Towards Human-UAV Physical Interaction and Fully Actuated Aerial Vehicles

Unmanned Aerial Vehicles (UAVs) ability to reach places not accessible to humans or other robots and execute tasks makes them unique and is gaining a lot of research interest recently. Initially UAVs were used as surveying and data collection systems, but lately UAVs are also efficiently employed in aerial manipulation and interaction tasks. In recent times, UAV interaction with the environment has become a common scenario, where manipulators are mounted on top of such systems. Current applications has driven towards the direction of UAVs and humans coexisting and sharing the same workspace, leading to the emerging futuristic domain of Human-UAV physical interaction. In this dissertation, initially we addressed the delicate problem of external wrench estimation (force/torque) in aerial vehicles through a generalized-momenta based residual approach. To our advantage, this approach is executable during flight without any additional sensors. Thereafter, we proposed a novel architecture allowing humans to physically interact with a UAV through the employment of sensor-ring structure and the developed external wrench estimator. The methodologies and algorithms to distinguish forces and torques derived by physical interaction with a human from the disturbance wrenches (due to e.g., wind) are defined through an optimization problem. Furthermore, an admittance-impedance control strategy is employed to act on them differently. This new hardware/software architecture allows for the safe human-UAV physical interaction through exchange of forces. But at the same time, other limitations such as the inability to exchange torques due to the underactuation of quadrotors and the need for a robust controller become evident. In order to improve the robust performance of the UAV, we implemented an adaptive super twisting sliding mode controller that works efficiently against parameter uncertainties, unknown dynamics and external perturbations. Furthermore, we proposed and designed a novel fully actuated tilted propeller hexarotor UAV. We designed the exact feedback linearization controller and also optimized the tilt angles in order to minimize power consumption, thereby improving the flight time. This fully actuated hexarotor could reorient while hovering and perform 6DoF (Degrees of Freedom) trajectory tracking. Finally we put together the external wrench observer, interaction techniques, hardware design, software framework, the robust controller and the different methodologies into the novel development of Human-UAV physical interaction with fully actuated UAV. As this framework allows humans and UAVs to exchange forces as well as torques, we believe it will become the next generation platform for the aerial manipulation and human physical interaction with UAVs

Decentralized MPC based Obstacle Avoidance for Multi-Robot Target Tracking Scenarios

In this work, we consider the problem of decentralized multi-robot target tracking and obstacle avoidance in dynamic environments. Each robot executes a local motion planning algorithm which is based on model predictive control (MPC). The planner is designed as a quadratic program, subject to constraints on robot dynamics and obstacle avoidance. Repulsive potential field functions are employed to avoid obstacles. The novelty of our approach lies in embedding these non-linear potential field functions as constraints within a convex optimization framework. Our method convexifies non-convex constraints and dependencies, by replacing them as pre-computed external input forces in robot dynamics. The proposed algorithm additionally incorporates different methods to avoid field local minima problems associated with using potential field functions in planning. The motion planner does not enforce predefined trajectories or any formation geometry on the robots and is a comprehensive solution for cooperative obstacle avoidance in the context of multi-robot target tracking. We perform simulation studies in different environmental scenarios to showcase the convergence and efficacy of the proposed algorithm. Video of simulation studies: \url{https://youtu.be/umkdm82Tt0M

Modeling, Control and Design Optimization for a Fully-actuated Hexarotor Aerial Vehicle with Tilted Propellers

International audienceMobility of a hexarotor UAV in its standard configuration is limited, since all the propeller force vectors are parallel and they achieve only 4 DoF actuation, similar, e.g., to quadrotors. As a consequence, the hexarotor pose cannot track an arbitrary trajectory over time. In this paper, we consider a different hexarotor architecture where propellers are tilted, without the need of any additional hardware. In this way, the hexarotor possess a 6 DoF actuation which allows to independently reach positions and orientations in free space and to be able to exert forces on the environment to resist any wrench for aerial manipulation tasks. After deriving the dynamical model of the proposed hexarotor, we discuss the controllability and the tilt angle optimization to reduce the control effort. An exact feedback linearization and decoupling control law is proposed based on the input-output mapping, considering the Jacobian and task acceleration, for non-linear trajectory tracking. The robustness of our approach is validated by simulation results

Short-term Outcomes in Patients with Carcinoma of the Esophagus and Gastroesophageal Junction Receiving Neoadjuvant Chemotherapy or Chemoradiation before Surgery. A Prospective Study

Background Neoadjuvant chemotherapy (NACT) and neoadjuvant chemoradiotherapy (NACRT) have been demonstrated to improve survival compared to surgery alone in esophageal carcinoma, but the evidence is scarce on which of these therapies is more beneficial, particularly with regard to resectability rates, postoperative morbidity and mortality, and histological responses. Objective This study compares the resectability, pathological response rates, and short-term surgical outcomes in patients with carcinoma of the esophagus or gastroesophageal junction receiving NACT or NACRT prior to surgery. Methods Patients with resectable carcinoma of the esophagus or gastroesophageal junction adenocarcinoma, squamous cell carcinoma, and adenosquamous histologies were enrolled in this well-matched prospective non-randomized study. Thirty-five patients were given NACT, and 35 NACRT. In the NACT group, 25 patients received three cycles of three-weekly carboplatin and paclitaxel, and 10 received three cycles of cisplatin/5-fluorouracil, while all the patients in the NACRT group received 41.4 Gy of radiotherapy concomitant with five cycles of weekly paclitaxel and carboplatin-based chemotherapy. Results Twenty-two patients in the NACT group and 33 patients in NACRT group had resection (P value = 0.0027). The percentage of microscopically margin-negative resection (R0 resection) was similar in both the groups (86% versus 88%). The incidences of surgical and non-surgical complications were similar in both the groups (P=0.34). There was no 30-day mortality. There was a trend toward more pathological complete regression in the NACRT group (P=0.067). The percentage of patients achieving complete tumor regression at the primary site (pT0) was significantly higher in the NACRT group. The down-staging effect on nodal status was similar in both the groups (P=0.55). There was a statistically significant reduction in tumor size in the NACRT group. The median numbers of nodes harvested and positive nodes were similar in both the groups. Conclusion Patients receiving NACRT had better resectability rates and pathological response rates, but similar postoperative morbidity compared to the NACT group