Special finite elements: Theoretical background and application

Specijalni konačni elementi (KE) koriste se za modeliranje posebnih fenomena u ponašanju konstrukcija. Izraz "specijalni" označava KE sa specifičnim svojstvima (parametri krutosti, ponašanje pod opterećenjem, itd.) i posebnom ulogom u modeliranju, po čemu se i bitno razlikuju od "standardnih" KE. Postoji više tipova specijalnih KE, ali se najčešće koriste: "nelinearna opruga" KE, "zazor" KE i "veza" KE. Na različitim će primjerima biti pokazane prednosti primjene specijalnih KE, posebno u modeliranju konturnih i prijelaznih uvjeta. Teorijska podloga data je samo u neophodnom obimu, zbog dobrog razumijevanja numeričkih aspekata primjene specijalnih KE.Special finite elements (FEs) are used for modeling of certain phenomena in structural behavior. The term "special" denotes FEs with specific characteristics (stiffness parameters, behavior under load, etc.) and a specific role in modeling, which is their main difference from "common" FEs. There are many types of special FEs, but the following are often used: so-called "nonlinear spring" FE, "gap" FE and "link" FE. Various examples will show many advances in the application of these FEs, especially in modeling of boundary and interface conditions. Theoretical background is given only in the amount necessary for proper understanding of numerical aspects of the application of special FEs

Influence of tool wear on the mechanism of chips segmentation and tool vibration

The tool wear has a significant impact on the cutting process and therefore tool wear monitoring is especially important for building intelligent machine tools which are capable of assessing their own states and reacting to important changes. This approach is based on the assumption that there exists a relationship between the spectrum of high-frequency vibrations measured on tool holder, in immediate vicinity of the cutting zone, and the tool wear degree. The wear causes changes in tool tip geometry, which has significant influence on the process of chip forming. At the same time, the erratic nature of chip forming process excites the cutting zone, generating a very broad spectrum of vibrations. Due to high input energy, these vibrations are very intensive, and spread through the entire machining system. In the paper, experimental results are shown which pertain to the relationship between the power spectral density (PSD) within 5 kHz to 50 kHz interval.Web of Science20111210

A model of collaborative process planning system (e-CAPP)

Današnja tendencija globalne konkurentnosti zahtijeva razvoj distribuiranih aplikacionih sustava koji se koriste u projektiranju proizvoda, pripremi proizvodnje, kao i izravno u procesu proizvodnje. Na ovaj način se stvaraju distribuirana projektantska i proizvodna okruženja koja nadilaze tradicionalna fizička i vremenska ograničenja. Primjenom Internet/intranet tehnologije povezuju se i integriraju geografski dislocirani projektanti, eksperti, sustavi, resursi i servisi. Analizom novih tendencija u planiranju i pripremi distribuirane proizvodnje uočena je potreba za razvojem kolaborativnog sustava u oblasti projektiranja tehnoloških procesa. Aktivnosti vezane za projektiranje tehnoloških procesa izrade se u distribuiranim okruženjima često realiziraju primjenom proširenog CAPP sustava čija je baza znanja proširena i unaprijeđena znanjem dislociranih eksperata. e-CAPP upravo predstavlja jedan takav kolaborativni sustav namijenjen projektiranju tehnoloških procesa izrade proizvoda.The current tendency of global competitiveness requires the development of distributed application systems that are used in the product design, the production preparation, as well as directly in the manufacturing processes. In this way, distributed design and production environments created actually exceed traditional physical and time constraints. The application of internet/intranet technologies enables the connection and integration of geographically dislocated designers, experts, systems, resources and services. After analysing new tendencies in planning and preparing the distributed manufacturing, a need to develop a collaborative system in the area of process planning is identified. Activities related to process planning in distributed environments are often realized by applying the extended CAPP system whose knowledge base is increased and improved by the knowledge of geographically dislocated experts. The e-CAPP represents exactly such a collaborative system which can be effectively applied in the area of process planning

A novel fully fast recovery EMG amplifier for the control of neural prosthesis

Ovaj članak predstavlja novo EMG (elektromiografsko) brzo oporavljivo pojačalo, koje se može koristiti kao sučelje za kontrolu neuronskih proteza. Osnova predloženog električnog kruga je standardno instrumentacijsko pojačalo implementirano pomoću tri operacijska pojačala s integratorom u negativnoj povratnoj petlji diferencijalnog pojačala. Standardno instrumentacijsko pojačalo s tri operacijska pojačala je modificirano uvođenjem analogne linije za kašnjenje između prvog stupnja (diferencijalni ulaz - diferencijalno izlazno pojačalo) i drugog stupnja (diferencijalno pojačalo). Glavna svrha analogne linije za kašnjenje je kašnjenje EMG signala i poticaj artefakta između prvog i drugog stupnja. Uvođenjem linije za kašnjenje u standardnom instrumentacijskom pojačalu s tri operacijska pojačala, pokazano je da se poticaj artefakta može otkriti prije nego što se pojavi na izlazu iz pojačala. Na taj način kontrolni sklopovi pojačala imaju dovoljno vremena da onemoguće integrator u diferencijalnom pojačalu, i spriječe nakupljanje naboja u kondenzatoru integratora. Također je pokazano da ova konfiguracija EMG pojačala ima ultra brzo vrijeme oporavka, tako da se može koristiti kao sučelje za kontrolu neuronskih proteza.This paper presents a novel EMG (electromyography) fast recovery amplifier, which can be used as a neural prosthesis control interface. The basis of the proposed circuit is standard three op-amp amplifier with integrator in the negative feed-back loop of the differential amplifier. The Standard three op-amp instrumentation amplifier has been modified by introducing analog delay line between the first stage (differential input - differential output amplifier) and the second stage (differential amplifier). The main purpose of the analog delay line is to delay EMG signal and the stimulus artifact between the first and the second stage. It is shown that by introducing a delay line in the standard three op-amp instrumentation amplifier, stimulus artifact can be detected before it appears at the output of the amplifier. Thus the control circuits of the amplifier have enough time to disable the integrator in the differential amplifier, and prevent charge accumulation in the integrators capacitor. It is also shown that this configuration of the EMG amplifier has ultrafast recovery time, so it can be used as a control interface of the neural prosthesis

Evaluation of Residual Stresses after Irregular Interrupted Machining

Residual stress occurs in many machined components and parts. Over time, several methods have been developed for the investigation of residual stress in the material – destructive and non-destructive. This article deals with the evaluation and comparison of residual stress in the material when machining steel C45 and 11CrMo9-10, when the tool enters into the cut and stands out in conditions of an interrupted cut. A non-destructive method, based on X-Ray diffraction, was applied to evaluate the residual stress. The points were measured on the last machined slat by using interrupted cut simulator. An irregular interrupted cut was achieved by gradually machining 4, 3, 2 and 1 slat. The experiments were realized in co-operation with the Faculty of Mechanical Engineering, VSB – Technical University of Ostrava, Czech Republic and the Faculty of Mechanical Engineering, the University of Žilina, Slovakia

Use of soft computing technique for modelling and prediction of CNC grinding process

Zbog složenosti procesa brušenja višeslojne keramike te osiguranja zahtijevane kvalitete proizvoda, odabir optimalnih tehnoloških parametara je izazovan zadatak za proizvođače. Osigurati traženu izlaznu kvalitetu proizvoda (paralelnost površina) u funkciji ulaznih parametara (stroj, operater stroja, folija i proizvodna linija) predstavlja glavni cilj istraživanja. "Tehnike mekog računalstva" dobivaju pozornost istraživača za modeliranje procesnih parametara složenih tehnoloških procesa. U ovom radu koristi se tehnika mekog računalstva poznata kao umjetne neuronske mreže (ANN) za modeliranje i predviđanje parametara tehnološkog procesa CNC brušenja višeslojne keramike. Rezultati su pokazali da ANN s algoritmom širenja unazad potvrđuje primjenu i na ovaj problem. Oblikovanjem različitih arhitektura ANN (pravila učenja, prijenosne funkcije, broj i strukture skrivenih slojeva i drugi) na setu podataka iz proizvodno – tehnološkog procesa ostvaren je najbolji rezultat RMS greške od 10,76 % u procesu učenja i 12,07 % u procesu validacije. Ostvareni rezultati potvrđuju prihvatljivost i primjenu ovog istraživanja u tehnološkoj i operativnoj pripremi proizvodnje.Due to the complexity of grinding process of multilayer ceramics, and the need for a specific product quality, the choice of optimal technological parameters is a challenging task for the manufacturers. The main aim of investigation is to secure the demanded final product quality (plane parallelism) in the function of input parameters (machine, machine operator, foil and production line). "Soft computing techniques" are becoming more interesting to the researchers for the modelling of processing parameters of complex technological processes. In this paper, a soft computing technique, known as the Artificial Neural Networks (ANN), is used for the modelling and prediction of parameters of technological process of CNC grinding of multilayer ceramics. The results show that the ANN with the back-propagation algorithm justifies the application also to this problem. By designing different architectures of ANN (learning rules, transfer functions, number and structure of hidden layers and other) on the set of data from the production - technological process, the best result of RMS error (10,76 %) in the process of learning and 12,07 % in the process of validation was achieved. The achieved results confirm the acceptability and the application of this investigation in the technological and operational preparation of production

APPLYING PRECEDENCE RELATIONSHIPS AND CAD/CAM SIMULATION IN TIME-BASED OPTIMIZATION OF PROCESS PLANNING

Optimization of process planning belongs to the group of combinatorial optimization problems which at the macro and micro level consists of the selection of machining operations, definition of sequences of machining operations and their grouping into processes, selection of manufacturing resources, machining parameters and strategies. The objective function used for evaluating process plans is mostly defined by manufacturing cost, manufacturing time, surface quality and surface accuracy. The main goal of this research refers to the process planning and optimization of manufacturing time by applying precedence relationships among machining operations, as well as the simulation technique within the CAD/CAM system. The precedence relationships are defined on the basis of dimensional, geometric, technological and economical precedence constraints. Based on these rules, precedence matrices for determining operation sequence for the given shaft part are formed, and afterwards, machining operations are grouped into appropriate processes. For the given rational variants of process plans, a simulation of machining process is performed within the Catia software system. The obtained output is the best variant of process plan for the shaft part on the basis of manufacturing time as the adopted objective function

A model of tool wear monitoring system for turning

Prikupljanje kvalitetnih i pravovremenih informacija o stanju alata u realnom vremenu predstavlja nužan uvjet za identifikaciju stupnja istrošenosti alata čime se u značajnoj mjeri poboljšava postojanost i kvaliteta procesa obrade. Ovaj rad se bavi definiranjem modela sustava za klasifikaciju istrošenosti alata uz poseban osvrt na modul za prikupljanje i obradu signala ubrzanja vibracija primjenom diskretnih "wavelet" transformacija (DWT) pri dekomponiranju signala. U radu je prikazan model razvijenog fuzzy sustava za klasifikaciju trošenja alata. Sustav sačinjavaju tri podsustava: za prikupljanje i obradu podataka, za klasifikaciju istrošenosti alata i odlučivanje. U okviru podsustava za prikupljanje i obradu podataka prikazana je izabrana metoda izdvajanja značajki. U okviru klasifikacije i grupiranja podataka prikazan je izabrani model fuzzy klasifikatora i provjera klasifikacije u eksperimentalnim laboratorijskim uvjetima. Primijenjeni model testiran je za zahvate uzdužne i poprečne obrade.Acquiring high-quality and timely information on the tool wear condition in real time, presents a necessary prerequisite for identification of tool wear degree, which significantly improves the stability and quality of the machining process. Defined in this paper is a model of tool wear monitoring system with special emphasis on the module for acquisition and processing of vibration acceleration signal by applying discrete wavelet transformations (DWT) in signal decomposition. The paper presents a model of the developed fuzzy system for tool wear classification. The system comprises three modules: module for data acquisition and processing, module for tool wear classification, and module for decision-making. The selected method for feature extraction is presented within the module for data classification and processing. The selected model for the fuzzy classifier and classification in experimental laboratory conditions is shown within data classification and clustering. The proposed model has been tested in longitudinal and transversal machining operations

Eksperimentalna analiza i MKE modeliranje vibracija reznog alata

Presented in this paper is a comparative analysis of vibrations, measured during machining process and modelled by FEM. Moreover, microscopic structure of chip cross section was analyzed in order to establish the frequency of lamellae generation and its influence on the total level of vibrations of the cutting tool. Based on the results thus obtained, a method was proposed which allows determination of tool wear degree through separation of reliable indicators from the high-frequency spectrum of the measured vibration signals. This investigation showed that the change of chip segmentation frequency significantly influences the output vibration signal within the high-frequency spectrum, and is a function of tool wear degree.U radu je dat usporedni pregled vibracija reznog alata izmjerenih u procesu obrade i modeliranih primjenom metode konačnih elemenata (MKE). Također, analizirana je mikroskopska strukture poprečnog presjeka odvojenih čestica sa ciljem utvrđivanja frekvencije stvaranja lamela i njihovog utjecaja na ukupnu razinu vibracija alata za obradu. Prikazom dobivenih rezultata postavljene su osnove za verifikaciju predložene metode određivanja stanja istrošenosti alata izdvajanjem pouzdanih pokazatelja iz visokofrekventnog dijela spektra signala izmjerenih vibracija. Provedeno istraživanje pokazalo je evidentan utjecaj promjene frekvencije segmentacije odvojenih čestica na odziv signala vibracija u visoko-frekventnom dijelu spektara, te ovisnost o promjeni stupnja istrošenosti reznog alata