Ratchet wheel a is secured rigidly on shaft 1. Link 2, rotating freely about fixed axis A of shaft 1, carries pawl 3 which turns about pin b and slides along this pin with slot d. With respect to link 2, shaft 1 can rotate only counterclockwise; when it starts to rotate clockwise, it is locked by pawl 3. Pawl 3 can be disengaged from ratchet wheel a by sliding its slot d along pin b.
$290$SL,SD$