JPH05224533A - Image forming device - Google Patents

Abstract

PURPOSE:To make a toner concentration constant when toner is absent, without being restricted almost the sensitivity of a detecting means used by changing a decision value according to the sensitivity of the detecting means used. CONSTITUTION:When the output voltage of a sensor exceeds an empty level, for instance, 5V, the fact is displayed for an operator by an operational panel, and a copying action is stopped before a defective image caused by blurring, etc., is produced. At this time, the empty level is changed according to the difference of the sensitivity of the sensor. In other words, the dispersion of the sensitivity of the sensor makes almost a normal distribution pattern. At this time, each sensor is classified into several ranks, according to the difference of the sensitivity of each sensor, for instance, into three ranks of A, B, and C, and one of plural empty levels prepared according to the ranks in advance, can be selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a developing device which uses a two-component developer composed of, for example, a toner and a carrier and keeps the toner density constant.

[0002]

2. Description of the Related Art As is well known, an electrophotographic image forming apparatus is provided with a developing device for visualizing an electrostatic latent image formed on a photosensitive drum (image carrier). There is.
This type of developing device is roughly classified into a two-component system and a one-component system.

In the former case, the toner is attached to carrier particles and carried to the outer periphery of the developing roller to form a developer layer, which is brought into contact with the surface of the photosensitive drum, and the electrostatic latent image formed on the photosensitive drum is formed. Coulomb force separates the toner from the carrier particles and attaches it to the latent image portion. The latter is to form a developer layer on the outer circumference of the developing roller with the toner alone, and similarly to adhere the toner to the latent image portion.

In any of the above cases, it is necessary to keep the toner concentration of the developer layer constant, and the former two-component developing device uses a toner concentration sensor which is an optical toner concentration detecting means.

Conventionally, as shown in FIG. 6, for example, toner is not replenished from a toner replenishing device when the output voltage of the sensor is smaller than a reference value, and toner is replenished only when it is larger than the reference value. The toner density is kept constant.

If the toner for replenishment in the toner replenishing device is used up, the toner cannot be replenished even if the toner replenishing device performs the replenishing operation, and if the image forming operation is continued in this state, the toner density will continue to decrease. Then, when the output voltage of the sensor at that time exceeds the empty level, it is displayed and the image forming operation is stopped.

However, as shown in FIG. 7, for example, the toner concentration sensors a, b, c, d, e, f, and g may have slight differences in individual sensitivity characteristics due to variations in manufacturing. Instead, the empty control is performed at a constant level. For this reason, as shown in FIG. 8, when the sensitivity characteristics greatly differ from each other as in the sensors a and g, the toner density at the time of empty can be widened, and the usable sensor is limited by the sensitivity characteristic. was there.

[0008]

As described above, in the prior art, in order to reduce the influence of variations in the sensitivity characteristics of the sensor, the sensor having similar characteristics was selected and used, which is expensive in terms of cost. There was a drawback.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus which is not limited by the sensitivity of the detecting means and can keep the toner density at the time of toner empty substantially constant.

[0010]

In order to achieve the above object, in an image forming apparatus of the present invention, an image having a two-component developer containing a toner and a carrier is contained and an electrostatic latent image is formed. Developing means for supplying the toner to the surface of the carrier, replenishing means for replenishing the developing means with toner, detecting means for detecting the toner concentration in the developing means, and the replenishing means according to the detection result of the detecting means. Control means for controlling the amount of toner replenishment by means of the above-mentioned means, judgment means for deciding that the amount of toner replenishment by the replenishing means has decreased based on the detection result of the detection means, and determination of a decrease in the amount of toner replenishment by this judging means. And a changing unit for changing the setting of the determination value for the above according to the sensitivity of the detecting unit.

Further, in the image forming apparatus of the present invention, a developing means for accommodating a two-component developer comprising a toner and a carrier and supplying the toner to the surface of an image carrier having an electrostatic latent image is provided. A replenishing means for replenishing the developing means with toner; a detecting means for detecting the toner concentration in the developing means; a control means for controlling the toner replenishing amount by the replenishing means according to the detection result of the detecting means; Determination means for determining that the toner supply amount by the supply means has decreased based on the detection result of the supply means, stop means for stopping the image forming operation according to the determination result of the determination means, and toner supply amount in the determination means. Change means for changing the setting of the determination value for determining the decrease of the ranks according to the sensitivity of the detection means It is configured.

[0012]

According to the present invention, since the judgment value can be changed according to the sensitivity of the detecting means to be used by the above means, the image forming operation can be stopped at the same toner density by the detecting means having different sensitivities. Is possible.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2 show an image forming apparatus according to the present invention.

The image forming apparatus has an apparatus main body 1 having an original table 2 made of transparent glass fixed on the upper surface thereof, and an original cover rotatably supported at one end on the upper surface of the main body 1 to cover the upper surface of the original table 2. 3 and upper and lower sheet feeding cassettes 4 and 5 that are detachably loaded in one side portion of the main body 1 and project from the one side portion.
And a tray 6 projecting from the other end of the main body 1 at the discharge end.

Inside the main body 1, an optical system consisting of an exposure lamp 7 and mirrors 8, 9 and 10 which reciprocate in the direction of arrow x along the lower surface of the original table 2 and reflected light by the exposure scanning of the optical system. Magnification varying lens block 11 and mirror 12
Photoconductor drum 13 that forms an image through the photoconductor drum 1
Developing device 14 for adhering toner to the electrostatic latent image formed on the surface of No. 3 to visualize (visualize) toner, and photoconductor drum 13
The copy paper P stored in the cassette 4 or 5 is transferred to the transfer charger 20 and the peeling charger 21 through the delivery roller mechanism 15 or 16 and the guide path 17 or 18 in synchronism with the rotation in the arrow y direction. Feed, photoconductor drum 1
A pair of registration rollers 22 that are brought into close contact with the surface of the sheet 3, a conveyor belt 23 that transfers the toner image through the transfer charger 20, and that conveys the copy paper P separated from the drum 13 by the separation charger 21. The transfer belt 23 includes a fixing roller pair 24 that is provided at the end of the transport belt 23 to fix the toner image on the copy sheet P, and a discharge roller pair 25 that is provided adjacent to the fixing roller pair 24. Pair 25
And then discharged onto the tray 6.

Further, on the periphery of the photosensitive drum 13,
A discharging charger 26 for discharging the drum 13 after transfer along the rotation direction, a cleaner 27 for removing toner adhering to the surface of the photosensitive drum 13 after discharging, and a discharging lamp for erasing the residual image on the drum 13. 28, and the photosensitive drum 1
A charger 29 is provided for charging the surface of No. 3 and forming an electrostatic latent image during exposure.

Further, in the main body 1, a cooling fan 30 for preventing a temperature rise and a plurality of microswitch groups for detecting the cassette size at the insertion tip positions of the cassettes 4, 5 are formed. Cassette size detectors 31, 32 and the like are provided.

The developing device 14 contains, for example, a two-component developer consisting of toner and carrier. The toner adheres to carrier particles and is carried to the outer periphery of the developing roller to form a developer layer to form a photosensitive drum. This is a two-component developing device which is brought into contact with the surface of the photosensitive drum 13 and separates toner from carrier particles by the Coulomb force of the electrostatic latent image formed on the photosensitive drum 13 and adheres to the latent image portion. The developing device 14 is a toner hopper 14 as a replenishing means for replenishing the toner that decreases with a copying operation (image forming operation).
a. FIG. 3 shows the two-component developing device 1 described above.
4 shows the configuration of No. 4.

That is, inside the casing 141, a pair of conveying rollers 142 and 143, which are developer conveying means whose axial direction is parallel to the axial direction of the photosensitive drum 13, and a developing roller 144 are provided.

The conveying rollers 142, 143 and the developing roller 144 are driven to rotate in the directions indicated by arrows X, Y, Z in the drawing by driving systems (not shown). Then, the developer 145 filled in the casing 141 is conveyed to the developing roller 144 side by the rotation of the conveying rollers 142 and 143, and the developer layer 145a is formed on the outer periphery of the developing roller 144. This developer layer 145a
Comes into contact with the surface of the photosensitive drum 13, and the above-described development is performed. In addition, 146 in the drawing is a spike control blade for making the thickness of the developer layer 145a formed on the outer periphery of the developing roller 144 uniform.

On the other hand, on the lower surface of the casing 141, a toner concentration sensor 51 as a detecting means is provided so as to face the conveying roller 142, and the toner concentration of the developer 145 conveyed along the conveying path 141a is detected. It is supposed to do. Here, a basic copy operation (normal copy) in the above-described image forming apparatus will be described.

For example, a document is placed on the document table 2,
It is assumed that the copy conditions such as the number of copies, the copy magnification, and the paper size are selected via an operation panel (not shown), and a copy start signal is input. Then, the document placed on the document table 2 is illuminated by the light from the exposure lamp 7 during reading.

The reflected light from the original is reflected by the mirrors 8, 9, 1.
An image is formed on the photoconductor drum 13 to which a predetermined charge has been applied in advance by the charger 29, through 0, the lens block 11 and the mirror 12. That is, the reflected light from the document is converted into an electrostatic pattern on the surface of the photoconductor drum 13 by slit exposure and becomes a latent image. The image formed as a latent image on the photoconductor drum 13 is developed by selectively attaching the toner supplied from the developing device 14 thereto.

In parallel with the series of operations so far, according to the designated paper size or original size and the image magnification,
The cassette containing the copy paper P of the optimum size is selected from one of the paper feed cassettes 4 and 5.
Then, by the corresponding delivery roller mechanism 15 or 16, one copy sheet P from the selected cassette is
Is withdrawn. This one copy sheet P is fed to each of the guide paths 17 or 18, and then the registration roller pair 22 aligns the leading edge of the image and the leading edge of the copy sheet P, and is fed toward the photoconductor drum 13. Will be sent.

In this way, the copy sheet P guided to the photoconductor drum 13 is attracted (adhered) by being attracted by the electric charge remaining on the photoconductor drum 13, and is already used for latent image formation. By supplying the charge having the same polarity as that of the electric charge given to the transfer unit 13 from the transfer charger 20, the toner attached to the photosensitive drum 13 is transferred to the copy sheet P.

The copy sheet P on which the toner has been transferred is released from being attracted to the photosensitive drum 13 by the action of the peeling charger 21, and the transport belt 2 is loaded with the toner.
3 sent up. Then, the toner is fixed (fixed) to the copy paper P by passing between the fixing roller pair 24. As described above, the copy sheet P on which the image of the original is copied is discharged to the tray 6 by the discharge roller pair 25 with the copy surface facing up (upward).

The photosensitive drum 13 after the copy paper P is separated is further rotated, and the surface of the photosensitive drum 13 is cleaned by the cleaner 27. That is, the surface of the photoconductor drum 13 is destaticized via the decharging charger 26, the residual toner is removed by the cleaner 27, and the charge distribution pattern on the surface is returned to the initial state by the decharging lamp 28. The state in which the copying of is possible is maintained. Next, the operation related to toner supply according to the present invention will be described.

Normally, when the above copying operation is repeated, the toner in the developing device 14 gradually decreases as the number of copies increases. Then, the toner concentration sensor 51 detects it as a voltage change. Then, the output voltage of the toner concentration sensor 51 has a certain reference value, for example, 4
When the voltage exceeds V, a toner replenishing mechanism (not shown) is operated, and the replenishment toner stored in the toner hopper 14a is supplied as in the conventional case.

In this way, the toner concentration in the developing device 14 is kept constant by controlling the toner replenishing mechanism and replenishing the toner from the toner hopper 14a only while the output voltage of the toner concentration sensor 51 exceeds the reference value. It is designed to be drunk.

In the toner replenishing operation, if the replenishment toner in the toner hopper 14a is exhausted, the toner cannot be replenished even if the replenishing operation is performed.
If the copying operation is continued in this state, the toner density will continue to decrease and the output voltage of the sensor 51 will also gradually increase. And
The output voltage of the sensor 51 is an empty level, for example, 5
When the voltage exceeds V, it is displayed to the operator by an operation panel (not shown), and the copying operation is stopped before a defective image such as a blur is generated.

Here, in order to eliminate the variation in the toner concentration at the time of emptying due to the variation in the sensitivity of the toner concentration sensor 51 due to various causes at the time of manufacture, in this embodiment, as shown in FIG. The empty level is changed according to the difference in sensitivity.

That is, the variation in the sensitivity of the sensor 51 has a substantially normal distribution type as shown in FIG.
Therefore, each sensor 51 is divided into several ranks, for example, three ranks A, B, and C according to the difference in sensitivity, and one of a plurality of empty levels prepared in advance according to the rank is set. It is designed to be selected. As a result, it is possible to reduce variations in toner density when the toner is empty, and also variations in image density at that time.

As a means for selecting the empty level, for example, the rank of the sensor 51 to be used is key-input from the operation panel and the level value corresponding to the input is read from the memory, or the developing device 14 in which the sensor 51 is incorporated. The information indicating the rank is attached to the developing device 1
When 4 is set in the image forming apparatus, the information may be read to automatically change the level value. As described above, the toner empty level can be changed according to the sensitivity of the toner density sensor used.

That is, the sensor is divided into several ranks according to the difference in sensitivity, and one of the empty levels is selected according to the rank. This allows
It is possible to stop the copying operation with the same toner density even with the sensors having different sensitivities. Therefore,
It is possible to use a sensor having any sensitivity, and moreover, it is possible to guarantee stable quality without variations in image density among the developing devices.

In the above embodiment, the case where the sensor is divided into three ranks according to its sensitivity has been described, but the present invention is not limited to this, and more accurate control can be realized by subdividing the rank. It is a thing. Further, the present invention can be applied not only to a copying machine but also to various image forming apparatuses using a two-component developing device such as a laser printer and a plain paper fax machine. Of course, various modifications can be made without departing from the spirit of the invention.

[0036]

As described above in detail, according to the present invention, there is provided an image forming apparatus which is not limited by the sensitivity of the detecting means and can make the toner density substantially constant when the toner is empty. it can.

[Brief description of drawings]

FIG. 1 is an external perspective view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of the image forming apparatus.

FIG. 3 is a configuration diagram similarly showing an example of a developing device.

FIG. 4 is a diagram showing a relationship between sensors classified into ranks and empty levels corresponding to the sensors.

FIG. 5 is a diagram showing a relationship between sensor sensitivity and rank.

FIG. 6 is a diagram shown for explaining a toner supply operation.

FIG. 7 is a diagram showing an example of variations in sensor sensitivity.

FIG. 8 is a diagram for explaining a conventional technique and its problems.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Device main body, 2 ... Original document stand, 4, 5 ... Paper feed cassette, 7
... exposure lamp, 13 ... photosensitive drum, 14 ... developing device,
14a ... Toner hopper (replenishing means), 20 ... Transfer charger, 24 ... Fixing roller pair, 29 ... Charger, 51 ... Toner density sensor (detecting means), 142, 143 ... Conveying roller, 144 ... Developing roller, 145 ... Developer.

Claims (2)

[Claims] 1. A developing unit that contains a two-component developer including a toner and a carrier and supplies the toner to the surface of an image carrier having an electrostatic latent image, and a replenishing unit that replenishes the toner to the developing unit. A detection unit for detecting the toner concentration in the developing unit; a control unit for controlling the toner replenishment amount by the replenishment unit according to the detection result of the detection unit; and a replenishment unit based on the detection result of the detection unit. The determination means for determining that the toner supply amount has decreased, and the changing means for changing the setting of the determination value for determining the decrease of the toner supply amount in the determination means according to the sensitivity of the detection means are provided. An image forming apparatus characterized by the above. 2. A developing means for containing a two-component developer comprising a toner and a carrier and supplying the toner to the surface of an image carrier having an electrostatic latent image, and a supplying means for supplying the toner to the developing means. A detection unit for detecting the toner concentration in the developing unit; a control unit for controlling the toner replenishment amount by the replenishment unit according to the detection result of the detection unit; and a replenishment unit based on the detection result of the detection unit. A determination unit that determines that the toner replenishment amount has decreased, a stop unit that stops the image forming operation according to the determination result of this determination unit, and a determination value setting for determining the reduction of the toner replenishment amount in the determination unit. The image forming apparatus is characterized in that the image forming apparatus is provided with a changing unit which is divided into ranks according to the sensitivity of the detecting unit and which changes corresponding to the rank. .