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Practical Approaches for Robot Dynamic Model Implementation for Control and Simulation Purposes
Abstract
A robot dynamic model is time variable, highly non-linear and characterized by coupling effects among the robot joints. Consequently, a derivation and implementation of a robot dynamic model, which is used for purposes of control, simulation, and mechanical design, often represents a challenging task. The last couple of decades saw a great amount of research with the aim to achieve better ease of use (development) and computational efficiency of robot dynamic algorithms. Recently, general-purpose robot modeler/simulator software that enables numerical calculation of robot inverse dynamics problem for user-developed robot model and input joint trajectories are being increasingly used by a wider range of robot developers for robot control purposes. In this study, two different practical approaches to account for robot dynamics for purposes of robot control, trajectory generation, mechanical design and simulation, are discussed. The first approach includes an efficient solution for forward dynamics using a novel modified recursive Newton–Euler algorithm, which is used for simulation, mechanical design, and trajectory generation. The second approach is based on modern software tools usage, for the purposes of simulation and control. Both strategies for implementation of robot dynamic model are based on developed 3D models of robots in CAD software and 3D modelers. Applied approaches are demonstrated in three different case studies. Discussion on the benefits of the presented approaches is given.KeywordsRobot dynamicsSimulationControlClosed-formNewton–EulerSoftware
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This paper presents a method for the
implementation of a robot forward kinematics algorithm that
complies with the Denavit-Hartenberg (DH) convention in Robot
Operating System (ROS). The integration of the algorithm in
ROS is based on the representation of DH parameters in dual
quaternion space. The main motivation for the presented
research is to make use of ROS powerful visualization tools
available in tasks that require robot forward kinematics
calculation while keeping the principles of DH robot modeling
convention. Implementation of the dual quaternion-based robot
forward kinematics algorithm in ROS is demonstrated using a
serial 6DoFs robot as an example.
Modern combat aircraft can fly at unusual orientations. The spatial disorientation trainer (SDT) examines a pilot's ability to recognise these orientations, to adapt to unusual positions and to persuade the pilot to believe in the aircraft instruments for orientation and not in his own senses. The SDT is designed as a four-degree-of-freedom (4DoF) manipulator with rotational axes. Through rotations about these axes, different orientations can be achieved; different acceleration forces acting on the pilot can also be simulated. In this paper, a control algorithm of an SDT that improves the quality and safety of the SDT motion while improving position accuracy and reducing servo errors is proposed. This control algorithm uses approximate inverse dynamics based on the recursive Newton–Euler algorithm, which accounts for the motors present in the system; it calculates motor torques, as well as the forces and moments acting on the SDT links based on the achievable velocities and accelerations of the robot links. This algorithm enables accurate dimensioning of the axes bearings and links as well. The maximum possible accelerations of the SDT links are calculated in each interpolation period based on the total moments of inertia for the axes of rotation of these links, mutual influences of the link accelerations on each other, and motor capabilities. The forces, moments and torques that act on the SDT links obtained with the suggested algorithm have lower magnitude and smoother profile. In this study, the forces and angular velocities that act on the simulator pilot in the SDT are calculated along with the roll and pitch angles of the gondola for these forces.
This paper presents OpenSYMORO, an open-source software package for symbolic modelling of robots. This software package is based on previous work detailed in [1]. However, the package in [1] was developed using Wolfram Mathematica and hence required Mathematica license for use. OpenSYMORO is mainly developed using the Python programming language and the source code will be publicly available. The new version provides support to model robots with flexible joints, floating base and wheeled mobile robots. This is in addition to supporting serial, tree structure and closed-loop robots. A visualisation tool to view the structure of the robot is also included.
Pilots of modern combat aircraft are exposed to the devastating effects of high acceleration forces. The pilots׳ ability to perform tasks under these extreme flight conditions must be examined. A centrifuge motion simulator for pilot training is designed as a 3DoF manipulator with rotational axes. Through rotations about these axes, acceleration forces that act on aircraft pilots are simulated. Because of the possibilities of present actuators, it is notably difficult to produce a centrifuge that can realise all of the desired changes of the acceleration forces completely accurately. For this reason, it is necessary to make a compromise in the centrifuge׳s design with regard to the motor choices and link designs. A new control algorithm that contains a new algorithm for the inverse dynamics of the robots (based on the recursive Newton–Euler algorithm) and that accounts for the possible motor actions has been developed in this study. This algorithm first calculates the successive actuator torques of the links, which are required for the given motion during each interpolation period. Next, the algorithm checks whether actuators can achieve these torques, and if they cannot, it calculates the maximal successive link angular accelerations that motors can achieve. Based on this, control unit sends appropriate control inputs. As a result, the quality of the motion control is improved, and a precise calculation of the forces and the moments that act on the centrifuge links (which is necessary to calculate the link strengths) is performed.
A development of a robot control system is a highly complex task due to nonlinear dynamic coupling between the robot links. Advanced robot control strategies often entail difficulties in implementation, and prospective benefits of their application need to be analyzed using simulation techniques. Computed torque control (CTC) is a feedforward control method used for tracking of robot’s time-varying trajectories in the presence of varying loads. For the implementation of CTC, the inverse dynamics model of the robot manipulator has to be developed. In this paper, the addition of CTC compensator to the feedback controller is considered for a Spatial disorientation trainer (SDT). This pilot training system is modeled as a 4DoF robot manipulator with revolute joints. For the designed mechanical structure, chosen actuators and considered motion of the SDT, CTC-based control system performance is compared with the traditional speed PI controller using the realistic simulation model. The simulation results, which showed significant improvement in the trajectory tracking for the designed SDT, can be used for the control system design purpose as well as within mechanical design verification.
Conventional methods for solving robot forward dynamics are characterized by high com- putational complexity. Recursive Newton-Euler algorithm (RNEA) is the most efficient com- putational method used for deriving a manipulator’s dynamic equations of motion. In order to solve robot forward dynamics using RNEA in the most widely used Walker and Orin’s method 1, it is necessary to execute RNEA n + 1 times, where n is the number of degrees- of-freedom (DoF). Herein, a simple and efficient method to solve forward dynamics using the modified RNEA (mRNEA) only once is presented. The proposed method is significantly more beneficial when used for robot simulations as it does not require calculating joint torques as inputs for forward dynamics unlike other methods. Further, an algorithm that calculates the joints’ accelerations based on forward dynamics while considering the ac- tuators’ force/torque saturations and achieves a realistic simulation of robot movements is presented. The proposed mRNEA, its application in the presented forward dynamics al- gorithm, and the efficiency of the presented algorithms are demonstrated using a serial 6-DoF robot as an example.
This paper presents a dynamic model-based design of a control system and an approach toward a drive selection of a centrifuge motion
simulator (CMS). The objective of the presented method is to achieve the desired performance while taking into account the complexity of the
control system and the overall device cost. An estimation of a dynamic interaction of the interconnected CMS links motions is performed using
the suitable inverse dynamics simulation. An algorithm based on the approximate inverse dynamics model is used within the drive selection
method. The model of the actuator’s mechanical subsystem includes the effective inertia (inertia reflected on the rotor shaft) calculated from
the inverse dynamics model. A centralized control strategy based on a computed torque method is considered and compared to traditional
decentralized motion controllers. To obtain an accurate comparison of the suggested control methods through a realistic simulation, structural
natural frequencies of the manipulator links are considered, and the actuator capabilities are taken into account. The control system design
and simulation methods and the drive selection strategies, presented here for the CMS, are applicable within the general robot manipulator’s
domain.
This paper presents advantages of using open architecture for the real-time control of robot manipulators, parallel kinematics machine tools and other multi-axis machining systems. In order to increase their competitiveness, companies need to follow the global economy requirements. The constant incorporation of new technologies into existing controllers and reduction in the development time and costs are the main objectives. An open architecture control (OAC) concept appears as a solution to deal with these requirements. This article explains the rationale for the development of OAC systems, presents the major international activities which propose various approaches to OACs and a series of controllers that have been developed using this design philosophy at the Lola Institute.
In this paper a new Robot Modeling/Simulation Toolbox for Matlab is presented. The primary purpose of this toolbox is to generate all the common equations required for robot control design. It can compute the kinematic and dynamic equations of a serial robot in closed-form. The toolbox generates codes for the most representative matrices of the robot dynamics. For example, the Inertia Matrix, Coriolis Matrix, Gravitational Torques Vector and most important the Robot Regressor can be computed in closed-form with symbolic representation. This toolbox uses the Denavit-Hartenberg (DH) and Euler-Lagrange Methodologies to compute the Kinematic and Dynamic models of the robot. Furthermore, it automatically generates useful code for these models, such as M-Files, Simulink model and C/C++ code, allowing easy integration with other popular Matlab toolboxes or C/C++ environments. The only requirement from the user are the DH parameters, making it an easy to use tool. For 3D visualization, the toolbox supports different methods. The primary contribution is the automation and simplification of the robot modeling process which is important for correct robot design and control. In addition, the easy to use GUI and simplified models allow rapid prototyping and simulation of robots and control design/validation. As a proof of concept, validation of the computed models of a real industrial robot is included, where the toolbox was used to compute all the robot models. Thereafter, using the motion equations generated by this toolbox, a Dynamic Compensation Control was designed and implemented on a Staubli TX-90 industrial robot in order to demonstrate how this toolbox simplifies the process.
This paper reviews some of the accomplishments in the field of
robot dynamics research, from the development of the recursive
Newton-Euler algorithm to the present day. Equations and algorithms are
given for the most important dynamics computations, expressed in a
common notation to facilitate their presentation and comparison
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