JP2007086660A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrict degradation of image quality such as fog or a density decrease resulting from toner deterioration, without wastefully consuming a toner when performing the forcible consumption operation of the toner. <P>SOLUTION: The degree of toner deterioration is judged by measuring the density of an intermediate image and checking the characteristics of development. Then, a necessary amount of the toner is forcibly consumed according to the degree of the toner deterioration. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus employing an electrophotographic method or electrostatic recording, such as a copying machine or a page printer.

  In an electrophotographic image forming apparatus, an electrostatic latent image formed on an image carrier is visualized as a toner image by a developing device.

  As one of such developing devices, various dry one-component developing devices have been proposed and put into practical use. For example, a contact development method is mentioned. Since this contact development method does not require a magnetic material, the apparatus can be simplified and miniaturized, and has many advantages such as the ability to form a color image by using a non-magnetic toner. .

  In the contact development method, development is performed by pressing or contacting the surface of the developing roller, which is a developer bearing member, with an image bearing member on which an electrostatic latent image is formed. Therefore, a developing roller having elasticity and conductivity is used. It will be necessary.

  In order to obtain a known developing electrode effect and bias effect, a conductive layer can be provided on the surface of the developing roller or in the vicinity of the surface, and a bias voltage can be applied as necessary.

  In the contact development method as described above, the image quality may be deteriorated, for example, the image density may become unstable or fogging may occur as the number of formed images increases. The decrease in image quality is mainly due to toner deterioration, and is mainly caused by the rubbing between the developing roller and the surface of the image carrier and the rubbing between the developing roller and the toner regulating blade.

In order to avoid such a situation, a method of forcibly consuming toner at a certain interval by detecting the number of printed sheets or the number of rotations of the developing roller is known (for example, see Patent Documents 1 to 6). By using this method, toner that has deteriorated around the developing roller can be consumed, and fresh fresh toner can be supplied to the developing roller, so that deterioration in image quality can be reduced. Further, in a state where the toner is likely to deteriorate in the latter half of the lifetime, the toner deterioration is suppressed by increasing the amount of toner to be replaced. There is a known method for forcibly consuming toner by predicting the degree of toner deterioration according to the number of prints and the number of rotations of the developing roller, such as changing the amount of toner to be forcibly consumed or increasing the interval for performing the forced consumption operation. It has been.
Japanese Patent No. 2733709 Japanese Patent No. 3389354 JP-A-8-314253 JP-A-9-34243 Japanese Patent Laid-Open No. 10-133531 JP 2000-181216 A

  In the above method, the amount of toner to be forcibly consumed is determined by predicting toner deterioration based on the number of printed sheets and the rotation time of the developing roller. However, with the diversification of current users, there are various usage methods. For this reason, depending on the method of use, the toner is forcibly consumed even if the toner deterioration is not a problem.

  Therefore, in view of the above problems, an object of the present invention is to always obtain stable image quality by directly detecting the toner state and performing optimum toner forced consumption.

  A typical configuration of an image forming apparatus according to the present invention for achieving the above object includes an image carrier on which a latent image is formed, and a developing unit that develops the latent image with a developer. In an image forming apparatus having a mode for executing a developer forced consumption operation for forcibly consuming developer from the developing means at a predetermined timing during image formation, the density of the developer image formed by the developing means is measured. The developer forced consumption operation is controlled based on a result measured by the density measuring unit.

  According to the present invention, the degree of developer deterioration is directly determined by measuring the density of the developer image formed by the developing means. Then, it is possible to determine whether or not to execute the forced developer consumption operation according to the determined deterioration level of the developer, and to eliminate the unnecessary forced developer consumption operation. Even if it is executed, a necessary amount of developer can be forcibly consumed. Accordingly, it is possible to always obtain a stable image quality without wasting the developer wastefully. The contents of control of the forced developer consumption operation are the amount of the developer to be forcibly consumed, the timing for forcibly consuming the developer, or both.

(1) Example of Image Forming Apparatus FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus according to the present invention. This image forming apparatus is an A4 size color laser printer using a transfer type electrophotographic process, a contact charging method, a one-component contact development method, and a four-drum method (inline method). Then, a full-color image is formed on a recording material (for example, paper, an OHP sheet) P according to input image information from an external host device 200 that is communicably connected to the main body control unit (controller: control means) 100. Can be output. The external host device 200 is a computer, an image scanner, or the like.

  Y, M, C, and K are first to fourth image forming units arranged in parallel from the bottom to the top in the image forming apparatus main body (hereinafter referred to as the apparatus main body). Then, an image of a developer (hereinafter referred to as toner) of each color of yellow (Y), magenta (M), cyan (C), and black (K) is formed.

  Each image forming unit has the same electrophotographic process mechanism except that the colors of toner images to be formed are different from each other. That is, each has a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1 as an image carrier and a contact charging roller 2 as a charging means for uniformly charging the surface of the photosensitive drum. Further, a laser scanner 3 (Y / M / C / K) as an exposure unit for forming an electrostatic latent image by irradiating light on the charging surface according to image information, and using the electrostatic latent image as a toner image It has a one-component contact developing device 4 (Y, M, C, K) as developing means for developing. Further, a transfer roller 5 as a transfer unit that transfers the toner image to the recording material P, and a flade cleaning device 6 as a cleaning unit that removes transfer residual toner on the surface of the photosensitive drum after the toner image is transferred to the recording material P. Have The color toners stored in the developing devices 4 (Y, M, C, and K) are yellow toner, magenta toner, cyan toner, and black toner, respectively.

  In each of the image forming units Y, M, C, and K described above, four process devices, that is, the photosensitive drum 1, the charging roller 2, the developing device 4, and the cleaning device 6, can be attached to and detached from the apparatus main body at once. The cartridge 7 (Y, M, C, K) is provided.

  Here, the process cartridge is a cartridge in which a charging unit, a developing unit, or a cleaning unit and an electrophotographic photosensitive member are integrally formed, and this cartridge can be attached to and detached from the image forming apparatus main body. In addition, at least one of the charging unit, the developing unit, and the cleaning unit and the electrophotographic photosensitive member are integrally formed into a cartridge, and the cartridge can be attached to and detached from the apparatus main body. Further, at least the developing means and the electrophotographic photosensitive member are integrally formed into a cartridge, and the cartridge can be attached to and detached from the apparatus main body.

  Each process cartridge (hereinafter abbreviated as a cartridge) is attached to and detached from the apparatus main body in a predetermined manner, and is mechanically and electrically coupled to the apparatus main body side by being mounted in a predetermined manner. As a result, the driven member (photosensitive drum, developing roller, toner supply roller, toner stirring paddle, etc.) on the cartridge side can be driven by the drive mechanism on the apparatus main body side. Further, it becomes possible to apply a predetermined bias to the charging roller / developing roller on the cartridge side from the high voltage power source on the apparatus main body side. In addition, the sensor on the cartridge side and the storage device 11 (Y, M, C, K) are brought into conduction with the control unit 100 on the apparatus body side.

  Reference numeral 8 denotes an endless recording material carrying belt (ETB: hereinafter abbreviated as “belt”), which is suspended from an upper drive roller 9a, a lower driven roller 9b, and a tension roller 9c. The belt 8 is disposed in the vertical direction over the entire image forming unit on the photosensitive drum 1 side of each of the image forming units Y, M, C, and K described above. In each image forming portion, the transfer roller 5 is pressed against the photosensitive drum 1 via the belt 8. A contact portion between each photosensitive drum 1 and the belt 8 is a transfer portion T.

  Reference numeral 9 denotes a paper feed mechanism disposed below the first image forming unit Y. Reference numeral 10 denotes a fixing device disposed on the upper side of the belt 8.

  A printing operation (printing operation) will be described. In accordance with a predetermined printing timing of the image forming sequence, each photosensitive drum 1 is rotationally driven in the counterclockwise direction of the arrow at a predetermined speed in each of the image forming units Y, M, C, and K. Then, the laser scanner 3 is driven. The belt 8 is rotationally driven at a speed corresponding to the rotational speed of the photosensitive drum 1 in the clockwise direction of the arrow. Further, the sheet feeding roller 9b of the sheet feeding mechanism unit 9 is driven at a predetermined control timing, and the recording material (transfer material) P stored in the sheet feeding cassette 9a is fed out, and the uppermost roller by the retard roller 9c. Only one recording material is separated and fed. The recording material is temporarily stopped by the registration roller 9d and waits for the rise of the laser scanner 3 in each image forming unit, stabilization of the photosensitive drum potential by the charging roller 2, and the like. The recording material is fed to the lower end portion of the belt 8 by the registration roller 9d in synchronism with the recording position and the image forming timing of the toner image in each image forming portion. The recording material P fed to the lower end of the belt is sandwiched between the nip portion of the belt 8 and the bias applying roller 9e, is electrostatically closely contacted with the surface of the belt 8, and is stably held. It is transported up.

  In each of the image forming units Y, M, C, and K, the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2 during the rotation process. The uniformly charged surface is subjected to scanning exposure with a laser beam L corresponding to the image signal of each color output from the laser scanner 3 to form an electrostatic latent image. That is, the first image forming unit Y performs exposure based on yellow image data to form an electrostatic latent image. In the second image forming unit M, exposure based on the magenta image data is performed to form an electrostatic latent image. In the third image forming unit C, exposure based on cyan image data is performed to form an electrostatic latent image. The fourth image forming unit K performs exposure based on the black image data to form an electrostatic latent image. The electrostatic latent image is developed as a toner image by the developing device 4.

  Printers are often used in combination with image exposure and reversal development. In the image forming apparatus of this embodiment, the surface of the photosensitive drum 1 is uniformly charged to a predetermined negative potential by the charging roller 2, and an electrostatic latent image is formed by image exposure for exposing the image information portion. Then, the electrostatic latent image is reversely developed by the developing device 4 of a one-component contact developing system using a negatively charged non-magnetic one-component developer (toner).

  As a result, a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are respectively provided at predetermined control timings on the surfaces of the photosensitive drums 1 of the first to fourth image forming units Y, M, C, and K. Is formed.

  The recording material P is in close contact with the belt 8 and is conveyed from the bottom to the top. In each transfer portion T of the first to fourth image forming portions Y, M, C, and K, the photosensitive drums. Each toner image of yellow, magenta, cyan, and black formed on one surface is superposed and transferred. A transfer bias having a polarity opposite to the charging polarity of the toner is applied to the transfer roller 5. As a result, the toner image on the surface of each photosensitive drum 1 is electrostatically transferred onto the surface of the recording material P.

  The recording material P that has received the superimposed transfer of the four color toner images is separated from the belt surface at the upper end portion of the belt 8 and introduced into the fixing device 10 where heat and pressure are applied. As a result, the toner images of a plurality of colors are permanently fixed on the surface of the recording material, and the full color image formed product is discharged out of the apparatus main body.

  In each image forming unit, the transfer drum is removed from the surface of the photosensitive drum after the transfer of the toner image onto the recording material P by the cleaning device 6 and is repeatedly used for image formation.

(2) Developing device 4
The developing device 4 will be described with reference to FIG. The developing devices 4 (Y, M, C, and K) of the first to fourth image forming units Y, M, C, and K only differ in the color of the contained developer (toner), and the structures are mutually different. The same. Reference numeral 41 denotes a developing container, in which a negatively chargeable nonmagnetic one-component toner (not shown) is accommodated as a developer.

A developing roller 42 as a developer carrying member is partially exposed to the outside of the developing container at an opening provided on the side of the developing container 41 facing the photosensitive drum, and disposed in parallel with the photosensitive drum 1. is there. The developing roller 42 has an outer conductive agent volume resistivity by dispersing such carbon ^{10 2} Ωcm~10 10 Ωcm silicones, low hardness rubber material or foam such as urethane, and is constituted by a combination thereof It is a semiconductive elastic roller having a diameter of 16 mm. The exposed portion of the developing roller 42 outside the developing container is brought into contact with the photosensitive drum 1 with a predetermined pressing force.

  Reference numeral 43 denotes a developer supply roller for the developing roller 42, which is an elastic roller made of sponge and having an outer diameter of 16 mm. The supply roller 43 is disposed in parallel with the developing roller in contact with the developing roller 42 in the developing container 41 on the side opposite to the photosensitive drum facing side of the developing roller 42.

  Reference numeral 44 denotes a developing blade as a developer layer thickness regulating member for the developing roller 42, which is disposed in contact with the upper surface of the developing roller 42. The developing blade 44 is a leaf spring made of SUS, and abuts against the developing roller 42 with a predetermined abutting pressure while being bent within an elastic range. The contact direction is a counter direction in which the tip on the free end side with respect to the contact portion is located upstream in the rotation direction of the developing roller 42.

  Reference numeral 45 denotes an agitation paddle as a developer agitating and conveying means for agitating the toner in the developing container 41 and conveying it to the supply roller 43 side. The stirring paddle 45 is disposed in parallel with the supply roller in the developing container 41 on the side opposite to the developing roller 42 side of the supply roller 43.

  The developing roller 42 is driven to rotate in the clockwise direction indicated by an arrow with a predetermined peripheral speed difference with respect to the photosensitive drum 1 in the forward direction with respect to the rotation of the photosensitive drum 1. In this embodiment, the process speed of the image forming apparatus, that is, the peripheral speed of the photosensitive drum 1 is 150 mm / sec, and the peripheral speed of the developing roller 42 is 225 mm / sec.

  The supply roller 43 is rotationally driven with a peripheral speed difference in the counter direction indicated by an arrow with respect to the rotation of the developing roller 42. The supply roller 43 supplies toner to the developing roller 42 and scrapes off toner remaining on the developing roller 42 without being developed.

  The stirring paddle 45 is driven to rotate at a predetermined speed in the counterclockwise direction of the arrow. Thereby, the toner in the developing container 41 is agitated and the toner is conveyed to the supply roller 43 side.

  When the toner supplied to the developing roller 42 by the supply roller 43 passes through the contact portion between the developing roller 42 and the developing blade 44, the toner is charged by frictional charging and restricted to a thin layer.

  That is, the toner is carried on the rotating developing roller 42 by sliding with the supply roller 43. When the carried toner passes through the contact portion with the developing blade 54 by the subsequent rotation of the developing roller 42, the toner is charged by frictional charging and is regulated to a uniform thin layer. Then, the toner layer is conveyed to a developing area which is a contact-opposed portion between the developing roller 42 and the photosensitive drum 1 by the subsequent rotation of the developing roller 42. Then, the toner layer receives the reflection force from the developing roller 42 by the charged electric charge and is supplied to the photosensitive drum 1 to develop the electrostatic latent image and visualize it as a toner image. Alternatively, the electrostatic latent image on the photosensitive drum is developed by the developing bias applied to the developing roller 42 by the toner layer, and visualized as a toner image.

  The toner remaining on the developing roller 42 without being subjected to the development is returned to the developing container 41 by the subsequent rotation of the developing roller 42 and scraped off from the developing roller 42 by sliding with the supply roller 43. The toner is supplied again to the developing roller 42 by the supply roller 43.

  In this embodiment, the supply roller 43 has two functions as toner supply and recovery means. However, the present invention is not limited to this, and the developer supply means and the developer recovery means are provided separately. It is also possible.

(3) Control System The main body control unit 100 includes a main body CPU 21 that is a central processing unit that controls the printing operation of the image forming apparatus. An image processing control unit 22 that performs image processing on image information input from the external host device 200 and a high-voltage output control unit 23 that performs output control of a high-voltage device that supplies high-voltage outputs such as a charging bias, a development bias, and a transfer bias. A laser drive control unit 24 that performs light emission control of the laser scanner 3 according to image information to be output is provided. A storage unit (read / write nonvolatile storage unit) 25 that stores setting values such as image forming process conditions, an image processing method, and image information transmitted from the external host device 200 is included. It has an IO control unit 26 that communicates with a storage device (read / write nonvolatile storage means) 11 (Y, M, C, K) mounted on each cartridge 7 (Y, M, C, K). Reference numeral 27 denotes an operation panel section of the apparatus main body, which includes a power switch, a display section, operation keys, and the like, and exchanges information with the main body CPU 21.

  When the cartridge 7 (Y, M, C, K) is attached to the apparatus main body, and when the power is turned on to the apparatus main body, the IO control unit 25 stores the storage device 11 (Y, M, C) attached to the cartridge. Communicate with K) to obtain various stored values such as process conditions and usage history.

  The stored value obtained by the IO control unit 25 is transmitted to the main body CPU 21 together with the stored value of the storage device unit 24, and is used as data when image formation is performed.

  Image information transmitted from the external host device 200 is processed by the image processing control unit 22 as image information that can be subjected to image processing such as edge processing and density adjustment to perform optimal image formation. The main body CPU 21 stores the stored value obtained from the storage device 11 (Y, M, C, K) of the cartridge 7 (Y, M, C, K) mounted on the apparatus main body, the image information after the image processing is completed, and Then, an optimum process condition value is calculated, and an image is formed with the optimum process condition value.

(4) Image Density Control The image forming apparatus of this embodiment includes a density sensor 12 for measuring the image density on the belt 8. The density sensor 12 is disposed so as to face the outer surface of the belt at the suspending portion of the belt 8 with respect to the driving roller 9a. The main body CPU 21 has a control mode for forming a toner image pattern for density control on the belt 8 for each image forming unit in order to control the image density of each image forming unit Y, M, C, and K. Then, the image density of the toner image pattern formed on the belt 8 is measured by the density sensor 12, and the density is calculated from the output of the density sensor 12, and according to the result, each image forming unit Y, M, C -K image density control is performed. The toner image pattern for density control formed on the belt 8 is removed from the belt by the cleaning device 13 disposed downstream of the density sensor 12 in the belt moving direction.

  Here, the position of the density sensor 12 is not limited to the belt 8, but can be provided on the photosensitive drum 1 of each of the image forming units Y, M, C, and K. That is, in each of the image forming units Y, M, C, and K, the density sensor 12 is disposed between the developing device 4 and the transfer unit T so as to face the photosensitive drum 1, and is used for density control formed on the photosensitive drum surface. The image density of the toner image pattern may be measured. At this time, a voltage having a polarity opposite to that during normal image formation is applied to the transfer roller 5 so that the toner image pattern for density control does not adhere to the belt 8 at the transfer portion T and reaches the cleaning device 6. To collect.

  In the image forming apparatus according to the present exemplary embodiment, only Dhalf control for controlling a halftone density is performed. It is known that the halftone changes depending on the toner state (toner deterioration condition). By performing Dhalf control, image processing is performed such that the relationship (input / output characteristics) of the output density to the input image signal that changes due to toner deterioration is always kept linear, and a stable halftone image density can be obtained. Become.

  When performing the Dhalf control, a halftone image of 16 gradations is created on the belt 8 for each color (each image forming unit), and the density is measured by the density sensor 12. FIG. 3 shows the relationship between the image density and the input image signal. The horizontal axis represents the input image signal (input data), and the vertical axis represents the result of the image density measured by the density sensor 12. Based on this result, image processing is performed so that the halftone density has a linear relationship according to the input image signal.

  In this embodiment, this Dhalf control is executed at certain intervals such as when the power of the apparatus main body is turned on, when the cartridge is replaced, and the number of printed sheets counter.

(5) Toner Forced Consumption Control Next, toner forced consumption control will be described.

  The toner present in the vicinity of the developing roller 42 and the supply roller 43 of the developing device 4 is deteriorated by rubbing between the developing roller 42 and the supply roller 43, between the developing roller 42 and the photosensitive drum 1, and between the developing roller 42 and the regulating blade 44. To do.

  Due to this toner deterioration, there are cases where the density cannot be maintained properly, the image is stuck, or fogging occurs. In order to suppress these problems, a forced toner consumption mode in which toner near the developing roller 42 and the supply roller 43 is forcibly consumed is executed at a predetermined timing. That is, at the time of non-image formation such as between papers and after rotation, similarly to the normal image formation, the uniformly charged photosensitive drum 1 is exposed to form an electrostatic latent image for forced toner consumption. Then, the electrostatic latent image is developed with toner. At this time, a voltage having a polarity opposite to that at the time of normal image formation is applied to the transfer roller 5 so that the toner image reaches the cleaning device 6 without being attached to the belt 8 at the transfer portion T and is collected. is there. By performing this forced toner consumption operation, fresh toner is supplied from the toner storage portion side in the developing container 41 to the vicinity of the developing roller 42 and the supply roller 43, so that image formation with proper image quality can be performed. become.

  Here, the interval between sheets means the transfer portion T in the continuous printing mode, after the trailing end of one recording material passes through the transfer portion T and before the leading end of the next recording material reaches the transfer portion T. This is a non-sheet passing state period of the recording material. In the post-rotation period, after the predetermined number of printing steps are completed, the main motor is continuously driven for a while to rotate the photosensitive drum 1 to perform a predetermined post-operation (pre-stop operation) of the image forming apparatus. This is the period to be executed.

  Conventional toner forced consumption control predicts the degree of toner degradation based on the number of printed sheets and the number of rotations of the developing roller, and forcibly consumes a predetermined amount of toner at a predetermined timing.

  On the other hand, in the present invention, the deterioration of the toner (developer) is directly detected, and the required amount is forcibly consumed at the required timing, thereby further improving the high image quality and image stability. It was possible to achieve.

  The toner forced consumption control of this embodiment will be described in more detail. In the toner forced consumption control of this embodiment, a halftone density is measured (detected) for each of the image forming units Y, M, C, and K by using a mechanism used in Dhalf control. Then, the degree of toner deterioration is determined from the result, and the toner forcible consumption operation is performed for each of the image forming units Y, M, C, and K accordingly.

  First, FIG. 4 shows the input / output characteristics of the latter half of the cartridge life and the initial stage by Dhalf control. It can be seen that the input / output characteristics in the latter half of the life are greatly deviated from the initial ones. In particular, a large deviation can be confirmed near the halftone density than near the low density or near the high density. A major factor of this change is toner deterioration. Therefore, toner deterioration is determined from the result of the input / output characteristics.

  In this embodiment, as shown in the control flow diagram of FIG. 5, the determination of toner deterioration is performed by comparing the halftone density of the input data 96 where the difference appears most. The control flow of FIG. 5 is applied to each of the image forming units Y, M, C, and K.

  The main body control unit 100 creates a halftone density image of the input data 96 for each color (each image forming unit) on the belt 8 at a predetermined timing, and measures the density with the density sensor 12 (steps S1 → S2). ).

  The timing at which halftone density measurement is executed is during non-development, and is basically performed every predetermined number of printed sheets or every time the developing roller rotates (rotational speed) is predetermined (predetermined rotational speed). Do. This is because the toner deterioration actually occurs due to the rotation of the developing roller if it is performed every time. Here, every 1500 sheets are considered. It may be performed when the power is turned on or when the cartridge is replaced. However, since the developing roller does not rotate at this time, it is considered that the toner deterioration does not advance, so that it is not necessary.

And the measured density data _{D A,} to compare the ideal density data _{D B} stored in the storage device 25 in advance the main body control unit 100 _(D A -D _{B) (step} S3). Difference at this time is time smaller than a predetermined value D _C does not enter the toner forced consumption mode. On the other hand, when the difference at this time is a predetermined value D _C or higher enters the toner forced consumption mode, performing the toner forced consumption operation at a predetermined interval (step S4). Further, halftone density measurement for toner forced consumption control is performed at a predetermined timing (steps S5 → S1 → S2). To stop the toner forced consumption mode when the difference is not yet when a predetermined value or more D _C continues toner forced consumption mode (step S4 → S5), it reaches a predetermined value D _C.

In this embodiment, keep the value of say 30 as an ideal density data D _B stored in the storage device 25 of the main control unit 100. Then, the difference between this value and the measured density D _A (D _{A -D B)} is at was 10 or more, determines that the toner deterioration has progressed, switched to the toner forced consumption mode (step S3 → S4).

  In this embodiment, in the forced toner consumption mode, every 50 printed sheets, an image having a width of 210 mm in the main scanning direction as the effective developing width and a width of 100 mm in the sub-scanning direction is exposed on the photosensitive drum 1 surface. A latent image is formed by lighting, and toner is consumed by developing the latent image. As a result, the toner in the vicinity of the developing roller is replaced, and the newly supplied toner can stably form a high-quality image.

Further, halftone density measurement in the toner forced consumption mode is performed every 500 sheets (step S5 → S1 → S2), as a result, release the toner forced consumption mode when the difference does not exceed the 10 that the predetermined value D _C Thus, the toner forced consumption operation is not executed. When the difference is still 10 or more, the toner forced consumption mode is continued, and the toner forced consumption operation is performed at the same pace (step S4).

  Conventionally, it is necessary to consume a large amount of toner in order to cope with the worst condition that the user uses for toner deterioration. In such a case, toner that has not deteriorated is forcibly consumed every certain number of printed sheets (or developing roller rotation time), and thus toner may be wasted. On the other hand, if the forced toner consumption is to be suppressed, the image quality may be slightly lowered when a low print image is printed. To solve such a problem, it is possible to appropriately forcibly consume toner according to the deterioration state by measuring the halftone density as described above and directly determining the deterioration degree of the toner. Become. Since the required amount can be consumed at the necessary timing, it is possible to always provide a stable and high-quality image without wastefully consuming the toner.

  In this embodiment, the halftone density measurement is performed at the input data 96. However, other input data may be used as long as the difference between the input data and the output density data based on the toner deterioration can be clearly understood. . Furthermore, the points to be compared do not have to be a single point. A halftone image for multiple points of input data can be formed and compared using the sum or average of the differences. It is possible to detect the degree of toner deterioration even by the method of comparing the two.

  The halftone density measurement timing (step S5) in the toner forced consumption mode does not have to be every 500 printed sheets, and may be a number suitable for the image forming apparatus to be used. Further, it is not necessary to use the number of printed sheets. For example, the developing roller rotation time can be used instead.

  Here, the Dhalf control and the forced toner consumption control are not linked in a special manner. However, it is also possible to link the timing of forced toner consumption control and Dhalf control. It is desirable to perform toner forced consumption control and perform Dhalf control after performing the toner forced consumption operation. As a result, halftone density correction is performed on the toner characteristics after the toner has been replaced by forced toner consumption, so that more stable image formation can be performed.

  The image forming apparatus used in the present embodiment has substantially the same configuration as that of the first embodiment, and there is a difference in toner forced consumption control.

In Example 1, switches to the toner forced consumption mode when was a constant value D _C or more there is a difference between the measured halftone density data D _A and the ideal density data D _B, carried forced toner consumption operation at predetermined intervals Is supposed to do.

In this embodiment, according to the difference D _D measurement data D _A and the reference density data D _B, it is characterized by controlling the interval at which the toner consumption force.

When the difference D _D is large, a shorter implementation interval toner forced consumption operation and the halftone density measurement in the toner forced consumption mode, suppressing the deteriorated quickly. When the difference D _D is small, frequent since it is not necessary to perform the toner forced consumption operation, toner deterioration while dropping the frequency of the toner forced consumption operation and the halftone density measurement to reduce toner consumption in the toner forced consumption mode Suppress.

Specifically, as the table shown in FIG. 6, in accordance with the difference D _D, it changes the implementation interval toner forced consumption operation and the halftone density measurement in the toner forced consumption mode. As in the control flow diagram of FIG. 7, the toner forced consumption mode entering when the difference D _C is 6 or more and less than 6 or more 8, less than 10 8 to less than 10 more than 12, then partitioned with 12 or more, respectively The toner forced consumption operation and halftone density measurement are surely performed at suitable intervals. This makes it possible to always perform stable image formation without wasting toner.

In this embodiment, in accordance with the difference D _D, but change the execution timing of the toner forced consumption operation and the halftone density measurement in the toner forced consumption mode, the present invention is not limited to this, changing the amount of toner consumed at a time It is possible to obtain similar effects.

  The image forming apparatus used in the present embodiment has substantially the same configuration as that of the first embodiment, and there is a difference in toner forced consumption control.

  In the first embodiment, it is considered that the halftone deviation is mostly caused by toner deterioration. However, in practice, the halftone shift varies somewhat depending on the environment and deterioration of the photosensitive drum. For this reason, in this embodiment, correction is performed in advance so as to eliminate the influence of the environment and the photosensitive drum deterioration, so that the toner deterioration degree is detected with higher accuracy and an appropriate toner forced consumption operation is performed.

  Specifically, environmental correction and photosensitive drum deterioration correction are performed on the reference density data stored in the storage device 25 of the main body control unit 100.

  An environmental sensor 14 (FIG. 1) for detecting temperature and humidity is provided at an appropriate position of the apparatus main body. Detection environment information (temperature and humidity information) of the environment sensor 14 is input to the main body CPU 21. The main body CPU 21 calculates the absolute water content from the detected temperature and humidity.

  As shown in FIG. 8, the input / output characteristics of a halftone image change depending on the environment (absolute water content). In a high temperature and high humidity (H / H) environment, the concentration tends to be higher than in a low temperature and low humidity (L / L) environment. Therefore, an environment table of reference density data as shown in FIG. 9 is stored in the storage device 25 of the main body control unit 100. The main body CPU 21 can eliminate the influence of the environment as much as possible by comparing with the reference density data calculated from the environment table, and can determine the degree of toner deterioration with higher accuracy. Here, the reference density data is calculated by linear interpolation between the table data. Reference density data of 21.6 (g / m ^ 3) and 1.0 (g / m ^ 3) are used for the high and low humidity sides other than the table environment.

  Another factor affecting the change in halftone is a change in the sensitivity of the photosensitive drum due to a reduction in the film thickness of the photosensitive drum 1. The abrasion amount of the photosensitive drum can be accurately determined by the photosensitive drum rotation time, the developing roller contact rotation time, and the photosensitive drum charging time.

  In addition, since there is a linear correlation between the photosensitive drum film thickness and the photosensitive drum sensitivity, it is possible to accurately predict the change in sensitivity of the photosensitive drum.

  Since the sensitivity tends to deteriorate when the life of the photosensitive drum is reduced as the life is advanced, the photosensitive drum having a thin film thickness (12 μm) at the end of the life and the photosensitive drum having a thick film thickness at the beginning of the life (20 μm) as shown in FIG. ) Shows a slight difference in input / output characteristics.

  In order to eliminate this difference, further correction is performed on the value of the environment correction table. The photosensitive drum scraping is 1 μm, and the reference density data is offset by 0.38. As a result, it is possible to accurately correct the change in halftone density due to deterioration of the photosensitive drum.

  The photosensitive drum scraping state indicates the usage history (the accumulated rotational speed of the photosensitive drum) stored in the storage device 11 (Y, M, C, K) of the cartridge 7 (Y, M, C, K) mounted on the apparatus main body. Etc.) is derived from the main body CPU 21.

  As described above, by performing the environmental correction and the photosensitive drum deterioration correction, it is possible to detect the deterioration state of the toner more accurately, and the forced toner consumption operation can be performed at an appropriate amount and at an appropriate interval. As a result, stable and high-quality image formation can be performed without wastefully consuming toner.

  Here, in the present invention, the developing device (developing means) is not limited to the contact developing type device using the nonmagnetic one-component developer of the embodiment. It may be a non-contact development type apparatus using a non-magnetic one-component developer, or a contact or non-contact development type apparatus using a magnetic one-component developer. Also, an apparatus using a two-component developer may be used.

  Further, the image forming method of the image forming apparatus is not limited to the electrophotographic method using a photoconductor as the image carrier. An electrostatic recording system using a dielectric material having no photosensitivity as an image carrier or a magnetic recording system using a magnetic material may be used. Further, the image forming apparatus is not limited to the transfer type image forming apparatus, and may be a direct type image forming apparatus.

Schematic diagram of image forming apparatuses of Examples 1, 2, and 3. Schematic of the developing device used in Examples 1, 2, and 3. Typical input / output characteristics of the developing device used in the examples I / O characteristics fluctuation diagram due to difference in life in Example 1 Toner forced consumption control flow chart of Embodiment 1 Table showing density difference, forced consumption operation execution interval, and halftone density measurement interval in the second embodiment Toner forced consumption control flow chart of Embodiment 2 I / O characteristics variation diagram due to environmental differences in Example 3 Table of moisture content and reference concentration data of Example 3 I / O characteristics variation diagram due to film thickness difference in Example 3

Explanation of symbols

  Y, M, C, K, 1st to 4th image forming unit, 1 ... Photosensitive drum (image carrier), 2 ... Charging roller, 3 (Y, M, C, K), Laser scanner 4 (Y, M, C, K) ··· Development device, 5 · · Transfer roller, 6 · · Cleaning device, 7 (Y · M · C · K) · · Process cartridge, 8 · · Recording material carrier belt , 9 .. Paper feed mechanism section, 10... Fixing device, 11 (Y, M, C, K)... Storage device mounted on cartridge, 12... Image density sensor, 14. Main body control unit, 200..External host device

Claims (5)

Development that includes an image carrier on which a latent image is formed and a developing unit that develops the latent image with a developer, and forcibly consumes the developer from the developing unit at a predetermined timing during non-image formation. In the image forming apparatus having a mode for executing the agent forced consumption operation,
An image forming apparatus comprising density measuring means for measuring the density of a developer image formed by the developing means, and controlling the developer forced consumption operation based on a result measured by the density measuring means. .   The image forming apparatus according to claim 1, wherein the developing unit is a one-component contact developing system.   The image forming apparatus according to claim 1, wherein the control content of the developer forcible consumption operation is the amount of developer to be forcibly consumed.   The image forming apparatus according to claim 1, wherein the control content of the developer forcible consumption operation is a timing for forcibly consuming the developer.   The image forming apparatus according to claim 1, wherein the developer image formed to measure the density is a halftone density image.