Papers by Keyword: Parallel Robot

Abstract: The paper presents the functional analysis of a parallel robotic system used for transperineal prostate biopsy. A simulation system to study the robot functional analysis was developed using the integrated MATLAB software. Given the fact that the robotic system is used in a medical environment, it has to meet certain safety requirements indicated by the medical doctors. In order to fulfill these needs an appeal to complex simulation software has to be made to help choosing the best kinematic solution for the robotic system. The designed simulation software offers a correlation between the structure of the robot and the surrounding medical environment, pointing out its workspace and possible configurations that might harm the human patient during the biopsy.

Abstract: Trajectory tracking control of compliant parallel robot is presented. According to the characteristics of compliant joint, the system model is derived and the dynamic equation is obtained based on the Lagrange method. Radial Basis Function (RBF) neural network control is designed to globally approximate the model uncertainties. Further, an itemized approximate RBF control method is proposed for higher identify precision. The trajectory tracking abilities of two control strategies are compared through simulation.

Abstract: The use of parallel manipulators in industrial is growing. Among key advantages of parallel manipulators versus their serial counterparts, is their improved end-effector positioning accuracy than open-loop mechanism. However, undesirable dimensional tolerance and joint clearance can decrease the positioning accuracy of the end-effector. In this article, Taguchi method is applied to a 3-PSP parallel manipulator to determine how dimensional tolerance and joint clearance affects the accuracy of its end effector. Because of random nature of dimensional tolerance, it is assumed that actual value of all kinematic parameters are normally distributed. Taguchi method is then used and effect of tolerance on accuracy for each of the manipulator kinematics parameters is obtained. Finally, a tolerance set resulting in best accuracy is predicted by the Taguchi method. This tolerance is verified with a new set of experiment.

Abstract: This work tends to deal with the multi-objective dynamic optimization problem of a three translational degrees of freedom parallel robot. Two global dynamic indices are proposed as the objective functions for the dynamic optimization: the index of dynamic dexterity, the index describing the dynamic fluctuation effects. The length of the linkages and the circumradius of the platforms were chosen as the design variables. A multi-objective optimal design problem, including constrains on the actuating and passive joint angle limits and geometrical interference is then formulated to find the Pareto solutions for the robot in a desired workspace. The Non-dominated Sorting Genetic Algorithm (NSGA-II) is adopted to solve the constrained nonlinear multi-objective optimization problem. The simulation results obtained shows that the robot can achieve better dynamic dexterity and less dynamic fluctuation simultaneously after the optimization.

Abstract: This paper proposed a new method to downgrade the kinematic mathematical model of parallel robots. A technique of complement mathematical models uses constraints to change the form of objective functions. An equivalent structure is used to replace the original structure of investigated robots. The difficulties encountered in solving problems having the transcendental form can be avoided by downgrading formula of the new mathematical model. The original formula which is usually in quaternary order can be downgraded to quadratic form. The main advantages of this method are understandable mathematical basis, high accuracy, and quick convergence. Carrying out solutions for pracitical kinematic problems of parallel robots becomes very promissable.

Abstract: The major disadvantage of the parallel robot is that the singular positions are comprised into the work space. The singular positions are the particular poses for parallel robot DELTA where the mobility of the structure is not longer zero when the actuators are locked. Present analysis is focused on the determinant value of the Jacobian matrix of the kinematic analysis equation system, written using Denavit – Hartenberg transformation matrices. The kinematic equations possess the algebraic and trigonometric character, so that the inverse singularity analysis can be formulated. By instantaneous mobility analysis of the moving platform of the parallel robots, the geometric conditions for the forward singularity configurations are identified. Finally, a numerical example is solved in order to illustrate the variation of the Jacobian determinant in the proximity of a singular position.

Abstract: The paper presents a new medical parallel robot for brachytherapy. Brachytherapy (BT) is a relatively new and efficient medical technique for cancer treatment that enables to deliver higher doses of radiation to more-specific areas of the body, compared to the conventional form of radiation therapy that projects radiation from a machine outside the body. BT implies the implant of radioactive seeds inside the tumor, through specific needles, thus affecting only the tumor while avoiding unnecessary irradiation of the healthy tissue. Compared to the most of the brachytherapy designed only for treating the prostate, the medical robot presented in the paper is designed for hard-to-reach areas (such as the retroperitoneal area or the mediastinum). An approach regarding the robot structural synthesis, kinematics is presented followed by some simulation results obtained for a specific BT needle trajectory.

Abstract: Brachytherapy (BT) is a modality to treat cancer by inserting needles into a patient to deliver radioactive sources direct to the diseased tissue. The efficiency of the treatment is determined by the positions of the needles. A robot can be used in order to increase the precision of the needles locations. This paper presents an approach for needle trajectory planning based on isomorphic mapping from a haptic device. A virtual reality environment has been modelled containing a 3D reconstructed abdominal model of the patient. Needle insertion using the BT robot is controlled using a Force Dimension Omega haptic device. The developed software application allows the users to practice robotic needle insertion and to determine the most appropriate locations for the BT needles.

Abstract: In order to achieve greater workspace motion, it’s designed a high aspect ratio 3-PPSR flexible parallel robot, driven by a piezoelectric motor, connected by flexible hinges, which has the advantages of simple structure, non singular, seamless, high motion precision. Because of the stiffness of the system directly affecting the motion accuracy, load bearing performance, according to the characteristics of high aspect ratio flexible hinge, It’s established the mathematical model of flexible hinge through finite element method. Using method of integral stiffness, conbined coordination equation with force balance equation, the flexible stiffness model of system is obtained. Finally, through using Ansys, it’s confirmed the validity of the theoretical model by comparing of the theoretical stiffness model results with the finite element analysis of the model results, to provide a reliable guarantee for optimization and analysis of kinematics and dynamics of flexible parallel robot.

Abstract: A 3-axis parallel loading mechanism, which works as a multi-axis load simulator, is proposed for reliability test of multi-axis CNC machine tools by exerting specific load spectrums on the spindle. To achieve efficient loading force control, dynamic model of the 3-DOF translational parallel robot is derived via the virtual work principle and is embedded into the control strategy to build a model-based control scheme. A mass distribution factor is introduced and the rotating inertia of the limbs is neglected to simplify the dynamics equations for better real-time control performance. This simplification method is verified by comparison with the complete dynamics model. Then the simplified dynamic model is integrated with a PI (proportional–integral) controller with feedforward to control the moving platform’s output force in the task space and this control strategy is verified through co-simulations with MATLAB/Simulink and ADAMS. Simulation results show that the proposed model-based PI controller is effective to control the three-dimensional output force of the 3-DOF translational parallel robot.