JPH11212351A - Electrophotographic recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent fogging from occurring even when the residual amount of toner in a developing device is reduced by changing a bias difference between voltage applied on a toner carrier and voltage applied on a supply roller corresponding to the detected residual amount of the toner. SOLUTION: The bias difference is formed between the voltage applied on a developing roller 15 and the voltage applied on the supply roller 14 in order to increase the supply amount of the toner from the roller 14 to the roller 15. For example, by applying the voltage of -300 V on the roller 15 and the voltage of $0450 V on the roller 14, respectively, the bias difference of 150 V is formed. Relating to this device, the bias difference changing means of a CPU 27 controls at least either the voltage applied on the roller 15 or the voltage applied on the roller 14 so that the bias difference may be small at the point when fogging density exceeds a tolerance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic recording apparatus.

[0002]

2. Description of the Related Art Conventionally, in a developing device of an electrophotographic recording apparatus, a developing roller and a supply roller are disposed inside,
The toner is supplied to the developing roller by the supply roller, and is then supplied to the photosensitive drum by the developing roller to form a toner image on the photosensitive drum.

FIG. 2 is a sectional view of a conventional electrophotographic recording apparatus. In the figure, 51 is a toner cartridge,
A hopper formed by the case of the developing device is disposed below the toner cartridge 51, and the toner 52 of the one-component developer dropped from the toner cartridge 51 stays in the hopper. 53 is a stirrer (shaker) formed in a crankshaft shape, 54 is a supply roller, and 55 is a developing roller.

Reference numeral 56 denotes a layer thickness regulating blade, 57 denotes a photosensitive drum, 58 denotes a charging roller, and 59 denotes a cleaning roller. Next, the operation of the developing device having the above configuration will be described. First, when a driving unit (not shown) is driven,
The stirrer 53, the supply roller 54, and the developing roller 55 are each rotated in the direction of the arrow. Then, the toner 52 staying in the hopper is supplied to the developing roller 55 with the rotation of the stirrer 53 and the supply roller 54.

Generally, the developing roller 55 and the supply roller 5
In the developing device having No. 4, in order to increase the amount of toner supplied from the supply roller 54 to the developing roller 55,
A potential difference, that is, a bias difference is formed between the voltage applied to the developing roller 55 and the voltage applied to the supply roller 54. For example, −300 is applied to the developing roller 55.
When a voltage of [V] is applied and a voltage of -450 [V] is applied to the supply roller 54, a bias difference of 150 [V] is formed.

The toner adhered in a layer on the surface of the developing roller 55 is thinned by a layer thickness regulating blade 56 to have a thickness of about several tens of microns. At this time, the toner 52 is charged by friction between the layer thickness regulating blade 56 and the developing roller 55. Then, the thinned and charged toner 52 is supplied to the developing roller 5.
5 is supplied to the photosensitive drum 57 with the rotation of 5.

On the other hand, the photosensitive drum 57 is rotated in the direction of the arrow, and the surface is uniformly charged by rotating the charging roller 58 in the direction of the arrow. Next, light is irradiated from the direction of arrow B by optical means (not shown) to form an electrostatic latent image on the photosensitive drum 57. Then, at the contact portion between the photosensitive drum 57 and the developing roller 55, that is, at the developing portion, the toner 52
Is attracted and adhered to the electrostatic latent image formed on the photosensitive drum 57 to form a toner image corresponding to the electrostatic latent image.

The toner image is transferred to a print medium such as paper (not shown) by a transfer device (not shown), and is fixed to the print medium by a fixing device (not shown). Printing is performed in this manner. Further, the toner 52 remaining on the photosensitive drum 57 after the transfer is completed is removed by rotating the cleaning roller 59 in the direction of the arrow.

[0009]

However, in the conventional electrophotographic recording apparatus, when the amount of the toner 52 in the hopper, that is, the remaining amount of the toner decreases, the toner 52 deteriorates. Then, the deteriorated toner 5
When the toner 2 is charged to the opposite polarity, in the developing section, the toner 52 is sucked and adhered to the portion of the photoreceptor drum 57 where the electrostatic latent image is not formed, and the phenomenon that the background is stained, that is, fogging occurs. Will happen.

In addition, since the proportion of the deteriorated toner 52 occupies as the remaining amount of toner decreases, the degree of fog on the photosensitive drum 57, that is, the fog density increases. FIG. 3 is a diagram showing the relationship between the remaining amount of toner and the fog density in a conventional developing device. In the figure, the horizontal axis represents the amount of remaining toner, and the vertical axis represents the fog density.

As shown in the figure, as the amount of remaining toner decreases, the fog density increases. An object of the present invention is to provide an electrophotographic recording apparatus capable of solving the problems of the conventional electrophotographic recording apparatus and preventing fogging from occurring even when the remaining amount of toner in the developing device is reduced. With the goal.

[0012]

For this purpose, in an electrophotographic recording apparatus according to the present invention, a toner carrier, a supply roller for supplying toner to the toner carrier, and a means for applying a voltage to the toner carrier are provided. Means for applying a voltage to the supply roller, toner remaining amount detecting means for detecting the remaining amount of toner in the developing device, and a voltage applied to the toner carrier in accordance with the detected remaining amount of toner. And a bias difference changing means for changing a bias difference between the bias voltage and a voltage applied to the supply roller.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of an electrophotographic recording apparatus according to an embodiment of the present invention, FIG. 4 is a perspective view of a driving portion of a stirrer of a developing device according to the embodiment of the present invention, and FIG. 5 is an embodiment of the present invention. FIG. 2 is a cross-sectional view of the electrophotographic recording device. In the figure, reference numeral 11 denotes a toner cartridge, and a hopper formed by a frame 25 of a developing device 26 is disposed below the toner cartridge 11, and a one-component developer dropped from the toner cartridge 11 into the hopper. Of the toner 12 stays. 13 is a stirrer made of a magnetic material formed in a crankshaft shape, 14 is a supply roller, and 15 is a developing roller as a toner carrier.

Reference numeral 16 denotes a layer thickness regulating blade, 17 denotes a photosensitive drum, 18 denotes a charging roller, 19 denotes a cleaning roller, and 20 denotes a toner remaining amount detecting means having a structure rotatable around a fulcrum A. A toner sensor 21 is a magnet embedded in the toner sensor 20, and a photo interrupter 22 is turned on / off in response to the operation of the lever 20a of the toner sensor 20.

Reference numeral 23 denotes a gear which is rotated by driving a driving means (not shown), and is supported by a frame 25. Reference numeral 24 denotes a projection attached to the gear 23. In the stirrer 13, the rotating shaft 13a
Is fitted (centered) in the center of the gear 23, but is supported independently of the gear 23, and can be engaged with the gear 23 in one direction to rotate. That is, when the gear 23 rotates in the direction of the arrow in FIG. 4, the projection 24 pushes the arm 13b of the stirrer 13 to rotate the stirrer 13 in the direction of the arrow.

Reference numeral 27 denotes the photo interrupter 2
2, a CPU for taking in the output signal of 2, a changeover switch 29,
A program ROM 31 stores a program for controlling the electrophotographic recording apparatus. Reference numeral 28 denotes a supply roller bias high-voltage power supply. The supply roller bias high-voltage power supply 28 is connected to the supply roller 14 of the developing device 26 and also to the developing roller 15 via a switch 29. . Reference numeral 30 denotes a developing roller bias high voltage power supply. The developing roller bias high voltage power supply 30
Connected to. The changeover switch 29 is connected to the CPU 27 and changes the voltage applied to the developing roller 15 to the voltage of the supply roller bias high voltage power supply 28 and the voltage of the development roller bias high voltage power supply 30 based on the instruction of the CPU 27. It is designed to switch.

Next, the operation of the developing device 26 having the above configuration will be described. First, the agitator 13, the supply roller 14, and the developing roller 15 are driven by driving the driving unit.
Are rotated in the directions indicated by the arrows, the toner 12 retained in the hopper is supplied to the developing roller 15 as the agitator 13 and the supply roller 14 rotate.

Generally, the developing roller 15 and the supply roller 1
In the developing device 26 having the number 4, in order to increase the supply amount of the toner 12 from the supply roller 14 to the development roller 15, the voltage between the voltage applied to the development roller 15 and the voltage applied to the supply roller 14 is increased. A bias difference is formed. For example, when a voltage of -300 [V] is applied to the developing roller 15 and a voltage of -450 [V] is applied to the supply roller 14, a bias difference of 150 [V] is formed.

The toner 12 adhered in a layer on the surface of the developing roller 15 is thinned by a layer thickness regulating blade 16 to a thickness of about several tens of microns. At this time, the toner 12 is charged by friction between the layer thickness regulating blade 16 and the developing roller 15. The thinned and charged toner 12 is supplied to the photosensitive drum 17 as the developing roller 15 rotates.

On the other hand, the photosensitive drum 17 is rotated in the direction of the arrow, and the surface is uniformly and uniformly charged by rotating the charging roller 18 in the direction of the arrow. Next, light is irradiated from the direction of arrow B by optical means (not shown) to form an electrostatic latent image on the photosensitive drum 17. Then, in the contact portion between the photosensitive drum 17 and the developing roller 15, that is, in the developing portion, the toner 12
Is attracted to and adheres to the electrostatic latent image formed on the photosensitive drum 17 to form a toner image corresponding to the electrostatic latent image.

The toner image is transferred to a print medium such as paper (not shown) by a transfer device (not shown), and is fixed to the print medium by a fixing device (not shown). Printing is performed in this manner. Further, the toner 12 remaining on the photosensitive drum 17 after the transfer is completed is removed by rotating the cleaning roller 19 in the direction of the arrow.

As shown in FIG. 5, when the stirrer 13 is placed at the position shown by the solid line, that is, when the crank pin portion 13c is near the bottom dead center,
The magnet 21 is attracted by the crank pin portion 13c, and the toner sensor 20 is placed at a position shown by a solid line.
To shield.

When the stirrer 13 is placed at a position other than the position shown by the solid line, for example, at the position shown by the broken line, the magnet 21 is not attracted by the crank pin portion 13c, and the toner sensor 20 is shown by the broken line by its own weight. The lever 20a does not block the photointerrupter 22 because the lever 20a is positioned at the right position. As described above, when the stirrer 13 is placed at a position other than the position shown by the solid line, the photo interrupter 22 turns on the output signal because it is not shielded by the lever 20a, and when the stirrer 13 is placed at the position shown by the solid line. , The output signal is turned off.

Therefore, by observing the waveform of the output signal of the photointerrupter 22, it is possible to know the time during which the stirrer 13 is placed at the position shown by the solid line. In the present embodiment, when the stirrer 13 is placed at a position other than the position indicated by the solid line, the output signal is turned on, and the stirrer 13 is turned on.
Is placed at the position shown by the solid line, the output signal is turned off. However, when the waveform of the output signal of the photointerrupter 22 is reversed and the stirrer 13 is placed at a position other than the position shown by the solid line, the output signal becomes When the stirrer 13 is turned off and is placed at the position shown by the solid line, the output signal can be turned on.

By the way, as described above, the stirrer 13
, The rotating shaft 13a is fitted into the center of the gear 23, but is supported independently of the gear 23.
Can be rotated in one direction with respect to
The stirrer 13 is rotated by pushing the arm 13b by the projection 24. Therefore, the stirrer 13
When the remaining amount of toner is sufficiently large, the arm 13b is rotated at a constant speed without separating from the protrusion 24 because the resistance of the toner 12 is always received. Arm 13b is separated from the projection 24 by its own weight.

Next, a method for detecting the remaining amount of toner in the electrophotographic recording apparatus having the above-described configuration will be described. FIG. 6 is a first diagram illustrating the operation of the stirrer according to the embodiment of the present invention, FIG. 7 is a second diagram illustrating the operation of the stirrer according to the embodiment of the present invention, and FIG. FIG. 9 is a third diagram showing an operation of the stirrer in the embodiment, FIG. 9 is a first diagram showing an output waveform of the photointerrupter in the embodiment of the present invention,
FIG. 10 is a second diagram showing an output waveform of the photo interrupter according to the embodiment of the present invention, and FIG. 11 is a third diagram showing an output waveform of the photo interrupter according to the embodiment of the present invention.
FIG. 12 is a diagram showing the relationship between the remaining amount of toner and the magnet suction time in the embodiment of the present invention. 6 to 8, the operation of the stirrer 13 is initially, 1
It is shown over time for 時 rotation, １ ／ rotation and 3/4 rotation. 12, the horizontal axis indicates the amount of remaining toner, and the vertical axis indicates the suction time t of the magnet 21 (FIG. 5) of the toner sensor 20 (FIG. 1).

As shown in FIG. 6, when the amount of remaining toner is sufficiently large, the agitator 13 always receives the resistance of the toner 12, so that the arm portion 13b does not separate from the protrusion 24 and is kept at a constant speed. Rotated. In this case, the output waveform of the photo interrupter 22 is as shown in FIG.

Here, the period of rotation of the gear 23 (FIG. 4) is T seconds, and the attraction time of the magnet 21 is t _n seconds (n
= 1, 2, 3,...), As shown in FIG.
The attraction time t of the magnet 21 in a state where the remaining amount of toner is sufficiently large is t ₁ as shown in FIG. As shown in FIG. 7, when the remaining amount of toner decreases to about half, the resistance of the toner 12 received by the stirrer 13 decreases. Since the portion 13b separates from the projection 24 by its own weight and tries to drop to the bottom dead center, the time during which the crank pin portion 13c is located near the bottom dead center becomes long. As a result, suction time t of the magnet 21, as shown in FIG. 10, it is a long t ₂ than t _1.

As shown in FIG. 8, when the remaining amount of the toner further decreases and the toner 12 hardly remains in the hopper, the time for the arm 13b to separate from the protrusion 24 becomes longer, and the crankpin since the time the part 13c is placed in the vicinity of the bottom dead center becomes longer, suction time t of the magnet 21, as shown in FIG. 11, the longer t ₃ than t _2.

Therefore, the toner remaining amount and the magnet 21
If the correlation with the suction time t is clear, the remaining amount of toner can be known by measuring the suction time t of the magnet 21. As shown in FIG. 12, as the remaining amount of toner decreases, the suction time t of the magnet 21 increases.
Becomes longer.

By the way, when the amount of the toner 12 when the hopper is filled with the toner 12 is 60 [g], the maximum value of the fog density allowed in a general use condition of the electrophotographic recording apparatus is as follows. It is about 10%, but the minimum value of the remaining amount of toner corresponding to the maximum value is about 17 to 18 g in FIG. Further, as shown in FIG. 12, suction time t of the magnet 21 when the toner remaining amount is about 17 to 18 [g] becomes t _x.

[0032] That is, suction time t of the magnet 21 is more than t _x, so that the fog density unacceptable. Therefore, the CPU27 measures the suction time t of the magnet 21, when the measured suction time t becomes t _x, so as to prevent the fog density increases. In FIG. 12, AR1 is an area where print fading occurs.

Next, the operation of the CPU 27 will be described. FIG. 13 is a diagram showing the relationship between the bias difference between the developing roller and the supply roller and the fog density in the embodiment of the present invention, and FIG. 14 is a flowchart showing the operation of the developing roller application bias switching process in the embodiment of the present invention. FIG. 15 is a diagram showing the relationship between the remaining amount of toner and the fog density in the embodiment of the present invention. In FIG. 13,
In FIG. 15, the horizontal axis shows the bias difference, the vertical axis shows the fog density, and in FIG. 15, the horizontal axis shows the remaining amount of toner, and the vertical axis shows the fog density.

As described above, in the developing device 26 having the developing roller 15 (FIG. 1) and the supply roller 14, the toner 12 from the supply roller 14 to the developing roller 15
In order to increase the supply amount (FIG. 5), the developing roller 15
, And a bias difference is formed between the voltage applied to the supply roller 14. For example, the developing roller 1
5, a voltage of -300 [V] is applied to the supply roller 14;
When a voltage of 450 [V] is applied, 150
A bias difference of [V] is formed.

As shown in FIG. 3, when the remaining amount of toner becomes 10 g, the fog density becomes 15 g.
〔%〕become. FIG. 13 shows that the bias difference is 150
It represents the fog density as it is reduced from [V].
In this case, as the bias difference becomes smaller, the fog density becomes lower, which is the maximum value of 10 which is allowable in a general use condition of the electrophotographic recording apparatus.
It turns out that it becomes lower than [%].

This is because the toner 12 is transferred from the developing roller 15 to the photosensitive drum 17 as the bias difference decreases.
It is considered that the suction force for sucking the toner is reduced, and the toner 12 having the deteriorated charging characteristic does not adhere to the portion of the photosensitive drum 17 where the electrostatic latent image is not formed. Therefore, the bias difference changing means (not shown) of the CPU27, the time at which the fog density exceeds the allowable range, i.e., when the suction time t of the magnet 21 becomes t _x, as a bias difference becomes smaller, If at least one of the voltage applied to the developing roller 15 and the voltage applied to the supply roller 14 is controlled, it is possible to prevent the fog density from increasing even if the remaining amount of toner decreases.

That is, the remaining amount of toner decreases and the toner 1
2 is deteriorated, and even if the deteriorated toner 12 is charged to the opposite polarity, the bias difference is reduced, so that the amount of the toner 12 supplied from the supply roller 14 to the developing roller 15 is reduced, and It is possible to prevent the toner 12 from adhering to the portion where the electrostatic latent image is not formed on the surface 17 and to cause fogging.

The fog density does not increase even if the ratio of the deteriorated toner 12 increases. When the voltage applied to the developing roller 15 can be changed by the developing roller bias high voltage power supply 30, the voltage of the developing roller bias high voltage power supply 30 is reduced without using the changeover switch 29. Thus, the voltage may be equal to the voltage of the supply roller bias high voltage power supply 28.

Furthermore, if the bias difference is small, the fog density can be lowered even if it is not always zero.
Therefore, it is not always necessary to make the voltage of the developing roller bias high voltage power supply 30 equal to the voltage of the supply roller bias high voltage power supply 28. Next, the flowchart will be described. Step S1 The CPU 27 executes the operation of the photo interrupter 2 according to the program stored in the program ROM 31.
The waveform of the output signal of No. 2 is monitored, and the attraction time t of the magnet 21 is measured. Suction time t in Step S2 magnet 21 determines whether shorter than t _x. If the suction time t is shorter than t _x , the process proceeds to step S3. If the suction time t is longer than t _x , the process proceeds to step S4. Step S3: When it is determined that the remaining amount of toner is sufficiently large, the bias difference changing means switches the changeover switch 29,
The voltage of the developing roller bias high voltage power supply 30 is applied to the developing roller 15, and the voltage of the supply roller bias high voltage power supply 28 is applied to the supply roller 14. For example, the developing roller 1
5 is supplied with a voltage of -300 [V], and
A voltage of 0 [V] is applied. Step S4: When it is determined that the remaining amount of toner is low, the bias difference changing unit switches the switch 29 to apply the voltage of the supply roller bias high voltage power supply 28 to the developing roller 15 and the supply roller 14. For example, a voltage of -450 [V] is applied to the developing roller 15 and the supply roller 14, respectively. As a result, the bias difference is set to zero.

As described above, the suction time t of the magnet 21 is
When the voltage of the supply roller bias high-voltage power supply 28 is applied to the developing roller 15 at the time when the time t has reached _tx , the relationship between the remaining amount of toner and the fog density is as shown by the solid line in FIG. The broken line indicates the relationship between the remaining amount of toner and the fog density in the related art. As can be seen from FIG. 15, it is possible to prevent the fog density from increasing even if the remaining amount of toner decreases.

The present invention is not limited to the above-described embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0042]

As described above in detail, according to the present invention, in an electrophotographic recording apparatus, a toner carrier,
A supply roller that supplies toner to the toner carrier, a unit that applies a voltage to the toner carrier, a unit that applies a voltage to the supply roller, and a remaining toner amount detector that detects a remaining amount of toner in the developing device Means for changing a bias difference between a voltage applied to the toner carrier and a voltage applied to the supply roller in accordance with the detected amount of remaining toner.

In this case, the remaining amount of toner is detected, and the bias difference is changed in accordance with the remaining amount of toner. Therefore, even if the remaining amount of toner is reduced and the toner is deteriorated and the deteriorated toner is charged to the opposite polarity, the bias difference is reduced, so that the electrostatic latent image on the photosensitive drum is not formed. It is possible to prevent the toner from adhering to the portion and causing fogging.

The fog density does not increase even if the ratio of the deteriorated toner increases.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electrophotographic recording apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional electrophotographic recording apparatus.

FIG. 3 is a diagram illustrating a relationship between a remaining toner amount and a fog density in a conventional developing device.

FIG. 4 is a perspective view of a driving portion of a stirrer of the developing device according to the embodiment of the present invention.

FIG. 5 is a cross-sectional view of the electrophotographic recording apparatus according to the embodiment of the present invention.

FIG. 6 is a first diagram illustrating an operation of the stirrer according to the embodiment of the present invention.

FIG. 7 is a second diagram showing the operation of the stirrer according to the embodiment of the present invention.

FIG. 8 is a third diagram showing the operation of the stirrer according to the embodiment of the present invention.

FIG. 9 is a first diagram illustrating an output waveform of the photointerrupter according to the embodiment of the present invention.

FIG. 10 is a second diagram illustrating an output waveform of the photointerrupter according to the embodiment of the present invention.

FIG. 11 is a third diagram showing an output waveform of the photo interrupter according to the embodiment of the present invention.

FIG. 12 is a diagram illustrating a relationship between a remaining amount of toner and a magnet suction time according to the embodiment of the present invention.

FIG. 13 is a diagram illustrating a relationship between a bias difference between a developing roller and a supply roller and fog density in the embodiment of the present invention.

FIG. 14 is a flowchart illustrating an operation of a developing roller application bias switching process according to the embodiment of the present invention.

FIG. 15 is a diagram illustrating a relationship between a remaining amount of toner and a fog density according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 14 supply roller 15 developing roller 20 toner sensor 26 developing device 27 CPU 28 high voltage power supply for supply roller bias 30 high voltage power supply for development roller bias

Claims (2)

[Claims] 1. A toner carrier, (b) a supply roller for supplying toner to the toner carrier, (c) means for applying a voltage to the toner carrier, and (d) the supply roller. Means for applying a voltage to the toner carrier, (e) a toner remaining amount detecting means for detecting the remaining amount of toner in the developing device, and (f) a voltage applied to the toner carrier in accordance with the detected remaining amount of toner. An electrophotographic recording apparatus comprising: a bias difference changing unit configured to change a bias difference between a voltage and a voltage applied to the supply roller. 2. The electrophotographic recording apparatus according to claim 1, wherein the bias difference changing unit changes a voltage applied to the toner carrier in accordance with the detected remaining amount of toner.