JPH10123769A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the toner concentration of a developing device in an adequate state in accordance with another image forming process condition and the change of environmental condition. SOLUTION: When the value of the driving voltage of a copy lamp is made to be >= an initial value Va+α by process control processing, developing performance is judged to be too high, so that a toner concentration reference value K is corrected to K+β. Thus, the toner concentration inside the developing device is increased to reduce the electrostatically charged amount of toner, so that the developing characteristic is deteriorated. On the contrary, when the value of the driving voltage of the copy lamp is made to be <= the initial value Va-α by the process control processing, the developing performance is judged to be too low, so that the toner concentration reference value K is corrected to K-β. Thus, the toner concentration inside the developing device is decreased to raise the electrostatically charged amount of the toner, and the developing characteristic is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a laser printer, and a facsimile for forming an image by an electrophotographic method using a two-component developer.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine for forming an image by an electrophotographic method, devices and consumables such as a charger, an exposure device, a photoconductor, and a developer are used. These devices and consumables cause characteristic changes due to environmental changes such as temperature and humidity, and characteristic changes due to aging. For this reason, the state of formation of an image obtained by charging and exposing the photosensitive member becomes unstable due to a change in the characteristics of the apparatus and consumables.

Therefore, conventionally, there has been proposed an image forming apparatus and an image forming method for stabilizing an image forming state by controlling image forming process conditions in accordance with the change in the characteristics. For example, JP-A-6-51
No. 551 discloses that a toner patch is formed at a predetermined position on the peripheral surface of a photoreceptor, and image forming process conditions such as a developing bias are corrected based on a density ratio between the toner patch and a non-image forming portion. An arrangement is disclosed. Japanese Patent Application Laid-Open No. 6-19259 discloses that the copy lamp voltage is changed every time a predetermined number of copies are completed, and the relationship between the output of the original density sensor and the developing bias voltage is changed according to the amount of change in the copy lamp voltage. Is disclosed. Further, in Japanese Patent Application Laid-Open No. Hei 6-11929, in the control of the process condition by the toner patch method, the amount of the toner remaining after the transfer process in the toner patch portion is detected, and the amount of the toner is defined as a predetermined standard. A configuration is disclosed in which a static elimination output is controlled based on a result of comparison with a value.

As described above, by executing a process control process different from the normal image forming process and automatically correcting the image forming process conditions affecting the image forming state, the image forming state can be maintained well. I have.

[0005]

However, in the conventional image forming apparatus, a single image forming process condition is automatically corrected by a process control process, and based on the correction state of the image forming process condition. There is no device that corrects the toner density in the developing device. For this reason, in the conventional image forming apparatus, there is a problem that the toner concentration of the developer, which greatly affects the image forming state, cannot be maintained in an appropriate state according to changes in other image forming process conditions and environmental conditions. there were.

SUMMARY OF THE INVENTION It is an object of the present invention to maintain the toner density of a developing device in an appropriate state in accordance with changes in other image forming process conditions and environmental conditions, and to provide a satisfactory toner without excessive or insufficient density and fog. An object of the present invention is to provide an image forming apparatus capable of forming an image of high quality.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a change in environmental conditions can be recognized from a correction state of an image forming process condition in a process control process. It is noted that by correcting the density, the toner density of the developing device can be maintained in an appropriate state according to changes in other image forming process conditions and environmental conditions.

For example, the charge amount of the toner in the developing device has been reduced in a high-temperature and high-humidity state and after being left for a long period of time. Since toner scattering occurs, it is necessary to reduce the toner concentration in the developing device. Conversely, during low-temperature and low-humidity conditions and during continuous image formation, the charge amount of the toner in the developing device is increased, and transferability is deteriorated due to a decrease in image density. is there. On the other hand, in the process control process for correcting the copy lamp voltage, the copy lamp voltage is increased in a high-temperature and high-humidity state and after being left for a long time, and the copy lamp voltage is decreased in a low-temperature and low-humidity state and continuous image formation.

Therefore, a change in environmental conditions can be recognized from the correction state of the image forming process conditions such as the copy lamp voltage in the process control processing, and the toner density of the developing device is corrected according to the correction state of the image forming process conditions. By doing so, it is possible to maintain the toner density of the developing device in an appropriate state according to changes in other image forming process conditions and environmental conditions.

According to a first aspect of the present invention, there is provided an image forming apparatus for performing a process control process for automatically correcting an image forming process condition other than a toner density of a developing device among image forming process conditions affecting an image forming state. It is characterized in that a correction for increasing or decreasing the toner density reference value of the developing device is performed based on a comparison result between an image forming process condition after correction by the process control process and a predetermined value set in advance.

Therefore, according to the first aspect of the present invention, the correction state of the image forming process condition is recognized from the comparison result between the image forming process condition after the correction by the process control process and a predetermined value, and development is performed. The toner density in the apparatus can be set to an appropriate state according to the correction state of the image forming process conditions.

According to a second aspect of the present invention, the correction amount of the toner density reference value of the developing device is changed according to a change state of the image forming process condition corrected by the process control process.

Therefore, according to the second aspect of the present invention, the correction amount of the toner density in the developing device is changed according to the change state of the image forming process condition, and the toner density of the developing device is maintained in a more appropriate state. Is done.

According to a third aspect of the present invention, after the correction for increasing or decreasing the toner density reference value of the developing device is performed, a process for matching the toner density in the developing device to the toner density reference value is performed. I do.

Therefore, according to the third aspect of the invention, the toner density in the developing device quickly matches the corrected toner density reference value.

According to a fourth aspect of the present invention, a current correction state is determined based on a history of correction states of the toner density reference value.

Therefore, in the invention described in claim 4, when correcting the toner density reference value, the history of the correction state up to that time is referred to. For example, a plurality of processes for increasing or decreasing the toner density reference value in the same direction are performed. When the number of times is consecutive, the toner concentration of the developing device is not excessively corrected.

According to a fifth aspect of the present invention, an upper limit value and a lower limit value are set in advance for the toner density reference value, and when the toner density reference value reaches the upper limit value or the lower limit value, another image processing is performed. It is characterized in that a process control for correcting the condition is executed. Therefore, in the invention described in claim 5, the toner density reference value is not corrected beyond the upper limit of the range in which the image quality can be maintained satisfactorily, and the image quality does not deteriorate due to fog.

[0019]

FIG. 1 is a schematic front view showing the internal structure of a copying machine which is an image forming apparatus according to an embodiment of the present invention. A copying machine 40 embodying the present invention includes a platen 1 having a reference plate 33 at a part of the bottom surface, a copy lamp 2,
A first mirror 3, a second mirror 4, a third mirror 5, a fourth mirror 6, a fifth mirror 7, a sixth mirror 8, a lens 9, a photosensitive drum 10, a charger 11, a developing device 12, a transfer device 13,
Cleaning device 1 provided with cleaning blade 15
4. Paper transport belt 16, fixing device 17, static elimination lamp 1
8, a blank lamp 19, a photo sensor 20, and a temperature / humidity sensor 31.

In the copying machine 40, when a document is placed on the upper surface of the document table 1 and a copy switch is operated on an operation panel (not shown), the copy lamp 2 and the mirrors 3 to 3 are operated.
Reference numeral 5 moves under the document table 1 in parallel with the document table 1 to expose and scan the image of the document. The light of the copy lamp 2 is reflected on the image surface of the document placed on the document table 1, and this reflected light passes through the mirrors 2 to 8 and the lens 9 to the photosensitive drum 10.
The light is distributed on the surface. The surface of the photoconductor drum 10 is charged with a single-polarity charge by the charger 11 prior to the light distribution of the reflected light of the document, and the surface of the photoconductive drum 10 is irradiated with the reflected light of the document. An electrostatic latent image is formed on the image. The electrostatic latent image is removed from the charge of the non-image portion by irradiation of light from the blank lamp 19, and then supplied with toner from the developing device 20 to be visualized as a toner image.

On the other hand, in synchronization with the rotation of the photosensitive drum 10, a sheet is fed between the photosensitive drum 10 and the transfer unit 13 from a feeding unit (not shown). The toner image formed on the surface of the photosensitive drum 10 is transferred to the surface of the sheet by corona discharge of the transfer device 13. The paper on which the toner image has been transferred is transported to the fixing device 17 by the paper transport belt 16. The fixing device 17 heats and pressurizes the sheet, melts the toner image on the sheet, and fixes the toner image on the sheet. The sheet that has passed through the fixing device 17 is discharged outside the copying machine 40 by a discharge roller (not shown). The surface of the photosensitive drum 10 on which the toner image has been transferred to the paper is subjected to removal of residual toner by a cleaning blade of a cleaning device 14 and removal of residual charge by a charge removing lamp 18, and then to irradiation of the next original reflected light. In addition, a charge is provided from the charger 11.

The developing device 12 includes a toner hopper 21 for replenishing the toner inside the developing device 12, a toner replenishing motor 22 driven at the time of replenishing the toner, and a non-magnetic sleeve supported at a position facing the photosensitive drum 10. 23, a magnet 24 disposed inside a non-magnetic sleeve 23, a stirring roller 2 pivotally supported inside a developing device 12 for storing a developer.
And a toner density sensor 26 for detecting the toner density of the developer in the developing device 12. The developer contained in the developing device 12 is stirred by the rotation of the stirring roller 25, and the carrier and the toner constituting the developer are frictionally charged. The toner is attracted to the surface of the non-magnetic sleeve 23 together with the carrier by the action of the magnet 24, and the photosensitive drum 1 is rotated by the rotation of the non-magnetic sleeve 23.
0 is conveyed to a position facing the surface of “0”. The toner adsorbed on the surface of the non-magnetic sleeve 23 is electrostatically adsorbed on the electrostatic latent image formed on the surface of the photoreceptor drum 10, and the electrostatic latent image is visualized.

FIG. 2 is a block diagram showing a partial configuration of the control unit of the copying machine. The toner supply motor 22, the toner density sensor 26, the A / D converter 28, the copy lamp driving circuit 30, and the like are connected to the CPU 29 constituting the control unit of the copying machine 40. The toner density sensor 26
For example, it is a magnetic permeability sensor that detects the toner density in the developer based on the magnetic permeability of the developer stored in the developing device 12. The developer contained in the developing device 12 is composed of a magnetic carrier and a non-magnetic toner. Therefore, when the proportion of the toner in the developer increases, the magnetic permeability of the developer decreases, and conversely, when the proportion of the toner in the developer decreases, the magnetic permeability of the developer increases. The CPU 29 supplies the detection signal of the photo sensor 20 together with the detection signal of the toner density sensor 26 to the amplifier 27 and the A / D converter 2.
8 is input. The CPU 29 controls ON / OFF of the toner supply motor 22 and the drive voltage of the copy lamp 2 based on the detection signal of the toner density sensor 26 and the detection signal of the photo sensor 20.

In the above-described development of the electrostatic latent image during the copying operation, only the toner in the developer contained in the developing device 12 is consumed, and in order to maintain the toner image density constant,
It is necessary to supply toner to the developing device 12. Therefore, the toner density is detected based on the magnetic permeability detected by the toner density sensor 26, and the detected value of the toner density and the CPU 2
9, when it is determined that the detected toner density is lower than the toner density reference value K in comparison with the toner density reference value K preset in FIG. Replenish toner inside.

Further, in the copying machine 40, a process control process is executed when the power is turned on under a predetermined condition or every fixed period (determined by the total number of copies or the total operating time). In this process control process, a toner patch is formed on the surface of the photosensitive drum 10 by an image forming process, and the density of the toner patch is detected by the photo sensor 20. As shown in FIG. 2, an output signal of the photo sensor 20 is amplified to a predetermined level by an amplifier 27, converted to digital data by an A / D converter 28, and input to a CPU 29. The CPU 29 corrects the parameters of the image forming process by controlling the drive voltage of the copy lamp 2 in the copy lamp drive circuit 30 based on the data input from the A / D converter 28.

That is, when the process control process is executed, first, the reference plate 33 arranged near the document placing surface of the document table 1 is irradiated by the copy lamp 2 and the reflected light is exposed through the exposure optical system. Light is distributed on the surface of the body drum 10. At this time, by changing the voltage of the copy lamp 2, a plurality of patch-like electrostatic latent images having different surface potentials are formed, and these patch-like electrostatic latent images are visualized by the developing device 12. As a result, a plurality of toner patches having different toner densities are formed, and the photo sensor 20 detects the toner densities of these toner patches.
The detection value of the photo sensor 20 for each of the plurality of toner patches is compared with a predetermined value P, and the voltage applied to the copy lamp 20 for the toner patch corresponding to the predetermined value P is changed to the voltage of the copy lamp 20 during a normal copying operation. Adopted as drive voltage.

Since the number of toner patches that can be created by changing the toner density is finite, there is not always a toner patch having a density that matches the predetermined value P. Therefore, when there is no toner patch having a density matching the predetermined value P, the voltage applied to the copy lamp 2 according to the detection values P1 and P2 (P1 <P <P2) of the photosensors 20 closest to the predetermined value P is determined. , The drive voltage of the copy lamp 2 during the copying operation is calculated. That is, assuming that the applied voltages of the copy lamp 2 corresponding to the detection values P1 and P2 of the photosensor 20 are V1 and V2, respectively, the relationship of V1 = aP1 + b (1) V2 = aP2 + b (2) Is satisfied, the values of a and b are obtained from Expressions (1) and (2), and the driving voltage V of the copy lamp 2 during the copying operation is obtained from V = aP + b (3).

By the above process control processing,
The drive voltage of the copy lamp 2 changes as shown in FIG. When the drive voltage V of the copy lamp 2 is set to a value equal to or more than the initial value Va + α by the process control process, it is determined that the developing property is too high, and the toner density reference value K is changed to K +
Correct to β. As a result, the toner is replenished so as to reduce the magnetic permeability of the developer contained in the developing device 12, and the charge amount of the toner, that is, the developability is reduced by increasing the toner concentration in the developer. . This state continues until the drive voltage V of the copy lamp 2 is reduced to a value equal to or less than the initial value Va-α in the subsequent process control processing.

Conversely, if the drive voltage V of the copy lamp 2 is set to a value equal to or less than the initial value Va-α by the process control process, it is determined that the developing property is too low, and the toner density reference value K is changed to K-β. To be corrected. As a result, the amount of toner supplied into the developing device 12 decreases, the magnetic permeability of the developer increases, and the toner density in the developer decreases, so that the developability increases. This state continues until the drive voltage V of the copy lamp 2 becomes equal to or more than the initial value Va + α in the subsequent process control processing. With the above processing, a stable copy image can be obtained over a long period of time.

In FIG. 3, the rotation time of the developing tank on the horizontal axis is the rotation time of the non-magnetic sleeve 23, that is,
This means the accumulated operating time from the time when the power to the developing device 12 is turned on, and does not include the time when the developing device 12 is not operating.

Further, even if the toner density reference value is changed, the toner density of the developer in the developing device 12 does not change immediately.
Immediately after the toner density reference value K is increased, toner is frequently supplied into the developing device 12, and the toner density reference value K is increased.
Is decreased, the toner density in the developing device 12 does not decrease unless the toner is consumed by repeating the copying operation. Therefore, as shown in part (a) of FIG. 3, after the toner density reference value K is changed, the value of the drive voltage V of the copy lamp 2 is changed to the initial value Va ± α until a predetermined time T elapses.
, The toner density reference value K is not changed correspondingly.

Further, when the toner density reference value K is changed to K + β, the toner density in the developing device 12 is increased and the developing property is reduced. As a result, the density of the toner patch formed on the surface of the photosensitive drum 10 is reduced. The drive voltage V of the copy lamp 2 should decrease due to the process control process. However, as shown in part (b) of FIG.
If the drive voltage V of the copy lamp 2 is continuously increased after changing the toner density reference value K to K + β, it is determined that a failure has occurred in the copying machine 40.

FIG. 4 is a flowchart showing a first example of the processing procedure of the control unit of the copying machine. When the timing for executing the process control process comes to a predetermined timing (s1), the CPU 29 constituting the control unit of the copying machine 40 determines that the elapsed time t from when the previous toner density reference value K was changed is t ≧ It is determined whether or not T (time T is a time until the toner density in the developing device 12 is stabilized after the toner density reference value K is changed) (s2). If t ≧ T in this determination, the process control process is not permitted, and the process returns to the normal copying operation. If t ≧ T, the process control process is allowed, a toner patch is formed, the correction value ΔV of the copy lamp voltage V by the process control process is calculated, and the copy lamp voltage is corrected (s3 to s5). Further, the copy lamp voltage V after the correction is the initial value V of the copy lamp voltage.
If it is equal to or more than a + α, the toner density reference value K is set to K + β
(S6, s7), and the corrected copy ramp voltage V
Is smaller than the initial value Va-α of the copy lamp voltage, the toner density reference value K is changed to K-β (s8, s).
9).

By this processing, it is possible to prevent excessive process control processing in a state where the toner concentration in the developing device 12 is not stable. In the above example, for example, α = 4 volts, β = 10 counts (value at which the toner density increases by 0.5%), and T = 200 seconds.

FIG. 5 is a flowchart showing a second example of the processing procedure of the control unit of the copying machine. The CPU 29
After the copy lamp voltage is corrected by the process control process (s11 to s13), it is determined whether or not the corrected copy lamp voltage V exceeds the initial value Va ± α of the copy lamp voltage (s14, s17). . The copy lamp voltage V after the correction is the initial value Va + of the copy lamp voltage.
If the value is equal to or more than α, the toner density reference value K is corrected to K + β, and then the set time of the rotation time of the stirring roller 25 in the developing device 12 is lengthened (s15, s16). The corrected copy lamp voltage V is the initial value V of the copy lamp voltage.
If it is equal to or less than a-α, the reference value K for the toner density correction
Is corrected to K-β, and then a black solid image is formed (s1
8, s19).

By this processing, the toner density reference value K is set to K
When the value increases to −β, a large amount of toner in the developing device 12 is consumed, so that the time until the toner concentration in the developing device 12 actually decreases can be reduced. Further, when the toner concentration reference value K is reduced to K + β, by sufficiently agitating the toner supplied in the developing device 12, the charge amount of the supplied toner can be quickly increased.

FIG. 6 is a flowchart showing a third example of the processing procedure of the control unit of the copying machine. The CPU 29
After the copy lamp voltage is corrected by the process control process (s21 to s23), it is determined whether or not the corrected copy lamp voltage V exceeds the copy lamp voltage initial value Va ± α (s24, s28). . The copy lamp voltage V after the correction is the initial value Va + of the copy lamp voltage.
If the toner density reference value K is increased in the previous process control when the value is equal to or more than α, the number of continuous corrections n of the toner density reference value K in the same direction up to the previous time is n.
Based on the correction value β (n−1) and the previous correction value β (n−1), the current correction value βn is calculated by βn = kβ (n−1) (where 0 <k <1), and the toner density reference value K
Is corrected to K + βn (s25, s26). If the toner density reference value K has not been decreased in the previous process control, the toner density reference value K is corrected to K + β (s27).

When the corrected copy ramp voltage V is equal to or less than the initial value Va-α of the copy ramp voltage and the toner density reference value K is decreased in the previous process control, the same The present correction value βn is calculated from βn = kβ (n−1) based on the continuous correction number n of the toner density reference value K and the previous correction value β (n−1) (where 0 <k <1). ), Toner density reference value K
Is corrected to K-βn (s29, s30). If the toner density reference value K has not been increased in the previous process control, the toner density reference value K is corrected to K-β (s31).

By this processing, the current correction amount can be adjusted based on the history of the correction state of the toner density reference value K, and the process of increasing or decreasing the toner density reference value K in the same direction is repeated plural times. In this case, it is possible to prevent the toner concentration in the developing device 12 from being excessively corrected. For example,
When α = 4 volts and β = 10 counts, k = 0.6.

FIG. 7 is a flowchart showing a fourth example of the processing procedure of the control unit of the copying machine. The CPU 29
After the copy lamp voltage is corrected by the process control process (s41 to s43), it is determined whether or not the corrected copy lamp voltage exceeds the initial value Va ± α of the copy lamp voltage (s44, s48). The copy lamp voltage V after the correction is the copy lamp voltage initial value Va ± α.
Is exceeded, the absolute value | ΔV / ΔT | of the variation ΔV of the copy lamp voltage per unit time ΔT is calculated and compared with a predetermined amount z (s45, s49). In this comparison, when | ΔV / ΔT | ≧ z, the toner density reference value K is corrected to K + jβ or K−jβ (1 <j) (s46, s50).

By this process, as shown in part (c) of FIG. 3, when the change in the copy lamp voltage due to the process control process is large and it can be determined that the toner density in the developing device 12 is extremely inappropriate. Thus, the toner density in the developing device 12 can be changed quickly. For example, when β = 7 counts, z = 0.064 volt / sec,
j = 1.4 (jβ = 10).

FIG. 8 is a flowchart showing a fifth example of the processing procedure of the control unit of the copying machine. By correcting the toner density reference value K to K ± β according to the process control, the copy lamp voltage V becomes (the initial voltage Va).
When the voltage changes in a short time from −α) to (initial voltage Va + α) or from (initial voltage Va + α) to (initial voltage Va−α), it is considered that the correction of the toner density reference value is excessive. Therefore, the CPU 29 measures the time Tα1 during which the copy lamp voltage changes from (initial voltage Va−α) to (initial voltage Va + α) and the time Tα2 during which the copy lamp voltage changes from (initial voltage Va + α) to (initial voltage Va−α). Then, by the correction by the process control (s61 to
(s63), when the copy ramp voltage exceeds (initial voltage Va + α) or (initial voltage Va−α), (s64, s6)
8) Compare time Tα1 or time Tα2 with predetermined time Y (s65, s69). In this comparison, the time Tα
1 or the time Tα2 is shorter than the predetermined time Y, the correction amount of the toner density reference value is set to + iβ or −iβ (0 <i
<1) (s66, s70).

By this processing, it is possible to prevent the toner density from being excessively corrected, and to set the toner density in the developing device 12 to an appropriate value. For example, after the toner density reference value is changed by + β = 15 counts, (initial voltage Va−
When the time Tα1 ≦ 1100 seconds from (8 volts) to (initial voltage Va + 8 volts), i = 0.6 and the toner density reference value is changed by −8 counts.

As shown in FIG. 9A, when the toner concentration in the developing device 12 is too high, the charge amount of the toner is reduced, and the image quality is reduced due to fog. Also,
If the toner concentration in the developing device 12 is too low, the image quality is degraded due to carrier drop. Therefore, an upper limit value Kmax and a lower limit value Kmin are provided for the toner density reference value,
It can be considered that the toner density reference value is not corrected beyond the upper limit Kmax and the lower limit Kmin.

As shown in FIG. 9B, even when the density in the developing device 12 is constant, the charge amount increases as the temperature and humidity decrease, and the charge amount decreases as the temperature and humidity increase. Therefore, it is conceivable that the external environment of the developing device 12 is measured by the temperature / humidity sensor 31, and the upper limit Kmax and the lower limit Kmin of the toner density reference value are changed based on the measurement result. For example, in a normal state, 50 ≦ S ≦ 120,
In the high temperature and high humidity state, 60 ≦ S ≦ 130, and in the low temperature and low humidity state, 40 ≦ S ≦ 100.

FIG. 10 is a flowchart showing a sixth example of the processing procedure of the control unit of the copying machine. CPU 29
Is corrected by the correction in the process control (s81
To s83), when the copy lamp voltage V becomes equal to or lower than the initial voltage Va-α, the current toner density reference value becomes the lower limit value K.
It is determined whether or not it is min (s86, s87). If the current toner density reference value is the lower limit Kmin, the correction for increasing the toner density reference value is not performed, and the voltage value Vb of the developing bias is corrected (s88).

By this processing, the toner density reference value is not corrected beyond the upper limit of the range in which good image quality can be maintained, and the image quality due to fog can be prevented from lowering. For example, when the toner density reference value is the lower limit value Kmin =
120, the copy ramp voltage is (initial voltage Va−4).
Volts), the developing bias voltage value vb
To 30 volts.

When the toner density reference value reaches the upper limit value or the lower limit value, image processing conditions other than the developing bias can be corrected.

[0049]

According to the first aspect of the present invention, a correction state of the image forming process condition is recognized from a comparison result between the image forming process condition after the correction by the process control process and a predetermined value set in advance. The toner density in the developing device can be set to an appropriate state according to the correction state of the image forming process conditions.

According to the second aspect of the present invention, the correction amount of the toner density in the developing device is changed according to the change state of the image forming process condition, and the toner density of the developing device is maintained in a more appropriate state. be able to.

According to the third aspect of the present invention, the toner density in the developing device can be made to quickly match the corrected toner density reference value.

According to the fourth aspect of the present invention, the current toner density reference value is corrected by referring to the history of the correction status of the toner density reference value so far. Even when the toner density is continuously increased and decreased in the same direction, it is possible to prevent the toner density of the developing device from being excessively corrected.

According to the fifth aspect of the invention, the toner density standard value is not corrected beyond the upper limit of the range in which the image quality can be maintained satisfactorily, so that the image quality can be reliably prevented from lowering due to fog.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing an internal structure of a copying machine which is an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a partial configuration of a control unit of the copying machine.

FIG. 3 is a diagram showing a change state of a copy lamp voltage and a toner density reference value in the copying machine.

FIG. 4 is a flowchart illustrating a first example of a processing procedure of a control unit of the copying machine.

FIG. 5 is a flowchart showing a second example of the processing procedure of the control unit of the copying machine.

FIG. 6 is a flowchart illustrating a third example of the processing procedure of the control unit of the copying machine.

FIG. 7 is a flowchart showing a fourth example of the processing procedure of the control unit of the copying machine.

FIG. 8 is a flowchart showing a fifth example of the processing procedure of the control unit of the copying machine.

FIG. 9 is a diagram showing a relationship between toner density and toner charge amount, and a relationship between environmental conditions and toner charge amount in a general copying machine including the copying machine according to the embodiment of the present invention.

FIG. 10 is a flowchart showing a sixth example of the processing procedure of the control unit of the copying machine.

[Explanation of symbols]

 2-copy lamp 10-photosensitive drum 12-developing device 21-toner hopper 26-toner density sensor 40-copier

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masayasu Narimatsu 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hiroo Naoi 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka (72) Inventor Eiji Saikou 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka Sharp Corporation

Claims (5)

[Claims] An image forming apparatus that performs a process control process for automatically correcting image forming process conditions other than the toner density of a developing device among image forming process conditions that affect an image forming state, the image forming device after the correction by the process control process is performed. An image forming apparatus, comprising: performing a correction for increasing or decreasing a toner density reference value of a developing device based on a comparison result between an image forming process condition and a predetermined value set in advance. 2. The image forming apparatus according to claim 1, wherein the correction amount of the toner density reference value of the developing device is changed according to a change state of the image forming process condition corrected by the process control process. 3. The image forming apparatus according to claim 1, wherein after the correction for increasing or decreasing the toner density reference value of the developing device is performed, a process for matching the toner density in the developing device to the toner density reference value is performed. . 4. The image forming apparatus according to claim 1, wherein a current correction state is determined based on a history of correction states of the toner density reference value. 5. An image forming apparatus according to claim 1, wherein an upper limit value and a lower limit value are set in advance for the toner density reference value, and a process control for correcting other image processing conditions when the toner density reference value reaches the upper limit value or the lower limit value. The image forming apparatus according to claim 1, wherein the image forming apparatus executes the processing.