In this work, an optimization-based control scheme for a bilateral teleopered unmanned aerial vehicle (UAV) is proposed using control barrier functions (CBFs) and passivity. We consider a human operator moving the position of an end effector of a haptic device as the velocity command input to the UAV. The CBF is applied as a constraint to maintain the collision-free motion of the UAV for safety. On the other hand, to preserve the stability of the system, we consider passivity as another constraint together, but it leads to undesired behavior of an optimal solution for haptic feedback. To deal with the issue, the strategy called energy tank for passivity is included to replace the condition of strict output passivity. The aforementioned designs are formalized as a quadratically constrained quadratic program (QCQP) to solve numerically. Through numerical examples, we have a comprehensive discussion about the features of the proposed controller with better safety. The experimental results verify the effectiveness of our method in practice.

This paper presents novel quadrotor structures composed of only clockwise rotors. A multirotor unmanned aerial vehicle (UAV) generally has both clockwise and counterclockwise rotors to counteract the torques from the rotors. While the proposed structures have only clockwise rotors, those rotors are tilted to cancel the torques around the yaw angle of the body. This paper investigates the conditions for the proposed structures to achieve static hovering. More specifically, we provide a guideline to design the rotor tilt angles of the proposed structure. Then, this paper presents the design example of the rotor tilt angles and develops a prototype of the proposed quadrotor. The cascaded controller is also developed for the proposed structure. Finally, experimental validation is conducted with a developed prototype and controller.

For a dynamical system, safety is typically guaranteed by constraining the system states within a set defined a priori. A popular approach is to use control barrier functions (CBFs) that encode safety using a smooth function. However, typical constructions of the smooth function do not account for any notion of safety uncertainty for the system inside the safe set. Although, one can formulate uncertainty in the dynamics of the model in a CBF framework, observability of unmodeled dynamics is difficult, particularly in an online setting. Addressing these drawbacks, we present a novel formulation for synthesizing the CBF smooth function by taking into account safety uncertainty using online measurements of the system states. This uncertainty is encoded by computing the posterior variance using Gaussian processes conditioned on past measurement states. Our approach only requires observability of system states rather than the system dynamics. By incorporating safety uncertainty, the safe set can be dynamically expanded or compressed. This is achieved by computing a local safety map online at the present location and identifying samples with minimal safety exceeding the current safety limit. As more data is collected, the safety margin increases. Hence, these minimally safe exploratory samples can be used to expand the current safe set incrementally. We validate our approach experimentally by expanding an initial safe set, along x and y positions independently, for a quadrotor with safety. The experiment video can be seen at: https://youtu.be/9qvOf1UpRPw.

This paper presents a method for biped gait generation along a predefined curve with fully stretched knees. First, we design a spatial gait pattern as a function of the traveled distance on the path without considering dynamics. Then, a consistent dynamic walking motion is obtained by optimization that minimizes the zero-moment point and the speed errors while considering the trade-off between kinematics and dynamics. This method generalizes the spatially quantized dynamics-based gait generation, which is our former method restricted to straight paths, to walk on arbitrary curves. The generated gaits are validated by dynamic simulation.

This article proposes a novel geometric method to investigate whether a multirotor unmanned aerial vehicle (UAV) can achieve static hovering, i.e., hoverability. Hoverability is indispensable for a multirotor UAV to conduct its tasks safely and should be satisfied even after its rotors fail to prevent accidents. The proposed geometric method reveals the relationship between the position of the center of mass (CoM) and the rotor placement of a multirotor UAV with upward-oriented rotors to satisfy hoverability. It can be applied to a multirotor UAV with any number and positioning of rotors. This article also demonstrates that our proposed method can be applied to the investigation of a robust structure against rotor failures. This investigation provides a geometric proof that a pentarotor UAV with robustness against an arbitrary rotor failure cannot be developed. Furthermore, a quantitative measure of hoverability is newly presented based on the analysis method. This enables us to design a multirotor UAV with an optimal structure by maximizing it. Finally, experimental validation is performed by using a hexrotor UAV whose CoM position is adjusted.