JP2008170624A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of eliminating an abnormal image by securely detecting and correcting a Vt difference arising from a linear velocity difference even if a variation in Vt (magnetic permeability output value) is caused by linear velocities of the developer stirring members of a developing device due to aging, an environmental change, or the like. <P>SOLUTION: During concentration adjustment process control, developer stirring operations are performed at different linear velocities. Output values Vt of the permeability sensor at the linear velocities are detected, and a difference between them is used as an amount of Vt linear velocity correction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, and a multifunction machine provided with at least one of them.

In recent full-color printers and copiers, the printing speed is slower for securing fixing energy and writing processing speed when printing on cardboard and OHP sheets, and higher speed is required for black printing because the speed is higher than full color. It becomes.
That is, one device has two or more image forming speeds.
As with the image forming speed, when the developer stirring speed is 2 linear speeds (linear speed) or higher, especially when the speed is half or double the standard speed, the agent balance is lost, the agent drops, and the left and right ID (image density) unevenness. Therefore, it is desirable that the developing stirring speed is 1 linear speed.
However, as the machine is reduced in size and cost, the developing device, the drive motor, and the gear are also reduced in size, and the speed is often changed at the same rate as the main body of the image forming apparatus due to layout and cost problems.

In a two-component development system that uses a magnetic permeability sensor (hereinafter referred to as “T sensor”) and performs toner replenishment control, the flow of the agent on the T sensor unit is caused by two or more developer stirring speeds. In contrast, the T sensor output value (hereinafter referred to as “Vt”) depending on the linear velocity is different. For this reason, the toner density (hereinafter referred to as “TC”) and the toner adhesion amount differ depending on the linear speed switching, and abnormal quality such as low ID at high speed, excessive ID at low speed, and transfer dust may occur.
It has been empirically known that the developer stirring member on the T sensor portion may be cut in order to eliminate the Vt linear velocity difference mechanically.
Patent Document 1 discloses a technique for determining a Vt linear velocity shift amount (correction amount) based on a Vt at the time of sheet passing at the time of linear velocity switching.

JP 2005-172868 A JP 2002-207357 A JP 2006-084671 A Japanese Patent No. 030226687

However, when the fluidity of the agent is poor due to a high TC or a high number of sheet passing agents, the agent in the T sensor unit stays and misdetects, or the bulk density state of the agent changes in the T sensor unit during continuous white paper passing (Bulk density decreases), and there is a problem that TC is supposed to be constant but it is determined that TC is high and erroneous detection is performed.
On the other hand, if a fin or mylar is attached to the developer agitating member on the T sensor unit and the agent is always fluidized, there is no change in the agent bulk density state at the time of agent retention in the T sensor unit or continuous white paper feed, Although false detection is eliminated, the linear velocity difference is increased.
When the agent is fluidized by fins or the like, it is necessary to correct the Vt difference due to the linear velocity. The correction amount is normally constant at normal temperature and humidity, but initially it will be shifted if the fluidity of the agent is different due to aging or the environment. May occur.

  The present invention provides an image forming apparatus capable of eliminating abnormal images by reliably detecting and correcting a Vt difference due to a linear velocity difference even when a deviation occurs in the Vt due to the linear velocity due to environmental changes or the like over time. And its purpose.

  In order to achieve the above object, according to the first aspect of the present invention, two-component developer containing toner and carrier is used, and toner density control is performed based on the detected value of the magnetic permeability sensor. An image forming apparatus having a developing device including a developer agitating member having a linear speed, having a mode for performing toner density control by process control, and performing density adjustment process control for density adjustment according to a result of the process control. At the time of density adjustment process control, the developer agitating operation with different linear velocities is performed, the output value Vt of the magnetic permeability sensor at these linear velocities is detected, and the difference is set as the Vt linear velocity correction amount.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, during the density adjustment process control, a developer stirring operation with different linear velocities before and after density adjustment is performed, and Vt at these linear speeds is detected The Vt correction amount of the toner density in the other region is also determined from the Vt linear velocity correction amount at different toner concentrations between the Vt before the density adjustment and the Vt after the density adjustment.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the Vt linear velocity correction mode is entered during density adjustment process control at a density different from the previous density adjustment process control.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the Vt linear velocity correction amount is determined at the time of density adjustment process control when a predetermined number of sheets are passed from the previous density adjustment process control. Features.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the Vt linear velocity correction amount is determined at the time of the density adjustment process control when a certain period of time has elapsed since the previous density adjustment process control. It is characterized by.

According to the first aspect of the present invention, according to the present invention, by detecting and correcting the Vt difference due to the linear velocity, it is possible to eliminate the Vt linear velocity difference due to the influence of the developer state (time and environment). It is possible to eliminate abnormal qualities such as low ID at high speed, excessive ID at low speed, transfer dust and the like that occur at the time of linear speed switching.
By entering the Vt linear velocity correction mode during the density adjustment process, Vt stabilized by developer agitation (the toner concentration and agent balance in the agent are stable) and immediately after that Vt detected during operation at another linear velocity ( By determining the Vt linear velocity correction amount based on the difference in the toner density stability in the agent, the accuracy of the Vt linear velocity correction amount can be increased and abnormal quality can be eliminated.

According to the invention described in claim 2, it is possible to detect the Vt linear velocity correction amount at two different types of TC = Vt.
According to the third aspect of the present invention, the operation can be eliminated in the same case as the previous TC and Vt ranges, and the waiting time of the user can be reduced.
According to the fourth aspect of the present invention, when there is no change in the agent state and there is no change in the Vt shift amount, the operation can be eliminated and the waiting time of the user can be reduced.
According to the fifth aspect of the present invention, since the period is managed, the change in the agent state can be managed more, the operation can be eliminated when there is no change in the Vt shift amount, and the waiting time can be further reduced.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
First, an overview of the overall configuration of the image forming apparatus according to the present embodiment will be described with reference to FIGS. 1 and 2. 1Y (yellow), 1M (magenta), 1C (cyan), and 1K (black) image forming units are arranged in parallel along the conveyance direction of the transfer paper 12 as a recording medium. Excluding the reference numerals for each color, each image forming unit has a photosensitive drum 2 as a cylindrical latent image carrier, and around the photosensitive drum 2 in order clockwise as charging means. Charging roller 3, writing device 4 for exposing the color-separated image data, developing device 5 having colored toner (yellow, magenta, cyan, black) corresponding to the color-separated image data, and transfer image of the toner image A transfer roller 6 as a transfer means for transferring to 12, a cleaning blade 7 as an element of a cleaning means for removing transfer residual toner on the photosensitive drum 2 after transfer, and the like are disposed.

The transfer paper 12 is supported by being wound around a plurality of rollers, and is transported by a transport belt 8 disposed so that the photosensitive drums are in rolling contact with each other.
After the paper is fed, the transfer paper 12 accommodated in the paper feed cassette is temporarily stopped by the pair of registration rollers 10, corrected for oblique displacement, and fed onto the transport belt 8. The transfer paper 12 sequentially conveyed to the respective image forming units by the conveyance belt 8 sequentially receives the transfer of the toner image on the photosensitive drum 2 by the transfer roller 6 at the respective transfer positions, and is fixed by the fixing device 14. Once fixed, a permanent full color image is formed. After the fixing, the transfer paper 12 is discharged to a paper discharge tray 16 by, for example, a paper discharge roller pair 15 and stacked. In FIG. 1, reference numeral 9 denotes a belt cleaning device for cleaning the conveyor belt 8, and reference numeral 13 denotes a manual feed tray.

  The developing device 5 is disposed on the side of the photosensitive drum 2, and as shown in FIG. 2, a part of the developing device 5 is exposed from the opening inside the developing casing in which the opening is formed toward the photosensitive drum 2. , A developing sleeve 17 made of a non-magnetic material as a developer carrying member carrying a two-component developer comprising toner and a magnetic carrier on its surface, and a magnet roller (not shown) as magnetic field generating means fixedly arranged inside the developing sleeve 17 1), a doctor 18 as a developer regulating member for regulating the amount of the developer carried and carried on the developing sleeve 17, screw-like developer agitating members 19, 20 and the like.

The toner density in the developing device 5 is consumed by the image data, and is almost obtained by replenishing the toner according to the image area and the value of the magnetic permeability sensor (hereinafter referred to as “T sensor”) C in the developing device 5. Kept constant.
In addition, a plurality of halftones and solid patterns formed on the photosensitive drum 2 or the conveyor belt 8 are processed once per 200 sheets (the number of sheets varies depending on the purpose and may be about 100 to 1000). The T sensor target value, the charging potential, and the light amount are set according to a mode in which the adhesion amount is converted by the sensor and set so that the target adhesion amount is obtained.
Unlike monochrome monochrome printers, color printers and copiers have many opportunities to continuously produce high-area images. Therefore, as shown in Table 1 (summarized carrier coverage of full-color printers and monochrome printers) It is necessary to control with TC (high carrier coverage).

Here, the shape of the developer stirring members 19 and 20 and the characteristics related to Vt will be described. FIG. 3 is a plan view of the periphery of the developer stirring members 19 and 20, and FIG. 4 is a plan view showing fins and mylars (stirring portions at positions facing the T sensor C) on the developer stirring member 19.
In FIG. 3, a partition member is provided between the developer agitating member 19 and the developer agitating member 20 for conveying the developer in the opposite directions, respectively, and the developer is transferred at the end in the longitudinal direction. The developer circulates in a loop.
In FIG. 4, the fin width is indicated by A, the Mylar width is indicated by B, and the T sensor is indicated by C.
FIG. 5 shows Vt-related characteristics when the Mylar width of the developer agitating member at a location facing the T sensor C is swung. FIG. 5 shows a case where the fin is fixed to 16 mm. The Vt-related characteristics mentioned here are: Vt linear velocity (linear velocity) shift amount when the Mylar width is changed (at the photosensitive member velocity of 125 to 185 mm / sec), T sensor sensitivity (V / wt%), The amount of decrease in Vt, (Vcnt when the initial agent is 5 wt%) is shown.

The graph of FIG. 5 shows the following contents.
(1) Vt linear velocity shift amount (125-185) ... Mylar width is increased from 0.07 V to 0.64 V with a change from 0 to 5.5 mm (mylar width is narrow and shift amount is reduced).
(2) T sensor sensitivity (V / wt%): The Mylar width is changed from 1 to 5.5 mm, and there is almost no change from 0.47 V to 0.50 V (not related to the Mylar width).
(3) Vt drop amount during air stirring: Mylar width is reduced from 0.66V to 0.09V due to a change from 0 to 4 mm (mylar width is wide and reduction is reduced).
(4) Vcnt at initial agent: Mylar width increased from 5.9 V to 8.1 V with a change from 0 to 5.5 mm.
The same tendency was observed when the fin width was swung with the Mylar width fixed.

Thereby, the following results are obtained.
(A) By increasing developer mixing property in the vicinity of the T sensor (widening the fin / mylar width), the Vt linear velocity shift amount is increased / the Vt decrease amount during idle stirring is decreased.
(B) Due to a decrease in developer mixing property in the vicinity of the T sensor (narrowing the fin / mylar width), the Vt linear velocity shift amount is small / the Vt decrease amount during empty stirring is large.
(C) The above (a) and (b) are in a trade-off relationship.
From these, it is understood that the Vt linear velocity difference (linear velocity difference) and the Vt decrease amount cannot be suppressed simultaneously under the mechanical conditions.

FIG. 6 is a characteristic diagram showing a change in Vt at the time of blank paper passing (no toner replenishment) in the initial agent when the T sensor portion has fins and mylars (see FIG. 7). FIG. 8 is a characteristic diagram showing a change in Vt when a blank sheet is fed (no toner replenishment) with a 50K sheet developer and a T sensor portion having fins and a mylar (see FIG. 7).
FIG. 9 is a characteristic diagram showing a change in Vt when a blank sheet is fed (no toner replenishment) when the T sensor portion has a fin cut and no mylar (see FIG. 10) with a 50K sheet passing developer. 6, 8, and 9, the j part of Vt is at standard speed, the k part is at high speed, the l part is at low speed, and 200 sheets are passed through each part.

In the initial agent shown in FIG. 6, the Vt linear velocity difference is about 0.1 V (difference between j and k parts, difference between l and j parts), but it becomes larger in the case of the 50K sheet paper developer shown in FIG. ing.
From this, it can be seen that the Vt linear velocity difference varies depending on the state of the developer, and it can be said that the Vt linear velocity correction amount cannot be a fixed value. In FIG. 9, the Vt linear velocity difference is eliminated even with the same 50K sheet passing developer, but the Vt decrease amount which is small in FIGS. 6 and 8 is large. Under mechanical conditions, it can be seen that if the Vt linear velocity difference is eliminated, a decrease in Vt occurs.
The Vt drop amount cannot be corrected because it varies depending on the amount of replenished toner, but the Vt linear velocity difference does not change as long as the developer fluidity is the same, and therefore does not need to be corrected frequently. Therefore, it can be said that the correction may be performed when the environment is switched or over time (long range such as 5K sheets, 10K sheets).

FIG. 11 shows a flowchart of the control operation in this embodiment.
When the density adjustment process is executed, if the number of sheets (period) is less than the previous density adjustment process, the normal density adjustment process is executed and the process ends.
When the number is greater than a certain number (period), when γ is within the target range, the process is completed once, so the Vt linear velocity correction mode is not entered. When γ is outside the target range, the density adjustment program is set, and two types of TC (Vt level) are obtained, so the Vt linear velocity correction mode is entered.
First, Vt_a1 of the process controller is read, and the developer is stirred at another linear speed b to read Vt_b1. The linear velocity correction number (Vt_a1−Vt_b1) at γ is determined. When the target γ is reached after replenishment / consumption, Vt_a2 of the last process control is read, and the developer is stirred at another linear speed b to read Vt_b2. The linear velocity correction number (Vt_a2−Vt_b2) at γ is determined. The correction amount is determined and reflected by the method shown in FIG. 12 below, and the process control is terminated.

As shown in FIG. 12, the linear velocity correction amount differs even when the Vt value is high (when it is high or low). Decide the amount.
When the sheet is fed at the linear velocity b, the Vt value of the linear velocity a (Vt_a) is calculated by Vt_b = Vt_b1 + (Vt_a−Vt_a1) × (Vt_b2−Vt_b1) / (Vt_a2−Vt_a1).

The development conditions of this embodiment are shown below.
Mechanical conditions:
Gap between the developing sleeve and the photosensitive drum (hereinafter referred to as GP) 0.4 to 0.6 mm
Gap between development sleeve and doctor blade (hereinafter referred to as GD) 0.4 to 0.6 mm
Development sleeve diameter 18φ
Photoconductor linear speed 60-250mm / sec
Ratio of developing roller linear velocity to photosensitive member linear velocity 1.1-1.8
Developer:
Carrier ferrite average 50-70μm
Toner Polyol resin, polyester resin Average particle size 6-7μm
Additive amount 0.5-2.0wt%
Carrier coverage 30-80%
Charge amount (Q / M) 10-30 μC / g

1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention. It is an expanded sectional view of the site | part of a developing device. It is a schematic plan view centering on the developer stirring member of the developing device. It is a side view which shows the fin and mylar on a developer stirring member. It is a graph which shows the Vt related characteristic when the Mylar width | variety of the developer stirring member of the location facing T sensor is shaken. It is a graph which shows Vt transition at the time of a white paper passing with a T sensor part with a fin and a mylar with an initial agent. FIG. 7 is a side view of a developer stirring member corresponding to the characteristics of FIG. 6. It is a graph which shows Vt transition at the time of a white paper passing with a T sensor part with a fin and a mylar having a 50K sheet paper developer. It is a graph which shows Vt transition at the time of a white paper passing without a T sensor part fin cut and a mylar without a 50K sheet paper developer. FIG. 10 is a side view of a developer stirring member corresponding to the characteristics of FIG. 9. It is a flowchart which shows control operation. It is a graph which shows the relationship between TC and Vt in each linear velocity.

Explanation of symbols

C Magnetic permeability sensor 5 Developing device 19, 20 Developer stirring member

Claims (5)

A two-component developer containing toner and carrier is used to control the toner concentration based on the value detected by the magnetic permeability sensor. The developing device has a developer stirring member having two or more linear velocities. In the image forming apparatus having a mode for controlling the toner density by the process control and performing the density adjustment process control for adjusting the density according to the result of the process control.
At the time of the density adjustment process control, the developer agitating operation with different linear velocities is performed, the output value Vt of the magnetic permeability sensor at these linear velocities is detected, and the difference is used as the Vt linear velocity correction amount. Image forming apparatus. The image forming apparatus according to claim 1.
During the density adjustment process control, developer agitation operations with different linear velocities are performed before and after density adjustment, Vt at these linear velocities is detected, and when the toner density is different between Vt before density adjustment and Vt after density adjustment. An image forming apparatus characterized in that a Vt correction amount of toner density in another region is also determined from a Vt linear velocity correction amount. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein a Vt linear velocity correction mode is entered during density adjustment process control at a density different from the previous density adjustment process control. The image forming apparatus according to claim 1 or 2,
An image forming apparatus characterized in that a Vt linear velocity correction amount is determined at the time of density adjustment process control when a predetermined number of sheets are passed from the previous density adjustment process control. The image forming apparatus according to claim 1 or 2,
An image forming apparatus characterized in that a Vt linear velocity correction amount is determined during density adjustment process control when a predetermined period of time has elapsed since the previous density adjustment process control.

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