An Improved Force Controller With Low and Passive Apparent Impedance for Series Elastic Actuators
An Improved Force Controller With Low and Passive Apparent Impedance for Series Elastic Actuators
复制标题
DOI：
10.1109/tmech.2020.2970532
复制
发表时间：
2020-06-01
影响因子：
6.4
通讯作者：
van der Kooij, Herman
中科院分区：
文献类型：
--
作者：
Rampeltshammer, Wolfgang F.;Keemink, Arvid Q. L.;van der Kooij, Herman
本文介绍了一种用于外骨骼、假体和人形机器人等步态机器人的串联弹性致动器的力控制器。因此，控制器需要增加执行器的带宽，降低其表观阻抗以抵抗干扰或与人类用户轻松交互，并稳定地与任何（动态）环境交互。对于步态来说，这些环境是不连续变化的，因此产生了规律的影响。在本文中，我们建议使用内环PD控制器来增加执行器的带宽，同时使用外环干扰观测器（DOB）来降低执行器的视阻抗。为了增加执行器的控制带宽，我们为PD控制器引入了一种新的调谐方法，该方法允许对被控对象的带宽和阻尼比进行独立调谐。通过降低视阻抗来抑制干扰的DOB会导致视阻抗变为非被动，从而导致执行器的潜在接触和耦合不稳定。为了与任何环境无条件稳定地相互作用，我们减小了DOB贡献，使其在保持无源的同时降低了表观阻抗。通过辨识转矩控制器的传递行为和执行器的视阻抗，在测试装置上对所提出的整定方法和DOB自适应进行了评估。实验结果表明，所提出的调谐方法可以分别对带宽和阻尼比进行调谐，而DOB自适应能够兼顾视阻抗的降低和无源性。
This article presents a force controller for series elastic actuators that are used in gait robots, such as exoskeletons, prostheses, and humanoid robots. Therefore, the controller needs to increase the bandwidth of the actuator, lower its apparent impedance for disturbance rejection or effortless interaction with a human user, and to stably interact with any (dynamic) environment. For gait, these environments are changing discontinuously, thus creating regular impacts. In this article, we propose the use of an inner-loop PD controller to increase the bandwidth of the actuator, alongside an outer-loop disturbance observer (DOB) to lower the apparent impedance of the actuator. To increase the controlled bandwidth of the actuator, we introduce a novel tuning method for the PD controller that allows for independent tuning of bandwidth and damping ratio of the controlled plant. The DOB, which is introduced to reject disturbances by lowering the apparent impedance, causes the apparent impedance to turn nonpassive, resulting in potential contact and coupled instability of the actuator. To enable unconditionally stable interactions with any environment, we scale down the DOB contribution such that it lowers the apparent impedance while remaining passive. The proposed tuning method and DOB adaptation were evaluated on a test setup by identifying the torque controller's transfer behavior and the apparent impedance of the actuator. The results of these tests showed that the proposed tuning method can separately tune bandwidth and damping ratio, whereas the DOB adaptation is able to tradeoff the reduction in the apparent impedance with its passivity.