Abstract:In order to improve the flexibility and wearability of exoskeleton, a wearable lower limb exoskeleton based on the flexible drive joint is designed. In view of the different focus points at different phases in the control of lower limb exoskeleton, a hybrid control strategy based on dual-mode switching is proposed. Firstly, a series elastomer based on double parallel springs is designed to solve the flexibility problem of the lower limb exoskeleton joint, and it is installed in the drive module of exoskeleton joint. The feedback of joint torque and position information is achieved through two encoders. Then, a dual-mode switching control strategy is proposed by analyzing the movement characteristics of the exoskeleton at different gait phases. The adaptive impedance control algorithm is adopted at the stance phase to improve stability and impact resistance, and the active disturbance rejection and fast terminal sliding mode control algorithm is adopted at the swing phase to improve response speed and tracking accuracy. Finally, control simulation and active-passive tracking experiments are carried out to verify the superiority of the proposed algorithm to traditional PID (proportional-integral-derivative) and active disturbance rejection control algorithms. The results of passive tracking experiment show that the convergence time can reach 0.28 s when the convergence range of joint error is ±5%. In the active tracking experiment, the maximum RMSEs (root mean squared errors) of the hip and knee joints are 0.47° and 1.28° respectively while the experimenters wear the exoskeleton. These experimental results show that the human movement intention can be tracked in real time by the proposed control algorithm, and the requirements for human-machine interaction flexibility are satisfied.
[1] 张玉明,吴青聪,陈柏,等.下肢软质康复外骨骼机器人的模糊神经网络阻抗控制[J].机器人, 2020, 42(4):477-484,493. Zhang Y M, Wu Q C, Chen B, et al. Fuzzy neural network impedance control of soft lower limb rehabilitation exoskeleton robot[J]. Robot, 2020, 42(4):477-484,493. [2] 贾斌,熊小桃,王家豪.机器人的现状及发展趋势探析[J]. 中国新技术新产品, 2019(16):117-118. Jia B, Xiong X T, Wang J H. Analysis on the status and development trends of the robotics[J]. China New Technologies and New Products, 2019(16):117-118. [3] 张琦,田梦倩,李伟强,等.复式套索人工肌肉驱动的下肢外骨骼的运动控制[J].机器人, 2021, 43(2):214-223. Zhang Q, Tian M Q, Li W Q, et al. Motion control of a lowerlimb exoskeleton actuated by compound tendon-sheath artificial muscles[J]. Robot, 2021, 43(2):214-223. [4] Chen C F, Du Z J, He L, et al. Active disturbance rejection with fast terminal sliding mode control for a lower limb exoskeleton in swing phase[J]. IEEE Access, 2019, 7:72343-72357. [5] 赵新刚,谈晓伟,张弼.柔性下肢外骨骼机器人研究进展及关键技术分析[J].机器人, 2020, 42(3):365-384. Zhao X G, Tan X W, Zhang B. Development of soft lower extremity exoskeleton and its key technologies:A survey[J]. Robot, 2020, 42(3):365-384. [6] Chen C F, Du Z J, He L, et al. Development and hybrid control of an electrically actuated lower limb exoskeleton for motion assistance[J]. IEEE Access, 2019, 7:169107-169122. [7] Sanchez-Villamañan M D C, Gonzalez-Vargas J, Torricelli D, et al. Compliant lower limb exoskeletons:A comprehensive review on mechanical design principles[J]. Journal of NeuroEngineering and Rehabilitation, 2019, 16. DOI:10.1186/s12984-019-0517-9. [8] Carpino G, Accoto D, Sergi F, et al. A novel compact torsional spring for series elastic actuators for assistive wearable robots[J]. Journal of Mechanical Design, 2012, 134(12). DOI:10.1115/1.4007695. [9] dos Santos W M, Caurin G A P, Siqueira A A G. Design and control of an active knee orthosis driven by a rotary series elastic actuator[J]. Control Engineering Practice, 2017, 58:307-318. [10] Long Y, Du Z J, Chen C F, et al. Development of a lower extremity wearable exoskeleton with double compact elastic module:Preliminary experiments[J]. Mechanical Sciences, 2017, 8(2):249-258. [11] Karavas N C, Tsagarakis N G, Caldwell D G. Design, modeling and control of a series elastic actuator for an assistive knee exoskeleton[C]//IEEE RAS and EMBS International Conference on Biomedical Robotics and Biomechatronics. Piscataway, USA:IEEE, 2012:1813-1819. [12] Cestari M, Sanz-Merodio D, Garcia E. Preliminary assessment of a compliant gait exoskeleton[J]. Soft Robotics, 2017, 4(2):135-146. [13] Zhu Y H, Yang J X, Jin H Z, et al. Design and evaluation of a parallel-series elastic actuator for lower limb exoskeletons[C]//IEEE International Conference on Robotics and Automation. Piscataway, USA:IEEE, 2014:1335-1340. [14] Shi D, Zhang W X, Zhang W, et al. A review on lower limb rehabilitation exoskeleton robots[J]. Chinese Journal of Mechanical Engineering, 2019, 32. DOI:10.1186/s10033-019-0389-8. [15] Chu A, Kazerooni H, Zoss A. On the biomimetic design of the Berkeley lower extremity exoskeleton (BLEEX)[C]//IEEE International Conference on Robotics and Automation. Piscataway, USA:IEEE, 2005:4345-4352. [16] Wang S Q, Wang L T, Meijneke C, et al. Design and control of the MINDWALKER exoskeleton[J]. IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2015, 23(2):277-286. [17] Lee S, Sankai Y. Power assist control for walking aid with HAL-3 based on EMG and impedance adjustment around knee joint[C]//IEEE/RSJ International Conference on Intelligent Robots and Systems. Piscataway, USA:IEEE, 2002:1499-1504. [18] Kim H, Shin Y J, Kim J. Design and locomotion control of a hydraulic lower extremity exoskeleton for mobility augmentation[J]. Mechatronics, 2017, 46:32-45. [19] Spong M W, Hutchinson S, Vidyasagar M. Robot modeling and control[J]. Industrial Robot, 2006, 33(5):403-403.