JPH0844200A - Image forming method for multicolor image - Google Patents

Abstract

PURPOSE:To obtain an image free from irregularities and also to prolong the endurance life of a photoreceptor without sustaining a vibration and an impact when a developing device positioned on a downmost-stream side is in developing operation by starting the developing operation of the developing device positioned on the downmost-stream side, simultaneously, starting driving a developing device positioned on an uppermost- stream side in a non-developing state. CONSTITUTION:When a 1st sheet is in developing operation, the developing device 14 positioned on the downmost-stream side in a moving direction of a photoreceptor 9 is driven, simultaneously, the developing device 11 positioned on the uppermost-stream side is driven in order to develop a 2nd sheet. But at this time, a developing bias for the developing device 11 on the uppermost-stream side is turned off. Thus, yellow developer for the uppermost-stream developing device 11 comes in contact with an electrostatic latent image on the 1st sheet to be developed by the developing device 14 on the downmost-stream side, but the developing bias is turned off, that is, the developing device 11 is made in the non-developing state, so that the electrostatic latent image is not developed substantially. Besides, the electrostatic latent image is developed with black toner, then the color mixture is completely inconspicuous even though the yellow developer sticks to the latent image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method for continuously forming multicolor images using a multicolor image forming apparatus such as a multicolor copying machine or a multicolor printer.

[0002]

2. Description of the Related Art In an electrophotographic multicolor image forming apparatus,
A plurality of developing devices, each containing a developer of a different color, are arranged around the photoconductor, and the developing device on the upstream side in the moving direction of the photoconductor is sequentially switched to the developing state for a multicolor image. -For example, a full-color image-is created.

By the way, in the above-mentioned image forming apparatus, the distance from the position where the image is exposed on the photoconductor to the developing position where each developing device opposes the photoconductor is the development on the downstream side in the moving direction of the photoconductor. It's as long as a bowl. Therefore, in order to continuously create a multicolor image in a short time, it is possible to start driving the most upstream developing device during the developing operation by the most downstream developing device and perform development at two locations at the same time.

[0004]

However, if the driving of another developing device (the most upstream developing device) is started during the development of one developing device (the most downstream developing device), the fluctuation of the driving load at the start thereof will occur. As a result, the speed of the developing roller provided in the developing device under development sharply decreases, and in the worst case, the developing device vibrates due to the impact of load fluctuation, and the image quality is disturbed on the image. Therefore, in the conventional multi-color image forming apparatus, after the development of the most downstream developing device is completed, the photosensitive member is rotated almost once, and then the most upstream developing device is driven to develop the second and subsequent sheets.
Therefore, there are problems in that it takes a long time to create a multicolor image and the life of the photoconductor is shortened due to extra rotation of the photoconductor.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention has been made to solve the above problems, and in a multicolor image forming apparatus, when a plurality of multicolor images are continuously formed, the most downstream At the same time that the developing operation of the developing device is started, the most upstream developing device is also driven in the non-developing state.

[0006]

According to the above method, at the same time when the developing operation of the most downstream developing device is started, the most upstream developing device is also driven in the non-developing state. That is, the driving of the most upstream developing device does not start while the most downstream developing device is in operation. Therefore, the image created by the most downstream developing device is not disturbed. Also, when the drive of the most upstream developing device is started, the electrostatic latent image to be developed by the most downstream developing device may pass through the development area of the most upstream developing device. Since the developing device of No. 1 is driven, it is kept in a non-developing state, so that the electrostatic latent image to be developed by the most downstream developing device is not developed by the most upstream developing device.

[0007]

【Example】

(1) Overall Structure: FIG. 1 shows a schematic structure of a multicolor image forming apparatus by an electrophotographic system, that is, a multicolor copying machine 1-.
The copying machine 1 includes an original platen 2 made of transparent plate glass and an original cover 3 for opening and closing the upper surface of the original platen 2, and the original is placed on the original platen 2 with the image surface to be copied facing downward. It is placed and covered with the opening / closing cover 3. Below the document platen 2, there is provided a scanning optical unit 5 which operates in the direction of arrow 4 along the lower surface of the document platen 2 and reads an image of a document placed on the document platen 2. The original image read in step (4) is decomposed into four-value (yellow, magenta, cyan, black) image data and stored in the image storage unit 6. The image data stored in the image storage unit 6 includes yellow, magenta, cyan,
It is sent to the laser exposure device 7 in the order of black, and the laser 8 corresponding to each image data is exposed on the electrostatic latent image carrier-that is, the photoconductor 9-.

The photosensitive member 9 is composed of a drum having a photosensitive layer on its outer peripheral portion, and is surrounded by a charging device 10, developing devices 11 and 12,
13, 14, a transfer device 15, a cleaning device 16, and a charge eliminating device 17 are provided. The photoconductor 9 is indicated by an arrow 18.
When rotated in the direction, the outer peripheral photosensitive layer is uniformly charged by the charger 10, and the charged area is exposed to the laser 8 as described above, so that electrostatic images corresponding to yellow, magenta, cyan, and black image data are obtained. Latent images are sequentially formed. These electrostatic latent images are developed by developing units 11, 12, 13 having yellow, magenta, cyan, and black toners, respectively.
The image is developed and visualized in 14 and is sequentially transferred to a transfer sheet (for example, paper) in the transfer device 15 to be superposed.
The toner not transferred to the transfer sheet is collected by the cleaning device 16. Further, the charge remaining on the photoconductor 9 is removed by the charge removing device 17 to prepare for the next development.

The transfer device 15 includes a transfer drum 19 which rotates in the direction of arrow 20. The transfer drum 19 is a chucking device 2 that holds the leading end of the transfer sheet on the outer peripheral portion.
1 is provided. A transfer charger 22 is provided in the inner space of the transfer drum 19 so as to face the photoconductor 9. In addition, in the vicinity of the moving path of the transfer drum 19, the first charge removing device 23, the sheet separating device 24, the second charge removing device 25, and the cleaning device 26 are sequentially provided on the downstream side of the transfer charger 22 in the rotation direction of the transfer drum 19. Is provided.

The transfer sheet 27 is supplied from a paper feeding unit 28, 29, or 30 and held by the chucking device 21 on the outer periphery of the transfer drum 19. Further, when the transfer drum 19 is rotated, it is sent to the facing portion (transfer area 31) between the photoconductor 9 and the transfer drum 19, and the yellow toner image is first transferred. Further, each time the transfer drum 19 makes one rotation, magenta, cyan, and black toner images are transferred onto the transfer sheet 27 in an overlapping manner. Note that the front end of the transfer sheet 27 is resist-adjusted with each toner image, and all the toner images are superposed without displacement.

When the transfer of all the toner images is completed, the transfer sheet 27 is destaticized by the first destaticizing device 23, separated from the transfer drum 19 by the separating device 24, and the toner is thermally fixed by the fixing device 32, so that the discharge tray is discharged. It is discharged to 33. On the other hand, the transfer drum 19 from which the transfer sheet 27 is removed is the second
The charge is removed by the static eliminator 25, and the cleaning device 26
To remove the residue.

(2) Developing devices 11-14: developing devices 11, 1
2, 13, 14 basically have the same configuration. To be more specific with reference to FIG. 2, the housing 34 of the developing units 11 to 14 has an opening 35 in the upper portion facing the photoconductor.
Are formed. Inside the opening 35, a developing roller 36 that slightly projects from the opening 35 and faces the photoconductor 9 is arranged. A smoke prevention sheet 38 is attached to the end of one wall 37 facing the outer peripheral surface of the developing roller 36, and the tip end thereof faces the photoconductor 9 in a non-contact manner. The other wall 3 facing the outer peripheral surface of the developing roller 36
A partition wall 40 is provided on the inner side of 9, and a dust and smoke suction chamber 41 having a photoconductor facing portion opened is formed between the wall 39 and the partition wall 40 and is connected to a suction device (not shown). There is.

The developing roller 36 has a magnet body 42 fixed in a non-rotating state, and an arrow 44 attached to the magnet body 42 to cover the magnet body 42.
And a developing sleeve 43 that is rotationally driven in the direction. The developing sleeve 43 is connected to a developing bias power source 45. Below the developing roller 36, a supply roller 46 is provided at a predetermined distance from the developing roller 36. Similar to the developing roller 36, the supply roller 46 is composed of a magnet body 47 fixed in a non-rotating state and a supply sleeve 48 which is exteriorly mounted on the magnet body 47 and is rotationally driven in the direction of arrow 49. The spike-height restricting plate 50 fixed to the outer peripheral surface of the supply sleeve 48 faces the outer peripheral surface of the supply sleeve 48 with a predetermined gap. A developer stirring screw 51 (which will be described later in detail) is provided below the supply roller 46, and is indicated by an arrow 52.
Developer that is rotated in the direction and is accommodated in the housing 34-that is, a two-component developer including toner and carrier-
Are to be mixed. Also, the housing 34
A toner concentration detection sensor 95 is provided at the bottom of the toner storage device so as to face the developer stirring screw 51, and the toner concentration contained in the developer can be detected.

As shown in FIG. 3, a plurality of magnetic poles are formed on each of the magnet bodies 42 and 47. In the drawings, N and S represent polarities, respectively. More specifically, the developing roller 36 is attached to the magnet body 42 of the developing roller 36.
A magnetic pole N1 is disposed as a developing magnetic pole at a portion facing the photosensitive member 9 and the photosensitive member 9. In addition, the sleeve rotation direction (direction of arrow 44) from the closest position between the developing roller 36 and the supply roller 46.
The magnetic pole N2 is disposed on the downstream side of the. The magnetic pole S1 is arranged between the magnetic poles N1 and N2, and the magnetic pole S2 is arranged downstream of the magnetic pole N1 in the rotation direction of the developing sleeve 43. On the other hand, the magnet sleeve 47 of the supply roller 46 is sandwiched between the magnet sleeve 47 and the developing sleeve 43 so as to sandwich the supply sleeve 48.
The magnetic pole S3 is arranged on the upstream side and the magnetic pole S4 having the same polarity is arranged on the downstream side with respect to the rotation direction, and the magnetic pole N3 is arranged on the upstream side in the rotation direction of the supply sleeve 48 from the facing portion of the spike height regulating plate 50.

In the above structure, the developer contained in the housing 34 is agitated by the agitating screw 51,
The toner and the carrier are each charged with a predetermined polarity.
Also, the developer drawn up by the stirring screw 51 is
It is supplied to the supply roller 46 in a region facing the magnetic pole N3,
It is held on the outer circumference of the supply sleeve 48 by the magnetic force of the magnetic pole N3. Further, the developer is conveyed in the same direction as the supply sleeve 48 rotates in the direction of the arrow 49, and is regulated by the spike height regulating plate 50 to form a pool. The developer that has passed between the height control plate 50 and the supply roller 46 is magnetic pole S3 and magnetic pole N2.
And is supplied to the developing sleeve 43 at the opposite portion. Then, by the rotation of the developing sleeve 43 in the direction of the arrow 44, the developer passes through the facing portion of the magnetic pole S1 and then moves to the facing portion of the developing magnetic pole N1, where it contacts the photoconductor 9 to transfer the electrostatic latent image to the toner. Visualize with. When the developer that has passed through the developing area passes through the facing portion of the magnetic pole S2, the developer is separated from the developing sleeve 43 by the repulsive magnetic field formed between the magnetic pole S2 and the magnetic pole S4 and falls onto the supply roller 46. Further, the repulsive magnetic field prevents the developer from entering between the developing sleeve 43 and the supply sleeve 48. And supply sleeve 48
The developer that has fallen to # 1 drops toward the stirring screw 51 and is stirred again by the stirring screw 51. The dust and smoke toner scattered from the opening 35 facing the photoconductor 9 is prevented from being scattered to the outside by the dust and smoke prevention sheet 38, and is sucked and collected through the dust and smoke suction chamber 41.

(3) Drive System of Developing Device: The drive system of the developing devices 11, 12, 13, and 14 will be described with reference to FIGS. 4 and 5. An input gear 54 is provided on the side wall 53 of the housing 34. . The input gear 54 is used for the developing devices 11, 12,
By mounting 13 and 14 on the copying machine 1, they are connected to the drive gear 55. The drive gear 55 is drivingly connected to the motor through a drive clutch corresponding to each developing device, and rotation of the drive gear 55 is transmitted to the input gear 54 by turning on the drive clutch. Further, the input gear 54 is drivingly connected to a gear 61 fixed to a rotating shaft 60 of the stirring screw 51 via idler gears 58 and 59 supported by the rotating shafts 56 and 57, respectively. The rotary shaft 60 and the rotary shaft 62 of the developing sleeve 43.
Pulleys 63 and 64 are fixed to the respective pulleys, and a belt 65 is stretched over these pulleys 63 and 64. A rotary shaft 67 is connected to a rotary shaft 56 of the idler gear 58 via an electromagnetic clutch 66. A pulley 68 fixed to the rotary shaft 67 and a pulley 70 fixed to a rotary shaft 69 of the supply sleeve 48 is attached to a belt 71. Has been bridged. The electromagnetic clutch 66 is held on the side wall 53 by the support frame 72.

According to this drive system, when the drive clutch (not shown) is turned on, the rotation of the drive gear 55 is transmitted to the rotary shaft 60 via the input gear 54, the idler gears 58 and 59, and the gear 61, and the stirring screw is rotated. 51 rotates in the direction of arrow 52. Further, when the rotary shaft 60 rotates, the rotary shaft 62 rotates via the pulleys 63, 64 and the belt 65, and the developing sleeve 43 rotates in the arrow 44 direction. The supply sleeve 48 is rotated via the pulleys 68 and 70 and the belt 71 by turning on the electromagnetic clutch 66 and connecting the rotary shaft 56 and the rotary shaft 67. That is, the supply sleeve 48 includes the developing sleeve 43 and the stirring screw 51.
In the state where is driven, the electromagnetic clutch 66 can be turned on or off to switch to a rotating or non-rotating state.

(4) Switching of developing device: the electromagnetic clutch 6
Under the control of 6, the developing units 11, 12, 13, and 14 are in a state where the developer is in contact with the photoconductor 9 (hereinafter referred to as “developer contact state”) and a state in which the developer is not in contact with the photoconductor 9. (Hereinafter, referred to as “developer non-contact state”). More specifically, referring to FIGS.
When the developing device is switched from the developer contact state to the developer non-contact state, when the electromagnetic clutch 66 is turned on while the drive clutch is turned on, the developing sleeve 43 and the stirring screw 51 rotate in the directions of arrows 44 and 52, respectively. At the same time, the supply sleeve 48 rotates in the direction of arrow 49.
As a result, the developer drawn up by the stirring screw 51 is supplied from the supply sleeve 48 to the developing sleeve 43, and the developer that has passed through the developing area is supplied to the supply sleeve 4.
It is sent back to the stirring screw 51 via 8 (see FIG. 6).

When the electromagnetic clutch 66 is turned off in this state, the rotation of the supply sleeve 48 is stopped. However, the developing sleeve 43 and the stirring screw 51 continue to rotate.
As a result, the developer drawn up from the stirring screw 51 stays near the spike height regulating plate 50 due to the magnetic force of the magnetic pole N3. Further, the developer held in the developing sleeve 43 is conveyed in the direction of the arrow 44 by the rotation of the developing sleeve 43 and drops to the supply sleeve 48, and there is almost no developer on the developing sleeve 43-that is, non-developing. State-
Is switched to.

On the contrary, when the developing device is switched from the non-contact state of the developer to the contact state of the developer, the developing sleeve 43 and the stirring screw 51 are rotated, and the electromagnetic clutch 66 is rotated.
Is turned on to rotate the supply sleeve 48. This allows
As shown in FIG. 9, the developer regulated by the spike height regulating plate 50 is simultaneously supplied from the supply sleeve 48 to the developing sleeve 43, conveyed to the developing area, and brought into contact with the photoconductor 9.
Therefore, the developing units 11, 12, 13, and 14 are quickly switched from the developer non-contact state to the developer contact state.

Here, the time from when the supply roller 46 stops rotating until the developer runs out in the developing area is the developing magnetic pole where the developer faces the developing area from the facing portion of the magnetic pole (developer receiving pole) N2. This corresponds to the time required to pass the facing portion of N1. Specifically, the peripheral speed of the developing sleeve 43 is set to 16
When the distance on the developing sleeve 43 from the facing portion of the magnetic pole N2 to the facing portion of the magnetic pole N1 is 23 mm, it is about 0.14 seconds. Therefore, rather than the trailing edge of the electrostatic latent image on the photosensitive member 9 being developed reaches the developing area,
If the rotation of the supply sleeve 48 is stopped as soon as the developer is conveyed from the facing portion of the magnetic pole N2 to the facing portion of the magnetic pole N1, the timing of stopping the development and the trailing end of the electrostatic latent image can be exactly matched. Further, by stopping the supply sleeve 48 at this timing, the most efficient developing device switching operation is achieved.

When the developing device is switched from the developer non-contact state to the developer contact state, the developer is magnetic pole N2 rather than the tip of the electrostatic latent image formed on the photoconductor 9 reaches the development area. The driving of the developing sleeve 43 or the like is started earlier than the time when the developing sleeve 43 is conveyed from the facing portion to the facing portion of the magnetic pole N1 (about 0.14 seconds in the above specific example). As a result, the tip of the electrostatic latent image and the developer enter the developing area at the same time, and the timings of the both can be matched. Further, by operating the developing device at such a timing, the most efficient switching operation can be achieved.

The switching timing of the developing device is shown in FIG.
Will be described in more detail with reference to. FIG. 10 shows the timing at which various devices operate with respect to the electrostatic latent image area of the first color (yellow in this embodiment) formed on the photoconductor 9, and the copy operation starts (time: t0). After that, when the exposure of the laser 8 corresponding to the image of the first color from the laser exposure device 7 is started on the photoconductor 9 (time: t1), the developing device 11 is driven after a predetermined time (time: t2). The developing device drive clutch for transmission is turned on, and the electromagnetic clutch 66
Is turned on, and the developing sleeve 43, the supply sleeve 48, and the stirring screw 51 simultaneously start driving. Then, after a predetermined time (time: t3), the power supply 45 is turned on to apply the developing bias VB to the developing sleeve 43, and the electrostatic latent image is developed from the leading end portion thereof. Here, the time from time t2 to time t3 is equal to the time when one point on the developing sleeve 43 stopped at the facing portion of the magnetic pole N2 moves to the developing area facing the magnetic pole N1.

When the developing operation by the developing device 11 is finished, when the image exposure from the laser exposure device 7 is finished (time: t4), the electromagnetic clutch 66 is turned off after a predetermined time (time: t5). As a result, the rotation of the supply sleeve 48 is stopped and the supply of the developer to the developing sleeve 43 is cut off. Then, after a predetermined time (time: t6), the developing device drive clutch is turned off, and the developing operation is completed. At the time when the electromagnetic clutch 66 is turned off, the developer is still present on the developing sleeve 48, and the magnetic pole N2 moves from the facing portion to the magnetic pole N1.
By the developer held up to the facing portion, the development up to the rear end of the electrostatic latent image is performed. In other words, at the time t5 when the electromagnetic clutch 66 is turned off, the developer is rotated by the rotation of the developing sleeve 43 from the facing portion of the magnetic pole N2 to the facing portion of the magnetic pole N1 at the time t5 when the trailing end of the electrostatic latent image passes through the developing area. It is set as soon as it is transported to.

(5) Structure and operation of stirring screw: The stirring screw 51 will be described in detail with reference to FIGS. The rotating shaft 60 of the stirring screw 51 is arranged in a toner replenishing passage 74 formed so as to project from the bottom portion of the housing 34 and the housing side wall 53, and the toner replenishing passage 74 is formed in the rotating shaft portion 75 located in the toner replenishing passage 74.
A replenishment blade 76 having a diameter slightly smaller than the inner diameter is provided.
In addition, the above-mentioned replenishment blade 7 is attached to the rotary shaft portions 77 and 78 included in the region up to the predetermined distance from both side walls of the housing 53.
Inflow side feed vanes 79 and outflow side feed vanes 8 having a diameter larger than 6
0 is provided. Further, on the rotary shaft portion 81 sandwiched between these feed blades 79, 80, these feed blades 79, 80
Feed blades 82 having a larger diameter than the above are provided at predetermined intervals. The rotary shaft 60, the supply blade 76, and the feed blades 79 and 80 form an inner screw 73.

An inflow pipe 83 having a diameter larger than that of the feed blade 79 and smaller than that of the central feed blade 82 is concentrically provided around the inflow side feed blade 79 adjacent to the toner replenishing path 74, and One end is fixed to the housing side wall 53. Further, the inflow pipe 83 is provided with a toner inflow opening 84, and the inflow opening 84 is directed upward at a predetermined angle. On the other hand, an outflow pipe 85 having the same diameter as the inflow pipe 83 is concentrically provided around the opposite outflow feed blade 80, and one end of the outflow pipe 85 is fixed to the other housing side wall 53. Further, the outflow pipe 85 has a toner outflow opening 86, and the outflow opening 86 faces downward.

A screw pipe 87 is externally fixed to the periphery of the large-diameter feed vane 82, and both ends of the screw pipe 87 are externally attached without contact with the inflow pipe 83 and the outflow pipe 85. Further, in the screw pipe 87, a plurality of openings 8 are provided in a portion that covers the inflow pipe 83 and the outflow pipe 85.
8, 89 are formed at equal intervals in the circumferential direction. Further, on the outer peripheral portion of the screw pipe 87, a protrusion 90 is spirally provided along the outer peripheral portion.

A stirring screw 51 having the above structure
When the rotation is transmitted to the rotating shaft 60 and rotates in the direction of arrow 52, the developer located inside the screw pipe 87 is conveyed in the direction of arrow 91 by the rotation of the feed blade 82, and the outflow opening of the outflow pipe 85. The screw pipe 87 through the opening 86 of the portion 86 and the screw pipe 87.
Spills outside. The developer on the outside of the screw pipe 87 is conveyed by the rotation of the protrusion 90 in the opposite direction, that is, the arrow 92 direction. Also, the developer is 90
Is pumped up and supplied to the supply roller 46.
The developer conveyed to the toner replenishment side without being supplied to the supply roller 46 is the opening 88 of the screw pipe 87.
And falls inside the inflow pipe 83 through the inflow opening 84 of the inflow pipe 83, and is conveyed in the direction of arrow 91 in the screw pipe 87 by the feed blades 79, 82 and 80. Then, the toner of the developer and the carrier conveyed in this manner are frictionally contacted with each other and are charged to a predetermined polarity.

When it is determined from the detection result of the toner concentration detecting sensor 95 that the toner concentration is lower than a predetermined reference concentration, toner is replenished to the toner replenishing path 74 from a toner replenishing device (not shown). The replenished toner is conveyed to the inside of the housing 34 based on the rotation of the toner replenishment blade 76, and is replenished to the developer conveyed through the inside of the inflow pipe 83 and the inside of the screw pipe 87. Further, the replenished toner is mixed with the developer and comes into contact with the carrier to be charged to a predetermined polarity and potential.

(6) Continuous copying operation: four developing units 11,
The control of the developing device when driving 12, 13, and 14 to continuously copy a multicolor image will be described with reference to the time chart of FIG. When a start signal is input to the copying machine 1 by turning on a print switch (not shown) or the like, the static eliminator 17 is turned on and the residual charge on the photoconductor 9 is removed. Further, the charger 10 is turned on to uniformly charge the outer peripheral surface of the photoconductor 9. After a predetermined time, the laser is exposed from the exposure device 7 to the charged area on the photoconductor 9, and the photoconductor 9 is exposed.
The electrostatic latent images Y1, M1, and C for the first sheet corresponding to the image data of yellow, magenta, cyan, and black are shown on the top.
1 and K1 are created at a constant timing. Developer 1
1, 12, 13, and 14 transmit driving force to the developing units 11, 12, 13, and 14 after a predetermined time from the start of exposure based on the image data of yellow, magenta, cyan, and black, respectively, and supply the developing sleeves 43, respectively. Sleeve 4
8. Rotate the stirring screw 51. The predetermined time from the start of exposure to the driving of the developing device depends on the distance from the exposure position to the developing area of each developing device, and is set longer for the developing device located on the downstream side in the rotation direction of the photoconductor 9. There is. At the same time when the driving of the developing devices 11, 12, 13, 14 is started, the developing sleeve 43 of each developing device is started.
To the developing biases VB (Y), VB (M), VB (C),
VB (K) is applied and the corresponding developing devices 11, 12, 1
3 and 14, the electrostatic latent images Y1, M1, C for the first sheet
1 and K1 are developed respectively.

When the drive is transmitted to the developing device 14 located on the most downstream side in the moving direction of the photoconductor 9 during the developing operation of the first sheet, at the same time, the most upstream is prepared for the development of the second sheet. The drive is transmitted to the developing device 11 located at. However, at this point, the developing bias V to the most upstream developing device 11 is
B (Y) is off. Therefore, although the yellow developer of the most upstream developing device 11 contacts the first electrostatic latent image K1 to be developed by the most downstream developing device 14, the developing bias VB (Y) is turned off. , That is, developing unit 11
Is a non-developed state, the electrostatic latent image K1 is not substantially developed. Further, since the electrostatic latent image K1 is developed with the black toner, even if the yellow developer may adhere to the electrostatic latent image K1, the color mixture is not noticeable at all.

The exposure start for the second image is the first
It is performed in agreement with the exposure timing of each color in the image formation of the first sheet. That is, the time from the formation of the black electrostatic latent image K1 for the first sheet to the formation of the yellow electrostatic latent image Y2 for the second sheet is the same for each electrostatic image for the first sheet. It is equal to the time interval for forming the latent images Y1, M1, C1, K1. Then, after a predetermined time from the start of image exposure of the second sheet, the developing device 14 is stopped and the developing operation for the black electrostatic latent image K1 of the first sheet ends. At this time, the developing device 11 is kept in a driving state. Then, at the same time when the driving of the developing device 14 is stopped, or when a predetermined time elapses thereafter, the developing bias VB (Y) is turned on and the developing device 11 develops the second electrostatic latent image Y2. Hereinafter, image formation is similarly performed.

(7) Other Embodiments: In the above embodiment, the developer in the developing device is switched between the contact state and the non-contact state with the photoconductor based on the turning on / off of the electromagnetic clutch 66. As shown in FIG. 14, each developing device 11, 1
2, 13 and 14 are rotatably supported about shafts 154, 155, 156 and 157 that support the input gears 54, and eccentric cams 158, 159 and 16 are provided.
The developer held by the developing roller 43 may be switched between the contact state and the non-contact state with the photoconductor 9 based on the rotations of 0 and 161.

Further, in the above embodiment, during continuous copying, the most upstream developing device 11 driven simultaneously with the most downstream developing device 14 is used.
In this case, the developing bias VB (Y) is turned off to keep the developing state in the driven state, but when the developing device of the type shown in FIG. 14 is used, the developing device is removed from the photoconductor. It is retracted and kept in a non-contact state with the developer, and the developing device is moved to bring the developer into contact with the photoconductor to switch to the developing state. Further, the developing sleeve may be switched between the developing state and the non-developing state by switching between the rotating state and the non-rotating state.

[0035]

As is apparent from the above description, according to the present invention, the most upstream developing device is driven in the non-developing state at the same time when the developing operation of the most downstream developing device is started. An image without disturbance is obtained without being subjected to vibration or shock during the developing operation of the developing device. Further, when a multicolor image is continuously formed, the photoconductor is not unnecessarily rotated, and the durable life of the photoconductor can be extended.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a multicolor copying machine.

FIG. 2 is a cross-sectional view of a developing device.

FIG. 3 is a magnetic field distribution diagram of a developing roller and a supply roller.

FIG. 4 is a perspective view showing a drive system of a developing device.

5 is a perspective view showing a drive system of the developing device together with FIG.

FIG. 6 is a diagram illustrating the movement of the developer inside the developing device.

FIG. 7 is a view for explaining the movement of the developer inside the developing device, following FIG.

FIG. 8 is a view for explaining the movement of the developer inside the developing device, following FIG. 7.

FIG. 9 is a view for explaining the movement of the developer inside the developing device, following FIG. 8. It is a perspective view of a stirring screw.

FIG. 10 is a perspective view of a stirring screw.

FIG. 11 is a sectional view of a developing device including a stirring screw.

FIG. 12 is a plan view showing the components of the stirring screw.

FIG. 13 is a time chart in the case of continuously copying a multicolor image.

FIG. 14 is a diagram showing another mechanism for switching the developing device between a developer contact state and a developer non-contact state.

[Explanation of symbols]

9 ... Photoconductor, 11 ... Developing device, 36 ... Developing roller, 46 ...
Supply roller, 51 ... stirring sleeve.

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[Procedure amendment]

[Submission date] November 15, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Delete

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Delete

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

(5) Structure and operation of stirring screw: The stirring screw 51 will be described in detail with reference to FIGS. The rotating shaft 60 of the stirring screw 51 is arranged in a toner replenishing passage 74 formed so as to project from the bottom portion of the housing 34 and the housing side wall 53, and the toner replenishing passage 74 is formed in the rotating shaft portion 75 located in the toner replenishing passage 74.
A replenishment blade 76 having a diameter slightly smaller than the inner diameter is provided.
In addition, the above-mentioned replenishment blade 7 is attached to the rotary shaft portions 77 and 78 included in the region up to the predetermined distance from both side walls of the housing 53.
Inflow side feed vanes 79 and outflow side feed vanes 8 having a diameter larger than 6
0 is provided. Further, on the rotary shaft portion 81 sandwiched between these feed blades 79, 80, these feed blades 79, 80
Feed blades 82 having a larger diameter than the above are provided at predetermined intervals. The rotary shaft 60, the supply blade 76, and the feed blades 79 and 80 form an inner screw 73.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yu Hama Michi 2-33 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka, Osaka International Building Minolta Co., Ltd. (72) Inventor ▲ Shinichi Yoshimoto Osaka-shi, Osaka 2-13-3 Azuchi-cho, Chuo-ku Osaka International Building Minolta Co., Ltd.

Claims (1)

[Claims] 1. A plurality of developing devices are arranged around a photoconductor,
In a multicolor image forming apparatus that sequentially drives a developing device on the upstream side with respect to the moving direction of a photoconductor to create a multicolor image, when a plurality of multicolor images are continuously formed, the development of the most downstream developing device is performed. An image forming method for a multicolor image forming apparatus, characterized in that, at the same time as the operation is started, the most upstream developing device is driven in a non-developing state.