| At present, there are some disadvantages, such as bad ability of anti-jamming, increasement ofhuman working load in application of a kind of professional helmet mounted display which has highcontrast, big enough angle of field. A novel helmet mounted display----helmet mounted display witha6URHS parallel manipulator (HMDPM) which can solve problems above by mean of parallelmanipulator is proposed, and several principal researches on improving system funciton are developedin this paper.Firstly, a dimensional design and its corresponding methodology for6URHS is investigated whilecharacteristics of head motion are considered as design criterions. A metod that descripts scale of headmotion by six-dimensional hyperellipsoid is investigated, and the characteristics of head motion inflight training are summarized based on datum from many experiments. In practice, design criterionsare classified into compulsory requirements and relaxable requirements, and the objective functionsregarding the kinematic performances of the6URHS are defined according to all criterions, while themathematical model of optimization is established in accordance with the principle of nonlinear leastsquares. The paper presents a novel methodology--modified nonlinear least squares based onCentroidal Voronoi Tesselations(CVT)--which initializes the design parameters with CVT and solvesthe optimization problem by means of the nonlinear least squares method, thus obtaining severalfeasible solutions The numerical simulations show that each design solution satisfies all thecompulsory criterions and the new method has a better ability for global optimization. Additionally,the best solution is determined by taking into account the optimization of relaxable requirements--dexterity in workspace, and the feasibility of the new method is further verified by analyzing thepartial indices of the optimal mechanism. The prototype machine is manufactured according to theoptimal scheme.Secondly, the kinematic analysis for manipulator of6URHS is developed, and the kinematicrelationship between leading screw, nut and platform is derived. Dynamic analysis of leg is carried outusing Newton-Euler method, and the Newton-Euler equations of whole leg and corresponding partsincluding nut are established respectively, and then the closed-form dynamic equation of6URHSparallel manipulator is established. Virtual machine, dynamic models of6URHS are buildedrespectively by SIMULINK and M file, and some comparison experiments about dynamic responseare developed, the results of experiments show that the veracity of the dynamic models of6URHS isas the same as virtual machine’s. Additionally, it is proved that it is essential to established6URHSdynamic model considering the dynamic characteristics of nut.Thirdly, the parameter identification and cooresponding methodology of HMDPM platformincluding helmet is studied. Requirments about parameter identification method being fit for HMDPMare summarized in accordance with system construction and operation. Continuous-discrete extensionkalman filter and hybrid unscented kalman filter which are modified based on extension kalman filterand unscented kalman filter respectively to be used in identification of continuous-discrete hybridsystem are developed; Some contrastive analysises are done by mean of simulation, and results showthat continuous-discrete unscented kalman filter is more excellence than Continuous-discreteextension kalman filter on computation velocity and accuracy. Taking advantage ofcontinuous-discrete unscented kalman filter, the real value of platform parameters are obtained, and contrastive analysis betweent actual value and CAD mdel value of platform parameters is carried out,the reasons resulting in difference between actual value and model value are investigated, and anslysisresults show that the difference is the reflection of reality and continuous-discrete unscented kalmanfilter has qualification to identify parameters of HMDPM platform online.Forthly, an active compliance control strategy and its kernels for HMDPM are investigated. Themethodology of predicting head motion based on force feedback and dynamic model of extensible legof parallel manipulator is proposed to plan trajectory. Based on the relationship between the length ofextensible leg and the position and orientation of platform, the information of head motion ispredicted by means of sensor datum and solution of dynamic model of extensible leg, and then it isused to be the desired trajectory of HMDPM position control. The inertia term and nonlinear term ofHMDPM dynamic model are calculated, and the compensations of them are considered in design ofHMDPM controller so that the generalized contact force between head and helmet will be controlledeasily while tracking control of head is progressing. The SimMechanics module in MATLAB isadopted to construct human-robot interactive model of HMDPM, and the feasibility of novel controlstrategy is verified by developing some related numerical simulations. The simulations show that headmotion will be predicted rapidly and exactly using the presented method, the stiffness of HMDPM andgeneralized contact force are reduced evidently by compensating inertia term and nonlinear term inHMDPM controller while tracking control of head is conducted well, and user’s comfort is enhancedobviously. Method to calculate generalized contact force which is based on system dynamic modeland force feedbacks is developed, and is applicated in experiment to test the effience of activecompliance control strategy, experiment results show that both system stiffness and generalizedcontact force can be decreased by making use of active compliance control strategy, and humanworking load is reduced simultaneously. Quantized analysis of influence that have resulted fromdifferent experiment condition is done, and the impersonality of experiment is approved to be well.Fifthly, system softwares operation environment is established by combining RTX and WindwosXP, then the instantaneity and performance of system are promoted and the frequency of system canattain500~1000HZ. Based on Visual Studio, system softwares such as system management software,prediction of head motion software, online identification software and so on, are developed bymodularizing system functions, and the graphic user interface of system management software andvirtual machine showing kinematic status of6URHS are also developed respectively adopting C++Builder and OpenGL, so it is possible to evaluate the reliability and efficiency of methods beforeadoption in practice. Thereby, the security of system will be improved and hardwares can be protectedfrom damage which is due to unexpected case, and then the practicability of softwares is approved tobe fine.Finally, Some comparison experiments are developed and carried out to test the tracking precision,stability and ability of anti—jamming of traditional electromagnetic tracker and HMDPM, and theresults show that the former is better than the latter on all three test aspects in two test environmentswhich are classified by metal object existence, and there is a serious meansurement distortion forelectromagnetic tracker in metal object environment. Several test items that are designed to analyzesystem performance are constituted in accordance with report 《AGARDAR-144》å'Œã€ŠMIL-STD-1558》. |
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