Mechanism Research Of A Hexapod Robot With Protectable Mechanical Legs

Since 1960s,hexapod robots have been developed into a kind of multi-legged robot with a variety of types.Due to some and even all of their actuators always swing with the mechanical legs,it is not esay to protect.This brings the hexapod robots have a high failure rate and low reliability while they work in the harsh environments,such as high humidity,high temperature and strong radiation.Therefore it is difficult for hexapod robots to perform dangerous tasks instead of human beings.The general protection method of driver and driver's accessories is applying the shelter and isolation while they operate in the severe environment.Hence the revolve or prismatic joint is designed as the driving joint,so as to protect the driver and its accessories.Further more,the driving joint is connected with the frame to make the corresponding driver and its accessories can be fixed on the frame.This kind of mechanical leg is called protectable mechanical leg.This paper does a lot of work to research and analyze the mechanisms of hexapod robot with protectable mechanical leg.Based on the G_F set theory,the kinematic characteristics and degree of freedom composition are analyzed for the leg mechanism and ankle joint of the proposed multi-legged robot in this paper.The structure layout and composition schemes of protectable leg mechanism are designed.The principle of type synthesis of protectable leg mechanism is proposed,and the method of judging the effectiveness of leg mechanism is given.Many 3-DOF passive walking mechanisms are synthesized,and the motion input points and input motion characteristics of these walking mechanisms are determined.Fifteen kinds of series-parallel hybrid protectable leg mechanisms and 8 kinds of parallel protectable leg mechanisms are synthesized.At the same time,a brief configuration scheme of these protectable leg mechanisms is made.The inverse position of a protectable leg mechanism is analyzed.The three-dimensional workspace of the foot endpoint is plotted by using the boundary search method.The jacobian matrix,hessian matrix and the driving static model of the leg mechanism are established.Moreover,the constraint jacobian matrix of the driving mechanism is solved based on the linear space theory.The adjoint relationship between the velocity and angular velocity of the endpoint of the driving mechanism and the walking mechanism is analyzed respectively.Based on the principle of virtual work,the dynamic model of the leg mechanism is established.To verify the correctness of the theoretical model,the kinematics and mechanics simulation of the leg mechanism are executed.Five kinds of whole mechanism types are given based on the principle of bionics.The configuration characteristics of these whole machines are analyzed.Using the closed-loop vector chain method,the transfer relationship between the motion input of the supporting leg and the motion output of the body of a hexapod robot is established.The velocity and acceleration of the supporting leg and swing leg are analyzed,and the formulas of velocity and acceleration of the center of mass of the components in the supporting leg and swing leg are given.The dynamic models of supporting leg and swing leg are solved.To verify the correctness of the theoretical model,the kinematics and mechanics simulation of the integrated hexapod robot are executed.The workspace evaluation index of the driving mechanism and the kinematics and static performance evaluation index of the leg mechanism are defined.Based on the defined performance evaluation index,the geometric parameters of the leg mechanism are selected by multi-objective optimization.Then,based on the dynamic model of the hexapod robot,the driving parameters of the hexapod robot are estimated.Based on the geometric parameters of the leg mechanism and the driving parameters of the hexapod robot,the whole design and experimental prototype of hexapod robot are designed and developed.The stability evaluation index of hexapod robot is defined,and the stability of hexapod robot in tripod,quadruped and pentapod gait is analyzed.The gait of hexapod robot across the obstacles,such as the ditch,the hillock and the stairway,is planned.The relationship between the ditch width and stride gait is summarized.A formula for calculating gait parameters of hexapod robot in gait adjustment stage during the stair gait is established.The research contents of this paper lay a theoretical foundation for the development and practical application of the hexapod robot with protectable mechanical legs.