Research On Control System Of Hydraulically Actuated Single-legged Hopping Robot

With the deepening of the multi-legged robot research,four types of multi-legged robot research are the key points among the robotics field.The first type is the multi-legged robot with the capability of large load transportation as a vehicle which can walk on the terrain while the wheeled vehicle can not.The second type is the multi-legged robot with dynamic motion of high speed,high efficiency and adaptability to all kinds of terrain.The third type is the multi-legged robot whose mechanical structure is designed based on bionics,improving the running speed.The fourth type is the multi-legged robot with the capability of various gaits,especially the dynamic gait.The dynamic gait research of legged robot is the core common research of the above-mentioned four types of robot.The single-legged robot has only one gait,the dynamic hopping gait.And meanwhile the single-legged hopping robot's mechanical structure is relatively simple and the robot is easily controlled.So that the single-legged hopping robot is the ideal platform for the research of dynamic gait of legged robot.The hopping proceduce of the single-legged hopping robot is the same with that of the multi-legged robot's single leg.The single leg alternately changed between flight phase and stance phase.The hopping cycle of the single-legged robot is composed of all the dynamic hopping events of the multi-legged robot's single leg.During the procedure,the single-leg interactives with environment.The contacting,friction and collision influence the control of the hopping robot and the dynamic stability.The thesis systematically develops the basic research of single-legged hopping robot,which includes robot kinematics,dynamics,contact model with ground,vertical hopping,height control and compliant touch-down.And the methods and theories are verified by the simulation and experiment,providing basis for the follow-up research of dynamic gait.The thesis is organized in logical and sequential chapters as follows:In chapter 1,the background and significance are introduced,the development situation of the domestic and foreign single-legged hopping robots are reviewed based on a large number of domestic and foreign literature,3 routes of the single-legged hopping robot research is analyzed.Furthermore,the control research situation of domestic and foreign single-legged hopping robots is intruoduced from 3 aspects,the control of prismatic-legged hopping,the articulated single-legged hopping and compliant touch-down of the legged hopping.Some domestic and foreign attractive and difficult research areas are analyzed.At last the research contents of this thesis are presented by considering providing the basic research of the dynamic gait locomotion of multi-legged robot which constitute the overall framework of the hydraulically actuated single-legged hopping robot systematic research.In chapter 2,considering design of the hydraulically driven single-legged robot,two aspects of bionics research of the robot design are proposed.Research of skeleton structure and joint angle of the large dogs' hind limb provided design reference for the robot's joint angle,limb length,as well as actuator layout.Research of joint angle interval and the reaction force of the end-effector on stance of hopping gait provided design reference for the hydraulic actuator parameters.The virtual prototype of robot was designed based on the design parameter by SolidWorks.The mass property parameter was obtained from toolbox of SolidWorks.The mechanical structure and hydraulic acutor parameters were verified by vertical hopping simulation in the software of Matlab/Simulink.And meanwhile the hydraulic system parameters were obtained by the simulation,which provided reference for the design of hydraulic system.The hydraulically actuated single-legged hopping robot has 2 active degree of freedom(DOF),they are extension/flexion of hip joint in sagittal plane and extension/flexion of knee joint in sagittal plane,respectively.Both limb length of upper leg and lower leg is 0.35 m.The hip joint angle range is[-50°,70°],while the knee joint angle range is[-140°,-20°].The piston diameter of the hydraulic cylinder is 0.02 m;the rod diameter of hydraulic cylinder is 0.01 m.The hydraulic system pressure is 16 MPa;and the average rate of flow of hydraulic system is 5.6×10-5 m3/s.The hydraulically actuated single-legged hopping robot platform consists of the single-legged hopping robot,hydraulic system and measurement and control system as well.Chapter 3 builds the vertical hopping simulation platform of hydraulic actuated single-legged hopping robot.The kinematics and dynamics of the single-legged hopping robot was modeled on the basis of deeply understanding and researching the theory of hopping robot.The nonlinear dynamics of hydraulic actuator on robot joints was built.Two types of contact model,the soft contact and the hard contact,were set up.The ground reaction force of both contact models to the end-effector was obtained.Furthermore,two kinds of methods to judge the touch-down and take-off condition were ananlyzed,which were zero-crossing of end-effector's postion and zero-crossing of ground reaction force to the end-effector.The four modules,which are dynamic model of hopping robot,dynamic model of hydraulic actuator,contact model and robot controller,were integrated by simulation software named Matlab/Simulink.In chapter 4,considering the vertical hopping research of the single-legged hopping robot,the vertical hopping control method is proposed based on the motion planning on stance.The SLIP model,mass-spring-damper model,CoM sinusoidal motion were analyzed and the dynamic integrated equation was solved.On Cartesian Space,robot's hip motion was mapped to the planned motion of the center of mass(CoM)by SLIP model and CoM sinusoidal motion.On joint space,the vertical hopping was realized with the joint trajectory planning based on the sine function.The PID controller and PD controller were adopted to track the joint motion of robot separately on flight phase and stance phase.The method of vertical hopping was verified by the simulation on the dynamic hopping simulation platform and then by the experiment on the hopping robot plateform.In Chapter 5,considering the compliant touch-down of the hydraulic actuated single-legged hopping robot with the purpose of releasing the effect of impulse to the robot system and its motion control the instant the hydraulically actuated legged-robot touches down with dynamic gait.Two types of solution are proposed.The first solution is designing the damping hole on the hydraulic actuator unit of the hopping robot.The compliant touch-down is realized by releasing the hydraulic impulse generated by the touch-down impulse of robot's end-effector.The second soluton is based on the robot joint motion planning on flight phase.The compliant touch-down condition was obtained by analyzing the dynamics of touch-down of vertical hopping.The compliant touch-down was realized by joint motion planning on flight phase.The experiment result shows that the effect of the hydraulic pressure releaseing is evident with the damping hole inside the hydraulic cylinder.With the same diameter of the damping hole,and the robot dropped from the same height without initial velocity,the end-effector's impulse with the active compliance strategy is smaller than that with the joint postion control strategy.Combined with the first compliance control method which the actuator unit of the hydraulically actuated single-leggd hopping robot has a damping hole with diameter of 1 mm,the experiment result of the control method based on the joint motion planning on flight showed that the hydraulic pressure of the hydraulic rodless chamber reduced from 6 MPa to 5 MPa the instant the robot touched down the ground.The effect of releasing hydraulic pressure is evident.In chapter 6,the vertical hopping control of the single-legged hopping robot was realized based on the active compliance control which is a typical cascade control structure.Different outer loops of active compliance control was adopted based on different phases.The inner loop of active compliance is the force control,including the force tracking control with hydraulic force and load force.Contiuous and stable vertical hopping of the single-legged hopping robot is realized on the vertical hopping simulatin platform and hopping robot platform.The hydraulic impulse of the rodless chamber of the joint hydraulic cylinder is controlled within a smaller value,compliant touch-down was realized during the procedure of dynamic hopping.Chapter 7 provides the summary of the thesis.The future work prospections and innovations are also included.