JPH0844188A - Developing device - Google Patents

Abstract

PURPOSE:To decide a toner replenishing time by using the detection value of a toner concentration sensor obtained at the end of operating a developing device but before a developing device is stopped instead of the detection value of the sensor until the output of the toner concentration sensor is stabilized at the start of operating the developing device, and to prevent the toner from being excessively replenished. CONSTITUTION:When the operation of the developing device is started in accordance with a copying start (step 1), the detection value Vtn of the toner concentration sensor is read at prescribed intervals (step 2), whether or not the output of the sensor is stabilized is judged based on the effect whether or not a difference between two front and back detection values Vtn-Vt(n-1) becomes equal to or below a prescribed value K1 (step 3). And while the output of the sensor is not stabilized, the toner replenishing time is decided by using the detection value Vto obtained at the end of the operation and stored when copying is finished but before the developing device is stopped and a reference value Vref instead of the detection value Vtn (steps 4-7).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device of an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and more specifically, a mixing ratio of a carrier and a toner in a two-component developer in the developing device ( (Hereinafter, referred to as toner concentration) by a toner concentration detector to control the toner replenishing device, a developing device for avoiding an adverse effect due to an apparent abnormality detection immediately after the toner concentration detector starts operating the developing device. Related to the improvement of.

[0002]

2. Description of the Related Art Conventionally, in a developing device equipped with a developing device for developing a latent image on a latent image bearing member using a two-component developer containing a carrier and a toner, the amount consumed by the development is reduced. A toner replenishing device for replenishing the toner in the developing device and a toner replenishing device for detecting the toner concentration in the developing device in order to keep the toner concentration in the developing device constant by replenishing the developing device with an appropriate amount of toner. A concentration detector and replenishment control means for controlling the toner replenishing device based on the detection result of the toner concentration detector.

In Japanese Patent Laid-Open No. 63-14181, the toner density detector of the type that detects a change in the magnetic permeability of the developer is used as a toner concentration detector if the operation of the developer is stopped for a certain period of time. Although the developer concentration does not change due to sinking due to its own weight, slight movement of the developer in the vicinity of the toner concentration detector that detects magnetic permeability, and change in the fluidity of the developer, etc. It has been pointed out that the apparent magnetic permeability of the toner concentration detector changes at the start of the operation, the toner concentration is detected lower than it actually is, and more toner than necessary is replenished. Then, in order to solve the problem, the publication discloses that "a detection state storage unit that stores a detection state of a developer concentration detection device at the end of the operation of the developing device, and a start state of the operation of the developing device,
When the detection state storage means stores an appropriate concentration,
There has been proposed a developer concentration control device characterized in that means for inhibiting the operation of the toner replenishing means for a certain period of time is provided.

[0004]

However, in the above structure, the operation of the toner replenishing means is prohibited for a certain period of time when the detection state storing means stores the proper density at the start of the operation of the developing device. The latent image cannot be developed during this fixed time. This is because if the latent image is developed within this fixed time, the toner density may decrease and the density of the developed image may be insufficient. This is clear from the specific example of the above publication, in which the period during which the operation of the toner replenishing means is prohibited is limited to the so-called preliminary rotation before the start of image formation. is there. Therefore, according to the above configuration,
It is necessary to set the preliminary rotation time after the start of the operation of the developing device to a time sufficient for eliminating the above-mentioned apparent abnormality detection, and the waiting time until the start of the image forming operation becomes longer accordingly. Was left.

It should be noted that such an apparent abnormality detection at the time of starting the operation of the developing device of the toner concentration detector indicates that a developer different from that during the continuing operation of the developing device is immediately after the operation of the developing device is stopped because the operation of the developing device is stopped. As long as there is a distribution or flow state, and this is a toner concentration detector that outputs an apparent detection output that is far from the actual toner concentration of the developer, it will detect changes in magnetic permeability. The developing device using a toner concentration detector of a method other than the toner concentration detector of the above method can also occur.

The present invention has been made in view of the above problems, and it is an object of the present invention to prevent excessive toner replenishment due to apparent abnormality detection at the start of operation of the developing device of the toner concentration detector. It is an object of the present invention to provide a developing device that can start a developing operation even when such an abnormality is detected and can obtain a developed image to a certain extent.

[0007]

In order to achieve the above object, the developing device according to claim 1 develops a latent image on a latent image carrier using a two-component developer containing a carrier and a toner. Developing device, a toner replenishing device that replenishes the toner to the developing device, a toner concentration detector that detects a mixing ratio of carrier and toner in the developing device, and the toner concentration detector In a developing device having a replenishment control means for controlling the toner replenishing device on the basis of the detection result of the mixture ratio, the detection value storage means for storing the detection value of the toner concentration detector at the end of the operation of the developing device. , After starting the operation of the developing device,
A determination means for determining whether or not the output of the toner concentration detector is stable by using the detection value of the toner concentration detector is provided, and the replenishment control means outputs the output of the toner concentration detector by the determination means. Is determined to be stable, the replenishment amount is determined using the detection value stored in the detection value storage means, and after it is determined to be stable, the detection value of the toner concentration detector is used. It is characterized in that the supply amount is determined.

According to a second aspect of the present invention, in the developing device according to the first aspect, the determination means performs detection before and after the detection by the toner density detector which is performed at a predetermined interval after the operation of the developing device is started. It is characterized in that it is configured to judge whether or not the output of the toner concentration detector is stable, depending on whether or not the difference between the detected values is within a predetermined range.

[0009]

In the developing device according to the first or second aspect, the detection value of the toner concentration detector is stored by the detection value storage means when the operation of the developing device is completed. Then, after the operation of the developing device is started, the determination means determines whether or not the output of the toner concentration detector is stable using the detection value of the toner concentration detector.

Until the determination unit determines that the output of the toner concentration detector is stable, the replenishment control unit determines the replenishment amount using the detection value stored in the detection value storage unit, Control the toner supply device. As a method of determining the replenishment amount, for example, a minimum replenishment amount assuming an average toner consumption amount for one image formation is used as a reference, and the reference replenishment amount is determined based on the detection result of the toner concentration detector. It is possible to use a method of determining so that the replenishment amount is increased or decreased. Here, as the detection result of the toner concentration detector in such a determination method, the detection value stored in the detection value storage means is used. To use.

After the determination means determines that the output of the toner concentration detector is stable, the replenishment control means determines the replenishment amount using the detection value of the toner concentration detector to replenish the toner. Control the device.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a developing device of an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. FIG. 1 is a schematic configuration diagram of the developing device according to the present embodiment. In this developing device, two developing rollers 2 and 2 composed of a rotary developing sleeve with a fixed magnet are provided in an opening facing the surface of a drum-shaped photosensitive member 1 as a latent image carrier, and a two-component developing device is provided. The developing device 3 contains a developer, and the toner hopper 4 contains the toner to be supplied to the developing device. In the developing device 3, in addition to the developing rollers 2 and 2, the paddle wheel 5 for supplying the developer to the developing rollers 2 and 2 along the bottom of the developing device casing, and the toner hopper 4 are replenished. A spheroidal plate 6 and the like for mixing the toner with the developer in the developing device 3 and stirring and supplying the developer to the paddle wheel 5 side are provided. In the toner hopper 4, a stirring member 7 that stirs the toner stored therein and sends it to the communication port side with the developing device 3 is rotatably provided, and the stirring member 3 is provided in the communication port.
There is provided a toner replenishing roller 8 for replenishing the developing device 3 with the toner picked up from the lower part of the toner hopper 4 by the rotation of the.

In the developing device, the toner concentration sensor 9 for detecting the change in magnetic permeability for detecting the toner concentration of the developer in the developing device 3 is provided with, for example, the bottom wall portion of the developing casing below the spheroidal plate 6. It is provided in. The detection signal of the toner concentration sensor 9 is read by the CPU 11 via the interface 10. A ROM 12 in which a sequence program for toner replenishment control, which will be described later, and the like are stored, and a RAM 13 in which various data and variables are stored are connected to the CPU 11. In addition, the CPU 11 uses the interface 10 to
A control signal is sent to the drive circuit 15 for the drive motor 14 of the toner supply roller 8. In this example, the toner replenishing roller 8 is driven by the dedicated drive motor 14, but instead of this, the toner replenishing roller 8 is supplied from a drive transmission system for inputting drive to the rotation in the developing device, for example, via a clutch. 8 may be driven.
In this case, the clutch is turned on / off by the CPU1.
By controlling with 1, the rotation of the toner supply roller 8 is controlled.

In this developing device, during the operation of the developing device, the rotating members 2, 5, 6 and the like in the developing device are driven by a driving device (not shown). This allows the elliptical plate 1
At 2, the developer is agitated and sent to the paddle wheel 5, the developer is supplied to the developing rollers 2 and 2 by the rotation of the paddle wheel 5, and further, the developing roller 2 and 2 are rotated to convey the developer to the surface of the photoconductor 1. Then, the latent image formed on the surface of the photoconductor 1 is developed. When the CPU 11 detects from the detection signal of the toner concentration sensor 9 that the toner concentration of the developer is lower than the predetermined concentration, it sends a control signal to the drive circuit 15 and the drive motor 14 outputs a predetermined amount. The toner replenishing roller 8 is rotationally driven so that the toner can be replenished. The toner is replenished into the developing device 3 by the rotation of the toner replenishing roller 8.

Next, the toner replenishment control according to this embodiment will be described in detail. FIG. 2A is a graph showing the relationship between the toner density in the developing device and the output value of the toner density sensor 9. As can be seen from this graph, the output value of the toner concentration sensor 9 of the present embodiment, which sees the change in magnetic permeability, becomes smaller as the toner concentration increases. The toner density indicated by Dref in this graph is a reference toner density for obtaining a good development density in the toner control of this embodiment, and the sensor output Vref corresponding to this is used as a reference value for toner density control.

FIG. 2B is a graph showing the relationship between the detected value Vt of the toner density sensor 9 during copying and the toner replenishment time, that is, the rotational drive time of the toner replenishing roller 8. As can be seen from this graph, the toner replenishment control of this embodiment is proportional to the difference between the detected value Vt and the control reference value Vref, and the larger the difference, the longer the toner replenishment time. The upper limit L is set for the toner replenishment time in order to prevent erroneous detection of the toner concentration sensor 9 for some reason and excessive toner replenishment.

It should be noted that the above-mentioned specific toner density Dr
The specific relationship between the value of ef, the detection value Vt shown in FIG. 2B, and the toner replenishment time is determined by the average toner consumption amount when copying an average original document and the detection by the toner density sensor 9. The value varies depending on the frequency of reading the value and the execution of the toner replenishing operation according to the result (the toner may not be replenished depending on the result), and is determined in advance by experiment. Hereinafter, in the present embodiment, it is assumed that the detection value of the toner density sensor 9 is read and the toner replenishment operation is executed according to the result of reading three times during one copy.

Here, in the developing device 3 of this embodiment, while the developing device 3 is in operation, the rotating members 2, 5 and 6 in the developing device 3 are rotated to recirculate the developer, so that the toner density is reduced. A constant developer flow is generated above the sensor 9. Then, when the operation of the developing device 3 is stopped, the circulation of the developer is also stopped, so that a certain amount of the developer stays above the toner concentration sensor 9. Then, if the developing device 3 is operated again after this stop, the developer recirculation occurs again, but for a while after the operation of the developing device is resumed after this stop, the amount of developer and the flow rate on the toner concentration sensor 9 change every moment. . Therefore, the output of the toner concentration sensor 9 does not correspond to the actual toner concentration of the developer. In FIG. 3A, the horizontal axis indicates time, and the vertical axis indicates the detection value of the toner concentration sensor 9, and a period a during which the developing device is operating and the developer is recirculating, and a constant time developing device after the period a Of the detected value V for the period b during which the stirring of the developer is stopped and the developing device is operated again after the period b until the developer is circulated and the toner concentration detection value Vt becomes stable.
It is a graph which showed change of t. As can be seen from this graph, the detected value Vt is the period b during which the operation of the developing device is stopped.
In the meantime, the value changes to a value larger than the detected value Vto when the developing device is stopped. Then, when the operation of the developing device is restarted thereafter, the detected value Vto ′ immediately before restarting changes to a small value and returns to the value Vto immediately before stop (when there is no toner consumption due to development).

As described above, the detection value Vt of the toner density sensor 9 is maintained for a while (for example, a period of about 2 to 3 continuous copies) after the developing device 3 is restarted after the stop.
Is unstable, and the detected value corresponds to a toner density lower than the actual toner density. Therefore, the detected value Vt during this period
If the toner replenishment time is determined using, there is a high possibility that excessive toner replenishment will cause background stains on the image.

Therefore, in this embodiment, the toner density sensor 9 is used when the operation of the developing device is restarted after the stop and the development is performed.
2b, the detected value Vt of the toner density sensor 9 immediately before the stop is used instead of the detected value Vt at that time. The toner replenishment time is determined from the relationship shown. Then, after determining that the detection value Vt of the toner density sensor 9 is stable, the toner replenishment time is determined from the relationship shown in FIG. 2B using the actual detection value Vt.

The determination as to whether or not the detected value Vt is stable is made, for example, with the graph shown in FIG.
As shown in (b), after the operation of the developing device is restarted after the stop, for example, the detected value V for normal toner density control
In the sampling timing of t, reads a detection value Vt, (difference Vt ₁ -Vt ₂ of Vt _1, for example, first detection value and the detection value of the second time and Vt ₂₎ the difference between the detected value of the sampling of tandem Is the comparison value k that was previously obtained by experiments
It can be performed by comparison depending on whether or not the value becomes 1 or less.

FIG. 4 shows a flow chart of such toner supply control, which is executed at the start of the operation of the developing device. First, the operation of the developing device 3 is started by copying start (step 1), and the detection value V of the toner density sensor 9 is detected.
tn is read (step 2) (n is a subscript indicating how many times the operation has been started). Then, it is determined whether or not the detected value is stable depending on whether or not the difference between the detected value Vtn and the read detected value Vt (n-1) immediately before that is larger than the comparison value K1 (step 3). Here, at the time of the first reading, the detection value Vto immediately before the stop of the developing device stored in the RAM 13 is used as the reading detection value immediately before. When it is determined that the detected value is not stable (Y in step 3), the toner replenishment time is determined using the detected value Vto stored in the RAM 13 just before the developing device is stopped and the reference value Vref. In addition, the toner supply roller 8 is rotationally driven (step 4). Then, it is judged whether or not a series of copying is completed (step 5), and if it is not completed, a wait time for setting a predetermined sampling interval, not shown in this flowchart, is set thereafter, and step 2 is executed. Return to step 3 until the detected value is determined to be stable in step 3 or copying is completed,
Detection value Vt stored in AM13 immediately before the stop of the developing device
The toner replenishment time is determined using o and the reference value Vref, and the toner replenishment roller 8 is rotationally driven (step 4). If it is determined in step 3 that the detected value Vt is stable (N in step 3), the process proceeds to step 6 to determine the toner replenishment time using the detected value Vt and the reference value Vref, and The toner replenishing roller 8 is rotationally driven (step 6), and thereafter, a waiting time for setting a predetermined sampling interval (not shown in this flowchart) is set until copying is completed,
Reading the detected value Vt (step 8) and the detected value Vt
And the determination of the toner replenishment time using the reference value Vref and the like (step 6) are repeated. Then, when it is determined that the copying is completed (Y in step 5 or 7), the detection value Vto at the completion of the copying, that is, at the end of the operation of the developing device is set to R above.
Store in AM13 (step 9).

As described above, according to the present embodiment, the stability of the output of the toner density sensor 9 is detected from the start of copying, and the control is performed using the sensor detection value Vto at the end of the previous copying until the output is stable. By doing so, excessive replenishment can be prevented, and the toner density can be controlled relatively appropriately, so that the background stain of the image due to the excessive replenishment can be effectively prevented.

[0024]

According to the developing device of the first or second aspect, when the output of the toner concentration detector is not stable after the operation of the developing device is started, the stored operation of the developing device is stopped. Since the replenishment amount is determined using the toner concentration detection value at the end of the previous developing unit operation, the replenishment amount required considering the normal toner consumption amount by the image forming operation based on the specific detection value. Can be determined. For example, even if the stored toner concentration detection value is within the proper toner concentration range, depending on the specific value, the toner consumed in the developing operation to be started may be expected to be replenished to some extent. Can be decided. Therefore, even if the development is started without waiting for the output of the toner concentration detector to stabilize, a somewhat good developed image can be obtained.

After the output of the toner concentration detector has stabilized, the toner replenishing device is controlled by determining the replenishment amount using the detection value of the toner concentration detector at that time, so that the toner of the actual developer is used. A good developed image can be obtained by appropriate toner replenishment based on the density.

Moreover, since it is determined whether the output of the toner concentration detector is stable, and whether the output of the toner concentration detector is stable is determined by using the detection value of the toner concentration detector,
The time required for the output of the toner concentration detector to stabilize is
Compared to the case of switching the determination of the replenishment amount as described above with a uniform setting including a sufficient margin, the actual toner concentration detector at that time is changed from the shortest time in the current situation. It is possible to switch to a good determination of the replenishment amount using the output.

In particular, according to the developing device of the second aspect, whether or not the difference between the detection values of the detection by the toner density detector performed at a predetermined interval after the operation of the developing device is started and after is within a predetermined range. Since it is determined whether or not the output of the toner density detector is stable, the algorithm of the determination means or the circuit configuration can be made relatively simple.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a developing device according to an embodiment.

FIG. 2A is a graph showing characteristics of a toner concentration sensor of the developing device. FIG. 6B is a graph showing the relationship between the toner concentration sensor detection value and the toner replenishment time.

FIG. 3A is a graph showing the relationship between the developing operation and the toner concentration sensor detection value. (B) is a graph for explaining the toner replenishment control according to the present embodiment.

FIG. 4 is a flowchart of the toner supply control.

[Explanation of symbols]

 1 Photoreceptor 2 Developing Roller 3 Developing Device 4 Toner Hopper 5 Paddle Wheel 8 Toner Supply Roller 9 Toner Density Sensor

Claims (2)

[Claims] 1. A developing device for developing a latent image on a latent image bearing member using a two-component developer containing a carrier and a toner, and a toner replenishing device for replenishing the toner to the developing device. A toner concentration detector for detecting a mixture ratio of carrier and toner in the developing device, and a replenishment control for controlling the toner replenishing device based on the detection result of the mixture ratio by the toner concentration detector. And a detection value storage unit for storing the detection value of the toner concentration detector at the end of the operation of the developing unit, and the detection value of the toner concentration detector after starting the operation of the developing unit. And a determination means for determining whether or not the output of the toner concentration detector is stable, and the replenishment control means controls the replenishment control means until the determination means determines that the output of the toner concentration detector is stable. The detected value stored in the detected value storage means There determines the supply amount, and the developing apparatus being characterized in that configured to determine a supply amount using the detection value of the toner density detector after it is determined that the stable. 2. The toner according to whether or not a difference between detection values before and after the detection by the toner concentration detector, which is performed at a predetermined interval after the operation of the developing device is started by the judgment means, is within a predetermined range. The developing device according to claim 1, wherein the developing device is configured to determine whether or not the output of the density detector is stable.