JP2007304360A - Adjusting method for developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adjustment method for a developing device whereby a conveyance bias can be constantly adjusted to an appropriate level despite a change in the amount of toner electrification and stable image quality can be ensured. <P>SOLUTION: The developing device 100 includes a magnetic roll 143 for holding two-component developer 145 supplied to a developing tank 142, and a developing roll 144 for holding toner thereon and developing an electrostatic latent image on an image carrier 110. The adjusting method for the developing device 100 has a bias voltage adjustment step in which bias voltages Vdc3 and Vdc4 applied to the magnetic roll 143 and developing roll 144 are adjusted so that the toner concentration of a pattern on the image carrier 110 or the pattern transferred to a transfer body becomes a predetermined toner concentration. This adjustment method includes a rotating-speed adjustment step in which based on a difference between the target difference voltage of each of the obtained bias voltages Vdc3 and Vdc4 and its predetermined standard difference voltage, the relative rotating speeds of the magnetic roll 143 and developing roll 144 are adjusted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic roll for holding a two-component developer composed of a carrier and toner filled in a developing tank in a brush shape, and an electrostatic formed on an image carrier holding the toner conveyed from the magnetic roll. A developing roller for developing a latent image, and adjusting the bias voltage applied to each of the magnetic roller and the developing roller to adjust the toner density of the pattern formed on the image carrier or the pattern after transfer to the transfer member The present invention relates to a method for adjusting a developing device including a bias voltage adjustment step for adjusting the toner density to a predetermined toner density.

  As a developing device incorporated in an electrophotographic image forming apparatus, Patent Document 1 discloses a stable image in which the toner layer thickness on the developing roller is always stabilized over a long period of time without making the developing device complicated, and there is no density change. In order to maintain the above, a solid pattern using a toner layer formed on the second turn after starting to apply the developing bias to the developing roll on the image carrier and the next rotation was formed. The toner layer thickness detection pattern arranged with the halftone pattern using the toner layer is visualized, and the toner layer thickness detection pattern on the image carrier or the toner layer thickness detection pattern transferred to the transfer body A developing method that detects the toner density with a density sensor and controls the difference voltage of the bias voltage between the magnetic roll and the developing roll based on the detected toner density, that is, the transport bias voltage. There has been proposed.

JP 2005-55841 A

  However, in the above-described conventional technology, the rotation speeds of the magnetic roll and the developing roll are fixed, and the charge amount of the toner filled in the developing tank is within the ideal charge amount range. If the charge amount of the toner fluctuates, it may be difficult to adjust the toner density.

  For example, although sufficient toner is supplied to the developing roll, depending on the relationship between the toner charge amount and the bias voltage between the image carrier and the developing roll, that is, the developing bias voltage, the image from the developing roll A necessary toner amount is not supplied to the carrier, and it is detected that the toner density of the halftone pattern is low, and it is determined that the toner amount of the developing roll is not sufficient. As a result, the adjusted transport bias voltage becomes too high, causing a leak between the developing roll and the magnetic roll, which may cause image defects such as black spots. Furthermore, if excessive toner is supplied to the developing roll, the distance between the developing roll and the magnetic roll is narrowed, causing a trouble in toner conveyance, which may cause toner scattering and agent leakage.

  Conversely, depending on the relationship between the charge amount of the toner and the development bias voltage, it is detected that the toner density of the halftone pattern is high and it is determined that the amount of toner supplied to the development roll is large. As a result, when the transport bias voltage is adjusted to be low, the amount of toner supplied from the magnetic roll cannot catch up with the amount of toner supplied from the developing roll to the image carrier, and the previous development history continues. There is a possibility that a development ghost that affects the development of this occurs.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-described conventional drawbacks, and an object of the present invention is to provide a method for adjusting a developing device that can always properly adjust the transport bias even when the charge amount of toner changes, and can ensure stable image quality. .

  In order to achieve the above-mentioned object, the first characteristic configuration of the developing device adjustment method according to the present invention comprises a carrier and a toner filled in a developing tank, as described in claim 1 of the claims. A magnetic roll that holds the two-component developer in a brush shape; and a developing roll that holds the toner conveyed from the magnetic roll and develops the electrostatic latent image formed on the image carrier. A bias voltage adjustment step for adjusting the bias voltage applied to each of the developing rolls so that the toner density of the pattern formed on the image carrier or the pattern after transfer to the transfer body becomes a predetermined toner density; A developing device adjustment method comprising: a target difference in bias voltage applied to each of the magnetic roll and the developing roll obtained in the bias voltage adjustment step Based on a deviation between pressure and the preset reference difference voltage lies in the is an adjustment method of a developing device with a magnetic roll and a rotational speed adjustment step of the adjusting the relative rotational speed of the developing roll.

  The major factors that determine the amount of toner supplied from the magnetic roll to the developing roll include the transport bias voltage ΔVc, which is the voltage difference between the bias voltages applied to the magnetic roll and the developing roll, and the toner in the developing tank. There are carrier ratio, that is, toner density T / C in the developing tank, relative rotation speed Nr of the magnetic roll and developing roll, and toner charge amount C, and ideal toner density T / C and ideal An ideal conveyance bias voltage ΔVc that is set based on the charge amount C of the toner and the ideal relative rotational speed Nr is used as the reference difference voltage.

  However, in actuality, the charge amount C of the toner varies depending on the type of printed matter, the number of printed sheets, and the like even if the toner density T / C is adjusted to be constant. Therefore, in the bias voltage adjusting step, the transport bias voltage ΔVc is adjusted in consideration of the change in the charge amount C of the toner, and the toner amount supplied to the developing roll is adjusted. Therefore, the carrier bias voltage ΔVc adjusted in the bias voltage adjustment step is often different from the reference difference voltage.

  By the way, a range in which the bias voltage applied to the magnetic roll and the developing roll can be adjusted in advance is determined in advance. Depending on the charge amount C of the toner, the upper limit of the adjustable range or the bias voltage may be set. If the situation continues, there is a possibility that the transport bias voltage ΔVc cannot be adjusted properly.

  According to the above-described configuration, the toner conveyance amount is mechanically adjusted by the rotation speed adjustment step based on the deviation between the target difference voltage obtained in the bias voltage adjustment step and the reference difference voltage. Even if there is a change in the charge amount, the adjustment value of the bias voltage applied to the magnetic roll and the developing roll can be maintained in a substantially constant range, and stable image quality can always be ensured.

  According to the second characteristic configuration described in the second aspect, in addition to the first characteristic configuration described above, the rotation speed adjustment step may be configured so that the predetermined toner density is obtained by the reference difference voltage. The point is to adjust the relative rotational speed.

  According to the above-described configuration, the bias voltage applied to the magnetic roll and the developing roll can always be stably adjusted even if the charge amount of the toner changes.

  In the third feature configuration, in addition to the first or second feature configuration described above, the bias voltage adjustment step is executed at a predetermined interval set in advance, and the rotation speed adjustment is performed. The step is that it is executed during the predetermined interval.

  According to the above-described configuration, even if the target difference voltage set this time becomes a value deviated from the reference difference voltage by the bias voltage adjustment step, the target adjusted in the bias voltage adjustment step executed next time Since the difference voltage can be brought close to the reference difference voltage, the target difference voltage can be quickly adjusted in the bias voltage adjustment step executed next time.

  In the fourth feature configuration, in addition to any one of the first to third feature configurations described above, the bias voltage adjustment step includes at least a predetermined low-voltage bias voltage applied to the developing roll. Solid pattern adjustment step of adjusting the bias voltage applied to the magnetic roll so that the density of the solid pattern formed on the image bearing member or the density of the solid pattern after transfer to the transfer body becomes a target solid density in a state of applying And after the solid pattern adjustment step, the magnetic roll so that the density of a predetermined halftone pattern formed on the image carrier or a predetermined halftone pattern after transfer to the transfer body becomes a target halftone density. And a halftone pattern for adjusting both bias voltages while maintaining a constant voltage difference between the bias voltages applied to each of the developing rolls. Consists of a down adjustment step lies in the predetermined toner concentration is the target solid density.

  In the bias voltage adjustment step, the amount of toner conveyed to the developing roll is appropriately adjusted in the solid pattern adjustment step, and then the gradation of toner density is ensured in the halftone pattern adjustment step.

  According to the configuration described above, the rotation speed adjustment step enables stable adjustment of the transport bias voltage in the solid pattern adjustment step.

  As described above, according to the present invention, it is possible to provide a method for adjusting a developing device that can always properly adjust the transport bias even when the charge amount of toner changes, and can ensure stable image quality. became.

  The developing device adjustment method according to the present invention will be described below.

  A printer as an example of an electrophotographic image forming apparatus including a developing device according to the present invention forms a toner image of each color component of MCYK based on a print job input from an external device as shown in FIG. An image forming unit 1, a sheet feeding unit 2 including a paper tray for supplying, conveying, and discharging a sheet as a recording medium, a conveying roller, an endless transfer member 31 supported by three rollers 30, A transfer unit 3 including a plurality of transfer rollers 32 and 33 arranged in contact with the transfer body 31, a fixing unit 4 for fixing a toner image transferred to a recording medium, and the external device. An interface unit 5 that performs data transmission and reception and a system control unit 6 that includes a microcomputer that performs overall control of the printer are included.

  The image forming unit 1 includes four photoconductor units 100 corresponding to M (magenta), C (cyan), Y (yellow), and K (black) colors arranged along the circumferential direction of the transfer body 31. A toner density sensor 11 that detects the density of each color based on the amount of light reflected from the toner pattern of each color carried on the transfer body 31 so that the toner density of the toner image to be formed is maintained at a predetermined toner density; As shown in FIG. 1, each photoconductor unit 100 includes an image carrier 110, a charging charger 120 along the circumferential direction of the image carrier 110, and a control unit 12 that controls the image forming unit 1. An exposure head 130, a developing device 140, a cleaner 150, a charge removal lamp 160, and the like are arranged.

  The image carrier 110 includes a photosensitive drum having a photosensitive member in which an amorphous silicon layer, which is a positively chargeable photoconductor, is deposited on the surface of an aluminum cylinder, and is positively charged by the charging charger 120. By the exposure from 130, the charge in the exposed portion is grounded through the cylinder.

  The toner density sensor 11 is disposed on the downstream side of the photoreceptor unit 100 disposed along the circumferential direction of the transfer body 31. The toner density sensor 11 will be described in detail. The toner density sensor 11 projects a single polarized light at a predetermined inclination angle with respect to the normal direction of the transfer body 31 as shown in FIG. The light unit 13 is disposed on the opposite side to the light projecting unit 13 with respect to the normal direction, and the reflected light from the transfer body 31 is the same as the first polarized light and the light projecting light. And a first and second light receiving parts 15 for receiving the first and second polarized lights, and the first and second light receiving parts 15 for receiving the first and second polarized lights. The toner density is detected from the light amount difference of the second polarized light.

  As shown in FIG. 1, the developing device 140 provided in each of the photoreceptor units 100 of M (magenta), C (cyan), Y (yellow), and K (black) colors corresponds to the corresponding colors. A toner cartridge 141 filled with the toner, a developer tank 142 that stirs the toner and carrier supplied from the toner cartridge 141, and a two-component developer 145 composed of the carrier and toner filled in the developer tank 142. A magnetic roll 143 for holding the magnetic brush 143l, and a developing roll for developing the electrostatic latent image formed on the image carrier 110 by holding the toner conveyed from the magnetic roll 143 as a toner thin layer 144l. 144.

  The magnetic roll 143 is composed of a rotating sleeve including a fixed magnet roller in which N poles and S poles are alternately magnetized, and a DC bias voltage (hereinafter referred to as “bias voltage”) Vdc3 is applied to the rotating shaft thereof. A high voltage circuit 143v is connected, and the rotation shaft is connected to a drive mechanism 146m composed of a motor and a speed reduction mechanism so that the magnetic roll 143 rotates in one direction at a predetermined rotation speed. The high voltage circuit 143v and the drive mechanism 146m are configured to be controllable.

  The developing roll 144 is made of uniformly charged aluminum, and a high-voltage circuit 144v for applying an AC bias voltage Vac4 and a bias voltage Vdc4 is connected to the rotation axis of the developing roll 144. Further, the developing roll 144 has a predetermined rotational speed. The rotating shaft is connected to a driving mechanism 146s including a motor and a speed reduction mechanism so as to rotate in one direction, and the high-voltage circuit 144v and the driving mechanism 146s can be controlled by the control unit 12.

  The control unit 12 sets a bias voltage at a predetermined interval set in advance, in this embodiment, when the cumulative operating time of the developing device 140 reaches a predetermined time or when the cumulative number of printed sheets reaches a predetermined number of printed sheets. It is configured to perform an adjustment step.

  In the bias voltage adjustment step, at least a solid pattern formed on the image carrier 110 with a predetermined low-voltage bias voltage Vdc4 (L) applied to the developing roll 144 or a solid pattern after transfer to the transfer body 31 A solid pattern adjusting step for adjusting the bias voltage Vdc3 applied to the magnetic roll 143 so that the density of the image becomes a target solid density, and a predetermined half formed on the image carrier 110 after the solid pattern adjusting step. Conveyance which is a difference voltage between bias voltages applied to the magnetic roll 143 and the developing roll 144 so that the tone pattern or the density of a predetermined halftone pattern after transfer to the transfer body 31 becomes a target halftone density. Both bias voltages are adjusted while maintaining the bias voltage ΔVc constant. Consisting of-safe tone pattern adjustment step.

  In the solid pattern adjustment step, the toner conveyed from the magnetic roll 143 to the developing roll 144 is adjusted so as not to be supplied excessively. In the halftone pattern adjustment step, the toner density level is adjusted. The tonality is adjusted.

  Note that the bias voltage adjustment step is not limited to the adjustment method described above, and in order to detect the toner layer thickness on the developing roller 144 on the image carrier 110 according to Patent Document 1, the development is performed. A toner layer in which a solid pattern using a toner layer formed on the second turn after applying the developing bias of the roller 144 and a halftone pattern using a toner layer formed during the next rotation are arranged The thickness detection pattern is visualized, and the toner layer thickness on the transfer body 31 to which the toner layer thickness detection pattern on the image carrier 110 or the toner layer thickness detection pattern on the image carrier 110 is transferred. The toner density in the detection pattern is detected by the toner density sensor 11, and the toner layer on the developing roller 144 is controlled to a predetermined layer thickness by the detected toner density. Such that adjustment method may be one using the other adjustment methods.

  During the predetermined interval, the control unit 12 preliminarily includes a target differential voltage, which is a differential voltage between bias voltages applied to the magnetic roll 143 and the developing roll 144 obtained in the bias voltage adjustment step, Based on a deviation from the set reference difference voltage, a rotation speed adjustment step is executed to adjust the relative rotation speed of the magnetic roll 143 and the developing roll 144 so that the target solid density is obtained by the reference difference voltage. Is configured to do.

  Here, the reference difference voltage is an ideal transport bias voltage ΔVc set based on an ideal toner density T / C, an ideal toner charge amount C, and an ideal relative rotational speed Nr. The reference difference voltage is a design value set in advance through experiments or the like.

  This will be described in detail below. When the cumulative operating time of the developing device 140, which becomes a predetermined interval, reaches a predetermined time or when the cumulative number of printed sheets reaches a predetermined number of printed sheets, the control unit 12 first performs a solid pattern adjusting step of the bias voltage adjusting step. As a result, the following adjustment is performed.

  Without changing the AC bias voltage Vac4 applied to the developing roll 144 rotating at the rotation speed Ns for each color photoconductor unit 100, the bias voltage Vdc4 is set to a predetermined low-voltage bias voltage Vdc4 (close to the minimum applied voltage). L) and applying a bias voltage Vdc3 of the first to fourth patterns to the magnetic roll 143 rotating at a rotation speed Nm, the toner image having four patterns on the image carrier 110. As shown in FIG. 4, the toner image is carried on the transfer body 31 and the toner density sensor 11 detects the toner density of each of the four patterns.

  As shown in FIG. 5, a memory (not shown) of the control unit 12 is obtained from a characteristic curve obtained from the transport bias voltage ΔVc which is a difference voltage between the bias voltage Vdc3 and the bias voltage Vdc4 (L) and the detected toner density. An optimum carrier bias voltage that becomes a target solid density at the time of solid pattern formation stored in the unit is obtained, and this is set as a target difference voltage ΔVc (O). The bias voltage Vdc3 (O) can be obtained from the target difference voltage ΔVc (O) and the bias voltage Vdc4 (L). When the bias voltages Vdc3 and Vdc4 applied to the magnetic roll 143 and the developing roll 144 are adjusted while maintaining the target differential voltage ΔVc (O), the toner is excessively transferred from the magnetic roll 143 to the developing roll 144. It is never supplied.

  Next, the control unit 12 performs the following adjustment as a half pattern adjustment step of the bias voltage adjustment step in order to ensure gradation.

  Similar to the formation of the solid pattern, several predetermined halftone patterns are formed on the image carrier 110 and transferred to the transfer body 31, and the toner density of the predetermined halftone patterns of the several patterns after transfer is changed. The bias voltages Vdc3 and Vdc4 are adjusted while maintaining the carrier bias voltage ΔVc (O) so that the target halftone density at the time of half pattern formation stored in a storage unit (not shown) of the control unit 12 is obtained.

  The control unit 12 sets the target differential voltage ΔVc (, which is a differential voltage between bias voltages applied to the magnetic roll 143 and the developing roll 144 obtained in the bias voltage adjustment step immediately before the predetermined interval elapses. O) and the reference voltage difference ΔVc (S) set in advance, in the solid pattern adjustment step of the bias voltage adjustment step performed after the predetermined interval has elapsed, the magnetic roll 143 and the developing roll Rotational speed for adjusting the relative rotational speed of the magnetic roll 143 and the developing roll 144 so that the target solid density can be obtained with the target differential voltage of the bias voltage applied to each of the 144 as the reference differential voltage ΔVc (S). Perform adjustment steps.

  In the rotation speed adjusting step, the ratio of the toner and the carrier in the developing tank 142, that is, the toner concentration T / C in the developing tank 142, which is stored in a storage unit (not shown) of the control unit 12 through experiments and the like in advance. And a rotational speed ratio Nr between the rotational speed Nm of the magnetic roll 143 and the rotational speed Ns of the developing roll 144, which is a relative rotational speed of the magnetic roll 143 and the developing roll 144, and a toner charge amount C. Same as the specific curve obtained by the solid pattern adjustment step of the bias voltage adjustment step from a plurality of characteristic curves of the transport bias voltage ΔVc and the toner density of the solid pattern carried on the transfer body 31 under different conditions. Or select the closest specific curve.

  The plurality of specific curves will be described. As shown in FIG. 6A, the values of the toner density T / C, the rotation speed ratio Nr, and the charge amount C of the toner, which are conditions, are 0 to z, 0 to y, and 0, respectively. Each is determined at predetermined intervals from the range up to x. Each of the plurality of specific curves is obtained for each condition of a value given from the range for the toner density T / C, the rotation speed ratio Nr, and the charge amount C of the toner through an experiment or the like. Further, it is a characteristic curve of the transport bias voltage ΔVc and the toner density of the solid pattern. For example, the specific curve shown in FIG. 6B is a specific curve obtained under the conditions at the point D in FIG. is there.

  Further, in the storage unit, in order to set the target differential voltage ΔVc (O) of the selected specific curve as the reference voltage value ΔVc (S), the relative rotational speeds of the magnetic roll 143 and the developing roll 144 are stored. The amount of change in the rotation speed ratio Nr between the rotation speed Nm of the magnetic roll 143 and the rotation speed Ns of the developing roll 144 is prepared and stored in advance through experiments or the like.

  Based on the information on the amount of change in the rotation speed ratio Nr stored in the storage unit, the control unit 12 keeps the rotation speed Ns of the developing roll 144 constant and the rotation speed Nm of the magnetic roll 143. Is changed to a preset rotation speed Nm (O), and the target differential voltage ΔVc (O) obtained at the next execution of the bias voltage adjustment step is adjusted to be the reference differential voltage ΔVc (S).

  Here, when the reference differential voltage ΔVc (S) is higher than the target differential voltage ΔVC (O) obtained in the bias adjustment step, the rotation speed Nm (O) is equal to the magnetic roll 143 and the developing roll. The rotation speed ratio Nr to 144 is set in advance to be small. Conversely, when the reference differential voltage ΔVc (S) is lower than the target differential voltage ΔVC (O), the rotation speed ratio Nr is set in advance. For example, in the specific curve shown in FIG. 7, since the target difference voltage ΔVc (O) is lower than the reference difference voltage ΔVc (S), the target difference voltage ΔVc (O) is reduced by reducing the rotation speed ratio Nr. Is adjusted to be the reference differential voltage ΔVc (S).

  Incidentally, as described above, when the specific curve obtained in the bias voltage adjustment step and the specific curve selected from the plurality of characteristic curves stored in the storage unit of the control unit 12 are not the same, or when the rotation speed adjustment step If there is a change in the toner charge amount after execution, there is a possibility that the target difference voltage ΔVc (O) obtained at the next execution of the bias voltage adjustment step does not completely match the reference difference voltage ΔVc (S). However, the difference is small and the influence on the image quality is small.

  Hereinafter, another embodiment will be described. In the above-described embodiment, the image bearing member 110 is a photoreceptor drum having a photoreceptor in which an amorphous silicon layer as a positively chargeable photoconductor is deposited on the surface of an aluminum cylinder. An OPC drum that is an organic photoconductor, or other types of photoconductive semiconductor drums in which the photoconductor is selenium or the like may be employed, and in this case, depending on the charging characteristics of the photoconductor, What is necessary is just to change suitably the two-component developer to employ | adopt.

  In the above-described embodiment, with respect to the adjustment of the relative rotational speed of the magnetic roll 143 and the developing roll 144, the control unit 12 keeps the rotational speed Ns of the developing roll 143 constant and the rotational speed Nm of the magnetic roll 144 is tested. However, the present invention is not limited to this, and only the rotation speed Ns of the developing roll 144 is changed, or the rotation speed Nm of the magnetic roll 143 and the development are changed. A configuration in which the rotation speed Ns of the roll 144 is changed together may be employed. However, when the rotation speed Ns of the developing roll 144 is changed, at least when the rotation speed Ns is lowered, the rotation speed of the image carrier 110 or the like needs to be changed accordingly. This is because if the rotation speed Ns of the developing roll 144 changes, the toner conveyance characteristics to the image carrier 110 change, and in particular, the influence is great when the rotation speed Ns of the developing roll 144 is lowered. Because.

  In the above-described embodiment, four patterns of toner images are formed in toner density detection. However, the present invention is not limited to this, and an optimal pattern of toner images is formed according to various conditions such as device characteristics, use conditions, and costs. The toner density of each pattern of the toner image may be detected, and the bias voltages Vdc3 and Vdc4 applied to the magnetic roll 143 and the developing roll 144 may be adjusted.

  In the above-described embodiment, the rotation speed adjustment step changes the rotation speed Nm of the magnetic roll 143 to the rotation speed Nm (O) set in advance through experiments or the like immediately before the predetermined interval elapses. The rotation speed of the magnetic roll 143 is changed between the execution of the bias voltage adjustment step and the execution of the next bias voltage adjustment step after the elapse of a predetermined interval. The relative rotational speed may be changed by changing the number Nm to the rotational speed Nm (O) set in advance through experiments or the like gradually or stepwise. In this case, since the relative rotational speed is changed gradually or stepwise, the influence on the image quality is small.

  In the above-described embodiment, the rotation speed adjustment step performs the target difference voltage ΔVc so that the predetermined toner density is obtained when the target difference voltage ΔVc (O) becomes the preset reference difference voltage ΔVc (S). The relative rotational speed is adjusted based on the deviation between (O) and the reference differential voltage ΔVc (S). For example, when the deviation is small, a bias voltage can be applied in the bias voltage adjustment step. If it is determined that there is little possibility to reduce the voltage range and the relative rotation speed is not changed and the deviation is large, the voltage range to which the bias voltage can be applied in the bias voltage adjustment step is high. It is good also as a structure which judges and changes the said relative rotational speed.

  In the above-described embodiment, the rotational speed adjustment step is executed immediately before the elapse of the predetermined interval, but may be executed during execution of the bias voltage adjustment step. For example, when the target voltage difference ΔVc (O) is obtained by executing the bias voltage adjustment step, the deviation is based on the deviation between the target voltage difference ΔVc (O) and the reference voltage difference ΔVc (S). When the difference is small, the rotation speed adjustment step is not executed by adopting the target difference voltage ΔVc (O). When the deviation is large, the rotation speed adjustment step is executed and the target difference voltage ΔVc (O ) May be adjusted to become the reference difference voltage ΔVc (S), and then the bias voltage adjustment step may be completed. In this case, adjustment in the bias voltage adjustment step takes time. When the bias voltage adjustment step is completed, an appropriate image quality can be reliably ensured.

  In the above-described embodiment, the reference differential voltage is an ideal conveyance bias that is set based on an ideal toner density T / C, an ideal toner charge amount C, and an ideal relative rotational speed Nr. Although it is assumed that the voltage is ΔVc, an ideal value that is set based on the ideal charge amount C and the ideal relative rotational speed Nr as a configuration that maintains the toner density T / C substantially constant. A good carrier bias voltage ΔVc may be used. Further, these factors may not be taken into consideration, and the adjustment range of the bias voltage applied to the magnetic roll and the developing roll may be set to a value that maximizes each adjustment range.

  The above-described embodiments are merely examples of the present invention, and the scope of the present invention is not limited by the description, and the specific configuration of each part is appropriately changed within the scope of the effects of the present invention. It goes without saying that it can be done.

Explanatory drawing of developing device Explanatory drawing of the printer in this embodiment Explanatory drawing of the toner density sensor which detects the toner density on the transfer body in this embodiment Explanatory drawing of the toner image of the pattern formed on the transfer body The graph which shows the relationship between a conveyance bias voltage and the toner density value (toner conveyance amount to a developing roll) of the solid pattern toner image on a transfer body (A) The figure used for description of the conditions at the time of calculating | requiring the several specific curve memorize | stored in the memory | storage part of a control part, (b) Explanatory drawing of a specific curve The figure used for explanation when adjusting the target differential voltage in the specific curve to the reference differential voltage

Explanation of symbols

12: Control unit 100: Photosensitive unit 140: Developing device 141: Toner cartridge 142: Developing tank 143: Magnetic roll 143l: Magnetic brush 143v: High voltage circuit (for magnetic roll)
144: Developing roll 144l: Toner thin layer 144v: High voltage circuit (for developing roll)
145: Two-component developer (toner and carrier)
146m: Drive mechanism (for magnetic roll)
146s: Drive mechanism (for developing roll)

Claims (4)

A magnetic roll that holds a two-component developer composed of a carrier and toner filled in a developing tank in a brush shape, and an electrostatic latent image formed on the image carrier by holding the toner conveyed from the magnetic roll. The toner density of the pattern formed on the image bearing member or the pattern after transfer to the transfer body by adjusting the bias voltage applied to each of the magnetic roll and the developing roll. A developing device adjustment method including a bias voltage adjustment step for adjusting so that:
Based on the deviation between the target differential voltage of the bias voltage applied to each of the magnetic roll and the developing roll obtained in the bias voltage adjusting step and a preset reference differential voltage, the relative of the magnetic roll and the developing roll A developing device adjustment method including a rotation speed adjustment step for adjusting a rotation speed.   The developing device adjustment method according to claim 1, wherein the rotation speed adjustment step adjusts the relative rotation speed so that the predetermined toner density is obtained by the reference difference voltage.   The developing device adjustment method according to claim 1, wherein the bias voltage adjustment step is executed at a predetermined interval set in advance, and the rotation speed adjustment step is executed during the predetermined interval.   In the bias voltage adjustment step, at least a predetermined low voltage bias voltage is applied to the developing roll, the solid pattern formed on the image carrier or the density of the solid pattern after transfer to the transfer body becomes the target solid density. A solid pattern adjusting step for adjusting a bias voltage applied to the magnetic roll, and a predetermined halftone pattern formed on the image carrier after the solid pattern adjusting step or a predetermined half-tone pattern formed on the transfer body A halftone pattern adjustment step for adjusting both bias voltages while maintaining a constant voltage difference between bias voltages applied to the magnetic roll and the developing roll so that the density of the halftone pattern becomes a target halftone density. 4. The method according to claim 1, wherein the predetermined toner density is the target solid density. Adjusting method of the developing device according to.