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This paper involves the investigation of the forward kinematic problem of three 4-DOF parallel robots, named as 4-PRUR1, 4-PRUR2, 4-PUU, performing 3 translations and one rotation, namely Schönflies motion. The foregoing parallel robots are special cases of 3 parallel robots, named as 4-PR′R′R″R″, 4-PR″R″R′R′ and 4-PR″R′R′R″, respectively, arisen from the type synthesis performed for 4-DOF parallel mechanisms with identical kinematic limb structures. Each robot has 4 identical kinematic chains and each chain consists of one prismatic active joint and 4 revolute passive joints. Due to different direction of revolute joints in each limb, 3 different architectures are considered in this paper. The forward kinematic problem is explored in seven-dimensional kinematic space using the so-called Study's parameters and LIA algorithm and eventually, it has been shown that an algebraic expression of degree 4 indicates the forward kinematic of each kinematic chains of parallel robots under study in this paper. Moreover, using homotopy continuation and comparison with resultant method, it reveals that the forward kinematic problem of this robots have up to 236,236 and 2 real solutions, respectively.

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This paper investigates the multi-objective optimization design of planar cable-driven parallel robots by using the evolutionary optimization algorithm. Since in cable-driven parallel robots, the cables should remain in tension in all configurations, the extent of the controllable workspace is considered as one of the design indices. This objective function is of utmost importance to the design of cable-driven parallel robots, since it considers the unidirectional properties of the cables in the analysis. In addition, in order for the robot to have suitable dexterity and accuracy and to be able to manipulate any arbitrary task in all the required directions, various kinematic indices such as global condition number, translational and rotational kinematic sensitivity indices are used. Through analysis of the conflict of these objectives within the workspace of the robot, it is shown that use of multi-objective optimization is an effective method to reach to a suitable trade-off. Furthermore, by applying multi-objective optimization methods such as the non-sorting genetic algorithm and the adaptive weighted particle swarm optimization algorithm, the optimal pareto front for the design parameters for the cable robot is obtained such that to draw a compromise between the robot designs.

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This paper aims at obtaining the dynamic models of twoconstraint-over parallel mechanisms (PM) with 3-DOF (degree of freedom) and 4-DOF, the Tripteron and the Quadrupteron. The reasoning used in this paper is based on a judicious concept in detaching the whole mechanism into several subsystems and consecutive synergies between kinematic analysis, Lagrangian and Newtonian approaches. In this regard, the mechanisms are made equivalent to some subsystems and the equations of kinematic constraints are derived for all subsystems. Afterwards upon resorting to Lagrangian approach and blending it with the latter kinematic relations, the dynamic model of each leg in task space is obtained. The dynamic model of the end- effector is written in virtue of Newton-Euler’s approach where yields to three differential equations. Finally, the problem leads to a system of 12 equations for the Tripteron and 16 equations for the Quadrupteron, which do not need usaul simplifications in such problems. For the sake of comparison, the results are put into contrast by the one obtained with a dynamic analyzer software. The results obtained by both approaches are coherent which affirms the correctness of the proposed algorithm.

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Static balancing is one of the most valuable strategies in manufacturing and industrial designing. This paper deals with the static balancing of parallel mechanisms. Using counter-weights and springs, and their combination, are the most popular methods in this procedure. In this article, theories and formulas of static balancing, by considering the end-effector with constant-weight, using counter-weights and springs are addressed. As case studies, three 3-DOF planar parallel mechanisms, namely, 3-RRR, 3-PRR and 3-RPR with constant-weight are investigated. A static balanced 3-RRR is modeled and validated in Adams software and fabricated using a combination of spring and counter-weight. This mechanism is manufactured in Human and Robot Interaction laboratory (TaarLab). Moreover, a cable parallel 3-DOF mechanism using static balancing concept is designed for which variable weight is considered at the end-effector. The crane benefits from static balancing of variable weight that causes the power actuators just use in relocation the counter-weight in XY plane that is obviously less than the power needed to relocate the main load across the gravity direction. The advantages of these kinds of mechanisms consist in reducing manufacturing and operation price, increasing the safety and using less power in actuators.

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Regarding the progress in technology and increase in the capabilities of the robots, one of the main challenges in the field of robotics is the problem of real-time and collision-free path planning of robots. This paper focuses on the problem of path planning of a 3-DOF decoupled parallel robot called Tripteron in the presence of obstacles. The proposed algorithm is a synergy-based algorithm of convex optimization, disjunctive programming and model predictive control. This algorithm has many advantages compared to previous methods reported in the literature including not getting stuck in the local optimums and finding the global optimum and high computational speeds. Finally, the algorithm will be implemented on a model of the real robot. It should be mentioned that this algorithm has been implemented using Gurobi optimization package with C++ programming language in Qt Creator environment and the simulation of the parallel mechanism is performed by the CAD2MAT package for MATLAB. Obtained results reveal that the maximum computational time at each step is less that one second which, for this particular application, could be regarded as a real-time algorithm.

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The sensitivity of the moving platform of parallel mechanisms to the uncertainties in the design and control stages is of paramount importance. The mechanism has to be designed such that the negative effect of the foregoing errors is minimized. The latter issue has encouraged many researchers to derive and propose relevant indices being responsible for outputting a metric representing the kinetostatic performance of parallel mechanisms. Most of such indices entail severe drawbacks in the sense of leading to physically inapplicable interpretation, which was considerably alleviated by the emergence of kinematic sensitivity. Nevertheless, none of the studies heretofore has investigated the influence of the uncertainties in the passive joints on the kinetostatic performance. In other words, the assumption has always been that the aforementioned errors are negligible. This paper proposes a novel formulation for the kinematic sensitivity index, which, apart from that of the active joints, takes the effect of the uncertainties in the passive joints into account, and brings about the advantage that the mechanism can be optimized and improved in terms of kinetostatic performance, together with the workspace. The formulation, for the sake of illustration and verification, is also applied to the 4-bar linkage and 3-RPR parallel mechanisms, as well as the Tripteron robot. The results of the implementation of the proposed kinematic sensitivity index, which takes the effect of the uncertainties in the passive joints into account, show that the values associated with the case-studies considered in this paper fall within the intervals 1-2.4, 0.1-0.9 and 0.6-2.2, respectively.

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This paper presents implementation of position control for planar cable-driven parallel robots using Visual servoing. 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 due to decreasing of the unknown parameters and computation time. In order to track the position of End-Effector, an online image processing procedure is developed and implemented. Finally, as the third contribution, two different controllers in classic and modern 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 demonstrate weaknesses in modeling the uncertainties although they represent acceptable performance. Due to the latter incapability, sliding mode controller is utilized and experimental tests represent effectiveness of this method. Result of the latter procedure is an inimitable operation on the desired task however, it suffers from chattering effect. Moreover, results of these controllers confirm accommodation between the model and robot. The whole procedure imposed, could be applied for any kind of cable-driven parallel robot.

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This paper deals with the collision-free path planning of planar parallel robot by avoiding mechanical interferences and obstacle within the workspace. For this purpose, an Artificial Potential Field approach is developed. As the main contribution of this paper, In order to circumvent the local minima problem of the potential fields, a novel approach is proposed which is a combination of Potential Field approach, Fuzzy Logic and also a novel algorithm consisting of Following Obstacle as well as Virtual Obstacle methods, as a hybrid method. Moreover, the inverse kinematic problem of the 3-RRR planar parallel robot is analyzed and then the aforementioned hybrid method is applied to this mechanism in singular-free case. It is worth mentioning that, in this paper, all the probable collisions, i.e., the collision between the mechanism and the obstacles and also among the links, are taken into accounts. Two general cases have been considered in collision-free path planning simulation; the first case considered a mobile robot in several workspaces and the second one was assigned to the 3-RRR planar parallel robot path planning. Results of the simulations, which are implemented in C programming language for the sake of real-time purposes. reveal that for the both cases, the newly proposed hybrid path planning method is efficient enough for the mobile robot, or the end-effector of the planar parallel robot to reach the goal without colliding with the obstacles.

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This article presents the mechanical design process of a mobile robot which is named TL-PR. Two separate algorithms are applied for obstacle avoidance purpose which are experimentally implemented on the proposed robot. The control board Arduino which is used for the under study robot is an open source board. In order to receive the images which are used for obstacle detecting and obstacle avoidance a Kinect sensor is installed in the proposed robot. The structure of TL-PR is a creative, simple and low cost structure. Two methods are used for obstacle avoidance which are implemented on the proposed robot. The first one is based on ultrasonic sensor. Five ultrasonic sensors are set around the proposed robot structure. The fuzzy control is used to manage the output data of the ultrasonic sensors and the rules of the fuzzy control are set on the MATLAB software. The second method which is used for obstacle detection and avoidance is based on image processing algorithm. A Kinect sensor is set on the top of the robot structure which is used for image processing for detecting the obstacles. The second method consists in processing the Visual Studio software and it run based on the OpenCV library. The proposed robot is a desirable platform for the @home robots. The laptop which is set on the robot made the robot compatible for implementing the various control and image processing algorithms.

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In this paper, kinematic and dynamic model of planar cable-driven parallel robots are introduced in general form which are verified for a constrained cable-driven parallel robot in Sim-mechanics. Path planning based on artificial potential field approach is considered to prevent collision between dynamic obstacle, end-effector and cables in order to achieve collision-free path. As well as to reduce energy consumption, cable tension constraints have been involved in optimization of path planning. This method is proposed to control a cable robot. Therefore, obstacles are distributed randomly in order to have a complex environment. By this way, cable tension constraint is studied as one of the most crucial challenges for cable driven robots. Moreover, Fmincon function of Matlab is applied in order to take into account the required constraints and maintain the limits for cables tension. The latter leads to solve the redundancy resolution which is a definite asset in controlling a cable-driven parallel robot. Finally, a four-cables driven parallel robot is controlled by using the so-called computed torque method for tracking the desired and optimized path. The method is explained and obtained results indicate the efficiency of the proposed approach.

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This paper focuses on the problem of finding object orientation around Yaw & Pitch & Roll angels. The object orientation is computed in a real time manner using a mono-camera and three points on a solid object in a machine vision software. Three points should be selected from environment at the beginning. In order to reduce wreckful effects of environmental lights on detecting colorful objects and also to reduce the number of used software filters, IR LEDs with 850nm invisible wavelength are used. Artificial Neural Network (ANN) is used for solving this problem since orientation's equations are nonlinear and real-time solving for them is impossible. For solving the problem a feed forward artificial neural network with one hidden layer and 21 nodes in that is used, which has 3 nodes for output layer and 6 nodes for input layer. For having high accuracy in ANN, output data is also obtained from a MPU-9150 installed on a 2-DOF orientional parallel robot and compared to ANN outputs. 7243 data from Roll and Yaw angles and 751 data from Pitch angle is obtained from MPU-9150 sensor and the later 2-DOF orientional parallel robot and 467 data remains nonuse for learning ANN. After learning the neural network, results compared to nonuse data for ANN learning and desire results obtained with 0.038 maximum error

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In this paper, based on the concept of natural orthogonal complement, an algorithm is devised to analyze the inverse and forward dynamics and dynamic sensitivity of n-linkage planar serial robots. The first goal is to derive the governing dynamic equations of a planar serial robot systematically, more precisely, number of the linkages, mass, moment of inertia and the length of the linkages are the inputs of the algorithm and the output will be the dynamics equations of the robot. As a comparison study, a planar serial mechanism, namely, dynamic modeling of 6R serial revolute manipulator is investigated and the results of the proposed algorithm are compared with other methods, i.e, Adams software and MatODE. In the next step, in order to develop a dynamic sensitivity analysis scheme, Sobol and EFAST methods are employed. By the use of the dynamic equations of the robots, the sensitivity of the actuating torques to the design parameters such as mass and length of the linkages is analyzed. Dynamic sensitivity of three planar serial robots namely, 2R-PSM, 3R-PSM and 6R-PSM is studied in two different configurations such as singular and isotropic. At the end, the effects of various angular velocities on the sensitivity of actuated torques to the design parameters are investigated. The obtained results reveal that the tolerance of uncertainty in the design parameters of robot affects the actuating torques significantly and also the Sobol’s method predict the sensitivity of the robot more precisely.

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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)

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In spite of several advantages of parallel robots, they generally have limited workspace. Therefore, it is of paramount importance to obtain the workspace by considering the mechanical interference. In this paper, the mechanical interference in planar parallel mechanisms, including interference between links and, collision between links and obstacles and between end-effector and obstacles, are investigated using geometrical reasoning. For this purpose, a new geometric method is proposed for collision detection in the workspace of planar parallel mechanisms based on the lines segment intersection. In this method, the configurations of the planar parallel robot are obtained in the entire workspace. Then, the interference of links with each other and obstacles, which are respectively modeled by line segment and polygon, are determined. Finally, the collision-free workspace of the parallel robot is obtained for a specified orientation of the moving platform. Moreover, in this paper, an index is presented which can be used for examining the workspace by considering mechanical interference. The foregoing index provides some insight into obtaining a well-conditioned workspace.  For the sake of validation, this method is implemented on two planar parallel robots, namely as 3-RRR and 3-PRR, for different working modes. The obtained results reveal that the ratio of the practical workspace to the theoretical workspace is decreased upon increasing the orientation of the end-effector for both clockwise and counterclockwise directions. Furthermore, due to differences in the number of the moving links, the mechanical interference-free workspace of 3-RRR parallel robot is usually more limited than 3-PRR parallel robot.

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This paper investigated the imitation of human motions by a NAO humanoid robot which can be regarded as a human-robot interaction research. In this research, first, human motion is captured by a Kinect 3-dimentional camera through a Robot Operating System (ROS) package. Captured motion is then mapped into the robot’s dimension due to the differences between human and humanoid robot dimensions. After performing the mapping procedure, the solution of both forward and inverse kinematic problem of the robot are solved. To this end, a “Distal” form of forward kinematics solution of the NAO humanoid robot is computed and based on the latter form an analytical inverse kinematics solution for the whole-body imitation purpose is used. The foregoing issue, as one of the contributions of this paper, can be regarded as one of the main reason for obtaining a smooth imitation. In order to keep the robot’s stability during the imitation, an ankle strategy based on a Linear Inverted Pendulum Model (LIPM) and the Ground projection of the Center of Mass (GCoM) criteria is introduced. Moreover, the latter LIPM is controlled by a Proportional-Integral-Derivative (PID) controller for two cases, namely, double and single support phases. Considering the limitation on the motion capture device, from experimental and simulation results obtained by implementing the proposed method on a NAO-H25 Version4 it can be inferred that the robot exhibits an accurate, smooth and fast whole-body motion imitation.

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In this paper, position control is addressed for a pneumatically actuated 6-DoF Gough-Stewart parallel robot. At first, dynamic model of the pneumatic system of each link of the robot which comprises a pneumatic actuator and a proportional electrical control valve is extracted. Unknown parameters of the obtained dynamic model consisting friction force, viscous coefficient and the parameters of the valve are identified by employing an evolutionary algorithm. Then, position control of the robot’s pneumatic actuator is performed based on designing Backstepping-Sliding Mode controller according to the nonlinear dynamic model of the pneumatic system. Moreover, kinematic equations of the 6-DoF parallel robot are achieved and a novel method is proposed, the so-called Geometry-based Quasi-Forward Kinematic, to the end of calculating the position of the end-effector of the robot without using expensive position sensors. Accordingly, kinematic closed-loop control of the parallel robot, which is based on simultaneous joint space and task space control, is investigated for trajectory tracking using potentiometers, a rotation sensor, and based on the computed position of the end-effector by the proposed method. Desired sinusoidal trajectories with pure motions and also complicated trajectories are tracked in which error of positions and rotations are lower than 2 (cm) and 3 (deg), respectively. The results reveal that the trajectory tracking control of the pneumatic 6-DoF Gough-Stewart parallel robot is performed properly based on the proposed control strategies and the novel method for calculating the position of the end-effector.

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This paper aims at proposing an algorithm for collision-free motion planning of two wheeled mobile robots. The proposed approach relies on discrete motion planning, convex optimization and receding horizon control (RHC) concepts. The proposed algorithm is employed for motion planning and control of a mobile robot in order to pass through an unknown environment both in simulation and practical implementation. In this regard, CVX package benefited from the Gurobi solver is employed to solve the optimization problem in the simulation. Moreover, in order to perform a collision-free motion planning, corresponding Robot Operating System (ROS) package with the intended mobile robot is employed to cooperate with the provided motion planner package. The provided package utilizes educational license of Gurobi optimizer solely to speed up solving proposed optimization problem and its built in branch and bound for Mixed Linear Integer Programming (MLIP). In order to keep the linear form of the constraints, a combination of the Velocity Obstacle (VO) in the first horizon and Bug method concept for the rest of the horizons is used. Obtained results show the reliability of this algorithm for safe collision avoidance. The reported results reveal this fact that by considering the maximum velocity of the E-puck, obtained computational time is less than 0.004 sec. in each stage which is fast enough for robot motion planning tasks.

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In this paper, we used a non-singular backstepping terminal sliding mode control approach to the unmanned aerial vehicle (quadrotor). In the first step, the governing dynamical equations were obtained based on the quadrotor considering all the effective parameters. The controller objective is limited to obtaining proper tracking of the desired positions (x, y, z) and the yaw angle (ψ), as well as maintaining the stability of the roll and pitch angles despite the presence of external disturbances. Controlling methods require complete information about system states that may be limited in practice. Even if all system conditions are available, it is interfered by noise, and also large number of applier sensors to measure states, makes the entire system more complex and costly. For this purpose, the Extended Kalman Filter (EKF) has been used as an observer. The extended Kalman filter is used as a speed observer and estimator of external disturbances such as wind force. Therefore, the use of a controller-observer is suggested to estimate the effects of external disturbances in order to compensate for them. The design method is based on the stability of Lyapunov. Simulation results show the promising performance and suitability of the observer-controller.

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