论文标题

可行性驱动的控制有限的DDP的方法

A Feasibility-Driven Approach to Control-Limited DDP

论文作者

Mastalli, Carlos, Merkt, Wolfgang, Marti-Saumell, Josep, Ferrolho, Henrique, Sola, Joan, Mansard, Nicolas, Vijayakumar, Sethu

论文摘要

差分动态编程(DDP)是一种直接的单射击方法,用于轨迹优化。它的效率来自对时间结构的开发(最佳控制问题固有的)和系统动力学的明确推出/集成。但是,它具有数值不稳定,与直接多个射击方法相比,它的初始化选项有限(允许对控件的初始化,但不能对状态进行初始化),并且缺乏对控制约束的正确处理。在这项工作中,我们通过可行性驱动的方法来解决这些问题,该方法调节数值优化过程中的动态可行性并确保控制限制。我们的可行性搜索模拟了只有动态约束的直接多重拍摄问题的数值解决。我们表明,我们的方法(命名为box-fddp)比Box-DDP+(一种单个拍摄方法)具有更好的数值收敛性,并且其收敛速率和运行时性能与使用内部点和主动集合算法在Knitro中可用的最先进的直接转录配方竞争。我们进一步表明,Box-FDP与最先进的非线性编程算法中的动态可行性误差降低了。我们通过为四足动物和人形机器人产生复杂而运动的运动来证明我们的方法的好处。最后,我们强调了Box-FDDP适用于腿部机器人中的模型预测控制。

Differential dynamic programming (DDP) is a direct single shooting method for trajectory optimization. Its efficiency derives from the exploitation of temporal structure (inherent to optimal control problems) and explicit roll-out/integration of the system dynamics. However, it suffers from numerical instability and, when compared to direct multiple shooting methods, it has limited initialization options (allows initialization of controls, but not of states) and lacks proper handling of control constraints. In this work, we tackle these issues with a feasibility-driven approach that regulates the dynamic feasibility during the numerical optimization and ensures control limits. Our feasibility search emulates the numerical resolution of a direct multiple shooting problem with only dynamics constraints. We show that our approach (named BOX-FDDP) has better numerical convergence than BOX-DDP+ (a single shooting method), and that its convergence rate and runtime performance are competitive with state-of-the-art direct transcription formulations solved using the interior point and active set algorithms available in KNITRO. We further show that BOX-FDDP decreases the dynamic feasibility error monotonically--as in state-of-the-art nonlinear programming algorithms. We demonstrate the benefits of our approach by generating complex and athletic motions for quadruped and humanoid robots. Finally, we highlight that BOX-FDDP is suitable for model predictive control in legged robots.

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