JPH0434479A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image with proper density by supplying toner to a 1st developing unit which controls image density and adjusting the toner concentration when a decrease in the image density or an image density decreasing state is detected. CONSTITUTION:When a detecting means 18 detects the toner concentration of the 1st developing unit decreases below a specific reference value, a toner supplementing means 21 supplements toner to the 1st developing unit 10 according to a 1st control mode. Further, when a measuring means 8 or 80 measures the decrease in the image density or a state wherein a picture element which affects the image density causes a decrease in the image density, the toner supplementing means 21 supplements toner to the 1st developing unit 10 according to a 2nd control mode. Thus, an image with proper density which is neither too thick nor too thin is 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 plan 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 opposed to each other. The developer filling rate of the developing area is set to be higher than that of the first developing device or 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 a conventional 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 by the first developing device, and then reproduced by the second developing device. be done. 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 affects the image density, decreases,
It becomes difficult to obtain a sufficient image a degree of FNi ("I=". Also,
If a factor that affects image density, such as the humidity at the location where the image forming apparatus is installed, decreases, the toner charge amount may increase and a sufficient density may not be ensured.

(Means for Solving the Problems) Therefore, the present invention provides a first magnetic brush type on the side of the photoreceptor.
A developing device and a second developing device are provided, each of which 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 developed by the first developing device. In an image forming apparatus configured to reproduce images using two developing devices, a detection means for detecting a toner concentration of a developer in the first developing device;
toner replenishing means for replenishing toner to the first developing device;
a first control mode in which the toner replenishing means is driven when the toner concentration falls below a predetermined standard/# degrees based on the detection result of the detection means; a measuring means for measuring, and a second control for driving the toner replenishing means when it is detected by the measuring means that a state that causes a decrease in image density or a decrease in the image (f;!iPt degree); mode.

(Function) According to the above configuration, when the detection means detects that the toner concentration of the first developing device becomes less than a predetermined reference value, the toner replenishing means replenishes the first developing device with toner according to the first control mode. Further, when the measuring means determines 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 toner replenishing means supplies toner to the first developing device according to the second control mode. will be replenished.

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

■ Image forming device configuration FIG. 1 shows the main parts of an image forming apparatus.

b) Photoconductor I Photoconductor I is a cylindrical body having a photoconductor layer on its outer peripheral surface, and is indicated by arrow a.
It is designed to rotate in the direction.

(11) Charging charger 2 The charging charger 2 has a wire 4 stretched inside a stabilizer plate 3 having a U-shaped cross section, a grid 5 provided in the opening, and the grid 5 facing the 5-light body l. It is placed parallel to this. Further, the wire 4 and the grid 5 are connected to a power source 6, and have high voltages vH□, V8. is now applied.

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

(iv) Developing device 10. 20 The first developing device IO and the second developing device 20 each include a developing roller 12 in an opening 11 facing the photoreceptor l.

The developing roller 12 includes a fixed magnet 13 having a plurality of magnetic poles on its outer periphery, and a sleeve I4 that rotates around the magnet 13 in the direction indicated by the arrow. Further, between the sleeve 14 and the photoreceptor 1, a developing cap D5 (Ds,
, D5. ) is ensured, and a regulating plate I5 is opposed to the upper outer circumferential surface of the sleeve 14 with a regulating cap D frame Dゎ=, Db2). Furthermore, the sleeve 14 is connected to a power source 70, and the developing bias voltage vB (VB, , VB
2) is applied.

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

The developing devices 10 and 20 are both equipped with a toner replenishment section 21. This toner replenishing section 21 has a conveyance path 22 provided at the bottom.
The conveyor blade 23 is provided with a conveyor blade 23, which is rotated by the drive of a motor 24, and toner is supplied from the toner replenishing unit 21 to the stirring unit 16.

Further, a photosensor 8 is provided on the upper part of the second developing device 20 so as to face the photoreceptor 1, and is designed to illuminate the outer circumferential surface of the photoreceptor 1 and detect its reflected light.

(v) Control device The control device CPU includes the aforementioned photo sensor 8° magnetic sensor 18, motor 24, power supplies 6, 70, and operation panel 10.
0 print switches 101 and the like are connected to each other, and receive and receive signals from the sensors, etc., and motors and the like are respectively driven based on the signals.

■ Multiple development operation The first developing device 10 and the second developing device 20 are driven almost simultaneously,
A multiple development operation for developing an electrostatic latent image on two surfaces of the photoreceptor 1 will be described.

Note that for the first developing device 10 and the second developing device 20, the developing gear D5+ of the first developing device IO is set to 0.6 mm, and the developing camp DS2 of the second developing device 20 is set to 1.2 mm. In addition, the regulation cap D61 of both developing devices 10.20
．． Db2 is both set to 0.5 mm.

Under these conditions, the photoreceptor 1 rotates in the direction of the arrow a, and the charging roller 2 applies a high voltage VHI to the wire 4 and a high voltage VHI to the grid 5.
H2 is applied, and the outer peripheral surface of the photoreceptor 1 passing through the charging area X1 is charged to a potential of ■□.

Next, the image area of the charged photoreceptor 1 is exposed to image light at the 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 1 is illuminated by the inter-image eraser 7 in the charge-eliminating area X3, and the charges in the area are erased.

Further, the electrostatic latent image on the photoreceptor 1 is
When passing through the portion facing the developing device 20, the toner is developed in the developing areas X, , X5, respectively.

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 packet 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 . As the material rotates, it is transported in the direction indicated by the arrow, and the amount of transport is limited by the regulating section 15.

Here, the developer regulated by the regulating section 15 flows backward and falls into the stirring section 16 . On the other hand, the developer that has passed through the regulation gear Dbl+Db2 between the regulation part 15 and the sleeve 14 forms a magnetic brush along the lines of magnetic force formed on the outer periphery of the sleeve by the magnetic force of the magnet I3. The developing area X4. is transported in the direction of the arrow, and the sleeve 14 and the photoreceptor 1 face each other. The outer peripheral surface of the photoreceptor 1 is rubbed with X5.

The developer that has passed through the development areas X, . . .

Therefore, development area X4. The surface of the photoreceptor l passing through X, comes into contact with the magnetic bras of the first developing device 10 and the second developing device 20, respectively, and changes the image area potential of the electrostatic latent image and the electric potential of the electrostatic latent image. 70
Bias Vb (Vb
, , Vb2), the charged toner electrostatically adheres to the electrostatic latent image area.

Here, the developing cap DS+ of the first developing device 10 is narrower than the developing cap I)st 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 the contact of the magnetic brush is also large, and most of the toner adhering to the electrostatic latent image of the thin line is collected by the magnetic brush, resulting in the removal of the toner from the thin line that has passed 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 the electrostatic latent images of loose images and normal 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 x5 is wider than the developing cap Ds+ of the first developing area X4.

Therefore, the probability that the magnetic brush will come into contact with the toner on the photoreceptor l is lower than that in the first development area Reproduced faithfully to the original. In addition, rough images and character images of normal thickness are reproduced with sufficient density.

(1) Single 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 3) 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 #1, 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 make the time length of one routine uniform for the hot 1 system in the contents of each subroutine below, and the various timers in each subroutine are counted based on the length of this 1 routine. Ru.

In step #3, a subroutine for copy control is executed, and if the print switch 101 is pressed, an image forming operation is executed by the subroutine. In step #4, other processing, such as adjusting the temperature of the fixing device, etc. The subroutine to do this is 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. 4) In this subroutine, in step #10, 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.

When OnEno/ is detected in step #10, the copy start flag FC3 is set to "'1" in step #11, the density detection flag FrD is set to "1" in step #12, and the process proceeds to step #13. . Note that the copy start flag FCS is a flag for determining whether or not to start a copy operation.

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

On the other hand, if on-edge is not detected in step #10, step #11.12 is not performed and step #12 is not detected.
Proceed to step 13.

In step #13, the copy start flag FC8 is “1”
If the copy start flag FC8 is "1", each step after step #14 is executed, and if the copy start flag FC8 is "0", the process returns to the main routine.

Therefore, while waiting for the print switch 101 to be pressed, steps #11 and 12 and steps #14 to #21 described below are not executed.

Next, in steps f14 to f19, image density detection,
Controls include density reference value switching, copy paper feeding and transport, optical system, and photoreceptor surroundings.

Subsequently, in the toner replenishment control subroutine of step #20, as shown in FIG. The reference voltage v1 input to the input terminal is compared. Note that the reference voltage input from the power supply device 31 to the comparator 30 is determined in a concentration reference value switching subroutine to be described later.

Furthermore, the voltage of the signal output from the magnetic sensor 18 is proportional to the toner concentration of the developer.

As a result of the comparison, if the reference voltage (1) is higher than the comparison voltage Vc, the toner concentration of the developer exceeds the reference toner concentration corresponding to the reference voltage V, so toner replenishment is not performed. If the reference voltage ■1 is lower than the comparison voltage Vc, the toner atf of the developer is lower than the reference toner concentration, so
The motor 24 is driven and the stirring section 16 of the developing device 10 or 20 is driven.
toner is replenished.

Finally, in step #20, it is determined whether or not the copying operation has been completed, and if the copying operation has been 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 5)
In this subroutine, it is determined in step #30 whether or not the concentration detection flag FID is 1", and the concentration detection flag FrD
If "," then 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 concentration detection processing sub-chin is completed, the concentration detection flag FID is reset to "0" in step #33.

Then, in step #34, the density reference value switching flag F~'I
Set C to the same value and return to the copy control subchin. The density reference value switching flag FMC is a flag for controlling switching of the reference toner density, which is a reference for determining whether the toner density in the developing device is appropriate.

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

Next, in step #41, 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 10 is driven to develop the pattern latent image and form a toner pattern image for density detection.

First, the photosensor 8 reads the reflection Is degree (image a degree) ID of the previous toner pattern image.

(v) One-time reference value switching subroutine (see FIG. 7) In this subroutine, in step #50, it is determined whether the density reference value switching flag FMC is "1".

This density reference value switching flag FMC is set to 1'' in step #34, as described above.

If the density reference value switching flag FMC is not "1", that is, if the image density ID is not detected, or if this density reference value switching subroutine has ended and a copy operation is being executed, the copy control subroutine Return to.

When the density reference value switching flag FMC is °I", the process advances to step #51 and the image density ID is compared with the first reference density ID. Then, if TD>ID, the image density ID or the first reference density is determined. ID, if it is darker (too much a), it is determined in step #52 whether the reference voltage Vl of the comparator 30 related to toner density control of the first developing device 10 is set to a low value VL.As a result of the determination, , or VL, the process returns to the copy control subroutine.

On the other hand, if Vl is set to vL, step #53
Proceed to step #54, switch the switch 32 of the power supply 31 to the power supply 35 side, switch the reference voltage ■ to V, (>VL), and set the concentration reference value switching flag FMC to "'".
O'' and returns to the copy control subroutine. As a result, toner replenishment from the toner replenishing section 21 is suppressed, the toner density of the first developing device 10 is lowered, and the image density is reduced to an appropriate density.

If it is determined in step #51 that rD>ID, that is, it is lower than the image density ID or the first reference density ID, then in step #55 the image density ID or the second reference density ID, (< ID, ) is lower (too thin).

If T D < ID 2, the process returns to the copy control subroutine.

If ID<ID, it is determined in step #56 whether the reference voltage vI input to the reference input terminal of the comparator 30 is set to a high value VH regarding the toner concentration control of the first developing device IO.

As a result of the determination, if Vl is not set to V□, the process returns to the copy control subroutine. On the other hand, ■ is V□
If the switch 32 of the power supply device 31 is set to the power supply 34 side in step #57, the reference voltage v6 is switched to V L (< V ) I), and the concentration reference value switching flag FMC is set in step #58. It is reset to "O" and returns to the copy control subroutine. This results in
Toner supply from the toner supply section 21 becomes active, and the first
The toner density in the developing device 10 increases, and the image density rises to an appropriate density.

Through the above-described processing, an image that is properly darkened without being too dark or too light can be obtained.

Note that when the toner concentration of the first developing device 10 is increased, toner may adhere to the background portion of the photoreceptor 1, but this toner has a weak electrical adhesion force with the photoreceptor 1, It is easily collected by the magnetic brush of the container 20. Therefore, there is no possibility that toner adheres to the recording medium and deteriorates the image quality.

(2) Other Embodiments In the above embodiments, a toner pattern image is formed on the photoreceptor 1 prior to multiple development, and the toner a degree is adjusted based on the image JIf. As shown, a humidity sensor 80 is provided near or inside the developing units 10 and 20, and when the humidity exceeds a predetermined reference value, the reference input voltage Vi of the comparator 30 is increased, and conversely, when the humidity falls below the reference value, Then, the reference input voltage Vi may be lowered.

(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 the image forming apparatus is in a state where image density is controlled, toner is replenished to the first developing device which controls the image density, and the toner density is adjusted.

Therefore, an image with appropriate density and excellent density reproducibility and fine line reproducibility can be obtained.

[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;
FIG. 2 is a diagram showing a circuit configuration related to toner concentration control of the control device. 3 to 7 are flowcharts for controlling the operation of the image forming apparatus. FIG. 3 is the main routine, FIG. 4 is the copy control subroutine, FIG. 5 is the image density detection subroutine, and FIG. 6 is the image forming apparatus. Detection processing subroutine, FIG. 7 shows a toner density switching subroutine. I: Photoreceptor, 8: Photosensor, IO: First developer, 20: Second developer, 18: Magnetic sensor,
21... Toner supply unit, CPU... Control device. Figure 2 fCPU Patent applicant Minolta Camera Co., Ltd. agent Patent attorney Aohaku Haka 1 person

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 the image forming apparatus, the image forming apparatus includes a detection means for detecting the toner concentration of the developer of the first developing device, a toner replenishing means for replenishing toner to the first developing device, and a detection result of the detecting device. a first control mode in which the toner replenishing means is driven when the toner density becomes equal to or less than a predetermined reference density; a measuring means for measuring the image density or a change in an element that influences the image density; An image forming apparatus comprising: a second control mode in which the toner replenishing means is driven when it is detected that the density has decreased or that the element is in a state that causes a decrease in image density.