JPH09160384A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a color image forming device capable of high speed output by allowing two developing devices to contact and separate with/from a latent image carrier alternately by a single driving means. SOLUTION: A guide shaft 48 is provided at the end of a black developing device 6 and arranged so that is may be engaged in a position guiding groove 49 provided on a side frame 36 and its leading end may be engaged in a groove part 51 provided on a can member 50. Similarly, a guide shaft 52 is also provided at the end of a cyan developing device 7 and disposed so that it may be engaged in a position guiding groove 53 provided on the side frame 36 and its leading end may be engaged in the groove part 51 provided on the cam member 50. The cam member 50 is driven to be normally and reversely rotated by a motor 54, and the developing devices 6 and 7 are moved by the rotation of the cam member. By moving two developing devices along a developing device guiding means by the single driving means, the constitution of a developing device moving mechanism is simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of moving a developing device having a developing roller for visualizing a latent image on a latent image bearing member with a developer to a position where it is separated from the latent image bearing member and in contact with the latent image bearing member. The present invention relates to an image forming apparatus including a developing device moving unit.

[0002]

2. Description of the Related Art As an image forming apparatus capable of forming a color image using an electrophotographic process, a plurality of developing devices are provided in the device, a developing device of a desired color is selected, and the developing device is moved through a moving path to a developing position. 2. Description of the Related Art An image forming apparatus that performs development by moving the image forming apparatus has been proposed.

As a conventional technique of the image forming apparatus of this system, for example, there is JP-A-63-220267, which is provided with a plurality of developing devices and is dedicated to a black developing device for a latent image carrier and other than black. When a developing device having a total of two developing positions dedicated to the color developing device and a color other than black is selected, and the selected developing device moves to the developing position through the moving path, the developing device close to the moving path The latent image is formed in order from the above color and development is performed.

[0004]

However, in the image forming apparatus disclosed in the above-mentioned Japanese Patent Laid-Open No. 63-220267, the image formation of two colors of black and a single color (for example, cyan, magenta and yellow) is performed. Although high-speed output is possible, in full-color image formation, when replacing the developing device at the developing position, there is only one movement path from the developing position to the standby position. There is a problem that the next developing device cannot be moved to the developing position until it moves to the standby position, that is, it takes time to switch the developing device and high-speed output cannot be performed.

Generally, when a full-color image is formed by using an electrophotographic process, it is necessary to use a developing device equipped with cyan, magenta, yellow, and black toners to form an image four times on a photoreceptor. Therefore, the time required for output is four times as long as that for forming a monochrome image. However, since the time required for actual image formation as in the above-mentioned conventional technique is further increased by the switching time of the developing device, the image formation time becomes long, which hinders high-speed output.

In the prior art, since the developing device is housed outside the main body of the apparatus, the desired developing device is selected outside the apparatus and then transferred to the inside of the main body. Therefore, the developing device moving mechanism and the moving path are complicated. In addition, the scale becomes large, which hinders the miniaturization of the device.

The present invention has been made in view of the above-mentioned prior art, and the time required for moving the developing device from the standby position to the developing position is not included in the time required for image output, and high-speed output is possible. Another object of the present invention is to provide a compact color image forming apparatus, and to provide a compact color image forming apparatus with a simple and compact moving mechanism of the developing device.

[0008]

In order to achieve the above object, an image forming apparatus according to claim 1 of the present invention comprises a latent image carrier which is charged and imagewise exposed to form an electrostatic latent image. A plurality of developing devices for visualizing the latent image on the latent image carrier,
In an image forming apparatus having a developing device moving means for moving the developing device to a developing position in contact with the latent image bearing member or a standby position separated from the latent image bearing member, the developing device moving means includes the developing device moving means. Engaging with the developing device guide means provided for each of the plurality of developing devices for guiding the developing device to the developing position or the standby position, and the developing device guide means of two developing devices of the plurality of developing devices. A structure which is constituted by a single driving means for moving two developing devices along the developing device guiding means, and which makes the two developing devices alternately come in contact with and separate from the latent image carrier by the single driving means. It is characterized by having done.

Further, in the image forming apparatus according to a second aspect of the present invention, the single driving unit can rotate in the forward and reverse directions, and the single driving unit rotates in one direction so that one of the two developing devices. Is separated from the latent image carrier, and the other is in contact with the latent image carrier.

Further, in the image forming apparatus according to a third aspect of the present invention, the developing device guide means has a pair of convex portions provided on both sides of an end portion of the developing device, and a pair provided on the apparatus main body side that engages with the convex portions. The developing device guide groove, wherein the drive means is a cam member having a groove portion that engages with the convex portion, and a motor capable of rotating in the normal and reverse directions to drive the cam member.

Further, the image forming apparatus according to claim 4 is
The image forming apparatus according to claim 5, further comprising a plurality of the developing device moving means.
And four developing devices are provided.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments.

FIG. 1 is a sectional view of an apparatus showing the overall construction of an embodiment of an image forming apparatus of the present invention, which is a printer apparatus capable of recording a color image. The schematic operation of the first embodiment will be described with reference to FIG.

In FIG. 1, a photoreceptor 1 which is a latent image carrier.
Is a nickel electroformed tube or an endless belt base material such as polyethylene terephthalate resin whose surface is coated with an aluminum layer coated with an organic photoconductor. The photoconductor drive rotates in the direction of arrow A by contacting the inner circumference of the base. It is rotationally driven by the roller 2. The photoreceptor 1 is not in the form of a belt,
The organic photoreceptor may be directly applied to the surface of the aluminum pipe material, and the photoreceptor driving roller 2 may be eliminated. A charging roller 3 as a charging unit is arranged on the outer periphery of the photoconductor 1, and a voltage of about -1200 V is applied from a high voltage power source (not shown) to make the surface of the photoconductor 1 uniform while rotating in contact with the photoconductor 1. Charge. Here, in this example, the charging roller 2 is used as the charging means, but a corona charger can also be used.

The photoreceptor 1 whose surface is uniformly charged by the charging means is selectively scanned and exposed by the laser scanning optical system 4 which is the exposing means as the first color in accordance with image information of black, for example, for black. Electrostatic latent image of is formed. In this example, the laser scanning optical system 3 was used as the exposing means, but it is also possible to use an exposing optical system composed of an LED array, a liquid crystal shutter or the like as the exposing means.

A photosensitive member auxiliary roller 5 for urging the photosensitive member 1 in the direction of abutting the photosensitive member driving roller 2 is arranged downstream of the laser scanning optical system 4 in the photosensitive member rotating direction. At the same time, the driving force from the photosensitive drum 1 is smoothly transmitted to the photoconductor 1, and at the same time, the exposure position on the photoconductor 1 is prevented from shifting due to the separation / contact operation of the developing device described later.

On the downstream side of the photosensitive member auxiliary roller 5 in the rotating direction of the photosensitive member, black, cyan, magenta, and yellow toners are stored as developers, respectively, and the developing devices 6 and 7 can be freely contacted to and separated from the photosensitive member 1. , 8 and 9 are arranged.

The structure of each developing device will be described with reference to FIG. FIG. 2 is a sectional view showing the configuration of the black developing device 6. In FIG. 2, the toner (not shown) filled in the developing device is agitated by the rotation of the agitator 10 for the purpose of preventing the toner from aggregating and uniformly depositing in the depth direction of FIG. The supply roller 11 is a roller in which a conductive elastic body is arranged on the outer periphery of a shaft member, is pressed by the developing roller 12 while rotating in the direction of arrow C, and supplies the toner to the developing roller 12 while frictionally charging the toner. The developing roller 12 supplied with the toner rotates in the direction of arrow D, and one end of the developing roller 12 has a developing device case 13.
The regulating member 15 fixed to the free end side of the leaf spring 14 fixed to the pressure roller presses the developing roller 12 to regulate the thickness of the toner layer to an appropriate amount. As the developing roller 12, an elastic member such as rubber is provided on the surface of the metal roller, or the surface of the metal roller is subjected to surface treatment with an appropriate surface roughness.
The regulating member 15 can be made of rubber, resin, metal or the like. The latent image on the photoconductor is visualized by the toner by bringing the developing device having such a configuration into contact with the photoconductor 1 and providing a potential difference between the photoconductor 1 and the developing roller 12 as necessary. It Further, the developing devices 7, 8 and 9 for other colors have the same structure.

Returning to FIG. 1, the electrostatic latent image for black formed by the laser scanning optical system 4 moves in advance from the position of the chain double-dashed line in the direction of arrow B with the rotation of the photosensitive member 1 in the direction of arrow A. And is developed by a black developing device 6 that is pressed against the photoconductor 1 to form a black toner image. At this time,
The developing devices 7, 8 and 9 for the other colors are separated from the photoconductor 1.

On the downstream side of the developing device in the rotation direction of the photoconductor, an intermediate transfer medium 16 is provided adjacent to the photoconductor 1 and the transfer medium roller 1 is provided.
It is wound around 7, 18, and 19 and is driven at the same speed as the peripheral speed of the photoconductor 1 by a driving source (not shown). The intermediate transfer medium 16 is made of a material such as polyester, polycarbonate, polyethylene terephthalate, or the like, to which a conductive agent such as carbon is applied, and is configured as a conductive film having an appropriate conductive resistance. The transfer medium roller 17 or 18 is connected to a high voltage power source (not shown), and a high voltage is selectively applied by a switch means (not shown). The photoconductor 1 is in contact with the intermediate transfer medium 8 supported between the transfer medium rollers 17 and 18 at the primary transfer portion 20. As described above, the black toner image formed on the surface of the photoconductor 1 reaches the primary transfer portion 20 as the photoconductor 1 rotates in the arrow A direction. At this time, the transfer medium roller 17 or 18
A voltage of about +2000 V is applied from a high voltage power source (not shown) to the black toner image formed on the surface of the photoconductor 1 at the primary transfer portion 20 and transferred to the intermediate transfer medium 16.

The photoconductor 1 having the black toner image transferred to the intermediate transfer medium 16 is further rotated in the direction of arrow A, and the toner remaining on the surface of the photoconductor 1 is scratched by a photoconductor cleaner 21 composed of a cleaner blade or the like. Taken, in addition,
The surface of the photoconductor 1 is uniformly exposed by the static eliminator 22 to remove the residual charges on the photoconductor 1 and the image can be formed again.

When the desired black toner image is completely transferred to the intermediate transfer medium 16, the black developing device 6 moves in the direction opposite to the arrow B and retracts to the initial standby position.

Subsequently, the second to fourth color images (magenta, cyan, yellow) are processed in the same procedure as the first color.
Are sequentially recorded on the intermediate transfer medium 16 in an overlapping manner.

When the superposition of the color toner images on the intermediate transfer medium 16 is completed, the recording sheets 24 stacked and placed on the recording sheet placing table 23 are started to be fed by the sheet feeding roller 25, and friction (not shown) is applied. Only the topmost sheet is fed by the separation type or claw separation type one-sheet separating means. The leading end of the recording sheet 24, which has been separated and fed, in the transport direction reaches the registration roller 26, which is temporarily stopped and stopped by clutch means (not shown). When the leading edge of the recording sheet 24 in the conveying direction is brought into contact with the nip portion of the registration roller 26, oblique feeding is corrected, and the registration roller 2 is synchronized with the position of the color toner image superimposed on the intermediate transfer medium 16.
When 6 starts to be driven by the clutch means (not shown), the feeding is restarted in the direction of the secondary transfer portion 27. As a result, the recording sheet 24 reaches the secondary transfer portion 27.

When the leading edge of the recording sheet 24 enters the secondary transfer portion 27, a voltage of about -2000 V is applied to the secondary transfer roller 28 from a high voltage power source (not shown), and the color formed on the surface of the intermediate transfer medium 16 is applied. Recording sheet 2 with toner image
4 is transferred to the surface. A transfer medium cleaner 29 composed of a cleaner blade or the like moves in the direction of arrow E and comes into contact with the intermediate transfer medium 16 that has finished transferring the color toner images, and the toner remaining on the surface of the intermediate transfer medium 16 is scraped off. When the scraping is completed, the transfer medium cleaner 29 moves in the direction opposite to the arrow E and retracts.

Recording sheet 2 on which a color toner image is transferred
4 is a heat roller 32 that is conveyed by a belt conveying device 30 and has a rod-shaped halogen lamp 31 inside;
The pressure roller 3 which is pressed against the heat roller 32 and rotates.
The recording sheet 24 having the color toner image transferred thereto is nipped and conveyed while being heated and pressed, and the toner image is fixed. The recording sheet 24 on which the toner image is fixed is discharged to the outside of the apparatus by the discharge roller group 35, and the color image recording is completed.

Next, the moving means for each developing device to move in and out of contact with the photosensitive member 1 will be described. FIG. 3 is a partial cross-sectional perspective view showing the structure of the separation / contact operation mechanism of the black developing device 6 and the cyan developing device 7 of the present image forming apparatus. In order to explain the engagement of each constituent member, each constituent member is axially arranged. It is distributed and arranged in. In FIG. 3, the developing device guides 37, 3 are provided on the side frame 36 that holds each component.
8, 39 are provided, the developing device guide 37 is provided with developing device guide grooves 40 and 41, the developing device guide 38 is provided with a developing device guide groove 42, and the developing device guide 39 is provided with a developing device guide groove 43. There is. Protrusions 44 and 45 are provided at the end of the black developing device 6, the protrusion 44 is engaged with the developing device guide groove 40, the protrusion 45 is engaged with the developing device guide groove 42, and the black developing device 6 is engaged with the developing device guide groove 40. And 4
It is held so that it can move in parallel in two directions. Similarly, in the cyan developing device 7, the projections 46 and 47 are provided in the developing device guide groove 4.
1 and 43 to engage with the developing device guide grooves 41 and 43.
It is held so that it can move in parallel with the direction.

On the other hand, a guide shaft 48 is provided at an end portion of the black developing device 6, engages with a position guide groove 49 provided on the side frame 36, and a tip of the shaft is provided with a groove portion 51 provided on the cam member 50. It is arranged to engage. Similarly, a guide shaft 52 is also provided at the end of the cyan developing device 7, engages with a position guide groove 53 provided on the side frame 36, and the tip of the shaft engages with a groove 51 provided on the cam member 50. It is arranged as follows. The cam member 50 can be driven to rotate forward and backward by a motor 54, and the black developing device 6 and the cyan developing device 7 move due to the rotation of the cam member.
Similarly, a mechanism for holding each developing device is also provided on the side frame side opposite to that of FIG. 3, and a cam gear provided on the outer periphery of the cam member 50 and a cam member provided on the opposite side with a transmission shaft 56. The black developing device 6 and the cyan developing device can be smoothly moved by transmitting the driving force to the.

That is, the projections 44, 45, 46, 47, the guide shafts 48, 52, and the developing device guide grooves 40, 41, 42, 4
3, the position guide grooves 49 and 53 are the developing device guide means of the present invention, the cam member 50 and the motor 54 are the drive means of the present invention, and the transmission gear 55 and the transmission shaft 56 are auxiliary mechanisms of the drive means.

Here, the arrangement of the black developing device 6 and the cyan developing device 7 and the developing device guide grooves 40, 41, 42,
A preferred positional relationship between the 43 and the position guide grooves 49 and 53 is shown in FIG. In FIG. 4, the developing roller 12 of the black developing device 6 and the developing roller 12 of the cyan developing device 7 are located at substantially the same position.
The cyan developing roller comes into contact with the photosensitive member 1 at the contact position 57.
As a result, the developing roller of which developing device is the photoconductor 1
Even if the photoconductor 1 is brought into contact with the photoconductor 1, the positions of elastic deformation of the photoconductor 1 are substantially the same, and the driving characteristics given to the photoconductor 1 by the respective developing rollers can be made substantially the same, so that the pressure contact developing condition can be made uniform and stable. realizable. Further, the developing device guide grooves 40, 41, 4
2 and 43 and the position guide grooves 49 and 53 are arranged in the black and cyan developing roller contact position 57 of the photoconductor 1.
Of the developing device guide grooves 40 and 42 and the position guide groove 49 with respect to the normal K in FIG.
It is desirable that the arrangement angle β of the 43 and the position guide groove 53 is 45 ° or less. By setting the arrangement angle β to be 45 ° or less, the force applied in the rotation direction of the photoconductor 1 when the developing device is brought into contact with the developing device can be made smaller than the force exerted in the contact direction of the developing roller, and the developing roller is actuated by the photoconductor. It becomes difficult for the developing roller to bite and the photosensitive member 1 to vibrate when it comes into contact with or separates from the photosensitive member 1. In addition, the magenta / yellow developing roller contact position 58
Is provided at a position (the angle γ is equal) which is line-symmetrical to the black / cyan developing roller contact position 57 with respect to the long-axis centerline L of the photosensitive member 1 so that the elastic deformation of the photosensitive member 1 and the developing roller are exposed. The drive characteristics given to the body 1 can be made the same as the black / cyan developing roller contact position 57.

Further, the operation of separating and contacting the black developing device 6 and the cyan developing device 7 with respect to the photosensitive member 1 will be described in more detail with reference to FIGS.

FIG. 5 is a partial sectional view of the image forming apparatus showing the positions of the black developing device 6 and the cyan developing device 7 when the entire device is in a stopped state, a standby state or a developing device exchange state. In this state, the black developing device 6 is biased in the direction of arrow F by the spring 57, the projections 44 and 45 are engaged with the developing device guide grooves 40 and 42, and are positioned,
The developing roller 12 is largely separated from the photoconductor 1. Similarly, the cyan developing device 7 is also biased in the direction of arrow G by the spring 58, the protrusions 46 and 47 are engaged with the developing device guide grooves 41 and 43 and positioned, and the developing roller 12 is largely separated from the photoconductor 1. There is. In this state, the agitator 10, the supply roller 11, and the developing roller 12 of each developing device are stopped.

FIG. 6 is a partial sectional view of the image forming apparatus showing the positions of the black developing device 6 and the cyan developing device 7 when the black developing device 6 is in the developing state and the cyan developing device 7 is in the standby state. . Before the image formation is started and before the electrostatic latent image for black formed on the photoconductor 1 reaches the black / cyan developing roller contact position 59, the motor 5
4, the cam member 50 rotates in the direction of arrow H, and the groove 5
1 moves the guide shaft 48, and the black developing device 6 moves in the direction of arrow B against the bias of the spring 57, while the agitator 10, the supply roller 11, and the developing roller 12 start rotating, and the black developing device 1 starts to rotate. The developing roller 12 of No. 6 contacts the photoconductor 1 at the contact position 59, and develops the electrostatic latent image for black. On the other hand, in the cyan developing device 7, the groove 51 has the guide shaft 5
2 and the projections 46 and 47 do not act on the developing device guide groove 4
Since the cam member 50 is engaged with the cam members 1 and 43, it does not move even when the cam member 50 rotates. At this time, the agitator 10, the supply roller 11, and the developing roller 12 are stopped. When the development of the electrostatic latent image for black is completed, the cam member 50 is rotated in the direction opposite to the arrow H by the motor 54, and the black developing device 6 returns to the state of FIG. 5 while the agitator of the black developing device 6 is being returned. 10, supply roller 11, developing roller 1
2 stops.

FIG. 7 is a partial sectional view of the image forming apparatus showing the positions of the black developing device 6 and the cyan developing device 7 when the black developing device 6 is in the standby state and the cyan developing device 7 is in the developing state. . The electrostatic latent image for cyan formed on the photoconductor 1 is in the black / cyan developing roller contact position 5
Before reaching 9, the cam member 50 is rotated by the motor 54 in the direction of the arrow I, the groove portion 51 moves the guide shaft 52,
While the cyan developing device 7 moves in the direction of the arrow J against the bias of the spring 58, the agitator 10, the supply roller 11, and the developing roller 12 start rotating, and the developing roller 12 of the cyan developing device 7 comes into contact with the contact position. At 59, it contacts the photoconductor 1 and develops the electrostatic latent image for cyan. On the other hand, in the black developing device 6, the groove 51 does not act on the guide shaft 48, and the protrusions 44 and 45 are formed.
Is engaged with the developing device guide grooves 40 and 42, the cam member 50 does not move even if it rotates, and the agitator 10,
The supply roller 11 and the developing roller 12 are stopped. When the development of the electrostatic latent image for cyan is completed, the cam member 50 is rotated by the motor 54 in the direction opposite to the arrow I, and the cyan developing device 7 returns to the state of FIG. , Supply roller 11, developing roller 1
2 stops.

The magenta developing device 8 and the yellow developing device 9 have the same structure as the black developing device 6 and the cyan developing device 7 so that the respective developing rollers are in contact with and separate from the photoconductor 1, and the description thereof is omitted. To do. The arrangement of each color developing device is not limited to the above position, and the arrangement of the four color developing devices may be arbitrarily changed.

With the above-mentioned structure, the four-color developing device is divided into two colors, and each two-color developing device is divided into one.
The developing roller of each developing device can be brought into contact with and separated from the photoconductor 1 by moving the two motors in forward and reverse operations.

In the image forming apparatus of this example, for the purpose of efficiently forming an image and obtaining an image forming output in a short time, for example, when the development of the first color is completed and the developing device of the first color is When operations such as charging, latent image recording, and transfer of a toner image from the latent image carrier are continued when the second-color developing device contacts the latent image carrier while being separated from the latent image carrier. There are many. When the one-component pressure contact developing system is applied to the developing device of such a color image forming apparatus, it is experimentally clear that the impact when the developing roller of each color comes into contact with the photoconductor adversely affects the image quality. It was Therefore, by appropriately controlling the peripheral speed of the developing roller of each color and the rotation speed of the motor for performing the contact / separation operation of each developing device, the impact when the developing roller contacts the photoconductor 1 is reduced. FIG. 8 shows a timing chart showing the peripheral speed control of each developing roller and the rotation speed control of the motor for performing the contact / separation operation of each developing device in the present invention.

In FIG. 8, when the photosensitive member 1 starts to rotate and reaches a predetermined peripheral speed V1, the laser scanning optical system starts rotating operation, and when the scanning optical system reaches a predetermined rotational speed, T
A black latent image is written on the photoconductor 1 between Bk. Further, the motor that moves the black developing device 7 and the cyan developing device 8 rotates while slowing up and slowing down during TR1, and the black developing roller contacts the photoconductor 1. Prior to this, the black developing roller starts to rotate at a peripheral speed V1 which is the same speed as the photosensitive member, and the developing roller and the photosensitive member 1 contact each other with the peripheral speed of the developing roller being V1. After the contact between the black developing roller and the photosensitive member 1, before the tip of the black latent image on the photosensitive member 1 reaches the developing position, the peripheral speed of the developing roller is gradually accelerated from V1 to V2 to obtain a suitable developing state. , TD1 to develop a black latent image. When the black development is completed, the peripheral speed of the developing roller is gradually reduced from V2 to V1 again, and the motor for moving the black developing device 7 and the cyan developing device 8 during TR3 slows up and slows in the direction opposite to TR1. The black developing roller is separated from the photoconductor 1 by rotating while being lowered, and stopped after the separation.

On the other hand, the motor for moving the magenta developing device 8 and the yellow developing device 9 rotates while slowing up and slowing down during TR2 in the middle of TD1, without waiting for the black developing roller to be separated from the photoconductor 1. On photoconductor 1
The movement in the direction is started, and the black developing and developing roller contacts the photoconductor 1 immediately after the separation is started. Before and after the contact, the magenta developing roller is subjected to the same speed control as the black developing roller, and the magenta latent image written by the scanning optical system during TM is developed during TD2. Development of magenta is completed, TR
The motor for moving the magenta developing device 8 and the yellow developing device 9 during 4 rotates in the direction opposite to TR2 while slowing up and slowing down, whereby the magenta developing roller is separated from the photoconductor 1. At that time, the magenta developing roller is subjected to the same speed control as the black developing roller,
Stop after separation.

Similarly, the cyan developing roller moved in TR3 immediately after the separation of the magenta developing roller comes into contact with the photosensitive member 1, and the cyan latent image written by the scanning optical system during TC is developed between TD3. , TR5 is separated from the photoconductor 1 and the cyan development roller is moved in TR4 immediately after the separation is started, the yellow development roller is brought into contact with the photoconductor 1 and the yellow latent image written by the scanning optical system is changed to TD4 during TY. The developing process is performed during the interval, and it is separated from the photoconductor 1 during TR6. A full-color image is obtained by transferring the toner images of the respective colors obtained by this series of operations onto the intermediate transfer medium 16 of FIG.

In FIG. 8, the peripheral speed of each developing roller and the peripheral speed of the photosensitive member are made equal to each other so that the impact on the photosensitive member during the separating operation of the developing roller is minimized. However, if the developing roller and the photoconductor are brought into contact with each other in a state where the peripheral speed of each developing roller and the peripheral speed of the photoconductor are completely the same, the development fog may become remarkable. The peripheral speed of the roller is 1 more than the peripheral speed of the photoconductor.
Fogging can be reduced by increasing the speed by about 0%. Therefore, the peripheral speed of each developing roller when it is brought into contact with and separated from the photoconductor is not necessarily completely the same as the peripheral speed of the photoconductor, and may be substantially constant.

By operating the apparatus of this example in the procedure described with reference to FIG. 8, for example, a preliminary operation for bringing the developing device for the second color close to the second developing position while developing the first color at the first developing position is performed. When the development of the first color is completed at the first development position, the development of the second color can be started immediately at the second development position. In addition, during the development of the second color, the retracting operation of the developing device for the first color to the standby position and the preliminary operation for bringing the developing device for the third color closer to the first developing position are performed, and the developing operation for the second color is performed at the second developing position. Immediately after the above, the development of the third color can be started at the first developing position. Therefore, the time for switching the developing device is not added to the time for image formation as compared with the above-mentioned conventional technique, and high-speed output of an image is possible.

Further, by constructing the developing device guide means and the drive means as shown in FIG. 3, TR3 and TR in FIG.
As shown in FIG. 4, when the developing devices 6, 7 or 8, 9 in the same group are replaced, the replacement operation can be performed by simply rotating the motor in one direction, and the compact and simple configuration and simple driving are possible. The developing device replacement operation can be realized by the control method.

Further, when the developing roller and the photosensitive member are brought into contact with or separated from each other, the peripheral speed of the developing roller of each developing device is made substantially equal to the peripheral speed of the photosensitive member, and then the developing roller is gradually brought into contact with the photosensitive member. The impact on the photoconductor during the separating operation of the developing roller is significantly reduced, and the image quality deterioration such as the color shift and the image blur due to the separating operation of the developing roller can be prevented. Further, the toner on the developing roller is not scattered due to the peripheral speed difference when the developing roller is brought into contact with the photoconductor, and the inside of the apparatus is not contaminated with the floating toner.

Further, by gradually increasing or decreasing the peripheral speed of the developing roller before and after the development to a speed substantially equal to the peripheral speed of the photosensitive member or a speed higher than the peripheral speed of the photosensitive member, the impact given to the photosensitive member at the time of shifting is extremely high. It becomes slight, there is no fogging, and
It is possible to obtain a high quality image having a sufficient image density.

[0046]

As described above, according to the image forming apparatus of the present invention, the two developing devices can be moved along the developing device guide means by the single driving means by the constitution of claim 1. The structure of the developing device moving mechanism can be simplified.

Further, according to the second aspect of the present invention, when the two developing devices are exchanged, the exchange operation can be performed only by rotating the driving means in one direction, and the development device exchange operation can be performed by a simple drive control method. Can be realized.

According to the third aspect of the invention, the developing device guide means and the driving means can be realized in a compact and simple structure.

Further, with the structure of claim 4 or 5, full-color image formation can be performed without including the time for moving the developing device from the standby position to the developing position in the time required for image output. High-speed output of images becomes possible.

[Brief description of the drawings]

FIG. 1 is an apparatus cross-sectional view showing the overall configuration of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a black developing device 6 according to an embodiment of the present invention.

FIG. 3 is a partial cross-sectional perspective view showing the structure of the separation / contact operation mechanism of the black developing device 6 and the cyan developing device 7 in the embodiment of the invention.

FIG. 4 is an arrangement of black developing device 6 and cyan developing device 7 and developing device guide grooves 40, 4 in the embodiment of the present invention.
FIG. 4 is a partial cross-sectional view showing a preferred positional relationship among 1, 42, 43 and position guide grooves 49, 53.

FIG. 5 is a partial cross-sectional view showing the positions of the partial developing device 6 and the cyan developing device 7 when the device is in the stopped state, the standby state, or the developing device replacement state in the embodiment of the present invention.

FIG. 6 is a partial cross-sectional view showing the positions of the black developing device 6 and the cyan developing device 7 when the black developing device 6 is in the developing state and the cyan developing device 7 is in the standby state in the embodiment of the invention.

FIG. 7 is a partial cross-sectional view showing the positions of the black developing device 6 and the cyan developing device 7 when the black developing device 6 is in the standby state and the cyan developing device 7 is in the developing state in the embodiment of the invention.

FIG. 8 is a timing chart showing the peripheral speed control of each developing roller and the rotation speed control of a motor that performs contact / separation operation of each developing device in the embodiment of the present invention.

[Explanation of symbols]

 1 ... Photosensitive member (latent image bearing member) 2 ... Photosensitive member driving roller 3 ... Charging roller 4 ... Laser scanning optical system 5 ... Photosensitive member auxiliary roller 6 ... Black developing device 7 ... Cyan developing device 8 ... Magenta developing device 9 ... Yellow Developing device 10 ... Agitator 11 ... Supply roller 12 ... Developing roller 13 ... Developing device case 14 ... Leaf spring 15 ... Restricting member 16 ... Intermediate transfer medium 17, 18, 19 ... Transfer medium roller 20 ... Primary transfer portion 21 ... Photoconductor cleaner 22 ... Static eliminator 23 ... Recording sheet mounting table 24 ... Recording sheet 25 ... Paper feeding roller 26 ... Registration roller 27 ... Secondary transfer section 28 ... Secondary transfer roller 29 ... Transfer medium cleaner 30 ... Belt transport device 31 ... Halogen lamp 32 ... Heat rollers 33, 34 ... Pressure roller 35 ... Paper discharge roller group 36 ... Side frames 37, 38, 39 ... Developing device Guide 40, 41, 42, 43 ... Developing device guide groove 44, 45, 46, 47 ... Protrusion 48, 52 ... Guide shaft 49, 53 ... Position guide groove 50 ... Cam member 51 ... Groove portion 54 ... Motor 55 ... Transmission gear 56 ... Transmission shafts 57, 58 ... Spring 59 ... Black / cyan developing roller contact position 60 ... Magenta / yellow developing roller contact position

Claims (5)

[Claims] 1. A latent image carrier that is charged and image-exposed to form an electrostatic latent image, a plurality of developing devices that visualize the latent images on the latent image carrier, and the developing device. An image forming apparatus having a developing device moving means for moving to a developing position in contact with the latent image bearing member or a standby position for separating from the latent image bearing member, wherein the developing device moving means places the developing device in the developing position. Alternatively, two developing devices that engage with the developing device guide means provided for each of the plurality of developing devices for guiding to the standby position and the developing device guide means of two of the plurality of developing devices are engaged. Is constituted by a single driving means for moving the developing device along the developing device guiding means, and the two developing devices are alternately brought into contact with and separated from the latent image carrier by the single driving means. Image forming apparatus. 2. The single drive means is capable of rotating in the forward and reverse directions, and when the single drive means rotates in one direction, one of the two developing devices is separated from the latent image carrier, The image forming apparatus according to claim 1, wherein the other is in contact with the latent image carrier. 3. The developing device guide means includes a pair of convex portions provided on both sides of an end portion of the developing device, and a pair of developing device guide grooves provided on the side of the main body of the device that engages with the convex portions. 3. The image forming apparatus according to claim 1, wherein the means is a cam member having a groove portion that engages with the convex portion, and a motor that drives the cam member and can rotate in the forward and reverse directions. 4. The image forming apparatus according to claim 1, further comprising a plurality of the developing device moving means. 5. The image forming apparatus according to claim 4, further comprising two developing device moving means and four developing devices.