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2.6 Safety Function
2.6.1 Overview
With the ALPHA7 Series, the servo amplifier output transistor is stopped by hardware circuit, and the
motor is slowly stopped (free-run stop) by opening (turning OFF) safety device connection connector
CN6 [EN1+] or [EN2+] input. This is the Cat.0 (uncontrolled stoppage) safety stop function (STO)
regulated by EN60204-1, and complies with functional safety standards.
If constructing a safety system, a safety shutoff device was required outside the servo amplifier,
however, this is no longer required by using the safety stop function (STO).
EN ISO 13849-1: 2015
Category
Performance level
Average diagnostic coverage
Response time / Fault reaction time
Mean time to dangerous failure for each
channel
EN 61508-1 to -7
EN 61800-5-2
Safety function
Safety level
Hardware fault tolerance
Safe failure fraction
Probability of failure per hour
Probability of failure on demand average [h
Proof test interval
The servo amplifier output cutoff function uses the safety stop function (STO) regulated by
IEC61800-5-2, however, this is not designed to completely cut off the power supply and motor
electrically. Consequently, depending on the servo system application, it will be necessary to
employ such mechanisms as a brake for mechanical locking, or motor terminal protection to prevent
electric shock in order to ensure the safety of end users.
The servo amplifier output cutoff function does not completely cut off the power supply and motor
electrically, and therefore the servo amplifier power supply should be completely cut off, and wiring
and maintenance work carried out after 5 minutes or longer have elapsed.
Voltage occurs at the servomotor terminals during free-run triggered by the output cutoff function,
and therefore maintenance, inspection, and wiring work should be carried out after ensuring that the
servomotor has come to a complete stop.
Failure to observe this could result in electric shock.
Table 2.6.1-1 Functional safety performance
-1
]
WARNING
CHAPTER 2 WIRING
3
e
90% or higher (DCave medium)
50 ms or less (response time)
62 years or longer (MTTFd)
Output torque OFF function (STO)
SIL3
1 (HFT)
90% or higher (SFF)
-8
Less than 1.5 x 10
(PFH)
-4
Less than 1.5 x 10
(PFDavg)
10 years
Safety Function
2
2-113
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