JP3301404B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used for developing an electrostatic latent image formed on an image carrier in an image forming apparatus such as a copying machine or a printer. A developer carrier to be held and an image carrier on which an electrostatic latent image is formed are provided so as to face each other with a required interval, and an AC voltage is applied to the developer carrier, and the developer carrier is In a developing device in which an AC electric field is applied between the image carrier and the developing device, the developer held on the developer carrier is supplied to an electrostatic latent image formed on the image carrier to perform development.
Even when the distance between the developer carrier and the image carrier fluctuates, the density of the formed image does not fluctuate greatly, and a good image having a stable image density can be obtained. The feature of the present invention resides in the following point.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, various developing devices have been used to develop an electrostatic latent image formed on an image carrier.

In such a developing device, a developer carrier is provided so as to be in contact with the image carrier, and the developer is guided by the developer carrier to a development area in contact with the image carrier to perform development. A developing device of a contact developing system, which is to be carried out, and a developer carrier are provided so as to face the image carrier at a predetermined interval, and the developer is used by the developer carrier to a developing area facing the image carrier. Then, an AC voltage is applied to the developer carrier to cause an AC electric field to act between the developer carrier and the image carrier, thereby supplying the developer to the electrostatic latent image formed on the image carrier. There is known a non-contact developing type developing apparatus which performs development by using a developing method.

Here, in the case of the above-described contact developing type developing device, since the developing is performed by bringing the developer into contact with the image bearing member,
Although excellent in the reproducibility of the electrostatic latent image formed on the image carrier, the developer also adheres to non-image portions where the electrostatic latent image is not formed, and fogging occurs in the formed image, There has been a problem that the surface of the image carrier is worn by the developer carrier.

On the other hand, in the case of a non-contact developing type developing device in which a developer carrying member is provided so as to be opposed to an image carrying member at a predetermined interval, the above-described problems in the contact developing type developing device are reduced. .

However, in the case of such a non-contact developing type developing apparatus, for example, the molding accuracy and the mounting accuracy of the image carrier and the developer carrier are poor, so that the image carrier and the developer carrier cannot be connected to each other. The distance may fluctuate, and when the distance between the developer carrier and the image carrier becomes smaller, the AC electric field acting between the developer carrier and the image carrier becomes stronger, and the density of the formed image becomes lower. On the other hand, when the distance between the developer carrier and the image carrier increases, the AC electric field acting between the developer carrier and the image carrier weakens, and the density of the formed image decreases. However, there is a problem that density unevenness or the like occurs in an image formed by the above method, and a good image having a stable image density cannot be obtained.

[0007]

According to the present invention, a developer is held on a developer carrier, and the developer is guided to a developing area opposed to the image carrier at a predetermined interval. To solve the above-described problem in a developing device in which an AC voltage is applied to the developing device to perform the development by supplying the developer from the developer carrier to the electrostatic latent image formed on the image carrier. It is an issue.

That is, according to the present invention, in the above-described developing device, when the distance between the developer carrier and the image carrier fluctuates, the change in the density of the formed image is suppressed. It is another object of the present invention to stably obtain a good image having a low density unevenness and a constant image density.

[0009]

In order to solve the above-mentioned problems, the developing device according to the present invention holds a developer on a developer carrier, and transfers the developer to the image carrier at a required distance. A developing device that supplies a developer to the electrostatic latent image formed on the image carrier by applying an AC voltage composed of a rectangular wave from a power supply to the developer carrier, A capacitor, a resistor, and a rectifying element are connected in parallel between the power supply and the developer carrier, and the rectifying element is connected by a voltage in a direction in which the developer is sent to the image carrier at the AC voltage having the rectangular wave. The connection was made in such a direction as to cut off the current.

Here, as in the developing device according to the present invention, when applying an AC voltage composed of a rectangular wave from a power source to a developer carrier opposed to the image carrier at a predetermined distance from the image carrier, a power source and a developer are used. A capacitor, a resistor, and a rectifying element are connected in parallel with the carrier, and the rectifying element is used to cut off the current caused by the voltage in the direction in which the developer is sent to the image carrier at the AC voltage having the rectangular wave. When represented by an equivalent circuit, the case of connecting to
A capacitor element C, a resistance element R, and a rectifier element Re connected in the above-described direction are provided between a power supply S and a capacitor element Cd composed of an image carrier and a developer carrier opposed to each other with a required interval. Are represented as circuits connected in parallel.

In such a circuit, when the power supply S outputs an AC voltage composed of a rectangular wave as shown by broken lines in FIGS. 2A and 2B, the rectifier element Re
Is connected in the direction of sending the developer to the image carrier at the AC voltage composed of the rectangular wave, that is, in the direction of interrupting the current caused by the voltage in the developing direction, so that the developer returns to the developer carrier, that is, When a voltage in the recovery direction acts, a current flows through the rectifier element Re, and a voltage Vd applied across the capacitor element Cd.
Becomes equal to the voltage peak value Vp1 in the recovery direction output from the power supply S.

On the other hand, the direction in which the developer is sent to the developer carrier,
That is, when the voltage in the developing direction acts, the voltage Vd applied across the capacitor element Cd is constituted by the voltage peak value Vp2 in the developing direction output from the power supply S, and the image carrier and the developer carrier. a capacitor element capacitance C ₁ of Cd that is expressed by the following equation by the capacitance C ₂ of the capacitor element C. _{Vd = Vp2 × C 2 / (} C 1 + C 2)

[0013] Here, the distance d between the image bearing member and the developer carrying member is reduced, the value of the capacitance C ₁ in the capacitor element Cd is increased, as shown by the solid line in FIG. 2 (A), a capacitor element Cd Is smaller than the voltage peak value Vp2 in the developing direction output from the power supply S. For this reason, the average voltage value VL 'of the AC voltage actually acting on the surface of the developer carrier moves in the collecting direction more than the average voltage value VL of the AC voltage output from the power supply S, and the development is suppressed. Become like As a result, even when the distance d between the image carrier and the developer carrier is reduced and the AC electric field acting between the image carrier and the developer carrier becomes stronger, the image to be formed is formed. Is prevented from increasing.

On the other hand, the distance d between the image carrier and the developer carrier
Is larger, the value of the capacitance C ₁ in the capacitor element Cd becomes smaller, and as shown by a solid line in FIG. 2B, the voltage Vd applied across the capacitor element Cd and the voltage peak in the developing direction output from the power source S The average voltage value VL ′ of the AC voltage actually acting on the surface of the developer carrying member is substantially the same as the average voltage value VL of the AC voltage output from the power source S, and the difference between the average voltage value VL ′ and the average voltage value The image density of the image to be reduced is less likely to decrease.

Therefore, in the developing device according to the present invention, even when the distance d between the image carrier and the developer carrier fluctuates, the change in image density of the formed image is suppressed, and the density unevenness is suppressed. Is reduced, and a good image having a constant image density can be stably obtained. In the developing device according to the present invention, the distance d between the image carrier and the developer carrier is opposed as described above.
When the image density is reduced, the density of the image to be formed is prevented from rising above a predetermined density, and when the distance d between the image carrier and the developer carrier is increased, the image to be formed is reduced. In order to obtain an image having a sufficient image density, since the image density of the developer is reduced and the difference in density between the two is reduced, the application of the developer It is necessary to increase the peak-to-peak value of the AC voltage to be applied, or to set the DC voltage high in a direction in which development is promoted.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a developing device according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings.

In the developing device of this embodiment, as shown in FIG. 3, a developer carrier 11 in the form of a roller is provided so as to face the image carrier 1 with a required distance d therebetween. The supply member 12 supplies the toner 2 accommodated therein to the developer carrier 11.

Then, the developer carrier 11 to which the toner 2 is supplied is rotated so that the toner 2 is transported by the developer carrier 11 and a regulating member 13 is provided on the surface of the developer carrier 11. To regulate the amount of the toner 2 conveyed by the regulating member 13 and frictionally charge the toner 2. The charged toner 2 faces the image carrier 1 via a required distance d. To the developing area. Here, as the developer carrier 11, for example, a metal roller whose surface has been blasted to have a ten-point average roughness Rz of about 7 μm is used. A plate material of stainless steel or phosphor bronze having a thickness of 0.08 mm to 0.2 mm is used, and the distance d between the image carrier 1 and the developer carrier 11 is generally set in the range of 150 to 250 μm.

Here, in the developing device of this embodiment, a capacitor 15 having a capacitance of 100 to 1000 pF and a resistance of 10 ⁶ are provided between the developer carrier 11 and the power supply 14. The resistor 16 and the rectifying element 17 such as a diode having a range of from 10 to 10 ⁹ Ω are connected in parallel, and the rectifying element 17 sends the toner 2 to the image carrier 1, that is, the developing direction. Are connected in such a direction as to block the current caused by the voltage.

In the developing device of this embodiment, the power supply 14 outputs a developing bias voltage obtained by superimposing an AC voltage consisting of a rectangular wave on a DC voltage, and this developing bias voltage is connected in parallel with the above-described parallel connection. The developer 2 is applied to the developer carrier 11 through the capacitor 15, the resistor 16, and the rectifier 17, thereby supplying the toner 2 held on the developer carrier 11 to the electrostatic latent image formed on the image carrier 1. And develop it.

After the development in this manner,
The toner 2 after the development is guided to the apparatus main body 10 by the developer carrier 11, and the toner 2 is removed from the developer carrier 11 by the removing member 18 and returned into the apparatus main body 10.

Here, as in the developing device of this embodiment, the developing bias voltage as described above is applied to the developer carrier 11 through a capacitor 15, a resistor 16, and a rectifying element 17 connected in parallel to perform development. In the case where the development is performed and the case where the development is performed by directly applying the developing bias voltage to the developer carrier 11 as described above, the voltage value of the DC voltage applied from the power supply 14 is changed to change the developing bias voltage. By changing the average voltage, development characteristics were examined when the distance d between the image carrier 1 and the developer carrier 11 was large and small, and the results are shown in FIG. In FIG. 4, as in the developing device of the embodiment, the developer carrying member 1 is supplied with the developing bias voltage through a capacitor 15, a resistor 16, and a rectifying element 17 connected in parallel.
1 is a solid line, and the developing bias voltage is directly applied to the developer carrier 11.
The development characteristics in the case where the development was performed by applying a voltage to are shown by broken lines.

As a result, when the developing bias voltage is applied to the developer carrier 11 through the capacitor 15, the resistor 16, and the rectifying element 17 connected in parallel as in the developing device of this embodiment, the developing is performed. As compared with the case where the developing bias voltage is directly applied to the developer carrier 11 to perform the development, the image density of the image carrier when the distance d between the image carrier 1 and the developer carrier 11 is large and when the interval is small is small. The difference is reduced, the change in image density when the distance d between the image carrier 1 and the developer carrier 11 fluctuates is suppressed, and a good image having a stable image density with less density unevenness is obtained. Was.

[0024]

Next, a developing device according to a specific embodiment of the present invention will be compared with a developing device according to a comparative example. It is clarified that even when the interval fluctuates, the change in image density is suppressed, and a good image with less density unevenness can be obtained.

Here, in the developing device of the embodiment, in the developing device of the above-described embodiment shown in FIG.
A capacitor 15 having a capacitance of 200 pF, a resistor 16 having a resistance value of 100 MΩ, and a rectifier 17 are connected in parallel between the developer carrier 11 and a power source 14.
7 interrupts the current caused by the voltage in the direction in which the toner 2 is sent to the image carrier 1. On the other hand, in the developing device of the comparative example, the power source 14 is directly connected to the developer carrier 11 without providing the capacitor 15, the resistor 16, and the rectifying element 17 between the power source 14 and the developer carrier 11. I tried to make it.

In each of the developing devices of the embodiment and the comparative example, the peak-to-peak value Vpp is 2.0 kV in the embodiment together with the DC voltage from the power supply 14, and the peak-to-peak value Vpp is 1 in the comparative example. An AC voltage consisting of a rectangular wave having a frequency of 2.6 kHz and a frequency of 2.5 kV is output, and the voltage value of the DC voltage output from the power source 14 is changed to change the average voltage of the developing bias voltage. The development characteristics of the case where the distance d between the substrate 1 and the developer carrier 11 was 0.15 mm and 0.20 mm were examined. FIG. 5 shows the result when the developing device of the example was used, and FIG. FIG. 6 shows the result when the developing device was used.
It was shown to. 5 and 6, the image carrier 1
When the distance d between the image carrier 1 and the developer carrier 11 is 0.15 mm, the result is indicated by a circle and a broken line, and when the distance d between the image carrier 1 and the developer carrier 11 is 0.20 mm, the result is indicated by a solid line. Indicated by

As a result, in the vicinity of the image density 1.5 at which a sufficient density image can be obtained, the distance d between the image carrier 1 and the developer carrier 11 is 0.15 mm, 0.20 mm
Comparing the image densities in the case of Example 1 and Example 2, the developing device of the comparative example showed a large difference in image density between the two images having the above-mentioned different intervals, but in the developing device of the example,
The difference in image density between the two is almost eliminated, and under the conditions of actual development, even if the distance d between the image carrier 1 and the developer carrier 11 fluctuates, density unevenness occurs in the formed image. And a good image having a constant image density can be stably obtained.

[0028]

As described above in detail, in the developing device of the present invention, when the AC voltage composed of a rectangular wave is applied from the power source to the developer carrier facing the image carrier at a required interval. Connecting a capacitor, a resistor, and a rectifying element in parallel between the power supply and the developer carrier,
Since this rectifying element cuts off only the current due to the voltage acting in the direction of sending the developer to the image carrier in the AC voltage composed of the rectangular wave, the developer is transferred to the image carrier on the surface of the developer carrier. Only the voltage acting in the direction of sending to the developing direction, that is, the developing
As the distance between the image carrier and the developer carrier becomes smaller and the acting AC electric field becomes stronger, the development is strongly suppressed, and the image when the distance between the image carrier and the developer carrier fluctuates. Changes in concentration have been suppressed.

As a result, in the developing device according to the present invention, even when the distance between the image carrier and the developer carrier fluctuates, the occurrence of density unevenness is reduced, and a good image having a constant image density is obtained. It has become stable.

[Brief description of the drawings]

FIG. 1 is a diagram showing an equivalent circuit of a circuit composed of a developing device and an image carrier according to the present invention.

FIG. 2 is a cross-sectional view of the developing device according to the present invention, in which the waveform of the AC voltage applied to the developer carrier and the waveform of the AC voltage actually acting on the surface of the developer carrier are different between the image carrier and the developer carrier; FIG. 4 is a diagram showing a state where the distance changes according to the facing distance.

FIG. 3 is a schematic explanatory view of a developing device according to an embodiment of the present invention in which a resistor and a rectifying element are connected in parallel between a developer carrier and a power supply.

FIG. 4 shows a case where the distance between the image carrier and the developer carrier is large and a case where the distance between the image carrier and the developer carrier is small in the developing device of the embodiment and the developing device in which an AC voltage is directly applied to the developer carrier from a power supply. FIG. 9 is a diagram comparing changes in development characteristics between the case and the case.

FIG. 5 is a diagram illustrating changes in development characteristics when the distance between the image carrier and the developer carrier is large and small in the developing device according to the embodiment of the present invention.

FIG. 6 is a diagram illustrating a change in development characteristics when the distance between the image carrier and the developer carrier is large and small in the developing device of the comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 2 Toner (developer) 11 Developer carrier 14 Power supply 15 Capacitor 16 Resistance 17 Rectifier d Space between image carrier and developer carrier

Continuation of the front page (56) References JP-A-58-68757 (JP, A) JP-A-61-94074 (JP, A) JP-A-3-271102 (JP, A) (58) Fields studied (Int .Cl. ⁷ , DB name) G03G 15/08 G03G 15/06 101

Claims (1)

(57) [Claims] The developer is held on a developer carrier, and the developer is guided to a developing area opposed to the image carrier at a predetermined distance from the image carrier. In a developing device that applies a voltage to supply a developer to an electrostatic latent image formed on an image carrier, a capacitor, a resistor, and a rectifier are connected in parallel between the power supply and the developer carrier. And a rectifying device connected to the rectifying element in such a direction as to block a current caused by a voltage in a direction in which the developer is sent to the image carrier at the AC voltage having the rectangular wave.