Cable Robot Performance Evaluation by Wrench Exertion Capability

Although cable driven robots are a type of parallel manipulators, the evaluation of their performances cannot be carried out using the performance indices already developed for parallel robots with rigid links. This is an obvious consequence of the peculiar features of flexible cables-a cable can only exert a tensile and limited force in the direction of the cable itself. A comprehensive performance evaluation can certainly be attained by computing the maximum force (or torque) that can be exerted by the cables on the moving platform along a specific (or any) direction within the whole workspace. This is the idea behind the index-called the Wrench Exertion Capability (WEC)-which can be employed to evaluate the performance of any cable robot topology and is characterized by an efficient and simple formulation based on linear programming. By significantly improving a preliminary computation method for the WEC, this paper proposes an ultimate formulation suitable for any cable robot topology. Several numerical investigations on planar and spatial cable robots are presented to give evidence of the WEC usefulness, comparisons with popular performance indices are also provided

Pick-and-place trajectory tracking control for cable-driven gangue sorting robots

The cable-driven parallel robots have the advantages of fast moving speed, large workspace and strong dynamic load carrying capacity, so they are employed to perform the pick-and-place operation of the target gangues quickly and accurately. However, due to the flexibility and the unidirectional characteristics of the cables, the cables must be kept in tension all the time, which makes the control of the robots face great challenges. At the same time, the dynamic impact, uncertainty of dynamic parameters, external interference and other factors caused by the process of the pick-and-place the target gangues will inevitably affect the motion accuracy of the end-grab of the robot, and even lead to the failure of the sorting of target gangues. Therefore, a robust adaptive fuzzy control strategy, which can ensure the motion accuracy of the end-grab of the cable-driven gangue sorting robots, is presented to overcome the disturbances of dynamic parameters and the influences of external interference in the process of picking and placing the gangues. Based on Lyapunov stability theory, the stability of the proposed control strategy is proved. The simulation analysis of the proposed control strategy is carried out through a spatial spiral trajectory and practical pick-and-place trajectory for the robot. The results show that the end-grab of the robot has a good tracking effect on the predetermined trajectory, and the maximum position tracking error and root mean square error are 2×10−2 m and 8.9867×10−4 m, respectively; and furthermore, the cable tensions are smooth and continuous, which satisfies the constraint conditions of the cable tensions. It is proved that the proposed robust adaptive fuzzy control strategy in this paper is effective and reliable for the trajectory tracking control of the cable-driven gangue sorting robots. This study can lay a good theoretical foundation for the further application of the cable-driven gangue sorting robots

Air vehicle simulator: an application for a cable array robot

The development of autonomous air vehicles can be an expensive research pursuit. To alleviate some of the financial burden of this process, we have constructed a system consisting of four winches each attached to a central pod (the simulated air vehicle) via cables - a cable-array robot. The system is capable of precisely controlling the three dimensional position of the pod allowing effective testing of sensing and control strategies before experimentation on a free-flying vehicle. In this paper, we present a brief overview of the system and provide a practical control strategy for such a system. ©2005 IEEE

Design, analysis, and control of a cable-driven parallel platform with a pneumatic muscle active support

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The neck is an important part of the body that connects the head to the torso, supporting the weight and generating the movement of the head. In this paper, a cable-driven parallel platform with a pneumatic muscle active support (CPPPMS) is presented for imitating human necks, where cable actuators imitate neck muscles and a pneumatic muscle actuator imitates spinal muscles, respectively. Analyzing the stiffness of the mechanism is carried out based on screw theory, and this mechanism is optimized according to the stiffness characteristics. While taking the dynamics of the pneumatic muscle active support into consideration as well as the cable dynamics and the dynamics of the Up-platform, a dynamic modeling approach to the CPPPMS is established. In order to overcome the flexibility and uncertainties amid the dynamic model, a sliding mode controller is investigated for trajectory tracking, and the stability of the control system is verified by a Lyapunov function. Moreover, a PD controller is proposed for a comparative study. The results of the simulation indicate that the sliding mode controller is more effective than the PD controller for the CPPPMS, and the CPPPMS provides feasible performances for operations under the sliding mode control

Discrete Cosserat Approach for Multi-Section Soft Robots Dynamics

In spite of recent progress, soft robotics still suffers from a lack of unified modeling framework. Nowadays, the most adopted model for the design and control of soft robots is the piece-wise constant curvature model, with its consolidated benefits and drawbacks. In this work, an alternative model for multisection soft robots dynamics is presented based on a discrete Cosserat approach, which, not only takes into account shear and torsional deformations, essentials to cope with out-of-plane external loads, but also inherits the geometrical and mechanical properties of the continuous Cosserat model, making it the natural soft robotics counterpart of the traditional rigid robotics dynamics model. The soundness of the model is demonstrated through extensive simulation and experimental results for both plane and out-of-plane motions.Comment: 13 pages, 9 figure