Center Of Motion Research Articles

Design of a Semi-Active Prosthetic Knee for Transfemoral Amputees: Gait Symmetry Research by Simulation

The key technology of the prosthetic knee is to simulate the torque and angle of the biological knee. In this work, we proposed a novel prosthetic knee operated in semi-active mode. The structure with ball-screw driven by the motor and the passive hydraulic damping cylinder was presented. A four-bar linkage was adapted to track the instantaneous center motion of human knee. The mathematical models of hydraulic cylinder damping and active torque were established to simulate the knee torque and angle. The results show that the knee torque symmetry index is smaller than 10% in the whole gait. The knee angle symmetry index value is 34.7% in stance phase and 11.5% in swing phase. The angle in swing phase is closer to the intact knee. The semi-active prosthetic knee could provide similar torque and angle of the biological knee in the simulation. It has shown good potential in improving the gait symmetry of the transfemoral amputee.

Optimal tool orientation in 3 + 2-axis machining considering machine kinematics

In 5-axis machining, the initial orientation and position of the part in the fixture on the machine table are chosen to avoid collisions and to ensure that axes ranges are respected. However, kinematics of the machine is rarely considered for workpiece setup optimization although it affects the tool path execution and machining time. Indeed, for complex surfaces, actual feedrate is often lower than the programmed one and can present strong slowdowns, which are critical for the tool cutting conditions and therefore the part quality. This article investigates the use of kinematic manipulability criteria to determine the best orientation of the workpiece setup to maximize the actual feedrate and reduce machining time. The modelling of maximum velocity, acceleration, and jerk of each axis by means of polytopes makes it possible to take advantage of the whole kinematic space of the machine more intuitively. Simulations and experiments are carried out in 3 + 2-axis machining on test parts with a ball-end tool. For stretched surfaces, while the tool centre motion is given by the machining strategy, the tool axis orientation is optimized jointly with the workpiece setup. Experiments confirm that actual feedrate raises faster to better respect the programmed cutting conditions along each path. As feedrate is also higher, machining time is reduced significantly.

Giant linear magnetoresistance in half-metallic Sr2CrMoO6 thin films

Linear magnetoresistance (LMR) is a special case of a magnetic-field induced resistivity response, which has been reported in highly disordered semiconductor systems and in topological materials. In this work, we observe LMR effect in half-metallic perovskite Sr2CrMoO6 thin films, of which the maximum MR value exceeds +1600% at 2 K and 14 T. It is an unusual behavior in ferrimagnetic double perovskite material like Sr2CrMoO6, which are known for intrinsic tunneling-type negative magnetoresistance. In the thin films, the high carriers’ density (~1022 cm−3) and ultrahigh mobility (~104 cm2 V−1 s−1) provide a low-resistivity (~10 nΩ·cm) platform for spin-polarized current. Our DFT calculations and magnetic measurements further support the half-metal band structure. The LMR effect in Sr2CrMoO6 could possibly originate from transport behavior that is governed by the guiding center motion of cyclotron orbitals, where the magnetic domain structure possibly provides disordered potential. The ultrahigh mobility and LMR in this system could broaden the applications of perovskites, and introduce more research on metallic oxide ferri-/ferro-magnetic materials.

Control Strategy for Direct Teaching of Non-Mechanical Remote Center Motion of Surgical Assistant Robot with Force/Torque Sensor

This paper presents a control strategy that secures both precision and manipulation sensitivity of remote center motion with direct teaching for a surgical assistant robot. Remote center motion is an essential function of conventional laparoscopic surgery, and the most intuitive way a surgeon manipulates a robot is through direct teaching. The surgical assistant robot must maintain the position of the insertion port in three-dimensional space during the four-degree-of-freedom motions such as pan, tilt, spin, and forward/backward. In addition, the robot should move smoothly when controlling it with the hands during the surgery. In this study, a six-degree-of-freedom collaborative robot performs the cone-shaped trajectory with pan and tilt motion of an end-effector keeping the position of the remote center. Instead of the bulky mechanically constrained remote center motion mechanism, a conventional collaborative robot is used to mimic the wrist movement of a scrub nurse. A force/torque sensor that is attached between the robot and end-effector estimates the surgeon’s intention. A direct teaching control strategy based on position control is applied to guarantee precise remote center position maintenance performance. A motion generation algorithm is designed to generate motion by utilizing a force/torque sensor value. The parameters of the motion generation algorithm are optimized so that the robot can be operated with uniform sensitivity in all directions. The precision of remote center motion and the torque required for direct teaching are analyzed through pan and tilt motion experiments.

Excitation of a Moving Oscillator

We calculate transition amplitudes and probabilities between the coherent and Fock states of a quantum harmonic oscillator with a moving center for an arbitrary law of motion. These quantities are determined by the Fourier transform of the moving center acceleration. In the case of a constant acceleration, the probabilities oscillate with the oscillator frequency, so that no excitation occurs after every period. Examples of oscillating and rotating motion of the harmonic trap center are considered too. Estimations show that the effect of excitation of vibration states due to the motion of the harmonic trap center can be observed in available atomic traps.

Trajectory control of planar closed chain fully compliant mechanism

This study presents the design, analysis, dynamical modeling and control of a planar, flexure based closed chain compliant mechanism. Mechanism is designed as a single piece and comprised of rigid-flexure links connected in series. Base links of the mechanism can be actuated through two servo motors and translated along the horizontal direction using two step motors. Two servo motors are mounted on a rail-cart system and carts are equipped with belt drive to enable horizontal displacement. Dynamical model of the mechanism is derived by adapting pseudo rigid body modeling method, vector closure loop equations, Euler’s laws of motion and geometric constraints. Mechanism is 3D printed using thermoplastic polyurethane filament (TPU), motion of the mechanism is video recorded and position of the tip along with the motion of center of each links are captured using image processing. Mathematical model is simulated in Matlab Simulink and validated with the experimental data. A reference trajectory drawn within the workspace of the mechanism on iPad is successfully traced in real time using the simplified model, mirror imaging program and inverse kinematics. The proposed mechanism can be utilized as a haptic device and a compliant manipulator in industrial applications where high precision and larger workspace is desired.

A Novel Load Cell-Supported Research Platform to Measure Vertical and Horizontal Motion of a Horse's Centre of Mass During Trailer Transport

During transport, horses are subjected to acceleration in three dimensions, rapid braking, turning, noise, and other stressors. The animal's ability to make postural corrections may be insufficient to prevent injury or distress, and so knowledge of the compensatory motion patterns of the horse in the trailer is a necessary precondition for smart design of transport systems. A custom two-horse trailer was built for this project. It had a horse compartment 1.85 m wide by 3.95 m long, with adjustable bulkheads and a centre divider separating the horses. The floor was instrumented with 24 shearbeam load cells to measure the vertical load imposed by each horse and its horizontal motion. Two horses were driven on a 56 km trip on both rural and urban roads. Load data were collected at 100 Hz for the 58-minute trip and were filtered with a cut-off frequency of 5 Hz using a Butterworth low-pass filter and then vertical acceleration computed. A pivot table counted sign reversals in the vertical acceleration signal, and vertical displacement was calculated using the fundamental frequency of the resulting acceleration data. Total vertical motion was calculated by making the negative displacements absolute and summing these with the positive displacements, and vertical work done was calculated by multiplying the force by the displacement measures. Horizontal motion was calculated by averaging the transverse and cranio-caudal position of the centre of pressure every second and adding the resultant displacements. Absolute vertical displacement of the two horses was 69.55 m and 97.56 m. In addition to the work done by standing, vertical work done in response to vibration was 322.4 kJ and 443.2 kJ. Horizontal excursion was 227.1 m and 243.0 m. This is a first effort to quantify the additional workload imposed on animals during transport, which will aid in the design of smart transport vehicles that will minimize the stress to horses.

Domain wall dynamics in the spinor Bose-Einstein condensates

A dynamical theory is presented for the domain wall in the spinor Bose-Einstein condensate of “effective” one dimension. The formulation is based on the time-dependent Landau-Ginzburg (LG) theory written in terms of the spinor order parameter. The procedure is carried out in such a way that an adiabatic change of the collective coordinates which are given by the kink position as well as the phase function built in the spinor, is adapted to the canonical term (alias geometric phase) in the LG Lagrangian. Two problems are discussed: The first one is to explore the translational motion of the kink center in the presence of the pinning potential, which results in the quantum potential problem. The other one concerns the steering of the domain wall by modulating the externally driven magnetic field assisted with dissipation. The present attempt would shed light on the spinor Bose-Einstein condensates from a novel viewpoint.

Analysis of the beats of separation sieve pans

To ensure high productivity of grain production reliable operation of grain cleaning equipment is required. The process of cleaning seed material is connected to significant vibration loads some of which have an impact on the separation process and the operational reliability of the machine components. To combat harmful vibrations a theoretical analysis of the beats occurring during the sieve separation of grain was made. The law of motion of the mass center of the sieve pan is derived as a function from time over a period of oscillating. The analytical solution of the obtained equation allows determining the horizontal and vertical displacements of the mass center at every moment of time. Based on this motion, accelerations and related inertial forces are determined. These forces take on sufficiently large values, which lead to beats of the indicated separation devices. To determine the forces leading to these beats, using the d’Alembert’s principle, equilibrium equations are compiled, the solution of which allows determining the total horizontal force and reaction force in the suspension. The equations of equilibrium include the forces of tension on bending of the suspension rods. It has been established that a rational choice of the geometric characteristics of these suspensions can significantly reduce the forces acting on the drive of the sieve pan and, as a result, on the horizontal and vertical runouts.

Analytical calculation of the orbital spectrum of the guiding centre motion in axisymmetric magnetic fields

Charged particle motion in axisymmetric toroidal magnetic fields is analysed within the context of the canonical Hamiltonian guiding centre theory. A canonical transformation to variables measuring the drift orbit deviation from a magnetic field line is introduced and an analytical transformation to action-angle variables is obtained, under a zero drift width approximation. The latter is used to provide compact formulas for the orbital spectrum of the drift motion, namely the bounce/transit frequencies as well as the bounce/transit averaged toroidal precession and gyration frequencies. These formulas are shown to have a remarkable agreement with numerically calculated full drift width frequencies and significant differences from standard analytical formulas based on a pendulum-like Hamiltonian description. The analytical knowledge of the orbital spectrum is crucial for the formulation of particle resonance conditions with symmetry-breaking perturbations and the study of the resulting particle, energy and momentum transport.

Dynamics of bright soliton in a spin–orbit coupled spin-1 Bose–Einstein condensate* *Project supported by the National Natural Science Foundation of China (Grant No. 11775253) and the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (Grant No. ZDBS-LY-7016).

We have investigated the dynamics of bright solitons in a spin–orbit coupled spin-1 Bose–Einstein condensate analytically and numerically. By using the hyperbolic sine function as the trial function to describe a plane wave bright soliton with a single finite momentum, we have derived the motion equations of soliton’s spin and center of mass, and obtained its exact analytical solutions. Our results show that the spin–orbit coupling couples the soliton’s spin with its center-of-mass motion, the spin oscillations induced by the exchange of atoms between components result in the periodical oscillation of center-of-mass, and the motion of center of mass of soliton can be viewed as a superposition of periodical and linear motions. Our analytical results have also been confirmed by the direct numerical simulations of Gross–Pitaevskii equations.

Hydraulic system based energy harvesting method from human walking induced backpack load motion

Considerable energy can be harvested from human motions, and energy generated by human walking induced backpack load motion is capable of powering mechatronic systems to reduce energy consumption effectively. This paper mainly deals with the design and performance analysis of the energy recovery system with backpack load based on fluid power transmission technique. The kinematics modeling of the displacement of the gravity center of human body during walking was conducted to describe the generation of mechanical energy within the human gait cycle. Combined with the experimental measurement of gait characteristics, the displacement of cyclical motion of the gravity center was obtained. The energy recovery mechanism was designed making use of the vibration excitation of the backpack load motion to directly convert the human walking induced mechanical energy into hydraulic energy and achieve energy storage with accumulator instantaneously. Through numerical simulation and experimental verification, the energy harvesting results under different walking speeds and backpack loads are analyzed. It is shown that the average output power of the recovery mechanism goes over 6 W at a walking speed of 1.53 m/s with a backpack load of 15 kg, and the captured energy can be increased with the higher speed and larger load. The characteristics of accumulator is critical to achieve continuous energy conversion with increase of walking time. The comparison indicated that the output power and power density of the system proposed in this paper is superior to those based on electric generation, which provided potential solution for energy saving of the hydraulic exoskeleton.

Вплив внутрішньої динаміки когерентних вихрових структур, що взаємодіють між собою, на генероване звукове поле

The article is dedicated to the glowing memory of the talented Ukrainian scientist-mechanic, professor, doctor of physical and mathematical sciences Vyacheslav Vladimirovich Meleshko. The sound fields of several coherent vortex structures interacting with each other were calculated using the moment model (MZS-model) of the first and second orders. In the first-order MZS-model, vortices are described by point vortices, in the second-order MZS-model--by Kirchhoff vortices. Sound fields as a result of vortex interaction are calculated using the Lighthill's acoustic analogy under Powell's formulation. The spectrum of the sound field in the description of coherent vortices by point vortices is characterized by a single frequency band, which reflects the motion of the vortex centers of vortices (large-scale vortex movements). Taking into account the inner vortex dynamics leads to the expansion of spectrum and level increasing of calculated sound: the lower band describes the motion of the vorticity centers of spots, the higher band describes the internal dynamics of the vorticity. It is shown that large-scale vortex movements can be modeled by point vortices, when the sound spectrum of distributed vortices is clearly divided into bands and the width of the lower frequency band is close to the width of the sound spectrum from point vortices. The presence of an upper frequency band in the sound field of interacting vortex spots does not allow us to describe the distributed vortices as point vortices when constructing a sound source, since such a simplification leads to a significant underestimation of the level of the calculated sound field.

Research and Implementation of the Sports Analysis System Based on 3D Image Technology

On the basis of existing research, this paper analyzes the algorithms and technologies of 3D image‐based sports models in depth and proposes a fusion depth map in view of some of the shortcomings of the current hot spot sports model methods based on 3D images. We use the 3D space to collect the depth image, remove the background from the depth map, recover the 3D motion model from it, and then build the 3D model database. In this paper, based on the characteristics of continuity in space and smoothness in time of a rigid body moving target, a reasonable rigid body target motion hypothesis is proposed, and a three‐dimensional motion model of a rigid body target based on the center of rotation of the moving target and corresponding motion is designed to solve the equation with parameters. In the case of unknown motion law, shape, structure, and size of the moving target, this algorithm can achieve accurate measurement of the three‐dimensional rigid body motion target’s self‐rotation center and related motion parameters. In the process of motion parameter calculation, the least square algorithm is used to process the feature point data, thereby reducing the influence of noise interference on the motion detection result and correctly completing the motion detection task. The paper gives the measurement uncertainty of the stereo vision motion measurement system through simulated and real experiments. We extract the human body motion trajectory according to the depth map and establish a motion trajectory database. For using the recognition algorithm of the sports model based on the 3D image, we input a set of depth map action sequences. After the above process, the 3D motion model is obtained and matched with the model in the 3D motion model database, and the sequence with the smallest distance is calculated. The corresponding motion trajectory is taken as the result of motion capture, and the efficiency of this system is verified through experiments.

Optimization of Operating Modes of a Train by the Haul Distance

The world community carries out large-scale research into reducing the consumption of electric power, while keeping living needs at the same level. Transport sector consumes a vast amount of electric energy, particularly, electric-driven rolling stock of railways. The paper deals with finding the trajectory of train motion, which is going to be the most energy efficient to run along. There is also presented analysis of specific power consumption for traction of trains of the largest Railway network in Russia. Criteria for optimization of freight trains handling with electric locomotives by the means of differential equation of motion of center of mass of a train. There is proposed a mathematical model for movement of a train and a theorem on dividing motion of the system into fast and slow components. Restrictions for state variables of a train and objectives for optimization of operation mode on the given locomotive run are formulated. The paper describes the solution of optimization with the use of innovative software for mathematical simulation through directed graphs (or digraphs) of movement of a freight train with an electric locomotive on the haul. A new Lagrange coefficient is proposed, which is the cost of time in units of specific power consumption. There are determined parameters that should be considered when developing a technical passport for a railway section.

Transport model of active particles in a tidal wetland flow

A concentration transport model has been formulated to characterize the transport of a mass of self-propelling active particles in an unsteady wetland flow at the phase-averaged scale. The vertical distribution and motion of mass center are rigorously derived for an active-particle cloud in the tidal wetland flow by use of the concentration moment method, while the longitudinal dispersivity is calculated by means of finite difference method. It is found that the distribution of total quantity of active particles in each streamline in the tidal wetland flow is identical to that in the fully developed wetland flow. The velocity and longitudinal dispersivity of mass center of the active-particle cloud eventually reach a stable oscillatory status for the case of tidal wetland flow rather than an asymptotic constant velocity which occurs in the steady wetland flow. The effects of dimensionless parameters on the amplitude, phase and period of the velocity of mass center and longitudinal dispersivity are discussed in detail for the active-particle cloud in the tidal wetland flow.

Dynamics of a pair of point vortices and a foil with parametric excitation in an ideal fluid

In this paper we obtain equations of motion for a vortex pair and a circular foil with parametric excitation due to the periodic motion of a material point. Undoubtedly, such problems are, on the one hand, model problems and cannot be used for an exact quantitative description of real trajectories of the system. On the other hand, in many cases such 2D models provide a sufficiently accurate qualitative picture of the dynamics and, due to their simplicity, an estimate of the influence of different parameters. We describe relative equilibria that generalize Föppl solutions and collinear configurations when the material point does not move. We show that a stochastic layer forms in the neighborhood of relative equilibria in the case of periodic motion of the foil's center of mass.

힘/토크 센서를 이용한 수술보조로봇의 원격중심운동 직접교시 알고리즘 연구

힘/토크 센서를 이용한 수술보조로봇의 원격중심운동 직접교시 알고리즘 연구

Specifics of the Distribution of Orbits of Long-Period Comets in the Inner Part of the Oort Cloud

Abstract—We investigate statistical patterns in the distribution of the orbits of long-period comets that belong to the inner region of the Oort cloud (with aphelion distances, Q, lying in the 50–2000 AU interval). We show that the distribution of aphelia is not random and such patterns can be due, in particular, to the presence of hypothetical massive bodies in the region considered. We varied the orbital parameters of such bodies to obtain two orbits such that each of them has the aphelia of 40 comets located within the 20-degree neighborhood of the orbit. This number is statistically significant. The orbits have the following parameters in the ecliptic coordinate system: P1: ΩP = 297°, iP = 24°, ωP = 322°, eP = 0.6, aP = 510 AU; P2: ΩP =92°, iP = 80°, ωP =327°, eP = 0.3, aP =1000 AU. For the adopted masses of these bodies we determined the minimum distances between their orbits and the orbits of the comets and estimated the number of aphelia located within the spheres of influence of these bodies. We found that the greatest number of aphelia are located near orbit P1. However, their number is insufficient to conclude that massive bodies actually move in the inferred orbits. It is remarkable that the planes of orbits P1 and P2 in the Galactic coordinate system have the same inclinations (40°) and longitudes of their ascending nodes are equal to 10° and 170°, i.e., the orbital planes are almost symmetric with respect to the direction toward the Galactic center. The concentration of orbital aphelia of the comets considered found in this study can therefore be due to the attraction from the Galactic center and/or complex motion of the Solar system.

Non-coplanar interplanetary flight simulation considering motion relative to the center of mass peculiarities of solar sail spacecraft

The paper is devoted to the non-coplanar interplanetary Earth–Venus flight of a spacecraft equipped with a non-perfectly reflecting solar sail, the magnitude and direction of acceleration from which is calculated taking into account specular and diffuse reflections, absorption and transmission of photons by the surface of the solar sail. The goal of the heliocentric motion is to transfer the solar sail spacecraft into the Hill sphere of Venus with zero hyperbolic excess of speed. A feature of the paper is the study of the motion of a non-perfectly reflecting solar sail spacecraft taking into account the motion relative to the center of mass. The problem is divided into three stages. At the first stage, a nominal program for controlling the motion of the spacecraft center of mass is formed. At the second stage, sufficient angular velocities are determined to ensure the obtained nominal control program and the parameters of the spacecraft controls – thin-film controls located along the perimeter of the solar sail – are calculated. The operating principle of the thin-film controls is quite simple. When the voltage applied to the thin-film controls changes, they become transparent or opaque, there is a difference in the normal components of the light pressure forces, which provides a control torque for changing the orientation of the spacecraft in space. At the third stage, the joint motion of the center of mass and relative to the center of mass of the spacecraft is simulated to demonstrate the feasibility of the obtained control program. As a result, a comparison is made of non-coplanar interplanetary Earth–Venus flights with and without thin-film control elements.