Research On Precise Positioning Algorithm Of Spatial Four-cable Drive

The four-cable actuated parallel mechanism is a kind of device which uses the suspension cable as the driving element in the workspace to realize the fast and accurate positioning of the end-effector.Its advantages of wide coverage area,simple structure and low cost are very suitable for indoor archaeology high-precision photography and meet the work requirements of the maximum operating space.In this paper,through the static modeling,cable length optimization and workspace performance analysis and other aspects of research,to achieve the precise positioning of four-cable drive and workspace maximization.First of all,in order to reduce the positioning error of the suspension system,the self-weight and elastic deformation factors of the suspension cable are fully considered,and the spatial four-cable catenary equation is derived by analyzing the inverse solution of the position of the actuator.In order to study the influence of the elastic deformation of the suspension cable on the positioning of the system,Newton iterative method is used to solve the position-forward equation.Based on the optimization theory,using the sequential quadratic programming algorithm,three different optimization objective functions are simulated to solve the optimization of the cable force and cable length,and the effects of the three methods are compared by simulation variation curves.The experimental data show that there is little difference between the three optimization effects,which can be selected according to the working requirements of the system.At the same time,SQP algorithm has fast convergence speed,clear and simple solution process,uniform distribution of four cable forces,and avoids virtual pull phenomenon and cable force overrun.In addition,the comparative simulation results of elastic deformations show that when the four-cable traction system is positioned in the entire workspace,especially the workspace boundary,the overall position of the end-effector will be greatly deviated if the elastic deformations of the suspension cables are not considered.Therefore,the elastic deformation of the suspension cable should be considered in the spatial four-cable actuated parallel mechanism to reduce the position error and achieve accurate positioning.Finally,based on the dimensionality reduction theory,the expression of the workspace boundary closed by the force screw was derived by using the constraint conditions of the normal operation of the four-cable driven parallel mechanism.The influence of different types of suspension cables and different specifications of actuators on the performance of the workspace of the system is analyzed,and the workspace of the four-cable-driven parallel mechanism is maximized under the condition that the system works normally.