Marco Santochi

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.

On-Line Sensing of Flank and Crater Wear of Cutting Tools

Abstract It is well known the high interest for on line sensing of tool wear with the aim of controlling machine tools productivity from the point of view of quality and quantity. Difficulties in this measurement are also known. This paper describes a sensor based upon the TV image analysis of a worn tool. The flank wear is measured observing the active cutting part from a proper direction and lighting the wearland by a fiber optic system. The crater wear is visualized by lighting the tool by a laser system developed by the authors; from the obtained image it is possible to extract the position and the dimensions of the crater and a complete mapping. By means of these system it is possible to evaluate classical parameters of tool wear and to have complete information about tool wear morphology. The paper describes also the software strategy developed for image analysis which has been studied as a compromise between measuring time and required precision. Experimental tests performed with the prototype on a NC lathe have shown good performances here described and discussed.

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.

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.

A Flexible Tool Wear Sensor for NC Lathes

Modern NC machine tools require a more and more exact monitoring and control of cutting process: this function must be per formal by simple and reliable sensors. A very important parameter is tool wear used to optimize cutting data, to control tool position and to change tools at the right time. A new type of tool wear sensor is described, whose working principle is a simple automatic analysis of the whole wearland TV image. The mechanical and optical structure of the sensor is particularly flexible to fit different kinds of tools mounted on a turret of a NC lathe. Many tests have been executed with different tools; results are reported and discussed. The good performances of this sensor make it particularly useful in the development of an ACO strategy, connected to a dynamic data bank inside the NC unit itself.

Robotized assembly of modular fixtures

Summary A prototype plant for the robotized assembly of modular fixtures for NC machining centers is described. After presenting a brief summary of the present tendencies relative to the design, preparation and management of the fixtures, the plant and its components are described in their general structure, posing particular focus on the geometric and functional features of the modular elements, designed in order to facilitate the automatic operations of manipulation and assembly. The plant is controlled by a software structured for design of fixture configuration, planning of the assembly sequence and off-line programming of the robot. Results obtained in assembly tests are also discussed, and emphasis is placed on the more critical aspects linked to the automation of this important operation. In conclusion, the possible applications of the automatic assembly of fixtures for FMS plants are proposed.