Link Robot Research Articles

FPGA-Based Fused Smart Sensor for Dynamic and Vibration Parameter Extraction in Industrial Robot Links

Intelligent robotics demands the integration of smart sensors that allow the controller to efficiently measure physical quantities. Industrial manipulator robots require a constant monitoring of several parameters such as motion dynamics, inclination, and vibration. This work presents a novel smart sensor to estimate motion dynamics, inclination, and vibration parameters on industrial manipulator robot links based on two primary sensors: an encoder and a triaxial accelerometer. The proposed smart sensor implements a new methodology based on an oversampling technique, averaging decimation filters, FIR filters, finite differences and linear interpolation to estimate the interest parameters, which are computed online utilizing digital hardware signal processing based on field programmable gate arrays (FPGA).

Robust visual servo control of robot manipulators with uncertain dynamics and camera parameters

In this paper, an image-based robust controller is designed to compensate uncertainties with image Jacobian and robot dynamics due to uncertain depth measurement and load variations. The proposed controller with eye-in-hand structure has separate terms to compensate each of uncertainties. The ultimately uniform boundedness of the closed-loop system is proved by the Lyapunov method. The performance of the proposed control system is demonstrated by experimental results of a 5-link robot manipulator with two degree of freedom.

LMI approach to robust unknown input observer design for continuous systems with noise and uncertainties

The full order robust unknown input observers for continuous systems are presented. The observers are designed for both linear and nonlinear systems considering both noise and uncertainties. First, an unknown input observer is designed for linear systems. The observer is derived based on linear matrix inequality (LMI) approach. Then the observer design problem is extended for a class of nonlinear systems whose nonlinear function satisfies the Lipschitz condition. The main advantage of these observers over the existing works on UIO design is that these can handle both noise and uncertainties simultaneously. The performance of the observers is demonstrated by applying it to the robust state estimation of single link robot arm.

Application of a Genetic Algorithm on the Assessment of the Capabilities of Cctuator Systems for Laser Mircro Adjustment

Laser forming with actuator systems is a very attractive process to meet the rising demand for accuracy in micro system technology. However, the actuator systems have to be designed specifically for the given adjustment task. A computer assisted design system for actuator systems for laser based micro adjustment has been developed which supports the designer by creating a number of optimized design choices from a starting design. A multiobjective genetic algorithm has been successfully applied to this task. The algorithm for evaluation of adjustment capability of the actuator system uses another single objective genetic algorithm to determine the forming capability of the actuator system. The approach is similar to the inverse kinematics algorithm used in robotics but also considers elastic forming. The irradiated components of the actuator system are treated as robotic links for which the amount of laser based forming are the link parameter. An elastic structural mechanic simulation of the actuator system with beam elements calculates the resulting adjustment movement of the actuator system. The research performed to develop a configuration of this algorithm specifically to the needs of actuator system design evaluation is presented in this paper.

U-model based learning feedforward control of MIMO nonlinear systems

In this paper, a learning feedforward controller (LFFC) using the U-model is proposed for a better tracking control of multivariable nonlinear systems over a finite time interval. The multivariable system is modelled using the U-model and the LFFC is established using Newton–Raphson method. U-model significantly simplifies the online synthesis of the feedforward control law. The proposed technique is verified on 2-link robot manipulator in real-time. The performance of the proposed U-model based LFFC is compared with a number of schemes under varying load conditions.

A cohesive modeling technique for theoretical and experimental estimation of damping in serial robots with rigid and flexible links

Dynamic model incorporating damping characteristics, namely joint damping and structural damping in flexible links, of the serial robots with rigid and flexible links is presented. A novel procedure, based on the unified approach of theoretical formulation and analysis of experimental data, is proposed for the estimation of damping coefficients. First, the dynamic model of a robotic system with rigid and flexible links is presented. Next, the modifications in the dynamic model due to the considerations of damping characteristics of joints and structural damping characteristics of the flexible links are presented. A systematic methodology based on analysis of data obtained from experiments is presented for estimation and determination of damping coefficients of rigid-flexible links. The determination of joint damping coefficients, is based on the logarithmic decay of the amplitude of the oscillations of robotic links, while the structural damping coefficients are estimated mainly using the modal analysis and the method of evolving spectra. The method of evolving spectra, based on the Fast Fourier Transform of the decay of the amplitude in structural vibrations of the robot links in progressive windows is used to estimate the structural damping ratios while the critical structural coefficients are determined using the modal analysis. The methodology is illustrated through a series of simple experiments on simple robotic systems. The experimental results are then compared with the simulation results incorporating the damping coefficients determined using the proposed procedure. The comparisons leads to the validation of the proposed dynamic modeling technique, modeling of the damping characteristics, and the method proposed for estimation of damping coefficients for rigid-flexible link robotic systems.

Extended and Unscented Kalman Filtering Applied to a Flexible‐Joint Robot with Jerk Estimation

Robust nonlinear control of flexible‐joint robots requires that the link position, velocity, acceleration, and jerk be available. In this paper, we derive the dynamic model of a nonlinear flexible‐joint robot based on the governing Euler‐Lagrange equations and propose extended and unscented Kalman filters to estimate the link acceleration and jerk from position and velocity measurements. Both observers are designed for the same model and run with the same covariance matrices under the same initial conditions. A five‐bar linkage robot with revolute flexible joints is considered as a case study. Simulation results verify the effectiveness of the proposed filters.

Two new design concepts for snake robot locomotion in unstructured environments

AbstractThis communication presents and justifies ideas related to motion control of snake robots that are currently the subject of ongoing investigations by the authors. In particular, we highlight requirements for intelligent and effcient snake robot locomotion in unstructured environments, and subsequently we present two new design concepts for snake robots that comply with these requirements. The first design concept is an approach for sensing environment contact forces, which is based on measuring the joint constraint forces at the connection between the links of the snake robot. The second design concept involves allowing the cylindrical surface of each link of a snake robot to rotate by a motor inside the link in order to induce propulsive forces on the robot from its environments. The paper details the advantages of the proposed design concepts over previous snake robot designs.

Mechatronic design and control of a planar cooperative robot

This paper presents the simple mechatronic design and control of a planar cooperative robot. The system consists of a pair of three link robots carrying an end-effector on one end of each. The cooperative robot system is driven through a controller designed in MATLAB. The computer is interfaced with this system by using a PIC16F84A and PIC16F877 based circuit. The controller takes in input of the initial and final position of the object that has to be moved and calculates the angles that need to exist between the links. The controller then evaluates the pulses that need to be given to the motors and transfers them to the PIC circuit through a serial port. The PIC in turn generates the signal required for each motor to move. An important point to note is that there is only a certain region in which both the robots can exist at the same time. Some points of robot 1 are out of bounds for robot 2 due to mechanical constraints. So an important concept here is of error handling. The cooperative action is achiev...

A calculation method of the reaction force and moment for a Delta-type parallel link robot fixed with a frame

SUMMARYThe paper presents a method of reaction force and moment calculation for a 3-RSS pure translational parallel link robot (Delta-type parallel robot), in which the inverse and forward kinematics of the parallel link robot are directly analyzed according to kinematic structure of the parallel robot. For dynamic analysis, the parallel robot is imaginarily parted into three serial ones, and their actual joint torques are determined by the virtual work principle. To obtain the reaction force and moment of the parallel robot acting on the base, which is the composition of the reaction forces and moments of the three serial robots, the Newton–Euler Method is adopted. To show the validity of the presented method, the simulation analysis and experimental results are given, the experimental results tally with the calculation value.

Computer-aided-symbolic dynamic modeling for Stewart-platform manipulator

SUMMARYThe Stewart platform manipulator is a fully kinematic linkage system that has major mechanical differences from typical serial link robots. It is a six-axis parallel robot manipulator with a high force-to-weight ratio and good positioning accuracy that exceeds that of a conventional serial link robot arm. This study examines the dynamic equations and control methodology for a Stewart platform. Because manual symbolic expansion of Stewart platform robot dynamic equations is tedious, time-consuming, and prone to errors, an automated derivation process is highly desired. The main goal of this work is to present an efficient procedure for computer generation of dynamic equations for a Stewart platform manipulator. As MATLAB has a powerful signal processing toolbox along with symbolic processing capabilities and is widely used as a common technical computing environment in many universities and research laboratories, the objective of this study was to develop a MATLAB-based approach for symbolic computation for a parallel linked robot. Additionally, a computed-torque control methodology is utilized for such a structure. Simulation results demonstrate the effectiveness of the proposed control methodology.

A fault-tolerant control framework for a class of non-linear networked control systems

In this article, a novel fault-tolerant control (FTC) framework is presented for a class of non-linear networked control systems (NCSs) with Markov transfer delays. First, the NCSs are modelled by non-linear discrete Takagi–Sugeno fuzzy model using Euler approximate method. Then, a sliding mode-based fault estimation technique is developed for such model. With the estimated state and fault information, the proposed FTC framework can maintain the input-to-state stability of the faulty NCSs. A flexible joint robot link example is included to show the efficiency of the proposed method.

로봇팔을 위한 중력보상기 연구

In this paper, a design and analysis of a gravity compensator which is a new device to reduce the joint torque of robots caused due to gravity is presented. Joints of all robots are loaded by large torques due to gravity. By applying the gravity compensator to the robot joints, the load torques applied to the robot joints are reduced by the repulsive force of the gravity compensator such that the size of the joint actuation motor can be reduced. In this paper, the structure and force relation of the gravity compensator are analyzed. The superior performance of the proposed gravity compensator is verified through experiments which measure the joint motor current caused by the load applied to the robot link.

Modeling, simulation and fuzzy control of an anthropomorphic robot arm by using Dymola

Analysis and fuzzy control of an anthropomorphic robot arm on a special trajectory is the subject of this paper. These types of systems are used in cutting operations on materials, joining materials by welding, material handling in remote and dangerous environments, packing of foods, inspection/testing electronic parts or medical products. This robot arm realizes the handling motion on a special trajectory. In this study, the first three links of Mitsubishi RV-2AJ Industrial Robot, are like an anthropomorphic arm, have been modeled and simulated by using Dymola. Kinematic equations have been obtained and mathematical model of this system has been formed by using Lagrange’s Equations. Fuzzy logic controller for the joint angles for the motion trajectory has been designed and the simulation results have been presented at the end of the study.

SVM Based Computed Torque for Robot Manipulator Control

Because of t he strong need of finding easy and robust methods to control robots, many solutions has been proposed in the literature. The computed torque method is a well established robot control technique which takes account of the dynamic coupling between the robot links. However, its main disadvantage lies on the assumption of an exactly known dynamic model which is not realizable in practice. To overcome this issue, we propose in this paper to estimate the dynamics model of the nonlinear system with a machine learning regression method, namely support vector regressor. Then the output of this regressor is thereafter in conjunction with a PD controller to achieve the tracking trajectory task of a robot manipulator.

Iterative feedback control of snake-like robot based on principal fibre bundle modelling

This paper is concerned with point-to-point control of a simple 3-link snake robot, which is a typical example of non-holonomic drift-free systems with complicated controllability structure. First, we give a mathematical model of the snake robot in the form of a system on a principal fibre bundle with the structure Lie group SE (2). Then we propose a set of piecewise-linear/sinusoidal periodic input, and an algorithm which determines its design parameters so that the net effect of the input is approximately equal to the desired displacement. Finally, we give an idea of improving this approximation by an online iterative tuning of the design parameters. Effectiveness of the proposed method is evaluated by numerical simulations.

Adaptation Dominant-Type Adaptive Learning Controller for Robot Manipulators Using a Forgetting Factor

This paper describes a new Adaptation Dominant-Type Adaptive Learning Controller (ADTALC) for trajectory tracking of robot manipulators. In this method, the torque of adaptive controller becomes much larger than the torque of learning controller when the joint angle trajectories converge to the desired ones. In this proposed controller, a forgetting factor is introduced, so that the torque of learning controller approaches zero. The stability of this proposed controller is proved by Lyapunov stability analysis, and its effectiveness is demonstrated by the computer simulation results of a 2-link robot manipulator. This proposed controller provides a novel approach for robot control system to achieve a high-speed and high-precision trajectory tracking.

Flatness-based and energy-based control for distributed parameter robotic systems

The paper presents a comparative study between flatness-based control and energy-based control when applied to flexible link robots. Flatness-based control is an open-loop nonlinear control method which is suitable for differentially flat systems i.e. systems the behavior of which is determined by a finite collection of quantities, consisting of the flat output and its derivatives. On the other hand energy-based control is a closed-loop control method, which unlike the absence of an explicit mathematical model of the flexible-link dynamics can succeed satisfactory performance of the associated control loop. The performance of flatness-based control is tested against energy-based control through simulation experiments.

ISoRA: Humanoid Robot Arm for Intelligent Haptic Interaction with the Environment

The paper concentrates on the development and control of the humanoid robot arm iSoRA, intended for operation in a dynamic unstructured environment. Optical torque sensors integrated into each joint enable measurement of contacting forces along the entire manipulator surface. A variable admittance control strategy was elaborated to increase the robot functionality and to achieve the human-like dynamics of interaction. The experimental results show that the proposed approach not only provides safe interaction of the robot arm with a person, but also improves the effectiveness of contact task performance. The paper also presents a novel concept of avoidance of an obstacle of unknown shape. The tactile sensory ability of the developed manipulator allows robot links to follow the object contour and to perform motion planning in the dynamic environment. The information on the applied normal force vector, object shape and target point coordinates is supplied to the motion planning system. The algorithms for contact point detection, object geometry recognition, and estimation of contacting object stiffness are detailed. The numerical simulation elicits a capability of the proposed method to approximate various object shapes precisely. The experimental results showed that the local admittance control and motion planner allowed the end-effector to follow the object contour in a very smooth, consistent manner while reaching the target point.

2A2-E11 動力学シミュレーションと進化型アルゴリズムを用いた不整地移動ロボットの構造最適化

A wheeled mobile mechanism with a passive and/or active linkage mechanism for travel in rough terrain is developed and evaluated. In our previous research, we developed a wheeled mobile robot which has six wheels and a passive linkage mechanism, and its maneuverability was experimentally verified. The ability to climb over a 0.20 m high bump, which is twice the height of the wheel diameter of 0.10 m, was achieved; and the mobile robot can climb up 0.15 m high continuous steps. In this research, we optimized the mobile robot linkage mechanisms and controller parameters by evolutionary algorithm and Open Dynamics Engine in numerical simulations. In simulations, though the default parameter mobile robot could climb up the 0.20 m high bump, it could not achieve climbing up the two kinds of stairs. On the other hand, the best parameter mobile robot could climb up the three kinds of typical environments.