Editing Safe torque off

[[File:sto.jpg|thumb|Motor velocity decaying to zero after STO has been activated.]]
Safe torque off a.k.a. STO is a motor drive function that disables drive's ability to direct any torque inducing power to the motor and also prevents unintentional motor power-up. STO is built with [https://en.wikipedia.org/wiki/Redundancy_(engineering) redundancy] a way that guarantees the torque removal torque even in the case of single failure of any component of the system.
==Usefulness==
Built-in STO in drive provides following
;Pros
*Eliminate the need of power cutting relay or contactor 
*Can provide dynamic braking of motor under STO condition instead of letting motor free-wheel which usually increases safety
*Reduce cost of safety circuity
*Simplify wiring
;Cons
*Most STO implementations not safe with brush DC motors and also may cause AC motor to lock-up in certain magnetic pole angle
==STO in Argon servo drive==
[[Argon (servo drive)]] has 4-way STO function making it one of the most fail safe implementations available. Safety is being provided by four simultaneous actions:
*Removing AC input power from power stage by the means of internal safety rated relay
*Cutting gate drive voltage from power stage rendering power stage inactive
*Activating dynamic braking of motor
*Software (firmware) disabling motor control