JP2001005284A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of simply preventing the change of image density caused by that a developer is stuck onto the surface of a developer carrying member of a developing machine without reducing productivity even when the developing machine not used for the developing is merely passed through a photoreceptor. SOLUTION: This image forming device is provided with a control means 8 for controlling potential relation between the developer carrying member 42 of the developing machine which is not used for the developing and the photoreceptor 1 so as to obtain potential difference generating an electric field in such a direction that the developer G is moved to the photoreceptor 1 side when the developing machine 40 (Y, M and C) of this developing device 4 which is not used for the developing is merely passed through the photoreceptor 1 and moved. Or it is provided with a control means 8 setting the carrying member 42 of the developing machine which is not used for developing in a floating state by electrically cutting it from a bias power source device when it is merely passed through the photoreceptor and moved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, or a multifunction machine using an electrophotographic method, and more particularly, to an image forming apparatus which sequentially moves through a developing position facing a photosensitive member. When developing an electrostatic latent image formed on a photoreceptor by electrophotography, only a developing device used for the development is exposed to light. The present invention relates to an image forming apparatus of a type used while facing a body.

[0002]

2. Description of the Related Art For example, as shown in FIG. 13, an image forming apparatus of this type is arranged so as to rotate in a certain direction (direction of arrow C in FIG. 13) in the vicinity of a drum-shaped photosensitive member 100. A developer transport member to which a single-color developer of black (B), yellow (Y), magenta (M), and cyan (C) is accommodated, respectively, and the developer is supplied with a developing bias. (A rotating developing sleeve or the like) 120 to transport and supply four developing machines 140B, 1 to a developing position DE facing the photoconductor 100.
An apparatus provided with a rotary movement type (rotary) developing apparatus 130 equipped with 40Y, 140M, and 140C is known.

The developing device 130 includes a rotating support 110
Is rotated intermittently (as if skipped) by a predetermined angle in the direction of arrow C, whereby a plurality of developing machines 14
0 (B, Y, M, C) sequentially moves through the developing position DE facing the photoconductor 100, and the photoconductor 100
Only the developing device 140 used for developing the electrostatic latent image formed at the developing position is switched and moved to face the photoconductor 100 at the developing position DE. Further, as a developing method of the developing device 130, for example, a two-component developer composed of a toner and a carrier is held in a spike shape on the development carrier member 120 to form a magnetic brush. Contact type two-component magnetic brush developing method in which development is performed while the surface of the photoconductor 1 is in contact with the surface of the photoconductor 1 is employed. Each developing device 140 indicated by a solid line in the drawing indicates a state in which the developing device 140 is at a standby position where none of the developing devices is opposed to the photoconductor 100, that is, at a home position HP during non-development. The machine 140a is in a state in which it is located at a developing position DE facing the photoconductor 100 due to the rotation of the rotary support 120.

When a color image is formed by such an image forming apparatus, usually, an electrostatic latent image for each color component of black, yellow, magenta, or cyan is sequentially formed on the photosensitive member 100, and each of the electrostatic latent images is formed. The rotation of the rotating support 110 in synchronization with the timing of forming the electrostatic latent image causes the four developing machines 140B, 140Y, 140M, and 140C to rotate.
Are sequentially moved from the home position HP to the developing position DE opposed to the photoconductor 100 in this order and stopped, and the electrostatic latent image for each color component is developed with the corresponding developer of each color. . That is, each developing machine 1
When the magnetic brush formed on the surface of the developer conveying member 120 rotating at 40 moves while contacting the photoconductor 100, the developer (toner T) on the magnetic brush is exposed to the developer conveying member 120 by the developing bias. The electrostatic field is electrostatically transferred to and adhered to the electrostatic latent image portion of the photoreceptor 100 by an electric field formed between the photoconductor 100 and the electrostatic latent image. Then, when the development by the last developing device 140C is completed, each developing device 14 of the developing device 130 (
0) is to return to the home position HP again by the rotation of the rotary support 110. Further, when a black-and-white image is formed, when a black electrostatic latent image is formed on the photoconductor 100, only the developing device 140 </ b> B containing the black developer is located at the developing position E facing the photoconductor 100. The electrostatic latent image is moved and stopped, and the electrostatic latent image is developed with a black developer. When the development is completed, the developing device 140B of the developing device 130 returns to the home position HP again. (See FIG. 4).

[0005]

Incidentally, in an image forming apparatus having such a developing device 130, a developing device 140 (Y, M, M) which is not used for development, such as when forming a black and white image, is used. In the case where C) simply passes through the photoconductor 100 without stopping, the surface corresponding to the portion passing through the photoconductor 100 in the developer conveying member 130 of the developing machine 140 (Y, M, C) not used for the development. The problem is that the developer (strictly speaking, toner) adheres directly so as to concentrate on the surface, and the density of the image portion corresponding to the portion of the developer conveying member 120 to which the developer adheres changes in the subsequent image formation. There is.

This phenomenon is presumed to occur as follows. First, as shown in FIG. 14, when a black-and-white image is formed, when development by the developing device 140B is completed as described above, the developing device 140B operates to return to the home position HP again. The developing device 140 (Y, M, C) that is not used for development is the rotating support 1
With the rotation of arrow 10 in the direction of arrow C, it simply passes through photoconductor 100. At this time, the surface of the photosensitive member 1 is in a state of being uniformly charged to charging potential V _H by the charging device, while the developing machine 140 (Y passing through the photosensitive member 1,
Each of the developer carrying members 120 of M and C) hardly rotates, and is in a state where only the developing bias is applied. Therefore, for example, a case where reversal development is performed using a negatively charged developer will be described. As shown in FIGS. 14 and 15, the charging potential V _H of the photosensitive member 100 and the potential of the developing bias are from the relationship between V _D, negatively charged developer G (toner T) moves through the magnetic brush (magnetic brush-like carrier Cr) by receiving an electric field in a direction to move to the developer conveying member 120 side And finally adheres to the surface of the transport member 120. Ta in FIG. 15 indicates the developer conveying member 120.
Toner attached to the surface of the toner. In this case, if the developer conveying member 120 is sufficiently rotated after the developer (Ta) is adhered and before the next developing step arrives, the developer adhered to the surface of the conveying member 120 Is gradually removed by the process of forming a new magnetic brush. However, in practice, the developer conveying member 120 hardly rotates and is used for the next developing process. This is likely to remain in a state of being attached to the surface of the conveying member 120. This tendency becomes more remarkable as the speed is higher.

As shown in FIG. 16, the portion W2 of the developer conveying member 120 to which the developer adheres has a potential equal to that of the other portion W1 by the charge (α) of the adhered developer. , W3, apparently higher (V _D +
α). As a result, when the portion W2 to which the developer has been attached is subjected to the next developing step as it is, the potential (V _D + α) at the portion W2 of the developer transport member 120 and the electrostatic latent image on the photosensitive member 1 Potential difference ΔV2 from the latent image potential (V _I )
Is different from the potential difference ΔV1 in the normal case, the amount of developer (the amount of adhesion) for developing the electrostatic latent image is also different, and the density of the image changes (in this example, the density is lower). It is presumed to be darker).

Japanese Patent Application Laid-Open No. Hei 9-80846 discloses that, in order to prevent an abnormal image caused by toner adhering to the developing sleeve, the image forming operation is interrupted when the developing machine is switched and the developing sleeve is stopped. A method of cleaning the developing sleeve by rotating the developing sleeve in two directions (a direction for removing the developer from the developing position during non-development) is described. However, in this method, the image forming operation must be temporarily stopped. There is a disadvantage that productivity is reduced because it is not necessary.

Accordingly, the present invention has been made in view of the above-mentioned problems, and even if a developing machine not used for development simply passes through the photoreceptor, the developer of the developing machine may be used. It is an object of the present invention to provide an image forming apparatus capable of easily preventing a change in image density caused by a developer adhering to a surface of a conveying member without reducing productivity.

[0010]

According to a first aspect of the present invention, there is provided a photosensitive member which is uniformly charged by a charging device and then exposed by an image exposure device to form an electrostatic latent image; A developer for developing the electrostatic latent image on the photoconductor is accommodated, and the developer is transported and supplied to a developing position facing the photoconductor by a developer transport member to which a developing bias is applied from a bias power supply. A developing device having a plurality of developing devices, wherein the developing devices sequentially move through a developing position facing the photoconductor, and only the developing devices used for development are provided. Assuming that the image forming apparatus is stopped at the developing position and arranged to face the photoconductor, when a developing machine not used for development of the developing device simply passes through the photoconductor and moves, Developer conveying member of developing machine An image forming apparatus in which the developer is provided with a control means for controlling an electric field in a direction to shift to the photoconductor side is potential difference so as to generate a potential relationship between the photoconductor.

The control means in the image forming apparatus according to the first invention is not particularly limited as long as it can execute the control for obtaining the above-mentioned potential difference.
For example, at least a portion of the photoreceptor corresponding to an area where a developer conveying member of a developing machine not used for development passes oppositely, has an electrostatic potential having a potential such that the developer is electrostatically transferred to the photoreceptor side. The image exposure apparatus is controlled so as to form a latent image.

[0012] The control means may include: a portion corresponding to a region of the photoconductor at which a developer conveying member of a developing machine not used for development passes oppositely; The charging device may be controlled so that the charging device is charged to such a potential as to be shifted.

Further, the control means may include an electric field for generating an electric field in a direction in which the developer is transferred to the photoconductor while the developer conveying member of the developing machine not used for the development passes at least facing the photoconductor. The bias power supply may be controlled so as to apply a developing bias composed of a potential.

A second invention which can achieve the above object is:
In the image forming apparatus based on the first aspect of the present invention, when a developing device not used for development of the developing device simply moves through the photosensitive member and moves, a developer conveying member of the developing device is electrically connected to a bias power supply device. This is an image forming apparatus provided with a control unit that cuts off in a floating state.

According to the first aspect of the present invention, even if a developing machine not used for development simply passes through the photoreceptor without stopping, the developer conveying member of the developing machine not used for the development is exposed to light. Since an electric field is generated between the developer and the body in a direction in which the developer moves to the photoconductor side, the developer does not adhere to at least the surface of the developer conveying member of the developing machine during the passage. However, in this case, the developer may adhere to the photoconductor side. According to the second aspect, the developer transport member of the developing device not used for the development is electrically disconnected from the bias power supply device to be in a floating state. Is greatly reduced (to a level at which fluctuations in image density do not pose a practical problem). Furthermore, the second aspect of the invention is particularly effective when applying a superimposed DC voltage to a DC voltage as a developing bias.

In the image forming apparatus according to the first and second aspects of the present invention, the developing device includes a plurality of developing machines mounted on a rotating support, and the developing device is rotated so that the developing position is opposed to the photosensitive member. In addition to the so-called rotary movement (rotary) method, a plurality of developing machines can be mounted on a linearly movable support and moved directly to the development position facing the photoreceptor by directly moving the support. A so-called linear movement (tandem) system can also be used.

As a developing method of the developing device, a contact type two-component magnetic brush developing method is usually applied, but a known one-component developing method may be applied. Further, as a developer conveying member in the developing machine, for example, when a contact type two-component magnetic brush developing method is applied, a developing roll composed of a cylindrical developing sleeve and a magnet disposed inside the cylinder is used. used. When a one-component developing method is applied, a developing roll mainly composed of a single body is used. As the developing bias, only a DC voltage may be applied, or a voltage obtained by superimposing an AC voltage on a DC voltage may be applied.

[0018]

[First Embodiment] FIG. 1 is a schematic diagram showing an embodiment of a color image forming apparatus to which the present invention is applied. In the figure, reference numeral 1 denotes a drum-shaped photoconductor arranged to rotate in the direction of arrow A, 2 denotes a charging device for uniformly charging the surface of the photoconductor 1, and 3 denotes a charged photoconductor 1
An image exposure device for exposing a light image corresponding to image information on the surface to form an electrostatic latent image, and a plurality of developing devices for developing the electrostatic latent image formed on the photoconductor 1 with a developer of a predetermined color A transfer device for electrostatically transferring a toner image formed on the photoconductor 1 by development onto the recording sheet P; and 6, a toner remaining on the surface of the photoconductor 1 after the transfer. It is a cleaning device for removing the like. The image exposure device 3 drives the semiconductor laser based on each image signal output through an image processing device that performs necessary processing on image information input from a document reading device or an external connection device (not shown) and holds the processed image information. Then, an optical writing scanning device (ROS) is used in which laser light LB emitted from the semiconductor laser is guided to the surface of the photoconductor 1 by a predetermined optical system to perform exposure scanning.

Reference numeral 10 denotes a transfer drum which rotates in the direction of arrow B in contact with the photosensitive member 1 at the transfer position, adsorbs the recording sheet P on the surface, and conveys the recording sheet P to the transfer position;
Denotes a sheet suction device including a charger 11a and a suction roll 11b for electrostatically sucking the recording sheet P supplied from a sheet feeding unit such as a sheet feeding tray (not shown) onto the surface of the transfer drum 10. A peeling device 13 for removing the recording sheet P from the surface of the transfer drum 11 while removing the charge, a charge removing device 13 for removing the charge of the transfer drum 11 after removing the recording sheet P, and a sticker 14 for attaching to the surface of the transfer drum 11 after the charge removal. This is a drum cleaning device for removing kimono.
Reference numeral 15 denotes a registration roll that feeds the recording sheet P to the sheet suction device 11 at a predetermined sheet feeding timing.

Further, reference numeral 7 denotes a fixing device having a heating roll 70 and a pressure roll 71 which rotate in a state where they are pressed against each other and allow the recording sheet P after the completion of transfer to pass through the pressed portion. This is a transport belt device that transports the peeled recording sheet P to the transfer device 7. Note that a dotted line with an arrow in the drawing indicates a main transport path of the recording sheet P.

As shown in FIGS. 1 and 2, the developing device 4 includes a two-component developer G of a single color of black, yellow, magenta, and cyan on a cylindrical rotating frame 41 which rotates in the direction of arrow C. (Developer composed of negatively charged toner T and positively charged magnetic carrier Cr)
Are stored in the developing units 40B, 40Y, 4
0M and 40C are mounted at equal intervals in this order (so as to be arranged at positions every 90 degrees).

These developing units 40B, 40Y, 40
Each of M and 40C employs a contact type two-component magnetic brush developing method. In order to hold and transport the contained two-component developer G in a spike shape, a magnet 42b is provided inside. A developing roller 42 as a developer conveying member composed of a cylindrical developing sleeve 42a is rotatably disposed by the developing sleeve 42a. In FIG. 2, reference numeral 43 denotes a screw-shaped developer supply rotating body (such as an auger) that circulates and conveys the stored developer G so as to pass near the rear of the developing roll 42 while stirring the developer G; A layer thickness regulating member 45 for regulating the height of the magnetic brush composed of the developer G formed on the surface of the developing sleeve 42 (developing sleeve 42a), and 45 is a new developer G transferred from a developer replenishing device (not shown). Is a replenishing member for replenishing the developing unit 40 with the developing unit 40, and a discharging member 46 for transferring the recovered used developer to a discharging unit when performing trickle development for recovering the used and overflowing developer G. .

In the non-developing state, the developing device 4 is located at a home position HP which is a standby position where none of the four developing units 40 face the photoconductor 1 (see FIG. 4A). By rotating the rotating frame 41 intermittently by a predetermined angle in the direction of arrow C,
The developing unit 40 (actually, the developing roll 42) is sequentially moved to the developing position DE facing the photoreceptor 1 and stopped, and the developing operation is executed at the developing position DE. Further, when each developing unit 40 is moved to the developing position DE and performs a developing operation, a predetermined developing bias is applied to the developing sleeve 42a from a bias power supply 49, and the developing roller 42 (developing sleeve 42). 42a) and the like are rotated. As the developing bias, at least a DC voltage is applied, but a DC voltage on which an AC voltage is superimposed is applied as necessary.

With respect to the application of the developing bias, an electrode terminal 48 for a contact connected to a bias power supply 49 is disposed near the developing position DE so as to pass through the developing sleeve 42a. When 42a moves to the developing position DE, it comes into contact with the electrode terminal 48 so as to be in an applicable state.
On the other hand, with respect to the rotation of the developing roll 40 and the like, a transmission gear that rotates while being connected to a rotation drive source such as an electric motor (not shown) is disposed near the development position DE. When the developing roller 42 (gear of the developing sleeve) moves to the developing position DE, the developing roller 42 is in a rotatable state by meshing.

FIG. 3 shows operation timings concerning the application of the developing bias and the rotation of the developing roll during the development of the developing unit 40. In other words, the developing unit 40 used for development is
When the developing sleeve 42a moves toward the developing position DE with the rotation in the direction of arrow C, first, a part of the developing sleeve 42a comes into contact with the contact electrode terminal 48, and then a developing bias is applied from the bias power supply 49. Further, the gear of the developing sleeve 42a meshes with the transmission gear in parallel with the contact operation with the electrode terminal 48, and the rotation drive source starts to rotate after the application of the developing bias. . Then, when the developing frame reaches the developing position DE, the rotation of the rotating frame 41 is stopped and the developing frame becomes ready for development. Also,
When the developing operation is completed, the rotating frame 41 starts to rotate again in the direction of the arrow C. First, the rotation drive source for rotating the developing sleeve 42a is stopped, and then the application of the developing bias is completed. Then, with the rotation of the rotating frame 41, the gear of the developing sleeve 42a is released from the meshing state with the transmission gear, and the developing sleeve 4a is released.
A part of 2a is released from the contact state with the electrode terminal 48. Reference numeral 41-O in FIG. 3 indicates the center of rotation of the rotating frame 41.

As shown in FIGS. 1 and 5, a developing unit 40 not used for development in a mode for forming a black and white image or the like simply passes through the photoreceptor 1 as shown in FIGS. In this case, the toner T of the developer G adheres to a portion of the photoreceptor 1 corresponding to a region through which the developing unit 40 (strictly speaking, the developing roll 42) that is not used for the development passes. Controller 8 that controls the operation of image exposure device 3 so as to form an electrostatic latent image (countermeasure latent image) In for preventing image formation.
Is connected to That is, this controller 8
When the case where a developing unit not used for development simply passes through the photoconductor arrives, the control of operating the image exposure device 3 to form the above-described countermeasure latent image In on the photoconductor 1 is executed. . In this case, the potential V _N of the countermeasure latent image In
Is in a state where a developing bias is applied during development.
The potential is set to such an extent that the toner T in the magnetic brush formed on the developing sleeve 42a of the developing roll 42 is at least electrostatically transferred to the photoconductor 1 side.

Next, the operation of the color image forming apparatus will be described.

First, when a full-color image is formed, the photosensitive member 1 rotating in the direction of arrow A is uniformly charged to a predetermined charging potential by the charging device 2, and then image exposure is performed by the image exposure device 3. Thus, an electrostatic latent image for black is formed.
Next, the rotating frame 41 of the developing device 4 rotates in the direction of arrow C in synchronization with the timing of forming the electrostatic latent image so that the developing unit 40B containing the black developer G faces the photosensitive member 1 from the home position HP. Development position DE
And stop (FIGS. 1 and 2).

The developing unit 40B that is moved to the development position DE is the principle as described above, together with a developing bias of a predetermined potential V _D from a bias power source 49 is applied to the developing sleeve 42a of the developing roller,
The developing sleeve 42a and the like start rotating in the direction indicated by the arrow in the figure. Thus, the developing position D facing the photoconductor 1 while forming a magnetic brush on the surface of the developing sleeve 42B in which the black developer G in the developing unit 40B rotates.
The toner T of the developer G is electrostatically transferred and adheres to the electrostatic latent image portion of the photoconductor 1 at the developing position DE at the developing position DE. As a result, a black toner image in which the electrostatic latent image is developed is formed on the photoconductor 1.

The black toner image on the photoreceptor 1 is conveyed to the transfer position facing the transfer device 5 by the rotation of the photoreceptor 1 and the recording sheet P supplied at this timing.
Is attracted to the transfer drum 10 rotating in the direction of arrow B by the sheet attracting device 11 and is conveyed to the transfer position.
As a result, the toner image on the photoconductor 1 is electrostatically transferred onto the recording sheet P by the operation of the transfer device 5.

When the transfer is completed, the toner remaining on the surface of the photosensitive member 1 is removed by the cleaning device 6, and the process proceeds to a step of forming an electrostatic latent image of the next color component. On the other hand, the recording sheet P on which the black toner image has been transferred is circulated while being attracted to the transfer drum 10, and is again conveyed to the transfer position in accordance with the transfer of the next toner image.

When the formation and transfer of the black toner image are completed in this way, the subsequent formation and development of an electrostatic latent image for each of the yellow, cyan and magenta color components and the development of the toner image obtained by the development are performed. The transfer is repeated in a similar manner. In particular, in the development,
As the rotating frame 41 in the developing device 4 rotates in the direction of arrow C, the developing position DE facing the photoconductor 1 is obtained.
, The yellow developing unit 40Y, the cyan developing unit 40C, and the magenta developing unit 40C.
C is moved and switched one by one in this order. The yellow, cyan, and magenta toner images formed on the photoreceptor 1 by the development are multiplex-transferred so as to be successively superimposed on the recording sheet P on the transfer drum 10 at the transfer position.

When the final color (cyan) toner image is transferred onto the recording sheet P, the recording sheet P is peeled off from the transfer drum 1 by the action of the peeling device 12, and then sent to the fixing device 7. Fixation is made. This allows
A fixed full-color image is formed on the recording sheet P. Further, in the developing device 4, when the development of the final color (cyan) is completed, the rotating frame 41 rotates in the direction of arrow C and returns to the home position HP again. Incidentally, when this full-color image is formed, the four developing units 40B, 40Y, 40M, and 40C start from the home position HP in this order, are sequentially moved to the developing position DE, and then return to the home position HP as they are. Therefore, the developing unit 40 not used for development does not simply pass through the photoconductor 1.

Next, the case of forming a black and white image will be described.

First, as shown in FIG. 4 and FIG.
Is charged by the charging device 2 at a predetermined charging potential V _H (for example, −70
After being uniformly charged to 0V), the electrostatic latent image I _B for black made from the image exposure is performed by the image exposure device 3 latent image potential V _I (e.g. -300 V) is formed. In the developing device 4, the rotation of the rotating frame 41 in the direction of arrow C causes the black developing unit 40B to move to the home position HP.
From FIG. 4A, the photosensitive member 1 is moved to a developing position DE (FIG. 4B).

[0036] Then, the electrostatic latent image I _B, in a state where the developing bias is applied having a predetermined potential V _D on the developing sleeve 42B of the developing unit 40B (e.g. -560V), black developer G (negative The toner is developed by the neutrally charged toner T). As described above, the black toner image formed on the photoreceptor 1 by this development is transferred to the recording sheet P attracted to the transfer drum 10 and conveyed, and then fixed by the fixing device 7. Thereby, a black and white image is formed.

On the other hand, when the development by the developing unit 40B is completed, the developing device 4 rotates the rotating frame 41 in the direction of arrow C, thereby causing the developing unit 40B to rotate.
Is returned to the home position HP. At this time, the developing units 40Y, 40M,
0C will simply pass through the photoreceptor 1 without stopping in this order (FIG. 4c). The rotating frame 4 at this time
1, the higher the speed, the faster the machine,
The speed at which each of the developing units 40 passes through the photoconductor 1 also increases. Thus, when the developing sleeve 42 of each developing unit 40 passes through the developing position DE, unlike the case of normal development, the developing sleeve 42 passes with almost no rotation.

In this image forming apparatus, when the developing unit 40B returns to the home position HP,
The image exposure device 3 is operated under the control of the controller 8, and as shown in FIG. 5, a predetermined potential V is applied to a portion of the photoreceptor 1 where the developing units 40Y, 40M, and 40C face each other. _A countermeasure latent image In of _N (for example, -500 V) is formed. In this example, the latent image In is placed on a portion of the photoconductor 1 which is an area from before the arrival of the developing unit 40Y until the passage of the developing unit 40C is completed.
Are formed continuously.

Thus, the photosensitive member 1 at the portion where the countermeasure latent image In is formed and the developing unit 4 not used for development.
As shown schematically in FIG. 6, an electric field En is formed between each of the developing sleeves 0Y, 40M, and 40C in such a direction that the negatively charged toner T moves to the photoconductor 1 side. As a result, the toner T on each of the developing sleeves 42 does not move to and adhere to the surface of each of the developing sleeves 42 when passing through the photoconductor 1. Also,
At this time, a part of the toner T may be electrostatically transferred and attached to the latent image In portion of the photoconductor 1 due to a potential relationship between the two, and the toner T is removed by the cleaning device 6. Therefore, there is no adverse effect on the subsequent image formation.

Therefore, even when the next image formation using the developing units 40Y, 40M, and 40C is performed after forming the black-and-white image, the image obtained by developing the developing units 40Y, 40M, and 40C is obtained. No concentration fluctuation occurs. For this reason, even if the next image formation may be performed continuously after the black and white image formation mode, it is possible to perform good image formation without density fluctuation.

[Embodiment 2] FIG. 7 is a schematic view of a main part showing another embodiment of a color image forming apparatus to which the present invention is applied (this is partially omitted from FIG. 1). 8 and 11). The color image forming apparatus according to the second embodiment differs from the first embodiment in that a charging device 2 (actually, a power supply controller thereof) is used instead of the image exposure device 3 as a control target of the controller 8 in the first embodiment. Has the same configuration as the image forming apparatus according to the first embodiment.

That is, the controller 8 in the second embodiment operates the charging device 2 when the case where the developing unit 40 not used for development simply passes through the photosensitive member 1 arrives, and the site corresponding to regions where the developing unit 40 is not used in the development passes opposite, and executes control to charge the charge potential V _M for different measures the potential V _H of the normal uniform charging. In this case, a countermeasure for the charge potential V _M, in a state where the developing bias during development is applied, electrostatically the toner T is at least a photosensitive member 1 side in the magnetic brush formed on the developing sleeve 42a of the developing roller 42 The potential is set to such a level as to make a transition. The potential V _M can be set to the same value as the latent image potential V _N of the countermeasure latent image In, but may be set to a different value.

In the case of this image forming apparatus, when the monochrome image forming mode is selected, the developing unit 40B
When the controller returns to the home position HP, the controller 8
, The charging device 2 is operated, and as shown in FIG. 5, for example, the developing units 40Y, 40M,
40C is charged to the charging potential for site measures a region passing opposite V _N (e.g. -500 V. This same as the potential V _M of the previous latent image an In). Thus, as in the first embodiment, when the toner T on each developing sleeve 42 in the developing unit 40 not used for development passes through the photoconductor 1, the toner T moves to the surface side of each developing sleeve 42. Does not adhere. Therefore, even if the next image formation may be continuously performed after the black and white image formation mode, it is possible to perform good image formation without density fluctuation.

[Embodiment 3] FIG. 8 is a schematic diagram showing a main part of another embodiment of a color image forming apparatus to which the present invention is applied. The color image forming apparatus according to the third embodiment includes:
The configuration is the same as that of the image forming apparatus according to the first embodiment except that a bias power supply 49 is used as a control target of the controller 8 in the first embodiment.

That is, the controller 8 according to the third embodiment operates the bias power supply 49 when the case where the developing unit 40 not used for development simply passes through the photoconductor 1 arrives, and operates the bias power supply 49. while developing unit 40 that is not used for development passes opposite, the potential V _D of the regular developing bias is to perform the control of applying the developing bias for measures of different potentials V _F. In this case, the potential V _F of the developing bias, the degree of potential negatively charged toner T is the electric field direction to shift at least the photosensitive member 1 side is generated in the developing magnetic brush formed on the sleeve 42a of the developing roller 42 Is set.

In the image forming apparatus, when the developing unit 40B returns to the home position HP when the monochrome image forming mode is selected, the bias power supply 49 is operated under the control of the controller 8, and as shown in FIG. The electric potential V is applied to each of the developing sleeves 42 only while the developing units 40Y, 40M, and 40C of the body 1 pass oppositely.
_F (for example, −720 V) is applied as a countermeasure developing bias. Thus, the photosensitive member 1 and the developing units 40Y,
10M and the developing sleeves 42C of FIG.
As shown schematically, an electric field Ef is formed in such a direction that the negatively charged toner T moves to the photoconductor 1 side. As a result, the toner T on each developing sleeve 42 is When passing through the developing sleeves 42
It does not move to and adhere to the surface of the surface. Therefore,
Even if the next image formation is performed continuously after the black and white image formation mode, it is possible to perform good image formation without density fluctuation.

[Embodiment 4] FIG. 11 is a schematic diagram showing a main part of another embodiment of a color image forming apparatus to which the present invention is applied. In the color image forming apparatus according to the fourth embodiment, as a control target of the controller 8 in the first embodiment, an electrode terminal 48 for a contact and a bias power supply (circuit)
The configuration is the same as that of the image forming apparatus according to the first embodiment, except that a switch means 50 for turning on and off the electrical connection between 49 is employed.

That is, the controller 8 according to the fourth embodiment allows the developing unit 40 that is not used for development to be used when the developing unit 40 not used for development simply passes through the photosensitive member 1 to arrive. Only during the opposing passage, the switch means 50 is operated to turn off the connection, and the developing sleeves 42 are electrically disconnected from the bias power supply 49 so as to be in a floating state. As such a switch means 50, for example, a means such as a relay is used.

In this image forming apparatus, when the developing unit 40B returns to the home position HP when the black and white image forming mode is selected, the switch means 50 is operated under the control of the controller 8, and as shown in FIG. Only when the developing units 40Y, 40M, and 40C of the body 1 face each other, the connection is turned off, and each developing sleeve 42 is connected to the bias power supply 4.
9 is electrically disconnected. As a result, the developing sleeves 42 are kept in a floating state, so that the toner T of each developing sleeve 42 does not move inside the magnetic brush toward the surface of the sleeve. This is particularly effective when a DC voltage on which an AC voltage is superimposed is applied as a developing bias.
Is suppressed to a very small amount even if it adheres to the photoconductor 1 (the toner adhered to the photoconductor 1 is thereafter removed by the cleaning device 6). Therefore, even if the next image formation may be continuously performed after the black and white image formation mode, it is possible to perform good image formation without density fluctuation.

[Other Embodiments] In the first to fourth embodiments, three developing units 40 which do not use latent image formation, charging, application of a developing bias, or electrical disconnection for development as countermeasures are used.
Although the case where Y, 40M, and 40C are executed in a state where they are continuous only at the part or between the photoconductors 1 is illustrated, the processing is intermittently performed only at the part or between the respective developing units where the developing sleeves 42 pass. You may do so. The developing unit not used for development is
Although the case where the monochrome image forming mode is selected is exemplified as a case where the image is simply passed, the present invention is not limited to this.
In addition, for example, three developing units 40Y, 40
In the case where image formation is performed using M and 40C (in this case, the development unit 40B is not used for development and simply passes so as to face the photoconductor), the same control by the controller 8 is performed. Can be set to Furthermore, although the case where reversal development is performed has been described as an example, a similar effect can be obtained in the case where regular development is performed. In addition, an image forming apparatus to which the present invention can be applied uses an intermediate transfer member instead of the transfer drum 10, and once transfers the toner image on the photoconductor 1 to the intermediate transfer member and then secondary-transfers the image onto the recording sheet P. The image forming apparatus may employ an intermediate transfer method.

[0051]

As described above, according to the image forming apparatus of the present invention, each control operation by the above-described control means is executed even if a developing machine not used for development simply passes through the photosensitive member. By simply doing so, it is possible to easily prevent a change in image density caused by the developer adhering to the surface of the developer conveying member of the developing machine. Further, when executing each control operation by this control means, it is not necessary to interrupt the image forming process operation, so that the above-mentioned effect can be obtained without lowering the productivity. Is also possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an image forming apparatus according to a first embodiment.

FIG. 2 is an enlarged explanatory view of a developing device.

FIG. 3 is an explanatory diagram showing a configuration example of operation timings regarding application of a developing bias and rotation of a developing sleeve of a developing unit.

FIG. 4 is an explanatory diagram showing a moving state and a position of a developing device when forming a black and white image.

FIG. 5 is an explanatory diagram showing each operation state over time when a black and white image is formed in the first embodiment (2).

FIG. 6 is an enlarged explanatory diagram illustrating a state of a developer and the like when a developer conveying member of a developing machine not used for development passes through a photoconductor in the first embodiment (2).

FIG. 7 is a schematic diagram illustrating a main part of an image forming apparatus according to a second embodiment;

FIG. 8 is a schematic diagram illustrating a main part of an image forming apparatus according to a third embodiment;

FIG. 9 is an explanatory diagram showing each operation state over time when a monochrome image is formed in the third embodiment.

FIG. 10 is an enlarged explanatory diagram illustrating a state of a developer and the like when a developer conveying member of a developing machine not used for development passes through a photoconductor in a third embodiment.

FIG. 11 is a schematic diagram illustrating a main part of an image forming apparatus according to a fourth embodiment;

12 is an explanatory diagram showing each operation state over time in forming a black and white image in Embodiment 4. FIG.

FIG. 13 is an explanatory diagram illustrating a main part of a conventional image forming apparatus including a developing device of a rotational movement type.

FIG. 14 is an explanatory diagram showing each operation state over time when forming a black-and-white image in the related art.

FIG. 15 is an enlarged explanatory view showing a state of a developer and the like when a developer conveying member of a developing machine not used for development passes through a photoconductor in a conventional technique.

FIG. 16 is a diagram for explaining a density fluctuation caused by a developer attached to a developer conveying member in the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor, 2 ... Charging device, 3 ... Image exposure device, 4 ... Developing device, 8 ... Controller (control means), 40 ... Developing unit (developing machine), 42 ... Developing sleeve (developer conveying member), 49 ... Bias power supply, G ... Developer, DE ... Development position.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AD16 BB24 BB33 BB34 BB63 2H073 BA02 BA04 BA09 BA13 BA41 CA03 CA22 2H077 AD06 AD35 AD36 BA03 BA08 DB08 DB12 DB13 DB14 EA01 GA13

Claims (5)

[Claims] 1. A photoconductor on which an electrostatic latent image is formed by being uniformly charged by a charging device and then exposed by an image exposure device, and a developer for developing the electrostatic latent image on the photoconductor. A developing device that includes a plurality of developing machines that are housed and transport the developer to a developing position facing the photoconductor by a developer transport member to which a developing bias is applied from a bias power supply, and supply the developer. The apparatus is arranged such that the plurality of developing machines sequentially move through the developing position facing the photoconductor, and only the developing machine used for development stops at the developing position and faces the photoconductor. In the image forming apparatus, when a developing device that is not used for developing the developing device simply moves through the photoconductor, the potential relationship between the developer conveying member of the developing device and the photoconductor is determined by the developer. To move to the photoconductor side An image forming apparatus comprising an electric field is provided with control means for controlling so that the potential differences occurring in. 2. The control device according to claim 1, wherein the developer electrostatically transfers the developer to the photoconductor at least to a portion of the photoconductor corresponding to a region where a developer conveying member of a developing machine not used for development passes oppositely. 2. The image forming apparatus according to claim 1, wherein the image exposure apparatus is controlled so as to form an electrostatic latent image having a potential of the order. 3. The control means electrostatically transfers the developer to the photoconductor at least in a portion of the photoconductor corresponding to a region where a developer conveying member of a developing machine not used for development passes oppositely. 2. The image forming apparatus according to claim 1, wherein the charging device is controlled so as to be charged to about a potential. 4. The control means according to claim 1, wherein said developing means includes a developer conveying member which is not used for development, and at least a potential at which an electric field is generated in such a direction that said developer moves toward said photosensitive member while said developer carrying member passes at least facing said photosensitive member. 2. The image forming apparatus according to claim 1, wherein a bias power supply is controlled so as to apply a developing bias. 5. A photoconductor on which an electrostatic latent image is formed by being uniformly charged by a charging device and then exposed by an image exposure device, and a developer for developing the electrostatic latent image on the photoconductor. A developing device that includes a plurality of developing machines that are housed and transport the developer to a developing position facing the photoconductor by a developer transport member to which a developing bias is applied from a bias power supply, and supply the developer. The apparatus is arranged such that the plurality of developing machines sequentially move through the developing position facing the photoconductor, and only the developing machine used for development stops at the developing position and faces the photoconductor. In the image forming apparatus, when a developing device not used for developing the developing device simply moves through the photoconductor, the developer conveying member of the developing device is electrically disconnected from the bias power supply device. Floatin An image forming apparatus characterized in that a control means for the state.