JP4750307B2 - Development device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device that develops, for example, an electrostatic latent image formed on an image carrier, and more particularly, to a developing device used in an image forming apparatus such as a copying machine, a printer, or a FAX.
[0002]
[Prior art]
FIG. 11 is a schematic sectional view of a conventional color image forming apparatus.
[0003]
The image forming apparatus of this example has a digital digital color image reader unit at the top and a digital color image printer unit at the bottom.
[0004]
In the reader unit, the original 30 is placed on the original platen glass 31, and the reflected light image from the original 30 exposed and scanned by the exposure lamp 32 is condensed on the full color sensor 34 by the lens 33 to obtain a color color separation image signal. The color-separated image signal is processed by a video processing unit (not shown) through an amplifier circuit (not shown) and sent to the printer unit.
[0005]
In the printer unit, a photosensitive drum 1 that is an image carrier is rotatably supported in the direction of arrow R1, and a pre-exposure lamp 11, a corona charger 2, an exposure optical system 3, and potential sensors 12 are provided around the photosensitive drum 1. Development unit 4 (4y, 4c, 4m, 4k), toner detection means 13 on drum, transfer device 5, cleaning device 6 and the like are arranged.
[0006]
The laser beam exposure optical system 3 receives an image signal from the reader unit, converts it to an optical signal by a laser output unit (not shown), reflects the laser beam by the polygon mirror 3a, passes through the lens 3b and the mirror 3c. Then, the surface of the photosensitive drum 1 is converted into an optical image E that is scanned into a latent image (raster scan).
[0007]
In the printer unit, at the time of image formation, first, the photosensitive drum 1 is rotated in the arrow direction R1, neutralized by the pre-exposure lamp 11, uniformly charged by the charger 2, and then irradiated with the light image E for each separated color. Then, an electrostatic latent image of each color is formed on the surface of the photosensitive drum 1.
[0008]
Next, a predetermined developing device 4 is operated for each separation color to develop the latent image on the photosensitive drum 1, and an image of toner based on resin is formed on the photosensitive drum 1. The developing units 4y, 4m, 4c, and 4k are made to approach the photosensitive drum 1 alternatively according to the latent image of the separated color by the operation of the eccentric cams 24y, 24c, 24m, and 24k.
[0009]
The recording material is transported from the recording material cassette 7 to the transfer device 5 by the transport system, and then supplied to the transfer position facing the photosensitive drum 1 by the transfer device 5. The toner image formed on the photosensitive drum 1 is transferred to the recording material supplied to the transfer position. In this example, the transfer device 5 includes a transfer drum 5a, a transfer charger 5b, an adsorption charger 5c, an opposing adsorption roller 5g, an inner charger 5d, and an outer charger 5e, and is pivotally supported so as to be rotationally driven. The recording material carrying sheet 5f is integrally adjusted in a cylindrical shape in the peripheral opening area of the transfer drum 5a. The recording material carrying sheet 5f uses a dielectric sheet such as a polycarbonate film.
[0010]
The recording material conveyed to the transfer device 5 is adsorbed to the recording material carrying sheet 5f by the adsorption charger 5c and the adsorption roller 5g, conveyed through the transfer position according to the rotation of the transfer drum 5a, and the toner on the photosensitive drum 1 The image is transferred onto the recording material by the transfer charger 5b.
[0011]
In this way, a desired number of color toner images are superimposed and transferred from the photosensitive drum 1 while rotating a desired number of times on the recording material that is attracted to and conveyed by the recording material carrying sheet 5f, thereby forming a full-color image. The
[0012]
In the case of the four-color mode, when the transfer of the four-color toner image is completed in this way, the recording material is separated from the transfer drum 5a by the action of the separation claw 8a, the separation push-up roller 8b, and the separation charger 5h, and heat fixing The paper is discharged to the tray 1 through the roller fixing device 9.
[0013]
On the other hand, after the transfer, the photosensitive drum 1 is subjected to the image forming process again after the residual toner on the surface is cleaned by the cleaning device 6.
[0014]
In the case of forming images on both sides of the recording material, after the recording material exits the fixing device 9, the conveyance path switching guide 19 is driven immediately, and after being guided to the reverse path 21 a through the discharge vertical path 20. Then, the recording material is temporarily stopped, and by reverse rotation of the reversing roller 21b, the recording material is withdrawn in the direction opposite to the feeding direction starting from the rear end when fed, and the recording material is turned over and stocked in the intermediate tray 22. Thereafter, the image is again sent to the transfer drum 5a, and an image is formed on the other surface of the recording material by the above-described image forming process, and the image is discharged to the discharge tray 10 through the fixing device 19.
[0015]
The toner on the recording material carrying sheet 5f of the transfer drum 5a after separating the recording material is scattered when powder is scattered and adhered from the photosensitive drum 1, the developing device 4, the cleaning device 6 or the like, or when the recording material is jammed (paper jam). And the oil on the recording material may adhere when the double-sided image is formed, but the fur brush 14, the backup brush 15, and the oil removing roller 16 that face each other through the recording material carrying sheet 5f. And cleaned by the backup brush 17 and then again subjected to the image forming process. Such cleaning is performed at the time of pre-rotation and post-rotation, and at any time when a jam (paper clogging) occurs.
[0016]
In this example, the transfer drum eccentric cam 25 is operated, and the cam follower 5i integrated with the transfer drum 5a is operated, whereby the gap between the recording material carrying sheet 5f and the photosensitive drum 1 is set at a predetermined interval. The configuration can be set to. For example, during standby or when the power is turned off, the distance between the transfer drum and the photosensitive drum can be increased so that the rotation of the transfer drum from the rotational drive of the photosensitive drum can be made independent.
[0017]
Further, the developing device 4 (4y, 4c, 4m, 4k) performs the developing operation in the series of image forming operations as follows. When the electrostatic latent image reaches a developing position facing the developing sleeve 41 of the developing device 4 by the rotation of the photosensitive drum 1, a developing bias in which AC and DC are superimposed on the developing sleeve 41 by a developing bias power source (not shown). , And the developing sleeve 41 is rotated in the B direction by a developing sleeve driving device (not shown) and pressurized by the developing pressurizing cam 24 (24y, 24c, 24m, 24k), and the latent image is developed in this state. To do.
[0018]
Further, when controlling the gradation of the toner image formed on the photosensitive drum (resulting in the toner image formed on the recording material) (when forming a halftone image), the density detection is performed on the photosensitive drum 1. The patch latent image is formed, the developing bias is applied to the developing sleeve 41 to develop the patch latent image with toner, and the density of the obtained patch image is read by the patch sensor 13. If the read image density does not reach the reference value, the image signal level is adjusted. By this adjustment, the exposure portion potential on the photosensitive drum exposed by the exposure optical system with respect to the image signal is adjusted, and the developed patch image density value at that time is fed back to the CPU 300 as an initial reference value. By performing this operation for each color, the gradation of the toner image of each color formed on the photosensitive drum can be optimized, and a halftone image can be formed satisfactorily.
[0019]
Further, when controlling the amount of toner to be replenished to the developing device 4 so that the concentration of the toner accommodated in the developing device 4 is kept almost constant, the toner is stored on the photosensitive drum 1 (for example, during image formation). For example, a patch image having a predetermined density is formed (between areas where a normal image is formed), and the output value of the sensor 13 is always constant, that is, accommodated in the developing device 4. By controlling the amount of toner to be replenished to the developing device 4 so that the toner density is kept substantially constant, the weight ratio (T / C ratio) between the toner and the carrier is optimized, and an image with the appropriate density is obtained. Obtainable.
[0020]
[Problems to be solved by the invention]
However, when controlling the gradation of the toner image formed on the photosensitive drum, and the amount of toner replenished to the developing device 4 so that the density of the toner stored in the developing device 4 is kept substantially constant. If the development electric field (development bias applied to the development sleeve) for developing both patch latent images is the same, the developer (toner) is loaded by the development electric field, and the life of the developer is reduced. Sometimes it would be shorter.
[0023]
  The present inventionEyesThe object is to provide a developing device capable of reducing the load applied to the developer and improving the lifetime of the developer while favorably performing image gradation control and developer replenishment control.
[0024]
Another object of the present invention is to provide a developing device capable of satisfactorily performing both image gradation control and developer replenishment control.
[0025]
Further objects of the present invention will become apparent upon reading the following detailed description.
[0026]
[Means for Solving the Problems]
  The above object is related to the present invention.PresentAchieved with imaging devices.
[0029]
  According to the present invention, in a developing device having a developer containing portion that contains a developer including toner and a carrier, and a developer carrying member that carries the developer,
  When the first latent image for controlling the amount of developer supplied to the developer accommodating portion is developed, a first developing bias to which a voltage containing an AC component is repeatedly applied is the developer carrier. When the second latent image for controlling the gradation of the image is developed, a period in which a voltage including an AC component is applied and a period in which a voltage including an AC component is not applied are A second developing bias provided alternately is applied to the developer carrier.A developing device is provided.
[0033]
  In the present invention, according to another embodiment,, ThroughDuring normal image formation, a bias that alternately includes a period in which a voltage including an AC component is applied and a period in which a voltage including an AC component is not applied.ButApplied to the developer carrierIs done.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, the present invention relates toPresentAn embodiment of the image apparatus will be described in more detail with reference to the drawings.
[0035]
Example 1
FIG. 1 is a schematic view showing an embodiment of an image forming apparatus provided with a developing device of the present invention. Developers 101Y to 101C (developing sleeves) for developing an electrostatic latent image on a photosensitive drum 128 as an image carrier. The developing bias applied to () can be switched.
[0036]
As shown in FIG. 1, the image forming apparatus includes a primary charger 121 as a charging unit, a laser 122 as an exposure unit, and three developing units as a developing unit around a photosensitive drum 128 that is an electrophotographic photosensitive member. 101Y, 101M, 101C, a transfer drum 127 as a recording material carrier, a cleaner 126 as a cleaning unit, and a fixing device 125 as a fixing unit. At a position between the transfer drum 127 of the photosensitive drum 128 and the developing device 101 (a position downstream of the developing unit and upstream of the transfer unit in the moving direction of the photosensitive drum) so as to face the photosensitive drum. An image density sensor 108 is installed as an image density detection means for detecting the density of the image density control patch image formed on the photosensitive drum 128, that is, the density of the detection toner image.
[0037]
The three developing devices 101 (101Y to 101C) are mounted on the developing rotator 106 at equal intervals in the circumferential direction, and can be selectively moved to the developing unit. These developing units 101 include a developing container 102 (102Y, 102M, 102C) as a developer containing portion, and a two-component developer in which a nonmagnetic toner and a magnetic carrier are mixed is accommodated therein. An opening is provided at a developing portion of each developing device 101 facing the photosensitive drum 128, and a developing sleeve 105 (105Y, 105M, 105C) as a developer carrying member is partially exposed to the opening. Inside the developing sleeve 105, a magnet (magnetic pole) as a magnetic field generating means is fixedly arranged in a non-rotating manner. Further, at the time of development, the developing sleeve and the photosensitive drum surface are configured to be separated from each other by a predetermined distance, but the magnetic brush formed on the developing sleeve is configured to contact the photosensitive drum surface.
[0038]
At the time of development, the developing sleeve 105 holds the two-component developer in the developing device 101 on the surface (a magnetic brush is formed and held on the surface of the developing sleeve at the time of development), and in the developing area facing the photosensitive drum 128. Transport. At this time, a developing bias, which will be described in detail below, is applied to the developing sleeve, and developer is electrostatically attached to the electrostatic latent image formed on the photosensitive drum 128 from the developing sleeve, and is visible on the photosensitive drum. An image is formed. The developer after developing the latent image is returned to the developing device 101 and collected according to the rotation of the developing sleeve 105.
[0039]
Inside each developing device 101, density sensors 107 (107Y, 107M, 107C) are installed as developer concentration detecting means for detecting the toner concentration of the housed developer. 103 (103Y, 103M, 103C) and a toner conveying screw 104 (104Y, 104M, 104C) are disposed (a cartridge system that can be attached to and detached from the image forming apparatus main body) and a toner supply screw 104 (104Y, 104M, 104C). Has been. The sensor 107 has a light emitting portion and a light receiving portion, and the light emitted from the light emitting portion receives reflected light reflected by the developer by the light receiving portion, thereby corresponding to the toner density accommodated in the developing device 101. The information to be detected is detected, and the CPU compares the detection result with the reference value. If the CPU determines that the toner density is low, the toner amount supplied from the toner cartridge 103 to the developing device 101 by the screw 104 is calculated and controlled based on this. With such a configuration, a shortage of toner consumed by image formation can be replenished, and the amount of toner (ratio of toner and carrier) in the developing device can be maintained substantially constant. .
[0040]
Three-color full-color image formation is performed as follows. The photosensitive drum 128 is rotated, and the surface of the photosensitive drum 128 is uniformly charged by the charger 121. Then, the surface of the photosensitive drum 128 is exposed by the laser 122 in accordance with the image information (image signal) of the document. An electrostatic latent image of the first color, for example, a yellow color component is formed, this latent image is developed by the yellow developing device 101Y, a yellow toner image is formed on the photosensitive drum 128, and the yellow toner image is transferred. The image is transferred to a recording material 124 such as a sheet on a transfer drum 127 or a light transmissive resin sheet (for OHP) by a transfer bias by a charger 123. The toner remaining on the photosensitive drum 128 after the transfer is removed by the cleaner 126.
[0041]
Next, the photosensitive drum 128 is charged again and exposed by the laser 122 to form an electrostatic latent image of the next color, for example, a magenta color component. During this time, the rotator 106 rotates 120 ° in the direction of the arrow, the magenta developing device 101M faces the photosensitive drum 128, and the formed latent image is developed by the developing device 101M, and a magenta toner image is formed on the photosensitive drum 128. obtain. This magenta toner image is transferred onto the recording material 124 on which the yellow toner image has already been transferred. In the same manner, a cyan toner image is formed and transferred onto the recording material 124 in a superimposed manner.
[0042]
When the three color toner images are superimposed and transferred on the recording material 124 in this way, the recording material 124 is peeled off from the transfer drum 127 and sent to the fixing device 125, where it is pressurized and heated, whereby the three color toners are transferred. The image is fixed to form a full-color permanent image, and the printed image (output image) is discharged out of the image forming apparatus.
[0043]
FIG. 2 is a diagram showing the potential of the photosensitive drum.
[0044]
The value when charged by the primary charger 121 on the photosensitive drum 128 is Vd, the charged potential of the photosensitive drum when the laser 122 emits 0 level light is V00, the photosensitive drum potential when ffhex light is emitted is Vff, and the developing bias dc When the component is Vdc, the fog removal potential Vback can be expressed by | Vdc−V00 |, and the development contrast Vcont can be expressed by | Vff−Vdc |. The photosensitive drum potential is Vp when the laser output for forming the latent image of the patch image is phex, and the contrast potentials Vcont and dp of the patch latent image are | Vp−Vdc |.
[0045]
When the image forming apparatus is initially installed or immediately after the toner supply container is replaced, it is stored in the ROM as a storage unit and is stored in a predetermined environment table (process conditions (exposure intensity, development bias, For example, a patch latent image is formed on the photosensitive drum 128 like Vcont and dp according to a process condition setting value such as a transfer bias stored in advance, and is used for controlling the toner latent patch latent image and image gradation. The patch latent image is developed into a patch image (this is called a digital patch image).
[0046]
When controlling the toner replenishment amount, as described above, the density of the patch image is detected by the image density detection sensor 108, and the detected output value is taken into the CPU as an initial value. The toner cartridge 103 is replenished to the developing device 101 so that the taken-in initial value and the density of the patch image for toner replenishment detected during the subsequent density control, that is, the sensor output value are the same. Control the amount of toner.
[0047]
In addition, without performing laser exposure on the photosensitive drum 128, the potential difference between the developing bias Vdc1 and the photosensitive drum potential Vd (the potential of the region that is charged by the charger 121 and not exposed) is used as the contrast potential of the patch latent image. Vcont, ap may be formed and developed to form a patch image for toner supply (this is referred to as an analog patch image). Even in this case, the initial value is set in the same manner as described above, and analog patch image formation and toner replenishment amount control are performed during the copy sequence (while a plurality of images are continuously formed on the photosensitive drum (on the recording material)). It can be performed.
[0048]
In the present invention, a latent image is formed by digital exposure, and the developed image is referred to as a digital image, and the latent image is referred to as a digital latent image. In this case, the latent image is referred to as an analog latent image, and the developed image is referred to as an analog image. Hereinafter, this designation is used as necessary.
[0049]
However, the characteristics of the photosensitive drum, particularly the photosensitivity characteristics, may change from those at the initial installation due to deterioration due to use of the photosensitive drum, fluctuation due to environment, and the like. For this reason, a difference is generated between the potential obtained by exposing the photosensitive drum with the laser output P and the initial potential to be originally obtained, and the image density formed on the photosensitive drum is desired by this potential difference. If toner replenishment control is performed with an image density value that includes this error, the toner density in the developing device falls outside the desired range, and the density of the formed image becomes excessively thin, There was a possibility that fogging occurred and an image was defective.
[0050]
Development in the developing unit to control the toner replenishment amount via the patch toner image for toner replenishment, with the removal of the photoconductor potential measurement sensor, which is a highly functional and expensive component, especially as cost and size are reduced There is a concern that variations in the concentration of the developer increase, the load applied to the developer increases, and adverse effects such as an increase in abnormal images such as fogging and a decrease in the life of the developer occur.
[0051]
Therefore, in this embodiment, in order to eliminate the variation in the potential of the laser irradiation portion on the photosensitive drum due to the change in the photosensitivity characteristic of the photosensitive drum, a patch latent image for toner replenishment is formed at a stable potential without laser exposure. Then, an analog patch forming method for developing this to form a patch image is adopted.
[0052]
This stabilizes the density of the patch image for toner replenishment and improves the detection accuracy of the patch image, thereby reducing the load applied to the developer and obtaining a stable output image with no fog. . Control as follows.
[0053]
The image forming apparatus in FIG. 1 has two high-voltage power supplies 100A and 100B as high-voltage power supplies for development bias connected to a CPU 300 as control means, and switches between development bias A and development bias B for each developing device 101. Can be applied. FIG. 3 shows a timing chart for switching the developing bias during image formation (“latent image” is the period during which the latent image is formed, “development” is the period during which the developing sleeve is rotating, and “developing bias A, B "Denotes the period during which the developing biases A and B are applied to the developing sleeve). FIG. 4 shows time waveforms of the developing biases A and B, which are alternating voltages applied to the developing sleeve (the horizontal axis represents time, and the vertical axis represents the voltage applied to the developing sleeve). FIG. 5 shows the development characteristics of the development biases A and B (the horizontal axis is the development contrast potential (absolute value), and the vertical axis is the patch image density detected by the sensor 108). FIG. 6 shows an image area and a non-image area on the photosensitive drum when images are continuously formed on a plurality of recording materials (arrows indicate the moving direction of the photosensitive drum).
[0054]
A part of the operation during the continuous image formation will be described with reference to FIG. 3. An electrostatic latent image of a normal image to be formed in the image area C on the photosensitive drum 128 is formed as a digital latent image, and the latent image is developed. When the developing position facing the developing device 101 is reached, a developing bias A shown in FIG. 4A is applied to the developing sleeve 105 of the developing device 101 from the high voltage power source 100A, and the latent image is developed. There is a non-image area E on the photosensitive drum 101 until an electrostatic latent image of the next normal image is formed, and a patch image for toner supply is formed on the non-image area E using the non-image area E. Then, toner replenishment control is performed.
[0055]
In the non-image area E, the photosensitive drum is not subjected to laser exposure, but only Vd is charged to form an analog latent image having a potential difference from the developing bias potential Vdc1, and the patch latent image is at the developing position. 4, the developing bias is switched from A in FIG. 4A to B in FIG. 4B, and development is performed with the switched developing bias B to form an analog patch image. When the next image area D reaches the developing position, the developing bias is switched from B to A again to develop the latent image of the output image on the image area D.
[0056]
The developing bias A in FIG. 4A includes a predetermined number of pulse portions of rectangular waves (alternating portions where an alternating electric field is formed by applying a voltage obtained by superimposing an alternating voltage and a direct current voltage to the developing sleeve), and a blank (A blank pulse bias) having a waveform having alternating portions (rest portions where a constant electric field is formed by applying only a DC voltage to the developing sleeve). When such a developing bias A is used, as shown in FIG. 5A, even if the toner density in the developing device fluctuates, it is difficult to reflect on the density of the image (toner image) formed on the photosensitive drum ( In the figure, with respect to the ideal solid line, the image density when the toner density in the developing device is varied is indicated by a dotted line), and the development characteristic can stabilize the image density. Due to the characteristic that the development bias A is less likely to be reflected in the toner image density in which the developer density is formed, if the developer density is controlled from the toner image density fluctuation in this development bias, the load on the developer tends to increase. There is a characteristic that the deterioration of the developer is accelerated.
[0057]
The developing bias B in FIG. 4B is a rectangular wave pulse bias, and repeatedly includes an alternating portion where an alternating electric field is formed by applying a voltage obtained by superimposing an alternating voltage and a direct current voltage to the developing sleeve. When such a developing bias B is used, as shown in FIG. 5B, the density of the image (toner image) to be formed (developed) is accurately reflected and reproduced with respect to the toner density in the developing device. (In the figure, the image density when the toner density in the developer is changed is indicated by a dotted line with respect to the ideal solid line, the developer density fluctuation amount is sensitive to the image density fluctuation amount.) Is reflected. This developing bias B is suitable for controlling the developer density because the toner image density formed with respect to the developer density fluctuation is sensitively changed, and the load on the developer tends to be small. There is a characteristic that deterioration of the developer can be suppressed.
[0058]
As described above, the development bias used for developing the patch latent image for toner replenishment control in the non-image area in the continuous copy sequence is set such that the toner image density fluctuation amount does not follow the developer density fluctuation amount. The developing bias A that stabilizes the image density is switched to the developing bias B that sensitively reflects the variation amount of the developer density in the variation amount of the image density.
[0059]
Further, since the patch image for toner replenishment is formed as an analog image by switching from the output image formed as a digital image in the image area, the patch image can be favorably formed in the non-image area. The reliability of the output value detected by the sensor can be increased, so that the load on the developer can be reduced, the density of the output image in the image area can be stabilized, and fogging can be eliminated.
[0060]
Further, in this embodiment, an interrupt sequence that operates at the post-rotation processing operation (cleaning of the photoconductor and transfer drum, etc.) after completion of normal image formation, pre-multi-rotation during the start-up of the machine body, and special timing. The image density is further stabilized by a special control sequence other than normal image formation.
[0061]
FIG. 7 is a development view of an image area, showing the formation of a patch image for gradation control of an image in a special control sequence other than during normal image formation. The arrow indicates the moving direction of the photosensitive drum. This is a mode for detecting whether or not the halftone image formed on the photosensitive drum (and consequently formed on the recording material) is properly expressed, and in accordance with the detection result, the exposure optical system By correcting the input image signal, the exposure portion potential on the photosensitive drum exposed by the exposure optical system is corrected. However, in addition to the yellow, magenta and cyan developing devices, the black developing device is mounted on the image forming apparatus of FIG.
[0062]
In this special control sequence, in the image area on the photosensitive drum 128, as shown in FIG. 7, a plurality of images are formed for each color of magenta (M), cyan (C), yellow (Y), and black (K). Tone control patches M1 to Mn, C1 to Cn, Y1 to Yn, K1 to Kn (M1 to Mn are developed latent images formed so as to have different densities in stages (C1 to Cn, The same applies to Y1 to Yn and K1 to Kn))). This development of the patch latent image is different from the development of the patch latent image for toner replenishment formed in the non-image area during continuous image formation on the plurality of recording materials described above. The developing bias A has such a characteristic that the density of the image formed with respect to the fluctuation amount does not follow and stabilizes.
[0063]
Then, the patch image for gradation control of the image is read by the detection sensor 108, and as shown in FIG. 8, a plot of the output image density with respect to the input image density signal input to the exposure optical system, that is, a characteristic curve can be obtained. it can. Then, the CPU creates a look-up table so that the characteristic curve becomes a linear output characteristic as shown by the dotted line, and then corrects the gradation of the image to be formed and the charged potential of the photosensitive drum. Thus, a more stable output image can be obtained. In FIG. 8, the horizontal axis represents an image density signal input to the exposure optical system (the signal is such that the density increases toward the right), and the vertical axis is formed by the image signal. This represents the density detected by the sensor 108 of the toner image obtained by developing the latent image.
[0064]
As described above, according to this embodiment, the normal output image in the image area is stabilized and the development in the non-image area is performed by switching the developing bias in the image area and the non-image area during image formation. In order to improve the reliability of the density detection output of the image for developer replenishment control, in the special sequence described above, for developing the latent image patch for image gradation control, for developer replenishment control in the non-image area described above By using a development bias that is different from that used for developing latent images, the patch image density detection output reliability for image tone control is improved, the load on the developer is reduced, and stable output without fogging. An image can be obtained.
[0065]
Example 2
In the first embodiment, the patch image formed in the non-image area on the photosensitive drum during the continuous image formation on a plurality of recording materials is an analog image. However, in this embodiment, the patch latent image is formed by laser exposure. A patch image of the digital image to be formed is formed, and the same effect as in the first embodiment can be obtained by this.
[0066]
In this embodiment as well, as in the first embodiment, a patch image is formed on the photosensitive drum in a special control sequence other than the normal image formation. In this embodiment, this is used as an analog patch image, and toner is used. Used for replenishment amount control.
[0067]
In the first embodiment, as shown in FIG. 1, two high-voltage power sources for developing bias are installed, ie, power sources 100A and 100B, and these are switched by hardware. In this embodiment, one high-voltage power source is used. As shown in FIG. 9, the power supply can generate two development biases. That is, with respect to the rectangular wave AC bias (development bias B), for example, if two cycles are oscillated, two cycles (two cycles are integer multiples that do not shift in phase) are not oscillated. If it is possible to generate an AC development bias waveform (development bias A) based on one cycle, the development bias A and the development bias B can be switched and generated by a single high-voltage power supply.
[0068]
The gradation control of the image in this embodiment will be described. As shown in FIG. 3, an electrostatic latent image of the output image is formed as a digital latent image in the image area C on the photosensitive drum 101, and the latent image is developed at the development position. When the value reaches, development is performed with the development bias A. Then, the laser output phex is exposed on the non-image area E on the photosensitive drum 101 until the electrostatic latent image of the next output image, and as shown in FIG. A patch latent image is formed as a digital latent image, developed, and further detected by the sensor 108 to control the gradation of the image.
[0069]
When the gradation control patch latent image reaches the development position, the development bias is maintained at the development bias A used for forming a normal image, and development is performed to form a digital patch image. When the next image area D reaches the developing position, the developing bias is further maintained at A, and the latent image of the output image on the image area D is developed.
[0070]
As described above, the development bias used for developing the patch image for controlling the gradation of the image in the non-image area in the copy sequence has a small fluctuation amount of the toner image density with respect to the fluctuation amount of the developer density in the developing device. That is, by maintaining the development bias A that stabilizes the density of the output image, the reliability of the detection output by the sensor 108 of the patch image for gradation control in the non-image area can be increased, and thereafter The gradation of the image to be formed can be corrected satisfactorily. Further, the load on the developer can be reduced, and the output image in the image area can be an image having a stable density and no fogging.
[0071]
Furthermore, a patch image for toner replenishment control is formed on the photosensitive drum in a special control sequence other than normal image formation, and this patch image is changed to an analog image different from the patch image being formed, and the development bias is developed. Switch to bias B. Thereby, the reliability of the detection output by the sensor 108 of the patch image for toner replenishment control can be improved, and the amount of toner replenished in the developing device can be optimized. Furthermore, the load applied to the developer can be reduced, and a stable output image without fogging can be obtained.
[0072]
In the above-described embodiments, the image forming apparatus that forms a color image using one photosensitive drum has been described as an example. However, the present invention is not limited to this, and recording that carries and conveys a recording material such as a conveyance belt is performed. A plurality of, for example, four, photosensitive drums are provided along the material carrier, and four color (Y, M, C, K) toner images on the four photosensitive drums are sequentially superimposed on the recording material and transferred onto the conveyance belt. Thus, the present invention can be applied to a tandem type image forming apparatus that obtains a full-color image on a recording material, and the same effect can be obtained by controlling the same.
[0073]
Also, as shown in FIG. 10, a plurality of, for example, four photosensitive drums are provided along an intermediate transfer belt 130 as an intermediate transfer member, and four colors (Y, M, C, K) on the four photosensitive drums are provided. The toner images are sequentially superposed on the intermediate transfer belt 130 for primary transfer, and then the four color toner images are collectively transferred onto the recording material conveyed by the conveying belt 127, so that full color is formed on the recording material. The present invention can also be applied to an intermediate transfer type image forming apparatus for obtaining an image. 10, the same reference numerals as those in FIG. 1 denote the same members, and a detailed description thereof will be omitted.
[0074]
In this case, the density of the patch image for toner replenishment control and the patch image for gradation control of the image can be detected on each photosensitive drum 128 (128Y to 128K). Installed on the downstream side of the image forming unit, the patch images for toner replenishment control for each color and the patch images for image gradation control are sequentially applied from the photosensitive drums 128Y to 128K onto the intermediate transfer belt 130 so as not to overlap each other. After the transfer, the density of the patch image for toner replenishment control of each color and the patch image for gradation control of the image may be detected on the intermediate transfer belt 130 by the detection sensor 108. According to this, since it is not necessary to install the detection sensor 108 in each of the photosensitive drums 128Y to 128K, the cost can be greatly reduced.
[0075]
Of course, also in the image forming apparatus for forming an image on the recording material on the recording material carrier described above, a patch image for controlling toner replenishment of each color and a patch image for controlling gradation of the image are obtained from the respective photosensitive drums 128Y to 128K. Transfer directly to the recording material carrying member so as not to overlap each other, and the density of the patch image for toner replenishment control of each color and the patch image for gradation control of the image on the recording material carrier by the single sensor 108. You may make it detect.
[0076]
It goes without saying that the same effects as those of the first and second embodiments can be obtained even if the detailed configuration of the embodiment described above is variously modified within the scope of the idea of the present invention.
[0077]
【The invention's effect】
As described above, according to the present invention, the first developing electric field for developing the first latent image for controlling the amount of developer replenished to the developer accommodating portion and the gradation of the image are controlled. Therefore, both the gradation control of the image and the replenishment control of the developer can be performed satisfactorily, and the developer can be applied to the developer. Such a load can be reduced and the life of the developer can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an embodiment of an image forming apparatus provided with a developing device of the present invention.
2 is a schematic diagram showing a potential on a photosensitive drum of the image forming apparatus of FIG.
FIG. 3 is a diagram showing a sequence in density control performed in the embodiment of FIG. 1;
4 is a diagram showing waveforms of two development biases A and B used in the embodiment of FIG.
FIG. 5 is a diagram illustrating development characteristics of development biases A and B in FIG. 4;
6 is a diagram illustrating an image area and a non-image area for forming an output image and a patch image on the photosensitive drum in the embodiment of FIG. 1;
7 is a schematic diagram showing a method of forming a patch image for gradation correction formed during non-image formation in the embodiment of FIG. 1. FIG.
8 is an explanatory diagram showing a correction method of a lookup table for tone correction based on density detection of the patch image of FIG. 7;
FIG. 9 is a diagram showing a method of forming waveforms of development biases A and B in another embodiment of the present invention.
FIG. 10 is a schematic diagram illustrating another example of an image forming apparatus to which the present invention is applicable.
FIG. 11 is a detailed view showing a conventional image forming apparatus.
[Explanation of symbols]
101Y-101C, 101K Developer
102Y to 102C toner density sensor
103Y to 103C toner cartridge
108 Image density sensor
122 laser
127 Transfer drum
128, 128Y-128K photosensitive drum
130 Intermediate transfer belt
100A, 100B High-voltage power supply for developing bias

Claims (2)

In a developing device having a developer container that contains a developer including toner and a carrier, and a developer carrier that carries the developer,
When the first latent image for controlling the amount of developer supplied to the developer accommodating portion is developed, a first developing bias to which a voltage containing an AC component is repeatedly applied is the developer carrier. When the second latent image for controlling the gradation of the image is developed, a period in which a voltage including an AC component is applied and a period in which a voltage including an AC component is not applied are A developing device, wherein a second developing bias provided alternately is applied to the developer carrying member . Normal image formation, claims and duration of voltage including an AC component is applied, a period in which no voltage is applied, including an AC component, the bias provided alternately, characterized in that it is applied to the developer carrying member Item 2. The developing device according to Item 1 .

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