Method of initializing pen recorder carriage position

A method of driving a pen recorder including a carriage supporting a rotatable drum with a plurality of pen units mounted thereon and a stepper motor for driving the carriage across a sheet of print paper through a print region in which the pen units can effect printing and a nonprint region in which the pen units can effect no printing, said method comprising the steps of:

• moving said carriage to a stopper position at an end of said nonprint region by rotating said stepper motor through a predetermined number of increments, thereby establishing a fixed relationship between the phase of said stepper motor and the position of said carriage;
• moving said carriage through said print region to allow a selected pen unit to effect printing on the sheet of print paper in a printing cycle;
• returning said carriage to a home position at an opposite end of said nonprint region after each printing cycle;
• and
• reprocating said carriage in an interval between said stopper position and said home position while angularly moving said rotatable drum until a desired pen unit is selected for a next printing cycle, said interval excluding said stopper position, so that said home position can be fixed with respect to said stopper position until all desired printing cycles are performed.