A computer-aided framework for manufacturability analysis of robot-made assemblies

Abstract

It has been proven that manufacturing enterprises could obtain signi cant savings, both in time and money, by making changes during the early phases of design of their products. This fact has lead to the development of a number of methodologies and software systems tailored to give designers tools to analyze manufacturability during the design stage. Two different approaches could be taken for analyzing the manufacturability of a given design. One is to use metrics based on different factors, like number of operations, complexity of the involved operations, etc. The other one is to simulate the manufacturing process to see if it is feasible to build the design without having to do a physical mock-up. In the case of robotic assembly of electro-mechanical devices, the second approach is more useful because detailed assembly plans are generated in order to do the analysis. In order to test if a given design could be manufactured by a speci c robotic cell, designers must answer a number of questions about sequencing, stability, xturing, grasping, motion planning and tool accessibility. Although several tools have been developed for computing some of the answers required by designers, they have been developed in an isolated fashion making hard the integration of their results. Each tool uses its own ob ject models, sets of constraints, scale factors, and base units leading to incompatibility problems when designers have to use the output from one tool as the input for another one. Unfortunately, these problems make designers would rather answer their questions empirically, one by one, and thus a system that integrates these tools is need. Such a system will relieve designers from the integration burden allowing them to focus on the creative aspects of their jobs. This thesis describes a computer-aided framework that enables the integration of software tools for manufacturability analysis. Based on a given description of the assembly, a feasible assembly sequence, a robotic cell model, a set of software tools and a description of the order in which the tools must be called, the framework is capable of giving detailed plans for the assembly (if they exist) or feedback about the manufacturability problems (when it is impossible to make the assembly in the given cell). The framework is designed in such a way the software tools do not have to be run locally, instead they could be run in any place in the world which can be accessed trough Internet. Two Web-accesible computer systems were implemented to accomplish this research; the rst one was developed as a mean to gure out the problems that must be tackled down to integrate several software tools, and the second one was developed to show the feasibility of building the proposed framework. The ma jor contributions of this research can be characterized as follows: De nition and formal speci cation of a central assembly-oriented data model which includes information about assemblies, robotic cells and constraints. The data model is based on a comprehensive domain ontology that enables the interoperation of manufacturability analysis software tools by managing information for chaining processes, storing solutions and giving feedback to the user. De nition of a modular framework for integration of software tools and feedback mechanisms. A black box integration approach is used allowing the software tools to be implemented in any computer language as long as they use the standard input/output system to read variables and output results. Constraint management is used as a communication mechanism between the tools. The integration of their solutions is made by testing each solution generated to keep coherence with the requirements of all the tools. Sockets are used to communicate with the software tools, so they could be run in any computer plugged to the World-Wide Web at any location around the world. A simple example was set and four tests were run in order to prove the main characteristics of the framework. Also, a survey was designed and applied to expert assembly designers to have an evaluation of the system's usefulness.