Optimal variable stiffness control: formulation and application to explosive movement tasks
Optimal variable stiffness control: formulation and application to explosive movement tasks
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DOI：
10.1007/s10514-012-9302-3
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发表时间：
2012-10-01
影响因子：
3.5
通讯作者：
Vijayakumar, Sethu
中科院分区：
文献类型：
--
作者：
Braun, David;Howard, Matthew;Vijayakumar, Sethu
人们普遍认为，一旦考虑到动态任务，柔顺驱动对机器人控制是有利的。然而，内在合规性的好处伴随着较高的控制复杂性。具体地说，通过顺应的致动器协调系统的运动，并找到导致更好性能的特定于任务的阻抗分布，这是众所周知的。在这里，我们提出了一个最优控制公式来计算电机的位置指令，以及相关的时变扭矩和刚度分布。为了证明这种方法的有效性，我们考虑了一个“爆炸性”的投球任务，其中利用柔顺驱动系统的内在动力学导致了任务性能的改善(即，投掷距离)。在这个例子中，我们表明：(I)所提出的控制方法能够根据特定的任务目标和系统动态来定制阻抗策略，(Ii)可以利用改变刚度的能力来获得更好的性能，(Iii)在具有可变物理柔度的系统中，本公式使得能够利用执行器的储能能力来改善任务性能。我们在数值仿真和两连杆变刚度机器人的硬件实验中对此进行了说明。
It is widely recognised that compliant actuation is advantageous to robot control once dynamic tasks are considered. However, the benefit of intrinsic compliance comes with high control complexity. Specifically, coordinating the motion of a system through a compliant actuator and finding a task-specific impedance profile that leads to better performance is known to be non-trivial. Here, we propose an optimal control formulation to compute the motor position commands, and the associated time-varying torque and stiffness profiles. To demonstrate the utility of the approach, we consider an "explosive" ball-throwing task where exploitation of the intrinsic dynamics of the compliantly actuated system leads to improved task performance (i.e., distance thrown). In this example we show that: (i) the proposed control methodology is able to tailor impedance strategies to specific task objectives and system dynamics, (ii) the ability to vary stiffness can be exploited to achieve better performance, (iii) in systems with variable physical compliance, the present formulation enables exploitation of the energy storage capabilities of the actuators to improve task performance. We illustrate these in numerical simulations, and in hardware experiments on a two-link variable stiffness robot.