Energy Consumption Analysis,Optimization And Power System Research For A Hydraulic Actuated Quadruped Robot

The legged animals in nature are highly adaptable to complex terrain such as rugged mountains,jungles,snow and ice,and can reach almost any part of the land surface.In view of the fact that the existing wheeled and tracked mobile robots cannot meet the application requirements of human beings in material transportation,disaster relief and geological exploration in complex terrain environment,in recent decades,researchers all over the world have developed a variety of legged robots with legged animals as bionic objects.Due to the advantages in movement speed,load capacity and stability,quadruped robots are favored by researchers.For legged robots,the main actuating mode can be divided into electrical,pneumatic and hydraulic,and the power supplies include high-density batteries and gasoline engines.Compared with electrical and pneumatic actuator,hydraulic actuator has high power density,which can meet the requirements of high load capacity and fast movement for field transportation of legged robot.In addition,the hydraulic drive system uses gasoline engine to provide energy,which can replenish quickly by adding fuel and has a long endurance,which is more suitable for field operation than the electric powered robot.Therefore,in the last decade,hydraulic actuated quadruped robots have developed rapidly.On the other hand,the energy utilization efficiency of the hydraulic drive system is low and the system generates serious heat.Therefore,measures must be taken to reduce the motion energy consumption of the hydraulic drive robot as much as possible.Besides,the dynamic load and walking state of the robot can easily cause the engine speed fluctuation.Therefore,the engine speed control algorithm with strong robustness must be designed.Aiming at the above problems,this paper takes SCalf-? hydraulic actuated quadruped robot as the research object,and establishes the energy model of robot motion,optimizes the trajectory of robot foot,and proposes a fuzzy feed-forward method based on flow estimation to control the engine rotating speed.The main research contents of this paper are as follows:1.In this paper,the SCalf-? quadruped robot was analyzed,both kinematics and dynamics models of the robot was established.A feet force distribution strategy based on the minimum norm method is proposed to obtain the complete expression of the joint torques,which lays a foundation for the establishment of energy model and flow matching of the hydraulic system.2.Based on the analysis of the characteristics of hydraulic friction forces the expression of the joint torques,a comprehensive energy model of the hydraulic actuated quadruped robot was established,including mechanical energy consumption and friction loss,and JCOT(Joint Cost of Transport)is proposed to value the joint power consumption conditions.Based on the most common used trot gait,the energy consumption characteristics of gait parameters such as step length,step height,standing height,gait cycle and duty cycle are analyzed.The gait parameters under typical scenarios are also acquired,which can provide a theoretical basis for the optimization of motion energy consumption of hydraulic actuated quadruped robot.This paper proposed a robot foot trajectory planning equation based on the Fourier series.The parameter selecting problem is converted into a optimization problem which uses the energy consumption of the robot as the objective function and the scope of joint movement as the optimization constraints.The Pattern Search Method is used to optimize the equation parameters,and the trajectory equation can be obtained.By comparing the energy consumption of the optimized trajectory with that of the cubic spline interpolated foot trajectory,the effectiveness of the optimized trajectory in energy consumption and motion control is proved.Based on the proposed energy efficient trajectory,the inverse kinematics is used to obtain the motions of the joints.The parameters of the hydraulic cylinder are used to estimation the hydraulic flow consumption,and the expected engine rotating speed can be determined.Besides,the hydraulic flows between the robot power system and the hydraulic system are also matched.To solve the problems of low output torque stiffness and rotating speed lag of fuel engine,a fuzzy feed-forward method based on flow estimation is proposed.Physical prototype experiments are made to verify the effectiveness and robustness of the method under different working conditions.