JP4489517B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that sequentially transfers a plurality of colors of visible images on an intermediate transfer member and then retransfers the plurality of color images on the intermediate transfer member to a recording medium to form a color image.

  In Patent Document 1, two developing units are arranged on each photoconductor provided in each of two image stations arranged around an intermediate transfer member, and the two developing units are switched to allow different colors on the photoconductor. A process of creating a visual image is performed on each of the two photoconductors, and each visible image is sequentially transferred onto the intermediate transfer member, and then the transferred image is retransferred to a sheet to form a color image. An image forming apparatus is described.

  According to the image forming apparatus of Patent Document 1, the developing roller of each color developing device is arranged at a predetermined distance from the surface of the photosensitive member, and a panning magnet for controlling the supply of toner to the developing roller is arranged. . Each developing device arranged around the photoconductor switches the development color by switching contact / non-contact of the toner layer between the developing roller and the photoconductor.

JP 2000-137362 A

  However, in the image forming apparatus configured to switch contact / non-contact of the toner layer to the photoconductor as in Patent Document 1, the photoconductor is in a state where the toner layer is in contact with the photoconductor and in a state where the toner layer is not in contact. The load for rotational drive is different. For this reason, there is a problem that the rotational speed of the photosensitive member fluctuates when the development color is switched. That is, if the development color is switched during the formation of the latent image on the photoconductor, the latent image on the photoconductor is disturbed. Further, when the development color is switched during the intermediate transfer from the photosensitive member to the intermediate transfer member, the image on the intermediate transfer member is disturbed. This will be described in more detail below.

  As shown in FIG. 14, in the process of transferring the cyan image formed on the photosensitive drum 101 to the intermediate transfer belt 102 by the developing device 100C, when the development color switching operation from cyan to yellow is started at the end of cyan development, Since the intermediate transfer from the photosensitive drum 101 to the intermediate transfer belt 102 is in operation, the cyan toner image on the intermediate transfer belt 102 is disturbed by the influence of the photosensitive drum speed fluctuation. Therefore, it is necessary to wait until the end of the intermediate transfer of the cyan image (see FIG. 15) before starting the developing color switching operation from cyan to yellow. In addition, if exposure of the yellow image by the optical writing unit 103 (see FIG. 16) is started at the time of FIG. 14, a developing color switching operation from cyan to yellow is performed during the exposure operation. The latent image on the photosensitive drum 101 is disturbed by the influence of the speed fluctuation of the 101. Therefore, it is necessary to wait for the start of exposure of the yellow image by the optical writing unit 103 until the end of the development color switching operation from cyan to yellow (see FIG. 16).

  Also, FIG. 17 shows a black image formed on the photosensitive drum 101 by the developing device 100K to the intermediate transfer belt 102. At the time when the black development is completed, black is changed to cyan to form the next full color image. This shows a case where the developing color switching operation is started. In this case, since the intermediate transfer from the photosensitive drum 101 to the intermediate transfer belt 102 is in operation, the image on the intermediate transfer belt 102 is disturbed due to the influence of the speed fluctuation of the photosensitive drum 101. Therefore, it is necessary to wait until the end of the intermediate transfer of the black image (see FIG. 18) before starting the development color switching operation from black to cyan. In addition, if exposure of the cyan image by the optical writing unit 103 is started at the time of FIG. 17, the developing color switching operation from black to cyan is performed during the exposure operation. Due to the influence, the latent image on the photosensitive drum 101 is disturbed. Therefore, it is necessary to wait for the start of exposure of the cyan image by the optical writing unit 103 until the end of the developing color switching operation from black to cyan (see FIG. 19).

In the image forming operation described above, as shown in FIGS. 16 and 19, there are areas on the intermediate transfer belt 102 where images cannot be formed.
Image formation impossible area = space a between the exposure position X and the intermediate transfer position T by the optical writing unit 103 + the distance b through which the image travels during the developing color switching operation
Therefore, it is necessary to increase the size of the intermediate transfer belt 102. This not only causes an increase in the size and cost of the apparatus, but also causes a problem that it is difficult to improve the image quality of the output image due to the influence of elongation, vibration, and the like due to a decrease in rigidity of the intermediate transfer belt 102.

  In particular, the problem of load fluctuation on the photosensitive drum 101 due to the development color switching is that the interval (developing gap) between the photosensitive drum 101 and the developing device (developing roller) 100 during the developing operation in the two-component developing method is highly accurate. For the setting, a roller member is rotatably mounted coaxially with the developing device (developing roller) 100, and the roller member is brought into contact with the surface of the photosensitive drum 101, or as in the one-component developing method. This is remarkable when the developing device (developing roller) 100 is brought into contact with the photosensitive drum 101 during the developing operation. The configuration using the abutting roller member can realize high image quality at low cost, and the one-component development method is advantageous for reducing the size and cost of the apparatus. Therefore, the downsizing of the image forming apparatus is a major obstacle to reducing the size and cost of the image forming apparatus and improving the image quality.

  An object of the present invention is to prevent image disturbance due to a development color switching operation and to realize high image quality.

  SUMMARY OF THE INVENTION An object of the present invention is to reduce the size and cost of an apparatus by reducing the size of an intermediate transfer member and to improve the image quality of an output image by increasing the rigidity of the intermediate transfer member.

According to a first aspect of the present invention, there is provided an image forming apparatus, wherein an image carrier on which a latent image is formed by exposure by an exposure device and an outer periphery of the image carrier are arranged side by side so as to be formed on the image carrier. A plurality of different color developing means for making visible latent images visible; development switching means for switching between a developing state and a non-developing state of the latent image formed on the image carrier of each developing means; An intermediate for transferring a multi-color image formed by sequentially transferring a visible image on the image carrier developed by switching the development color sequentially by switching the development means by the development switching means to a recording medium A transfer member, and a circumference of the image carrier from a position facing the developing unit located most downstream in the rotation direction of the image carrier to a transfer position with the intermediate transfer member. The length L1, 1 <v × t and (v:: rotational linear velocity of the image bearing member surface, t developing switching means time to switch to a developing condition developing means from the non-developing state).
The development switching unit is configured such that the rear end of the visible image formed on the image carrier by the predetermined development unit is located on the most downstream side in the rotation direction of the image carrier among the development units. After passing the opposite position of the developing means, the developing means corresponding to the color of the visible image to be formed next is switched from the non-development state to the development state.

Therefore, the circumferential length L1 of the image carrier from the position facing the developing unit located on the most downstream side in the image carrier rotating direction to the transfer position with the intermediate transfer member is used as the image during the development color switching operation by the development switching unit. The development switching means has a rear end of a visible image formed on the image carrier by the predetermined development means, and the image is not included in each of the development means. The developing means corresponding to the color of the visible image to be formed next is switched from the non-development state to the development state after passing through the position opposite to the development means located on the most downstream side in the rotation direction of the carrier. Thus, the intermediate transfer operation of the developed image is completed at the timing when the load variation of the image carrier due to the development color change occurs, and the image is disturbed even if the rotational speed variation of the image carrier occurs. It does not occur. For this reason, an area where an image cannot be formed on the intermediate transfer member is an image non-formation region = the interval between the exposure position by the exposure device and the position opposite to the developing unit located on the most downstream side in the image carrier rotation direction + development color switching operation Thus, the intermediate transfer member can be downsized because the range of the distance traveled by the image is obtained. As a result, image disturbance can be prevented by avoiding fluctuations in the speed of the image carrier during intermediate transfer, so that the quality of the output image can be improved, and the peripheral length of the intermediate transfer member can be reduced. Not only can cost reduction be realized, but also higher image quality can be achieved by increasing the rigidity of the intermediate transfer member.

According to a second aspect of the invention, in the image forming apparatus according to claim 1 Symbol placement, the developing unit, the relative latent image formed on the image bearing member performs a visible image by the two-component developing method And a positioning member that maintains a distance between the surface of the developing means and the surface of the image carrier in a developed state by contacting the image carrier.

  Therefore, in the case of adopting a configuration in which the positioning member is brought into contact with the surface of the image carrier in order to set the interval (development gap) between the image carrier and the developing means during the developing operation in the two-component development method with high accuracy. Since the influence of the collision between the positioning member and the image carrier at the moment when the development state is changed by the development color switching operation from the non-development state is large, the effect of this configuration is great. That is, along with the improvement of the image quality due to the high development gap accuracy by the positioning member, the effect of image disturbance due to the avoidance of the speed fluctuation of the image carrier during the process operation is great, so it is possible to achieve a significant increase in image quality, and further downsizing the apparatus, Cost reduction is also possible.

According to a third aspect of the present invention, there is provided an image carrier on which a latent image is formed by exposure by an exposure device, and a latent image formed on the image carrier that is arranged in parallel facing the outer periphery of the image carrier. A plurality of different color developing means for making visible images, a development switching means for switching between a development state and a non-development state of the latent image formed on the image carrier of each of the development means, and the development switching means An intermediate transfer body for transferring a multi-color image formed by sequentially transferring a visible image on the image carrier developed by sequentially switching a development color by switching each developing means to a recording medium; A circumferential length L1 of the image carrier from a position opposed to the developing means located on the most downstream side in the rotation direction of the image carrier among the developing means to a transfer position with the intermediate transfer member, L1 <v × t ( : Rotational linear velocity of the image bearing member surface, t: developing switching means and time to switch to a developing condition developing means from the non-developing state).
The development switching unit is configured such that the rear end of the visible image formed on the image carrier by the predetermined development unit is located on the most downstream side in the rotation direction of the image carrier among the development units. After passing the position opposite to the developing means, the developing means corresponding to the color of the visible image to be formed next starts switching from the non-developing state to the developing state, and the developing means changes from the non-developing state to the developing state. Almost at the same time, the switching of the developing means forming the visible image from the developing state to the non-developing state is started.

Therefore, the circumferential length L1 of the image carrier from the position facing the developing unit located on the most downstream side in the image carrier rotating direction to the transfer position with the intermediate transfer member is used as the image during the development color switching operation by the development switching unit. The development switching means has a rear end of a visible image formed on the image carrier by the predetermined development means, and the image is not included in each of the development means. After passing through the position facing the developing means located on the most downstream side in the rotation direction of the carrier, the developing means corresponding to the color of the visible image to be formed next starts switching from the non-developing state to the developing state. At substantially the same time when the non-developed state of the developing means to complete the switching to the developing state, to start switching to the non-developing state from developing state of the developing means to form a visible image, a non-developing form The load fluctuation of the image carrier accompanying the completion of switching from the development state to the development state and the load fluctuation of the image carrier accompanying the start of switching from the development state to the non-development state occur at the same timing. The intermediate transfer operation is completed and the exposure operation of the latent image developing device to be developed next is not started, and the image is not disturbed even if the rotation speed of the image carrier changes. As a result, image disturbance can be prevented by avoiding speed fluctuations of the image carrier during intermediate transfer and latent image formation, so that the output image can be improved in image quality and the circumference of the intermediate transfer member can be reduced. Not only can the apparatus be miniaturized and the cost can be reduced, but the intermediate transfer body can be made more rigid, resulting in higher image quality.

According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect , the opposite of the developing means located on the most upstream side in the rotation direction of the image carrier among the developing means from the exposure position by the exposure device. The circumferential length L2 of the image carrier to the position is L2> v × t.

  Therefore, the distance L2 between the exposure position by the exposure apparatus and the position facing the developing means located on the most upstream side in the rotation direction of the image carrier is made larger than the distance (v × t) that the image travels during the development color switching operation. Therefore, it is possible to reliably prevent image defects in which cyan is developed with respect to the latent image to be developed in yellow when the developing color is switched from the cyan developing means located on the most upstream side to the next yellow developing means. become. As a result, it is possible to prevent image disturbance due to avoiding speed fluctuations of the image carrier during the process operation, and it is possible to reliably prevent deterioration in image quality such as color mixing and to achieve a significant increase in image quality.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third aspect , the developing means visualizes the latent image formed on the image carrier by a one-component developing method. In the development state, the surface of the developing means comes into contact with the surface of the image carrier.

  Therefore, when the developing means is brought into contact with the image carrier during the developing operation as in the one-component development method, the development color switching operation from the non-development state where the developing means comes into contact with the image carrier to the developed state is completed. The effect of this configuration is great because the influence of the development color switching operation from the development state in which the developing means is separated from the image carrier to the non-development state is large. That is, since the effect of image disturbance due to avoiding speed fluctuations of the image carrier during the process operation is great, a significant increase in image quality can be achieved. Since the length can be reduced, the device can be greatly reduced in size and cost.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the developing means other than the developing means located on the most downstream side in the rotation direction of the image carrier among the developing means. The developing means is disposed on the developing means in which the rear end of the formed visible image is located on the most downstream side in the rotation direction of the image carrier after the completion of the visible image formation on the latent image formed on the image carrier. A test patch for density detection in image compensation control is formed before passing through the opposing position.

  Therefore, the test patch for process control is intended to detect the image density, and there is no problem even if there is some variation in position. Therefore, by forming the process control test patch in an area where an output image cannot be formed due to the influence of the speed fluctuation of the image carrier, the area of the image carrier or the intermediate transfer body can be effectively used. As a result, the area of the image carrier and the intermediate transfer member can be used effectively, so that the apparatus can be downsized, the cost can be reduced, and the printing speed can be improved.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, after the development color switching by the development switching means is completed, the switched development means is the latent image that has started formation. A density detection test patch in the image compensation control is formed before the image reaches a position where the images face each other.

  Therefore, the test patch for process control is intended to detect the image density, and there is no problem even if there is some variation in position. Therefore, by forming the process control test patch in an area where an output image cannot be formed due to the influence of the speed fluctuation of the image carrier, the area of the image carrier or the intermediate transfer body can be effectively used. As a result, the area of the image carrier and the intermediate transfer member can be used effectively, so that the apparatus can be downsized, the cost can be reduced, and the printing speed can be improved.

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, a plurality of the image carriers are provided, and a plurality of color images are formed on the intermediate transfer body using the image carriers. Form.

  Accordingly, since the number of developing units arranged between the exposure position which is an image formation impossible area and the most downstream development position can be reduced, the interval between the exposure position and the most downstream development position can be reduced. In other words, since the image forming load area is reduced, it is possible to further reduce the size of the intermediate transfer member, and it is possible to significantly reduce the size and cost of the apparatus and to increase the rigidity and vibration of the intermediate transfer member. The output image can be further improved in image quality, and the printing speed is greatly improved compared to the configuration using one image carrier.

  According to the first aspect of the present invention, image disturbance can be prevented by avoiding speed fluctuations of the image carrier during intermediate transfer, so that it is possible to achieve high image quality of the output image, and the circumference of the intermediate transfer member. Since the reduction can be achieved, not only can the apparatus be reduced in size and cost, but also higher image quality can be achieved by increasing the rigidity of the intermediate transfer member.

According to the second aspect of the present invention, the image quality is improved by improving the development gap accuracy by the positioning member, and the effect of the image disturbance by avoiding the speed fluctuation of the image carrier during the process operation is great. In addition, it is possible to reduce the size and cost of the apparatus.

According to the third aspect of the present invention, image disturbance can be prevented by avoiding speed fluctuations of the image carrier during intermediate transfer and latent image formation, so that the output image can be improved in image quality and the intermediate transfer body can be realized. Therefore, not only can the apparatus be miniaturized and the cost can be reduced, but also higher image quality can be achieved by increasing the rigidity of the intermediate transfer member.

According to the fourth aspect of the invention, it is possible to prevent image disturbance due to avoiding speed fluctuation of the image carrier during the process operation, and to surely prevent deterioration in image quality such as color mixing, thereby achieving a significant increase in image quality. it can.

According to the invention described in claim 5, since the effect of image disturbance due to avoiding the speed fluctuation of the image carrier during the process operation is great, a significant improvement in image quality can be achieved, and the developing means can be reduced in size by adopting the one-component developing system. In addition, the circumference of the intermediate transfer member can be reduced, so that a significant reduction in the size and cost of the apparatus can be realized.

According to the invention described in claim 6, since the area of the image carrier and the intermediate transfer member can be used effectively, the apparatus can be downsized, the cost can be reduced, and the printing speed can be improved.

According to the seventh aspect of the present invention, the area of the image carrier and the intermediate transfer member can be used effectively, so that the apparatus can be downsized, the cost can be reduced, and the printing speed can be improved.

According to the eighth aspect of the invention, since the image forming load area is reduced, the intermediate transfer member can be further reduced in size, and the apparatus can be greatly reduced in size and cost. Rigidity can prevent elongation, vibration, and the like, achieve higher image quality of the output image, and greatly improve the printing speed compared to the configuration using one image carrier.

[First embodiment]
A first embodiment of the present invention will be described with reference to FIGS. In this embodiment, a color copying machine is applied as an image forming apparatus.

  Here, FIG. 1 is a side view showing a schematic structure of the color copying machine 1, and FIG. 2 is a side view showing a schematic structure of the printer engine 3. As shown in FIG. 1, a printer engine 3, a fixing device 4, a paper feed cassette 5 and the like are provided in a main body case 2 of a color copying machine 1 which is an image forming apparatus. A scanner 6 that reads an image of a document is provided on the upper part of the main body case 2.

  The scanner 6 includes an exposure lamp 8 that exposes a document (not shown) placed on the contact glass 7, an exposure scanning unit 8 that includes a reflection mirror that sequentially reflects reflected light from the document surface, an imaging lens 9, It is composed of an RGB-compatible CCD (Charge Coupled Device) image sensor 10 or the like. The light emitted from the exposure lamp is reflected by the original surface, and the reflected light from the original surface is sequentially reflected by the reflection mirror and then received by the CCD image sensor 10. The light received by the CCD image sensor 10 is photoelectrically converted into an electrical signal (analog signal), converted into a digital signal, and then subjected to image processing by an image processing unit (not shown).

  The printer engine 3 includes a photosensitive drum 11 that is an image carrier that is driven to rotate counterclockwise, a charging device 12 that is disposed around the photosensitive drum 11, an optical writing unit that is an exposure device using a semiconductor laser, and the like. 13, a developing unit 14, an intermediate transfer belt 16 as an intermediate transfer member, a transfer device 17, and the like. During image formation by the printer engine 3, the outer peripheral surface of the photosensitive drum 11 is uniformly charged by the charging device 12, and image processing is performed by the image processing unit toward the outer peripheral surface of the uniformly charged photosensitive drum 11. A laser beam corresponding to the image data is emitted from the optical writing unit 13, and an electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 11. The electrostatic latent image is developed with toner from the developing unit 14 to form a toner image.

  Here, as shown in FIG. 2, the developing unit 14 stores a developing device 15K that stores black (K) toner, a developing device 15M that stores magenta (M) toner, and a yellow (Y) toner. The developing device 15Y has a four-color developing device (developing means), which is a developing device 15C containing cyan (C) toner. These developing devices 15K, 15M, 15Y, and 15C are connected to a development switching mechanism 18, respectively. The development switching mechanism 18 functions as a development switching means, and prevents color mixing due to the toner of the other development devices moving to the photosensitive drum 11 when one development device is operating. In addition, the non-operating developing devices are moved away from the peripheral surface of the photosensitive drum 11 so that the toner of these developing devices does not contact the photosensitive drum 11.

  That is, each developing device 15 storing toners of cyan, yellow, magenta, and black is moved by the development switching mechanism 18 so that the first color (for example, cyan) developing device 15C is opposed to the photosensitive drum 11. The toner is attached to the electrostatic latent image on the photosensitive drum 11 and developed as a cyan toner image. An intermediate transfer belt 16 is disposed at the primary transfer position T1 of the photosensitive drum 11, and this cyan toner image is in contact with the photosensitive drum 11 and rotates clockwise on the intermediate transfer belt 16. Primary transfer.

  Such a primary transfer process is sequentially performed for the other three colors, that is, yellow, magenta, and black, and four color toner images are superimposed on the intermediate transfer belt 16.

In the color copying machine 1 of the present embodiment, as shown in FIG. 2, the developing device 15K located on the most downstream side in the rotation direction of the photosensitive drum 11 among the developing devices 15K, 15M, 15Y, and 15C. The circumferential length L1 of the photosensitive drum 11 from the opposite position K to the transfer position T1 with the intermediate transfer belt 16 is
L1 <v × t (v: linear rotation speed of the surface of the photosensitive drum 11, t: time for the development switching mechanism 18 to switch the developing device 15 from the non-development state to the development state)
And

Further, as shown in FIG. 2, the developing device 15C that is located on the most upstream side in the rotation direction of the photosensitive drum 11 among the developing devices 15K, 15M, 15Y, and 15C from the exposure position by the optical writing unit 13 is opposed to the developing device 15C. The circumferential length of the photosensitive drum 11 from the facing position C of the developing device 15C located on the most upstream side to the facing position K of the developing device 15K located on the most downstream side is L3. When the maximum length (image area) in the rotation direction of the photosensitive drum 11 of the image transferred onto the intermediate transfer belt 16 is L4 and the circumferential length of the intermediate transfer belt 16 is L5,
v × t <L5-L4-L3-L2
It is.

  The color toner image formed on the intermediate transfer belt 16 is transferred onto the recording medium P by the transfer device 17 located at the secondary transfer position T2. This recording medium P is fed from the paper feed cassette 5 or the manual feed tray 22 provided on the side surface of the main body case 2.

  The recording medium P on which the color toner image has been transferred is conveyed by the conveying belt 19 and fixed by the fixing device 4. The recording medium P fixed by the fixing device 4 is discharged onto the discharge tray 20 or sent to the reverse tray 21 for image formation on the back surface.

  The color copying machine 1 has a controller 51 for controlling each part as shown in FIG. The controller 51 includes a central processing unit (CPU) 52 that centrally controls each unit such as the scanner 6 and the printer engine 3, a read only memory (ROM) 53 that stores various programs executed by the CPU 52, and a work area of the CPU 52. RAM (Random Access Memory) 54 or the like that functions as a bus line 55 is connected. The CPU 52 is connected to a motor 50 that controls the rotation of each unit, an actuator 18a of the development switching mechanism 18, and the like.

  Next, a characteristic image forming operation among the image forming operations of the color copying machine 1 of the present embodiment will be described.

  First, the process of starting the exposure of the yellow image from the process of transferring the cyan image formed on the photosensitive drum 11 to the intermediate transfer belt 16 will be described with reference to FIGS. In the color copying machine 1 according to the present embodiment, in the step of transferring the cyan image formed on the photosensitive drum 11 to the intermediate transfer belt 16, after the cyan development by the developing device 15C is completed (see FIG. 4), When passing the position K facing the developing device 15K, the developing switching mechanism 18 starts the developing color switching operation to the yellow image by the developing device 15Y (see FIG. 5). The exposure (exposure position X) of the yellow image from the writing unit 13 is started (see FIG. 6).

  Next, the process of starting the exposure of the cyan image from the process of transferring the black image formed on the photosensitive drum 11 to the intermediate transfer belt 16 will be described with reference to FIGS. In the color copying machine 1 of the present embodiment, in the step of transferring the black image formed on the photosensitive drum 11 to the intermediate transfer belt 16, after the black development by the developing device 15K is completed (that is, the rear end of the black image is the developing device 15K). The development switching mechanism 18 starts the development color switching operation to a cyan image by the development switching mechanism 18 (see FIG. 7), and after completion of the development switching operation to the cyan image, the optical writing is performed. The cyan image exposure (exposure position X) from the unit 13 is started (see FIG. 8).

In this way, the distance L1 from the facing position K of the developing device 15K to the primary transfer position T1 that is the transfer position with respect to the intermediate transfer belt 16 is made smaller than the distance (v × t) that the image travels during the development color switching operation. At the same time, after the rear end of the developed image has passed the facing position K of the developing device 15K, the developing device 15 (15K, 15M, 15Y, 15C) that performs the next development is switched from the non-development state to the development state. When the development color is switched from color to black, it is possible to reliably prevent image defects in which black is developed with respect to latent images to be developed in other colors, and at the timing when load fluctuation of the photosensitive drum 11 occurs due to development color switching. The intermediate transfer operation of the developed image has been completed, and the image is not disturbed even if the rotational speed fluctuation of the photosensitive drum 11 occurs. For this reason, as shown in FIGS. 6 and 8, the region where an image cannot be formed on the intermediate transfer belt 16 is
Image non-formable area = space A between the exposure position X and the facing position K of the developing device 15K + the distance B the image travels during the development color switching operation
Thus, the intermediate transfer belt 16 can be downsized.

  Further, here, the distance (v × t) B that the image travels during the developing color switching operation is defined as the distance between the circumferential length L5 of the intermediate transfer belt 16 and the image region L4 and the exposure position X to the facing position K of the developing device 15K ( By making the distance smaller than the distance excluding L3 + L2), the exposure operation of the latent image to be developed from the optical writing unit 13 is started at the timing when the load fluctuation of the photosensitive drum 11 occurs due to the development color switching. Therefore, even if the rotational speed fluctuation of the photosensitive drum 11 occurs, the image is not disturbed.

  As described above, by reducing the size of the intermediate transfer belt 16, it is possible to reduce the size and cost of the apparatus, and also to prevent the elongation, vibration, and the like by increasing the rigidity of the intermediate transfer belt 16, thereby increasing the output image. Image quality can be realized.

  In particular, in order to set the interval (development gap) between the photosensitive drum 11 and the developing device 15 (15K, 15M, 15Y, 15C) during the developing operation in the two-component developing method with high accuracy, the developing device 15 (15K, 15M). , 15Y, 15C), a roller member (not shown) that is a positioning member is rotatably mounted on the same axis, and the roller member is brought into contact with the surface of the photosensitive drum 11 in a non-development state. Since the influence of the collision between the roller member and the photosensitive drum 11 at the moment when the developing state is changed by the developing color switching operation from is large, the effect of this configuration is great.

  It should be noted that after the development of the image, until the rear end of the developed image passes the opposing position K of the developing device 15K, or after the exposure by the optical writing unit 13, the developing device 15 (15K, 15M, 15Y, 15C) until the opposite position is reached, the position accuracy of the image cannot be compensated for by the speed fluctuation of the photosensitive drum 11 due to the developing color switching operation, so that an image for output cannot be formed. The test patch for control is intended to detect the image density, and there is no problem even if there is some variation in position. Therefore, an area in which an output image cannot be formed due to the influence of the speed fluctuation of the photosensitive drum 11 (the rear end of the visible image formed after the visible image formation on the latent image formed on the photosensitive drum 11 is completed). After the development color switching by the development switching mechanism 18 is completed until it passes the position K facing the developing device 15K, the latent image that has been formed until it reaches the position facing the switched developing device 15 is reached. By forming a process control test patch, the areas of the photosensitive drum 11 and the intermediate transfer belt 16 can be used effectively. Since test patch formation for process control is described in JP-A-2002-214866, description thereof is omitted here.

As described above, according to the present embodiment, the circumference of the photosensitive drum 11 from the facing position K of the developing device 15K located on the most downstream side in the rotation direction of the photosensitive drum 11 to the transfer position T1 with the intermediate transfer belt 16 is achieved. By making the length L1 smaller than the distance (v × t) that the image travels during the development color switching operation by the development switching mechanism 18, at the timing when the load fluctuation of the photosensitive drum 11 occurs due to the development color switching, the development is performed. The intermediate transfer operation of the image thus completed is completed, and the image is not disturbed even if the rotational speed fluctuation of the photosensitive drum 11 occurs. For this reason, an area where an image cannot be formed on the intermediate transfer belt 16 is
Non-image forming area = the distance between the exposure position X of the optical writing unit 13 and the facing position K of the developing device 15K + the distance the image travels during the developing color switching operation, and the intermediate transfer belt 16 can be downsized. . As a result, image disturbance can be prevented by avoiding fluctuations in the speed of the photosensitive drum 11 during intermediate transfer, so that the quality of the output image can be improved, and the circumference of the intermediate transfer belt 16 can be reduced. Not only can the size and cost be reduced, but the rigidity of the intermediate transfer belt 16 can be increased to further increase the image quality.

  Further, the distance (v × t) that the image travels during the development color switching operation by the development switching mechanism 18 is developed from the peripheral length L5 of the intermediate transfer belt 16, the image area L4, and the exposure position X by the optical writing unit 13. By making the distance smaller than the distance excluding the interval (L3 + L2) between the opposing positions K of the device 15K, the optical writing of the latent image to be developed next is performed at the timing when the load fluctuation of the photosensitive drum 11 occurs due to the development color switching. The exposure operation from the embedding unit 13 is not started, and the image is not disturbed even if the rotational speed fluctuation of the photosensitive drum 11 occurs. As a result, image disturbance can be prevented by avoiding fluctuations in the speed of the photosensitive drum 11 during the formation of the latent image, so that higher image quality can be achieved.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIGS. In addition, the same part as 1st Embodiment mentioned above is shown with the same code | symbol, and abbreviate | omits description. The present embodiment is different from the first embodiment described above in the image forming operation.

In the color copying machine 1 of the present embodiment, as shown in FIG. 2, from the exposure position X by the optical writing unit 13, the developing device 15K, 15M, 15Y, 15C is the most in the rotation direction of the photosensitive drum 11. The circumferential length L2 of the image carrier up to the facing position C of the developing device 15C located on the upstream side,
L2> v × t (v: linear rotation speed of the surface of the photosensitive drum 11, t: time for the development switching mechanism 18 to switch the developing device 15 from the non-development state to the development state)
And

  Here, the process of starting the exposure of the yellow image from the process of transferring the cyan image formed on the photosensitive drum 11 to the intermediate transfer belt 16 will be described with reference to FIGS. In the color copying machine 1 according to the present embodiment, in the step of transferring the cyan image formed on the photoconductive drum 11 to the intermediate transfer belt 16, the position K where the rear end of the cyan image faces the developing device 15K after the cyan development is completed. When it passes, the developing switching mechanism 18 starts the switching operation of the developing device 15Y to the developing state (see FIG. 9). Simultaneously with the end of the switching operation of the developing device 15Y to the developing state by the developing switching mechanism 18, the switching operation of the developing device 15C to the non-developing state is started, and then the yellow image exposure (exposure) from the optical writing unit 13 is started. Position X) is started (see FIG. 10).

  Next, the process of starting the exposure of the cyan image from the process of transferring the black image formed on the photosensitive drum 11 to the intermediate transfer belt 16 will be described with reference to FIGS. In the color copying machine 1 of the present embodiment, in the step of transferring the black image formed on the photosensitive drum 11 to the intermediate transfer belt 16, after the black development by the developing device 15K is completed (that is, the rear end of the black image is the developing device 15K). ), The developing switching mechanism 18 starts the switching operation of the developing device 15C to the developing state (see FIG. 11). Then, simultaneously with the end of the switching operation of the developing device 15C by the development switching mechanism 18 to the developing state, the switching operation of the developing device 15K to the non-developing state is started, and then the exposure (exposure) of the cyan image from the optical writing unit 13 is started. Position X) is started (see FIG. 12).

  In this way, after the rear end of the developed image has passed the facing position K of the developing device 15K, the developing device 15 (15K, 15M, 15Y, 15C) that performs the next development is switched from the non-development state to the development state. Then, development of the developing device 15 (15K, 15M, 15Y, 15C) that was developing at the same time as the switching of the developing device 15 (15K, 15M, 15Y, 15C) that performs the development from the non-development state to the development state is completed. In order to start switching from the non-development state to the non-development state, the load variation of the photoconductor drum 11 accompanying the completion of the switch from the non-development state to the development state and The load fluctuation occurs at the same timing, and at the generation timing, the intermediate transfer operation of the developed image is finished and the next development is performed. Exposure operation from the optical writing unit 13 of the image has not been started, turbulence does not occur in the image even if the rotation velocity fluctuation of the photoreceptor drum 11 is generated. Further, the distance L2 between the exposure position X and the facing position C of the developing device 15C is made larger than the distance (v × t) that the image travels during the development color switching operation, so that the yellow color is changed when developing color is changed from cyan to yellow. Image defects in which cyan is developed with respect to the latent image to be developed can be reliably prevented.

  In particular, when the developing device 15 (15K, 15M, 15Y, 15C) is brought into contact with the photosensitive drum 11 during the developing operation as in the one-component developing method, the developing device 15 (15K, 15M, 15Y, 15C) is in contact with the development color switching operation from the non-development state to the development state, and the development state in which the developing device 15 (15K, 15M, 15Y, 15C) is separated from the non-development state. The effect of this configuration is great because the influence of the start of the development color switching operation to the development state is large.

  In the printer engine 3 of the color copying machine 1 according to each embodiment, only one photosensitive drum 11 provided with four developing devices 15 (15K, 15M, 15Y, 15C) is used on the intermediate transfer member 16. However, the present invention is not limited to this, and a multicolor image is formed on an intermediate transfer member using a plurality of image carriers (photosensitive drums, etc.) provided with a plurality of developing devices. You may apply to the structure to do. In the following, a two-station recording system using two photoreceptors provided with a plurality of developing devices (for details, see Japanese Patent Application Laid-Open Nos. 10-177286 and 11-125968) will be briefly described.

  FIG. 13 is a schematic configuration diagram showing a main part of the color copying machine 1 that uses two photosensitive drums 11a and 11b in which a plurality of developing devices are arranged in parallel and forms a full-color image on the intermediate transfer belt 16. As shown in FIG. Such a configuration is characterized in that the size of the apparatus can be reduced and the printing speed can be increased as compared with a configuration using a single photosensitive drum 11 (for details, refer to Japanese Unexamined Patent Application Publication No. 2002-214868). .

  In this color copying machine 1, at the time of image formation, the photosensitive drums 11a and 11b, which are two image carriers, are rotated in the counterclockwise direction, and the surfaces thereof are uniformly charged by the charging devices 12a and 12b. Exposure is performed according to image information input by the embedding units 13a and 13b to form an electrostatic latent image. Then, the two-color developing devices 15C and 15M of cyan and magenta, the two-color developing devices 15Y and 15K of yellow and black) are moved by the development switching mechanism 18, and the developing device 15C of the first color (for example, cyan) is moved. The developing device 15Y for the second color (for example, yellow) is positioned at the developing position facing the photoconductive drum 11b at the developing position facing the photoconductive drum 11a, and toner is applied to the electrostatic latent image on the photoconductive drum 11a. The toner is attached and developed as a cyan toner image, and the toner is attached to the electrostatic latent image on the photosensitive drum 11b to be developed as a yellow toner image. The cyan toner image and the yellow toner image are primary-transferred at primary transfer portions T11 and T12 on an intermediate transfer belt 16 that is an intermediate transfer member that contacts the photosensitive drums 11a and 11b and rotates counterclockwise. Transcribed. Then, the primary transfer process is sequentially performed for the other two colors, that is, magenta and black, and the four color toner images are superimposed on the intermediate transfer belt 16. These four color toner images are collectively transferred to the recording medium P conveyed from a paper feed cassette (not shown) by the transfer device 17 at the secondary transfer portion T2 to form a full color image. Obtainable.

  When the above configuration is applied, the number of the developing devices 15 arranged between the exposure position X, which is an image formation impossible area, and the most downstream development position can be reduced. Therefore, the interval between the exposure position X and the most downstream development position can be reduced. Can be reduced. In other words, since the image forming load area is reduced, the intermediate transfer belt 16 can be further reduced in size, and the apparatus can be greatly reduced in size and cost. The output image can be further improved in image quality, and the printing speed is greatly improved compared to the configuration using the photoconductor as one image carrier.

  In each embodiment, an example in which a color copying machine is applied as an image forming apparatus has been described. However, the present invention is not limited to this and can be applied to a color laser printer or the like.

  In each embodiment, the photosensitive drum 11 (11a, 11b) is used as the image carrier. However, the present invention is not limited to this. For example, a photosensitive belt or the like may be used.

  Furthermore, in each embodiment, the intermediate transfer belt 16 is used as an intermediate transfer member, but the present invention is not limited to this, and for example, an intermediate transfer drum, an intermediate transfer roller, or the like may be used.

1 is a side view showing a schematic structure of a color copying machine according to a first embodiment of the present invention. It is a side view showing a schematic structure of a printer engine. FIG. 2 is a block diagram showing electrical connection of each part built in a color copying machine. FIG. 7 is an explanatory diagram illustrating a part of a process of starting exposure of a yellow image from a process of transferring a cyan image formed on a photosensitive drum to an intermediate transfer belt. FIG. 7 is an explanatory diagram illustrating a part of a process of starting exposure of a yellow image from a process of transferring a cyan image formed on a photosensitive drum to an intermediate transfer belt. FIG. 7 is an explanatory diagram illustrating a part of a process of starting exposure of a yellow image from a process of transferring a cyan image formed on a photosensitive drum to an intermediate transfer belt. FIG. 7 is an explanatory diagram illustrating a part of a process of starting exposure of a cyan image from a process of transferring a black image formed on a photosensitive drum to an intermediate transfer belt. FIG. 7 is an explanatory diagram illustrating a part of a process of starting exposure of a cyan image from a process of transferring a black image formed on a photosensitive drum to an intermediate transfer belt. FIG. 10 is an explanatory diagram illustrating a part of a process of starting exposure of a yellow image from a process of transferring a cyan image formed on a photosensitive drum to an intermediate transfer belt in a color copying machine according to a second embodiment of the present invention. FIG. 7 is an explanatory diagram illustrating a part of a process of starting exposure of a yellow image from a process of transferring a cyan image formed on a photosensitive drum to an intermediate transfer belt. FIG. 7 is an explanatory diagram illustrating a part of a process of starting exposure of a cyan image from a process of transferring a black image formed on a photosensitive drum to an intermediate transfer belt. FIG. 7 is an explanatory diagram illustrating a part of a process of starting exposure of a cyan image from a process of transferring a black image formed on a photosensitive drum to an intermediate transfer belt. It is a side view which shows schematic structure of the modification of a printer engine. It is explanatory drawing which shows a part of process of starting exposure of a yellow image from the process of transferring the cyan image formed in the conventional photoconductor drum to an intermediate transfer belt. It is explanatory drawing which shows a part of process of starting exposure of a yellow image from the process of transferring the cyan image formed in the conventional photoconductor drum to an intermediate transfer belt. It is explanatory drawing which shows a part of process of starting exposure of a yellow image from the process of transferring the cyan image formed in the conventional photoconductor drum to an intermediate transfer belt. It is explanatory drawing which shows a part of process of starting exposure of a cyan image from the process of transferring the black image formed in the conventional photoconductor drum to an intermediate transfer belt. It is explanatory drawing which shows a part of process of starting exposure of a cyan image from the process of transferring the black image formed in the conventional photoconductor drum to an intermediate transfer belt. It is explanatory drawing which shows a part of process of starting exposure of a cyan image from the process of transferring the black image formed in the conventional photoconductor drum to an intermediate transfer belt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Image carrier 13 Exposure apparatus 15 Developing means 16 Intermediate transfer body 18 Development switching means

Claims (8)

An image carrier on which a latent image is formed by exposure by an exposure device;
A plurality of different color developing means that are arranged in parallel to the outer periphery of the image carrier and visualize the latent image formed on the image carrier;
Development switching means for switching between a development state and a non-development state of the latent image formed on the image carrier of each of the development means;
A plurality of color images formed by sequentially transferring visible images on the image carrier developed by sequentially switching development colors by switching the development means by the development switching means are transferred to a recording medium. An intermediate transfer member;
With
A circumferential length L1 of the image carrier from a position facing the developing unit located on the most downstream side in the rotation direction of the image carrier among the developing units to a transfer position with the intermediate transfer member,
L1 <v × t (v: linear rotation speed of the image carrier surface, t: time for the development switching means to switch the development means from the non-development state to the development state)
And,
The development switching unit includes the development unit in which a rear end of a visible image formed on the image carrier by the predetermined development unit is located on the most downstream side in the rotation direction of the image carrier among the development units. Switching from the non-development state to the development state for the developing means corresponding to the color of the visible image to be formed next,
An image forming apparatus . Before Symbol developing means, the relative latent image formed on the image bearing member, it performs a visible image by the two-component developing method, the developing unit surface in the developing state by contact with the image bearing member and the image has a positioning member that maintains the spacing of the support surface, according to claim 1 Symbol placing the image forming apparatus, characterized in that. An image carrier on which a latent image is formed by exposure by an exposure device;
A plurality of different color developing means that are arranged in parallel to the outer periphery of the image carrier and visualize the latent image formed on the image carrier;
Development switching means for switching between a development state and a non-development state of the latent image formed on the image carrier of each of the development means;
A plurality of color images formed by sequentially transferring visible images on the image carrier developed by sequentially switching development colors by switching the development means by the development switching means are transferred to a recording medium. An intermediate transfer member;
With
A circumferential length L1 of the image carrier from a position facing the developing unit located on the most downstream side in the rotation direction of the image carrier among the developing units to a transfer position with the intermediate transfer member,
L1 <v × t (v: linear rotation speed of the image carrier surface, t: time for the development switching means to switch the development means from the non-development state to the development state)
age,
The development switching unit includes the development unit in which a rear end of a visible image formed on the image carrier by the predetermined development unit is located on the most downstream side in the rotation direction of the image carrier among the development units. The developing unit corresponding to the color of the visible image to be formed next starts switching from the non-development state to the development state, and the development unit switches from the non-development state to the development state. Upon completion of almost simultaneously, starts switching to non-development state from the developing state of the developing means to form a visible image, images forming device you wherein a. The circumferential length L2 of the image carrier from the exposure position by the exposure apparatus to the position facing the developing means located on the most upstream side in the rotation direction of the image carrier among the developing means is L2> v × t. The image forming apparatus according to claim 3 . The developing means visualizes the latent image formed on the image carrier by a one-component development method, and the developing means surface is in contact with the surface of the image carrier in a developed state. The image forming apparatus according to claim 3 , wherein the image forming apparatus is in contact with each other. The developing means other than the developing means located on the most downstream side in the rotation direction of the image carrier among the developing means, after the completion of the visible image formation on the latent image formed on the image carrier, Forming a test patch for density detection in image compensation control until the rear end of the formed visible image passes through a position facing the developing means located on the most downstream side in the image carrier rotation direction; the image forming apparatus according to any one of claims 1 to 5, characterized in that. After the development color switching by the development switching means is completed, the switched development means forms a density detection test patch in the image compensation control until the latent image that has started forming reaches the position facing it. to an image forming apparatus according to any one of claims 1 to 5, characterized in that. Wherein a plurality of the image bearing member, using said respective image carrier to form a plurality of colors image on the intermediate transfer member, the image forming apparatus according to any one of claims 1 to 7, characterized in that.

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