Lever 1 turns about fixed axis A . Levers 2 and 3 turn independently of each other about fixed axis B . Lever 1 has two lugs a and levers 2 and 3 have lugs b. As lever 1 is oscillated, its lugs a alternately engage lugs b of levers 2 and 3 . At this the other lever (lever 2 as illustrated) is forced by spring 4 against pin d mounted at axis A, compressing the spring. When lever 1 is released it will be returned by spring 4 and the first lever (lever 3 as illustrated) to its initial (central) position.
$144$SL,L$