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1.
Development of a mathematical model for the dynamic optimization of batch reactors, and MINLP synthesis of plug-flow reactors in complex networks
Marcel Ropotar, Zdravko Kravanja, 2007, izvirni znanstveni članek

Opis: This paper describes the development of a robust and efficient reactor model suitable for representing batch and plugflow reactors (PFRs) in different applications. These would range from the nonlinear (NLP) dynamic optimization of a stand-alone batch reactor up to the mixed-integer nonlinear (MINLP) synthesis of a complex reactor network in overall process schemes. Different schemes for the Orthogonal Collocation on Finite Element (OCFE) and various model formulations, in the case of MINLP model, were studied in order to increase the robustness and efficiency of the model. A deterministic model for known kinetics was obtained for batch and PFR reactors and extended for uncertainties in process parameters and reaction kinetics when the kinetics is unknown. Different variations of the developed model were applied to certain problems, as examples. The first motivating example was the dynamic optimization of batch reactor and the second the MINLP synthesis of a process scheme for the production of allyl chloride. The NLP version of the model with moving finite elements was found to be the most efficient for representing a batch reactor in the dynamic optimization example, and PFR trains in the process synthesis example.
Ključne besede: batch reactor, orthogonal collocation, off-line optimization, on-line optimization, flexibility, uncertainty
Objavljeno: 31.05.2012; Ogledov: 1145; Prenosov: 5
.pdf Polno besedilo (520,87 KB)

2.
New approach to uncertainty evaluation in the calibration of gauge block comparators
Andrej Godina, Bojan Ačko, Marjan Družovec, 2007, izvirni znanstveni članek

Opis: Gauge blocks (GBs) are being calibrated by two methods: interferometric calibration and calibration by mechanical comparison to reference GB. While interferometric method represents primary level, comparison is more suitable for calibrating industrial GBs because of lower costs and shorter calibration time. Although no significant changes in equipment happened in last decade, improvements in mechanical comparison are on-going. In addition to the uncertainty of the reference GB calibration, uncertainty of the GB comparator is the most important contribution to total uncertainty of the mechanical calibration. The article introduces a new approach for evaluating the uncertainty of GB comparator calibration. The uncertainty budget and results of analytical and experimental evaluation of all contributions are presented. This approach results in lower end-effect uncertainty and a slightly higher length dependent uncertainty, in comparison with the uncertainty evaluation procedure as described in EA document EA-10/02.
Ključne besede: measurements, calibration, measuring uncertainty, gauge block, comparator, CMC, mechanical comparison
Objavljeno: 31.05.2012; Ogledov: 960; Prenosov: 10
URL Polno besedilo (0,00 KB)

3.
Simulation of line scale contamination in calibration uncertainty model
Marjan Družovec, Bojan Ačko, Andrej Godina, Tatjana Welzer Družovec, 2008, izvirni znanstveni članek

Opis: Precise calibration of quartz line scales is very important for assuring traceability of microscopic measurements. Very significant influence in calibration uncertainty budget is represented by uncertainty of line centre detection. Line centre is usually detected through video signal processing using different types of algorithms. This paper is presenting calibration procedure that was developed in the Laboratory for Production Measurement at the Faculty of Mechanical Engineering in Maribor. It is focused in uncertainty analysis and especially in the influence of line scale contamination on determination of line centre position. Different types of line scale contamination like dirt spots, scratches, line edge incorrectness, and line intensity were simulated in order to test the ability of the line centre detection algorithm to eliminate such influences from the measurement results.
Ključne besede: line scale, calibration, uncertainty, video-positioning system, simulation
Objavljeno: 31.05.2012; Ogledov: 720; Prenosov: 5
URL Polno besedilo (0,00 KB)

4.
Measurement uncertainty in calibration of measurement surface plates flatness
Andrej Gusel, Bojan Ačko, Vedran Mudronja, 2009, izvirni znanstveni članek

Opis: Ravno merilno površino, kot je to na primer merilna plošča, lahko smatramo kot izhodišče za izvajanje večine meritev oblike in lege merjenih objektov. Da bi merilne plošče v ta namen zadovoljivo uporabljali, moramo najprej zagotoviti, da so res ravne in primerne za meritve. Ravnost merilne ploskve ugotavljamo posredno, tako da najprej določimo premost posameznih linij, ki so sestavni del merilne mreže. Te linije so še dodatno razdeljene na merilne korake, ki so prirejeni meram merilne opreme. Premost merilne linije izračunamo z merjenjem nagiba posameznega merilnega položaja za vsako linijo posebej, neravnost celotne površine pa tako, da rezultate po linijah povežemo v celoto. Osnove, postopki in merilne naprave za izvajanje meritev so torej znani, neznanka pa ostaja negotovost tovrstne kalibracije merilne površine. Meritev brez ustrezno izražene negotovosti ne pomeni ničesar, zato moramo zagotoviti, da bomo lahko negotovost določili. Pričujoči članek predstavlja nov pristop določanja merilne negotovosti pri merjenju ravnosti, ki temelji na uporabi metode Monte Carlo. Pri tem celoten merilni sistem razstavimo na posamezne komponente ter ocenimo njihovo veličino in vplive le teh, meritve pa simuliramo. Zanima nas tudi vpliv parametrov merilne mreže na meritev.
Ključne besede: production measurements, length measurements, measuring uncertainty, calibration, uncertainty measurement, flatness measurement
Objavljeno: 31.05.2012; Ogledov: 762; Prenosov: 9
URL Polno besedilo (0,00 KB)

5.
Thread gauge calibration for industrial applications
Tadeja Primožič Merkač, Bojan Ačko, 2010, izvirni znanstveni članek

Opis: There are two most commonly used methods for calibration of thread rings, with different measuring uncertainty. The method of mechanical sensing with two balls is mostly used on one-axial measuring machines and on coordinate measuring machines. However, the method of calculating the core diameter of the thread ring combined with the technique of adaptation (in accordance with the method of the smallest squares) is used on the profile scanner. The required tolerances, which are very narrow for adjustable and laboratory thread ring, so the measuring uncertainty may be too high when using the method of mechanical sensing with two balls, and the low quality of some control rings, are the decisive factors for choosing an appropriate method in the industry. This also depends on the laboratoryćs capability of executing a specific method. The measurements of the core diameter of thread rings, which are the main topic of this article, were included into an international inter-comparison in which the main subject was the same thread ring as the one mentioned in this article.
Ključne besede: thread ring gauge, calibration, pitch diameter, measurement uncertainty, dimensional measurements
Objavljeno: 31.05.2012; Ogledov: 747; Prenosov: 3
URL Polno besedilo (0,00 KB)

6.
Calibration of electronic levels using a special sine bar
Bojan Ačko, 2005, izvirni znanstveni članek

Opis: Electronic levels are designated for the precise measurement of inclination angles within the range of +- 3 mm/m. They are very often used for checking the straightness of machine tool guides as well as the flatness of different kindsof machine tool tables and surface plates. Typical resolution of such instruments is 1 m/m. Electronic levels are calibrated by using very precise angle generators. One such generator is a sine bar. Sine bars are cheap and enable fast and simple calibrations. Commercial sine bars however are not precise enough. We, therefore, decided to design a special sine bar, which would be able to generate angles within an uncertainty of 1 mžm. This sine barwas designed by the laboratory staff and manufactured in our workroom. We have also created a calibration procedure, which has already been accredited. Uncertainty analysis, including experimental measurements, shows that the planned uncertainty has been reached. The sine bar design, calibration procedure and uncertainty evaluation are presented in this article.
Ključne besede: production measurements, measuring uncertainty, calibration, inclination angles, flatness measurements, sine bar, electronic level
Objavljeno: 01.06.2012; Ogledov: 988; Prenosov: 11
URL Polno besedilo (0,00 KB)

7.
Uncertainty of nitrate and sulphate measured by ion chromatography in wastewater samples
Brigita Tepuš, Marjana Simonič, 2007, izvirni znanstveni članek

Opis: This paper presents an evaluation of measurement uncertainty regarding the results of anion (nitrate and sulphate) concentrations in wastewater. Anions were determined by ion chromatography (EN ISO 10304-2, 1996). The major sources of uncertainty regarding the measurement results were identified as contributions to linear least-square or weighted regression lines, precision, trueness, storage conditions, and sampling. Determination of anions in wastewater is very important for the purification procedure, especially the amount of nitrate in waste and potable waters. The determined expanded uncertainty was 6% for nitrate anions and 8.3% for sulphate anions. The difference between measurement uncertainties determined by the two methods, the weighted and linear least-square methods is negligible.
Ključne besede: wastewater, nitrates, sulphates, measurements, measuring uncertainty
Objavljeno: 01.06.2012; Ogledov: 816; Prenosov: 13
.pdf Polno besedilo (254,17 KB)

8.
Possibilities of using three-dimensional optical scanning in complex geometrical inspection
Tadej Tasič, Miodrag Hadžistević, Bogdan Valentan, Vojko Pogačar, Jože Balič, Bojan Ačko, Tomaž Brajlih, Igor Drstvenšek, 2011, izvirni znanstveni članek

Opis: Brezkontaktno optično zajemanje, merjenje in digitalizacija postajajo vedno bolj razširjeni postopki v sistemih zagotavljanja kakovosti. Prednosti optičnega skeniranja v primerjavi s konvencionalnimi kontaktnimi merilnimi postopki so preprosto zajemanje, visoka gostota pridobljenih podatkov ter povezava med povratnim inženirstvom in preverjanjem oblike. Optični skener se zaradi trirazsežnega zajemanja podatkov pogosto obravnava kot alternativa koordinatni merilni napravi. Prednost optičnega skeniranja je predvsem večja hitrost zajemanja podatkov, medtem ko natančnost še ne dosega ravni koordinatne merilne tehnike. Ta prispevek obravnava možnosti uporabe optičnega skenerja pri preverjanju natančnosti izdelave. Predstavljen je primer, pri katerem je za preverjanje natančnosti izdelka uporabljen optični skener GOM ATOS II. V prvem delu prispevka je predstavljeno specifično področje preverjanja natančnosti medicinskih vsadkov. Predstavljene so prednosti, zaradi katerih je optično skeniranje pri takšnih izdelkih primernejše od koordinatnega merjenja. V drugem delu prispevka so predstavljeni rezultati optičnega zajemanja geometrije merilnih kladic ter merilna negotovost postopka. V zadnjem delu je predstavljena neposredna primerjava rezultatov optičnega skeniranja in koordinatnega merjenja krogle. Glede na rezultate merjenja merilnih kladic in primerjave rezultatov merjenja krogle smo dokazali, da je natančnost optičnega skenerja GOM ATOS II primerna za preverjanje oblike medicinskih vsadkov z ozirom na zahtevano natančnost izdelka pred samim operacijskim posegom. Nadaljnje raziskave na tem področju bodo namenjene predvsem ločevanju in vrednotenju merilnih pogreškov optičnega zajemanja, ki so posledica nenatančnosti same naprave ter pogreškov, ki nastajajo zaradi naknadne poobdelave (poligonizacije) zajetih podatkov. Preizkus natančnosti optičnega sistema je bil omejen na merjenje merilnih kladic in na primerjavo meritve krogle s koordinatno merilno napravo. Prispevek predstavlja izvirno področje preverjanja natančnosti izdelave kompleksnih geometrijskih oblik. Predstavljena sta postopek zajemanja in poobdelave podatkov ter metoda preizkusa natančnosti naprave. Prispevek je namenjen vsem, ki se ukvarjajo s preverjanjem kompleksnih geometrijskih oblik, saj se bo z razvojem novih sistemov za optično zajemanje oblik povečevala tudi njihova natančnost. Te naprave bodo zato postajale vedno pomembnejše na širšem področju zagotavljanja kakovosti in ne samo na specifičnem primeru, predstavljenem v tem članku.
Ključne besede: 3D optical scanning, uncertainty of measurement, geometry inspection, rapid manufacturing, reverse enginering, quality assurance
Objavljeno: 10.07.2015; Ogledov: 374; Prenosov: 11
URL Polno besedilo (0,00 KB)

9.
Optimal robust motion controller design using multi-objective genetic algorithm
Andrej Sarjaš, Rajko Svečko, Amor Chowdhury, 2014, izvirni znanstveni članek

Opis: This paper describes the use of a multi-objective genetic algorithm for robust motion controller design. Motion controller structure is based on a disturbance observer in an RIC framework. The RIC approach is presented in the form with internal and external feedback loops, in which an internal disturbance rejection controller and an external performance controller must be synthesised. This paper involves novel objectives for robustness and performance assessments for such an approach. Objective functions for the robustness property of RIC are based on simple even polynomials with non-negativity conditions. Regional pole placement method is presented with the aims of controllers% structures simplification and their additional arbitrary selection. Regional pole placement involves arbitrary selection of central polynomials for both loops, with additional admissible region of the optimized pole location. Polynomial deviation between selected and optimized polynomials is measured with derived performance objective functions. A multi-objective function is composed of different unrelated criteria such as, robust stability, controllers' stability and time performance indexes of closed loops. The design of controllers and multi-objective optimization procedure involve a set of the objectives, which are optimized simultaneously with a genetic algorithm - Differential evolution.
Ključne besede: disturbance observer, DOB, uncertainty systems, optimal robust control, multi-objective optimization, differential evolution
Objavljeno: 15.06.2017; Ogledov: 47; Prenosov: 0
.pdf Polno besedilo (2,22 MB)

10.
Contingency factors influencing implementation of physical asset management practices
Damjan Maletič, Matjaž Maletič, Basim Al-Najjar, Katerina Gotzamani, Maria Gianni, Kalinowski, Boštjan Gomišček, 2017, izvirni znanstveni članek

Opis: Purpose: The purpose of this empirical study is to examine the role of two contingency factors, i.e. uncertainty and competitiveness in relation to physical asset management (PAM) practices as well as to maintenance key performance indicators. The research is based on a premise that PAM, which was defined by risk management practices, performance assessment practices, life cycle management practices, and policy & strategy practices, has become an indispensable element of strategic thinking of asset owners as well as maintenance and asset managers. The purpose of this study is to advance the understanding of how organizations that face high or low level of uncertainty and competitiveness respond in terms of PAM deployment. Methodology/Approach: This study employed a data set based on a large-scale survey among organizations in six European countries (i.e. Slovenia, Poland, Greece, Sweden, Turkey and Slovakia). Data were collected from 138 organizations located in the above-mentioned countries to conduct the study. Findings: The results show that organizations that are faced with high level of uncertainty and competitiveness are more engaged in the deployment of PAM practices. Moreover, results show that when organizations are facing high levels of competitiveness they are using KPIs to a greater extent than organizations under low levels of competitiveness. Originality/value: From a theoretical perspective, this study contributes to the contingency theory by providing empirical evidence whether a context-dependent approach to PAM is needed. The findings also provide insights for managers on how to respond to the competitive pressure as well as how to customize PAM practices in order to adapt to the changes in dynamic organizational environment.
Ključne besede: physical asset management, maintenance, uncertainty, competitiveness
Objavljeno: 06.04.2017; Ogledov: 214; Prenosov: 3
.pdf Polno besedilo (675,00 KB)

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