How many turns must the link-driven driving sheave rotate to fully open or close the doors?

The correct answer reflects the mechanism of how link-driven driving sheaves operate in elevator systems. In typical elevator door operation, the sheave, which is a pulley-like component, must rotate a specific amount to engage the door mechanism fully.

In this case, one-half of a turn of the link-driven driving sheave is sufficient to either fully open or fully close the doors. This design is efficient and allows for quick and reliable operation without requiring excessive movement or energy. Understanding this aspect of the sheave's mechanics is crucial for maintaining and troubleshooting elevator systems effectively.

A full turn would typically exceed the necessary movement, leading to unnecessary wear on components. Similarly, one and a half turns would imply an over-rotation, while two turns would definitely be excessive for a simple open or close operation. Therefore, recognizing that one-half of a turn is adequate is key to understanding the functionality of the system.