Bulletin of the Polish Academy of Sciences Technical Sciences

The paper presents a universal architectural pattern and an associated specification method that can be applied in the design of robot control systems. The approach describes the system in terms of embodied agents and proposes a multi-step decomposition enabling precise definition of their inner structure and operation. An embodied agent is decomposed into effectors, receptors, both real and virtual, and a control subsystem. Those entities communicate through communication buffers. The activities of those entities are governed by FSMs that invoke behaviours formulated in terms of transition functions taking as arguments the contents of input buffers and producing the values inserted into output buffers. The method is exemplified by applying it to the design of a control system of a robot executing one of the most important tasks for a service robot, i.e. picking up, by a position–force controlled robot, an object located using an RGB-D image acquired from a Kinect. Moreover in order to substantiate the universality of the presented approach we present how classical, known from the literature, robotic architectures can be expressed as systems composed of one or more embodied agents.

The paper discusses a two-machine flow shop problem with minimization of the sum of tardiness costs, being a generalization of the popular NP-hard single-machine problem with this criterion. We propose the introduction of new elimination block properties allowing for accelerating the operation of approximate algorithms of local searches, solving this problem and improving the quality of solutions determined by them.

In the paper a new, state space, non integer order model of an one-dimensional heat transfer process is proposed. The model uses a new operator with Mittag-Leffler kernel, proposed by Atangana and Beleanu. The non integer order spatial derivative is expressed by Riesz operator. Analytical formula of the step response is given, the convergence of the model is discussed too. Theoretical results are verified by experiments.

One of the main problems of multivariable cost functions in model predictive control is the choice of weighting factors. Two finite control set model predictive control algorithms, applied to the three-phase active rectifier with an LCL filter, are described in the paper. The investigated algorithms, i.e. PCi_cu_c and PCi_gi_cu_c, implement multivariable approaches applying line (grid) current, capacitor voltage and converter current. The main problem dealt with in the paper is the choice of optimum values of the cost function weighting factors. The values of the factors calculated using the method proposed in the paper are very close to the values represented by the lowest THDi of the line current. Moreover, simulations verifying the equations used in the prediction of controlled values, i.e. line current, capacitor voltage and converter current, are presented. Both simulation and experimental results are presented to verify effectiveness of the investigated control strategies under change of the load (P = 5 kW and 2.5 kW), during transient states, under unbalanced and balanced line voltage.

FEM (finite element method) is an essential and powerful numerical method that can explicitly optimize the design process of electrical devices. In this paper, the employment of FEM tools such as SolidWorks, COMSOL and ANSYS is proposed in order to aid electrical apparatuses engineering and modeling – those are arc chambers of modular circuit breakers. Procured models of arc chambers have been undergoing simulations concerning heating, electric potential distribution, electric charge velocity and traverse paths. The data acquired has been juxta-positioned against experimental data procured in the Short-Circuit Laboratory, Warsaw University of Technology. The reflection of the theoretical approach was clearly noted in the experimental results. Mutual areas of the modeled element expressed the same physical properties and robustness errors when tested under specific conditions – faithfully reflecting those which were experimented with. Moreover, the physical phenomena essential for electrical engineering could be determined already at the model stage. This procedure proved highly valuable during designing/engineering work in terms of material economy.

The article presents the essentials of reactance compensation of unbalanced loads in three-phase four-wire systems powered by a sinusoidal and asymmetrical voltage source. The whole of compensation and symmetrization is based on the Currents’ Physical Components (CPC) theory. Reactance compensation, i.e. compensation based solely on inductors and capacitors, in four-wire systems requires the device to be included in a star (Y) structure in order to compensate for the reactive current (reactive power) and the current at the neutral conductor caused by zero sequence asymmetry, and for the device in a delta (∆) structure to allow compensation of the reactive current (reactive power) and current, causing asymmetry of the negative sequence.

The main topic of the paper is the large signal averaged model of a switch-mode flyback power converter. The use of the large-signal averaged models of switching converters allows for fast simulation of power systems. The known averaged models of a flyback are based on the state-space averaging or switch-averaging approach. The model presented in the paper is derived with the use of the separation of variables approach and include parasitic resistances of all converter components. The limitations of the model accuracy are discussed. The calculations based on the averaged model are compared with detailed full-wave simulations and measurements results.

The paper analysed the influence of current frequency on the thermal field of the insulated busbar. Its physical model consist of two hollow cylinders and a solid cylinder with different material properties. In turn, the mathematical model is a system of heat conduction equations with the appropriate set of the boundary, initial and continuity conditions. The problem was solved using the modified Green’s method. As a result, the following characteristics and parameters of the busbar were determined as a functions of frequency: heating curves, local time constants, steady-state current ratings, and stationary temperature profiles. The results were positively verified by finite element method.

In this work, experiments were carried out to quantify the behaviour of friction stir welded (FSW) AA5082-AA7075 butt joints under tensile loading and completely reversed fatigue loading. Different samples were prepared to identify optimum tool rotational and travel speeds to produce FSW AA5082-AA7075 butt joints with the maximum fatigue life. ANOVA was performed, which confirmed that both tool speed and tool rotational speed affect the tensile strength of the weld. The samples exhibit a considerable difference in their fatigue life and tensile strength. This difference can be accounted to the presence of welding defects such as surface defects and porosity. S-N curve plotted for the sample shows a significantly high fatigue life at the lower stress ranges. Fracture surfaces were also analysed under scanning electron microscope (SEM). Study of the fracture surface of the sample that failed under fatigue loading showed that the surface was mainly divided in two zones. The first zone was the area of fatigue crack growth where each stress cycle, slowly and gradually, helped in the growth of the crack. The second zone was the region of fast fracture where the crack growth resulted in the failure of the joint instantaneously. The fracture surface study of the sample that failed under tensile loading showed that the mode of failure was ductile in nature.

The paper deals with analysis of samples made of Inconel 718 nickel superalloy, produced using direct metal laser sintering (DMLS), known as “sintering”, and precision casting technologies. The theoretical part is focused on the characteristics of producing samples of the nickel superalloy by modern additive methods (those for processing metallic materials) and by the conventional technology of precision casting. The practical part involves the investigation of the mechanical properties and texture of the surfaces of the tested samples. A significant part of this study is devoted to analysis of fracture surfaces and EDX experimental testing of TEM lamella by using of electron microscopy methods. The conclusions of this paper include a discussion, evaluation and explanation of both technologies applied on tested samples. Finally, the main benefits of using modern additive technologies in the design and production of heat-resistant components of turbochargers are discussed.

The amorphous Mg-based alloys may be used as metallic biomaterials for resorbable orthopedic implants. The Mg-Zn-Ca metallic glasses demonstrate variable in time degradation rate in simulated body fluid. In this work the Mg₆₆Zn₃₀Ca₄ alloy was chosen as a substrate for coatings. This paper reports on the surface modification of a Mg₆₆Zn₃₀Ca₄ metallic glass by plasma electrolytic oxidation (PEO). The structure characterization of uncoated Mg₆₆Zn₃₀Ca₄ alloy was performed by using TEMand XRD method. The immersion tests of coated and uncoated Mg₆₆Zn₃₀Ca₄ alloy were carried out in Ringer’s solutionat 37°C. The volume of released hydrogen by immersion tests was determined. The coatings structure and chemical composition after immersion tests by SEM/EDS were studied. Based on SEM images of surface structure samples, immersion tests results and hydrogen evolution measurement was proposed the course of corrosion process in Ringer’s solution for Mg-based metallic glasses with PEO coating. Results of immersion tests in Ringer’s solution allowed to determine the amount of evolved hydrogen in a function of time for Mg₆₆Zn₃₀Ca₄ metallic glass and sample with PEO coating. In comparison to the non-coated Mg₆₆Zn₃₀Ca₄ alloy, the sample with PEO layer showed a significantly decreased hydrogen evolution volume.

One of the ways to decrease thermal conductivity is nano structurization. Cobalt triantimonide (CoSb3) samples with added indium or tellurium were prepared by the direct fusion technique from high purity elements. Ingots were pulverized and re-compacted to form electrodes. Then, the pulsed plasma in liquid (PPL) method was applied. All materials were consolidated using rapid spark plasma sintering (SPS). For the analysis, methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with a laser flash apparatus (LFA) were used. For density measurement, the Archimedes’ method was used. Electrical conductivity was measured using a standard four-wire method. The Seebeck coefficient was calculated to form measured Seebeck voltage in the sample placed in a temperature gradient. The preparation method allowed for obtaining CoSb3 nanomaterial with significantly lower thermal conductivity (10 Wm^–1K^–1 for pure CoSb₃ and 3 Wm^–1K^–1 for the nanostructured sample in room temperature (RT)). The size of crystallites (from SEM observations) in the powders prepared was about 20 nm, joined into larger agglomerates. The Seebeck coefficient, α, was about –200 µVK^–1 in the case of both dopants, In and Te, in microsized material and about –400 µVK^–1 for the nanomaterial at RT. For pure CoSb3, α was about 150 µVK^–1 and it stood at –50 µVK^–1 for nanomaterial at RT. In bulk nanomaterial samples, due to a decrease in electrical conductivity and inversion of the Seebeck coefficient, there was no increase in ZT values and the ZT for the nanosized material was below 0.02 in the measured temperature range, while for microsized In-doped sample it reached maximum ZT = 0.7 in (600K).

This paper concerns measurements and calculations of low frequency noise for semiconductor layers with four-probe electrodes. The measurements setup for the voltage noise cross-correlation method is described. The gain calculations for local resistance noise are performed to evaluate the contribution to total noise from different areas of the layer. It was shown, through numerical calculations and noise measurements, that in four-point probe specimens, with separated current and voltage terminals, the non-resistance noise of the contact and the resistance noise of the layer can be identified. The four-point probe method is used to find the low frequency resistance noise of the GaSb layer with a different doping type. For n-type and p-type GaSb layers with low carrier concentrations, the measured noise is dominated by the non-resistance noise contributions from contacts. Low frequency resistance noise was identified in high-doped GaSb layers (both types). At room temperature, such resistance noise in an n-type GaSb layer is significantly larger than for p-type GaSb with comparable doping concentration.

1) Background: the modeling, characterization, transformation and propagation of high-power CW laser beams in optical (including fiberoptic) trains and in the atmosphere have become hot topics in laser science and engineering in the past few years. Single-mode output is mandatory for high-power CW laser applications in the military field. Moreover, an unstationary, dynamic operation regime is typical. Recognized devices and procedures for laser-beam diagnostics could not be directly applied because of dynamic behavior and untypical non-Gaussian profiles. 2) Methods: the Wigner transform approach was proposed to characterize dynamically variable high-power CW laser beams with significant deterministic aberrations. Wavefront-sensing measurements by means of the Shack-Hartmann method and decomposition into an orthogonal Zernike basis were applied. 3) Results: deterministic aberration as a result of unstationary thermal-optic effects depending on the averaged power of the laser output was found. Beam quality determined via the Wigner approach was changed in the same way as the measurements of the beam diameter in the far field. 4) Conclusions: such an aberration component seems to be the main factor causing degradation in beam quality and in brightness of high-power CW laser beams.

This paper presents the results of a numerical analysis of nitride-based edge-emitting lasers with an InGaN/GaN active region designed for continuous wave room temperature emission of green and blue light. The main goal was to investigate whether the indium thin oxide (ITO) layer can serve as an effective optical confinement improving operation of these devices. Simulations were performed with the aid of a self-consistent thermal-electrical-optical model. Results obtained for green- and blue-emitting lasers were compared. The ITO layer in the p-type cladding was found to effectively help confine the laser mode in the active regions of the devices and to decrease the threshold current density.

In this article, the authors propose and investigate a new concept of HAPS aerostat design in a modular form, which allows for sequential increasing or decreasing of the total volume, up to the desired size. In its initial form, the aerostat has relatively small dimensions but its central cylindrical part is multi-segmented and can be easily extended. The application of controllable construction couplings enables precise control of the aerostat expansion process and significantly improves its vertical mobility. The paper describes details of telescopic aerostat construction, presents a mathematical model of its vertical motion and investigates numerically two volume control strategies aimed at maximization of operation efficiency and minimization of operation cost. The results obtained reveal the main problems that have to be addressed and the factors that play a key role in design of such telescopic aerostats and control of their vertical mobility.

The study presented research on the possibility of using acoustic emission to detect and analyze the development of the alkali-silica reaction (ASR) in cement mortars. The experiment was conducted under laboratory conditions using mortars with reactive opal aggregate, accelerating the reaction by ensuring high humidity and temperature, in accordance with ASTM C227. The progress of corrosion processes was monitored continuously for 14 days. The tests were complemented with measurements of the expansion of the mortars and observations of microstructures under a scanning electron microscope. The high sensitivity of the acoustic emission method applied to material fracture caused by ASR enabled the detection of corrosion processes already on the first day of the test, much sooner than the first recorded changes in linear elongation of the specimens. Characteristic signal descriptors were analyzed to determine the progress of corrosion processes and indicate the source of the cracks. Analysis of recorded 13 AE parameters (counts total, counts to peak, duration, rise time, energy, signal strength, amplitude, RMS, ASL, relative energy, average frequency, initial frequency and reverberation frequency) indicates that the number of counts, signal strength and average frequency provide most information about the deleterious processes that occur in the reactive aggregate mortars. The values of RA (rise time/amplitude) and AF (average frequency) enabled the classification of detected signals as indicating tensile or shear cracks. The acoustic emission method was found suitable for monitoring the course of alkali-aggregate reaction effects.