Motion Of System Research Articles

Diffusion induced flow on a wedge-shaped obstacle

In this paper the problem of evolution of diffusion induced flow on a wedge-shaped obstacle is analyzed numerically. The governing set of fundamental equations is solved using original solvers from the open source OpenFOAM package on supercomputer facilities. Due to breaking of naturally existing diffusion flux of a stratifying agent by the impermeable surface of the wedge a complex multi-level vortex system of compensatory fluid motions is formed around the obstacle. Sharp edges of the obstacle generate extended high-gradient horizontal interfaces which are clearly observed in laboratory experiments by high-resolution Schlieren visualization. Formation of an intensive pressure depression zone in front of the leading vertex of the wedge is responsible for generation of propulsive force resulting in a self-displacement of the obstacle along the neutral buoyancy horizon in a stably stratified environment. The size of the pressure deficiency area near the sharp vertex of a concave wedge is about twice that for a convex one. This demonstrates a more intensive propulsion mechanism in case of the concave wedge and, accordingly, a higher velocity of its self-movement in a continuously stratified medium.

An MEMS-based multiple electro-rheological bending actuator system with an alternating pressure source

This paper presents a novel MEMS-based electro-rheological (ER) bending actuator system with an alternating pressure source for micro-scale applications with multiple microactuators. The ER bending actuator system is based on rectification of alternating flows by synchronized control valves using a liquid crystal as a working fluid. It enables the number and size of supply and return pipes to be reduced. In addition, the working principle of the alternating pressure system makes all critical hydraulic components such as the pump, valves and hydraulic actuators suitable for MEMS fabrication. In this paper, the bending parts featuring high-aspect-ratio and three-dimensional structures were realized by a newly developed PDMS micromolding process which was achieved by a separation process using poly (vinyl alcohol) (PVA) sacrificial layers dissolved by water ultrasonication with proper external forces. Control valves called ER microvalves were fabricated by standard silicon micromachining and their characteristics were investigated. The fabricated 1.6-mm long ER bending actuator demonstrated bi-directional motions that achieved a displacement of 1.1mm (radius of curvature of 1.2mm) and a rise time of 1.1s. In addition, the characteristics of the tip displacements vs. applied voltages are also presented. The experimental results showed that this system is promising for control systems of high power, high-speed and miniature motion with large strokes.

Probing the Role of Mobility in the Collective Motion of Nonequilibrium Systems.

By systematically varying the mobility of self-propelled particles in a 2D lattice, we experimentally study the influence of particle mobility on system's collective motion. Our system is intrinsically nonequilibrium due to the lack of energy equipartition. By constructing the covariance matrix of spatial fluctuations and solving for its eigenmodes, we obtain the collective motions of the system with various magnitudes. Interestingly, our structurally ordered nonequilibrium system exhibits properties almost identical to disordered glassy systems under thermal equilibrium: the modes with large overall motions are spatially correlated and quasilocalized while the modes with small collective motions are highly localized, resembling the low- and high-frequency modes in glass. More surprisingly, a peak similar to the boson peak forms in our nonequilibrium system as the number of mobile particles increases, revealing the possible origin of the boson peak from a dynamic aspect. We further illustrate that the spatially correlated large-movement modes can be produced by the cooperation of highly active particles above a threshold fraction, while the localized small-movement modes can be created by adding individual inactive particles. Our study clarifies the role of mobility in collective motions, and further suggests a promising possibility of extending the powerful mode analysis approach to nonequilibrium systems.

Development of automatic control system of underwater complex branch with flexible connections

Synthesis of automatic control systems (ACS) of spatial motion of underwater systems with flexible connections (USFC) forms the actual scientific problem. Own nonlinearity remotely operated underwater vehicle (ROV) enhanced nonlinearity flexible connections that make up USFC. Synthesis of ACS and USFC link forms the basis for automatic control of both onelink and multilink USFC. The method of the formalization of USFC structure is in the form of a graph model. It is represented on the basis of defined-controlled units of USFC. The method of inverse dynamics is synthesized from the regulators spatial movement of TPA and cable winches to control the length of the flexible part of the issued bonds. A BAC USFC link, which includes TPA, a cable winch and synthesized regulators, is the basis for the automation of spatial movement of onelink and multilink USFC. Computer simulation work of NAO investigates USFC link. The result is quite satisfactory for the automatic management of objects of such complexity.

Comparison of the XPM and UCAC4 catalogs

The systematic differences between the stellar positions and proper motions of the XPM and UCAC4 catalogs have been obtained in the form of decompositions into vector spherical harmonics by taking into account the magnitude equation. The systematic components have been extracted with a probability of at least 0.98 by dividing 41 316 676 stars into groups corresponding to 12 J magnitude bins with a width of 0.5m for mean values from 10m.25 to 15m.75. A study of the systematic differences between the equatorial coordinates suggests that the range of systematic differences between the XPM and UCAC4 positions exceeds the corresponding range of differences between PPMXL and UCAC4 by a factor of 5, especially for bright stars in the range being investigated. Analysis of the orientation of the XPM and UCAC4 reference frames has shown that their mutual rotation is 2–4 mas around the X axis and 7–10 mas around the Z axis. These angles depend on the magnitude of stars. Since two systems of proper motions are given in the XPM catalog, XPMx and XPMp, we have decomposed the proper motion differences XPMx–XPMp into vector spherical harmonics and found these differences to be free from the magnitude equation. An important fact is that the first-order zonal coefficients have turned out to be greatest in absolute value. The toroidal coefficient t1,0,1,0 found has shown that the XPMx and XPMp reference frames of proper motions rotate relative to each other around the Z axis with an angular velocity of 0.45 mas yr−1. It should be added that the range of systematic differences XPMx–XPMp is 2.1 mas yr−1 in right ascension and 1.7 mas yr−1 in declination. The angular velocities of mutual rotation of the XPMp and UCAC4 reference frames change within the range from 0.6 to 2.2 mas yr−1, while the analogous range for the XPMх and UCAC4 catalogs is 0.3–1.8 mas yr−1. The angular velocity and coordinates of the pole of the mutual rotation axis depend on the magnitude of stars. The parameters of the mutual rotation around the Z axis derived from the differences XPMx–UCAC4 and XPMp–UCAC4 change from 0.03 ± 0.06 to 1.73 ± 0.06 mas yr−1 and from 0.49 ± 0.06 to 2.19 ± 0.06 mas yr−1, respectively. Based on our analysis, we have shown that the XPMcatalog actually comprises two catalogs, XPM(XSC) and XPM(PSC), in which the stellar positions coincide at the standard epoch J2000 and differ at any other epoch. The decomposition coefficients of the systematic differences XPM–UCAC4 we obtained allow the stellar positions and proper motions from one catalog to be reduced to the system of the other catalog by taking into account this duality.

High-precision motion control of a stage with pneumatic artificial muscles

Pneumatic artificial muscles (PAMs) have been applied in bionic robots, welfare devices, and parallel manipulators because of their many advantages over traditional actuators; such advantages include their high power-to-weight ratio, high power-to-volume ratio, high degree of safety, and stick-slip-free operation. However, significant nonlinearities in PAMs cause low controllability and limit their application. This research aims to provide a practical controller design method for high-precision motion of PAM mechanisms, and this paper proposes a simple and practical controller design method. This controller is designed based on our previous positioning controller and includes a phase-lead element that reduces residual vibration and a simple modified feed-forward element that improves its following ability. The proposed controller design procedure can be easily implemented in PAM mechanisms without an exact dynamic model. This system's motion control performance was evaluated experimentally. The positioning results indicate that the maximum steady-state error is reduced to 0.7μm and that the transient response's overshoot is eliminated using a reconstructed step-like reference signal. The experimental results show that the maximum errors are less than 2 and 5μm under 0.1- and 0.5-Hz sinusoidal tracking control, respectively. Moreover, the designed control system's robustness for positioning and tracking was examined in experiments using an additional mass.

Accuracy of Kinematic Positioning Using Global Satellite Navigation Systems under Forest Canopies

A harvester enables detailed roundwood data to be collected during harvesting operations by means of the measurement apparatus integrated into its felling head. These data can be used to improve the efficiency of wood procurement and also replace some of the field measurements, and thus provide both less costly and more detailed ground truth for remote sensing based forest inventories. However, the positional accuracy of harvester-collected tree data is not sufficient currently to match the accuracy per individual trees achieved with remote sensing data. The aim in the present study was to test the accuracy of various instruments utilizing global satellite navigation systems (GNSS) in motion under forest canopies of varying densities to enable us to get an understanding of the current state-of-the-art in GNSS-based positioning under forest canopies. Tests were conducted using several different combinations of GNSS and inertial measurement unit (IMU) mounted on an all-terrain vehicle (ATV) “simulating” a moving harvester. The positions of 224 trees along the driving route were measured using a total-station and real-time kinematic GPS. These trees were used as reference items. The position of the ATV was obtained using GNSS and IMU with an accuracy of 0.7 m (root mean squared error (RMSE) for 2D positions). For the single-frequency GNSS receivers, the RMSE of real-time 2D GNSS positions was 4.2–9.3 m. Based on these results, it seems that the accuracy of novel single-frequency GNSS devices is not so dependent on forest conditions, whereas the performance of the tested geodetic dual-frequency receiver is very sensitive to the visibility of the satellites. When post-processing can be applied, especially when combined with IMU data, the improvement in the accuracy of the dual-frequency receiver was significant.

SU‐E‐T‐648: Quality Assurance Using the RADPOS System for 4D Radiotherapy with CyberKnife

Purpose:The CyberKnife robotic radiosurgery system uses Synchrony respiratory motion compensation, which requires independent performance verification. In this work, the RADPOS 4D dosimetry system's motion measurements are compared with internal fiducial position measurements. In addition, RADPOS measurements are compared with Synchrony's predictive correlation model, which is based on internal fiducial and external LED marker position measurements.Methods:A treatment plan was created for a lung insert containing fiducials, RADPOS detector, and Solid Water tumor phantom. Two Quasar Respiratory Motion Phantoms (Q1 and Q2) and two RADPOS detectors (R1 and R2) were used: Q1 simulated lung motion with a lung insert moving in the superior/inferior direction, while Q2 simulated chest motion with a chest platform moving in the anterior/posterior direction. Before treatment, R1 was secured inside of the tumor phantom within Q1, while LED markers and R2 were positioned on the chest platform of Q2. Two treatment delivery cases were studied: isocentric plan (I) and non‐isocentric patient plan (P). Four motion cases were studied: no motion (0), sinusoidal and in‐phase (1), sinusoidal and out‐of‐phase (2), patient waveform and out‐of‐phase (3). A coordinate alignment algorithm was implemented, allowing RADPOS and model position data to be compared within the fiducial coordinate system.Results:The standard deviation of the differences between RADPOS and fiducial position measurements was below 0.6 mm for all experimental cases. The standard deviation of the differences between RADPOS and model position data was 1.0, 1.5, and 1.6 mm along the primary direction of motion for case I1, I2, and P3, respectively.Conclusion:Our work demonstrates that RADPOS is a useful tool for independent quality assurance of CyberKnife treatment with Synchrony respiratory compensation. RADPOS and fiducial position measurement closely match, and RADPOS confirms the effectiveness of CyberKnife's Synchrony motion tracking.This work was supported by OCAIRO (Ontario Consortium for Adaptive Interventions in Radiation Oncology) grant.

Experimental verification of a hybrid dynamical model of the church bell

In this paper we present a hybrid model of church bell. The dynamical system of yoke-bell-clapper is nonlinear and discontinuous. We use the Lagrange equations of the second type to derive formulas that describe the system's motion. The energy between the bell and the clapper is transmitted via impacts, here modeled using a coefficient of energy restitution. The values of the system's parameters have been determined basing on the measurements of the biggest bell ‘‘The Heart of Lodz’’ in the Cathedral Basilica of St Stanislaus Kostka, Lodz, Poland. Using the same bell we also validate the model by comparing the results of numerical simulations with experimental data. The presented results show that the described model is a reliable predictive tool which can be used both to simulate the behavior of the existing yoke-bell-clapper systems as well as to design the yokes and predict the motion of new bells.

Tolerance Analysis of Rotating Mechanism Based on Skin Model Shapes in Discrete Geometry

Geometric deviations are inevitably observable on every manufactured workpiece. These deviations affect the function and quality of mechanical products and have therefore to be controlled by geometric tolerances. Computer-aided tolerancing aims at supporting design, manufacturing, and inspection by determining and quantifying these effects of geometric deviations on the product quality and the functional behaviour. However, most established tolerance representation schemes imply abstractions of geometric deviations and are not conform with the standards for geometric dimensioning and tolerancing. These limitations led to the development of a Skin Model inspired framework for the tolerance analysis, which is based on a representation of non-ideal workpieces employing discrete geometry representation schemes, such as point clouds and surface meshes. In this contribution, this Skin Model inspired framework for computer aided tolerancing is extended to systems in motion and applied to the tolerance analysis of rotating mechanism with higher kinematic pairs. For this purpose, the generation of non-ideal part representatives, as well as their processing with algorithms for registration and computational geometry are highlighted. Finally, the results are visualized and interpreted. The procedure as well as the simulation model itself are shown in a case study of a disk cam mechanism.

Vibration energy harvesting from a piezoelectric bistable system with two symmetric stops

Random vibration energy is widely existing in the environment. To efficiently harvest it, many researchers have designed lots of harvesters up till now. A lot of research works have found that when a harvester with bistable piezoelectric energy is excited by stochastic forces, if the intensity of them is low, the system's motion will be trapped in a single potential well. This will result in a low output voltage. In order to overcome the difficult of it and improve the harvesting efficiency, we develop an impact facility with two stops and incorporate it to a bi-stable energy harvester. This design can improve the harvesting efficiency greatly. First the electromechanical coupling equations are derived based on the Euler-Bernoulli beam theory and Kirchhoff's law. Then, we analyze the symmetric stops' effect on the potential function and the elastic restoring force of the system. Results show that both the potential energy and the magnitude of restoring force will be enhanced when collision takes place. Furthermore, we investigate the impact's effect on the system's dynamic responses and efficiency at harmonic excitation. Results reveal that a well designed impact can transform an intrawell motion into an interwell, and then increase the output voltage. And the chaotic motion can be changed into the large amplitude periodic one. Then, the harvester's dynamic responses under random excitations at a low intensity are obtained by using Euler-Maruyama method. Results indicate that the collision gaps can greatly influence the efficiency of the energy harvester. Collisions between the beam and the stops can force the system to oscillate between two potential wells more frequently. According to the relationship between the gap and the standard deviation of output voltage, we know that there exists an optimal collision gap for a definite intensity of stochastic excitation. The bistable energy harvester with this optimal gap will oscillate between the two wells frequently, and output a large voltage. Moreover, the collision stiffness can influence the system's performance as well. With the increase of collision stiffness, the system will exhibit a more frequently jumping between the two potential wells, but the stiffness has a limitation, exceeding which it cannot increase the frequency of jumping and improve the output power any more. So by properly designing the collision gap and stiffness, the system can most frequently jump between the two wells with a large amplitude of displacement, hence can attain the highest harvesting efficiency.

Nonlinear Response Characteristics of Giant Magnetostrictive-Piezoelectric Composite Sensors

The nonlinear magnetoelectric response characteristics of a giant magnetostrictive-piezoelectric composite sensor in harmonic magnetic fields are described in this paper. Nonlinear differential items are introduced to explain the hysteresis phenomena of a giant magnetostrictive material. The nonlinear dynamic model of giant magnetostrictive-piezoelectric composite sensors in harmonic magnetic fields is developed, and the dynamic response of the system is obtained. The numerical and experimental results show that there are multiple frequencies in the response of the system, and the system's motions change from periodic orbits to chaos with the increase in the level of outside excitation. The results of this study are helpful for the optimal design and improvement of giant magnetostrictive-piezoelectric composite sensors.

Resonance oscillations in some systems with aftereffect

Non-linear systems, described by Volterra integro-differential equations, with a characteristic equation possessing a pair of pure imaginary roots with other roots with negative real parts are considered. A small limit periodic perturbation, specified by a time function, which tends exponentially with time to periodic oscillations, the frequency of which is equal to the frequency of the oscillations in the linearized system, acts on the system. The problem of the rotational motions of a solid plate in an air flow, taking into account the nonstationarity of the flow in the framework of the model which takes into account the nonstationarity by introducing integral terms into the moments of the aerodynamic forces, is considered. Amplitude equations, which solve the problem of the existence in the system of limit periodic rotational oscillations, which occur due to the action of a small perturbation of the flow when there is resonance, are constructed from third-order terms. An assertion is presented which generalizes the result previously obtained regarding the existence in the system of limit periodic motions, when the perturbation is specified by a function of time, having a derivative of bounded variation. The motions, indicated earlier, approach periodic oscillations, represented by absolutely converging Fourier series. The generalization relates to a class of perturbations, specified by continuous or piecewise-continuous functions of time.

Brownian motions with one-sided collisions: the stationary case

We consider an infinite system of Brownian motions which interact through a given Brownian motion being reflected from its left neighbor. Earlier we studied this system for deterministic periodic initial configurations. In this contribution we consider initial configurations distributed according to a Poisson point process with constant intensity, which makes the process space-time stationary. We prove convergence to the Airy process for stationary the case. As a byproduct we obtain a novel representation of the finite-dimensional distributions of this process. Our method differs from the one used for the TASEP and the KPZ equation by removing the initial step only after the limit $t\to\infty$. This leads to a new universal cross-over process.

Stability of multifinger action in different state spaces.

We investigated stability of action by a multifinger system with three methods: analysis of intertrial variance, application of transient perturbations, and analysis of the system's motion in different state spaces. The "inverse piano" device was used to apply transient (lifting-and-lowering) perturbations to individual fingers during single- and two-finger accurate force production tasks. In each trial, the perturbation was applied either to a finger explicitly involved in the task or one that was not. We hypothesized that, in one-finger tasks, task-specific stability would be observed in the redundant space of finger forces but not in the nonredundant space of finger modes (commands to explicitly involved fingers). In two-finger tasks, we expected that perturbations applied to a nontask finger would not contribute to task-specific stability in mode space. In contrast to our expectations, analyses in both force and mode spaces showed lower stability in directions that did not change total force output compared with directions that did cause changes in total force. In addition, the transient perturbations led to a significant increase in the enslaving index. We consider these results within a theoretical scheme of control with referent body configurations organized hierarchically, using multiple few-to-many mappings organized in a synergic way. The observed volatility of enslaving, greater equifinality of total force compared with elemental variables, and large magnitude of motor equivalent motion in both force and mode spaces provide support for the concept of task-specific stability of performance and the existence of multiple neural loops, which ensure this stability.

Is the solar system's galactic motion imprinted in the Phanerozoic climate?

A new δ18O Phanerozoic database, based on 24,000 low-Mg calcitic fossil shells, yields a prominent 32 Ma oscillation with a secondary 175 Ma frequency modulation. The periodicities and phases of these oscillations are consistent with parameters postulated for the vertical motion of the solar system across the galactic plane, modulated by the radial epicyclic motion. We propose therefore that the galactic motion left an imprint on the terrestrial climate record. Based on its vertical motion, the effective average galactic density encountered by the solar system is . This suggests the presence of a disk dark matter component.

Free vibrations and seismic resistance of three-layer non-homogeneous orthotropic rectangular plates

The problem of seismic resistance and free vibration of three-layer non-homogeneous, orthotropic rectangular plates, which layers are made of various, continuously non-homogeneous materials, is considered in the paper. It is assumed that elasticity characteristics of the material for layers are continuous functions of the plate thickness coordinate. Using the Kirchhoff-Love hypothesis for the entire thickness of the element, the expressions for forces and moments were obtained, as well as integrated stiffness characteristics for the three-layer orthotropic plate under consideration were determined. In general form, equation systems of the plate motion in both exact and approximate formulations were obtained. In the approximate formulation of the problem, two motion equations of the problem with respect to the deflection and the stress function were obtained. For the case of the plate pin-edge fixing, the problem solution was made and the formula for determining free vibrations of the plate was found. When making numerical calculations, the elasticity characteristics of the material for layers were taken as linear in relation to the thickness coordinates.

Self-Correcting Pattern Recognition System of Surface EMG Signals for Upper Limb Prosthesis Control

Pattern recognition methods for classifying user motion intent based on surface electromyography developed by research groups in well-controlled laboratory conditions are not yet clinically viable for upper limb prosthesis control, due to their limited robustness in users' real-life situations. To address this problem, a novel postprocessing algorithm, aiming to detect and remove misclassifications of a pattern recognition system of forearm and hand motions, is proposed. Using the maximum likelihood calculated by a classifier and the mean global muscle activity of the forearm, an artificial neural network was trained to detect potentially erroneous classification decisions. This system was compared to four previously proposed classification postprocessing methods, in both able-bodied and amputee subjects. Various nonstationarities were included in the experimental protocol to account for challenges posed in real-life settings, such as different contraction levels, static and dynamic motion phases, and effects induced by day-to-day transfers, such as electrode shifts, impedance changes, and psychometric user variability. The improvement in classification accuracy with respect to the unprocessed classifier ranged from 4.8% to 31.6%, depending on the scenarios investigated. The system significantly reduced misclassifications to wrong active classes and is thus a promising approach for improving the robustness of hand prosthesis controllability.

V6-10 NOVEL PERCUTANEOUS NAVIGATION SYSTEM INTEGRATING GPS TECHNOLOGY WITH MOVABLE TABLET DISPLAY OF SURGICAL 3D MODEL FOR TARGETED FOCAL THERAPY: INITIAL EXPERIENCES IN HUMAN BODY.

INTRODUCTION AND OBJECTIVES: We present the first application of a percutaneous navigation system (Translucent Medical, Inc.) integrating GPS technology with a movable tablet display of virtual three dimensional (3D) models. The surgical tools and movable tablet display are tracked by GPS technology and digitally aligned with each other. The system displays real-time internal anatomy, superimposed surgical tools, and navigation aids (i.e. predictive puncture line). The objectives of this study were to assess the feasibility and accuracy of the system in targeted therapy for the prostate and kidney in cadaver. METHODS: Gold fiducial-markers (CIVCO Medical), which served as target centers of the virtual tumors (target-fiducial), were implanted in parenchyma of the kidney and prostate. A pre-op CT scan was obtained. The CT-DICOM data were transferred to the system to reconstruct into 3D surgical models. A needle with built-in GPS sensors was used as a therapeutic puncture needle. When the system indicated coincidence of the needle-tip and target-fiducial, another fiducial (treatment-fiducial) was placed through the outer-sheath of the therapeutic needle. A post-op CT was acquired to assess digitized distance between the 2 fiducials. For each target-fiducial, two placements of a treatment-fiducial were attempted (from two different skin incisions >20mm distant). RESULTS: Real-time display of the puncturing trajectory superimposed within the 3D model was used to successfully navigate the targeting in all procedures. Navigation was enhanced by color-coded changes to the needle-icon, indicating whether or not the current trajectory was on line to intersect the surgical target. Median time to target was 43 sec. Mean distance from needle-tip to target was 2.5mm (as calculated by the tracking system). Distance between the paired treatment-fiducials was 7.7mm. Distance between target-fiducial and treatment-fiducial was 16.6mm in the prostate and 12.0mm in the kidney. In an analysis of each axial component, errors were significantly greater along z-axis (p<0.01), likely due to the intra-operative pushing down the organ during the puncture, resulting in possible rotation, shift, or deformation of the soft-tissue organ. CONCLUSIONS: This virtual navigation system, integration of GPS-technology with movable tablet display, is promising for percutaneous interventions. In order to minimize possible errors, further work is needed to augment the tracking system of intra-corporeal motions or deformations of the organs.

Control of Uncertain Nonlinear Multibody Mechanical Systems

Descriptions of real-life complex multibody mechanical systems are usually uncertain. Two sources of uncertainty are considered in this paper: uncertainties in the knowledge of the physical system and uncertainties in the “given” forces applied to the system. Both types of uncertainty are assumed to be time varying and unknown, yet bounded. In the face of such uncertainties, what is available in hand is therefore just the so-called “nominal system,” which is our best assessment and description of the actual real-life situation. A closed-form equation of motion for a general dynamical system that contains a control force is developed. When applied to a real-life uncertain multibody system, it causes the system to track a desired reference trajectory that is prespecified for the nominal system to follow. Thus, the real-life system's motion is required to coincide within prespecified error bounds and mimic the motion desired of the nominal system. Uncertainty is handled by a controller based on a generalization of the concept of a sliding surface, which permits the use of a large class of control laws that can be adapted to specific real-life practical limitations on the control force. A set of closed-form equations of motion is obtained for nonlinear, nonautonomous, uncertain, multibody systems that can track a desired reference trajectory that the nominal system is required to follow within prespecified error bounds and thereby satisfy the constraints placed on the nominal system. An example of a simple mechanical system demonstrates the efficacy and ease of implementation of the control methodology.