Michael A. Wesley

An algorithm for planning collision-free paths among polyhedral obstacles

This paper describes a collision avoidance algorithm for planning a safe path for a polyhedral object moving among known polyhedral objects. The algorithm transforms the obstacles so that they represent the locus of forbidden positions for an arbitrary reference point on the moving object. A trajectory of this reference point which avoids all forbidden regions is free of collisions. Trajectories are found by searching a network which indicates, for each vertex in the transformed obstacles, which other vertices can be reached safely.

AUTOPASS: an automatic programming system for computer controlled mechanical assembly

This paper describes an experimental very high level programming system for computer controlled mechanical assembly. AUTOPASS (AuTomated Parts Assembly System). The AUTOPASS language is oriented towards objects and assembly operations, rather than motions of mechanical assembly machines. It is intended to enable the user to concentrate on the overall assembly sequence and to program with English-like statements using names and terminology that are familiar to him. To relate assembly operations to manipulator motions, the AUTOPASS compiler uses an internal representation of the assembly world. This representation consists of a geometric data base generated prior to compilation and updated during compilation; it thus represents the state of the world at each assembly step. The level of the language has been chosen to provide a high degree of assistance to the user without the systems having to perform artificial intelligence type problem solving operations.

A geometric modeling system for automated mechanical assembly

Very high level languages for describing mechanical assembly require a representation of the geometric and physical properties of 3-D objects including parts, tools, and the assembler itself. This paper describes a geometric modeling system that generates a data base in which objects and assemblies are represented by nodes in a graph structure. The edges of the graph represent relationships among objects such as part-of, attachment, constraint, and assembly. The nodes also store positional relationships between objects and physical properties such as material type. The user designs objects by combining positive and negative parameterized primitive volumes, for example, cubes and cones, which are represented internally as polyhedra. The data base is built by invoking a procedural representation of the primitive volumes, which generates vertex, edge, and surface lists of instances of the volumes. Several applications in the automatic assembly domain have been implemented using the geometric modeling system as a basis.

OYSTER: a study of integrated circuits as three-dimensional structures

This paper presents a design for a software system (OYSTER) for the parametric simulation and analysis of the fabrication steps of very large scale integrated circuit devices. The system is based on a solid geometric modeling approach in which the component parts of an integrated circuit are represented at any step as three-dimensional solid objects in a geometric data base. The simulation of a fabrication step transforms the data base representation of the geometry and the relations among component parts from their state before the step to their state after the step. At any step, and particularly after the final step, the component parts may be analyzed automatically to determine geometric, mechanical, thermal, and electrical properties. Statistical effects may be incorporated to allow investigation of alignment tolerance build-up and yield. A prototype study is described in which an existing geometric modeling system is used to transform a set of planar masks for an FET device through 28 process steps into 3-D models which are used to compute device capacitances.

Construction and Use of Geometric Models

In this chapter the role of a comprehensive engineering data base in design, manufacture, assembly, and inspection has been developed. By means of examples and references to the literature it has been shown that many of the ingredients are already technically feasible. It remains to be seen whether the outstanding problems are solvable, and which areas are or will become economically feasible.

GENERATION OF SOLID MODELS FROM TWO-DIMENSIONAL AND THREE-DIMENSIONAL DATA

Many important CAD data bases exist only in wire frame (three-dimensional edge and vertex) or projection (two-dimensional planar view) form. In order to exploit the many advantages of computer-based solid modeling, the data descriptors of the objects in these data bases must be converted to solid form. This paper surveys methods for performing the transformation automatically, describes one polyhedral algorithm in some detail, and explores the degree of automation that is both possible and practicable.