Unwanted Motion Research Articles

Hexapod orthogonal periarticular slack-wire stabilization technique: Surgical tip for accurate orthogonal metaphyseal frame mounting

Introduction: The use of hexapod circular external fixators in the treatment of various orthopedic conditions has become more common in recent years. One of the principle mounting requirements is that the fixator is orthogonally aligned to the mechanical axis of the limb. This creates the optimal mechanical environment for bone formation as any forces exerted on the fixator are transmitted as axial forces to the limb while eliminating unwanted motions such as rotation and shear. We describe a method to reliably obtain orthogonal mounting of periarticular rings during hexapod circular external fixator application. The technique is fast, accurate, and uses components readily available on all hexapod external fixator systems. Methods: The “hexapod orthogonal periarticular slack-wire stabilization (HOPSS) technique” uses a untensioned/slack wire as the second fixation element following the transverse reference wire. A wire fixation bolt is attached to the ring, and a second wire (slack wire) is placed through the wire fixation bolt to allow insertion in an antero–posterior direction. The wire is advanced through the near cortex and onto the far cortex after which the wire fixation bolt can be tightened and a final image intensifier check can be done. The technique can be used for the application rings to the metaphysis of long bones. Discussion: Orthogonal mounting for Ilizarov all-wire frames has been a crucial part of the surgical technique and has long been accepted as it promotes axial micromotion that supports callus formation and union and eliminated parasitic motion at the bone ends. The described technique uses readily available instruments and components to assist with perfect orthogonal mounting. Conclusions: The hexapod orthogonal periarticular slack-wire technique is a simple method for obtaining more accurate orthogonal mounting. It is quick and effective and does not require any additional equipment.

ISAR Autofocus Imaging Algorithm for Maneuvering Targets Based on Phase Retrieval and Gabor Wavelet Transform

The imaging issue of a rotating maneuvering target with a large angle and a high translational speed has been a challenging problem in the area of inverse synthetic aperture radar (ISAR) autofocus imaging, in particular when the target has both radial and angular accelerations. In this paper, on the basis of the phase retrieval algorithm and the Gabor wavelet transform (GWT), we propose a new method for phase error correction. The approach first performs the range compression on ISAR raw data to obtain range profiles, and then carries out the GWT transform as the time-frequency analysis tool for the rotational motion compensation (RMC) requirement. The time-varying terms, caused by rotational motion in the Doppler frequency shift, are able to be eliminated at the selected time frame. Furthermore, the processed backscattered signal is transformed to the one in the frequency domain while applying the phase retrieval to run the translational motion compensation (TMC). Phase retrieval plays an important role in range tracking, because the ISAR echo module is not affected by both radial velocity and the acceleration of the target. Finally, after the removal of both the rotational and translational motion errors, the time-invariant Doppler shift is generated, and radar returned signals from the same scatterer are always kept in the same range cell. Therefore, the unwanted motion effects can be removed by applying this approach to have an autofocused ISAR image of the maneuvering target. Furthermore, the method does not need to estimate any motion parameters of the maneuvering target, which has proven to be very effective for an ideal range–Doppler processing. Experimental and simulation results verify the feasibility of this approach.

Reduction of unwanted swings and motions in floating wind turbines

A novel strategy to reduce unwanted swings and motions in floating wind turbines is presented. At above rated wind speeds, the platform, on which the wind turbine is mounted, causes the generator speed control loop to become unstable. The proposed strategy assures stability of the control loop by an additive adjustment of the measured generator speed using tower fictitious forces. The developed strategy is independent of the platform and wave dynamics.

Stability of Intracavitary Applicator Placement for HDR Brachytherapy of Cervix Cancer

Cervical cancer is often treated with a combination of external beam radiation therapy (EBRT) and high-dose rate (HDR) intracavitary brachytherapy (ICBT). An intrauterine ring and tandem (R&T) are inserted through the vagina until they reach the cervix and uterus, where the dose is prescribed. The goals of this study were to investigate the stability of intracavitary applicator placement during patient transfer and to evaluate the dosimetric impact of displacement. 14 patients with cervical cancer were analyzed. Three sets of orthogonal fluoroscopic radiographs were obtained in the HDR suite after the insertion and prior to treatment: pre-CT fluoroscopic radiograph with patient in the lithotomy position, pre-CT fluoroscopic radiograph with patient in the legs down position, and post-CT fluoroscopic radiograph with patient in the legs down position. Applicator position post-CT was compared to the pre-CT radiographs to determine if the position changed during patient transfer. The displacement was measured in the anterior-posterior, medio-lateral, and superior-inferior directions, as well as the degree of rotation. To study the dosimetric impact of applicator shifts on dose to organs at risk (OARs), the R&T were shifted virtually in the BrachyVision treatment planning system. The OARs studied included the bowel, sigmoid, rectum and bladder. 5mm shifts were made in the superior-inferior, medio-lateral and anterior-posterior direction. 3 rotations were made in the pitch, yaw and roll directions. Applicator shifts were analyzed in only one direction at a time. The dosimetric impact on OARs was evaluated by comparing DVH-based criteria from the original and shifted/rotated plans. The average displacements were 1.90 ± 0.47mm laterally, 2.97 ± 0.58mm longitudinally and 9.50 ± 1.48mm anterior-posterior. The average rotation on the PA radiograph was 0.97 ± 0.21° and 2.55 ± 0.61° on the LAT radiograph. 5mm anterior-posterior shifts had the greatest effect on dose to OARs. On average, 5mm ANT shifts had the greatest effect on the D2cc values of the bowel. There was a 13.69% increase in dose. 5mm ANT shifts also affected bladder dose, with a 36.47% increase in dose. 5mm POST shifts increased rectal dose by 28.61%. Other directional shifts were minimal. The largest effect on OAR dose due to rotation was to the sigmoid when the applicator shifted in the POST pitch direction. As a result, the dose increased by 4.66%. Other changes in dose were minimal. Patient transfer resulted in applicator shifts and rotations that had a measurable effect on dose to OARs. The displacements were the result of either a direct shift or rotation of the applicator. However, the dose differences reported in this study represent the worst-case scenarios, since the surrounding tissues and organs may move with the applicators. Additional tracking of these shifts and rotations may clarify the sources of these unwanted motions and suggest possible mitigation strategies.

Parasitic Inclinations in Cable-Driven Parallel Robots using Cable Loops

Cable-Driven Parallel Robots (CDPRs) also noted as wire-driven robots are parallel manipulators with flexible cables instead of rigid links. A CDPR consists in a base frame, a Moving-Platform (MP) and a set of cables connecting in parallel the MP to the base frame. CDPRs are well-known for their advantages over the classical parallel robots in terms of large workspace, reconfigurability, large payload capacity and high dynamic performance. In spite of all the mentioned advantages, one of the main shortcomings of the CDPRs is their limited orientation workspace. The latter drawback is mainly due to cable interferences and collisions between cables and surrounding environment. Hence, a planar four-Degree-of-Freedom (DoF) under-constrained CDPR with an articulated MP is introduced and studied in this paper. The end-effector is articulated through a cable loop, which enables the robot to obtain a modular pose determination, namely orientation and positioning. As a result, the mechanism under study has an unlimited and singularity-free orientation workspace in addition to a large translational workspace. It should be noted that some unwanted rotational motions of the moving platform, namely, parasitic inclinations, arise due to the cable loop. Finally, those parasitic inclinations are modeled and assessed for the mechanism at hand.

Removing Unclassified Hand Tremor Motion from Computer Mouse Input with Neural Networks

An artificial neural network based filter to remove unwanted tremor-induced motion in computer mouse input is presented and tested. A method to efficiently capture appropriate training data is shown to be important in the operation and training of the neural network filter. The architecture of the neural network as well as the numerous design choices are presented and explained. A simulation study proves the artificial neural network is successful at removing a simulated Parkinson’s tremor from computer mouse movements even with minimal training data. Resulting tremor-free motion estimated by the artificial neural network is shown to be similar to normal tremor free computer mouse movements.

Vibration Control Using a Dedicated Inertial Sensor

The Compact Linear Collider (CLIC) project is right in the development phase. In this prospect, the main objective of the final focus stabilization is to succeed in damping ground motion vibration at the sub-nanometer scale to avoid any unwanted motion of the two last final focus magnets. Active vibration control using high-resolution industrial seismic sensors has already shown its limits in the desired range of attenuation [4–100] Hz. Hence, a dedicated inertial sensor has been designed, tuned to fit CLIC requirements. It doesn’t contain any feedback or coil which would linearize its dynamic in its bandwidth [0.1–100] Hz, avoiding electrical noise or thermal noise, and when used for active control, enhancing its performances thanks to the internal resonance. An analytical modeling of the sensor dynamic behavior also shown experimentally gives a first internal resonance around 11 Hz. This paper is complemented by a comparative measurement with high precision industrial sensors. A noise level 2.5 times better (0.04 nm at 4 Hz) has been achieved. This sensor has also been tested in the context of vibration rejection with a sub-nanometer active vibration rejection support. Experimental results have been compared with the one obtained with the state-of-the-art industrial sensors. Vertical seismic motion attenuation results have shown unprecedented performances. A damping ratio of 8.5 has been achieved at 4 Hz, leading to an rms displacement of the support of 0.25 nm thanks to the active support prototype and the dedicated sensor.

Muscular and neuromotor control and learning in the athletic horse

Athletic performance or the kinematics of locomotion is ultimately the result of the actions of muscles. Muscular actions differ depending on the muscle group involved with anatomical and functional properties depending on the primary roles of the muscle; from stabilisation to powering locomotion. The functional (contractile and metabolic) properties of a muscle are determined by its fibre type or relative fibre type proportions in the muscle. The actions of muscle require the coordination of the nervous system with muscle contraction to produce movement or resist movement to avoid unwanted motion and tissue damage. The coordination of muscular action with the nervous system is termed neuromotor control and it requires precise proprioceptive input from the periphery, processing and input from the central nervous system (including learned or trained movements) and involves timing of muscle recruitment as well as muscle contraction. Training of muscles involves training for strength (or force generation) and stamina with measureable physiological changes with training including increased fibre size, alterations in fibre type, alterations in glycogen concentrations and lactate transport and alterations in mitochondrial and capillary density. As well as standard athletic training, skills training can make the difference in athletic performance and injury prevention in the equine athlete. This involves training of neuromotor control; training motor skills by motor relearning and conditional learning. Practical specific training techniques can be used in injury prevention, rehabilitation post injury and maintenance of the athlete. In this review we will focus on the thoracolumbar and hindlimb areas of the horse and review the importance of muscular control of locomotion, neuromotor control, the physiological effects of training and practical ways to maximise performance potential by specific physiotherapy skills training.

Using a moving aerial platform to detect and localise a low probability of intercept radar

In this study, the problem of detecting and finding the location of a low probability of intercept (LPI) radar is investigated. A method based on using two electronic support antennas mounted on a moving aircraft is proposed and it is proved that the phase difference between the signals received by the two antennas can be used to detect and localise an LPI radar. In addition, the effect of the aircraft random displacements on the proposed method performance is discussed and a modification to compensate for unwanted motions is introduced. Simulation results show the effectiveness of the method for detecting very low signal-to-noise ratio signals, and the proposed method performance is compared with the short-time Fourier transform method.

Movement correction in DCE-MRI through windowed and reconstruction dynamic mode decomposition

Images of the kidneys using dynamic contrast-enhanced magnetic resonance renography (DCE-MRR) contains unwanted complex organ motion due to respiration. This gives rise to motion artefacts that hinder the clinical assessment of kidney function. However, due to the rapid change in contrast agent within the DCE-MR image sequence, commonly used intensity-based image registration techniques are likely to fail. While semi-automated approaches involving human experts are a possible alternative, they pose significant drawbacks including inter-observer variability, and the bottleneck introduced through manual inspection of the multiplicity of images produced during a DCE-MRR study. To address this issue, we present a novel automated, registration-free movement correction approach based on windowed and reconstruction variants of dynamic mode decomposition (WR-DMD). Our proposed method is validated on ten different healthy volunteers’ kidney DCE-MRI data sets. The results, using block-matching-block evaluation on the image sequence produced by WR-DMD, show the elimination of 99% of mean motion magnitude when compared to the original data sets, thereby demonstrating the viability of automatic movement correction using WR-DMD.

Hydrodynamic characteristics of a separated heave plate mounted at a vertical circular cylinder

In this study, a wave flume experiment was performed with a scaled floating model to optimise the design of a floating body and control unwanted motions due to the offshore environment. A cylindrical test model was chosen as a standard and classical representative design of a floating structure in an ocean environment. The attachment of a heave plate at the bottom of the floating structure has been suggested as an effective tool to control its motion. However, the associated hydrodynamic effects, particularly the added mass variation, need to be investigated. Therefore, a scaled cylindrical model with a height of 300mm, an outer diameter of 60mm, and various heave plates was designed, manufactured, and tested. The motion responses of a scaled model in a water flume (i.e. forced oscillation, free decay, and regular wave response) were analysed. The results were compared for similar cylindrical models with various heave plates attached at different gaps from the cylinder bottom, different oscillating frequencies, and different Keulegan–Carpenter (KC) numbers. An empirical formula was formulated to calculate the added mass of the combined structure of the cylinder and heave plate. The results indicated that varying the heave plate diameter had the most significant effect on the added mass compared to the gap and KC (0.2–1.4). The added mass coefficient of the combined cylinder and heave plate was below 0.05, while KC varies from 0.2 to 1.4 and the gap ratio (Dg/(0.5Dc+0.5Dp)) varied between 0.2 and 1.2. The peak heave response amplitude operator (RAO) for the combined cylinder and heave plate was 40% less than that of the cylinder without a heave plate.

Development of estimated disturbance rejection feedback for an armoured vehicle using active front wheel steering

An unwanted yaw motion occurred at the centre of gravity (CG) of the wheeled armoured vehicle caused by the impulse force generated during gun turret firing. The recoil force from the gun fire tends to create instability conditions for the armoured vehicle during firing condition and affects the dynamic performance of armoured vehicle in lateral direction. In this paper, an active safety system, active front wheel steering (AFWS) system using estimated disturbance rejection feedback (EDRF) embodiment is proposed to reject the unwanted yaw disturbance and stabilise the armoured vehicle. Besides, the proposed control strategy is also used to re-position the armoured vehicle back to its initial position. Therefore, a summation moment reference input is used to counter back the unwanted firing moment occurred due to gun firing impulse at CG of the armoured vehicle. The armoured vehicle is evaluated via simulation analysis in term of yaw rate, yaw angle, vehicle sideslip angle, lateral acceleration and lateral displacement. Significant improvements up to 75% have been achieved by using the proposed control strategy of AFWS system to reject the external disturbance due to the firing force.

Trajectory generation to suppress oscillations in under-constrained cable-driven parallel robots

Cable-driven parallel robots (CDPRs) have many advantages over conventional link-based robot manipulators in terms of acceleration due to their low inertia. This paper concerns about under-constrained CDPRs, which have a less number of cables than six, often used favorably due to their simpler structures. Since a smaller number of cables than 6 are employed, however, their payloads have extra degrees of motion freedom and exhibit swaying motions or oscillation. In this paper, a scheme to suppress unwanted oscillatory motions of the payload of a 4-cable-driven CDPR based on a Zero-vibration (ZV) input-shaping scheme is proposed. In this method, a motion in the 3-dimensional space is projected onto the independent motions on two vertical planes perpendicular to each other. On each of the vertical plane, the natural frequency of the CDPR is computed based on a 2-cable-driven planar CDPR model. The precise dynamic model of a planar CDPR is obtained in order to find the natural frequency, which depends on the payload position. The advantage of the proposed scheme is that it is possible to generate an oscillation-free trajectory based on a ZV input-shaping scheme despite the complexity in the dynamics of the CDPR and the difficulty in computing the natural frequencies of the CDPR, which is required in any ZV input-shaping scheme. To verify the effectiveness of the proposed method, a series of computer simulations and experiments were conducted for 3- dimensional motions with a 4-cable-driven CDPR. Their results showed that the motions of the CDPR with the proposed method exhibited a significant reduction in oscillations of the payload. However, when the payload moves near the edges of its workspace, the improvement in oscillation reduction diminished as expected due to the errors in model projection.

Flow control for suppression of self-excited rolling oscillation at high angles of attack

A cruciform-finned slender body can excite a limit-cycle rolling oscillation at high angles of attack. To suppress the unwanted motions, flow control approaches should be employed if the aerodynamic control surfaces lose control efficiency at high angles of attack. As a promising technology, the ns-dielectric barrier discharge plasma actuator has been successfully used in high-speed and high-Reynolds-number flow control applications. The present work employs a π-type ns-dielectric barrier discharge plasma actuator and vortex generators to suppress self-excited rolling oscillation at α = 50°. The free-to-roll tests show that the plasma actuator ignited at F+ ∼ 1.5 and that the vortex generators can suppress rolling oscillation. The flow patterns from particle image velocimetry measurement at different cross-sections and rolling angles suggest that the vorticity decrease of the leeward vortices may be the control mechanism for the plasma actuator. For the vortex generators, evident modification of the flow field structure can be observed due to the vortices generated from the vortex generators, which decreases the rolling moment induced by the asymmetry vortices to suppress the self-excited rolling oscillation.

Tracking control in x-y plane of an offshore container crane

A tracking controller is proposed for a crane attached to a mobile harbor (MH) equipped with a dual-stage trolley system, to dynamically position a container from the MH to the container ship or vice versa. Wave-induced motions of the MH and container ship occur during loading and unloading operations owing to external disturbances such as waves. However, a challenging task is to move a payload with unwanted swing motions accurately to the loading and unloading positions on a moving target vessel. To solve this problem, a dynamic MH crane model is derived in three-dimensional space, with roll, pitch, and heave motions caused by sea-wave disturbances. The MH crane model is then linearized to design a tracking controller and the parameters of the linearized model are obtained by carrying out the system identification process. A preview tracking control method that includes feedback and feed-forward control with the predicted target position in the x-y plane in the near future is utilized. Through numerical simulations and experiments with a scaled model, the tracking performance of the proposed dynamic positioning control system is considered when sinusoidal roll and pitch motions of the MH are generated to mimic the wavy sea environment.

Experimental investigation of roll characteristics of a cruciform-finned slender body

Next-generation aircraft and missile are required to have extreme maneuverability, which should maintain stability at high angle of attack. However, the unsteady flow field surrounding the air vehicle would affect the aerodynamics loads and induce unwanted nonlinear motions, of which the rolling motions are usually generated. In order to investigate the unsteady rolling characteristics of a cruciform-finned slender body, the free-to-roll and force measurement tests including particle image velocimetry measurement have been conducted comprehensively. Different types of rolling motion, trimming at equilibrium positions, self-excited rolling oscillation, and self-excited spinning are observed during the free-to-roll experiment depending on the different angles of attack. The force measurement results show that the rolling motions are related to both the static and dynamic stabilities of the rolling moment at balance points. The stabilities of the rolling moment would change as the angle of attack for the model increases. At last, the flow field results from particle image velocimetry measurement indicate that the unsteady rolling motions may be induced by the interaction between the asymmetry vortices and strake wings, fins.

Phase-aware echocardiogram stabilization using keyframes

This paper presents an echocardiogram stabilization method designed to compensate for unwanted auxilliary motion. Echocardiograms contain both deformable cardiac motion and approximately rigid motion due to a number of factors. The goal of this work is to stabilize the video, while preserving the informative deformable cardiac motion. Our approach incorporates synchronized side information, extracted from electrocardiography (ECG), which provides a proxy for cardiac phase. To avoid the computational expense of pairwise alignment, we propose an efficient strategy for keyframe selection, formulated as a submodular optimization problem. We evaluate our approach quantitatively on synthetic data and demonstrate its benefit as a preprocessing step for two common echocardiogram applications: denoising and left ventricle segmentation. In both cases, preprocessing with our method improved the performance compared to no preprocessing or other alignment approaches.

On the coupled dynamics of small spacecraft and elastic deployable appendages

A thorough investigation of the dynamics of finite-mass satellites with a deployable elastic arm is presented. This work is focused on the interaction between spacecraft rigid body motion and its flexible arm dynamics during the deployment process. The classical Newton–Euler formulation and the Lagrangian approach are applied to the study of the dynamics of spacecraft and its deploying arm. Utilizing a non-Newtonian floating frame to define the arm elastic deformation field, the interactions between the spacecraft and its moving arm have been simulated. Complete equations of motion show that the spacecraft motion induces dynamical stiffness on the arm; in addition, axial and lateral motions of the deploying elastic arm change the spacecraft mass-characteristics and thus influence the spacecraft’s rigid body motions. The overall dynamic behavior is highly dependent on spacecraft mass characteristics in addition to the “arm deployment time (ADT)”. The results of case studies clearly indicate that some assumptions previously applied in appendage dynamic analysis are not conservative and produce erroneous results. This study realistically investigates the dynamics of elastic deploying appendages by considering finite-mass characteristics for small and massy spacecraft. The results reveal that for massive spacecraft the arm’s flexible dynamics is mainly excited through deployment, while for small spacecraft the energy transfers to the arm base and the spacecraft rigid body motion is considerably stimulated. Moreover, this work has further highlighted the effects of ADT in the overall system response. The findings of this work show that the energy distribution between arm’s elastic dynamics and spacecraft rigid body motions is an important factor in the design of any control system to limit unwanted arm-tip motions.

Modeling, Validation, and Control of Electronically Actuated Pitman Arm Steering for Armored Vehicle

In this study, 2 DOF mathematical models of Pitman arm steering system are derived using Newton’s law of motion and modeled in MATLAB/SIMULINK software. The developed steering model is included with a DC motor model which is directly attached to the steering column. The Pitman arm steering model is then validated with actual Pitman arm steering test rig using various lateral inputs such as double lane change, step steer, and slalom test. Meanwhile, a position tracking control method has been used in order to evaluate the effectiveness of the validated model to be implemented in active safety system of a heavy vehicle. The similar method has been used to test the actual Pitman arm steering mechanism using hardware-in-the-loop simulation (HILS) technique. Additional friction compensation is added in the HILS technique in order to minimize the frictional effects that occur in the mechanical configuration of the DC motor and Pitman arm steering. The performance of the electronically actuated Pitman arm steering system can be used to develop a firing-on-the-move actuator (FOMA) for an armored vehicle. The FOMA can be used as an active safety system to reject unwanted yaw motion due to the firing force.

Tunable damping in the Heusler compoundCo2−xIrxMnSi

Here we report on the realization of tuning the intrinsic damping in the half-metallic Heusler compound ${\mathrm{Co}}_{2}\mathrm{MnSi}$ by substituting Co by Ir. The work includes theoretical calculations and experimental measurements on bulk and thin films samples. Control of damping is to remove unwanted magnetization motion and suppress signal echoes through uncontrolled precession of the magnetization for future implementation of this material into, e.g., current perpendicular plane--giant-magnetoresistance sensors. Density functional calculations revealed stable magnetization and increasing damping parameter with Iridium concentration, whereas the half metallicity could be retained. The calculations are consistent with experimental results from bulk and thin film samples of this report and elucidate the linear dependence of the Gilbert damping parameter on the substituent concentration. This report again demonstrates the inherent tunability of Heusler compounds, which constitutes a pivotal feature of this material class.