JP2013044790A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a uniform toner stirring sequence performed for all cartridges may involve stirring unnecessary cartridges and therefore productivity may be decreased because of time required for the toner stirring sequence.SOLUTION: Toner images are formed near both ends in a main scanning direction of an intermediate transfer body before performing a toner stirring sequence, and a density difference between the toner images is calculated to control duration for performing the toner stirring sequence from the calculated density difference. Accordingly, downtime that is generated through the toner stirring sequence performed for uniform and fixed duration is suppressed, and thereby a decrease in productivity brought about by a decrease in through-put can be suppressed.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a laser beam printer, and a facsimile.

  2. Description of the Related Art Conventionally, an image forming apparatus employs a system in which a developing unit that accommodates toner is formed into a cartridge and the cartridge can be attached to and detached from the image forming apparatus body. According to this method, the user can perform maintenance of the image forming apparatus without depending on the service person, so that convenience can be improved. However, in this method, if a cartridge is not used for a long period of time and kept in a certain posture, a toner called a tapping phenomenon occurs in which the toner stored in the storage unit is biased toward one side and is solidified. There is a possibility. When image formation is performed with a cartridge in which tapping has occurred, there is a possibility that the amount of toner supply will not be stable and unevenness in image density will occur.

  In order to eliminate such a tapping state, Patent Document 1 discloses a method in which a stirring operation for stirring the toner is performed for a certain period of time before starting image formation.

JP-A-11-184200

  However, in the method disclosed in Patent Document 1, image formation is started after a uniform toner stirring operation regardless of whether or not the toner needs to be stirred. Therefore, for example, even when it is not necessary to perform the toner agitation operation for a fixed amount, since the image formation is performed after the agitation operation is completed, the time required for the toner agitation becomes a downtime, and the downtime As a result, the throughput may decrease and the productivity may decrease.

  The invention according to the present application has been made in view of the above situation, and suppresses a decrease in productivity due to a decrease in throughput by suppressing a downtime caused by stirring the toner. With the goal.

  To achieve the above object, a plurality of image carriers, a plurality of developers for forming toner images on each of the plurality of image carriers, and a plurality of developers are accommodated in the developers. An image forming apparatus having a plurality of agitating means for agitating the developed developer and a transfer body onto which a toner image formed on the image carrier is transferred, wherein the developing device is arranged in the longitudinal direction of the developing device. Detecting means for detecting a first density at a first position and a second density at a second position of the toner image formed on the image carrier at a position and transferred to the transfer body; Control means for controlling a stirring operation by the stirring means based on a difference between the first density and the second density detected by the detecting means and a predetermined threshold value.

  According to the configuration of the present invention, it is possible to suppress a decrease in productivity due to a decrease in throughput by suppressing a downtime caused by stirring the toner.

Schematic configuration diagram of an image forming apparatus Block diagram showing system configuration of image forming apparatus FIG. 1 is an enlarged main sectional view of the process cartridge 9a of FIG. Flowchart for explaining operation for controlling time of toner stirring sequence The figure which showed the intermediate transfer body 80 when the toner image 218d was primary-transferred The graph which showed the relationship between the density difference of toner image 218dR and 218dL, and the implementation time of a toner stirring sequence A flowchart for explaining an operation of forming a toner image again in the middle of the toner stirring sequence and determining whether or not to continue the toner stirring sequence based on the density difference. The figure which showed the intermediate transfer body 80 when a toner stirring sequence was implemented 3 times. Flowchart for explaining an operation for simultaneously cleaning a toner image formed for toner stirring sequence and a toner image formed for image density control The figure which showed the intermediate transfer body 80 when image density control was implemented after implementing a toner stirring sequence twice.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a laser printer as an image forming apparatus. First, the configuration of the entire image forming apparatus will be described. In the following description, the first station is a yellow (Y) toner image forming station, the second station is a magenta (M) toner image forming station, and the third station is a cyan (C) color. The toner image forming station No. 4 and the fourth station are black (K) toner image forming stations.

  Reference numeral 1a denotes a photosensitive drum as an image carrier. The photosensitive drum 1a is formed by laminating a plurality of functional organic materials including a carrier generation layer that generates a charge by exposure on a metal cylinder, a charge transport layer that transports the generated charge, and the outermost layer is an electrical layer. Low conductivity and almost insulating. Reference numeral 2a denotes a charging roller as charging means. The charging roller 2a is brought into contact with the photosensitive drum, and as the photosensitive drum 1a rotates, the surface of the photosensitive drum 1a is uniformly charged without being driven to rotate. A DC voltage or a voltage superimposed with an AC voltage is applied to the charging roller 2a, and discharge occurs in a small air gap on the upstream and downstream sides from the contact nip portion between the surface of the charging roller 2a and the photosensitive drum 1a. 1a is charged. Reference numeral 3a denotes a cleaning unit for cleaning the transfer residual toner on the photosensitive drum 1a. Reference numeral 8a denotes a developing unit as developing means. The developing unit 8a includes a developing roller 4a, a stirring unit 5a, a nonmagnetic one-component developer 6a, and a developer application blade 7a. Each of the members 1a to 8a is an integrated process cartridge 9a that is detachable from the image forming apparatus. Here, as an example, the developer is a non-magnetic single component, but a two-component developer of toner and carrier may be used.

  Reference numeral 11a denotes exposure means, which is composed of a scanner unit or LED array that scans laser light with a polygon mirror, and irradiates the photosensitive drum 1a with a scanning beam 12a that is modulated based on an image signal. Each of the charging roller 2a, the developing roller 4a, and the primary transfer roller 81a includes a charging bias power source 20a that is a voltage supplying unit to the charging roller 2a, a developing bias power source 21a that is a voltage supplying unit to the developing roller 4a, and a primary transfer. It is connected to a primary transfer bias power source 84a which is a means for supplying voltage to the roller 81a. The above is the configuration of the first station, and the second, third, and fourth stations have the same configuration, and thus description thereof is omitted here. In the following description, the first station will be described as a representative for convenience of explanation, but the second, third, and fourth stations can be similarly configured and controlled. For the same members as those in the first station, the suffixes after the numbering are b, c, and d corresponding to the second, third, and fourth stations, respectively. Note that the image forming apparatus according to the present embodiment is a so-called tandem system, and the first to fourth cartridges are arranged at unique positions.

  The intermediate transfer member 80 is supported by two rollers, that is, a secondary transfer counter roller 86 and a driving roller 14 as a stretching member, and an appropriate tension is maintained. By driving the drive roller 14, the intermediate transfer member 80 moves in the forward direction at substantially the same speed with respect to the photosensitive drums 1a to 1d. The intermediate transfer member 80 rotates in the direction of the arrow, and the primary transfer roller 81a is disposed at a position facing the photosensitive drum 1a with the intermediate transfer member 80 interposed therebetween. Further, a static elimination member 23a is disposed on the downstream side of the primary transfer roller 81a in the rotation direction of the intermediate transfer member 80. The drive roller 14, the charge removal member 23a, and the secondary transfer counter roller 86 are electrically grounded.

  The photosensitive drum 1a as an image carrier is configured by applying an organic photoconductor layer (OPC) to the outer peripheral surface of an aluminum cylinder. Both ends of the photosensitive drum 1a are rotatably supported by flanges, and are driven to rotate counterclockwise with respect to the drawing by transmitting a driving force from a driving motor (not shown) to one end. The charging unit 2a is a conductive roller formed in a roller shape. The charging unit 2a is brought into contact with the surface of the photosensitive drum 1a, and the surface of the photosensitive drum 1a is uniformly applied by applying a charging bias voltage by a power source (not shown). It is to be charged. The exposure means 11a has a polygon mirror, and this polygon mirror is irradiated with image light corresponding to an image signal from a laser diode (not shown). The developing means is in contact with the surface of the toner storage unit and the photosensitive drum storing toners of black, cyan, magenta, and yellow, respectively, and is driven to rotate by a driving unit (not shown) and developed by a developing bias power source (not shown). It is composed of developing rollers 4a to 4d and the like that perform development by applying a voltage.

  In addition, primary transfer rollers 81 a to 81 d that are in contact with the intermediate transfer body 80 are provided alongside the intermediate transfer body 80 so as to face the photosensitive drums 1 a to 1 d. These primary transfer rollers 81a to 81d are connected by primary transfer bias power sources 84a to 84d, and positive charges are applied from the primary transfer rollers 81a to 81d to the intermediate transfer member 80 in contact with the photosensitive drums 1a to 1d. The negative color toner images on the photosensitive drums 1a to 1d are sequentially transferred to form a multicolor image.

  When feeding the recording material P as paper from the main body cassette 16, the main body cassette bottom plate 29 is raised by driving the cassette pickup roller 17, and the recording material P installed in the main body cassette 16 is pushed up. The uppermost sheet of the recording material P pushed up comes into contact with the cassette pickup roller 17, and the recording material P is separated and fed one by one by the rotation of the cassette pickup roller 17. Are transferred to the contact portion between the secondary transfer roller 82 and the intermediate transfer member 80.

  The recording material P fed from the main cassette 16 or the manual feed tray 30 is conveyed to the secondary transfer unit by the registration roller 18. The intermediate transfer member 80 is circulated by the drive roller 14 so as to electrostatically attract the toner images formed on the photosensitive drums 1a to 1d. As a result, a multicolor image is formed on the outer periphery of the intermediate transfer member 80, and the image formed on the belt is conveyed to a contact portion between the secondary transfer roller 82 and the intermediate transfer member 80, which is the secondary transfer position. When the toner image on the intermediate transfer member 80 is transferred to the recording material P, an electric field is formed on the secondary transfer counter roller 86 disposed opposite to the intermediate transfer roller 82 by applying a voltage to the secondary transfer roller 82. Dielectric polarization is generated between the transfer member 80 and the recording material P to generate an electrostatic adsorption force therebetween.

  The fixing unit 19 applies heat and pressure to fix the toner image on the recording material, and includes a fixing belt (not shown) and an elastic pressure roller (not shown). The elastic pressure roller sandwiches the fixing belt and forms a fixing nip portion with a predetermined width with a predetermined pressure contact force with a belt guide member (not shown). In a state where the fixing nip portion rises to a predetermined temperature and is temperature-controlled, the recording material P on which the unfixed toner image conveyed from the image forming portion is formed is between the fixing belt and the elastic pressure roller in the fixing nip portion. The image surface is conveyed upward, that is, facing the fixing belt surface. In the fixing nip portion, the image surface is in close contact with the outer surface of the fixing belt, and the fixing nip portion is nipped and conveyed together with the fixing belt. In the process where the recording material P is nipped and conveyed together with the fixing belt through the fixing nip portion, the fixing belt heats the unfixed toner image on the recording material P and heat fixes the recording material P. The fixed recording material P is discharged to the discharge tray 36.

  FIG. 2 is a block diagram illustrating a hardware configuration and functions for explaining an example of a system configuration of the image forming apparatus. The host computer 200 transmits print data (character code, graphic data, image data, process conditions, etc.) described in a page description language such as PCL to the controller unit 201. The controller unit 201 receives print data from the host computer 200. The received print data is sequentially analyzed for each color to generate image information that is a bitmap composed of dot data necessary for forming an image with the printer (hereinafter referred to as image expansion), and to the engine control unit 202. Send sequentially. Here, as an example, a method of developing an image by the controller unit 201 has been described. However, the image development is not necessarily performed by the controller unit 201. For example, the image may be developed by the host computer 200 and the image information may be transmitted to the controller unit 201.

  The engine control unit 202 serving as a control unit forms an image based on image information sequentially input from the controller unit 201, and thus forms a latent image on the photosensitive drum 1, forms a toner image of each color, primary transfer, and secondary. A series of image forming operations such as transfer and fixing processing are controlled. The process from the formation of the latent image to the primary transfer (hereinafter referred to as a printing operation) is performed in parallel with the image development. An interface unit 210 connects the engine control unit 202 and the controller unit 201. The interface unit 210 includes a serial communication unit 203 and an image forming signal communication unit 204. The serial communication unit 203 receives a command or signal transmitted from the controller unit 201 to the engine control unit 202, and sends a signal requesting the status of the image forming apparatus or image information from the engine control unit 202 to the controller unit 201. Send. The image forming signal communication unit 204 receives image information transmitted from the controller unit 201 to the engine control unit 202. Here, the control means is the engine control unit 202, but the control means is not limited to this. For example, the control means may be formed by dividing the objects controlled by the engine control unit 202 and the controller unit 201 into two. Is possible.

  211 is a CPU that controls each control unit and communication unit in the engine control unit 202, and compares data sent to the controller unit 201 with data stored in a ROM (not shown) of the engine control unit. It is. The CPU 211 controls a home position mark (hereinafter also referred to as an HP mark) 218b on the intermediate transfer member 80, a sensor control unit 218 that controls an optical sensor 218a and 218c that detects a toner image 218d, the intermediate transfer member 80, and the photosensitive drum 1. The drive control unit 217 that controls the above is controlled. The CPU 211 controls generation of a vertical synchronization signal (hereinafter also referred to as a / TOP signal) for starting a printing operation and a horizontal synchronization signal output from the scanner unit. Further, the image forming control unit 212, the fixing control unit 213, the paper feed control unit 214, the high voltage control unit 215, and the nonvolatile memory control unit 216 that perform control related to the printing operation such as a scanner motor and a laser output are controlled.

  FIG. 3 is an enlarged schematic configuration diagram of the process cartridge 9a. In FIG. 3, the developing unit 8a for stirring the toner will be described. The developing unit 8a is composed of the following members. A developing roller 4a as a developer carrying member that contacts the photosensitive drum 1a and rotates in the direction of the arrow in the figure. Developer application blade 7a as a developer regulating member. An agitation unit 5a as an agitation member for agitating the conveyed non-magnetic one-component developer 6a and transporting it to the developing roller 4a. In this embodiment, the stirring unit 5a has been described with a rotatable plate-like stirring member as an example. However, if the developer can be stirred, stirring members having other shapes such as a screw shape or a roller shape may be used. May be. Moreover, it is good also as a stirring part combining those two or more.

  Next, with reference to FIG. 4 to FIG. 6, control of necessity of toner agitation operation (hereinafter also referred to as toner agitation sequence) and control of execution time of the toner agitation sequence in the present embodiment will be described. In the present embodiment, description will be made assuming that a cartridge that may need to be subjected to the toner stirring sequence is a yellow cartridge. A toner image is formed by the yellow cartridge, the density difference of the formed toner image is detected, and the execution time of the toner agitation sequence is determined according to the density difference.

  FIG. 4 is a flowchart for explaining the operation of controlling the time of the toner stirring sequence. In step S401, the CPU 211 forms a toner image 218d on the photosensitive drum 1a. In step S <b> 402, the CPU 211 primarily transfers the formed toner image 218 d onto the intermediate transfer body 80. The positions where the toner images are formed are in the vicinity of both ends of the developing roller 4a in the main scanning direction. By transferring the toner image to the intermediate transfer member 80, the toner image is in the vicinity of both ends in the main scanning direction in the image area of the intermediate transfer member 80 as shown in FIG.

  FIG. 5 shows the intermediate transfer member 80 when the toner image 218d is primarily transferred. The toner image 218d is primarily transferred as toner images 218dR and 218dL in the vicinity of both ends in the main scanning direction in the image region on the intermediate transfer member 80. The toner images are formed at two different positions of the toner images 218dR and 218dL in order to calculate the execution time of the toner agitation sequence from the difference in density between the two toner images. The length PL and the width PW of the toner images 218dR and 218dL are formed as lengths and widths so that the density sensor 218c can reliably detect the density. Note that the toner image 218d is a general term that combines the toner image 218dR and the toner image 218dL. Further, here, the density sensor 218c for detecting the toner image on the intermediate transfer member 80 has been described as an example. However, for example, in order to detect the toner image on the photosensitive drum of each color, a sensor is arranged on each photosensitive drum. It is also possible to detect the toner image on the photosensitive drum.

  In step S403, the CPU 211 starts detection of the density of the toner images 218dR and 218dL transferred to the vicinity of both ends in the main scanning direction of the intermediate transfer body 80 using the detected HP mark 218b as a reference. In step S404, the CPU 211 determines whether the density detection of the toner images 218dR and 218dL has been completed by the density sensor 218c. When the density of the toner images 218dR and 218dL is detected by the density sensor 218c, the CPU 211 calculates the density difference between the toner images 218dR and 218dL in S405. The densities of the toner images 218dR and 218dL are handled as digital values from 0 to 255. Therefore, the value that the density difference can take is also from 0 to 255 deg. The state where the density difference is generated in the toner images 218dR and 218dL is a state in which the toner is biased and solidified in one of the longitudinal directions of the developing unit 8.

  In step S406, the CPU 211 determines the execution time of the toner agitation sequence according to the calculated density difference between the toner images 218dR and 218dL. FIG. 6 is a graph showing the relationship between the density difference between the toner images 218dR and 218dL and the execution time of the toner stirring sequence. When the density difference is less than 65 deg, it is determined that the toner is sufficiently stirred, and the toner stirring sequence is not performed. Thereafter, as the density difference increases, the execution time of the toner stirring sequence is increased. For example, when the density difference is 65 deg, the execution time is 6 seconds as a predetermined time, when the density difference is 125 deg, the execution time is 30 seconds, and when the density difference is 200 deg or more, the execution time is 60 seconds. To do. In this way, by controlling the execution time of the toner agitation sequence depending on whether or not the toner image density difference exceeds a predetermined value (threshold value), an appropriate time according to the condition of the toner in the cartridge is obtained. It is possible to perform the toner stirring sequence. Note that the threshold in the present embodiment is, for example, 65 deg, 125 deg, 200 deg, or the like described above. The relationship between the density difference shown here and the execution time of the toner stirring sequence is merely an example, and the threshold for determining the execution time is appropriately determined depending on the stirring speed, the characteristics of the toner component, the environmental temperature, the detection capability of the darkness sensor, and the like. It is possible to set. Although the toner stirring sequence by rotating the stirring unit 5a as the stirring means has been described here, it is possible to use stirring members of other shapes such as a screw shape or a roller shape. At that time, since the stirring force varies depending on the shape of the stirring member, the stirring time is appropriately set according to the stirring member. The subsequent control is the same as that described in the present embodiment, and the toner agitation sequence can be performed.

  In step S407, the CPU 211 causes the cleaning unit 3a to clean the toner images 218dR and 218dL formed on the intermediate transfer member 80. In step S <b> 408, the CPU 211 determines whether the execution time of the toner agitation sequence obtained from the calculated density difference is zero. If the execution time is not 0, in S409, the CPU 211 performs the toner agitation sequence for the calculated execution time. When the execution time is 0 or when the toner agitation sequence in S409 is started, in S410, the CPU 211 determines whether the cleaning and the toner agitation sequence are completed, and ends the toner agitation sequence when completed.

  In this way, a toner image is formed by a cartridge that may need to be subjected to a toner agitation sequence, for example, when it is new or has not been subjected to image formation for a long time. In this embodiment, the cartridge that may need to perform the toner agitation sequence is a yellow cartridge. However, the agitation sequence can be performed for other cartridges by calculating the density difference in the same procedure. . Further, when there are a plurality of cartridges that may need to be subjected to the toner stirring sequence, the density difference may be calculated by the same procedure for each. By determining the density difference, it is possible to detect the deviation of the developer from the density difference of the formed toner image, rather than performing a toner stirring sequence for a predetermined time, and it is appropriate for the state of the developer. It is possible to perform the toner agitation sequence in a long execution time. Therefore, it is possible to suppress a decrease in productivity due to a decrease in throughput by suppressing a downtime generated by performing the toner agitation operation at a uniform time.

(Second Embodiment)
In the first embodiment, the method of controlling the execution time of the toner agitation sequence according to the state of the toner by forming a toner image before performing the toner agitation sequence and detecting the density difference has been described. In this embodiment, after determining that the toner agitation sequence is necessary, a toner image is formed again during the toner agitation sequence, and it is determined whether to continue the toner agitation sequence based on the density difference. A method for performing control with higher accuracy will be described. The description of the configuration of the image forming apparatus and the like similar to those of the first embodiment is omitted here.

  FIG. 7 is a flowchart for explaining an operation of forming a toner image again during the toner stirring sequence and determining whether or not to continue the toner stirring sequence based on the density difference. It should be noted that the same steps as those in the flowchart of FIG.

  In step S701, the CPU 211 compares the density difference between the toner image 218dR and the toner image 218dL with a predetermined value (threshold value), and determines whether the density difference is equal to or less than a predetermined value (here, 65 deg or less as an example). To do. If the density difference is larger than the predetermined value, in S702, the CPU 211 performs a toner stirring sequence for 6 seconds. Here, as an example, the case where the toner stirring sequence is performed for 6 seconds has been described, but the present invention is not limited to 6 seconds. When using other types of stirring members such as screws or rollers, it is possible to perform a toner stirring sequence according to these members. FIG. 8 is a diagram of the intermediate transfer member 80 when the toner stirring sequence is performed three times. The toner image 218d is primarily transferred in the vicinity of both ends in the main scanning direction in the image area on the intermediate transfer member 80 so that the toner images 218dR1, 218dL1, 218dR2, 218dL2, 218dR3, and 218dL3 do not overlap each other. The interval PI between the toner images is formed with a length and a width so that the density sensor 218c can reliably detect the leading edge and the trailing edge of the toner image. Here, as an example, the toner images are formed in the vicinity of both end portions, but the present invention is not limited to this. For example, one may be formed at the end portion and the other at the center portion. Also, here, an example is shown in which the toner image is formed at a position where there is no deviation in the sub-scanning direction (the direction perpendicular to the longitudinal direction of the developing device), but the present invention is not limited to this. It may be shifted. Although an example in which a plurality of toner images are detected is shown here, a single toner image that extends over two density sensors may be formed.

  If the density difference is smaller than the predetermined value, the CPU 211 causes the cleaning unit 3a to clean the toner image formed on the intermediate transfer body 80 in S703. In step S <b> 704, the CPU 211 determines whether the cleaning is completed. When the cleaning is completed, the toner agitation sequence ends.

  Thus, during the toner agitation sequence, a toner image is formed, the density difference is detected, and it is determined whether or not to continue the toner agitation sequence according to the density difference. This makes it possible to detect the deviation of the developer from the density difference between the formed toner images, instead of uniformly performing the toner agitation sequence. The toner agitation sequence can be performed in an appropriate execution time according to the state of the developer. Can be performed. Therefore, it is possible to suppress a decrease in productivity due to a decrease in throughput by suppressing a downtime generated by performing the toner agitation operation at a uniform time.

(Third embodiment)
In the first embodiment and the second embodiment, the method of determining whether or not to perform the toner stirring sequence by forming a toner image has been described. In the present embodiment, a method for suppressing a decrease in productivity by simultaneously cleaning a toner image formed for a toner stirring sequence and a toner image formed for image density control will be described.
Note that the description of the configuration of the image forming apparatus, etc., which is the same as in the first embodiment or the second embodiment is omitted here.

  First, image density control will be described. The engine control unit 202 forms a latent image based on the patch pattern data transmitted from the controller unit 201. Then, the formed latent image is developed, and a toner image (patch) 218d for image density control is primarily transferred onto the intermediate transfer member 80. In the present embodiment, a patch pattern generating unit 205 that generates a patch pattern is mounted on the controller unit 201. However, the patch pattern generation unit 205 may be mounted on the engine control unit 202 instead of the controller unit 201. The engine control unit 202 is provided with a density sensor 218c as image density detection means. The density sensor 218c measures the density of the patch 218d by irradiating the patch 218d formed on the intermediate transfer body 80 with light from the light emitting element and receiving the reflected light from the light receiving element. The density of the patch 218d detected by the density sensor 218c is converted into a digital value from 0 to 255 by the sensor control unit 218 and transmitted to the CPU 211. The engine control unit 202 performs image density control using the digital value of the image density detected by the density sensor 218c and transmitted from the sensor control unit 218. Image density control in the present embodiment includes maximum density control (Dmax control) for adjusting the maximum density of an image to a predetermined density, and gradation control (Dhalf control) for adjusting the gradation characteristics of an image to a predetermined characteristic.

  FIG. 9 is a flowchart for explaining the operation of simultaneously cleaning the toner image formed for the toner stirring sequence and the toner image formed for image density control. Note that the same steps as those in the flowcharts of FIGS. 4 and 7 are given the same reference numerals, and description thereof will be omitted.

  If the CPU 211 determines in step S701 that the toner image density difference is equal to or less than a predetermined value, in step S901, the CPU 211 forms a density control patch. In step S <b> 902, the CPU 211 primarily transfers the formed toner image onto the intermediate transfer body 80. In step S903, the CPU 211 starts detecting the density of the toner image transferred to the detected intermediate transfer member 80 by the density sensor 218c. In step S904, the CPU 211 determines whether the density detection of the toner image is completed by the density sensor 218c. When the density of the toner image is detected by the density sensor 218c, the CPU 211 performs image density control according to the detected density in S905. When the image density control is performed, in step S906, the CPU 211 causes the cleaning unit 3a to clean the toner image formed on the intermediate transfer member 80. In step S907, the CPU 211 determines whether the cleaning is completed. When the cleaning is completed, the toner agitation sequence ends.

FIG. 10 is a diagram of the intermediate transfer member 80 when the image density control is performed after the toner stirring sequence is performed twice. The toner images 218dR1, 218dL1, 218dR2, 218dL2 and the image density control patches K0-7, Y0-7, M0-7, C0-7 are primarily transferred so as not to overlap each other. The interval between the toner images 218dR1, 218dL1, 218dR2, 218dL2 and the image density control patch is PI. Further, the length of the toner images 218dR1, 218dL1, 218dR2, 218dL2 is PL1, the length of the image density control patch is PL2, and the peripheral length of the intermediate transfer member 80 is L. Then, on the intermediate transfer member 80,
(L− (PL2 × 4 + PI × 4)) ÷ (PL1 + PI) (1)
The number of toner images 218d calculated by the equation (1) can be formed on the intermediate transfer member 80.

  In this way, the toner image density difference is detected, and it is determined whether or not to continue the toner agitation sequence according to the density difference. Accordingly, it is possible to perform the toner stirring sequence in an appropriate execution time according to the state of the toner, instead of performing the toner stirring sequence uniformly. Further, a toner image for image density control is formed, and cleaning is performed simultaneously with the toner image for toner stirring sequence. Therefore, by suppressing the downtime that occurs due to the toner stirring sequence and the image density control, it is possible to suppress a decrease in productivity due to a decrease in throughput.

80 Intermediate transfer member 218a Optical sensor 218b HP mark 218c Density sensor 218d Toner image 221 CPU

Claims (9)

A plurality of image carriers;
A plurality of developing units for forming a toner image on each of the plurality of image carriers;
In each of the plurality of developing devices, a plurality of stirring means for stirring the developer contained in the developing device;
A transfer body to which a toner image formed on the image carrier is transferred,
The first density of the first position of the toner image formed on the image carrier at the position in the longitudinal direction of the developer by the developing unit and transferred to the transfer body, and the second of the second position of the toner image. Detecting means for detecting the concentration of
An image forming system comprising: a control unit configured to control a stirring operation by the stirring unit based on a density difference between the first density and the second density detected by the detection unit and a predetermined threshold value. apparatus.   The image forming apparatus according to claim 1, wherein the control unit performs a stirring operation by the stirring unit when the density difference detected by the detection unit exceeds the threshold value.   The image forming apparatus according to claim 2, wherein the control unit controls to increase a time for performing the stirring operation by the stirring unit as the density difference increases.   The control unit forms a toner image again before the stirring operation by the stirring unit is completed, detects the first density of the toner image and the second density of the toner image by the detection unit, and 4. The method according to claim 1, wherein whether or not the stirring operation by the stirring unit is continued is determined based on a difference between the first concentration and the second concentration and a predetermined threshold value. 5. 2. The image forming apparatus according to item 1.   The detection means includes a first sensor that detects a density of a first position of the toner image, and a second sensor that detects a density of a second position of the toner image. Item 5. The image forming apparatus according to any one of Items 1 to 4.   6. The toner image according to claim 1, wherein the toner image is formed on the image carrier at positions of both ends in the longitudinal direction of the developing device, and is transferred to the transfer member. Image forming apparatus.   7. The toner image according to claim 1, wherein the toner image is formed on the image carrier at a position not deviated in a direction orthogonal to the longitudinal direction of the developing device, and transferred to the transfer member. The image forming apparatus described in the item. A cleaning means for cleaning the toner image of the transfer body;
A toner image for controlling the stirring operation by the stirring unit and a toner image for controlling the image density are respectively transferred to the transfer body, and the toner images transferred to the transfer body are cleaned by the cleaning unit. The image forming apparatus according to claim 1. An image carrier;
A developing device for forming a toner image on the image carrier;
In the developing unit, an image forming apparatus having stirring means for stirring the developer accommodated in the developing unit,
Detection by which the developing device detects a first density at a first position of a toner image formed on the image carrier at a position in a longitudinal direction of the developing device and a second density at a second position of the toner image. Means,
An image forming system comprising: a control unit configured to control a stirring operation by the stirring unit based on a density difference between the first density and the second density detected by the detection unit and a predetermined threshold value. apparatus.

Images