关键词:双足机器人;欠驱动;步态切换;不平整地面;控制方法 Abstract The stability control of underactuated 3-D biped robot is still a hard nut to crack, as a result of locomotion characteristics which mix high dimension, strong nonlinearity and underactuation. Some traditional control methods, such as event-based feedback control and PD control, are poor in robustness and weak in resistance to external disturbances. Through observation, it is certain that humans adjust gaits tactically to regain stability when they are affected by external disturbances, by contrast with trying to keep the stability sustained by only one gait which is quite limited. Inspired by this, a control method based on gait transition is proposed for the underactuated 3-D biped robot. First of all, taking the minimum energy consumption as the optimization goal, a multi group of gait and step gait is designed as the reference gait to build a gait library by nonlinear optimization method. Secondly, to obtain an optimal performance in terms of the balance between the stability and input torques, a multi-objective gait transition function is established. Finally, a reference gait that minimizes the gait transition function is obtained by solving a quadratic optimization problem, and it is then used as the walking gait for the next step with the purpose of using gait library (multiple trajectories) method to reach the goal of improving robustness. In the simulation experiment, using the proposed gait transition control method, the underactuated 3-D biped robot can walk through the rough ground with the relative height varying within the range [20,20] mm without falling down, in contrast to the failure of previous one-gait control method. The results show the effectiveness of the method.
为说明该步态切换策略能够有效提高行走鲁棒性, 参考文献[34]中的地面高度设置, 以摆动腿落地时, 地面接触高 在[ 20,20] mm (约为4%的腿长)内随机变化的不平整路面作为扰动 (摆动腿落地后, 直到发生下一次碰撞前, 地面高度不再变化). 实验中共测试100 步, 并进一步假设 以每20步为一个周期, 即 , 如图5 所示. 显示原图|下载原图ZIP|生成PPT 图5随机生成路面高度 (以20步为一个循环). -->Fig.5Profile of randomly generated ground heights (every 20 steps as a period) -->
图6所示为机器人关节角度和角度速的相图, 仅采用基于事件的控制方法时, 机器人在三步之后相图呈发散状, 即机器人摔倒. 然而, 采用本文基于步态切换的控制方法, 通过切换不同的步态, 机器人能够有效克服地面高度的随机变化, 通过不平整地面, 如图7所示. 显示原图|下载原图ZIP|生成PPT 图6基于事件控制下的关节角度和角速度, 其中黑点为起始位置. -->Fig.6Joint angles and angular velocities under the event-based control, where the red solid circle is the initial position -->
显示原图|下载原图ZIP|生成PPT 图7步态切换控制下20步内的关节角度和角速度, 其中黑点为起始位置. -->Fig.7Joint angles and angular velocities within 20 steps under the gait transition control, where the red solid circle is the initial position -->
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