JP2001125365A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a defect that image density fluctuates in accordance with a rapid change of the electrostatically charged quantity of developer, as for an image forming device for controlling toner concentration. SOLUTION: The image forming device is provided with a latent image forming means 3 for forming a latent image on an image carrier, a developing device 5 for developing the latent image by the developer constituted of toner and carrier, a toner replenishing device 12 for replenishing the toner to the developing device, a toner concentration detecting means 13 for detecting the mixture ratio of the toner to the carrier in the developer in the developing device, a reference image density detecting means 15 for detecting the density of the reference image formed on the image carrier, and a correcting means for correcting the target value of the toner concentration detecting means based on the detection value of the reference image density detecting means so that the detection value may become a prescribed target value, and in the case a fixing temperature set when a power is supplied is equal to or below a prescribed temperature, besides, in the case the integrated number of image-formed sheets counted after the power is supplied is equal to or below a prescribed value, the target value of the toner concentration detecting means is varied at prescribed intervals at the time of continuously forming the images.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile, a plotter and the like, and more particularly, to an image forming apparatus using a two-component developing apparatus and having a characteristic in a toner density control method. Related to the device.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine using an electrophotographic system, a two-component developing apparatus is often used as one of developing apparatuses. Further, the following is known as a toner density control system of a two-component developing device. : The density of a reference pattern image formed on an image carrier such as a photoreceptor is detected by a reflection type sensor (hereinafter referred to as a P sensor) as a reference image density detecting means, and toner replenishment control is performed according to the detected value. Things to do. : A unit for performing toner replenishment control according to a detection value of a toner concentration sensor (hereinafter, referred to as a T sensor) as a toner concentration detection unit for detecting a change in apparent magnetic permeability of a developer in a developing device.

In the above-mentioned method, when a toner image is transferred from an image carrier to a transfer material, a contact transfer method in which the transfer material is brought into contact with the image carrier using a transfer roller or a transfer belt is used. However, since a reference pattern cannot be formed during image formation, there is a problem that a toner image becomes unstable during continuous copying (or printing). In addition, the above-described method has a problem that it is impossible to follow a change in the developing ability due to the deterioration of the developer and environmental fluctuation, and a variation in the developing conditions of the developer and each machine.

Therefore, a toner replenishment control system has been used in which the above methods are combined to compensate for each other's problems. FIG. 10 shows a flowchart of a control operation of the copying machine showing one example. In FIG. 10, when copying is completed, (1) it is determined whether or not the accumulated number of sheets has reached 10 since the previous P sensor detection. If the total number has reached 10, (2) a reference pattern is created and its density is detected by a P sensor and stored in a memory. (3) If the current copy job is a continuous copy job of eight or more sheets, then (4) the detection value of the P sensor:
From Vp = Vsp / Vsg, the correction value of the T sensor: ΔVtref is determined according to Table 1 below. Next, (5) the target value of the T sensor: Vtref is calculated according to Vtref = Vtp + ΔVtref, where the output of the T sensor at the time of detecting the P sensor is Vtp, and the target value: Vtref is stored in the memory.

[0005]

[Table 1]

If the total number of copies since the previous P-sensor detection has not reached 10 when copying is completed, (6) the total number is stored in the memory. In this way, the target value of the T sensor: Vtref is determined, and the toner supply amount for each copy (image formation) is determined by the difference between the detected value of the T sensor for each copy: Vt and the target value: Vtref: ΔVt = Vt
From −Vtref, the toner replenishment time is determined from the coefficient α in Table 2 below.

[0007]

[Table 2]

By controlling as described above, the problem of control using only the T sensor, which cannot follow the change in developing ability due to the aging of the developer, environmental fluctuation, and variation in developing conditions for each machine, is corrected by the P sensor. Also, during continuous copying using the contact transfer device, the replenishment control is performed based on the detection value of the T sensor, so that the image becomes stable.

[0009]

However, the following problems also occur in the above-described combination system of the P sensor and the T sensor. For example, when the image forming apparatus is not used for a long time, such as at night, the charge amount Q / m of the developer (toner) may decrease.

Here, a description will be given with reference to FIG. 11 showing the relationship between the toner concentration: TC and the charge amount: Q / m. The developer, which was controlled at point A (TC1, Q / m1) on the previous day, has its charge amount: Q / m reduced by standing, and when the power is turned on the next day, the state at point B (TC1, Q / m2) is reached. Become. For example, in this state, if ten copies are taken several times and the P sensor detection and the update of the target value Vtref of the T sensor are performed several times, it is determined that the P sensor is dark because Q / m is low. , TC1 to make Q / m2 Q / m1
The target value of the toner concentration is changed so as to change from to TC2. Since the Q / m of the developer does not rise during the intermittent (small number of copies) copying, c
An appropriate image is obtained at the point (TC2, Q / m1).

However, if a large number of continuous copies of 500 or 1000 sheets are made immediately in this state, the charge amount of the developer also increases, and the toner density is determined by the T sensor.
Since the control is performed at C2, Q / m becomes high, and the control is performed at the point D in FIG. Originally, TC1 at point A in FIG.
Is appropriate, but it is not possible to respond to a sudden increase in Q / m because the P sensor cannot be detected between copies, and control is performed by TC2. In comparison, there is a problem that the image density is lowered at the end of copying.

If the Q / m drops significantly, as shown in FIG. 12 (the relationship between the toner density: TC and the T sensor output: VT), the T sensor output: VT also changes. This is because the change in the charge amount of the toner: Q / m changes the bulk density and fluidity of the developer. Here, an example will be described. Example 1: TC1, V
In the case where the control is performed at T1, if continuous copying is performed immediately after the power is turned on the next day, the Q / m decreases. Since the control is performed at the same VT1, the TC increases to TC3. In this case, when the Q / m is reduced and the developing capacity is increased, the toner density further increases, resulting in excessive image density and background contamination. Example 2: If it was controlled by TC1 and VT1 the day before, the power supply was turned on the next day.
After N, take 10 copies, detect P sensor and Vtr
When ef is updated, Vtref becomes approximately VT2 in FIG. Thereafter, when a large number of copies are continuously made, the control is performed using VT2, so that the Q / m of the developer increases and TC
2, the toner density decreases. In this case, the toner density becomes lower than the appropriate control level TC1 when the charge amount of the developer rises, and as a result, the image density greatly differs at the start end of the large-volume copy.

As described above, the conventional method of controlling the toner density in an image forming apparatus using a two-component developing device has a disadvantage that the image density fluctuates due to a rapid change in the charge amount of the developer. Was.

The present invention has been made in view of the above circumstances, and in an image forming apparatus which performs toner density control using a two-component developing apparatus, image density fluctuation occurs due to a rapid change in the amount of charge of a developer. It is an object of the present invention to solve the problem of the problem.

[0015]

According to another aspect of the present invention, there is provided an image forming apparatus, comprising: a latent image forming unit configured to form a latent image on an image carrier; A developing device that develops the upper latent image with a developer including a toner and a carrier, a toner replenishing device that replenishes the developing device with a toner, and a toner that detects a mixing ratio of the toner and the carrier of the developer in the developing device Density detecting means, forming a reference latent image for detection on the image carrier at predetermined intervals, and detecting the density of the reference image for detection obtained by developing with the developing device; A correction unit configured to correct a target value of the toner density detection unit based on the detection value so that a detection value of the reference image density detection unit with respect to the detection reference image becomes a predetermined target value; The temperature is the prescribed temperature When below, when imaging cumulative number from power is below a predetermined value, and changes the target value of the toner density detection means at predetermined intervals during continuous image formation.

Further, in the image forming apparatus according to the second aspect,
Latent image forming means for forming a latent image on an image carrier, a developing device for developing the latent image on the image carrier with a developer comprising toner and carrier, and a toner replenishing device for replenishing the developing device with toner And a toner concentration detecting means for detecting a mixture ratio of the toner and the carrier of the developer in the developing device, and forming a detection reference latent image on the image carrier at predetermined intervals, and developing the latent image by the developing device. Reference image density detection means for detecting the density of the detection reference image obtained by the detection, and based on the detection value such that the detection value of the reference image density detection means for the detection reference image becomes a predetermined target value. A correction unit for correcting the target value of the toner density detection unit, and a timer for counting a time from the end of the image forming operation to the start of the next image forming operation. Continuous work according to time It characterized in that it sometimes changes the target value of the toner density detection means at predetermined intervals.

Further, in the image forming apparatus according to the third aspect, in addition to the configuration of the first or second aspect, the total change amount of the target value during continuous image formation is limited. Further, in the image forming apparatus according to the fourth aspect, the first, second, or third aspect is provided.
In addition to the above configuration, the total change amount of the target value during continuous image formation during a predetermined period is limited. Furthermore, in the image forming apparatus according to the fifth aspect, in addition to the configuration of the first, second, third, or fourth aspect, it is preferable that the target value of the toner density detection unit that is changed at predetermined intervals during continuous image formation is limited. Features.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention. In FIG.
Reference numeral 1 denotes an image carrier. Around the image carrier 1, a charging device 2, a writing system 3, an erase 4, a developing device 5, a contact transfer device 6, a P sensor 15, a cleaning device 8,
A charge removing device 9 and the like are provided, and a fixing device 7 is provided downstream of the transfer device 6 in the transfer material transport direction. It should be noted that illustrations of a paper feeding unit (a paper feeding cassette, a paper feeding tray, etc.) and a paper feeding device (a paper feeding roller, a transport roller, a registration roller, etc.) of the transfer paper P are omitted.

The image carrier 1 is a drum-shaped photosensitive member in the illustrated example, but a belt-shaped photosensitive member may also be used. The charging device 2 charges the surface of the image carrier 1 uniformly. For example, a contact charging device such as a charging roller is used, but a non-contact charging device such as a corona charger may be used. The writing system 3 includes the charged image carrier 1
Is a means for forming an electrostatic latent image on a document 16 in the example shown in FIG.
b, and illuminates the reflected light image from the document 16 with mirrors 3c, 3d, 3e, an imaging lens 3f, and mirrors 3g, 3g.
h, 3i, the image carrier 1 is exposed. In addition, a laser beam modulated according to image information by a laser scanning optical system is exposed on the image carrier 1 to form an image. Light-emitting diodes (L
ED) There are various methods such as a method of driving an array or the like to write an image. The erase 4 irradiates light from a light source such as an LED, for example, to erase the charged charges outside the image forming area on the image carrier, and forms a latent image of the detection reference pattern on the image carrier. It can be used as a means. The detection reference pattern latent image can be formed by either the writing system 3 or the erase 4. The developing device 5 develops the latent image on the image carrier with a two-component developer including a toner and a carrier to visualize the latent image.
The developing roller 11 for carrying and transporting the developer, a developing unit 10 containing a developer supply member, a stirring member, and the like, a toner replenishing unit 12 containing toner, and the toner in the toner replenishing unit 12 to the developing unit 10 The image forming apparatus includes a toner replenishing roller 14 for replenishing the toner, a toner density sensor (T sensor) 13 for detecting a toner density (mixing ratio of toner and carrier) in the developing unit, and the like. The transfer device 6 transfers a visible image on an image carrier to a transfer material such as transfer paper P. In the illustrated example, the transfer device 6 is a contact transfer type transfer device using a transfer belt 6a. And a transfer device using a transfer roller, and a non-contact transfer type transfer device using a transfer charger. P
The sensor 15 is a reflection type sensor including a light emitting element and a light receiving element, and detects the density of a reference pattern image created on an image carrier. The cleaning device 8 removes residual toner and the like on the image carrier after transfer using a blade, a brush roller, or the like. The charge removing device 9 removes the charge remaining on the image carrier after cleaning by light irradiation or the like. The fixing device 7 includes, for example, a heating roller having a heat source and a pressure roller, and fixes an unfixed toner image on the transfer paper P.

In the image forming apparatus having the configuration shown in FIG. 1, when an image forming (copying or printing) operation is started, first, the image carrier 1 is uniformly charged by the charging device 2, and is electrostatically charged by the writing system 3. A latent image is formed. Then, after the extra charges outside the image forming area are erased by the erase 4, the latent image on the image carrier 1 is developed by the developer carried by the developing roller 11 of the developing device 5 to become a visible image. . Then, the transfer paper P is fed to the transfer device 6 from a paper feed unit (not shown) at the timing when the visible image (toner image) on the image carrier 1 comes to the position of the transfer device 6. Then, the toner image on the image carrier 1 is transferred to the transfer paper P at the nip portion of the transfer belt 6a. Then, the transfer paper P after the transfer is conveyed toward the fixing device 7 by the transfer belt 6a, and the toner image is fixed on the transfer paper P by the fixing device 7. On the other hand, the residual toner is removed from the surface of the image carrier 1 after the transfer by the cleaning device 8, and the residual charge is removed by the charge removing device 9.

In the image forming apparatus shown in FIG. 1, when detecting the image density of the visible image on the image carrier, the image carrier 1 is uniformly charged by the charging device 2, and then the writing system 3 or the erase system is erased. 4, a detection reference latent image (reference pattern latent image) is formed on the image carrier 1 at predetermined intervals, and this latent image is developed by the developing device 5 to form a detection reference image (reference pattern image). I do. Then, the density of the reference pattern image is detected by the P sensor 15. The developing device 5
The toner density (mixing ratio of toner and carrier) in the developing unit 10 is detected by a toner density sensor (T sensor) 13. Here, as the normal toner replenishment control, for example, a control operation as described in “Prior Art” is performed. In this case, as described above, the image density is changed due to a rapid change in the charge amount of the developer. There was a problem that fluctuation occurred.

Therefore, in this image forming apparatus,
(1) The target value of the toner density sensor (T sensor) 13 based on the detection value such that the detection value of the P sensor 15 with respect to the detection reference image becomes a predetermined target value: Vtref
When the fixing temperature at power-on is equal to or lower than a predetermined temperature, when the total number of images formed since power-on is equal to or lower than a predetermined value, the toner density is determined at predetermined intervals during continuous image formation. Target value of the sensor (T sensor) 13: Vtref
Or (2) correcting the target value of the toner density sensor detecting means based on the detected value so that the detected value of the P sensor 15 with respect to the detection reference image becomes a predetermined target value. And a timer that counts the time from the end of the imaging operation to the start of the next imaging operation, and performs continuous imaging according to the time from the end of the imaging operation to the start of the next imaging operation. The target value Vtref of the toner density sensor (T sensor) 13 is changed at predetermined intervals (claim 2). Further, in the image forming apparatus according to the present invention, (3) In addition to the configuration of (1) or (2), the total amount of change of the target value during continuous image formation is limited (Claim 3) or (4). (3) In addition to the above (1), (2) or (3), the total amount of change of the target value during continuous image formation during a predetermined period is limited (claim 4), or
(5) In addition to the above (1), (2), (3) or (4), the target value of the toner density detecting means (T sensor) which is changed at predetermined intervals during continuous image formation is limited. It has a configuration.

Hereinafter, an embodiment of a specific control operation in the image forming apparatus of the present invention will be described. A correcting means for correcting a target value: Vtref of the toner density sensor (T sensor) 13 is shown in the figure of the image forming apparatus. The microcomputer in the control unit does not perform the control operations and calculations shown in the following embodiments. The control unit includes a microcomputer, various control circuits, input / output circuits, memories such as ROM and RAM, various counters, timers, and the like.

[0024]

(Embodiment 1) First, an embodiment of claim 1 will be described. FIG. 2 shows an example of a control operation in the image forming apparatus according to the present invention. In this embodiment, when the fixing temperature at the time of turning on the power is 100 ° C. or lower, it is determined that the leaving time since the last use of the machine is long, and the control operation of FIG. 2 is executed. In this embodiment, as shown in FIG. 2, the total number of image formation from 100 ° C. or lower is 5K (K = 1
000) or less, and the normal toner supply operation described above is performed when the number of copies is equal to or more than 5K, and counting is started when the total number of image formations is equal to or less than 5K. The target value of the T sensor: Vtref is calculated every 100 sheets, and the target value: Vtref is set to 0.06V.
Lower it by one. That is, the corrected target value Vtref (n
ew) is Vtref (n), where Vtref (old) is the target value before correction.
ew) = Vtref (old) −0.06. Here, FIG. 4 shows changes in the target value: Vtref and the image density: ID of the T sensor when this embodiment is carried out. According to the present embodiment, even when the charge amount of the developer (toner): Q / m increases during continuous copying, the toner concentration: TC also gradually increases by decreasing the T sensor target value: Vtref as described above. , It is possible to maintain a good image density without a decrease in density even during continuous copying.

(Embodiment 2) Next, a second embodiment of the present invention will be described. In the embodiment of the present invention, the fixing temperature at the time of turning on the power is used as a reference. However, in order to more accurately detect the leaving time, a timer is provided in the control unit of the image forming apparatus main body, and the time between image forming jobs is set. Measuring is more effective. FIG. 3 shows an example of the control operation in the image forming apparatus of the present invention. In the image forming apparatus of the present embodiment, although not particularly shown, measurement of the elapsed time is started by the timer at the end of the image forming operation. Then, the timer is stopped together with the next image forming instruction (copy start in this embodiment), and the elapsed time from the end of the previous image forming is set. And the elapsed time is 2
If the time is shorter than the time, the normal toner supply control described above is performed. If the elapsed time is 2 hours or more, the target value of the T sensor: V at predetermined intervals during continuous image formation according to the elapsed time.
Change tref. For example, if the image is left overnight (about 10 hours), the T sensor target value: Vtref is reduced by 0.06 V for every 100 images to be formed, so that the charge amount: Q / m increases and the image density: ID Prevent the decline. In this case, the same effect as in FIG. 4 of the first embodiment is obtained. Further, in this example, Q / m was reduced due to long-term leaving (eg, leaving for 72 hours or more) due to long-term rest, and opening time (eg, opening time of 2 to 9 hours) was created between operations. As shown in FIG. 3, even for a slight decrease in Q / m or the like in the case, the idle time is directly measured, and the target value of the T sensor: Vtref is determined at a predetermined interval during continuous image formation according to the elapsed time. Since the change is performed, more accurate Vtref correction can be performed.

In the first and second embodiments, the target value of the T sensor as the toner density detecting means: V
Although the interval at which tref is changed is set to the number of images to be formed, a similar effect can be obtained by changing the interval according to the drive time of the developing device, the drive time of the image carrier, and the like.

(Third Embodiment) Next, a third embodiment will be described. In the first and second embodiments (the first and second embodiments), the target value: Vtref of the T sensor is corrected as the number of continuous copies increases, and, for example, four times (450 in the first embodiment). 24V) and 14 times for 1450 sheets (0.84 V in the first embodiment), which may naturally be excessively corrected. Thus, in the present embodiment, in addition to the control of the first or second embodiment, control is performed so as to limit the total change amount of the target value during continuous image formation. FIG. 5 shows an example of the control operation in the image forming apparatus according to the third aspect. In the embodiment shown in FIG.
In addition to the control operation (FIG. 2), the number of changes of the target value Vtref of the toner density detecting means (T sensor) in one job is counted, and the maximum value of the number of changes (total change amount) is set to 5.
Times (when the change amount for each time is 0.06 V, the total change amount is 0.3 V), so that no further change is made. As a result, as the number of formed images increases, it is possible to prevent the target value: Vtref from being changed without reproduction, and to prevent the toner density from excessively increasing.

(Embodiment 4) Next, an embodiment of claim 4 will be described. In the third embodiment (third embodiment), for example, when 1 to 500 (500 continuous copies at one time) is performed a plurality of times, the correction of the target value: Vtref of the T sensor during the job is performed each time. This may be performed and the correction may be excessive. Therefore, in the present embodiment, control is performed so as to limit the total amount of change of the target value during continuous image formation during a predetermined period (for example, during a period from power ON to OFF). FIG. 6 shows an example of a control operation in the image forming apparatus according to the fourth aspect. In the embodiment of FIG. 6, in addition to the control operation of the third embodiment (FIG. 5), the target value of the T-sensor: Vtref after the power is turned on is changed 10 times (total shift amount). If the change amount per time is 0.06 V, the total change amount is 0.6 V)
By limiting the total number of shifts (all changes) of the target value: Vtref, excessive correction is prevented.

Here, as a specific embodiment of the first, third, and fourth aspects, a target of the T sensor in a case where a copy operation of 1000 sheets is repeated three times after the power is turned on and ten copies are made, FIG. 7 shows a change in the value: Vtref, and FIG. 8 shows a change in the detection value: Vsp / Vsg of the P sensor. In FIG.
Vsp / Vsg = 0.1 is the target value of control (target value of the detection value of the P sensor), but at present (conventional control) Vsp / Vsg = 0.1
Vsg is large, and the image density is low. Further, in the embodiment of the present invention, Vsp / Vsg is small and no decrease in density is observed, but as the copy is taken, Vsp / Vsg is increased.
Is too small. On the other hand, in the third embodiment, since the correction amount in one job is limited, Vsp / Vsg is greatly increased as in the first embodiment.
Is no longer removed. Further, in the embodiment of the present invention, by limiting the integrated value of the correction amount, the density reduction and the excessive density are suppressed, and a very good result is obtained.

(Embodiment 5) Next, a fifth embodiment will be described. In the above-described fourth embodiment (an embodiment of claim 4), by setting a limit on the integrated value of the correction amount, a decrease in density and an excessive density are suppressed, and a very good result is obtained. It may be. For example, 1 to 50 (50 continuous copies at one time) from power-on
Is repeated 60 times, the charge amount of the developer: Q /
m is sufficiently high. Therefore, after this,
When 000 copies are made, the target value of the T sensor is:
Since Vtref is corrected, the toner density increases.
Therefore, in the present embodiment, control is performed so as to limit the target value: Vtref of the T sensor that is changed at a predetermined interval during continuous image formation. FIG. 9 shows an example of a control operation in the image forming apparatus according to the fifth aspect. In the embodiment shown in FIG.
In addition to the control operation (FIG. 6), the target value of the T sensor: Vtr so that at least soiling and toner scattering do not occur.
If the target value: Vtref is 1.5 V or more, the target value: Vtref during the job is updated, but if the target value: Vtref becomes 1.5 V or less, the Target value: Vtref correction is stopped. As a result, a problem caused by an excessive rise in toner density can be avoided.

In the above-described third to fifth embodiments, the case where the control operation of the third to fifth embodiments is applied to the control operation of the first embodiment has been described. The same effect can be obtained by applying the control operations of claims 3 to 5 to the control operation of the example. Further, in the case of combination with the embodiment of the second aspect, it is naturally possible to change the limit value of the correction amount in one job according to the idle time, and the image becomes more stable. Further, in the above embodiment, the toner replenishment coefficient α described in the description of the related art is used.
Is the difference between the T sensor detection value: Vt and the target value: Vtref: V
Although a fixed value based on t-Vtref (Table 2) is used, in the case of an image forming apparatus using a digital optical system such as a laser scanning optical system as a writing system, the number of written pixels and Vt-Vtre
A method of determining the coefficient α of toner replenishment by using the f value together can be used, and even in such a method, the present embodiment can be used without any problem.

[0032]

As described above, in the image forming apparatus according to the first aspect, when the fixing temperature at the time of power-on is equal to or lower than a predetermined temperature, the number of integrated images since power-on is equal to or lower than a predetermined value. Sometimes, by changing the target value of the toner density detecting means at predetermined intervals during continuous image formation, it is possible to avoid a decrease in image density during continuous image formation due to a change in toner charge amount. Further, in the image forming apparatus according to the second aspect, the target value of the toner density detecting means is changed at predetermined intervals during continuous image formation according to the time from the end of the image formation operation to the start of the next image formation operation. Accordingly, the toner density can be controlled more accurately than the configuration of the first aspect.

In the image forming apparatus according to the third aspect,
In addition to the configuration of the first or second aspect, by limiting the total change amount of the target value at the time of continuous image formation, it is possible to perform continuous copying (printing) as compared with the first or second aspect. The resulting excessive correction of the toner density target value can be prevented. Further, in the image forming apparatus according to the fourth aspect, in addition to the configuration of the first, second or third aspect, the total change amount of the target value during continuous image formation during a predetermined period is limited. 3, the overcorrection of the toner density can be more accurately prevented. Furthermore, in the image forming apparatus according to the fifth aspect, in addition to the configuration of the first, second, third, or fourth aspect, the target value of the toner density detecting unit that is changed at predetermined intervals during continuous image formation is limited. As a result, it is possible to prevent an excessive increase in the toner density as compared with the configuration of the first, second, third or fourth aspect, and it is possible to surely prevent the background from being soiled and the toner from scattering.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present invention.

FIG. 2 is a flowchart illustrating an example of a control operation in the image forming apparatus according to the first embodiment.

FIG. 3 is a flowchart illustrating an example of a control operation in the image forming apparatus according to claim 2;

FIG. 4 shows a case where the control according to claim 1 shown in FIG. 2 is performed.
FIG. 7 is a diagram illustrating changes in a target value of the T sensor: Vtref and an image density: ID with respect to the number of copies.

FIG. 5 is a flowchart illustrating an example of a control operation in the image forming apparatus according to the third embodiment.

FIG. 6 is a flowchart illustrating an example of a control operation in the image forming apparatus according to claim 4;

FIG. 7 is a view showing a specific embodiment of the first, third, and fourth aspects, wherein after power-on, ten copies are taken, and
FIG. 10 is a diagram illustrating a change in a target value: Vtref of the T sensor when the copying operation of 000 sheets is repeated three times.

FIG. 8 is a view showing a specific embodiment of the first, third, and fourth aspects, wherein after power-on, ten copies are taken, and
FIG. 9 is a diagram illustrating a change in the detection value: Vsp / Vsg of the P sensor when the copying operation of 000 sheets is repeated three times.

FIG. 9 is a flowchart illustrating an example of a control operation in the image forming apparatus according to claim 5;

FIG. 10 is a flowchart illustrating an example of a control operation of a conventional copier.

FIG. 11 is a diagram showing a relationship between toner concentration: TC and charge amount: Q / m in a conventional copying machine.

FIG. 12 shows the toner concentration in a conventional copier: TC and T
It is a figure which shows the relationship of sensor output: VT.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image carrier 2 charging device 3 writing system (line image forming means) 4 erase 5 developing device 6 transfer device 7 fixing device 8 cleaning device 9 static eliminator 10 developing unit 11 developing roller 12 toner replenishing unit (toner replenishing device) 13 toner Density sensor (toner density detecting means) 14 Toner supply roller 15 P sensor (reference image density detecting means)

Claims (5)

[Claims] A latent image forming means for forming a latent image on the image carrier; a developing device for developing the latent image on the image carrier with a developer comprising toner and a carrier; A toner replenishing device for replenishing, a toner concentration detecting means for detecting a mixture ratio of toner and carrier of a developer in the developing device, and forming a detection reference latent image on the image carrier at predetermined intervals; Reference image density detection means for detecting the density of the detection reference image obtained by development by the developing device, and the detection value of the reference image density detection means for the detection reference image so as to be a predetermined target value. A correction means for correcting the target value of the toner density detection means based on the detection value is provided. , For a predetermined time during continuous imaging In the image forming apparatus characterized by changing the target value of the toner density detection means. A latent image forming means for forming a latent image on the image carrier, a developing device for developing the latent image on the image carrier with a developer comprising a toner and a carrier, and A toner replenishing device for replenishing, a toner concentration detecting means for detecting a mixture ratio of toner and carrier of a developer in the developing device, and forming a detection reference latent image on the image carrier at predetermined intervals; Reference image density detection means for detecting the density of the detection reference image obtained by development by the developing device, and the detection value of the reference image density detection means for the detection reference image so as to be a predetermined target value. A correction means for correcting the target value of the toner density detection means based on the detected value; and a timer for counting a time from the end of the image forming operation to the start of the next image forming operation. Depending on the time until the image operation starts Te image forming apparatus characterized by changing the target value of the toner density detection means at a predetermined interval during continuous image formation. 3. The image forming apparatus according to claim 1, wherein a total change amount of a target value during continuous image formation is limited. 4. An image forming apparatus according to claim 1, wherein a total change amount of a target value during continuous image formation during a predetermined period is limited. 5. An image forming apparatus according to claim 1, wherein a target value of said toner density detecting means, which is changed at predetermined intervals during continuous image formation, is limited.