JP5760380B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device and an image forming apparatus.

In an electrophotographic image forming apparatus, a housing for storing a two-component developer composed of toner and a carrier, a developing roll having a function of receiving the developer in the housing and carrying it to the vicinity of the position of the photoreceptor, and the developer in the housing Some include a developer stirring member that stirs internally and a developer conveying member that supplies the stirred developer to the developing roll.
In such a developing device, if the developer is not circulated within the housing, the toner adhering to the photoreceptor may generate uneven density or low-charged toner, which may adversely affect image quality such as fogging. In order to improve the circulation of the developer, there is a technique in which both are arranged so that the distance between the developing roll and the paddle wheel (developer conveying member) becomes a predetermined value (see Patent Document 1). ).

Japanese Patent Laid-Open No. 11-219031

  An object of the present invention is to improve the transport efficiency of a developer from a conveyance body to a developing roll while maintaining the circulation of the developer inside the developing device.

According to the first aspect of the present invention, there is provided the developer filled in the housing such that the height of the powder surface relative to the housing and the bottom surface of the housing is not less than the first value and not more than the second value. When the developing roller consists of a blade provided on the rotary shaft and the rotary shaft, wherein disposed opposite to the developing roller, and a paddle for conveying toward the developer to the developing roll, a bottom surface of said housing Adjusting means for adjusting the amount of the developer in the housing so that the height of the powder surface as a reference is maintained between the first value and the second value; The axis of the rotating shaft is provided at a position lower than the first value with respect to the bottom surface of the housing, and the highest point of the blades with respect to the bottom surface of the housing is higher than the second value. , the paddle, in the highest reaches point The vane Te is rotated in the direction toward the developing roller, wherein a developer a developing unit, characterized in that to carry on said developing roller in the vertical direction above the height of the powder surface.

The invention according to claim 2 further includes drive means for driving the developing roll and the paddle so that a ratio between the rotational speed of the developing roll and the rotational speed of the paddle is within a predetermined range. The developing device is characterized in that the blade has a flat plate shape having one side in a direction parallel to the rotation axis.

Invention of claim 3, wherein the blade is shaped Ri is Do and a first blade and a second blade is the same, normal to the plane of the second blade surface of the first blade The developing unit according to claim 2, wherein the developing unit is parallel to the normal line.

According to a fourth aspect of the present invention, the blade includes a first blade, a second blade, and a third blade, and at least one of the first blade, the second blade, and the third blade. The developing device according to claim 2, wherein a length in a direction perpendicular to the rotation axis is smaller than that of the other blades .

According to a fifth aspect of the present invention, there is provided an electrostatic latent image formed on the photoconductor including the developing device according to any one of the first to fourth aspects, a photoconductor, an exposure device, and a charging device. An image forming unit that develops the toner using a developer supplied from the developing device, a transfer unit that transfers the developed image to a recording medium, and a fixing unit that fixes the transferred image. Forming device .

According to the first to fifth aspects of the present invention, as compared with the case where the height of the developer filled in the housing of the developing device is not maintained in a range determined with respect to the transport body, the transport roll to the developing roll. It is possible to improve the transport efficiency of the developer to and to prevent a decrease in the transport efficiency of the developer from the conveyance body to the developing roll.

2 is a diagram schematically illustrating an internal structure of the image forming apparatus 1. FIG. The top view of the developing device 20b. Sectional drawing of the developing device 20b. 2 is a diagram illustrating functions of the image forming apparatus 1. FIG. The figure showing the other aspect of the paddle 213. FIG. The figure showing the other aspect of the paddle 213. FIG. The figure showing the other aspect of the paddle 213. FIG. The figure showing the other aspect of the paddle 213. FIG.

<Embodiment>
1. Configuration FIG. 1 is a diagram schematically showing the internal structure of an image forming apparatus 1. The image forming apparatus 1 is roughly divided into a sheet storage unit 10, a drum unit 20a, a developing unit 20b, and a fixing unit 30. The developer used in the image forming apparatus 1 is a so-called two-component developer composed of toner (colored particles) finally attached to the paper P and powder that is a carrier for charging the toner. .
The paper feed storage unit 10 accumulates paper P that is an image recording medium. When the printing process is started, the paper P is aligned and transport timing adjusted by the transport rolls 40, 41a, and 41b, and the electrostatic latent image formed by the drum unit 20a is transferred to the transfer roll 42, and heated. The image is fixed by the roll 301 and the pressure roll 302, and is discharged out of the apparatus through the transport rolls 43a and 43b. The drum unit 20a includes a photosensitive drum 201, a charging device 203, an exposure device 202, a toner removing member 204, and the like. The charging device 203 charges the photosensitive drum. The exposure device 202 irradiates the photosensitive drum 201 with laser light based on image data to be formed. As a result, an electrostatic latent image is formed on the photosensitive drum 201. The toner removing member 204 removes excess developer on the photosensitive drum 201.

  FIG. 2 is a diagram of the developing device 20b as viewed from the z direction. FIG. 3 is an enlarged view of the developing device 20b when viewed from the same direction as in FIG. Hereinafter, a description will be given with reference to FIGS. 2 and 3. The developing device 20b includes a housing 217, a first conveying member 211, a second conveying member 212, a paddle 213, a developing roll 214, a layer thickness regulating member 215, and a toner supply port 216. The first transport member 211, the second transport member 212, the paddle 213, and the developing roll 214 each have a rotation shaft in the y direction, and are respectively rotatably fixed to the housing 217 at both ends of the rotation shaft. That is, these members are arranged so that the positions of the rotation axes are in the order of the first conveying member 211, the second conveying member 212, the paddle 213, and the developing roll 214 in the positive direction from the negative x-axis. It arrange | positions so that a rotating shaft may become all parallel. In FIG. 2, the layer thickness regulating member 215 is not shown. Gears (not shown) are provided at the ends of the respective rotation shafts of the first conveyance member 211, the second conveyance member 212, the paddle 213, and the developing roll 214, and the gears are connected to each other, and a motor (not shown). )), Each member rotates about its rotation axis. Since there is a gear connection, the rotation speed ratio (circumferential speed ratio) of each rotary shaft is fixed to a preset value. The rotation speed ratio can be adjusted by changing the size of the gear. For example, if the average of the rotation speeds of the four members of the first transport member 211, the second transport member 212, the paddle 213, and the developing roll 214 is 1, the rotation speed of each member is in the range of 0.8 to 1.2. The size of the gear is determined so that

A partition wall W is provided between the first transport member 211 and the second transport member 212. The partition wall W forms the first storage chamber R1 and the second storage chamber R2. At both ends of the partition wall W in the y direction, connection ports 220L and 220R that connect the first storage chamber R1 and the second storage chamber R2 are formed. The 1st conveyance member 211 consists of the screw-shaped blade | wing 211S formed in the rotating shaft 211a and the rotating shaft. Similarly, the 2nd conveyance member 212 consists of the rotating shaft 212a and the screw-shaped blade | wing 212S formed in the rotating shaft. The paddle 213 includes a rotation shaft 213a and two blades 213f. The developing roll 214 includes a metal member (not shown) serving as a rotation shaft and a magnet roll (not shown) in which a plurality of magnetic poles are arranged in the rotation direction, and a rotating body (surface) in contact with the developer. A cylindrical member having a developing sleeve). The layer thickness regulating member 215 is a cylindrical member made of a magnetic material. The blade 213f is composed of two blades having the same shape and has one side in a direction parallel to the rotation shaft 213a (y direction). The normal of the surface of the first blade and the normal of the surface of the second blade Are parallel (= two blades are fixed in a straight line).
The outer diameters of the first transport member 211 and the second transport member 212 (that is, the length in the direction perpendicular to the rotation axis of the blades) are equal. The outer diameter of the paddle 213 is smaller than the outer diameter of the second transport member 212. The outer diameter of the developing roll 214 is smaller than the outer diameter of the second conveying member 212 and larger than the outer diameter of the paddle 213. The outer diameter of the layer thickness regulating member 215 is smaller than the outer diameter of the paddle 213.

  In the first storage chamber R1, a toner supply port 216 (not shown in FIG. 2) is provided at the end in the y direction on the connection port 220L side, and toner is supplied from a toner cartridge (not shown) as needed. 1 is supplied to the storage chamber R1. The supplied toner is agitated with the carrier in the first storage chamber R1 and charged. The supplied toner is agitated with the carrier by the rotating first conveying member 211 in the first storage chamber R1. At the same time, the first transport member 211 transports the first storage chamber R1 in the direction of arrow A. Part of the developer that has reached the other end in the y direction enters the second storage chamber R2 via the connection port 220R (arrows B and C). The developer that has entered the second storage chamber R2 is transported in the direction of arrow D by the rotating second transport member 212. At this time, a part of the developer being conveyed is guided to the developing roll 214 by the action of the paddle 213 rotating in the direction of the arrow, and moves on the surface of the developing roll 214 as the developing roll 214 rotates. Toner contained in a part of the developer moving on the surface of the developing roll 214 adheres to the photosensitive drum 201 from the developing roll 214 by electrostatic attraction. At this time, the amount of the developer placed on the developing roll 214 is limited by the layer thickness regulating member 215. The remaining toner that has not adhered is lowered on the developing roll 214 with the rotation of the developing roll 214 and is guided to the paddle 213 again. A part of the toner is agitated by the rotation of the paddle 213, and the arrow D Conveyed in the direction. Part of the developer that has arrived at one end in the y direction by the second transport member 212 enters the first storage chamber R1 through the connection port 220L (arrows E and F). In this way, the developer circulates in the developing device 20b, and toner is supplied to the drum unit 20a as necessary.

  As shown in FIG. 3, the developing device 20 b is fixed in the direction perpendicular to the z direction (that is, the horizontal direction) in the image forming apparatus 1. More specifically, the bottom of the housing 217 (the bottom of the portion where the developer is present) is a surface perpendicular to the z direction, so that when the second conveying member 212 is not rotating, the development is performed. The powder surface of the agent is also approximately horizontal. The heights (= positions in the z direction) at which the rotation axes of the first transport member 211, the second transport member 212, the paddle 213, the developing roll 214, and the layer thickness regulating member 215 are fixed are different. Specifically, assuming that the bottom of the housing 217 is a height reference (= zero height), the rotation axes of the first conveyance member 211 and the second conveyance member 212 are provided at the same height. The rotating shaft of the developing roll 214 is provided above the rotating shafts (212a and 213a) of the second conveying member 212 and the paddle 213. The central axis of the layer thickness regulating member 215 is fixed above the rotation axis of the developing roll 214. The rotation shaft 213 a of the paddle 213 is fixed below the rotation shaft 212 a of the second transport member 212.

  In the above arrangement, the height of the developer (hereinafter referred to as “powder surface ht”) is always higher than the axial center position hl of the rotating shaft of the paddle 213 with reference to the bottom of the second storage chamber R2 portion of the housing 217. And the maximum reach point hu of the paddle 213 (= “height at which the rotating shaft 213a is fixed” + “length of the blade 213f”) is maintained below the developer in the housing 217. The amount is controlled. In other words, the paddle 213 is fixed so that the fixed position of the rotation shaft is below ht with respect to the given powder surface ht, and the highest point of reaching the paddle 213 is above ht. The length of the blade 213f is determined.

  In the initial state, the developer is filled so as to be within a predetermined powder surface range as described above. However, the amount of developer decreases with the image forming process. This is because the amount of carrier in the developing device 20b is approximately unchanged, while the toner is consumed every time the image forming process is executed. Therefore, in the image forming apparatus 1, the toner is replenished from the toner supply port 216 so as to supplement the consumed toner so that the powder level of the developer is always kept in the above-described certain range. Yes. As a method of determining the toner replenishment timing and replenishment amount, for example, a sensor for measuring the magnetic permeability is provided in the first storage chamber R1, the concentration of the developer in the first storage chamber R1 is measured, and the result is used. Then, the height of the powder surface in the second storage chamber R2 is calculated. More specifically, the correspondence between the developer concentration and the information such as the rotation speed of the first conveying member 211 and the second conveying member 212 is stored in advance as a table, and the toner is stored by referring to the table. What is necessary is just to determine the timing and quantity of injection | throwing-in. In addition to calculating the amount of developer (powder surface height) from the toner concentration, a contact sensor is provided in the second storage chamber R2 to directly measure the powder surface height in the second storage chamber R2. May be.

  In the above configuration, the paddle 213 is an example of a transport body, the drum unit 20a is an example of an image forming unit, the transfer roll 42 is an example of a transfer unit, and the fixing unit 30 is an example of a fixing unit.

By adopting the arrangement according to the above-described embodiment, the transport efficiency of the developer from the paddle 213 to the developing roll 214 is improved. The reason is as follows. If the maximum reach point of the paddle 213 is less than hl (the maximum reach point of the paddle 213 is located below the powder level ht), the development existing above the maximum reach point of the paddle 213 Since the rotational force of the blade 213f is not transmitted to the agent particles, the ratio of the developer particles carried onto the developing roll 214 is small in the developer conveyed near the paddle 213. In other words, in this situation, since the fixed position of the paddle 213 is too low or the length of the blade 213f is too small with respect to the amount of developer, the amount carried to the developing roll 214 is small, and the paddle 213 to the developing roll 214 is small. The transport efficiency of developer to is not good.
On the contrary, when the fixed position of the rotating shaft 213a of the paddle 213 is above the powder surface ht, the blade 213f and developer particles are in contact with each other at a position lower than the rotating shaft 213a. At this time, the blade 213f is inclined downward from the horizontal, and from this state, most of the developer particles receiving the force due to the rotation of the blade 213f are spilled from the blade 213f while being scraped upward. Thus, the vicinity of the developing roll 214 cannot be reached. That is, in this case, it can be said that the fixed position of the paddle 213 is too high with respect to the amount of the developer. In this case, the developer transport efficiency also deteriorates.

As described above, based on the knowledge that the transport efficiency varies depending on the position of the powder surface ht and the highest point of the rotation shaft 213a and the blade 213f of the paddle 213, in the present embodiment, the transport from the paddle 213 to the developing roll 214 is performed. The developer powder level is controlled and the paddle 213 is fixed and the outer diameter is designed so that the efficiency is the highest.
In order to improve the transport efficiency, it is conceivable to increase the amount of developer in the housing or increase the rotational speed of the paddle 213. However, if the amount of the developer in the housing 217 is unnecessarily increased, the circulation of the developer in the entire housing 217 is deteriorated. Further, for example, if the rotational speed is to be increased only for the paddle 213, it is necessary to provide a speed change mechanism or the like, which makes it difficult to reduce the size of the apparatus. In this respect, in this embodiment, since a small amount of developer is used, the circulation property is good, and it is not necessary to provide a mechanism for changing the rotational speed of the paddle 213, which contributes to downsizing of the entire apparatus. Further, since the transport efficiency from the paddle 213 to the developing roll 214 is good, when a large amount of toner is consumed in one transfer process (for example, when forming a so-called solid image), the toner is conveyed to the developing roll 214 in the immediately subsequent transfer process. Situations where toner is insufficient (so-called white spots) are less likely to occur.

  In the above description, it is assumed that the powder surface ht is constant in the y direction (= always horizontal), but in practice, the developer concentration may vary depending on the location in the developing device 20b. . In general, the developer flow tends to stagnate near the center in the y direction than in the vicinity of the center. Therefore, the height of the powder surface tends to be lower at the center in the y direction than at the end. Further, such powder surface variations (developer bias) may depend on the total amount of developer in the developing device 20b and the rotation speeds of the first transport member 211, the second transport member 212, and the paddle 213. Even when there is a variation in the powder level as described above, it is preferable to control the height of the powder level so that it falls within a range where the lower limit value is hl and the upper limit value is hu. However, it is a case where the variation width of the powder surface is hu−hl or more (that is, there is a place where it is locally hu or more or hl or less), and the average value of the powder surface height is hl or more hu If maintained within the following range, the developer transport efficiency is improved as described above when viewed as the entire developing device 20b. In this case, it is more preferable if the average value of the powder surface height is exactly halfway between the position of the rotary shaft 213a and the highest point (that is, (hu + hl) / 2).

2. Operation FIG. 4 is a diagram illustrating functions of the image forming apparatus 1.
The image forming apparatus 1 includes a CPU 100, a memory 110, an input / output unit 120, and a bus 130 that connect them, which are not illustrated in the above-described drawings, and control each unit of the image forming apparatus 1 described above. The The CPU 100 realizes an image forming function 101 and a developing device control function 102 when roughly classified. The image forming function 101 is a function for controlling operations of the drum unit 20a, the fixing unit 30, the transport roll, and the like. The developing device control function 102 is a function for controlling operations related to the developing device 20b, and includes a powder level detection function 1021, a powder level adjustment function 1022, and a drive control function 1023. The powder level detection function 1021 is a function of controlling a toner concentration sensor (not shown) provided in the housing 217 and acquiring an output signal from the toner concentration sensor. The powder level adjustment function 1022 determines the amount and timing of toner to be injected into the housing 217 from the toner cartridge (not shown) through the toner supply port 216 based on the output signal from the density sensor, and injects the toner. This is a function for controlling a mechanism (not shown). The CPU 100 that realizes the powder level adjustment function 1022 is an example of an adjustment unit. The drive control function 1023 is a motor (not shown) connected to a gear (not shown) provided at each end of the rotation shaft of the first conveying member 211, the second conveying member 212, the paddle 213, and the developing roll 214. This is a function for controlling the driving of The input / output means 120 includes hardware such as a numeric keypad and a touch panel that accepts input of user instructions or displays information such as processing status.

<Modification>
As described above, the blades of the paddle 213 are not limited to a mode in which the blades are composed of two blades having the same shape, and the two blades are fixed in a straight line. The number of blades is not limited to two as in the above embodiment, but may be one, for example. When a plurality of blades are provided, the angle between two adjacent blades in a plane perpendicular to the rotation axis is not limited to 180 °.
5A to 5D illustrate other modes of the blade 213f.
The mode shown in FIG. 5A has three blades 213f having the same shape. The angle between adjacent blades is 120 degrees. According to this shape, the space formed between two adjacent blades exerts the effect of holding the developer particles. Therefore, the amount of developer supplied to the developing roll 214 per rotation of the paddle 213 increases.
The form shown in FIG. 5B has three blades 213f having the same shape, two of which have the same height from the shaft, and the remaining one is higher than the other two. The length (outer diameter) is shortened. The angle between adjacent blades is 120 degrees. In the case of this mode, compared with FIG. 5A, the amount of the blade held between the blades per rotation is reduced, but the flow of the developer is smoothed accordingly. Transportation efficiency may improve.
In the form shown in FIG. 5C, the blade 213f is not flat and the cross section is curved.
In the form shown in FIG. 5D, a paddle 213 is formed by embedding a shaft inside a single flat blade 213f, instead of having a wing projecting on the rotating shaft 213a.

  In the above embodiment, an example in which a set of drum units 20a and a developing device 20b are provided to form an image with one color (for example, black) has been described. A set of 20a and developing device 20b may be provided. Even in this case, in each developing device 20b, the relationship between the height ht of the powder surface, the fixed position of the shaft center of the paddle 213, and the outer diameter is the same as the arrangement relationship shown in the above embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Paper feed accommodating part, 20a ... Drum unit, 20b ... Developing device, 30 ... Fixing unit, 40a, 40b, 41a, 41b, 43a, 43b ... Transport roller 42: Transfer roll 100 ... CPU 110 ... Memory 120 ... Input / output means 130 ... Bus 101 ... Image forming function 102 ... Development , 201 ... photosensitive drum, 204 ... toner removal member, 203 ... charging device, 202 ... exposure device, 211 ... second transport member, 212 ... first transport 213... Development roller 215... Layer thickness regulating member 216... Toner supply port 211 a, 212 a, 213 a... Rotating shaft, 211 f, 212 f, 213 f. Feather, 2 7 ... Housing, 301 ... Heating roll, 302 ... Pressure roll, 1021 ... Powder level detection function, 1022 ... Powder level adjustment function, 1023 ... Drive control function, P ...・ Paper, R1 ... first storage chamber, R2 ... second storage chamber, W ... partition wall

Claims (5)

A housing;
A developer filled in the housing such that the height of the powder surface relative to the bottom surface of the housing is a first value or more and a second value or less;
A developing roll;
A paddle comprising a rotating shaft and blades provided on the rotating shaft, disposed opposite the developing roll, and transporting the developer toward the developing roll;
Adjusting means for adjusting the amount of the developer in the housing such that the height of the powder surface relative to the bottom surface of the housing is maintained between the first value and the second value; ,
Have
The axis of the rotating shaft is provided at a position lower than the first value with respect to the bottom surface of the housing, and the highest point of the blades with respect to the bottom surface of the housing is higher than the second value. ,
The paddle rotates in a direction in which the blades are directed toward the developing roll at the highest reaching point, and conveys the developer onto the developing roll vertically above the height of the powder surface. . Drive means for driving the developing roll and the paddle so that the ratio between the rotational speed of the developing roll and the rotational speed of the paddle is within a predetermined range;
The developing device according to claim 1, wherein the blade has a flat plate shape having one side in a direction parallel to the rotation axis. The vane is Ri Do and a first blade and a second blade shape is the same,
Developing device according to claim 2, characterized in that the normal of the surface normal and the second blade surface prior Symbol first blade are parallel. The blade is composed of a first blade, a second blade, and a third blade,
The length of a direction perpendicular to the rotation axis of at least one of the first blade, the second blade, and the third blade is smaller than that of the other blades. The developing device according to 1. A developing device according to any one of claims 1 to 4,
An image forming unit that has a photoconductor, an exposure device, and a charging device, and that develops the electrostatic latent image formed on the photoconductor using a developer supplied from the developer;
A transfer portion for transferring the developed image to a recording medium;
A fixing unit for fixing the transferred image;
An image forming apparatus.

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