JPH0926699A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a high-quality image by highly electrifying developer to be compatible with the restriction of ghost caused thereby while effectively avoiding the damage of a developer carrier and the deterioration of the developer. SOLUTION: In this developing device which is provided with the developer carrier 2 in a developing housing and where an auxiliary developer carrier 4 is disposed on the downstream side of the carrier 2 in the moving direction of a latent image carrier 1 ; at least the developer by an amount equivalent to one rotation of the carrier 2 is transferred to the carrier 1 side in a dummy image forming stage other than an ordinary image forming stage, and the transferred developer is transferred to the carrier 4 side in a non-contact state and recovered to the carrier 2 side in the non-contact state. Or at least the developer by the amount equivalent to one rotation of the carrier 2 is transferred to the carrier 4 in the non-contact state and recovered to the carrier 2 side in the non-contact state. Furthermore, the dummy image forming stage is executed only under high humidity environment according to humidity information from a humidity detection means 11 as necessary.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a printer using an electrophotographic technique, and particularly, a developing ghost is generated in a type using a magnetic one-component developer. The present invention relates to an improvement of a magnetic one-component developing device that suppresses the above-mentioned phenomenon.

[0002]

2. Description of the Related Art In a conventional magnetic one-component developing device, as shown in FIG. 14, for example, a developing housing 103 having a developing opening on the latent image carrier 101 side and containing a magnetic one-component developer 110 is provided. A developer carrier 102 disposed facing the developing opening of the developing housing 103,
A developer regulating member 104 that regulates the amount of developer adhering to the developer carrying body 102 is provided so as to contact the developer carrying body 102 on the opposite side of the latent image carrying body 101. The developer carrying member 102 includes a magnet roll 102a in which a plurality of magnetic poles are fixedly arranged, and a cylindrical sleeve 102b rotatably supported around the magnet roll 102a. Is a high voltage AC power supply 1
05 and the DC power supply 106, a bias voltage composed of a DC superimposed AC voltage is selectively applied via the switch 107.

In such a developing device, the magnetic one-component developer 110 contained in the developing housing 103 is used.
Is held on the surface of the developer carrying member 102 by the magnetic force of the magnet roll 102a, is rubbed against the surface of the developer carrying member 102 when passing through the developer regulating member 104, and forms a thin layer of the developer. To be done. By the rubbing between the developer 110 and the surface of the developer carrying member 102, the developer is triboelectrically charged and an electric charge is given. The developer 110 thinned by the developer regulating member 104 is conveyed to the development area A by the rotation of the sleeve 102b of the developer carrying member 102, and then the developer carrying member 102 to which the developing bias is applied and the latent image. An electric field formed between the electrostatic latent image on the image carrier 101 and the electrostatic latent image causes the developer having electric charges to fly to the electrostatic latent image on the latent image carrier 101 for development.

[0004]

However, as a problem peculiar to the one-component developing system, there is a developing ghost. This is because the triboelectric charge amount of the developer is the developer carrier 102.
Becomes larger due to repeated friction with the surface of the sleeve 102b, and it is difficult to replace the developer on the surface of the developer carrying member 102, so that the developer regulating member 104 and the developer carrying member 102 pass each time. Sleeve 102b
This occurs because the particle size distribution of the developer conveyed on the surface shifts to the smaller diameter side, so that the developing performance differs between the developer consuming portion and the non-consuming portion of the developer on the surface of the sleeve 102b.

As a means for solving such a technical problem, conventionally, a method of directly mechanically scraping off the residual developer on the developer carrying member with a scraper has been used. However, in the first place, in order to hold and convey the developer on the developer carrier, it is necessary to roughen the surface roughness of the developer carrier, and the residual developer on the roughened surface was scraped off directly with a scraper. As a result, not only is it extremely difficult to completely remove the residual developer, but it is necessary to bring the scraper into strong contact with the surface of the developer carrier to some extent, which accelerates damage to the developer carrier and the scraper. There is a defect.

Therefore, as a means other than the method of scraping with a scraper, 10 ² to 10 containing conductive fine particles is used.
-Provide a resin layer of ^-6 Ωcm or less on the sleeve surface, and distribute the secondary particles of 1.0 μm or less at the developer size level in the outermost surface layer to promote leakage of the developer surface charge and develop There is one in which a development ghost is eliminated by preventing an increase in the charge amount of the developer (for example, Japanese Patent Laid-Open No.
276174). However, in this type, the charge amount of the developer is reduced, and the charge amount is not sufficient for proper development, especially in a high humidity environment, and the development ghost is improved, but blurring and There is a technical problem that the halftone is rough and the gradation reproducibility is poor, and the overall image quality is low.

As another method, an electric field generating roll is provided at a corresponding position between the repelling magnetic poles in the developer carrying member, and a scraper is brought into contact with the electric field generating roll.
There is one in which the residual developer on the surface of the developer carrier is transferred to the electric field generating roll side, and the developer held on the electric field generating roll surface is scraped off by a scraper (for example, JP-A-2-275977). . However, in this type, since the developer adhered to the electric field generation roller is mechanically scraped by a scraper, stress is applied to the developer, which causes a technical problem of accelerating the deterioration of the developer. I will end up.

In view of the above, the present invention effectively prevents damage to the developer carrying member and deterioration of the developer, and at the same time, achieves high image quality by suppressing the ghost and high image quality by suppressing the ghost. The purpose is to obtain a component developing device.

[0009]

The development ghost is extremely bad after a few consecutive prints having the same non-image portion (portion where the developer is not consumed), and is unlikely to appear in a solid image or a halftone image. Occurrence after solid image printing is slight. The present invention pays attention to this point and intentionally tries to always create a state after solid image printing. That is, in the developing device according to the present invention, as shown in FIG. 1A, the developer carrying member 2 facing the latent image carrying member 1 carrying the electrostatic latent image is disposed in the developing housing 3. In a developing device for visualizing an electrostatic latent image on the latent image carrier 1 with the developer carried on the developer carrier 2, in a developing housing with respect to the moving direction of the latent image carrier 1. In the dummy image forming process other than the normal image forming process, at least one round of the developer carrying member 2 in the auxiliary developer carrying member 4 disposed close to the downstream side of the developer carrying member 2 in 3 To the latent image carrier 1 side by transferring the developer on the developer carrier 2 over the area corresponding to the dummy development execution means 5 and the auxiliary developer carrier 4. On the other hand, the dummy developed image Td formed on the latent image carrier 1 is not contacted electrostatically or magnetically. Developer transfer means 6 for transferring the developer in a state, and developer recovery means 7 for returning the developer transferred on the auxiliary developer carrier 4 to the developer carrier 2 side in a non-contact state magnetically or electrostatically. It is characterized by having.

In another developing device according to the present invention, as shown in FIG. 1B, a developing agent carrier 2 facing a latent image carrier 1 carrying an electrostatic latent image is provided on a developing housing 3. In the developing device, which is disposed inside and visualizes the electrostatic latent image on the latent image carrier 1 with the developer carried on the developer carrier 2, the movement of the latent image carrier 1 The auxiliary developer carrying member 4 disposed close to the developer carrying member 2 in the developing housing 3 with respect to the direction, and at least the developer carrying member in the dummy image forming process other than the normal image forming process. A developer transfer means 8 for transferring the developer on the developer carrying member 2 to the side of the auxiliary developer carrying member 4 in an electrostatically or magnetically non-contact state over an area corresponding to one round of the body 2. , The developer transferred by the developer transfer means 8 is magnetically or electrostatically transferred to the developer carrier 2 side. It is characterized in that a developer collecting means 9 for returning a non-contact state.

In such a technical means, the latent image carrier 1 uses a photoconductor when an electrostatic latent image is formed by light and a dielectric when an electrostatic latent image is formed by ions. The design may be appropriately changed according to the type of the latent image forming means, and the configuration thereof may be drum-shaped, belt-shaped or the like, the charging means positive / negative, the exposure method, or the like. As the developer carrying member 2, a magnet member having a plurality of magnetic poles arranged therein may be fixedly installed in a rotatable developing sleeve as long as it can carry and convey the developer.
Conversely, a magnet member may be rotatably provided in the fixed developing sleeve. Further, the developing system may be contact or non-contact. As the material of the developing sleeve, a resin sleeve of phenol or the like, a metal sleeve of aluminum or stainless steel, or a metal sleeve having an aluminum oxide layer or metal plating or a resin coating film of acrylic, epoxy, polyester, or the like on the surface is used. in use.

Further, as the auxiliary developer carrying member 4, the same structure as the developer carrying member 2 may be adopted, but in the developer transferring means 6 and 8 and the developer collecting means 7 and 9, it is not necessary. As long as the developer can be transferred in the contact state, it does not matter whether the sleeve is used or the magnet member is not used.

Further, the dummy development executing means 5 may be appropriately selected as long as it can form the dummy development image Td on the latent image carrier 1, and for example, at least on the latent image carrier 1. A method is used in which a solid or halftone dummy latent image is formed on the entire surface of the area corresponding to one round of the developer carrier 2 and the dummy latent image is developed with the developer of the developer carrier 2. At this time, from the viewpoint of suppressing the amount of developer consumption, it is preferable to form a halftone dummy latent image rather than a solid dummy latent image. Further, as the charging means and the exposing means (not shown) for forming the dummy latent image on the latent image carrier 1, an original device may be provided, but from the viewpoint of cost reduction, it is existing. It is preferable to use the above.

Further, it is difficult to transfer 100% of the developer developed on the latent image carrier 1 to the auxiliary developer carrier 4. Therefore, a small amount of the developer that does not contribute to image formation remains on the latent image carrier 1 and more developer than is originally required for image formation is consumed. Therefore, the formation range of the dummy developed image Td is preferably the minimum range required for eliminating the history of the developer carrying member 2 (one round of the developer carrying member 2). Regarding the device invention of FIG. 1 (b),
Since the developer is directly transferred to the auxiliary developer carrier 4 without passing through the latent image carrier 1, it is not necessary to consider the developer remaining on the latent image carrier 1, but the process of the dummy image forming step From the viewpoint of shortening the time, the range of formation of the transferred and developed image of the developer transfer means 8 is the minimum range required to eliminate the history of the developer carrier 2 (a round of the developer carrier 2). Min) is preferred.

Regarding the execution timing of each functional means (5 to 7 or 8, 9) in the dummy image forming process, it may be executed at any timing other than the normal image forming process. It does not matter whether the number is once or twice or more, as long as the development ghost can be prevented from occurring. Furthermore, the dummy development executing means 5,
The method for controlling the developer transfer means 6 and 8 and the developer recovery means 7 and 9 may be usually automatically executed by using a microcomputer or the like, but is manually operated at an arbitrary timing. There is no problem in doing so.

Further, from the viewpoint of effectively utilizing the recovered developer, in the dummy image forming step, the developer transferred to the auxiliary developer carrier 4 is promptly recovered by the developer recovery means 7, 9. However, for example, a temporary stock section is provided in the vicinity of the auxiliary developer carrying member 4, the stock section is temporarily collected, and the temporarily collected development is performed at a predetermined timing later. You may make it collect | recover the agent collectively to the developer carrying body 2 side.

The developer transfer means 6 and 8 may be appropriately selected as long as they electrostatically or magnetically transfer the developer in a non-contact state, but the developer transfer is easily performed. From the point of view of performing the transfer, it is preferable to electrostatically transfer by applying a bias for forming the transfer electric field.

Further, the developer collecting means 7 and 9 may return the developer in a non-contact state electrostatically or magnetically. Particularly, from the viewpoint of cost reduction, the auxiliary developer carrying member. 4 is fixedly provided at a position where the developer carrier 2 and the developer carrier 2 face each other, and a magnetic pole pattern is used that magnetically attracts the developer from the auxiliary developer carrier 4 toward the developer carrier 2 side. Is preferred.

From the viewpoint of avoiding wasteful consumption of the developer, in the developing device according to the present invention,
A humidity detecting means 11 for detecting the ambient environment humidity, and a dummy image forming prohibiting means 12 for prohibiting the dummy image forming step under the condition that the humidity detecting means 11 determines that the ambient environment is high humidity. It is preferable to add. According to the dummy image formation prohibiting means 12, the dummy image forming process is executed only in a low humidity environment where the distribution of the charge amount of the developer becomes large by using the humidity information of the humidity sensor or the like, and the development ghost is efficiently generated. To be prevented.

[0020]

In the technical means as described above, FIG.
The operation of the device invention of (a) will be described. The following dummy image forming process is executed at a predetermined timing other than the normal image forming process. First, the dummy development executing means 5 forms a dummy electrostatic latent image on the latent image carrier 1 by using, for example, a charging means and an exposing means (not shown), and at the same time as that, develops the latent image carrier 1 and the developing means. The developer is conveyed to the developing area, which is a position close to the agent carrier 2. The transported developer is transferred to the dummy electrostatic latent image on the latent image carrier 1 in the developing region over at least a region corresponding to one round of the developer carrier 2, and the dummy developed image Td is transferred. To create. Thereafter, the dummy developed image Td is conveyed to a position where the latent image carrier 1 and the auxiliary developer carrier 4 are close to each other, and is electrostatically or magnetically transferred to the auxiliary developer carrier 4 side by the developer transfer means 6. To the non-contact state. Further, the developer transferred onto the auxiliary developer carrying member 4 is conveyed to a position where the auxiliary developer carrying member 4 and the developer carrying member 2 are close to each other, and the developer collecting means 7 moves the developer to the developer carrying member 2 side. Electrostatically or magnetically recovered in a non-contact state, returned to the developer housing portion side in the developing housing 3, and the dummy image forming step is completed.

Next, the operation of the device invention of FIG. 1B will be described. In the same figure, in the dummy image forming step, first, the developer transfer means 6 is operated, and the developer on the developer carrier 2 is at least extended over the region corresponding to one round of the developer carrier 2. It transfers to the side of the carrier 4 electrostatically or magnetically in a non-contact state. After that, the developer collecting means 9 operates to collect the developer transferred to the auxiliary developer carrying member 4 to the developer carrying member 2 side in a non-contact state magnetically or electrostatically, and the developer is stored in the developing housing 3. The process returns to the developer accommodating portion side, and the dummy image forming process is completed.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. First Embodiment FIG. 2 is a first embodiment of an image forming apparatus in which the developing device according to the present invention is incorporated and is a schematic sectional view. In the figure, reference numeral 21 is a photoconductive photosensitive drum having a surface layer made of a negatively charged organic photosensitive member on the surface, 22 is a charger for charging the photosensitive drum 21, and 23 is on the charged photosensitive drum 21. An exposure device such as a laser for writing a predetermined electrostatic latent image (including those in a normal image forming process and a dummy image forming process to be described later), and 24 is a photosensitive drum 2
A developing device for developing the electrostatic latent image on 1 with a magnetic one-component developer 30, 25 is a transfer device for transferring a visible image (developed image) by the developer on the photosensitive drum 21 to a recording sheet (not shown), Two
6 is a static eliminator for removing residual charges on the photosensitive drum 21, 2
A cleaner 7 removes the residual developer on the photosensitive drum 21. In a normal image forming process of such an image forming apparatus, the surface of the photosensitive drum 21 is uniformly charged by the charger 22 and then the light based on the image signal is irradiated by the exposing device 23 to, for example, an image portion. -100V, background part-
An electrostatic latent image of 360 V is formed, visualized by the developing device 24, and transferred to a recording sheet (not shown).

The developing device 24 in this embodiment is
The photosensitive drum 21 side is provided with a developing housing 31 in which a developing opening is opened and in which the magnetic one-component developer 30 is stored. A developing roller 32 is provided at a portion of the developing housing 31 facing the developing opening. And a predetermined area between the developing roller 32 and the photosensitive drum 21 is disposed in the developing area A so as to be close to the developing roller 32.
It is supposed to function as. In this embodiment, the developing roll 32 is provided with a plurality of magnetic poles arranged inside along the circumferential surface thereof and a magnet roll 33 fixedly installed so as not to rotate, and rotatably arranged outside thereof. The magnet roll 3 is composed of a cylindrical sleeve 34 and
As the magnetic pole configuration of 3, a 4-pole configuration in which N poles and S poles are alternately arranged (specifically, 4-pole configuration of N1, S1, N2, S2) is used, while the sleeve 34 is A cylinder made of a non-magnetic metal such as aluminum or stainless steel, or a surface of which is subjected to a chemical treatment (plating or the like) for preventing leakage or a resin coat is used.

Further, a bias voltage composed of a DC voltage superimposed AC voltage is selectively applied to the sleeve 34 by a high voltage AC power supply 35 and a DC power supply 36 via a switch 37, so that the developing roll 32 and the photosensitive drum 21 are brought close to each other. In the developing area A, an alternating electric field is generated between the surface of the photosensitive drum 21 and the grounded electrode below the photoreceptor layer. In the present embodiment, the bias voltage has, for example, an AC component frequency of 2.4 kHz, a peak-to-peak voltage of 2000V, and a DC component of -250V.

Further, in this embodiment, reference numeral 40
Is a developer layer thickness regulating member that regulates the layer thickness of the developer carried on the developing roll 32. The soft elastic body 41 is pressed against the surface of the developing roll 32, and one end is fixedly supported and its free end. A spring plate 42 around which the soft elastic body 41 is fixed
It is composed of The contact position of the soft elastic body 41 with respect to the developing roll 32 is the rotational direction of the developing roll 32 with respect to the reference line connecting the position where the developing roll 32 is closest to the photosensitive drum 21 and the center of the magnet roll 33. The position is 170 ° on the upstream side, and is installed so that the free end of the spring plate 42 faces the upstream side in the rotation direction of the developing roller 32. In this embodiment, the soft elastic body 41 has a width of 15 m.
m, thickness 1 mm, rubber hardness 50 °, silicone rubber, spring plate 42 is 0.1 mm thick stainless steel plate (SUS304CSP3 / 4 material, tensile strength 95 kgf
/ Mm ² and proof stress 68 kgf / mm ² ).

Further, an expansion housing portion 31a bulging downward is formed below the accommodation space of the developing roller 32 of the development housing 31, and the photosensitive drum 21 side of the expansion housing portion 31a is connected to the developing opening. Auxiliary roll 50 is disposed inside the expansion housing portion 31a. The auxiliary roll 50 is provided so as to face the photosensitive drum 21 and the developing roll 32, and the gap between the auxiliary roll 50 and the photosensitive drum 21 is 100 μm to
The gap between the auxiliary roll 50 and the developing roll 32 is set to about 1 mm to 3 mm while being set to about 350 μm.

The auxiliary roll 50 includes a magnet roll 51 having a plurality of magnetic poles arranged along its peripheral surface and fixedly installed so as not to rotate.
1. Cylindrical sleeve 52 rotatably arranged outside 1
As the magnetic pole configuration of the magnet roll 51, a three-pole configuration in which N poles and S poles are alternately arranged (specifically, three-pole configuration of N3, S3, N4) is used. Two N
The roll, that is, the position between the N3 pole and the N4 pole is the developing roll 3
It is arranged to face the S2 pole of No. 2. Meanwhile, the sleeve 52
As the cylinder, a cylinder made of non-magnetic metal such as aluminum or stainless steel or a surface of which is subjected to a chemical treatment (plating or the like) for preventing leakage or a resin coat is used.

Further, a bias voltage, which is a DC voltage superimposed AC voltage, is selectively applied to the auxiliary roll 50 by a high voltage AC power supply 53 and a DC power supply 54 via a switch 55, so that the auxiliary roll 50 and the photosensitive drum 21 are separated from each other. An alternating electric field is generated between the grounded electrode and the grounded electrode under the photoconductor layer on the surface of the photosensitive drum 21 in the adjacent region.
In the present embodiment, the bias voltage has a frequency of the AC component of 2.4 kHz and a peak-to-peak voltage of 200, for example.
0V, DC component is 50 to 300V.

Further, in this embodiment, the microcomputer shown in FIG. 3 is used as a control system for controlling a normal image forming process and a dummy image forming process described later. In the figure, each output of the copy switch 61 and the like is input as data to the control unit 70 via the input interface 71. The control unit 70 has a central processing unit (hereinafter referred to as CPU) 7
2. Random access memory (hereinafter referred to as RAM) 73
And a read-only memory (hereinafter referred to as ROM) 74. The ROM 74 has a program (FIG. 4) for executing the normal image forming process and the dummy image forming process.
Is stored, the CPU 72 executes the program based on the given data via the input interface 71, and the output interface 75
The respective devices such as the charging device 22, the exposing device 23, the developing device 24, and the transferring device 25 are controlled via the.

Next, the operation of the developing device according to this embodiment will be described with reference to the flow chart shown in FIG. Taking a copy job for making a plurality of copies as an example, first, after setting the number of copies, the copy switch 6
When 1 is turned on (step A), the control unit 70
Starts its operation so as to execute one normal copy cycle (normal image forming process), as shown in steps B and C of FIG. At this time, the switch 37 is closed and a predetermined bias voltage (developing bias) is applied to the developing roll 32, while the switch 55 is opened and the auxiliary roll 50 is opened.
Is in a floating state. In such a state, a normal copy cycle is performed. That is, the photosensitive drum 21 is uniformly charged by the charging device 22, an electrostatic latent image is formed on the charged surface of the photosensitive drum 21 by the exposing device 23, and the electrostatic latent image is developed by the developing device 24.

In the developing step at this time, the developer 30 in the developing housing 31 is adsorbed on the surface of the developing roll 32 which rotates in the same tangential direction as the photosensitive drum 21, and the soft elastic body of the developer layer thickness regulating member 40. 41 by developing roll 3
2 Rub on the surface. As a result, the developer 30 is thinned and the developer 30 is provided with an appropriate electric charge. The thinned developer 30 is conveyed to the developing area A by the rotation of the developing roll 32, and a large amount of the developing agent having an appropriate electric charge is generated in the alternating electric field generated in the gap between the developing roll 32 and the photosensitive drum 21. 30 particles of the agent fly and reciprocate. Further, due to this reciprocating motion, the particles of the developer 30 collide with each other, and the developer 30 as a whole becomes cloud-shaped. The cloud of the developer 30 is attracted to the latent image portion on the photosensitive drum 21 by the DC component of the bias voltage,
The development is completed.

After that, the visible image (developed image) by the developer on the photosensitive drum 21 reaches the transfer portion of the transfer device 25 as the photosensitive drum 21 moves. At this time, the photosensitive drum 2
Although the developed image on No. 1 passes through the auxiliary roll 50 portion, since the auxiliary roll 50 is in a floating state, there is no concern that a part of the developed image on the photosensitive drum 21 will be transferred to the auxiliary roll 50 side. The developed image on the drum 21 is not destroyed. Then, when the developed image is transferred to a recording sheet (not shown) by the transfer device 25, the static eliminator 26 and the cleaner 27 return the photosensitive drum 21 to the initial state again, and the normal one copy cycle is completed.

After confirming that one normal copy cycle is completed, as shown in steps D and E of FIG. 4, the copy job is temporarily stopped and the dummy cycle (dummy image forming step) is executed again. Start operation. The concept of the dummy cycle according to this embodiment is as follows. That is, the developer layer on the surface of the developing roll 32, in which the developer is consumed by the development, is re-formed by being rubbed against the surface of the developing roll 32 by the soft elastic body 41 of the developer layer thickness regulating member 40 again. At this time, the characteristics of the re-formed developer layer are different between the portion where the developer is consumed (image portion) and the portion where the developer is not consumed (non-image portion). Specific characteristics include a particle size distribution, a carry amount, and a charge amount distribution.The particle size distribution shifts to a small particle size side in the non-image part, the carry amount increases in the non-image part, and the charge amount distribution varies. It becomes broad in the non-image part. This tendency is slight up to one print in the non-image area, but it appears remarkably when two or more prints in the same non-image area position are the same, and different developer characteristics cause development ghost. it is conceivable that.
Therefore, in the present embodiment, a solid black or halftone latent image is formed on the photosensitive drum 21 at least once around the developing roller 32 before or after printing so that the non-image portion does not continue beyond one print. The developer is consumed over the entire circumference of the developing roll 32 by performing the minute formation and developing in the same manner as the normal developing.

More specifically, the dummy cycle according to this embodiment is as shown in FIGS.
(A) Dummy development step, (b) Developer transfer step, (c)
It consists of a developer recovery process.

(A) Dummy developing step As in the normal copy cycle, the switch 37 is closed and the bias voltage (-VB1) consisting of the DC voltage superimposed AC voltage is applied to the developing roll 32. In this state,
The control unit 70 charges the photosensitive drum 21 uniformly (-V0) by the charger 22, and controls the exposure unit 23 to perform exposure so that the charging potential decreases from (-V0) to (-V1). A halftone electrostatic latent image is formed on the photosensitive drum 21 by the length (L) of one round of the developing roller 32.
Then, the developer 30 for one round of the developing roll 32 has a potential difference (Δ) between the bias voltage (−VB1) and the image portion potential (−V1).
V), and a dummy developed image 30a is formed on the photosensitive drum 21. At this time, the amount of developer consumed in the dummy cycle can be minimized by optimally setting the magnitude of the value of the potential difference (ΔV).

(B) Toner Transfer Process Also, unlike the normal copy cycle, the switch 55 is closed and the bias voltage (+ VB2), which is a DC voltage superimposed AC voltage, is applied to the auxiliary roll 50. On the other hand, the dummy developed image 30a on the photosensitive drum 21 has a potential of approximately (-V1). Therefore, the dummy developed image 30a attached on the photosensitive drum 21 is not transferred to the auxiliary roll 50 and the photosensitive drum 21.
After being separated from the photosensitive drum 21 and caused to fly by a direct current superposition alternating electric field between the photosensitive drum 21 and the auxiliary roller 50, it is transferred from the photosensitive drum 21 to the auxiliary roll 50 by the magnetic attraction force of the auxiliary roll 50.

(C) Developer Collecting Step When the dummy developed image 30a on the photosensitive drum 21 is completely transferred to the auxiliary roll 50 side, the transferred developer 30 is rotated in the same tangential direction as the photosensitive drum 21 and the auxiliary roll 5 is rotated.
It is conveyed to a position facing the developing roller 32 with a magnetic force of zero. At this position, due to the repulsive force between the N3 pole and the N4 pole of the auxiliary roll 50, the magnetic poles are separated from the auxiliary roll 50 and, at the same time, between the magnetic poles N3 and N4 and the magnetic pole S2 on the developing roll 32 side. Is transferred to the developing roll 32 side by the magnetic force of
Reused. At this time, when the bias voltage is applied to the auxiliary roll 50, the electrostatic field acts in the direction in which the transfer of the developer 30 is hindered, but in this embodiment, the gap between the auxiliary roll 50 and the developing roll 32 is 1 to 3 mm
Therefore, the electric field strength between the auxiliary roll 50 and the developing roll 32 is correspondingly reduced, and the developer 30 can be transferred by the magnetic attraction force.

In order to ensure the transfer operation of the developer 30 from the auxiliary roll 50 to the developing roll 22, for example, when the dummy developer 30a on the photosensitive drum 21 is transferred to the auxiliary roll 50, the switch 55 is moved. The auxiliary roll 50 may be brought into an electrically floating state by not opening an electrostatic field between the auxiliary roll 50 and the developing roll 32.

When such a dummy cycle is completed,
As shown in step F of FIG. 4, the operations C to E are repeated until the copy job for the set number of sheets is completed, and when the set number of sheets is reached, the copying is ended.

As described above, the problem of deterioration of the developer that occurs in eliminating the development ghost can be solved by the non-contact method of recovering the developer, and the problem of excessive consumption of the developer can be solved by recycling the developer. It will be possible.

In the above embodiment, the developing roll 32 is used.
Although the DC voltage superimposed AC voltage is applied to both the auxiliary roll 50 and the auxiliary roll 50, the present invention is not limited to this. For example, only the DC voltage component -250V may be applied to the developing roll 32, Or, auxiliary roll 5
Although it is possible to apply only the DC voltage component to 0,
In this case, the DC voltage is 300 to 1000V.

Further, the first embodiment and the comparative example (see FIG. 1)
When the developing device shown in FIG. 4 was mounted on an actual machine), the developer layer formation state and the image performance were examined, and the results shown in Table 1 below were obtained. In Table 1, 1 is a comparative example, 2 to 5 are different types of latent images in the dummy cycle of the first embodiment, which are solid black and printing area ratio 7 respectively.
A halftone of 0%, a halftone with a printing area ratio of 50%, and a halftone with a printing area ratio of 30%.

[0043]

[Table 1]

According to Table 1, the lower the density difference (ghost) in the image part / non-image part, the better.
It was confirmed that solid black, 70% halftone, and 50% halftone were improved, but it was confirmed that 30% halftone had a printing area ratio that was too low and the improvement effect was insufficient.

Further, when the efficiency of collecting the developer adhering to the photosensitive drum 21 onto the auxiliary roll 50 was examined in the modes 2 to 5 of the first embodiment, the results shown in Table 2 below were obtained. .

[0046]

[Table 2]

From Table 2, it is understood that the transfer of the developer from the photosensitive drum 21 onto the auxiliary roll 50 is not 100% complete. At this time, since solid black remains in the photosensitive drum 21 without being completely collected by the auxiliary roll 50, in order to suppress excessive consumption of the developer, the latent image in the dummy cycle execution has a printing area ratio of 50% to 70%. %
It is judged that the halftone of is good.

Second Embodiment FIG. 7 shows an image forming apparatus incorporating a second embodiment of the developing device to which the present invention is applied. Note that components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted here. The developing device according to this embodiment is substantially the same as that of the first embodiment, but in addition to the configuration of the first embodiment, a humidity sensor 62 for detecting environmental humidity in which the image forming apparatus is installed is provided inside the apparatus body. Have The humidity information from the humidity sensor 62 is shown in FIG.
As shown in the flowchart of FIG. 8, the control unit 70 of the present embodiment takes in a dummy cycle after the normal copy cycle only when the humidity is less than 55%. Do not execute the dummy cycle when the humidity is 55% or more, for example, switch 3
7 is opened to turn off the application of the bias voltage to the developing roll 32.

The reason why the humidity reference value is 55% is that the development ghost is 30% as shown in Table 3 below.
5 remarkably occurs in low humidity environment below RH
It is based on the experimental data that it is slight in a high humidity environment of 5% RH or more. Table 3 shows a comparative example (Fig. 1).
10) R in different humidity environment for the developing device shown in FIG.
The developer layer formation state and the image performance were examined under H, 30% RH, 55% RH, and 85% RH.

[0050]

[Table 3]

Therefore, according to this embodiment, the dummy cycle is executed only in the low humidity environment in which the development ghost remarkably occurs, and the dummy cycle is not executed in the high humidity environment in which the development ghost is slight. It is possible to suppress the consumption of the developer as much as possible as compared with the first embodiment.

In this embodiment, the humidity sensor 62
However, the humidity information is not limited to this, and for example, in a type in which the transfer current value of the transfer device is controlled according to a change in humidity, this humidity If the transfer current value of the transfer device, which changes according to information, is used instead of the humidity sensor, more inexpensive control becomes possible.

Third Embodiment FIG. 9 shows a third embodiment of a developing device to which the present invention is applied.
2 shows an image forming apparatus in which the is incorporated. Embodiment 1
Constituent elements similar to those are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof is omitted here. Unlike the first embodiment, the developing device according to the present embodiment creates a dummy developed image on the photosensitive drum 21, and directly transfers the developer for one round of the developing roller 32 to the auxiliary roller 50 and then collects it. By doing so, it is intended to obtain the same effect as that of the first embodiment. In the present embodiment, there is no bias power source applied to the auxiliary roll 50,
By providing the switch 56, it is possible to selectively create a grounded or electrically floating state. Further, the control system (see FIGS. 3 and 4) of the developing device according to the present embodiment is configured to realize the following dummy cycle.

The dummy cycle according to this embodiment is
As shown in FIGS. 10 and 11, (a) developer transfer step and (b) developer recovery step. (A) Developer Transfer Process At the start of the dummy cycle, the switch 56 is closed and the auxiliary roll 50 is grounded. At this time, since a bias voltage composed of a DC voltage superimposed AC voltage is applied to the developing roll 32, an alternating electric field is generated in a region where the developing roll 32 and the auxiliary roll 50 are close to each other. Then, due to this alternating electric field, the developer 30 for one round of the developing roll 32 is transferred to the auxiliary roll 50 side.

(B) Developer Collecting Step After that, when one round of the developer 30 on the developing roll 32 is transferred to the auxiliary roll 50 side, the switch 56 is opened,
The auxiliary roll 50 is in an electrically floating state. Then, the transferred developer 30 is conveyed by the rotational movement of the sleeve 52 only by the magnetic force, and when it reaches the portion facing the developing roll 32 again, the repulsive force between the N3 pole and the N4 pole of the auxiliary roll 50 is the same. As a result, the magnetic force between the magnetic poles N3 and N4 and the magnetic pole S2 on the developing roll 32 side is transferred to the developing roll 32 side at the same time as it is separated from the auxiliary roll 50, and is reused.

In this way, the dummy cycle can be executed without producing a dummy developed image on the photosensitive drum 21.

Fourth Embodiment FIG. 12 shows a developing device according to a fourth embodiment of the present invention. Note that components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted here. The basic configuration of the developing device according to this embodiment is substantially the same as that of the first embodiment, but unlike the first embodiment, an auxiliary magnet 80 is used instead of the auxiliary roll 50. That is, the auxiliary magnet 80 is an electromagnet,
For example, a coil 82 is wound around a rod-shaped magnetic body 81 rotatable in a predetermined angle range, the coil 82 is connected to a DC power source 84 via a switch 83, and the switch 83 is opened / closed to selectively cause the coil 82. It is designed to be energized. Further, the control system of the developing device according to this embodiment is configured so as to realize the dummy cycle as shown in FIGS. 13 (a) and 13 (b).

The dummy cycle in this embodiment includes (a) dummy developing step and developer transferring step, and (b)
It consists of a developer transfer step. (A) Dummy development step and developer transfer step First, the same dummy development step as in Embodiment 1 is performed,
The developer 30 for one round of the developing roll 32 is
Transfer to the top. At this time, the auxiliary magnet 80 is shown in FIG.
As shown in FIG.
Of the rod-shaped magnetic body 81. Since the switch 83 is closed and the coil 82 is energized, the auxiliary magnet 80 functions as an electromagnet having both ends of the rod-shaped magnetic body 81 as magnetic poles N and S. There is. In such a state, when the dummy developed image 30a transferred onto the photosensitive drum 21 reaches a position facing the auxiliary magnet 80, the dummy developed image 30a on the photosensitive drum 21 is magnetically attracted by the auxiliary magnet 80. Transferred to the 80 side.

(B) Developer Collecting Step When all the dummy developed images 30a on the photosensitive drum 21 are transferred to the side of the auxiliary magnet 80, the auxiliary magnet 80 rotates by a predetermined angle as shown in FIG. 13 (b). , Rod-shaped magnetic body 81
Of the developer 30 stops at a position substantially facing the magnetic pole S2 of the developing roll 32, and at this stage, the switch 83 is opened. Then, the coil 82 is de-energized, and the auxiliary magnet 80 does not function as an electromagnet. For this reason, the holding force of the developer 30 held by the auxiliary magnet 80 disappears, and the developer 30 on the auxiliary magnet 80 is transferred to the developing roll 32 side by the magnetic force toward the magnetic pole S2 on the developing roll 32 side and re-generated. Used.

[0060]

As described above, according to the present invention,
As a dummy image forming process other than the normal image forming process,
At least one round of the developer for one round of the developer carrier is once developed from the developer carrier to the latent image carrier, and is recovered via the auxiliary developer carrier, or from the developer carrier to the auxiliary developer carrier. Since it is directly transferred and collected, the characteristic difference between the image portion and the non-image portion in the developer layer on the developer carrying member can be minimized, and the development ghost can be suppressed to a small extent. By recycling the developer used in the dummy image forming step, it is possible to effectively prevent excessive consumption of the developer. Further, in order to prevent the development ghost, the charge amount of the developer is not reduced, so that the high image quality due to the high charge of the developer can be effectively realized. Further, since the developer used in the dummy image forming step is transferred and collected by a non-contact method, the stress of the developer can be suppressed to be less than that of the type using a mechanical means such as a scraper. The life of can be extended more.

Further, in the type in which the dummy developed image is formed on the latent image carrier, the ordinary latent image forming means can be effectively used, so that there is an effective concern that the apparatus cost unnecessarily increases. It can be avoided. If the electrostatic or magnetic method is optimally selected as the non-contact method for transferring and recovering the developer in the dummy image forming process, the transfer and recovery operation of the developer can be easily realized. can do. Further, by utilizing the fact that the development ghost is related to humidity, it is possible to efficiently execute the dummy image forming step by using humidity information from a humidity sensor or the like.

[Brief description of drawings]

1A and 1B are explanatory views showing the configurations of different developing devices according to the present invention.

FIG. 2 is a first embodiment of a developing device to which the present invention is applied.
FIG. 3 is an explanatory view showing an image forming apparatus in which is incorporated.

FIG. 3 is a block diagram showing a control system of the developing device according to the first embodiment.

FIG. 4 is a flowchart showing processing contents of a control system used in the first embodiment.

5A to 5C are explanatory views schematically showing a dummy cycle of the developing device according to the first embodiment.

FIG. 6 is an explanatory view showing each operation principle of FIGS. 5 (a) to 5 (c).

FIG. 7 is a second embodiment of a developing device to which the present invention is applied.
FIG. 3 is an explanatory view showing an image forming apparatus in which is incorporated.

FIG. 8 is a flowchart showing the processing contents of the control system of the developing device according to the second embodiment.

FIG. 9 is a third embodiment of the developing device to which the present invention is applied.
FIG. 3 is an explanatory view showing an image forming apparatus in which is incorporated.

10A to 10B are explanatory views schematically showing a dummy cycle of the developing device according to the third embodiment.

FIG. 11 is an explanatory diagram showing each operation principle of FIGS. 10 (a) and 10 (b).

FIG. 12 is an explanatory diagram showing an image forming apparatus incorporating a developing device according to a fourth embodiment of the present invention.

13A and 13B are explanatory views schematically showing a dummy cycle of the developing device according to the fourth embodiment.

FIG. 14 is an explanatory diagram showing an example of a conventional developing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Latent image carrier, 2 ... Developer carrier, 3 ... Development housing, 4 ... Auxiliary developer carrier, 5 ... Dummy development execution means,
6 ... Developer transfer means, 7 ... Developer recovery means, 8 ... Developer transfer means, 9 ... Developer recovery means, 11 ... Humidity detection means,
12 ... Dummy image formation inhibiting means

Claims (6)

[Claims] 1. A latent image carrier (1) carrying an electrostatic latent image.
The developer housing (2) facing the developer housing (3)
In the developing device, which is disposed in the developer carrier and visualizes the electrostatic latent image on the latent image carrier (1) with the developer carried on the developer carrier (2), the latent image carrier is provided. Auxiliary developer carrying member (4) arranged close to the downstream side of the developer carrying member (2) in the developing housing (3) with respect to the moving direction of the body (1) and other than the normal image forming process. In the dummy image forming step, the developer on the developer carrier (2) is transferred to the latent image carrier (1) side over at least the area corresponding to one round of the developer carrier (2). A latent image carrier (1) with respect to the dummy developer executing means (5) for forming a dummy developed image (Td) and the auxiliary developer carrier (4).
Developer transfer means (6) for transferring the dummy developed image (Td) formed above in an electrostatic or magnetic non-contact state
And a developer recovery means (7) for returning the developer transferred onto the auxiliary developer carrying member (4) to the developer carrying member (2) side in a non-contact state magnetically or electrostatically. A developing device characterized by the above. 2. A latent image carrier (1) carrying an electrostatic latent image.
The developer housing (2) facing the developer housing (3)
In the developing device, which is disposed in the developer carrier and visualizes the electrostatic latent image on the latent image carrier (1) with the developer carried on the developer carrier (2), the latent image carrier is provided. Auxiliary developer carrying member (4) arranged close to the downstream side of the developer carrying member (2) in the developing housing (3) with respect to the moving direction of the body (1) and other than the normal image forming process. In the dummy image forming step, the developer on the developer carrying body (2) is statically moved toward the auxiliary developer carrying body (4) side over at least a region corresponding to one round of the developer carrying body (2). A developer transfer means (8) for transferring electrically or magnetically in a non-contact state, and a developer transferred by the developer transfer means (8) magnetically or electrostatically to the developer carrier (2) side. And a developer collecting means (9) for returning the contactlessly in a non-contact state. 3. The dummy development executing means (5) according to claim 1, wherein the dummy development executing means (5) is solidly spread over the entire area of the latent image carrier (1) corresponding to at least one round of the developer carrier (2). A developing device, wherein a dummy halftone dummy image is formed, and the dummy latent image is developed by the developer of the developer carrying member (2). 4. The developer transfer means (6) or (8) according to claim 1 or 2, wherein the latent image carrier (1) or the developer carrier (2) and the auxiliary developer carrier ( 4) A developing device for applying a bias for forming a transfer electric field for transferring the developer to and from 4). 5. The developer collecting means (7) or (9) according to claim 1 or 2, wherein the developer collecting means (7) or (9) is fixed at a position where the auxiliary developer carrier (4) and the developer carrier (2) face each other. And a magnetic pole pattern that magnetically attracts the developer from the auxiliary developer carrying member (4) toward the developer carrying member (2) side. 6. The humidity detecting means (11) according to claim 1, wherein the ambient environment humidity is detected, and the ambient environment is judged to be high humidity by the humidity detecting means (11). A developing device comprising: a dummy image formation inhibiting means (12) for inhibiting a dummy image formation process under conditions.