JP2012013986A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that is capable of reducing waste of toner and restoring deteriorated charging property of toner while suppressing reduction of availability than before.SOLUTION: The image forming apparatus forms a plurality of toner patches having different amounts of attached toner by changing the development potential between an image carrier and a developer carrier (S5); detects the amounts of attached toner of the respective formed toner patches (S6); performs regression analysis of pairs of the development potential and the amount of attached toner of the respective toner patches and derives a linear function showing the correlation of the development potential and the amount of attached toner (S7); determines whether or not the inclination of the derived linear function is equal to or smaller than a reference inclination (S8); and if it is determined that the inclination is equal to or smaller than the reference inclination, considers that the development property of the toner is deteriorated and performs a restoration process of the development property (S9).

Description

  The present invention relates to an image forming apparatus, and more particularly to control of a developing potential.

In an image forming apparatus, when developing an electrostatic latent image formed on a photoreceptor, toner is charged by stirring with a stirring screw or the like provided in a developing unit. However, when the image forming apparatus has been idle for a long period of time, the chargeability and fluidity of the toner may be significantly deteriorated, which may cause a decrease in the density of the printed image and image fogging.
Therefore, when the image forming apparatus has been inactive for a long time and resumes operation, the toner is agitated for a predetermined time before starting the execution of the print job, and the toner (old toner) remaining in the developing unit for a long time is discharged and discharged. The chargeability and fluidity of the toner are recovered by performing processing such as supply of new toner (hereinafter referred to as pretreatment).

  In addition to this, in Patent Document 1, the development potential is adjusted. Specifically, a plurality of toner patches having different toner adhesion amounts are created on the surface of the photosensitive member or transfer medium by changing the developing potential, and the toner adhesion amounts of these toner patches are detected by a sensor. Then, a development characteristic (linear function) representing the relationship between the development potential and sensor detection value for each toner patch is derived. A development potential corresponding to a predetermined sensor value is calculated from the linear function, and the calculated development potential is used in the developing device.

JP 2006-47855 A

However, the chargeability and fluidity of the toner may not be sufficiently recovered even if the above pretreatment is performed. As an example, this corresponds to the case where the power supply of the image forming apparatus is stopped for a longer period of time than usual and toner chargeability and fluidity have deteriorated more than expected.
This also applies to the case where pages with a low printing area ratio are continuously printed even though the image forming apparatus is operating. At this time, the amount of toner consumed is small, and the stirring of the toner is repeated. As a result, more severely stressed and physically deteriorated toner remains in the developing device than usual when the power supply of the image forming apparatus is simply stopped. Such toner is difficult to be charged by stirring, and is desirably discharged.

  As described above, when the chargeability and fluidity of the toner are not sufficiently recovered in the pretreatment as described above, it is considered to stir the toner for a longer time and to increase the discharge amount of the old toner as means for recovering these. It is done. However, if the stirring of the toner is uniformly extended for a long time, the print job cannot be executed during this time, and the availability as an image forming apparatus is impaired. Further, if the amount of discharged old toner is increased uniformly, toner waste becomes significant.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of reducing waste of toner and recovering toner development performance while suppressing reduction in availability as compared with the prior art.

In order to solve the above problems, the present invention provides an image forming apparatus including a developing unit that develops an electrostatic latent image formed on an image carrier to form a toner image, the image carrier and a developer. A patch forming means for forming a plurality of toner patches having different toner adhesion amounts by changing a development potential with the carrier; a detection means for detecting the toner adhesion amounts of the toner patches; and development for each of the toner patches. A derivation means for performing linear regression analysis on a set of potential and toner adhesion amount, deriving a linear regression equation with development bias as an independent variable and toner adhesion amount as a dependent variable;
Determining means for determining whether or not the slope relating to the independent variable is equal to or less than a reference slope; and when it is determined that the slope is equal to or less than the reference slope, the developing performance is regarded as a reduction in toner developing performance. Execution means for executing the recovery process.

Since the image forming apparatus of the present invention has the above-described configuration, the execution performance recovery process is limited to a case where it is considered that the toner development performance is deteriorated. Development performance can be recovered.
Further, the execution unit may stir the toner for a second stirring time longer than the first stirring time when the slope of the coefficient of the independent variable is larger than the reference slope as the recovery process.

According to this configuration, the toner is stirred for the second stirring time longer than the first stirring time when the toner developing performance is not lowered only when the toner developing performance is lowered. Chargeability and fluidity can be sufficiently recovered.
Further, the execution means may extend the second stirring time as the slope of the coefficient of the independent variable is smaller.

According to this configuration, as the toner developing performance is less deteriorated, the stirring time can be shortened, so that the reduction in availability can be further suppressed.
Further, the execution unit may forcibly discharge the toner in the developing unit as the recovery process.
According to this configuration, the toner in the developing means is forcibly discharged only when the developing performance of the toner is lowered. Therefore, a predetermined amount of toner is uniformly discharged regardless of whether the developing performance of the toner is lowered or not. Compared with the case of discharging, toner waste can be reduced.

  Further, after the recovery process, the patch forming unit further changes the development potential to form a plurality of toner patches having different toner adhesion amounts, and the detection unit is further formed after the recovery process. The toner adhesion amount of each toner patch is detected, and the deriving means further performs a linear regression analysis on a set of the development potential and the toner adhesion amount for each toner patch formed after the recovery process, and develops a bias. Is an independent variable, and a linear regression equation having a toner adhesion amount as a dependent variable is derived, and the image forming apparatus further determines that a slope related to the independent variable in the linear regression equation derived after the recovery processing is a reference slope. If it exceeds, a development potential corresponding to a predetermined target toner adhesion amount is obtained using a linear regression equation derived after the recovery process, and the obtained development potential is It is also possible to perform development to the developing means.

  According to this configuration, since the development characteristics are again verified and the development potential is acquired in a state where the chargeability and fluidity of the toner are sufficiently recovered by the pretreatment, a stable image can be formed with an appropriate development potential. it can.

1 is a schematic cross-sectional view illustrating an overall configuration of a printer according to an embodiment of the present invention. It is a cross-sectional view showing a configuration example of a developing unit according to an embodiment of the present invention. FIG. 4 is a diagram illustrating an example of a toner pattern formed on an intermediate transfer belt. It is a figure which shows an example of a development characteristic. 2 shows an overall control flow of image stabilization processing and preprocessing according to the present embodiment. It is a control flow of preprocessing performed by the preprocessing execution unit. It is a figure which shows the relationship between a light quantity and a sensor value about an exposure process. It is a figure which shows the relationship between a primary transfer voltage and a detected electric current value.

<Overall configuration>
An image forming apparatus according to an embodiment of the present invention will be described.
FIG. 1 is a schematic cross-sectional view showing an overall configuration of a printer 1 as an example of an image forming apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the printer 1 includes an image processing unit 3, a paper feeding unit 4, a fixing unit 5, and a control unit 60. The printer 1 is connected to a network (for example, a LAN) and is connected to an external terminal device (not shown). When a print job execution instruction is received, a toner image composed of yellow, magenta, cyan, and black is formed based on the instruction, and a full-color image is formed by multiple transfer of these toner images. Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are represented as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.

The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K corresponding to the colors Y to K, an optical unit 10, an intermediate transfer belt 11, a toner pattern detection sensor 36, and the like.
The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y disposed around the photosensitive drum 31Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like. A Y-color toner image is formed on the drum 31Y.

The other image forming units 3M to 3K have the same configuration as the image forming unit 3Y, and the reference numerals are omitted in FIG.
The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13, and is rotationally driven in the direction of arrow A.
The optical unit 10 includes a light emitting element such as a laser diode, emits a laser beam L for forming an image of Y to K colors by a drive signal from the control unit 60, and exposes and scans the photosensitive drums 31Y to 31K.

By this exposure scanning, electrostatic latent images are formed on the photosensitive drums 31Y to 31K charged by the chargers 32Y to 32K. The electrostatic latent images are developed by the developing units 33Y to 33K, and Y to K color toner images are superimposed on the same positions on the intermediate transfer belt 11 and primarily transferred onto the photosensitive drums 31Y to 31K. It is executed at different timings.
The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 11 by the electrostatic force acting on the primary transfer rollers 34Y to 34K to form a full-color toner image, and further move toward the secondary transfer position 46.

  On the other hand, the paper feed unit 4 includes a paper feed cassette 41 that stores the recording sheets S, a feed roller 42 that feeds the recording sheets S in the paper feed cassette 41 one by one onto the transport path 43, and a fed recording sheet S. Are provided with a timing roller pair 44 for taking the timing of feeding the toner to the secondary transfer position 46, and the recording sheet S is transferred from the paper feeding unit 4 to the secondary transfer position in accordance with the movement timing of the toner image on the intermediate transfer belt 11. The toner images on the intermediate transfer belt 11 are collectively transferred onto the recording sheet S by the action of the secondary transfer roller 45.

The recording sheet S that has passed the secondary transfer position 46 is conveyed to the fixing unit 5, and the toner image (unfixed image) on the recording sheet S is fixed to the recording sheet S by heating and pressurization in the fixing unit 5. Thereafter, the sheet is discharged onto the discharge tray 72 via the discharge roller pair 71.
<Configuration of development unit>
FIG. 2 is a cross-sectional view illustrating a configuration example of the developing unit 33Y.

Since the developing units 33Y to 33K have the same configuration, only the developing unit 33Y will be described, and the description of the developing units 33M to 33K will be omitted.
As shown in the figure, the developing unit 33Y includes a developing housing 50, a developing roller 51, a conveying screw 52, a stirring screw 53, a regulating member 54, a replenishing unit 55, and a developing drive including a motor that rotationally drives the developing roller 51. Unit 104, a drum driving unit 105 including a motor that rotationally drives the photosensitive drum 31Y, a bias power source 106 that applies a development potential to the developing roller 51 during development, and operations of the development driving unit 104, the drum driving unit 105, and the bias power source 106 A development control unit 103 that performs control is included. Also, in the figure, an overall control unit 100 that controls the overall operation of the printer 1 and is related to the development unit included in the control unit 60 shown in FIG. 1, an image stabilization processing control unit 101, and a preprocessing control unit 102. Are described together.

The developing housing 50 is elongated along the axial direction of the developing roller 51 (perpendicular to the paper surface: hereinafter referred to as “axial direction”), the developer D is accommodated therein, and the partition walls 503 are formed in the vertical direction. Thus, the upper developing chamber 501 and the lower stirring chamber 502 are divided.
The developing chamber 501 and the agitating chamber 502 are communicated with each other through the first communication portion at one end side in the axial direction (hereinafter referred to as “device front side”), and the other end side (hereinafter referred to as “device rear side”). The portions located on the “side” are communicated with each other via the second communication portion, and constitute a circulation conveyance path for the developer D accommodated in the development housing 50.

The developing roller 51 is rotatably supported in a direction indicated by an arrow B in a portion of an opening 57 provided in a position facing the photosensitive drum 31Y in the developing chamber 501, and carries a developer D on the surface thereof to carry a photosensitive member. It is conveyed to a development position (development nip) facing the drum 31Y.
In accordance with the developing potential applied to the developing roller 51 by the bias power source 106 and the potential on the surface of the photosensitive drum 31Y, the toner is conveyed to the surface of the photosensitive drum 11 in the developing nip.

  The conveying screw 52 is disposed in the developing chamber 501 at a position facing the photoconductive drum 31Y with the developing roller 51 interposed therebetween, and is rotatably supported in a parallel posture along the axial direction, and is accommodated in the developing chamber 501. The developer D being conveyed is supplied to the developing roller 51 while conveying the developer D being conveyed from the front side of the apparatus toward the rear side along the axial direction. The developer D conveyed by the conveying screw 52 toward the rear side of the apparatus in the developing chamber 501 is sent to the stirring chamber 502 located below through the second communication portion.

The agitating screw 53 is disposed in the agitating chamber 502 and is rotatably supported in a parallel posture along the axial direction. The agitating screw 53 agitates the developer D sent from the developing chamber 501 via the second communicating portion. In order to prevent solidification in the chamber 502 and to maintain fluidity, stirring is performed while transporting toward the direction opposite to the transport direction of the transport screw 52, that is, toward the front side of the apparatus.
The developer D transported toward the front side of the apparatus by the stirring screw 53 is sent to the developing chamber 501 located above through the first communication portion, and again by the transporting screw 52 disposed in the developing chamber 501, It is conveyed toward the rear side of the device. The developing roller 51, the conveying screw 52, and the agitating screw 53 are driven to rotate in the direction indicated by the arrow in FIG. The development drive unit 104 is driven according to the control of the development control unit 103. Note that the developing roller 51, the conveying screw 52, and the like may be separately driven by a separate motor instead of a single driving motor.

The regulating member 54 is arranged so that the tip thereof has a predetermined gap with the surface of the developing roller 51, and the gap so that the amount of developer on the surface of the developing roller 51 becomes an appropriate amount at the developing position. The amount of developer passing through is regulated.
The replenishing unit 56 accommodates a one-component developer (hereinafter sometimes referred to as “toner”), and replenishes the developing housing 50, here, the stirring chamber 502.

  Specifically, the developer for replenishment is replenished every certain amount and every certain time (for example, several seconds) while the developing roller 51, the conveying screw 52, and the stirring screw 53 are rotating. Replenishment of developer increases the amount of developer D in the development housing 50. However, since an amount of developer corresponding to the replenishment amount is discharged to the outside from a discharge port (not shown), development is performed. The amount of the agent D does not continue to increase and is maintained at a substantially constant amount.

For the replenishment toner, a replenishment operation is performed in accordance with an instruction from the development control unit 103. That is, the development control unit 103 detects the remaining amount of toner during rotation of the developing roller 51, the conveying screw 52, etc. during an image forming operation, and replenishes the replenishment unit 56 with toner so that the toner becomes a constant amount. Instruct. When the replenishing unit 56 receives an instruction from the development control unit 103, the replenishing unit 56 replenishes the designated amount of toner.
<Configuration of Image Stabilization Control Unit>
In the printer 1, the fatigue of the photosensitive drum 31 and the toner and changes in diameter, changes in environmental conditions such as humidity and temperature around the printer 1, changes in the device configuration such as the installation of a new unit, and the like. Concentration may deteriorate.

The image stabilization processing control unit 101 adjusts the developing potential in the developing unit 33 (33Y to 33K) and returns the image density to an appropriate one at a predetermined timing in order to compensate for the above-described deterioration of the image density. The operation of the image stabilization processing to be performed is controlled.
In the present embodiment, the image stabilization processing is satisfied immediately after the power is turned on, and the stabilization processing start conditions such as the elapsed time from the previous execution of the image stabilization processing, the number of prints, changes in environmental conditions, and whether or not the unit is replaced. It will be executed if In other words, the image stabilization process may be performed in a transient state before the print job is executed, such as when the power is turned on, or in a steady state in which the print job is executed, but the density of the image to be formed deteriorates. In some cases, the execution of the print job is temporarily prohibited when it is considered that the print job has been performed.

Whether or not the stabilization processing start condition is satisfied is determined by the overall control unit 100, and when the satisfaction is detected, the overall control unit 100 performs image stabilization for the image stabilization processing control unit 101. An instruction to start processing is transmitted.
For example, the overall control unit 100 includes a clock, records the date and time when the image stabilization process was executed, and the elapsed time since the previous execution of the image stabilization process has passed a predetermined time (for example, 2 days). In such a case, it is determined that the stabilization processing start condition has been satisfied. In addition, the overall control unit 100 counts the number of printouts since the previous image stabilization process was performed, and determines that the stabilization process start condition has been satisfied when the number has reached 1000. The overall control unit 100 includes a temperature sensor and monitors the temperature using the temperature sensor. Then, the temperature when the image stabilization process was executed last time is recorded, and when the temperature difference from the current temperature exceeds 10 ° C., it is determined that the stabilization process start condition is satisfied. The overall control unit 100 determines that the stabilization process start condition has been satisfied when the configuration of the image forming apparatus has changed, such as when a new unit is mounted after the previous image stabilization process. Further, the overall control unit 100 may determine that the stabilization processing start condition has been satisfied when it is detected that a predetermined number of pages having a low printing area ratio have continued. Details of printing a page with a low printing area ratio will be described later.
The stabilization processing start condition is not limited to these, and a condition that can determine that the image density may be deteriorated may be used.

In the following description of image stabilization processing, preprocessing, etc., only Y color will be described to avoid redundant description. Even if not explicitly shown, the same processing as in the case of Y color is performed for each of the colors M, C, and K.
The image stabilization processing control unit 101 includes a patch formation control unit 111, a density detection control unit 112, and a development characteristic verification unit 113.

When receiving an instruction to start image stabilization processing from the overall control unit 100, the patch formation control unit 111 receives four toner patterns (hereinafter referred to as toners) having a width WP and a length LP as shown in FIG. Also referred to as a patch or a solid patch.) Control for forming TP1 to TP4 on the intermediate transfer belt 11 at intervals KP is performed.
Specifically, the patch formation control unit 111 controls the charger 32Y via the development control unit 103 to charge the photosensitive drum 31Y. After charging the photoconductor drum 31Y, the patch formation control unit 111 controls the optical unit 10 via the development control unit 103, and electrostatic latent images corresponding to TP1, TP2, TP3, and TP4 are formed on the photoconductor drum 31Y. Let it form. Thereafter, the patch formation control unit 111 develops the electrostatic latent image corresponding to TP1 by applying the development potential DV1 to the bias power source 106 via the development control unit 103. Similarly, electrostatic latent images corresponding to TP2, TP3, and TP4 are developed by applying development potentials DV2, DV3, and DV4, respectively. Here, the development potentials DV1, DV2, DV3, and DV4 are 120V, 160V, 200V, and 240V, for example. Then, the patch formation control unit 111 controls the primary transfer roller 34Y via the development control unit 103, and primarily transfers the four developed toner patterns onto the intermediate transfer belt 11. Through the above processing, a toner pattern as shown in FIG. 3 is formed on the intermediate transfer belt 11.

The patch formation control unit 111 notifies each development potential value (development potential value) used for development to the development characteristic verification unit 113. Although the number of toner patches is four in this embodiment, the number is not limited to this.
The density detection control unit 112 uses the toner pattern detection sensor 36 to detect the density (toner adhesion amount) of each toner pattern formed on the intermediate transfer belt 11.

  Here, the toner pattern detection sensor 36 will be briefly supplemented. The toner pattern detection sensor 36 is an optical sensor having a light emitting unit and a light receiving unit (not shown). The light emitting unit irradiates light in the infrared to visible light region toward the toner pattern. The light receiving unit receives that the irradiated light returns by regular reflection or irregular reflection and returns a value (hereinafter referred to as a sensor detection value) corresponding to the intensity of the received light to the development characteristic verification unit 113. Output. The detection sensor value decreases as the toner amount on the intermediate transfer belt 11 increases and the exposure of the belt surface decreases.

The toner pattern on the intermediate transfer belt 11 is removed by a cleaning mechanism (not shown) after the sensor detection value is acquired by the toner pattern detection sensor 36.
The development characteristic verification unit 113 receives the development potential value from the patch formation control unit 111, receives the sensor detection value corresponding to each development potential value from the density detection control unit 112, and derives and verifies the development characteristic using these values.

As an example, the development characteristic verification unit 113 receives four development potential values DV1 to DV4 from the patch formation control unit 111, and receives sensor detection values (SD1 to SD4) corresponding to DV1 to DV4 from the density detection control unit 112, respectively. Assume that you received it.
FIG. 4 is a diagram for explaining the development characteristics, and four points P1 (DV1, SD1) represented by a set of a development potential value received by the development characteristic verification unit 113 and a sensor detection value (density value). , P2 (DV2, SD2), P3 (DV3, SD3), P4 (DV4, SD4) are plotted.

  The development characteristic verification unit 113 obtains a primary regression equation (development characteristic) representing the relationship between P1 to P4 by linear regression analysis which is a known technique. In this embodiment, a linear regression analysis (y = ax + b) is obtained by a known least square method as an example of linear regression analysis, with development bias as an independent variable (x) and toner adhesion amount as a dependent variable (y). However, other methods may be used as long as a linear regression equation representing the correlation from P1 to P4 can be derived.

In FIG. 4, the graph (b) represents the development characteristics.
The development characteristic verification unit 113 considers that the development characteristic is deteriorated when the development characteristic slope (slope related to the independent variable) a is equal to or lower than a predetermined slope lower limit (0.0035 as an example). Is determined to be necessary. This is because even when a development potential is applied during development, the amount of toner that moves to the photosensitive drum 31Y is often insufficient. In this case, a preprocessing execution instruction is notified to the preprocessing control unit 102. Specifically, the pretreatment is processing for stirring the toner and discharging the old toner in order to restore the development characteristics. Details of the preprocessing will be described later.

  On the other hand, when the slope a of the development characteristic exceeds a predetermined slope lower limit (when it is not determined that pre-processing needs to be executed), the development characteristic verification unit 113 holds the development characteristic in advance. A development potential value (TDV) corresponding to the target sensor detection value (TSD) is obtained. Then, the development characteristic verification unit 113 notifies the development control unit 103 of TDV as the development potential applied to the bias power source 106.

Note that execution of a print job is prohibited during execution of this image stabilization process.
However, the time required for the image stabilization process is about 3 seconds in a printer having a maximum printing speed of about 30 sheets / minute, which is shorter than the time required for the pre-processing described later. Therefore, even if it is performed in a timely manner, it is considered that the availability of the printer 1 is hardly impaired.
Note that the development potential value (TDV) corresponding to the target density value (TSD) is acquired from the current development characteristics without performing pre-processing, and this TDV is set in the development unit 33Y to perform the subsequent development. If this is done, even if the amount of toner in the solid portion is sufficient in the development result, a halftone portion (so-called rustling) phenomenon, a phenomenon that gradation continuity cannot be ensured, etc. will occur. sell. Further, leak noise may also occur in the solid portion. When these phenomena occur, the image quality of the printed material is greatly degraded.

In the present embodiment, since the image stabilization processing is performed again after performing the preprocessing described later, such a problem does not occur.
Note that image stabilization processing and pre-processing described later are processing performed when the print image is not stable. Therefore, in the printer 1, while the image stabilization process and the preprocess are being executed, the print job is accepted, but the print job is not executed.
<Pre-processing execution unit 102>
The preprocessing execution unit 102 executes preprocessing as a preliminary process of the image stabilization process in order to recover the deteriorated development characteristics. For example, the pre-processing includes toner agitation processing and old toner discharge processing. Further, execution of a print job is prohibited during execution of preprocessing. Therefore, when the power is turned on, the start of execution of the print job is delayed until the image stabilization process and the preprocess are completed.

  The pre-process is executed after the image stabilization process as described above, when the development characteristic slope a calculated in the image stabilization process is equal to or lower than a predetermined slope lower limit. Then, after the development characteristics are recovered by the preprocessing, the image stabilization processing is performed again. If the development characteristic slope a calculated in the image stabilization process is equal to or lower than the predetermined slope lower limit, the pre-processing is performed again. Thereafter, the pre-processing and the image stabilization process are repeatedly executed until the development characteristic slope a exceeds a predetermined slope lower limit. On the other hand, if sufficient development characteristics are obtained in the first image stabilization processing, the preprocessing is not executed. Further, if it is determined that sufficient development characteristics can be obtained in the second and subsequent image stabilization processing, the subsequent preprocessing is not performed.

Hereinafter, the toner agitation process and the old toner discharge process will be described in detail, and then the operation of the preprocessing execution unit 102 will be described.
The toner stirring process is a process for sufficiently stirring the developer in the developing unit 33Y. By this stirring process, the toner is triboelectrically charged, and the toner having an insufficient charge amount is raised to the original charge amount level.

If the toner is left for about 1 to 2 days, the charge amount is reduced to about 50 to 60% when the normal charge amount is 100%. This charge amount can be recovered to about 85 to 100% by the toner stirring process.
The time for sufficient stirring is, for example, about 36 seconds, but is not limited thereto, and may be changed according to the characteristics of the apparatus and toner. In the present embodiment, as will be described in detail later, the toner agitation for about 6 seconds equivalent to the so-called normal agitation processing time and the toner agitation for about 36 seconds described above are separately used.

Further, the toner (old toner) staying in the developing portion for a long time is reduced in volume due to the influence of gravity or the like, so that the fluidity is lowered. However, the toner fluidity can be recovered by the toner stirring process. If the fluidity is low, the mixing property of the old toner and the new toner, which is a short period after being replenished to the developing unit, cannot be made uniform, and it becomes difficult to keep the charging property stable.
In addition, the remaining amount of the toner post-treatment agent is smaller in the old toner than in the new toner. The toner post-treatment agent is inorganic fine particles added to the toner for several percent for the purpose of sufficiently providing fluidity and chargeability. These inorganic fine particles are buried in the toner particles during mixing and agitation, or are released from the toner particles, which causes a decrease in fluidity and chargeability with repeated use.

  As described above, when the old toner having insufficient fluidity and chargeability and the new toner having sufficient fluidity and chargeability are mixed, the fluidity and chargeability are locally increased as a whole. There are high and low parts. If such a toner is used as it is for development, even if the amount of toner in the solid portion is sufficient in the printing result on the sheet, the halftone portion is blurred particularly (so-called rust), the floor There may be a phenomenon that the continuity of the tone cannot be secured. Further, leak noise or the like may occur in the solid portion. When these phenomena occur, the image quality of the printed material is greatly degraded.

In the old toner discharge process, old toner with low developability in the developing unit 33Y is forcibly discharged, so that a constant amount of toner is consumed and new toner (new toner) is replenished in the developing unit 33Y. It is processing to do. As a result, the ratio of the old toner in the developing unit 33Y is greatly reduced and the ratio of the new toner is increased, so that the charging property and fluidity are restored to a sufficient state.
This old toner discharge process is particularly effective when it is performed when a predetermined number of pages having a low printing area ratio continue. When pages with a low printing area ratio continue for a predetermined period or more, changes in the physical properties of the toner surface due to stress, coarse particles due to aggregation, unevenness of the holding state on the developing roller, and increase in fog toner and internal contamination May cause. In such a case, it is difficult to be charged even if the toner stirring process is performed, and it is difficult to recover the charged amount once lowered to a predetermined level.

As an example, it is determined as follows whether or not a predetermined number of pages having a low print area ratio have continued.
Each time one printout is made, the preprocessing execution unit 102 fixes the print area ratio (the area of the printable portion of the recording sheet S and the toner actually) per printed result to be printed out. The ratio to the area of the printed portion is calculated (for printing on a recording sheet that is not A4 size, it is converted to A4 size). This calculation is performed by analyzing the image data of an image to be printed on the recording sheet S, and the area of the portion where the toner is fixed on the recording sheet S and the printable area of the recording sheet S. This can be done by calculating the ratio with the area.

  Then, the reference print area ratio in the recording sheet S (corresponding to an area ratio of 2% in an A4 size recording sheet) is compared with the calculated print area ratio, and if the reference is not reached, the difference is cumulatively added. . When the total area ratio (total difference area ratio) obtained by cumulative addition is equal to or larger than the area ratio corresponding to the area of 30 A4 size recording sheets, the toner has an area equivalent to 10% of the A4 size recording sheet. A discharge pattern is created on the intermediate transfer belt 11 in the same manner as in the toner patch formation. Thereafter, the old toner is discharged by removing the toner discharge pattern on the intermediate transfer belt 11 by a cleaning mechanism (not shown).

In addition, when the old toner discharge process is performed, the charge amount of the old developer is decreased when the charge amount of the old toner is excessive, such as being placed in a low humidity environment, or by being placed in a high humidity environment. In this case, the charge amount of the whole toner is restored to the original charge amount by supplying new toner.
<Control of Image Stabilization Processing and Preprocessing in Image Forming Apparatus>
FIG. 5 shows an overall control flow of image stabilization processing and preprocessing according to the present embodiment.

  First, the overall control unit 100 monitors the start conditions of the image stabilization process, and if the conditions are satisfied (S1), determines whether or not the print job is being executed (S2). When the print job is being executed (S2: Y), the process waits until the print job is completed (S3). When the print job is not being executed (S2: N, S3: Y), the execution of the print job is prohibited ( S4) The image stabilization process control unit 101 is notified of the start of the image stabilization process.

The patch formation control unit 111 in the image stabilization processing control unit 101 forms a toner patch for detecting development characteristics using a plurality of development potentials (S5).
The density detection control unit 112 measures each density of the plurality of toner patches using the toner pattern detection sensor 36, and notifies the development characteristic verification unit 113 of the measured density (S6).
The development characteristic verification unit 113 verifies the development characteristics (S7).

The development characteristic verification unit 113 determines whether or not the inclination of the development characteristic indicating the development characteristic is equal to or less than a predetermined inclination (0.0035) (S8).
When it is determined that the inclination is equal to or less than the predetermined inclination (S8: YES), the preprocessing execution unit 102 is instructed to execute the preprocessing. Upon receiving the preprocessing execution instruction, the preprocessing execution unit 102 executes preprocessing (S9), and proceeds to S2.

If the slope of the development characteristic graph is not less than or equal to the predetermined value (S8: NO), the development characteristic value is considered to be good, and a development potential value at which a target sensor detection value (TSD) is obtained based on the development characteristic. (TDV) is calculated and set as the developing potential in the developing section 33 (S10). Then, the overall control unit 100 permits execution of the print job (S11).
<Operation of preprocessing execution unit>
FIG. 6 is a detailed flow of the preprocessing (S9) performed by the preprocessing execution unit 102.

The preprocessing execution unit 102 stores the date and time when the previous printout was performed. The timepiece may be the one provided in the overall control unit 100 or the preprocessing execution unit 102.
The date and time when the previous printout was performed may be stored by the overall control unit 100 and received by the preprocessing execution unit 102 from the overall control unit 100.

The preprocessing execution unit 102 compares the previous printout date with the current time, and determines whether a predetermined period has elapsed since the previous printout date (S21).
If it is determined that the predetermined period has elapsed (S21: Y), it is determined whether or not a predetermined number of pages having a low printing area ratio are continued (S22). When it is determined that a predetermined number or more of pages with a low printing area ratio are continuous (S22: Y), a toner discharge process is performed (S23), and then a toner agitation process (S24) is performed.

In the toner stirring process in S24, the toner is stirred for 36 seconds longer than normal (6 seconds).
In S22, when it is not determined that a predetermined number or more of pages having a low printing area ratio are continued (S22: N), a toner agitation process (S24) is performed, and the process ends.
If it is not determined in S21 that printing has not been performed for a predetermined period (S21: N), it is next determined whether or not a predetermined number or more of pages having a low printing area ratio are continued (S25).
When it is determined that a predetermined number or more of pages with a low printing area ratio are continuous (S25: Y), a toner discharge process is executed (S26), then a toner agitation process (S27) is executed, and the process ends. The toner agitation process in S27 is normal toner agitation with a shorter execution time (6 seconds) than the toner agitation process performed in S24.

In S25, if it is not determined that a predetermined number or more of pages with a low printing area ratio are continued (S25: N), a toner agitation process (S27) is executed, and the process ends.
The values of 6 seconds and 36 seconds, which are the toner agitation time of the toner agitation processing (S24), depend on the setting of the developing unit, the used toner, and the like. It is assumed that the optimum numerical value is obtained through experiments.

As described above with reference to FIGS. 5 and 6, the preprocessing and the image stabilization process are repeated until sufficient development characteristics are obtained. On the other hand, the first image stabilization process is sufficient. If the development characteristics are obtained, pre-processing is not executed. Further, if it is determined that sufficient development characteristics can be obtained in the second and subsequent image stabilization processing, the subsequent preprocessing is not performed.
Therefore, in anticipation of the deterioration of the chargeability and fluidity of the toner as compared with the conventional case, the amount of toner agitation is set longer than usual and the amount of old toner discharged Compared to the normal setting, the execution of the print job is permitted at an early stage and the printer becomes ready for printing, and the toner development characteristics may be recovered while reducing waste of toner. It is thought that there are many.
<Modified examples>
Although the present invention has been described based on the above embodiment, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention. Of course.
(1) As a method for controlling the developing potential applied between the developer carrying member and the image carrying member, a method of controlling by applying a DC voltage as the developing potential (hereinafter referred to as DC control), development. There is a method (hereinafter referred to as duty control) in which control is performed using a DC voltage superimposed with an alternating voltage as a potential. The horizontal axis of the development characteristics indicates the development potential, but the upper limit of the development potential that can be set in advance is limited by the rating of the power source.

When the slope of the derived development characteristic is too small, the TDV may exceed the rating when the potential (TDV) necessary for obtaining the predetermined density (TSD) is obtained from the development characteristic line.
In this case, control may be performed by switching between direct current control and duty control. According to the duty control, the development potential exceeding the upper limit can be instantaneously applied while suppressing the average potential of the development potential to the rated upper limit value. Specifically, direct current control is performed in a range where the development potential is equal to or less than a predetermined bias, and duty control is performed in a range exceeding the predetermined bias.

However, when performing duty control, if the amplitude of the AC component is increased, the maximum potential difference generated between the photosensitive member potential and the developing roller potential increases, and leakage may occur due to the potential difference becoming too large.
Therefore, when setting the development potential, parameters such as the execution time of the toner agitation processing and toner discharge processing described above are changed depending on whether the control method is the DC control range or the Duty control range. Thus, the occurrence of leaks or the like may be suppressed by verifying the development characteristics.
(2) With respect to the exposure conditions, the optimum light amount may be calculated by the same process as the development characteristic derivation in the above-described embodiment.

In advance, a ladder-like detection pattern is imaged on the intermediate transfer belt while varying the amount of light, and the sensor values (SD1 to SD4) relating to the ladder corresponding to the respective light amounts (LI1 to LI4) are obtained by the toner pattern detection sensor 36. . An example in which the light amount and the sensor value are plotted is shown in FIG.
By using the graph of FIG. 7 and reading the light amount LI0 (target value) from which the target sensor value SD0 (density) is obtained from the graph of FIG. 7, it is possible to obtain the optimal light amount LI0 for performing exposure. .
(3) As for the value of the primary transfer voltage used for primary transfer, an optimum voltage may be obtained as follows. As for the primary transfer voltage, unlike the case of the development characteristics described above, the toner pattern is not formed, and each of the predetermined primary transfer voltages TV1 (0 V) and TV2 (2.0) is applied, At this time, transfer currents TI1 and TI2 flowing through the transfer roller are obtained.

FIG. 8 is a graph plotting the sets (TV1, TI1) and (TV2, TI2) of the primary transfer voltage and the current value.
Then, as shown in FIG. 8, linear interpolation is performed between the set (TV1, TI1) and (TV2, TI2) of the primary transfer voltage and the current value. By determining the primary transfer voltage (TV0) corresponding to the target detected current value TI0 (15 μA) from the linear function indicating the linearly interpolated graph, the optimum primary transfer voltage is obtained, and the transfer characteristics are determined. Can be improved.
(4) γ correction may be further performed after acquiring the development potential that can obtain the target density value (sensor detection value TSD) described in the above embodiment.

  In the γ correction, when data representing each gradation in the image data is printed as an actual image, each gradation and the density corresponding to each gradation are corrected when there is no predetermined relationship. In general, a gradation value and a density value corresponding to each gradation are in a proportional relationship (has linear characteristics). First, toner patches corresponding to a plurality of gradations are formed, and the toner density for each toner patch is obtained by the toner pattern detection sensor 36 as in the above-described embodiment.

The relationship between each gradation value and the corresponding density value is derived by linear regression analysis, etc., and when the derived characteristic does not show a linear characteristic, a correction curve for returning to the linear characteristic is calculated and applied. To do.
As in this modification, the development characteristics are detected in advance, and γ correction is executed under conditions set in advance so that this is within the appropriate range, so that it is affected by roughness in the low density area and noise. Thus, it is possible to avoid a case where the gradation curve has a discontinuous characteristic.
(5) In the above embodiment, in order to derive the development characteristics, the toner amount of the toner patch formed on the intermediate transfer belt 11 is detected by the sensor. However, the present invention is not limited to this. For example, it may be performed on a toner image formed on a photoreceptor, or may be performed by reading a toner image fixed on paper with a scanner or the like.

In the development process, one-component development in which the developer is composed only of toner is used. However, the present invention is not limited to this, and two-component development or the like may be used.
(6) The target adhesion amount (TSD), sensor value, and the like are examples, and the values may vary depending on design changes. Note that the target adhesion amount (TSD) does not always have to be a constant level, and a value input by a user or maintenance personnel for image adjustment may be used.
(7) The pre-processing execution condition may be changed more finely according to the inclination a of the development characteristics. For example, the smaller the value of a, the longer the stirring time of the toner in the developing unit may be. As a result, when the current development characteristics are relatively good, the pretreatment time is reduced, and when the development characteristics are deteriorated, the pretreatment time is lengthened. Appropriate pretreatment is possible.
(8) The present invention may be the method described above. Further, the present invention may be a computer program that realizes these methods by a computer, or may be a digital signal composed of the computer program.

The present invention also provides a computer-readable recording medium such as a flexible disk, hard disk, CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray Disc). ), Recorded in a semiconductor memory or the like. Further, the present invention may be the computer program or the digital signal recorded on these recording media.
(9) The above embodiment and the above modifications may be combined.

  The image forming apparatus of the present invention is suitable for MFPs (multifunction peripherals), printers, and the like that require high image quality, power saving, resource saving, and the like. And used in offices.

DESCRIPTION OF SYMBOLS 1 Printer 3M-3K Image forming part 4 Paper feed part 5 Fixing part 12 Drive roller 30 Recording sheet 31Y-31K Photosensitive drum 32Y-32K Charger 33M-33K Developing part 34Y-34K Primary transfer roller 35Y Cleaner 36 Toner pattern detection sensor 51 Developing Rollers 52, 53 Agitating Screw 56 Supply Unit 60 Control Unit 100 Overall Control Unit 101 Image Stabilization Control Unit 102 Preprocessing Execution Unit 103 Development Control Unit 104 Development Drive Unit 105 Drum Drive Unit 106 Bias Power Supply 111 Patch Formation Control Unit 112 Density detection control unit 113 Development characteristic verification unit

Claims (5)

An image forming apparatus including a developing unit that develops an electrostatic latent image formed on an image carrier to form a toner image,
Patch forming means for changing the developing potential between the image carrier and the developer carrier to form a plurality of toner patches having different toner adhesion amounts; and
Detecting means for detecting the toner adhesion amount of each of the toner patches;
Deriving means for performing linear regression analysis on a set of development potential and toner adhesion amount for each of the toner patches, deriving a linear regression equation with development bias as an independent variable and toner adhesion amount as a dependent variable;
Determination means for determining whether or not a slope related to the independent variable is a reference slope or less;
An image forming apparatus, comprising: an execution unit configured to execute a recovery process of the developing performance on the assumption that the developing performance of the toner is deteriorated when it is determined that the inclination is equal to or less than the reference inclination. The said execution means stirs the toner for a second stirring time longer than the first stirring time when the slope of the coefficient of the independent variable is larger than the reference slope as the recovery process. The image forming apparatus described. The image forming apparatus according to claim 2, wherein the execution unit lengthens the second stirring time as the slope of the coefficient of the independent variable is smaller. The image forming apparatus according to claim 1, wherein the execution unit forcibly discharges toner in the developing unit as the recovery process. The patch forming means, after the recovery process,
A plurality of toner patches having different toner adhesion amounts are formed by changing the development potential,
The detection means further detects a toner adhesion amount of each toner patch formed after the recovery process,
The deriving means further performs a linear regression analysis on a set of the development potential and the toner adhesion amount for each toner patch formed after the recovery process, the development bias as an independent variable, and the toner adhesion amount as a dependent variable. Deriving a linear regression equation
The image forming apparatus further includes:
When the slope relating to the independent variable in the linear regression equation derived after the recovery process exceeds the reference slope, the linear regression equation derived after the recovery process is used to correspond to a predetermined target toner adhesion amount. The image forming apparatus according to claim 1, wherein a developing potential is acquired, and the developing unit performs development with the acquired developing potential.

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