Posture Control Of Parallel Manipulator Driven By Pneumatic Cylinders

To realize an industrial pneumatic parallel mechanism which satisfies the demand of low-cost for the large amount applications case,the topic of this thesis was chosen as the high precision posture control of pneumatic parallel manipulator.The ordinary pneumatic cylinders were used as the actuators for a common working status.The basic algorithm was the adaptive robust method based on the back-stepping concept and the dynamic model of the mechatronic system.Meanwhile,this method has the good abilities to inhibit the influence caused by parameters uncertainties and modeling error.The real-time updated adaptive matrix and least square method helped the online parameters estimation working successfully based on the indirect adaptive robust control theory.Moreover,according to the actual cases,the improvements of the algorithms were focused on the load identification,cleadzone compensation and pressure observer design,which have significantly expanded the universalities and adaptabilities of the controller.In order to integrate the controller into an embedded hardware for the industrial applications,an embedded board that suited the production type based on DSP was designed.At the same time,a newly method to reduce the valves switching properties was proposed,which was useful for the noise decreasing purpose.The thesis has six chapters.The first chapter is the introduction,mainly for the researches de?velopments on aspects of parallel robots,pneumatic elements and testing,pneumatic servo control,mechatronic system modeling and control,advanced nonlinear control methods.It was empha?sized that in the field of pneumatic parallel manipulator posture control,especially the stage lifted by cylinders which has the good load capacity and value in industrialization,the current control precision of posture tracking could not meet the requirements.The controller design,adaptability and industrial interfaces should be improved significantly.However,the recent studies on the single cylinder control method proved that the adaptive robust method must be an effective solution.The second chapter described the modelling processes of the whole mechatronic system.It includes the 3-RPS platform kinematic and dynamic analysis,pressure-flowrate testing and analyz?ing of proportional valve,friction properties discussion,dynamic and thermodynaimic processes of the pneumatic cylinder.Based on those modules of modeling,the whole dynamic functions were established,which could describe the motion and pressure features accurately and laid a solid basement for the controller design in next chapter.In the third chapter,firstly the basic principles of adaptive parameters identification were introduced by the linearization of the dynamic functions and the establishing of the regression matrix and parameters vectors.The least square method was used as the basic calculation of the unknown parameters with the restriction due to the fading factor,updated rate and physical boundaries.The single cylinder controller design steps were discussed following the adaptive estimation section.The detailed expressions and calculations were all demonstrated in this section as well as the stability proof,which was conducted by the Lyapunov method.Based on the single cylinder's control concept,the controller structure for 3-RPS system was established by converting the parameters into the vector and matrix form.Similarly,the stability of multiple system controller was also shown in the related section.In the last section of chapter,the simulation and experimental results are shown and discussed.Based on the experimental results in Chapter 3,to improve the performance in common work-ing cases of the 3-RPS pneumatic manipulator,the newly proposed developments were discussed in the fourth chapter.There are mainly four focused aspects:1)To enhance the transient response rate of the stage,the fast compensation part was added in to the robust design,which was effective to estimate the low frequency part of the unmodeled part and system interference.By applying this approach,the system bandwidth was expanded and the precision was also improved.2)Due to the different deadzone value of each proportional valve,it could not be set as constant in controller but has to be estimated online.The deadzone online compensation method was integrated into the controller design to satisfy the actual demand of large amount applications.3)The big differ-ence between the initial estimation value and real value of unknown parameters might cause the jittering phenomenon and non-converging parameters estimation results.To solve this problem,the load identification process was introduced into the control sequences.Based on these three progresses on the control methods,the universality of controller was greatly enhanced and most of the obstacles on the way of industrialization were cleared.The fifth chapter gives the application example of the 3-RPS pneumatic manipulator and the related researches.The experiments results were shown in the figures in each section.First is the virtual reality simulator solution with the motion function.The target motion trajectories could be generated by a manually analog signal sampler.The experience of the virtual reality was realized by the posture tracking as the scene changing during the program execution.In order to untying the restriction caused by the PXI controller,an embedded hardware was developed based on DSP with the same performance comparing with the former equipment.Moreover,the noise that oc-curred during the slowly motion situation could be a big disadvantage which influence the users'experience.A method based on the motion and velocity analysis of piston rod was proposed to decrease the noise while ensuring the tracking accuracy.In the final chapter of my thesis,a summary of my works was listed in the first section.To make it a real mature controller production based on adaptive robust method,a few solutions that should be done in the future were listed and the possibilities were discussed.It would not be far to see this kind of parallel pneumatic manipulator with a much better tracking performance become a widely used production,as well as the contributions were done successfully in the related fields.