Kinematics,Gait Planning And Stability Analysis For Quadruped Robots With Twisting Trunks

Most of traditional quadruped robots are equipped rigid trunks.For natural quadrupeds,all of them have flexible trunks that could perform active motions.They always move their trunks when they are walking,running,bounding,turning or climbing.It is easy to image that the trunk motion plays important role in natural quadrupeds' daily life.Inspired by natural quadrupeds,this thesis proposed quadruped robots with dexterous trunks,which can move or change their form actively.It is of significance to investigate the quadruped robots with dexterous trunks and impacts of dexterous trunk on the performance of quadruped robots.The main contents of this thesis contain four aspects as follow.1.The bionic characteristics of the quadruped robots with dexterous trunks.Through observing behaviors of natural quadrupeds,revealing three basic motion style of the natural quadrupeds' trunks as motions of twisting,arching and twisting-arching.To find a serial of mechanisms in forms of open loops and close loops those can imitate these three motions.Adding these mechanisms into the design of quadruped robots leads to quadruped robots with dexterous trunks.Therefore,the dexterous trunks can be classified as dexterous twisting trunks,dexterous arching trunks and dexterous twisting-arching trunks.The bionics characteristics of the quadruped robots with dexterous trunks are embodied in the imitation of the three trunk motions.2.The kinematics and workspace of quadruped robots with dexterous twisting trunk.The coordinates of the mass center and hip locations of the robot are solved based on formula of mass center coordinates and matrix transformation respectively.This is the main content of the forward kinematics of the robot which deferring to that of quadruped robots with rigid trunks.The expression of joint angles of legs in terms of the coordinates of the foot tips is found out when a certain twisting angle is known,which is the main content of the inverse kinematics.Base on the kinematics,the trunk workspace and leg workspace of the robot are obtained through calculating the locations of mass center and foot tips respectively.By comparing with rigid trunk quadruped robots,it is found that the dexterous twisting trunk could enlarge the workspace of the robot.The work in this part is the fundamental of the gait planning and stability analysis.The dexterous twisting trunk will impact the gait and stability of the robot through the workspace.3.The gait planning for the quadruped robot with dexterous trunk.The gait planning is one of the basic research points of quadruped robots.This thesis solves the planning of continuous static gait and trot gait.For the continuous static gait,through the observation of geckos,the motion events of the gait are pointed out.The relation between the stride length and the twisting angle is found out based on the leg workspace and geometric method.By comparing with rigid trunk quadruped robots,it is found that the dexterous twisting trunk could lengthen the stride length of the robot.Then the monotonicity of stride length relative to twisting angle is solved.Based on the work above,the largest stride length of this gait is solved.The problem of kinematic margin is solved based on the geometric model and numerical calculation.As a result,the continuous static gait is implemented.In respect of trot gait,through the observation of lizards,the motion events of this gait are pointed out.Using the methods similar to those used in continuous static gait,the relation between stride length and the trunk twisting angle is solved.The trajectory of the mass center is solved based on the zeromoment point theory.Then the change rule of the trunk twisting angle is solved.As a result,the trot gait is implemented.At last the simulations and experiments are conducted to verify feasibilities of the gaits.It is proved that the dexterous twisting trunk can improve the locomotion speed of quadruped robots.4.The stability analysis for the quadruped robot with dexterous trunk.The stability analysis is one of the basic research points as well.From the view point of longitudinal stability margin and tumble stability,the static stability and dynamic stability are investigated respectively.The longitudinal stability margin is studied in the continuous static gait.The tumble stability is investigated when the robot stands suffering impacts from outside.The relations between the trunk twisting angle and two stability criteria are revealed.By comparison with the rigid trunk robot,it is proved that the dexterous twisting trunk can improve the stability of the robot.At last the simulations and experiments are conducted to verify the conclusions above.It is proved that the dexterous twisting trunk can improve the stability of quadruped robots.