Published papers

© 2019 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. In this study, a signal-processing method for the landing radar of a lunar lander is proposed using deep learning. To perform a precise landing, measurement of the relative velocity with respect to the surface is essential. To measure the velocity, the landing radar irradiates the surface with a pulse wave and observes the Doppler shift. High-precision measurement on complex terrains, such as a crater or slope, has always been the problem of landing radar because the irradiated terrain causes a deformation of the reflected pulse wave and strongly affects the measurement accuracy. A system is proposed in this study that performs measurements with high accuracy on complex terrains using convolutional neural networks. In the proposed method, spectrograms are used as input data to consider the effect of irradiated terrain on the measurement data. Experiments show that our method not only improves the measurement accuracy compared with the existing method but also can be implemented from the viewpoint of execution time. Moreover, this paper attempted to deepen the network architecture and input irradiated terrain data simultaneously. It was confirmed that the measurement accuracy was further improved by this enhancement.

Recent research on flight-deck interval management technology, including the findings of a flight-test demonstration conducted by NASA, led to the development of an alternative control logic for flight-deck interval management, termed as “interval management–speed planning.” As this logic demonstrated promising results in numerical simulations, for the first time, test pilots and airline pilots were invited to evaluate the system in an Airbus A320 simulator, using an avionics setup similar to the one employed in NASA’s flight test, on an approach for the Tokyo International Airport. A qualitative and quantitative survey was conducted in which the pilots’ opinions pertaining to their acceptance of the interval management operation and comprehension of the system behavior using both the original and alternative control logic, as well as a modified graphical user interface, were sought. The results indicated that the new control logic was well accepted by the pilots, confirming some of the results and hypotheses from the numerical simulation; nevertheless, it was indicated that further research on the user interface is needed to make full use of the logic’s capability.

Objective: To test the hypothesis that varus thrust visualized during gait is associated with a higher prevalence of low back pain (LBP) in individuals with knee osteoarthritis (OA). Methods: Individuals with knee OA (Kellgren/Lawrence grade ≥1) underwent a gait observation to assess varus thrust. The participants identified LBP and its severity using questionnaires. Logistic regression analyses were performed to examine the association between varus thrust and LBP. Results: We included 205 participants (mean age 68.19 years; 72.20% women). A total of 45 participants (22.0%) showed varus thrust in their painful knee, in whom 31 (68.89%) and 18 (40.00%) were identified as having any LBP and moderate-to-severe LBP (numerical rating scale ≥4 points), respectively. Patients with varus thrust demonstrated a 3.6-fold higher risk of the presence of moderate-to-severe LBP (95% confidence interval [95% CI] 1.62–8.10). In patients with LBP, the presence of varus thrust was associated with more severe LBP intensity (proportional odds ratio 2.25 [95% CI 1.02–4.96]). Conclusion: This study highlights the novel relationship between varus thrust and LBP, which supports the idea of a biomechanical link, the so-called knee–spine syndrome. These findings provide new insight for clarifying the pathogenesis of LBP related to knee OA.

The need for early detection and intervention for age-related health deterioration via home-based health monitoring systems is growing with global population aging. Health deterioration is typically evaluated using questionnaires, but obtaining frequent responses is difficult. Although stair walking involving a high physical load is suitable for assessing health deterioration, uniform assessment using home-based systems is difficult because different stair designs result in different movements. There is currently insufficient research on differences in evaluation performance between different stair designs. The current study aimed to develop an objective index to assess difficulties in activities of daily living (ADLs) as an indicator of health deterioration by observing stair walking, and to investigate the effects of stair dimensions on the relationship between the index and health deterioration. We hypothesized that knee joint positions during stair ascent would be associated with health deterioration, and developed the “Stepping in Level” index, reflecting the knee joint position when stepping in, obtained using a markerless depth information-based system. Seventy elderly people ascended two types of stairs (steep: 33.7°; shallow: 28.2°) and completed a questionnaire regarding ADL difficulty. We used a generalized linear mixed model to investigate the ability of “Stepping in Level” to explain ADL difficulty. The results revealed that “Stepping in Level” was able to explain ADL difficulty, and steep stairs were more suitable than shallow stairs for assessment. Our system enables daily assessment of difficulty in ADLs and detection of subtle changes in daily life. The current findings could inform design guidelines for health monitoring.

This study proposes a terrain relative navigation (TRN) method to estimate spacecraft positions in the shadowed regions of the moon with high precision by combining the camera image and the synthetic aperture radar (SAR) data. TRN, which estimates the position of a spacecraft by comparing the preliminary terrain information stored in a database with the observed terrain, is an effective method of correcting the drift errors of inertial measurement units (IMUs). Optical cameras are primarily used for TRN sensors to observe the terrain; however, shadow images do not have enough characteristic points to match with the database. SAR is a form of radar that can generate high-resolution photo-like images, regardless of light conditions. In this study, we propose the use of SAR as navigation sensors and demonstrate effectiveness of SAR.

© 2018, The Author(s). This systematic review with a meta-analysis aimed to summarize the current evidence of the effectiveness of mesenchymal stem cell (MSC) treatment for knee osteoarthritis (OA) and to examine whether rehabilitation is an effect modifier of the effect estimate of MSC treatment. A literature search yielded 659 studies, of which 35 studies met the inclusion criteria (n = 2385 patients; mean age: 36.0–74.5 years). The meta-analysis results suggested that MSC treatment through intra-articular injection or arthroscopic implantation significantly improved knee pain (standardized mean difference [SMD]: −1.45, 95% confidence interval [CI]: −1.94, −0.96), self-reported physical function (SMD: 1.50, 95% CI: 1.09, 1.92), and cartilage quality (SMD: −1.99; 95% CI: −3.51, −0.47). However, the MSC treatment efficacy on cartilage volume was limited (SMD: 0.49; 95% CI: −0.19, 1.16). Minor adverse events (knee pain or swelling) were reported with a wide-ranging prevalence of 2–60%; however, no severe adverse events occurred. The evidence for these outcomes was “very low” to “low” according to the Grades of Recommendation, Assessment, Development and Evaluation system because of the poor study design, high risk of bias, large heterogeneity, and wide 95% CI of the effects estimate. Performing rehabilitation was significantly associated with better SMD for self-reported physical function (regression coefficient: 0.881, 95% CI: 0.049, 1.712; P = 0.039). We suggest that more high quality randomized controlled trials with consideration of the potential rehabilitation-driven clinical benefit would be needed to facilitate the foundation of effective MSC treatment and regenerative rehabilitation for patients with knee OA.

© 2018 by the authors. In deregulated electricity markets, minimizing the procurement costs of electricity is a critical problem for procurement agencies (PAs). However, uncertainty is inevitable for PAs and includes multiple factors such as market prices, photovoltaic system (PV) output and demand. This study focuses on settlements in multi-period markets (a day-ahead market and a real-time market) and the installation of energy storage systems (ESSs). ESSs can be utilized for time arbitrage in the day-ahead market and to reduce the purchasing/selling of electricity in the real-time market. However, the high costs of an ESS mean the size of the system needs to be minimized. In addition, when determining the size of an ESS, it is important to identify the size appropriate for each role. Therefore, we employ the concept of a "slow" and a "fast" ESS to quantify the size of a system's role, based on the values associated with the various uncertainties. Because the problem includes nonlinearity and non-convexity, we solve it within a realistic computational burden by reformulating the problem using reasonable assumptions. Therefore, this study identifies the optimal sizes of ESSs and procurement, taking into account the uncertainties of prices in multi-period markets, PV output and demand.

© 2020 Elsevier B.V. Recently, there have been several studies on the research and development of service robots, such as reception or waiter robots for facilities and companion robots for support of baggage transportation or guidance in public spaces. Several experimental results in real environments have been reported. To realize socially acceptable human–robot interaction for service robots, human recognition, including not only position but also body direction, around the robot is important. Using an RGB-D camera, it is possible to detect the posture of a person. However, because the viewing angle of the camera is narrow, it is difficult to recognize the environment around the robot with a single device. This study proposes the estimation of the body direction based on the gait, that is, not only the position and velocity, but also the state of the legs (stance or swing phase), using laser range sensors installed at shin height. We verify the effectiveness of the proposed method for several patterns of movement, which are seen when a person interacts with the service robot and evaluate measurement accuracy.

© 2013 IEEE. For the evaluation of pathological gait, a machine learning-based estimation of the vertical ground reaction force (vGRF) using a low-cost insole is proposed as an alternative to costly force plates. However, learning a model for estimation still relies on the use of force plates, which is not accessible in small clinics and individuals. Therefore, this paper presents a force plate-free learning from a single leg stance (SLS) and natural walking measured only by the insoles. This method used a linear least squares regression that fits insole measurements during SLS to body weight in order to learn a model to estimate vGRF during walking. Constraints were added to the regression so that vGRF estimates during walking were of proper magnitude, and the constraint bounds were newly defined as a linear function of stance duration. Moreover, a lower bound for the estimated vGRF in mid-stance was added to the constraints to enhance estimation accuracy. The vGRF estimated by the proposed method was compared with force platforms for 4 healthy young adults and 13 elderly adults including patients with mild osteoarthritis, knee pain, and valgus hallux. Through the experiments, the proposed learning method had a normalized root mean squared error under 10% for healthy young and elderly adults with stance durations within a certain range (600-800 ms). From these results, the validity of the proposed learning method was verified for various users requiring assessment in the field of medicine and healthcare.

© 2019 The Japan Society for Aeronautical and Space Sciences. Increasing air traffic and airport congestion calls for solutions to improve traffic throughput. In this paper, we evaluate one solution, Flight-deck Interval Management and its underlying logic, particularly in terms of its utility. An environment to simulate traffic engaged in interval management on the most common arrival routes toward Tokyo International Airport was set up and run as a large-scale Monte Carlo simulation on the K-Supercomputer. The results show that under low wind conditions in particular, spacing goal times with a standard deviation of less than 5 s can be achieved and a speed tolerance mode can reduce the number of speed commands without compromising performance.

© 2020 The Authors Background: Postmenopausal women are at risk of fall and fracture with the physical decline. Distal radius fracture (DRF) is considered as the primary fragility fracture, and women with this fracture showed poor results in the usual Timed Up-and-Go (TUG) test, indicating a decline in balance and physical ability. The detailed physical characteristics of female DRF patients have not been extensively examined. Research question: Is the novel laser TUG system able to detect and analyze the detailed gait characteristics in patients with DRF whose physical ability has tended to decline? Methods: In this cross-sectional case control study, the gait characteristics of 32 female patients with DRF who had undergone surgery were evaluated at 2 weeks postoperatively with a laser TUG system to analyze the detailed leg motion during normal TUG test. Forty-three age- and sex-matched non-fractured women were evaluated by the laser TUG system as controls. Lifestyle and present illness were corrected at the time of TUG measurement. Detailed data during laser TUG in both groups were compared statistically, and odds ratio and thread shod of the fracture was elucidated through a logistic regression analysis. Results: DRF patients showed slower speed and had to do more steps to complete the TUG test. Furthermore, asymmetric trajectory and significantly further distance from the marker were observed. Thirteen steps to complete the TUG test was the thread shod of DRF. Significance: Detailed gait characteristics of patients with DRF were detected by the laser TUG system. The gait decline and abnormality could be one of the reasons of consecutive fragility fracture. To prevent secondary fragility fractures, this system can be useful for screening.

© 2018 Background: Lumbopelvic pain (LPP) is one of the most common discomforts during pregnancy. However, few studies have evaluated relation between LPP and gait in pregnancy quantitatively. Research question: This study aimed to investigate the relation between the LPP and gait characteristics such as symmetry, stability, and the degree of motion during pregnancy. Methods: Gait data were collected for fifty-two pregnant women between the third and tenth month of pregnancy on smooth, horizontal walkway by using inertial measurement sensor units attached to the participants’ lumbar. The degrees of trunk movement, movement symmetry, gait variability, and symmetry of rotation were expressed as the root mean square (RMS), autocorrelation peak (AC), coefficient of variance (CV), and the degree of asymmetry at the approximate amount of angular variation (DA) respectively, which were calculated from measured acceleration data and angular velocity data. An independent t-test was performed to investigate differences in these gait parameters between LPP group and pain free group classified according to the presence or absence of the pain, which is evaluated by using a questionnaire. In addition, LPP group was divided into 5 subgroups based on the types of pain, and the differences between the groups were also investigated by using a one way ANOVA. Results: Rotational asymmetry was observed in movement of the roll direction of the LPP patients. The DA of the roll angle of the LPP group was significantly greater than that in the pain free group (0.140 ± 0.093 vs. 0.077 ± 0.053, respectively; p = 0.004). In the analysis of pain complications, the significant difference in DA of roll angle, and CV of yaw angle were observed. Significance: The results indicated that motion asymmetry of both rotation and translation increased significantly in LPP patients’ gait.

© 2019, Springer Nature B.V. Controlling a drone using head-mounted display induces virtual reality (VR) sickness. From previous research, it is known that angular velocity is one of the contributing factors to induce VR sickness, however for drones, linear motion and the interaction between linear and angular motion often occur during operation. In this research, we investigate the effect of each conditions experimentally and proposes a method of controlling a drone to reduce VR sickness. We designed a system that does not make user’s head fixed at one point but allows to move the head freely. At the same time, the head orientation and direction are synced with the drone’s attitude to reduce sensory conflict. Two controllers were compared: joystick control and head control. We tested with a real system and conducted experiments on subjects to verify its effect. The proposed controller reduced angular velocity in the frequency range 0.1 to 10 Hz where a vestibular system becomes most sensitive, and it is demonstrated that reducing sensory conflict contributes to the reduction of VR sickness.

© 2020 Elsevier Ltd Laser range sensor-based timed up and go (laser-TUG) test can evaluate performance in TUG subtasks (sit-to-walk [STW], walking a short distance, and turning). This study aimed to test the hypothesis that weaker hip abductor muscle strength is more significantly associated with slowed turning speed than with the other TUG subtasks (STW and straight walking) after controlling for quadriceps muscle strength in patients with knee osteoarthritis (OA). Community-dwelling participants with knee OA (Kellgren and Lawrence [K&L] grade ≥ 1; mean age, 68.6 years; 70.3% women) underwent laser-TUG. Spatiotemporal gait parameters in TUG and the TUG subtasks were evaluated as outcome measures. The isometric muscle strength of the hip abductor and quadriceps was measured using a hand-held dynamometer. Multiple linear regression analysis was performed to examine the relationship between muscle strength as an independent variable and spatiotemporal parameters as dependent variables. The relative importance of hip abductor muscle strength was determined using the percentages of unique variance. Participants with weaker hip abductor muscle strength demonstrated 0.094 m/s slower turning speed after adjustment for covariates including quadriceps muscle strength. The unique variance explained by hip abductor muscle strength in turning speed was 2.1%. However, no significant relationships were confirmed between weak hip abductor muscle strength and the time to perform TUG and the straight walking (forward and return) phase. These findings indicate that turning motion may be more sensitive to aggravated hip abductor muscle weakness and may show better response to hip muscle strengthening exercises. Longitudinal studies are warranted to elucidate this issue.

© 2020 Elsevier B.V. This paper proposes a novel control system design for a two-wheeled service robot that follows a person as an assistant without knowing the person's destination. For this kind of service robot, the key skill is to realize human-friendly movement. However, appropriate motion always changed depending on the situation. For instance, when the robot is close and person turns toward it, it is important to suppress the robot's acceleration. Likewise, if the person turns away from the robot, the robot should maintain its position within an appropriate area. Therefore, to deal with various required movements, our control system is able to change its properties automatically and suitably depending on the situation by using weights of the cost function in nonlinear model predictive control (NMPC) as a function of the relative distance between the person and the robot. Unlike previous methods, our design includes only one controller. Consequently, we are able to take into account system stability. Moreover, owing to proposing in NMPC framework, it is easy to extend our method by adopting other recognition or goal-setting methods. We conducted simulations using actual human walking data taken by the robot's laser range sensors. The experiments demonstrate that the robot can follow a person who performs U-turn, confirming that our method can produce human-friendly robot movement in a practical scene.

© 2001-2011 IEEE. An insole-based estimation of the vertical ground reaction force (vGRF) is proposed as an alternative to costly force plates for the evaluation of pathological gait. However, machine learning techniques for estimation still rely on the use of force plates. Moreover, measuring plural walking steps in order to prevent overfitting induces fall risks and physically taxes the patients. Therefore, this paper presents an accessible and efficient learning scheme for the insole-based estimation of vGRF. In this system, we employ a low-cost scale as an alternative to force plates. Then, we use Gaussian process regression (GPR) to learn a model in order to estimate vGRF without overfitting of small-sized data sets corrupted by measurement errors and noise of the devices. In addition, we propose a 'one-step learning' scheme based on a probabilistic data augmentation. This approach augments actual measurements of a minimum (just one) walking step to a virtual data set for plural steps by considering their typical variability between steps. In experiments, the GPR models learned from two walking steps estimated vGRF with mean errors of 8% or under for entire/local magnitudes. Moreover, the learning from one step with probabilistic augmentation enhanced the estimation accuracy.

© 2018 Osteoarthritis Research Society International Objective: To test the hypothesis that the interaction between low back pain (LBP) and knee pain intensity contributes to the disability level of individuals with knee osteoarthritis (OA). Design: Community-dwelling participants with knee OA (Kellgren/Lawrence [K/L] grade ≥1) were enrolled. LBP and its severity were identified using questionnaires. Knee pain severity and disability level were evaluated using the Japanese Knee Osteoarthritis Measure (JKOM) subscale. Multiple linear regression analyses were performed to examine the effect of the LBP–knee pain interaction, an independent variable, on disability, a dependent variable. Results: A total of 260 participants (age, 48–88 years; 77.7% women) were included. Of them, 151 (58.1%) had LBP. The LBP–knee pain interaction was significantly associated with disability after the adjustment for covariates. A post-hoc subgroup analysis revealed that the relationship between knee pain intensity and disability level was higher in individuals with LBP (beta: 0.621 points; 95% confidence interval [CI]: 0.511 to 0.731 points) than in those without LBP (beta: 0.402 points; 95% CI: 0.316 to 0.487 points). Conclusions: LBP interacts with knee pain intensity and contributes to disability level in individuals with knee OA. Coexisting LBP and knee pain had a stronger impact on disability level than LBP or knee pain alone. These findings highlight the potential deteriorative effects of the LBP–knee interaction on disability. Maximal treatment effects for disability might be achieved when LBP and knee pain are targeted simultaneously, rather than separately.

© 2018 The Author(s). Background: While abnormal rearfoot posture and its relationship to patellofemoral (PF) pain has been thoroughly discussed in the literature, its relationship to patellofemoral osteoarthritis (PFOA) has not been determined. This study aimed to examine whether rearfoot posture is associated with a higher prevalence of radiographic PFOA in a compartment-specific manner in patients with medial tibiofemoral osteoarthritis (TFOA). Methods: Participants from orthopedic clinics (n=68, age 56-90 years, 75.0% female), diagnosed with radiographic medial TFOA (Kellgren/Lawrence [K/L] grade≥2) were included in this study. The presence of PFOA and static rearfoot posture were evaluated using a radiographic skyline view and a footprint automatic measurement apparatus, respectively. The relationship between rearfoot posture and PFOA was examined using analysis of covariance and propensity score-adjusted logistic regression analysis. Results: On average, patients with coexisting PFOA and medial TFOA (n=39) had an inverted calcaneus 3.1° greater than those with isolated medial TFOA (n=29). Increased calcaneus inverted angle was significantly associated with a higher probability of the presence of medial PFOA (odds ratio: 1.180, 95% confidence interval: [1.005, 1.439]; p=0.043). Calcaneus inverted angle was not associated with higher odds of lateral PFOA presence based on the adjusted values. Conclusions: The presence of an inverted rearfoot was associated with PFOA. Although these findings do not clearly indicate a biomechanical link between rearfoot posture and PFOA, this study shed light on the potential relationship between altered rearfoot posture and PFOA, as can be seen between rearfoot abnormality and PF pain.

© 2019, Springer Nature Switzerland AG. One of the most basic tasks that a dual-arm robot does is pick-up and place work. Pick-up and place work consists of tasks in which the robot carries objects from a start position (initial position) to a goal position. The following three important points should also be considered when the dual-arm robot does this work efficiently: (1) collision avoidance of the arms, (2) which arm should move an object, and (3) the order in which the objects should be picked up and placed. In addition, dual-arm robot has operation range constraints. Depending on the position relationship between a start position and goal position, unless both arms are used, the object may not be transferred to a goal position. In this paper, we define the transfer path which must use both arms as “shared transfer path”. First, we use mixed integer linear programming (MILP) based planning for the pick-up and place work to determine which arm should move an object and in which order these objects should be moved while considering the dual-arm robot’s operation range. Second, we plan the path using the rapidly exploring random tree (RRT) so that the arms do not collide, enabling the robot to perform efficient pick-up and place work based on the MILP planning solution. The effectiveness of proposed method is confirmed by simulations and experiments using the HIRO dual-arm robot.

© 2019 by Xin Ning. Published by the American Institute of Aeronautics and Astronautics, Inc. This paper proposes a simultaneous control method for small satellites mounted with a communication antenna; the objective is to reduce the time involved in satellite maneuver and antenna motion. Recently, small Earth observation satellites have been utilized, even though agile large angle satellite attitude maneuver has been in demand. Small Earth observation satellites acquire high-resolution data, resulting in an increase in the time required for data communication. Therefore, it has become important to ensure that small Earth observation satellites are capable of being maneuvered rapidly so that communication time can be extended by using a data relay system. The purpose of this study is to extend the time for Earth observation and data communication even if satellite has model uncertainty or space disturbance. In order to achieve this, we propose a simultaneous control method for satellite maneuver and antenna motion by using a nonlinear programming problem (NLP) and robust servo control method by using the state dependent Riccati equation (SDRE).