Manipulating Parts with an Array of Pins: A Method and a Machine
To appear at the Ninth International Symposium of Robotics Research,
Snowbird, Utah, October 1999.
Sebastien Blind, Christopher McCullough, Srinivas Akella, and Jean Ponce
Beckman Institute for Advanced Science and Technology
University of Illinois at Urbana-Champaign
Urbana, IL 61801
Abstract
This paper explores the manipulation of polygonal parts using a
simple device consisting of a grid of retractable pins 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, or bounce out or fall through. We
control the set of equilibrium part configurations by selecting the
set of actuated pins. Our objective is to automatically compute pin
actuation sequences that bring the part to a goal configuration,
without predicting the exact part motion between equilibria. Our
approach is based on constructing the capture region of each part
equilibrium, i.e., the maximal subset of the part's configuration
space such that any motion starting within it is guaranteed to reach
the equilibrium. Reorienting a part reduces to constructing 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, and then finding paths in this graph from
initial to goal states. We have implemented an algorithm to generate
the capture regions and these paths, and have conducted experiments on
a prototype Pachinko machine.