Flexible Link Research Articles

Machine-Learning-Based 3-D Channel Modeling for U2V mmWave Communications

Unmanned aerial vehicle (UAV) millimeter wave (mmWave) technologies can provide flexible link and high data rate for future communication networks. By considering the new features of three-dimensional (3D) scattering space, 3D velocity, 3D antenna array, and especially 3D rotations, a machine learning (ML) integrated UAV-to-Vehicle (U2V) mmWave channel model is proposed. Meanwhile, a ML-based network for channel parameter calculation and generation is developed. The deterministic parameters are calculated based on the simplified geometry information, while the random ones are generated by the back propagation based neural network (BPNN) and generative adversarial network (GAN), where the training data set is obtained from massive ray-tracing (RT) simulations. Moreover, theoretical expressions of channel statistical properties, i.e., power delay profile (PDP), autocorrelation function (ACF), Doppler power spectrum density (DPSD), and cross-correlation function (CCF) are derived and analyzed. Finally, the U2V mmWave channel is generated under a typical urban scenario at 28 GHz. The generated PDP and DPSD show good agreement with RT-based results, which validates the effectiveness of proposed method. Moreover, the impact of 3D rotations, which has rarely been reported in previous works, can be observed in the generated CCF and ACF, which are also consistent with the theoretical and measurement results.

The application of a optimal controller for the flexible joint robot

This paper describes the operation of a single Degree of Freedom (DOF) flexible robotic arm by the optimal controller. The derived model is based on Euler- Lagrange approach, while the first and second-order (super twisting) Sliding Mode Control (SMC) is proposed as a nonlinear control strategy. Exploration of a flexible robotic arm with using state-of-the-art controllers is essential for practical applications. This is even more refreshing when these arms have joints that work independently of each other to create a smooth connection between the joints, but it still ensures the natural properties like a real human arm. This system has many similarities with the flexible link system of the MIMO model in its operational state analysis. Control laws must be followed by logical rules in a coherent whole. The next step is to design a controller to fit the structure of the system. The author also compared the use of the above controller with a system without using any controller to determine the effectiveness of using the above controller.

Control Strategy and Corresponding Parameter Analysis of a Virtual Synchronous Generator Considering Frequency Stability of Wind Power Grid-Connected System

The doubly-fed induction generator (DFIG) based on the control strategy of constant parameter virtual synchronous generator (VSG) can cause problems of sharp frequency variations in the grid-connected system, long adjustment times, and large overshoot of the active power output from the DFIG. Aiming at dealing with the above-mentioned problems, a VSG control strategy with an independent flexible link (IFLVSG) is proposed in this paper without changing the parameters and structure of the VSG, so that the moment of inertia and damping coefficient can be flexibly adjusted according to the change of the system frequency, so as to improve the system frequency stability. To form a complete selection scheme for control parameters in IFL, the state space equation including IFLVSG control is established, and the advantages of exponential IFL are highlighted by using the sensitivity calculation method. At the same time, in order to improve the analysis efficiency, the main control parameters affecting the frequency stability of the system are selected according to the sensitivity value. Finally, the root locus analysis method is used to reveal the influence law of the main control parameters on the frequency stability of the system. The formed scheme provides a theoretical basis for the selection of control parameters.

LNG export diversification and demand security: A comparative study of major exporters

Global demand for liquefied natural gas (LNG) has doubled over the past decade. The long-term outlook for natural gas is strongest among the fossil fuels. Specifically, LNG is expected to play an increasing role in meeting global natural gas demand, as it provides a flexible link between geographically separated suppliers and customers. In the context of the growing role of LNG in the global energy system, this paper focuses on the world's five largest LNG exporters: Australia, Qatar, the United States of America (USA), Russia and Malaysia. In 2021, they accounted for three-quarters of the global supply. By focusing on exporters, the paper addresses the bias in energy policy literature, which is largely concerned with energy importers. The paper engages in a comparative analysis of LNG exports by five suppliers by considering the extent of their diversification. Focusing on the 2009–2021 period, the paper leverages eight variables to explain patterns of diversification of LNG exports among suppliers and over time. The paper finds that the geographical location and gas price differential across regional markets have the most explanatory power. This finding has significant policy implications for the behaviour of LNG exporting states, demonstrating high sensitivity to economic factors.

Two hybrid model-based control strategies for a flexible parallel planar manipulator

Designers can reduce the inertia of moving parts of a robotic manipulator aiming for energy efficiency. Nevertheless, this design option could yield undesired vibrations due to its lighter components, requiring control strategies for their mitigation. In addition, other challenges arise when designing parallel manipulators since the control strategies cannot use a direct measurement of the manipulator end-effector’s pose and their coupling dynamics. This work proposes two hybrid model-based control design strategies for a 3RRR parallel manipulator with flexible links in this work. Both strategies have two feedback loops, one of which exploits the encoder’s measurements and the inverse kinematic model of the manipulator considering rigid links. The difference between the strategies is related to the feedback signal used in the second feedback loop that exploits an LQR/LQG strategy. The first strategy uses the end-effector’s pose measured by a limited frame camera, while the second uses the end-effector’s pose derived from a reduced-order finite element model. These strategies are experimentally compared with a PID strategy for assessing their assets and limitations. The steady-state error was lower when using the model-based control strategies. Moreover, the second strategy responds faster than the first for the evaluated tasks.

Vibration Control for Flexible Manipulators With Event-Triggering Mechanism and Actuator Failures.

This article focuses on flexible single-link manipulators (FSLMs) under boundary control and in-domain control. The actuators of the system include the dc motor at the end of the joint and m piezoelectric controllers installed at the flexible link, which is regarded as an Euler-Bernoulli beam. The problem of the infinite number of actuator failures, including the partial loss of the effectiveness and total loss of effectiveness, is solved by the adaptive compensation method. By introducing the relative threshold strategy, the event-triggered control (ETC) scheme is proposed to achieve angle regulation and vibration suppression while reducing the communication burden between the controllers and the actuators. The Lyapunov direct method is utilized to prove that the system is uniformly ultimately bounded and both the angular tracking error and elastic displacement converge to a neighborhood of zero. Numerical simulation results are provided to demonstrate the effectiveness of the proposed control law.

End-effector trajectory tracking of flexible link parallel robots using servo constraints

We apply the concept of servo constraints to end-effector trajectory tracking control of parallel robots with structural link flexibilities. Such servo constraints deliver the inverse robot model where solution approaches via projections are proposed, which transform the resulting differential-algebraic equations to ordinary differential equations. The applicable solution process depends on the existence and stability of the internal dynamics. When using the exact end-effector of flexible link robots as output, this internal dynamics is usually unstable. Then a two-point boundary value problem is considered in the framework of stable inversion to obtain the noncausal solution offline. This solution is used as a feedforward control, which is initially combined only with actuator feedback control. To also account for errors within the link flexibility, the well-known linear–quadratic regulator is adapted to end-effector trajectory tracking based on differential-algebraic equations. Finally, we propose a systematic input–output feedback linearization approach, which uses servo constraints for flexible link parallel robots. Here a minimum phase system is obtained by tracking a redefined end-effector output, which is an approximation of the exact end-effector position. All control concepts are validated experimentally with a parallel robot having a highly flexible link. The results allow us to compare different control approaches and show the superior performance of controllers that rely on a flexible multibody model in contrast to classical rigid multibody modeling.

Adaptive vibration control for constrained moving vehicle-mounted nonlinear 3D rigid-flexible manipulator system subject to actuator failures

This paper proposes an active adaptive fault-tolerant control scheme for position tracking and vibration suppression of a constrained moving rigid-flexible manipulator system (RFMS) in three-dimensional (3D) space. The investigated RFMS comprises four parts: a vehicle, a rotatable base, a rigid link, and a flexible link, which is first modeled using nonlinear partial differential equations (PDEs) in terms of Hamilton’s principle. The system may suffer from unknown actuator faults, and the proposed control strategy can compensate for the faults without knowing the fault type and information. The displacement constraint of the vehicle can be ensured by using the barrier Lyapunov function. In the presence of unknown actuator faults and the displacement constraint, the angular position tracking of rigid link, flexible link and rotatable base, and vehicle position tracking can be realized. At the same time, the vibration of the flexible link can be effectively suppressed. The closed-loop system is proven to be asymptotically stable via employing the extended LaSalle’s invariance. Numerical simulations are carried out to verify the effectiveness of the proposed control protocol.

Tip Position Control and Vibration Suppression of a Planar Two-Link Rigid-Flexible Underactuated Manipulator.

When a flexible link manipulator lacks a joint motor, how to use the remaining motors to achieve the control objective is a challenge, and the research in this direction is limited. This article presents a tip position control and vibration suppression approach for a planar two-link rigid-flexible (TLRF) underactuated manipulator with a passive first joint. First, we establish a dynamic model of the system by using the assumed mode method (AMM) and the Lagrangian modeling method. Then, we obtain the dynamic coupling relationship of the two links based on the dynamic model. According to this dynamic coupling relationship, we find that the passive rigid link can be controlled indirectly by controlling the active flexible link. Thus, we calculate the target angles of the two links by using the inverse kinematic method and design a controller for the active flexible link to stabilize it at its target angle and to suppress its vibration. Next, we optimize the parameters of this controller by using the genetic algorithm (GA). GA helps us simultaneously stabilize the passive rigid link at its target angle while realizing the control objective of the active flexible link. The simulation results demonstrate the effectiveness of the proposed control approach.

Dynamic Modeling of a Flexible-Link Flexible-Joint System with Tip Mass Considering Stiffening Effect

This paper presents the dynamic model of a flexible-link, flexible-joint manipulator system with a considerable stiffening effect of the flexible link. A gripper, along with tip mass, is attached at one end of the flexible link. By employing the extended Hamilton’s principle, a nonlinear governing equation of motion is derived along with several boundary constraints. Under the assumption of small deformation in free vibration, a simplified motion equation is deduced to determine the natural frequencies of the mechanical system. Four parameters of the system are selected to carry out the sensitivity study on frequency. The results show that the second frequency mainly depends on the mass of tip payload. Moreover, the third frequency is significantly affected by the moment inertia of tip payload. Regarding the constant angular motion, the finite element method is adopted to analyze the dynamic model by considering the stiffening effect. The frequency results are obtained which show a higher stiffness of the Single Flexible-link Flexible-joint (SFF) system with the angular velocity increasing. The influence of three factors (i.e., payload mass, length of the flexible link, and angular velocity) on the fundamental natural frequencies are discussed, which show instinct characteristics of the flexible manipulator system.

Fast 2.5D and 3D inversion of transient electromagnetic surveys using the octree-based finite-element method

Two efficient implementations of 3D and 2.5D modeling and inversion are presented to be applicable to large-scale transient electromagnetic (TEM) method explorations. The key novel features are (1) forward response and Jacobian calculations are implemented using the octree-based finite-element method, (2) a mirror approach is used to build a 2.5D inversion scheme for further efficiency, and (3) a flexible link between the forward mesh and inversion model is applied on 3D and 2.5D schemes based on the voxel formulation. We compare the performance of the new implementations with 3D modeling using tetrahedral meshes, with respect to speed and memory requirements. The 3D octree algorithm requires less than 1/3 of the computational time compared with a 3D tetrahedral scheme for equivalent accuracy. The 2.5D octree algorithm further speeds up the process by reducing the computational time by another factor of two. The inversion uses the Levenberg-Marquart approach minimizing the least-squares criterion of the objective function. We determine the utility of our inversion approach on a synthetic example and a field example. In the synthetic example, the 3D octree inversion result finds superior resolution of a 3D anomaly compared with a 1D result, whereas the 2.5D inversion result is, expectedly, between the 1D and 3D results, but with favorable computational expenses compared with the full 3D solution. The field data set contains 200 soundings, and we perform a 3D inversion on the full survey. A 24-sounding section is then selected for the 2.5D inversion. The 2.5D inversion result finds resistivity features similar to the 3D inversion result at the selected profile. Hence, we conclude that the presented implementations are capable of handling relatively large TEM surveys on modern computational platforms. This could be smaller subsets of production-size surveys where 2D and 3D effects are pronounced.

The dynamic analysis of the joint trolley movement and hoisting mechanism in the tower crane

The task of this paper is to research the simultaneous use of trolley and hoisting mechanism by the tower crane with a beam jib. To conduct research, a dynamic model of joint movement of mechanisms has been developed, which takes into account the main movement of drive mechanisms and oscillating movement of the load on a flexible suspension and links of mechanisms with elastic properties. A mathematical model of the motion of mechanisms is constructed on the basis of a dynamic model with the help of Lagrange equations of the second kind. For a specific jib system of the tower crane, dynamic calculations were performed using the developed mathematical model. According to the results of the calculations, a dynamic analysis of the joint movement of trolley and hoisting mechanism was carried out. The analysis revealed significant dynamic and energy overloads of mechanisms during transients (start, braking) and the presence of high-frequency oscillations in the links with elastic properties and low-frequency oscillations of the load on a flexible suspension.
 To reduce the overload of crane mechanisms in the areas of transients and eliminate oscillations during steady traffic, it is recommended to optimize traffic modes and develop drive control systems to implement the desired traffic modes.

Vibration control and calculating inverse dynamics of the rigid-flexible two-link manipulator T-R

The dynamics and control of flexible link manipulators (FLMs) are increasing in industrial robotics research. In which the problem of inverse dynamics of the flexible link manipulators is a problem that has been studied little and has no general solution. In this paper, an approximation method is presented to calculate the reverse dynamics of the serial manipulators with rigid-flexible links. The linearization of the motion equations for a rigid-flexible translation and rotation two-link manipulator (manipulator T-R) is addressed. The vibration control and calculating inverse dynamics of a periodic rigid-flexible two-link manipulator T-R are studied. The Taguchi method is used for the design of gain values of the controller PD for the manipulator. The results of numerical simulation show the efficiency and usefulness of the proposed approximation method.

Research on vibration suppression and trajectory tracking control strategy of a flexible link manipulator

Residual vibrations caused by point-to-point motions reduce the positioning accuracy and dynamic performance of flexible link manipulators, and the trajectory planning method, a well-known open-loop control strategy, has been proven to effectively suppress the residual vibration in point-to-point motion. However, this open-loop control method has limitations in dealing with model uncertainty and disturbance problems. In this paper, a control strategy based on dynamics-based trajectory planning and fuzzy self-tuning PD (FST PD) controller is proposed, and applied to achieve residual vibration suppression and trajectory tracking of a flexible link manipulator. To improve the trajectory tracking performance under external disturbances, this control strategy is combined with a linear extended state observer (LESO). Firstly, the dynamic model of the system is deduced using the floating reference frame and Lagrange equation. On this basis, the objective function to minimize the lateral deformation of the tip is constructed, and then the optimal trajectory is obtained by using the Crossbreeding PSO (CBPSO) algorithm. Secondly, the optimal trajectory is used as the desired trajectory to suppress residual vibration, and the FST PD controller combined with the LESO is used to achieve high-precision trajectory tracking control of the flexible link manipulator. Finally, the effectiveness and feasibility of the composite control strategy is verified through multiple simulations. The proposed method can provide support for vibration suppression of flexible link manipulators; meanwhile, the controller structure of this method is simple and easy to implement, and the use of sensors/actuators and other equipment in the system is reduced, which effectively reduces the economic cost.

Vibration characteristics of flexible manipulator based on EVO trajectory effect by the constraints and parameters variation

This paper studies the vibration control effect for manipulators with both flexible link and flexible joint according to the energy-vibration-optimal (EVO) trajectory planning method effect by the constraint conditions and structure parameters. First, a dynamic model of the flexible joint-flexible link arm is established following the assumed modal method and Lagrange principle. The optimization model is then proposed and discretized using the Particle Swarm Optimization (PSO) trajectory planning method and the trajectory optimization of discrete result algorithm, taking into account both residual oscillation and energy consumption. Following that, the numerical trajectory optimization results and their vibration suppression effect analysis by different constraint conditions, such as driving constraints, time constraints, and joint stiffness, are compared and discussed. The results show that the optimization velocity trajectory tends to a S-shaped trajectory and a convex trajectory respectively with the increase of driving velocity constraint and acceleration constraint respectively, while the sufficient planning time can make the less energy consumption. The parameter variations of length, cross-sectional area and next link lumped mass of have a significant impact on the residual oscillation of the flexible arm, with length having the most influence, whereas joint stiffness has little influence on the residual oscillation of the flexible link. The processing accuracy of length, cross-sectional area and end quality parameters must be ensured, while joint stiffness accuracy requirements can be slightly relaxed during the actual processing. Finally, experiments show that the optimization method is effective at vibration suppression. While the small variations of the end mass have significant influence on the vibration suppression effect, the residual vibrations of the parameter variation ones are all larger than the original parameter one. Meanwhile, as the mass of the manipulator increases, so does its energy consumption.

Dynamic model and integrated optimal controller of hybrid arms robot for laser contour machining

The hybrid arms robot (HAR) is a new modified robot which consists of a rigid link (RL) and a flexible link (FL), and it carries a laser head at the end-effector for laser contour machining (CM). The HAR is inspired from a rigid-flexible links manipulator (RFLM) and the aim is to bring the advantages of flexible link manipulators (FLMs) to industrial robots. The HAR gains the advantages of lightweight robots and FLMs such as fast response, less power consumption due to using small actuators, low cost, and safe to surrounding operators. However, the HAR has the drawback of a tip vibration caused by the flexibility of the second FL and leads to a position error at the end-effector position. Furthermore, the HAR has more parameters to be incorporated in a dynamic model such as the tip vibration, the laser head weight, and a force generated by the assist gas pressure. This research aims to obtain the dynamic model of the HAR using the finite element method (FEM) in conjunction with the Lagrangian equation and to propose an integrated optimal controller (IOC) which is an integration of a linear quadratic regulator (LQR) and a fuzzy logic controller (FLC). The derived dynamic model of the HAR is efficient due to the close match response with the SimMechanics model response of the HAR. The proposed IOC is tested for point-to-point (PTP) position control of the HAR and demonstrates improved response and better capability for the tip vibration suppression. The proposed IOC also reveals enhanced triangular CM trajectory, rhombic CM trajectory, and circular CM trajectory of the HAR laser head compared to the LQR performance in a proper cutting speed to ensure the machining quality.

Evaluation of Cost-Effective Flexible High-Speed Data Exchange Links for Heterogeneously Integrated Multi-Chip Modules and Boards

With increasing complexity and heterogeneity, miniaturized integrated system on both multi-chip module and printed circuit board levels relies more and more on high-speed point-to-point serial signal transmission links as the backbone of inter-chip data signal exchange network, which are inevitably accompanied by signal integrity problems such as loss, reflection, and crosstalk. The difficulties in the physical design phase of interconnect routing for high-speed link on densely occupied package interposers or printed circuit boards and the associated planar area overhead (keep-out zone for the crosstalk prevention and impedance matching, etc.), as well as the relevant cost in manufacturing, performance analysis and actual measurement or evaluation, are also sharply increasing; furthermore, the interconnects implemented on interposer or printed circuit board substrate are physically inflexible, and the corresponding microsystems are not suitable for emerging applications that generally demand good deformability and good conformality to 3-dimensionally shaped mounting surface. How to simultaneously elevate the cost-effectiveness, signal transmission performance and physical flexibility of the high-speed link, while keeping low profile of the whole module, has become one of the major challenges in the evolution of micro/nano system technology. Accordingly, this paper proposes a cable-based point-to-point link method, which adopts physically flexible and widely available off-the-shell cables that can be assembled onto the surface of the interposers or boards as a potential cost-effective solution to the challenge mentioned above. Universal Serial Bus, micro-coaxial cables, and Twinax cables are explored as candidates. The full links for each cable, from one of the paired connectors to another, are physically modeled and validated by an electromagnetic full-wave structural simulation tool, with key components of each type of link taken into considerations. The simulated results and the measured results from vector network analyzers are compared, which verifies the effectiveness of our proposal.

Organizational and legal issues in streamlining the horizontal structural connection between central and local public bodies

The article reveals the reasons for the lack of coordination functions and horizontal links in the apparatus of public authorities in the Republic of Moldova. The object of the research is a complex of legal and non-legal relations, multiparty, which arise in the initial stages of the formation of unstable organizational structures, linear-functional, of the central public administration bodies. The aim of this paper is to develop methods for streamlining the relationships and structures of the functional matrix at all levels of governance and self-government. Ways to weaken the multiparty factor are proposed by developing self-regulatory organizations of entrepreneurs and delegating them to state functions. The relevance of the topic is due to the fact that the lack of flexible links and coordination structures between the governing bodies, in the conditions of constant conflicts between party leaders, can lead to problems that call into question the very existence of the state. The author also argues that concrete measures need to be taken in order to combat imperfect legal rules in the form of tightening control over departmental regulation and establishing a permanent review of legislation. Based on the author’s experience in using the various questionnaires and surveys in his monographs, it is proposed, in drafting each new bill, to conduct a content analysis of current regulatory acts in the relevant field or industry and, from a scientific point of view, reach a final decision on whether such a regulatory act can be adopted. It is proposed to formulate at the state level and include in the legislation the various strategic objectives of promoting cooperation in the field of scientific and technological progress and small business.

Practical adaptive position feedback regulator for parallel robots with bounded inputs

This paper addresses the regulation problem of parallel robots by a proportional derivative plus desired gravity compensator (PD-DGC) controller. Due to inaccurate measurements, unmodeled dynamics, and vibrations specially in cable-driven robots and external disturbance in practice, the model of the robot is often plagued with kinematic and dynamic uncertainties. In this paper, two new generations of PD-DGC controller, namely adaptive with respect to the parameters in gravity term, and time-varying PD-DGC in the presence of bounded disturbance, are proposed. Toward not requiring accurate velocity measurement, PD-DGC with merely position feedback in complement to the time-varying controller is designed in the presence of bounded control efforts. Incorporating both methods to establish a simple but strong robust adaptive controller is also investigated by adding an extra assumption on adapted parameters. The asymptotic stability of the closed-loop system is analyzed by the Lyapunov direct method. Experimental results on 2-DOF eye surgery and 3-DOF flexible link ARAS cable-driven robot demonstrate the effectiveness of the proposed approaches in practice.

Calibration for a robotic drilling system with secondary encoders based on a novel enhanced rigid-flexible coupling model

PurposeThis paper aims to propose a novel model and calibration method to improve the absolute positioning accuracy of a robotic drilling system with secondary encoders and additional axis.Design/methodology/approachThe enhanced rigid-flexible coupling model is developed by considering both kinematic parameters and link flexibility. The kinematic errors of the robot and the additional axis are considered with a model containing 27 parameters. The elastic deformation errors of the robot under self-weight of links and end-effector are estimated with a flexible link model. For calibration, an effective comprehensive calibration method is developed by further considering the coordinate systems parameters of the drilling system and using a two-step process constrained Levenberg–Marquardt identification method.FindingsExperiments are performed on the robotic drilling system that contains a KUKA KR500 R2830 industrial robot and an additional lifting axis with a laser tracker. The results show that the maximum error and mean error are reduced to 0.311 and 0.136 mm, respectively, which verify the effectiveness of the model and the calibration method.Originality/valueA novel enhanced rigid-flexible coupling model and a practical comprehensive calibration method are proposed and verified. The experiments results indicate that the absolute positioning accuracy of the system in a large workspace is greatly improved, which is conducive to the application of industrial robots in the field of aerospace assembly.