Method of automatic zero adjustment of an injection-molding machine and an apparatus therefor

In a method of zero return for an axis driven by means of a servomotor of an injection-molding machine, a method of automatic zero adjustment of an injection-molding machine, comprising the steps of:

• (a) driving the servomotor to move the axis from a zero return start position toward a reference point;
• (b) storing a preset coordinate position of the reference point as a current coordinate position of the axis when the servomotor further rotates to take a predetermined rotational-angle position after the axis reaches a deceleration position situated short of said reference point the current coordinate position having a memory value;
• (c) updating the memory value of said current coordinate position while moving the axis toward an absolute position whose coordinate position is known;
• (d) correcting said preset coordinate position of the reference point using a correction value calculated on the basis of the memory value of said current coordinate position and the known coordinate position of said absolute position when the axis reaches said absolute position;
• (e) updating the memory value of said current coordinate position while moving the axis toward said reference point;
• and
• (f) replacing said memory value with said preset coordinate position of the reference point when said memory value reaches said corrected reference point coordinate position.