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This device can be used not only to achieve the parallelism between the surface on which it is fixed and the horizontal plane, but also to accomplish desired tilt angles around the two axis. The device consists of two main components: microcontroller development board and gyroscope sensor. The updating frequency of the displayed values is 10 Hz, these being displayed in the same time for both axes, presenting also the feature of holding the displayed values. At the same time, the device can perform the recalibration, which can also be used for the rescaling to a certain desired angle, thus simplifying the achievement of it. The measurement accuracy is two tenths of a degree, this being high considering the price and the characteristics of the components used. At the end, the designed device is appreciated as being useful, quite simple to implement and easy to operate.

The paper describes the way of a system dimensioning required to achieve a linear displacement measurement. The system is based on a microcontroller and an incremental encoder. Taking into account the needing of electronic parameter adaptation at the interfacing of the incremental encoder and the microcontroller, a constructive-functional optimization is accomplished. The sensibility of displacement measurement is given by the number of pulses per angular unit, the microcontroller processing and counting speed as well as the efficiency of implemented algorithm and source code. At the dimensioning of electronic circuit is also requested to consider the possibility of perturbation inducing due to the electromagnetic interference of own sources or from environment.

Early detection of cracks in engineering structures by vibration-based methods requires monitoring systems that can evaluate natural frequencies with high accuracy. This paper introduces a method for estimating the natural frequencies using features extracted from the vibrational response of structures excited to cross through the resonance. To this aim, an open-loop acoustic system able to ensure bidirectional excitation, in swept-sine or short-time mode, with controllable parameters was developed. Analyzing the structural response at the crossing area through the resonance, two particularities on which the method is based have been revealed. The first refers to the symmetry of the frequency shift at peak amplitude from the natural frequency, if positive and negative sweep rates are applied. Therefore, the natural frequency can be found as the average of the frequency values at the resonance. Also, the necessary time to achieve the peak amplitude after passing through the natural frequency is similar, irrespective to the sign of the sweep rate. This accomplishment allows finding the natural frequency from a graphical representation. Frequency estimation made for a test structure by employing the two procedures lead to convergent results. Comparing these results to those achieved by impulsive excitation, a better precision was remarked at the swept-sine excitation. With regard the simplicity, rapidity and stability of the method, the swept-sine excitation has been proved as the most effective.

The DC-DC non-isolated Buck converter is based on a sliding-mode controller (BC-SMC) accomplished with an Arduino Uno R3 development board. The converter aims to supply and charge portable devices (PDs) with variable DC voltage requirements in a range of 2.5 to 24 V and a power up to 300 W. The input is connected to a DC power supply of 30 V and 11 A. BC-SMC ensures the output voltage setup and control, it also limits the current that is supplied to the PD. The BC-SMC can switch between current control, when the PD charging process is at the beginning stage, or the voltage control at the end of charge or when simply supplying the PD. After testing the BC-SMC, it shows good performance, supplying up to 50 A for 5 V or lower voltage requirements, or more than 10 A at the 24 V, the highest voltage limit. The BC-SMC was developed to be included in a more complex equipment, which is targeted to connect to any electrical DC energy source, in a range of 1.5 to 300 V, and supply PDs with electrical requirements between: 2.5–30V and 0–50 A.

This paper describes the design of a 3D printer fire detection system (3DP-FDS) with a GSM connection, its purpose being to avoid fire accidents. The key feature of the system is the ability to send an alert via a short message service (SMS) when a fire is detected. 3DP-FDS consists of an Arduino Uno R3 development board, SIM800L GSM/GPRS modem module, KY-026 flame sensor module and a Li-Ion battery package. The flame sensor performs the fire sensing on the digital output, comparing the detected value to the selected DC value from development board. Then, the development board sends a message to the GSM module that delivers it. The supervised active area is limited by the flame sensor 1 m detection distance and 60° angle, it being enough to cover the printer build volume and framework. A maximum time frame of 5 seconds has been accomplished, between the flame detection and the message receiving by the user. Also, the system can safely work for more than six hours without network supply. 3DP-FDS helps users to improve their safety standards and it can also be involved in other safety scenarios.

The paper presents a procedure to precisely estimate the natural frequencies of structures. It implies the acoustic excitation of the structure and the evaluation of the frequencies from the response signals, involving an advanced method developed by the authors. The study is performed on a cantilever beam. To demonstrate the efficiency of the contrived procedure, the values of the frequencies by applying this procedure are compared whit those obtained by standard frequency estimation made for the response to an impulsive excitation.

Nowadays high-speed microcontrollers are employed to accomplish many applications in different domains, due to their flexible characteristics and structures. In this paper, the microcontroller algorithm performs a fast time-frequency analysis by discrete Fourier transform (DFT) on variable time portions of the vibration signal. System can be easily customized so that a spectrum with variable range and density is achieved. Also, the real-time microcontroller based system (R-TMBS) has been thought as a stand-alone system as well as to be included in a more complex system, which can function in closed-loop, when the system feedback is obtained via R-TMBS.

SMA-based (Shape Memory Alloy) actuators with thermal activation are widely implemented in a large area of equipments and devices, but they have an important limitation in the low force produced. The force increases with the dimension, which gives new issues in the control of the requested energy for activation. This happens more often when the SMA actuator is driven by electrical current intensity. Here, a solution for SMA control at low voltage and high intensity is proposed, involving pretty usual devices in handy schematics. The solution was tested and proved as effective in such cases.

Vibration-based damage detection methods able to recognize cracks in the early state require accurate frequency evaluation in order to identify small modal changes. Because of higher order, the natural frequencies are rapidly damped, time history provides insufficient information if standard frequency estimations are performed. This paper introduces a method of overlaying multiple spectra achieved by iterative truncation of the original signal. In this way, the spectral bin number becomes much higher and the identification of real natural frequencies is easier. Also, an original damage detection algorithm based on the frequency shift is described that considers the first six bending vibration modes occurred due to damage. These are in direct relation to the modal strain energy stored at the damage location. The effectiveness of the detection method is proved using real structures in some damage scenarios. Thus, it was shown that even if a crack reduces the beam’s transversal cross section by only 6%, it can be clearly detected.

The present paper describes research results considering the automatic control of a prehension module using a dual shape memory alloy (SMA) actuator. The offspring targeted a high-speed prehension appliance by means of adjusting constants of a PID controller. Furthermore, SMA springs are individually driven according each one’s particularities, aiming at prolonging life of dual SMA actuator, with respect to parametric values given by manufacturer. Problem of process control is approached from few perspectives: automatic control, software implementation and electronic performance, the first being the one subjected to following discussion.

This paper suggests a structure for prosthetic hand myoelectric-based control systems and a set of evolving Takagi-Sugeno-Kang (TSK) fuzzy models to characterize mathematically the finger dynamics of the human hand for the myoelectric control of prosthetic hands. The fuzzy models represent the reference models in myoelectric-based control systems, the model outputs are the flexion percentages that correspond to the midcarpal joint angles, and the model inputs are the myoelectric signals obtained from eight myoelectric sensors. Different numbers of additional model inputs obtained from past inputs and/or outputs are considered. The structure and parameters of the fuzzy models are evolved by an incremental online identification algorithm (IOIA). The evolving TSK fuzzy models for one finger are tested against the experimental data, and a comparison with similar TSK fuzzy models evolved by another IOIA and a neural network model with similar number of parameters is included.

In this paper we show that it is possible to learn high performance model reference controllers using a model-free Q-learning approach, based on input-output (IO) samples collected from the controlled process. Under observability assumptions for the process, virtual extended state-space process models of different orders are built from the IO collected samples. We prove that state-space control of these virtual processes is equivalent to IO control of the initial process. For the virtual state-space process, high performance nonlinear Neural Network (NN) state-feedback controllers are learned based on the IO data collected from the initial process, to achieve output model-reference tracking control. Control learning is a two-step model-free process: an IO model-free controller first drives the process exploration of a wide operating range for IO samples collection that are then used to model-free learn the NN controllers. The approach is successfully validated on a highly nonlinear coupled aerodynamic system.

The paper presents the design of several classical low-cost control systems (CSs) with Integral Controllers (I), Proportional-Integral Controller (PI), Proportional-Integral-Derivative Controller (PID) and adaptive Proportional-Integral control systems dedicated to the level control of vertical three-tank systems (V3TS). To design the proposed control solutions, the least-squares identification leads to the parameters of the transfer functions of the simplified models of V3TS. The CSs consist of several SISO control loops with separately tuned I, PI and PID controllers and adaptive PI controller. The Modulus Optimum method is applied to initially tune the parameters of the controllers. A comparative study of the suggested control structures is also given and validated by real-time experimental results.

The paper presents three design methods for the position control of a mechatronics application characterized by rigid body dynamics and a discontinuously variable parameter (inertia). The techniques are useful because the control structure with state feedback does not assure reduced settling times, phase margins of 60° (or smaller) and a zero steady-state control error. The Modulus Optimum method (MO-m) is applied to initially tune the parameters of the continous-time controllers and the backwards difference method is used for discretizing these parameters. A set of digital and experimental results for the position control systems using the proposed and developed control solutions validate the suggested techniques. A comparative analysis of the three proposed control structures is also given in order to highlight how the specified control system performance was achieved.

Accurate frequency evaluation is very important in the damage detection processes because the dynamic response is less sensitive to damage. Therefore, to be able to detect transverse cracks in early stage, it is necessary to read precisely the frequencies. In the literature are presented several methods, more or less complex and resource consuming, destined to improve the frequencies readability. In practical applications simple and fast methods for frequency evaluation are requested; the process should be adequate to be automated. The paper presents an original method for identifying the correct frequency of generated or acquired signals. The method is based on the analysis of the original signal cropped by rectangular windows in order to rearrange successively the spectral lines aiming to find the highest peak achieved in a region of interest for the frequency-amplitude pairs.

The goal of the paper is to accomplish the response regarding the force-displacement characteristic evolution, of a Shape Memory Alloy (SMA) actuator element. This reveals the first research stage in controlling the SMA behavior, providing important information about the heating-cooling time intervals. Step excitation of the SMA is performed by few values of electric current intensity, which produces the heating of SMA element up to 90-95 oC. To meet the testing requirements, an adequate test stand has been set up, consisting of sensors for force, displacement and temperature. The analog values provided by sensors were acquired and afterwards analyzed. The values of temperature, displacement and force were achieved, and their characteristic evolution has been performed. Thus, the time intervals are resulted and some other important aspects have been observed, regarding the delay between parameters and the temperature overshoot

In this paper, a signal processing algorithm to accurately estimate the natural frequencies of structures for early recognition and assessment of cracks is proposed. In standard frequency estimation, the precision increases if the frequency resolution is improved. A finer resolution is achieved by increasing the analysis time interval. Nowadays, there are many other methods to improve the spectrum resolution, as the interpolation of spectral lines, zero-padding, zoom-FFT and so on. The proposed algorithm stepwise crops the acquired vibration signal and performs a spectral analysis. Superposing these spectra, an overlapped spectrum, with a dramatically increased resolution, results. This spectrum offers the possibility to identify very precisely the natural frequencies, even for damages in early stage. The algorithm was tested on generated and real-world signals and was proved to work well, even in the case of fast damped or short signals.

Frequency and magnitude evaluation are two of the main signal analysis tasks in the electrical power systems. This paper presents a simple and robust algorithm which enables an accurate estimation of the harmonic parameters of signals with unknown frequency. Differing from the existing approaches, frequency and magnitude of harmonic waves are simultaneously and precisely identified. The proposed algorithm can be applied in spectral estimation as well as in system identification, signal reconstruction, and other important signal processing issues. Algorithm operational efficiency was proved by frequency and amplitude estimation of generated signals with known frequency achieved their aim.

The paper presents results obtained for the cooling process of a new-designed SMA-based wave generator (SMA-WG), which represents the deforming component of a harmonic drive. SMA-WG is driven by two-way SMA elements and, due to this, it does not require a driving motor. Correct SMA-WG operation supposes a simulated rotational ellipse performed by SMA elements, which is achieved by a cyclical control of temperature. SMA heating is electrically controlled, but for rapid cooling, a forced air flow is aimed. Therefore, SMA-WG design must involve special characteristics determined by numerical flow simulation.

The investigation of relevant scientific literature regarding gear modeling enabled us to discover a significant number of papers dating back several decades and continuing to the present. The purpose of the dynamic models was quite diverse, but all modeling efforts share the goal of replicating the complex physics of power transmission through gear interaction. This paper investigates the relevant aspects regarding the dynamic modeling of gear transmissions, starting with the simplest model (1DOF), then developing it into a model with three degrees of freedom (3DOF) and finishing with six degrees of freedom model (6DOF).

This paper relates the lubrication influence on the Xylan 1052 coating applied as the surface layer of a testing disk. By pressing a coated and uncoated bearing ball against the surface of coated disk having different rotational speeds, wear evolution diagrams have been achieved. Tests were performed in three specific conditions, when the disk coated surface is: dry, under poor or continuous lubrication. These conditions allow understanding the influence of poor or continuous lubrication on the behavior of coated disk surface at the contact stress. Such conditions could practically occur due to some problems appearing in industrial environment.

Assuming that vibration and noise amplitude depend on coating thickness, here were performed important tests about wear of the Xylan 1052 coating. Applying variable contact stress by different load pressures on a disk coated, and keeping the rotational speed constant, a wear evolutions diagram has resulted. Also, a diagram with the wear evolutions of Xylan 1052 coating has been achieved by using the same load pressure and varying the rotational speed. This information offers significant knowledge about Xylan 1052-film wearing, reflecting an appreciation of the running-in period and the coating thickness. Further on, the proper working time is accomplished, as well as the minimum coating thickness whereas the covering becomes irrelevant to use.

By monitoring the vibration response of mechanical or civil engineering systems, the modal parameter changes due to materials or geometrical properties can be observed. Fine frequency shift identification is decisive to determine particularly small changes and thereby small cracks or damages. This paper firstly presents some existing methods to accurately find the frequency values. All these methods show non-linear, relevant errors in interpretation. Afterward a simple method is proposed, consisting in iterative decreasing of the number of samples from the original signal, performing a standard frequency analysis for each truncated signal and finally overlapping of achieved spectra. Thus, the resulted spectrum has a much fine resolution due to the important addition of spectral lines. In this way a more accurate identification of frequencies is possible. In fact, the relevant frequency is accomplished under a lobe shape. In the peak position of this lobe the best frequency value can be clearly identified. With the help of these more accurate frequency values, modal analysis becomes more reliable and efficient.

In the framework of the paper, we analyze some theoretical and practical aspects regarding the identification of the induction motor. The problem is important in the synthesis of different driving systems with automatic induction motors, usually with variable speed of rotations. The performances in the transitory and stationary regime of these quick adjustment systems are influenced by the precision of the mathematical model of the chosen driving motor. We present different mathematical models of the induction motor, obtained in an experimental way

We are proposing a software simulation model that could be used for the contact stress determination in the case of a new type of Xylan 1052-coated cylindrical toothed wheel gearing. It shows the contact stress distribution and displacements into the Xylan 1052 fluoropolymer coating that was applied to the surfaces of tooth flank. It represents a necessity due to the fact that, as it's well known, the strength of plastic material is much less than the strength of steel material.

In this paper is presented a contact stress calculation algorithm for a new type of cylindrical toothed wheel. This new type consists in the application of a Xylan 1052 fluoropolymer film on the surface of a metal toothed wheel. Due to the fact that the steel strength, in any case is better than the plastic strength, the main issue which appears is at the contact between the two homologous flank surfaces.

This paper introduces a method to identify damages in beam-like structures by analyzing the natural frequency changes of the first six transversal vibration modes. A correlation between the damage location and frequency change is established for each mode separately, by considering the modal strain energy stored in that location. The mathematical relation describing this correlation is used to characterize the dynamic behavior of a beam with a damage of known position and to derive its Damage Location Indicator (DLI) as a six-term vector. The method consists in comparing the vectors describing the damage at any possible location along the beam with the Damage Signature (DS), which is achieved from the measurements that compare the beam's frequencies in healthy and damaged state. A modified Kullback-Leibler Divergence is used to assess the damage location. In order to permit early damage assessment, an improved frequency evaluation algorithm was developed. It is based on signal truncation and consequent spectral lines rearrangement, in order to accurately find the strongest spectral components. The effectiveness of the proposed method is demonstrated by simulations and experiments.

The presence of corrosion influences the dynamic behaviour of plates, by modifying its natural frequencies and mode shapes. Many methods to assess damages in structural elements are known, but they mainly address to the geometric discontinuities, where mass loss is insignificant. In some of the prior research, we have got success in achieving a mathematical relation between damage geometry and frequency shifts. Since the mass decrease is also associated with numerous corrosion mechanisms, the idea of this paper is to establish the influence of mass changes in the natural frequencies of plates and including this information in a baseline, to apply it in processes for corrosion assessment. Thus, by research the evaluation of frequency changes due to mass loss and stiffness decrease has been followed. The finite element analysis was performed, considering corroded area as being simulated by a constantly decreasing plate thickness. In this way, is highlighted the correlation between frequency changes in the transversal vibration modes and mass loss. The dependency between mass loss and frequencies is accomplished, as a mathematical relation as well. This relation is associated with another relation, who predicts the frequency decreases due to stiffness reduction, in order to find the curves of frequency shifts and promote them as a baseline for corrosion assessment. Also, a corrosion assessment method, based on the contrived frequency shift curves, has been developed and proved as reliable and easily applicable.

This paper presents an enhanced method that accurately identifies natural frequencies of structures, via an important improvement of spectral lines density. Spectral lines density increases due to the superposition of many spectra, each spectrum being accomplished by subtracting certain number of samples from the original signal and using the power spectral density analysis. The newly achieved overlapped-spectrum shows important additions to spectral line number and makes more accurately identification of frequencies in the peak position of relevant amplitudes. In this way, modal analysis becomes more reliable and efficient. Method application assumes small frequency changes and the advantage of establishing more precisely the position and dimension of damage. The analysis of all results explicitly indicates an important assessment in the evaluation of frequency. Considering relevant aspects, it can be appreciated that the approached method offers a new development way in the vibration-based damage detection, allowing de possibility to perform more accurate evaluation of frequencies and introducing new features into the domain.

NOWADAYS, THE DAMAGE SEVERITY EVALUATION IN MECHANICAL STRUC-TURES MADE OF BEAMS IS MOSTLY PERFORMED BY ANALYZING THE NATURAL FREQUENCY SHIFT. THE NON-ISOTROPIC MATERIALS, AS THE MULTI-LAYERED ONES, ARE WIDE-SPREAD IN INDUSTRIAL APPLICATIONS, FOR INSTANCE DUE TO THEIR INTERESTING PHYSIC-MECHANICAL PROPERTIES. THUS, A DEEPER APPROACH OF MULTI-LAYERED BEAMS BECOMES AN IMPORTANT REQUEST IN THE RESEARCH DOMAIN. IN THIS PAPER, THE ACCOMPLISHMENT OF DAMAGE SEVERITY IN MULTI-LAYERED BEAMS IS MORE COMPREHENSIVELY CHARAC-TERIZED BY INTRODUCING A NEW WAY TO HIGHLIGHT THE CRACK EVOLUTION AS A FUNCTION OF STORED ENERGY. IT IS WELL KNOWN THAT THE ENERGY STORED IN A BEAM WITHOUT DAMAGE IS GREATER THAN THE ENERGY OF THAT DAMAGED BEAM. AS A CONSEQUENCE, THE BEAM DEFLECTION CAN BE RELATED TO THE STORED ENERGY. IN THIS REGARD, THE POSSIBILITY TO SPLIT THE DAMAGE LOCALIZATION AND THE DAMAGE SEVERITY ASSESSMENT HAS BEEN PROVEN, AND ALSO THE GRAPHICAL EVOLUTION OF THE NATURAL FRE-QUENCY SHIFT HAS BEEN ACHIEVED AS A FUNCTION OF THE CRACK DEPTH. THE RESULTS ACHIEVED BY THE FINITE ELEMENT METHOD (FEM) AND EXPERIMENTAL TESTS ARE GIVEN IN TABLES AND GRAPHICS. FOR THE FIRST FIVE VIBRATION MODES, A COMPARISON WAS MADE BETWEEN FREQUENCIES ACCOMPLISHED BY ANALYTICAL, NUMERICAL AND EXPERIMENTAL ANALYSES, IN ORDER TO GIVE MORE CREDIBILITY TO THE ACCURACY OF THE RESEARCH DATA PRESENTED IN THIS PAPER.