JP4438051B2 - Image forming apparatus - Google Patents

Description

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

  In an electrophotographic image forming apparatus, image formation is generally performed by image forming processes of charging, exposure, development, transfer, fixing, and cleaning. That is, after the surface of the photosensitive member is uniformly charged, exposure according to image information is performed to form an electrostatic latent image. The electrostatic latent image is developed as a toner image with toner, and the toner image is transferred from the photoreceptor onto a recording material such as paper. The photoreceptor after the toner image transfer is cleaned by removing the transfer residual toner remaining on the surface. On the other hand, the recording material after transfer of the toner image is heated and pressurized to fix the toner image on the surface. This completes image formation.

  As a developer used in the above-described image forming apparatus, a two-component developer in which a non-magnetic toner and a magnetic carrier are mixed is widely used with the recent improvement in image quality and speed of a full-color image forming apparatus. This two-component developer can achieve high image quality and high speed of a full-color image forming apparatus. On the other hand, the toner / carrier mixing ratio (toner concentration) in the developing device changes depending on toner consumption. It is difficult to always keep the toner density at an appropriate level. When the toner density is inappropriate, various image defects such as density fluctuation, roughness, fogging, carrier adhesion, and toner scattering occur. For this reason, in forming a high-quality and highly-stabilized image, it is very important to accurately detect the toner density and appropriately control the supplied toner amount.

  Therefore, as a means for detecting the toner density, a change in the physical characteristics of the two-component developer itself, for example, a change in the reflection density of the developer or a change in the magnetic permeability is directly detected by the density sensor, and the detection result There is a method of controlling the amount of supplied toner based on this.

  However, this method has a problem in that it cannot be accurately controlled when the toner charge amount fluctuates due to environmental fluctuations such as temperature and humidity or deterioration with time. In other words, even if the toner density is appropriate, if the toner charge amount fluctuates due to environmental fluctuations or carrier deterioration, the coupling force between the toner and the carrier fluctuates, and the amount of toner movement on the photosensitive member fluctuates. Therefore, it is very difficult to maintain a stable image density.

  Therefore, a reference image (patch image) is formed by developing the reference latent image formed on the photosensitive member, the reflection density of the patch image is detected by the density sensor, and the toner density of the developer is detected. There is a method of controlling the amount of supplied toner based on the detection result.

  In such a toner patch detection method, since the target of detection is the toner adhesion amount formed on the photoconductor, more precisely speaking, the toner density of the developer is not directly controlled to be constant. For this reason, even when the toner charge amount fluctuates due to environmental fluctuations such as temperature and humidity or deterioration with time, it is possible to always maintain an appropriate toner density in image formation.

  By the way, as the image forming apparatus continues to be used for a long time, the toner in the toner storage unit storing the replenished toner disappears. Therefore, it is necessary to encourage the supply of new toner. As this toner remaining amount detecting means, a piezo method, an antenna method, a light detection method, and the like have been proposed and implemented. As another method, there is a method that uses both the toner patch detection method and the toner presence / absence detection means and the toner density control means. Specifically, it is determined that there is no toner when the detection output of the patch image is less than or equal to a predetermined value, or when the output less than or equal to the predetermined value continues for a plurality of times. Since this method can perform both toner presence / absence detection and toner density control with a single sensor, there is no need to provide a dedicated sensor for toner presence / absence detection, and this method is very cost effective.

  However, since this method detects toner presence / absence and toner density control with a single sensor, simply looking at the detection output of the patch image is really no toner, or because of factors other than toner density It is difficult to determine whether the concentration is low. In order to increase the accuracy of the toner presence / absence determination, it is sufficient to set the reference value of the patch image density when determining the absence of toner. However, the normal image density is greatly reduced in the vicinity of the absence of toner. This is not preferable for practical use. On the other hand, if the reference value is set higher, the decrease in density can be suppressed, but the risk of erroneous determination of the presence or absence of toner increases.

Accordingly, when the patch image is detected by the density sensor and the detection level of the density sensor does not satisfy a certain reference value, a forced toner supply operation is performed. Thereafter, the re-formed patch image is detected by the density sensor, and if the detection level still does not satisfy the reference value, it is determined that there is no toner. If it is determined that there is no toner, after the toner cartridge is replaced with a new toner cartridge, the toner forcible replenishment operation is performed again. After that, the formed patch image is detected by the density sensor. It is known to cancel (Patent Document 1).
Japanese Patent Laid-Open No. 5-66669

  However, in the above-described means, when the toner density is recovered again by the toner replenishment operation, the toner density may be rapidly increased, and various problems such as image density failure, toner scattering, and fixing failure occur.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus for determining whether or not image formation (including determination of the presence or absence of toner remaining in a toner container) can be performed based on the detected density of a reference toner image (patch image). It is determined that the amount of toner remaining in the container is an amount that cannot continue image formation, and the time from returning to the state where image formation is prohibited is shortened as much as possible. An object of the present invention is to realize and provide an image forming apparatus capable of suppressing the rise.

The present invention includes a developing device that develops an electrostatic image formed on an image carrier, a replenishing unit that replenishes toner in a toner container to the developing device, a density sensor that detects the density of a reference toner image, An image forming apparatus comprising: a control unit that controls a replenishment operation of the replenishing unit according to the output of the density sensor; and a determination unit that determines whether image formation can be performed according to the output of the density sensor.
An image forming apparatus capable of executing a determination mode for interrupting an image forming operation and determining whether image formation can be performed when the density of the reference toner image is equal to or lower than a predetermined density based on a detection result of the density sensor,
The determination mode is based on a first process for performing a replenishment operation of the replenishing means so that a first predetermined amount of toner is replenished to the developing device, and a determination toner image formed after the first process. In this mode, if the density of the determination toner image does not return to a predetermined density, the replenishment operation by the replenishing unit and the formation of the determination toner image are repeatedly executed. Is a possible mode,
The determining means determines the amount of toner to be replenished per replenishment operation of the replenishing means in the mode when the number of replenishment operations of the replenishing means performed in the mode reaches a predetermined number. The replenishment operation of the replenishing means is changed so that the second predetermined amount is smaller than the first predetermined amount from the predetermined amount .

  According to the present invention, when image formation is prohibited, the time required to return to a state where image formation can be started based on the output of the density sensor can be shortened as much as possible. Furthermore, the amount of toner required for forming the reference toner image can be reduced as much as possible. Further, when returning, it is possible to prevent an image formation defect by suppressing a sudden increase in toner density.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each drawing, what attached | subjected the same code | symbol has the same structure or effect | action, The duplication description about these shall be abbreviate | omitted suitably.

  FIG. 1 shows an image forming apparatus according to Embodiment 1 as an example of an image forming apparatus according to the present invention. The image forming apparatus shown in the figure is an electrophotographic four-color full-color printer, and the figure schematically shows a schematic configuration thereof.

  The configuration of a printer (hereinafter referred to as “image forming apparatus”) will be described with reference to FIG.

  The printer shown in FIG. 1 (hereinafter referred to as “image forming apparatus”) includes a drum-type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 as an image carrier. The photosensitive drum 1 is supported so as to be rotatable in the arrow R1 direction. Around the photosensitive drum 1, a primary charger (charging means) 2, an exposure device (exposure means) 3, a developing device (developing means) 4, and an intermediate transfer are arranged almost sequentially from the upstream side along the rotation direction. A belt 5 and a cleaning device (cleaning means) 6 are disposed. A transfer conveyance belt 7 is disposed below the intermediate transfer belt 5, and a fixing device (fixing unit) is disposed downstream of the transfer conveyance belt 7 along the conveyance direction (arrow A direction) of the recording material P. ) 8 is provided.

  In the present embodiment, the photosensitive drum 1 having a diameter of 60 mm is used. As shown in FIG. 2, the photosensitive drum 1 is formed by coating a photosensitive layer 1b made of a normal organic photoconductive layer (OPC) on the outer peripheral surface of a grounded drum base 1a made of a conductive material such as aluminum. A protective layer (OCL) 1c having excellent wear resistance is applied and formed thereon. Of these layers, the photoreceptor layer 1b is composed of four layers: an undercoat layer (CPL) 1b1, an injection blocking layer (UCL) 1b2, a charge generation layer (CGL) 1b3, and a charge transport layer (CTL) 1b4. The photosensitive layer 1b is usually an insulator, and has a feature that it becomes a conductor when irradiated with light of a specific wavelength. This is because holes (electron pairs) are generated in the charge generation layer 1b by light irradiation, and these become the charge carriers. The charge generation layer 1b is made of a phthalocyanine compound having a thickness of 0.2 μm, and the charge transport layer 1c is made of polycarbonate in which a hydrazone compound having a thickness of about 25 μm is dispersed. The photosensitive drum 1 is rotationally driven in the direction of the arrow R1 at a predetermined process speed (circumferential speed) by a driving means (not shown).

  In the present embodiment, a scorotron type corona discharger is used as the primary charger 2. This corona discharger is formed by covering the discharge wire 2a with a metal shield 2b opened on the photosensitive drum 1 side.

  In the present embodiment, as the exposure device 4, a laser scanner that turns on / off laser light in accordance with image information is used. The laser beam generated from the exposure device 3 is applied to the surface of the charged photosensitive drum 1 through a reflection mirror. Thereby, the electric charge of the laser beam irradiated portion is removed, and an electrostatic latent image is formed.

  In the present embodiment, the developing device 4 employs a rotational development method. A rotating body 4A that is driven to rotate in the direction of arrow R4 by a motor (not shown) around a shaft 4a, and four developing devices mounted thereon, that is, black, yellow, magenta, and cyan developing devices 4Y, 4M, 4C, 4K. When a black developer image (toner image) is formed on the photosensitive drum 1, development is performed by the black developing device 4 </ b> K at the development position D close to the photosensitive drum 1. Similarly, when a yellow toner image is formed, the rotating body 4A is rotated by 90 °, and the developing unit 4Y for yellow is disposed at the development position D to perform development. Magenta and cyan toner images are formed in the same manner. In the following description, when it is not necessary to distinguish colors, it is simply referred to as a developing device.

  The above-described intermediate transfer belt 5 is stretched over a drive roller 10, a primary transfer roller (primary transfer charger) 11, a driven roller 12, and a secondary transfer counter roller 13. The rotation of the drive roller 10 causes an arrow R5. Rotate in the direction. A belt cleaner 14 is in contact with the intermediate transfer belt 5. Further, the above-described transfer conveyance belt 7 is stretched around the drive roller 15, the secondary transfer roller 16, and the passive roller 17, and rotates in the direction of arrow R 7 as the drive roller 15 rotates. The transfer roller 8 described above has a fixing roller 18 with a built-in heater (not shown) and a pressure roller 20 in contact with the fixing roller 18 from below.

  The operation of the image forming apparatus configured as described above will be described.

  In FIG. 1, the surface of the photosensitive drum 1 charged by the primary charger 2 is exposed by the exposure device 3 to form an electrostatic latent image on the photosensitive drum 1. A toner image is formed on the photosensitive drum 1 by adhering toner to the electrostatic latent image by a developer containing a developer (toner) of a desired color. This toner image is transferred onto the intermediate transfer belt 5 by applying a primary transfer bias to the primary transfer roller 11 from a primary transfer bias application power source 11a.

  When four-color full-color image formation is performed, first, a black toner image is formed on the photosensitive drum 1 by the black developing device 4K, and the black toner image is primarily transferred onto the intermediate transfer belt 5. The toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 after the primary transfer is removed by the cleaning device 6. Next, the rotating body 4A is rotated by 90 °, the yellow developing device 4Y is disposed at the developing position D, a yellow toner image is formed on the photosensitive drum 1, and the black toner image on the intermediate transfer belt 5 is formed. A yellow toner image is primarily transferred and superimposed.

  This operation is also sequentially performed in the magenta developing unit 4M and the cyan developing unit 4C, and the four color toner images are superimposed on the intermediate transfer belt 5. Thereafter, by applying a secondary transfer bias to the secondary transfer roller 16, the four-color toner images on the intermediate transfer belt 5 are secondarily collected onto the recording material P carried on the transfer conveyance belt 7. Transcript.

  The recording material P onto which the toner image has been transferred is peeled off from the transfer conveyance belt 7 and is heated and pressed by the fixing roller 18 and the pressure roller 20 of the fixing device 8 to fix the toner image on the surface. As a result, a four-color full-color image is formed. After the secondary transfer, toner (transfer residual toner) remaining on the intermediate transfer belt 5 is removed by the belt cleaner 14.

  In the case of performing monochromatic image formation, the electrostatic latent image formed on the photosensitive drum 1 is developed by a developing unit that contains toner of a desired color. This toner image is primarily transferred onto the intermediate transfer belt 5 and then immediately transferred onto the recording material P as a secondary transfer. The recording material P onto which the toner image has been transferred is peeled off from the transfer conveyance belt 7 and heated and pressurized by the fixing device 8 to fix the toner image on the surface.

  In the present embodiment, the image density detection sensor 21 faces the surface of the photosensitive drum 1 on the downstream side of the development position D along the rotation direction of the photosensitive drum 1 and on the upstream side of the primary transfer roller 11. Has been placed.

  Next, with reference to FIG. 3, the developing devices 4Y, 4M, 4C, and 4K for the respective colors mounted on the rotating body 4A in FIG. 1 will be described. The developing container 22 of the developing unit contains a two-component developer containing nonmagnetic toner and a magnetic carrier, and the toner concentration in the developer in the initial state is about 8% by weight. This value should be properly adjusted according to the toner charge amount, the carrier particle size, the configuration of the image forming apparatus, etc., and does not necessarily have to follow this value.

  The toner in the developer consumed by the development is supplied from a toner container 23 that is detachably installed in the vicinity of each developing device of the rotating body 4A.

  When the developing device is moved to the developing position D, the developing area facing the photosensitive drum 1 is opened, and the developing sleeve 24 is rotatably arranged so as to be partially exposed to the opening.

  Inside the developing sleeve 24, a fixed magnet 25 as a magnetic field generating means is included. The developing sleeve 24 is made of a non-magnetic material, and rotates during the developing operation in the direction of arrow R24 shown in FIG. 3, that is, in the direction of movement from the top to the bottom in the direction of gravity in the developing region. The two-component developer is held in layers and is carried and conveyed to the development area, and the developer is supplied to the development position D facing the photosensitive drum 1 to develop the electrostatic latent image formed on the photosensitive drum 1.

  In order to adjust the amount of the developer conveyed to the developing region to an appropriate amount, a regulating blade (developer regulating member) is provided so as to face the developing sleeve 24 on the upstream side of the developing region along the rotation direction of the developing sleeve 24. ) 26 is provided. The regulating blade 26 regulates the layer thickness of the developer on the developing sleeve 24.

  The developer after developing the electrostatic latent image is conveyed according to the rotation of the developing sleeve 24 and collected in the developing container 22. Further, the developer container 22 is provided with a first circulation screw 27a (a side closer to the development sleeve 24) and a second circulation screw 27b (a side far from the development sleeve 24) as developer agitating / conveying means. Thus, the developer in the developing container 22 is circulated and mixed and stirred. In the present embodiment, the developer circulation direction is the direction from the back surface side to the front surface side in FIG. 3 on the first circulation screw 27a side, and the reverse direction from the front surface side to the back surface side on the second circulation screw 27b side. It has become.

  The two-component developer described above consumes the toner in the developer as the number of image forming sheets (number of copies) increases. The consumed toner is replenished into the developer container 22 from the developer replenishment port 22a provided in the developer container 22 through the developer replenishment port 23a provided in the toner container 23 through the replenishment conveyance path 28. . The replenished toner is replenished upstream of the second circulation screw 27b of the developing container 22 in the developer conveying direction. The toner is mixed and agitated with the developer already in the developing container 22 and the developed developer conveyed by the first circulation screw 27a. In this way, the developer is handed over to the first circulation screw 27a in a well-stirred state, and is supplied to the developing sleeve 24 again. A supply screw (toner supply means) 30 is provided in the supply conveyance path 28. The rotation time of the replenishing screw 30 is controlled by the CPU 29 as a control means, and thereby the amount of toner to be replenished to the developing device is adjusted.

  Next, a toner patch detection method in the present embodiment will be described.

  First, when an image forming apparatus is initially installed, it is stored in a backup memory, and a predetermined environment table (process conditions corresponding to temperature and humidity information (exposure intensity, development bias, transfer bias setting values of process conditions such as A reference toner image (hereinafter referred to as a patch image) is formed under the image forming conditions based on the stored one)). That is, by performing laser exposure on the charged photosensitive drum 1, a patch latent image is formed, and the patch latent image is developed to form a patch image. This is called a digital patch image method. Further, without performing laser exposure on the photosensitive drum 1 (it can also be said that light is emitted so that the exposure level becomes zero), the developing bias and the photosensitive drum potential (charged by the primary charger 2, but by the exposure device 3). The patch potential may be formed by forming a contrast potential of the patch latent image based on a potential difference with respect to the potential of the region not exposed) and developing the contrast potential. This is called an analog patch image method. When controlling the toner replenishment amount, a specific patch target signal value is compared with the density of the patch image for toner replenishment detected during the subsequent density control, that is, the sensor output value. The CPU controls the amount of toner to be replenished from the toner container 23 to the developing container 22 so that they are the same.

  In this embodiment, a latent image formed by digital exposure is called a digital latent image, and an image obtained by developing this digital latent image is called a digital image. In order to distinguish these from each other, when a patch image is formed without performing the above-described exposure, the latent image is referred to as an analog latent image, and an image obtained by developing the latent image is referred to as an analog image. Hereinafter, these designations are used as necessary.

  However, when the above-described digital patch image method is adopted, the characteristics of the photosensitive drum 1, particularly the photosensitivity characteristics, may change compared to the initial installation due to deterioration due to use of the photosensitive drum 1, changes due to the environment, and the like. It was. For this reason, a difference occurs between the potential obtained by exposing the photosensitive drum 1 with the laser output of the exposure device 3 and the potential at the initial setting that should be originally obtained, and the image density formed on the photosensitive drum 1 is reduced. This potential difference deviates from a desired value. If toner replenishment control is performed using an image density value that includes this error, the toner density in the developing device may be outside the desired range, causing image density fluctuations, toner fogging, and the like, leading to image defects. there were.

  Development in the developing unit is particularly useful for controlling the toner replenishment amount based on the patch image for toner replenishment in a state where the photoconductor potential measurement sensor, which is a highly functional and expensive component, has been removed along with cost reduction and miniaturization. The variation in the concentration of the developer is increased, the load applied to the developer is increased, and there is a possibility that adverse effects such as an increase in abnormal images such as fogging and a decrease in the life of the developer may occur.

  Therefore, in the present embodiment, in order to eliminate the variation in the potential of the laser irradiation portion on the photosensitive drum 1 due to the change in the photosensitivity characteristics of the photosensitive drum 1, the patch latent image for toner supply is stabilized without laser exposure. An analog patch forming method is employed in which a patch image (reference toner image) is formed by forming with a potential and developing it.

  As described above, the rotation time of the replenishment screw 30 is controlled by the CPU 29, whereby the amount of toner to be replenished to the developing device is adjusted. Toner supply for controlling the rotation time is adjusted. The control means will be specifically described below.

  When the image forming operation is repeated, the toner in the developer container is consumed and the toner concentration in the developer is lowered. Therefore, it is preferable to control the toner concentration within a desired range by appropriately replenishing the toner. In the present invention, the first toner supply control means for controlling the rotation time of the toner supply screw based on the video count number of the image density signal of the image information signal of a copy original or the like, and the reference toner image (reference toner) on the photosensitive drum. Image), the density signal of the reference toner image is detected by a density detection sensor, the density signal is compared with an initial reference signal stored in advance, and the first toner supply control is performed based on the comparison result. A system using a second toner supply control means for correcting the driving time of the toner supply section determined by the means is used.

In the combined method, the toner density is controlled mainly by the video count method. In the video count method, the level of the output signal of the image signal processing circuit is counted for each pixel, and this count is added up for the pixels of the original paper size, thereby obtaining the video count per original (for example, A4 size). The maximum video count number per frame is 400 dpi and 256 tones (3844 × 10 ⁶ ). This video count number corresponds to the expected toner consumption, and an appropriate replenishment screw rotation time is determined from a conversion table showing a correspondence relationship between the video count number and the toner supply screw rotation time, and the toner is accordingly determined. Is replenished.

  In this embodiment, the rotation time of the toner supply screw is selected only from an integer multiple of a predetermined unit time (unit block supply). In this embodiment, the rotation time of the toner supply screw per unit block is set to 0.3 seconds, and the rotation time of the toner supply screw per image is 0.3 seconds or an integral multiple thereof. Limited. FIG. 4 shows a specific state of toner supply.

  For example, when the rotation time of the toner supply screw obtained from the above video count number through the conversion table is 0.42 seconds, the number of unit block replenishment supplied per image in the next image forming operation is 1 ( The rotation time of the toner supply screw is 0.3 seconds), and the remaining toner supply for 0.12 seconds is stored as a surplus and added to the rotation time of the toner supply screw obtained from the next video count. The The flow of the above processing is shown in FIG.

  As described above, an advantage of limiting the rotation time of the toner supply screw to only an integral multiple of the predetermined unit time is that the amount of toner replenishment once is stabilized. If toner is replenished in accordance with the rotation time of the toner supply screw obtained from the video count number, the rotation time becomes very short when the video count number is small. If the rotation time is short, the influence of the rise time and fall time of the drive motor that drives the toner supply screw becomes large, and there is a problem that the toner replenishment amount is not stable. Therefore, the toner replenishment amount is stabilized by always setting a constant rotation time as in this embodiment.

  In the video count method, if there is a difference between the expected toner consumption and the actual toner consumption, the developer concentration gradually deviates from the appropriate range, so a predetermined interval (a predetermined number of times of image formation is performed). It is preferable to correct the toner replenishment amount using the patch detection method (hereinafter referred to as “patch detection mode”). In this embodiment, the interval is set for every 50 small size originals (for example, A4 portrait).

  When the number of images formed reaches 50 and the operation timing of the patch detection mode is reached, an electrostatic latent image of a reference toner image having a certain area is formed on the photosensitive drum, and this is developed with a predetermined development contrast voltage. The density signal of the reference toner image is detected by an optical sensor 90 facing the photosensitive drum. The density signal Vsig is compared with the initial reference signal Vref previously recorded in the memory. When Vsig−Vref <0, it is determined that the density of the patch image is low, that is, the developer density is low, and the difference between Vref and Vsig Therefore, the necessary toner replenishment amount and the corresponding rotation time of the toner supply screw are determined, and the rotation time is corrected in a form added to the rotation time determined by the video count method. Conversely, when Vsig−Vref ≧ 0, it is determined that the density of the patch image is high, that is, the developer density is high, and the amount of unnecessary toner and the corresponding stop time of the toner supply screw are determined from the difference between Vref and Vsig. This time is corrected by subtracting it from the rotation time determined by the video count method. By performing such control, it is possible to correct a deviation in toner density. FIG. 6 shows a processing flow when the video count method and the patch detection method are used together.

  In this embodiment, the density signal of the reference toner image is detected on the photosensitive drum. However, the reference toner image formed on the photosensitive drum is transferred onto the intermediate transfer member 5, and the density signal after the transfer is transferred. Can be detected by an optical sensor arranged in the vicinity of the intermediate transfer member 5.

  Further, when the rotation time of the toner supply screw is increased from the detection result of the patch detection mode, that is, when the number of unit block replenishment is added, only one block is added per image as shown in FIG. ing. That is, when adding 10 blocks as the number of unit block replenishment from the detection result in the patch detection mode, it is not added at once, but one block is added per image, and additional correction is performed over 10 images. To complete. By performing such control, it is possible to prevent the toner density in the developing device from rapidly increasing and causing fogging and scattering.

  Next, toner presence / absence detection in this embodiment will be described. In this embodiment, the toner cartridge 23 (toner container) or the like is not provided with sensors for detecting the presence / absence of toner, and the presence / absence of toner is detected and determined by the CPU using the sensor output used for patch detection. Then, when the CPU determines that the remaining amount of toner in the toner cartridge is an amount that is difficult to continue image formation in the future, control is performed to prohibit image formation. That is, the CPU determines whether or not the image formation can be continued in addition to the toner presence / absence determination in the toner cartridge based on the detected density of the patch image. In this embodiment, in the configuration in which the toner cartridge is installed in the image forming apparatus and the toner is sequentially supplied, the presence / absence of toner in the toner cartridge is determined based on the detected density of the patch image. Alternatively, the image forming apparatus may be provided with a large capacity toner hopper, and the presence or absence of toner in the toner hopper may be determined based on the detected density of the patch image. In this case, toner is supplied from the toner cartridge to the toner hopper.

  As a result, it is possible to reduce the cost for the sensor for detecting the presence or absence of toner. An operation flow of toner presence / absence detection is shown in FIG.

  The density signal Vsig detected in the patch detection mode is compared with a predetermined density signal lower limit value Vlimit (S2), and it is determined whether or not the lower limit value is exceeded. If the lower limit value is exceeded, the CPU determines that there is still enough toner in the toner cartridge, and the toner replenishment amount is corrected so that one block is added per image as described above (S3). ). If it is less than the lower limit, the CPU determines that the remaining amount of toner in the toner cartridge is low, and enters the toner remaining amount detection mode. During the transition to this mode, the image formation is prohibited, and this fact is displayed on the liquid crystal display unit of the image forming apparatus or notified to a personal computer or the like connected to the image forming apparatus via a network cable.

  Here, the toner remaining amount detection mode in this embodiment will be described below with reference to FIG.

  First, the rotating body 4 rotates so that the developing device that has entered the toner remaining amount detection mode comes to the developing position.

  Then, the toner supply screw is forcibly rotated for 4 seconds (time not depending on the output of the patch sensor) to forcibly replenish the toner, and the developing device is simultaneously idled for 4 seconds (that is, the developer stirring operation is performed). Do). Thereafter, a toner patch image is formed, and this density signal is detected by a sensor. At this time, if the detected signal value exceeds the density signal lower limit value Vlimit, the toner remaining amount detection mode ends here, and the state where image formation is prohibited is returned to a state where image formation is possible.

  However, if the density signal lower limit value Vlimit is still below, the toner supply screw rotates again for 4 seconds, and the developing device also idles simultaneously for 4 seconds. Then, a series of steps for forming a toner patch image is executed again, and this density signal is detected by a sensor. At this time, when the detected signal value is equal to or lower than the density signal lower limit value Vlimit, the above operation is repeatedly performed a predetermined number of times (number of times = H) (in this embodiment, 5 times).

  After that, even if the above operation is repeated a predetermined number of times (5 times), if the detected signal value is less than or equal to the density signal lower limit value Vlimit, the time is shorter than that during the forcible replenishment operation, that is, forced for 2 seconds. In this case, when the detected signal value is equal to or lower than the density signal lower limit value Vlimit, this operation is repeated a predetermined number of times (number of times = J) (in this embodiment, 5 times).

  If the detected signal value is still below the density signal lower limit value Vlimit, the CPU determines that there is no toner, and notifies the replacement of the toner cartridge (outputs a signal that prompts replacement).

  The output destination of this signal is a liquid crystal display section as display means provided on the upper part of the image forming apparatus main body. When the image forming apparatus is connected to a personal computer or the like via a network and has a function as a printer, the signal may be output to the personal computer or the like via the network.

  Thus, as shown in FIG. 8, the forced replenishment operation for 4 seconds is performed 5 times, and then the forced replenishment operation for 2 seconds is performed 5 times. During forced replenishment, the developer is idled simultaneously for 4 seconds.

  As described above, in this embodiment, in the toner remaining amount detection mode, the driving time (toner replenishment amount) of the toner replenishment screw per time at the time of forced replenishment is changed according to the number of repetitions of the above steps, and the initial step Control is performed so that the number of processes in the later stage is less than that in the process.

  That is, when the toner remaining amount detection mode is entered, the toner concentration is lowered, so the toner concentration is increased quickly by increasing the amount of toner replenished per time. When the toner concentration increases to some extent, the toner concentration is gradually increased by decreasing the toner replenishment amount per time.

  As described above, in the toner remaining amount detection mode, by changing the replenishment amount per one time during the forcible replenishment operation, it is possible to determine the presence / absence of toner in a short time and to detect erroneous detection of toner presence / absence. It is possible to prevent and suppress a rapid increase in toner density.

  Here, if the replenishment amount per one time in the forcible replenishment operation is increased from the beginning of the toner remaining amount detection mode, the toner density rapidly increases, causing various problems such as toner scattering, fogging, and poor image density. Problem has occurred.

  In addition, if the amount of replenishment per time during the forced replenishment operation is reduced from the beginning of the toner remaining amount detection mode, an abrupt increase in toner concentration can be suppressed, but it takes time to increase the toner concentration, and the A lot of time has occurred.

  On the other hand, when it is determined that there is no toner and a new toner cartridge filled with toner is mounted and installed, the above-described toner remaining amount detection mode is entered again, and the presence or absence of toner is determined by performing the same steps and operations. In this case, the time from the replacement of the toner cartridge until the image can be formed can be shortened as much as possible, the erroneous detection of the presence / absence determination of toner can be prevented, and the rapid increase in toner density can be suppressed. be able to. Furthermore, it is possible to prevent image formation defects that occur when the first image is formed after returning to a state where image formation is possible.

  As described above, according to the present embodiment, in the image forming apparatus that determines the presence / absence of toner remaining in the toner cartridge by the toner patch detection method, it is possible to detect the presence / absence of toner in a short time and to prevent erroneous detection of the toner presence / absence determination. In addition, an image forming apparatus capable of suppressing an abrupt increase in toner density has been realized and provided.

  Next, Example 2 will be described. Note that the image forming process in the present embodiment is almost the same as that of the first embodiment described above, and a duplicate description is omitted.

  In the first exemplary embodiment, the patch image is formed every time the forced supply operation is repeated in the toner remaining amount detection mode. However, when a large amount is forcibly replenished in the first half of the toner remaining amount detection sequence (when the replenishment is performed 5 times in 4 seconds in the first embodiment), the toner density is recovered to a certain degree of speed. It was rare for the patch concentration to recover to the desired value (Vlimit). Therefore, in this embodiment, at the beginning of the toner remaining amount detection sequence, the forcible replenishment operation is performed without performing toner patch detection, and after the toner density is recovered to some extent, the toner patch detection is performed while repeating the forcible replenishment operation. It was. Details will be described below with reference to FIG.

  First, the rotating body 4 rotates so that the developing device that has entered the toner remaining amount detection mode comes to the developing position. Then, the toner supply screw is forcibly rotated for 12 seconds to forcibly supply the toner, and the developing unit is simultaneously idled for 12 seconds. During this time, toner patch detection is not performed.

  Thereafter, a forced replenishment operation for 4 seconds is performed according to FIG. 9, and then toner patch detection is performed. When the detected signal value exceeds the density signal lower limit value Vlimit, the toner remaining amount detection mode ends, and an image can be formed.

  On the other hand, when the detected patch signal value is equal to or lower than the density signal lower limit value Vlimit, this operation is repeated a predetermined number of times (number of times = J) (in this embodiment, twice).

  After that, even if the above operation is repeated a predetermined number of times (twice), if the detected signal value is equal to or lower than the density signal lower limit value Vlimit, the time is shorter than that during the forcible replenishment operation, that is, forcing for 2 seconds. In this case, when the detected signal value is equal to or lower than the density signal lower limit value Vlimit, this operation is repeated a predetermined number of times (number of times = J) (in this embodiment, 5 times). If the detected signal value is still below the density signal lower limit value Vlimit, it is determined that there is no toner, and the replacement of the toner cartridge is notified (a signal for prompting replacement is output).

  As described above, at the beginning of the toner remaining amount detection sequence, the forcible replenishment operation is performed without detecting the toner patch, and after the toner density is recovered to some extent, the toner patch detection is performed while the forcible replenishment operation is repeated. The number of extra toner patch detections was reduced. As a result, it was possible to reduce the amount of toner consumed by detecting the toner patch, and further to reduce the time during which image formation was prohibited (the time when the mode was changed), that is, the downtime.

  Next, Example 3 will be described. Note that the image forming process in the present embodiment is almost the same as that of the first embodiment described above, and a duplicate description is omitted.

  In general, it is known that the charging performance of the carrier is lowered by the deterioration of the carrier at the end of the life of the developer.

  In such a case, for example, when a new filled toner cartridge is mounted after it is determined that there is no toner, the toner replenished by the forced replenishment operation after the toner remaining amount detection mode is not sufficiently charged, fogging, image Concentration fluctuation occurred rarely.

  Therefore, in this embodiment, when it is determined that the toner is present by performing the toner remaining amount detection mode in the first and second embodiments, the developing device that has performed the toner remaining amount detection mode does not stop after the toner remaining amount detection mode ends. The idling operation was performed for 30 seconds. As a result, even when a large amount of toner is supplied in the toner remaining amount detection mode at the end of the life of the developer, the replenished toner is sufficiently agitated with the developer, particularly the carrier, and the frictional charging is performed well. No fogging or image density fluctuation occurred.

1 is a longitudinal sectional view schematically showing a schematic configuration of an image forming apparatus according to the present invention. It is a longitudinal cross-sectional view which shows typically the layer structure of a photosensitive drum. It is a longitudinal cross-sectional view which shows the structure of a developing device. It is a figure explaining the mode of the unit block supply which concerns on Example 1. FIG. FIG. 6 is a diagram illustrating a toner supply flow by a video count method according to the first exemplary embodiment. FIG. 6 is a diagram illustrating a toner supply flow when the video count method and the patch detection method according to the first embodiment are used together. FIG. 6 is a diagram illustrating an operation flow of toner presence / absence detection according to the first exemplary embodiment. FIG. 6 is a diagram illustrating a flow of a toner remaining amount detection sequence according to the first exemplary embodiment. FIG. 10 is a diagram illustrating a flow of a toner remaining amount detection sequence according to the second embodiment.

Claims (1)

A developer that develops an electrostatic image formed on the image carrier, a replenishing unit that replenishes toner in a toner container to the developer, a density sensor that detects a density of a reference toner image, and a density sensor An image forming apparatus comprising: a control unit that controls a replenishment operation of the replenishing unit according to an output; and a determination unit that determines whether image formation can be performed according to an output of the density sensor.
An image forming apparatus capable of executing a determination mode for interrupting an image forming operation and determining whether image formation can be performed when the density of the reference toner image is equal to or lower than a predetermined density based on a detection result of the density sensor,
The determination mode is based on a first process for performing a replenishment operation of the replenishing means so that a first predetermined amount of toner is replenished to the developing device, and a determination toner image formed after the first process. In this mode, if the density of the determination toner image does not return to a predetermined density, the replenishment operation by the replenishing unit and the formation of the determination toner image are repeatedly executed. Is a possible mode,
The determining means determines the amount of toner to be replenished per replenishment operation of the replenishing means in the mode when the number of replenishment operations of the replenishing means performed in the mode reaches a predetermined number. An image forming apparatus , wherein the replenishment operation of the replenishing means is changed so that a predetermined amount is changed to a second predetermined amount smaller than the first predetermined amount .

Images