Manipulating Parts with an Array of Pins: A Method and a Machine
To appear in the International Journal of Robotics Research,
2001.
Sebastien Blind, Christopher McCullough, Srinivas Akella, and Jean Ponce
Abstract
This article investigates the manipulation of polygonal parts using a
simple device consisting of a grid of retractable pins mounted on a
vertical plate. This ``Pachinko machine'' is intended as a
reconfigurable parts feeder for flexible assembly. A part dropped on
this device may come to rest on the actuated pins, bounce out, or fall
through. We propose a novel algorithm for part reorientation. Its
input consists of the shape of a part, its initial position and
orientation, and a goal configuration, and its output is a sequence of
pin actuations that will bring the part to the goal configuration. The
proposed approach does not attempt to predict the part motion between
the equilibria associated with the active pins in the output sequence;
instead, it constructs the capture region of each equilibrium, i.e.,
the maximal subset of the part's configuration space such that any
motion starting within it is guaranteed to end at the
equilibrium. Assuming frictionless contacts and dissipative dynamics,
reorienting a part reduces to finding a path from initial to goal
states in a directed graph whose nodes are the equilibria and whose
arcs link pairs of nodes such that the first equilibrium lies in the
capture region of the second one. The proposed approach has been
implemented on a prototype of the Pachinko machine, and initial
experiments are presented.