Manipulating Parts with an Array of Pins: A Method and a Machine

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. The authors 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.