JP4544217B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for detecting a current flowing in a specific electrical load.

In an image forming apparatus, there is a case where it is desired to detect a current flowing in an electrical load that the image forming apparatus has. For example, in Patent Document 1 below, since the impedance changes immediately after the medium enters between the photosensitive drum and the transfer roller, constant voltage control is performed until just before printing, and the current flows to the transfer roller at that time. The current is detected by the current monitor circuit, thereby calculating the current impedance. Then, after printing is started, an appropriate transfer voltage is applied to the transfer roller according to the impedance.
JP-A-9-160402

By the way, the technique disclosed in Patent Document 1 has a configuration in which a current monitor circuit is provided on the transfer roller side in order to detect the current flowing through the transfer roller. For this reason, the wiring with the control circuit that performs the constant voltage control or the like becomes long, and there is a possibility that accurate current detection cannot be easily performed because of being easily affected by noise or the like.
The present invention has been completed based on the above situation, and an object of the present invention is to provide an image forming apparatus capable of accurately detecting a current flowing through a specific electric load.

As a means for achieving the above object, an image forming apparatus according to the invention of claim 1 includes a belt stretched around the belt and a belt that contacts the belt, and electrically adheres to the belt. The belt is sandwiched between a first cleaning roller that sucks, a second cleaning roller that electrically sucks the deposit sucked by the first cleaning roller, and the first cleaning roller, and is grounded to a predetermined potential. generating a pressing roller, a first voltage generating circuit for generating a first voltage applied to the first cleaning roller, the applied to the second cleaning roller, the second voltage is larger absolute value than the first voltage A second voltage generating circuit that detects the first current flowing through the first voltage generating circuit according to the first voltage, and the second voltage according to the second voltage. A second current detection circuit that detects a second current flowing through the circuit; a third current calculation unit that calculates a third current flowing through the first electrical load based on the first current and the second current; The second voltage generation circuit includes a transformer, and the first voltage generation circuit includes a first output terminal connected to the first cleaning roller and the second voltage connected to the second cleaning roller. A shunt circuit connected between a second output terminal of the generation circuit and configured to flow a current between a predetermined reference potential line and a secondary winding of the transformer; and a current flowing through the shunt circuit is controlled. And a control circuit that adjusts the voltage at the first output terminal to the first voltage, and the first current detection circuit is provided between the first output terminal and the reference potential line. A first resistance, and a voltage of the first resistance And the first current is detected based on a resistance value of the first resistor, and the third current calculation unit is configured to detect a third current flowing in the belt from a difference value between the first current and the second current. Is calculated .
The “image forming apparatus” of the present invention may be not only a printing apparatus such as a printer (for example, a laser printer), but also a facsimile machine, or a multifunction machine having a printer function and a reading function (scanner function). . Further, as long as the belt has the belt, the development unit is not limited to a tandem (single pass) system having an image carrier for each development unit, and each development unit performs development on a common image carrier. (Single drum) system may be used. Furthermore, either a direct transfer method in which a developer image is directly transferred to a recording medium or an intermediate transfer method in which a developer image is indirectly transferred through an intermediate transfer belt may be used.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the second voltage generation circuit includes a transformer, and the second current detection circuit includes a secondary of the transformer. A second resistor is provided between the side winding and the ground line, and the second current is detected based on a terminal voltage of the second resistor and a resistance value of the second resistor.

<Invention of Claim 1>
According to this configuration, the impedance between the first cleaning roller and the pressing roller is, for example, not limited to a print medium (not limited to a paper print medium such as paper but a plastic print medium such as an OHP sheet) on the belt. The current flowing there also changes, and there is a risk that the belt will be damaged, for example, if a current exceeding a predetermined value flows. Therefore, it is particularly desirable to perform current detection using the present invention.

In addition, the direction of the current flowing through the first output end may change depending on the load state on the first cleaning roller and the second cleaning roller , but the third current is based on a common calculation formula regardless of which direction the current flows. Can be requested.

Further , according to this configuration, the first current can be detected by a relatively simple method.

< Invention of Claim 2 >
According to this configuration, the second current can be detected by a relatively simple method.

An embodiment of the present invention will be described with reference to FIGS.
1. Overall Configuration of Printer FIG. 1 is a schematic cross-sectional view showing the internal configuration of a color laser printer (hereinafter simply referred to as “printer 1”) 1 as an image forming apparatus of the present embodiment.
A printer 1 illustrated in FIG. 1 includes a toner image forming unit 4, a paper conveying belt 6 as a belt member, a fixing unit 8, a paper feeding unit 9, a stacker 12, and a control unit 10, and a printing medium. As a result, four color images corresponding to image data input from the outside are formed on the paper P.

  The toner image forming unit 4 includes four developing units 51Y, 51M, 51C, and 51B and yellow, magenta, cyan, and black toners T (stored in these developing units 51Y, 51M, 51C, and 51B. For each of the four toner image forming steps according to an example of the developer (see FIG. 2), the photosensitive drum 3 as the photosensitive member, the charger 31 for uniformly charging the photosensitive drum 3, and the photosensitive after the charging A scanner unit 41 is provided as an exposure unit that exposes the surface of the body drum 3 with laser light to form an electrostatic latent image according to image data. Note that most of the scanner unit 41 is not shown, and only a portion where laser light is finally emitted is shown.

Hereinafter, the configuration of each component will be described in detail. In the following description, when it is necessary to distinguish each color, it is necessary to add a suffix of Y (yellow), M (magenta), C (cyan), and B (black) to each part code. If there is not, the subscript is omitted.
The photosensitive drum 3 of the toner image forming unit 4 is formed of a substantially cylindrical member, and four of them are arranged in a horizontal direction at substantially equal intervals so as to be rotatable. As the substantially cylindrical member of the photosensitive drum 3, for example, a member in which a positively chargeable photosensitive layer is formed on an aluminum base material is used. The aluminum base material is grounded to the ground line of the printer 1.

  Further, the charger 31 is a so-called scorotron type charger. The charger 31 is opposed to the photosensitive drum 3 and extends in the width direction thereof. The charging wire 32 is accommodated in the photosensitive drum 3 side. The surface of the photosensitive drum 3 is charged to a positive polarity (for example, +700 V) by applying a high voltage to the charging wire 32. The shield case 33 has a structure in which a grid is provided in the open portion on the photosensitive drum 3 side. By applying a specified voltage to the grid, the surface of the photosensitive drum 3 is substantially the same as the grid voltage. Charged to potential.

The scanner unit 41 is disposed on each photosensitive drum 3 on the downstream side of the charger 31 in the rotation direction of the photosensitive drum 3, and emits laser light corresponding to one color of image data input from the outside from the light source. The laser beam is emitted and scanned with a mirror surface of a polygon mirror that is rotationally driven by a polygon motor, and is irradiated onto the surface of the photosensitive drum 3.
When the scanner unit 41 irradiates the surface of the photosensitive drum 3 with laser light corresponding to the image data, the surface potential of the irradiated portion is reduced (+150 to +200 V), so that the photosensitive drum 3 An electrostatic latent image is formed on the surface.

  Each of the developing units 51Y, 51M, 51C, and 51B includes a developing unit case 55 that stores toner T of each color and a developing roller 52 as a developing unit. Thus, the developing roller 52 is disposed on the downstream side of the scanner unit 41 so as to contact the photosensitive drum 3. Each developing unit 51 charges the toner T to “+” (positive polarity), supplies the toner T to the photosensitive drum 3 as a uniform thin layer, and at the contact portion between the developing roller 52 and the photosensitive drum 3, With respect to the “+” (positive polarity) electrostatic latent image formed on the photosensitive drum 3, a toner T charged to “+” (positive polarity) is carried by the reversal development method, and the electrostatic latent image is formed. Develop.

  The developing roller 52 is formed in a cylindrical shape using a conductive silicone rubber or the like as a base material, and a coating layer of a resin containing fluorine or a rubber material is formed on the surface. The toner T stored in the developing unit case 55 is a positively chargeable non-magnetic one-component toner, and yellow, magenta, cyan toner, and black, respectively, according to the developing units 51Y, 51M, 51C, and 51B. Toner T is accommodated.

  The paper feed unit 9 is provided at the lowermost part of the apparatus, and includes a storage tray 91 that stores the paper P and a pickup roller 92 that feeds the paper P. The paper P stored in the storage tray 91 is picked up one by one from the paper feeding unit 9 by the pickup roller 92 and is sent to the paper transport belt 6 through the transport roller 98 and the registration roller 99.

  The sheet transport belt 6 is narrower than the width of the photosensitive drum 3 and is endlessly configured to travel integrally with the sheet P while the sheet P is supported on the upper surface. It is bridged between. In addition, transfer rollers 61 are provided in the vicinity of positions facing the respective photosensitive drums 3 with the paper transport belt 6 interposed therebetween. Then, as the driving roller 62 rotates, the surface of the sheet conveying belt 6 facing the photosensitive drum 3 moves from the right in the drawing to the left in the drawing as shown in FIG. The paper P sent from the rollers 99 is sequentially conveyed to the photosensitive drum 3 and sent to the fixing unit 8.

A cleaning roller 105 ( an example of a “first cleaning roller”) as a removing unit is provided at a position near the driven roller 63 on the surface of the paper conveying belt 6 that is turned back by the driving roller 62.

  FIG. 2 is an explanatory diagram illustrating in detail the configuration of the toner removing unit 100 including the cleaning roller 105. As shown in FIG. 2, the cleaning roller 105 has a configuration in which a foam material made of silicone is provided around a shaft member 105 </ b> A extending in the width direction of the paper transport belt 6. A predetermined first bias voltage V <b> 1 is applied to a metal electrode roller 104 (an example of a “pressing roller”) provided at an opposing position so as to rotate while contacting the paper transport belt 6. Established. With this first bias voltage V 1, the toner T (an example of “attachment”) attached to the paper transport belt 6 is removed by the cleaning roller 105. For example, if the electrode roller 104 is connected to the ground line and grounded, and a bias (for example, −1200 V) having a polarity opposite to the polarity of the toner T is applied to the cleaning roller 105, the toner T is attracted to the cleaning roller 105. Can be removed. The cleaning roller 105 is driven by a driving unit (not shown) so that the contact portions with the paper transport belt 6 are in opposite directions.

Further, the cleaning roller 105 includes a metal recovery roller 106 that removes the toner T adhering to the cleaning roller 105 from the cleaning roller 105 (for example, a structure in which an iron material is plated with Ni or a structure made of stainless steel). ( An example of a “second cleaning roller”) and a storage box (storage container) 107 for storing the toner T removed from the cleaning roller 105 are provided. A rubber cleaning blade 108 is in contact with the collection roller 106, and this cleaning blade 108 functions to scrape off the toner T adhering to the collection roller 106. A reverse polarity bias (for example, −1600 V) whose absolute value is larger than the bias to the cleaning roller 105 is applied to the collection roller 106.

  Returning to FIG. 1, the transfer roller 61 has a transfer bias (for example, −10 to −15 μA) opposite in polarity to the charging polarity of the toner T between the transfer roller 61 and the photosensitive drum 3 by the negative voltage current source 112. The toner image formed on the photosensitive drum 3 when applied is transferred to the paper P conveyed by the paper conveying belt 6.

The fixing unit 8 includes a heating roller 81 and a pressure roller 82, and heats and presses the paper P on which the toner image is transferred while nipping and conveying the paper P by the heating roller 81 and the pressure roller 82. Thus, the toner image is fixed on the paper P.
A stacker 12 is formed on the upper surface of the printer 1. The stacker 12 is provided on the paper discharge side of the fixing unit 8 and accommodates the paper P discharged from the fixing unit 8. The control unit 10 includes a control device using a CPU (not shown) and controls the overall operation of the printer 1.

2. Configuration of High Voltage Control Device On the control board 10A of the control unit 10, a bias is applied to each electric load provided in the printer 1, such as the transfer roller 61, the developing roller 52, the charger 31, the toner removing unit 100, and the like. A high-voltage control device 120 that generates a voltage is mounted. FIG. 3 shows the components that generate the bias voltage (first bias voltage V1, second bias voltage V2) to the toner removing unit 100.

  Specifically, on the control board 10A, a first bias generation circuit 121 (an example of “first voltage generation circuit”), a second bias generation circuit 122 (an example of “second voltage generation circuit”), For example, a PWM (Pulse Width Modulation) control circuit 123 configured by an application specific integrated circuit (ASIC) is provided.

(1) Second Bias Generation Circuit The second bias generation circuit 122 generates a second bias voltage V2 (an example of “second voltage”, for example, a target value of −1600 V) to be applied to the collection roller 106, and is a PWM signal. A smoothing circuit 124, a transformer drive circuit 125, a boosting / smoothing rectification circuit 126, and an output voltage detection circuit 127 are provided. Among these, the PWM signal smoothing circuit 124 plays a role of receiving and smoothing the PWM signal S 1 from the PWM port 123 A of the PWM control circuit 123 and applying it to the transformer drive circuit 125. The transformer drive circuit 125 is configured to flow an oscillation current through the primary winding 126A of the boosting / smoothing rectifier circuit 126 based on the received PWM signal S1.

  The step-up / smoothing rectifier circuit 126 includes a transformer (transformer) 128, a diode 129, a smoothing capacitor 130, and the like. The transformer 128 includes a secondary winding 126B, a primary winding 126A, and an auxiliary winding 126C. One end of the secondary winding 126B is connected to a connection line 131 connected to the roller shaft of the collection roller 106 via a diode 129 and a second output terminal t2 (an example of a “second output end”). Further, the smoothing capacitor 130 and the discharge resistor 133 are connected in parallel to the secondary winding 126B, respectively.

  With such a configuration, the oscillation voltage of the primary winding 126A is boosted and rectified in the boosting / smoothing rectifier circuit 126 and applied to the roller shaft of the recovery roller 106 as the second bias voltage V2.

  The output voltage detection circuit 127 is connected to the auxiliary winding 126 </ b> C of the transformer 128 of the step-up / smoothing rectifier circuit 126 and the PWM control circuit 123. The output voltage detection circuit 127 is configured to detect an output voltage Vf generated between both ends of the auxiliary winding 126C and to input the detection signal S2 to the A / D port 123B of the PWM control circuit 123. Since the output voltage Vf is proportional to the second bias voltage V2 that is the output voltage of the secondary winding 126B, the PWM control circuit 123 causes the PWM signal S1 so that the output voltage Vf becomes a predetermined constant value. A constant voltage control is performed to change the second bias voltage V2 to a target value (for example, -1600 V) by appropriately changing the duty ratio of the second bias voltage V2.

(2) First Bias Generation Circuit The first bias generation circuit 121 generates a first bias voltage V1 (an example of “first voltage”, for example, a target value of −1200 V) to be applied to the cleaning roller 105. In the embodiment, the first bias voltage V1 to be applied to the cleaning roller 105 is generated based on the second bias voltage V2 generated by the second bias generation circuit 122. Specifically, the first bias generation circuit 121 mainly includes a shunt circuit 140 and a shunt current control circuit 141 (an example of a “control circuit”). The shunt circuit 140 is a current adjustment element connected between the first output terminal t1 (an example of “first output end”) connected to the connection line 142 connected to the cleaning roller 105 and the second output terminal t2. As a transistor 143. More specifically, the pnp transistor 143 has a collector connected to the second output terminal t2 side, an emitter connected to the first output terminal t1 side, and a base connected to the second output terminal t2 via the input resistor 144. Connected to the side. The emitter (first output terminal t1) of the transistor 143 is connected to a predetermined reference potential (for example, a positive potential of 3.3v) V3 line via feedback resistors R1 and R2 (an example of “first resistor”). ing. The reference potential V3 is not limited to + 3.3V as long as it is a potential at which a contact potential V4 described later does not become negative.

  The shunt current control circuit 141 is connected to the PWM port 123 of the PWM control circuit 123 via the photocoupler 145, and controls the base potential of the transistor 143 according to the PWM signal S4 output from the PWM port 123. Thus, it plays a role of adjusting the amount of shunt current is flowing through the shunt circuit 140. In the PWM control circuit 123, the contact potential V4 between the feedback resistors R1 and R2 is input to the A / D port 123E as the detection signal S5. Since this contact potential V4 is proportional to the first bias voltage V1 that is the output voltage of the first bias generation circuit 121, the PWM control circuit 123 causes the PWM signal to be such that the contact potential V4 becomes a predetermined constant value. Constant voltage control is performed to set the first bias voltage V1 to a target value (for example, -1200 V) by appropriately changing the duty ratio of S4. The photocoupler 145 serves to isolate the current on the PWM control circuit 123 side so as not to be mixed with a first current i1 described later.

3. Monitoring Method of Belt Current Flowing through the Paper Conveying Belt Now, the impedance of the cleaning roller 105, which is a resistor, the paper conveying belt 6, and the paper P on the paper conveying belt 6 vary greatly depending on the temperature and humidity of the printer 1. Accordingly, the belt current ib (an example of “third current”) flowing through the paper transport belt 6 also varies. Sheet conveying belt 6, flows a constant current or overcurrent (e.g. 100 .mu.A), such as pitting, because there is a risk of damage, it is necessary to monitor the belt current ib. Further, since the paper conveyance belt 6 and the cleaning roller 105 are deteriorated depending on the use frequency, it is necessary to measure the impedance and grasp the replacement time.

  However, since the path and direction of the current flowing between the toner removal unit 100 and the high-voltage control device 120 change depending on the load state between the cleaning roller 105 and the paper conveyance belt 6, the accuracy at a predetermined position on the toner removal unit 100 side is changed. The belt current ib cannot be measured well. Specifically, for example, when a large amount of toner T adheres to the paper transport belt 6, the impedance between the paper transport belt 6 and the cleaning roller 105 increases, and the voltage drop here increases. Then, since the first bias voltage V1 becomes lower than the target value (−1200 V), the shunt current control circuit 141 causes the base current of the transistor 143 to decrease the shunt current is in order to return it to the target value. The collector-emitter voltage (terminal voltage between the first output terminal t1 and the second output terminal t2) is increased by being controlled. At this time, a part of the first current i1 flowing from the reference potential V3 line via the feedback resistors R1 and R2 flows into the collecting roller 106 via the first output terminal t1 and the cleaning roller 105.

  On the other hand, for example, when the paper conveyance belt 6 is sandwiched with high nip force between the cleaning roller 105 and the electrode roller 104 with high humidity, the impedance between the paper conveyance belt 6 and the cleaning roller 105 is reduced. The voltage drop here is also reduced. Then, since the first bias voltage V1 becomes higher than the target value (−1200 V), in order to return this to the target value, the shunt current control circuit 141 causes the base current of the transistor 143 to increase the shunt current is. The collector-emitter voltage (terminal voltage between the first output terminal t1 and the second output terminal t2) is decreased by being controlled. At this time, a part of the current ib ′ of the belt current ib flows into the first output terminal t1 and merges with the first current i1. As described above, the path and direction of the current flowing between the toner removing unit 100 and the high-voltage control device 120 change depending on the load state between the cleaning roller 105 and the paper transport belt 6.

  Therefore, in the present embodiment, first, the second current i2 (= current ic (from the recovery roller 106 via the second output terminal t2 to the secondary winding) A configuration is provided for detecting the current flowing into 126B + the shunt current is). Specifically, the other end of the secondary winding 126B of the step-up / smoothing rectifier circuit 126 is connected to the ground line via a current measuring resistor 132 (an example of “second resistor”). A detection signal S3 corresponding to the terminal voltage Vd of the measuring resistor 132 is taken into the A / D port 123C of the PWM control circuit 123. The second current i2 flows through the current measuring resistor 132, and the terminal voltage Vd also changes according to the current value. The PWM control circuit 123 can calculate the second current i2 from the terminal voltage Vd and the resistance value rd of the current measuring resistor 132. Therefore, the current measuring resistor 132 and the PWM control circuit 123 function as a “second current detection circuit”.

  Further, the PWM control circuit 123 can calculate the first current i1 from the contact potential V4 taken into the A / D port 123E, the reference potential V3, and the resistance values r1 and r2 of the feedback resistors R1 and R2. . Therefore, the feedback resistors R1 and R2 and the PWM control circuit 123 function as a “first current detection circuit”.

  Here, when the impedance between the paper transport belt 6 and the cleaning roller 105 decreases and the current ib ′ flows into the first output terminal t1, the belt current ib can be expressed by the following equation.

[Equation 1]
ic + ib ′ = (Vd / rd) −i1
i1 = (V3-V1) / (r1 + r2)
ib = ic + ib ′ = (Vd / rd) − {(V3−V1) / (r1 + r2)}
On the other hand, when the impedance between the paper transport belt 6 and the cleaning roller 105 increases and the current i1 ′ flows into the collecting roller 106 via the first output terminal t1 and the cleaning roller 105, the belt current ib is expressed by the following equation. Can be represented.

[Equation 2]
ic = (Vd / rd)- (i1-i1 ')
i1 = (V3-V1) / (r1 + r2)
ib = ic− i1 ′ = (Vd / rd) − {(V3−V1) / (r1 + r2)}
As a result, the equations for calculating the belt current ib are the same in Equations 1 and 2. This means that the belt current ib can be calculated by the same formula (Formula 1 and 2) regardless of whether the current ib ′ or the current i1 ′ flows. The PWM control circuit 123 reads information related to the above formula from a memory (not shown), and calculates the belt current ib as needed according to this formula. Accordingly, at this time, the PWM control circuit 123 functions as a “third current calculation unit”.

  For example, when the belt current ib by the above calculation process is equal to or greater than a predetermined value (for example, a current value slightly smaller than a level at which the paper transport belt 6 is damaged), the PWM control circuit 123 determines that the belt current ib is the predetermined value. Switch to the constant current control to make the following constant values. Further, the PWM control circuit 123 calculates the impedance of the cleaning roller 105 and the sheet conveying belt 6 from the belt current ib obtained by the calculation process and the current value of the first bias voltage V1 or the second bias voltage V2, and this value is calculated. When the predetermined value or more is reached, it is determined that it is time to replace the cleaning roller 105 and the like, and a message to that effect is displayed on a display unit (not shown) of the printer 1 to notify the user.

4). Effects of the present embodiment (1) According to the present embodiment, as described above, the first current i1 and the second current i2 used for the calculation of the belt current ib are not on the toner removing unit 100 side. Since the current flows through each bias generation circuit 121, 122 on the control board 10A side, it can be detected on the control board 10A side. For this reason, unlike the conventional configuration in which a current monitor circuit is provided on the electrical load side, wiring from the control board to the current monitor circuit becomes unnecessary, and for example, the influence of noise on the wiring can be reduced.

  (2) Also, when the impedance between the paper transport belt 6 and the cleaning roller 105 is reduced and the current ib ′ flows into the first output terminal t1, the impedance between the paper transport belt 6 and the cleaning roller 105 is also large. Thus, even when the current i1 ′ flows into the collecting roller 106 via the first output terminal t1 and the cleaning roller 105, the belt current ib can be calculated using the same formula (Formulas 1 and 2). Can be simplified.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

( 1 ) In the above embodiment, the first bias voltage V1 and the second bias voltage V2 are described as examples having a negative polarity. However, the first bias voltage V1 and the second bias voltage V2 may have a positive polarity. The opposite is true.

( 2 ) The belt may be, for example, an intermediate transfer belt in addition to the paper transport belt 6.

( 3 ) In addition to the toner T, the adhering material may be paper powder or the like.

1 is a schematic cross-sectional view illustrating an internal configuration of a printer according to an embodiment of the invention. Explanatory drawing showing in detail the configuration of the toner removal unit Block diagram of components that generate a bias voltage to the toner removal unit

1. Printer (image forming device)
6. Paper transport belt (belt)
104 ... Electrode roller (pressing roller)
105 ... cleaning low-La (the first cleaning roller)
106 ... recovered low La (second cleaning roller)
121... First bias generation circuit (first voltage generation circuit)
122. Second bias generation circuit (second voltage generation circuit)
123 ... PWM control circuit (current detection circuit, third current detection unit)
132 ... Current measurement resistor (second resistor)
140 ... Shunt circuit 141 ... Shunt current control circuit (control circuit)
i1 ... first current i2 ... second current ib ... belt current (third current)
is ... Shunt current (current flowing in the shunt circuit)
R1, R2 ... Feedback resistor (first resistor)
t1 ... 1st output terminal (1st output terminal)
t2 ... second output terminal (second output terminal)
T ... Toner (attachment)
V1 ... first bias voltage (first voltage)
V2 ... second bias voltage (second voltage)

Claims (2)

A belt stretched around the belt,
A first cleaning roller that contacts the belt and electrically attracts deposits on the belt;
A second cleaning roller for electrically sucking the deposits sucked by the first cleaning roller;
A pressing roller that sandwiches the belt with the first cleaning roller and is grounded to a predetermined potential;
A first voltage generation circuit for generating a first voltage to be applied to the first cleaning roller ;
A second voltage generation circuit that generates a second voltage that is applied to the second cleaning roller and that has an absolute value greater than the first voltage;
A first current detection circuit for detecting a first current flowing through the first voltage generation circuit in response to the first voltage;
A second current detection circuit for detecting a second current flowing in the second voltage generation circuit in response to the second voltage;
A third current calculator ,
The second voltage generation circuit has a transformer.
The first voltage generation circuit is connected between a first output terminal connected to the first cleaning roller and a second output terminal of the second voltage generation circuit connected to a second cleaning roller, and a predetermined reference potential line A shunt circuit for passing a current between the secondary winding of the transformer and a control circuit for controlling a current flowing in the shunt circuit to adjust a voltage of the first output terminal to the first voltage; Comprising
The first current detection circuit includes a first resistor provided between the first output terminal and the reference potential line, and the first current detection circuit includes the first resistor based on the voltage of the first resistor and the resistance value of the first resistor. 1 current detection configuration,
The image forming apparatus , wherein the third current calculation unit calculates a third current flowing through the belt from a difference value between the first current and the second current . The second current detection circuit has a second resistor provided between the secondary winding of the transformer and a ground line, and the terminal voltage of the second resistor and the resistance value of the second resistor are The image forming apparatus according to claim 1, wherein the second current is detected based on the first current.

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