Gino Dini

Automated sequencing and subassembly detection in assembly planning

Abstract This paper describes a procedure for the selection of the subassemblies and the assembly sequences of a product, applied in an assembly planning software system named FLAPS (Flexible Assembly Planning System), under development at the institute of mechanical technology of the University of Pisa. This procedure is based on a mathematical model of the product, obtained through the definition of 3 matrices: the interference matrix, the contact matrix and the connection matrix. The possible subassemblies are automatically detected by satisfying some mathematical conditions applicable to these matrices. For each subassembly and for the whole product, all the possible assembly sequences are generated, whose number can be successively reduced according to some optimization criteria. At the end, a meaningful example is reported to show the possibilities of the method.

Computer Aided Disassembly Planning: State of the Art and Perspectives

Abstract In the last two decades, the problems related to the preservation of the environment and the resources of the planet have been dramatically highlighted by different phenomena (thinning of ozone layer, greenhouse effect, decreasing of forests, air pollution, increasing difficulties in the industrial and domestic waste management, etc.). In order to face this situation, the governments have begun to apply rules to control some aspects of the industrial production and energy. Consequently, the environment has become an interesting issue also for the researchers. A key-point in these new techniques, grouped under the name of “sustainable development”, is the disassembly and recycling of the end-of-life goods, necessary to minimize the environmental impact of discarded materials and energy consumption. In this keynote paper the state of the art of the software tools developed to help the designer and the dismantler in the optimization of the disassembly-for-recycling of discarded goods is discussed. The architecture of a complete and general computer aided disassembly planning system is described and a number of system developed both in the academic institutes and in the industry are shown together a review and classification of the different adopted solutions.

Generation of Optimized Assembly Sequences Using Genetic Algorithms

Abstract This paper describes a method based on genetic algorithms for the generation and the evaluation of assembly sequences. Genetic algorithms are here used to drastically reduce the high computational time, usually necessary to evaluate the best assembly sequences, owing to ‘combinatorial explosion’ phenomena. The generation of optimized sequences is performed using an appropriate fitness function which takes into account simultaneously the geometrical constraints, the minimization of gripper changes and object orientations, and the possibility of grouping similar assembly operations (screwing, pressing, etc.). The paper also presents the chromosome structure used in the system, the genetic operators and, finally, a meaningful example of application.

Dynamic scheduling of FMS using a real-time genetic algorithm

The paper presents a genetic algorithm capable of generating optimised production plans in flexible manufacturing systems. The ability of the system to generate alternative plans following part-flow changes and unforeseen situations is particularly stressed (dynamic scheduling). Two contrasting objectives represented by the reduction of machine idle-times, thanks to dynamic scheduling computation and the reduction of the makespan, are taken into account by the proposed system. The key-point is the real-time response obtained by an optimised evolutionary strategy capable of minimising the number of genetic operations needed to reach the optimal schedule in complex manufacturing systems.

A disassembly planning software system for the optimization of recycling processes

This paper describes the methods and algorithms adopted in a software system for the generation of optimized disassembly plans to be used in recycling of end-of-life goods. Three aspects of the system are particularly emphasized: the integration with CAD; the capability to automatically detect the subassemblies of the product; and the capability to auto matically generate all the feasible disassembly sequences. The selection of the best disassembly plan is made on the basis of the maximum profit achievable from the recycling of components, calculated according to the information contained in a database and concerning the market, the available tools, etc. A meaningful example of application is reported and discussed in detail, analysing the system performance in different situations, e.g. different market conditions, different deterioration of the good, application of different kinds of disassembly operations.

COATS: an Expert Module for Optimal Tool Selection

Abstract After an introduction in which the usefulness of expert systems in the field of process planning is discussed, the paper describes an expert module for fully automatized tool selection in turning operations: the module is a part of a process planning package developed by the authors. The structure of the module includes a knowledge base where production rules IF-THEN can be easily created, edited and deleted by means of an interactive program and a dictionary without being a software specialist, in order to fit the module to different industrial environments. Each rule must be written together with a “weight” evaluated upon the basis of each tool parameter and its influence on cutting process: a reference guide is given for this purpose. After consulting the rules the module proposes the best toolholder-insert couples found in properly created tool files. The “score” of each tool selected is computed by rules weight. Tests carried out have given good results some of which are here described. Then an approach to self learning is described, which allows the module to improve its knowledge base upon the basis of experience, properly evaluated by a monitoring and diagnostic program: automatic creation of new rules is so possible. The advantages of this module are flexibility and possibility to be directly connected with workshop environment.

A Sensor-Integrated Tool for Cutting Force Monitoring

Abstract This paper describes the development of a new concept of cutting tools using strain gages for the measurement of forces in turning operations. The basic idea is the integration of the sensor within the tool shank, in order to obtain a system which is easy to use, easy to install and capable of transmitting data to the CNC through wireless equipment. In particular, the output signal of the measurement bridge is amplified and sent to an external data acquisition system by infra-red transmission. The present paper reports the design principles and the results of some machining tests illustrating the behaviour of the tool in different cutting conditions.

KAPLAN: a Knowledge-Based Approach to Process Planning of Rotational Parts

Abstract This paper describes a generative CAPP system named KAPLAN (Knowledge based Approach to process PLANning) studied for the fully automatic generation of production plans of rotational parts. The program structure is based on knowledge base techniques and the knowledge required for the plan generation is represented by IF-THEN rules, easily adaptable to every workshop environment by means of an user interface. An integration between CAD and CAPP obtained by means of a design module has allowed a complete and effective management of data flow in a full automatic way up to the production plan with all the needed information. The used technique allows to generate all the possible plans for a mechanical part and to select the best one according to the selection criteria stored in the knowledge base. The program is a part of a more complex CAPP system, together with other modules for the complete planning of the work done in a FMS cell installed in the Institute of Mechanical Technology of Pisa. The paper reports some meaningful examples of cases efficiently solved by KAPLAN.

Optimization of Disassembly Sequences for Recycling of End-of-Life Products by Using a Colony of Ant-Like Agents

In this paper the problem of recycling of end-of-life goods is approached using a computer-aided technique named Ant Colony Optimization system. The need of disassembly for recycling and the opportunity of using computer-aided techniques, AI tools in particular, are discussed. The basic concepts of Ant Colony Optimization systems are also introduced. The main topics related to a future application of this methodology to a software system able to support the designer in choosing the best disassembly sequences of products are discussed.

Sensor Technology in Assembly Systems

Abstract This paper describes the present state of the art of sensor technology in automated assembly and analyzes the trends of research performed in the last years. After having examined which are the main reasons for using sensors, the assembly operations requiring sensors are shown. Then the working principles of the most diffused sensors are described together with open problems and some examples of typical applications: force, tactile, optical and vision, mechanical probes and positional sensors. In addition the paper examines the main trends of present research with special reference to new types of sensors, to new application areas, to sensor fusion and artificial intelligence for their management. Finally typical industrial assembly applications are described where sensors have been successfully used.