Research On Motion And Operation Cooperative Control Of Two Wheeled-leg Arm Robot Based On Distributed Model

The research object of this paper is a two wheeled-leg arm robot.This type of robot has the advantages of wheeled efficient movement ability,uneven terrain adaptability,arm operation ability,etc.It can adapt to the human working environment and has the potential to interact and collaborate with humans.However,due to the complex wheel-leg-arm composite structure,the lack of static stability margin,and the existence of real-time multi-point interaction between the wheel/arm and the environment,the control of the two wheeled-leg arm robot is very difficult.Therefore,how to integrate dynamic stability control into the wheel-leg-arm coordinated control and give full play to the wheeled motion ability,the terrain adaptability of the leg structure and the arm's working ability are important problems that need to be solved in the control of the two wheeled-leg arm robot.In recent years,advanced theoretical results and engineering prototypes for two wheeled-leg arm robots have continuously appeared,and their high dynamic motion capabilities have also set off a research boom in this field.Combining with the current development status,this article focuses on the movement and operation requirements of two wheeled-leg arm robots.The robot multi-mode control method,terrain adaptation method,wheel-leg-arm coordinated planning and control method are studied respectively.The main contents and innovations are as follows:1.The establishment of the kinematic model and dynamic stability analysis of the two wheeled-leg arm robot are the basis of motion and operation control.Firstly,based on the kinematics transfer relationship of the distributed model,the kinematics models of the wheeled-leg subsystem,the two wheeled-leg system,and the two wheeled-leg arm robot are established respectively.Secondly,it compares and analyzes the difference in the coupling relationship between the point foot type and the wheel foot type mechanism,locates the influence of the under-actuation characteristics on the attitude control,an extended internal horizontal posture state space model of wheeled-leg is established,and describes the posture changes of the wheel foot type system.Thirdly,based on the general point mass model,the dynamic stability constraint conditions of the two wheeled-leg system are analyzed,and model predictive controller is constructed to transform the horizontal acceleration into the internal horizontal attitude acceleration.Finally,an inverse kinematics control framework is designed to extend the internal horizontal posture,and the internal horizontal posture phase diagram is used to describe the convergence process of various unbalanced initial postures to the dynamic equilibrium point.2.The wheeled-leg dynamics model of the two wheeled-leg system can be used to plan the wheeled-leg-torso interaction force as a joint torque and drive the wheeled-leg subsystem to output the resultant force that pushes the torso's motion.Firstly,the initial state quantity is added to the under-actuated degree of freedom of the of the wheeled-leg subsystem's wheel-floating base,and the wheeled-leg integrated full-drive dynamics model is established with the interaction force of wheeled-leg and torso as the end output force.Then,a distributed control framework with the torso pose as task space is proposed,and the torso resultant force and joint torque are planned hierarchically.Finally,the proposed two wheeled-leg system walking and jumping motion planner and the multi-mode state machine are integrated with the control framework to realize the wheel-leg coordinated walking and jumping compliance control in the sagittal plane.3.When the two wheeled-leg system moves in uneven terrain,the adjustment of the wheeled-leg posture and the dynamic stability of the full body movement can be realized by planning the joint torque.Firstly,analyze the characteristics of the left and right wheeled-leg posture in the dynamic balance state of the two wheeled-leg system when moving on uneven terrain,release the standing height and internal horizontal posture constraints,and define the posture angle constraints describing the relationship between them.Secondly,analyze the overdrive phenomenon in the three-dimensional motion of the torso subsystem,use the active driving force at the end of the wheeled-leg to eliminate the linearly related passive driving force,and establish a complete mapping relationship between the resultant torso force and the active driving force of the wheeled-leg.Thirdly,a virtual force distribution method based on the wheeled-leg attitude angle constraint is proposed to realize the posture coordination of the left and right wheeled-legs.At the same time,a terrain adaptation strategy based on ankle joint torque compensation is proposed,so that when the slope angle changes,it can quickly converge and stabilize in a new balanced posture.Finally,carry out simulation and physical platform experiment verification.4.For the requirements of torso-arm coordinated motion and arm end force output of two wheeled-leg arm robot,firstly,a multi-task space planning method based on hierarchical optimization is proposed,which can achieve reference trajectory planning for two different priority task spaces simultaneously,eliminating the redundant of whole body motion planning.Secondly,a load adaptive estimator is designed based on the torso dynamics model to estimate the interaction force online between the arm and the environment.Thirdly,based on the two-level table-car model,the wheeled-leg-torso-arm force transmission is analyzed,and a virtual generalized force feedforward compensation method for arm motion and operate based on torso generalized force planning is proposed to improve the dynamic stability of motion and work.Finally,a physical environment simulation experiment is carried out.