JP2010060755A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, for outputting a high-quality image even just after starting by rapidly estimating the current image flow state of a photoreceptor without depending on a temperature humidity sensor or a heater, and appropriately controlling exposure. <P>SOLUTION: In pre-rotation for image formation, fifty test electrostatic images 1s are formed on a photosensitive drum 1 and detected by 10 potential sensors 30, whereby image flow states at 100 points on the surface of the photosensitive drum 1 are measured. A correction map of exposing conditions which reflects the image flow states at 100 points on the surface of the photosensitive drum 1 is formed, and main image formation is started. In the image formation, the exposing quantity per pixel in each position on the surface of the photosensitive drum 1 is adjusted according the correction map to recover the toner adhesion quantity of pixels lost by image flow. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an electrostatic image by exposing the surface of a charged photoreceptor, and more particularly to exposure control in which image flow is not noticeable even when an image is formed in a state where the surface resistance of the photoreceptor is lowered.

  The surface of the charged photoreceptor 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 photoreceptor is transferred to a transfer medium (recording material or intermediate transfer). An image forming apparatus to be transferred to a body is widely used.

When the photosensitive member is charged using a contact charging device such as a charging roller or a non-contact charging device such as a corona charger, discharge products such as nitrogen oxide NO _X accumulate on the surface of the photosensitive member. There is a possibility that. Further, when a toner image is transferred from a photosensitive member to a transfer medium using a contact type transfer device such as a transfer roller or a non-contact type transfer device such as a corona charger, the same applies to the surface of the photosensitive member. Discharge products can accumulate.

  When the discharge product is accumulated on the surface of the photoreceptor and left in a high-humidity environment, an image defect such as image flow tends to occur in the initial image formation after activation (see FIG. 11). That is, the surface resistance of the photosensitive member is reduced due to moisture adsorption through the discharge product, and the charged dark portion potential VD and the exposed bright portion potential VL leak between the exposure and the development, thereby causing an electrostatic image. The potential distribution of the will collapse. As a result, the width of the electrostatic image to which the toner adheres exceeding the developing voltage Vdc is reduced, so that the line image becomes thin, and the charge amount of the electrostatic image that attracts the toner exceeding the developing voltage Vdc is reduced. The image density decreases (see FIG. 9).

  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. Here, based on the output of the temperature / humidity sensor, the drum heater is operated only when the humidity is high enough to cause image flow. By waiting for image formation and raising the surface temperature of the photoconductor, the adsorbed moisture is evaporated to recover the surface resistance of the photoconductor.

  Patent Documents 2 and 3 disclose a potential sensor that can detect a change in potential distribution of an electrostatic image accompanying a decrease in surface resistance of a photoreceptor. The potential sensor has an electrode member that forms a cylindrical surface in the main scanning direction and is arranged in non-contact with the photosensitive member, and a voltage signal corresponding to a differential waveform of the potential distribution of the electrostatic image as the photosensitive member rotates. Is output.

  Patent Document 4 discloses an image forming apparatus that divides the surface of a photosensitive drum into a number of regions, measures potentials, and adjusts the laser exposure amount in each region in accordance with the potential measurement results.

JP 2002-40876 A Japanese Patent Laid-Open No. 11-183542 JP 2004-77125 A JP 2004-258482 A

  When the photosensitive member of the waiting image forming apparatus is always heated using a heater, power consumption increases, running cost increases, and there is a problem from the viewpoint of energy saving. However, as shown in Patent Document 1, when the heater is stopped during standby and the heater is energized for each image formation to wait for image formation until it reaches a certain temperature, the image formation start waiting time increases. As a result, the productivity of the image forming apparatus is impaired.

  Therefore, there has been proposed a control in which image formation is immediately started by adjusting only the exposure conditions while maintaining the surface resistance lowered by moisture absorption without using a heater. A temperature / humidity sensor is installed to measure temperature and humidity, and in high humidity conditions where image flow is likely to occur, the potential distribution is expanded to increase the exposure intensity and ensure the development width and density even with low surface resistance. An electrostatic image is formed.

  However, even if the temperature and humidity conditions at the time of starting the image forming apparatus are constant, the degree of image flow that actually occurs is large depending on the individual differences and usage history of the photoconductor, the charging device, the transfer device, the cleaning device, etc. Change. It is difficult to set the exposure intensity so that the image flow can be offset properly under only the temperature and humidity conditions, because many factors come together to vary the accumulated amount and accumulation distribution of the current discharge products on the photoconductor. .

  The present invention provides an image forming apparatus capable of outputting a high-quality image even immediately after startup by quickly estimating the current image flow state of a photoreceptor and appropriately controlling exposure without relying on a temperature / humidity sensor or a heater. The purpose is to provide.

  The image forming apparatus of the present invention includes a photosensitive member, a charging unit that charges the photosensitive member, an exposure unit that exposes the charged photosensitive member to form an electrostatic image, and a toner. Development means for developing and forming a toner image and transfer means for transferring the toner image carried on the photosensitive member to a transfer medium passing through a transfer portion are provided. A detecting unit capable of detecting a change in a potential distribution of the electrostatic image accompanying a decrease in the surface resistance of the photosensitive member; a predetermined electrostatic image is written on the photosensitive member and detected by the detecting unit; Control means for controlling the exposure means based on the detection result of the predetermined electrostatic image so as to increase the amount of applied toner according to the amount of decrease in surface resistance.

  In the image forming apparatus of the present invention, the collapse state of the potential distribution of the test electrostatic image formed on the photosensitive member is detected by using the potential sensor, so that the current image flow of the photosensitive member to be imaged from now on is detected. Exposure conditions that accurately reflect the state can be set.

  Therefore, a high-quality image can be output immediately after startup by quickly estimating the current image flow state of the photoconductor and appropriately controlling exposure without relying on a temperature / humidity sensor or a heater.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, as long as exposure conditions and exposure data are adjusted according to the detection result of the test electrostatic image using the potential sensor, a part or all of the configuration of the embodiment is replaced with the alternative configuration. Other embodiments can also be implemented.

  In this 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 or an image forming apparatus that uses a recording material conveyance belt is also described. Can be implemented.

  In addition, about the general matter regarding the image forming apparatus and electric potential sensor which are shown by patent documents 1-4, 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.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of a configuration of an image forming apparatus to which a potential sensor is attached, and FIG. 2 is an explanatory diagram of an arrangement of the potential sensor.

  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.

  Around the rotating photosensitive drum 1, 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 arranged.

  The charging roller 2, which is an example of a charging unit, is applied with an oscillating voltage obtained by superimposing an AC voltage on a DC voltage from a power source D <b> 3 and is driven to rotate by the photosensitive drum 1. Charge to potential VD.

  An exposure apparatus 3 which is an example of an exposure unit writes an electrostatic image of an image by scanning the charged photosensitive drum 1 with a laser beam and reducing it to a bright portion potential VL. An electrostatic image corresponding to the image information is formed on the photosensitive drum 1 using an infrared laser beam (wavelength λ = 780 nm) that is binary-modulated in accordance with image information read by an image scanner (not shown).

  A developing device 4 as an example of a developing unit develops the electrostatic image formed on the photosensitive drum 1 with toner to form a toner image. In the developing device 4, a negatively charged toner is carried on a developing sleeve 4s that rotates around a fixed magnetic pole 4m, and is selectively attached to the exposed bright portion potential VL portion of the photosensitive drum 1 to statically. Reverse development of the image.

  The transfer roller 5, which is an example of a transfer unit, transfers a toner image from the photosensitive drum 1 to the recording material P by applying a positive DC voltage having a polarity opposite to the charging polarity of the toner from the power source D <b> 4.

  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 toner image charged to the negative polarity and carried on the photosensitive drum 1 is transferred to the recording material P which is fed to the transfer portion T1 and is nipped and conveyed.

  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. In addition, 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. At this time, a part of the discharge product entangled with the toner stagnating at the tip of the cleaning blade 6b is also removed. For this reason, if the photosensitive drum 1 continues to rotate, the surface resistance of the photosensitive drum 1 gradually recovers with the removal of moisture and discharge products through rubbing, and image symptom is gradually reduced.

  As shown in FIG. 2 with reference to FIG. 1, the potential sensor 30 is brought into contact with the surface of the photosensitive drum 1 between the exposure position by the exposure device 3 and the development position by the development device 4 in the main scanning direction. Several are arranged. A total of ten potential sensors 30 are arranged along the generatrix of the cylindrical surface of the photosensitive drum 1 and detect changes in the surface potential of the photosensitive drum 1 at ten positions in the width direction.

  An origin sensor 1 r, which is an example of an angle discriminating unit, is attached to the rotating shaft of the photosensitive drum 1 in order to discriminate individual angular positions in the rotation direction of the photosensitive drum 1. Starting from the origin signal generated by the origin sensor 1 r for each rotation of the photosensitive drum 1, the control unit 110 sets 10 angle regions every 36 degrees in the rotation direction of the photosensitive drum 1.

  The controller 110 forms a test electrostatic image 1 s that is 3 dots wide and uniformly continuous in the main scanning direction on the photosensitive drum 1 and detects it by the potential sensor 30 before the start of image formation. A total of 50 test electrostatic images 1s are written at five equal intervals with respect to 10 angular regions.

  The controller 110 detects 50 test electrostatic images 1 s written on the photosensitive drum 1 with ten potential sensors 30 and measures the image flow state at 100 locations on the surface of the photosensitive drum 1. Then, a correction map of exposure conditions reflecting the image flow states at 100 positions on the surface of the photosensitive drum 1 is formed, and actual image formation is started. At the time of image formation, the exposure amount per pixel at each position on the surface of the photosensitive drum 1 is adjusted according to the correction map to recover the toner adhesion amount of pixels lost due to image flow.

  As a method of adjusting the exposure amount per pixel, as will be described later, a method of changing the emission intensity of the laser beam at each position in the main scanning direction (Example 1), and a method of changing the area of dots forming pixels. There is a method (Example 3). Both methods may be combined.

  Further, the image flow at each individual position that will occur when an image is formed at that time is estimated from the output of the potential sensor 30, and the image adjusted so that the image flow is appropriately canceled at each position. Image formation may be performed using data. Alternatively, a γ correction curve that cancels the decrease in the toner adhesion amount due to the image flow may be obtained, and the image data of the image to be formed from this is corrected as a whole.

  Immediately after the start of image formation, since the surface resistance of the photosensitive drum 1 is low and the output of the potential sensor 30 is greatly reduced, the exposure amount per pixel is greatly increased so that a large image flow can be offset. As the image formation is accumulated, the surface resistance of the photosensitive drum 1 is gradually recovered and the output of the potential sensor 30 is gradually increased. Therefore, the increase in the exposure amount is gradually reduced according to the recovery of the output. Then, when the output of the potential sensor 30 recovers to a predetermined level, the process shifts to normal image formation without adjustment.

<Photoconductor>
FIG. 3 is an explanatory diagram of the structure of the photosensitive layer of the photosensitive drum.

  The image forming apparatus 100 employs a photosensitive drum 1 in which the surface hardness of the photosensitive layer 1b is increased by irradiation with an electron beam. In the case of the photosensitive drum 1 having high hardness, the wear rate of the photosensitive layer 1b is 1/4 or less than that of the conventional one. Image formation can be continued up to the number of sheets. On the other hand, in the high-hardness photosensitive drum 1, the discharge product that has been removed with the surface wear remains on the surface of the photosensitive drum 1, and image flow due to the discharge product is likely to occur.

  As shown in FIG. 3, the photosensitive drum 1 includes a conductive layer 1c, an intermediate layer 1d, a charge generation layer 1e, a charge transport layer 1f, and a protective layer 1g on the surface of an aluminum cylinder base layer 1a having a diameter of 30 mm and a length of 360 mm. A photosensitive layer 1b is formed.

  The conductive layer 1c was formed by the following procedure. 50 parts of conductive titanium oxide powder coated with tin oxide containing 10% antimony oxide (parts by weight, the same applies hereinafter), 25 parts of phenol resin, 20 parts of methyl cellosolve, and 5 parts of methanol were prepared. Then, 0.002 part of silicone oil (polydimethylsiloxane polyoxyalkylene copolymer, average molecular weight 3000) is added to the formulation, and the mixture is dispersed for 2 hours in a sand mill apparatus using φ1 mm glass beads to adjust the conductive layer 1c. The paint for was formed. This paint was applied onto the base layer 1a by a dip coating method and dried at 140 ° C. for 30 minutes to form a conductive layer 1c having a thickness of 20 μm.

  The intermediate layer 1d was formed by the following procedure. 5 parts of N-methoxymethylated nylon was dissolved in 95 parts of methanol to prepare a coating material for the intermediate layer 1d. This paint was applied onto the conductive layer 1c by a dip coating method and then dried at 100 ° C. for 20 minutes to form a 0.6 μm intermediate layer 1d.

  The charge generation layer 1e was formed by the following procedure. An oxytitanium phthalocyanine having a black peak at 9.0, 14.2, 23.9, and 27.1 degrees with a black angle 2θ ± 0.2 degrees in X-ray diffraction of CuKα was prepared. 3 parts of oxytitanium phthalocyanine, 3 parts of polyvinyl butyral (trade name ESREC BM2, manufactured by Sekisui Chemical Co., Ltd.) and 35 parts of cyclohexanone were dispersed for 2 hours in a sand mill using a φ1 mm glass bead. Thereafter, 60 parts of ethyl acetate was added to the formulation to prepare a coating for the charge generation layer 1e. This coating material was applied onto the intermediate layer 1d by a dip coating method and then dried at 50 ° C. for 10 minutes to form a charge generation layer 1e having a thickness of 0.2 μm.

  The charge transport layer 1f was formed by the following procedure. For charge transport layer 1f, 10 parts of styryl compound of structural formula (4) and 10 parts of polycarbonate resin having repeating units of structural formula (5) are dissolved in a mixed solvent of 50 parts of monochlorobenzene and 30 parts of dichloromethane. The coating solution was adjusted.

  This coating solution was dip-coated on the charge generation layer 1e and then dried at 120 ° C. for 1 hour to form a charge transport layer having a thickness of 20 μm.

  The protective layer 1g was formed by the following procedure. A coating for 1 g of the protective layer was prepared by dissolving 60 parts of the hole transporting compound of the structural formula (3) in a mixed solvent of 50 parts of monochlorobenzene and 50 parts of dichloromethane. The coating material for 1 g of the protective layer contained 30 wt% of tetrafluoroethylene resin as fluorine atom-containing resin particles with respect to the total weight of the protective layer 1 g.

  After coating this coating solution on the charge transport layer 1f, an electron beam was irradiated under conditions of an acceleration voltage of 150 KV and an irradiation dose of 50 KGy in an atmosphere having an oxygen concentration of 10 ppm. Subsequently, a heat treatment was performed for 10 minutes under the same atmosphere at a temperature of 100 ° C. of the photosensitive drum 1 to form a protective layer 1 g having a thickness of 5 μm. In this manner, a photosensitive drum 1 as an electrophotographic photosensitive member in which the surface hardness of the photosensitive layer 1b was increased by electron beam irradiation was obtained.

After leaving the photosensitive drum 1 for hardness test in an environment of 25 ° C. and 50% humidity for 24 hours, using a microhardness measuring device Fischerscope H100V (Fischer), HU (universal hardness value) and elastic deformation The rate was determined. As a result, HU was 190 N / mm ² and We (elastic deformation rate) was 46%.

The photosensitive drum 1 for mounting on the actual machine was mounted on an image forming apparatus iR3045 (manufactured by Canon Inc.). Then, in a normal environment (20 ° C./50% RH), an image with an applied toner amount of 0.025 g / A4 size was intermittently tested for 100,000 sheets, and the photosensitive layer 1b before and after the test was tested. The film thickness was measured with an eddy current film thickness meter (Fisher). The amount of abrasion was calculated by calculating how much the film thickness was cut compared to the initial film thickness, and dividing the number by the number of rotations of the photosensitive drum 1 under test to calculate the amount of abrasion with a unit of μm / 10,000 rotations. As a result, the shaving amount of the imageable area on the photosensitive drum 1 was 0.1 μm / 10,000 rotations.
<Electric potential sensor>

  4 is an explanatory diagram of the configuration of the potential sensor, FIG. 5 is an explanatory diagram of a manufacturing method of the potential sensor, FIG. 6 is an explanatory diagram of an electrode pattern, and FIG. 7 is an explanatory diagram of an output circuit of the potential sensor.

As shown in FIG. 4, the potential sensor 30 is formed in a thin plate-like appearance having a thickness of 100 μm, a width of 2.5 mm, and a length of 20 mm in which a resin film as an example of an insulating film is laminated, and an electrode member is embedded therein. The semi-cylindrical surface at the tip is brought into contact with the photosensitive drum 1. The potential sensor 30 slidably rubs the photosensitive drum 1 on the outer surface of a resin film having a thickness of 25 μm disposed so as to cover the electrode member on the curved surface, so that the facing distance between the electrode member on the curved surface and the photosensitive drum 1 is 25 μm. Hold on. The insulating property and the insulating film, a sense of high resistance enough to form a capacitor between the electrode member is a photosensitive drum, specifically 1 × 10 or more ¹⁰ Omega · cm in specific resistance desirable.

  The potential sensor 30 is supported by the image forming apparatus 100 in a cantilever manner, and a tip portion is brought into contact with the photosensitive drum 1 with a predetermined angle of inclination. The potential sensor 30 is configured such that a contact pressure with respect to the photosensitive drum 1 is set by a bending reaction force of the thin plate portion, and a high resistance material covering the surface of the cylindrical electrode surface is brought into contact with the photosensitive drum 1 to thereby contact the electrode surface. And the photosensitive drum 1 are set to face each other.

  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.

As shown in FIG. 5, 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. 5 (a), the silver paste is screen-printed and adhered to the substrate film layer 31 of the PET film, and the L-shaped detection electrode portion 32a and the connection wiring portion shown in FIG. 4 (a). A thin film of 32b was formed.

  As shown in FIG. 5B, 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. 5C, the PET film was attached as a film layer 35 from above.

  As shown in FIG. 5 (d), the adhesive was further applied as a second adhesive layer 36 from above with a bar coater to a thickness of 20 μm and dried.

  As shown in FIG. 5 (e), it was bent at a distance of 20 mm from one end in the length direction and was completely attached.

  The thin film electrode layer 32 is formed into a thin film by vacuum deposition or sputtering formation of a metal thin film on the substrate film layer 31 on which a mask having openings corresponding to the detection electrode portions 32a and the connection wiring portions 32b is overlaid. Also good.

  In addition, a pattern of the detection electrode portion 32a and the connection wiring portion 32b is formed by forming and etching a resist pattern on a metal thin film adhered to the entire surface of the substrate film layer 31 by vacuum deposition or sputtering. A thin film may be formed.

  For example, as in the case of creating a flexible printed circuit board, a circuit pattern may be projected and exposed on a resist layer to form a resist pattern, and a metal thin film exposed from the resist layer may be removed by etching to form a thin film.

  As shown in FIG. 6A, 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 in order to ensure insulation of the thin film electrode layer 32. 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.

  The connection wiring part 32b may be branched in a T shape from the center of the detection electrode part 32a as shown in FIG. 6B, and the detection electrode part as shown in FIG. 6C. You may branch from the arbitrary positions of 32a.

  In the potential sensor 30, the substrate film layer 31 is folded back at a predetermined curvature so as to be positioned at a distance between the photosensitive drum 1 and the electrode surface. The thin film electrode layer 32 is in close contact with the inner surface of the folded region of the substrate film layer 31, and the detection electrode portion 32a along the folded line is formed as a thin film as a thin film pattern. The center layer 33 is disposed in close contact with the inner surface of the substrate film layer 31 so as to give the substrate film layer 31 a predetermined curvature. The overlapping portion of the substrate film layer 31 and the center layer 33 has a length that can be bent in a plane perpendicular to the folding line of the substrate film layer 31. 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. 7, 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 signal processing circuit 120 is connected to the potential sensor 30, and the output analog voltage signal is A / D converted and taken into the control unit 110 to measure the peak voltage, thereby forming a photosensitive drum without forming a toner image. 1 is determined. The potential sensor 30 has an electrode member (32a) long in the main scanning direction opposed to the photoconductor at a predetermined distance, and the potential of the electrostatic image in the main scanning direction passing through the electrode member (32a) as the photoconductor rotates. A voltage signal corresponding to the differential waveform of the distribution is output.

  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. By making the detection electrode portion 32a face the photosensitive drum 1 through the substrate film layer 31, a voltage signal corresponding to a change in the surface potential of the photosensitive drum 1 is taken out from the detection electrode portion 32a. 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, 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.

  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.

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)

  Accordingly, the output of the potential sensor 30 changes by 10% even if the distance d between the electrodes of 25 μm is changed by 2.5 μm due to the eccentric rotation of the photosensitive drum 1, and 90% of the normal peak value is 90% of the threshold value. Thus, it is impossible to determine the image flow.

  When the tip of the potential sensor 30 comes into contact with the photosensitive drum 1 perpendicularly, the contact pressure becomes unstable, and the potential sensor 30 tends to cause so-called chatter vibration. Will increase. Even when the angle is less than 5 degrees close to the vertical, the followability to the eccentric rotation of the photosensitive drum 1 is deteriorated, and noise accompanying fluctuations in the inter-electrode distance d increases.

  On the other hand, when it exceeds 80 degrees, which is close to the horizontal, the potential sensor 30 feels abdomen, the critical detection electrode part 32a and the photosensitive drum 1 do not face each other well, and the output decreases.

  The linear pressure applied to the potential sensor 30 is preferably 0.01 mg / mm to 10 g / mm. When the linear pressure is less than 0.01 mg / mm, the signal is not stable because there is almost no contact. On the other hand, when the linear pressure exceeds 10 g / mm, the potential sensor 30 is worn in a short period of time, or the photosensitive drum 1 is scratched.

  Since the amount of change in potential due to the movement of the test electrostatic image 1s is detected as a differential value of the potential distribution, the amount of change in potential increases as the rotational speed of the photosensitive drum 1 increases to some extent, and the output increases to increase sensitivity. Specifically, a peripheral speed (process speed) of 50 to 1000 mm / sec can be handled, and an image flow of 100 to 800 mm / sec can be detected with high accuracy.

<Charging means>
As shown in FIG. 1, the image forming apparatus 100 uses a roller charging method that is a contact method as a charging method, and uses a roller transfer method that is a contact method as a transfer method. The contact-type charging method using the charging roller 2 has a lower applied voltage than the non-contact type charging method using a corona discharger, so that the cost of the power source D3 can be reduced. Further, since the discharge current is smaller than that of the non-contact system, the amount of ozone generated is small, and the environmental measures are excellent. However, as an embodiment, a non-contact system or an injection system may be used.

  The charging roller 2 is provided with an elastic layer 2b on a conductive support (using a round bar of metal material such as iron, copper, stainless steel, aluminum and nickel) 2a, and the elastic layer 2b is made conductive. ing. If the thickness of the elastic layer 2b is in the range of 1 to 500 mm, it can be used sufficiently. As a method for imparting conductivity to the elastic layer 2b, a conductive agent having an electron conduction mechanism such as carbon black, graphite, or conductive metal oxide is dispersed in an elastic material such as rubber. You may mix the electrically conductive agent which has ion conduction mechanisms, such as an alkali metal salt and a quaternary ammonium salt. A rubber material such as natural rubber, ethylene propylene rubber (EPDM), or styrene butadiene rubber (SBR) with conductivity is foamed, and the resistance value is adjusted to less than 1010 Ω · cm to form an outer diameter of 14 mm. Yes.

  The power source D3 applies an oscillating voltage obtained by superimposing a predetermined DC voltage Vdc on a sinusoidal AC voltage controlled at a constant current to a frequency of 1.8 kHz and a total current of 2000 μA to the charging roller 2.

<Developing means>
The developing method of the electrostatic image formed on the photoreceptor is roughly divided into the following four types.
(1) One-component non-contact development: Magnetic toner is coated on the developing sleeve with a blade or the like, and the magnetic toner is conveyed by magnetic force and developed in a non-contact state with respect to the photoreceptor.
(2) One-component contact development: The toner coated as described above is developed in contact with the photoreceptor.
(3) Two-component contact development: A developer obtained by mixing a magnetic carrier with a non-magnetic toner is conveyed by magnetic force and developed in contact with a photoreceptor.
(4) Two-component non-contact development: The above two-component developer is developed in a non-contact state.

  At present, the two-component contact development (3) is often used from the viewpoint of high image quality, full color, and development stability. In the present embodiment, (1) one-component non-contact development is described, but any of them may be adopted. Generally, the toner on the developing sleeve is not completely developed to the photosensitive member side, and the toner is also present on the developing sleeve immediately after development. This tendency is particularly strong in jumping development using magnetic toner, and the development efficiency is not so high.

  As the one-component developer used in the image forming apparatus 100, magnetic black toner produced by a pulverization method was used. Specifically, a binder resin, a colorant, a magnetic material, a charge control agent, and other additives are sufficiently mixed by a Henschel mixer or a ball mill mixer, and melted using a heat kneader such as a kneader or an extruder. It is mild and meaty. Thus, the resins are compatible with each other, the melted and kneaded product is cooled and solidified, the solidified product is pulverized, and then the pulverized product is classified to obtain a magnetic toner.

  Generally, silica or the like is externally added to the magnetic toner in order to stabilize charged performance against environmental fluctuations and improve fluidity. In the image forming apparatus 100, 1.0 part by weight of hydrophobic silica (volume average particle size 10 nm) whose surface of the silica base is hydrophobized with a silane coupling agent and silicone oil is added to 100 parts by weight of the magnetic toner. is doing. Titanium oxide (volume average particle size 50 nm) is externally added by 0.8 parts by weight. Further, in order to increase the removal efficiency of the discharge product adhered to the photosensitive drum 1 by the cleaning device 6, 1 part by weight of strontium titanate generally used as an abrasive was added. The abrasive particles used are oxides such as cerium oxide, silicon oxide, aluminum oxide and titanium oxide, carbides such as silicon carbide and tungsten carbide, nitrides such as silicon nitride and titanium nitride, and other general organic particles. Can be substituted.

<Cleaning means>
FIG. 8 is an explanatory diagram of the cleaning blade.

  The cleaning device 6 includes a cleaning blade 6b, a toner container 6a, a scattering prevention sheet, and a conveying screw. Transfer residual toner and the like are present on the photosensitive drum 1 after the transfer process, but these are toners that could not contribute to the transfer, and generally have a small particle diameter, external additives, and the like. These inclusions are removed from the photosensitive drum 1 by the cleaning blade 6b constituting the cleaning device 6. The transfer residual toner removed from the cleaning blade 6b is collected into a waste toner box (not shown) by a conveying screw.

  In the image forming apparatus 100, the surface of the photosensitive drum 1 is repeatedly used to form a toner image. Therefore, after the transfer to the recording material P, the transfer residual toner that remains on the photosensitive drum 1 without being transferred. Must be removed sufficiently.

  Various methods have been put to practical use as methods for removing the transfer residual toner, but a method of scraping the transfer residual toner from the photosensitive drum 1 using the cleaning blade 6b is widely used. The method using the cleaning blade 6b is suitable for downsizing the entire system at low cost, and is excellent in removal efficiency of transfer residual toner.

  The material of the cleaning blade 6b is preferably a material that has high hardness and high elasticity, is excellent in wear resistance, mechanical strength, oil resistance, and ozone resistance, and does not damage the photosensitive drum 1. Materials having appropriate elasticity and hardness such as polyurethane rubber, styrene-butadiene copolymer, chloroprene, butadiene rubber, chlorosulfonated polyethylene rubber, fluorine rubber, and chloroprene rubber can be used.

  As shown in FIG. 8, in this embodiment, a cleaning blade 6b made of polyurethane rubber is integrally held at the tip of the sheet metal 6e, and a predetermined set angle θ = 23 degrees with respect to the photosensitive drum 1 and the amount of intrusion. The contact is made under the condition of δ = 1.30 mm.

<Control means>
As shown in FIG. 7 with reference to FIG. 1, the printer control unit 111 performs necessary calculations according to a predetermined control program and control data to control each unit of the image forming apparatus 100. The exposure apparatus 3 is controlled to write a test electrostatic image 1 s on the photosensitive drum 1, and the image flow state of the test electrostatic image 1 s is measured through the potential sensor 30.

  The image processing unit 130 converts image data captured by an image scanner mounted on the image forming apparatus 100 into exposure image data. The document image formed on the individual image sensor 131 via the lens is input as luminance data of black and converted into an analog electric signal by the individual image sensor 131. The converted image information is input to an analog signal processing unit (not shown), subjected to sample & hold, dark level correction, and the like, and then analog / digital converted by the A / D conversion unit 132.

  The shading correction unit 133 performs shading correction on the digitized signal, and corrects variations in individual image pickup elements for reading a document and variations in light distribution characteristics of a document illumination lamp. Thereafter, it is sent to the logarithmic conversion unit 134.

  The logarithmic conversion unit 134 stores a table for converting input luminance data into density data, and converts the luminance data into density data by outputting a table value corresponding to the input data. Thereafter, the image is scaled to a desired magnification by the scaling processing unit 135 and input to the γ correction unit 136.

  When the density data is output, the γ correction unit 136 performs data conversion using a table that considers the characteristics of the printer, and adjusts the output according to the density value set by the operation unit. Thereafter, it is sent to the binarization unit 137.

  The binarization unit 137 binarizes the multi-value density data and sets the density value to “0” or “255”. The 8-bit image data is binarized and converted into 1-bit image data of “0” or “1”, and the amount of image data stored in the image memory unit 140 is reduced.

  However, when the image is binarized, the number of gradations of the image is changed from 256 gradations to two gradations. Therefore, when image data having a large halftone such as a photographic image is binarized, the image is generally greatly deteriorated. For this reason, it is necessary to perform pseudo halftone expression using binary data. Here, an error diffusion method is used as a technique for performing pseudo halftone expression using binary data.

  In this method, if the density of an image is greater than a certain threshold, the density data is “255”, and if the density is less than a certain threshold, the density data is “0”. Then, the difference between the actual density data and the binarized data is distributed to surrounding pixels as an error signal. The error is distributed by multiplying an error caused by binarization by a weighting factor on a matrix prepared in advance and adding it to surrounding pixels. As a result, the average density value of the entire image is stored, and exposure image data in which the halftone is expressed in a pseudo binary manner is formed.

  The binarized exposure image data is sent to the image memory unit 140 and stored therein. Further, since image data from an externally connected computer is processed into exposure image data binarized by the external I / F processing unit 150, it is sent to the image memory unit 140 as it is.

  The image memory unit 140 includes a high-speed page memory unit 141 and a large-capacity hard disk 144 capable of storing a plurality of pages of exposure image data. The plurality of exposure image data stored in the hard disk 144 is output in the order corresponding to the editing mode designated by the operation unit of the image forming apparatus 100. The exposure image data output from the image memory unit 140 is sent to the smoothing unit 146 in the printer unit 145.

  The smoothing unit 146 interpolates the exposure image data so that the line end portion of the binarized image is smooth, and outputs the exposure image data to the exposure control unit 147. The exposure control unit 147 operates the exposure device 3 using the exposure image data to form an electrostatic image of the image on the photosensitive drum 1.

  The image memory unit 140 includes a page memory unit 141 composed of a memory such as a DRAM and a hard disk 144 that is a large-capacity storage device. The image memory unit 140 writes the exposure image data from the external I / F processing unit 150 and the image processing unit 130 to the page memory unit 141 via the memory controller unit 142. Also, exposure image data is read out to the printer unit 145 via the memory controller unit 142, and image input / output access to the hard disk 144, which is a large-capacity storage device, is performed.

  The memory controller unit 142 generates a DRAM refresh signal for the page memory unit 141. Also, arbitration of access to the page memory 141 from the image I / F processing unit 150, the image processing unit 130, and the hard disk 144 is performed. Further, in accordance with instructions from the CPU, control is performed on the write address to the page memory unit 141, the read address from the page memory unit 141, the read direction, and the like.

  As a result, the CPU controls a function of arranging a plurality of document images in the page memory unit 141 and performing a layout, outputting the image to the printer unit 145, a function of cutting out and outputting only a part of the image, and an image rotation function.

<Image flow>
FIG. 9 is an explanatory diagram of an electrostatic image in which image flow occurs, FIG. 10 is an explanatory diagram of an image in which no image flow has occurred, and FIG. 11 is an explanatory diagram of an image in which image flow has occurred.

As shown in FIG. 1, the charging roller 2 is charged with a discharge by being applied with a high AC voltage, and therefore, the surface of the photosensitive drum 1 has various nitrogen oxides NO _X and ozone compounds X−. A discharge product called O ₃ is deposited. Since the transfer roller 5 also transfers the toner image with electric discharge, these discharge products are deposited 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 photosensitive drum 1 easily absorbs moisture as the image formation is accumulated. Resistance tends to decrease.

  The accumulated discharge products tend to be immediately scraped off even in a normal pre-rotation operation when the image forming apparatus 100 is activated if the scraping amount of the photosensitive drum 1 is about the conventional level. It ’s hard to be. However, when the amount of scraping is less than one-tenth of that of the conventional drum 1 as in the photosensitive drum 1, the discharge product is not easily scraped off due to the rubbing of the cleaning blade 6b, and the image flow is likely to occur.

  In addition, it was confirmed that the charging device using the corona charger, the transfer device, and the charging device using the injection charging method using the magnetic brush charger are exposed to the discharge to deposit the discharge product. Has been. For this reason, the charging method and the transfer method for implementing the present invention are not limited to the method of bringing the roller member into contact.

  As shown in FIG. 9, 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.

  When the surface of the photosensitive drum 1 is started at a low temperature or in a high humidity environment, the discharge product tends to adsorb moisture in the atmosphere and reduce the surface resistance of the photosensitive drum 1. For this reason, the light portion potential VL and the dark portion potential VD are likely to leak, and the slope of the potential distribution at the edge of the test electrostatic image 1s becomes gentle, and the positive and negative peak voltages of the differential waveform output signal output from the potential sensor 30 Becomes lower.

  When the surface resistance of the photosensitive drum 1 decreases, the potential distribution of the test electrostatic image 1s changes from an ideal rectangular shape to a Gaussian distribution shape. The important factors governing the toner adhesion amount to the electrostatic image are the development contrast Vcont, which is the potential difference between the DC voltage Vdc used in development and the bright portion potential VL, and the electrostatic image width W1 across the DC voltage Vdc. When the development contrast Vcont is small, the depth of the electrostatic image becomes shallow, the toner adhesion amount per area is reduced, and the image density is lowered. When the electrostatic image width W1 is reduced, the output line width is reduced. As a result, the reproducibility of the pixel density tends to deteriorate on the photosensitive drum 1 and the output image, the image density decreases and the line width decreases, and a so-called image-flowed image in which blurring or blurring occurs is formed. It will be.

  As shown in FIG. 1, using a photosensitive drum 1 that has been subjected to a 100,000 sheet passing image test to easily generate an image flow, the image flow is performed under a high temperature and high humidity environment (HH: 30 ° C., 80% RH). Experiments were performed.

  As shown in FIG. 10 with reference to FIG. 1, using a photosensitive drum 1 that is easy to generate an image flow, 40 test electrostatic images (line width 2 dots 80 μm) 1s in the main scanning direction, A4 Continuous image formation of 10,000 sheets was performed intermittently on plain paper of size size. As shown in FIG. 10, 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.

  In this manner, a test electrostatic image 1 s was formed on the photosensitive drum 1 in the state of the photosensitive drum having different image flow levels, and the potential distribution of the test electrostatic image 1 s was measured using the potential sensor 30. The temperature and humidity, the photosensitive drum 1, the stop time, the stop environment, and the like were varied to intentionally generate different image flows, and the correlation with the peak value of the output signal of the charging sensor 30 was examined.

  As a result, a high correlation was confirmed between the degree of image flow of the formed image and the peak voltage of the output signal of the potential sensor 30. Thus, it was confirmed that by measuring the peak voltage of the detection signal of the test electrostatic image 1s using the potential sensor 30, the occurrence of image flow on the photosensitive drum 1 at that time can be sufficiently predicted. It has been found that the state of the image flow can be accurately estimated by the magnitude of the peak voltage of the output signal, and it can be accurately determined how much image flow will occur when an image is formed.

  As shown in FIG. 7, the control unit 110 controls the exposure apparatus 3 to write the test electrostatic image 1 s, and at the timing when the test electrostatic image 1 s passes through the potential sensor 30, Capture output. The positive and negative peak voltages output from the potential sensor 30 correspond to the slope of the edge of the potential distribution of the test electrostatic image 1s. The control unit 110 estimates the occurrence of image flow by comparing 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.

  At this time, the line width W1 of the test electrostatic image 1s is preferably 20 to 2000 μm, and more preferably 40 μm to 1000 μm. Within this range, it is possible to accurately determine the image flow using an electrostatic image.

  As shown in FIG. 1, the image flow is likely to occur after being left for a long time after the image forming apparatus 100 is stopped, and hardly occurs during the continuous operation of the image forming apparatus 100. This is because the discharge product, which is one of the causes of the image flow, continues to be scraped off by the rubbing of the cleaning blade 6b of the cleaning device 6 during the operation of the image forming apparatus 100.

  Further, regarding moisture adsorption to the photosensitive drum 1 which is a direct cause of image flow, the radiant heat of the fixing device 8 and the frictional heat of the cleaning blade 8b maintain the surface temperature of the photosensitive drum 1 high during image formation. Yes. During image formation, the surface of the photosensitive drum 1 is in a drying direction from the surroundings due to a temperature difference, and moisture adsorption is prevented. However, after a certain amount of time has passed after the image forming apparatus 100 is stopped, the temperature of the photosensitive drum 1 decreases to the same temperature as the surroundings. Therefore, the surface of the photosensitive drum 1 is more than the surroundings by the amount that the discharge product has improved hygroscopicity and hydrophilicity. It becomes easy to adsorb moisture.

  Therefore, the controller 110 exposes the pixels until the image flow is substantially eliminated immediately after the start of the image forming apparatus 100, or until the image flow is substantially eliminated immediately after restart after waiting in the sleep mode. Correct.

  However, the image flow does not occur uniformly over the entire surface of the photosensitive drum 1. Depending on the accumulation distribution of discharge products on the surface of the photosensitive drum 1, the state of the outside air flowing around the photosensitive drum 1, the difference in the cooling rate after stopping, etc., it appears at different levels for each position on the surface of the photosensitive drum 1. . In particular, in areas where the corona charger or charging roller was faced during a stop, the discharge product attached to the corona charger or charging roller is exposed to the phenomenon of sublimation and re-adhesion. Accumulation is significant, and a larger image flow is likely to occur than in other parts.

  For this reason, if the pixel exposure conditions are uniformly corrected in the entire image to cancel the image flow, the image density unevenness and line width unevenness due to the correction may occur, and the image quality may be impaired. .

  Therefore, the control unit 110 measures the image flow state (surface resistance) at 100 locations on the surface of the photosensitive drum 1 using the potential sensor 30, and corrects the exposure condition of the pixel on the entire surface of the photosensitive drum 1 (148). Form. Then, according to the correction map, the exposure conditions of the pixels are corrected at different levels for each position on the surface of the photosensitive drum 1, thereby making the influence on the entire image caused by the correction unnoticeable.

  The control unit 110 writes a predetermined electrostatic image on the photosensitive member and detects it by the detection means (30), and increases the toner loading amount of the pixel in accordance with the amount of decrease in the surface resistance of the photosensitive member. The exposure means (3) is controlled based on the detection result of the image (1s).

<Example 1>
FIG. 12 is an explanatory diagram of exposure control in the first embodiment, FIG. 13 is an explanatory diagram of measurement of the image flow state of the photosensitive drum, and FIG. 14 is a diagram of test electrostatic image writing in the first and second rotations of the previous rotation. It is explanatory drawing. FIG. 15 is an explanatory diagram of the change of the output signal when the potential sensor passes through one angle region, FIG. 16 is an explanatory diagram of the relationship between the laser exposure amount and the peak value of the output signal, and FIG. FIG. 6 is a diagram illustrating a peak value of an output signal in a photosensitive drum state. FIG. 18 is a diagram showing an example of the relationship between the laser exposure amount before and after the correction, and FIG. 19 is a control flowchart of the first embodiment.

  As shown in FIG. 12A with reference to FIG. 1, when the surface resistance of the photosensitive drum 1 decreases, the potential distribution of the test electrostatic image 1s exposed in a rectangular shape becomes a Gaussian curve. For this reason, in the potential distribution, the potential becomes equal to or lower than the developing voltage Vdc (− direction), and the width of the region where the toner adheres becomes narrower and the height becomes lower.

  For this reason, as shown in FIG. 12B, assuming that a Gaussian curve is formed, the exposure intensity is increased so that the width and height of the area to which the toner adheres approach a rectangular potential distribution. to correct. As a result, even when the surface resistance of the photosensitive drum 1 is lowered, a toner image having a line width and density that cancels out some of the image flow can be developed and output to the recording material P.

  In order to accurately correct the exposure intensity for each position on the surface of the photosensitive drum 1, it is necessary to measure the current image flow state (the degree of decrease in surface resistance) for each position on the surface of the photosensitive drum 1. . Then, in order to measure the image flow state at each position, the output signal of the potential sensor 30 is detected in the photosensitive drum 1 that is going to perform image formation from the initial state where no image flow occurs at each position. It is necessary to measure how much the peak voltage is decreasing.

As shown in FIG. 13, in Example 1, first, the image flow level at each position L _WXYZ on the photosensitive drum 1 is detected using the photosensitive drum 1 having a diameter of 30 mm in a state where no image flow occurs.

  In the image forming apparatus 100, while the photosensitive drum 1 is pre-rotating immediately before performing the image forming operation, the test electrostatic image 1 s is exposed to a region corresponding to one circumferential length of the photosensitive drum 1. 50 lines are written in the sub-scanning direction of the drum 1. The test electrostatic image 1s is formed in a direction perpendicular to the rotation direction of the photosensitive drum 1 (main scanning direction or longitudinal direction of the photosensitive drum 1), and is approximately three times the writing resolution 600 dpi (laser beam spot diameter 42.3 μm). It has a width of 127 μm.

  Then, the peak value of the output signal, which is a differential waveform of the potential distribution of each test electrostatic image 1s, was read by the potential sensors 30 provided at equal intervals in the longitudinal direction of the photosensitive drum 1. At this time, if the area of the circumferential length of the photosensitive drum 1 is divided into ten angular areas 1 to 10, the length of one angular area is 10 minutes of the circumferential length of 94.2 mm. 1 is 9.42 mm.

Here, in order to distinguish the measurement data of the potential sensor 30 at each position on the surface of the photosensitive drum 1, the data collection position on the photosensitive drum 1 is denoted as L _WXYZ . W (W = 1, 2, 3, 4, 5) represents the number of rounds of the pre-rotation of the photosensitive drum 1. The angle region on the photosensitive drum 1 is represented by X (X = 1, 2, 3, 4, 5, 6, 7, 8, 9, 0). The number of the test electrostatic image 1s in each angle region is represented by Y (Y = 1, 2, 3, 4, 5). The position at which the output of the potential sensor 30 in the longitudinal direction of the photosensitive drum 1 is measured is represented by Z (Z = 1, 2, 3, 4, 5, 6, 7, 8, 9, 0). Thereby, for example, the data collection position on the innermost side of the first line in the angle region 8 of the third rotation of the previous rotation is denoted as L ₃₈₁₀ .

  As shown in FIG. 14A, five test electrostatic images 1s in which the exposure amount of the laser, that is, the depth of the electrostatic image is changed in five stages for each angle region, from the thinnest, etc. Write to the interval. Then, one set of five test electrostatic images 1s is drawn in all angular regions while the photosensitive drum 1 makes one round.

  As shown in FIG. 14B, the order of the depth of the electrostatic image in the test electrostatic image 1s of 5 pieces is changed in the order of the ring after the second rotation of the photosensitive drum 1 after the second rotation. Finally, a pre-rotation is performed five times to draw a test electrostatic image 1s having five different depths at all positions.

First, a test electrostatic image was formed and measured on a new photosensitive drum 1 in which no image flow occurred during the pre-rotation of image output immediately after the first start in the morning in a high-temperature and high-humidity environment. At this time, as shown in FIG. _15A , an output signal whose peak voltage changes in five steps corresponding to Y = 1 to 5 was measured from the potential sensor 30 of L _11Y1 .

Thereafter, a test electrostatic image was formed and measured on the photosensitive drum 1 on which 100,000 images were formed during the pre-rotation of image output immediately after the start of the morning in a high-temperature and high-humidity environment. At this time, as shown in FIG. 15B, an output signal having an overall peak value level lower than that of FIG. _15A was measured from the potential sensor 30 of L _11Y1 .

  As shown in FIG. 12 (a), when 100,000 images are formed, the potential distribution of the test electrostatic image 1s changes from a rectangular shape to a Gaussian distribution, and the inclination of the edge becomes gentle. Compared with the drum 1, the peak value of the output signal (differential waveform of potential distribution) decreases.

  As shown in FIG. 14B, the peak value of the output signal is changed by changing the laser exposure amount. This is due to the potential distribution of the edge of the electrostatic image depending on the depth of the electrostatic image to be formed. This is because the maximum value of the slope of the curve changes.

  As shown in FIG. 16, regarding the new photosensitive drum 1 (solid line) and the photosensitive drum 1 (broken line) on which 100,000 images have been formed, the relationship between the five levels of laser exposure and the peak value of the output signal is shown. The plot was smoothed after approximating each point with a straight line. Then, it was confirmed that the inclination of the potential distribution at the edge of the test electrostatic image 1s, in other words, the depth and width of the test electrostatic image 1s depend on the laser exposure amount.

The relationship (solid line) drawn during the pre-rotation of the photosensitive drum 1 where no image flow occurs and the relationship (dashed line) drawn during the pre-rotation of the photosensitive drum 1 where image flow occurs (a broken line) peak value of the output signal at _k decreases to S _'k from S _k. On the photosensitive drum 1 (broken line) in which 100,000 sheets of image formation are accumulated with respect to the new photosensitive drum 1 (solid line), the peak value of the output signal decreases from S _k to S ′ _k .

Then, by premium laser exposure from E _k to E _n, 10 million copies but the photosensitive drum 1 obtained by accumulating the image formation (dashed line), the peak value of the photosensitive drum 1 (solid line) par of the output signal of the new state Is obtained. As a result, even with the photosensitive drum 1 (broken line) where image flow occurs, a toner image close to the development width and development density on the photosensitive drum 1 (solid line) where image flow does not occur can be developed.

  As shown in FIG. 19 with reference to FIG. 7, when the image forming job is input, the control unit 110 starts the pre-rotation (S11), and the test electrostatic image 1s over 5 rotations as described above. Is detected and detected by the potential sensor 30 (S12).

  The control unit 110 compares the peak value measured with the new photosensitive drum 1 with the peak value measured this time for the test electrostatic image 1s of the third laser exposure amount, and if the decrease in the peak value is less than 5%. (NO in S13), normal image formation is performed (S16).

  However, when the peak value measured this time has decreased by 5% or more (YES in S13), the relationship between the laser exposure amount and the peak value of the output signal shown in FIG. Ask for.

Then, set the current laser exposure amount E ₂ for 100 each position on the photosensitive drum 1, to set the laser exposure amount E ₂ was smoothed as laser exposure amount does not change suddenly between adjacent each position (S14). That is, a control map of the laser exposure amount on the surface of the photosensitive drum 1 is formed.

Further, after the start of image formation, so as to reduce gradually the laser exposure amount toward the normal level, 1, 2, and 3 after the start of image formation, ..., the laser exposure amount E ₂ of the n-th set The exposure amount correction unit 148 holds the exposure amount (S15).

  The exposure amount correction unit 148 is a memory in which an exposure amount correction map drawn by the number of image formations is recorded. The exposure control unit 147 causes the exposure apparatus 3 to output the laser exposure amount set in the laser exposure amount control map in synchronization with the writing of the exposure image data (S16).

  An example of a technique for controlling the laser light source in synchronization with image writing by individually setting the laser exposure amount in each region on the surface of the photosensitive drum is described in Japanese Patent Application Laid-Open No. 2004-258482. There is a way.

<Example 2>
As shown in FIG. 12 (a) with reference to FIG. 1, in the photosensitive drum 1 in which 100,000 sheets of image formation are accumulated, the potential distribution of the test electrostatic image 1s changes from a rectangular shape to a Gaussian distribution edge. The inclination of the is loosened. If image formation is performed in this state, a good image in which no image flow has occurred is developed, and an image that is partially or wholly reduced in density or blurred is developed.

  As in the case of the photosensitive drum 1 used in Example 1, a new photosensitive drum 1 was used even if the exposure was performed at a certain laser intensity under the condition that an image flow having a sufficient accumulated image formation and reduced surface resistance occurred. An image different from the case is output. In other words, an almost ideal electrostatic image is formed on the photosensitive drum 1 where no image flow occurs, and the toner image is developed on the photosensitive drum 1 as it is, and is transferred and fixed to the recording material P. On the other hand, in the photosensitive drum 1 in which image flow occurs, an almost ideal electrostatic image is formed at the moment of exposure. However, since the surface resistance of the photosensitive drum 1 is low, the electric charge moves instantaneously. Thus, the potential distribution is different from that of the original electrostatic image. If development, transfer, and fixing are performed in this state, an image stream is generated on the output image.

  In the first embodiment, in order not to cause these phenomena on the output image, the laser exposure amount is adjusted to a value specific to each position based on the image flow level detected by the potential sensor 30 in the test electrostatic image 1s. Thus, the development result was corrected. In the second embodiment, the electrostatic image collapse state is grasped in advance by a procedure different from that of the first embodiment, and the laser exposure amount is changed so that an ideal toner image is developed. Form an image.

As shown in FIG. 7 with reference to FIG. 13, the analog voltage signal detected by the potential sensor 30 at the position _LW111 is amplified by the amplifier circuit 121 and A / D converted by the AD converter 122. This digital data is sent to the CPU of the printer control unit 111. In the CPU, the relationship between the five types of peak voltages obtained at the position _LW111 and the five types of laser exposure amounts are approximated by straight lines, and the values obtained by smoothing them with curves are used as the values of the current photosensitive drum 1. The image is stored in the memory as a table of image flow levels at the position _LW111 .

This is compared with a table of the laser exposure amount and peak value of the photosensitive drum 1 without image flow at the position _LW111 , and if the change in the peak value is less than 5%, it is determined that the change has not occurred, and is left as it is. Normal image formation is performed.

However, if the peak value has decreased by 5% or more, it is determined that the surface resistance has greatly decreased, and the decrease at the position _LW111 is calculated. Then, the laser exposure amount is calculated so that the laser exposure amount has a peak value that should be originally obtained, and this result is fed back to the exposure condition correction unit 148. As a result, the exposure condition correction unit 148 instructs the exposure control unit 145 to increase the laser exposure amount.

More specifically, as shown in FIGS. 16 and 17, first, the depth of the electrostatic image drawn at the position _LW111 during the pre-rotation is determined, and the laser exposure amount E _k corresponding thereto is determined.

When irradiated onto the photosensitive drum 1 which is not an exposure amount E _k generated image flow, the peak value of the potential distribution detected becomes S _k. When the peak value S _k is obtained, a good image without image flow is output. However, when the peak value is smaller than S _k , the electrostatic image is different from the originally drawn electrostatic image. As a result, image flow occurs.

Indeed if the image deletion was exposed at an exposure amount E _k to the photosensitive drum 1 occurs, look like the broken line in FIG. 16, when comparing the case of the same electrostatic image, the peak value becomes the S _'k can not be put away obtain the desired peak value S _k, the image flow occurs.

Therefore, it is necessary to change to a desired laser exposure amount so that the peak value S _k can be obtained in this state, but when the relationship with the peak value in the state where there is no image flow is S _k = S ′ _n . to change the laser exposure amount to E _n. Further, 'in the case of _{n, S'} S _k ≠ S locates _n 'S satisfies the relationship of _{n' n-1 that <S} k <S, changes the laser exposure to _{E n.} FIG. 18 shows an example of the relationship between the laser exposure amount before and after correction. Thus, as the amount of laser exposure from a table stored in the memory is E _n, the result is fed back to the exposure condition correction unit 148. As a result, the depth of the electrostatic image at the time of development is almost the same as that when no image flow occurs, and the toner image is developed almost as ideal, and the image flow cannot be confirmed on the output image.

  As a result, even when the photosensitive drum 1 in which image flow occurs is used, the image flow level of the photosensitive drum 1 can be grasped on-time by incorporating the above sequence during the pre-rotation. Then, by feeding back the result to the laser exposure amount, it was possible to always obtain a good image with no image flow.

In the present embodiment has described the case of position _{L W111} as an example, the same procedure in the case of the position _{L WXYZ} other than the position _{L W111.} Regarding the correction of the laser exposure amount at a position where the potential sensor 30 is not installed in the main scanning direction of the photosensitive drum, the position where the potential sensor 30 is installed so that the laser exposure amount is smooth and continuous in the main scanning direction. Complementation is performed based on the laser exposure amount after correction in.

  Further, when the relative humidity in the vicinity of the photosensitive drum 1 is low, an image flow hardly occurs. Therefore, an electronic humidity sensor 125 is attached in the image forming apparatus 100 to monitor the relative humidity in the vicinity of the photosensitive drum 1. .

  The humidity sensor 125 is an electric resistance type humidity sensor that detects relative humidity by utilizing the change in impedance of the sensor element depending on the amount of moisture in the moisture sensitive film. When the moisture sensitive film is a polymer, negative ions in the polymer cause ionic conduction by surrounding moisture (humidity) and exist as mobile ions. The mobile ion concentration changes due to a change in the moisture content of the moisture-sensitive film due to an increase or decrease in humidity, and this is measured as a change in impedance so that the relative humidity can be detected. The electric resistance value of the polymer moisture-sensitive film changes exponentially and becomes high resistance when the relative humidity is in the range of 0 to 20% RH, making it difficult to detect the relative humidity. However, the occurrence of the image flow becomes remarkable in a high humidity environment, and further, there is an advantage that a conversion circuit for extracting an electric signal from the humidity sensor 125 is simple, downsized, and cost can be easily reduced.

  For this reason, in Example 1, using the electric resistance type humidity sensor 125, the result detected by the humidity sensor 125 is converted into an absolute moisture amount, and the absolute moisture amount in the vicinity of the photosensitive drum 1 is 10 g / kg or more. In the case of the above, the above operation was performed. Thereby, even if it compared with the result when absolute water content is 10 g / kg or less, a difference does not appear but a favorable image was obtained.

<Example 3>
20 is an explanatory diagram of exposure control in the third embodiment, FIG. 21 is an explanatory diagram of exposure width and exposure length control, and FIG. 22 is an explanatory diagram of the relationship between the dot size in the photosensitive drum rotation direction and the peak value of the output signal. FIG. FIG. 23 is a diagram showing the peak value of the output signal in each photosensitive drum state according to the dot size, and FIG. 24 is a diagram showing an example of the relationship between the dot size before and after correction.

  As shown in FIG. 20A with reference to FIG. 1, when the surface resistance of the photosensitive drum 1 decreases, the potential distribution of the test electrostatic image 1s exposed in a rectangular shape becomes a Gaussian curve. For this reason, in the potential distribution, the potential becomes equal to or lower than the development voltage Vdc (− direction), and the width of the region where the toner adheres becomes narrower and the height becomes lower.

  Therefore, as shown in FIG. 20B, assuming a Gaussian potential distribution, the pixels are configured so that the width and height of the area to which the toner adheres approach a rectangular potential distribution. The dot size to be corrected is increased and corrected. As a result, even when the surface resistance of the photosensitive drum 1 is lowered, a toner image having a good line width and density that offsets the image flow can be developed and output to the recording material P.

That is, in Example 2, the depth of the electrostatic image at each position L _WXYZ on the photosensitive drum 1 was changed by changing the laser exposure amount. On the other hand, in Example 3, the depth of the electrostatic image is not changed, and the size of the dots constituting each electrostatic image is set to the level of image flow measured using the potential sensor 30. Change accordingly. As a result, image flow symptoms that actually occur are reduced.

Further, in Example 1, a test electrostatic image 1s having a 3-dot width of 127 μm was drawn during the pre-rotation, but in Example 3, a test electrostatic image having a 1-dot width of 42.3 μm that makes the image flow difference clear. Draw 1s. This is because the image flow level at each position L _WXYZ is detected by changing the dot size of the test electrostatic image 1s. At this time, the size of each dot is expressed as S (a, b).

  As shown in FIG. 21A, a in S (a, b) represents the number of dots in the sub-scanning direction of the photosensitive drum 1, and b represents the number of dots in the main scanning direction. As shown in FIG. 21B, S (2, 1) is defined by defining the size of 2 dots in the sub-scanning direction of the photosensitive drum 1 and 1 dot in the main scanning direction as a new one dot. is there. As shown in FIG. 21C, S (1, 2) is defined by defining the size of one dot in the sub-scanning direction and two dots in the main scanning direction of the photosensitive drum 1 as a new one dot. is there.

  As shown in FIG. 13, in Example 1, five types of test electrostatic images 1 s having different electrostatic image depths were formed by changing the laser exposure amount in five steps at each angular position. On the other hand, in Example 2, there are five sizes of S (1, 1), S (2, 1), S (2, 2), S (3, 1), and S (3, 3). Using the corrected dots, a test electrostatic image 1s having a line width of 1 dot is formed.

  The size of the dots in the main scanning direction of the photosensitive drum 1 is almost insensitive because each dot forms a line, and the change in the peak value of the output signal of the potential sensor 30 is less than 5%. . Therefore, only the number of dots in the sub-scanning direction (rotation direction) of the photosensitive drum 1 will be discussed below.

  As shown in FIG. 20A, the image flow tends to become more prominent as the line width becomes thinner. As shown in FIG. 20B, the image flow occurs when the line width becomes larger. It becomes difficult to do. In Example 3, since the test electrostatic image 1s is drawn when the dot size is changed and the substantial line width is increased, if the line has a certain width, almost no image flow can be confirmed. Further, in the main scanning direction of the photosensitive drum 1, it is considered that the output of the potential sensor 30 was hardly sensitive because the width and depth did not change because the dots overlapped.

  As shown in FIGS. 22 and 23, the relationship between the dot size in the rotation direction (sub-scanning direction) of the photosensitive drum 1 and the peak value of the output signal is plotted for smoothing. As the line width in the sub-scanning direction becomes thicker, it can be confirmed that the difference between the state without image flow and the state with image flow is reduced.

Using this relationship, a test electrostatic image 1s is formed in order to measure the current image flow state during the pre-rotation before image formation, as in the second embodiment. For example, when the peak value is S _k at the dot size D _k at the position L _11Y 1, the peak value is S ′ _k when the photosensitive drum 1 in which the image flow is generated is used.

In this state, an image flow occurs and a defect can be confirmed in the output image. Therefore, it is necessary to change the size of dots in the sub-scanning direction to form an electrostatic image so that the desired signal intensity _Sk is obtained. There is. For this reason, when the relationship with the peak value in a state where there is no image flow is S _k = S ′ _n , the dot size is changed to D _n . If S _k ≠ S ′ _n, a search is made for S _n that satisfies the relationship S ′ _n−1 <S _k <S ′ _n , and the dot size is changed to D _n . This change in dot size can be realized by feeding back to the exposure condition correction unit 148 in the same manner as in the second embodiment. FIG. 24 shows an example of the relationship between dot sizes before and after correction.

Such correction is performed on the exposure image data at each position _LXYZ of the photosensitive drum 1. As for dot size correction at a position where the potential sensor 30 is not installed in the main scanning direction of the photosensitive drum, the potential sensor 30 is installed so that the dot size is smooth and continuous in the main scanning direction. Complementation is performed based on the corrected dot size at the corrected position. As a result, as in the second embodiment, a good image with no image flow can be output on the output image.

Incidentally, in Embodiment 3, a case has been described position _{L W111,} also perform the same operation when the position _{L WXYZ} other than the position _{L W111,} absolute water content of the photosensitive drum 1 near was 10 g / kg or more A sufficiently good image could be output by performing the above operation only in some cases.

It is explanatory drawing of a structure of the image forming apparatus which attached the potential sensor. It is explanatory drawing of arrangement | positioning of an electric potential sensor. It is explanatory drawing of a structure of the photosensitive layer of a photosensitive drum. 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 a cleaning blade. 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. 6 is an explanatory diagram of exposure control in Embodiment 1. FIG. It is explanatory drawing of the measurement of the image flow state of a photosensitive drum. It is explanatory drawing of writing of the test electrostatic image in the 1st rotation of the pre-rotation, and the 2nd rotation. It is explanatory drawing of the change of an output signal when an electric potential sensor passes through one angle area | region. It is explanatory drawing of the relationship between a laser exposure amount and the peak value of an output signal. It is the figure which showed the peak value of the output signal of each photosensitive drum state by the amount of laser exposure. It is the figure of an example which showed the relationship between the laser exposure amount before correction | amendment and after correction | amendment. 3 is a flowchart of control according to the first embodiment. It is explanatory drawing of the exposure control in Example 3. FIG. It is explanatory drawing of control of exposure width and exposure length. FIG. 6 is an explanatory diagram of a relationship between a dot size in a photosensitive drum rotation direction and a peak value of an output signal. FIG. 6 is a diagram illustrating a peak value of an output signal in each photosensitive drum state depending on a dot size. It is an example of the relationship between the dot size before and after correction.

Explanation of symbols

1 Photoconductor (Photosensitive drum)
2 Charging means (charging roller)
3 Exposure means (exposure equipment)
4 Development means (developing device)
5 Transfer means (transfer roller)
6 Cleaning device 8 Fixing device 30, 41 Detection means (potential sensor)
31 Insulating film (substrate film layer)
32 Electrode pattern (thin film electrode layer)
32a detection electrode part 32b connection wiring part 34 first adhesive layer 35 film layer 36 second adhesive layer 100 image forming apparatus 110 control means (control part)
120 signal processing circuit 130 image processing unit 140 image memory unit 145 printer unit 148 exposure condition correction unit

Claims (6)

A photosensitive member, a charging unit for charging the photosensitive member, an exposure unit for exposing the charged photosensitive member to form an electrostatic image, and developing the electrostatic image using toner to form a toner image. In an image forming apparatus comprising: a developing unit; and a transfer unit that transfers a toner image carried on the photoconductor to a transfer medium that passes through a transfer unit.
Detecting means capable of detecting a change in potential distribution of the electrostatic image accompanying a decrease in surface resistance of the photoreceptor;
Based on the detection result of the predetermined electrostatic image so that the predetermined electrostatic image is written on the photosensitive member and detected by the detection means, and the amount of applied toner is increased in accordance with the reduction amount of the surface resistance of the photosensitive member. An image forming apparatus comprising: a control unit that controls the exposure unit.   The potential sensor differentiates the potential distribution of the electrostatic image in the main scanning direction passing through the electrode member as the photosensitive member rotates with an electrode member long in the main scanning direction facing the photosensitive member at a predetermined distance. The image forming apparatus according to claim 1, wherein a voltage signal corresponding to a waveform is output. A plurality of the potential sensors are arranged in the main scanning direction of the photoconductor,
The image forming apparatus according to claim 2, wherein the control unit controls the exposure unit so that an exposure amount per pixel is increased as the position in the main scanning direction has a lower peak voltage of the voltage signal. An angle discriminating means for discriminating individual angular positions in the rotation direction of the photoconductor,
The control means detects the predetermined electrostatic images formed at the individual angular positions by a plurality of the potential sensors, and sets an exposure amount per pixel for each position of the surface of the photoconductor. 4. The image forming apparatus according to claim 3, wherein the exposure unit is controlled.   The potential sensor includes a thin film electrode layer in which an insulating film folded to form a cylindrical surface at the tip and an electrode pattern formed to form a cylindrical surface in close contact with the inner surface of the folded insulating film And a central layer bonded to the substrate film layer and the thin film electrode layer so as to give a predetermined curvature to the cylindrical surface of the electrode pattern. The image forming apparatus described.   The potential sensor inclines the thin plate-like side surface so as to protrude the cylindrical surface of the tip toward the rotation direction of the photoconductor, and slides the cylindrical surface of the tip on the photoconductor, 6. The image forming apparatus according to claim 5, wherein a contact pressure with respect to the photosensitive member is set by a bending reaction force.

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