Research On The Rolling Motion Generation Of A Robot Based On Closed Chain Five-bow-shaped-bar Linkage

The mobile performance is the key technology of the robot to complete the tasks in a complicated environment,while the main way to develop new types of mobile robots with an efficient and high speed movement is study from nature.Organisms in nature have developed many excellent environmental adaptations through long-term evolution and could be learned and imitated by human beings.Bionics research shows that some organisms can perform rolling movement with the trunk and limbs as rolling elements,which is different from the rolling of wheels with fixed-axis.Inspired by nature,a varity of rolling robots have been developed by researchers.However,most of them adopt traditional structural link as the component,which makes the robot move at a lower speed and hard to overcome the impact force from the ground that will affect the stability.In order to overcome the above shortcomings,this paper put forword a novel rolling robot based on closed chain five-bow-shaped-bar linkage,which can be propelled forward by the change of the shape and also can avoid the impact force from ground,resulting a smooth and continuous rolling movement.The main works of this paper are as follows:Firstly,the mechanical structure is designed using bow shaped bar according to the theories of morphology and symmetry.The robot is composed by five modular bow shaped bars connected end to end,and each module has the same structural parameters and centroid distribution through weight balancing.The generalized coordinates are defined in the kinematics model,and then the relationships between the active and passive joints are obtained.Moreover,the coordinates,velocities and accelerations of the center of mass are deduced in D-H method.By regarding the dynamic rolling as the rolling of a disk,the inertia moment of the robot relative to the contact point is calculated out.Secondly,the constraints and mechanism of dynamic rolling are analyzed.The trendency of the work space of the center of mass as well as the maximum centroid offset along with the rolling angle is obtained through Monte Carlo algorithm.The non-linear coupling model of the rolling acceleration about the three generalized coordinates is established and numerically decoupled to obtain the maximum acceleration of the robot.Then,four schemes of rolling laws,such as sine curve,triangle,trapezoid and correction trapezoid,are used to solve the joint solution space.The line between the initial and target positions in the solution space is used as the reference trajectory to optimize the joint trajectory with the goal of minimum modal between the joint position and the reference trajectory.The stability of the dynamic rolling is analyzed by zero-moment point(ZMP)method,according to the results of joint trajectory planning.Then the ZMP curve relative to the contact point is figured out,which shows that the sharp change in the rolling acceleration of the robot will cause a vibration in the ZMP curve,thus,affect the stability.Thirdly,the Lagrangian equation of the dynamic rolling is established in the non-redundant driving condition,according to the kinetic and potential energies,as well as nonholonomic constraints of the dynamic rolling.By substituting the joint trajectory into the Lagrangian equation,the generalized forces are obtained corresponding to the four given acceleration laws.Fourthly,the ability of obstacle negotiation is analyzed by regarding the contact point between the robot and obstacle as a fulcrum,then,it could be seem as an optimization problem of the COG with constraints.In this way,the height model of obstacle negotiation is established with the structural parameters and the horizontal distance between the robot and obstacle.And the tendency of the height of the obstacle that the robot can overcome is figured out in the rolling angle axis in numerical method.Moreover,the joint trajectory during the obstacle overcoming course is planned with the principle of minimal path of the center of mass,according to the range of the center of mass and its concave characteristic.The dynamics of the obstacle overcoming is analyzed to acquire the friction coefficient to ensure the robot's non-slip movment in the obstacle overcoming process.Finally,a prototype testing platform and the closed-loop control system are designed to verify the theoretical analysis.And the difference between the planning result and sensor signal is used to control the joint.The study of this paper has a great significance,as it develops the theory of movement of the closed chain linkage mechanism and explores the application of a new type of movement method.