JP2007102009A - Image forming apparatus and control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To steadily convey paper in an inexpensive configuration in a monochrome image formation mode higher in speed than a full-color image formation mode. <P>SOLUTION: The image forming apparatus includes a high output motor for a black cartridge 7d, and low output motors for color cartridges 7a to 7c. In the monochrome image formation mode that is higher in speed than the full-color image formation mode, the respective developing rollers of the color cartridges 7a to 7c are separated from corresponding photoreceptor drums and are not driven, thereby only the photoreceptor drums 1a to 1d are rotated in contact with electrostatic conveyance belt 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for forming an image on a transfer material and a control method thereof, and more particularly to an electrophotographic color image forming apparatus and a control method thereof.

  Conventionally, an image forming apparatus including a plurality of image forming units using an electrophotographic system has been proposed. For example, each image forming unit forms a toner image of a different color, and in order to transfer the color image by sequentially superimposing the formed toner images on the recording material, an electrostatic conveyance belt or the like that carries the recording material A multi-transfer type image forming apparatus provided with a transfer body is known. In addition, a color image forming apparatus having an intermediate transfer body that temporarily forms each color toner image on the intermediate transfer body using the intermediate transfer body and collectively transfers the formed toner image onto a recording material has been proposed. .

This color image forming apparatus is generally called a tandem system, and can set a printing speed fast, so that it has conventionally been configured as a general color image forming apparatus. (For example, refer to Patent Document 1.)
Further, in recent years, the user has proposed replacing the conventional monochrome machine with the printing speed in the monochrome image forming mode in the color image forming apparatus faster than the printing speed in the color image forming mode.

  In this case, since the replacement from the monochrome machine is proposed to the user, it is necessary to make the configuration of the color image forming apparatus cheaper. In the case of a configuration having an intermediate transfer member, the configuration of the apparatus is complicated and often expensive. Therefore, a configuration using an electrostatic conveyance belt that is simpler than the configuration having an intermediate transfer member is often employed. .

  Hereinafter, the state in the monochrome image forming mode in the conventional color image forming apparatus will be described with reference to FIG.

In the figure, the transfer roller 12a to 12c and the photosensitive drums 1a to 1c are separated from each other, the sheet 43 is adsorbed, and the sheet 43 is conveyed by rotating the electrostatic transfer belt 11. Yes. At this time, the black image forming unit is rotationally driven by the motor 42d, and the motors 42a to 42c that drive the color image forming unit are stopped.
JP 2003-215878 A

  However, in the above-described conventional example, the sheet conveying force in the monochrome image forming mode is a state where the photosensitive drums 1a to 1c are separated from each other. For this reason, when a state occurs in which the electrostatic conveyance belt is not sufficiently attracted to the sheet, the sheet may be peeled off from the electrostatic conveyance belt to cause a paper jam.

  The state where the suction force of the electrostatic conveyance belt is not sufficient is, for example, a case where the environment in which the apparatus is installed is a high temperature and high humidity environment (for example, temperature 30 ° C./humidity 80%). In a high-temperature and high-humidity environment, the paper adsorbs moisture, so that the resistance value of the paper decreases and the charge is likely to leak, making it difficult to impart charge to the paper.

  As a countermeasure, there is a method in which the photosensitive drums of all color image forming units are brought into contact with transfer rollers to increase the conveying force. However, in a printer in which the printing speed in the monochrome image forming mode as described above is higher than that in the full-color image forming mode, it is necessary to cope with the high-speed monochrome printing speed. Therefore, the output of the motors 42a to 42c for driving the color image forming unit needs to be the same as the output of the motor 42d for driving the black image forming unit, which increases costs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of performing stable sheet conveyance with an inexpensive apparatus configuration and a control method therefor. And

  It is another object of the present invention to provide an image forming apparatus and a control method therefor that can perform stable sheet conveyance with an inexpensive configuration while preventing consumption of a process cartridge.

  The present invention also provides an image forming apparatus capable of realizing a higher-speed monochrome image forming operation with a low-cost configuration and capable of stably transporting paper at a high speed, and a control method therefor.

  In order to achieve the above object, an image forming apparatus of the present invention includes a plurality of image carriers, a plurality of developing members for developing a latent image formed on the image carrier with a developer, and the plurality of members. A first abutting / separating means for selectively abutting and separating the developing member and the plurality of image carriers, and the transfer unit for transferring the image developed on the image carrier onto a transfer material. A conveying means for conveying a body; a second abutting / separating means for selectively abutting and separating the conveying means and the plurality of image carriers; and the plurality of image carriers and the plurality of developing members. A plurality of driving means for driving, a first image forming mode for forming an image using all of the plurality of image carriers, and a second for forming an image using one of the plurality of image carriers. Control means for switching between image forming modes, the control means, In the second image forming mode, the first abutting / separating means controls the developing member that is not used for image formation among the plurality of developing members so as to be separated from the image carrier, and the second Control is made so that all the image carriers are brought into contact with the transporting means by the contact / separation means.

  Further, the control method of the image forming apparatus of the present invention includes a plurality of image carriers, a plurality of developing members for developing a latent image formed on the image carrier with a developer, and the plurality of developing members. A first abutting / separating means for selectively abutting and separating a plurality of image carriers and a plurality of the image carriers, and conveying the transfer member to transfer an image developed on the image carrier onto a transfer material Driving means, a second abutting / separating means for selectively abutting and separating the conveying means and the plurality of image carriers, and driving the plurality of image carriers and the plurality of developing members. A first image forming mode in which an image is formed using all of the plurality of image carriers, and one of the plurality of image carriers. Mode for switching between the second image forming mode for forming an image using one of the two When switching to the second image forming mode and the switching step, the first abutting / separating means separates the developing member, which is not used for image formation, from the plurality of developing members from the image carrier. And a control step of controlling all the image bearing members to contact the conveying means by the second contact / separation means.

  As described above, according to the present invention, it is possible to perform stable sheet conveyance with an inexpensive configuration.

  In addition, according to the present invention, it is possible to perform stable sheet conveyance with an inexpensive configuration while preventing consumption of the process cartridge.

  Further, according to the present invention, it is possible to realize a higher-speed monochrome image forming operation with an inexpensive configuration, and it is possible to perform high-speed and stable paper conveyance.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[Entire configuration of image forming apparatus]
First, the overall configuration of the image forming apparatus will be described with reference to FIG. FIG. 2 is a longitudinal sectional view showing the overall configuration of a full-color laser beam printer 100 which is an aspect of the image forming apparatus.

  An image forming apparatus 100 shown in the figure includes four photosensitive drums 1a, 1b, 1c, and 1d arranged in parallel in the vertical direction. The photosensitive drum 1 (1a, 1b, 1c, 1d) is rotationally driven counterclockwise in the drawing by a driving means (not shown). Around the photosensitive drum 1, a charging device 2 (2a, 2b, 2c, 2d) for uniformly charging the surface of the photosensitive drum 1 is disposed in order according to the rotation direction. Further, a scanner unit 3 (3a, 3b, 3c, 3d) that irradiates a laser beam based on image information to form an electrostatic latent image on the photosensitive drum 1, and attaches toner to the electrostatic latent image to form a toner image. The developing devices 4 (4a, 4b, 4c, 4d) for developing are arranged. Then, the electrostatic transfer unit 5 for transferring the toner image on the photosensitive drum 1 to the transfer material S, and the cleaning device 6 (6a, 6b, 6c, 6) for removing the transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer. 6d) is provided.

  Here, the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning device 6 are integrally formed into a cartridge to form a process cartridge 7 (7a, 7b, 7c, 7d). Hereinafter, the photosensitive drum 1 will be described in detail.

  The photoconductor drum 1 is configured by applying an organic photoconductive layer (OPC photoconductor) to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, for example. Both ends of the photosensitive drum 1 are rotatably supported by support members, and a driving force from a driving motor (not shown) is transmitted to one end, thereby rotating counterclockwise in the figure. Driven.

  As the charging device 2, a contact charging type can be used. The charging member is a conductive roller formed in the shape of a roller. The roller is brought into contact with the surface of the photosensitive drum 1, and the surface of the photosensitive drum 1 is made uniform by applying a charging bias voltage to the roller. In this way, it is charged.

  The scanner unit 3 is disposed at substantially the same level as the corresponding photosensitive drum 1 in the vertical direction. Image light corresponding to an image signal is irradiated to a polygon mirror 9 (9a, 9b, 9c, 9d) rotated at high speed by a scanner motor (not shown) by a laser diode (not shown) in the scanner unit 3. The image light reflected by the polygon mirror 9 selectively exposes the uniformly charged surface of the photosensitive drum 1 through the imaging lens 10 (10a, 10b, 10c, 10d) to form an electrostatic latent image. It is configured to do.

  Each of the developing devices 4a, 4b, 4c, and 4d is composed of a developing device that stores toner of each color of yellow, magenta, cyan, and black. The developing unit has a toner container for storing toner, and has a mechanism for detecting the remaining amount of toner by detecting the light transmission time by transmitting the LED light into the toner container.

  Further, in the developing device 4, in order to extend the life of the process cartridge 7 and to reduce the cost per print sheet, when the image is not formed, the developing roller 41 is separated and stopped so that the developing roller 41 and Consumption of the photosensitive drum 1 is suppressed.

  Next, the contact operation and the separation operation of the developing device 4 with respect to the photosensitive drum 1 will be described with reference to FIG. First, FIG. 3A shows a state in which the photosensitive drum 1 and a developing roller 41 that supplies toner as a developer provided in the developing device 4 are in contact with each other. In this state, the photosensitive drum 1 and the developing roller 41 are rotationally driven by a driving motor (not shown), and toner can be conveyed to the photosensitive drum 1 exposed by the image writing laser beam to form an image.

  FIG. 3B shows a state where the photosensitive drum 1 and the developing roller 41 that supplies toner as a developer are separated from each other. Compared to FIG. 3A, the developing unit moves in the direction of the arrow. In this state, the developing roller 41 is separated from a driving motor (not shown) and is stopped, so that no image is formed. At this time, since the photosensitive drum 1 and the driving motor are not separated, the photosensitive drum 1 can be rotationally driven in conjunction with the driving motor.

An electrostatic transport 11 that circulates and moves so as to face and face all the photosensitive drums 1a, 1b, 1c, and 1d is provided. The electrostatic transport 11 is composed of a film-like member having a thickness of about 150 μm having a predetermined volume specific resistance (10 ¹¹ to 10 ¹⁴ Ω · cm). The electrostatic transport 11 is supported by rollers in the vertical direction with four shafts, and circulates and moves so that the transfer material S is electrostatically attracted to the outer peripheral surface on the left side in the drawing to bring the transfer material S into contact with the photosensitive drum 1. To do. Thereby, the transfer material S is transported to the transfer position by the electrostatic transport 11, and the toner image on the photosensitive drum 1 is transferred to the recording material according to the electrostatic transport.

  The transfer roller 12 (12a, 12b, 12c, 12d) is arranged in parallel at a position in contact with the inside of the electrostatic transport 11 and facing the four photosensitive drums 1a, 1b, 1c, 1d. A positive charge is applied from the transfer roller 12 to the transfer material S via the electrostatic transport 11, and the electric field generated by the charge causes the recording material S in contact with the photosensitive drum 1 to be negatively charged on the photosensitive drum 1. Toner image is transferred.

  The electrostatic transport 11 is a belt having a circumferential length of about 700 mm and a thickness of 150 μm. The belt is stretched around four rollers of a driving roller 13, driven rollers 14 a and 14 b and a tension roller 15, and rotates in the direction of the arrow in the figure. As a result, the electrostatic conveyance 11 described above circulates and the toner image is transferred while the transfer material S is conveyed from the driven roller 14a side to the driving roller 13 side.

  The paper feed unit 16 feeds and conveys the transfer material S to the image forming unit, and a plurality of transfer materials S are stored in the paper feed cassette 17. At the time of image formation, a sheet feeding roller 18 (for example, a half-moon shaped roller) feeds the uppermost sheet S on the sheet feeding cassette 17. The leading edge of the sheet S comes into contact with the registration roller pair 19 and temporarily stops. After the loop is formed, the electrostatic transport 11 starts rotating, and the registration roller pair 19 starts rotating so as to synchronize the image writing position. It is transported to the electric transport 11.

  The fixing unit 20 fixes a plurality of color toner images transferred to the transfer material S, and includes a heating roller 21a that rotates, and a pressure roller 21b that presses and applies heat and pressure to the transfer material S. Consists of. Downstream of this, there is a paper discharge roller pair 25, and the paper discharge roller 25 discharges the transfer material S out of the apparatus main body.

  In addition, a paper discharge sensor (not shown) is disposed between the fixing roller pair 21 and the paper discharge roller pair 25, so that the transfer material S can be reliably discharged out of the main body or wound around the fixing roller pair 21. I am monitoring for this. That is, the transfer material S to which the toner image on the photosensitive drum 1 is transferred is conveyed by the fixing roller pair 21 when passing through the fixing unit 20, and is given heat and pressure by the fixing roller pair 21. As a result, the toner images of a plurality of colors are fixed on the surface of the transfer material S.

  A double-sided conveyance path for double-sided recording is formed on the back surface of the electrostatic conveyance unit 5. A pair of conveyance rollers 28 and 29 are arranged vertically on the double-side conveyance path, and convey the transfer material S downward in the drawing. At the lowest point, a U-turn conveyance path 30 is provided to change the sheet conveyance direction, and the transfer material S guided to the U-turn conveyance path 30 is re-fed to the registration roller pair 19 and is applied to both sides of the recording material S. Perform image formation.

  As an image forming operation, the process cartridges 7a, 7b, 7c, and 7d are sequentially driven in accordance with the printing timing, and the photosensitive drums 1a, 1b, 1c, and 1d are rotated counterclockwise in the drawing according to the drive. It is rotationally driven in the direction. Then, the scanner units 3 corresponding to the respective process cartridges 7 are sequentially driven. By this driving, the charging roller 2 applies a uniform charge to the peripheral surface of the photosensitive drum 1. Then, the scanner unit 3 exposes the circumferential surface of the photosensitive drum according to an image signal to form an electrostatic latent image on the circumferential surface of the photosensitive drum 1. A developing roller 41 in the developing device 4 forms (develops) a toner image on the circumferential surface of the photosensitive drum 1 by transferring toner to a low potential portion of the electrostatic latent image.

  At the timing when the leading edge of the toner image on the peripheral surface of the photosensitive drum 1a at the most upstream side is rotated and conveyed to a point facing the electrostatic conveyance 11, the printing start position of the transfer material S coincides with the opposite point. As described above, the registration roller pair 19 starts rotating and feeds the transfer material S to the electrostatic transport 11.

  The transfer material S is pressed against the outer periphery of the electrostatic transport 11 so as to be sandwiched between the electrostatic attraction roller 22 and the electrostatic transport 11. At that time, by applying a voltage between the electrostatic transport 11 and the electrostatic attraction roller 22, charges are induced in the transfer material S that is a dielectric and the dielectric layer of the electrostatic transport 11, and the transfer material is It is configured to electrostatically attract to the outer periphery of the electrostatic transport 11. As a result, the transfer material S is stably adsorbed to the electrostatic transport 11 and transported to the most downstream transfer section.

  While being conveyed in this manner, the toner image on each photoconductive drum 1 is sequentially transferred to the transfer material S by an electric field formed between each photoconductive drum 1 and the transfer roller 12.

  The transfer material S to which the four color toner images are transferred is separated from the electrostatic conveyance 11 by the curvature of the belt driving roller 13 and is carried into the fixing unit 20. After the toner image is thermally fixed by the fixing unit 20, the transfer material S is discharged out of the main body by the paper discharge roller pair 25 with the image surface facing down from the paper discharge unit 31.

  Next, the double-sided printing operation will be described in detail. When the printer body receives the double-sided printing signal, the paper discharge sensor detects that the transfer material S has passed through the fixing roller pair 21. In response to the detection signal, the paper discharge roller pair 25 rotates in the reverse direction and guides the transfer material S to the double-sided conveyance path. The transfer material S that has entered the double-sided conveyance path is conveyed by the conveyance rollers 28 and 29 through the U-turn conveyance path 30 to the registration roller pair 19. Thereafter, the printing is completed by the same image forming process as the front surface printing, and the transfer material S is discharged from the paper discharge unit 31 to the outside of the main body.

  Next, a characteristic operation of the present embodiment, that is, an operation at the time of printing in the monochrome image forming mode will be described with reference to FIG.

  When printing is executed in the monochrome image forming mode, the operation of the motors 42a to 42d, which are drive sources, is started with the developing rollers 41a to 41c being separated. At this time, the motors 42 to 42c do not need to drive the developing rollers 41a to 41c for color image formation, and only the photosensitive drums 1a to 1c of the cartridges 7a to 7c need to be driven. Therefore, about half of the output torque of the motors 42a to 42c is sufficient as compared with full color image formation.

  Therefore, the motors 42 to 42c can rotate at a monochrome rotation speed that is faster than the rotation speed in the full-color image forming mode. That is, when the photosensitive drum is rotated in the monochrome image forming mode, the load torque is reduced to about half that in the color image forming mode due to the separation of the developing roller, so that the rotation speed can be increased. .

  In this embodiment, for example, a stepping motor used for driving the photosensitive drum and the developing roller can be used as the motor. FIG. 4 shows the relationship between the load torque of the stepping motor, the motor rotation speed, and the motor output. In the figure, the horizontal axis indicates the rotational speed of each motor, and the vertical axis indicates the load torque (solid line in the figure) and the motor output (dashed line in the figure).

  In FIG. 4, the color image forming unit motor is set so that the motor is driven at a position ((1) in FIG. 4) where the maximum output of the motor is obtained when printing a full-color image with the largest load.

  As shown in FIG. 4, if the load torque is reduced, the rotational speed can be set large. Therefore, in the color mode, the developing roller can be separated to reduce the load torque and increase the rotational speed. In the stepping motor having the characteristics shown in FIG. 4, the number of revolutions can be increased to about 1.3 times ((2) in FIG. 4).

  Thereafter, when printing is started and the sheet 43 is conveyed, the sheet 43 is nipped and conveyed by the photosensitive drums 1a to 1c and the transfer rollers 12a to 12c, so that it reaches the black image forming unit without causing paper jam. Is possible.

  FIG. 10 is a control block diagram of the image forming apparatus in the present embodiment.

  The control in the present embodiment is comprehensively executed by the controller 200 of FIG. The controller 200 is a control unit including a CPU and a RAM or a ROM. By outputting control signals from the controller 200 to the motors 42a to 42d and 44, the photosensitive drum 1 (1a to 1d), the developing roller 41 (41a to 41d), and the driving roller 13 are driven and controlled. Also, the controller 200 outputs a signal for driving and controlling a contact / separation mechanism (not shown) in the contact / separation operation of each developing roller and the joint separation operation of the photosensitive drum and the electrostatic conveyance belt 11. The operation is controlled by.

  FIG. 5 is a flowchart for explaining a sequence at the time of image formation in this embodiment. This sequence is executed by the controller 200 of FIG.

  In S11, printing is started in the image forming apparatus.

  In S12, it is determined whether the print mode is a monochrome image formation mode or a full color image formation mode. If the print mode is the full color image formation mode, the development roller and the transfer roller of the image forming unit for all colors are brought into contact in S14 and printing is performed in the full color mode. , Printing is completed in S15. It is assumed that the image forming mode is designated in advance by the user or instructed from a host computer (not shown) connected to the image forming apparatus.

  The operation state of the image forming apparatus in the full color image forming mode is the state shown in FIG.

  If the print mode is the monochrome image formation mode in S12, the development roller and the transfer roller in the black image formation unit are brought into contact with each other in S13, the development rollers in the other image formation units are separated from each other, and printing is performed in the monochrome image formation mode. , Printing is completed in S15. The operation state of the image forming apparatus at this time is as shown in FIG.

  In this embodiment, as a motor for driving the cartridge 7d for monochrome image formation in a higher-speed monochrome image formation mode, it is necessary to provide a high output motor for driving the photosensitive drum and the developing roller. . However, in the monochrome image forming mode, the cartridges 7a to 7c for color image formation need only drive the photosensitive drum, so that a motor having a lower output than the motor for driving the cartridge 7d can be used.

  In addition, it is possible to suppress the consumption of the color process cartridge by separating the developing roller from being driven.

  As described above, according to the present invention, in the monochrome image forming mode, the developing roller of the developing device is separated from the photosensitive drum, and the photosensitive drum is rotated while the photosensitive drum alone is in contact with the transfer roller. It is possible to rotate at high speed. An inexpensive low output motor can be used as the motor for the color image forming unit. Therefore, it is possible to perform stable sheet conveyance with an inexpensive apparatus configuration while preventing the process cartridge from being consumed.

  A second embodiment of the present invention will be described.

  Since the configuration of the image forming apparatus in this embodiment is the same as that of the first embodiment, the description of the configuration is omitted. Further, the control block diagram of the image forming apparatus is the same as that of the first embodiment, and the description thereof is omitted.

  In this embodiment, a sufficient conveyance force cannot be ensured only by the adsorption force of the electrostatic conveyance belt, and it corresponds to monochrome printing in a specific mode (for example, a thin paper image formation mode) using a recording material in which a paper jam is likely to occur. This is different from the first embodiment.

  In the thin paper image forming mode, particularly when the environment is high temperature and high humidity, a sufficient conveying force cannot be secured. In other words, the paper (thin paper) absorbs moisture in high-temperature and high-humidity usage, so that the resistance value of the paper is lowered and the attractive force to the electrostatic conveyance belt is weakened. Thin paper does not have a thickness compared to plain paper, and its stiffness is weak. Therefore, in the above-described device configuration (a configuration in which paper is transported from the lower side to the upper side), the paper (thin paper) bends and becomes static when the adsorption force becomes weaker. It will be separated from the electroadsorption belt.

  In this embodiment, it is a thin paper image forming mode, and control as described below is executed particularly when the apparatus environment is high temperature and high humidity.

  FIG. 4 is a flowchart for explaining the sequence at the time of image formation in this embodiment.

  In S51, printing is started in the image forming apparatus.

  In S52, it is determined whether the print mode is the monochrome image formation mode or the full color image formation mode. If the print mode is the full color mode, the developing roller and transfer roller of the image forming unit for all colors are brought into contact with each other and printing is performed in the full color mode. Printing is complete. It is assumed that the image forming mode is designated in advance by the user or instructed from a host computer (not shown) connected to the image forming apparatus.

  The operation state of the image forming apparatus in the full-color image forming mode is the state shown in FIG.

  If the print mode is the monochrome image formation mode in S52, it is determined in S53 whether or not the paper type to be printed is thin paper. If it is determined that the paper is thin in S53, the developing roller of the black image forming unit is contacted in S54, the developing roller of the other image forming unit and the transfer roller of all colors are contacted, and printing is performed in the monochrome image forming mode. In step S57, printing is completed. The operation state of the image forming apparatus at this time is the same as the state shown in FIG.

  If the print mode is the monochrome image forming mode and the paper type to be printed is not thin paper, the developing roller and transfer roller of the black image forming unit are brought into contact with each other in S56, and the developing roller and transfer roller of the other image forming unit And printing in the monochrome image forming mode. Thereafter, printing is completed in S57. The operation state of the image forming apparatus at this time is as shown in FIG.

  In this example, the specific mode is the thin paper image forming mode and the high temperature and high humidity environment is described as an example. However, the present invention is not limited to this, and it is not always necessary to use thin paper. For example, the paper can be applied to a case where the paper is easily peeled off from the electrostatic conveyance belt, such as coated paper, OHT, or thick paper.

  As described above, according to the present exemplary embodiment, in a situation where the electrostatic conveyance belt cannot secure a sufficient conveyance force, the developing roller of the color image forming unit is separated and the photosensitive drum is brought into contact with the transfer roller to rotate. To drive. As a result, it is possible to perform stable paper conveyance with an inexpensive configuration while preventing the process cartridge from being consumed even in various situations.

  A third embodiment of the present invention will be described.

  Since the configuration of the image forming apparatus in the present embodiment is the same as that in the first and second embodiments, description regarding the configuration is omitted. Further, the control block diagram of the image forming apparatus is the same as that of the first embodiment, and the description thereof is omitted.

  This embodiment is characterized in that a DC brushless motor is used instead of the stepping motor as described in the first embodiment as the drive source for the image forming unit of the color image forming apparatus in the first and second embodiments. It is.

  6A and 6B are diagrams for explaining the characteristics of the motor in this embodiment. FIG. 6A shows the characteristics of a DC brushless motor, and FIG. 6B shows the characteristics of a stepping motor. In the figure, the horizontal axis indicates the rotation speed of each motor, and the vertical axis indicates torque (solid line in the figure) and output (dashed line in the figure).

  As a motor for a color image forming unit, the motor is driven at a position ((A) (3) and (B) (1) in FIG. 9) where the maximum output of the motor is obtained when printing a full color image with the largest load. When the photosensitive drum is rotated in the monochrome image forming mode, the load torque is reduced to about half by separating the developing roller (solid arrow in the figure), so that the rotation speed can be increased (broken arrow in the figure). . Here, in the case of a DC brushless motor, it is possible to increase the rotational speed to the middle of the maximum rotational speed and the rotational speed of (3) (≈maximum rotational speed / 2), that is, about 1.5 times (FIG. 9). (4)).

  On the other hand, in the case of a stepping motor, the output torque drops sharply at a rotational speed higher than the maximum output speed, so the rotational speed can be increased only up to about 1.3 times. No ((2) in FIG. 9). Therefore, if a motor with the same output is used as the color image forming unit motor, the DC brushless motor is faster than the stepping motor in the monochrome mode in which only the photosensitive drum is driven. It becomes possible to cope with.

  In this example, although a DC brushless motor has been described as an example, a DC motor having similar characteristics may be used as a drive source.

  As described above, according to the present embodiment, a DC brushless motor (or DC motor) is used as a motor for the image forming unit, so that when a developing roller is separated, another motor such as a stepping motor is used. Can be rotated at a high speed. As a result, an inexpensive configuration can be realized, and stable paper conveyance can be performed in a higher-speed monochrome image forming mode.

1 is a diagram illustrating an image forming apparatus in a monochrome mode according to a first embodiment of the present invention. FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus according to a first embodiment of the present invention. It is a figure explaining the contact-separation of the developing device concerning 1st Example of this invention. It is a figure explaining the motor characteristic which concerns on 1st Example of this invention. It is a figure explaining the sequence which concerns on 1st Example of this invention. It is a figure explaining the sequence concerning the 2nd Example of the present invention. It is a figure explaining the image forming apparatus at the time of the full color mode concerning 2nd Example of this invention. It is a figure explaining the motor characteristic concerning the 3rd example of the present invention. It is a figure explaining the state at the time of the monochrome image formation mode in the conventional image forming apparatus. 2 is a control block diagram of the image forming apparatus of the present invention. FIG.

Explanation of symbols

1a, 1b, 1c, 1d Photosensitive drum 11 Electrostatic conveying belts 12a, 12b, 12c, 12d Transfer roller 13 Drive roller 14a, 14b Driven roller 15 Tension roller 41a, 41b, 41c, 41d Developing roller 42a, 42b, 42c, 42d, 44 Motor 43 Paper 200 Controller

Claims (11)

A plurality of image carriers;
A plurality of developing members for developing the latent image formed on the image carrier with a developer;
First contact / separation means for selectively contacting and separating the plurality of developing members and the plurality of image carriers;
Conveying means for conveying the transfer body in order to transfer the image developed on the image carrier onto a transfer material;
Second contact / separation means for selectively contacting and separating the transport means and the plurality of image carriers;
A plurality of driving means for driving the plurality of image carriers and the plurality of developing members;
Control means for switching between a first image forming mode for forming an image using all of the plurality of image carriers and a second image forming mode for forming an image using one of the plurality of image carriers. Have
The control means controls the developing member that is not used for image formation among the plurality of developing members to be separated from the image carrier by the first contact / separation means in the second image forming mode, In addition, the image forming apparatus is characterized in that the second abutting / separating means controls to bring all the image carriers into contact with the conveying means.   In the second image forming mode, the control unit is configured to perform the first contact when the transfer material is a predetermined type of transfer material and the installation environment of the apparatus is a high temperature and high humidity environment. Control so that all the developing members are in contact with the image carrier by the separation means, and control so that all the image carriers are in contact with the transport means by the second contact / separation means. The image forming apparatus according to claim 1.   In the first image forming mode, the control unit controls the first contact / separation unit to contact all the developing members to the image carrier, and the second contact / separation unit 3. The image forming apparatus according to claim 1, wherein all the image bearing members are controlled to contact the conveying unit. 4.   The plurality of image carriers are image carriers for forming images of a plurality of colors, respectively, and the first image forming mode is a mode for forming images of a plurality of colors, and the second image forming mode. The image forming apparatus according to claim 1, wherein the image forming apparatus is a mode for forming a monochrome image.   The image forming apparatus according to claim 1, wherein an image forming speed in the second image forming mode is higher than an image forming speed in the first image forming mode.   The image forming apparatus according to claim 1, wherein the driving unit includes a DC motor or a DC brushless motor. A plurality of image carriers, a plurality of developing members for developing a latent image formed on the image carrier with a developer, and the plurality of developing members and the plurality of image carriers are selectively applied. A first abutting / separating means for contacting and separating; a conveying means for conveying the transfer body to transfer an image developed on the image carrier onto a transfer material; the conveying means; and the plurality of images. An image forming apparatus comprising: a second contact / separation unit that selectively contacts and separates the carrier; and a plurality of drive units for driving the plurality of image carriers and the plurality of developing members. A control method,
A mode switching step for switching between a first image forming mode for forming an image using all of the plurality of image carriers and a second image forming mode for forming an image using one of the plurality of image carriers. When,
When switching to the second image forming mode, the first contact / separation means controls the developing member that is not used for image formation among the plurality of developing members to be separated from the image carrier; and A control step of controlling all the image bearing members to contact the conveying means by the second contact / separation means;
A control method for an image forming apparatus, comprising:   Further, when the transfer material is a predetermined type of transfer material and the installation environment of the apparatus is a high temperature and high humidity environment when the mode is switched to the second image forming mode, the first contact / separation is performed. Control for controlling all the developing members to contact the image carrier by means, and control for bringing all the image carriers to contact the conveying means by the second contact / separation means 8. The method of controlling an image forming apparatus according to claim 7, further comprising steps.   Further, when the mode is switched to the first image forming mode, the first contact / separation means controls all the developing members to contact the image carrier and the second contact / separation means. 9. The method of controlling an image forming apparatus according to claim 7, wherein control is performed so that all the image carriers are brought into contact with the transport unit.   10. The image formation according to claim 7, wherein the first image formation mode is a color image formation mode, and the second image formation mode is a monochrome image formation mode. Device control method.   11. The image forming apparatus according to claim 7, wherein an image forming speed in the second image forming mode is higher than an image forming speed in the first image forming mode. Method.

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