Mechanism for describing an algebraic curve
Articulated Mechanims Basis. Applications

This question has been central to kinematics for several centuries, and its origins can be traced back to Watt, with the drawing of a straight line. It's important to understand the theoretical and practical implications. There's a big difference between generating a curve and reproducing one.

Let's illustrate this with the circle:

• by tracing the edge of a coin with a pencil, we draw a circle that is the reproduction of an existing circle;

• with one instrument, the compass, we can generate any circle of given radius, i.e. of given equation.

For the right, the answer is much more difficult:

• the common drawing of the line with the ruler is the reproduction of an existing line;

• ...