Motion And Error Analysis Of Omni-directional Robot Based On Screw Theory

Omni-directional mobile robots have been widely used with high mobility.When the omni-directional mobile robots are used as mobile platforms for the mobile assembly robots,the assembly becomes more flexible and convenient,but the high-precision requirements of robot are higher.In this paper,the omni-directional mobile assembly robot developed by the laboratory is taken as the research object to explore the method of improving the assembly precision.Firstly,the omni-directional mobile robot assembly structure is introduced and analyzed simply.The virtual principle of connecting rod and the screw theory are used to establish the omnidirectional mobile platform kinematics model and parallel assembly platform kinematics model respectively.The error model of the omni-directional mobile platform and parallel assembly platform are respectively established by using the method of virtual principle of connecting rod and the screw theory.Then the relationships between the motor driven errors,bar length errors,the hinge clearance errors and the posture errors of end assembler are presented.Meanwhile the deformation of the parallel assembly platform is analyzed with the external force,and the compensation model of deformation errors is built.Finally,simulations of the kinematics model and the error model are presented.By observing the simulation results of kinematics model,the paper haves obtained the effectiveness of the method of screw theory in establishing kinematics model.By comparing the simulation results of error model,the paper obtains two methods to improve the assembly accuracy of the omni-directional mobile assembly robot: one is from the control aspect and the other is from the processing.