Crank 1 of four-bar linkage DCBA rotates about fixed axis D. Rocker arm 2, turning about fixed axis A, is a quadrant of which portion b has gear teeth. In one revolution of crank 1, toothed link 3 makes two half-revolutions, one in each direction. The lengths of the motion and dwell periods of link 3 are adjusted by changing the length of rocker arm 2. The initial position of link 3 is adjusted by turning sector a about axis A with respect to rocker arm 2. Concave and concentric surfaces c serve to lock link 3 during its dwell periods. To enable the mechanism to pass through its extreme (dead-centre) positions, pins e on sector a enter slots d of link 3.
$1751$GL,D$