JP2002072663A - Image forming device - Google Patents

Abstract

(57) [Summary] [Problem] Inductance ATR and video count AT
By changing the ratio of the toner supply control by R, even if there is an environmental change during the image forming operation or a change in the bulk density of the developer due to the developer being left, the error of the toner density control is eliminated. SOLUTION: During an image forming operation under toner supply control by an inductance ATR, a current toner density is detected by an inductance head, and a difference | ac between a current signal value a and a signal value c at the time of previous image formation is obtained. If | is 0.4 V or more, the control is switched to the combined supply control including the video count ATR. Combined supply control starts with video count AT
Starting from a toner replenishment ratio P (χ) of R of 100% and a toner replenishment ratio of 0% by the inductance ATR, linearly decreasing with P (χ) according to the number of image formations に corresponding to the difference value, the predetermined number When the number reaches N, the combination control ends, and the flow returns to the original toner supply using only the inductance ATR.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copier, a printer, and a recorded image display for developing a visible image by developing an electrostatic latent image formed on an image carrier by an electrophotographic method, an electrostatic recording method, or the like. Apparatus, image forming apparatus such as facsimile,
More particularly, the present invention relates to an image forming apparatus provided with a developer concentration control device for appropriately controlling the toner concentration of a two-component developer.

[0002]

2. Description of the Related Art In general, as a developing device provided in an electrophotographic or electrostatic recording type image forming apparatus, a developing apparatus using a two-component developer mainly composed of a non-magnetic toner and a magnetic carrier is known. In particular, in a color image forming apparatus that forms a full-color or multi-color image by an electrophotographic method, most developing devices use a two-component developer from the viewpoint of the color of the image.

As is well known, the toner concentration of a two-component developer, that is, the ratio of the weight of the toner to the total weight of the carrier and the toner, is a very important factor in stabilizing image quality. The toner of the developer is consumed at the time of development, and the toner density changes. Therefore, the toner concentration of the developer is detected by a developer concentration control device (ATR) in a timely manner, the toner is replenished to the developing device according to the change, and the toner concentration of the developer is constantly controlled to be constant. Is maintained.

Heretofore, various types of developer concentration control devices have been put into practical use due to differences in detection means for detecting the toner concentration of the developer in the developing device.

For example, a developer carrying member of a developing device (in general, a developing sleeve is often used as a developer carrying member, and is referred to as a “developing sleeve” in the following description) or a developer carrying path of a developing device. Then, an optical type toner concentration detecting means is installed, and it is determined that the reflectance when the detecting means irradiates the developer on the developing sleeve or the developer in the developing device with the toner concentration differs depending on the toner concentration of the developer. There is a developer concentration control device that detects and controls the toner concentration of the developer in the developing device.

Alternatively, an inductance head is provided as a toner concentration detecting means in the developing device, and the fact that when the toner concentration of the developer changes, the apparent magnetic permeability due to the mixing ratio of the carrier and the toner of the developer changes. hand,
There is a developer concentration control device of an inductance detection type which detects a toner concentration of a developer in a developing device and controls a replenished toner amount by comparing a detected value with a reference value.

Further, the density of a patch image formed on an image carrier (in general, a photosensitive drum is often used as an image carrier, and is hereinafter referred to as a "photosensitive drum"), is used to determine the density of the patch image on the surface of the photosensitive drum. When the detected value is lower than the initial set value, the toner is supplied to the developing device until the detected value is lower than the initial set value, and as a result, the toner in the developer in the developing device is detected. There is a developer concentration control device of a type in which the concentration is indirectly maintained at a desired value.

Furthermore, a video count for estimating the amount of toner consumed in the development of the image based on the video count number of the image density obtained by reading the image information signal by a CCD sensor or the like, and supplying the corresponding amount of toner. There is also a developer concentration control device called a system.

However, the above-described method of detecting the toner density from the reflectance when light is applied to the developer on the developing sleeve or the developer in the developing device is performed when the detecting means becomes dirty due to toner scattering or the like. There is a problem that the toner density cannot be detected accurately.

The method of indirectly controlling the toner density from the patch image density on the photosensitive drum cannot secure a space for forming a patch image or a space for installing a detecting means due to downsizing of a copying machine or an image forming apparatus. There are problems such as.

On the other hand, in the developer concentration control device (video count ATR) based on the video count method, the amount of toner replenishment is calculated and replenished each time an image forming operation is performed. In this case, it is possible to quickly control the toner concentration to an appropriate value as compared with the former two. However, if a difference occurs between the toner consumption calculated from the video count and the toner replenishment amount by the toner hopper due to the accuracy of the toner hopper or the like that replenishes the toner, when the number of formed images becomes large, It will gradually deviate from the proper toner concentration,
It is difficult to control the developer concentration only by the video count method.

On the other hand, the developer concentration control device (inductance detection ATR) of the inductance detection type does not have the above-mentioned problem. In this method, for example, when it is detected that the apparent magnetic permeability of the developer is large, the ratio of the carrier particles in the developer in a certain volume is increased, which means that the toner concentration is reduced. When replenishment is started, on the contrary, when the apparent magnetic permeability decreases, the proportion of the carrier in the developer in a certain volume decreases, which means that the toner concentration has increased, so the toner replenishment is stopped. The toner density is controlled based on the above method.

[0013]

However, when the image forming apparatus is not operated for a long period of time and the developer is left for a long period of time, the inductance detection ATR is used immediately after the image forming operation is resumed, immediately after the image forming operation is resumed, due to environmental changes and toner during the period of being left. There has been a problem that the sensor output changes due to a change in the bulk density of the developer due to a change in the charge amount or the like, even though the toner density has not changed.

That is, although the toner concentration of the developer in the developing device is constant, it is detected that the amount of the developer in a certain volume near the inductance detecting sensor has changed. As a result, an output signal indicating that the toner has been reduced is output and the toner is replenished even though the toner is not consumed, or an output signal indicating that the toner is not reduced even though the toner amount is reduced. And a problem such as not supplying toner occurs.

In the former case, there arises a problem that the image density is increased, fogging, scattering and the like occur due to excessive supply of toner. In the latter case, problems such as image deterioration and low image density due to a decrease in the amount of toner in the developer are caused. These problems are caused by a change in the bulk density of the developer, for example, when the stop time (leaving time) from when the image forming apparatus is stopped to when it is operated again is long, or when the use environment of the apparatus main body fluctuates greatly during that time. The larger, the more noticeable.

As means for solving this problem, at the time of image formation, the detection signal value of the inductance detection sensor and
When the difference from the detection signal value at the time of the previous image formation is large, that is, when it is detected that the change in the bulk density of the developer is large, the control is switched to the toner replenishment control by the video count ATR, or A method such as switching to supply control may be considered.

In the toner replenishment control by the video count ATR, as described above, the toner replenishment amount is calculated and replenished each time an image forming operation is performed. Therefore, the toner is excessively replenished or replenished due to a change in the bulk density of the developer. Shortages can be temporarily avoided.

However, as described above, if there is a difference between the toner consumption calculated from the video count and the toner replenishment amount by the toner hopper, the initial appropriate There is a possibility that the density gradually deviates from the toner density. Therefore, after a certain period of time, it is necessary to return to the original toner replenishment control using only the inductance ATR. However, if the method of returning to the original value and the timing are not proper, the toner density may be out of an appropriate range. The nature was high.

Accordingly, an object of the present invention is to change the ratio of toner replenishment control by the two density control devices, the inductance ATR and the video count ATR, to change the environment due to the image forming operation or to determine whether the developer is left unattended. An object of the present invention is to provide an image forming apparatus capable of eliminating an error in toner density control caused by a change in the density and preventing the occurrence of an image defect due to the error.

[0020]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
Forming an electrostatic latent image on the image carrier corresponding to the image information signal;
In an image forming apparatus that develops the electrostatic latent image by a developing unit using a two-component developer in which a toner and a carrier are mixed to form a visible image, and transfers the visible image to a transfer material, an apparent appearance of the developer Is detected, based on a comparison result between the obtained detection signal value and a predetermined reference signal value,
A first developer density control device for controlling a replenishing operation of a replenishing unit for replenishing toner to the developing unit, and a second developer controlling a replenishing operation of the replenishing unit based on a video count number of a density signal of an image information signal. A developer concentration control device, wherein the first developer concentration control device compares a detection signal value detected at the time of current image formation with a detection signal value detected at the time of previous image formation, and detects the detected signal value. If the difference is equal to or more than a predetermined value, the control of the replenishing operation of the replenishing means is switched to the combined replenishment control by the first developer concentration control device and the second developer concentration control device, The image forming apparatus is characterized in that, after the combined supply control is continued for a time determined by a difference between the detection signals, the combined supply control is terminated.

According to the present invention, the replenishment ratio of the toner by the first developer concentration control device and the second developer concentration control device is linearly determined by the elapsed time from the start of the combined supply control. To change. The time for which the combined replenishment control is continued is determined based on the number of formed images. The time for continuing the combined supply control is determined based on the operation time of the developer stirring member of the developing unit. The time during which the combined supply control is continued is determined based on the video count of the density signal of the image information signal. The image carrier and the developing unit are integrated to constitute a process cartridge that can be attached to and detached from the image forming apparatus main body, and the process cartridge is detected by the first developer concentration control device during the previous image formation. A nonvolatile memory for storing the detection signal value;

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 An image forming apparatus to which the present invention can be applied forms a latent image corresponding to an image information signal on an image carrier such as a photosensitive member or a dielectric by an electrophotographic system, an electrostatic recording system, or the like. This latent image is developed by a developing device using a two-component developer mainly composed of toner and carrier to form a visible image (toner image),
Various types of visible images can be used as long as they are transferred to a transfer material such as paper and fixed by a fixing unit to form a permanent image on the transfer material.

First, an overall configuration of an embodiment of an image forming apparatus according to the present invention will be described with reference to FIG. In this embodiment, a case where the present invention is applied to an electrophotographic digital copying machine will be described. However, the present invention is equally applicable to various other image forming apparatuses of an electrophotographic type and an electrostatic recording type.

In FIG. 1, an image of a document 31 to be copied is projected by a lens 32 onto an image pickup device 33 such as a CCD. The image sensor 33 decomposes the image of the document 31 into a number of pixels and generates a photoelectric conversion signal (analog signal) corresponding to the density of each pixel as an image signal. Image sensor 3
3 is sent to an image signal processing circuit 34, where it is converted into a pixel image signal having an output level corresponding to the density of the pixel, and sent to a pulse width modulation circuit 35. Can be

The pulse width modulation circuit 35 has a width (time length) corresponding to the level of each input pixel image signal.
Is formed and output. That is, as shown in FIG. 3A, a wider drive pulse W is applied to a high-density pixel image signal, and a narrower drive pulse S is applied to a low-density pixel image signal. , A drive pulse I having an intermediate width is formed for a medium-density pixel image signal.

The laser drive pulse output from the pulse width modulation circuit 35 is supplied to the semiconductor laser 36, and the semiconductor laser 36 is irradiated with the laser light 3 for a time corresponding to the pulse width.
6a emits and emits light. Therefore, the semiconductor laser 36 is driven for a longer period of time for the high-density pixels, and is driven for a shorter period of time for the low-density pixels. Therefore, the photosensitive drum 40 is exposed to a high-density pixel in a longer range in the main scanning direction by the optical system described below.
For a low density pixel, a shorter range is exposed in the main scanning direction. That is, the dot size of the electrostatic latent image differs according to the density of the pixel. Therefore, it goes without saying that the toner consumption for the high density pixels is larger than that for the low density pixels. In FIG. 3D, the electrostatic latent images of the low, medium and high density pixels are indicated by L, M and H, respectively.

The laser light 36a emitted from the semiconductor laser 36 is swept by a rotating polygon mirror 37, and is fixed by a lens 38 such as an f / θ lens and a fixed mirror 39 for directing the laser light 36a toward the photosensitive drum 40 as an image carrier. Is spot-formed on the photosensitive drum 40. Thus, the laser beam 36a scans the surface of the photosensitive drum 40 in a direction (main scanning direction) substantially parallel to the rotation axis of the photosensitive drum 40, and forms an electrostatic latent image on the surface of the photosensitive drum 40.

The photosensitive drum 40 is a drum-shaped electrophotographic photosensitive member having amorphous silicon, selenium, OPC and the like on its surface and rotating in the direction of the arrow. 42 uniformly charges. Thereafter, exposure scanning is performed with a laser beam modulated in accordance with the image information signal described above, whereby an electrostatic latent image corresponding to the image information signal is formed. This electrostatic latent image is reversely developed by a developing device 44 using a two-component developer 43 in which a toner and a carrier are mixed to form a visible image (toner image). Here, the reversal development is a development method in which a toner charged to the same polarity as the latent image is attached to a region of the photoconductor exposed to light, and the toner is visualized.

This toner image is applied to two rollers 45 and 46.
The transfer charger 4 is mounted on a transfer material 48 held on a transfer material carrying belt 47 which is stretched between and is driven endlessly in the direction of the arrow in FIG.
9 is transcribed.

Note that only one image forming station (including a photosensitive drum 40, an exposing unit 41, a primary charging unit 42, a developing unit 44, and the like) is illustrated for simplicity of description.
In the case of a color image forming apparatus, for example, four image forming stations for each color of cyan, magenta, yellow and black are sequentially arranged on the transfer material carrying belt 47 along the moving direction thereof, and An electrostatic latent image of each color obtained by color-separating the image of the document on the photosensitive drum is sequentially formed, developed by a developing device having a toner of a corresponding color, and conveyed while being held on a transfer material carrying belt 47. The image is transferred onto the transfer material 48 in a superimposed manner.

The transfer material 48 to which the toner image has been transferred is
It is separated from the transfer material carrying belt 47 and transported to a fixing device (not shown), where it is fixed and formed into a permanent image. Further, the residual toner remaining on the photosensitive drum 40 after the transfer is
Thereafter, it is removed by the cleaner 50.

FIG. 2 shows an example of the developing device 44. As shown in the drawing, the developing device 44 is arranged to face the photosensitive drum 40, and the inside thereof is a partition wall 51 extending vertically.
The first chamber (developing chamber) 52 and the second chamber (stirring chamber) 53
It is divided into and. In the first chamber 52, a non-magnetic developing sleeve 54 that rotates in the direction of the arrow as a developer carrying member is disposed.
5 is fixedly arranged. The developing sleeve 54 carries and conveys a layer of a two-component developer (including a magnetic carrier and a non-magnetic toner) whose layer thickness is regulated by a blade 56, and transfers the developer in a developing area opposed to the photosensitive drum 40.
To develop the electrostatic latent image. In order to improve the development efficiency, that is, the rate at which toner is applied to the latent image, a development bias voltage in which a DC voltage is superimposed on an AC voltage is applied to the development sleeve 54 from a power supply 57.

The first chamber 52 and the second chamber 53 are provided with developer stirring screws 58 and 59, respectively. The screw 58 stirs and conveys the developer in the first chamber 52, and the screw 59 is provided with the toner 63 supplied by the rotation of the conveying screw 62 from a toner discharge port 61 of a toner replenishing tank 60 described later, and the developing device 44. The toner 43 inside the developer 43 is agitated and conveyed to make the toner concentration of the developer 43 uniform and recover. In the partition wall 51, a developer passage (not shown) for communicating the first chamber 52 and the second chamber 53 with each other at the front and rear ends in FIG. 2 is formed. Due to the conveying force of 59, the developer in the first chamber 52 whose toner density has been reduced due to the consumption of the toner by the development moves from one passage into the second chamber 53, and the toner density is recovered in the second chamber 53. The developer is moved from the other passage into the first chamber 52.

Now, in order to correct the change in the developer concentration in the developing device 44 due to the development of the electrostatic latent image, the developing device 4
In the present embodiment, the first chamber (developing chamber) 52 of the developing unit 44 is controlled to supply toner to the developing unit 4.
The output signal from the inductance head 20 installed on the bottom wall of the developing unit 44, specifically, the developing chamber 52
There is provided a developer concentration control device of an inductance detection type which detects the actual toner concentration of the developer 43 in the inside and replenishes the toner by comparison with a reference value.

As described above, the two-component developer contains a magnetic carrier and a non-magnetic toner as main components, and when the toner concentration of the developer 43 (the ratio of the toner weight to the total weight of the carrier and the toner) changes, the magnetic carrier The apparent magnetic permeability changes depending on the mixing ratio of the toner and the non-magnetic toner.
When this apparent magnetic permeability is detected by the inductance head 20 and converted into an electric signal, as shown in FIG.
This electric signal, that is, the detection signal (V) changes almost linearly according to the toner density (T / D ratio (%)). That is, the output signal from the inductance head 20 is
This corresponds to the actual toner concentration of the two-component developer in the developing device 44.

The output signal from the inductance head 20 is supplied to one input of a comparator 21 shown in FIG. The other input of the comparator 21 is supplied with a reference signal corresponding to an apparent magnetic permeability of the developer 43 at a specified toner density (an initial set value of the toner density) from the reference voltage signal source 22. Therefore, the comparator 21 compares the specified toner density with the actual toner density in the developing device, and the detection signal of the comparator 21 as a result of comparing the two input signals is supplied to the CPU 67.

The CPU 67 controls the toner supply time based on the detection signal from the comparator 21. For example, the developer 43 detected by the inductance head 20
If the actual toner concentration of is smaller than the specified value,
That is, if the toner supply is insufficient, the CPU 67
Operates the conveying screw 62 of the toner replenishing tank 60 so as to replenish the insufficient toner to the developing device 44. That is, based on the detection signal from the comparator 21, the screw rotation time required to supply the insufficient toner to the developing device 44 is calculated, and the motor driving circuit 69 is controlled to rotate the motor 70 by that time. Then, the insufficient toner is supplied to the developing device 44.

When the actual toner concentration of the developer 43 detected by the inductance head 20 is higher than a specified value, that is, when the toner is excessively replenished, the CPU 67 The amount of excess toner in the developer is calculated based on the detection signal. Then, when an image is formed from a document, toner is supplied so as to eliminate the excess toner amount, or an image is formed without supplying the toner until the excess toner amount is consumed. The control is performed such that an image is formed without using the toner and the excess toner is consumed, and when the excess toner is consumed, the toner replenishing operation is performed as described above.

The control of the above replenishment operation will be further described with reference to the flowchart of FIG.

First, when the image forming operation is started (step S501), toner density detection starts (S502). Next, the detection value a from the inductance head 20 is input to the comparator 21 (S503),
1 is compared with the reference value b from the reference voltage signal source 22 (S5).
04), and sends the detected voltage difference (ab) to the CPU 67 to determine whether (ab)> 0 (S505, S5).
06), if (ab)> 0 (YES), that is, if the toner density is lower than the reference value, the toner supply time is determined (S507). Next, toner supply is performed for the determined toner supply time (S508), and the process returns to the start of step S502.

If (ab) <0 in step S506 (NO), that is, if the toner concentration is higher than the reference value, the process returns to the start without supplying toner.

In the inductance detection ATR used in this embodiment, the optimum toner density (6% in this embodiment) is too high, toner scattering occurs, and if it is too low, the image density becomes low. The reference value of the detection signal is adjusted to 2.5 V. If the detection signal of the sensor is larger than the reference value (for example, 3.0 V), the toner is replenished. If the detection signal of the sensor is small (for example, 2.0 V), the toner supply is stopped. However, the present invention is not limited to the above signal processing, and the circuit configuration may be changed. The reference value may be a value other than 2.5 V. When the toner density is lower than the optimum value, the detection signal of the sensor is reduced, and when the toner density is higher than the optimum value, the detection signal is increased. Unishi and may be.

As described above, when an image forming apparatus such as a copying machine or a printer is left unoperated for a certain period of time, the apparent magnetic permeability of the developer changes due to a change in the bulk density of the developer. In spite of the fact that the toner density is constant, a change occurs in the detection signal of the inductance detection type ATR, and an error may occur in the toner density control.

For example, as shown in FIG. 6, when the optimum toner concentration (T / D ratio) of the developer is 6% (FIG. 6C),
The detection signal value from the inductance head 20 is 2.5 V
(FIG. 6B), and the optimum toner density is maintained until immediately before the idle period. However, when the image forming apparatus is not operated after being left for a long time (FIG.
The bulk density of the developer changes due to factors such as a change in the temperature and humidity of the use environment of the apparatus main body and a change in the toner charge amount (FIG. 6A). (Note that
FIG. 6A illustrates the case where the bulk density is increased by leaving the apparatus unattended.) In some cases, the detection signal at the time when the operation of the apparatus is restarted may change significantly.

In such a case, the inductance detection type ATR used in the present embodiment has the circuit configuration shown in FIG.
As shown in FIG. 6B, when the detection signal value is higher than the reference value (2.5 V in this embodiment), it is determined that the ratio of the carrier in the developer is large, that is, the toner concentration is low. As shown in (c), there is a problem that the toner is excessively replenished and becomes stable in a portion higher than the original optimum toner concentration. Further, although not shown here, the detection signal value may be low depending on the situation of the neglect. In such a case, there is a problem that the toner is not supplied and the toner density is stabilized at a position lower than the optimum value.

Therefore, in the present embodiment, excessive replenishment and insufficient replenishment of toner due to a change in the detection signal of the inductance detection system ATR due to the image forming apparatus being left unattended are prevented, and the toner is immediately started after the image forming operation is started. In order to be able to control the density within an appropriate range, the developer density control of the inductance detection ATR is performed in combination with the video count method which is the second developer density control means. The above-mentioned disadvantages are eliminated.

First, the video count method for the image density of the image information signal will be described with reference to FIG.

In the toner replenishment control by the video count method, the level of the output signal of the image signal processing circuit 34 shown in FIG. 1 is counted for each pixel. This counting is performed as follows. First, the pulse width modulation circuit 35
Is supplied to one input of an AND gate 64, and a clock pulse (a pulse shown in FIG. 3B) from a clock pulse oscillator 65 is supplied to the other input of the AND gate. Therefore, as shown in FIG. 3C, the laser drive pulses S, I,
The number of clock pulses corresponding to each pulse width of W,
That is, the number of clock pulses corresponding to the density of each pixel is output. The number of clock pulses is accumulated by the counter 66 for each image, and the video count is calculated (for example, the maximum video count of one A4 size sheet is 400 dpi, 3884 × 10 ⁶ at 256 gradations). The pulse integration signal C1 for each image from the counter 66
The (video count number) corresponds to the amount of toner consumed from the developing device 44 to form one toner image corresponding to the image of the document 31. Therefore, the video count number is supplied to the CPU 67, and an appropriate toner supply time is determined from a conversion table in the RAM 68 that indicates the correspondence between the video count number and the toner supply time.

In this embodiment, the video count system is used as the second developer concentration control device, but it operates based on the following control.

First, as shown in FIG. 1, a detection signal from the inductance head 20 is stored in a recording and holding device 23 such as a non-volatile memory whenever image formation is performed. At the time of the next image formation, the record holding device 2
3 is supplied to one input of the second comparator 24, and the other input is an inductance head at the time of current image formation. The detection signal a from the control unit 20 is input, and the difference is sent to the second CPU 25. Second CPU 25
Then, it is determined whether or not the difference = | a−c | is equal to or greater than a predetermined value. Based on the result, the subsequent developer concentration control is continued only by the first concentration control device using the inductance detection method. It is determined whether to perform the control or to switch to the control using the second developer concentration control device based on the video count method.

In this embodiment, the threshold value for determining whether to switch to the combined control is set to 0.4V. As a result of study, the difference | in the image forming apparatus according to the present embodiment
If a−c | is equal to or greater than this value, excessive replenishment of toner,
Alternatively, the lack of replenishment becomes remarkable, and the fluctuation of the T / D ratio exceeds the allowable range. However, it is needless to say that the threshold value is not limited to this value, and an optimum value is set according to the configuration of the image forming apparatus.

If the toner replenishment control by the video count method is performed, the amount of toner consumed for each image forming operation is predicted, and the toner replenishment amount is calculated and replenished accordingly. Can be temporarily avoided.

However, since this method is a replenishment based on prediction, the control of this method alone causes a large amount of image forming operation, so that the difference between the toner consumption amount and the supply amount causes the developer concentration to fall out of an appropriate range. There is a risk that it will come off gradually. Also, even if the bulk density of the developer changes after being left for a long period of time, it gradually adapts to the environment as the image forming apparatus continues to operate, eliminates packing of the developer due to agitation, and recovers the toner charge amount. It is considered that the density gradually approaches the bulk density suitable for the environment.

Therefore, both the toner replenishment control means are used in combination, and immediately after the operation of the apparatus which has been left for a long time is started, the toner replenishment control is mainly performed by the video count method, and the inductance is gradually increased as the image forming operation time elapses. If the switching is performed so as to mainly perform the toner supply control of the detection method, the toner supply control according to the actual state of the developer can be performed.

Therefore, in the present embodiment, the following combination replenishment control is performed.

In general, the change in the bulk density of the developer due to standing becomes larger as the environmental change during standing and the standing time become longer, so that the difference | ac of the detection signals detected by the inductance head is accordingly increased. | Also increases. That is, the fact that the difference between the detection signals is large means that
It is considered that it takes time for the developer to adapt to the environment or to recover the charge amount.

FIG. 7 is a graph showing the time from when the output is increased by leaving the toner density of 2.5 V to the original detection output of the toner density until the output returns to the original state due to idle rotation. It can be seen that the larger the fluctuation of the detection output due to the neglect (the larger the fluctuation of the bulk density of the developer), the longer the time required for the detection output to recover.
Therefore, the time for using both the inductance detection method and the video count method for toner replenishment is changed depending on the magnitude of the difference between the detection signals. That is, the combination replenishment control is terminated after a predetermined time determined by the magnitude of the difference value of the detection signal has elapsed.

As described above, while the operation of the image forming apparatus is continued, it is considered that the developer gradually adapts to the environment and gradually approaches a bulk density suitable for the environment. When the developer is not familiar with the environment, increase the ratio of toner replenishment by the video count method at the beginning, reduce the error of toner replenishment immediately after standing, and use the inductance detection method when the developer has adapted to the environment over time. Increasing the ratio of toner replenishment prevents the developer concentration from being out of the proper range due to the difference between the toner consumption amount and the supply amount, so that the developer concentration is always controlled within the proper range. .

This will be specifically described with reference to the flowchart shown in FIG.

During the image forming operation, the current signal value a is detected by the inductance head (step S801),
The signal value c at the time of the previous image formation is read from the nonvolatile memory (S802), and the two are compared by the second comparator 24 (S803). The difference | ac |
When it is detected that the voltage is 4 V or more, the mode is switched to the combined replenishment control. The time length for performing the combined replenishment control, that is, the duration of the combined replenishment control is determined according to the magnitude of the difference at that time. Since the number of formed images corresponds to the image forming time,
In the present embodiment, the duration of the combined supply control is determined as the number of image formations (S804).

That is, the number N of formed images for which the combined replenishment control is performed is as follows: N = │ac│ × A (A is a constant, where A = 10
0), and the ratio P (χ) of toner supply by the video count method after χ sheets from the start of the combined supply control is represented by P (χ) = 100− (χ / N) × 100.

That is, immediately after switching to the combined supply control, the toner supply ratio P (χ) =
Starting with 100%, the toner supply ratio by the inductance detection method = 0%, the toner supply is started, and the toner supply ratio by the video count method is linearly changed to P (χ).
When the number of image formation reaches a predetermined N number, P (χ) = P (N) = 0%, and the flow returns to the original toner detection method using only the inductance detection method. FIG. 9 shows how the toner replenishment ratio P (χ) changes according to the video count method.

For example, when the difference value of the detection signal is 0.5 V, the number N of sheets for which the combined supply control is continued is determined as N = 0.5 × 100 = 500, and the combined supply control is started. (S805).
The toner replenishment ratio P (χ) by the video count method after 100 sheets is P (χ) = 100− (100/500) × 100 = 80
%, And the toner supply time obtained by the inductance detection method at that time is 500 ms (ms = 10
^-3 seconds), and assuming that the toner replenishment time obtained by the video count method is 20 ms, the actual toner replenishment time T
Is calculated as follows: T = 0.2 × 500 + 0.8 × 20 = 116 (ms) Then, this ratio gradually decreases with an increase in the number of image formation sheets, and after 500 sheets, P (χ) = 0, and the combined supply control ends (S806).

Immediately after the combined replenishment control is started, the developer has not yet been adapted to the environment and the charge amount has not been sufficiently recovered. In a state where the developer has been adjusted to the environment after a certain period of time and the charge amount has been recovered, it is desirable that the ratio of toner supply by the inductance detection method is large. Therefore, as described above, the method of linearly changing the toner supply ratio by the two developer concentration control means and gradually reducing the toner supply ratio by the video count method is based on the state of the developer at each time. This is very excellent in that toner can be supplied in a timely manner.

As described above, the time for continuing the replenishment control in combination with the video count method is determined based on the difference (| ac |) between the detection signals detected by the inductance detection method. As a result, the larger the variation in the bulk density of the developer, the longer the time for performing the combined supply control can be made, so that it is possible to perform the appropriate combined supply control according to the magnitude of the variation in the bulk density. Further, by changing the ratio of toner replenishment by the two developer density control means linearly according to the number of image formations after the start of the combined replenishment control, toner replenishment in accordance with the state of the developer at each time is achieved. It is now possible to do it.

By performing such control, even when the bulk density of the developer changes due to standing, the developer concentration is prevented from suddenly changing due to the fluctuation of the detection signal of the inductance detection sensor, and the toner density is increased. It has become possible to prevent image quality deterioration such as scattering, fogging and low image density due to toner density reduction.

Embodiment 2 In this embodiment, the time during which the combined supply control is continued is controlled by the screw 58 (or the screw 5) which is a developer stirring member.
It was determined based on the operation time of 9).

Since the recovery of the bulk density of the developer is directly related to the driving of the stirring member, determining the time for continuing the combined supply control based on this operation time will make the actual state of the developer more effective. The reflected control can be performed.

That is, the operation time t of the developer stirring member for performing the combined replenishment control is t = │ac│ × B (B is a constant, here B = 400
0), and the toner supply ratio P (y) by the video count method after the stirring member has operated for y seconds after starting the combined supply control is: P (y) = 100− (y / t) × 100 expressed. For example, when the difference value of the detection signal is 0.5 V, the operation time t of the developer stirring member that continues the combined supply control is t = 0.5 × 4000 = 2000 (sec), and the stirring member The toner replenishment ratio P (y) by the video count method after the operation for 500 seconds is as follows: P (y) = 100− (500/2000) × 100 = 7
5%.

According to the structure of this embodiment, the developer which has been left alone and has a large change in the bulk density, or the developer in which the bulk density is stable due to the subsequent large-volume image forming operation, can be used for more actual development. Since the toner replenishment control can be performed according to the state of the developer, the developer concentration can be controlled within a more appropriate range.

Embodiment 3 In this embodiment, the time during which the combined supply control is continued is determined based on the video count of the density signal of the image information signal.

Even when the developer is held between the carriers for a long period of time and the toner is pressed between the carriers, the shape and surface properties of the toner are changed and the bulk density is changed. Then, when the toner is replaced by replenishing the toner, the developer returns to substantially the initial bulk density. Since the integrated video count number corresponds to the actual toner replacement amount, it is possible to perform control reflecting the actual toner state.

According to the structure of this embodiment, the developer which is left immediately after the bulk density is largely changed and the developer in which the bulk density is stabilized by the subsequent large-volume image forming operation can be used for more actual development. Since replenishment control can be performed in accordance with the state of the toner present in the developer, the developer concentration can be controlled within a more appropriate range.

Embodiment 4 In this embodiment, at least the photosensitive drum 40 and the developing device 44 are integrated as a process cartridge in the image forming apparatus of FIG. 1, and this process cartridge is configured to be detachable from the main body of the image forming apparatus. Is the feature.

By making the process unit into a cartridge in this manner, replacement by the user becomes possible, and the maintenance performance can be greatly improved.

However, since the user can exchange the process cartridges, it is assumed that some users may use a plurality of process cartridges for one image forming apparatus. In this case, the process cartridge being used is left outside the apparatus main body. When the process cartridge is used again, the control described in the first to third embodiments must be performed.

Therefore, a non-volatile memory is provided in the process cartridge, and the detection signal detected during the image forming operation is stored in the non-volatile memory as needed.
With this configuration, the detection signal detected during the previous image forming operation can always be read out regardless of how the process cartridge is used or left unattended. Appropriate developer concentration control can be performed immediately after resuming use.

Thus, in an image forming apparatus using a process cartridge having excellent maintainability, even if the bulk density of the developer changes due to the process cartridge being left unattended, the development signal is changed by the detection signal of the inductance detection sensor. This makes it possible to prevent the agent concentration from abruptly changing and to prevent image quality deterioration such as scattering and fogging due to an increase in toner concentration, and image density thinning due to a decrease in toner concentration.

In each of the embodiments described above, the case where the present invention is applied to an electrophotographic digital copying machine has been described. However, the present invention is applicable to various other electrophotographic and electrostatic recording systems. This is equally applicable to image forming apparatuses such as copying machines and printers. For example, the present invention can be applied to an image forming apparatus that performs shading of an image by a dither method. The present invention is also applicable to an image forming apparatus that prints out an image based on an image information signal output from a computer or the like instead of copying a document. In the present invention, it goes without saying that various modifications and changes can be made to the configuration of the image forming apparatus and the control system as needed.

[0081]

As described above, according to the present invention,
Forming an electrostatic latent image on the image carrier corresponding to the image information signal;
This electrostatic latent image is developed using a two-component developer in which a toner and a carrier are mixed to form a visible image, and the resulting visible image is transferred to a transfer material in an image forming apparatus. A first developer density control device for controlling the replenishing operation of the toner replenishing means based on a comparison result between the detected signal value and a predetermined reference signal value, and a density of the image information signal. A second developer density control device for controlling a replenishing operation of the toner replenishing means based on a video count number of the signal, wherein the first developer density control device detects a detection signal value detected at the time of image formation and a previous image The detection signal values detected at the time of formation are compared, and if the difference between the detection signal values is equal to or more than a predetermined value, the replenishing operation of the replenishing means is performed by the first developer concentration control device and the second developer concentration. Complementary use by controller Switch to control, and since a predetermined time determined by the difference between the detection signal value has to perform control so as to terminate the combined supply control after a lapse,
It is possible to prevent an error from occurring in the toner density control after resuming the image forming operation due to the change in the bulk density before and after the developer is left, so that good image formation can be performed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a schematic configuration diagram illustrating a developing device included in the image forming apparatus of FIG. 1;

FIG. 3 is a waveform diagram illustrating a method of counting image information signals in the image forming apparatus of FIG.

FIG. 4 is an explanatory diagram showing how a detection signal from an inductance head provided in the developing device of FIG. 2 changes according to a change in toner concentration of a developer.

FIG. 5 is a flowchart illustrating a basic operation of toner supply control by an inductance detection method performed in the embodiment of FIG. 1;

FIG. 6 is an explanatory diagram showing the relationship between the bulk density of a developer, a toner density detection signal of an inductance detection method, and the T / D ratio of a developer before and after an idle period in a conventional toner supply control along an image forming time. It is.

FIG. 7 is an explanatory diagram showing that when a toner density detection signal rises due to being left, the time required until the detection signal recovers differs depending on the degree of increase.

FIG. 8 is a flowchart illustrating a basic operation of combined supply control performed in the embodiment of FIG. 1;

FIG. 9 is an explanatory diagram showing a state of a change in the ratio of toner replenishment by the video count method during the combined replenishment control.

[Explanation of symbols]

 Reference Signs List 20 inductance head 21 comparator 40 photosensitive drum 44 developing device 66 counter 67 CPU

Claims (6)

[Claims] An electrostatic latent image corresponding to an image information signal is formed on an image carrier, and the electrostatic latent image is developed by a developing unit using a two-component developer in which a toner and a carrier are mixed to form a visible image. In the image forming apparatus that transfers the visible image to a transfer material, an apparent magnetic permeability of the developer is detected, and based on a comparison result between the obtained detection signal value and a predetermined reference signal value. A first developer density control device for controlling a replenishing operation of a replenishing device for replenishing toner to the developing device, and a second controlling a replenishing operation of the replenishing device based on a video count number of a density signal of an image information signal. The first developer concentration control device compares the detection signal value detected at the time of the current image formation with the detection signal value detected at the time of the previous image formation, and detects the detection signal. If the difference between the values is greater than In this case, the control of the replenishing operation of the replenishing means is switched to the combined replenishment control by the first developer concentration control device and the second developer concentration control device, and is determined by the difference between the detection signals. An image forming apparatus, wherein after the combined supply control is continued for a time, the combined supply control is terminated. 2. A toner supply ratio between the first developer concentration control device and the second developer concentration control device,
The image forming apparatus according to claim 1, wherein the image forming apparatus linearly changes according to an elapsed time after starting the combined supply control. 3. The image forming apparatus according to claim 1, wherein the time during which the combined supply control is continued is determined based on the number of images to be formed. 4. The image forming apparatus according to claim 1, wherein a time for continuing the combined supply control is determined based on an operation time of a developer stirring member of the developing unit. 5. The image forming apparatus according to claim 1, wherein a time during which the combined supply control is continued is determined based on a video count of a density signal of the image information signal. 6. The image carrier and the developing means are integrated to constitute a process cartridge detachable from the main body of the image forming apparatus. The image forming apparatus according to claim 1, further comprising a non-volatile memory that stores a detection signal value detected during image formation.