Link Manipulator Research Articles

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.

Prescribed finite-time tracking control with input buffer for a manipulator system

The prescribed finite-time trajectory tracking control problem with input buffer is investigated for a linkage manipulator system. The backstepping method is used to design the prescribed finite-time trajectory tracking controller. A new prescribed finite-time performance function is proposed, which can more easily regulate control performance. With the help of this performance function, a constraint control law is designed for the tracking error, and a better transient performance than the existing prescribed finite-time performance function can be obtained under the same parameter conditions for the trajectory tracking process of the manipulator system. At the same time, a control input buffer function is designed, which solves both the overvoltage problem of control input caused by the overlarge position error of the manipulator and the problem that the manipulator system is difficult to start under heavy load. The simulation experiments verify the effectiveness and superiority of the proposed controller.

Design of fixed-time sliding mode control using variable exponents

This paper proposes the design of a robust fixed-time sliding mode controller for a second-order nonlinear system with matched and unmatched uncertainties. First, a fixed-time stable scalar dynamics with a variable exponent is introduced. We establish the global fixed-time stability results for the proposed dynamics using Lyapunov analysis. The maximum convergence time has been derived in terms of the design parameters, which is independent of the initial conditions. These results are then extended to solve the robust fixed-time stabilization for uncertain nonlinear second-order system. Specifically, we proceed with the sliding mode control design, where the sliding surface and the control law are motivated by the proposed scalar dynamics. Moreover, the proposed design is free from singularity and guarantees fixed-time robust stabilization. Simulation results with comparative analysis has been included. Further, experimental validation on a single link manipulator is provided to demonstrate the performance of the proposed approach.

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.

An application of natural matrices to the dynamic balance problem of planar parallel manipulators

Abstract This paper introduces a simplified matrix method for balancing forces and moments in planar parallel manipulators. The method resorts to Newton’s second law and the concept of angular momentum vector, yet it is not necessary to perform the velocity and acceleration analyses, tasks that were normally unavoidable in seminal contributions. With the introduction of natural matrices, the proposed balancing method is independent of the time and the trajectory generated by the moving links of parallel manipulators. The effectiveness of the method is exemplified by balancing two planar parallel manipulators.

Research on the change of the combined moment of inertia for two-link manipulator with angular coordinate system

The main of the problems of the development of two-link manipulators with an angular coordinate system is the lack of effective and universal control systems capable of implementing energy-intensive modes of movement. This is due to the design features of the pointer system of such manipulators and the methods of their use. During the operation of the manipulator, significant dynamic loads occur in its drive system, which create oscillations of the mechanical system and reduce the accuracy of work. The control system must also effectively compensate for such dynamic variations. Dynamic equations of motion used to build manipulator control controllers, which allow taking into account various features of using manipulators. These mathematical models necessarily contain one of the characteristics in the form of the combined moment of inertia of the mechanical system, which is important in the calculation of differential equations and the determination of kinematic parameters of motion. In this article, the combined moments of inertia of the boom system of a two-link manipulator with an angular coordinate system are determined. A study was carry out and it shown that the nature of the change in the combined moments of inertia influenced by the modes of movement of the boom system links. The results of the study showed that the combined moment of inertia of the boom system of the manipulator is not a constant value, which does not change uniformly under special operating conditions of the machine. To determine the combined moments of inertia, the method of bringing the kinetic energy of the moving system to the drive mechanism was apply. This is relevant, because in the future it will be necessary to adjust the unevenness of the movement of the manipulator links by the drive itself. The study was conduct for a typical linear motion mode and a motion mode with a change in speed along a parabolic trajectory.

Design and Simulation of an Innovative Modular Four-Bar Linkage Robotic Arm: Analysis and Applications

In response to the issues of traditional manipulators, such as difficulty in controlling the terminal posture during motion, low control precision, and complex structure, a modular mechanical arm based on a parallel four-bar terminal posture maintenance mechanism has been designed to meet the special requirements of terminal posture maintenance. By analyzing the motion mechanism of the manipulator, the shape space of the manipulator, the terminal position space, and the relationships of forward and inverse kinematics have been derived. A simulation model of the linkage manipulator was established in the Robotic Toolbook for Matlab environment, and structural simulation analysis and kinematic equation verification were conducted. The end positioning and attitude control of different manipulators are simulated by Matlab programming. The working space of the manipulators is calculated by Monte Carlo method, and compared with that of traditional planar manipulators. The results show the validity of the kinematics equation and the rationality of the end positioning control scheme of the linkage manipulator. Finally, the experiment verifies that the attitude retention rate of the modular decoupling manipulator is 97.78% under high load, which verifies the reliability of this scheme. In addition, the manipulator can simplify the complexity of the mechanical structure and complete the control requirements of the terminal attitude under the premise of increasing the working space as much as possible, which lays a foundation for the design and optimization of the manipulator in the field of modular terminal attitude.

Task and motion planning using mixed integer linear programming for solving fetch-and-carry tasks by a mobile manipulator

This manuscript describes a TAsk and Motion Planning (TAMP) method for mobile manipulators. We focus on fetch-and-carry tasks, and we aim to simultaneously generate both a sequence of actions and a motion sequence for each action. The number of factors to be considered in solving such a problem, and the interactions among them are complex due to the multifaceted characteristics of mobile manipulation. As a result, straightforwardly performing simultaneous TAMP may require a significant amount of processing time. Therefore, we reduce the complexity of the problem by formulating fetch-and-carry planning for a Mixed Integer Linear Programming (MILP) problem. The proposed method can obtain the sequence of actions and the movement of the mobile manipulator in less than one second in many cases. The effectiveness of the proposed method is verified in environments in which delivery objects and obstacles are placed in various patterns, using a robot with an omnidirectional mobile platform and a serial link manipulator.

Latent Space Representations for Marker-Less Realtime Hand-Eye Calibration.

Marker-less hand-eye calibration permits the acquisition of an accurate transformation between an optical sensor and a robot in unstructured environments. Single monocular cameras, despite their low cost and modest computation requirements, present difficulties for this purpose due to their incomplete correspondence of projected coordinates. In this work, we introduce a hand-eye calibration procedure based on the rotation representations inferred by an augmented autoencoder neural network. Learning-based models that attempt to directly regress the spatial transform of objects such as the links of robotic manipulators perform poorly in the orientation domain, but this can be overcome through the analysis of the latent space vectors constructed in the autoencoding process. This technique is computationally inexpensive and can be run in real time in markedly varied lighting and occlusion conditions. To evaluate the procedure, we use a color-depth camera and perform a registration step between the predicted and the captured point clouds to measure translation and orientation errors and compare the results to a baseline based on traditional checkerboard markers.

Predefined-Time Adaptive Neural Tracking Control for a Single Link Manipulator with an Event-Triggered Mechanism.

This paper introduces an adaptive trajectory-tracking control method for uncertain nonlinear systems, leveraging a time-varying threshold event-triggered mechanism to achieve predefined-time tracking. Compared to conventional time-triggering approaches, the employment of a time-varying threshold event-triggered mechanism significantly curtails communication resource wastage without compromising the system's performance. Furthermore, a novel adaptive control algorithm with predefined timing is introduced. This method guarantees that tracking errors converge to within a small vicinity of the origin within a predefined timeframe, ensuring all signals in the closed-loop system remain bounded. Moreover, by adjusting a controller-related parameter, we can predefine the upper bound of the convergence time. Finally, the efficacy of the control scheme is corroborated by simulation results obtained from a nonlinear manipulator system.

A Method for Simulating the Positioning Errors of a Robot Gripper

The research is aimed at creating a methodology for increasing the positioning accuracy of an industrial robot and minimizing the vibration of the robot gripper by applying machine learning based on the developed mathematical model for estimating the positioning error. Two components of positioning accuracy are considered: geometric and kinematic errors and elastic static deformations. The dynamic error in the partial system of motion of the robot manipulator links is analyzed. The equation of partial motions is obtained from Lagrange’s differential equation of motion of the II kind. The system of differential equations for the positioning error was solved analytically by Euler’s method. An example of modeling the position and orientation error of the gripper due to temperature deformations of the third link for the manipulator scheme is given. An example of the modeling of static deformations and errors of the manipulator with elastic pliability of the robot links is given. An example of dynamic error modeling in a partial system of motion of the robot links is given. The proposed method of modeling robot gripper positioning errors makes it possible to increase the positioning accuracy of the industrial robot and minimize the vibration of the gripper. Having a mathematical model of positioning errors, it is possible to compensate for the positioning error by changing the speed of movement of the gripper reference point before determining the direct kinematic task.

Режими роботи маніпулятора ремонтно-евакуаційної машини

With modern methods of conducting military operations, the system of technical support of the troops is of great importance. One of the ways to increase the effectiveness of the system of technical support of troops is the use of armored repair and evacuation vehicles. It is possible to increase the technical capabilities of armored repair and evacuation vehicles by modernizing existing models, or creating qualitatively new vehicles that take into account the specifics of use and characteristic combat damage of modern weapons and military equipment, the type of engine of the military vehicle, its weight and dimensions and other characteristics. Improvement and modernization of armored repair and evacuation vehicles allows to ensure their effectiveness. Armored repair and evacuation vehicles demonstrate high efficiency when carrying out operations to extract or lift damaged or stuck, blocked, bogged down, sunken military equipment. In these cases, the traction force of the armored recovery vehicle's own engine is used or its own specialized means of evacuation: crane winches, polyspatch systems, crane booms together with power hydraulic cylinders of their drive, levers, other evacuation equipment. Features of the lifting and loading equipment include such modes of operation as lifting loads from a solid surface, detaching the load from a viscous surface, dragging at different angles to the support surface, and getting stuck. The most difficult in terms of dynamic overloads of all elements of the hydraulic manipulator is the mode of partial immersion and dense sticking of the load in clay soil, when after separation from it, the load under the action of the forces of elastic deformations of the suspension flies up to the height of a significant relaxation of the suspension and reaching the upper point, where its speed is zero, falls down on an elastic suspension. At the same time, a three-fold overload of the manipulator links is observed.

Configuration reconstruction and all-joint synchronous measurement based on vision for segmented linkage manipulator of rigid-flexible dual-arm space robot

A rigid-flexible dual-arm space robot offers promising potential for on-orbit operation due to complementary strengths of its rigid and flexible manipulators. The rigid manipulator has the advantage of large payload capacity and high motion accuracy. The segmented linkage flexible manipulator is ideal for maneuvering in narrow, unstructured environments like internal satellite inspections and maintenance, due to its flexibility and slender body. However, there are inevitable tracking errors due to the multiple cable-driven mechanisms in the flexible manipulator. It’s difficult to get the configuration and end pose of flexible manipulator without adding external sensors. To address these issues, this paper presents a method for configuration reconstruction and all-joint synchronous measurement of the flexible manipulator. The flexible manipulator is captured by the stereovision system mounted on the rigid manipulator. The links’ equivalent center points are recognized by central moment method and edge line extraction method based on the natural characteristics. Joint-to-link kinematic model of flexible manipulator is established to measure joint angles and reconstruct configuration. Several simulations and experiments are carried out to validate the proposed method. The experimental results showed links’ average measurement position errors were less than 13 mm and joint angles reconstructed using the proposed method had an error of approximately 0.35°. These results demonstrate the accuracy and robustness of the proposed method.

Comparative Analysis of Spiral Dynamic Algorithm and Artificial Bee Colony Optimization for Position Control of Flexible Link Manipulators

Comparative Analysis of Spiral Dynamic Algorithm and Artificial Bee Colony Optimization for Position Control of Flexible Link Manipulators

Kinematic and Dynamic Modeling of 3DOF Variable Stiffness Links Manipulator with Experimental Validation

Variable stiffness link (VSL) manipulators are robotic arms that can adjust their link stiffness in real time to improve their adaptability and precision. They are particularly useful in industrial environments where safe collaboration with human workers is required. However, modeling and controlling these non-linear systems is a major challenge due to their complexity. This research paper presents a mathematical model for a 3DOF VSL manipulator, which is the first step towards optimizing performance, improving safety, and reducing costs. The accuracy and reliability of the model are demonstrated through verification experiments that strengthen confidence in its validity for engineering and scientific research. This study contributes to the understanding of the dynamics of VSL manipulators and provides insights for future advances in the use of such robots. By using the proposed model, the efficiency and precision of VSL manipulators can be improved while ensuring safe human–robot interaction in various industrial applications.

Tendon-Driven Continuum Robots for Aerial Manipulation—A Survey of Fabrication Methods

Aerial manipulators have seen a rapid uptake for multiple applications, including inspection tasks and aerial robot–human interaction in building and construction. Whilst single degree of freedom (DoF) and multiple DoF rigid link manipulators (RLMs) have been extensively discussed in the aerial manipulation literature, continuum manipulators (CMs), often referred to as continuum robots (CRs), have not received the same attention. This survey seeks to summarise the existing works on continuum manipulator-based aerial manipulation research and the most prevalent designs of continuous backbone tendon-driven continuum robots (TDCRs) and multi-link backbone TDCRs, thereby providing a structured set of guidelines for fabricating continuum robots for aerial manipulation. With a history spanning over three decades, dominated by medical applications, CRs are now increasingly being used in other domains like industrial machinery and system inspection, also gaining popularity in aerial manipulation. Fuelled by diverse applications and their associated challenges, researchers have proposed a plethora of design solutions, primarily falling within the realms of concentric tube (CT) designs or tendon-driven designs. Leveraging research works published in the past decade, we place emphasis on the preparation of backbones, support structures, tendons, stiffness control, test procedures, and error considerations. We also present our perspectives and recommendations addressing essential design and fabrication aspects of TDCRs in the context of aerial manipulation, and provide valuable guidance for future research and development endeavours in this dynamic field.

Precision motion control of rotary flexible link manipulators using polynomial input trajectories and feedback control

This paper aims to develop a high-precision controller for a flexible link manipulator using polynomial reference, feedforward input, and feedback control. The control objective is to move the tip of the flexible link to a target position as quickly as possible without exciting its resonant modes. Upon a frequency response-based system identification, a frequency-domain feedback controller is designed for reference tracking. The controller includes a proportional-integral controller, a lead filter, and a set of notch filters to control the rigid body and the flexible link dynamics. A set of polynomial reference and feedforward input trajectories are then designed to improve the tracking performance and minimize residual vibrations. The conventional polynomial reference is generated based on the rigid body motion of the system. A revised polynomial reference generation method is then developed by adding flexible motions to the conventional reference. Simulations and experimental tests indicate significant improvements in the performance of the control system using the revised polynomial trajectories.

Tracking control of flexible link manipulator with joint space constraints

Abstract A controller design with system uncertainties, external disturbances, and joint space constraints for a flexible link manipulator (FLM) is presented in this paper. To overcome the lumped disturbance and ensure that the joint space constraints are not violated, a finite-time extended state observer (ESO) and a barrier Lyapunov function are constructed. Using Lyapunov’s theory, the error of the system is proved to be semi-globally ultimately uniformly bounded without violating the constraints. Finally, the rationality of the proposed methodology is verified by numerical simulation.

Retrieving a file binder from a bookshelf using pseudo-curved trajectory generation for a foldable robotic hand

Human-assistive robots need to perform trajectory making for and control of a robotic hand along the many rotating mechanisms in our living spaces. If such trajectory control can be performed without high-cost sensors, certainly a significant cost reduction in building the robot will be achieved. This paper describes a method of retrieving a file binder by generating a pseudo-curved trajectory for tilting it using a simple system. A simple claw mechanism with a switch sensor to grasp an object was designed and 3D-printed, and it was attached to a 6-DOF foldable robotic hand developed by the authors. A method for generating a pseudo-curved trajectory using the switch sensor was developed, and the robotic hand was successfully moved along this trajectory to tilt and grasp a file binder to retrieve it from a bookshelf. Experiments to clarify the success rate were also conducted, and it was found that the results depend on the rotational speed of manipulator links and the vibration of the claw mechanism link. A rubber sponge was added to give flexibility to the claw mechanism, which significantly improved the success rate. Furthermore, a control system to recover from tilting failure was constructed, and its effectiveness was validated by experiments.

Finite Element Method-Based Dynamic Modeling Framework for Flexible Continuum Manipulators

Abstract Flexible continuum manipulators (FCMs) are gaining importance because of their maneuverability and pliability in confined and complex spaces, where rigid link manipulators underperform. However, the dynamic behavior and control of the FCM are quite challenging due to its complex nonlinear behavior. In this study, a finite element-based dynamic model framework is derived that accounts for the geometric nonlinearities and inertial effects. An experimental setup of tendon-driven FCM, consisting of a flexible backbone, is developed to validate the model. The modal analysis of the model is in agreement with the analytical solutions, with less than 10% error. The model is also validated for various loading conditions on the tip-actuated tendon-driven FCM. The steady-state tip position predictions are within 15% of the ground truth.