Cooperative Motion Research Articles

Insights into Entropy Change of β2 Relaxation in Retraction of Uniaxially Stretched Polyimide Films

AbstractStretching has been extensively applied for decades in the production of polyimide (PI) materials with improved mechanical, electrical, and thermal properties. Meanwhile, a detailed understanding of the molecular motions during stretching is still limited. Herein, the thermomechanical behaviors of uniaxially stretched PI films prepared from 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride (BPDA) and 2,2′‐bis (trifluoromethyl) benzidine (TFDB) are studied, and the possible molecular motions responsible for the sub‐glass transition temperature (Tg) stretchability and retraction after stretching are systematically investigated. Based on X‐ray diffraction and dynamic mechanical analysis, it is revealed that both the sub‐Tg stretchability and retraction correlates with β2 relaxation, which originates from the highly cooperative molecular motions of conformational rotations involving segmented BPDA units. A thermodynamic model is established and applied for the analysis of the retraction behaviors of stretched BPDA‐TFDB PI films. It is found that the increase of entropy under stretching plays a significant role in most retraction cases. However, as the stretching temperature increases, the α relaxation‐correlated large‐scale molecular motions emerge. Such motions partially counterbalance the conformational rotations of BPDA segments, leading to an enhanced contribution of enthalpy decrease during the retraction of BPDA‐TFDB PI films.

Molecular Dynamics Simulations of Ammonium-Based Acrylate Polymerized Ionic Liquids

Polymerized ionic liquids (polyILs) are interesting materials that may find application as the electrolyte in electrochemical devices provided that they can be made with sufficiently high ion conductivities. The continuous optimization requires the understanding of the ion transport in available materials. In this work, a group of ammonium-based acrylate polyILs were examined as the candidates with engineered side chains containing long linker and various alkyl tails. Classical molecular dynamics simulations were performed to investigate the mechanism of ion transport. For all simulated systems, the diffusion coefficients were higher than previously investigated polyILs with imidazolium vinyl cations directly bonded to the backbones. Diffusivity was further improved when the tail length increased from methyl to propyl, but this trend did not persist for butyl and longer tails. The higher diffusion coefficient generally coexisted with less ion pair association, lower dynamical heterogeneity, and suppressed string-like cooperative motion. It was affirmed that only a few counterions were fast-moving for effective hopping, and the counterions exhibited smoother motion in acrylate polyILs than the imidazolium-based polyIL with a shorter side chain. For better ion transport, this work suggested that long linker and intermediate tails in the polymerized ions appeared to be the attractive candidates.

Surface-mediated dynamic cooperative motions in azobenzene polymer films

Surface-mediated dynamic cooperative motions in azobenzene polymer films

Surface-mediated dynamic cooperative motions in azobenzene polymer films

Abstract Azobenzene (1,2-diphenyldiazene in IUPAC name) is a widely studied, simple, rodlike photochromic molecule. The trans- (E) to cis- (Z) photoisomerization of this molecule was discovered a long time ago (nearly 90 yr). Nevertheless, the allure and utility of this molecule never faded and it has not surrendered a leading position among many other organic photochromic molecules. New applications for photoswitching molecular and macromolecular systems are still being proposed extensively. By linking the azobenzene molecule to liquid crystals (LCs) and polymer systems, a number of fascinating motility functions have been newly realized. This article overviews our research activities using azobenzene-containing monolayers and LC polymer films. The topics range across surface photoalignment of LCs, both from solid surface and free surface; photoalignment of hierarchical structures such as mesohybrids and block copolymers; photomechanical motions and morphological switching in block copolymer monolayers; high-density brushes of azobenzene side chain LC polymers (SCLCPs); photo-triggered mass migrations in azobenzene SCLCP films; and polymer motions via Marangoni flow, etc. Demonstrations of these dynamic photofunctions are expected to provide great opportunities for practical smart applications.

Cooperative Dynamic Motion Planning for Dual Manipulator Arms Based on RRT*Smart-AD Algorithm.

Intelligent manufacturing requires robots to adapt to increasingly complex tasks, and dual-arm cooperative operation can provide a more flexible and effective solution. Motion planning serves as a crucial foundation for dual-arm cooperative operation. The rapidly exploring random tree (RRT) algorithm based on random sampling has been widely used in high-dimensional manipulator path planning due to its probability completeness, handling of high-dimensional problems, scalability, and faster exploration speed compared with other planning methods. As a variant of RRT, the RRT*Smart algorithm introduces asymptotic optimality, improved sampling techniques, and better path optimization. However, existing research does not adequately address the cooperative motion planning requirements for dual manipulator arms in terms of sampling methods, path optimization, and dynamic adaptability. It also cannot handle dual-manipulator collaborative motion planning in dynamic scenarios. Therefore, in this paper, a novel motion planner named RRT*Smart-AD is proposed to ensure that the dual-arm robot satisfies obstacle avoidance constraints and dynamic characteristics in dynamic environments. This planner is capable of generating smooth motion trajectories that comply with differential constraints and physical collision constraints for a dual-arm robot. The proposed method includes several key components. First, a dynamic A* cost function sampling method, combined with an intelligent beacon sampling method, is introduced for sampling. A path-pruning strategy is employed to improve the computational efficiency. Strategies for dynamic region path repair and regrowth are also proposed to enhance adaptability in dynamic scenarios. Additionally, practical constraints such as maximum velocity, maximum acceleration, and collision constraints in robotic arm applications are analyzed. Particle swarm optimization (PSO) is utilized to optimize the motion trajectories by optimizing the parameters of quintic non-uniform rational B-splines (NURBSs). Static and dynamic simulation experiments verified that the RRT*Smart-AD algorithm for cooperative dynamic path planning of dual robotic arms outperformed biased RRT* and RRT*Smart. This method not only holds significant practical engineering significance for obstacle avoidance in dual-arm manipulators in intelligent factories but also provides a theoretical reference value for the path planning of other types of robots.

Synchronization of multiple rigid body systems: A survey.

The multi-agent system has been a hot topic in the past few decades owing to its lower cost, higher robustness, and higher flexibility. As a particular multi-agent system, the multiple rigid body system received a growing interest for its wide applications in transportation, aerospace, and ocean exploration. Due to the non-Euclidean configuration space of attitudes and the inherent nonlinearity of the dynamics of rigid body systems, synchronization of multiple rigid body systems is quite challenging. This paper aims to present an overview of the recent progress in synchronization of multiple rigid body systems from the view of two fundamental problems. The first problem focuses on attitude synchronization, while the second one focuses on cooperative motion control in that rotation and translation dynamics are coupled. Finally, a summary and future directions are given in the conclusion.

A robust MPC approach for platooning control of automated vehicles with constraints on acceleration

This paper deals with the issue of robust model predictive control (MPC)-based automated vehicle platooning control under acceleration constraints. A unified framework is established to characterize the dynamics of cooperative longitudinal motion of the vehicle platoon with parameter uncertainties as well as the saturated control input. More specifically, the parameter uncertainties are described by norm bounded, and the saturated control input is assumed to be sector-bounded. The coordinated platoon behaves like a linear model where the deviations from the reference spacing and velocity are selected as the state variables. The main objective of this paper is to develop a robust MPC-based platooning control such that the controlled vehicular platoon can track the leading vehicle under the acceleration constraint and parameter uncertainties, meanwhile maintaining safety and resource management. By solving the optimization problem, sufficient conditions for MPC-based platooning control system stability in the mean-squared sense and performance analysis are provided and the controller gain is obtained at each instant. Finally, multi-vehicle cases are conducted to demonstrate the feasibility of the developed control algorithm.

Dynamic heterogeneity in Pd40Ni40P20 glass-forming metallic melt and crystallization behavior probed by quasi-elastic neutron scattering and ultrafast scanning calorimetry

The intrinsic heterogeneity of metallic glasses is hidden in long-range disordered structures. Due to the lack of a long-range ordered structure, it is difficult to construct the structure-property relationship in metallic glasses. However, relaxation dynamics provides a powerful approach to understanding metallic glasses. State-of-the-art quasi-elastic neutron scattering (QENS) and ultrafast scanning calorimetry are used to study the atomic relaxation dynamics, dynamic heterogeneity, diffusion coefficient and crystallization behavior of the Pd40Ni40P20 metallic glass. The presence of dynamic heterogeneity in the Pd40Ni40P20 glass-forming metallic melt is evaluated from the dynamic susceptibility, which is derived from the QENS self-intermediate scattering function. The dynamic heterogeneity increases gradually with decreasing temperature, and a dynamic crossover arises at approximately 1235 K, which is related to the cooperative motion of atoms. Ultrafast scanning calorimetry combined with conventional calorimetry provides heating and cooling rates over seven orders of magnitude, allowing us to study how the liquid thermal history affects glass formation, glass transition, and crystallization. The critical cooling rate required for glass formation is directly determined. A continuous-heating-transformation diagram for crystallization is constructed. This study will improve our understanding of the atomic relaxation dynamics mechanism and intrinsic heterogeneity in metallic glasses.

Research on AGV cart control system based on fuzzy PID control

Abstract As an important carrier of intelligent logistics, AGV can effectively reduce the labor cost of factories and warehouses. With the comprehensive promotion of “smart manufacturing”, the manufacturing industry has a stronger demand for automated AGV logistics systems. This paper firstly analyzes the principle of fuzzy PID controller and establishes its kinematic model to obtain the intrinsic relationship between the motion form and the speed of each driving wheel. Secondly, through the data measured and fed back by the fuzzy PID control system, the AGV driving angle deviation and position deviation are used as the input of the fuzzy controller; its fuzzy deviation correction technology is applied to realize the path correction of the AGV and ensure the stable operation of the AGV through the cooperative motion control technology. Finally, MATLAB software establishes the joint simulation model of the AGV fuzzy PID control system. The results show that through the two algorithms of PID control and fuzzy PID control correction test, the fuzzy PID controller system corrects the deflection efficiency by 47.41%; in the kinematic test, the path tracking efficiency is increased by 30.76%, the distance correction efficiency is increased by 69.56%, the angle correction efficiency is increased by 69.56%, and the average performance is increased by 53.44%. Through the two comparisons, it is concluded that the fuzzy controller designed in this paper has the advantages of fast response speed, good stability, and strong deflection correction performance, which substantially improves the speed and accuracy of intelligent search of intelligent vehicles.

Output Constrained Control of Lower Limb Exoskeleton Based on Knee Motion Probabilistic Model With Finite-Time Extended State Observer

Due to randomness and uncertainty of individual walking gait, this study uses the sparse Gaussian process (SGP) to construct a knee motion probabilistic model related to its corresponding hip motion. Since the SGP can quantify output uncertainty, a time-varying constrained boundary of knee position is presented to guarantee the operator's safety and comfort in human-exoskeleton cooperative motion. First, a low-cost gait acquisition system (called CJD-1) composed of inertial measurement unit is constructed to collect the operator's gait information. Then, a virtual interaction torque field and an output-dependent universal barrier function are designed to realize the coordinated transformation of the time-varying constrained boundary generated by the SGP. Hence, the exoskeleton joint position is constrained by the desired output constrained boundary, which is complied with the operator's gait law. Then, a backstepping controller with a finite-time extended state observer is proposed to estimate and compensate unmeasured joint velocity and lumped uncertainty. The effectiveness of the proposed control scheme is verified by both simulations and experimental results of human-exoskeleton cooperative motion.

Implementation of cross-scale plane micro-scratching process driven by hybrid piezoelectric actuation

The atomic force microscope tip-based mechanical machining technique has been used to fabricate complex micro-structures successfully. However, the machining scope and depth are limited, which holds back this technique severely. This work presents the design and evaluation of a piezoelectric manufacturing system (PMS) for implementation of cross-scale (large scale and high resolution) plane micro-scratching. The PMS has the two-dimensional (2D) micro-machining ability with depths up to 0.98 μm in the millimeter machining scope through the combination of a travel range XY positioning stage and a three-degree-of-freedom (3-DOF) sandwich piezoelectric manipulator. The tracing property of the PMS is feasible for large scale machining by controlling the multi-axis cooperative motion of the 2-DOF stage. The experiments show that the micro-triangles and micro-circles arrays with dimensions from 40 μm to 400 μm are machined successfully. The deviations of the position determination and machined depths for all the micro-structures are less than 5%. Further, it is verified that the manipulator has potential to be used in vibration-assisted cutting to improve machining quality. To sum up, the PMS shows great prospects in the applications of machining cross-scale and large depth planar micro-structures.

Cooperative Lane-Change Motion Planning for Connected and Automated Vehicle Platoons in Multi-Lane Scenarios

Multi-vehicle motion planning (MVMP) has become an emerging paradigm in connected and automated vehicles (CAVs). The cooperative lane-change movements with the coexistence of platoons and CAVs are typical scenarios on the muti-lane roads. This paper proposes an optimal control framework with the advantages of completeness and universality for platoons and CAVs’ cooperative lane-change motion planning in different task scenarios. Two typical cooperative scenarios are designed for the subsequent study of optimal modeling. The platoons’ reconfiguration and original shape maintenance are considered to reflect the universality of moving objects and the diversity of cooperative tasks. Approximately geometric contour models, dynamic externally tangent rectangle and inflated rectangle, are utilized to describe the platoon’s profile. Analytical complete collision avoidance constraints among different motion objects are constructed effectively. Other necessary constraints and the weighted cost function that minimizes lane-change time and motion energy are comprehensively considered. The optimal control models are established for the desired scenarios. Moreover, a numerical solution method combined with the simultaneous direct collocation method based on the trapezoidal rule and the barrier function method is proposed to obtain the optimal schemes. Simulation and contrast experiments are conducted for two scenarios. The results indicate that the cost function’s weight coefficients and specific lane-change tasks influence the cooperative motion planning effects and verify that the proposed optimal control framework is of reasonability, effectiveness, and unification.

Enhancement of Hydrate Stability through Substitutional Defects.

Cytosine monohydrate (CM) and anhydrate crystal forms reversibly interconvert under high temperatures or high humidity conditions. Here, we demonstrate through defect engineering the ability to expand the thermal stability range of CM through the targeted creation of quantifiable defects in low-level concentrations. Twelve different molecular dyes with a variety of core structures and charges were screened as potential dopants in CM. CM-dye phases prepared with Congo red (CR), Evans blue (EB), and Azocarmine G (AG) exhibited the highest inclusion levels (up to 1.1 wt %). In these doped isomorphous materials, each dye is presumed to substitute for 4-7 cytosine molecules within the low-rugosity (102) planes of the CM matrixes, thereby creating a quantifiable substitutional defect and an impediment to the cooperative molecular motions which enable the transformation to the anhydrate. Dehydration of materials with these engineered defects requires significantly higher temperatures and proceeds with slower kinetics compared to pure CM. The CM-dye phases also exhibit a reduction in the thermal expansion along key crystallographic axes and yield dehydration products with altered particle morphologies.

A polynomial-time hybrid solver for multi-agent motion navigation against deadlocks

In the cooperative multi-agent pathfinding and motion planning, given a unique start position and a unique goal position for each agent, all agents are able to pursue their own goals without colliding with each other. To aim at realizing the collision-free motion of the agents within the tractable time, this work proposes a polynomial-time solver, called the HBD-AOI, hybridizing centralized and decentralized schemes. Firstly, an algorithm of centralized pathfinding is utilized to plan the optimal paths of all agents. Afterwards, each of the agents updates the local motion pattern to tracks its own planned waypoints with the obstacle avoidance in a decentralized manner. Furthermore, to resolve unavoidable egoistic conflicts occurring in the decentralized scheme, a centralized intervener with the route replanning is invoked to coach the involved agents to abort the existing deadlocks. Bounded by an amount of time, the performances of the proposed and benchmarked algorithms are simulated on the same instance, from the evaluated testbeds that consists of various maps and scenarios. In the simulations, it is proved that this work outperforms other benchmarked algorithms for all presented instances in the term of the success rate. The experimental results are also demonstrated to verify the feasibility of the proposed methodology.

The Role of Double-Tentacled Cooperative Kinematics on the Hydrodynamics of a Self-propelled Swimmer

In this study, we proposed an underwater robotic swimmer integrating dual-actuated composite tentacles. We employed overlapping grid technology to manipulate virtual swimmers and performed simulations of incompressible viscous flow. To facilitate the distinction between three driving modes (the reverse, homologous, and interlace modes), the rear flexible module of the swimmer was divided into three components: thigh links, calf links, and caudal fins. The cooperative motion mechanism behind the double-tentacled module exhibited special hydrodynamic properties. Under the same kinematic parameters, the reverse mode exhibited the best energy-saving and propulsion effect, whereas the homologous mode was affected by lateral energy loss, thus resulting in the worst propulsion effect. However, the joint system exhibited anti-interference and spanwise flexibility. The interlace mode produced a certain error in the lateral displacement, and the propulsion efficiency was between the former two modes. Compared with traditional fish-like robots, the diverse actuation morphologies of the swimmer reported in this study exhibit extremely powerful self-propelled functionality, and its key features, including the geometry of an aquatic squid and the kinematics of the stretched body-caudal fin pattern, offer insights into the analysis of self-propelled hydrodynamics.

Determination of cooperatively rearranging regions in a binary glass former

Cooperative motions are important for understanding the divergence of viscosity of glassy materials at a finite temperature, since the elementary process of the structural relaxation occurs within the smallest cooperative region as suggested by Adam and Gibbs. On the basis of the definition of a cooperatively rearranging region (CRR) by Adam and Gibbs and by Odagaki, we determine the size of CRR for the Kob–Andersen model as a function of temperature using molecular dynamics simulations. We first confine particles in a spherical region and, varying the radius of that region, we determine the CRR size as the smallest radius of the region in which particles can change their relative positions. The size of the CRR increases as the temperature is reduced and seems to diverge below the glass transition temperature. The temperature dependence of the number of particles in the CRR obeys the equation derived from the Adam–Gibbs relation and the Vogel–Fulcher–Tammann equation.

Comparative Study of High-Resolution LysB29(Nε-myristoyl) des(B30) Insulin Structures Display Novel Dynamic Causal Interrelations in Monomeric-Dimeric Motions

The treatment of insulin-dependent diabetes mellitus is characterized by artificial supplementation of pancreatic β-cell ability to regulate sugar levels in the blood. Even though various insulin analogs are crucial for reasonable glycemic control, understanding the dynamic mechanism of the insulin analogs may help to improve the best-protracted insulin analog to assist people with type 1 diabetes (T1D) to live comfortably while maintaining tight glycemic control. Here, we present the high-resolution crystal structure of NN304, known as insulin detemir, to 1.7 Å resolution at cryogenic temperature. We computationally further investigated our crystal structure’s monomeric-dimeric conformation and dynamic profile by comparing it with a previously available detemir structure (PDB ID: 1XDA). Our structure (PDB ID: 8HGZ), obtained at elevated pH, provides electrostatically triggered minor movements in the equilibrium between alternate conformational substates compared to the previous structure, suggesting it might induce an intermediate state in the dissociation pathway of the insulin detemir’s hexamer:dihexamer equilibrium. Supplemented with orientational cross-correlation analysis by a Gaussian network model (GNM), this alternate oligomeric conformation offers the distinct cooperative motions originated by loose coupling of distant conformational substates of a protracted insulin analog that has not been previously observed.

Nonequilibrium molecular dynamics for accelerated computation of ion–ion correlated conductivity beyond Nernst–Einstein limitation

Condensed matters with high ionic conductivities are crucial in various solid devices such as solid-state batteries. The conduction is characterized by the cooperative ionic motion associated with the high carrier density. However, the high cost of computing correlated ionic conductivities has forced almost all ab initio molecular dynamics (MD) to rely on the Nernst–Einstein dilute-solution approximation, which ignores the cross-correlation effect. Here we develop a chemical color-diffusion nonequilibrium MD (CCD-NEMD) method, which enables to calculate the correlated conductivities with fewer sampling steps than the conventional MD. This CCD-NEMD is demonstrated to well evaluate the conductivities in the representative solid electrolyte bulk Li10GeP2S12 and Li7La3Zr2O12. We also applied CCD-NEMD to the grain boundary of Li7La3Zr2O12 and demonstrated its applicability for calculating interfacial local conductivities, which is essential for investigating grain boundaries and composite electrolytes. CCD-NEMD can provide further accurate understanding of ionics with ionic correlations and promote developing solid devices.

Programming-Based Optimal Learning Sliding Mode Control for Cooperative Dual Ship-Mounted Cranes Against Unmatched External Disturbances

When lifting and transporting large payloads in the marine environment, the dual ship-mounted crane system plays a very important role for cargos transportation, which exhibits strong load capacity and high flexibility. However, apart from the nonlinearity and underactuation characteristic, some unknown or uncertain unmatched wave disturbances may also cause positioning errors, which may induce various risks during the transportation process; besides, lots of existing methods ignore a part of the cooperative crane motions, and the control issue of dual ship-mounted crane system with five degrees of freedoms (5 DOF) is still open. In terms of the aforementioned problems, an adaptive dynamic programming (ADP)-based optimal learning sliding mode controller is proposed in this paper. Specifically, under the frame of adaptive dynamic programming, the Hamilton-Jacobi-Bellman (HJB) equation can be addressed. Then, based on the gradient attenuation algorithm, critic neural networks (NNs) are trained depending on the designed updating law and the approximate optimal learning controller can be obtained. Lyapunov techniques and Lasalle’s invariance principle are used to guarantee asymptotic stability of the dual ship-mounted cranes system. Finally, a series of simulation results are depicted to show the effectiveness of the proposed optimal learning sliding mode controller. Note to Practitioners—In this paper, the control problem of a 5 DOF dual ship-mounted cranes system with unmatched wave disturbance is studied. Due to the complex nonlinear characteristics of the dual ship-mounted cranes and the need to consider the cooperative lifting and wave disturbances, the operation of the dual ship-mounted cranes are very challenging. Moreover, it brings more difficulties to the design of this kind of controller due to its nonlinear underactuated property. Existing control methods for dual ship-mounted cranes are based on linearized or oversimplified crane models, or require accurate model. To solve these kinds of problems, this paper proposes a new control approach for dual ship-mounted cranes suffering from unmatched wave disturbances to achieve satisfactory performance. The stability analysis of the closed-loop systems equilibrium point is implemented by Lyapunov techniques, implying that the accurate positioning and fast payload swings suppression against unmatched wave disturbances are achieved concurrently. In the future studies, we will apply the proposed control method to industrial dual ship-mounted cranes systems to improve their working safety and efficiency.

Chemotaxis of two chiral squirmers

External gradients can strongly influence the collective behavior of microswimmers. In this paper, under an external linear chemical gradient, we study the behavior of two hydrodynamically interacting self-propelled chiral swimmers in the low-Reynolds number regime. We use the generalized squirmer model called the chiral squirmer, a spherically shaped body with an asymmetric surface slip velocity, to represent the swimmer. We find that the external gradient favors the attraction between the swimmers and, in some situations, leads to a bounded state in which the swimmers move in a highly synchronous manner. Furthermore, due to this cooperative motion, these swimmers reach the chemical target faster than individual swimmers. This study may help in understanding the collective behavior of chiral swimmers and in designing synthetic microswimmers for targeted drug delivery.