Apparatus for automatically adjusting offset correction values for current detectors

An automatic offset adjusting apparatus (4) for current detectors (5, 11) in a digital controller for a servo motor (10) is constructed so that, when errors occur in offset correction values (c1, c2) due to a temperature change and the like while the servo motor (10) is in operation, an electrical angle detecting unit (26) detects a ripple of the torque of the servo motor (10), on the basis of a ripple of a torque command value (b), and detects a first electrical angle, where the torque command value (b) becomes maximum, and a second electrical angle, where the torque command value (b) becomes minimum, based on an electrical angle signal (f) of the servo motor, a judgement unit (27) judges whether or not offset correction errors have occurred on the basis of a difference between the first and second electrical angles, and, if the judgement unit (27) judges that the offset correction errors have occurred, a correction unit (30) adds adjustment values for the offset correction values (c1, c2) corresponding to the first electrical angle to the respective offset correction values (c1, c2) to update the offset correction values (c1, c2), whereby the correction of the offset correction values (c1, c2) is automatically carried out even while the servo motor (10) is in operation, thereby preventing generation of the ripple of the torque of the servo motor (10).