JPH10240072A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the existence of unnecessary toner and to prevent disturbance of the surface potential of a photoreceptor due to residual toner by recovering the unnecessarily sticking toner on the photoreceptor by a developing roller. SOLUTION: At the same time that the photoreceptor 1 is driven, an electrifier 14, the developing roller 18, and a supply roller 22 are activated. As a result, an unelectrified area from the electrifier 14 to the developing roller 18 is subjected to toner development by the developing roller 18 despite the absence of image data. The toner 20 attracted to the photoreceptor 12 is electrified by the electrifier 14. Only after the rear end of the toner 20 attracted to the photoreceptor 12 passes under an exposure unit 16, the exposure unit 16 is activated. That is, when the surface of the photoreceptor 12 subjected to the second electrification by the electrifier 14 reaches to the position of the exposure unit 16, exposure is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus,
In particular, the present invention relates to an image forming apparatus applied to, for example, a copying machine, a laser printer, a facsimile, and the like using an electrophotographic system.

[0002]

2. Description of the Related Art As shown in FIG. 6, a conventional image forming apparatus 1 including a photoconductor (photoconductor drum) 3 rotating around a central axis 2, for example, is related to the photoconductor 3 as shown in FIG.
At least charging means 4, exposure means 5 and developing means 6
Are arranged in this order from the upstream side in the rotation direction, and when starting an image forming operation, all the means are activated at the same time, and a predetermined image forming process is performed.

[0003]

In the prior art, as described above, at least the charging means 4, the exposing means 5 and the developing means 6 are activated simultaneously with the start of the image forming operation. The section shown, that is, the section where charging from the charging means 4 to the developing means 6 is not performed is performed in the developing means 6 despite the absence of image data to be formed.
Develops toner (a black solid image is formed)
There was such a problem.

Therefore, conventionally, a voltage having a polarity opposite to the developing bias voltage is applied to the developing means 6 for a predetermined period from the start of the operation, so that a section from the charging means 4 to the developing means 6 becomes unnecessary. Since development was not performed, a circuit for that purpose had to be provided, and there was a disadvantage that the cost was increased. Further, in the image forming apparatus in which the developing unit 6 is not provided with a unit for applying a voltage of the opposite polarity, and the untransferred toner on the photoreceptor is collected by a cleaning unit (for example, a cleaning blade) (not shown), the toner is There was also a problem that it was wasted.

SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide an image forming apparatus capable of forming a good image at low cost without generating useless developer (toner).

[0006]

SUMMARY OF THE INVENTION The present invention relates to a photosensitive member having a displaceable surface, a charging means provided at a fixed position for charging the surface of the photosensitive member, and a photosensitive member provided at the fixed position for statically charging the photosensitive member. In an image forming apparatus including an exposure unit for forming an electrostatic latent image and a developing unit for developing the electrostatic latent image into a toner image, the surface of the photoconductor after the second charging by the charging unit is exposed to the exposure unit. The image forming apparatus is characterized in that the exposure means is activated when it is displaced to a position.

[0007]

When the photosensitive member is driven, the charging means and the developing means are activated. Therefore, a section from the charging unit to the developing unit (a section indicated by A in FIG. 6) is developed with the toner by the developing unit. The toner adsorbed on the photoreceptor surface is uniformly charged by the charging unit without being transferred to the transfer material. When the end of the toner-developed section (A) passes through the exposure means, that is, when the surface of the photoconductor after the second charging by the charging means is displaced to the position of the exposure means, the exposure means Activated for the first time. Therefore, the toner charged to a predetermined potential by the charging unit and unnecessarily adsorbed to the photoconductor moves to the developing unit due to the potential difference. That is, the toner adsorbed on the photoreceptor despite no image data is collected by the developing unit.

[0008]

According to the present invention, the toner adsorbed on the photoreceptor immediately after the start of the operation is recovered by the developing means, so that it is possible to prevent the generation of useless toner, and furthermore, the developing means uses the developing bias voltage and Does not need to apply a reverse polarity voltage. In addition, since the toner is unnecessarily adhered to the photoreceptor and the position is exposed after the toner is collected, a stable good image can be obtained without disturbing the potential of the photoreceptor surface due to the residual toner.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus 10 according to this embodiment shown in FIG.
Includes a photoreceptor 12 that is rotatably driven in the direction of the arrow and has a displaceable surface. The surface of the photoreceptor 12 has a charger 1 as a charging unit fixedly disposed on the upper left side thereof.
4 uniformly charges to, for example, -700V.

An exposure device (exposure means) 16 such as a laser beam is fixedly arranged at the upper right of the photoconductor 12, and an original light image formed by the exposure device 16 is incident on the photoconductor 12. Thereby, an electrostatic latent image (negative image) of, for example, -100 V is formed on the surface of the photoconductor 12. On the right side of the photoconductor 12, a developing roller 18 as a developing unit is arranged so as to be in contact with the surface of the photoconductor 12. The developing roller 18 is formed of an elastic body such as urethane. On the surface of the developing roller 18, for example, a negative-polarity, non-magnetic one-component developer (hereinafter, referred to as “toner”) 20 is carried. A supply roller 22 and a developing container 24 are arranged in relation to the developing roller 18.

The developing container 24 contains or stores the toner 20. An agitator 26 that agitates the toner 20 and supplies the toner 20 to the supply roller 22 is disposed substantially at the center of the developing container 24. Therefore, the toner 20 stored or stored in the developing container 24 is supplied to the developing roller 18 by the supply roller 22. Also,
The developing roller 18 has a developing bias voltage of-
A DC voltage of 300 V is applied to the supply roller 22 by, for example,-
A DC voltage of 400 V is applied respectively. When the toner 20 has a positive polarity, the polarity of the voltage applied to the developing roller 18 and the supply roller 22 is also positive.

Above the developing roller 18, an elastic blade 28 elastically contacting the surface thereof is disposed, and the elastic blade 28 causes the toner 20
Is regulated to form a thin toner layer. Further, a transfer device 30 is disposed below the photoreceptor 12, and thereby electrostatically attracts the toner image to a transfer material (not shown) such as paper. The transfer unit 30 is supplied with a transfer bias voltage having a polarity (positive polarity) opposite to the developing bias voltage.

In such an image forming apparatus 10, the electrophotographic process is repeated around the photoreceptor 12. That is, the surface of the photoconductor 12 is charged to, for example, −700 V by the charger 14, and −100 V is exposed by exposing the document image.
A V electrostatic latent image is formed. The electrostatic latent image is developed with the developing roller 18 to which a developing bias voltage of, for example, -300 V is applied. Then, the developed toner image on the photoconductor 12 is transferred to a transfer material by the transfer device 30. The untransferred toner that has not been transferred to the transfer material and remains on the surface of the photoconductor 12 is again guided to the charger 14 while adhering to the photoconductor 12, and is uniformly charged with the photoconductor 12, or The toner is collected on the developing roller 18 by a background electric field formed between the body 12 and the developing roller 18.

However, since the developing bias voltage is applied to the developing roller 18 at the same time when the charging is started by the charging device 14, the charging device 14 applies the developing bias voltage to the developing roller 18 even though there is no image data to be formed. This causes a problem that the developing section 18 performs toner development on the section (section indicated by A in FIG. 2). Therefore, conventionally, a voltage having a polarity opposite to the developing bias voltage is applied to the developing roller 18 for a predetermined period at the same time as the start of the image forming operation, thereby preventing unnecessary toner development. Therefore, it is necessary to provide a circuit for applying a voltage of the opposite polarity, and there is a problem that the cost is increased.

On the other hand, in the embodiment shown in FIG. 1, when the end position of the section where toner is developed by the developing roller 18 (the section indicated by A in FIG. 2) passes through the exposure unit 16, that is, the charging unit 14 When the surface of the photoconductor 12 is displaced to the position of the exposure device 16 after the second charging, the exposure device 16 is activated for the first time, and the toner 20 unnecessarily attracted to the photoconductor 12 is developed by the developing roller. 18
It is configured to be collected by. These image forming operations are controlled by the CPU 32 shown in FIG.

That is, when an instruction to start an image forming operation is given by a key input or the like, the CPU 32 controls the driver 34 to turn on the main motor 36 in step S1 in FIG. Thereby, the photoconductor 12 is driven. In the next step S3, a predetermined voltage is applied from the power supply 38 to the charger 14, the developing roller 18 and the supply roller 22. That is, in step S3, the charger 14, the developing roller 18, and the supply roller 22
Is activated. Therefore, a black solid image is formed in the section indicated by A in FIG. 2 of the photoconductor 12 as described above. Then, in step S5,
It is determined whether or not a predetermined period has elapsed since the power was supplied to the charger 14, and if "YES" is determined there, the exposure unit 16 is activated in step S7.

That is, the image forming apparatus 10 of this embodiment
Includes a timer counter 40, and the timer counter 40
Thus, after the charger 14 is activated, the time during which the photoreceptor 12 has rotated by one turn and the distance from the charger 14 to the exposure device 16 (the section indicated by B in FIG. 2) is counted. That is, when the surface of the photoconductor 12 is displaced to the position of the exposure device 16 after the second charging by the charging device 14, the exposure by the exposure device 16 is started for the first time. Therefore, in FIG.
The toner 20 in the section indicated by is -70 by the charger 14.
After being charged to 0 V, it is collected by the developing roller 18 without being exposed by the exposure device 16. If “NO” is determined in the step S5, “YE
This process is repeated until S ″ is determined.

When the exposure device 16 is activated, in a succeeding step S9, the CPU 32 determines whether or not a predetermined period has elapsed since the exposure device 16 was turned on. In the next step S11, a transfer bias voltage is applied to the transfer device 30, and the toner image is transferred to a transfer material (not shown). Then, in step S13, it is determined whether or not exposure of image data corresponding to one page to be formed has been completed.
When S "is determined, in the following step S15,
The exposure unit 16 is disabled. In the next step S17,
The CPU 32 determines whether or not a predetermined period has elapsed since the disabling of the exposure unit 16, and if "YES" is determined there, disables the transfer unit 30 in step S19.

Then, in step S21, the CPU 32
Determines whether the continuous print mode is selected, that is, whether there is image data of another page to be formed. If “YES” is determined there, the process proceeds to step S5, and steps S5 to S5 are performed.
The operation of 19 is repeated. If "NO" is determined in the step S5, that is, if the continuous print mode is not selected, in the step S23,
The paper ejection sensor 42 is activated, thereby detecting whether or not the transferred transfer paper has been discharged out of the apparatus.
When it is confirmed that the transfer paper has been discharged, the CP
U32 disables the charger 14, the developing roller 18 and the supply roller 22 in step S25, stops the photoconductor 12 in step S27, and ends all the operations.

According to this embodiment, the toner 20 unnecessarily adsorbed to the photosensitive member 12 immediately after the start of the operation is collected by the developing roller 18 (developing container 24), so that no waste toner is generated. Further, unlike the conventional case, it is not necessary to apply a voltage having a polarity opposite to the developing bias voltage to the developing roller 18. Further, since the portion where the toner is unnecessarily adsorbed (the section indicated by A in FIG. 2) passes through the exposing device 16, the exposing device 16 is activated for the first time. The surface potential of the photoconductor 12 is not disturbed. Therefore, a stable image can be obtained at low cost.

In the above embodiment, the photosensitive member 12 is formed in a cylindrical (drum) shape.
5, it is needless to say that the present invention can also be applied to a belt-shaped member shown in FIG. Although the embodiment in which the electrophotographic process is performed using the negatively charged photoconductor 12 has been described, an image forming apparatus using the positively charged photoconductor 12 and toner having the same polarity as the electrophotographic process is similar to the above-described embodiment. The effect of can be obtained.

[Brief description of the drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention;

FIG. 2 is an explanatory diagram showing a part of the operation of the embodiment in FIG. 1;

FIG. 3 is a block diagram showing a part of the embodiment in FIG. 1;

FIG. 4 is a flowchart showing a part of the operation of the embodiment in FIG. 1;

FIG. 5 is an illustrative view showing another embodiment;

FIG. 6 is an illustrative view showing a conventional technique;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 12 ... Photoconductor 14 ... Charging device 16 ... Exposure device 18 ... Developing roller 20 ... Toner 22 ... Supply roller 32 ... CPU 40 ... Timer counter

Claims (1)

[Claims] A photosensitive member having a displaceable surface; charging means provided at a fixed position for charging the surface of the photosensitive member; forming an electrostatic latent image on the charged photosensitive member provided at a fixed position. An image forming apparatus that includes an exposure unit that performs the second charging by the charging unit and a developing unit that develops the electrostatic latent image into a toner image. Characterized in that the exposure means is activated when displaced to the position of
Image forming device.