An Active helideck testbed for floating structures based on a Stewart-Gough platform

A parallel robot testbed based on Stewart-Gough platform called Active-helideck is designed, developed and tested as a helicopter floating helideck. The objective of this testbed is to show the advantages of helicopters that use an active helideck upon landing on and taking off from ships or from offshore structures. Active-helideck compensates simulated movements of a ship at sea. The main goal of this study is to maintain the robot’s end effector (helideck) in a quasi-static position in accordance to an absolute inertial frame. Compensation is carried out through the coordinate action of its six prismatic actuators in function of an inertial measurement unit. Moreover, the simulation of the sea movement is done by a parallel robot called ship platform with three degrees of freedom. The ship platform is built with a vertical oscillation along the z axis, i.e. heave, and rotates on remaining axes, i.e. roll and pitch. Active helideck is able to compensate simulated movements by considering the ship as an inertial frame as observed in the experiment

Real Coded Mixed Integer Genetic Algorithm for Geometry Optimization of Flight Simulator Mechanism Based on Rotary Stewart Platform

Featured Application Low-cost flight simulators with electric rotary actuators and optimized geometry for flight simulation. Designing the motion platform for the flight simulator is closely coupled with the particular aircraft's flight envelope. While in training, the pilot on the motion platform has to experience the same feeling as in the aircraft. That means that flight simulators need to simulate all flight cases and forces acting upon the pilot during flight. Among many existing mechanisms, parallel mechanisms based on the Stewart platform are suitable because they have six degrees of freedom. In this paper, a real coded mixed integer genetic algorithm (RCMIGA) is applied for geometry optimization of the Stewart platform with rotary actuators (6-RUS) to design a mechanism with appropriate physical limitations of workspace and motion performances. The chosen algorithm proved that it can find the best global solution with all imposed constraints. At the same time, the obtained geometry can be manufactured because integer solutions can be mapped to available discrete values. Geometry is defined with a minimum number of parameters that fully define the mechanism with all constraints. These geometric parameters are then optimized to obtain custom-tailored geometry for aircraft flight simulation

Análise, simulação e controle de um sistema de compensação de movimento utilizando um manipulador plataforma de stewart acionado por atuadores hidráulicos

O mecanismo Plataforma de Stewart é um manipulador do tipo paralelo, com seis graus de liberdade, boa relação peso/carga e alta rigidez. Tais características conferem a este tipo de manipulador propriedades superiores de precisão em relação aos manipuladores seriais. Neste trabalho, o controle de um Manipulador Plataforma de Stewart (MPS) acionado por atuadores hidráulicos é estudado com o objetivo de compensação de movimentos para viabilização de transferência de cargas e pessoas em ambiente naval.Visando ao desenvolvimento de um protótipo experimental, o manipulador é estudado considerando a situação em que se encontra sobreposto a um segundo MPS que tem por objetivo simular o movimento da maré, sendo ambos MPS considerados desacoplados dinamicamente. Neste contexto, o estudo envolve a análise cinemática e dinâmica do manipulador incluindo, também, a dinâmica dos cilindros hidráulicos. Além disso, são estudadas unidades de medição inercial (IMU) utilizando-as como instrumento para medição do movimento da base a ser compensado. O projeto do controlador do sistema de atenuação de movimento faz uso da técnica de Torque Computado (TC). A análise de estabilidade, feita separadamente para o sistema mecânico e hidráulico, baseou-se da teoria de Lyapunov. Simulações realizadas considerando trajetórias similares às do movimento de um navio são utilizadas. Para compensação do movimento são utilizados, também, sinais provenientes de uma IMU. Por meio de simulação, comprova-se que o sistema proposto é capaz de compensar adequadamente os movimentos da base estudados.The Stewart platform mechanism is a parallel manipulator with six degrees of freedom, high load/weight ratio and high stifness. These properties give them a better accuracy when compared to serial manipulators. This work focuses on study of electrohydraucally Stewart Platform Manipulators (MPS) to enable compensation of vessels motions for load and personell transfer in sea. Aimed at developing an experimental prototype, a second MPS is placed underneath the rst MPS to simulate vessels motions and so both manipulators are considered dynamically decoupled. In this sense, the kinematics and dynamics of this manipulator are presented, as well as a mathematical model of the hydraulic actuator. Furthermore, special attention is given to the study of inertial measurement units (IMU) which is used as an instrument for measuring the motion to be compensated. Controller design for the compensation system is developed considering compute torque theory which consider the system separated in two: mechanical and hydraulic. The Lyapunov criteria is used to guarantee closed loop stability for each subsystem. Simulations are performed considering similar vessel motions. Signals provided from a comercial IMU are used for motion compensation. The control compensation performance is veri ed by means of computer simulations