Angular Limitation Research Articles

Multi-constrained predictive optimal control for spacecraft attitude stabilization and tracking with performance guarantees

This paper investigates a novel predictive control approach for spacecraft attitude stabilization and tracking problems with consideration of performance constraints, angular velocity limitation and control saturation. First, the prescribed performance control (PPC) structure and barrier Lyapunov function (BLF) are utilized to design the cost function of optimal control problem. Subsequently, a multi-constrained predictive optimal controller for spacecraft attitude stabilization and tracking with performance guarantees is devised via exploiting an explicit receding horizon optimization control strategy under actuator saturation. Compared with the existing methods, the major merit of the proposed one lies in the semi-analytic solving scheme of optimal control problems with high computing efficiency and simultaneous handling of multiple constraints without increasing computational burden. Finally, two illustrative examples are employed to validate the effectiveness of the proposed control method.

Electro-Hydraulic Servo-Pumped Active Disturbance Rejection Control in Wind Turbines for Enhanced Safety and Accuracy

Aiming at the high accuracy and high robustness position control of servo pump control in the pitch system of a wind turbine generator, this paper proposes an active disturbance rejection controller (ADRC). The ADRC considers pitch angular velocity and acceleration limits. According to the kinematics principle of the pump-controlled pitch system, the relationship between the pitch angular velocity and acceleration limit and the displacement of the hydraulic cylinder is established. Through the method of theoretical analysis, the nonlinear relationship expression between pitch angle and hydraulic cylinder displacement is obtained, and the linearization of pitch angular velocity control is realized; the formula for b0 (the estimated value of the input gain of the system) of the pump-controlled pitch system is obtained by the method of modeling and analysis, b0 is the key parameter for the design of the ADRC; the stability of the controller parameters is proved through the stability analysis and simulation analysis, and the design of the self-immobilizing controller with pitch angular velocity and acceleration limitation is the completed ADRC design. Finally, a joint simulation platform of AMESim and MATLAB as well as a physical experiment platform of electro-hydraulic servo pump-controlled pitch control is constructed, and the effectiveness of the proposed control method is verified through simulation and experiment. The results show that compared with the unrestricted ADRC and PID, the velocity-acceleration-limited ADRC can effectively improve the control effect of the angular velocity and acceleration of the paddle, smooth the startup process, improve the safety of the system, and have better position control accuracy and anti-jamming ability.

Impact of strength of fault current path on the operation of decoupled double synchronous reference frame – phase locked loop

This paper studies the performance of decoupled double synchronous reference frame - phase locked loop (DDSRF-PLL) synchronizing method during grid fault. The study is carried out using Matlab/Simulink. The contribution of the paper is to reveal that if the DDSRF-PLL proposed in many papers is used, the control system of network side converter (NSC) may become unstable during a symmetrical grid fault. The instability problem appears only when certain tuning parameters of DDSRF-PLL are used and the fault current path is weak. Thus, the problem may not be easily detected. This paper emphasizes that it is mandatory to use PI-controller with integrator anti windup in the loop filter of DDSRF-PLL. In addition, the impact of angular frequency limitation range on the fault ride through performance is evaluated with comparative simulations.

Variably polarized superradiant THz source employing crossed undulator configuration

We propose a variably polarized high-power THz source based on a crossed undulator configuration optimized for superradiant emissions from a short-pulsed electron beam. It generates arbitrary polarization by superimposing orthogonal linear polarization from two planar undulators. The phase difference is adjusted by slightly varying the path length of the first radiation in the phase shifter located between the undulators, enabling continuous and fast polarization manipulation. To realize the crossed undulator scheme based on superradiance in the THz region, it is necessary to maintain an extremely short electron bunch length of the order of 100 fs or less throughout the two undulators. We have designed a prototype system with an R56-variable triple-bend phase shifter that enables isochronous electron beam transport. Through theoretical and numerical analyses, we found that although polarization has significant observation angle dependence, a degree of polarization higher than 0.9 and a significant radiation intensity can be obtained under an appropriate angular limitation. Depending on the electron beam current and the number of undulator periods, it is estimated that the effective intensity under an angular limitation for a degree of circular polarization of 0.9 can reach the order of 100 mW on average.

Calculating multiple scattering from a time-varying undulating sea surface using a full-wavefield multistage algorithm

The sea-surface interface between ocean and air is time varying and can be spatially rough as a result of wind, tides, and currents; the shape of this interface changes over time under the influence of wind, tides, etc. As a result, waves impinging on the sea surface are continuously scattered. In the case of marine seismic, the multiple-scattered waves propagate downward into the underwater formation and result in complex seismic responses. To understand the structure of the responses, we have adopted a multistage algorithm for computing the scattered waves at the sea surface. Specifically, we first extrapolate the upgoing incident waves stepwise using thin-slab approximation from the scattering theory based on the De Wolf approximation of the Lippmann-Schwinger equation. Then, we implement the air-water boundary condition at the sea surface. Finally, we use the irregular boundary processing technique to compute the time-varying undulating sea-surface scattered waves from different scattering stages. To overcome the angular limitation of the original parabolic approximation, we introduce a multidirectional parabolic approximation based on computational electromagnetics. Numerical tests indicate that the multistage algorithm presented here can accurately calculate sea-surface scattered waves and should be useful in investigating the structure of marine seismic responses.

Radio Counterparts of Gamma-Ray Sources in the Cygnus Region

The view of the gamma-ray universe is being continuously expanded by space high energy (HE) and ground based very-high energy (VHE) observatories. Yet, the angular resolution limitation still precludes a straightforward identification of these gamma-ray emitting sources. Radio observations are an effective tool for searching their possible counterparts at lower energies because the same population of relativistic electrons responsible for radio emission can also produce HE/VHE emission via inverse-Compton scattering. The Cygnus region is crowded by many gamma-ray sources, most of them remaining unidentified. In order to find possible counterparts to unidentified gamma-ray sources, we carried out a deep survey of the Cygnus region using the Giant Metrewave Radio Telescope at 610 MHz and 325 MHz. We did a detailed search for counterparts in the error circle of HE/VHE sources. We report 36 radio sources found in the error ellipse of 15 HE sources, and 11 in those of VHE sources. Eight sources have very steep radio spectral index alpha <-1.5, which are most likely to be pulsars and will be followed up for periodicity search. Such a significant number of pulsar candidates within the error circle of HE/VHE sources prompts fresh look at the energetics and efficacy of pulsars and pulsar wind nebulae in this context.

Improving Surface Current Estimation From Geostationary Ocean Color Imager Using Tidal Ellipse and Angular Limitation

AbstractSea surface currents (SSCs) in coastal regions can be mapped from successive optical images observed by satellite. We implemented the maximum cross‐correlation (MCC) algorithm to Geostationary Ocean Color Imager‐derived total suspended matter in the East China Sea in this study. We developed a new data filtering method to improve the accuracy of SSC vector sequence using estimated tidal ellipse. The proposed method eliminated spurious vectors by considering direction order and suitable angular limitation. The obtained average velocity of SSC reached 0.72 m/s, which was close to the buoy‐measured average speed of 0.64 m/s. Compared with existing spurious vector eliminating method, the average angular error was improved significantly by 28–38% and the average relative magnitude error was improved by 3% in the case study.

Non-kinematic calibration of industrial robots using a rigid–flexible coupling error model and a full pose measurement method

Abstract This study addresses the non-negligible flexibility problem of industrial robots and describes a rigid–flexible coupling error model for robot non-kinematic calibration. Simulation confirms that compliance errors are major sources of inaccuracies and affect robot accuracy with geometric errors. To reduce the impact of measurement noise and improve calibration performance, an enhanced approach is proposed for full pose measurement and identification optimisation. This approach is based on the self-adaption particle swarm optimisation (SAPSO) algorithm with a dual-index (i.e. observability index O1 and identification accuracy index Omin) and a modified Levenberg–Marquardt algorithm, which considers external constraints (i.e. structural interference and angular limitation). Simulation results illustrate that the 36 error parameters of the proposed error model can be identified with improved accuracy and stability using the proposed approach. Finally, experimental results obtained with a Staubli TX60L robot with a FARO laser tracker are introduced to demonstrate the practical effectiveness of our approach in robot accuracy improvement.

Next-generation lithography for 22 and 16 nm technology nodes and beyond

In this paper, next-generation lithography (NGL) for the 22 and 16 nm technology nodes and beyond is reviewed. A broad range of topics, including history, technologies, critical challenges, and the most plausible candidates are discussed. The 22 and 16 nm technology nodes rely on NGL. NGLs have been extensively studied. Because of technological issues, the semiconductor industry has stopped pursuing several NGLs, such as X-ray proximity lithography, ion projection lithography, and scattering with angular limitation projection electron lithography. Currently, the primary candidate technologies are extreme ultraviolet lithography (EUVL), maskless lithography (ML2), and nanoimprint lithography (NIL), with EUVL being the leading candidate. Since EUVL was first proposed in 1988, many studies have been conducted. Currently, there is no "show stopper" for EUVL. Moreover, challenges are present in almost all aspects of EUVL technology. Almost all primary semiconductor manufacturing companies plan to implement commercial pre-production step-and-scan exposure tools in 2011. However, EUVL power at an intermediate focusing level has not yet met the volume manufacturing requirements. EUVL resists have been significantly improved recently, but there is still a critical need to meet requirements on resolution, line width roughness, and sensitivity. Creating a defect-free EUVL mask is another obstacle to the application of EUVL. ML2 and NIL, like EUVL, have also undergone significant progress recently, but throughput, defect control, and cost remain the critical impediments for practical application.

The Development of a New Orthosis (Neuro-Orthosis) for Patients with Carpal Tunnel Syndrome

Static wrist orthoses (SWOs) are used in the treatment of carpal tunnel syndrome (CTS) with some drawbacks. As an alternate approach to SWOs, an active closed-loop wrist control strategy based on the principles of functional electrical stimulation was proposed to limit wrist movements. The purpose of the study was to determine whether the proposed 'neuro-orthosis' (NeO) system resulted in less restriction in the hand compared to clinically accepted custom-made SWOs while limiting the wrist movements. A case-control study was designed to determine the specific effects of the system on patients with CTS. A total of 24 right-handed female volunteers (12: CTS, 12: healthy) participated in the study. Function, dexterity, and strengths were measured under three different testing conditions: without orthosis, with SWO, and with the NeO system. Maximum angles in one subtest while the NeO system was on and off and general discomfort levels in SWO and NeO test conditions were recorded. The NeO system resulted in less restriction with respect to SWO and provided considerable angular limitation compared to placebo. It was concluded that the proposed prototype control system can be a good candidate to limit the wrist movements in place of SWOs with a better degree of freedom in patients with CTS.

Calculation of Stress Fields Near Notch Roots in Real Life Structures Subjected to In-Plane and Out-of-Plane Deformations

Abstract The authors proposed a practical method for estimating stress fields near a notch in a real structure under in-plane loading in the previous paper. In this method, boundary conditions of a region near a notch are determined reasonably, using the stress field expression and stress components measured by strain gages on the boundary. Therefore, in this method, precise estimation of the stress fields can be performed in a real structure whose boundary conditions are hard to grasp. In this paper, we develop this method further so that it can be used for notches under out-of-plane loading or simultaneous in-plane and out-of-plane loading. A straight boundary near a notch and non-symmetric boundary conditions are investigated as factors lowering the calculation precision. Consequently, there is the angular limitation of a notch in application of this method. However calculation results are accurate enough for most cases.

Processing and interpretation of EBSD data gathered from plastically deformed metals

The use of electron backscattered diffraction (EBSD) for the investigation of dislocation boundary microstructures formed during plastic deformation of metals is discussed. A quantitative description is given of the angular resolution limitation in EBSD mapping. The ability of filtering using orientation averaging to improve the angular resolution of the EBSD data is then considered. Orientation filtering is tested using both simulated EBSD maps where a certain orientation noise function and level are assumed and additionally by direct comparison of EBSD and orientation measurements taken in the transmission electron microscope from the same region of a thin foil. Orientation filtering results in an improvement of data quality, but filtering can also introduce artefacts that cannot be distinguished from real microstructural features. The main limitation at present in developing specific recommendations for the use of filtering methods is that more information is required about the nature of the orientation noise at or near dislocation boundaries.

Monte Carlo simulation of electron transmission through masks in projection electron lithography

We have calculated electron energy loss spectrum for electrons transmitted through a mask in projection electron lithography by Monte Carlo simulation based on the dielectric function model and Mott elastic scattering cross section. A good agreement between simulation and experiment is obtained. The calculation results of the transmission and contrast for the masks in scattering angular limitation for projection electron lithography show that the contrast is dominated by the thickness of scattering layer (thicker the scattering layer higher the contrast), but is less affected by the thickness of the supporting membrane. Furthermore, with the increasing aperture angle the transmission increases but the contrast reduces, and the contrast decreases with increasing primary energy of electrons.

シリアルリンクロボットの跳躍パターン生成

This paper discusses jumping pattern generation for a serial link robot so that it can jump as high as possible under torque limitation. By applying GA for determining torque assignment, we obtain various jumping patterns with respect to the torque limitation under the mass of robot. With the increase of the torque limitation, double-leg based jump, single-leg based jump, and spring-type jump, are generated for high jump. Under the joint angular limitation, we also obtain an interesting solution where one end of the link is first lifted up and the other end finally kicks the ground strongly.

Optical inspection of next generation lithography masks

For the last 5years a joint venture has pursued a research program studying and enhancing the ability of optical inspection tools to meet the inspection needs of extreme ultraviolet (EUV) and other next generation lithographies (NGLs). In this article we present a survey of results we have obtained for patterned inspection of NGL masks. The NGL technologies that we have studied include two electron projection lithographies, EUV, and step and flash imprint lithography (SFIL). We discuss the sensitivity of the inspection tools and mask design factors that affect tool sensitivity. In contrast to conventional photomask inspection, which primarily utilizes transmitted light for inspection, almost all NGL mask inspections are performed in reflected light. Much of the work has been directed towards EUV mask inspection and how to optimize the mask to facilitate inspection. Early EUV masks had an optical contrast of 40% or lower. Our partners have succeeded in making high contrast EUV masks ranging in contrast from 70% to 98%. Die to die and die to database inspections, at a wavelength of 257nm, of EUV masks have been achieved with a sensitivity that is comparable to what can be achieved with conventional photomasks, with a minimum detected defect size of 80nm square defects. We have inspected scattering with angular limitation projection electron-beam masks successfully. Electron-beam stencil masks, such as that used in projection reduction exposure with variable axis immersion lenses, pose a problem in that their high aspect ratio of mask thickness to minimum feature width results in low resolution transmission images. Reflected light images provide high-resolution images suitable for inspection, but will not be sensitive to defects below the inspection surface. We have run inspections on SFIL masks in die to die, reflected light in an effort to provide information concerning possible cumulative damage due to imprinting and to provide feedback on defect densities, types and sizes to improve the masks. Our defect sensitivity on SFIL masks is approximately 100nm, though we cannot run at the highest sensitivity due to large numbers of nonprogrammed defects. We have also used an inspection system, at a wavelength of 364nm, to inspect both unpatterned EUV substrates (no coatings) and blanks (with EUV multilayer coatings), and demonstrated a sensitivity of approximately 100nm to polystyrene latex spheres. This information has helped drive down the defect densities on EUV blanks and substrates by some three orders of magnitude. Extensions of conventional optical lithography have pushed out the introduction of NGL technology to the 33nm or possibly the 22nm node. Mask inspection technology will need substantial improvements in resolution to meet the NGL inspection requirements below the 45nm node.

Ultrasound Inverse Scattering Computed Tomography under the Angular Illumination Limitation

Transmission ultrasound inverse scattering computed tomography is expected to be useful for breast cancer screening, because it provides the quantitative sound speed reconstruction of tissue properties. For the realization of the system, however, large-scale ring array acquisition systems are required and hardware cost becomes very high. To resolve this problem, four linear array probes are placed around the rectangular perimeter of the target region. By this means, system may be realized at a lower cost and may still be compatible with conventional B mode imaging. In this system, a limitation on the illumination angle is imposed based on the range achievable with electronic scanning by the four linear arrays. Hence, ill-posedness caused by the lack of angular view information becomes a serious problem. As a resolution to this problem, a hybrid method using both angular and frequency diversity observations is employed, so that low-frequency scattering signal components are incorporated into the image reconstruction calculations. To examine the method numerically, scattered data are synthesized for tissue-like rectangular test objects through rigorous calculations using the finite difference method. From the results of the reconstructed images, it is demonstrated that the precision of the sound speed and reproducibility of the object shape is almost satisfactory, even when the illumination view is limited over an extremely narrow range.

Simple Estimation Method for Stress Field near a Notch in Real Structures with Strain Gages (2nd Report, A Thin Plate under Anti-Plane Deformation or both In-Plane and Anti-Plane Deformation)

The authors proposed a practical method for estimating the stress fields near a notch in a real structure under in-plane loading in the previous paper. In this method, boundary conditions of a region near a notch are determined reasonably, using the stress field expression and stress components by strain gages on the boundary. Therefore, in this method, precise estimation of the stress fields can be performed in real structure whose boundary conditions are hard to grasp. In this paper, we have developed this method so that it can be used for notches under anti-plane loading or both in-plane and anti-plane loading. A straight boundary near a notch and non-symmetric boundary conditions are investigated as factors lowering the estimation precision. Consequently, there is the angular limitation of a notch in application of this method. However estimation results accurate enough for practically were obtained in the most cases.

Monte Carlo simulation of electron transmission through the scattering masks with angular limitation for projection electron lithography

We calculated electron energy loss and angular distributions for electrons transmitted through masks for electron projection lithography by a Monte Carlo (MC) simulation method. After comparing the improved continuous slowing down approximation model, the direct MC model, and the intensive direct MC model, the last model was used. The energy loss distributions calculated by the latter two models are much better than by the first model and the intensive direct MC model can be applied to more materials than the direct MC model. The effect of mask thickness on energy loss, transmission, and contrast was analyzed. We found that, for a W/Cr/Si3N4 mask, the thicker the scattering layer the wider the angular distribution, the lower the transmission, and the higher the contrast. But the thickness of the membrane Si3N4 layer has less effect on the contrast.

Modeling and development of a deep silicon etch process for 200 mm election projection lithography mask fabrication

Gravitation toward a dry silicon etch process for electron projection lithography (EPL) mask fabrication is beneficial because of the concomitant increase in the available membrane area. In order to help understand the complex Bosch etch process and its dependence upon hardware design and process parameters for scattering with angular limitation in projection election beam lithography (SCALPEL) mask fabrication, a combined equipment and feature scale model has been employed. For case studies such as varying the deposition cycle time or ramping the bias power, computed sidewall profiles from the model deviate from experimental data by only about 5.5%. Given the extreme complexity of the Bosch process, this correlation is considered excellent. The best experimental Bosch etch conditions produce SCALPEL substrates with an effective silicon etch rate of 2.7 μm/min, 6.1% etch uniformity, selectivity to tetraethyl orthosilicate &amp;gt;240:1, and average strut sidewall angles of 87.4°. Introduction of hardware into the chamber results in partially blocking the transport of important etch and polymer deposition species to the wafer, thereby altering the etch and passivation rates. The provided learning is applicable to projection reduction exposure with variable axis immersion lenses format EPL masks as well.

Mask blank fabrication, pattern transfer, and mounting distortion simulations for the 8-in. format SCALPEL mask

The electron-beam projection lithography technique known as scattering with angular limitation projection electron-beam lithography (SCALPEL) is capable of producing linewidths of 100 nm and smaller, making it a leading candidate for replacing the current lithographic technique, deep ultraviolet (DUV). Critical to the success of SCALPEL is the creation of a low-distortion mask. Finite element modeling allows for the efficient identification of pattern-specific distortions of the mask membrane. Results pertinent to the current design of the 8-in. format mask are presented.