Petri Networks in the Planning of Discrete Manufacturing Processes

This chapter puts forward characteristics of selected issues of manufacturing processes planning using the Petri networks technique. It includes references to the extensive literature concerning the use of Petri networks in computer aided planning of discrete production processes. Diversity of these problems is high as it refers both to the methods of modeling and simulation of the course of manufacturing processes, the issue of optimizing these processes and production systems, representation of knowledge on production parts of equipment and integration of planning and production activities in general. The work puts forward example use of a temporary, priority Petri network for modeling and optimizing production systems and manufacturing operations as well as an example of fuzzy interference using the Petri network mechanism

OPTIMAL FEED RATE CONTROL STRATEGIES FOR FRICTION DRILLING

The presented paper contains the results of research aimed at developing optimal strategies for controlling the feed rate in the friction drilling process. In particular, the use of linear variable feed rate for individual drilling stages and adaptive feed rate control have been tested. The experiments were carried out with the use of a CNC machine tool equipped with an axial force and torque sensor. Correlation between thrust force and torque was shown, respectively, in relation to the feed drive load and the drive of machine tool spindle. Based on this, a feed rate sensorless control strategy was created to protect against excessive and long-term overload both of the tool and the drives. The following assessment criteria were considered: drilling cycle time, maximum values of thrust and torque, maximum values of feed drive load and drive of machine tool spindle, maximum power and energy effect in the form of work necessary to perform during the drilling process and forming the hole flange. The obtained test results, made for low-carbon steel with a tungsten carbide tool, indicate the advantage of the approach based on the linear variable feed rate and adaptive control over the traditional drilling process based on the step change of the feed rate, according to the recommendations given by the tool manufacturers

A hybrid approach for manufacturability analysis

S u m m a r y The paper describes a practical solution for knowledge acquisition of expert process planners and/or experienced machinists with sets of heuristic rules. This fuzzy approach enables to perform manufacturability analysis. Therefore, proposed knowledge system can help in identifying of potential manufacturing problems early in design stage and in determining of machining precedence constraints (hard constraints) in situation of feature volumetric interaction. Special class Weighted Priority Petri Nets and Genetic Algorithms have been used to analyse and optimize the results. Finally, an illustrative example of hole making has been used to demonstrate the proposed methodology. Keywords: CAPP, design for manufacturing, Petri nets, computational intelligence Hybrydowa metoda analizy produktywności S t r e s z c z e n i e W pracy przedstawiono praktyczne rozwiązanie problemu akwizycji wiedzy eksperta w projektowaniu procesów i/lub doświadczonych operatorów obrabiarek, reprezentowanej w postaci zbioru heurystycznych reguł. Rozmyte podejście pozwala na prowadzenie analizy technologiczności proponowanego rozwiązania. Opracowana metoda jest pomocna w identyfikacji potencjalnych problemów wytwórczych juŜ na etapie projektowania konstrukcyjnego. Pozwala określić ograniczenia krytyczne dla relacji procedencji, wynikające z wzajemnych objętościowych interakcji pomiędzy formami elementarnymi występującymi w projektowanym wyrobie. UŜyto specjalnych klas wagowych, priorytetowych sieci Petriego i algorytmu genetycznego dla analizy i optymalizacji wyników. Zaproponowane podejście przedstawiono na przykładzie ustalania sekwencji obróbki otworów, uwzględniającej technologiczność rozwiązania

Alternative Methods for Estimating Plane Parameters Based on a Point Cloud

Non-contact measurement techniques carried out using triangulation optical sensors are increasingly popular in measurements with the use of industrial robots directly on production lines. The result of such measurements is often a cloud of measurement points that is characterized by considerable measuring noise, presence of a number of points that differ from the reference model, and excessive errors that must be eliminated from the analysis. To obtain vector information points contained in the cloud that describe reference models, the data obtained during a measurement should be subjected to appropriate processing operations. The present paperwork presents an analysis of suitability of methods known as RANdom Sample Consensus (RANSAC), Monte Carlo Method (MCM), and Particle Swarm Optimization (PSO) for the extraction of the reference model. The effectiveness of the tested methods is illustrated by examples of measurement of the height of an object and the angle of a plane, which were made on the basis of experiments carried out at workshop conditions

Modeling the Work of Multi-spindle Machining Centers with the Petri Nets

The article presents the results of the simulation studies concerning the impact of random production interruptions on the efficiency of multi-spindle machining centers. Four different machining center configuration models were developed using a dedicated class of stochastic Petri nets. In addition to the number of machine spindles, the number of simultaneously mounted parts, loading time of parts, their machining time, and reliability parameters regarding the frequency of machine interruptions caused by random factors were also taken into account as model parameters. A series of virtual tests was carried out for machining processes over a period of 1000 hours of operation. Analysis of the results confirmed the purpose of conducting simulation tests prior to making a decision regarding the purchase of a multispindle milling center. This work fills the existing research gap, as there are no examples in the technical literature of evaluating the effectiveness of multi-spindle machining centers

Measurement of Energy Consumption During a Thermal Drilling Cycle

Praca przedstawia zagadnienie dotyczące pomiaru i analizy zużycia energii w trakcie cyklu wiercenia termicznego. Przedstawiono oparte na tokarce CNC stanowisko badawcze, którego elementem wyposażenia był eksperymentalny układ poboru energii oparty o licznik energii elektrycznej oraz siłomierz. Zastosowane urządzenia pomiarowe pozwalały na rejestrację obciążenia sieci energetycznej, obciążenia napędów obrabiarki, siłę osiową, moment hamujący wiertło, aktualne obroty wrzeciona obrabiarki, pozycję wiertła względem obrabianego materiału i wartości rejestrów parametrów pomocniczych w strategii adaptacyjnego sterowania posuwem. Rozważano dwa przypadki cyklu wiercenia: wykonanie pojedynczego otworu oraz wykonanie szeregu otworów w jednym cyklu. Testowano pięć strategii sterowania posuwem w trakcie cyklu wiercenia, w tym adaptacyjne sterowanie posuwem i rekurencyjną metodę optymalizacji posuwu. Dla porównania wykonano także otwory tradycyjnymi wiertłami krętymi HSS. Na podstawie uzyskanych rezultatów badań można stwierdzić, że metoda wiercenia ciernego może być zaliczona do energooszczędnych metod wykonywania otworów w elementach cienkościennych.The work presents the issue of measuring and analyzing energy consumption during a thermal drilling cycle. A research stand based on a CNC lathe was presented, the equipment of which was an experimental energy consumption system based on an electricity meter and a force gauge. The measuring devices used allowed for recording the load on the power grid, the load on the machine tool drives, the axial force, the drill braking torque, the current rotation of the machine tool spindle, the position of the drill in relation to the workpiece and the values of auxiliary parameter registers in the strategy of adaptive feed control. Two cases of a drilling cycle were considered: making a single hole and making a series of holes in one cycle. Five feed control strategies were tested during the drilling cycle, including adaptive feed control and a recursive feed optimization method. For comparison, holes were also made with traditional HSS twist drills. Based on the obtained test results, it can be concluded that the friction drilling method can be included in the energy-saving methods of making holes in thin-walled elements

Simulation tests of adaptive control strategies for CNC machine tools

The issue addressed in the article concerns the current needs and possibilities of computer-aided design of adaptive control strategies in machining processes. A simulative method of selecting the adaptive feed control strategy while rough turning materials difficult to machine, effective and inexpensive in its implementation, based on controlling the load placed on the machine's drives, has been presented. The results of a number of virtual tests of the proposed feed control strategy have been included, while paying particular attention to the stability of the machining process during moments of sudden change in the machining allowance. The obtained results meet the accepted quality indicators of the control algorithm. At the same time, the experiences collected by the author while conducting the tests confirmed the complexity of the issue and the resulting necessity to implement a comprehensive simulation testing program

Method of Selecting a Rational Strategy in Sustainable Friction Drilling

The presented paper contains a description of a new method of determining the optimum feed rate for a waste-free, energy-efficient drilling process being a friction drilling. Previous experience has shown that the energy required to drill a hole by friction drilling is closely correlated with the drilling cycle time. Based on the authors' own experience, the thesis was put forward that the optimum feed rate during the drilling procedure should be variable but smooth. Additional evaluation criteria for the developed method were the drilling cycle time, the maximum values of the axial force and torque, the maximum values of the feed drive and machine spindle drive load, as well as the energy consumption. The test rig was based on a numerically controlled machine tool, equipped with an axial force and torque sensor, and additional dedicated measuring devices for measuring energy consumption. The results of the study indicate the high competitiveness of the developed approach, compared to the feed rate control strategies in a friction drilling cycle known from the literature. The proposed approach for selecting the longitudinal feed rate can quickly gain a significant number of applications. Studies have shown that optimally planned feed rates can reduce energy intensity by up to 47%