Statistical Wiener process model for vibration signals in accelerated aging processes of electric motors

This research describes random process modeling of the accelerated aging process based upon the mechanical degradation in induction motors. In order to show this aging effect, vibration measurements are considered at the end of each aging cycle, which gradually cause to bearing damage in the motor. In this manner, the accelerated aging study comprises seven aging stage sequentially and collected data set is presented as seven aging cycles and one initial cycle. Hence total aging process is represented by a set of the sequential vibration signals for initial and aged cases. Since the vibration signals are random values which represent the Gaussian distribution character in each period of measurement and this character can be conveyed to the next stage with a scaling of the signal related to elapsed time, the process reminds the Brownian motion or the so-called random walk and it is expected that the degradation can be described as a Wiener process. Examining the collected data proves that in the statistical manner, this compact data set reflects the properties of a non-stationary random process and it is expressed by the Wiener Process Model (WPM) as a statistical approach. This property of the process will be helpful to estimate the residual useful life (RUL) of the bearings in induction motors with high accuracy

Design considerations of a MEMS cantilever beam switch for pull-in under electrostatic force generated by means of vibrations

This study is about investigation of design considerations of a MEMS switch that is considered to pull in under electrostatic force generated by a piezoelectric based voltage generator inside the MEMS. Here the energy source to drive the piezoelectric device is vibrations the whole system undergoes. In this study, a new approach is brought to calculate the pull-in voltage easily and effectively under certain assumptions. There are a number of conditions the switch has to meet such as its robustness against environmental vibrations. Some are discussed in brief. Following the design considerations a series of MEMS switches are fabricated and the pull-in voltages are measured in order to compare the true data with calculations and simulations. Numerical results prove the validity of the new approach to calculate the pull-in voltage, and experimental results coincide greatly with the calculations. Several materials are investigated to be used in the design of the cantilever beam and finally a beam structure is proposed that fits best for overall specifications

Implementation Possibilities of Standard Site Method Sub-cases for EMC Antenna Calibrations in Non-ideal Site Conditions

Today, a number of engineering issues require electromagnetic compatibility (EMC) tests, in turn triggering the need for EMC-antenna calibrations. In this framework, experimenters seek accurate and time-saving solutions. Basically, standard site method (SSM) ANSI C63.5-2006 stipulates the near-to-ideal conditions on an empty and vast land, where three antennas are used for antenna factor determination. In our previous work, we investigated the suitability of narrow test sites for antenna calibration according to three-antenna SSM-ANSI-C63.5-2006, whose usability was validated under certain conditions. In the present study, we expand our research by applying the sub-cases of using a known antenna and identical antennas specified in the standard in order to shorten the calibration process. The results reveal that the methods for various calibrations are useful for successfully running the process even in non-ideal sites and help significantly reduce the experimentation time, considering the uncertainty limits specified in EMC test standards

Design considerations of a MEMS cantilever beam switch for pull-in under electrostatic force generated by means of vibrations

This study is about investigation of design considerations of a MEMS switch that is considered to pull in under electrostatic force generated by a piezoelectric based voltage generator inside the MEMS. Here the energy source to drive the piezoelectric device is vibrations the whole system undergoes. In this study, a new approach is brought to calculate the pull-in voltage easily and effectively under certain assumptions. There are a number of conditions the switch has to meet such as its robustness against environmental vibrations. Some are discussed in brief. Following the design considerations a series of MEMS switches are fabricated and the pull-in voltages are measured in order to compare the true data with calculations and simulations. Numerical results prove the validity of the new approach to calculate the pull-in voltage, and experimental results coincide greatly with the calculations. Several materials are investigated to be used in the design of the cantilever beam and finally a beam structure is proposed that fits best for overall specifications

A Method To Improve Accuracy In Digital Multimeters

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1990Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 1990Bu tezde, dijital mültimetrelerde hatanın azaltılması için bir yöntem önerilmiştir. Burada önemli olan husus, hata azaltılırken maliyetin aşırı yükselmesine neden olmamaktır. Dijital aletlerde doğruluğa en çok etkiyen eleman A/D çeviricidir. Ve bu elemanda hız ile doğruluk ters orantılıdır. Her iki özelliğin iyileştirilmesi ise ileri teknoloji ile mümkün olabilmekte dir ki, bu da maliyetin çok artması demektir. Bu tezde uygulanan yöntemin prensibi, ölçme süresinin uzamasına göz yumarak, ölçüle cek işaretlerden alınan örnekler arasındaki süreyi açmaya dayanmaktadır. Aynı zamanda, tezde yenilik olarak sunulan düşünce doğrultusunda- işaretin frekans değişimi de takip edil mektedir. Bu nedenle tam periyodik işaret durumuna göre örnek sayısını artırmaya gerek kal mamaktadır. Böylelikle doğruluğu yüksek, fakat ucuz A/D çeviriciler kullanılarak amaca ulaşıla bilmektedir. Birinci bölümde, uygulanacak yöntemin tanıtılmasına hazırlık teşkil eden düşünceler açık lanmıştır. Buna göre, ideal halde, genlik ve frekansı hiç değişmeyen, yani tam periyottu işaret lerde ölçme süresi, ilâve bir hata söz konusu olmaksızın, istenildiği kadar uzatılabilir. İkinci bölümde konunun teorisi ele alınmıştır. Burada, işaretlerden alınan örneklerle ortala ma ve efektif değerlerin hesabı açıklanmış, ardından genlik ve frekanstaki değişimlerin ölçme sonucuna etkisi incelenmiştir. Yukarıda sözü edilen yöntem, bu tez kapsamına giren ve geri lim (U), akım (I), aktif güç (P), reaktif güç (Q), ve güç katsayısı (k) ölçen cihazın gerçeklenmesin- de, U ve I işratlerinden her periyotta 1 örnek alınarak uygulanmıştır. Bu tezde, örneklerin alına cağı anların uygun biçimde kaydırılması ile, -belli sınırlar içinde - tam periyodik işaret durumuna göre örnek sayısı artırılmadığı halde, frekans modülasyonunun doğuracağı hata miktarının, di ğer hatalar yanında ihmal edilebilecek mertebede kalacağı gösterilmiştir, işaretin biçimi değiş mediği sürece örnek sayısını belirleyici tek faktör, orijinal işaret içindeki en yüksek harmonik derecesi olarak kalacaktır. Genlik modülasyonlu halde ise, modüle eden işaretin periyodunun tesbitindeki güçlükler nedeniyle, hatanın azaltılması amacına yönelik özel bir önlem alınmamış tır. Üçüncü bölümde gerçeklenen devrenin katlan teker teker tanıtılmıştır. Dördüncü bölümde hata analizi yapılmış, toplam hatanın %0.5 ile %1 arasında kaldığı he saplanmıştır. Beşinci bölümde çeşitli fonksiyonların (U, I, P, Q, k) hesabına ilişkin yazılım ele alınmıştır. Altıncı bölümde, gerçeklenen cihaz ile doğruluğu bilinen bazı cihazların ölçü sonuçları kar şılaştırılmış, çeşitli dalga şekilleri için, cihazın, hesaplanan hata sınırları içinde doğru ölçme yaptı ğı tesbit edilmiştir. Sonuç olarak kullanılan yöntemin, dijital mültimetrelerin doğruluk ve maliyetine olumlu kat kısı olduğu, ve önemli uygulama alanları bulunduğu belirtilmiştir.The most critical device of a digital multimeter, effecting the accuracy, is the Analog / Digital Converter (ADC). By this element, the speed is inversely proportional to the accu racy, unless an advanced technology is used. In this thesis, a new method is proposed to reduce error in digital multimeters, without causing the cost to increase extremely. The principal of this method is based upon the fact, that the time interval between the samples taken from the measured signal, will be widened, hereby accepting the measur ing period also to enlarge. Besides that, -according to the method developed in this work- the frequency change of the signal will be followed, which has the advantage, that the number of the samples is not needed to be increased compared with the case of fully periodic waveform. Thus, it will be possible to use cheap, but high accurate ADC to achieve our aim. Any periodic function with the amplitude X, can be defined as x(t) = X. P(cot), where P (cot) is a periodic function with its peak values +1 and -1. If the amplitudes of the har monics higher than the n-th order are small enough to be ignored, then we have to take 2n samples per period for real time processing. This means a sampling period of n I con. But if we are sure of the amplitude remaining unchanged, in other words, if the signal is fully periodic, so, after taking one sample, we can wait m periods to pass before taking the next sample; and in the m-th period, the sample will be taken after an advance of n I con. Thus, the measuring period will be lenghtened to 2- (2nm + 1). re / co instead of 2- n / co. In practice, we generally want to measure either RMS values of signals, or power, which is the average value of the multiplication of two similar signals. For all these meas urements, it is very convenient to use a microprocessor to process the samples. As it is also explained in the second part of this thesis, for periodic signals, the follow ing items can be shown easily: 1) The average value of the 2n samples / period is equal to the mean value of the sig nal. 2) The square root of the average value of the 2n samples / period is equal to the RMS value of the signal. 3) The average value of the multiplication of 2n samples / period each from two signals is equal to the mean power, considering the one signal to be the current, and the other the voltage. But here, one point is important to draw attention to: Although according to Nyquist criterium, the number of the samples / period (N) may be chosen N > 2n, in practice, one should choose N > 2n, to avoid the possibility, that all samples coincide with zero- cross ing points of the n-th order harmonic. In this thesis, the proposed method is used by selecting m = 1. Accordingly the sam pling points are shown in Fig. 1. 1st zero crossing 2nd z. c. (i+1)stz.c. Figure 1 - Sampling points for m = 1 Using this method, an instrument has been developed to measure RMS- values of volt- age and current, mean power, reactive power (according to the formula: Q = V U2. I2 - P2 ), and power factor k= P / Ul. In part 2, it has further been analyzed, at which rate the frequency (FM) / amplitude (AM) modulation effects the total error. In the case of FM, actually there is no concern about additional error, if one can follow the frequency change, and accordingly shift samples to appropriate points. This is be cause, the amplitude remaining unchanged means the RMS-value being the same as in the case of fully periodic waveform (no modulation). But the impossibility of the prediction of the duration of the current period (T) led us here to determine the sampling points as i-l t"i= £Tk + TM.(G-l)/N) k=l i£2 and the first sampling point (i = 1) is the first zero crossing point of the signal 1st zero crossing 2nd z. c. Ti/32 32nd z. c. * t * t 31T31/32 Figure 2 - Sampling points in the case of FM (for m = 1) The instrument developed here, is designed to measure signals with nmax = 15. Thus N is chosen to be N = 32 (Fig.2). Calculations show, that by using the method developed in this work and explained VIII -* Load Figure 3 - Block schematic of the circuit above, FM will not have considerable effect upon total error, as far as the signals in prac tice are concerned. According to this method, the 'Pulse Timing Circuit' (Fig. 3) will be synchronized with each voltage zero-crossing (positive to negative), which is assumed to be the beginning of the new period. Thus the frequency change will be followed and the effect of FM upon total error will be minimized. But in the case of AM, the RMS-value is not directly proportional to the amplitude of the signal. This means one has to determine the period of the modulated signal in order to define the right positions for samples; or the measuring period should be taken large enough to keep additional error within negligible limits. Because of the inconvenience of either of these two alternatives, with our instrument we did not try to measure signals with minimum error, which are effected by AM. In part 3, the block diagram (Fig. 3) of the realized circuit is given first, and then various parts are explained in detail. On Fig. 3, the functioning of the system can be explained briefly as follows: A certain ratio of the voltage on the network is applied to the zero-crossing detector (ZCD). This stage is followed by a pulse timing circuit (PTC), which performs the task, to produce pulses at appropriate moments. These pulses are used to trigger two sample- hold circuits (SHC), one for current, the other for voltage. The samples taken will be transferred to the microprocessor (u.P) across an analog-to-digital converter (ADC). After completion of taking 32 samples each from voltage and current, the u.P performs calcula tions according to the selected function and the result will be displayed. The fourth part handles the error analysis. Studying each stage seperately shows, that the most critical stage is the PTC. By this stage the most effective property on the error is the frequency of the crystal, being used to clock the CMOS-ICs. Thus to reduce the er ror, the frequency is to be increased. For our application, the frequency is chosen 1 MHz., causing an approximate error of 0.2 % for this stage. The ADC has a 12-bit resolution, with an absolute error of 1.22 mV (Reference volt age: 5 V). IX C Start J Display <- 00 Wait for interrupt Load u and i samples Determine selected function Perform according subroutine Display Figure 4 - Flow chart of the program Programming the u.P is explained in Part 5. The flow chart of the program is given in Fig. 4. In the sixth part, results of some measurements are given to prove the quality of the realized instrument. The results are compared with those of instruments, of which the ac curacy is known. Thus, it is shown, that the proposed method is a cheap solution to re duce error in digital multimeters. Finally, in the concluding part, some important properties of the study are reviewed, and some further considerations are explained, such as to make use of the instrument to build up an accurate digital Watt-hour meter (Wh-meter).DoktoraPh.D

Position Control of Flexible Manipulator using PSO-tuned PID Controller

Flexible manipulators have been tried to use due to their advantages such as the requirement of low drive power because of low weight, low power consumption, higher load capacity, high-speed operation, small actuators and low production costs. These advantages of flexible manipulators are due to their structural flexibility in joints or links. However, the flexibility causes vibrations in the end effector both on the move and after the force that causes the movement is removed. It takes some time to dampen these vibrations. In this study, particle swarm optimization (PSO)-tuned PID controller is used to control the position of the flexible manipulator directly and indirectly to reduce the vibration of the manipulator. The fitness function selected for the PSO includes parameters related to both the desired time response and vibration. Thus, the optimal PID parameters found with PSO control the position of the flexible manipulator and ensure low vibration

A New Algorithm for Dynamic Vestibular System Analysis with Wearable Pressure and Motion Sensors

Objective: Balance is a complex state that requires integrating information from many systems into various levels of the nervous system and the actions of commands from the central nervous system and the musculoskeletal system. Postural control is the ability to maintain body position against forces that threaten the individual's orientation or balance. In our study, a mobile prototype system was used to create equilibrium data of subjects and generate a set of normal values, diseases and fuzzy decisions

Performance Comparison of ML Methods Applied to Motion Sensory Information for Identification of Vestibular System Disorders

This study is the first step gone to develop a Machine Learning (ML) algorithm to be applied to sensory information collected from people to identify Vestibular System (VS) disorders. Three ML methods, the Support Vector Machine (SVM), SVM with Gaussian Kernel and Decision Tree are compared to determine the one with the highest accuracy to use for VS analysis. These methods are applied to the data set collected from groups both of healthy and suffering from VS disorders. All three methods had computation time in tens of milliseconds providing the possibility of real time processing in the field of identification of diseases related to VS imperfections. The assessment of the algorithms was based on processing of 22 features extracted from the dataset. SVM with Gaussian Kernel performed best with 81.3% accuracy. Following this step, some addition and removal of features is made to observe their effect on the training model. We noticed that some features are discriminative that they have significant influence on the overall accuracy. Thus, as a next step, the objective of this work is to apply some feature selection methods to find the most discriminative features to decrease the algorithm complexity while increasing the system accuracy. The ultimate goal of our study is to develop a ML algorithm embedded in wearable devices in order to diagnose people with VS-problems in their daily life

A novel surgical technique for treatment of symptomatic Tarlov cysts

Background The aim of this retrospective study was to describe a novel, simple surgical technique for the treatment of symptomatic Tarlov cysts. Methods A total of 40 patients with symptomatic Tarlov cysts, admitted to our tertiary center between 1998 and 2019 constituted the study group. All patients underwent microsurgical puckering of the cyst, the technique we described to prevent a recurrence. Patients' symptoms, radiological findings, intraoperative findings, and clinical results were evaluated. Results Of the 40 patients (5 males, 35 females) whose charts were reviewed, the mean age was 28.4 (range, 17-61) years. The mean follow-up was 8 (range, 3 months to 21 years) years. Preoperatively, the most common symptoms were leg pain and numbness of the lower extremity. Postoperatively, no major complications were observed. Clinical progression was halted in all patients; 33 (82%) patients recovered completely and seven (17%) patients reported partial recovery. Cystic cavity persisted radiologically in five (12%) patients, decreased in size in 30 (75%) patients, and regressed completely in the remaining five (12%) patients. None of the patients had permanent neurological deficits. Conclusion Puckering of the cyst membrane is a safe and easy-to-perform surgical technique for symptomatic Tarlov cysts. This technique can be used almost in all cases instead of the commonly used microsurgical cyst excision or cyst fenestration