JPH08146768A - Developing device - Google Patents

Abstract

PURPOSE: To keep the developer carrying force of a developing roller proper. CONSTITUTION: A pressure sensor 45 is arranged near the developing roller 32. The developer is carried to an electrostatic latent image on a photoreceptor 7 by the rotation of the sleeve 32b of the developing roller 32. The pressure sensor 45 detects a change in the pressure of the developer on its surface. When the pressure detected by the sensor 45 is low, the device judges that the developer carrying force is decreased, and therefore it increases the rotating speed of the sleeve 32b by a carrying force control means 60. Consequently an amount that the developer is carried is increased. When the pressure detected by the sensor 45 is high, the rotating speed of the sleeve 32b is decreased. As a result, the amount that the developer is carried is decreased and image density is made stable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for visualizing an electrostatic latent image formed on a surface of a photoconductor by a two-component developer in an electrophotographic image forming apparatus such as a copying machine or a laser printer. .

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a laser printer, as a means for developing an electrostatic latent image on a photosensitive member, a sleeve surrounding a developing roller is rotated and a magnetic brush is applied to the sleeve surface. A developing device is widely used in which a magnetic brush is formed and the magnetic brush slides on the electrostatic latent image. In recent years, the speed of image forming apparatuses has been increased. For example, a high-speed model having a copy speed of 40 (sheets / minute) has a copy speed of 30 (sheets / sheet).
If you try to use the developing device used in the conventional model as it is, the rotation speed (rotation speed) of the sleeve of the developing roller is fixed, and the image quality characteristic of the magnetic brush is fixed. Therefore, there is a problem that, for example, a document image with solid black or many characters may have a blur, and on the other hand, a document image with halftone may have a problem that the reproducibility of the density change deteriorates. ing.

On the other hand, in order to obtain a good image by increasing the contrast in accordance with the original image or, conversely, by improving the halftone reproducibility, Japanese Patent Laid-Open No. 233467/1990 discloses that A developing device is disclosed that includes a sleeve that supports a magnetic brush that is rotatably provided around a magnet roll, and a drive device that rotates the sleeve at different rotational speeds. In this developing device, the rotation speed of the sleeve can be switched between high speed rotation (300 rotations / minute) and low speed rotation (200 rotations / minute) by the operator operating an operation button provided on the copying machine main body. Is usually set to high speed rotation,
If the original is solid black or has many characters, copy at high speed. When the original is a halftone image such as a photograph, the rotation speed of the sleeve is switched to low speed rotation by the operation button to perform copying.

[0004]

However, in a developing device using a two-component developer composed of a carrier and a toner, image quality deterioration such as decrease in image density and increase in fog usually occurs as the number of copies increases. Occurs. Many of these causes are due to deterioration of the developer and changes in the toner concentration. Further, not only the deterioration of the developer but also the development system that conveys the developer to the electrostatic latent image on the surface of the photoreceptor is often caused. Therefore, in the developing device disclosed in Japanese Unexamined Patent Publication No. 1-233467, the rotation speed of the sleeve of the magnet roll is simply switched according to the original, so that it is not possible to prevent the decrease in image density due to the deterioration of the developer. There is a problem that the developing performance cannot be kept constant.

In another conventional developing device, deterioration of image quality is prevented by detecting the toner concentration of the developer with a transmittance sensor or the like and controlling the toner concentration of the developer to be always constant. However, if the developer cannot be conveyed to the electrostatic latent image on the photoconductor in an appropriate amount in a stable state, the image density is changed. In other words, even if the toner density of the developer is kept constant, a problem such as a change in image density is caused due to a change in the developer carrying force by the magnet roll itself. It has reached the present without any measures taken.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a developing device for stabilizing the image density by appropriately maintaining the conveying force of the developer by the developing roller.

[0007]

As shown in FIG. 1, a means for solving the problems according to the present invention includes a developing roller 32 rotatably supported in a developing tank 30 and a spike of a developer on the developing roller 32. A doctor 35 for regulating is internally provided, and a carrying force detecting means (pressure sensor) for detecting the carrying force of the developer carried to the electrostatic latent image formed on the surface of the photoconductor 7 by the rotation of the developing roller 32. 45 and the conveying force detecting means 45
And a carrying force control means 60 for making the carrying force of the developer constant based on the detection result. The carrying force control means 60 controls the rotation speed of the developing roller 32.

In order to accurately detect the developer carrying force, the carrying force detecting means 45 is arranged upstream of the doctor 35 near the developing roller in the developer carrying direction so as not to affect the image quality. , The carrying force of the developer is controlled except during the development.

Further, a toner concentration control means 61 for keeping the toner concentration of the developer constant is provided, and the toner concentration is controlled except when the developer carrying force is controlled.

[0010]

In the above means for solving problems, the conveying force detecting means 4
5 detects the developer conveyed to the electrostatic latent image on the photoconductor 7 by the rotation of the developing roller 32. At this time, the carrying force detecting means 45 detects the developer on the upstream side of the doctor 35 in the developer carrying direction, so that the carrying force of the developer is accurately detected. If it is determined that the developer carrying force is not appropriate based on the detection result, the carrying force control means 60 controls the rotation speed of the developing roller 32 to keep the developer carrying force constant. In this way, since the carrying force control is performed at times other than during development, the image density is stabilized without affecting the image quality.

Further, the toner density of the developer is detected except when the carrying force is controlled, and the toner density control means 61 keeps the toner density of the developer constant, thereby obtaining a more stable image density.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A copying machine according to an embodiment of the present invention is, as shown in FIG. 2, a document placing table 2 provided on an upper portion of a copying machine main body 1.
An exposure device 6 including a lamp 3, a lens 4 and a mirror 5, a photoconductor 7 on which an electrostatic latent image is formed and rotationally driven by a drive device (not shown), and a main charger 8 for uniformly charging the photoconductor surface. , A developing device 9 that develops by attaching toner to the electrostatic latent image on the surface of the photoconductor, a transfer charger 10 that transfers the toner image on the surface of the photoconductor to a sheet, and a sheet on which the toner image is transferred on the surface of the photoconductor. A peeling charger 11 for peeling the surface of the photoconductor, a cleaning device 12 for cleaning the surface of the photoconductor, a destaticizing device 13 for destaticizing the electrostatic charge on the surface of the photoconductor, and a paper feeding device 15 for guiding the paper from the paper feeding cassette 14 to the photoconductor 7 side. And a conveyor belt 16 for conveying the paper separated from the surface of the photoconductor, and the paper from the conveyor belt 16 is pressed and heated by the upper and lower two heating rollers 17, 18 to fix the toner. A fixing device 19 which is constructed from the sheet discharge roller 21 for feeding the paper to the discharge tray 20. An exposure unit 22 is irradiated with the reflected light from the exposure device 6. When the power switch is turned on and the heating rollers 17, 18 of the fixing device 19 reach a sufficient temperature, copying is possible.

As shown in FIG. 1, the developing device 9 includes a developing tank 30 in which a two-component developer composed of a carrier and a toner is stored.
And a toner replenishing section 31 for replenishing the developing tank 30 with toner, the developing tank 30 being rotatably supported by the developing tank 32, and a pair of rotatable stirring rollers 33, 34 for stirring the developer. A doctor 35 for controlling the rising of the developer on the developing roller 32 and a toner concentration detection sensor 36 for detecting the toner concentration of the developer are incorporated. Reference numeral 37 is a discharge port for discharging the developer to the outside, and 38 is a shutter for opening and closing the discharge port 37.

The toner replenishing section 31 comprises a toner hopper 40 mounted on the upper part of the developing tank 30 and a toner replenishing roller 42 arranged at a toner replenishing port 41 of the toner hopper 40 communicating with the developing tank 30. Roller 42
When the toner density detection sensor 36 detects a decrease in the toner density of the developer, the toner density detection sensor 36 is driven via a drive unit (not shown) such as a toner motor or the like in response to a signal from a control unit.

The toner concentration detecting sensor 36 is a magnetic permeability sensor which converts the magnetic permeability of the developer into a voltage and outputs the voltage, and is fixed to the tank wall of the developing tank 30 so as to face the stirring roller 34. The toner concentration detection sensor 40 has a characteristic that its output voltage increases when the toner consumption in the developing tank 30 increases and the toner concentration decreases.

The developing roller 32 is disposed facing the photoconductor 7, is fixed to the developing tank 30, and magnetically attracts the developer to form a magnetic brush. It is composed of a cylindrical sleeve 32b loosely rotatably fitted, and the sleeve 32b is driven in multiple stages via a drive device (not shown) composed of a DC servo motor or the like in response to a signal from a control unit described later.

The doctor 35 is made of, for example, an extruded aluminum product or stainless steel.
Is fixed to the developing tank 30 with a space of about 0.5 mm from the sleeve surface.

The developing device 9 is provided with a carrying force detecting means for detecting the carrying force of the developer carried to the electrostatic latent image formed on the surface of the photoconductor by the rotation of the sleeve 32b of the developing roller 32. Has been. The carrying force detecting means is a pressure sensor 45, which is arranged on the upstream side of the doctor 35 in the developer carrying direction, and has a distance (about 0.5 m) between the doctor surface and the sleeve surface with respect to the sleeve surface.
m) and is attached to the developing tank 30 at intervals of 5 mm or less. The pressure sensor 45 changes the movement amount (conveyance amount) of the developer per unit area on the sleeve surface due to the deterioration of the developer and the change of fluidity, that is, It detects a pressure change, converts it into a voltage, and outputs it. The output voltage decreases when the pressure applied to the pressure sensor 45 increases, and the output voltage increases when the pressure applied to the pressure sensor 45 decreases. ing. The closer the distance between the pressure sensor 45 and the surface of the sleeve is, the better. However, if the distance is too close, the pressure sensor 45 impedes the flow of the developer, and the effect appears on the image. On the contrary, if the distance is too far, the change in the pressure of the developer cannot be properly detected, and as a result of the experiment, it is set as described above (preferably 1.0 mm to
2.5 mm spacing).

On the upper surface of the copying machine body 1, a copy start switch, a key input section for setting the number of copies, copy contents, etc., and an LED for copy contents, the status of each section, etc.
Is provided or an operation panel (not shown) including a display unit for displaying pictograms or the like on the liquid crystal display panel is provided, and the copier is provided with each operation based on the contents set by the switches and keys on the operation panel. A control unit 50 that comprehensively controls the operation of the apparatus is provided.

The control unit 50, as shown in FIG.
A D / A converter 52 for converting a control signal from the CPU 51 into an analog signal, and the toner motors 53 and D based on the analog signal converted by the D / A converter 52.
Driver circuit 5 for controlling the rotation of the C servo motor 54, etc.
And 5. The CPU 51 has a function of sending a control signal to each unit based on the contents set by the user to execute a normal copy cycle or the like, and based on the output signal from the pressure sensor 45, the development in the developing roller 32 is performed. A conveying force control means 60 for making the conveying force of the agent constant,
Toner concentration control means 61 for keeping the toner concentration of the developer constant based on the output signal from the toner concentration detection sensor 36.
Are provided.

The carrying force control means 60 controls the rotational speed of the sleeve 32b of the developing roller 32 based on the detection result of the carrying force of the developer by the pressure sensor 45, and the reference voltage to which the output voltage from the pressure sensor 45 is set. If the value is lower than the value, it is determined that the developer carrying force is strong (the carrying amount is large), and the rotation speed of the sleeve 32b is reduced. If the output voltage is higher than the reference value, the developer carrying force is decreased. It is determined that the sleeve 32b is weak (the amount of conveyance is small), and the rotation speed of the sleeve 32b is increased.

In the control unit 50, the developer carrying force control by the carrying force control means 60 is performed at a time other than copying, that is, at the time of pre-rotation after the power switch is turned on (during the preheating period) or as shown in FIG. The copy start switch is turned on and the setting is performed after A seconds have elapsed since the drive of the main motor and the DC servo motor 54 of the developing roller 32 was started. Further, the copy cycle is started B seconds after the conveyance force control is completed.

The toner concentration control means 61 controls the drive of the toner replenishing roller 42 according to the toner concentration detection result of the toner concentration detection sensor 36, and the output voltage from the toner concentration detection sensor 36 becomes higher than the reference value. At this time, it is determined that the toner concentration of the developer has decreased, and the toner replenishing roller 42 is driven by the toner motor 53. Then, the toner concentration control is set to be performed at the time other than the developer carrying force control, that is, from the start of the copy cycle to the stop of the rotation of the sleeve 32b of the developing roller 32 as shown in FIG. .

The adjusting operation for stabilizing the image density in the copying machine constructed as described above will be described with reference to the timing chart of FIG. 4 and the flowcharts of FIGS. First, when the copy start switch is pressed,
DC of the developing roller 32 while the main motor is driven
The servo motor 54 is driven to rotate the sleeve 32b at the set speed. Then, the developer in the developing tank 30 is agitated by the agitating rollers 33 and 34 and is supplied to the developing roller 32 side, and the developer adsorbed on the sleeve surface is regulated by the doctor 35 so that the ears of the developer can be prevented.
The developing roller 32 is moved by the rotation of 2b.

At this time, if the amount of the developer conveyed to the photoconductor 7 changes due to a change in the state such as the deterioration of the developer or the decrease in the attracting force of the developer on the developing roller 32, the image density is changed. Change and defective development occurs. Therefore, in order to keep the amount of developer conveyed to the photoconductor 7 side properly, it is necessary to detect the amount of developer conveyed, and the pressure sensor 45 detects the amount of developer conveyed on the upstream side of the doctor 35 in the conveying direction. Is detected. In other words, if the pressure sensor 45 is arranged in the area downstream of the doctor 35 before sliding contact with the electrostatic latent image of the photoconductor 7, it interferes with the spikes regulated by the doctor 35, and thus the developer spikes. There is a problem that a standing defect occurs and affects an image. Further, in the area of the photoconductor 7 after sliding contact with the electrostatic latent image, the developer after development is detected, and it is not possible to detect an appropriate developer conveyance amount. .

The pressure sensor 45 converts the amount of developer conveyed, that is, the pressure of the developer applied to the sensor surface into a voltage, and continuously transmits the output voltage to the controller 50. During the preheating period immediately after the switch is turned on or immediately after the developing roller 32 is activated, the flow of the developer is unstable, and accurate information on the pressure change of the developer cannot be obtained. After the roller 32 is activated, it waits for A seconds, during which the output signal from the pressure sensor 45 is not read.

After a lapse of A seconds, the CP of the control unit 50
U51 reads the output voltage sent from the pressure sensor 45 and compares the output voltage with the set reference value. And when this output voltage is higher than the reference value,
It is determined that the developer carrying force is weak, and the rotation speed of the sleeve 32b is increased. Then, the amount of developer conveyed by the sleeve 32b increases, the output voltage of the pressure sensor 45 decreases, and when the output voltage from the pressure sensor 45 reaches a reference value, the rotation speed of the sleeve 32b increases. Stop and finish the rotation speed setting. Sleeve 32b
The rotational speed at this point is maintained, and copying is performed at this rotational speed thereafter.

On the other hand, when the output voltage from the pressure sensor 45 is lower than the reference value, it is judged that the developer carrying force is strong, and the rotation speed of the sleeve 32b is lowered to carry the carried developer. The amount decreases and the output voltage of the pressure sensor 45 decreases. Then, when the output voltage reaches the reference value, the reduction of the rotation speed of the sleeve 32b is stopped, and thereafter, the sleeve 32b rotates at the rotation speed at this point.

After the lapse of B seconds, the CP of the control unit 50
U51 judges that the setting of the rotation speed of the sleeve 32b is completed, and the copying process is started based on the contents set by the user through the operation panel. At this time, the sleeve 32b of the developing roller 32 is driven at the set rotation speed until the next copy start switch is pressed.

When the copy process starts, the CPU 51 of the control unit 50 reads the output voltage from the toner concentration detection sensor 36 and controls the toner concentration of the developer. At this time, it is determined whether the output voltage from the toner concentration detection sensor 36 is higher or lower than the reference value,
When the output voltage is high, it is determined that the toner concentration of the developer is low, and the toner motor 53 is driven. Then, the toner supply roller 42 rotates, and the toner hopper 40
The toner inside is replenished from the toner replenishing port 41 into the developing tank 30. After that, when the output voltage from the toner concentration detection sensor 36 reaches the reference value, it is determined that the toner concentration of the developer has become appropriate, and the driving of the toner motor 53 is stopped,
The rotation of the toner supply roller 42 stops and the toner supply is completed. Then, the toner concentration control is repeatedly performed until the main motor and the sleeve 32b of the developing roller 32 are stopped after the copying process is completed.
When the output voltage from the toner concentration detection sensor 36 is lower than the reference value, the toner motor 53 is not driven.

In this way, the sleeve 3 of the developing roller 32 is
Since the change in the pressure of the developer conveyed by 2b is detected and the rotation speed of the sleeve 32b is controlled based on the detection result, the developer conveying force is always maintained properly. Therefore, even if the developer deteriorates, the rotation speed of the sleeve 32b is changed to increase the developer conveying force, and a constant amount of the developer is always conveyed to the electrostatic latent image on the surface of the photoconductor. The density is stable, development defects such as fog are suppressed, and stable image quality can be obtained.

Then, between the time when the copy start switch is pressed and the time when copying is started, the developing roller 32
Since the rotation speed of the sleeve 32b is controlled after a slight delay after the rotation of the sleeve 32b, it is possible to detect an accurate change in the carrying force in a state where the flow of the developer is stable. That is, if the rotation speed of the sleeve 32b is changed during copying, naturally there is an inflection point at which the developer conveying force changes, and the flow of the developer becomes temporarily unstable, leading to a change in image quality. , Sleeve 32b except during copying
By controlling the rotation speed of (1), stable image density can be obtained during copying, and development failure such as image quality change does not occur.

Further, since the pressure sensor 45 is arranged on the upstream side of the doctor 35 in the developer conveying direction, an appropriate pressure change of the developer can be detected, and the spike of the developer on the sleeve surface can be detected. It has no adverse effect. Moreover, since the pressure sensor 45 is arranged at a position within 5 mm wider than the distance between the sleeve 32b and the doctor 35 with respect to the sleeve surface, it does not hinder the flow of the developer and causes a problem on the image. Do not give. Therefore, since appropriate information on the pressure change of the developer can be obtained, the rotation speed of the sleeve 32b can be reliably controlled, and the image density can be stabilized.

Furthermore, since the toner concentration of the developer is controlled during copying other than when the rotational speed of the sleeve 32b is controlled, which is performed when the flow of the developer is unstable, a stable toner concentration can be obtained and a further image can be obtained. The concentration can be stabilized.

The present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention. For example, in this embodiment, the rotation speed of the sleeve 32b of the developing roller 32 is controlled to keep the developer carrying force constant, but the bias voltage applied to the developing roller 32 is controlled to control the magnetic force of the magnet body 32a. The carrying force of the developer may be made constant by changing the force. Further, the amount of developer conveyed to the developing roller 32 side may be adjusted by controlling the rotation speeds of the stirring rollers 33 and 34.

Then, the pressure sensor 45 is used as the developer carrying force detecting means to detect the amount of movement of the developer by the change in the pressure of the developer. It may be detected directly.

Further, the developer carrying force control is performed between the time when the copy start switch is turned on and the time when the copy process is started. However, it may be performed during the preheating period after the power switch is turned on or after the copy process is completed.

[0038]

As is apparent from the above description, according to the present invention, the conveying force of the developer conveyed by the developing roller is detected, and the rotation speed of the developing roller is controlled on the basis of the detection result. Therefore, even if the developer deteriorates, the developer conveying force is always kept proper. Therefore, a constant amount of developer is always conveyed to the electrostatic latent image on the surface of the photoconductor, so that the image density is stable, development defects such as fogging are suppressed, and good image quality can be obtained. Further, even if the developer deteriorates, good image quality can be obtained, so that the developer can be used for a long time, the frequency of replacement of the developer can be reduced, and resource saving can be achieved.

Since the developer carrying force is controlled at times other than during development, a stable image density can be obtained during development, and development failure such as image quality change does not occur. Moreover, since the conveying force detecting means is arranged on the upstream side of the doctor in the conveying direction of the developer, an appropriate change in the conveying force of the developer can be detected, and the spikes of the developer on the surface of the developing roller by the doctor can be detected. Will not be adversely affected. Therefore, the developer carrying force can be reliably controlled and the image density can be stabilized.

Further, since the toner concentration of the developer is controlled except when the developer carrying force is controlled so that the flow of the developer becomes unstable, a stable toner concentration is obtained and the image density is further stabilized. Is planned.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a developing device according to an embodiment of the present invention.

[Fig. 2] Overall configuration of copier

FIG. 3 is a block diagram of a control unit.

FIG. 4 is a timing chart showing an image density adjusting operation.

FIG. 5 is a flow chart of developer carrying force control.

FIG. 6 is a flowchart of toner density control

[Explanation of symbols]

 7 Photoreceptor 30 Developing Tank 32 Developing Roller 35 Doctor 45 Pressure Sensor 60 Conveying Force Control Means 61 Toner Density Control Means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G03G 15/09 Z

Claims (5)

[Claims] 1. A developing device in which a developing roller, which is rotatably supported, and a doctor, which regulates the rising of the developer on the developing roller, are provided in a developing tank. Carrying force detecting means for detecting the carrying force of the developer carried to the electrostatic latent image formed on the surface of the sheet, and carrying force for making the carrying force of the developer constant based on the detection result of the carrying force detecting means. A developing device comprising: a control unit. 2. The developing device according to claim 1, wherein the carrying force control means controls the rotation speed of the developing roller. 3. The developing device according to claim 1, wherein the carrying force of the developer is controlled by the carrying force control means except during development. 4. The developing device according to claim 1, wherein the carrying force detecting means is arranged upstream of the doctor near the developing roller in the developer carrying direction. 5. The developing device according to claim 3, further comprising a toner density control unit that keeps the toner density of the developer constant, and the toner density is controlled except when the developer carrying force is controlled.