Image forming apparatus

Abstract

To accurately control a surface potential of an image carrier to a desired potential with a simple circuit configuration.SOLUTION: An image forming apparatus comprises: an image carrier; a power supply that generates a voltage subjected to constant voltage control; a voltage application member to which the voltage generated by the power supply is applied; a current detection unit that detects a current flowing from the power supply to the voltage application member; and a control unit that controls output voltage of the power supply. The control unit acquires, from the current detection unit, a first current feedback signal generated immediately after the start of output from the power supply, and a second current feedback signal generated after the lapse of a predetermined time from the start of output from the power supply, and calculates output current based on the first current feedback signal and the second current feedback signal.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, surface potential control techniques for image carriers, such as photoreceptors, have been known, which involve detecting the state of a charged component and controlling the voltage applied to the charged component in order to set the surface potential of the image carrier to a desired potential.

[0003] For example, to reduce errors when detecting the charging current of an image carrier, there is a technique to store the voltage of the current feedback signal in an unloaded state (no-load current) and determine the load current by subtracting the no-load current from the voltage of the current feedback signal when a load is connected. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, conventional technology requires a constant current and constant voltage control switching mechanism for high-voltage power supplies used for charging, which complicates the circuit configuration and increases the circuit size and cost.

[0005] Furthermore, in the case of a technology that subtracts the no-load current from the voltage of the current feedback signal when a load is connected, it is necessary to obtain the voltage of the current feedback signal in the no-load state. Therefore, if one tries to implement this in actual use, it is necessary to provide a mechanism to separate the contact with the charging roller, or to obtain the voltage of the current feedback signal with the PCDU (Photo Conductor Development Unit) in an unset state, which complicates the circuit configuration and increases the circuit size and cost.

[0006] The present invention has been made in view of the above, and aims to provide an image forming apparatus that can control the surface potential of an image carrier to a desired potential with high precision using a simple circuit configuration. [Means for solving the problem]

[0007] To solve the above-mentioned problems and achieve the objective, the present invention provides an image forming apparatus comprising: an image carrier; a power supply that generates a constant voltage controlled voltage; a voltage application member to which the voltage generated by the power supply is applied; a current detection unit that detects the current flowing from the power supply to the voltage application member; and a control unit that controls the output voltage of the power supply, wherein the control unit obtains from the current detection unit a first current feedback signal generated immediately after the start of output from the power supply and a second current feedback signal generated after a predetermined time has elapsed from the start of output from the power supply, and the first current feedback signal voltage and the second current feedback signal The difference between the voltage and the current detection unit divided by the resistance value of the current detection unit. The output current is calculated based on this. [Effects of the Invention]

[0008] According to the present invention, the surface potential of the image carrier can be controlled to a desired potential with high precision using a simple circuit configuration. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing an example of the mechanical structure of an image forming apparatus according to the first embodiment. [Figure 2] Figure 2 is a schematic diagram showing an example of the overall configuration for an electrophotographic process using an image forming apparatus according to the first embodiment. [Figure 3] Figure 3 is a block diagram showing the configuration of the high-voltage power supply and control board in the image forming apparatus according to the first embodiment. [Figure 4] Figure 4 shows a photoreceptor drum and a charging roller according to the first embodiment. [Figure 5] Figure 5 shows an example of the circuit configuration of the high-voltage power supply of the image forming apparatus according to the first embodiment. [Figure 6] Figure 6 is a timing chart showing an example of the relationship between the charging DC control signal, the charging DC voltage Vc, the surface potential Vd0 of the photoreceptor drum, the charging current Iout, and the voltage FBV of the current feedback signal in the first embodiment. [Figure 7]Figure 7 is a flowchart showing an example of the calculation process for the charging current Iout and the charging applied voltage Vc by the image forming apparatus 1 according to the first embodiment. [Figure 8] Figure 8 is a timing chart showing an example of the relationship between the charging DC control signal, the charging DC voltage Vc, the surface potential Vd0 of the photoreceptor drum, the charging current Iout, and the voltage FBV of the current feedback signal in the second embodiment. [Modes for carrying out the invention]

[0010] An embodiment of the image forming apparatus will be described in detail below with reference to the attached drawings.

[0011] (First embodiment) Figure 1 is a schematic diagram showing an example of the mechanical structure of an image forming apparatus 1 according to the first embodiment. The image forming apparatus 1 according to this embodiment is a digital multifunction device having a copying function, a printer function, a facsimile function, etc. The copying function, printer function, and facsimile function can be sequentially switched and selected using the application switching key on the control panel. When the copying function is selected, it enters copying mode; when the printer function is selected, it enters printer mode; and when the facsimile mode is selected, it enters facsimile mode.

[0012] The image formation process in the image forming apparatus 1 will be briefly explained using the copying mode as an example. In copying mode, a stack of documents is sequentially fed to the image reading device 3 by the automatic document feeder (ADF) 2. The image reading device 3 then reads the image information from the documents. The image information read from the documents is converted into optical information by the writing unit 4, which acts as a writing means, via the image processing means.

[0013] The photoreceptor drum 6 is uniformly charged by a charger (not shown), and then exposed to light information from the writing unit 4 to form an electrostatic latent image. This electrostatic latent image on the photoreceptor drum 6 is developed by the developing device 7 to form a toner image. This toner image is transferred to the transfer paper by the transport belt 8, and the toner image is fixed to the transfer paper by the fixing device 9 before it is discharged.

[0014] Figure 2 is a schematic diagram showing an example of the overall configuration for the electrophotographic process by the image forming apparatus 1 of the first embodiment.

[0015] The high voltage generated by the high-voltage power supply 10 is applied to the charging roller 21, which acts as a voltage application member, and the photoreceptor drum 6 is uniformly charged. Subsequently, exposure is performed by the exposure device 22 according to the image information signal, and an electrostatic latent image is formed on the photoreceptor drum 6. Then, the toner image is developed by the developing device 7, and the toner image on the photoreceptor drum 6 is transferred to the intermediate transfer belt 24 by applying the high voltage generated by the high-voltage power supply 11 to the primary transfer roller 23.

[0016] The toner image transferred to the intermediate transfer belt 24 is transferred to the recording material by a secondary transfer unit (not shown), and then fixed to the recording material by a fixing device 9 to obtain an image. In addition, if a static eliminator 25 is provided in the image forming apparatus 1, the static eliminator 25 removes the charge from the surface of the photoreceptor drum 6, and then a charging treatment is performed. In the case of color printing, there are four similar configurations, and the toner image is transferred to the intermediate transfer belt for each color, and then proceeds to the secondary transfer unit and fixing device 9.

[0017] In the image forming apparatus 1 according to this embodiment, in order to detect the charging current when charging the photoreceptor drum 6, which serves as the image carrier, the sum of the output current (charging current) and the internal current of the high-voltage power supply flows into a current detection resistor in the high-voltage power supply 10.

[0018] When a charging current is generated, both the output current (charging current) and the internal current flow into the current sensing resistor. However, once the photoreceptor drum 6 is sufficiently charged and no more charging current is generated, only the internal current flows in. By taking the difference between the two, only the charging current can be calculated. This allows for accurate detection of the charging current with a simple configuration. The following describes this embodiment in detail.

[0019] Figure 3 is a block diagram showing the configuration of the high-voltage power supply and control board in the image forming apparatus 1 according to the first embodiment.

[0020] The high-voltage power supply 10 generates a high voltage to be applied to the charging roller 21. As shown in Figure 3, the high-voltage power supply 10 includes a charging DC bias generation unit 101, a charging AC bias generation unit 102, and a charging DC current detection unit 103. The magnitude and timing of the output are determined by a PWM (Pulse Width Modulation) signal, which is a control signal sent from the control board 30. The charging DC bias and charging AC bias can each be controlled by the control signal.

[0021] The DC bias generation unit 101 generates a DC voltage. The AC bias generation unit 102 generates an AC voltage. Then, a superimposed charge bias, which is the DC voltage generated by the DC bias generation unit 101 and the AC voltage generated by the AC bias generation unit 102, is applied to the photoreceptor drum 6.

[0022] The DC current detection unit 103 detects the DC component of the current flowing from the high-voltage power supply 10 to the photoreceptor drum 6, generates a current feedback signal converted to voltage, and sends it to the control board 30. Note that the AC bias generation unit 102 may be omitted in the configuration.

[0023] The control board 30 controls the high-voltage power supply 10. The control board 30 outputs a PWM signal, which is a DC charging control signal, to the high-voltage power supply. As shown in Figure 3, the control board 30 includes an arithmetic processing unit 302 and a memory 301.

[0024] The arithmetic processing unit 302 receives a current feedback signal generated by the charged DC current detection unit 103 of the high-voltage power supply 10, calculates the charged DC bias to be applied based on the current feedback signal, and outputs a charged DC control signal based on the charged DC bias to the high-voltage power supply 10. In this way, the arithmetic processing unit 302 controls the surface potential of the photoreceptor drum 6 to the desired potential. The arithmetic processing unit 302 corresponds to the control unit. Details of the arithmetic processing unit 302 will be described later.

[0025] Memory 301 temporarily stores the current feedback signal received by the arithmetic processing unit 302, the calculated DC bias, and other data.

[0026] Figure 4 shows the photoreceptor drum 6 and the charging roller 21 according to the first embodiment. The charging current can be expressed by the following equation (1-1).

[0027]

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[0028] Here, I out V is the charging current, Z is the impedance between the charging roller 21 and the GND (ground) of the photoreceptor drum 6, and V is the impedance between the charging roller 21 and the GND (ground). c V is the DC voltage of the charge. d0 This is the surface potential of the photoreceptor drum 6 near the nip of the charging roller 21.

[0029] Let's explain using the example of charging the photoreceptor drum 6 to a negative polarity. For example, if Z = 25 MΩ and the photoreceptor surface is charged from 0 V to -700 V (V c = -700V, V d0 =0V), from equation (1-1) above, it can be calculated as in equation (1-2), I out It can be seen that this will result in negative polarity.

[0030] FIG. 5 is a diagram showing an example of the circuit configuration of the high-voltage power supply 10 of the image forming apparatus 1 according to the first embodiment. As shown in FIG. 1, the high-voltage power supply 10 mainly includes a bleeder resistor 105, a current detection resistor 106, a voltage monitor 107, a control unit 108, and a drive circuit 109.

[0031] The voltage monitor 107 monitors the output voltage of the high-voltage power supply 10 and sends it to the control unit 108. The control unit 108 controls the drive circuit 109 based on the output voltage received from the voltage monitor 107. Specifically, the control unit 108 includes the charging DC bias generation unit 101 and the charging AC bias generation unit 102 described above.

[0032] In the present embodiment, the arithmetic processing unit 302 of the control board 30 calculates the charging current I, which is the output current, based on the first current feedback signal generated immediately after the start of output from the high-voltage power supply 10 and the second current feedback signal generated after a predetermined time has elapsed since the start of output from the high-voltage power supply 10. out That is, the arithmetic processing unit 302 of the control board 30 calculates the charging current I, which is the output current, based on the difference between the voltage FBV_1 of the first current feedback signal generated immediately after the start of output from the high-voltage power supply 10 and the voltage FBV_1 of the second current feedback signal generated after a predetermined time has elapsed since the start of output from the high-voltage power supply 10. out More specifically, the arithmetic processing unit 302 calculates the charging current I, which is the output current, based on the difference between the voltage FBV_1 of the first current feedback signal and the voltage FBV_2 of the second current feedback signal generated after the elapse of the time when the photosensitive drum 6 makes one rotation as the predetermined time since the start of output. out This will be described in detail below.

[0033] The current detection resistor 106 is used to detect the charging current I. out As shown in Equation (2-1), the voltage FBV of the current feedback signal can be expressed as the product of the resistance value R of the current detection resistor 106 and the current I flowing through the current detection resistor 106. The current detection resistor 106 corresponds to the current detection unit and also corresponds to the charging DC current detection unit 103 in FIG. 3. det and the current I flowing through the current detection resistor 106. det The current detection resistor 106 corresponds to the current detection unit and also corresponds to the charging DC current detection unit 103 in FIG. 3.

[0034] The bleeder resistor 105 controls the internal current I when a voltage is output. INT A current flows, and the internal current I INT As shown in equation (2-3), the output voltage V out and the resistance value R of the bleeder resistor 105 INT It can be expressed as the quotient of . Here, since the output voltage is negative, I INT This also results in negative polarity.

[0035] Here, as shown in Figure 5, the current flowing through the current sensing resistor 106 (sensing current) I is given by equation (2-2). det The internal current I INT and the output current of the high-voltage power supply 10 (charging current: I out It can be expressed as the sum of ). Therefore, the voltage FBV of the current feedback signal can be derived from equation (2-1) using equations (2-2) and (2-3) as shown in equation (2-4). Thus, the charging current I out This can be derived from equation (2-4) using equation (2-5).

[0036]

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[0037] Here, FBV is the voltage of the current feedback signal, R det The resistance value of current sensing resistor 106 is I. det I is the current flowing through the current sensing resistor 106 (sensing current). out This is the output current (charging current or static elimination current) of the high-voltage power supply 10, I INT V is the internal current. out The output DC voltage of the high-voltage power supply 10, R INT This is the resistance value of the bleeder resistor 105.

[0038] For example, R det = 5kΩ, V out = -700V, I out = -30uA, R INT Assuming an impedance of 2MΩ, the voltage FBV of the current feedback signal can be calculated as shown in equation (3-1).

[0039]

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[0040] At this time, V out R is the DC output setting value for charging, INT V is estimated from the resistance constant and substituted into the formula, but in reality it varies depending on the individual, temperature and humidity, load conditions, etc., which becomes an error in the calculation of FBV. For example, in the above example, V out +3% variation (V out =-721V), R INT The variation is -1% (R INT If the resistance is 1.98MΩ, then FBV will be 1.97V. With these varying values, equation (2-5) gives I out Working backwards, we get -44uA as shown in equation (3-2), which is a large variation of approximately 47% compared to the true value (-30uA).

[0041] Figure 6 shows the charging DC control signal and the charging DC voltage V in the first embodiment. c , the surface potential V of the photoreceptor drum 6 d0 , charging current I out This is a timing chart showing an example of the relationship between the voltage FBV of the current feedback signal. In Figure 6, the horizontal axis represents time. Note that the image forming apparatus 1 according to this embodiment is configured not to include a static eliminator such as a static elimination lamp that removes static charge before charging.

[0042] When a DC charging control signal is input from the control board 30, the DC charging voltage V c This outputs a DC voltage V, and consequently the photoreceptor drum 6 becomes charged. c It becomes charged. According to equation (1-1), the current sensing resistor 106 takes time (t) for the photoreceptor drum 6 to complete one rotation, i.e., one full rotation. OPC ) Charge current I out and internal current I INT As the current flows, the voltage FBV_1 of the first current feedback signal is generated according to equation (4-1).

[0043] Here, if we let the diameter of the photoreceptor drum 6 be Φ and the linear velocity be λ, then t OPC =Φ × π / λ

[0044]

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[0045] From the time the charging DC control signal is turned on, the time equivalent to one rotation of the photoreceptor drum 6 (t OPC ) After the passage of time, V c Since the photoreceptor drum 6, which is charged, comes into contact with the charging roller 21, the V in equation (1-1) d0 =V c Therefore, the charging current I out = 0. Therefore, in equation (2-4), I out = 0, but I INT As current flows, a voltage FBV of the current feedback signal is generated. This is called the voltage FBV_2 of the second current feedback signal. Therefore, the voltage FBV_2 of the second current feedback signal is calculated by equation (4-2).

[0046] The arithmetic processing unit 302 of the control board 30 calculates the difference (ΔFBV) between the voltage FBV_1 of the first current feedback signal and the voltage FBN_2 of the second current feedback signal. This difference (ΔFBV) is calculated as shown in equation (4-3), which is the charge voltage V out , the resistance value R of the bleeder resistor 105 INT This results in an equation that does not depend on the charging current I, and the effects of these variations can be ignored. out This can improve the detection accuracy.

[0047] At this time, the charged DC voltage V out This is the set value for the charged DC output, and the resistance value R of the bleeder resistor 105. INT This value is estimated from the resistance constant and substituted into the formula, but in reality, it varies depending on the individual, temperature and humidity, load conditions, etc., resulting in an error in the calculation of the current feedback signal voltage FBV. For example, in the above example, the charged DC voltage V out The peel has a +3% variation (V out =-721V), resistance value R of bleeder resistor 105 INT The variation is -1% (R INTIf the resistance is 1.98 MΩ, the voltage FBV of the current feedback signal will be 1.97 V. With these varying values, the charging current I can be calculated from equation (2-5). out Working backwards, we obtain -44uA, as shown in equation (5), which is a large variation of approximately 47% compared to the true value (-30uA).

[0048]

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[0049] The above charging current I out Using this, the surface potential V of the photoreceptor drum 6 d This can be predicted. Since the photoreceptor drum 6 becomes charged by accumulating charge on its surface, charging the photoreceptor drum 6 can be considered equivalent to charging a capacitor. For this reason, equation (6-1) holds true between the charge Q and the charging potential of the photoreceptor drum 6. Here, C is the capacitance of the photoreceptor drum 6.

[0050] Here, since this charge Q is expressed by equation (6-2), equation (6-3) holds. Differentiating both sides of equation (6-3) gives equation (6-4). Surface potential V of the photoreceptor drum 6 before charging. d0 , charged with applied voltage V c Assuming constant, V c =V d Therefore, equation (6-5) holds true.

[0051] Furthermore, since equation (6-6) holds, the charging current I is as shown in equation (6-7). out and the surface potential V of the photoreceptor drum 6 d We can derive the relationship between these two.

[0052]

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[0053] The calculation processing unit 302 of this embodiment calculates the charging current I using equation (2-5) above. outApplying this to equation (6-7), the surface potential V of the photoreceptor drum 6 is obtained. d Predict and determine the appropriate V d The charging applied voltage V is such that this occurs. c This is adjusted. As a result, in this embodiment, abnormal images caused by poor charging, such as background stains and faint images, can be suppressed.

[0054] Next, the charging current I by the image forming apparatus 1 according to the first embodiment out and the applied charging voltage V c The calculation process for the current I will be explained. Figure 7 shows the charging current I by the image forming apparatus 1 according to the first embodiment. out and the applied charging voltage V c This is a flowchart showing an example of the calculation process.

[0055] First, the high-voltage power supply 10 starts applying a DC voltage to the charging roller 21 (S101). Next, immediately after the start of applying the DC voltage, the arithmetic processing unit 302 obtains the voltage FBV_1 of the first current feedback signal using equation (4-1) (S102). Then, the arithmetic processing unit 302 calculates the time t from the start of applying the DC voltage until the photoreceptor drum 6 completes one rotation. OPC Wait for the results to unfold (S103).

[0056] The time t for the photosensitive drum 6 to rotate one full turn OPC Once the time has elapsed, the arithmetic processing unit 302 obtains the voltage FBV_2 of the second current feedback signal immediately after the start of application of the charged DC voltage using equation (4-2) (S104). Then, the arithmetic processing unit 302 calculates the difference between the voltage FBV_1 of the first current feedback signal and the voltage FBV_2 of the second current feedback signal using equation (4-3) (S105).

[0057] Next, the arithmetic processing unit 302 calculates the charging current I from equation (2-5). out Calculate the calculated I out Therefore, using equation (6-7), the surface potential V of the photoreceptor drum 6 can be calculated. d The calculation unit 302 then calculates the desired surface potential V (S106). d The next charging applied voltage V cCalculate it (S107).

[0058] Thus, in this embodiment, the arithmetic processing unit 302 calculates the charging current I which is the output current based on the first current feedback signal generated immediately after the start of output from the high-voltage power supply 10 and the second current feedback signal generated after a predetermined time has elapsed since the start of output from the high-voltage power supply 10. out More specifically, the arithmetic processing unit 302 calculates the charging current I which is the output current based on the difference between the voltage FBV_1 of the first current feedback signal generated immediately after the start of output from the high-voltage power supply 10 and the voltage FBV_2 of the second current feedback signal generated after a predetermined time has elapsed since the start of output from the high-voltage power supply 10. out Even more specifically, the arithmetic processing unit 302 calculates the charging current I which is the output current based on the difference between the voltage FBV_1 of the first current feedback signal and the voltage FBV_2 of the second current feedback signal generated after the elapse of the time when the photoreceptor drum 6 has rotated once as the predetermined time since the start of output. out Calculate it.

[0059] Therefore, according to this embodiment, the above difference does not depend on the charging voltage V, the resistance value R of the bleeder resistor 105, and the influence of these variations can be ignored, so the detection accuracy of the charging current I can be improved. As a result, according to this embodiment, with a simple circuit configuration, the surface potential of the photoreceptor drum 6 can be controlled to a desired potential with high accuracy. out , and does not depend on the resistance value R of the bleeder resistor 105, and the influence of these variations can be ignored, so the detection accuracy of the charging current I can be improved. As a result, according to this embodiment, with a simple circuit configuration, the surface potential of the photoreceptor drum 6 can be controlled to a desired potential with high accuracy. INT can be improved. As a result, according to this embodiment, with a simple circuit configuration, the surface potential of the photoreceptor drum 6 can be controlled to a desired potential with high accuracy. out Moreover, in this embodiment, since the arithmetic processing unit 302 detects the surface potential of the photoreceptor drum 6 from the calculated output current, a desired photoreceptor surface potential can be obtained from the detected current, and the occurrence of abnormal images can be prevented.

[0060] Also, in this embodiment, since the arithmetic processing unit 302 detects the surface potential of the photoreceptor drum 6 from the calculated output current, a desired photoreceptor surface potential can be obtained from the detected current, and the occurrence of abnormal images can be prevented.

[0061] Note that a gap may be provided between the photoreceptor drum 6 and the charging roller 21 so that the photoreceptor drum 6 is charged in a non-contact manner with the charging roller 21.

[0062] (Second Embodiment) In the first embodiment, the difference between the voltage FBV_1 of the first current feedback signal immediately after the start of application of the charging DC voltage and the voltage FBV_2 of the first current feedback signal after the elapse of the time during which the photosensitive drum 6 makes one rotation from the start of application of the charging DC voltage is obtained, and based on this difference, the charging current I which is the output current out is calculated.

[0063] In this second embodiment, based on the voltage PBV_1 of the first current feedback signal generated immediately after the start of output from the high-voltage power supply 10 and the voltages of the plurality of second current feedback signals generated after the elapse of time for each of the plurality of rotations when the photosensitive drum 6 makes a plurality of rotations from the start of output from the high-voltage power supply 10, the charging current I which is the output current out is calculated.

[0064] The configuration of the image forming apparatus 1 according to the second embodiment, the configuration and circuit configuration of the high-voltage power supply 10, and the configuration of the control board 30 are the same as those of the first embodiment.

[0065] FIG. 8 is a timing chart showing an example of the relationship among the charging DC control signal, the charging DC voltage V c , the surface potential V d0 of the photosensitive drum 6, the charging current I out , and the voltage FBV of the current feedback signal in the second embodiment. In FIG. 8, the horizontal axis represents time.

[0066] In the second embodiment, in consideration of the case where due to deterioration of the photosensitive drum 6 or the charging roller 21 or the like, the photosensitive drum 6 cannot be sufficiently charged within the time t OPC for one rotation (that is, the surface potential V d of the photosensitive drum 6 does not converge), it is assumed that the photosensitive drum 6 is sufficiently charged within the time for two rotations (2 × t OPC ).

[0067] When the charging DC control signal is input from the control board 30, the charging DC voltage V c is output, and accordingly, the photosensitive drum 6 is charged to V c . According to equation (1-1), in the current detection resistor 106, within the time t OPCCharging current I out _1' and internal current I INT As the current flows, the voltage FBV_1' of the first current feedback signal is generated according to equation (7-1).

[0068]

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[0069] Time t from the ON of the charging DC control signal to the time it takes for one rotation of the photoreceptor drum 6 OPC After some time, the charged photoreceptor drum 6 comes into contact with the charging roller 21, but due to deterioration of the photoreceptor drum 6 and the charging roller 21, V d0 <V c Therefore, I in equation (1-1) out =I out _2' (≠0) is obtained, and the voltage FBV of the current feedback signal is generated. If this voltage is called FBV_2', then FBV_2' is given by equation (7-2).

[0070] From the time the DC charging control signal is turned on until the time it takes for the photoreceptor drum 6 to complete two rotations (2 × t) OPC ) After the passage of time, V c Since the photoreceptor drum 6, which is charged, comes into contact with the charging roller 21, the V in equation (1-1) d0 =V c And so, I out = 0. In equation (2-4), Iout = 0, but the internal current I INT As current flows, a voltage FBV of the current feedback signal is generated. If this voltage is denoted as FBV_3', then FBV_3' is given by equation (7-3).

[0071] In the example above, the photoconductor drum 6 is V c The current required to charge it is I out _1+I out It can be said that _2. Therefore, the arithmetic processing unit 302 calculates "FBV_1'+FBV_2'-2×FBV_3'" (ΔFBV) as shown in equation (7-4), thereby determining the charged voltage V out , the resistance value R of the bleeder resistor INTΔFBV can be calculated independently of the charging voltage V. out , the resistance value R of the bleeder resistor INT The effect of variations can be ignored, and the charging current I out This can improve the detection accuracy.

[0072] Generalizing the above, if it takes N cycles to sufficiently charge the photoreceptor drum 6, then the voltage of the current feedback signal for the Nth cycle of the photoreceptor drum 6 is FBV N Therefore, the arithmetic processing unit 302 can calculate ΔFBV using equation (8-1).

[0073]

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[0074] Then, the arithmetic processing unit 302 calculates the charging current I from ΔFBV according to equation (2-5). out By calculating this, we can determine the charging current I required to sufficiently charge the photoreceptor drum 6. out It is possible to calculate this.

[0075] The method for determining the Nth cycle is, for example, the voltage of the current feedback signal (FBV) at the Nth cycle. N ) and the voltage of the current feedback signal (FBV) for the N-1 cycle. N-1 ) difference (ΔFBV N_N-1 ) is a predetermined threshold (V th If the value falls below (8-2), that is, if equation (8-2) is satisfied, it can be determined that the photoreceptor drum 6 is sufficiently charged. However, the method for determining N is not limited to this.

[0076] In this embodiment, both the DC bias-only charge and the AC+DC superimposed bias are possible, but generally, the AC+DC superimposed bias allows for sufficient charging of the surface potential of the photoreceptor drum 6, so N is smaller in the AC+DC superimposed bias case.

[0077] If the control is performed using the average value of the applied voltage over one rotation of the photoreceptor drum 6, under low temperature and low humidity conditions, the surface potential of the photoreceptor drum 6 may not reach the target potential after one rotation, resulting in control errors.

[0078] Therefore, in this embodiment, the charging current I, which is the output current, is determined based on the voltage PBV_1 of the first current feedback signal generated immediately after the start of output from the high-voltage power supply 10, and the voltages of multiple second current feedback signals generated after a time has elapsed for multiple rotations when the photoreceptor drum 6 has rotated multiple times from the start of output from the high-voltage power supply 10. out It is calculating this.

[0079] Therefore, according to this embodiment, the output current can be calculated with high accuracy even when the charging roller 21 deteriorates under low temperature and low humidity conditions (such as when using a roller that has been used for a long time), or when it is difficult to apply a potential to the photoreceptor drum 6. As a result, according to this embodiment, even under low temperature and low humidity conditions, the surface potential of the photoreceptor drum 6 can be controlled to a desired potential with high accuracy using a simple circuit configuration.

[0080] In the above embodiment, the image forming apparatus of the present invention is described using an example in which it is applied to a multifunction device having at least two functions from among a copy function, a printer function, a scanner function, and a facsimile function. However, it can be applied to any image forming apparatus such as a copier, printer, or facsimile machine. [Explanation of symbols]

[0081] 1. Image forming apparatus 6. Photoconductor drum 10 High-voltage power supply 21 Electrostatic roller 30 Control board 101 Charged DC bias generation unit 102 Charged AC bias generation unit 103 Charge DC current detection unit 105 Bleeder resistor 106 Current sensing resistor 107 Voltage Monitor 108 Control Unit 109 Drive Circuit [Prior art documents] [Patent Documents]

[0082] [Patent Document 1] Japanese Patent Publication No. 2000-81773

Claims

1. Image carrier and, A power supply that generates a constant voltage controlled voltage, A voltage applying member to which the voltage generated by the aforementioned power supply is applied, A current detection unit for detecting the current flowing from the power supply to the voltage application member, The system comprises a control unit that controls the output voltage of the power supply, The control unit obtains a first current feedback signal generated immediately after the start of output from the power supply and a second current feedback signal generated after a predetermined time has elapsed since the start of output from the power supply from the current detection unit, and calculates the output current based on the value obtained by dividing the difference between the voltage of the first current feedback signal and the voltage of the second current feedback signal by the resistance value of the current detection unit. Image forming apparatus.

2. The control unit calculates the output current based on the value obtained by dividing the difference between the voltage of the first current feedback signal and the voltage of the second current feedback signal, which is generated after a predetermined time has elapsed from the start of output from the power supply until the image carrier has rotated once, by the resistance value of the current detection unit. The image forming apparatus according to claim 1.

3. The control unit detects the surface potential of the image carrier from the calculated output current. The image forming apparatus according to claim 1 or 2.

4. The aforementioned power supply outputs a superimposed bias of DC and AC. The image forming apparatus according to any one of claims 1 to 3.

5. A gap is provided between the image carrier and the voltage application member, and the image carrier is charged without contact with the voltage application member. An image forming apparatus according to any one of claims 1 to 4.

Images