Shut-Off Function (Sto, Ss1) - Mitsubishi Electric MELSEC Q Series Programming Manual

1 OVERVIEW

1.4.4 Shut-off function (STO, SS1)

(1) STO function disables energy supply to the servo motor by electrical shut-off. The
function does not mechanically disconnect electricity from the motor. Therefore, it
cannot prevent exposure to electric shock, install a magnet contactor or a molded
case circuit breaker to the main circuit power supply (L1, L2, and L3) of the servo
amplifier.
(2) STO function can disable the energy to servo motor by the electrical shutoff. This
function does not guarantee the procedure of stopping the servo motor and
deceleration control.
(3) SS1 function only guarantees the delay time before STO becomes effective.
(4) If SS1 delay time is shorter than servo motor deceleration time, or forced stop
function has an error, STO becomes effective during motor rotation, dynamic
brake stop or free-run stop is activated.
(5) Even if STO function becomes effective with a STO switch, voltage may be left in
the servo motor due to the inherent delay of the equipment.
(6) When the servo amplifier is replaced, make sure that new one is the same type as
the old one. After installation, make sure to check the performance of safety
observation function before operating the system.
(7) Check the safety at a certain cycle, or with machinery which is defined by the
safety standard to prevent the accumulation of failures. Check the safety at least
once a day regardless of system safety level.
(8) If a power module of a servo amplifier shorted at the upper and lower positions,
the servo motor axis rotates half at maximum. For a linear servo motor, the
primary side will move a distance of pole pitch.
(9) Make sure to supply STO input signals (STO1, STO2) from one power supply.
Otherwise, the STO function may not function properly due to a sneak current,
failing to bring the STO shut-off state.
(10) For the STO I/O signals of the STO function, supply power by using a safety extra
low voltage (SELV) power supply with the reinforced insulation.
1 - 12