Flexible Manipulator Research Articles

All-optical group velocity manipulation in Mach-Zehnder fiber interferometers incorporating with Brillouin random lasing resonance

We proposed and experimentally demonstrated a novel scheme of light group velocity control via a Mach-Zehnder fiber interferometer incorporated with Brillouin random lasing resonance in a half-open linear cavity. A theoretical model of the proposed Brillouin random lasing resonance-based Mach-Zehnder interferometer (BRLR-MZI) for the light group velocity manipulation was derived, predicting optical power-dependent transmittance spectrum shift as well as the enhancement of the temporal advancement. Thanks to Brillouin random lasing-induced fast light effect, the proposed scheme not only achieves a flexible all-optical manipulation of its transmittance spectrum but also overcomes the saturation effect for the light speed control based on a traditional MZI. In experimental validation, sinusoidally modulated signals with the modulation frequency of 160 kHz ultimately experienced a maximum advancement of 4031 ns (corresponding to the group index of 0.875), which exhibits an advancement improvement of 1364 ns compared with the traditional MZI-based scheme. It suggests a promising platform for exploring applications in fields of all-optical signal processing, microwave photonic, and ultra-sensitive fiber sensing.

Epsilon-near-zero gratings for polarization selectivity.

Zero-index materials have emerged as a topic of significant scientific interest in recent years. In this Letter, we investigate the electromagnetic properties of epsilon-near-zero (ENZ) gratings composed of materials with near-zero effective permittivity. Our study reveals that ENZ gratings exhibit a unique polarization selectivity that is opposite to that observed in perfect conductor gratings. Furthermore, we demonstrate that hybrid gratings combining perfect conductors and ENZ materials can block omnidirectional electromagnetic waves of any polarization. In addition, we propose a practical design of the ENZ and hybrid gratings based on dielectric ENZ MMs, exhibiting excellent polarization selectivity and blocking effect. Our research presents a promising approach for the flexible manipulation of polarizations using ENZ gratings.

Drift current-induced tunable near-field energy transfer between twist magnetic Weyl semimetals and graphene

Abstract Both the nonreciprocal surface modes in Weyl semimetal (WSM) with a large anomalous Hall effect and the nonreciprocal photon occupation number on a graphene surface induced by the drift current provide a promising way to manipulate the nonreciprocal near-field energy transfer. Interestingly, the interactions between nonreciprocities are highly important for research in (thermal) photonics but remain challenging. In this study, we theoretically investigated the near-field radiative heat flux transfer between a graphene heterostructure supported by a magnetic WSM and a twist-Weyl semimetal (T-WSM). The nonreciprocal surface mode could be changed by the separation space between two Weyl nodes and the twist angle. Notably, we found that in the absence of a temperature difference between two parallel plates, nonequilibrium fluctuations caused by drift currents led to the transfer of near-field radiative heat flux. Furthermore, these nonreciprocal surface modes interacted with the nonreciprocal photon occupation number in graphene to achieve flexible manipulation of the near-field heat flux size and direction. Additionally, graphene adjustable flux in the case of a temperature difference between the two plates was also discussed. Our scheme can provide a reference for near-field heat flux regulation in nonequilibrium systems.

Programmable optical meta-holograms

Abstract The metaverse has captured significant attention as it provides a virtual realm that cannot be experienced in the physical world. Programmable optical holograms, integral components of the metaverse, allow users to access diverse information without needing external equipment. Meta-devices composed of artificially customized nano-antennas are excellent candidates for programmable optical holograms due to their compact footprint and flexible electromagnetic manipulation. Programmable optical meta-holograms can dynamically alter reconstructed images in real-time by directly modulating the optical properties of the metasurface or by modifying the incident light. Information can be encoded across multiple channels and freely selected through switchable functionality. These advantages will broaden the range of virtual scenarios in the metaverse, facilitating further development and practical applications. This review concentrates on recent advancements in the fundamentals and applications of programmable optical meta-holograms. We aim to provide readers with general knowledge and potential inspiration for applying programmable optical meta-holograms, both intrinsic and external ways, into the metaverse for better performance. An outlook and perspective on the challenges and prospects in these rapidly growing research areas are provided.

Adaptive Quantized Control of Flexible Manipulators Subject to Unknown Dead Zones

This article proposes an adaptive control for a flexible manipulator (FM) under the influence of distributed disturbances, unknown dead zones, and input quantization. First, the hybrid effect of the unknown dead zone and input quantization is formulated and represented based on some essential transformations. Then, an adaptive robust quantized control with online updating laws is developed to address the uncertainty of the dead zone, ensure robustness and angle position, and dampen the vibration in the FM system. Subsequently, the Lyapunov theoretical analysis is employed to ensure the bounded stability of the system. Finally, numerical simulations and experiments with a Quanser platform are given to further verify the feasibility and superiority of the designed scheme.

Uncertainty-Aware Haptic Shared Control With Humanoid Robots for Flexible Object Manipulation

Uncertainty-Aware Haptic Shared Control With Humanoid Robots for Flexible Object Manipulation

High-Precision Tip Tracking of a Flexible Link Manipulator Using Two-Time Scale Adaptive Robust Control

A flexible link manipulator (FLM) has advantages of greater payload-to-manipulator-weight ratio, safer operation, and lower energy consumption compared with the rigid manipulator, which has promising demands in various industrial and aerospace applications. However, the internal dynamics of the system is easy to be unstable due to its nonminimum phase characteristics, and there exists severe parametric uncertainties and uncertain nonlinearities in its dynamics, which has brought many difficulties in the precise tip tracking control and effective vibration suppression. In this article, the entire mathematical model of the FLM is established with assumed mode method and actuator dynamics. Then, the system is decomposed into a slow subsystem and a fast subsystem through introducing an adjustable time-scale factor according to a new output redefined dynamics with uncertainties from truncated vibration modes and unknown disturbances of system. A two-time scale adaptive robust control (TTSARC) scheme, which consists of an adaptive robust control for the slow subsystem and a state feedback control for the fast subsystem, is proposed to effectively handle parametric uncertainties and uncertain nonlinearities as well as improve behavior of internal dynamics. Moreover, the clear connection of achievable performances and control parameters based on the stability analysis of the entire system is addressed. The experimental results indicate that precise tip tracking with small link deflection for the FLM working on different conditions can be achieved with the proposed TTSARC.

Detection, Clinical Application, and Manipulation of RNA Modifications.

ConspectusWith increasing research interest, more than 170 types of chemical modifications of RNA have been characterized. The epigenetic modifications of RNA do not alter the primary sequence of RNA but modulate the gene activity. Increasing numbers of regulatory functions of these RNA modifications, particularly in controlling mRNA fate and gene expression, are being discovered. To gain a deeper understanding of the biological significance and clinical prospects of RNA modifications, the development of innovative labeling and detection methodologies is of great importance. Owing to the dynamic features of RNA modifications and the fact that only a portion of genes are modified, detection methods should accurately reveal the precise distribution and modification level of RNA modifications. In general, detection methodologies identify specific RNA modifications in two ways: (1) enriching modification-containing RNAs; and (2) altering the Watson-Crick base pairing pattern to produce truncation or mutation signatures. Additionally, it is important to develop flexible and accurate manipulation tools that enable the installation or removal of RNA modifications at specific positions to investigate the biological functions of a single site. With the development of detection and manipulation methods, the scientific understanding of the biological functions of RNA modifications has increased, paving the way for applications of RNA modifications in disease diagnosis and treatments.In this Account, we provide a brief summary of recent efforts to develop methodologies for detecting RNA modifications. Through the evolution of these detection techniques, our team has uncovered the potential biological roles of RNA modifications in diseases such as diabetic cardiovascular complications, viral infections, and hematologic malignancies. We mainly summarize the recently developed strategies for manipulating RNA modifications. The advent of these programmable editing tools allows for the precise installation or removal of RNA modifications at specific positions. As a result, the biological functions of RNA modifications at these specific loci could be identified, further advancing our knowledge in this field.With this Account, we anticipate providing chemical and biological researchers with comprehensive strategies to discover the underlying mechanisms of RNA modification-mediated biological processes. Although the field of RNA modifications has undergone rapid progress in recent years, our understanding of most of these RNA modifications remains incomplete. We hope to inspire efforts to expand the toolbox for investigating RNA modifications and promote translational research on epigenetics in clinical diagnosis and treatment.

Optical and electrical dual-mode tactile sensor with interlinked interfaces recording normal force and slip for closed-loop robotics

The rapid development of electronic skin will allow disabled people and intelligent robots to interact more effectively with their surroundings. Nevertheless, it remains challenging to simultaneously capture multi-dimensional personalized information (including pressure and slip sensation) through simple device structure design with high stability under complex mechanical conditions. Here, a tactile sensor with simple structure and reliable performance (withstand considerable stretching, twisting, bending, and vibration) is designed for pressure and slip sensing. It is implemented by optical and electrical dual-mode sensing mechanisms and high toughness interlinked interface strategy (interfacial toughness ∼ 33.69 Jm−2, nearly 5 times higher than control sample). This device is composed of a periodic microstructured piezoresistive layer and a triboelectrification-induced electroluminescent (TIEL) layer, both of which are based on the quasi-homogeneous PDMS (polydimethylsiloxane) composite. The whole device possesses the characteristics of lightness, flexibility, and light-transmitting. Besides, the device could automatically locate and track the slip motion while detecting the normal pressure in a large range (0–––1,000 kPa). As an application demonstration, the sensor is installed on a flexible manipulator and combined with the closed-loop control system. Compared to a single electrical mode, the optical and electrical dual-mode tactile sensor could more accurately monitor the sliding of the clamped object, adjust the clamping force instantly, and avoid object slipping. The unique performance of the device shows great potential in trajectory recognition, artificial limbs, intelligent robots, and human–machine interfaces.

Enhancing robustness and noise rejection in flexible joint manipulators: an optimized sliding mode controller with enhanced gray wolf optimization for trajectory tracking

The objective of this study is to enhance the performance of a nonlinear three-rigid-link manipulator (RLM) with a focus on trajectory tracking, robustness against disturbances and noises, and adaptability to joint flexibility. To achieve this, we have employed an optimized sliding mode controller with a proportional integral derivative (PID) sliding manifold. The tuning process involves selecting the critical gains of the controller that minimizes the integral time absolute error (ITAE), serving as the objective function (OBJF) to optimize the performance of the robot manipulator. To identify the optimal gains of the controller, we have utilized a new optimization algorithm known as memory enhanced linear population size reduction gray wolf optimization (MELGWO). The efficacy of this algorithm is compared to other existing optimization methods in the literature. Moreover, this research has delved into the impact of joint flexibility on the robot system’s performance. Encouragingly, the results demonstrate that the optimized SMC–PID with MELGWO adaptation can effectively address joint flexibility while maintaining acceptable performance levels.

Impact of Added Passive Compliance On the Performance of Tip-Actuated Flexible Manipulators

Abstract With their inherent compliance, flexible manipulator systems (FMSs) are increasingly finding new applications, such as robotic surgeries requiring safe interaction with the environment. While force-controlled FMSs are desirable, an added passive, compliant element can enhance safety while preserving performance. This paper explores the effects of added compliance on tip-actuated FMSs. A detailed analysis compares the impacts of additional compliance, and comparisons are made with a baseline no-compliance case. It is observed that the series compliance provides added safety but with some compromise on performance and stability. In contrast, parallel compliance improves stability and performance without compromising safety in interaction. While similar insights have been well-understood in the context of rigid-link robots, it is interesting to observe that additional series compliance in tip-actuated flexible manipulators is undesirable, unlike for rigid-link robots.

Optical anapole modes in hybrid metal–dielectric nanoantenna for near-field enhancement and optical sensing

Metal–dielectric nanostructures in the optical anapole modes are essential for light–matter interactions due to the low material loss and high near-field enhancement. Herein, a hybrid metal–dielectric nanoantenna composed of six wedge-shaped gold (Au) nanoblocks as well as silica (SiO2) and silicon (Si) nanodiscs is designed and analyzed by the finite element method (FEM). The nanoantenna exhibits flexibility in excitation and manipulation of the anapole mode through the strong coupling between the metal and dielectrics, consequently improving the near-field enhancement at the gap. By systematically optimizing the structural parameters, the electric field enhancement factors at wavelengths corresponding to the anapole modes (AM1 and AM2) can be increased to 518 and 1482, respectively. Moreover, the nanoantenna delivers great performance in optical sensing such as a sensitivity of 550 nm/RIU. The results provide guidance and insights into enhancing the coupling between metals and dielectrics for applications such as surface-enhanced Raman scattering and optical sensing.

Symmetry‐Induced Selective Excitation of Topological States in Su–Schrieffer–Heeger Waveguide Arrays

The investigation of topological state transition in carefully designed photonic lattices is of high interest for fundamental research, as well as for applied studies such as manipulating light flow in on‐chip photonic systems. Herein, the topological phase transition between symmetric topological zero modes (TZM) and antisymmetric TZMs in Su–Schrieffer–Heeger mirror symmetric waveguides is reported. The transition of TZMs is realized by adjusting the coupling ratio between neighboring waveguide pairs, which is enabled by selective modulation of the refractive index in the waveguide gaps. Bidirectional topological transitions between symmetric and antisymmetric TZMs can be achieved with proposed switching strategy. Selective excitation of topological edge mode is demonstrated owing to the symmetry characteristics of the TZMs. The flexible manipulation of topological states is promising for on‐chip light flow control and may spark further investigations on symmetric/antisymmetric TZM transitions in other photonic topological frameworks.

Integrated lithium niobate optical mode (de)interleaver based on an asymmetric Y-junction.

Lithium niobate on insulator (LNOI) platforms promise unique advantages in realizing high-speed, large-capacity, and large-scale photonic integrated circuits (PICs) by leveraging lithium niobate's attractive material properties, which include electro-optic and nonlinear optic properties, low material loss, and a wide transparency window. Optical mode interleavers can increase the functionality of future PICs in LNOI by enabling optical mode division multiplexing (MDM) systems, allowing variable mode assignment while maintaining high channel utilization and capacity. In this Letter, we experimentally demonstrate an optical mode interleaver based on an asymmetric Y-junction on the LNOI platform, which exhibits an insertion loss of below 0.46 dB and modal cross talk of below -13.0 dB over a wavelength range of 1500-1600 nm. The demonstrated mode interleaver will be an attractive circuit component in future high-speed and large-capacity PICs due to its simple structure, scalability, and capacity for efficient and flexible mode manipulation on the LNOI platform.

Neural Network-Based Cooperative Trajectory Tracking Control for a Mobile Dual Flexible Manipulator.

For a mobile dual flexible manipulator (MDFM) system, this article focuses on the problem of cooperative trajectory tracking under unknown dynamics and time-varying trajectories. The dynamic model of the wheeled mobile manipulator system in 2-D space is established. Taking into account the unmodeled dynamics of the system, unknown terms of the system are approximated by integrating the radial basis function neural network (RBFNN) structure. By introducing the servo system, the cooperative trajectory tracking control (CTTC) strategy is designed, which realizes the system's cooperative operation, time-varying trajectory tracking, and vibration suppression. The performance of the proposed control scheme is verified through theoretical analysis and numerical simulations.

Dynamic modeling and vibration suppression for double flexible manipulator with a tip payload

Dynamic modeling and vibration suppression for double flexible manipulator with a tip payload

Distributed robust‐multivariate‐observer‐based FDI attacks estimation for nonlinear multi‐agent systems with directed graphs

AbstractThis article investigates the distributed robust estimation problem for false data injection (FDI) attacks in nonlinear multi‐agent systems with directed graphs. To approximate the realistic attack scenario, the case where both the actuator network channel and sensor network channel suffering from FDIs are considered, and the attack signals contain time‐varying circumstances. A novel distributed robust‐multivariate‐observer (DRMO) strategy is developed such that the online estimation of FDI attack dynamics can be realized with the partially unknown nonlinear dynamics, attack transient increments, and disturbances impact being eliminated. The designed DRMO scheme only depends on the received compromised/uncompromised measurement output information on the account that whole state information cannot be measured directly. Finally, two simulation examples, including a network of four one‐link flexible joint manipulator systems with comparisons to existing methods, are given to show the effectiveness of the proposed scheme.

Multimodal Imaging for Validation and Optimization of Ion Channel-Based Chemogenetics in Nonhuman Primates.

Chemogenetic tools provide an opportunity to manipulate neuronal activity and behavior selectively and repeatedly in nonhuman primates (NHPs) with minimal invasiveness. Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are one example that is based on mutated muscarinic acetylcholine receptors. Another channel-based chemogenetic system available for neuronal modulation in NHPs uses pharmacologically selective actuator modules (PSAMs), which are selectively activated by pharmacologically selective effector molecules (PSEMs). To facilitate the use of the PSAM/PSEM system, the selection and dosage of PSEMs should be validated and optimized for NHPs. To this end, we used a multimodal imaging approach. We virally expressed excitatory PSAM (PSAM4-5HT3) in the striatum and the primary motor cortex (M1) of two male macaque monkeys, and visualized its location through positron emission tomography (PET) with the reporter ligand [18F]ASEM. Chemogenetic excitability of neurons triggered by two PSEMs (uPSEM817 and uPSEM792) was evaluated using [18F]fluorodeoxyglucose-PET imaging, with uPSEM817 being more efficient than uPSEM792. Pharmacological magnetic resonance imaging (phMRI) showed that increased brain activity in the PSAM4-expressing region began ∼13 min after uPSEM817 administration and continued for at least 60 min. Our multimodal imaging data provide valuable information regarding the manipulation of neuronal activity using the PSAM/PSEM system in NHPs, facilitating future applications.SIGNIFICANCE STATEMENT Like other chemogenetic tools, the ion channel-based system called pharmacologically selective actuator module/pharmacologically selective effector molecule (PSAM/PSEM) allows remote manipulation of neuronal activity and behavior in living animals. Nevertheless, its application in nonhuman primates (NHPs) is still limited. Here, we used multitracer positron emission tomography (PET) imaging and pharmacological magnetic resonance imaging (phMRI) to visualize an excitatory chemogenetic ion channel (PSAM4-5HT3) and validate its chemometric function in macaque monkeys. Our results provide the optimal agonist, dose, and timing for chemogenetic neuronal manipulation, facilitating the use of the PSAM/PSEM system and expanding the flexibility and reliability of circuit manipulation in NHPs in a variety of situations.

Intelligent flexible manipulator system based on flexible tactile sensing (IFMSFTS) for kiwifruit ripeness classification.

Consumers all throughout the world enjoy kiwifruit. After harvest, there are as much as 20-25% of kiwifruit lost along the entire industrial chain. An intelligent flexible manipulator system based on flexible tactile sensing (IFMSFTS) was created to automatically and intelligently classify kiwifruit ripeness in order to minimize loss. The flexible manipulator is coupled with the flexible tactile sensor. When kiwifruits are being gripped by the manipulator, the flexible sensor perceives their firmness, and the mapping relationship between firmness and ripeness allows for the prediction and evaluation of the kiwifruit's ripeness. Principal component analysis (PCA) is employed to minimize the dimension of the sample firmness data set. K-Nearest neighbor (KNN) and support vector machine (SVM) classifiers are utilized to train and test the data. The findings indicate that PCA-KNN's classification accuracy is 97.5% and PCA-SVM's classification accuracy is 96.24%. The first is a better fit. IFMSFTS can precisely classify ripeness, effectively address the issue of fruit loss, and realize the sustainable and clean production of fruit by sensing the firmness of kiwifruit and relying on the mapping link between firmness and ripeness. © 2023 Society of Chemical Industry.

Consensus tracking and vibration control for multiple single-link flexible manipulators with input signal quantization

This study examines consensus tracking and vibration control of a multiagent system consisting of multiple single-link flexible manipulators with input signal quantization. The dynamics of each flexible manipulator are described by fourth-order partial differential equations (PDEs). A logarithmic quantizer with changeable parameters is adopted to quantize control inputs, and adaptive laws are designed to compensate for the effect caused by quantization. A distributed adaptive boundary control protocol is proposed based on the PDE model to ensure all manipulators track the desired angular position and eliminate vibrations without knowledge of quantizer parameters. The proposed control protocol is proven to ensure the uniformly bounded stability of the closed-loop system. Simulations are carried out under three cases to illustrate the effectiveness of the designed strategy.