JP2006003815A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformly charge the surface of a photoreceptor without increasing the time of charging the photoreceptor surface in an image forming apparatus which carries out image formation by developing an electrostatic latent image formed on a photoreceptor. <P>SOLUTION: A printer is equipped with: a discharge wire 29b to discharge between the wire and the surface of a photoreceptor drum 27 in a charging region to charge the surface of the photoreceptor drum 28; a grid electrode 29a disposed between the photoreceptor drum 27 surface and the discharge wire 29b to control the current running both; a cleaning brush 51 to detect the potential of the photoreceptor drum 27 surface in an uncharged region; and resistors 95a to 95e to change the potential of a grid electrode 29a in accordance with the detection result of the potential of the photoreceptor drum 27 surface and to correct the charge amount for charging the photoreceptor drum 27 surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus in which an electrostatic latent image is formed by exposing a charged photoreceptor, and image formation is performed by developing the electrostatic latent image.

  The image forming apparatus as described above includes a discharge electrode for performing discharge with the photosensitive member and a grid electrode for performing discharge control, and is formed even when the surrounding environment changes. Some devices are equipped with a device for making the grid voltage applied to the grid electrode constant so that the density of the image becomes constant (see, for example, Patent Document 1).

An apparatus for making the grid voltage constant mounted in the image forming apparatus includes a circuit that divides the grid voltage by a fixed resistor, and the amount of current flowing through the grid electrode so that the voltage divided by this circuit becomes constant. To control.
JP-A-3-279773

  However, in the image forming apparatus described above, the grid voltage applied to the grid electrode is constant. Even if the grid voltage is constant, the grid electrode is charged by the discharge electrode for reasons such as deterioration of the surface of the photoreceptor or change of environment. If there is a variation in the potential of the surface of the photoconductor before being applied, it is difficult to uniformly charge the surface of the photoconductor.

  Specifically, for example, as shown in FIG. 5, when the grid voltage is constant at X and the surface potential of the photoreceptor before charging is A, charging of the photoreceptor surface is started. The surface potential of the photoconductor increases as shown by a solid line, and the surface potential of the photoconductor at the end of charging reaches C, which is a potential between the surface potential A of the photoconductor before charging and the grid voltage X. In addition, when the surface potential of the photosensitive member before charging is lower than A and the grid voltage is constant, the surface potential of the photosensitive member increases as indicated by a two-dot chain line, and after charging, The surface potential of the photoconductor increases only to D. For this reason, the surface potential of the photosensitive member before charging becomes a potential lower by δ than that in the case of A, and the surface of the photosensitive member cannot be uniformly charged.

  In order to solve this problem, it is sufficient to sufficiently charge the surface of the photosensitive member with the discharge electrode. Specifically, for example, the moving (rotating) speed of the photosensitive member is reduced, the grid electrode is It is conceivable to increase the area that can be charged by the discharge electrode. However, when such a solution is executed, there are problems that it takes a long time to form an image and it becomes difficult to arrange the grid electrodes.

  Therefore, in view of such problems, in an image forming apparatus that forms an image by developing an electrostatic latent image formed on a photoconductor, the photoconductor is not increased in time for charging the surface of the photoconductor. It is an object of the present invention to allow the surface to be uniformly charged.

  In order to achieve the above object, the invention according to claim 1 is provided with a photoconductor and a charging unit for charging the surface of the photoconductor, and the electrostatic latent image is charged on the photoconductor charged by the charging unit. An image forming apparatus for forming an image, developing an electrostatic latent image formed on the photoreceptor with a developer, and transferring a visible image developed with the developer to a recording medium, the charging unit And a charge amount correcting unit that corrects an amount of charge when the charging unit charges the surface of the photoconductor based on a potential of the surface of the photoconductor before being charged by the charging.

  Therefore, according to such an image forming apparatus, even when there is a variation in the potential of the surface of the photosensitive member before charging by the charging unit, charging by the charging unit is not performed without increasing the time for charging the surface of the photosensitive member. Later, the surface of the photoreceptor can be uniformly charged.

  The image forming apparatus according to claim 1, wherein the surface of the photoconductor has an endless structure having a predetermined circumferential length and is configured to be rotationally driven in the circumferential direction during image formation. 2, the charging unit charges the surface of the photosensitive member when the surface of the photosensitive member that is driven to rotate passes through a charging region that can be charged by the charging unit, and the charge amount correcting unit is in the vicinity of the charging region. It is desirable to correct the amount of charge when the charging means charges the surface of the photoconductor based on the potential of the uncharged region located upstream in the rotation direction of the photoconductor.

  According to such an image forming apparatus, since the uncharged area is located in the vicinity of the charged area, the surface of the photoreceptor is not affected electrically in the area from the uncharged area to the charged area. Can do. For this reason, the charge amount can be corrected satisfactorily.

  Furthermore, in the image forming apparatus according to claim 2, the charging unit may include a roller, a brush, or the like for contacting the surface of the photosensitive member and charging the surface of the photosensitive member. It is preferable to configure as described in item 3. In other words, the charging means is disposed between the discharge electrode for discharging to and from the surface of the photoconductor to charge the surface of the photoconductor in the charging region, and between the surface of the photoconductor and the discharge electrode. A grid electrode for controlling a current flowing between the surface and the discharge electrode), and the charge amount correction means detects the potential of the surface of the photoreceptor in the uncharged region, and the grid is determined according to the detection result. What is necessary is just to comprise so that the electric potential of an electrode may be fluctuate | varied.

According to such an image forming apparatus, it is possible to control the amount of charge given to the surface of the photoconductor only by changing the potential of the grid electrode, so that the amount of charge can be easily controlled.
According to a third aspect of the present invention, in the image forming apparatus according to the third aspect, as described in the fourth aspect, the charging unit is configured such that the potential of the grid electrode is a predetermined value according to the potential of the surface of the photoreceptor detected by the charge amount correcting unit. It is preferable to control so that.

  According to such an image forming apparatus, when the potential of the surface of the photoreceptor before charging is a certain value, the potential of the grid electrode that is a reference when charging the surface of the photoreceptor is set to the surface of the photoreceptor before charging. It can be controlled to be a constant potential corresponding to the potential.

  Further, in the image forming apparatus according to claim 3 or 4, the charge amount correction means includes a surface contact means arranged so as to come into contact with the surface of the photoreceptor in the uncharged area as described in claim 5. It is desirable to use this surface contact means to detect the surface potential of the photoreceptor.

According to such an image forming apparatus, the surface contact means can reliably detect the potential of the surface of the photoreceptor before charging.
Further, in the image forming apparatus according to claim 5, the charge amount correction unit shunts a part of the current flowing through the grid electrode to the surface contact unit side as described in claim 6, and the surface contact unit side It is preferable to detect the potential on the surface of the photoreceptor in accordance with the amount of current shunted.

According to such an image forming apparatus, since a part of the current flowing through the grid electrode is shunted to the surface contact means side, a power source for supplying current to the surface contact means can be eliminated.
Further, in the image forming apparatus according to claim 5 or 6, the surface contact means is preferably a cleaning means for cleaning the surface of the photosensitive member as described in claim 7.

  According to such an image forming apparatus, the surface contact means can serve both as a function for detecting the potential of the surface of the photosensitive member and as a cleaning means. In comparison, the number of parts can be reduced.

  8. The image forming apparatus according to claim 7, wherein the recording medium is made of paper, the developer is made of a positively chargeable toner, the charging means is a discharge electrode and a grid electrode, and the surface of the photoreceptor in an uncharged area. In the case where the voltage is applied so as to be higher than the first potential, the charge amount correcting means supplies the cleaning means to the surface of the photoconductor in the uncharged area. It is desirable to apply a voltage that is higher than this potential and remove the paper dust adhering to the surface of the photoreceptor by the cleaning means.

  In other words, since the material of paper has a characteristic that it is easily negatively charged, when the paper is used as a recording medium, the discharge electrode, the grid electrode, and the cleaning unit have a higher potential than the surface of the photoreceptor. The cleaning means can adsorb the paper dust adhering to the surface of the photoreceptor.

Therefore, according to such an image forming apparatus, it is possible to satisfactorily remove the paper dust adhering to the surface of the photoreceptor by the cleaning unit.
Further, in the image forming apparatus according to any one of claims 5 to 8, the charge amount correction unit calculates a potential difference between the potential of the grid electrode and a predetermined reference potential as described in claim 9. It is preferable that a voltage dividing unit that divides a grid voltage to be expressed is provided, and a potential of the grid electrode is changed by supplying a current to the surface contact unit from a voltage dividing point of the voltage dividing unit.

  According to such an image forming apparatus, when the current supplied to the surface contact means fluctuates, the potential of the grid electrode can be naturally fluctuated, and an apparatus for monitoring the current is not necessary. The forming apparatus can have a simple configuration.

Further, in the image forming apparatus according to claim 9, it is desirable that the voltage dividing means is composed of a plurality of resistors as described in claim 10.
According to such an image forming apparatus, since the plurality of resistors are used for the voltage dividing unit, the configuration of the voltage dividing unit can be simplified.

  In the image forming apparatus according to any one of claims 3 to 10, the rotating speed of the photosensitive member reaches a potential at which the potential on the surface of the photosensitive member after passing through the charging region substantially matches the potential of the grid electrode. More preferably, as described in claim 11, the potential of the surface of the photoreceptor after passing through the charged region is a potential between the potential before passing through the charged region and the potential of the grid electrode. It is desirable that the speed is set so as to reach an intermediate potential.

  According to such an image forming apparatus, even if the photosensitive member is rotated at a high speed, the charged surface potential of the photosensitive member can be made constant.

Embodiments according to the present invention will be described below with reference to the drawings.
FIG. 1 is an external view showing a printer 1 to which the present invention is applied.
As shown in FIG. 1, a printer 1 as an image forming apparatus is a laser printer, for example, and includes a paper feed tray 6, a paper discharge tray 46, vent holes 62 a and 62 b, and a display that displays the status of the printer 1. A unit 60, an operation unit 61 that performs operation settings of the printer 1, and a power switch 63 that is a main switch of the printer 1 are provided.

The paper feed tray 6 is detachably attached to the bottom of the main casing 2 and is used for stacking and storing paper 3 (recording medium: see FIG. 2) therein.
The paper discharge tray 46 is used to hold the paper 3 on which an image has been formed by the printer 1 and discharged.

The vent holes 62a, 62b are for facilitating the release of heat in the main body casing 2, and are constituted by a number of long holes.
Further, the operation unit 61 determines “+” and “−” keys for selecting various setting items for setting the operation of the printer 1, and setting items selected by the “+” and “−” keys. A “SET” key or the like is provided.

  The display unit 60 includes a liquid crystal display device, for example, and displays the number of pages printed by the printer 1 (page counter) and the operation state of the printer 1 such as an abnormality. In addition, when the operation unit 61 is operated by the user, the display unit 60 displays various modes (a page counter mode for informing the number of printed sheets, a position informing mode for informing an error position when an error occurs, a user An image (character) for setting the buzzer (not shown) that sounds a buzzer (not shown) when the operation unit 61 is operated or when an error occurs is displayed. Therefore, the user can perform various settings by operating the operation unit 61 while viewing the image displayed on the display unit 60.

Next, the inside of the main body casing 2 will be described with reference to FIG. FIG. 2 is a side cross-sectional view of the main part of the printer 1.
In FIG. 2, the printer 1 includes, in a main body casing 2, a feeder unit 4 for feeding paper 3 and an image forming unit 5 for forming a predetermined image on the fed paper 3. Yes.

  The feeder unit 4 includes the sheet feeding tray 6 described above, a sheet pressing plate 7 provided in the sheet feeding tray 6, a sheet feeding roller 8 and a sheet feeding pad provided above one end of the sheet feeding tray 6. 9, paper dust removing rollers 10 and 11 provided on the downstream side in the conveyance direction of the paper 3 with respect to the paper feed roller 8, and a resist provided on the downstream side in the conveyance direction of the paper 3 with respect to the paper dust removing rollers 10 and 11 And a roller 12.

  The paper pressing plate 7 is swingably supported at the far end with respect to the paper feed roller 8 so that the near end can be moved in the vertical direction, and from the back side. It is biased upward by a spring (not shown). Therefore, the sheet pressing plate 7 is swung downward against the urging force of the spring, with the end far from the sheet feeding roller 8 as a fulcrum as the amount of stacked sheets 3 increases. The paper feed roller 8 and the paper feed pad 9 are disposed to face each other, and the paper feed pad 9 is pressed toward the paper feed roller 8 by a spring 13 disposed on the back side of the paper feed pad 9. . The uppermost sheet 3 on the sheet pressing plate 7 is pressed toward the sheet feeding roller 8 by a spring (not shown) from the back side of the sheet pressing plate 7, and the sheet feeding roller 8 and the sheet feeding are rotated by the rotation of the sheet feeding roller 8. After being sandwiched between the pads 9, the sheets are fed one by one. The fed paper 3 is sent to the registration roller 12 after the paper dust is removed by the paper dust removing rollers 10 and 11. The registration roller 12 includes a pair of rollers, and sends the paper 3 to the image forming unit 5 after a predetermined registration.

  The feeder unit 4 further includes a multi-purpose tray 14, a multi-purpose side feed roller 15 and a multi-purpose side feed pad 25 for feeding the sheets 3 stacked on the multi-purpose tray 14. The multi-purpose-side paper feed roller 15 and the multi-purpose-side paper feed pad 25 are arranged so as to face each other. The paper feed pad 25 is pressed toward the multi-purpose side paper feed roller 15. The sheets 3 stacked on the multi-purpose tray 14 are fed one by one after being sandwiched between the multi-purpose side feed roller 15 and the multi-purpose side feed pad 25 by the rotation of the multi-purpose side feed roller 15. Paper.

Next, the image forming unit 5 includes a scanner unit 16, a process unit 17, a fixing unit 18, and the like.
The scanner unit 16 is provided at an upper portion in the main casing 2 and includes a laser light emitting unit (not shown), a polygon mirror 19 that is rotationally driven, lenses 20 and 21, reflectors 22, 23, and 24, and the like. A laser beam based on predetermined image data emitted from the light emitting unit passes or reflects in the order of the polygon mirror 19, the lens 20, the reflecting mirrors 22 and 23, the lens 21, and the reflecting mirror 24, as indicated by a chain line, and will be described later. The surface of the photosensitive drum 27 as the photosensitive member of the process unit 17 is irradiated with high-speed scanning.

  The process unit 17 is disposed below the scanner unit 16 and, as shown in FIG. 2, a photosensitive drum 27, a developing cartridge 28, a scorotron, and the like in a drum cartridge 26 that is detachably attached to the main casing 2. A mold charger 29, a transfer roller 30, and a cleaning brush 51 are provided.

  The developing cartridge 28 is detachably attached to the drum cartridge 26, and includes a developing roller 31, a layer thickness regulating blade 32, a supply roller 33, a toner box 34, and the like.

  The toner box 34 is filled with positively charged non-magnetic one-component toner. Examples of the toner include polymers such as styrene monomers such as styrene, acrylic monomers such as acrylic (C1 to C4) acrylate and alkyl (C1 to C4) methacrylate, and suspension polymerization. A polymerized toner obtained by copolymerization by a known polymerization method is used. Note that such a toner is blended with a colorant such as carbon black, wax, or the like. Then, the toner in the toner box 34 is agitated by the rotation of the agitator 36 supported by the rotation shaft 35 provided at the center of the toner box 34 in the arrow direction (clockwise direction), and is provided in the toner box 34. Released from the toner supply port 37. Note that a toner remaining amount detection window 38 is provided on the side wall of the toner box 34 and is cleaned by a cleaner 39 supported by the rotary shaft 35.

  A supply roller 33 is disposed at a side position of the toner supply port 37 so as to be rotatable in the direction of the arrow (counterclockwise), and the developing roller 31 faces the supply roller 33 in the direction of the arrow ( It is arranged to be rotatable counterclockwise. The supply roller 33 and the developing roller 31 are in contact with each other in a state where each of them is compressed to some extent.

  The supply roller 33 has a metal roller shaft covered with a roller made of a conductive foam material. The developing roller 31 has a metal roller shaft covered with a roller made of a conductive rubber material having no magnetic characteristics. More specifically, the roller part of the developing roller 31 has a urethane rubber or silicone rubber coating layer containing fluorine on the surface of a roller body made of conductive urethane rubber or silicone rubber containing carbon fine particles. It is covered. A developing bias is applied to the developing roller 31.

  In addition, a layer thickness regulating blade 32 is disposed in the vicinity of the developing roller 31. The layer thickness regulating blade 32 includes a pressing portion 40 having a semicircular cross section made of insulating silicone rubber at the tip of a blade body made of a metal leaf spring material. 28, the pressing portion 40 is configured to be pressed against the developing roller 31 by the elastic force of the blade body.

  The toner discharged from the toner supply port 37 is supplied to the developing roller 31 by the rotation of the supplying roller 33. At this time, the toner is positively frictionally charged between the supplying roller 33 and the developing roller 31, and further developed. The toner supplied onto the roller 31 enters between the pressing portion 40 of the layer thickness regulating blade 32 and the developing roller 31 with the rotation of the developing roller 31, where it is further sufficiently frictionally charged and constant. It is carried on the developing roller 31 as a thin layer.

  The photosensitive drum 27 is disposed at a side position of the developing roller 31 so as to be able to rotate in the arrow direction (clockwise direction) so as to face the developing roller 31. The photosensitive drum 27 has a drum main body grounded and a surface portion formed of a positively chargeable photosensitive layer made of polycarbonate or the like. The photosensitive drum 27 is configured to be rotationally driven by power from a main motor (not shown).

  The scorotron charger 29 includes a grid electrode 29a and a discharge wire 29b as a discharge electrode. The scorotron charger 29 is disposed above the photosensitive drum 27 at a predetermined interval so as not to contact the photosensitive drum 27. ing. The scorotron charger 29 is a positively charged scorotron charger that generates corona discharge from a discharge wire 29b such as tungsten. By adjusting the potential of the grid electrode 29a, the surface of the photosensitive drum 27 is applied. It is configured to be uniformly charged to positive polarity. The scorotron charger 29 has a limited area (charging area: see FIG. 4) where the surface of the photoreceptor can be charged, and can charge an area of approximately 20 degrees in angle.

  The surface of the photosensitive drum 27 is first uniformly charged positively by the scorotron charger 29 as the photosensitive drum 27 rotates, and then exposed by high-speed scanning of the laser beam from the scanner unit 16. Then, an electrostatic latent image based on predetermined image data is formed.

  Next, the electrostatic charge formed on the surface of the photosensitive drum 27 when the positively charged toner carried on the developing roller 31 comes into contact with the photosensitive drum 27 by the rotation of the developing roller 31. The latent image, that is, the surface of the photosensitive drum 27 that is uniformly positively charged, is supplied to an exposed portion that is exposed to a laser beam and the potential is lowered, and is visualized by being selectively carried. Thereby, reversal development is achieved.

  The transfer roller 30 is disposed below the photosensitive drum 27 so as to face the photosensitive drum 27, and is supported by the drum cartridge 26 so as to be rotatable in an arrow direction (counterclockwise direction). The transfer roller 30 is configured such that a metal roller shaft is covered with a roller made of an ion conductive rubber material, and a transfer bias (transfer forward bias) is applied during transfer. Therefore, the visible image carried on the surface of the photosensitive drum 27 is transferred to the paper 3 while the paper 3 passes between the photosensitive drum 27 and the transfer roller 30.

  The cleaning brush 51 is formed by weaving a large number of conductive hairs into a woven fabric, and the tips of the many hairs are arranged so as to contact the surface of the photosensitive drum 27. A cleaning bias having a higher potential than the surface potential of the photosensitive drum 27 before charging is applied to these hairs, and a region where a large number of hairs are in contact with the photosensitive drum 27 (uncharged region: see FIG. 4). Thus, the paper dust adhering to the photosensitive drum 27 is collected.

  The fixing unit 18 is disposed on the downstream side of the process unit 17, and includes a fixing roller 41 having a gear, a pressing roller 42 that presses the fixing roller 41, and a downstream side of the fixing roller 41 and the pressing roller 42. A pair of conveying rollers 43 provided in the apparatus is provided. The fixing roller 41 is made of metal and includes a halogen lamp for heating, and the sheet 3 passes between the fixing roller 41 and the pressing roller 42 through the toner transferred onto the sheet 3 in the process unit 17. The sheet 3 is fixed by heating and pressurizing, and then the sheet 3 is conveyed to the sheet discharge path 44 by the conveying roller 43. The paper 3 sent to the paper discharge path 44 is sent to the paper discharge roller 45 and is discharged onto the paper discharge tray 46 by the paper discharge roller 45.

  In addition, the printer 1 is provided with a reverse conveyance unit 47 in order to form images on both sides of the paper 3. The reverse conveyance unit 47 includes a paper discharge roller 45, a reverse conveyance path 48, a flapper 49, and a plurality of reverse conveyance rollers 50.

  The paper discharge roller 45 includes a pair of rollers and is configured to be able to switch between forward rotation and reverse rotation. As described above, the paper discharge roller 45 rotates in the forward direction when the paper 3 is discharged onto the paper discharge tray 46, but rotates in the reverse direction when the paper 3 is reversed.

  The reverse conveyance path 48 is provided along the vertical direction so that the paper 3 can be conveyed from the paper discharge roller 45 to a plurality of reverse conveyance rollers 50 disposed below the image forming unit 5. The upstream end is disposed near the paper discharge roller 45, and the downstream end is disposed near the reverse conveyance roller 50.

  The flapper 49 is provided so as to be able to swing so as to face a branch portion between the paper discharge path 44 and the reverse conveyance path 48, and the paper reversed by the paper discharge roller 45 by excitation or non-excitation of a solenoid (not shown). 3 is configured to be able to be switched from the direction toward the paper discharge path 44 to the direction toward the reverse conveyance path 48.

  A plurality of reverse conveyance rollers 50 are provided in a substantially horizontal direction above the paper feed tray 6, and the most upstream reverse conveyance roller 50 is disposed near the rear end of the reverse conveyance path 48, and The most downstream reverse conveying roller 50 is provided so as to be disposed below the registration roller 12.

  When images are formed on both sides of the paper 3, the reverse conveying unit 47 is operated as follows. That is, when the sheet 3 having an image formed on one side is sent from the sheet discharge path 44 to the sheet discharge roller 45 by the transport roller 43, the sheet discharge roller 45 rotates forward with the sheet 3 interposed therebetween. The paper 3 is once transported to the outside (the discharge tray 46 side), and when the majority of the paper 3 is sent to the outside and the rear end of the paper 3 is sandwiched between the paper discharge rollers 45, the paper 3 rotates forward. To stop. Next, the paper discharge roller 45 rotates in the reverse direction, and the flapper 49 switches the transport direction so that the paper 3 is transported to the reverse transport path 48, and the reverse transport path 48 in the reverse direction of the paper 3. To be transported. When the conveyance of the paper 3 is completed, the flapper 49 is switched to the original state, that is, the state where the paper 3 sent from the conveyance roller 43 is sent to the paper discharge roller 45. Next, the sheet 3 conveyed in the reverse direction to the reverse conveyance path 48 is conveyed to the reverse conveyance roller 50, reversed from the reverse conveyance roller 50 in the upward direction, and sent to the registration roller 12. The paper 3 conveyed to the registration roller 12 is turned over and sent again to the image forming unit 5 after a predetermined registration, whereby a predetermined image is formed on both sides of the paper 3.

  Note that position sensors 64 to 67 for detecting the position of the sheet 3 are arranged in the conveyance path through which the sheet 3 passes. More specifically, the position sensor 64 is disposed immediately before the registration roller 12, and the position sensor 65 is disposed immediately after the registration roller 12. The position sensor 66 is disposed immediately after the fixing roller 41, and the position sensor 67 is disposed immediately before the paper discharge roller 45.

  Next, a control system in the printer 1 will be described with reference to FIG. FIG. 3 is a block diagram showing an electrical connection relationship between the control device 70 built in the printer 1 and each unit located in the periphery thereof.

  The control device 70 is connected to the above-described image forming unit 5 and operation unit 61, position sensors 64 to 67, various motors 84 such as a main motor serving as a power source for the sheet conveying system of the printer 1. Then, the control device 70 follows the instructions from the user input via various motors 84 or the like, or the instructions from various information processing devices (such as personal computers) input via the network. And the operation unit 61 is controlled.

  The control device 70 includes a CPU 71, a ROM 72, a RAM 73, and a well-known microcomputer centering on a bus line 76 that connects these components.

The control device 70 further includes an image formation control unit 79, a motor drive unit 78, a signal input unit 81, a network interface 74 (network I / F), and the like.
The image forming control unit 79 controls the image forming unit 5 in accordance with a command from the CPU 71.

The motor drive unit 78 transmits a drive pulse to each of the various motors 84 in accordance with a command from the CPU 71 to drive the various motors 84.
The signal input unit 81 takes in a command signal from a user input via the operation unit 61 and detection signals from the position sensors 64 to 67 into the control device 70, and these input signals can be processed by the CPU 71. Convert to signal.

The network interface 74 is used for data communication with an external information processing apparatus (such as a personal computer) via a network.
The image forming control unit 79, the motor driving unit 78, the signal input unit 81, and the network interface 74 are connected to the CPU 71, ROM 72, and RAM 73 via the bus line 76.

  In such a printer 1, when the CPU 71 receives a print request from an external information processing apparatus via a network, the CPU 71 then executes an image formation control unit 79 or the like according to print data (image formation data) transmitted via the network. Various motors 84 are driven and controlled, and an image based on the print data is formed on the paper 3 while the paper 3 is conveyed.

  Further, during image formation, the position sensors 64 to 67 detect the presence / absence of the sheet 3 at each sensor position, and the CPU 71 uses the driving pulses transmitted from the motor driving unit 78 to the various motors 84 and the position sensors 64 to 67. In association with the detection, when the sheet 3 does not exist at a position where the sheet 3 should exist or when the sheet 3 exists at a position where the sheet 3 should not exist, a paper jam (paper jam) is notified.

  Furthermore, when various errors are detected based on the detection by the position sensors 64 to 67, the CPU 71 stops the operation of the image forming unit 5 and executes a process for prohibiting the image forming operation.

  In particular, the image forming unit 5 described above includes a charge amount correction unit 90 (see FIG. 3) for controlling the amount of charge on the surface of the photosensitive drum 27 by the scorotron charger 29. In response to a signal input from the correction unit 90, a command is sent to the image formation control unit 79 to send a signal with a duty ratio controlled to the charge amount correction unit 90.

Next, the charge amount correction unit 90 will be described in detail with reference to FIG. FIG. 4 is an explanatory diagram schematically showing the charge amount correction unit 90 and each unit located in the vicinity thereof.
The charge amount correction unit 90 includes a PWM signal smoothing circuit 91, a transformer drive circuit 92, a booster / rectifier circuit 93, a constant voltage circuit 94, a plurality of resistors 95 a to 95 e, and a diode 96.

Hereinafter, each part constituting the charge amount correction unit 90 will be described in detail.
The PWM signal smoothing circuit 91 receives a signal whose duty ratio is controlled from the control device 70, smoothes the signal, and outputs a DC signal proportional to the duty ratio of the signal.

The transformer drive circuit 92 receives the DC signal output from the PWM signal smoothing circuit 91 and outputs an AC signal having a frequency corresponding to the voltage of the DC signal.
The booster / rectifier circuit 93 receives the AC signal output from the transformer drive circuit 92, boosts the AC signal, and rectifies and smoothes the boosted AC signal to generate a high voltage (for example, about 7000 V). Generate.

  Part of the high voltage generated by the booster / rectifier circuit 93 is output to the constant voltage circuit 94, and most of the generated high voltage is applied to the discharge wire 29b of the scorotron charger 29 as a discharge voltage. Applied.

  The constant voltage circuit 94 is a known constant voltage circuit, and the constant voltage generated by the constant voltage circuit 94 (higher than the surface potential of the photosensitive drum 27 before charging) is applied to the developing roller 31 as a developing bias. As applied.

The plurality of resistors 95 a to 95 e are arranged on the control device 70 side and the cleaning brush 51 side from the branch point 97.
That is, resistors 95c and 95d are disposed on the path from the grid electrode 29a to the control device 70, and the resistor 95a is disposed on the path from the grid electrode 29a to the cleaning brush 51.

  The resistor 95e has one end connected to the terminal on the control device 70 side of the resistor 95d and the resistor 95b, and the other end grounded. The resistor 95b has one end connected to a terminal on the control device 70 side of the resistor 95d and the other end connected to a terminal on the cleaning brush 51 side of the resistor 95a.

  The diode 96 has an anode connected to the connection point between the resistor 95 a and the resistor 95 b, and a cathode connected to the cleaning brush 51. The diode 96 is provided to prevent a current from flowing from the photosensitive drum 27 to the cleaning brush 51 when the surface potential of the photosensitive drum 27 becomes lower than that of the cleaning brush 51.

  The charge amount correction unit 90 generates a bias to be applied to the discharge wire 29b and the developing roller 31 by the PWM signal smoothing circuit 91, the transformer drive circuit 92, the boosting / rectifying circuit 93, and the constant voltage circuit 94. Then, the charge amount correction unit 90 removes a current (hereinafter referred to as a current (Ig) flowing through the grid electrode 29 a) excluding a current flowing through the surface of the photosensitive drum 27 among the current discharged from the discharge wire 29 b as a branch point. At 97, the current is divided into a current (If) flowing through the resistors 95c and 95d and a current (Ic) flowing through the resistor 95a. Further, the current flowing from the connection point between the resistor 95a and the resistor 95b to the cleaning brush 51 is Ic ′. Then, the control device 70 controls the PWM signal smoothing circuit 91 so that the current (If + Ic−Ic ′) flowing through the resistor 95e becomes constant (precisely, the potential of the signal input to the control device 70 becomes constant). The input signal is controlled by the control device 70.

  Here, when the potential of the surface of the photosensitive drum 27 in contact with the cleaning brush 51 becomes low, the current (Ic ′) passed through the cleaning brush 51 increases. For this reason, when the control device 70 controls the PWM signal so that the current flowing through the resistor 95e does not decrease, the current (Ig) increases and the potential of the grid electrode 29a increases.

  Even when the current (Ic ′) flowing through the cleaning brush 51 changes, the current (Ig) flowing through the grid electrode 29a is constant at that moment. When it becomes low, the current (If + Ic−Ic ′) flowing through the resistor 95e decreases. At this time, the potential at the connection point between the resistor 95d and the resistor 95e drops, but at this time, the control device 70 determines that the potential at the connection point between the resistor 95d and the resistor 95e is constant. The duty ratio of the signal input to the signal smoothing circuit 91 is controlled.

  Next, changes in the surface potential of the photosensitive drum 27 charged by the scorotron charger 29 will be described with reference to FIG. FIG. 5 is a graph showing the relationship between the surface potential of the photosensitive drum 27 and the charging time by the scorotron charger 29.

  When charging of the surface of the photosensitive drum 27 is started by the scorotron charger 29, for example, the potential of the grid electrode 29a is X and the potential of the surface of the photosensitive drum 27 is A as shown in FIG. In this case, the surface potential of the photosensitive drum 27 rises, and when charging for a sufficiently long time, the surface potential of the photosensitive drum 27 reaches the potential of the grid electrode 29a.

  By the way, since the charging time is not sufficient, the surface potential of the photosensitive drum 27 after charging only rises to C, which is a potential between the surface potential A of the photosensitive drum 27 before charging and the potential X of the grid electrode 29a. . Therefore, when the surface potential of the photosensitive drum 27 before charging is B, which is lower than A, and the potential of the grid electrode 29a is constant, the potential of the photosensitive drum 27 after charging is D. Therefore, the surface potential of the photosensitive drum 27 before charging is lower by δ than the case of A.

  For this reason, in this embodiment, even if the surface potential of the photosensitive drum 27 before charging is different by changing the potential of the grid electrode 29a by the plurality of resistors 95a to 95e, The surface potential of the photosensitive drum 27 is made the same.

  That is, when the surface potential of the photosensitive drum 27 before charging is low (for example, when the potential is B), the potential of the grid electrode 29a is increased so that the potential of the surface of the photosensitive member increases more quickly. Therefore, the surface potential of the photosensitive drum 27 after charging is C. As a result, the surface of the photosensitive drum 27 can be uniformly charged.

  Here, the charging means in the present invention corresponds to the control device 70, the PWM signal smoothing circuit 91, the transformer drive circuit 92, the booster / rectifier circuit 93, the constant voltage circuit 94, the grid electrode 29a, and the discharge wire 29b in the present embodiment. To do.

The charge amount correcting means corresponds to the resistors 95a and 95b, the cleaning brush 51, and the path from the branch point 97 to the cleaning brush 51.
Here, the grid means 29a and the discharge wire 29b in this embodiment correspond to the charging means in the present invention.

The voltage dividing means corresponds to the resistors 95a and 95b.
The surface contact means and the cleaning means correspond to the cleaning brush 51.
In the printer 1 described in detail above, the discharge wire 29b for charging the surface of the photosensitive drum 27 by discharging between the surface of the photosensitive drum 27 in the charging region, and the surface of the photosensitive drum 27 and discharging. The grid electrode 29a is arranged between the wire 29b and controls the current flowing between them (between the surface of the photoconductive drum 27 and the discharge wire 29b), and the potential of the surface of the photoconductive drum 27 in the uncharged region. The potential of the grid electrode 29a is changed in accordance with the cleaning brush 51 for detection and the detected result of the detected potential on the surface of the photosensitive drum 27 to correct the amount of charge when the surface of the photosensitive drum 27 is charged. Resistors 95a to 95e. Here, a part of the current flowing through the grid electrode 29a is shunted to the cleaning brush 51 side by the branch point 97, and the resistors 95a to 95e are photosensitive in accordance with the amount of current shunted to the cleaning brush 51 side. It is configured to naturally detect the potential of the surface of the body drum 27.

  Therefore, even if the potential of the surface of the photosensitive drum 27 before charging by the scorotron charger 29 varies, the charging by the scorotron charger 29 is performed without increasing the time for charging the surface of the photosensitive drum 27. Later, the surface of the photosensitive drum 27 can be uniformly charged.

  In addition, since the charge amount correction unit 90 diverts a part of the current flowing through the grid electrode 29a to the cleaning brush 51 side at the branch point 97, a power source for supplying current to the cleaning brush 51 may be unnecessary. it can.

Furthermore, since the amount of charge applied to the surface of the photosensitive drum 27 can be controlled simply by changing the potential of the grid electrode 29a, the amount of charge can be easily controlled.
Next, the surface of the photosensitive drum 27 has an endless structure having a predetermined circumferential length and is configured to be rotationally driven in the circumferential direction during image formation. The scorotron charger 29 is a photosensitive material that is rotationally driven. The surface of the photosensitive drum 27 is charged when the surface of the photosensitive drum 27 passes through a charging area that can be charged by the scorotron charger 29. The cleaning brush 51 is disposed in contact with an uncharged area located in the vicinity of the charged area and upstream of the photosensitive drum 27 in the rotation direction.

  Therefore, since the uncharged area is located in the vicinity of the charged area, it is possible to prevent the surface of the photosensitive drum 27 from being electrically affected in the area from the uncharged area to the charged area. For this reason, the charge amount can be corrected satisfactorily.

  The control device 70 is configured to control the potential of the grid electrode 29a to be a predetermined value according to the potential of the surface of the photosensitive drum 27 detected by the resistors 95a to 95e.

  Accordingly, when the potential of the surface of the photosensitive drum 27 before charging is a certain value, the potential of the grid electrode 29a serving as a reference when charging the surface of the photosensitive drum 27 is set to the surface of the photosensitive drum 27 before charging. It can be controlled to be a constant potential corresponding to the potential.

Further, the cleaning brush 51 is used to detect the surface potential of the photosensitive drum 27.
Therefore, the potential of the surface of the photosensitive drum 27 before charging can be reliably detected by the cleaning brush 51.

Further, the cleaning brush 51 is used for detecting the surface potential of the photosensitive drum 27 and for cleaning the surface of the photosensitive drum 27.
Therefore, the number of components can be reduced as compared with the case where components having each function are arranged.

  Further, a voltage that is higher than the potential of the surface of the photosensitive drum 27 in the uncharged area is applied to the discharge wire 29b and the grid electrode 29a. This printer 1 is positively charged as a developer. An image is formed using toner. Then, the charge amount correction unit 90 applies a voltage that is higher than the potential of the surface of the photosensitive drum 27 in the uncharged region in accordance with the current supplied to the cleaning brush 51, and the cleaning brush 51 The paper dust adhered to the surface of the photosensitive drum 27 is configured to be removed.

Therefore, the paper dust attached to the surface of the photosensitive drum 27 can be satisfactorily removed by the cleaning brush 51.
The rotating speed of the photosensitive drum 27 is a constant speed such that the potential on the surface of the photosensitive drum 27 after passing through the charging region reaches an intermediate potential between the potential before passing through the charging region and the potential of the grid electrode 29a. Is set.

Therefore, even if the photosensitive drum 27 is rotated at a high speed, the charged surface potential of the photosensitive drum 27 can be made constant.
The resistors 95a to 95e are configured to divide a grid voltage representing a potential difference between the potential of the grid electrode 29a and a predetermined reference potential, and in particular, cleaning is performed from the voltage dividing points of the resistors 95a and 96b. By supplying a current to the brush 51, the potential of the grid electrode 29a is changed.

  Therefore, when the current supplied to the cleaning brush 51 fluctuates, the potential of the grid electrode 29a can be naturally fluctuated, and a device for monitoring the current is not necessary, so that the printer 1 has a simple configuration. be able to.

The embodiment of the present invention is not limited to the above-described embodiment, and can take various forms as long as it belongs to the technical scope of the present invention.
For example, in this embodiment, the scorotron charger 29 that charges the surface of the photosensitive drum 27 without contacting the photosensitive drum 27 is used. However, the photosensitive drum 27 comes into contact with the surface of the photosensitive drum 27. You may comprise so that the surface of this may be charged. In this case, the photosensitive drum 27 may be charged by bringing a roller, a brush or the like into contact with the surface of the photosensitive member.

  In the present embodiment, when the current flowing through the resistors 95a and 95b changes, the potential of the grid electrode 29a naturally changes. However, such a configuration is not particularly necessary. The surface potential of the photosensitive drum 27 before charging may be detected by a sensor, and the control device 70 may be configured to change the potential of the grid electrode 29a based on the detection result. In this case, for example, the control device 70 may be configured to change the resistance values of the resistors 95c and 95d based on the detection result of the sensor.

  Furthermore, in the present embodiment, the cleaning brush 51 is brought into contact with the surface of the photoconductor to detect the surface potential of the photoconductor drum 27. However, the present invention is not limited to the brush, and may be a roller, a blade, or the like. Further, the potential on the surface of the photoreceptor may be detected by a non-contact type sensor.

Moreover, the connection method of the several resistors 95a-95e is not restricted to the connection method as described in FIG. 4, For example, you may make it show in FIG.
That is, as shown in FIG. 6, the resistors 95f to 95h are connected in series, the terminal on the resistor 95f side is connected to the grid electrode 29a, and the terminal on the resistor 95h side is grounded. In this state, the current flowing to the cleaning brush 51 is taken out from the connection point between the resistor 95f and the resistor 95g, and the current returning to the control device is taken out from the connection point between the resistor 95g and the resistor 95h.

  Even if it does in this way, the same effect is acquired.

It is a schematic sectional drawing which shows a laser printer. It is a schematic diagram which shows a part of scanner unit which comprises a laser printer. FIG. 3 is a block diagram illustrating an electrical connection relationship between units included in the printer. It is explanatory drawing which shows typically the electric charge amount correction | amendment part and each part located in the periphery. 3 is a graph showing a relationship between a surface potential of a photosensitive drum and a charging time by a scorotron charger. It is explanatory drawing which shows the modification of the connection method of a resistor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Printer, 5 ... Image formation part, 16 ... Scanner unit, 17 ... Process unit, 18 ... Fixing unit, 26 ... Drum cartridge, 27 ... Photoconductor drum, 28 ... Developing cartridge, 29 ... Scorotron type charger, 29a ... Grid electrode, 29b ... discharge wire, 30 ... transfer roller, 31 ... developing roller, 34 ... toner box, 51 ... cleaning brush, 70 ... control device, 78 ... motor drive unit, 79 ... image formation control unit, 81 ... signal input , 90... Charge amount correction unit, 91... PWM signal smoothing circuit, 92... Transformer drive circuit, 93... Boosting / rectifying circuit, 94 .. constant voltage circuit, 95 a to 95 e.

Claims (11)

A photoreceptor, and charging means for charging the surface of the photoreceptor,
An electrostatic latent image is formed on the photosensitive member charged by the charging unit, the electrostatic latent image formed on the photosensitive member is developed with a developer, and a visible image developed with the developer is recorded on a recording medium. An image forming apparatus for transferring to
An image comprising: a charge amount correcting unit that corrects a charge amount when the charging unit charges the surface of the photoconductor based on a potential of the surface of the photoconductor before being charged by the charging unit. Forming equipment. The surface of the photoreceptor has an endless structure having a predetermined circumference, and is configured to be rotationally driven in the circumferential direction during image formation,
The charging unit charges the surface of the photosensitive member when the surface of the rotating photosensitive member passes through a charging region that can be charged by the charging unit;
The charge amount correcting means is a charge amount when the charging means charges the surface of the photoconductor based on a potential of an uncharged area located in the vicinity of the charging area and upstream in the rotation direction of the photoconductor. The image forming apparatus according to claim 1, wherein: The charging means includes
A discharge electrode for discharging between the surface of the photoreceptor and charging the surface of the photoreceptor in the charging region;
A grid electrode disposed between the surface of the photoreceptor and the discharge electrode for controlling a current flowing between the two,
3. The image forming apparatus according to claim 2, wherein the charge amount correction unit detects a potential of the surface of the photoreceptor in the uncharged region, and varies the potential of the grid electrode according to the detection result. .   4. The image according to claim 3, wherein the charging unit controls the potential of the grid electrode to be a predetermined value in accordance with the potential of the surface of the photoreceptor detected by the charge amount correcting unit. Forming equipment.   The charge amount correcting means includes surface contact means arranged to contact the surface of the photoreceptor in the uncharged region, and detects the potential of the surface of the photoreceptor using the surface contact means. The image forming apparatus according to claim 3.   The charge amount correcting unit diverts a part of the current flowing through the grid electrode to the surface contact unit side, and detects the potential of the surface of the photoconductor according to the amount of current divided to the surface contact unit side. The image forming apparatus according to claim 5.   The image forming apparatus according to claim 5, wherein the surface contact unit is a cleaning unit for cleaning the surface of the photoreceptor. The recording medium is made of paper,
The developer comprises a positively charged toner,
The charging means applies a voltage to the discharge electrode and the grid electrode such that the potential becomes higher than the potential of the surface of the photoreceptor in the uncharged region,
The charge amount correcting means applies a voltage to the cleaning means so as to be higher than the potential of the surface of the photoconductor in the uncharged region, and removes the paper dust attached to the surface of the photoconductor by the cleaning means. The image forming apparatus according to claim 7, wherein the image forming apparatus is removed.   The charge amount correcting means includes voltage dividing means for dividing a grid voltage representing a potential difference between the potential of the grid electrode and a predetermined reference potential, and a current is supplied to the surface contact means from the voltage dividing point of the voltage dividing means. The image forming apparatus according to claim 3, wherein the potential of the grid electrode is changed by supplying the voltage.   The image forming apparatus according to claim 9, wherein the voltage dividing unit includes a plurality of resistors.   The circumferential speed of the photoconductor is set at a constant speed so that the potential on the surface of the photoconductor after passing through the charged region reaches an intermediate potential between the potential before passing through the charged region and the potential of the grid electrode. The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus.

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