Motional Degrees Of Freedom Research Articles

Intracage vibrations and Zeeman effect in Y3N@C80 single-molecule transistors

Clusterfullerenes, which contain a cluster rather than single-atom inclusions, exhibit more complex internal structures and greater degrees of freedom for motion. Trimetallic nitride clusterfullerenes have attracted significant attention due to their diversity and potential applications, among which Y3N@C80 stands out for its charge-transfer characteristics in electronic excitations, owing to the unique distribution of molecular orbitals near the Fermi level. Here, we have fabricated single-molecule transistor devices using Y3N@C80. Transport measurements at liquid helium temperature revealed a series of excited state energy levels, which were matched to corresponding vibrational modes through comparison with Raman spectra and density functional theory calculations. Additionally, we measured charge-state-dependent magnetic responses, revealing the electron and spin-filling patterns of the molecular orbitals in Y3N@C80. These results enhance our understanding of the dynamics and molecular spin–orbit characteristics of clusterfullerenes, indicating their potential for multifunctional applications.

Submersible Position Prediction Model Based on HMM and Six Degrees of Freedom Motion

Submersible Position Prediction Model Based on HMM and Six Degrees of Freedom Motion

Nonlinear dynamic modeling and vibration analysis for flexible tethered satellite systems under large deformations

The escalating threat posed by space debris necessitates innovative approaches for its removal. This article presents a comprehensive mathematical modeling and dynamic analysis of a flexible tethered satellite system (FTSS) in the post-capture phase, taking into account nonlinear strain effects for the flexible appendages. The FTSS consists of a rigid central body satellite, two identical flexible panels, and a towing mass that manipulates the satellite through a tether. We develop a detailed dynamic model that accurately represents the system’s three-dimensional motion, incorporating the rigid body’s 6 degrees of freedom (DOF), the tether’s 3 DOF motion, and two modal generalized coordinates for each panel. The extended Hamilton method is employed to derive this model, enabling us to investigate the conditions under which nonlinear strain considerations become critical. The findings of this article reveal that nonlinear strain effects can profoundly impact the system’s dynamics under certain geometric and forcing conditions, often overlooked in previous studies. In these scenarios, the panel strains exceed the linear regime, necessitating the use of nonlinear models for accurate representation. This work emphasizes the importance of incorporating nonlinear strain terms in the dynamic analysis of FTSSs, particularly when dealing with large deformations and high-amplitude vibrations encountered in debris removal applications.

Modelling and Control of 6- Degrees of Freedom movement Using Fuzzy Logic

Modelling and Control of 6- Degrees of Freedom movement Using Fuzzy Logic

Dynamical active particles in the overdamped limit

Mobile microscopic bodies, such as motile cells, can be modelled phenomenologically as ‘active particles’ which can move against external forces by depleting an internal energy depot. The microscopic mechanisms underlying such ‘active’ behaviour must ultimately obey fundamental physics: energy depots must actually consist of dynamical degrees of freedom, such as chemical reaction coordinates, which in some way couple to the particle’s motional degrees of freedom. As a step towards connecting phenomenological models with microscopic dynamical mechanisms, recent papers have studied the minimalistic dynamical mechanism of a ‘dynamical active particle’, and shown how nonlinear couplings can allow steady energy transfer from depot to motion, even in the presence of weak dissipation. Most real active particles move through viscous environments, however, and are strongly damped. Here we therefore generalize the dynamical active particle into the overdamped regime. We find that its mechanism still operates, and in particular allows the overdamped active particle to travel just as far against friction as the undamped model, by moving at a slower average speed. Our results suggest that active particle phenomenology can indeed be consistent with comprehensible dynamical mechanisms, even in strongly dissipative environments.

Performance-based target reliability analysis of offshore wind turbine mooring lines subjected to the wind and wave

Reliability assessment is a crucial aspect of the design and operation of structures, particularly in balancing safety and cost considerations. This paper introduces a novel method for evaluating the performance-based target reliability of floating wind turbine platforms in offshore environments. The method focuses on the platform's motion modes and wave frequencies, which significantly influence the system's structural integrity and performance. An improved limit state function is proposed to enhance the accuracy of reliability calculations, specifically for steady-state conditions. The platform's six degrees of freedom motions are carefully analyzed to investigate their dependence on wave frequencies. By considering the time response of these motions and accounting for uncertainties in wave characteristics, wave impact directions, and wind effects, a comprehensive reliability analysis is conducted to assess the stability modes of the platform. This paper introduces the term 'Reliability Performance-Based' (RPB) analysis as a new concept to evaluate the system's reliability at a given performance level. Furthermore, an optimal target reliability index is defined to address the economic aspect of the design process. The proposed methodology's PEB analysis focuses on capturing uncertainties in wave characteristics and wind effects on floating wind turbine platforms. This includes a detailed examination of wave and wind-induced loads and their propagation through the system concerning its performance level. Statistical models were integrated to quantify these uncertainties, applying Monte Carlo simulations to assess their effects on the platform's reliability. This approach allows for a nuanced understanding of the interactions between environmental factors and structural responses, enhancing the precision of our reliability assessments. It enables the consideration of economic efficiency alongside safety, ensuring a balanced approach to the design and operation of the floating wind turbine platform. By providing a comprehensive reliability assessment framework, it aids in the optimization of design and decision-making processes for floating wind turbine platforms.

A new industrially magnetic capsule MedRobot integrated with smart motion controller

Capsule medical robots with unique application advantages have broad prospects for gastrointestinal detection, targeted drug delivery, medical assistance, and other fields. However, due to the complexity of the gastrointestinal environment and the limitations of the space magnetic field, robust motion control of capsule robots is still a challenge. Using a permanent magnet (NdFeB) as a space magnetic source, a capsule robot manipulation instrument with an integrated motion intelligent control approach is proposed in this work. First of all, a steering fixture controlling a permanent magnet is designed, and a manipulation instrument capable of five degrees of motion freedom is built with low cost and high accuracy. Furthermore, an integrated motion control approach, consisting of a primary motion subsystem and an auxiliary motion subsystem, is presented, where the motion route of the capsule robot is planned. A parallel optimization strategy is adopted to improve the traditional Gray Wolf Optimization Algorithm, the improved version of which is utilized to tune the parameters of controllers. Finally, some experiments of the designed capsule robot are carried out in different planes and slopes, as well as simulated stomach and real pig stomach, respectively. The results show that the motion characteristics are continuous and stable, and the average position error is 4.2 mm, which meets the application requirements.

Unsteady aerodynamics of the floating offshore wind turbine due to the trailing vortex induction and airfoil dynamic stall

The trailing vortex induction effect and the airfoil dynamic stall are two main sources of the wind turbine unsteady aerodynamics. The unsteady aerodynamics of the floating offshore wind turbine (FOWT) is more complicated than its monopile counterpart due to the existence of the additional six degrees of freedom motion (6-DOF) of the floating platform. This paper focuses on the unsteady aerodynamics of the FOWT under surge condition results from the trailing vortex induction and airfoil dynamic stall, especially the resulting hysteresis effect, by adopting the free vortex wake (FVW) method coupled with the dynamic stall model. The reasons and manifestations of the hysteresis effect are discussed, and the effect of the operation conditions on the hysteresis effect of the FOWT are analyzed. Besides, other unsteady aerodynamic phenomena associated with the hysteresis effect are also included. Results show that, when the FOWT operates under surge condition, there exists a phase lag between the loads response and the variation of the rotor inflow velocity, which is a manifestation of the hysteresis effect. With the variation of the operation conditions of the FOWT, the phenomena such as dynamic stall, blade-wake interaction and the transition of the operation state may occur, and the manifestation of the hysteresis effect will be different.

Deep reinforcement learning and decoupling proportional-integral-derivative control of a humanoid cable-driven hybrid robot

Aiming at the application of robots in service, medical treatment, rehabilitation, and other fields, a humanoid cable-driven hybrid robot by imitating the structure of human arm is designed in this article. The robot is composed of a cable–spool–pulley system, series mechanism, and coaxial spherical parallel mechanism, which can achieve six degrees of freedom movement in space. A challenge with cable driving is that the movement of the rear end joints (such as pitch and roll) can alter the length or tension of the cable driven by the frontend joints, resulting in joint coupling. This interference can lead to a decrease in the motion accuracy of the robotic arm. In addition, it also affects the durability of cables or mechanical components such as bearings and pulleys. Considering the joint motion coupling phenomenon caused by the cable-driven, the decoupling method is proposed, and the kinematic model of the robot is established. To solve the nonlinear coupling characteristics and the uncertainty of the dynamics parameters, a controller is proposed for the humanoid cable-driven hybrid robot, combining proportional-integral-derivative (PID) control based on decoupling method (DC-PID) and the double delay deep deterministic policy gradient (TD3) deep reinforcement learning algorithm. The trajectory tracking of the end-effector position and orientation are controlled by using DC-PID and TD3. And the simulation results show that the proposed control method has good trajectory tracking and convergence performance according to trajectory tracking error and training reward. Finally, the humanoid cable-driven hybrid robot prototype is developed. The experimental results of coupling compensation show that the average maximum error of the joint is reduced by 77.58% after considering the coupling compensation of the joint. The results of the controller validation experiments show that the DC-PID controller reduces the maximum error in each axis by 11.54%, 35.29%, and 40.16%, respectively, compared to the open-loop experiments.

Dielectric Elastomer-Based Actuators: A Modeling and Control Review for Non-Experts

Soft robotics are attractive to researchers and developers due to their potential for biomimicry applications across a myriad of fields, including biomedicine (e.g., surgery), the film industry (e.g., animatronics), ecology (e.g., physical ‘animats’), human–robot interactions (e.g., social robots), and others. In contrast to their rigid counterparts, soft robotics offer obvious actuation benefits, including their many degrees of freedom in motion and their potential to mimic living organisms. Many material systems have been proposed and used for soft robotic applications, involving soft actuators, sensors, and generators. This review focuses on dielectric elastomer (DE)-based actuators, which are more general electro-active polymer (EAP) smart materials. EAP-based soft robots are very attractive for various reasons: (a) energy can be efficiently (and readily) stored in electrical form; (b) both power and information can be transferred rapidly via electrical phenomena; (c) computations using electronic means are readily available. Due to their potential and benefits, DE-based actuators are attractive to researchers and developers from multiple fields. This review aims to (1) provide non-experts with an “easy-to-follow” survey of the most important aspects and challenges to consider when implementing DE-based soft actuators, and (2) emphasize current solutions and challenges related to the materials, controls, and portability of DE-based soft-actuator systems. First, we start with some fundamental functions, applications, and configurations; then, we review the material models and their selection. After, we outline material limitations and challenges along with some thermo-mechano-chemical treatments to overcome some of those limitations. Finally, we outline some of the control schemes, including modern techniques, and suggest using rewritable hardware for faster and more adaptive controls.

AI-Driven solid-state device to enable natural control of upper-extremity robotic exoskeletons

The paper introduces the ‘Smart Handle’, a compact, lightweight, fully solid-state control device based on machine learning (ML) models, enabling intuitive manipulation across all three degrees-of-freedom (DOF) of translation and orientation. This handle-type control device utilizes low-cost, easily accessible sensors and materials. It addresses the need for natural control mechanisms in upper-extremity exoskeletons used in rehabilitation and occupational settings, offering position and orientation trajectories crucial for kinematic models. Additionally, individuals with motor difficulties using mobility chairs could benefit from its ability to learn and interpret diverse inputs as control commands. Through empirical study, it was demonstrated that the device adeptly learns and outputs continuous translation and rotation information from training sets focused on single DOF motions. Personalized calibration enables consistent movement classification with over 95% accuracy. Successful proof-of-concept experiments were conducted in exoskeleton and wheeled robot control applications, showcasing the Smart Handle's adaptability and reliability in diverse settings. This research underscores the device's potential across multiple domains, providing a foundation for enhanced intuitive control mechanisms in various technological applications.

An experimental study on the aerodynamic loads of a floating offshore wind turbine under imposed motions

Abstract. The rotor of a floating wind turbine is subject to complex aerodynamics due to changes in relative wind speeds at the blades and potential local interactions between blade sections and the rotor near wake. These complex interactions are not yet fully understood. Lab-scale experiments are highly relevant for capturing these phenomena and provide means for the validation of numerical design tools. This paper presents a new wind tunnel experimental setup able to study the aerodynamic response of a wind turbine rotor when subjected to prescribed motions. The present study uses a 1:148 scale model of the DTU 10 MW reference wind turbine mounted on top of a 6 degrees of freedom parallel kinematic robotic platform. Firstly, the thrust variation of the turbine is investigated when single degree of freedom harmonic motions are imposed by the platform, with surge, pitch and yaw being considered in this study. For reduced frequencies greater than 1.2, it is found that the thrust variation is amplified by up to 150 % compared to the quasi-steady value when the turbine is subject to pitch and surge motions, regardless of the amplitude of motion. A similar behaviour is also noticed under yaw motions. Secondly, realistic 6 degrees of freedom motions are imposed by the platform. The motions are derived from FAST simulations performed on the full-scale turbine coupled with the TripleSpar floater, and the tests aim at exploring the thrust force dynamics for different sea states and wind conditions, obtaining reasonable agreement with the simulations. Finally, the work shows the capabilities of an off-the-shelf hexapod to conduct hybrid testing of floating offshore wind turbines in wind tunnels, as well as its limitations in performing such tests.

RC-SLAM: Road Constrained Stereo Visual SLAM System Based on Graph Optimization.

Intelligent vehicles are constrained by road, resulting in a disparity between the assumed six degrees of freedom (DoF) motion within the Visual Simultaneous Localization and Mapping (SLAM) system and the approximate planar motion of vehicles in local areas, inevitably causing additional pose estimation errors. To address this problem, a stereo Visual SLAM system with road constraints based on graph optimization is proposed, called RC-SLAM. Addressing the challenge of representing roads parametrically, a novel method is proposed to approximate local roads as discrete planes and extract parameters of local road planes (LRPs) using homography. Unlike conventional methods, constraints between the vehicle and LRPs are established, effectively mitigating errors arising from assumed six DoF motion in the system. Furthermore, to avoid the impact of depth uncertainty in road features, epipolar constraints are employed to estimate rotation by minimizing the distance between road feature points and epipolar lines, robust rotation estimation is achieved despite depth uncertainties. Notably, a distinctive nonlinear optimization model based on graph optimization is presented, jointly optimizing the poses of vehicle trajectories, LPRs, and map points. The experiments on two datasets demonstrate that the proposed system achieved more accurate estimations of vehicle trajectories by introducing constraints between the vehicle and LRPs. The experiments on a real-world dataset further validate the effectiveness of the proposed system.

An investigation on coupling analysis and vibration rectification of vibration isolation system for strap-down inertia measurement unit

ABSTRACT The development and deployment of high-precision positioning and orientation systems rely heavily on strap-down inertial measurement units (IMU), which are an integral part of aircraft navigation and launch systems. However, careful study and ongoing use of microelectromechanical systems inertial sensor assemblies (MEMS ISA) present the challenge of vibration disturbances that can significantly degrade the performance of IMU. To alleviate this problem, this paper proposes a vibration isolation system (VIS) based on a motion decoupling mechanism. The designed VIS dynamically decouples 6 degrees of freedom motion, effectively isolating the IMU from external vibrations while allowing free movement, thereby significantly improving control of vibration-induced motion changes. Our approach is validated through finite element simulations and random vibration tests, showing that the proposed VIS effectively reduces transmission measurement errors in IMU. The sensitivity of MEMS ISA to various vibration amplitudes and frequencies can lead to severe vibration correction errors. Therefore, reducing noise and offset is critical for systems that must operate reliably in harsh environments. This study not only explores vibration correction, but also provides a feasible solution through VIS design that can significantly reduce noise and deviation, helping to improve the durability and accuracy of the system. This research is clear that integrating well-designed VIS can significantly improve the resilience and accuracy of MEMS-based inertial systems, paving the way for more robust applications in the aerospace and defense industry.

Drosophila Larvae-Inspired Soft Crawling Robot with Multimodal Locomotion and Versatile Applications.

Soft crawling robots have been widely studied and applied because of their excellent environmental adaptability and flexible movement. However, most existing soft crawling robots typically exhibit a single-motion mode and lack diverse capabilities. Inspired by Drosophila larvae, this paper proposes a compact soft crawling robot (weight, 13 g; length, 165 mm; diameter, 35 mm) with multimodal locomotion (forward, turning, rolling, and twisting). Each robot module uses 4 sets of high-power-density shape memory alloy actuators, endowing it with 4 degrees of motion freedom. We analyze the mechanical characteristics of the robot modules through experiments and simulation analysis. The plug-and-play modules can be quickly assembled to meet different motion and task requirements. The soft crawling robot can be remotely operated with an external controller, showcasing multimodal motion on various material surfaces. In a narrow maze, the robot demonstrates agile movement and effective maneuvering around obstacles. In addition, leveraging the inherent bistable characteristics of the robot modules, we used the robot modules as anchoring units and installed a microcamera on the robot's head for pipeline detection. The robot completed the inspection in horizontal, vertical, curved, and branched pipelines, adjusted the camera view, and twisted a valve in the pipeline for the first time. Our research highlights the robot's superior locomotion and application capabilities, providing an innovative strategy for the development of lightweight, compact, and multifunctional soft crawling robots.

Negative-temperature pressure in black holes

The concept of negative temperature is unique to quantum physics and describes systems that are hotter than any positive-temperature system. For decades, negative temperatures have been shown in a number of spin systems, but experiments only recently demonstrated atomic ensembles with negative temperatures in their motional degrees of freedom. An observed behavior of such negative-temperature ensembles is that despite highly attractive forces between an arbitrary number of particles, there is a self-stabilization against collapse. Negative temperatures are only possible in quantum systems because there exists upper bounds on the energy of particles —a property not found in classical physics. Here we consider whether event horizons set up similar upper limits within black holes, giving rise to negative-temperature systems just within event horizons. Combining black-hole thermodynamics with experimentally observed negative-temperature effects could imply a quantum-based outward pressure in black holes.

Modelling and analysis for the dynamic behavior of 6-DOF motion platform used for simulating aerospace mechanical environment

As high carrying capacity, high frequency response and high precision control performance are presented, the 6 degree of freedom (DOF) motion platform is chosen as the aerospace device to implement mechanical environment simulation experiment on the ground. In this paper, a dynamic model of the 6 DOF motion platform is firstly developed based on the Newton-Euler method. Then the attitude determination and the driving force are analyzed by solving the dynamic equations. Furthermore, a parametric modelling method for the 6 DOF motion platform is proposed and applied to obtain the expansion amounts and the driving forces of the 6 hydraulic rods in the motion platform by adopting the Adams software. Results show a good agreement with the computation results of the theory dynamic model, which demonstratesthe validity of the proposed modelling method for analysis of the dynamic behavior of the 6-DOF motion platform.

Dynamic process and dynamic-stall phenomenon on blade sections of a floating horizontal-axis wind turbine caused by the platform's pitch motion

Floating horizontal-axis wind turbines (FHAWTs) experience six degrees of freedom motion in space with their floating platforms. Such dynamic process may induce complex dynamic flow and variable local load on the blades, however, still insufficiently understood from a perspective of unsteady aerodynamics. In this study, the local aerodynamic load in the dynamic process induced by the platforms’ pitch motion is investigated by computational fluid dynamics. Our results indicate that the axial force of each blade section fluctuates significantly over time, with varying levels of fluctuation among the blade sections. The pressure distributions around the blade sections also vary significantly. Additionally, we observe the light dynamic stall phenomenon that cause stronger lift in upstroke and weaker lift in downstroke, and the flow separation and reattachment process during the dynamic stall demonstrates a delayed response relative to instantaneous changes in the angle of attack. The load variations due to the dynamic process and dynamic stall can lead to severe fatigue and extreme loads on the surface and structure of the blades. These findings suggest that quasi-steady analysis, which neglects the dynamic process, is not sufficient for accurately predicting the blade loads under pitch motion. Furthermore, we find that the fatigue-load properties vary with location on a blade section, with the leading and trailing edges being more susceptible to fatigue problems. These results highlight the importance of considering the potential harmful effects of pitch motion in the design of FHAWTs.

An integrated dynamic modeling method for underwater vehicle with hull, propeller and rudder

An integrated motion simulation and dynamic modeling method is proposed, which takes into account the mutual influences of hull, propeller and rudder. Using Computational Fluid Dynamics (CFD) in a single simulation, all hydrodynamic coefficients, including those for the rudder and propeller, can be determined. Taking SUBOFF model as the object, the dynamics model was established based on the simplified equation of six degrees of freedom motion in space. The hydrodynamic coefficients were identified by using sliding time window and normal distribution methods. The results show that in comparison with the experimental hydrodynamic coefficients, the error of the predicted hydrodynamic coefficients is very small, and the force and moment curves fitted by dynamic equation are very close to those monitored by CFD simulation. This proves the reliability of the established dynamic model and the correctness of the parameter identification method.

Experimental study of floating bridge global response when subjected to waves and current

The present paper investigates the wave- and current-induced responses of the Bjørnafjord phase 5 K12 floating bridge concept based on small-scale model tests. Due to the extensive length of the bridge concept combined with relatively small wave heights governing the design, the experimental model represents a truncated section of the original bridge concept. This truncated section includes a stay-cable tower and ten floating pontoons supporting a horizontally curved bridge girder at varying altitude. The bridge girder truncation points coincide with the tower column and the location just above the first moored pontoon. The girder boundary conditions are simplified as fixed for all degrees of freedom (DOF) on either side of the model while allowing for free rotation around the longitudinal and vertical axes at the location above the otherwise moored pontoon. The instrumentation of the experimental model includes three DOF translational motions captured at 13 locations along the bridge and six DOF motion of each pontoon. Force transducers are used to capture axial forces in all ten tower stay-cables and at the two ends of the bridge girder, while strain gauges capture shear forces and bending- and torsional moments measured at 12 locations along the bridge girder.The dynamic properties of the model are investigated by subjecting the model to both regular waves and broad-banded, long-crested waves, propagating at two different wave directions corresponding to waves travelling in and out of the fjord. These tests are performed with and without collinear current to investigate the effect of current on the bridge responses. Subsequently, the effect of current is investigated for two important long-crested wave conditions, i.e. the 100-year wind wave condition and the 10000-year swell wave condition. For both wave conditions the model tests are performed without current and with 1-year and 10-year current velocities, respectively. Finally, the short-term response from the long-crested wind and swell wave conditions without current are compared to those of short-crested waves without current.Results show that both current and the directional distribution of the waves have a significant influence on the structural responses. It is recommended that both effects are properly accounted for in any future design.