| Stewart parallel mechanism has become a hotspot in the field of robotics because of its high rigidity, simple structure, strong load capacity and other advantages. Stewart parallel mechanism is widely used in automobile driving simulation system of parallel machine tools, flight simulator and other fields. With the emphasis on agricultural development of our country, the Stewart parallel mechanism is also used in the field of the recurrence of road spectrum information and the bump test on farm equipment by the road spectrum information. The calculation and selection of the parts of the driving system In this paper are made after determining the drive mood. The transfer function of the system of the cylinder controlled by valve is made to further improve. The effects of the two control strategies of PID control method and H∞ robust control method are compared in the simulation process. According to the domestic and foreign development trend, application fields and research methods, the main content put forward in this paper is as follow:(1) The system structure and working principle of Stewart parallel mechanism are introduced. The main advantages of hydraulic control system are elaborated as the drive system of the Stewart parallel mechanism; The calculation and selection of the key components in the hydraulic control system are also introduces, including the hydraulic valve, the hydraulic cylinder and so on. Combined with the knowledge of spatial mechanism, the transformation rule of spatial coordinates is introduced and the forward and inverse solution of position, solution of Jacobian matrix and velocity analysis are all accomplishd. The operation mechanism in the singularity and the condition number of Jacobian matrix are all calculated.(2) After analyzing the transfer function between the displacement of the valve core and the extension displacement of the telescopic rod in the system of cylinder controlled by valve, the mathematical model of the hydraulic control system of the Stewart parallel mechanism is deducted by adding the transfer function between the displacement of the valve spool and the input current; After analyzing the transfer function between the input flow of the cavity without rod and the extension displacement of the telescopic rod in the system of cylinder controlled by valve, the mathematical model of the hydraulic control system of the Stewart parallel mechanism is deducted by adding the transfer function between the output flow of valve and the input current. Based on the two methods, the high-resolution feedback device is proposed to analysis and optimize hydraulic control system; The control algorithm for the reproduction of road spectrum information is proposed.(3) Three-dimensional software Solidworks is used to build the model and assemble the model of the whole Stewart parallel mechanism. The three-dimensional model is imported into the kinematics simulation software ADAMS through the conversion interface between the software. The positive and inverse kinematics simulation is carried out to verify the correctness of the model. The working principle and the ideal effect of two the control strategy(PID control and H∞ robust control) are analyzed. The hydraulic simulation software AMESIM is used to carry out the loop modeling according to the hydraulic control system. The results are compared and analyzed through the parallel connection of PID control and H∞ robust control in the system simulation. The advantages and disadvantages of the two control schemes are compared and analyzed, and the related ideas are put forward in the following research.(4) Servo valve static characteristic test system is used to test the static performance of the selected chosen servo valve of the hydraulic control system and its static performance curves of the servo valve are obtained. Then the performance parameters are calculated and compared with the sample data. The corresponding positive and inverse solutions of the Stewart parallel mechanism are tested, and the results are analyzed and compared. And the further research work is put forward. |
PDF Full Text Request