This is a sequence of linkages that open a door. The first shows the door is a lever hinged at its fulcrum that is opened and closed by moving any point.
The next linkage adds a linear actuator to move the point on the door. The result is a four-bar linkage known as a slider-crank linkage. The next sheet provides a construction that coordinates the open and closed positions with the rotation of an input crank. This is a four-bar linkage known as a crank-rocker.
The final construction yields a four-bar linkage known as a function generator that coordinates the open and closed positions of the door with specific angles for the input crank.