scholarly journals Modeling Dynamic Ankle Mechanical Impedance in Relaxed Muscle

2011 ◽  
Author(s):  
Hyunglae Lee ◽  
Neville Hogan
Keyword(s):  
Estimation Method ◽  
Frontal Plane ◽  
Mechanical Impedance ◽  
Standing Position ◽  
Order Model ◽  
Hill Model ◽  
Complex Zero ◽  
Ankle Impedance ◽  
Limb Posture ◽  
Better Than

This paper presents identification and modeling of dynamic ankle mechanical impedance in relaxed muscles. A multi-variable estimation method using a wearable therapeutic robot enabled clear interpretation of dynamic ankle impedance both in the sagittal and frontal planes. Estimation results showed that dynamic ankle behavior apparently cannot be reconciled with a simple 2nd order model. Measurements in a seated and standing position verified that ankle impedance changes substantially depending on lower-limb posture. Identification results were fitted with a modified Hill model with a mass between the muscle and tendon elements. When coupled with foot inertia, either singly or antagonistically, this model successfully captured the dynamic behavior of the ankle impedance both in the seated and standing positions up to 20 Hz. At least a 4th order model having 2 complex zero and 1 complex pole pairs was required to describe relaxed ankle impedance either in the sagittal or frontal plane up to 20Hz. In the seated position, a 6th order model was slightly better than the 4th order model but with the expense of complexity, and a 8th order model might be used to describe dynamic ankle behavior up to 30∼40Hz.

Instrumented Walkway for Estimation of the Ankle Impedance in Dorsiflexion-Plantarflexion and Inversion-Eversion During Standing and Walking

2015 ◽  
Author(s):  
Evandro M. Ficanha ◽  
Guilherme Ribeiro ◽  
Mohammad Rastgaar Aagaah
Keyword(s):  
Degrees Of Freedom ◽  
Force Plate ◽  
Mechanical Impedance ◽  
Standing Position ◽  
Camera System ◽  
Ankle Impedance ◽  
System A ◽  
Human Ankle ◽  
Applied Forces ◽  
And Inversion

This paper describes in detail the fabrication of an instrumented walkway for estimation of the ankle mechanical impedance in both dorsiflexion-plantarflexion (DP) and in inversion-eversion (IE) directions during walking in arbitrary directions and standing. The platform consists of two linear actuators, each capable of generating ±351.3 N peak force that are mechanically coupled to a force plate using Bowden cables. The applied forces cause the force plate to rotate in two degrees of freedom (DOF) and transfer torques to the human ankle to generate DP and IE rotations. The relative rotational motion of the foot with respect to the shin is recorded using a motion capture camera system while the forces applied to the foot are measured with the force plate, from which the torques applied to the ankle are calculated. The analytical methods required for the estimation of the ankle torques, rotations, and impedances are presented. To validate the system, a mockup with known stiffness was used, and it was shown that the developed system was capable of properly estimating the stiffness of the mockup in two DOF with less than 5% error. Also, a preliminary experiment with a human subject in standing position was performed, and the estimated quasi-static impedance of the ankle was estimated at 319 Nm/rad in DP and 119 Nm/rad in IE.

scholarly journals UAV Based Estimation of Forest Leaf Area Index (LAI) through Oblique Photogrammetry

2021 ◽  
Vol 13 (4) ◽  
pp. 803
Author(s):  
Lingchen Lin ◽  
Kunyong Yu ◽  
Xiong Yao ◽  
Yangbo Deng ◽  
Zhenbang Hao ◽  
...  
Keyword(s):  
Leaf Area Index ◽  
Leaf Area ◽  
Point Cloud ◽  
Forest Canopy ◽  
Estimation Method ◽  
Vertical Direction ◽  
Estimation Accuracy ◽  
3D Point Cloud ◽  
Area Index ◽  
Better Than

As a key canopy structure parameter, the estimation method of the Leaf Area Index (LAI) has always attracted attention. To explore a potential method to estimate forest LAI from 3D point cloud at low cost, we took photos from different angles of the drone and set five schemes (O (0°), T15 (15°), T30 (30°), OT15 (0° and 15°) and OT30 (0° and 30°)), which were used to reconstruct 3D point cloud of forest canopy based on photogrammetry. Subsequently, the LAI values and the leaf area distribution in the vertical direction derived from five schemes were calculated based on the voxelized model. Our results show that the serious lack of leaf area in the middle and lower layers determines that the LAI estimate of O is inaccurate. For oblique photogrammetry, schemes with 30° photos always provided better LAI estimates than schemes with 15° photos (T30 better than T15, OT30 better than OT15), mainly reflected in the lower part of the canopy, which is particularly obvious in low-LAI areas. The overall structure of the single-tilt angle scheme (T15, T30) was relatively complete, but the rough point cloud details could not reflect the actual situation of LAI well. Multi-angle schemes (OT15, OT30) provided excellent leaf area estimation (OT15: R2 = 0.8225, RMSE = 0.3334 m2/m2; OT30: R2 = 0.9119, RMSE = 0.1790 m2/m2). OT30 provided the best LAI estimation accuracy at a sub-voxel size of 0.09 m and the best checkpoint accuracy (OT30: RMSE [H] = 0.2917 m, RMSE [V] = 0.1797 m). The results highlight that coupling oblique photography and nadiral photography can be an effective solution to estimate forest LAI.

Physical fitness of rhythmic gymnasts depending on age and level of sports achievements

2020 ◽  
Vol 30 (91) ◽  
pp. 29-36
Author(s):  
Katarzyna Sterkowicz-Przybycień ◽  
Paula Fundament
Keyword(s):  
Physical Fitness ◽  
Body Height ◽  
Age Groups ◽  
Standing Position ◽  
Time Duration ◽  
Balance Test ◽  
Eyes Closed ◽  
Fitness Tests ◽  
Rhythmic Gymnasts ◽  
Better Than

Aim. The aim of this study was to compare the indices of physical development, frequency and time duration of training, and the results of physical fitness tests depending on age and level of sports achievements among rhythmic gymnasts. Materials and methods. The study comprised 36 rhythmic gymnasts: Gr1 (n=13, 9.0±1.0 years), Gr2 (n=11, 11.36±0.5 years), Gr3 (n=12, 14.27±0.7 years). After standardised sports interview, the groups with lower level of sports achievements (LSL) (n=20) and higher level of sports achievements (HSL) (n=16) were defined. Measurements of body height and mass were performed. The study participants performed the broad jump test, Unipedal Stance Test with Eyes Open (UPST-EO) and Eyes Closed (EC), and the rhythmic gymnastics specific coordinative test with a hoop. Results. The number of training sessions per week and their duration did not depend on age. The results of the broad jump were significantly different for groups Gr1, Gr2 and Gr3 (F=27.02, p<0.01). The average results for the 3 trials of UPST-EO in Gr2 and Gr3 were better than in Gr1 (F=5.51, p=0.008). The average result of UPST-EC for Gr3 was also significantly better than for Gr1 (W=9.53, p=0.008). The hoop test showed differences for all age groups Gr1<Gr3<Gr2 (F=11.55, p<0.001). HSL athletes were significantly different from LSL in frequency and duration of training, average results from 3 trials of UPST-EO, UPSTEC and the best result of UPST-EC (p<0.05). Conclusions. Differences between groups in physical fitness tests results depended on gymnasts’ age and showed their usefulness in the control of training at a particular stage of sports development. HSL gymnasts predominated over LSL in results of the one-leg standing position postural balance test with eyes opened and closed. The detected differences can be useful for coaches in identifying and developing gymnastic talent.

scholarly journals Interpretation of the Directional Properties of Voluntarily Modulated Human Ankle Mechanical Impedance

2010 ◽  
Author(s):  
Patrick Ho ◽  
Hyunglae Lee ◽  
Mohammad A. Rastgaar ◽  
Hermano Igo Krebs ◽  
Neville Hogan
Keyword(s):  
Muscle Activation ◽  
Mechanical Impedance ◽  
In Vivo Studies ◽  
General Representation ◽  
Quantitative Characterization ◽  
Ankle Impedance ◽  
Human Ankle ◽  
Electromyographic Recording

This article presents the results of two in-vivo studies providing measurements of human static ankle mechanical impedance. Accurate measurements of ankle impedance when muscles were voluntarily activated were obtained using a therapeutic robot, Anklebot, and an electromyographic recording system. Important features of ankle impedance, and their variation with muscle activity, are discussed, including magnitude, symmetry and directions of minimum and maximum impedance. Voluntary muscle activation has a significant impact on ankle impedance, increasing it by up to a factor of three in our experiments. Furthermore, significant asymmetries and deviations from a linear two-spring model are present in many subjects, indicating that ankle impedance has a complex and individually idiosyncratic structure. We propose the use of Fourier series as a general representation, providing both insight and a precise quantitative characterization of human static ankle impedance.

scholarly journals A New Flexible Version of the Lomax Distribution with Applications

2018 ◽  
Vol 7 (5) ◽  
pp. 120
Author(s):  
T. H. M. Abouelmagd
Keyword(s):  
Estimation Method ◽  
Good Alternative ◽  
Model Parameters ◽  
Data Sets ◽  
Suitable Model ◽  
Lifetime Data ◽  
New Model ◽  
The Right ◽  
New Distribution ◽  
Better Than

A new version of the Lomax model is introduced andstudied. The major justification for the practicality of the new model isbased on the wider use of the Lomax model. We are also motivated tointroduce the new model since the density of the new distribution exhibitsvarious important shapes such as the unimodal, the right skewed and the leftskewed. The new model can be viewed as a mixture of the exponentiated Lomaxdistribution. It can also be considered as a suitable model for fitting thesymmetric, left skewed, right skewed, and unimodal data sets. The maximumlikelihood estimation method is used to estimate the model parameters. Weprove empirically the importance and flexibility of the new model inmodeling two types of aircraft windshield lifetime data sets. The proposedlifetime model is much better than gamma Lomax, exponentiated Lomax, Lomaxand beta Lomax models so the new distribution is a good alternative to thesemodels in modeling aircraft windshield data.

A Modified DFT-Based Channel Estimation Method for OFDM-RoF System

2014 ◽  
Vol 989-994 ◽  
pp. 3521-3525
Author(s):  
Li Qun Huang ◽  
Peng Zhang ◽  
Guang Yang
Keyword(s):  
Channel Estimation ◽  
High Frequency ◽  
Estimation Method ◽  
Frequency Component ◽  
High Frequency Component ◽  
Improved Method ◽  
Frequency Components ◽  
Influence Of Noise ◽  
Changing Rate ◽  
Better Than

In this paper, we present a modified discrete Fourier transform (DFT)-based channel estimation method. The conventional DFT-based method will produce additional high frequency component in the channel impulse response, and degrade the accuracy of channel estimation. The modified algorithm can eliminate additional high frequency components by extending the LS estimate in frequency domain with a symmetric signal of its own, and selects the useful paths by calculating the changing rate of energy. Thus, the proposed algorithm become more accurate. The simulation results show the new algorithm can reduce the influence of noise on channel estimation efficiently, and the performance of the improved method is better than the LS and conventional DFT algorithm.

Stochastic Estimation of Human Ankle Mechanical Impedance in Lateral/Medial Rotation

2014 ◽  
Author(s):  
Evandro M. Ficanha ◽  
Mohammad Rastgaar
Keyword(s):  
Degrees Of Freedom ◽  
Muscle Activation ◽  
Transfer Functions ◽  
Linear Time ◽  
Mechanical Impedance ◽  
Linear Time Invariant ◽  
Ankle Impedance ◽  
Human Ankle ◽  
Medial Rotation ◽  
The Difference

This article compares stochastic estimates of human ankle mechanical impedance when ankle muscles were fully relaxed and co-contracting antagonistically. We employed Anklebot, a rehabilitation robot for the ankle to provide torque perturbations. Surface electromyography (EMG) was used to monitor muscle activation levels and these EMG signals were displayed to subjects who attempted to maintain them constant. Time histories of ankle torques and angles in the lateral/medial (LM) directions were recorded. The results also compared with the ankle impedance in inversion-eversion (IE) and dorsiflexion-plantarflexion (DP). Linear time-invariant transfer functions between the measured torques and angles were estimated for the Anklebot alone and when a human subject wore it; the difference between these functions provided an estimate of ankle mechanical impedance. High coherence was observed over a frequency range up to 30 Hz. The main effect of muscle activation was to increase the magnitude of ankle mechanical impedance in all degrees of freedom of ankle.

A Height Estimation Method Based on Joint Time Delay and Phase Estimation for Wideband InSAR or InSAS

2012 ◽  
Vol 605-607 ◽  
pp. 1105-1109
Author(s):  
Sen Zhang ◽  
Jin Song Tang ◽  
He Ping Zhong
Keyword(s):  
Time Delay ◽  
Cross Correlation ◽  
Estimation Method ◽  
Simulated Data ◽  
Time Delay Estimation ◽  
Phase Estimation ◽  
Height Estimation ◽  
Common Information ◽  
Correlation Estimation ◽  
Better Than

In this paper, a new height estimation method based on joint time delay and phase estimation is proposed, which can solve the contradiction between the dimensions of the observing space and the hypothesis of spatial stationarity. It can improve the performance and robustness of time delay estimation by utilizing the neighboring pixels’ common information though spatial processing. The simulated data varifies the perfermance of the proposed method. The result is that its performance is better than the cross correlation estimation method.

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