用精确二阶导数提升装配运动规划的鲁棒性,大幅减少物理仿真次数。
Robust Rigid Body Assembly via Contact-Implicit Optimal Control with Exact Second-Order Derivatives
- 基于可微物理仿真和精确二阶导数,实现高效装配路径优化
- 实测成功率超99%,显著优于传统方法
- 适合需要高精度与鲁棒性的工业装配场景
机器人装配运动规划长期依赖强化学习与采样方法,需大量物理仿真。本文提出一种样本高效的鲁棒最优控制方法,通过利用精确的二阶导数信息,显著减少规划过程中的物理仿真步数。构建了可微分物理仿真器,为数值求解器提供二阶解析导数,并实现从导数信息到精确接触模拟的无缝衔接。通过借鉴内点法的平滑策略,使碰撞检测与接触求解问题的解具备可微性。提出改进的线性规划型碰撞检测公式,高效实现目标函数及一、二阶导数计算。进一步构建多场景轨迹优化问题,增强对仿真-现实差异的鲁棒性。实验证明,该方法在真实场景中超过99%的成功率。研究还分析了接触动力学平滑近似与鲁棒建模对成功率的影响,并在多种钉孔装配任务中验证了使用精确海森矩阵相较于常用近似方法的优势。
原文摘要 · Abstract (English)
Efficient planning of assembly motions is a long standing challenge in the field of robotics that has been primarily tackled with reinforcement learning and sampling-based methods by using extensive physics simulations. This paper proposes a sample-efficient robust optimal control approach for the determination of assembly motions, which requires significantly less physics simulation steps during planning through the efficient use of derivative information. To this end, a differentiable physics simulation is constructed that provides second-order analytic derivatives to the numerical solver and allows one to traverse seamlessly from informative derivatives to accurate contact simulation. The solution of the physics simulation problem is made differentiable by using smoothing inspired by interior-point methods applied to both the collision detection as well as the contact resolution problem. We propose a modified variant of an optimization-based formulation of collision detection formulated as a linear program and present an efficient implementation for the nominal evaluation and corresponding first- and second-order derivatives. Moreover, a multi-scenario-based trajectory optimization problem that ensures robustness with respect to sim-to-real mismatches is derived. The capability of the considered formulation is illustrated by results where over 99\% successful executions are achieved in real-world experiments. Thereby, we carefully investigate the effect of smooth approximations of the contact dynamics and robust modeling on the success rates. Furthermore, the method's capability is tested on different peg-in-hole problems in simulation to show the benefit of using exact Hessians over commonly used Hessian approximations.
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