JP2003316143A - Developing device image forming apparatus, and discrimination method for presence of developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely detect that a developer is not supplied, by utilizing a sensor for measuring a toner concentration. <P>SOLUTION: Change characteristics of a detection output V<SB>l</SB>of a toner concentration sensor 41 for a control voltage Vc are obtained beforehand, and a difference between detection output Vlmin and Vlmax respectively corresponding to a minimum voltage Vcmin and a maximum voltage Vcmax of a control voltage Vc surely exceeds a threshold Vs=1.5 V while the developer is supplied to a developing vessel 46, and therefore, it is judged that the developer is supplied to the developing vessel 46 when the difference is equal to or larger than the threshold Vs, and it is judged that the developer is not supplied to the developing vessel 46 when the difference is smaller than the threshold Vs. Since the control voltage Vc obtained when the detection output V<SB>l</SB>of the toner concentration sensor 41 is the threshold Vs=1.5 V is derived and set, output characteristics of the toner concentration sensor 41 can be optimized. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device using a developer obtained by mixing toner and carrier, an image forming apparatus, and a method for determining the presence / absence of a developer.

[0002]

2. Description of the Related Art In an image forming apparatus of this type, a developer in which a toner and a carrier are mixed is stirred in a container to charge the developer, and the toner in the developer is placed on an image carrier. The electrostatic latent image is adhered to the electrostatic latent image, the electrostatic latent image is developed, a toner image is formed on the image carrier, and the toner image on the image carrier is transferred and fixed on a recording sheet. Further, the toner concentration of the developer in the container is detected, and when the toner concentration decreases, the toner is replenished to the container to keep the toner concentration constant.

As a method of detecting the toner density, there is a method of using an L detection toner density sensor, for example. This L
The coil of the detection toner concentration sensor is arranged at a position in contact with the developer, and this sensor measures the magnetic permeability of the developer corresponding to the toner concentration. Actually, the higher the toner concentration in the developer, the lower the carrier concentration of the magnetic substance,
The magnetic permeability of the developer is lowered.

The density measurement based on the magnetic permeability is excellent in that it enables constant measurement and has no influence on the image forming process. The toner density is measured by this sensor, the toner is replenished according to the measured toner density, and the toner density is kept substantially constant.

This L detection toner density sensor is, for example, T
It is provided as a programmable toner sensor (trade name) manufactured by DK Corporation. This sensor includes an oscillation circuit including the above coil and a frequency / voltage conversion circuit, and exhibits a negative characteristic that the voltage of the detection output decreases as the toner concentration increases. Further, the voltage of the detection output can be adjusted by changing the control voltage. This is because the output characteristic of the sensor is not always constant, the output characteristic changes depending on the mounting position of the sensor coil, or the output characteristic of the sensor is not stable and stable for a completely new developer. This is because.

Here, when the developer in which the toner and the carrier are mixed is completely new, the charge of the toner is lowered because the developer is in a substantially stationary state and insufficiently agitated during long-term storage. The repulsive force between the toners is also decreasing, and the number of carriers per unit volume is increasing. At this time, even if the carrier concentration is constant, the magnetic permeability of the developer becomes high, so that the voltage of the detection output of the sensor becomes large and the measured toner concentration becomes lower than the actual concentration. When this new developer is agitated, the charge amount of the toner gradually increases with the lapse of time and eventually becomes saturated, and along with this, the detection output of the sensor decreases and stabilizes. Therefore, when the developer is replaced with a new one, a predetermined time (for example, 3 minutes)
Stirring is performed to stabilize the detection output of the sensor, and then the control voltage of the sensor is changed to adjust the voltage of the detection output of the sensor so that the measured toner concentration matches the actual concentration. It was

[0007]

By the way, in a developer in which toner and carrier are mixed, the charge retention ability of the toner deteriorates with the lapse of usage time. For this reason, it is necessary to replace the developer with a new one after every tens of thousands of recording.

However, at the time of exchanging the developer, even if the container in which the developer is not put is set by mistake and the stirring operation of the developer is performed, the permeability of the empty space (air) is low and the sensor is Since the detection output is low,
As in the case of stirring the new developer, the detection output of the sensor is lowered and regarded as stable, and the adjustment work of the control voltage of the sensor may be completed. In this state, since there is no developer, the image is not recorded even when the image forming operation is executed, and it may take a wasteful time to solve this trouble.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and it is possible to reliably detect the non-addition of the developer by using a sensor for measuring the toner density. An object of the present invention is to provide a developing device, an image forming device, and a developer presence / absence determining method.

[0010]

In order to solve the above problems, the present invention provides a magnetic permeability for detecting the magnetic permeability of a developer by generating a magnetic field intersecting with a developer obtained by mixing toner and carrier. Based on the sensor and the detection output of the magnetic permeability sensor,
In a developing device including a control unit that controls the toner concentration of the developer, the control unit changes the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor to change the amount of change in the detection output of the magnetic permeability sensor. Then, the amount of change in the detected output is compared with a preset threshold value to determine the presence or absence of the developer.

According to the present invention having such a configuration, the control voltage applied to the magnetic permeability sensor is changed to obtain the amount of change in the detection output of the magnetic permeability sensor, and the amount of change in the detection output is preset. The presence or absence of the developer is determined by comparing the threshold value with the threshold value. Here, if there is a developer, since there is also a carrier of a magnetic material in the developer, the permeability sensor detects the permeability of the developer, and when the control voltage changes,
The detection output of the magnetic permeability sensor also changes greatly. On the other hand, if there is no developer, since there is no carrier of magnetic material, the permeability sensor detects the permeability of the empty space (air). The detection output of the magnetic susceptibility sensor does not change. Therefore, the presence or absence of the developer can be reliably determined based on the characteristic of the detection output of the magnetic permeability sensor with respect to the control voltage.

If the toner concentration is sufficient and necessary, the carrier concentration of the magnetic material is low, the permeability of the developer is low, and the permeability of the empty space (air) is also low. The presence or absence of the developer cannot be determined only by the detection output itself.

Further, according to the present invention, if the change amount of the detection output of the magnetic permeability sensor is less than the threshold value, the control means determines that there is no developer, and the change amount of the detection output of the magnetic permeability sensor is the threshold value. If it is above, it is determined that the developer is present.

As described above, if the developer is present, the magnetic carrier is also present. Therefore, the magnetic permeability of the developer is detected by the magnetic permeability sensor, and the magnetic permeability changes when the control voltage changes. The detection output of the sensor also changes greatly. Also,
Without a developer, there is no magnetic carrier, so
The magnetic permeability sensor detects the magnetic permeability of an empty space (air), and the detection output of the magnetic permeability sensor does not change even if the control voltage changes. Therefore, if the change amount of the detection output of the magnetic permeability sensor is less than the threshold value and small, it is determined that there is no developer, and if the change amount of the detection output of the magnetic permeability sensor is more than the threshold value and large, there is the developer. Can be determined.

Next, the present invention is based on a magnetic permeability sensor for detecting the magnetic permeability of the developer by generating a magnetic field intersecting with the developer formed by mixing toner and carrier, and the detection output of the magnetic permeability sensor. In the developing device including a control unit for controlling the toner concentration of the developer, the control unit changes the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor, and the maximum value and the minimum value of the control voltage are changed. The difference between the detection outputs of the magnetic permeability sensors corresponding to the value is obtained, and the difference is compared with a preset threshold value to determine the presence or absence of the developer.

Also according to the present invention having such a configuration, based on the characteristic of the detection output of the magnetic permeability sensor with respect to the control voltage,
The presence or absence of the developer can be reliably determined.

Further, according to the present invention, if the change amount of the detection output of the magnetic permeability sensor is less than the threshold value, the control means determines that there is no developer, and the change amount of the detection output of the magnetic permeability sensor is the threshold value. If it is above, it is determined that the developer is present.

Also in this case, it is determined that there is no developer if the amount of change in the detection output of the magnetic permeability sensor is small, and that there is the developer if the amount of change in the detection output of the magnetic permeability sensor is large.

Further, in the present invention, the determination by the control means is executed during the idling period in which the developer is stirred without image formation.

As described above, if the determination is performed by the control means during the idling period in which the developer is agitated without image formation, the developing device is not burdened.

Next, the image forming apparatus of the present invention exposes the developing device of the present invention, an image carrier that forms an electrostatic latent image developed by the developer of the developing device, and the image carrier, And an exposure device that forms an electrostatic latent image on the image carrier.

That is, the present invention includes an image forming apparatus provided with the developing device of the present invention.

Further, the method for judging the presence or absence of the developer of the present invention is
The magnetic field that intersects with the developer is generated from the magnetic permeability sensor during the idling period when the developer is mixed with toner and carrier without image formation, and the magnetic permeability of the developer is measured by the magnetic permeability sensor. While detecting, the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor is changed to obtain the change amount of the detection output of the magnetic permeability sensor, and the change amount of the detection output is compared with a preset threshold value. Therefore, the presence or absence of the developer is determined.

Also according to such a method of the present invention, based on the characteristic of the detection output of the magnetic permeability sensor with respect to the control voltage,
The presence or absence of the developer can be reliably determined.

[0025]

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

FIG. 1 schematically shows an embodiment of the image forming apparatus of the present invention. The image forming apparatus of the present embodiment forms an image by an electrophotographic method,
An exposure scanning unit 10 and an image forming unit 20 are provided.

In the exposure scanning section 10, the control section 30 receives an image signal from an external host computer or the like. The control unit 30 performs necessary processing on this image signal,
Image data is formed, a drive signal corresponding to this image data is output to the laser diode 11, and the laser light emitted from the laser diode 11 is modulated. The laser light is collimated by the collimator lens 12, and then reflected and deflected by the polygon mirror 14 driven to rotate at a constant speed by the motor 13. The image forming unit 20 passes through the fθ lens 15 and the folding mirror 16. It is incident on the surface of the photosensitive drum 21, and the surface of the photosensitive drum 21 is exposed and scanned.

In the image forming unit 20, while rotating the photosensitive drum 21 in one direction, the residual toner on the surface of the photosensitive drum 21 is removed by the cleaner 22, and the eraser lamp 2 is used.
The surface of the photosensitive drum 21 is neutralized by irradiating the surface of the photosensitive drum 21 with the light of No. 3, and the surface of the photosensitive drum 21 is uniformly charged by the charging charger 24.
The surface of the photosensitive drum 21 is exposed and scanned by the laser light from the exposure scanning unit 10 to form an electrostatic latent image on the surface of the photosensitive drum 21, and the electrostatic latent image on the surface of the photosensitive drum 21 is developed by a developing device. 25 to develop a toner image on the surface of the photosensitive drum 21. On the other hand, in synchronization with the rotation operation of the photosensitive drum 21, a recording sheet (not shown) is pulled out from the sheet cassette 27 by the sheet feeding roller 26, and the recording sheet is conveyed by the timing rollers 28 and the conveyor belt 29. The toner image on the surface of the photosensitive drum 21 is transferred to a recording sheet by the transfer charger 31. Further, the recording sheet is fixed by the conveyance belt 29 to the fixing device 3
After being conveyed to 2, the recording sheet is heated and pressed by the fixing device 32 to fix the toner image on the recording sheet, and then the recording sheet is discharged to the discharge tray 34 by each discharge roller 33.

The exposure scanning unit 10 is pivotably supported by a hinge so as to be openable and closable upward so that the toner container of the developing device 25 can be replaced and a paper jam generated in the image forming unit 20 can be processed. I have to.

FIG. 2 shows the photosensitive drum 21 and the developing device 2.
5 is a side view showing FIG. The developing device 25 is of a dry two-component magnetic brush developing type that uses a developer obtained by mixing toner and a carrier of magnetic material, and includes a toner container 43 for storing toner and a toner residual amount for detecting the residual amount of toner. A quantity sensor 48, a developing container 46 containing a developer, a toner replenishing roller 47 for replenishing toner from the toner container 43 to the mixing and stirring chamber of the developing container 46, and a toner and magnetic carrier in the mixing and stirring chamber. The stirring rollers 45 and 45 that stir and frictionally charge, the toner concentration sensor 41 that detects the toner concentration in the mixing and stirring chamber, and the developing roller 44 that supplies toner from the mixing and stirring chamber to the surface of the photosensitive drum 21. I have it. By the supply of toner from the developing device 25, toner is attached to the electrostatic latent image on the surface of the photoconductor drum 21, and the electrostatic latent image is developed to form a toner image.

The developing roller 44 is formed by inserting a magnet roller for generating a magnetic field into a cylindrical sleeve made of a non-magnetic metal such as aluminum alloy, brass and SUS304 stainless steel. The toner in the developer is supplied to the surface of the photoconductor drum 21 while being attracted to the surface of the sleeve by rotating only the sleeve.

The toner density sensor 41 has a detection surface 41.
a is always in contact with the developer and is arranged apart from the developing roller 44. Since the toner concentration sensor 41 detects the magnetic permeability of the developer, it needs to be separated from the developing roller 44 to avoid the influence of the magnet roller of the developing roller 44.

FIG. 3 is a block diagram showing a control device 30 for controlling the image forming apparatus, a toner density sensor 41, and the like. The control device 30 includes a CPU 31, a ROM 3
2 and RAM 33 and the like.

The CPU 31 measures the toner remaining amount of the toner container 43 based on the detection output of the toner remaining amount sensor 48, and when the remaining amount of the toner falls below a specified amount, displays a message prompting the toner replenishment. It is displayed on the section 52. Or C
The PU 31 displays various other messages on the display unit 52. Further, the CPU 31 inputs the detection output (voltage) Vl from the toner concentration sensor 41 to measure the toner concentration in the developer and controls the control voltage adjusting circuit 59,
The control voltage Vc applied to the toner density sensor 41 is controlled. When the toner concentration in the developer becomes less than the specified value, the CPU 31 drives and controls the motor 56 for rotating the toner replenishing roller 47 through the toner replenishing motor drive circuit 57, and rotates the toner replenishing roller 47 to cause the toner to replenish the toner. The mixing and stirring chamber of the developing container 46 is replenished from the container 43. Further, the CPU 31 controls the rotation of the stirring rollers 45, 45 and the developing roller 44 of the developing device 25.

The ROM 32 stores a program for controlling the entire image forming apparatus and a program for controlling the toner density in the developer. RAM33 is C
It is used as a working area of the PU 31, and stores various data such as the detection output Vl of the toner concentration sensor 41.

Further, the toner concentration sensor 41 is provided with a terminal TI for inputting an operating voltage, an output terminal TL for the detection output Vl, a terminal TC for inputting a control voltage Vc, a ground terminal G and the like. The toner concentration sensor 41 generates a magnetic field intersecting with the developer, detects the magnetic permeability of the developer, and outputs a detection output Vl indicating the magnetic permeability. The developer is a mixture of a toner containing a resin or the like as a main component and a magnetic carrier. Therefore, when the toner concentration is high, the carrier concentration is low and the magnetic permeability of the developer is low. On the contrary, when the toner concentration is low, the carrier concentration is high and the magnetic permeability of the developer is high.

FIG. 4 is a graph showing the output characteristics of the toner density sensor 41. Here, the toner concentration is 5% by weight.
The following control voltages Vcmin, Vcz, Vc are used.
Each output characteristic is shown for each max. As is clear from the output characteristics of the toner concentration sensor 41, the higher the toner concentration and the lower the magnetic permeability of the developer, the lower the detection output Vl, and conversely, the lower the toner concentration and the lower the developer concentration. The higher the magnetic permeability, the higher the detection output Vl.

Further, as shown in the graph of FIG. 5, the control voltage Vc of the toner density sensor 41 is proportional to the detection output Vl. Here again, a developer having a toner concentration of 5% by weight is used.
Considering that the voltage range of the detection output Vl of the toner concentration sensor 41 is specified, the control voltage Vc is adjusted so that the detection output Vl of the toner concentration sensor 41 has a voltage value substantially in the center of the specified voltage range. Therefore, it is necessary to optimize the output characteristics of the toner concentration sensor 41. For example, the control voltage Vc is set so that the detection output Vl of the toner density sensor 41 becomes 1.5V.
Adjust. This 1.5V is applied to the developing container 46 described later.
It is adopted as the threshold value Vs used for determining the presence / absence of the developer in the inside.

Further, as described above, it is necessary to periodically replace the developer in which the toner and the carrier are mixed with a new developer. When this new developer is stirred, the magnetic permeability of this developer gradually increases. The output Vl of the toner concentration sensor 41 also decreases and stabilizes accordingly. The graph of FIG. 6 shows the characteristics of the detection output Vl of the toner concentration sensor 41 with respect to the stirring time, and shows the characteristics a, b and c for each of the three types of new developers. As is clear from the graph of FIG. 6, the detection output Vl of the toner concentration sensor 41 decreases and stabilizes with the passage of stirring time. Therefore, when the developer is replaced with a new one, it is stirred for a predetermined time (for example, 3 minutes) to stabilize the detection output Vl of the toner concentration sensor 41, and then the control voltage Vc is adjusted to adjust the toner concentration sensor. It is desirable to set the detection output Vl of 41 to 1.5V.

By the way, even when the developer container 46 not filled with the developer is mistakenly set and the developer is agitated when the developer is replaced, an empty space (air) in the developer container 46 is generated. Since the magnetic permeability is low and the detection output Vl of the toner concentration sensor 41 is low, the detection output Vl of the toner concentration sensor 41 decreases and is regarded as stable, as when a new developer is stirred. It is possible. Therefore, it is desirable to determine the presence / absence of the developer in the developing container 46 before adjusting the control voltage Vc of the toner concentration sensor 41.

If the developing container 46 is empty,
Since the empty space of the developing container 46 is detected by the toner concentration sensor 41, the toner concentration sensor 41 is simply
Of the control voltage Vc from the minimum voltage Vcmin to the maximum voltage Vcmax, as is apparent from the detection output Vlmin of the toner concentration sensor 41 when the magnetic permeability is low in the graph of FIG. Even then, the detection output Vlmin of the toner concentration sensor 41 is maintained.

Further, when the developer is loaded in the developing container 46, the carrier of the magnetic material of the developer is detected by the toner concentration sensor 41, so that the control voltage is as shown in the graph of FIG. When Vc changes from the minimum voltage Vcmin to the maximum voltage Vcmax, the detection output Vl of the toner concentration sensor 41 changes greatly. This change amount is obtained by the toner concentration sensor 41 when the toner concentration during development is 5% by weight.
Detection output Vl (= 1.5V) of 2 times or more.

Therefore, the control voltage Vc is changed from the minimum voltage Vcmin to the maximum voltage Vcmax, and the toner density sensor 4
If the change characteristic of the detection output Vl of 1 is obtained, the presence or absence of the developer in the developing container 46 can be determined based on the change characteristic of the detected output Vl.

Therefore, in the present embodiment, when the developer is replaced, the change characteristic of the detection output Vl of the toner concentration sensor 41 with respect to the control voltage Vc is obtained according to the flowchart of FIG. 7, and based on the change characteristic of the detection output Vl. The presence or absence of the developer in the developing container 46 is determined, and then the control voltage Vc is adjusted and the detection output Vl of the toner concentration sensor 41 is set to 1.5 V to optimize the output characteristic of the toner concentration sensor 41. ing. Next, the process of the flowchart of FIG. 7 will be described.

First, during the periodic maintenance and inspection of the image forming apparatus, if the developer in the developing container 46 is replaced with a new one, the developing container 46 is set in the image forming apparatus at a predetermined position, and then the image is formed. The main power switch of the forming apparatus is turned on to start the image forming apparatus, and the initial setting button 51 is turned on. In response to the initialization button 51 being turned on, the CPU 31 of the control device 30 inhibits the rotation of the toner supply roller 47, and also starts the rotation of the stirring rollers 45, 45 of the developing device 25 to cause the inside of the developing container 46. The idling drive for stirring the developer is started (step S101).

Subsequently, the CPU 31 sets the control voltage Vc of the toner concentration sensor 41 to the minimum voltage Vcmin (step S102) and samples the detection output Vlmin of the toner concentration sensor 41 (step S103) to obtain the minimum voltage Vcmin. The detection output Vlmin is stored in the RAM 33 in association with each other. Further, the CPU 31 uses the toner concentration sensor 4
The control voltage Vc of 1 is increased stepwise by a change width of ΔVc (for example, ΔV = 0.25V), and the detection output V of the toner concentration sensor 41 is increased each time the control voltage Vc is increased stepwise.
l is sampled and stored in the RAM 33 in association with the control voltage Vc and the detection output Vl (step S10).
4). Finally, the CPU 31 raises the control voltage Vc of the toner concentration sensor 41 to the maximum voltage Vcmax (step S105), and the detection output Vlmax of the toner concentration sensor 41.
Is sampled (step S106), and the maximum voltage Vcm
The ax and the detection output Vlmax are stored in the RAM 33 in association with each other. As a result, the change characteristic of the detection output Vl of the toner concentration sensor 41 with respect to the control voltage Vc is stored in the RAM 33.

In this way, the change characteristic of the detection output Vl of the toner concentration sensor 41 is obtained, and after 3 minutes have elapsed from the start of rotation of the stirring rollers 45, 45, the CPU 31 stops the stirring rollers 45, 45 and drives the idling drive. Is stopped (step S107). Then, the CPU 31 reads out the respective detection outputs Vlmin and Vlmax corresponding to the minimum voltage Vcmin and the maximum voltage Vcmax from the RAM 33, obtains the difference between the respective detection outputs Vlmin and Vlmax, and sets the difference to a preset threshold Vs = 1. .5 V (step S10
8) If this difference is less than the threshold Vs (step S10)
8 is “No”), and it is considered that the developer has not been charged into the developing container 46. Here, when the developer is not supplied, the empty space of the developing container 46 is detected by the toner concentration sensor 41 as described above, and therefore the toner concentration is changed even if the control voltage Vc is changed. The detection output Vlmin of the sensor 41 is always maintained, the difference between the detection outputs Vlmin and Vlmax of the toner concentration sensor 41 becomes 0, and this difference becomes less than the threshold value Vs. Therefore, if this difference is less than the threshold value Vs, it can be considered that the developer has not been added.

When it is determined that the developer has not been added, the CPU 31 displays on the display unit 52 a message prompting the developer to be added (step S111).

If the difference is equal to or more than the threshold value Vs ("Yes" in step S108), the CPU 31 considers that the developer is in the developing container 46. Here, when the developer is supplied, the carrier of the magnetic material of the developer is detected by the toner concentration sensor 41 as described above, so that the respective detection outputs Vlmin and Vlmax of the toner concentration sensor 41 are detected. Is approximately twice the threshold value Vs, and this difference is certainly greater than or equal to the threshold value Vs. Therefore, if this difference is greater than or equal to the threshold value Vs, it can be considered that the developer has been added.

When the CPU 31 considers that the developer has been applied, the CPU 31 refers to the change characteristic of the detection output Vl of the toner concentration sensor 41 in the RAM 33 to refer to the toner concentration sensor 4
The control voltage Vc when the detection output Vl of 1 becomes the threshold value Vs = 1.5V is derived, the control voltage Vc is stored in the RAM 33, and the control voltage Vc is stored in the toner concentration sensor 41.
In addition to this (step S109), image formation is awaited (step S110).

As described above, in this embodiment, the change characteristic of the detection output Vl of the toner concentration sensor 41 with respect to the control voltage Vc is obtained, and when the developer is being supplied to the developing container 46, the minimum voltage Vcmin and the maximum voltage Vcmax. The difference between the detection outputs Vlmin and Vlmax corresponding to
Since it surely exceeds 1.5 V, if the difference is equal to or more than the threshold value Vs, it is considered that the developer is put in the developing container 46, and if the difference is less than the threshold value Vs, the developer is not included. It is considered that the developing container 46 has not been charged. Further, the toner concentration sensor 4 for the control voltage Vc
Since the control voltage Vc when the detection output Vl of the toner concentration sensor 41 reaches the threshold value Vs = 1.5V is derived and set by using the change characteristic of the detection output Vl of No. 1, the output of the toner concentration sensor 41 is set. The characteristics can be optimized.

Further, since the apparatus of this embodiment is realized by utilizing the existing toner density sensor 41 and the like and only adding the program, the cost does not increase.

Further, since the presence / absence of the developer and the optimization of the output characteristic of the toner density sensor 41 are performed during the idling operation, the developing device and the image forming device are not burdened.

[0054]

As described above, according to the present invention, the control voltage applied to the magnetic permeability sensor is changed to obtain the change amount of the detection output of the magnetic permeability sensor, and the change amount of the detection output is calculated in advance. The presence or absence of the developer is determined by comparing with the set threshold value. Here, if the developer is present, since the magnetic carrier in the developer is also present, the magnetic permeability of the developer is detected by the magnetic permeability sensor, and when the control voltage changes, the magnetic permeability of the magnetic permeability sensor changes. The detection output changes greatly. On the other hand, if there is no developer, there is no magnetic carrier, so the permeability sensor detects the permeability of the empty space (air), and even if the control voltage changes,
The detection output of the magnetic permeability sensor hardly changes. Therefore, the presence or absence of the developer can be reliably determined based on the characteristic of the detection output of the magnetic permeability sensor with respect to the control voltage.

Further, according to the present invention, if the change amount of the detection output of the magnetic permeability sensor is less than the threshold value and small, it is determined that there is no developer, and the change amount of the detection output of the magnetic permeability sensor is equal to or more than the threshold value. If it is large, it is determined that the developer is present.

Further, according to the present invention, since the determination is performed by the control means during the idling period in which the developer is stirred without image formation, the developing device is not burdened.

[Brief description of drawings]

FIG. 1 schematically shows an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a side view showing a photosensitive drum and a developing device in the apparatus of FIG.

3 is a block diagram showing a control device for controlling the apparatus of FIG. 1, a toner concentration sensor, and the like.

FIG. 4 is a graph showing output characteristics of a toner concentration sensor.

FIG. 5 is a graph showing the characteristics of the detection output with respect to the control voltage of the toner density sensor.

FIG. 6 is a graph showing a characteristic of a detection output of the toner concentration sensor with respect to stirring time.

FIG. 7 is a flowchart showing processing by the apparatus of FIG.

[Explanation of symbols]

21 photoconductor drum 25 Developing device 43 toner container 48 Toner level sensor 46 developer container 47 Toner supply roller 45 stirring roller 44 developing roller 41 Toner density sensor 30 control device 31 CPU 32 ROM 33 RAM

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Jun Yamaguchi             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F term (reference) 2H077 AA12 AB06 AB14 AC04 AD06                       DA10 DA15 DA42 DA52 DA78                       DA80 DA82 DB08 DB10 DB14                       DB18 DB25 EA03

Claims (7)

[Claims] 1. A magnetic permeability sensor for detecting a magnetic permeability of a developer by generating a magnetic field intersecting with a developer formed by mixing toner and carrier, and based on a detection output of the magnetic permeability sensor,
In a developing device including a control unit that controls the toner concentration of the developer, the control unit changes the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor to change the amount of change in the detection output of the magnetic permeability sensor. A developing device, characterized in that the presence or absence of a developer is determined by comparing the amount of change in the detected output with a preset threshold value. 2. The control means determines that there is no developer when the amount of change in the detection output of the magnetic permeability sensor is less than a threshold value, and the developing means when the amount of change in the detection output of the magnetic permeability sensor is greater than or equal to the threshold value. The developing device according to claim 1, wherein it is determined that the developer is present. 3. A magnetic permeability sensor for detecting magnetic permeability of the developer by generating a magnetic field intersecting with the developer formed by mixing toner and carrier, and based on the detection output of the magnetic permeability sensor,
In a developing device provided with a control unit for controlling the toner concentration of the developer, the control unit changes the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor so that the maximum value and the minimum value of the control voltage are changed. A developing device, wherein a difference between detection outputs of corresponding magnetic permeability sensors is obtained, and the presence or absence of a developer is determined by comparing the difference with a preset threshold value. 4. The control means determines that there is no developer if the amount of change in the detection output of the magnetic permeability sensor is less than the threshold value, and the developing unit if the amount of change in the detection output of the magnetic permeability sensor is not less than the threshold value. The developing device according to claim 3, wherein it is determined that the developer is present. 5. The developing device according to claim 1, wherein the determination by the control unit is executed during an idling period in which the developer is stirred without image formation. 6. The developing device according to claim 1, an image carrier that forms an electrostatic latent image developed by the developer of the developing device, and the image carrier, which is exposed to light. An image forming apparatus comprising: an exposure device that forms an electrostatic latent image on an image carrier. 7. The magnetic permeability of the developer is generated by generating a magnetic field intersecting with the developer during an idling period in which the developer obtained by mixing toner and carrier is agitated without image formation. While detecting with a permeability sensor,
By changing the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor, the change amount of the detection output of the magnetic permeability sensor is obtained,
A method for determining the presence or absence of a developer, characterized in that the presence or absence of a developer is determined by comparing the amount of change in the detection output with a preset threshold value.