Developing device and image forming apparatus including passing developer amount changing mechanism

1. A developing device that circulates developer including carrier and toner in a circulation passage having first and second conveyance passages by conveying the developer in a first conveyance direction in the first conveyance passage and conveying the developer in a second conveyance direction in the second conveyance passage, so that the developer is supplied to a developing roller provided along one of the first and second conveyance passages, the developing device comprising:

a first conveyance member provided in the first conveyance passage and driven to rotate to convey the developer in the first conveyance direction;

a communicating passage through which the developer flows from the first conveyance passage to the second conveyance passage;

a second conveyance member provided in the second conveyance passage and driven to rotate to convey the developer that has flowed through the communicating passage in the second conveyance direction;

a discharge passage extending from an end portion of the first conveyance passage located downstream in the first conveyance direction;

a passing developer amount changing mechanism configured to change an amount of developer per unit time passing through the communicating passage, according to a pressure applied to the developer at a junction between the first conveyance passage and the discharge passage, wherein the passing developer amount changing mechanism comprises a detection unit configured to acquire information indicating fluctuations of the pressure applied to the developer at the junction; and

a movement control unit to control a moving unit based on the acquired information to change a size of an opening of the communicating passage.

2. The developing device of claim 1 , further comprising

a third conveyance member that is provided in the discharge passage and driven to rotate to convey the developer in a direction opposite to the first conveyance direction by applying a conveyance force that is smaller than a conveyance force applied by the first conveyance member.

3. The developing device of claim 2 , wherein

each of the first and third conveyance members is a screw formed by helically winding a blade around the same rotary shaft in an opposite direction.

4. The developing device of claim 1 , wherein

the passing developer amount changing mechanism increases the amount of developer per unit time as the pressure applied to the developer at the junction increases.

5. The developing device of claim 4 , wherein

the passing developer amount changing mechanism changes the amount of developer per unit time by changing a size of an opening of the communicating passage from which the developer flows into the communicating passage.

6. A developing device that circulates developer including carrier and toner in a circulation passage having first and second conveyance passages by conveying the developer in a first conveyance direction in the first conveyance passage and conveying the developer in a second conveyance direction in the second conveyance passage, so that the developer is supplied to a developing roller provided along one of the first and second conveyance passages, the developing device comprising:

a first conveyance member provided in the first conveyance passage and driven to rotate to convey the developer in the first conveyance direction;

a communicating passage through which the developer flows from the first conveyance passage to the second conveyance passage;

a second conveyance member provided in the second conveyance passage and driven to rotate to convey the developer that has flowed through the communicating passage in the second conveyance direction;

a discharge passage extending from an end portion of the first conveyance passage located downstream in the first conveyance direction; and

a passing developer amount changing mechanism configured to change an amount of developer per unit time passing through the communicating passage, according to a pressure applied to the developer at a junction between the first conveyance passage and the discharge passage,

wherein the passing developer amount changing mechanism is a valve made of a flexible material comprising a base fixed to a wall of the communicating passage so as to partially block an opening of the communicating passage and bend as pressure applied to the developer at the junction increases.

7. The developing device of claim 6 , wherein

the valve has a tapered portion that tapers toward a tip thereof.

8. A developing device that circulates developer including carrier and toner in a circulation passage having first and second conveyance passages by conveying the developer in a first conveyance direction in the first conveyance passage and conveying the developer in a second conveyance direction in the second conveyance passage, so that the developer is supplied to a developing roller provided along one of the first and second conveyance passages, the developing device comprising:

a first conveyance member provided in the first conveyance passage and driven to rotate to convey the developer in the first conveyance direction;

a communicating passage through which the developer flows from the first conveyance passage to the second conveyance passage;

a second conveyance member provided in the second conveyance passage and driven to rotate to convey the developer that has flowed through the communicating passage in the second conveyance direction;

a discharge passage extending from an end portion of the first conveyance passage located downstream in the first conveyance direction; and

a passing developer amount changing mechanism configured to change an amount of developer per unit time passing through the communicating passage, according to a pressure applied to the developer at a junction between the first conveyance passage and the discharge passage,

wherein the passing developer amount changing mechanism is a valve made of a flexible material provided at the communicating passage so as to partially block an opening of the communicating passage and bend as pressure applied to the developer at the junction increases, and the valve has a flexible portion that becomes more flexible closer to a tip thereof.

9. The developing device of claim 6 , wherein

the valve is made of one of a foamed elastic material and a resin film.

10. The developing device of claim 5 , wherein

the passing developer amount changing mechanism includes:

a shutter that is swingably supported by a supporter provided at the communicating passage;

a forcing mechanism configured to apply a force to swing the shutter toward the first conveyance passage; and

a swing prohibiting mechanism configured to prohibit the shutter from swinging toward the first conveyance passage further than a predetermined position where the shutter partially blocks the opening of the communicating passage,

as the pressure applied to the developer at the junction increases, the shutter swings toward the second conveyance passage against the force applied by the forcing mechanism, thereby increasing the size of the opening of the communicating passage.

11. The developing device of claim 10 , wherein

the predetermined position is a position where the opening of the communicating passage is maximally blocked by the shutter.

12. The developing device of claim 5 , wherein

the passing developer amount changing mechanism includes;

a shutter configured to partially block the opening of the communicating passage, and the moving unit is configured to move the shutter in the communicating passage.

13. An image forming apparatus for forming an image by developing an electrostatic latent image on a photoreceptor using a developing device that circulates developer including carrier and toner in a circulation passage having first and second conveyance passages by conveying the developer in a first conveyance direction in the first conveyance passage and conveying the developer in a second conveyance direction in the second conveyance passage, so that the developer is supplied to a developing roller provided along one of the first and second conveyance passages, wherein

the developing device includes:

a first conveyance member provided in the first conveyance passage and driven to rotate to convey the developer in the first conveyance direction;

a communicating passage through which the developer flows from the first conveyance passage to the second conveyance passage;

a second conveyance member provided in the second conveyance passage and driven to rotate to convey the developer that has flowed through the communicating passage in the second conveyance direction;

a discharge passage extending from an end portion of the first conveyance passage located downstream in the first conveyance direction;

a passing developer amount changing mechanism configured to change an amount of developer per unit time passing through the communicating passage, according to a pressure applied to the developer at a junction between the first conveyance passage and the discharge passage, wherein the passing developer amount changing mechanism comprises a detection unit configured to acquire information indicating fluctuations of the pressure applied to the developer at the junction; and

a movement control unit to control a moving unit based on the acquired information to change a size of an opening of the communicating passage.

14. The image forming apparatus of claim 13 , wherein

the developing device further includes

a third conveyance member that is provided in the discharge passage and driven to rotate to convey the developer in a direction opposite to the first conveyance direction by applying a conveyance force that is smaller than a conveyance force applied by the first conveyance member.

15. The image forming apparatus of claim 13 , wherein

the passing developer amount changing mechanism increases the amount of developer per unit time as the pressure applied to the developer at the junction increases.

16. The image forming apparatus of claim 15 , wherein

the passing developer amount changing mechanism changes the amount of developer per unit time by changing a size of an opening of the communicating passage from which the developer flows into the communicating passage.

17. An image forming apparatus for forming an image by developing an electrostatic latent image on a photoreceptor using a developing device that circulates developer including carrier and toner in a circulation passage having first and second conveyance passages by conveying the developer in a first conveyance direction in the first conveyance passage and conveying the developer in a second conveyance direction in the second conveyance passage, so that the developer is supplied to a developing roller provided along one of the first and second conveyance passages, wherein

the developing device includes:

a first conveyance member provided in the first conveyance passage and driven to rotate to convey the developer in the first conveyance direction;

a communicating passage through which the developer flows from the first conveyance passage to the second conveyance passage;

a second conveyance member provided in the second conveyance passage and driven to rotate to convey the developer that has flowed through the communicating passage in the second conveyance direction;

a discharge passage extending from an end portion of the first conveyance passage located downstream in the first conveyance direction; and

a passing developer amount changing mechanism configured to change an amount of developer per unit time passing through the communicating passage, according to a pressure applied to the developer at a junction between the first conveyance passage and the discharge passage,

wherein the passing developer amount changing mechanism is a valve made of a flexible material comprising a base fixed to a wall of the communicating passage so as to partially block an opening of the communicating passage and bend as pressure applied to the developer at the junction increases.

18. The image forming apparatus of claim 16 , wherein

the passing developer amount changing mechanism includes:

a shutter that is swingably supported by a supporter provided at the communicating passage;

a forcing mechanism configured to apply a force to swing the shutter toward the first conveyance passage; and

a swing prohibiting mechanism configured to prohibit the shutter from swinging toward the first conveyance passage further than a predetermined position where the shutter partially blocks the opening of the communicating passage,

as the pressure applied to the developer at the junction increases, the shutter swings toward the second conveyance passage against the force applied by the forcing mechanism, thereby increasing the size of the opening of the communicating passage.

19. The image forming apparatus of claim 16 , wherein

the passing developer amount changing mechanism includes;

a shutter configured to partially block the opening of the communicating passage, and the moving unit is configured to move the shutter in the communicating passage.