Powder conveying device and image forming apparatus

An aspect of the invention is a powder conveying device including a conveying passage where powder is conveyed from a first powder accommodating chamber toward a second powder accommodating chamber, in the conveying passage, a conveying member including a rotating shaft rotatable, and a blade member spirally provided around the rotating shaft and enable to convey the powder by rotation of the rotating shaft, an intake region including an intake port through which the powder is taken in from the first powder accommodating chamber, a first conveying region arranged on a downstream side of the intake region in a conveying direction of the powder, and a second conveying region arranged on a downstream side of the first conveying region in the conveying direction, a conveyable volume of the powder per one revolution of the conveying member at the second conveying region being lower than that at the first conveying region.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-000143 filed Jan. 5, 2009.

BACKGROUND

Technical Field

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

SUMMARY

In accordance with an aspect of the invention, a powder conveying device includes: a conveying passage in which powder is conveyed from a first powder accommodating chamber toward a second powder accommodating chamber, the powder being accommodated in the first powder accommodating chamber and the second powder chamber; a conveying member that is disposed in the conveying passage, and includes a rotating shaft that is rotatable, and a blade member that is spirally provided around the rotating shaft, and can convey the powder by rotation of the rotating shaft; an intake region that is formed on the conveying passage where the conveying member is disposed, and includes an intake port through which the powder is taken in from the first powder accommodating chamber; a first conveying region that is formed on the conveying passage where the conveying member is disposed, and is arranged on a downstream side of the intake region in a conveying direction of the powder; and a second conveying region that is formed on the conveying passage where the conveying member is disposed, and is arranged on a downstream side of the first conveying region in the conveying direction, a conveyable volume of the powder per one revolution of the conveying member at the second conveying region being lower than that at the first conveying region.

DETAILED DESCRIPTION

Entire Configuration of Image Forming Apparatus according to an Exemplary Embodiment

An entire configuration of an image forming apparatus according to an exemplary embodiment of the invention will be described.FIG. 1is a schematic diagram illustrating the entire configuration of the image forming apparatus of the exemplary embodiment.

An image forming apparatus10includes a recording medium accommodating unit12, an image forming section14, a transporting unit16, a fixing device18, and a recording medium discharge unit20. A recording medium P such as a sheet is accommodated in the recording medium accommodating unit12. The image forming section14forms a toner image in the recording medium P. The transporting unit16transports the recording medium P from the recording medium accommodating unit12to the image forming section14. The fixing device18fixes the toner image formed by the image forming section14to the recording medium P. The recording medium P to which the toner image is fixed by the fixing device18is discharged at the recording medium discharge unit20.

The image forming section14includes image forming units22Y,22M,22C, and22K, a intermediate transfer belt24, a first transfer roller26, and a second transfer roller28. The image forming units22Y,22M,22C, and22K form yellow (Y), magenta (M), cyan (C), and black (K) toner images, respectively. The toner images formed by the image forming units22Y,22M,22C, and22K are transferred to the intermediate transfer belt24that is an example of an intermediate transfer member. The first transfer roller26that is an example of a first transfer member transfers the toner images formed by the image forming units22Y,22M,22C, and22K to the intermediate transfer belt24. The second transfer roller28that is an example of a secondary transfer member transfers the toner images, transferred to the intermediate transfer belt24, to the recording medium P.

Each of the image forming units22Y,22M,22C, and22K includes a photosensitive drum30rotated in one direction (counterclockwise inFIG. 1). The photosensitive drum30is an image carrier in which an electrostatic latent image is formed in a surface thereof.

A charging device32, an exposure device34, a development device36, an eraser device38, and a toner removing device40are provided around each photosensitive drum30in that order from the upstream side in the rotating direction of the photosensitive drum30. The charging device32charges the surface of the photosensitive drum30. The exposure device34exposes the surface of the charged photosensitive drum30to form an electrostatic latent image in the surface of the photosensitive drum30. The development device36develops the electrostatic latent image formed in the surface of the photosensitive drum30, thereby forming a toner image. The eraser device38erases charge from the surface of the photosensitive drum30after the toner image is transferred to the intermediate transfer belt24. The toner removing device40removes toner remaining on the surface of the photosensitive drum30after the toner image is transferred to the intermediate transfer belt24.

Toner accommodating chambers58are provided above the intermediate transfer belt24, and the toner accommodating chamber58is an example of a first powder accommodating chamber in which the toner is stored (accommodated). The toner accommodating chambers58are provided in the image forming units22Y,22M,22C, and22K, respectively. The toner is supplied from the toner accommodating chamber58to the development device36of each of the image forming units22Y,22M,22C, and22K.

The development device36includes a development chamber36A in which a developer including the toner and a magnetic carrier is accommodated, and the development chamber36A is an example of a second powder chamber in which the powder is accommodated. A conveying member36B and a development roller36C are provided in the development chamber36A. The conveying member36B conveys the developer while stirring the developer. The development roller36C that is an example of a developer retaining member retains the developer conveyed by the conveying member36B. The toner retained by the development roller36C adheres to the surface of the photosensitive drum30to develop the electrostatic latent image.

A toner conveying device60is provided between the toner accommodating chamber58and the development chamber36A. The toner conveying device60is as a powder conveying device that conveys the powder, and the toner conveying device60conveys the toner from the toner accommodating chamber58toward the development chamber36A. A configuration of the toner conveying device60is described later.

The toner conveying device60of the exemplary embodiment may be used to a case in which powder except for the toner is conveyed. For example, the toner conveying device60may be used to powder except for the toner whose fluidity is changed by a change in environmental conditions or production conditions.

The intermediate transfer belt24is entrained about a facing roller42, and a driving roller44, and a support roller46. The facing roller42faces the second transfer roller28. The intermediate transfer belt24is circularly moved in one direction (clockwise inFIG. 1) while being in contact with the photosensitive drums30.

A toner removing unit48is provided on the intermediate transfer belt24in order to remove the toner remaining on the intermediate transfer belt24.

The first transfer roller26faces the photosensitive drum30so as to sandwich the intermediate transfer belt24with the photosensitive drum30. A first transfer position is formed between the first transfer roller26and the photosensitive drum30. The toner image on the photosensitive drum30is first-transferred to the intermediate transfer belt24in the first transfer position. In the first transfer position, the first transfer roller26transfers the toner image on the surface of the photosensitive drum30to the intermediate transfer belt24by a pressing force and an electrostatic force.

The second transfer roller28faces the facing roller42so as to sandwich the intermediate transfer belt24with the facing roller42. A second transfer position is formed between the second transfer roller28and the facing roller42. The toner image on the intermediate transfer belt24is second-transferred to the recording medium P in the second transfer position.

The transporting unit16includes a delivery roller50and pairs of transporting rollers52. The delivery roller50delivers the recording medium P accommodated in the recording medium accommodating unit12. The pair of transporting rollers52transports the recording medium P delivered by the delivery roller50to the second transfer position while sandwich the recording medium P therebetween.

The fixing device18is disposed on the downstream side of the second transfer position in the transporting direction to fix the toner image which is transferred in the second transfer position to the recording medium P.

A pair of transporting rollers54and a pair of discharge rollers56are disposed in this order on the downstream side of the fixing device18in the transporting direction. The pair of transporting rollers54transports the recording medium P while sandwiching the recording medium P therebetween. The pair of discharge rollers56discharges the recording medium P to the recording medium discharge unit20.

An image forming operation forming an image in the image forming apparatus of the exemplary embodiment will be described below.

In the image forming apparatus10of the exemplary embodiment, when the image is formed in the recording medium P, the pair of transporting rollers52transports the recording medium P delivered from the recording medium accommodating unit12to the second transfer position.

On the other hand, in the intermediate transfer belt24, the toner images formed by the image forming units22Y,22M,22C, and22K are superposed to form the color image. The color image formed on the intermediate transfer belt24is transferred to the recording medium P transported to the second transfer position.

The recording medium P to which the toner image is transferred is transported to the fixing device18, and the transferred toner image is fixed by the fixing device18. The pair of discharge rollers56discharges the recording medium P to which the toner image is fixed to the recording medium discharge unit20. In this manner, the series of image forming operation is performed.

Configuration of Toner Conveying Device according to an Exemplary Embodiment

A configuration of the toner conveying device of the exemplary embodiment will be described below.FIG. 2is a schematic diagram illustrating the configuration of the toner conveying device of the exemplary embodiment.

The toner conveying device60of the exemplary embodiment includes a conveying passage62and a conveying member64. The toner is conveyed from the toner accommodating chamber58toward the development chamber36A through the conveying passage62. The conveying member64is disposed in the conveying passage62to convey the toner.

The toner accommodating chamber58is formed in a toner storage container82in which the toner is accommodated. For example, the toner storage container82is structured by a toner cartridge. The toner is accommodated in the toner cartridge that is detachably attached into the image forming apparatus10.

The conveying passage62is formed by the inside of a conveying pipe72and the inside of a conveying pipe74. The conveying pipe72is horizontally extended. The conveying pipe74is coupled to one end of the conveying pipe72, and the conveying pipe74is vertically extended. The conveying member64is disposed in the conveying pipe72.

The conveying member64is formed into a conveying screw, and the conveying member64includes a rotating shaft64A and a blade member64B. The blade member64B is spirally provided around the rotating shaft64A, and the blade member64B can convey the toner by the rotation of the rotating shaft64A.

A gear portion66is provided at one end (right end inFIG. 2) of the rotating shaft64A. The gear portion66is meshed with a gear portion68provided in a driving shaft70of a driving portion (not illustrated). Therefore, the driving shaft70is rotated by a driving force of the driving portion, and the torque of the driving shaft70is transmitted to the rotating shaft64A through the gear portions68and66. The rotating shaft64A to which the torque of the driving shaft70is transmitted is rotated to convey the toner by the blade member64B.

A crank76is coupled to the other end of the rotating shaft64A to convert rotational motion of the rotating shaft64A into reciprocating motion. One end of a spiral wound coil78is coupled to the crank76. Therefore, the crank76converts the rotational motion of the rotating shaft64A into the reciprocating motion to vertically move the coil78.

In the conveying pipe72, an intake region T having an intake port80is formed on the conveying passage62where the conveying member64is disposed. The toner is taken in the conveying pipe72from the toner accommodating chamber58through the intake port80. The intake port80is formed below the toner accommodating chamber58and at an upper portion of the conveying pipe72. The toner falling from the toner accommodating chamber58is taken in the conveying passage62in the conveying pipe72through the intake port80.

In the intake region T, the conveying member64conveys the toner taken in through the intake port80to the downstream side. The intake region T ranges from one end (a portion of a chain double-dashed line80A) of the intake port80to the other end (a portion of a chain double-dashed line80B).

In the conveying pipe72, a first conveying region H1is formed on the conveying passage62where the conveying member64is disposed. The first conveying region H1is disposed on the downstream side of the intake region T in the conveying direction. In the first conveying region H1, the conveying member64conveys the toner conveyed from the intake region T to the downstream side.

In the conveying pipe72, a second conveying region H2is formed on the conveying passage62where the conveying member64is disposed. The second conveying region H2is disposed on the downstream side of the first conveying region H1in the conveying direction. In the second conveying region H2, the conveying member64conveys the toner conveyed from the first conveying region H1to the downstream side.

In the second conveying region H2, a conveyable volume per one revolution of the conveying member64is lower than that of the first conveying region H1. Specifically, in the second conveying region H2, a diameter (shaft diameter) of the rotating shaft64A of the conveying member64is larger than that of the first conveying region H1.

For example, the diameter of the rotating shaft64A ranges is equal to or more than 8 mm and equal to or less than 9 mm in the second conveying region H2in a case where the rotating shaft64A has the diameter of 3 mm in the intake region T and first conveying region H1.

In this case, an outer diameter of the blade member64B is set to 12 mm, an inner diameter of the conveying pipe72(passage width of conveying passage62) is set to 14 mm, and one pitch of blade member64B is set to 14 mm. Note that this “one pitch” means a distance from one vertex of the blade member64B to another vertex of the blade member64B, which is adjacent to the one vertex in an axial direction of the rotating shaft64A.

For example, the second conveying region H2has a length ranging equal to or more than one pitch and equal to or less than two pitches (1-2 pitches) of the blade member64B, the first conveying region H1has a length ranging equal to or more than a half pitch and equal to or more than one and a half pitch (0.5-1.5 pitch) of the blade member64B, and the intake region T has a length of one and a half pitch (1.5 pitch) of the blade member64B.

In the drawings, the letter A designates a diameter of the rotating shaft64A, the letter B designates an outer diameter of the blade member64B, and the letter C designates an inner diameter of the conveying pipe72.

In the second conveying region H2, the configuration in which the conveyable volume per one revolution of the conveying member64is lower than that of the first conveying region H1is not limited to the configuration in which the diameter of the rotating shaft64A of the conveying member64in the second conveying region H2is larger than that of the first conveying region H1. For example, as illustrated inFIG. 4, in the second conveying region H2, the outer diameter of the blade member64B of the conveying member64may be smaller than that of the first conveying region H1, and the inner diameter of the conveying pipe72(the passage width of conveying passage62) is smaller than that of the first conveying region H1.

At this case, when the outer diameter of the blade member64B of the conveying member64in the first conveying region H1differs from that in the second conveying region H2, the first conveying region H1may be equal to the second conveying region H2in the inner diameter of the conveying pipe72(the passage width of conveying passage62).

In the second conveying region H2, the configuration in which the conveyable volume per one revolution of the conveying member64is lower than that of the first conveying region H1may be a configuration in which the diameter of the rotating shaft64A of the conveying member64in the second conveying region H2is larger than that of the first conveying region H1, and the outer diameter of the blade member64B of the conveying member64in the second conveying region H2is smaller than that of first conveying region H1.

In the second conveying region H2, the configuration in which the conveyable volume per one revolution of the conveying member64is lower than that of the first conveying region H1may be a configuration in which the one pitch of the blade member64B of the conveying member64in the second conveying region H2is smaller than that of the first conveying region H1. (“1 pitch (H2)” is smaller than “1 pitch (H1)”, seeFIG. 12)

Note that, as the configuration in which the conveyable volume per one revolution of the conveying member64of the second conveying region H2is lower than that of the first conveying region H1, any of the above mentioned configurations of “the diameter of the rotating shaft64A of the conveying member64in the second conveying region H2is larger than that of the first conveying region H1”, “the outer diameter of the blade member64B of the conveying member64in the second conveying region H2is smaller than that of the first conveying region H1”, “the inner diameter of the conveying pipe72(the passage width of conveying passage62) in the second conveying region H2is smaller than that of the first conveying region H1”, and “one pitch of the blade member64B of the conveying member64in the second conveying region H2is smaller than that of the first conveying region H1” may be combined.

EVALUATION

Evaluation performed to Examples 1 and 2 and Comparative Examples 1 to 3 will be described below. In the evaluation, in the configuration of the exemplary embodiment, one pitch of the blade member64B is set to 14 mm, the length of the intake region T is set to one and a half pitches of the blade member64B, the length of the first conveying region H1is set to one and a half pitches of the blade member64B, and the length of the second conveying region H2is set to two pitches of the blade member64B.

The evaluation is performed while the diameter of the rotating shaft64A, the outer diameter of the blade member64B, and the inner diameter of the conveying pipe72are set in each of Examples 1 and 2 and Comparative Examples 1 to 3.

The evaluation is performed by computing a toner conveying amount (dispense rate) per unit time of one toner cartridge using the toner to which a thermal stress is applied by keeping in a high-temperature environment and the toner to which no thermal stress is applied.

For Example 1, in the intake region T, the first conveying region H1, and the second conveying region H2, the inner diameter of the conveying pipe72is set to 14 mm and the outer diameter of the blade member64B is set to 12 mm. In the intake region T and the first conveying region H1, the diameter of the rotating shaft64A is set to 3 mm. In the second conveying region H2, the diameter of the rotating shaft64A is set to 9 mm (seeFIG. 2).

As a result of evaluation of Example 1, a difference in dispense rate between the toner to which the thermal stress is applied and the toner to which no thermal stress is applied is 3% as illustrated inFIG. 3.

Although the absolute value of the dispense rate is lowered, the absolute value of the dispense rate may be increased by enhancing the rotating speed for rotating and driving of the rotating shaft64A as needed or by enlarging the outer diameter of the blade member64B of the conveying member64.

For Example 2, the diameter of the rotating shaft64A is set to 3 mm in the intake region T, the first conveying region H1, and the second conveying region H2. In the intake region T and the first conveying region H1, the inner diameter of the conveying pipe72is set to 14 mm and the outer diameter of the blade member64B is set to 12 mm. In the second conveying region H2, the inner diameter of the conveying pipe72is set to 9.5 mm and the outer diameter of the blade member64B is set to 8.5 mm (seeFIG. 4). As a result of evaluation of Example 2, the difference in dispense rate between the toner to which the thermal stress is applied and the toner to which no thermal stress is applied is 7% as illustrated inFIG. 5.

Comparative Example 1

For Comparative Example 1, in the intake region T, the first conveying region H1, and the second conveying region H2, the inner diameter of the conveying pipe72is set to 14 mm, the outer diameter of the blade member64B is set to 12 mm, and the diameter of the rotating shaft64A is set to 3 mm (seeFIG. 6).

As a result of evaluation of Comparative Example 1, the difference in dispense rate between the toner to which the thermal stress is applied and the toner to which no thermal stress is applied is 25% as illustrated inFIG. 7.

Comparative Example 2

For Comparative Example 2, in the intake region T, the first conveying region H1, and the second conveying region H2, the inner diameter of the conveying pipe72is set to 14 mm, the outer diameter of the blade member64B is set to 12 mm, and the diameter of the rotating shaft64A is set to 9 mm (seeFIG. 8).

As a result of evaluation of Comparative Example 2, a difference in dispense rate between the toner to which the thermal stress is applied and the toner to which no thermal stress is applied is 33% as illustrated inFIG. 9.

Comparative Example 3

For Comparative Example 3, in the intake region T, the first conveying region H1, and the second conveying region H2, the inner diameter of the conveying pipe72is set to 14 mm and the outer diameter of the blade member64B is set to 12 mm.

In the intake region T, the diameter of the rotating shaft64A is set to 3 mm. In the first conveying region H1and the second conveying region H2, the diameter of the rotating shaft64A is set to 9 mm (seeFIG. 10).

As a result of evaluation of Comparative Example 3, the difference in dispense rate between the toner to which the thermal stress is applied and the toner to which no thermal stress is applied is 27% as illustrated inFIG. 11.

The differences in dispense rate between the toner to which the thermal stress is applied and the toner to which no thermal stress is applied are 25%, 33%, 27% in Comparative Examples 1 to 3. On the other hand, the differences in dispense rate are improved to 3% and 7% in Examples 1 and 2.

In Comparative Example 3, the improvement is not achieved although the conveyable volume per one revolution of the conveying member64is made different between in the intake region T and in the first conveying region H1and the second conveying region H2. That is, it is understood it is important to make different the conveyable volume per one revolution of the conveying member64between in the first conveying region H1and in the second conveying region H2such as like Examples 1 and 2.

This may be because: although the toner amount taken in between the blade members64B of the conveying member64from the toner accommodating chamber58in the intake region T is varied due to the difference in fluidity of the toner, the variation occurred in the intake region T is absorbed therefore stabilize the toner conveying amount by providing “a part where the toner conveyable amount is large” and “a part where the toner conveyable amount is small” in this order in the toner conveying region subsequent to the intake region T.

The invention is not limited to the exemplary embodiment described above, but various modifications, changes, and improvements can be made without departing from the scope of the invention.