Putting physics in control-the example of robotics

It is argued that scalar summarizing properties, such as energy conservation or entropy production, often can be used effectively in the design of controllers for multi-input nonlinear physical systems. For instance, the conservation of total mechanical energy allows one to show simply the stability of simple proportional-derivative position controllers for robot manipulators, and it can also be systematically used to design trajectory controllers for these systems. Similarly, explicitly accounting for dissipative dynamics makes possible the use of the intrinsically stabilizing nature of certain disturbance terms such as viscous friction. Related approaches also can be of use in addressing problems of robustness to high-frequency unmodeled dynamics. The development points toward a more ´handcrafted,´ physically motivated approach to nonlinear control system design.<>