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Operating Manual Linear ACTUSAFE CMFS(L)
OM-ENGLISH-Failsafe-Linear-16xx-V2.00-2022.03.03
3 Functional Description of the CM FS(L) Failsafe Drive
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Functional Description of the CM FS(L) Failsafe Drive
In normal operation, the actuator is operated by the motor (1). Via a worm gear stage (2) and a planetary gear train (3),
the motor drives the spindle nut of a ball screw (4). The sun gear shaft of the planetary gear train is fixed in place by an
operating current brake (5).
The ball screw converts the rotational movement of the gear unit into linear motion, which, on the one hand, tension the
spring (6), which acts as an energy storage device. On the other hand, the linear motion is transmitted to the valve stem
(8) via a spring-loaded spindle pin (7).
There are no engaging or disengaging elements between the motor, the energy storage device and the fitting shaft in the
actuator. All the gear unit components are permanently engaged.
While moving against the fail-safe direction, the electric motor has to move both the valve and the energy storage device
(spring) for the fail-safe stroke.
If the supply for the operating current brake is interrupted (by a power failure, or intentionally to trigger a fail-safe stroke,
the actuator will no longer be held, and the energy stored in the spring will be converted into kinetic energy. The actuator
starts, forced by the spring, to move the valve in the failsafe position. In this case, the entire gear chain of the actuator with
the exception of the worm gear stage will be moved until the end stop of the valve is reached. The spring-loaded spindle
pin (7) dampens the stop to protect the valves seat.
Owing to this operating principle, neither an initialising stroke nor resetting of the actuator is required after a failsafe stroke.
As soon as the power supply is restored, the actuator is ready for operation.
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Figure 2:
1. . . Motor, 2. . . Worm gear stage, 3. . . Planetary gear train, 4. . . Ball screw, 5. . . Electrical holding brake,
6. . . Spring, 7. . . spring-loaded spindle pin, 8. . . valve stem
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