JPH0212284A - Developing device - Google Patents

Abstract

PURPOSE:To restrain the occurrence of a sleeve ghost by moving a developing sleeve along the axial direction of an image carrier and developing an image. CONSTITUTION:During development, a pinion 12 driven by a normally and reversely rotating motor 12a and a rack 13 reciprocate a developing unit 4 in a direction parallel to the shaft of a photosensitive drum 1. As a result, the way that toner is used on the developing sleeve 4a can be uniform in the shaft direction. Consequently, the value of triboelectrification due to charging up developer is almost close to a constant value in the axial direction of the developing sleeve 4a, whereby a sleeve ghost that the history of a previously printed pattern appears as density difference can be minimized.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer, and particularly to a developing device in an image forming apparatus that uses an electrostatic transfer process. .

[Conventional technology]

In conventional developing devices, the former consumes more developer in the printing and non-printing areas than the latter (there is less charge-up, so the tripo charge of the developer can be kept low compared to the latter). However, the disadvantage is that the difference directly affects the development characteristics.

[Problem to be solved by the invention] In particular, when using a negative charging developer, changes in triboelectric charge are likely to be reflected in density fluctuations, so solid black images etc. may occur while printing a certain printing pattern. This has the disadvantage that so-called "sleeve ghosts" tend to occur, where the history of previously printed patterns appears as a difference in density.

[Means for solving problems]

The gist of the present invention is to provide a developing device in an electrophotographic image forming apparatus, which is characterized in that a developing sleeve is reciprocated along an axial direction to perform development.

By reciprocating the developing sleeve along the axial direction of the image carrier, the amount of toner on the developing sleeve is made uniform in the axial direction, thereby reducing the value of triboelectric charge caused by developer charge-up. As a result, it is possible to suppress the occurrence of so-called "sleeve ghost" in which the history of previously printed patterns appears as a density difference.

〔Example〕

FIG. 9 is a schematic diagram of an electrophotographic printer as an image forming apparatus to which the present invention is applied.

In the figure, 1 is a photoreceptor as an image carrier, and in this example, a drum-shaped photoreceptor (hereinafter referred to as a photoreceptor drum)
is used.

The photosensitive drum 1 is rotated at a predetermined circumferential speed in the direction of the arrow in the figure, and after the drum surface is uniformly charged to a negative polarity by a negative charger 2, an image is formed by an image exposure beam 3 such as a laser beam. Exposure is performed to form an electrostatic latent image.The electrostatic latent image is formed by causing negatively charged toner to adhere to the bright potential area exposed to the laser beam by the developing sleeve 4a of the developing device 4. (Reversal development) Visualized as a toner image.

Next, the transfer material P is synchronized with the rotation of the photosensitive drum l and fed between the drum l and a transfer charger 5, and the toner image on the photosensitive drum l is sequentially transferred to the transfer material P by the transfer charger 5. transcribed. The transfer material P on which the toner image has been transferred is separated from the photosensitive drum l by a separation charger 6, and then sent to a fixing device 8 by a transfer material conveying unit 7, where the toner image is fixed on the transfer material P. be done.

On the other hand, the toner remaining on the photosensitive drum l without being transferred to the transfer material P is collected by the cleaner 9, and the electric charge on the photosensitive drum l is reduced by exposing the drum surface to light by the pre-exposure device 10, thereby reducing the surface resistance. The electric charge is transmitted through the lowered photosensitive drum 1 and eliminated, and is prepared for the next image forming process.

[Embodiment 1] FIG. 1 shows an embodiment of the present invention, and is a plan view seen from above. 1 is a photosensitive drum, 4 is a developing device, 4a is a developing sleeve, 11 is a drive motor for the developing sleeve 4a, 12.13
is a pinion 12. for sliding (reciprocating) the developing device 4a in the axial direction. There are 13 racks. Pinion 12.
The rack 13 constitutes a developing sleeve moving device 21.

a pinion 12 driven by a reversible motor 12a;
During development, the developing device 4 is caused to reciprocate in a direction parallel to the axis of the photosensitive drum 1 by the rack 13. As a result, the toner on the developing sleeve 4a is consumed uniformly in the axial direction.

As shown in FIGS. 2 and 3, the reciprocating motion may be in the form of a sine wave or a shape close to a rectangular wave, with the vertical axis representing the amount of movement and the horizontal axis representing the time axis.

As a result, the value of tribo due to developer charge-up approaches a constant value in the axial direction of the developing sleeve 4a,
The so-called "sleeve go signal" in which the history of the previously printed pattern appears as a density difference, 15 is the laser as the image signal writing light source, 16 is the laser driver for making the laser 15 emit light, 17 is the laser ON time 18 is an integration counter for adding up the laser OFF time, 19 is a timer that generates the time required for the developing sleeve to make one revolution, and 17.18 is added to the integration counter for each time. Reset.2
0 is an arithmetic/control circuit; 17. The ratio of the laser ON time and laser OFF time integrated in step 18, R-(Laser ON
The amount of movement of the developing sleeve is determined by calculating the cumulative time/cumulative laser OFF time). 21 is a developing sleeve moving device (first
Means of illustration 12a, 12. 13 can be used. ),
22 is a driver for operating the device. Reference numeral 23 is a register for determining the maximum value of the laser OFF time in the main scanning direction and calculating the amount of movement.

FIG. 5 shows an example of a pattern printed on a sheet of paper, and the shaded areas indicate the printed portions. Cases are classified into ■ and ■ according to the ratio of the printing area to the white background, that is, the printing rate.

FIG. 6 is a timing chart of the second embodiment of the present invention.

Next, the above configuration will be explained. When an image signal is generated, the laser 08 time integration counter 17 and the laser OFF are activated.
The time integration counter 18 counts the ON and OFF times, and the cumulative ratio of the laser ON time and laser OFF time within the area determined by the length of one rotation of the developing sleeve and the paper width, R
= (laser ON cumulative time/laser OFF cumulative time) Calculate one rotation of the sleeve. (Hereinafter abbreviated as "integration ratio R".

) On the other hand, the maximum value of the laser OFF time in the main scanning direction of the laser 15 (the maximum value is the paper width) is determined using the register 23, and the amount of movement corresponding to the maximum value is determined.

The above integration counter 17. 18, and the contents of the register 23 are reset after calculating the integration ratio R within the area determined by the length of one rotation of the developing sleeve and the paper width.

- In case ■, the integration ratio R is RAT, (for example, 0.
02) Laser OFF time is MAX! :: The corresponding length is a, which is the width of the paper, and in this case, the developing sleeve 4a is moved in the axial direction by the length of the paper width.

- In case ■, the integration ratio R is R>T2 (for example, 0.
7) And the length corresponding to the laser OFF time MAX is b
become. However, in reality, if the laser is turned off completely across the width of the paper on a white background between characters, the maximum value will be the width of the paper, but in this case, when comparing the maximum values, it will not be considered as the maximum value and the information will be canceled. shall judge. In this case, since R has a value close to 1, it is considered that sleeve ghosts are unlikely to occur, so the developing sleeve does not move.

・In case ◎, the integration ratio R falls within the following range.

TI (for example, 0.02)≦R≦72 (for example, 0.7) and the length corresponding to the laser OFF time MAX is C. In this case, the developing sleeve 4a is moved in the axial direction by a length of 0 minutes.

Case (2) is the remaining amount other than case (2) and ◎. (However, when the image signal is turned off, the integration ratio R is calculated and the same control is performed.

Further, although not shown, a developing sleeve movement amount integration circuit is provided. Axial length of photosensitive drum l (photosensitive area) I! ,,
If the length of the developing sleeve 4a in the axial direction is 12, then 12
=21. Set the length to . First, photosensitive drum 1! , /2 and 12/2 of the developing sleeve 4c match, the photosensitive drum starts moving toward either the drive gear side or the opposite side, calculates the cumulative value of the amount of movement, and calculates lx. After moving by /2, start moving in the opposite direction. Then, the developing sleeve movement amount integrating circuit is reset at the time when the locations Ill/2 and 12/2 match again.

Thereafter, the same operation is repeated.

By performing the above-mentioned control operation, the value of tribo due to charge-up of the developer approaches a constant value in the axial direction of the developing sleeve 4a, and the history of the previously printed pattern can appear as a density difference. .

This makes it possible to suppress the occurrence of so-called "sleeve ghosts."

[Example 3] In Example 2, the developing device 4 was moved in the axial direction during paper transfer, but in reality, it was too short to do this, and the image may have tails or other problems. If an undesirable effect occurs, the developing device 4 may be moved in the axial direction after the previous image formation ends, before the next image formation starts, or before or after the image formation starts.

FIG. 7 shows a third embodiment of the present invention, in which 14 is an image signal, 15 is a laser as a light source for writing the image signal, 16 is a laser driver for causing the laser 15 to emit light, and 17 is an integrated laser ON time. 18 is an integration counter for integrating laser OFF time, 2o
The arithmetic and control circuit calculates the ratio of the laser ON time and the laser OFF time integrated at 17°18, R=(laser ON integrated time/laser OFF integrated time), and determines the amount of movement of the developing sleeve.

21 is a developing sleeve moving device for moving the developing sleeve 4a by the amount of movement, and 22 is a driver for moving the device. Reference numeral 23 is a register for determining the maximum value of the laser OFF time in the main scanning direction and calculating the amount of movement.

FIG. 8 is a timing chart of Embodiment 3 of the present invention.

Next, the above configuration will be explained. When an image signal is generated, the laser 08 time integration counter 17 and the laser OFF are activated.
The time integration counter 18 counts the ON and OFF times, and the cumulative ratio R of the laser 08 hours and the laser OFF time within the paper area (within one page) of the previously printed pattern
' = (Laser ON cumulative time/Laser OFF cumulative time) (
1 page). (Hereinafter, it will be abbreviated as "integration ratio R'J.") On the other hand, find the maximum value of the laser OFF time in the main scanning direction of the laser I5 in the register 23, and find the movement 1 corresponding to it. (The maximum value is the paper width) Integration counter 17. 18, movement amount calculation register 2
The contents of 3 are reset when the image signal is turned off and there is a paper interval.

・If there is one page of the case, the integration ratio R' is R'
<T (for example, 0.02), and the length a corresponding to the laser OFF time MAX is the paper width, and in this case, the developing sleeve 4a is moved in the axial direction by the length of the paper width.

・If there are l pages in case ■, the integration ratio R' is R'
> T2 (e.g. 0.7) and laser OFF time MA
The length corresponding to X is b. However, in reality, if the laser is turned off completely across the width of the paper on a white background between characters, the maximum value will be the width of the paper, but in this case, when comparing the maximum values, it will not be considered as the maximum value and the information will be canceled. The decision shall be made based on the following. In this case, since R' has a value close to 1, it is considered that sleeve ghosts are unlikely to occur, so the developing sleeve does not move.

・If there are l pages in case ◎, the integration ratio R' falls within the following range.

T, ≦R'≦T2 and the length corresponding to the laser OFF time MAX is C. In this case, the developing sleeve 4a is moved in the axial direction by a length of 0 minutes.

The contents and effects of the sleeve movement amount integration circuit are the same as in the second embodiment, so a description thereof will be omitted.

[Example 4] In Examples 2 and 3, the amount of movement of the developing sleeve was determined for the three cases of case ■ and ◎, but in Example 2, the amount of movement of the developing sleeve was basically determined based on the paper width and the developing sleeve 1. Although the integration ratio within the area defined by the circumference has been calculated, the integration ratio may also be calculated by dividing the vertical length of the paper into five equal parts, for example.

Furthermore, the amount of movement of the developing sleeve is the length f of the photosensitive drum,
There is no need to limit it to 11/2 of 11/2, and it may be thicker (or smaller) than this.

Further, in the present invention, a laser is used as the image signal writing light source, but the light source may be a light emitting diode, liquid crystal shutter, or the like.

〔Effect of the invention〕

As explained above, according to the present invention, by reciprocating or moving the developing sleeve along the axial direction of the image carrier, the toner on the developing sleeve is consumed uniformly in the axial direction. The tripod value due to developer charge-up approaches a constant value in the axial direction, and as a result, it is possible to suppress the occurrence of so-called "sleeve ghost", where the history of previously printed patterns appears as a density difference. becomes.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a developing device embodying the present invention, FIGS. 2, 4 and 6 are block diagrams and timing charts of the second embodiment of the present invention, and FIGS. 7 and 8 are diagrams of the third embodiment of the present invention. 3 is a block diagram and a timing chart of an embodiment. FIG. FIG. 5 shows the print pattern (■) of the second embodiment of the present invention. It is a diagram showing the state of O9■. FIG. 9 is a schematic diagram of an electrophotographic printer as an image forming apparatus to which the present invention is applied. 1... Image carrier 4... Developing device 4a ・
・Developing sleeve 12 ・Pinion 13 ・・
・Rack 17 ... Laser ON time cumulative count 18 ...
Laser OFF time integration counter 19...Developing sleeve-period timer 20...Arithmetic control circuit 22...Developing sleeve movement driver 23...Laser OFF time MAX & movement amount calculation register Developing sleeve moving device

Claims (3)

[Claims] (1) In an electrophotographic image forming apparatus, a developing device is characterized in that a developing sleeve is moved along the axial direction of an image carrier to perform development. (2) The developing device according to claim 1, wherein the developing sleeve is moved along the axial direction of the image carrier during image formation to perform development, depending on the value of the printing ratio within a specific area. Device. (3) Depending on the value of the printing ratio within a specific area, the developing sleeve is moved along the axial direction of the image carrier during the conveyance interval of the transfer material or during the forward rotation or backward rotation to prepare for the next development. The developing device according to claim 1, characterized in that: