The Coulomb pump: a novel parts feeding method using a horizontally-vibrating surface

Abstract

Part feeders, which separate and orient parts prior to packing and insertion, are critical components of an assembly line. Existing feeders utilize off-plane vibrations of a rigid structure to convey parts along a track. Repeated part hopping/landing phases are concerns if parts are delicate and/or high positioning accuracy is required. Here we consider a simpler feeder design in which parts are in permanent contact with a horizontally-vibrating flat plate. Each vibration is a "pump-like" motion along a single degree of freedom: the plate spends more time moving forward than backward. Parts are propelled forward since dynamic friction is fixed and independent of the relative velocity at the interface. In designing plate vibration profiles we consider issues of waveform simplicity, bandwidth, and feed rate performance. Both bang-bang and sinusoidal control waveforms are analyzed. Expressions are derived for equilibrium feed rates for both waveforms; dynamic simulation is used to verify the analysis. A prototype of the proposed feeder has been implemented with cheap mechanical parts. A simple experiment with the device is presented.