摘要
This paper presents a control algorithm for push recovery, which particularly focuses on the hip strategy when an external disturbance is applied on the body of a standing under-actuated biped. By analyzing a simplified dynamic model of a bipedal robot in the stance phase, it is found that horizontal stability can be maintained with a suitably controlled torque applied at the hip. However, errors in the angle or angular velocity of body posture may appear, due to the dynamic coupling of the transla- tional and rotational motions. To solve this problem, different hip strategies are discussed for two cases when （1） external dis- turbance is applied on the center of mass （CoM） and （2） external torque is acting around the CoM, and a universal hip strategy is derived for most disturbances. Moreover, three torque primitives for the hip, depending on the type of disturbance, are designed to achieve translational and rotational balance recovery simultaneously. Compared with closed-loop control, the advantage of the open-loop methods of torque primitives lies in rapid response and reasonable performance. Finally, simulation studies of the push recovery of a bipedal robot are presented to demonstrate the effectiveness of the proposed methods.
目的:稳定站立和姿态保持是双足机器人正常作业的前提,但各种不确定的外部扰动不可避免。机器人需要通过协调关节运动使其快速恢复到原先的稳定站立状态。创新点:本文提出一种开环bang-bang-bang控制方法,根据扰动情况设计髋关节力矩曲线,可以同时恢复欠驱动双足机器人的平衡状态和身体姿态。与闭环控制相比,本方法恢复更为迅速。方法:首先,将外力扰动情况分为3类:1)外力通过质心,扰动仅改变平衡状态不改变身体姿态;2)外力矩扰动,扰动仅改变身体姿态不改变平衡状态;3)外力不通过质心,扰动同时改变平衡状态和身体姿态(图2)。然后,针对不同扰动情况提出对应的3种开环bang-bang-bang控制方法以及对应的髋关节力矩曲线:1)针对扰动情况1的STB控制(式14),在恢复水平稳定状态的同时不改变原先的身体直立姿态;2)针对扰动情况2的ATB控制(式18),在恢复身体直立姿态的同时不改变水平稳定状态;3)针对扰动情况3的UTB控制(式32),可以同时恢复水平稳定状态以及原先的身体直立姿态。并证明了针对最大可恢复范围内的扰动,本文的控制方法都可以同时恢复双足机器人的平衡状态和身体姿态。最后,通过4组仿真实验验证了本文方法的有效性和相比闭环控制的快速性。结论:针对欠驱动双足机器人站立的扰动恢复问题,提出一种基于髋策略的bang-bang-bang控制方法。该方法可迅速同时恢复机器人的平衡状态及身体姿态。
基金
Project supported by the National Natural Science Foundation of China （Nos. 51405430 and 61473258） and the National High-Tech R＆D Program （863） of China （No. 2012AA041703）
