JP4067862B2 - Developing device, image forming apparatus, and method for determining presence / absence of developer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device using a developer obtained by mixing toner and a carrier, an image forming apparatus, and a developer presence / absence determination method.
[0002]
[Prior art]
In this type of image forming apparatus, the developer in which the toner and the carrier are mixed is stirred in a container to charge the developer, and the toner in the developer is converted into an electrostatic latent image on the image carrier. Then, the electrostatic latent image is developed to form a toner image on the image carrier, and the toner image on the image carrier is transferred to a recording sheet and fixed. Further, the toner density of the developer in the container is detected, and when the toner density decreases, the toner is supplied to the container to maintain the toner density constant.
[0003]
As a method for detecting the toner density, for example, there is a method using an L detection toner density sensor. The coil of the L detection toner density sensor is arranged at a position in contact with the developer, and the magnetic permeability of the developer corresponding to the toner density is measured by this sensor. Actually, the higher the toner concentration in the developer, the lower the carrier concentration of the magnetic material and the lower the magnetic permeability of the developer.
[0004]
This density measurement based on magnetic permeability is excellent in that it can always be measured and does not affect the image forming process at all. The sensor measures the toner density, replenishes the toner according to the measured toner density, and keeps the toner density substantially constant.
[0005]
This L detection toner density sensor is provided as, for example, a programmable toner sensor (trade name) manufactured by TDK Corporation. This sensor includes an oscillation circuit including the 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 characteristics of the sensor are not always constant, and the output characteristics change depending on the mounting position of the coil of the sensor, or the output characteristics of the sensor are not stable and constant for a completely new developer. Because.
[0006]
Here, when the developer in which the toner and the carrier are mixed is completely new, the developer is almost stationary during the long-term storage and the stirring is insufficient. The repulsive force also decreases, and the number of carriers per unit volume increases. At this time, even if the carrier concentration is constant, the magnetic permeability of the developer increases, so that the voltage of the detection output of the sensor increases, and the measured toner concentration becomes lower than the actual concentration. When the new developer is stirred, the charge amount of the toner gradually increases with time, and eventually becomes saturated. As a result, the detection output of the sensor also decreases and stabilizes. For this reason, when the developer is replaced with a new developer, stirring is performed for a predetermined time (for example, 3 minutes) to stabilize the detection output of the sensor, and then the control voltage of the sensor is changed to change the voltage of the detection output of the sensor. And adjusting the measured toner density to match the actual density.
[0007]
[Problems to be solved by the invention]
By the way, the developer in which the toner and the carrier are mixed is deteriorated in the charge holding ability of the toner as the usage time elapses. For this reason, it is necessary to replace the developer with a new one every time tens of thousands of sheets are recorded.
[0008]
However, when replacing the developer, even if the container without the developer is set in error and the developer is agitated, the permeability of the empty space (air) is low, and the sensor output is low. Therefore, in the same manner as when a new developer is agitated, the detection output of the sensor is considered to be stable due to a decrease, and the adjustment of the control voltage of the sensor may be completed. In this state, since there is no developer, an image is not recorded even when an image forming operation is executed, and a wasteful time may be spent for solving this trouble.
[0009]
Accordingly, the present invention has been made in view of the above-described conventional problems, and a developing device capable of reliably detecting the non-input of the developer by using a sensor for measuring the toner density, An object is to provide an image forming apparatus and a developer presence / absence determination method.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention generates a magnetic field that crosses a developer formed by mixing toner and a carrier, and detects a permeability of the developer, and a detection output of the permeability sensor. And a control unit for controlling the toner density of the developer, the control unit changes the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor, and detects the output of the magnetic permeability sensor. The change amount of the detected output is obtained, and the change amount of the detected output is compared with a preset threshold value to determine the presence or absence of the developer.
[0011]
According to the present invention having such a configuration, the amount of change in the detected output of the magnetic permeability sensor is obtained by changing the control voltage applied to the magnetic permeability sensor, and the amount of change in the detected output is set to a preset threshold value. In comparison, the presence or absence of the developer is determined. Here, if there is a developer, there is also a magnetic carrier in the developer, so the permeability of the developer is detected by the permeability sensor, and when the control voltage changes, the permeability sensor The detection output also changes greatly. On the other hand, if there is no developer, there is no carrier of magnetic material, so the permeability sensor detects the permeability of the empty space (air), and even if the control voltage changes, the permeability does not change. The detection output of the magnetic sensor does not change. Therefore, the presence or absence of the developer can be reliably determined based on the detection output characteristic of the magnetic permeability sensor with respect to the control voltage.
[0012]
If the toner concentration is sufficient and sufficient, the magnetic carrier concentration is low, the magnetic permeability of the developer is low, and similarly the magnetic permeability of the empty space (air) is low. The presence of the developer cannot be determined by itself.
[0013]
Further, according to the present invention, the control means determines that there is no developer if the change amount of the detection output of the magnetic permeability sensor is less than the threshold value, and if the change amount of the detection output of the magnetic permeability sensor is equal to or greater than the threshold value. For example, it is determined that the developer is present.
[0014]
As described above, if there is a developer, there is also a magnetic carrier, so the permeability of the developer is detected by the permeability sensor. When the control voltage changes, the permeability sensor detects it. The output also changes greatly. Further, 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 permeability sensor The detection output does not change. Therefore, if the change amount of the detection output of the magnetic permeability sensor is less than the threshold value and is small, it is determined that there is no developer, and if the change amount of the detection output of the magnetic permeability sensor is equal to or greater than the threshold value, the developer is present. Can be determined.
[0015]
Next, according to the present invention, a magnetic field sensor that detects the magnetic permeability of the developer by generating a magnetic field intersecting with the developer obtained by mixing the toner and the carrier, and the development based on the detection output of the magnetic permeability sensor. And a control unit for controlling the toner concentration of the agent, the control unit changes the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor to correspond to the maximum value and the minimum value of the control voltage. The difference between the detection outputs of the magnetic permeability sensors is determined, and the difference is compared with a preset threshold value to determine the presence or absence of the developer.
[0016]
Also according to the present invention having such a configuration, the presence or absence of the developer can be reliably determined based on the characteristics of the detection output of the magnetic permeability sensor with respect to the control voltage.
[0017]
Further, according to the present invention, the control means determines that there is no developer if the change amount of the detection output of the magnetic permeability sensor is less than the threshold value, and if the change amount of the detection output of the magnetic permeability sensor is equal to or greater than the threshold value. For example, it is determined that the developer is present.
[0018]
Also here, if the change amount of the detection output of the magnetic permeability sensor is small, it is determined that there is no developer, and if the change amount of the detection output of the magnetic permeability sensor is large, it is determined that the developer is present.
[0019]
In the present invention, the determination by the control means is executed during an idling period in which the developer is stirred without image formation.
[0020]
In this way, if the determination by the control means is executed during the idling period in which the developer is stirred without image formation, a burden is not applied to the developing device.
[0021]
Next, an image forming apparatus according to the present invention includes a developing device according to the present invention, an image carrier that forms an electrostatic latent image developed by the developer of the developing device, and an image carrier that is exposed to the image carrier. And an exposure device that forms an electrostatic latent image on the body.
[0022]
That is, the present invention includes an image forming apparatus provided with the developing device of the present invention.
[0023]
Further, the developer presence / absence determination method of the present invention generates a magnetic field intersecting with the developer from the magnetic permeability sensor during an idling period in which the developer formed by mixing the toner and the carrier is stirred without forming an image. Then, while detecting the magnetic permeability of the developer by the magnetic permeability sensor, the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor is changed to obtain the amount of change in the detection output of the magnetic permeability sensor, and this detection The amount of change in output is compared with a preset threshold value to determine the presence or absence of the developer.
[0024]
Also with such a method of the present invention, 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.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0026]
FIG. 1 schematically shows an embodiment of an image forming apparatus of the present invention. The image forming apparatus according to the present embodiment forms an image by an electrophotographic method, and includes an exposure scanning unit 10 and an image forming unit 20.
[0027]
In the exposure scanning unit 10, the control unit 30 receives an image signal from an external host computer or the like. The control unit 30 performs necessary processing on the image signal to form image data, outputs a drive signal corresponding to the image data to the laser diode 11, and laser light emitted from the laser diode 11. Modulate. The laser light is collimated by the collimating lens 12, then reflected and deflected by the polygon mirror 14 driven to rotate at a constant speed by the motor 13, and the image forming unit 20 passes through the fθ lens 15 and the folding mirror 16. Is incident on the surface of the photosensitive drum 21, and the surface of the photosensitive drum 21 is exposed and scanned.
[0028]
In the image forming unit 20, while rotating the photosensitive drum 21 in one direction, residual toner on the surface of the photosensitive drum 21 is removed by the cleaner 22, and the surface of the photosensitive drum 21 is irradiated with light from the eraser lamp 23. The surface of the photosensitive drum 21 is neutralized, and the surface of the photosensitive drum 21 is uniformly charged by the charging charger 24, and then the surface of the photosensitive drum 21 is exposed and scanned with the laser beam from the exposure scanning unit 10. Thus, an electrostatic latent image is formed on the surface of the photosensitive drum 21, and the electrostatic latent image on the surface of the photosensitive drum 21 is developed by the developing device 25 to form a toner image on the surface of the photosensitive drum 21. On the other hand, in synchronization with the rotation of the photosensitive drum 21, a recording sheet (not shown) is pulled out from the sheet cassette 27 by the paper feed roller 26, and this recording sheet is pulled by the respective timing rollers 28 and the conveying belt 29. The toner image on the surface of the photosensitive drum 21 is transferred onto a recording sheet by the transfer charger 31. Further, the recording paper is conveyed to the fixing device 32 by the conveying belt 29, the recording paper is heated and pressurized by the fixing device 32 to fix the toner image on the recording paper, and then the recording paper is discharged by each discharge roller 33. The paper is discharged to the paper tray 34.
[0029]
The exposure scanning unit 10 is pivotally supported by a hinge so as to be openable and closable 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. .
[0030]
FIG. 2 is a side view showing the photosensitive drum 21 and the developing device 25. The developing device 25 is of a dry two-component magnetic brush developing method using a developer obtained by mixing toner and a magnetic carrier, and includes a toner container 43 that contains toner, and a toner residue that detects the remaining amount of toner. An amount sensor 48, a developer container 46 for containing 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. Stirring rollers 45 and 45 for stirring and friction charging, a toner concentration sensor 41 for detecting the toner concentration in the mixing and stirring chamber, and a developing roller 44 for supplying toner from the mixing and stirring chamber to the surface of the photosensitive drum 21. I have. By supplying the toner from the developing device 25, the toner adheres to the electrostatic latent image on the surface of the photosensitive drum 21, and the electrostatic latent image is developed to form a toner image.
[0031]
The developing roller 44 is obtained by inserting a magnetic roller that generates a magnetic field into a cylindrical sleeve made of a non-magnetic metal such as aluminum alloy, brass, or SUS304 stainless steel. The toner in the developer is supplied to the surface of the photosensitive drum 21 by rotating only the sleeve while adsorbing the toner.
[0032]
The toner density sensor 41 is arranged such that its detection surface 41 a is always in contact with the developer and is separated from the developing roller 44. Since the toner density sensor 41 detects the magnetic permeability of the developer, the toner density sensor 41 needs to be separated from the developing roller 44 to avoid the influence of the magnet roller of the developing roller 44.
[0033]
FIG. 3 is a block diagram showing the control device 30 and the toner density sensor 41 for controlling the image forming apparatus. The control device 30 includes a CPU 31, a ROM 32, a RAM 33, and the like.
[0034]
The CPU 31 measures the remaining amount of toner in the toner container 43 based on the detection output of the toner remaining amount sensor 48, and informs the display unit 52 that the toner is urged to be replenished when the remaining amount of toner falls below a specified amount. indicate. Alternatively, the CPU 31 displays other various messages on the display unit 52. Further, the CPU 31 inputs the detection output (voltage) Vl from the toner density sensor 41 to measure the toner density in the developer or controls the control voltage adjustment circuit 59 to be applied to the toner density sensor 41. The control voltage Vc 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 supply roller 47 through the toner supply motor drive circuit 57, and rotates the toner supply roller 47 so that the toner becomes toner. The mixing 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 and 45 and the developing roller 44 of the developing device 25.
[0035]
The ROM 32 stores a program for controlling the entire image forming apparatus and a program for controlling the toner density in the developer. The RAM 33 is used as a working area for the CPU 31 and stores various data such as the detection output Vl of the toner density sensor 41.
[0036]
The toner density sensor 41 includes a terminal TI for inputting an operating voltage, an output terminal TL for a detection output Vl, a terminal TC for inputting a control voltage Vc, a ground terminal G, and the like. The toner density sensor 41 generates a magnetic field crossing 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 mainly composed of a resin or the like and a magnetic carrier. For this reason, when the toner concentration is high, the carrier concentration is low and the magnetic permeability of the developer is lowered. Conversely, when the toner concentration is low, the carrier concentration increases and the magnetic permeability of the developer increases.
[0037]
FIG. 4 is a graph showing the output characteristics of the toner density sensor 41. Here, a developer having a toner concentration of 5% by weight is used, and each output characteristic is shown for each control voltage Vcmin, Vcz, Vcmax. As apparent from the output characteristics of the toner concentration sensor 41, the detection output Vl decreases as the toner concentration increases and the developer permeability decreases, and conversely, the toner concentration decreases and the developer concentration decreases. The higher the permeability, the higher the detection output Vl.
[0038]
Further, as shown in the graph of FIG. 5, the control voltage Vc of the toner density sensor 41 and the detection output Vl are proportional. 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 becomes a voltage value approximately at the center of the specific voltage range. Therefore, it is necessary to optimize the output characteristics of the toner density sensor 41. For example, the control voltage Vc is adjusted so that the detection output Vl of the toner density sensor 41 is 1.5V. This 1.5 V is adopted as a threshold value Vs used for determining the presence or absence of the developer in the developing container 46 described later.
[0039]
In addition, as described above, it is necessary to periodically replace the developer mixed with the toner and the carrier with a new one. When the new developer is stirred, the magnetic permeability of the developer gradually decreases. As a result, the detection output Vl of the toner density sensor 41 decreases and stabilizes accordingly. The graph of FIG. 6 shows the characteristics of the detection output Vl of the toner density sensor 41 with respect to the stirring time, and shows the characteristics a, b, and c for each of three types of new developers. As apparent from the graph of FIG. 6, the detection output Vl of the toner concentration sensor 41 decreases and stabilizes as the stirring time elapses. For this reason, when the developer is replaced with a new developer, the developer 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.
[0040]
By the way, even when the developer container 46 to which the developer has not been charged is erroneously set and the developer is agitated when the developer is replaced, the permeability of the empty space (air) in the developer container 46 is high. Since the detection output Vl of the toner density sensor 41 is low, the detection output Vl of the toner density sensor 41 may be considered to be stable due to a decrease, as in the case of stirring a new developer. obtain. Therefore, it is desirable to determine the presence or absence of the developer in the developing container 46 prior to the adjustment of the control voltage Vc of the toner concentration sensor 41.
[0041]
Here, when the developing container 46 is empty, the empty space of the developing container 46 is detected by the toner density sensor 41, so that not only the detection output Vl of the toner density sensor 41 is lowered, but also The graph of FIG. As is apparent from the detection output Vlmin of the toner concentration sensor 41 when the magnetic permeability is low, the detection output Vlmin of the toner concentration sensor 41 is maintained even when the control voltage Vc changes from the minimum voltage Vcmin to the maximum voltage Vcmax. The
[0042]
Further, when the developer is put in the developer container 46, the carrier of the developer magnetic material is detected by the toner concentration sensor 41. The graph of FIG. As apparent from FIG. 4, when the control voltage Vc changes from the minimum voltage Vcmin to the maximum voltage Vcmax, the detection output Vl of the toner density sensor 41 changes greatly. This amount of change is more than twice the detection output Vl (= 1.5 V) of the toner density sensor 41 when the toner density during development is 5% by weight.
[0043]
Therefore, if the control voltage Vc is changed from the minimum voltage Vcmin to the maximum voltage Vcmax and the change characteristic of the detection output Vl of the toner density sensor 41 is obtained, the development in the developing container 46 is based on the change characteristic of the detection output Vl. The presence or absence of the agent can be determined.
[0044]
Therefore, in the present embodiment, when changing the developer, 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 the developing container is determined based on the change characteristic of the detection output Vl. 46, the presence or absence of the developer is determined, and thereafter, the control voltage Vc is adjusted, the detection output Vl of the toner density sensor 41 is set to 1.5 V, and the output characteristics of the toner density sensor 41 are optimized. Next, the process of the flowchart of FIG. 7 will be described.
[0045]
First, during regular maintenance and inspection of the image forming apparatus, when the developer in the developing container 46 is replaced with a new one, the developing container 46 is set in a predetermined position in the image forming apparatus, and then the image forming apparatus The main power switch is turned on to start the image forming apparatus, and the initial setting button 51 is turned on. In response to the ON of the initial setting button 51, the CPU 31 of the control device 30 prohibits the rotation of the toner replenishing roller 47 and starts the rotation of the stirring rollers 45, 45 of the developing device 25 so that the inside of the developing container 46 The idling drive of stirring the developer is started (step S101).
[0046]
Subsequently, the CPU 31 sets the control voltage Vc of the toner density sensor 41 to the minimum voltage Vcmin (step S102), samples the detection output Vlmin of the toner density sensor 41 (step S103), and samples the minimum voltage Vcmin and the detection output Vlmin. Are stored in the RAM 33 in association with each other. Further, the CPU 31 increases the control voltage Vc of the toner density sensor 41 stepwise with a change width of ΔVc (for example, ΔV = 0.25V), and each time the control voltage Vc increases stepwise, the toner concentration sensor 41. The detection output Vl of 41 is sampled, and the control voltage Vc and the detection output Vl are associated with each other and stored in the RAM 33 (step S104). Finally, the CPU 31 raises the control voltage Vc of the toner density sensor 41 to the maximum voltage Vcmax (step S105), samples the detection output Vlmax of the toner density sensor 41 (step S106), the maximum voltage Vcmax 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 density sensor 41 with respect to the control voltage Vc is stored in the RAM 33.
[0047]
Thus, the change characteristic of the detection output Vl of the toner density sensor 41 is obtained, and when 3 minutes have elapsed from the start of rotation of each stirring roller 45, 45, the CPU 31 stops each stirring roller 45, 45 and stops idling driving. (Step S107). Then, the CPU 31 reads out the detection outputs Vlmin and Vlmax corresponding to the minimum voltage Vcmin and the maximum voltage Vcmax from the RAM 33, obtains a difference between the detection outputs Vlmin and Vlmax, and sets the difference as a preset threshold value Vs = 1. .5V (step S108), and if this difference is less than the threshold value Vs (“No” in step S108), it is considered that the developer is not put into the developing container 46. Here, when the developer is not charged, since the empty space of the developing container 46 is detected by the toner concentration sensor 41 as described above, even if the control voltage Vc changes, the toner concentration The detection output Vlmin of the sensor 41 is always maintained, the difference between the detection outputs Vlmin and Vlmax of the toner density sensor 41 is 0, and this difference is less than the threshold value Vs. Therefore, if this difference is less than the threshold value Vs, it can be considered that the developer is not charged.
[0048]
If the CPU 31 determines that the developer has not been input, the CPU 31 displays on the display unit 52 a prompt to input the developer (step S111).
[0049]
If the difference is equal to or greater than the threshold value Vs (“Yes” in step S108), the CPU 31 considers that the developer has been put into the developing container 46. Here, when the developer is supplied, the magnetic carrier of the developer is detected by the toner concentration sensor 41 as described above, and therefore 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 surely equal to or greater than the threshold value Vs. Therefore, if this difference is equal to or greater than the threshold value Vs, it can be considered that the developer is supplied.
[0050]
If the CPU 31 considers that the developer is supplied, the CPU 31 refers to the change characteristic of the detection output Vl of the toner density sensor 41 in the RAM 33, and the detection output Vl of the toner density sensor 41 becomes the threshold value Vs = 1.5V. Control voltage Vc is derived, this control voltage Vc is stored in the RAM 33, this control voltage Vc is added to the toner density sensor 41 (step S109), and image formation is waited (step S110).
[0051]
As described above, in this embodiment, a change characteristic of the detection output Vl of the toner density sensor 41 with respect to the control voltage Vc is obtained, and corresponds to the minimum voltage Vcmin and the maximum voltage Vcmax when the developer is put in the developer container 46. Since the difference between the respective detection outputs Vlmin and Vlmax surely exceeds the threshold value Vs = 1.5 V, if this difference is equal to or greater than the threshold value Vs, it is considered that the developer is put in the developing container 46, and If this difference is less than the threshold value Vs, it is considered that the developer is not put into the developing container 46. Further, using the change characteristic of the detection output Vl of the toner density sensor 41 with respect to the control voltage Vc, the control voltage Vc when the detection output Vl of the toner density sensor 41 becomes the threshold value Vs = 1.5 V is derived and set. Therefore, the output characteristics of the toner density sensor 41 can be optimized.
[0052]
Further, since the apparatus of the present embodiment is realized by using the existing toner density sensor 41 and the like and only by adding a program, it is possible to avoid an increase in cost.
[0053]
Furthermore, since the determination of the presence or absence of the developer and the optimization of the output characteristics of the toner density sensor 41 are performed during the idling operation, there is no burden on the developing device and the image forming apparatus.
[0054]
【The invention's effect】
As described above, according to the present invention, the control voltage applied to the magnetic permeability sensor is changed to determine the amount of change in the detected output of the magnetic permeability sensor, and the amount of change in the detected output is set to a preset threshold value. In comparison, the presence or absence of the developer is determined. Here, if there is a developer, there is also a magnetic carrier in the developer, so the permeability of the developer is detected by the permeability sensor, and when the control voltage changes, the permeability sensor The detection output changes greatly. On the other hand, if there is no developer, there is no carrier of magnetic material, so the permeability sensor detects the permeability of the empty space (air), and even if the control voltage changes, the permeability does not change. The detection output of the magnetic susceptibility sensor hardly changes. Therefore, the presence or absence of the developer can be reliably determined based on the detection output characteristic of the magnetic permeability sensor with respect to the control voltage.
[0055]
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 is small, it is determined that there is no developer, and the change amount of the detection output of the magnetic permeability sensor is greater than or equal to the threshold value. For example, it is determined that the developer is present.
[0056]
Furthermore, according to the present invention, since the determination by the control means is executed during the idling period in which the developer is stirred without image formation, it is not necessary to place a burden on the developing device.
[Brief description of the 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, a toner density sensor, and the like for controlling the device of FIG. 1; FIG.
FIG. 4 is a graph showing output characteristics of a toner density sensor.
FIG. 5 is a graph showing a characteristic of a detection output with respect to a control voltage of the toner density sensor.
FIG. 6 is a graph showing characteristics of detection output of a toner density sensor with respect to stirring time.
FIG. 7 is a flowchart showing processing by the apparatus of FIG.
[Explanation of symbols]
21 Photosensitive drum
25 Development device
43 Toner Container
48 Toner level sensor
46 Developer container
47 Toner supply roller
45 Stirrer roller
44 Developing roller
41 Toner density sensor
30 Control device
31 CPU
32 ROM
33 RAM

Claims (8)

A magnetic field sensor that detects the magnetic permeability of the developer by generating a magnetic field that crosses the developer formed by mixing the toner and the carrier, and controls the toner density of the developer based on the detection output of the magnetic permeability sensor. A developing device comprising a control means;
The control means changes the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor, obtains a change amount of the detection output of the magnetic permeability sensor corresponding to the change of the control voltage, and calculates the change amount of the detection output. A developing device that determines the presence or absence of a developer by comparing with a preset threshold value.   The control means determines that there is no developer if the change amount of the detection output of the magnetic permeability sensor is less than the threshold value, and determines that the developer is present if the change amount of the detection output of the magnetic permeability sensor is equal to or greater than the threshold value. The developing device according to claim 1, wherein: A magnetic field sensor that detects the magnetic permeability of the developer by generating a magnetic field that crosses the developer formed by mixing the toner and the carrier, and controls the toner density of the developer based on the detection output of the magnetic permeability sensor. A developing device comprising a control means;
The control means changes the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor to determine the difference between the detection outputs of the magnetic permeability sensors corresponding to the maximum value and the minimum value of the control voltage. Is compared with a preset threshold value to determine the presence or absence of the developer.   The control means determines that there is no developer if the change amount of the detection output of the magnetic permeability sensor is less than the threshold value, and determines that the developer is present if the change amount of the detection output of the magnetic permeability sensor is equal to or greater than the threshold value. The developing device according to claim 3, wherein: Determination by the control means, a developing device according to any one of claims 1 to 4, characterized in that it is performed during the idling period for stirring the developer without image formation. A developing roller that supplies a developer obtained by mixing toner and carrier to the surface of the electrostatic latent image carrier, a magnetic permeability sensor that generates a magnetic field crossing the developer, and detects the magnetic permeability of the developer; In a developing device comprising control means for controlling the toner concentration of the developer based on the detection output of the magnetic sensor,
The magnetic permeability sensor is arranged at a position where the detection surface is always in contact with the developer and separated from the developing roller,
The control means changes the control voltage for controlling the magnetic field strength applied to the permeability sensor during the idling period in which the developer is stirred without image formation and before adjusting the control voltage of the permeability sensor. Thus, the change amount of the detection output of the magnetic permeability sensor corresponding to the change of the control voltage is obtained, and the change amount of the detection output of the magnetic permeability sensor is compared with a preset threshold value. A developing device characterized in that if there is less than a threshold, it is determined that there is no developer, and if the amount of change in the detection output of the magnetic permeability sensor is greater than or equal to the threshold, it is determined that there is developer. A developing device according to any one of claims 1 to 6,
An image carrier that forms an electrostatic latent image developed by the developer of the developing device;
An exposure device that exposes the image carrier to form an electrostatic latent image on the image carrier;
An image forming apparatus comprising: During the idling period in which the developer formed by mixing the toner and the carrier without stirring the image is generated, a magnetic field crossing the developer is generated from the magnetic permeability sensor, and the magnetic permeability of the developer is determined by the magnetic permeability sensor. While detecting, the control voltage for controlling the magnetic field strength applied to the magnetic permeability sensor is changed, the change amount of the detection output of the magnetic permeability sensor corresponding to the change of the control voltage is obtained, and the change amount of the detection output is calculated. A developer presence / absence determination method, wherein the presence / absence of developer is determined by comparing with a preset threshold value.

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