Dither Amplitude Research Articles

Adaptive bias control of optical IQ modulator with low LFM dither and strong fluctuation resistance.

An innovative approach has been proposed for adaptive bias control in optical IQ modulators. In contrast to traditional approaches that utilize sine dither, this method employs a linear frequency modulated (LFM) signal as the dither, associated with the fractional Fourier Transform (FrFT) to extract the bias point drift. The LFM signal, after undergoing FrFT, transforms into a compressed signal (CS) with energy concentration in the fractional domain. Utilizing this signal for bias point monitoring, the proposed method demonstrates robust bias control even in the presence of substantial interferences, as substantiated by comprehensive simulations and experimental investigations. Remarkably, in a 20-Gbaud 16QAM signal transmission, the proposed approach achieves stable control of the bias point for over 4 hours, even in the presence of voltage fluctuations, while effectively reducing the dither amplitude by half. Furthermore, it maintains a low bit error rate (BER) below 10-5 even under intentional external interference.

Effective Frequency Lock-In Changes of a Ring Laser Gyroscope Due to Harmonic Components of Dithering Signal

The frequency lock-in phenomenon is the most important error factor that degrades the performance of a ring laser gyroscope by causing a non-linear output to the rotational angular velocity input. To solve the problem of frequency lock-in, a mechanical dithering technique has been proposed and most successfully and widely applied to date. In addition, in the case of dithering with a sinusoidal signal of a single-frequency component, the theoretical background is well established. However, in actual applications, it is almost impossible to implement a perfect single sinusoidal signal owing to various electrical and mechanical constraints. In general, although the occupied portion is smaller than the fundamental frequency component, the dithering signal inevitably includes harmonics. Therefore, it is essential to analyze the influence of the corresponding harmonic component to accurately predict the frequency lock-in characteristics of a ring laser gyroscope. In this study, it is assumed that the dithering signal has odd harmonics, and through numerical experiments, the frequency lock-in widths of the ring laser gyroscope according to the dithering amplitude change and the effectiveness of improving the related characteristics according to the application of random dithering are analyzed. The analysis confirmed that the resonance condition, including the higher harmonics of mechanical dithering, can be a major variable that determines the frequency lock-in characteristics of the ring laser gyroscope. To improve the relevant performance of the ring laser gyroscope, in-depth research from that point of view is necessary.

Illumination-Resilient Lane Detection by Threshold Self-Adjustment Using Newton-Based Extremum Seeking

The ability to detect lane markings under varying lighting conditions is essential for autonomous mobile robots and automatic vehicle driving assistance systems. Because the object color information is subject to illumination variation, this article presents a novel and computationally efficient algorithm based on the extremum-seeking method to achieve illumination-resilient lane detection and path-following tasks for autonomous driving. Lane detection is performed in the hue-saturation-value color space by distinguishing the colored lane marks from the background. The system’s inputs are the upper and lower thresholds in each of the hue, saturation, and value channels. We define a cost function as the combination of detection accuracy and lane coverage to evaluate the algorithm performance. Two extremum-seeking schemes, one with fixed dither amplitudes and another with adaptive dither amplitudes, are designed to adjust the system inputs to minimize the cost function. The two proposed methods are validated and compared through video-based simulation studies and scaled-car field experimental tests.

Evading generated-image detectors: A deep dithering approach

In this paper, an end-to-end and black-box deep dithering model is proposed as an anti-forensic measure against general generated-image detectors. Firstly, we show the limitations of conventional generated-image simulator, and propose to use VQ-VAE as an effective alternative to simulate the image generation process. The general end-to-end anti-forensic framework using deep dithering model for generated images is then presented, which generates imperceptible spatial additive dithering to evade the fake-image detectors for various image generation models. The contrastive learning strategy is employed to train the deep dithering model, as we use real images and their VQ-VAE simulated fake images as positive and negative samples respectively, which could greatly eliminate the generative patterns on various generated images. In addition, the dithering amplitude constraint is also adopted to maintain the visual fidelity of dithered images and prevent them from degradation in visual quality. The experimental results show that our proposed deep dithering approach could effectively eliminate the generative artifacts on various GAN based generated images, and outperforms other state-of-the-art generated-image anti-forensic methods.

Systematic fuzzy Navier–Stokes equations for aerospace vehicles

PurposeTo prove the effectiveness of the proposed design method, this study aims to propose the Fisher equation and temperature cooling fins that control high-speed aerospace vehicles.Design/methodology/approachA new approach whereby the control of aerospace vehicles can be achieved by fuzzy controller and appropriate Navier–Stokes equations in this article. The design of the controller based on models of Navier–Stokes equations simplified complex mathematical simulations and approximations.FindingsIf the fuzzy controller cannot stabilize the system, the Navier–Stokes fuzzy function is injected into the system as a controller tool, and the system is asymptotically stabilized by adjusting the fuzzy parameters.Originality/valueThe simulation results show that if the tuning frequency is high enough, the fuzzy controller and fuzzy observer can create chaotic movements by adjusting the dither amplitude appropriately. The demonstration of the Fisher equation and the temperature-cooled fin control problem for high-speed aerospace vehicles has displayed the benefits of combining fuzzy control with the Navier–Stokes equation.

Model-Based Predictive Control and Dithering Control for an Integrated Gasoline Engine and Three-Way Catalytic Converter System

Abstract Controls of integrated gasoline engine and aftertreatment systems are critical for fuel efficiency improvement and emission regulation. This paper aims to develop novel model-based three-way catalytic converter (TWC) controls to reduce the fuel consumption and tailpipe emissions for a gasoline engine. A model-based dither control and a nonlinear model predictive control (MPC)-based control are presented, respectively. The proposed TWC dither control utilizes a systematically designed dither cycle configuration (including dithering amplitude, offset, and frequency) based on a control-oriented model, with the capability to adapt the dither cycle configuration to various engine operating conditions. The MPC control can optimize engine air–fuel ratio (AFR) to maintain the oxygen storage of TWC at a desired level and thus meet the tailpipe NOx, CO, and HC emission requirements. The efficacies of both model-based TWC controls are validated in simulation with MPC control improving CO emission conversion efficiencies by 8.42% and 4.85% in simplified US06 and urban dynamometer driving schedule (UDDS) driving cycles, when compared to a baseline dithering-based AFR control. Meanwhile, NOx emission conversion efficiency is maintained above the required limit of 95%, while the fuel efficiency remains at the same level as the baseline control methodology.

Designing Limit-Cycle Suppressor Using Dithering and Dual-Input Describing Function Methods

This paper described a method to design a limit-cycle suppressor. The dithering technique was used to eliminate self-sustained oscillations or limit cycles. Otherwise, the Dual Input Describing Function (DIDF) method was applied to design dither parameters and analyze the existence of limit cycles. This method was done in a nonlinear system with relay nonlinearity using three standard dither signals, namely sine, triangle, and square waves. The aim of choosing varying dithers was to investigate the effect of dither shapes and the minimum amplitude required for the quenching strategy. First, the possibility and amplitude of limit cycles were determined graphically on the DIDF curve. Then, the minimum amplitude of dither was calculated based on the DIDF analysis. Finally, a simulation was built to verify the analytical work using a digital computer. The simulation results were related to the analysis results. It was evident that the dithering technique is a simple way to suppress limit cycles in a nonlinear system. This paper also presented that dither is an amplitude function, and square-wave dither has the minimum amplitude to quench limit cycles.

Uncertainty Estimation in Extremum Seeking Control of Unknown Static Maps

This letter proposes a design of extremum seeking controllers that guarantees precise convergence of the control system to the unknown optimizer of a measured unknown cost function. The approach introduces an uncertainty estimation technique that provides an estimate of the worst case uncertainty associated with the unknown optimizer. An uncertainty set update algorithm is proposed to reduce the radius of the uncertain set as new data is received. The radius of the uncertainty set is used to reduce the required dither amplitude. The convergence to the unknown optimum and the removal of the dither signal are achieved simultaneously. Asymptotic convergence of the extremum seeking control system to the unknown minimizer is achieved in the absence of measurement noise. A simulation example is provided to demonstrate the effectiveness of the approach.

O2 dosage as a descriptor of TWC performance under lean/rich dithering in stoichiometric natural gas engines

The effects of oscillations in gas composition, known as lean/rich dithering, on the performance of a commercial Pd-based three-way catalyst (TWC) for stoichiometric natural gas (NG) engines were evaluated using synthetic exhaust flow reactor experiments. Under simulated NG exhaust conditions, NO conversion was intimately correlated to CH4 conversion at slightly fuel-rich operating conditions. CH4 conversion significantly varied with lambda (or O2 concentration) and depended on the direction of the lambda change. The dynamic CH4 conversion is likely related to the change of catalyst oxidation state and structures of Pd active sites. The CH4-NO cross-over point was found at a rich-biased lambda rather than stoichiometry. Compared to static operation, catalyst performance was much higher under a realistic dithering condition. The impacts of dithering parameters including amplitude and frequency on CH4 and NO conversions were explored. O2 dosage is proposed as an effective descriptor of the TWC dithering performance. In the O2-dosage space, the performance of distinct dithering parameters collapse, helping to elucidate the fundamental influence of dithering parameters on TWC performance. With the help of O2 dosage, an optimal operating window leading to high CH4 and NO conversions was identified. A higher dithering amplitude is required to keep the catalyst in a reduced state for higher CH4 and NO conversions, while an appropriate O2 dosage that does not exceed the breakthrough OSC is necessary to avoid excess O2 that results in NO slip. The dithering amplitude and O2-dosage-metric maps provide a new method for studying dynamic TWC performance and identifying optimum operation strategies.

The Algorithm of Direct Current Smooth Filtering Based on the Minimum Resource Consumption in FPGA

The algorithm of direct current smooth filtering was proposed in this paper to satisfy the requirement of minimum resource consumption in FPGA and to meet the goal of calculation period in minimum length. In this work, the detail circuit was designed by FPGA and the key circuit was simulated by the modalism. The result of board-level test is shown that the dither amplitude of original direct current was decreased significantly at 90%. The amplitude was in the stable state to reach expected smoothing effects.

Design of Adaptive Voltage Dither Control Framework Based on Spectral Analysis for Nonlinear Piezoelectric Actuator

Advances in miniaturization of micromachines are receiving considerable industrial attention, with a crucial aspect of research being on precision positioning and manipulation at the micro-nanoscale. Nanopositioners are precision mechatronic systems designed to deal with objects at extremely precise resolution wherein piezoelectric actuators have a high potential to impact emerging markets. However, the major bottleneck in harvesting the advantages of piezoelectric actuator for nanopositioning is the presence of inherent nonlinearity, mostly hysteresis, along with the presence of external dynamical disturbance, and traditional feedback controller cannot handle. Dithering has been used in the parlance of piezoelectric actuation as a surprisingly simple yet powerful means of enhancing system performance. This research presents the design framework of an adaptive voltage dither control logic based on spectral analysis of the system output using normalized harmonic ratio. The proposed controller adaptively tunes the intensity of dither amplitude depending on the system response to an optimum value that yields satisfactory results. A commercially available piezo-actuator has been used to model the system along with hysteresis using Dahl model, and system parameters have been identified experimentally. Performance of the proposed controller has been investigated by subjecting the plant model to several real-time perturbations like plant parameter variation, sinusoidal motion tracking, multi-amplitude multi-frequency input signal, external disturbances like Gaussian and impulse, step response, etc., and with the results showing better control performance and disturbance rejection capability as compared to traditional feedback control.

A method to obtain the gain coefficient and dithering amplitude of multi-dithering algorithm in coherent beam combining system based on threshold testing

We reported a new approach for obtaining proper gain coefficient and dithering amplitude of multi-dithering algorithm in coherent beam combination via threshold-testing technique. Through this approach, two parameters can be set based on obtaining threshold with actual signal intensity varying. To clarify the new method, we demonstrated the coherent beam combination of two channels experimentally, which results coincided well with the simulations. The experimental results indicate that this method is an effective way to improve the performance of coherent beam combination systems.

Benchmarking modern algorithms to holographically create optical tweezers for laser-cooled atoms

ABSTRACTWe discuss and compare three methods to generate holograms for optical tweezers: simple rounding, Floyd–Steinberg error diffusion dithering and mixed-region amplitude freedom (MRAF). These schemes are optimized for producing large arrays of tightly focused luminous spots. The algorithms are compared in terms of their speed, efficiency and accuracy, for periodic arrangements of traps; an arrangement of particular interest for the trapping and manipulation of single laser-cooled atoms in the field of quantum computing. We simulate the image formation using each of a binary amplitude modulating digital mirror device (DMD) and a phase modulating spatial light modulator (PSLM) as the display element. While a DMD allows for fast frame rates, the slower PSLM is more efficient and provides higher accuracy with a quasi-continuous variation of phase. We discuss the relative merits of each algorithm for use with both a DMD and a PSLM, allowing one to choose the ideal approach depending on the circumstances.

Modeling of three-way catalytic converter performance with exhaust mixtures from dithering natural gas-fueled engines

The behavior of a three-way catalytic converter (TWC) to treat the exhaust from a natural-gas fueled engine in fuel dithering conditions was evaluated by numerical simulation. A validated comprehensive and thermodynamically consistent surface reaction mechanism was utilized to model the natural gas engine exhaust conversion in the TWC at dithering conditions. The mechanism was implemented in a tank-in-series model to study the TWC behavior while air to fuel ratio was cyclically varied (dithering conditions). The simulation results were evaluated by comparison with data collected from a TWC operated at dithering conditions. The microkinetic reaction model predicted the post catalyst total hydrocarbon (THC), NO and CO concentrations well when 5 reaction steps out of 115 elementary steps were modified. Both simulations and experiments showed that TWC window widened in the dithering conditions, particularly dithering yielded improved NO conversion as compared to steady state operation at higher air to fuel ratios. Simulations showed that this was due to a higher number of surface vacancies with dithering that improved NO adsorption and surface reaction. Both dithering parameter including amplitude and frequency was modeled and the results indicated there is an optimal dithering amplitude to achieve lower exhaust emission, larger dithering amplitude decreased the THC conversion because the air fuel ratio shifted to the fuel rich side. Simulations indicated that the dithering frequency did not noticeably impact the exhaust conversion simply because the transition time is relative short.

Frequency Response of Laser Gyroscopes in a Wide Range of Rotation Velocities

The laser gyro frequency response is studied by means of numerical simulation using a phase equation. The calculation results are compared to the results of experimental measurements on a precision dynamic test-bench. Quantitative relationship between the threshold value of static lock-in zone and frequency response distortions is established. Numerical methods helped to obtain and experimentally confirm the quantitative dependence of frequency response distortion on the amplitude and frequency of meander-shaped dither. It is shown that the dither shape significantly affects the frequency response form. Furthermore, it is demonstrated that frequency-response distortions depend on conditions of its measurement, in particular, on the time. The conducted research allows dither parameters to be optimized with a view to increase the accuracy of measurements using laser gyroscopes.

A New Method for Maintaining Constant Dither Amplitude in Low Frequency PWM

Various controls for fluid flow and pressure are now required in related industries, and the pulse width modulation (PWM) and dithering techniques have become essential for the proport ...

Dither in a rolling airframe flight vehicle with a two-position actuator: An amplitude distribution approach

Rolling airframe manoeuvring is a type of manoeuvre in which the missile provides continuous roll during flight. Cross-coupling between the angle of attack and sideslip in rolling airframe missiles (RAMs) yields a coning motion around the flight path. As the pitch and yaw cross-coupling effect decreases, the radius of this coning motion decreases and the accuracy of the control system increases. Two-position (on–off) actuators are used in most RAMs. The presence of a two-position actuator in a feedback system makes its characteristics non-linear. A high-frequency signal so-called dither is applied to compensate for the non-linearity effect of the actuator characteristic in the feedback system and to stabilize the coning motion. The amplitude distribution function (ADF) method in dither analysis shows that the smoothed non-linearity characteristic can be computed as the convolution of the original non-linearity and the ADF of the dither signal. According to the four-degrees-of-freedom (4-DOF) equations of RAMs in a non-rolling frame and regarding various dither signals through the ADF approach on a two-position actuator, an analytical condition for dither amplitude in coning motion stability of RAMs is derived. It was shown that the triangular signal with specified amplitude and high enough frequency led to a smoother response of two-position actuators. Finally, by applying beam-riding guidance to a RAM, the performance of dithers for decreasing the distance of the missile from the centre of the beam is validated through simulations. It is illustrated that applying the triangular dither resulted in minimal error.

Effects of lateral tip control in CD-AFM width metrology

Critical dimension atomic force microscopes (CD-AFMs) use flared tips and two-dimensional sensing and position control of the tip-sample interaction to enable scanning of features with near-vertical or reentrant sidewalls. Sidewall sensing usually involves lateral dither of the tip, which was the case in the first two generations of CD-AFM. Current, third-generation instruments also have a fast dither tube actuation (FDTA) mode where a control algorithm and fast response piezo actuator are used to position the tip in a manner that resembles touch-triggering of coordinate measuring machines (CMMs). All methods of tip position control, however, induce an effective tip width that may deviate from the actual geometrical tip width. When lateral dithering is involved, this effect is readily understood as the addition of a dither envelope to the geometrical tip width.The effective tip width is a key correction parameter for accurate feature width measurements and is typically estimated using a tip calibration procedure. However, the possibility exists of small errors in the estimated tip width due to variations and dependencies of the effective width on tip, tool, material, and environmental parameters. We are investigating this possibility through a systematic study of the dependence of the apparent width on measurement mode, dither amplitude, tip type, and sample composition. While we believe that there are potential effects that should be considered carefully, we also conclude, particularly for silicon features, that most potential biases can be removed by performing the calibration and measurement exercises under the same conditions.

Energy harvesting from the PV Hybrid Power Source

In this paper it is proposed a Maximum Power Point (MPP) tracking technique for the photovoltaic (PV) system based on an advanced Extremum Seeking (aES) control that improves both basic performances of the ES control schemes: guaranteed convergence and proved internal robustness. Beside these features that are necessary in case of unmodeled dynamics, other features such as higher search speed and improved accuracy of the MPP tracking process are demonstrated. Thus, different irradiance sequences are used to test the performances of the MPP tracking process, where each of them could represent a worse scenario than in reality. Analysis in the frequency domain reveals the main relationships between the aES control parameters (the values of closed loop gain and dither amplitude) and the performance indicators (the search speed and tracking accuracy). If the dither amplitude is set to be proportional with the magnitude of the first harmonic of the PV power processed in the ES control loop, then the aES control will exhibit a negligible power ripple after the MPP was caught. Therefore, the proposed aES control outperforms all ES control schemes in overall power efficiency.

FC energy harvesting using the MPP tracking based on advanced extremum seeking control

In this paper is proposed a Maximum Power Point (MPP) tracking technique for the Fuel Cell (FC) stacks based on advanced Extremum Seeking (aES) control that improves the basic performances of the ES control schemes: a guaranteed convergence and proved internal robustness. Other features such as higher search speed and improved tracking accuracy are demonstrated for the proposed aES control, besides these features that are necessary in case of unmodeled dynamics. The analysis on the frequency domain reveals the relationships between the main aES control parameters, the values of closed loop gain and dither amplitude, and the design performance indicators, the speed of search and accuracy of MPP finding, respectively. If the dither amplitude is set to be proportional with the magnitude of first harmonics of the processed FC power, then the reference current used in the FC current control loop will have an insignificant ripple after the MPP is caught. Thus, a reduced FC power ripple will appear. Therefore, if the search speed is set to be the same for all ES control schemes, then the proposed aES control outperforms all classical ES control schemes in overall power efficiency. Moreover, the aES search speed will proportionally increase with the loop gain and the dither amplitude. Note that here the dither has the amplitude set by the first harmonic of the FC power, being a time variable that have high value during the searching phase. This accelerates MPP searching up to the FC safe limits. Finally, this means a controllable time to shortly find the next MPP on dynamical operation of the FC stack. First harmonic of the FC power becomes almost zero after MPP is caught. Thus, higher tracking accuracy that means an economy on fuel consumption is obtained. The simulations performed show that above mentioned performances are effective for the aES control operating in both ripple- and dither-based modes of the grid connected FC inverters.