CAREER: Planning and Control for Overconstrained Mechanisms

这个教师早期职业发展（Career）项目研究的目标是产生混合估计器、运动规划算法和控制策略，这些策略将协同工作，以保证在非结构化环境中面对多个接触界面时的性能和稳定性。将开发一个超约束多点机械臂原型，并将规划和控制方法应用于该系统，以演示对摩擦界面细节不敏感的操作。多点接触在许多操作任务中是常见的。示例包括用于分布式或微操作、车辆和传统机器人抓取的阵列。尽管所有这些应用都受到了极大的关注，但之前的工作还没有提供一种能够处理接触状态中固有不确定性的分析方法——接触状态表示给定的接触是否卡住、滑动或脱离接触。这些接触状态之间的非平滑过渡对动力学有很大的影响；因此，系统地减轻这些非光滑效应引起的负面性能是很重要的。此外，这些系统经常被过度驱动，因此每个接触接口都是独立铰接的。这导致了机构名义上的运动过度约束——也就是说，所有点接触之间的运动关系不能同时得到满足。由于对摩擦力和法向力建模的细节敏感，因此有必要对当前接触状态进行估计，并将接触状态纳入运动规划和控制中。为了装配的目的，制造通常需要重新定位和重新定向对象。为了实现这一点，通常使用多个致动器，这些致动器由于摩擦相互作用而与物体发生粘滑接触。众所周知，执行器的物理特性，特别是它们与物体的相互作用是难以精确建模的。因此，非常需要对这些低级细节不敏感的操作策略。此外，许多交通工具，如最初的火星探测器，都有一种机械设计，可以保证某些车轮在运行过程中一定会打滑。然而，哪个车轮打滑取决于未知的环境条件。因此，在这种情况下，也有必要制定运动规划策略，即使在环境产生的大量不确定性存在的情况下也能保证工作。该项目将通过制定战略来满足这些需求，这些战略在面对固有的不确定性时保证了性能。从短期来看，该项目将有助于宏观制造业和车辆控制，从长期来看，可能会影响微观制造业。

The goal of this Faculty Early Career Development (CAREER) Program research is to produce hybrid estimators, motion planning algorithms, and control strategies that will work in concert to guarantee performance and stability in the face of multiple contact interfaces in an unstructured environment. An overconstrained multiple point manipulator prototype will be developed and planning and control methods will be applied to this system to demonstrate manipulation that is not sensitive to the particulars of the frictional interfaces. Multiple point contact is common in many manipulation tasks. Examples include arrays for distributed or micro manipulation, vehicles, and traditional robotic grasping. Although all of these applications have received a great deal of attention, no previous works have provided an analytical approach capable of dealing with the inherent uncertainties in the contact state--the state that represents whether a given contact is sticking, slipping, or is out of contact. These nonsmooth transitions between contact states have a dramatic impact on the dynamics; hence, it is important to systematically mitigate the negative performance these nonsmooth effects induce. Moreover, these systems are often overactuated, so that each contact interface is independently articulated. This leads to mechanisms that are nominally kinematically overconstrained--that is, the kinematic relationships between all the point contacts cannot be simultaneously satisfied. Which constraint is broken is sensitive to details of friction and normal force modeling, so it is necessary to estimate the current contact state and incorporate the contact state into the motion planning and control.Manufacturing often involves the need to reposition and reorient objects for purposes of assembly. To accomplish this, multiple actuators are often used, and these actuators experience stick and slip contact with the object due to frictional interactions. The physics of the actuators and, in particular, their interaction with the object are notoriously difficult to model accurately. Hence, there is a strong need for manipulation strategies that are not sensitive to these low-level details. Moreover, many vehicles, such as the original Mars rover, have a mechanical design that guarantees that some of the wheels must slip during operation. However, which wheels slip is dependent on unknown environmental conditions. Hence, in this situation as well there is a need to develop motion planning strategies that are guaranteed to work even in the presence of substantial uncertainty arising from the environment. This project will contribute to these needs by developing strategies that have guaranteed performance in the face of inherent uncertainty. In the short term this project will contribute to macro-scale manufacturing and vehicle control, and in the long-term will likely impact micro-scale manufacturing.