JPH09292775A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent carrier sticking, toner-image scatter, etc., on a latent-image carrier by making at least one parameter different between image formation using one color and image formation using a plurality of colors at the same time out of parameters which affect an image process from the electrification of an image carrier to the separation of a transfer medium. SOLUTION: Out of the parameters, including an application voltage to a carrier recovery roll 61, which affect the image formation process from the electrification of the photoreceptive drum 8 to the separation of the transfer medium, at least one parameter is made different between the image formation using the one color and image formation using the plurality of colors at the same time. As the parameter it is preferable to use the application voltage to the recovery roll 61. To make a copy using the two colors at the same time, a voltage in which a DC voltage of -350V superposed on an AC voltage of 1.5kV with 1kHz is applied to the carrier recovery roll 61. To make a copy using the one color, black, only an AC voltage of 1.5kV with 1kHz is applied to it. Switching between the application voltages is carried out in such a manner that when a copy mode is set through an operation panel, a switching element 64 is switched to a terminal (a) or (b) according to it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a laser beam printer, and a facsimile, and more particularly to an image forming apparatus capable of monochromatic and simultaneous bicolor image formation.

[0002]

2. Description of the Related Art Conventionally, as a technique relating to an image forming apparatus capable of forming a single color image and a simultaneous two-color image of this kind, for example, Japanese Patent Publication No. 3-60435 (JP-A-58-169).
No. 160). The developing device according to Japanese Patent Publication No. 3-60435 has a color and a charging polarity different from those of a monochromatic toner developing mechanism for accommodating monochromatic toner along a moving path of a recording medium supporting an electrostatic latent image. A two-color toner developing mechanism for accommodating two-color toner is disposed, the operation of the two-color toner developing mechanism is stopped when a single-color toner image is formed, and the operation of the single-color toner developing mechanism is stopped when a two-color toner image is formed. The control mechanism is provided.

However, in the developing device according to this proposal, the developing mechanism for two-color toner used when simultaneously forming images of two colors mixes two kinds of toners having different charging polarities into one developing mechanism. Since the toners having different charging polarities are electrostatically attracted to each other, it is difficult to separate the two kinds of toners having different colors, and color mixing occurs, and only an image with poor quality is obtained. The problem is that it is not a very realistic technology. Further, in the developing mechanism for two-color toner, it is necessary to store and supply two kinds of toner in one developing mechanism, so that the developing mechanism itself becomes large and at the same time the cost increases, and at the same time, the photosensitive drum Since it is necessary to arrange a large-sized developing mechanism for two-color toner in addition to the developing mechanism for single-color toner, it is necessary to use a photosensitive drum having a large diameter, and the image forming apparatus becomes large. There is a problem.

Therefore, the applicant of the present invention has already proposed a technique relating to an image forming apparatus capable of solving the problems such as the color mixture of two color toners, and capable of favorably forming an image of a single color and two colors at the same time. It has also been commercialized.

The image forming apparatus proposed by the applicant is, for example, as follows. As shown in FIG. 19, this image forming apparatus uniformly charges the surface of the photosensitive drum 100 by the primary charger 101 during the simultaneous two-color image formation, and then the image reading apparatus 102.
The image of the first color of the original read by the image exposing device 103 is exposed at the first exposure position to form an electrostatic latent image, and the electrostatic latent image is formed by the first developing device 104.
To develop with color toner of a predetermined polarity. Subsequently, the image of the second color is exposed on the photosensitive drum 100 by the image exposure device 103 at the second exposure position to form an electrostatic latent image, and the electrostatic latent image is formed on the second developing device 10.
5, the color toner of the first developing device 104 is developed with black toner having a polarity opposite to that of the color toner. In this image forming apparatus, the two color toner images of color and black formed on the photosensitive drum 100 as described above are transferred to the auxiliary transfer corotron 10.
After charging to the same polarity as the black toner by the charging of 6, the transfer toner is transferred onto the transfer paper 112 conveyed from any of the plurality of paper feed cassettes 108 to 111 by the charging of the transfer corotron 107, and The transfer paper 112 on which the two color toner images have been transferred is separated from the surface of the photoconductor drum 100 by the charge removal of the separation corotron 108, is subjected to a fixing process by the fixing device 113, and is discharged onto the discharge tray 114, and the two colors are simultaneously formed. The image forming process of the image is completed.

In addition to the simultaneous two-color image formation, the above-mentioned image forming apparatus can form not only a monochrome single color image but also a single color image, double-sided image, single-sided image formation, and the like. When performing double-sided image formation or the like, the transfer sheet 112 on which an image has been formed is not discharged as it is, and the transfer path 11 is not discharged.
5 and the intermediate tray 116, and the sheet is conveyed to the image forming section again with the front and back reversed or in the same state.
Double-sided image formation is performed.

[0007]

However, the prior art described above has the following problems. That is, in the case of the image forming apparatus proposed by the present applicant, in order to meet the recent demand for higher image quality, the first and second developing devices 104 and 10 that perform color and black development, respectively.
5 uses a two-component developer using a carrier having a small particle size, and toner is formed by one or both of the first electrostatic latent image and the second electrostatic latent image formed on the photosensitive drum 100. And developing with a two-component developer consisting of a carrier.

At this time, in the first developing device 104, if the potential contrast of the electrostatic latent image formed on the surface of the photosensitive drum 100 is large, as shown in FIG. The fringe electric field F having an extremely high value is formed, and the carrier C having a polarity opposite to that of the toner T may adhere to the portion where the fringe electric field F is formed. When the potential cotrust between the background potential of the electrostatic latent image and the developing bias potential applied to the developing sleeve is large, as shown in FIG. 21 (in the case of reversal development),
Carrier C receives repulsive force due to the developing bias potential,
The carrier C may adhere to the background portion. Further, also in the second developing device 105, when the potential contrast between the background potential of the electrostatic latent image and the developing bias potential applied to the developing sleeve is large, as shown in FIG. The carrier C may receive a repulsive force due to the developing bias potential, and the carrier C may adhere to the background portion. FIG.
Indicates that the carrier is attached.

As described above, when the carrier C adheres to the surface of the photosensitive drum 100, the carrier C has a particle diameter of about several times to 10 times that of the toner T, and therefore the surface of the photosensitive drum 100. The toner image developed on the transfer paper 112
At the time of transfer to the upper side, the distance between the photosensitive drum 100 and the transfer paper 112 at the portion where the carrier C is attached becomes large. Therefore, there is a problem that the charging of the transfer corotron 107 does not sufficiently act on the toner on the photoconductor drum 100, and a transfer failure occurs at that portion. Further, if the carrier C adheres to the surface of the photoconductor drum 100, the carrier C may damage the cleaner that cleans the photoconductor drum 100. Further, the carrier C itself may be transferred onto the transfer paper 113, which may cause image blurring such as character blurring.

In the case of the image forming apparatus proposed by the applicant of the present invention, the image forming device 2 formed on the photosensitive drum 100 is used.
In order to make the polarities of the color toner images uniform, charging is performed by the auxiliary transfer corotron 106. This auxiliary transfer corotron 106 is also used when the black image is formed in addition to the simultaneous two-color image formation. The black toner image formed on the drum 100 is charged. Therefore, particularly when a black monochromatic image is formed, the black toner image formed on the photosensitive drum 100 is charged with the same polarity as the charging polarity of the toner image.
Therefore, there is a problem in that the toner may scatter due to the electrostatic repulsive force and the image quality of fine lines made of black toner may deteriorate.

As described above, in the case of the image forming apparatus proposed by the applicant of the present application, simultaneous development is performed with toners having different polarities, and the carrier of one or both developing devices is on the photosensitive drum 100. However, there is a problem that the image quality may be deteriorated due to the scattering of toner or the scattering of toner. Therefore, in the image forming apparatus proposed by the present applicant, in order to suppress the occurrence of such problems, the charging potential of the photoconductor drum 100 and the developing device 10 are reduced.
The developing biases of Nos. 4 and 105, the applied voltage to the auxiliary transfer corotron 106, and the like were set to a level at which deterioration of image quality due to carrier adhesion or toner scattering does not pose a problem. As a result, in the case of the image forming apparatus proposed by the applicant of the present application, there is a problem that it is difficult to sufficiently satisfy the image quality for both single color and simultaneous two colors.

[0012] Among these problems, as a technique for solving the problem due to carrier adhesion to the photosensitive drum, Japanese Utility Model Laid-Open No. 2-140547 and Japanese Utility Model Laid-Open No. 3-12263 proposed by the present applicant are disclosed. In addition, Japanese Patent Laid-Open No. 6-1
No. 19,707 has been already proposed.

The copying machine proposed by the present applicant in Japanese Utility Model Laid-Open No. 2-140547 mentioned above has a charging unit, an image writing exposure unit, a developing unit, a transfer unit and a cleaning unit at a position facing the outer peripheral side of the latent image carrier. And a developing unit which is provided so as to be movable toward and away from the latent image carrier, and at least one of which constitutes the developing unit is formed by a developing device containing a two-component developer. In the copying machine, a conductive plate is made to face a portion of the developing device which is close to the latent image carrier, and biasing voltage sources having opposite polarities are connected to and disconnected from the conductive plate through a switching means. It is configured to connect as possible.

Further, the developing device of the applicant of the present invention, which is disclosed in Japanese Utility Model Laid-Open No. 3-12263, is composed of a toner and a carrier around a rotatable developer carrier in which a magnet is arranged in a fixed state. A magnetic brush of component developer is formed to develop the electrostatic latent image formed on the surface of the latent image carrier, and a magnet is fixed inside the developer carrier near the developer carrier and is rotatable. In a developing device in which a carrier for removing carrier is disposed and the carrier attached to the surface of the latent image carrier is removed by the carrier for removing carrier and the magnet, The magnet of
The magnetic poles are not provided near the closest position, and the magnetic poles of the same polarity are arranged at the opposite positions.

Further, the developing device of the image forming apparatus according to the above-mentioned Japanese Patent Laid-Open No. 6-119707 comprises a developing magnetic pole and at least one carrying magnetic pole arranged on the rear side of the developing magnetic pole, and A developer carrying member is provided in which the polarity of the carrying magnetic pole adjacent to the developing magnetic pole is different from the polarity of the developing magnetic pole, and toner and carrier are the main components on the developer carrying body. In a developing device for forming a magnetic brush of a component developer to develop an electrostatic latent image formed on a photoconductor, a member for collecting a carrier separated from the developer carrier is adjacent to the developing magnetic pole. In addition to being provided in the vicinity of the carrying magnetic pole, a magnetic pole having the same polarity as the developing magnetic pole is provided in the carrier collecting member. Further, according to the present invention, a bias voltage is applied to the developer carrying member and the carrier collecting member, and the carrier collecting member has the same or a large value as the bias voltage applied to the developer carrying member. It also includes a configuration for applying a polar voltage.

However, in the case of the copying machine according to Japanese Utility Model Laid-Open No. 2-140547, a conductive plate is made to face a portion of the developing device which is close to the latent image carrier, and the conductive plate is provided with a switching means. It is configured such that bias applying voltage sources having opposite polarities are connected to each other so that they can be disconnected and connected, and the carrier adhering on the latent image carrier is electrostatically removed by a conductive plate. However, there is a problem in that the carrier attracting force is weak only by the electrostatic force and the carrier adhered on the latent image carrier cannot be removed sufficiently effectively. Also, this actual Kaihei 2-1
In the case of the copying machine according to Japanese Patent No. 40547, since biasing voltage sources having opposite polarities are connected to the conductive plate via the switching means in a connectable / disconnectable manner, a voltage is applied to the conductive plate. Two power supplies that generate voltages with different polarities are required as bias voltage sources,
There is a problem that the cost becomes higher accordingly.

Further, in the case of the developing device according to Japanese Utility Model Laid-Open No. 3-12263, a rotatable removal carrier carrier which is arranged in the vicinity of the developer carrier and in which a magnet is arranged in a fixed state is used. Therefore, by applying a predetermined voltage to the removed carrier carrier, it is possible to effectively remove the carrier attached to the surface of the latent image carrier. However, in the case of this developing device, since the voltage applied to the removed carrier carrier is always constant,
There is a problem that the carrier adhering to the surface of the latent image carrier cannot be removed sufficiently effectively during the formation of a monochromatic image.

Further, the developing device of the image forming apparatus according to the above-mentioned Japanese Patent Laid-Open No. 6-119707 includes a structure for applying a bias voltage to the developer carrying member and the carrier collecting member. A voltage of the same polarity as the bias voltage applied to the developer carrying member or having a large value is applied to the carrier recovery member. However, when a voltage having the same polarity as the bias voltage applied to the developer carrying member is applied to the carrier collecting member in this manner, the second developing device is operated by the carrier collecting member during simultaneous two-color image formation. There is a problem that the developed color toner of the first developing device 104, which is charged to the opposite polarity to the toner of 105, is adsorbed, and the color toner image is blurred and color mixture occurs.

Therefore, the present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to form an image forming apparatus capable of forming both a single-color image and a simultaneous two-color image. In addition, it is possible to surely prevent carrier adhesion to the latent image carrier and scattering of the toner image, and also surely prevent the toner image developed on the image carrier from being attracted by the downstream developing means. It is an object of the present invention to provide an image forming apparatus capable of satisfying both the image quality of both a monochrome image and a simultaneous two-color image.

[0020]

That is, the invention described in claim 1 of the present invention is provided in a plurality of developing means using toners having different charging polarities and colors and at least one developing means. Carrier recovery means for recovering the carrier attached on the image carrier by magnetic force and electrostatic force, and a plurality of developing means for developing a plurality of electrostatic latent images formed on the image carrier uniformly charged. By developing with, toner images of a plurality of colors are simultaneously formed on the image carrier,
After the toner images of these plural colors are aligned by the auxiliary transfer charging means, they are transferred onto the transfer medium by the transfer charging means, and the transfer medium on which the toner images are transferred is separated from the image carrier. In the image forming apparatus capable of simultaneously forming images of a plurality of colors in addition to the single color image of
Among the parameters that affect the image forming process from the charging of the image carrier including the voltage applied to the carrier recovery unit to the separation of the transfer medium, at least one parameter is used for simultaneous multi-color image formation during single-color image formation. It is configured to change depending on the time of formation.

Further, the invention described in claim 2 of the present invention is configured such that the parameter is the voltage applied to the carrier recovery means.

Further, the invention described in claim 3 of the present invention is configured such that the parameter is the voltage applied to the developer carrying member of the developing means.

Further, the invention described in claim 4 of the present invention is configured such that the parameter is at least one of an applied voltage and a current value of the transfer charging means.

Further, the invention described in claim 5 of the present invention is configured such that the parameter is at least one of the applied voltage and the current value of the pre-transfer charging means.

Further, in the invention described in claim 6 of the present invention, the parameters are both the voltage applied to the carrier collecting means and the voltage applied to the developer carrying member of the developing means. It was done.

Further, in the invention described in claim 7 of the present invention, the parameter is at least one of the applied voltage and current value of the transfer charging means and at least one of the applied voltage and current value of the pre-transfer charging means. It is configured to be both.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

FIG. 2 shows an electrophotographic copying machine as an embodiment of the image forming apparatus according to the present invention.

This electrophotographic copying machine has a composite function of performing simultaneous two-color copying, so-called 1-pass two-color copying, color single-color copying, double-sided copying, single-sided multiplex copying, etc. in addition to ordinary black single-color copying. It has become a copy machine. Also, the paper feed cassettes that feed the paper are all housed inside the main body of the copier, as in modern copiers, so the paper feed cassette does not project outside the device, and paper feeding operations Can be easily done from the front of the copier, and requires a small installation space.
It has a neat appearance and a nice-looking structure.

In the electrophotographic copying machine, as shown in FIG. 2, the image of the original to be copied is read by the original reading device 2 arranged at the upper end of the copying machine main body 1 together with the color information. Once converted into an electrical signal. The image information of the document converted into the electric signal is subjected to predetermined image processing as necessary, and then the laser scanning unit 3
(Hereafter, ROS [Raster Output Sca
Abbreviation of ner]. ), It is converted into an optical signal again, and scanning exposure is performed on the photosensitive drum described later. This R
As shown in FIG. 3, the OS 3 reflects the two semiconductor lasers 4 and 5 and the laser beam Bm emitted from these semiconductor lasers 4 and 5 on the reflecting surface during the rotating operation to bring them into a predetermined scanning range. A polygon mirror 6 that guides it across, a polygon motor 7 for rotating the polygon mirror 6, and a beam Bm from the polygon mirror 6.
, A mirror 10 for reflecting the beam Bm to a first exposure position and a second exposure position on the photosensitive drum 8, respectively. 11 and mirrors 12 and 13.

The ROS 3 scans the two laser beams Bm emitted from the semiconductor lasers 4 and 5 which oscillate according to the image signal, by the polygon mirror 6 along the axial direction of the photosensitive drum 8. At the two exposure positions, the first and second exposure positions, which are determined by the mirror 11 and the mirror 13, on the photoconductor drum 8, image exposure according to the image signal can be performed simultaneously or selectively.

By the way, as the photosensitive drum 8,
For example, a material using an organic photoconductive material (OPC) is used, but the material is not limited to this. As shown in FIG. 4, the photosensitive drum 8 is rotatably arranged in the direction of the arrow by a driving unit (not shown).
The surface of the photosensitive drum 8 is, as shown in FIG.
By the primary charger 14, a predetermined negative voltage (for example,
After being uniformly charged to −750 V), the image is scanned and exposed by the ROS 3 as described above at either or both of the first and second exposure positions depending on the copy mode.
An electrostatic latent image is formed on the surface.

At that time, when two-color simultaneous copying is performed, exposure is performed by image writing for exposing only the image portion at the first exposure position, and as shown in FIG. A latent image is formed. As shown in FIG. 5, the first electrostatic latent image is developed by the first developing device 15 with negative polarity toner, for example, in red by a reversal development method. After that, at the second exposure position, exposure is performed by background lighting that exposes the background portion, and a second electrostatic latent image is formed as shown in FIG. This second electrostatic latent image is, as shown in FIG.
The second developing device 16 normally develops black with positive polarity toner by a regular developing method.

In addition, normal black copying, color monochromatic copying,
In the case of double-sided copying or single-sided multiplex copying, the image is exposed and developed at the first or second exposure position as needed.

The above-mentioned first and second developing devices 15 and 16
Are operated at the same time or selectively. When two-color copying is performed at the same time, they are operated at the same time, and when one-color copying is performed, only one developing device is close to the photosensitive drum 8. It moves to the developed position and operates selectively.
Further, in the first developing device 15, toners of colors such as red and blue are used, and when performing simultaneous two-color copying or color monochromatic copying, the image of a predetermined color is developed and the second developing device 15 is used. In the developing device 16, black toner is normally used, and black monochromatic copying and simultaneous two-color copying are performed.

As shown in FIG. 4, the toner images developed by the first and second developing devices 15 and 16 are positively charged with the same polarity as the black toner by the auxiliary transfer corotron 17, as shown in FIG. First and second developing devices 15, 16
The polarity of the toner image developed by is aligned to the positive polarity as shown in FIG.

After that, as shown in FIG. 2, the toner image formed on the photosensitive drum 8 is transferred from any one of a plurality of paper feed cassettes 18 to 21 arranged inside the main body 1 of the copying machine.
Transfer paper 2 of a predetermined size supplied through paper feed roller 23a, transport roller 23, and registration roller 24
2 is transferred from the photosensitive drum 8 by charging the transfer corotron 25, as shown in FIGS.
The transfer paper 22 to which the toner image is transferred is separated from the photosensitive drum 8 as shown in FIG. 5 by the charge removal of the separation corotron 26, and then transferred to the fixing device 28 by the conveyor belt 27 as shown in FIG. The toner image is conveyed and fixed on the transfer paper 22 by heat and pressure. The transfer paper 22 on which the toner image is fixed remains as it is in the normal copy mode or the simultaneous two-color copy mode.
Discharged on top.

However, in the above-mentioned modes such as double-sided copying and single-sided multiplex copying, the transfer sheet 2 having the toner image fixed thereon is used.
No. 2 is not ejected onto the ejection tray 29 as it is, but the conveyance direction is switched by a switching means (not shown), and is conveyed to the image forming unit again via the conveyance path 30 and the intermediate tray 31 as it is or the inside and outside is turned upside down. Then, a predetermined toner image is copied. Then, after such transfer and fixing of the predetermined image is repeated, the transfer paper 22 is first discharged onto the discharge tray 29.

As shown in FIG. 4, the surface of the photosensitive drum 8 from which the transfer paper 22 is separated is left by the exposure of the erase lamp 33 after the residual toner, paper dust and the like are removed by the cleaning device 32. The charges are erased, and the next copying process is prepared.

FIG. 6 shows a first developing device used in the electrophotographic copying machine. This first developing device 15
Is detachably mounted on the copying machine main body 1 via a holding portion (not shown), and can be replaced with a developing device of another color as required.

As shown in FIG. 6, the first developing device 15 has a developing roll 3 as a developer carrying member, which is disposed in the opening of the housing 35 so as to face the photosensitive drum 8.
6 and the partition wall 3 on the back side of the developing roll 36.
7, a first screw auger 38 and a second screw auger 39, which are provided side by side, and these augers 38, 3
9 provided on the upper side of 9 through the receiving plate 40
The screw auger 41 and the main part thereof are configured. A toner box 44 having a toner agitating coil auger 42 and a toner transporting screw auger 43 is integrally provided on the back side of the housing 35.

Inside the first developing device 15, a two-component developer 45 composed of a color toner T of a predetermined color and a carrier C which is a magnetic particle is stored. Further, inside the toner box 44, color toner T of a predetermined color is
Is stored.

First, the developing roll 36 is composed of a cylindrical sleeve 46 which rotates in the direction of the arrow and a magnet roll 47 which is fixedly arranged inside the sleeve 46, and the spikes arranged above the developing roll 36. The standing restricting member 48 scrapes off the excess developer 45 to form a predetermined amount of magnetic brush on the outer peripheral surface thereof.

On the other hand, the screw augers 38, 39,
Reference numeral 41 denotes a rotary shaft that is driven to rotate at a low speed by a drive motor via a drive gear (not shown), and a conveying blade that is formed in a spiral shape along the length direction of these rotary shafts, and Regarding the first screw auger 38,
The carrier blade is made of non-magnetic stainless steel material (non-magnetic SUS3
04), so that it is not affected by the magnetic force of the magnet roll 47.

An opening (not shown) for supplying the toner conveyed by the second screw auger 39 to the first screw auger 38 is provided at one end side in the longitudinal direction of the partition wall 37. Cage, on the other hand, the receiving plate 4
The second screw auger 39 is also provided on both end sides in the longitudinal direction of 0.
An opening (not shown) for the toner conveyed by the abutment of the side wall of the housing 35 to move to the third screw auger 41, and the toner conveyed by the third screw auger 41 are transferred to the first screw auger 41. And an opening (not shown) for supplying to 38,
As a result, the toner replenished from the toner box 44 is transferred to the second screw auger 39 and the third screw auger 4
While being conveyed from No. 1 to the first screw auger 38, it is sufficiently stirred and charged with the developer 45, and is supplied to the developing roll 36 by the first screw auger 38.

Further, in the first developing device 15, a bias roll 49 for removing the positive polarity toner charged to the polarity opposite to the regular polarity is provided on the downstream side of the development roll 36 in the opening of the housing 35. The bias roll 49 is applied with a negative voltage having the same polarity as the regular toner charging polarity.

As shown in FIG. 4, the first developing device 15 has a crank-shaped rotating rod 50 arranged at its rear end and an engaging portion for engaging with a crank portion 50a of the rotating rod 50. The retracting means composed of 51 or the like can move to a developing position close to the photosensitive drum 8 and a non-developing position separated from the photosensitive drum 8 as needed.

In this embodiment, the toner agitating coil auger 42 provided in the toner box 44 is provided.
As the toner agitation coil-shaped auger 42, a blade for conveyance made of plastic, metal, or the like may be integrally attached to the toner agitation auger 42 as required.

That is, in the first developing device 15,
The toner in the toner box 44 may be biased to one side due to impact such as attachment / detachment or left for a long time with one side held downward. In such a case, erroneous detection of no toner or toner box 44 may occur. There is a case where the toner supply failure from the developing device 15 into the developing device 15 occurs and the toner concentration in the developing device 15 is extremely lowered.

Therefore, even if the toner in the toner box 44 is biased to one side by using the one in which the conveying blades are integrally attached as described above as the coil stirring coil auger 42, Since the toner agitating coil-shaped auger 42 is provided with the carrying blade, it is possible to exert a sufficient toner carrying force, and the developing device 15
Immediately after the start of the operation, the toner in the toner box 44 can be conveyed to the normal state, so that it is possible to prevent the erroneous detection of the absence of toner and the reduction in the density due to the toner supply failure.

FIG. 7 shows a second developing device used in the electrophotographic copying machine according to this embodiment.

As shown in FIG. 7, the second developing device 16 has a developing roll 5 as a developer carrier, which is disposed in the opening of the housing 52 so as to face the photosensitive drum 8.
3, the first and second screw augers 54 and 55 provided on the inner side of the housing 52, and the toner T that is agitated while being sequentially conveyed by the first and second screw augers 54 and 55. A two-component developer 56 composed of the carrier C and a paddle 57 for supplying the developer 56 to the developing roll 53 constitute a main part thereof, and one side surface of the housing 52 accommodates a toner (not shown). A toner box and a toner supply screw auger for supplying toner from the toner box to the inside of the housing 52 are provided.

Inside the housing 52 of the second developing device 16, a two-component developer 56 consisting of black toner T and carrier C which is magnetic particles is contained.

First, the developing roll 53 comprises a cylindrical sleeve 58 which rotates in the direction of the arrow, and a magnet roll 59 which is fixedly arranged inside the cylindrical sleeve 58, and the spikes arranged above the developing sleeve 58. The surplus developer 56 is scraped off by the standing regulating member 60, and a predetermined amount of magnetic brush is formed on the outer peripheral side thereof.

The magnet roll 59 disposed inside the developing sleeve 58 is provided at a predetermined position on the outer periphery thereof in order to obtain a predetermined developing characteristic and a developer conveying characteristic, as shown in FIG. A plurality of magnetic poles having a predetermined polarity are arranged. That is, on the outer circumference of the magnet roll 59, the S1 pole is located at the closest position to the photosensitive drum 8,
N2 poles are magnetized at positions different by 0 degrees. In addition, the S2 pole is formed in the vicinity of the bristling regulation member 60.
The N3 pole is magnetized between the 2 pole and the S1 pole, and the N1 pole is magnetized near the N2 pole between the S1 pole and the N2 pole.

On the other hand, the screw augers 54, 55
Is composed of rotary shafts that are driven to rotate at a low speed by a drive motor via a drive gear (not shown), and conveying blades formed in a spiral shape along the length direction of these rotary shafts. Further, regarding the first screw auger 54, the conveying blade thereof has a non-magnetic stainless steel material (non-magnetic SUS30
4) or a synthetic resin member (a material to which toner is hard to adhere, for example, polycarbonate), and is not affected by the magnetic force of the magnet roller 59.

The toner T supplied into the developing device 15 by the conveying means provided at the end of the second screw auger 55 is agitated with the developer 56 containing the carrier C by the second screw auger 55. After that, while being conveyed to the first screw auger 54 via the second screw auger 55 to be sufficiently stirred and charged, it is conveyed from the first screw auger 54 to the paddle 57,
It is adapted to be supplied to the developing roll 53 via the paddle 57.

In the opening of the housing 52 of the first developing device 16, a carrier collecting roll 61 as a carrier carrying member is arranged downstream of the developing roll 53 so as to face the photosensitive drum 8. The carrier recovery roll 61 is rotatable in the direction of the arrow by a driving unit (not shown). Inside the carrier recovery roll 61, the carrier recovery magnet roll 62 is disposed in a fixed state. Further, a scraper 63 for removing the carrier C captured on the carrier recovery roll 61 is provided on the outer peripheral surface of the carrier recovery roll 61.
Is abutted. In the carrier recovery roll 61, the closest position of the photosensitive drum 8 is the S pole,
It is magnetized so that different positions are the N poles.

By doing so, the developing sleeve 58
Magnet roll 59 and carrier recovery roll 61 inside
As shown in FIG. 7, the magnet roll 62 of No. has no magnetic pole at the closest position, and the magnetic poles of S1 pole and S pole and N1 and N pole of the same polarity are arranged at opposing positions. Is configured to.

In this illustrated example, the magnet roll 59 in the developing sleeve 58 and the magnet roll 62 of the carrier recovery roll 61 are set to the closest position where no magnetic pole is provided.
Although the case of taking a fairly wide area has been described, the present invention is not limited to this. For example, if the magnetic poles are not provided in the areas located within 45 degrees on both sides of the closest position, that is, 90 degrees. good.

As shown in FIG. 4, the second developing device 16 has a crank-shaped rotating rod 64 arranged at its rear end and an engaging portion for engaging with the crank portion 64a of the rotating rod 64. A retracting unit composed of 65 or the like can move to a developing position close to the photosensitive drum 8 and a non-developing position separated from the photosensitive drum 8 as needed.

In this embodiment, the magnet roll 62 in the carrier recovery roll 61 is the developing sleeve 58.
Both ends are 3mm compared to the inner magnet roll 59
It is set to be long.

By doing so, the developing sleeve 58
In the area other than the magnetized width, the electric potential on the photoconductor drum 8 may be lowered to the background electric potential due to the exposure by the erase lamp 33, and the carrier easily attaches to the surface of the photoconductor drum 8. Has become. Therefore, by setting the magnet roll 62 in the carrier collecting roll 61 to be long, the carrier collecting roll 61 can reliably remove the carriers attached to both ends of the photoconductor drum 8.

By the way, in this embodiment, at least one of the parameters that affect the image forming process from the charging of the image carrier to the separation of the transfer medium, including the voltage applied to the carrier recovery means is used. The parameter is configured to be changed between a single color and a plurality of simultaneous colors, and the voltage applied to the carrier collecting means is used as the parameter.

That is, in this embodiment, as shown in FIG. 1, the carrier recovery roll 61 has an AC voltage of 1.5 kV and a frequency of 1 kHz and a DC voltage of −350 at the time of simultaneous two-color copying.
The voltage that superimposes V is AC voltage of 1.5k when the color is black.
It is configured to apply V, 1 kHz only. Switching the applied voltage to the carrier recovery roll 61 is as follows.
When the copy mode is set by the operation panel of the copying machine, the switching element 64 for switching is switched to the terminal a side at the time of simultaneous two-color copying and to the terminal b side at the time of single color according to the setting of the copy mode. Be seen.

In the above embodiment, when a single color is used, A
The C voltage is applied only at 1.5 kV and 1 kHz, and the direct current voltage is not applied. However, the present invention is not limited to this, and is higher than the DC voltage of −350 V which is the applied voltage at the time of simultaneous two-color copying. A high voltage of -100V or -50V may be applied, or a DC voltage of +50 to +300.
A voltage of about V may be applied.

With the above-described structure, the image forming apparatus according to the present embodiment is capable of simultaneously printing a single color image as follows.
In an image forming apparatus capable of forming both color images, it is possible to reliably prevent the carrier from adhering to the latent image carrier and sufficiently satisfy the image quality of both the single color image and the simultaneous two-color image. It is possible.

That is, in order to copy the image of the original in the electrophotographic copying machine, as shown in FIG. 2, after the image is exposed on the surface of the photosensitive drum 8 by the ROS 3 in accordance with the image signal, The electrostatic latent image formed on the surface of the photosensitive drum 8 is developed by a magnetic brush of a two-component developer including toner T and carrier C by one or both of the first developing device 15 and the second developing device 16. .

At this time, in the first developing device 15, as shown in FIG. 20, when the potential contrast of the electrostatic latent image formed on the surface of the photosensitive drum 8 is large, as described above, the latent image is formed. A fringe electric field F having an extremely high potential is formed in the peripheral portion, and the carrier C having a polarity opposite to that of the toner T may adhere to the portion where the fringe electric field F is formed. When the potential cotrust between the background potential of the electrostatic latent image and the developing bias potential applied to the developing sleeve 46 is large, as shown in FIG. 21 (in the case of reversal development), the carrier C is at the developing bias potential. Due to the repulsive force, the carrier C may adhere to the background portion. Furthermore, also in the second developing device 16,
When the potential contrast between the background potential of the electrostatic latent image and the developing bias potential applied to the developing sleeve 58 is large, the carrier C is repelled by the developing bias potential as shown in FIG. 22 (in the case of regular development). The carrier C may be attached to the background portion due to the force.

As shown in FIG. 7, the carrier C attached to the surface of the photosensitive drum 8 is a voltage applied to the carrier recovery roll 61 disposed on the downstream side of the developing sleeve 58 of the second developing device 16. And the magnetic force of the S pole of the magnet roll 62 disposed inside the carrier recovery roll 61, and is captured by the surface of the carrier recovery roll 61 and removed from the surface of the photoconductor drum 8. . After that, the carrier C is conveyed with the rotation of the carrier recovery roll 61, scraped by the scraper 63 contacting the surface of the carrier recovery roll 61, and recovered inside the developing device 16.

At this time, in the simultaneous two-color copying mode, the switching element 64 is switched to the terminal a side of the carrier recovery roll 61 as shown in FIG.
A voltage obtained by superimposing a DC voltage of −350 V on an AC voltage of 1.5 kV and 1 kHz is applied. Therefore, the carrier recovery roll 61 has an AC voltage of 1.5 kV and 1 kHz.
In addition, since the DC voltage of −350V is applied, the toner T of the developed first developing device 15 charged to the same polarity as the DC voltage of −350V adheres to the carrier recovery roll 61. Can be reliably prevented,
The carrier C adhering to the surface of the photosensitive drum 8 can be removed without disturbing the color toner image formed by the first developing device 15, image quality deterioration due to carrier adhering can be prevented, and good image quality can be achieved simultaneously. A two-color image can be obtained.

On the other hand, the carrier recovery roll 61 has
As shown in FIG. 1, in the black monochromatic mode, the switching element 64 is switched to the terminal b side, and only the AC voltage of 1.5 kV and 1 kHz is applied. Therefore, the carrier recovery roll 61 has an AC voltage of 1.5 kV,
Since only 1kHz is applied and the DC voltage becomes 0V,
This 0V DC voltage is a voltage on the positive polarity side in view of the negative polarity, which is the charging polarity of the carrier C used in the second developing device 16, and therefore is a voltage between the carrier C and the carrier recovery roll 61. In addition, the electrostatic adsorption force is greater than that in simultaneous two-color copying, and the carrier C adhering to the surface of the photosensitive drum 8 can be removed more effectively than in simultaneous two-color copying. It is possible to prevent deterioration, and it is possible to obtain a black monochromatic image with good image quality.

FIG. 18 shows changes in the carrier recovery rate when the DC voltage applied to the carrier recovery roll 61 of the second developing device 16 is changed.

As is apparent from FIG. 18, when the voltage applied to the carrier recovery roll 61 in the black monochromatic mode is changed from the negative voltage to 0 V, the carrier recovery rate is significantly improved.

Second Embodiment FIG. 8 shows a second embodiment of the present invention. The same parts as those in the first embodiment will be designated by the same reference numerals. Of the parameters that affect the image forming process from the charging of the image carrier including the voltage applied to the carrier collecting unit to the separation of the transfer medium, at least one parameter is set for single color and simultaneous multiple colors. The voltage applied to the developer carrying member of the developing means is used as the parameter.

That is, in the second embodiment, as shown in FIG. 8, the developing sleeve 58 of the second developing device 16 is
A DC voltage of -400V is applied during simultaneous two-color copying, and a DC voltage of -350V is applied during black monochrome. Switching the voltage applied to the developing sleeve 58 is
When the copy mode is set by the operation panel of the copying machine, the switching element 65 for switching is switched to the terminal a side at the time of simultaneous two-color copying and to the terminal b side at the time of single color according to the setting of the copy mode. Be seen.

Although in the above-described embodiment, only the DC voltage is applied to the developing sleeve 58, the present invention is not limited to this, and the AC voltage is superimposed and applied to the developing sleeve 58. In this case, at least one of the voltage value and the frequency of the AC voltage applied to the developing sleeve 58 is configured to be switched simultaneously or independently with the DC voltage between simultaneous two-color and single-color. May be.

In such a case, when carrying out simultaneous two-color copying in the electrophotographic copying machine, the developing bias voltage applied to the developing sleeve 58 of the second developing device 16 is switched to the DC voltage of -400V, and the developing bias voltage of FIG. As shown in, the potential difference between the background portion of the electrostatic latent image and the developing bias voltage is set to be smaller than that in the case of a single color, so that the developing property of the second developing device 16 is slightly suppressed and the developer of the second developing device 16 is suppressed. It is possible to reliably prevent the developed color toner image from being disturbed by the magnetic brush, and to obtain a good simultaneous two-color image.

On the other hand, when performing black monochromatic copying in the electrophotographic copying machine, the developing bias voltage applied to the developing sleeve 58 of the second developing device 16 is a DC voltage of -350V.
5, the potential difference between the background portion of the electrostatic latent image and the developing bias voltage is set to be larger than that at the time of simultaneous two-color copying, so that the developing property by the second developing device 16 is improved. Then, a clear black toner image can be formed by the second developing device 16, and a good black monochromatic image can be obtained.

FIG. 14 shows the result of a visual sensory test to confirm the state in which the image disturbance of the color toner image occurs when the developing bias voltage applied to the developing sleeve 58 is changed. is there.

As is apparent from FIG. 14, by setting the developing bias voltage applied to the developing sleeve 58 of the second developing device 16 at the time of simultaneous two-color copying to be low, the occurrence of image disturbance of the color toner image is good. You can see that it is suppressed to. Further, in FIG. 15, in order to confirm the level (amount) of the carrier transferred onto the transfer paper 22 when the developing bias voltage applied to the developing sleeve 58 is changed at the time of performing black monochromatic copying, the visual check is performed. 15 shows the result of the sensory test by the method shown in FIG. 15, and as is clear from FIG. 15, by increasing the developing bias voltage applied to the developing sleeve 58 of the second developing device 16 at the time of black monochromatic copying, the transfer paper 22 can be printed. It can be seen that the level (amount) of carriers that are transferred can be reduced.

The other structure and operation are the same as those in the first embodiment, and the description thereof will be omitted.

Third Embodiment FIG. 9 shows a third embodiment of the present invention. The same parts as those in the first embodiment will be designated by the same reference numerals. Of the parameters that affect the image forming process from the charging of the image carrier including the voltage applied to the carrier collecting unit to the separation of the transfer medium, at least one parameter is set for single color and simultaneous multiple colors. The voltage applied to the carrier recovery means and the voltage applied to the developer carrier of the developing device are used as the above parameters.

That is, in the third embodiment, as shown in FIG. 9, the carrier recovery roll 61 has an AC voltage of 1.5 kV and 1 kHz and a DC voltage of -35 when performing simultaneous two-color copying.
The voltage that superimposes 0V is AC voltage 1.5k
It is configured to apply V, 1 kHz only. Switching the applied voltage to the carrier recovery roll 61 is as follows.
When the copy mode is set by the operation panel of the copying machine, the switching element 64 for switching is switched to the terminal a side at the time of simultaneous two-color copying and to the terminal b side at the time of single color according to the setting of the copy mode. Be seen.

Moreover, in the third embodiment, as shown in FIG. 9, the developing sleeve 58 of the second developing device 16 is provided with a DC voltage of -400 V for simultaneous two-color copying and D for single color.
It is configured to apply a C voltage of -350V. When the copy mode is set by the operation panel of the copying machine, the switching voltage of the voltage applied to the developing sleeve 58 is set to the switching element 65 for switching in accordance with the setting of the copy mode, and the terminal a side at the time of simultaneous two-color copying. In the case of a single color, it is performed by switching to the terminal b side.

As described above, in the simultaneous two-color copying mode and the single-color copying mode, by simultaneously switching both the voltage applied to the carrier recovery roll 61 and the voltage applied to the developing sleeve 58 of the developing device 16, Drum 8
Effective removal of the carrier adhering to the upper portion and prevention of disturbance of the color toner image can be achieved at the same time, and a better simultaneous two-color image and a single-color image can be obtained.

The other structure and operation are the same as those in the first embodiment, and the description thereof will be omitted.

Fourth Embodiment FIG. 10 shows a fourth embodiment of the present invention. The same parts as those of the first embodiment will be designated by the same reference numerals and will be described below. Of the parameters that affect the image forming process from the charging of the image carrier including the voltage applied to the carrier collecting unit to the separation of the transfer medium, at least one parameter is set for single color and simultaneous multiple colors. The voltage applied to the transfer charging means is used as the parameter.

That is, in the fourth embodiment, as shown in FIG.
As shown in FIG.
AC black voltage of 3.3kV, 4
A voltage obtained by superimposing a DC constant current of −280 μA on 85 kHz is used as an AC voltage of 3.3 kV and 485 kH when a single color of the first developing device 15 alone is used or when two colors are simultaneously used.
DC current of z-280 μA or more (for example,
It is configured to apply a superimposed voltage of about -330 μA). When the copy mode is set by the operation panel of the copying machine, the switching voltage of the voltage applied to the transfer corotron 25 is changed according to the setting of the copy mode. Is switched to the terminal a side in the case of single color or simultaneous two-color copying, and to the terminal b side in the case of black single color by only the second developing device 16.

As described above, the voltage applied to the transfer corotron 25 is set to the AC current of 3.3 kV and 485 kHz when the black color is generated by the second developing device 16 alone.
By switching to a voltage in which a DC constant current of 280 μA is superimposed, the transfer current by the transfer corotron 25 can be slightly suppressed. Therefore, when the black toner image originally charged to the positive polarity and further charged to the positive polarity having the same polarity by the auxiliary transfer corotron 17 is transferred onto the transfer paper 22, the transfer current by the transfer corotron 25 is slightly increased. By suppressing, the disturbance of the black toner image at the time of transfer due to an excessive transfer current can be prevented, and a good black monochromatic image can be obtained.

On the other hand, the voltage applied to the transfer corotron 25 is set to an AC voltage of 3.3 kV and 485 k when a single color of the first developing device 15 alone is used or when two colors are simultaneously copied.
The transfer current by the transfer corotron 25 can be increased by switching to a voltage obtained by superimposing a DC constant current of −280 μA or more on Hz (for example, about −330 μA). Therefore, when the toner image containing the color toner that is originally negatively charged and positively charged with the opposite polarity by the auxiliary transfer corotron 17 is transferred onto the transfer paper 22, the transfer corotron is used. By increasing the transfer current by 25, a two-color image or color single-color image containing color toner whose polarity is reversed by the auxiliary transfer corotron 17 can be satisfactorily transferred by a sufficient transfer current, and good simultaneous two-color Alternatively, a color monochromatic image can be obtained.

FIG. 16 shows the results of a visual sensory test to confirm the state in which the image disturbance of the color toner image and the black toner image occurs when the direct current flowing through the transfer corotron 25 is changed. It is a thing.

As is apparent from FIG. 16, the DC current flowing through the transfer corotron 25 at the time of simultaneous two-color copying is -33.
By increasing the voltage to about 0 μA and switching the DC constant voltage to about −280 μA during black copying, it is possible to reduce the level of image disturbance, and to perform good transfer of both the color toner image and the black toner image. I understand.

The other structure and operation are the same as those in the first embodiment, and the description thereof will be omitted.

Embodiment 5 FIG. 10 also shows Embodiment 5 of the present invention,
The same parts as those of the first embodiment will be described with the same reference numerals. In the fifth embodiment, the transfer of the transfer medium from the charging of the image carrier including the voltage applied to the carrier collecting unit is performed. Among the parameters that affect the image forming process up to the above, at least one parameter is configured to be changed between a single color and a plurality of simultaneous colors. At least one of the applied voltage and the current value of the auxiliary transfer unit is used as the parameter. One is used.

That is, in the fifth embodiment, as shown in FIG.
As shown in, the AC voltages 3.3 kV and 485 k are applied to the auxiliary transfer corotron 17 when transferring a single color or simultaneous two colors.
A voltage obtained by superimposing a DC constant current of +67 μA on the Hz is connected to the ground when only the second developing device 15 is in the black monochromatic state, and is switched so that the AC voltage and the DC voltage are both 0V. There is. When the copy mode is set by the operation panel of the copying machine, the switching of the voltage applied to the auxiliary transfer corotron 17 causes the switching element 67 for switching according to the setting of the copy mode, and the terminal a during simultaneous two-color copying. To the side of the terminal b when the second developing device 16 alone is black.

Thus, the auxiliary transfer corotron 17
When the voltage applied to the second developing device 16 is black monochromatic, the discharge by the auxiliary transfer corotron 17 can be prohibited by connecting to the ground and switching both the AC voltage and the DC voltage to 0V. . Therefore, it is originally charged positively and the auxiliary transfer corotron 1
It is possible to prevent the black toner image from being disturbed by the electrostatic repulsive force of the same polarity by receiving the positive polarity charge of the same polarity by 7.

On the other hand, the voltage applied to the auxiliary transfer corotron 17 is set to an AC voltage of 3.3 kV at the time of simultaneous two-color transfer.
By switching to a voltage obtained by superimposing a DC constant current of DC current +67 μA on 485 kHz, auxiliary charging by the auxiliary transfer corotron 17 can be favorably performed. Therefore, originally, the negatively charged color toner can be positively charged to the positive polarity having the opposite polarity by the charging of the auxiliary transfer corotron 17, and the toner image containing the color toner is satisfactorily transferred onto the transfer paper 22. It is possible to obtain a good color monochromatic image and a simultaneous two-color image.

FIG. 17 shows the results of a visual sensory test to confirm the state in which the black toner image is disturbed when the direct current flowing through the auxiliary transfer corotron 17 is changed.

As is apparent from FIG. 17, when the black color is monochromatic, it is connected to the ground and both the AC voltage and the DC voltage are set to 0 V, so that the image disturbance due to the scattering of the black toner image is almost prevented, and it is preferable. It turns out that it is possible to obtain various images.

The other structure and operation are the same as those in the first embodiment, and the description thereof will be omitted.

Sixth Embodiment FIG. 10 also shows a sixth embodiment of the present invention.
The same parts as those in the first embodiment will be described by giving the same reference numerals. In the sixth embodiment, the transfer medium is separated from the charging of the image carrier including the voltage applied to the carrier collecting means. Among the parameters affecting the image forming process up to the above, at least one parameter is configured to be changed between a single color and a plurality of simultaneous colors, and at least the applied voltage and the current value of the transfer charging unit are used as the parameters. One of them and at least one of the applied voltage and the current value of the auxiliary transfer means are used.

That is, in the sixth embodiment, as shown in FIG.
As shown in FIG.
AC black voltage of 3.3kV, 4
A voltage obtained by superimposing a DC constant current of −280 μA on 85 kHz is used as an AC voltage of 3.3 kV and 485 kH when a single color of the first developing device 15 alone is used or when two colors are simultaneously used.
DC current of z-280 μA or more (for example,
It is configured to apply a superimposed voltage of about -330 μA).

Moreover, in the sixth embodiment, as shown in FIG. 10, AC voltages of 3.3 kV and 485 kH are applied to the auxiliary transfer corotron 17 when transferring a single color or simultaneous two colors.
A voltage obtained by superimposing a DC constant current of +67 μA on z is connected to the ground when only the second developing device 15 is in a black monochromatic state and is switched so that both AC voltage and DC voltage of 0 V are applied. There is.

By doing so, the fourth embodiment described above is performed.
It is possible to obtain the action and effect having both the action and effect of the fifth embodiment, and it is possible to obtain a better simultaneous two-color image and a black single-color image.

The other structure and operation are the same as those in the first embodiment, and the description thereof will be omitted.

Seventh Embodiment FIG. 11 shows a seventh embodiment of the present invention. The same parts as those in the first embodiment will be designated by the same reference numerals and will be described below. Of the parameters that affect the image forming process from the charging of the image carrier including the voltage applied to the carrier collecting unit to the separation of the transfer medium, at least one parameter is set for single color and simultaneous multiple colors. The charge voltage of the image carrier is used as the parameter.

That is, in the seventh embodiment, FIG.
As shown in, a primary charger 14 that uniformly charges the surface of the photoconductor drum 8 is provided with the photoconductor drum 8 at the time of simultaneous two-color transfer.
A voltage such that the surface charging voltage becomes −700 V is applied from the high-voltage power supply 69 through two resistors and a varistor element, and when the second developing device 15 alone is in a black single color, the surface charging voltage of the photosensitive drum 8 is A voltage of −750 V is applied from the high-voltage power supply 69 via one resistor and a varistor element. When the copy mode is set by the operation panel of the copying machine, the switching of the voltage applied to the primary charger 14 is performed by the switching element 68 for switching according to the setting of the copy mode.
The second developing device 16
In the case of a black monochromatic color due to only, it is performed by switching to the terminal b side.

As described above, the charging voltage of the surface of the photosensitive drum 8 by the primary charger 14 is set to − during black monochromatic copying.
By switching to 750 V, the potential difference between the charging voltage on the surface of the photosensitive drum 8 corresponding to the image portion of the electrostatic latent image and the developing bias voltage can be made large, and the developing property of the second developing device 16 can be improved. Therefore, a good black monochromatic image can be obtained.

On the other hand, the charging voltage applied to the surface of the photosensitive drum 8 by the primary charger 14 is set to -700 when copying two colors at the same time.
By switching to V, the potential difference between the charging voltage and the developing bias voltage on the surface of the photosensitive drum 8 corresponding to the background portion of the electrostatic latent image can be reduced in the first developing device 15, and the first developing device 15 The phenomenon that the carrier adheres to the surface of the photoconductor drum 8 due to the above can be suppressed, and the carrier adhesion can be suppressed, so that a good simultaneous two-color image can be obtained.

The other structure and operation are the same as those in the first embodiment, and the description thereof will be omitted.

Eighth Embodiment FIG. 12 shows an eighth embodiment of the present invention. The same parts as those in the first embodiment will be designated by the same reference numerals. Of the parameters that affect the image forming process from the charging of the image carrier including the voltage applied to the carrier collecting unit to the separation of the transfer medium, at least one parameter is set for single color and simultaneous multiple colors. The number of revolutions of the developer carrying member is used as the parameter.

That is, in the eighth embodiment, as shown in FIG.
As shown in, the first developing device 15 and the second developing device 16
Is configured to be driven by one drive motor 70, and an AC motor is used as the drive motor 70.
The drive motor 70 itself has switching terminals 71 and 72 for switching between 50 Hz and 60 Hz. Therefore, the voltage applied to the drive motor 70 is controlled by the relay switch 73.
By switching between the terminal 71 on the Hz side and the terminal 72 on the 60 Hz side, the rotational speed of the drive motor 70 composed of the AC motor can be changed, and as a result, the drive motor 70
Developing sleeve 5 of the second developing device 16 driven by
The number of rotations of 8 can be switched. When the copying mode is set by the operation panel of the copying machine, the number of rotations of the developing sleeve 58 of the second developing device 16 is switched by setting the terminal of the switching element 74 at the time of simultaneous two-color copying according to the setting of the copying mode. By switching the terminal of the relay switch 73 to the a side and switching the terminal of the switching element 74 to the b side and the terminal of the relay switch 73 to the b side when the second developing device 16 alone is black in color. Be seen.

As described above, the rotational speed of the developing sleeve 58 of the second developing device 16 is set to 50 Hz in the simultaneous two-color copying.
By switching to the terminal a on the side, it is possible to switch to a relatively low speed side, the developing property by the developing sleeve 58 of the second developing device 16 is suppressed, and the color toner image already formed on the photosensitive drum 8 is formed. It can be prevented from being disturbed.

On the other hand, the rotational speed of the developing sleeve 58 of the second developing device 16 can be switched to the relatively high speed side by switching to the terminal b on the 60 Hz side during black monochromatic copying and color monochromatic copying. Second developing device 1
The developing property of the developing sleeve 58 of No. 6 can be improved, and black and color toner images can be satisfactorily formed on the photosensitive drum 8.

The other structure and operation are the same as those in the first embodiment, and therefore the description thereof is omitted.

Ninth Embodiment FIG. 13 shows a ninth embodiment of the present invention. The same parts as those in the first embodiment will be designated by the same reference numerals and will be described. Of the parameters that affect the image forming process from the charging of the image carrier including the voltage applied to the carrier collecting unit to the separation of the transfer medium, at least one parameter is set for single color and simultaneous multiple colors. The gap between the image carrier and the developer carrier is used as the parameter.

That is, in the ninth embodiment, FIG.
As shown in (a), at the time of simultaneous two-color transfer, the gap between the photoconductor drum 8 and the developing sleeve 58 of the second developing device 16 is set relatively large so as to be 0.85 mm to 1.00 mm, As shown in FIG. 13 (b), the photosensitive drum 8 and the second
The gap between the developing device 16 and the developing sleeve 58 is, for example, 0.
It is configured to be relatively small so as to be 75 mm. The photosensitive drum 8 and the second developing device 16
The gap between the developing sleeve 58 and the developing sleeve 58 is switched between the shaft 80 of the developing sleeve 58 of the second developing device 16 according to the copy mode.
This is performed by rotating a contact member 81, which is mounted coaxially with the contact member 81 and is in contact with the axial end portion of the surface of the photosensitive drum 8, by a solenoid 82 attached to the other end of the contact member 81. The large-aperture portion 83 of the butting member 81 is brought into contact with the surface of the photoconductor drum 8 at the time of simultaneous two-color copying, and the butting member 81 is made at the time of black monochromatic copying.
The portion 84 having a small radius is abutted on the surface of the photosensitive drum 8.

As described above, the gap between the photosensitive drum 8 and the developing sleeve 58 of the second developing device 16 is set to be relatively large during simultaneous two-color copying, and the developing property of the second developing device 16 is slightly lowered. By doing so, it is possible to prevent the second developing device 16 from disturbing the developed color toner image, and it is possible to obtain a good simultaneous two-color image.

On the other hand, the gap between the photoconductor drum 8 and the developing sleeve 58 of the second developing device 16 is set to be relatively small at the time of black monochromatic copying to improve the developing property of the second developing device 16. A black toner image can be satisfactorily obtained by the second developing device 16.

The other structure and operation are the same as those in the first embodiment, and the description thereof will be omitted. It is needless to say that any two or three or more of the first to ninth embodiments may be combined as appropriate.

[0122]

According to the present invention, which has the above-described structure and operation, in an image forming apparatus capable of forming both a single-color image and a simultaneous two-color image, carrier adhesion to a latent image carrier or a toner image. It is possible to surely prevent the scattering of toner particles and the like, and it is possible to surely prevent the toner image developed on the image bearing member from being attracted by the developing device on the downstream side. It is possible to provide an image forming apparatus capable of sufficiently satisfying both image qualities, and further, it is possible to provide excellent image quality at a low cost without requiring major modification of the apparatus. However, the range of selection is widened, and it is possible to save the labor of newly designing a developer.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a main part of an electrophotographic copying apparatus according to an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram showing an electrophotographic copying apparatus according to an embodiment of an image forming apparatus according to the present invention.

FIG. 3 is a perspective view showing a ROS.

FIG. 4 is a configuration diagram showing a main part of an electrophotographic copying apparatus according to an embodiment of an image forming apparatus according to the present invention.

FIG. 5 is an explanatory diagram showing an image forming process.

FIG. 6 is a cross-sectional configuration diagram showing a first developing device.

FIG. 7 is a cross-sectional configuration diagram showing a second developing device.

FIG. 8 is a configuration diagram showing a main part of an electrophotographic copying apparatus according to Embodiment 2 of the present invention.

FIG. 9 is a configuration diagram showing a main part of an electrophotographic copying apparatus according to a third embodiment of the present invention.

FIG. 10 is a configuration diagram showing a main part of an electrophotographic copying apparatus according to Embodiments 4 to 6 of the present invention.

FIG. 11 is a configuration diagram showing a main part of an electrophotographic copying apparatus according to a seventh embodiment of the present invention.

FIG. 12 is a configuration diagram showing a main part of an electrophotographic copying apparatus according to Embodiment 8 of the present invention.

13 (a) and 13 (b) are configuration diagrams showing a main part of an electrophotographic copying apparatus according to Embodiment 9 of the present invention.

FIG. 14 is a graph showing the relationship between the developing bias and the degree of occurrence of image distortion.

FIG. 15 is a graph showing the relationship between the developing bias and the degree of occurrence of carrier adhesion.

FIG. 16 is a graph showing the relationship between the transfer current value and the degree of occurrence of image distortion.

FIG. 17 is a graph showing the relationship between the current value of the auxiliary transfer corotron and the degree of occurrence of toner scattering.

FIG. 18 is a graph showing the relationship between the current value of the auxiliary transfer corotron and the degree of occurrence of toner scattering.

FIG. 19 is a block diagram showing a conventional electrophotographic copying apparatus.

FIG. 20 is an explanatory diagram showing a mechanism in which carrier adhesion occurs.

FIG. 21 is an explanatory diagram showing a mechanism of carrier adhesion.

FIG. 22 is an explanatory diagram showing a mechanism in which carrier adhesion occurs.

FIG. 23 is an explanatory diagram showing a mechanism in which carrier adhesion occurs.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 photoconductor drum, 14 temporary charger, 15 first developing device, 16 second developing device, 17 auxiliary transfer corotron, 25 transfer corotron, 26 separation corotron, 5
8 developing sleeve, 61 carrier recovery roll, 64
Switching element.

Claims (7)

[Claims] 1. A plurality of developing means using toners having different charging polarities and colors, and a carrier collecting means provided in at least one developing means for collecting carriers adhered on an image carrier by magnetic force and electrostatic force. And developing a plurality of electrostatic latent images formed on the image carrier uniformly charged, by a plurality of developing means, to simultaneously form a toner image of a plurality of colors on the image carrier, After the toner images of these plural colors are aligned by the auxiliary transfer charging means, they are transferred onto the transfer medium by the transfer charging means, and the transfer medium on which the toner images are transferred is separated from the image carrier. In the image forming apparatus capable of simultaneously forming a plurality of color images in addition to the single color image, the image from the charging of the image carrier including the voltage applied to the carrier collecting unit to the separation of the transfer medium is performed. An image forming apparatus, wherein at least one parameter among parameters affecting an image forming process is changed between a single-color image formation and a simultaneous multi-color image formation. 2. The image forming apparatus according to claim 1, wherein the parameter is a voltage applied to the carrier recovery means. 3. The image forming apparatus according to claim 1, wherein the parameter is a voltage applied to the developer carrying member of the developing unit. 4. The image forming apparatus according to claim 1, wherein the parameter is at least one of an applied voltage and a current value of the transfer charging unit. 5. The image forming apparatus according to claim 1, wherein the parameter is at least one of an applied voltage and a current value of the pre-transfer charging unit. 6. The image forming apparatus according to claim 1, wherein the parameters are both the voltage applied to the carrier recovery means and the voltage applied to the developer carrying member of the developing means. 7. The method according to claim 1, wherein the parameter is at least one of an applied voltage and a current value of the transfer charging means and at least one of an applied voltage and a current value of the pre-transfer charging means. Image forming device.