JP3251117B2 - Toner density control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a facsimile,
The present invention relates to a toner density control device that controls a mixture ratio of a toner and a carrier of a developer in a developing device in an image forming apparatus such as a printer.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, a facsimile, and a printer, an electrostatic latent image is formed on an image carrier such as a photosensitive drum or a photosensitive belt, and the electrostatic latent image is developed. The developer is developed by a developer and transferred to a transfer material such as transfer paper or a transfer belt. Generally, a mixture of a carrier and a toner is used as the developer, and the toner is consumed in developing the electrostatic latent image. The toner is supplied from the toner replenishing device to the developing device, and the mixture ratio (toner density) of the developer carrier and the toner in the developing device is detected by the toner density sensor, and the toner density control device outputs the detected value of the toner density sensor. The mixing ratio between the carrier and the toner is controlled to a predetermined value by controlling the toner replenishing device based on the toner replenishing amount to the developing device.

[0003] Conventionally, as a toner density control device, there is a device for changing a toner density control reference value in a stepwise manner as described in Japanese Patent Application Laid-Open No. 3-138673, and when a power supply is turned on / off. Japanese Patent Application Laid-Open No. 3-148679 discloses a method for properly controlling the toner density. However, there is no device in which toner density control is correctly performed at the start of a job of a developing device.

FIG. 3 shows an example of a developing device used in an electrophotographic image forming apparatus. 2. Description of the Related Art In an electrophotographic image forming apparatus, for example, a copying machine, when a start button is pressed and turned on, image formation (copying) is continuously and repeatedly performed for a set number of sheets set by an operation unit. At the time of image formation, the image carrier 11 composed of, for example, a photosensitive drum is rotated by a main motor and uniformly charged by a charging device, and then an image is written by image exposure by an exposure device to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 12 and transferred to a transfer material such as transfer paper by the transfer device.

The developing device 12 comprises a developing device 12a and a toner replenishing device 12b. In the developing device 12a, a developer in which a carrier and a toner are mixed is stored in a developing container 13, and a stirrer 14 formed of an elliptical plate, a stirrer 15 formed of stirring blades, developing rollers 16, 17 and a roller 18 stand by ( At the time of non-image formation), it is stopped, and at the time of image formation, it is driven to rotate by a developing device driving means comprising a developing motor and operates.

That is, the developer in the developing container 13 is stirred by the elliptical plate 14 and the stirring blade 15 and is conveyed to the developing roller 16, and the developing rollers 16, 17 are provided with magnets inside and the developing roller 16 is stirred. The developer conveyed by the wings 15 is magnetically attracted and conveyed with rotation. The developer on the developing roller 16 is scraped off by a doctor member 19 at a portion having a certain thickness or more.
And between the developing roller 16 and the developing roller 1
7 and passes between the image carrier 11 and the developing roller 17.

The electrostatic latent image on the image carrier 11 is
Is developed by the developer passing between the developing roller 16 and the developing roller 16, and the developer passing between the image carrier 11 and the developing roller 16 and 17 returns to the inside of the developing container 13, and again the elliptic plate 14 and the stirring Stirred by the wings 15. Further, the developer scraped off from the developing roller 16 by the doctor member 19 falls into the developing container 13 via the separator 20 and the roller 18, and is again stirred by the elliptical plate 14 and the stirring blade 15. In this way, the developer in the developing container 13 develops the electrostatic latent image on the image carrier 11 while circulating during image formation, and stops during standby.

In the toner replenishing device 12b, the agitator 38 and the replenishing roller 39 are rotated by the toner replenishing motor, and the toner in the hopper is supplied from the replenishing port 40 to the developing device 12b.
a, and the toner from the toner replenishing device 12b falls through the roller 18 into the developing container 13 to
4, mixed with the developer by the stirring blade 15 and stirred. The agitator 38 functions to stir the toner in the hopper,
It functions to carry the toner replenished from the toner bottle to the back of the hopper.

A toner concentration sensor 21 is attached to the lower side of the elliptical plate 14 in the developing container 13 and detects a mixture ratio (toner concentration) of the developer carrier and the toner in the developing container 13. Toner density control apparatus, for example, a toner supply amount determined by the magnitude of the output value V _T and the reference value V _REF of the toner density sensor 21, developing devices 12a toner by the toner supply amount and the determined from the toner supply device 12b
The toner replenishing motor of the toner replenishing device 12b is controlled so that the toner is replenished to the toner, and the toner concentration of the developer is controlled to a predetermined value.

[0010]

Figure 9 [0005] represents the output value V _T of the toner density sensor 21, 10 is the output value V of the toner density and the toner density sensor 21 of the developer in the developer container 13
_Shows the relationship with _T. Toner density control unit determines the toner supply amount depending on the magnitude of the output value V _T and the reference value V _REF of the toner density sensor 21. When the output value V _T of time (A) to the toner concentration sensor 21 to the developing device 12a developer running is refluxed exhibit stable value as V _T0, the developing device 12a is stopped ( 3B, the output value _VT of the toner density sensor 21 shows a high value such as _VT0 'depending on the state of the developer above the toner density sensor 21 (the toner density detection area of the toner density sensor 21). The reason why the toner density sensor 21 erroneously detects the toner density is that the elliptical plate 14
Is changed, the amount of the developer above the toner density sensor 21 changes.

When a predetermined time (C) elapses after the operation of the developing device 12a, the output value V _T of the toner density sensor 21 is output.
Also shows a stable value, but the output value V _T0 ′ of the toner density sensor 21 when the developing device 12a is stopped does not always show the same value, and when V _T0 ′ shows a high value V _T0 ″, toner output value V _T of the density sensor 21 a long time to stabilize (C ') is applied.

While the toner density control device is not stable (C), that is, immediately after the start of image formation, the toner density sensor 2
By controlling the toner density in the first output value V _T, the difference between the output value V _T and the reference value V _REF of the toner density sensor 21 is large, it is determined that the developer is insufficient toner in the toner supply device 12b Excessive toner supply is performed, and the image carrier 11
It causes the background image to be stained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a toner density control apparatus which can solve the above-mentioned drawbacks and can eliminate the problem caused by erroneous detection of the toner density detection means immediately after the start of image formation.

[0014]

In order to achieve the above object, according to the first aspect of the present invention, a developer in which a carrier and a toner are mixed is housed and operated at the time of image formation to act on the image carrier with the developer. In a toner concentration control device of an image forming apparatus having a developing device for developing an electrostatic latent image and a toner replenishing device for replenishing toner to the developing device, a developer mixture in the developing device has a mixing ratio of toner and toner. A toner concentration detecting means for detecting the toner concentration, and controlling the toner replenishing device based on a detection result of the toner concentration detecting means to control a toner replenishing amount to the developing device. by adding a predetermined correction value to the detected value of the means by controlling the toner supply device based on the value and control means for controlling the amount of toner supplied to the developing device, the control
Means is provided for controlling the toner concentration when the developing device is stopped.
The detection value of the degree detection means is V _T0 ′, at the end of the previous image formation.
When the detected value of the toner density detecting means is _VTO ,
Can, wherein the value of the difference between the _{V T0} 'and the _{V T0}
By changing the fixed time, the correction value is calculated as the time after the start of image formation.
The intercept is determined by a linear function, and the intercept is defined as V _T0 and V _T0 ′.
The correction value is changed by determining the difference
It is obtain things.

[0015]

[0016]

[0017]

According to the first aspect of the invention, the control means adds a predetermined correction value to the detection value of the toner density detection means for a certain time after the start of image formation, and controls the toner replenishing device based on the value. The toner supply amount to the developing device is controlled. And
The control means detects the toner concentration when the developing device is stopped.
The detected value of the output means is V _T0 ′, and the
When the detection value of the toner concentration detection means is a _{V T0, V T0}
Changing the predetermined time by the value of the difference between V _{T0 'and,} before
The correction value is determined by a linear function of the time after the start of image formation.
Is determined by the value of the difference between _VT0 and _VT0 '.
Changes the correction value.

[0018]

[0019]

[0020]

FIG. 1 shows a circuit configuration of an embodiment of the present invention.
FIG. 2 shows an operation flow of this embodiment. This example is
This is an embodiment of the invention according to claim 1, which is an example of a toner concentration control device for controlling the mixing ratio of the toner and the carrier of the developer in the developing device shown in FIG. A control unit 31 formed by using a microcomputer also serves as a control unit of an electrophotographic image forming apparatus including a copying machine using the developing device shown in FIG. When the start signal is input, the respective parts of the image forming apparatus are controlled so that the image forming operation (copying operation) is continuously and repeatedly performed by the number set by the operation unit 32 as described above. At the time of image formation, the control unit 31 rotates a developing device driving unit 37 including a developing motor via a driver 36, and the developing motor 3
7 rotates the elliptical plate 14, the stirring blade 15, the developing rollers 16, 17 and the roller 18.

The output signal of the toner density sensor 21 is A / D converted by an A / D converter 33 and input to the control unit 31. Control unit 31 constitutes a control means for controlling the toner density, toner replenishment determines the toner supply amount depending on the magnitude of the output value V _T and the reference value V _REF of the toner density sensor 21 as described above, that this decision The toner replenishing motor 35 of the toner replenishing device 12b is controlled via the driver 34 to control the toner concentration of the developer to a predetermined value so that the toner is replenished from the toner replenishing device 12b to the developing device 12a by the amount.

The control unit 31, by controlling the toner density in a stable non output value V _T of the image formation start immediately after the toner density sensor 21, the difference between the output value V _T and the reference value V _REF of the toner density sensor 21 Is large, so that the developer is determined to be short of toner, and the toner replenishing device 12b performs excessive toner replenishment, thereby eliminating the problem of causing background contamination of the image on the image carrier 11 and the like. For a fixed time t immediately after the start of image formation, the toner density sensor 21
Adding the correction value to the output value V _T.

Further, as described above, the output value V _T0 ′ of the toner density sensor 21 when the developing device 12 a is stopped does not always indicate the same value, and if V _T0 ′ indicates a high value V _T0 ”, toner output value V _T of the density sensor 21 a long time to stabilize (C ') is applied. Then, the control unit 31,
As shown in FIG. 4, the toner density sensor 21 is changed by changing the predetermined time t according to the difference between _VT0 and _VT0 '.
Output value V _T of the correction of the output value V _T of the toner density sensor 21 corresponding to the time (C) to be stabilized.

Further, as shown in FIG. 5, the control section 31 sets the correction value y to a function of the time x from the start of image formation, for example, a linear function y = ax + b (a: constant), thereby controlling the toner density sensor 21. corrects the output value V _T of the toner density sensor 21 at a value close to the output waveform, V as shown in FIG. 6
By changing the correction value by changing the b-intercept with the value of the difference between _T0 and V _T0 ′, excessive or insufficient correction is reduced.

FIG. 7 shows the output value V _T of the toner density sensor 21 from the time when the continuous copying operation for the previous set number of sheets is completed to the time when the continuous copying operation for the next set number of sheets is started.
Indicates that the toner density sensor 2 has been
1 of the output value V _T it takes a certain time t to stabilize.
The controller 31 reads the output value V _T0 of the toner density sensor 21 via the A / D converter 33 when the continuous image forming operation (copying operation for the set number of sheets) is completed as shown in FIG. The output value _VT0 'of the toner density sensor 21 when the developing device 12a is completely stopped is read through the A / D converter 33.

[0026] Then, the control unit 31, the V _T0 'value of the difference between the output value V _T0 of the last that has been stored in the memory image forming operation at the end of the toner density sensor 21 (V _T0' -
Calculates V _T0), a table showing the relationship between the (V _T0 '-V _T0) by, as shown in FIG. 4 in the non-volatile memory (V _{T 0'} -V _T0) and the correction time t, Fig. 6 The correction time and the respective values t ₁ and b ₁ of the b-intercept are determined according to a table showing the relationship between (V _T0 ′ −V _T0 ) and the b-intercept as shown in FIG.

When the start button of the operation unit 32 is turned on and the image formation is started, the control unit 31 measures the time after the start of the image formation and determines whether or not this time is smaller than the time t _1. , the time after the start of image formation by calculating a correction value y from the time and the b ₁ after the image formation start by the function y = ax + b if the t ₁ is smaller than the output value V _T of the toner density sensor 21 The result is added to the reference value V
_The toner replenishing amount is determined by the magnitude of _REF, and the toner replenishing motor 35 of the toner replenishing device 12b is controlled via the driver 34 so that the toner is replenished from the toner replenishing device 12b to the developing device 12a by the toner replenishing amount. Then, the toner concentration of the developer is controlled to a predetermined value.

When the time after the start of image formation is equal to or longer than the time t ₁ , the control section 31 performs the above-described normal toner density control, that is, the output value V _T of the toner density sensor 21. And the reference value V _REF , the toner replenishing amount is determined. The toner in the toner replenishing device 12 b is supplied via the driver 34 so that the toner is replenished from the toner replenishing device 12 b to the developing device 12 a by the determined toner replenishing amount. The supply motor 35 is controlled to control the toner concentration of the developer to a predetermined value.

When the image forming operation for the set number of sheets is completed, the control section 31 changes the output value V _T0 of the toner density sensor 21 to A.
The data is read via the / D converter 33 and stored in the memory.
Thus, the conventional apparatus had been determined toner supply amount depending on the magnitude of the output value V _T and the reference value V _REF of the toner density sensor 21 shown in FIG. 7, in this embodiment of the toner density sensor 21 since the output value V _T determines the toner supply amount depending on the magnitude of correction as shown in FIG. 8 and V _T and the reference value V _REF after the correction by adding a correction value, immediately after the image formation start toner density sensor It is possible to eliminate the problem caused by the erroneous detection of 21.

In the above embodiment, the amount of the developer above the toner density sensor 21 changes during non-image formation due to a change in the position of the elliptical plate 14 and the like, and the toner density sensor 21 erroneously detects the toner density. The present invention can be similarly applied to a case where the toner amount in the toner density detection area of the density sensor 21 changes during non-image formation due to another cause and the toner density sensor 21 erroneously detects the toner density. Although the above-described embodiment is an example in which the present invention is applied to a copying machine, the present invention is applied to an electrophotographic apparatus such as a facsimile or a printer having a developing device which operates during image formation and circulates a developer in which a carrier and a toner are mixed. The same effect can be obtained by applying the present invention to an image forming apparatus such as an image forming apparatus and an electrostatic recording method.

[0031]

As described above, according to the first aspect of the present invention, a developer in which a carrier and a toner are mixed is stored and operated at the time of image formation, and an electrostatic latent image on an image carrier is actuated by the developer. In a toner density control device of an image forming apparatus having a developing device for developing and a toner replenishing device for replenishing toner to the developing device, a toner density detecting device for detecting a mixing ratio of a carrier of the developer in the developing device and the toner. Means for controlling the toner replenishing device based on the detection result of the toner density detecting means to control the toner replenishing amount to the developing device, and for a certain period of time after the start of image formation, the detected value of the toner density detecting means. Control means for controlling the toner replenishing device based on the value and adding the predetermined correction value to control the toner replenishment amount to the developing device. Cheap It is possible to eliminate the problem that it is determined that the developer is not sufficient for the toner with the output value that is not used and that the toner replenishment device performs excessive toner replenishment, which causes the image on the image carrier to become dirty. it can.

Further, the detected value of the toner density detecting means when the developing device is stopped V _T0 ', the detection value of the toner density detecting means at the time of previous image formation completion V _T0
, The control means makes the V _T0 and the V _T0 ′
Since changing the predetermined time by the value of the difference between, until the output value of the toner concentration detection means it is also not exhibit the usual same value of the output value V _{T0 'toner} density detecting means when the developing unit is stopped to stabilize The output value of the toner concentration detecting means corresponding to the time can be corrected.

Furthermore, in particular said control means, said determining a correction value at the time of the primary function of the post-image formation start, determine its intercept on the value of the difference between the V _{T0 'and} the V _T0
Therefore, since the correction value is changed , excess or deficiency of correction can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention.

FIG. 2 is a flowchart showing an operation flow of the embodiment.

FIG. 3 is a cross-sectional view illustrating an example of a developing device.

FIG. 4 is a characteristic diagram showing a relationship between (V _T0 ′ −V _T0 ) and a correction time in the embodiment.

FIG. 5 is a characteristic diagram showing a relationship between a time x after the start of a copying operation and a correction value y in the embodiment.

FIG. 6 is a characteristic diagram showing the relationship between (V _T0 ′ −V _T0 ) and the b-intercept in the embodiment.

Is a waveform diagram showing an output value V _T of the toner density sensor to when the 7 next set number of sheets of copying operation from the time the previous setting number of sheets of copying operation in the above embodiment is completed is started .

FIG. 8 is a waveform chart showing an output value of the toner density sensor after correction in the embodiment.

9 is a waveform diagram showing an output value V _T of the toner density sensor.

FIG. 10 is a characteristic diagram illustrating a relationship between a toner density and an output value of a toner density sensor.

[Explanation of symbols]

 21 Toner density sensor 31 Control unit 35 Toner supply motor

Claims (1)

(57) [Claims] A developing device for storing a developer in which a carrier and a toner are mixed and operating at the time of image formation to develop an electrostatic latent image on an image carrier with the developer; and supplying toner to the developing device. A toner concentration control device for an image forming apparatus having a toner replenishing device, wherein a toner concentration detection device for detecting a mixture ratio of a carrier and a toner of a developer in the developing device, and a detection result of the toner concentration detection device. The toner replenishing device is controlled to control the amount of toner replenishment to the developing device, and a predetermined correction value is added to the detection value of the toner concentration detection means for a certain time after the start of image formation, and based on the value, Control means for controlling a toner replenishing device to control a toner replenishment amount to the developing device , wherein the control means comprises:
When the developing device is stopped,
The detected value is _VT0 ', the toner at the end of the previous image formation.
When the detected value of the density detecting means is _VT0 , the _VT0
Varying said predetermined time by the value of the difference between the V _{T0 '}
The correction value is determined by a linear function of the time after the start of image formation.
Because, the value of the difference between the _{V T0} 'The sections and the _{V T0}
Therefore the toner density control apparatus characterized by changing the correction value by determining.