Papers by Keyword: Stewart Platform

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Authors: Yong Shi, Wen Tao Liu
Abstract: In order to identify the geometrical parameters of parallel kinematics machines tools (PKM), a new parameters identification method is presented. The identification method is proposed based on a pose discrepancy model, which is deduced from the error between the nominal and measurement relative distance of two different spatial locations of the moving platform. In the identification method, an error sensitivity matrix, which expresses the sensitivity between the pose error and geometrical structural parameters error of PKM, can be created with numerical methods. The results of different numerical methods are analyzed. A measurement method to get the precise lengths of legs is presented, which decrease the number of identified parameters. In an experiment, the error of PKM is reduced from 6.71mm to 1.144mm. Therefore, the identification method is verified effective and feasible.
Authors: Frank Janse van Vuuren, Yoon Soo Kim, Kristiaan Schreve
Abstract: Most hexapods that are currently available on the market are expensive and have extremely high positional and orientation accuracies. Although the positional accuracy is high the viewing angle is limited to 60°. These hexapods are designed with a small viewing angle, as they are not optimised for radio telescopes. The aim of this work is to highlight the various factors that should be considered during the design of a 6-3 Stewart platform for pointing applications. These factors are illustrated by presenting the case study of a small custom hexapod that is designed, built and tested. Modelling of the Platform is performed through the implementation of existing kinematic and dynamic models that could be verified through comparison to simulation results in literature. Components designed for the hexapod include the linear drives, base joints, platform joints, electronic controller and graphical user interface. The design process is documented and design decisions clearly motivated. Performance of the Stewart platform is measured with an inclinometer and the ability of the platform to track a sun simulation path is presented. Specifications which the hexapod is able to achieve include a viewing angle of 120˚±0.3˚ and the ability to carry a payload of 1kg.
Authors: Qiang Li, Hong Bo Yan
Abstract: A novel method is introduced. Simplify Stewart platform by using of group technology. Six legs 6-6 Stewart Platform is transformed into three group legs Stewart platform by way of geometrical knowledge and numerical analysis. Make emulational program of Matlab 6.5 to validate the method of direct kinematics. Velocity and precision of computing are advanced by repeatedly optimizing of method. The method is scientific and novel.
Authors: Qi Shuai Liu, Xi Yang, Wei Di Jin
Abstract: This paper devotes to address the problem of the singularity of the Stewart platform, which is different from the serial mechanism. An algorithm has been constructed; also, by solving a minimum problem, it finds a alternative path to instead the preliminary path, in which there are several singular configurations. At the end of this paper, a numerical case has been developed and gives two points on the preliminary path. By applying this algorithm, a singularity-free path can be found to avoid the singularities in the preliminary path and ill-condition. So, this algorithm can be proven practical.
Authors: T. Nagarajan, S. Krishnan, A.M.A. Rani, Victor Amirtham, T.V.V.L.N. Rao, Winson Ambaraj, Ramanathan Ramiah
Abstract: This paper analyses the result of the ongoing experimental research on the operational behavior of SMA in medical and robotics application. SMA are the materials that have the ability to return their original shape when subjected to the appropriate thermo mechanical interaction. SMA finds very wide applications in various facets of robotic equipments and industrial automation. They are easy to manufacture, low cost and can be integrated with human operations without any large scale safety requirements. Three SMA wires with diameters of 0.254 mm, 0.381 mm and 0.508 mm were experimented to measure the displacement of the wire with various bias forces. The 0.25 mm wire is best suited for generating substantial displacement. The displacement may be used to create CPM (Continues Passive Motion) for the Stewart platform for ankle rehabilitation therapy.
Authors: Martin Ramsauer, Michael Kastner, Paolo Ferrara, Ronald Naderer, Hubert Gattringer
Abstract: This paper investigates the sensorless detection and evaluation of inner oscillations of unknown test objects mounted on a compliant test bench. The principle of the sensorless analysis is that test objects are not totally rigid in reality. This means one or more parts of the test objects are oscillating with different eigenfrequencies compared to their rigid equivalent. By comparing eigenfrequencies of both (rigid and fault test object) oscillating parts are detectable. The aim of this experiment is to demonstrate the use of a 6 DOF compliant Stewart platform (alternatively used in a simulation environment) to generate frequency sweeps in all degrees of freedom, to get a sensorless detection of vibrations in unknown objects. For this purpose only the preexisting sensors applied for the control of the hexapod should be used. The detection of loose parts by shaking objects can be done by a complex robotic manipulation task. Being designed for flexible use by small and medium-sized enterprises, the robotic Stewart platform (hexapod) will adapt autonomously to different test objects leading to a highly flexible robot.
Authors: Wei Meng, Zu De Zhou, Quan Liu, Qing Song Ai
Abstract: Multiple Degrees of Freedom (DOF) parallel robots possess the advantages of being compact structure, great stiffness, stability and high accuracy, so such platforms have been widely used in application areas as diverse as the spacecraft motion simulators, radio telescopes, and medical rehabilitation devices. In this paper, after giving a brief review on the control strategies for parallel robot, a 6-DOF robot system for medical purposes based on simulation as well as real environment is established. In order to improve the position tracking accuracy for such objects with time-varying and nonlinear parameters, a practical fuzzy adaptive controller is designed based on the kinematics of parallel platform, where fuzzy inference units are utilized to modify the PID parameters in real-time by using the position feedback from the robot actuators. Finally, both virtual and actual experiment results demonstrate that the proposed algorithm is able to effectively reduce the position tracking errors compared with the traditional PID controller, and the reliability and feasibility of such parallel robotic system can also be guaranteed.
Authors: Chao Li, Jian Qin Mao
Abstract: Multiple degree-of-freedom (DOF) vibration isolation is essential for precision control of space-borne structures and weapon systems. A new design and analysis of actuators employing magnetostrictive material TbDyFe is presented. Then, this paper studies the design and control problems of a six DOF Stewart platform using the concept of cubic configuration. Optimal geometry for the sensor configuration to get best signal is designed. To control the smart structure, a real time computer control system is built. Improved robust adaptive filtering algorithm based on nonlinear constitutive relation proposed in this paper and used in the computer control system. More than 20 dB of vibration attenuation is achieved in real-time experiments.
Authors: Fang Hua Liu, Hong Tao Wu
Abstract: The parallel structure of the sensor, which based on Stewart platform, has a direct impact on the technical quota. This article uses Genetic Algorithm to parameterize the model of the sensor. Take the isotropy target of the sensor as objective function, and take five basic structural parameters of the Stewart platform as design variables. Then it optimizes the structure of the sensor. Then apply the virtual prototype technology of ADAMS to simulate. At last, it found the transformation relation between the isotropy target of the sensor and each parameter. It can offer an important gist for optimizing the structure of the sensor.
Authors: Yen Chieh Mao, Dai Jia Juan, Sheng An Wen, Wen Chi Tsai, Jheng Ting He
Abstract: Gait rehabilitation is an important process of medical treatments on lower extremity injuries for human neuromusculoskeletal system. Benefiting from the medical device automation technology in recent years, robots achieve the rehabilitation in a professional, precise and continuous manner by integrating mechatronics, automation, computer science and communication technologies, improving the qualities provided by human therapists, the labor-intensive works. This research proposes a Stewart Platform-based measurement system for human gait rehabilitation and test purposes. Related works are collected and analyzed, fetching a brief understanding of the market. Human gait model is constructed in 3D Studio Max and the CAD model is established in Solidworks. This research forms the mathematic models of kinetics and dynamics and performs the footplate posture simulations by using these models.
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