JP2019020657A - Image formation apparatus - Google Patents

Abstract

To allow proper setting of the transfer voltage by detecting the current in the state where the actual voltage applied to a transfer roller reaches the reference voltage.SOLUTION: An image formation apparatus detects the voltage and current (S2) by changing the voltage applied to a secondary transfer outer roller over from the secondary transfer voltage to the reference voltage before correction (S1), determines whether or not there is the voltage that reaches the set voltage (S4), out of the voltage detected to the voltage changeover timing starting changeover to the secondary transfer voltage (S3), expands the next sheet interval for the prescribed time (S10) when there is no voltage that reaches the set voltage (NO in S4), changes the voltage changeover timing (S11), repeats processing, corrects the reference voltage using the voltage within a prescribed range out of the detected voltage and the corresponding current (S5) when there is the voltage that reaches the set voltage (YES in S4), and can set the transfer voltage using the current detected in the state where the voltage applied to the secondary transfer outer roller reaches the reference voltage.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus using electrophotographic technology, such as a printer, a copying machine, a facsimile machine, or a multifunction machine.

  As an image forming apparatus, an intermediate transfer type image forming apparatus is known in which a toner image formed on a photosensitive drum is primarily transferred to an intermediate transfer belt, and the toner image primarily transferred to the intermediate transfer belt is secondarily transferred to a recording material. ing. There is also known a direct transfer type image forming apparatus that directly transfers a toner image formed on a photosensitive drum onto a recording material. The toner image formed on the intermediate transfer belt or the photosensitive drum is transferred onto a recording material at a transfer nip portion formed by bringing a conductive transfer roller into contact with the intermediate transfer belt or the photosensitive drum. In order to transfer the toner image to the recording material, a transfer voltage is applied to the transfer roller by a high voltage power source.

  The transfer roller has an electrical resistance value that changes due to a change in environment (for example, temperature and humidity) or deterioration due to long-term use. When an image forming job for continuously forming images on a large number of recording materials does not change the transfer voltage even though the electric resistance value of the transfer roller changes, a target current suitable for transfer flows to the transfer nip portion. Transfer defects may occur. In view of this, an apparatus has been proposed that performs an inter-sheet ATVC (Active Transfer Voltage Control) between a recording material and a recording material that passes through a transfer nip portion each time an image is formed on a predetermined number of recording materials during an image forming job. (Patent Document 1). In the inter-sheet ATVC, a current detected in response to the application of a reference voltage that allows a target current to flow through the transfer nip when there is no recording material, and a transfer roller obtained in advance during an image forming job pre-rotation, etc. The reference voltage is corrected on the basis of the voltage-current characteristics. Then, the sum of the corrected reference voltage and a predetermined voltage (referred to as a paper sharing voltage or the like) determined in advance according to, for example, the type of the recording material is set as a new transfer voltage.

Japanese Patent No. 3847875

  Recently, in order to further increase the productivity of the image forming apparatus, the process speed at the time of image formation is improved, and the distance between the recording material and the recording material that are continuously conveyed (referred to as “between paper” for convenience) is shortened. It is hoped that. When the paper interval is shorter than the conventional one, when the voltage applied to the transfer roller in the paper interval ATVC is switched from the transfer voltage to the reference voltage, the actual voltage (referred to as the actual voltage) applied to the transfer roller is the reference voltage. The current is likely to be detected during the voltage transition before reaching. Conventionally, the reference voltage is corrected based on the current detected during the voltage transition (specifically, the falling of the voltage from the transfer voltage to the reference voltage), and even if the transfer voltage is set based on the corrected reference voltage, The transfer voltage was not set properly and image defects were likely to occur.

  The present invention has been made in view of the above-described problem. Even when the electric resistance value of the transfer roller changes, the current is detected in a state where the actual voltage applied to the transfer roller reaches the reference voltage in the inter-sheet ATVC, and the transfer voltage An object of the present invention is to provide an image forming apparatus capable of appropriately setting the image quality.

  The image forming apparatus according to the present invention includes an image carrier that carries and rotates a toner image, a transfer nip formed in contact with the image carrier, and a transfer voltage applied to the image on the recording material. A transfer member that transfers a toner image on the carrier, a power source that applies a voltage to the transfer member, a voltage detection unit that detects a voltage applied to the transfer member from the power source, and a current that flows through the transfer member Current detection means for detecting the voltage, and the voltage applied to the transfer member during a predetermined period in which a corresponding region between the recording material and the recording material passes through the transfer nip during an image forming job. The first transfer voltage applied when passing through the transfer nip portion is switched to a reference voltage having an absolute value lower than the first transfer voltage, and the voltage applied to the transfer member is changed from the first transfer voltage to the reference. Electric A second transfer voltage applied to the transfer member during image formation based on the voltage detected by the voltage detection means and the current detected by the current detection means within a predetermined time from the start of switching to And a control unit capable of executing a setting mode to be set, and the control unit is configured to record the recording material and the subsequent recording material based on a voltage detected by the voltage detection unit by the predetermined time in the setting mode. The distance between the materials is changed.

  According to the present invention, the transition of the voltage that does not reach the reference voltage by the predetermined time by changing the interval between the recording material and the recording material based on the voltage detected by the predetermined time from the start of switching. The second transfer voltage can be set appropriately without using the current detected inside.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. Schematic which shows a control part. The flowchart which shows the inter-paper ATVC of this embodiment. 5 is a timing chart for explaining current detection of the inter-sheet ATVC according to the embodiment. The timing chart explaining other embodiment. The figure explaining front rotation ATVC. 9 is a timing chart for explaining current detection of a conventional inter-sheet ATVC. The figure explaining correction | amendment of a reference voltage. 6 is a timing chart for explaining current detection of a conventional inter-sheet ATVC when the inter-sheet interval is short. FIG. 2 is a schematic diagram illustrating a direct transfer type image forming apparatus.

<Image forming apparatus>
The image forming apparatus of this embodiment will be described. First, the configuration of the image forming apparatus of this embodiment will be described with reference to FIG. An image forming apparatus 1 shown in FIG. 1 is a tandem intermediate transfer type full color printer in which image forming units 3Y, 3M, 3C, and 3K of yellow, magenta, cyan, and black are arranged along an intermediate transfer belt 2. Of course, the image forming apparatus 1 is not limited to this, and may be a mono-color printer including only one black image forming unit 3K.

  In the image forming unit 3Y, a yellow toner image is formed on the photosensitive drum 4Y and is primarily transferred to the intermediate transfer belt 2. In the image forming unit 3M, a magenta toner image is formed on the photosensitive drum 4M, and transferred onto the yellow toner image on the intermediate transfer belt. In the image forming units 3C and 3K, a cyan toner image and a black toner image are formed on the photosensitive drums 4C and 4K, respectively, and are sequentially transferred onto the intermediate transfer belt 2.

  The image forming units 3Y, 3M, 3C, and 3K are configured in substantially the same manner except that the color of toner used in the developing devices 7Y, 7M, 7C, and 7K is different from yellow, magenta, cyan, and black. Therefore, hereinafter, the image forming unit 3Y will be described in detail, and the image forming units 3M, 3C, and 3K will be described by replacing Y at the end of the symbol with M, C, and K.

  In the image forming unit 3Y, a charging roller 5Y, an exposure device 6Y, a developing device 7Y, a primary transfer roller 8Y, and a drum cleaning device 9Y are disposed so as to surround the photosensitive drum 4Y. The photosensitive drum 4Y is a drum-shaped electrophotographic photosensitive member in which a photosensitive layer is formed on the outer peripheral surface of an aluminum cylinder, for example, and is rotated in the direction of arrow R1 in the drawing at a predetermined process speed by a motor (not shown).

  The charging roller 5 </ b> Y charges the surface of the photosensitive drum 4 </ b> Y to a uniform negative dark potential by applying a charging voltage obtained by superimposing an AC voltage on a negative DC voltage. The exposure device 6Y writes an electrostatic latent image of the image on the surface of the charged photosensitive drum 4Y by scanning with a rotating mirror a laser beam obtained by ON-OFF modulating the scanning line image data obtained by developing the separation color image of each color.

  The developing device 7Y supplies toner to the photosensitive drum 4Y to develop the electrostatic latent image into a toner image. In the developing device 7Y, the developing sleeve 7S disposed on the surface of the photosensitive drum 4Y with a slight gap is rotated in the counter direction with respect to the photosensitive drum 4Y at a predetermined process speed. The developing device 7Y contains, for example, a two-component developer containing a non-magnetic toner having a negative charging characteristic and a magnetic carrier having a positive charging characteristic. The two-component developer is carried on the developing sleeve 7S, and the photosensitive drum 4Y. To the opposite part. By applying a developing voltage, in which an AC voltage is superimposed on a DC voltage, to the developing sleeve 7S, the negatively charged toner is transferred to the exposed portion of the photosensitive drum 4Y having a relatively positive polarity and electrostatically charged. The latent image is reversely developed. In FIG. 1, the developing sleeve 7S is described only in the developing device 7Y, but the developing devices 7M, 7C, and 7K also have the developing sleeve 7S.

  The primary transfer roller 8Y presses the intermediate transfer belt 2 to form a primary transfer portion T1 between the photosensitive drum 4Y and the intermediate transfer belt 2. A primary transfer power supply (not shown) is connected to the primary transfer roller 8Y, and the primary transfer power supply applies a positive primary transfer voltage to the primary transfer roller 8Y, whereby a negative electrode on the photosensitive drum 4Y (on the photosensitive member). The toner image charged to be neutral is transferred to the intermediate transfer belt 2. In the drum cleaning device 9Y, for example, a cleaning blade made of a polyurethane material is in contact with the surface of the photosensitive drum 4Y, and the transfer residual toner that passes through the primary transfer portion T1 and remains on the photosensitive drum 4Y is collected by the cleaning blade. .

  The intermediate transfer belt 2 as an image carrier is an intermediate transfer body that can rotate in contact with the photosensitive drums 4Y to 4K. The intermediate transfer belt 2 is supported around a tension roller 31, a driving roller 32, and a secondary transfer inner roller 33, and is driven by the driving roller 32 to rotate. The intermediate transfer belt 2 moves in the same direction (arrow R2 direction in the figure) as the rotation direction of the photosensitive drums 4Y to 4K (arrow R1 direction in the figure) at a position where it contacts the photosensitive drums 4Y to 4K.

  The four color toner images transferred onto the intermediate transfer belt (on the intermediate transfer member) by the image forming units 3Y to 3K are conveyed to the secondary transfer unit T2 which is a transfer nip unit, and are recorded on the recording material P (paper, OHP sheet). Secondary transfer to a sheet material). The recording material P is taken out from the recording material cassette 101 by the pickup roller 102, separated one by one, and sent out to the conveyance path. The recording material P on the conveyance path is sent to the secondary transfer portion T2 in time with the toner image on the intermediate transfer belt 2. Then, the recording material P on which the four color toner images are secondarily transferred is sent to the fixing device 40, and the toner image on the recording material is heated and fixed. The recording material P on which the toner image is fixed is discharged out of the machine body.

  The secondary transfer portion T2 as a transfer nip portion is formed by pressing the secondary transfer outer roller 34 toward the secondary transfer inner roller 33 with the intermediate transfer belt 2 interposed therebetween. The secondary transfer outer roller 34 as a transfer member is made of, for example, an ion conductive foamed rubber (for example, NBR, EPDM, urethane or the like in which a surfactant is injected on a metal shaft, or an ion conductive polymer. A roller formed with an elastic layer (such as a rubber layer). A secondary transfer power supply 50 with a variable supply voltage is connected to the secondary transfer outer roller 34. In the present embodiment, the secondary transfer inner roller 33 is connected to the ground potential (0 V), while the secondary transfer power supply 50 applies a positive secondary transfer voltage having a polarity opposite to that of the toner to the secondary transfer outer roller 34. By applying this, a transfer electric field is generated in the secondary transfer portion T2. The secondary transfer outer roller 34 responds to the transfer electric field by transferring the four color toner images transferred to the intermediate transfer belt 2, that is, the toner images charged with negative polarity of yellow, magenta, cyan, and black, to the secondary transfer unit. Secondary transfer can be performed collectively to the recording material P conveyed to T2.

<Control unit>
The image forming apparatus 1 according to the present embodiment includes a control unit 200 as a control unit. The control unit 200 will be described with reference to FIG. The controller 200 may be connected to various devices such as a motor and a power source for operating the image forming apparatus 1 other than those shown in the drawing, but the illustration and description thereof are omitted here because they are not the gist of the invention.

  The control unit 200 as a control unit performs various controls of the image forming apparatus 1 such as an image forming operation, and includes a CPU 201 (Central Processing Unit) and a memory 202 such as a ROM, a RAM, or a hard disk device. The memory 202 stores various data such as various programs such as an image forming job, a reference voltage, a paper sharing voltage, a secondary transfer voltage, which will be described later, and a plurality of current values to be passed during a pre-rotation ATVC which will be described later. The control unit 200 can execute various programs stored in the memory 202, and can execute the various programs to operate the image forming apparatus 1. Note that the memory 202 can also temporarily store arithmetic processing results and the like accompanying the execution of various programs.

  The image forming job is a series of periods from the start of image formation to the completion of the image forming operation based on a print signal for forming an image on the recording material P. Specifically, it refers to the period from pre-rotation (preparation operation before image formation) after receiving a print signal (job input) to post-rotation (operation after image formation). It is a period that includes the interval. In the present specification, “between sheets” (when paper is not passed) is a predetermined area in which a corresponding region between the recording material P and the recording material P passes through the secondary transfer portion T2 (see FIG. 1) during an image forming job. It is a period.

  In addition to the CPU 201 and the memory 202, the control unit 200 includes a constant voltage control circuit 301, a constant current control circuit 302, a voltage detection circuit 303, a current detection circuit 304, and a voltage generation circuit 305. These constant voltage control circuit 301, constant current control circuit 302, voltage detection circuit 303, current detection circuit 304, and voltage generation circuit 305 are arranged on a substrate (not shown) and control the secondary transfer power supply 50 (see FIG. 1). . The CPU 201 can transmit a constant voltage setting signal to the constant voltage control circuit 301, a constant current setting signal to the constant current control circuit 302, and a transfer clock signal to the voltage generation circuit 305. On the other hand, the CPU 201 can acquire a voltage detection signal from the voltage detection circuit 303 and a current detection signal from the current detection circuit 304. The CPU 201 can perform sampling by performing A / D conversion on the voltage detection signal acquired from the voltage detection circuit 303 and the current detection signal acquired from the current detection circuit 304.

  Based on the constant voltage setting signal and constant current setting signal transmitted from the CPU 201, the constant voltage control circuit 301 and the constant current control circuit 302 operate. In response to this, the voltage generation circuit 305 generates a voltage (output signal) to be applied to the secondary transfer outer roller 34 (see FIG. 1). In this way, a voltage is applied to the secondary transfer outer roller 34 by the secondary transfer power supply 50. A voltage detection circuit 303 as voltage detection means detects a voltage from the voltage generation circuit 305, and the detected voltage is output to the constant voltage control circuit 301 and the CPU 201 as an analog voltage detection signal (Vsns). A current detection circuit 304 as current detection means detects a current from the voltage generation circuit 305, and the detected current is output to the constant current control circuit 302 and the CPU 201 as an analog current detection signal.

  The operation of the control unit 200 will be described in more detail. The constant voltage control circuit 301 includes an operational amplifier (IC301) and a diode (D301). The constant current control circuit 302 includes an operational amplifier (IC302) and a diode (D302). The voltage detection circuit 303 includes resistors (R303 and R304). The current detection circuit 304 includes an operational amplifier (IC303) and a resistor (R305). The voltage generation circuit 305 includes a resistor (R301, R302), a transistor (Q301), a transformer (T301), and an FET (Q302).

  The voltage generation circuit 305 adjusts the voltage on the primary side of the transformer (T301) by the transistor (Q301) based on the constant voltage setting signal or the constant current setting signal, and drives the primary side of the transformer (T301) according to the transfer clock signal. Thus, a voltage (output signal) is generated. The voltage detection circuit 303 detects the voltage applied to the secondary transfer outer roller 34 by dividing the voltage generated by the voltage generation circuit 305 with resistors (R303, R304), and sends the voltage to the constant voltage control circuit 301 and the CPU 201. Output (voltage detection signal). The constant voltage control circuit 301 can perform feedback control so that the voltages of the constant voltage setting signal and the voltage detection signal match. That is, if the voltage detection signal is larger than the constant voltage setting signal, the output is controlled by the operational amplifier (IC301) so that the voltage output from the voltage generation circuit 305 is reduced. On the other hand, if the voltage detection signal is smaller than the constant voltage setting signal, the output is controlled by the operational amplifier (IC301) so that the voltage output from the voltage generation circuit 305 is increased.

The current detection circuit 304 detects the current flowing through the secondary transfer outer roller 34 based on the voltage generated by the voltage generation circuit 305 (current detection signal). The current (Ib) flowing through the secondary transfer outer roller 34 can be expressed by the following equation 1 using the current detection signal (Isns) detected by the current detection circuit 304. Note that “Vref” in Equation 1 is a predetermined voltage applied to the non-inverting input terminal (+) side of the operational amplifier (IC 303) of the current detection circuit 304.
Isns = Ib * resistance value of resistance (R305) + Vref Equation 1

  The constant current control circuit 302 can perform feedback control so that the currents of the constant current setting signal and the current detection signal match. That is, if the current detection signal is larger than the constant current setting signal, the output is controlled by the operational amplifier (IC 302) so that the voltage output from the voltage generation circuit 305 is reduced. On the other hand, if the current detection signal is smaller than the constant current setting signal, the output is controlled by the operational amplifier (IC 302) so that the voltage output from the voltage generation circuit 305 is increased. Thus, the voltage applied to the secondary transfer outer roller 34 is adjusted.

  The diode (D301) of the constant voltage control circuit 301 and the diode (D302) of the constant current control circuit 302 compare the output of the constant voltage control circuit 301 and the output of the constant current control circuit 302. A signal for increasing the voltage output from the voltage generation circuit 305 is input to the base of the transistor (Q301) of the voltage generation circuit 305. During constant voltage control, the output of the operational amplifier (IC301) operates so as to be larger than the output of the operational amplifier (IC302), and the output of the operational amplifier (IC302) is ground (GND) by comparing the constant current setting signal and the current detection signal. Works like sticking to a level. On the other hand, during constant current control, the output of the operational amplifier (IC302) operates so as to be larger than the output of the operational amplifier (IC301). The output of the operational amplifier (IC301) is ground level by comparing the constant voltage setting signal and the voltage detection signal. It works to stick to.

  Next, a method for setting the secondary transfer voltage will be described. Since the toner image on the intermediate transfer belt 2 (on the image carrier) is transferred to the recording material P during the image forming job, the control unit 200 applies a constant secondary transfer voltage to the secondary regardless of the amount of toner related to image formation. Constant voltage control applied to the outer transfer roller 34 is performed. However, it is necessary to apply a secondary transfer voltage so that a target current for transferring the toner image flows to the secondary transfer portion T2. If the current flowing through the secondary transfer portion T2 is smaller than the target current, a transfer failure may occur in which the toner image is not sufficiently transferred from the intermediate transfer belt 2 to the recording material P. Conversely, the current flowing through the secondary transfer portion T2 Is larger than the target current, an abnormal discharge may occur in the secondary transfer portion T2. In order to avoid this, it is necessary to flow a current that does not cause a transfer failure or abnormal discharge in the secondary transfer portion T2 to the secondary transfer portion T2 as a target current.

  Therefore, the control unit 200 performs the pre-rotation ATVC when the image forming job is pre-rotated. The pre-rotation ATVC is control for setting, as a reference voltage, a voltage that allows a target current to flow through the secondary transfer portion T2 when the recording material P does not pass through the secondary transfer portion T2. Done in Since the reference voltage that allows the target current to flow changes according to changes in the environment (for example, temperature and humidity) and changes in the electrical resistance value of the secondary transfer outer roller 34 due to long-term use, the control unit 200 is Rotate ATVC is performed. Also in the present embodiment, the pre-rotation ATVC is executed at the time of the first image forming job that is started after the cumulative number of image-formed recording materials P exceeds a predetermined number (for example, 1000 sheets), for example. Is done.

<Pre-rotation ATVC>
The pre-rotation ATVC will be briefly described with reference to FIG. 6 with reference to FIG. 1 and FIG. The control unit 200 sequentially applies a plurality of currents (I1 and I2 in FIG. 6) stored in the memory 202 to the secondary transfer outer roller 34 in order, so that the corresponding test voltages (V1 in FIG. 6) are supplied. , V2) are applied in order. However, one current (I1) has a current value smaller than the target current, and the other current (I2) has a current value larger than the target current. Then, the control unit 200 performs linear approximation using the P1 point (I1, V1) and the P2 point (I2, V2) in FIG. 6 corresponding to these (Y = (I2-I1) / (V2-V1)). This is regarded as the voltage-current characteristic (VI characteristic) of the secondary transfer outer roller 34 and stored in the memory 202. Then, according to the voltage-current characteristic (Y), the control unit 200 calculates the difference (ΔI) between the target current and the current (I1) smaller than the target current, the voltage (V1) applied when the current (I1) is passed, A reference voltage (Vb = V1 + ΔI / Y) is obtained and stored in the memory 202.

  As described above, the reference voltage (Vb) obtained by the pre-rotation ATVC is a voltage that allows a target current to flow through the secondary transfer portion T2 when the recording material P does not pass through the secondary transfer portion T2. It is. On the other hand, the secondary transfer voltage applied to the secondary transfer outer roller 34 during the image forming job is a target current applied to the secondary transfer portion T2 when the recording material P is passing through the secondary transfer portion T2. If the voltage is not able to flow, there is a risk of causing a transfer failure or the like. Therefore, when setting the secondary transfer voltage, in addition to the electrical resistance value of the secondary transfer outer roller 34, it is necessary to consider the electrical resistance value of the recording material P that passes through the secondary transfer portion T2. Therefore, the control unit 200 determines the secondary transfer voltage applied to the secondary transfer outer roller 34 at the time of the image forming job as the paper sharing voltage (Vp) in consideration of the reference voltage (Vb) and the electrical resistance value of the recording material P. ) And the sum. That is, the reference voltage becomes a reference when setting the secondary transfer voltage. Note that the paper sharing voltage (Vp) is a voltage value (predetermined voltage) that varies depending on the temperature and humidity obtained by an environmental sensor (not shown) mounted on the apparatus main body, the type of the recording material P, and the front or back side of the paper. Are pre-assigned and stored in the memory 202.

  However, as described above, when images are continuously formed on a large number of recording materials P, the electrical resistance value of the secondary transfer outer roller 34 may change. Nevertheless, if the secondary transfer voltage based on the reference voltage (Vb) set by the above-described pre-rotation ATVC is continuously applied, it is difficult for the target current to flow to the secondary transfer portion T2, and image defects may occur. . Therefore, the control unit 200 executes the inter-sheet ATVC and corrects the reference voltage every time image formation is continuously performed on a predetermined number (for example, 100) of recording materials P. In a general paper interval ATVC, a two-way paper non-passage is performed based on a current value detected by performing constant voltage control and a voltage / current characteristic of the secondary transfer outer roller 34 obtained by the above-described pre-rotation ATVC. The reference voltage is corrected to a voltage value that allows the target current to flow to the next transfer portion T2.

<Conventional paper-to-paper ATVC>
Here, a conventional inter-sheet ATVC will be described with reference to FIGS. Here, the reference voltage (Vb1) set by the pre-rotation ATVC is 2500 V, the reference voltage (Vb2) corrected by the inter-sheet ATVC is 2400 V, and the paper sharing voltage (Vp) of the recording material P is 500 V. Further, it is assumed that the interval between sheets is 100 ms, the time required for the voltage fall associated with the voltage switching applied to the secondary transfer outer roller 34 is 40 ms, and the time required for the voltage rise associated with the voltage switching is 20 ms. In this case, the time for current detection when the reference voltage is applied is 40 (100-40-20) ms. In addition, the black circle in FIG. 7 shows the electric current detection timing by CPU201 (refer FIG. 2).

  In view of the fact that the voltage-current characteristic of the secondary transfer outer roller 34 is actually non-linear, in order to obtain the reference voltage (Vb1) with high accuracy, a voltage at which a current equivalent to that at the time of transfer can be passed between sheets, that is, the reference voltage. It is desirable to detect the current while applying a voltage as close as possible to (Vb1). The control unit 200 (see FIG. 2) executes the inter-sheet ATVC after completing the transfer to the recording material P1 with the secondary transfer voltage. In the example shown in FIG. 7, the secondary transfer voltage of the recording material P1 immediately before executing the inter-sheet ATVC is the first of the sum of the reference voltage (Vb1: 2500V) and the paper sharing voltage (Vp: 500V). The target voltage (3000 V) is set.

  The control unit 200 switches the voltage to be applied to the secondary transfer outer roller 34 from the first target voltage (3000 V) to the reference voltage (Vb1: second target voltage (2500 V)) set in the pre-rotation ATVC. The control unit 200 detects the current value in five times at intervals of 8 ms, for example, after the second target voltage has been reached, that is, at least the time required for the voltage to fall (see solid line A in the figure). ), The detected current value is averaged. As the averaging process, for example, the remaining three current values excluding the maximum current value and the minimum current value among the detected five current values are averaged.

  As shown in FIG. 8, the control unit 200 obtains a difference (ΔIb1) between the averaged current value (Ib1) and the target current (Itrg). A reference voltage correction amount (ΔVb = ΔIb1 / Y) is obtained according to the obtained current difference (ΔIb1) and the voltage-current characteristic (Y) obtained by the pre-rotation ATVC. This reference voltage correction amount (ΔVb: -100V, for example) is added to the second target voltage (Vb1) (Vb2 = Vb1 + ΔVb) to obtain a corrected reference voltage (Vb2). Then, in order to form an image on the next recording material P2 that passes through the secondary transfer portion T2, the sum of the corrected reference voltage (2400V) and the paper sharing voltage (500V) is applied as the secondary transfer voltage applied during image formation. A third target voltage (2900V) is set (see FIG. 7). According to this, the current flowing through the secondary transfer outer roller 34 becomes a current indicated by “Ib2” in FIG. 8, and an error from the target current is “ΔIb2”. That is, by correcting the reference voltage, the error between the current flowing through the outer secondary transfer roller 34 and the target current can be reduced from “ΔIb1” before correction to “ΔIb2” after correction.

  Recently, in order to further increase the productivity of the image forming apparatus, the process speed at the time of image formation is increased and the gap between sheets is made as short as possible. When the interval between the sheets is shortened (for example, 80 ms), the time required for the voltage fall (40 ms) and the time required for the voltage rise (20 ms) do not change, so that the current can be applied to the current detection with the reference voltage applied. Time is shortened (20 ms). FIG. 9 shows the current detection timing of the conventional inter-sheet ATVC when the inter-sheet interval is shortened (black circle in FIG. 9). Here, since current detection is performed at intervals of 10 ms, the number of current values that can be detected in one paper interval is one.

  As shown in FIG. 9, when the interval between sheets is shortened, the current can be detected only once or twice at a time when the second target voltage (Vb1) is applied in one interval between sheets. This makes it difficult to average the current values and obtain a current value (Ib1: see FIG. 6) suitable for correcting the reference voltage. Accordingly, as indicated by a solid line A in FIG. 9, the reference voltage is corrected by averaging a plurality of current values obtained by performing the inter-sheet ATVC between a plurality of (for example, five times) sheets. The current value used for is obtained. In the example shown in FIG. 9, the secondary transfer voltage is set to the third target voltage (2900 V) from the sixth sheet, which is the first recording material after the correction of the reference voltage.

  However, in practice, the time required for the voltage to fall with the voltage switching from the secondary transfer voltage to the second target voltage may change due to a change in the electrical resistance value of the secondary transfer outer roller 34 or the like. In that case, as indicated by a dotted line B in FIG. 9, the current may be detected before reaching the second target voltage (Vb1). Alternatively, when the paper interval is shortened in the past, even if a plurality of currents can be detected in one paper interval as indicated by the dotted line B in FIG. There was something. In other words, it is necessary to ensure the time required for the voltage rise due to switching from the second target voltage to the secondary transfer voltage between the sheets.If the sheet interval is shortened, the actual voltage becomes the second target voltage. There is no time for starting the current detection after waiting for the arrival. In this case, the current may be detected before reaching the second target voltage. Conventionally, when the reference voltage is corrected based on the current detected before reaching the second target voltage, it is difficult to correct the reference voltage appropriately. This is because, in the prior art, on the assumption that the reference voltage has been reached, the reference voltage is corrected by actually measuring only the current without actually measuring the voltage. Therefore, even when a secondary transfer voltage based on the corrected reference voltage is applied, transfer failure, abnormal discharge, etc. are caused, and image defects such as “strong missing” and “weak missing” may occur.

<Inter-paper ATVC of this embodiment>
In the present embodiment, in view of the above points, in the inter-sheet ATVC, when the current can be detected only during the voltage falling due to the voltage switching from the secondary transfer voltage to the second target voltage (reference voltage), The inter-paper ATVC is performed again after the next inter-paper interval is expanded. That is, the paper interval is expanded until the current can be detected in the state where the second target voltage is reached by the paper interval ATVC, and the reference voltage can be corrected according to the current detected in the state where the second target voltage is reached. ing. FIG. 3 shows a flowchart of the inter-sheet ATVC of this embodiment. In the inter-sheet ATVC of this embodiment, the control unit 200 (see FIG. 2) sets a predetermined value (for example, 100) as the number of recording materials P on which images are continuously formed as information relating to image formation time during an image formation job. This is the control (setting mode) that is executed between the sheets whenever it exceeds. In addition, here, in order to make the explanation easy to understand, a case where the next sheet interval is widened will be described as an example, but the present invention is not limited thereto. Depending on the case, an appropriate paper interval such as a next paper interval (that is, skipping one) may be used instead of the next paper interval.

  As shown in FIG. 3, when starting the inter-sheet ATVC (in the setting mode), the controller 200 applies the voltage applied to the secondary transfer outer roller 34 to the secondary transfer voltage applied when the previous recording material P passes. Is switched to the reference voltage before correction (second target voltage) (S1). Here, the reference voltage stored in the memory 202 (see FIG. 2) is switched. The reference voltage is a voltage that is lower in absolute value than the secondary transfer voltage. Then, the control unit 200 detects the voltage and current at predetermined intervals according to the voltage switching (S2). The voltage detection and current detection are performed until a predetermined time from the start of switching to the reference voltage, more specifically, from the voltage switching timing at which switching to the secondary transfer voltage applied to the next recording material P2 is started after switching to the reference voltage. Performed before (NO in S3). The voltage switching timing is determined according to the length between sheets and the time taken for the voltage to rise when switching from the reference voltage to the secondary transfer voltage, and is stored in the memory 202. For example, when the interval between sheets is 65 ms and the time taken for the voltage to rise is 15 ms, the voltage switching timing is 50 (65-15) ms. For example, when the interval between sheets is 100 ms and the time taken for the voltage to rise is 20 ms, the voltage switching timing is 80 (100-20) ms.

  When the predetermined voltage switching timing has elapsed (YES in S3), the control unit 200 executes the next process of S4. Among the voltages detected until the predetermined voltage switching timing (within a predetermined time), the control unit 200 detects a voltage that has reached a set voltage (for example, 2500 ± 20 V) within a predetermined range from the second target voltage (reference voltage). It is determined whether or not there is (S4). When there is a voltage within the predetermined range (a voltage that has reached the set voltage) (YES in S4), the control unit 200 considers that the reference voltage has been reached, and, as will be described later, the detected voltage within the predetermined range. The reference voltage is corrected using the voltage and the current detected correspondingly (S5). The corrected reference voltage is stored (updated) in the memory 202. Then, the control unit 200 obtains the secondary transfer voltage by adding the paper sharing voltage to the corrected reference voltage (S6), and determines the voltage applied to the secondary transfer outer roller 34 from the reference voltage (second target voltage). Switching to the secondary transfer voltage (third target voltage) is started (S7). If the paper gap is different from the paper gap before execution of the paper gap ATVC (see S10 described later), the control unit 200 returns the paper gap to the length at the start of the image forming job (original paper gap) (S8). ), The inter-paper ATVC ends. When the sheet interval is returned to the original sheet interval, the voltage switching timing is also returned to the length at the start of the image forming job.

  On the other hand, when there is no voltage within the predetermined range (NO in S4), the controller 200 changes the voltage applied to the secondary transfer outer roller 34 from the reference voltage (second target voltage) to the secondary transfer voltage (third target voltage). Switching to voltage is started (S9). In this case, the control unit 200 considers that the reference voltage has not been reached, does not correct the reference voltage, and prepares to perform the inter-sheet ATVC again between the next sheets, so that the next sheet is separated from the current sheet. A predetermined time (for example, 20 ms) is extended from the interval (S10). Further, the control unit 200 delays the voltage switching timing for switching the voltage applied to the secondary transfer outer roller 34 from the reference voltage to the secondary transfer voltage during the subsequent setting mode in accordance with the change between the sheets (S11). For example, when the time required for the voltage to rise is 15 ms and the interval between sheets is changed from 65 ms to 85 ms, the voltage switching timing is changed after 50 ms and 70 ms after the start of the interval between sheets. Then, the control unit 200 waits for processing until the next sheet interval comes (S12). During processing standby, the recording material P is passing through the secondary transfer portion T2. When the next sheet interval comes, the control unit 200 returns to the process of step S1 and repeats the above-described process, that is, executes the sheet interval ATVC again.

  Concretely, it demonstrates using FIG.4 and FIG.8. Here, a case where the reference voltage (Vb1) set by the pre-rotation ATVC is 2500 V, the reference voltage (Vb2) corrected by the inter-sheet ATVC is 2400 V, and the paper sharing voltage (Vp) of the recording material P is 500 V is shown. That is, the secondary transfer voltage of the recording material P1 immediately before execution of the inter-sheet ATVC is (first transfer voltage) 3000V. Also, the original sheet interval (before change) is 65 ms, the transition time required for the voltage fall associated with the voltage switching applied to the secondary transfer outer roller 34 is 30 ms or 55 ms, and the transition time required for the voltage rise associated with the voltage switching. Was set to 15 ms. In this case, the voltage switching timing to the secondary transfer voltage is 50 (65-15) ms after the start of the interval between sheets. In the present embodiment, black circles in FIG. 4 represent voltage and current detection timing.

  As shown in FIG. 4, the controller 200 (see FIG. 2), after finishing the secondary transfer on the recording material P1, rotates the voltage applied to the secondary transfer outer roller 34 from the secondary transfer voltage (3000V) to the front. The reference voltage set in ATVC (second target voltage: 2500 V) is changed. The voltage and current are detected regardless of whether or not the actual voltage has reached the reference voltage. In this embodiment, the voltage and current are sampled at intervals of 8 ms, for example.

  As shown by a solid line A in FIG. 4, when there is a voltage within a predetermined range, it is considered that the voltage has reached the reference voltage, and the control unit 200 determines that the voltage within the predetermined range and the voltage are within the predetermined range. The reference voltage is corrected based on the corresponding detected current. At this time, when there are a plurality of voltages within the predetermined range, the voltages and the corresponding currents are averaged, and the reference voltage is corrected using the averaged voltage value and current value. If there are not a plurality of voltages within the predetermined range, the averaging process is not performed, and the reference voltage may be corrected using the detected voltage value and current value. That is, based on the voltage (Vb1) and current value (Ib1) obtained by actual measurement, the reference voltage correction amount (ΔVb: −100 V) is obtained as described above (see FIG. 8), and thus the reference voltage is obtained. Is corrected and reset as the corrected reference voltage (Vb2). The secondary transfer voltage (second transfer voltage) to be applied to the next recording material P2 is a third target voltage (2900V) which is the sum of the corrected reference voltage (2400V) and the paper sharing voltage (500V). Set to Thus, by correcting the reference voltage by the inter-sheet ATVC, the error between the current flowing through the secondary transfer outer roller 34 and the target current is changed from “ΔIb1” before correction to “ΔIb2” after correction, as shown in FIG. Can be made smaller.

  As indicated by a dotted line B in FIG. 4, when there is no voltage within the predetermined range, it is considered that the voltage has not reached the reference voltage, and the control unit 200 performs a predetermined interval (20 ms) between the next sheets. In addition to changing the voltage, the timing for switching to the secondary transfer voltage is changed. Then, the control unit 200 executes the inter-sheet ATVC again at the next inter-sheet interval. Nevertheless, when there is no voltage within the predetermined range, the control unit 200 further changes the next paper interval and voltage switching timing. That is, as indicated by a dotted line C in FIG. 4, the sheet interval and the voltage switching timing are changed until a voltage within a predetermined range is detected, and the sheet interval ATVC is repeated between the sheets with different times. The control unit 200 corrects the reference voltage based on the voltage within the predetermined range thus obtained and the current detected corresponding to the voltage. For example, if the average voltage obtained by averaging the voltages within a predetermined range is 2550V, and the reference voltage correction amount is −100V, the corrected reference voltage is 2450V. In this case, the secondary transfer voltage applied to the next recording material P2 passing through the secondary transfer portion T2 is a third target voltage (the sum of the corrected reference voltage (2450V) and the paper sharing voltage (500V)). 2950V). In the case of the present embodiment, the reference voltage correction amount may be obtained using the reference voltage (second target voltage) set in the previous rotation ATVC without using the voltage (Vb1) obtained by actual measurement. .

  As described above, in this embodiment, in the inter-sheet ATVC, the voltage applied to the secondary transfer outer roller 34 is measured, and it is considered that the voltage applied to the secondary transfer outer roller 34 has reached the reference voltage. In this state, the current flowing through the secondary transfer outer roller 34 can be detected. In order to do so, if the falling of the voltage applied to the secondary transfer outer roller 34 is not in time for the voltage switching timing to start switching to the secondary transfer voltage, the voltage switching timing is changed together with the sheet interval as described above. Yes. According to this, even if the electrical resistance value of the secondary transfer outer roller 34 is changed, it is detected in a state where the voltage has reached the reference voltage without using the current detected during the voltage fall caused by voltage switching. The reference voltage can be corrected using the current. Therefore, a secondary transfer voltage that does not cause transfer failure or abnormal discharge can be applied, and image defects such as “strong missing” and “weak missing” are less likely to occur. In addition, since only the paper interval is temporarily expanded during the execution of the paper interval ATVC, a good image can be obtained without significantly reducing the productivity related to image formation.

<Other embodiments>
In the embodiment described above, the reference voltage is corrected without performing the averaging process when there are not a plurality of voltages that have reached the set voltage in one paper interval ATVC, but this is not restrictive. If there are not a plurality of voltages that have reached the set voltage in one paper-to-paper ATVC, a plurality of voltages (voltages that have reached the set voltage) obtained by performing the paper-to-paper ATVC a plurality of times and currents detected correspondingly An averaging process may be performed on each to correct the reference voltage.

  In the above-described embodiment, it is determined whether or not there is a voltage that has reached the set voltage in one paper interval (see S4 in FIG. 3), and when there is no voltage that has reached the set voltage, the next paper interval is determined. However, the present invention is not limited to this. For example, as shown in FIG. 5, when the inter-sheet ATVC is performed between a plurality of times (for example, five times) of the same length, and there is no voltage that reaches the set voltage at a predetermined number of times (for example, three times) or more. In addition, the interval between the next sheets (here, the sixth time) may be increased and the voltage switching timing may be changed. Alternatively, when the inter-paper ATVC is performed between a plurality of papers of the same length and there is a continuous paper space without a voltage reaching the set voltage (for example, three times), the next paper space is expanded or The voltage switching timing may be changed.

  In the above-described embodiment, the intermediate transfer type image forming apparatus has been described as an example, but the present invention is not limited thereto. In the above-described embodiment, when the image forming apparatus 1 is a mono-color printer, a toner image is transferred from one photosensitive drum 4K serving as an image carrier onto a recording material P conveyed to a conveying belt 250 as shown in FIG. The present invention can also be applied to a direct transfer type image forming apparatus in which is transferred directly.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Image carrier (intermediate transfer body, intermediate transfer belt), 4Y-4K ... Image carrier (photosensitive body, photosensitive drum), 34 ... Transfer member (2) Secondary transfer outer roller), 50 ... power supply (secondary transfer power supply), 200 ... control means (control unit), 303 ... voltage detection means (voltage detection circuit), 304 ... current detection means ( Current detection circuit), P ... recording material, T2 ... transfer nip (secondary transfer)

Claims (11)

An image carrier that carries and rotates a toner image;
A transfer member that abuts against the image carrier to form a transfer nip, and a transfer voltage is applied to transfer a toner image on the image carrier to a recording material;
A power source for applying a voltage to the transfer member;
Voltage detecting means for detecting a voltage applied to the transfer member from the power source;
Current detection means for detecting a current flowing through the transfer member;
During an image forming job, when a recording material passes through the transfer nip portion, a voltage applied to the transfer member in a predetermined period in which a corresponding region between the recording material passes through the transfer nip portion. Is switched from the first transfer voltage applied to the reference voltage to an absolute value lower than the first transfer voltage, and the voltage applied to the transfer member is switched from the first transfer voltage to the reference voltage. By time, a setting mode for setting a second transfer voltage to be applied to the transfer member during image formation can be executed based on the voltage detected by the voltage detection unit and the current detected by the current detection unit Control means,
The control means changes the interval between the subsequent recording material and the recording material based on the voltage detected by the voltage detecting means by the predetermined time during the setting mode.
An image forming apparatus. In the setting mode, the control means switches the voltage applied to the transfer member to the first transfer voltage during the subsequent setting mode based on the voltage detected by the voltage detection means by the predetermined time. Change the voltage switching timing,
The image forming apparatus according to claim 1. The control means does not set the second transfer voltage when the voltage applied to the transfer member does not reach a set voltage within a predetermined range in the setting mode.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The predetermined time is a time until the voltage applied to the transfer member starts to be switched to the first transfer voltage.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. When the voltage detected by the voltage detection unit reaches the set voltage by the predetermined time, the control unit corresponds to the voltage that has reached the set voltage among the detected voltages and the voltage. Setting the transfer voltage based on the current detected by the current detection means and the voltage-current characteristics of the transfer member;
The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus. The control means includes a plurality of voltages detected by the voltage detection means in response to sequentially passing a plurality of currents having different sizes through the transfer member during a pre-rotation of the image forming job, and the plurality of currents. The voltage-current characteristic is obtained based on
The image forming apparatus according to claim 5. When the second transfer voltage is set, the control unit returns the changed recording material-to-recording material interval and the changed voltage switching timing at the start of the image forming job.
The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. The control unit starts the setting mode every time information relating to an image forming time exceeds a predetermined value during an image forming job.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The information relating to the image formation time is the number of recording materials on which image formation has been performed.
The image forming apparatus according to claim 8. The image carrier is a photoconductor in which an electrostatic latent image is developed into a toner image by a developer.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The image carrier is an intermediate transfer member to which a toner image on a photosensitive member developed with a developer is transferred.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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