To rapidly feed industrial parts on an assembly line, Carlisle et al. (1994) proposed a flexible part feeding system that drops parts on a flat conveyor belt, determines position and orientation of each part with a vision system, and then moves them into a desired orientation. When a part is grasped with two hard finger contacts and lifted, it pivots under gravity into a stable configuration. The authors refer to the sequence of picking up the part, allowing it to pivot, and replacing it on the table as a pivot grasp. The authors show that under idealized conditions, a robot arm with four degrees of freedom (DOF) can move (feed) parts arbitrarily in 6 DOF using pivot grasps. This paper considers the following planning problem: Given a polyhedral part shape, coefficient of friction, and a pair of stable configurations as input, find pairs of grasp points that will cause the part to pivot from one stable configuration to the other. For a part with n faces and m stable configurations, the authors give an O(m/sup 2/n log n) algorithm to generate the m/spl times/m matrix of pivot grasps. When the part is star-shaped, this reduces to O(m/sup 2/n). Since pivot grasps may not exist for some transitions, multiple steps may be needed. Alternatively, the authors consider the set of grasps where the part pivots to a configuration within a "capture region" around the stable configuration; when the part is released, it will tumble to the desired configuration. Both algorithms are complete in that they are guaranteed to find pivot grasps when they exist.

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No abstract available.

To rapidly feed industrial parts on an assembly line, Carlisle et. al. (1994) proposed a flexible part feeding system that drops parts on a flat conveyor belt, determines the pose of parts with a vision system and manipulates them into a desired pose. A robot arm with 4-DOF is capable of moving parts through 6-DOF when equipped with a passive pivoting axis between the parallel jaws of its gripper. We refer to these actions as pivot grasps. This paper considers the planning problem. Given a polyhedral part shape, coefficient of friction and a pair of stable configurations as input, find pairs of grasp points that will cause the part to pivot from one stable configuration to the other. For some transitions, pivot grasps may not exist. For a part with n faces and m stable configurations, we give an O(m/sup 2/n log n) algorithm to generate the m/spl times/m matrix of pivot grasps. When the part is star shaped, this reduces to O(m/sup 2/n). We also study a generalization that considers "capture regions" around stable configurations. Both algorithms are complete in that they are guaranteed to find pivot grasps when they exist.

When manipulating parts, it is important to determine the orientation of the part with respect to the gripper. This orientation may not be known precisely or may be disturbed by the act of grasping. In some cases, it is possible to use mechanical compliance to orient parts during grasping. Goldberg (1993) showed that any part with polygonal boundary can be oriented and grasped in this manner using a parallel-jaw gripper. Many of the curves currently used in engineering design are algebraic but nonlinear. Although these curves can be approximated as polygons for the purpose of visualization, such approximations can lead to false conclusions about mechanical behavior. In this paper we consider the class of parts whose planar projection has a piecewise algebraic convex hull. Our primary result is a proof that a grasp plan exists for any such part. We give a planning algorithm that produces the shortest plan and runs in time O(n/sup 2/ log n+N), where n is the number of transitions in the grasp function and N is the length of the plan produced. We believe this to be the first paper to address the problem of manipulating algebraic parts when nothing is know about their initial orientation.>

To be cost effective and highly precise, many industrial assembly robots have only four degrees of freedom (DOF) plus a binary pneumatic gripper. Such robots commonly permit parts to be rotated only about a vertical axis. However it is often necessary to reorient parts about other axes prior to assembly. In this paper the authors describe a way to orient parts about an arbitrary axis by introducing a rotating bearing between the jaws of a simple gripper. Based on this mechanism, the authors are developing a rapidly configurable vision-based system for feeding parts. In this system, a camera determines initial part pose; the robot then reorients the part to achieve a desired final pose. The authors have implemented a prototype version in their laboratory using a commercially-available robot system.>

Automatic recognition of parts is an important problem with applications in sorting parts for packing and assembly. Our objective is to recognize parts using inexpensive, widely-available robot hardware as an alternative to machine vision. Specifically, our aim is to determine the shape of a polygonal part from a sequence of diameter (width) measurements made by grasping the part with an instrumented parallel-jaw gripper. Since complete determination of shape is not possible using just diameter measurements, we consider the problem of recognizing a part from a known (finite) set of parts. Given a set of parts with a total of N faces, of which n are stable, we first construct an internal representation of the stable faces in O(N+n/sup 4/) time. Then we give two off-line planning algorithms: one constructs an optimal sensing plan in time O(n/sup 4/2/sup n/) the other constructs a suboptimal sensing plan in time O(n/sup 2/ log n). Neither plan requires more than n+1 online measurements.>

K.Y. Goldberg (1990) described an algorithm for orienting planar polygonal parts using a modified parallel-jaw gripper. The authors extend this algorithm to handle parts with curved edges. They define a generalized polygon as a planar figure made up of piecewise linear and circular edges, and a generalized polygonal part as one of constant cross section, the convex hull of which is a generalized polygon. For this class of parts a complete algorithm for determining an optimal parts-orienting strategy is presented.>

Manufacturing processes often produce a stream of parts that must be oriented precisely before assembly. Given the description of an n-sided planar polygonal part, K.Y. Goldberg (Ph.D. Diss., Carnegie-Mellon Univ., 1990) presents an O(n/sup 3/) serial algorithm that produces an optimal sequence of gripper actions to orient the part up to symmetry using a sensorless parallel jaw gripper. The authors consider an online version of this problem and given an O(n) parallel solution for it on an n*n mesh-connected computer.>