JP4539673B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an image forming apparatus including an image carrier and a plurality of developing units provided corresponding to different color developers is known (see Patent Document 1). In this case, the developer left untransferred when a paper jam occurs or the waste developer composed of a developer when a density pattern (density patch) is generated for calibration, etc. After being removed from the body, the conveyance belt, the intermediate transfer belt, or the like, the black developer is collected in a developing device containing the black developer.

As a result, the waste developer containing different color developers is collected in a developing device containing the black developer, thereby reducing the influence of color mixing.
JP 2004-279474 A

  However, even with the configuration described above, it is inevitable that the color of the black developer changes due to the inclusion of a developer having a color different from black.

  The present invention has been completed based on the above circumstances, and an object thereof is to provide an image forming apparatus in which a change in color is suppressed when a developer is collected in a developing device.

The present invention has been completed based on the above circumstances, and the first invention is an image forming apparatus, which is provided corresponding to an image carrier and developers of different colors. A plurality of developing units; transfer means for transferring a developer image formed on the image carrier by the developing unit to a target; and a developer transferred to the target in units of the plurality of developers A control means for executing a recovery process for collecting in a developing device corresponding to a developer having the largest charge amount per unit, and a measurement means for measuring a charge amount per unit amount of each developer. The means determines a developer having the largest charge amount per unit amount among the plurality of developers based on the measurement result of the measurement means .

The inventors have developed a developer having a charge amount per unit amount larger than that of other developers even when developers of different colors are mixedly accommodated in one developer. The present invention was conceived by utilizing the phenomenon that the image is preferentially developed on the image carrier. That is, according to the first invention, the developer that stores the developer having the largest charge amount per unit amount among the plurality of developers corresponds to the developer recovered from the object and the developer. Color developer (the developer originally stored in the developing device) is mixed. In this state, when a developer image is formed on the image carrier, the developer of the color corresponding to the developing device has the largest amount of charge per unit amount among the plurality of developers. The developer of the color corresponding to the developing device is selectively developed. As a result, it is possible to reliably suppress a change in the color of the developer during development.
Further, since the developer having the largest charge amount per unit amount can be determined by measuring with the measuring means, the developing device containing the developer having the largest charge amount per unit amount is developed with other colors. The agent can be reliably recovered. Thereby, it can suppress reliably that the color of a developing agent changes.

  The developer may be a one-component system composed only of toner, a two-component system including toner and carrier, or a multiple-component system including three or more components. The charge amount per unit amount is, for example, a charge amount with respect to a reference unit amount, such as a unit mass of the developer, a unit volume of the developer, or a charge amount per toner particle constituting the developer. Say.

According to a second aspect of the present invention, the apparatus according to the first aspect further comprises determination means for determining whether the remaining amount of the developer previously stored in the developing unit has reached a predetermined amount M (> 0). The control unit allows the developing device to perform a developing process for forming the developer image on the carrier when the determination unit does not determine that the remaining amount has reached the predetermined amount M, and the remaining amount is equal to the predetermined amount M. When it is determined that the value has reached, the development processing is prohibited.

  When the collection process is executed, the developer for collecting the developer contains a color developer corresponding to the developer and the developer collected by the collection process. When a developer image is formed on the image carrier in this state, the color developer corresponding to the developing device is selectively consumed. Then, all the color developer corresponding to the developing unit is consumed, and there is a concern that only the collected developer remains in the developing unit. If development processing is executed in this state, a developer image different from the color of the developer corresponding to the developing device may be formed.

In view of the above points, in the second invention, when it is determined that the remaining amount of the developer accommodated in the developing unit has reached a predetermined amount (> 0), the development processing is prohibited. Thereby, it is possible to prevent the developer image from being formed only by the collected developer, and thus it is possible to prevent the color of the developer image from changing.

According to a third aspect , in the second aspect , an exposure unit that exposes the image carrier, and a generation unit that generates a light ON / OFF signal for causing the exposure unit to emit light based on bitmap data. First counting means for counting an ON signal among the light ON / OFF signals, and first integrating means for accumulating and storing the count number of the ON signal obtained by the first counting means, The determining means determines the remaining amount of developer corresponding to the developing device in which the developer transferred to the object is collected based on the count number stored in the first integrating means.

  As described above, when the developer of the color corresponding to the developing device is selectively consumed, there is a concern that only the collected developer remains in the developing device. For this reason, there is a problem that it is impossible to detect whether or not the remaining amount of the developer corresponding to the developing device has become 0 by simply detecting the remaining amount of the developer in the developing device.

According to the third aspect , the remaining amount of the developer of the color corresponding to the developing device can be surely known based on the count number stored in the first integrating means.

A fourth invention is the one according to the second invention, wherein a developing roller is provided in the developing device for adhering the developer to the image carrier, and a second count for counting the number of rotations of the developing roller. And a second accumulating unit that accumulates and stores the number of rotations of the developing roller obtained by the second counting unit, and the determination unit sets the rotation number stored in the second accumulating unit. Based on this, the remaining amount of developer corresponding to the developing device from which the developer transferred to the object is collected is determined.

According to the fourth aspect of the invention, the remaining amount of developer of the color corresponding to the developing device can be surely known based on the number of rotations of the developing roller stored in the second integrating means.

  The number of rotations is not the number of rotations (rotation speed) of the developing roller per unit time but the number of rotations (amount) of the developing roller.

According to a fifth invention, in any one of the first to fourth inventions, when the recovery process is not executed, a plurality of the image carriers provided corresponding to the developing devices are used as the object. When carrying out the recovery process, the image carrier corresponding to a different developer from the developer from which the developer transferred to the object is recovered among the plurality of image carriers, Separation means for separating the object is provided.

According to the fifth invention, in the recovery process, the image carrier corresponding to the developing device different from the developing device in which the developer transferred to the target is recovered does not come into contact with the target. As a result, it is possible to prevent the developer transferred to the object from adhering to an image carrier corresponding to a developing device different from the developing device from which the developer transferred to the object is collected, and thus color mixing can be suppressed. .

According to a sixth invention, in any one of the first to fifth inventions, the object is movable relative to the image carrier, and the object moves along a direction in which the object moves relatively. A plurality of the image carriers corresponding to the developing units, and the image carrier corresponding to the developing unit from which the developer transferred to the object is collected is relatively It is provided at the most upstream position in the moving direction.

According to the sixth invention, in the recovery process, the developer transferred to the target object comes into contact with the image carrier corresponding to the developer that collects the developer, and the developer in the developer corresponding to the image carrier. To be recovered. As a result, it is possible to prevent the developer transferred to the object from adhering to an image carrier corresponding to a developing device different from the developing device from which the developer transferred to the object is collected, and thus color mixing can be suppressed. .

According to a seventh invention, in any one of the first to sixth inventions, a holding unit that temporarily collects and holds the developer attached to the object, and the developer collected in the holding unit And applying means for applying a holding bias voltage for holding the holding portion to the holding portion, and the control means causes the applying means to apply a reverse bias voltage having a polarity opposite to the holding bias voltage to the holding portion. Thus, after the developer held in the holding unit is returned to the object, the collection process is executed.

According to the seventh aspect , the developer transferred to the object is temporarily held by the holding unit. As a result, when the developer is transferred to the object, the collection process does not have to be executed immediately.

  According to the present invention, even when the developer is collected in the developing device, it is possible to suppress a change in the color of the developer during development.

<Embodiment 1>
(Entire printer configuration)
Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a side sectional view showing a schematic configuration of a direct tandem type printer 4 that employs a non-magnetic one-component developing system as an example of an image forming apparatus of the present invention. In the following description, the right side in FIG.

  The printer 4 is configured by housing a printing unit 6 in a main body casing 5. A sheet (an example of an object) 1 that is a recording medium is stacked on a supply tray 7 provided at the bottom of the main casing 5. The sheet 1 stacked on the uppermost position in the supply tray 7 is sent out to the registration roller 9 as the paper supply roller 8 provided above the front end of the supply tray 7 rotates. The registration roller 9 corrects the skew of the sheet 1 and then conveys the sheet 1 onto the belt unit 20 of the printing unit 6.

  The printing unit 6 includes a belt unit 20, a process unit 21, a fixing device 22, and the like. The belt unit 20 has a configuration in which a belt (an example of an object) 2 is stretched between a pair of front and rear support rollers 13. When the belt 2 is driven, the sheet 1 on the belt 2 is conveyed from the upstream side (front side) to the downstream side (rear side) in the moving direction.

  The process unit 21 performs black (BK), cyan (C), yellow (Y), magenta in order from the upstream side of the moving direction of the sheet 1 along the moving direction (arrow A) of the belt 2 that conveys the sheet 1. The image forming units 3BK, 3C, 3Y, and 3M are provided corresponding to the developers of the respective colors (M). The image forming units 3BK, 3C, 3Y, and 3M include four developing units 10BK, 10C, 10Y, and 10M that are provided corresponding to the developers of the respective colors and store the corresponding color developers.

  In this embodiment, the charge amount per unit amount of the magenta developer is the largest as compared with the developer of other colors. The charge amount per unit amount is, for example, a charge amount with respect to a reference unit amount such as a unit mass of the developer, a unit volume of the developer, or a charge amount per toner particle constituting the developer. Say.

  Each color developer accommodated in each developing device 10BK, 10C, 10Y, 10M is supplied to each developing roller 13BK, 13C, 13Y, 13M by rotation of each supply roller 19BK, 19C, 19Y, 19M. Between each of the supply rollers 19BK, 19C, 19Y, and 19M and each of the developing rollers 13BK, 13C, 13Y, and 13M, triboelectric charging is performed. The surface of each image carrier (for example, a photosensitive drum) 11BK, 11C, 11Y, and 11M is first uniformly charged to a positive polarity by each charger 16BK, 16C, 16Y, and 16M as it rotates. Thereafter, exposure is performed by light from each of the exposure units 17BK, 17C, 17Y, and 17M, and an electrostatic latent image corresponding to an image to be formed on the sheet 1 is formed.

  Next, by the rotation of each developing roller 13BK, 13C, 13Y, 13M, the toner on each developing roller 13BK, 13C, 13Y, 13M is supplied to the surface of each image carrier 11BK, 11C, 11Y, 11M, and electrostatic latent The image is visualized. Thereafter, the developer images carried on the surfaces of the image carriers 11BK, 11C, 11Y, and 11M are obtained by transferring the sheet 1 to the image carriers 11BK, 11C, 11Y, and 11M and a transfer unit (for example, a transfer roller) 12BK, While passing between 12C, 12Y and 12M, the images are sequentially transferred onto the sheet 1 by a transfer bias applied to the transfer means 12BK, 12C, 12Y and 12M.

  The transferred sheet 1 is conveyed to the fixing device 22 by the belt unit 11 where the developer image transferred onto the sheet 1 is thermally fixed. Then, the heat-fixed sheet 1 is discharged onto a discharge tray 14 provided on the upper surface of the main casing 5.

  The printer 4 according to this embodiment is a so-called cleanerless printer 4 that does not have a cleaner for removing the developer attached to the belt 2. A so-called transfer residual toner (developer) remaining on the surface of each of the image carriers 11BK, 11C, 11Y, and 11M at the time of transfer is adopted as a simultaneous development cleaning system that collects them in the developing units 10BK, 10C, 10Y, and 10M. is doing.

(Separation means)
The image carriers 11BK, 11C, 11Y, and 11M are in contact with the belt 2. The transfer units 12BK, 12C, 12Y, and 12M are in contact with the belt 2 in a state where the belt 2 is sandwiched between the corresponding color image carriers 11BK, 11C, 11Y, and 11M.

  On the other hand, as shown in FIG. 2, the image forming units 3BK, 3C, 3Y are provided with separating means 23BK, 23C, 23Y for separating the image forming units 3BK, 3C, 3Y from the belt 2. Although omitted in FIG. 2, the image forming unit 3M is also provided with a separation unit having a similar structure.

  A link 24BK is provided at the right end of the spacing means 23BK in the drawing. Although omitted in FIG. 2, the other image forming units 3C, 3Y, 3M are also provided with links having a similar structure. Hereinafter, the separation means 23BK will be described as an example.

  The rotational force of a motor (which may be a rotary solenoid) 25BK provided at the tip of the link 24BK is transmitted to the separating means 23BK via the link 24BK, and moves the separating means 23BK in the left-right direction in FIG. Then, the shaft 27BK fitted in the crank-shaped guide hole 26BK provided in the separating means 23BK moves in the vertical direction along the guide hole 26BK. As a result, the image forming unit 3BK provided with the shaft 27BK moves up and down integrally with the developing device 10BK, the image carrier 11BK, the charger 16BK, and the exposure device 17BK. Thus, the image carrier 11BK of the image forming unit 3BK can be separated from the belt 2.

  Similarly to the above, the image carriers 11C, 11Y, and 11M of the other image forming units 3C, 3Y, and 3M can be separated from the belt 2. The image carriers 11BK, 111C, 11Y, and 11M can be selectively separated from the belt 2 by the separation means provided for each of the image forming units 3BK, 3Y, 3C, and 3M.

(Electrical configuration of printing system)
FIG. 3 is a block diagram showing an electrical configuration of a printing system including the above-described printer 4 and one or a plurality of computers 40 connected to the printer 4 via a communication line 37.

  The printer 4 includes a CPU 30 (an example of a control unit, a determination unit, a generation unit, and a first count unit), a ROM 31, a RAM (an example of a first integration unit) 32, an operation unit 34, a display unit 35, and the printing unit 6 described above. A network interface 36, a motor 25, a charging control circuit 50, a developing bias circuit 51, a transfer bias circuit 52, and the like.

  The ROM 31 stores various programs for controlling the operation of the printer 4 such as print processing, which will be described later. The CPU 30 stores the processing results in the RAM 32 in accordance with the program read from the ROM 31, and stores the processing results of the printer 4. Control the behavior.

  The operation unit 34 includes a plurality of buttons, and various input operations such as an instruction to start printing can be performed by the user. The display unit 35 includes a liquid crystal display and a lamp, and can display various setting screens and operation states. The network interface 36 is connected to an external computer 40 or the like via a communication line 37, and mutual data communication is possible.

  The CPU 30 controls the movement of the image forming units 3BK, 3C, 3Y, and 3M in the vertical direction by controlling the rotation direction of the motor 25.

  The charging control circuit 50 applies a high voltage to the chargers 16BK, 16C, 16Y, and 16M to cause corona discharge, thereby uniformly charging the surfaces of the image carriers 11BK, 11C, 11Y, and 11M (for example, 700V). (See FIG. 4). When the surfaces of the image carriers 11BK, 11C, 11Y, and 11M are exposed by the exposure devices 17BK, 17C, 17Y, and 17M to form an electrostatic latent image, the potential of the electrostatic latent image is lowered to, for example, about 150V. (See FIG. 4).

  The developing bias circuit 51 is connected to the developing rollers 18BK, 18C, 18Y, and 18M, and applies a developing bias voltage (for example, 550 V) to the developing rollers 18BK, 18C, 18Y, and 18M (see FIG. 4).

  The transfer bias circuit 52 is connected to the transfer units 12BK, 12C, 12Y, and 12M, applies a transfer bias to the transfer units 12bK, 12C, 12Y, and 12M by constant current control (for example, −10 μA to −15 μA). A voltage (for example, 1.5 kV) for generating a reverse transfer bias having a polarity different from that of the transfer bias is applied (see FIG. 4).

  When the user inputs a print command on the computer 40, the computer 40 creates data for printing using application software, and converts the data into PDL (page description language) using a printer driver to create print data. The computer 40 transmits this print data to the printer 4 via the communication line 37.

(Recovery processing)
FIG. 5 shows an example when the sheet 1 is jammed. As described above, the black image forming unit 3K is provided on the upstream side (right side in the drawing) of the cyan image forming unit 3C. The black developer 28BK transferred from the image forming unit 3K may adhere to the surface of the belt 2.

  For example, if the user forcibly pulls the sheet 1 downstream in the movement direction (right side in the figure), the belt 2 rotates in the direction of arrow A (downstream) due to friction with the sheet 1. Sometimes. Then, for example, the image carrier 11BK that is in contact with the belt 2 rotates in the clockwise direction in the drawing due to the frictional force with the belt 2. As a result, the developer 28R adhering to the sheet 1 or the belt 2 may be rotated to the image carrier 11BK and adhere to the image carrier 11BK. During the jam handling operation, there is a possibility that the user may touch a part in the printer 4, so that no transfer bias is applied to the transfer means 12C so that the user does not get an electric shock. For this reason, the force that draws the black developer 28BK toward the belt 2 is hardly applied. For example, the black developer 28BK on the belt 2 adheres to the cyan image carrier 11C by van der Waals force or the like. May end up.

  When the image forming operation on the sheet 1 is executed in this state, as shown in FIG. 6, the black developer 28BK and the cyan developer 28C are mixed on the cyan image carrier 11C. Become. As a result, the black developer 28BK is mixed with the sheet 1 in an area where the cyan developer 28C is supposed to be transferred.

  Therefore, in this embodiment, before executing the image forming operation, the CPU 30 collects the developer 28R attached to the image carriers 11BK, 11Y, 11C, and 11M during the jam processing as follows. In the following description, the suffixes BK, C, M, and Y are omitted for configurations common to the respective colors (black, yellow, cyan, and magenta).

  First, as shown in FIG. 7, the CPU 30 drives the belt 2 by the belt unit 20 with the transfer bias applied to the transfer means 12 by the transfer bias circuit 52, and develops the image attached to the image carrier 11 during the jam processing. The agent 28R is transferred to the belt 2 (S306, S307). At this time, the developer 28R is transferred to a position on the belt 2 as shown in FIG. Further, the CPU 30 drives the belt 2 by the half circumference by the belt unit 20 (FIG. 7, S308). At this time, the developer 28R moves to, for example, the position shown in FIG.

  Subsequently, the CPU 30 causes the transfer bias circuit 52 to stop applying the transfer bias (FIG. 7, S309). As a result, the force attracted toward the belt 2 hardly acts on the developer 28R transferred to the belt 2.

  The CPU 30 drives the motor 25 to move the image forming units 3BK, 3Y, 3C upward, and separates the image carriers 11BK, 11Y, 11C from the belt 2 (S310). At this time, only the image carrier 11M is in contact with the belt 2 (see FIG. 2).

  The CPU 30 applies a reverse transfer bias voltage (for example, 1.5 kV) only to the transfer unit 12M corresponding to the developer having the largest charge amount (magenta in the present embodiment) (S311). This generates a force that electrically draws the developer 28R from the magenta transfer unit 12M side to the magenta image carrier 11M side. Further, the CPU 30 applies a first reverse bias voltage (voltage lower than the surface potential of the image carrier 11M) having a polarity opposite to the developing bias to the magenta developing roller 18M by the developing bias circuit 51 (S312). As a result, a force that electrically draws the developer 28R from the image carrier 11M side to the developing roller 18M side is generated.

  Thereafter, the CPU 30 causes the belt unit 20 to drive the belt 2 by the length of one circumference (S313). Then, the developer 28R moves to the magenta image carrier 11M, further moves to the magenta developing roller 18M, and is collected by the magenta developing device 10M (see FIG. 10). At this time, as described above, since the image carriers 11BK, 11Y, and 11C are separated from the belt 2, they do not come into contact with the developer 28R. Thereby, it is possible to prevent the developer 28R from being mixed into the developing devices 11BK, 11Y, and 11C via the image carriers 11BK, 11Y, and 11C. When S313 ends, the CPU 30 brings the image carriers 11BK, 11Y, and 11C into contact with the belt 2 (S314).

(Selective development)
By the above recovery processing, the magenta developer 28M originally stored in the magenta developing device 10M and the recovered developer 28R are mixed in the same developing device 10M.

  In the present embodiment, as described above, the magenta developer 28M has the largest amount of charge per unit amount. Therefore, when the developing process is executed in a state where the magenta developer 28M and the collected developer 28R are mixed in the developing device 10M, the magenta developer 28M is placed on the image carrier 11M corresponding to magenta. It is developed preferentially (selectively) (see FIG. 11). As a result, even when the developer 28R is collected in the developing device 10M corresponding to magenta, it is possible to suppress a change in the color of the magenta developer 28M.

  In this regard, when the developer 28R is collected in the predetermined developing device 10 without considering the charge amount per unit amount of the developer, the developer having a large charge amount per unit amount when the development process is executed. Is selectively developed, it is impossible to prevent a change in color.

(Print processing)
FIG. 12 is a flowchart illustrating the flow of print processing executed by the printer 4 under the control of the CPU 30.

  When the power is turned on (S90) and printing is possible, the CPU 30 of the printer 4 starts the printing process shown in FIG. The CPU 30 first executes the initial process S100 and then monitors whether or not data is received via the communication line 37 (S101). If there is received data (S101: Y), the received data for one page is expanded into bitmap data in the area used as a page buffer in the RAM 32 (S102).

  The CPU 30 continuously monitors whether or not received data has been received (S103). If there is received data (S103: Y), the RAM 32 is different from the page buffer in which the bitmap data has already been developed. Using the area as a new page buffer, the received data for the next page is expanded into bitmap data, and the contents of the page buffer in which the bitmap data has already been expanded are printed by the printing unit 6 (S104).

  Subsequently, the CPU 30 executes a count process in S105. As shown in FIG. 13, the CPU 30 generates a light ON / OFF signal that causes the magenta exposure device 17M to emit light based on each bit of the bitmap data (S201), and counts the number of ON signals (S202). The CPU 30 transmits the count number to the RAM 32 and stores the total number of count numbers (S203). The CPU 30 calculates the usage amount of the magenta developer 28M based on the count number stored in the RAM 32 (S204) and the usage amount of developer per bit (S205) stored in the ROM 31. (S206).

  When the CPU 30 executes the collecting process, the developing device 10M from which the developer 28R is collected is in a state where the magenta developer 28M and the developer 28R are mixed. When the CPU 30 executes the developing process in this state, the color developer 28M corresponding to the developing device 10M is selectively consumed. Then, all of the magenta developer 28M is consumed, and there is a concern that only the developer 28R remains in the developing device 10M corresponding to magenta. If the development process is executed by the CPU 30 in this state, a developer image different from the color of the magenta developer 28M may be formed.

  Therefore, in this embodiment, the CPU 30 (an example of a determination unit and a control unit) determines whether the remaining amount of the magenta developer 28M has reached a predetermined amount M (> 0), and the CPU 30 (the control unit). For example, when it is not determined that the remaining amount of the magenta developer 28M has reached the predetermined amount, the developing device 10M allows the developing process to form the developer image on the image carrier 11M, and the remaining amount reaches the predetermined amount. When it is determined that the development processing has been performed, the development processing is prohibited.

  Then, as described above, the CPU 30 develops the developer corresponding to the developing device 10M based on the total number of counts stored in the RAM 32 and the usage amount of the developer 28M per ON signal stored in the ROM 31. The remaining amount of 28M is determined.

  Accordingly, the remaining amount of the magenta developer 28M can be surely known based on the count number stored in the RAM 32. When it is determined that the remaining amount of the developer 28M accommodated in the developing device 10M has reached a predetermined amount (> 0) (S207: Y), the development processing is prohibited, so that the collected development is performed. Since it is possible to prevent the developer image from being formed only by the agent 28R, it is possible to prevent the color of the magenta developer 28M from changing.

  If the CPU 30 does not determine that the usage amount of the developer 28 has reached the predetermined amount M (S207: N), the CPU 30 ends the counting process and returns to the main routine.

  In FIG. 12, after the counting process S105, the CPU 30 determines whether or not a jam of the sheet 1 has occurred in S106, and if it is determined that a jam has occurred (S106: Y), in S107. Perform jam processing.

  As shown in FIG. 7, the CPU 30 causes the belt unit 20 to stop the belt 2 in the jam processing S106 (S301). The CPU 30 displays an error display on the display unit 35 of the printer 4 (S302), and instructs the user to perform jam processing. The CPU 30 determines whether or not the user has opened an openable / closable cover (not shown) provided on the main casing 5 for the jam processing (S303). If the user opens the cover (S303: Y), executes the jam processing, and then closes the cover again (S304: N), it is determined in S305 whether the cause of the jam has been resolved.

  When the cause of the jam is resolved (S305: Y), the CPU 30 executes the collection process as described above (S306 to S314). After executing S314, the CPU 30 returns to the main routine.

  After completing the jam processing S107, the CPU 30 causes the printing unit 6 to print the contents of the page buffer previously developed in the image for one page in S108. Then, count processing S105 is performed and it returns to S106.

  If the CPU 30 does not detect a paper jam in S106, the CPU 30 returns to S103 and monitors whether there is received data for the next page.

  If the CPU 30 determines in S103 that there is no received data for the next page (S103: N), the CPU 30 causes the printing unit 6 to print the contents of the bitmap data expanded in the page buffer (S109).

  The CPU 30 executes the counting process S105 in the same manner as described above, and determines whether or not a paper jam has occurred. When the occurrence of paper jam is detected (S110: Y), the jam processing S107 is executed in the same manner as described above, and then the print processing S109 and the count processing S105 are executed. If the CPU 30 does not detect the occurrence of a jam in the sheet 1 in S110, the CPU 30 monitors whether there is received data (S101).

  As described above, according to the present embodiment, since the magenta developer 28M has the largest charge amount per unit amount, the collected developer is contained in the same developing device 10. When a developer image is formed on the image carrier 11 in a state where the 28R and the developer 28M having a color corresponding to the developer 10M are mixed, the color corresponding to the developer 10M is formed on the image carrier 11M. The developer 28M is selectively developed. As a result, it is possible to suppress a change in the color of the magenta developer 28M corresponding to the developing device 10M that collects the developer 28R.

  According to the present embodiment, the CPU 30 sets magenta corresponding to the developing device 10M based on the total number of counts stored in the RAM 32 and the usage amount of the developer 28 per ON signal stored in the ROM 31. The remaining amount of developer 28M (developer 28M originally contained in the developing device) can be calculated reliably. When it is determined that the remaining amount of the developer 28 accommodated in the developing device 10M has reached the threshold value, the printing process is stopped, so that it is possible to suppress the change in the color of the developer 10M.

  Further, in the present embodiment, the image carrier 11BK, 11Y, 11C different from the image carrier 11M corresponding to magenta M is subjected to the recovery process while being separated from the belt 2 by the separation means 23BK, 23Y, 23C. It has come to be. As a result, the developer 28R transferred to the belt 2 is transferred to the image carriers 11BK, 11Y, and 11C corresponding to the different developers 10BK, 10Y, and 10C from the developer 10M from which the developer 28R transferred to the belt 2 is collected. Can be prevented, so that color mixing can be further suppressed.

<Embodiment 2>
Next, a second embodiment of the present invention will be described with reference to FIGS.
FIG. 14 shows an electrical configuration of the image forming apparatus according to the present embodiment. The printer 4 is the same as that of the first embodiment except that the printer 4 includes a current sensor (an example of a measuring unit) 60 that detects a current value of a current (development current) flowing between the developing roller 18 and the image carrier 11. About the same part, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

  Here, the density of the printed image is proportional to the amount of developer deposited per unit area. The developer adhesion amount is determined by the current flowing from the developing roller to the image carrier during development and the charge amount per unit mass of the developer (hereinafter referred to as Q / M). That is, the current that flows from the developing roller to the image carrier during development represents the amount of charge that has moved from the developing roller to the image carrier due to the movement of the developer per unit time. Dividing by Q / M makes it possible to determine the amount of developer movement (developer adhesion amount).

On the other hand, even when the image carrier is charged by the charger and not exposed by the exposure device, if the potential of the developing roller is different from the potential of the image carrier, the developing current (hereinafter referred to as this The developing current at that time is referred to as “non-image portion developing current”). Here, when the relationship between the non-image area development current and the Q / M of the toner when the development bias is fixed to a constant value V b 0 was examined, the non-image area development current I w and Q / M The relationship is expressed as the following equation (1). Note that e 1, f 2 and g are constants.
Q / M = eIw ² + fIw + g (1)

  As described above, the developing current Iw when the image carrier is charged by the charger and not exposed by the exposure device depends on the Q / M value of the toner.

  Therefore, if the development current is measured in a state where the image carrier is not exposed, the Q / M of the toner can be obtained based on the measured development current.

  The above equation (1) is stored in the ROM 31 of the printer 4.

  FIG. 15 shows a flowchart of print processing according to the present embodiment. After the power is turned on (S90), the CPU 30 executes the initial process S100 and then measures the charging characteristics of the developer of each color (S400).

  In S <b> 400, the CPU 30 causes the developing bias circuit 50 to apply a current detection developing bias Vb <b> 0 determined in advance as a value for detecting the developing current to the developing roller 18 for a certain period of time. The current detection developing bias Vb0 is the developing bias Vb0 which is a condition when the above-described equation (1) stored in the ROM 71 is obtained. That is, it is adapted to the condition that Q / M can be obtained using the equation (1).

  Here, the application of the current detection developing bias Vb0 is completed before the electrostatic latent image formed by the exposure operation by the exposure device 17 is started for a certain period of time during which the current detection developing bias Vb0 is applied. Is set. That is, the charger 16 starts the charging operation at a timing earlier than the timing at which the first part of the image forming area where the electrostatic latent image is formed by the exposure device 16 during the printing operation. It has become.

  In S400, the current value of the developing current (non-image portion developing current Iw) is detected by the current sensor 60 during application of the current detecting developing bias Vb0. Specifically, while the image carrier 11 rotates once, current values are detected in a plurality of states in which the rotation position of the image carrier 11 (contact position between the image carrier 11 and the developing roller 18) is different. The average is taken. By doing so, it is possible to prevent the influence of the eccentricity of the image carrier 11 and the change in the surface characteristics in the circumferential direction and the erroneous detection, thereby improving the reliability of the detected value.

  Subsequently, the CPU 30 acquires the above-described formula (1) stored in the ROM 31, and calculates the Q / M of the developer by substituting the detected development current Iw into the formula (1).

  The CPU 30 compares the Q / M of each color developer calculated as described above, and determines which color developer has the highest Q / M. Thereafter, the CPU 30 stores in the RAM 32 the developer having the largest Q / M color in S401.

  Thereafter, the CPU 30 determines whether or not the cover of the main casing 5 has been opened in S402, and if it is determined that the cover has not been opened (S402: N), print data is received via the communication line 37. It is monitored whether or not it is performed (S101). The subsequent processing is the same as S101 to S110 in FIG. 12 of the first embodiment, and thus a duplicate description is omitted.

  When the cover of the main casing 5 is opened in S402 (Y), the CPU 30 measures the developer charging characteristics when the cover is closed (S403: N) (S400).

  In the first embodiment, the developer having the largest charge amount per unit amount is described as magenta, for example. However, the charge amount of the developer gradually decreases due to deterioration during use. And not all developers are deteriorated in the same way. For this reason, for example, even when magenta has the highest charge amount per unit amount when it is new, the charge amount per unit amount of developer different from magenta may become the largest as a result of deterioration during use. In such a case, when the developer 28M is collected in the developing device 10M corresponding to magenta, when the CPU 30 executes the printing process, the developer of other colors is selectively developed from the developing device 10M corresponding to magenta. The desired color will change.

  In the present embodiment, the CPU 30 can reliably collect the developer 28R in the developing device 10 corresponding to the developer having the largest Q / M by measuring Q / M. Thereby, it is possible to reliably suppress a change in the color of the developer corresponding to the developing device 10 from which the developer 28R has been collected.

<Embodiment 3>
16 and 17 show Embodiment 3 of the present invention. FIG. 16 shows an electrical configuration of the image forming apparatus according to the present embodiment. The printer 4 is the same as that of the first embodiment except that it includes a rotation sensor (an example of a second count unit) 61 that detects the number of rotations of the developing roller 18. Therefore, the same portions are denoted by the same reference numerals and redundant descriptions are provided. Omitted.

  FIG. 17 is a flowchart showing the flow of the counting process S105 executed by the CPU 30. In the present embodiment, as shown in FIG. 17, the CPU 30 uses the rotation sensor 61 to count the number of rotations of the developing roller 18M corresponding to magenta (S500). The rotation speed means not the rotation speed (the rotation speed per unit time) but the rotation amount.

  The CPU 30 transmits the count number to a RAM (an example of the second integrating means) 32 and stores the total number of count numbers (S501). The CPU 30 uses the amount of magenta developer 28M based on the count number stored in the RAM 32 (S502), the developer usage amount per rotation of the developing roller 18M stored in the ROM 31, and (S503). Is calculated (S504). Further, the CPU 30 determines the remaining amount of the developer 28M corresponding to the developing device 10M based on the usage amount of the magenta developer 28M.

  Accordingly, the remaining amount of the magenta developer 28M can be surely known based on the count number stored in the RAM 32. When it is determined that the remaining amount of the developer 28M stored in the developing device 10M has reached a predetermined amount (> 0) (S505: Y), the print processing is prohibited (S506). Since it is possible to prevent the developer image from being formed only by the developed developer 28R, it is possible to prevent the color of the magenta developer 28M from changing.

<Embodiment 4>
FIG. 18 shows a fourth embodiment of the present invention. In the present embodiment, magenta (M), cyan (C), yellow (Y), yellow (Y), in order from the upstream side (right side in the figure) along the moving direction (arrow line A) of the belt 2 that conveys the sheet 1. The configuration is substantially the same as in the first embodiment except that four image forming units 3M, 3C, 3Y, and 3BK are provided corresponding to the developer of each color of black (BK). Are denoted by the same reference numerals and redundant description is omitted.

  According to the present embodiment, in the recovery process, the developer 28R transferred to the belt 2 comes into contact with the image carrier 10M corresponding to magenta having the largest charge amount per unit amount, and corresponds to the image carrier 10M. Is collected in the developing device 10M. As a result, the developer 28R transferred to the belt 2 can be prevented from coming into contact with the image carriers 11BK, 11Y, and 11C corresponding to black, yellow, and cyan. As a result, it is possible to prevent the developer 28R from adhering to the image carriers 11BK, 11Y, and 11C different from the image carrier 11M corresponding to the developer having the largest amount of charge per unit amount, thereby reliably suppressing color mixing. it can.

  Further, according to the present embodiment, the developer 28R transferred to the belt 2 first comes into contact with the collecting image carrier 10M provided at the most upstream side, and therefore, is different from the image carrier 10M. The step of separating the image carriers 11BK, 11Y, and 11C from the belt 2 can be omitted.

<Embodiment 5>
19 to 22 show a fifth embodiment of the present invention. As shown in FIG. 19, in the present embodiment, a sensor 15 for detecting a test pattern formed on the belt 13 is provided facing the surface of the belt 13.

  Further, below the belt 2, a brush (holding portion) 73 that is rotated by a motor (not shown) is disposed at a position that contacts the lower surface of the belt 2. The brush 73 comes into contact with the belt 2 to remove the developer 28R attached to the belt 2 from the belt 2.

  A holding case 70 having a box shape is disposed below the brush 73 so that the developer 28R removed from the belt 2 by the brush 73 is received from below so as not to scatter.

  Opposing means (opposing roller) 71 for applying a holding unit bias voltage is provided between the brush 73 and the opposite side of the belt 2 with respect to the brush 73. A holding unit bias circuit 72 shown in FIG. 20 is connected to the facing means 71 and the brush 73. The CPU 30 causes the holding unit bias circuit 72 to apply a holding unit bias voltage between the facing unit 71 and the brush 73. The holding unit bias voltage includes a holding bias voltage for temporarily collecting and holding the developer on the brush 73, and a second reverse bias voltage (an example of a reverse bias voltage) for returning the developer to the belt 2. One of them is selectively applied.

  Since the configuration other than the above is substantially the same as that of the first embodiment, the same members are denoted by the same reference numerals, and redundant description is omitted.

  In the present embodiment, as shown in FIG. 21, the CPU 30 causes the image forming units 3BK, 3C, 3Y, 3M to execute a test process for forming a test pattern on the belt 2 in a predetermined pattern. The CPU 30 applies a transfer bias to each image carrier 11BK, 11Y, 11C, 11M (S601), and causes each image forming unit 3BK, 3Y, 3C, 3M to print a test pattern in a predetermined pattern on the belt 2 (see FIG. S602). Next, the CPU 30 causes the sensor 15 to detect the test pattern. At this time, if a mixed color is detected in the magenta test pattern having the largest charge amount per unit amount (S603: Y), the CPU 30 prohibits the print processing (S604). Thereby, when CPU30 performs a printing process, it can suppress beforehand that other colors are mixed with magenta.

  For example, when the above-described test process is completed, the CPU 30 causes the belt unit 20 to drive the belt 2 and causes the brush 73 to which a holding bias is applied to contact the belt 2 to adhere to the belt 2. The developer is removed from the belt 2 and temporarily held on the brush 73.

  As shown in FIG. 22, when the CPU 30 does not execute the print process, the developer held by the brush 73 is changed to a developer 11 (in this embodiment, magenta in the present embodiment) corresponding to the developer having the largest charge amount. To the developing device 11M) corresponding to.

  The CPU 30 applies a second reverse bias voltage for returning the developer to the belt 2 between the brush 73 and the facing unit 71 by the holding unit bias circuit 72 (S700). Application of the second reverse bias voltage generates a force that electrically draws the developer from the brush 73 side to the belt 2 side. The CPU 30 causes the developer held by the brush 73 to be supplied from the brush 73 to the belt 2 by rotating the brush 73 by a motor (not shown) simultaneously with the application of the second reverse bias voltage (S702). As a result, the developer adheres to the belt 2. Further, the CPU 30 causes the belt unit 20 to drive the belt 2 by the half circumference (S703).

  Next, the CPU 30 causes the holding unit bias circuit 72 to stop applying the second reverse bias voltage (S704). Thereby, there is no force to draw the developer attached to the belt 2 to the belt 2 side.

  Subsequent steps are the same as S309 to S314 in FIG.

  When the above test process is executed, it is necessary to collect the developer adhered on the belt 2 before executing the print process. However, if the collection process is executed each time the test process is executed, the test process time becomes longer as a whole.

  According to the present embodiment, for example, when a test process is executed, the developer attached to the belt 2 can be temporarily held on the brush 73. As a result, the collection process does not have to be executed immediately after the test process is completed, so that the test process time can be reduced as a whole.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) The developer 28 in this embodiment is exemplified by four-color development of yellow, magenta, cyan, and black, but is not limited to this, and may be two-color development of red and black. Color or four or more developers 28 may be used.
(2) In this embodiment, the developing method is a contact type, but is not limited to this, and a non-contact developing method may be used.
(3) The present embodiment is a tandem color printer that employs a direct transfer system, but is not limited thereto, and may be a tandem color printer that employs an intermediate transfer system, or a 4-cycle color printer. It may be.

1 is a side sectional view of an image forming apparatus according to a first embodiment. The principal part expanded side sectional view which shows the state which act | operated the separation means Block diagram showing electrical configuration Schematic diagram showing various bias voltages Schematic showing the movement of developer during jam processing Schematic diagram showing a state in which a developer of another color adheres to the image carrier Flow chart showing jam processing Enlarged side sectional view of the main part showing the intermediate process of jam processing Enlarged side sectional view of the main part showing the intermediate process of jam processing Schematic diagram showing the recovery process Schematic diagram showing a state where a developer having a large charge amount per unit amount is selectively developed Flow chart showing print processing Flow chart showing count processing The block diagram which shows the electric constitution of Embodiment 2. 10 is a flowchart illustrating print processing of the printer according to the second embodiment. The block diagram which shows the electric constitution of Embodiment 3. Flowchart showing the counting process of the third embodiment Side sectional view showing a configuration of a printer according to a fourth embodiment. Side sectional view showing a configuration of a printer according to a fifth embodiment. The block diagram which shows the electric constitution of Embodiment 5. Flow chart showing test process Flowchart showing holding unit developer recovery process

4. Printer (image forming device)
10BK, 10Y, 10C, 10M ... developer 11BK, 11Y, 11C, 11M ... image carrier 12BK, 12Y, 12C, 12M ... transfer means 17BK, 17Y, 17C, 17M ... exposure unit 18BK , 18Y, 18C, 18M ... developing roller 23BK, 23C, 23Y ... separating means 30 ... CPU (control means, judging means, generating means, first counting means)
32 ... RAM (first integration means, second integration means)
60 ... Current sensor (measuring means)
61 ... Rotation sensor (second counting means)
72. Holding unit bias circuit (applying means)
73 ... Brush (holding part)

Claims (7)

An image bearing member, a transfer unit that transfers the different colors and a plurality of developing units provided corresponding to the developer, the object a developer image formed on the image carrier by the developing unit, wherein Control means for performing recovery processing for recovering the developer transferred to the object in a developer corresponding to the developer having the largest charge amount per unit amount among the plurality of developers ; Measuring means for measuring the charge amount per unit amount,
The control unit is an image forming apparatus that determines a developer having the largest charge amount per unit amount among the plurality of developers based on a measurement result of the measurement unit. A determination unit configured to determine whether or not a remaining amount of the developer previously stored in the developing unit has reached a predetermined amount M (> 0), and the control unit determines whether the remaining amount is a predetermined amount by the determination unit; When it is not determined that M has been reached, the developing device permits development processing for forming the developer image on the carrier, and when it is determined that the remaining amount has reached a predetermined amount M, the development processing is prohibited. The image forming apparatus according to claim 1. An exposure unit that exposes the image carrier, a generation unit that generates a light ON / OFF signal for causing the exposure unit to emit light based on bitmap data, and an ON signal among the light ON / OFF signals is counted. First counting means, and first integrating means for accumulating and storing the count number of the ON signal obtained by the first counting means, wherein the determining means is stored in the first integrating means. The image forming apparatus according to claim 2, wherein the remaining amount of the developer corresponding to the developer in which the developer transferred to the object is collected is determined based on the count number . A developing roller provided in the developing unit for adhering the developer to the image carrier, a second counting unit for counting the number of rotations of the developing roller, and the developing obtained by the second counting unit. Second accumulating means for accumulating and storing the rotation speed of the roller, and the determination means collects the developer transferred to the object based on the rotation speed stored in the second accumulating means. The image forming apparatus according to claim 2 , wherein the remaining amount of the developer corresponding to the developing device is determined . When the recovery process is not performed, the plurality of image carriers provided corresponding to the developing units are brought into contact with the object, and when the recovery process is performed, the plurality of image carriers among the image bearing member corresponding to the developing device is different from the developing device in which the developer transferred to the object is recovered, any of claims 1 to 4 comprising a separating means for separating from said object 2. The image forming apparatus according to item 1 . The object is movable relative to the image carrier, and a plurality of the image carriers are arranged side by side corresponding to the developing units along a direction in which the object moves relatively. cage, the image bearing member corresponding to the developing devices developer transferred on the object is recovered, according to claim 1 or claim wherein the object is provided on the most upstream position in the direction of relative movement the image forming apparatus according to any one of 5. A holding unit that temporarily collects and holds the developer attached to the object, and an application unit that applies a holding bias voltage that holds the developer collected by the holding unit in the holding unit, The control unit causes the application unit to return the developer held in the holding unit to the object by applying a reverse bias voltage having a polarity opposite to the holding bias voltage to the holding unit. the image forming apparatus according to any one of claims 1 to 6 to perform the recovery process.

Images