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Статті в журналах з теми "PHASE ERROR BANDWIDTH"
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Torfs, D., J. De Schutter, and J. Swevers. "Extended Bandwidth Zero Phase Error Tracking Control of Nonminimal Phase Systems." Journal of Dynamic Systems, Measurement, and Control 114, no. 3 (September 1, 1992): 347–51. http://dx.doi.org/10.1115/1.2897354.
Повний текст джерелаАнотація:
This paper describes a new feedforward algorithm for accurate tracking control of nonminimal phase systems. Accurate feedforward calculation involves a prefilter design using the inverse system model. Nonminimal phase systems cause problems with this prefilter design, because unstable zeros become unstable poles in the inverse model. The zero phase error tracking control algorithm (ZPETC) consists of a substitution scheme, which removes the unstable zeros. This scheme introduces a small gain error, which increases with frequency, but no phase error. This paper investigates additional properties which give more insight into the ZPETC algorithm, and allow to improve it. The improved algorithm is based on the same substitution scheme as ZPETC, but adds additional feedforward terms to compensate for the gain error. These additional terms increase the frequency range for which the overall transfer function has only limited gain error, without introducing phase errors. The additional feedforward terms repeatedly reduce the tracking error proportional to ε2, ε4, ε6, …, where ε is the ZPETC tracking error. The new feedforward algorithm or new substitution scheme is therefore called “extended bandwidth zero phase error tracking control algorithm” (EBZPETC). Experimental results on a one-link flexible robot compares both methods.
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Huang, Yi Cheng, Shu Ting Li, and Kuan Heng Peng. "Precision Motion of Iterative Learning Controller Using Adaptive Filter Bandwidth Tuning by Improved Particle Swarm Optimization Technique." Applied Mechanics and Materials 376 (August 2013): 349–53. http://dx.doi.org/10.4028/www.scientific.net/amm.376.349.
Повний текст джерелаАнотація:
This paper utilized the Improved Particle Swarm Optimization (IPSO) technique for adjusting the gains of PID and the bandwidth of zero-phase Butterworth Filter of an Iterative Learning Controller (ILC) for precision motion. Simulation results show that IPSO-ILC-PID controller without adaptive bandwidth filter tuning have the chance of producing high frequencies in the error signals when the filter bandwidth is fixed for every repetition. However the learnable and unlearnable error signals should be separated for bettering control process. Thus the adaptive bandwidth of a zero phase filter in ILC-PID controller with IPSO tuning is applied to one single motion axis of a CNC table machine. Simulation results show that the developed controller can cancel the errors efficiently as repetition goes. The frequency response of the error signals is analyzed by the empirical mode decomposition (EMD) and the Hilbert-Huang Transform (HHT) method. Errors are reduced and validated by ILC with adaptive bandwidth filtering design.
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Zhao, Lei, Lei Shi, and Congying Zhu. "New Nonlinear Second-Order Phase-Locked Loop with Adaptive Bandwidth Regulation." Electronics 7, no. 12 (November 23, 2018): 346. http://dx.doi.org/10.3390/electronics7120346.
Повний текст джерелаАнотація:
Synchronization of large acquisition bandwidth brings great challenges to the traditional second-order phase-locked loop (PLL). To address the contradiction between acquisition bandwidth and noise suppression capability of the traditional PLL, a new second-order PLL coupled with a nonlinear element is proposed. The proposed nonlinear second-order PLL regulates the loop noise bandwidth adaptively by the nonlinear module. When a large input–output phase error occurs, this PLL reduces the frequency offset quickly by taking advantage of the large bandwidth. When the phase error is reduced by the loop control, the proposed PLL suppresses noises by using the small bandwidth to increase the tracking accuracy. Simulation results demonstrate that the tracking speed of the proposed PLL is increased considerably, and its acquisition bandwidth is increased to 18.8 kHz compared with that of the traditional second-order PLL (4 kHz).
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Passafiume, Marco, Giovanni Collodi, Edoardo Ciervo, and Alessandro Cidronali. "A Novel TDoA-Based Method for 3D Combined Localization Techniques Using an Ultra-Wideband Phase Wrapping-Impaired Switched Beam Antenna." Electronics 10, no. 17 (September 2, 2021): 2137. http://dx.doi.org/10.3390/electronics10172137.
Повний текст джерелаАнотація:
This paper presents a novel Time Difference of Arrival-based approach suitable for single-anchor positioning systems, implemented by phase wrapping-impaired array antenna. With the latter being a typical occurrence in large Switched Beam Antenna (SBA) operating in the low microwave range. The proposed method takes advantage from the large bandwidth of radio link, established between the anchor and the positioning target, by generating an unambiguous equivalent phase relationship between antenna array elements. The technique is validated by adopting a relatively large SBA antenna operating in the 4.75–6.25 GHz bandwidth, and capable to position a target in a 3D domain. Experimental data, carried out in the 4–7 GHz frequency bandwidth, show that by dealing properly with the inherent constraint of phase wrapping issues, it is possible to get a significant improvement on the elevation angle with respect to methods not capable to deal with phase reconstruction and thus operating in a phase-less context. Combining range and angle errors, the associated cumulative distribution function error in 90% of cases shows an error of 0.13 m.
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Cruz, Madson Pereira, Rodolfo Novellino Benda, Maria Flávia Soares Pinto Carvalho, Guilherme Menezes Lage, Maria Teresa Cattuzzo, and Herbert Ugrinowitsch. "Bandwidth knowledge of results persists on motor skills acquisition." Motricidade 14, no. 2-3 (October 17, 2018): 107–14. http://dx.doi.org/10.6063/motricidade.14294.
Повний текст джерелаАнотація:
The aim of this study was to investigate the short and long-term effects of the bandwidth KR in learning of the absolute and relative dimensions of a motor skill. Twenty-two undergraduate students divided into two groups: G15 who received KR when the relative error exceeded 15%; and G0, with KR after every trial. The study consisted of an acquisition phase, and the volunteers practiced 100 trials with a target time of 850 ms and relative of 22.2%, 44.4% and 33.3% between the first and second, second and third, third and fourth keys, respectively. This phase, KR related to relative time (relative error) was provided according to the group. KR of total target time was available to both groups after all trials. Three retention tests with ten trials were conducted 10 minutes, 24 hours and one week after the acquisition phase. The results showed that G15 had a smaller relative error than G0. This study allows concluding that bandwidth KR in relation relative time error showed its effects in the consistency of relative time. These effects persisted even after seven days after the acquisition phase in a delayed retention test.
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Song, Young-Jin, Thomas Pany, and Jong-Hoon Won. "Theoretical Upper and Lower Limits for Normalized Bandwidth of Digital Phase-Locked Loop in GNSS Receivers." Sensors 23, no. 13 (June 25, 2023): 5887. http://dx.doi.org/10.3390/s23135887.
Повний текст джерелаАнотація:
Determining the loop noise bandwidth and the coherent integration time is essential and important for the design of a reliable digital phase-locked loop (DPLL) in global navigation satellite system (GNSS) receivers. In general, designers set such parameters approximately by utilizing the well-known fact that the DPLL is stable if the normalized bandwidth, which is the product of the integration time and the noise bandwidth, is much less than one. However, actual limit points are not fixed at exactly one, and they vary with the loop filter order and implementation method. Furthermore, a lower limit on the normalized bandwidth may exist. This paper presents theoretical upper and lower limits for the normalized bandwidth of DPLL in GNSS receivers. The upper limit was obtained by examining the stability of DPLL with a special emphasis on the digital integration methods. The stability was investigated in terms of z-plane root loci with and without the consideration of the computational delay, which is a delay induced by the calculation of the discriminator and the loop filter. The lower limit was analyzed using the DPLL measurement error composed of the thermal noise, oscillator phase noise, and dynamic stress error. By utilizing the carrier-to-noise density ratio threshold which indicates the crossing point between the measurement error and the corresponding threshold, the lower limit of the normalized bandwidth is obtained.
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Ferrari, Mauro, and Luca Piattella. "0.8–8 GHz 4-bit MMIC phase shifter for T/R modules." International Journal of Microwave and Wireless Technologies 7, no. 3-4 (May 21, 2015): 317–26. http://dx.doi.org/10.1017/s1759078715000793.
Повний текст джерелаАнотація:
This paper presents the design approach and test results of a full passive, decade bandwidth GaAs MMIC, composed by a phase shifter (PS) with a cascaded absorptive single pole double throw switch, suitable for transmitter/receiver modules in active electronically scanned array. The proposed PS – fabricated using a UMS GaAs 0.25 PHEMT process – combines all-pass filters with high-pass filters, in order to provide less than 13 dB insertion loss, less than ±20° phase error and less than ±2.5 dB amplitude error in the 0.8–8 GHz bandwidth.
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Kim, Kyeong-Rok, and Jae-Hyun Kim. "Wideband Waveform Generation Using MDDS and Phase Compensation for X-Band SAR." Remote Sensing 12, no. 9 (May 1, 2020): 1431. http://dx.doi.org/10.3390/rs12091431.
Повний текст джерелаАнотація:
This study investigated wideband waveform generation using a field programmable gate array (FPGA) for X-band high-resolution synthetic aperture radar (SAR). Due to the range resolution determined by the bandwidth, we focused on wide bandwidth generation while preserving spectrum quality. The proposed method can generate wide bandwidth using a relatively low system clock. The new approach was designed in Simulink and implemented by very-high-speed-integrated-circuits hardware description language (VHDL). We also proposed a hardware structure in accordance with the proposed method. Signal connections of FPGA and digital analog converter (DAC) are described in the design of the proposed hardware structure. The developed X-band waveform generator using the proposed method output the desired pulse waveform. For the reduction of phase error and improvement of spectrum quality at the X-band, phase error compensation and pre-distortion were applied to the waveform generator. The results of the simulation and the hardware output demonstrate that the variation and standard deviation of the phase error were improved within the frequency spectrum. Accordingly, the proposed method and the developed waveform generator have the potential to produce a high-resolution image of the area of interest.
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Torfs, Dirk, and Joris De Schutter. "Optimal Feedforward Prefilter With Frequency Domain Specification for Nonminimum Phase Systems." Journal of Dynamic Systems, Measurement, and Control 118, no. 4 (December 1, 1996): 791–95. http://dx.doi.org/10.1115/1.2802359.
Повний текст джерелаАнотація:
The paper shows the influence of the location of unstable zeros on the tracking performance of feedforward prefilters. Unstable zeros are divided into a number of classes. It is shown that existing feedforward prefilters (Zero Phase Error Tracking Control (ZPETC), E-filter, Extended Bandwidth ZPETC, ...) perform well for two classes, but fail for a particular class of unstable zeros. For this class, a characteristic frequency, fc, exists such that the induced gain error attenuates all frequencies of the reference trajectory f ≤ fc and amplifies frequencies f > fc. Hence, it is impossible to freely select the tracking bandwidth. Therefore, an optimal feedforward prefilter for discrete time nonminimum phase systems is presented to deal with this class of unstable zeros. As in the ZPETC method, the prefilter compensates for unstable zeros in the inverse system model, retains the zero phase property, and introduces small gain errors. But in addition, the design minimizes a cost function for which a least square solution is found. A frequency and time domain analysis shows the superior performance of the presented optimal prefilter design even for trajectory with high frequency components.
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Vyomal N, Pandya, P. Rahul Reddy, and Abhishek Choubey. "Bandwidth Estimation Algorithm of WestwoodNR for Wireless Network." International Journal of Engineering & Technology 7, no. 2.16 (April 12, 2018): 114. http://dx.doi.org/10.14419/ijet.v7i2.16.11521.
Повний текст джерелаАнотація:
Two widely known parameters of Transmission Control Protocol (TCP) used to control the flow of packets are Congestion Window (cwnd) & Slow Start Threshold (ssthresh). After congestion, slow start phase or fast-retransmit phase come in action wherein TCP has an important role in the reduction of these parameters. This is in response to packet loss identified by TCP. This in turn will cause unnecessary reduction of data flow & degradation of TCP throughput. Researchers have developed some algorithms to come out of this problem, WestwoodNR is one of them. WestwoodNR is using Bandwidth Estimation algorithm to estimate available bandwidth, to make effective use of available network capacity even after the congestion episode. It allows higher values of ssthresh & cwnd when it enters the fast-retransmit phase and slow start phase. In turn this algorithm claims better performance in terms of bandwidth utilization. The focus of this paper is on error recovery mechanisms suitable for WestwoodNR operating over the wireless sub path. These mechanisms have to address the increased bit error probability and temporary disruptions of wireless links. The efficiency of WestwoodNR within wireless scenarios is investigated and possible modifications that lead to higher performance are pointed out.
Дисертації з теми "PHASE ERROR BANDWIDTH"
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Lin, Jinsong, and Kamilo Feher. "BANDWIDTH EFFICIENCY AND BER PERFORMANCE OF ENHANCED AND FEC CODED FQPSK." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/607727.
Повний текст джерелаАнотація:
International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, CaliforniaBit error rate (BER) and bandwidth efficiency of several variations of enhanced Feher patented quadrature phase shift keying (FQPSK) [1] are described. An enhanced FQPSK increases the channel packing density of that of the IRIG 106-00 standardized FQPSK-B by approximately 50% in adjacent channel interference (ACI) environment. As the bandwidth efficiency of FQPSK-B DOUBLES (2×) that of pulse code modulation/Frequency modulation (PCM/FM) [5], the enhanced FQPSK, with a simpler transceiver than FQPSK-B, has a channel packing density of TRIPLE (3×) that of PCM/FM. One of the other enhanced FQPSK prototypes has an end to end system loss of only 0.4 dB at BER=1x10^(-3) and 0.5 dB at BER=1x10^(-4) from ideal linearly amplified QPSK theory. The enhanced FQPSK has a simple architecture, thus is inexpensive and has small size, for ultra high bit rate implementation. With low redundancy forward error correction (FEC) coding which expands the spectrum by approximately 10%, further improvement of about 3-4.5dB E N b o is attained with NLA FQPSK-B and enhanced FQPSK at BER=1x10^(-5) .
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Law, Eugene, and Kamilo Feher. "FQPSK VERSUS PCM/FM FOR AERONAUTICAL TELEMETRY APPLICATIONS; SPECTRAL OCCUPANCY AND BIT ERROR PROBABILITY COMPARISONS." International Foundation for Telemetering, 1997. http://hdl.handle.net/10150/609732.
Повний текст джерелаАнотація:
International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, NevadaThe aeronautical telemetry community is investigating alternative modulation methods to the commonly used non-return-to-zero (NRZ) pulse code modulation (PCM)/frequency modulation (FM). This paper outlines the important characteristics being investigated. Measured data comparing the spectral occupancy and bit error probability (BEP) performance of PCM/FM with that of a prototype constant envelope Feher’s quadrature phase shift keying (FQPSK) modulator and demodulator will also be presented. Measured results in several radio frequency bands demonstrate that the 99.99% and -60 dBc bandwidths of filtered FQPSK are only approximately one-half of the corresponding bandwidths of optimized PCM/FM even when the signal is non-linearly amplified. The signal energy per bit to noise power spectral density (E /N ) required for a BEP of 1×10 b 0 -5 for non-optimized FQPSK was approximately 12 dB which is approximately the same as limiter discriminator detected PCM/FM.
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KUMAR, AJAY. "DESIGN OF DIGITAL PHASE SHIFTER WITH VARIOUS ORDERS OF BPF." Thesis, 2011. http://dspace.dtu.ac.in:8080/jspui/handle/repository/13879.
Повний текст джерелаАнотація:
M.TECHThis thesis presents the theory and a design method for distributed digital phase shifters, where both the phase‐error bandwidth and the return‐loss bandwidth are considered simultaneously. The proposed topology of each phase bit consists of a transmission‐line (TL) branch and a bandpass filter (BPF) branch. The BPF branch uses grounded shunt quarter wavelength stubs to achieve phase alignment with the insertion phase of the TL branch. By increasing the number of transmission poles of the BPF branch, the returnloss bandwidth can be increased. Analysis of the BPF topology with one, two, and three transmission poles is provided. The design parameters for 22.5 , 45 , 90 , are provided for bandwidths of 30%, 50%. The three bit digital phase shifter is designed with minimum phase shift of 22.50 and maximum phase provided is 157.50. Results of all three bit phase shifts are produced and their respective phase errors and return losses are compared.
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Uttarwar, Tushar. "A digital multiplying delay locked loop for high frequency clock generation." Thesis, 2011. http://hdl.handle.net/1957/25739.
Повний текст джерелаАнотація:
As Moore���s Law continues to give rise to ever shrinking channel lengths, circuits are becoming more digital and ever increasingly faster. Generating high frequency clocks in such scaled processes is becoming a tough challenge. Digital phase locked loops (DPLLs) are being explored as an alternative to conventional analog PLLs but suffer from issues such as low bandwidth and higher quantization noise. A digital multiplying delay locked loop (DMDLL) is proposed which aims at leveraging the benefit of high bandwidth of DLL while at the same time achieving the frequency multiplication property of PLL. It also offers the benefits of easier portability across process and occupies lesser area.
The proposed DMDLL uses a simple flip-flop as 1-bit TDC (Time Digital Converter) for Phase Detector (PD). A digital accumulator acts as integrator for loop filter while a ��-�� DAC in combination with a VCO acts like a DCO. A carefully designed select logic in conjunction with a MUX achieves frequency multiplication. The proposed digital MDLL is taped out in 130nm process and tested to obtain 1.4GHz output frequency with 1.6ps RMS jitter, 17ps peak-to-peak jitter and -50dbC/Hz reference spurs.Graduation date: 2012
Частини книг з теми "PHASE ERROR BANDWIDTH"
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Rodriguez, Erick Gonzalez, Yuliang Zheng, Holger Maune, and Rolf Jakoby. "Future Reconfigurable Radio Frontends for Cognitive Radio and Software Defined Radio." In Advances in Wireless Technologies and Telecommunication, 544–66. IGI Global, 2015. http://dx.doi.org/10.4018/978-1-4666-6571-2.ch020.
Повний текст джерелаАнотація:
Cognitive Radio (CR) and Software Defined Radio (SDR), concepts which were mere proposals to solve the population of services over the past two decades, are now enabled by novel materials and components to offer fully reconfigurable devices. Thus, a convergence of services can be attained within a reduced, or even single RF (Radio Frequency) signal path in the device. A solid design of reconfigurable frontends, from the RF part to the digital baseband, should consider different criteria to better exploit the available spectrum. Examples of such criteria are scattering parameters and phase linearity of components at a defined carrier frequency, RF signal bandwidth, and signal quality in terms of Error Vector Magnitude and Bit Error Rate. In this chapter, a general perspective to achieve smarter air interfaces is studied and discussed by setting out strategies based on CR and SDR techniques for the implementation and integration of future reconfigurable RF-Frontends.
Тези доповідей конференцій з теми "PHASE ERROR BANDWIDTH"
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Schäffer, Christian. "Determination of the Microwave Phase Error in Switchable Optical Time Delay Networks for Phased Array Antennas." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/cleo_europe.1996.cthi52.
Повний текст джерелаАнотація:
Switchable optical true time delay (TTD) networks are used for the control of phased array antennas and for microwave signal processing in the optical domain. Photonic networks are used because of their wide instantaneous bandwidth.
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Lin, Maoliu, Zhe Zhang, and Qinghua Xu. "The Accurate and Robust Estimation of Phase Error and its Uncertainty of 50GHz Bandwidth Sampling Circuit." In TENCON 2006 - 2006 IEEE Region 10 Conference. IEEE, 2006. http://dx.doi.org/10.1109/tencon.2006.344105.
Повний текст джерела
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Fienup, J. R. "Characterization of the Hubble Space Telescope point spread function using phase retrieval." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.mqq1.
Повний текст джерелаАнотація:
Characteristics of the Hubble Space Telescope (HST) that affect image deblurring are described, with emphasis on the phase errors that are determined by phase retrieval algorithms. The aberrations of the HST are determined from the measured point spread functions (PSFs) by phase retrieval algorithms of two types: nonlinear least squares optimization over coefficients of Zernike polynomials and iterative transform algorithms. In either case, accurate and comprehensive optical system models are needed to satisfy stringent requirements on the retrieved phase error, both for the purpose of building appropriate correction optics and for analytic computation of space variant PSFs for image deblurring. This paper describes phase retrieval algorithms incorporating a system model that involves multiple-plane propagation through the system and weighted error metrics that allow for bad CCD pixels to be ignored. Analytic expressions of the gradient of the error metric, with respect to either polynomial coefficients or point-by-point phase maps, are derived that allow for a full gradient calculation to be performed with a small number of fast Fourier transforms (FFTs) independent of the number of parameters. Other system characteristics that hinder image deconvolution are described, including the telescope jitter, the space-variant nature of the system, finite spectral bandwidth, and image undersampling.
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Xu, Luhua, Weijia Li, Jinsong Zhang, Deng Mao, Md Samiul Alam, Yannick D’Mello, Santiago Bernal, Zixian Wei, and David V. Plant. "Broadband High-Performance 2×2 MMI 3-dB Coupler Enabled by SWG Lateral Cladding for the Silicon-on-Insulator Platform." In Optical Fiber Communication Conference. Washington, D.C.: Optica Publishing Group, 2023. http://dx.doi.org/10.1364/ofc.2023.th2a.5.
Повний текст джерелаАнотація:
We demonstrate a high-performance silicon photonic 2×2 MMI 3-dB coupler enabled by SWG lateral cladding. Measured imbalance below 0.3 dB and phase error below 1.83° are achieved over a 130 nm bandwidth covering the C-band.
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Sun, Guangyoung. "Orbit Motion Tracking Control for Rotating Machine With Magnetic Suspensions." In ASME 2005 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/detc2005-84249.
Повний текст джерелаАнотація:
Conventional use of active magnetic bearings (AMB) focuses on keeping a rotor centered at the zero reference. In this research, a control algorithm is developed for an alternate task of tracking high-bandwidth sinusoidal targets: whirling and conical motions. To increase robustness to the parametric uncertainty and the nonlinearity of inherent AMB dynamics, the sliding mode control is developed based on an original nonlinear AMB model with an uncertain magnetic force constant. Performance indices, such as the I2R power loss, the tracking error and the phase lag, are compared for the two target motions, and they are also utilized to find an optimal bias current of the actuators. Simulation results show that the rotor follows the two high-bandwidth large motion targets with low tracking error and phase lag in the presence of parametric uncertainty. Orbit motion tracking control has a variety of potential applications in rotating machinery such as active rotating stall control, in which seal clearance is required to follow a sinusoidal dynamic motion.
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Lee, Kyeong Ha, Seung Guk Baek, and Ja Choon Koo. "Real-Time High Bandwidth Feedforward Position Control of Electro-Hydraulic Actuator Using Non-Minimum Phase Inverse Model." In ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/detc2017-67628.
Повний текст джерелаАнотація:
In this paper, real-time feedfoward position control algorithm of electro-hydraulic actuator (EHA) is proposed. To reduce nonlinearity of EHA, model uncertainty and disturbance, feedback system with proportional-integral-derivative (PID) controller is used. The feedback system is estimated as linear dirsrete time transfer function by recursive least squares algorithm. Feed-forward controller using inverse model generates filtered signals that compensate magnitude and phase of feedback system. For high bandwidth control, fast sample rate is necessary and it causes NMP zeros of estimated transfer function. The NMP transfer function is inversed by zero phase error tracking control (ZPETC) method and the inverse model is used to feedforward controller. The real-time experiment is conducted by NI-CompactRio and Labview, and the simulation is programmed in MATLAB/Simulink. The results of simulation verify the validity of proposed control strategy.
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Xi, Wei, Guoxiao Guo, and Jie Yu. "A Robust Servo Demodulation Algorithm to Compensate for Head Velocity Induced Error." In ASME 2013 Conference on Information Storage and Processing Systems. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/isps2013-2901.
Повний текст джерелаАнотація:
The fast growing areal density and continuous increasing demand of IOPS and throughput in hard disk drive present great challenges to servo systems on the performance of the track-follow accuracy and seek time. A high bandwidth servo system is required to meet the demand. However, the performance of the servo systems is ultimately limited by the resolution of the position signal which is demodulated form embedded servo sector. Inside the servo sector, the servo track address combining with the servo bursts provide a global position signal of read/write head. The servo track address, which is commonly encoded as gray code, provides coarse position information. Whereas the servo bursts carries the position error signal (PES) to determine the fine position information. There are multiple servo pattern schemes that have been used in hard disk drive, for example, amplitude based servo pattern, phase pattern, and dual frequency pattern [1]. The servo track address and servo bursts span multiple magnetic cycles. The head position is assumed to be unchanged when it travels through the servo sector. The assumption is valid when head is track-following or seeking at low velocity. However, when the head seeks with high velocity, the assumption induces large PE demodulation error, since the head can move as much as a few tracks when it travels through the servo sector. Thereby, it prevents us to use high servo bandwidth for pushing seeking performance. To tackle this problem, we proposed a robust PE demodulation algorithm which can eliminate the head velocity introduced error. The new demodulation algorithm can be generally applied to any servo pattern schemes. The paper is organized as follows. The servo burst modeling and problem formulations are introduced in section I. The velocity based PE demodulation algorithm is presented in section II. The paper concludes with simulation and experiment results.
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Pan, J. J., F. Q. Zhou, Y. Shi, and S. X. Li. "Effective Apodized Phase Mask For Optimum FBGs." In The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1998. http://dx.doi.org/10.1364/cleo_europe.1998.cfb3.
Повний текст джерелаАнотація:
FBGs are promising devices for DWDM networks [1]. Phase mask (PM) technique is one of the most versatile techniques for massive production of FBGs. However, ever increasing requirements of DWDM put stringent requirements on FBG sidelobe suppression and spectral skirt sharpness. In this paper, we report a detailed comparison of different apodization profiles with emphasis on narrow linewidth, sharp spectral skirt and a large figure of merit which is the ratio of bandwidth at -0.5 dB to that at -25 dB. Effective apodized PM was fabricated by using e-beam writing and reactive ion-milling (RIM) with stitching error-free. For a gaussian apodized FBG. it has a gaussian refractive index modulation, an inverse gaussian index background and a constant average index change along the FBG with no unwanted dispersion. FBG apodization using PM dithering technique suffers some drawbacks for pulsed UV excimer lasers and for very high UV photosensitive fibers. Scanning writing apodized FBG technique needs double UV exposures for FBG writing and background index change resulting in a lower control accuracy and a lower fabrication efficiency. Using apodization aperture and amplitude masks have the similar problems of double exposure and lower control accuracy resulting unwanted dispersion. Apodized PM technique is an efficient method for qualified DWDM FBGs production with a simple setup and an excellent fabrication repeatability.
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Gamiz, Victor L. "Low Light Level Fringe Visibility Estimation with Adaptive Optics." In Adaptive Optics. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/adop.1995.pd3.
Повний текст джерелаАнотація:
The source image spectrum obtained by imaging interferometry is derived from measurements of the interference fringe visibility and phase from pairs of apertures. Most interesting sources are dim and of small angular extent requiring observations in the low light level regime over large baselines. The use of large individual apertures increases the amount of light but requires some form of adaptive optics to mitigate the effects of the atmosphere and maintain the spatial coherence across baselines. We outline the mathematical formalism for quantifying the error in estimating the fringe visibility and phase with varying amounts of spectral bandwidth, radiometric signal-to-noise, atmospheric seeing, individual aperture diameter, baseline dimension, fringe tracking, tilt removal, and higher order Zernike mode removal. This work describes the proper aperture wavefront covariances across arbitrary baselines with the proper Kolmogorov atmospheric statistics, assumed independent by other works. Photon noise, detector noise, and spectral bandwidth dependent photon counting statistics are included. The effects from the use of single mode fiber optics to transport the beams are also described. Numerical results describing the sensitivity of the fringe estimates to the above parameters are presented for typical array geometries for observing geosyncronous satellites.
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Wong, N. C., and John L. Hall. "High-performance laser frequency stabilization using an external electrooptic phase shifter." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.ft6.
Повний текст джерелаАнотація:
A simple and effective laser frequency stabilization technique uses a high finesse optical cavity (5-MHz FWHM) as the frequency discriminator and an external ADP phase modulator to supply the necessary high-speed laser frequency correction. This is supplemented by a lightweight laser PZT for mid- and low-frequency corrections. The fast frequency servo has a unity gain frequency near 2 MHz, while its low-frequency gain rolls off below 50 kHz where the PZT loop becomes dominant. The FM noise spectrum of our single-mode argonion laser output extends up to 300 kHz but is dominated by water-induced fluctuation of 1.8-MHz rms frequency excursion at 600 Hz. In closed loop operation, the high-frequency noise is suppressed down to the measurement noise level, i.e., the frequency servo error point shows an apparent noise level well below the shot noise level. This is the key achievement toward obtaining an ultranarrow laser linewidth. The present residual linewidth of 70-kHz rms is due to insufficient gain at low frequencies to suppress the water-induced FM noise at 600 Hz. We believe this can be readily corrected by increasing the low-frequency gain with a region of steeper gain slope vs frequency in the PZT channel. Alternatively, adding an acoustooptic modulator as a fast frequency shifter1 will certainly provide the needed bandwidth. An argon laser linewidth of just a few kilohertz is expected.