JP4617129B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image of a copying machine, a printer, a recorded image display device, a facsimile machine or the like that develops an electrostatic latent image formed on an image carrier by an electrophotographic method, an electrostatic recording method, or the like to form a visible image. The present invention relates to a forming apparatus.

  Conventionally, in a developing process for developing an electrostatic latent image in an image forming process using an electrophotographic method or an electrostatic recording method, charged toner particles are imaged by utilizing the electrostatic interaction of the electrostatic latent image. In this step, a developer image (toner image) is formed by moving the toner image onto the electrostatic latent image on the carrier. In general, among the methods for developing such an electrostatic latent image, a two-component developing method employing a two-component developer in which toner is dispersed in a medium called a carrier is particularly required to have high image quality. It is preferably used for full-color copying machines and full-color printers.

  As an embodiment of the two-component developing device, as shown in FIG. 11, the developer supplied to the surface of the developing sleeve 41 that is a developer carrying member by the developer stirring and conveying means 43 and 44 is supplied to the developing sleeve 41. It is held in the state of a magnetic brush by the magnetic force of a magnet roller (not shown) which is a cylindrical magnetic field generating means contained therein, and this is opposed to the photosensitive drum 1 which is an image carrier based on the rotation of the developing sleeve 41. In addition to being transported to the developing area of the developing section 41, the magnetic brush is trimmed by the blade 42, which is a developer head height regulating member on the developing sleeve 41, so that the amount of developer transported to the developing area is properly maintained. Is provided.

  The two-component developer includes toner and carrier, but in the two-component developing device, the toner consumed by being subjected to the developing operation is properly replenished, and the ratio of the toner and the carrier is “the amount of toner”. It is controlled to keep the “density” constant.

  More specifically, the inside of the developing device is partitioned into a developing chamber 47 and a stirring chamber 48 by a partition extending in the vertical direction, and the developing chamber 47 and the stirring chamber 48 include two-component development including a non-magnetic toner and a magnetic carrier. The agent is contained. In the developing chamber 47 and the agitating chamber 48, screw type first and second developer agitating / conveying means 43 and 44, respectively, are arranged as described above, and the developers in the developing chamber 47 and the agitating chamber 48 are arranged. Are to be stirred and conveyed.

  The first agitating / conveying means 43 is disposed substantially parallel to the bottom of the developing chamber 47 along the axial direction of the developing sleeve 41, that is, along the developing width direction, and the blade member is spirally formed around the rotation axis. The screw structure is provided and rotates to convey the developer in the developing chamber 47 in one direction along the axial direction of the developing sleeve 41 at the bottom of the developing chamber 47.

  The second agitating and conveying means 44 has a screw structure in which a blade member is provided in a spiral shape around the rotation axis in a direction opposite to that of the first agitating and conveying means 43, and the first agitating and conveying means 44 is provided at the bottom of the agitating chamber 48. It is arranged substantially parallel to the conveying means 43 and rotates in the same direction as the first agitating and conveying means 43 to convey the developer in the agitating chamber 48 in the direction opposite to the first agitating and conveying means 43.

  The second agitating / conveying means 44 agitates the toner supplied from the toner supply tank 60 to the upstream side of the second agitating / conveying means 44 and the developer already in the agitating chamber 48 under the developer concentration control. The developer is transported and the developer concentration (toner concentration), which is the weight of the toner relative to the total weight of the developer, is made uniform. By this stirring, the toner and the carrier are rubbed, and the toner retains an appropriate charge amount by frictional charging.

  A partition wall 46 exists between the first stirring and conveying means 43 and the second stirring and conveying means 44, and the inside of the developing device is divided into a developing chamber 47 and a stirring chamber 48. As shown in FIG. 3, developer passages 46 a and 46 b are formed at both ends so that the developing chamber 47 and the agitating chamber 48 communicate with each other, and the conveying forces of the first and second agitating and conveying means 43 and 44 are formed. Thus, the developer in the developing chamber 47 in which the toner is consumed by being subjected to the developing operation and the density of the toner is lowered is configured to move from the other passage into the stirring chamber 48. Thus, the developer is circulated between the developing chamber 47 and the stirring chamber 48 by the rotation of the first and second stirring and conveying means 43 and 44.

  As means for detecting the toner concentration in the circulating developer (concentration detection means), a detection means using an inductance sensor 45 for detecting the toner-carrier ratio from the magnetic permeability of the developer has been conventionally known. Yes.

  In the developing device having the above-described configuration, the inductance sensor 45 is provided in the upstream portion of the developer circulation in the stirring chamber 48 as shown in FIG. When it is determined that the toner density detected by the inductance sensor 45 is insufficient with respect to the originally determined target density, the toner replenishment port 6a (see FIG. Replenish toner from 11). This developer concentration control means is referred to as inductance ATR. As described above, the density of the toner in the developer is controlled to a constant density by the inductance ATR.

  However, depending on the state of the developer, the bulk density of the developer may vary, and a difference may appear between the value detected by the inductance sensor 45 and the actual toner concentration. In particular, when left in a high-humidity environment for a long time, the toner and the carrier are aggregated, and the bulk density is increased as calculated in the normal printing operation. As a result, the apparent magnetic permeability increases and it is determined that the toner is insufficient, and the toner is replenished even though the toner density is actually appropriate. As a result, the target toner concentration may deviate.

  As a countermeasure, a method is known in which a toner consumption amount per page is determined from a cumulative value of the number of print pixels in an image information signal per page, and a control means (video count ATR) for supplying toner is used in combination with an inductance ATR. It has been.

  That is, when the detected density of the inductance sensor 45 and the target density are greatly deviated, the toner supply control by the inductance ATR is stopped and switched to the video count ATR, assuming that the image forming apparatus may be left for a long time. The toner concentration in the actual developer is prevented from deviating from a predetermined value (see Patent Document 1).

However, with the diversification of user needs in recent years, there is a need for an image forming apparatus that can improve image quality, extend the service life, and can withstand various usage situations. However, the conventional method is effective for stabilizing the toner concentration when left for a long period of time, but is not effective for the variation of the toner concentration due to the gradual change of the developer state. I couldn't respond enough. Therefore, there is a need for a more advanced developer concentration control method.
JP 2003-131439 A

  SUMMARY OF THE INVENTION An object of the present invention is to suppress an image density variation caused by developer density control such as fogging and image density reduction by suppressing fluctuations in toner density due to a gradual change in developer state as much as possible. A forming apparatus is provided.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the first aspect of the present invention is an image carrier on which an electrostatic latent image is formed based on an image information signal,
A developing device containing a developer including toner and a carrier, and developing the electrostatic latent image with the toner;
Toner supply means for supplying toner to the developing device;
Density detecting means for detecting the density of toner in the developing device;
First developer concentration control means for determining a toner replenishment amount based on a value of a detection signal from the density detection means and a reference value for density control, and operating the toner replenishment means;
Second developer concentration control means for determining a toner replenishment amount based on a cumulative value of the number of print pixels of the image information signal and operating the toner replenishment means;
Based on the toner replenishment amount determined by the first developer concentration control means and the toner replenishment amount determined by the second developer concentration control means, the density control in the first developer concentration control means. Determining means for determining whether to change the reference value of
An image forming apparatus comprising:

According to a second aspect of the present invention, there is provided an image carrier on which an electrostatic latent image is formed based on an image information signal;
A developing device containing a developer including toner and a carrier, and developing the electrostatic latent image with the toner;
Toner supply means for supplying toner to the developing device;
Density detecting means for detecting the density of toner in the developing device;
First developer concentration control means for determining a toner replenishment amount based on a value of a detection signal from the density detection means and a reference value for density control, and operating the toner replenishment means;
Second developer concentration control means for determining a toner replenishment amount based on a cumulative value of the number of print pixels of the image information signal and operating the toner replenishment means;
Based on the toner replenishment amount determined by the first developer concentration control means and the toner replenishment amount determined by the second developer concentration control means, the developer by the first developer concentration control means Switching means for switching from density control to developer density control by the second developer density control means;
An image forming apparatus comprising:

  The image forming apparatus of the present invention calculates the amount of developer replenishment obtained by each of the two developer concentration control means, and performs operations such as correcting the developer concentration control method according to the calculation result. As a result, it is possible to suppress the change in the toner density due to the gradual change of the developer state as much as possible, and to suppress the occurrence of image defects.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the following embodiments are intended to limit the scope of the present invention only to those unless otherwise specified. is not. Further, the material, shape, etc. of the members once described in the following description are the same as those in the first description unless otherwise described.

Example 1
Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

  An image forming apparatus to which the present invention can be applied, for example, forms an electrostatic latent image corresponding to an image information signal on an image carrier such as a photosensitive member or a dielectric by an electrophotographic method, an electrostatic recording method, or the like. Is developed by a developing device using a two-component developer mainly composed of toner particles and carrier particles to form a visible image (toner image), and the visible image is transferred onto a transfer material such as paper, and is used as a fixing unit. It is sufficient if it has a structure that makes a permanent image.

  First, an overall configuration of an example of an image forming apparatus to which the present invention can be applied will be described with reference to FIGS. In this embodiment, the present invention is applied to an electrophotographic full-color printer, but it goes without saying that the present invention is equally applicable to various image forming apparatuses such as an electrophotographic system and an electrostatic recording system. .

  First, according to the image forming apparatus shown in FIG. 1, a desired image to be output is decomposed into a large number of pixels from the image reading apparatus or computer 33 through the image information processing apparatus 32 and sent to the printer side. At this stage, it is converted into a pixel image signal that is image data corresponding to the density of each pixel.

  A drum-shaped photosensitive member (photosensitive drum) 1 serving as an image carrier is an electrophotographic photosensitive drum having amorphous silicon, selenium, OPC, or the like on its surface and rotating in the direction of an arrow. Are uniformly charged by the primary charger 2.

  The pixel image signal is input to the pulse width modulation circuit 31, and a laser driving pulse corresponding to the pixel image signal is supplied to the semiconductor laser 3 which is an exposure unit as a latent image forming unit, and corresponds to the pulse width. Make it emit light only for the time you want. On the photosensitive drum 1, a relatively long range is exposed for high density pixels in the main scanning direction, and a short range is exposed for low density pixels, and the area gradation corresponding to the image information signal is exposed. An electrostatic latent image having the following is formed (latent image forming step).

  This electrostatic latent image is developed by a developing device 4 using a two-component developer in which toner particles and carrier particles are mixed, and a visible image (toner image) is formed (developing step). The formed toner image is transferred to a transfer material 90 held on a transfer material carrier (transfer material carrier belt) 91 driven endlessly in the direction of the arrow by the action of a transfer roller 92 as a transfer means ( Transfer process). The toner image transferred to the transfer material 90 is fixed by a fixing unit (not shown) provided on the downstream side of the transfer material 90 to be a permanent image (fixing step), and a desired image formed product is provided. . The residual toner on the photosensitive drum 1 after the toner image is transferred is removed by the cleaning device 5 to prepare for the next image formation.

  For the sake of simplicity, FIG. 1 shows one image forming station (photosensitive drum 1, exposure device 3, primary charging device 2, developing device 4) in which the above-described image forming process for one color is performed. Only the cleaning device 5 and the like are included). As shown in FIG. 2, in a color image forming apparatus using a plurality of colors, for example, four image forming stations Y, M, C, and Bk for each color of cyan, magenta, yellow, and black are provided with a transfer material carrying belt 91. It is set as the structure arrange | positioned sequentially along the moving direction on the top. The color separation toner images for each color of the original formed on the photosensitive drums 1 of the image forming stations Y, M, C, and Bk are sequentially transferred to the transfer material 90 held and conveyed by the transfer material carrying belt 91. In the same manner, the image is fixed and a full color image is obtained. Note that the configurations of the image forming units in the stations Y, M, C, and Bk are the same except for the color of the developer.

  Next, the details of the developing device 4 installed in the printer will be described with reference to FIG. The configuration of the developing device 4 is substantially the same as the configuration shown in FIG. 11 described above except for the toner replenishing means, and the developing device 4 is arranged to face the photosensitive drum 1, and the inside thereof is A partition 46 extending in the vertical direction is divided into a first chamber (developing chamber) 47 and a second chamber (stirring chamber) 48. In the developing chamber 47, a non-magnetic developing sleeve 41, which is a hollow cylindrical body rotating in the direction of the arrow, is disposed as a developer carrier, and a magnet (not shown) serving as a magnetic field generating means is disposed in the developing sleeve 41. ) Is fixedly arranged. The developing sleeve 41 carries and transports a layer of a two-component developer (including a magnetic carrier and non-magnetic toner) whose layer thickness is regulated by a blade 42 which is a developer regulating member, and in a development region facing the photosensitive drum 1. A developer is supplied to the photosensitive drum 1 to develop the electrostatic latent image.

  In order to improve the developing efficiency, that is, the application rate of toner to the latent image, a developing bias voltage in which a DC voltage is superimposed on an AC voltage is applied to the developing sleeve 41 from a power source (not shown).

  In the developing chamber 47 and the agitating chamber 48, first and second developer agitating means (developer agitating screws) 43 and 44 are arranged as developer frame members and conveying means, respectively. The first screw 43 agitates and conveys the developer in the developing chamber 47, and the second screw 44 and the toner supplied from the toner replenishing tank 60 by the toner replenishing device 6 serving as a toner replenishing unit and the inside of the developing device 4 already exist. The developer in the container is agitated and conveyed to make the toner density uniform.

  The partition wall 46 that partitions the developing chamber 47 and the stirring chamber 48 is formed with developer passages 46a and 46b that allow the developing chamber 47 and the stirring chamber 48 to communicate with each other on the front side and the rear side shown in FIG. The developer in the developing chamber 47 in which the toner is consumed by the development due to the conveying force of the screws 43 and 44 and the toner concentration is lowered moves from one passage 46 b into the stirring chamber 48, and in the stirring chamber 48. The developer whose toner density has been recovered is configured to move from the other passage 46 a into the developing chamber 47.

  The toner replenishing device 6 as toner replenishing means includes a conveying screw 61 and a conveying screw 61 that connect a developer replenishing tank 60 containing toner as a replenishing developer and a toner replenishing port 6 a to the developing device 4. Drive motor 62, and a drive circuit 63 for controlling the drive motor 62. Then, the rotation time of the conveying screw 61 is calculated according to the developer (toner) supply amount determined by the developer concentration control means selected by the CPU 67, the motor driving circuit 63 is controlled, and the motor 62 is operated for that time. The developing device 4 is replenished with a predetermined amount of toner.

  As the developer concentration control means executed by the CPU 67, two methods can be selected. In either case, the toner amount for the shortage is obtained, the replenishment toner amount by the toner replenishing device 6 is controlled, and the toner to the developing device 4 is controlled. Carry out replenishment. As this selectable developer concentration supply means, in this embodiment, an inductance ATR executed by the main first developer concentration control means and a video executed by the subsequent second developer concentration control means. A combined method of count ATR is adopted. Here, the two types of developer concentration control means used in this embodiment will be described in detail.

  The inductance ATR as the first developer concentration control means includes, in the developing device 4, an inductance sensor 45 that is a density detection means for detecting the apparent permeability of the two-component developer including toner particles and carrier particles. The sensor 45 detects the density of the toner contained in the developing device 4 and determines the toner replenishment amount based on the difference between the detection signal value (output value) based on the detection result and the reference value for toner replenishment control. This is a control method for operating the replenishing device 6. On the other hand, the video count ATR as the second developer concentration control means is a control means for operating the toner replenishing device 6 based on the cumulative value of the number of print pixels of the image information signal.

  The inductance ATR as the first developer concentration control means will be described in detail.

  As shown in FIG. 3, the developing device 4 is provided with an inductance sensor 45 on the side wall upstream of the developer circulation in the stirring chamber 48. The output electric signal from the inductance sensor 45 changes substantially linearly according to the toner concentration.

  In the configuration shown in FIG. 1, detection data obtained by AD converting the electrical signal output from the inductance sensor 45 is sent to a CPU 67 that executes developer replenishment amount control means. The CPU 67 is connected to a nonvolatile memory RAM 68 that is a storage means.

  Here, in the RAM 68, detection data (initial value) corresponding to the prescribed toner density in the initial setting value is stored from the inductance sensor 45 via the CPU 67, and a predetermined “correction value” corresponding to the temperature and humidity is stored. A table is also stored in advance. In this embodiment, the “correction value” and the “initial value” corresponding to the above temperature and humidity are read from the RAM 68 to the CPU 67 and added to obtain the “reference value”.

Then, the CPU 67 calculates the detection data newly obtained from the inductance sensor 45 and the “reference value”, and determines it as a toner replenishment amount corresponding to the difference. Then, the rotation time of the conveying screw 61 corresponding to the toner replenishment amount is calculated, the motor driving circuit 63 is controlled, and the motor 62 is rotated and driven for that time. The conveying screw 61 rotates for the above-described time, and supplies a shortage of toner from the toner supply tank 60 to the developing device 4. That is, the toner supply amount is controlled by controlling the driving time of the motor 62.

  The toner concentration here is the weight ratio (%) between the toner and the developer (toner and carrier), and is basically controlled to 8.0% in this embodiment.

  However, only by controlling the developer concentration by the inductance ATR, even if the toner concentration is the same, the magnetic permeability changes because the bulk density changes depending on the state of the developer. As a result, an error may occur in the amount of toner to be replenished.

  For example, when a high printing rate image is continuously printed, a large amount of toner is replenished, so that the charge of the toner is reduced and the bulk density is increased. Therefore, the magnetic permeability increases and it is determined that the toner is insufficient. In order to compensate for the shortage, the toner is further replenished, so that the toner charge amount is further reduced and the bulk density is further increased. If the toner concentration is too high, problems such as fogging will occur.

  On the other hand, when the low printing rate image is continuously output, since the toner is not replaced, the toner in the developing device 4 has an excessive charge, and the bulk density of the developer is reduced. The permeability decreases due to the decrease in the bulk density, and if there is a lot of toner, false detection will occur. As a result, toner replenishment can be suppressed, resulting in insufficient toner replenishment, which can lead to a vicious circle that further leads to overcharging of the toner. When a high density image is printed in such a state, it may be difficult to obtain a sufficient density.

  Therefore, in order to correct the erroneous detection of the inductance ATR due to the developer state as described above and maintain the toner density at an appropriate value, in this embodiment, as the second developer density control means, Based on the total number of print pixels of the information signal, developer concentration control is performed by a video count ATR that operates the toner replenishing device 6.

  The video count ATR in this embodiment will be described below.

  As shown in FIG. 1, a laser drive pulse corresponding to a print pixel image signal transmitted from a pulse width modulation circuit 31 is supplied to one input of an AND gate 64, and the other input is supplied from a clock pulse oscillator 65. Supply clock pulses.

  The number of clock pulses corresponding to the pulse width of the laser drive pulse, that is, the number of clock pulses corresponding to the density of each pixel is output from the AND gate 64. The clock pulses are integrated for each image by the counter 66 to calculate the video count number.

  This video count number corresponds to the amount of toner consumed to form one toner image. The CPU 67 that performs toner replenishment control reads a conversion table indicating the correspondence between the video count number and the toner replenishment time provided in the RAM 68 from the video count number, and controls the driving time of the motor 62 as described above. The toner is replenished so as to compensate for the consumed toner amount.

  That is, in the inductance ATR, the density of the toner in the developing device 4 is directly detected by the inductance sensor 45 which is a density detection means, and the difference between the detected value and the reference value is used as the toner replenishment amount, whereas the video count ATR Then, the amount of toner consumed is calculated from the number of video counts and used as the replenishment amount.

  Conventionally, as described in Patent Document 1, when the detected density by the inductance sensor 45 in the inductance ATR is greatly deviated from the initial value and the reference value in consideration of the environment, the developer density control means is used as the video count ATR. However, it was not possible to sufficiently cope with the gradually changing developer state.

  Therefore, in this embodiment, a new developer concentration control method using both the inductance ATR and the video count ATR is executed. That is, the toner replenishment amount is always determined and calculated, and when the difference between the toner replenishment amounts obtained by both is small, the toner replenishment device 6 is operated by the inductance ATR, but there is a large difference in the toner replenishment amount. If this occurs, a countermeasure is taken by performing some predetermined operation on the developer concentration control means.

  In this embodiment, when there is a large difference between the replenishment amounts obtained by the inductance ATR and the video count ATR, specifically, there is a determination means for determining to change the reference value of the inductance ATR. This will be described with reference to the flowchart of this developer concentration control step shown in FIG.

  After image formation is started (S401), the developer replenishment control by the inductance ATR is continued while calculating the toner replenishment amounts x and y from the inductance ATR and the video count ATR until the cumulative value of the number of printed sheets reaches the Nth sheet. (S402, S403).

  When the cumulative value of the number of printed sheets reaches N (S403), the cumulative value X up to the Nth sheet actually supplied with toner by the inductance ATR and the cumulative toner supply amount Y by video count are calculated (S404).

  In S404, if normal, X and Y indicate substantially the same value. However, when there is a problem that the toner is consumed due to fogging or the density is not increased depending on the state of the developer, there is a difference between the replenishment amount X of the inductance ATR and the video count replenishment amount Y. .

  The difference is calculated, and when the difference is larger than the predetermined value A1 (S405 yes), it is determined that fogging has occurred, that is, the actual toner density may be high, and the toner density is determined. In order to decrease, the reference value of the inductance ATR is switched to be controlled with the new reference value a1 (S406).

  The difference is equal to or less than the predetermined value A1 (S405 no), but when the replenishment amount X of the inductance ATR with respect to the video count replenishment amount Y becomes a predetermined ratio A2 or less (S408 yes), the image density is low. In other words, it is determined that there is a possibility that the actual toner density is low, and the reference value of the inductance ATR is switched to be controlled with the new reference value a2 in order to increase the toner density (S409).

  After switching to the new reference value a1 or a2, a toner replenishment or toner consumption sequence is performed so that the output value of the detection (inductance detection) by the inductance sensor 45 is substantially equal to the new reference value a1 or a2. (S407, S410). A toner replenishment and toner consumption sequence will be described later.

  Thereafter, all accumulated values are reset and image formation is performed (S411).

  Then, the replenishment amount of the video count ATR and the inductance ATR is calculated, and when it is equal to or less than the predetermined value A1 and the predetermined ratio A2 (S408 no), the reference value remains unchanged and the accumulated value is reset and image formation is performed. Perform (S411).

  If the predetermined value A1 is too small, there is a possibility that the reference value is switched due to a slight inductance detection flare or video count error. On the other hand, if the predetermined value A1 is set to a large value, the reference value cannot be switched until the fogging or density reduction becomes a considerably bad level, so that the effect of suppressing the original defective image is lost.

  Regarding the predetermined ratio A2, if the value is too large, there is a possibility of erroneous detection, and if the value is small, the reference value will not be switched until the image defect level becomes bad.

  Also, regarding the number of printed sheets N, if a small number of sheets are judged, the possibility of erroneous detection due to an error increases. Conversely, if the number of sheets is too large, it takes a long time to make a judgment after a fog occurs. Printing an image.

  Furthermore, if the new reference values a1 and a2 are changed too much, the density of the excessive toner changes, and conversely, the problem arises that the fog and the image density are low. On the contrary, if the fluctuation range is small, it is difficult to obtain the effect of suppressing various problems because the toner density wants to fluctuate much.

  Therefore, in this embodiment, the cumulative number N of printed sheets is 30 in A4 conversion, the predetermined value A1 is 500 mg, and the predetermined ratio A2 is 0.8. The new reference value a1 is set to 95% of the original reference value a, and the new reference value a2 is set to 105% of the original reference value a.

  As described above, in the image forming apparatus used in this embodiment, the toner replenishment amount is always calculated from the inductance detection and the video count detection. As a result, even if there are some errors in the inductance ATR and the video count ATR, even if problems such as fogging and low density occur, it can be judged until it gets worse, and changing the reference value to the new reference value will not cause any harmful effects. It has become possible to suppress the occurrence of defective images.

  Here, a toner replenishment and toner consumption sequence, which is an operation of the toner replenishing device 6 for adjusting the inductance detection output value to the new reference values a1 and a2 performed in S407 and S410, will be described.

  Setting the reference value to the new reference value a1 means controlling the toner density to be low, but the amount of toner consumed is small depending on the print rate of the output image. It takes time to reach the output value. Therefore, in this embodiment, in order to forcibly consume the toner, the photosensitive drum 1 is exposed during non-image formation, and the toner is forcibly developed. The developed toner is collected by the cleaning device 5 without being transferred, so that no problem occurs when the next image is formed. As a result, the output value quickly reaches the target reference value a1.

  Since setting the reference value to the new reference value a2 means controlling the toner density to be high, it is necessary to replenish toner. The toner supply device 6 is operated while rotating the stirring screws 43 and 44 and the developing sleeve 41 in order to sufficiently stir the replenished toner so as to have an electric charge, so that the toner is gradually replenished, and the output value of the inductance detection Replenishment was carried out until was almost equal to the new reference value.

  By doing so, it is possible to change the reference value without causing adverse effects such as fogging by supplying toner at once.

  By providing the special sequence after changing the reference value as described above, since the toner density is surely changed, it is possible to surely suppress the problem that the fog and the image density are already reduced at the next image formation.

  In the present embodiment, that is, in this embodiment, it is determined by the toner replenishment amount determined by the inductance sensor ATR as the first developer concentration control means and the video count ATR as the second developer concentration control means. By calculating the toner replenishment amount and changing the reference value of the inductance sensor ATR based on the calculation result, even if the toner concentration controlled by the inductance ATR varies depending on the developer state, the toner supply amount is quickly In addition, since the inductance ATR is corrected, it is possible to suppress the occurrence of a defective image even when the developer state gradually changes.

  The predetermined value A1, the predetermined ratio A2, and the cumulative number of printed sheets N are optimum values in this embodiment, and the optimum values vary depending on the configuration of the developing device, and are not limited to these values.

  Further, the new reference values a1 and a2 are also increased or decreased by 5% such as 95% and 105% of the reference values in this embodiment. However, the present invention is not limited to this. Increase / decrease) and significant changes (for example, increase / decrease by 10%) are possible.

Example 2
The configuration used in the present embodiment is almost the same as that of the image forming apparatus described in the first embodiment. However, in this embodiment, in order to match the output value of the inductance detection with the new reference value, image formation can be continuously performed without performing a special sequence of forced toner consumption operation or forced toner supply operation. is there.

  In the first embodiment, when the new reference values a1 and a2 are changed to the new reference values a1 and a2 in the flowchart shown in FIG. 4 (S406 and S409), the forced toner consumption operation or the forced toner is used to match the inductance detection output value and the new reference value. A special sequence called replenishment operation was executed (S407, S410). However, if such a special sequence is performed, the user cannot perform image formation until this sequence is completed.

  In order to reduce such user stress, the inductance detection output value is adjusted to the new reference value while image formation is being performed. After the reference value is changed to the new reference value, there is naturally a difference between the replenishment amounts of the inductance ATR and the video count ATR. Therefore, if the replenishment amount of the inductance ATR and the video count ATR is calculated and controlled immediately after switching the reference value, the toner density is not stabilized. For this reason, the replenishment amount of the inductance ATR and the video count ATR are not compared and controlled until the predetermined number of sheets R for which the toner density is considered to be stable after the new reference value is set.

  This will be described with reference to the flowchart of this developer concentration control step shown in FIG.

  Here, from S501 to S504, the same steps as S401 to S404 shown in FIG. 4 are performed, and similarly, the toner replenishment amount is calculated by the inductance ATR and the video count ATR (S505, S507), and the difference X When -Y is larger than A1 (S505 yes), the inductance ATR reference value a is changed to a1 (S506), and when the ratio X / Y of X to Y is smaller than A2 (S505 no S507 yes), the reference value a is changed to a2 (S508).

  However, after that, without performing forced toner consumption or forced toner supply operation, the toner density is stabilized using the inductance ATR while performing normal image formation (S509), and a predetermined number of sheets considered to be stable. When R printing is completed (S510), the accumulated value is reset (S511). After resetting, the process returns to S501 to form an image.

  Further, the replenishment amounts of the video count ATR and the inductance ATR are calculated, and when the value is equal to or smaller than the predetermined value A1 and equal to or larger than the predetermined ratio A2 (S507 no), image formation is performed after resetting the accumulated value without changing the reference value. This is performed (S512).

  As a result, the toner density can be set to a desired value without interrupting image formation and performing a special sequence. After that, the state of the toner density can be determined and the inductance ATR and the video count ATR can be detected. By restarting the developer concentration control by calculating the replenishment amount, more stable developer concentration control can be performed.

  In this embodiment, the predetermined number R is set to 100. In this configuration, it was confirmed that when the image printing rate was 5%, the toner density was stable at the target density at this number. However, depending on the configuration of the developing device, this number may be insufficient or even a smaller number may be stable, and is not limited to this value.

  In this embodiment, the developer concentration control is resumed by calculating the replenishment amount after the new reference value is set after the predetermined number of prints. However, the output value of the inductance detection is almost the same as the newly set reference value. When the values become the same, it is also possible to restart the developer concentration control by calculating the replenishment amount of the video count ATR and the inductance ATR.

  This will be described with reference to the flowchart of this developer concentration control step shown in FIG.

  Here, the same steps as S401 to S404 shown in FIG. 4 are performed from S601 to S604, and similarly, the toner replenishment amount is calculated by the inductance ATR and the video count ATR (S605, S609), and the difference X When -Y is larger than A1 (S605 yes), the inductance ATR reference value a is changed to a1 (S606), and when the ratio X / Y of X to Y is smaller than A2 (S605 no S609 yes), the reference value a is changed to a2 (S610). After changing the reference value, the image forming operation is continued without performing the forced toner consumption or the forced toner supply operation, and the inductance ATR is performed (S607, S611). Image formation is continued until the inductance output value becomes equal to the new reference value (S608, S612 no), and it is considered that the toner density is stable when the output value becomes equal to the new reference value (S608, S612 yes). Again, in order to control the toner density by calculating the replenishment amount of the inductance ATR and the video count ATR, the accumulated value is reset, and the process returns to S601 (S613).

  As described above, by changing the toner density to a new reference value using the inductance ATR while continuing image formation, the user can change the toner density to an optimum level without feeling stress. In addition, since this method is more reliable than determining whether the toner is stable by the number of sheets, the developer concentration control by the replenishment amount calculation can be resumed at an appropriate timing.

Example 3
The configuration used in this embodiment is almost the same as the image forming apparatus having the configuration described in the first embodiment. However, in this embodiment, the developer concentration control is switched from the inductance ATR to the video count ATR according to the calculation result of the toner replenishment amount determined by the inductance ATR and the video count ATR, and the calculated value is an appropriate value. If it returns to (2), it is the characteristics that it switched to the inductance ATR.

  When the replenishment amount of the inductance ATR and the video count ATR is calculated and the replenishment amount by the inductance ATR is large, there is a possibility that fogging occurs or the image density is more than necessary. Since this phenomenon occurs because the toner concentration is high, it is necessary to lower the toner concentration.

  Further, when the replenishment amount of the inductance ATR is small, it means that there is no density on the photosensitive drum 1. Since this phenomenon occurs when the toner is excessively charged and the toner density becomes low, it is necessary to increase the toner density.

  In the first and second embodiments, the reference value of the inductance ATR is changed to change the toner density. However, in this embodiment, a switching means for switching the developer density control means from the inductance ATR to the video count ATR is used. Therefore, the toner density is changed indirectly.

  Hereinafter, a method of changing the toner density by switching means for switching from the inductance ATR to the video count ATR will be described.

  When the replenishment amount of the inductance ATR is larger than the replenishment amount of the video count ATR, by changing to the video count ATR, an amount smaller than the toner amount to be replenished by the inductance ATR is replenished. Therefore, since the replenishment amount is smaller than the actual toner consumption amount, the toner density gradually decreases in the lower direction.

  When the replenishment amount of the inductance ATR is small, switching to the video count ATR replenishes a larger amount than the amount to be replenished with the inductance ATR. For this reason, since the replenishment amount is larger than the actual toner consumption amount, the toner density gradually changes in the higher direction.

  After the replenishment amount is calculated in this way, the developer density control is switched from the inductance ATR to the video count ATR according to the calculation result, whereby the toner density can be changed in the target direction. As a result, various problems (fogging, low concentration) that were occurring could be suppressed.

  However, if control is continued with the video count ATR after switching to the video count ATR, errors in the video count ATR accumulate and the toner density may deviate significantly from the target density. For this reason, in this embodiment, switching from the video count ATR to the inductance ATR again prevents the toner density from greatly deviating from the target density.

  The developer concentration control of this embodiment will be specifically described with reference to the flowcharts of FIGS.

  The flowchart shown in FIG. 7 shows a developer concentration control method starting from a point in time when the developer concentration control means is not switched in one image formation.

  Here, when image formation is started (S701), it is first determined whether the developer concentration control means (main ATR) for actually replenishing toner is an inductance ATR or a video count ATR (S702).

  When the inductance ATR is used, toner replenishment control using the inductance ATR is executed as it is during image formation, and the cumulative value of the number of printed sheets continues to the Nth sheet (S703, S704).

  When the cumulative value reaches N sheets (S704 yes), the cumulative value X up to the Nth sheet actually supplied with toner by the inductance ATR and the cumulative toner supply amount Y by video count are calculated (S705).

  When the difference between the replenishment amount X of the inductance ATR and the replenishment amount Y of the video count ATR is calculated and becomes larger than a predetermined value A1, there is a possibility that fogging has occurred, that is, the actual toner density is high. There is a possibility that when the supply amount X of the inductance ATR with respect to the video count supply amount Y becomes equal to or less than the predetermined ratio A2 (S706 yes), the image density is thin, that is, the actual toner density is low. Judge that there is sex. At that time, the main ATR is switched to the video count ATR (S707).

  After switching to the video count ATR, all accumulated values are reset once and image formation is performed (S708).

  If it is not more than the predetermined value A1 and not less than the predetermined ratio A2 (S706 no), all the accumulated values are reset once (S708), and the developer density detection method performs image formation with the inductance ATR.

  Next, the control for returning to the normal inductance ATR from the state controlled by the video count ATR will be described. As shown in FIG. 8, even when the main ATR is the video count ATR, the toner replenishment amounts x and y required for the inductance ATR and the video count ATR until the number of printed sheets reaches M as in the case where the inductance ATR is the main. Are accumulated (S801, S802, S803).

  Then, cumulative values X and Y of the replenishment amounts of the inductance ATR and the video count ATR are calculated (S804), and the difference and ratio are calculated (S805).

  If the difference between the cumulative values X and Y is a value smaller than the predetermined value B1 and the ratio of the cumulative value X to Y is larger than the predetermined ratio B2 (S805 yes), it is determined that no fogging or low density has occurred, Switching to the normal inductance ATR (S806). At this time, all accumulated values are reset (S807). Thereafter, the flow returns to the density control for calculating the toner replenishment amount based on the inductance ATR and the video count ATR shown in the flowchart of FIG.

  If the difference between the cumulative values X and Y is equal to or greater than the predetermined value B1, or the ratio of the cumulative value X to Y is equal to or smaller than the predetermined ratio B2 (S805 no), it is still fogging and the concentration is still light. After determining and resetting the accumulated value (S808), the developer density control by the video count ATR is continued.

  In this example, A1, A2, and the cumulative number N of prints were the same as in Example 1, the cumulative number of prints M was 50, the predetermined value B1 was 0 mg, and the predetermined ratio B2 was 1.0. As a result, the fogging and the low concentration were restored, and then the normal inductance ATR was restored, and the recurrence of the fogging and the low concentration could be suppressed.

  However, the predetermined values A1 and B1, the predetermined ratios A2 and B2, and the cumulative number of printed sheets N and M are optimum values in the present embodiment, and the optimum values vary depending on the configuration of the developing device and the like. The value is not limited to this value.

  Further, in this embodiment, when switching from the video count ATR to the inductance ATR, it is determined whether to return or leave the replenishment amount from the inductance ATR and the video count ATR again, but when a certain number of sheets are printed, A method of automatically returning to the inductance ATR may be used.

  For example, according to the flowchart shown in FIG. 9, when the main ATR is the video count ATR, image formation is continued until the number of printed sheets reaches Q (S901, S902). Switching (S903), the accumulated value of the number of printed sheets is reset (S904), and the process returns to the developer concentration control for calculating the toner replenishment amount by the inductance ATR and the video count ATR as shown in the flowchart of FIG.

  However, it is desirable to set the number Q of prints, which is the timing for switching at this time, to a number that can sufficiently recover the fog.

  As described above, in this embodiment, it is determined by the toner replenishment amount determined by the inductance ATR as the first developer concentration control means and the video count ATR as the second developer concentration control means. According to the calculation result, the developer concentration control to be executed is switched from that based on the inductance ATR to that based on the video count ATR. By switching the developer concentration control to that based on the inductance ATR again, even if the toner concentration controlled by the inductance ATR varies depending on the state of the developer, the inductance ATR is corrected immediately. Even if the changes gradually, the occurrence of defective images can be suppressed. It has become possible.

  The first to third embodiments are not all independent, and are performed based on the result of calculating a predetermined toner replenishment amount in the first developer concentration control means and the second developer concentration control means. With regard to the predetermined operation, particularly the fog reduction control method after detecting the fog, it is possible to further obtain the fog reduction effect by combining them.

  In addition, as a transfer material carrier, an intermediate transfer member 91a is used instead of the transfer material carrier as in the configuration in which a drum-like member is used instead of the transfer material carrier belt 91, or in the image forming apparatus shown in FIG. A structure in which the toner images are superimposed on the intermediate transfer member 91a and primarily transferred to the intermediate transfer member 91a and then transferred to the transfer material 90 from the intermediate transfer member 91a to the transfer material 90 by the secondary transfer unit 92a. Although not shown, the present invention can be applied to various image forming apparatuses such as a configuration in which a developing device is mounted on a rotating body and sequentially faces one photosensitive drum.

1 is a partial schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. It is an upper view which shows an example of a developing device. 3 is a flowchart illustrating an example of a developer concentration control process according to the present invention. 6 is a flowchart illustrating another example of a developer concentration control process according to the present invention. 6 is a flowchart illustrating another example of a developer concentration control process according to the present invention. 6 is a flowchart illustrating another example of a developer concentration control process according to the present invention. 6 is a flowchart illustrating another example of a developer concentration control process according to the present invention. 6 is a flowchart illustrating another example of a developer concentration control process according to the present invention. It is a schematic block diagram which shows the other example of the image forming apparatus which concerns on this invention. It is a schematic block diagram which shows an example of a developing device.

Explanation of symbols

1 Photosensitive drum (image carrier)
4 Developing device 6 Toner supply device (toner supply means)
45 Inductance sensor (concentration detection means)

Claims (8)

An image carrier on which an electrostatic latent image is formed based on an image information signal;
A developing device containing a developer including toner and a carrier, and developing the electrostatic latent image with the toner;
Toner supply means for supplying toner to the developing device;
Density detecting means for detecting the density of toner in the developing device;
First developer concentration control means for determining a toner replenishment amount based on a value of a detection signal from the density detection means and a reference value for density control, and operating the toner replenishment means;
Second developer concentration control means for determining a toner replenishment amount based on a cumulative value of the number of print pixels of the image information signal and operating the toner replenishment means;
Based on the toner replenishment amount determined by the first developer concentration control means and the toner replenishment amount determined by the second developer concentration control means, the density control in the first developer concentration control means. Determining means for determining whether to change the reference value of
An image forming apparatus comprising: The determining means calculates a toner replenishment amount X determined by the first developer concentration control means and a toner replenishment amount Y determined by the second developer concentration control means, and XY The reference value is changed so that the toner density is lower than the toner density corresponding to the reference value used in the calculation of X when the value is larger than a first predetermined value. The image forming apparatus according to 1. The determining means calculates a toner replenishment amount X determined by the first developer concentration control means and a toner replenishment amount Y determined by the second developer concentration control means, and X / Y The reference value is changed so that the toner density becomes higher than the toner density corresponding to the reference value used in the calculation of X when the value is smaller than a second predetermined value. The image forming apparatus according to 1 or 2. An image carrier on which an electrostatic latent image is formed based on an image information signal;
A developing device containing a developer including toner and a carrier, and developing the electrostatic latent image with the toner;
Toner supply means for supplying toner to the developing device;
Density detecting means for detecting the density of toner in the developing device;
First developer concentration control means for determining a toner replenishment amount based on a value of a detection signal from the density detection means and a reference value for density control, and operating the toner replenishment means;
Second developer concentration control means for determining a toner replenishment amount based on a cumulative value of the number of print pixels of the image information signal and operating the toner replenishment means;
Based on the toner replenishment amount determined by the first developer concentration control means and the toner replenishment amount determined by the second developer concentration control means, the developer by the first developer concentration control means Switching means for switching from density control to developer density control by the second developer density control means;
An image forming apparatus comprising: The switching unit calculates a toner replenishment amount X determined by the first developer concentration control unit and a toner replenishment amount Y determined by the second developer concentration control unit, and XY The image forming apparatus according to claim 4, wherein the switching is performed when the value is larger than a first predetermined value. The switching unit calculates a toner replenishment amount X determined by the first developer concentration control unit and a toner replenishment amount Y determined by the second developer concentration control unit, and X / Y The image forming apparatus according to claim 4, wherein the switching is performed when the value is smaller than a second predetermined value. The switching unit performs an operation of switching from developer concentration control by the first developer concentration control unit to developer concentration control by the second developer concentration control unit, and then performs the first developer concentration control. Based on the toner replenishment amount determined by the means and the toner replenishment amount determined by the second developer concentration control means, the first development from the developer concentration control by the second developer concentration control means. The image forming apparatus according to claim 4, wherein the image forming apparatus is switched to developer density control by an agent density control unit. The switching means performs an operation of switching from developer density control by the first developer density control means to developer density control by the second developer density control means, and then forms a predetermined number of images. The image forming apparatus according to claim 4 , wherein at the time, the developer density control is performed by the first developer density control unit.

Images