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Aerial unperching of multirotors has received little attention as opposed to perching that has been investigated to elongate operation time. This study presents a new aerial robot capable of both perching and unperching autonomously on/from a ferromagnetic surface during flight, and a switching controller to avoid rotor saturation and mitigate overshoot during transition between free-flight and perching. To enable stable perching and unperching maneuvers on/from a vertical surface, a lightweight ($\approx$ $1$ \si{kg}), fully actuated tiltrotor that can hover at $90^\circ$ pitch angle is first developed. We design a perching/unperching module composed of a single servomotor and a magnet, which is then mounted on the tiltrotor. A switching controller including exclusive control modes for transitions between free-flight and perching is proposed. Lastly, we propose a simple yet effective strategy to ensure robust perching in the presence of measurement and control errors and avoid collisions with the perching site immediately after unperching. We validate the proposed framework in experiments where the tiltrotor successfully performs perching and unperching on/from a vertical surface during flight. We further show effectiveness of the proposed transition mode in the switching controller by ablation studies where large overshoot and even collision with a perching site occur. To the best of the authors' knowledge, this work presents the first autonomous aerial unperching framework using a fully actuated tiltrotor., Comment: 7 pages, 10 figures, 2024 IEEE International Conference on Robotics and Automation (ICRA) accepted

This study presents a new hardware design and control of a minimally actuated 5 control degrees of freedom (CDoF) quadrotor-based tiltrotor. The proposed tiltrotor possesses several characteristics distinct from those found in existing works, including: 1) minimal number of actuators for 5 CDoF, 2) large margin to generate interaction force during aerial physical interaction (APhI), and 3) no mechanical obstruction in thrust direction rotation. Thanks to these properties, the proposed tiltrotor is suitable for perching-enabled APhI since it can hover parallel to an arbitrarily oriented surface and can freely adjust its thrust direction. To fully control the 5-CDoF of the designed tiltrotor, we construct an asymptotically stabilizing controller with stability analysis. The proposed tiltrotor design and controller are validated in experiments where the first two experiments of $x,y$ position tracking and pitch tracking show controllability of the added CDoF compared to a conventional quadrotor. Finally, the last experiment of perching and cart pushing demonstrates the proposed tiltrotor's applicability to perching-enabled APhI., Comment: 7 pages, 10 figures, 2023 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) accepted

This paper introduces a new paradigm that integrates the concepts of particle abrasion and breakage. Both processes can co-occur under loading as soil particles are subjected to friction as well as collisions between particles. Therefore, the significance of this integrating paradigm lies in its ability to address both abrasion and breakage in a single framework. The new paradigm is mapped out in a framework called the 'particle geometry space.' The x-axis corresponds to the surface-area-to-volume ratio ($A/V$), while the y-axis represents volume ($V$). This space facilitates a holistic characterization of the four-particle geometry features, i.e., shape (${\beta}$) and size ($D$) as well as surface area ($A$) and volume ($V$). Three distinct paths (abrasion, breakage, and equally-occurring abrasion and breakage processes), three limit lines (breakage line, sphere line, and average shape-conserving line), and five different zones are defined in the particle geometry space. Consequently, this approach enables us to systematically relate the extent of co-occurring abrasion and breakage to the particle geometry evolution., Comment: 10 pages, 5 figures; Introduced a new term 'particle geometry space'; Improved readability and fixed minor typos

In this study, a new concept of a wheelchair-towing robot for the facile electrification of manual wheelchairs is introduced. The development of this concept includes the design of towing robot hardware and an autonomous driving algorithm to ensure the safe transportation of patients to their intended destinations inside the hospital. We developed a novel docking mechanism to facilitate easy docking and separation between the towing robot and the manual wheelchair, which is connected to the front caster wheel of the manual wheelchair. The towing robot has a mecanum wheel drive, enabling the robot to move with a high degree of freedom in the standalone driving mode while adhering to kinematic constraints in the docking mode. Our novel towing robot features a camera sensor that can observe the ground ahead which allows the robot to autonomously follow color-coded wayfinding lanes installed in hospital corridors. This study introduces dedicated image processing techniques for capturing the lanes and control algorithms for effectively tracing a path to achieve autonomous path following. The autonomous towing performance of our proposed platform was validated by a real-world experiment in which a hospital environment with colored lanes was created., Comment: Submitted to Intelligent Service Robotics

Existing multirotor-based cargo transportation does not maintain a constant cargo attitude due to underactuation; however, fragile payloads may require a consistent posture. The conventional method is also cumbersome when loading cargo, and the size of the cargo to be loaded is limited. To overcome these issues, we propose a new fully-actuated multirotor unmanned aerial vehicle platform capable of translational motion while maintaining a constant attitude. Our newly developed platform has a cubic exterior and can freely place cargo at any point on the flat top surface. However, the center-of-mass (CoM) position changes when cargo is loaded, leading to undesired attitudinal motion due to unwanted torque generation. To address this problem, we introduce a new model-free center-of-mass position estimation method inspired by the extremum-seeking control (ESC) technique. Experimental results are presented to validate the performance of the proposed estimation method, effectively estimating the CoM position and showing satisfactory constant-attitude flight performance., Comment: 8 pages, 8 figures, submitted to IEEE RA-L

People of a race appear different but share a 'phenotypic trait' due to a common genetic origin. Mineral particles are like humans: they appear different despite having a same geological origin. Then, do the particles have some sort of 'phenotypic trait' in the geometries as we do? How can we characterize the phenotypic trait of particle geometries? This paper discusses a new perspective on how the phenotypic trait can be discovered in the particle geometries and how the 'variation' and 'average' of the geometry can be quantified. The key idea is using the power-law between particle surface-area-to-volume ratio ($A/V$) and the particle volume ($V$) that uncovers the phenotypic trait in terms of ${\alpha}$ and ${\beta}^*$: From the log-transformed relation of $V = (A/V)^{\alpha} {\times} {\beta}^*$, the power value ${\alpha}$ represents the relation between shape and size, while the term ${\beta}^*$ (evaluated by fixing ${\alpha}$ = -3) informs the angularity of the average shape in the granular material. In other words, ${\alpha}$ represents the 'variation' of the geometry while ${\beta}^*$ is concerned with the 'average' geometry of a granular material. Furthermore, this study finds that $A/V$ and $V$ can be also used to characterize individual particle shape in terms of Wadell's true Sphericity ($S$). This paper also revisits the $M = A/V {\times} L/6$ concept originally introduced by Su et al. (2020) and finds the shape index $M$ is an extended form of $S$ providing additional information about the particle elongation. Therefore, the proposed method using $A/V$ and $V$ provides a unified approach that can characterize the particle geometry at multiple scales from granular material to a single particle. Ref.: Su, Y.F., Bhattacharya, S., Lee, S.J., Lee, C.H., Shin, M.: A new interpretation of three-dimensional particle geometry: M-A-V-L. Transp. Geotech. 23, 100328 (2020)., Comment: 30 pages, 15 figures, 8 tables; No difference from arXiv:2110.14469v1 except the first page stamp and the header on the manuscript

Deep Learning Recommendation Models (DLRM) are widespread, account for a considerable data center footprint, and grow by more than 1.5x per year. With model size soon to be in terabytes range, leveraging Storage ClassMemory (SCM) for inference enables lower power consumption and cost. This paper evaluates the major challenges in extending the memory hierarchy to SCM for DLRM, and presents different techniques to improve performance through a Software Defined Memory. We show how underlying technologies such as Nand Flash and 3DXP differentiate, and relate to real world scenarios, enabling from 5% to 29% power savings., Comment: 14 pages, 5 figures