JP3318052B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for use in an image forming apparatus such as a copying machine, a facsimile, a printer, and the like. More specifically, the present invention relates to a method in which a developer on a developer carrier is brought into contact with a toner supply member. The present invention relates to a developing device for replenishing toner from a toner replenishing member to a developer on a developer carrier.

[0002]

2. Description of the Related Art It is conventionally known to use a developing device having the above-mentioned structure in an image forming apparatus such as a copying machine, a facsimile, a printer or the like (see, for example, JP-A-59-113).
463 and JP-A-59-111663).

[0003]

In this type of developing device, a bias voltage is applied to each of the developer carrying member and the toner replenishing member, and the toner on the toner replenishing member is moved by the potential difference between the two. To supply the toner to the two-component developer. At this time, breakdown (leakage) occurs through the carrier present between the developer carrier and the toner supply member depending on the potential difference. That is, the developer carrying member, the developer, and the toner replenishing member are brought into a conductive (short) state, and the voltage applied to each of the developer carrying member and the toner replenishing member follows the higher absolute value. , Both have the same potential.

At the time of toner replenishment, since a higher voltage is applied to the toner replenishing member than to the developer carrying member on the charging polarity side of the toner particles, the voltage is applied to the developer carrying member. The development bias voltage VS becomes equal to the supply bias voltage VH applied to the toner supply member, and the development bias voltage is increased. That is, the developing bias voltage largely deviates from a predetermined voltage determined by the relationship between the latent image of the image carrier and the surface potential of the background portion, and causes abnormalities such as band-like background soiling and shading in the image. Will be.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent the deterioration of image quality such as background contamination even when a short circuit occurs between a developer carrying member and a toner supply member. It is to provide a developing device.

[0006]

[0007]

[0008]

[0009]

Means for Solving the Problems To achieve the above object,
According to the first aspect of the present invention, there is provided a developer carrier for carrying a two-component developer having a toner and a carrier, a developing bias voltage applying means for applying a predetermined potential VS to the developer carrier, A toner replenishing member which is carried in a thin layer and partially or wholly has conductivity; and a replenishing bias voltage applying means for applying a predetermined potential different from the potential VS of the developer carrier to the toner replenishing member. A developing device for replenishing toner from the toner replenishing member to the two-component developer on the developer carrier by contacting the two-component developer on the developer carrier with the toner replenishing member; When the output current of the bias voltage application unit becomes larger than a predetermined reference value, the output of the supply bias voltage application unit is stopped, and the supply bias voltage application unit of the toner supply member is electrically floated. In which it characterized in that a control means for state.

According to a second aspect of the present invention, in the developing device according to the first aspect , when the allowable current of the supply bias voltage applying means is IHlimit, the predetermined reference value is IHlim.
Using the value of it, the value of the current IHt by the toner replenished from the toner replenishing member to the developer carrying member is represented by IHlimi
It is characterized by being smaller than the value of t.

[0011]

As shown in FIG. 2 (a), a predetermined potential (including zero potential) applied to the developer carrying member is VS, and a predetermined potential different from VS applied to the toner supply member is VH, Assuming that the potential of the developer carrying member (hereinafter referred to as background suppressing potential) required to suppress the adhesion of the toner to the background at the potential VG on the image carrying member is VGS, VH-VS during image formation.
Is larger than the average absolute value of VGS-VS during image formation, as shown in FIG. 2B, the conductive portion of the developer carrier and the toner replenishing member is in an electrically short state. The absolute value of the potential difference between the potential VG of the background of the image carrier and the potential VS 'of the developer carrier (hereinafter referred to as the background potential) is determined by the potential VG of the background of the image carrier and the background. It becomes smaller than the absolute value ΔVGS of the potential difference from the suppression potential VGS (hereinafter referred to as the background suppression potential), and a band-like background stain or shading occurs at a corresponding position on the image.

[0012]

[0013]

[0014]

Therefore, in the first aspect of the present invention, when the output current of the replenishment bias voltage applying means becomes larger than a predetermined reference value, an electric short circuit occurs between the developer carrier and the toner replenishing member. By determining that the short-circuit state has occurred, it is possible to prevent a change in the potential VS of the developer carrying member when the short-circuit state has occurred. By setting the application unit in an electrically floating state, it is possible to prevent the generation of an electric field that causes the toner to move in the opposite direction from the developer carrier to the toner supply member.

According to the second aspect of the present invention, when the output current of the replenishing bias voltage applying means becomes larger than the permissible current of the replenishing bias voltage applying means than IHlimit, the electric connection between the developer carrier and the toner replenishing member is established. It is determined that a short circuit has occurred, and the output of the replenishment bias voltage applying means is stopped, thereby preventing a change in the potential VS of the developer carrier at the time of the short circuit. By setting the replenishing bias voltage applying unit of the member to an electrically floating state, it is possible to prevent the generation of an electric field such that toner moves in the reverse direction from the developer carrier to the toner replenishing member.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a developing device used in an electrophotographic copying machine (hereinafter referred to as a copying machine) as an image forming apparatus will be described. FIG. 1 is a schematic configuration diagram of a developing device 1 according to the present embodiment. As shown in FIG. 1, a developing roller 2 is provided so that a part thereof is exposed from an opening toward a photosensitive drum 20 as an image carrier. The developing roller 2 includes a plurality of magnets (not shown) at predetermined positions, and includes a developing sleeve 2a and the like which rotate independently of the magnets. And the developing device 1
Inside, a toner supply roller 3 as a toner supply member, an upper conveying screw 6, a lower conveying screw 7, and a developing doctor 8 also serving as a left side wall of the developing device 1 are disposed so as to face the developing sleeve 2a. ing. Further, a sponge roller 9 for supplying toner and a thinning blade 10 are disposed so as to contact the surface of the toner supply roller 3.
An agitator 11 and a toner conveying screw 12 are disposed above the sponge roller 9.

The developing sleeve 2a is made of a conductive non-magnetic material such as aluminum. A developing bias voltage is applied to the developing sleeve 2a by a developing bias power source 4 as a developing bias voltage applying means. I have. The toner replenishing roller 3 includes a core member made of a conductive material such as a metal, and a resistor layer (surface layer) laminated and fixed on a peripheral surface of the core member. Examples of the material of the resistor layer include rubber materials such as NBR (nitrile rubber) and silicone rubber mixed with carbon, and resin materials such as fluororesin. Alternatively, the toner supply roller 3 may be entirely made of metal such as aluminum or stainless steel without providing the resistor layer. The sponge roller 9 may be formed by winding a metal core bar that has been subjected to a conductive treatment by dispersing carbon in foamed polyurethane or the like. As the material of the thinning blade 10, a material having an appropriate elasticity such as a thin metal such as carbon steel, a rubber material such as silicone rubber, and a resin material such as fluororesin is used. The materials for the toner supply roller 3, the sponge roller 9, and the thinning blade 10 are selected in consideration of the charge polarity of the toner, the required charge amount, and the like.

The upper transport screw 6 is surrounded by a gutter-shaped screw casing 30 and rotates in a predetermined direction to transfer a two-component developer (hereinafter referred to as developer) in the screw casing 30 from the back side to the front side. It is designed to be transported. The screw casing 30 has an opening for taking in the developer at the rear end and an opening for dropping the developer at the front end, each having a length of about 10 mm in the front-rear direction. A pumping magnet having a length of about 10 mm in the front-rear direction is disposed above the rear end of the upper conveying screw 6, and the magnetic force of the magnet draws the developer into the screw casing 30 through the opening for taking in the developer. The drug is taken in. The lower transport screw 7 rotates in a predetermined direction in a developer reservoir above the developing roller 2, and transports the developer from the near side to the far side of the developing device 1.

The inside of the developing device 1 has a supply roller seal 13 whose lower end is attached to the unit peripheral wall and whose upper end contacts the toner supply roller 3 at a predetermined pressure, the toner supply roller 3, the thinning blade 10, and a thinner at the lower end. A partition constituted by a blade holder 14 having an upper portion attached to the upper portion of the stratification blade 10 and an upper end portion attached to the peripheral wall of the unit has a developing agitating chamber in which the developing roller 2 and the like are disposed, an agitator 11 and the like. It is partitioned into a toner storage chamber. The toner accommodating chamber accommodates toner sent from a toner tank (not shown) via an upper toner conveying screw 12, and the developing agitating chamber accommodates a developer including a carrier and toner. In the figure,
Reference numeral 16 denotes a right casing that forms the right side surface of the toner storage chamber, reference numeral 17 denotes an upper cover that forms the upper surface of the storage chamber, reference numeral 18 denotes a developer supply port cover that forms the upper surface of the development stirring chamber, and reference numeral 19 denotes Denotes a developing casing constituting the lower surface of the developing stirring chamber.

The toner in the developer is a toner particle alone or a powdery substance to which an additive is added, and the carrier in the developer is, for example, iron powder or each particle thereof coated with a resin. The thing etc. are used.

A developing bias voltage is applied to the developing sleeve 2a of the developing roller 2 rotating counterclockwise by the developing bias power supply 4, and the developing roller is rotated clockwise by the developer carried on the developing sleeve 2a. The electrostatic latent image formed on the photosensitive drum 20 is developed. When this developing operation is performed, the test pattern formed on the photosensitive drum 20 in advance is also developed, and the optical density of the visualized test pattern is measured by the image density detecting element 15 such as an optical image density sensor. Is detected. This detection result is compared with the reference density level, and the current toner density in the developer is determined. If it is determined that the toner density is low, the toner replenishing roller 3 disposed close to the developing roller 2 When the supply clutch is turned on, it rotates counterclockwise.

A sponge roller 9, a thinning blade 10, and a supply roller seal 13 are pressed against the peripheral surface of the toner supply roller 3 over the entire area in the axial direction. The sponge roller 9 rotating at the same time rubs the toner on the toner supply roller 3, is conveyed with the rotation of the toner supply roller 3, and is continuously thinned on the toner supply roller 3 by the thinning blade 10. The toner thinned on the toner replenishing roller 3 is charged with a predetermined polarity, in this example, negative polarity, by a series of frictional actions, and the toner is magnetized and conveyed onto the developing roller 2. It is taken into the developer by contact and electrical action. In this way, the toner is replenished into the developer, and the toner concentration in the developer is kept within a certain range.

The developer having passed between the developing roller 2 and the toner replenishing roller 3 is further transferred to the screw casing 30.
Pass below. At this time, at least a part of the developer on the rear end of the developing roller 2 is
Is taken into the screw casing 30 through the opening for taking in the developer. The taken-in developer is conveyed to the near side by the upper conveyance screw 6 and then falls onto the developing roller 2 from the opening for dropping the developer. The developer and the screw casing 30 from the opening for dropping the developer
The developer that has passed under the screw casing 30 without being taken into the inside forms a developer pool above the developing roller 2, and is moved by the lower conveyance screw 7 in the developer pool to the front side of the developing device 1. Transported to the back side from The developer stirred by the upper and lower conveying screws 6 and 7 is carried on the developing roller 2 by the magnetic force of the developing roller 2, and is regulated to a predetermined thickness by the developing doctor 8. Transported to the department.

As described above, the toner sufficiently charged by the toner replenishing roller 3 is supplied into the developer carried on the developing roller 2, so that the insufficiently charged toner remains on the developing roller 2. The replenishment toner is actually replenished on the developer pool that has been peeled off from the developer reservoir, mixed with the developer in the developer reservoir, agitated and frictionally charged, and then supplied to the developing roller 2 as compared with the conventional developing device. The time until the toner is used for development is short, and the responsiveness of the toner supply control is increased. Further, since there is little need for the toner to be triboelectrically charged by the developer, the total amount of the developer accommodated in the developing device 1 can be reduced as compared with the conventional developing device.

The surface of the toner replenishing roller 3 carries a triboelectrically charged toner, contacts the developer on the developing roller 2, and causes a potential difference between the developing sleeve 2a and the toner replenishing roller 3 (hereinafter, referred to as a toner replenishing roller 3). The toner on the toner supply roller 3 is supplied into the developer by the supply potential. More specifically, the replenishing operation will be described. A developing bias voltage of, for example, −600 (V) is applied to the developing sleeve 2 a by the developing bias power supply 4, and the voltage application unit of the toner replenishing roller 3, that is, in this example, A replenishing bias power source 5 as a replenishing bias voltage applying means applies, for example, -800 to the conductive core member 3a.
The replenishment bias voltage (V) is applied, and the negative toner particles on the toner replenishing roller 3 are drawn toward the developer on the developing roller 2 by the potential difference between the two, and the toner is replenished into the developer. .

FIG. 2A shows the photosensitive drum 2 at this time.
The surface potential distribution V (x) in the circumferential direction of 0, the potential VS of the developing sleeve 2a to which the developing bias voltage is applied, the potential VH of the conductive core member of the toner supply roller 3 to which the supply bias voltage is applied, and the like are shown. Here, VG is the potential of the background portion on the photosensitive drum 20, and VGS is the potential (= background suppression potential) of the developing sleeve 2a necessary to suppress the adhesion of the toner to the background portion. The background suppression potential (= | VGS−VG |), which is the absolute value of the potential difference between the background potential VG and the background suppression potential VGS, is represented by ΔVGS. In the present embodiment, the background potential, which is the potential difference between the potential VG of the background portion on the photosensitive drum 20 and the potential VS of the developing sleeve 2a, is considered in consideration of unevenness of exposure and deterioration of various characteristics with time. It is set sufficiently higher than the background suppression potential ΔVGS. For example, the background potential is set to about twice the background suppression potential ΔVGS.

When the developing bias voltage and the replenishing bias voltage are applied to the developing sleeve 2a and the core member 3a of the toner replenishing roller 3, respectively, the electrical connection between the developing sleeve 2a and the core member 3a is suddenly made. A short circuit state (hereinafter, this state is referred to as a short circuit state). As shown in FIG. 2B, the potential VS 'of the developing sleeve 2a in this short state is the difference between the potential VS of the developing sleeve 2a before the short state and the potential VH of the core member of the toner supply roller 3. Between the potentials. Then, as shown in FIG. 2B, if the potential VS 'of the developing sleeve 2a in the short-circuit state is located between the background suppression potential VGS and the background portion potential VG, a corresponding A band-like background stain or light and shade occurs at the position where the image appears.

Therefore, in the present embodiment, the developing bias power supply 4, the replenishment bias power supply 5, and the like are configured so that background contamination and shading do not occur on the image even when the short circuit occurs suddenly .

For example, as shown in FIG. 3, the developing bias voltage is set so that the average supply potential | VH-VS | during image formation is smaller than the average background suppression potential | VGS-VS | during image formation. and sets the value of the supply bias voltage. As a result, when a short circuit occurs suddenly, the potential VS 'of the developing sleeve 2a becomes a substantially intermediate value between VH and VS before the short state, and the potential VG of the background portion on the photosensitive drum 20 And developing sleeve 2
a potential | VS 'which is a potential difference from the potential VS'
-VG | becomes larger than the background suppression potential | VGS-VS |. Therefore, even if a short circuit occurs suddenly, background stains and shading do not occur on the image.

In a color copying machine or a printer, the background potential cannot be set to be much larger than the background suppression potential in order to accurately reproduce a highlighted portion. Since the absolute value of the potential difference between the surface potential of the image portion on the surface 20 and the potential of the developing sleeve 2a (hereinafter referred to as developing potential) itself is small, the average supply potential | VH-VS | It is desirable to set the average background suppression potential ΔVGS (= | VGS−VS |) to about one-fifth.

Further, for example, the developing device 1 is set so that the background potential | VS'-VG | when the short-circuit state occurs is made larger than the background suppression potential | VGS-VG |.
, For example, the internal output voltage VS0 of the developing bias power supply 4 and the output impedance R
S and the values of the internal output voltage VH0 and output impedance RH of the supply bias power supply 5 are set.

The formula for showing a setting example of the values of [0033] the upper Symbol circuitry
It may be obtained as follows. FIG. 4 shows an electrical equivalent circuit in which the main components of the developing device 1 are taken into consideration. Here, VP is the surface potential of the photosensitive drum 20, RSP
Is the electric resistance of the developer between the developing sleeve and the photosensitive drum,
RSH is the electrical resistance of the developer between the developing sleeve and the toner supply roller, and RHr is the resistor layer (surface layer) of the toner supply roller 3.
Is the electric resistance of the charged toner moving toward the photosensitive drum 20 due to development, and IHt is the current due to the charged toner moving toward the developing sleeve 2a due to toner supply. Also, in order to express the short state equivalently,
Switches SW1 and SW2 for short-circuiting RHr and RSH are connected to each other.

An equation expressing the potential VS of the potential of the developing sleeve 2a based on the equivalent circuit of FIG. Here, RH '= RH + RHr + RSH.

VS = VS0−IS · RS = VS0− {IDt + (VS0−Vp) / RSP− (VH0−VS0 + IH)
tRHr) / RH '} / (1 / RS + 1 / RSP + 1 / RH')

IS, I when not in a normal short state
H, VS, and VH are expressed as in Equations 2 to 5, respectively. Here, WD is the image forming width, vp is the process speed, and (M /
A) D is the toner density (developing amount per unit area) on the photosensitive drum 20, (Q / M) D is the average specific charge of the developed toner,
WH is the toner supply width, vR is the peripheral speed of the toner supply roller 3,
(M / A) H is the toner density (density) on the toner supply roller 3, and (Q / M) H is the average specific charge on the toner supply roller 3. The RSP and RSH respectively include the electrical resistance of the photoconductor itself of the photoconductor drum 20 and the toner supply roller 3.
In general, the values of RSP and RSH when not in a normal short-circuit state are very large, and the current I flowing between the developing sleeve and the photosensitive drum is not included.
D, and most of the current I H flowing between the conductive core member, the developing sleeve of the toner supply roller, a current due to movement of the respective charged toner IDt, to be IHt to.

## EQU2 ## IS = ID−IH ≒ IDt−IHt = WD · vp · (M / A) D · (Q / M) D−IH

## EQU3 ## IH = IHt + IHr ≒ IHt = WH.vR. (M / A) H. (Q / M) H

VS = VS0−RS · IS ≒ VS0−RS · (IDt−IHt)

VH = VH0−RH · IH ≒ VH0−RH · IHt

Specific values (RS = 1) in the above equations 2 to 5
80 kΩ, WD = 300 mm, vp = 75 mm / sec, (M / A) D
= 1 mg / cm ² , (Q / M) D = 20 μc / g, RH = 360 kΩ,
WH = 260 mm, vR = 250 mm / sec, (M / A) H = 0.
Substituting 3 mg / cm ² and (Q / M) H = 4 μc / g), Equations 4 and 5 become as follows.

## EQU6 ## VS = VS0-0.8V

VH = VH0−0.28V

Considering that the background suppression potential is several hundred volts, the voltage drop at the output impedances RS and RH of the power sources 4 and 5 can be ignored. That is, VS ≒ VS0 and VH ≒ VH0.

By the way, the potential difference between VS (background) when developing the background portion of the electrostatic latent image on the photosensitive drum 20 and VS (solid) when developing the solid portion is expressed by the following equation. Can be described as shown in Expression 8.

VS (background) −VS (solid) = IDt (solid) / (1 / RS)
+ 1 / RSP + 1 / RH ')

The fact that the value of VS (background) -VS (solid) in Equation 8 is large means that the potential VS of the developing sleeve 2a changes depending on the solid area ratio of the document, and a stable image cannot be obtained. Means that In order to cope with this inconvenience, it is necessary to make the value of VS (background) -VS (solid) in Expression 8 sufficiently small, and it is sufficient that any one of RS, RSP and RH 'is sufficiently small. Where RSP and RH '
Includes the electrical resistance of the developer itself, the electrical resistance at the contact portion between the photosensitive drum 20 and the developer, and the electrical resistance at the contact portion between the toner replenishing roller 3 and the developer. In practice, the above-mentioned problem is dealt with by making RS sufficiently small. That is, Equation 9 is a condition that RS should satisfy.

[Mathematical formula 9] RS ≪ (VS0−Vp) / IDt (solid)

When the surface charge on the photosensitive drum 20 leaks to the developing sleeve 2a through the developer or conversely, the charge is injected from the developing sleeve 2a onto the photosensitive drum 20 through the developer, an image is formed on the image. Traces of contact of the developer ears may remain. Therefore, in general, in order to stabilize the development, the current I flowing through the developer in the development area is
Dr = (VS−VP) / RSP ≒ (VS0−VP) / RSP must be kept within a certain range. Empirically, this range is substantially the same as the current IDt due to the movement of the charged toner in the development area,
Less than that is desirable. That is, Equation 10 holds.

[Expression 10] IDt ≧ IDr ≒ (VS0−VP) / RSP

In Expression 1, when the conditions shown in Expressions 9 and 10 are taken into consideration, an approximate expression representing the potential VS of the developing sleeve 2a is as shown in Expression 11.

VS = VS0− (VH0−VS0 + IHtRHr) · RS /
(RS + RH + RHr + RSH)

In the short state, not only the electric resistance RHr of the resistor layer of the toner replenishing roller 3 becomes substantially zero, but also the voltage applied to the developer is increased and the developer is easily short-circuited. It can be considered to be almost zero. That is, in FIG. 4, both SW1 and SW2 are ON.
You can think that it becomes. Accordingly, an approximate expression representing the absolute value of the potential VS 'of the potential of the developing sleeve 2a when the short-circuit state occurs is derived from Expression 11, and Expression 12 is obtained.

| VS '| ≒ | VS0 + (VH0−VS0) RS /
(RS + RH) |

In the equation (12), for example, RS / (RS
+ RH) is smaller than | VGS-VS | / | VH-VS |, by setting the values of the circuit elements RS, RH, VS0, and VHO, | VS'-VG |> | VGS-VG. Holds, and the background potential at the time of short-circuiting | V
S'-VG | becomes larger than the background suppression potential | VGS-VS |. Therefore, even if a short circuit occurs suddenly, background stains and shading do not occur on the image.

Using the above equation (11), an equation representing the absolute value ΔVS of the potential difference of the potential of the developing sleeve 2a between when the developing sleeve 2a is not in the short state and when it is in the short state is derived as follows. However, in this example, it is assumed that only SW1 in FIG. 4 is turned ON and only RHr = 0 holds in the short state.

ΔVS = | VH0−VS0 | · RS / | RS + RH + RSH | − | VH0−VS0 + IHt · RHr | · RS / | RS + RH + RHr + RSH |

In the case where there is no normal short circuit, FIG.
As shown in FIG. 5A, VSａVS0, but when a short circuit occurs, VS fluctuates as shown in FIG. 5B, which may adversely affect the image. Therefore, for example, by setting RS to a sufficiently small value in Equation 13, or by setting the value of each circuit element so as to satisfy (RS + RH + RSH) ≒ (VH0−VS0) / IHt, the potential difference ΔVS becomes the predetermined value. , The potential VS of the developing sleeve 2 is stabilized, and as a result, the background potential becomes extremely stable, so that there is no problem on the image. In particular, an original having many halftones such as a color image can be faithfully reproduced. Also, for example, by setting the value of RHr sufficiently smaller than the value of | VH0−VS0 | / IHt, the potential difference ΔVS can be made smaller than the predetermined value.

Further, Rp <| VS−VGS | between the conductive core member of the toner supply roller 3 and the supply bias power supply 5.
/ IS, a protection resistor Rp that satisfies / IS, and RS / (RS + RH
+ Rp) may be set so that the value of each circuit element RS, RH, Rp, VS0, VH0 is smaller than | VGS-VS | / | VH-VS | . As a result, even when a short circuit occurs, the change in the potential VS of the developing sleeve 2a becomes small, and the image is not disturbed. Furthermore, | VS'-VG |>
| VGS-VG | holds, and the ground potential | VS'-VG | at the time of short-circuiting becomes larger than the ground suppression potential | VGS-VS |. Background stains and shading do not occur. "

Setting the values of the circuit elements as described above
On the image when the short-circuit suddenly occurs due to
Although the occurrence of skin stains and shading can be prevented, in the present embodiment , the output current IH of the replenishment bias power supply 5 has its allowable current IHlimi
When the value becomes larger than the value of t, it is determined that a short circuit has occurred, and the control unit that turns off the supply bias power supply 5
It is provided in the supply bias power supply 5. In this way, the supply
By turning off the bias power supply 5, the absolute value of the potential VH of the conductive core member of the toner
A line larger than the absolute value of the potential VG of the background portion on the ram 20
In the matter under, suddenly in a case that became a short state
Also , the potential of the developing sleeve 2a does not change.
Further, even when the short circuit occurs suddenly, an electric field such that the toner moves in the reverse direction from the developing sleeve 2a to the toner replenishing roller 3 is not generated, and the toner replenishment to the developing sleeve 2a sharply decreases. Never do. Further, the value of the current IHt due to the movement of the charged toner supplied from the toner supply roller 3 onto the developing sleeve 2a is determined by the above IHlimit.
Of the toner supply roller 3 and the developing sleeve 2 in a normal case where the short-circuit state is not established.
During the toner replenishment to a, there is no possibility that the output of the replenishment bias power supply 5 is stopped, and an appropriate replenishment operation is maintained. Although the control unit in this example is provided in the supply bias power supply 5, it may be provided separately from the supply bias power supply 5.

In this embodiment , the developing bias power supply 4
When the output current IS is larger than the value of the allowable current ISlimit, or when the output current IH of the replenishment bias power supply 5 becomes larger than the value of the allowable current IHlimit, it is determined that a short circuit has occurred. 4 or a control unit for turning off the supply bias power supply 5 is provided in the supply bias power supply 5, and Rp> | VH-VS | / ISlimit and Rp
<| VH−VS | / IHlimit
Between the conductive core member of the toner supply roller 3 and the supply bias power supply 5, and between the developing sleeve 2a and the development bias power supply 4
May be provided in any one or both . Thus, even when a short circuit occurs suddenly, the potential VS of the developing sleeve 2a can be kept within a range in which background contamination does not occur.

As described above, in this embodiment, the case of the N / P development system using the negatively charged photoconductor and toner has been described. However, the present invention is limited to the charging polarity of the photoconductor and toner. And can be applied to a P / P development system.

[0050]

[0051]

[0052]

[0053]

Effects of the Invention According to the present invention, when the output current of the supply bias voltage applying means is larger than a predetermined reference value, between the developer carrying member and the toner supply member is electrically shorted By stopping the output of the replenishment bias voltage applying means when it is determined that the toner supply member is in the state, the potential of the developer carrying member does not change.
The absolute value of the potential VH is the absolute value of the potential VG of the background portion on the image carrier.
If it is larger than this, there is an effect that background contamination and shading do not occur on the image even if the short circuit occurs suddenly. Further, by setting the supply bias voltage applying section of the toner supply member to an electrically floating state, an electric field such that toner moves in the reverse direction from the developer carrying member to the toner supply member is not generated. There is an effect that the amount of toner supplied to the agent carrier is not suddenly reduced.

According to the invention of claim 2 , in addition to the effect of claim 1 , by setting the value of the current IHt by the toner supplied from the toner supply member to the developer carrying member to be smaller than the value of IHlimit. When toner is supplied from the toner replenishing member to the developer carrying member when there is no electrical short between the developer carrying member and the toner replenishing member, the output of the replenishing voltage applying means may stop. Since it disappears, there is an effect that a proper supply operation is maintained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a developing device according to an embodiment.

FIG. 2A is an explanatory diagram of a surface potential distribution of a photoconductor and potentials of a developing sleeve and a toner supply roller in a developing device according to a conventional example. FIG. 3B is an explanatory diagram of the same surface potential distribution and the same potential when the developing sleeve and the toner supply roller are short-circuited.

FIG. 3 is an explanatory diagram of a surface potential distribution of a photosensitive member and potentials of a developing sleeve and a toner supply roller in the developing device according to the embodiment.

FIG. 4 is an explanatory diagram of an electrical equivalent circuit of the developing device according to the embodiment.

FIG. 5A is an explanatory diagram of a surface potential distribution of a photoreceptor and a potential of a developing sleeve and a toner supply roller in a developing device according to another embodiment. FIG. 3B is an explanatory diagram of the same surface potential distribution and the same potential when the developing sleeve and the toner supply roller are short-circuited.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Developing device 2 Developing roller 2a Developing sleeve 3 Toner replenishing roller 4 Developing bias power supply 5 Replenishing bias power supply 20 Photoconductor drum

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takayuki Maruta 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company Limited (72) Inventor Kazuyuki Sugihara 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Nobuo Takami 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Co., Ltd. (72) Takuji Yoneda 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Inside Ricoh Company (72) Inventor Kaoru Yoshimatsu 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Company (56) References JP-A-2-251875 (JP, A) JP-A-2-278273 (JP, A) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G03G 13/06-13/095 G03G 15/06-15/095

Claims (2)

(57) [Claims] 1. A developer carrier for carrying a two-component developer having a toner and a carrier, and a predetermined voltage applied to the developer carrier.
A developing bias voltage applying means for applying a potential V S, a toner replenishing member which carries the toner in a thin layer and has a part or all of conductivity, and a potential V S of the developer carrier on the toner replenishing member. Replenishing bias voltage applying means for applying a different predetermined potential VH, wherein the two-component developer on the developer carrying member is brought into contact with the toner replenishing member, whereby In the developing device for replenishing toner to the two-component developer, the output current of the replenishment bias voltage applying means is set in advance.
When the replenishment bias becomes larger than a predetermined reference value,
Stopping the output of the voltage applying means, and
The supply bias voltage application section of the
A developing device provided with control means . 2. The allowable current of said supply bias voltage applying means.
Is defined as IHlimit, the value of IHlimit is used as the predetermined reference value,
-Toner supplied from the supply member to the developer carrier
Current IHt is smaller than the value of IHlimit.
The developing device according to claim 1, wherein: