JPH06118786A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a copying machine capable of obtaining optimum image quality corresponding to the kind of original for images requiring gradation, high resolution. etc. CONSTITUTION:In the original requiring the gradation like the image of a photographic style, a first developing mode is set by a developing mode input device 91 and the peripheral speed of the developing roll 4 at the time of developing is set almost the same as that of a photosensitive drum 1. Moreover, an AC bias on which a DC is superimposed or a pulse bias that the time ratio of high and low voltage parts is about 1:1 can be applied to the developing roll 4 as well. On the other hand, in the original requiring the high resolution like the image including many fine lines of a character, a table, etc., a second developing mode is set and the peripheral speed of the developing roll 4 at the time of developing is set higher than that of the photosensitive drum 1. Moreover, a DC bias or the pulse bias that the time ratio of the high and low voltage parts is about 2:3-1:10 (the case of N/P development) can be applied to the developing roll 4.

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 a copying machine, a facsimile or a printer, and more specifically, to a developer carrier by selectively retaining an electric charge on the surface of the developer carrier. Form many small closed electric fields on the body,
Image formation in which a developer is carried in multiple layers on the developer carrier by the minute closed electric field and the latent image on the image carrier is visualized by using the developer carried by the developer carrier. It relates to the device.

[0002]

2. Description of the Related Art In an image forming apparatus in which a latent image is formed on an image bearing member and visualized by a developer, a one-component system developing apparatus is used from the viewpoints of downsizing of the developing apparatus, cost reduction, high reliability and the like. A developing device using an agent is advantageous. Particularly for colorization, it is advantageous to use a non-magnetic one-component developer because of its high transparency. As a developing device using a one-component developer (hereinafter, referred to as toner), a developer carrier that carries toner on its surface and conveys it along a predetermined circulation path including a developing region, and a storage means for storing toner And a developer supply unit for supplying the toner stored in the developer storage unit to the developer support unit to supply the toner to the developer developer support unit (for example, Japanese Patent Laid-Open Publication No. Sho-Sho). 60-
229057 and JP-A-61-42672).

Here, the optimum toner adhesion amount and toner charge amount on the developer carrier in the developing method using non-magnetic toner will be described. The amount of toner deposited on the developer carrying member, the toner adhesion amount of about 0.6~1.0mg / cm ² on the image bearing member, the toner adhesion amount of about 0.5~0.7mg / cm ² on paper transfer Is desirable. Further, the toner adhesion amount on the image carrier and the transfer paper depends not only on the toner adhesion amount on the developer carrier but also on the peripheral speed difference between the image carrier and the developer carrier in the developing region. .

However, according to this type of developing device which has been put into practical use, the toner layer on the developer carrying member is one layer, and the toner adhesion amount on the developer carrying member is 0.2 to 0. ．
It was as small as 5 mg / cm ² . Therefore, in order to obtain the desired toner adhesion amount on the image bearing member or the like, it is necessary to set the peripheral speed of the developer bearing member to 2 to 4 times the peripheral speed of the image bearing member. Thus, when the rotation of the developer carrier is set high in order to cover the insufficient toner adhesion amount on the developer carrier, not only is it difficult to increase the image forming speed, but also, for example, a solid image. There is also a phenomenon of "from the trailing edge of the toner" in which the density of the trailing edge portion becomes high when the portion is developed.
This phenomenon is not a big problem for black-and-white images, but for color images there is a problem that the color is transmitted through the toner and the color is visualized, so that the density is high at the trailing edge, and especially in the case of superimposed images, there is a color difference. .

In order to obtain a desired toner adhesion amount on the image bearing member without causing such a phenomenon "from the trailing edge of the toner", the peripheral speed of the developer bearing member is adjusted. It is necessary to approach the peripheral speed, i.e., near constant velocity development, and increase the toner adhesion amount on the developer carrying member as compared with the conventional one. Specifically, in order to secure a sufficient amount of toner adhered on the image carrier or transfer paper at almost constant speed development, the amount of toner adhered on the developer carrier should be determined by a contact development method with good development efficiency. It is required to be at least 0.8 mg / cm ² or more, and at least 1.0 mg / cm ² or more in the non-contact development method having poor developing efficiency. In order to obtain such a toner adhesion amount on the developer carrying member, the toner layer thickness must be two or more layers.

Moreover, if the toner layer on the developer carrying member conveyed to the developing area contains uncharged toner or reversely charged toner, it may cause deterioration of development transfer, background stain, resolution deterioration and the like. Therefore, the toner charge amount is 5 to 1 as an average charge amount.
0 μc / g is desirable. Further, it is desirable that the toner charge amount distribution is a stable distribution in which there are few relatively low-charged toners that cause sharpness and deterioration of resolution and scumming.

As described above, a multi-layered toner layer of two or more layers having an average charge amount of 5 to 10 μc / g with a stable charge distribution is contained on the developer carrier without containing the uncharged toner or the oppositely charged toner. If it is formed on the body, the image forming speed can be increased and constant speed development for preventing "from the trailing edge of the toner" is possible.

Therefore, the applicant of the present invention, as a means for adhering a desired amount of toner having a stable charge amount on a developer carrier, as a developer carrier, the surface is regularly or irregularly distributed in a minute area. Using a developer carrier composed of a dielectric part and a grounded conductive part, the toner is triboelectrified at a pressure contact part between the developer carrier and a developer supply member rotating at a position in contact with the surface of the developer carrier, Further, the dielectric portion is triboelectrically charged by the developer supply member and the toner to form a large number of minute closed electric fields in the vicinity of the surface of the developer carrier, and the triboelectrically charged toner is carried by the minute closed electric field on the developer carrier. A developing device for supporting multiple layers on the body has been proposed (for example, Japanese Patent Application No. 2-1
5110). According to the developing device of the invention of the prior application, it becomes possible to form a multi-layer toner layer having a stable charge amount on the developer carrying member.

[0009]

However, in the construction of the developing device of Japanese Patent Application No. 2-15110, the multi-layered toner layer is formed on the developer carrying member, and the electric field for starting the development with the toner is started. (Threshold electric field)
However, the threshold electric field depends on the adhesive force between the toners in each layer of the multi-layered toner layer, and the threshold electric field is different for the first layer toner, the second layer toner, and the third layer toner. There is a problem that it is difficult to control the gradation.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optimum image according to the type of original such as an image requiring gradation and an image requiring high resolution. An object of the present invention is to provide an image forming apparatus capable of obtaining quality.

[0011]

In order to achieve the above object, a large number of minute closed electric fields are formed on a developer carrier by selectively retaining electric charges on the surface of the developer carrier. Then, the developer is carried in multiple layers on the developer carrying body by the minute closed electric field, and the latent image on the image carrying body is visualized by using the developer carried by the developer carrying body. An image forming apparatus according to claim 1, wherein the image forming apparatus according to claim 1 drives the developer carrier so that the surface of the image carrier moves, and the developer carrier for the surface of the image carrier connected to the drive means. A drive control means for controlling the moving speed of the surface of the body, and a first developing mode which is connected to the drive control means and in which the surface of the developer carrier moves at substantially the same speed as the moving speed of the surface of the image carrier. And the surface of the developer carrying member moves faster than the moving speed of the surface of the image carrying member. It is characterized in that provided and a mode switching means for switching the second developing mode.

An image forming apparatus according to a second aspect of the present invention is connected to the bias voltage applying means for applying a DC bias voltage or a bias voltage which changes periodically to the developer carrier, and is connected to the bias voltage applying means. A first development mode in which a bias voltage that changes periodically is applied to the developer carrier;
A mode switching means for switching between a second developing mode for applying a DC bias voltage to the developer carrier is provided.

According to another aspect of the image forming apparatus of the present invention, a bias voltage applying unit that applies a bias voltage that changes periodically to the developer carrier, and a bias voltage applying unit that is connected to the bias voltage applying unit. Application time A of a voltage for generating an electric field that causes the developer to move toward the developer carrying member and application time B of a voltage that generates an electric field that causes the developer to move toward the image carrying member A bias voltage control means for controlling a ratio between the bias voltage control means and the bias voltage control means, and a first developing mode for applying a bias voltage to the developer carrier, the bias voltage having an application time A substantially equal to the application time B. A mode switching means for switching between a second developing mode in which a bias voltage whose application time A is longer than said application time B is applied to the developer carrying member is provided.

[0014]

According to the image forming apparatus of the present invention, the user determines which of the first developing mode and the second developing mode is appropriate according to the type of the image of the original, and operates the mode switching means. The appropriate one of the first development mode and the second development mode is selected according to the type of the original. Alternatively, the type of the original is automatically read and determined by the original reading device provided in the mode switching means, and the first developing mode corresponding to the type of the original is set based on the output value of the reading device. An appropriate one of the second developing modes is selected. For example, in the case of a document requiring gradation such as a photographic image, the first developing mode is selected by the mode switching means. Then, the drive means is controlled by the drive control means, and the surface of the developer carrier moves at substantially the same speed as the moving speed of the surface of the image carrier. When development is performed in this state, the above "from the trailing edge toner" does not occur and the image density becomes uniform. On the other hand, in the case of a document requiring high resolution such as an image including many thin lines such as characters and tables, the second developing mode is selected by the mode switching means. Then, the drive means is controlled by the drive control means, and the surface of the developer carrier moves faster than the moving speed of the surface of the image carrier. When development is performed in this state,
The above-mentioned "from the trailing edge toner" occurs, and thin lines such as characters and tables become thick.

According to another aspect of the image forming apparatus of the present invention, the user determines which of the first developing mode and the second developing mode is appropriate depending on the type of the image of the original, and operates the mode switching means. The appropriate one of the first development mode and the second development mode is selected according to the type of the original. Alternatively, the type of the original is automatically read and determined by the original reading device provided in the mode switching means, and the first developing mode corresponding to the type of the original is set based on the output value of the reading device. An appropriate one of the second developing modes is selected. For example, in the case of originals that require gradation, such as photographic images,
The first developing mode is selected by the mode switching means. Then, the bias voltage applying means applies a periodically changing bias voltage to the developer carrying member. When development is performed in this state, the electric field generated between the image carrier and the developer carrier causes the developer to reciprocate between the developer carrier and the image carrier. Receive strong power. On the other hand, in the case of a document requiring high resolution such as an image including many thin lines such as characters and tables, the second developing mode is selected by the mode switching means. Then, a DC bias voltage is applied to the developer carrying member by the bias voltage applying means. When development is performed in this state, the developer is less likely to adhere to the non-image portion of the latent image on the image carrier.

In the image forming apparatus according to the third aspect of the present invention, the user determines which of the first developing mode and the second developing mode is appropriate depending on the type of the image of the original, and operates the mode switching means. The appropriate one of the first development mode and the second development mode is selected according to the type of the original. Alternatively, the type of the original is automatically read and determined by the original reading device provided in the mode switching means, and the first developing mode corresponding to the type of the original is set based on the output value of the reading device. An appropriate one of the second developing modes is selected. For example, in the case of originals that require gradation, such as photographic images,
The first developing mode is selected by the mode switching means. Then, the bias voltage control means controls the bias voltage application means for applying a bias voltage that changes periodically to the developer carrier, and an electric field that moves the developer to the developer carrier side is controlled. The application time A of the voltage to be generated is substantially equal to the application time B of the voltage to generate an electric field that causes the developer to move to the image carrier side. When development is performed in this state, the electric field generated between the image carrier and the developer carrier causes the developer to reciprocate between the developer carrier and the image carrier. Receive strong power. On the other hand, in the case of a document requiring high resolution such as an image including many thin lines such as characters and tables, the second developing mode is selected by the mode switching means. Then, the bias voltage control means controls the bias voltage application means for applying a bias voltage that changes periodically to the developer carrier, and an electric field that moves the developer to the developer carrier side is controlled. The application time A of the generated voltage is longer than the application time B of the voltage for generating the electric field for moving the developer toward the image carrier, for example, doubled. When the development is performed in this state, the time for which the development is accelerated becomes shorter and the time for which the developer is removed from the non-image area becomes longer.

[0017]

Embodiments Embodiments in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. First, the first embodiment will be described. Figure 2
FIG. 2 is a front view showing a schematic configuration of a developing device used in the copying machine according to this embodiment. The photoconductor drum 1 as an image carrier is driven to rotate clockwise in the arrow direction at a peripheral speed of 120 mm / sec, for example. A developing device 2 is arranged on the right side of the photosensitive drum 1. Around the photosensitive drum 1, a well-known charging device, exposure optical system, and
A transfer / separation device, a cleaning device, and a charge removal device (all not shown) are provided. The developing device 2 of this embodiment is
A casing 3 having an opening facing the surface of the photosensitive drum 1.
And a developing roller 4 as a developer carrying member which is partially exposed from the opening and is driven to rotate counterclockwise at a predetermined peripheral speed, and an arrow in a state of being pressed against the right side portion of the developing roller 4. A toner supply roller 5 as a developer supply member that is driven to rotate in a clockwise direction, and a non-magnetic one-component developer housed in a hopper portion as a developer storage means formed on the right side in the casing 3. An agitator 6 for supplying (hereinafter referred to as toner) 7 to the surface of the toner supply roller 5 and agitating the toner in the hopper, and a developing roller 4.
And a layer thickness leveling plate 8 as a developer regulating member for leveling the thickness of the toner layer on the developing roller 4 conveyed to the developing area A which is the portion facing the photoconductor drum 1 by the rotation of. There is.

As shown in FIG. 2, the developing roller 4 may be arranged to face the surface of the photosensitive drum 1 in the developing area A with a predetermined gap therebetween so as to perform non-contact developing. Contact development may be performed by disposing the upper toner layer so as to contact the surface of the photoreceptor 1.

Further, the developing roller 4 has a bias power source 2
1, an appropriate developing bias voltage, for example, DC, AC, AC with superimposed DC, or pulse voltage is applied. Particularly in the case of non-contact development, it is desirable to apply a voltage having an alternating component with good flight conditions (AC, AC with superimposed DC, or pulse voltage).

The developing roller 4 of the present embodiment has a structure shown in FIG.
As shown in (b), a developing roller 4 is used in which a dielectric portion 41 capable of holding electric charges on the surface and a grounded conductor portion 42 are exposed in a mixed manner in a small area. Figure 3
3A is a plan view of the surface of the developing roller 4, and FIG.
It is sectional drawing when it cut | disconnects by the aa cutting line of (a).
The size of the dielectric portion 41 is, for example, 50 to 200 in diameter.
Set to about μm. It is arranged that the dielectric parts 41 are dispersed randomly or according to a certain rule. As the area ratio of both parts, it is preferable that the area of the dielectric part 41 is in the range of 40 to 70% of the whole. As the material of the dielectric portion 41, a material having a resistance value such that electric charges are not accumulated by frictional charging by the toner supply roller 5 is used. To form the surface layer portion shown in the figure, for example, the surface of the cored bar roller is knurled to form a predetermined groove, and then an insulating resin, for example, is coated, and then the surface is cut to form a cored bar. The resin can be formed by exposing the resin in the groove as the dielectric portion 41 on the surface.

The toner supply roller 5 is provided with a sponge layer 52, which is an elastic foam, on a core metal 51, and a large number of voids are formed on the surface of the sponge layer 52 so that the toner can be retained at least in the vicinity of the surface. The hole is open. The sponge layer 52 will be described later in detail. The material of the sponge layer 52 and the fibrous member of the toner supply roller 5 is the toner 7 in the triboelectrification series so that the toner and the development roller 4 can be contacted with the development roller 4 to give a desired triboelectrification. It is desirable to use a material that is intermediate between the material described above and the material of the surface portion of the developing roller 4.

The toner supply roller 5 is supported, for example, at a position where it comes into pressure contact with the surface of the developing roller 4 by a predetermined amount, and the surface moves in the same direction as the surface of the developing roller 4 at the contact portion with the developing roller 4. It is driven so as to rotate in the forward direction. The peripheral speed of the toner supply roller 5 is set to, for example, about 0.5 to 2.5 times the peripheral speed of the developing roller 4. Further, the core metal 51 of the toner supply roller 5 is supplied with the same voltage as that applied to the developing roller 4 by the bias power source 22 or toner frictionally charged to a predetermined polarity from the toner supply roller 5 side to the developing roller 4 side. A voltage may be applied so as to form an electric field between the developing roller 4 and the electrostatic force toward the side.

The agitator 6 supplies the toner 7 contained in the hopper to the surface of the toner supply roller 5 and agitates the toner 7. The agitator 6 has the shape of the hopper, the fluidity of the toner 7 and its own weight. If the toner can be supplied to the surface of the toner supply roller 5, it may be omitted.

The layer-thickness leveling plate 8 has a light contact pressure of about 10 to 20 g / cm for non-contact development and a contact pressure of about 30 g / cm for contact development. It is arranged so as to abut on 4. In the case of contact development, the contact pressure is set to be relatively high because in the case of contact development, the development transfer rate to the photosensitive drum 1 side is relatively high.
The appropriate toner adhesion amount above is, for example, 0.8 to 1.0 mg /
This is because it is relatively small at about cm ² . As the material of the layer-thickness leveling plate 8, as in the case of the surface material of the toner supply roller 5, the toner material on the charge series and the dielectric 4 are used.
It is desirable to adopt one located between one material.

A more specific aspect of this embodiment will be described below as a specific example. (1) Developing roller 4 ・ By knurling on the surface of a metal core roller having a diameter of 25 mm, a groove having a depth of 0.1 mm and a groove width of 0.2 mm is formed with a pitch of 0.3.
It was formed into an iris shape with an mm of 45 degrees. -Coating the surface of this core metal roller with an epoxy-modified silicone resin (SR2115: trademark, manufactured by Toray),
The dielectric layer was coated by drying at 100 ° C. for about 30 minutes. The surface of this roller was cut to expose the cored bar portion as a conductor portion 42 on the surface, and the resin portion filled and left in the knurled groove was used as the dielectric portion 41. At this time, the total area of the conductor portion 42 is set to 50% of the whole (therefore, the total area of the dielectric portion 41 is set to 50% of the whole). (2) Toner supply roller 5 ・ Consists of a sponge roller having a diameter of 14 mm having a sponge layer 52 having a resistivity of about 1 × 10 ⁶ Ωcm on the cored bar roller 51,
This was placed in pressure contact with the developing roller 4 so as to bite into it at a biting amount of 1 mm. As the conductive sponge layer 52, foamed polyurethane in which carbon is kneaded is used. The average pore diameter of the surface of this sponge roller is 0.2.
Was 0.3 mm. (3) Layer-thickness leveling plate 8 ・ An elastic plate having a thickness of 2 mm is attached to the developing roller 4 by 10 to 10.
It was placed in contact with a contact pressure of 20 g / cm. -Urethane rubber was used for this elastic plate. (4) Development bias 21, development gap-The development roller 4 has, for example, a peak-to-peak voltage of 1000 Vp-p, 1000H in which DC of -500V is superimposed.
An AC bias of Z was applied (instead of this, -800V
DC bias may be applied).・ Development gap was set to 150 μm. (5) Photoreceptor 1-OPC-Negative latent images were uniformly charged so that the background part was -850V and the writing part (image part) was -100V. (6) Toner 7: A negatively charged toner using a non-magnetic styrene acrylic resin and a polyester resin was used.・ 0.5 wt% of SiO ₂ fine powder was added as an external additive.

In the above structure, the toner supply roller 5
The toner 7 contained in the hopper is supplied to the surface by the agitator 6. The toner 7 supplied to the toner supply roller 5 is carried on the surface of the sponge layer 52 or in the holes, and is directed toward the contact portion B between the toner supply roller 5 and the developing roller 4 by the clockwise rotation of the toner supply roller 5. Be transported.

The friction between the developing roller 4, the toner 7 and the toner supplying roller 5 causes the dielectric portion 4 of the developing roller 4 to move.
1 is given a charge having a polarity opposite to the desired toner charging polarity (charge having the same polarity as the photoconductor charge in normal development and charge having the opposite polarity to the photoconductor charge in reversal development).
In the above-described specific example of this embodiment, since the reversal development is performed using the toner 7 that is negatively charged, the dielectric portion 41 is positively charged. Then, as indicated by electric lines of force E in FIG. 3B, a microfield (a minute closed electric field) is formed on the developing roller 4.

On the other hand, since the surface of the toner supply roller 5 moves in the same direction as the surface of the developing roller 4, the toner 7 carried on the toner supply roller 5 slides between the developing roller 4 and the toner supply roller 5. Then, most of them are charged to a desired polarity (in the normal development, the polarity is opposite to the photoconductor charge, and in the reversal development, it is the same polarity as the photoconductor charge). In the above specific example of this embodiment, the toner 7 is negatively charged.

Then, the charged toner 7 on the toner supply roller 5 is electrostatically attracted by the electric field E of the microfield on the developing roller 4, and adheres to the surface of the developing roller 4 in multiple layers. As a result, the developing roller 4 exits the contact portion B in a state where the sufficiently charged toner 7 is carried in multiple layers. In this embodiment, the surface of the toner supply roller 5 is moved in the same direction as the surface of the developing roller 4, so that the toner 7 on the toner supply roller 5 is separated from the developing roller 4 and the toner supply roller 5. The toner supply roller 5 rotates and the toner is almost charged.
The uncharged or weakly charged toner 7 from the hopper is not supplied onto the developing roller 4 that has passed the contact portion B.

The toner layer on the developing roller 4 that has passed through the contact portion B is rubbed to a uniform thickness by the layer-thickness leveling plate 8 that is in light contact with the developing roller 4 to form a uniform thin layer. ,
When the developing roller 4 rotates, it is conveyed to the developing area A. At this time, the toner adhesion amount on the developing roller 4 is 1.5 to 2.0.
A toner layer having mg / cm ² and an average charge amount of 8 to 15 μC / g is formed. Then, in the developing area A, the development is performed while the surface of the developing roller 4 to which the optimum developing bias is applied by the contact or non-contact developing method and the surface of the photosensitive drum 1 move at a substantially constant speed.

The toner remaining on the surface of the developing roller 4 without adhering to the surface of the photosensitive drum 1 when passing through the developing area A is mechanically and electrically scraped off by the toner supply roller 5. Further, the electric charge on the developing roller 4 is also made constant by the frictional charging by the toner supply roller 5, whereby the surface of the developing roller 4 is initialized.

In the structure of the conventional developing device, the threshold electric field at the time of development depends on the inter-toner adhesive force in each layer of the multi-layered toner layers, and the threshold electric field is, for example, the first layer. The toner, the toner of the second layer, and the toner of the third layer are different from each other, which makes it difficult to control the gradation of the image.

In view of this, in this embodiment, the peripheral speed of the photosensitive drum 1 is one of the developing conditions depending on the type of original such as an original requiring gradation and an original requiring high resolution. The peripheral speed of the developing roller 4 is switched. The configuration of the characteristic portion of this embodiment will be described below. In the present embodiment, as shown in the control block diagram of FIG. 1, the rotation driving device 4 as a driving unit that rotationally drives the developing roller 4.
3, a rotation control device 4 as drive control means for the developing roller 4.
4, a developing roller bias power source 21, a bias control device 211 as a developing bias voltage control unit, and a mode switching unit 9 are provided. The rotation control device 44 is
The peripheral speed of the developing roller 4 with respect to the peripheral speed of the photosensitive drum 1 is controlled via the rotation driving device 43. In addition, in FIG.
A block diagram of a control configured so as to be commonly used in a second embodiment and a third embodiment described later is shown.

As the mode switching means 9, a mode input device 91 for inputting a developing mode constituted by a push button or the like which can be operated by the user, a main control portion 92 constituted by a CPU, a memory and the like, and I / O part 93
Is provided. Further, the mode input device 91 is
The user sets the first development mode for a document of an image that requires gradation, such as a photographic image,
The second developing mode can be set for a document of an image that requires high resolution such as an image including many thin lines such as a table.

In the above-described structure, in the case of a document requiring gradation such as a photographic image, the user operates the mode input device 91 to select the first developing mode. The signal of the setting data corresponding to the first developing mode is input to the main control unit 92 via the I / O unit 93.
Then, a control signal corresponding to the first development mode is sent from the main control unit 92 to the rotation control device 44 via the I / O unit 93, and the peripheral speed of the developing roller 4 at the time of development is the peripheral speed of the photosensitive drum 1. The drive condition of the rotation drive device 43 is set so as to be substantially the same as the speed. Then, at the time of image formation, the developing roller 4 is rotationally driven by the rotation driving device 43 at the above peripheral speed to perform development.

On the other hand, in the case of a document requiring a high resolution such as an image including many thin lines such as characters and tables, the user operates the mode input device 91 to select the second developing mode. The signal of the setting data corresponding to the second developing mode is input to the main control unit 92 via the I / O unit 93. Then, from the main control unit 92 via the I / O unit 93,
A control signal corresponding to the second developing mode is sent to the rotation control device 44 so that the peripheral speed of the developing roller 4 during development becomes higher than the peripheral speed of the photosensitive drum 1, for example, the peripheral speed of the developing roller 4 is exposed. The drive condition of the rotary drive device 43 is set so as to be 1.2 to 1.4 times the peripheral speed of the body drum 1. Then, at the time of image formation, the developing roller 4 is rotationally driven by the rotation driving device 43 at the above peripheral speed to perform development.

As described above, according to the first embodiment, at the time of development in the case of a document requiring gradation such as a photographic image,
Since the peripheral speed of the developing roller 4 is set to be substantially the same as the peripheral speed of the photosensitive drum 1, the above "from the trailing edge toner" does not occur and a solid image with a uniform image density can be obtained. . On the other hand, the peripheral speed of the developing roller 4 is set to be higher than the peripheral speed of the photosensitive drum 1 at the time of development of a document in which high resolution is required such as an image including many thin lines such as characters and tables. Therefore, the above "from the trailing edge toner" occurs,
Thin lines such as characters and tables become thicker, and clear images can be obtained.

Next, the second embodiment will be described. Second
In the embodiment, the type of developing bias voltage applied to the current roller 4, which is one of the developing conditions, is switched according to the type of original such as an original requiring gradation and an original requiring high resolution. There is. In the developing device according to the second embodiment,
Except for the developing bias voltage applied to the developing roller 4, the configuration is the same as that of the first embodiment shown in FIG. 2, and therefore description thereof will be omitted. The configuration of the characteristic portion of the second embodiment will be described below based on the control block diagram of FIG.

In the second embodiment, the developing roller bias power source 21 is configured to be able to freely apply a DC voltage, an AC voltage on which a DC voltage is superimposed, a pulse voltage or the like to the developing roller 4. Further, a bias control device 211 is provided as a developing bias voltage control means for controlling the types of bias voltage such as DC voltage and AC voltage applied to the developing roller 4. In the second embodiment, the user operates the mode input device 91 to select the first development mode in the case of a document that requires gradation such as a photographic image. The signal of the setting data corresponding to the first developing mode is sent to the main control unit 9 via the I / O unit 93.
Entered in 2. Then, the main control unit 92 to the I / O unit 9
3, a control signal corresponding to the first developing mode is sent to the bias control device 211, and the developing bias voltage at the time of development is set to the electrostatic latent image on the photosensitive drum 1 as shown in FIG. A voltage 21a which is a voltage that periodically changes centered on a potential approximately midway between the image portion and the non-image portion of the image, specifically 1200Vp-p, and a DC voltage of -500V superimposed on an AC voltage of 750Hz. The bias application condition of the bias power supply 21 is set so that Then, at the time of image formation, the bias voltage 21a is applied to the developing roller 4 by the bias power source 21 to develop the image.

On the other hand, in the case of a document requiring a high resolution such as an image including many thin lines such as characters and tables, the user operates the mode input device 91 to select the second developing mode. The signal of the setting data corresponding to the second developing mode is input to the main control unit 92 via the I / O unit 93. Then, from the main control unit 92 via the I / O unit 93,
A control signal corresponding to the second developing mode is sent to the bias controller 211, and the developing bias voltage at the time of developing is as shown in FIG.
As shown in (b), the bias application condition of the bias power supply 21 is set so that the DC voltage 21b is -800V. When the image is formed, the bias power source 21
As a result, the bias voltage 21b is applied to the developing roller 4 and development is performed.

In the second embodiment, in order to prevent the phenomenon that the trailing edge of the toner is shifted, the developing roller 4 is rotated as follows.
The surface moving direction in the developing area is the same as that of the photosensitive drum 1, and the peripheral speed thereof is substantially equal to the peripheral speed of the photosensitive drum 1, that is, about 120 mm / sec in this example. There is. However, in the contact development, if the development is completely constant speed, there is no difference in speed between the surface of the photosensitive drum 1 and the surface of the developing roller 4, so that the physical development is performed regardless of the potential of the surface of the photosensitive drum 1. Toner may adhere.
In order to prevent this, the peripheral speed of the developing roller 4 is set to be slightly higher. For example, the peripheral speed ratio (1 peripheral speed of the photosensitive drum: 4 peripheral speed of the developing roller) is 1: 1.05 to 1.1.
Is preferred. With such a peripheral speed ratio, the above-mentioned trailing edge toner deviation is not noticeable.

As described above, according to the second embodiment, at the time of development in the case of a document requiring gradation such as a photographic image,
The developing roller 4 is applied with the above-mentioned bias voltage 21a which periodically changes around a potential substantially in the middle between the image portion and the non-image portion of the electrostatic latent image on the photosensitive drum 1. The electric field generated between the developing roller 4 and the developing roller 4 allows the toner 7 to reciprocate between the developing roller 4 and the photosensitive drum 1, so that the developing process is performed, so that a smooth halftone image is obtained. be able to. On the other hand, the DC voltage 21b is applied to the developing roller 4 at the time of development in the case of a document requiring high resolution such as an image including many thin lines such as characters and tables.
Is applied, it becomes difficult for the toner 7 to adhere to the non-image portion of the electrostatic latent image on the photosensitive drum 1, there is no "bleeding" at the edge of the thin line such as characters and tables, and the contrast is large and clear. And a sharp image can be obtained.

Next, a third embodiment will be described. Third
In the embodiment, as in the second embodiment, it is applied to the current roller 4, which is one of the developing conditions, according to the type of the original such as the original requiring gradation and the original requiring high resolution. The type of development bias voltage is switched. The developing device according to the third embodiment has the same configuration as that of the first embodiment shown in FIG. 2 except for the developing bias voltage applied to the developing roller 4, and the description thereof will be omitted. The configuration of the characteristic portion of the third embodiment will be described below based on the control block diagram of FIG.

In the third embodiment, the developing roller bias power source 21 is constructed so as to be able to freely apply the AC voltage, the pulse voltage, etc., on which the DC voltage is superimposed, to the developing roller 4. Further, a bias control device 211 is provided as a developing bias voltage control means for controlling the types of bias voltage such as DC voltage and AC voltage applied to the developing roller 4. The bias control device 211 controls the type of the bias voltage applied to the developing roller 4, and the application time A of the voltage for generating an electric field for moving the toner 7 to the developing roller 4 side in one cycle of the bias voltage. , The ratio of the voltage for applying the voltage for generating the electric field that causes the toner 7 to move to the photosensitive drum 1 side to the application time B can be controlled.

In the third embodiment, the user operates the mode input device 91 to select the first developing mode in the case of an original requiring gradation such as a photographic image. It The signal of the setting data corresponding to the first developing mode is input to the main control unit 92 via the I / O unit 93. Then, from the main control unit 92 via the I / O unit 93,
A control signal corresponding to the first developing mode is sent to the bias controller 211, and the developing bias voltage at the time of developing is as shown in FIG.
As shown in (a), a voltage that cyclically changes centering on a potential approximately midway between the image portion and the non-image portion of the electrostatic latent image on the photosensitive drum 1, specifically, the high potential portion −1000V. , A low potential part 0V, a frequency of 1200 Hz, and a bias voltage of the bias power source 21 is applied so that the application time A of the low potential part is substantially the same as the application time B of the high potential part. Conditions are set. Then, at the time of image formation, the bias voltage is applied to the developing roller 4 by the bias power source 21 to develop the image.

On the other hand, in the case of a document requiring a high resolution such as an image containing many thin lines such as characters and tables, the user operates the mode input device 91 to select the second developing mode. The signal of the setting data corresponding to the second developing mode is input to the main control unit 92 via the I / O unit 93. Then, from the main control unit 92 via the I / O unit 93,
A control signal corresponding to the first developing mode is sent to the bias controller 211, and the developing bias voltage at the time of developing is as shown in FIG.
As shown in (b), a voltage that cyclically changes around a potential substantially midway between the image portion and the non-image portion of the electrostatic latent image on the photosensitive drum 1, specifically, the high potential portion −1000V. , The low potential part is 0 V, the frequency is 1200 Hz, and the application time A of the low potential part is longer than the application time B of the high potential part, for example, the time ratio of the application time A and the application time B is 2: 3-1. : Bias power supply 2 so that a pulsed voltage 21d of about 10 is obtained.
The bias application condition of 1 is set. Then, at the time of image formation, the bias voltage is applied to the developing roller 4 by the bias power source 21 to develop the image.

The developing roller 4 in the third embodiment is driven under the same conditions as in the second embodiment.

As described above, according to the third embodiment, at the time of development in the case of a document requiring gradation such as a photographic image,
The bias voltage 21 is applied to the developing roller 4 so that the application time A of the high potential portion is substantially the same as the application time B of the low potential portion.
Since c is applied, the toner 7 is reciprocally moved between the developing roller 4 and the photosensitive drum 1 by the electric field generated between the photosensitive drum 1 and the developing roller 4, and the developing process is performed. Is performed, a smooth halftone image can be obtained. On the other hand, at the time of development of a document requiring a high resolution such as an image including many thin lines such as characters and tables, the application time A of the high potential portion is higher than the application time B of the low potential portion on the developing roller 4. Long bias voltage 21d
Is applied, the time to accelerate development is shortened,
The toner 7 is removed from the non-image area for a long time, and a clear and sharp image having a large contrast in thin lines such as characters and tables can be obtained.

In this embodiment, the mode switching means 9 is constructed so that the user can judge the type of the original and input the corresponding development mode.
A document reading device such as a scanner for discriminating the type of the document is provided therein, and the optimum developing mode for the image of the document is automatically set based on the output value of the document reading device without user's operation. It may be configured as follows.

In this embodiment, the reversal development method is used, but the normal development method can also be applied. In the case of this regular development method, the material of the dielectric portion 41 of the developing roller 4 is Teflon resin, polyethylene resin, the toner supply roller 5, and the material of the layer thickness leveling plate 8 is polyurethane resin, polycarbonate resin, or toner 7. Polystyrene resin, acrylic resin or the like can be used as the material. Then, as an appropriate developing bias 21, for example, -20
0V is used.

[0051]

According to the image forming apparatus of the present invention, the surface of the developer carrier is the surface of the image carrier at the time of development in the case of a document requiring gradation such as a photographic image. Since it is set to move at substantially the same speed as the surface moving speed, the above "from the trailing edge toner" does not occur, and a solid image with uniform image density can be obtained. On the other hand, at the time of development of a document requiring high resolution such as an image containing many thin lines such as characters and tables, the surface of the developer carrier should move faster than the moving speed of the surface of the image carrier. Since it is set, the above-mentioned "from the trailing edge toner" occurs, the thin lines such as characters and tables become thick, and a clear image can be obtained.
As described above, there is an effect that the optimum image quality can be obtained according to the type of document.

According to the image forming apparatus of the second aspect, at the time of development in the case of a document requiring gradation such as a photographic image, a bias voltage which periodically changes is applied to the developer carrying member. Since the developer is applied while being subjected to a force such that the developer reciprocates between the developer carrying member and the image carrying member, a smooth halftone image can be obtained. . On the other hand, since a DC bias voltage is applied to the developer carrying member during development in the case of a document requiring high resolution such as an image containing many thin lines such as characters and tables, a latent image of the image carrying member is formed. It becomes difficult for the developer to adhere to non-image areas, and "bleeding" occurs at the edges of thin lines such as characters and tables.
It is possible to obtain a clear and sharp image with no contrast and large contrast. As described above, there is an effect that the optimum image quality can be obtained according to the type of document.

According to the image forming apparatus of the third aspect, the developer moves to the developer carrying member side at the time of development in the case of a document requiring gradation such as a photographic image. The application time A of the voltage for generating the electric field is set to be substantially equal to the application time B of the voltage for generating the electric field so that the developer moves to the image carrier side. Since development is performed while receiving a reciprocating force between the agent carrier and the image carrier, a smooth halftone image can be obtained. On the other hand, at the time of developing a document requiring high resolution such as an image including many thin lines such as characters and tables, the application time A is set to be longer than the application time B, so that the development is accelerated. The developing time is shortened, the time for removing the developer from the non-image area is lengthened, and a clear and sharp image having a large contrast in thin lines such as characters and tables can be obtained.
As described above, there is an effect that the optimum image quality can be obtained according to the type of document.

[Brief description of drawings]

FIG. 1 is a block diagram showing control of a developing roller of a developing device used in a copying machine according to an embodiment.

FIG. 2 is a front view showing a schematic configuration of a developing device used in the copying machine according to the embodiment.

3A is a plan view showing a part of the surface of the developing roller 4 of the developing device, and FIG. 3B is a sectional view of the surface portion.

FIG. 4A is a timing chart of the developing bias voltage when the first developing mode is set in the second embodiment,
FIG. 6B is a timing chart of the developing bias voltage when the second developing mode is set in the same embodiment.

FIG. 5A is a timing chart of the developing bias voltage when the first developing mode is set in the third embodiment,
FIG. 6B is a timing chart of the developing bias voltage when the second developing mode is set in the same embodiment.

[Explanation of symbols]

 2 developing device 4 developing roller 7 toner 9 mode switching means 21 developing roller bias power source 41 dielectric part 42 conductor part 43 rotation drive device 44 rotation control device 91 mode input device 92 main control part 93 I / O part 211 bias control device

Front Page Continuation (72) Inventor Yuichi Ueno 1-3-6 Nakamagome, Ota-ku, Tokyo In Ricoh Company (72) Inventor Akira Sawada 1-3-3 Nakamagome, Ota-ku, Tokyo In Ricoh Company

Claims (3)

[Claims] 1. A large number of minute closed electric fields are formed on the developer carrying body by selectively retaining electric charges on the surface of the developer carrying body, and the minute closed electric fields are formed on the developer carrying body. In the image forming apparatus, in which the developer is carried in multiple layers, and the latent image on the image carrier is visualized by using the developer conveyed by the developer carrier, the development is performed so that the surface moves. Drive means for driving the agent carrier, drive control means connected to the drive means for controlling the moving speed of the surface of the developer carrier relative to the surface of the image carrier, and connected to the drive control means, A first surface of the developer carrying member moves at substantially the same speed as the moving speed of the surface of the image carrying member.
An image forming apparatus comprising: a mode switching unit that switches between a developing mode and a second developing mode in which the surface of the developer carrier moves faster than the moving speed of the surface of the image carrier. 2. A large number of minute closed electric fields are formed on the developer carrying body by selectively retaining electric charges on the surface of the developer carrying body, and the minute closed electric fields are formed on the developer carrying body. In an image forming apparatus in which a multi-layered developer is carried on and the latent image on the image carrier is visualized by using the developer conveyed by the developer carrier, a DC bias is applied to the developer carrier. A bias voltage applying unit that applies a voltage or a bias voltage that changes periodically, and a first development mode that is connected to the bias voltage applying unit and that applies a bias voltage that changes periodically to the developer carrier, An image forming apparatus comprising: a mode switching unit that switches between a second developing mode in which a DC bias voltage is applied to the developer carrier. 3. A large number of minute closed electric fields are formed on the developer carrying body by selectively retaining electric charges on the surface of the developer carrying body, and the minute closed electric fields are formed on the developer carrying body. In an image forming apparatus in which a developer is carried in a multi-layered manner and a latent image on the image carrier is visualized by using the developer carried by the developer carrier, Bias voltage applying means for applying a bias voltage that changes to a voltage, and a voltage that is connected to the bias voltage applying means and that generates an electric field in one cycle of the bias voltage so that the developer moves to the developer carrying member side. A bias voltage control means for controlling the ratio of the application time A of the developer to the application time B of the voltage for generating an electric field that causes the developer to move to the image carrier side; and a bias voltage control means connected to the bias voltage control means. The application time A is approximately equal to the application time B Mode switching means for switching between a first developing mode in which a large bias voltage is applied to the developer carrier and a second developing mode in which a bias voltage whose application time A is longer than the application time B is applied to the developer carrier. An image forming apparatus comprising: