JP2006106629A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing unnecessary consumption of toner, cleaning failure, and sticking of carrier. <P>SOLUTION: In the image forming apparatus having a means 6 for detecting an amount of toner attached to an image carrier 1, the timing of the application of a development bias is altered according to the result of the detection obtained by the means 6 at the start of the image carrier. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus.

In the image forming apparatus in which the electrophotographic process means is disposed around the image carrier, the image carrier is started by a motor, but it takes several hundreds of milliseconds until the speed of the motor is stabilized at the start of startup. For this reason, the time until the portion where the image carrier is charged reaches the developing position varies due to the start-up of the motor.
On the other hand, the rising of the power pack applied to the charger also requires several tens to several hundreds of msec, so that even if the motor is at a constant speed, it takes a time for the rising until it is normally charged.

As described above, the variation at the time of starting the image bearing member has the following problems for the electrophotographic image forming apparatus adopting the negative positive system.
Usually, while an uncharged image carrier passes through the development position, a development bias reverse to the normal one is applied, the background stain is suppressed, and the normal development bias is switched at the timing when the charged portion comes.
However, due to variations in start-up time of the image carrier (this includes not only the motor alone but also variations in the load applied to the image carrier), the arrival of the charged portion of the image carrier at the development position varies. Become.
This will be described with reference to the example of FIG. FIG. 2 is a diagram showing the measurement results of the potential of the image bearing member and the developing bias at the developing position. 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 developing bias and the charging potential move at the timing (2), so that only a very small amount of toner is attached to the B portion.
However, in the case of a motor that rises quickly, the relationship is as in (1), and carrier adhesion occurs in the portion A in the figure. On the other hand, when the motor rises slowly, or when the torque increases due to changes over time or the environment, the relationship shown in (3) occurs, and the toner in part C is consumed excessively and the cleaning load increases. It may increase and lead 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 activated.
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that solves the above-described problems and can suppress wasteful toner consumption, poor cleaning, and occurrence of carrier adhesion.

In order to achieve the above object, an invention according to claim 1 is an image forming apparatus having a toner adhesion amount detecting means for detecting a toner adhesion amount on an image carrier, and the toner adhesion when the image carrier is activated. The development bias application timing is changed based on the detection result of the amount detection means.
According to a second aspect of the present invention, there is provided at least two or more developing sleeves and bias applying means for simultaneously applying a developing bias to each developing sleeve, and a target toner adhesion amount at the time of starting the image carrier is obtained. It is characterized in that T / 1000 × S ≧ L, where T (msec) to reach, distance L (mm) between developing sleeves, and linear velocity S (mmsec) of the image carrier.

According to the present invention, since the development bias application timing is corrected according to the toner adhesion at the time of starting the image carrier, it is possible to eliminate carrier adhesion, unnecessary toner consumption, and poor cleaning regardless of the environment and time. it can.
In addition, the above-described effects can be obtained when a plurality of developing sleeves are provided and a developing bias is applied simultaneously.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram around an image forming unit of an image forming apparatus according to an embodiment of the present invention. Around the image carrier (photosensitive drum) 1 that is rotated by a motor (not shown), the charging charger 2, the writing optical system 3, the first developing sleeve 4-1, and the second developing sleeve 4-2 are arranged in the order of the electrophotographic process. A developing device 4, a transfer belt 5, a P (photo) sensor 6 as a toner adhesion amount detection means, a cleaning blade 7, and a charge removal lamp 8 are arranged, and an image is formed by a known electrophotographic process.
Example 1
FIG. 2B is a diagram showing a state where toner and carrier adhering portions generated when the motor is turned on are monitored by a P sensor.
Even when the carrier is attached, since the carrier is not uniformly attached to the entire surface of the image carrier 1, the output of the P sensor is merely a thin pulse as shown in FIGS. Further, when the start-up of the motor is slow, the number of toner adhering portions increases, so that the time when the output value of the P sensor 6 is low as shown in FIGS.
As described above, the P sensor 6 can determine the timing of the development bias and the rising of the charging, and therefore, the development bias ON timing is adjusted in steps S1 to S9 in the flow of FIG. That is, when the main motor is turned on (S1), P sensor sampling is started (S2), and it is determined whether or not P sensor output Vsp <3.0 (S3). When the condition is satisfied, time measurement is started (S4), it is determined whether or not the P sensor output Vsp> 3.0 (S5), and it is further determined whether 20 msec has elapsed with Vsp> 3.0 (S6). When 20 msec elapses, time measurement is started (S7), sampling of the P sensor is terminated (S8), and the VB ON timing correction time is calculated and stored in the memory (S9).
In this embodiment, the time when the output of the P sensor 6 is 3 V or less is measured, and the VB ON timing is adjusted so that this time becomes the target time. For example, when the target time of Vsp <3V is 50 msec and the actually measured time is 80 msec, the toner adheres more than the target of 30 msec.
Therefore, the next job is controlled by delaying the VB ON timing by 30 msec from the target. By performing this operation for each job, it is possible to follow environmental fluctuations and rise fluctuations due to temporal torque fluctuations. As a result, wasteful toner consumption and carrier adhesion can be prevented.

(Example 2)
In this example,
Distance L (mm) between sleeves at the farthest distance = 18
Photoconductor linear velocity S (mmsec) = 500
And
In this embodiment, the time T (msec) required to reach the target toner adhesion amount at the time of starting the image carrier is set to 50 msec with the aim of Vsp <3V. That is, T / 1000xS = 25 ≧ L = 18.
For example, if the target time is 20 msec, T / 1000xS = 10 <L = 18.
This is a state in which carrier adhesion does not occur at the second sleeve (sleeve close to the transfer position) 4-2, but the developing bias rises at the position of the first sleeve (sleeve close to the writing position) 4-1. A state in which no carrier easily adheres will occur (see FIG. 4). By setting the target value to the above formula, it is possible to obtain an appropriate timing without carrier adhesion.

1 is a configuration diagram around an image forming unit of an image forming apparatus according to an embodiment of the present invention. FIG. (A) is a figure which shows the measurement result of the electric potential and developing bias of the image carrier in a development position, (b) is a figure which shows a mode that the toner and the carrier adhesion part which generate | occur | produce at the time of motor ON were monitored with the P sensor. . 3 is a flowchart showing a control operation in the image forming apparatus of the present invention. It is a figure which shows the part which a carrier adheres easily.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Charging charger 3 Writing optical system 4 Developing apparatus 4-1 First developing sleeve 4-2 Second developing sleeve 5 Transfer belt 6 P sensor (toner adhesion amount detecting means)
7 Cleaning blade 8 Static elimination lamp

Claims (2)

  In an image forming apparatus having a toner adhesion amount detecting means for detecting the toner adhesion amount on the image bearing member, the development bias application timing is determined based on the detection result of the toner adhesion amount detecting means when the image bearing member is activated. An image forming apparatus that is changed.   At least two or more developing sleeves and bias applying means for simultaneously applying a developing bias to each developing sleeve, and a time T (msec) until reaching the target toner adhesion amount at the time of starting the image carrier 2) The image forming apparatus according to claim 1, wherein T / 1000 × S ≧ L when the distance between the developing sleeves is L (mm) and the image carrier linear velocity is S (mmsec).

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