JP2009003271A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain an image defect caused by variance of vibration of a developing unit in a rotary developing device when performing changeover selecting operation of each developing unit to a developing position. <P>SOLUTION: The respective developing units 3 of the rotary developing device 2, at least one of which is unequally arranged with respect to a rotating holding body 4, have a developer holding body 5 rotationally moving while holding developer and capable of being brought into contact with/separated from an image holding body 1 via a position regulating member 6 at the developing position. A developing controller 10 has a changeover selecting means 11 for successively changing over and selecting the respective developing units 3 to be used to the developing position in a mode in which an image is developed to a visible image with compound color, and a changeover speed varying means 12 for varying the changeover speed of the respective developing units 3 by the changeover selecting means 11 in accordance with positional relation between the adjacent developing units 3 so that the changeover speed can be higher at least in the case a distance in a periphery direction between the adjacent developing units 3 is long compared with the case when it is short. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

A conventional image forming apparatus using a rotary developing device is widely known (see, for example, Patent Documents 1 to 3).
In Patent Documents 1 and 2, the operation timing of each developing device of the rotary developing device is defined, and the time from when the developing device is separated from the photoreceptor to the time when the next developing device comes into contact is determined as a plurality of developing devices. Techniques are disclosed for making them different between devices.
Patent Document 3 discloses a mode in which developing devices are unevenly arranged with respect to a rotating holder in a rotary developing device.

JP 2006-243193 A (Best Mode for Carrying Out the Invention, FIG. 9) JP 2006-243194 A (Best Mode for Carrying Out the Invention, FIG. 9) JP 2007-3961 A (Best Mode for Carrying Out the Invention, FIG. 2)

  The technical problem of the present invention is to suppress image defects caused by variations in the vibration of the developing device during the switching selection operation in the switching selection operation to each development position of the rotary developing device.

  According to the first aspect of the present invention, an image holding body that circulates and rotates at a predetermined speed and holds an electrostatic latent image, and the electrostatic latent image held on the image holding body is visualized in a single color or a composite color. In this state, a plurality of developing devices are mounted on a rotating holder that can rotate in one direction, and each developing device stops rotating at the developing position and a standby position other than the developing position, and the developing device stops rotating at the developing position. The image forming apparatus includes a rotary developing device that the developing device is driven to be developable, and a development control device that controls the rotary developing device, wherein each developing device of the rotary developing device is rotated. A developer holding body that is at least one unevenly arranged with respect to the holding body, and that holds the developer so as to rotate and can be brought into contact with and separated from the image holding body via a position regulating member at the development position. And the development control device visualizes the composite color The switching selection means for sequentially switching and selecting each developing device to be used with respect to the developing position in the mode, and at least adjacent to each other so as to be faster than when the circumferential distance between adjacent developing devices is long An image forming apparatus comprising: a switching speed varying unit configured to change a switching speed of each developing unit by the switching selection unit according to a positional relationship between the developing units.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the switching speed variable means changes the switching speed of each developing device so that the switching times of adjacent developing devices are substantially equal. There is provided an image forming apparatus.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the switching selection unit determines the timing of the separating operation of the developer holder relative to the image carrier when switching between adjacent developers is selected. The image forming apparatus is characterized in that they are set to be equal to each other.
According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the switching selection unit determines the contact operation timing of the developer holding body with respect to the image holding body when switching between adjacent developing devices is selected. The image forming apparatus is set after the transfer operation of the visible image by the developing device before switching is completed.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the switching selecting means determines the contact operation timing of the developer holding body with respect to the image holding body when switching between adjacent developing devices is selected. The image forming apparatus is set before the electrostatic latent image writing operation on the image forming apparatus.

According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, the switching speed varying means is configured so that the acceleration at the time of rising or falling is substantially equal when switching between the developing devices is selected. An image forming apparatus characterized by changing a switching speed.
According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, the switching speed variable means regulates the switching time of each developing device by adjusting the maximum value of the switching speed of each developing device. The image forming apparatus is characterized.
According to an eighth aspect of the present invention, in the image forming apparatus according to the first aspect, the switching speed variable means can change a switching speed of each developing device in accordance with a change in the rotational speed of the image carrier. An image forming apparatus characterized by the above.

According to the first aspect of the present invention, it is possible to suppress image defects caused by variations in the vibration of the developing device during the switching selection operation in the switching selection operation to each development position of the rotary developing device.
According to the second aspect of the present invention, the contact timing of the developer holding body with respect to the image holding body can be set substantially equal, and the variation in the vibration of the developing device can be reduced, so that the image defect caused by the variation in the vibration is more effective. Can be suppressed.
According to the third aspect of the present invention, it is possible to easily set the switching time of the developing device by the switching selection means. Further, the change point of the tracking pressure of the developing device with respect to the image holding member can be made equal between the respective colors, and the color shift at the time of transfer can be reduced.
According to the fourth aspect of the present invention, it is possible to reduce the influence on the transfer operation of the visible image due to the vibration of the developing device.

According to the fifth aspect of the present invention, it is possible to reduce the influence on the electrostatic latent image writing operation due to the vibration of the developing device.
According to the sixth aspect of the present invention, it is possible to suppress an increase in impact force due to the contact or separation operation of the developer holding member with respect to the image holding member.
According to the seventh aspect of the invention, the desired switching time can be easily defined by adjusting the maximum value of the switching speed.
According to the eighth aspect of the invention, it is possible to easily realize the optimization of the switching selection operation of each developing device in accordance with the change in the rotation speed of the image carrier.

First, an outline of an embodiment model of an image forming apparatus to which the present invention is applied will be described.
Outline of Embodiment Model FIG. 1 shows an outline of an embodiment model of an image forming apparatus.
In the same figure, the image forming apparatus is unidirectional so as to visualize the electrostatic latent image held by the image holding body 1 holding the electrostatic latent image and the electrostatic latent image held in the image holding body 1 in a single color or a composite color. rotation mounted a plurality of developing devices 3 (3 a to 3 d) to the rotary support 4 possible rotation stop at each of the developing devices 3 are developing position _{P 1} and the developing position _{P 1} other than the standby position _P 2 to P ₄ of the In addition, the developing device 3 includes a rotary developing device 2 that is driven to be developed in a state where the developing device 3 is stopped at the developing position P ₁ , and a development control device 10 that controls the rotary developing device 2. It is a thing.
Rotary developing device 2 of this type, a developing device 3 initial standby All of the developing device 3 is a developing position P ₁ the initial standby position so as not to face the when image formation job is not performed (not shown) It is designed to prevent unnecessary outflow of toner and carrier to the image carrier 1 and accumulation of developer, and to keep the developing performance of each developing device 3 good. Many.

In the present embodiment model, at least one of the developing devices 3 (3a to 3d) of the rotary developing device 2 (3a in FIG. 1) is unevenly arranged with respect to the rotating holder 4, and the developer. There has been a developing agent holding member 5 contactable spaced through the position regulating member 6 with respect to the image carrier 1 at a rotational moving and the developing position P ₁ is held. Reference numeral 7 denotes a developing container in which a developer is accommodated.
Here, as a factor that at least one of the developing devices 3 is unevenly arranged with respect to the rotation holder 4, for example, a developer supply container 8 for supplying developer to the rotation holder 4 is arranged, and The case where the capacity | capacitance of the developer supply container 8 differs according to the usage frequency of a developer is mentioned. In this case, for example, when the capacity of the developer supply container 8 attached to the developing device 3a is larger than the developer supply container 8 of the other developing devices 3 (3b to 3d), the installation space increases. Therefore, the circumferential distance β between the adjacent developing devices 3 (for example, 3a to 3d) becomes longer than the circumferential distance α between the other developing devices 3, and the developing devices 3 are unevenly arranged. It becomes.
Note that the number of the developing devices 3 that are unevenly arranged is not limited to one, and includes a plurality of cases.
Further, from the viewpoint of solving the technical problem of preventing vibration variation of the developing device 3 at the time of contact or separation, the developer holding body 5 is positioned relative to the image holding body 1 by a position regulating member 6 (tracking roll, etc.) It is assumed that contact and separation are possible via

In addition, the development control device 10 has a switching selection means 11 for sequentially switching and selecting each developing device 3 to be used for the developing position in a mode for visualizing a composite color, and at least a circumference between adjacent developing devices 3. The switching speed of each developing device 3 by the switching selection means 11 is changed from, for example, v _α to v _β in accordance with the positional relationship between the adjacent developing devices 3 so that the direction distance becomes longer when the direction distance is long. Any switching speed variable means 12 may be used.
Here, the “mode for visualizing with a composite color” in the switching selection means 11 is normally full color, but also includes, for example, a two-color mode including black.
Further, the switching selection means 11 realizes a series of switching selection operation processes of the developing device 3 and includes a contact / separation operation of the developer carrier at the development position in addition to the rotation operation of the rotation holding body 4.
Further, the switching speed variable means 12 changes the switching speed of each developing device 3 by the switching selection means 11, and the change mode is at least when the circumferential distance between adjacent developing devices 3 is long and short. It is necessary to adjust the switching time so that the switching time becomes substantially equal regardless of the positional relationship between the developing devices 3.

Further, as a preferable mode of the switching selection means 11, from the viewpoint of making the change point of the tracking pressure of the developing device 3 with respect to the image holding body 1 equal between the respective colors and reducing the color shift at the time of transfer, the adjacent development is performed. An example is an embodiment in which the timing of separating the developer holding body 5 with respect to the image holding body 1 at the time of selecting the switching of the developing device 3 is set equally among the developing devices 3.
In consideration of the influence on the transfer operation of the visible image, the switching selecting unit 11 determines the contact operation timing of the developer holding body 5 with respect to the image holding body 1 when switching between the adjacent developing devices 3 is selected. 1 is set after the transfer operation of the visible image by the developing device 3 before switching is completed.
Further, in consideration of the influence on the writing operation of the electrostatic latent image, the switching selection unit 11 determines the contact operation timing of the developer holding body 5 with respect to the image holding body 1 when switching between the adjacent developing devices 3 is selected. What is set before the operation of writing the electrostatic latent image on the holding body 1 is mentioned.

Further, as a preferable mode of the switching speed varying means 12, from the viewpoint of reducing the variation in vibration when switching the developing device 3 is selected, each developing device is set so that the switching times of the adjacent developing devices 3 are substantially equal. The thing which changes the switching speed of the device 3 is mentioned.
Further, as a method for shortening the switching time of the developing device 3, it is conceivable to set a large acceleration at the time of rising and falling when the developing device 3 is switched, but if this acceleration is increased, the developer retention is increased. Since there is a concern that the impact force associated with the contact or separation operation of the body 5 may increase, from the viewpoint of suppressing this, the switching speed varying means 12 is configured so that the acceleration at the time of rising or falling is switched between the developing devices 3. A mode in which the switching speed of each developing device 3 is changed so as to be substantially equal at the time of selection is preferable.
Furthermore, in order to shorten the switching time of the developing device 3 without increasing the acceleration as described above, the switching speed varying means 12 can adjust each developing device 3 by adjusting the maximum value of the switching speed. It is preferable to define the switching time of the device 3.
Further, since the switching selection operation time of the developing device 3 changes in accordance with the change in the rotation speed of the image carrier 1, the switching speed variable means 12 is used to make the switching selection operation of the developing device 3 smooth. It is preferable that the switching speed of each developing device 3 can be changed in accordance with a change in rotational speed of 1.

Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.
Embodiment 1
―Overall configuration of image forming device―
FIG. 2 shows Embodiment 1 of an image forming apparatus to which the present invention is applied.
In the figure, an image forming apparatus includes an image forming unit 21 using an electrophotographic method, a recording material supply unit 22 provided below the image forming unit 21 and supplying a recording material S to the image forming unit 21. And an image reading unit 23 provided on the image forming unit 21 for reading a document image.
In the present embodiment, the image forming unit 21 is an exposure for writing an electrostatic latent image, for example, an image carrier 30 such as a photoconductor, a charger 31 for charging the image carrier 30, and a charged image carrier 30. A device 32; a rotary developing device 40 that visualizes the electrostatic latent image formed on the image carrier 30 with, for example, a single-color or full-color toner; and a toner image on the image carrier 30 as a recording material. An intermediate transfer member 33 that holds the toner image on the intermediate transfer member 33 intermediately, a primary transfer unit 34 that primarily transfers the toner image on the image holding member 30 to the intermediate transfer member 33, and residual toner on the image carrier 30. A cleaning device 35 for cleaning, a secondary transfer device 36 for secondary transfer of the toner image on the intermediate transfer member 33 to the recording material S, and a fixing device 37 for fixing the toner image transferred on the recording material S It has.
Further, the image forming unit 21 is appropriately provided with a conveyance member (conveyance roll or conveyance belt) 38 capable of conveying the recording material S supplied from the recording material supply unit 22, and discharges the fixed recording material S. A recording material discharge receptacle 39 to be accommodated is disposed. Reference numeral 45 denotes an intermediate cleaning device that cleans residual toner on the intermediate transfer member 33.
Here, although the electrophotographic method is adopted in the present embodiment, the image holding body 30 may be any one that holds an electrostatic latent image and visualizes it with the rotary developing device 40. A dielectric or the like may be used, and an electrostatic latent image may be written on the dielectric by a writing device such as a charger or ions.
The recording material supply unit 22 includes a plurality of recording material containers 24 in which the recording material S is accommodated. The recording material S is sequentially fed out by a feeder 25 attached to the recording material container 24, and an appropriate number of the recording materials S are accommodated. The conveying member 26 supplies the image forming unit 21 with it.
Further, the image reading unit 23 reads a document on a document table 27 and converts the optical information into electronic information via a photoelectric conversion element 28. In FIG. 2, reference numeral 29 denotes a display for displaying various information.

Next, the rotary developing device 40 used in the present embodiment will be described in detail.
As shown in FIG. 3, the rotary developing device 40 includes a rotatable rotation holding body 41, and a plurality of developing devices 50 (specifically, 50 a to 50 d) are mounted on the rotation holding body 41. . Each of the developing devices 50 uses, for example, a two-component developer of four colors of black (K), yellow (Y), magenta (M), and cyan (C).
In particular, in the present embodiment, the rotary developing device 40 has a development position P ₁ as a setting position of each developing device 50, and a position opposite to the rotation direction of the rotary holder 41. The standby positions P _{2 to} P ₄ are set for each predetermined angle toward the front, and an initial standby position P ₀ is set so that none of the developing devices 50 faces the development position P ₁ when the rotary developing device 40 is not used. .

In particular, in the present embodiment, the developing devices 50 (50 a to 50 d) are arranged unevenly with respect to the rotation holder 41. Specifically, in this example, the black (K) developing device 50a is arranged at a position different from the other developing devices 50b to 50d, and between the black (K) developing device 50a and the yellow (Y) developing device 50b, The circumferential distance between the yellow (Y) developing unit 50b and the magenta (M) developing unit 50c and between the magenta (M) developing unit 50c and the cyan (C) developing unit 50d is α, and the cyan (C) developing unit 50d and black ( K) The circumferential distance between the developing devices 50a is set to β (> α).
Such uneven arrangement of the developing devices 50 (50a to 50d) depends on the size of the developing device 50 being different, and in this example, the developer of the black (K) developing device 50a that is frequently used. Since the replenishment container 80 is larger than the other developing devices 50b to 50d, the installation space for the black (K) developing device 50a is secured larger than that of the other developing devices 50b to 50d.

―Overall configuration of developer―
In this embodiment, the developing device 50, for example, as shown in FIGS. 4 and 5, the developer is accommodated to face the image carrier 30 at the developing position P ₁ comprising an open and color component toner and carrier And a roll-shaped developer holder 52 is rotatably disposed at a portion facing the opening of the developer container 51, and on the back side of the developer holder 52 of the developer container 51. Is configured such that a pair of agitating and conveying members 53 and 54 are rotatably arranged along the rotation axis direction of the developer holding member 52, and a partition plate 55 is provided in the developing container 51 positioned between the agitating and conveying members 53 and 54. The developer passage ports 56 and 57 are opened near both ends of the partition plate 55, and a developer circulation path 58 through which the developer conveyed by the agitating and conveying members 53 and 54 circulates through the passage ports 56 and 57. It is intended to secure The
Here, the developer holding body 52 is provided with a magnetic pole member 52b in which an appropriate number of magnetic poles are arranged inside a rotatable non-magnetic cylindrical body 52a. A layer thickness regulating member 59 that regulates the layer thickness of the developer conveyed to the area is disposed so as to face the gap.
The pair of agitating and conveying members 53 and 54 are, for example, provided with spiral blades 61 and 62 around the rotating shaft 60, and the agitating and conveying members 53 and 54 have the same helical blades 61 and 62. The developer is transported in the opposite direction when rotated in the direction.
Note that reverse spiral blades 63 and 64 are provided at both ends of the agitating and conveying members 53 and 54 so that the developer can be circulated and conveyed through the passage ports 56 and 57.

―Developer supply mechanism―
Further, in the present embodiment, the developing device 50 includes a developer supply mechanism 70. In this embodiment, since a developer discharge mechanism to be described later is added, toner containing a carrier is used as the replenishment developer.
The developer supply mechanism 70 is provided with a developer supply path 71 on the side away from the developer holder 52 along the longitudinal direction of the developer circulation path 58 of the developer container 51, and along the developer supply path 71. The developer conveying member 72 is rotatably arranged, and a delivery port 73 between the developer supply path 71 and the developer circulation path 58 is provided on the downstream side of the developer conveying direction by the developer conveying member 72. It is what I did.
The developer conveying member 72 is provided with a spiral blade 76 around the rotary shaft 75 in the same manner as the agitating / conveying members 53 and 54, and the rotating blade 41 rotates when the helical blade 76 is in a drive stopped state. Then, the developer can be moved in a direction away from the delivery port 73 in the developer supply path 71.
Furthermore, a developer supply port 74 is provided upstream of the developer supply path 71 in the developer transport direction, and a developer supply container 80 is connected to the developer supply port 74.
The developer supply container 80 has, for example, a cylindrical shape, and is divided into a storage chamber and a collection chamber. A spiral spring-shaped conveyance member is provided inside the storage chamber, and is connected via a developer supply port 74. Thus, the developer is supplied to the developer supply path 71.
In particular, in the present embodiment, the developer replenishment container 80 is set larger in the one attached to the black (K) developing device 50a than the one attached to the other developing devices 50b to 50d.

―Developer discharge mechanism―
In the present embodiment, the developing device 50 includes a developer discharge mechanism 90 that can discharge excess developer.
As shown in FIGS. 5 and 6A and 6B, the developer discharging mechanism 90 is a portion in which the stirring and conveying member 54 on the side away from the developer holding body 52 in the developer circulation path 58 is accommodated. And provided on the side wall of the developing container 51 facing the passage port 56.
The developer discharge mechanism 90 has a developer discharge port 91 opened at an appropriate position on the side wall of the developer container 51, and an open / close lid 92 is rotatably provided in the developer discharge port 91. The open / close lid 92 assists the developer discharging operation when the developer in the developer circulation path 58 increases and the amount of the developer exceeds a predetermined amount. When the position of the toner is changed, the developer is closed to prevent excessive discharge of the developer.

―Position control mechanism―
Further, in this embodiment, the developing unit 50, as shown in FIG. 7, the developing position P ₁ in the image carrier 30 and the relative positional relationship between the developer carrier 52 is able position restricting position restricting mechanism 95 It has.
The position restricting mechanism 95 is provided with, for example, position restricting rolls 96 and 97 coaxially at both ends of the developer holding member 52, and the image holding member 30 is brought into contact with the image holding member 30. The gap g between the developer holding body 52 and the developer holding body 52 is regulated to be constant.
One position restricting roll 96 is pressed and urged toward the image carrier 30 by an urging member 98 such as a spring that presses the entire developing device 50, and the other position restricting roll 97 is interposed via the drive transmission mechanism 103. Thus, when a rotational driving force acts on the developer holding body 52, the developer holding body 52 is pressed and urged toward the image holding body 30 in the direction of the rotational driving force.

―Control system―
FIG. 8 shows a control system for the rotary developing device according to this embodiment.
In the figure, reference numeral 100 denotes a control device composed of a microcomputer or the like, which performs drive control and density control of the rotary developing device 40.
Target drive control of the rotary developing device 40, developer carrier 52 of the drive motor 102, the developing unit 50 at the developing position P ₁ for driving the rotary holder 41 via a drive transmission mechanism 101 such as a gear, stirred A driving motor 104 that drives the conveying members 53 and 54 and the developer conveying member 72 via a drive transmission mechanism 103 such as a gear or a clutch. The image forming mode (monochromatic black mode (BW mode), full color from the operation unit 110 is provided. The control device 100 receives an instruction signal such as a mode (FC mode) and a signal from the rotation detector 120 that detects that the rotation holder 41 has rotated, and performs predetermined drive control on the drive motors 102 and 104. A signal is sent out. As the rotation detector 120, an encoder for detecting the rotation operation of the rotation holder 41 is used.
Further, the density control of the rotary developing device 40 is performed by, for example, a toner in the developer from a density detector (for example, using a detector that detects magnetic permeability) 130 that can detect the toner density of the developer in the developer 50. The density is grasped, and the developer supply operation is controlled based on the density.
The density detection method is not limited to the method of directly detecting from the developer in the developing device 50. For example, as shown by a two-dot chain line in FIG. 8, an image density detection pattern is formed on the image carrier 30. May be detected by the optical density detector 131.

―Switching selection control of rotary developing device―
In particular, in the present embodiment, the control device 100 executes the switching selection control process shown in FIG. 9 for the rotary developing device 40.
In the figure, the control device 100 first checks the image forming mode and determines a switching selection procedure for the developing devices 50 (50a to 50d).
For example, in the full color mode, it is determined to switch and select the developing device 50 (50a to 50d) in the order of yellow (Y) → magenta (M) → cyan (C) → black (K).
Then, the control device 100 determines whether or not the switching selection is cyan (C) → black (K). If the selection is cyan (C) → black (K), both developing units 50 (50d, 50d, Since the circumferential distance between 50a) is β (> α), the switching speed is set to v _β (> v _α ).
On the other hand, when the switching selection is other than cyan (C) → black (K), yellow (Y) → magenta (M), magenta (M) → cyan (C), cyan (C) → black (K) In this case, since the circumferential distance between the developing devices 50 is α, the switching speed is set to v _α .

At this time, the setting of the switching speeds v _α and v _β between the developing devices 50 is performed as follows.
For example, as shown in FIG. 10, assuming that the previous image forming process with a predetermined color (for example, yellow (Y)) is performed, the image forming process uses an exposure device 32 (abbreviated as ROS in FIG. 10). Image writing processing is performed, and thereafter development processing is performed by a yellow (Y) developing device 50b (abbreviated as Dev in FIG. 10) of the rotary developing device 40, and then the primary transfer device 34 (in FIG. 10). The primary transfer process is abbreviated as 1stBTR).
When the development processing by the yellow (Y) developing device 50b is completed, the rotary holding body 41 of the rotary developing device (abbreviated as “Rotary” in FIG. 10) 40 rotates, and the switching selection of the developing device 50 (in this example, yellow) (Y) Development unit 50b → Magenta (M) switching to development unit 50c) is performed.
At this time, the switching speed of the developing device 50 is set to v _α , and this switching speed v _α is selected so as to satisfy at least the following limiting conditions.

The limiting condition here is that the end point of the switching selection operation from the yellow (Y) developing device 50b to the magenta (M) developing device 50c is after the completion of the primary transfer operation by the primary transfer device 34, and the yellow ( Y) When the switching selection operation from the developing device 50b to the magenta (M) developing device 50c ends, image writing processing by the exposure device 32 (abbreviated as ROS in FIG. 10) in the next color image forming process is started. It must be the previous OK area.
That is, if you do not satisfy the former Restriction (Figure 10 indicated by a solid line), the following magenta (M) developing unit 50c is in contact via the position regulating mechanism 95 on the image carrier 30 at the developing position P ₁ Sometimes, the developing device 50b vibrates, and this vibration affects the primary transfer processing by the primary transfer device 34 of the yellow (Y), and there is a concern that horizontal stripes as image defects may occur.
On the other hand, when the latter restriction condition is not satisfied (indicated by a dotted line in FIG. 10), vibration at the time of switching selection of the next magenta (M) developing device 50c causes image writing processing by the exposure device 32 of magenta (M). There is a concern that impulse banding as an image defect occurs.

When the previous image forming process is cyan (C) and the subsequent image forming process is black (K), switching selection of the developing device 50 (in this example, the cyan (C) developing device 50d → black is selected). (K) Selection of switching to the developing device 50a) is performed.
At this time, the switching speed of the developing device 50 is set to v _β instead of v _α , and this switching speed v _β is also selected so as to satisfy at least the following limiting conditions.
The limiting condition in this case is that the end point of the switching selection operation from the cyan (C) developing device 50d to the black (K) developing device 50a is after the completion of the primary transfer operation by the primary transfer device 34, and cyan ( C) When the switching selection operation from the developing device 50d to the black (K) developing device 50a ends, the image writing process by the exposure device 32 (abbreviated as ROS in FIG. 10) in the next color image forming process is started. It must be the previous OK area.
If such a switching selection of the developing device 50 is performed, assuming that the switching speed is used as v _α , the circumferential distance between the developing devices 50 becomes longer from α to β. The switching time increases, and in particular, there is a high concern that the image writing process by the exposure device 32 in the next color image forming process will be affected.

The rotation speed of the image carrier 30 may be uniform or may vary depending on the image forming mode.
For example, when the rotation speed of the image carrier 30 is changed in the image forming mode (for example, the full color standard mode or the full color high image quality mode), the image forming process time of each color changes and the time between the image forming processes also changes. Can happen.
At this time, the switching speeds v _α and v _{β of the} developing device 50 satisfy the above-described limiting conditions under the condition that the rotation speed of the image carrier 30 (image forming process speed: corresponding to the process speed) is changed according to the image forming mode. If not, it is preferable to variably set the switching speeds v _α and v _β according to the process speed change so as to satisfy the restriction condition.

-Operation timing when selecting developer switching-
In this embodiment, switching selection operation of the developing unit 50, developing process is separated developing device 50 has been completed from the developing position P _1, the developing device 50 the position regulating mechanism then used in the developing position P ₁ 95 Is placed in contact with each other.
At this time, as shown in FIG. 11A, the switching selection operation of the developing device 50 is performed in a standby state in which power can be supplied in advance after the drive motor 102 in FIG. 8 is turned on (Rotary_Mot_ON in FIG. 11). Rotary_Mot_Hi_Low is set to Hi level, and after the writing process of the image (previous Image) in the previous image forming process is completed, a timing control signal for specifying the switching selection operation (Rotary_Mot_Clock in FIG. 11) is sent. Is done.
In the present embodiment, the timing control signal (Rotary_Mot_Clock in FIG. 11) is selected when any one of the developing devices 50 is selected (black (K) → yellow (Y), yellow (Y) → magenta (M), magenta. (M) → Cyan (C) and Cyan (C) → Black (K) have the same drive start timing and have substantially the same drive time (switching time).
For this reason, in the present embodiment, the separation and contact operation timings to the image carrier 30 associated with the switching selection operation of each developing device 50 (50a to 50d) are substantially equal, and the vibration of the developing device 50 is correspondingly increased. Variations are reduced, and image misregistration due to each image forming process is suppressed to a small extent.

On the other hand, in the comparative form of FIG. 11B, the timing control signal (Rotary_Mot_Clock of FIG. 11) is selected during the switching selection operation of the developing device 50 other than cyan (C) → black (K). The drive start timing is the same and the drive time (switching time) is substantially the same. However, in the switching selection operation of the developing device 50 of cyan (C) → black (K), another switching selection is performed. The drive start timing is delayed as compared with the time of operation, and the drive time (switching time) is substantially the same.
In such a comparison mode, the driving start timing in the switching selection operation of the developing device 50 of cyan (C) → black (K) is only X compared to the switching selection operation of the developing device 50 between other colors. Due to the delay, the change point of the tracking pressure of the developing device 50 with respect to the image holding body 30 between the colors at the time of separation is different, and there is a concern that the color shift at the time of the transfer operation may be increased accordingly. There is a concern that the timing of the contact operation with the image carrier 30 is deviated, and the variation in the vibration of the developing device 50 is increased accordingly, and the positional deviation of the image in each image forming process is increased.

Here, the switching selection operation of each developing device in the present embodiment is summarized as shown in FIG.
In the drawing, the switching selection operation of the developing device 50 is different between the developing device 50 of cyan (C) → black (K) and the developing devices 50 of other colors.
In particular, between the developing devices 50 of colors other than cyan (C) → black (K), the circumferential distance is α, the switching speed is v _α , and the switching time is t _α . At this time, the acceleration at the rise and fall (when switching is selected) in the switching selection operation between the developing devices 50 is a constant value m, and the maximum value of the switching speed is v _α (max).
On the other hand, between cyan (C) → black (K) developing devices 50 (50d, 50a), the circumferential distance is β (> α), and the switching speed is v _β (> t _α ). The switching time is approximately t _α ± Δt, similar to that between the developing devices 50 of other colors. At this time, although the switching speed _vβ is set to be high, the acceleration at the time of rising and falling (when switching is selected) in the switching selection operation between the developing devices 50 remains the constant value m, and the switching speed is The maximum value is v _β (max). Therefore, even if the switching speed is set faster from t _alpha to v _beta, since the acceleration is not increased, a situation in which impact force at the time of contact operation of the developing device 50 to the image carrier 30 is increased unnecessarily not, It is possible to easily set the high-speed switching speed v _β using the maximum value v _β (max) of the switching speed.

It is explanatory drawing which shows the outline | summary of embodiment model of the image forming apparatus with which this invention is applied. 1 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to a first embodiment. 2 is an explanatory diagram illustrating an outline of a rotary developing device of the image forming apparatus according to Embodiment 1. FIG. It is explanatory drawing which shows the detail of the developing device mounted in the rotary developing apparatus shown in FIG. FIG. 5 is a cross-sectional explanatory view taken along line VV in FIG. 4. (A) is explanatory drawing which shows the detail of the developer discharge port vicinity of Embodiment 1, (b) is the principal part perspective view. FIG. 5 is a sectional view taken along line VII-VII in FIG. 4. FIG. 3 is an explanatory diagram showing a control system (drive control system, density control system) used in the first embodiment. FIG. 9 is a flowchart showing a switching selection control process of the rotary developing device employed in the control system of FIG. 8. FIG. 10 is an explanatory diagram showing switching selection operation timing of each developing device of the rotary developing device. (A) is a timing chart showing a switching selection operation of each developing device in Embodiment 1, and (b) is a timing chart showing a switching selection operation of each developing device in a comparative embodiment. FIG. 10 is an explanatory diagram summarizing an example of switching selection operation of each developing device of the rotary developing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image holding body, 2 ... Rotating developing device, 3 (3a-3d) ... Developing device, 4 ... Rotating holding body, 5 ... Developer holding body, 6 ... Position control member, 7 ... Developing container, 8 ... Developing supply container, 10 ... developing control unit, 11 ... switching selection means, 12 ... switching speed changing means, P 1 _... developing _{position, P} 2 to P 4 _... waiting position

Claims (8)

An image carrier that circulates and rotates at a predetermined speed and holds an electrostatic latent image;
A plurality of developing devices are mounted on a rotary holding body that can be rotated in one direction so that the electrostatic latent image held on the image holding body is visualized as a single color or a composite color. A rotary developing device that stops rotating at a standby position other than the developing position, and that the developing device is driven to be developable in a state where the developing device stops rotating at the developing position;
An image forming apparatus including a development control device that controls the rotary development device,
At least one of the developing devices of the rotary developing device is unevenly arranged with respect to the rotating holder,
A developer holding body that holds the developer, rotates, and can be brought into contact with and separated from the image holding body via a position regulating member at the development position;
The development control device includes a switching selection means for sequentially switching and selecting each developing device to be used for the development position in a mode for visualizing a composite color.
Switching that changes the switching speed of each developing device by the switching selection means according to the positional relationship between the adjacent developing devices so that at least the circumferential distance between adjacent developing devices is faster than when the circumferential distance is short An image forming apparatus comprising: a speed varying unit. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the switching speed changing means changes a switching speed of each developing device so that a switching time of adjacent developing devices becomes substantially equal. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the switching selecting unit sets the operation timing of separating the developer holding member from the image holding member when switching between adjacent developing devices is set equally among the developing devices. The image forming apparatus according to claim 1.
The switching selection means sets the contact operation timing of the developer holding member with respect to the image holding member when switching between adjacent developing devices is selected after the transfer operation of the visible image by the developing device before switching on the image holding member is completed. An image forming apparatus. The image forming apparatus according to claim 1.
The switching selection means sets the contact operation timing of the developer holding body with respect to the image holding body when switching between adjacent developing devices is selected before the electrostatic latent image writing operation to the image holding body. Image forming apparatus. The image forming apparatus according to claim 1.
The switching speed varying means changes the switching speed of each developing device so that the acceleration at the time of rising or falling becomes substantially equal when switching of each developing device is selected. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the switching speed variable means regulates a switching time of each developing device by adjusting a maximum value of a switching speed of each developing device. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the switching speed variable means is capable of changing a switching speed of each developing device in accordance with a change in the rotational speed of the image carrier.

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