Flexible Link Research Articles

Exploration and analysis of a generalized one-parameter item response model with flexible link functions.

This paper primarily analyzes the one-parameter generalized logistic (1PGlogit) model, which is a generalized model containing other one-parameter item response theory (IRT) models. The essence of the 1PGlogit model is the introduction of a generalized link function that includes the probit, logit, and complementary log-log functions. By transforming different parameters, the 1PGlogit model can flexibly adjust the speed at which the item characteristic curve (ICC) approaches the upper and lower asymptote, breaking the previous constraints in one-parameter IRT models where the ICC curves were either all symmetric or all asymmetric. This allows for a more flexible way to fit data and achieve better fitting performance. We present three simulation studies, specifically designed to validate the accuracy of parameter estimation for a variety of one-parameter IRT models using the Stan program, illustrate the advantages of the 1PGlogit model over other one-parameter IRT models from a model fitting perspective, and demonstrate the effective fit of the 1PGlogit model with the three-parameter logistic (3PL) and four-parameter logistic (4PL) models. Finally, we demonstrate the good fitting performance of the 1PGlogit model through an analysis of real data.

Behaviour of cold-formed steel framed shear walls with slitted sheathing under lateral loading

Cold-formed steel (CFS) framed shear walls (CFS-SWs) with steel sheathing have emerged as promising lateral-force-resisting members in mid-rise buildings of seismic regions. This paper presents a combined experimental and numerical study on a new type of steel sheathed CFS-SWs, whose novel feature is the use of central CFS sheathing with vertical slits. Five full-scale wall specimens were tested under monotonic and cyclic lateral loading to examine the performance of the shear walls. Then a finite element (FE) modelling of CFS-SWs with slitted steel sheathing was established and verified by the experimental data. Further analyses on the parametric effects and the load-carrying mechanism of CFS-SWs with slitted sheathing were conducted. It is found that the slitted sheathing alleviates the premature damage of boundary studs and mitigates the tremors as well as noises during the loading. The wall with slitted sheathing shows good ductility with a 22.84% higher ductility factor than the wall with non-slitted sheathing. The width-to-thickness ratio and the height-to-width ratio of the flexural links between the slits have considerable effects on the stiffness as well as the peak load of the wall. Lastly, the ultimate lateral resistance of CFS-SWs with slitted sheathing was estimated using a simplified method.

Fractional Control of a Class of Underdamped Fractional Systems with Time Delay—Application to a Teleoperated Robot with a Flexible Link

This work addresses the robust control of processes of the form G(s)=K·e−τ·s/(1+T·sλ) with 1<λ≤2. A new method for tuning fractional-order PI and PD controllers is developed. The stability is assessed based on the frequency domain tuning of the regulators to control such delayed fractional-order underdamped processes. In order to analyze the closed-loop stability and robustness, the new concept of Robust High-Frequency Condition is introduced. The analysis based on that demonstrates that each controller has a different region of feasible frequency specifications, and, in all cases, they depend on their fractional integral or derivative actions. Finally, an application example, the position control of a teleoperated manipulator with a flexible link, is presented. Simulations and experiments illustrate that the region of feasible frequency specifications defined at low and high frequencies allows us to obtain robust controllers that fulfill frequency requirements.

Deep reinforcement learning with reward shaping for tracking control and vibration suppression of flexible link manipulator

This paper puts forward a novel deep reinforcement learning control using deep deterministic policy gradient (DRLC-DDPG) framework to address the reference tracking and vibration suppression problem of rotary flexible link (RFL) manipulator. Specifically, this study attempts to address the continuous action space DRLC problem through DDPG algorithm and presents a Lyapunov function based reward shaping approach for guaranteed deep reinforcement learning (DRL) convergence and enhanced speed of training. The proposed approach synthesizes the hard and soft constraints of the flexible manipulator as a constrained Markov decision problem (MDP) and evaluates the performance of DRLC-DDPG framework through hardware in loop (HIL) testing to realize precise servo tracking and suppressed vibration of the flexible manipulator. For identifying the dynamical model of the RFL, an empirical Auto-Regressive eXogenous (ARX) model using the closed loop identification technique is built. Moreover, to extract the true states (servo angle and deflection angle) from the actual measurements, which typically have the influence of sensor noise, an adaptive Kalman filter (AKF) is augmented with the DRLC scheme. The experimental results of DRLC-DDPG scheme compared with those of the model predictive control (MPC) for several test cases reveal that the proposed scheme is superior to MPC both in terms of trajectory tracking and robustness against the external disturbances and model uncertainty.

Fractional-Order Models of Damping Phenomena in a Flexible Sensing Antenna Used for Haptic Robot Navigation

In this paper, two types of fractional-order damping are proposed for a single flexible link: internal and external friction, related to the material of the link and the environment, respectively. Considering these dampings, the Laplace transform is used to obtain the exact model of a slewing flexible link by means of the Euler–Bernoulli beam theory. The model obtained is used in a sensing antenna with the aim of accurately describing its dynamic behavior, thanks to the incorporation of the mentioned damping models. Therefore, experimental data are used to identify the damping phenomena of this system in the frequency domain. Welch’s method is employed to estimate the experimental frequency responses. To determine the best damping model for the sensing antenna, a cost function with two weighting forms is minimized for different model structures (i.e., with internal and/or external dampings of integer- and/or fractional-order), and their robustness and fitting performance are analyzed.

Wasserstein barycenter for link prediction in temporal networks

Abstract We propose a flexible link forecast methodology for weighted temporal networks. Our probabilistic model estimates the evolving link dynamics among a set of nodes through Wasserstein barycentric coordinates arising within the optimal transport theory. Optimal transport theory is employed to interpolate among network evolution sequences and to compute the probability distribution of forthcoming links. Besides generating point link forecasts for weighted networks, the methodology provides the probability that a link attains weights in a certain interval, namely a quantile of the weights distribution. We test our approach to forecast the link dynamics of the worldwide Foreign Direct Investments network and of the World Trade Network, comparing the performance of the proposed methodology against several alternative models. The performance is evaluated by applying non-parametric diagnostics derived from binary classifications and error measures for regression models. We find that the optimal transport framework outperforms all the competing models when considering quantile forecast. On the other hand, for point forecast, our methodology produces accurate results that are comparable with the best performing alternative model. Results also highlight the role played by model constraints in the determination of future links emphasising that weights are better predicted when accounting for geographical rather than economic distance.

Hybrid Controller for a Single Flexible Link Manipulator

In this study, the dynamic modeling and step input tracking control of single flexible link is studied. The Lagrange-assumed modes approach is applied to get the dynamic model of a planner single link manipulator. A Step input tracking controller is suggested by utilizing the hybrid controller approach to overcome the problem of vibration of tip position through motion which is a characteristic of the flexible link system. The first controller is a modified version of the proportional-derivative (PD) rigid controller to track the hub position while sliding mode (SM) control is used for vibration damping. Also, a second controller (a fuzzy logic based proportional-integral plus derivative (PI+D) control scheme) is developed for both vibration damping and hub position tracking. A comparison is made between the performances of these two controllers. The Hybrid controller with PD and SM shows better tracking behavior than obtained from the suggested fuzzy (PI+D)2 controller for a single link flexible manipulator.

Vibration and Position Control of a Two-Link Flexible Manipulator Using Reinforcement Learning

In recent years, industries have increasingly emphasized the need for high-speed, energy-efficient, and cost-effective solutions. As a result, there has been growing interest in developing flexible link manipulator robots to meet these requirements. However, reducing the weight of the manipulator leads to increased flexibility which, in turn, causes vibrations. This research paper introduces a novel approach for controlling the vibration and motion of a two-link flexible manipulator using reinforcement learning. The proposed system utilizes trust region policy optimization to train the manipulator’s end effector to reach a desired target position, while minimizing vibration and strain at the root of the link. To achieve the research objectives, a 3D model of the flexible-link manipulator is designed, and an optimal reward function is identified to guide the learning process. The results demonstrate that the proposed approach successfully suppresses vibration and strain when moving the end effector to the target position. Furthermore, the trained model is applied to a physical flexible manipulator for real-world control verification. However, it is observed that the performance of the trained model does not meet expectations, due to simulation-to-real challenges. These challenges may include unanticipated differences in dynamics, calibration issues, actuator limitations, or other factors that affect the performance and behavior of the system in the real world. Therefore, further investigations and improvements are recommended to bridge this gap and enhance the applicability of the proposed approach.

Optimal Design of Flexible-Link Mechanisms With Desired Load-Displacement Profiles

Robot mechanisms that exploit compliance can perform complex tasks under uncertainty using simple control strategies, but it remains difficult to design mechanisms with a desired embodied intelligence. In this paper, we propose an automated design technique that optimizes the desired load-displacement behavior of planar flexible-link mechanisms. To do so, we replace a subset of rigid with flexible links in an existing mechanism, and optimize their rest shape. We demonstrate the efficacy of our approach on a set of examples, including two fabricated prototypes, illustrating applications for grasping and locomotion tasks.

Addressing Model Uncertainties and External Disturbances in Optimal Robust Control for Vibration Reduction in a Flexible Link Manipulator

Addressing Model Uncertainties and External Disturbances in Optimal Robust Control for Vibration Reduction in a Flexible Link Manipulator

Dynamic Modelling of the Spring Attached Two-Link Planar Manipulator

Robot dynamics is required for simulation, control, analysis of robot motion planners and controllers. There are a number of dynamic modelling investigations of robots with the different approaches and these investigations mostly focus on the link flexibility, joint friction or actuator dynamics. In addition to that these studies present dynamic model without any attached linear or torsion springs. In this study, the dynamic modelling of a two-link rigid manipulator with attached torsion springs is presented using the Lagrangian approach. The Lagrangian approach is a variational method that relies on the potential and kinetic energy of the mechanism, making it well-suited for the analysis of the two-link planar manipulator considered in this study. Initially, the two-link mechanism equations of motion are derived without any attached torsion springs. Subsequently, two torsion springs are attached to the joints of the mechanism, and the existing equations of motion are modified accordingly. The study also presents the kinetic, potential and total energies of the two link-manipulator, angular positions of the links and their velocities. By considering the dynamic modelling of the torsion spring attached two-link rigid manipulator, this study contributes to understanding and analysis of the two-link manipulators and the dynamic effects of the attached springs.

Generalized Functional Observer for Descriptor Nonlinear Systems—A Takagi-Sugeno Approach

This paper concerns the design of a generalized functional observer for Takagi–Sugeno descriptor systems. Furthermore, a generalized structure is herein introduced for purposes of estimating linear functions of the states of descriptor nonlinear systems represented into a Takagi–Sugeno descriptor form. The originality of the functional generalized observer structure is that it provides additional degrees of freedom in the observer design, which allows for improvements in the estimation against parametric uncertainties. The effectiveness of the developed design is illustrated by a nonlinear model of a single link robotic arm with a flexible link. A comparison between the functional generalized observer and the functional proportional observer is given to demonstrate the observer performances.

Mathematical Model of Flexible Link Dynamics in Marine Tethered Systems Considering Torsion and its Influence on Tension Force

Abstract The rigidity in bending of a flexible link (is an important characteristic that should be considered during regular service conditions. The tension and bending with torsion of wire ropes are also significant factors. This study proposed a method to calculate the vectors of the generalised forces of bending of flexible links. One of the causes of torsional stresses in the power plant of underwater tethered systems is the interaction with ship equipment, such as spiral winding on the winch drum, friction on the flanges of the pulleys or winch drums, and bends on various blocks and rolls that cause torsion. The source of torsional stresses in the FL may also be related to manufacturing, storage, transportation, and its placement on the ship’s winch drums. Torsion can lead to a decrease in the tensile strength due to load redistribution between power elements, or even a violation of their structure. In some cases, torsion significantly affects the movement of the underwater tethered system as a whole. The development of a mathematical model to describe the marine tethered systems dynamics, taking into account the effect of torsion, is important and relevant. The mathematical model of the marine tethered systems dynamics was improved and solved by accounting for the generalised forces of the torsion rigidity of the flexible link, using an algorithm and computer program. The influence of the bending and torsional rigidity of the FL on its deflection and tensile strength were considered based on the example of two problems. The developed program’s working window image shows the simulated parameters and the initial position of the flexible link. The results show that torsion has almost no effect on the shape of the a flexible link’s deflection in the X0Z plane, but leads to a deviation from the X0Z plane when calculating the static deflection of the flexible link. When the carrier vessel is stationary and the submersible vehicle has no restrictions on movement and has positive buoyancy, torsion leads to a three-dimensional change in the shape of the flexible link both in the X0Z plane and in the X0Y plane. The tension force of the flexible link along its length is distributed unevenly, and the torsion of the flexible link can lead to significant changes in its shape, the trajectory of towed objects, and the forces acting on the elements of the marine tethered systems

Improving the Seismic Performance of Eccentrically Braced Frames Using Tie Elements

In Eccentrically Braced Frames (EBFs), link beams in lower storeys may experience a high risk of vulnerability due to the nondistribution of plastic hinges in the frame height and this problem leads to the formation of the soft storey. To mitigate such vulnerabilities, successive link beams can be tied throughout the structure height employing tie elements to develop a tied EBF (TBF) system. Unlike many studies on K-TBFs with shear link beams, limited investigations have evaluated the performance of single diagonal TBFs and K-TBFs with flexural link beams. In this study, K-EBFs/TBFs refer to EBFs/TBFs having link beams with two braces and single diagonal EBFs/TBFs refer to EBFs/TBFs having link beams with one brace. K-EBFs with flexural link beams have drawn the attention of designers because these frames make more space in the architectural design to create larger openings. Accordingly, improving the performance of K-EBFs with flexural link beams is one of this research objectives. The results comparison for 18 2D EBFs with different storeys including K-EBF with shear behavior, K-EBF with flexural behavior, and single diagonal EBF with shear behavior indicated that tie elements in these models can increase energy dissipation capacity and distribute plastic hinges in the structure height. The results exhibited that not only this system performance was considerably improved using tie elements, but also offered better resistance against progressive collapse.

Dynamic Analysis of a Delta Parallel Robot with Flexible Links and Joint Clearances

Delta robot is a lightweight parallel manipulator capable of accurately moving heavy loads at high speed and acceleration along a spatial trajectory. This intensive dynamic process may have a significant impact on the end-effector trajectory precision and motor behavior. The paper highlights the influence on the dynamic behavior of a Delta robot by considering individual and combined effects of clearances and friction in the spherical joints, as well as the flexibility of the rod elements. The CAD modeling of the Delta robot and its motion simulation on a representative spatial trajectory where the maximum allowed values of speed and acceleration are reached were performed using the Catia and Adams software packages. The obtained results show that the methods used were successfully applied and the effects are mutually interconnected, but not cumulative.

Seismic resistance of buckling restrained steel slit panels with X-Shaped restrainers

Steel slit panels (SSPs) serving as lateral load-resisting systems are steel plates (SPs) with rows of vertical slits forming a series of flexural links. The main deficiencies of SSPs subjected to shear forces are fair seismic performance characteristics due to either out-of-plane deformation of long links or fracture of relatively short links. To alleviate this problem, novel buckling restrained SSPs with X-shaped restrainers (referred to as XSSPs) are proposed in the current study. The restrainers are placed on both sides of SSPs to restrain only out-of-plane buckling of links. Refined finite element models of these systems are established and verified by the experiments. The explicit analysis is conducted on these models to evaluate the effects of different patterns of X-shaped restrainers on the seismic performance of these systems. Other parameters considered in this work, include the width-to-thickness ratio of the links, the length-to-width ratio of the links, the number of rows of links, and the width of edge stiffeners. It is found from the results that the hysteresis responses of XSSPs are rather stable with a large energy dissipation capacity. The pinching enhancement is particularly high in cases with a lower length-to-width ratio of the links. Applyin more restrainers in XSSPs models with a lower width-to-thickness ratio and a higher length-to-width ratio of the links improved the strength and the initial stiffness significantly. The strength and stiffness increases due to using diagonal X-shaped restrainers can reach up to 400% and 900%, respectively. The XSSPs have exhibited superior energy dissipation increases more than two times compared with the corresponding SSPs and SPs.

Bayesian Index Models for Heterogeneous Treatment Effects on a Binary Outcome.

This paper develops a Bayesian model with a flexible link function connecting a binary treatment response to a linear combination of covariates and a treatment indicator and the interaction between the two. Generalized linear models allowing data-driven link functions are often called "single-index models" and are among popular semi-parametric modeling methods. In this paper, we focus on modeling heterogeneous treatment effects, with the goal of developing a treatment benefit index (TBI) incorporating prior information from historical data. The model makes inference on a composite moderator of treatment effects, summarizing the effect of the predictors within a single variable through a linear projection of the predictors. This treatment benefit index can be useful for stratifying patients according to their predicted treatment benefit levels and can be especially useful for precision health applications. The proposed method is applied to a COVID-19 treatment study.

Modeling and fuzzy control of flexible manipulator link with moving end effector

In this paper, a flexible robotic arm system was designed and constructed based on the aspect ratio of flexible arms. The mathematical modeling was derived using finite element method. In addition, necessary information about the dynamic behavior of the suggested system was collected and used to design controllers based on knowledge of fuzzy logic theory. The purpose of building the flexible robotic arm was to perform different movements while ensure the accuracy of the derived mathematical dynamic model. This was achieved by comparing the experimental responses with theoretical ones where both systems were controlled through control strategies designed on the basis of fuzzy logics. The resulted control system is a 2-input, 1-output system. Different fuzzy controllers were suggested in addition to the non-conventional fuzzy control method (Fuzzy Control). This includes traditional-fuzzy control method with PID as well as PD controllers.The results showed that the error ratio between theoretical and practical responses does not exceed 16% in Fuzzy Control method and 11% in the PD-Fuzzy Control and 9% in the PID-Fuzzy Control method. This mismatch is due to the nonlinearities and friction effects between the different mechanical parts that have not be considered. In addition, the overshoot percentage also does not exceed 7% in the first and second methods and 8% in the third method. All outcomes are scientifically discussed and analyzed to obtain the best approach to design a high performance flexible robotic arm system.

Transmission characteristics analysis and disturbance compensation control strategy for two-inertia system with a flexible link

Transmission characteristics analysis and disturbance compensation control strategy for two-inertia system with a flexible link

Dynamics modeling method dedicated to system models with open- and closed-loop structures subjected to kinematic and task based constraints

The paper presents a development of an automated computational procedure for constrained dynamics (CoPCoD) dedicated to derivation of dynamical models of mechanical systems, e.g. manipulators, both ground and space or mobile robotic systems, which can be composed of rigid and flexible links. They may be subjected to constraints, which are referred to as programmed, which may come from performance requirements, e.g. work or services a system is dedicated to. The CoPCoD structure offers systematic modeling of either open or closed loop constrained structures and results in computationally efficient numerical dynamical equations derivation. The CoPCoD development has its background in the generalized programmed motion equations (GPME) algorithm developed successfully for rigid models of mechanical systems subjected to high order nonholonomic constraints, however, the GPME was not fully automated for computer equation derivations. The two main motivations that underlie the CoPCoD development are to extend the GPME to flexible system models and make it fully automated to computer equation derivations for large classes of systems. The paper presents the general scheme of the CoPCoD architecture and examples which illustrate its application advantages.