Research On Cable-suspended Parallel 3D Printing Robot

As an emerging rapid prototyping technology in the era of intelligent manufacturing,3D printing technology has become more and more widely used.At present,3D printers generally adopt tandem type and parallel type mechanisms as executing mechanisms,which are more suitable for printing small-size,high-precision models,but are not suitable for printing models with large volumes and low accuracy requirements.In this paper,based on the idea of improving the workspace of 3D printers,a cable-suspended parallel 3D printing robot which use a 6-cable and 6-DOF cable-suspended parallel mechanism as actuator is developed,and the lower control system based on stm32 and the upper control system based on windows are developed.These constitute the experimental platform for 3D printing robots.Because the cables will sag under its own weight,this paper analyzes the kinematics model of the robot when the cable is treated as the straight line and the catenary,and analyzes the dynamic model of robot based on the Lagrangian method for the cable-suspended parallel 3D printing robots.The final simulation results show that for a small span cable-suspended parallel 3D printing robot,there is almost no difference in the cable length between the catenary model and the linear model.In this case,the cable linear model can be directly used for motion control,thereby reducing the complexity of the control process.But for large-span cable-suspended parallel 3D printing robot,where the rope bends heavily,the cable must be analyzed as a catenary model.The working space and the movement performance of cable-suspended parallel 3D printing robot's print head are closely related to its structure,in this paper,a sequential connection method and a cross connection method between the static platform and the print head were designed.The global condition number of the Jacobian matrix in the entire workspace is used as the performance index of the print head during 3D printing robot's movement.Based on the dynamic model of the cable-suspended parallel 3D printing robot,the influence of the position of the print head,the connection point of the rope,the angle of the print head,and the size of the print head on the print head workspace and the global condition number were studied in both two connection methods.Finally,the closed-loop vector method was used to analyze the motion error of the print head of the cable-suspended parallel 3D printing robot,the print head motion error model was established,the relationship between the print head motion error,the robot structure error and the rope length error was obtained.Because the cable length error is hard to measure,a cable length prediction algorithm is designed based on the neural network prediction method.Finally,a motion error compensation method is designed.Simulation and experimental results show that the motion error after error compensation is obviously smaller than the motion error before error compensation.