JP3412972B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image of a copying machine or a printer such as an electrophotographic system or an electrostatic recording system in which toner is attached to an electrostatic image formed on an image carrier to make it visible. Forming apparatus

[0002]

2. Description of the Related Art Conventionally, there is known a developer concentration control device (ATR) for controlling toner replenishment from a hopper as a toner replenishing container into a developing device in order to keep a predetermined amount of toner in the developing device. For toner replenishment control, for example, a method of detecting the amount of toner in the developing device by irradiating the toner in the developing device with light and detecting the amount of reflected light is known. This method is not suitable when it is difficult to reflect.

On the other hand, in order to predict the amount of toner in the developing device, a toner patch as a reference toner image corresponding to a predetermined density is formed on an image carrier or the like, and the density of this toner patch is optically detected by a sensor. It is known. It is necessary to form such a toner patch at a timing such that the toner patch is not transferred from the image carrier to the transfer material. Therefore, when performing continuous copying, it is preferable to perform it before the image formation of the first sheet or after the image formation of the last sheet. When the number of images formed by continuous copying is very large, the toner amount in the developing device may fluctuate greatly.Therefore, even during copying, the copying is interrupted every time a predetermined number of images are formed to form a toner patch. Is preferred. In order to reduce the frequency of interruption, it is preferable to make the predetermined number as long as possible.

[0004]

If the sensor for optically detecting the amount of toner in the developing device is not provided as described above, the following problem will occur if a sensor for detecting the amount of remaining toner is provided in the toner hopper. It was

That is, the toner remaining amount detection sensor in the toner hopper may erroneously detect that toner is present even when there is no toner.

Therefore, even if the toner in the hopper becomes empty, the toner cannot be supplied to the developing device,
In the toner patch detection method, the toner in the developing device is reduced because a toner patch is formed only every time a predetermined number of images are formed, which is relatively large during continuous copying. It was sometimes formed in large quantities.

Further, in recent years, a first hopper that replenishes toner to the developing device and a first hopper that replenishes toner to the first developing device in order to reduce the amount of toner replenished to the developing device at one time by reducing the size of the developing device. It was desired to have two hoppers.

On the other hand, it has been desired to improve the replenishment accuracy of the toner replenishment amount from the second hopper to the first hopper, and the toner replenishment amount from the hopper to the developing device when the hopper is single.

[0009]

SUMMARY OF THE INVENTION The present invention which solves the above-mentioned problems includes a developing device for developing an electrostatic image formed on an image carrier with toner, and a first toner container for replenishing the developing device with toner. A first sensor that detects the amount of toner in the first toner container; and a second toner container that replenishes the first toner container with toner according to the detection output of the first sensor, An image forming apparatus having a second sensor for detecting the amount of toner in the second toner container, wherein the first sensor is used even though the detection output of the second sensor indicates the presence of toner. When the absence of toner is repeatedly detected for a predetermined number of times, it is determined that it is an abnormality detection of the second sensor.

[0010]

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

First, the overall construction of an embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. Although a four-drum type digital full-color copying machine is shown in the present embodiment, it goes without saying that the present invention is equally applicable to various other image forming apparatuses such as a monochrome electrophotographic type and an electrostatic recording type.

This color image forming apparatus is capable of forming a visible image (toner image) of each color of yellow, magenta, cyan and black in the main body of the apparatus.
The fourth four image forming sections Pa, Pb, Pc and Pd are arranged linearly, and each of the image forming sections Pa to Pd is arranged.
Are dedicated photoconductor drums 1a, 1b, 1 serving as image carriers.
c and 1d, respectively. Each photoconductor drum 1a to 1d
Are driven to rotate in the direction of the arrow shown in the figure, and there are dedicated image forming process means around them, for example, the charging means 2.
a, 2b, 2c, 2d, image exposure means 3a, 3b, 3c, 3d such as a laser scanner, developing means 4a, 4b, 4c,
4d, and cleaning means 5a, 5b, 5c, 5d, etc. are provided.

Recording material carrying means, in this example, a recording material carrying belt 8 which moves endlessly in this example, is provided between a plurality of rollers below the photosensitive drums 1a to 1d of the image forming sections Pa to Pd. The transfer charging means 6a, 6b, 6c, and 6d are arranged in the interior. Further, a sheet feeding section is arranged on the right side of the recording material carrying belt 8 in the figure, and a fixing means 7 is arranged on the opposite side thereof, that is, on the left side of the figure. Further, a pair of registration rollers 13 for feeding the recording material P at a timing is arranged between the paper feeding portion and the recording material carrying belt 8. The recording material P is fed from the paper feeding portion to the registration rollers. The recording material carrying belt 8 is fed and held via the recording material carrying belt 13.
Of the image forming units Pa to
The Pd is sequentially transferred to the transfer area.

In the above-mentioned structure, the recording material P sent out from the paper feeding section is temporarily stopped when its leading edge is slightly sandwiched by the registration rollers 13, and the first image forming section P is then stopped.
It is sent out at the same timing as the image forming process a, and is fed onto the recording material carrying belt 8. This first
In the image forming portion Pa, the image data of the yellow component color in the original image is scanned with a laser beam or the like on the photosensitive drum 1a uniformly charged by the charging means 2a to form an electrostatic latent image of the yellow component color. To be done. This electrostatic latent image becomes a yellow visible image with yellow toner attached by the developing means 4a.

On the other hand, the recording material P is carried while being carried on the recording material carrying belt 8, and in the transfer area below the photosensitive drum 1a of the first image forming portion Pa, the operation of the transfer charging means 6a causes the photosensitive member to be carried out. The yellow visible image formed on the drum 1a, that is, the toner image is transferred onto the recording material P. While the yellow toner image is thus transferred onto the recording material P, an electrostatic latent image of a magenta component color is formed on the second image forming portion Pb, and this electrostatic latent image is magenta by the developing means 4b. The recording material P is a toner image and the recording material P is the second image forming portion Pb.
When the magenta toner image is conveyed to the lower transfer area of the photosensitive drum 1b, the magenta toner image is transferred to the transfer area, and is transferred in a state of being superposed on the yellow toner image on the recording material P by the action of the transfer charging means 6b. To be done.

Hereinafter, the third and fourth image forming portions Pc and Pd will be described.
In the same manner, similarly to the first and second image forming portions Pa and Pb, cyan and black toner images are sequentially formed, and these are sequentially formed on the recording material P conveyed by the recording material carrying belt 8. Toner images are multi-transferred.

When the image forming process is completed, the recording material P is separated from the recording material carrying belt 8 and fixed by the fixing means 7.
Then, the desired full-color image is obtained by batch fixing. The residual toners are removed from the photosensitive drums 1a to 1d of the image forming portions Pa to Pd after the transfer by the cleaning units 5a to 5d to prepare for the subsequent latent image formation.

A two-component developing system is used in which each color of yellow (Y), magenta (M), cyan (C), and black (Bk) is provided with a toner and a carrier, and the mixing ratio of the toner and the carrier is maintained at a predetermined ratio. Developer concentration control device (A
TR).

In the Y, M and C image forming stations,
The optical ATR sensors 9a, 9 are used to correct the changed toner density in the developing devices 4a, 4b, 4c by developing the latent image.
b and 9c are provided in the developing devices for the respective colors, and toner is supplied to the developing devices from a toner hopper (not shown) based on the detection signal thereof.

As described above, Y, M, and C adopt the optical ATR system, and have a density detection sensor (hereinafter referred to as an ATR sensor) in the developing device. The optical ATR method utilizes the property that the toner reflects the infrared light and the carrier absorbs the infrared light,
The amount of light reflected by light irradiation is detected. Bk uses a carbon toner having a high cost merit. Since the carbon toner absorbs infrared light, it is not suitable to use this optical ATR method in the developing device.

Therefore, it is preferable that BK adopt a method different from the optical ATR method. The BK ATR method will be described below.
FIG. 6 is a diagram showing an image processing unit for forming a latent image and a fourth image forming station (Bk) including a toner hopper. (First to third stations are omitted from the drawing.) The latent image formation will be described in detail with reference to the drawing. First, the image of the original 80 is read by the CCD 81, the obtained analog image signal is amplified to a predetermined level by the amplifier 82, and the analog-digital converter (A / D converter) 8
3 converts into a digital image signal of 8 bits (0 to 255 gradations). Next, this digital image signal is supplied to a .gamma. Converter (a converter which is composed of a 256-byte RAM in this example and performs density conversion by a look-up table method) 84, and is .gamma. Input to the device (D / A converter) 85. Here, the digital image signal is converted again into an analog image signal and supplied to one input of the comparator 87. The other input of the comparator 87 is supplied with a triangular wave signal of a predetermined cycle generated from the triangular wave generating circuit 86, and the analog image signal supplied to one input of the comparator 87 is compared with this triangular wave signal and pulsed. It is width modulated. This pulse-width-modulated binary image signal is directly input to the laser drive circuit 88, and the laser diode 8
9 is used as a signal for on / off control of light emission. The laser light emitted from the laser diode 89 is scanned in the main scanning direction by a well-known polygon mirror 90, and f / θ
It is irradiated onto the photosensitive drum 1d, which is an image carrier rotating in the direction of the arrow, through the lens 91 and the reflection mirror 92,
An electrostatic latent image will be formed.

Further, a video count type developer density control device is provided in order to correct the changed toner density in the developing device 4d due to the development of the latent image, and the output level of the digital image signal for each pixel is adjusted. The toner has been added up and the toner is being replenished as predicted. That is, the analog-digital converter 8
The output level of the image signal converted into the digital signal by 3 is integrated for each pixel, and the output level is calculated by the video counter 93.
Is converted into a video count number and sent to the CPU 94. CP
U94 converts the video count number into a replenishment amount, drives the motor 104 for a corresponding time, and rotationally drives the toner conveying screw 102 in the toner replenishment tank 101 that contains the toner T. An appropriate amount of toner is replenished therein to keep the toner density in the developing device 4d constant.

However, since the above-mentioned video count system is a predicted replenishment, if the toner replenishment amount from the hopper deviates from the expected value due to a change in the fluidity of the toner in the hopper, etc. The toner density of the developer deviates from the initial setting value.

A second developer concentration control device is provided for the purpose of correcting the deviation of the toner concentration of the developer.
It is used in combination with the first developer concentration control device of the video count system. This second developer concentration control device is operated at a predetermined timing to perform laser exposure and development on the photoconductor drum 1d to form a patch-shaped reference image, and to determine the toner concentration of the patch-shaped reference image. It is detected by the optical detection means 10 to determine whether the toner is over-replenished or insufficient, and the next video count number from the video counter 93 is corrected based on this determination, and the CPU
The toner replenishment signal from 94 is corrected.

The detecting means 10 is preferably provided downstream of the transfer position in the moving direction of the photosensitive drum 1d in order to prevent toner contamination, but may be provided upstream of the transfer position in the moving direction of the drum 1d. is there.

The timing of forming the reference image on the photosensitive drum is the timing at which the reference image is not transferred onto the transfer material. Normally, a plurality of images are continuously formed by inputting a single image formation start signal to the apparatus (for example, pressing a copy button once). During continuous copying, before the image formation on the first sheet or after the image formation on the last sheet is completed,
Alternatively, the reference image may be formed between the sheets (between the transfer materials). However, a system using a transfer belt has a problem in forming a reference image between sheets. In other words, there is a problem that a part of the toner, which is the reference image, is transferred to the belt, and when the belt makes a round, the back side of the next transfer material is stained. In order to avoid this problem, it is preferable that the photosensitive drum and the transfer belt are once separated at the time of forming the reference image (when passing the transfer nip). The separating operation is performed by lowering the transfer belt. During this time, Bk
Not only the transfer process of other colors cannot be performed, but image formation is temporarily interrupted even during continuous copying.

As described above, it is not preferable to frequently perform the above-described patch detection ATR because the image forming operation is interrupted. In this embodiment, the patch detection ATR is set to be performed at intervals of 100 sheets of transfer material during continuous copying. In this way, the density is corrected by the patch detection ATR, but the stability of the developer density is limited to the predictive replenishment performance by the video count method for 100 sheets without the patch detection operation during continuous copying. As a result, the toner replenishment amount from the toner hopper is required to be highly accurate.

Here, how much precision is specifically required will be described. The highest replenishment accuracy is required when the toner consumption amount (replenishment amount) is the largest. That is, the severest condition is that the original image is a solid image (about 1 g / sheet) and the maximum number of settable continuous copies is performed. Further, the narrower the toner density allowable range, the more severe the replenishment accuracy is required. The maximum number of continuous copies is 100, which is the patch detection interval, and the toner density allowable range is ± 1.
If the weight% and the amount of the developer in the developing device are 500 g, the toner replenishment accuracy is required to be about ± 5%.

Therefore, by forming the toner hopper in two stages in series and controlling the powder surface height of the lower hopper within a predetermined range, changes in the bulk density (fluidity change) of the toner are suppressed and replenishment accuracy is improved. I am measuring.

According to the experiment conducted by the inventor, the replenishment accuracy of the conventional toner hopper (hopper having a single toner tank) is about ± 20 to 30%, whereas this toner hopper is about ± 5%. The accuracy has improved dramatically.

Next, the structure and operation of the toner hopper will be described with reference to FIGS.

The first toner replenishing device A includes a first toner container 101 for containing the toner T and a first carrying screw 102 for carrying the toner T in the container to the developing device 4d.
And a powder surface detection sensor 103 for detecting the powder surface (level surface) of the toner T in the container. Further, the second toner replenishing device B stores the toner T in a first toner container 111 and a second toner container 111 having a toner capacity larger than that of the first toner container 101.
Second conveying screw 1 for conveying to the toner replenishing device A
12, a remaining amount detection sensor (second sensor) 113 for detecting that the remaining amount of toner in the container is low, a stirring member 114 for loosening the toner in the container, and the like. As shown in FIG. 8, the stirring member 114 has a diameter of 1.4 m.
It is rotatably provided on the shaft 116 in a linear shape of m. A wiper 117 for cleaning the detection surface of the sensor 113 is rotatably provided on the shaft 116.

Next, the operation of this embodiment will be described.
When the copying process starts, as described above, the toner replenishment time is calculated based on the video count number, the first motor 104 is driven only during the calculated time, and the first conveying screw 102 is driven through the drive transmission member. Is rotatively driven, and a part of the toner T stored in the first toner container 101 is conveyed and replenished to the developing device 4d.

By supplying the toner to the developing device 44, the powder surface of the toner T in the first toner container 101 is lowered. Therefore, when the powder surface detection sensor (first sensor) 103 detects the powder surface, the second toner replenishing device B supplies a predetermined amount of toner. For example, the detection output of the powder surface detection sensor 103 is supplied to the CPU, a drive signal is sent from this control circuit to the second motor 115 to drive the second motor 115 for a predetermined time, and the second conveying screw 112 is moved to the predetermined direction. It is rotationally driven for a time, and a predetermined amount (small amount) of the toner T stored in the second toner container 111 is conveyed and replenished into the toner container 101 of the first toner replenishing device A.

By performing this operation, the height of the powder surface of the toner T in the toner container 101 of the first toner replenishing device A can be constantly and approximately kept constant.

As a result, the fluctuation of the pressure applied to the lower toner in the first toner container 101 becomes small, and the fluctuation of the bulk density becomes small. Therefore, highly accurate toner supply can be performed.

A case where the above-mentioned remaining amount detecting sensor 113 and powder surface detecting sensor 103 make an erroneous detection will be described.

In this embodiment, a piezoelectric powder level sensor is used as the toner residual detection sensor (powder surface detection sensor). In this piezoelectric sensor, a failure in which a crack occurs in the piezoelectric element due to the impact of the sensor surface rarely occurs. In this case, since the oscillation becomes defective, erroneous detection is made such that there is toner even when there is no toner.

Further, in order to prevent the powder surface from being detected due to the toner adhering to the surface of the toner sensor, it is preferable to provide a sensor wiper to wipe off the toner on the surface of the sensor. The sensor wiper has a diameter of 0.
Although a wire spring material of about 3 mm is used, if the wiper is deformed for some reason, a problem that the toner sensor does not function as a cleaning member and the toner remains in the toner present due to the adhered toner occurs very rarely.

As described above, when an abnormality occurs in the piezoelectric element or the wiper, the toner remains in the state of having toner. Therefore, the toner in the hopper eventually becomes empty, and the toner in the hopper eventually becomes empty. Toner cannot be replenished.

When this situation is reached, the following problems occur in the above-mentioned video count system + patch detection system device.

In the video count + patch detection method, as described above, during continuous copying, the density of the developer is detected only at a predetermined interval (interval of 100 sheets of transfer material) by patch detection, so that toner is supplied from the hopper. Even if a defect (insufficiency) occurs, the apparatus cannot wait for the next patch detection density measurement in a state where it cannot make a self-judgment. During this period, for example, when the image duty is high and the toner consumption of the developing device is large, the density of the developer sharply drops, and a large amount of image formation with image deterioration is performed. Further, when the amount of toner in the developing device is reduced, the carrier adheres to the photosensitive drum. The image formed at this time becomes an abnormal image due to low toner density and carrier adhesion, and the carrier goes to the cleaner blade and the fixing roller via the photosensitive drum and the transfer material, which causes damage to these members. Further, when the developer also flows out due to the carrier adhesion, it cannot be recovered only by replenishing the toner, so that the developer needs to be replaced with a new one.

The hoppers of the Y, M and C developing units are also Bk.
Similarly, a two-stage hopper may be used, and a sensor for detecting the toner amount may be provided in each of the upper hopper and the lower hopper.
You may have only one hopper. However, even if an abnormality occurs in the hopper (especially the sensor) and the toner cannot be replenished from the hopper, the abnormality can be judged relatively early by detecting the toner concentration in the developing device by the optical ATR method. it can.

Therefore, the abnormality can be judged and the maintenance can be performed by the service person in a state where the image deterioration (image quality deterioration) is relatively small. Further, the developer can be used as it is by simply replenishing the toner in a shortage.

As described above, when there is no sensor for detecting the toner concentration in the developing device, it is desired to detect the abnormality of the toner hopper (especially the abnormality of the piezoelectric element or the wiper) at an early stage. .

Next, the control of the Bk developing device will be described in more detail.

FIG. 1 is a sequence chart showing the operation of the two screws during continuous copying. The transfer material is A3 size, 15 CPM (1 cy in 4 seconds)
cle). FIG. 1A shows the case where a solid image with the largest replenishment amount (an image in which toner is attached to the entire image formable area) is formed, and FIG. 1B shows the image d.
It is assumed that the duty is low and the supply amount is small.

In FIG. 1 (a), the first screw 102 replenishes about 1 g of toner for 2 seconds based on the video count amount. The first sensor 103 is 1s from the start of image formation.
After ec, it is detected whether or not there is a predetermined amount of toner, and if it is detected that there is no toner, the second screw 112 is rotated for a predetermined time. The predetermined time is 1 sec. 2nd screw 1
The toner transport capacity of 12 is 1.5 of the first screw 102.
The toner is replenished to the first hopper 101 for about 1.5 g in 1 second. The first screw 102 turns three times (3 seconds) and the second screw 112 turns twice (2 seconds
ec) As it rotates, 3 g is replenished, and the amount of coming and going of the first hopper 101 is balanced. Therefore, the toner presence / absence determination by the first sensor 103 is based on the fact that the presence of the toner is repeated twice in the time series. In reality, since the amount of replenishment varies, the number of times the first sensor 103 does not continue toner is 1 to 4 times. It has been experimentally confirmed that toner is present once or twice. If the supply amount to the first hopper 101 is low as shown in FIG.
The output of the sensor 103 is that toner is normally present, and sometimes toner is absent. From this, it can be considered that there is no normal state in which no toner (instruction to supply toner to the second hopper) continues five times or more.

FIG. 1C is a chart showing a case where the toner sensor (residual detection sensor) 113 of the second hopper 111 has failed and is in an abnormal state. Since the residual detection sensor 113 erroneously determines that toner is present due to a failure, the amount of toner in the second hopper 111 decreases, and the transport amount of the second screw 112 gradually decreases as the powder surface approaches the second screw 112. I will do it.

In this case, even if the first sensor 103 detects the absence of toner and drives the second screw 112, the replenishment amount from the second screw 112 is too small to catch up with it.
The first sensor 103 continuously repeats the toner absence determination. In the present embodiment, it is determined that the first sensor 103 has detected the absence of toner for the seventh consecutive time, and the next image forming interruption operation is started. When it is determined that there is an abnormality, the user or service person is warned of the abnormality of the hopper on the display unit of the device. Actually, all the papers being fed into the apparatus must be discharged, so that the operation is complicated, but is omitted here.

Further, in addition to the abnormality of the toner sensor and the wiper, if the stirring member 114 is assembled wrongly or is damaged, the replenishment of the second hopper 111 is similarly caused.
By detecting an abnormality, these defects can be discovered.

What is important here is that the developing device is fed from the first hopper 101 until the abnormality is determined (in this case, during the seven copies until the tonerless detection by the first sensor 103 continues seven times). That is, the toner replenishment amount to 4d is reduced and the concentration of the developer is not reduced. Therefore, the capacity of the first hopper 101 is the maximum toner amount for seven sheets (about 7
A larger amount of toner than that of g) is stored so that the abnormality detection works before the first hopper 101 becomes empty.

As described above, even if the toner sensor 113 of the second hopper 111 is broken (or the sensor wiper is deformed), the abnormality can be detected before the supply failure to the developing device 4d occurs, and the above-described operation is performed. It is possible to output a large amount of images with image deterioration and avoid problems such as carrier adhesion. In addition, since the cause of the abnormality can be specified in the hopper, the service person can use the developing device 4d or AT.
Since there is no need to suspect an abnormality in R, service time and labor can be greatly reduced.

<Reference Example> In the above embodiment, the case where the sensor 113 of the second hopper 111 is abnormal is described, but in this reference example, the first hopper 10 is used.
A case where an abnormality occurs in the first sensor unit 103 will be described.

FIG. 2 is a flow chart of the same formula as in FIG. FIG. 2 is based on the assumption that some abnormality occurs when the second to third copies are made, for example, the toner adheres to the surface of the sensor 103 so badly that the wiping ability of the wiper is exceeded. is there. First as shown in FIG.
Since the sensor 103 does not give the replenishment instruction to the second hopper 111 while judging that the toner is present, the first hopper 10
The toner in 1 is gradually approaching the sky. If this state continues as it is, the problem of lowering the density of the developer still occurs.

Here, the operation in a normal state will be reviewed. As can be seen from FIGS. 1A and 1B, when the replenishment duty is low, the frequency of the absence of toner is low as the determination of 103 of the 1st sensor. However, no matter how low the replenishment duty is, the powder surface in the first hopper 101 will be low as long as the replenishment is being performed, so that the absence of toner will be detected sometime. The amount of decrease in the powder surface is naturally proportional to the amount of toner supplied from the first screw 102. Also, the second screw 1
When 12 is driven and toner is replenished from the second hopper 111, the powder surface returns to a predetermined range centered on the height of the first sensor 103. Therefore, by estimating the amount of decrease of the powder surface after the toner supply from the second hopper 111 is stopped from the toner conveyance amount of the first screw 102, the powder surface is abnormally decreased, that is, the first surface. Sensor 1
It is possible to detect that an abnormality has occurred in 03 and the toner supply from the second hopper 111 is stopped.

FIG. 3 is a flow chart for performing the above control, which will be described below. Copying is started by inputting an image formation start signal (copy button ON, etc.) from the outside, and image formation is started. Since the toner replenishment amount itself from the first hopper 101 cannot be measured, the driving time of the first screw 102 of the first hopper 101 is integrated as a correlated value. The replenishment amount is S, and the replenishment time ΔS is added. Then, when the integrated amount reaches a predetermined value (here, 14 sec), it is determined to be abnormal. This part will be described later. If the integrated amount is smaller than the predetermined value, the first toner sensor 101 detects the presence or absence of a predetermined amount of toner, and resets the integrated amount if toner is detected, and proceeds to the next without resetting if toner is detected. . This routine is repeated until the continuous copying is completed. FIG. 4 shows changes in the integrated amount based on this flow in a normal state (in the case of a solid image and a low duty) and in an abnormal state. In the case of a solid image, the accumulated amount is 0 to 4 seconds, and in the case of an image having a low duty, the rocking is repeated from 0 to 3 seconds. This is because even if the powder surface in the first hopper 101 is lowered due to the replenishment from the first screw 102, the toner is supplied from the second hopper 111 by the toner absence detection of the sensor 103 and the powder surface is returned to the original range. It is similar to what is done. As shown in FIG. 4C, if the first sensor 103 is abnormal and is not reset, the integrated amount increases steadily. At this time, since the powder surface is abnormally lowered in proportion to the accumulated amount, when the accumulated amount reaches a predetermined value (14 sec), it is judged as abnormal, the copying operation is stopped, and the display unit of the apparatus displays. Display an error display. The predetermined value was set to 14 sec, which is calculated by converting seven solid images in accordance with the detection of an error on the seventh continuous image in the above-described embodiment. The first embodiment
As described above, according to the experimental results, the number of times toner is continuously present during a solid image is about 1 to 2 times, so that the cumulative amount is 6 sec assuming that the toner is continuous 2 times, which is sufficiently small compared with the predetermined value of 14 sec. Since it is a value, there is no possibility that the abnormality detection will be activated by mistake.

As described above, even in the present reference example, even if an abnormality occurs in the toner sensor unit 103, trouble can be prevented.

The above embodiment can detect the abnormality of the second hopper 111, and this reference example can detect the abnormality of the first hopper 101. Normally, it is unlikely that two sensors will fail at the same time, so by implementing both of them, measures will be taken without omission.

Although the driving time of the screw 102 is used as the integrated amount in this reference example, the video count amount may be used.

Next, in the examples and reference examples, the second hopper 1
A preferable example of the position of the sensor 113 in 11 will be described. FIG. 5 shows the second hopper 111 to the first hopper 1
6 is a graph showing the change over time in the toner supply amount to 01. The area u1 is the toner replenishment amount to the first hopper 101 when the powder surface height of the second hopper 111 is above the agitating portion V by the agitating member 114, and the area v1 is the powder surface height to the agitating portion V. It is the amount of toner supplied to the first hopper 101 at a certain time. Here, the stirring portion V refers to a region below the uppermost position of the rotation locus of the stirring member 114 shown in FIG. Regions U and V in FIG. 6 showing the powder surface height of the hopper are u1 and v1 in the replenishment amount graph (FIG. 5), respectively.
It is an area corresponding to. As can be seen from FIG. 5, the area u1
In the above, the toner supply amount to the first hopper 101 is reasonably stable, but the powder surface is in the area v1
So the supply is increasing. When the powder surface is in the region V, the toner replenishment amount increases because the toner is better loosened by rotating the stirring member 114 without the pressure of the toner from above, and the air can be easily taken in from the powder surface. It is considered that the fluidity of the toner increased as a result of the two points.

As described above, in the system for replenishing toner by using the video count method, improving the toner replenishment accuracy is extremely important for stabilizing the concentration of the developer. The position of the residual detection sensor 113 is arranged above the stirring area V as shown in FIG. 6 to prevent the powder surface from entering the area V. As a result, the toner supply amount is stable only in the area u1 as shown in FIG. Regarding the replenishment accuracy, in the areas u1 and v1, the range of about 10% is improved to about 6% if only the area u1 is used.

Further, in the optical ATR system, if the accuracy of toner replenishment from the hopper can be improved, it is possible to prevent a ripple of density which occurs when the replenishment amount is excessive and a low density and stable phenomenon which occurs when the replenishment amount is small. Therefore, it is preferable to set the position of the residual detection sensor 113 described above.

[0065]

As described above, according to the present invention, the abnormality detection of the second sensor can be judged according to the detection output of the first sensor. Therefore, the image caused by the defective toner supply to the developing device can be detected. Problems such as deterioration can be avoided in advance. Further, since the cause of the trouble can be identified as the abnormality detection of the second sensor, the maintenance load can be reduced.

[0066]

[Brief description of drawings]

FIG. 1 is a sequence chart diagram illustrating an example.

FIG. 2 is a sequence chart diagram illustrating a reference example.

FIG. 3 is a flowchart illustrating a reference example.

FIG. 4 is a graph showing an integrated amount for explaining a reference example.

FIG. 5 is a graph showing a supply amount from a hopper.

FIG. 6 is a schematic diagram showing a latent image forming and fourth image forming station.

FIG. 7 is a sectional view of the image forming apparatus.

FIG. 8 is an enlarged view of first and second hoppers.

[Explanation of symbols]

A First toner replenishing device B Second toner replenishing device 102 first screw 112 Second screw 103 first toner sensor 113 Second Toner Sensor 4d Bk developing device

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-4-73672 (JP, A) JP-A-7-175372 (JP, A) JP-A-5-323791 (JP, A) JP-A-7- 311501 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/08 114 G03G 15/08 115 G03G 15/08 507

Claims (3)

(57) [Claims] 1. A developing device for developing an electrostatic image formed on an image bearing member with toner, a first toner container for supplying toner to the developing device, and an amount of toner in the first toner container. A first sensor for detecting, a second toner container for replenishing toner to the first toner container in accordance with a detection output of the first sensor, and a toner amount in the second toner container are detected. An image forming apparatus having a second sensor, wherein the first sensor repeatedly detects the absence of toner a predetermined number of times even though the detection output of the second sensor indicates the presence of toner; An image forming apparatus, characterized in that it is determined to be an abnormality detection of a second sensor. 2. The image forming apparatus according to claim 1, wherein when the second sensor fails, the detection output of the second sensor indicates that toner is present. 3. A cleaning member for cleaning the detection surface of the second sensor, wherein the second member is provided when the cleaning member fails.
The image forming apparatus according to claim 1, wherein the detection output of the sensor of (1) indicates that toner is present.