Parallel Robots

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Identifiability of the Dynamic Parameters of a Class of Parallel Robots in the Presence of Measurement Noise and Modeling Discrepancy

Journal Title, Volume, Page: 
Mechanics Based Design of Structures and Machines: An International Journal Volume 36, Issue 4, 2008
Year of Publication: 
2008
Authors: 
Miguel Díaz-Rodríguez
Departamento de Tecnología y Diseño, Facultad de Ingeniería, Universidad de Los Andes, Mérida, Venezuela
Vicente Mata
Departamento de Ingeniería Mecánica y Materiales, Universidad Politécnica de Valencia, Valencia, España
Nidal Farhat
Departamento de Ingeniería Mecánica y Materiales, Universidad Politécnica de Valencia, Valencia, España
Current Affiliation: 
Department of Mechanical Engineering, Faculty of Engineering, An-Najah National University, Nablus, P.O. Box 7, Palestine
Sebastian Provenzano
Departamento de Tecnología y Diseño, Facultad de Ingeniería, Universidad de Los Andes, Mérida, Venezuela
Preferred Abstract (Original): 
Advanced model based control schemes and the solution of the direct dynamic problem requires accurate knowledge of the dynamic parameters of robotic systems, mainly the inertial properties of the links and the friction parameters at the kinematic joints. A well known and a very useful tool for their determination is through a dynamic identification process. Normally, in this process, only a subset of the dynamic parameters of a robot, known as “base parameters”, can be identified. When parameter identification is performed experimentally, not all the aspects of the robot can be modeled in detail. Moreover, measurement variables are affected by noise. These sources of error lead to the fact that not all the base parameters can be properly identified. Therefore, in this paper, the identifiability of the dynamic parameters of a class of parallel robot, in the presence of noise in measurement and discrepancy in modeling, is addressed. The analysis is carried out by means of a simulated robot and over an actual parallel 3-RPS robot.
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Dynamic Simulation of a Parallel Robot: Coulomb Friction And Stick–Slip In Robot Joints

Journal Title, Volume, Page: 
Robotica, Volume 28, Issue 01, January 2010, pp 35-45
Year of Publication: 
2010
Authors: 
Nidal Farhat
Departamento de Ingeniería Mecánica y de Materiales, Universidad Politécnica de Valencia, Spain
Current Affiliation: 
Department of Mechanical Engineering, Faculty of Engineering, An-Najah National University, Nablus, P.O. Box 7, Palestine
Vicente Mata
Departamento de Ingeniería Mecánica y de Materiales, Universidad Politécnica de Valencia, Spain
Álvaro Page
Departamento de Física Aplicada, Universidad Politécnica de Valencia, Spain
Miguel Dıaz-Rodriguez
Departamento de Tecnología y Diseño, Facultad de Ingeniería, Universidad de Los Andes, Venezuela
Preferred Abstract (Original): 
Dynamic simulation in robotic systems can be considered as a useful tool not only for the design of both mechanical and control systems, but also for planning the tasks of robotic systems. Usually, the dynamic model suffers from discontinuities in some parts of it, such as the use of Coulomb friction model and the contact problem. These discontinuities could lead to stiff differential equations in the simulation process. In this paper, we present an algorithm that solves the discontinuity problem of the Coulomb friction model without applying any normalization. It consists of the application of an external switch that divides the integration interval into subintervals, the calculation of the friction force in the stick phase, and further improvements that enhance its stability. This algorithm can be implemented directly in the available commercial integration routines with event-detecting capability. Results are shown by a simulation process of a simple 1-DoF oscillator and a 3-DoF parallel robot prototype considering Coulomb friction in its joints. Both simulations show that the stiffness problem has been solved. This algorithm is presented in the form of a flowchart that can be extended to solve other types of discontinuity.
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Identification of Dynamic Parameters of A 3-DOF RPS Parallel Manipulator

Journal Title, Volume, Page: 
Mechanism and Machine Theory Volume 43, Issue 1, January 2008, Pages 1–17
Year of Publication: 
2008
Authors: 
Nidal Farhat
Departamento de Ingeniería Mecánica y de Materiales, Universidad Politécnica de Valencia, C/Camino de Vera s/n, 46022 Valencia, Spain
Current Affiliation: 
Department of Mechanical Engineering, Faculty of Engineering, An-Najah National University, Nablus, P.O. Box 7, Palestine
Vicente Mata
Departamento de Ingeniería Mecánica y de Materiales, Universidad Politécnica de Valencia, C/Camino de Vera s/n, 46022 Valencia, Spain
Alvaro Page
Departamento de Física Aplicada, Universidad Politécnica de Valencia, C/Camino de Vera s/n, 46022 Valencia, Spain
Francisco Valero
Departamento de Ingeniería Mecánica y de Materiales, Universidad Politécnica de Valencia, C/Camino de Vera s/n, 46022 Valencia, Spain
Preferred Abstract (Original): 

In this paper, the dynamic parameters, both inertial and frictional, of a 3-DOF RPS parallel manipulator are identified considering two important issues: the physical feasibility of the identified inertial parameters and the use of nonlinear friction models in the identification process in order to model the friction phenomenon at robot joints. The dynamic model of the parallel manipulator is obtained starting from the Gibbs–Appell equations of motion along with the Gauss principle of Least Action, and these equations of motion are rewritten in a/their linear form with respect to the inertial parameters of the mechanical system. At this point, in accordance with the friction model considered, either linear or nonlinear, two types of dynamic models are dealt with: the totally and the partially linear with respect to the parameters to be identified. In order to solve the identification problem when nonlinear friction models are included, a nonlinear constrained optimization problem will be formulated and solved, instead of the Least Square Method, which is valid only for linear identification problems. It must be mentioned that the above-mentioned optimization problem will include the physical feasibility of the identified parameters in its formulation. The proposed procedure will be verified against a virtual parallel manipulator and finally, experimental identification processes are carried out over an actual parallel manipulator and a comparison is made between the LSM and the optimization process in the case of linear friction models, and between the linear and nonlinear friction models in the optimization process.

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