Safe torque off
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 (thus motor can still produce torque but cannot rotate more than 1/2 revolutions)
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
The cutting of AC power makes Argon safe even with DC motor and does not allow AC motor lock up.
In no event the Product Information or parts hereof shall be regarded as guarantee of conditions or characteristics. The Product Information or any part thereof may also not be regarded as a warranty of any kind. No liability of any kind shall be assumed by Author with respect to Product Information or any use made by you thereof, nor shall Author indemnify you against or be liable for any third party claims with respect to such information or any use thereof.
As content of this Wiki may be edited by user community, Granite Devices Oy or it's affiliates do not take any responsibility of the contents of this Wiki. Use information at your own risk. However, Granite Devices staff attempts to review all changes made to this Wiki and keep information trustworthy.
Without written consent, Granite Devices' Products or Intellectual Property shall not be used in situations or installations where living beings, material property, or immaterial property could be harmed by the operation, features or failures of Product. Products may only be used in a way where hazards like moving parts, electric shock, laser radiation, or fire can't be realized even if the content of this Wiki would suggest otherwise.
