JPH11305499A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably accurately detect the residual amount of developer with respect to an image forming device provided with a developing system capable of obtaining appropriate image density and a distinct image having no fogging even in the case of using small-grain-size toner, and changing the components of AC voltage such as peak-to-peak voltage, frequency and duty ratio according to some conditions. SOLUTION: The time when pre-rotation is performed being a stage other than an image forming stage is set as a toner residual amount detecting stage. In the residual amount detecting stage, toner residual amount is detected by impressing the AC voltage whose duty ratio on a (V-) side is made constant, that is, 50% on the developing sleeve of a developing device regardless of the change of the duty ratio of the AC voltage at the time of controlling the image density. In the image forming stage, the image density is controlled by changing the duty ratio of the developing bias to a ratio in accordance with the desired image density.

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 to which an electrophotographic method such as a copying machine, a printer, a facsimile or the like is applied.

[0002]

2. Description of the Related Art As an example of a conventional electrophotographic image forming apparatus, an image forming apparatus of a reversal developing system is known.

As shown in FIG. 11, this image forming apparatus comprises an image carrier 1 on which a photosensitive layer is provided on a grounded conductive substrate and on which an image is formed, and a charging device (which uniformly charges the image carrier). A charging roller) 2, an exposure device (not shown) for irradiating exposure light 9 for drawing an electrostatic latent image on the surface of the image carrier 1, and developing the latent image on the image carrier 1 with a developer 7 A developing device 3 for visualizing the image, a transfer roller 4 for transferring the toner image onto the transfer paper P, a fixing device 10 for fixing the toner image on the transfer paper P, and a transfer residue remaining on the image carrier 1 And a cleaning device 5 for cleaning the toner.

[0004] Toner 7 is a black magnetic toner obtained by blending, for example, 100 parts by weight of a magnetic substance, 100 parts by weight of a styrene acrylic resin, and 2 parts by weight of an iron complex of a monoazo dye as a negative charge control agent. , And the average particle size is 9 μm.

[0005] In the image formation by the electrophotographic process of the image forming apparatus, during the latent image process on the image carrier 1, first, the surface of the image carrier 1 is uniformly charged by the charging roller 2 and the image carrier 1 is charged. Is set as a dark portion potential Vd. After that, the surface of the image carrier 1 is exposed to exposure light 9 such as a laser beam, and the exposed portion is set as a bright portion potential Vl, and the surface of the image carrier 1 is statically controlled by a dark portion potential Vd portion and a bright portion potential Vl portion. An electrostatic latent image is formed.

In the developing process, the charged toner 7 is held on a developing sleeve 3a which is a developer holding member of the developing device 3, and an appropriate gap is provided between the developing sleeve 3a and the image carrier 1. Above, by applying a predetermined DC voltage + AC voltage, the toner 7 is adhered only to the light portion potential Vl without adhering to the dark portion potential Vd, and an image is formed on the image carrier 1 by the toner 7.

The behavior of the toner 7 in the above development will be described in detail. The toner 7 has a negative polarity for frictional charging with the elastic blade 3b and the like, and most of the toners 7 have a negative charging polarity due to frictional charging. Further, the dark portion potential portion Vd and the light portion potential Vl portion on the image carrier 1 are also set so as to show a negative potential.

Conventionally, the developing bias in such a system is obtained by superimposing a DC voltage of Vdc and an AC voltage Vpp of a rectangular wave having a duty ratio of 50% on a DC voltage of Vdc, as shown in FIG. When the minus side of the developing bias indicates the maximum voltage (V-) in absolute value, the toner 7 flies from the developing sleeve 3a onto the image carrier 1 with respect to the Vl portion, and the plus side on the opposite side is the maximum. When indicating the voltage (V +),
The flying toner 7 is transferred from the image carrier 1 to the developing sleeve 3.
a, and the flying and pulling back are repeated.

| (V −) − Vl |> | (V +) − Vl | (1) As a result of this repetitive motion, the negatively charged toner 7 becomes lighter on the image carrier 1. Attach to the part potential Vl part.

(V-) with respect to the dark portion potential portion Vd,
The behavior of the toner 7 at (V +) also behaves in the same manner at each voltage, but here, | (V −) − Vd | <| (V +) − Vd | (2) Therefore, the toner 7 hardly adheres to the dark portion potential Vd on the image carrier 1.

Accordingly, a voltage value which satisfies the equations (1) and (2), which is an electric field sufficient for the toner 7 to fly between the developing sleeve 3a and the image carrier 1, is expressed by Vd,
By setting Vl, (V-), and (V +), an image was formed on the image carrier 1 with the toner 7. In order to satisfy such a condition, the difference between (V−) and (V +), that is, Vpp is increased, and Vd and Vd are increased.
It is necessary to take sufficient contrast with l.

FIG. 13 shows a conventional example of numerical values, where (V −) = − 1200 V, (V +) = + 400 V,
Vd = -600V, Vl = -150V, Vdc = -40
0 V, Vpp = 1800 V, frequency = 2000 Hz, duty ratio = 50%, and the gap between the image carrier 1 and the developing sleeve 3a is 280 μm.

The charge amount of the toner 7 varies depending on the use condition and use environment of the developing device 3. To obtain an image having an appropriate density with respect to the change in the charge amount of the toner 7, Vd is required. , Vl, the appropriate (V-) and (V +) change. For this reason, the image forming apparatus usually uses the image density control device to control the developing sleeve 3 against Vd and Vl.
DC voltage (Vdc) applied between a and the image carrier 1
Is changed in accordance with the use condition of the developing device 3 (Vpp = constant at this time), so that an image with an appropriate density can be output.

However, the charging polarity of the toner 7 is not all the same, and the distribution of the charging of the toner 7 on the developing sleeve 3a is, in addition to the main polarity (minus) as shown by the hatched portion in FIG. There is a small amount of polarity (plus) so-called inverted toner.

In order to reduce the image density, such an inverted toner changes the DC voltage (Vdc) to Vl and (V
When the contrast between-and-is set to be small, the contrast between Vd and (V +) increases, so that the toner 7 flies to a region of the dark portion potential Vd where the toner 7 does not originally fly. Also, if the DC voltage (Vdc) is set so as to increase the contrast between Vl and (V-) to increase the image density, the contrast between Vd and (V-) also increases. The toner of the main polarity also flies to the region of the dark portion potential Vd. In this manner, these toners cause image defects such as so-called fog images that stain a white image (white background portion).

In recent years, as the quality of an image has been improved, the particle size of the toner 7 has been reduced, and as a result, the number of toners having insufficient charge has increased, and as a result, the level of fog has deteriorated. Even when an appropriate potential is set so that no fog occurs, V
Since the latitude (permissible range) of the set width of d, Vl, (V-), and (V +) is narrowed, D is required to change the density.
When the C voltage (Vdc) was changed, the proper Vd,
There is a problem that the balance between Vl, (V-) and (V +) is lost, and a fog image is generated.

[0017]

By the way, the developing device 3
One of the methods for detecting the remaining amount of toner is antenna residual detection. As shown in FIG. 11, a metal detecting rod (antenna) 14 is arranged in the developing container 3c of the developing device containing the toner 7 in parallel with the longitudinal direction of the developing sleeve 3a and applied to the developing sleeve 3a. Utilizing the fact that the current value flowing through the detection rod 14 due to the AC voltage of the developing bias changes when the electric capacity between the detection rod 14 and the developing sleeve 3 changes, the remaining amount of the toner 7 in the developing container 3c is utilized. Is to be detected.

However, the components (the peak-to-peak voltage, the frequency, and the like) constituting the AC voltage of the developing bias applied to the developing sleeve 3a are changed depending on the change of the image density and other conditions.
In a developing system having a sufficient image density and a clear image without fogging by changing the duty ratio), the current value flowing through the detection rod 14 fluctuates due to the change of the AC voltage component. A problem that a large amount of remaining toner cannot be detected.

Accordingly, it is an object of the present invention to provide a proper image density and a clear image without fog even with a small particle size toner, and an AC voltage such as a peak-to-peak voltage, a frequency and a duty ratio depending on various conditions. An object of the present invention is to make it possible to accurately and stably detect the remaining amount of the developer in an image forming apparatus having a developing system that changes the components.

[0020]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier, an electrostatic latent image formed from a dark potential portion and a light potential portion obtained by charging the surface of the image carrier and exposing the developer, Developing means for developing and visualizing using, density control means for controlling the density of the obtained visible image, and a detecting means for detecting the remaining amount of the developer of the developing means, the developing means, A developer holding member opposed to the image carrier with a predetermined gap therebetween, and in the development, applying a voltage obtained by superimposing an AC voltage between the developer holding member and the image carrier; The density control means controls the density of the visible image by changing at least one of a plurality of components constituting an AC voltage applied to the developer holding member, and controls the density of the developer. The amount detecting means is disposed in the developing means in parallel with the developer holding member. An image forming apparatus having a rod-shaped detection member, wherein the remaining amount of the developer is detected by measuring a current induced in the detection member by an AC voltage applied to the developer carrier. A developer remaining amount detection process as a process other than the image forming process, and in the developer remaining amount detection process, regardless of a change in an AC voltage component at the time of density control by the density control means, the developer An image forming apparatus characterized in that an AC voltage in which the plurality of components are set to a predetermined constant value is applied to a holding member to detect the remaining amount of the developer.

According to the present invention, when the electric field between the peak voltage on the side of causing the developer having the peak value of the AC voltage to fly the image carrier to the image bearing member and the light portion potential portion is 4.1 V / μm or more, The electric field between the peak voltage on the side to be caused and the dark portion potential portion is 3.5 V / μm or less, and the electric field between the peak voltage on the side where the developer is pulled back from the image carrier and the dark portion potential portion is 2.8.
V / μm or less, and at the time of density control by the density control means, the component that changes the AC voltage is the duty ratio of the AC voltage, and the duty ratio is set to 20 to
It can be changed in the range of 50%.

According to another aspect of the present invention, an electrostatic latent image formed from an image carrier and a dark portion potential portion and a bright portion potential portion obtained by charging and exposing the surface of the image carrier is exposed. A plurality of developing means for developing and visualizing using a developer, a plurality of density control means for controlling the density of the obtained visible image, and a plurality of detecting the remaining amount of the developer in each developing means And each of the developing units has a developer holding member opposed to the image carrier with a predetermined gap therebetween, and the developing is performed by the image carrier on the developer holding member. The concentration control unit changes at least one of a plurality of components constituting the AC voltage applied to the developer holding member. By controlling the density of the visible image, each of the developer amount detection means, A bar-shaped detection member is disposed in the image means in parallel with the developer holding member, and the remaining amount of the developer is detected by measuring a current induced in the detection member by an AC voltage applied to the developer carrier. In the image forming apparatus performed by the above, the image forming apparatus has a developer remaining amount detection process as a process other than the image forming process, and in the developer remaining amount detection process, Irrespective of the change in the component of the AC voltage, applying the AC voltage in which the plurality of components have a predetermined constant value to the developer holding member of each of the developing units to detect the remaining amount of the developer. The image forming apparatus is a feature.

According to the present invention, when the electric field between the peak voltage on the side of causing the developer having the peak value of the AC voltage to fly to the image carrier and the light potential portion is 4.1 V / μm or more, The electric field between the peak voltage on the side to be caused and the dark portion potential portion is 3.5 V / μm or less, and the electric field between the peak voltage on the side where the developer is pulled back from the image carrier and the dark portion potential portion is 2.8.
V / μm or less, and at the time of density control by each of the density control means, the component that changes the AC voltage is the duty ratio of the AC voltage.
It can be changed in the range of ５０50%.

According to the present invention, the current induced in the detecting member of each of the developing means is converted into a voltage and measured, and each of the measured voltages is compared with a respective reference voltage.
The remaining amount of the developer can be detected. Instead of applying an AC voltage in which the plurality of components have a predetermined constant value to the developer holding member of each of the developing units, the currents induced in the detection members of each of the developing units are the same, At least one of a plurality of components is stored in a developer holding member of a developing unit.
Applying the changed AC voltage, comparing each of the measured voltages with the same reference voltage, the remaining amount of the developer can be detected, and the component that changes the AC voltage is the AC voltage. It is a duty ratio.

Further, an alternating voltage is applied to the developer holding member of each of the developing means, the plurality of components having a predetermined constant value. At this time, the current induced in the detecting member of each of the developing means is the same. The distance between the detection member of each of the developing units and the developer holding member is changed, and the measured voltages are compared with the same reference voltage to detect the remaining amount of the developer. It can be carried out. Further, the process of temporarily transferring the visible image obtained by the development to the intermediate transfer body for a plurality of colors can be repeated, and thereafter, the visible images for a plurality of colors can be collectively transferred to a transfer material. The average particle size of the developer can be 6.5 μm or less.

[0026]

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

Embodiment 1 An important feature of the present invention is that in an image forming apparatus having an image density control device, it is possible to accurately and stably detect the remaining amount of developer in the developing device.
Since the configuration of the image forming apparatus of this embodiment is basically the same as the conventional image forming apparatus shown in FIG. 11, FIG. 11 will be referred to below as needed in the description of the present invention.

The image forming apparatus includes an image carrier 1, a charging roller 2, a developing device 3, a transfer roller 4, a cleaning device 5, a fixing device 10, and the like.

The developing device 3 includes a developing container 3 c containing the magnetic toner 7, a developing sleeve 3 a disposed at an opening of the developing container 3 c facing the image carrier 1, and a developing sleeve 3.
It is composed of an elastic blade 3b and the like abutting on the upper portion of the frame a.

The toner 7 is obtained by kneading 100 parts by weight of a magnetic material, 100 parts by weight of a styrene acrylic resin, and 2 parts by weight of an iron complex of a monoazo dye as a negative charge control agent, and pulverizing the mixture to obtain 100 parts by weight of toner particles. Parts by weight of silica and 1.2 parts by weight of silica.
m.

The toner 7 adheres to the surface of the developing sleeve 3a by the magnetic force of the developing magnet incorporated in the developing sleeve 3a, and is directed toward the developing section facing the image carrier 1 with the rotation of the developing sleeve 3a. Conveyed. During the conveyance, the toner 7 is regulated by the elastic blade 3b, is negatively triboelectrically charged, and is formed into a thin toner layer having a predetermined thickness.

A gap of about 280 μm is always formed between the image carrier 1 and the developing sleeve 3a by disposing rollers at both ends of the developing sleeve 3a in contact with both ends of the image carrier 1. ing. A rectangular wave AC voltage is applied as a developing bias between the image carrier 1 and the developing sleeve 3a.

At this time, the conductive base of the image carrier 1 is grounded, whereas the peak value of the developing bias applied to the developing sleeve 3a is (V −) = − 1400V,
(V +) = 0 V, the frequency is set to 2000 Hz,
The duty ratio of the rectangular wave is 35% on the (V-) side, and (V +)
Side is set to 65%. Further, by the charging by the charging roller 2 during the latent image process, the dark portion potential on the surface of the image carrier 1 is changed to Vd.
= −600 V, and the exposure by the laser beam exposure light 9 is set so that the bright portion potential of the exposed portion on the surface becomes Vl = −150 V.

The setting of these potentials is as shown in FIG. 1. With this, in the image forming apparatus of this embodiment, (V
−) And Vd are 2.86 V / μm, and (V−) and Vd
The electric field between I and Vd is 4.46 V / μm, and the electric field between (V +) and Vd is 2.14 V / μm. In the present embodiment, the image density is changed by changing the duty ratio of the developing bias (AC voltage).
On the −) side, it is 28 to 41%, and the fluctuation of the image density due to this is Vdc ± 150 in the conventional method of changing the image density by changing the DC value (Vdc) of the developing bias.
This is equivalent to changing V.

FIG. 2 shows the relationship between image density and fog in this embodiment together with the case of the conventional example. The density is 600d
The fog is represented by the line width of four dot lines in the pi image, and the fog is represented as a difference (%) of the reflection density after the white image formation with respect to the reference paper before the image formation.

In FIG. 2, a dotted line A represents the case of the conventional example, and the image density and the fog when the DC value (Vdc) of the developing bias is changed by the potential setting of the developing and latent image shown in FIG. Relationship. At this time, the developing bias DC
The value varies from -250V to -550V, and the dotted line A
The curve is such that the fog value has a minimum value with respect to the line width variation.

This is because, in a region where the line width is large, the contrast between Vl and (V−) becomes large, and Vd and (V−) become large.
, The amount of toner flying to the dark portion potential Vd also increases. Further, in a region where the line width is small, the contrast between Vl and (V-) decreases, and the contrast between Vd and (V +) increases.
This is due to the phenomenon that the amount of the inverted toner flying to the dark portion potential Vd increases.

The alternate long and short dash line B is the case of the conventional example, and Vd is Vd in the development and the potential setting of the latent image in FIG.
This is a relationship between image density and fog when the duty ratio of the developing bias is changed at constant values of c = −400 V and Vpp = 1800 V. At this time, the duty ratio of the developing bias varies from 40% to 60% on the (V−) side.

The dashed-dotted line B indicates that in a region where the line width is large,
By increasing the duty ratio on the (V−) side, V
Since the toner flight time between 1 and (V−) increases, the line width increases, and the flight time between Vd and (V−) also increases, so that the amount of toner flying to the dark portion potential Vd increases. However, at this time, since the potential difference between Vd and (V−) is not so large for the toner to fly, even if the flying time increases, the amount of the toner flying to the dark portion potential Vd does not increase so much.

On the other hand, in the region where the line width is small, the duty ratio on the (V +) side is increased, so that the potential difference between Vd and (V +) is sufficient for the inverted toner to fly to the dark portion potential Vd. Since the reversal toner is large, the flying amount of the reversal toner to the dark portion potential Vd portion sharply increases as the flying time increases.

The solid line C shows the case of this embodiment, and shows the relationship between image density and fog when the duty ratio of the developing bias is changed in the development and latent image potential setting shown in FIG. At this time, the duty ratio of the developing bias is changed from 28 to 41% on the (V-) side. Solid line C
The fog value increases as the line width increases, but the increase is very small. This is because, in a region where the line width is large, the toner flying time between Vl and (V-) increases by increasing the duty ratio on the (V-) side, so that the line width increases and Vd and Vd increase. Since the flying time with (V−) also increases, the amount of toner flying to the dark portion potential Vd increases.

However, the one-dot chain line B is (V −) = − 120
0V, Vd = -600V, and the solid line C is (V −) = −
1400 V, Vd = −600 V, and the potential difference between Vd and (V−) is set to be larger for the solid line C and to increase the fog amount, but the same line on the thicker side of the line width is set. In the width, the duty ratio on the (V−) side is 60% for the dashed line B and 41% for the solid line C. The solid line C has a shorter toner flight time than the dashed line B.
The fog value is slightly higher than the dashed line B.

On the other hand, in the region where the line width is small, (V +)
By increasing the duty ratio on the side, the line width is reduced, but the potential difference between Vd and (V +) is sufficiently small for the inversion toner to fly. The amount of the reversal toner flying to the portion is very small.

Here, (V−) and Vl, (V−) and V
d, the relationship between (V +) and Vd will be described.

In the relationship between (V−) and Vl, the reproducibility of the black image portion increases as the electric field intensity increases. At the electric field intensity a1 = 4.46 V / μm in the case of this embodiment,
The relationship between the duty ratio and the image density on the (V-) side of the developing bias is compared with the case where the conventional electric field intensity a2 = 3.75 V / μm and the intermediate electric field intensity a0 = 4.1 V / μm. As shown in FIG. The image density is 600 dpi
Are indicated by the line width of 40 dot lines. The duty ratio on the (V-) side of the developing bias is 50 to 20.
%, An electric field strength of 4.1 V / μm or more is required to obtain a sufficient line concentration of 1.4 or more.

In the relationship between (V−) and Vd, the fog level is better as the electric field intensity is smaller. When the electric field intensity is changed (b0 = 3.5 V / μm, b2 = 3.8 V /) with respect to the electric field intensity b1 = 2.86 V / μm (2.14 V / μm in the conventional developing system) in this embodiment. μ
FIG. 4 shows the relationship between the duty ratio and the fog on the (V−) side of the developing bias of m). Thus, when the duty ratio on the (V-) side of the developing bias is between 50% and 20%, in order to keep the fog at a good level of 3% or less, the electric field strength is set to 3.5 V / μm or less. There is a need.

In the relationship between (V +) and Vd, the lower the electric field intensity, the better the fog level. The relationship between the duty ratio and the fog amount on the developing bias (V +) side at the electric field intensity c1 of 2.14 V / μm in the case of the present embodiment is shown by the conventional electric field intensity c2 = 3.57 V / μm and the intermediate value. FIG. 5 shows a comparison with the case where the electric field strength c0 = 2.8 V / μm.

When the duty ratio on the (V-) side of the developing bias is between 50 and 20% (at this time, the duty ratio on the (V +) side is 50-80%), the fog is reduced to 3% or less. In order to maintain the level, the electric field intensity must be set to 2.8 V / μm or less.

As described above, according to the developing system of this embodiment, even if the developing ability changes depending on the use environment and the use condition (the number of images formed), the proper image density is always maintained in the black image area and the white area is maintained. Thus, a good image without fog can be obtained for a long period of time.

When the remaining amount of the toner 7 in the developing container 3c of the developing device 3 is to be detected by the residual antenna detection, in this embodiment, the duty ratio of the AC for the developing bias is changed to change the image. Since the density control method for changing the density is adopted, there is a problem that the remaining amount of toner cannot be accurately detected.

The principle of the antenna residual detection will be described.
When a developing bias is applied to the developing sleeve 3a of the developing device 3, a current is induced in a detection rod (antenna) 14 arranged in the developing container 3c in parallel with the longitudinal direction of the developing sleeve 3a, as shown in FIG. Then, a current flows through the detection rod 14. At this time, since there is a difference in the relative permittivity and the resistance between the toner 7 and the air, when the amount of the toner 7 changes between the developing sleeve 3a and the detection rod 14, the impedance (capacitance) between them changes. Since the current flows through the detection rod 14 according to the impedance, the remaining amount of the toner 7 can be detected from the current.

Therefore, as shown in FIG. 6, the current flowing through the detection rod 14 is rectified by a rectifier circuit 64 and converted into a DC voltage (toner remaining amount detection voltage) 65.
Compared with the reference voltage 67, the toner 7 in the developing container 3c
Is to detect the remaining amount.

Now, as shown in FIG. 7A, when the reference voltage 67 has a duty ratio of 50% for the AC voltage of the developing bias.
%. This duty ratio 50
When a developing bias of% is applied to the developing sleeve 3, an induced current as shown in FIG. 7B flows through the detecting rod 14, and the area of the current value (shaded area) is converted into a voltage to convert the reference voltage 6
7, the remaining toner amount can be detected.

Next, as shown in FIG. 8A, when the duty ratio corresponding to the AC voltage of the developing bias is changed (for example, the duty ratio is 25%) and applied, as shown in FIG. 7 (b), an induced current flows, and the voltage obtained by converting the area (shaded area) of this current value changes according to the changed duty ratio. Even when compared with the voltage 67, the remaining toner amount cannot be accurately detected.

Therefore, in the present invention, a step of detecting the remaining amount of toner is provided in a step other than the image forming step, and the remaining amount of toner is controlled regardless of the change in the duty ratio of the AC voltage of the developing bias at the time of image density control. In the detection process, the remaining amount of toner is detected by setting the duty ratio of the AC of the developing bias applied to the developing sleeve 3a to a predetermined constant value.

In this embodiment, the duty ratio on the (V−) side of the AC component of the developing bias is set to 50%.
As shown in FIG. 9, during the pre-rotation before the image forming process, this developing bias was applied to the developing sleeve 3a to detect the amount of remaining toner. Next, in the image forming process, the image density was controlled by changing the duty ratio of the developing bias to a ratio corresponding to the desired image density.

Therefore, according to the present embodiment, a desired image density can be obtained at the time of image formation, while an accurate remaining amount can be detected at the time of detecting the remaining amount of toner. Not clear images could be obtained.

In the above description, the detection of the remaining amount of toner has been described in connection with the case where the image density is controlled by changing the duty ratio of the developing bias. However, the present invention is not limited to this. In the density control method of changing the image density by changing the AC voltage component such as the frequency, the AC component (the peak-to-peak voltage, the frequency, and the duty ratio) of the developing bias is set to a predetermined constant value. , As well.

Embodiment 2 FIG. 10 is a schematic view showing another embodiment of the image forming apparatus of the present invention. In the first embodiment, a black and white image forming apparatus having one developing device 3 is used. However, as shown in FIG. 10, a color image forming apparatus having a plurality of developing devices, for example, Color developing units 3M, 3C, 3Y, 3
B is a full-color image forming apparatus.

The image carrier 1 rotates in the direction of the arrow, the surface of the image carrier 1 is uniformly and uniformly charged by the charging roller 2, and the potential of the surface of the image carrier 1 becomes the dark portion potential Vd. afterwards,
The surface of the image carrier 1 is exposed by exposure light 9 such as a laser beam, and the exposed portion becomes a bright portion potential Vl, so that an electrostatic latent image is formed on the surface of the image carrier 1. This latent image is developed by the first developing device 3M of magenta (M), and a magenta toner image of the first color is formed on the image carrier 1.

At this time, the second developing device 3C for cyan (C)
The operation of the third developing unit 3Y for yellow (Y) and the fourth developing unit 3B for black (B) is off, and the magenta toner image of the first color on the image carrier 1 is the second to fourth developing unit. Container 3C
3B, reaches the transfer nip area in contact with the intermediate transfer body 30 as the image carrier 1 rotates.

The intermediate transfer body 30 is provided with an elastic layer 32 of 10 ⁸ Ωcm or more on a pipe-shaped core metal 31.
The magenta toner image on the image carrier 1 is transferred to the surface of the intermediate transfer body 30 by a voltage having a polarity opposite to that of the toner applied to the intermediate transfer body 30 by the primary transfer power supply 33 (primary transfer).

After the transfer of the toner image of the first color is completed, the surface of the image carrier 1 is cleaned by the cleaning device 5, and then the image forming process for the cyan image of the second color is started. In the image forming process for the second color, only the second developing device 3C operates,
The other developing units 3M, 3Y, and 3B are turned off, and the second color cyan toner image is formed on the image carrier 1 by the procedure described above. The image is transferred by being superimposed on the magenta toner image of the color.

Similarly, the third color yellow toner image,
A black toner image of the fourth color is formed, and is transferred onto the surface of the intermediate transfer body 30 so as to overlap the previous image.

Next, one sheet of transfer paper P is taken out from the paper supply cassette 13 by the paper supply roller 15, passes through the transfer paper guide 11, and enters the transfer nip area where the intermediate transfer body 30 and the belt transfer member 45 abut. The toner image of four colors on the intermediate transfer body 30 is inserted into the transfer paper P by a voltage having a polarity opposite to that of the toner applied to the conductive roller 41 from the secondary transfer power supply 46.
Are collectively transferred to the surface (secondary transfer).

The belt transfer member 45 has a transfer belt 40 stretched around the conductive roller 41 and the drive roller 42. During the primary transfer, the conductive roller 41 is separated from the intermediate transfer body 30 as shown by a two-dot chain line so as not to disturb the primary transferred image on the intermediate transfer body. Sometimes, as shown by the solid line, the intermediate transfer member 3
0 to form a transfer nip area with the intermediate transfer body 30.

The transfer paper P on which the toner images of four colors have been transferred and which has exited the transfer nip area passes through the conveyance guide 12 and is fixed by the fixing device 1.
When the toner image reaches 0, the four color toner images are heated and pressed to be fixed on the surface of the transfer paper P as four color full color images.

The four developing units 3M to 3B are the same as those of the first embodiment.
Is slightly different in that the developing device 3 used is a magnetic toner, but the basic configuration of the device is almost the same.
3B is the same as that in the first embodiment.

The development in each of the developing devices 3M to 3B is performed by providing a fixed gap between the developing sleeve 3a holding the toner and the image carrier 1, and applying an AC voltage between them. . The electric field between the voltage on the flying side of the toner to the image carrier 1 having the peak value of the AC voltage and the light portion potential Vl is 4.1 V / μm or more, and the voltage on the flying side and the dark portion potential Vd Electric field between parts is 3.5V
/ Μm or less, and the electric field between the voltage on the toner retraction side of the image carriers 1 and the dark portion potential Vd is 2.8 V / μm.
It is as follows.

The image density is changed by changing the duty ratio of the AC voltage of the developing bias between 20% and 50% on the flight side.

The detection of the remaining amount of toner in each of the developing units 3M to 3B is carried out in a process other than the image forming process, and the detection of the remaining amount of toner is performed by determining the duty ratio of the AC voltage of the developing bias applied to the developing sleeve 3a. Was performed as a constant value. As a result, even in the density control method in which the image density is changed by changing the duty ratio of the AC voltage of the developing bias, accurate detection of the remaining amount of toner can be stably performed.

At this time, if the toners of the developing units 3M to 3B have the same impedance for all four colors, the reference voltage for detecting the remaining amount of toner may be one, but the magnetic toner is used for the black toner, and the magnetic toner is used for the other three colors. When a non-magnetic toner is used as the toner, the impedance differs between the magnetic toner and the non-magnetic toner. Therefore, two reference voltages, a reference voltage for the magnetic toner and a reference voltage for the non-magnetic toner, are provided. Perform detection. If the impedances of the four color toners are different, a reference voltage is provided for each toner, and the remaining amount of toner is detected.

In this embodiment, a developing bias in which the duty ratio on the (V-) side of the AC voltage is 50% is used for each of the developing units 3M to 3B, as shown in FIG. At the time of pre-rotation before the image forming process, this developing bias is applied to the developing sleeve 3a, and the current value detected by the detecting rod 14 is converted into a voltage by the detecting circuit of FIG. By doing so, each of the developing devices 3M to 3B
The remaining amount of the toner in was detected.

Then, in the image forming process, the duty ratio of the developing bias was changed to a ratio corresponding to the desired image density, and the image formation was performed while controlling the image density.

According to this embodiment, a desired image density can be obtained at the time of image formation, while an accurate remaining amount can be detected at the time of detecting the remaining amount of toner. Thus, the present embodiment has a sufficient image density and has no fog. A clear image could be obtained.

In the above description, the detection of the remaining amount of toner is based on the method of controlling the image density by changing the duty ratio of the developing bias, but as described in the first embodiment,
The present invention can also be applied to detection of the remaining amount of toner in a density control method for changing an image density by changing an AC voltage component such as a peak-to-peak voltage and a frequency of a developing bias.

Embodiment 3 In Embodiment 2, a plurality of developing units 3M of a color image forming apparatus are used.
A plurality of reference voltages are provided when detecting the remaining amount of toner of ~ 3B. However, providing a plurality of reference voltages by changing the reference voltage according to each of the developing devices 3M ~ 3B has a large variation and the detection of the remaining amount of toner. Circuits are also expensive.

Therefore, in the present embodiment, the reference voltage is the same for the plurality of developing units 3M to 3B, and if the remaining amount of toner in each of the developing units 3M to 3B is the same, the current induced in each detection rod 14 The duty ratio for the AC voltage of the developing bias is set separately according to the impedance of the toner of the developing devices 3M to 3B so that the values are equal. Therefore, the same remaining amount detecting circuit can be used for the developing units 3M to 3B.

In this embodiment, since the same remaining amount detecting circuit and the same reference voltage are used in the plurality of developing units 3M to 3B, the detection error can be reduced and the detecting circuit can be made inexpensive. Can be.

In the case where non-magnetic toner is used for magenta, cyan, and yellow and magnetic toner is used for black, the impedance of the non-magnetic toner is generally higher than that of the magnetic toner. The duty ratio on the −) side is 50% for the non-magnetic toner and 2 for the magnetic toner.
5% was applied to the developing sleeve 3a, and the remaining amount of toner was detected. As a result, the toner remaining amount detection voltage can be equalized in the four developing devices 3M to 3B, and the remaining toner amount can be detected with the same reference voltage.

In the above description, the detection of the remaining amount of toner has been described in the developing method in which the image density is changed by changing the duty ratio of the developing bias. The present invention can also be applied to the detection of the remaining amount of toner in the developing method in which the image density is changed by changing the voltage component.

Embodiment 4 This embodiment is different from Embodiment 2 in that when detecting the remaining amount of toner in the developing units 3M to 3B, a developing bias having the same duty ratio for the AC voltage is applied to these developing sleeves 3a. However, at this time, when the remaining toner amounts of the developing devices 3M to 3B are equal, the developing sleeve 3a is previously set so that the current values induced in the respective detection rods 14 are the same.
The detection rod 14 was installed at a different distance.

When a non-magnetic toner is used for magenta, cyan, and yellow and a magnetic toner is used for black, the impedance of the non-magnetic toner is generally higher than that of the magnetic toner, so that the non-magnetic toner is used in the developing units 3M to 3Y. The distance La between the developing sleeve 3a and the detecting rod 14 is smaller than the distance Lb between the developing sleeve 3a and the detecting rod 14 in the developing unit 3B for magnetic toner, that is, La <Lb.

In this embodiment, the toner remaining amount detection voltage can be made equal in the four developing units 3M to 3B, and the toner remaining amount can be detected by the same reference voltage.

Also in this embodiment, the present invention can be applied to the detection of the remaining amount of toner in the developing method of changing the image density by changing the AC voltage components such as the peak-to-peak voltage and the frequency of the developing bias.

In the first to fourth embodiments described above, an example is shown in which one toner remaining amount detection rod 14 is provided in the developing container 3c. However, a plurality of detection rods 14 may be provided.
Further, the detection rod 14 may rotate and have a function of stirring the toner.

[0087]

As described above, according to the present invention,
Density control means for controlling the density of a visible image by changing at least one of a plurality of components of an AC voltage of a voltage obtained by superimposing an AC voltage and a DC voltage applied to a developer holding member of a developing means. In the image forming apparatus provided with
A detecting member is provided in the developing unit, and an induced current flowing through the detecting member is detected by an AC voltage applied to the developer holding member, and when detecting the remaining amount of the developer, the remaining amount of the developer other than the image forming process is used. An amount detection process is provided, and in the developer remaining amount detection process, a plurality of components are set to a predetermined constant value in the developer holding member regardless of a change in the AC voltage component during the density control by the density control unit. Since the AC voltage is applied and the remaining amount of the developer is detected by the induced current flowing through the detecting member, accurate detection of the remaining amount of the developer can be performed stably,
Further, with good density control, it is possible to obtain an appropriate image density and a clear image without fog even with a small particle size toner.

In an image forming apparatus having a plurality of developing means, instead of applying an AC voltage having a plurality of components to a predetermined constant value to a developer holding member of each developing means, each developing means is provided with a plurality of developing means. By applying an alternating voltage in which at least one of a plurality of components is changed to the developer holding member, the currents induced in the detecting members of the respective developing units are made equal to each other. When the induced current flowing through the developing device is converted into a voltage and compared with the reference voltage, the same reference voltage can be used, and the remaining amount of the developer in each developing unit can be detected at low cost and with high reliability.

[Brief description of the drawings]

FIG. 1 is a diagram showing a developing bias waveform and an image potential setting in an embodiment of the image forming apparatus of the present invention.

FIG. 2 is a diagram showing the relationship between image density (line width) and fog in the embodiment of FIG. 1 together with the case of a conventional example.

FIG. 3 shows the electric field intensity a1 = 4.46 in the embodiment of FIG.
The relationship between the duty ratio on the (V−) side of the developing bias and the image density at V / μm is expressed by the conventional electric field intensity a2 =
3.75 V / μm and an intermediate electric field intensity a0 =
It is a figure shown in comparison with the case in 4.1V / micrometer.

FIG. 4 shows the electric field intensity b1 = 2.86 in the embodiment of FIG.
FIG. 10 is a diagram illustrating a relationship between the fog and the duty ratio on the (V−) side of the developing bias when the electric field intensity is changed with respect to V / μm.

FIG. 5 shows the electric field strength c1 = 2.14 in the case of the embodiment of FIG.
The relationship between the duty ratio and the fog amount on the (V +) side of the developing bias at V / μm is expressed by the conventional electric field strength c2 =
3.57 V / μm and the intermediate electric field strength c0 =
It is a figure shown in comparison with the case of 2.8V / μm.

FIG. 6 is an explanatory diagram illustrating a detection principle of a toner remaining amount detection unit provided in the image forming apparatus of the present invention.

FIG. 7 is a diagram showing an AC voltage with a duty ratio of 50% applied to a developing sleeve of the developing unit and a current flowing through a detection rod of the remaining toner amount detecting unit at that time in the embodiment of FIG.

FIG. 8 is a diagram showing an AC voltage having a duty ratio of 25% applied to a developing sleeve of the developing unit and a current flowing through a detection rod of the remaining toner amount detecting unit at that time in the embodiment of FIG.

9 is a diagram showing a sequence of toner remaining amount detection and image formation in the embodiment of FIG.

FIG. 10 is a schematic view showing another embodiment of the image forming apparatus of the present invention.

FIG. 11 is a schematic view showing a conventional image forming apparatus.

12 is a diagram illustrating a developing bias waveform and an image potential setting in the image forming apparatus of FIG. 11;

13 is a diagram illustrating a numerical example of a developing bias waveform and an image potential setting of FIG. 12;

FIG. 14 is a diagram illustrating a charge amount distribution of toner on a developing sleeve of a developing device installed in the image forming apparatus of FIG. 11;

[Description of Signs] 1 Image carrier 2 Charging roller 3 Developing device 3a Developing sleeve 3M to 3B Developing device 7 Toner 14 Detecting rod 30 Intermediate transfer member 65 Developer detecting voltage 66 Comparator 67 Reference voltage P Transfer paper

Claims (10)

[Claims] An electrostatic latent image formed from an image carrier and a dark potential portion and a bright potential portion obtained by charging and exposing the surface of the image carrier is exposed to a developer. Developing means for developing and visualizing, density controlling means for controlling the density of the obtained visible image, and detecting means for detecting the remaining amount of the developer in the developing means, wherein the developing means comprises an image carrier And a developer holding member opposed to the image carrier with a predetermined gap therebetween, and the development is performed by applying a voltage obtained by superimposing an AC voltage between the developer holding member and the image carrier. The density control unit controls the density of the visible image by changing at least one of a plurality of components constituting an AC voltage applied to the developer holding member, and the developer amount detection unit Is a rod-shaped detection member arranged in the developing means in parallel with the developer holding member. An image forming apparatus having a member, wherein the detection of the remaining amount of the developer is performed by measuring a current induced in the detection member by an AC voltage to the developer carrier; A developer remaining amount detection process is performed as a process other than the formation process, and in the developer remaining amount detection process, the developer holding member is independent of a change in an AC voltage component during density control by the density control unit. An image forming apparatus for detecting the remaining amount of the developer by applying an AC voltage in which the plurality of components are set to a predetermined constant value. 2. An electric field between the peak voltage of the peak value of the AC voltage at which the developer is caused to fly to the image carrier and the bright portion potential portion is at least 4.1 V / μm, and the peak at which the developer is caused to fly is provided. The electric field between the voltage and the dark potential section is 3.5 V / μ
m or less, the electric field between the peak voltage on the side where the developer is pulled back from the image carrier and the dark portion potential portion is 2.8 V / μm or less, and when the density control is performed by the density control means, the AC voltage is changed. The component is the duty ratio of the AC voltage,
2. The image forming apparatus according to claim 1, wherein the duty ratio is changed in a range of 20 to 50% on the flight side. 3. An electrostatic latent image formed from an image bearing member and a dark potential portion and a bright potential portion obtained by charging and exposing the surface of the image bearing member using a developer. A plurality of developing means for developing and visualizing, a plurality of density control means for controlling the density of the obtained visible image, and a plurality of detecting means for detecting the remaining amount of the developer in each developing means. Wherein each of the developing means has a developer holding member opposed to the image carrier with a predetermined gap therebetween, and the developing is performed by applying an AC voltage between the developer holding member and the image carrier. Is applied by applying a voltage on which the visible image is superimposed, by changing at least one of a plurality of components constituting an AC voltage applied to the developer holding member. The developer amount detecting means controls the density of the developer, and the developer amount detecting means stores the developer in the developing means. An image forming device that has a rod-shaped detection member disposed in parallel with the holding member, and that the remaining amount of the developer is detected by measuring a current induced in the detection member by an AC voltage applied to the developer carrier; In the apparatus, the image forming apparatus has a developer remaining amount detection process as a process other than the image forming process, and in the developer remaining amount detection process, a change of an AC voltage component at the time of density control by the density control unit. Irrespective of the above, an AC voltage in which the plurality of components are set to a predetermined constant value is applied to a developer holding member of each of the developing units, and the remaining amount of the developer is detected. . 4. An electric field between the peak voltage of the peak value of the AC voltage at which the developer is caused to fly to the image carrier and the bright portion potential portion is at least 4.1 V / μm, and the peak at which the developer is caused to fly is provided. The electric field between the voltage and the dark potential section is 3.5 V / μ
m or less, and the electric field between the peak voltage on the side where the developer is pulled back from the image carrier and the dark potential portion is 2.8 V / μm or less. 4. The image forming apparatus according to claim 3, wherein the component to be changed is a duty ratio of the AC voltage, and the duty ratio is changed in a range of 20 to 50% on the flight side. 5. The method according to claim 1, wherein the current induced in the detecting member of each of the developing units is converted into a voltage and measured, and each of the measured voltages is compared with a respective reference voltage to detect the remaining amount of the developer. The image forming apparatus according to claim 3, wherein the image forming apparatus performs the operation. 6. Instead of applying an AC voltage in which the plurality of components have a predetermined constant value to the developer holding member of each of the developing units, the currents induced in the detecting members of the respective developing units become the same. As described above, an AC voltage in which at least one of a plurality of components is changed is applied to the developer holding member of each of the developing units, and the measured voltages are compared with the same reference voltage, and the remaining amount of the developer is compared. 6. The image forming apparatus according to claim 5, wherein the amount is detected. 7. The image forming apparatus according to claim 6, wherein the component that changes the AC voltage is a duty ratio of the AC voltage. 8. An alternating voltage in which the plurality of components are set to a predetermined constant value is applied to a developer holding member of each of the developing units, and at that time, the same current is induced in the detection member of each of the developing units. The distance between the detection member of each of the developing units and the developer holding member is changed, and the measured voltages are compared with the same reference voltage to detect the remaining amount of the developer. The image forming apparatus according to claim 5, wherein the operation is performed. 9. The method according to claim 3, wherein the step of temporarily transferring the visible image obtained by the development to an intermediate transfer member is repeated for a plurality of colors, and thereafter, the visible images for a plurality of colors are collectively transferred to a transfer material. Item 8. The image forming apparatus according to any one of Items 8. 10. The image forming apparatus according to claim 1, wherein the average particle diameter of the developer is 6.5 μm or less.