JP3515864B2 - Electrostatic latent image 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 an electrostatic latent image developing device.

[0002]

2. Description of the Related Art As an electrostatic latent image developing device for developing an electrostatic latent image formed on a latent image bearing member such as a photoconductive photosensitive member, one using a developer made of powdery one-component toner is known. It is known (Japanese Patent Laid-Open No. 64-62675).

In a developing apparatus using a powdery one-component toner, generally, a toner is supplied to a developing roller by a supply roller and a thin layer forming roller regulates the layer thickness to form a uniform thin layer of toner on the peripheral surface of the developing roller. The formed thin layer of toner is conveyed to the developing unit by the rotation of the developing roller and provided for development.

In order to perform good development with such an electrostatic latent image developing device, the function of the thin layer forming roller for forming a thin layer of toner on the peripheral surface of the developing roller is always kept in good condition. is necessary. The main cause of deteriorating the function of the thin layer forming roller is that the toner adheres to the peripheral surface of the thin layer forming roller with time. Therefore, it is necessary to take measures to prevent the toner from sticking to the thin layer forming roller.

In the electrostatic latent image developing device described in Japanese Patent Laid-Open No. 64-62675, the edge portion of the toner scraping blade is brought into pressure contact with the peripheral surface of the thin layer forming roller so that the toner is adhered to the peripheral surface of the thin layer forming roller. The toner is prevented from sticking by preventing it from adhering and accumulating. Although this method is effective, since a large frictional resistance acts on the rotation of the thin layer forming roller, the driving torque of the thin layer forming roller becomes large and the mechanical energy consumption in the electrostatic latent image developing device becomes large. turn into.

Another known method for preventing toner from sticking to the peripheral surface of the thin layer forming roller is to reduce the stress of the toner that causes toner sticking in the electrostatic latent image developing device. (Japanese Patent Laid-Open No. 6-214452). This method is also considered effective, but it is not always easy to mechanically adjust the electrostatic latent image developing device to conditions that reduce the stress on the toner, and it is also easy to maintain the adjustment state for a long time. Not.

[0007]

SUMMARY OF THE INVENTION According to the present invention, the state of the thin layer forming roller can always be kept in a good state without using an auxiliary member such as a toner scraping blade, and a mechanical adjustment therefor. It is an object to realize an electrostatic latent image developing device that is also easy.

[0008]

The electrostatic latent image developing device of the present invention is an apparatus for "visualizing an electrostatic latent image formed on a latent image carrier by a developer made of powder of one component toner. And has a developing roller, a supply roller, and a thin layer forming roller (claim 1).

The "developing roller" rotates while holding the toner on the peripheral surface in a thin layer, and conveys the held toner to the developing section. The “supply roller” contacts the developing roller via the toner and supplies the toner to the peripheral surface of the developing roller.

The "thin layer forming roller" regulates the layer thickness of the toner supplied to the peripheral surface of the developing roller to realize a thin layer of toner having a desired layer thickness on the peripheral surface of the developing roller.

The thin layer forming roller elastically comes into pressure contact with the developing roller and the supply roller via the toner. The supply roller has a relative peripheral speed difference at the contact portion with respect to the thin layer forming roller, and scrapes off the toner adhering to the peripheral surface of the thin layer forming roller by frictional force. In this way, it is possible to prevent toner from remaining on and adhering to the peripheral surface of the thin layer forming roller,
The condition of the peripheral surface of the thin layer forming roller can always be kept in the initial good condition.

The "pressure contact force of the thin layer forming roller against the supply roller and the developing roller" is set to an appropriate value in advance,
The adjustment may be set at the time of shipment of the image forming apparatus, but a pressure contact force adjusting mechanism for adjusting the pressure contact force may be provided so that the adjustment can be performed at any time ( claim 3 ). This pressure contact force can be made to "act on the thin layer forming roller" ( claim 4 ). In this case, the "pressure contact force with respect to the developing roller" and the "pressure contact force with respect to the supply roller" may be adjusted independently, or the "independent force" is applied to the thin layer forming roller so that the magnitude and direction thereof are changed. It is also possible to adjust and set the pressure contact force to the developing roller and the supply roller.

In the above-mentioned electrostatic latent image developing device , "voltage applying means" is provided, an electric field "direction of pushing the toner from the supply roller and the thin layer forming roller toward the developing roller", and "from the thin layer forming roller". The electric field in the direction of pushing the toner toward the supply roller can be applied ( claim
Item 5 ) As described above, while electrically promoting the toner supply from the supply roller to the developing roller, the removal of the toner adhering to the thin layer forming roller by the supply roller can be electrically promoted.

In the electrostatic latent image developing device according to the first aspect, the developing roller, the supply roller, and the thin layer forming roller "rotate in the same direction ", and the electrostatic latent image developing device according to the second aspect.
, The developing roller and the thin layer forming roller rotate in the same direction, and the supply roller rotates in the opposite direction to the both rollers .

The surface roughness of the peripheral surfaces of the developing roller and the thin layer forming roller is Ra, and can be set to an appropriate value of 40% or less of the average particle diameter of the toner ( claim 6 ). The latent electrostatic image developing device of the present invention "is rotated by one short time thin layer forming roller to the forward and reverse directions, stripping the toner staying on the developing roller a developing roller cleaning mode" may have (claim 7, 8 ).

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a latent image carrier 4 which is a photoconductive photosensitive member forms an electrostatic latent image by a known appropriate method and rotates in the arrow direction to develop an electrostatic latent image. The powder is visualized by the device as a developer by the one-component toner 7. The obtained visible image is transferred and fixed on the recording paper by an appropriate transfer method. Development hopper 10 for storing a predetermined amount of toner 7
In addition to the developing roller 1, the thin layer forming roller 2 and the supply roller 3, an agitator 5 and a pressure adjusting mechanism 6 are provided inside. The thin layer forming roller 2 is elastically pressed against the developing roller 1 and the supply roller 3 via the toner 7. That is, the press contact force adjusting mechanism 6 applies an adjustable press contact force: F to the shaft center of the thin layer forming roller 2 ( claim 3,
4 ). The press contact force adjusting mechanism 6 is capable of rotating and adjusting as shown in the figure with the shaft portion of the thin layer forming roller 2 as the center of rotation.
By this rotation adjustment, the direction of the pressure contact force F can be changed. Therefore, by adjusting the “size and direction” of the pressure contact force F, the thin layer forming roller 2 can be pressed against the developing roller 1 and the supply roller 3 with a desired pressure contact force, and the development can be performed by adjusting the pressure contact force. It is possible to adjust the “charge amount” and “thin layer thickness” of the toner on the roller, and it is possible to effectively deal with the case where the charging characteristics of the toner change due to environmental changes. Pressure contact force: F is preferably in the range of 10 to 80 g / cm.

When the agitator 5 is rotated as shown,
The agitator 5 sends the toner 7 toward the supply roller 3 while stirring and frictionally charging the toner 7. The agitated toner 7 is captured on the peripheral surface of the supply roller 3, moves with the rotation of the roller 3, and is supplied to the peripheral surface of the developing roller 1. At this time, the toner 7 is frictionally charged by friction with the developing roller 1 and is held on the peripheral surface of the developing roller 1.

The toner 7 held on the developing roller 1 moves as the developing roller 1 rotates, and is triboelectrically charged while being regulated by the thin layer forming roller 2 to form a uniform thin layer. In this way, a "uniform thin layer of uniformly charged toner" is formed on the peripheral surface of the developing roller 1. The uniform thin layer of the toner 7 is conveyed to the developing section (the portion where the developing roller 1 and the latent image carrier 4 are in proximity or in contact) by the rotation of the developing roller 1 and is provided for development. The toner 7 attached to the thin layer forming roller 2 when the toner layer thickness on the developing roller 1 is regulated is peeled off from the peripheral surface of the thin layer forming roller 2 by the supply roller 3 and removed.

As the toner 7, either magnetic toner or non-magnetic toner can be used, and high resistance toner or low resistance toner can be used. The developing roller 1 can be configured as a metal roller made of aluminum or stainless steel,
A silicone rubber, an ethylene propylene (EPDM) rubber, a butadiene rubber, a hydrin rubber or the like “rubber material” or a nylon or polyimide or the like “resin material” may be configured to have a certain degree of hardness. When "magnetic toner" is used as the toner, it is necessary to form a "magnetic field for magnetically retaining the toner on the peripheral surface of the developing roller", but when the developing roller is a metal roller,
A permanent magnet may be provided in the inner space of the metal sleeve forming the roller peripheral surface to generate the above magnetic field. When the developing roller is a rubber roller or a resin roller, ferrite is mixed in rubber or resin of the roller material. Then, the magnetic field can be generated.

The surface of the developing roller 1 may be coated with a resin such as silicon in order to obtain a specific charging characteristic and a specific resistance value, and the "volume resistivity" is 10 ⁰ depending on the composition of the resin and the coating thickness. It can be adjusted within the range of 10 ¹² Ω · cm.

The thin layer forming roller 2 is advantageously made of a rubber material such as silicon rubber, ethylene propylene rubber or hydrin rubber and has a relatively low hardness. However, the developing roller 1 is made of a rubber roller and has a relatively low hardness. In this case, the thin layer forming roller 2 may be a metal roller. When the thin layer forming roller 2 is a rubber roller, its hardness is 30
60 degrees, the resistance can be used in a relatively wide range of ^{10 0} ~10 10 Ω · cm.

The peripheral surface of the supply roller 3 is made of "compressible elastic material". A polyurethane foam material is suitable as a material forming the peripheral surface portion. The surface of the supply roller 3 is
The peripheral surface portion may have a suitable roughness, and the peripheral surface portion may have a sponge-like small hole or a rubber peripheral surface mechanically roughened.

The surfaces of the developing roller 1 and the thin layer forming roller 2 are relatively finely roughened by sandless blasting or a polishing sheet so as to easily hold the toner, but the surface roughness is R.
It is preferable that "a" is "30 to 40% of the average particle diameter of the toner" ( claim 6 ). As described above, since the developing roller 1 and the thin layer forming roller 2 are elastically pressed against each other “through the toner”, when both rollers rotate with a relative peripheral speed difference,
The powder toner present between the two rollers acts as a "lubricant", enabling smooth rotation of both rollers. However, when the surface roughness of each of these rollers exceeds 40% of the average particle diameter of the toner, the relatively small particle diameter of the toner particles is fitted into the concave and convex portions on the peripheral surface of the roller. Become. In such a case, a portion where the peripheral surface of the developing roller and the peripheral surface of the thin layer forming roller come into direct contact with each other, the frictional force between both rollers increases, and the driving torque of the developing roller and the thin layer forming roller remarkably increases. Therefore, a powerful motor will be needed as a drive source.

As in the case of implementing the invention described in claim 5 , between the supply roller 3 and the developing roller 1, the supply roller 3 is provided.
When an "electric field" is generated between the thin layer forming roller 2 and the thin layer forming roller 2, carbon black or the like is mixed in the rubber elastic material forming the peripheral surface portion of the supply roller 3 to reduce the electric resistance of the peripheral surface portion to 10 ⁵
Ω · cm or less, the thin layer forming roller 2 also
When this is used as a rubber roller, carbon black or the like can be mixed into the rubber material to adjust the electric resistance of the peripheral surface portion to a desired value.

The pressure contact force between the developing roller 1 and the thin layer forming roller 2 is about 0.05 to 0.1 mm when the one of them is a metal roller and the other is a rubber roller of relatively low hardness. Is suitable. When the pressure contact force between the two exceeds the above-mentioned level, the drive torque in the drive system remarkably increases, and when the pressure contact force is less than the above-mentioned level, "deviation" due to mechanical error between members causes the formation on the peripheral surface of the developing roller 1. Non-uniformity occurs in the thin layer thickness of the toner
Proper development cannot be performed. As for the pressure contact force between the thin layer forming roller 2 and the supply roller 3, it is appropriate that the thin layer forming roller 2 "cuts into the supply roller 2" to have a size of digging into the supply roller 2.

The supply roller 3 has a relative peripheral speed difference at the contact portion with respect to the developing roller 1 and the thin layer forming roller 2. When the peripheral speed of the developing roller 1 is 1, the peripheral speed of the supply roller 3 is 0.7 to 1 (the supply roller 3 is the developing roller 1).
If the rollers are rotated in the same direction as the above, even if the peripheral speeds of both rollers are the same, a peripheral speed difference occurs between the contacting portions thereof, and the peripheral speed of the thin layer forming roller 2 is preferably 0.3 to 0.8. Is.

When the pressure contact force and the peripheral speed difference between the three rollers are appropriately set as described above, the toner is uniformly and favorably charged due to stirring and friction with each roller, and the thin layer forming roller 2
As a result, a “toner layer having a uniform thickness” is formed on the peripheral surface of the developing roller 1. The peripheral surface of the thin layer forming roller 2 is rubbed by the supply roller 3 to scrape off the adhered toner by a frictional force, so that the toner is always prevented from sticking and is kept in a good state. Further, this frictional force does not generate a large resistance torque to the thin layer forming roller 2.

In the case of carrying out the invention described in claim 5 , the voltage applying means 8 as shown in FIG. 2 is used to direct the toner (in the example shown in the drawing, negative toner) from the supply roller 3 and the thin layer forming roller 2 toward the developing roller 1. The electric field acts in a direction of pushing the toner) and the electric field acts in a direction of pushing the toner from the thin layer forming roller 2 toward the supply roller 3. By applying the electric field in this way, it is possible to easily and surely supply the toner to the developing roller 1, and to electrically promote the toner peeling from the thin layer forming roller 2 by the supplying roller 3.

On the basis of the bias potential (negative polarity) applied to the developing roller 1 for development, the potential applied to the thin layer forming roller 2 is about −30 to −100 V, which is a minus potential. And the potential applied to the supply roller 3 is −100 to 200 than the bias potential.
A potential of minus about V is suitable.

In the embodiment shown in FIG. 1, all of the developing roller 1, the thin layer forming roller 2 and the supply roller 3 are rotated in the same direction (counterclockwise) ( claim 1 ), but in the embodiment shown in FIG. By rotating the supply roller 3 in the clockwise direction, the supply roller 3 is in the opposite direction to the rotation direction (counterclockwise direction) of the other two rollers ( claim 2 ).

1 and 2, in the space 9 surrounded by the three rollers, the toner peeled off from the developing roller 1 by the thin layer forming roller 2 and the thin layer forming roller 2 are removed. The toner peeled off by the supply roller 3 (see FIG.
Toner) (in the case of FIG. 2) brought in by the rotation of the supply roller 3, and these toners are mainly caused by the rotation of the thin layer forming roller 2 and the supply roller 3.
It is discharged from the space portion 9 to the outside.

In the embodiment shown in FIG. 1, the thin layer forming roller 2 is used.
And the supply roller 3 rotate in the same direction, and the peripheral surfaces move in opposite directions at their contact portions, so that toner is discharged from the space 9 (is discharged in the rotational direction of the roller having a high peripheral speed).
It is difficult to increase the efficiency of the above, and the accumulation of toner in the space 9 is likely to increase. However, in the embodiment of FIG. 2, the movement direction of the peripheral surfaces of both rollers is at the contact portion between the thin layer forming roller 2 and the supply roller 3. Since they are in the same direction, the toner can be efficiently discharged from the space portion 9.

The toner formed as a thin layer on the peripheral surface of the developing roller 1 is used for development when passing through the "developing section", and the toner passing through the developing section without contributing to the development is supplied to the supply roller. It is rubbed by 3 and peeled off from the developing roller 1. This "peeling" is not always performed 100%. In particular, in the embodiment of FIG. 2, it is difficult to increase the efficiency of the above-mentioned peeling because the peripheral surfaces of both the developing roller 1 and the supply roller 3 move in the same direction at the contact portion.

As described above, the toner is likely to gradually accumulate on the peripheral surface of the developing roller 1 over time, even if it is not fixed. Therefore, the thin layer forming roller 2 can be rotationally driven in both forward and backward directions, and the "developing roller cleaning mode in which the thin layer forming roller is rotated in both forward and backward directions for a short time to remove the toner accumulated on the developing roller" is set. It is possible to perform the above-mentioned mode periodically or as needed to restore the state of the peripheral surface of the developing roller 1 to the initial state ( claims 7 and 8 ).

[0035]

EXAMPLE An electrostatic latent image developing device as shown in FIG. 1 was constructed.

The toner 7 is a "color compatible magnetic toner", that is, a resin containing polyester, polyol, styrene-acryl, etc. as the main component, and silica as an external additive in addition to the coloring material and the charge polarity control agent. A toner to which ferrite, magnetite, or the like was added in order to impart magnetism was used. The particle size distribution range is 4 to 10 μm, the average particle size is 7.5 μm, and the volume resistivity is 10 ¹² Ω · cm or more, which is a relatively high resistance and is negatively charged.

The developing roller 1 is an aluminum roller having a diameter of 20 mm, and a permanent magnet for forming a magnetic field is provided in the inner space of the aluminum sleeve. Thin layer forming roller 2
Is made of rubber material, diameter: 15mm, resistance: 1
It is 0 ⁵ Ω · cm. The supply roller 3 is made of polyurethane foam material (having a resistance of 10 ⁵ Ω · cm or less mixed with carbon black) on the peripheral surface of the core metal roller. Thickness: 4.5 m
The diameter is 15 mm, and the peripheral surface has a sponge-like small hole structure.

By setting the pressure of these three rollers 1, 2 and 3 to an appropriate pressure within the range of the pressure contact described above, the developing roller 1 is 0.05 with respect to the thin layer forming roller 2.
The thin layer forming roller 2 bites into the supply roller 3 by approximately 2 mm. The pressure contact force was set as described above using the pressure contact force adjusting mechanism 6 shown in FIG.

As shown in FIG. 1, all the three rollers 1 to 3 are rotated counterclockwise, the peripheral speed of the developing roller 1 is set to 100 mm / sec, and the peripheral speed of the thin layer forming roller 2 is 30. ˜80 mm / sec, and the peripheral speed of the supply roller 3 was appropriately set in the range of 70 to 100 mm / sec.

Further, according to the average particle diameter of the toner: 7.5 μm, the surface roughness of the peripheral surfaces of the developing roller 1 and the thin layer forming roller 2 is 3 μm or less, which is 40% or less of the above average particle diameter in Ra. Ra was set to 2.5 μm as an appropriate roughness.

Furthermore, by using the voltage applying means 8 as shown in FIG. 2, the bias voltage (negative polarity) of the developing roller 1 is used as a reference, and the thin layer forming roller 2 is more -30 to 10 than that.
Applying a potential of less than 0V to the supply roller 3,
A potential of −100 to 200 V less than the bias potential was applied.

The development of the electrostatic latent image was repeated for a long period of time in this way, but good development was always realized, and the surface of the thin layer forming roller 2 was checked with time. It was possible to maintain the state without sticking.

The supply roller 3 supplies toner to the developing roller 1 by scooping up the toner through a sponge-like small hole on the surface. If the toner is clogged in the small hole with time, the supply roller 3 It is considered that the apparent hardness of the peripheral surface portion of the toner increases, the elastic recovery force decreases, and the toner supply function deteriorates. Therefore, as described above, the thin layer forming roller 2 is pressed into the supply roller by about 2 mm and the pressing force is applied. To make it easier for the toner that has entered the small holes to be discharged.

In the above embodiment, the supply roller 3 is rotated clockwise and the pressure contact force between the two rollers is set so that the developing roller 1 bites into the supply roller 3 by about 0.8 to 1.5 mm. , The peripheral speed of the supply roller 3 is 80 to 15
When set to 0 mm / sec (peripheral speed of developing roller 1: 100 mm / sec), the toner charge amount is -3.
~-7μC / g, the supply amount to the developing roller 1 is per unit area 1-1.5 g / cm ^2, it was sufficient to as the charge amount toner supply amount. Further, the surface condition of the thin layer forming roller 2 was always able to maintain the initial good condition.

In each of the above embodiments, the "developing roller cleaning mode" was executed, and the peripheral surface of the developing roller could be kept in a good condition.

[0046]

According to the present invention, a novel electrostatic latent image forming device can be realized. With this configuration, the electrostatic latent image developing device can always keep the peripheral surface of the thin layer forming roller in a good condition at the beginning, so that good development can always be realized. Further, it is not necessary to press the toner scraping blade against the thin layer forming roller, and the toner is present as a lubricant between the three rollers that are in contact with each other, so that each roller can be rotated with a low driving torque, Since the appropriate range of the pressure contact force and the peripheral speed difference is wide, the electrostatic latent image developing device can be easily adjusted and set.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining only a characteristic part of another embodiment of the present invention.

[Explanation of symbols]

1 developing roller 2 Thin layer forming roller 3 supply rollers 4 Latent image carrier 7 toner

Claims (8)

(57) [Claims] 1. A device for visualizing an electrostatic latent image formed on a latent image bearing member by a developer made of powder of one-component toner, the toner being held in a thin layer on the peripheral surface. A developing roller that rotates to convey the toner to the developing unit, a supply roller that contacts the developing roller via the toner and supplies the toner to the peripheral surface of the developing roller, and a toner supplied to the peripheral surface of the developing roller. And a thin layer forming roller that realizes a thin layer of toner having a desired layer thickness on the circumferential surface of the developing roller by controlling the layer thickness of the thin layer forming roller with respect to the developing roller and the supplying roller. The developing roller, the supply roller, and the thin layer forming roller are elastically pressed against each other via toner.
Both rotate in the same direction, and the supply roller has a relative peripheral speed difference at the contact portion with respect to the thin layer forming roller, so that the supply roller has the peripheral surface of the thin layer forming roller. An electrostatic latent image developing device characterized in that the toner adhered to is scraped off by a frictional force. 2. A device for visualizing an electrostatic latent image formed on a latent image bearing member by a developer consisting of powder and one-component toner, the toner being held in a thin layer on the peripheral surface. A developing roller that rotates to convey the toner to the developing unit, a supply roller that contacts the developing roller via the toner and supplies the toner to the peripheral surface of the developing roller, and a toner supplied to the peripheral surface of the developing roller. And a thin layer forming roller that realizes a thin layer of toner having a desired layer thickness on the circumferential surface of the developing roller by controlling the layer thickness of the thin layer forming roller with respect to the developing roller and the supplying roller. The developing roller and the thin-layer forming roller rotate in the same direction due to elastic contact with the toner.
The supply roller rotates in the opposite direction of both rollers.
Since the supply roller has a relative peripheral speed difference at the contact portion with the thin layer forming roller, the supply roller scrapes the toner adhering to the peripheral surface of the thin layer forming roller by frictional force. An electrostatic latent image developing device characterized by being dropped. 3. The electrostatic latent image developing device according to claim 1, further comprising a pressure contact force adjusting mechanism for adjusting a pressure contact force of the thin layer forming roller with respect to the developing roller and the supply roller. Latent image developing device. 4. The electrostatic latent image developing device according to claim 3, wherein the pressing force adjusting mechanism applies a pressing force to the thin layer forming roller. 5. The electrostatic latent image developing device according to claim 1, wherein an electric field is applied in a direction to push the toner from the supply roller and the thin layer forming roller toward the developing roller, and An electrostatic latent image developing device comprising: a voltage applying unit that applies an electric field in a direction of pushing the toner from the thin layer forming roller toward the supply roller. 6. The electrostatic latent image developing device according to claim 1, wherein the surface roughness of the peripheral surface of the developing roller and the thin layer forming roller is
An electrostatic latent image developing device, wherein Ra is set to an appropriate value of 40% or less of the average particle diameter of the toner. 7. An electrostatic latent image formed on a latent image carrier.
Is visualized as a powder with a developer of one-component toner
A device that holds the toner in a thin layer on the peripheral surface and rotates to remove the toner.
Develops the toner by bringing it into contact with the developing roller that is conveyed to the developing section and the toner via the toner.
The supply roller supplying the peripheral surface of the roller and the layer thickness of the toner supplied on the peripheral surface of the developing roller are regulated.
A thin layer of toner with the desired layer thickness on the peripheral surface of the developing roller.
A developing roller and a supplying roller.
Is elastically pressed against the toner through the toner, and the supply roller is in contact with the thin layer forming roller.
By having a relative peripheral speed difference in
The roller removes the toner attached to the peripheral surface of the thin layer forming roller.
It is made to scrape off by frictional force, and the thin layer forming roller is rotated in both forward and reverse directions for a short time.
The developing roller that removes the toner that has accumulated on the developing roller.
Static electricity characterized by having a cleaning mode
Latent image developing device. 8. The electrostatic latent image developing device according to claim 1, wherein the thin layer forming roller is rotated in both forward and reverse directions for a short period of time,
An electrostatic latent image developing device having a developing roller cleaning mode for removing the toner accumulated on the developing roller.