Difference between revisions of "Safe torque off"

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[[File:sto.jpg|thumb|Motor velocity decaying to zero after STO has been activated.]]
 
[[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 produce torque with motor and also prevents unintentional motor start-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.
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Safe torque off a.k.a. STO is a motor drive function that disables drive's ability to produce torque with motor and also prevents unintentional motor start-up. STO is built with [https://en.wikipedia.org/wiki/Redundancy_(engineering) redundancy] a way that guarantees the removal of torque even in the case of single failure of any component of the system.
 
==Usefulness==
 
==Usefulness==
 
Built-in STO in drive provides following
 
Built-in STO in drive provides following

Revision as of 21:29, 15 June 2013

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 produce torque with motor and also prevents unintentional motor start-up. STO is built with redundancy a way that guarantees the removal of 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