JPH0434470A - Image forming device - Google Patents

Abstract

PURPOSE:To correct image density so that it may be in an optimum state by adjusting a developing gap in either of a 1st developing device and a 2nd developing device 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 which influences the image density by a detecting means for detecting the image density or the change in the element which influences the image density, the controlling means is actuated, and the napping height controlling gap Db in either of the 1st developing device and the 2nd developing device is made wider by an adjusting means 40. Thus, the developer filling ratio in either of the developing devices is increased and the image density can be kept in the optimum state.

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 static latent image on the photoreceptor is first developed by the first developing device, and then reproduced by 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 image forming apparatus, for example,
When the humidity at the location where the image forming apparatus is installed decreases, the toner charge amount increases and a sufficient density may not be ensured.

(Means for Solving the Problems) Accordingly, the present invention provides two-component developer that is held on the outer periphery of a sleeve that rotates around a magnet, and the developer that is transported to a developing area where the sleeve and the photoconductor face each other. A magnetic brush type first developing device and a second magnetic brush type developing device are arranged to adjust the amount by a regulating plate facing the sleeve with a predetermined brush height regulating gap.
A developing device is provided, toner of the same color is stored in a first developing device and a second developing device, and the electrostatic latent image on the photoreceptor is developed by the first developing device and then reproduced by the second developing device. In the image forming apparatus, the image forming apparatus includes an adjusting means for adjusting a height regulating cap of at least one of the first developing device and the second developing device, and detecting a change in image density or an element affecting the image density. and a detection means for operating the adjustment means when it is detected, based on the detection result of the detection means, that the image density has decreased or that the element is in a state that causes a decrease in the image density. , control means for narrowing the brush height regulation gap of at least one of the second developing devices;
It has been established.

(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 operates and the adjustment means The brush height regulation gap of at least one of the first developing device and the second developing device becomes wider.

As a result, the developer filling rate of at least one of the developing devices increases, and the image density is maintained at an appropriate level.

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

10 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 with a photoreceptor layer on its outer circumferential surface, and is indicated by the arrow a.
It is designed to rotate in the direction.

(ii) During charging 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 arranged parallel to the photoreceptor l. A grid 5 faces the photoreceptor 1. In addition, the wire 4 and the grid 5 are connected to the power source 6
are connected to the terminals, so that high voltages VMI and VW can be applied to them, respectively.

(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.

(iv) Developing Unit 10.20a, Schematic Structure In the first developing unit 10 and the second developing unit 20, the developing roller 12 is disposed in the 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 fixed magnet 13 in the direction of arrow a. Development gap D s (D sl, D
J is secured.

Further, a regulating plate 15 is provided above the sleeve 14, and the distance between the regulating plate 15 and the sleeve 14 (hereinafter referred to as "regulating gap") D, (D, , D□) is an adjusting device described later. 40 can be switched.

The bucket roller 17 is located at the rear of the developing section 11 (left side in the figure).
A magnetic sensor 18 is installed at the bottom of the stirring section 16.

The toner replenishing device 21 includes a replenishing roller 2 on a conveyance path 22 at the bottom.
3 is arranged, and the conveyance path 22 is connected to the stirring section 16. The replenishing roller 23 is drivingly connected to a motor 24, and by driving the motor 24, the toner contained in the toner replenishing device 21 can be replenished to the agitating section 16.

Further, a photosensor 8 is provided above the second developing device 20 so as to face the photoreceptor 1 .

b. Adjustment Device 40 As shown in FIGS. 2 to 4, in the adjustment device 40, the regulation plate 15 moves in the directions of arrows c and c'' so that it can approach and move away from the sleeve 14. Regulation plate 1
Racks 44° 44 are formed on both ends of the 5.

The shaft 41 is arranged parallel to the regulating plate 15, is rotatably supported by a bearing portion (not shown), and is rotated by a motor 43. In addition, pinions 42 are provided on both ends of the shaft 41.
．． 42 are provided, and these pinions 42 and 42 are engaged with racks 44 and 44 at both ends of the regulating plate.

The movable contact 45 is provided on the regulating plate 15, and fixed contacts 46 and 47 are arranged below and above it, respectively.

Therefore, when the motor 43 is rotated normally and the shaft 41 is rotated in the direction of arrow m, the regulation plate 15 approaches the sleeve 14, and the regulation gap D narrows. On the other hand, when the motor 43 is reversed and the shaft 41 is rotated in the direction of arrow n, the regulation plate 15 is separated from the sleeve 15, and the regulation gap D widens. Further, the regulation gap Db is set to l when the movable contact 45 is in contact with the fixed contact 46, and Dw is set when the movable contact 45 is in contact with the fixed contact 47. In this example, Dw=Q, 5 mm, and DN=0.2 mm are set.

(v) Control device The control device CPU is connected to the above-mentioned photo sensor 8° magnetic sensor 18, motor 24.43, power supplies 6, 70, print switch 101 of the operation panel 100, etc. A signal receiver is attached, and motors and the like are driven based on the signals.

■ Multiple development operation The first developer 810 and the second developer 20 are driven almost simultaneously,
A multiple development operation in which the electrostatic latent image on the photoreceptor I is developed twice will be described.

Note that the developing cap D, (D, , ) of the first developing device 10 is opened at 06, and the developing cap Ds (D5.) of the second developing device 20 is opened.
is set to 1.2 mm.

Further, the regulation gap DbI in the first development period 10 is wide (0.5 mm), and the regulation gap D□ in the second developing device 20 is wide (0.5 mm).
is set to be narrow (0.2 mm). however,
The regulation gap set in this manner is also appropriately switched by regulation gap switching control described later.

When the photoreceptor 1 rotates in the direction of arrow a in this state, the charger 2 applies a high voltage V Hl % to the wire 4 and a high voltage V, l to the grid 5, and the surface of the photoreceptor 1 passing through the charging area is charged to a potential of V□.

Next, the exposure position X! is placed on the image area of the charged photoreceptor 1! The image light is exposed at
i, 'il images are formed.

Subsequently, the non-image area of the photoreceptor 1 is illuminated by the inter-image eraser 7 in the charge removal area X, and the charges in the area are erased.

Further, the electrostatic latent image on the photoreceptor l is transferred between the first developing device 10 and the second developing device
When passing through the portion facing the developing device 20, the toner is developed in the developing areas X, , X, 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 a bucket roller 17 and supplied to the developing roller 12 .

The developer supplied to the developing roller 12 is held on the outer periphery of the sleeve 14 by the magnetic force of the magnet 13, and is conveyed in the direction of the arrow as the sleeve 14 rotates, and the amount of conveyance is limited by the regulating portion 15. be done.

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 regulating gears D, D, between the regulating part 15 and the sleeve 14 is
The photoconductors are conveyed in the direction of the arrow while forming magnetic brushes along the magnetic lines of force formed on the outer periphery of the sleeves by the magnetic force of the magnets 13, and the photoconductors are transported in the developing area X4°X, where the sleeve I4 and the photoconductor 1 face each other. Rub the outer peripheral surface of 1.

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, 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. will be collected.

Therefore, development area X4. The surface of the photosensitive weight passing through X contacts the magnetic brushes 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 power source 70.
The developing bias voltage v applied to the sleeve 14 from
The charged toner electrostatically adheres to the electrostatic latent image area based on the development potential difference with e (Va+, V□).

Here, the regulation gap Ds+(=0.
6 mm) is the developing gear of the second developing device 20, ps2 (1,
2mm). Therefore, development area
In No. 4, 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 fine line electrostatic latent image is collected by the magnetic brush, resulting in the first development area X being i! ! The amount of toner adhering to the thin line electrostatic latent image is small.

On the other hand, an electrostatic latent image of a solid image or a normal character image has sufficient toner attached to it, and is reproduced with sufficient density even if it is subjected to the scraping action of the magnetic brush.

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

Here, as mentioned above, the development gap D of the development area
s= (=1.2 mm) is wider than the development gap D□ (0.6 mm) of the development area X4.

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

(1) Single Image Density Control Image iI degree control performed during the multiple development described above will be explained with reference to the attached flowchart.

(i) Main routine (see Figure 5) In the main routine, when power is supplied to the image forming apparatus and the program starts, the control unit CPU is initialized in step #1, and each component device is set to the initial mode. Set.

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 constant regardless of the contents of each subroutine described 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 the 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.

(ii) Copy control subroutine (see FIG. 6) In this subroutine, in step #1o, 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 on-edge is detected in step #10, the copy start flag FCS is set to "1" in step #ll,
In step #12, the concentration detection flag FID is set to "1" and the process proceeds to step #13. Note that the copy start flag FC3 is a flag for determining whether or not to start a copy operation.

Further, the ia U detection flag FID is a flag for determining whether or not to execute a concentration detection process, which will be described later.

On the other hand, if on-edge is not detected in step #10, do not perform steps #11 and 12 (step #12).
Proceed to step 13.

In step #13, the copy start flag FC3 is “1”
It is determined whether or not the copy start flag FC8 is "0", and when the copy start flag FC8 is "0", each step after step #14 is executed, and when the copy start flag FCS is "0", the program returns to the main routine.

Therefore, while waiting until the print switch 101 is pressed, steps 111.12 and steps #14 to #21 described below are not executed.

Next, in steps #I4 to #19, image ff11 degree detection, regulation gap switching, copy paper feeding/transport, optical system,
Controls around the photoreceptor, toner replenishment, etc. are performed.

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 supply toner to the agitation unit 16. replenished,
The toner concentration in the stirring section 16 is maintained constant.

Subsequently, in step #20, it is determined whether or not the copying operation is completed, and if the copying operation is completed, step #21 is performed.
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 7)
In this subroutine, it is determined in step #30 whether the concentration detection flag FID is "1", and the concentration detection flag FI
If D 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 product 8 processing subroutine 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 "O" in step #33, the regulation gap switching flag FMC is set to 1" in step #34, and the copy control sub-chin The regulation gap switching flag FMC is a flag for executing regulation gap switching processing after the image density detection processing is completed.

(!V) Concentration detection processing subroutine (see Fig. 8) This subroutine is executed immediately after the print switch 10I is pressed. First, in step #40, the charger 2 is turned on, and the wire 4 and the grid 5 are connected to the power supply 6. A predetermined high voltage is applied, and the outer peripheral surface of the photoreceptor 1 rotating in the direction of arrow a is charged to a constant potential.

Next, in step #41, the inter-image eraser 7 is turned on and the individual light emitting diodes are turned on and off 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.

Finally, the photo sensor 8 reads the reflection density (image fii) ID of the toner pattern image.

(v) Development mode switching subroutine (see FIG. 9) In this subroutine, in step #50, it is determined whether the development mode switching flag FMC is "1".

As described above, this development mode switching flag FMC is set to "1" at the time when the detection of the image density ID is completed.

Now, when the development mode switching flag FMC is not 1'',
That is, if the image density ID has not been detected or if the development mode switching subroutine ends and a copy operation is being executed, the process returns to the copy control subroutine.

When the development mode switching flag FMC is "1", the image density ID and the first reference density IDl are compared in step #51. Then, if ID>ID, and the image density ID is darker (too much a) than the first reference density ID, step #52
If the regulation gear knob D &l is relatively wide, (=0
．． 5 mm). This determination is made based on the signal input through the fixed contact 47.

As a result of the judgment, if the regulation gap D□ is wide, step #
At 53, the motor 43 is driven to rotate normally, and the shaft 41 is rotated in the direction of arrow m to bring the regulating plate 15 closer to the sleeve 14. On the other hand, if the developing gap DD+ is not wide, the process proceeds to step #54.

In step #54, it is determined whether the regulation gap D Il+ has shifted to a narrow state due to normal rotation of the motor 43. This determination is made based on the signal input through the fixed contact 46. As a result of the determination, the fixed contact 46 and the movable contact 4
5 is in contact with the regulating gear, y7'D, is in a narrow state (D
b, = 0.2 mm), the forward rotation of the motor 43 is turned off in step #55, and then the development mode switching flag FMC is reset to "0" in step #56, and the copying process is started. Return to control subroutine. On the other hand, if there is no contact with either the movable contact 45 or the fixed contact 46, the process returns to the copy control subroutine.

If it is determined in step 351 that rD>ID is not true, that is, the image density ID is lower than the first reference density ID, then in step #57 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 rD<ID, the regulation gap Db+ is set to a relatively narrow state (D) in step #58.

0.2 mm). This determination is made based on the signal input through the fixed contact 46. As a result of the determination, if the regulation gap D a+ is narrow, the motor 43 is driven in the reverse direction in step #59, and the shaft 41 is driven in the direction of the arrow n.
direction to separate the regulating plate 15 from the sleeve 14. On the other hand, if the regulating gear knob Dbl is not narrow, the process proceeds to step #60.

In step #6o, the regulation plate 1 is rotated by the reverse rotation of the motor 43.
5 moves in the direction of arrow C' force, and the movable contact 45 becomes the fixed contact 4.
7 and the regulation gap D, 1 is wide (D, = 0
．． 5mm).

If the regulation plate 15 is moving in the direction of arrow C', the process returns to the copy control subroutine.

When it is detected that the regulation gap D has become wide (D, = 0.5 mm) due to contact between the movable contact 45 and the fixed contact 47, the drive of the motor 43 is stopped in step #61, and the drive of the motor 43 is stopped in step #61. At step 62, the development mode switching flag FMC is reset to "0" and the process returns to the copy control subroutine.

In this manner, when multiple development processing is executed, the first developing device 10 uses the image density ID before performing the multiple development processing.
is the second reference density ID, and when it is thinner than the regulation gap D
bI is widened, and when the image density ID is darker than the first reference density ID, the regulation gap D□ is narrowed, and the image density ID
is set between ID and ID.

Therefore, an image with an appropriate density that is neither too dark nor too light can be obtained.

(2) Other Embodiments In the above embodiments, a toner pattern image is formed on the photoreceptor 1 prior to multiple development, and the regulation gap D'll 1 is adjusted based on the image density. As shown in FIG. 1, a humidity sensor 80 is provided near or inside the development WIO, 20, and when the humidity exceeds a predetermined reference value, the development gap is widened, and conversely, when the humidity becomes below the reference value, the regulation gap is increased. You may narrow it down.

Further, the first developing device 10 is driven to form a toner pattern image, and the regulation gap Dbl is adjusted based on the image density rD. In the case of multiple development, this is the second
Only a small amount of toner is supplied from the developing device 20 to the electrostatic latent image.
Since most of the toner in the toner image of the final image is supplied by the first developing device IO, the density of the final image can be determined by measuring the image density of the toner image formed by the first developing device 10. It is from.

However, the pattern latent image is transferred to the first developer 10 and the second developer 2.
It is also possible to perform overlapping development at 0 and adjust the regulation gap based on the image density.

In this case, the photosensor 8 is attached to the lower part of the second developing device 20, for example.

In addition to adjusting the regulation gear Db of the first developing device 10, the regulation gear knob Db of the second developing device 20 is also adjusted. Alternatively, two developing units 10. '20
Both regulation gears Dbl+Db2 may be adjusted.

Further, in the gap adjustment device 40 that adjusts the restriction gap D, the restriction plate I5 is moved using a gear mechanism to adjust the restriction gap Db, but the gap adjustment device is not limited to the above embodiment. .

(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 state of
The image density is corrected to an appropriate state by adjusting the regulation gap of at least one of the second developing devices.

Therefore, appropriate? ! It is possible to obtain images with IV and excellent density reproducibility and fine line reproducibility.

[Brief explanation of drawings]

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 partial sectional view of the developing device, FIG. 3 is a side view of the regulation gap adjustment device, and FIG. 4 is a front view of the regulation cap adjustment device. 5 to 9 are flowcharts showing operation control of the image forming apparatus, in which FIG. 5 is a main routine, FIG. 6 is a copy control subroutine, FIG. 7 is an image density detection subroutine, and FIG. 8 is an image detection subroutine. Processing subroutine, FIG. 9 shows a regulation gear knob switching subroutine. DESCRIPTION OF SYMBOLS 1...Photoreceptor, 10...1st developing device, 20...2nd
Developing device, 11... Developing roller, 40... Regulation gear knob adjustment device, D jl+ D sr" developing gear knob, D
bl+ Dbl...Regulatory gap. Patent applicant Minolta Camera Co., Ltd. agent Patent attorney Haka 1 person

Claims (1)

[Claims] (1) A two-component developer is held on the outer periphery of a sleeve that rotates around a magnet, and the amount of developer to be conveyed to the development area where the sleeve and the photoconductor face each other is controlled by a predetermined height regulating gap in the sleeve. A magnetic brush type first developer and a second developer are provided which are adjusted by opposing regulating plates, and the first developer and the second developer contain toner of the same color, and the toner is placed on the photoreceptor. Developing the electrostatic latent image with a first developer,
In an image forming apparatus that subsequently reproduces an image with a second developing device, an adjusting means for adjusting a brush height regulation gap of at least one of the first developing device and the second developing device;
a detection means for detecting image density or a change in an element that affects the image density, and based on the detection result of the detection means,
When it is detected that the image density has decreased or that the element is in a state that causes a decrease in the image density, the adjusting means is operated to adjust the brush height regulation gap of at least one of the first developing device and the second developing device. An image forming apparatus comprising: a narrowing control means.