JP6601368B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that develops an electrostatic latent image using a developer obtained by mixing a toner and a carrier, and more particularly to a technique for determining the degree of deterioration of a carrier.

  In an image forming apparatus, for the purpose of image formation, a developer composed of toner and a carrier is mixed, and the toner in the developer is applied to the electrostatic latent image on the image carrier, and the electrostatic latent image is applied to the image carrier. Develop the image. Further, when the toner in the developer is consumed and reduced, the toner is replenished. On the other hand, since the carrier in the developer is continuously used, the surface of the carrier particle is worn or reduced in diameter, and the carrier deteriorates. For this reason, it is necessary to replace the developer itself in accordance with the deterioration degree of the carrier.

  For example, Patent Document 1 discloses an image forming apparatus that forms an electrostatic latent image on an image carrier and develops the electrostatic latent image with developer toner supplied from a developing device to form an image. The average area ratio is obtained by detecting the area ratio of the image formed by developing the electrostatic latent image, and the driving distance of the developer is detected, and the life of the developer is determined from the average area ratio and the driving distance of the developer. What is to be determined is described.

  In Patent Document 2, the electrostatic capacity value of the carrier after development existing on the developing sleeve is obtained, and the obtained electrostatic capacity value is compared with the electrostatic capacity value of the carrier when not used. An image forming apparatus for obtaining a deterioration state of an agent is shown.

JP 2005-331719 A JP 2009-15046 A

  Here, the degree of deterioration of the developer carrier varies greatly depending on the use environment such as temperature and humidity. However, in Patent Document 1, since the influence of the use environment on the carrier is not taken into account, it is impossible to know the exact carrier deterioration degree according to the use environment.

  In Patent Document 2, it is necessary to provide a special device for measuring the capacitance value of the carrier on the developing sleeve, which complicates the configuration of the image forming apparatus and increases the cost.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to more accurately determine the degree of deterioration of the carrier in the developer without complicating the configuration of the image forming apparatus.

An image forming apparatus according to an aspect of the present invention contains an image carrier that carries an electrostatic latent image, a developer obtained by mixing a toner and a carrier, and the toner of the developer is placed on the image carrier. A developing device that applies an electrostatic latent image to develop the electrostatic latent image, a toner replenishing unit that replenishes toner to the developing device, and a toner detecting unit that detects the toner concentration of the developer in the developing device And the output of the toner detection unit from the time when the toner is supplied to the developing device by the toner supply unit shows a ripple, and then the output of the toner detection unit converges to a value within a predetermined range. A control unit that determines the degree of deterioration of the carrier based on a relaxation time that is a time required to do;
And Ts0 is the relaxation time before the carrier is deteriorated, and it is compared with an actual printing rate before the carrier deteriorates to determine whether to reduce the productivity in order to maintain the image quality. The initial follow-up printing rate used is P0, the relaxation time when the carrier deteriorates is Tsx, and compared with the actual printing rate when the carrier deteriorates, the productivity is maintained in order to maintain the image quality. Assuming that the correction follow-up printing rate used for determining whether or not to decrease is Px, the control unit obtains the correction follow-up printing rate Px based on the following equation (2), and Px = (Ts0 / Tsx) × P0. (2) The control unit compares the actual print rate with the corrected follow-up print rate Px when the carrier deteriorates, and the actual print rate is larger than the corrected follow-up print rate Px. In order to maintain the image quality, it is determined that the productivity is reduced, and the larger the actual printing rate, the longer the (i) developer aging time, or (ii) the interval between printed recording papers The control to lengthen the length is performed .

  According to the present invention, the degree of deterioration of the carrier in the developer can be determined more accurately without complicating the image forming apparatus.

1 is a cross-sectional view showing an embodiment of an image forming apparatus of the present invention. FIG. 2 is a cross-sectional view illustrating a photosensitive drum, a developing device, and the like in the image forming apparatus of the present embodiment. 1 is a block diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment. 6 is a graph showing a change in an output value of a toner density sensor from the time when toner is supplied. It is a graph which shows the characteristic of relaxation time with respect to the number of printed recording sheets. (A) is a graph showing the relationship between the printing rate and productivity so that fogging does not occur in a state where the follow-up printing rate is fixed to the minimum value of 30%, and (B) is a corrected follow-up printing rate of 30% or 35. 5 is a graph showing the relationship between the printing rate and productivity so that fogging does not occur after adjusting to%.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing an embodiment of the image forming apparatus of the present invention. The image forming apparatus 1 of the present embodiment is an MFP (multifunction machine) having a plurality of functions such as a copy function, a printer function, a scanner function, and a facsimile function. The image forming apparatus 1 includes an image reading unit 11 and an image forming unit 12.

  The image reading unit 11 includes a scanner that optically reads a document, and generates image data indicating an image of the document.

  The image forming unit 12 prints an image indicated by the image data generated by the image reading unit 11 on the recording paper P. The image forming unit 3M for magenta, the image forming unit 3C for cyan, and the image forming unit 3C for yellow An image forming unit 3Y and a black image forming unit 3Bk are provided. In each of the image forming units 3M, 3C, 3Y, and 3Bk, the surface of the photosensitive drum 4 is uniformly charged, the surface of the photosensitive drum 4 is exposed, and an electrostatic latent image is formed on the surface of the photosensitive drum 4. The electrostatic latent image on the surface of the photosensitive drum 4 is developed into a toner image, and the toner image on the surface of the photosensitive drum 4 is transferred to the intermediate transfer belt 5 by the primary transfer roller 6. As a result, a color toner image (image) is formed on the intermediate transfer belt 5. This color toner image is secondarily transferred onto the recording paper P conveyed through the conveyance path 8 from the paper supply unit 7 in the nip region N between the intermediate transfer belt 5 and the secondary transfer roller 9.

  Thereafter, the recording paper P is heated and pressurized by the fixing device 15, the toner image on the recording paper P is fixed by thermocompression bonding, and the recording paper P is discharged to the discharge tray 17 through the discharge roller pair 16.

  Further, four toner containers 18 are provided above the image forming units 3M, 3C, 3Y, and 3Bk. Each toner container 18 stores magenta toner, cyan toner, yellow toner, and black toner, and these toners are respectively supplied to the image forming units 3M, 3C, and 3Y through respective paths (not shown). , And 3Bk developing device 22 (shown in FIG. 2).

  FIG. 2 is a cross-sectional view showing one set of the photosensitive unit 21 and the developing device 22 in each of the image forming units 3M, 3C, 3Y, and 3Bk. As shown in FIG. 2, a photoconductor unit 21, a developing device 22, and a primary transfer roller 6 are provided for each of the image forming units 3M, 3C, 3Y, and 3Bk. The photoconductor unit 21 includes a photoconductor drum 4, a charge eliminating unit 24 that neutralizes the surface of the photoconductor drum 4, a cleaning unit 25 that cleans toner remaining on the surface of the photoconductor drum 4, and a uniform surface of the photoconductor drum 4. A charging unit 26 and the like for charging are provided. The developing device 22 includes a developing roller 27, a developing bias applying unit 29 that applies a developing bias in which an AC voltage and a DC voltage are superimposed on the developing roller 27, a developer containing unit 31 that contains a developer, and a developer. Two screws 32 to be conveyed, a supply roller 33 for supplying the developer to the developing roller 27, and the like are provided.

  The developer accommodated in the developer accommodating portion 31 is a two-component developer obtained by mixing toner and carrier. In the developer accommodating portion 31, two conveyance paths 36 extending in the rotation axis direction of the photosensitive drum 4 (the depth direction in FIG. 2) are formed in parallel. Both ends of these transport paths 36 are connected to form a developer transport transport path. The two screws 32 circulate and convey the developer through the circulation and conveyance path, mix the developer toner and carrier, and charge the toner by stirring the toner and carrier.

  The developing roller 27 approaches or contacts the photosensitive drum 4. A developer is applied to the surface of the developing roller 27 via the supply roller 33. The toner carried on the surface of the developing roller 27 includes a developing roller 27 to which a developing bias in which an AC voltage and a DC voltage are superimposed is applied by a developing bias applying unit 29, and a photosensitive drum charged with a potential V0 (patented). An example of the image carrier in the claims) Due to the electrostatic force between 4, the image carrier moves from the surface of the developing roller 27 to the surface of the photosensitive drum 4 and adheres. Thereby, the electrostatic latent image on the surface of the photosensitive drum 4 is developed with toner. Further, a transfer bias voltage is applied to the primary transfer roller 6, and by applying this transfer bias voltage, the toner image carried on the surface of the photosensitive drum 4 is drawn toward the primary transfer roller 6 side, The toner image is transferred to the intermediate transfer belt 5.

  On the other hand, the developer container 31 of the developing device 22 is provided with a toner concentration sensor 35 (an example of a toner detector in the claims) that detects the toner density in the developer container 31. The toner concentration sensor 35 is a magnetic permeability sensor, and detects the magnetic permeability of the developer in the developer container 31. Based on the detected magnetic permeability, a toner concentration (ratio of toner to carrier, so-called T / C) is obtained. For example, when the amount of carrier in the developer within the detection range by the toner concentration sensor 35 is small, a high toner concentration is detected, and when the amount of carrier in the developer facing the toner concentration sensor 35 is large, the toner concentration is low. Is detected.

  When the toner of the developer in the developer container 31 is consumed and the toner density is lowered, the toner is transferred from the toner container 18 to the circulation conveyance path of the developer container 31 based on the output value of the toner density sensor 35. The toner and carrier of the developer are uniformly mixed by the two screws 32, and the toner density is restored.

  FIG. 3 is a functional block diagram showing the main internal configuration of the image forming apparatus 1. As shown in FIG. 3, the image forming apparatus 1 includes a control unit 41, a display unit 42, an operation unit 44, a storage unit 45, a control unit 51, a toner supply unit 47, an image reading unit 11, an image forming unit 12, and a toner density. A sensor 35 and the like are provided. These components can transmit / receive data or signals to / from each other through a bus.

  The display unit 42 includes a liquid crystal display (LCD), an organic EL (Organic Light-Emitting Diode) display, and the like.

  The operation unit 44 includes hard keys such as a numeric keypad, a determination key, and a start key.

  The storage unit 45 includes a RAM, a large capacity HDD (Hard Disk Drive), and the like.

  The controller 51 adjusts the amplitude VP, frequency F, and duty ratio Du of the AC voltage, and adjusts the value of the DC voltage to control the developing bias.

  The toner replenishing unit 47 is a toner replenishing mechanism that replenishes toner from the toner container 18 to the circulation conveyance path of the developer storage unit 31 of the developing device 22. The toner replenishing unit 47 is driven under the control of the control unit 51. The developing bias applying unit 29 is a part of the developing device 22.

  The control unit 41 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like. The control unit 41 functions as the control unit 51 and the display control unit 53 when the control program stored in the ROM or the storage unit 45 is executed by the CPU. In addition, each said structure of the control unit 41 may be comprised by a hard circuit, respectively, not based on the operation | movement based on a program.

  The control unit 51 governs overall operation control of the image forming apparatus 1.

  The display control unit 53 controls the display unit 42 to display a setting item input screen or an information input screen necessary for the image forming process.

  Here, in the developing device 22 of the image forming apparatus 1, since the carrier in the developer is continuously used, the surface of the carrier particle is worn or reduced in diameter, and the carrier is deteriorated. For this reason, it is necessary to determine the lifetime and the deterioration degree of the carrier.

  Therefore, in the present embodiment, when the controller 51 replenishes toner from the toner container 18 to the developer container 31 of the developing device 22 by the toner replenishing unit 47, the output value of the toner density sensor 35 from this replenishment point is set. Ripple is generated, and the degree of carrier deterioration is determined based on the attenuation characteristic from the peak value of the output value. In the present embodiment, attention is paid to the fact that the attenuation characteristic changes according to the degree of deterioration of the carrier. Thereby, in this embodiment, even if the deterioration degree of the carrier changes depending on the use environment such as temperature and humidity, the deterioration degree of the carrier can be accurately determined according to the actual condition of use in this use environment. Yes. In the present embodiment, since the existing toner density sensor 35 is used, it is not necessary to add a special device, and the configuration of the image forming apparatus 1 is not complicated and the cost is not increased.

  The process for determining the deterioration degree of the carrier will be described in detail. When the toner is replenished from the toner container 18 to the developer accommodating portion 31, the toner concentration of the developer is remarkably increased at the replenishment portion of the toner, and the development in which the toner concentration is remarkably increased by the two screws 32. The agent is circulated and conveyed. When the developer passes through the location where the toner density sensor 35 is disposed, initially, the toner density in the developer portion is relatively high, and the developer is circulated and conveyed through the circulation conveyance path, so that the toner concentration sensor 35 is disposed. Each time the position is repeatedly reached, the toner density of the developer portion decreases and converges to a predetermined specified density.

  The output value of the toner density sensor 35 reaches a maximum peak value at the first passage of the developer portion, reaches a lower peak value at the second passage, and then further decreases and is predetermined. Converge to a value within a certain range. That is, after the toner supply unit 47 supplies toner to the developing device 22, the output of the toner density sensor 35 shows a ripple, and then the output of the toner density sensor 35 converges to a value within a predetermined range. To do. The control unit 51 determines the degree of carrier deterioration based on the attenuation characteristic indicated by the output value of the toner density sensor 35.

  Next, an example of determination of the deterioration degree of the carrier based on the attenuation characteristic of the output value of the toner density sensor 35 will be described.

First, the specifications and conditions of the image forming unit as shown in FIG. 2 are set as follows, for example.
[Printing speed] 26 sheets / min [Photosensitive drum peripheral speed] 164.92 mm / sec
[Photosensitive drum diameter] 24 mm
[Gap between photosensitive drum and developing roller] 0.30 mm
[Photoconductor] OPC
[Photosensitive drum surface potential] V0 = 450V
[Developing roller diameter] 16mm
[Development roller surface shape] Knurl 80 μm 120 [Development roller speed] 263.89 mm / sec
Peripheral speed ratio of 1.6 to the photosensitive drum
[Developing roller bias voltage] DC bias voltage Vd = 350V
AC bias voltage Va amplitude voltage VP = 1200 V, frequency = 4 KHz,
Duty ratio 50%
[Toner] 6.8 μm, Positively Charged “Toner Concentration Sensor” Magnetic Permeability Sensor Under such specifications and conditions, the output value of the toner concentration sensor 35 is determined from the time when the toner is supplied to the developer container 31. 4, the horizontal axis indicates the time t that has elapsed since the toner replenishment time, and the vertical axis indicates the output value y of the toner density sensor 35. The characteristic U1 shown in the graph of FIG. 4 is a change in the output value y of the toner density sensor 35 over time.

  As is apparent from this characteristic U1, the output value of the toner density sensor 35 shows a ripple from the toner replenishment time (0 sec in FIG. 4), and this output value reaches the first peak value PV1 (maximum). After decreasing and reaching the second low peak value PV2, the amplitude attenuates and eventually converges.

  Here, the output value of the toner density sensor 35 is y, the constant is A, and the amplitude indicated by the output value y of the toner density sensor 35 is the amplitude at the peak value PV1 from the amplitude at the peak value PV1. The time until decay to 1 / e (an example of a value within the predetermined range described above) is defined as the relaxation time Ts, the time elapsed from the time of toner replenishment is defined as t, and the toner and the carrier are uniformly distributed at a specified ratio. Assuming that the output value y of the toner density sensor 35 is a constant C, the characteristic U1 indicating the change in the output value y of the toner density sensor 35 in the graph of FIG. 4 is expressed by the following equation (a). .

y = A × et / Ts × sin θ + C (a)
Since sin θ = 1 when the output value y reaches the peak value, the characteristic U2 of the curve connecting the peak values of the output value y is expressed by the following equation (b).

y = A × et / Ts + C (b)
Furthermore, in the above formula (b), the constant C which does not affect the relaxation time Ts is removed and the logarithm of both sides is taken, the following formula (1) is derived.

ln (y) = ln (A) -t / Ts (1)
Note that ln is a natural logarithmic function.

  Since the equation (1) derived in this way has only the variable “t”, the relaxation time can be obtained by obtaining the peak value of two or more output values y and the time t when each peak value arrives. Ts can be calculated. In order to obtain the peak value of two or more output values y, it is optimum that the output value y of the toner density sensor 35 swells from the time of toner supply.

  The control unit 51 controls the toner replenishing unit 47 to repeatedly sample the output value y of the toner density sensor 35 from the time of replenishment when the toner is replenished from the toner container 18 to the developer storage unit 31. The peak value of the two output values y is determined. And the control part 51 calculates | requires the time t of these peak values, and calculates relaxation time Ts based on said (1) using the peak value of these output values y and each time t. The time t is counted by a timer built in the control unit 41, and the control unit 51 obtains the time t from the timer.

  The control unit 51 calculates the relaxation time Ts from the output value y of the toner density sensor 35 targeting such a developer, and determines the degree of carrier degradation based on the relaxation time Ts.

  The control unit 51 uses the relaxation time Ts as an index indicating the degree of deterioration of the carrier of the developer. That is, when the time required from when the toner is replenished until the toner and the carrier are uniformly mixed changes according to the degree of deterioration of the carrier, the amplitude of the output value y is 1 of the peak value PV1. The relaxation time Ts until it decays to / e changes in the same way. Based on this, the control unit 51 determines the degree of carrier degradation from the relaxation time Ts.

  The graph of FIG. 5 shows the relaxation time Ts that changes with the number of printed sheets of recording paper P under the condition that only the toner is replenished without replenishing the carrier of the developing device 22 or replacing the developer. The characteristics are shown. The graph of FIG. 5 shows the initial relaxation time Ts, relaxation time Ts after printing 40K sheets at intervals of 2 sheets, and relaxation time Ts after printing 140K sheets at intervals of 2 sheets. Has been. As is clear from the graph of FIG. 5, the carrier deteriorates as the number of printed sheets increases, and the relaxation time Ts increases as the number of printed sheets increases. Therefore, the relaxation time Ts increases according to the degree of deterioration of the carrier. Is clear. Based on this, the control unit 51 determines that the longer the relaxation time Ts, the greater the degree of carrier degradation (the degree of progress of degradation is greater). The display control unit 53 causes the display unit 42 to display the determined degree of carrier degradation.

  Further, in this embodiment, even if the usage environment such as the temperature and humidity around the developing device 22 changes greatly, the influence of this usage environment change affects the developer in the developing device 22 that is a detection target by the toner density sensor 35. It is reflected in. Then, the control unit 51 calculates the relaxation time Ts from the output value y of the toner density sensor 35 targeting such a developer, and determines the degree of carrier deterioration based on the relaxation time Ts. For this reason, according to the present embodiment, it is possible to accurately determine the degree of carrier deterioration even when the usage environment changes.

As described above, in this embodiment, the carrier deterioration degree can be accurately determined based on the relaxation time Ts based on the output value of the toner density sensor 35 without being affected by the use environment such as temperature and humidity. Further, since the existing toner density sensor 35 is used, it is not necessary to add a special device.
[Application Example 1]
According to the above-described embodiment, even when the use environment of the image forming apparatus 1 changes, the degree of carrier deterioration can be accurately determined.

Therefore, in the application example 1, the control unit 51 accurately determines the life of the carrier and the replacement time of the developer based on the degree of deterioration of the carrier. For example, when the relaxation time Ts reaches a preset threshold value, the control unit 51 determines that it is a developer replacement time. The display control unit 53 causes the display unit 42 to display a message for prompting replacement of the developer.
[Application 2]
When the carrier deteriorates, the surface of the carrier particle is worn or reduced in diameter, and the electric resistance of the carrier is lowered. In this case, not only the toner of the developer carried on the surface of the developing roller 27 but also the carrier of the developer moves from the developing roller 27 to the surface of the photosensitive drum 4 and adheres. This is called carrier development. This carrier development not only deteriorates the image quality, but also causes damage to the surface of the photosensitive drum 4 and the surface of the intermediate transfer belt 5.

  However, in this carrier development, the control unit 51 increases the amplitude voltage VP of the AC bias voltage Va applied to the developing roller 27, increases the frequency F, or increases the forward / reverse duty ratio Du. Can be suppressed. Alternatively, the carrier development can also be suppressed by the controller 51 reducing the difference (V0−Vd) between the surface potential V0 of the photosensitive drum 4 and the DC bias voltage Vd applied to the developing roller 27.

  Therefore, in the application example 2, the control unit 51 adjusts the amplitude voltage VP, the frequency F, the forward / reverse duty ratio Du, and the DC bias voltage Vd of the AC bias voltage Va in the development bias applying unit 29 according to the degree of carrier deterioration. Thus, carrier development is suppressed. When the relaxation time Ts becomes equal to or greater than a preset threshold value, the control unit 51 determines each value of the amplitude voltage VP, the frequency F, and the forward / reverse duty ratio Du of the AC voltage Vc that is set in advance according to the relaxation time Ts. And a bias control instruction indicating the value of the DC voltage Vd is output to the developing bias applying unit 29. Based on the bias control instruction, the developing bias applying unit 29 sets each value of the amplitude voltage VP, the frequency F, the forward / reverse duty ratio Du of the AC voltage Vc, and the value of the DC voltage Vd, and sets the relaxation time Ts. A corresponding developing bias is generated and applied to the developing roller 27. Thereby, it is possible to suppress the carrier development when the deterioration of the carrier progresses.

  For example, when the relaxation time Ts is equal to or greater than a preset threshold value, the control unit 51 increases each value of the amplitude voltage VP, the frequency F, the forward / reverse duty ratio Du of the AC voltage Vc, and the DC voltage as the relaxation time Ts increases. A bias control instruction for increasing the value of Vd is output to the developing bias applying unit 29.

When the relaxation time Ts becomes equal to or greater than a preset threshold, the control unit 51 determines (1) each value of the amplitude voltage VP, the frequency F, and the forward / reverse duty ratio Du of the AC voltage Vc according to the relaxation time Ts, (2) Only one of the DC voltage Vd (1) or (2) may be controlled.
[Application Example 3]
When the carrier deteriorates, the particle surface of the carrier is worn or reduced in diameter, and the bulk density of the carrier in the developer increases. In this case, the toner density sensor 35 does not perform detection according to the substance, and the detected magnetic permeability of the developer becomes higher than the original, and the toner density lower than the original is detected. For this reason, it is determined that the ratio of the toner to the carrier is low, and the toner is excessively replenished based on this ratio, leading to a decrease in image quality.

Therefore, in the application example 3, the control unit 51 corrects the output value of the toner density sensor 35 according to the degree of carrier deterioration. For example, as the relaxation time Ts increases, the control unit 51 corrects and reduces the output value of the toner concentration sensor 35, that is, the magnetic permeability of the developer detected by the toner concentration sensor 35. Thereby, even if the carrier is deteriorated, the ratio of the toner to the carrier can be accurately determined, and the toner can be replenished accurately.
[Application Example 4]
In a situation where high-density printing is performed continuously, the toner is replenished as needed, but the time for which the toner is charged by the carrier is shortened, so the amount of toner charge is reduced and toner fog occurs. For this reason, when the printing rate per unit time becomes larger than a certain criterion (hereinafter referred to as a follow-up printing rate), the developer agitation time (developer aging time) in the developer container 31 of the developing device 22. ) Is extended to maintain the charge amount of the toner. Alternatively, when the printing rate per unit time becomes larger than the follow-up printing rate, the interval of the recording paper P to be printed is lengthened. That is, when the printing rate per unit time is larger than the follow-up printing rate, productivity is lowered to maintain image quality.

  Here, since the charge imparting ability of the toner by the carrier decreases as the carrier deteriorates, the follow-up printing rate is changed according to the actual charge imparting ability of the carrier, that is, according to the degree of deterioration of the carrier. However, conventionally, since there is no means for measuring the deterioration degree of the carrier while the image forming apparatus 1 is in operation, the follow-up printing rate is fixed at the minimum value, which makes efficient operation of the image forming apparatus 1 possible. It was hindering.

  Therefore, in application example 4, the control unit 51 varies the follow-up printing rate in accordance with the degree of carrier deterioration. For example, the relaxation time before the carrier deteriorates is Ts0, and compared with the actual printing rate before the carrier deteriorates, the initial follow-up used for determining whether to reduce the productivity in order to maintain the image quality. Whether the print rate is P0, the relaxation time when the carrier is deteriorated is Tsx, and is compared with the actual print rate when the carrier is deteriorated to determine whether to reduce the productivity in order to maintain the image quality Let Px be the correction follow-up printing rate used in the above. The control unit 51 obtains a corrected follow-up printing rate Px based on the following equation (2).

Px = (Ts0 / Tsx) × P0 (2)
Then, the control unit 51 obtains the actual printing rate based on the number of prints of the recording paper P and the change in the toner density detected by the toner density sensor 35, and compares the actual printing rate with the corrected follow-up printing rate Px. When the actual printing rate becomes larger than the corrected follow-up printing rate Px, it is determined that the productivity is lowered in order to maintain the image quality. The larger the actual printing rate, (i) the aging time of the developer Control such as lengthening or (ii) lengthening the interval of the recording paper P to be printed is performed to prevent the occurrence of toner fog. Thereby, compared with the case where the follow-up printing rate is fixed, it is possible to suppress a decrease in productivity while preventing the occurrence of toner fog.

  FIG. 6A is a graph showing the relationship between the printing rate and productivity in a state where the follow-up printing rate is fixed at 30% of the minimum value as in the prior art. FIG. 6B is a graph showing the relationship between the printing rate and productivity when the corrected follow-up printing rate Px is adjusted to 30% or 35% based on the above equation (2). As is clear from the comparison between the graph of FIG. 6A and the graph of FIG. 6B, the actual print rate without reducing the image quality and productivity by changing the correction follow-up print rate Px. The range expands.

  As described above, in the above application examples 2, 3, and 4, the feedback control, which has not been performed in the past, is performed to feed back the relaxation time Ts0 corresponding to the degree of deterioration of the carrier, and the bias of the developing roller 27. By controlling the output value of the toner density sensor 35 or the follow-up printing rate, the effects described above can be obtained.

  In the above embodiment, an image forming apparatus is illustrated as an embodiment of the image forming apparatus of the present invention. However, this is merely an example, and a copier, a printer, a facsimile machine, or the like may be used.

  Further, the configuration and processing of the above-described embodiment described with reference to FIGS. 1 to 6 are only one embodiment of the present invention, and are not intended to limit the present invention to the configuration and processing.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Image reading part 12 Image forming part 4 Photosensitive drum 22 Developing apparatus 27 Developing roller 29 Developing bias application part 35 Toner density sensor 41 Control unit 42 Display part 44 Operation part 45 Storage part 47 Toner replenishment part 51 Control part 53 Display controller

Claims (6)

An image carrier for carrying an electrostatic latent image;
A developing device that contains a developer obtained by mixing toner and a carrier, applies the toner of the developer to the electrostatic latent image on the image carrier, and develops the electrostatic latent image;
A toner replenishing section for replenishing toner to the developing device;
A toner detector for detecting the toner concentration of the developer in the developing device;
After the output of the toner detection unit from the time when the toner is supplied to the developing device by the toner supply unit shows a ripple, until the output of the toner detection unit converges to a value within a predetermined range. based on the time required is relaxation time, and a control unit that determines the degree of deterioration of the carrier,
The relaxation time before the carrier deteriorates is set to Ts0, and compared with an actual printing rate before the carrier deteriorates, an initial stage used for determining whether to reduce the productivity in order to maintain the image quality. Whether the follow-up printing rate is P0, the relaxation time when the carrier deteriorates is Tsx, and compared with the actual printing rate when the carrier deteriorates, is productivity lowered to maintain image quality? If the correction follow-up printing rate used to determine whether or not is Px,
The control unit obtains the corrected follow-up printing rate Px based on the following equation (2):
Px = (Ts0 / Tsx) × P0 (2)
The control unit compares the actual print rate with the corrected follow-up print rate Px when the carrier deteriorates, and maintains the image quality when the actual print rate becomes larger than the corrected follow-up print rate Px. Therefore, it is determined that the productivity is reduced, and the larger the actual printing rate, the longer the aging time of the developer (i) the longer the aging time of the developer, or (ii) the longer the interval between the recording sheets to be printed. apparatus. The elapsed time since toner is supplied to the developing device by the toner supply unit is t, the output of the toner detection unit is y, the constant is A, and the amplitude indicated by the output of the toner detection unit is a peak value. When Ts is a relaxation time as a time from the amplitude at the time of showing the peak value to 1 / e of the amplitude at the time of showing the peak value,
The control unit uses at least two elapsed times t when the output of the toner detection unit becomes a peak value and the next peak value, and outputs y of the toner detection unit at the respective elapsed times t, The image forming apparatus according to claim 1, wherein the relaxation time Ts is derived from (1), and the deterioration degree of the carrier is determined using the relaxation time Ts as an index of the deterioration degree of the carrier.
ln (y) = ln (A) -t / Ts (1)   The image forming apparatus according to claim 1, wherein the control unit determines a lifetime of the carrier based on the determined degree of deterioration of the carrier.   The image forming apparatus according to claim 1, wherein the control unit corrects a surface potential of the image carrier according to the determined degree of deterioration of the carrier. The developing device has a developer carrying member that carries the developer and imparts the developer to an electrostatic latent image on the image carrier,
The image forming apparatus according to claim 1, wherein the control unit corrects a developing bias applied to the developer carrying member based on the determined degree of deterioration of the carrier.   The image forming apparatus according to claim 1, wherein the control unit corrects an output of the toner detection unit based on the determined degree of deterioration of the carrier.