Patent ID: 8556379

Claim:
An image forming apparatus comprising: a first carriage having a recording head that ejects black liquid droplets and is movable in a main scanning direction; and a second carriage having a recording head that ejects color liquid droplets, the second carriage being detachably attachable to the first carriage within a scanning range of the first carriage in the main scanning direction, wherein the first carriage has a mount to place the second carriage thereon, and the mount of the first carriage is disposed relative to the second carriage such that the second carriage is lowered toward the mount of the first carriage in a direction of ejection of the liquid droplets to attach the second carriage to the first carriage, and wherein the second carriage is attached to the first carriage during full-color printing, and the second carriage and the first carriage move in the main scanning direction together while attached to each other to perform full-color printing, an attachment and detachment position at which the first carriage and the second carriage are attached to, and detached from, each other is determined relative to a reference position of the first carriage in the main scanning direction, wherein the first carriage further comprises a protrusion that contacts a lateral plate disposed at one end of the scanning range of the first carriage in the main scanning direction to determine the reference position of the first carriage in the main scanning direction.