parallel robot

This paper examines a parallel robot with 5 degrees of freedom with a linear platform. Parallel robots, have a restricted workspace, and singularities make the workspace even more confined. So the behavior of the robot in the working place is examined by focusing on kinematics and dynamics. To do kinematic analysis, the constraint equations are developed using the geometric relations, and the speed and acceleration equations of the robot are derived. The jacobian matrix is then calculated using the screw theory, and the state of the singularities in the workspace is determined based on the jacobian matrix. Considering the singularity and physical and geometric limitations, an algorithm for calculating the workspace is presented. In addition, the kinematic index of dexterity is investigated using the jacobian matrix as a measure of the robot's closeness to the singular configurations. The results of solving kinematic and dynamic problems are validated with the output of the simulation in MATLAB software.

Since forward kinematics in parallel robots has more difficulty and often does not lead to an analytical solution, in most studies, inverse kinematics has been preferred for parallel robot calibration. In this study, a technique was presented that does not need to completely solve direct kinematics. With the help of the forward kinematics, variation of the end effector with respect to the deviation of the kinematics parameters has been calculated. Then, by linearizing the equations, the possibility to use the linear least squares has been provided. The presented model like Zero-Reference model and Product of Exponential Formula, only uses one fixed reference frame and unlike D-H model does not have singularity problems. In the simulation, it was shown that the algorithm with a small number of selected poses and with high speed in a fraction of a second by a few iterations reaches an answer in the range of nanometers. Also, by using stereo vision, the presented theory was experimentally examined and shown that the proposed algorithm can reach the accuracy of the measuring instrument, similar to the simulation results.

In most research on parallel cable robots, control input energy norm (with two-squared cost function), also known as the least-squares method is widely used, but in addition to the advantages of this method, such as smoothness and differentiable, in the case of the current cable robot, where the cable structure has a physical meaning only in the positive range, using the linear cost function is sufficient in terms of mathematical modeling. With this replacement, without compromising the convexity, the optimization problem on the robot is solved with the low tensile limit and the high rupture limit, and the equal constraint tensile strength of the cables and the moving platform. The simulation results show that while the mentioned the alternative in the cost function does not have a significant effect on solving the optimization problem with numerical methods, the reduction in the average elapsed time to achieve the optimal solution is about 3 times, compared to the analytical method with the two-squared cost function, and is obtained at least 80 times that of numerical methods.

Parallel robots have a lot of compared to their counterparts, serial robots, such as higher accuracy, more load to weight ratio, and higher stiffness, which contribute to their various, and precise applications. Stiffness of the robot, as one of the most crucial parameters which should be considered in of the robot, the desired application. In this paper, an experimental study is investigated on evaluation of the robot’s stiffness and the errors corresponding to of the mechanism, which indicate the displacement of -effector of the robot with respect to external imposed forces. The aim of this paper is to evaluate the stiffness and the errors due to the softness behavior of the mechanism of a 3 degree of freedom (3-DoF) parallel robot; for this end, the amount of transfer of the final executor to the applied load is simulated. First, the 3-DoF decoupled robot is introduced and its features are expressed and the stiffness of the mechanism is modeled using Finite Element Method (FEM). Then, of the mechanism is determined in different positions of the end-effector by considering predefined boundary conditions. In order to evaluate the obtained model of the robots’ stiffness, a novel experimental setup is developed to measure the stiffness of the mechanism. By employing the setup, of the robot is measured in different conditions. Finally, the output results of the stiffness model are compared to the experimental tests. The results reveal that the 3-DoF decoupled parallel robot shows a proper stiffness behavior. Hence, it can be employed in various applications with high precision.

Because of the fact that cable-driven parallel robot ​possess limited moment resisting/exerting capabilities and relatively small orientation workspaces, in this paper, a method for determination of optimal configuration of reconfigurable cable-driven parallel robots is presented to improve their performance. In such robots, actuators can move the cable attachment points on the base with respect to the motion of the end-effector in its trajectory. In the determined configuration, any external wrench on the end-effector can be balanced, using cable forces for all poses near to a pose of the robot. The largest wrench-closure circular zone centered at an arbitrary point of a trajectory for a given range of orientation around a reference orientation of the end-effector is computed. Taking the area of such zone into account and with the aim of enlarging them, the optimal configuration of the robot is determined. The optimal configuration is found by appropriately changing the position of the moving attachment points on the base of the robots. By applying this procedure on a number of points on a given trajectory iteratively, proper actuation schemes are obtained. In this paper, this method is utilized for reconfigurable planar cable-driven parallel robots and the quality of their actuation schemes is compared with the robots with fixed cable attachment points on

The production and grinding of rotating parts with parallel and angular misalignment is one of the topics issues in the field of Manufacturing engineering. To connect these types of parts to the grinding machine, it is necessary to use three jaw chuck or Jig & Fixtures that are complicated and Time-consuming. This study examines the feasibility of using the 6RUS parallel robot as a six-degree of freedom chuck in the grinding machine. This research will include the design of the 6RUS robot and the reverse kinematics and robot workspace, and then examine the feasibility of using the robot as a six-degree of freedom chuck, which will analyze strain and frequency stress in finite element software includes.

One of the principle design stages of the machine tools, especially based on parallel mechanisms is the deflection analysis of its structure under machining forces. In this paper a new four degrees of freedom parallel robot with three translational and one rotational degrees of freedom was investigated to find the best design configuration. At first the kinematics and force analysis of the mechanism as the base of design analysis considering the load distribution on its various components were implemented. Then, deflection of the different components of structure under external torque and forces on the moving platform was obtained. To confirm the force relations and static analysis of the mechanism, the structure of robot by the FEM in ANSYS environment was analyzed. At last, the results of theoretical relations calculated by the MATLAB were compared with the simulated results obtained by the FEM. It was found a good consequently, the agreement between these two of the proposed design method.

Many efforts have been done in recent years to decrease the required time for analysis of FKP (Forward Kinematics Problem) of parallel robots.This paper starts with developing kinematics of a parallel robot and finishes with a suggested algorithm to solve forward kinematics of robots. In this paper, by combining the artificial neural networks and a 3rd-order numerical algorithm, an improved hybrid strategy is proposed in order to increase the accuracy and speed of forward kinematics analysis of parallel manipulators. First, an approximate solution of the forward kinematics problem is produced by the neural network. This approximate solution is then considered as the initial guess for the 3rd order Newton-Raphson numerical technique. By applying Stewart-Gough parallel manipulator, the efficiency of the proposed method is evaluated. It is shown that replacing the Newton-Raphson algorithm by the 3rd-order one leads to a reduction of the iterations required to reach the desired accuracy level and thus a reduction of the FKP analysis time. Finally, Stewart robot is used to simulate the movement of jaw. This novel algorithm can be applied to any forward kinematics of serial or parallel robots.

Simulation of the four degree of freedom parallel robot (Quattrotaar) is subjective of this paper. The mathematical model of the parallel robot is obtained too. The workspace is optimized for Non-singular kinematic type-2. Artificial Bees Colony algorithm and Particle Swarm Optimization algorithm as overall exploring algorithms are implemented and the results are compared to each other. Neglect of any intrinsic complexity of the optimization problem the results show the capability of both methods for this robot parameters design. Comparison of the results indicates the Particle Swarm Optimization algorithm runs faster than Artificial Bees Colony algorithm. The exploring volume consists of a plan with 500 mm x 500 mm dimension which moves in a vertical direction from 500 mm to 1000 mm. One of the important hints of the paper is a 90-degree rotation of end effector around vertical axis Z. This rotation is caused more flexibility and dexterity for the robot. A 3-D model of Quattrotaar parallel robot is created by Computer Aided Design software and finally, Quattrotaar is fabricated in Human and Robot Interaction Laboratory (Taarlab).

Unlike serial manipulators, forward kinematic problem (FKP) of parallel robots is highly complicated and its analytical solution is not generally le. Therefore, in most cases numerical methods are used to solve this problem which are relatively time consuming. On the other hand, reducing the duration of FKP analysis is an essential task for applications like real-time control. In this paper, artificial neural networks and a 3rd-order numerical algorithm are combined and a new hybrid strategy is proposed for forward kinematics analysis of parallel manipulators which significantly increases the speed of the FKP solution. In the proposed method, an approximate solution of the FKP is first produced by the neural network. This solution is next considered as an initial guess for the 3rd-order numerical technique which solves the nonlinear forward kinematics equations and obtains the answer with a desired level of accuracy. The proposed method is applied to a spatial 3-PSP parallel manipulator. The results show that using this method will lead to a 35 percent reduction in number of iterations and a 12 percent reduction in the FKP analysis time, while maintaining high level of solution accuracy.

In this paper, a multivariate statistical method called Principal Components Analysis, PCA, is utilized for detection faults in a 3-PSP parallel manipulator. This statistical method transfers original correlated variables into a new set of uncorrelated variables. PCA method can be used to determine the thresholds of statistics and calculate square prediction errors of new observations for checking the system when a fault occurs in the robot. To investigate on the ability of the PCA method for faults detection of the robot, a nonlinear model-based controller called Computed Torque Control, CTC, is designed. In this control scheme, rigid-body inverse dynamics model of the robot is utilized to linearize and to cancel the nonlinearity in the controlled system. Also, instead of using the robot prototype model, direct dynamics of the robot is used in the robot-control system. In this paper, two faults are artificially applied to the robot-control system. These two faults consist of faults in servo drive or servo motors and faults in joints clearances or position sensors. Finally, these faults are applied on the robot throughout a desired end-effector trajectory and the resultant outputs are obtained for both with and without faults in the manipulator. Consequently, the desired and faulty outputs are compared and faults detection using PCA method for the robot is performed.

Parallel mechanisms are widely being used in industrial applications such as machine tool، metrology، earthquake simulator، fly simulator، medical equipment and etc. These mechanisms have some limitations like having erratic workspace، singular points in the workspace and complexity of control systems. These limitations should be studied for suitable usage of parallel mechanisms. In this article، a four degree of freedom parallel mechanism (three linear and one rotation degrees of freedoms) is proposed as machine tool and being studied and its workspace and singularity analysis are done by solving the kinematic relations and using Matlab software. So، at first the inverse and direct kinematic equations of mechanism were solved and then an algorithm is used to determine the workspace and singular points of proposed parallel mechanism. Finally، to investigate the results of workspace analysis the structure has been modeled in Solidworks software and the inverse kinematic relation and the obtained workspace have been validated using the simulation. At the last، to investigate the quality of robot performance and its dexterity in workspace، global condition index of mechanism using Jacobean matrix is calculated for different orientations of moving platform.

A modified measure for the parallel cable driven robots is presented in this paper. These robots have additional advantages compared to other robots and even the parallel structures، but they are readily exposed to disturbances. The presence of external wrench (Force-Moment) may be the cause of violation against the motion constraint. The stability measure proposes a number between zero and one that could be the criterion for the evaluation of the robot''s ability while returning to its original equilibrium which was influenced by external disturbances. To offer a stability measure، Gibbs-Appell equations and acceleration energy are used. Robot kinematic and dynamic modeling based on Newton-Euler’s method calculates the measure. To illustrate the capabilities of the proposed measure، a 6 DOF cable robot with six cables is simulated. The results of the two simulations are presented and analyzed. The stability measure is depended to kinematic parameters and also to kinetics parameters as cables tension at the beginning of motion. Therefore using the proposed measure one can better evaluate the stability within the wider range of parallel cable robots.