Liquid supply device and image forming apparatus

1. A liquid supply device which supplies ejection liquid to a plurality of ejection heads from a liquid tank, comprising:

a supply pipe which connects the liquid tank to the plurality of ejection heads, an upstream end portion of the supply pipe being connected to the liquid tank, a downstream side of the supply pipe being branched into a plurality of branch pipes having different numbers of branches by means of a plurality of ramifying sections, ends of the plurality of branch pipes being respectively connected to the plurality of ejection heads; and

a flow path resistance altering device which alters a flow path resistance in at least one of flow paths from the plurality of ramifying sections to the plurality of ejection heads,

wherein branch pipes having a relatively small number of branches among the plurality of branch pipes are connected to ejection heads having a relatively high ejection frequency among the plurality of ejection heads.

2. The liquid supply device as defined in claim 1 , wherein:

each of the plurality of ejection heads has a plurality of nozzles forming liquid ejection ports; and

a line head having a long nozzle row is constituted by aligning the plurality of ejection heads.

3. The liquid supply device as defined in claim 1 , wherein the branch pipe having a smallest number of branches by means of the ramifying sections among the plurality of branch pipes is connected to the ejection head having a highest ejection frequency among the plurality of ejection heads.

4. The liquid supply device as defined in claim 3 , wherein:

each of the plurality of ejection heads has a plurality of nozzles forming liquid ejection ports; and

a line head having a long nozzle row is constituted by aligning the plurality of ejection heads.

5. The liquid supply device as defined in claim 4 , wherein the ejection head having the highest ejection frequency is disposed in a central portion of an arrangement of the plurality of ejection heads forming the line head.

6. The liquid supply device as defined in claim 4 , wherein the ejection head having the highest ejection frequency is disposed in one end portion of an arrangement of the plurality of ejection heads forming the line head.

7. The liquid supply device as defined in claim 1 , further comprising:

a pressure measuring device which is arranged in the branch pipe after a branch by means of the ramifying section and upstream of the ejection head; and

a flow path resistance control device which controls the flow path resistance altering device according to a measurement result of the pressure measuring device in such a manner that supply pressures of the plurality of ejection heads are substantially equal to each other.

8. The liquid supply device as defined in claim 7 , wherein the flow path resistance control device controls the flow path resistance altering device so as to close at least one of the flow paths to at least one of the plurality of ejection heads that is not ejecting the liquid.

9. The liquid supply device as defined in claim 1 , wherein the flow path resistance altering device comprises a mechanism which alters a cross-sectional area of a pipe forming the flow path.

10. An image forming apparatus comprising the liquid supply device as defined in claim 1 , the image forming apparatus forming an image on a recording medium by means of the liquid ejected from the ejection heads.

11. The image forming apparatus as defined in claim 10 , further comprising a flow path resistance control device which functions as a recording density correction device which suppresses variation in recording density between the plurality of ejection heads by controlling the flow path resistance altering device so as to adjust a supply pressure at each of the plurality of ejection heads.