Safe Torque off function 203Operation principle1. The Safe torque off activates (the activation switch is opened, or safety relaycontacts open).2. STO inputs on the drive control unit de-energize.3. The control unit cuts off the control voltage from the drive IGBTs.4. The control program generates an indication as defined by parameter 31.22 (referto the firmware manual of the drive).5. Motor coasts to stop (if running). The drive cannot restart while the activationswitch or safety relay contacts are open. After the contacts close, a new startcommand is required to start the drive.Start-up including acceptance testTo ensure safe operation of the Safe torque off function, validation is required. Thefinal assembler of the machine must validate the function by performing anacceptance test.The acceptance test must be performed:• at initial start-up of the safety function• after any changes related to the safety function (circuit boards, wiring,components, settings, etc.)• after any maintenance work related to the safety function. Authorized personThe acceptance test of the safety function must be carried out by an authorizedperson with expertise and knowledge of the safety function. The test must bedocumented and signed by the authorized person. Acceptance test reportsSigned acceptance test reports must be stored in the logbook of the machine. Thereport shall include documentation of start-up activities and test results, references tofailure reports and resolution of failures. Any new acceptance tests performed due tochanges or maintenance shall be logged into the logbook.
