Image forming device

Abstract

To prevent fogging toner during image formation, while preventing carrier adhesion in a period from when the rotation speed of a developing roller is started to decrease from a speed during image formation until when the rotation speed of the developing roller becomes zero.SOLUTION: In an image forming apparatus, an absolute value of a difference (Vback) between a surface potential of a developer carrier to which a development bias is applied by development bias application means and a surface potential of an image carrier to which an electrification bias is applied by electrification bias application means in a period after the completion of image formation and from when driving means starts decreasing the rotation speed of the developer carrier from a speed during image formation until when the rotation speed of the developer carrier becomes zero, is smaller than the absolute value of the difference (Vback) between the surface potential of the developer carrier to which the development bias is applied by the development bias application means and the surface potential of the image carrier to which the electrification bias is applied by the electrification bias application means during image formation.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with a developing device that develops an electrostatic latent image formed on an image carrier. [Background technology]

[0002] The image forming apparatus includes a photosensitive drum (image carrier), a charging device that charges the image carrier, and a developing device having a developing roller (developer carrier) that carries a developer containing toner and carrier to develop the electrostatic latent image formed on the image carrier.

[0003] Patent Document 1 describes an image forming apparatus that changes Vback between sheets during a continuous image forming job according to the number of sheets to be imaged. Note that Vback refers to the potential difference between the surface potential (non-image portion potential) Vd of the photoconductor drum charged by the charging device and the DC component Vdc of the developing bias. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-128320 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to the inventors' study, it was found that immediately after the image formation is completed and the rotation speed of the developing roller starts to be decelerated from the speed during image formation, the phenomenon in which carrier adheres to the non-image portion of the photosensitive drum (carrier adhesion) is more likely to occur than during image formation. This is related to the fact that while the rotation speed of the developing roller is stable during image formation, immediately after the image formation is completed and the rotation speed of the developing roller starts to be decelerated from the speed during image formation, the rotation speed of the developing roller is not stable due to the stoppage of the rotation drive of the developing roller.

[0006] In general, when the absolute value of Vback is reduced, carrier adhesion tends to be suppressed more than when the absolute value of Vback is increased. Therefore, in order to suppress carrier adhesion during the period from when the rotation speed of the developing roller starts to decelerate from the speed during image formation until the rotation speed of the developing roller becomes zero, it is conceivable to uniformly reduce the absolute value of Vback after the start of image formation. On the other hand, when the absolute value of Vback is reduced, the force of attraction of toner to the developing roller is weakened more than when the absolute value of Vback is increased, so that toner (fog toner) is more likely to adhere to the non-image portion of the photosensitive drum.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing carrier adhesion during the period from when the rotation speed of the developing roller starts to be decelerated from the speed during image formation until the rotation speed of the developing roller becomes zero, while suppressing fog toner during image formation. [Means for solving the problem]

[0008] In order to achieve the above object, an image forming apparatus according to an aspect of the present invention has the following configuration: a developing device including an image carrier, a developing container containing a developer containing a toner and a carrier, and a rotatable developer carrier carrying the developer to develop an electrostatic latent image formed on the image carrier; a driving means for driving the developer carrier to rotate, a developing bias application means for applying a developing bias to the developer carrier, a charging bias application means for applying a charging bias to the image carrier, and a control means for controlling the driving means, wherein an absolute value of a difference between a surface potential of the developer carrier to which the developing bias has been applied by the developing bias application means and a surface potential of the image carrier to which the charging bias has been applied by the charging bias application means at a position facing the developer carrier, during a period from when an image formation is completed and when the rotation speed of the developer carrier starts to be decelerated from the rotation speed of the developer carrier during image formation until the rotation speed of the developer carrier becomes zero, is the charging bias applying means applies the charging bias to the image carrier so that the surface potential of the image carrier at the facing position facing the developer carrier becomes a first potential during the image formation, and applies the charging bias to the image carrier so that the surface potential of the image carrier at the facing position facing the developer carrier becomes a second potential different from the first potential after the image formation is completed, and the control means controls the driving means to decelerate the rotation speed of the developer carrier from the rotation speed of the developer carrier during the image formation after the image formation is completed and the surface potential of the image carrier at the facing position facing the developer carrier becomes the second potential. It is characterized by: Effect of the Invention

[0009] According to the present invention, it is possible to suppress carrier adhesion during the period from when the rotational speed of the developing roller starts to decelerate from the speed during image formation until the rotational speed of the developing roller becomes zero, while suppressing fog toner during image formation. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram for explaining a configuration of an image forming apparatus according to a first embodiment. [Diagram 2] 1 is a cross-sectional view illustrating a configuration of a developing device according to a first embodiment. [Diagram 3]FIG. 4 is a diagram showing a sequence of an image forming operation (image creating operation) according to the first embodiment. [Figure 4] FIG. 10 is a diagram showing a sequence of an image forming operation (image creating operation) according to the second embodiment. [Diagram 5] FIG. 13 is a diagram showing a sequence of an image forming operation (image creating operation) according to the third embodiment. [Figure 6] FIG. 13 is a diagram showing a sequence of an image forming operation (image creating operation) according to the fourth embodiment. [Figure 7] FIG. 13 is a diagram showing a sequence of an image forming operation (image creating operation) according to the fifth embodiment. [Figure 8] FIG. 11 is a diagram showing a sequence of an image forming operation (image creation operation) in a conventional example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the present invention, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the present invention. The present invention can be implemented in various applications, such as printers, various printing machines, copiers, FAX machines, and multifunction machines.

[0012] [First embodiment] (Configuration of Image Forming Apparatus) FIG. 1 is a diagram showing the configuration of an in-line type (four-drum type) color image forming apparatus 100. As shown in FIG.

[0013] Image forming apparatus 100 has four image forming sections (image forming units): an image forming section that forms a yellow image, an image forming section that forms a magenta image, an image forming section that forms a cyan image, and an image forming section that forms a black image. These four image forming sections are arranged in a row at regular intervals. Hereinafter, when the subscripts A, B, C, and D are added to a reference symbol, they indicate the respective yellow, magenta, cyan, and black members (or devices), and when there is only a reference symbol without a subscript, they indicate a member (or device) that is not related to color.

[0014] Each image forming unit is provided with a photoconductor drum 1A, 1B, 1C, or 1D, which is an image carrier. The photoconductor drums 1A, 1B, 1C, and 1D are negatively charged organic photoconductors having a photosensitive layer on a drum base made of aluminum or the like, and are rotated at a predetermined process speed by a drive device.

[0015] Around each of the photoconductor drums 1A, 1B, 1C, and 1D, there are arranged charging rollers 2A, 2B, 2C, and 2D, developing devices 4A, 4B, 4C, and 4D, and primary transfer rollers 61A, 61B, 61C, and 61D, respectively.

[0016] Here, an image forming unit using a charging roller 2 made of conductive rubber as a charging device will be described in detail. The charging roller 2 is rotatably supported by bearing members at both ends of the core metal, maintaining a constant axial distance. The charging roller 2 is also biased toward the photosensitive drum 1 by a pressure spring, and is pressed against the surface of the photosensitive drum 1 with a predetermined pressure. The charging roller 2 rotates following the rotation of the photosensitive drum 1, and a charging bias of predetermined conditions is applied to the core metal of the charging roller 2. As a result, the surface of the photosensitive drum 1, which rotates in contact with the charging roller 2, is contact-charged to a predetermined polarity and potential.

[0017] Furthermore, above each of the photoconductor drums 1A, 1B, 1C, and 1D, there is disposed exposure means (exposure devices) 3A, 3B, 3C, and 3D, respectively, for forming an electrostatic latent image on the surface of the charged photoconductor drum 1. The exposure devices 3 are electrically connected to an image processing unit 9, and form an electrostatic latent image in response to an output image signal transmitted from the image processing unit 9.

[0018] The developing means (developing devices) 4A, 4B, 4C, and 4D contain yellow toner, cyan toner, magenta toner, and black toner, respectively. The developing rollers 44A, 44B, 44C, and 44D are rotated by the respective driving means (developing motors) and develop the electrostatic latent images formed on the surfaces of the photoconductor drums 1A, 1B, 1C, and 1D to form toner images.

[0019] At positions facing the image forming units, an intermediate transfer body, rotatable endless intermediate transfer belt 62, is disposed. The intermediate transfer belt 62 is tensioned by a drive roller 65, a secondary transfer opposing roller 63, and a tension roller 66. The intermediate transfer belt 62 is rotated (moved) in the direction of the arrow (counterclockwise direction) by the drive of the drive roller 65 connected to a motor. The toner images that reach positions facing the primary transfer rollers 61A, 61B, 61C, and 61D of the intermediate transfer belt 62 are transferred from the photosensitive drum 2 to the intermediate transfer belt 62 by a primary transfer voltage.

[0020] The secondary transfer opposing roller 63 contacts the secondary transfer roller 64 via the intermediate transfer belt 62 to form a secondary transfer portion. A belt cleaning device 67 is disposed on the outer side of the intermediate transfer belt 62 to remove and collect residual toner remaining on the surface of the intermediate transfer belt 62.

[0021] In addition, downstream of the secondary transfer section where the secondary transfer opposing roller 63 and the secondary transfer roller 64 abut in the rotation direction of the intermediate transfer belt 62, a fixing device 7 is provided to perform heat and pressure processing to fix the toner to the transfer material.

[0022] Cleaning members (drum cleaning devices) 8A, 8B, 8C, and 8D for cleaning residual toner on the surfaces of the photoconductor drums 1A, 1B, 1C, and 1D are arranged around the photoconductor drums 1A, 1B, 1C, and 1D, respectively.

[0023] The configuration of the developing device 4 is shown in a cross-sectional view in FIG.

[0024] The developing device 4 has a developing container 45 that contains a developer containing toner and a carrier. The developing container 45 is partitioned into an agitating chamber 46a and a developing chamber 46b by a partition wall 43, and the developer is circulated between the agitating chamber 46a and the developing chamber 46b. A screw 45a that agitates and transports the developer in the agitating chamber 46a is disposed in the agitating chamber 46a. A screw 45b that agitates and transports the developer in the developing chamber 46b is disposed in the developing chamber 46b.

[0025] The developing device 4 also includes a developer regulating member 42. The developer regulating member 42 regulates the amount of developer carried by the developing roller 44.

[0026] The developer contained in the developing device 4 (developing container) is a two-component developer in which negatively charged non-magnetic toner and magnetic carrier are mixed. The non-magnetic toner is a resin such as polyester or styrene that contains colorants and wax components, and is pulverized or polymerized to form a powder. The magnetic carrier is a core made of resin particles kneaded with ferrite particles or magnetic powder, with a resin coating on the surface.

[0027] We will now explain the process of developing toner onto the photoconductor drum 1 in the development area. After the photoconductor drum 1 is uniformly charged to a charging potential Vd [V] by the charging roller 2, the image area is exposed by the exposure device 3 to an exposure potential Vl [V].

[0028] A high-voltage power supply (charging bias application means) applies a DC voltage (charging DC bias) or a voltage obtained by superimposing an AC voltage on a DC voltage (charging DC+AC bias) to the charging roller 2. The charging DC bias or charging DC+AC bias is applied to the photoconductor drum 1 via the charging roller 2 that is in contact with the photoconductor drum 1.

[0029] Further, a DC voltage (developing DC bias) or a voltage obtained by superimposing an AC voltage on a DC voltage (developing DC+AC bias) is applied to the developing roller 44 by a high-voltage power supply (developing bias application means).

[0030] When the DC component voltage of the developing roller 44 is Vdc [V], the absolute value of the difference between the exposure potential V1 and this potential is called Vcont, |Vdc-V1|, which creates an electric field that carries the toner to the image portion.

[0031] Moreover, the absolute value |Vdc-Vd| of the difference between the DC voltage Vdc and the charging potential Vd is called Vback, which creates an electric field that pulls the toner back in the direction from the photosensitive drum 1 toward the developing roller 44. This is provided to suppress the phenomenon in which the toner (fog toner) adheres to the non-image portion of the photosensitive drum 1 (the so-called fogging phenomenon).

[0032] When the absolute value of Vback is increased, the force attracting the toner to the developing roller becomes stronger compared to when the absolute value of Vback is decreased, so that toner (fog toner) tends to be less likely to adhere to non-image areas of the photosensitive drum 1. On the other hand, when the absolute value of Vback is decreased, the phenomenon in which carrier adheres to non-image areas of the photosensitive drum (carrier adhesion) tends to be suppressed compared to when the absolute value of Vback is increased.

[0033] Note that the charging potential Vd of the photosensitive drum 1 has a dark decay. Therefore, the charging potential Vd immediately after the charging bias is applied to the photosensitive drum 1 and the charging potential Vd at the time when the charged position of the photosensitive drum 1 reaches the position facing the developing roller 44 due to the rotation of the photosensitive drum 1 are different values.

[0034] The first embodiment is concerned with a phenomenon (fogging phenomenon) occurring at the position where the photosensitive drum 1 faces the developing roller 44. For this reason, the charging potential Vd does not refer to the value of the charging potential Vd immediately after a charging bias is applied to the photosensitive drum 1, but refers to the value of the charging potential Vd at the time when the charged position of the photosensitive drum 1 reaches the position facing the developing roller 44 due to the rotation of the photosensitive drum 1. This also applies to other potentials such as the latent image potential V1 of the photosensitive drum 1.

[0035] (Conventional example) Before describing the sequence of the image forming operation (image creation operation) according to the first embodiment, the sequence of the image creation operation in a conventional example will be described with reference to Fig. 8. Fig. 8 shows the rotational drive of the developing roller 44 from during the image creation operation to the end of the image creation operation, the developing DC bias applied to the developing roller 44, the value of the charging potential Vd at the position where the photosensitive drum 1 faces the developing roller 44, and a timing chart in the conventional example.

[0036] 8, during image formation, a charging bias is applied to the charging roller 2 by a high-voltage power supply (charging bias application means), and the photosensitive drum 1 is uniformly charged (Vd=-900V) at the position facing the developing roller 44. In addition, a developing DC bias (Vdc=-740V) is applied to the developing roller 44 by the high-voltage power supply (developing bias application means). The charging potential Vd and the developing DC bias Vdc of the photosensitive drum 1 are in a stable state, and the fogging potential difference Vback at this time is 160V.

[0037] When the image creation operation (image formation) is completed, the rotational drive of the developing roller 44 begins to stop and the rotational speed of the developing roller 44 begins to decelerate, but the fog removal potential difference Vback (=160 V) at this time remains the same value as during image formation.

[0038] Then, after the rotation speed of the developing roller 44 becomes zero (after the developing roller drive stop point), the charging bias to the charging roller 2 by the high-voltage power supply (charging bias application means) starts to stop (the absolute value of the charging bias to the charging roller 2 starts to decrease uniformly). When the position where the charging bias of the photosensitive drum 1 starts to stop due to the rotation of the photosensitive drum 1 reaches the position opposite the developing roller 44, the developing DC bias to the developing roller 44 by the high-voltage power supply (developing bias application means) starts to stop.

[0039] In the conventional operation, the carrier adhesion amount and the fog toner amount were measured when the absolute value of Vback was changed to 60V, 110V, 160V, and 210V. In the conventional operation, the carrier adhesion amount and the fog toner amount were measured when the absolute value of Vback during image formation was changed. The results are shown in Table 1. In addition, in the conventional operation, the absolute value of Vback was changed during the period from when the rotation speed of the developing roller 44 started to be decelerated from the speed during image formation to when the rotation drive of the developing roller 44 stopped. The results of measuring the carrier adhesion amount and the fog toner amount at this time are shown in Table 2. Note that the period from when the rotation speed of the developing roller 44 started to be decelerated from the speed during image formation to when the rotation drive of the developing roller 44 stopped means the period from when the rotation drive of the developing roller 44 started to be stopped to when the rotation speed of the developing roller 44 becomes zero.

[0040] Regarding the carrier adhesion items in Tables 1 and 2, "◯" indicates that the degree of carrier adhesion is at a level that is acceptable for image quality, and "×" indicates that the degree of carrier adhesion is at a level that is unacceptable for image quality. Regarding the fog toner items in Tables 1 and 2, "◯" indicates that the degree of fog toner is at a level that is acceptable for image quality, and "×" indicates that the degree of fog toner is at a level that is unacceptable for image quality. Note that an unacceptable level for image quality means that image defects have occurred.

[0041] [Table 1]

[0042] [Table 2]

[0043] In this experiment, the image forming apparatus 100 was used to stop the operation during the image formation of a solid white image (i.e., an image with an image ratio of 0%), and the carrier and fog toner adhering to the photosensitive drum 1 were collected with tape. The amount of carrier adhesion was measured by counting the number of carrier particles in an area of ​​3 cm x 3 cm, and the number of carrier particles was counted by 1 cm. 2 The number of carrier particles adhering per unit area was calculated. The amount of fog toner was measured by measuring the density using an X-Rite 500 color reflection densitometer manufactured by X-Rite Corporation.

[0044] During image formation, when Vback is 210V or more, the degree of carrier adhesion becomes a level that is unacceptable for image quality. In contrast, during the period from when the rotation speed of the developing roller 44 starts to be decelerated from the speed during image formation until the rotation speed of the developing roller 44 becomes zero, when Vback is 160V or more, the degree of carrier adhesion becomes a level that is unacceptable for image quality. On the other hand, regarding the fog toner, during image formation, when Vback is 110V or less, the degree of fog toner becomes a level that is unacceptable for image quality. In contrast, during the period from when the rotation speed of the developing roller 44 starts to be decelerated from the speed during image formation until the rotation speed of the developing roller 44 becomes zero, when Vback is 60V or less, the degree of fog toner becomes a level that is unacceptable for image quality. From the above results, it can be seen that the optimal Vback at which image defects due to carrier adhesion and fog toner do not occur is different between during image formation and the period from when the rotation speed of the developing roller 44 starts to be decelerated from the speed during image formation until the rotation speed of the developing roller 44 becomes zero.

[0045] Next, the sequence of the image forming operation (image creation operation) in the first embodiment will be described with reference to Fig. 3. Fig. 3 shows the rotational drive of the developing roller 44 from during the image creation operation to the end of the image creation operation, the developing DC bias applied to the developing roller 44, the value of the charging potential Vd at the position where the photosensitive drum 1 faces the developing roller 44, and a timing chart in the first embodiment.

[0046] 3, during image formation, a charging bias is applied to the charging roller 2 by a high-voltage power supply (charging bias application means), and the photosensitive drum 1 is uniformly charged (Vd=-900V) at the position facing the developing roller 44. In addition, a developing DC bias (Vdc=-740V) is applied to the developing roller 44 by a high-voltage power supply (developing bias application means). The charging potential Vd and the developing DC bias Vdc of the photosensitive drum 1 are in a stable state, and the fogging potential difference Vback (imaging Vback) at this time is 160V.

[0047] When the image formation operation is completed, the charging bias to the charging roller 2 is changed and set so that Vd=-850V when the photosensitive drum 1 is in a position facing the developing roller 44. After the photosensitive drum 1 reaches Vd=-850V when the photosensitive drum 1 is in a position facing the developing roller 44, the rotational speed of the developing roller 44 starts to be decelerated, and the fogging potential difference Vback at this time is 110V. In addition, in FIG. 3, Vback during the period from when the rotational speed of the developing roller 44 starts to be decelerated from the speed during image formation until the rotational speed of the developing roller 44 becomes zero is indicated as "Vback at stop".

[0048] After the rotational drive of the developing roller 44 stops (i.e., after the rotational speed of the developing roller 44 becomes zero), the high-voltage power supply (charging bias application means) starts to stop applying the charging bias to the charging roller 2 (the absolute value of the charging bias to the charging roller 2 starts to decrease uniformly). Then, when the position where the charging bias application means started to stop applying the charging bias to the photosensitive drum 1 reaches the opposing position to the developing roller 44 due to the rotation of the photosensitive drum 1, the developing bias application means starts to stop applying the developing DC bias to the developing roller 44.

[0049] 3, during the period from when the rotation speed of the developing roller 44 starts to be decelerated from the speed during image formation until the rotation speed of the developing roller 44 becomes zero, Vback (stop Vback) is set to 110 V, thereby suppressing carrier adhesion. Also, during image formation, Vback (imaging Vback) is set to 160 V, thereby suppressing fog toner and carrier adhesion during image formation.

[0050] In the first embodiment described above, the stop time Vback is set to be smaller than the image formation Vback. According to the first embodiment, it is possible to suppress the carrier adhesion during the period from when the rotation speed of the developing roller 44 starts to be decelerated from the speed during image formation until the rotation speed of the developing roller 44 becomes zero, while suppressing the fog toner during image formation.

[0051] 3, when changing from the imaging Vback to the stop time Vback, an example is described in which the charging DC bias is changed while keeping the developing DC bias (Vdc=-740V) to the developing roller 44 constant, but this is not limiting. As long as the stop time Vback satisfies the relationship that it is smaller than the imaging Vback, a modified example in which the developing DC bias is also changed in addition to changing the charging DC bias may be used.

[0052] [Second embodiment] Next, a second embodiment will be described. The basic configuration of the second embodiment is the same as that of the first embodiment. Therefore, elements having substantially the same or corresponding functions and configurations as those of the first embodiment are given the same reference numerals, and detailed descriptions are omitted, and only the components unique to the second embodiment will be described in detail.

[0053] The sequence of the image forming operation (image creation operation) in the second embodiment will be described with reference to Fig. 4. Fig. 4 shows the rotational drive of the developing roller 44 from during the image creation operation to the end of the image creation operation, the developing DC bias applied to the developing roller 44, the value of the charging potential Vd at the position where the photosensitive drum 1 faces the developing roller 44, and a timing chart in the second embodiment.

[0054] In the first embodiment described above, the rotational drive of the developing roller 44 starts to be decelerated after the photosensitive drum 1 reaches Vd=-850V (after Vback reaches 110V) at the position facing the developing roller 44. However, if the rotational drive of the developing roller 44 starts to be decelerated immediately after the photosensitive drum 1 reaches Vd=-850V at the position facing the developing roller 44, there is a possibility that the rotational speed of the developing roller 44 will be changed in a state in which the potential of the photosensitive drum 1 is not sufficiently stable. In such a state, the rotational speed of the developing roller 44 is not controlled to the optimal Vback for suppressing carrier adhesion and fog toner, so there is a risk of carrier adhesion and fog toner occurring.

[0055] On the other hand, after the margin time until the charging potential Vd of the photosensitive drum 1 becomes stable has elapsed (about 100 msec in the second embodiment), the potential of the photosensitive drum 1 becomes sufficiently stable. For this reason, it is preferable to start decelerating the rotational drive of the developing roller 44 after 100 msec has elapsed since the charging potential of the photosensitive drum 1 after Vback has been changed to 110 V reaches the opposing position of the developing roller 44. In other words, after the image formation is completed, the charging position of the photosensitive drum 1 to which the charging bias is applied so that the surface potential of the photosensitive drum 1 becomes Vd=-850 V reaches the position where the photosensitive drum 1 faces the developing roller 44. It is preferable to start decelerating the rotational speed of the developing roller 44 from the speed during image formation within 100 msec or more from the time of this arrival and until the photosensitive drum 1 makes one rotation from the time of the arrival.

[0056] On the other hand, from the viewpoint of productivity, it is preferable to perform the stopping operation after image formation in a short time. Therefore, after the charged potential of the photosensitive drum 1 after changing Vback to 110V reaches the opposing position of the developing roller 44, the rotational drive of the developing roller 44 starts to be decelerated at least until the photosensitive drum 1 rotates once (216 msec in the second embodiment). This prevents the timing of starting to decelerate the rotational drive of the developing roller 44 (the start point of stopping the drive of the developing roller 44) from being delayed more than necessary, thereby suppressing a decrease in productivity.

[0057] 4, in the second embodiment, the time t from when the charged potential Vd of the photosensitive drum 1 after Vback is changed to 110V reaches the opposing position of the developing roller 44 until the rotational drive of the developing roller 44 starts to be decelerated is set as follows: That is, the time t is controlled to be 100 msec or more, calculated from the time when the charged potential of the photosensitive drum 1 after Vback is changed to 110V reaches the opposing position of the developing roller 44, until the time required for the photosensitive drum 1 to make one rotation. Note that in FIG. 4, the time when the charged potential of the photosensitive drum 1 after Vback is changed to 110V reaches the opposing position of the developing roller 44 is indicated as the "end point of change of drum potential at the opposing position of the developing roller".

[0058] In the second embodiment, after image formation is completed, the charging position of the photosensitive drum 1, to which a charging bias is applied so that the surface potential of the photosensitive drum 1 becomes Vd=-850V, reaches a position where the photosensitive drum 1 faces the developing roller 44. The drive motor is controlled so that the rotational speed of the developing roller 44 starts to decelerate from the speed during image formation within 100 msec or more from the time of this arrival and until the photosensitive drum 1 rotates once from the time of the arrival.

[0059] As a result, in the second embodiment, the timing at which the rotational drive of the developing roller 44 starts to be decelerated (the point at which the driving of the developing roller 44 starts to be stopped) is not delayed more than necessary, and therefore a decrease in productivity can be suppressed. Also, in the second embodiment, similarly to the first embodiment, it is possible to suppress the carrier adhesion during the period from when the rotational speed of the developing roller 44 starts to be decelerated from the speed during image formation until the rotational speed of the developing roller 44 becomes zero, while suppressing the fog toner during image formation.

[0060] [Third embodiment] Next, a third embodiment will be described. The basic configuration of the third embodiment is the same as that of the first embodiment. Therefore, elements having substantially the same or corresponding functions and configurations as those of the first embodiment are given the same reference numerals, and detailed descriptions are omitted, and only the components unique to the third embodiment will be described in detail.

[0061] The sequence of the image forming operation (image creation operation) in the third embodiment will be described with reference to Fig. 4. Fig. 5 shows the rotational drive of the developing roller 44 from during the image creation operation to the end of the image creation operation, the developing DC bias applied to the developing roller 44, the value of the charging potential Vd at the position where the photosensitive drum 1 faces the developing roller 44, and a timing chart in the third embodiment.

[0062] In the first embodiment described above, when the image formation operation is completed, the charging potential Vd of the photoconductor drum 1 during image formation is changed from the first charging potential (Vd1=-900V) to the second charging potential (Vd2=-850V). However, if a step occurs in the charging potential on the photoconductor drum 1 due to the charging potential Vd of the photoconductor drum 1 being changed in a short period of time, there is a risk of carrier adhesion or toner fogging occurring at the position on the photoconductor drum 1 where the charging potential is changed.

[0063] 5, Vback during the period from when the image formation operation is completed until the rotational drive of the developing roller 44 starts to decelerate is set as follows. That is, Vback during this period is controlled to a value different from Vback1 during image formation and Vback2 during the period from when the rotational speed of the developing roller 44 is decelerated from the speed during image formation until the rotational speed of the developing roller 44 becomes zero. It is preferable that Vback during the period from when the image formation operation is completed until the rotational drive of the developing roller 44 starts to decelerate is set to be equal to or higher than Vback1 during the period from when the rotational drive of the developing roller 44 starts until it reaches the speed during image formation, and equal to or lower than Vback2 during image formation.

[0064] In the example of FIG. 5, Vback during the period from the end of the image forming operation to the start of deceleration of the rotational drive of the developing roller 44 is achieved by changing the charging potential Vd of the photosensitive drum 1 while keeping the development DC bias Vdc to the developing roller 44 constant. The absolute value of Vback during the period from the end of the image forming operation to the start of deceleration of the rotational drive of the developing roller 44 is set to be greater than the absolute value of Vback at rest and smaller than the absolute value of the image forming Vback. Note that the Vback at rest refers to Vback during the period from the start of deceleration of the rotational speed of the developing roller 44 from the speed during image formation to the time when the rotational speed of the developing roller 44 becomes zero. Also, the image forming Vback refers to Vback during image formation (after the start point of the image forming operation).

[0065] As a result, in the third embodiment, the step of the charging potential Vd on the photosensitive drum 1 can be reduced, and carrier adhesion and fog toner can be suppressed. Also, in the third embodiment, similar to the first embodiment, carrier adhesion can be suppressed during the period from when the rotation speed of the developing roller 44 starts to be decelerated from the speed during image formation until the rotation speed of the developing roller 44 becomes zero, while fog toner can be suppressed during image formation.

[0066] [Fourth embodiment] Next, a fourth embodiment will be described. The basic configuration of the fourth embodiment is the same as that of the first embodiment. Therefore, elements having substantially the same or corresponding functions and configurations as those of the first embodiment are given the same reference numerals, and detailed descriptions are omitted, and only the components unique to the fourth embodiment will be described in detail.

[0067] The sequence of the image forming operation (image creation operation) in the fourth embodiment will be described with reference to Fig. 6. Fig. 6 shows the rotational drive of the developing roller 44 from during the image creation operation to the end of the image creation operation, the developing DC bias applied to the developing roller 44, the value of the charging potential Vd at the position where the photosensitive drum 1 faces the developing roller 44, and a timing chart in the fourth embodiment.

[0068] In the first embodiment described above, Vback is controlled to be constant during the period from when the rotation speed of the developing roller 44 starts to be decelerated from the speed during image formation until the rotation speed of the developing roller 44 becomes zero. However, the optimal value of Vback for carrier adhesion and fog toner varies depending on the rotation speed of the developing roller 44. In particular, immediately after the rotation drive of the developing roller 44 starts to be stopped, the rotation speed of the developing roller 44 is slower than during image formation, so Vback is smaller than the optimal value and there is a risk of fog toner being generated. Also, immediately before the rotation speed of the developing roller 44 becomes zero, Vback is larger than the optimal value and there is a risk of carrier adhesion being generated.

[0069] Therefore, in the fourth embodiment, as shown in FIG. 6, carrier adhesion and fogging toner are suppressed by controlling Vback according to the rotation speed of the developing roller 44 which is driven to rotate by a driving means (developing motor).

[0070] In the fourth embodiment, the same control as in the first embodiment is performed for the operation from the end of the image forming operation to the start of stopping the rotational drive of the developing roller 44. Therefore, a description of the operation from the end of the image forming operation to the start of stopping the rotational drive of the developing roller 44 will be omitted, and a detailed description will be given of the operation from the start of decelerating the rotational speed of the developing roller 44 from the speed during image formation to the time when the rotational speed of the developing roller 44 becomes zero.

[0071] When the image forming operation is completed, the photosensitive drum 1 is in a stable state with the first charging potential (Vd1=-900V) and the developing DC bias (Vdc=-740V), and in this state, the rotational drive of the developing roller 44 is started to be stopped. At this time, Vback is 160V.

[0072] After the rotation speed of the developing roller 44 starts to be decelerated from the speed during image formation, the charging DC bias is changed stepwise so that the charging potential Vd of the photosensitive drum 1 changes from the first charging potential to the second charging potential as the rotation speed of the developing roller 44 decreases. Specifically, after the rotation speed of the developing roller 44 starts to be decelerated from the speed during image formation, the charging DC bias is changed stepwise so that the charging potential of the photosensitive drum 1 changes from -900V to -850V as the rotation speed of the developing roller 44 decreases. Then, Vback becomes 110V when the stepwise change of the charging DC bias is completed.

[0073] 6, the point in time when the rotational drive of the developing roller 44 is stopped (i.e., the point in time when the rotational speed of the developing roller 44 becomes zero) is indicated as the "developing roller drive stop point." Also, in FIG. 6, Vback after the rotational drive of the developing roller 44 is stopped is indicated as the "post-stop Vback."

[0074] In the fourth embodiment, by executing the control shown in Fig. 6, it is possible to control to an optimum Vback according to the rotation speed of the developing roller 44. Therefore, in the fourth embodiment, it is possible to suppress carrier adhesion and fog toner during the period from when the rotation drive of the developing roller 44 starts to stop until when the rotation drive of the developing roller 44 stops (the rotation speed of the developing roller 44 becomes zero). Also, in the fourth embodiment, like the first embodiment, it is possible to suppress carrier adhesion during the period from when the rotation speed of the developing roller 44 starts to decelerate from the speed during image formation until when the rotation speed of the developing roller 44 becomes zero, while suppressing fog toner during image formation.

[0075] [Fifth embodiment] Next, a fifth embodiment will be described. The basic configuration of the fifth embodiment is the same as that of the first embodiment. Therefore, elements having substantially the same or corresponding functions and configurations as those of the first embodiment are given the same reference numerals, and detailed descriptions are omitted, and only the components unique to the fifth embodiment will be described in detail.

[0076] The sequence of the image forming operation (image forming operation) in the fifth embodiment will be described with reference to Fig. 6. Fig. 7 shows the rotational drive of the developing roller 44 from during the image forming operation to the end of the image forming operation, the developing DC bias applied to the developing roller 44, the value of the charging potential Vd at the position where the photosensitive drum 1 faces the developing roller 44, and a timing chart in the fourth embodiment.

[0077] During image formation or when operating at the same Vback as during image formation, an error, paper jam, or the like may occur, and image forming apparatus 100 may be stopped in an emergency. During an emergency stop, it is of course necessary to stop the drive of various members including developing roller 44 and the application of voltage to various members. Furthermore, during an emergency stop, it is desirable to issue an instruction to stop the drive of various members and the application of voltage to various members as quickly as possible.

[0078] In the first to fourth embodiments described above, the operation is based on the assumption that the image forming operation is normally completed. In the first to fourth embodiments described above, the charging DC bias is varied in multiple steps to control Vback in order to suppress carrier adhesion and fog toner, while driving various members and applying voltage to various members are stopped.

[0079] On the other hand, in the fifth embodiment, in the event of an emergency stop, the driving of various members and the application of voltage to the various members are immediately stopped as shown in Fig. 7. By controlling in this way, it is possible to stop the image forming apparatus 100 in a short period of time compared to the case where the termination process is performed while varying the charging DC bias stepwise.

[0080] [Other embodiments] The present invention is not limited to the above-described embodiments, and various modifications (including organic combinations of the respective embodiments) are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0081] In the above embodiment, when Vback is changed at each timing, the charging DC bias is changed while the developing DC bias Vdc to the developing roller 44 is kept constant, but this is not limited to the above example. As long as Vback is changed so as to satisfy the magnitude relationship of Vback at each timing in the above embodiment, a modified example in which the developing DC bias is also changed in addition to changing the charging DC bias may be used.

[0082] In the above embodiment, the image forming apparatus 100 is configured to use the intermediate transfer belt 62 as shown in Fig. 1, but the present invention is not limited to this. It is also possible to apply the present invention to an image forming apparatus configured to transfer the image by directly contacting the recording medium with the photosensitive drum 1 in sequence. [Explanation of symbols]

[0083] 1 Photoconductor drum 2. Charging device 4. Developing device 44 Developing roller 45 Developer container 100 Image forming device

Claims

1. An image carrier; a developing device including a developer container that contains a developer containing a toner and a carrier, and a rotatable developer carrier that carries the developer to develop an electrostatic latent image formed on the image carrier; A driving means for rotating the developer carrying member; a developing bias applying means for applying a developing bias to the developer carrying member; a charging bias applying means for applying a charging bias to the image carrier; A control means for controlling the driving means; Equipped with an absolute value of a difference between a surface potential of the developer carrier to which the developing bias is applied by the developing bias application means and a surface potential of the image carrier to which the charging bias is applied by the charging bias application means at a position facing the developer carrier, during a period from when the rotational speed of the developer carrier starts to be decelerated from the rotational speed of the developer carrier during image formation until when the rotational speed of the developer carrier becomes zero after image formation is completed is smaller than an absolute value of a difference between a surface potential of the developer carrier to which the developing bias is applied by the developing bias application means and a surface potential of the image carrier to which the charging bias is applied by the charging bias application means at a position facing the developer carrier, during image formation; the charging bias applying means applies the charging bias to the image carrier during the image formation so that a surface potential of the image carrier at a position facing the developer carrier becomes a first potential, and applies the charging bias to the image carrier after the image formation is completed so that a surface potential of the image carrier at a position facing the developer carrier becomes a second potential different from the first potential; The control means controls the driving means so as to decelerate the rotation speed of the developer carrier from the rotation speed of the developer carrier during the image formation after the image formation is completed and after the surface potential of the image carrier at the opposing position facing the developer carrier becomes the second potential.

1. An image forming apparatus comprising:

2. The control means controls the drive means so as to decelerate the rotational speed of the developer carrier from the rotational speed of the developer carrier during the image formation after the image formation is completed and 100 msec has elapsed since the surface potential of the image carrier at the opposing position facing the developer carrier becomes the second potential.

2. The image forming apparatus according to claim 1,

3. The control means controls the drive means so as to decelerate the rotational speed of the developer carrier from the rotational speed of the developer carrier during the image formation, during the period from when the surface potential of the image carrier at the opposing position facing the developer carrier becomes the second potential until when the image carrier rotates once after the image formation is completed.

3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

4. The control means controls the drive means so as to decelerate the rotational speed of the developer carrier from the rotational speed of the developer carrier during the image formation, during a period from when the image formation is completed and when 216 msec has elapsed since the surface potential of the image carrier at the opposing position facing the developer carrier becomes the second potential.

3. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

5. A surface potential of the developer carrier to which the developing bias is applied by the developing bias application means during the period from when the image formation is completed and when the rotational speed of the developer carrier starts to be decelerated from the rotational speed of the developer carrier during the image formation until the rotational speed of the developer carrier becomes zero is the same as a surface potential of the developer carrier to which the developing bias is applied by the developing bias application means during the image formation.

5. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

Images