JPH03260670A - 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 toner concentration of the developing device or the electrostatic charging potential of a photosensitive body. CONSTITUTION:A pattern latent image is formed on a photosensitive body 1 and developed by the 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 voltage of a power source 104 which is inputted in a comparator 103 is decreased and the developing device 10 is replenished with toner to recover the toner concentration. 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. or has been proposed.

First, a pattern latent image formed on the surface of a photoconductor 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. If the density is lower than a predetermined standard density, the developer is refilled with toner (hereinafter referred to as rAIDc).
It is called "law". ).

Another method is to install a magnetic sensor in the developing device to measure the toner concentration of the developer, that is, the weight mixing ratio of toner to carrier, and if the measured toner concentration is less than the standard toner concentration, toner is replenished into the developing device. Method (hereinafter referred to as rATDc
It is called "law". ).

When comparing the two, the ATDC method calculates the image density indirectly by measuring the toner density, whereas the ATDC method calculates the image density indirectly by measuring the toner density.
The method measures the image density of the actual image formed on the photoreceptor,
Based on this, toner a degree control is performed, so it can be said that this method is highly reliable.

By the way, conventionally, as an image forming apparatus, the time opening W1-30
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. It has been proposed that the image be developed again using two developing units.

In this image forming apparatus, the first developer ensures image density, the second developer faithfully reproduces fine lines to the original, and an image with excellent density reproducibility and fine line reproducibility is formed.

Therefore, strict image density control is not necessarily required for the second developer, which aims to improve the reproducibility of fine lines, but highly accurate image density control is performed for the first developer, which aims to ensure image density. In this case, it is preferable to mainly manage the image density using the more reliable AIDC method.

(Problem to be Solved by the Invention) However, the image density is determined by the formation conditions of the electrostatic latent image and the setting conditions of the developing device. That is, a decrease in image density is not caused only by a decrease in toner concentration of the developer, but may also occur due to poor bias conditions or charging conditions.

For this reason, even if the toner concentration is normal, if the image density has decreased due to bias failure, for example, if toner is replenished to the developing device according to the AIDC method, the toner concentration of the developer will be higher than necessary. This has the problem of causing background fog on the image and causing toner scattering, resulting in contamination of peripheral equipment.

(Means for Solving the Problems) Accordingly, the present invention provides an image forming apparatus that develops electrostatic latent images multiple times by driving the plurality of developing devices simultaneously, which detects the cause of image density reduction and corrects the problem. It is an object of the present invention to provide an image forming apparatus that restores image density through appropriate control.

In view of the above object, the present invention includes a photoconductor (1), a first developer (10) and a second developer (11) of magnetic brush type, and includes a photoconductor (1) formed on the photoconductor (1). In an image forming apparatus in which an electrostatic latent image is developed in a first developer (10) and then further developed in a second developer (11), a pattern latent image (Pl) is formed on the photoreceptor (1). Image forming means (
2, 9), and the pattern latent image (Pl) is transferred to a first developing device (
10) to form a first toner pattern image (T P ,
) is applied to the first developing device (10) to apply a bias having the same polarity as the toner charge polarity to form a second pattern image on the photoconductor. - a second pattern image forming mode (step 524) for forming a toner pattern image (TPt); a 1v image density measuring means (17); (TP,) and the image density detection mode (steps S21, 24) for detecting the image density (DI+Dt) of the second toner pattern image (TP),
i. a first comparison mode (step 523) for comparing the image density (Dl) of the first toner pattern image (T P , ) with a first reference density (DA); vii
Image density (D) of the second toner pattern image (TP2)
, ) and a second reference density (Da) (step 525); density (DA) and lower than the image density (D2) of the second toner pattern image (TP, ) or the second reference density (D, ), toner is supplied to the first developing device (10). The toner replenishment mode (step 826) is set such that the image density (D,) of the first toner pattern image (T P , ) is lower than the first reference density (DA), and the second toner pattern image (T P image density (D
, ) is higher than the second reference density (DB), a charge potential change mode (step 527) is provided in which the charge potential (V O ) of the photoreceptor (1) is increased.

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

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

In the figure, a photoreceptor 1 is a cylindrical body having an organic photoreceptor layer on its outer periphery, and is designed to rotate at a speed of 150 IIlffi/sec in the direction of arrow a.

Around the photoreceptor 1, along the direction of rotation, there are a charger 2, an inter-image eraser 9, a first developer 10, a second developer 11, a transfer charger 12, a separation charger 13, a cleaning device 14, and a main eraser 15. is placed.

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 grid covering an opening of the charge stabilizing plate 3 facing the photoconductor 1. A power supply #6 is connected to the charge wire 4, and another power source 7 is connected to the grid mesh 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 developing device 10, 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 cap DS+, and has a regulating plate 23a or a regulating cap D on its upper outer peripheral surface.
b+ and are connected to a power source 24H, and are designed to rotate at a speed of 143.64 rpm in the direction of the arrow.

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 and front sides of the wall 25a, and a bucket roller 28a and a conveyance blade 29a can be driven to rotate in the conveyance paths 26a and 27a, respectively. It is located in

The toner concentration detection sensor 30a is provided at the bottom of the front conveyance path 26a, and is configured to detect the toner concentration of the developer contained in the conveyance path 26.

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, and is provided with a photosensor 17 on the upper side facing the photoreceptor 1.

Note that 20a is a developing roller, 21b is a magnet, 22b is a sleeve, 23b is a regulating plate, 24b is a power source, 25b is a wall, 26b is a front conveyance path, 27b is a rear conveyance path, 28b is a bucket roller, and 29b is a conveyance path. A blade, 30b is a toner concentration detection sensor, 31b is a toner replenishment unit, 3.2b is a replenishment roller, 33b is a motor, D is a regulation cap, Ds
t indicates a developing cap.

FIG. 2 shows the circuit configuration of the image forming apparatus.

In this figure, outputs V, V, V3 of the photo sensor 17 and toner concentration detection sensors 30a and 30b are input to comparison input terminals of comparators 101, 103, and 105, respectively. On the other hand, comparators 101, 103,
The reference input terminal of 105 is connected to power supplies 102 and 10, respectively.
A reference voltage is applied from 4,106. The outputs of the comparators 101, 103, and 105 are output to the control device 100.

The control device 100 also includes a power source 6. 7. 24a24
b, the operation signal is output to the motors 33a and 33b.

Ru.

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

In the first developing device 10, the developer is circulated and conveyed through conveyance paths 26a and 27a by a packet roller 28a and a 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 26H.
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 via a bucket roller 28a. The developer supplied to the developing roller 20a is attracted by the magnetic force of the magnet body 21a and held on the outer periphery of the sleeve 22a, and is conveyed in the direction of the arrow mark in a magnetic brush state based on the rotation of the sleeve 22a, and is conveyed in the direction of the arrow mark by the regulation cap D. Only the developer that has passed through the sleeve 22a and the opposing area of the photoreceptor l (hereinafter referred to as
This is called the "development area." ) Brushing after passing through sl.

It falls into the front conveyance path 26a at the portion facing the troller 28a and is mixed with the developer.

The toner concentration of the developer is detected by the toner concentration detection sensor 30a, and the signal thereof is output to the comparator 103. on the other hand,
A signal corresponding to the reference concentration is inputted to the comparator 103 from the power supply 104 . The comparator 103 detects the voltage V3 of the two signals.
．． The magnitude of V is compared, and if V<V, that is, the toner density is below the reference density, a signal is output to the control device 100.

The control device 100 drives the motor 33a based on the signal from the comparator 103, and transfers the toner from the toner replenishing section 31a to the rear conveyance path 2.
Toner is replenished to 7a, and the toner concentration of the developer is adjusted to maintain a constant value.

The second developing device 12 performs the same processing as the first developing device 10. 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 gear +'yb Ds
+・0.6mm, Dst=1.0■-1 regulation gap Dbl, D5. =0.511II11, and the biases VB and □ applied from the power supplies 24a and 24b to the sleeves 23a and 23b are both set to 150V.

While the photoreceptor 1 is rotating in the direction of arrow a, the charger 2 has a charge wire 4 connected to the power source 6 by approximately -
A voltage of 5KV is applied to the grid mesh 4 and the power supply 7 is applied.
A bias of about -600V is applied from . the result,
The surface of the photoreceptor I passing through the charging region X1 is charged to -600V.

The charged surface of the photoreceptor 1 is exposed to image light 8 in the exposure area X, and an electrostatic latent image corresponding to the image to be reproduced is formed.

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 static elimination area X3, and the charges in the non-image area are erased.

The electrostatic latent image that has passed through the static elimination area X3 is transferred to the first development area
4, toner is supplied from the developer passing through the development area X4 as the sleeve 22a rotates, based on the electrostatic contrast between the bias VB (150V) and the potential of the electrostatic latent image area. 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 X, and bias VB! Based on the electrostatic contrast between (=150V) and the electrostatic latent image potential, toner is again supplied from the second developing device 11 and an image is reproduced.

As described above, development area X4. The toner image formed at Xs is transferred by discharge of the transfer charger 12 onto the recording medium 16, which is brought to the transfer area x8 in synchronization with the toner image.

The recording medium I6 to which the toner image has been transferred is stored in the separate charger 1.
The toner image is separated from the surface of the photoreceptor 1 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 I5 erases any residual charges in preparation for the next charging.

Here, in both the first developing device 10 and the second developing device 11, the regulation gap D bl+ Db! are the same (=0.5n+
+++), 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 gap Dli1 of the first development area X4 is 0.
．． 611II11, second development area X, development gap D s! is set to 1, Omm, so the frequency of contact of the developer to the photoreceptor 1 is as follows:
is higher than the second development area X.

Therefore, sufficient toner is supplied to the electrostatic latent image passing through the first development area X4, and solid images and character images of normal thickness are visualized with the necessary density. but,
Since the frequency of contact with the developer is high, the toner adhering to the surface of the photoreceptor 1 is often scraped off, and the reproducibility of fine lines is not necessarily good.

Continuation (In the second development area
Here, the toner adhering to the thin line electrostatic latent image passes through the development area X5 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.

■1 Image density control 3. About image density control of the image forming apparatus. This will be explained with reference to the flowcharts in FIGS.

(i) Copy control routine (see Figure 3) In this routine, in step Sll it is determined whether 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 control subroutine to be described later.

When the execution of the image density control subroutine is completed, a paper feed conveyance control subroutine, an optical system control subroutine, and a photoconductor rotation subroutine are executed in steps S13 to S15, respectively, and then a toner replenishment control routine is executed in step S16 (not shown). Return to main routine.

(11) Image density control subroutine (see FIGS. 4 and 56) 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. 5, 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. 7, the inter-image eraser 9 is blinked to form a pattern latent image P (step 535), and the first developer 1o is driven to form the pattern latent image P1 as shown in the figure. Toner pattern image TP
.

Visualize as. Also, the image density of the toner pattern 1TP1 is read by the photosensor 17 (step 5).
36).

In step S22, the toner pattern image TP on the photoreceptor 1 is
, the bias voltage VBI of the developing sleeve 22b of the second developing device 11 is changed to -500V.

As a result, as shown in FIG. 9, the positively charged toner constituting the toner pattern image TP is collected into the sleeve 22b by electric force. Therefore, the toner of the toner pattern image TP is not wasted,
The second developing device 11 is used for development.

Subsequently, in step (S23), the photo sensor 1
A signal of voltage V1 corresponding to the image density from 7 to 7 is output to the comparison input terminal of the comparator 101. Also, the comparator 101
A signal of voltage V corresponding to the first reference concentration DA is inputted from the power supply 102 to .

Note that the first reference concentration DA is a concentration that regulates the lower limit. Then, the comparator 101 calculates the image density D1 and the reference density D based on the voltages V, , V, of the input signals.
Compare the size of A.

As a result, if ■, <■, (D, DA), that is, the image density, is lower than the first reference density DA, the comparator 10
1 outputs a signal to the control device 100, and the control device 100 executes the process of step (S24).

In step (S24), another image density detection/s+ turn is formed and the image density is read.

Specifically, as shown in FIG. 6, 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 VB+ of the first developing device 10 is switched to +500V (step 538), and the positively charged toner is electrically repelled to fly toward the photoreceptor 1, forming a toner pattern image TP shown in FIG. The photo sensor 17 reads the image density (step 539). Note that, like the toner pattern image TP, the toner constituting the toner pattern image TP is removed in step S22.
The voltage is electrically recovered by the sleeve 22b to which 00V is applied. Therefore, toner is not wasted.

Subsequently, in step S25, based on the voltage V1 of the signal input from the photosensor 17 to the comparator 101 and the voltage L' of the signal manually input from the power supply 102, the image density is determined and the second reference density D8 is determined. Compare the size of.

Then, V1\V2'(D!<DB), that is, the image density of the toner pattern image TP, is the second reference density D.
If it is lower than a, the cause of the decrease in image density is the developing device 10.
The setting conditions are as follows. The reason for this is that, as described above, the toner pattern image TP is created with the photoreceptor 1 in an uncharged state, eliminating factors that affect the deterioration of the photoreceptor 1 and charging.

Therefore, in step S26, in order to restore the toner density of the first developing device 10, the voltage V4 of the power supply 104 input to the comparator 103 is lowered to restore the image density.

On the other hand, if ■1'≧V2' (D2≧D8), that is, the image density of the toner pattern image TP is higher than the second reference density DB, the image density D1 of the toner pattern image TP
The fact that DA is lower than the reference value DA can be judged to be caused by the latent image forming conditions such as deterioration of the photoreceptor or charging, contrary to the above-mentioned case.

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 ■. is increased, and 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, lowering the reference voltage 4 input to the comparator 102 increases the toner density and restores the image density. If the decrease in image density is due to deterioration or charging of the photoreceptor, the charging potential is V. is adjusted.

That is, the image density can be recovered 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 satisfies the first reference density DA, the process advances to step S29.

In step S29, the image density is compared with a third reference density DC. Note that the third reference concentration DC is a concentration that regulates the upper limit, and is set by changing the output of the power supply 102.

As a result of the comparison, if D, ≦DC1, that is, the image density is located between the lower limit regulation density DA and the upper limit regulation density DC, and the density is appropriate (DA<D, ≦DB), the process advances to step S28.

D, > Da, that is, if the image density D1 exceeds the upper limit regulation density and is too dark, the process proceeds to step S30, and it is determined whether the voltage v4 is lowered by the signal input from the power supply 104 to the comparator 103. However, if the voltage has been lowered, the output voltage v4 of the power supply 104 is increased in step S31 to reduce the image density. Conversely, if the voltage V4 has not been lowered, the image density is lowered by changing the charging conditions in step S32.

In step S32, it is determined whether or not the output of the power source 7 is in a high voltage output state, and if it is in a high voltage output state, step S32 is performed.

In step S33, the output of the power source 7 is lowered to reduce the charged potential of the photoreceptor 1 (■). and then proceed to step 828.
If the output of the other type #, 7 is in a low voltage output state, step S2
Proceed to step 8.

In step (S28), the output of the power supply 24a is changed to return the developing bias to VB--150V, and a normal image forming state is established.

,@,,,,,,,(this?,actual,@,Example: In the above description, when it is determined that the image density created by the first developing device 10 is less than a predetermined reference value, the toner density detection sensor 30a The image density is restored by adjusting the output of the power supply 104 corresponding to the reference density to be compared with the output of the toner replenishing motor 33a. The image density may be restored by restoring the density.

Further, the toner pattern images TP, , TP, are generated by the second developing device 1.
1 or may be collected by the cleaning device 14. In this case, especially for the second toner pattern image TP, the developing bias VB+ is set to 5
The time during which the voltage is set to 00V is shortened as much as possible, and the range of the pattern image TP that does not interfere with image density detection is made small (to suppress wasteful consumption of toner).

Further, the photosensor 17 may be provided above the second developing device 11 or may be provided below the cleaning device 14.

Furthermore, in the embodiment, the developer filling rate in the developing area facing the developing sleeve or the electrostatic latent image carrier of the developing device is made higher in the first developing device 10 than in the second developing device 11. , an example in which the development gap D 81 of the first development device 10 is made smaller than the development gap DS of the second development device 11 has been described;
Either the regulation gap D of the developing device 11 is made larger, or the circumferential speed of the sleeve of the first developing device 10 is increased compared to that of the second developing device 1.
The circumferential speed of the first sleeve is set to be higher than the circumferential speed of the first sleeve, so that the amount of developer conveyed to the developing area X4 of the first developing device 10 is larger than the amount of developer conveyed to the developing area X5 of the second developing device 11. Also good.

(Effects of the Invention) As is clear from the above description, in the image forming apparatus according to the present invention, in image density control of an image forming apparatus that develops the same electrostatic latent image multiple times using a plurality of developing devices, Determine whether the cause of the decrease in image density is due to the developing device settings or the pattern latent image formation conditions. If the cause is due to the developing device settings, increase the toner density of the developing device and If the cause is due to the image forming conditions, the charge potential on the photoreceptor is changed.

Therefore, even though the toner concentration of the developer is maintained at an appropriate level, toner is not replenished to the developer, thereby preventing image quality defects and producing high-quality images without background fog etc. Can you get it?

[Brief explanation of drawings]

FIG. 1 is a sectional view of main parts of the image forming apparatus, FIG. 2 is a control circuit diagram, and FIG. 3 is a flowchart of a copy control routine.
FIG. 4 is a flowchart of a subroutine for AIDC control, FIG. 5 is a flowchart of a subroutine for forming toner pattern images, etc., FIG. 6 is a flowchart for subroutines for forming toner pattern images, etc., and FIG. 7 is a flowchart for forming toner pattern images on a photoreceptor. FIG. 8 is a perspective view showing the toner pattern image formed on the photoreceptor, and FIG. 9 is a perspective view showing the toner scraping situation of the second developing device. FIG. DESCRIPTION OF SYMBOLS 1... Photoreceptor, 2... Charger, 9... Inter-image eraser, 10... First developer, 11... Second developer,
20a, 20b--developing roller, 22a, 22b--sleeve, 23a, 23b--regulating member, 24a. 24b... Power supply, 40... Gap adjustment device, 100
Control device, 101, 103, 105... Comparator, 10
2.104,106...Reference voltage, D,,,D,. ...Development gap, Dbl, Dbt...Regulation gap, PP,...Pattern latent image, TP,, TP,...Toner pattern image. Figure 7 Figure 8 Figure 9

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 toner replenishment mode in which toner is replenished to the first developing device; and 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. An image forming apparatus comprising: a charge potential change mode for increasing the charge potential of the photoreceptor when the charge potential of the photoreceptor is high.