Electric press
The electric press is provided with a main CPU 1 and a sub CPU 3 , the main CPU 1 being responsive to a signal from a servo driver 10 to give an detecting signal to a relay 2 when a ram 51 is located in a predetermined position, thereby to give a mute signal to an area sensor 30 and the sub CPU 3 being responsive to a signal from an encoder 9 to give a detecting signal to a relay 4 when the ram is located in a predetermined position, thereby to give a mute signal to the area sensor 30 . The main CPU 1 and sub CPU 3 watch each other, that is, the main CPU 1 checks the output of a relay 4 and turns the relay 2 off when the mute signal is not produced from the relay 4 . The conditions of sub CPU and main CPU are compared with each other. In case the two conditions are in accord with each other, it is decided that the relay 4 is out of order. The sub CPU 3 makes the same check operation in connection with the relay 2.
1. An electric press having a ram that is movable relative to a work to be processed and having an area sensor connected thereto for detecting a person entering a predetermined area in connection with the electric press, said electric press comprising:
detecting means for detecting a predetermined condition of the electric press;
signal producing means that is structured and arranged to produce a signal to invalidate said area sensor whenever the detecting means detects that said electric press is in the predetermined condition; and
watching means for determining whether or not watching said signal producing means if said signal producing means is operating correctly; wherein
said detecting means includes a first detecting means and a second detecting means;
said signal producing means includes a first signal producing means and a second signal producing means;
said watching means includes a first watching means for watching if said first signal producing means is normally operating and a second watching means for watching if said second signal producing means is normally operating,
said first and second signal producing means being prevented from producing the signal for invalidating the area sensor in case one of said first and second signal producing means is not normally operating.
2. The electric press as defined in claim 1 , wherein
said first detecting means is responsive to the drive signal from the drive motor of said electric press to detect said predetermined condition of said electric press;
said second detecting means is operated to detect the position of the ram of said electric press, thereby to detect said predetermined condition of said electric press.
3. The electric press as defined in claim 1 , further comprising: a sub-central processing unit for realizing said first watching means which watches if said first signal producing means is normally operating and for realizing said second signal producing means, and a main central processing unit for realizing said second watching means which watches if said second signal producing means is normally operating and for realizing said first signal producing means.
4. The electric press as defined in claim 1 , wherein said predetermined condition of said electric press is a condition wherein said ram is in a standby position.
5. The electric press as defined in claim 1 , wherein said predetermined condition of said electric press is a condition wherein said ram is in the process of moving to a standby position.