JP2000112222A - Toner concentration control method/toner concentration control device/picture forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately control toner concn. employing only a toner concn. detection without using an optical sensor detection system. SOLUTION: Let Vt be the output of a toner concn. detecting means which detects the toner concn. in the developing device that supplies toner to the non-developed image forming on an image carrying body to produce an image. Then, a comparison is made between the output Vt and a reference value Vref. Based on the result of the comparison, the method controls the toner concn. in the developing device by controlling the toner supply to the device by a toner supplying means. In the method, let Vt1 be the output of the toner concn. detecting means when the developing device is turned off in a previous time. Moreover, let Vt2 be the output of the means when the device is newly turned on. Then, a comparison is made between the outputs Vt1 and Vt2. Based on the comparison, a compensation value ΔVref of the value Vref and the change in the value ΔVref due to the number of picture forming sheets are determined. After having newly turned on the device, an output Vt3 of the means at a prescribed time is compared with the output Vt2. If a difference ΔVtc between the outputs Vt2 and Vt3 exceeds a prescribed threshold value, the value ΔVref and its change due to the number of picture forming sheets are updated with other values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner density control method, a toner density control device, and an image forming apparatus.

[0002]

2. Description of the Related Art An image is formed by forming a latent image on an image carrier, supplying toner to the formed latent image by a developing device to visualize the image, and transferring and fixing the visualized toner image to the image carrier. Forming apparatuses are widely known as digital or analog copying apparatuses, laser printers, facsimile apparatuses, and the like. The powder developer used for developing the latent image is a complex mixture containing a carrier, a fluidity adjusting material, and the like in addition to the toner.
When the development is performed, the toner in the developer is consumed and decreases, and the toner concentration in the developer decreases. For this reason, toner is supplied to the developer as needed. If the toner concentration in the developer is too high, the toner image will be stained with the background and the resolution will be reduced. If the toner concentration is too low, the image density of the toner image will be reduced or the toner image will be rubbed. Therefore, the toner supply is controlled to adjust the toner concentration in the developer in the developing device to an appropriate range. Basically, the toner density control is based on “the output of the toner density detecting means: Vt,
Reference value: Vref, and based on the result, control toner supply to the developing device by the toner supply means. " The reference value: Vref is a value obtained by converting the toner density that requires toner replenishment into the developer into the output of the toner density detecting means. Therefore, “Vt−Vref =
Assuming that “K”, when “K ≧ 0”, the toner supply amount increases as K increases.

[0003] By the way, the image forming apparatus may be moved for moving, or may be left unused for a long time in a high-temperature and high-humidity office that has been cooled down during a summer vacation or the like. In this case, when the image forming apparatus is newly operated, the output of the toner replenishing unit may be "shifted from an appropriate output value". This can be caused by the inclination of the developing device when the image forming device is moved or mechanical vibration, which may cause "change in the packing state of the developer in the developing device", or cause the image forming device to operate at a high temperature.・ The amount of charge of the developer has decreased due to being left inactive for a long time in a high humidity environment, or the bulk density has changed, or
It is conceivable that these causes are caused by a combination. In such a case, the output of the toner density detecting means does not give the correct toner density. Therefore, if the toner replenishment is performed based on the toner density detection result, the toner replenishment amount may be excessive or insufficient. As a result, there is a possibility that the toner concentration in the developer cannot be controlled within an appropriate range. As a method for dealing with such a problem, a toner image is obtained by forming a reference latent image pattern on an image carrier while detecting the toner concentration in the developer by a toner concentration detecting unit, and developing the latent image pattern. A method is known in which the reflection density of the image portion and the non-image portion of the reference toner image is detected by an optical sensor, and the reference value: Vref is corrected based on the result (JP-A-8-202137). Although this method is effective, it requires two types of detection, that is, detection by a toner concentration detection unit and detection by an optical sensor. Therefore, the toner concentration control is complicated. The cost is likely to be high because a density detecting means and an optical sensor are required.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to realize proper toner density control only by toner density detection without using a detection system using an optical sensor.

[0005]

According to the present invention, there is provided a toner density control method for detecting a toner density in a developing device for supplying a toner to a latent image formed on an image carrier to visualize the latent image. Means for controlling the toner density in the developing device by comparing the output of the means: Vt with the reference value: Vref, and controlling the toner supply to the developing device by the toner replenishing means based on the result. The features are as follows. That is, the output of the toner concentration detecting means: Vt1 when the developing device was last turned off (the operation state immediately before the developing device stopped functioning) and the toner when the new developing device was turned on (when the developing device was driven again). Output of density detecting means: V
t2 is compared, and based on the comparison result, "reference value: correction value of Vref: ΔVref and change of correction value: ΔVref depending on the number of formed images" are determined. Further, the output of the toner concentration detecting means at a predetermined time after the new developing device is turned on: V
t3 is compared with the output: Vt2, and when the difference between the two: ΔVtc exceeds a predetermined threshold value, the “correction value: ΔVref and the change due to the number of image formed” is changed to another one (claim 1).
According to a second aspect of the present invention, there is provided the toner density control method according to the first aspect, wherein the toner is supplied from when a new developing device is turned on to when the output: Vt3 of the toner density detecting means is obtained. Based on the correspondence between toner supply and output: Vt3, difference between output: Vt2 and output: Vt3: ΔV
tcc is corrected to “ΔVtc2”, and the corrected ΔVtc2
Is larger than a predetermined threshold, the reference value: the correction value of Vref:
It is characterized in that ΔVref and the change due to the number of formed images are changed to different values.

[0006] The toner concentration control device of the present invention is "a device for controlling the toner concentration in the developing device", and has a toner concentration detecting means, a toner replenishing means, and a control means. The "toner density detecting means" is a means for detecting the toner density in the developing device. "Toner supply means"
This is a means for supplying toner to the developing device. "Control means"
Is the output of the toner density detecting means: Vt and the reference value: Vref
And control means for controlling toner supply to the developing device by the toner supply means based on the result. This control means performs the following control. That is, the output of the toner concentration detecting means when the developing device was turned off last time: Vt1,
The output of the toner density detecting means when the new developing device is turned on is compared with Vt2, and based on the comparison result, the reference value is Vre.
The correction value of f: ΔVref and the change of the correction value: ΔVref depending on the number of formed images are determined, and the output of the toner density detecting means at a predetermined point in time after the new developing device is turned on: V
t3 is compared with the output: Vt2, and when the difference: ΔVtc exceeds a predetermined threshold value, the correction value: ΔVref and the change due to the number of formed images are changed to different values to control the toner supply means. Do. The toner concentration control device according to claim 4,
4. The toner density control device according to claim 3, wherein the control means outputs the toner supply and output: Vt3 when the toner supply is performed from the time when the new developing device is turned on until the output of the toner density detection means: Vt3 is obtained. The difference between the output: Vt2 and the output: Vt3: ΔVtc is corrected based on the correspondence between
2, when the corrected ΔVtc2 exceeds a predetermined threshold,
Reference value: Correction value of Vref: ΔVref and its change due to the number of formed images are changed to different values, and the toner replenishing means is controlled ”.

In the toner density control device according to the third or fourth aspect, a "magnetic permeability sensor for detecting the magnetic permeability of the developer" can be used as the toner density detecting means. 6. The toner density control device according to claim 3, wherein the output of the toner density detecting means is V.
The “predetermined time point” for capturing t3 is “an operation time equivalent to three or three image forming processes” from the start of the image forming operation.
Has elapsed (claim 6). 7. The toner density control device according to claim 3, wherein a correction value of the reference value: Vref: ΔVref, and a correction value: Δ.
The change in Vref due to the number of formed images is ΔVt (= Vt2
−Vt1) in the control means as a table, and when ΔVtc exceeds a predetermined threshold value, the control means:
Vt3−Vt1 is newly set as ΔVt, and based on the above table, the reference value: the correction value of Vref: ΔVref, and the correction value: ΔV
ref can be determined according to the change due to the number of formed images (claim 7). The image forming apparatus according to the present invention is configured such that “a latent image is formed on an image carrier, a toner is supplied to the formed latent image by a developing device, and the developed toner image is transferred to the image carrier. An image forming apparatus for fixing, comprising the toner density control device according to any one of claims 3 to 7 (claim 8). The formation of the latent image on the image carrier is described as “the image carrier is a photoconductive photoconductor,
It may be performed by "charging and exposure" or by "position selective charging of the surface of the image carrier as a dielectric or uniform charging and position selective discharging". The form of the image carrier can be cylindrical, sheet-like, endless or endless belt-like. The “image carrier” may be ordinary transfer paper or an overhead projector (OH
A plastic sheet (OHP sheet) for P) may be used. The transfer of the toner image to the image carrier may be performed by a “direct transfer method” in which the toner image is directly transferred from the image carrier to the image carrier, or a “intermediate transfer medium” such as an intermediate transfer belt from the image carrier. The transfer may be performed by an “intermediate transfer method” in which the image is transferred to the image carrier via the above method.

[0008]

FIG. 2 schematically shows only an essential part of an embodiment of an image forming apparatus according to the present invention. The photoconductive photoconductor 5 as an image carrier is formed in a cylindrical shape and is rotatable in the direction of the arrow. Around the photoreceptor 5, a charging roller 6 (which may be a corona charger) as a charging means, a developing device 7, a registration roller 10, a transfer separator 8, and a cleaning device 9 are provided. Between the device 7 is an "exposure unit using the exposure light 4". Reference numeral 14 denotes a fixing device. The developing device 7 stores therein “powder developer” which is a mixture of toner, carrier, and the like, and carries the developer by holding the developer on the peripheral surface of the developing roller 71 and transporting the developer to a developing unit. ing. When image formation is performed, the photoconductor 5 rotates at a constant speed in the direction of the arrow, and its peripheral surface is uniformly charged by the charging roller 6.
The uniformly charged photoreceptor surface is exposed by exposure light (an original light image projected by an image forming optical system or a writing light by an optical writing device such as an optical scanning device) 4 in an exposure section, and a latent image is formed. It is formed. This latent image is supplied with toner by the developing device 7 to be visualized. The development is performed by "normal development" when the latent image is a positive latent image formed by the original light image, and by "reverse development" when the latent image is a negative latent image formed by the writing light. The visualized toner image is transferred and fixed to transfer paper S as an image carrier. That is, the transfer paper S is sent to the transfer unit by the registration roller 10 with the timing of the movement of the toner image due to the rotation of the photoconductor 5. In the transfer section, the toner image is transferred by the transfer separator 8 and then separated from the photoconductor 5. The separated transfer paper S has the toner image fixed by the fixing device 14 and is discharged out of the device. The photoconductor 5 after the transfer of the toner image is cleaned by the cleaning device 9 to remove the residual toner and the like.

The developing device 7 has a magnetic permeability sensor 11 (hereinafter abbreviated as a T sensor 11) as "toner concentration detecting means" for detecting "toner concentration in a powdery developer" in the device. ) Is provided, and its output is input to the microprocessor unit 1 as “control means”. The microprocessor unit 1 controls toner supply based on the output of the T sensor 11. That is, a hopper 13 is provided in the developing device 7, and the toner T stored in the hopper 13 is supplied to the developing device by the rotation of the toner supply roller 12. The toner replenishment amount is adjusted by the time during which the toner replenishment roller 12 is driven to rotate. That is, the amount of toner to be supplied is proportional to the rotation driving time of the toner supply roller 12. The toner replenishing roller 12 and the hopper 13 constitute “toner replenishing means”, and the microprocessor 1 controls the “driving time” of the toner replenishing roller 12. The toner density control basically means "comparing the output: Vt of the T sensor 11 with a reference value: Vref, and controlling the toner supply to the developing device by the toner supply means based on the result". The T sensor 11 detects the magnetic permeability of the developer, but since the magnetic permeability of the developer increases as the toner density decreases, the output Vt of the T sensor 11 increases as the toner density decreases. The reference value: Vref is a value obtained by converting the toner density that requires toner replenishment into the developer into the output of the T sensor. Therefore, assuming that “Vt−Vref = K”, “K ≧
When "0" is reached, the toner supply amount is increased as K increases. Note that the microprocessor unit 1 appropriately samples the output of the T sensor 11 when the developing device 7 is on, but particularly when the developing device is turned on from the on-state (for example, when the developing device 7 is on). As for the output of the T sensor 11 (when the “main switch is turned off”), the last value automatically sampled is stored in the memory of the microprocessor unit 1. The stored contents at this time are read out as "output of toner density detecting means at the time of previous development device off: Vt1" when a new development device is turned on.

Since the toner is not consumed when the developing device is off, when the developing device is newly turned on, that is, when the new developing device is turned on, the output of the T sensor: Vt2 is essentially the value of the previous time. The output of the toner concentration detecting means when the developing device is off should be the same as Vt1. Nevertheless, Vt1 ≠ Vt2 may be caused by the reason that “the image forming apparatus is moved in place” while the developing apparatus is turned off, as described above. When the image forming apparatus is moved, the change in the packing state of the developer in the developing apparatus caused by the inclination of the developing apparatus when the image forming apparatus is moved, or mechanical vibration, or the image forming apparatus is exposed to high temperature and high humidity. A “change in the bulk density of the developer” due to a decrease in the charge amount of the developer due to the non-operating state for a long time, or a combined influence of these causes may be considered. Also,
When the toner supply is performed immediately before the developing device is turned off and the developing device is turned off in a state where the toner concentration is high only in the vicinity of the T sensor, the T sensor is turned off at the time when the developing device is turned off. If the high density of the toner is detected, the output becomes Vt2 <Vt1 when the new developing device is turned on (the high density state near the T sensor is eliminated by the preliminary stirring), and the developing device is turned off. If the high density of the toner is not detected by the T sensor at the time, the output when the new developing device is turned on (the high density state is detected) is Vt2> Vt1.
Even if the outputs of the T sensor: Vt1 and Vt2 become “Vt1 ≠ Vt2”, there is no toner consumption while the developing device is off, so the toner amount in the developer does not change during this time, and therefore, With the new developing device turned on, the output of the T sensor gradually approaches "Vt1 (output corresponding to the toner density)" as the preliminary stirring is performed. Thus, bringing the state of the developer closer to the state when the developing device was used last time is referred to as “starting up the developer”.

When the developer continues to start up the developer, the output of the T sensor changes with time from a new ON state of the developing device, and approaches the previous output: Vt1. It has been found that the “pattern of output change (referred to as a recovery pattern)” differs depending on the cause of Vt1 ≠ Vt2.

Referring to FIG. 3, the horizontal axis is time, and the vertical axis is the output of the T sensor 11. Time: 0 is “when the new developing device is turned on”. Therefore, the output at time: 0: Vt
Is the output: Vt2 in the above description. Each curve 3-
1-3 to 6 show "representative recovery patterns".
First, looking at the recovery pattern 3-1 in FIG. 3, in the recovery pattern 3-1 the T sensor output: Vt2 (Vt (t = 〇)) when the new developing device is turned on is the same as when the previous developing device was turned off. Output: equal to Vt1. in this case,
Since the T sensor 11 properly detects the toner density, the toner density control may be performed by "consisting with the previous control". Next, looking at the recovery pattern 3-2, this indicates that "the image forming apparatus has been operated at a high temperature for a certain period of time.
The output pattern of the T sensor 11 when the developing device is newly turned on: Vt2 is the output when the developing device was previously turned off: Vt2.
higher than t1. That is, in this state, the toner concentration in the developer is detected to be lower than the actual one. In this recovery pattern, the output: Vt of the T sensor decreases exponentially with time, and finally matches the recovery pattern 3-1.

The recovery patterns 3-3 to 3-6 are caused by a change in the packing state of the developer or a toner replenishment immediately before the last time the developing device was turned off. In these cases, in the recovery pattern, the output: Vt of the T sensor greatly changes in a short time after the new developing device is turned on, but the subsequent changes match the recovery patterns 3-1 and 3-2. . Therefore,
After the new developing device on a predetermined point: output at t _3: Looking at Vt3, at this point, output: Vt3 is seen to become an output that matches the recovery pattern of recovery patterns 3- or 3-2 . That is, in the present invention, the "predetermined time" at which the output of the toner density detecting means: Vt3 should be obtained
Are recovery patterns 3-3 to 3-5 in FIG.
Is set to an appropriate time after the recovery pattern 3-1 or 3-2 is matched. At this point, the effects of the "change in the packing state of the developer" and the "toner replenishment immediately before the developing device was turned off" have been eliminated. Here, considering what happens when normal toner density control is performed in the case of the recovery pattern 3-2 in FIG. 3, the output: Vt2 in this recovery pattern
However, since the output is originally "should be" higher than Vt1, the detected toner density is detected to be lower than the actual toner density in the developer. Therefore, if the output: Vt2 is larger than the reference value: Vref, toner supply is performed. Due to this toner replenishment, the amount of toner in the developer becomes excessive, which may cause background contamination and the like. Accordingly, in such a case, the output of the T sensor: Vt1, Vt
Then, t2 is compared, and a correction value: ΔVref of the reference value: Vref is determined based on the comparison result. That is, when Vt2−Vt1 is larger than a certain value, the reference value is changed from “Vref to Vref + ΔVre”.
By increasing it to f, toner replenishment is suppressed. On the other hand, in the recovery pattern 3-2, the output: Vt gradually decreases with time and approaches the recovery pattern 3-1. For this reason, if the correction value: ΔVref is fixed, in a situation where toner is consumed due to repetition of the image forming operation, the toner in the developer gradually becomes insufficient to suppress toner replenishment. At the end, the image density is reduced or the toner image is rubbed. In order to avoid this, as the image forming operation is repeated, that is, as the number of formed images increases, the correction value: ΔVre
f needs to be "gradually changed". What has been described above is “toner density control when the output change of the T sensor 11 follows the recovery pattern 3-2”, which is referred to as “first control”.

The first control is to compare the output of the toner density detecting means when the previous developing device was turned off: Vt1 with the output of the toner density detecting means when the new developing device was turned on: Vt2, and based on the comparison result. , Reference value: Vref correction value:
This control is to determine ΔVref and the “change in the number of image formations” of the correction value ΔVref.

By the way, a recovery pattern cannot be specified only by the output of the T sensor: Vt2 when a new developing device is turned on. Referring to FIG. 4, when the output of the T sensor when the new developing device is turned on: Vt2 is as shown in FIG.
It is not possible to determine whether the subsequent transition of Vt shifts according to the recovery pattern 3-7 or shifts toward the recovery pattern 3-2 according to the recovery pattern 3-5. In such a case, the "first control" is "control based on the premise that the T sensor output: Vt changes according to the recovery pattern 3-7". If the output: Vt changes in accordance with the recovery pattern 3-5, in such a case, if the toner density control is performed according to the first control, the toner density in the developer increases as the number of image formation increases. They quickly fall into shortages. To avoid this, after the new developing device on a predetermined time: the output of the toner density detection means in t _3: Vt3 said output: Vt2
Compare with That is, when taking the difference between the outputs: Vt2 and Vt3, when the output: Vt follows the recovery pattern 3-5,
The difference is ΔVtcb, and the output: Vt is the recovery pattern 3.
When following −7, the difference is ΔVtca, ΔVtcb>
ΔVtca. From this, when there is a change in the packing state of the developer when the new developing device is turned on or the effect of toner supply immediately before the last developing device is turned off, the difference between the outputs of the T sensor: Vt2 and Vt3: ΔVtc is large. Therefore, when the above-mentioned difference: ΔVtc exceeds a predetermined threshold value, the correction value: ΔVref and the change due to the number of formed images are changed to different values to obtain the actual recovery pattern. Can be controlled along the line. This control is called “second control”.

In the embodiment of the "image forming apparatus" described with reference to FIG. 2, the microprocessor unit 1 as control means performs the above control.

That is, the toner density control device of the image forming apparatus described in the above embodiment is a device for controlling the toner density in the developing device 7, and detects the toner density in the developing device. Means 11 and developing device 7
The output of the output of the toner replenishment means 12 and 13 for replenishing the toner to the toner and the output of the toner density detection means 11 are set to Vt,
ref, and based on the result, control means 1 for controlling toner supply to the developing device by the toner replenishing means. The control means 1 controls the output of the toner density detecting means when the developing device was turned off last time. : Vt1 is compared with the output of the toner density detecting means Vt2 when the new developing device is turned on, and based on the comparison result, the reference value: the correction value of Vref: ΔV
and ref, the correction value: with determining the change due to the number of image formation .DELTA.Vref, after a new developing device on a predetermined time: the output of the toner density detection means in t _3: Output the Vt3: compared to Vt2, both When the difference ΔVtc exceeds a predetermined threshold value, the correction value ΔVref and the change due to the number of formed images are changed to different values to control the toner replenishing means (Claim 3). Detecting means 11
Is a magnetic permeability sensor for detecting the magnetic permeability of the developer. It will be apparent that the toner density control device implements the toner density control method according to the present invention. Further, the “image forming apparatus” forms a latent image on the image carrier 5, supplies toner to the formed latent image by a developing device 7, and visualizes the latent image. 4. An image forming apparatus for transferring and fixing to a body, according to claim 3.
(Claim 8).

In the above description, if toner is supplied between the time when a new developing device is turned on and the time when the output: Vt3 of the toner density detecting means is obtained, the output: Vt3 is a value obtained when the toner is not supplied. And affects the second control. To avoid this effect, when the toner supply is performed, the "toner supply and output: Vt3
And a difference between the output: Vt2 and the output: Vt3: ΔVtc is corrected to ΔVtc2, and the corrected ΔVtc2
Is greater than a predetermined threshold, the reference value: the correction value of Vref:
ΔVref and the change due to the number of formed images may be changed to another one (claim 2). In this case, the microprocessor unit 1 as the control means outputs the output of the toner concentration detecting means: Vt3
(Because the microprocessor unit 1 issues a toner replenishment command, the presence or absence of toner replenishment can be detected by the microprocessor unit based on this fact because the microprocessor unit 1 issues a toner replenishment command).
Based on the correspondence with Vt3, the difference between the output Vt2 and the output: Vt3: ΔVtc is corrected to ΔVtc2, and the corrected ΔVtc is set.
When c2 exceeds a predetermined threshold value, the control of the toner replenishing means is performed by changing the correction value of the reference value: Vref: ΔVref and the change due to the number of image formation to another value (claim 4).

[0019]

EXAMPLES Specific examples will be described below. The image forming apparatus is as described with reference to FIG. Although the toner concentration in the developer is detected by the T sensor, in a developer in an appropriate state, the relationship between the toner concentration detected by the T sensor and the output of the T sensor: Vt is as shown in FIG. The reference value: Vref used for toner density control in an appropriate state is “2.5 V”. As the first control, the output of the T sensor: the difference between Vt1 and Vt2: ΔVt (V
t2-Vt1), the "correction step" is set to 1 to
5 for each of these correction steps.
Table 1 shows a correction value of Δref: ΔVref and a change of the correction value: ΔVref depending on the number of image formed.

[0020]

[Table 1]

The predetermined point in time when the output: Vt3 is fetched is set to a point in time when three image forming processes have elapsed from the start of the image forming operation. At this point (the number of processes), if it is too long, the correction is delayed, and if it is too short, the difference between Vt2 and Vt3 is small and the sensitivity is low. In this embodiment, it is appropriate to set the number of processes: three or after a developing operation time equivalent thereto. FIG. 1 is a flowchart illustrating a procedure of toner density control associated with image formation. When the main switch is turned on, a T sensor output: Vt1, which is a toner density signal corresponding to the "toner density when the developing device was turned off (main switch off)" stored in the memory of the microprocessor unit, is called. Will be At the same time, the developing device is driven (the new developing device is turned on), and the T sensor output: Vt2, which is the current toner density signal, is sampled and taken in. Then, ΔVt (= Vt2−Vt1) is calculated, and the correction step: n (1 to 5) is determined according to the above Table 1 according to the value of ΔVt, and the reference value: Vre.
The correction value of Δf: ΔVref and the “change due to the number of image formed” of the correction value: ΔVref are determined. For example, Vt1 =
Assuming that 2.1 V, Vt2 = 2.45 V and ΔVt is 0.35, the correction step at this time is n = 4, and the correction value: ΔVref is 0. 4, 0.3 to 41 to 40, 0.2 to 41 to 80, 0.1 to 81 to 150, 0 for 151 or more
Is set to Therefore, the corrected reference value: Vref '
Is the reference value corrected with the number of image formed and the number of image formed: Vref ′ = Vref + ΔVref 1-20 3.4V 21-40 3.3V 41-80 3.2V 81-150 3.1V 151-3.0V Will be set as follows. As described above, the reference value is gradually set lower with an increase in the number of formed images, so that “suppression of toner supply” is gradually alleviated, and
It is possible to prevent "the toner in the developer gradually decreases".

When the output: Vt2 is sampled, the developing device is turned off and enters a standby state. Wait in this state,
When the print switch is turned on and the copy operation as the “image forming process” is started, the developing device is turned on, and the output of the T sensor: Vt is “corrected” determined according to the above-mentioned image formation number. Reference value: Vref '". When Vt>Vref', toner supply is performed. After the main switch is turned on, the image forming process 3
The T sensor output: Vt3 at the time when the number of times has elapsed is captured. Then, ΔVtc (= Vt3−Vt2) is calculated, and it is determined whether or not the result satisfies “0 ≦ ΔVtc <0.2”. When “0 ≦ ΔVtc <0.2” is satisfied,
The toner supply control (the above-described first control) is performed according to the above-defined conditions. When “0 ≦ ΔVtc <0.2” is not satisfied, that is, when ΔVtc is larger by two or more correction steps or smaller than an assumed change, the correction amount is reviewed. The correction amount is reviewed as follows. That is, the output: Δt from Vt1 and Vt2
Vt = Vt3−Vt1 is calculated, the new ΔVt is used as ΔVt in Table 1 above, a new correction step is specified, and a correction value by the newly specified correction step is:
The toner replenishment is controlled by selecting ΔVref and the change depending on the number of formed images. For example, in the above case,
While Vt1 = 2.1V and Vt2 = 2.45V, Vt3 =
2.15, when ΔVtc = 0.3, Vt3−V
2. Assuming that t1 = 0.05, the reference value Vref 'corrected by the new correction step n = 1 is the number of image formations together with the number of image formations. The corrected reference value Vref' = Vref + ΔVref 1 to 20 1 V 21 to 3.0 V will be set.

In this manner, the toner density can be controlled according to the recovery pattern. Hereinafter, the correction value is switched every time the number of image formations to be switched is reached. However, each time the number of copies set by the user is completed, the job is set to “job end” for image formation, and a standby state is set. That is, in the above-described embodiment, the correction value of the reference value: Vref: ΔVref and the change of the correction value: ΔVref depending on the number of formed images are ΔVt (= Vref).
t2−Vt1) and the control means 1 as a table (Table 1)
When ΔVtc exceeds a predetermined threshold value, the control means newly sets Vt3−Vt1 as ΔVt based on the table and corrects the reference value: the correction value of Vref: ΔVref, and the image of the correction value: ΔVref. The change according to the number of sheets to be formed is determined (claim 7). A second embodiment described below is a case where the toner density control method according to the second aspect is performed. FIG. 7 shows a control procedure as a flowchart. Until the "copy operation" which is an image forming process is started, it is the same as in the above-described embodiment. It is assumed that the copy operation has started and, for example, toner has been supplied for 6 seconds between three copies.
At this time, “the toner supply time is accumulated”. "Correspondence relationship between toner supply and output: Vt" is as shown in FIG. For this reason, if the toner supply for 6 seconds enters between the three copies, the output: Vt3 in the relationship between the toner supply and the output: Vt3.
t3 drops by about 0.1V. That is, since the output: Vt3 is lower by 0.1 V than when there is no toner replenishment, the above determination is made with a value obtained by adding 0.1 V to the aforementioned ΔVtc: Vtc2. That is,
Vtc + 0.1 = Vtc2 and “0 ≦ ΔVtc2 <0.2”
Is a condition for determining whether to review the correction value. Except for this point, the other points are the same as those in the above-described embodiment. That is, in this embodiment, toner supply and output:
Based on the relationship of Vt3, the difference between output: Vt2 and output: Vt3:
.DELTA.Vtc is corrected to .DELTA.Vtc2. When the corrected .DELTA.Vtc2 exceeds a predetermined threshold, the reference value: Vref correction value: .DELTA.Vr
The toner density control is performed by changing ef and the change due to the number of formed images to different ones.
4). As described above, in the present invention, the correction of Vref is performed based on the value of ΔVt, but the correction can be similarly applied to the value of Vt. Depending on the value of ΔVt, not only the correction of Vref, but also the pre-stirring (idling) driving time of the developing device may be changed to add the startup of the developer after a long pause. That is, it is also effective to make a correction to make the pre-stirring time longer when ΔVt is large and to make it shorter when ΔVt is small.

[0024]

As described above, according to the present invention, it is possible to effectively prevent insufficient toner density control during a new use of the image forming apparatus after a long period of non-use, thereby realizing good image formation. it can.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating toner density control according to an embodiment.

FIG. 2 is a diagram for explaining an embodiment of the image forming apparatus of the present invention.

FIG. 3 is a diagram for explaining a change in the output: Vt of the toner density detecting means after a new developing device is turned on.

FIG. 4 is a diagram for explaining a toner density control method according to the present invention.

FIG. 5 is a diagram illustrating a correspondence relationship between an output: Vt of a T sensor and a toner density in the embodiment.

FIG. 6 is a diagram illustrating a correspondence relationship between a toner supply time and an output of a T sensor: Vt in the embodiment.

FIG. 7 is a flowchart for explaining toner density control according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microprocessor unit (control means) 5 Photoreceptor (image carrier) 7 Developing device 11 T sensor (toner density detecting means) 12 Toner supply roller 13 Hopper

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masanori Kawasumi 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (reference) 2H027 DA38 DA45 DD07 DE04 DE07 DE09 EA06 EC06 EE08 HB09 2H077 DA10 DA22 DA42 DA52 DB02 9A001 JJ35

Claims (8)

[Claims] An output: Vt of a toner density detecting means for detecting a toner density in a developing device for supplying a toner to a latent image formed on an image carrier and visualizing the latent image is compared with a reference value: Vref. And controlling the toner concentration in the developing device by controlling the toner replenishment to the developing device by the toner replenishing device based on the result. Vt1 is compared with the output of the toner density detecting means when the new developing device is turned on: Vt2, and based on the comparison result,
Reference value: Vref correction value: ΔVref, and the correction value: ΔVre
f, the output of the toner density detection means at a predetermined time after the new developing device is turned on: Vt3 is compared with the output: Vt2, and the difference between the two: ΔVtc is a predetermined threshold value. If it exceeds, the toner density control method characterized in that the correction value: ΔVref and the change due to the number of formed images are changed to different values. 2. The toner density control method according to claim 1, wherein the output of the toner density detecting means from the time the new developing device is turned on is:
When toner supply is performed before Vt3 is obtained, the output: Vt3 is determined based on the correspondence between the toner supply and the output: Vt3.
Difference between t2 and output: Vt3: ΔVtc is corrected to ΔVtc2. When the corrected ΔVtc2 exceeds a predetermined threshold value, the reference value: the correction value of Vref: ΔVref and the change due to the number of image formed are different. A toner density control method characterized by changing to a toner concentration control method. 3. An apparatus for controlling a toner concentration in a developing device, comprising: a toner concentration detecting means for detecting a toner concentration in the developing device; a toner replenishing means for replenishing toner to the developing device; The output of the detection means: Vt, the reference value: Vref
And control means for controlling toner supply to the developing device by the toner replenishing means based on a result of the comparison. Then, the output of the toner density detecting means when the new developing device is turned on is compared with Vt2, and based on the comparison result, the correction value of the reference value: Vref: ΔVref and the change of the correction value: ΔVref depending on the number of formed images. At the same time, after the new developing device is turned on, the output: Vt3 of the toner density detecting means at a predetermined time after the start of the image forming operation at a predetermined time is compared with the above output: Vt2, and the difference between the two:
When ΔVtc exceeds a predetermined threshold, the correction value: ΔVre
A toner density control device, wherein f and the change due to the number of formed images are changed to different ones to control the toner replenishing means. 4. The toner density control device according to claim 3, wherein the control means outputs an output of the toner density detection means from a time when a new developing device is turned on.
When toner supply is performed before Vt3 is obtained, the output: Vt is determined based on the correspondence between the toner supply and the output: Vt3.
Difference between 2 and output: Vt3: ΔVtc is corrected to ΔVtc2,
When the corrected ΔVtc2 exceeds a predetermined threshold value, the correction value of the reference value: Vref: ΔVref and the change due to the number of formed images are changed to different values to control the toner replenishing means. Toner concentration control device. 5. The toner density control device according to claim 3, wherein the toner density detection means is a magnetic permeability sensor for detecting the magnetic permeability of the developer. 6. The toner density control device according to claim 3, wherein the predetermined time is equivalent to three or three times of the image forming process from the start of the image forming operation. A toner density control device characterized in that the operation time has elapsed. 7. The toner density control device according to claim 3, wherein a reference value: a correction value of Vref: ΔVref, and the correction value: ΔVre.
The change of f due to the number of formed images is ΔVt (= Vt2−Vt).
1) is stored in the control means as a table according to the above. When the ΔVtc exceeds a predetermined threshold value, the control means newly sets Vt3−Vt1 to ΔVt based on the table,
Reference value: Vref correction value: ΔVref, and the correction value: ΔVre
a toner density control device, wherein f is a change depending on the number of formed images. 8. An image in which a latent image is formed on an image carrier, a toner is supplied to the formed latent image by a developing device to visualize the image, and the visualized toner image is transferred and fixed to the image carrier. An image forming apparatus, comprising: the toner density control device according to any one of claims 3 to 7.