Mehdi Tale Masouleh

Singularity Conditions of 3T1R Parallel Manipulators With Identical Limb Structures

This paper deals with the singularity analysis of parallel manipulators with identical limb structures performing Schonflies motions, namely, three independent translations and one rotation about an axis of fixed direction (3T1R). Eleven architectures obtained from a recent type synthesis of such manipulators are analyzed. The constraint analysis shows that these architectures are all over-constrained and share some common properties between the actuation and the constraint wrenches. The singularities of such manipulators are examined through the singularity analysis of the 4-\underline RUU parallel manipulator. A wrench graph representing the constraint wrenches and the actuation forces of the manipulator is introduced to formulate its superbracket. Grassmann-Cayley Algebra is used to obtain geometric singularity conditions. Based on the concept of wrench graph, Grassmann geometry is used to show the rank deficiency of the Jacobian matrix for the singularity conditions. Finally, this paper shows the general aspect of the obtained singularity conditions and their validity for 3T1R parallel manipulators with identical limb structures.

Determination of Singularity-Free Zones in the Workspace of Planar 3-P̱RR Parallel Mechanisms

This paper presents an algorithm for the determination of singularity-free zones in the workspace of the planar 3-PRR mechanism. The mathematical derivation of the algorithm is first given. Numerical examples are then included to demonstrate the application of the proposed approach.

An experimental study on the vision-based control and identification of planar cable-driven parallel robots

This paper presents the implementation of a vision-based position control for planar cable-driven parallel robots. The main contribution of this paper contains three objectives. First, a method is used toward kinematic modeling of the robot using four-bar linkage kinematic concept, which could be used in online control approaches for real-time purposes. In order to ensure positive tension in cables, as a basic essential property, static and dynamic equations of robot are also obtained. Second, in order to track the position of End-Effector, an online image processing procedure is developed and implemented. Finally, as the third contribution, different control approaches are applied in order to validate the model with plant and obtain the most promising controller. As classic controller, pole placement approach is suggested and results reveal weaknesses in modeling the uncertainties. Due to the latter incapability, sliding mode controller is utilized and experimental tests represent effectiveness of this method. However, the chattering phenomenon in the beginning of the robot operation is the main insufficiency of this controller. Hence, in order to present a more accurate controller, adaptive sliding mode controller working alongside with an identification method on the model is applied. The provided identification procedure is based on Recursive Least Square approach, which rebates the effects of uncertainties in the parameters of the model. Moreover, results of these controllers confirm accommodation between the model and robot. The proposed procedure could be well applied for any kind of planar cable-driven parallel robot.

Determining the maximal singularity-free circle or sphere of parallel mechanisms using interval analysis

This paper proposes a systematic algorithm based on the interval analysis concept in order to obtain the maximal singularity-free circle or sphere within the workspace of parallel mechanisms. As case studies the 3-RPR planar and 6-UPS parallel mechanisms are considered to illustrate the relevance of the algorithm for 2D and 3D workspaces. To this end, the main algorithm is divided into four sub-algorithms, which eases the understanding of the main approach and leads to a more effective and robust algorithm to solve the problem. The first step is introduced to obtain the constant-orientation workspace and then the singularity locus. The main purpose is to obtain the maximal singularity-free workspace for an initial guess. Eventually, the general maximal singularity-free workspace is obtained. The main contribution of the paper is the proposition of a systematic algorithm to obtain the maximal singularity-free circle/sphere in the workspace of parallel mechanisms. The combination of the maximal singularity-free circle or sphere with the workspace analysis by taking into account the stroke of the actuators, as additional constraint to the latter problem, is considered. Moreover, the center point of the circle/sphere is not restrained to a prescribed point.

Dynamic analysis of Hexarot: axis-symmetric parallel manipulator

In this study, the kinematics and dynamics of a six-degree-of-freedom parallel manipulator, known as Hexarot, are evaluated. Hexarot is classified under axis-symmetric robotic mechanisms. The manipulator comprises a cylindrical base column and six actuated upper arms, which are connected to a platform through passive joints and six lower arms. The actuators of the mechanism are located inside a cylindrical-shaped base, which allows the mechanism to rotate infinitely about the axes of the latter column. In the context of kinematics, the inverse-kinematic problem is solved using positions, velocities, and accelerations of the actuated joints with respect to the position, orientation, and motion of the platform. Accordingly, the main objective of this study is to dynamically model the manipulator using the Newton–Euler approach. For validation, the obtained dynamic model of the Hexarot manipulator is simulated in MATLAB based on the formulations presented in this paper. The kinematic and dynamic models of the manipulator are simulated for a given motion scenario using MATLAB and ADAMS. The results of the mathematical model obtained using MATLAB are in good agreement with that using the ADAMS model, confirming the effectiveness of the proposed mathematical model.

Path tracking and obstacle avoidance of a FPGA-based mobile robot (MRTQ) via fuzzy algorithm

In this paper, a fuzzy algorithm is implemented on a FPGA-based mobile robot, called MRTQ (Mobile Robot of University of Tehran & Qazvin Azad University)-which could be regarded as an embedded system-for line tracking and obstacle avoidance purposes. MRTQ is a mobile robot platform which is developed for industrial researches and education purposes. As the first step, for the sake of validity of the proposed fuzzy rules, 30 rules in total are envisaged. Then, preliminary simulations are implemented in MATLAB. Moreover, as the main contribution of this work, the foregoing rules are implemented on FPGA. Several practical tests reveal the effectiveness of the proposed fuzzy rules for which MRTQ was able to track the path more precisely and softly in different speeds and avoid the detected obstacle through the path readily.

Feasible Kinematic Sensitivity in Cable Robots Based on Interval Analysis

The kinematic sensitivity has been recently proposed as a unit-consistent performance index to circumvent several shortcomings of some notorious indices such as dexterity. This paper presents a systematic interval approach for computing an index by which two important kinematic properties, namely feasible workspace and kinematic sensitivity, are blended into each other. The proposed index may be used to efficiently design different parallel mechanisms, and cable driven robots. By this measure, and for parallel manipulators, it is possible to visualize constant orientation workspace of the mechanism where the kinematic sensitivity is less than a desired value considered by the designer. For cable driven redundant robots, the controllable workspace is combined with the desired kinematic sensitivity property, to determine the so-called feasible kinematic sensitivity workspace of the robot. Three case studies are considered for the development of the idea and verification of the results, through which a conventional planar parallel manipulator, a redundant one and a cable driven robot is examined in detail. Finally, the paper provides some hints for the optimum design of the mechanisms under study by introducing the concept of minimum feasible kinematic sensitivity covering the whole workspace.

Experimental study on the model-based control of a 2-degree-of-freedom spherical parallel robot camera stabilizer based on multi-thread programming concept

This article aims at proposing a real-time controller for a camera stabilizer using a 2-degree-of-freedom spherical parallel robot with simultaneous display of the control results using multi-threading programming concept. The main contribution of this article can be regarded as employing (a) a 2-degree-of-freedom spherical parallel robot as a camera stabilizer, (b) introducing approximated model and Jacobian model, and (c) using multi-thread programming in order to create equal conditions for comparing accuracy of designed controllers and simultaneous controlling and running of graphical user interface. The experimental setup consists of a 2-degree-of-freedom spherical parallel robot in which a camera is attached to its end-effector plus a 3-degree-of-freedom passive rotational platform, which provide the possibility to apply random perturbations on the base of the foregoing 2-degree-of-freedom spherical parallel robot. At the end-effector of the robot, a 6-degree-of-freedom sensor is installed which sends rotational data to a micro controller, wirelessly. To this end, transceiver boards are constructed to create connection between PC controller and micro-controller. A PC controller is designed in order to ensure that the installed cameras orientation will remain fixed for a prescribed orientation. In this regard, a controller without encoder and a Jacobian-based controller are employed for the under study spherical 2-degree-of-freedom parallel robot. Then, multi-thread programming is used to eliminate complexities of controller structures. Based on the experimental results obtained by implementing both controller, outputs are compared and mean error of each control method and the related RMSE are reported for the sake of proposing the most promising controller.

Optimal motion planning of redundant planar serial robots using a synergy-based approach of convex optimization, disjunctive programming and receding horizon

This paper is focused on the optimal motion planning of redundant planar serial robots, by avoiding obstacles within its workspace. A synergy-based algorithm between convex optimization, disjunctive programming and receding horizon is proposed to the end of achieving advantages such as finding the global optimum solution and low computational time. For the purpose of the problem, different cost functions can be considered, including among others, transition time, energy usage or path length. In addition, kinematic and dynamic relations of the robots under study are expressed as constraints of the problem and since they are non-convex functions, they are approximated by convex constraints. The proposed algorithm is simulated for 3-DOF and 4-DOF redundant planar serial robots in the presence of static and dynamic obstacles using the CVX package in MATLAB and the Gurobi optimization package in the Qt Creator environment. Finally, the proposed approach is implemented on a real 4-DOF planar serial robot via the Gurobi optimization package using the C++ programming language. Results reveal that using a moving horizon is a proper and reliable method to be used for real-time purposes compared with other approaches suggested in the literature. The average computational time at each step is less than 0.3 seconds.

Collision-free workspace of parallel mechanisms based on an interval analysis approach

This paper proposes an interval-based approach in order to obtain the obstacle-free workspace of parallel mechanisms containing one prismatic actuated joint per limb, which connects the base to the end-effector. This approach is represented through two cases studies, namely a 3-RPR planar parallel mechanism and the so-called 6-DOF Gough–Stewart platform. Three main features of the obstacle-free workspace are taken into account: mechanical stroke of actuators, collision between limbs and obstacles and limb interference. In this paper, a circle(planar case)/spherical(spatial case) shaped obstacle is considered and its mechanical interference with limbs and edges of the end-effector is analyzed. It should be noted that considering a circle/spherical shape would not degrade the generality of the problem, since any kind of obstacle could be replaced by its circumscribed circle/sphere. Two illustrative examples are given to highlight the contributions of the paper.