JP4335201B2 - Developing device and image forming apparatus - Google Patents

Description

  In the present invention, a developer in which a toner and a carrier are mixed is attached to the peripheral surface of a magnetic roll to charge the toner, and the charged toner is moved onto the developing roll to be attached to the peripheral surface of the developing roll. The present invention relates to a so-called hybrid developing device that develops an electrostatic latent image formed on the peripheral surface of the photosensitive drum by moving toner from the peripheral surface of the developing roll to the peripheral surface of the photosensitive drum. The present invention also relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and a composite machine using such a developing device.

  FIG. 6 is a configuration diagram showing a schematic configuration of a developing device according to the background art. The developing device shown in FIG. 6 is a so-called hybrid developing device, a magnetic cylindrical magnetic roll 101, a cylindrical developing roll 102 disposed opposite to the magnetic roll 101, and a photosensitive member on the peripheral surface. And a cylindrical photosensitive drum 103 having the above structure. Then, the peripheral surface of the photosensitive drum 103 is charged by a charging device (not shown), and exposed by an exposure device (not shown) so that an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 103. It has become.

  Further, a developer in which a carrier made of a magnetic material and a toner are mixed is supplied to the peripheral surface of the magnetic roll 101 from a toner container (not shown), and the charged developer is supplied to the peripheral surface of the magnetic roll 101. To be attached. Then, the magnetic roll 101, the developing roll 102, and the photosensitive drum 103 were rotated, and as shown in FIG. 7, the magnetic roll 101 was charged by applying a high voltage to the magnetic roll 101 and the developing roll 102. Formed on the peripheral surface of the photoconductive drum 103 by causing toner to fly and causing the charged toner to adhere to the peripheral surface of the developing roll 102 in a layered manner and then causing the charged toner to fly from the developing roll 102 to the photoconductive drum 103. The electrostatic latent image is developed with toner.

An image forming apparatus using such a developing device performs image formation on the recording paper by transferring the toner image formed on the peripheral surface of the photosensitive drum 103 onto the recording paper, heating, and fixing. (For example, refer to Patent Document 1).
JP 2005-55837 A

  By the way, in the developing device as described above, when the development of the electrostatic latent image formed on the peripheral surface of the photosensitive drum 103 is started, that is, when voltage application to the magnetic roll 101 and the developing roll 102 is started, the magnetic roll The toner adhering to the peripheral surface 106 between the peripheral surface position 104 of the developing roll 102 facing the 101 and the peripheral surface position 105 of the developing roll 102 facing the photosensitive drum 103 is The position 104 is supplied to the photosensitive drum 103 and used for development until the position 104 moves to a position facing the photosensitive drum 103 as the developing roll 102 rotates.

  Then, the toner attached to the peripheral surface 106 is not supplied from the magnetic roll 101 to the developing roll 102 after the start of development. For example, the toner attached to the peripheral surface of the developing roll 102 during the previous image formation Become. For this reason, the toner adhered to the peripheral surface 106 has been adhered to the peripheral surface of the developing roll 102 for a long time. As a result, the adhesion strength becomes strong, and the toner supply amount from the peripheral surface 106 of the developing roll 102 to the photosensitive drum 103 is increased. And the image density immediately after the start of development (arrow 107 in FIG. 7) may become inconvenient.

  Further, for example, it may be possible to prevent the toner from firmly adhering to the peripheral surface 106 of the developing roll 102 by removing the toner adhering to the peripheral surface of the developing roll 102 after the previous image formation. However, in this case, at the start of image formation, toner is not attached to the peripheral surface 106 of the developing roll 102 or only a small amount of toner is attached. As a result of the toner not being supplied to the body drum 103 or the toner supply amount becoming extremely small, there is a problem that an image is not formed or the image density becomes extremely thin.

  The present invention has been made in view of the above problems, and in a hybrid developing device, a developing device capable of reducing a decrease in the amount of toner supplied to the photosensitive drum immediately after the start of image formation. The purpose is to provide. It is another object of the present invention to provide an image forming apparatus that can reduce the decrease in image density immediately after the start of image formation using such a developing device.

  In order to achieve the above-described object, the developing device according to the first means of the present invention causes a developer in which toner and a carrier are mixed to adhere to the peripheral surface of the magnetic roll and charges the toner. The toner is caused to fly from the magnetic roll onto the developing roll to adhere to the peripheral surface of the developing roll, and from the peripheral surface of the developing roll, the toner is allowed to fly to the peripheral surface of the photosensitive drum, thereby In the developing device that develops the electrostatic latent image formed on the peripheral surface of the drum, the magnetic roll and the photosensitive drum are disposed to face the developing roll, respectively, and a rotation driving unit that rotates the developing roll A first voltage applying unit that applies a first voltage to the magnetic roll so as to cause the toner to fly from the magnetic roll onto the developing roll; A second voltage applying unit that applies a second voltage to the developing roll so as to cause the toner to fly from the peripheral surface of the developing roll to the peripheral surface of the photosensitive drum after the first voltage is applied by the unit; With.

  According to this configuration, the toner charged by applying the first voltage to the magnetic roll by the first voltage applying unit flies onto the developing roll. Thereafter, the toner charged by applying the second voltage to the developing roll by the second voltage applying unit is ejected to the peripheral surface of the photosensitive drum, and the electrostatic formed on the peripheral surface of the photosensitive drum. Since the latent image is developed, it is possible to reduce the use of toner that is firmly attached to the peripheral surface of the developing roll before the first voltage is applied to the magnetic roll by the first voltage applying unit. Therefore, it is possible to reduce a decrease in the image density immediately after the start of development due to a decrease in the amount of toner supplied from the developing roll to the photosensitive drum due to the toner adhering firmly.

  Further, in the above developing device, the second voltage application unit is located at a position facing the magnetic roll when application of the first voltage by the first voltage application unit is started. The second voltage is applied to the developing roll after the peripheral surface position of the roll has moved to a position facing the photosensitive drum.

  According to this configuration, the peripheral surface position of the developing roll at the position facing the magnetic roll when the second voltage application unit starts applying the first voltage by the first voltage application unit, that is, After the peripheral surface position of the developing roll to which toner is newly supplied from the magnetic roll has moved to the position facing the photosensitive drum, the second voltage is applied to the developing roll, that is, from the developing roll to the photosensitive drum. Since the toner is supplied, it is possible to reduce the use of the toner that is firmly attached to the peripheral surface of the developing roll before the application of the first voltage to the magnetic roll by the first voltage applying unit for the development. Thus, it is possible to reduce the decrease in the image density immediately after the start of development due to a decrease in the amount of toner supplied from the developing roll to the photosensitive drum due to the firmly adhered toner.

  In the developing device described above, the second voltage application unit may rotate at least the developing roll by the rotation driving unit after the application of the first voltage by the first voltage application unit is started. Thus, the second voltage is applied to the developing roll after the elapse of time when the position facing the magnetic roll on the peripheral surface of the developing roll moves to the position facing the photosensitive drum. Is what you do.

  According to this configuration, at least the developing roll is rotated by the rotation driving unit after the application of the first voltage by the first voltage applying unit is started, that is, the toner supply from the magnetic roll to the developing roll is started. As a result, the second voltage is applied to the developing roll after the elapse of the time when the position facing the magnetic roll on the peripheral surface of the developing roll moves to the position facing the photosensitive drum. After the peripheral surface position of the developing roll at the position facing the magnetic roll at the start of application of the first voltage by the voltage applying unit of the first moving to the position facing the photoconductive drum, the first application to the developing roll is performed. 2 can be applied.

  In the developing device described above, the first voltage application unit outputs a voltage obtained by superimposing an AC voltage on a DC voltage as the first voltage.

  According to this configuration, the voltage obtained by superimposing the AC voltage on the DC voltage by the first voltage application unit is applied to the magnetic roll as the first voltage, so that a predetermined amount of toner is instantaneously transferred (flighted) to the developing roller. ).

  In the developing device described above, the second voltage application unit outputs a voltage obtained by superimposing an AC voltage on a DC voltage as the second voltage.

  According to this configuration, the voltage obtained by superimposing the AC voltage on the DC voltage by the second voltage application unit is applied to the developing roll as the second voltage. Therefore, the toner adhering to the developing roll is activated and the photosensitive roll is activated. The developability of the electrostatic latent image formed on the body drum can be improved.

  In the developing device described above, the second voltage application unit may further include a leading position of an electrostatic latent image formed on the peripheral surface of the photosensitive drum as the photosensitive drum rotates with the developing roll. When the counter position is reached, a second voltage is applied to the developing roll.

  According to this configuration, after the first voltage is applied by the first voltage application unit, or at the position facing the magnetic roll when the application of the first voltage by the first voltage application unit is started. The position of the peripheral surface of the developing roll that has been moved to the position facing the photosensitive drum or the position facing the magnetic roll when the application of the first voltage by the first voltage applying unit is started. After the peripheral surface position of the developing roller has moved to the position facing the photosensitive drum, the leading position of the electrostatic latent image formed on the peripheral surface of the photosensitive drum is further developed with the rotation of the photosensitive drum. Since the second voltage is applied to the developing roll by the second voltage application unit when the position facing the roll is reached, the toner firmly adhered from the top of the electrostatic latent image as described above. Toner from developing roll to photosensitive drum It is possible to reduce the image density immediately after the start of development amount fed is decreased becomes thin.

  The image forming apparatus according to the second means of the present invention forms an image by transferring the toner image formed on the photosensitive drum by the developing device described above to a recording sheet.

  According to this configuration, the electrostatic latent image on the photosensitive drum is developed using the developing device described above, and the toner image formed on the photosensitive drum is transferred to the recording paper to form an image. Therefore, it is possible to reduce the decrease in image density immediately after the start of development.

  In the developing device having such a configuration, the toner charged when the first voltage is applied to the magnetic roll by the first voltage applying unit flies onto the developing roll. Thereafter, the toner charged by applying the second voltage to the developing roll by the second voltage applying unit is ejected to the peripheral surface of the photosensitive drum, and the electrostatic formed on the peripheral surface of the photosensitive drum. Since the latent image is developed, it is possible to reduce the use of toner that is firmly attached to the peripheral surface of the developing roll before the first voltage is applied to the magnetic roll by the first voltage applying unit. Therefore, it is possible to reduce a decrease in the image density immediately after the start of development due to a decrease in the amount of toner supplied from the developing roll to the photosensitive drum due to the toner adhering firmly.

  The image forming apparatus having such a configuration reduces a decrease in image density immediately after the start of development due to a decrease in the amount of toner supplied from the developing roll to the photosensitive drum due to the toner firmly adhered to the developing roll. The electrostatic latent image on the photosensitive drum is developed using a developing device capable of developing, and the toner image formed on the photosensitive drum is transferred to recording paper to form an image. It can reduce that a density | concentration becomes thin.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted. FIG. 1 is a diagram schematically showing an internal configuration of an image forming apparatus using a developing device according to an embodiment of the present invention. An image forming apparatus 1 illustrated in FIG. 1 is a tandem type color printer, and is provided on a paper feed cassette 10, a transfer conveyance unit 20 provided on the top of the paper feed cassette 10, and an upper part of the transfer conveyance unit 20. The image forming unit 30, the fixing unit 40 disposed on the left side of the transfer conveyance unit 20, a first conveyance path 50 that guides the recording paper P set in the paper feed cassette 10 to the transfer conveyance unit 20, And a second transport path 60 that guides the recording paper P on which the fixing process has been performed by the fixing unit 40 to the discharge tray 80.

  The paper feed cassette 10 stores recording paper P therein, picks up the stored recording paper P one by one by a paper feed roller (not shown), and discharges it to the first transport path 50 side. The image forming unit 30 includes image forming units 30K, 30Y, 30M, and 30C that form toner images of black (K), yellow (Y), magenta (M), and cyan (C), respectively. Since the image forming units 30K to 30C have the same configuration, only the image forming unit 30K will be described.

  The image forming unit 30K includes a photosensitive drum 31, a charger 32, an exposure device 33, a developing device 34, and a cleaner unit 35. The photosensitive drum 31 is a cylindrical member, receives a driving force from a motor (not shown), and rotates in a clockwise direction (A direction in the drawing). The exposure device 33 includes a light source such as a light emitting diode or a laser diode, and irradiates the photosensitive drum 31 charged by the charger 32 with an optical signal corresponding to the image data, thereby generating an electrostatic latent image of the image data. Form. A toner box 341 for storing black (K) toner and supplying K toner to the developing device 34 is disposed above the developing device 34.

  The photosensitive drum 31 is formed by forming a photosensitive material on the outer peripheral surface of a cylindrical drum. As the photosensitive material used for the photosensitive drum 31, for example, a positively charged organic photosensitive member (positive OPC) can be used. When a positively charged organic photoconductor is used as the photosensitive material, there is little generation of ozone or the like, and the charging is stable.In particular, even when the film thickness of the positively charged organic photoconductor having a single layer structure changes due to long-term use, It is suitable for long-life systems because there is little change in photosensitive characteristics and image quality is stable. In addition, an amorphous silicon photoreceptor may be used as the photosensitive material.

  In addition, by setting the film thickness of the positively charged organic photoconductor on the photoconductor drum 31 to about 20 μm to 40 μm, the life of the photoconductor drum 31 can be extended. When the film thickness of the positively charged organic photoreceptor is less than 20 μm, the generation of black spots increases due to dielectric breakdown when the film thickness reaches 10 μm due to the decrease in the film thickness due to use. On the other hand, if the thickness of the positively charged organic photoconductor exceeds 40 μm, the sensitivity is lowered and the image is reduced.

  For example, the charger 32 charges the positively charged organic photoreceptor formed on the outer peripheral surface of the photoreceptor drum 31 to, for example, 400V. As the exposure device 33, a semiconductor laser or an LED (Light Emitting Diode) can be used. As the output light of the exposure device 33, when the photosensitive material of the photosensitive drum 31 is a positively charged organic photosensitive member, a wavelength of about 770 nm is preferable, and for an amorphous silicon photosensitive member, a wavelength of about 685 nm is preferable.

  Then, after charging the positively charged organic photoconductor of the photoconductor drum 31 to 400 V by the charger 32, for example, when the exposure device 33 exposes the LED light with a wavelength of 770 nm, the potential of the exposed portion is set to about 70V. As a result, the potential of the portion exposed by the exposure device 33 is lowered, and the potential of the non-exposed portion is maintained at 400 V. Therefore, the exposure device 33 is placed on the outer peripheral surface (positively charged organic photoreceptor) of the photosensitive drum 31. An electrostatic latent image is formed based on the exposure by.

  The developing device 34 includes a magnetic roll 11, a developing roll 12, a stirring mixer 342, and a paddle mixer 343. The agitation mixer 342 and the paddle mixer 343 mix the toner supplied from the toner box 341 and the carrier and agitate them to charge them, and supply them to the magnetic roll 11.

As the carrier, a ferrite carrier having a volume resistivity of 10 ⁸ Ωcm and a silicone resin coating, a saturation magnetization of 40 emu / g, and an average particle diameter of 35 μm can be used. In this case, for example, when the average particle size exceeds 50 μm, the stress of the carrier increases and the toner supply amount to the developing roll 12 decreases because the toner concentration cannot be increased. As the carrier, a magnetite carrier, Mn ferrite, Mn-Mg ferrite, or the like can be used. These carriers may be used as they are, but it is also possible to use them after surface treatment within a range that does not increase the appropriate resistance.

  In this embodiment, the mixing ratio of the toner is 5 to 20% by weight, preferably 5 to 15% by weight, based on the total amount of the carrier and the toner. If the mixing ratio of the toner is less than 5% by weight, the toner charge amount becomes high and a sufficient image density cannot be obtained, and if it exceeds 20% by weight, a sufficient charge amount cannot be obtained. The image forming apparatus may be scattered and contaminated, or toner fog may occur on the image.

  FIG. 2 is a configuration diagram showing in detail an example of the configuration of the magnetic roll 11, the developing roll 12, and the photosensitive drum 31. The magnetic roll 11 has a magnetic body therein, and when supplied with a developer composed of the toner 13 and the carrier 14 mixed and stirred by the stirring mixer 342 and the paddle mixer 343, the magnetic roll 11 has a magnetic force based on the internal magnetic body. Thus, the carrier 14 is attracted to the outer peripheral surface to form the magnetic brush 15 and the magnetic brush 15 is accompanied by the toner 13.

  In FIG. 2, the magnetic roll 11 rotates counterclockwise, and the layer thickness of the magnetic brush 15 is regulated by a regulating blade 345 disposed in the vicinity of the magnetic roll 11 with a minute interval. The space | interval of the control blade 345 and the magnetic roll 11 is 0.3 mm-1.5 mm, for example. The distance between the magnetic roll 11 and the developing roll 12 is, for example, 0.2 mm to 0.5 mm, and preferably about 0.3 mm to 0.4 mm.

  Further, a DC voltage source 16 and an AC voltage source 17 are connected in series to the magnetic roll 11, and the AC voltage Vac 1 output from the AC voltage source 17 is added to the DC voltage Vdc 1 output from the DC voltage source 16. Superimposed and applied. As a result, the toner 13 flies and is supplied to the outer peripheral surface of the developing roll 12 disposed so as to face the magnetic roll 11, thereby forming a toner layer 131. In this case, a series circuit of the DC voltage source 16 and the AC voltage source 17 corresponds to an example of the first voltage application unit, and a voltage in which the AC voltage Vac1 is superimposed on the DC voltage Vdc1 corresponds to an example of the first voltage. is doing.

  The thickness of the toner layer 131 is set to, for example, 50 μm, preferably 30 μm to 70 μm. This thickness is a value corresponding to about 5 to 10 layers of the toner 13 when the average particle size of the toner 13 is 7 μm.

  The DC voltage Vdc1 is set to 400 V, for example, and the AC voltage Vac1 is set to have a P-P of 500 V and a phase opposite to the AC voltage Vac2 described later, thereby improving the toner supply performance from the magnetic roll 11 to the developing roll 12. As shown, the collecting action of the unused developer from the developing roll 12 to the magnetic roll 11 can be increased without adversely affecting the developing roll 12 and the photosensitive drum 31.

  The developing roll 12 is a cylindrical rotating body whose sleeve is made of, for example, conductive aluminum. For example, the developing roll 12 rotates counterclockwise in the same direction as the magnetic roll 11 and opposite to the photosensitive drum 31. It is like that. The sleeve material may be a uniform conductor, and SUS, conductive resin coating, or the like can be applied. Further, the developing roll 12 is disposed so that the outer peripheral surface thereof has a distance of about 250 μm from the outer peripheral surface of the photosensitive drum 31 (positively charged organic photoconductor). The distance between the developing roll 12 and the photosensitive drum 31 can be set to, for example, 150 μm to 400 μm, and preferably 200 μm to 300 μm. If the distance between the developing roll 12 and the photosensitive drum 31 is smaller than 150 μm, it causes fogging, and if it is larger than 400 μm, it becomes difficult to cause the toner 13 to fly from the developing roll 12 to the photosensitive drum 31, and a sufficient image density. Can not get. Further, it becomes a factor that causes selective development.

  A DC voltage source 18 and an AC voltage source 19 are connected in series to the shaft of the developing roll 12, and an AC voltage output from the AC voltage source 19 to a DC voltage Vdc 2 output from the DC voltage source 18. Vac2 is superimposed and applied to the sleeve via the shaft. Then, the toner 13 is supplied by flying from the toner layer 131 formed on the outer peripheral surface of the developing roll 12 to the photosensitive drum 31. In this case, a series circuit of the DC voltage source 18 and the AC voltage source 19 corresponds to an example of the second voltage application unit, and a voltage in which the AC voltage Vac2 is superimposed on the DC voltage Vdc2 corresponds to an example of the second voltage. is doing.

  The DC voltage Vdc2 is, for example, 100 V, and the AC voltage Vac2, for example, is Vpp of 1.5 kV, a frequency of 3.0 kHz, and a duty of 30%. The waveform of the AC component of the AC voltage Vac2 is preferably a rectangular wave.

  As described above, the AC voltage Vac2 is superimposed on the DC voltage Vdc2 and applied to the conductive sleeve of the developing roll 12 to activate the toner 13 attached to the outer peripheral surface of the developing roll 12. As a result, the photosensitive member is activated. The developability of the electrostatic latent image formed on the positively charged organic photoreceptor of the drum 31 can be improved, and the recoverability of the toner 13 from the developing roll 12 to the magnetic roll 11 can be improved.

  Incidentally, in order to stabilize the image density in continuous printing, it is necessary to periodically remove the toner 13 from the developing roll 12 and refresh. The toner 13 is always refreshed if the toner 13 is peeled off from the developing roll 12 at the end of development, but it takes time to form the stable toner layer 131 on the outer peripheral surface of the developing roll 12 again. If the toner 13 is peeled off from the developing roll 12, the printing speed is reduced.

  On the other hand, according to the developing device 34 shown in FIG. 2, the developability for the electrostatic latent image formed on the positively charged organic photoreceptor of the photosensitive drum 31 without removing the toner 13 from the developing roll 12 every time development is completed. In addition, the recovery of the toner 13 from the developing roll 12 to the magnetic roll 11 can be improved, so that the stability of continuous printing can be improved.

  Further, in order to increase the supply amount of the toner 13 to the photosensitive drum 31, if the peripheral speed of the developing roller 12 is set to 1.5 times or more the peripheral speed of the photosensitive drum 31, the toner can be shortened in a short time. 13 can be taken in and out. Further, when the peripheral speed of the magnetic roll 11 is set to 1 to 2 times the peripheral speed of the developing roll 12, the toner replacement is promoted. In this case, the rotation direction of the magnetic roll 11 is preferably opposite to the rotation direction of the developing roll 12.

  Further, by changing the DC voltage Vdc2 while applying the AC voltage Vac2 to the developing roll 12 at the end of the development, the toner 13 adhering in a layered manner to the sleeve of the developing roll 12 is collected in the magnetic roll 11 and The toner 13 can be replaced.

The saturated toner amount of the toner layer 131 is determined by the difference between the DC voltage Vdc2 output from the DC voltage source 18 and the DC voltage Vdc1 output from the DC voltage source 16. For example, when the DC voltage Vdc1 is set to 150 V and the DC voltage Vdc2 is set to 400 V, a toner layer 131 of about 1.0 mg / cm ² is obtained on the second turn of the developing roll 12. The adjustment of the layer thickness of the toner layer 131 is basically obtained by the potential difference of Vdc2−Vdc1, but there are cases where factors such as the charge amount of the toner 13 and the strength of the magnetic force of the magnetic roll 11 are also affected.

  Further, the amount of toner supplied from the developing roll 12 to the photosensitive drum 31 changes according to the image data to be formed, so that, for example, when a high-density image is formed, the voltage of Vdc2-Vdc1 is increased. A uniform image can be obtained by adjusting the potential difference between the DC voltage Vdc2 and the DC voltage Vdc1 in accordance with the image data. When performing high density printing continuously, it is advantageous to set the value of Vdc2-Vdc1 slightly higher.

Further, when the toner amount of the toner layer 131 is 0.5 mg / cm ² or less, the followability of density when a high density image is continuous is lowered, and image unevenness is likely to occur. On the other hand, when the toner layer 131 exceeds 1.5 mg / cm ² , the development ghost is noticeable and the toner scattering tends to be noticeable. The layer thickness of the toner layer 131 also depends on the charge amount of the toner 13, and when the toner charge amount is 10 μC / g or less, particularly 5 μC / g or less, the scattering of the toner 13 increases due to the increase in the layer thickness of the toner layer 131. . On the other hand, when the toner charge amount is 20 μC / g or more, the developability of the electrostatic latent image on the photosensitive drum 31 is lowered due to the decrease in the layer thickness of the toner layer 131.

  The toner layer 131 is collected by the magnetic brush 15 held on the magnetic roll 11, and a new developer is carried to the developing roll 12 through the regulating blade 345. It is important to define the particle size distribution of the toner 13 in order to avoid selective developability. Generally, the particle size distribution of the toner 13 is measured with a coal counter, and the spread of the particle size distribution is expressed by the ratio of the volume distribution average diameter to the number distribution average diameter. In order to prevent selective development, it is important to reduce the ratio. When the distribution is wide, toner having a relatively small particle size is deposited on the developing roll in continuous printing, and developability is lowered.

  Then, the toner 13 is supplied to the electrostatic latent image formed on the photosensitive drum 31 as described above, and developed, thereby forming a toner image. The K toner image formed on the photosensitive drum 31 is transferred to the recording paper P or the transfer belt 21 by the transfer roller 22. The cleaner unit 35 removes toner adhering to the surface of the photosensitive drum 31 to which the K toner image is transferred.

  The transfer conveyance unit 20 includes a transfer belt 21, a transfer roller 22, a right roller 23, and a left roller 24. The right roller 23 is disposed below the image forming unit 30K, and the left roller 24 is disposed below the image forming unit 30C. The transfer belt 21 is an endless belt stretched between the right roller 23 and the left roller 24, and is rotated at a constant speed in a counterclockwise direction (direction B) by the right roller 23 and the left roller 24. The The transfer belt 21 is made of a heat-resistant resin material such as polyimide resin. Four transfer rollers 22 are disposed on the inner peripheral side of the transfer belt 21 and at positions facing the four photosensitive drums 31. The transfer roller 22 is made of a conductive rubber material or the like, and transfers each color toner image formed on the photosensitive drum 31 onto the recording paper P or transfer belt.

  The fixing unit 40 includes a heat shielding box 41, a fixing roller 42 with a built-in heater, and a pressure roller 43. The toner image is fixed on the recording paper P by heating and conveying the recording paper P on which the toner image is formed. Let

  FIG. 3 is a block diagram showing an example of the electrical configuration of the image forming apparatus 1 shown in FIG. The image forming apparatus 1 illustrated in FIG. 3 includes a paper transport mechanism 201, an operation panel 401, a communication I / F unit 501, an image forming unit 30, and a control unit 2. The paper transport mechanism 201 is configured by a drive mechanism such as a motor or a gear, for example, and various types of paper feed cassette 10, transfer transport unit 20, transport path 50, and transport path 60 in accordance with a control signal from the control unit 2. The recording paper P stored in the paper feed cassette 10 is transported by driving the transport rollers and belt.

  The operation panel 401 includes, for example, a liquid crystal display and the like, and includes a display 402 that displays an operation state of the image forming apparatus 1 and operation keys 403 for a user to input a print execution instruction and various setting instructions. The communication I / F unit 501 is a communication interface circuit such as USB (Universal Serial Bus) or Ethernet (registered trademark), for example, from another information processing device connected to the outside of the communication I / F unit 501 such as a personal computer. The received communication signal, for example, image data or a signal indicating an image formation instruction is converted into data in a format that can be processed by the control unit 2 and output to the control unit 2.

  The image forming unit 30 includes a rotation driving unit 301, an exposure device 33, DC voltage sources 16 and 18, and AC voltage sources 17 and 19. The rotation drive unit 301 is configured using, for example, a motor, various gears, and the like, and in accordance with a control signal from the control unit 2, the agitation mixer 342, the paddle mixer 343, the magnetic roll 11, the developing roll 12, and the photosensitive drum. 31 is rotationally driven. The DC voltage sources 16 and 18 and the AC voltage sources 17 and 19 output DC voltages Vdc1 and Vdc2 and AC voltages Vac1 and Vac2, respectively, in response to a control signal from the control unit 2.

  The control unit 2 includes, for example, a CPU (Central Processing Unit) that executes predetermined arithmetic processing, a ROM (Read Only Memory) that stores a predetermined control program, and a RAM (Random Access Memory) that temporarily stores data. And the peripheral circuits and the like, and by executing a control program stored in the ROM, operations of the sheet transport mechanism 201, the operation panel 401, the communication I / F unit 501, and the image forming unit 30 are performed. To control.

  Next, a characteristic operation of the image forming apparatus 1 configured as described above will be described. First, for example, image data transmitted from a personal computer connected to the outside of the communication I / F unit 501 is received by the communication I / F unit 501. Then, in response to a control signal from the control unit 2, the recording paper P fed out from the paper feed cassette 10 by the paper transport mechanism 201 is transported to the photosensitive drum 31 in the image forming unit 30 </ b> K via the transport path 50. At the same time, the agitation mixer 342, the paddle mixer 343, the magnetic roll 11, the developing roll 12, and the photosensitive drum 13 are rotationally driven by the rotation driving unit 301.

  Then, the developer composed of the toner 13 and the carrier 14 is stirred by the stirring mixer 342 and the paddle mixer 343, and the toner 13 is charged. Further, as shown in FIG. 2, the toner 13 and the carrier 14 are attached to and held on the outer peripheral surface of the magnetic roll 11 to form the magnetic brush 15, and the magnetic brush 15 is attached to the regulating blade 345 as the magnetic roll 11 rotates. The thickness of the magnetic brush 15 is made constant by passing between the magnetic roller 11 and the magnetic roll 11. Further, the outer peripheral surface of the photosensitive drum 31 is charged by the charger 32.

  Next, the controller 2 performs an exposure operation by the exposure device 33 based on the image data received by the communication I / F unit 501, and an electrostatic latent image corresponding to the image data is formed on the outer peripheral surface of the photosensitive drum 31. It is formed.

  Next, after the AC voltage Vac1 output from the AC voltage source 17 is superimposed on the DC voltage Vdc1 output from the DC voltage source 16 and applied to the magnetic roll 11 in accordance with the control signal from the control unit 2, The AC voltage Vac2 output from the AC voltage source 19 is superimposed on the DC voltage Vdc2 output from the DC voltage source 18 and applied to the developing roll 12. FIG. 4 is an explanatory diagram showing application timings of the DC voltage Vdc1, the AC voltage Vac1, the DC voltage Vdc2, and the AC voltage Vac2. In the waveform V1 shown in FIG. 4, “ON” indicates a state where both the DC voltage Vdc1 and the AC voltage Vac1 are applied, and “OFF” indicates a state where neither the DC voltage Vdc1 nor the AC voltage Vac1 is applied. Similarly, in the waveform V2 shown in FIG. 4, “ON” indicates a state where both the DC voltage Vdc2 and the AC voltage Vac2 are applied, and “OFF” indicates a state where neither the DC voltage Vdc2 nor the AC voltage Vac2 is applied. Yes.

  FIG. 5 is an explanatory diagram for explaining an example of operations of the magnetic roll 11, the developing roll 12, and the photosensitive drum 31. At timing T <b> 1, the circumferential surface position “a” of the developing roll 12 is a position facing the magnetic roll 11 (the closest position). At time T1, when the DC voltage Vdc1 and the AC voltage Vac1 are applied to the magnetic roll 11, the toner 13 held on the outer peripheral surface of the magnetic roll 11 is developed by the potential difference between the magnetic roll 11 and the developing roll 12. The roller 12 flies to the circumferential surface position a of the roll 12, and the circumferential surface position a moves in the direction of the photosensitive drum 31 indicated by the arrow 121 as the developing roll 12 rotates, and a toner layer 131 is formed on the outer circumferential surface of the developing roll 12. Is done.

  The developing roller 12 is rotated by the rotation driving unit 301, and at the timing T2 when the circumferential surface position a moves and reaches the position b facing the photosensitive drum 31, the DC voltage Vdc2 and the AC voltage Vac2 are changed to the developing roller 12. To be applied. The timing at which the DC voltage Vdc2 and the AC voltage Vac2 are applied to the developing roll 12 may be after the timing T2.

  In this case, for example, the time T during which the outer peripheral surface of the developing roll 12 rotates from the position facing the magnetic roll 11 to the position facing the photosensitive drum 31 by rotating the developing roll 12 by the rotation driving unit 301 is measured in advance. The time T is set in advance as a timer value of a timer circuit (not shown), for example, and the control unit 2 uses the DC voltage source 16 and the AC voltage source 17 to set the DC voltage Vdc1 and After the application of the AC voltage Vac1 to the magnetic roll 11 is started, the DC voltage source 18 and the AC voltage source 19 detect the DC voltage Vdc2 and the AC voltage after detecting that at least the time T has elapsed using the timer circuit described above. The voltage Vac2 may be applied to the developing roll 12.

  Further, for example, the rotation amount of the developing roll 12 is detected using a rotation amount detection sensor such as a rotary encoder (not shown), and the control unit 2 detects the developing roll at the position facing the magnetic roll 11 at the timing T1. When the rotation amount of the developing roller 12 corresponding to the movement of the circumferential surface position a of 12 to the position b facing the photosensitive drum 31 or a rotation amount larger than that is detected by the rotation amount detection sensor described above. The DC voltage Vdc2 and the AC voltage Vac2 may be applied to the developing roll 12 by the DC voltage source 18 and the AC voltage source 19.

  Here, the circumferential surface position (closest position) of the photosensitive drum 31 at the position b facing the circumferential surface position a of the developing roll 12 at timing T2 is defined as c. Then, when the DC voltage Vdc2 and the AC voltage Vac2 are applied to the developing roll 12 at the timing T2, the toner 13 held in layers on the outer peripheral surface of the developing roll 12 due to the potential difference between the developing roll 12 and the photosensitive drum 31. However, the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 31 is developed with the rotation of the photosensitive drum 31 and the toner is developed. An image is formed.

  Then, at the timing when the photosensitive drum 31 rotates and the peripheral surface position c faces the transfer roller 22, the transfer conveyance unit 20 conveys the leading end portion of the recording paper P to the opposed position between the photosensitive drum 31 and the transfer roller 22. Then, the black (K) toner image on the photosensitive drum 31 is transferred to the recording paper P. As a result, the toner image is transferred from the leading end of the recording paper P.

  Thereafter, similarly, the yellow (Y), magenta (M), and cyan (C) toner images are transferred to the recording paper P by the image forming units 30Y, 30M, and 30C, and transferred to the recording paper P by the fixing unit 40. The black (K), yellow (Y), magenta (M), and cyan (C) toner images are fixed, conveyed by the conveyance path 60, and discharged to the discharge tray 80.

  As described above, according to the image forming apparatus 1 shown in FIG. 1, when the application of the AC voltage Vac1 and the DC voltage Vdc1 is started by the DC voltage source 16 and the AC voltage source 17 (timing T1), it faces the magnetic roll 11. After the peripheral surface position a of the developing roll 12 at the position, that is, the peripheral surface position a holding the toner 13 supplied from the magnetic roll 11 at the timing T <b> 1, moves to the position b facing the photosensitive drum 31. The DC voltage Vdc2 and the AC voltage Vac2 are applied to the developing roll 12 by the DC voltage source 18 and the AC voltage source 19, that is, the toner 13 held at the peripheral surface position a is supplied to the peripheral surface position c of the photosensitive drum 31. Since the electrostatic latent image on the photosensitive drum 31 is developed by the toner 13 held at the circumferential surface position c, before the development operation is started, In example adhering to the outer peripheral surface of the developing roller 12 in the previous image formation, it is never used toner 13 was firmly adhered. Therefore, by using the toner 13 that has adhered to the outer peripheral surface of the developing roll 12 before the start of the developing operation, the amount of toner supplied from the developing roll 12 to the photosensitive drum 31 decreases, and immediately after the start of development (in FIG. 4). It is suppressed that the image density during the period of time T) becomes thin.

  Further, the AC voltage Vac2 is set to a voltage at which the toner 13 does not fly from the developing roller 12 to the photosensitive drum 31 unless the DC voltage Vdc2 is applied. For example, when the AC voltage Vac2 is supplied to the developing roll 12 by the AC voltage source 19, the toner 13 remaining in a minute amount on the outer peripheral surface of the developing roll 12 is vibrated. Then, when the toner on the developing roll 12 finally returns to the magnetic roll 11, a phenomenon occurs in which the toner is rearranged with directionality in the thickness direction.

  That is, a relatively large toner having a low chargeability vibrates, and a small toner hardly moves and stays on the surface of the developing roll 12. This results in a high charge toner array in the lower layer and a low charge toner array in the upper layer. In particular, when the toner layer is thin, the tendency of rearrangement works strongly, causing a problem that high charge adheres firmly to the lower layer. In this state, when a new toner layer is formed on the toner firmly adhered to the lower layer, the charging properties of the lower layer portion 13 and the upper layer portion toner 13 are further separated, and the lower layer toner 13 is further fixed to the developing roll 12. As a result, the supply amount of the toner 13 from the developing roll 12 to the photosensitive drum 31 varies, and there is a possibility that uneven development density occurs.

  However, according to the image forming apparatus 1 shown in FIG. 1, since neither the DC voltage Vdc1 nor the AC voltage Vac2 is applied to the developing roll 12 during the period of time T, the toner layers are rearranged as described above. Is reduced, and uneven development density is reduced.

  Although an example in which the DC voltage Vdc2 and the AC voltage Vac2 are applied to the developing roll 12 after the elapse of time T after the DC voltage Vdc1 and the AC voltage Vac1 are applied to the magnetic roll 11 is shown, the DC voltage Vdc1 and the AC voltage are exchanged. It is sufficient that the DC voltage Vdc2 and the AC voltage Vac2 are applied to the developing roll 12 after the voltage Vac1 is applied to the magnetic roll 11, and it is not necessary to apply the DC voltage Vdc2 and the AC voltage Vac2 after elapse of time T or more. Absent. Even if the time from when the DC voltage Vdc1 and the AC voltage Vac1 are applied to the magnetic roll 11 to when the DC voltage Vdc2 and the AC voltage Vac2 are applied to the developing roll 12 is less than the time T, the DC voltage If the DC voltage Vdc2 and the AC voltage Vac2 are applied to the developing roll 12 after the Vdc1 and the AC voltage Vac1 are applied to the magnetic roll 11, they firmly adhere to the outer peripheral surface of the developing roll 12 before the start of the developing operation. Therefore, the amount of toner supplied from the developing roll 12 to the photosensitive drum 31 is reduced by the toner 13 that is firmly attached, and the image density immediately after the start of development is reduced. Can be reduced.

  Further, the AC voltage source 17 may not be provided, and the toner 13 may be caused to fly from the magnetic roll 11 to the developing roll 12 by supplying the DC voltage Vdc1 output from the DC voltage source 16 to the magnetic roll 11. Further, the AC voltage source 19 may not be provided, and the toner 13 may be caused to fly from the developing roll 12 to the photosensitive drum 31 by supplying the DC voltage Vdc2 output from the DC voltage source 18 to the developing roll 12. .

  Further, as an example of the image forming apparatus 1, an example in which the present invention is applied to a color printer has been shown. However, the image forming apparatus 1 may be an image forming apparatus such as a copying machine, a facsimile, or a complex machine thereof. Moreover, a monochrome image forming apparatus may be used.

1 is a diagram schematically illustrating an internal configuration of an image forming apparatus using a developing device according to an embodiment of the present invention. It is a block diagram which shows an example of a structure of a magnetic roll, a developing roll, and a photoreceptor drum in detail. FIG. 2 is a block diagram illustrating an example of an electrical configuration of the image forming apparatus illustrated in FIG. 1. FIG. 3 is an explanatory diagram showing application timings of DC voltage and AC voltage to the magnetic roll shown in FIG. 2 and application timings of DC voltage and AC voltage to the developing roll. FIG. 3 is an explanatory diagram for explaining an example of operations of a magnetic roll, a developing roll, and a photosensitive drum shown in FIG. 2. It is a block diagram which shows schematic structure of the developing device which concerns on background art. It is explanatory drawing for demonstrating operation | movement of the developing device which concerns on background art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Control part 11 Magnetic roll 12 Developing roll 13 Toner 14 Carrier 15 Magnetic brush 16, 18 DC voltage source 17, 19 AC voltage source 20 Transfer conveyance part 30 Image forming part 31 Photosensitive drum 32 Charger 33 Exposure apparatus 34 Developing Device 35 Cleaner 40 Fixing Unit 201 Paper Conveying Mechanism 301 Rotation Drive Unit 342 Stir Mixer 343 Paddle Mixer 345 Regulatory Blade Vac1, Vac2 AC Voltage Vdc1, Vdc2 DC Voltage

Claims (6)

A developer in which a toner and a carrier are mixed is attached to the circumferential surface of the magnetic roll, the toner is charged, and the charged toner is moved from the magnetic roll onto the developing roll, thereby moving the developer onto the circumferential surface of the developing roll. In a developing device that develops an electrostatic latent image formed on the peripheral surface of the photosensitive drum by attaching and moving the toner from the peripheral surface of the developing roll to the peripheral surface of the photosensitive drum.
The magnetic roll and the photosensitive drum are respectively arranged to face the developing roll,
A rotation drive unit for rotating the developing roll;
A first voltage applying unit that applies a first voltage to the magnetic roll to move the toner from the magnetic roll onto the developing roll;
After the first voltage is applied by the first voltage application unit, a second voltage is applied to the developing roll so as to move the toner from the peripheral surface of the developing roll to the peripheral surface of the photosensitive drum. A second voltage application unit ,
In the second voltage application unit, the circumferential surface position of the developing roll that was at the position facing the magnetic roll when the application of the first voltage by the first voltage application unit was started is A developing device that applies the second voltage to the developing roll after moving to a position facing the photosensitive drum. A developer in which a toner and a carrier are mixed is attached to the circumferential surface of the magnetic roll, the toner is charged, and the charged toner is moved from the magnetic roll onto the developing roll, thereby moving the developer onto the circumferential surface of the developing roll. In a developing device that develops an electrostatic latent image formed on the peripheral surface of the photosensitive drum by attaching and moving the toner from the peripheral surface of the developing roll to the peripheral surface of the photosensitive drum.
The magnetic roll and the photosensitive drum are respectively arranged to face the developing roll,
A rotation drive unit for rotating the developing roll;
A first voltage applying unit that applies a first voltage to the magnetic roll to move the toner from the magnetic roll onto the developing roll;
After the first voltage is applied by the first voltage application unit, a second voltage is applied to the developing roll so as to move the toner from the peripheral surface of the developing roll to the peripheral surface of the photosensitive drum. A second voltage application unit,
The second voltage applying unit is configured such that at least the developing roll is rotated by the rotation driving unit after the application of the first voltage by the first voltage applying unit is started. wherein the elapsed time since the time to move to a position facing the opposite position to the photosensitive drum with the magnetic roll in the circumferential surface, der Revealed image device to perform the application of the second voltage to the developing roller . The developing device according to claim 1, wherein the first voltage application unit outputs a voltage obtained by superimposing an AC voltage on a DC voltage as the first voltage. The developing device according to claim 1, wherein the second voltage application unit outputs a voltage obtained by superimposing an AC voltage on a DC voltage as the second voltage.   The second voltage application unit is further configured such that when the leading position of the electrostatic latent image formed on the peripheral surface of the photosensitive drum reaches a position facing the developing roll as the photosensitive drum rotates. The developing device according to claim 1, wherein a second voltage is applied to the developing roll.   An image forming apparatus for forming an image by transferring a toner image formed on the photosensitive drum by the developing device according to claim 1 onto a recording sheet.

Images