JPH03260669A - Image forming device - Google Patents

Abstract

PURPOSE:To faithfully reproduce density and a thin line by discriminating whether the cause of the lowering of image density is the set condition of a developing device or a pattern latent image forming condition and controlling the rotating speed of a developing sleeve or the electrostatic charging potential of a photosensitive body. CONSTITUTION:A pattern latent image is formed on a photosensitive body 1 and developed by a 1st developing device 10 to form a 1st toner pattern image TP1. Then, the density D1 of the TP1 is detected by a density sensor 17. Next, an electrostatic charger 2 is turned off and the bias of the developing device 10 is switched to +500V to form a 2nd toner pattern image TP2, and the density D2 is read by the sensor 17. When D1<DA and D2<DB hold between 1st reference density DA and 2nd reference density DB, the revolving speed of a motor 43 is made high to accelerate the revolving speed of the sleeve 22a so that a developing material carried to a developing area is increased to recover the image density. When D1<DA and D2>DB hold, the electrostatic charging potential of the photosensitive body 1 is made high. Thus, the density and the thin line are faithfully reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic copying process.

(Prior Art) Conventionally, with respect to image forming apparatuses such as copying machines and printers that form toner images using a two-component developer consisting of toner and carrier, the following two methods have been used to optimize image density. is proposed.

First, a pattern latent image formed on the surface of a photoreceptor is visualized as a toner pattern image using a developing device, and the image density of this toner pattern image is read by a reflective photosensor. Predetermined basis TJJ: If it is lower than i8 degrees, the method of replenishing toner to the developing device (hereinafter referred to as
It is called "rAIDc method". ).

Another method is to install a magnetic sensor in the developing device and measure the toner concentration of the developer, that is, the mixing ratio of 1-toner to carrier, and the measured toner concentration is the standard. How to replenish toner (hereinafter referred to as l'
It is called the ``AT I) C method''. ).

When comparing the two methods, the ATDC method indirectly calculates the degree of image per image by measuring the concentration of i-ner, whereas the AI
The DC method can be said to be a highly reliable method because it measures the image density of an actual image formed on a photoreceptor and performs 1-ner density control based on this.

By the way, conventionally, as an image forming apparatus,
In Japanese Patent No. 7783, two magnetic brush developing devices containing toner of the same color are provided on the side of a photoreceptor, and these developing devices are driven almost simultaneously to transfer the electrostatic latent image developed by the first developing device to the second magnetic brush developing device. A method has been proposed in which the image is developed again using two developing units.

In this image forming apparatus, the first developing device secures the image density, and the second developing device develops fine lines exactly as expected, thereby forming an image with excellent density reproducibility and fine line reproducibility.

Therefore, strict image density control is not necessarily necessary for the second developing device, which aims to achieve fine line reproducibility of 1.
For the first developing device whose purpose is to ensure image density, it is necessary to perform highly accurate image density control, and in this case, it is preferable to manage image density by the more reliable AIDC method.

(Problem to be Solved by the Invention) However, the image density is determined by the formation condition (I) of the electrostatic latent image and the setting conditions of the developing device. This is not caused by the heat, but may be caused by poor bias conditions or charging conditions.

For this reason, even if the toner density is normal, if the image density has decreased due to bias failure, for example, when toner is replenished to the developing device using the AIDC method, the toner in the developer will be 714 degrees or more than necessary. '', which causes problems such as background fog on the image and toner scattering, resulting in contamination of peripheral equipment.

In order to solve this problem, is it possible to use the ATDC method in combination and regulate the upper limit so that the toner concentration of the developer does not exceed a predetermined value? If this is the case, a problem arises in that the necessary image density cannot be guaranteed.

(Means for Solving the Problems) Accordingly, the present invention provides an image forming apparatus that simultaneously drives the plurality of developing devices to develop multiple electrostatic latent images,
It is an object of the present invention to provide an image forming apparatus that detects the cause of a decrease in haze and restores image density through appropriate control corresponding to the cause.

Under the above [1], the present invention comprises a photoreceptor (1), a magnetic brush type first developer (10) and a second developer (11), After developing the electrostatic latent image with the first developer 2N (10), the second developer (11
), the image forming apparatus comprises a pattern latent image forming means (2, 9) for forming a pattern latent image (I),) on the photoreceptor (1); a first pattern image forming mode (step 521) in which a first toner pattern image (TP, ) is developed by the first developing device (10); a second pattern image forming mode (step 524) in which a second toner pattern image (TP2) is formed on the photoreceptor by applying a bias of the same polarity as the image density measuring means (17);
), and (2) the image density measuring means (17) measures the first toner pattern image (TP, ) and the second toner pattern image (TP,
, ), an image density detection mode (step S21, 524) for detecting the image density (Dl), (D,) of the first toner pattern image (the image density (Dl) of the TPO and the first reference density); (a first comparison mode (step 523) in which D is compared with
The image density of the toner pattern image (TP2) of
a second comparison mode (step 525) in which the image density (Dl) of the first toner pattern image ("rp,) is compared with the reference density (D8) of vi.
D and the second toner pattern image (T P
When the image density (D,) of t) is lower than the second reference density (DB), the first developing device (10) and the second developing device (1
1) at least one of the sleeves (22a, 2
2b) rotation speed adjustment mode (step 826) in which the rotation speed is increased; Image density (D,) of toner pattern image (TPt) of No. 2
A charge potential change mode (step 527) in which the charge potential (VO) of the photoreceptor (1) is halved when the charge potential (VO) is higher than the second reference density (D, , ) is provided.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

1. Configuration of image forming device FIG. 1 shows the main parts of an image forming apparatus.

In the figure, photoreceptor I is a cylindrical body having an organic photoreceptor layer on its outer periphery, and is designed to rotate in the direction of arrow a at a speed of 50 mm/sec.

Around the photoconductor 1, a charging charger 2, an inter-image eraser 9, a first developer IO1, a second developer 11, a transfer charger 12, a separation charger 13, a cleaning device 14, and a main eraser 15 are arranged along the rotation direction of the photoconductor 1. It is arranged.

The charger 2 includes a charge stabilizing plate 3 arranged parallel to the photoconductor 1, a charge wire 4 stretched over the charge stabilizing plate 3, and a green domain unit covering an opening of the charge stabilizing plate 3 facing the photoconductor 1. 5, a power supply 6 is connected to the charge wire 4, and another power supply 7 is connected to the grid, tome, and /yu 5.

The first developing device 10 is a magnetic brush type developing device using a two-component developer consisting of toner and carrier.

In the first developer 2g10, the developing roller 20a is composed of a fixed magnet body 21a and a cylindrical sleeve 22a.

The sleeve 22a faces the photoreceptor 1 with a developing gap Ds1, and has a regulating plate 23a or a regulating gap D on its upper outer peripheral surface.
b+, and are connected to the power source 24a.

Further, as shown in FIG. 2, the rotation speed of the sleeve 22a can be adjusted by a rotation control device 40. In this rotation control device 40, a gear 45 is attached to the drive shaft 44 of the drive motor 43, and the gear 45 meshes with the gear 42 provided on the drive shaft /II of the sleeve 22a.

The rear space of the developing roller 20a is connected to the front conveyance path 2 by a wall 25a.
6a and a rear conveyance path 27a, which are connected to each other via passages (not shown) provided on the back side and the front side of the wall 25a, and the rear conveyance path 26a.

27a, brush meter roller 28a1 and conveyance blade 29, respectively.
It is arranged so that it can be rotated. In addition, the conveyance path 26
A, 27a contains a developer, and the l/toner concentration is measured by a toner concentration detection sensor 30a provided at the bottom of the front conveyance path 26a.

The toner supply section 31a stores toner, and the toner is supplied to the rear conveyance path 27a by driving the supply roller 32a with a motor 33a.

The second developing device 11 has almost the same configuration as the first developing device 10, or does not include a sleeve rotation control mechanism;
This developing device is different from the first developing device 10 in that a photosensor 17 is provided in the upper part facing the photoreceptor 1.

In addition, 20a is a developing roller, 21b is a magnet body, 22b
is the sleeve, 23b is the regulation plate, 24b is the power supply, 25 b
is the wall, 26b is the front conveyance path, 27b is the rear conveyance path, 28
b is a bucket roller, 29b is a conveyance blade, 30b is a toner concentration detection sensor, 31b is a toner replenishment section, 32b is a replenishment roller, 33b is a motor, D is a regulation cap, DS
t indicates the development gap.

FIG. 3 shows the circuit configuration of the image forming apparatus. This circuit is mainly composed of a control device 100, and includes a comparator 102,
The signals of the toner concentration detection sensors 30a, 30b and other signals are input, and when operation signals are output to the power supplies 6, 724a, 24b, motors 33a, 33b, and motor 43, other signals are output as well. There is.

g,,,,,,..., statue, raccoon dog The processing contents of the control device 100 will be explained below.

First, the operation of the first developing device 10 will be explained.

In the first developing device 10, the developer care roller 28a
It is circulated and conveyed through the conveyance paths 26a and 27a by the conveyance blade 29a. That is, the developer in the front transport path 26a is transported from the back side to the front side, and is sent to the rear transport path 27a via the communication path at the front end.

Further, the developer in the rear conveyance path 27a is conveyed from the front side to the back side, and passes through the communication path at the rear end to the front conveyance path 26a.
sent to. The developer is mixed while being transported through the transport paths 26a and 27a, and the toner is triboelectrically charged to a positive polarity and the carrier to a negative polarity.

Further, the developer transported through the front transport path 26a is supplied to the developing roller 20a by a bucket roller 28a. The developer supplied to the developing roller 20a is attracted by the magnetic force of the magnet 21a and held on the outer periphery of the sleeve 22a, and is conveyed in the direction of the arrow in a magnetic brush state based on the rotation of the sleeve 22a, and is conveyed in the direction of the arrow by the regulating cap Db. Only the developer that has passed through □ is transferred to the opposing area between the sleeve 22a and the photoreceptor 1 (hereinafter referred to as "
"Development area". ) X4, and while in contact with the photoreceptor l, the developing gap I)5. After passing through, it falls into the front conveyance path 26a at a portion opposite to the bucket roller 28a and is mixed with the developer.

The toner concentration of the developer is detected by the toner concentration detection sensor 30a, and when it is determined that it is lower than a predetermined reference concentration, the motor 33a is driven, and the toner is replenished from the toner replenishing section 31a to the rear conveyance path 27a, and the developer is The toner density is maintained almost constant. .

In the second developing device 11, the same processing as in 10 is performed on the first developing image "A". Therefore, the explanation will be omitted.

Next, a description will be given of multiple development processing in which an electrostatic latent image formed on the outer peripheral portion of the photoreceptor 1 is developed by rotating the first developing device 10 and the second developing device 11 substantially simultaneously. At this time, the first
In the developing device 10 and the second developing device 11, the developing cap Ds+
"0.6mm+ Dstl, On+n+, Regulation key+'
The sleeve 23a is set to 0, 5 mm, and the sleeve 23a
Bias V Bl+V B2 applied to 23b are both set to -I50V.

While the photoreceptor 1 is rotating in the direction of the arrow a, the charger 2 is connected to the churn wire 4 by the power source 6.
A voltage of 6KV is applied and the grid is turned on.

A bias of approximately -600V is applied to the terminals 4 and 4 from the power supply 7. As a result, the photoreceptor l passing through the charged area
The surface of is charged to -600V.

The surface of the charged photoreceptor 1 is imaged in the exposure area X2.
The light 8 is exposed to form an electrostatic latent image corresponding to the image to be reproduced.

The surface of the photoreceptor 1 on which the electrostatic latent image has been formed is illuminated by the inter-image eraser 9 in the defrosting area x3, thereby erasing the charges in the non-image area.

The electrostatic latent image that has passed through the static elimination area X3 is transferred to the first development area
When passing through 4, bias ■8. Based on the electrostatic contrast between (150V) and the potential of the electrostatic latent image portion, toner is supplied from the developer passing through the development area X4 as the sleeve 22a rotates, and is developed as a toner image.

The electrostatic latent image that has passed through the first development area X4 is conveyed to the second development area
Toner is supplied again from the developing device 11 and the image is reproduced.

As described above, the toner images formed in the development areas X, .

The recording medium 16 onto which the toner image has been transferred is transferred to a separate charger 1.
The toner image is separated from the surface of the photoreceptor l at step 3, and the toner image is heated and fixed by a fixing device.

On the other hand, the cleaning device 14 removes residual toner from the surface of the photoreceptor 1 that has passed through the portion facing the separation charger 13, and the main eraser 15 erases the residual charge to prepare for the next charging.

Here, in both the first developing device 10 and the second developing device 11, the regulation gap D b l + D b t is the same (=0
．． 5 mm), and the amount of developer conveyed to the development areas X, , X, per unit time is set to be the same.

On the other hand, the development cap Ds of the first development area X4 is 0.
6 mm, the developing cap D5° of the second developing area X is 1
．． omm, the frequency of contact of the developer with the photoreceptor l is higher in the first development area X4 than in the second development area X5.

Therefore, sufficient toner is supplied to the electrostatic latent image passing through the first development area X4, and a loose image or a letter image with the thickness of a letter is visualized with the necessary density. but,
Due to the high frequency of contact with the developer, the surface of the photoreceptor 1 is often scraped off with a number of I-toners, and the reproducibility of fine lines is not necessarily good.

In the subsequent second development area X5, the frequency of contact of the developer with the photoreceptor 1 is low, and therefore the scraping effect of the developer is small.
Here, the toner that has formed on the thin line electrostatic latent image passes through the development area X without being scraped off.

Therefore, on the image reproduced on the recording medium 16, solid images and ordinary character images are reproduced with sufficient density, and even thin lines are reproduced faithfully to the original.

4. Regarding image density control of image forming apparatus. This will be explained with reference to the flowcharts in FIGS.

(Copy control routine (see FIG. 4)) In this routine, in step S11, it is determined whether or not a print key (not shown) has been pressed, and if it is determined that the print key has been pressed, the process advances to step S12. Executes an image density detection routine to be described later.

When the image density control routine is completed, a paper feed conveyance control subroutine, an optical system control subroutine, and a photoconductor rotation subroutine are respectively executed in steps S13 to Si2.
The li supply control routine is executed and the process returns to the main routine (not shown).

(11) Image density control subroutine (see FIG. 5) In this subroutine, in step S21, a toner pattern image for image density detection is created, and the image density is detected. Specifically, as shown in FIG. 6, the outer periphery of the photoreceptor 1 rotating in the direction of arrow a is charged by the charger 2 (step 534). Next, as shown in FIG. 8, in step 535), the inter-image eraser 9 is blinked to form a pattern latent image 1)1, and the first developing device 10 is driven to form the pattern latent image 1)l. Toner pattern image TP shown in the figure
Visualize as. Further, the image density of the toner pattern image 1''P is read by the photosensor 17 (step 836).

In step S22, the toner pattern image 1' on the photoreceptor 1 is
In order to scrape off the toner of P, the bias voltage of the developing sleeve 22F of the second developing device 11 is increased. .

Change to -500V.

As a result, as shown in FIG. 10, the positively charged toner constituting the toner pattern image T I) is collected into the sleeve 22b by the electric force.

Therefore, the toner of the toner pattern image T P is not wasted and is used for development in the second developing device 11 .

Subsequently, in step (S23), a signal corresponding to the image density is input from the photosensor 17 to the comparison input terminal of the comparator 102. In addition, the comparator 102 includes a power supply 10
1 to a voltage signal corresponding to the first reference concentration DA is input. Note that the first base i11 degree DA is a concentration that regulates the lower limit. Then, the comparator 102 compares the voltages of the respective input signals.

As a result, D , < DA, that is, the image density D1 or the first
If it is lower than the base r$ concentration DA, the comparator 102 outputs a signal to the control device +00, and the control device 100 executes the process of step (S24).

In step (S24), another image density detection pattern is formed and its image density is read.

Specifically, as shown in FIG. 7, the charger 2 is turned off while the photoreceptor is rotating (step 537).
, the surface of the photoreceptor 1 is maintained in an uncharged state. That is,
The image density obtained as a result is kept in a state in which factors causing deterioration of the charger 2 and the photoreceptor 1 are not included. Next, the bias 1, 1 of the first developing device 10 is switched to +500V (Step 538), and the positively charged toner is electrically repelled to fly toward the photoconductor 1, and the toner shown in FIG. Forming a pattern image T P , and increasing the image density,
is read by the photosensor 17 (step 539). Note that the toner constituting the toner pattern image TPt is as follows:
Similarly to the toner pattern image TP, the step S22
The voltage is electrically recovered by the sleeve 22b to which 1,500 cm is applied. Therefore, toner is not wasted.

Subsequently, in step S25, the second reference density D8 and the image density D8 are compared.

If D<Dゎ, that is, the image density of the toner pattern image TP is lower than the second reference density, the cause of the decrease in image density lies in the setting conditions of the developing device 10. The reason for this is that, as mentioned above, the l/ner pattern image TP was created with the photoreceptor I left in an uncharged state and the factors affecting the deterioration and charging of the photoreceptor I divided by tJF. be.

Therefore, in step 326, the rotational speed of the motor 43 is increased, the rotational speed of the sleeve 22a is increased, and the amount of developer conveyed to the development area X4 is increased to restore the image density.

On the other hand, D, ≧D8, that is, the toner pattern image TP.

If the image density RI is higher than the second reference density DB,
The image density of the toner pattern image TP is the reference value [)A
Contrary to the above-mentioned case, the reason why the value is lower than that is considered to be due to the latent image forming conditions such as deterioration of the photoreceptor or charging.

Therefore, in step S27, the output of the bias power supply 7 of the grid mesh 5 is increased.

As a result, the charged potential of the photoreceptor 1 is ■. Then, the image density is restored.

As described above, if the cause of the decrease in image density is due to the setting conditions of the first developing device 10, the image density can be restored by increasing the rotation speed of the motor 43 and increasing the amount of developer conveyed to the development area X4. If the reduction in image density is due to photoreceptor deterioration or charging, then the charging potential is V. or adjusted. That is, the image density can be restored by eliminating the cause of the decrease in image density.

If it is determined in step S23 that DA≦D1, that is, the image density D1 or the first reference density DA is satisfied, the process advances to step S29.

In step S29, the image density D1 is compared with a third reference density DC. Note that the third reference concentration is is the concentration that regulates the upper limit.

As a result of comparison, D, ≦Dc, that is, image density or lower limit ring '1
13 degrees I) Located between A and the upper limit regulation concentration DC
If the F concentration state (DA×DI≦D[l), the process advances to step 328.

1)+>I)c, that is, image density D1 or upper limit regulation density■
] If the density exceeds 3, proceed to step S30,
It is determined whether the rotation speed of the motor 43 in the rotation control device 40 has increased. If the number of revolutions is 2, the number of revolutions of the motor 43 is reduced in accordance with the density difference in step S3 to reduce the image density. Conversely, if the rotational speed of the motor 43 has not increased, the process proceeds to step S32 without reducing the rotational speed, and the image density is lowered depending on the charging conditions.

In step S32, it is determined whether or not the output of the power source 7 is in a high voltage output state. If the output is in a high voltage output state, the output of the power source 7 is lowered in step S33, and the charged potential of the photoreceptor 1 is set to ■. The process proceeds to step 828, and if the output of the power source 7 is in a low voltage output state, the process proceeds to step 328.

In step (S28), the output of the voltage source 124a is changed to return the developing bias to Va=-150V, resulting in a normal image forming state.

H, =, side-saving lumberjack I41 In the above explanation, when it is assumed that the cause of the decrease in image density is in the first developing device 10, it is assumed that the rotation speed of the first developing device sleeve 22a is adjusted or the rotation speed of the second developing device sleeve 22a is adjusted. A rotation control device may be provided in the container 11, and the image density may be restored by adjusting the rotation speed of the second developing sleeve 22b or by adjusting the rotation speed of both sleeves 22a and 22b.

Furthermore, in the above description, the toner pattern image TP.

TP is assumed to be collected in the second developing device 11, or may be collected in the cleaning device 4. In this case, especially for the second toner pattern image TP, the time for setting the developing bias VB) to 500V is as short as possible, and the pattern image TP is made small within a range that does not interfere with image density detection. Try to reduce wasteful consumption.

Further, the photosensor 17 is connected to the second developing device 1711 (D
It may be provided in a part of the cleaning device 14 or in the lower part of the cleaning device 14.

Furthermore, in the above embodiment, the developer filling rate of the developing area where the developing sleeve of the developing device faces the static T4 latent image carrier is
Did we explain an example in which the developing cap DS+ of the first developing device 10 is made smaller than the developing cap D9 of the second developing device 11 in order to make the first developing device 10 higher than the second developing device 11? The regulation gap D of the first developing device 10 is the second developing device 'r? jll regulation gap Db2, or the circumferential speed of the sleeve of the first developing device 10 is made larger than the circumferential speed of the sleeve of the second developing device 11.
The amount of developer conveyed to the developing area X4 of
The amount of developer may be greater than the amount of developer transported to one development area x5.

(Effects of the Invention) As is clear from the following explanation, in the image forming apparatus according to the present invention, the image density control of the image forming apparatus in which the same electrostatic latent image is developed multiple times using a plurality of developing units. In,
Is the cause of the decrease in image density or is it the setting conditions of the developing device?
Ill determine whether the cause is due to the pattern latent image formation conditions, and if the cause is due to the setting conditions of the developing device, adjust the rotation speed of the sleeve, and if the cause is due to the latent image formation conditions, adjust the charged potential of the photoreceptor. That's what I do.

Therefore, even though the toner concentration of the developer is maintained appropriately, toner is not further replenished to the developer, and a high-quality image without background fog etc. can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the main parts of the image forming apparatus, Fig. 2 is a front view of the rotation control device, Fig. 3 is a control circuit diagram, Fig. 4 is a flowchart of the copy control routine, and Fig. 5 is for AIDC control. Flowchart of the subroutine, FIG. 6 is a flowchart of the subroutine for forming a toner pattern image, etc.
The figure is a flowchart of a subroutine such as forming a toner pattern image, FIG. 8 is a perspective view showing a pattern latent image formed on a photoconductor and a developed toner pattern image, and FIG. 9 is a diagram showing a pattern latent image formed on a photoconductor-L. FIG. 10 is an explanatory view showing the toner scraping action of the second developing device. DESCRIPTION OF SYMBOLS 1. Photoreceptor, 2... Charging charger, 9... Inter-image eraser, 10... First developing device, 11... Second developing device, 2
Q a, 2Q b-developing roller, 22a, 22b sleeve, 23a, 23b--regulating member, 24 a24
b...Power supply, 40...Rotation control device, D S,, D
s2 development gap, D bl+ D b2...Regulation cap, P)),...Pattern latent image, i' P l+
i'P... Toner pattern image.

Claims (1)

[Claims] (1) A photoreceptor, a magnetic brush type first developer and a second developer, and the electrostatic latent image formed on the photoreceptor is transferred to the first developer.
An image forming apparatus that develops the image using the developing device and then further develops the image using the second developing device, further comprising: a pattern latent image forming means for forming a pattern latent image on the photoreceptor; and developing the pattern latent image using the first developing device. a first pattern image forming mode in which a first toner pattern image is formed; and a second pattern image forming mode in which a bias having the same polarity as the toner charging polarity is applied to the first developing device to form a second toner pattern image on the photoreceptor. a second pattern image forming mode; an image density measuring means; an image density detection mode in which the image density measuring means detects the image density of the first toner pattern image and the second toner pattern image; a first comparison mode that compares the image density of the toner pattern image with a first reference density; and a second comparison mode that compares the image density of the second toner pattern image with a second reference density. , when the image density of the first toner pattern image is lower than the first reference density, and the image density of the second toner pattern image is lower than the second reference density,
A rotation speed adjustment mode in which the rotation speed of the sleeve of at least one of the first developing device and the second developing device is increased; An image forming apparatus comprising: a charging potential change mode for increasing the charging potential of the photoreceptor when the image density of the toner pattern image is higher than a second reference density.