Developing device and image forming apparatus

1. A developing device comprising:

a developing roller that carries a developer;

a developing tank that supplies the developing roller with the developer replenished from a replenishing port, the developing tank including a first developing tank, a second developing tank, and a connecting part including a connecting path for circulating the developer between the first developing tank and the second developing tank formed between the first developing tank and the second developing tank;

a discharger that has a discharge port connecting to the developing tank and discharges the developer from the developing tank;

a supply amount acquirer that acquires a supply amount of the developer to be supplied to the developing tank;

a discharge amount acquirer that acquires a discharge amount of the developer to be discharged through the discharge port;

a developer amount adjuster that adjusts an amount of the developer in the developing tank, the developer amount adjuster including at least one of a partition member that moves to change a width of the connecting path of the connecting part and a conveyance member that conveys the developer in the developing tank while stirring the developer in the developing tank; and

a hardware processor that controls the at least one of a position of the partition member and a speed of conveyance of the conveyance member to adjust the amount of the developer in the developing tank to a value within a predetermined range, in accordance with the acquired supply amount and the acquired discharge amount of the developer.

2. The developing device according to claim 1 , wherein

the first developing tank is connected to the discharger on a downstream side in a moving direction of the developer, and supplies the developer to the developing roller; and

the second developing tank is connected to the replenishing port on an upstream side in a conveying direction of the developer.

3. The developing device according to claim 2 , wherein

the discharge amount acquirer acquires the discharge amount of the developer from a result of detection performed by a bulk detection sensor that detects bulkiness of the developer in the first developing tank.

4. The developing device according to claim 3 , wherein

the bulk detection sensor detects the bulkiness by measuring magnetic permeability of the developer in the first developing tank.

5. The developing device according to claim 3 , wherein

the bulk detection sensor is disposed immediately before the discharge port in the moving direction of the developer.

6. The developing device according to claim 2 , wherein

the developer amount adjuster includes the partition member that moves to change the width of the connecting path in the connecting part, and

the hardware processor causes the partition member to move, to adjust the amount of the developer in the first developing tank to a value within the predetermined range.

7. The developing device according to claim 2 , wherein

the developer amount adjuster includes the conveyance member that conveys the developer in the developing tank to the discharge port while stirring the developer in the developing tank, and

the hardware processor controls speed of conveyance of the developer being conveyed by the conveyance member, to adjust the amount of the developer in the first developing tank to a value within the predetermined range.

8. The developing device according to claim 6 , wherein

the partition member is capable of reciprocating in one of a width direction and a height direction of the connecting path.

9. The developing device according to claim 6 , wherein

the connecting path includes: an upstream-side path for supplying the first developing tank with the developer replenished from the replenishing port into the second developing tank; and a downstream-side path for returning the developer in the first developing tank into the second developing tank, and

the partition member is located on the opposite side from the discharge port, and is movable to change width of the upstream-side path.

10. The developing device according to claim 2 , wherein

the supply amount acquirer acquires the supply amount from a replenishment amount of the developer supplied to the second developing tank from the replenishing port or coverage of an image printed on a paper sheet.

11. The developing device according to claim 3 , wherein

the hardware processor determines whether the amount of the developer in the first developing tank is outside a predetermined range in accordance with a result of detection performed by the bulk detection sensor and the supply amount, and, when determining that the amount of the developer in the first developing tank is outside the predetermined range, controls the developer amount adjuster to adjust the amount of the developer in the first developing tank to a value within the predetermined range.

12. The developing device according to claim 11 , wherein,

when a value detected by the bulk detection sensor exceeds a threshold value, the hardware processor determines that the amount of the developer in the first developing tank is outside the predetermined range.

13. The developing device according to claim 11 , wherein

the hardware processor collates values of the acquired discharge amount of the developer and the acquired supplied amount of the developer, and, from a result of the collation, determines whether the amount of the developer in the first developing tank is outside the predetermined range.

14. The developing device according to claim 13 , wherein,

when the result of the collation shows that transitions of the discharge amount and the supply amount do not match, the hardware processor determines that the amount of the developer in the first developing tank is outside the predetermined range.

15. The developing device according to claim 12 , wherein

at least one of the threshold value is set on each of an upper limit side and a lower limit side.

16. The developing device according to claim 12 , wherein,

when a value detected by the bulk detection sensor exceeds the threshold value for a certain period of time or longer, the hardware processor determines that the amount of the developer in the first developing tank is outside the predetermined range.

17. The developing device according to claim 3 , wherein

the developer amount adjuster includes: the partition member that moves to change the width of the connecting path in the connecting part; and the conveyance member that conveys the developer in the developing tank to the discharge port while stirring the developer in the developing tank, and

the hardware processor preferentially controls a position of the partition member.

18. The developing device according to claim 17 , wherein

two thresholds are set on each of an upper limit side and a lower limit side,

when a value detected by the bulk detection sensor exceeds a first threshold value on one of the upper limit side and the lower limit side, the hardware processor controls the position of the partition member, and,

when a value detected by the bulk detection sensor exceeds a second threshold value on one of the upper limit side and the lower limit side, the hardware processor controls speed of conveyance of the developer being conveyed by the conveyance member.

19. The developing device according to claim 18 , wherein

the hardware processor determines

whether to preferentially control the speed of conveyance of the developer being conveyed by the conveyance member, in accordance with a speed at which a value detected by the bulk detection sensor exceeds the first threshold value on one of the upper limit side and the lower limit side.

20. An image forming apparatus comprising the developing device according to claim 1 .