Recently, the utilization of aerial manipulators for performing pushing tasks in non-destructive testing (NDT) applications has seen significant growth. Such operations entail physical interactions between the aerial robotic system and the environment. End-effectors with multiple contact points are often used for placing NDT sensors in contact with a surface to be inspected. Aligning the NDT sensor and the work surface while preserving contact, requires that all available contact points at the end-effector tip are in contact with the work surface. With a standard full-pose controller, attitude errors often occur due to perturbations caused by modeling uncertainties, sensor noise, and environmental uncertainties. Even small attitude errors can cause a loss of contact points between the end-effector tip and the work surface. To preserve full alignment amidst these uncertainties, we propose a control strategy which selectively deactivates angular motion control and enables direct force control in specific directions. In particular, we derive two essential conditions to be met, such that the robot can passively align with flat work surfaces achieving full alignment through the rotation along non-actively controlled axes. Additionally, these conditions serve as hardware design and control guidelines for effectively integrating the proposed control method for practical usage. Real world experiments are conducted to validate both the control design and the guidelines.

翻译：近年来，在无损检测应用中利用空中机械臂执行推动任务的需求显著增长。此类操作涉及空中机器人系统与环境之间的物理交互。通常采用具有多个接触点的末端执行器，以使无损检测传感器与被检测表面保持接触。要在维持接触的同时对齐无损检测传感器与工作表面，需要末端执行器尖端的所有可用接触点均与工作表面接触。采用标准的全位姿控制器时，由于建模不确定性、传感器噪声和环境扰动引起的干扰，常会出现姿态误差。即使微小的姿态误差也可能导致末端执行器尖端与工作表面之间接触点的丢失。为在这些不确定性中保持完全对齐，我们提出一种控制策略，该策略选择性地停用角运动控制，并在特定方向上启用直接力控制。具体而言，我们推导出两个必须满足的关键条件，使得机器人能够通过沿非主动控制轴的旋转实现与平坦工作表面的被动对齐，从而达到完全对齐。此外，这些条件可作为硬件设计和控制准则，以有效集成所提出的控制方法用于实际应用。我们进行了真实世界实验以验证控制设计和相关准则。