US 5,442,563 AGranted

Backward assembly planning with DFA analysis

AssigneeThe United States of America as represented by the Adminstrator of the National Aeronautics and Space Administration

InventorSukhan Lee

Life of this patent

Estimating the term…

patentgrep

Loading patent…

Abstract

An assembly planning system that operates based on a recursive decomposition of assembly into subassemblies, and analyzes assembly cost in terms of stability, directionality, and manipulability to guide the generation of preferred assembly plans. The planning in this system incorporates the special processes, such as cleaning, testing, labeling, etc. that must occur during the assembly, and handles nonreversible as well as reversible assembly tasks through backward assembly planning. In order to increase the planning efficiency, the system avoids the analysis of decompositions that do not correspond to feasible assembly tasks. This is achieved by grouping and merging those parts that can not be decomposable at the current stage of backward assembly planning due to the requirement of special processes and the constraint of interconnection feasibility. The invention includes methods of evaluating assembly cost in terms of the number of fixtures (or holding devices) and reorientations required for assembly, through the analysis of stability, directionality, and manipulability. All these factors are used in defining cost and heuristic functions for an AO* search for an optimal plan.

Claims13

Dependent claims

A method of selecting and performing a sequence of sub-assembly operations to construct an assembly said assembly containing a plurality of assembly parts, said method comprising:

identifying all direct subassemblies of said assembly, said identifying comprising:
(a) identifying potential subassemblies of said assembly,
(b) for each potential subassembly, determining whether said potential subassembly is a direct subassembly of said assembly by:
(1) determining whether there is a common axis of separation between said potential subassembly and the remainder of said assembly,
(2) determining whether said potential subassembly is stable, and
(3) determining whether there is a direct unobstructed path between said potential subassembly and the remainder of said assembly;
representing said assembly as a tree of AND and OR nodes beginning with all direct subassemblies as bottom nodes of said tree and concluding with said assembly as the top node of said tree, said AND nodes corresponding to required decompositions of said assembly, said OR nodes corresponding to alternative decompositions of said assembly;
computing a local cost of each OR node of said tree, said computing comprising at least one of the following steps:
(a) determining the number of reorientations of said assembly parts required to construct said direct subassembly given initial orientations of said assembly parts, and
(b) determining the number of mating operations required to construct said direct subassembly;
computing a heuristic cost of each OR node corresponding to said local cost comprising computing a cost of holding said direct subassembly multiplied by a cost of internal stability of said direct subassembly;
combining said local cost and heuristic cost of each OR node of said tree to form a combined cost;
eliminating OR nodes of higher combined costs;
and
performing an assembly operation of subassemblies corresponding to said tree after the elimination of OR nodes of higher combined costs.

12 more elements

A method of selecting and performing a sequence of sub-assembly operations to construct an assembly said assembly containing a plurality of assembly parts, said method comprising:

identifying all direct subassemblies of said assembly, said identifying comprising:
(a) identifying potential subassemblies of said assembly,
(b) for each potential subassembly, determining whether said potential subassembly is a direct subassembly of said assembly by:
(1) determining whether there is a common axis of separation between said potential subassembly and the remainder of said assembly,
(2) determining whether said potential subassembly is stable, and
(3) determining whether there is a direct unobstructed path between said potential subassembly and the remainder of said assembly;
representing said assembly as a tree of AND and OR nodes beginning with all direct subassemblies as bottom nodes of said tree and concluding with said assembly as the top node of said tree, said AND nodes corresponding to required decompositions of said assembly, said OR nodes corresponding to alternative decompositions of said assembly;
computing a local cost of each OR node of said tree, said computing comprising at least:
one of the following steps:
(a) determining the number of reorientations of said assembly parts required to construct said direct subassembly given initial orientations of said assembly parts,
(b) determining the number of mating operations required to construct said direct subassembly, and,
(c) determining a relative cost of holding devices to stabilize said direct subassembly and the remainder of said assembly, and determining the relative cost due to reorientation of said assembly parts;
computing a heuristic cost of each OR node corresponding to said local cost comprising computing a cost of holding said direct subassembly multiplied by a cost of internal stability of said direct subassembly;
displaying to an operator a table for each of said OR nodes summarizing all of factors of said local cost and heuristic cost;
combining said local cost and heuristic cost of each OR node of said tree to form a combined cost;
eliminating OR nodes of higher combined costs;
and
performing an assembly operation of subassemblies corresponding to said tree after the elimination of OR nodes of higher combined costs.

15 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/258,908Filed 9 Jun 1994 · continuation
Priority: 28 Aug 1992
Granted: 15 Aug 1995
Term ends: Not estimatedThe source records don’t support an estimate.

Classification8 codes

G05B 19/41805
Total factory control, i.e. centrally controlling a plurality of machines, e.g. direct or distributed numerical control [DNC], flexible…:…
G06F 30/00
Computer-aided design [cad]
G05B 2219/31053
From computer integrated manufacturing till monitoring: planning, generate assembly plans
G06F 2111/04
Details relating to CAD techniques: constraint-based CAD