Position Signal Research Articles

Impact dynamics of a free-falling reference test mass in space

Outer space may constitute a privileged environment for experiments involving impacts. In fact, disturbing phenomena like drag or weight forces are negligible and a nearly pure free-fall state may be achieved for the impacting bodies. The case analysed in this manuscript comes from the initialization of the science phase of a space mission (LISA Pathfinder, flown in 2015), in which an extended metallic body – starting from a caged configuration – was released to free-fall inside a spacecraft by a dedicated mechanism, the grabbing positioning and release mechanism (GPRM). During the release phase, the test mass (TM) experienced some impacts with the GPRM end effector, before being electrostatically controlled to its nominal position, i.e. still in the centre of the hosting electrode housing. The impact dynamics of the TM therefore resulted critical, since it helped reduce its kinetic energy with respect to the spacecraft. In this paper, the TM position and attitude telemetry signals are analysed, and the impacts coefficient of restitution is calculated, providing reference values for similar space instruments, where a free-falling reference body is used (for instance, for geodesy and/or spacecraft navigation).

Five-axis path smoothing based on sliding convolution windows for CNC machining

Tiny linear toolpaths widely used in five-axis CNC machine tools only meet G0 continuity at the junctions of adjacent paths, the tangential and curvature discontinuities at the corners result in decelerations and fluctuations of machine tools. Although the corner smoothing for the three-axis tool path is relatively mature, the five-axis tool pose path smoothing is still difficult to plan due to the nonlinear motions of the rotational axes and the parameter synchronization between the tool center point (TCP) path and the tool orientation vector (TOV) path. Therefore, this paper aims to extend the smoothing scopes of previously presented mixed tiny path smoothing method based on sliding convolution windows for three-axis CNC machining (Zhang et al. in Journal of Manufacturing Process 102:685–699, [19]). Compared with the previous work, this paper converts the five-axis tool pose path into the tool position signal and tool orientation signal, and the interpolation points of the two path signals in the convolution window are directly processed on the basis of the synchronous motions of all axes. The original parameter synchronization relationship between the TCP path and the TOV path is still maintained. Besides, the smoothing error prediction model is constructed. The proposed five-axis path smoothing method has been integrated into a self-developed open-architecture CNC system and its effectiveness for the five-axis path optimization is validated via the simulation and experiment.

Founding the Wnt gene family: How wingless was found to be a positional signal and oncogene homolog.

The Wnt family of developmental regulators were named after the Drosophila segmentation gene wingless and the murine proto-oncogene int-1. Homology between these two genes connected oncogenesis to cell-cell signals in development. I review how wingless was initially characterized, and cloned, as part of the quest to identify developmental cell-to-cell signals, based on predictions of the Positional Information Model, and on the properties of homeotic and segmentation gene mutants. The requirements and cell-nonautonomy of wingless in patterning multiple embryonic and adult structures solidified its status as a candidate signaling molecule. The physical location of wingless mutations and transcription unit defined the gene and its developmental transcription pattern. When the Drosophila homolog of int-1 was then isolated, and predicted to encode a secreted proto-oncogene homolog, it's identity to the wingless gene confirmed that a developmental cell-cell signal had been identified and connected cancer to development.

Prescribed performance tracking control of multi-link robotic manipulator with uncertainties

<p style='text-indent:20px;'>This paper addresses the trajectory tracking problem with prescribed performance for a multi-link robotic manipulator subject to unknown dynamics and external disturbances. A predefined performance function is adopted to describe tracking errors' desired transient and steady-state performance. Then, the output error dynamics with performance constraints are transformed into an equivalent unconstrained system, whose stabilization is sufficient to guarantee the prescribed performance of the original system. An extended state observer with a friction model is designed to approximate unknown dynamics together with the unmeasurable velocity state, which extends the applicability of the proposed controller to manipulators with only position signals available. The friction model is lumped into it to improve the precision and velocity of estimation. It is proved via Lyapunov analysis that the proposed controller can theoretically guarantee the satisfaction of prescribed performance in the presence of uncertainties. The simulation results verify the reliability and effectiveness of the proposed method.</p>

Position Signal and Non-conduction Phase Current Based Fault Diagnosis Method of Position Sensor for Doubly Salient Electromagnetic Motor

Position Signal and Non-conduction Phase Current Based Fault Diagnosis Method of Position Sensor for Doubly Salient Electromagnetic Motor

Leveraging Multi-LEO Satellite Signals for Opportunistic Positioning

Leveraging Multi-LEO Satellite Signals for Opportunistic Positioning

Vision-Based UAV Self-Positioning in Low-Altitude Urban Environments.

Unmanned Aerial Vehicles (UAVs) rely on satellite systems for stable positioning. However, due to limited satellite coverage or communication disruptions, UAVs may lose signals for positioning. In such situations, vision-based techniques can serve as an alternative, ensuring the self-positioning capability of UAVs. However, most of the existing datasets are developed for the geo-localization task of the objects captured by UAVs, rather than UAV self-positioning. Furthermore, the existing UAV datasets apply discrete sampling to synthetic data, such as Google Maps, neglecting the crucial aspects of dense sampling and the uncertainties commonly experienced in practical scenarios. To address these issues, this paper presents a new dataset, DenseUAV, that is the first publicly available dataset tailored for the UAV self-positioning task. DenseUAV adopts dense sampling on UAV images obtained in low-altitude urban areas. In total, over 27K UAV- and satellite-view images of 14 university campuses are collected and annotated. In terms of methodology, we first verify the superiority of Transformers over CNNs for the proposed task. Then we incorporate metric learning into representation learning to enhance the model's discriminative capacity and to reduce the modality discrepancy. Besides, to facilitate joint learning from both the satellite and UAV views, we introduce a mutually supervised learning approach. Last, we enhance the Recall@K metric and introduce a new measurement, SDM@K, to evaluate both the retrieval and localization performance for the proposed task. As a result, the proposed baseline method achieves a remarkable Recall@1 score of 83.01% and an SDM@1 score of 86.50% on DenseUAV. The dataset and code have been made publicly available on https://github.com/Dmmm1997/DenseUAV.

Five-Meter Nonmagnetic Telescopic Tubular Mast: Design, Test, and On-Orbit Application

Space deployable masts, as one of the most widely used branches of space deployable structures, can provide driving, positioning, and transmission functions for spacecraft in orbit, which are irreplaceable in complex space activities. The nonmagnetic telescopic tubular mast (NMTTM) is designed and manufactured by the Shenyang Institute of Automation, Chinese Academy of Sciences, aboard the SATech-01 satellite to keep the magnetic probe assembly away from magnetic interference and realize global magnetic field measurement. The NMTTM can withstand complicated vibration and shock during rocket launching in the retracted state of 0.95 m, while it can be stably released and deployed to 5.28 m in orbit. NMTTM was successfully launched into Sun-synchronous orbit on 27 July 2022, fully deployed, and generated the positioning signal after a duration of 19 min and 16 s for the deployment process on 7 November. This paper focuses on the whole process of NMTTM from mission requirements to structure design and manufacture, through to releasing, deployment, and locking technology, environmental simulation tests, up to on-orbit deployment verification, which provides valuable experience for the subsequent development and application of large-scale space deployable masts.

Analog Position Estimation for Enhanced Stability and Fidelity of Haptic Systems.

In this paper, we propose three methods to compute low-latency analog position where two of them fuse encoder and rate gyro signals. While one method is based on gyro with bias correction using encoder information, the other one is encoder-referenced combined with a resettable integrator to minimize the staircase form of encoder signals. Experiments on a one degree-of-freedom haptic simulation system have shown that a low-latency analog position with an accuracy over 98% compared to the sampled encoder signal can be obtained. The analog position signals are then utilized to produce analog viscoelastic virtual environments to assess and benchmark the proposed methods through uncoupled stability and perceived fidelity tests. The results have shown that a virtual stiffness range larger than 400% can be obtained with enhanced fidelity compared to common digital implementations.

Sensorless Speed Control of PMSM in Low-Speed by High Frequency Pulsating Injection with Double Modulation Error Compensation

A novel improvement scheme for the High Frequency Pulsating Injection-Sinusoidal (HFPI-S) method that considers the error function is proposed and implemented for PMSM sensorless control. The limitations in extracting the error function and dealing with signal noise at low-speed could appear the estimation errors in rotor position within the HFPI-S system. In this study, a new model for the proposed method, including the addition of dual modulation as error compensation in the process of extracting rotor position and enhancing the observer for conventional rotor position signals was focused. The results of this study showed that the extraction of the error function that is expanded could obtain more accurate results. Therefore, the addition of dual modulation and the observer enhancement could be effectively applied to maintain the accuracy of rotor position estimation even under low-speed and loaded conditions.

Epigenetic landscape of intestinal cell line HT29 cocultured with Lacticaseibacillus.

Aim: To investigate the changes in epigenetic landscape of HT29 cells upon coculture with the Lacticaseibacillus.Materials & methods: Histone and m6A mRNA modifications were examined by biochemical and NGS-based methods including western blotting, colorimetric assays, ChIP-Seq and direct mRNA sequencing. LC-MS was performed to identify Lacticaseibacillus secretome.Results: In cocultured HT29 cells global enrichment of H3K9ac and H3K4me3 and depletion of H3K9me3 mark was observed; mean genic positional signals showed depletion of H3K9ac and H3K4me3 at the TSS but enrichment in the upstream region; m6A methylation was altered in mRNAs corresponding to specific gene pathways; Lacticaseibacillus HU protein interacts with histone H3.Conclusion: Lacticaseibacillus can epigenetically alter specific genetic pathways in human intestinal cells.

Tool Dynamics-induced Surface Topography Error in Fast Tool Servo-Based Diamond Turning of Micro Dome Arrays

Micro dome arrays are applied as moulds to injection/press moulding to produce micro lens arrays. Fast tool servo (FTS) based diamond turning is a promising technique for manufacturing such micro dome arrays with high accuracy and machining efficiency. In this study, cutting of micro dome array (MDA) on copper with FTS was performed to evaluate the dynamics behaviour of the tool servo and its effects on surface topography. Results show that local surface speed dramatically affects the servo dynamics behaviour. When the local surface speed is higher than a critical value, overcutting and wavy patterns could be formed on the cut-in area of the domes and exit area, which is caused by the servo response and its limitation. By capturing and analysing the position signal and correlating it with the surface topography of the generated dome surface and considering its limitations, an effective strategy for optimizing micro dome array machining parameters was proposed. MDA cutting tests with optimized cutting conditions achieved a significantly improved form accuracy. This study will guide the optimal use of FTS systems in machining micro structured surfaces.

Integration of Laser Communication and Aiming Based on High Sensitivity Beam Position Signal Extraction (Invited)

Integration of Laser Communication and Aiming Based on High Sensitivity Beam Position Signal Extraction (Invited)

Research on control strategy of pneumatic soft bionic robot based on improved CPG.

To achieve the accuracy and anti-interference of the motion control of the soft robot more effectively, the motion control strategy of the pneumatic soft bionic robot based on the improved Central Pattern Generator (CPG) is proposed. According to the structure and motion characteristics of the robot, a two-layer neural network topology model for the robot is constructed by coupling 22 Hopfield neuron nonlinear oscillators. Then, based on the Adaptive Neuro-Fuzzy Inference System (ANFIS), the membership functions are offline learned and trained to construct the CPG-ANFIS-PID motion control strategy for the robot. Through simulation research on the impact of CPG-ANFIS-PID input parameters on the swimming performance of the robot, it is verified that the control strategy can quickly respond to input parameter changes between different swimming modes, and stably output smooth and continuous dynamic position signals, which has certain advantages. Then, the motion performance of the robot prototype is analyzed experimentally and compared with the simulation results. The results show that the CPG-ANFIS-PID motion control strategy can output coupled waveform signals stably, and control the executing mechanisms of the pneumatic soft bionic robot to achieve biological rhythms motion propulsion waveforms, confirming that the control strategy has accuracy and anti-interference characteristics, and enable the robot have certain maneuverability, flexibility, and environmental adaptability. The significance of this work lies in establishing a CPG-ANFIS-PID control strategy applicable to pneumatic soft bionic robot and proposing a rhythmic motion control method applicable to pneumatic soft bionic robot.

A muon high-resolution pseudorange measurement method: Application to muon navigation in confined spaces

Confined spaces such as polar regions, deep earth and deep ocean are crucial navigation scenarios where traditional navigation techniques have difficulty in obtaining external signals for positioning. The cosmic ray muons, which carry the spatial and energetic information, are easy to penetrate these confined spaces. Therefore, the unique muon characteristic provides a new perspective to estimate detector position, which can be considered using in confined spaces navigation. In this paper, a well-developed theory of muon navigation is established by combining a muon pseudorange measurement method. Moreover, an Equivalent Velocity Calculation Model (EVCM) and a Muon Sequence Matching Technology (MSMT) are proposed. The first model corrects flight pseudorange error caused by the relativistic energy loss and the second technology compensates the random error in pseudorange measurement. Further, a series of simulations are performed to analyze the muon events number which can be received by detector in different scenarios with the variations of zenith angle, detector area, varied detector plates gap, and muon flight distance. Meanwhile, the simulation results demonstrate that the muon navigation update rate every 10 minutes can reach 5.989 in confined spaces at 100 m, and further pseudorange error analysis indicates that the meter-level positioning accuracy can be acquired. Finally, we construct a muon coincidence measurement scheme and verify that the laws of the muon positioning system for high-energy muons are consistent with the simulation results.

Controlling the Position of the DC Motor using PID, and the Sliding Mode Algorithm

With the development of information technology and smart technology to meet the Industrial Revolution 4.0, and to meet life requirements. Automatic control devices require high-precision control quality. Therefore, in this paper, we focus on researching the Sliding mode controller to improve the control quality compared to PID controller. First, the sliding mode control is designed using the Lyapunov algorithm. Next, the process of simulating the position signal of a DC motor with a PID controller is compared with a sliding mode control to prove the effectiveness of the proposed controller.

Observation and Analysis of VLF Nocturnal Multimode Interference Phenomenon based on Waveguide Mode Theory

Very low frequency (VLF) signals are propagated between the ground-ionosphere. Multimode interference will cause the phase to show oscillatory changes with distance while propagating at night, leading to abnormalities in the received VLF signal. This study uses the VLF signal received in Qingdao City, Shandong Province, from the Russian Alpha navigation system to explore the multimode interference problem of VLF signal propagation. The characteristics of the effect of multimode interference phenomena on the phase are analyzed according to the variation of the phase of the VLF signal. However, the phase of VLF signals will also be affected by the X-ray and energetic particles that are released during the eruption of solar flares, therefore the two phenomena are studied in this work. It is concluded that the X-ray will not affect the phase of VLF signals at night, but the energetic particles will affect the phase change, and the influence of energetic particles should be excluded in the study of multimode interference phenomena. Using VLF signals for navigation positioning in degraded or unavailable GPS conditions is of great practical significance for VLF navigation systems as it can avoid the influence of multimode interference and improve positioning accuracy.

Human Walking Direction Detection Using Wireless Signals, Machine and Deep Learning Algorithms.

The use of wireless signals for device-free activity recognition and precise indoor positioning has gained significant popularity recently. By taking advantage of the characteristics of the received signals, it is possible to establish a mapping between these signals and human activities. Existing approaches for detecting human walking direction have encountered challenges in adapting to changes in the surrounding environment or different people. In this paper, we propose a new approach that uses the channel state information of received wireless signals, a Hampel filter to remove the outliers, a Discrete wavelet transform to remove the noise and extract the important features, and finally, machine and deep learning algorithms to identify the walking direction for different people and in different environments. Through experimentation, we demonstrate that our approach achieved accuracy rates of 92.9%, 95.1%, and 89% in detecting human walking directions for untrained data collected from the classroom, the meeting room, and both rooms, respectively. Our results highlight the effectiveness of our approach even for people of different genders, heights, and environments, which utilizes machine and deep learning algorithms for low-cost deployment and device-free detection of human activities in indoor environments.

Design and Implementation of Multiple Signal Demodulation Device Based on FPGA

To meet the requirements of other aircraft flight test tasks for multiple types of engines and achieve a device matching multiple engine flight test tasks, a design scheme of a multi-signal demodulation device based on FPGA is proposed. This demodulation device collects and demodulates data such as throttle lever position signal, altitude speed, and switch value. It converts and analyzes the data in series and parallel through FPGA and forwards it to various interfaces such as the EEC interface and airborne testing system. According to the interface protocol requirements, it is converted into signals of types such as RS422, ARINC429, and Ethernet. This multi-signal demodulation device has broad application prospects.

Relative contribution of lateral vestibular neuron and abducens internuclear neuron inputs to the discharge activity of medial rectus motoneurons

Medial rectus motoneurons mediate nasally directed horizontal eye movements. These motoneurons receive two major excitatory inputs, from the abducens internuclear neurons (ABD Ints) and neurons of the lateral vestibular nucleus whose axons course through the ascending tract of Deiters (ATD). In the present work, we have recorded in the alert chronic cat preparation the discharge activity of these two premotor neurons simultaneously with eye movements, to discern their relative contribution to the firing pattern of medial rectus motoneurons. ABD Int discharge was accurately correlated with eye movements, displaying high sensitivities to eye position and eye velocity. ATD neurons also discharged in relation to spontaneous and vestibular eye movements but showed significantly lower eye position and eye velocity sensitivities. Outstandingly, ATD neurons presented a significantly lower eye position threshold for recruitment compared to both ABD Ints and medial rectus motoneurons. Therefore, ATD neurons exhibited eye position and velocity signals during spontaneous and vestibular eye movements, which were of lower magnitude than those of ABD Ints, but due to their low recruitment threshold, they could play a significant role in facilitating ABD Int signal transmission onto medial rectus motoneurons.