Automatic object release in magnetic and electrostatic levitation systems

A method is described for automatic release of a levitated object without external control commands in levitation systems (such as magnetic and electrostatic levitation). The key aspect is an integral action in the controller. Examples of a zero-power controller for magnetic levitation and a proportional-integral-derivative (PID) controller for electrostatic levitation are presented. Automatic release of the levitated object is a consequence of the controller behavior when the levitated object has a temporary forced position error. In a pick and place task that uses non-contact levitation techniques, a position error is induced at placing. Automatic release simplifies the task of placing, as no external command is required. The principle of this release method is explained and analyzed using a zero-power controller in a magnetic levitation system. For electrostatic levitation, which is analogous to magnetic levitation, experimental results of an automatic release based on PID-control are presented. A general guideline is derived to tune the controller settings so as to achieve automatic release, and this is supported by experiments.