Abstract: A vertical position of a ram is directly detected by a ram position detector. A first speed arithmetic operating portion determines a first ram moving speed on the basis of a change of the detected position. A second speed arithmetic operating portion determines a second ram moving speed on the basis of a rotational number of a servo motor which is determined by a servo motor rotational number detector. A comparing portion compares the first ram speed with the second ram speed, and when a difference is equal to or more than a predetermined amount, a judging portion judges that an abnormality exists so as to immediately stop the servo motor and stop an operation.

Abstract: A vertical position of a ram (5U) is directly detected by a ram position detecting means (11), and a first speed arithmetic operating portion (65) determines a first ram moving speed on the basis of a change of the detected position. At the same time, a second speed arithmetic operating portion (67) determines a second ram moving speed on the basis of a rotational number of a servo motor (39) which is determined by a servo motor rotational number detecting means (40). A comparing portion (69) compares the first ram speed with the second ram speed, and in the case that a difference is equal to or more than a predetermined amount, a judging portion (71) judges that an abnormality exists so as to immediately stop the servo motor (39) and stop a working.