Continuous Yaw Research Articles

The impact of yaw attitude models on precise orbit determination: The latest blocks of GNSS satellites and their yaw models

The GNSS satellites do not maintain nominal attitude when the solar elevation angle falls into a predetermined threshold, resulting in a period of abnormal yaw attitude which will degrade the accuracies of the orbit and clock products. This paper investigates in depth the distribution rules of GPS/GLONASS/Galileo/BDS satellites’ eclipse periods and analyses in detail the correction characteristics of each model in eclipse periods. The models used are GPS IIF and GLONASS-M for GPS IIIA and GLONASS-K modernized satellites, respectively, and the continuous yaw models for BDS-3 and Galileo satellites. Finally, an experimental analysis of the improvement of each block of satellite eclipse periods’ orbital accuracy is conducted. The results indicate that most satellites’ orbital accuracy is improved by 35.0 % to 50.0 % following yaw correction, but only by 29.0 % and 18.0–35.2 % for GPS IIIA satellites and BDS-3 satellites.

Yaw Rate Prediction and Tilting Feedforward Synchronous Control of Narrow Tilting Vehicle Based on RNN

The synchronous control of yaw motion and tilting motion is an important problem related to the lateral stability and energy consumption of narrow tilting vehicles. This paper proposes a method for the tilting control of narrow tilting vehicles: tilting feedforward synchronous control. This method utilizes a proposed novel prediction method for yaw rate based on a recurrent neural network. Meanwhile, considering that classical recurrent neural networks can only predict yaw rate at a given time, and that yaw rate prediction generally needs to analyze a large amount of computer vision data, in this paper, the yaw rate is represented by a polynomial operation to predict the continuous yaw rate in the time domain; this prediction is realized using only the driving data of the vehicle itself and does not include the data generated by computer vision. A prototype experiment is provided in this work to prove the advantages and feasibility of the proposed tilting feedforward synchronous control method for narrow tilting vehicles. The proposed tilting feedforward synchronous control method can ensure the synchronous response of the yaw motion and the tilting motion of narrow tilting vehicles.

Adaptive nonlinear control for 4‐DOF ship‐mounted rotary cranes

SummaryThe swing characteristics of the load of ship‐mounted rotary cranes is very complicated, due to the rotation of the boom. Especially, when the crane is operating at sea, it is subject to some disturbances caused by waves, which makes the precise control of the load more difficult. We study the control problem of a four degree of freedom ship‐mounted rotary crane with continuous yaw and roll disturbances in this paper. Specifically, we propose an adaptive controller and the adaptive laws can be updated in real‐time depending on the state of the system and the disturbance. This method does not require linearization of the crane dynamic equations, therefore, the crane can get great control performance even if it is far from the equilibrium point. Comparative experiments demonstrate that the proposed method has excellent anti‐disturbance ability.

Effects of display lag on vection and presence in the Oculus Rift HMD

Head-mounted display (HMD)-based virtual reality (VR) is ideally suited for presence and generating compelling visual experiences of self-motion, but users can suffer from side effects associated with head-to-display lag. We used the Oculus Rift HMD (consumer release – CV1) to simulate forward self-motion in depth. Observers made continuous yaw head movements at approximately 0.5 Hz or 1.0 Hz while viewing these self-motion simulations. We examined the perceptual effects of increasing the display lag, by adding lag to the baseline lag of the system (estimated to be approximately 5.3 ms or 0.5 frames per second). We found that increasing the head-to-display lag up to 212 ms reduced the presence and the strength of vection. In addition, faster (1.0 Hz) head oscillations were found to generate weaker presence and vection in the virtual environment than the slower (0.5 Hz) head oscillations. We also found that a positive correlation between vection and presence (found previously) persists across a wide range of head-to-display lags, and, increasing lag from a very low baseline level still impaired both experiences. Both vection and presence in virtual environments can therefore be impaired by either increasing head-display lag or making more rapid angular head movements.

Continuous rotational motion in birefringent particles using two near-orthogonally polarized optical tweezers beams at different wavelengths with low ellipticity

Continuous yaw (in-plane) rotation of an optically trapped birefringent particle is conventionally achieved by illuminating with light of high ellipticity. This ellipticity has to be high enough to make the tilt of the washboard potential bypass the confining effect of the corrugation. Here by using a novel technique, we generate continuous rotations of a 3 µm sized spherical birefringent particle with ellipticity lower than that permissible with a single optical tweezers beam. We use two lasers, near-orthogonally polarized, with similar intensities at wavelengths of 1064 and 975 nm to obtain continuous rotations, just by making one of the beams elliptically polarized, but well lower than that permissible by the washboard potential. The maximum rotation frequency we achieve with the present configuration is 5 Hz which can be increased by simultaneously increasing the two laser intensities.

A brain-inspired localization system for the UAV based on navigation cells

Purpose To solve problems of low intelligence and poor robustness of traditional navigation systems, the purpose of this paper is to propose a brain-inspired localization method of the unmanned aerial vehicle (UAV). Design/methodology/approach First, the yaw angle of the UAV is obtained by modeling head direction cells with one-dimension continuous attractor neural network (1 D-CANN) and then inputs into 3D grid cells. After that, the motion information of the UAV is encoded as the firing of 3 D grid cells using 3 D-CANN. Finally, the current position of the UAV can be decoded from the neuron firing through the period-adic method. Findings Simulation results suggest that continuous yaw and position information can be generated from the conjunctive model of head direction cells and grid cells. Originality/value The proposed period-adic cell decoding method can provide a UAV with the 3 D position, which is more intelligent and robust than traditional navigation methods.

Precise orbit determination of BDS-3 satellites using B1C and B2a dual-frequency measurements

Compared to the BeiDou regional navigation satellite system (BDS-2), the BeiDou global navigation satellite system (BDS-3) includes the newly designed B1C and B2a signals, which are compatible with the L1 and L5 frequencies of the global positioning system (GPS). Considering that the precise orbit determination (POD) of the BDS-3 constellation is currently restricted to the legacy B1I and B3I signals, we reported the POD performance of BDS-3 satellites using B1C and B2a dual-frequency measurements. Nine globally distributed Multi-GNSS Experiment (MGEX) stations were selected to determine the orbits of BDS-3 satellites during the period of July 2019. The results show that B1C/B2a-based POD enables an average three-dimensional root-mean-square error (3D RMS) of 24.2 cm, and the precision is better than 6 cm in the radial component in a comparison of two-day overlapping arcs. Satellite laser ranging (SLR) validation achieves an overall precision of 6.8 cm in RMS differences. Compared to the B1I/B3I-based POD results, the quality of B1C/B2a-based orbits is improved by approximately 9% across the whole BDS-3 constellation, indicating that the new B1C/B2a signals can be employed for the superior POD performance of BDS-3 satellites. Moreover, we investigated the behavior of the solar radiation pressure (SRP), which is generally considered one of the primary error sources in BDS-3 medium earth orbit (MEO) dynamic orbit determination. The ECOM7 SRP model has a better POD performance in continuous yaw steering (CYS) mode than the ECOM5 and ECOM9 SRP models. The results also show that there is no degradation in the orbit precision of BDS-3 MEO satellites when the elevation angle of the sun above the orbital plane (β angle) varies within the range of − 4° to + 4°.

Dual-steering mode based on direct yaw moment control for multi-wheel hub motor driven vehicles: Theoretical design and experimental assessment

One of the main challenges for multi-wheel hub motor driven vehicles is the coordination of individual drivetrains to improve mobility and stability in the steering process. This paper proposes a dual-steering mode based on direct yaw moment control for enhancing vehicle steering ability in complex environments. The control system is designed as a hierarchical structure, with a yaw moment decision layer and a driving force distribution layer. In the higher-level layer, the objective optimization function is constructed to obtain the slip steering ratio, which represents the degree of vehicle slip steering in the dual-steering mode. A yaw moment controller using active disturbance rejection control theory is designed for continuous yaw rate control. When the actual yaw rate of the vehicle deviates from the reference yaw rate obtained by the vehicle reference model and the slip steering ratio, the yaw moment controller is actuated to determine the yaw moment demand for vehicle steering. In the lower-level layer, there is a torque distribution controller based on distribution rules, which meets the requirement of yaw moment demand without affecting the total longitudinal driving force of the vehicle. For verifying the validity and feasibility of the dual-steering mode, simulations were conducted on the hardware-in-loop real-time simulation platform. Additionally, corresponding real vehicle tests were carried out on an eight-wheel prototype vehicle. Test results were generally consistent with the simulation results, thereby demonstrating that the proposed dual-steering mode reduces steering radius and enhances the steering performance of the vehicle.

Reactive Postural Responses to Continuous Yaw Perturbations in Healthy Humans: The Effect of Aging.

Maintaining balance stability while turning in a quasi-static stance and/or in dynamic motion requires proper recovery mechanisms to manage sudden center-of-mass displacement. Furthermore, falls during turning are among the main concerns of community-dwelling elderly population. This study investigates the effect of aging on reactive postural responses to continuous yaw perturbations on a cohort of 10 young adults (mean age 28 ± 3 years old) and 10 older adults (mean age 61 ± 4 years old). Subjects underwent external continuous yaw perturbations provided by the RotoBit1D platform. Different conditions of visual feedback (eyes opened and eyes closed) and perturbation intensity, i.e., sinusoidal rotations on the horizontal plane at different frequencies (0.2 Hz and 0.3 Hz), were applied. Kinematics of axial body segments was gathered using three inertial measurement units. In order to measure reactive postural responses, we measured body-absolute and joint absolute rotations, center-of-mass displacement, body sway, and inter-joint coordination. Older adults showed significant reduction in horizontal rotations of body segments and joints, as well as in center-of-mass displacement. Furthermore, older adults manifested a greater variability in reactive postural responses than younger adults. The abnormal reactive postural responses observed in older adults might contribute to the well-known age-related difficulty in dealing with balance control during turning.

Visual Fixation and Continuous Head Rotations Have Minimal Effect on Set-Point Adaptation to Magnetic Vestibular Stimulation

Background: Strong static magnetic fields such as those in an MRI machine can induce sensations of self-motion and nystagmus. The proposed mechanism is a Lorentz force resulting from the interaction between strong static magnetic fields and ionic currents in the inner ear endolymph that causes displacement of the semicircular canal cupulae. Nystagmus persists throughout an individual's exposure to the magnetic field, though its slow-phase velocity partially declines due to adaptation. After leaving the magnetic field an after effect occurs in which the nystagmus and sensations of rotation reverse direction, reflecting the adaptation that occurred while inside the MRI. However, the effects of visual fixation and of head shaking on this early type of vestibular adaptation are unknown.Methods: Three-dimensional infrared video-oculography was performed in six individuals just before, during (5, 20, or 60 min) and after (4, 15, or 20 min) lying supine inside a 7T MRI scanner. Trials began by entering the magnetic field in darkness followed 60 s later, either by light with visual fixation and head still, or by continuous yaw head rotations (2 Hz) in either darkness or light with visual fixation. Subjects were always placed in darkness 10 or 30 s before exiting the bore. In control conditions subjects remained in the dark with the head still for the entire duration.Results: In darkness with head still all subjects developed horizontal nystagmus inside the magnetic field, with slow-phase velocity partially decreasing over time. An after effect followed on exiting the magnet, with nystagmus in the opposite direction. Nystagmus was suppressed during visual fixation; however, after resuming darkness just before exiting the magnet, nystagmus returned with velocity close to the control condition and with a comparable after effect. Similar after effects occurred with continuous yaw head rotations while in the scanner whether in darkness or light.Conclusions: Visual fixation and sustained head shaking either in the dark or with fixation inside a strong static magnetic field have minimal impact on the short-term mechanisms that attempt to null unwanted spontaneous nystagmus when the head is still, so called VOR set-point adaptation. This contrasts with the critical influence of vision and slippage of images on the retina on the dynamic (gain and direction) components of VOR adaptation.

Direct yaw moment control actuated through electric drivetrains and friction brakes: Theoretical design and experimental assessment

A significant challenge in electric vehicles with multiple motors is how to control the individual drivetrains in order to achieve measurable benefits in terms of vehicle cornering response, compared to conventional stability control systems actuating the friction brakes. This paper presents a direct yaw moment controller based on the combination of feedforward and feedback contributions for continuous yaw rate control. When the estimated sideslip exceeds a pre-defined threshold, a sideslip-based yaw moment contribution is activated. All yaw moment contributions are entirely tunable through model-based approaches, for reduced vehicle testing time. The purpose of the controller is to continuously modify the vehicle understeer characteristic in quasi-static conditions and increase yaw and sideslip damping during transients. Skid-pad, step-steer and sweep steer tests are carried out with a front-wheel-drive fully electric vehicle demonstrator with two independent drivetrains. The experimental test results of the electric motor-based actuation of the direct yaw moment controller are compared with those deriving from the friction brake-based actuation of the same algorithm, which is a major contribution of this paper. The novel results show that continuous direct yaw moment control allows significant “on-demand” changes of the vehicle response in cornering conditions and to enhance active vehicle safety during extreme driving maneuvers.

Orienting eye movements and nystagmus produced by translation while rotating (TWR)

Sinusoidal translation while rotating at constant angular velocity about a vertical axis (translation while rotating, TWR) produces centripetal and translational accelerations along the direction of translation and an orthogonal Coriolis acceleration due to the translation in the rotating frame. Thus, a Coriolis acceleration is produced along the bitemporal axis when oscillating along the naso-occipital axis, and along the naso-occipital axis when oscillating along the bitemporal axis. Together, these components generate an elliptically rotating acceleration vector that revolves around the head in the direction of rotation at the frequency of oscillation. Here we studied the orienting and compensatory responses of rabbits during TWR. Combinations of centripetal and translational accelerations were held constant at 0.5 g, and oscillation frequencies were varied from 0.01-0.33 Hz. The amplitude of the Coriolis acceleration increased with the frequency of translation. Naso-occipital translation caused vergence and pitch at all frequencies and roll at higher frequencies, and bitemporal translation produced roll at all frequencies and vergence and pitch at higher frequencies. The sensitivity of each ocular orienting component to linear acceleration was comparable across the different oscillation frequencies. TWR also induced continuous yaw nystagmus with slow phase velocity in the direction of rotation of the acceleration vector. Thresholds for appearance of nystagmus were 0.05 Hz, corresponding to a Coriolis acceleration of 0.06 g. Mean slow phase velocity for a rotating linear acceleration vector produced by 0.5 g along the translation axis and 0.34 g of Coriolis acceleration along the orthogonal axis were approximately 9 degrees /s. Eye velocities during TWR were similar to those generated by off-vertical axis rotation (OVAR), but were opposite in direction with regard to head rotation, following the direction of the rotating acceleration vector in both paradigms. Both are produced by activation of velocity storage in the vestibular system. One important difference between TWR and OVAR is that the head is always upright with regard to gravity during TWR. We speculate that the brain may use these low amplitude rotating linear accelerations to generate eye velocities that help to orient gaze when making turns during normal locomotion.

Design and Operational Aspects of All-Electric Thruster Control Systems for Geostationary Satellites

Results of an all-electric thruster control concept study for geostationary satellites are presented. Early work on this type of system emphasized feasibility rather than design and operational aspects. Conservative estimates of 1975 technology were used as guides in selecting possible thruster combinations and component sites to satisfy basic mission requirements and constraints. The present work goes beyond 1975 technology to that of the late 1970's and considers innovations in hardware and operational techniques which may permit significant reductions in control system weight and components. Finally, recommendations regarding thruster development and satellite design compatible with optimum all-electric control systems are offered. It is concluded that, for systems without momentum wheels or gyros, three orthogonal components of control torque and continuous yaw sensing are required to ensure a stable automatic control system. Furthermore, alternating use of different inclination control thrusters will be highly desirable if these thrusters are canted away from the orbit normal direction due to plume impingement problems.