P2 is divided by the resistors R15 and R16, which are the third voltage detector, and is input to the A/D port 3 of the ASIC IC1. The ASIC IC1 performs constant voltage control of the ICL positive power supply V2 based on the voltage input to the A/D port 3. FIG. In order to prevent a negative voltage from being input to the A/D port 3 of the ASIC IC1 when the negative power supply V3 is turned on, the input voltage to the A/D port 3 is set to 3.3 V via a diode D6 and a resistor R17. Since it is pulled up by the voltage divided by R18, it is a positive potential voltage. Also, the anode voltage of the diode D5, which is the output voltage of the negative power supply V3, is divided by the resistors R13 and R14, which are the first voltage detectors, and input to the A/D port 2 of the ASIC IC1. The ASIC IC1 performs constant voltage control of the negative power supply V3 based on the voltage input to the A/D port 2 . Although the resistors R13 and R14 are provided in the rectifier circuit RE2 in FIG. 7, they may be provided in the rectifier circuit RE1. In that case, the bleeder resistor R2 is provided in the rectifier circuit RE2.

(current detection circuit)
The current detection circuits IS1 and IS2 detect load currents flowing through the secondary transfer roller P1 and the ICL brush P2, respectively, and output the detected load current values to the A/D ports 4 and 5 of the ASIC IC1. The current detection circuit IS1 (first current detection section) comprises an operational amplifier IC2, capacitors C4, C5 and C6, resistors R7, R8, R10 and R11, and a detection resistor R9. A voltage obtained by dividing a voltage of 3.3 V by resistors R7 and R8 is input to the non-inverting input terminal (+) of the operational amplifier IC2. Since the inverting input terminal (-) is imaginary short-circuited with the non-inverting input terminal (+), it is maintained at substantially the same potential as the non-inverting input terminal (+). Therefore, the voltage input to the ASIC IC1 through the A/D port 4 flows from the voltage of the inverting input terminal (-) of the operational amplifier IC2, that is, the voltage input to the non-inverting input terminal (+) to the detection resistor R9. The voltage value is a voltage drop corresponding to the load current. Similarly, the current detection circuit IS2 (second current detection section) comprises an operational amplifier IC3, capacitors C8, C9 and C10, resistors R19, R20, R22 and R23, and a detection resistor R21. A voltage obtained by dividing a voltage of 3.3 V by resistors R19 and R20 is input to the non-inverting input terminal (+) of the operational amplifier IC3. Since the inverting input terminal (-) is imaginary short-circuited with the non-inverting input terminal (+), it is maintained at substantially the same potential as the non-inverting input terminal (+). Therefore, the voltage input to the ASIC IC1 through the A/D port 5 flows from the voltage of the inverting input terminal (-) of the operational amplifier IC3, that is, the voltage input to the non-inverting input terminal (+) to the detection resistor R21. The voltage value is a voltage drop corresponding to the load current.

(Operation during image formation)
During image formation, a toner image is formed on the photosensitive drum P5, and a transfer voltage applied from a primary transfer power source (not shown) to the primary transfer pad P6 transfers the toner image on the photosensitive drum P5 to the ITB P4 (image carrier). transcribed to After that, when a positive transfer voltage is applied from the secondary transfer positive power supply V1 to the secondary transfer roller P1 (transfer portion) under the control of the ASIC IC1, the toner image on the ITB P4 (on the image carrier) is transferred. , ITB P4 and the recording material sandwiched between the secondary transfer roller P1. In this embodiment, the image forming unit that forms an image on a recording material includes a photosensitive drum P5, a primary transfer pad P6, a secondary transfer roller P1, an ICL brush P2, and an ITB P4. Further, the toner remaining on the ITB P4 without being transferred onto the recording material is removed by applying a positive voltage from the ICL positive power supply V2 to the ICL brush P2 (cleaning section) under the control of the ASIC IC1. Temporarily recovered at P2. At this time, the current value of the secondary transfer current, which is the load current flowing through the secondary transfer roller P1, can be detected by the current detection circuit IS1. A secondary transfer current flows from the secondary transfer positive power supply V1 through the secondary transfer roller P1 to the ground (hereinafter referred to as "GND") of the drive roller P3 that rotates the ITB P4. Then, the secondary transfer current returns from the GND of the operational amplifier IC2 to the secondary transfer positive power supply V1 via the operational amplifier IC2, the resistor R10, the detection resistor R9, and the bleeder resistor R2. A reference voltage obtained by dividing a voltage of 3.3 V by resistors R7 and R8 is input to the non-inverting input terminal (+) of the operational amplifier IC2, and controlled so that an imaginary short-circuit with the inverting input terminal (-) is established. . Therefore, the current detection circuit IS1 detects the current value of the secondary transfer current flowing through the secondary transfer roller P1 as a potential difference in the detection resistor R9, and outputs it as a detection voltage. A detection voltage output by the current detection circuit IS1 is input to the ASIC IC1 via the A/D port 4. FIG.

Similarly, the current value of the ICL current, which is the load current flowing through the ICL brush P2, can be detected by the current detection circuit IS2. The ICL current flows from the ICL positive power supply V2 through the ICL brush P2 to the GND of the drive roller P3, from the GND of the operational amplifier IC3 through the operational amplifier IC3, the resistor R22, the detection resistor R21, the bleeder resistors R14 and R13, Return to ICL positive power supply V2. A reference voltage obtained by dividing a voltage of 3.3 V by resistors R19 and R20 is input to the non-inverting input terminal (+) of the operational amplifier IC3, and is controlled so that an imaginary short-circuit with the inverting input terminal (-) is established. . Therefore, the current detection circuit IS2 detects the current value of the ICL current flowing through the ICL brush P2 as a potential difference in the detection resistor R21, and outputs it as a detection voltage. A detection voltage output by the current detection circuit IS2 is input to the ASIC IC1 via the A/D port 5. FIG.

(Behavior during cleaning process)
On the other hand, during the cleaning process, ASIC IC1 turns on the negative power supply V3. The negative voltage supplied from the negative power supply V3 is supplied to the secondary transfer roller P1 through the bleeder resistor R1 and is also supplied to the ICL brush P2 through the resistor R12. Due to the negative voltage applied to the secondary transfer roller P1, the toner adhering to the secondary transfer roller P1 is transferred to the ITB P4 and removed from the secondary transfer roller P1. Further, the toner temporarily collected by the ICL brush P2 is ejected (transferred) to the ITB P4 by a negative voltage applied to the ICL brush P2. After that, the toner transferred to the ITB P4 is transferred to the photosensitive drum P5 by the transfer voltage applied to the primary transfer pad P6, and a waste toner container in a cartridge (not shown) having the photosensitive drum P5 and performing image formation. to be recovered.

The thick solid-line arrow shown in FIG. 7 indicates the path of the current (hereinafter referred to as “secondary transfer negative current”) flowing through the secondary transfer roller P1 when a negative voltage is applied to the secondary transfer roller P1. . At this time, part of the secondary transfer negative current flows through the path 1 to the detection resistor R9 of the current detection circuit IS1 for the secondary transfer current. Part of the secondary transfer negative current also flows through the path 2 to the detection resistor R21 of the current detection circuit IS2 for the ICL current. Therefore, the current detection circuit IS1 and the current detection circuit IS2 cannot correctly detect the load current flowing through the secondary transfer roller P1 and the ICL brush P2, respectively. cannot be controlled to set the voltage and current to desired values.

[Overview of secondary transfer power supply and ITB cleaning power supply]
FIG. 1 is a circuit diagram schematically showing the secondary transfer power supply and the ICL power supply of the power supply device provided in the image forming apparatus having the ITB P4 of the first embodiment. In addition, in FIG. 1, the same components as in FIG. 7 described above are denoted by the same reference numerals, and descriptions thereof are omitted. The difference between FIG. 1 of this embodiment and FIG. 7 of the conventional example is that between the rectifier circuits RE1 and RE2 connected to the current detection circuits IS1 and IS2 and the input terminal to which the output voltage from the piezoelectric transformer T1 is input. Secondly, the capacitor C1, which is the separator, is arranged in series. As a result, when the negative power supply V3 is turned on, the current path 1 flowing through the current detection circuit IS1 and the current path 2 flowing through the current detection circuit IS2 are separated by the capacitor C1. As a result, the current detection circuits IS1 and IS2 can acquire correct current detection results of the load currents flowing through the secondary transfer roller P1 and the ICL brush P2, respectively. An AC voltage is output from the piezoelectric transformer T1, and an AC-coupled AC voltage is output to the terminal of the capacitor C1 on the rectifier circuit RE2 side. Therefore, the arrangement of the capacitor C1 does not affect the circuit operation of the negative power supply V3.

[Secondary transfer negative current and detection voltage of current detection circuit]
FIG. 2 shows the secondary transfer negative current and current detection when the negative power supply V3 in the circuit diagram of FIG. 1 of this embodiment and FIG. FIG. 4 is a diagram showing an example of a detection voltage of circuit IS1; The horizontal axis of FIG. 2 indicates the current value of the load current (unit: μA), and the vertical axis indicates the detection voltage (unit: V). In the graph shown in FIG. 2, the plots indicated by circles are the detection results of the current detection circuit IS1 of FIG. 1 of this embodiment, and the plots indicated by squares are of the current detection circuit IS1 of FIG. This is the detection result. In the conventional circuit configuration, as described above, the secondary transfer negative current flowing through the secondary transfer roller P1 flows not only through the current detection circuit IS1 but also through the current detection circuit IS2. Therefore, even if the value of the secondary transfer negative current is changed, the detection voltage of the current detection circuit IS1 hardly changes, and a correct load current detection result cannot be obtained. On the other hand, in the circuit configuration of this embodiment, by providing the capacitor C1, the secondary transfer negative current flowing to the secondary transfer roller P1 flows only to the current detection circuit IS1, and the current is cut off by the capacitor C1. It does not flow into circuit IS2. Therefore, when the value of the secondary transfer negative current is changed, the detection voltage output from the current detection circuit IS2 also changes linearly, and it can be seen that a correct detection result is obtained.

In addition, in the circuit configuration of FIG. 1, a correct detection result is similarly obtained for the detection voltage of the current detection circuit IS2 that detects the current flowing through the ICL brush P2 by turning on the negative power supply V3. That is, in the circuit configuration of this embodiment, by providing the capacitor C1, the ICL negative current, which is the negative current flowing through the ICL brush P2, flows only through the current detection circuit IS2, and the current is cut off by the capacitor C1. It does not flow into circuit IS1. Therefore, when the value of the ICL negative current is changed, the detection voltage output from the current detection circuit IS2 also changes linearly as in the graph of FIG. 2, and correct detection results can be obtained.

[Current path when voltages from positive and negative power supplies are superimposed]
FIG. 3 is a diagram showing current paths in the circuit of FIG. 1 when the ICL positive power supply V2 and the negative power supply V3 are on and the secondary transfer positive power supply V1 is off. In the state shown in FIG. 3, a negative voltage is applied to the secondary transfer roller P1 from the negative power supply V3, and a positive voltage is applied to the ICL brush P2 from the ICL positive power supply V2. ing. A thick solid arrow indicates a current path of a secondary transfer negative current that flows through the secondary transfer roller P1 when a negative voltage is applied to the secondary transfer roller P1. On the other hand, the thick dashed arrow indicates the current path of the ICL positive current flowing through the ICL brush P2 when a positive voltage is applied to the ICL brush P2 from the ICL positive power supply V2. In this way, there are cases where voltages from power sources of both positive and negative polarities are superimposed and applied to the same load.

As described above, in the case of the conventional circuit configuration shown in FIG. 7, when voltages from power sources of both positive and negative polarities are superimposed, a current path such as path 2 shown in FIG. It also affected the detection result of the ICL current by the current detection circuit IS2. On the other hand, in the case of this embodiment, as shown in FIG. 3, the secondary transfer negative current flows through the following routes. That is, the secondary transfer negative current flowing from the negative power supply V3 to the secondary transfer roller P1 flows through the detection resistor R9, the resistor R10, and the operational amplifier IC2 to the GND of the operational amplifier IC2, and then from the GND of the driving roller P3 via the bleeder resistor R1. and return to the negative power supply V3. Further, the ICL current flowing from the ICL positive power supply V2 to the ICL brush P2 flows to the GND of the drive roller P3, passes through the GND of the operational amplifier IC3, the operational amplifier IC3, the resistor R22, the detection resistor R21, the bleeder resistors R14 and R13, Return to ICL positive power supply V2. At this time, the terminal of the ICL positive power supply V2 on the rectifier circuit RE2 side becomes a negative voltage obtained by rectifying and smoothing the AC voltage of the piezoelectric transformer T1. A voltage obtained by summing the negative voltages of T1 is output. The ICL positive power supply V2 inputs the voltage divided by the resistors R15 and R16 to the A/D port 3 of the ASIC IC1 to perform feedback control. Therefore, the ASIC IC1 controls the ICL positive power supply V2 so that the positive voltage to be applied to the ICL brush P2 is output. As described above, in this embodiment, even when the voltage from the power source of both positive and negative polarities is superimposed, the current path is cut off by the capacitor C1. The load current flowing through P2 can be detected correctly.

[Load characteristics of piezoelectric transformer]
FIG. 4 is a diagram schematically showing load characteristics of the piezoelectric transformer T1 used for the negative power supply V3. The horizontal axis of FIG. 4 represents the impedance (unit: MΩ) of the load to which the piezoelectric transformer T1 supplies the output voltage, and the vertical axis represents the peak voltage (unit: V), which is the maximum voltage that the piezoelectric transformer T1 can apply. showing. "Initial" and "Terminal" on the horizontal axis indicate the life of the load that supplies the output voltage of the piezoelectric transformer T1. It indicates the end of the usable period of the load. As shown in FIG. 4, as the impedance of the load increases, the absolute value of the peak voltage that can be applied to the load by the piezoelectric transformer T1 increases.

In general, the impedance of the secondary transfer roller P1 and the ICL brush P2 used in an electrophotographic image forming apparatus rises due to electrical deterioration, in which the resistance changes when current flows. Normally, the maximum voltage that can be applied is designed so that a predetermined voltage can be supplied even when the load impedance is the smallest within the range of load impedance that can vary according to product specifications. That is, the maximum voltage that can be applied to the load is designed as the peak voltage Vs when the load impedance in FIG. 4 is small with a certain margin taken into account. The circuit configuration of this embodiment shown in FIG. 1 enables the load current to be detected by the current detection circuits IS1 and IS2 even when the negative power supply V3 is turned on. Therefore, the output voltage of the negative power supply V3 is supplied to the ASIC IC1 based on the current detection results of the current detection circuits IS1 and IS2 and the applied voltage value input via the A/D port 2 of the negative power supply V3. It is possible to calculate the combined impedance of the load The combined impedance here is the impedance including the impedance in the circuit such as the resistor R2 in addition to the secondary transfer roller P1 and the ICL brush P2.

As shown in FIG. 4, as the load impedance of the piezoelectric transformer T1 increases, the absolute value of the peak voltage that can be output increases. Therefore, using this characteristic of the piezoelectric transformer T1, the ASIC IC1 raises the absolute value of the maximum voltage that can be applied according to the value of the detected load impedance. As a result, the maximum voltage that the piezoelectric transformer T1 can apply to the secondary transfer roller P1 and the ICL brush P2, whose load impedance has increased due to the deterioration of the current, up to a voltage considering a certain margin for the peak voltage Ve in FIG. can be raised. In general, the reason why it is necessary to apply a higher voltage to the load is that current of a predetermined current value is applied to the secondary transfer roller P1 and the ICL brush P2 whose load impedance has increased due to deterioration in current flow. . As a result, the specifications of the device can be satisfied by increasing the maximum voltage that can be applied according to the load impedance. As a result, the high-voltage output of the high-voltage power supply device, which is required due to deterioration of the process members such as the secondary transfer roller P1 and the ICL brush P2, can be handled without increasing the cost and circuit area. be able to.

As described above, the load current can be correctly detected even when a power supply device in which a plurality of power supplies that supply output voltages of the same polarity to the load are shared is turned on. In addition, the same effect can be obtained even when output voltages of positive and negative power sources are superimposed. Also, as described above, it is possible to increase the output voltage of the high-voltage power supply device without increasing the cost or increasing the circuit area. In this embodiment, as shown in FIG. 1, the negative power supply V3 is composed of the piezoelectric transformer T1. Effects similar to those of the present embodiment can be obtained.

As described above, according to this embodiment, the load current can be correctly detected even when the power supply unit is shared.

In Example 1, the ASIC IC1 performs constant voltage control for the secondary transfer positive power supply V1, the ICL positive power supply V2, and the negative power supply V3. In a second embodiment, a circuit configuration for performing both constant voltage control of the secondary transfer negative voltage and constant current control of the ICL negative voltage in the negative power supply V3 will be described.

[Overview of secondary transfer power supply and ITB cleaning power supply]
FIG. 5 is a circuit diagram schematically showing the secondary transfer power supply and the ICL power supply of the power supply device provided in the image forming apparatus having the ITB P4 of the second embodiment. In FIG. 5, the same components as in FIG. 1 of the first embodiment described above are assigned the same reference numerals, and descriptions thereof are omitted. FIG. 5 of this embodiment differs from FIG. 1 of Embodiment 1 in that the secondary transfer negative voltage is set to a predetermined constant voltage by a Zener diode ZD1 (constant voltage supply unit). In this embodiment, similarly to FIG. 1 of the first embodiment, the capacitor C1 is connected in series between the input terminals of the rectifier circuits RE1 and RE2 to which the current detection circuits IS1 and IS2 are respectively connected. The arrangement points are the same.

In FIG. 5, a circuit in which a Zener diode ZD1 and a diode D7 are connected in series is added to the circuit diagram of FIG. 1 of the first embodiment. The diode D7 has a cathode terminal connected to the current path from the secondary transfer power source to the secondary transfer roller P1, an anode terminal connected to the anode terminal of the Zener diode ZD1, and a cathode terminal of the Zener diode ZD1 connected to GND. there is The diode D7 is arranged to prevent current from flowing through the Zener diode ZD1 when the secondary transfer positive power supply V1 is turned on.

In the circuit configuration of the first embodiment shown in FIG. 1, when the load impedance of the secondary transfer roller P1 is ZP1, in terms of an equivalent circuit, the load impedance ZP1 is connected in parallel with a circuit in which resistors R3 and R4 are connected in series. relationship. Here, the combined impedance of the load impedance ZP1 and the series-connected resistors R3 and R4 is expressed as (ZP1//(R3+R4)). Assuming that the anode voltage of the diode D2 is VD2 and the resistance value of the resistor R1 is R1, the voltage VP1 applied to the secondary transfer roller P1 can be expressed by the following (Equation 1).
VP1=VD2×(ZP1//(R3+R4))/(R1+(ZP1//(R3+R4))) (Formula 1)

From (Equation 1), it can be seen that the voltage VP1 applied to the secondary transfer roller P1 changes according to the load impedance ZP1 of the secondary transfer roller P1. In general, the ion-conducting conductive material used for the secondary transfer roller P1 has a large amount of change in load impedance depending on the environment, so the load impedance ZP1 of the secondary transfer roller P1 also changes greatly. As a result, the voltage VP1 applied to the secondary transfer roller P1 changes greatly depending on the environment. Therefore, as shown in FIG. 5 of this embodiment, by disposing the Zener diode ZD1, a predetermined constant voltage can be applied to the secondary transfer roller P1 regardless of changes in the load impedance ZP1 of the secondary transfer roller P1 caused by the environment. can be applied.

Further, by disposing the Zener diode ZD1, constant voltage control is performed on the secondary transfer roller P1, so that constant current control can be performed on one ICL brush P2. For example, when a negative voltage is applied to the ICL brush P2 from the negative power supply V3 and the toner temporarily collected by the ICL brush P2 is ejected to the ITB P4, if the load impedance of the ICL brush P2 increases due to deterioration of the current flow, A predetermined current value may not be ensured. As a result, there are cases where sufficient transfer residual toner cannot be discharged. Therefore, with the circuit configuration of this embodiment, constant current control of the ICL negative power supply is performed, the current flowing through the ICL brush P2 is detected by the current detection circuit IS2, and the output voltage of the negative power supply V3 is adjusted. Control can be performed such that a desired ICL negative current flows. As a result, when discharging the transfer residual toner from the ICL brush P2, the ASIC IC1 can sufficiently discharge the transfer residual toner through optimum control.

As described above, in a power supply device in which a plurality of power supplies that supply output voltages of the same polarity to loads are shared, constant current control can be performed, and constant voltage control can be performed for other loads. be able to. In the above-described embodiment, the primary transfer pad P6 for transferring the toner image on the photosensitive drum P5 to the ITB P4, the secondary transfer roller P1 for transferring the toner image on the ITB P4 to the recording material, and the ICL brush P2 are provided. An example of an image forming apparatus has been described. Among image forming apparatuses, there is not only a secondary transfer method, but also an image forming apparatus of a method in which a recording material is conveyed by a conveying belt and a toner image on a photosensitive drum is transferred onto the conveyed recording material. In such a conveying belt type image forming apparatus, a toner image on a photosensitive drum is directly transferred to a conveying belt in order to detect color misregistration on a recording material. At that time, a high voltage is applied to the cleaning brush in order to clean the toner transferred to the conveying belt, and the power supply device described above can be applied.

As described above, according to this embodiment, the load current can be correctly detected even when the power supply unit is shared.

The power supply device having the secondary transfer power source and intermediate transfer belt cleaning power source described in Embodiments 1 and 2, and the current detection circuit for detecting the load current flowing through the secondary transfer roller and the ICL brush is an image forming apparatus. It can be applied as a power supply. The configuration of an image forming apparatus to which the power supply devices of Embodiments 1 and 2 are applied will be described below.

[Configuration of Image Forming Apparatus]
A laser beam printer will be described as an example of an image forming apparatus. FIG. 6 shows a schematic configuration of a laser beam printer 128 (hereinafter referred to as printer 128), which is an example of an electrophotographic printer. The printer 128 has four photosensitive drums 101, 102, 103, and 104, and uses an in-line full-color laser beam to obtain a full-color image by forming four-color toner images at once using the intermediate transfer belt 123 and superimposing them. is a printer. Charging rollers 111 to 114 and developing rollers 105 to 108, which are developing devices, are arranged around the photosensitive drums 101 to 104, and process cartridges 115 to 118, which are units of these rollers, are detachable from the main body of the printer 128. there is

Next, the process cartridge 115 will be described in detail. Since the other three process cartridges 116 to 118 have the same configuration, description thereof will be omitted. The process cartridge 115 includes a rotatably supported photosensitive drum 101. The photosensitive drum 101 is driven to rotate in the arrow direction (clockwise direction) in the figure by a drum motor (not shown), which is driving means. A charging roller 111 is arranged above the photosensitive drum 101. The charging roller 111 is pressed toward the center of the photosensitive drum 101 by a pressing means (not shown), and is driven to rotate as the photosensitive drum 101 rotates. . Further, since a charging voltage is applied to the charging roller 111 by a charging high-voltage power supply (not shown), the surface of the photosensitive drum 101 is uniformly contact-charged.

The surface of the photosensitive drum 101 charged by the charging roller 111 is irradiated with the laser beam L1 from the laser scanner 109 . The laser scanner 109 scans while turning on/off the laser beam L1 based on image information to expose the photosensitive drum 101 and forms an electrostatic latent image on the photosensitive drum 101 according to the image information. The laser scanner 109 has a configuration for performing exposure for yellow and magenta, and the laser scanner 110 has a configuration for performing exposure for cyan and black.

A developing roller 105 is rotatably disposed on the downstream side in the rotational direction of the irradiation position of the laser beam L1 on the photosensitive drum 101, and toner is supplied from a developer container (not shown). A developing voltage is applied to the developing roller 105 from a high-voltage power supply for development (not shown), so that toner adheres to the electrostatic latent image, which is the exposed portion of the surface of the photosensitive drum 101, and the electrostatic latent image becomes a toner image. is rendered as

A primary transfer pad 119 composed of a grounded metal core and a conductive layer is disposed downstream of the photosensitive drum 101 in the rotational direction, with the intermediate transfer belt 123 interposed therebetween. The primary transfer pad 119 is pressed against the surface of the photosensitive drum 101 to form a transfer nip portion between the photosensitive drum 101 and the primary transfer pad 119 . The intermediate transfer belt 123 is sandwiched between the transfer nips. Therefore, the charged toner image is transferred from the surface of the photosensitive drum 101 to the surface of the intermediate transfer belt 123 by the potential difference between the potential of the surface of the photosensitive drum 101 and the transfer voltage applied from the primary transfer power source (not shown) to the primary transfer pad 119 . be transcribed. Toner remaining on the photosensitive drum 101 after the toner image has been transferred to the intermediate transfer belt 123 is removed by a cleaner (not shown).

The intermediate transfer belt 123 is stretched by three rollers including a roller 136 facing the secondary transfer roller 126, a tension roller 125, and the like, and is driven to rotate in the arrow direction (counterclockwise direction) in the figure. The toner images of each color formed on the photosensitive drums 101 to 104 are sequentially transferred onto the intermediate transfer belt 123 and then formed by the secondary transfer roller 126 and the counter roller 136 as the intermediate transfer belt 123 rotates. It is conveyed to the secondary transfer section. On the other hand, the recording medium P stacked in the paper feed cassette 140 is fed from the paper feed cassette 140 by the paper feed roller 144, conveyed toward the secondary transfer section by the convey roller 131, and is detected by the registration sensor 132. Stop when the tip is detected. Then, the recording medium P that has stopped and waited at the registration sensor 132 is re-conveyed at the timing when the toner image on the intermediate transfer belt 123 coincides with the secondary transfer portion. Re-feeding the recording medium P from a paused state is called re-feeding. The image is transferred onto the recording medium P at the transfer section without positional deviation. At this time, a transfer voltage is applied between the secondary transfer roller 126 and the opposing roller 136 from a power source 161 which will be described later. Toner remaining on the intermediate transfer belt 123 without being transferred onto the recording medium P is collected by the cleaning section 180 .

The recording medium P onto which the toner image has been transferred is conveyed to the fixing device 127 . The fixing device 127 has a rotatably arranged fixing roller 157 and a pressure roller 156 that rotates while being pressed against the fixing roller 157 . A heater (not shown) is provided inside the fixing roller 157, and the temperature of the surface of the fixing roller 157 is adjusted by controlling the power supplied to the heater. When the recording medium P is conveyed to the fixing device 127, the fixing roller 157 and the pressure roller 156 rotate at a constant speed. The medium P is pressurized and heated from both the front and back sides at a constant pressure and temperature. As a result, the unfixed toner image on the surface of the recording medium P is melted and fixed on the recording medium P to form a full-color image. The recording medium P on which the full-color image is fixed passes through a fixing paper discharge sensor 130 arranged at the exit of the fixing device 127 and is discharged onto a paper discharge tray 129 above the printer 128 .

The printer 128 includes a controller 170 that controls the image forming operation by the process cartridges 115 to 118, which are image forming units, and the conveying operation of the recording medium P. FIG. Also, the ASIC 175 corresponding to the ASIC IC1 of the first and second embodiments controls the power supply device 160 based on instructions from the controller 170 . The power supply device 160 has power supplies 161 , 162 , 163 and the like that generate various voltages to be supplied to each device in the printer 128 . A power supply 161 is a secondary transfer positive power supply that supplies a positive DC voltage to the secondary transfer roller 126 corresponding to the secondary transfer roller P1 in the first and second embodiments. It corresponds to the power supply V1. The power supply 162 is an intermediate transfer belt cleaning power supply that supplies a positive DC voltage to the cleaning unit 180 corresponding to the ICL brush P2 of the first and second embodiments, and corresponds to the ICL positive power supply V2 of the first and second embodiments. A power supply 163 is a negative power supply that supplies a negative DC voltage to the secondary transfer roller 126 and the cleaning unit 180, and corresponds to the negative power supply V3 in the first and second embodiments. Further, the power supply device 160 has a current detection circuit for detecting the current flowing through the secondary transfer roller 126 and the current flowing through the cleaning unit 180, which corresponds to the current detection circuits IS1 and IS2 of the first and second embodiments.

During image formation, a positive transfer voltage is applied from the power supply 161 to the secondary transfer roller 126 under the control of the ASIC 175 . Then, the toner image on the intermediate transfer belt 123 corresponding to ITB P4 in Examples 1 and 2 is transferred onto the recording medium P sandwiched between the intermediate transfer belt 123 and the secondary transfer roller 126 . Further, the toner remaining on the intermediate transfer belt 123 without being transferred onto the recording medium P is temporarily transferred to the cleaning section 180 by applying a positive voltage from the power supply 162 to the cleaning section 180 under the control of the ASIC 175 . to be recovered. The facing roller 136 corresponds to the driving roller P3 of the first and second embodiments.

On the other hand, when the ASIC 175 turns on the power source 163 during the cleaning process, the negative voltage supplied from the power source 163 is also supplied to the secondary transfer roller 126 and the cleaning section 180 . The toner attached to the secondary transfer roller 126 is transferred to the intermediate transfer belt 123 and removed from the secondary transfer roller 126 by the negative voltage applied to the secondary transfer roller 126 . Further, the toner collected by the cleaning unit 180 is discharged (moved) onto the intermediate transfer belt 123 by the negative voltage applied to the cleaning unit 180 . After that, the toner transferred to the intermediate transfer belt 123 corresponds to the photosensitive drum P5 of Examples 1 and 2 due to the transfer voltage applied to the primary transfer pad 119 which corresponds to the primary transfer pad P6 of Examples 1 and 2. It is transferred (moved) to the photosensitive drum 101 . Then, the toner transferred to the photosensitive drum 101 is removed by a cleaner (not shown) of the photosensitive drum 101 . In the current detection circuit of the power supply device 160, even when the voltage from the power supply of both positive and negative polarities is superimposed, the current path is cut off by the capacitor C1, so the load current flowing through the secondary transfer roller 126 and the cleaning unit 180 is detected. can be detected correctly.

As described above, according to this embodiment, the load current can be detected correctly even when the power supply unit is shared.

C1 capacitors IS1, IS2 current detection circuit P1 secondary transfer roller P2 ICL brushes RE1, RE2 rectifying circuit T1 piezoelectric transformer V1 secondary transfer positive power supply V2 ICL positive power supply V3 secondary transfer negative power supply and ICL negative power supply

Claims (15)

a first power supply that outputs an alternating voltage;
a first rectifying unit and a second rectifying unit connected to the first power supply unit for rectifying the AC voltage output from the first power supply unit and outputting a DC voltage having a predetermined polarity;
a second power supply unit and a third power supply unit that output a DC voltage having a polarity opposite to the predetermined polarity;
a first current detection unit for detecting a current flowing through a first load supplied with a voltage obtained by superimposing the output voltage of the first rectification unit and the output voltage of the second power supply unit;
a second current detection unit for detecting a current flowing through a second load supplied with a voltage obtained by superimposing the output voltage of the second rectification unit and the output voltage of the third power supply unit;
a separation unit that separates the current flowing through the first current detection unit and the current flowing through the second current detection unit;
A power supply device comprising: The separating section includes an input terminal of the first rectifying section to which the alternating voltage from the first power supply section is input, and a second rectifying section to which the alternating voltage from the first power supply section is input. 2. The power supply device according to claim 1, wherein the capacitor is connected in series with the input terminal of the . The first rectification unit or the second rectification unit has a first voltage detection unit that detects the DC voltage output by the first rectification unit or the second rectification unit,
The second power supply unit has a second voltage detection unit that detects the DC voltage output by the second power supply unit,
3. The power supply device according to claim 2, wherein the third power supply section has a third voltage detection section that detects the DC voltage output from the third power supply section. A control unit that controls output voltages of the first power supply unit, the second power supply unit, and the third power supply unit,
Based on detection results of the first voltage detection unit, the second voltage detection unit, and the third voltage detection unit, the control unit controls the first power supply unit, the second power supply unit, 4. The power supply device according to claim 3, wherein the output voltage of said third power supply unit is controlled. 5. The power supply device according to claim 4, wherein the second voltage detection section and the third voltage detection section output detection results of positive potential voltage to the control section. The control unit controls detection results of the first current detection unit and the second current detection unit, detection results of the first voltage detection unit, the second voltage detection unit, and the third voltage detection unit. and calculating the impedance of the first load and the second load based on the detection result, and the first power supply unit according to the calculated impedance of the first load and the second load 6. The power supply device according to claim 4, wherein the output voltages of the second power supply unit, and the third power supply unit are controlled. When the DC voltage of the opposite polarity is not output from the second power supply unit and the DC voltage of the predetermined polarity is output from the first rectifying unit, a predetermined voltage is applied to the first load. 7. The power supply device according to claim 6, further comprising a constant-voltage supply unit that supplies the . 8. The power supply device according to claim 7, wherein the constant voltage supply section has a diode and a Zener diode. The control unit controls the first power supply unit and the third power supply so that current having a constant current value is supplied to the second load based on the detection result of the second current detection unit. 9. The power supply device according to claim 8, wherein the power supply device controls a unit. 10. The power supply device according to any one of claims 1 to 9, wherein said first power supply unit has a piezoelectric transformer. The power supply device according to any one of claims 1 to 10, wherein the first rectifier and the second rectifier have diodes. an image forming unit for forming an image;
a power supply device that supplies a high voltage to the image forming unit,
The power supply device
a first power supply that outputs an alternating voltage;
a first rectifying unit and a second rectifying unit connected to the first power supply unit for rectifying the AC voltage output from the first power supply unit and outputting a DC voltage having a predetermined polarity;
a second power supply unit that outputs a DC voltage having a polarity opposite to the predetermined polarity;
a third power supply unit that outputs a DC voltage having a polarity opposite to the predetermined polarity;
a first current detection unit for detecting a current flowing through a first load supplied with a voltage obtained by superimposing the output voltage of the first rectification unit and the output voltage of the second power supply unit;
a second current detection unit for detecting a current flowing through a second load supplied with a voltage obtained by superimposing the output voltage of the second rectification unit and the output voltage of the third power supply unit;
a separation unit that separates the current flowing through the first current detection unit and the current flowing through the second current detection unit;
An image forming apparatus comprising: The image forming unit includes an image carrier that carries an image, a transfer unit that transfers the image on the image carrier to a recording material, and a cleaning unit that cleans the image carrier,
13. The image forming apparatus according to claim 12, wherein a voltage output from said first power supply section is supplied to said transfer section and said cleaning section. the DC voltage output from the second power supply unit is supplied to the transfer unit;
14. The image forming apparatus according to claim 13, wherein the DC voltage output from the third power supply section is supplied to the cleaning section. further comprising a photosensitive drum on which an image is formed;
15. The image forming apparatus according to claim 13, wherein the image carrier is an intermediate transfer belt onto which the image formed on the photosensitive drum is transferred.

Images