Active and variable stiffness adjustment strategy for legs of quadruped robot for stable transition between soft and hard ground
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摘要: 針對四足機器人在變剛度地面環境下動態行進時易出現姿態不穩定的問題，本文提出了一種機器人腿部主動變剛度實時調節策略，該策略根據機器人著地后的機身和腿部的運動狀態實時估計出著地腿和地面的耦合剛度，并將前后腿與地面耦合剛度的差值補償到相應的著地腿上。該策略能夠使機器人著地后迅速適應不同剛度特性的地面，特別是地面剛度相差較大的情況。通過搭建Simulink-SimMechanics仿真平臺，對角腿在同一剛度地面和變剛度地面兩種不同的著地環境，對僅利用常規姿態反饋控制、腿部主動變剛度調節策略與常規姿態反饋控制聯合方式進行了對比實驗。結果表明，通過腿部主動變剛度調節策略的作用，四足機器人在軟硬地面過渡時實現對機身俯仰角和滾轉角的補償修正，調控效果優于單獨通過常規姿態反饋控制。Abstract: Quadruped bionic robots are favored by development experts because of their broad application prospects, such as interstellar exploration, educational companionship, and social inspections. Quadruped robots were developed and inspired by mammals, which are known to exist in most areas on the earth's land surface. However, quadruped robots cannot achieve such an ideal state due to various reasons. At present, the adaptive problem of quadruped robots under a complex and changeable terrain has made significant progress, as reported in related literature. However, the case of robots that are as flexible as mammals in nature and meet the needs of multi-functional and multi-scenarios are still poorly understood. A quadruped robot is prone to posture instability when dynamically traveling in a ground environment with variable rigidity. This work proposes a real-time adjustment strategy of the active variable stiffness of the legs. This strategy estimates the landing in real time based on the motion state of the fuselage and legs after the robot touches the ground. The coupling stiffness of the legs and the ground and the difference between the coupling stiffness of the front and rear legs and the ground is compensated to the corresponding landing legs. This enables the robot to quickly adapt to the ground with different stiffness characteristics after landing, especially when the ground stiffness differs greatly. The Simulink-SimMechanics simulation platform is established with the diagonal legs on the same stiffness ground and on different ground environments with variable stiffness. The active leg stiffness adjustment strategy combined with conventional attitude feedback control is tested, and results are compared with those using only a conventional attitude feedback control. Results show that through the active variable stiffness of the legs, the quadruped robot realizes the compensation and correction of the pitch and roll angle of the fuselage during the transition between soft and hard ground. Moreover, the control effect is better than that of the conventional attitude feedback control alone.
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圖 8 腿部狀態. (a) 腿1、2狀態; (b) 腿3、4狀態
Figure 8. State of each leg: (a) states of the first and second legs; (b) states of the third and fourth legs
圖 9 機身側向運動. (a) 機身側向位移; (b) 機身滾轉角; (c) 機身滾轉角速度
Figure 9. Lateral movement of the fuselage: (a) lateral displacement of the fuselage; (b) roll angle of the fuselage; (c) roll angular velocity of the fuselage
圖 10 機身俯仰運動. (a) 機身俯仰角; (b) 機身俯仰角速度
Figure 10. Pitching motion of the fuselage: (a) pitch angle of the fuselage; (b) pitch angular velocity of the fuselage
圖 11 變剛度地面下單獨采用cAFC的仿真視頻截圖
Figure 11. Simulation video screenshot of the cAFC alone under the ground with variable stiffness
圖 12 變剛度地面下cAFC與aVSL聯合作用的仿真視頻截圖
Figure 12. Simulation video screenshot of the combined action of cAFC and aVSL under the ground with variable stiffness
圖 13 變剛度地面下的側向運動. (a) 變剛度地面下的側向位移; (b) 變剛度地面下的機身滾轉角; (c) 變剛度地面下的機身滾轉角速度
Figure 13. Lateral motion under the ground with variable stiffness: (a) lateral displacement under the ground with variable stiffness; (b) roll angle under the ground with variable stiffness; (c) roll angular velocity under the ground with variable stiffness
圖 14 變剛度地面下的機身俯仰運動. (a) 變剛度地面下的機身俯仰角; (b) 變剛度地面下的機身俯仰角速度
Figure 14. Pitching motion under the ground with variable stiffness: (a) pitch angle under the ground with variable stiffness; (b) pitch angular velocity under the ground with variable stiffness
中文字幕在线观看表 1 模型的重要參數
Table 1. Important parameters of the model
Parameters Value Length, width, and height of the fuselage/m 0.35、0.18、0.03 Weight/kg 5.103 Thigh length/m 0.16 Calf length/m 0.16 Acceleration of gravity/(m?s?2) 9.80665 Original length of equivalent leg / m 0.2771 Initial angle of swing joint (rad) 0 Initial angle of hip joint / rad ?π/6 Initial angle of knee joint / rad π/3 Initial horizontal speed of the fuselage / (m?s?1) 1 Initial height of the fuselage / m 0.3 
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