Impedance Modulation and Feedback Corrections in Tracking Targets of Variable Size and Frequency

2006 ◽  
Vol 96 (5) ◽  
pp. 2750-2759 ◽  
Author(s):  
Luc P. J. Selen ◽  
Jaap H. van Dieën ◽  
Peter J. Beek
Keyword(s):  
Mechanical Impedance ◽  
Task Demands ◽  
Target Size ◽  
Movement Variability ◽  
Tracking Accuracy ◽  
Task Execution ◽  
Tracking Errors ◽  
Impedance Modulation ◽  
Movement Frequency ◽  
Stiffness And Damping

Humans are able to adjust the accuracy of their movements to the demands posed by the task at hand. The variability in task execution caused by the inherent noisiness of the neuromuscular system can be tuned to task demands by both feedforward (e.g., impedance modulation) and feedback mechanisms. In this experiment, we studied both mechanisms, using mechanical perturbations to estimate stiffness and damping as indices of impedance modulation and submovement scaling as an index of feedback driven corrections. Eight subjects tracked three differently sized targets (0.0135, 0.0270, and 0.0405 rad) moving at three different frequencies (0.20, 0.25, and 0.33 Hz). Movement variability decreased with both decreasing target size and movement frequency, whereas stiffness and damping increased with decreasing target size, independent of movement frequency. These results are consistent with the theory that mechanical impedance acts as a filter of noisy neuromuscular signals but challenge stochastic theories of motor control that do not account for impedance modulation and only partially for feedback control. Submovements during unperturbed cycles were quantified in terms of their gain, i.e., the slope between their duration and amplitude in the speed profile. Submovement gain decreased with decreasing movement frequency and increasing target size. The results were interpreted to imply that submovement gain is related to observed tracking errors and that those tracking errors are expressed in units of target size. We conclude that impedance and submovement gain modulation contribute additively to tracking accuracy.

scholarly journals Estimation of the Two Degrees-of-Freedom Time-Varying Impedance of the Human Ankle

2018 ◽  
Vol 12 (1) ◽  
Author(s):  
Evandro Ficanha ◽  
Guilherme Ribeiro ◽  
Lauren Knop ◽  
Mo Rastgaar
Keyword(s):  
Degrees Of Freedom ◽  
Mechanical Impedance ◽  
Heel Strike ◽  
Time Varying ◽  
Two Degrees Of Freedom ◽  
Impedance Modulation ◽  
Ankle Stiffness ◽  
Human Ankle ◽  
Stiffness And Damping ◽  
And Inversion

An understanding of the time-varying mechanical impedance of the ankle during walking is fundamental in the design of active ankle-foot prostheses and lower extremity rehabilitation devices. This paper describes the estimation of the time-varying mechanical impedance of the human ankle in both dorsiflexion–plantarflexion (DP) and inversion–eversion (IE) during walking in a straight line. The impedance was estimated using a two degrees-of-freedom (DOF) vibrating platform and instrumented walkway. The perturbations were applied at eight different axes of rotation combining different amounts of DP and IE rotations of four male subjects. The observed stiffness and damping were low at heel strike, increased during the mid-stance, and decreases at push-off. At heel strike, it was observed that both the damping and stiffness were larger in IE than in DP. The maximum average ankle stiffness was 5.43 N·m/rad/kg at 31% of the stance length (SL) when combining plantarflexion and inversion and the minimum average was 1.14 N·m/rad/kg at 7% of the SL when combining dorsiflexion and eversion. The maximum average ankle damping was 0.080 Nms/rad/kg at 38% of the SL when combining plantarflexion and inversion, and the minimum average was 0.016 Nms/rad/kg at 7% of the SL when combining plantarflexion and eversion. From 23% to 93% of the SL, the largest ankle stiffness and damping occurred during the combination of plantarflexion and inversion or dorsiflexion and eversion. These rotations are the resulting motion of the ankle's subtalar joint, suggesting that the role of this joint and the muscles involved in the ankle rotation are significant in the impedance modulation in both DP and IE during gait.

scholarly journals Impedance of the Human Ankle During Standing for Posture Control

2018 ◽  
Author(s):  
G. A. Ribeiro ◽  
E. Ficanha ◽  
L. Knop ◽  
M. Rastgaar
Keyword(s):  
Mechanical Impedance ◽  
Posture Control ◽  
Resultant Force ◽  
Order System ◽  
Time Varying ◽  
Ankle Impedance ◽  
Impedance Modulation ◽  
Human Ankle ◽  
Stiffness And Damping ◽  
Antagonistic Muscles

The stiffness and damping of anatomical joints can be modulated by muscle co-contraction, where antagonistic muscles contract simultaneously, increasing both the joint’s stiffness and damping. In a second order system, the mechanical impedance, or simply impedance, is a function of the system’s inertia, damping, and stiffness. The ankle impedance can be defined as the resultant force due to an external motion perturbation. The impedance modulation of the human ankle is required for stable walking. The estimation of the time-varying impedance modulation of the human ankle is the focus of research by different groups [1,2].

Dynamic Characterization of an Integral Squeeze Film Bearing Support Damper for a Supercritical CO2 Expander

2017 ◽  
Author(s):  
Bugra Ertas ◽  
Adolfo Delgado ◽  
Jeffrey Moore
Keyword(s):  
High Speed ◽  
Dynamic Performance ◽  
Mechanical Impedance ◽  
Squeeze Film ◽  
Fluid Inertia ◽  
Inertia Effects ◽  
Damping Behavior ◽  
Impedance Testing ◽  
Stiffness And Damping ◽  
Onset Of Cavitation

The present work advances experimental results and analytical predictions on the dynamic performance of an integral squeeze film damper (ISFD) for application in a high-speed super-critical CO2 (sCO2) expander. The test campaign focused on conducting controlled orbital motion mechanical impedance testing aimed at extracting stiffness and damping coefficients for varying end seal clearances, excitation frequencies, and vibration amplitudes. In addition to the measurement of stiffness and damping; the testing revealed the onset of cavitation for the ISFD. Results show damping behavior that is constant with vibratory velocity for each end seal clearance case until the onset of cavitation/air ingestion, while the direct stiffness measurement was shown to be linear. Measurable added inertia coefficients were also identified. The predictive model uses an isothermal finite element method to solve for dynamic pressures for an incompressible fluid using a modified Reynolds equation accounting for fluid inertia effects. The predictions revealed good correlation for experimentally measured direct damping, but resulted in grossly overpredicted inertia coefficients when compared to experiments.

Modeling and trajectory tracking control of a two-wheeled mobile robot: Gibbs–Appell and prediction-based approaches

Robotica ◽  
2018 ◽  
Vol 36 (10) ◽  
pp. 1551-1570 ◽  
Author(s):  
Hossein Mirzaeinejad ◽  
Ali Mohammad Shafei
Keyword(s):  
Trajectory Tracking ◽  
Dynamic Models ◽  
Sliding Mode ◽  
Tracking Accuracy ◽  
Wheeled Mobile Robots ◽  
Tracking Errors ◽  
Trajectory Tracking Control ◽  
Control Laws ◽  
Control Approach ◽  
Prediction Time

SUMMARYThis study deals with the problem of trajectory tracking of wheeled mobile robots (WMR's) under non-holonomic constraints and in the presence of model uncertainties. To solve this problem, the kinematic and dynamic models of a WMR are first derived by applying the recursive Gibbs–Appell method. Then, new kinematics- and dynamics-based multivariable controllers are analytically developed by using the predictive control approach. The control laws are optimally derived by minimizing a pointwise quadratic cost function for the predicted tracking errors of the WMR. The main feature of the obtained closed-form control laws is that online optimization is not needed for their implementation. The prediction time, as a free parameter in the control laws, makes it possible to achieve a compromise between tracking accuracy and implementable control inputs. Finally, the performance of the proposed controller is compared with that of a sliding mode controller, reported in the literature, through simulations of some trajectory tracking maneuvers.

scholarly journals Development of a magnetic tracking system for monitoring soil movements induced by geohazards

2019 ◽  
Vol 92 ◽  
pp. 17007 ◽  
Author(s):  
Xiaoyu Chen ◽  
Rolando P. Orense
Keyword(s):  
Magnetic Fields ◽  
Permanent Magnets ◽  
Tracking System ◽  
Soil Liquefaction ◽  
Small Scale ◽  
Interior Point Algorithm ◽  
Tracking Accuracy ◽  
Tracking Errors ◽  
Magnetic Tracking ◽  
Soil Movements

In the study of geotechnical hazards, such as soil liquefaction and landslides, the analysis of soil movements is always one of the major preoccupations. An efficient movement sensing technique requires the tracking of subsurface soil for the purpose of examining the mechanism involved. A magnetic tracking system is therefore proposed, with permanent magnets as trackers and magnetometers as receivers. When permanent magnets, deployed within the soil to serve as excitation sources, move with soil body during a geotechnical event, they generate static magnetic fields whose flux densities are related with the positions and orientations of the magnets. Magnetometers are used as receivers to detect the generated magnetic fields, which can be further used in calculating the magnets' locations and orientations based on appropriately developed algorithms. Comparison between situations where the trackers are exposed to air and embedded within soil was conducted to evaluate the influence of soil (wet and dry) on the tracking accuracy. Also, multi-objective tracking is realized by using the particle swarm optimization (PSO) technique combined with interior-point algorithm. The tracking errors are evaluated and applications of the proposed system in small-scale laboratory tests for geohazards are discussed.

scholarly journals Rotordynamic Force Coefficients of Pocket Damper Seals

2006 ◽  
Vol 128 (4) ◽  
pp. 725-737 ◽  
Author(s):  
B. Ertas ◽  
A. Gamal ◽  
J. Vance
Keyword(s):  
Dynamic Pressure ◽  
Mechanical Impedance ◽  
Experimental Tests ◽  
Impedance Method ◽  
Force Density ◽  
Frequency Dependent ◽  
Force Coefficients ◽  
Cross Axis ◽  
Positive Direct ◽  
Stiffness And Damping

This paper presents measured frequency dependent stiffness and damping coefficients for 12-bladed and 8-bladed pocket damper seals (PDS) subdivided into four different seal configurations. Rotating experimental tests are presented for inlet pressures at 69 bar (1000 psi), a frequency excitation range of 20–300 Hz, and rotor speeds up to 20,200 rpm. The testing method used to determine direct and cross-coupled force coefficients was the mechanical impedance method, which required the measurement of external shaker forces, system accelerations, and motion in two orthogonal directions. In addition to the impedance measurements, dynamic pressure responses were measured for individual seal cavities of the eight-bladed PDS. Results of the frequency dependent force coefficients for the four PDS designs are compared. The conclusions of the tests show that the eight-bladed PDS possessed significantly more positive direct damping and negative direct stiffness than the 12-bladed seal. The results from the dynamic pressure response tests show that the diverging clearance design strongly influences the dynamic pressure phase and force density of the seal cavities. The tests also revealed the measurement of same-sign cross-coupled (cross-axis) stiffness coefficients for all seals, which indicate that the seals do not produce a destabilizing influence on rotor-bearing systems.

scholarly journals Rotordynamic Force Coefficients of Pocket Damper Seals

2006 ◽  
Author(s):  
B. Ertas ◽  
A. Gamal ◽  
J. Vance
Keyword(s):  
Dynamic Pressure ◽  
Mechanical Impedance ◽  
Impedance Method ◽  
Force Density ◽  
Frequency Dependent ◽  
Force Coefficients ◽  
Direct Stiffness ◽  
Cross Axis ◽  
Positive Direct ◽  
Stiffness And Damping

This paper presents measured frequency dependent stiffness and damping coefficients for 12 and 8 bladed pocket damper seals (PDS) subdivided into 4 different seal configurations. Rotating experimental test are presented for inlet pressures at 69 bar (1,000 psi), a frequency excitation range of 20–300 Hz, and rotor speeds up to 20,200 rpm. The testing method used to determine direct and cross-coupled force coefficients was the mechanical impedance method, which required the measurement of external shaker forces, system accelerations, and motion in two orthogonal directions. In addition to the impedance measurements, dynamic pressure responses were measured for individual seal cavities of the 8 bladed PDS. Results of the frequency dependent force coefficients for the 4 PDS designs are compared. The conclusions of the test show that the 8 bladed PDS possessed significantly more positive direct damping and negative direct stiffness than the 12 bladed seal. The results from the dynamic pressure response tests show that the diverging clearance design strongly influences the dynamic pressure phase and force density of the seal cavities. The tests also revealed the measurement of same-sign cross-coupled (cross-axis) stiffness coefficients for all seals, which indicate that the seals do not produce a de-stabilizing influence on rotor-bearing systems.

Radar Target Tracking Error Research Using Kalman Filter-Based Algorithms

2012 ◽  
Vol 239-240 ◽  
pp. 1184-1187
Author(s):  
Qian Long Chai ◽  
Yu Long Bai ◽  
Cun Hui Dong
Keyword(s):  
Kalman Filter ◽  
Target Tracking ◽  
Unscented Kalman Filter ◽  
Tracking Error ◽  
Substantial Effect ◽  
Specific Model ◽  
Radar Target ◽  
Tracking Accuracy ◽  
Tracking Errors ◽  
Radar Systems

The methods of radar target tracking have a substantial effect on the accuracy of the whole radar systems. The basic principles and implementing steps of the Extended Kalman filter (the EKF) and the Unscented Kalman filter (the UKF) are briefly introduced. The main sources of radar observation errors and the limitation of the current methods are analyzed. According to the requirements of tracking a CV target, the EKF and the UKF are used to simulate the experiments by establishing the specific model of radar target tracking. The results show that the tracking errors can be constrained within a certain range and the whole systems also have the high tracking accuracy.

scholarly journals Distributed Adaptive Coordinated Control of Multiple Euler–Lagrange Systems considering Output Constraints and Time Delays

Complexity ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Hongde Qin ◽  
Xiaojia Li ◽  
Yanchao Sun
Keyword(s):  
Coordinated Control ◽  
Tracking Accuracy ◽  
Tracking Errors ◽  
Simulation Experiments ◽  
Control Laws ◽  
The Neural Network ◽  
Output Constraints ◽  
Control Schemes ◽  
Virtual Leader ◽  
Coordinated Tracking

In this paper, we mainly investigate the coordinated tracking control issues of multiple Euler–Lagrange systems considering constant communication delays and output constraints. Firstly, we devise a distributed observer to ensure that every agent can get the information of the virtual leader. In order to handle uncertain problems, the neural network technique is adopted to estimate the unknown dynamics. Then, we utilize an asymmetric barrier Lyapunov function in the control design to guarantee the output errors satisfy the time-varying output constraints. Two distributed adaptive coordinated control schemes are proposed to guarantee that the followers can track the leader accurately. The first scheme makes the tracking errors between followers and leader be uniformly ultimately bounded, and the second scheme further improves the tracking accuracy. Finally, we utilize a group of manipulator networks simulation experiments to verify the validity of the proposed distributed control laws.

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