Research On Workspace And Dimension Synthesis Method Of A Fully Constrained Flexible Cable Traction Parallel Mechanism

With the rapid development of China’s economy,by the end of 2020,the number of civil aviation aircraft in China has reached 6747,and the airport passenger throughput has accumulated 420 million person times,and these numbers still have an increasing trend.With the increase of the number of civil aircraft,there is an urgent need for an equipment that can quickly and conveniently inspect the aircraft skin.According to the actual requirements of aircraft skin inspection,an aircraft upper surface inspection system based on CRPM4-3T parallel mechanism is designed in this thesis.The main work completed is as follows:An aircraft upper surface skin inspection system based on CRPM4-3T parallel mechanism is designed.The system is composed of CRPM4-3T parallel mechanism,PTZ and camera.The kinematics of CRPM4-3T parallel mechanism is analyzed,and the kinematics position inverse solution equation and velocity inverse solution equation of the mechanism are deduced.The correctness of the kinematic model is verified by kinematic simulation.The cable force distribution method of CRPM4-3T parallel mechanism is studied.Because the cable force solution of the mechanism is not unique,the cable force distribution problem is transformed into the value of the general solution factor of non-homogeneous linear equations by establishing the force balance equation.Two distribution strategies about the general solution factor are proposed and compared.It is concluded that the distribution strategy with minimum cable force variance has better performance in cable force fluctuation and continuity.Based on the vector closure principle,the workspace of CRPM4-3T parallel mechanism is solved,and the influence law of moving platform load on workspace is analyzed.The static stiffness model of CRPM4-3T parallel mechanism is established.The research shows that the cable force stiffness plays a leading role in the overall stiffness.The translational stiffness of the mechanism along the X,Y and Z directions in the workspace is compared and analyzed.It is determined that the stiffness performance along the Z axis restricts the stiffness performance of the whole mechanism.The variation laws of workspace volume,stiffness mean index and stiffness standard deviation index under different rope layout and detection radius ratio are studied.Using the ideal point method,the multi-objective scale synthesis of the mechanism is carried out,and the optimal scale parameters are calculated.The stiffness numerical evaluation index and stiffness fluctuation evaluation index are established,and different weighting coefficients are selected to evaluate the mechanism at different positions in the workspace.