JP2000267430A - Image forming method and apparatus - Google Patents

Abstract

(57) [Problem] To provide an image forming method and an image forming apparatus for always forming an image having a constant quality regardless of the type of the image. SOLUTION: A developing unit is configured to carry a developer including a toner and a magnetic carrier to a developing area opposed to an image carrier, and to be held at a predetermined interval from the developer carrier. A developer regulating member that regulates the amount of the developer carried by the developer carrying member to the developing area; and a portion near the developer carrying member downstream of the developer regulating member with respect to the moving direction of the developer carrying member. And an electrode member 37,
An electric field control unit that controls an electric field formed between the electrode member 37 and the developer carrier 31, and the electric field control unit forms an image of the electric field formed between the electrode member 37 and the developer carrier 31. An image forming method for controlling according to information and an image forming apparatus to which the method is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus for forming an image by developing an electrostatic latent image using a developer comprising a toner and a magnetic carrier.

[0002]

2. Description of the Related Art As an image forming apparatus, there are a digital copying machine, a printer, a facsimile and the like, and many products have already been put to practical use. The principle of image formation is to uniformly charge the surface of a photoconductive image carrier (photoreceptor), perform image exposure using a light beam controlled based on image data, and form an electrostatic latent image. It is developed with toner, and the toner image is transferred and fixed to a transfer material to obtain a recorded matter. The image carrier after the transfer of the toner image is cleaned by a cleaning device, and if necessary, is subjected to charge elimination and used in the next image forming step. With respect to these products, requirements from the standpoint of customers include high reliability including durability, low cost, good operability, and the like, and an even stronger requirement is a high level of image quality. As one of the components that influences the level of achievement of this requirement, the development system greatly affects.

[0003] Among electrophotographic and other developing methods in an image forming method using a powder toner, a two-component developing method is known as a method particularly excellent in high-speed response and stability over time. In particular, it is known as a mainstream technology in the field of products such as copiers and laser printers. In the two-component developing system, the developer is held and transported on the surface of a non-magnetic sleeve in which a magnet is provided inside the developer carrier, and the developer is made into a brush shape (hereinafter, referred to as a “magnetic brush”). The toner is selectively adhered to the latent image surface by the electric field between the image carrier on which the electrostatic latent image is formed and the sleeve to which the electric bias is applied, in contact with or close to the image carrier, thereby developing the image. Is performed. The two-component developer used here comprises a toner and a carrier. The carrier is a magnetic material, and is held and conveyed to the sleeve by a magnet inside the sleeve. The toner has a charge when it comes into contact with the carrier, adsorbs on the carrier, moves with the carrier, and is transferred to the image carrier according to the electrostatic latent image, and the toner corresponding to the consumption amount is normally newly supplied. You. The carrier stays in the developing device, mixes with the supplied toner, and contributes to the conveyance and charging of the toner.

[0004] As the type of carrier, a carrier coated with a resin using a magnetic material such as iron powder, ferrite or magnetite as a core material, or a carrier in which magnetite fine powder or the like is dispersed in a resin (binder) is generally used. The resistance of the carrier is controlled to an appropriate value by the coating agent and the binder, and the durability of the carrier is improved. In the two-component developing method, a periodically changing bias (hereinafter, referred to as an AC bias) is applied to a developer carrying member that conveys a developer, so that the developer carrying member and the image carrying member on which a latent image is formed are formed. Many developing methods have been proposed and put into practical use, in which a periodic electric field is formed between the substrate and a developing ability and an image quality are improved. Here, it is generally known that when the peak-to-peak voltage of the AC bias is increased, the developing ability and the image quality are greatly improved. However, when an AC bias is applied, a phenomenon in which toner adheres to a non-image portion (background portion) (referred to as “fog” or “background stain”) tends to occur. This is due to the toner having a low charge amount (hereinafter, referred to as “weakly charged toner”).
For example, a charge amount measuring device (for example, product name “E-spa
rt analyzer ". 8), the charge amount distribution of the toner is measured. As compared with a developer having little toner whose charge amount is distributed around 0 as shown in FIG. 8A, the toner distributed around 0 as shown in FIG. A relatively large amount of developer resulted in a large amount of fog.

[0005] This can be interpreted as follows. Since the weakly charged toner has a small electrostatic adhesion to the carrier, it easily floats in the developer, and the binding received from the electrostatic latent image and the developing bias is small. Will be higher. In particular, since the AC bias generates a strong electric field momentarily, floating toner is likely to be generated. On the other hand, an electrode is provided in the vicinity of the developer carrier outside the development area of the developer carrier, and a bias is applied to the electrode to improve the developing ability of the developer and prevent toner scattering. Methods are conventionally known. For example, Japanese Patent Application Laid-Open No. 6-27820 proposes that a developer conveying guide member having a shape along the outer peripheral surface of a developer sleeve (developer carrier) is provided, and a developer conveying guide member having the same polarity as a developing bias is provided on the developer conveying guide member. This is an electrostatic latent image developing device that can improve the developing efficiency by applying a voltage. In addition, Japanese Unexamined Patent Publication
Japanese Patent Application Laid-Open No. -102767 proposes that an electrode for biasing the toner of the developer toward the developer carrier is provided at a position upstream of the regulating member for regulating the developer in the moving direction of the developer carrier. Accordingly, the developing device has the effect of increasing the toner concentration of the formed developer layer, obtaining a high-quality image, and preventing toner scattering. Japanese Patent Application Laid-Open No. 8-44177 proposes a developing device in which an auxiliary electrode is provided in a developer circulation path in the developing device and an AC bias is applied thereto. Due to the action of the oscillating electric field, the toner and the carrier of the developer are once separated from each other, and the newly replenished toner is uniformly mixed and controlled to a predetermined charge amount in a short time, so that fog and image density decrease. Can be prevented. Also, JP-A-8-17
Japanese Patent Application Laid-Open No. 1282 proposes a developing device in which an electrode to which a DC voltage having the same polarity as the charged polarity of the developer is applied is provided downstream of the developing area to prevent toner scattering.
Japanese Patent Application Laid-Open No. 8-202139 proposes that an auxiliary electrode is provided in a developer transport path, and when a toner concentration is below a lower limit of an allowable value, a toner replenishment mode is set to a toner supply mode. Is a developing device that stops AC and applies an AC bias to the auxiliary electrode. The newly supplied toner is uniformly mixed with the existing developer by the action of the oscillating electric field, and has an effect of preventing fogging. Also, Japanese Patent Application Laid-Open No. 8-240
No. 972 proposes a developing device in which a toner scattering suppression electrode is disposed so as to face a developing sleeve (developer carrier), and the toner is pressed against the developing sleeve side by the action of an electric field to reduce toner scattering. Has the effect of suppressing.

[0006]

However, the above proposal has the following problems. Depending on the image to be formed, an image including many photographs and graphs has a large toner adhesion area, and conversely, has a small toner adhesion area almost at the center of a line drawing. When the toner adhesion area on the image is large, a lot of toner is used in the development area.
Accordingly, it is necessary to supply the toner to the developer layer on the developing sleeve. For this reason, there is a problem that a large amount of toner must be charged to a predetermined charge amount in a short time. On the other hand, when the toner adhesion area on the image is small, the toner consumption in the developing area is small, and therefore, there is a problem that the charge amount of the toner must be suppressed so as not to be too large. These problems need to be dealt with by any device. In particular, if the toner charge amount is too high, the developing ability is reduced, and the required image density may not be obtained. This is problematic when forming images having similar properties. On the other hand, there is an image forming apparatus that switches the recording density and forms an image with high resolution when necessary. In such an apparatus, when forming an image having a high resolution, it is desirable to increase the charge amount of the toner in order to improve the reproducibility of the electrostatic latent image. Conversely, when forming an image having a low resolution, It is necessary to suppress the charge amount of the toner and secure the developing ability.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to provide an image forming method and an image forming apparatus which always form an image having a constant quality regardless of the type of the image. To provide. It is still another object of the present invention to provide an image forming method and an image forming apparatus capable of maintaining a developing ability according to a recording density even when the recording density of an image changes.

[0008]

According to a first aspect of the present invention, an electrostatic latent image is formed on an image carrier by performing image exposure based on image information. Latent image forming means for forming, means for developing an electrostatic latent image to form a toner image on an image carrier, transfer means for transferring a toner image on the image carrier to a transfer material, and toner on the transfer material An image forming method using an image forming apparatus having a transfer unit for fixing an image to a transfer material, wherein the developing unit includes: a developer carrying member that transports a developer including a toner and a magnetic carrier to a developing area facing the image carrying body; A developer regulating member that is held at a fixed interval from the developer carrier and regulates the amount of developer that the developer carrier conveys to the developing area; and a developer regulating member that moves in a direction in which the developer carrier moves. An electrode member is further provided near the developer carrier on the further downstream side, and An electric field control unit that controls an electric field formed between the electrode member and the developer carrier, wherein the electric field control unit converts an electric field formed between the electrode member and the developer carrier into image information. This is an image forming method that is controlled in accordance with this. According to a second aspect of the present invention, in the image forming method according to the first aspect, the electric field control unit controls an electric field formed by the electrode member according to the number of colored images included in the image information. The invention according to claim 3 is
3. The image forming method according to claim 1, wherein an average density of the document is detected from image information of the document read by the image reading device, and an electric field formed by the electrode member is controlled according to the average density value. It is a forming method. Claim 4
The latent image forming means for performing image exposure based on the image information to form an electrostatic latent image on the image carrier,
Means for developing the electrostatic latent image to form a toner image on the image carrier, transfer means for transferring the toner image on the image carrier to a transfer material, and transfer for fixing the toner image on the transfer material to the transfer material And an image forming apparatus comprising:
A developer carrier that transports a developer composed of a toner and a magnetic carrier to a development area facing the image carrier; and a developer that is held at a fixed distance from the developer carrier and transports the developer carrier to the development area. A developer regulating member that regulates the amount of toner, and an electrode member in the vicinity of the developer carrier downstream of the developer regulating member with respect to the direction of movement of the developer carrier, and the electrode member and the developer carrier. And an electric field control unit that controls an electric field formed between the image forming apparatus and the image forming apparatus according to image information. According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the fourth aspect, wherein the electric field control unit controls an electric field formed by the electrode member according to the number of colored images included in the image information. According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect, the image forming apparatus further comprises an image reading device for reading the optical information of the document, and an average of the document detected by the image reading device. An image forming apparatus includes an electrolysis control unit that controls an electric field formed by an electrode member according to a density value. The invention according to claim 7 is
Latent image forming means for performing image exposure based on image information to form an electrostatic latent image on the image carrier, means for developing the electrostatic latent image to form a toner image on the image carrier, and image carrier In an image forming method using an image forming apparatus having a transfer unit that transfers a toner image on a body to a transfer material and a transfer unit that fixes the toner image on the transfer material to the transfer material, the developing unit faces the image carrier. A developer carrier that transports a developer composed of a toner and a magnetic carrier to a developing area to be developed; and a developer carrier that is held at a fixed interval from the developer carrier and regulates an amount of the developer that is transported to the developing area. A developer regulating member, an electrode member near the developer carrier downstream of the developer regulating member with respect to the direction of movement of the developer carrier, and an electric field formed between the electrode member and the developer carrier. An electric field control unit for controlling the electric field control, The image forming apparatus controls an electric field formed between the electrode member and the developer carrier according to image information, and the latent image forming means forms an electrostatic latent image on the image carrier according to the image information. It is a forming method. Claim 8
The invention described in (1) is the image forming method according to (1) or (7), wherein the electric field formed between the electrode member and the developer carrier includes a vibration component. According to a ninth aspect of the present invention, there is provided a latent image forming means for performing image exposure on a pixel basis based on image information to form an electrostatic latent image on an image carrier, and developing the electrostatic latent image to carry an image. An image forming apparatus comprising: a unit configured to form a toner image on a body; a transfer unit configured to transfer the toner image on the image carrier to a transfer material; and a transfer unit configured to fix the toner image on the transfer material to the transfer material. The latent image forming means can perform image exposure by switching the number of pixels per unit area, and the developing means transports a developer comprising a toner and a magnetic carrier to a developing area facing the photoconductor 20. Carrier, a developer regulating member that is held at a fixed interval from the developer carrier, and regulates the amount of developer that the developer carrier conveys to the development area;
An electrode member is provided near the developer carrier downstream of the developer regulating member with respect to the direction of movement of the developer carrier, and an electric field formed between the electrode member and the developer carrier is converted into image information. This is an image forming apparatus including an electric field control unit that performs control in accordance with the control. According to a tenth aspect of the present invention, in the image forming apparatus according to the fourth or ninth aspect, the electric field formed between the electrode member and the developer carrier includes a vibration component. .

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing a basic configuration of an image forming apparatus according to an embodiment of the present invention. The image forming method according to claim 1 will be described with reference to FIG. FIG. 2 is a system block diagram of an image forming method for forming an image using external image data such as a computer. The photoconductor 20 corresponds to an image forming body, and is a photoconductor 20 formed by applying or vapor-depositing a photoconductor on a substrate made of a conductor. Specifically, an OPC organic photoconductor is formed on an aluminum substrate. The photosensitive member 20 is formed by applying a body, and rotates at a constant rotation speed during image formation. The charging roller 21 is a charging unit for charging the photoconductor 20 to a uniform potential, and the writing device 1 performs image exposure on the charged photoconductor 20 using a laser beam to form the photoconductor 2.
The developing device 30 contains a two-component developer, and forms the electrostatic latent image on the photosensitive member 2 on which the electrostatic latent image is formed.
0 is a means for developing the toner. Then, as shown in FIG. 2, image data is input to the writing device 1 from an external device 3 such as a computer.

The operation of forming a latent image by this image forming method will be described in detail. First, image information is input from a computer or the like via an interface. The image data converted to the bitmap image is transferred to the LD drive unit 11 and causes the laser light to blink on a pixel basis. The laser beam is applied to the photoreceptor 20 of the image forming apparatus to form an electrostatic latent image. Here, the number of pixels (hereinafter, referred to as “color pixels”) to which toner is to be attached after image data is formed in pixel units in the interface unit 10 (hereinafter, referred to as “color pixels”) is referred to as an image identification unit. Count at 15. The image identification unit 15 compares the number of colored pixels with a predetermined value, and sends the result to the electric field control unit. Note that the image identification unit 15 may provide two or more thresholds and perform three or more classifications instead of the two-stage determination. Further, the image identification section 15 does not necessarily need to identify from the information of the entire image, but may identify from information of a part of the image. In accordance with the output image data input to the writing device 1 and the transport timing of the photoconductor 20 and the rotation timing of the polygon mirror 12, the signal generator 10 of the writing device 1
A semiconductor laser drive signal is output to the LD drive unit 11 from the input output image data, and the LD drive unit 11 serving as a writing light source generates a laser beam according to the input semiconductor laser drive signal. The laser beam generated by the LD driving unit 11 is rotationally scanned by a rotating polygon mirror 12, its optical path is bent by a mirror 14 via an fθ lens 13, and is charged to a uniform potential in advance by a charging roller 2121. Raster scanning is performed by main scanning that is performed by projecting on the peripheral surface of the body 20 and sub-scanning that is performed by rotation of the photoconductor 20, and an electrostatic latent image is formed on the photoconductor 20.

The electrostatic latent image formed on the photoreceptor 20 is reversibly developed by a developing device 30 containing a two-component developer and a latent image on the photoreceptor 20 is developed by a developing sleeve 31 which is a developer conveying member. The toner T is developed by the method. The developing sleeve 31 keeps a predetermined gap from the photoconductor 20.
The base of the photoconductor 20 is grounded, and the developing sleeve 31
Is applied with a bias voltage of DC voltage,
Toner development is performed by a contact development method using a two-component developer to form a toner image on the photoconductor 20. The transfer / separation device 22 transfers the toner image formed on the photoconductor 20 in the transfer area to a recording paper, separates the recording paper on which the toner image has been transferred from the photoconductor 20, and transfers the toner image. The recording paper thus separated is separated from the photoconductor 20. The recording paper is fed one by one from a paper feed cassette 25 and supplied by a pair of transport rollers 24. The recording paper separated by the separation device 23 is sent to the fixing device 50, where the toner T on the transfer paper is melted and fixed by the heat generating roller 51 and the pressure roller 52, and the discharge tray 57 outside the device is discharged by the discharge roller 57. Is discharged to
Further, the cleaning device 40 collects the toner T remaining on the photoconductor 20 from which the recording paper has been separated by the separation device 23,
The cleaning blade 41 is used to clean the photoconductor 20 so that a new image is formed. The cleaning blade 41 removes the toner T remaining without being transferred from the photoconductor 20. Clean the photoconductor 20,
Further, the toner T removed from the photoconductor 20 is collected.

Here, when the developing device 30 develops the latent image on the photoconductor 20 with the toner T, the charge amount of the toner T is controlled by the electrode member 37 provided in the developing device 30. FIG. 3 is a schematic diagram showing a basic configuration of the developing device 30 used in the image forming method according to one embodiment of the present invention. The developing device 30 includes a developing sleeve 31 (developer carrier), a doctor blade 35, an internal magnet 36, stirring members 32 and 33, and the like. As will be described later, the developing device 30 contains a developer including a magnetic carrier C and a toner T. The developing sleeve 31 is a cylindrical member composed of a non-magnetic conductive member, and rotates in the direction of the arrow (counterclockwise) in the figure. A plurality of fixed magnets are provided inside. A developing bias of −600 V is applied to the developing sleeve 31 from the power supply V1. The developer pool has two stirring members 32 and 33 for moving the developer in opposite directions. Further, in the vicinity of the developing sleeve 31, a developing area of the developer (here, the developing area means "an area where the toner T can move from the developing sleeve 31 to the photoconductor 20 on which the electrostatic latent image is formed"). ) Is provided with a doctor blade 35 for regulating the transport amount. On the developing sleeve 31, the developer is held in a brush shape by a magnetic field formed by a magnet (called “magnetic brush”), and is conveyed counterclockwise as the developing sleeve 31 rotates. At this time, the transport amount of the developer is regulated by the doctor blade 35. Since the doctor blade 35 needs to maintain a uniform distance from the developing sleeve 31, it is desirable that the material be a metal such as stainless steel or aluminum. A magnet is provided in the developing sleeve 31 in the developing area. Developing sleeve 31
By generating a large magnetic flux density component in a direction perpendicular to the surface, carrier adhesion and carrier scattering can be prevented, and development efficiency can be ensured.

As shown in FIG. 3, an electrode member 37 is provided downstream of the doctor blade 35 when viewed from the rotation direction of the developing sleeve 31. A periodically changing voltage is applied to the electrode member 37 to generate a constant or periodically changing electric field (hereinafter, referred to as “alternate electric field”) with the developing sleeve 31. The electrode member 37 faces the developing sleeve 31 with a certain area. The electrode member 37 is made of a conductive material such as a metal. Developing sleeve 3
When an alternating electric field is formed between the electrode 1 and the electrode material, the toner T receives a periodic force. FIG. 4 shows the direction of the alternating electric field in the region between the developing sleeve 31 and the electrode material. The alternating electric field is periodically formed so as to move particles having charges of a specific polarity in opposite directions to each other, excluding a state of zero, that is, a state where no electrostatic force acts. In FIG. 4, reference numeral t1 denotes a time zone in which a force for attracting the toner T to the electrode member 37 is applied, and reference numeral t2 denotes a time zone in which a force for attracting the toner to the developing sleeve 31 is applied. In each time zone, a strong electric force acts on the toner T. Note that t1 / (t1
+ T2) is defined as a duty ratio. That is, the duty ratio is a temporal ratio in which the electric field is directed in a direction to draw the toner T to the electrode member 37.

FIG. 5 is a diagram schematically showing a contact state between the toner T and the carrier C. FIG. 5A shows that the toner T has not passed through a space between the developing sleeve 31 and the electrode member 37. FIG. 5B is a view schematically showing a contact state in which the toner T has just started to contact the carrier C. FIG. 5B shows the toner T after passing through a space between the developing sleeve 31 and the electrode member 37. FIG. 4 is a view schematically showing a contact state between a carrier C and a carrier C; As shown in FIG. 5A, the toner T is initially in contact with the carrier C with a large contact area. Although the charge amount of the entire toner T particles is relatively small, the contact area between the toner T and the carrier C is large because the contact area with the carrier C is large. When a force in a predetermined corresponding direction is received in a time zone of t1 in FIG.
1 from the carrier C which is magnetically bound on it. When a force in a predetermined corresponding direction is received in the time zone of t2 in FIG. 4, the toner T collides again with the surface of the carrier C.
This state is repeated periodically, and the toner T becomes the carrier C
Repeat separation and collision from the surface. Toner T is carrier C
When the collision occurs, as shown in FIG. Electric charges having opposite polarities are generated on the toner T side and the carrier C side of the contact portion. By repeating such collisions, the charge holding portion on the surface of the toner T gradually spreads, and the total charge amount of the toner T particles increases. After the developer has passed through the space between the developing sleeve 31 and the electrode member 37, the toner T and the carrier C are attached as shown in FIG. 5B. Therefore, despite the large charge amount of the toner T, the adhesion between the toner T and the carrier C is small. Thereafter, as the developing sleeve 31 rotates, the developer escapes from the area where the alternating electric field is applied. The developer is further conveyed to the developing area as the developing sleeve 31 rotates. In the developing area, the magnetic brush formed by the internal magnet 36 comes into contact with the photoconductor 20, and the toner T moves by the electric field formed between the voltage of the developing sleeve 31 and the electrostatic latent image on the photoconductor 20. When the toner T is consumed in the developing process, the toner T
Is supplied from a toner bottle (toner supply container). The replenished toner T is mixed with the developer in the developing device 30 by the stirring members 32 and 33 described above. Two stirring members 3
The developer transported by the developing sleeves 2 and 33 is the developing sleeve 3
When it reaches the vicinity of 1, it is pumped up to the developing sleeve 31 by the action of the internal magnet 36. With the configuration of the developing device 30 described above, the developer that has passed the doctor blade 35 has a large charge amount of the toner T and a small contact area between the toner T and the carrier C. May be relatively small. As a result, the developing ability is improved, and the adhesion of the toner T to the background is reduced. Further, since the charge amount of the entire toner is large, the responsiveness of the toner T to the electrostatic latent image, that is, the acceleration of the toner T toward the electrostatic latent image on the photoconductor 20 is large, and the toner T is more faithful to the electrostatic latent image. A toner image can be obtained, and the resolution and the like are improved.

A typical example of the two-component developer used here is a carrier C having a core made of ferrite particles having a maximum magnetization of 60 emu / g and a particle size of 50 μm, the surface of which is coated with a silicone resin; Average particle size is 7.5 μm
And a toner T containing a thermoplastic resin as a main component and colored with carbur black at a toner concentration of 5 wt.% (Meaning that the carrier C: the toner T is 95: 5 by mass ratio). is there. The toner T tends to be negatively charged when it comes into contact with the carrier C, and has a charge amount of about −25 μC / g in an initial state. These numerical values and materials are merely examples, and do not limit the content of the invention. Further, for example, the diameter of the developing sleeve 31 is 20 m.
m, an image forming apparatus is used in which the linear velocity of the developing sleeve 31 is 480 mm / s with respect to the linear velocity of the photosensitive member 20 of 240 mm / s. The process specifications of these image forming apparatuses are also merely an embodiment of the present invention.

(Embodiment 2) An image forming method according to claim 2 will be described. According to a second aspect of the present invention, the electric field control unit causes the image identification unit 15 to output the electrode member 3 according to the identification result.
7 is an image forming method for controlling a bias applied to the reference numeral 7.
When the number of colored pixels is less than a predetermined value, the amount of toner consumption is small and the replacement of the toner T is small, so it is necessary to control the toner T to prevent the charge amount of the toner T from becoming excessive. Therefore, in such a case, the electrode member 37 shown in FIG. 3 is set to the same potential as the developing sleeve 31 or a bias is applied to the electrode member 37 so that the difference from the developing sleeve 31 is relatively small. When the number of colored pixels is equal to or larger than a predetermined value, the toner consumption is large and the toner T is frequently replaced. Therefore, it is necessary to charge the toner T supplied to the developer layer on the developing sleeve 31 in a relatively short time. is there. Therefore, in such a case, a bias is applied to the electrode member 37 so that the toner T is actively moved between the electrode member 37 and the developing sleeve 31 to increase the charge amount. An example in which a high-quality image is obtained by controlling the DC component of the bias applied to the electrode member 37 will be specifically described. At this time, the bias applied to the electrode member 37 is only DC or a combination of DC and AC. In the latter case, the DC component here is the time integrated average value of the bias waveform.

If the number of colored pixels is less than a predetermined value, the charge amount of the toner T may be increased as described above and the developing ability may be reduced.
To the same level as the developing bias -600V. Conversely, if the number of colored pixels is greater than or equal to a predetermined value,
Since the toner T is frequently replaced as described above, the toner charge amount is reduced, and the developing capability is excessive, so that fogging may easily occur. To correct this, the bias applied to the electrode member 37 is set to a minus side from the developing bias −600 V, that is, the toner T is drawn to the developing sleeve 31. As a result, a situation arises in which the toner density is high on the developing sleeve 31 side of the magnetic brush and low on the tip end side. In this state, fogging on the background becomes less likely to occur, and the toner T moved to the developing sleeve 31 contacts the carrier C, so that the toner charge amount gradually increases.

(Embodiment 3) An image forming method according to an eighth aspect of the present invention is an image forming method in which an electric field formed between the electrode member 37 and the developer carrying member includes a vibration component. Here, an example in which the voltage of the AC bias (peak-to-peak value) for the electrode member 37 is controlled will be described. When the number of colored pixels is less than the predetermined value, the charge amount of the toner T tends to increase and the developing ability tends to decrease. Therefore, the peak-to-peak value applied to the electrode member 37 is reduced to prevent this. The change in the toner charge amount is reduced. As a result, the charge amount of the toner T is prevented from becoming too high. Conversely, when the number of colored pixels is equal to or more than a predetermined value, the charge amount of the toner T is reduced, the developing capacity is excessive, and fogging tends to occur. By increasing the peak value, the separation and reattachment of the toner T and the carrier C are promoted. As a result, the supplied toner T is charged in a short time. In addition to the above control, for example, the duty ratio and frequency of the AC component may be changed. By controlling the bias applied to the electrode member 37 as described above, it is possible to provide a stable image forming method that does not vary according to the type of image. Therefore, claims 4, 5 and 1
As described in Item 0, by applying the image forming method according to Claims 1, 2 and 8, it is possible to provide a stable image forming apparatus which does not vary according to the type of image. it can.

(Embodiment 4) An image forming method according to claim 7 will be described with reference to FIG. The other parts except the contents described below have the same configuration as the first embodiment. Here, FIG.
FIG. 3 is a system block diagram of an image forming method of reading optical information of a document by a device such as a scanner using a CCD image pickup device or the like of an image reading unit and converting the data into image data such as electric signals to form an image. The original is read by the image reading device 4 to obtain read image data. The read image data is subjected to image processing by an image processing device to create output image data, and the created output image data is temporarily stored in the image memory. Next, the output image data stored in the image memory of the image processing apparatus is read out at the time of recording and input to the image forming apparatus. An image is formed by this image forming apparatus. The image forming process performed by the image forming apparatus is performed as follows. Here, the image reading section 4 calculates the average density value of the entire document and sends it to the image identification device. The average density of the entire document may be calculated from the average value of the data read by the CCD image sensor, or a result obtained by determining the reflectance by another optical sensor may be used. When the average density value of the document is less than the predetermined value, since the toner consumption in the subsequent image formation is small and the replacement of the toner T is small, it is necessary to control so that the charge amount of the toner T does not become excessive.

Therefore, in such a case, the electrode member 37 is set to the same potential as the developing sleeve 31 or a bias is applied to the electrode member 37 so that the difference from the developing sleeve 31 is reduced. When the average density value of the original is equal to or more than a predetermined value, the toner consumption is large and the toner T is frequently replaced. Therefore, it is necessary to charge the toner T supplied to the developer layer on the developing sleeve 31 in a relatively short time. There is. Therefore, in such a case, a bias is applied to the electrode member 37 so that the toner T is actively moved between the electrode member 37 and the developing sleeve 31 to increase the charge amount. Specifically, when the average density of the document is large, the same as when the number of colored pixels of the third embodiment is equal to or more than a predetermined value, and when the average density of the document is small, the number of colored pixels of the third embodiment is the predetermined value. It is desirable to perform control in the same way as when it is less than. By controlling the bias applied to the electrode member 37 as described above, it is possible to provide a stable image forming method that does not change depending on the type of the read image. Therefore, claim 9
As described above, by applying the image forming method according to the seventh aspect, it is possible to provide a stable image forming apparatus that does not vary depending on the type of image.

(Embodiment 5) An image forming method according to claim 3 will be described with reference to FIG. The other parts except the contents described below have the same configuration as the first embodiment. Here, FIG.
FIG. 1 is a system block diagram of an image forming method for forming an image based on external image data such as a printer.
First, image information from a computer or the like is input via an interface. The image data converted to the bitmap image is transferred to the LD driving unit 11 and causes the laser light to blink on a pixel basis. The laser light is irradiated on the photoconductor 20 of the image forming apparatus, and an electrostatic latent image is formed. Hereinafter, a toner image is formed as described in the first embodiment. A recording density setting unit sets the number of pixels per unit area on an image (hereinafter, referred to as “recording density”), and signals the interface unit 10, the LD driving unit 11, the electric field control unit, and the image forming apparatus to specify the recording density. Send. The interface unit 10 converts the image information into pixel-based image data according to the recording density, and transmits the image data to the LD driving unit 11. L
The D drive unit 11 performs image exposure on the photoconductor 20 of the image forming apparatus by setting an image transfer clock, a scanning speed of laser light, and the like according to the recording density. In the image forming apparatus,
The rotation speed and the like of the photoconductor 20 are set according to the recording density, and a toner image is formed. The electric field control unit controls the bias applied to the electrode member 37 as described below according to the recording density. When the recording density is high, it is preferable to increase the charge amount of the toner T in order to adhere the toner T faithfully to a portion where the spatial frequency of the electrostatic latent image is high (that is, a fine image). Therefore, a bias is applied to the electrode member 37 so that the toner T is actively moved between the electrode member 37 and the developing sleeve 31 to increase the charge amount. When the recording density is low, it is important to supply a sufficient amount of toner T to a portion where the spatial frequency of the electrostatic latent image is low. Therefore, the electrode member 37 is set to the same potential as the developing sleeve 31 or Is applied to the electrode member 37 so that the difference between the two is relatively small.

An example of the condition setting will be described below.

[Table 1] (*): Time average As a result, a high-quality image can be obtained even at a low recording density of 600 dpi. In addition, the recording density of 120
Even at 0 dpi, a high-quality image can be obtained regardless of whether the bias applied to the electrode member 37 is superimposed on DC or AC. By controlling the bias applied to the electrode member 37 as described above, it is possible to provide a stable image forming method that does not change depending on the type of the read image. Therefore, as described in claim 6, by applying the image forming method according to claim 3, it is possible to provide a stable image forming apparatus that does not change according to the type of image.

[0024]

As described above, in the image forming method according to the first aspect, the electrode member located near the developer carrying member and provided downstream of the developer regulating member and downstream of the developing region. By switching the applied bias according to the image information, the toner density and the toner charge amount can be appropriately controlled, so that stable image quality can always be maintained according to the content of the image. Further, in the image forming apparatus according to the fourth aspect of the present invention to which this image forming method is applied, similarly, it is possible to always maintain a stable image quality according to the content of the image. In the image forming method according to the second aspect, by switching the bias applied to the electrode member in accordance with the number of colored pixels, the toner charging amount is excessively increased when toner replacement is small, and the developing ability is reduced. Not
Further, when the toner replacement is large, the replenished toner is not charged in a short time to cause fogging or toner scattering, so that stable image quality can be always maintained. Further, in the image forming apparatus according to the fifth aspect of the present invention, it is possible to always maintain a stable image quality without causing an adverse effect when the charge amount of the toner is too high or too low. it can. In the image forming method according to the third aspect, in the image forming apparatus having the image reading unit, the average density of the document is obtained, and the bias applied to the electrode member is switched according to the average density. Because the toner charge does not rise too much and the developing capacity does not decrease, and when toner replacement is large, the replenished toner is charged in a short period of time so that fogging and toner scattering do not occur. Stable image quality can be maintained. Further, this image forming method is applied.
In the image forming apparatus described in (1), stable image quality can always be maintained. According to the image forming method of the present invention, in the image forming apparatus capable of performing image formation by switching the recording density, the bias applied to the electrode member near the developer carrier is switched according to the recording density. ,
Since the toner charge amount can be controlled, when the recording density is high, the toner adheres faithfully to the spatial frequency portion of the electrostatic latent image,
When the recording density is low, sufficient toner can be supplied to a portion of the electrostatic latent image where the spatial frequency is low. Further, in the image forming apparatus according to the ninth aspect of the present invention, the amount of toner charge can be controlled, so that the toner can be supplied in accordance with the magnitude of the spatial frequency, and high quality image quality can always be obtained. Can be maintained. In the image forming method according to the eighth aspect, since the movement of the toner and the carrier can be made more efficient by including the vibrating portion in the electric field formed between the electrode member and the developer carrier, the charge amount of the toner is increased. It is possible to improve the control accuracy and perform image formation in a stable state according to various situations. Further, in the image forming apparatus according to the tenth aspect of the present invention, the accuracy of controlling the charge amount of the toner is improved, and the image can be formed in a stable state according to various situations. .

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a basic configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a system block diagram of an image forming method for forming an image using external image data such as a computer.

FIG. 3 is a schematic diagram showing a basic configuration of a developing device used in an image forming method according to an embodiment of the present invention.

FIG. 4 shows the direction of an alternating electric field in a region between a developing sleeve and an electrode material.

FIG. 5 is a diagram schematically illustrating a contact state between a toner and a carrier. FIG. 5A is a diagram schematically illustrating a contact state in which the toner has just started to contact the carrier without passing through the space between the developing sleeve and the electrode member. FIG. 5B is a diagram schematically illustrating a contact state between the toner and the carrier after passing through a space between the developing sleeve and the electrode member.

FIG. 6 is a diagram illustrating a CCD of an image reading unit that converts optical information of a document into an image;
Read with a device such as a scanner using an image sensor, etc.
FIG. 3 is a system block diagram of an image forming method for forming an image by converting the image data into image data such as an electric signal.

FIG. 7 is a system block diagram of an image forming method for forming an image based on image data from an external device such as a printer.

FIG. 8 is an example of measurement of a toner charge amount distribution by a charge amount measuring device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 writing device 2 image forming device 3 external device such as computer 4 image reading device 10 interface unit 11 LD driving unit 12 polygon mirror 13 lens 14 mirror 15 image identification unit 20 photoconductor 21 charging roller 22 transfer / separation device 24 transport roller Reference Signs List 25 paper feed roller 26 paper feed cassette 30 developing device 31 developer sleeve 32 first stirring member 33 second stirring member 34 partition plate 35 doctor blade 36 internal magnet 37 electrode member 38 toner supply roller 40 cleaning device 41 cleaning blade 50 fixing device C carrier T toner V1, V2 Power supply

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 15/08 507X (72) Inventor Hiroshi Yasutomi 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Company, Ltd. (72) Inventor Hirokatsu Suzuki 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H027 DA10 DE02 EA05 EC02 ED09 EE06 EF09 2H077 AD02 AD06 AD13 AD36 AE04 AE08 CA02 DA08 DA63 DB08 EA03 EA15 FA25

Claims (10)

[Claims] 1. A latent image forming means for performing image exposure based on image information to form an electrostatic latent image on an image carrier, and developing the electrostatic latent image to form a toner image on the image carrier. Means, a transfer means for transferring the toner image on the image carrier to the transfer material, and a transfer means for fixing the toner image on the transfer material to the transfer material, wherein the developing means comprises: A developer carrier that transports a developer composed of a toner and a magnetic carrier to a development area facing the image carrier; and a developer that is held at a fixed distance from the developer carrier and transports the developer carrier to the development area. A developer regulating member that regulates the amount of the developer carrier, an electrode member near the developer carrier downstream of the developer regulating member with respect to the direction of movement of the developer carrier, and further, an electrode member and the developer carrier. An electric field control unit that controls an electric field formed between the Image forming method, wherein the electric field control section is controlled in accordance with an electric field formed between the electrode member developer carrying member to the image information. 2. The image forming method according to claim 1, wherein the electric field control unit controls an electric field formed by the electrode member according to the number of colored images included in the image information. 3. The image forming method according to claim 1, wherein an average density of the document is detected from image information of the document read by the image reading device, and an electrode member is formed according to the average density value. An image forming method comprising controlling an electric field. 4. A latent image forming means for performing image exposure based on image information to form an electrostatic latent image on an image carrier, and developing the electrostatic latent image to form a toner image on the image carrier. Means, a transfer unit for transferring the toner image on the image carrier to the transfer material, and a transfer unit for fixing the toner image on the transfer material to the transfer material, wherein the developing unit comprises: an image carrier; A developer carrier that conveys a developer composed of toner and a magnetic carrier to an opposing development area; and a developer carrier that is held at a fixed distance from the developer carrier and regulates an amount of the developer conveyed to the development area. A developer regulating member, and an electrode member in the vicinity of the developer carrier downstream of the developer regulating member with respect to the direction of movement of the developer carrier, and between the electrode member and the developer carrier. An electric field control unit that controls an electric field to be formed in accordance with image information An image forming apparatus comprising and. 5. The image forming apparatus according to claim 4, wherein the electric field control unit controls an electric field formed by the electrode member according to the number of colored images included in the image information. 6. The image forming apparatus according to claim 4, further comprising: an image reading device for reading optical information of the document, wherein the image information corresponds to an average density value of the document detected by the image reading device. An image forming apparatus comprising: an electrolysis control unit that controls an electric field formed by the electrode member. 7. A latent image forming means for performing image exposure based on image information to form an electrostatic latent image on an image carrier, and developing the electrostatic latent image to form a toner image on the image carrier. Means, a transfer means for transferring the toner image on the image carrier to the transfer material, and a transfer means for fixing the toner image on the transfer material to the transfer material, wherein the developing means comprises: A developer carrier that transports a developer composed of a toner and a magnetic carrier to a development area facing the image carrier; and a developer that is held at a fixed distance from the developer carrier and transports the developer carrier to the development area. A developer regulating member that regulates the amount of the developer carrier, an electrode member near the developer carrier downstream of the developer regulating member with respect to the direction of movement of the developer carrier, and further, an electrode member and the developer carrier. An electric field control unit that controls an electric field formed between the The electric field control unit controls an electric field formed between the electrode member and the developer carrier according to image information, and the latent image forming unit forms an electrostatic latent image on the image carrier according to the image information. An image forming method characterized by forming. 8. The image forming method according to claim 1, wherein an electric field formed between the electrode member and the developer carrier includes a vibration component. 9. A latent image forming means for performing image exposure on a pixel basis based on image information to form an electrostatic latent image on an image carrier, and developing the electrostatic latent image to form a toner image on the image carrier. Forming a latent image on a transfer material; and transferring the toner image on the transfer material onto the transfer material. Can perform image exposure by switching the number of pixels per unit area, and a developing unit transports a developer including a toner and a magnetic carrier to a development region facing the image carrier. A developer regulating member that is held at a constant interval with the developer carrying member and regulates an amount of the developer carried by the developer carrying member to the developing region; a downstream side of the developer regulating member with respect to a moving direction of the developer carrying member; An electrode member near the developer carrier And an image forming apparatus, characterized in that it comprises an electric field control section for controlling in response the electric field formed in the image information between the electrode member and the developer carrying member. 10. The image forming apparatus according to claim 4, wherein the electric field formed between the electrode member and the developer carrier includes a vibration component.