Functional Safety; Safety Torque Shutdown (Sto) Overview; Sto Module In Servo Drive - Servotronix CDHD2S User Manual

Troubleshooting

9. Functional Safety

9.1 Safety Torque Shutdown (STO) Overview

Functional safety in CDHD2S servo drives is implemented through the Safe Torque Off (STO)
function. Activating the Safe Torque Off (STO) function will cause the drive to stop supplying power
to control motor movement. STO ensures that the energy generated by no torque can continue to
act on the motor, and prevents the drive from accidentally starting or the motor from rotating when
it remains connected to the power supply.
The advantage of STO integration using standard safety technology (using electromechanical
switchgear) is that it eliminates separate components and does not require associated wiring and
servicing.
In addition, the switching time of this function is shorter than the switching time of
electromechanical components in traditional safety concepts.
Note: When the STO function is in effect, the STO circuit power is removed and the motor
power is disabled.
The STO function is defined in the standard EN/IEC61800-5-2 and is related to uncontrolled
stop that complies with the IEC60204-1 standard Category 0 Stop.
Standard EN/IEC61800-5-2 specifies functional safety requirements for adjustable velocity
electric drive systems. According to the requirements of this standard, when the STO function is in
effect, no power is applied to the motor to make it move.
The STO function can be used when power needs to be removed to prevent accidental start-
up.
Warning: Drives with suspended loads must be equipped with an additional mechanical safety
block (e.g. motor brake) because the drive cannot control the load when STO is active.
If the load is not properly protected, it may cause serious personal injury.
The STO function in CDHD2S removes the power provided by the power module gate drive,
suppressing the PWM pulses generated by driving IGBT, as shown in the figure below.

9.2 STO Module in Servo Drive

At present, there are many types of STO modules used in different CDHD2S servo drives:
STO_A3, STO_A4 and STO_A5 only generate the positive power supply voltage for the gate
⚫
drive.
STO_B generates both positive and negative supply voltages for the gate drive.
⚫
Product Dimensio
series ns
—241
—
Input voltage Nominal output current
Table 9-1
circuit
STO STO
compliance