Contact can be conceptualized as a set of constraints imposed on two bodies that are interacting with one another in some way. The nature of a contact, whether a point, line, or surface, dictates how these bodies are able to move with respect to one another given a force, and a set of contacts can provide either partial or full constraint on a body's motion. Decades of work have explored how to explicitly estimate the location of a contact and its dynamics, e.g., frictional properties, but investigated methods have been computationally expensive and there often exists significant uncertainty in the final calculation. This has affected further advancements in contact-rich tasks that are seemingly simple to humans, such as generalized peg-in-hole insertions. In this work, instead of explicitly estimating the individual contact dynamics between an object and its hole, we approach this problem by investigating compliance-enabled contact formations. More formally, contact formations are defined according to the constraints imposed on an object's available degrees-of-freedom. Rather than estimating individual contact positions, we abstract out this calculation to an implicit representation, allowing the robot to either acquire, maintain, or release constraints on the object during the insertion process, by monitoring forces enacted on the end effector through time. Using a compliant robot, our method is desirable in that we are able to complete industry-relevant insertion tasks of tolerances <0.25mm without prior knowledge of the exact hole location or its orientation. We showcase our method on more generalized insertion tasks, such as commercially available non-cylindrical objects and open world plug tasks.

翻译：接触可被概念化为施加于相互作用的两个物体上的一组约束。接触的性质（点、线或面）决定了在给定力作用下物体相互运动的方式，而一组接触可对物体运动提供部分或完全约束。数十年的研究探索了如何显式估算接触位置及其动力学特性（如摩擦属性），但所研究方法计算成本高昂，且最终结果常存在显著不确定性。这阻碍了接触密集型任务的进一步发展——例如通用轴孔插入这类对人类看似简单的操作。本文不显式估算物体与孔洞间的单个接触动力学特性，转而通过研究柔顺接触构型（compliance-enabled contact formations）来解决该问题。更正式地，接触构型根据施加于物体可用自由度上的约束进行定义。我们摒弃对单个接触位置的估算，将该计算抽象为隐式表征，使机器人能在插入过程中通过监测末端执行器随时间变化的受力情况，获取、维持或释放对物体的约束。借助柔顺机器人，本方法可在无需预先获知精确孔位或朝向的前提下，完成公差小于0.25mm的工业相关插入任务。我们进一步展示了该方法在通用插入任务（如商用非圆柱体零件及开放环境插头插拔任务）中的有效性。