JP2005345915A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of eliminating carrier sticking, toner wasting, and cleaning defects. <P>SOLUTION: The image forming apparatus electrostatically discharges an image carrier 1 by a writing means 3 of forming an electrostatic latent image on the image carrier 1 in starting up the image carrier 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus using a negative positive system.

  An image carrier (photosensitive drum, photosensitive belt, and intermediate transfer member) of an electrophotographic image forming apparatus is activated and rotated by a motor. There are several times until the motor speed is stabilized at the start of activation. It takes 100 msec. For this reason, the time until the charged portion on the image carrier reaches the developing position varies depending on the rise time of the motor. On the other hand, since it takes several tens to several hundreds of milliseconds for the power pack to be applied to the charger, even if the motor is at a constant speed, it takes time for the power pack to be charged normally.

As described above, the variation at the time of starting the image carrier has the following problems for the image forming apparatus adopting the negative positive system. That is, normally, during the period when the non-charged part on the image carrier passes through the developing device, the development bias reverse to the normal one is applied to suppress the background stain and the normal development is performed at the timing when the charged part comes. Switching to bias. However, due to variations in the starting time of the image carrier (which includes variations in the load on the image carrier as well as the motor alone), the arrival of the charged portion of the image carrier at the development position varies. .
This will be described with reference to the example of FIG. FIG. 5 shows the measurement of the potential of the image carrier and the development bias at the development position. Usually, the developing bias VB is switched from the reverse polarity (+ here) to the normal polarity (−) after a certain time from the motor ON. Normally, the relationship between the developing bias VB and the charging potential VD indicated by the broken line b is as shown in the figure, so that only a very small amount of toner needs to be attached to the hatched region 11 in FIG.
However, in the case of a motor that rises quickly, the charging potential VD is shown as a broken line a, and the development bias VB and the charging potential VD are in the relationship shown in the figure, and carrier adhesion occurs in the hatching region 12 portion. End up. On the other hand, when the torque increases due to a slow-starting motor or due to changes over time or environment, the charging potential VD is shown as a solid line c, and the development bias VB and the charging potential VD are in the relationship shown in the figure. Therefore, extra toner is consumed in the hatched area 13. Also, the cleaning load may increase, leading to poor cleaning. As described above, in an image forming apparatus using an electrophotographic system of a negative positive system, useless toner consumption, cleaning failure, and carrier adhesion may occur due to unstable factors when the image carrier is started.
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can eliminate carrier adhesion, waste of toner, and poor cleaning.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier that is rotationally driven by a motor, a charging unit that charges the image carrier, and optical information written on a charged portion of the image carrier. In an image forming apparatus comprising a writing unit that forms an electrostatic latent image, a developing unit that develops an electrostatic latent image, and a control unit, the control unit carries the image by the writing unit when the image carrier starts to rotate. It is characterized by neutralizing the body.
According to a second aspect of the present invention, the controller stops the charge removal by the writing means after the image carrier has reached a constant speed.
According to the third aspect of the present invention, the distance from the writing position to the developing position closest to the writing position is L (mm), the linear velocity of the image carrier is S (mm / sec), and the actual rise time of the developing means is determined. When T (msec) is set, it is configured to satisfy the relationship of T ≦ L / S × 1000.

  In the present invention, when the image carrier is activated, the intended purpose can be achieved by discharging the image carrier by the writing means for forming an electrostatic latent image on the image carrier.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of an image forming system of the image forming apparatus. Around the image carrier 1 rotated by a motor, a charging device (charging means) 2, a writing device (optical writing system, writing means) 3, a developing device (developing means) 4, a transfer device (transfer means) 5, and a cleaning The devices 6 are arranged in the order of the electrophotographic process, and a well-known electrophotographic process is executed under the control of a control unit (not shown). The potential sensor 7 is a sensor that detects the potential of the image carrier 1.
One feature of the present invention resides in that the control unit neutralizes the image carrier by the writing means 3 when the rotation of the image carrier 1 is started.
Another feature resides in that the control unit stops static elimination by the writing means after the image carrier has reached a constant speed.
Further, another feature is that the distance from the writing position to the developing position closest to the writing position is L (mm), the linear velocity of the image carrier is S (mm / sec), and the actual rise time of the developing means is T (Msec), T ≦ L / S × 1000.
[Example 1]
FIG. 2 is an explanatory diagram of the first embodiment. In the first embodiment, a motor having a rise time of 600 msec or less is used as a motor (not shown) for driving the image carrier 1. As shown in FIG. 2B, charging, writing, and developing reverse bias are turned ON simultaneously with the motor ON, and the static elimination by the writing device 3 is turned OFF at 600 msec when the motor is at a constant speed.
The developing bias VB of the developing device 4 is controlled at a timing in consideration of switching, rise time, and layout distance, so that the charging potential VD and the developing bias of the image carrier 1 are stabilized at a stable timing as shown in FIG. VB relationship can be maintained. As a result, the image carrier 1 can be started at a stable timing without being affected by variations in torque for driving the image carrier 1, motors, or variations in rising of the charging potential VD.
In the case where the potential sensor 7 is mounted, by detecting the potential (VL in FIG. 2A) after neutralization by the writing device 3, and controlling the reverse bias of development according to VL, Problems such as carrier adhesion due to VL fluctuations can be prevented.

[Example 2]
FIG. 3 is an explanatory diagram of the second embodiment. In the second embodiment, it is determined whether the speed is constant by detecting a lock signal of the motor, and the start timing of the image carrier 1 is determined. In the second embodiment, the H signal is output when the rotational speed of the motor becomes ± 1%. As a result, image formation can be started with a minimum waiting time at the time of activation. In particular, when the motor is temporarily stopped for the cleaning by the cleaning device 6 during the continuous image formation or the creation of the reference pattern and the motor is started immediately, the minimum waiting time compared with the first embodiment described above. There is an advantage that it is sufficient.
[Example 3]
FIG. 4 is an explanatory diagram of the third embodiment. In Example 3, the distance L from the actual writing position to the image carrier 1 to the developing position closest to the writing position L = 30 (mm), the linear velocity S of the image carrier 1 = 360 (mm / sec) When the actual rising time T of the developing device 4 is T = 70 (msec), the time to reach the developing position is longer than T = 70 (msec), L / S × 1000 = 83 (msec).
If such a relationship is satisfied, the developing bias VD is switched at a timing of L / S × 1000-T (msec) even after the neutralization of the image carrier 1 by the writing device 3 is stopped at the same time as the motor becomes constant speed. Thus, the image carrier 1 can be started at a stable timing without being affected by variations in torque for driving the image carrier 1, variations in motor, or variations in rising of the charging potential VD. In the case of the third embodiment, the “actual rise time T of the developing device 4” is an actual measurement time from when the reverse bias OFF is switched to the normal developing bias VD until 80% of the predetermined output.
If this relationship is not satisfied, it is necessary to extend the timing for stopping the neutralization of the writing device 3 in consideration of the rise of the developing bias, and it takes time to start up. Here, the time from the reverse bias is T, but when the reverse bias is not applied (for example, when VL is high and there is no fear of background contamination), 80% of the predetermined output from the normal development bias ON. It is reasonable to set the time as T.

1 is a configuration diagram of an image forming system of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is an explanatory diagram of the first embodiment. Explanatory drawing of Example 2. FIG. Explanatory drawing of Example 3. FIG. FIG. 6 is an explanatory diagram of a conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image carrier 2, Charging device, 3 Writing device, 4 Developing device, 5 Transfer device, 6 Cleaning device, 7 Potential sensor

Claims (3)

An image carrier that is rotated by a motor, a charging unit that charges the image carrier, a writing unit that writes optical information on a charged portion of the image carrier to form an electrostatic latent image, and develops the electrostatic latent image In an image forming apparatus comprising a developing means and a control unit,
An image forming apparatus characterized in that the control unit neutralizes the image carrier by the writing means when the rotation of the image carrier is started.   The image forming apparatus according to claim 1, wherein the control unit stops the neutralization by the writing unit after the image carrier has reached a constant speed. When the distance from the writing position to the developing position closest to the writing position is L (mm), the linear velocity of the image carrier is S (mm / sec), and the actual developing means rise time is T (msec), The image forming apparatus according to claim 2, wherein the image forming apparatus is configured to satisfy a relationship of T ≦ L / S × 1000.

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