Optimal Design For Six-degrees-of-free Dompa Rallel Mechanism Of Overloaded And Redundant

Parallel mechanism has a strong advantage on stiffness, bearing capacity, dynamicand it is widely used in motion simulation, parallel kinematics machinesandmicropositioner. The characteristics of the parallel mechanism in differentapplications have different requirements. The parallel mechanism has to take a largeload while it is used as the output section of the motion simulator especially as the shipsimulator and armored vehicles simulator. Therefore, how to improve the carryingcapacity and the drive performance of the parallel mechanism has a great significance tothe development of the motion simulator industry. In this dissertation, an optimal designmethod of electric redundant6DOF parallel mechanism is proposed. This method canimprove drive capability of the system,it can avoid high cost of hydraulic driveandshortcomings of complex maintenance at the same time. The main contents andresults are as follows:The redundant parallel mechanism which consists of six electric legs and threepneumatic redundancy legs is proposed. The electric leg is the active leg and it is usedto ensure the movement of the parallel mechanism. The pneumatic leg is the ancillaryleg and it is used to assist the electric leg to balance the platform and the load. Whilethere is no redundancy support, the work done by gravity is only supported by the activeleg.By adding the redundancy support,the energy consumption of the drive motor isreduced, because the work done by gravity and the potential energy of the gas springcan convert each other.The kinematics and dynamics of the redundant6DOF parallel mechanism areanalyzed with Newton-Euler method, and the kinetic equation is obtained. In thisdissertation, in order to improve system performance and reduce the system’s internalenergy loss, the change of the peak force of the active leg is analyzed. In this process,the optimization objective is to reduce the driving force peak of the active leg, thevariable is redundancy driving force and the radius of hinge point on the redundantleg.Six kinds of the1DOF movements of the platform,eleven kinds of the2DOF of movement and two typical motion conditions are optimized and simulated. The resultshows that while the redundant legs output a constant force, the peak of the active legsdriving force can be effectively reduced by selecting the appropriate radius of the hingepoint and the appropriate redundant driving force.Coordinates position of the hingepoint and the power range of the redundant legs are determined.In order to verify thefeasibility of the optimized result, themodel of the redundant6DOF Parallel mechanismis established inSimMechanics tool box of Matlab, and the optimization results of the1DOF and the2DOF are verified. Simulation result shows that peak forces of differentmovements are reduced, the minimum of reduction is17.2%and the maximum ofreduction is57.63%.Redundant6DOF Parallel mechanism is controlled with fuzzy PID control method.In order to make the control system simpler, the output of the redundant leg is set as aconstant value and the control of the redundant leg is not considered. A control systemis built with the SimMechanics model, and then the sinusoidal tracking characteristicsand the step response characteristics of the system are simulated. The satisfactory resultcan be obtainedby controlling the Stewart Platform with the fuzzy PID control method.