Design of a flexible parts feeding system

This paper describes the design and implementation of a flexible parts feeding system. While flexibility encompasses every part of the workcell design, including hardware and control software, the ability to feed parts in a wide variety of sizes and shapes is crucial. Conventional feeding methods, such as vibratory bowl feeders, are not practical for flexible workcells because of their specialized nature. This system is composed of three conveyors working together. The first conveyor is inclined and lifts parts from a bulk hopper in a quasisingulated manner. Parts fall from the first conveyor onto the second, horizontally mounted, conveyor. An underlit window at the end of the second conveyor presents a silhouette image of the parts to a vision system. After the pose of a part has been determined, a robotic arm is used to acquire it. Parts which are in unfavorable orientations or are overlapping are returned to the bulk hopper by a third conveyor. Guidelines for part design which improve the feeding system’s performance are also presented. 1. Survey of Previous Approaches Flexible parts feeding has been and continues to be the most difficult and elusive piece of the agile puzzle. As current trends in production continue towards agility12, non-flexible feeder designs become less and less viable. Rapid changeover between products and rapid introduction of new assemblies is hampered if the feeders cannot be quickly reconfigured34. Several current designs are discussed below. Genex, Inc. markets a feeder (also called the Adept FlexFeeder 250) that has seen limited commercial use56. This feeder uses a short horizontal conveyor to hold bulk parts. An underlit window located in the end of a second horizontal conveyor, mounted below and forward of the first, is used to present parts to the vision system. A third conveyor returns unused parts to a bucket which transports them to the first conveyor for recirculation. The FPF 2000, marketed by Intelligent Automated Systems, uses a different approach. A bin with a trap door is used to drop parts onto a vibrating plate. The plate ends on an underlit conveyor which presents the parts to the vision system. A second conveyor returns unused parts to a bucket which drops them back into the bin for re-feeding. Robotic Production Methods Inc. has designed several feeders which utilize a similar technique6. Parts are lifted from a hopper using a conveyor belt or a vibrating plate. In one design, parts are presented in a vision window that uses overhead lighting; and in another, specialized modular tooling plates are used for orientation. In either case, parts not in the correct orientation fall back into the hopper. AT&T has a feeding system that uses a combination of vibrating plates covered with structured carpet to transport parts around a rectangular loop. At one end, a vision system employing overhead lighting is used for pose estimation.