JP5945923B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine. Specifically, a toner image obtained by developing a latent image on a latent image carrier with a two-component developer is finally formed on a recording material. The present invention relates to an image forming apparatus that performs image formation by transferring to the above.

  When toner in a two-component developer (hereinafter simply referred to as “developer”) that is circulated and conveyed along the developer circulation conveyance path in the developing device (developing means) is consumed by image formation, The toner is supplied to the developer by the toner supply means. The following methods are known as conventional toner replenishment control methods employed in this toner replenishment.

For example, a toner density detection unit is provided at a predetermined location (toner detection location) on a circulation transport path for circulating and transporting the developer in the developing device, and the toner density detected by the toner density detection unit is used as a target toner density. A necessary target toner supply amount is calculated. A control method is known in which replenished toner is replenished to the developer all at once or at regular intervals so that the calculated target toner replenishment amount is replenished. Hereinafter, this control method is referred to as feedback supply control (FB supply control).
In addition, toner consumption that is expected to be consumed by developing the latent image from pixel writing information (image information) used when the exposure device (latent image forming means) forms the latent image on the latent image carrier. (Predicted value) is obtained. A control method is also possible in which the target toner replenishment amount is calculated from the calculated predicted value, and the replenishment toner is replenished to the developer all at once or at regular intervals so that the target toner replenishment amount of toner is replenished. Are known. Hereinafter, this control method is referred to as feedforward supply control (FF supply control).
Also, a control method that combines FF supply control with FB supply control has been proposed.

  In the FF replenishment control, if the target toner replenishment amount is accurate and the toner of the target toner replenishment amount is accurately replenished, as shown in FIG. The density is stable at the target toner density. However, in general, there are individual differences in toner replenishing devices, and the amount of toner replenished per unit replenishing operation (unit toner replenishing amount) differs depending on the individual toner replenishing device. In other words, the toner replenishing ability varies depending on the individual toner replenishing device. Even if the same toner replenishing device is used, the usage environment such as the temperature and humidity of the place where the image forming apparatus on which the toner replenishing device is installed is installed, the remaining amount of toner in the toner replenishing device, and the gear for driving the toner replenishing device. Unit toner replenishment amount (replenishment capability) varies depending on factors such as motor deterioration. Therefore, even if an accurate target toner supply amount is calculated, the actual toner supply amount does not become the target toner supply amount, and a supply error occurs.

  Patent Document 1 discloses an image forming apparatus capable of correcting a replenishment error caused by an error in a unit toner replenishment amount. In this image forming apparatus, first, prior to the toner supply operation, the toner density before toner supply is detected by the toner density detection means. Thereafter, a target toner replenishment amount is calculated from the detection result of the toner density detection means, and a toner replenishment operation for replenishing the toner of the target toner replenishment amount is executed. After this toner replenishment operation, the toner concentration after toner replenishment is detected by the toner concentration detecting means. At this time, if the target toner replenishment amount calculated from the detection result of the toner concentration detection means before replenishment is accurate and the toner of the target toner replenishment amount is replenished accurately, the toner concentration after toner replenishment is Should match the target toner density. However, in reality, the toner concentration after the toner replenishment does not match the target toner concentration because the toner of the target toner replenishment amount is not accurately replenished due to the replenishment error due to the individual difference of the toner replenishing devices.

  In the image forming apparatus disclosed in Patent Document 1, the difference in toner density before and after toner replenishment is multiplied by the toner replenishment amount per unit toner density difference to calculate a replenishment error due to the current toner replenishment. Since the toner replenishment amount per unit toner density difference can be obtained with high accuracy in advance, the replenishment error calculated here is between the target toner replenishment amount and the actually replenished toner replenishment amount with high accuracy. Match the error. The ratio between the target toner replenishment amount calculated at the current toner replenishment and the replenishment error is used as a correction coefficient (correction value), and the target toner replenishment amount is calculated using this correction coefficient at the time of subsequent toner replenishment.

  When performing toner replenishment with FF replenishment control while continuously printing images with the same image area ratio, if the unit toner replenishment amount is insufficient with respect to the set value, a replenishment operation corresponding to the accurate target toner replenishment amount is performed. Even if it is carried out, the actual toner supply amount becomes smaller than the target toner supply amount every time. Therefore, as shown in FIG. 23, the actual toner density gradually decreases (thinner). Similarly, when the unit toner replenishment amount is excessive with respect to the set value, the actual toner replenishment amount is larger than the target toner replenishment amount every time, so that the actual toner density is as shown in FIG. It gradually gets higher (darker).

  On the other hand, for example, when toner supply is performed by combining FF supply control and FB supply control while continuously printing images with the same image area ratio, the toner concentration in the developer is changed to the target toner concentration over time as shown in FIG. It is possible to stabilize. That is, when the unit toner replenishment amount is insufficient or excessive with respect to the set value, the actual toner replenishment amount gradually deviates from the target toner replenishment amount even if the toner is replenished by the FF replenishment control. However, when the actual toner density deviates from the target toner density beyond the allowable range, the toner supply amount is corrected by the FB supply control. As a result, when images having the same image area ratio are continuously printed, the actual toner density converges to the target toner density over time as shown in FIG.

  However, in the FB replenishment control, after detecting that the actual toner replenishment amount deviates from the target toner replenishment amount beyond the allowable range, the detection result is reflected in the toner replenishment operation. In contrast, toner supply is delayed. Therefore, as shown in FIG. 24, the actual toner density converges to the target toner density after a certain period of time has elapsed since the start of continuous printing of images having the same image area ratio. The initial period (unstable period) is far from the target toner density.

  In addition, when an image having a different image area ratio is continuously printed after the actual toner density has converged to the target toner density, the actual toner supply amount gradually deviates from the target toner supply amount again. As a result, as described above, the toner supply amount is corrected by the FB supply control, and the toner density change as shown in FIG. 24 is repeated again. Therefore, when the unit toner replenishment amount is insufficient or excessive with respect to the set value, in the toner replenishment control in which the FB replenishment control is simply combined with the FF replenishment control, the content of the image information (image area ratio, etc.) changes each time. Since the actual toner supply amount deviates from the target toner supply amount, it is difficult to stabilize the actual toner concentration at the target toner concentration.

  On the other hand, in the conventional image forming apparatus described in Patent Document 1 described above, the period from the detection of the toner concentration before toner replenishment to the detection of the toner concentration after toner replenishment in order to calculate the correction coefficient, the image The forming operation cannot be executed. This is because if the toner is consumed during this period, an error (replenishment error) between the target toner replenishment amount by the toner replenishment and the actual toner replenishment amount replenished by the toner replenishment is calculated from the toner density difference before and after the toner replenishment. This is because an appropriate correction coefficient cannot be calculated because it cannot be calculated. Therefore, in the conventional image forming apparatus described in Patent Document 1, it is necessary to provide a period in which only the toner replenishing operation is performed without executing the image forming operation in order to calculate the correction coefficient. There was a problem that increased.

,
The present invention has been made in view of the above problems, and an object of the present invention is to increase the standby time of the image forming operation in calculating the correction value for correcting the replenishment error, and to actually measure the correction value. An object of the present invention is to provide an image forming apparatus capable of stabilizing a toner density at a target toner density.

In order to achieve the above object, the present invention provides a latent image carrier, a latent image forming means for forming a latent image on the latent image carrier based on image information, and a surface of the developer carrier. The two-component developer is conveyed to the development area by the rotation of the developer carrier, and the toner in the two-component developer is adhered to the latent image on the surface of the latent image carrier in the development area. A developing device for developing, a toner replenishing means for executing a toner replenishing operation to the two-component developer in the developing device, and a target toner replenishing amount calculated from the image information based on the image information. A toner replenishment control unit that calculates a target operation amount of the toner replenishment unit to be replenished by the toner replenishment unit and controls a toner replenishment operation of the toner replenishment unit according to the target operation amount; The latent image is developed by a developing device. In an image forming apparatus that forms an image by finally transferring a toner image formed on a carrier onto a recording material, a correction value storage unit that stores a correction value for correcting the target operation amount, and the developing device A predetermined value between the toner density detected by the toner density detecting means for detecting the toner density of the two-component developer and the toner density detecting means controlled by the toner replenishing control means, and the target toner density. When the above difference occurs, the correction value is calculated based on the difference, and the correction value update processing is performed to update the correction value stored in the correction value storage unit to the calculated correction value. includes a processing unit, the toner supply control means calculates a first target toner supply amount based on the image information, the toner density and the target preparative detected by the toner concentration detecting means The second target toner supply amount is calculated based on the difference value between the density and the final target toner supply amount corresponding to the total value of the first target toner supply amount and the second target toner supply amount. The target motion amount before correction to be replenished is calculated, and the target motion amount before correction is corrected by the correction value stored in the correction value storage means, and the corrected target motion amount after correction is applied to the toner supply means. The toner supply operation is controlled, and the correction value update processing means calculates the correction value based on the accumulated value of the second target toner supply amount used for calculating the target operation amount in the toner supply operation within a predetermined period. It is characterized by that.

  In the present invention, since toner supply is controlled by FF supply control based on image information, if the actual toner supply amount does not match the target toner supply amount and a supply error occurs, as shown in FIG. As a result, the difference between the toner density and the target toner density gradually opens. At this time, even if the FF supply control based on the image information is performed, the difference between the toner density and the target toner density indicates that a supply error has occurred. Therefore, in the present invention, based on this knowledge, when a difference greater than a specified value occurs between the toner density and the target toner density by controlling the toner replenishment operation by the toner replenishment control means, the toner replenishing means is based on the difference. A correction value for correcting the target motion amount is calculated. By controlling the toner replenishment operation in accordance with the target operation amount corrected by the correction value calculated in this way, the deviation between the actual toner replenishment amount and the target toner replenishment amount by the FF replenishment control is reduced, and the replenishment error is reduced. It is reduced. Therefore, when an image is formed after the correction value is calculated in this way, unlike the case where the above-described FF supply control and FB supply control are simply combined, any image area ratio image is formed. However, the toner density can be stabilized at the target toner density from the beginning of the image formation.

  In addition, the toner density used for calculating the correction value is a toner density that has fluctuated due to control of the toner supply operation by the toner supply control means, that is, FF supply control based on the image information. This toner density needs to be detected while performing the image forming operation, and does not increase the waiting time of the image forming operation in calculating the correction value for correcting the replenishment error.

  As described above, according to the present invention, it is possible to stabilize the actual toner density at the target toner density without increasing the standby time of the image forming operation in calculating the correction value for correcting the replenishment error. An excellent effect is obtained.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 3 is a schematic diagram illustrating a configuration of a process unit for generating a Y toner image in the printer. FIG. 3 is an explanatory diagram showing a development unit configuration around a developer circulation conveyance path in which the developer circulates in the development unit in the process unit. FIG. 3 is a block diagram illustrating an example of a control system that executes toner supply control according to the embodiment. 5 is a flowchart showing a flow of toner supply control. FIG. 6 is an explanatory diagram for explaining a calculation process of a final target toner supply amount in the embodiment. It is explanatory drawing about FB replenishment control in embodiment. FIG. 10 is an explanatory diagram showing a change in toner density before updating a correction value. FIG. 9 is an explanatory diagram illustrating a proportional replenishment amount calculated by a proportional replenishment method with respect to toner density fluctuation as illustrated in FIG. 8. FIG. 9 is an explanatory diagram illustrating an integrated replenishment amount calculated by an integral replenishment method with respect to toner density fluctuation as illustrated in FIG. 8. 6 is a graph showing a change in toner density in a print job when the toner density is greatly deviated from a target toner density at the time of ending the print job. 6 is a graph showing a change in toner density in a print job when the print job is started from a state where the toner density is significantly different from a target toner density. FIG. 6 is an explanatory diagram for explaining a method of determining an initial density threshold used for determining whether or not the toner density at the start of a print job is out of a target range. 10 is a flowchart showing a flow of toner supply control in Modification 2. 10 is a flowchart showing a flow of toner replenishment control in Modification 3. 10 is a flowchart showing a flow of toner replenishment control in Modification 4. 14 is a graph showing a change in toner density in a print job when the print job is started from a state in which the toner density greatly deviates from a target toner density in Modification 4. FIG. 10 is an explanatory diagram when it is determined that a toner density stable section in which the toner density is stable. FIG. 10 is an explanatory diagram when it is determined that the toner density is not stable. 10 is a flowchart showing a flow of toner supply control in Modification 5. (A) is explanatory drawing which shows the total image formation time in the case of performing correction value calculation regularly in the conventional apparatus which required the time for exclusive use for calculating a correction value. (B) is explanatory drawing which shows the total image formation time in the case of performing correction value calculation with the same frequency, performing the same image formation as the conventional apparatus in embodiment. FIG. 4 is an explanatory diagram showing a state in which the toner concentration in the developer is stable at the target toner concentration from the initial time to time. FIG. 7 is an explanatory diagram showing a state where the toner density in the developer deviates from the target toner density when toner is replenished in a state where the unit toner replenishment amount is not appropriate when toner replenishment is performed only by FF replenishment control. When toner replenishment is performed by combining FF replenishment control with FB replenishment control, if toner replenishment is performed when the unit toner replenishment amount is not appropriate, the toner concentration in the developer eventually converges to the target toner concentration. It is explanatory drawing which shows a state.

An embodiment in which the present invention is applied to an electrophotographic printer (hereinafter simply referred to as “printer”) as an image forming apparatus will be described below.
First, a basic configuration of the printer according to the present embodiment will be described.
FIG. 1 is a schematic configuration diagram illustrating a printer according to the present embodiment.
This printer includes four process units 1Y, 1C, 1M, and 1K for yellow, magenta, cyan, and black (hereinafter referred to as Y, C, M, and K). These use Y, C, M, and K toners of different colors as image forming substances for forming an image, but the other configurations are the same.

FIG. 2 is a schematic diagram showing a configuration of a process unit 1Y for generating a Y toner image.
The process unit 1Y includes a photoreceptor unit 2Y and a developing unit 7Y. The photoconductor unit 2Y and the developing unit 7Y are configured to be detachable from the printer main body as a process unit 1Y. However, in a state where it is detached from the printer main body, the developing unit 7Y can be attached to and detached from a photosensitive unit (not shown).

The photoreceptor unit 2Y includes a drum-shaped photoreceptor 3Y as a latent image carrier, a drum cleaning device 4Y, a static eliminator (not shown), a charging device 5Y, and the like.
The charging device 5Y, which is a charging unit, uniformly charges the surface of the photoreceptor 3Y, which is driven to rotate clockwise in FIG. 2 by a driving unit (not shown), by the charging roller 6Y. Specifically, a charging bias is applied from a power source (not shown) to the charging roller 6Y that is driven to rotate counterclockwise in FIG. 2, and the charging roller 6Y is brought close to or in contact with the photosensitive member 3Y, whereby the photosensitive member 3Y. Is uniformly charged. Instead of the charging roller 6Y, another charging member such as a charging brush may be used in proximity or contact. Further, a charger that uniformly charges the photosensitive member 3Y by a charger method, such as a scorotron charger, may be used. The surface of the photoreceptor 3Y uniformly charged by the charging device 5Y is exposed and scanned by a laser beam emitted from an optical writing unit 20 serving as a latent image forming unit, which will be described later, and carries an electrostatic latent image for Y.

FIG. 3 is an explanatory diagram showing the configuration of the developing unit around the developer circulation conveyance path where the developer circulates in the developing unit.
As shown in FIGS. 2 and 3, the developing unit 7 </ b> Y that is a developing device has a first conveying screw 8 </ b> Y as a developer conveying means disposed in the developer stirring and conveying path 9 </ b> Y. Further, a second conveying screw 11Y as a developer conveying means is disposed in the developer supply conveying path 14Y. Further, the developing unit 7Y includes a toner concentration sensor 10Y including a magnetic permeability sensor as a toner concentration detecting unit, a second conveying screw 11Y as a developer conveying unit, a developing roll 12Y as a developer carrying member, and a developer regulating member. The doctor blade 13Y is also provided. In these two transport paths, a Y developer (not shown) that is a two-component developer composed of a magnetic carrier and a negatively chargeable Y toner is accommodated.

  The first conveying screw 8Y is rotationally driven by a driving means (not shown) to convey the Y developer in the developer stirring and conveying path 9Y to the front side in FIG. 2 (direction of arrow A in FIG. 3). The Y developer in the middle of conveyance is supplied by a toner concentration sensor 10Y fixed on the first conveyance screw 8Y to the replenishment point (in this embodiment, the developer agitation conveyance path) facing the toner replenishing port 17Y in the developer agitation conveyance path 9Y. The toner concentration of the Y developer passing through a predetermined detection location (near the downstream end of the developer stirring and conveying path 9Y in the present embodiment) located downstream of the developer circulation direction in the vicinity of the upstream end of 9Y) is detected. . Then, the Y developer conveyed to the downstream end of the developer agitation conveyance path 9Y by the first conveyance screw 8Y enters the upstream end of the developer supply conveyance path 14Y from the end communication port 18Y.

  The second transport screw 11Y in the developer supply transport path 14Y is rotationally driven by a driving unit (not shown) to transport the Y developer to the back side in FIG. 2 (in the direction of arrow A in FIG. 3). In this way, the developing roll 12Y is arranged in a posture parallel to the second conveying screw 11Y above the second conveying screw 11Y that conveys the Y developer in FIG. The developing roll 12Y has a configuration in which a fixedly arranged magnet roller 16Y is included in a developing sleeve 15Y as a developer carrying member made of a non-magnetic sleeve that is driven to rotate counterclockwise in FIG. . A part of the Y developer conveyed by the second conveying screw 11Y is pumped up to the surface of the developing sleeve 15Y by the magnetic force generated by the magnet roller 16Y. Then, after the layer thickness is regulated by a doctor blade 13Y disposed so as to maintain a predetermined gap from the surface of the developing sleeve 15Y, the layer is conveyed to a developing region facing the photosensitive member 3Y, and is transferred onto the photosensitive member 3Y. Y toner is adhered to the electrostatic latent image for Y. This adhesion forms a Y toner image on the photoreceptor 3Y. The Y developer that has consumed Y toner by the development is returned onto the second conveying screw 11Y as the developing sleeve 15Y rotates. Then, the Y developer transported to the downstream end of the developer supply transport path 14Y by the second transport screw 11Y returns to the upstream end of the developer stirring transport path 9Y through the end communication port 19Y. In this way, the Y developer is circulated and conveyed in the developing unit.

  The Y toner image formed on the photoreceptor 3Y is intermediately transferred to an intermediate transfer belt 41 that is an intermediate transfer body. The drum cleaning device 4Y of the photoreceptor unit 2Y removes toner remaining on the surface of the photoreceptor 3Y after the intermediate transfer process. As a result, the surface of the photoreceptor 3Y subjected to the cleaning process is neutralized by a neutralizing device (not shown). By this charge removal, the surface of the photoreceptor 3Y is initialized and prepared for the next image formation. Similarly, in the process units 1C, 1M, and 1K for other colors, C toner images, M toner images, and K toner images are formed on the photoreceptors 3C, 3M, and 3K, and the intermediate transfer belt 41 is subjected to intermediate transfer. Is done.

  An optical writing unit 20 is disposed below the process units 1Y, 1C, 1M, and 1K in FIG. The optical writing unit 20 irradiates the photoconductors 3Y, 3C, 3M, and 3K of the process units 1Y, 1C, 1M, and 1K with the laser light L emitted based on the image information. As a result, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 3Y, 3C, 3M, and 3K, respectively. The optical writing unit 20 deflects the laser light L emitted from the light source by the polygon mirror 21 that is rotationally driven by a motor, and passes through the photoreceptors 3Y, 3C, 3M, and 3K via a plurality of optical lenses and mirrors. Is irradiated. Instead of such a configuration, an LED array may be used.

  A first paper feed cassette 31 and a second paper feed cassette 32 are disposed below the optical writing unit 20 so as to overlap in the vertical direction. In each of these paper feed cassettes, a plurality of recording papers P, which are recording materials, are stored in a stack of recording papers, and a first paper feed roller is placed on the top recording paper P. 31a and the second paper feed roller 32a are in contact with each other. When the first paper feed roller 31a is driven to rotate counterclockwise in FIG. 1 by driving means (not shown), the uppermost recording paper P in the first paper feed cassette 31 is vertically oriented on the right side of the cassette in FIG. The paper is discharged toward the paper feed path 33 arranged so as to extend. When the second paper feed roller 32a is rotated counterclockwise in FIG. 1 by driving means (not shown), the uppermost recording paper P in the second paper feed cassette 32 is discharged toward the paper feed path 33. The A plurality of transport roller pairs 34 are arranged in the paper feed path 33, and the recording paper P fed into the paper feed path 33 is sandwiched between the rollers of the transport roller pair 34 while being fed between the paper feed paths 33. 1 is conveyed from the lower side to the upper side in FIG. A registration roller pair 35 is disposed at the end of the paper feed path 33. The registration roller pair 35 temporarily stops the rotation of both rollers as soon as the recording paper P sent from the conveyance roller pair 34 is sandwiched between the rollers. Then, the recording paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.

  Above each process unit 1Y, 1C, 1M, and 1K in FIG. 1, a transfer unit 40 is disposed to endlessly move the intermediate transfer belt 41 counterclockwise in FIG. In addition to the intermediate transfer belt 41, the transfer unit 40 includes a belt cleaning unit 42, a first bracket 43, a second bracket 44, and the like. Also provided are four primary transfer rollers 45Y, 45C, 45M, 45K, a secondary transfer backup roller 46, a drive roller 47, an auxiliary roller 48, a tension roller 49, and the like. The intermediate transfer belt 41 is endlessly moved counterclockwise in FIG. 1 by the rotational driving of the driving roller 47 while being stretched around these rollers. The four primary transfer rollers 45Y, 45C, 45M, and 45K sandwich the intermediate transfer belt 41 that moves endlessly between the photoreceptors 3Y, 3C, 3M, and 3K to form primary transfer nips, respectively. Yes. A transfer bias having a polarity opposite to that of the toner (in this embodiment, a positive polarity) is applied to the inner peripheral surface of the intermediate transfer belt 41. The intermediate transfer belt 41 sequentially passes through the primary transfer nips for Y, C, M, and K along with the endless movement thereof, and the photoreceptors 3Y, 3C, 3M, and 3K are disposed on the outer peripheral surface thereof. The upper color toner images are primarily transferred so as to overlap each other. As a result, a four-color superimposed toner image (hereinafter referred to as “four-color toner image”) is formed on the intermediate transfer belt 41.

  The secondary transfer backup roller 46 sandwiches the intermediate transfer belt 41 with the secondary transfer roller 50 disposed outside the loop of the intermediate transfer belt 41 to form a secondary transfer nip. The registration roller pair 35 described above feeds the recording paper P sandwiched between the rollers toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 41. The four-color toner image on the intermediate transfer belt 41 is affected by the secondary transfer electric field formed between the secondary transfer roller 50 to which the secondary transfer bias is applied and the secondary transfer backup roller 46, and the influence of the nip pressure. The secondary transfer is batch-transferred onto the recording paper P in the secondary transfer nip. Then, combined with the white color of the recording paper P, a full color toner image is obtained.

  Untransferred toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 41 after passing through the secondary transfer nip. This is cleaned by the belt cleaning unit 42. In the belt cleaning unit 42, the cleaning blade 42a is brought into contact with the front surface of the intermediate transfer belt 41, whereby the transfer residual toner on the belt is scraped off and removed.

  The first bracket 43 of the transfer unit 40 swings at a predetermined rotation angle about the rotation axis of the auxiliary roller 48 as the solenoid (not shown) is turned on / off. In the case of forming a monochrome image, the printer according to the present embodiment rotates the first bracket 43 a little counterclockwise in the drawing by driving the solenoid described above. By this rotation, the Y, C, and M primary transfer rollers 45Y, 45C, and 45M are revolved counterclockwise in the drawing around the rotation axis of the auxiliary roller 48, whereby the intermediate transfer belt 41 is moved to the Y direction. , C and M photoconductors 3Y, 3C and 3M. Of the four process units 1Y, 1C, 1M, and 1K, only the K process unit 1K is driven to form a monochrome image. Accordingly, it is possible to avoid exhaustion of the process units due to wastefully driving the process units for Y, C, and M during monochrome image formation.

  A fixing unit 60 as a fixing unit is disposed above the secondary transfer nip in the figure. The fixing unit 60 includes a pressure heating roller 61 that includes a heat source such as a halogen lamp, and a fixing belt unit 62. The fixing belt unit 62 includes a fixing belt 64, a heating roller 63 containing a heat source such as a halogen lamp, a tension roller 65, a driving roller 66, a temperature sensor (not shown), and the like. Then, the endless fixing belt 64 is endlessly moved in the counterclockwise direction in FIG. 1 while being stretched by the heating roller 63, the tension roller 65, and the driving roller 66. In the process of endless movement, the fixing belt 64 is heated from the back side by the heating roller 63. A pressure heating roller 61 that is driven to rotate in the clockwise direction in FIG. 1 is in contact with the surface of the fixing belt 64 that is heated in this manner. Thereby, a fixing nip where the pressure heating roller 61 and the fixing belt 64 abut is formed.

  Outside the loop of the fixing belt 64, a temperature sensor (not shown) is disposed so as to face the front surface of the fixing belt 64 with a predetermined gap, and the fixing belt 64 just before entering the fixing nip. Detect surface temperature. This detection result is sent to a fixing power supply circuit (not shown). The fixing power supply circuit performs on / off control of power supply to the heat generation source included in the heating roller 63 and the heat generation source included in the pressure heating roller 61 based on the detection result of the temperature sensor. As a result, the surface temperature of the fixing belt 64 is maintained at about 140.degree. The recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 41 and then fed into the fixing unit 60. Then, in the process of being conveyed from the lower side to the upper side in the drawing while being sandwiched by the fixing nip in the fixing unit 60, the full-color toner image is applied to the recording paper P by being heated or pressed by the fixing belt 64. To settle.

  The recording paper P subjected to the fixing process in this manner is discharged outside the apparatus after passing between the rollers of the paper discharge roller pair 67. A stack unit 68 is formed on the upper surface of the housing of the printer main body, and the recording paper P discharged to the outside by the discharge roller pair 67 is sequentially stacked on the stack unit 68.

  Above the transfer unit 40, toner cartridges 72Y, 72C, 72M, and 72K, which are four toner containers that respectively store Y toner, C toner, M toner, and K toner, are disposed. The color toners in the toner cartridges 72Y, 72C, 72M, and 72K are appropriately supplied to the developing units 7Y, 7C, 7M, and 7K of the process units 1Y, 1C, 1M, and 1K by the toner replenishing device 70, respectively. The toner cartridges 72Y, 72C, 72M, and 72K are detachable from the printer main body independently of the process units 1Y, 1C, 1M, and 1K.

Hereinafter, toner replenishment control, which is a characteristic part of the present invention, will be described.
In this embodiment, the toner replenishment operation can be executed independently for each of yellow, magenta, cyan, and black, but the toner replenishment operations are the same. Therefore, in the following description, description of color-coded codes Y, C, M, and K is omitted.

FIG. 4 is a block diagram illustrating an example of a control system that executes toner supply control according to the present embodiment.
In the control system shown in FIG. 4, the toner density information is input from the toner density sensor 10 attached to the developing unit 7 to the control device 100 as the toner replenishment control means. Further, image information used for forming a latent image is input from the optical writing unit 20 to the control device 100. The control device 100 according to the present embodiment executes toner supply control using both FB supply control using toner density information and FF supply control using image information.

FIG. 5 is a flowchart showing the flow of toner supply control in the present embodiment.
When a print job is input (S1), first, the toner concentration of the developer in the developing unit 7 is detected by the toner concentration sensor 10 (S2). In the present exemplary embodiment, the unit of toner concentration will be described by the mass ratio [wt%] of toner and carrier. Further, the amount of toner is expressed by mass [g], and will be described as a positive value when the toner is replenished and a negative value when the toner is consumed.

  When the toner density is detected in this way, it is determined whether or not the detection result is within the target range (S3). This target range is set, for example, within a range from the target toner density to a specified value (initial density threshold). At this time, if the detected toner density is within the target range (Yes in S3), the correction value update flag is turned ON (S4), and integration of the FB replenishment amount described later in the print job is started (S5). ). The integrated value of the FB replenishment amount is stored in the storage device 101. On the other hand, when the detected toner density is out of the target range (No in S3), the correction value update flag is turned OFF (S6), and the FB replenishment amount in the print job is not integrated.

Subsequently, an image forming operation in accordance with the contents of the input print job is started (S7), and the control device 100 performs optical writing when forming a latent image for the current image formation on the photoconductor 3. Image information used by the unit 20 is acquired (S8). The acquired image information is stored in the storage device 101. Specifically, the image information here refers to, for example, the toner adhesion amount to the photoreceptor 3 per unit image area or the image area ratio per unit image area (when the predetermined toner adhesion amount is 1). The ratio of the amount of toner adhering to the unit image area). The unit image area here can be arbitrarily set, for example, the area of one sheet of paper on which an output image is formed, or the area of one region obtained by further dividing the area of one sheet of paper. Further, for example, the area of the output image output within a specified time may be the unit image area. However, if the unit image area is set to be large, for example, the area of a plurality of sheets of paper is set as the unit image area, the timing for obtaining the image information is delayed, and therefore the supply operation start timing of the FF supply control may be delayed. Therefore, it is desirable that the unit image area be as small as possible.
Note that the image information is any information as long as it is information that can specify the toner adhesion amount (toner amount consumed by the developing unit) that adheres to the photoreceptor by the image forming operation corresponding to the image information. Good.

Further, the control device 100 detects the toner concentration of the developer in the developing unit 7 by using the toner concentration sensor 10 (S9). The detected toner density report is stored in the storage device 101. Further, the control device 100 reads out from the storage device 101 the correction value calculated by the method described later during the previous image forming operation (S10). Thereafter, the control device 100 uses the image information acquired in S4 and the toner density detected by the toner density sensor 10 in S9, and the toner replenishment amount (before correction) necessary to set the toner density to the target toner density. Target toner replenishment amount) is calculated. Then, using the correction value read in S10, the target toner supply amount before correction is corrected, and the final target toner supply amount is calculated (S11). In this embodiment, the final target toner supply amount (target operation amount) is calculated from the following equation (1). How to correct the pre-correction target toner supply amount using the correction value It is determined appropriately.
Target toner supply amount = Target toner supply amount before correction x Correction value (1)

FIG. 6 is an explanatory diagram for explaining a final target toner supply amount calculation process in the present embodiment.
Based on the image information from the optical writing unit 20, the control device 100 predicts the amount of toner consumed by the image forming operation based on the image information, and is necessary for suppressing a decrease in toner density due to the toner consumption. The toner supply amount (FF supply amount) is calculated. In addition, the control device 100 restores the current toner density to the target toner density based on the difference value between the toner density information from the toner density sensor 10 and the target toner density stored in the storage device 101. A necessary toner supply amount (FB supply amount) is calculated. Then, the control device 100 adds the FB replenishment amount and the FF replenishment amount calculated in this way, and calculates the added value as the target toner replenishment amount before correction. After calculating the pre-correction target toner supply amount, the control device 100 corrects the pre-correction target toner supply amount using the correction value stored in the storage device 101.

FIG. 7 is an explanatory diagram of the FB replenishment control in the present embodiment.
In the FB replenishment control of this embodiment, the sum of the proportional replenishment amount calculated by the proportional replenishment method and the integral replenishment amount calculated by the integral replenishment method is calculated as the FB replenishment amount. In the proportional replenishment method, a toner replenishment amount (proportional replenishment amount) proportional to the difference value between the detected toner density and the target toner density is calculated. In the integral replenishment method, the difference value between the detected toner density and the target toner density is integrated over time, and a toner replenishment amount (integrated replenishment amount) proportional to the integral value is calculated.

  The proportional supply amount calculated by the proportional supply method with respect to the toner density fluctuation as shown in FIG. 8 is as shown in FIG. In the proportional replenishment method, the proportional replenishment amount increases as the difference value between the detected toner density and the target toner concentration increases, the proportional replenishment amount decreases as the difference value decreases, and the difference value becomes zero. If the toner density matches the target toner density, the proportional replenishment amount is also zero.

  On the other hand, the integrated replenishment amount calculated by the integral replenishment method with respect to the toner density fluctuation as shown in FIG. 8 is as shown in FIG. In the integral replenishment method, when the difference between the detected toner concentration and the target toner concentration starts to be small, the integral replenishment amount is small. When the difference between the detected toner concentration and the target toner concentration continuously occurs, the integral replenishment amount Gradually increases. Also, in the integral replenishment method, even if the difference value between the detected toner density and the target toner concentration becomes zero, the integral replenishment amount is calculated according to the accumulated difference value so far. Unlike the above, the integral replenishment amount does not become zero. Therefore, even when the actual toner replenishment amount is insufficient or excessive with respect to the target toner replenishment amount, and the toner density fluctuation only by the FF replenishment control shows the behavior as shown in FIG. By performing toner replenishment of the FB replenishment amount including the replenishment amount, the shortage or excess can be corrected, and the toner density can be brought close to the target toner density.

  The final target toner replenishment amount calculated in S11 is stored in the storage device 101. However, since the correction value has not yet been calculated in the first image forming operation, the storage device 101 stores the initial correction value in advance. Remember me. At the time of the first image forming operation, the final target toner supply amount is calculated using this initial value. This initial value may be an arbitrary value, but if the initial value is too large or too small, the amount of toner replenishment will be excessive or too small during the first image forming operation. Therefore, it is desirable to set the initial value to a value in which the target toner supply amount before correction is directly calculated as the final target toner supply amount.

  When the calculation of the final target toner supply amount is completed, the control device 100 controls the toner supply operation of the toner supply device 70 so that the toner of the target toner supply amount is supplied to the developing unit 7 (S12). If there is an image to be formed next (Yes in S13), the process returns to S8, the image information is acquired, the target toner replenishment amount is calculated again, and the toner is replenished (S8 to S12). ).

  When there are no more images to be formed next (No in S13), the image forming operation is terminated (S14). Then, it is determined whether or not the correction value update flag is ON (S15). If the correction value update flag is OFF (No in S15), the process is ended as it is. On the other hand, when the correction value update flag is ON (Yes in S15), the control device 100 determines the integrated value of the FB replenishment amount stored in the storage device 101 (according to the FB replenishment control performed during the current print job). (Total toner replenishment amount) is acquired (S16), and the update process of the correction value to be used next time is executed using this (S17).

  In the correction value update processing of the present embodiment, the control device 100 selects the correction value change amount according to the selection condition shown in Table 1 below according to the FB replenishment amount integrated value in the print job acquired in S16. . Then, the control device 100 adds the selected correction value change amount to the current correction value stored in the storage device 101, and sets this as a new correction value. Thereafter, the control device 100 rewrites the correction value stored in the storage device 101 with a new correction value. The storage area for storing the correction value is preferably a non-volatile memory so that the stored correction value is not lost even when the power is turned off.

  In the present embodiment, the update threshold value 1 is set to a value larger than zero, and the update threshold value 2 is set to a value smaller than zero. When “FB replenishment amount integrated value ≧ update threshold 1”, it indicates that toner replenishment during the print job was in the following situation. In other words, the actual toner density is the target toner even though the FF replenishment control performed during the print job supplies toner for the amount of FF replenishment (the amount of toner consumed by image formation of the print job). Therefore, the toner is supplied by the FB supply amount by the FB supply control so that the difference between the actual toner density and the target toner density generated by the FF supply control is compensated. This situation can be said to have occurred because the actual replenishment amount is insufficient in consideration of the relatively high accuracy of the FF replenishment amount calculated in the FF replenishment control.

  That is, it can be understood from the result that “FB replenishment amount integrated value ≧ update threshold 1” that the actual replenishment amount is insufficient. In this embodiment, when “FB replenishment amount integrated value ≧ update threshold value 1”, as shown in Table 1, a correction value change amount 1 that takes a positive value is selected, and this correction value change amount 1 is The current correction value in the storage device 101 is added. As a result, the new correction value is larger than the current correction value, and the final target toner replenishment is performed even when the same amount of toner is replenished by the FF replenishment control during the next and subsequent toner replenishment operations. A large amount will be calculated. As a result, the toner replenishment error corresponding to the FF replenishment amount by the FF replenishment control becomes smaller at the next and subsequent toner replenishment operations, and the FB replenishment amount integrated value at the next and subsequent toner replenishment operations becomes smaller than the current one.

  On the other hand, when “FB replenishment amount integrated value ≦ update threshold 2”, it indicates that the toner replenishment during the print job was in the following situation. In other words, the actual toner density is the target toner even though the FF replenishment control performed during the print job supplies toner for the amount of FF replenishment (the amount of toner consumed by image formation of the print job). Therefore, the toner supply is limited by the FB supply amount by the FB supply control, and the difference between the actual toner density and the target toner density generated by the FF supply control is reduced. This situation occurs because the actual replenishment amount is excessive.

  That is, it can be understood from the result that “FB replenishment amount integrated value ≦ update threshold 2” that the actual replenishment amount is excessive. In the present embodiment, when “FB replenishment amount integrated value ≦ update threshold value 2”, as shown in Table 1, the correction value change amount 2 that takes a negative value is selected, and this correction value change amount 2 is The current correction value in the storage device 101 is added. As a result, the new correction value is smaller than the current correction value, and the final target toner replenishment is performed even when the same FF replenishment amount of toner is replenished during the next and subsequent toner replenishment operations. The amount is calculated with a small amount. As a result, the toner replenishment error corresponding to the FF replenishment amount by the FF replenishment control becomes smaller at the next and subsequent toner replenishment operations, and the FB replenishment amount integrated value at the next and subsequent toner replenishment operations becomes smaller than the current one.

  By repeatedly performing such correction value update processing, the toner replenishment error corresponding to the FF replenishment amount by the FF replenishment control can be finally reduced or made zero. In this case, the toner density can be stabilized at the target toner density only by the FF supply control. For this reason, the FB replenishment control is not performed, and the FB replenishment amount integrated value is almost zero, so the correction value update process is not performed. However, even if the amount of toner replenishment operation is the same, the actual replenishment amount changes due to environmental changes, deterioration over time, etc., so that the toner concentration cannot be stabilized at the target toner concentration again only by FF replenishment control. In this case, the correction value updating process is performed again.

  Here, if the actual toner replenishment amount coincides with the target toner replenishment amount, the FB replenishment control is not performed because the toner concentration is stabilized at the target toner concentration only by the FF replenishment control. The value is zero. However, in actuality, the FB replenishment amount is not limited even if the actual toner replenishment amount matches the target toner amount due to noise in the toner density detection or the bias of the toner in the developer circulating in the developing unit 7. Normally, the integrated value does not become zero. Therefore, in this embodiment, the range in which the FB replenishment amount integrated value is larger than the update threshold 2 and smaller than the update threshold 1 is set as an error range (allowable range), the correction value change amount is set to zero, and the correction value The update is not performed. As a method for determining the appropriate update threshold value 1 and update threshold value 2, for example, the maximum value and the minimum value of the FB supply amount integrated value when the actual toner supply amount matches the target toner supply amount are obtained by experiments in advance. For example, a method of estimating and setting the maximum value as the update threshold value 1 and the minimum value as the update threshold value 2 may be used.

  Further, since the set values of the correction value change amount 1 and the correction value change amount 2 become the correction value resolution as they are, the correction accuracy of the replenishment error becomes higher as the absolute value is set smaller. On the other hand, if the absolute value of the correction value change amount is set too small, the correction value update count that is repeated until the replenishment error is corrected increases, which takes time. In consideration of these, it is desirable that the set values of the correction value change amount 1 and the correction value change amount 2 are set to absolute values as large as possible within a range where necessary correction accuracy can be obtained.

  In this embodiment, when the toner density detected before starting the image formation of the input print job is out of the target range (No in S3), the correction value update flag is turned OFF (S4). The correction value update process (S17) is not executed. The reason will be described below.

FIG. 11 is a graph showing the toner density fluctuation in the print job when the toner density deviates greatly from the target toner density when the print job is completed.
In the situation shown in FIG. 11, for example, since a replenishment error occurs during the print job, the difference between the toner density and the target toner density gradually opens, and as a result, FB replenishment control is performed. Although the toner density approaches the target toner density by the execution of the FB replenishment control, the image formation is completed before the toner density approaches the target toner density. The FB replenishment amount calculated by the FB replenishment control at this time is calculated so as to compensate for the deviation between the toner density and the target toner density caused by the replenishment error of the FF replenishment control during the print job. Therefore, a high correlation between the integrated value of the FB replenishment amount by the FB replenishment control and the replenishment error by the FF replenishment control is maintained. Therefore, since it is possible to grasp whether the actual toner supply amount is excessive or insufficient from the integrated value of the FB supply amount, it is updated to an appropriate correction value. Is improved.

FIG. 12 is a graph showing a change in toner density in a print job when the print job is started from a state where the toner density greatly deviates from the target toner density.
If the toner density cannot be sufficiently close to the target toner density as shown in FIG. 11 during the previous print job, the toner density and the target toner density before the start of the current print job are set as shown in FIG. Is away. In this case, the FB replenishment control is performed in the toner replenishment operation during the current print job, and the toner amount (initial error) corresponding to the difference between the toner density at the start of the current print job and the target toner density is compensated. The density gradually approaches the target toner density. The FB replenishment amount calculated by the FB replenishment control at this time not only compensates for the deviation between the toner density and the target toner density caused by the replenishment error due to the FF replenishment control, but also the difference between the initial toner density and the target toner density. Calculate the value to compensate. Therefore, the correlation between the FB replenishment amount integrated value by the FB replenishment control and the replenishment error by the FF replenishment control collapses, and it is accurately grasped from the FB replenishment amount integrated value whether the actual toner replenishment amount is excessive or insufficient. Can not do it.

  Therefore, if the correction value is updated even when there is a difference between the initial toner density and the target toner density, for example, a correction value that can appropriately correct the replenishment error is set. Even in this case, the correction value may be updated because the FB supply control is performed. In this case, although it is not necessary to update the correction value, the correction value is updated, so that a replenishment error occurs in the next and subsequent toner replenishment operations.

FIG. 13 is an explanatory diagram for explaining a method of determining an initial density threshold used for determining whether or not the toner density at the start of a print job is out of the target range.
Originally, if there is even a slight difference between the toner density at the beginning of the print job and the target toner density, the toner replenishment amount to compensate for the difference is included in the FB replenishment amount integrated value. A strict correlation between the replenishment amount integrated value and the replenishment error cannot be obtained. However, as described above, the toner density detection value includes a slight error or fluctuation due to noise in toner density detection, bias of the toner in the developer circulating in the developing unit 7, and the like.

  For this reason, in this embodiment, a range (target toner density ± initial density threshold range) until the target toner density is separated by the initial density threshold is set as an error range (allowable range), and the initial toner density in the print job falls within this range. If it is maintained, the correction value update flag is set to ON even if it does not completely match the target toner density. For example, the initial density threshold setting value is obtained by estimating the maximum value and the minimum value when the toner density of a developer whose toner density is known is detected by a toner density sensor by experiments in advance. For example, a method for setting an initial density threshold value may be used.

  At this time, if the detected toner density tends to swing to a higher side than the target toner density or conversely tends to swing to a lower side, the initial density threshold value is a plus side or a minus side with respect to the target toner density. The target range may be set by setting individual values for each side. In addition, when the detected toner density can only swing to the higher side than the target toner density or to the lower side, the initial density threshold is set only on the positive side with respect to the target toner density. The target range may be set only on the minus side. Further, when the toner density sensor has a low detection resolution and a constant toner density value is detected even if the actual toner density fluctuates within the target range (for example, the detection resolution is a toner density of 1 [wt%]). However, when the width of the target range is about 0.1 [wt%], the detected toner density matches the target toner density without setting the initial density threshold (without setting the target range). You may judge by whether or not.

[Modification 1]
Next, a modified example of the correction value update process in the present embodiment (hereinafter, this modified example is referred to as “modified example 1”) will be described.
In the correction value update process of the first modification, the control device 100 selects the correction value change amount according to the selection condition shown in Table 2 below according to the FB replenishment amount integrated value in the print job acquired in S16. To do. In the above embodiment, there are three selection condition categories, but in the first modification, there are five selection condition categories.

  For example, when the FB replenishment amount integrated value is a positive value, the correction value is updated so as to increase the correction value. However, by increasing the update threshold and increasing the selection condition, the FB replenishment amount integrated value The amount of change in the correction value that varies depending on the magnitude can be changed to return the extent to which the correction value is increased. The same applies when the FB replenishment amount integrated value is a negative value. In the first modification, four update thresholds having a relationship of update threshold 3> update threshold 1> 0> update threshold 2> update threshold 4 are prepared, but the number of update thresholds is not limited thereto. .

  The larger the difference between the toner concentration and the target toner concentration, the larger the FB replenishment amount integrated value. Therefore, a larger FB replenishment amount integrated value indicates that the toner concentration is far away from the target toner concentration. This indicates that the current correction value is significantly different from the appropriate correction value. Therefore, in the first modification, when the FB replenishment amount integrated value is large, the large correction value change amounts 3 and 4 are adopted to largely update the correction value until the correction value is corrected to an appropriate correction value. To shorten the time.

  On the other hand, a small FB replenishment amount integrated value indicates that the difference between the toner density and the target toner density is small, and this indicates that the deviation between the current correction value and the appropriate correction value is small. Therefore, in the first modification, when the FB replenishment amount integrated value is small, the correction value is finely updated by adopting the small correction value change amounts 1 and 2, and the correction value is corrected to an appropriate correction value with high accuracy. I am doing so.

[Modification 2]
Next, a description will be given of a modification of the method for determining whether or not to perform the correction value update process in the present embodiment (hereinafter, this modification is referred to as “Modification 2”).
FIG. 14 is a flowchart showing the flow of toner supply control in the second modification.
In the above embodiment, the integrated value of the FB replenishment amount in the print job is detected (S5, S16), the correction value change amount is selected according to the FB replenishment amount integrated value, and the updated correction value is calculated. ing. On the other hand, in the second modification, the FB replenishment amount integrated value is not detected, but the correction value change amount is selected according to the integral replenishment amount calculated in the FB replenishment control, and the updated correction value is calculated.

  As described above, the FB replenishment amount calculated by the FB replenishment control is a total value of the proportional replenishment amount and the integral replenishment amount. As shown in FIG. 9, the proportional replenishment amount becomes zero when the toner concentration matches the target toner concentration. However, the integral replenishment amount is equal to the target toner concentration as shown in FIG. However, the value does not become zero, and a value corresponding to the history (the difference between the toner density and the target toner density) is calculated. That is, even when the actual toner replenishment amount is insufficient, the toner replenishment amount is equal to the target toner concentration over time, and the proportional replenishment amount of the FB replenishment amount is zero. The integral replenishment amount of is taking a positive value to compensate for the shortage. Conversely, even when the actual toner replenishment amount is excessive, the toner concentration is consistent with the target toner concentration over time and is stabilized because the proportional replenishment amount of the FB replenishment amount is zero. This is because the integral replenishment amount takes a negative value to reduce the excess amount.

  Therefore, the value of the integrated replenishment amount is acquired at the end of the print job (S21), and the control device 100 selects the correction value change amount according to the selection conditions shown in Table 3 below according to the integrated replenishment amount. Specifically, when “integrated replenishment amount ≧ update threshold A”, a correction value change amount 1 that is a positive value is selected, and the correction value change amount 1 is selected as the current correction value in the storage device 101. Add to. As a result, the new correction value is larger than the current correction value, and the final target toner replenishment is performed even when the same amount of toner is replenished by the FF replenishment control during the next and subsequent toner replenishment operations. A large amount will be calculated. On the other hand, if “integrated replenishment amount ≦ update threshold B”, a correction value change amount 2 that is a negative value is selected, and this correction value change amount 2 is added to the current correction value in the storage device 101. . As a result, the new correction value is smaller than the current correction value, and the final target toner replenishment is performed even when the same FF replenishment amount of toner is replenished during the next and subsequent toner replenishment operations. The amount is calculated with a small amount.

  According to the second modification, the correction value change amount is selected according to the integral replenishment amount calculated in the FB replenishment control performed during the print job, and the updated correction value is calculated. The process of integrating and storing the FB replenishment amount becomes unnecessary. Therefore, the calculation load due to the integration of the FB replenishment amount is eliminated, and a storage area for storing the FB replenishment amount integrated value is not required.

[Modification 3]
Next, a modified example (hereinafter, this modified example is referred to as “modified example 3”) of the execution timing of the correction value update process in the present embodiment will be described.
In the present embodiment, the target toner density value may be changed during a print job. For example, when performing image density adjustment control that is performed periodically during a print job, a target toner density is changed according to the result of detecting a toner adhesion amount by forming a toner patch having a predetermined image density in a non-image area. There is a case. When the target toner density value is changed in this way, the amount of toner corresponding to the difference between before and after the change of the target toner density is included in the FB replenishment quantity. Correlation with is broken.

FIG. 15 is a flowchart showing the flow of toner replenishment control in the third modification.
In the third modification, when the target toner density is changed during the print job (Yes in S31), it is determined whether the correction value update flag is ON (S32), and the correction value update flag is ON. If there is (Yes in S32), the control device 100 acquires the FB replenishment amount integrated value up to this point (S33), and uses this to update the correction value to be used next time (S34). As a result, the correction value update process can be performed using the FB replenishment amount integrated value before the target toner density change in which the correlation between the FB replenishment amount integrated value and the replenishment error is maintained. Can be updated.

In the third modification, the correction value update flag is turned OFF after the correction value update process is performed in this way (S35). As a result, the correction value update process is not performed after the completion of image formation. Therefore, it is possible to prevent the correction value update process from being performed using the FB replenishment amount integrated value after the target toner density change in which the correlation between the FB replenishment amount integrated value and the replenishment error is broken.
In the third modification, instead of the FB replenishment amount integrated value, an integrated replenishment amount of the FB replenishment amount may be used as in the second modification.

[Modification 4]
Next, another modified example of the method for determining whether or not to execute the correction value update process in the present embodiment (hereinafter, this modified example is referred to as “modified example 4”) will be described.
FIG. 16 is a flowchart showing the flow of toner supply control in the fourth modification.
In the above embodiment, the toner density is detected before starting the image formation of the input print job (S2), and it is determined whether or not to execute the correction value update processing after the print job is finished according to the detection result. (S3, S4, S6, S15). On the other hand, in the fourth modification, it is determined whether or not to execute the correction value update process depending on whether or not the toner density is stable at the end of the print job. In the fourth modification, as in the case of the second modification, the FB replenishment amount integrated value is not detected, and the correction value change amount is selected and updated according to the integral replenishment amount calculated in the FB replenishment control. However, the same applies to the case where the updated correction value is calculated in accordance with the FB replenishment amount integrated value.

  In the fourth modification, when the toner density is stable (Yes in S41), the value of the integrated replenishment amount is acquired at the end of the print job (S21), and the above table is displayed according to the integrated replenishment amount. According to the selection condition shown in FIG. 3, a correction value change amount is selected and correction value update processing is performed (S22). On the other hand, when the toner density is not stable (No in S41), the correction value update process is not performed.

FIG. 17 is a graph showing a change in toner density in a print job when the print job is started from a state where the toner density greatly deviates from the target toner density.
In the above embodiment, as shown in FIG. 17, when the toner density at the beginning of the print job is greatly deviated from the target toner density, an appropriate correction value cannot be calculated, so that the correction value update process is not performed. . On the other hand, according to the fourth modification, even when the toner density at the start of the print job greatly deviates from the target toner density, if the toner density is stable at the target toner density (within the toner density stable section). If so, an appropriate correction value can be calculated.

  In other words, as described above, even when the toner density at the start of the print job is greatly deviated from the target toner density, the FB supply control is performed in the toner supply operation during the print job. It approaches the density and becomes stable near the target toner density. In the period until the toner density is stabilized at the target toner density, the FB replenishment amount calculated by the FB replenishment control includes a part that compensates for the difference between the initial toner density and the target toner density. Therefore, from the integrated value of the FB replenishment amount or the integrated replenishment amount of the FB replenishment amount during this period, it is accurately grasped whether the actual toner replenishment amount matches the target toner replenishment amount, or is excessive or insufficient. I can't.

  On the other hand, when the toner density becomes stable in the vicinity of the target toner density (within the toner density stable section), the FB replenishment amount no longer includes the difference between the initial toner density and the target toner density. Not included. At this time, the proportional replenishment amount of the FB replenishment amount is zero, but the integrated replenishment amount of the FB replenishment amount takes an appropriate value, so that even if the actual toner replenishment amount is insufficient or excessive, The toner density can be stabilized near the target toner density. Specifically, when the actual toner replenishment amount is insufficient, the integral replenishment amount of the FB replenishment amount takes a positive value to compensate for the shortage, so that the toner concentration is stabilized at the target toner concentration. The state can be maintained. Similarly, when the actual toner replenishment amount is excessive, the integral replenishment amount of the FB replenishment amount takes a negative value to limit the excess amount, so that the toner density is stable at the target toner concentration. Can be maintained.

In other words, as long as the toner density is stable in the vicinity of the target toner density (within the toner density stable section), the initial toner density may or may not be far from the target toner density. From the value of the integral supply amount of the supply amount, it is possible to grasp whether the actual toner supply amount is insufficient or excessive. Therefore, according to the fourth modification, it is possible to execute the correction value update process for updating the correction value to an appropriate value even if the initial toner density is far from the target toner density.
According to the fourth modification, even if the target toner density is changed during the print job, if the toner density is stable at the end of the print job image formation, the image formation of the print job is performed. The correction value update process can be performed after the completion.

18 and 19 are explanatory diagrams for explaining an example of a method for determining whether or not the toner density is stable (whether or not the toner density is stable).
As shown in FIG. 18, the change amount of the toner density between the image formation end time and the time that is back by the specified judgment time is a range (target toner density ± determination threshold value) that is separated from the target toner density by the judgment threshold. If it is within the range, it is determined that the toner density is stable, and if it is out of the range, it is determined that the toner density is not stable.

  The range is defined by providing the determination threshold in this way, as described above, due to toner density detection noise, toner bias in the developer circulating in the developing unit 7, and the like. This is because the detected value includes a slight error or fluctuation. The determination threshold value may be determined in the same manner as the initial density threshold value in the above embodiment.

  Also, instead of comparing the toner density at the image formation end time with the target toner density, the change in the toner density is observed within the determination time. The toner density temporarily changes to a value near the target value. This is because it is possible to accurately determine whether the toner density is stably changing in the vicinity of the target toner density. For example, the determination time may be set to a time for the developer to make a round in the developing unit. In this case, it can be confirmed whether or not the toner density is stable in all the developers in the developing unit.

[Modification 5]
Next, still another modified example of the method for determining whether or not to execute the correction value update process in the present embodiment (hereinafter, this modified example is referred to as “modified example 5”) will be described.
FIG. 20 is a flowchart showing the flow of toner replenishment control in the fifth modification.
In the fifth modification, the condition for determining whether to execute the correction value update process is combined with the condition in the second modification and the condition in the fourth modification to increase the frequency of executing the correction value update process. .

  In the second modification, when the toner density is out of the target range before the start of image formation of the input print job (No in S3, S6), the correction value update process after the end of the print job is not performed (S15). No). On the other hand, in the fifth modification, even when the toner density is out of the target range before starting the image formation of the input print job (No in S3, S6), the toner density at the end of the image formation is stable. If so (No in S15, Yes in S51), correction value update processing after the print job is completed is executed.

  In the fourth modification, when the toner density at the end of image formation is not stable (No in S41), the correction value update process after the end of the print job is not performed. On the other hand, in the fifth modification, even if the toner density at the end of image formation is not stable, if the toner density is within the target range before the start of image formation for the input print job (Yes in S3). , S4, S15 Yes), correction value update processing after the print job is completed is executed.

  That is, in the fifth modification, either the condition that the toner density is within the target range before the start of the image formation of the input print job or the condition that the toner density at the end of the image formation is stable. If this is satisfied, the correction value update process is executed.

  In addition, according to the present embodiment, including each of the above-described modifications, it is possible to perform a parallel operation with the image forming operation without providing a dedicated time for calculating and updating the correction value (a time during which the image forming operation cannot be performed). A correction value can be calculated. Therefore, the replenishment error can be corrected without increasing the waiting time for the image forming operation. Further, in the case of a conventional apparatus that requires a dedicated time for calculating a correction value, as shown in FIG. 21 (a), it is periodically performed between image forming (print job) and image forming. While it is necessary to include a dedicated time for calculating the correction value, in the case of the present embodiment, as shown in FIG. The correction value can be calculated and updated without entering. As a result, when correction values are calculated at the same frequency while performing the same image formation as in the conventional apparatus, the time required for all image formation can be shortened by ΔTime at the maximum, as shown in FIG. .

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A latent image carrier such as the photosensitive member 3, a latent image forming unit such as an optical writing unit 20 that forms a latent image on the latent image carrier based on image information, and a developer carrier such as the developing roll 12. The two-component developer carried on the surface of the toner is conveyed to the development region by rotation of the developer carrier, and the toner in the two-component developer is adhered to the latent image on the surface of the latent image carrier in the development region. A developing device such as a developing unit 7 that develops the latent image, a toner replenishing unit such as a toner replenishing device 70 that performs a toner replenishing operation to the two-component developer in the developing device, and the image information. Then, a target operation amount (target toner replenishment amount, etc.) of the toner replenishing unit for replenishing the toner for the target toner replenishment amount calculated from the image information by the toner replenishing unit is calculated, and the target operation amount is To control the toner supply operation of the toner supply means And a toner replenishment control means such as a control device 100, and the toner image formed on the latent image carrier by being developed by the developing device is finally transferred onto the recording material to form an image. In the image forming apparatus, the correction value storage means such as the storage device 101 that stores the correction value for correcting the target operation amount, the toner concentration sensor 10 that detects the toner concentration of the two-component developer in the developing device, etc. When the difference between the toner density detected by the toner density detecting means and the target toner density is greater than a predetermined value by controlling the toner replenishing operation by the toner replenishing control means, the difference ( The correction value is calculated based on the FB replenishment amount integrated value or the integral replenishment amount), and a correction value update process is performed to update the correction value stored in the correction value storage means to the calculated correction value. The toner replenishment control unit includes a correction value update processing unit such as the control device 100, and the toner replenishment control unit is configured to perform the correction of the toner replenishment unit according to the corrected target operation amount corrected by the correction value stored in the correction value storage unit. The toner supply operation is controlled.
Since toner supply is controlled by FF supply control based on image information, a difference between the toner density and the target toner density indicates that a supply error has occurred. In this aspect, when a difference greater than a specified value occurs between the toner density and the target toner density, a correction value for correcting the target operation amount of the toner replenishing means is calculated based on the difference, thereby reducing the replenishment error. It is possible to calculate an appropriate correction value. In addition, the standby time for the image forming operation is not increased in calculating the correction value.

(Aspect B)
In the aspect A, the toner replenishment control unit calculates a first target toner replenishment amount such as an FF replenishment amount based on the image information, and the toner concentration detected by the toner concentration detection unit, the target toner concentration, The second target toner supply amount such as the FB supply amount is calculated based on the difference value between the first target toner supply amount and the final target toner supply amount corresponding to the total value of the first target toner supply amount and the second target toner supply amount. A target operation amount before correction for replenishing toner is calculated, and a toner replenishing operation of the toner replenishing means is controlled according to the target operation amount after correction after the target operation amount before correction is corrected by the correction value. And
According to this, until the toner replenishment operation is performed using the updated correction value, it is possible to converge the toner density away from the target toner density to the target toner density by the FB replenishment control.

(Aspect C)
In the aspect B, the correction value update processing means calculates the correction value based on the accumulated value of the second target toner supply amount used for calculating the target operation amount in the toner supply operation within a predetermined period. Features.
Since the cumulative value of the second target toner supply amount (FB supply amount integrated value) is highly correlated with the supply error, an appropriate correction value can be calculated. In particular, according to this aspect, even when the toner density is not stable at the target toner density when calculating the correction value, if the initial toner density in the predetermined period is close to the target toner density, an appropriate correction value is set. Can be calculated.

(Aspect D)
In the aspect C, there is provided target toner density changing means for changing the target toner density when a predetermined target toner density changing condition is satisfied, and the correction value update processing means is configured to change the target toner density within the predetermined period. The correction value update processing is performed when the density changing means changes the target toner density.
According to this, since the correction value is calculated based on the accumulated value of the second target toner supply amount that is not affected by the change in the target toner density, an appropriate correction value can be calculated.

(Aspect E)
In any one of the above aspects B to D, the toner replenishment control means is configured to supply a second target toner replenishment based on a time integral value of a difference value between the toner density detected by the toner density detecting means and the target toner density. An amount is calculated, and the correction value update processing means calculates the correction value based on the time integral value.
Since the time integral value of the difference value between the toner density and the target toner density (integrated replenishment amount of the FB replenishment amount) is highly correlated with the replenishment error, an appropriate correction value can be calculated. In particular, according to this aspect, if the toner density at the time of calculating the correction value is stable at the target toner density, an appropriate correction value can be calculated.

(Aspect F)
In the aspect E, the correction value update processing unit performs the correction value update processing when the toner density detected by the toner density detection unit is maintained within a target range including the target toner density. To do.
According to this, it is possible to stably calculate an appropriate correction value from the time integral value of the difference value between the toner density and the target toner density (integrated replenishment amount of the FB replenishment amount).

(Aspect G)
In any one of the above aspects A to F, the correction value storage means is a nonvolatile memory.
According to this, since the correction value can be held even when the power source is turned off, an appropriate correction value before turning on the power can be used as the correction value immediately after turning on the power, and at the time of image formation immediately after turning on the power. Also, proper toner replenishment can be performed.

(Aspect H)
In any of the above aspects A to G, a plurality of the toner replenishing means are provided, and the toner replenishing control means individually controls the plurality of toner replenishing means, and the correction value update processing means Is characterized in that the correction value update processing is individually performed for the plurality of toner replenishing means.
According to this, a replenishment error based on individual differences among a plurality of toner replenishing units mounted on the same image forming apparatus can be corrected appropriately.

(Aspect I)
In any one of the aspects A to H, the correction value update processing unit repeatedly performs the correction value update process after a predetermined period.
According to this, the toner replenishment error can be corrected with an appropriate correction value according to the latest situation.

(Aspect J)
In the above aspect I, the predetermined period is a fixed period determined in advance or a period determined in accordance with a use environment or an accumulated toner consumption amount.
According to this, the correction value that can appropriately correct the toner replenishment error can be updated at an appropriate timing.

DESCRIPTION OF SYMBOLS 3 Photoconductor 7 Developing unit 10 Toner density sensor 20 Optical writing unit 41 Intermediate transfer belt 70 Toner replenishing device 72 Toner cartridge 100 Control device 101 Storage device

JP 2007-304524 A

Claims (9)

A latent image carrier;
Latent image forming means for forming a latent image on the latent image carrier based on image information;
The two-component developer carried on the surface of the developer carrier is transported to the development area by the rotation of the developer carrier, and the toner in the two-component developer is transferred to the latent image carrier surface on the surface of the latent image carrier. A developing device that adheres to the image and develops the latent image;
Toner replenishing means for performing a toner replenishing operation to the two-component developer in the developing device;
Based on the image information, a target operation amount of the toner replenishing means for replenishing the toner for the target toner replenishment amount calculated from the image information by the toner replenishing means is calculated, and according to the target operation amount Toner supply control means for controlling the toner supply operation of the toner supply means,
In an image forming apparatus for forming an image by finally transferring a toner image formed on the latent image carrier by being developed by the developing device onto a recording material,
Correction value storage means for storing a correction value for correcting the target movement amount;
Toner density detecting means for detecting the toner density of the two-component developer in the developing device;
When the difference between the toner density detected by the toner density detecting means and the target toner density is more than a specified value by controlling the toner replenishing operation by the toner replenishing control means, the correction value is calculated based on the difference. Correction value update processing means for performing correction value update processing for updating the correction value stored in the correction value storage means to the calculated correction value,
The toner replenishment control means calculates a first target toner replenishment amount based on the image information, and a second target toner based on a difference value between the toner density detected by the toner density detection means and the target toner density. A replenishment amount is calculated, and a target operation amount before correction for replenishing the toner corresponding to the final target toner replenishment amount according to the sum of the first target toner replenishment amount and the second target toner replenishment amount is calculated. Controlling the toner replenishment operation of the toner replenishing means according to the corrected target motion amount after correction , wherein the previous target operation amount is corrected by the correction value stored in the correction value storage means ;
The correction value update processing means calculates the correction value based on a cumulative value of the second target toner supply amount used for calculating the target operation amount in the toner supply operation within a predetermined period. apparatus. The image forming apparatus according to claim 1 .
A target toner density changing means for changing the target toner density when a predetermined target toner density changing condition is satisfied;
The image forming apparatus, wherein the correction value update processing unit performs the correction value update processing when the target toner density changing unit changes the target toner density within the predetermined period. The image forming apparatus according to claim 1 , wherein
The toner replenishment control means calculates a second target toner replenishment amount based on a time integral value of a difference value between the toner density detected by the toner density detection means and the target toner density;
The image forming apparatus, wherein the correction value update processing unit calculates the correction value based on the time integral value.   A latent image carrier;
  Latent image forming means for forming a latent image on the latent image carrier based on image information;
  The two-component developer carried on the surface of the developer carrier is transported to the development area by the rotation of the developer carrier, and the toner in the two-component developer is transferred to the latent image carrier surface on the surface of the latent image carrier. A developing device that adheres to the image and develops the latent image;
  Toner replenishing means for performing a toner replenishing operation to the two-component developer in the developing device;
  Based on the image information, a target operation amount of the toner replenishing means for replenishing the toner for the target toner replenishment amount calculated from the image information by the toner replenishing means is calculated, and according to the target operation amount Toner supply control means for controlling the toner supply operation of the toner supply means,
  In an image forming apparatus for forming an image by finally transferring a toner image formed on the latent image carrier by being developed by the developing device onto a recording material,
  Correction value storage means for storing a correction value for correcting the target movement amount;
  Toner density detecting means for detecting the toner density of the two-component developer in the developing device;
  When the difference between the toner density detected by the toner density detecting means and the target toner density is more than a specified value by controlling the toner replenishing operation by the toner replenishing control means, the correction value is calculated based on the difference. Correction value update processing means for performing correction value update processing for updating the correction value stored in the correction value storage means to the calculated correction value,
  The toner replenishment control means calculates a first target toner replenishment amount based on the image information, and based on a time integral value of a difference value between the toner density detected by the toner density detection means and the target toner density. A second target toner supply amount is calculated, and a pre-correction target operation amount for supplying toner corresponding to the final target toner supply amount according to the sum of the first target toner supply amount and the second target toner supply amount is calculated. And controlling the toner replenishing operation of the toner replenishing means according to the corrected post-correction target motion amount obtained by correcting the pre-correction target motion amount with the correction value stored in the correction value storage means,
  The image forming apparatus, wherein the correction value update processing unit calculates the correction value based on the time integral value. The image forming apparatus according to claim 3 or 4 ,
The image forming apparatus, wherein the correction value update processing unit performs the correction value update processing when the toner density detected by the toner density detection unit is maintained within a target range including a target toner density. The image forming apparatus according to any one of claims 1 to 5 ,
The image forming apparatus, wherein the correction value storage means is a non-volatile memory. The image forming apparatus according to any one of claims 1 to 6 ,
A plurality of toner replenishing means;
The toner replenishment control means individually controls the plurality of toner replenishment means.
The image forming apparatus, wherein the correction value update processing unit performs the correction value update processing individually for the plurality of toner supply units. The image forming apparatus according to any one of claims 1 to 7 ,
The image forming apparatus, wherein the correction value update processing unit repeatedly performs the correction value update processing after a predetermined period. The image forming apparatus according to claim 8 .
The image forming apparatus according to claim 1, wherein the predetermined period is a predetermined fixed period or a period determined according to a use environment or an accumulated toner consumption amount.

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