Link Manipulator Research Articles

Istraživanje prilagodljivosti cevi od ugljeničnih vlakana kod serijskog manipulatora

This work describes the investigation on adapting the carbon fiber tube for building lightweight serial manipulator links. The carbon fiber is chosen based on its significant properties such as lightweight and superior mechanical strength, as an alternative to the existing conventional alloys such as steel and aluminium. A serial manipulator also suffers from a few disadvantages. A typical serial manipulator generally has a structure weight to payload ratio of approximately 200:1, which in turn drastically increases the power and torque requirements of the link actuators. So, there is a need to address this serious problem by investigating the lightweight construction for robot arm links through alternative designs. Such a design will significantly decrease the power requirements of the robot arm without compromising on stability. A comparative study has been done considering three different materials: steel, aluminium and carbon fiber using finite element analysis to check payload capability and stress concentrations.

Control of flexible single-link manipulators having Duffing oscillator dynamics

Abstract Unwanted vibrations caused by the commanded motions lower the positioning accuracy and degrade the control performance of flexible link manipulators. Much work has been devoted to the dynamics and control of flexible link manipulators. However, there are few studies dedicated to the flexible link manipulators having Duffing oscillator dynamics. This paper develops a new model for a flexible single-link manipulator by assuming large mechanical impedance in the drives or large inertia of the motor hub and by considering the flexibility of the single-link manipulator. The derived model includes an infinite number of uncoupled Duffing oscillators by ignoring the modal coupling effects. Two new methods are presented for controlling the vibrations of the flexible manipulator governed by Duffing oscillators. One is designed for the single-mode Duffing oscillator, and the other is for the multi-mode Duffing oscillators. A comparison of these two methods is made using the results of numerical simulations and experimental measurements. Experimental investigations are also performed on a flexible single-link manipulator to validate the dynamic behavior of Duffing oscillators and the effectiveness of the new control methods.

Design and development of non‐perfluorinated ionic polymer metal composite‐based flexible link manipulator for robotics assembly

In this article, a noble ionic polymer metal composite (IPMC) based on sulfonated polyvinyl alcohol (SPVA) and 1‐ethyl‐3‐methylimidazolium tetrachloro aluminate (IL) with deposited Pt was fabricated and used to develop flexible link manipulator. The proposed IPMC was fabricated by simple solution casting method using SPVA and IL with deposited Pt metal by electroless plating method. Herein, SPVA polymer membrane acts as a medium for metal ion migration, and the Pt act as the surface conductive electrode on both sides of the membrane surface. Experimental characterizations such as scanning electron microscopy, cyclic voltammetry and linear sweep voltammetry, load characterization, and actuation performance confirm the excellent electrochemical and electromechanical response as compared with the other reported IPMCs. This method of fabrication exhibits significant advantages, such as the easy process of fabrication using non‐toxic materials. A two‐link flexible manipulator was developed, where the electromechanical behavior of polymer‐based actuator provides an important step for robotic assembly. This shows the potential of flexible compliant fingers and joints in flexible link manipulator for robotic assembly. POLYM. COMPOS., 40:2582–2593, 2019. © 2018 Society of Plastics Engineers

Study on kinematics and inverse dynamics of legged mobile manipulator for determining feet-terrain reaction forces and joint torques

Legged mobile manipulator is a robotic system that consists of a serial manipulator rigidly mounted on a multi-legged platform. Its high mobility and dexterity makes this robotic system more suitable to be used in disaster management and space applications, where there will be an uneven and unstructured terrain. However, its high power consumption and low stability under external disturbances are the challenges to be solved. In this paper, an attempt is made to determine the feet-terrain reaction forces and joint actuating torques, which ensures the minimum power consumption. Initially, the kinematic model of the robotic system is developed using general-purpose rigid body analysis. Newton–Euler approach is then utilized to formulate the coupled dynamics of this multi-body system. The developed inverse dynamics model considers the inertial effects of the manipulator and moving legs on the trunk body and stationary legs. However, it has no unique solution due to its high redundancy. Therefore, it has been formulated as an optimization problem in order to minimize the power consumption after satisfying some functional constraints. The performance of the developed approach has been tested on computer simulations. The results show that the developed model can efficiently study the kinematics and dynamics of the legged mobile manipulator and also explain the nature of shifting of center of gravity of the combined robotic system due to the movement of the manipulator links. The developed model is a generalized one and it can be used for carrying out stability analysis and designing suitable controller for the combined robotic system.

Adaptive fuzzy tracking control of robot manipulators actuated by permanent magnet synchronous motors

This paper presents a model-free controller for robot manipulators driven by permanent magnet synchronous motors (PMSM). The contribution of this paper is merging the electrical and mechanical equations of the robotic system to simplify the controller design procedure. In other words, due to the fact that the manipulator links are the load torques of the PMSMs, the uncertainties related to the manipulator dynamics have been transferred to the voltage equations of the PMSMs. Uncertainties including external disturbances and system dynamics are estimated and compensated in the control law using adaptive fuzzy systems. In contrast to most previous related works that ignore the PMSM electrical equations, both the electrical and mechanical equations are taken into consideration. Based on the Barbalat's lemma, the asymptotic convergence of the tracking error to zero is guaranteed. The case study is an articulated manipulator driven by PMSMs. In comparison with a robust controller for a single-link manipulator actuated by PMSM, the proposed method is superior due to faster and smoother responses.

Analytical Method for Determination of Internal Forces of Mechanisms and Manipulators

This paper presents a theory for the analytical determination of internal forces in the links of planar linkage mechanisms and manipulators with statically determinate structures, considering the distributed dynamic loads. Linkage mechanisms and manipulators were divided into elements and joints. Discrete models were created for both the elements and the entire mechanism. The dynamic equations of equilibrium for the discrete model of the elements and the hinged and rigid joints, under the action of longitudinal and transverse distributed dynamic trapezoidal loads, were derived. In the dynamic equations of the equilibrium of the discrete model of the elements and joints, the connections between the components of the force vector in the calculated cross-sections and the geometric, physical, and kinematic characteristics of the element were established for its plane-parallel motion. According to the developed technique, programs were created in the Maple system, and animations of the motion of the mechanisms were produced. The links were constructed with the intensity of transverse- and longitudinal-distributed dynamic loads, bending moments, and shearing and normal forces, depending on the kinematic characteristics of the links.

Modeling and control of flexible link manipulators for unmodeled dynamics effect

Flexible link manipulators are mostly prefered in applications where energy consumption and faster operation are critically important. Since distributed nature of flexibility makes the system depend on not only time variable but also a spatial variable, the dynamics of flexible structures are expressed by partial differential equations. In the virtue of this kind of modeling, the designers encounter with infinite dimensional systems which means that the system has an infinite number of degrees of freedom. To cope with infinite dimensional systems, one of the most relevant techniques is to truncate the model into a definite order. However, this may yield the unmodeled dynamics that cause performance degradation and even instability. In this paper, the main motivation is to propose control techniques to compensate unwanted effects of unmodeled dynamics which may occur in truncation process. In order to achieve this goal, the linear quadratic Gaussian and the weighted [Formula: see text] controller design are adopted. The performances of the designed controllers are demonstrated on the experimental setup. Besides this motivation, traditional lumped parameter model of the flexible link manipulator which is widely seen in the literature is considered and the superiority of the partial differential equation model is shown on the experimental setup.

Robust Interval Type-2 Fuzzy Sliding Mode Control Design for Robot Manipulators

This paper develops a new robust tracking control design for n-link robot manipulators with dynamic uncertainties, and unknown disturbances. The procedure is conducted by designing two adaptive interval type-2 fuzzy logic systems (AIT2-FLSs) to better approximate the parametric uncertainties on the system nominal. Then, in order to achieve the best tracking control performance and to enhance the system robustness against approximation errors and unknown disturbances, a new control algorithm, which uses a new synthesized AIT2 fuzzy sliding mode control (AIT2-FSMC) law, has been proposed. To deal with the chattering phenomenon without deteriorating the system robustness, the AIT2-FSMC has been designed so as to generate three adaptive control laws that provide the optimal gains value of the global control law. The adaptation laws have been designed in the sense of the Lyapunov stability theorem. Mathematical proof shows that the closed loop control system is globally asymptotically stable. Finally, a 2-link robot manipulator is used as case study to illustrate the effectiveness of the proposed control approach.

Sensorless Reaction Force Estimation of the End Effector of a Dual-arm Robot Manipulator Using Sliding Mode Control with a Sliding Perturbation Observer

We estimated the reaction force for assembly work with a three-link dual-arm robot manipulator using sliding mode control with a sliding perturbation observer (SMCSPO) without using a force sensor. The sliding perturbation observer (SPO) is used to estimate the reaction force of the end effector without using any sensor. The SPO estimates the perturbation, which consists of the parameter uncertainties, nonlinear terms, and disturbances such as the reaction force. During assembly, the most effective perturbation term is close to the reaction force, so we assumed that the estimated perturbation is the same as the reaction force. The estimated perturbation was compared with the reaction force from the dynamics of the manipulator using a simulation with the SimMechanics toolbox of MATLAB/SIMULINK. The simulation results show the performance of the SMCSPO and that the reaction force can be estimated using the SPO without any sensor. The method can improve the structural reduction of link manipulator robots and decrease costs.

EAST in-vessel operation manipulator with failure recovery ability

The Robotics Institute of SJTU has been involved in the development of an in-vessel maintenance operation manipulator system for China’s Experimental Advanced Superconducting Tokamak (EAST) since 2007. Previous work primarily focused on the basic operating principle and extreme environment endurance. In this paper, the failure recovery feature is introduced for the first time for an in-vessel manipulator system. Based on a summary of previous research, we propose a new serial link structured manipulator with failure recovery ability. The main structure of the new manipulator is presented, including the baking cask, manipulator deployment platform, serial link manipulator main body and dual-drive push-rod structure, which gives the manipulator its failure recovery ability. Additionally, the manipulator in-vessel deployment process is simulated on a computer, and basic kinematics analysis is performed to evaluate the feasibility of the proposal.

Learning of operator hand movements via least angle regression to be teached in a manipulator

In this document, a control system is developed to allow a manipulator to learn and plan references from demonstrations given by an operator hand. Data entry is acquired by a sensor and is learned by the generalized learning model with least angle regression to create a desired reference in three dimensional space. A fifth reference profile is employed to smooth the desired reference. Direct and inverse kinematics are gotten to represent the transformation between the three dimensional space and each of the manipulator links. A dynamic model is gotten using Newton–Euler formulation. An evolving proportional derivative (PD) control is applied to get that the manipulator end effector follows the operator hand movements. The monitoring and control systems are implemented in an embedded platform for testing purposes.

Design and qualification tests of a robotic joint module for tokamak in-vessel manipulator use

PurposeThis paper aims to present the design and a prototype experiment of a robotic joint module for tokamak in-vessel manipulator-related research; the results will promote the adaptation of current in-vessel inspection manipulator to achieve full tokamak in-vessel environment compatibility.Design/methodology/approachA flexible metallic bellow-enclosed working chamber is used to protect the main servo drive components, the active cooling method for high temperature protection and the servo control structure simplification for high radiation endurance. A joint module prototype is manufactured and tested under a similar in-vessel environmental condition for extreme condition protection validation and basic servo control ability evaluation.FindingsThe joint module prototype successfully survived the similar in-vessel environment tests and proved good mobility via closed-loop servo control. A conceptual design of a serial linkage manipulator with joint module structure is proposed for future in-vessel inspection manipulator development.Originality/valueThe proposed joint module uses common industrial servo components to achieve its full extreme in-vessel environment compatibility. Different from traditional metallic bellow application in a vacuum environment to produce a linear movement result, the proposed joint module aims to achieve rotating movement directly from the metallic bellow structure, thereby reducing the joint structure space requirement, simplifying the vacuum environment movement transmission structure and increasing the vacuum environment compatibility degree.

Dynamic Modeling and Control of a Flexible Link Manipulators with Translational and Rotational Joints

Flexible link manipulators are widely used in many areas such the space technology, medical, defense and automation industries. They are more realistic than their rigid counterparts in many practical conditions. Most of the investigations have been confined to manipulators with only rotational joint. Combining such systems with translational joints enables these manipulators more flexibility and more applications. In this paper, a nonlinear dynamic modeling and control of flexible link manipulator with rigid translational and rotational joints is presented. This model TR (Translational-Rotational) is developed based on single flexible link manipulator with only rotational joint. Finite element method and Lagrange approach are used to model and build equations of the motion. PID controller is designed with parameters (Kp, Ki, Kd) which are optimized by using Particle Swarm Optimization algorithm (PSO). Errors of joints variables and elastic displacements at the end-effector point are reduced to warrant initial request. The results of this study play an important role in modeling generalized planar flexible two-link robot and in selecting the suitable structure robot with the same request.

Derivation of motion equation for mobile manipulator with viscoelastic links and revolute–prismatic flexible joints via recursive Gibbs–Appell formulations

This paper investigates the dynamic equations of an N-flexible link manipulator with revolute–prismatic joints while considering the effects of manipulator locomotion by the mobile platform bound by non-holonomic kinematic constraints. Such constraints, in addition to creating dynamic interaction between manipulator and platform, cause serious motion limitations and introduction of more computational complexity. The manipulator’s flexible links are modeled by the assumed mode method, where the Timoshenko beam theory is used for the substitution of the assumed mode shapes. The internal and external damping effects are also studied for the model precision. Moreover, revolute–prismatic joints in each arm are exploited to develop the robot mobility. The new joint structure makes it possible to use mobile manipulators with long flexible links. However, in regard to the variations of links length caused by prismatic joints, time-varying dynamic equations are obtained, leading to comparatively complex and lengthy formulations. Therefore, the Gibbs–Appell formulation is utilized as an alternative to the Lagrange equations to facilitate the process of deriving the motion equations. In addition, the non-dimensional form of the Timoshenko beam theory mode shapes is recommended to circumvent the computation of time step mode shapes. It is also necessary to examine the system tip-over stability based on long and variable-length arms, lightweight base, and widespread environmental factors using the zero moment point methods. Finally, a numerical simulation for a mobile manipulator, with two flexible links and revolute–prismatic joints is carried out to demonstrate the performance of the presented model for such complex systems. Different amounts of link elasticity and the effects of internal and external damping coefficients are separately studied. The results are verified by recent fixed base flexible manipulators employing revolute–prismatic joints as well as the IUST Revolute–Prismatic joints experimental setup incorporating rigid links.

Mode shape analysis, modal linearization, and control of an elastic two-link manipulator based on the normal modes

• Global vibration modes of two-link flexible manipulators are calculated. • Effects of uncertainties and design parameter are studied in modal space. • A modal linearization method is proposed for flexible manipulators. • A control scheme based on the linear model is simulated. Accurate determination of mode shapes and resonant frequencies of high-speed slender robotic arms, known as flexible link manipulators, is fundamental for mechanical design, dynamic analysis, identification, and control of the manipulators. This paper presents a Finite Element (FE) modeling, modal analysis, linearization, and control of a Two-Link Flexible Manipulator (TLFM) based on the global vibration modes, which are essentially more precise than the component mode analysis used in most previous studies. The resonant frequencies and the global vibration modes are employed, then, for analyzing the influence of configuration and payload variations, as well as architecture variations using a prismatic joint in the upper arm. The Modal Assurance Criterion (MAC) is adopted as a tool for comparing the mode shapes. Finally, based on the system modes and MAC calculations, a new modal control scheme is proposed for a multi-stage rest-to-rest maneuver of the manipulator.

Obstacle avoidance handling and mixed integer predictive control for space robots

This paper presents a novel obstacle avoidance constraint and a mixed integer predictive control (MIPC) method for space robots avoiding obstacles and satisfying physical limits during performing tasks. Firstly, a novel kind of obstacle avoidance constraint of space robots, which needs the assumption that the manipulator links and the obstacles can be represented by convex bodies, is proposed by limiting the relative velocity between two closest points which are on the manipulator and the obstacle, respectively. Furthermore, the logical variables are introduced into the obstacle avoidance constraint, which have realized the constraint form is automatically changed to satisfy different obstacle avoidance requirements in different distance intervals between the space robot and the obstacle. Afterwards, the obstacle avoidance constraint and other system physical limits, such as joint angle ranges, the amplitude boundaries of joint velocities and joint torques, are described as inequality constraints of a quadratic programming (QP) problem by using the model predictive control (MPC) method. To guarantee the feasibility of the obtained multi-constraint QP problem, the constraints are treated as soft constraints and assigned levels of priority based on the propositional logic theory, which can realize that the constraints with lower priorities are always firstly violated to recover the feasibility of the QP problem. Since the logical variables have been introduced, the optimization problem including obstacle avoidance and system physical limits as prioritized inequality constraints is termed as MIPC method of space robots, and its computational complexity as well as possible strategies for reducing calculation amount are analyzed. Simulations of the space robot unfolding its manipulator and tracking the end-effector’s desired trajectories with the existence of obstacles and physical limits are presented to demonstrate the effectiveness of the proposed obstacle avoidance strategy and MIPC control method of space robots.

A New Approach to the Rigid Finite Element Method in Modeling Spatial Slender Systems

The static and dynamic analysis of slender systems, which in this paper comprise lines and flexible links of manipulators, requires large deformations to be taken into consideration. This paper presents a modification of the rigid finite element method which enables modeling of such systems to include bending, torsional and longitudinal flexibility. In the formulation used, the elements into which the link is divided have seven DOFs. These describe the position of a chosen point, the extension of the element, and its orientation by means of the Euler angles Z[Formula: see text]Y[Formula: see text]X[Formula: see text]. Elements are connected by means of geometrical constraint equations. A compact algorithm for formulating and integrating the equations of motion is given. Models and programs are verified by comparing the results to those obtained by analytical solution and those from the finite element method. Finally, they are used to solve a benchmark problem encountered in nonlinear dynamic analysis of multibody systems.

Control of Serial Link Manipulator Using a Fractional Order Controller

This paper proposes a fractional-order controller for serial link manipulator to track desired trajectories in the joint space. The proposed control strategy consists of two main parts. First, a PID fractionional controller is developed using five parameters. By adding the extra degrees of freedom, the fractional order controller can achieve better control performance than the conventional PID controller. In contrast of the first part of the proposed controller which depends on the error between the desired and real values, the second part depends on the robot dynamics. This proposed control law guarantees the global asymptotic stability of the tracking errors. This global stability is proved using Lyapunov theory. The control strategy is tested ona 2 DOF robot manipulator. Simulation results and the comparison with the computed torque approach show the effectiveness of the approach with good tracking performance.

ANALYSIS OF AIR-SPRING FOR A LINK OF HYPER-REDUNDANT MANIPULATOR

Urgency of the research. This research paper deals with a designing and analyzing of link for hyper-redundant manipulator/mechanism. The paper investigates 6-DOF manipulator link, consisting of pneumatic as well as electromagnetic actuators. A motion of upper platform of the link is reached by pneumatic actuators, namely air-springs. The main focus of this research is analysis of air-spring and its properties. From this reason FEM analysis is done in software SolidWorks. In the conclusion the results are discussed. Pneumatic actuators can play interesting role in order to be possible to change the mechanical properties of the manipulators. Target setting. Analysis of air-spring actuator for hyper-redundant manipulator. Actual scientific researches and issues analysis. Most of robotic arms consist of electrical actuators. Using pneumatic actuators the manipulator gets new properties like changing stiffness. Uninvestigated parts of general matters defining. Air-springs are still in the process of investigation from the view of mechanisms actuator. The research objective. In the paper simulations and analysis of the air-spring are done. The statement of basic materials. This paper investigates the area of modeling in software SolidWorks. At first CAD model of new segment for hyperredundant manipulator is introduced and its basic parts are described. Then, in the preprocessing phase, the detailed steps of its setup SolidWorks computation core were described. The second half of the article is to focus on the calculation and assessment of simulation results. Conclusions. The paper introduces new kind of manipulator link. The link is analyzed and tested by simulation.

An Updating Method for Finite Element Models of Flexible‐Link Mechanisms Based on an Equivalent Rigid‐Link System

This paper proposes a comprehensive methodology to update dynamic models of flexible‐link mechanisms (FLMs) modeled through ordinary differential equations. The aim is to correct mass, stiffness, and damping matrices of dynamic models, usually based on nominal and uncertain parameters, to accurately represent the main vibrational modes within the bandwidth of interest. Indeed, the availability of accurate models is a fundamental step for the synthesis of effective controllers, state observers, and optimized motion profiles, as those employed in modern control schemes. The method takes advantage of the system dynamic model formulated through finite elements and through the representation of the total motion as the sum of a large rigid‐body motion and the elastic deformation. Model updating is not straightforward since the resulting model is nonlinear and its coordinates cannot be directly measured. Hence, the nonlinear model is linearized about an equilibrium point to compute the eigenstructure and to compare it with the results of experimental modal analysis. Once consistency between the model coordinates and the experimental data is obtained through a suitable transformation, model updating has been performed solving a constrained convex optimization problem. Constraints also include results from static tests. Some tools to improve the problem conditioning are also proposed in the formulation adopted, to handle large dimensional models and achieve reliable results. The method has been experimentally applied to a challenging system: a planar six‐bar linkage manipulator. The results prove their capability to improve the model accuracy in terms of eigenfrequencies and mode shapes.