Image forming apparatus and method for correcting landing positions of liquid droplets

An image forming apparatus comprising:

• a first carriage movable in a main scanning direction and having at least two first recording heads offset laterally from each other to eject black liquid droplets;
• a second carriage separatably dockable with the first carriage and having a second recording head to eject color liquid droplets;
• a pattern forming unit to control the at least two first recording heads to form on a recording medium adjustment patterns for correcting a shift in landing positions of the liquid droplets ejected from the at least two first recording heads, the at least two first recording heads forming multiple rows of the adjustment patterns in a sub-scanning direction perpendicular to the main scanning direction, each of the adjustment patterns including at least two reference patterns and a measured pattern sandwiched by the two reference patterns aligned in the main scanning direction;
• a pattern detector provided to the first carriage to read the adjustment patterns, the pattern detector successively reading at least two rows of the multiple rows of the adjustment patterns formed in the sub-scanning direction without docking and separation of the first and second carriages;
• and
• a landing position corrector to determine one of a distance between the measured pattern and at least one of the two reference patterns and a scanning time of the first carriage based on a result obtained by the pattern detector and correct the shift in the landing positions of the liquid droplets.