Existing industrial parts feeders move parts through a sequence of mechanical filters that reject parts in unwanted orientations. These feeders require the design of specialized devices such as baffles, cutouts, nests, or traps for each part. In a paper published in Algorithmica (one of three), we described a programmable apparatus that uses a vibrating surface for sensorless, non-prehensile manipulation, where parts are systematically positioned and oriented without sensor feedback or force closure. The idea is to generate and change the dynamic modes of a vibrating surface. Depending on the node shapes of the surface, the position and orientation of the parts can be actively controlled. Our research goal is to develop a science base for manipulation using programmable force fields.
The vibrating surface creates a two-dimensional force vector field. By chaining together sequences of force fields, the equilibrium states of a part in the field can be cascaded to obtain a desired final state. We describe efficient polynomial-time algorithms that generate sequences of force fields for sensorless positioning and orienting of planar parts, and we show that these strategies are complete. Finally we consider parts feeders that can only implement a finite set of force fields. We show how to plan and execute strategies for these devices, and discuss the tradeoff between mechanical complexity and planning complexity.