5.2 HWBB Function
5.2.1 Risk Assessment
5-4
5.2.1
Risk Assessment
When using the HWBB function, you must perform a risk assessment of the servo system in
advance to confirm that the safety level of the standards is satisfied. Refer to the following sec-
tion for details on the standards.
Compliance with UL Standards, EU Directives, and Other Safety Standards
Note: To meet performance level e (PLe) in EN ISO 13849-1 and SIL3 in IEC 61508, the EDM1 signal must be mon-
itored by the host controller. If the EDM1 signal is not monitored by the host controller, the levels will be safety
performance level c (PLc) and SIL1.
The following hazards exist even when the HWBB function is operating. These hazards must be
included in the risk assessment.
•
The Servomotor will move if an external force is applied to it (for example, gravity on a vertical
axis). Implement measures to hold the Servomotor, such as installing a separate mechanical
brake.
•
If a failure occurs such as a Power Module failure, the Servomotor may move within an elec-
tric angle of 180
°
. Ensure safety even if the Servomotor moves.
The rotational angle or travel distance depends on the type of Servomotor as follows:
•
Rotary Servomotor: 1/6 rotation max. (rotational angle calculated at the motor shaft)
•
Direct Drive Servomotor: 1/20 rotation max. (rotational angle calculated at the motor shaft)
•
Linear Servomotor: 50 mm max.
•
The HWBB function does not shut OFF the power to the SERVOPACK or electrically isolate it.
Implement measures to shut OFF the power supply to the SERVOPACK before you perform
maintenance on it.
•
The HWBB function of a
Σ
-7W/
Σ
-7C SERVOPACK shuts off the current to the motors for
both axes at the same time. You cannot shut off the current to the motor for just one axis.
Build the system so that a hazardous condition will not result if the current to the motors for
both axes is shut off.
5.2.2
HWBB State
The HWBB state is when the /HWBB1 or /HWBB2 signal is OFF, the HWBB function is active,
and the current to the motor is turned OFF with a hardwired circuit.
If the /HWBB1 or /HWBB2 signal turns OFF and the HWBB function is activated, the SERVO-
PACK will be in the following status.
The following examples use the
Σ
-7W SERVOPACK with MECHATROLINK-III commands. If you
use a
Σ
-7C SERVOPACK, you will need to use Controller Section commands instead of MECHA-
TROLINK-III commands.
Important
