| Legged animals,such as human,horse,tiger,leopard,etc.,not only have highly flexible moving and operating capabilities,but also have strong adaptability such as jungles,rugged mountains,steep rock surfaces,which are not available on wheeled or tracked mobile robots.In material transportation,field exploration,security patrol,ruins search and rescue,etc.,they have wide application prospects.In recent years,many research have been committed to the research and development in many kinds of legged robots,especially the quadruped robots with excellent stability,flexibility and load capacity.The driving modes of the active joints of quadruped robots can be divided into two main categories:electrical and hydraulic.Compared with electrical,the hydraulic has high power density and hard load characteristics,which make the robot have a larger load capacity and impact resistance.However,the hard load characteristics of the hydraulic drive can easily cause impact force when the robot's feet are in contact with the ground,which has a great impact on the leg structure,electrical components,connecting parts and the stability of the robot.In addition,the high energy consumption is also the bottleneck restricting the development of the hydraulically actuated quadruped robot.To solve the above problems,the hydraulic servo actuator with passive compliance was proposed from the actual application requirements of the quadruped robot SCalf-?,and related researches were carried out from several aspects The main research contents are as follows:1.The hydraulic servo actuator with passive compliance(HPCA)is proposed,which is characterized by the design of the miniature accumulator and check valve on a hydraulic cylinder with original structure.Then the numerical and simulation models are built by Simulink and AMESim,respectively.The cushioning characteritics,pressure-flow characteritics and frequency response are analyzed.The physical prototype is designed and integrated.After that the working principle,numerical and simulation modeling and passive compliance characteritics are verified through experiments.2.A leg experimental platform of the quadruped robot SCalf-? actuated by HPCA is designed,and its forward/reverse kinematics and dynamics models are derived.Then the compliance method characterized by incorporating dynamic feedforward control and joint angle feedback control items into virtual model is proposed.The simulation model of SCalf-? is established by AMESim software.After that the dynamic characteristics of the quadruped robot during gait execution and the interaction between robot's feet and the ground are analyzed.The results prove the effectiveness of HPCA on the passive compliance of the legged robot and the better compliance effect of the combination of active and passive compliance.3.Based on trotting gait and the foot trajectory planned by the combination of quantic spline interpolation curve and straight line,the movement track and load characteristics of the actuator when the separation points between the foot and the ground are at different positions are analyzed.By summing up,the energy-saving laws of HPCA in the supporting phase and swing phase,as well as the absorption of the pressure jump when the symmetrical valve controls the asymmetric cylinder are revealed.The energy-saving effects of HPCA are verified by simulation and experiments.4.Based on the analysis of the actuator's trajectory which affects the energy consumption of the quadruped robot,the foot trajectory planning method characterized by using segmented cubic spline interpolation curve in the swing phase is proposed.The time tf of the foot which is measured from the ground to the highest point was always introduced into the foot trajectory equations by the way of the piecewise programming in the swing phase to change the time ratio between the piston extension and retraction,and with the help of energy consumption model of the actuator,the impact of the gait cycle T,the step length L and the time tfon the energy consumption of the quadruped robot SCalf-? actuated by OHA was studied;Based on the simulation model built in AMESim,the energy saving ability of the HPCA with the energy efficient trajectory was verified by simulation. |
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