Research On Spatial Trajectory Control Of Pneumatic Manipulator

The automatic gumming manipulator system has been widely used in the automobile windshield glass gumming. It is particularly critical to control the trajectory tracking of the manipulator. Furthermore, the glue flammability brings the pneumatic drive working mode a highly competitive position. Therefore, the main purpose of this research is to develop a multi-DOF manipulator by using a pneumatic position servo system, and to study the spatial trajectory control of this manipulator. This work will provide a solid foundation for the industrial application of the automobile windshield glass gumming.A three DOF serial joint pneumatic manipulator control system was developed based on the gumming requirements and the existing conditions. The pneumatic proportional flow valve controlled cylinder system was used in the power mechanism of the single joint (the waist, the main arm and the lower arm). Firstly, the basic elements and the operating principle of the pneumatic manipulator are introduced. Then, the kinematics model of the pneumatic manipulator was established. The forward and inverse kinematics analysis has been carried out. Several typical kinds of trajectory simulation results were obtained by using inverse angle angles planning trajectory method, based on the pneumatic manipulator kinematics model. Finally, a planning trajectory theoretical guidance which can be suitable for the characteristics of pneumatic position servo system was proposed.The joint dynamic characteristics are the theoretical basis for the manipulator joint control. In this paper, the dynamic equations of the pneumatic manipulator were deduced and simplified reasonably. The dynamics simulation results show that the gravity torque is the major part of the driving torque when the end point of pneumatic manipulator is at a low speed. Thus, according to the above simplified joint dynamic equations, a control method on the gravity compensation torque with planning trajectory was presented. In addition, the gravity torque changing law with main arm and lower arm joints angles was obtained. It can provide a reference for the planning trajectory. The experiments verify the validity of this compensation method.The computation linearized models of the pneumatic manipulator joints were built. Compared with the identified model in the pneumatic manipulator joints identification experiment, the characteristics in low frequency is as same as the computation models. This result shows that the theoretical model is correct. By considering the complex characteristics of the pneumatic system, the pole-placement controller was designed as the control strategy for the single joint pneumatic position servo system based on the computation linearized models. The system pole configuration region was analyzed, by taking the different loads, the different traces, the different conditions and the different control models into account. The system closed-loop dominant poles which can meet well with the multiple task conditions were obtained. A flutter compensation method was investigated, for describing the cylinder creeping phenomenon when the pneumatic position servo system was at a low speed. The superposition sine flutter signal was used to produce the alternate minimal motion in cylinder and decrease the system nonlinear effect caused by the friction. Thus it can diminish the cylinder creeping phenomenon. The relationship between the frequency and the amplitude of the sine flutter signal and the system characteristics was obtained. A model of co-simulation based on Simulink/ADAMS was built. The simulation results show that the coupling characteristics in the joints were obvious and the tracking error in the tri-joints moving together was bigger than the single joint moving. The characteristic experiments of the pneumatic manipulator single joint were performed. The results show that the system has a good tracking performance and robustness.There is obvious coupling phenomenon in the joints of the serial pneumatic manipulator. According to the mathematic model of the electro-pneumatic proportional flow valve controlling a linear cylinder and the simplified equations of the joints, the decoupling dynamic equations of the dual-joint (the main arm and the lower arm) were obtained. And the relationship between the joint angular acceleration and the joint coupling inertial torque was analyzed. According to the gravity compensation and working condition parameters, the decoupling controller of the dual-joint was also designed. It is obvious that this method can eliminate the effect of joints coupling and can improve the system dynamic characteristics.Finally, the spatial trajectory control experiments of the pneumatic manipulator were performed. The compositions of the manipulator and the real-time control system which can meet the multi-joint multi-task were introduced. In addition, the single-joint pole–placement controller, the gravity compensation torque with the planning trajectory control method and the decoupling compensation control method were used in the joint control in the pneumatic manipulator. The experiments of the manipulator spatial trajectory tracking with tri-joints combined moving were carried out. The spatial line, the spatial circular and the car windshield 1:2 glass shape were tracked, respectively. The experimental results show that the tracking error of the manipulator end point is small; the average relative tracking error of the trajectory in Cartesian coordinate axes is less than 2%; the tri-joints'moving is in a good synchronization; and the manipulator end point velocity fluctuation is maintained in 10%. The above performances show that the pneumatic manipulator meets well with the industrial gumming precision and the uniformity requirement. The present work provides a support for the industrial application of the pneumatic manipulator.