Unsmooth Motion Research Articles

Quantification of Cycling Smoothness in Children with Cerebral Palsy

Smoothness is a hallmark of skilled, coordinated movement, however, mathematically quantifying movement smoothness is nuanced. Several smoothness metrics exist, each having its own limitations and may be specific to a particular motion such as upper limb reaching. To date, there is no consensus on which smoothness metric is the most appropriate for assessing cycling motion in children with cerebral palsy (CP). We evaluated the ability of four preexisting metrics, dimensionless jerk, spectral arc length measure, roughness index, and cross-correlation; and two new metrics, arc length and root mean square error, to quantify the smoothness of cycling in a preexisting dataset from children with CP (mean age 13.7 ± 2.6 years). First, to measure the repeatability of each measure in distinguishing between different levels of un-smoothness, we applied each metric to a set of simulated crank motion signals with a known number of aberrant revolutions using subjects’ actual crank angle data. Second, we used discriminant function analysis to statistically compare the strength of the six metrics, relative to each other, to discriminate between a smooth cycling motion obtained from a dataset of typically developed children (TD), the control group (mean age 14.9 ± 1.4 years), and a less smooth, halted cycling motion obtained from children with CP. Our results show that (1) ArcL showed the highest repeatability in accurately quantifying an unsmooth motion when the same cycling revolutions were presented in a different order, and (2) ArcL and DJ had the highest discriminatory ability to differentiate between an unsmooth and smooth cycling motion. Combining the results from the repeatability and discriminatory analysis, ArcL was the most repeatable and sensitive metric in identifying unsmooth, halted cycling motion from smooth motion. ArcL can hence be used as a metric in future studies to quantify changes in the smoothness of cycling motion pre- vs. post-interventions. Further, this metric may serve as a tool to track motor recovery not just in individuals with CP but in other patient populations with similar neurological deficits that may present with halted, unsmooth cycling motion.

Computer-controlled finishing via dynamically constraint position-velocity-time scheduler

In a Computer Numerical Controlled (CNC) finishing process, the target material removal from an optical surface is guided by the convolution between the influence function of a machine tool and its dwell time at certain points over the surface. To reduce dynamics stressing and increase machining efficiency, the dwell time must be converted to varying velocities, which are the actual inputs to the machine tool controller. Conventionally, the conversion assumed constant acceleration and relied on linear motion interpolation, which caused discontinuities in velocities. This unsmooth motion affects the material removal distribution, and, thus, the accuracy of the finished surface shape. Many modern CNC machines support the smoother, cubic-polynomial interpolated Position-Velocity-Time (PVT) motion mode; however, the conventional scheduler may fail to provide suitable velocities for the PVT. This study answers this challenge by proposing a novel PVT-based velocity scheduler that achieves smooth motion while considering CNC dynamic limits. Firstly, the principle of the PVT is explained, and the PVT-based velocity scheduler is formulated. Secondly, a quadratic programming is used to optimize the velocities by imposing the CNC dynamic constraints and the C1 continuities (zeroth and first derivatives are continuous) simultaneously. Thirdly, the smoothness and accuracy of the scheduled velocities are studied on different kinds of tool paths via simulation. Finally, a sub-0.3 nm level surface finishing experiment using ion beam figuring is demonstrated to verify the feasibility of the proposed method. The PVT-based scheduler and simulator code is open-sourced.

Adaptive edge-based mean shift for drastic change gray target tracking

Numerous tracking approaches have been proposed recently, however, existing approaches can hardly be applied to drastic change gray target tracking because of their vulnerability to unsmooth motion and appearance discontinuity caused by drastic change gray target. We aim to address this problem by proposing an adaptive edge-based mean shift algorithm, where edges are utilized as feature rather than intensity. We propose a method to construct the feature space by employing a combination of edge images to overcome the inadequate representation of single edge feature space. The feature space provides sufficient information for representing targets. In addition, a detection module is proposed to cope with targets whose gray value distributions change drastically. The detection module can detect the target in a specific region which is automatically adjusted according to the target size of former frame; therefore it offers our algorithm the ability to obtain precise target region and target position. By automatically updating the tracker using currently detected target information, our algorithm becomes adaptive to the changes in target's size and shape. Intensive experiments show that our algorithm outperforms state-of-the-art algorithms in tracking drastic change gray targets.

Novel Similarity-Invariant Line Descriptor and Matching Algorithm for Global Motion Estimation

We present a new and fast line descriptor and matching algorithm to geometrically register video frames that are deformed by a similarity transformation and contain line segments but with very low texture details, such as navigation maps. Line segments are extracted from the frames, and each line is described with a novel line descriptor that does not depend on pixel intensities. The described lines are then matched together and the matches are input to an outlier removal algorithm in order to estimate the parameters of the transformation describing the global motion between the frames. We propose a method for fast parameter estimation of the transformation using line segments instead of points. Additionally, we apply this algorithm in the testing and error detection context of navigation systems, in which we show how to detect map jump artifacts that could occur during the development of these systems, leading to a jerky and unsmooth motion between the frames. The proposed descriptor and its matching algorithm are shown to be fast enough for online use and very robust against a wide range of translation, rotation, and scale changes. Furthermore, the error detection algorithm allows to detect almost all map jump artifacts while maintaining a very low number of false alarms.

Influence of electrolyte concentration on microchannel oil-in-water emulsification using differently charged surfactants

The purpose of this study was to investigate the formation characteristics of oil-in-water (O/W) emulsion droplets in the presence of electrolyte by microchannel (MC) emulsification using differently charged surfactants. Droplet formation was conducted by pressurizing a dispersed phase (refined soybean oil) via 23,348 asymmetric through-holes micro fabricated on a 24mm×24-mm silicon chip into a continuous phase in the presence of a surfactant (1.0wt%) and an electrolyte (NaCl) (0–1.0mol/L). Monodisperse O/W emulsions with an average droplet diameter (dav,drop) of 26μm and a coefficient of variation (CV) below 5% were produced from the asymmetric through-holes when the NaCl concentration was lower than a threshold level that is 0.3mol/L for sodium dodecyl sulfate (SDS) and 0.5mol/L for polyoxyethylene (20) sorbitan monolaurate (Tween 20). Further increase in the NaCl concentration resulted in increase of the dav,drop and CV of the resultant O/W emulsions, which is due to unstable and unsmooth motion of the oil–water interface during droplet formation. In the presence of SDS, it was found that interfacial tension must be higher than a threshold level (c.a. 0.9mN/m) in order to achieve stable droplet formation by MC emulsification. The ζ-potential on the droplet and chip surfaces was negative, and their absolute value decreased with increasing the NaCl concentration. The ζ-potential results also indicated that repulsive electrostatic interaction between the droplet and chip surfaces in the presence of NaCl is high for SDS and negligible for Tween 20. The difference in their electrostatic interaction is assumed to affect the smoothness of droplet formation and the behavior of the droplets formed.

Temporal presentation protocols in stereoscopic displays: Flicker visibility, perceived motion, and perceived depth

Most stereoscopic displays rely on field-sequential presentation to present different images to the left and right eyes. With sequential presentation, images are delivered to each eye in alternation with dark intervals, and each eye receives its images in counter phase with the other eye. This type of presentation can exacerbate image artifacts including flicker, and the appearance of unsmooth motion. To address the flicker problem, some methods repeat images multiple times before updating to new ones. This greatly reduces flicker visibility, but makes motion appear less smooth. This paper describes an investigation of how different presentation methods affect the visibility of flicker, motion artifacts, and distortions in perceived depth. It begins with an examination of these methods in the spatio-temporal frequency domain. From this examination, it describes a series of predictions for how presentation rate, object speed, simultaneity of image delivery to the two eyes, and other properties ought to affect flicker, motion artifacts, and depth distortions, and reports a series of experiments that tested these predictions. The results confirmed essentially all of the predictions. The paper concludes with a summary and series of recommendations for the best approach to minimize these undesirable effects.

Energy-Based Control of a Haptic Device Using Brakes

This paper proposes an energy-based control method of a haptic device with electric brakes. Unsmooth motion is frequently observed in a haptic system using brakes during a wall-following task. Since it is generally known that a haptic system using brakes is passive due to brake's characteristics, its energy behavior has seldom been investigated. However, force distribution at the end effector reveals that the unsmooth motion of a haptic system using brakes represents active behavior of the system in the specific direction. A force control scheme is proposed that computes the gain for smooth motion by considering the energy behavior of a system. Experiments show that smooth wall following is possible with a proposed force control scheme.

Design and control of a planar haptic device with passive actuators based on passive force manipulability ellipsoid (FME) analysis

In this paper, we propose an optimal design for a passive haptic device with brakes and its control method. The inability of a brake to generate torque significantly affects the performance of a multi-DOF haptic device, in that a desired force can be generated only approximately in some workspace and, in some cases, the device may become stuck contrary to the user's intention. In this research, these limitations are analyzed by means of the so-called passive force manipulability ellipsoid. Through the analysis, performance indices are developed for evaluating the limitations associated with passive haptic devices. Optimization is conducted for a 5-bar mechanism with redundant actuation, and a coercive force approximation scheme is developed to avoid unsmooth motion during the wall-following task along the virtual wall. It is experimentally shown that the performance in relation to the limitations is greatly improved for the optimized mechanism. © 2005 Wiley Periodicals, Inc.

Design and control of a planar haptic device with passive actuators based on passive force manipulability ellipsoid (FME) analysis

In this paper, we propose an optimal design for a passive haptic device with brakes and its control method. The inability of a brake to generate torque significantly affects the performance of a multi-DOF haptic device, in that a desired force can be generated only approximately in some workspace and, in some cases, the device may become stuck contrary to the user's intention. In this research, these limitations are analyzed by means of the so-called passive force manipulability ellipsoid. Through the analysis, performance indices are developed for evaluating the limitations associated with passive haptic devices. Optimization is conducted for a 5-bar mechanism with redundant actuation, and a coercive force approximation scheme is developed to avoid unsmooth motion during the wall-following task along the virtual wall. It is experimentally shown that the performance in relation to the limitations is greatly improved for the optimized mechanism. © 2005 Wiley Periodicals, Inc.

NURBS interpolator for constant material removal rate in open NC machine tools

Conventionally used linear or circular interpolators are undesirable for the precision machining of 3D free-form surfaces for the following reasons: the transmission errors due to the huge number of point data, discontinuity of curve segmentation, and unsmooth motion speed. In this regard, modern CNC machine tools are designed with a function for machining arbitrary parametric curves. However, these systems do not consider controlling feedrate adaptively, which dominates the quality of the machining process. This paper proposes a NURBS interpolator based on the adaptive feedrate control for the constant material removal rate. This is accomplished by varying feedrate using the curvature of a surface. The curvature-compensated feedrate system has important potential applications in ensuring part accuracy and protecting the cutting tool. The simulated and experimental results show it is applicable to real machining.

On the Chandler wobble. I. Theory

This paper introduces the idea that there exists a nutation separation layer in the superficial zone of the Earth, thereby sets up a new model of nutation. The equations of motion are derived and solved. It is proved that the separation layer is “soft”, and is probably located at a depth of 300 km from the surface. Its allowable minimum thickness is less than 1 km and its viscosity is on the order of 10 10 poise, like pitch at 15 °C. The results show that the main peak of the Chandler wobble (CW) is double, one being the nutational frequency of the inner main body, the other , the outer component. The beat between the two frequencies produces the 40-yr period in the amplitude of the CW. The two amplitudes interact so they do not differ greatly in size, their approximate ratio being 1 to 0.7. The famous amplitude-period relation of the CW is a direct result of this paper. The sudden changes in the polar trace and the 180° phase change in 1924–1926 are essentially the same phenomenon determined by relative changes in the two frequencies. The value of Q for the CW of between 30 and 60 deduced by previous workers from observations is a false Q, the true Q is around 200, in agreement with the value from seismic waves. This paper also predicts that apart from the two main frequencies, there is a series (more than one pair) of secondary frequencies symmetrically located on either side. The time constant of the CW is about 70 yr and it can be approximately maintained by excitation by earthquakes. Its unsmooth motion is one that zigzags about the mean trace.