Simple Kinematic Research Articles

Tracking a Mobile Robot in a UWB-sensor Grid

This work presents the development of a tracking system for a three-wheeled omnidirectional mobile robot. This kind of robot can perform rotation and translation in any pose. The arc-length segment described by the omni-wheels controls the trajectory of the robot. We present a simplified kinematic model in state-space. The observation system is based on an UltraWide Band ranging sensor. Finally made the state estimation using some classic positioning algorithms and compare the results against Finite Impulse Response Filter state estimators.

On the origin of shear-band network patterns in ductile shear zones

Ductile yielding of rocks and similar solids localize shear zones, which often show complex internal structures due to the networking of their secondary shear bands. Combining observations from naturally deformed rocks and numerical modelling, this study addresses the following crucial question: What dictates the internal shear bands to network during the evolution of an initially homogeneous ductile shear zone? Natural shear zones, observed in the Chotonagpur Granite Gneiss Complex of the Precambrian craton of Eastern India, show characteristic patterns of their internal shear band structures, classified broadly into three categories: type I (network of antithetic low-angle Riedel (R) and synthetic P-bands), type II (network of shear-parallel C and P/R bands) and type III (distributed shear domains containing isolated undeformed masses). Considering strain-softening rheology, our two-dimensional viscoplastic models reproduce these three types, allowing us to predict the condition of shear band growth with a specific network pattern as a function of the following parameters: normalized shear zone thickness, bulk shear rate and bulk viscosity. This study suggests that complex anastomosing shear-band structures can evolve under simple shear kinematics in the absence of any pure shear component.

The Effect of a Weak Asthenospheric Layer on Surface Kinematics, Subduction Dynamics and Slab Morphology in the Lower Mantle

AbstractOn Earth, the velocity at which subducting plates are consumed at their trenches (termed “subduction rate” herein) is typically 3 times higher than trench migration velocities. The subduction rate is also 5 times higher than estimated lower mantle slab sinking rates. Using simple kinematic analyses, we show that if this present‐day “kinematic state” operated into the past, the subducting lithosphere should have accumulated and folded beneath near‐stationary trenches. These predictions are consistent with seismic tomography, which images localized and widened lower‐mantle slab piles. They are, however, at odds with most dynamic‐subduction models, which predict rapid trench retreat and inclined slabs in the mantle transition zone. We test the hypothesis that a weak asthenospheric layer (WAL), between the lithosphere‐asthenosphere boundary and 220 km depth, compatible with geophysical constraints, can remedy the discrepancies between numerical models and observations. The WAL lubricates the base of the lithosphere, increases the subduction rate while reducing trench retreat. As a consequence, simulations featuring a WAL predict slab accumulation at the mantle transition zone, and thicker, folded slabs in the lower mantle. A WAL viscosity only 2–5 times lower than that of the adjacent mantle is sufficient to shift subduction regimes toward a mode of vertical slab sinking and folding beneath near‐stationary trenches, across a wide range of model parameters, producing surface and slab velocities close to those observed at the present‐day. These findings provide support for the existence of a weak asthenosphere beneath Earth's lithosphere, complementing independent evidence from various geophysical data.

Constraining the Charm-Yukawa coupling at the Large Hadron Collider

We present theoretical results for the sensitivity of charm Yukawa coupling measurements in future high-luminosity LHC runs in three channels: Vector Boson Fusion (VBF), W Higgs-strahlung and Z Higgs-strahlung production of a Higgs boson and its subsequent decay into charm quarks. To reduce the overwhelmingly large backgrounds and to reduce false positives, we apply a set of simple kinematic and jet feature cuts and feed neural network data structures of three types; jet features, jet images and particle level features. To facilitate straightforward comparison with experimental studies [1,2], we express our results in terms of signal strengths [3].

Optimization design and experimental validation of a vortex-based suction cup for a climbing AUV

This paper presents a climbing AUV, which is able to work in both swimming and climbing modes. The key issue in the design of a climbing robot is the choice of a reliable adhesion technique. Due to its great performance as regards payload, motion speed, simple system kinematics and gripping over a wide range of surfaces, a vortex-based suction cup is adopted to provide adhesion effect for the climbing motion of the AUV. Since the vortex-based suction cup is the core component of the vehicle, this paper mainly focuses on the structural and operational optimization of the suction cup by both Computational Fluid Dynamics (CFD) simulations and experimental validation. The proposed CFD simulation method is firstly verified by uncertainty study. The uncertainty analysis results indicate that the proposed simulation model and settings are reliable as reasonable agreements are found when comparing the computed results from varied grid size, iteration number, and time step cases. The total numerical uncertainties of the CFD simulation method for adhesion force and torque prediction are 1.50% and 1.46% of the average simulated values, respectively. In the CFD simulations, we investigate the effects of some key structural and operational parameters on the adhesion performance of the suction cup, including the vane number of impeller, the shape of cup shell, the adhesion gap (distance between cup bottom and wall surface), and the rotation rate of impeller. It can be concluded that more rotation rate of impeller can generate more adhesion force and more torque; smaller adhesion gap can produce more adhesion force but less torque; cup wall with inclined angle can increase the adhesion force and decrease the torque; the adhesion performance of the suction cup is less sensitive to the vane number of the impeller. CFD simulation results provide the basic design guidelines for the development of suction cup prototype. In the experiments, a specially designed testing platform is built up to validate and compare the performance of a set of suction cup prototypes, varied by different impeller and cup shell combinations. We compare the CFD simulation and experiment results of a 10-vane suction cup at a range of rotation rate conditions. The reasons of the discrepancy between CFD simulation and experiment results are mainly due to the open-loop control of the drive motor and the underestimate of the rotation rate in the experiments. The experimental results indicate that the effects of the structural and operational parameters on the generated adhesion performance are very complicated, and the effect of the structural parameters on the adhesion performance is influenced by the operational parameters, while the rotation rate and the adhesion gap play the key roles.

Inchworm Inspired Multimodal Soft Robots With Crawling, Climbing, and Transitioning Locomotion

Although many soft robots, capable of crawling or climbing, have been well developed, integrating multimodal locomotion into a soft robot for transitioning between crawling and climbing still remains elusive. In this work, we present a class of inchworm-inspired multimodal soft crawling-climbing robots (SCCRs) that can achieve crawling, climbing, and transitioning between horizontal and vertical planes. Inspired by the inchworm’s multimodal locomotion, which depends on the “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> ” deformation of the body and controllable friction force of feet, we develop the SCCR by 1) three pneumatic artificial muscles based body designed to produce “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> ” deformation; 2) two negative pressure suckers adopted to generate controllable friction forces. Then a simplified kinematic model is developed to characterize the kinematic features of the SCCRs. Lastly, a control strategy is proposed to synchronously control the “ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> ” deformation and sucker friction forces for multimodal locomotion. The experimental results demonstrate that the SCCR can move at a maximum speed of 21 mm/s (0.11 body length/s) on horizontal planes and 15 mm/s (0.079 body length/s) on vertical walls. Furthermore, the SCCR can work in confined spaces, carry a payload of 500 g (about 15 times the self-weight) on horizontal planes or 20 g on vertical walls, and move in aquatic environments.

A novel kinematics and statics correction algorithm of semi-cylindrical foot end structure for 3-DOF LHDS of legged robots

In this paper, aiming at the problem that the ideal modeling point of the foot end deviates from the actual contact point due to the rolling effect of the semi-cylindrical foot end in leg hydraulics drive system (LHDS), a novel and relatively simple kinematics and statics correction algorithm is proposed. This algorithm can effectively improve the accuracy of LHDS kinematics and statics, and it is still applicable when the body and the contact surface are at different angles. Firstly, this paper deduces the kinematics and statics when the foot end of LHDS is regarded as the point foot, analyzes and calculates the deviation under common working conditions. Secondly, in view of this phenomenon, a kinematics correction algorithm based on virtual DOF and a statics correction algorithm based on translation theorem of forces are proposed respectively. Finally, the proposed algorithm is verified by LHDS performance test platform under various working conditions. The results show that after applying the kinematics correction algorithm, the trajectory deviation reduction rate of the hip joint is over 65%; after applying the statics correction algorithm, the deviation reduction rate of foot end contact force is over 43%. The related research results can be applied to any similar foot end, which has engineering application value.

The Impact of Matrix Rheology on Stress Concentration in Embedded Brittle Clasts

AbstractFrictional failure is the dominant deformation mechanism for rocks in the upper crust while in the middle crust rocks begin to deform viscously. Within this transition, brittle and viscous phases coexist, forming semi‐frictional materials. While semi‐frictional deformation on large scales might play an important role in understanding the transition between earthquakes and slow slip/creep, it can also be observed at smaller scales. Here, we use field observations of the Papoose Flat pluton in eastern California to study deformation of heterogeneous materials during shearing. Clast concentration varies between 2% and 12% by area. Field and microscopic observations show that the matrix deforms viscously, while the clasts fail in a brittle manner. We systematically document clast concentration and spacing with respect to clast fracturing and observe increasing frictional failure of clasts with increasing clast concentration. To test which matrix viscosities impose enough stresses on the clasts to lead to frictional deformation, we complement field observations with 2D numerical models. Maps with 7% by area randomly placed circular clasts are created and deformed under simple shear kinematic conditions. We test different matrix viscosities, from constant low and high viscosity (1017 and 1019 Pa.s, respectively), to dislocation creep for granite. Clasts in the vicinity of other clasts are affected by stresses around their neighbors. This effect decreases with increasing clast distance. Our field observations and numerical results suggest that the viscous phase can impose significant stresses onto the brittle phase, causing failure even at very low clast concentrations and in the absence of clast‐clast interactions.

Observation of significant Doppler shift in deuterium-deuterium neutron energy caused by neutral beam injection in the large helical device

The compact neutron emission spectrometer (CNES) having a tangential sightline was installed to observe a significant Doppler shift of the neutron energy due to the high-energy tangential neutral beam (NB) injections in the Large Helical Device (LHD) for understanding of the energy distribution of fast-ion. The CNES is based on a 1-inch diameter and 1-inch height EJ301 liquid scintillator coupled with a conventional 1-inch photomultiplier tube. The histogram of the integrated pulse signal (Qtotal) during different NBs heating phases measured by the CNES shows that the edge of Qtotal changes depending on NB directions. Using the simple derivative unfolding technique, the neutron energy spectra were unfolded from the measured Qtotal histogram. Peaks of the neutron energy shift to 2.0 MeV, 2.42 MeV, and 3.0 MeV according to the injection direction of NBs. The obtained neutron energy is almost consistent with the virgin deuterium-deuterium neutron energy evaluated by the simple two-body kinematics considering the sightline of CNES, NB injection angle, and NB injection energy.

Approximate field measures for ionic polymer-metal composite materials and a simplified order-of-magnitude actuator model

As the field of soft robotics grows and new applications for this technology are discovered, the use of simplified models for the soft actuators found in these devices will be critical. In this study we explore arguments based on the magnitude of field gradients that arise in the ionic polymer-metal composite (IPMC) under large applied voltages and their use for approximating measures of the fields inside the polymer. Using the order-of-magnitude based arguments provides exceptional results for quantifying the field measures of maximum ionic concentration and electric potential within the bulk of the polymer. These measures are leveraged to reconstruct the fields themselves in such a way that the internal bending moments generated inside the actuator may be approximated. With the internal moments, a simplified kinematic model may be used to formulate the steady-state actuator response of the IPMC. This actuator model shows a great deal of accuracy as compared to a full multiphysics model, and we discuss the prospects for future development of this model to account for dynamic actuation.

Reduced kinematic multiscale model for tissue engineering electrospun scaffolds

To this day, there is still a need for a direct relationship between the microscopic material properties and network microstructure configuration with the macroscopic mechanical response in order to optimize the design loops of biomimetic electrospun grafts. Multiscale mechanical modeling arises as a useful alternative, which allows to represent the individual nanofibers mechanical response and how the interaction between fibers results in the final macroscopic behavior. In this work, a micromechanical model that accounts for fiber interaction, progressive straightening (i.e. progressive recruitment) and reorientation is presented. An RVE is generated by means of a virtual deposition algorithm that mimics the electrospinning process itself, thus obtaining geometries that resemble the observed electrospun microstructure. These geometries were then validated by comparison with analysis of SEM images, taking special interest in the diameter, orientation and tortuosity distributions. Then, an elastic–plastic constitutive law for the nanofibers is implemented along with a simplified kinematic description that results in a significant reduction of the number of Degrees of Freedom of the discretized mechanical equilibrium problem. Finally, the micromechanical model is validated against uniaxial tensile tests of electrospun PLLA bone-shaped samples, reproducing the experimentally observed behavior while employing realistic geometric and constitutive parameters to characterize the fibers.

Kinematic modelling and design of a tendon actuated soft manipulator

Soft robots have garnered significant attention in recent years due to their ability to perform complex and organic motions, while being simple in structure. In particular, soft manipulators have enabled safer collaboration with humans and larger margins of error in applications such as grasping. Unfortunately, the lack of conventional mechanical joints and a large variety of designs necessitate the development of specialized kinematic models. In this paper, we present a novel mathematical framework for kinematic modelling of multi-section soft manipulators actuated by four pulling tendons per section embedded in an elastic, deformable material such as silicone. We use piecewise constant curvature approximation to capture the shape of the manipulator and derive an analytical forward kinematic mapping. Further, we accompany this model with a simple and effective numerical inverse kinematics approach. Finally, we develop a hardware prototype and perform a qualitative validation of both the forward and inverse kinematics. Our experiments indicate that this kinematic model is a feasible for the proposed robot design.

Improved Λp Elastic Scattering Cross Sections between 0.9 and 2.0 GeV/c as a Main Ingredient of the Neutron Star Equation of State.

Strange matter is believed to exist in the cores of neutron stars based on simple kinematics. If this is true, then hyperon-nucleon interactions will play a significant part in the neutron star equation of state. Yet, compared to other elastic scattering processes, there is very little data on Λ-N scattering. This experiment utilized the CEBAF Large Acceptance Spectrometer (CLAS) detector to study the Λp→Λp elastic scattering cross section in the incident Λ momentum range 0.9-2.0 GeV/c. These are the first data on this reaction since the 1970s. The new cross sections have significantly better accuracy and precision than the existing world data, and the techniques developed here can also be used in future experiments.

Neutron energy spectrum measurement using CLYC7-based compact neutron emission spectrometer in the Large Helical Device

Tangential compact neutron emission spectrometer (CNES) based on the Cs2LiYCl6:Ce with 7Li-enrichment (CLYC7) scintillator is newly installed in the Large Helical Device (LHD). Measurement of neutron energy spectrum was performed using CNES in tangential neutral beam (NB) heated deuterium plasma discharges. The Doppler shift of neutron energy according to the direction of tangential NB injection has been obtained. When the fast ions moving away from the CNES, lower shifted neutron energy is obtained, whereas the upper shifted neutron energy is obtained when the fast ions moving toward the CNES. The obtained neutron energy is almost consistent with the virgin deuterium-deuterium neutron energy evaluated by the simple two-body kinematic calculation.

A suggested simple design and inverse kinematics for a multi-degrees-of-freedom robot arm

In this paper, architecture for the robot arm and a mathematical model was suggested to simplify the inverse kinematics that describes the movement and orientation of this end-effector. Although this design contains eight degrees of freedom, all the angular displacements and velocities could be formulated as functions of the three coordinates of the end-effecter starting point. These three values are enough to set the end-effector at the desired point in the workspace, and with the desired orientation. The tip of the end-effecter could be equipped with a grabber or any attached manufacturing tool. To check the reliability of the introduced mathematical model, a simple model for the arm was built using aluminum beams. The joints are actuated by stepper motors that are controlled by a microprocessor. The model executed the positioning and orientation of the end-effector with an accuracy of about 93% of any traveled distance. This lack of accuracy may be accounted for by the low resolutions of the used motors. In this study, the positioning and orientation were only considered, and future work is required for the analysis of loads and power capacities

Derivation of “n = 2j-3” statically determinant spatial truss formula by modified Chebychev–Grübler–Kutzbach criterion

Truss is a structural twin of kinematic mechanism. A truss is specially used to support the roof, rocket launch structures, telecom towers, and bridges as structural entities. They have a great tendency to bear heavy load and withstand impact loading conditions. In this paper, spatial truss formula “n = 2j-3” is derived using a simple kinematic approach and Grübler criterion. A primitive hit and trial method based on stability and mobility is used to separate stable trusses followed by mathematical analysis. In addition, a modification of Grübler criterion is introduced in this work to especially understand and derive the truss equation. Connectivity constants are incorporated further evolve the understanding of stability and mobility in 2D structures. Finally, the complex Grübler criterion is reduced to the simple truss equation.

Pose2Sim: An End-to-End Workflow for 3D Markerless Sports Kinematics-Part 1: Robustness.

Being able to capture relevant information about elite athletes’ movement “in the wild” is challenging, especially because reference marker-based approaches hinder natural movement and are highly sensitive to environmental conditions. We propose Pose2Sim, a markerless kinematics workflow that uses OpenPose 2D pose detections from multiple views as inputs, identifies the person of interest, robustly triangulates joint coordinates from calibrated cameras, and feeds those to a 3D inverse kinematic full-body OpenSim model in order to compute biomechanically congruent joint angles. We assessed the robustness of this workflow when facing simulated challenging conditions: (Im) degrades image quality (11-pixel Gaussian blur and 0.5 gamma compression); (4c) uses few cameras (4 vs. 8); and (Cal) introduces calibration errors (1 cm vs. perfect calibration). Three physical activities were investigated: walking, running, and cycling. When averaged over all joint angles, stride-to-stride standard deviations lay between 1.7° and 3.2° for all conditions and tasks, and mean absolute errors (compared to the reference condition—Ref) ranged between 0.35° and 1.6°. For walking, errors in the sagittal plane were: 1.5°, 0.90°, 0.19° for (Im), (4c), and (Cal), respectively. In conclusion, Pose2Sim provides a simple and robust markerless kinematics analysis from a network of calibrated cameras.

Semi-Automated Procedure to Estimate Nonlinear Kinematic Hardening Model to Simulate the Nonlinear Dynamic Properties of Soil and Rock

The strain-dependent nonlinear properties of ground materials, such as shear modulus degradation (G/Gmax) and damping, are of significant importance in seismic-related analyses. However, the ABAQUS program lacks a comprehensive procedure to estimate parameters for a built-in model. In this study, a nonlinear kinematic hardening (NKH) model with three back-stress values was used, which allows better fitting to the backbone curves compared to the simplified nonlinear kinematic hardening (SNKH) model previously proposed. Instead of modeling in ABAQUS, a semi-automated procedure was implemented in MATLAB, which can predict shear stress–shear strain hysteretic loops, to find the fitting parameters to the target G/Gmax and/or damping curves. The procedure was applied for three soil and two rock samples, and the results indicate a good match between model and target backbone curves, which proves the application of the procedure and the NKH model in simulating the nonlinear properties of ground materials.

Kinematics analysis and workspace optimization for a 4-DOF 3T1R parallel manipulator

A four degrees-of-freedom (DOF) Parallel Manipulator (PM) with a 4PPa-2PaR configuration has been proposed to generate 3-DOF Translational and 1-DOF Rotational (3T1R) motions in our early work. It has the advantages of symmetric geometry, simple kinematics and infinite extension of translational workspace along its linear guide direction. However, its V-type assembly mode results in a long distance between its moving platform and the base, which makes its stiffness and accuracy lower. Besides, its the other two translational workspaces are limited due to its kinematic singularities. To overcome such limitations, the PM is modified by utilizing its M-type assembly mode and placing an offset angle to the last parallelogram mechanism. To simplify the displacement analysis, a geometrical projection method is employed, while a closed-loop vector approach is used for its instantaneous kinematic analysis. Both singularity and workspace issues are investigated. An optimization algorithm based on Genetic Algorithm is proposed to maximize the reachable workspace. The optimization result indicates that the workspace is significantly increased. A prototype of the M-type PM is fabricated to validate the effectiveness of the modified design.

Trajectory tracking control of quadcopters under tunnel effects

There are many potential applications to utilise aerial robots in hazardous tunnel-like environments. For example, aiding human operators with inspections of small railway culverts or mineral mappings of mining tunnels. Nevertheless, such confined environments pose many challenges for quadcopters to navigate through. Suspended dust particles, poor lighting conditions and featureless/excessive features in the surroundings make localisation difficult. Furthermore, the fluid interactions between the rotors’ downwash and the surfaces of the surroundings create aerodynamic disturbances, which threaten the quadcopter’s stability and increase its risk of collision in the restricted confined space, not to mention the longitudinal wind gusts. This paper presents our findings on the characteristics of these aerodynamic disturbances, the Tunnel Effects for quadcopters, in a 1.5m(W) x 1.5m(H) square cross section tunnel through a series of experiments. A semi-autonomous system is proposed with self-stabilisation in the vertical and lateral axes while a pilot provides commands in heading and the longitudinal direction of the tunnel for performing required tasks such as tunnel wall inspections. We propose a cross-sectional localisation scheme using Hough Scan Matching with a simple kinematic Kalman filter for providing reliable vertical and lateral position information. An integral backstepping (IBS) controller is designed and implemented to enable quadcopters to robustly fly in tunnel-like confined environments. The proposed system is tested in simulated tunnel environments and a real railway tunnel with various reference trajectories, and the IBS controller has shown superior tracking performance in comparison with a PID controller despite of the existence of the Tunnel Effects.