Lever 1 turns about fixed axis B. Two-armed pawl 2 turns about fixed axis C and one of its ends slides along lever 1. Lever 4 turns about fixed axis D and has rigidly secured hammer a. Pin d of lever 4 slides along key 3 which turns about fixed axis A. Lever 1, subject to a constant torque, is held against rotation by pawl 2. When key 3 is depressed, lever 4 is turned and hammer a strikes rod b which, in turn, turns pawl 2, freeing lever 1. Spring 5 applies force to hold pawl 2 against lever 1.
$486$SL,K$