Research On Redundantly Restrained Cable-driven Parallel Mechanism For Simulating Force

Taking the return simulation of re-entry module from moon,which is the purpose in the third-step of Chinese Lunar Exploration Program,as application background,this paper studies on the theory and application problems of vector force output by the redundantly restrained cable-driven parallel mechanism.Focusing on a redundantly restrained cable driven parallel mechasnism of 9-63 configuration,a systematic research on vector force output is made in this paper,which contains the study and verified experiments of configuration design,redundant cable force distribution,vibration characteristic and applying strategy of disturbing force based on the force-position combination control.Accroding to requirement of motion in low-gravity environment,a cable-driven parallel mechanism of 9-63 configuration is proposed using the basic theory.The definition and the calculating method of the force-control workplace based on the established kinematics model are presented considering the unilateral force feature of cables.To evaluate performances of the isotropy and stiffness characteristic in the force-control workspace,two indexes which are homogeneous stiffness condition number and homogeneous average stiffness are introduced.The structural parameters of the cable-driven paralled mechanism are given.The redundantly restrained cable-driven parallel mechanism of 9-63 configuration can be equivalent to a motion superimposed system of 9-cable tensioning support system and the upper 6 cables with the generalized external force.The indexes of overall tension force used for sustaining tension of cables and overall power consumption by the tension force is established.By the indexes,a cable force optimized distribution method based on the null space vector and preload adjustment of redundantly restrained cable-driven parallel mechanism is proposed.Using the cable force distribution method,the strategy of vector force output by cable driven parallel robot is presented and the simulation analyses of re-entry module behave during the launch and its landing in low-gravity environment is made.By differential transformation and geometric theory,the overall stiffness model considering effects of cable force for cable-driven parallel mechanism is establishedbased on Hessian matrix,which is used in the research of the stiffness distribution in the force-control workspace.A simplified calculating method of low-order natural frequency is proposed by dynamic model of parallel mechanism and Taylor expansion.Then the distribution of natural frequency in workplace and the area containing performance jump,which should be avoided,are presented.The use of the force-position combination control will cause the fluctuation of cable force.By analyses the effects of period of fluctuations,fluctuation amplitude and preload on system behave,the period of fluctuations is distinguished as the key parameter for the force-position combination control strategy.Establishing the indexes about cable force variation and the sensitivity of displacement,the control priority of each cable is defined.Then the applying strategy of disturbing force is proposed considering the sensitivity of cable forces and the output performance of vector force by cable-driven parallel mechanism is given.The experiment platform is established.A series of verification experiments are conducted by the experiment platform.The results of the motion experiment indicate that the experiment platform satisfies the requirement of motion simulation experiment in low-gravity environment.The experiment results of launch and landing applied disturbing force experiment confirm that the force distribution method and applying strategy of disturbing force based on the force-position combination control proposed in this paper can be used to conduct the simulation experiment of the launch process in low-gravity.Outputing vector force by cable-driven parallel mechanism is verified in this paper.