7-2
7
1. Safety function
Supplement
Outline
Outline description of safe torque off (STO)
The safe torque off (STO) function is a safety function that shuts the motor current
and turns off motor output torque by forcibly turning off the driving signal of the servo
driver internal power transistor. For this purpose, the STO uses safety input signal and
hardware (circuit).
When STO function operates, the servo driver turns off the servo ready output signal
(S-RDY) and enters safety state.
This is an alarm condition and the 7-seg LED on the front panel displays the error code
number.
Safety precautions
When using the STO function, be sure to perform equipment risk assessment to ensure
that the system conforms to the safety requirements.
Even while the STO function is working, the following potential safety hazards exist.
Check safety in risk assessment.
The motor may move when eternal force (e.g. gravity force on vertical axis) is
exerted on it. Provide an external brake, etc., as necessary to secure the motor. Note
that the purpose of motor with brake is holding and it cannot be used for braking
application.
When parameter Pr5.10 Sequence at alarm is set to free run (disable dynamic
brake), the motor is free run state and requires longer stop distance even if no
external force is applied. Make sure that this does not cause any problem.
When power transistor, etc., becomes defective, the motor will move to the extent
equivalent of 180 electrical angle (max.). Make sure that this does not cause any
problem.
The STO turns off the current to the motor but does not turn off power to the servo
driver and does not isolate it. When starting maintenance service on the servo driver,
turn off the driver by using a different disconnecting device.
External device monitor (hereafter EDM) output signal is not a safety signal. Do not use
it for an application other than failure monitoring.
Dynamic brake and external brake release signal output are not related to safety
function. When designing the system, make sure that the failure of external brake
release during STO condition does not result in danger condition.
When using STO function, connect equipment conforming to the safety standards.
Note
Related page
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Summary of Contents for MINAS A5 Series
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