3D Walking Research Articles

Helium diffusion in pure hematite (α-Fe2O3) for thermochronometric applications: A theoretical multi-scale study

He diffusion coefficient in iron oxide α-hematite crystal has been determined using computational multi-scale approach in the purpose of geological dating as He is produced during U-Th-Sm decay in this mineral. Natural hematite samples are generally made of nanometric to micrometric scale crystals leading to the difficulty to determine the total He diffusion behavior. A multi-scale theoretical approach will so bring new information on the He diffusion coefficient in 3D. Investigations, at microscopic scale, of helium insertion and atomic jumps into hematite crystal have been performed by DFT and transition state theory. The minimum path energy of helium migration between interstitial sites and its position at transition state are determined by the climbing image-Nudged Elastic Band method.Based on the microscopic results the 3D random walk of helium, in the hematite crystal, has been simulated by the Kinetic Monte Carlo method. The diffusion coefficient has been determined:D3D(cm2/s)=9.32×10-3e-1.63eVkBT.The calculated activation energy, for a perfect crystal, is in very good agreement with experiment data showing that He diffusion in hematite is controlled only by the crystal structure. These results give the 3D He diffusion and permit to determine that He is highly retain in crystal at surface temperature, with closure temperature of 83 and 154°C for grain size of 0.1 and 10μm respectively. These diffusion coefficient data can so be used in the future for a better interpretation of geological ages.

Urban density, diversity and design: Is more always better for walking? A study from Hong Kong

Many cities in China have undergone rapid urbanization and are experiencing a decline in residents' physical activity levels. Previous studies have reported inconsistent findings on the association between 3D's (density, diversity, design) and walking behavior, and few studies have been conducted in China. The aim of this study was to identify the association between objectively measured 3D's and different domains of walking (transport vs. leisure) in Hong Kong, China. A survey was conducted in 2014 to collect walking data and relevant individual data from 1078 participants aged 18–65. The participants were randomly selected from 36 Hong Kong housing estates with different built environment and neighborhood socioeconomic status (SES). Built environment factors—population design, land-use mix and street intersection density—were assessed using a geographic information system. Multi-level regression was used to explore the associations between walking behavior and built environment factors, while adjusting for covariates. Two out the three D's—land-use mix and street connectivity—are not significantly related to any domains of walking. Furthermore, the third D, population density, is only positively related to walking for transport and walking for leisure in the lower range of density, while is negatively related to walking for leisure in the higher range of density. The findings suggest that the association between original 3D's and walking may vary in different urban contexts. The policy or planning strategy—using three D's to promote physical activity—may be ineffective or even counterproductive in large and already dense cities in China.

3D exemplar-based random walks for tooth segmentation from cone-beam computed tomography images.

Tooth segmentation is an essential step in acquiring patient-specific dental geometries from cone-beam computed tomography (CBCT) images. Tooth segmentation from CBCT images is still a challenging task considering the comparatively low image quality caused by the limited radiation dose, as well as structural ambiguities from intercuspation and nearby alveolar bones. The goal of this paper is to present and discuss the latest accomplishments in semisupervised tooth segmentation with adaptive 3D shape constraints. The authors propose a 3D exemplar-based random walk method of tooth segmentation from CBCT images. The proposed method integrates semisupervised label propagation and regularization by 3D exemplar registration. To begin with, the pure random walk method is to get an initial segmentation of the teeth, which tends to be erroneous because of the structural ambiguity of CBCT images. And then, as an iterative refinement, the authors conduct a regularization by using 3D exemplar registration, as well as label propagation by random walks with soft constraints, to improve the tooth segmentation. In the first stage of the iteration, 3D exemplars with well-defined topologies are adapted to fit the tooth contours, which are obtained from the random walks based segmentation. The soft constraints on voxel labeling are defined by shape-based foreground dentine probability acquired by the exemplar registration, as well as the appearance-based probability from a support vector machine (SVM) classifier. In the second stage, the labels of the volume-of-interest (VOI) are updated by the random walks with soft constraints. The two stages are optimized iteratively. Instead of the one-shot label propagation in the VOI, an iterative refinement process can achieve a reliable tooth segmentation by virtue of exemplar-based random walks with adaptive soft constraints. The proposed method was applied for tooth segmentation of twenty clinically captured CBCT images. Three metrics, including the Dice similarity coefficient (DSC), the Jaccard similarity coefficient (JSC), and the mean surface deviation (MSD), were used to quantitatively analyze the segmentation of anterior teeth including incisors and canines, premolars, and molars. The segmentation of the anterior teeth achieved a DSC up to 98%, a JSC of 97%, and an MSD of 0.11 mm compared with manual segmentation. For the premolars, the average values of DSC, JSC, and MSD were 98%, 96%, and 0.12 mm, respectively. The proposed method yielded a DSC of 95%, a JSC of 89%, and an MSD of 0.26 mm for molars. Aside from the interactive definition of label priors by the user, automatic tooth segmentation can be achieved in an average of 1.18 min. The proposed technique enables an efficient and reliable tooth segmentation from CBCT images. This study makes it clinically practical to segment teeth from CBCT images, thus facilitating pre- and interoperative uses of dental morphologies in maxillofacial and orthodontic treatments.

An optimal jerk-stiffness controller for gait pattern generation in rough terrain

In this paper, an optimal jerk stiffness controller is proposed to produce stable gait pattern generation for bipedal robots in rough terrain. The optimal jerk controller is different from the point-to-point and via-Point conventional approaches as trajectories are planned in the Cartesian space system whereas control laws are expressed in the joint space. Its major contribution resides in the generation of stable semi elliptic Cartesian trajectories during the swing phase that do combine benefits of trigonometric and polynomial functions. The stiffness controller is designed without gravity compensation and ensures for the robotic system elastic and stable contact forces with the ground during the impact and the double support phases. Not only, the control strategy proposed needs very few sensors to be implemented but also it ensures robustness to sensory noise and safety with rough terrain. Simulation performed on a 12 DOF bipedal robot shows the performances of the control laws combined to produce a 3D stable walking cycles without shaking in uneven terrain.

From Passive Dynamic Walking to Passive Turning of Biped walker

Dynamically stable biped robots mimicking human locomotion have received significant attention over the last few decades. Formerly, the existence of stable periodic gaits for straight walking of passive biped walkers was well known and investigated as the notion of passive dynamic walking. This study is aimed to elaborate this notion in the case of three dimensional (3D) walking and extend it for other maneuvers, specifically curved walking or turning. For this purpose, the motion of a general 3D compass gait model on a ramp has been analyzed theoretically in detail. A comprehensive dynamic modeling with respect to the vertical fixed frame is used based on Lagrangian and augmented methods. In addition to 3D passive straight walking, the results confirm the existence of some passive turning motions for the biped walker towards the steepest decent of the ramp. It was shown that the value of passive turning is strictly concerned to the value of initial perturbed condition of the walker, especially to the value of heading angle. A parameter analysis was also accompanied to examine the change in the characteristics of such passive motions caused by the change in model parameters.

Using the Generalized Inverted Pendulum to Generate Less Energy-Consuming Trajectories for Humanoid Walking

AbstractThis paper proposes an analysis of the effect of vertical position of the pivot point of the inverted pendulum during humanoid walking. We introduce a new feature of the inverted pendulum by taking a pivot point under the ground level allowing a natural trajectory for the center of pressure (CoP), like in human walking. The influence of the vertical position of the pivot point on energy consumption is analyzed here. The evaluation of a 3D Walking gait is based on the energy consumption. A sthenic criterion is used to depict this evaluation. A consequent reduction of joint torques is shown with a pivot point under the ground.

Evaluation of Microstructure and Transport Properties of Deteriorated Cementitious Materials from Their X-ray Computed Tomography (CT) Images.

Pore structure, tortuosity and permeability are considered key properties of porous materials such as cement pastes to understand their long-term durability performance. Three-dimensional image analysis techniques were used in this study to quantify pore size, effective porosity, tortuosity, and permeability from the X-ray computed tomography (CT) images of deteriorated pastes that were subjected to accelerated leaching test. X-ray microtomography is a noninvasive three-dimensional (3D) imaging technique which has been recently gaining attention for material characterization. Coupled with 3D image analysis, the digitized pore can be extracted and computational simulation can be applied to the pore network to measure relevant microstructure and transport properties. At a spatial resolution of 0.50 μm, the effective porosity (φe) was found to be in the range of 0.04 to 0.33. The characteristic pore size (d) using a local thickness algorithm was found to be in the range of 3 to 7 μm. The geometric tortuosity (τg) based on a 3D random walk simulation in the percolating pore space was found to be in the range of 2.00 to 7.45. The water permeability values (K) using US NIST Permeability Stokes Solver range from an order of magnitudes of 10−14 to 10−17 m2. Indications suggest that as effective porosity increases, the geometric tortuosity increases and the permeability decreases. Correlation among these microstructure and transport parameters is also presented in this study.

Optimized 3D stable walking of a bipedal robot with line-shaped massless feet and sagittal underactuation

This paper seeks to provide a method for optimizing 3D bipedal walking with satisfactory energy efficiency, provable stability and one degree of underactuation. Following the studies of the planar biped RABBIT, we propose a 3D robot with massless line feet which serve as sagittal rotation axes when lying flat on the ground. Using this configuration and the control method based on virtual constraints and feedback linearization, the walking stability can be verified by the restricted scalar Poincaré map of the zero dynamics of the system, and periodic gaits can be obtained analytically as in the case of planar bipeds with point feet. A line-foot contact model is adopted to ensure one degree of underactuation. Unlike most published contact models of bipedal walking, this model also prevents possible yaw movements of the feet on the ground. In addition, we adopt an output function named “symmetry outputs” with the desired outputs parameterized by Bézier coefficients and postural parameters, and the gait optimization is performed using a SQP algorithm. According to the results obtained from a bipedal model with a height of 1.5 m and a weight of 39 kg, the optimization program is capable of calculating stable periodic gaits with a speed between 0.2 m/s and 1.5 m/s.

自由度凍結の解除と弾性体によるヒトに近い3次元歩行

Recent study of passive walking is developed complicatedly. In previous study, 3D passive walking used to comprise pelvis mechanism and human foot mechanism. In this study, we aim to develop a 3D passive walking in a more stable state. We focused on human thenar and hypothenar, and developed variable rigidity mechanism using elasticity. Further, according to the principle of releasing fixed degree of freedom, we developed an ankle system, resulting in more smooth human-like walking.

Optimal gait planning for humanoids with 3D structure walking on slippery surfaces

SUMMARYIn this study, a gait optimization routine is developed to generate walking patterns which demand the lowest friction forces for implementation. The aim of this research is to fully address the question “which walking pattern demands the lowest coefficient of friction amongst all feasible patterns?”. To this end, first, the kinematic structure of the considered 31 DOF (Degrees of Freedom) humanoid robot is investigated and a closed-form dynamics model for its lower-body is developed. Then, the medium through which the walking pattern generation is conducted is presented. In this medium, after designing trajectories for the feet and the pelvis, the joint space variables are obtained, using the inverse kinematics. Finally, by employing a genetic algorithm (GA), an optimization process is conducted to generate walking patterns with the minimum Required Coefficient Of Friction (RCOF). Six parameters are adopted to parameterize the pelvis trajectory and are exploited as the design variables in this optimization procedure. Also, a parametrical study is accomplished to address the effects of some other variables on RCOF. For comparison purposes, a tip-over Stability Margin (SM) is defined, and an optimization procedure is conducted to maximize this margin. Finally, the proposed gait planning procedure is implemented on SURENA III, a humanoid robot designed and fabricated in CAST, to validate the developed simulation procedure. The obtained results reveal merits of the proposed optimal gait planning procedure in terms of RCOF.

Two eyes are identical to one: Three-dimensional motor tracking of visual targets

The threshold for detecting stereoscopic motion is notably higher than that for detecting the equivalent fronto-parallel motion. Thus, for small excursions, an apparently stationary line can easily be seen as moving by simply closing one eye - two eyes being less sensitive than one (Tyler, 1971). Here, we used a 3D tracking paradigm to examine motion perception with a continuous motor task. Observers used a cursor to track a target as it moved in a 3D Gaussian random walk. In the main experiment, each eye saw a veridical 2D projection of a square target and cursor moving in 3D. A Leap Motion controller was used to move the cursor by simply pointing at the target location. The controller was calibrated such that there was a one-to-one mapping between finger movement and simulated cursor movement. Tracking data were analyzed by computing the cross-correlograms (CCGs) between the target and cursor velocities for each of the three cardinal motion directions, and assessing the lag, peak correlation, and width of the CCGs. Responses to the depth component of the motion were markedly weaker and more sluggish than responses to the fronto-parallel directions. Further experiments revealed that these depth responses were identical when either only horizontal disparity information was available or when a disparity-only target was viewed monocularly. Our primary finding was that depth tracking is worse than fronto-parallel tracking, but this was simply due to the much smaller amplitudes of projected fronto-parallel motion that motion-in-depth produces. We did not find evidence for the stereo-motion suppression observed with traditional psychophysics, nor did we find a need to invoke a specific disparity processing mechanism. Rather, continuous tracking behavior is parsimoniously explained by reliance on the 2D projections of 3D motion. Meeting abstract presented at VSS 2015. Language: en

Impact of apatite chemical composition on (U-Th)/He thermochronometry: An atomistic point of view

The quantification of the different parameters influencing He diffusion in apatite is an important issue for the interpretation of (U-Th)/He thermochronometric ages. Key issues include understanding the role of chemical composition and the mechanism modifying diffusivity by radiation damage, both requiring a realistic description at the atomic level. In this contribution, we restrict ourselves on the influence of the chemical composition especially on the effect of Cl-atoms on the He diffusion in the damage-free apatite crystal. For this purpose, a multi-scale theoretical diffusion study has been conducted using periodic Density Functional Theory calculations for two different apatite compositions (pure fluorine apatite and apatite with one chlorine and 3 fluorine atoms per cell called Cl0.25-apatite) representative of damage-free crystals. Different He insertion sites and diffusion pathways are first investigated. The Density Functional Theory approach coupled to the Nudged Elastic Band method is used to determine the energy barriers between the insertion sites. A statistical method, based on Transition State Theory, is used to compute the jump rate between sites and the different results are used as output for a 3D random walk simulation, which determines the diffusion trajectories and the diffusion coefficients. The calculated diffusion coefficients for pure F-apatite exhibit a slightly anisotropic behavior with an activation energy Ea=95.5kJ/mol and a frequency factor D0=1.9×10−3cm2/s along the c axis; Ea=106.1kJ/mol and D0=4.1×10−3cm2/s in the plane orthogonal to c. Closure temperatures for a 60μm grain radius and 10°C/Ma cooling rate range from 33 to 36°C and depend on crystal geometry for a given grain size. Surprisingly, even though He diffusion is strongly blocked across the Cl atoms in Cl0.25-apatite, where Ea is significantly higher (166.7kJ/mol), He atoms can still diffuse along the c axis through workaround pathways. Closure temperatures are dependent on the Cl content in the crystal lattice and can be ∼12°C higher for Cl0.25-apatite than for F-apatite. These results show that various Cl contents lead to a more He retentive diffusivity in addition to their impact on damage-annealing rate. The results of this study are in good agreement with experimental results and demonstrate that a proper Density Functional Theory treatment allows to characterize He diffusion in damage-free apatite. This opens new avenues to a reliable method of quantifying rare gas diffusion in mineral structures.

Emotion Interaction with Virtual Reality Using Hybrid Emotion Classification Technique toward Brain Signals

Human computer interaction (HCI) considered main aspect in virtual reality (VR) especially in the context of emotion, where users can interact with virtual reality through their emotions and it could be expressed in virtual reality. Last decade many researchers focused on emotion classification in order to employ emotion in interaction with virtual reality, the classification will be done based on Electroencephalogram (EEG) brain signals. This paper provides a new hybrid emotion classification method by combining self- assessment, arousal valence dimension and variance of brain hemisphere activity to classify users’ emotions. Self-assessment considered a standard technique used for assessing emotion, arousal valence emotion dimension model is an emotion classifier with regards to aroused emotions and brain hemisphere activity that classifies emotion with regards to right and left hemisphere. This method can classify human emotions, two basic emotions is highlighted i.e. happy and sad. EEG brain signals are used to interpret the users’ emotional. Emotion interaction is expressed by 3D model walking expression in VR. The results show that the hybrid method classifies the highlighted emotions in different circumstances, and how the 3D model changes its walking style according to the classified users’ emotions. Finally, the outcome is believed to afford new technique on classifying emotions with feedback through 3D virtual model walking expression.

Principle and method of speed control for dynamic walking biped robots

In this paper, the method of speed control for 3D biped robots is addressed. First, the primary principle of speed control by regulation of input energy is studied, the feature of which is to regulate the speed and the step length synchronically. The method of Poincaré mapping is used to prove the stability of speed control in the common range. Second, a method of speed control for an 18 DOFs bipedal 3D robot, which is characterized by the two-point-foot, is proposed. The method is developed on the basis of the 3D walking pattern proposed previously, with the new function of speed regulation being added in. The simulations show that the performances of regular walking, acceleration, and deceleration are effective and stable, and therefore verify the feasibility of the proposed method. Furthermore, some walking features, such as the walking efficiency and lateral control, are demonstrated.

Stable walking of 3D compass-like biped robot with underactuated ankles using discrete transverse linearization

In this study, a walking manner of a spatial compass-like biped robot with underactuated ankles is presented. This biped robot has 3 degrees of freedom with only one actuator. The hip joint is equipped with a constraint mechanism to lock the angle when it retracts to a desired value. With the Poincare shooting method, a limit cycle of 3D walking gait on level ground is obtained. This limit cycle is unstable by checking the Jacobian of the Poincare map. We use this limit cycle as a reference trajectory and then introduce a method based on discrete transverse linearization to transform the reference trajectory tracking problem to a stabilization problem of a discrete periodic linear system. Thus, the classical discrete-time linear quadratic regulator is recalled to solve the stabilization problem. That is, a stable walking control law is obtained for the proposed 3D robot with a constraint mechanism.

Performance Analysis and Feedback Control of ATRIAS, A Three-Dimensional Bipedal Robot

This paper develops feedback controllers for walking in 3D, on level ground, with energy efficiency as the performance objective. Assume The Robot Is A Sphere (ATRIAS) 2.1 is a new robot that has been designed for the study of 3D bipedal locomotion, with the aim of combining energy efficiency, speed, and robustness with respect to natural terrain variations in a single platform. The robot is highly underactuated, having 6 actuators and, in single support, 13 degrees of freedom. Its sagittal plane dynamics are designed to embody the spring loaded inverted pendulum (SLIP), which has been shown to provide a dynamic model of the body center of mass during steady running gaits of a wide diversity of terrestrial animals. A detailed dynamic model is used to optimize walking gaits with respect to the cost of mechanical transport (CMT), a dimensionless measure of energetic efficiency, for walking speeds ranging from 0.5 (m/s) to 1.4 (m/s). A feedback controller is designed that stabilizes the 3D walking gaits, despite the high degree of underactuation of the robot. The 3D results are illustrated in simulation. In experiments on a planarized (2D) version of the robot, the controller yielded stable walking.

Controlled Reduction with Unactuated Cyclic Variables: Application to 3D Bipedal Walking with Passive Yaw Rotation.

This paper shows that viscous damping can shape momentum conservation laws in a manner that stabilizes yaw rotation and enables steering for underactuated 3D walking. We first show that unactuated cyclic variables can be controlled by passively shaped conservation laws given a stabilizing controller in the actuated coordinates. We then exploit this result to realize controlled geometric reduction with multiple unactuated cyclic variables. We apply this underactuated control strategy to a five-link 3D biped to produce exponentially stable straight-ahead walking and steering in the presence of passive yawing.

Relationship Between Knee Walking Kinematics and Muscle Flexibility in Runners

Decreased flexibility in muscles and joints of lower extremities is commonly observed in runners. Understanding the effect of decreased flexibility on knee walking kinematics in runners is important because, over time, altered gait patterns can make runners vulnerable to overuse injuries or degenerative pathologies. To compare hamstring and iliotibial-band (ITB) flexibility and knee kinematics in runners and nonrunners. A descriptive, comparative laboratory study. Hamstring and ITB flexibility were measured with the active knee-extension test and the modified Ober test, respectively, in both groups of participants. Three-dimensional (3D) walking kinematic data were then recorded at the knee using a motiontracking system. 18 runners and 16 nonrunners. Knee-extension angle (hamstring flexibility) and hip-adduction angle (ITB flexibility). Knee kinematic parameters of interest included knee angle at initial contact, peak knee angles, and knee-angle range in all planes of movement. The runners had a significantly less flexible ITB than the nonrunners (hip adduction [-] and adduction [+] angles, 3.1° ± 5.6° vs -.4° ± 4.5°; P < .001). The runners demonstrated a greater mean tibial external-rotation angle at initial contact (7.3° ± 5.8° vs 2.0° ± 4.0°; P = .01) and a smaller mean peak tibial internal-rotation angle (-1.6° ± 3.0° vs -4.2° ± 3.2°; P = .04) than the nonrunners. This study provides new insight into the relationship between muscle flexibility and 3D knee kinematics in runners. This supports the premise that there is an association between muscle flexibility and transverse-plane knee kinematics in this population.

Influence of neuromuscular noise and walking speed on fall risk and dynamic stability in a 3D dynamic walking model

Older adults and those with increased fall risk tend to walk slower. They may do this voluntarily to reduce their fall risk. However, both slower and faster walking speeds can predict increased risk of different types of falls. The mechanisms that contribute to fall risk across speeds are not well known. Faster walking requires greater forward propulsion, generated by larger muscle forces. However, greater muscle activation induces increased signal-dependent neuromuscular noise. These speed-related increases in neuromuscular noise may contribute to the increased fall risk observed at faster walking speeds. Using a 3D dynamic walking model, we systematically varied walking speed without and with physiologically-appropriate neuromuscular noise. We quantified how actual fall risk changed with gait speed, how neuromuscular noise affected speed-related changes in fall risk, and how well orbital and local dynamic stability measures predicted changes in fall risk across speeds. When we included physiologically-appropriate noise to the ‘push-off’ force in our model, fall risk increased with increasing walking speed. Changes in kinematic variability, orbital, and local dynamic stability did not predict these speed-related changes in fall risk. Thus, the increased neuromuscular variability that results from increased signal-dependent noise that is necessitated by the greater muscular force requirements of faster walking may contribute to the increased fall risk observed at faster walking speeds. The lower fall risk observed at slower speeds supports experimental evidence that slowing down can be an effective strategy to reduce fall risk. This may help explain the slower walking speeds observed in older adults and others.

A coordination-based CPG structure for 3D walking control

SUMMARYIn most of our daily motion tasks, the coordination between limbs is very crucial for successful execution of the tasks. In this paper, coordination among oscillators controlling in Cartesian space is studied to control bipedal walking. In our method, phase adjustment among oscillators is considered as one of the key issues to achieve coordination. A new phase adjustment method is proposed. With this method, an oscillator is able to coordinate other oscillators and maintain a desired phase relationship. This property is important for the walking control especially when external perturbations are given. To simplify the relationship between oscillators in a central pattern generator (CPG), a hierarchical CPG structure is adopted, where a main oscillator will be used to adjust other oscillators. In the simulation, the walking motion controlled by the CPG controller converges to a stable pattern even with external perturbations. We have implemented the controller in both the simulation model and real hardware robot.