JP2007322727A - Power supply, image forming apparatus, and control unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To insure that process conditions of a mechanism used as a load can be exactly adjusted by exactly discriminating an electrostatic capacitance of the load at a low cost with simple configuration. <P>SOLUTION: There are provided an AC transformer 1024 which boosts the AC voltage of an AC power supply for biasing and is connected to the load to constitute a series resonance circuit, a frequency controller 1011 which detects the resonance frequency of the AC transformer 1024, a capacitance discrimination section 1013 which discriminates the capacitance of the development device 50 used as the load from a resonance frequency detected by the frequency controller 1011, and a controller 101 which changes and controls the development bias of the development device 50 based on the capacitance discriminated by the capacitance discrimination section 1013. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply apparatus, an image forming apparatus, and a control apparatus, and more particularly to a technique for setting conditions such as a developing bias to an appropriate value in accordance with a change with time.

In an electrophotographic image forming apparatus, toner is supplied from a developing device to an electrostatic latent image on the surface of a photosensitive drum to form a toner image, and the toner image is transferred onto a recording sheet by a transfer roller. Thus, the toner image is fixed on the recording paper. In the developing process by the developing device, it is necessary to change and set the developing bias voltage or the like to an appropriate value in accordance with a change with time of the developing device or a change in the surrounding environment. As a technique for setting the developing bias voltage or the like to an appropriate value, for example, paying attention to a change in the capacitance of a mechanism serving as a load of the power supply device, the capacitance is measured to determine the process conditions of the developing device. There is a technology to control. For example, an image forming apparatus that controls the developing bias voltage by measuring the amount of toner tribo (see Patent Document 1 below), or an image forming apparatus that measures capacitance from the oscillation frequency of a self-excited oscillation circuit (Patent Document 2 below). Have been proposed).
JP 2004-102181 A JP 2001-290349 A

  However, in the case of the image forming apparatus disclosed in each of the above patent documents, the configuration for measuring the capacitance is complicated, and there is a problem that the cost is high. In addition, there is a conventional technique for measuring the capacitance by measuring the load current of the transformer for boosting the AC voltage. In this case, the error is small if the load is only the capacitance component, but actually the resistance component is not. Because there is an error.

  The present invention has been made in order to solve the above-described problems. It is possible to accurately determine the capacitance of a load with a simple configuration and low cost, and to accurately adjust the process conditions of a mechanism serving as a load. It is for the purpose.

The invention described in claim 1 of the present invention boosts the AC voltage of the bias AC power source and is connected to a load to form a series resonance circuit;
Resonance frequency detection means for detecting the resonance frequency of the transformer;
Capacitance determination means for determining the capacitance of the load from the resonance frequency detected by the resonance frequency detection means;
And a control unit that changes and controls a process condition of the mechanism serving as the load based on the capacitance determined by the capacitance determination unit.

The invention according to claim 5 boosts the AC voltage of the bias AC power source, and also detects a resonance frequency of a transformer connected to a load and constituting a series resonance circuit,
Capacitance determination means for determining the capacitance of the load from the resonance frequency detected by the resonance frequency detection means;
And a control unit configured to change and control a process condition of the mechanism serving as the load based on the capacitance determined by the capacitance determination unit.

  In these configurations, the resonance frequency detection means detects the resonance frequency of the transformer that forms the series resonance circuit with the load, and the capacitance determination means determines the capacitance of the load from the detected resonance frequency. Then, the control means changes and controls the process condition of the mechanism serving as a load based on the capacitance. Here, since the configuration for detecting the resonance frequency and obtaining the capacitance from the resonance frequency is employed, the capacitance can be determined with a simple configuration and at a low cost. The load can be equivalent to a parallel connection of a capacitance and a resistor. However, since the capacitance is dominant, it is possible to accurately determine the capacitance from the detected resonance frequency.

  The invention according to claim 2 is the power supply device according to claim 1 or 2, wherein the resonance frequency detecting means sweeps the frequency of the AC voltage, and the primary current of the transformer is The lowest frequency is detected as the resonance frequency.

  In this configuration, when the transformer resonates, the reactive power is reduced and the efficiency is improved. Based on the fact that the primary current of the transformer is reduced, the resonance frequency detecting means performs the frequency sweep of the AC voltage on the primary side of the transformer. By detecting the frequency at which the current has the lowest value as the resonance frequency, the resonance frequency can be accurately detected. In addition, the resonance frequency can be detected with a simple configuration without requiring a complicated configuration.

  Further, the invention according to claim 3 is the power supply device according to claim 1, wherein the capacitance determination means stores a capacitance corresponding to a plurality of resonance frequencies. And a capacitance specifying unit that specifies the capacitance of the load by reading out the capacitance corresponding to the resonance frequency detected by the resonance frequency detecting means from the capacitance storage unit. is there.

  According to this configuration, since the capacitance specifying unit reads the capacitance corresponding to the resonance frequency detected by the resonance frequency detecting unit from the capacitance storage unit, the capacitance of the load is specified. The determination of the capacitance of the load based on the detected resonance frequency can be realized with a simple configuration.

The invention according to claim 4 is a power supply device according to any one of claims 1 to 3,
An image carrier on which an electrostatic latent image is formed;
A developer carrying member that attaches a developer to the image carrying member; and a developing bias applying unit that applies a developing bias voltage to the developer carrying member; and a developing unit serving as a load of the transformer;
The control unit is an image forming apparatus that sets a developing bias voltage applied to the developer carrying member by the developing bias applying unit based on the capacitance determined by the capacitance measuring unit.

  According to this configuration, the resonance frequency detecting means detects the resonance frequency of the transformer that constitutes the series resonance circuit with the load, and the electrostatic capacity determination means detects the electrostatic frequency of the developing bias applying means from the detected resonance frequency. The capacity is discriminated, and the control means changes and controls the developing bias voltage of the developing bias applying means. As a result, it is possible to accurately determine the capacitance of the developing bias applying means with a simple configuration and low cost.

  According to the first and fifth aspects of the invention, it is possible to accurately determine the capacitance of the load with a simple configuration and low cost.

  According to the second aspect of the present invention, the resonance frequency can be accurately detected with a simple configuration without requiring a complicated configuration.

  According to the third aspect of the present invention, the determination of the capacitance of the load based on the detected resonance frequency can be realized with a simple configuration.

  According to the fourth aspect of the present invention, it is possible to accurately determine the capacitance of the developing bias applying unit with a simple configuration and low cost.

  Hereinafter, a power supply apparatus, an image forming apparatus, and a control apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of a printer to which a power supply device and a control device according to an embodiment of the present invention are applied. A printer (an example of an image forming apparatus) 10 includes a sheet storage unit 12 that stores sheets P to be subjected to a printing process, and one sheet (a transfer target) that is fed from a sheet bundle P1 stored in the sheet storage unit 12. The apparatus main body 11 includes an image forming unit 13 that performs an image transfer process on the material P) and a fixing unit 14 that performs a fixing process on the paper P on which the transfer process has been performed by the image forming unit 13. In addition, a paper discharge unit 15 for discharging the paper P on which the fixing process has been performed by the fixing unit 14 is provided on the top of the apparatus main body 11.

  A predetermined number (one in the present embodiment) of paper cassettes 121 is provided in the paper storage unit 12 so as to be detachable from the apparatus main body 11. A pickup roller 122 is provided at the upstream end (right side in FIG. 1) of the paper cassette 121 to feed out the paper P one by one from the paper bundle P1. The paper P fed out of the paper cassette 121 by driving the pickup roller 122 is supplied to the image forming unit 13 through the paper feed conveyance path 123 and the registration roller pair 124 provided at the downstream end of the paper feed conveyance path 123. Paper.

  The image forming unit 13 performs a transfer process on the paper P based on image information transmitted from a computer or the like. The image forming unit 13 is configured such that the charging roller 30, exposure light, and the like along the peripheral surface of the photosensitive drum (image carrier) 20. A device 40, a developing device 50, a transfer roller 60, and a drum cleaning device 70 are provided.

  The photosensitive drum 20 is for forming an electrostatic latent image and a toner image (visible image) along the electrostatic latent image on the peripheral surface. For example, an amorphous silicon layer is laminated on the peripheral surface. Yes.

  The charging roller 30 forms a uniform charge on the peripheral surface of the photoconductive drum 20, and charges the photoconductive drum 20 while being rotated while the peripheral surface is in contact with the peripheral surface of the photoconductive drum 20. Give. The power supply device for charging bias according to the present invention is provided in the printer 10 in order to supply a charging bias voltage to the charging roller 30.

  The exposure device 40 irradiates the peripheral surface of the rotating photosensitive drum 20 with a laser beam to which intensity is applied based on image data transmitted from an external device such as a computer, so that the circumference of the photosensitive drum 20 is rotated. An electrostatic latent image is formed on the peripheral surface of the photosensitive drum 20 by erasing the charge of the laser beam irradiated portion on the surface.

  The developing device (developing unit) 50 supplies toner to the peripheral surface of the photosensitive drum 20 to attach the toner to the portion where the electrostatic latent image is formed on the peripheral surface, and thereby the peripheral surface of the photosensitive drum 20. To form a toner image. The developing device 50 includes a mag roller 501 (developer carrying member) for attaching a developer to the photosensitive drum 20, and a developing bias applying unit (developing bias applying means) 502 for applying a developing bias voltage to the mag roller 501. An AC voltage from a power supply device (details will be described later) according to an embodiment of the present invention is applied to the developing device 50 (developing bias applying unit 502).

  The transfer roller 60 transfers a positively charged toner image formed on the peripheral surface of the photosensitive drum 20 to the paper P with respect to the paper P sent to a position immediately below the photosensitive drum 20. A negative charge having a polarity opposite to that of the toner image is applied to the paper P.

  Accordingly, the paper P that has reached the position immediately below the photosensitive drum 20 is pressed and held between the transfer roller 60 and the photosensitive drum 20, while the toner image on the circumferential surface of the positively charged photosensitive drum 20 is negatively charged. The sheet P is peeled off toward the surface of P, whereby the transfer process is performed on the sheet P.

The fixing unit 14 performs a fixing process by heating the toner image of the paper P that has been subjected to the transfer process by the image forming unit 13, and includes a heat roller 141 in which an energizing heating element is mounted, and the heat roller 141. The pressure roller 142 is arranged so that the peripheral surfaces are opposed to each other at the lower part. Then, the paper P after the transfer process is composed of a heat roller 141 that is driven to rotate clockwise around the roller center, and a pressure roller 142 that is driven to rotate counterclockwise around the roller center. By passing through the nip portion between them, heat from the heat roller 141 is obtained and the fixing process is performed. The paper P subjected to the fixing process is discharged to the paper discharge unit 15 through the paper discharge conveyance path 143.

  The paper discharge unit 15 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 151 for receiving the discharged paper P is formed at the bottom of the recess.

  Next, the configuration of the power supply apparatus 100 according to an embodiment of the present invention will be described. FIG. 2 is a circuit diagram showing a power supply device according to an embodiment of the present invention. The power supply apparatus 100 according to an embodiment of the present invention boosts the AC voltage of a bias AC power supply and supplies it as a developing bias to the developing apparatus 50. The developing device 50 that is a load of the power supply device 100 is shown by an equivalent circuit in which a capacitor and a resistor are connected in parallel. Further, the developing device 50 is connected in series with an AC transformer 1024 described later to constitute a series resonance circuit.

  The power supply apparatus 100 includes a control unit 101, an AC (alternating current) voltage generation circuit 102, a DC (direct current) voltage generation circuit 103, and a voltage detection circuit 104.

  The control unit 101 performs control necessary for generating and correcting the development bias. The control unit 101 includes a frequency control unit 1011, a voltage detection unit 1012, and a capacitance determination unit 1013.

  The frequency control unit (resonance frequency detection means) 1011 generates and outputs a clock signal (HVCLK) that determines the frequency of the AC component of the developing bias voltage. The frequency control unit 1011 performs control to sweep the frequency of the AC component of the developing bias voltage when detecting the resonant frequency of the series resonant circuit including the AC transformer 1024 and the developing device 50 connected in series. Further, the resonance frequency detection unit 1015 included in the frequency control unit 1011 resonates the frequency when the voltage detection unit 1012 detects the lowest voltage indicating resonance when sweeping the frequency of the AC component of the development bias voltage. The frequency is stored, and the value of the resonance frequency is sent to the capacitance storage unit 1016.

  The voltage detection unit (frequency detection unit) 1012 sequentially acquires voltage values at each frequency from the voltage detection circuit 104 when the frequency control unit 1011 performs frequency sweeping at the time of detecting the resonance frequency. The voltage detection unit 1012 sends an instruction signal to the resonance frequency detection unit 1015 when the acquired voltage value becomes the minimum value, and causes the resonance frequency detection unit 1015 to detect the frequency at the time of the minimum voltage value as the resonance frequency. .

  An electrostatic capacity determination unit (electrostatic capacity determination unit) 1013 determines the electrostatic capacity of the developing device 50 based on the resonance frequency detected by the resonance frequency detection unit 1015. The capacitance determining unit 1013 includes a capacitance storage unit 1016 and a capacitance specifying unit 1017. The electrostatic capacity storage unit 1016 stores a table indicating a relationship with each electrostatic capacity corresponding to a plurality of resonance frequencies. The capacitance specifying unit 1017 specifies the capacitance of the developing device 50 by reading out the capacitance corresponding to the resonance frequency detected by the resonance frequency detection unit 1015 from the capacitance storage unit 1016.

  Note that the developing device 50 serving as a load of the AC transformer 1024 has its mag roller coupled to the photosensitive drum in a contact state or a non-contact state. The developing device 50 serving as a load can be equivalent to a parallel connection of a capacitor (capacitance) and a resistor (resistance), but the capacitance is dominant. This capacitance varies depending on the film thickness of the photoconductor drum, the dielectric constant of the toner, the amount of tribo, the gap between the roller and the photoconductor, etc. Can be corrected to an optimum value.

  Based on the capacitance thus identified, the control unit (control means) 101 changes the AC voltage control signal output to the AC amplitude control circuit 1021, thereby changing the AC voltage amplitude of the bias AC power supply. Thus, the developing bias is controlled to a value corresponding to the specified capacitance.

  The AC (alternating current) voltage generation circuit 102 includes an AC amplitude control circuit 1021, a frequency control circuit 1022, an AC transformer driving circuit 1023, and an AC transformer (transformer) 1024. The AC amplitude control circuit 1021 is a circuit that controls the amplitude of the AC voltage of the bias AC power supply, and controls the amplitude based on an AC voltage control signal from the control unit 101. The frequency control circuit 1022 converts the AC voltage control signal from the AC amplitude control circuit 1021 into a rectangular wave using the clock signal output from the frequency control unit 1011. The AC transformer drive circuit 1023 amplifies the rectangular wave signal by the amplifier circuit U1 and outputs the amplified signal to the AC transformer 1024 for boosting the AC voltage. When the AC transformer 1024 is driven in this way, an AC voltage of about 1.6 KVp-p, for example, is generated at the OUTPUT end. This AC voltage is applied to the mag roller or sleeve roller of the developing device 50.

  The DC voltage generation circuit 103 includes a DC voltage control circuit 1031 and a DC voltage supply unit 1032. The DC voltage control circuit 1031 turns on / off the output of the DC voltage by the DC voltage supply unit 1032 based on the analog DC voltage control signal output from the control unit 101. The DC voltage supply unit 1032 is connected to the secondary side of the AC transformer 1024 that generates an AC component.

  The voltage detection circuit (frequency detection means) 104 is a circuit that detects the voltage of the amplifier circuit of the AC transformer drive circuit 1023 that drives the AC transformer 1024. When the AC transformer 1024 resonates with the developing device 50 as a load, the reactive power is reduced, so that the efficiency is improved and the primary current (drive current) of the AC transformer 1024 is reduced. Therefore, the frequency at which the drive current decreases most during the frequency sweep of the frequency control unit 1011 is the resonance frequency. Based on this, the voltage detection circuit 104 is provided for detecting the drive current of the AC transformer 1024 based on the fluctuation of the voltage of the AC transformer 1024.

  The voltage value detected by the voltage detection circuit 104 is output to the voltage detection unit 1012 of the control unit 101 through the operational amplifier U2. As described above, when the frequency control unit 1011 sweeps the frequency of the AC component of the developing bias voltage when detecting the resonance frequency, the voltage of the amplifier circuit U1 of the AC transformer driving circuit 1023 at the time of the sweep is detected by the voltage detection. It is sequentially detected by the circuit 104. When the voltage detection unit 1012 detects the minimum voltage value, the voltage detection unit 1012 outputs an instruction signal that causes the resonance frequency detection unit 1015 to detect the frequency at the time when the minimum voltage value is detected as the resonance frequency.

  That is, when the power supply device 100 is driven, Q3 is first turned on by the DC voltage control signal from the control unit 101, and the developing bias DC voltage generated at the output terminal OUTPUT is set to zero. Next, the AC voltage control signal sets the amplitude of the AC voltage of the bias AC power supply. Then, the AC signal HVCLK for driving the transformer from the control unit 101 enters the base of Q2, and the AC voltage is converted into a rectangular wave and amplified by the amplifier circuit U1. By driving the AC transformer 1024 with this amplified AC voltage, an AC voltage of about 1.6 KVp-p, for example, is generated at the OUTPUT end. This AC voltage is applied to the mag roller or sleeve roller of the developing device 50.

  On the other hand, when a load current flows with an AC voltage applied to the mag roller or sleeve roller, the drive current on the primary side of the AC transformer 1024 for boosting the AC voltage also fluctuates. Therefore, the drive current of the AC transformer 1024 can be detected by measuring the current of the transistor built in the amplifier circuit U1.

  R1 of the voltage detection circuit 104 shown in FIG. 2 is a resistor that detects the drive current of the AC transformer 1024. Since the voltage generated at both ends of R1 is proportional to the drive current, if the voltage drop generated at both ends of R1 is amplified by the operational amplifier U2 and A / D converted by the control unit 101, the increase or decrease of the drive current is increased. It can be read as a digital value.

  The control device according to the present invention includes a voltage detection circuit 104, a voltage detection unit 1012, a frequency control unit 1011, a capacitance determination unit 1013, and a control unit 101.

  Next, development bias change control by the power supply apparatus 100 will be described with reference to FIG. 2 and FIGS. 3 to 5. 3 is a flowchart showing development bias change control by the power supply apparatus 100, FIG. 4 is a graph showing the relationship between the sweep frequency and the detected voltage, and FIG. 5 is a graph showing the relationship between the resonance frequency and the capacitance. .

  First, the control unit 101 determines whether or not the development bias change mode (capacitance measurement mode) is set by the operator (S1). Here, when the development bias change mode is set (YES in S1), the development bias change control after S2 is entered. When the developing bias change mode is not set (NO in S1), drive control of the power supply device 100 is performed when the developing device 50 is driven during normal image formation (S8). Here, the control unit 101 determines whether or not to enter development bias change control depending on whether or not the development bias change mode is set. However, when the printer 10 is turned on, the development bias change is determined. Regardless of whether the mode is set, it is preferable to enter the development bias change control. This is to enable development processing with an optimum development bias according to the state of the developing device 50 and the surrounding environment when the power is turned on.

  When the development bias change control is entered, the frequency control unit 1011 sweeps the frequency of the AC component of the development bias voltage in order to detect the resonance frequency of the AC transformer 1024 with the development device 50 as a load (S2). During this frequency sweep, the voltage detection circuit 104 sequentially detects the voltage of the amplifier circuit of the AC transformer drive circuit 1023 that drives the AC transformer 1024 and outputs the voltage to the voltage detection unit 1012. The voltage detection unit 1012 detects whether or not the voltage of the amplifier circuit of the AC transformer driving circuit 1023 sent from the voltage detection circuit 104 has reached the minimum voltage value (S3). Here, the voltage detection unit 1012 regards the voltage to be detected as the lowest point, not the absolute value. That is, instead of determining whether the voltage value to be detected has reached a predetermined value, the lowest voltage value among the voltage values obtained during the frequency sweep is detected.

  When the voltage detection unit 1012 detects that the voltage of the amplifier circuit of the AC transformer drive circuit 1023 has reached the minimum voltage value (YES in S3), the voltage detection unit 1012 sends an instruction signal for causing the resonance frequency detection unit 1015 to acquire the resonance frequency. (S4). Receiving the instruction signal from the voltage detection unit 1012, the resonance frequency detection unit 1015 detects the frequency at which the lowest voltage value is detected by the voltage detection unit 1012 as the resonance frequency (S5).

  When the frequency of the AC component of the developing bias voltage is swept, for example, as shown in FIG. 4, the voltage of the amplifier circuit U1 of the AC transformer driving circuit 1023 changes according to the frequency. As described above, when the AC transformer 1024 resonates with the developing device 50 as a load, the reactive power is reduced, the efficiency is improved, and the primary current of the AC transformer 1024 is reduced. Accordingly, the frequency at which the minimum voltage value is reached in FIG. 4 is the resonance frequency.

  The capacitance determination unit 1013 reads the capacitance corresponding to the resonance frequency detected by the resonance frequency detection unit 1015 from the capacitance storage unit 1016 (S6). For example, as shown in FIG. 5, the capacitance changes in accordance with the resonance frequency. Therefore, the capacitance storage unit 1016 includes a plurality of resonance frequencies and capacitances corresponding to the resonance frequencies. Is stored.

  Based on the identified capacitance, the control unit 101 changes the AC voltage control signal output to the AC amplitude control circuit 1021, thereby changing the amplitude of the AC voltage of the bias AC power supply, and developing the AC voltage control signal. The developing bias of the apparatus 50 is set to a value suitable for the received capacitance (S7).

  By performing such development bias change control, the capacitance can be accurately determined with a simple configuration and low cost.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above embodiment, FIG. 2 shows the power supply device 100 according to one embodiment of the present invention as a power supply device for development bias, but the power supply device 100 according to one embodiment of the present invention It can be applied as a power supply device for use, for example, a charging bias, and the charging bias can be changed and controlled to an appropriate value in accordance with the capacitance.

  Further, it is possible to detect the presence / absence of toner in the developing device 50, the remaining amount of toner, and the like based on a change in electrostatic capacitance detected by the power supply device 100.

1 is a diagram illustrating a schematic configuration of a printer to which a power supply device and a control device according to the present invention are applied. It is a circuit diagram which shows the power supply device which concerns on one Embodiment of this invention. It is a flowchart which shows the development bias change control by a power supply device. It is a figure which shows the relationship between a sweep frequency and a detection voltage with a graph. It is a figure which shows the relationship between a resonant frequency and an electrostatic capacitance with a graph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Printer 100 Power supply device 20 Photosensitive drum 30 Charging roller 40 Exposure apparatus 50 Development apparatus 501 Mag roller 502 Development bias application part 101 Control part 1011 Frequency control part 1012 Voltage detection part 1013 Capacitance discrimination part 1015 Resonance frequency detection part 1016 Electrostatic Capacitance storage unit 1017 Capacitance specifying unit 102 AC voltage generation circuit 1021 Amplitude control circuit 1022 Frequency control circuit 1023 Transformer drive circuit 1024 AC transformer 103 DC voltage generation circuit 1031 DC voltage control circuit 1032 DC voltage supply unit 104 Voltage detection circuit U1 Amplification Circuit U2 operational amplifier

Claims (5)

A transformer that boosts the AC voltage of the bias AC power source and is connected to a load to form a series resonance circuit;
Resonance frequency detection means for detecting the resonance frequency of the transformer;
Capacitance determination means for determining the capacitance of the load from the resonance frequency detected by the resonance frequency detection means;
A power supply apparatus comprising: control means for changing and controlling process conditions of the mechanism serving as the load based on the capacitance determined by the capacitance determination means.   2. The power supply device according to claim 1, wherein the resonance frequency detection unit sweeps the frequency of the AC voltage and detects the frequency at which the primary side current of the transformer is the lowest value as the resonance frequency.   The electrostatic capacity discriminating means includes an electrostatic capacity storage unit that stores each electrostatic capacity corresponding to a plurality of resonance frequencies, and an electrostatic capacity corresponding to the resonance frequency detected by the resonance frequency detecting means. The power supply device according to claim 1, further comprising: a capacitance specifying unit that specifies the capacitance of the load by reading from the capacitance storage unit. A power supply device according to any one of claims 1 to 3,
An image carrier on which an electrostatic latent image is formed;
A developer carrying member that attaches a developer to the image carrying member; and a developing bias applying unit that applies a developing bias voltage to the developer carrying member; and a developing unit serving as a load of the transformer;
The image forming apparatus in which the control unit sets a developing bias voltage applied to the developer carrying member by the developing bias applying unit based on the capacitance determined by the capacitance measuring unit. Resonance frequency detection means for boosting the AC voltage of the bias AC power source and detecting the resonance frequency of a transformer connected to a load and constituting a series resonance circuit;
Capacitance determination means for determining the capacitance of the load from the resonance frequency detected by the resonance frequency detection means;
A control device comprising: control means for changing and controlling a process condition of the mechanism serving as the load based on the capacitance determined by the capacitance determination means.

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