Research On Design Theory And Application Of Multidimensional Vibration Isolation Platform Based On Parallel Mechanisms

One dimensional vibration has been deeply studied at home and abroad.Sphere of learning has ripe theory and technology in one dimensional vibration.But people are very poor in multidimensional vibration.If we put the theory and technology which are used in single dimensional vibration into multidimensional vibration,the structure will be complicated and it may don't work.So it is very important to study multidimensional vibration and seek for theory and technology for multidimensional vibration isolation.The basic vibration isolation principle for multidimensional vibration was put forward at the beginning of the paper.Multidimensional vibration isolation platform is composed of up platform,down platform and parallel mechanisms.The parallel mechanisms should be put between the up platform and the down platform.The freedom of the parallel mechanism should be accordance with the dimension of the vibration.The number of the dimension of vibration may be 6,5,4,3,2 so,number of the freedom of the parallel mechanism should be 6,≥5,≥4,≥3,≥2.The matrix of location and posture was introduced and the independent output number was given.Dependence judgment on the motion of mechanism and demarcation of independent output were discussed.The paper also introduced virtual restraint of mechanism, inactive joint,driving joint,single open chain restraint degree,and parallel mechanism coupling degree to lay a foundation to mechanism type synthesis.The multidimensional vibration isolation platform was chosen by type synthesis and ADAMS simulation.It has 6 freedoms.Its mechanism's adjoining legs meet at right angles.The legs of the mechanism are6-SOC{-S-P-S-}.The two mechanisms are put back to back.The platform is easy to design and make,has the advantage of stability.The platform can isolate vibration along x axis,along y axis,along z axis,round x axis,round z axis.The acceleration amplitude along y axis is much less than 1.The platform can't isolate vibration round y axis(vertical axis).The platform has much value though it can't isolate vibration round vertical axis.In the first place,angular acceleration of up platform is almost the same as that of the down platform.Secondly,the angular accelerations of the up platform and down platform are much less than the angular acceleration round other axis.So,we needn't attach much importance to the angular acceleration round vertical axis.Thirdly,as compared with translation along y axis,the probability of rotation round vertical axis is low.Simulation shows that spring stiffness coefficient and damping coefficient have influence on the vibration of the platform and damping coefficient has more influence than the spring stiffness coefficient.The platform can also isolate vibration when it is driven by sine force,sine torsion and when it is driven by different length impulse.The forward and inverse position analyses are done with coordinates transition,and the calculation is done by programming with MATLAB to verify forward and inverse position analyses.The workspace is searched with MATLAB program in right-angle coordinate space.It's necessary to adjust damping because it has influence on vibration isolation.The miniature cylinder is used as a translational joint as well as a damper.Get rid of the gas pipe,fix flow regulating valves at "air in","air out",and make the cylinder become a damper.As a multidimensional vibration isolation platform which is used in vehicle,for example,a multidimensional vibration isolation sickbed, transient response has most influence on system.To reduce the instantaneous amplitude of the up platform and to make it decay rapidly are important.So,the damping ratio of the platform is decided according to performance index of transient response of two order system.Experiments show the platform isolate vibration better when the damping ratio of the leg is 0.707.Free vibration equation of the platform was established and the solution was found.Nature frequency is lower than 5 Hz.The platform can avoid resonance by changing spring stiffness coefficient and the length of the parallel mechanism.The solution shows that the vibration of the up platform decays rapidly.The characteristic valves display the parameters which are related with decay.In order to establish the forced vibration equation easily,when we found the vehicle's vibration we didn't take into account the mass of sickbed and patient because it is much lighter than that of vehicle.After we found the vehicle's vibration,we regarded the up platform as vibrator and regarded the vehicle as a moving basement.The accelerations of the up platform,down platform were measured in length,in width,in height.The experiments show that the platform isolates vibration in length,in width,in height.It has better vibration isolation effect when the damping ratio is 0.707.In a word,the multidimensional vibration isolation platform is a new idea and breakthrough in vibration isolation field.The platform is simple and practical.It can be used in many fields.