Implementing Lensless Cameras in Autonomous Robotic Systems

The open-source Robot Operating System (ROS) is a mixed and scalable P2P network-based robotics framework. We examine lensless compressive imaging using a hardware apparatus assembly having an imaging sensor, but no lens. Cameras with lenses have been the standard, but several factors constrain their application. Lensless cameras may reduce the cost, size, and weight of image processing as we move away from use of expensive lenses in robot designs. Lensless cameras can be used also in applications such medicine, where apparatus size is very important. To support our objective we show how ROS applications are developed and most importantly how one can build applications that allows users to complete useful tasks in a timely manner with high performance

Free vibrations of planar serial frame structures in the case of axially functionally graded materials

This paper considers the problem of modal analysis and finding the closed-form solution to free vibrations of planar serial frame structures composed of Euler-Bernoulli beams of variable cross-sectional geometric characteristics in the case of axially functionally graded materials. Each of these beams is performing coupled axial and bending vibrations, where coupling occurs due to the boundary conditions at their joints. The numerical procedure for solving the system of partial differential equations, after the separation of variables, is reduced to solving the two-point boundary value problem of ordinary linear differential equations with nonlinear coefficients and linear boundary conditions. In this case, it is possible to transfer the boundary conditions and reduce the problem to the Cauchy initial value problem. Also, it is possible to analyze the influence of different parameters on the structure dynamic behavior. The method is applicable in the case of different boundary conditions at the right and left ends of such structures, as illustrated by an appropriate numerical example

Free vibrations of planar serial frame structures in the case of axially functionally graded materials

This paper considers the problem of modal analysis and finding the closed-form solution to free vibrations of planar serial frame structures composed of Euler-Bernoulli beams of variable cross-sectional geometric characteristics in the case of axially functionally graded materials. Each of these beams is performing coupled axial and bending vibrations, where coupling occurs due to the boundary conditions at their joints. The numerical procedure for solving the system of partial differential equations, after the separation of variables, is reduced to solving the two-point boundary value problem of ordinary linear differential equations with nonlinear coefficients and linear boundary conditions. In this case, it is possible to transfer the boundary conditions and reduce the problem to the Cauchy initial value problem. Also, it is possible to analyze the influence of different parameters on the structure dynamic behavior. The method is applicable in the case of different boundary conditions at the right and left ends of such structures, as illustrated by an appropriate numerical example

The annulling of the sudden appearance of an unbalance in rotary machines by using active magnetic bearings

The application of magnetic bearings has become more frequent during the last 20 years and represents a significant aspect of improvements in the construction of machines with rotary motion. With the advancement of technology, the number of applications in which magnetic bearings have found their application is increasing. In this paper, it is shown how the effect of magnetic forces can annul the negative influence of unbalance, which suddenly appeared in a rotor supported in active magnetic bearings. Such cases may occur in operation due to breakage and rotor parts falling off (e.g., fan blades), which will lead to a sudden change in the mass balance of the rotor system and dislocation of the centre of mass in relation to the geometric centre of the rotor. In the paper, a mathematical model of the dynamic behaviour of a rigid rotor in active magnetic bearings was developed. The model is nonlinear and has five degrees of freedom and can only be solved numerically. The Newmark beta method and the Newton-Raphson method were used to solve the system of nonlinear differential equations. The results of the simulation showed the advantages of using active magnetic bearings for annulling sudden occurrences of unbalance in rotary machines

Closed-form solution for the free axial-bending vibration problem of structures composed of rigid bodies and elastic beam segments

In this paper, the coupled axial-bending vibration of planar serial frame structures composed of rigid bodies and Euler-Bernoulli beam segments is considered. The corresponding mode orthogonality conditions for this kind of structures are derived. It is assumed that the mass centers of rigid bodies have both the transverse and the axial eccentricity with respect to beam neutral axes and that the mass centers are located in the plane in which the rigid bodies perform planar motion. The system responses to initial excitation in the case of distinct as well as repeated natural frequencies are considered. Theoretical considerations are accompanied by four numerical examples.This is the peer reviewed version of the article: Tomović, A.; Šalinić, S.; Obradović, A.; Grbović, A.; Milovančević, M. Closed-Form Solution for the Free Axial-Bending Vibration Problem of Structures Composed of Rigid Bodies and Elastic Beam Segments. Applied Mathematical Modelling 2020, 77, 1148–1167.[https://doi.org/10.1016/j.apm.2019.09.008

COUPLED TRANSVERSE AND LONGITUDINAL VIBRATIONS OF EULER-BERNOULLI AND TIMOSHENKO BEAMS OF FUNCTIONALLY GRADED MATERIALS

У дисертацији се анализира проблем линеарних хармонијских осцилација еластичних греда од функционално градијентних материјала чије се карактеристике мењају по уздужној оси греде. С обзиром на могућности моделовања материјала тако да својим карактеристикама, могу да задовоље структурне и естетске захтеве, повећан је обим њиховог коришћења у реалним конструкцијама. Ови материјали могу се примењивати у широком спектру различитих инжењерских области, као што су биомедицинско инжењерство, енергетика, ваздухопловно инжењерство, грађевинарство и многе друге. Анализа статичких и динамичких карактеристика еластичних греда, с обзиром на њихову примену у бројним инжењерским конструкцијама је од посебног значаја за савремену технику. У дисертацији се анализирају уздужне и попречне осцилације, као и спрегнуте попречне и уздужне осцилације еластичних греда, чији се попречни пресек и карактеристике материјала мењају по уздужној оси греде. Спрезање уздужних и попречних модова осциловања одређено је општим начином ослањања греде. С обзиром на природу функционално градијентних материјала анализира се промена густине и модула еластичности по уздужној оси греде. Приликом формирања модела, греда се посматра као механички систем са бесконачно много степени слободе. Понашање оваквог система описује се парцијалним диференцијалним једначинама са променљивим коефицијентима. За изведене једначине одређени су аналитички записи модела ослањања греде у општем случају, користећи системе опруга и крутих тела на крајевима греде. На основу ових записа анализира се спрезање попречних и уздужних осцилација. Раздвајањем пороменљивих, дужине и времена, код хармонијских осцилација формиран је систем обичних диференцијалних једначина којима се једначине своде на модални облик. Једначине се своде на бездимензиони облик који је у одређеним случајевима погодан за извршавање потребних израчунавања. У поступку алгебарског свођења крутости опруга на бездимензиони облик, њихове вредности своде се на јединични интервал, што представља додатно нумеричко упрошћавање. С обзиром на формирани систем обичних диференцијалних једначина са дефинисаним контурним условима, проблем израчунавања сведен је на решавање двотачкастог граничног проблема. Решавање проблема врши се симболичко-нумеричким методом почетних параметара (SNMIP). Овај модел представља модификацију метода почетних параметара (Бидермановог метода) и не захтева примену итеративних процедура приликом израчунавања. Такође, даје се пример примене метода гађања на решавање осцилација греда променљивог попречног пресека и променљивих карактеристика материјала дуж подужне осе греде (аксијално функционално градијентних греда). Услови ортогоналности модова осциловања еластичних греда изводе се на основу претходно одређеног аналитичког облика контурних услова за дефинисане почетне услове у општем смислу. Користећи услове ортогоналности модова осциловања изводе се интеграционе константе у временској функцији. Тиме се добија решење проблема осциловања еластичних греда променљивог попречног пресека од функционално градијентних материјала у затвореном облику. Као верификација примене симболичко-нумеричког метода почетних параметара у решавању тачних диференцијалних једначина кретања даје се упоредни приказ резултата добијених овим методом и оних који су одређени користећи метод крутих сегмената. Такође, разматра се примена симболичко-нумеричког метода почетних параметара за одређивање жељене сопствене фреквенције с обзиром на различите масене и механичке карактеристике механичког система.The problem of linear harmonic vibration of elastic axially functionally graded (AFG) beams whose characteristics change along longitudinal axes is analyzed in the presented dissertation. The implementation of modern procedures in designing functionally gradient (FG) materials have caused the increased use of later materials in real-life engineering structures, due to the fact that they may satisfy specific structural and aesthetic demands. Thus, FG materials may be used to overcome a wide range of engineering problems in various areas, i.e., biomedical engineering, energy industry, airspace engineering, civil engineering, etc. and that is why the static and dynamic analysis is of special importance in modern engineering. In the dissertation the longitudinal and transverse vibration problems as well as coupled transverse and longitudinal vibration problems of AFG elastic beams are analyzed. The coupling of longitudinal and transverse mode shapes is achieved by the implementation of general boundary conditions. With respect to the nature of FG materials, the changes of mass density and elasticity modulus are analyzed along the beam longitudinal axes. An elastic beam is treated as a mechanical system with an infinite number of degrees of freedom and its behavior is described by partial differential equations with variable coefficients. For presented problems, the equations of motion are derived and boundary conditions are presented in a symbolic manner. Based on later writings, the coupling of mode shapes is analyzed. Using the method of separation of variables, namely longitude and time, the system of ordinary differential equations is formed and the equations are written in the modal form. The equations are written in the non-dimensional form, which may be suitable for practical calculations. In this process, stiffness coefficients are reduced to the unit interval that presents further numerical simplification. Based on the formed system of ordinary differential equations with defined boundary conditions, the computational problem is reduced to the two point boundary value problem. The presented problem is solved using the symbolic-numeric method of initial parameters (SNMIP). This model presents modification of the method of initial parameters (Biderman’s method) and does not require the application of iterative procedures. Also, the example of the shooting method application for solving vibration problem of AFG beams is presented. Orthogonality conditions of mode shapes are derived with respect to general boundary conditions and further used for the derivation of integration constants in the time function. Thus, the vibration problem of elastic AFG beams with variable cross-sectional characteristics is solved in the closed form. The comparative analysis of the results obtained by SNMIP and those obtained by rigid element method is implemented in order to verify the presented procedures. The use of SNMIP in the determination of desired natural frequencies with respect to various mass and mechanical characteristics of the system is also discussed

On the torque transmission by a Cardan-Hooke joint

Proučavana je kinemtika i dinamika Kardan-Hukovog zgloba. Kinematička analiza se bazira na teoriji složenog kretanja krutog tela. Dinamička analiza Kardan-Hukovog zgloba je izvršena na bazi Lagranževih jednačina druge vrste. Kardan-Hukov zglob je analiziran u uslovima promenljive ugaone brzine pogonskog (ulaznog) vratila zgloba. Razmatrane su dve varijante zgloba: (1) ravan pogonske viljuške se poklapa sa ravni vratila; (2) ravan pogonske viljuške je normalna na ravan vratila. Izveden je izraz kojim se opisuje prenos obrtnog momenta Kardan-Hukovim zglobom. Izvedeni izraz sadrži članove koji potiču od inercije ulaznog i izlaznog vratila kao i od inercije krsta Kardan-Hukovog zgloba. Teorijska razmatranja su propraćena numeričkim primerom.Kinematics and dynamics of a Cardan-Hooke joint are investigated. Kinematic analysis is based on the kinematic chain rule for angular velocity vectors. Dynamics of the Cardan-Hooke joint is analyzed by means of the Lagrange equations of the second kind. The Cardan-Hooke joint is analysed under varying operating conditions, that is, it is assumed that the input shaft has variable angular velocity. Two cases are considered: (1) the driving yoke plane coincides with the plane of the shafts; (2) the driving yoke plane is normal to the plane of the shafts. An expression for torque transmission in a Cardan-Hooke joint in varying operating conditions was developed. The expression contains terms representing inertia of the shafts and the cross of the Cardan-Hooke joint. Theoretical considerations are accompanied by a numerical example

Електронске особине и морфологија танких филмова органских материјала добијених комбинаторијалним напаравањем из гасне фазе

There is an ongoing interest in organic materials due to their application in various organic electronic devices. However stability of organic materials limits their potential use. They are prone to degradation both during the working life and storage. One of the main causes is extrinsic degradation, under the influence of oxygen and moisture. This problem can be solved by encapsulation of devices. However no encapsulation is perfect. In the first part of this work a study of degradation of thin films of N,N′-bis(3- methylphenyl)-N,N′-bis(phenyl)benzidine (TPD) and 4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl (DPVBi) under UV irradiation in air is given. Films of both materials are stable in vacuum, but readily degrade in the presence of oxygen. Thus, the necessary condition for degradation is the simultaneous presence of UV light and oxygen. Chemical analysis of irradiated films by NMR, mass and infrared spectroscopy revealed presence of oxidized species (impurities). These impurities are responsible for increased morphological stability of irradiated films and quenching of photoluminescence. Only small amount of impurities, 0.4 % (0.2 %) for TPD (DPVBi), causes 50 % decrease of photoluminescence. This implies a non-trivial mechanism of quenching. For both molecules it was found that distance between impurities is smaller or equal to exciton diffusion length, which is the necessary condition for quenching. Following mechanism of quenching is proposed: exciton diffuses by hopping form one DPVBi (TPD) to another through FRET in a random walk manner. If, during its lifetime, it comes to proximity of an impurity, a Dexter-type energy transfer occurs and PL is quenched. Findings of DPVBi study are important because they show that even a small amount of oxygen that penetrates a DPVBi layer would impair luminescence efficiency of a device. Moreover, the absorption of own radiation (for DPVBi and TPD both) would additionally contribute to the rate of degradation of a device. It is reasonable to expect that transport properties would also be affected when materials are used as a holetransporting layer in OLEDs.Постоји велики интерес за органске материјале због њихове примене у различитим органским електронским уређајима. Међутим стабилност орагнских материјала ограничава њихову примену. Они су подложни деградацији не само за време операције уређаја већ и за време складиштења. Један од главних узрока је деградација услед спољних утицаја: светлости, влаге и кисеоника. Овај проблем може да се превазиђе путем енкапсулације уређаја, али ниједан вид енкапсулације није савршен. У првом делу рада биће изложена студија деградације танких филмова N,N′- bis(3-methylphenyl)-N,N′-bis(phenyl)benzidine (TPD) и 4,4′-bis(2,2-diphenylvinyl)- 1,1′-biphenyl (DPVBi) под утицајем УВ зрачења у ваздуху. Филмови оба материјала су стабилни у вакууму, али деградирају у присуству кисеоника. Дакле, непоходан услов за деградацију, потребно је истовремено присуство УВ светлости и кисеоника. Хемијска анализа осветљених филмова извршена уз помоћ NMR, масене и инфрацрвене спектроскопије показала је присуство оксидованих врста (нечистоћа). Нечистоће су одговорне за повећану морфолошку стабилност осветљених филмова и гашење фотолуминесценције. Мала количина нечистоћа, 0.4 % (0.2 %) у случају TPD (DPVBi), изазива пад интензитета фотолуминесценције од 50 %. Ово имплицира нетривијални механизам гашења фотолуминесценције. За оба молекула је нађено да је растојања између нечистоћа мање или приближно једнако дужини дифузије ексцитона што је неопходан услов за гашење фотолуминесценције. Предложен је механизам гашења: ексцитони дифундују у скоковима од једног до другог молекула DPVBi (TPD) случајним ходом путем Форстеровог резонатног трансфера енергије. Ако у току свог времена живота ексцитон дође у близину нечистоће долази до Декстеровог трансфера енергије и гашења фотолуминесценције. Резултати студије за DPVBi молекул су важни зато што показују да и мала количина кисеоника у слоју DPVBi може озбиљно да утиче на фотолуминесцентну ефикасност уређаја. Штавише, апсорпција сопственог зрачења (код оба молекула, DPVBi и TPD) ће додатно да допринесе брзини деградације уређаја. Разумно је претпоставити да ће и транспортне особине бити нарушене у случају када се ови материјали користе као слој за транспорт шупљина у органским светлећим диодама

Free vibration of axially functionally graded Timoshenko cantilever beam with a large rigid body attached at its free end

The problem of natural frequency computing of an axially functionally graded (AFG) Timoshenko cantilever beam of a constant cross-sectional area is considered. The longitudinal and transverse vibrations of the cantilever beam are coupled because of the boundary conditions at its right end, where the eccentrically displaced rigid body is attached. Once the variables are separated, the procedure of solving the system of partial differential equations is reduced to solving the two-point boundary value problem of ordinary linear differential equations with nonlinear coefficients and linear boundary conditions. In this case, it is possible to transfer boundary conditions and to reduce the problem to the Cauchy problem of initial conditions. Also, it is possible to analyze the influence of various parameters on the values of natural frequencies. The impact of the cross-sectional area on natural frequency is analyzed and illustrated by a numerical example

Free vibration of axially functionally graded Timoshenko cantilever beam with a large rigid body attached at its free end

The problem of natural frequency computing of an axially functionally graded (AFG) Timoshenko cantilever beam of a constant cross-sectional area is considered. The longitudinal and transverse vibrations of the cantilever beam are coupled because of the boundary conditions at its right end, where the eccentrically displaced rigid body is attached. Once the variables are separated, the procedure of solving the system of partial differential equations is reduced to solving the two-point boundary value problem of ordinary linear differential equations with nonlinear coefficients and linear boundary conditions. In this case, it is possible to transfer boundary conditions and to reduce the problem to the Cauchy problem of initial conditions. Also, it is possible to analyze the influence of various parameters on the values of natural frequencies. The impact of the cross-sectional area on natural frequency is analyzed and illustrated by a numerical example