Synergistic morphology and feedback control for traversal of unknown compliant obstacles with aerial robots

Animals traverse vegetation by direct physical interaction using their entire body to push aside and slide along compliant obstacles. Current drones lack this interaction versatility that stems from synergies between body morphology and feedback control modulated by sensing. Taking inspiration from nature, we show that a task-oriented design allows a drone with a minimalistic controller to traverse obstacles with unknown elastic responses. A discoid sensorized shell allows to establish and sense contacts anywhere along the shell and facilitates sliding along obstacles. This simplifies the formalization of the control strategy, which does not require a model of the interaction with the environment, nor high-level switching conditions for alternating between pushing and sliding. We utilize an optimization-based controller that ensures safety constraints on the robot's state and dampens the oscillations of the environment during interaction, even if the elastic response is unknown and variable. Experimental evaluation, using a hinged surface with three different stiffness values ranging from 18 to 155.5 N mm rad-1, validates the proposed embodied aerial physical interaction strategy. By also showcasing the traversal of isolated branches, this work makes an initial contribution toward enabling drone flight across cluttered vegetation, with potential applications in environmental monitoring, precision agriculture, and search and rescue.

Transmission efficiency of one tooth difference sine tooth profile planetary reducer

The structural size of space exploration and unmanned aerial vehicle manipulator is required to be as small as possible, and the weight must be as light as possible. However, the existing reducers have difficulties in achieving lightweight robot joint drive systems. For it, this paper proposes a single tooth difference continuous sine tooth profile K-H-V type planetary reducer in which pin type equi-speed output mechanism is used. Concerning the reducer, its structural composition and meshing characteristics are analyzed. Based on the findings, the meshing pair's force, the friction coefficient, and the meshing efficiency are investigated. The force and bearing efficiency of the planetary gear are studied, and the efficiency of the equi-speed output mechanism in addition to the total efficiency of the reducer are determined. Moreover, the efficiency of the reducer prototype is measured and compared to the calculated efficiencies. The results show that the gear modulus, the input speed, the surface roughness, and the lubricating oil viscosity have a significant effect on the meshing efficiency. Furthermore, the efficiency of the eccentric bearings is significantly lower than that of the non-eccentric bearings. Therefore, it can be increased by tuning the pressure angle, the tooth number of planetary gear, the tooth height, and the distribution circle radius of the pinhole. In addition, the power loss of the output mechanism has the greatest effect on transmission efficiency. Reducing the center distance, the inner diameter of the rotating arm bearing, and the tooth number of planetary gear, as well as increasing the outer diameter of the pin shaft can reduce the power loss of the output mechanism. The experimental efficiency of the reducer prototype is 82.47%, its computational efficiency is 83.72%, and its error is 1.25%, verifying the correctness of the efficiency calculation method.

Robust Global stabilization of aerial continuum manipulation systems via hybrid feedback

In this paper, the control problem of aerial continuum manipulation systems (ACMSs) is considered. This study introduces a new platform for ACMSs in which a quadrotor is equipped with a tendon-bent concentric tube continuum robot. The decoupled dynamic modeling of ACMSs is utilized to derive the proposed feedback control law. The control design process is split into two distinct control loops. In the first loop, a terminal synergetic controller is presented to control the continuum robot's tip to track the desired trajectory. In the second loop, an improved synergetic controller is introduced to control the position and velocity of the quadrotor, which ensures asymptotic stability of the origin of the error dynamic. Moreover, in this loop a hybrid feedback law is designed to operate with the improved synergetic controller, which overcomes topological obstructions and globally stabilizes the attitude of the quadrotor. Furthermore, the stability of the resultant closed-loop system is verified utilizing the Lyapunov stability theorem. The efficiency and advantages of the proposed controller are verified by a comparative analysis in simulations.

Construction and management of smart campus: Anti-disturbance control of flexible manipulator based on PDE modeling

With the rapid development of smart campus, this paper studies the attitude tracking control of flexible manipulator (FM) in colleges and universities under elastic vibration and external disturbances. First, different from the traditional modeling based on ordinary differential equations (ODEs), the partial differential equations (PDEs) dynamic model of a manipulator system is established based on the Hamilton principle (HP). Second, the boundary control condition of the end system of the manipulator is introduced to adjust the vibration of the manipulator. Furthermore, a Proportional-Derivative (PD) boundary control (PDBC) strategy is proposed by the Lyapunov function to suppress the vibration of the manipulator. Finally, a numerical comparison simulation based on MATLAB/SIMULINK further verifies the robustness and anti-disturbance performance of the control method proposed in this paper.

Drone-assisted collection of environmental DNA from tree branches for biodiversity monitoring

The protection and restoration of the biosphere is crucial for human resilience and well-being, but the scarcity of data on the status and distribution of biodiversity puts these efforts at risk. DNA released into the environment by organisms, i.e., environmental DNA (eDNA), can be used to monitor biodiversity in a scalable manner if equipped with the appropriate tool. However, the collection of eDNA in terrestrial environments remains a challenge because of the many potential surfaces and sources that need to be surveyed and their limited accessibility. Here, we propose to survey biodiversity by sampling eDNA on the outer branches of tree canopies with an aerial robot. The drone combines a force-sensing cage with a haptic-based control strategy to establish and maintain contact with the upper surface of the branches. Surface eDNA is then collected using an adhesive surface integrated in the cage of the drone. We show that the drone can autonomously land on a variety of branches with stiffnesses between 1 and 10³ newton/meter without prior knowledge of their structural stiffness and with robustness to linear and angular misalignments. Validation in the natural environment demonstrates that our method is successful in detecting animal species, including arthropods and vertebrates. Combining robotics with eDNA sampling from a variety of unreachable aboveground substrates can offer a solution for broad-scale monitoring of biodiversity.

Collecting critically endangered cliff plants using a drone-based sampling manipulator

Kauaʻi, an island within the Hawaiʻi archipelago, is home of a unique flora that contains 250 single-island endemic plant species. Threats have led to a significant population decrease where 97% of these plant species are now listed as endangered, critically endangered, or extinct. Vertical cliff habitats on Kauaʻi work as refugia to protect plants from their stressors. However, this habitat makes conservation work particularly difficult, forcing scientists, and botanists to use risky and time-consuming methods such as abseiling to access remote plant populations. Here we present the Mamba, the first aerial system capable of sampling plants on cliffs. This system is operated by two pilots and consists of an actively controlled platform suspended by a long cable under a lifting drone. Eleven otherwise inaccessible samples from five critically endangered species were collected during the first field trials on Kauaʻi Island. The samples are currently surviving in nurseries, demonstrating that the Mamba can be used to complete the conservation life cycle for organisms located in difficult areas, from location to collection, then cultivation and outplanting.

Dynamic Stiffness Enhancement of the Quadcopter Control System

Vibrations often result in fatigue breakage in quadcopter flight operations. Reducing the vibration effect is the main important issue for quadcopter flight. Enhanced dynamic stiffness is required in the quadcopter control system for the vibration rejection ability. In this paper, the dynamic stiffness of the quadcopter control system is constructed and is used as an index for the performance of the quadcopter control system to resist an external oscillatory load. To rapidly reduce the vibration effect, a repetitive controller is introduced in the quadcopter control system, where the direct dynamic stiffness and the quadrature dynamic stiffness with variable frequencies are proposed. A theoretical model of the dynamic stiffness of the quadcopter control system is established by analyzing the definition of dynamic stiffness. Simulated and experimental results show that the magnitudes of the direct dynamic stiffness with the proposed repetitive controller are larger than those without the repetitive controller. The quadrature dynamic stiffness with the proposed repetitive controller is relatively smooth compared to that without the proposed repetitive controller, which can be used to verify the stability being improved by the designed repetitive controller. In addition, the magnitudes of the loss factor of the quadcopter control system with the repetitive controller are lower than those without the repetitive controller.

Precise Cable-Suspended Pick-and-Place with an Aerial Multi-robot System

This work introduces the G-Fly-Crane, a proof-of-concept aerial multi-robot system designed to demonstrate the advantage of using multiple aerial robots as a valuable tool for novel construction techniques, not requiring the use of heavy engines and costly infrastructures. We experimentally demonstrate its capability to perform pick-and-place and manipulation tasks in a construction scenario, with an increased payload capacity and dexterity compared to the single robot case. The system is composed of three aerial robots connected to a platform by three pairs of cables. The platform is equipped with a gripper, enabling the grasping of objects. The paper describes in detail the hardware and software architecture of our prototype and explains the implemented control methods. A shared control strategy incorporates the human operator in the control loop, thus increasing the overall system reliability when performing complex tasks. The paper also discusses the next steps required to bring this technology from indoor laboratory conditions to real-world applications.

Aerial Tele-Manipulation with Passive Tool via Parallel Position/Force Control

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.