PRINTER

PURPOSE:To make it possible to detect the deterioration of operation margin due to increase in load torque by reducing the drive torque of a pulse motor and checking the operation margin corresponding to the difference between the drive torque of the pulse motor and the load torque of a mechanical part. CONSTITUTION:An operation margin corresponding to the difference between the drive torque of a pulse motor 5 and the load torque of mechanical parts 1 to 4, 6, 7, 12 is checked by reducing the driving torque of the pulse motor 5. Consequently, it is possible to detect the diminution of the operation margin subsequent to an increase of the load torque by reducing the drive torque of the pulse motor 5. Thus an abnormal increase of load torque due to a temporal change or dust settlement in a sliding part can be detected as a possible caused for erroneous operation by a simple and quick way.