Tracking Control And Motion Distribution Of Omnidirectional Mobile Robot Based On Decoupled Active Caster Wheels

Mobile robot based on decoupled active caster wheels is a new type of omnidirectional mobile robot,which is particularly suitable for goods-carriage in small spaces and has high socioeconomic value.The special configuration of this type of robot not only realizes the omnidirectional movement function,but also makes the challenge of driving redundancy to the system,causing difficulties in motion control.In order to promote the development of omnidirectional mobile robots based on decoupling active caster wheels,which can be truly applied in practical industries,this paper makes in-depth research on motion control which is the key technology of this type of robot.We propose a concept of hierarchical control for omnidirectional mobile robot system with decoupling active caster wheels,which is based on the kinematic model and the dynamic model.The upper layer implements trajectory tracking control and the lower layer implements motion distribution.Firstly,the development of omnidirectional mobile robots is introduced,and advantages of decoupling active caster wheels to achieve omnidirectional movement towards robots are highlighted.And then the key research contents of mobile robot motion control are summarized.Secondly,we design an omnidirectional mobile robot composed of two decoupled active casters,and explain the working principle of decoupled active caster wheel.And then the degree of freedom of mobile robot based on the decoupled active caster wheels is calculated.Based on the series-parallel theory,an active caster wheel can be regarded as a three-degree-of-freedom robotic arm,and mobile robot can be regarded as a platform with multiple robotic arms.Under ideal motion conditions,kinematic and static model of the robot are constructed.Based on galil's hardware servo drive system and ROS-based software system,the robot control system is built.In terms of tracking control based on the kinematic model,we analyze the slip interference of casters,and establishe a kinematic model of omnidirectional mobile robot considering slip interference.Based on the multi-sensor information fusion technology,the speed estimation and position estimation of robot's motion state are realized,and the slip is estimated.A dynamic model of the tracking error during the movement of the mobile robot is established,and the upper-level trajectory tracking controller is designed in combination with the backstepping method.The caster speeds are distributed based on inverse kinematics,sliding compensation is introduced into the joint end,and overall control frame of robot system is established.Then,we analyze the influence of control parameters on the stability of robot system,and verify the effectiveness of control method by simulation and experiments.In order to further study the robot's motion control,we explore from the perspective of dynamics.Considering the non-holonomic constraint characteristics of caster wheels,a dynamic model of omnidirectional mobile robot and a simplified friction model are established based on the first type of Lagrangian equation.For the convenient of upper layer controller design,we translate it into an overall dynamic model in the workspace.Based on sliding mode theory,the upper trajectory tracking controller is designed.In terms of lower-level torque distribution,the constraint problem is transformed into an optimization problem,and the Lagrangian multiplier method is used to solve the optimization problem so as to minimize the internal force of the robot.Then,the stability of the system is analyzed,and the effect of the controller is verified through simulation experiments.This paper proposes a hierarchical trajectory tracking controller based on the kinematics model and dynamics model of omnidirectional mobile robot with decoupled active caster wheels,which takes the redundant driving characteristics of omnidirectional mobile platform into account.We hope this technology can support omnidirectional mobile platform application and promote its development.