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The paper presents a way of accomplishing a non-contact excitation by electromagnetic waves generated from a system that includes WiFi microcontroller, H-Bridge and coil. The ESP 32 microcontroller software achieves PWM signal, which follows’ a sinusoidal shape of variable frequency. The PWM signal drives the H-bridge resulting in a more powerful electric signal that also drives the coil, accomplishing in this way the pseudo-sine electromagnetic wave. The source code from microcontroller provides variable frequency and working period as well. The main features of the system are 0.5 to 3000 Hz, working periods between 0.1 and 10 seconds, the possibility to achieve more than one working period with standby periods in between.

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.

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.

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.

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 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.