Repeated Impact-Based Capture of a Spinning Object by a Dual-Arm Space Robot

This paper presents detumbling and capture of space debris by a dual-arm space robot for active space debris removal missions. Space debris, such as a malfunctioning satellite or a rocket upper stage, often has uncontrolled tumbling motion. It also has uncertainties in its parameters, such as inertial characteristics or surface frictional roughness. These factors make the debris capture missions difficult to accomplish. To cope with such challenging missions, we propose a detumbling and capture control method for a dual-arm robot based on repeated impact capable of suppressing the debris motion by repeatedly utilizing an effect of a passive damping factor in the contact characteristics. In this paper, as the initial step of a study on the repeated impact-based capture method, we assume that the capture target is a rocket upper stage that can be simply modeled as a cylindrical body and mainly has angular velocity motion in its principle axis of inertia. A motion tracking control law of an end-effector of the robot arm is introduced to maintain the repeated impact. The proposed control method enables the robot to accomplish the detumbling and capture without precise estimation of the inertial characteristics and surface frictional roughness of the debris. The validity of the proposed method is presented by numerical simulations and planar microgravity experiments using an air-floating system. In particular, the experimental evaluation shows the fundamental feasibility of the proposed method, and thus, the result contributes to a practical application

Mobility Analysis of Hopping and Tumbling Motion in Microgravity

This paper presents the analyses of the tumbling and hopping mobility of a novel moving mechanism on small celestial bodies in microgravity. The robot consists of an inner motor with a flywheel and eight elastic spikes connected to the perimeter of the robot. The tumbling and hopping motion of the robot can be switched by controlling the torque of the motor. Hence, the robot can traverse a large region with high moving accuracy. In this paper, we conduct several numerical simulations to analyze the characteristics of the mobility by assigning various values of elastic and damping coefficient of spikes, and the torque of the motor. The results are useful to construct the feasible motion planning for real missions.International Symposium on Artificial Intelligence, Robotics and Automation in Space (i-SAIRAS 2020), October 19-23, 2021, Los Angles, CA, USA（新型コロナ感染拡大に伴い、オンライン開催に変更

Tumbling and Hopping Locomotion Control for a Minor Body Exploration Robot

This paper presents the modeling and analysis of a novel moving mechanism "tumbling" for asteroid exploration. The system actuation is provided by an internal motor and torque wheel; elastic spring-mounted spikes are attached to the perimeter of a circular-shaped robot, protruding normal to the surface and distributed uniformly. Compared with the conventional motion mechanisms, this simple layout enhances the capability of the robot to traverse a diverse microgravity environment. Technical challenges involved in conventional moving mechanisms, such as uncertainty of moving direction and inability to traverse uneven asteroid surfaces, can now be solved. A tumbling locomotion approach demonstrates two beneficial characteristics in this environment. First, tumbling locomotion maintains contact between the rover spikes and the ground. This enables the robot to continually apply control adjustments to realize precise and controlled motion. Second, owing to the nature of the mechanical interaction of the spikes and potential uneven surface protrusions, the robot can traverse uneven surfaces. In this paper, we present the dynamics modeling of the robot and analyze the motion of the robot experimentally and via numerical simulations. The results of this study help establish a moving strategy to approach the desired locations on asteroid surfaces.2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), October 25, 2020 - January 24, 2021, Las Vegas, NV, USA （新型コロナ感染拡大に伴い、現地開催中止

Terrain-Dependent Slip Risk Prediction for Planetary Exploration Rovers

Wheel slip prediction on rough terrain is crucial for secure, long-term operations of planetary exploration rovers. Although rough, unstructured terrain hampers mobility, prediction by modeling wheel–terrain interactions remains difficult owing to unclear terrain conditions and complexities of terramechanics models. This study proposes a vision-based approach with machine learning for predicting wheel slip risk by estimating the slope from 3D information and classifying terrain types from image information. It considers the slope estimation accuracy for risk prediction under sharp increases in wheel slip due to inclined ground. Experimental results obtained with a rover testbed on several terrain types validate this method

Free-carrier dynamics and band tails in Cu[2] ZnSn (S[x]Se[1−x] )[4] : Evaluation of factors determining solar cell efficiency

We investigated the composition-dependent photocarrier dynamics in Cu[2] ZnSn(S[x]Se[1−x])[4] (CZTSSe) single crystals using various types of steady-state and time-resolved optical spectroscopy. Photoluminescence spectroscopy shows that the band-tail states formed below the band edge decrease monotonically with increasing Se content. THz time-resolved spectroscopy clarifies that an increase in the Se content leads to a shorter lifetime of the free photocarriers. A trade-off between the composition-dependent band-tail density and the free-carrier lifetime occurs in CZTSSe single crystals. Our experimental results provide insights into the physics behind the low and composition-dependent conversion efficiency of CZTSSe-based solar cells

Bilateral Renal Cell Carcinoma and its Treatment

A report is presented on two cases of bilateral renal cell carcinoma together with a review of the literature. Bilateral renal cell carcinoma is rare and there is much controversy concerning its treatment. Our current experience supports conservative therapy for bilateral renal cell carcinoma

Flame retardance-donated lignocellulose nanofibers (LCNFs) by the Mannich reaction with (amino-1,3,5-triazinyl)phosphoramidates and their properties

Nitrogen/phosphorus-containing melamines (NPCM), a durable flame-retardant, were prepared by the successive treatment of ArOH (Ar = BrnC6H5−n, n = 0, 1, 2, and 3) with POCl3 and melamine monomer. The prepared flame-retardants were grafted through the CH2 unit to lignocellulose nanofibers (LCNFs) by the Mannich reaction. The resulting three-component products were characterized using FT-IR (ATR) and EA. The thermal behavior of the NPCM-treated LCNF fabric samples was determined using TGA and DSC analyses, and their flammability resistances were evaluated by measuring their Limited Oxygen Index (LOI) and the UL-94V test. A multitude of flame retardant elements in the fabric samples increased the LOI values as much as 45 from 20 of the untreated LCNFs. Moreover, the morphology of both the NPCM-treated LCNFs and their burnt fabrics was studied with a scanning electron microscope (SEM). The heat release lowering effect of the LCNF fabric against the water-based paint was observed with a cone calorimeter. Furthermore, the mechanical properties represented as the tensile strength of the NPCM-treated LCNF fabrics revealed that the increase of the NPCM content in the PP-composites led to an increased bending strength with enhancing the flame-retardance