Research On Performance Of High Speed Pneumatic Cylinder Based On New Cushion Structure

Air and inert gas are taken as working medium in pneumatic transmission and control technology with minimal impact on the surrounding environment and easy to be realized in long distance transmission and centralized gas supply.In addition,rapid response,convenience in speed-control,easy to manipulate are also its advantage.So pneumatic transmission and control technology has been widely used in the field of industrial automation.Pneumatic cylinders are essential components in pneumatic transmission system,whose performance has directly effect on the performance and reliability of pneumatic systems.The phenomenon of shock and vibration often happens for pneumatic cylinder because of high compressibility of gas medium,which weakening the life of pneumatic cylinder in a great extent.Therefore,great attention should be paid for the research of cushion structure and cushion control technology in the field of engineering technology.In order to improve the cushion performance of high-speed pneumatic cylinder and broaden the regulating range and stability of good cushion state,dynamic modeling simulation and experimental research of high speed pneumatic cylinder with built-in pressure release valve,new cushion structure scheme and dynamic modeling,multi-objective particle swarm optimization on new cushion structure,the realization of new cushion structure and test verification and other related work were developed.Since extending process and retracting process of pneumatic cylinder have the similar law,based on reasonable simplification and function principle analysis on pneumatic cylinder,the dynamic model for retracting process of pneumatic cylinder including gas thermodynamics equation,the mechanical system dynamics equation,pneumatic cylinder friction model and so on were established according to different stage and module.At the same time dynamic performance test platform based on LabVIEW was established,mainly including such work as pneumatic drive circuit design,machining and installation of test bench,hardware circuit design,and compiling multi-channel interrupt program.Speed oscillation or shock would bring great difficulty in friction test and modeling,the information of friction work was obtained by means of test and finite element analysis before and after the cylinder entering into cushion stage.Furthermore,the parameters of friction model were obtained by parameter fitting method.The dynamic performance of the pneumatic cylinder was simulated after the fitted friction model was introduced into dynamics simulation model of pneumatic cylinder.The test results of the dynamic performance of the pneumatic cylinder were compared with simulation results with corresponding working conditions.The comparison results showed that dynamic performance of the pneumatic cylinder can be evaluated and analyzed correctly by the established dynamic mathematical model.The dynamic performance experiment of high speed pneumatic cylinder with built-in pressure under various working conditions approved that pressure release valve often opened and closed repeatedly,the exhaust velocity and opening pressure could not be well matched,the stable adjustment range was very narrow.Therefore,three kinds of structures schemes which could improve the cushioning performance of cylinder were proposed.After comparison of these schemes,the combination adjusting structure composed of cushion chamber clearance volume of pneumatic cylinder and cushion valve adjusting structure were determined.The cushion valve adjusting structure was composed of pressure regulating valve,exhaust valve,one-way valve,fixed volume chamber and related throttle channel.Based on equal diversion point data of parameter interval,simulation analysis of combination adjusting structure was made.It revealed that optimum cushion performance can be obtained through step adjustment.Two regulating stages of cushion chamber clearance volume and pressure adjusting valve both had approximate linear control law,but the relevant parameters need to be optimized in order to gain better cushion regulating range and stability.The parameters of the new cushion structure were numerous,these various parameters influenced each other,taking into account that longer travel time meaned the possibility of velocity fluctuation would become greater and shorter travel time meaned the piston is more likely to collide on cover.Structure and dynamic parameters were optimized by multi-objective particle swarm optimization algorithm based on non-dominated sorting in which stroke time and piston terminal speed were taken as the optimization goal,optimal goal solution set comprised of travel time and piston terminal velocity was obtained with good convergence rate by introducing crowding distance and mutation strategy.In order to realize the better stability of cushion adjustment,the central point of the optimal solution set was selected as the optimal solution.Optimal cushion regulating characteristics and good cushion adjustment range were obtained by simulation under two kinds of work condition such that load mass fixed and maximum piston changing,and maximum piston speed fixed and load mass changing.The simulation results showed that the new cushion structure had the advantages of wider adjustment range and better adjustment stability.In order to verify the feasibility of the new cushion structure in improving the cushioning performance,design and trial manufacture of new cushion structure were carried out based on the optimized structure parameters.after the new cushion structure was installed in the dynamic performance test platform of pneumatic cylinder,test and analysis were carried out in various working conditions,comparative analysis showed that experimental test and simulation analysis had little difference in step regulation scope and regulation conversion points.After the analysis of the main reasons for the difference,the integrated structure of cushion chamber clearance volume and cushion valve was designed finally.New cushion structure had better cushion regulating characteristic compared to traditional pressure release cushion valve,the regulation range and stability had been improved with different work conditions.The cushion performance of high speed pneumatic cylinder with new cushion structure can be improved greatly,engineering application scope will be expanded,and the service life of the pneumatic cylinder will also be prolonged.