Patent ID: 8308272

Claim:
An image forming apparatus comprising: a first carriage having a first recording head to eject black liquid droplets, movable in a main scanning direction; a second carriage having a second recording head to eject color liquid droplets, separatably dockable with the first carriage within a main scanning range of the first carriage; a first positioning unit to position the second carriage relative to the first carriage in a sub-scanning direction perpendicular to the main scanning direction, the first positioning unit comprising: a reference shaft provided to one of the first and second carriages and extending in the main scanning direction; and notched positioning members provided to the other one of the first and second carriages to engage the reference shaft; a second positioning unit provided to at least one of the first and second carriages to position the second carriage relative to the first carriage in a rotary direction rotating around the reference shaft, the second positioning unit contacting the other one of the first and second carriages in the rotary direction upon docking of the first and second carriages; and a third positioning unit to position the second carriage relative to the first carriage in the main scanning direction, the third positioning unit comprising: a positioning member; grooved members provided parallel to each other in the sub-scanning direction, the grooved members being provided to one of the carriages and the positioning member; and shafts provided parallel to each other in the sub-scanning direction to engage the grooved members, the shafts being provided to the other of the carriages and the positioning member.