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This work presents a stability analysis and experimental assessment of a visual control algorithm applied to a redundant planar parallel robot under uncertainty in relation to camera orientation. The key feature of the analysis is a strict Lyapunov function that allows the conclusion of asymptotic stability without invoking the Barbashin-Krassovsky...
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Citations
... Visual servoing is a sensor-based closed-loop control that takes one or several cameras as sensors and closes the control loop by using the image features extracted from the camera signal. Several researches focused on using visual servoing for parallel robot control [5][6][7][8][9]. In past years, different image features have been ✩ This paper was recommended for publication by Associate Editor Jun Wu. * Corresponding author at: École Centrale de Nantes, France. ...
... In past years, different image features have been ✩ This paper was recommended for publication by Associate Editor Jun Wu. * Corresponding author at: École Centrale de Nantes, France. proposed to have good performance in terms of accuracy for controlling parallel robots, for example, the observation of robot legs [5,6] or the observation of features put on the robot platform [7][8][9][10]. ...
This paper proposes a sensor-based design methodology in order to design a Delta robot with guaranteed accuracy performance for a dedicated sensor-based controller. This sensor-based design methodology takes into account the accuracy performance of the controller in the design process in order to find optimal geometric parameters of the robot. Three types of controllers are envisaged to be applied to the Delta robot, leading to three different optimal designs: leg-direction-based visual servoing, line-based visual servoing and image moment visual servoing. Based on these three controllers, positioning error models taking into account the error of observation coming from the camera are developed, and the controller singularities are analyzed. Then, design optimization problems are formulated in order to find the optimal geometric parameters and relevant parameters of the camera for the Delta robot for each type of controller. Prototypes of Delta robots have been manufactured based on the obtained optimum design parameters in order to test the performance of the pair {robot-controller}.
... The parallel mechanism experimental platform (as depicted in Figure 3) can be employed to validate the trajectory tracking accuracy performance. 49,50 The experimental platform mainly consists of the parallel mechanism and vision sensor system. The parallel mechanism as shown in Figure 1 can move according to the expected trajectory by changing the torque/force of the four actuated motors. ...
In this article, the trajectory tracking control is developed by implementing a non-singular terminal sliding mode control for the redundantly actuated parallel mechanism system. The proposed control scheme could guarantee that the tracking errors converge to zero asymptotically. The problem of singularity with regard to conventional terminal sliding mode control scheme can be eliminated with the presented novel non-singular terminal sliding mode surface as well. The corresponding stability of the proposed control scheme has also been proved theoretically in terms of Lyapunov method. In addition, simulations and experiments are conducted for trajectory tracking to validate the effectiveness of the proposed scheme. The illustrative results demonstrate that the proposed scheme is available to solve the uncertainties and external disturbances with self-tuning in real time. Furthermore, the prominent characteristics of the presented control scheme are quick convergence, high accuracy, and high robustness, which can achieve excellent tracking performance as compared with computed torque control scheme and conventional sliding mode control scheme.
... A visual servo control system, where a camera is used to track the position of the moving platform and the kinematic model is then used to provide the joint position feedback, was introduced in [155]. An algorithm for visual servo control that is capable of dealing with uncertain camera orientations was discussed in [156]. A visual servo-control scheme that addresses RPKMs and uses the dynamic properties of the mechanism to solve the kinematic redundancy was suggested in [157]. ...
Parallel kinematic mechanisms (PKM) have received particular attention due to their higher stiffness, increased payload capacity, and agility, when compared to their serial counterparts. Despite these significant advantages, however, most PKM designs, typically, yield limited workspace, problematic singularities, and configuration-dependent stiffness. In response, mechanism redundancy has emerged as an effective tool to address these and other problems. In this paper, we present an in-depth discussion of past research on PKM redundancy. The methodical review of the pertinent literature, first, introduces the concept of redundancy based on the number of actuators and the number of degrees of freedom required to perform a task and, then, discusses the two main types of redundancy according to the mobility of the mechanism, i.e., kinematic and actuation redundancy. Subsequently, research on the design aspects of redundant PKMs, including the various criteria used for design optimization is detailed. Primary advantages of PKM redundancy include workspace enlargement, singularity elimination/ avoidance, and improved joint-torque distribution. In this paper, these advantages are discussed in contrast to the main challenges redundant mechanisms present, such as in motion planning and control, and calibration. Other issues of PKM redundancy, briefly, presented herein for completeness are fault-tolerance, reconfigurability, cable-driven and hyper-redundant PKMs.
... (iii) Robust system [21,22] against system parameter uncertainties and external disturbance can be achieved. ...
A novel self-repairing control scheme is proposed for a helicopter with unknown disturbance. Firstly, a disturbance observer is introduced to observe the disturbance of the system, which can produce corresponding control signals according to the disturbance signals. Secondly, an integral sliding mode controller is designed to compensate the unobserved disturbance and uncertainties. All of the closed-loop poles can be arbitrarily placed and the output errors converge to zero effectively through the controller. Besides, a robust closed-loop system against disturbance and parameter uncertainties is achieved. In addition, quantum information technique is used to increase the self-repairing control accuracy of helicopter. Finally, simulation results demonstrate the effectiveness and feasibility of the proposed self-repairing control scheme.
... Nowadays, considering what we know and the literature available, this task has been solved particularly well by Miyazaki laboratory (although the system has not been able to beat an expert human player). It should be mentioned that there are types of robots that have not been used in order to solve this task, such as parallel robots [30]. However, thanks to the position of the actuators, parallel robots are ideal for achieving high speeds and acceleration at the end of the robot. ...
Playing the game of Ping-Pong is a challenge to human abilities since it requires developing skills, such as fast reaction capabilities, precision of movement and high speed mental responses. These processes include the utilization of seven DOF of the human arm, and translational movements through the legs, torso, and other extremities of the body, which are used for developing different game strategies or simply imposing movements that affect the ball such as spinning movements. Computationally, Ping-Pong requires a huge quantity of joints and visual information to be processed and analysed, something which really represents a challenge for a robot. In addition, in order for a robot to develop the task mechanically, it requires a large and dexterous workspace, and good dynamic capacities. Although there are commercial robots that are able to play Ping-Pong, the game is still an open task, where there are problems to be solved and simplified. All robotic Ping-Pong players cited in the bibliography used at least four DOF to hit the ball. In this paper, a spherical bat mounted on a 3-DOF parallel robot is proposed. The spherical bat is used to drive the trajectory of a Ping-Pong ball.
Planar two-legged parallel robots with three degrees of freedom have been suggested in the literature as a solution to reduce the leg interference problem of their conventional three-legged counterparts, and since then have attracted considerable attention. This paper presents a singularity analysis of these robots. Three alternatives, namely the robots with 2-RRR, 2-RPR, and 2-PRR structures are considered. Type I, II, and III singularity conditions are obtained taking into account all possible actuation schemes. Several singularity-free actuation schemes are enumerated and discussed. The performed analysis also shows that adjustable designs are possible for manipulators with 2-PRR structures to have singularity-free operation. The proposed design concept and its effectiveness are illustrated through numerical examples.
Previous works on parallel robots have shown that their visual servoing using the observation of their leg directions was possible. There were, however, found two main results for which no answer was given. These results were: 1) the observed robot that is composed of n legs could be controlled in most cases using the observation of only m leg directions ( ), and 2) in some cases, the robot did not converge to the desired end-effector pose, even if the observed leg directions did (i.e., there was not a global diffeomorphism between the observation space and the robot space). Recently, it was shown that the visual servoing of the leg directions of the Gough–Stewart platform and the Adept Quattro was equivalent to controlling other virtual robots that have assembly modes and singular configurations different from those of the real ones. These hidden robot models are tangible visualizations of the mapping between the observation space and the real robots Cartesian space. Thanks to this concept, all the aforementioned points pertaining to the studied robots were answered. In this paper, the concept of the hidden robot model is generalized for any type of parallel robots controlled using visual servos based on the observation of elements other than the end-effector, such as the robot legs into motion. It is shown that the concept of the hidden robot model is a powerful tool that gives useful insights about the visual servoing of robots and that it helps define the necessary features to observe in order to ensure the controllability of the robot in its whole workspace. All theoretical concepts are validated through simulations with an Adams mockup linked to Simulink.
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