Link Manipulator Research Articles

Hybrid vibration control of a Two-Link Flexible manipulator

This research work deals with tip vibration control of a Two-Link Flexible manipulator using hybrid control technique. This technique involves the implementation of unconstrained viscoelastic damping layer on the links in conjunction with active damping using piezoelectric sensors and actuators. Mathematical modelling of the complete system is done using the finite element approach in the inertial frame. Viscoelastic damping is modelled using Kelvin–Voigt elements for which a damping matrix is derived. Active damping is modelled as time-dependent uniformly distributed load applied by the piezoelectric actuator on the flexible link working under feedback control. The angular and linear velocities of the tips of flexible links are used for direct feedback. The unconstrained viscoelastic damping layer effectively reduces the vibrations of the system. The effectiveness of the active control depends upon the relative position of sensors and actuators on the links. The novelty of the work lies in control of torsional and flexural vibrations through the application of passive and active damping methods to the non-inertial frames represented by the manipulator links.

Adaptive containment control of multi-leader fleet of underwater vehicle-manipulator autonomous systems carrying a load

ABSTRACTThis paper addresses the problem of a fleet containment under the leader-follower strategy with direct topology. The complete fleet navigation, guidance and control have been designed using adaptive control and the artificial potential field formation-based approach. The framework is developed to control the navigation and formation of a fleet of underwater vehicle-manipulator systems (UVMs). The proposed containment control approach is a distributed cascade control structure composed of a navigation and guidance controller and a tracking controller. For the path tracking control, adaptive is applied to the general equations of motion of the underwater vehicle equipped with a 3 link manipulator owing to its ability to achieve fast and robust adaptation. Potential field like control has been used for navigation and guidance. The objective is to ensure robust formation maintenance while in motion or in a standby position. Simulation results show the performance of the control approach even when subjected to ocean disturbances.

Quadrature lumped parameter models for flexible long links of manipulators. Part II. Tests and application

Quadrature lumped parameter models for flexible long links of manipulators. Part II. Tests and application

Adaptive back stepping fast terminal sliding mode control of robot manipulators actuated by pneumatic artificial muscles: continuum modelling, dynamic formulation and controller design

Pneumatic Artificial Muscles (PAMs) also called braided pneumatic actuators were invented by Mckibben to help the Polio patients. When the internal bladder is pressurized the actuator gets shorter which can produce a tensile force. PAMs are widely used in bio robotic as well as industrial, medical and rehabilitation robotic applications due to their salient advantages such as high power to weight ratio, flexibility and low cost. However, PAMs exhibit highly non-linear characteristics due to nonlinear mechanical properties of the inner tube and geometrically complex behavior of the outer shell. To use PAMs in engineering applications it is necessary to have an accurate relationship between produced axial force, contraction ratio and applied internal pressure. In this work, a continuum mechanics based model is extended to calculate actuation force of PAMs which is essential in calculation of the required internal pressure as the input signal for control of PAM-based systems. Moreover, dynamic model of a 2-link robot manipulator actuated by PAMs is presented and an adaptive back stepping fast terminal sliding mode controller is applied. Robustness of the utilized method against external disturbances and parameter uncertainties is also investigated. Comparing the model results with experimental data, it is observed the model well predicts mechanical behavior of PAMs. Furthermore, positions and tracking errors are compared with results of an adaptive sliding mode controller. Simulation results obviously demonstrate fast and accurate tracking performance of the applied controller. The developed model can be widely used in design of rehabilitation and also industrial robotic systems.

Numerical study of the hydraulic excavator overturning stability during performing lifting operations

This article presents a numerical study of the stability of a hydraulic excavator during performing lifting operations. A planar dynamic model is developed with six degrees of freedom, which considers the base body elastic connection with the terrain, the front digging manipulator links, and the presence of the freely suspended payload. Differential equations describing the excavator dynamic behavior are obtained by using the Lagrange formalism. Numerical experiments are carried out to study the excavator dynamic stability under different operating conditions during the motion along a vertical straight-line trajectory. It is shown that the arising inertial loads during the movement of the links along the vertical trajectory, combined with the payload swinging and the motion of the base body, decreases the excavator stability. It was found that the excavator stability during following vertical straight-line trajectory decreases considerably in the lower part of the vertical trajectory. If the stability coefficient is close to 1, the payload swinging can cause the separation of a support from the terrain; nevertheless, the excavator stability can be restored. A method for tire stiffness and damping coefficients estimation is presented. The validation of the dynamical model is performed by the use of a small-scale elastically mounted manipulator.

Speed Control of BLDC Using NARMA-L2 Controller in Single Link Manipulator

The BLDC motors are widely used in industrial applications. The load characteristic and controller are important to obtain optimum performance in the speed control of the BLDC motor because some problems are occurred in speed control of nonlinear loads which is used the conventional control methods. The single link manipulator used in robotic applications is a nonlinear system for control algorithms. The load of motor is determined on considering the conversion ratio of the reducer box. In this study, a single link manipulator system consist of BLDC motor, reducer gearbox and robot arm is controlled by using NARMA-L2 controller as known modern control method in used the control of the nonlinear systems. The NARMA-L2 controller is based on neural network. The single link manipulator system is analyzed by using MATLAB/Simulink environment. The speed control of the BLDC motor is performed in conditions the constant and nonlinear load. The results show that the speed control of BLDC motor is performed the high performance in nonlinear loads.

Gain Tuning for High-Speed Vibration Control of a Multilink Flexible Manipulator Using Artificial Neural Network

Abstract Flexible manipulators are associated with merits such as low power consumption, use of small actuators, high-speed, and their low cost due to fewer materials’ requirements than their rigid counterparts. However, they suffer from link vibration which hinder the aforementioned merits from being realized. The limitations of link vibrations are time wastage, poor precision, and the possibility of failure due to vibration fatigue. This paper extends the vibration control mathematical foundation from a single link manipulator to a three-dimensional, two links flexible manipulator. The vibration control theory developed earlier feeds back a fraction of the link root strain to increase the system damping, thereby reducing the strain. This extension is supported by experimental results. Further improvements are proposed by tuning the right proportion of root strain to feed back, and the timing using artificial neural networks. The algorithm was implemented online in matlab interfaced with dSPACE for practical experiments. From the practical experiment done in consideration of a variable load, neural network tuned gains exhibited a better performance over those obtained using fixed feedback gains in terms of damping of both torsional and bending vibrations and tracking of joint angles.

Impact of Viscoelastic Hinged Dampers on Formation of the Stress State of Mobile Machine Manipulators

This research aims the influence analysis of the resistance forces created by viscoelastic dampers in the cylindrical hinges of the manipulators of the transport and technological machines, as well as to the effectiveness of oscillation damping of the metal structure during operation. The construction of the hinged dampers that has been designed by the authors is original. The mathematical model of joint operation of the cylindrical hinge with an excessive backlash and viscoelastic damper has been formed in the article. It is shown that the determinative role of viscous resistance forces involves irreversible energy dissipation of the oscillating rotary movement of the neighboring manipulator links due to oscillating displacement of the hinge pin within the backlash limits in the hinge until the oscillations fade completely. The quantitative analysis of the effectiveness of reducing impact load of the metal structure is performed; moreover the dependence correlations of dynamic process characteristics and engineering factors of the hinged dampers have been determined. Depending on the correlation between stiffness and viscosity of the damper, the effect of viscous resistance forces may not practically occur; it may lead to intensive damping of oscillatory displacement of the hinge pin within the clearance limits. In the latter case, the oscillation process becomes aperiodic with practically complete fading within one oscillation of the hinge pin.

Robust Active Disturbance Rejection Control For Flexible Link Manipulator

SummaryThis paper presents an advanced robust active disturbance rejection control (ADRC) for flexible link manipulator (FLM) to track desired trajectories in the joint space and minimize the link’s vibrations. It has been shown that the ADRC technique has a very good disturbance rejection capability. Both the internal dynamics and the external disturbances can be estimated and compensated in real time. The proposed robust ADRC control law is developed to solve the problems existing in the original version of the ADRC related to the disturbance estimation errors and the variation of the parameters. Indeed, these parameters cannot be included in the existing disturbances and then be estimated by the extended state observer. The proposed control law is based on the sliding mode technique, which considers the uncertainties in the control gains and disturbance estimation errors. Lyapunov theory is used to prove the closed-loop stability of the system. The proposed control strategy is simulated and tested experimentally on one FLM. The effect of the observer bandwidth on the system performance is simulated and studied to select the best values of the bandwidth frequency. The simulation and experimental results show that the proposed robust ADRC has better performance than the traditional ADRC.

Development of system of automatic control of robotic arm drive

Currently, the scope of application of robotic systems and complexes is expanding significantly. The introduction of industrial robots is one of the most promising areas of complex automation of production processes, which will significantly increase labor productivity and save people from monotonous, difficult and harmful work. Many tasks are solved by facilitating robotic manipulators to facilitate human performance and to achieve higher quality and accuracy of production. Thus, thanks to the development of automatic control systems, information technologies and their application in the creation of modern robotic systems, the opportunity has emerged to release a person from work that poses a threat to his life and health. When using manipulator robots, an important task is to develop a control system that provides positioned movement of the links of the manipulator. The main task of the automatic drive control system is to form and implement a set of control effects, in accordance with technological requirements. In this work we propose a system of automatic control of the actuator of the manipulator, which provides positioned movement of the manipulator link along a given trajectory. Using the tables of originals and images of typical functions for which continuous Laplace transforms and Z-transforms are calculated, a discrete linear steady-state mathematical model of the robot-manipulator automatic control system is constructed. The parameters of the corrective devices of the system of automatic control of the electric actuator of the robot manipulator were made, which allowed to improve the characteristics of the transient process, namely: to reduce the time of over-regulation and the duration of the transient. The obtained results of the simulation of transients allow to confirm that the synthesized parameters of the corrective devices for the analog automatic control system can be used in the digital automatic control system of the electric actuator of the robot manipulator.

Quadrature lumped parameter models for long flexible links of manipulators. Part I. Design of the models

Quadrature lumped parameter models for long flexible links of manipulators. Part I. Design of the models

Quasi fixed-time fault-tolerant control for nonlinear mechanical systems with enhanced performance

A novel quasi fixed-time prescribed performance control approach is investigated for mechanical systems with consideration of unknown dynamics and actuator faults. First, a fixed-time stable performance function is developed to quantitatively characterize the transient and steady-state responses. Then, a quasi fixed-time adaptive controller with a pretty simple computational structure is devised based on the developed performance function. Different from the existing finite-time/fixed-time control schemes, the prominent advantages are twofold: (1) no fractional-order state or output information is required, wherein, the order of the states involved in the developed controller just equals to one. (2) the fixed convergence time can be prespecified by the uses instead of relying on several parameters. Finally, applications to a 2-link robotic manipulator are employed to validate the effectiveness of the proposed control approach.

Robustness and Disturbance Rejection of PD/H-∞ Integrated Controller for Flexible Link Manipulator System

Robustness and Disturbance Rejection of PD/H-∞ Integrated Controller for Flexible Link Manipulator System

Prescribed performance control of one-DOF link manipulator with uncertainties and input saturation constraint

In this paper, we mainly address the position control problem for one-degree of freedom &#x0028 DOF &#x0029 link manipulator despite uncertainties and the input saturation via the backstepping technique, active disturbance rejection control &#x0028 ADRC &#x0029 as well as predefined tracking performance functions. The extended state observer &#x0028 ESO &#x0029 is employed to compensate uncertain dynamics and disturbances, and it does not rely on the accurate model of systems. The tracking differentiator &#x0028 TD &#x0029 is utilized to substitute the derivative of the virtual control signals, and the explosion of complexity caused by repeated differentiations of nonlinear functions is removed. The auxiliary system is used to deal with the control input limitation, and the tracking accuracy and speed are improved by predefined tracking performance functions. With the help of the input-to-state stability &#x0028 ISS &#x0029 and Lyapunov stability theories, it is proven that the tracking error can be gradually converged into arbitrarily small neighborhood of the origin, and the tracking error is adjusted by suitable choice of control parameters. The simulation results are presented for the verification of the theoretical claims.

Energy-based Hamiltonian approach in H∞ controller design for n-degree of freedom mechanical systems

This paper studies the energy-based approach for controller design of -degree of freedom mechanical systems. In this approach, the Hamiltonian function, which is the sum of kinetic and potential energies of the system, is considered as the Lyapunov function for stability analysis. The stability analysis is done based on the port-controlled Hamiltonian (PCH) model. In this regard, two theorems are given and proved that the proposed controllers lead to disturbance attenuation for both absolutely known system model and unknown ones with parametric uncertainties. In the case of parametric uncertainties, the energy-based controller has an adaptive approach. Performance of proposed controllers is illustrated through simulations taken on a 2-link robot manipulator system, which validate the theoretical achievements of this paper.

Topology Optimization Of Industrial Manipulator-Link Considering Dynamic Loading

Abstract In the present work, mass of an industrial manipulator-link is minimized using topology optimization method. Topology optimization is established substantial method for mass reduction of structural and machine components. A single link of manipulator is considered for optimization. For optimizing the design region, minimum compliance is chosen as objective function. While robotic arm rotates continuously about a fixed end, applied force acts dynamically on the other end. In such case topology obtained at one angular position is not optimum for other angular positions. Hence, a single topology is not sufficient for dynamic loading condition. Here, a weighted density parameter approach is proposed to consider the dynamic effect and produce a single weighted-topology. To compare the performance of weighted-topology, performance values such as maximum Von-Mises stress and deflection are computed at all discrete angular positions. A MATLAB based routine is developed to generate the weighted-topology and to simulate the performance values. Further, the obtained results are validated using simulation software ANSYS Workbench 18.1. The optimal design of weighted-topology is proven as better compare to any other individual topologies at different angular positions.

Sliding Mode Fractional Order Control for a Single Flexible Link Manipulator

Sliding Mode Fractional Order Control for a Single Flexible Link Manipulator

Designing and Modelling of Nonlinear Controller

Researchers and control engineers have long struggled with the challenge of creating a non-linear controller. Multiple inputs and outputs are available to the robotic manipulators. The focus of this research is on two types of link manipulators. Automation has reduced the number of workers needed to deliver a thorough description of NPID controller dynamics and control structure. NPID was shown to be superior to other proportional integral and derivative controllers because of the nonlinear multiplier it uses in conjunction with the integral controller. Welding, underwater robotics, the industrial painting industry, spot welding, and a slew of other applications all use this controller. It was possible to eliminate the drawbacks of traditional PID controllers while also improving the overall advantages by merging PID controllers with fuse logic, resulting in the development of both of these resilient technologies

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.