Dynamics of a Ship-Mounted Two-DoF Manipulator Case: Effect of Sea State to the Manipulator Joint Torque

This paper is concerned with the study of the kinematic and kinetic analysis of a slider crank linkage using D'Alembert's principle. The links of the considered mechanism are assumed to be rigid. The analytical solution to observe the motion (displacement, velocity, and acceleration), reactions at each joint, torque required to drive the mechanism and the shaking force have been computed by a computer program written in MATLAB language over one complete revolution of the crank shaft. The results are compared with a finite element simulation carried out by using ANSYS Workbench software and are found to be in good agreement. A graphical method (relative velocity and acceleration method) has been also applied for two phases of the crank shaft (q2 = 10° and 130°). The results obtained from this method (graphical) are compared with those obtained from analytical and numerical method and are found very acceptable. To make the analysis linear the friction force on the joints and sliding interface are neglected. All results, in this work, are obtained when the crank shaft turns at a uniform angular velocity (w2 = 188.5 rad/s) and time dependent gas pressure force on the slider crown.

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GPS Surface Reflection for Ionosphere and Sea State Determination

10.21236/ada624667 ◽

2001 ◽

Author(s):

Stephen J. Katzberg ◽

Lloyd A. Linstrom

Keyword(s):

Sea State ◽

Surface Reflection ◽

State Determination

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Verification of Finger Joint Stiffness Estimation Method With Soft Robotic Actuator

Frontiers in Bioengineering and Biotechnology ◽

10.3389/fbioe.2020.592637 ◽

2020 ◽

Vol 8 ◽

Author(s):

Xiang Qian Shi ◽

Ho Lam Heung ◽

Zhi Qiang Tang ◽

Kai Yu Tong ◽

Zheng Li

Keyword(s):

Estimation Method ◽

Joint Stiffness ◽

Ground Truth ◽

Clinical Score ◽

Metacarpophalangeal Joint ◽

Finger Joint ◽

Joint Torque ◽

Hand Rehabilitation ◽

Stiffness Characteristic ◽

Modified Ashworth Scale

Stroke has been the leading cause of disability due to the induced spasticity in the upper extremity. The constant flexion of spastic fingers following stroke has not been well described. Accurate measurements for joint stiffness help clinicians have a better access to the level of impairment after stroke. Previously, we conducted a method for quantifying the passive finger joint stiffness based on the pressure-angle relationship between the spastic fingers and the soft-elastic composite actuator (SECA). However, it lacks a ground-truth to demonstrate the compatibility between the SECA-facilitated stiffness estimation and standard joint stiffness quantification procedure. In this study, we compare the passive metacarpophalangeal (MCP) joint stiffness measured using the SECA with the results from our designed standalone mechatronics device, which measures the passive metacarpophalangeal joint torque and angle during passive finger rotation. Results obtained from the fitting model that concludes the stiffness characteristic are further compared with the results obtained from SECA-Finger model, as well as the clinical score of Modified Ashworth Scale (MAS) for grading spasticity. These findings suggest the possibility of passive MCP joint stiffness quantification using the soft robotic actuator during the performance of different tasks in hand rehabilitation.

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An Analytical Method for Dynamic Wave-Related Errors of Interferometric SAR Ocean Altimetry under Multiple Sea States

Remote Sensing ◽

10.3390/rs13050986 ◽

2021 ◽

Vol 13 (5) ◽

pp. 986

Author(s):

Yao Chen ◽

Mo Huang ◽

Yuanyuan Zhang ◽

Changyuan Wang ◽

Tao Duan

Keyword(s):

Electromagnetic Scattering ◽

Analytical Method ◽

Wave Spectrum ◽

High Accuracy ◽

Sea State ◽

Error Budget ◽

Ocean Topography ◽

Mean Square Errors ◽

Dynamic Wave ◽

Wide Swath

The spaceborne interferometric synthetic aperture radar (InSAR) is expected to measure the sea surface height (SSH) with high accuracy over a wide swath. Since centimeter-level accuracy is required to monitor the ocean sub-mesoscale dynamics, the high accuracy implies that the altimetric errors should be totally understood and strictly controlled. However, for the dynamic waves, they move randomly all the time, and this will lead to significant altimetric errors. This study proposes an analytical method for the dynamic wave-related errors of InSAR SSH measurement based on the wave spectrum and electromagnetic scattering model. Additionally, the mechanisms of the dynamic wave-related errors of InSAR altimetry are analyzed, and the detailed numerical model is derived. The proposed analytical method is validated with NASA’s Surface Water and Ocean Topography (SWOT) project error budget, and the Root-Mean-Square Errors (RMSEs) are in good agreement (0.2486 and 0.2470 cm on a 0.5 km2 grid, respectively). Instead of analysis for a typical project, the proposed method can be applied to different radar parameters under multiple sea states. The RMSEs of Ka-band under low sea state, moderate sea state, and high sea state are 0.2670, 1.3154, and 6.6361 cm, respectively. Moreover, the RMSEs of X-band and Ku-band are also simulated and presented. The experimental results demonstrate that the dynamic wave-related errors of InSAR altimetry are not sensitive to the frequencies but are sensitive to the sea states. The error compensation method is necessary for moderate and higher sea states for centimetric accuracy requirements. This can provide feasible suggestions on system design and error budget for the future interferometric wide-swath altimeter.

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Upper-Limb Isometric Force Feasible Set: Evaluation of Joint Torque-Based Models

Biomechanics ◽

10.3390/biomechanics1010008 ◽

2021 ◽

Vol 1 (1) ◽

pp. 102-117

Author(s):

Nasser Rezzoug ◽

Vincent Hernandez ◽

Philippe Gorce

Keyword(s):

Upper Limb ◽

Isometric Force ◽

Joint Torque ◽

Force Distribution ◽

Prediction Errors ◽

Feasible Set ◽

Joint Torques ◽

Motor Abilities ◽

Capacity Evaluation ◽

Measured Force

A force capacity evaluation for a given posture may provide better understanding of human motor abilities for applications in sport sciences, rehabilitation and ergonomics. From data on posture and maximum isometric joint torques, the upper-limb force feasible set of the hand was predicted by four models called force ellipsoid, scaled force ellipsoid, force polytope and scaled force polytope, which were compared with a measured force polytope. The volume, shape and force prediction errors were assessed. The scaled ellipsoid underestimated the maximal mean force, and the scaled polytope overestimated it. The scaled force ellipsoid underestimated the volume of the measured force distribution, whereas that of the scaled polytope was not significantly different from the measured distribution but exhibited larger variability. All the models characterized well the elongated shape of the measured force distribution. The angles between the main axes of the modelled ellipsoids and polytopes and that of the measured polytope were compared. The values ranged from 7.3° to 14.3°. Over the entire surface of the force ellipsoid, 39.7% of the points had prediction errors less than 50 N; 33.6% had errors between 50 and 100 N; and 26.8% had errors greater than 100N. For the force polytope, the percentages were 56.2%, 28.3% and 15.4%, respectively.

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