Basic Googling on the mechanical generation of oscillating motion (moving something back and forth in the manner of a windshield wiper or a flapping wing) from a source of circular motion comes up with a concept known as a "four-bar linkage" or "crank rocker". For example, this video shows very clearly a simple way to create a windshield-wiper motion:
The problem is, this doesn't look anything like a windshield wiper. It has a bar attached to the tip of the "wiper" pulling it back and forth along its arc. But in an actual windshield wiper (or wing, for that matter) the moving force comes from the base, not the tip.
So how do you go about generating oscillating motion from the base of the oscillating device, windshield-wiper style? Assume you're starting with a motor providing circular motion, as in the video.