Large Angular Motion Research Articles

Nonlinear Modeling and Vibration Response Analysis of a Dual-Rotor System with an Inter-Shaft Graphite Seal

The inter-shaft graphite seal is a common structure in the dual-rotor system, and may generate nonlinear lateral excitation when there is large relative angular motion at the seal position. This paper represents the first attempt to study the nonlinear behaviors of a dual-rotor system with inter-shaft graphite seal excitations. First, an excitation model of the inter-shaft graphite seal is proposed by the analytical method. This model is then introduced into the beam finite element model of a dual rotor system, and the dynamic equations of the whole system are finally obtained. The vibration responses under the effect of the inter-shaft seal are clarified by analyzing 3D waterfall plots, rotor orbits, and time and frequency domain waveforms. The results show that the inter-shaft seal can lead to vibration coupling between HP and LP rotors. The axial spring stiffness and contact end face friction coefficient of the graphite seal have a significant effect on rotor vibration. When those two parameters are small, only coupling vibration phenomena can be observed, i.e., the rotation frequency of one rotor can be observed in another rotor vibration. With the increase in axial spring stiffness or contact end face friction coefficient, multiple modes of LP and HP rotors are excited, which dominates the vibration behaviors of the dual rotor system.

An improved attitude estimation algorithm for suppressing magnetic vector disturbance based on extended Kalman filter

This paper proposes an improved attitude estimation algorithm based on the extended Kalman filter (EKF), and it is applied to suppress the accuracy reduction in attitude estimation caused by fusing magnetometer data under large angular motion. In the proposed attitude estimation structure, the approximate variance of the estimated horizontal northbound magnetic vector is used to dynamically adjust the participation of magnetometer data in attitude estimation, as the approximate variance increases significantly under large angular motion and fusing magnetometer data will reduce estimation accuracy. A three-axis position-velocity controlled turntable is used to conduct rocking experiments for validating the proposed attitude estimation algorithm. The results show a significant improvement in yaw angle estimation accuracy with the proposed attitude estimation algorithm and correspondingly enhance the distribution of pitch and roll angle errors.

Risk of Revision After Vertebral Augmentation for Osteoporotic Vertebral Fracture: A Narrative Review.

Osteoporotic vertebral fractures (OVFs) can hinder physical motor function, daily activities, and the quality of life in elderly patients when treated conservatively. Vertebral augmentation, which includes vertebroplasty and balloon kyphoplasty, is a commonly used procedure for OVFs. However, there have been reports of complications. Although serious complications are rare, there have been instances of adjacent vertebral fractures, cement dislocation, and insufficient pain relief due to cement failure, sometimes necessitating revision surgery. This narrative review discusses the common risks associated with vertebral augmentation for OVFs, such as cement leakage and adjacent vertebral fractures, and highlights the risk of revision surgery. The pooled incidence of revision surgery was 0.04 (0.02-0.06). The risks for revision are reported as follows: female sex, advanced age, diabetes mellitus, cerebrovascular disease, dementia, blindness or low vision, hypertension, hyperlipidemia, split type fracture, large angular motion, and large endplate deficit. Various treatment strategies exist for OVFs, but they remain a subject of controversy. Current literature underscores the lack of substantial evidence to guide treatment strategies based on the risks of vertebral augmentation. In cases with a high risk of failure, other surgeries and conservative treatments should also be considered as treatment options.

Actively Tunable Spectral Filter for Compact Hyperspectral Camera Using Angle‐Sensitive Plasmonic Structures

AbstractHyperspectral imaging provides enhanced classification and identification of veiled features for diverse biomedical applications such as label‐free cancer detection or non‐invasive vascular disease diagnostics. However, hyperspectral cameras still have technical limitations in miniaturization due to the inherently complex and bulky configurations of conventional tunable filters. Herein, a compact hyperspectral camera using an active plasmonic tunable filter (APTF) with electrothermally driven spectral modulation for feature‐augmented imaging is reported. APTF consists of angle‐sensitive plasmonic structures (APS) over an electrothermal MEMS (Microelectromechanical systems) actuator, fabricated by combining nanoimprint lithography, and MEMS fabrication ona 6‐inch wafer. APS have a complementary configuration of Au nanohole and nanodisk arrays supported on asilicon nitride membrane. APTF shows a large angular motion at operational voltages of 5–9 VDC for continuous spectral modulation between 820 and 1000 nm (45 nm/V). The compact hyperspectral camera was fully packaged with a linear polarizer, APTF and amonochromatic camera, exhibiting asize of 16 mm (ϕ) × 9.5 mm (h). Feature‐augmented images of subcutaneous vein and a fresh fruit have been successfully demonstrated after the hyperspectral reconstruction and spectral feature extraction. This functional camera provides a new compact platform for point‐of‐care or in vivo hyperspectral imaging in biomedical applications.

Binocular camera calibration based on dual update strategy weighted differential evolution particle swarm optimization

Aiming at the problem of camera calibration with multi-parameters in space target pose measurement, a novel calibration method based on dual update strategy weighted differential evolution particle swarm optimization was proposed . An adaptive judgment factor was constructed to control the usage proportion of weighted differential evolution (WDE) algorithm and particle swarm optimization (PSO) algorithm in each iteration process, which allowed the PSO or WDE algorithm to update individuals according to the probability laws. Moreover, through the information exchange mechanism, the individual obtained by the WDE operation was adopted to guide the individual evolution process operated by PSO algorithm. The proposed WDEPSO algorithm could ensure the diversity and effectiveness of the individual evolution of the population, and it was coupled with the camera nonlinear calibration model and parameters. Consequently, the proposed method could simultaneously realize the combined nonlinear and global continuous optimization, which overcomed the local convergence problem caused by the limited feature points arise from the saturated light intensity of the target space ambient. Experiments suggest that the objective function value optimized by the WDEPSO method is smaller, and the proposed method obtains the higher calibration accuracy. The standard gague measurement error obtained by the calibration parameters is less than 0.40 mm, the reconstruction attitude accuracy of the target under large angular motion is better than 0.30°, as well as the repeatability measurement results are stable.

A Novel Fault-Tolerant Navigation and Positioning Method with Stereo-Camera/Micro Electro Mechanical Systems Inertial Measurement Unit (MEMS-IMU) in Hostile Environment.

Visual odometry (VO) is a new navigation and positioning method that estimates the ego-motion of vehicles from images. However, VO with unsatisfactory performance can fail severely in hostile environment because of the less feature, fast angular motions, or illumination change. Thus, enhancing the robustness of VO in hostile environment has become a popular research topic. In this paper, a novel fault-tolerant visual-inertial odometry (VIO) navigation and positioning method framework is presented. The micro electro mechanical systems inertial measurement unit (MEMS-IMU) is used to aid the stereo-camera, for a robust pose estimation in hostile environment. In the algorithm, the MEMS-IMU pre-integration is deployed to improve the motion estimation accuracy and robustness in the cases of similar or few feature points. Besides, a dramatic change detector and an adaptive observation noise factor are introduced, tolerating and decreasing the estimation error that is caused by large angular motion or wrong matching. Experiments in hostile environment showing that the presented method can achieve better position estimation when compared with the traditional VO and VIO method.

Inertially Stabilized Platform for Airborne Remote Sensing Using Magnetic Bearings

Multiaxis gimbal configurations are commonly used in the line of sight stabilization systems for airborne remote sensing. Although these configurations are cost-effective, system performances deteriorate in the case of large payload, due to nonlinear friction and bandwidth limit of the servo loops. In this paper, a novel maglev dual-stage inertially stabilized platform is described, which encompasses a two-axis gimbal assembly as the coarse stage and a 5-DOF (degree of freedom) magnetic bearing as the fine stage. The coarse stage is mounted on the aircraft consisting of a lateral gimbal and an elevation gimbal to isolate the large angular motion of the vehicle and provide coarse pointing. The payload instrument is suspended in the elevation gimbal utilizing an electromagnetic bearing with vernier gimbaling capability to compensate the residual angular motion of the gimbal. An actual prototype of the proposed platform was designed and fabricated to illustrate the framework. The performance of the magnetic suspension system is investigated through experiments. Detailed models are established for the magnetic suspension system and the gimbal stabilizing system to develop the control strategy of the dual-stage system. Finally, the effectiveness of the design is demonstrated through simulation studies, where a 3.5 times stabilization precision improvement is prefigured compared to a reference conventional gimbal system.

Large Angle Silicon-on-Insulator Tilting Actuator with Kinematic Excitation and Simple Integrated Parallel-Plate Electrostatic Transducer

We report on the novel architecture and operational principle of an electrostatically actuated large angle tilting microelectromechanical (MEMS) actuator with kinematic excitation. The device transforms and amplifies small linear out-of-plane motion of a parallel-plate transducer into a large angular motion of a tilting element attached to the transducer with a certain offset using an elastic torsion axis. The actuator, which is distinguished by the single layer robust architecture and incorporating the simple integrated electrostatic transducer, was fabricated from a silicon-on-insulator (SOI) substrate using a common deep reactive ion etching (DRIE) based process. Detailed modeling of the device was followed by the experimental characterization of the actuator. Large tilting angles were observed in experiments, consistenty with the theoretical prediction. An optical peak to peak angle of 37.5° was measured under relatively low actuation voltages. Our theoretical and experimental results collectively demonstate the feasibility of the suggested apporach and show that simple electrostatic actuation combined with the dynamic amplification results in efficient large amplitude operation of tilting devices.

3D Motion and geometric information system of single-antenna radar based on incomplete 1D range data

A 3D motion and geometric information system of single-antenna radar is proposed, which can be supported by spotlight synthetic aperture radar (SAR) system and inverse SAR (ISAR) system involving relative 3D motion of the rigid target. In this system, applying the geometry invariance of the rigid target, the unknown 3D shape and motion of the radar target can be reconstructed from the 1D range data of some scatterers extracted from the high-resolution range image. Compared with the current 1D-to-3D algorithm, in the proposed algorithm, the requirement of the 1D range data is expanded to incomplete formation involving large angular motion of the target and hence, the quantity of the scatterers and the abundance of 3D motion are enriched. Furthermore, with the three selected affine coordinates fixed, the multi-solution problem of the reconstruction is solved and the technique of nonlinear optimization can be successfully utilized in the system. Two simulations are implemented which verify the higher robustness of the system and the better performance of the 3D reconstruction for the radar target with unknown relative motion.

Bidirectional electrothermal electromagnetic torsional microactuators for large angular motion at dc mode and high frequency resonance mode operation

This paper presents a novel design of a bidirectional torsional micromirror utilizing vertically driven electrothermal electromagnetic silicon beam actuators to generate large angular motion in both static mode and high-frequency resonance mode with low operational voltages. The microactuators are fabricated on a silicon-on-insulator (SOI) wafer using three photo masks in order to form two different thicknesses of single crystal silicon (SCS) device layer and backside cavities. When the driving bias is applied to the device in the static mode operation, four buckle beams placed alongside the torsion bars are subjected to thermal expansion and buckle in the vertical direction generating torsional displacement of the micromirror with respect to two torsion bars, the center of rotation. The direction of buckle is controlled by the Lorentz force caused by the current flowing through the silicon beams to be buckled in the magnetic field applied, enabling the bidirectional motion of the torsional micromirror. At resonance, Lorentz force itself drives the actuator instead of thermal expansion force from the buckle beams. The maximum static angular displacement of the torsional actuator is 13.42° (26.84°, optical angle) under a driving dc voltage of 7.5 V. In the resonance mode operation, the measured angular displacement is 8.22° (16.44°, optical angle) at 10.64 kHz under sinusoidal driving voltages of 0 to 4.4 V.

Thermally driven torsional micromirrors using pre-bent torsion bar for large static angular displacement

This paper presents one- and two-degree-of-freedom (DOF) torsional micromirrors driven by in-plane thermal actuators for large static angular motion at low operational voltage. The micromirror actuator is fabricated on a silicon-on-insulator (SOI) wafer using three photomasks to form two different thicknesses on the device layer and to define backside holes. The thin layer beam connected to the thick layer torsion bar is pulled by the in-plane thermal actuator, twisting the torsion bar and therefore inducing angular motion of the mirror. The proposed pre-bent torsion bar design enhances the angular motion significantly and suppresses unnecessary translational motion. The fabricated 1-DOF micromirror is driven to the maximum optical scan angle of 6.5° at 13 V dc. For a 2-DOF micromirror, optical scan angles of 5.4° and 5.2° are achieved in each direction of rotation at 11 V dc.

Molecular structures, conformations, force fields and large amplitude motion of cis-3-chloro-2-propen-1-ol as studied by quantum chemical calculations and gas electron diffraction augmented with quantum chemical calculations on 2-propen-1-ol

B3LYP and MP2(F) quantum chemical calculations have been performed for 2-propen-1-ol using the cc-pVTZ basis set. Five stable conformations are detected and related to the two conformations observed experimentally. The calculated normal frequencies are scaled for two conformers and their assignments are compared. Similar quantum chemical calculations predict three stable conformers for cis-3-chloro-2-propen-1-ol. Quantum chemical force field calculations reveal large amplitude motions about the C C bond for all conformers. Least-squares refinements of the gas electron diffraction data using a mixture of two static conformers verify the presence of these two conformers. The agreement with the experimental data for this type of refinements is not satisfactory which indicates that large amplitude models should be used. Describing the torsions about the C C bond as frame work vibrations in harmonic large amplitude angular motion of Gaussian distributions for two conformations improved the agreement with the experimental data considerably. The root-mean-square angular amplitude of the torsions for the two conformations refined to 28.6(12)° and 21.4(46)°, with dihedral angles C C C O equal to −125.5(17)° and 180(fixed)°, respectively. Some r a distances (Å) and r α angles (degrees) obtained are: r(C C) = 1.5044(20), r(C C) = 1.3435(16), r(C O) = 1.4299(14) and r(C Cl) = 1.7366(19), <(C C C) = 125.60(12), <(C C O) = 111.0(2), <(C C Cl) = 123.61(10). Parenthesized values are [ σ 2 lsq + (0.001 × r) 2] 1/2 for bond distances, where σ lsq is the least-squares standard deviation. For the angles σ lsq is given. There is good agreement between the experimental results and the quantum chemical calculations.

Large angle SOI tilting actuator with integrated motion transformer and amplifier

In this work we report on the novel architecture and operational principle of a tilting actuator with integrated motion transformer and amplifier fabricated using single structural layer of silicon on insulator (SOI) wafer and demonstrate the functionality of the device both theoretically and experimentally. The device incorporates an integrated compliant motion amplifier realized as an eccentric elastic torsion link that transforms small out-of-plane motion of the parallel-plate electrostatic transducer into large amplitude angular motion of the tilting element. A feasibility study and evaluation of design parameters were performed using a lumped model of the device and coupled three-dimensional simulation. Experimental and model results indicate that this generic architecture, combining simple fabrication process with robustness of SOI-based devices, is efficient for static and resonant operation of various tilting microdevices.

A linear/angular interferometer capable of measuring large angular motion

A novel linear and angular interferometric heterodyne system, capable of measuring large angular motion, is proposed. The interferometric system has a high linear-displacement resolution of 1.24 nm while the angular-displacement resolution can reach 0.0025 arcsec. By combining the advantages of the interferometer with a retroreflector and the interferometer with a plane-mirror reflector, the proposed interferometric measurement system allows a desirable transverse motion and rotational motion along any of the three orthogonal directions. Using a retroreflector with a diameter of 38.1 mm, the translational range in the transverse directions is no less than 20 mm × 10 mm while the angular range along any axis is no less than 10°. The angular readings can be used to compensate the linear outputs in real time when the Abbe error occurs. This ability has been demonstrated by the experiments.

Passive dynamic controllers for nonlinear mechanical systems

A methodology for model-independent controller design for controlling the large angular motion of multibody dynamic systems is outlined. The controlled system may consist of rigid and flexible components that undergo large rigid body motion and small elastic deformations. Control forces/torques are applied to drive the system and at the same time suppress the vibrations due to flexibility of the components. The proposed controller consists of passive second-order systems that may be designed with little knowledge of the system parameters, even if the controlled system is nonlinear. Under rather general assumptions, the passive design assures that the closed-loop system has guaranteed stability properties. Unlike positive real controller design, stabilization can be accomplished without direct velocity feedback. In addition, the second-order passive design allows dynamic feedback controllers with considerable freedom to tune for desired system response and to avoid actuator saturation. After developing the basic mathematical formulation of the design methodology, simulation results are presented to illustrate the proposed approach applied to a flexible six-degree-of-freedom manipulator.

Adaptive suppression of biodynamic interference in helmet-mounted displays and head teleoperation

This paper addresses errors caused by vibration or turbulence in airborne helmet displays and teleoperation. It is shown by analysis and computer simulations that a modified version of the least-mean-squares adaptive noise suppression algorithm facilitates the separation of the large voluntary head movements from the vibrationinduced small nonvoluntary head motion. Thus, the effects of the biodynamic interference can be essentially removed. The results also indicate that errors in head-tracking teleoperated devices can essentially be suppressed. Extensive man-in-the-loop laboratory simulations that validate the method are described. YSTEM teleoperation by pilot head motion and presentation of computer-gene rated symbols and flight information in helmet-mounte d displays is emerging as a promising technology in modern avionic systems. Head teleoperation is potentially an effective method for instinctive and rapid aiming of radar antennas, missile seeker heads, or laser designators. In addition, it relieves the hands of the pilot for other vital manual tasks in increasingly complex airborne environments. Helmet-mounted displays (HMD) can, in principle, be the ultimate solution in merging computer-generated displays with the outside scene, thus embracing the entire field of view available to the pilot. Therefore, the HMD potentially relieves the pilot from the troublesome need to share his attention between the all-aspect outside scene and a restrictive cockpitmounted panel or head-up display. However, a potential shortcoming of head teleoperation and HMDs is their vulnerability to biodynamic interference resulting from vibration, atmospheric turbulence, or self-induced vehicle motion. These interferences can cause substantial random aiming errors and apparent display blurring that may seriously impair pilot performance. Two kinds of biodynamic interference exist, namely, 1) additive interferences due to nonvoluntary limb motions caused by, and correlated with, vibration,1'2 and 2) nonadditive interferences resulting from the disturbances in the central nervous system caused by the body and head vibrations, uncorrelated with them, but monotonically increasing with their intensity.3'4 Head vibration causes relative angular motion of the HMD with respect to the line of sight of the eye, which is inertially stabilized by the vestibular system. Consequently, as a result of the apparent display shift, image blurring occurs, resulting in substantial degradation of reading speed and probability of correct character recognition.5'6 This neuromotor stabilization, known as the vestibulo-ocular reflex (VOR), is effective in the frequency range of 2-10 Hz.7 Wells and Griffin6'8 conducted experiments to cancel this blurring by shifting the display in the opposite direction with an amplitude equal to the measured head motion which was determined by an approximate double integration of head angular acceleration. They succeeded in demonstrating the effectiveness of the concept, but the imperfection of the integration caused substantial transients in the display position in the presence of large angular head motion.

Dynamic Interactions of Link Elasticity and Clearance Connections in Planar Mechanical Systems

This study is an investigation of the effects of clearances and link flexibility on the stresses in joints of high speed mechanisms. A general large angular motion mathematical model is developed using an efficient mathematical formulation based on displacement functions. Numerical solution of the model reveals that over a wide operating range, link flexibility consistently reduces joint bearing stresses. The possibility of developing simple design procedures for quantitative prediction of joint bearing stresses is discussed.