# Aerial Tele-Manipulation with Passive Tool via Parallel Position/Force Control +
###### Abstract  
This paper addresses the problem of unilateral contact interaction by an under-actuated quadrotor UAV equipped with a passive tool in a bilateral teleoperation scheme. To solve the challenging control problem of force regulation in contact interaction while maintaining flight stability and keeping the contact, we use a parallel position/force control method, commensurate to the system dynamics and constraints in which using the compliant structure of the end-effector the rotational degrees of freedom are also utilized to attain a broader range of feasible forces. In a bilateral teleoperation framework, the proposed control method regulates the aerial manipulator position in free flight and the applied force in contact interaction. On the master side, the human operator is provided with force haptic feedback to enhance his/her situational awareness. The validity of the theory and efficacy of the solution are shown by experimental results. This control architecture, integrated with a suitable perception/localization pipeline, could be used to perform outdoor aerial teleoperation tasks in hazardous and/or remote sites of interest. a 202118 September 2021 26 September  
a manipulation tool. This manipulation tool is either an active robotic arm manipulator or a passive tool. When dexterous manipulation by an aerial manipulator is not required, for example, when the robot is intended to apply desired force vectors to an object in order to push, inspect, or probe its surface, or when the normal grippers are not effective, for example, for an object with a wide flat surface, the use of a lightweight passive tool is preferable to a heavier active arm manipulator, as the smaller payload imposed to the aerial robot results in a more energy-efficient system and longer operational flight time. Moreover, simplicity and low weight of a passive tool allow the usage of a broader range of UAVs. Despite significant achievements in the fully autonomous control of drones, limited problem-solving capabilities, inadequacy in unexpected environmental conditions, legal restrictions, and imperfect position control [8] often require the presence of human operator(s) in aerial manipulation tasks. In bilateral teleoperation schemes, the human capabilities are enhanced by providing them with tangible interaction information of the remote side in the form of force and motion feedbacks (haptic feedback), besides the traditional visual feedback. In this paper, we propose an aerial manipulation solution using passive tools with a compliant end-effector. Applying a desired force profile in a uni-lateral contact, and at the same time maintaining the flight stability, that is, position and orientation control, and keeping the contact stable, that is, to avoid losing contact and sliding over the contact surface, represents a challenging control problem, especially when it is performed with an under-actuated aerial manipulator in a bilateral teleoperation loop. Fully-actuated aerial manipulators have been demonstrated to be more effective for this kind of application [8; 9; 10; 11] but consume more energy due to internal forces. That is why the use of under-actuated UAVs is investigated in this work. Our aerial manipulator is a quadrotor UAV equipped with a lightweight passive tool rigidly attached to the top of it (Figures 1 and 2). The end-effector has a mechanical damper on its surface to smooth free flight to contact transition, and a passive compliant spherical joint to keep the contact while changing the orientation. This compliant mechanism, along with appropriate control policy conforming with the system constraints, allows involving all the robot's degrees of freedom to generate the desired force vector. The desired motion and force of the aerial manipulator are attained using a _parallel position/force control_ scheme within a bilateral teleoperation control framework. The proposed control scheme regulates the aerial manipulator pose in free flight and the applied force in contact conditions.