JP2002357991A - Image forming device - Google Patents

Abstract

(57) [Summary] [Problem] By performing sequential residual detection during initialization,
During the initialization, the presence / absence of a developing cartridge loaded in each rotary station is detected. By performing the above, the effects of detecting the presence or absence of the developing cartridge and reducing costs can be obtained. SOLUTION: A developing bias generating means 1 for generating a developing bias, a developing bias applying means 2 for applying a voltage generated by the developing bias generating means to a developing roller in a developing cartridge, and a capacitance between a detection electrode and the developing roller are determined. The capacitance detecting means 3 to be detected, based on the result of comparison and amplification between the developing bias generating means and the capacitance detecting means,
The apparatus further includes a toner remaining amount detecting unit 4 for detecting an amount of toner in the developing cartridge, and sequentially performs residual detection during initialization to detect the presence or absence of each developing cartridge during initialization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic process, and more particularly, to the detection of the presence or absence of a cartridge using a device for detecting the remaining amount of toner.

[0002]

2. Description of the Related Art A schematic configuration of a conventional electrophotographic image forming apparatus having a toner remaining amount detecting means will be described.

FIG. 8 is a sectional view of a conventional image forming apparatus. 100 is an image forming apparatus, 101 is a DC controller. The scanner unit 102 includes a laser unit 103 that emits a laser beam L, a polygon mirror 104 that horizontally scans the laser beam L, a scanner motor 105 that rotates the polygon mirror 104 at a constant speed, an fθ lens 106 that forms an image of the laser beam L, BD indicating starting point of scanning
It comprises a photodetector 107 for detecting a signal and a reflection mirror 108. The laser light L is modulated on / off by an image signal sent from the DC controller 101 to the laser unit 103.

Reference numeral 109 denotes a developing cartridge which can be attached to and detached from the image forming apparatus.
11. It has a stirring rod 112 for stirring the toner.

A rotary unit 113 accommodates four developing units (109y, 109m, 109c, 109Bk).

Reference numeral 114 denotes a photosensitive drum unit that can be attached to and detached from the image forming apparatus 100, and includes a photosensitive drum 115, a waste toner storage unit 116, and a charger 117. In the figure,
Reference numeral 118 denotes a transfer belt, and 119 denotes a transfer belt cleaner.

Reference numeral 120 denotes a cassette for storing recording paper, and 12
1 is a pickup roller for picking up recording paper from a cassette, 122 and 123 are rollers for feeding recording paper,
124 is a conveyance path for conveying the recording paper, 125 and 126 are conveyance rollers, 127 and 128 are registration rollers, 129 is a transfer roller, 130 is a conveyance belt, 131
Denotes a fixing device, and 132 and 133 denote paper discharge rollers.

Next, an image forming operation by an electrophotographic method in a conventional example will be described. DC controller 101
The image signal is transmitted to the laser unit 103 in the scanner unit 102 based on the BD signal detected by the photodetector 107. The laser unit 103 generates a laser beam L based on the image signal.

The laser beam L is applied to a polygon mirror 104, fθ
Charger 1 via lens 106 and reflection mirror 108
The photosensitive drum 11 charged to a predetermined voltage by 17
5, and a latent image based on the image signal is formed on the photosensitive drum 115.

The latent image formed on the photosensitive drum 115 is
The toner image is developed by the developing roller 110. Then, each color 109y, 109 of the developing cartridge 109 is
By sequentially switching m, 109c, and 109Bk, each toner image is developed on the photosensitive drum 115. The image of each color is sequentially transferred to the transfer belt 118, and an image in which four colors of toner are overlapped is formed on the transfer belt.

The fixing roller of the fixing device 131 is internally heated by a halogen heater. By passing through the fixing roller, the toner of each color is melted by heat and fixed as an image, and is discharged to the outside from the paper discharge port by the discharge rollers 132 and 133.

The fixing roller has heaters built in at the top and bottom, and a thermistor element for detecting the surface temperature is in contact with each surface, so that the temperature can be separately monitored and on / off controlled by microcomputer control. .

On the other hand, the recording paper accommodated in the recording paper cassette 120 is picked up by the pickup roller 121 at a predetermined timing, and is picked up by the picture paper rollers 122 and 1.
The transport roller 23 transports the paper to the transport path 124 by the transport roller 12.
5, 126, the registration rollers 127, 1
The sheet is fed up to just before 28 and temporarily stops. Then, at predetermined timing, the registration ports 127, 12
8 is re-fed.

Then, the toner image on the transfer belt 118 is transferred onto the recording paper by the transfer roller 129.

The toner image transferred onto the recording paper is fused to the recording paper by the fixing device 131 with pressure and heat to form a permanent image. After that, the recording paper having the permanent image is discharged to the outside of the image forming apparatus 100 by the discharge rollers 132 and 133.

Next, a method of detecting the remaining amount of toner in a conventional example will be described. FIG. 9 shows a configuration for detecting the remaining amount of toner in a conventional example. Those described in FIG. 8 are denoted by the same reference numerals and description thereof is omitted.

Reference numeral 134 denotes a conductive antenna electrode. 1
35 is a capacitance detecting means, 136 is a reference capacitor C
r, 137 and 138 are diodes, 139 is a constant voltage source,
140 is a reference voltage detection resistor, 141 is a reference voltage detection capacitor, 142 and 143 are diodes, 144 is an antenna electrode output voltage detection resistor, 145 is an antenna electrode output voltage detection capacitor, 146 is an operational amplifier, and 147 is a clamp diode. 148, a high-voltage power supply; 149, a developing bias generator; 150, a DC controller 101;
CPU.

Next, the operation of detecting the remaining amount of toner in the conventional example will be described. First, in the developing bias generator 149, a developing bias in which an AC voltage is superimposed on a DC voltage is generated. The developing bias is applied to the reference capacitor 136 in the capacitance detecting means 135 and the developing roller 110.

The reference capacitor 136 generates an alternating current according to the reference capacitor capacitance Cr.

On the other hand, the electrostatic capacity (hereinafter referred to as Ct) between the developing roller 110 and the antenna electrode 134 is applied to the antenna electrode 134.
An alternating current is generated according to.

The AC current flowing through the reference capacitor 136 is rectified by the resistor 140 and the capacitor 141 via the diode 137 and converted into a DC voltage vr1. Here, the positive input of the operational amplifier 146 is connected to a constant voltage source 139.
Of the DC voltage vr2 (4.0 V) and the DC voltage vr1 are input.

On the other hand, an alternating current flowing through the antenna electrode 134 is rectified by a resistor 144 and a capacitor 145 via a diode 142 and converted into a DC voltage, and is input to a negative input of an operational amplifier 146.

With the above circuit configuration, the operational amplifier 1
Reference numeral 46 outputs a voltage vs corresponding to a difference between the capacitance Cr of the reference capacitor 136 and the capacitance Ct between the developing roller 110 and the antenna electrode 134. Here, the operational amplifier 1
The output voltage Vs at 46 has characteristics expressed by the following equation.

Vs = 4.0−A × (Ct−Cr) × f × Vpp (Equation 1) where A is a predetermined constant, Ct is the capacitance between the developing roller 110 and the antenna electrode 134, and Cr is a reference. Capacitor 1
36, f is the AC frequency of the developing bias, Vp
p is a Peak to Peak voltage of the developing bias.

The output voltage Vs is controlled by a diode 147 connected to the output terminal of the operational amplifier 146.
It is suppressed to below 150 input rated voltage. Hereafter, Vs
Is referred to as a capacitance detection voltage.

FIG. 10 shows the relationship between the capacitance Ct between the developing roller 110 and the antenna electrode 134 and the capacitance detection voltage Vs.

Ce is the capacitance between the developing roller 110 and the antenna electrode 134 when the toner is empty (Empty);
Cf is a capacitance between the developing roller 110 and the antenna electrode 134 when the toner is full (Full), and Cr
= Ce.

Since the toner as a developer has a higher dielectric constant than air, the developing roller 110 and the antenna electrode 134
The more toner is distributed between the developing rollers 110,
The capacitance Ct between the antenna electrodes 134 increases,
The capacitance detection voltage Vs decreases. Thus, the remaining amount of toner can be detected by detecting the capacitance detection voltage Vs.

FIG. 11 is a flow chart of a conventional method for detecting the remaining amount of toner. First, image formation is started in S501, and a developing bias is generated by the developing bias generator 149 in S502.

In step S503, the capacitance detection voltage vs.
The analog / digital conversion is performed by the analog input unit 150, and the CPU 150 detects the detection voltage Vs. S504
Then, the CPU 150 converts the detection voltage Vs into a remaining toner amount based on a conversion table stored in a storage device (not shown), and detects the remaining toner amount in S505. And S5
At 06, for example, a detection result is notified to a display unit (not shown).

Other conventional methods for detecting the remaining amount of toner will be described below.

1. A light emitting element and a light receiving element are provided, and if there is toner between the light emitting element and the light receiving element, light is not received, and the remaining amount of the toner is determined (using the light shielding property of the toner).

2. The remaining amount of the toner is determined based on the weight of the toner container (using the weight of the toner).

3. The number of printed sheets is counted and stored from the start of use by a storage unit that can be written as needed.

[0035]

In the conventional toner remaining amount detection method (sequential remaining amount detection) using an antenna electrode, the presence or absence of a developing device (hereinafter, referred to as CRG) is not detected.

For this reason, CR is used also as the detection level of the sensor in the toner remaining amount detecting means using the light transmission type sensor.
G presence detection was being performed.

However, when the presence or absence of CRG is detected by the toner remaining amount detecting means using the light transmission type sensor,
Due to toner contamination due to the durability of the image forming apparatus, the light transmission type sensor cannot obtain a good reflected light level,
RG presence detection cannot be performed.

Further, the detection of the presence or absence of CRG by the light transmission type sensor has a drawback that the configuration of the image forming apparatus is complicated and the cost is high.

[0039]

SUMMARY OF THE INVENTION The present invention has been made for the purpose of solving the above problems, and has the following arrangement as means for achieving the object.

In the present invention, at least one or more developing devices (hereinafter referred to as CRG) and voltage generating means (hereinafter referred to as developing bias generating means) for generating a voltage (hereinafter referred to as developing bias) including an AC voltage component. ), A voltage application unit that applies a voltage generated by the developing bias generation unit, at least one or more detection electrodes (hereinafter, referred to as antenna electrodes), and a capacitance between the voltage application unit and the antenna electrodes. Rotary-driven image forming, comprising: capacitance detecting means for detecting; and toner remaining amount detecting means for detecting a remaining amount of a developer (hereinafter, referred to as toner) in a CRG based on a detection result by the capacitance detecting means. The apparatus is characterized in that the presence or absence of CRG is detected based on the detection level of the remaining amount of toner by the remaining toner amount detecting means.

Or at least one or more CRGs;
Developing bias generating means for generating a developing bias, a voltage applying unit for applying a voltage generated by the developing bias generating means, at least one or more antenna electrodes, and a capacitance between the voltage applying unit and the antenna electrodes A rotary drive type image forming apparatus comprising: a capacitance detection unit for detecting the voltage; and a voltage conversion unit for converting the capacitance obtained by the capacitance detection unit into a DC voltage. It is characterized in that the presence or absence of a developing device at each rotary station is detected based on the voltage value level by the converting means.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to examples of an image forming apparatus.

[0043]

FIG. 1 is a block diagram showing the configuration of an "image forming apparatus" according to a first embodiment. The functions described in the above-described conventional example are assigned the same numbers, and detailed descriptions thereof will be omitted.

In FIG. 1, 1 is a developing bias generating means for generating a developing bias, 2 is a developing bias applying means for applying the voltage generated by the developing bias generating means 1 to the developing roller 110 in the developing cartridge 109, and 3 is an antenna. Capacitance detecting means 4 for detecting a capacitance between the electrode 134 and the developing roller 110, and a toner 4 in the developing cartridge 109 based on a result of comparison and amplification between the developing bias generating means 1 and the electrostatic capacity detecting means 3. It is a toner remaining amount detecting means for detecting the amount.

FIG. 2 is a flowchart for explaining the operation of this embodiment. FIG. 3 is a table showing the relationship between the toner remaining amount detection range and the CRG presence / absence detection range, and FIG. 4 is a table showing the relationship between the toner remaining amount detection voltage value and the CRG presence / absence detection voltage value. 3 and FIG. 4 will be used to describe the following.

In FIG. 2, when the initialization of the image forming apparatus is started, in step S201, the developing cartridge 1 of the first color is formed.
09 comes to the development position. Then, a developing bias is generated by the developing bias generating means 1 of FIG. 1 (S202).

The developing bias is applied to the developing roller 110 in the first color developing cartridge 109 that has reached the developing position (S203), and the capacitance is detected through the antenna electrode 134 (S204).

The detected capacitance is compared and amplified with the developing bias for detecting the remaining amount of toner of the first color to detect the level of the remaining amount of toner (S205).

At S206, the detection results are shown in FIGS.
If the detected voltage value is 4.0 V or less as shown in FIG.
9 is present (S207), and if the detected voltage value is 4.0 V or more, the developing cartridge 109 is classified as no (S208), and the CPU 15 in the DC controller 101 is classified.
0 (S209).

When the detection of the remaining amount of toner in the first color developing cartridge 109 is completed in S209, the counter is incremented by one in S210, and n = S in S211.
If it is not 4, the process returns to S201, where the second color developing cartridge 109 is moved to the developing position, and the remaining toner amount detection operation and the presence / absence of CRG are performed. The above sequence is sequentially performed for each of the four developing cartridges (109M, 109C,
9Y, 109Bk). And S21
Only when n = 4 with 1, the process proceeds to S212.

In S212, if all of the detection results of the remaining toner amount of the four developing cartridges stored in the CPU 150 in the DC controller 101 in S209 have passed through S207, the toner The remaining amount detection ends.

However, if at least one of the detection results has passed through S208, the process proceeds to S213, in which the user is notified that there is no n-color developing cartridge, and the initialization of the image forming apparatus is stopped. The stop release is performed by loading the insufficient n-color developing cartridge in S214.
The initialization of the image forming apparatus is performed again.

As described above, when the initialization is completed, the presence or absence of CRG can be accurately detected and the user can be notified.

In the present embodiment, a configuration has been described in which one antenna electrode detects the presence or absence of CRG. However, a configuration in which a plurality of antenna electrodes are inserted into each developing cartridge 109 may be used to detect the presence or absence of CRG. Also,
Although the threshold for determining the presence or absence of CRG is set to 4.0 V, the threshold can be set freely depending on the difference in the mechanical structure around the image forming apparatus and the developing cartridge 109. Although the number of the developing cartridges 109 is set to n = 4, it may be set to a desired number. Depending on the timing in the image forming operation, the number of detected toner remaining amounts may be equal to or less than the developing force-the number of cartridges. Is also possible. Further, the detection of the remaining amount of toner and the detection of the presence or absence of CRG during the initialization have been described.

(Embodiment 2) FIG. 5 is a block diagram showing the configuration of Embodiment 2. The functions described in the above-described conventional example are assigned the same numbers, and detailed descriptions thereof will be omitted.

In FIG. 5, 1 is a developing bias generating means for generating a developing bias, 2 is a developing bias applying means for applying the voltage generated by the developing bias generating means 1 to the developing roller 110 in the developing cartridge 109, and 3 is an antenna. The capacitance detecting means 5 for detecting the capacitance between the electrode 134 and the developing roller 110 is a voltage converting means for converting the capacitance detected by the above-mentioned capacitance detecting means into a DC voltage.

FIG. 6 is a flowchart for explaining the operation of this embodiment. FIG. 7 shows capacitance detection and CRG
The relationship with the presence / absence detection range is shown in a table, and FIG. 7 is used to describe the operation of this embodiment.

In FIG. 6, when the initialization of the image forming apparatus is started, in step S601, the developing cartridge 1 of the first color is set.
09 comes to the development position. Then, a developing bias is generated by the developing bias generating means 1 of FIG. 5 (S602).

The developing bias is applied to the developing roller 110 in the first color developing cartridge 109 that has reached the developing position (S603), and the capacitance is detected through the antenna electrode 134 (S604).

The detected capacitance is converted into a DC voltage in S605, and is compared and amplified with the voltage generated by the developing bias generating means 1.

In step S606, as shown in FIG. 7, the detected voltage value is set at 4.0 V as a threshold. If the detected voltage value is 4.0 V or less, the developing cartridge 109 is present (S607), and the detected voltage value is 4 If the voltage is equal to or higher than 0.0 V, the developing cartridge 109 is classified as no (S608) and stored in the CPU 150 in the DC controller 10 (S609).

When the detection of the capacitance of the first color developing cartridge 109 is completed in S609, the counter is incremented by one in S610, and n = 4 in S611.
If not, the flow returns to S601 to move the second color developing cartridge 109 to the developing position, and the capacitance detection operation and the determination of the presence or absence of CRG are performed.

The above-described sequence is sequentially performed with four developing cartridges (109M, 109C, 109Y, and 109Bk).
Execute for Then, only when n = 4 in S611, the process proceeds to S612.

In S612, if all the detection results of the electrostatic capacity detection results for the four developing cartridges already stored in the CPU 150 in the DC controller 101 in S609 have passed through S607,
The capacitance detection ends.

However, if at least one of the detection results has passed through S608, the process proceeds to S613, where the user is notified that there is no n-color developing cartridge, and the initialization of the image forming apparatus is stopped.

When the stop is released, the image forming apparatus is initialized again by loading the insufficient n-color developing cartridge in step S614.

As described above, when the initialization is completed, the presence or absence of CRG can be accurately detected and the user can be notified.

In the present embodiment, a configuration has been described in which one antenna electrode detects the presence or absence of CRG. However, a configuration in which a plurality of antenna electrodes are inserted into each developing cartridge 109 may be used to detect the presence or absence of CRG. Also,
Although the threshold for determining the presence or absence of CRG is set to 4.0 V, the threshold can be set freely depending on the difference in the mechanical structure around the image forming apparatus and the developing cartridge 109. Although the number of the developing cartridges 109 is set to n = 4, the number may be set to a desired number, and the number of detected capacitances may be set to be equal to or less than the number of the developing cartridges depending on the timing of the image forming operation. It is. Furthermore, the detection of the capacitance and the detection of the presence or absence of the CRG during the initialization have been described. However, the present invention is not limited to this.

In this embodiment, when the above-mentioned initialization is completed, the presence or absence of CRG can be accurately detected and the user can be notified.

Further, the configuration has been described in which one antenna electrode detects the presence or absence of CRG. However, a configuration in which a plurality of antenna electrodes are inserted into each developing device 109 may be used to detect the presence or absence of CRG.

Further, the threshold value for judging the presence or absence of CRG is set to 4.0 V. However, the threshold value can be freely set depending on the difference in the mechanical structure around the image forming apparatus and the developing cartridge 109.

Then, the number of the developing cartridges 109 is set to n.
= 4, but may be set to a desired number, and the number of detected capacitances may be equal to or less than the number of developing cartridges depending on the timing of the image forming operation.

In the present invention, the detection of the capacitance and the presence / absence of CRG during the initialization have been described. However, the present invention is not limited to this, and the detection may be performed at a timing other than the initialization.

[0074]

As described above, according to the present invention, a developing bias is applied during initialization of an image forming apparatus, and the presence or absence of CRG at each rotary station is detected based on the detection result from the capacitance detecting means. There are effects that can be done.

Further, since the light transmission type CRG presence / absence detection system can be eliminated, the cost can be greatly reduced.

Further, as in the case of the light transmission type sensor, the presence of CRG cannot be detected due to toner contamination due to the durability of the image forming apparatus.
It is possible to perform G presence detection.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a toner remaining amount detecting unit according to a first embodiment.

FIG. 2 is a flowchart of toner remaining amount detection in the first embodiment.

FIG. 3 illustrates a relationship between a remaining amount of toner and a detection voltage according to the first exemplary embodiment.

FIG. 4 is a diagram illustrating the detection voltage of the remaining amount of toner and C in the first embodiment.
Relation of RG presence detection voltage

FIG. 5 is a configuration diagram of a capacitance detection unit according to a second embodiment.

FIG. 6 is a flowchart of capacitance detection according to the second embodiment.

FIG. 7 shows a relationship between capacitance and detection voltage in the second embodiment.

FIG. 8 is a configuration diagram of an image forming apparatus in a conventional example.

FIG. 9 is a configuration diagram of a toner remaining amount detecting unit in a conventional example.

FIG. 10 shows a relationship between a remaining amount of toner and a detection voltage in a conventional example.

FIG. 11 is a flowchart for detecting the remaining amount of toner in a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 developing bias generating means 2 developing bias applying means 3 electrostatic capacity detecting means 4 developer remaining amount detecting means 100 image forming apparatus 101 DC controller 102 scanner unit 103 laser unit 104 polygon mirror 105 scanner motor 106 fθ lens 107 photodetector 108 Reflecting mirror 109 Developing cartridge 110 Developing roller 111 Toner container 112 Stirrer bar 113 Rotary unit 114 Photosensitive drum unit 115 Photosensitive drum 116 Waste toner container 117 Charger 118 Transfer belt 119 Transfer belt cleaner 120 Cassette 121 Pickup rollers 122, 123 Feed roller 124 transport path 125, 126 transport roller 127, 128 registration roller 129 transfer roller 130 transport belt 13 Fixing devices 132, 133 Discharge roller 134 Antenna electrode 135 Capacitance detecting means 136 Reference capacitor Cr 137, 138 Diode 139 Constant voltage power supply 140 Reference voltage detecting resistor 141 Reference voltage detecting capacitor 142, 143 Diode 144 Antenna electrode output voltage detecting resistor 145 Antenna electrode output voltage detection capacitor 146 Operational amplifier 147 Clamp diode 148 High voltage power supply 149 Developing bias generator 150 CPU

Continued on the front page F-term (reference) 2H027 DA01 DA27 DD02 DE05 DE07 DE10 EA05 EA15 EC06 EC09 EC20 ED09 EE07 EF06 ZA01 2H030 AA07 AD16 AD19 BB24 BB33 BB34 2H073 BA01 BA13 BA25 BA41 BA45 CA22 2H077 AD35 BA09 DA15 DA24 DA59 DA15 DA15 DA24 DA15 DA24 DA15 DB14 GA13

Claims (12)

[Claims] A voltage generator configured to generate a voltage including an AC voltage component; a voltage application unit configured to apply a voltage generated by the voltage generator;
At least one or more detection electrodes, capacitance detection means for detecting capacitance between the voltage applying unit and the detection electrodes, and a developer in a developing device based on a detection result by the capacitance detection means In a rotary drive type image forming apparatus having a developer remaining amount detecting means for detecting a remaining amount, the presence or absence of a developing device is detected by a detection level of the remaining developer amount by the developer remaining amount detecting means. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the detection of the presence or absence of the developing device based on the detection level of the remaining amount of the developer is performed during initialization of the image forming apparatus. 3. The image forming apparatus according to claim 1, wherein the developing device is at least one cartridge detachable from a main body. 4. The image forming apparatus according to claim 1, wherein at least one of the voltage applying units is a developing roller. 5. The image forming apparatus according to claim 1, wherein said image forming apparatus is a rotary-driven color image forming apparatus for at least two colors. 6. The image forming apparatus according to claim 1, wherein the developing device has a voltage application unit that applies a voltage generated by the voltage generation unit. 7. At least one or more developing devices, voltage generating means for generating a voltage including an AC voltage component, and a voltage applying unit for applying a voltage generated by the voltage generating means.
At least one or more detection electrodes, capacitance detection means for detecting capacitance between the voltage applying unit and the detection electrodes, and converting the capacitance obtained by the capacitance detection means into a DC voltage An image forming apparatus of a rotary drive type having a voltage conversion unit, wherein the presence or absence of a developing unit at each rotary station is detected based on a voltage value level of the voltage generation unit and the voltage conversion unit. 8. The image forming apparatus according to claim 7, wherein the detection of the presence or absence of the developing device based on the voltage value level by the voltage applying unit and the voltage conversion unit is performed during initialization of the image forming apparatus. 9. The image forming apparatus according to claim 7, wherein the developing device is at least one or more cartridges detachable from a main body. 10. At least one of said voltage applying units,
The image forming apparatus according to claim 7, wherein the image forming apparatus is a developing roller. 11. The image forming apparatus according to claim 7, wherein the image forming apparatus is a rotary-driven color image forming apparatus for at least two colors. 12. The image forming apparatus according to claim 7, wherein the developing device has a voltage application unit that applies a voltage generated by the voltage generation unit.