Flexible Manipulator Research Articles

Full Forward Kinematics of Lower-Mobility Planar Parallel Continuum Robots

In rigid lower-mobility parallel manipulators the motion of the end-effector is partially constrained due to a combination of passive kinematic pairs and rigid components. Translational mechanisms, such as the Delta manipulator, are the most common ones among this type of mechanisms. When flexible elements are introduced, as in Parallel Continuum Manipulators, the constraint is no longer rigid, and new challenges arise in performing certain motions depending on the degree of compliance. Mobility analysis shifts from being purely a geometric issue to one that heavily relies on force distribution within the mechanism. Simply converting classical lower-mobility rigid parallel mechanisms into Parallel Continuum Mechanisms may yield unexpected outcomes. This work, making use of a planar parallel continuum Delta manipulator, on the one hand, presents two different approaches to solve the Forward Kinematics of planar continuum manipulators, and, on the other hand, explores some challenges and issues in assessing the resultant workspace for different design alternatives of this kind of flexible manipulators.

Topology optimization of a superconducting photonic crystal power beam splitter

The design of photonic crystals using novel materials holds significant importance in constructing high-performance, next-generation photonic crystal devices. In this study, aiming at the requirements for enhanced transmission and selectivity, we utilized a topology optimization method based on the method of moving asymptotes (MMA) to realize a high-temperature superconducting photonic crystal power splitter with low transmission loss and selectivity effects, which allows for flexible control and manipulation of optical signals. The method addresses the shortcomings of traditional scanning techniques, such as low efficiency and high resource consumption, by allowing for multi-parameter optimization. This improvement enhances the precision and effectiveness of the numerical computational iterative process. The research offers insights into the design of novel optical devices.

Parametric global mode method for dynamical modeling and response analysis of a rotating and length-varying flexible manipulator

Rotating and Length-Varying Flexible Manipulators (RLVFMs) benefit from the ability to transform their length to adapt to complex and demanding workspaces but suffer from increased complexity in nonlinear dynamical characteristics and thus difficulties in modeling. To provide an in-depth understanding of the RLVFMs, this paper proposes a novel dynamical modeling approach for the RLVFMs, called the Parametric Global Modal Method (PGMM), and presents a framework to study their nonlinear responses. It is capable of addressing time-varying boundary conditions and describing the elastic deformation of all flexible components with only one set of modal coordinates. A low-dimensional dynamical model of a RLVFM is developed. The natural characteristic results obtained from the models developed by the PGMM and the finite element method (FEM) are compared for verifications of the PGMM. Via a convergence analysis of responses, the high precision of the model developed by the PGMM is verified to be achieved by using only the first two modes. On this basis, the dynamic responses and computational efficiency of the low-dimensional model are validated through experiments and finite element method (FEM) simulations. Moreover, the responses of the RLVFM under operations of rapid maneuvering are studied and a potential vibration control strategy for the RLVFM is preliminarily demonstrated. This work provides a new way of developing advanced dynamical modeling methods of reconfigurable and deformable multi-component mechanisms for their dynamical design, response analysis, and system control.

Flexible switchable mid-infrared metalens optical tweezer based on VO2

Metasurface has developed rapidly since its advent because of its powerful control over electromagnetic waves, but most traditional metasurface can only passively realize a single fixed function, which limits its application and development in integrated systems. To modulate electromagnetic waves more flexibly and efficiently, here, we first propose what we believe to be a novel scheme to design a switchable metalens by utilizing the phase change materials VO2 and double-layer metasurface modulation. The metalens designed by the proposed scheme can achieve flexible conversion between the transmitted focusing and reflected focusing through changing the phase state of VO2. Then, we investigate the optical force phenomenon of these metalenses, the simulation results indicating that the proposed switchable metalens can achieve stable particle manipulation under both the transmission and reflection modes. This makes it a promising device in flexible optical manipulation, and this reversible tuning will also show significant application potentials in biology, medicine, optical communication and other fields.

Position control of single link flexible manipulator: a functional observer-based output feedback sliding mode approach

Position control of single link flexible manipulator: a functional observer-based output feedback sliding mode approach

A Combined Strategy for Path Planning of Tensegrity Manipulators Considering Structural Stability

Abstract A strategy combining an improved rapidly exploring random tree (RRT) method with the artificial potential field (APF) method is proposed for the path planning of flexible tensegrity manipulators considering typical complex constraints, such as structural stability, obstacle avoidance, and cable no-slackening. The relationship between the node displacements and the elongations of active members is established for the kinematic analysis of tensegrity manipulators. The rest lengths of active members are taken as the design variables for the generation of a random tree. The guide node is utilized for goal-biased samplings to expedite the exploration toward the final configuration, while the APF method is introduced to ensure that the obtained elongations of active members can satisfy the constraint of obstacle avoidance. The proportion of random and goal-biased samplings is adaptively adjusted based on the sampling success rate. Futile random samplings can be significantly reduced by dynamically modifying the random sampling range according to the obtained configuration nearest to the final configuration. The computational procedure of the proposed method is presented. An illustrative flexible tensegrity manipulator is employed to demonstrate the adaptability of the proposed path planning method to complex constraints, especially structural stability.

Micromotor based on single fiber optical vortex tweezer

Optical micromotors are powerful tools for trapping and rotating microparticles in various fields of bio-photonics. Conventionally, optical micromotors are built using bulk optics, such as microscope objectives and SLMs. However, optical fibers provide an attractive alternative, offering a flexible photon platform for optical micromotor applications. In this paper, we present an optical micromotor designed for 3D manipulation and rotation based on a single fiber optical vortex tweezer. A tightly focused vortex beam is excited by preparing a spiral zone plate with an ultrahigh numerical aperture of up to 0.9 at the end facet of a functionalized fiber. The focused vortex beam can optically manipulate and rotate a red blood cell in 3D space far from the fiber end facet. The trapping stiffness in parallel and perpendicular orientations to the fiber axis are measured by stably trapping a standard 3-µm silica bead. The rotational performance is analyzed by rotating a trimer composed of silica beads on a glass slide, demonstrating that the rotational frequency increases with rising optical power and the rotational direction is opposite to the topological charge of the spiral zone plate. The proposed fiber micromotor with its flexible manipulation of microparticle rotation circumvents the need for the precise relative position control of multiple fiber combinations and the use of specialized fibers. The innovations hold promising potential for applications in microfluidic pumping, biopsy, micromanipulation, and other fields.

Neural Network Adaptive Inverse Control of Flexible Joint Space Manipulator Considering the Influence of Gravity.

With the aim of correcting the problem of trajectory tracking control of a flexible joint space manipulator in environments with different gravity, a neural network adaptive inverse control algorithm based on singular perturbation theory is proposed to resist the disturbance caused by system uncertainty. Firstly, the dynamic model of a flexible joint space manipulator with the influence of gravity is established, and then the system is divided into a fast subsystem and a slow subsystem using singular perturbation theory. The velocity feedback control rate is designed for the fast subsystem to suppress the elastic vibration caused by the joint flexibility. For the slow subsystem, the uncertain term and known term are separated by the inverse control algorithm, where the uncertain term is approximated online by the RBF neural network, and the robust control rate is designed to compensate for the approximation error. The simulation results show that the control method can not only effectively reduce the high-frequency vibration caused by the flexible joint but also resist the system disturbance so that a good track control effect is achieved.

Free vibration of flexible two links manipulator with variable cross-sectional areas

This paper demonstrated the free vibration of a planar two-link flexible manipulator with harmonic drivers and non-uniformity in the cross-section of links. A dynamic model has been developed that incorporates flexibilities in both link and joint experiencing harmonic vibration, with joint flexibility modeled as torsional spring-inertia components combination. Two links were modeled based on Von Karman’s nonlinear strain relations and theory of the Euler-Bernoulli beam. The nonlinear governing equations were derived using the extended Hamilton’s principle for planar two-link flexible manipulators with variable cross-sections for each link. The coefficients of the obtained partial differential equations were as a function of spatial coordinates and were reduced to the ordinary differential equations for a family of cross-section geometries with exponentially varying widths of rectangular sections of each link. The frequency equation was obtained and analytical solutions of the vibration were achieved for different exponential shapes of each link (widening and narrowing beam for each link). Natural frequencies and mode shapes were presented for varying cross-section areas of the links. The effects of the end masses, payload, beam mass density, flexural rigidity ratio, and joint frequency were investigated on the mode shapes and natural frequencies when the power of the exponential function of the cross-sectional areas of two links was varied. The numerical results were verified with experimental results.

Topological interface and corner states of flexural waves in metamaterial plates with glide-symmetric holes

This study investigates the topological localization and propagation of flexural waves in metamaterial plates with perforated holes exhibiting glide symmetry. The dispersion relations of flexural waves in this mechanical system exhibit four-fold Dirac degeneracies at the M point of the Brillouin zone. By properly adjusting the rotation angles of the perforated holes, these degeneracies can be lifted up to create omnidirectional bandgaps, enabling nontrivial topological phases. Both numerical and experimental results demonstrate multiple topological states of flexural waves in the developed elastic metaplates, including dual-band helical interface states and anisotropic interface/corner states. The simple perforated metaplates with glide-symmetric holes provide novel, manufacturable platforms for the flexible manipulation of topological flexural waves, greatly facilitating potential applications such as energy harvesting and signal enhancement.

Full-space trifunctional metasurface with independent control of amplitude and phase for circularly polarized waves

Abstract Flexible and diverse manipulation of electromagnetic (EM) waves in half space (reflection or transmission) has facilitated strong aspiration toward full-space wave control. However, it remains challenging to achieve independent amplitude and phase control, which seriously hinder the real-world applications. Herein, an innovative strategy of trifunctional metasurface is proposed to independently and simultaneously manipulate the amplitude and phase of circular polarized waves in full space. The multifunctional design is composed of double-layer anisotropic metasurface sandwiched with a bandpass frequency selective surface, with a frequency-direction multiplexed paradigm for on-demand control of both amplitude and phase across three independent channels. To validate the concept, a multifunctional metadevice is designed and verified by simulations and experiments, showcasing arbitrary near-field and far-field power modulation in full space. Lateral and axial bifocal metalenses with desired intensity distribution are designed in two reflection channels at 9 GHz, while multibeam generator with desired spatial scatterings and power allocations is designed in transmissive channel at 13 GHz. The finding paves the way for attaining multifunctional metadevices with amplitude and phase modulation in full space, which have potential applications in high-quality imaging and high-capacity communication systems.

High-Fidelity Supramolecular Chirality Transportation Enabled Through Chalcogen Bonding.

The formation of asymmetric microenvironments in proteins benefits from precise transportation of chirality across multiple levels through weak bonds in the folding and assembly process, which inspires the rational design and fabrication of artificial chiral materials. Herein, the chalcogen bonding-directed precise transportation of supramolecular chirality toward multiple levels is reported to aid the fabrication of chiroptical materials. Benzochalcogenadiazole (O, S, Se) motifs are conjugated to amino acid residues, and the solid-state assemblies afforded selective supramolecular chirality with handedness depending on the kinds of chalcogen atoms and amino acids. The chalcogen-N sequence assisted by hydrogen bonding synergistically allows for the complexation with pyrene conjugated aryl carboxylic acids to give macroscopic helical structures with active circular dichroism and circularly polarized luminescence, of which handedness is precisely determined by the pristine chiral species. Then the further application of chiral benzochalcogenadiazole motifs as seeds in directing handedness of benzamide via symmetry breaking is realized. Behaving as the dopants, embedding into the matrix of benzophenone induces the room temperature phosphorescence, whereby the thermal chiroptical switch is fabricated with color-tunable phosphorescent circularly polarized luminescence. This work utilized benzochalcogenadiazole-based chiral building units to accomplish precise transportation of supramolecular chirality in coassemblies with high-fidelity, achieving flexible manipulation of chiroptical properties and macroscopic helical sense.

PID Controller Parameter Tuning Based on a Modified Differential Evolutionary Optimization Algorithm for the Intelligent Active Vibration Control of a Combined Single Link Robotics Flexible Manipulator

This paper introduces some of the various techniques of vibration control and optimization for the purpose of vibration reduction and balancing. Here, in this research by comprising three of the most effective variational techniques now, a Modified Differential Evolutionary Optimization Algorithm (MDEOA) method is suggested to handle the challenge of adjusting the PID controller parameters for the Intelligent Active Vibration Control (IAVC) of a Combined Single Link Robotics Flexible Manipulator (CSLRFM) in order to reduce the undesired effects of vibration. The Crossover Probability Factor (CPF) as the Certain Ratio (CR) and the Mutation Factor (MF) of the algorithm are gradually altered during algorithm iteration to enhance the method's performance during optimization. On this foundation, the PID controller parameter tuning and the issue of CSLRFM mechanical vibrations are addressed using the MDEOA method. This research suggests an evolutionary algorithm that incorporates the variational techniques mentioned above, which will be combined by a certain ratio, and the specific computational procedure. In this strategy, a Strictly Bearish Distributed Exponential Function (SBDEF) has been used as the main target and the criteria and indicators for evaluating and measuring the optimal performance of differential evolution are the Integral Absolute Error (IAE) rate and the PID controller parameter values. According to simulation findings, the technique can be used to optimize the PID controller parameters settings for the IAVC of the CSLRFM and a reduction in the mechanical vibrations. Simulation results illustrate the effectiveness of the proposed MDEOA strategy which is significantly and quite satisfactory about 25 to 30 (%) better than comparing to the other algorithms in improvement stabilization and vibration control of CSLRFM.

Smart Photovoltaic Windows for Next-Generation Energy-Saving Buildings.

The global energy system transforming from fossil fuels to renewable green energy through the adaption of innovative and dynamic green technologies. Energy-saving buildings (ESBs) are attracting extensive attention as intelligent architectures capable of significantly reducing the energy consumption for heating, air-conditioning, and lighting. They provide comfortable working and living environment by regulating and harnessing solar energy. Smart photovoltaic windows (SPWs) offer a promising platform for designing ESBs due to their unique feature. They can modulate solar energy based on dynamic color switching behavior under external stimuli and generate electrical power by harvesting solar energy. In this review, the-state-of-art of strategies and technologies are summarized putting SPWs toward high-efficiency ESBs. The SPWs are systematically categorized according to the working principle and functional component. For each type of SPWs, material and architecture engineering are focused on to optimize operation mode, optical modulation capability, photovoltaic performance and durability for giving ESBs flexible manipulation, extraordinary energy-saving effect, and high electricity power. In addition, the challenges and opportunities in this cutting-edge research area are discussed, with the aim of promoting the development of advanced multifunctional SPWs and their application in high efficiency ESBs.

Semi-Analytical Design of PDE Endpoint Controller for Flexible Manipulator With Non-Homogenous Boundary Conditions

Semi-Analytical Design of PDE Endpoint Controller for Flexible Manipulator With Non-Homogenous Boundary Conditions

Optimized Control of 3DOF Variable Stiffness Link Manipulator Using Feedback Linearization PD and Sliding Mode Approaches

Purpose: This study focuses on the control of a 3-degree-of-freedom (3DOF) variable stiffness flexible links manipulator, employing diverse control techniques to address the challenges associated with its inherent structural flexibilities. Variable Stiffness Link (VSL) manipulators offer enhanced adaptability and safety in various applications by dynamically adjusting their link stiffness. This feature allows them to optimize performance for different tasks, from delicate operations to robust industrial use. However, the variable stiffness introduces complex nonlinear dynamics, significantly complicating precise control and necessitating advanced control strategies. Methodology: The research investigates two advanced control methods: linearized feedback proportional-derivative (PD) control and sliding mode control (SMC). These techniques are employed for both position and trajectory control of the system, aiming to maintain precise joint angles while minimizing oscillations in the end effector. The controller designs for both linearized feedback PD and sliding mode control are presented, including stability analyses using Lyapunov theory. Experimental work is conducted to evaluate the effectiveness of both control strategies. Findings: The results demonstrate that both controllers achieve satisfactory performance in managing the complex dynamics of the flexible link system. The linearized feedback PD controller shows good tracking capabilities across the three joints while the sliding mode controller exhibits superior performance. Comparative analysis reveals that while both controllers effectively maintain stability and achieve precise trajectory tracking, the sliding mode controller displays marginally better performance in terms of steady-state errors and robustness to system nonlinearities. Unique contribution to theory, policy and practice: This research contributes to the advancement of control techniques for flexible manipulators, offering promising solutions for improving the performance and reliability of this manipulator for automation applications.

Optomechanical entanglement manipulation and switching in a squeezed-cavity-assisted optomechanical system

Quantum entanglement is pivotal in modern quantum technologies, spanning applications from quantum networks to quantum metrology. Controllable quantum entanglement in cavity optomechanical systems has been an enduring pursuit. We propose a unique method for flexible manipulation and switching of optomechanical entanglement in a squeezed-cavity-assisted optomechanical system consisting of a χ(2)-nonlinear optical cavity and an optomechanical cavity. Squeezing the nonlinear optical cavity through parametric pumping allows effective control of light-light and light-vibration interactions within the system. This capability of the squeezed system plays a key role in manipulating quantum entanglement. We find that quantum entanglement between the unsqueezed cavity mode and the mechanical mode can be effectively regulated by adjusting the pump laser parameters. Furthermore, by turning the phase of the pump, we can achieve highly flexible quantum switching between entanglement and separability. Additionally, we demonstrate increased entanglement between the squeezed cavity mode and the mechanical mode when completely suppressing the pump-induced optical input noise. Our findings pave the way not only towards the manipulation and protection of fragile quantum entanglement but also to achieve photon-phonon quantum control by exploiting quantum squeezing.

Tip and vibration control of space robots using estimated flexible coordinates

This paper provides an extension to previous work on end-effector control of flexible space manipulators. Those works considered the use of a special output called the μ-tip rate for feedback control of desired end-effector trajectories with simultaneous vibration control. Implementation of this special output requires measurement of end-effector position or the use of flexible forward kinematics to determine it. For the latter, one requires measurements of the joint angles and flexible coordinates. The second of these is difficult to measure in space scenarios, so this paper looks at the use of an estimation scheme to approximate it and use it in a task-space control law. Multiple simulations are conducted to investigate the use of these approximated elastic coordinates in robustly controlling a one-link and two-link flexible manipulator with a payload mass. The error between desired and actual trajectory is calculated, and the results are juxtaposed with results from a joint-space feedback scheme. There is an emphasis on comparing the estimated elastic coordinates with the actual simulated coordinates. Using the estimated elastic coordinates to determine the end-effector location via forward kinematics, yielded similar results to when the actual elastic coordinates were used. Overall, the estimation equation used is shown to provide reasonable end-effector tracking results with the end-effector being able to track various types of trajectories.

A novel combined control of flexible single-link manipulator based on singularly perturbed theory

PurposeThis study aims to improve the control accuracy and antidisturbance performance of the manipulator with the flexible link, a combined controller, which combines the novel backstepping sliding mode controller based on the extended state observer (ESO) and super-twisting sliding mode controller.Design/methodology/approachFirst, the dynamic of the system is constructed by Lagrange method and assumed mode method, and then the dynamic is decoupled by the singular perturbation theory to obtain the slow-varying subsystem and fast-varying subsystem. For the slow-varying subsystem, the novel backstepping sliding mode controller based on ESO is used to achieve joint tracking. For the fast-varying subsystem, the super-twisting sliding mode controller is used for vibration suppression. At the same time, to suppress chattering, the tanh function is used to replace the sign function in the reaching law.FindingsThe simulation results show that the combined control has better trajectory tracking performance, antiinterference performance and vibration suppression performance than traditional sliding mode control (SMC).Originality/valueA novel backstepping sliding mode controller based on ESO is designed to guarantee the performance of the tracking trajectory. The new controller improves the converge rate. A super-twisting sliding mode controller, which can stabilize the fast-varying subsystem, is used to suppress the vibration of flexible link.

Fuzzy PI vibration suppression control strategy for space double flexible telescopic manipulator with fractional disturbance observer

The space double flexible telescopic manipulator (SDFTM) with time-varying length, is called the space flexible manipulator and can carry out reciprocating linear telescopic motion along its axis. It possesses characteristics such as lightweight flexibility, small space occupation, large turning radius, and a wide working range. These features can assist astronauts in performing complex tasks in dangerous outer space environments and offer broad application prospects. However, due to the highly nonlinear and time-varying length characteristics of the space flexible manipulator, its dynamic modeling becomes more complex and challenging. Moreover, during the rotation of the space flexible manipulator, its inherent flexible behavior can trigger vibration phenomena, significantly impacting the execution accuracy of on-orbit tasks. Therefore, proposing control methods to address vibration issues is an effective approach. Thus, achieving stable and precise operation of the space flexible manipulator necessitates the precise establishment of its dynamic model and the development of high-precision control algorithms, which have become key research directions. Firstly, a time-varying dynamic modeling method of the space manipulator is proposed by combining the Lagrange principle and flexible beam vibration theory. Unlike the traditional method, which only considers the limit length of the space manipulator under static conditions, the dynamic process of the space manipulator presented during actual operation is fully considered, which greatly improves the modeling accuracy. Then, a time-varying model based on the fuzzy PI real-time control strategy (FD-FZPI) with fractional order disturbance observer (FO-DOB) is proposed. Based on the robust stability principle, a more accurate FO-DOB is proposed based on integer order DOB, coupled with a fuzzy PI controller to compensate for the external disturbance and modeling error of the space manipulator. Finally, numerical simulation analysis is carried out, and the results show that the average parameter difference between the time-varying dynamic model and the static dynamic model can reach about 5.2 %, which indicates the accuracy of the proposed dynamic modeling method. At the same time, the proposed FD-FZPI control strategy achieves about 14.6 % performance improvement over the traditional DOB-PI control method, indicating that the proposed control strategy can effectively suppress the flutter fluctuation of the space manipulator and achieve accurate and stable dynamic tracking.