JP2010060756A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which enhances accuracy and reproducibility of control to be performed on the basis of results obtained by detecting a predetermined electrostatic image by securing the SN ratio of an output signal from a potential sensor to be high even when charging or development is performed by using a voltage including an AC voltage. <P>SOLUTION: By forming a test electrostatic image on a photosensitive drum 1 and detecting it by the potential sensor 30 when starting up the image forming apparatus first in one day, the image deletion state (lowering state of surface resistance) of the photosensitive drum 1 is measured, and run time of image deletion restoring sequence is set according to the results of measurement. Oscillating voltage is applied to a charging roller 2 so as to electrify the photosensitive drum 1 by 1/6 of peripheral length of the photosensitive drum 1, and the test electrostatic image is written by an exposure device. Before the test electrostatic image approaches the potential sensor 30, the oscillating voltage is turned off. Thus, high frequency noise caused by AC current of high voltage high frequency included in the oscillating voltage does not appear in the output signal from the potential sensor 30, thereby measuring accuracy of the image deletion state is enhanced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  An image forming apparatus that performs charging or development using a voltage including an alternating voltage, and more specifically, detects an electrostatic image on a passing photosensitive member with the electrode surface facing the photosensitive member between the charging unit and the developing unit. It is related with the control which raises the SN ratio at the time of doing.

  The surface of a charged photoconductor (photosensitive drum, etc.) is exposed to form an electrostatic image, the electrostatic image is developed with toner to form a toner image, and the toner image carried on the photoconductor is used as a recording material or intermediate An image forming apparatus for transferring to a transfer body is widely used. Some image forming apparatuses include a charging unit that applies an oscillating voltage in which an AC voltage is superimposed on a DC voltage to a transfer member (transfer roller or the like) to charge the surface of the photoreceptor to a predetermined dark portion potential. . Also, many image forming apparatuses apply an oscillating voltage obtained by superimposing an alternating voltage on a direct current voltage to a developer bearing member (developing sleeve, etc.) carrying a charged toner, thereby converting the electrostatic image on the photosensitive member into a toner. Developing means for developing the image is provided.

  In the image forming apparatus, if discharge products generated in processes involving discharge such as charging and transfer accumulate on the surface of the photoconductor, the hygroscopicity increases and the surface resistance of the photosensitive drum decreases, and the image is formed immediately after the image formation. An image defect called flow tends to occur.

  Patent Document 1 discloses an image forming apparatus that evaporates water on the surface of a photoconductor by heating and heating it with a drum heater while idling the photoconductor to prevent image flow.

  In Patent Document 2, in order to judge the image flow state of a photoconductor, a cylindrical electrode surface is opposed to the photoconductor at an interval of 10 to 100 μm, and an electrostatic image on the photoconductor passing therethrough has a dot size. An example of detection means for detecting with resolution is shown. This detection means detects a predetermined electrostatic image formed in parallel with the electrode surface with a predetermined line width, and outputs an output voltage corresponding to a differential waveform of the potential distribution of the electrostatic image.

  In Patent Document 3, a charged potential (surface defect) of a photoconductor is detected with dot size resolution in a state where an outer surface of an insulating film covering the periphery of a cylindrical surface of a wire electrode is in contact with the photoconductor. An example of the detecting means is shown.

JP 2002-40876 A Japanese Patent Laid-Open No. 11-183542 JP 2004-77125 A

  In order to prevent image flow, it is considered to arrange the detection means shown in Patent Documents 1 and 2 between the charging means and the developing means and adjust the heating conditions for preventing image flow shown in Patent Document 1. It was done. At this time, if the charging unit using the oscillating voltage in which the AC voltage is superimposed on the DC voltage and the developing unit using the oscillating voltage in which the AC voltage is superimposed on the DC voltage, the SN ratio of the output signal of the detecting unit is large. It turned out to be reduced.

  In the detection means disclosed in Patent Documents 2 and 3, minute changes in the electric field when an electrostatic image passes through the electrode surface are picked up by the electrode surface facing the photoconductor. For this reason, even if it is slightly away from the electrode surface, if a high voltage and high frequency AC voltage of several kV and several kHz is used in the charging means and the developing means, large radio noise generated by the AC voltage is picked up through the electrode surface. End up.

  Therefore, even when the predetermined electrostatic image is written equally on the photosensitive member using the exposure unit, the output signal when the predetermined electrostatic image is detected by the detection unit greatly varies due to the influence of noise. When the predetermined electrostatic image is detected, the SN ratio of the output signal of the detection means is lowered, and the accuracy and reproducibility of the heating control of the photosensitive member based on the detection result cannot be ensured.

  According to the present invention, even when charging or development is performed using a voltage including an AC voltage, the SN ratio of the output signal of the detection unit is ensured to be high, and the accuracy of the control performed based on the detection result of a predetermined electrostatic image. Another object of the present invention is to provide an image forming apparatus capable of improving reproducibility.

  The image forming apparatus of the present invention forms an electrostatic image by exposing the photoconductor, a charging unit that charges the photoconductor using a voltage including an alternating voltage, and the photoconductor charged by the charging unit. An exposure unit; a developing unit that develops the electrostatic image with toner; and an electrostatic image on the photosensitive member that is passed between the charging unit and the developing unit with the electrode surface facing the photosensitive member. And detecting means for detecting. Then, after controlling the charging unit so that a predetermined electrostatic image is formed, the charging unit is configured to reduce the AC voltage of the charging unit at least during a period in which the predetermined electrostatic image is detected by the detection unit. Control means for controlling the means is provided.

  In the image forming apparatus according to the present invention, the AC voltage used in the charging unit is reduced until the predetermined electrostatic image reaches the detection unit after charging the rotation region of the photosensitive member on which the predetermined electrostatic image is formed. The Since the AC voltage of the charging unit decreases before the predetermined electrostatic image to be detected reaches the detection unit, when the predetermined electrostatic image reaches the detection unit, noise caused by the AC voltage is detected by the detection unit. It becomes difficult to output. During a period when a predetermined electrostatic image is detected, a state in which noise due to the AC voltage of the charging unit is low continues.

  Therefore, even when charging is performed using a voltage including an AC voltage, the SN ratio of the output signal of the detection means can be ensured higher than when a predetermined electrostatic image is passed while the AC voltage is high. As a result, the accuracy and reproducibility of the control performed based on the detection result of the predetermined electrostatic image is increased.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, as long as the detection unit detects a predetermined electrostatic image in a state where the AC voltage is lowered than usual, a part or all of the configuration of the embodiment is replaced with the alternative configuration. This embodiment can also be implemented.

  In the first embodiment, an image forming apparatus that directly transfers a toner image from a photosensitive drum to a recording material in a sheet-fed manner will be described. However, an image forming apparatus that uses an intermediate transfer belt and an image forming apparatus that uses a recording material conveyance belt. But it can be done.

  In the second embodiment, an image forming apparatus using an intermediate transfer belt will be described. However, the image forming apparatus using a recording material conveyance belt can also be implemented.

  In addition, about the general matter regarding the image forming apparatus and electric potential sensor which are shown by patent documents 1-3, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted. In addition, the reference symbols in parentheses shown in the configuration names used in the claims are examples for assisting understanding of the invention, and are not intended to limit the configuration to the corresponding members in the embodiments. Absent.

<First Embodiment>
FIG. 1 is an explanatory diagram of a configuration of an image forming apparatus to which a potential sensor is attached.

  As shown in FIG. 1, the image forming apparatus 100 forms a toner image on the photosensitive drum 1 and transfers it to the recording material P at the transfer portion T1. The sheet P to which the toner image is transferred is sent to the fixing device 8 to fix the toner image.

  A charging roller 2, an exposure device 3, a developing device 4, a transfer roller 5, a cleaning device 6, and a potential sensor 30 are disposed around a photosensitive drum 1 that is an example of a photosensitive member. The photosensitive drum 1 is composed of an electrophotographic photosensitive member containing a compound in which at least the surface layer of a conductive cylindrical aluminum substrate is cured by polymerization or crosslinking, and is rotated by an image forming apparatus main body (not shown). It is supported freely. An amorphous silicon optical semiconductor can also be used as the photosensitive layer.

  The charging roller 2, which is an example of a charging unit, rotates in contact with the photosensitive drum 1 in a state where an oscillating voltage obtained by superimposing an AC voltage on a DC voltage is applied from the power source D 3, thereby causing the photosensitive drum 1 to have a uniform negative polarity. Charge to dark part potential VD.

  The exposure apparatus 3, which is an example of an exposure unit, scans the photosensitive drum 1 charged to the dark portion potential VD with a laser beam (wavelength λ = 780 nm) and reduces the potential of the exposed portion to the bright portion potential VL. An electrostatic image is formed.

  The developing device 4 which is an example of a developing unit develops the electrostatic image formed on the photosensitive drum 1 with a negatively charged toner to form a toner image. The developing device 4 rubs the photosensitive drum 1 by carrying toner on the developing sleeve 4s rotating around the fixed magnetic pole 4m. By applying an oscillating voltage in which an AC voltage is superimposed on the developing voltage Vdc from the power source D4 to the developing sleeve 4s, the toner is transferred to the bright portion potential VL portion of the photosensitive drum 1 and the electrostatic image is reversely developed.

  The transfer roller 5, which is an example of a transfer unit, is in contact with the photosensitive drum 1 to form a transfer portion T <b> 1 that sandwiches and conveys the recording material P. The toner image charged negatively and carried on the photosensitive drum 1 is transferred to the recording material P that is nipped and conveyed by applying a positive DC voltage from the power source D1 to the transfer roller 5.

  The recording material P is taken out from the cassette 20 and separated one by one by the separation roller 21, conveyed from the conveyance roller 22 to the registration roller 23, and waits. The registration roller 23 sends the recording material P to the transfer portion T1 in synchronization with the toner image carried on the photosensitive drum 1.

  The cleaning device 6 rubs the photosensitive drum 1 with the cleaning blade 6b to remove the transfer residual toner attached to the surface of the photosensitive drum 1 that has passed through the transfer portion T1. Further, during the image formation, the cleaning device 6 rubs the rotating photosensitive drum 1 with the cleaning blade 6 b and frictionally heats it, thereby evaporating water adhering to the surface of the photosensitive drum 1. For this reason, when the photosensitive drum 1 continues to rotate, the surface resistance of the photosensitive drum 1 gradually recovers as moisture is removed through rubbing.

  The potential sensor 30 is disposed in contact with the photosensitive drum 1 between the exposure position of the exposure device 3 and the development position of the development device 4, and detects a predetermined electrostatic image formed during non-image formation.

<Electric potential sensor>
2 is an explanatory diagram of the configuration of the potential sensor, FIG. 3 is an explanatory diagram of the manufacturing method of the potential sensor, FIG. 4 is an explanatory diagram of the electrode pattern, FIG. 5 is an explanatory diagram of the output circuit of the potential sensor, and FIG. It is explanatory drawing of an output voltage.

  As shown in FIG. 2, the potential sensor 30 is formed in a thin plate-like appearance having a thickness L1 = 100 μm, a width L2 = 2.5 mm, and a length L3 = 20 mm in which resin films are laminated, and electrode members are embedded therein. The semi-cylindrical surface at the tip is brought into contact with the photosensitive drum 1.

  The potential sensor 30 is cantilevered from the main body of the image forming apparatus, and a tip portion thereof is in contact with the photosensitive drum 1 with a predetermined angle of inclination. A contact pressure with respect to the photosensitive drum 1 is set by a bending reaction force of the thin plate portion. ing. The potential sensor 30 contacts the outer surface of an insulating film layer having a thickness of 25 μm covering the surface of the electrode surface with the photosensitive drum 1 so that the facing distance between the curved surface of the electrode surface and the photosensitive drum 1 is 25 μm. Is set.

  A contact line where the potential sensor 30 contacts the photosensitive drum 1 is positioned in parallel with a straight line (cylindrical generating line) that crosses the surface of the photosensitive drum 1 in the axial direction. For this reason, the edge of the electrostatic image 1 s formed on the photosensitive drum 1 in the main scanning direction passes through the contact line of the potential sensor 30 almost simultaneously.

  The substrate film layer 31 of the potential sensor 30 is folded at a predetermined curvature so as to form a cylindrical surface that contacts the photosensitive drum 1. The thin film electrode layer 32 is formed as a thin film pattern, and constitutes a semi-cylindrical curved detection electrode portion 32 a that is in close contact with the inner surface of the folded region of the substrate film layer 31. The center layer 33 is bonded to the inner surface of the substrate film layer 31 so as to give a predetermined curvature to the substrate film layer 31 and the thin film electrode layer 32. The overlap of the substrate film layer 31 and the center layer 33 constitutes a thin plate-like appearance of the potential sensor 30 and can be bent elastically. The thin-film electrode layer 32 includes a connection wiring portion 32 b that is connected to the detection electrode portion 32 a and is fixed to the inner side surface of the substrate film layer 31 so that wiring can be performed on the opposite side of the folded region of the substrate film layer 31.

As shown in FIG. 3, the potential sensor 30 was manufactured under the following conditions.
Substrate film layer 31, film layer 35: Lumirror (trademark) manufactured by Toray: PET film, thickness 25 μm, width 2.5 mm, length 45 mm, Young's modulus 2.7 GPa, resistivity 1 × 10 ¹⁵ Ω · cm
Thin film electrode layer 32: Silver paste made by Shinto Chemitron: K-3424, resistance 1.59 × 10 ⁻⁶ Ωcm
Detection electrode part 32a: width 212 μm, length 2 mm, thickness 10 μm
Connection wiring part 32b: width 0.5 mm
First adhesive layer 34, second adhesive layer 36: Olivevine (trademark) manufactured by Toyo Ink, acrylic pressure-sensitive adhesive, thickness 20 μm

  As shown in FIG. 3A, the silver paste was screen-printed on the substrate film layer 31 of the PET film, and the L-shaped detection electrode portion 32a and the connection wiring portion 32b shown in FIG. 4 were formed into a thin film.

  As shown in FIG. 4, in order to ensure insulation of the thin film electrode layer 32, the electrode pattern of the thin film electrode layer 32 is formed closer to the inner side than the edge of the substrate film layer 31. The detection electrode portion 32a is formed in a planar shape along the folding line 33s on the inner side surface where the substrate film layer 31 is folded. The connection wiring part 32b is arranged continuously to the detection electrode part 32a so that the pad 32c can be wired on the opposite side of the return line 33s.

  As shown in FIG. 3B, an acrylic pressure-sensitive adhesive was applied as a first adhesive layer 34 adhesive from above with a bar coater to a thickness of 20 μm and dried.

  As shown in FIG. 3C, the PET film was attached as a film layer 35 from above.

  As shown in (d) of FIG. 3, the adhesive was further applied thereon as a second adhesive layer 36 with a bar coater to a thickness of 20 μm and dried.

  As shown in FIG. 3 (e), it was bent at a distance of 20 mm from one end in the length direction and was completely attached.

  As shown in FIG. 5, the potential sensor 30 is attached so as to be inclined by 15 degrees with respect to the normal line of the photosensitive drum 1 and to have a pressure of 0.1 g / mm.

  The controller 110 controls the exposure device 3 before the image formation is started to form a test electrostatic image 1 s that is 2 dots wide and continuously continuous in the main scanning direction on the photosensitive drum 1. When the photosensitive drum 1 rotates in the direction of the arrow R1, the test electrostatic image 1s of the bright portion potential VL formed on the surface of the photosensitive drum 1 charged to the dark portion potential VD passes through the potential sensor 30. When the detection electrode unit 32 a faces the photosensitive drum 1 at a certain distance, a voltage signal corresponding to a change in the surface potential of the photosensitive drum 1 is extracted from the detection electrode unit 32.

  In the process in which the test electrostatic image 1s approaches and approaches the potential sensor 30, an induced current flows out from the detection electrode portion 32a, and a positive voltage signal is output. Thereafter, in the process in which the test electrostatic image 1 s moves away through the potential sensor 30, an induced current flows into the detection electrode portion 32 a and a negative voltage signal is output. In this way, as shown in FIG. 6A, an output corresponding to the differential waveform of the potential distribution of the test electrostatic image 1s is extracted from the potential sensor 30.

  As shown in FIG. 6A, the potential sensor 30 outputs the peak of the output voltage at the rise and fall of the potential distribution of the test electrostatic image. The positive / negative peak value Vp of the output voltage corresponds to the slope of the edge of the potential distribution of the test electrostatic image 1s. The control unit 110 measures the peak value Vp of the output voltage of the potential sensor 30 to determine the image flow state on the photosensitive drum 1 without forming a toner image.

  The control unit 110 takes in the output of the potential sensor 30 through the signal processing circuit 120. The output voltage of the potential sensor 30 is amplified by the amplifier circuit 121, converted to a digital value by the AD converter circuit 122, and taken into the control unit 110. The control unit 110 compares the measured peak voltage against a reference value measured in a low temperature and low humidity (LL) environment when the photosensitive drum 1 is in a new state.

Consider a case in which the potential on the photosensitive drum 1 side is changed by regarding the detection electrode portion 32a and the surface of the photosensitive drum 1 as a capacitor facing each other with an electrode distance d. At this time, the voltage V output when the induced current enters and exits the detection electrode portion 32a changes according to the inter-electrode distance d. Therefore, the output of the potential sensor 30 is caused by the eccentric rotation of the photosensitive drum 1 or the vibration of the potential sensor 30. V fluctuates.
V = Q / C = k × Q × d / S (k: constant, d: distance between electrodes, S: electrode area)

  Therefore, the output of the potential sensor 30 changes by 10% only by changing the distance d between the electrodes of 25 μm by 2.5 μm due to the eccentric rotation of the photosensitive drum 1 or the like. However, since the tip of the potential sensor 30 is in contact with the photosensitive drum 1, a mechanism and control for keeping the distance between the detection electrode portion 32 a and the photosensitive drum 1 constant is unnecessary. Following the eccentric rotation of the photosensitive drum 1, the facing interval can be kept constant with the thickness of the substrate film layer 31.

  The potential sensor 30 is in contact with the surface of the photosensitive drum 1 at an angle so that the tip protrudes in the rotational direction within a plane perpendicular to the width direction of the photosensitive drum 1. By making the contact in this way, the frictional force with respect to the photosensitive drum 1 lifts the potential sensor 30 and reduces the contact pressure. Therefore, even if the photosensitive drum 1 rotates eccentrically, the potential sensor 30 can maintain a stable small contact pressure. Can keep track of the surface precisely.

<Image flow>
7 is an explanatory diagram of an electrostatic image in which image flow occurs, FIG. 8 is an explanatory diagram of an image in which no image flow has occurred, FIG. 9 is an explanatory diagram of an image in which image flow has occurred, and FIG. 10 is an output of a potential sensor. FIG.

As shown in FIG. 1, since the charging roller 2 performs charging accompanied by the discharge of the AC voltage, the discharge of various nitrogen oxides NO _X and ozone compounds X—O ₃ is formed on the surface of the photosensitive drum 1. Product accumulates. Since the transfer roller 5 also transfers the toner image with discharge, these discharge products are accumulated on the surface of the photosensitive drum 1.

  When discharge products accumulate on the surface of the photosensitive drum 1, the hydrophilicity of the surface increases and moisture in the air is adsorbed during the stop period. Therefore, the surface of the photosensitive drum 1 absorbs moisture as the image formation is accumulated. Surface resistance tends to decrease.

  As shown in FIG. 7, when the photosensitive drum 1 charged to the dark portion potential VD is exposed and the test electrostatic image 1s is written, immediately after the exposure, the potential of the exposed portion decreases to the bright portion potential VL. Thus, the slope of the edge of the potential distribution is steep. However, if the surface resistance of the photosensitive drum 1 is reduced, the charge moves on the surface of the photosensitive drum 1 from exposure to development, the edge of the potential distribution of the test electrostatic image 1s is broken, and the inclination becomes gentle. The peak value of the potential also decreases. As a result, the line width W2 of the image developed using the DC voltage Vdc by the developing device is narrower than the line width W1 when the surface resistance of the photosensitive drum 1 is not reduced. Further, the potential difference H2 between the DC voltage Vdc, which is the development contrast, and the peak of the potential distribution is lower than the potential difference H1 when the surface resistance of the photosensitive drum 1 is not lowered, and the toner adhesion amount is reduced to reduce the image density. Decreases.

  Image flow is likely to occur after the image forming apparatus 100 has been left for a long time after being stopped, and is unlikely to occur during continuous operation of the image forming apparatus 100. This is because the discharge product continues to be scraped off by the rubbing of the cleaning blade 6 b of the cleaning device 6 during the operation of the image forming apparatus 100. Further, during the image formation, the surface temperature of the photosensitive drum 1 is kept higher than the surroundings due to the temperature difference because the radiant heat of the fixing device 8 and the frictional heat of the cleaning blade 6b maintain the surface temperature of the photosensitive drum 1 high. This is because moisture adsorption is suppressed.

  However, after a certain amount of time has passed after the image forming apparatus 100 is stopped, the temperature of the photosensitive drum 1 drops to the same temperature as the surroundings. Therefore, the discharge product adheres to the surface of the photosensitive drum 1 and the hygroscopicity and hydrophilicity are increased. It will be easier to adsorb moisture than the surroundings.

  First, an experiment to generate an image stream under a high-temperature and high-humidity environment (HH: 30 ° C., 80% RH) using the photosensitive drum 1 that has been subjected to a 100,000 sheet passing image test to easily generate an image stream. went. Using the photosensitive drum 1 that facilitates the occurrence of image flow, 40 images of the test electrostatic image (line width 2 dots 80 μm) 1s in the main scanning direction, 10,000 sheets intermittently on a regular sheet of A4 size transverse feed The sheets were continuously imaged. As shown in FIG. 8, no image flow occurred at this point.

  The photosensitive drum 1 was left overnight and the same image was formed the first morning. Then, an image flow occurred, and a part of the line image became white and thin as shown in FIG.

  Next, a test electrostatic image 1 s was formed on the photosensitive drum 1 to output an image, and the potential distribution of the test electrostatic image 1 s was measured using the potential sensor 30. By varying the temperature and humidity, the photosensitive drum 1, the stop time, the stop environment, etc., image flows of different degrees were intentionally generated, and the correlation with the peak value of the output signal of the potential sensor 30 was examined.

  As shown in FIG. 10, the test electrostatic image 1s was detected by the potential sensor 30 under various conditions with different image flow levels, the output signal was recorded, and then a character image having a line width of 100 μm was formed. As a result, image flows having different levels were reproduced as character images, and detection signals of the test electrostatic image 1s corresponding to the image flow levels were collected. The rate of change in the figure is based on the signal level 120 mV of the output signal from the new photosensitive drum 1 measured in advance as a reference signal, and the peak voltage changed by what percentage from the reference signal under each image flow condition. It was shown numerically.

  As a result, a high correlation was confirmed between the degree of image flow of the formed image and the peak voltage of the collected output signal. Further, when the image flow of the character image can be confirmed visually, it has been confirmed that the peak voltage is reduced by approximately 15% or more with respect to the output signal from the new photosensitive drum 1 measured in advance. . Thus, it was confirmed that the occurrence of image flow can be sufficiently predicted by measuring the peak voltage of the detection signal of the test electrostatic image 1s using the potential sensor 30. The state of the image flow is accurately estimated based on the magnitude of the peak voltage, the degree of blur of the actual character image is also determined, and it can be accurately determined whether or not the image flow is generated when the image is actually formed.

  In order to recover the surface resistance of the photosensitive drum 1, the image forming apparatus 100 waits for image formation, idles the photosensitive drum 1, and frictionally heats the photosensitive drum 1 by sliding of the cleaning blade 6 b. This idling time is set according to the peak voltage of the output signal of the potential sensor 30, and as shown in FIG. 6B, the idling time is set longer as the peak voltage Vp is lower. However, as shown in Patent Document 1, the surface resistance may be recovered using a drum heater. In this case, the energization time of the drum heater may be set longer as the peak voltage Vp is lower.

  In any case, in the first startup sequence in the morning, the test electrostatic image 1s is measured using the potential sensor 30, and the control time for restoring the surface resistance of the photosensitive drum 1 is set according to the measurement result. Then, after the control for recovering the surface resistance is performed for the set time, the photosensitive drum 1 is stopped and the first start sequence in the morning is completed.

<Charging means>
FIG. 11 is an explanatory diagram of an output signal of a potential sensor that detects a test electrostatic image while the vibration voltage is in an ON state, and FIG. 12 is an explanatory diagram of an output signal of the potential sensor that detects the test electrostatic image by turning off the vibration voltage. It is.

  As shown in FIG. 5, the charging roller 2 includes an elastic layer 2b made of a rubber material formed with a sponge on a conductive support (using a round bar made of a metal material such as iron, copper, stainless steel, aluminum and nickel) 2a. The elastic layer 2b is provided with conductivity. If the thickness of the elastic layer 2b is in the range of 1 to 500 mm, it can be used sufficiently.

  An oscillating voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging roller 2 from a power source D3. The oscillating voltage includes an AC voltage whose voltage value periodically changes with time, and the AC voltage preferably has a peak-to-peak voltage that is twice or more the discharge start voltage when only the DC voltage is applied. The waveform of the AC voltage is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or a pulse wave, but a sine wave that does not include a harmonic component is preferable from the viewpoint of reducing charging noise.

  The power source D3 outputs an AC voltage having a frequency of 1.8 kHz and performs constant current control with a total current of 2000 μA. The DC voltage superimposed on the AC voltage is set equal to the charging target (dark part potential VD) of the photosensitive drum 1. That is, the DC voltage VD applied to the charging roller 2 is copied onto the surface of the photosensitive drum 1 with a bidirectional discharge due to the AC voltage.

  During normal image formation, if the oscillating voltage applied to the charging roller 2 is turned off, normal charging and normal electrostatic image writing cannot be performed. Therefore, application of the oscillating voltage is interrupted until the image formation is completed. There is nothing. However, when the potential sensor 30 detects the test electrostatic image 1s in a state where the vibration voltage is applied to the charging roller 2, high level noise appears in the output waveform measured by the oscilloscope as shown in FIG. Since radio wave noise is generated due to the influence of the AC voltage included in the vibration voltage, the potential sensor 30 serves as an antenna to pick up the noise.

  Therefore, in the image forming apparatus 100, when the oscillating voltage is applied to the charging roller 2 to charge the rotating region where the test electrostatic image 1s is formed, the oscillating voltage is turned off. Thereby, when the potential sensor 30 detects the test electrostatic image 1s, no radio wave noise is generated, and an output waveform with less noise is obtained as shown in FIG.

<Developing means>
The developing device 4 is roughly configured by a developing sleeve 4s and a hopper for supplying a developer to the developing sleeve 4s. The developing sleeve 4 s is disposed so as to maintain a constant gap of 0.3 mm along the longitudinal direction between the developing sleeve 4 s and the photosensitive drum 1.

  As a developer, a one-component magnetic negative polarity toner was used. As the developer, a two-component developer composed mainly of a nonmagnetic negative toner and a magnetic carrier, or a one-component developer composed of a magnetic toner may be used.

  An oscillating voltage obtained by superimposing an alternating voltage (Vpp = ˜1.2 kV) on a negative direct current voltage (Vdc = ˜−350 V) is applied to the developing sleeve 4s. The magnetic toner carried on the surface of the developing sleeve 4s is conveyed to the developing position and is urged by the DC voltage Vdc in the process of reciprocating between the photosensitive drum 1 and the developing sleeve 4s in response to the AC voltage. The image is transferred from 4 s to the electrostatic image on the photosensitive drum 1.

  During normal image formation, normal development becomes impossible if the vibration voltage applied to the developing sleeve 4s is turned off. Therefore, the application of vibration voltage is not interrupted until the image formation is completed. However, when the potential sensor 30 detects the test electrostatic image 1s in a state where an oscillating voltage is applied to the developing sleeve 4s, a high level noise appears in the output waveform measured by the oscilloscope as shown in FIG. Since radio wave noise is generated due to the influence of the AC voltage included in the vibration voltage, the potential sensor 30 serves as an antenna to pick up the noise.

  Therefore, in the image forming apparatus 100, the vibration voltage applied to the developing sleeve 4s is turned off throughout the process of forming the test electrostatic image 1s and measuring with the potential sensor 30. As a result, radio noise is not generated, and an output waveform with less noise is obtained from the potential sensor 30, as shown in FIG.

<Example 1>
FIG. 13 is a control flowchart of the first embodiment, and FIG. 14 is a timing chart of application of vibration voltage to the charging roller.

  As shown in FIG. 13 with reference to FIG. 5, when the user turns on the power of the image forming apparatus 100, the fixing temperature adjustment sensor 8s determines whether the image forming apparatus 100 has been operated for the first time (one morning) on the day (S11). ).

  In the morning (YES in S11), the installation environment of the apparatus is determined by the in-machine environment sensor 100s. In the case of a high humidity environment (YES in S12), rotation of the photosensitive drum 1 is started (S13).

  When the photosensitive drum 1 rotates at a predetermined speed, application of an oscillating voltage to the charging roller 2 is started (S14). When the charged rotation area of the photosensitive drum 1 reaches the exposure position, exposure of the test electrostatic image 1s is started with the above-described line width and pitch (S15).

  The application of the oscillating voltage to the charging roller 2 is turned off 50 msec before the first test electrostatic image 1s reaches the measurement position of the potential sensor 30 (S16). Then, the state of the test electrostatic image 1s on the surface of the photosensitive drum 1 is measured by the potential sensor 30 (S17).

  When the peak value of the output voltage of the potential sensor 30 is lower by 15% or more than the reference value (no image flow) measured in the new state, the control unit 110 determines that the image flow is present (S18). YES), an image flow elimination sequence is executed (S19).

  After completion of the image flow elimination sequence (S19) or when the peak value of the output voltage of the potential sensor 30 has not decreased by 15% or more compared to the reference value (no image flow) (NO in S18), the photosensitive drum 1 Is stopped (S20).

  Subsequently, a pre-rotation sequence is started as a test operation of the main body in order to confirm the energization state of the charging roller 2 and the operation status of the fixing device 8 and the transport unit in advance (S21). Then, after the pre-rotation sequence (S21) is completed, “Copying is possible” is displayed on the operation unit 108 (S22), and the copying operation is accepted.

  Note that if it is not the morning (NO in S11) or not in the high humidity environment (NO in S12), the image pre-removal sequence (S19) is unnecessary, and thus the normal pre-rotation sequence is immediately executed (S21).

  In the control of the first embodiment, as shown in FIG. 10, the execution time of the image flow elimination sequence is set according to the rate of decrease in the peak value of the output signal of the potential sensor 30. However, the image flow elimination sequence may be started without setting the execution time. The process of writing the test electrostatic image 1s on the photosensitive drum 1 at a predetermined time (for example, every 20 seconds) and re-measurement with the potential sensor 30 may be repeated until the rate of decrease in the peak value becomes 15% or less.

  As shown in FIG. 14 with reference to FIG. 1, the outer diameter of the photosensitive drum 1 is Φ30 mm, and the outer diameter of the charging roller 2 is Φ16 mm. The exposure position of the scanning line by the exposure device 3 is set at an angle of 60 ° along the rotation direction with the charging roller 2 as a base point. Further, the tip of the potential sensor 30 abuts at an angle of 80 ° along the rotation direction from the charging roller 2 as a base point, and the developing device 4 develops at an angle of 90 ° along the rotation direction from the charging roller 2 as a base point. The sleeve 4s is opposed.

  The photosensitive drum 1 rotates at a process speed of 110 mm / sec to form an image. When the photosensitive drum 1 starts to rotate at a predetermined speed, the vibration voltage described above is applied to the charging roller 2. The delay time of the rise and fall of the oscillating voltage is 50 msec.

  The circumferential length of the photosensitive drum 1 from the charging position to the exposure position of the scanning line at the rotation angle position of 60 ° on the circumference of the photosensitive drum 1 having an outer diameter of Φ30 mm is about 15.7 mm. The arrival time from the charging position to the exposure position of the scanning line is about 142 msec because it travels about 15.7 mm at a peripheral speed of 110 mm / sec. However, since the rise of the oscillation voltage has a delay of 50 msec, scanning line exposure is started 192 msec after the start of charging. The line width (sub-scanning direction length) of the test electrostatic image 1s written by the exposure apparatus 3 is about 100 μm with a 2-dot width.

  The circumferential length of the photosensitive drum 1 from the charging position to the measurement position of the potential sensor 30 at the rotation angle position of 80 ° on the circumference of the photosensitive drum 1 having an outer diameter of Φ30 mm is about 20.85 mm. When 104 μm = 0.1 mm test electrostatic images 1s are written at intervals of 0.1 mm over a circumference of about 20.85 mm, about 104 test electrostatic images 1s can be formed.

  In Example 1, before the charged area of the photosensitive drum 1 reaches the contact position of the potential sensor 30, the test electrostatic image 1s is reduced to 50 msec = 5.5 mm in consideration of the delay time 50 msce of the oscillating voltage fall. As soon as is approaching the measurement position, the oscillating voltage is stopped early.

  For this reason, the peripheral area where the test electrostatic image 1s can be formed is reduced to 15.35 mm, but the test electrostatic image 1s of 100 μm = 0.1 mm is spaced by 0.1 mm over the peripheral length of 15.35 mm. In this case, about 76 test electrostatic images 1s can be formed. And since generation | occurrence | production of the radio wave noise by the oscillating voltage applied to the charging roller 2 can be prevented, the electric potential sensor 30 does not need to be influenced by noise.

<Example 2>
In the control of Example 1, the vibration voltage applied to the charging roller 2 was turned off before the first test electrostatic image reached the measurement position of the potential sensor 30. On the other hand, in Example 2, before the first test electrostatic image reached the measurement position of the potential sensor 30, only the AC voltage of the oscillating voltage applied to the charging roller 2 was reduced. By reducing the peak-to-peak voltage Vpp of the AC voltage to 1/2 to 1/50 of the normal time, the amplitude of radio noise is reduced, and the noise level appearing in the output signal of the potential sensor 30 is reduced to 1/2 to 1/50. Lowered to.

  As a result, as shown in FIG. 12, the potential distribution of the test electrostatic image 1s can be measured with little noise, and the control time of the image flow elimination sequence (S19: FIG. 13) can be set appropriately with less error.

  In the second embodiment, the configuration of the image forming apparatus 100 is as described with reference to FIGS. 1 to 13, and the flowchart and the time chart of the first embodiment are described with reference to FIGS. 13 and 14. Just as you did.

  In the second embodiment, before the charged area of the photosensitive drum 1 reaches the potential sensor 30, the high voltage of the charging roller 2 is applied as early as 50 msec = 5.5 mm in consideration of the falling 50 msce of the oscillation voltage of the charging roller 2. To do. And since the value of the peak voltage Vpp of an alternating voltage is reduced to 1/2 to 1/50 and generation | occurrence | production of a high frequency noise is reduced, there exists an effect which stabilizes the signal at the time of a measurement.

  In addition, it is good also as control which reduces a voltage to 1/2 to 1/50 in the whole oscillating voltage which superimposed the alternating voltage. In any case, since the generation of radio noise due to the oscillating voltage can be reduced, the influence of noise that the potential sensor 30 picks up unnecessarily is reduced.

<Example 3>
FIG. 15 is a flowchart of control of the third embodiment, and FIG. 16 is a timing chart of application of vibration voltage to the charging roller.

  In the control of Example 1, only the image flow state in the charging area until the application of the oscillating voltage was turned off, that is, the rotation area of 15.35 mm in the circumferential length of 94.2 mm of the photosensitive drum 1 having a diameter of 30 mm was measured. On the other hand, in the third embodiment, the charged area is sequentially fed every rotation of the photosensitive drum 1, and the image flow state is measured for all rotation areas of the photosensitive drum 1 having a peripheral length of 94.2 mm by a plurality of rotations. A predetermined electrostatic image (1 s) is formed on the rotation region of the photosensitive member (1) that has passed through the charging means (2) in which the AC voltage is reduced, without reducing the AC voltage in the next rotation. Thus, a predetermined electrostatic image (1s) is formed on the entire circumference of the photoconductor (1) through a plurality of rotations of the photoconductor (1) and detected by the detection means (30).

  In the control of the third embodiment, the timing at which the vibration voltage is started to be applied to the charging roller 2 and the timing at which the vibration voltage to be applied to the charging roller 2 is turned off are controlled in the same manner as in the first embodiment. As a control sequence, only the vibration voltage application start timing at each rotation is adjusted so that the vibration voltage is applied at the current rotation starting from the position where the vibration voltage was turned off at the previous rotation. Different from Example 1. Therefore, in the flowchart of FIG. 15, the steps common to the first embodiment are denoted by the same reference numerals as those in FIG.

  As shown in FIG. 15 with reference to FIG. 5, when the photosensitive drum 1 rotates at a predetermined speed, application of an oscillating voltage to the charging roller 2 is started (S14). When the charged rotation area of the photosensitive drum 1 reaches the exposure position, exposure of the test electrostatic image 1s is started (S15).

  The application of the oscillating voltage to the charging roller 2 is turned off 50 msec before the first test electrostatic image 1s reaches the measurement position of the potential sensor 30 (S16). Then, the test electrostatic image 1s is measured using the potential sensor 30 (S17).

  The control unit 110 counts the number of measurements in order to measure the image flow state by dividing the entire circumference of the photosensitive drum 1 into six times. When the number of measurements is 1 to 5 (YES in S25), the next measurement is performed, but when the number of measurements is 6 (NO in S25), the measurement is terminated and the state of the image flow is determined (S18). .

  When the number of times of measurement is 1 to 5 (YES in S25), the application of the vibration voltage to the charging roller 2 is turned ON 50msec before the position where the vibration voltage was turned off by the previous rotation reaches the charging position (S26). . Then, writing of the test electrostatic image 1s is started 50 msec after the position where the application of the vibration voltage is turned on reaches the exposure position (S15).

  As shown in FIG. 16, in Example 3, the image flow state is measured by 15.35 mm per rotation when the circumferential length of the photosensitive drum 1 is 94.2 mm. For this reason, the measurement of the image flow state of the entire circumference is completed with six rotations of the photosensitive drum 1. The circumference of the photosensitive drum 1 is normally charged 15.35 mm at each of the six rotations to form a test electrostatic image 1s (S15), and an image is generated using the potential sensor 30 with the vibration voltage turned off (S16). The flow state is measured (S17).

  When the number of rotations from the first time reaches 6 (YES in S28), control unit 110 completes the measurement of the image flow state.

  When the peak value of the output voltage of the potential sensor 30 is lower by 15% or more than the reference value (no image flow), the control unit 110 determines that there is an image flow (YES in S18), and the image flow. A cancellation sequence is executed (S19). The execution time of the image flow cancellation sequence is set so that the rotation region where the image flow state is most remarkable on the entire circumference of the photosensitive drum 1 can be returned to the normal range, and the image flow cancellation sequence is executed (S19).

  After completion of the image flow elimination sequence (S19) or when the peak value of the output voltage of the potential sensor 30 has not decreased by 15% or more compared to the reference value (no image flow) (NO in S18), the photosensitive drum 1 Is stopped (S20).

  Subsequently, a pre-rotation sequence is started as a test operation of the main body in order to confirm the energization state of the charging roller 2 and the operation status of the fixing device 8 and the transport unit in advance (S21). Then, after the pre-rotation sequence (S21) is completed, “Copying is possible” is displayed on the operation unit 108 (S22), and the copying operation is accepted.

  Note that if it is not the morning (NO in S11) or not in the high humidity environment (NO in S12), the image pre-removal sequence (S19) is unnecessary, and thus the normal pre-rotation sequence is immediately executed (S21).

  As shown in FIG. 16 with reference to FIG. 5, the photosensitive drum 1 forms an image at a process speed of 110 mm / sec. In the first rotation measurement, when the photosensitive drum 1 starts rotating at a predetermined speed, the vibration voltage of the charging roller 2 is applied. Stable charging becomes possible after a rise time of 50 msec.

  The distance from the charging position to the exposure position is about 15.7 mm corresponding to 60 degrees, and at a moving speed of 110 mm / sec, the arrival time from the charging position to the exposure position is about 142 msec. However, since the rising of the oscillation voltage exists for 50 msec, the exposure starts after 192 msec.

  The line width of the test electrostatic image 1s is about 100 μm. Before the test electrostatic image 1s (charged region) formed on the photosensitive drum 1 reaches the potential sensor 30, the vibration voltage is applied to the charging roller 2 in consideration of the falling 50 msce of the power supply D3 of the charging roller 2. Stop. That is, the application is stopped as early as 50 msec = 5.5 mm.

  For this reason, the formation area of the test electrostatic image 1s is 15.35 mm, and ON / OFF of the exposure is repeated with a width of 100 μm = 0.1 mm, so that approximately 76 test electrostatic images 1s can be formed. . The state of image flow on the surface of the photosensitive drum 1 can be measured by the potential sensor 30 without being affected by noise due to the vibration voltage of the charging roller 2.

  In the second rotation measurement, since the photosensitive drum 1 has already been rotated at a constant speed, the application of the vibration voltage is started 5.5 mm = 50 msec earlier than the position of the photosensitive drum 1 where the vibration voltage was previously stopped. Thereby, since the rising time of the oscillating voltage is 50 msec, stable charging at the second rotation is started from the position where normal charging was completed last time. As in the first rotation, the exposure starts after 192 msec. Before the charging area of the second rotation reaches the potential sensor 30, the vibration voltage of the charging roller 2 is stopped, and the measurement of the test electrostatic image 1s by the potential sensor 30 is executed in a state where the vibration voltage is stopped.

  Hereinafter, at the third rotation, the charging area is formed by connecting to the end of the charging area at the second rotation and the test electrostatic image 1s is written, and at the fourth rotation, the end of the charging area at the third rotation is connected. A charged area is formed and a test electrostatic image 1s is written. In this way, the same sequence is repeated, and the measurement of the image flow state through six rotations on the entire circumference of the photosensitive drum 1 (94.2 mm in this example) is completed.

  As a result, it is possible to measure the image flow state on the surface of the photosensitive drum 1 with the potential sensor 30 for the entire circumference of the photosensitive drum 1 without being affected by noise due to the vibration voltage of the charging roller 2.

<Example 4>
FIG. 17 is a time chart of the control of the fourth embodiment.

  In Example 1, before the potential sensor 30 measured the test electrostatic image 1s, the vibration voltage of the charging roller 2 was turned off to suppress noise in the output signal of the potential sensor 30 that detected the test electrostatic image 1s. In the fourth embodiment, the vibration voltage of the developing sleeve 4s is turned OFF in addition to the vibration voltage of the charging roller 2 to further suppress noise in the output signal of the potential sensor 30 that detects the test electrostatic image 1s. The control of the vibration voltage of the charging roller 2 has been described with reference to the flowchart of FIG.

  As shown in FIG. 5, when a vibration voltage is applied to the developing sleeve 4 s of the developing device 4 when measuring the test electrostatic image 1 s with the potential sensor 30, the alternating voltage component of the vibration voltage generates high-frequency radio noise. . Since the potential sensor 30 measures the induced current due to the surface electric field of the photosensitive drum 1 using the antenna-like electrode member, the high frequency noise generated from the developing sleeve 4s is carried on the detection signal as noise, and the correct measurement is performed. Make it difficult.

  Therefore, in the fourth embodiment, no oscillating voltage is applied to the developing sleeve 4 s during the period in which the image flow state of the photosensitive drum 1 is measured using the potential sensor 30. Since it is not necessary to develop the test electrostatic image 1s, not only the AC voltage but also the DC voltage Vdc is not applied. Thereby, generation | occurrence | production of a high frequency noise is suppressed and the output signal of the electric potential sensor 30 at the time of measurement of the test electrostatic image 1s is stabilized.

  The photosensitive drum 1 rotates at a process speed of 110 mm / sec, and a test electrostatic image 1 s having a line width of about 100 μm is formed in order to measure the image flow state of the photosensitive drum 1 with the potential sensor 30. A plurality of test electrostatic images 1s having a width of 0.1 mm are still formed on the photosensitive drum 1 after the image flow state of the photosensitive drum 1 is measured by the potential sensor 30.

  Therefore, if a normal vibration voltage is applied to the developing sleeve 4s, the toner image of the test electrostatic image 1s is developed, and then the transfer roller 5 is contaminated with toner, and the inside of the apparatus is also contaminated with toner. End up.

  Therefore, when measuring the image flow state of the photosensitive drum 1, switching to a low vibration voltage different from that during normal image formation can reduce toner contamination in the apparatus and suppress the consumption of excess toner.

  By the way, there are a reversal development system and a regular development system as a method of applying an oscillating voltage to the development sleeve 4s.

  First, a reversal development system in which the negative toner is placed on a low charged potential with the dark portion potential VD of the photosensitive drum 1 being −700 V and the bright portion potential VL after exposure being −100 V will be described. During normal image formation, an AC voltage of 1.8 kHz and a DC voltage of −300 V (fogging removal potential) are applied to the developing sleeve 4 s at AC 1.2 KVpp. The voltage conditions for charging and development are not limited to this example.

  When the mode for measuring the image flow state of the photosensitive drum 1 is entered, the oscillating voltage applied to the developing sleeve 4s turns off the AC voltage and switches the DC voltage off. By doing so, the potential of the developing sleeve 4 s becomes relatively lower than −100 V on the photosensitive drum 1, and it is possible to reduce the transfer of the negative toner to the photosensitive drum 1 and to reduce the toner scattered in the apparatus. At the same time, it is possible to suppress the consumption of excess toner when measuring the image flow state of the photosensitive drum 1.

  Next, a normal development system in which the negative toner is placed on a high charged potential assuming that the dark portion potential VD of the photosensitive drum 1 is +700 V and the bright portion potential VL after exposure is +100 V will be described. During normal image formation, an AC voltage of 1.8 kHz and a DC voltage of +300 V (fogging removal potential) are applied to the developing sleeve 4 s at AC 1.2 KVpp. The voltage conditions for charging and development are not limited to this example.

  As shown in FIG. 17 with reference to FIG. 5, when the mode for measuring the image flow state of the photosensitive drum 1 is entered, the oscillating voltage applied to the developing sleeve 4s turns off the AC voltage and sets the DC voltage to + 800V. Switch. By doing so, the potential of the developing sleeve 4 s becomes relatively higher than +700 V on the photosensitive drum 1, and it is possible to reduce the amount of toner scattered in the apparatus by reducing the transfer of the negative toner to the photosensitive drum 1. At the same time, it is possible to suppress the consumption of excess toner when measuring the image flow state of the photosensitive drum 1.

<Second Embodiment>
FIG. 18 is an explanatory diagram of a configuration of the image forming apparatus according to the second embodiment.

  As shown in FIG. 18, the image forming apparatus 200 of the second embodiment is a full-color electrophotography in which yellow, magenta, cyan, and black image forming portions PA, PB, PC, and PD are arranged along the intermediate transfer belt 51. An image forming apparatus.

  In the image forming portion PA, a yellow toner image is formed on the photosensitive drum 1 </ b> A and is primarily transferred to the intermediate transfer belt 51. In the image forming portion PB, a magenta toner image is formed on the photosensitive drum 1B, and is primarily transferred onto the yellow toner image on the intermediate transfer belt 51. In the image forming units PC and PD, a cyan toner image and a black toner image are formed on the photosensitive drums 1C and 1D, respectively, and similarly, the toner images on the intermediate transfer belt 51 are overlapped with each other and sequentially primary transferred.

  The four-color toner images primarily transferred to the intermediate transfer belt 51 are transported to the secondary transfer portion T2 as the intermediate transfer belt 51 rotates, and are collectively transferred to the recording material P fed to the secondary transfer portion T2. Next transferred. The recording material P onto which the toner image has been secondarily transferred at the secondary transfer portion T2 is heated and pressurized by the fixing device 8 to fix the toner image on the surface and then discharged to the outside. The fixing device 8 exemplifies a method using a roller, but the fixing method is not limited to the roller method, and a belt fixing method may be used.

  The recording material P is taken out from the cassette 20 and separated one by one by the separation roller 21, conveyed from the conveyance roller 22 to the registration roller 23, and waits. The registration roller 23 sends the recording material P to the transfer portion T1 in synchronization with the toner image carried on the photosensitive drum 1.

  The intermediate transfer belt 51 is supported around a driving roller 52, a counter roller 53, and a tension roller 54, and is driven by the driving roller 52 to rotate in the direction of arrow R2.

  The image forming portions PA, PB, PC, and PD are configured substantially the same except that the colors of toner used in the attached developing devices 4A, 4B, 4C, and 4D are different from yellow, magenta, cyan, and black. Hereinafter, the image forming unit PA will be described, and the image forming units PB, PC, and PD will be described by replacing A at the end of the reference code with B, C, and D.

  A charging roller 2A, an exposure device 3A, a developing device 4A, a primary transfer roller 5A, a cleaning device 6A, and a potential sensor 30A are disposed around a photosensitive drum 1A that is an example of a photosensitive member.

  The charging roller 2A, which is an example of a charging unit, is applied with an oscillating voltage obtained by superimposing an AC voltage on a DC voltage, and charges the photosensitive drum 1A to a uniform dark potential VD having a negative polarity. The charging means is not limited to the charging roller, and a scotron type or blade type charger may be used.

  The exposure apparatus 3A, which is an example of an exposure unit, scans the laser beam on the photosensitive drum 1A charged to the dark portion potential VD, and forms an electrostatic image of the image by lowering the potential of the exposed portion to the bright portion potential VL. .

  The developing device 4A, which is an example of a developing unit, develops the electrostatic image formed on the photosensitive drum 1A with a negatively charged toner to form a toner image. The developing device 4A stirs a two-component developer in which a magnetic carrier is mixed with a nonmagnetic toner to charge the nonmagnetic toner to a negative polarity and a magnetic carrier to a positive polarity, and stands on a developing sleeve that rotates around a fixed magnetic pole. The photosensitive drum 1A is rubbed against the photosensitive drum 1A. By applying an oscillating voltage in which an AC voltage is superimposed on the developing voltage Vdc to the developing sleeve, the toner is transferred to the bright portion potential VL portion of the photosensitive drum 1A, and the electrostatic image is reversely developed.

  A primary transfer roller 5 </ b> A, which is an example of a transfer unit, forms a primary transfer portion T <b> 1 between the photosensitive drum 1 </ b> A and the intermediate transfer belt 51. The toner image charged negatively and carried on the photosensitive drum 1A is primarily transferred to the intermediate transfer belt 51 by applying a positive DC voltage to the primary transfer roller 5A. The transfer means is not limited to the transfer roller, and a blade type or corotron type transfer device may be used.

  The cleaning device 6A rubs the photosensitive drum 1A with a cleaning blade to remove transfer residual toner adhering to the surface of the photosensitive drum 1A that has passed through the primary transfer portion T1. In addition, the cleaning device 6A causes the rotating photosensitive drum 1A to rub against the rotating photosensitive drum 1A during frictional heating to evaporate water adhering to the surface of the photosensitive drum 1A. For this reason, when the photosensitive drum 1A continues to rotate, the surface resistance of the photosensitive drum 1A gradually recovers as moisture is removed through rubbing. Although the cleaning device 6A uses a cleaner blade type, a system using a fur brush can naturally be used.

  The potential sensor 30A is disposed in contact with the photosensitive drum 1A between the exposure position of the exposure device 3A and the development position of the developing device 4A, and is formed during non-image formation in order to measure the image flow state of the photosensitive drum 1A. A predetermined electrostatic image is detected.

<Example 5>
FIG. 19 is a flowchart of control according to the fifth embodiment.

  In the control of the fifth embodiment, in each of the image forming units PA, PB, PC, and PD shown in FIG. 18, the potential sensor is used with the vibration voltage applied to the charging roller turned off, as in the first embodiment. A test electrostatic image is measured. Further, in the starting sequence in the morning, the control is the same as that of the first embodiment, except that the image flow state is sequentially measured with a plurality of photosensitive drums. Accordingly, in FIG. 19, the same reference numerals are assigned to the controls common to the first embodiment, and a duplicate description is omitted.

  As shown in FIG. 18, the image forming apparatus 200 includes a plurality of photosensitive drums 1A, 1B, 1C, and 1D. For this reason, when an oscillating voltage is applied to the charging rollers 2A, 2B, 2C, and 2D and charging is performed simultaneously with the photosensitive drums 1A, 1B, 1C, and 1D, high-frequency noise is generated from the charging rollers 2A, 2B, 2C, and 2D. To do.

  For this reason, if it is attempted to simultaneously measure the image flow state with the photosensitive drums 1A, 1B, 1C, and 1D using the potential sensors 30A, 30B, 30C, and 30D, high-frequency noise generated from the charging roller of another adjacent image forming unit. Affected by. Since the potential sensors 30A, 30B, 30C, and 30D measure the weak electric fields of the photosensitive drums 1A, 1B, 1C, and 1D that pass therethrough, noise is added to the detection signal due to high-frequency noise generated from the charging roller, Correct measurement becomes difficult.

  Therefore, while measuring the image flow state of the photosensitive drum 1A by the potential sensor 30A, the vibration voltages for charging and developing are turned off by the image forming units PB, PC, and PD. While the image flow state of the photosensitive drum 1B is measured by the potential sensor 30B, the charging and developing vibration voltages are turned off by the image forming units PA, PC, and PD. While the image flow state of the photosensitive drum 1C is being measured by the potential sensor 30C, the charging and developing vibration voltages are turned off by the image forming portions PA, PB, and PD. While the image flow state of the photosensitive drum 1D is being measured by the potential sensor 30D, the charging and developing vibration voltages are turned off by the image forming portions PA, PB, and PC. This has the effect of suppressing the influence of noise and stabilizing the signal during measurement.

  As shown in FIG. 19 with reference to FIG. 5, the measurement of the image flow state of the photosensitive drum 1B of the image forming unit PB is completed after the measurement (S31) of the image flow state of the photosensitive drum 1A of the image forming unit PA is completed. (S32). Thereafter, after the measurement of the image flow state of the photosensitive drum 1B of the image forming unit PB is completed (S32), the process proceeds to the measurement of the image flow state of the photosensitive drum 1C of the image forming unit PC (S33). Thereafter, after the measurement of the image flow state of the photosensitive drum 1C of the image forming unit PC (S33) is completed, the process proceeds to the measurement of the image flow state of the photosensitive drum 1D of the image forming unit PD (S34). Thereby, the output signals when the potential sensors 30A, 30B, 30C, and 30D detect the photosensitive drums 1A, 1B, 1C, and 1D are stabilized. Then, after the measurement of the image flow state on each of the photosensitive drums 1A, 1B, 1C, and 1D is completed, the control is performed in the form according to the first embodiment.

<Example 6>
FIG. 20 is a flowchart of control according to the sixth embodiment.

  The control of the sixth embodiment is the same as that of the fifth embodiment except that the order of measuring the image flow state is different between the image forming units PA, PB, PC, and PD shown in FIG.

  As shown in FIG. 20 with reference to FIG. 18, in the sixth embodiment, after the image flow state measurement (S41) of the photosensitive drums 1A and 1C of the image forming unit PA and PC is completed, the image forming unit PB, The process proceeds to measurement of the image flow state of the photosensitive drums 1B and 1D of the PD (S42). After the image forming state PA and PC simultaneously measure the image flow state with the vibration voltage turned off at the image forming portions PB and PD (S41), the image forming portion with the vibration voltage turned off at the image forming portions PA and PC. The image flow state is measured simultaneously with PB and PD (S42).

  Since radio noise decreases as the distance from the transmission source increases, if the vibration voltage is turned off at the adjacent image forming unit, the output of the potential sensor does not have to be turned off at all other image forming units. The signal to noise ratio is significantly increased.

  Therefore, while measuring the image flow state of the photosensitive drums 1A and 1C by the potential sensors 30A and 30C (S41), the image forming units PB and PD turn off the charging and developing vibration voltages. While measuring the image flow state of the photosensitive drums 1B and 1D with the potential sensors 30B and 30D (S42), the image forming portions PA and PC turn off the charging and developing vibration voltages.

  This has the effect of suppressing the influence of noise and stabilizing the signal during measurement. The output signals when the potential sensors 30A, 30B, 30C, and 30D detect the photosensitive drums 1A, 1B, 1C, and 1D are stabilized, and the measurement accuracy of the image flow state is increased.

It is explanatory drawing of a structure of the image forming apparatus which attached the potential sensor. It is explanatory drawing of a structure of an electric potential sensor. It is explanatory drawing of the manufacturing method of an electric potential sensor. It is explanatory drawing of an electrode pattern. It is explanatory drawing of the output circuit of an electric potential sensor. It is explanatory drawing of the output voltage of an electric potential sensor. It is explanatory drawing of the electrostatic image which an image flow generate | occur | produces. It is explanatory drawing of the image in which the image flow does not generate | occur | produce. It is explanatory drawing of the image which the image flow generate | occur | produced. It is explanatory drawing of the relationship between the output of an electric potential sensor, and an image flow state. It is explanatory drawing of the output signal of the electric potential sensor which detected the test electrostatic image with the vibration voltage ON state. It is explanatory drawing of the output signal of the electric potential sensor which turned off the oscillating voltage and detected the test electrostatic image. 3 is a flowchart of control according to the first embodiment. 6 is a timing chart of application of vibration voltage to the charging roller. 10 is a flowchart of control according to the third embodiment. 6 is a timing chart of application of vibration voltage to the charging roller. 10 is a time chart of control in Embodiment 4. It is explanatory drawing of a structure of the image forming apparatus of 2nd Embodiment. 10 is a flowchart of control in Embodiment 5. 10 is a flowchart of control in Embodiment 6.

Explanation of symbols

1 Photosensitive drum 2 Charging means (charging roller)
3 Exposure means (exposure equipment)
4 Development means (developing device)
5 Transfer roller 6 Cleaning device 8 Fixing device 30 Potential sensor 31 Substrate film layer 32 Thin film electrode layer 32a Detection electrode portion 32b Connection wiring portion 34 First adhesive layer 35 Film layer 36 Second adhesive layer D3, D4 Power supply 100 Image forming device 110 Control unit 120 Signal processing circuit

Claims (7)

A photosensitive member; a charging unit that charges the photosensitive member using a voltage including an alternating voltage; an exposure unit that exposes the photosensitive member charged by the charging unit to form an electrostatic image; and the electrostatic image Developing means for developing the toner with toner, and detecting means for detecting an electrostatic image on the photosensitive member passing through the charging member and the developing member with the electrode surface facing the photosensitive member. In the image forming apparatus,
After controlling the charging unit so that a predetermined electrostatic image is formed, the charging unit is controlled so as to reduce the AC voltage of the charging unit at least during a period in which the predetermined electrostatic image is detected by the detection unit. An image forming apparatus comprising control means for controlling.   The control means forms the predetermined electrostatic image without reducing the AC voltage in the next rotation with respect to the rotation area of the photosensitive member that has passed through the charging means in which the AC voltage has decreased. 2. The image forming apparatus according to claim 1, wherein the predetermined electrostatic image is formed on the entire circumference of the photoconductor through a plurality of rotations of the photoconductor and detected by the detection unit. A photosensitive member; a charging unit that charges the photosensitive member; an exposure unit that exposes the photosensitive member charged by the charging unit to form an electrostatic image; and the electrostatic image using a voltage including an AC voltage. Developing means for developing the toner with toner, and detecting means for detecting an electrostatic image on the photosensitive member passing through the charging member and the developing member with the electrode surface facing the photosensitive member. In the image forming apparatus,
An image forming apparatus comprising: a control unit that controls the developing unit so as to reduce an AC voltage of the developing unit at least during a period in which the predetermined electrostatic image is detected by the detecting unit. Another charging means for charging another photosensitive member arranged in proximity to the photosensitive member using a voltage including an alternating voltage;
2. The control unit according to claim 1, wherein the control unit controls the another charging unit so as to reduce an AC voltage of the another charging unit during a period in which the predetermined electrostatic image is detected by the detection unit. 4. The image forming apparatus according to any one of items 3 to 3. Another developing means for developing an electrostatic image formed on another photosensitive member arranged in the vicinity of the photosensitive member with toner using a voltage including an alternating voltage;
2. The control unit according to claim 1, wherein the control unit controls the another developing unit so as to reduce an AC voltage of the another developing unit at least during a period in which the predetermined electrostatic image is detected by the detecting unit. 4. The image forming apparatus according to any one of items 3 to 3.   The image forming apparatus according to claim 1, wherein the control unit stops the AC voltage before the predetermined electrostatic image approaches the detection unit.   The detection means includes an insulating film and a thin film electrode layer in close contact with the film, and the outer surface of the film folded back so that the thin film electrode layer forms a curved surface inside the film. The image forming apparatus according to claim 1, wherein the predetermined electrostatic image is detected in a state of being in contact with a body.

Images