JPH0434466A - Image forming device - Google Patents

Abstract

PURPOSE:To recover image density by adjusting the developing bias voltage of a 1st developing device for controlling the image density and increasing a developing potential difference between the potential of an electrostatic latent image part and the developing bias voltage in the case of detecting the lowering of the image density, or the state where the image density is about to lower. CONSTITUTION:In the case of detecting the lowering of the image density, or the state where the lowering of the image density is brought by an element by a detecting means 8 or 80 for detecting the image density or the change in the element which influences the image density, the developing bias voltage VB1 of the 1st developing device 10 is changed so that the potential difference between the developing bias VB1 and the potential of the electrostatic latent image part VH2 may be increased by a controlling means CPU. Thus, the image with the optimum density neither too thick nor too thin can be obtained.

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 method using a magnetic brush developing device.

(Prior Art) Conventionally, as the image forming apparatus, a first developing device and a second developing device containing a developer containing toner of the same color are arranged on the side of a photoconductor, and a sleeve and a photoconductor are connected to each other. JP-A-1-307783 discloses a device in which the developer filling rate of the opposing developing areas is set so that the first developing device is higher than the second developing device.
It is proposed in the publication.

Note that the developer filling rate is a value obtained by dividing the amount of developer transported to the development area by the distance between the photoreceptor and the development roller.

In this image forming apparatus, when the first developing device and the second developing device are driven almost simultaneously, the electrostatic latent image on the photoreceptor is first developed in the first developing device, and then reproduced in the second developing device. Ru. As a result, it is possible to obtain an image with an image density equivalent to that of the original image and excellent reproducibility of fine lines.

(Problems to be Solved by the Invention) However, even in the above-mentioned image forming apparatus, when the toner density of the first developing device, which particularly affects the image density, decreases,
It becomes difficult to secure a sufficient number of images. Furthermore, even if the toner a-density is appropriate, if factors that affect the image R11 degree, such as the iN degree of the installation position of the image forming apparatus, decrease, the toner charge amount will increase and sufficient density may not be ensured. be.

(Means for Solving the Problems) Therefore, the present invention provides the image forming apparatus with a detection means for detecting an image density or a change in an element that affects the image density, and a detection means for detecting a decrease in the image density or a change in the image density. When an element is detected to have entered a state that results in a decrease in image density,
A control means is provided for changing the developing bias voltage of the first developing device so that a potential difference between the developing bias voltage and the potential of the electrostatic latent image portion increases. .

(Function) According to the above configuration, when the detection means detects that the image density has decreased, or that an element that affects the image density is in a state that causes a decrease in the image density, the control means changes the developing bias voltage, It is switched so that the voltage difference between the developing bias voltage and the potential of the electrostatic latent image portion becomes larger.

(Implementation! IA+) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

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

(i) Photoreceptor 1 Photoreceptor 1 is a cylindrical body having a photoreceptor layer on its outer peripheral surface, and is indicated by the arrow a.
It is designed to rotate in the direction.

(11) Charger 2 The charger 2 has a wire 4 stretched inside a stabilizing plate 3 having a U-shaped cross section, a grid 5 provided in the opening, and the grid 5 facing the photoreceptor l. It is placed parallel to this. Further, the wire 4 and the grid 5 are connected to a power source 6, so that high voltages V)I, VH, can be applied to them, respectively.

Note that in this embodiment, VMl=-6K VSVot=
It is 600v.

(iii) Inter-image eraser 7 The inter-image eraser 7 includes light emitting diodes in multiple stages, and is arranged in parallel with the photoreceptor 1, so that each light emitting diode can be turned on or off as desired.

(1v) Developing device 10. 20 The first developing device 10 and the second developing device 20 are provided with a developing roller 2 in an opening 11 facing the photoreceptor 1.

The developing roller 12 is composed of a fixed magnet 13 having a plurality of magnetic poles on its outer periphery, and a sleeve 14 that rotates around the magnet 13 in the direction of the arrow. , development gear Ds (D,,,D,,)
is ensured. Further, the upper outer peripheral surface of the sleeve 14 is provided with a regulating plate 1 with a regulating gap Dゎ (D□, D□).
5 is facing. Furthermore, the sleeve 14 is connected to the power supply device 7.
By switching the connection to the first power supply 71 or the second power supply 72 with the switch 73, the developing bias voltage V□ can be selectively switched to ■8 or a lower voltage VL. It looks like this. In this embodiment, ■□=-150V, vt-100V. Further, the power supply device 70 of the second developing unit 20 includes power supplies 71 and 72 like the first developing unit 10, although the power supplies 71 and 72 are omitted from the drawing.

A stirring section 16 is formed at the rear (left side in the figure) of the opening 11, and a bucket roller 17 is arranged in this stirring section I6. Further, a magnetic sensor 18 is provided at the bottom of the stirring section 16.

Both developing devices WI0.20 are equipped with a toner replenishing section 21. This toner replenishing section 21 has a conveyance path 22 provided at the bottom.
The toner replenishing section 21 is provided with a conveying blade 23, which is rotated by the drive of a motor 24, and the toner replenishing section 21 replenishes the agitating section 16 with toner.

Further, a photosensor 8 is provided on the upper part of the second developing device 20 so as to face the photoreceptor 1, and illuminates the outer peripheral surface of the photoreceptor 1 and detects the reflected light.

(v) Control device The control device CPU includes the aforementioned photosensor 8 magnetic sensor 15, motor 24.5L electric motor t7.6, power supply device 70, and operation panel 100.

The sensors 101 and the like are connected to receive signals from the sensors and the like, and the motors and the like are driven and controlled based on the signals.

(2) Multiple development operation The first developing device 10 and the second developing device 20 are driven almost simultaneously,
A multiple development operation in which the electrostatic latent image on the photoreceptor 1 is developed twice will be described.

Note that in the first developing device 10 and the second developing device 20, the developing gear knob DS+ of the first developing device IO is set to 0.6 mm, and the developing gear knob DS2 of the second developing device 20 is set to 1.2 mm. Both developers to, 20 regulation gear knob Dt+1lDb
2 are both set to 0.5 mm. In addition, the power supply device 70
In this case, the switch 73 is connected to the power supply 71, and the developing bias N voltage is set to VB+=Vnt=-150V.

Under these conditions, the photoreceptor 1 rotates in the direction of arrow a, and the charging charger 2 applies a high voltage vHl % to the wire 4 and a high voltage V□ to the grid nod 5, and the outer peripheral surface of the photoreceptor 1 passing through the charged area is charged to a potential of V□2=600V.

Next, the image area of the charged photoreceptor 1 is exposed to image light at exposure position X, and an electrostatic latent image corresponding to the image to be reproduced is formed.

Subsequently, the non-image area of the photoreceptor l is illuminated by the inter-image eraser 7 in the charge removal area X3, and the charges in the area are erased.

Furthermore, the electrostatic latent image on the photoreceptor 1 is
When passing through the portion facing the developing device 20, the developing areas X4. Developed with Xs.

The following operations are performed in the first developing device 10 and the second developing device 20.

The developer is mixed and agitated by the rotation of the packet roller 17, and the toner and carrier come into frictional contact and are charged to opposite polarities. Further, the developer is scooped up by the throat roller 17 and supplied to the developing roller 12.

The developer supplied to the developing roller 12 is attracted by the magnetic force of the magnet 13 and held on the outer circumference of the sleeve 14, and is conveyed in the direction of the arrow as the sleeve 14 rotates. be done.

Here, the developer regulated by the regulating section 15 flows backward and falls into the stirring section 16 . On the other hand, the regulation gap V, (Db,) between the regulation part 15 and the sleeve 14.

The developer that has passed through Do) is conveyed in the direction of the arrow while forming a magnetic brush along the lines of magnetic force formed on the outer periphery of the sleeve by the magnetic force of the magnet body 13, so that the sleeve 14 and the photoreceptor 1 face each other. The outer peripheral surface of the photoreceptor 1 is rubbed in the development areas X- and Xs.

The developer that has passed through the development areas X, , X continues to be conveyed in the direction indicated by the arrow as the sleeve 14 rotates, and is released from the magnetic force of the magnet 13 at the portion facing the packet roller 17 and falls into the stirring section 16. .

Therefore, the surface of the photoreceptor l passing through the development areas x, x', is connected to the first developer IO and the second developer 20, respectively.
The charge is applied to the sleeve 14 based on the development potential difference between the image area potential of the electrostatic latent image and the development bias voltage V (Vb, , V, 2) applied to the sleeve 14 from the power supply 70. The banded toner electrostatically adheres to the electrostatic latent image area.

Here, the developing gap Ds+ of the first developing device 1O is narrower than the developing cap D52 of the second developing device 20. Therefore, in the development area X4, the frequency of contact of the developer with the electrostatic latent image is high, and sufficient toner adheres to the electrostatic latent image. However, the toner scraping effect due to contact with the magnetic brush is also large, and much of the toner adhering to the thin line electrostatic latent image is collected by the magnetic brush, resulting in the thin line passing through the first development area X4. The amount of toner adhering to the electrostatic latent image is small. On the other hand, sufficient toner adheres to electrostatic latent images such as dark images and ordinary character images, and they are reproduced with sufficient density even if they are subjected to the scraping action of the magnetic brush.

Next, toner is again supplied to the electrostatic latent image conveyed to the development area X, and the thin line is again visualized as a toner image.

Here, the developing cap D52 of the second developing area X is wider than the developing cap D51 of the first developing area X4.

Therefore, the probability that the magnetic brush comes into contact with the toner on the photoreceptor 1 is lower than that in the first development area Images are faithfully reproduced to the original. Furthermore, solid images and character images of normal thickness are reproduced with sufficient density.

(3) 3-Image Density Control The image density control performed during the multiple development described above will be explained with reference to the attached flowchart.

(i) Main routine (see Figure 2) In the main routine, when the power is turned on to the image forming apparatus and the program starts, the control device CPU is initialized in step #l, and each component device is set to the initial mode. Ru.

In step #2, the internal timer initialized in step #1 is started. This internal timer is used to keep the time length of one routine constant regardless of the contents of each subroutine below, and the various timers in each subroutine are counted based on the length of this one routine. .

In step #3, a copy control subroutine is executed, and if the print switch 101 is pressed, an image forming operation is executed by this subroutine.

In step #4, other processes, such as a subroutine for adjusting the temperature of the fixing device, are called and executed. Since the contents of this subroutine are unrelated to the present invention, a description thereof will be omitted.

In step #5, it is determined whether the internal timer set in step #2 has expired, and after waiting for the internal timer to expire, the process returns to step #2.

(11) Copy control subroutine (see FIG. 3) In this subroutine, in step #IO, it is detected whether the print switch 101 of the image forming apparatus is on-edge.

Note that on-edge refers to a state in which the signal input from the print switch 101 to the control device CPU changes from off to on.

If it is detected in step #10 that it is on/7, the copy start flag FCS is set to 1" in step #]1,
In step #12, the concentration detection flag FID is set to "1" and the process proceeds to edge knob #13. Note that the copy start flag FC3 is a flag for determining whether or not to start a copy operation.

Further, the density detection flag FID is a flag for determining whether or not to execute density detection processing, which will be described later.

On the other hand, if on-edge is not detected in step #1O, step #11.12 is not performed and step #10 is not detected.
Proceed to step 13.

In step #13, it is determined whether the copy start flag FCS is "1" or not, and when the copy start flag FC8 is "1", each step after step #14 is executed, and when the copy start flag FCS is "0". Returns to the main routine.

Therefore, while waiting until the print switch 101 is pressed, step #lL12 and step #1 described below are performed.
Processes #14 to #21 are never executed.

Next, in steps #14 to #18, control of the image (Ll!), density detection, density reference value switching, copy paper feeding/conveyance, optical system, and photoreceptor is performed.

Next, in step #19, in the toner replenishment control subroutine, the toner concentration is measured by the signal from the magnetic sensor 18, and based on the result, if the toner concentration is less than a predetermined reference concentration, the motor 24 is driven to stir the toner. Part 16
toner is replenished.

Finally, in step #20, it is determined whether or not the copying operation has been completed, and if the copying operation is completed, step #21
Then, the copy start flag FC3 is reset to "0" and the process returns to the main routine.

(iii) Image density detection subroutine (see Figure 4)
In this subroutine, it is determined in step #30 whether the concentration detection flag FID is 1'', and the concentration detection flag FID is
If the density detection flag FID is "1", step #31 is executed, and if the density detection flag FID is not "1", the process returns to the copy control sub-chin.

In step #31, a concentration detection processing sub-chin is executed. The details of this process will be described later.

In step #32, it is determined whether the processing of the density detection processing sub-chin has been completed, and if it has not been completed, the process returns to the copy control sub-chin. When the density detection processing sub-chin is completed, the density detection flag FID is reset to "0" in step #33, the bias switching flag FMC is set to "BI" in step #34, and copy control is performed. This bias switching flag FMC is set to the developing bias voltage VIi of the first developing device 10.
This is a flag for executing l+ switching processing.

(1v) Concentration detection processing subroutine (see Figure 5) In this subroutine, first, in step #40, the charger 2 is turned on, and a predetermined high voltage is applied to the wire 4 and grid 5 from the power supply 6, and in the direction of arrow a. The outer peripheral surface of the rotating photoreceptor 1 is charged to a constant potential.

Next, in step 341, the inter-image eraser 7 is turned on, and the individual light emitting lights are blinked to form a pattern latent image of a predetermined size on the outer peripheral surface of the photoreceptor 1 for image density detection.

Subsequently, in step #42, the first developing device IO is driven to develop the pattern latent image and form a toner pattern image for density detection.

Finally, the foot sensor 8 reads the reflection density (image density) rD of the toner pattern image.

(v) Bias switching subroutine (see Figure 6) In this subroutine, the bias switching flag F is set in step #50.
Determine whether MC is "l".

As described above, this bias switching flag FMC is set to 1'' in step #34.

Now, when the bias switching flag FMC is not “L”,
That is, if the image density ID has not been detected or if the bias switching subroutine ends and a copy operation is being executed, the process returns to the copy control subroutine.

When the bias switching flag FMC is “1”, step 3
51, the image density ID and the first reference density TIED are compared. Then, if ID>ID, the image density ID or the first
Group d1. If the density is higher than a degree ID (too much a), in step #52, the developing bias voltage ve of the first developing device 10 is increased.
It is determined whether or not + is set to a low value vL (=-100V).

As a result of the determination, if VBI is not set to vL, the process returns to the copy control subroutine.

On the other hand, if V□ is set to VL, step #53
, and set the developing bias voltage VBI to a high value vII (,=
-150V), the bias switching flag FMC is reset to "0" in step #54, and the process returns to the copy control subroutine.

As a result, the electrostatic latent image image portion potential V,! , and the developing bias voltage Vゎ shift from the relationship shown in FIG. 8 to the relationship shown in FIG. 7, the developing potential difference (v, ut v□) becomes smaller and the image density decreases.

If it is determined in step #51 that ID>ID is not true, that is, the image density rD is lower than the first reference density ID, then in step #55 the image density ID is lower than the second reference density I.
It is determined whether it is lower (too thin) than D, (< ID,).

If fD<ID, it is determined in step #56 whether the developing bias voltage VB is set to a high value vH. If the developing bias voltage VB is not set to V)I, the process returns to the copy control subroutine. On the other hand, the developing bias voltage V11. is a high value V,
(If set to , Ste.

Switch step #56 to VB and VL (=100V), and set bias switching flag FMC to “O” in step #58.
and returns to the copy control subroutine. As a result, the electrostatic latent image image area potential V8 and the developing bias voltage VB+ shift from the relationship shown in FIG. 7 to the relationship shown in FIG. becomes higher.

Through the above processing, an image with an appropriate density that is neither too dark nor too light can be obtained.

Note that when the developing bias voltage VB of the first developing device 10 is lowered, toner may adhere to the background portion of the photoreceptor 1, but this toner has a weak electrical adhesion force with the photoreceptor 1, 2. It is easily collected by the magnetic brush of the developing device 20. However, there is no chance that background fog will occur on the image and the image quality will deteriorate.

(2) Other Embodiments In the above embodiments, a toner pattern image is formed on the photoreceptor 1 prior to multiple development, and the developing bias voltage v, 1 is changed based on the image density. As shown in FIG. 1, a humidity sensor 80 is provided near or inside the developing device 10, 20, and when the humidity exceeds a predetermined reference value, the developing potential difference is reduced, and conversely, when the humidity becomes below the reference value, the humidity sensor 80 is installed. The developing potential difference may be increased.

(Effects of the Invention) As is clear from the above description, in the present invention, in an image forming apparatus that simultaneously drives a plurality of developing devices to develop the same electrostatic latent image multiple times, the image density decreases or the image density decreases. When it is detected that a state has been reached, the developing bias voltage of the first developing device that controls the image density is adjusted, and the developing potential difference between the electrostatic latent image area potential and the developing bias voltage is increased to increase the developing potential of the image. The concentration will be restored.

Therefore, it is possible to obtain an image with appropriate density and excellent density reproducibility and fine line reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a cross section of main parts and a circuit configuration of an image forming apparatus;
Figures 2 to 6 are flowcharts showing operation control of the image forming apparatus, in which Figure 2 is the main routine, Figure 3 is the copy control subroutine, Figure 4 is the image density detection subroutine, and Figure 5 is the image detection. The processing subroutine, FIG. 6 is a toner density switching subroutine, and FIGS. 7 and 8 are diagrams showing the relationship between developing bias voltage and image density. DESCRIPTION OF SYMBOLS 1... Photoreceptor, 8... Photo sensor, 10... First developer, 20... Second developer, 18... Magnetic sensor, 2. 1... Toner supply unit, 70... Power supply device, 71.7
2...Power supply, V! l,, V□...Developing bias voltage, CPU...Control device. Patent applicant: Minolta Camera Co., Ltd. Agent: Patent attorney: 1 person: 1 person: Figure 6, Figure 7, Figure 8.

Claims (1)

[Claims] (1) A magnetic brush type first developer and a second developer are located on the side of the photoreceptor.
A developing device is provided, each of these developing devices contains toner of the same color, the electrostatic latent image on the photoreceptor is first developed by the first developing device, and then the electrostatic latent image is reproduced by the second developing device. In an image forming apparatus configured to form an image, a detection means for detecting an image density or a change in an element affecting the image density;
When the detecting means detects that the image density has decreased or that the element has become in a state that causes a decrease in image density, the developing bias voltage of the first developing device is adjusted to be equal to the developing bias voltage of the electrostatic latent image image. 1. An image forming apparatus comprising: a control means for changing the potential difference with respect to a partial potential to increase.