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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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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.

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Kinematic performance indices are used to have an evaluation of the potential efficiency of the robots. Some of these items are designing the optimal structure, trajectory planning, programming, and evaluation of behavior of the robot in positioning and orienting with desired rates or resolution. These indices will be used when the robot has even translational or rotational degrees of freedom (DoF). Due to dimensional incompatibility of the Jacobian entries in the complex DoF’s robots with both types of DoF’s, performance indices such as Jacobian condition index and associate singular values, are not applicable. In this paper, inhomogeneity of Jacobin matrix has been resolved by introducing a new Jacobian matrix which is called Cartesian Jacobian Matrix (CJM). Cartesian Jacobian Matrix maps Cartesian velocity vector of End-Effector (EE) to the joint space velocity vector. As a case study, the suggested method has been used for a Tricept parallel kinematic manipulator. Moreover, considering Local Conditioning Index (LCI) and associated singular values through the workspace have been led to structure optimization of the robot in order to have maximum positioning and orienting rates of EE through the maximum cuboid workspace. The optimization has been performed by Genetic algorithm via GA toolbox of MATLAB 2012 software.

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This paper presents a comparative study on the dexterity and manipulability of three planar 1-RRR, 2-RRR and 3-RRR manipulators.After derivation of the Jacobian matrix of three manipulators, they are transformed to a homogeneous form to include components with homogenous physical units. The condition number of each Jacobian matrix is calculated. Since the condition number changes in general between 1 to ∞, its inverse is used for definition of the local condition index.A zero value for this index indicates that the Jacobian matrix is singular and consequently, the robot has the worse manipulability. On the other hand, the robot indicates the best manipulability and dexterity when this index is close to one. Furthermore, the effect of changing the platform angle on the local condition index is investigated. The manipulability of three manipulators is then compared to each other for the platform angle for which the maximum local condition index is resulted. The results show that the 3-RRR manipulator has a better dexterity than other manipulators at the platform angles less than 90 degree.For the angles greater than 90 degree, the 1-RRR manipulator has a greater local condition index which indicates more dexterity. Finally, the maximum local condition index is compared for each robot at its own workspace and common workspace of three robots.The results verify that this index has almost identical values for the already mentioned workspaces for each robot.Based on the manipulability distribution, the global condition index of theses robots are checked.The results confirm the superiority of the 3-RRR robot.

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Cable-Driven Parallel Robot has many advantages. However, the problems of cable collision between each other and environment, the lacks proper structure and non-positive cable tension prevent the spread of them. Therefore, connecting a serial manipulator to mobile platform improve the ability to object manipulation. This paper investigates the multi-objective optimization structure design and comparative study of spatial constrained and suspended cable-driven parallel robot. By install serial manipulators possess a full hybrid robot’s features. The workspace volume, kinematic stiffness and sensitivity are three sets of optimization criteria. The workspace volume calculated by a novel approach of combination constraints as prevent cables collisions with each other, cable collision with moving platform, uncontrollability and singularity of the robot. First, examine range of the forces and torque reaction of the serial manipulator to moving platform. Then, the evolutionary optimization genetic algorithm use for the multi-objective optimization of constrained and suspended spatial cable-driven parallel robot structure to achieve proper Pareto front confrontation. The Pareto front reconciliation of these three criteria will be discussed. The constrained and suspended optimize by same criteria will compare in the same conditions. It is verified that the constrained structure significantly reduced actuation energy for manipulate a serial robot, supply greater workspace and manipulability. The result of this study used for manufacturing and development of a prototype spatial cable-driven parallel robot (RoboCab).

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Parallel manipulators are mechanisms with closed kinematic chains which have been developed in different forms, but these manipulators have several drawbacks such as small workspace, existence of singular points in their workspace, and complex kinematics and dynamics equations that lead to increase of difficulty in their control. In spite of this, this mechanism has been being conventionally used in many different industrial applications such as machining, motion simulators, medical robots, etc. To overcome these drawbacks, design and manufacturing of a manipulator with three translational degrees of freedom are provided. Design of this manipulator was based on the possibility of three translational motions for its end-effector. The manipulator degrees of freedom are obtained via screw theory. Basic features, consisting of forward and inverse kinematics, workspace and singularity analyzes and also velocity analysis, are considered in this paper. A numerical algorithm is implemented to determine the workspace regarding applied joint limitations and the design parameters were extracted based on to achieving to the desired workspace. The robot motion is created by using of pneumatic actuators which receive their command from a pneumatic servo valve. After design steps, the required elements were provided and assembled in a robotic lab. Finally, the simulation results have transparently approved the improved robots.

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Hexapod walking robots can be employed for both walking and manipulation purposes. When manipulating, they have 6 degrees of freedom for top platform, high rigidity, high load capacity, high speed, and accuracy. On the other hand, it is very well known that they have limited workspace when they are fixed in place for manipulation. Designing a hexapod robot resulting in a maximized workspace can greatly affect the efficiency of the robot when manipulating. Since radially symmetric hexapod walking robots can be modeled as three 2-RPR planar parallel mechanisms, we have used the methods and calculations that used in this kind of mechanism for designing a radially symmetric hexapod walking robot. In this paper, after a thorough review on existing methods for calculating and improving 2-RPR planar parallel mechanism workspace, an algorithm is presented, which results in a maximized reachable workspace. The merit of the method is that there is no need to calculate the workspace volume when maximizing the workspace volume. Also, following this algorithm is necessary for design of the maximized-workspace robot. In other words, the output of the presented optimization algorithm is a set of robot kinematic parameters, which guarantees the maximized volume of the robot’s reachable workspace.

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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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Robotic arms are widely used for 2D desktop applications. In this paper, a new mechanism for a planar robotic arm is presented. In addition to having the benefits of both series of parallel robots, the proposed mechanism also eliminates the disadvantages of both categories. The arm made on the same side as the parallel arms has rigidity, strength and precision, and other positive features of the parallel arms, and on the other hand, like the serial arms, due to the lack of singular points inside the workspace, has a large, symmetrical and also be able to move continuously in the entire workspace. The kinematics relations for the arm are derived, and a controller based on AVR microcontroller & computer for the arm are introduced. The results indicate an improvement in arm performance and the removal of singular points from within the workspace.

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Parallel robots, which have several advantages over serial robots, have been one of the important industrial developments to increase the efficiency of controllable devices. Parallel structures have more suitable features such as higher rigidity, higher movement speed, non-cumulative errors and flexibility of the end-effecter pose. However, the workspace of parallel robots, compared to serial robots, faces limitations due to the existence of multiple kinematic chains, as well as the complexities related to robot control. Small size of workspace is one of the main challenges of parallel robots. Designing moving platform of a parallel robot is of the factors affecting the workspace of the robot. C4 is a four-dof parallel robot that is developed based on the three-dof Delta robot. In current study, the influence of the moving platform design on the workspace and efficiency of the robot has been investigated. After the initial overall design of the robot, three proposed modes for the moving platform have been investigated by considering the robot's kinematic parameters and robot error analysis. According to the results of the workspace and the robot efficiency analyses, the most efficient design has been selected.