The effects of an object’s height and weight on force calibration and kinematics when post-stroke and healthy individuals reach and grasp

Impairment in force regulation and motor control impedes the independence of individuals with stroke by limiting their ability to perform daily activities. There is, at present, incomplete information about how individuals with stroke regulate the application of force and control their movement when reaching, grasping, and lifting objects of different weights, located at different heights. In this study, we assess force regulation and kinematics when reaching, grasping, and lifting a cup of two different weights (empty and full), located at three different heights, in a total of 46 participants: 30 sub-acute stroke participants, and 16 healthy individuals. We found that the height of the reached target affects both force calibration and kinematics, while its weight affects only the force calibration when post-stroke and healthy individuals perform a reach-to-grasp task. There was no difference between the two groups in the mean and peak force values. The individuals with stroke had slower, jerkier, less efficient, and more variable movements compared to the control group. This difference was more pronounced with increasing stroke severity. With increasing stroke severity, post-stroke individuals demonstrated altered anticipation and preparation for lifting, which was evident for either cortical lesion side.

Multi-frequency passive and active microrheology with optical tweezers

Optical tweezers have attracted significant attention for microrheological applications, due to the possibility of investigating viscoelastic properties in vivo which are strongly related to the health status and development of biological specimens. In order to use optical tweezers as a microrheological tool, an exact force calibration in the complex system under investigation is required. One of the most promising techniques for optical tweezers calibration in a viscoelastic medium is the so-called active–passive calibration, which allows determining both the trap stiffness and microrheological properties of the medium with the least a-priori knowledge in comparison to the other methods. In this manuscript, we develop an optimization of the active–passive calibration technique performed with a sample stage driving, whose implementation is more straightforward with respect to standard laser driving where two different laser beams are required. We performed microrheological measurements over a broad frequency range in a few seconds implementing an accurate multi-frequency driving of the sample stage. The optical tweezers-based microrheometer was first validated by measuring water, and then exemplarily applied to more viscous medium and subsequently to a viscoelastic solution of methylcellulose in water. The described method paves the way to microrheological precision metrology in biological samples with high temporal- and spatial-resolution allowing for investigation of even short time-scale phenomena.

Theory of Uncertainty Analysis with Application to Naval Hydrodynamics

The modern methodology for quantifying the quality of experimental data is uncertainty analysis. Current methods are reviewed with some examples primarily from naval hydrodynamics. The methods described are applicable to fluids engineering. The history of uncertainty analysis, US and international standards on uncertainty analysis, verification and validation standards for computational fluid dynamics, and instrument calibration are discussed. One important result is that random loading in force calibration can produce a lower uncertainty estimate than sequential loading. Statistically, the calibration results for the slope and intercept are the same for the two methods in the example thrust calibration, but the uncertainty in random loading is factor of three smaller than sequential loading.

Research on static force calibration technology of fatigue test system

The fatigue test system is the main equipment to test the fatigue load performance of anchorage, but for a long time, due to the lack of calibration basis and the lack of effective traceability way, it is unable to calibrate the equipment. This paper analyzes the structure and working principle of the fatigue test system, and determines its measurement technical indicators and requirements through investigation and test verification. The calibration method of static force value is studied and verified by experiments. The uncertainty of static force calibration results is evaluated, and the static force calibration technology of fatigue test system with uncertainty better than 0.50% is formed, which lays a good foundation for the calibration of this kind of equipment.

Calibration of cyclic force with inertial force correction to a fatigue testing machine

The accuracy between a dynamic force and a static force applied on a specimen by a fatigue machine is usually not the same. By establishing physical vibration models of fatigue machines, it is concluded that the error of a cyclic force is mainly caused by the inertial force of the vibration mass between the machine sensor and the specimen. After the inertial force is exactly corrected, the force displayed on the machine would be consistent with the real force on the specimen. A standard dynamic force calibration sensor (DFCS) with an inertial force correction method has been used to do calibration of fatigue testing machines in this paper. Compared with the replica test-piece method, the two calibration results are close to each other.

Investigations on nonlinear deformation phenomena in a force calibration system

Previous investigations show, in force calibration and measurement systems that are based on electromagnetic force compensation (EMFC), deformations of the flexure hinges can cause significant contributions to the uncertainty of the system. A Simulink model of the Planck-Balance 2 (PB2) is established in MATLAB according to the CAD model. <br />The results are compared to simplified analytical models and the results obtained from measurement.