JP2011133527A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a leakage of current while preventing a change in image density in continuous printing, even if the electric property of a coat layer varies. <P>SOLUTION: An image forming apparatus includes: a first roller 11 that conveys toner by carrying and rotating the toner with the coat layer 59 and supplies, to a photoreceptor drum, the toner at a first part facing the photoreceptor drum; a first voltage generation section 67 for superimposing DC voltage output from a first DC power source 73 on AC voltage output from a first AC power source 75, and applying them to the first roller 11 in order to scatter the toner carried by the coat layer 59 at the first part; a first measuring section 69 for measuring the alternating current that is output from the first AC power source 75 and flows in the first roller 11; and a first control section 71 for controlling the alternating current that is output from the first AC power source 75 and flows in the first roller 11 by adjusting the frequency of the alternating current output from the first AC power source 75 based on the alternating current measured by the first measuring section 69. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that supplies toner from a roller to a photosensitive drum by applying a DC voltage and an AC voltage superimposed on the roller.

  In the electrophotographic technology, the electrostatic latent image formed on the photosensitive drum is developed by supplying toner from a roller called a developing roller to the photosensitive drum. As a method of supplying the toner, a DC voltage and an AC voltage are superimposed and applied to the developing roller, whereby the toner carried by the developing roller is caused to fly and the toner is supplied to the photosensitive drum. In some cases, a resinous coating layer containing a conductive material is formed on the peripheral surface of the developing roller, and toner is carried on the coating layer. When such a developing roller is used, the electrical properties (resistance value, capacitance, dielectric constant, etc.) of the coating layer affect the performance of the image forming apparatus due to environmental changes and the like. In view of the above problems, a technique for obtaining a good developed image by making the alternating current of the alternating voltage applied to the developing roller provided with the conductive rubber layer a constant current has been proposed (for example, Patent Document 1). See paragraphs 0076 to 0088)).

JP 7-28335 A

  However, if the amount of charge accumulated in the coating layer during continuous printing increases, a phenomenon in which the image density changes occurs. If the resistance value of the coating layer is reduced, the amount of electric charge accumulated in the coating layer can be suppressed, so that the phenomenon that the image density changes can be prevented. However, current leakage occurs between the photosensitive drum and the developing roller.

  The margin of the resistance value of the coat layer that can simultaneously prevent the phenomenon of current leakage and the phenomenon of image density change decreases as the printing speed of the image forming apparatus increases. In the coat layer formed on each developing roller, variations in electrical properties are inevitably generated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of both preventing the phenomenon of current leakage and preventing the phenomenon of changing the image density during continuous printing even if the electrical properties of the coating layer vary. And

  An image forming apparatus according to an aspect of the present invention that achieves the above object has an image carrier and a peripheral surface on which a coat layer is formed, and rotates while carrying toner on the coat layer. The coating layer includes a first roller that conveys toner and supplies the toner to the image carrier at a first facing portion that faces the image carrier, a first DC power source, and a first AC power source. In order to cause the toner carried in step 1 to fly at the first opposing location, the DC voltage output from the first DC power supply and the AC voltage output from the first AC power supply are superimposed to overlap the toner. A first voltage generating unit to be applied to the first roller; a first measuring unit for measuring an AC current output from the first AC power source and flowing through the first roller; and the first measurement. The first AC power source based on the AC current measured at the section A first control unit that controls the alternating current output from the first alternating current power source and flowing through the first roller to a constant current by adjusting the frequency of the alternating current output from the first alternating current power source. To do.

  According to this configuration, the alternating current that is output from the first alternating current power source that generates the alternating voltage applied to the first roller and flows through the first roller is set to a constant current, and the constant current control is performed using the alternating current frequency. Running by adjusting. For this reason, even if the electrical properties of the coating layer vary, both the prevention of the phenomenon of current leakage between the first roller and the image carrier and the prevention of the phenomenon of changing the image density by continuous printing are achieved. Can do. This configuration can be applied to both a two-component developer and a one-component developer.

  In the above-described configuration, the two-component developer is conveyed by rotating while carrying the two-component developer, and the toner in the two-component developer is removed from the first component at a second facing portion facing the first roller. A second roller to be supplied to the roller, a second DC power source and a second AC power source, and the toner in the two-component developer carried by the second roller is caused to fly at the second facing portion. For this purpose, a second voltage generator that applies a DC voltage output from the second DC power supply and an AC voltage output from the second AC power supply to the second roller in a superimposed manner; A second measuring unit that measures an AC current output from the second AC power source and flows through the second roller; and the second measuring unit based on the AC current measured by the second measuring unit. By adjusting the AC frequency output from the AC power supply A second control unit for controlling the alternating current output from the second AC power supply through the second roller to the constant current, it is possible to further comprise a.

  According to this configuration, the alternating current output from the second AC power source that generates the AC voltage applied to the second roller and flowing through the second roller is set to a constant current, and this constant current control is performed using the AC frequency. Running by adjusting. For this reason, even if there are variations in the electrical properties of the coating layer, both the prevention of the phenomenon of current leakage between the first roller and the second roller and the prevention of the phenomenon of changing the image density during continuous printing are achieved. be able to.

  The said structure WHEREIN: The sheet resistance value of the said coating layer can be made into 1.0E + 5 or more and 1.0E + 9 or less.

  According to this configuration, the sheet resistance value of the coating layer is embodied as 1.0E + 5 or more and 1.0E + 9 or less as a range of variation in the electrical properties of the coating layer.

  In the above configuration, the image bearing member may include amorphous silicon.

  According to this configuration, when the photosensitive member of the image carrier is amorphous silicon, even if the electrical properties of the coat layer vary, the phenomenon of current leakage is prevented and the image density changes due to continuous printing. Both prevention can be achieved.

  According to the present invention, even if the electrical properties of the coat layer vary, it is possible to achieve both the prevention of a current leak phenomenon and the prevention of a phenomenon in which the image density changes during continuous printing.

1 is a diagram illustrating an outline of an internal structure of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus. FIG. 2 is a view showing a cross section of a pair of photosensitive drums and a developing device provided in the image forming apparatus. FIG. 4 is a diagram illustrating a process in which toner in a two-component developer is supplied from a developing device to a photosensitive drum. FIG. 2 is a block diagram illustrating a configuration of a first power supply unit provided in the image forming apparatus. FIG. 3 is a block diagram illustrating a configuration of a second power supply unit provided in the image forming apparatus. It is a figure which shows the experimental result which shows that the resistance value of a coat layer influences a leak phenomenon and a density | concentration change phenomenon. It is a figure which shows the measured value of the alternating current which flows between a 1st roller and a photosensitive drum, and the alternating current which flows between a 1st roller and a 2nd roller. 6 is a flowchart illustrating an example of constant current control when toner is supplied to a photosensitive drum. 6 is a flowchart illustrating an example of constant current control when supplying toner in a two-component developer to a first roller. FIG. 5 is a diagram illustrating a process in which a one-component developer is supplied from a developing device to a photosensitive drum.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an outline of the internal structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 is a tandem color printer. The image forming apparatus 1 includes a sheet storage unit 110, an image forming unit 130, and a fixing unit 160.

  The sheet storage unit 110 is disposed at the lowermost part of the image forming apparatus 1 and includes a sheet tray 111 that can store a bundle of sheets P. The paper tray 111 is inserted into the image forming apparatus 1 and attached. When replenishing the paper P, the paper tray 111 is pulled out from the image forming apparatus 1. In the bundle of sheets P stored in the sheet tray 111, the uppermost sheet P is fed out toward the sheet conveyance path 115 by driving the pickup roller 113. The paper P is transported to the image forming unit 130 through the paper transport path 115.

  The image forming unit 130 forms a toner image on the conveyed paper P. The image forming unit 130 includes a magenta unit 133M, a cyan unit 133C, a yellow unit 133Y, and a black unit 133K, which are arranged in tandem according to the order in which the toner images are transferred to the transfer belt 131. These units have the same configuration, and a magenta unit 133M will be described as an example.

  The magenta unit 133M includes a photosensitive drum 135. Around the photosensitive drum 135, a charger 137, an exposure device 139, a developing device 141, and a cleaner 143 are arranged. The charger 137 uniformly charges the peripheral surface of the photosensitive drum 135. The exposure device 139 generates light corresponding to magenta data in the image data transmitted from a personal computer or the like, and irradiates the circumferential surface of the uniformly charged photosensitive drum 135. As a result, an electrostatic latent image corresponding to the magenta data is formed on the peripheral surface of the photosensitive drum 135. In this state, by supplying magenta toner from the developing device 141 to the peripheral surface of the photosensitive drum 135, a toner image corresponding to magenta data is formed on the peripheral surface.

  The transfer belt 131 can move in the D direction (clockwise) while being sandwiched between the photosensitive drum 135 and the primary transfer roller 145. The toner image corresponding to the magenta data is transferred from the photosensitive drum 135 to the transfer belt 131. The magenta toner remaining on the peripheral surface of the photosensitive drum 135 is removed by the cleaner 143. The above is the description of the magenta unit 133M.

  A toner image corresponding to magenta data is transferred to the transfer belt 131, and a toner image corresponding to cyan data is transferred onto the toner image. Similarly, a toner image corresponding to yellow data and a toner corresponding to black data are transferred. The image is transferred in layers. As a result, a color toner image is formed on the transfer belt 131. This color toner image is transferred by the secondary transfer roller 149 onto the paper P conveyed from the paper storage unit 110 described above.

  The sheet P on which the color toner image is transferred is sent to the fixing unit 160. The fixing unit 160 includes a heating roller 161 and a pressure roller 163. The paper P on which the color toner image is transferred is sandwiched between these rollers. As a result, heat and pressure are applied to the color toner image, and the color toner image is fixed to the paper P. The paper P is discharged to the paper discharge unit 169.

  FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 has a configuration in which a paper storage unit 110, an image forming unit 130, a fixing unit 160, a control unit 200, an operation display unit 300, a first power supply unit 61, and a second power supply unit 63 are connected to each other via a bus. Have The sheet storage unit 110, the image forming unit 130, and the fixing unit 160 have been described with reference to FIG.

  The control unit 200 includes a micro processing unit (MPU), a read only memory (ROM), a random access memory (RAM), and an image memory. The MPU performs control necessary for operating the image forming apparatus 1 on the hardware constituting the image forming apparatus 1. The ROM stores software necessary for controlling the operation of the image forming apparatus 1. The RAM is used for temporary storage of data generated during execution of software, storage of application software, and the like. The image memory temporarily stores image data (such as image data transmitted from a personal computer).

  The operation display unit 300 is provided with operation keys and a display screen. The display screen displays various operations and details of operations.

  The first power supply unit 61 and the second power supply unit 63 supply a voltage obtained by superimposing a DC voltage and an AC voltage to the developing device 141 and apply the superimposed voltage to the rollers in the developing device 141. The first power supply unit 61 and the second power supply unit 63 will be described in detail later.

  Next, the configuration and operation of the developing device 141 will be described. FIG. 3 is a view showing a cross section of a pair of the photosensitive drum 135 and the developing device 141. FIG. 4 is a diagram illustrating a process in which the toner 53 in the two-component developer 51 is supplied from the developing device 141 to the photosensitive drum 135. The photosensitive drum 135 is an example of an image carrier. Reference numeral 55 denotes a carrier constituting the two-component developer 51. In FIG. 3, the two-component developer 51, the toner 53, and the carrier 55 are omitted. Since the elements constituting the developing device 141 and the like are expressed by omitting the thickness, they are not hatched.

  The configuration and operation of the developing device 141 will be described mainly with reference to FIG. 3, and will be described with reference to FIG. 4 as necessary. The developing device 141 includes a first roller 11, a second roller 13, stirring screws 15 and 17, and a casing 19 that accommodates them.

  The stirring screws 15 and 17 are disposed in the stirring chamber 21 in the housing 19. The stirring chamber 21 is divided into two stirring spaces 25 and 27 by a partition plate 23. The stirring screw 17 is disposed in the stirring space 25, and the stirring screw 15 is disposed in the stirring space 27. Two-component developer 51 is accommodated in the stirring spaces 25 and 27. The two-component developer 51 is stirred by rotating the stirring screws 15 and 17. As a result, the toner 53 and the carrier 55 are frictionally charged, and the toner 53 and the carrier 55 are electrostatically coupled. Among the two-component developer 51 in this state, the two-component developer 51 accommodated in the stirring space 27 is pumped up to the second roller 13 by a magnetic force as shown in FIG.

  The second roller 13 is called a magnetic roller, and is disposed in the housing 19 so as to face the stirring screw 15. The second roller 13 covers the second non-rotating portion 29 in a state having a gap with the second peripheral surface 31 provided in the second non-rotating portion 29. The second non-rotating portion 29 has a thick cylindrical shape, and the shaft 33 is rotatably disposed in the cylinder. The second roller 13 is fixed to the shaft 33. The second roller 13 rotates in the rotation direction R2 along the second peripheral surface 31 as the shaft 33 rotates.

  A magnetic pole N 1, a magnetic pole S 1, a magnetic pole S 2, a magnetic pole N 2, and a magnetic pole S 3 are arranged on the second peripheral surface 31 along the rotation direction R 2 of the second roller 13. The magnetic poles N1 to N2 are N poles, and the magnetic poles S1 to S3 are S poles. Although an example in which the number of magnetic poles is five has been described, it may be an odd number.

  The magnetic pole S <b> 2 is disposed to face the stirring screw 15. The two-component developer 51 in which the toner 53 and the carrier 55 are electrostatically coupled as described above is pumped up from the stirring space 27 by the magnetic force of the magnetic pole S2 and is rotated in the rotation direction R2 as shown in FIG. 2 is sucked onto the second roller 13.

  A magnetic pole N2, a magnetic pole S3, a magnetic pole N1, and a magnetic pole S1 are arranged in this order on the downstream side of the rotation direction R2 with respect to the magnetic pole S2. A magnetic field for attracting (supporting) the two-component developer 51 to the second roller 13 in the state of a magnetic brush is formed by the magnetic force of these magnetic poles. As shown in FIG. 4, the second roller 13 rotates in the rotation direction R2 while carrying the two-component developer 51 in a magnetic brush state, so that the two-component developer 51 passes over the magnetic pole N2 and the magnetic pole S3. Then, it is conveyed onto the magnetic pole N1. In the middle of this, the thickness of the two-component developer 51 carried on the second roller 13 is regulated by the blade 35.

  The magnetic pole N1 is disposed toward the second facing portion 37 where the second roller 13 and the first roller 11 face each other. The magnetic pole N1 has a function of forming a magnetic field at the second facing portion 37.

  At the second facing portion 37, the toner 53 in the two-component developer 51 is supplied to the first roller 11 that rotates in the rotation direction R1. Specifically, as shown in FIG. 4, only the toner 53 is attracted to the first roller 11 and attracted to the first roller 11 by the electric force in a state where the carrier 55 is attracted to the second roller 13. .

  The two-component developer 51 including the toner 53 that has not been supplied to the first roller 11 is carried by the second roller 13 and conveyed onto the magnetic pole S1. Since no magnetic field is formed between the magnetic poles S1 and S2, the two-component developer 51 is peeled off from the second roller 13, guided to the stirring chamber 21, and reused.

  The first roller 11 will be described. The first roller 11 is disposed in the housing 19 so as to face the second roller 13. The first roller 11 covers the first non-rotating portion 39 in a state having a gap with the first peripheral surface 41 provided in the first non-rotating portion 39. The first non-rotating portion 39 has a thick cylindrical shape, and a shaft 43 is rotatably disposed in the cylinder. The first roller 11 is fixed to the shaft 43. The first roller 11 rotates in the rotation direction R1 along the first peripheral surface 41 as the shaft 43 rotates. The rotation direction R1 is the same direction as the rotation direction R2 of the second roller 13, and is clockwise in this embodiment.

  A magnetic pole S <b> 4 is disposed on the first peripheral surface 41 so as to face the second facing portion 37. Since the polarity of the magnetic pole S4 is S, the magnetic field attracting each other is formed by the magnetic pole S4 and the magnetic pole N1 at the second facing portion 37. Thereby, a strong magnetic brush can be formed between the magnetic pole S4 and the magnetic pole N1.

  The first roller 11 faces a toner supply port 45 provided in the housing 19. The developing device 141 is attached to the image forming apparatus 1 with the toner supply port 45 facing the photosensitive drum 135. In this state, the first roller 11 and the photosensitive drum 135 face each other at the first facing portion 47.

  The first roller 11 sucks the toner 53 at the second facing portion 37, and conveys the toner 53 by rotating in the rotation direction R1 while carrying the toner 53. Then, the toner 53 is supplied to the photosensitive drum 135 at the first facing portion 47. Specifically, the photosensitive drum 135 rotates in the rotation direction R3 opposite to the rotation directions R1 and R2. The conveyed toner 53 is attracted by the electrostatic latent image formed on the peripheral surface of the photosensitive drum 135 and moves to the photosensitive drum 135. As a result, the electrostatic latent image on the peripheral surface of the photosensitive drum 135 is developed, and a toner image is formed on the peripheral surface. A transfer belt 131 in contact with the photosensitive drum 135 is disposed on the photosensitive drum 135. The transfer belt 131 moves in the D direction, and the toner image is transferred to the transfer belt 131.

  As shown in FIG. 4, the toner 53 in the two-component developer 51 carried by the second roller 13 is supplied to the first roller 11 at a second facing portion 37. Further, the toner 53 carried by the first roller 11 is supplied to the photosensitive drum 135 at the first facing portion 47. In such supply, since the toner 53 is supplied by flying at the first facing portion 47 and the second facing portion 37, a DC voltage and an AC voltage are applied to the first roller 11 and the second roller 13. A superimposed voltage is applied.

  The superimposed voltage applied to the first roller 11 is supplied from the first power supply unit 61. The superimposed voltage applied to the second roller 13 is supplied from the second power supply unit 63. FIG. 5 is a block diagram showing the configuration of the first power supply unit 61, and FIG. 6 is a block diagram showing the configuration of the second power supply unit 63.

  As shown in FIG. 5, one end of the first power supply unit 61 is grounded via a capacitor 65. The other end of the first power supply unit 61 serves as an output end and is connected to the first roller 11. Although not shown in FIG. 4, a coat layer 59 is formed on the peripheral surface 57 of the first roller 11. The coat layer 59 is a resin layer containing a conductive material. The toner 53 is carried on the coat layer 59.

  The first power supply unit 61 includes a first voltage generation unit 67, a first measurement unit 69, and a first control unit 71. The first voltage generator 67 includes a first DC power source 73 and a first AC power source 75. These power sources 73 and 75 are connected in series. In the first DC power source 73, the AC generated by the transformer 77 is rectified by the diode 79 to generate DC. In the first AC power supply 75, AC is generated by the transformer 81. A voltage obtained by superimposing the DC voltage output from the first DC power supply 73 and the AC voltage output from the first AC power supply 75 is applied to the first roller 11. As a result, the toner 53 carried on the coat layer 59 flies at the first facing portion 47 shown in FIG. 4 and is supplied to the photosensitive drum 135.

  The first measuring unit 69 is configured by a circuit that measures an alternating current that is output from the first alternating current power source 75 and flows through the first roller 11 and detects a load current. The first control unit 71 controls the DC voltage and current output from the first DC power supply 73 and the AC voltage and current output from the first AC power supply 75.

  As shown in FIG. 6, one end of the second power supply unit 63 is grounded via a capacitor 65. The other end of the second power supply unit 63 serves as an output end and is connected to the second roller 13. Since the second power supply unit 63 has the same configuration as the first power supply unit 61, the description thereof is omitted. The second voltage generation unit 83, the second measurement unit 85, the second control unit 87, the second DC power supply 89, and the second AC power supply 91 are respectively connected to the first voltage generation unit 67 and the first measurement. This corresponds to the unit 69, the first control unit 71, the first DC power source 73, and the first AC power source 75.

  In the present embodiment, by adjusting the frequency of the alternating current output from the first alternating current power supply 75, the alternating current output from the first alternating current power supply 75 and flowing through the first roller 11 is controlled to a constant current, and One feature is that the AC frequency output from the second AC power supply 91 and flowing through the second roller 13 is controlled to a constant current by adjusting the frequency of the AC output from the second AC power supply 91. Thereby, both the prevention of the phenomenon of current leakage and the prevention of the phenomenon of changing the image density by continuous printing can be achieved without being affected by the variation of the resistance value of the coat layer 59. Hereinafter, “the phenomenon of current leakage” may be abbreviated as “leakage phenomenon”, and “the phenomenon of image density changing by continuous printing” may be abbreviated as “density changing phenomenon”.

  As a premise for understanding this effect, it is proved by experiments that the variation in the resistance value of the coat layer 59 affects the leak phenomenon and the concentration change phenomenon. And according to this embodiment, it demonstrates that the said effect is acquired even if the resistance value of the coating layer 59 has dispersion | variation.

  The experimental conditions were as follows.

<Experimental machine>
Kyocera Mita 500ci remodeling machine
<Toner>
500ci toner for Kyocera Mita
<Photosensitive drum 135>
Diameter: 30mm
Material: Amorphous silicon Runout: 40 μm
Bright potential: 250V
Dark potential: about 10V
Peripheral speed: 300mm / s
Toner amount used for development for solid image formation: 0.6 mg / cm ²
<First roller 11 (developing roller)>
Diameter: 16mm
Runout: 10 μm
Magnetic pole: 45mT magnetic pole S4
Reference value for the gap (first facing portion 47) with respect to the photosensitive drum 135: 120 μm
Peripheral speed ratio with the photosensitive drum 135: 1.6 times Applied voltage: DC 50V, AC 1.4Kvp-p, duty ratio 40%
Toner amount carried by first roller 11 (coat layer 59): 0.45 mg / cm ²
Material of the coat layer 59: Silicon modified urethane coat Method of forming the coat layer 59: The coat layer 59 was formed in the following steps. (1) A step of diluting a silicon-modified urethane-based resin with butanone. (2) A step of preparing a mixed solution by mixing 6% of ketjen carbon black with this diluted solution using zircon beads as a medium. (3) A step of stirring the mixed solution with a ball mill for 24 hours. (4) A step of spray-coating using the mixed solution after stirring and baking in an oven at about 120 ° C. for 30 minutes.
<Second roller 13 (magnetic roller)>
Diameter: 16mm
Surface: Anodized with a thickness of 15 μm after blasting or grooving Magnetic pole: 5 magnetic poles (magnetic pole S1, magnetic pole S2, magnetic pole S3, magnetic pole N2, magnetic pole N1 of 95 mT)
Gap with the first roller 11 (second facing portion 37): 300 μm
Peripheral speed ratio with the first roller 11: 1.5 times Applied voltage: DC 300 V, AC 0.6 Kvp-p, duty ratio 60% (reverse phase of AC voltage applied to the first roller 11)
Amount of magnetic brush passing under blade 35: 35 mg / cm ²

  The experimental method was as follows.

  The sheet resistance values Ω / □ of the coating layer 59 formed on the peripheral surface of the first roller 11 (developing roller) are (1) 1.0E + 5, (2) 1.0E + 6, and (3) 1.0E + 7, respectively. , (4) 1.0E + 8 and (5) 1.0E + 9, five developing devices 141 satisfying the above experimental conditions were prepared.

  For each of the five developing devices 141, 100 solid images were continuously printed.

  If a dot pattern was formed on the printed solid image, it was determined that current leakage occurred.

  The density of the printed solid image was measured using a reflection densitometer. When the density difference between the first solid image and the 100th solid image is less than 0.05, it is classified into three cases: 0.05 or more and 0.10 or less, and greater than 0.10. did.

  The experimental results are as shown in FIG. ○ in the column for preventing leakage phenomenon indicates that no current leakage has occurred, and x indicates that current leakage has occurred. In the column of density change phenomenon prevention, ◯ indicates that the difference in image density is smaller than 0.05, Δ indicates 0.05 or more and 0.10 or less, and x indicates that the difference is greater than 0.10.

  As can be seen from the experimental results, if the resistance value of the coat layer 59 is large, the leak phenomenon can be prevented, but the concentration change phenomenon occurs. On the other hand, if the resistance value of the coat layer 59 is small, the density change phenomenon can be prevented, but a leak phenomenon occurs.

  When the sheet resistance value of the coat layer 59 is near 1.0E + 7, both the prevention of the leak phenomenon and the prevention of the density change phenomenon can be achieved. However, the variation in resistance value inevitably occurs in the formation of the coat layer 59.

  As for the density change phenomenon, good results are obtained if the resistance value is 1.0E + 7 or less. Therefore, the experiment was performed in a situation where charges are easily accumulated in the first roller 11, that is, in a more severe situation. In a low temperature environment, the toner is easily charged. Further, if the position of the solid image is at the front end portion of the sheet, it is difficult for the first roller 11 to accumulate charges. Considering these, 100 sheets of printing were continuously performed to form a solid image only on the rear edge of the sheet in a low temperature environment (temperature 8 ° C., humidity 10%). During this printing, an alternating current flowing between the first roller 11 and the photosensitive drum 135 and an alternating current flowing between the first roller 11 and the second roller 13 were measured.

  As a result, even if the sheet resistance value was 1.0E + 7 or less, the density change phenomenon prevention was Δ. This is probably because the charge accumulated in the coat layer 59 increases as the toner charge amount increases, and as a result, the potential difference between the first roller 11 and the second roller 13 decreases.

  The measured alternating current value is shown in FIG. The values of the alternating current at the time of printing on the first sheet, the tenth sheet, the twentieth sheet,..., The 100th sheet are shown. It turned out that the alternating current value has fallen several sheets after printing the first sheet.

  Therefore, the same experiment was performed by controlling the alternating current to a constant current by adjusting the alternating voltage vp-p applied to the first roller 11. In this control, the AC voltage was increased to 2 Kvp-p, but a leak phenomenon occurred. Further, although the density change phenomenon could be prevented, a sufficient margin could not be obtained.

  Further, a similar experiment was performed by changing the difference between the DC voltage applied to the first roller 11 and the DC voltage applied to the second roller 13 to 300V. The density change phenomenon could not be prevented, and a ghost image corresponding to one round of the first roller 11 was generated.

  The same experiment was conducted by controlling the alternating current to a constant current by adjusting the alternating current frequency, which is one of the features of this embodiment. As a result, when the sheet resistance value Ω / □ is (1) 1.0E + 5, (2) 1.0E + 6, (3) 1.0E + 7, (4) 1.0E + 8, (5) 1.0E + 9 The prevention of phenomenon and change in concentration was ○. If the alternating current is controlled to a constant current by adjusting the alternating current frequency, the range of the resistance value (also referred to as the dielectric constant) of the coat layer 59 capable of preventing both the leak phenomenon and the concentration change can be expanded. I understood. Therefore, variations in electrical properties of the coat layer 59 can be absorbed.

  This constant current control is performed when the toner 53 is supplied from the first roller 11 to the photosensitive drum 135 and the toner 53 in the two-component developer 51 is supplied from the second roller 13 to the first roller 11 shown in FIG. It is executed when you do. FIG. 9 is a flowchart of an example of constant current control when supplying the toner 53 to the photosensitive drum 135, and FIG. 10 is a constant current when supplying the toner 53 in the two-component developer 51 to the first roller 11. It is a flowchart of an example of control.

  The constant current control shown in FIG. 9 will be described. As shown in FIGS. 4 and 5, the DC voltage output from the first DC power source 73 and the first AC power source are applied to the first roller 11 that rotates while carrying the toner 53 on the coat layer 59. The alternating voltage output from 75 is superimposed and applied. As a result, the toner 53 carried by the coat layer 59 is caused to fly at the first facing portion 47 and supplied to the photosensitive drum 135. During this supply, the alternating current flowing between the first roller 11 and the photosensitive drum 135 is controlled to a constant current of 2200 μA according to the flow shown in FIG.

  When the toner 53 is supplied to the photosensitive drum 135, the first measuring unit 69 measures the AC current output from the first AC power source 75 and flowing through the first roller 11 (step S1). The alternating current data measured by the first measurement unit 69 is sent to the first control unit 71. The first controller 71 determines whether the measured alternating current is 2200 μA (step S3).

  If the measured alternating current is not 2200 μA (No in step S3), the first controller 71 sets the frequency of the alternating current output from the first alternating current power source 75 based on the alternating current measured in step S1. adjust. As a result, the AC output from the first AC power supply 75 and flowing through the first roller 11 is controlled to a constant current of 2200 μA (step S5). If the measured AC current is smaller than 2200 μA, control is performed to increase the frequency of the AC output from the first AC power supply 75. On the other hand, if the measured alternating current is larger than 2200 μA, control is performed to lower the frequency of the alternating current output from the first alternating current power supply 75.

  When the processing in step S5 is completed or the current measured in step S3 is 2200 μA (Yes in step S3), it is determined whether all printing (printing for the 100th sheet in the present embodiment) is completed (step S7). . When all the printing is completed (Yes in step S7), the process of supplying the toner 53 from the first roller 11 to the photosensitive drum 135 is completed. If printing has not ended (No in step S7), the process returns to step S1.

  The constant current control shown in FIG. 10 is executed simultaneously with the constant current control shown in FIG. As shown in FIGS. 4 and 6, the DC voltage output from the second DC power supply 89 and the second AC power supply 91 are applied to the second roller 13 that rotates while carrying the two-component developer 51. The AC voltage output from is superimposed and applied. As a result, the toner 53 in the two-component developer 51 carried by the second roller 13 is caused to fly at the second facing portion 37 and supplied to the first roller 11. During this supply, the alternating current flowing between the first roller 11 and the second roller 13 is controlled to a constant current of 800 μA according to the flow shown in FIG.

  When the toner 53 in the two-component developer 51 is supplied to the first roller 11, the second measuring unit 85 outputs an alternating current flowing through the second roller 13 that is output from the second AC power source 91. Measure (Step S11). The alternating current data measured by the second measuring unit 85 is sent to the second control unit 87. The second controller 87 determines whether the measured alternating current is 800 μA (step S13).

  If it is not 800 μA (No in step S13), the second control unit 87 adjusts the AC frequency output from the second AC power supply 91 based on the AC current measured in step S11. As a result, the AC output from the second AC power supply 91 and flowing through the second roller 13 is controlled to a constant current of 800 μA (step S15).

  If the process in step S15 is completed or if Yes in step S13, it is determined whether all printing has been completed (step S17). If all printing has been completed (Yes in step S17), the process of supplying the toner 53 in the two-component developer 51 from the second roller 13 to the first roller 11 is completed. If printing has not ended (No in step S17), the process returns to step S11.

  As described above, according to the present embodiment, a constant current is generated between the first roller 11 and the photosensitive drum 135 by changing the AC output from the first AC power supply 75 and flowing through the first roller 11. The alternating current flowing between the first roller 11 and the second roller 13 is made constant by making the alternating current flowing constant current and making the alternating current output from the second alternating current power supply 91 and flowing through the second roller 13 constant. Constant current. These constant current controls are executed by adjusting the AC frequency. For this reason, even if the electrical properties of the coat layer 59 vary, it is possible to prevent both the phenomenon of current leakage and the phenomenon of image density change during continuous printing. The phenomenon that current leaks here means a phenomenon that current leaks between the first roller 11 and the photosensitive drum 135 and between the first roller 11 and the second roller 13.

  The range of variation in electrical properties of the coat layer 59 is, for example, a range in which the sheet resistance value of the coat layer 59 is 1.0E + 5 or more and 1.0E + 9 or less.

  When amorphous silicon is used as the photosensitive member of the photosensitive drum 135, the shake accuracy of the photosensitive drum 135 tends to deteriorate due to the manufacturing method of the photosensitive drum 135. As a result, the amount of fluctuation in the gap (first opposed portion 47) between the photosensitive drum 135 and the first roller 11 increases, and the image tends to be uneven. In order to prevent unevenness of the image, it is necessary to increase the electric field between the photosensitive drum 135 and the first roller 11. Therefore, the resistance value of the coat layer 59 must be increased in order to prevent current leakage. However, as described with reference to FIG. 7, if the resistance value of the coat layer 59 is increased, a density change phenomenon occurs.

  As described above, according to the present embodiment, both the prevention of the phenomenon of current leakage and the prevention of the phenomenon in which the image density gradually changes during continuous printing without being affected by the variation in the electrical properties of the coat layer 59. it can. Therefore, this embodiment is effective even when the photosensitive member of the photosensitive drum 135 is amorphous silicon.

  The present invention can also be applied to an image forming apparatus using a one-component developer. FIG. 11 is a diagram illustrating a process in which the one-component developer is supplied from the developing device to the photosensitive drum. Components that are the same as or equivalent to the components shown in FIG. A one-component developer made of magnetic toner 101 is supplied from the supply roller 103 to the first roller 11.

  11 differs from the first roller 11 shown in FIG. 4 in that the first non-rotating portion 39 has six magnetic poles S1 to S3 and N1 to N3. The magnetic pole S <b> 1 is disposed toward the first facing portion 47. A magnetic pole S1, a magnetic pole N1, a magnetic pole S2, a magnetic pole N2, a magnetic pole S3, and a magnetic pole N3 are arranged along the rotation direction R1 of the first roller 11.

  A coat layer 59 shown in FIG. 5 is formed on the peripheral surface of the first roller 11 shown in FIG. 11 in the same manner as the first roller 11 shown in FIG. The first roller 11 conveys the magnetic toner 101 by rotating while carrying the magnetic toner 101 on the coat layer 59, and the magnetic toner 101 is transferred to the photosensitive drum 135 at a first facing portion 47 facing the photosensitive drum 135. To supply.

  The superimposed voltage applied to the first roller 11 shown in FIG. 11 is supplied from the first power supply unit 61 in the same manner as the first roller 11 shown in FIG. For the constant current control of alternating current in the case of a one-component developer, the flowchart shown in FIG. 9 can be applied.

  Also in the case of a one-component developer, the same effect as in the case of the two-component developer described above can be obtained if the alternating current is controlled to a constant current by adjusting the alternating current frequency by the first power supply unit 61 shown in FIG. be able to. That is, even if there is variation in the electrical properties of the coat layer 59, it is possible to achieve both the prevention of the phenomenon of current leakage and the prevention of the phenomenon of changing the image density by continuous printing.

  In this embodiment, the printer is described as an example of the image forming apparatus 1. However, the image forming apparatus 1 according to this embodiment can be applied to a copier, a facsimile machine, and a multifunction machine having these functions.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 1st roller 13 2nd roller 37 2nd opposing location 47 1st opposing location 51 Two-component developer 53 Toner 55 Carrier 57 Peripheral surface of 1st roller 59 Coat layer 61 1st Power supply unit 63 Second power supply unit 67 First voltage generation unit 69 First measurement unit 71 First control unit 73 First DC power supply 75 First AC power supply 83 Second voltage generation unit 85 Second Measurement unit 87 Second control unit 89 Second DC power supply 91 Second AC power supply 101 Magnetic toner 103 Supply roller 135 Photosensitive drum (image carrier)

Claims (4)

An image carrier;
It has a peripheral surface on which a coat layer is formed, conveys the toner by rotating while carrying the toner on the coat layer, and carries the image at a first facing portion facing the image carrier. A first roller for feeding to the body;
A first DC power source and a first AC power source, and the DC voltage output from the first DC power source for causing the toner carried on the coat layer to fly at the first facing location; A first voltage generator for applying an alternating voltage output from the first alternating current power source to the first roller;
A first measurement unit that measures an alternating current output from the first alternating current power source and flowing through the first roller;
By adjusting the AC frequency output from the first AC power source based on the AC current measured by the first measurement unit, the first AC power source outputs the first AC power source. An image forming apparatus comprising: a first control unit that controls alternating current flowing through the roller to a constant current. The two-component developer is transported by rotating while carrying the two-component developer, and the toner in the two-component developer is supplied to the first roller at a second facing portion facing the first roller. A second roller;
A second direct current power source and a second alternating current power source, from which the second direct current power source causes the toner in the two-component developer carried by the second roller to fly at the second opposite location. A second voltage generator for applying the output DC voltage and the AC voltage output from the second AC power source to the second roller in a superimposed manner;
A second measuring unit for measuring an alternating current output from the second alternating current power source and flowing through the second roller;
By adjusting the frequency of the alternating current output from the second alternating current power source based on the alternating current measured by the second measurement unit, the second alternating current power source outputs the second alternating current power source. The image forming apparatus according to claim 1, further comprising: a second control unit that controls the alternating current flowing through the roller to a constant current.   The image forming apparatus according to claim 1, wherein the coating layer has a sheet resistance value of 1.0E + 5 or more and 1.0E + 9 or less.   The image forming apparatus according to claim 1, wherein the photoconductor of the image carrier includes amorphous silicon.

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