Apparatus and method for centering a printing screen over an object

A screen printing apparatus comprising:

• a positioning stage for fixedly positioning an object;
• a plate arranged above said positioning stage;
• a plurality of printing squeegees which are movable horizontally on said plate such that when a printing paste is applied to said plate, said printing paste is printed through said plate onto the object;
• a lifter for moving said positioning stage to a predetermined printing position in a vicinity of a lower surface of said plate;
• a plurality of horizontal drivers connected to said positioning stage for moving said positioning stage in two directions which are substantially perpendicular to each other;
• a positioning controller for calculating a central position of a pattern on said plate from only one reference position and a size of an outer periphery of the object which corresponds to the size of the pattern, said positioning controller being capable of controlling said horizontal drivers to move said positioning stage so that said central position corresponds to a center of the object, wherein said only one reference position is the position at which the pattern is attached to said plate;
• a carry-in conveyor for feeding the object onto said positioning stage along a predetermined transferring direction, said carry-in conveyor being arranged away from said positioning stage, said carry-in conveyor having a carry-in object support surface on which the object is placed before the object is fed onto said positioning stage from said carry-in object support surface, said carry-in object support surface being positioned within the same plane as an object support surface of said positioning stage;
• and
• a carry-out conveyor for transferring the object on said positioning stage along said transferring direction, said carry-out conveyor being arranged away from said positioning stage, said carry-out conveyor having a carry-out object support surface on which the object is placed after the object is fed from said positioning stage to said carry-out object support surface, said carry-out object support surface being positioned within the same plane as said object support surface of said positioning stage.