Force Control Strategy of Five-Digit Precision Grasping With Aligned and Unaligned Configurations

Objective To investigate the digit force control during a five-digit precision grasp in aligned (AG) and unaligned grasping (UG) configurations. Background The effects of various cylindrical handles for tools on power grasp performance have been previously investigated. However, there is little information on force control strategy of precision grasp to fit various grasping configurations. Method Twenty healthy young adults were recruited to perform a lift-hold-lower task. The AG and UG configurations on a cylindrical simulator with force transducers were adjusted for each individual. The applied force and moment, the force variability during holding, and force correlations between thumb and each finger were measured. Result No differences in applied force, force correlation, repeatability, and variability were found between configurations. However, the moments applied in UG were significantly larger than those in AG. Conclusion The force control during precision grasp did not change significantly across AG and UG except for the digit moment. The simulator is controlled efficiently with large moment during UG, which is thus the optimal configuration for precision grasping with a cylindrical handle. Further research should consider the effects of task type and handle design on force control, especially for individuals with hand disorders. Application To design the handle of specific tool, one should consider the appropriate configuration according to the task requirements of precision grasping to reduce the risk of accumulating extra loads on digits with a cylindrical handle.

Force Myography-Based Human Robot Interactions via Deep Domain Adaptation and Generalization

Estimating applied force using force myography (FMG) technique can be effective in human-robot interactions (HRI) using data-driven models. A model predicts well when adequate training and evaluation are observed in same session, which is sometimes time consuming and impractical. In real scenarios, a pretrained transfer learning model predicting forces quickly once fine-tuned to target distribution would be a favorable choice and hence needs to be examined. Therefore, in this study a unified supervised FMG-based deep transfer learner (SFMG-DTL) model using CNN architecture was pretrained with multiple sessions FMG source data (Ds, Ts) and evaluated in estimating forces in separate target domains (Dt, Tt) via supervised domain adaptation (SDA) and supervised domain generalization (SDG). For SDA, case (i) intra-subject evaluation (Ds ≠ Dt-SDA, Ts ≈ Tt-SDA) was examined, while for SDG, case (ii) cross-subject evaluation (Ds ≠ Dt-SDG, Ts ≠ Tt-SDG) was examined. Fine tuning with few “target training data” calibrated the model effectively towards target adaptation. The proposed SFMG-DTL model performed better with higher estimation accuracies and lower errors (R2 ≥ 88%, NRMSE ≤ 0.6) in both cases. These results reveal that interactive force estimations via transfer learning will improve daily HRI experiences where “target training data” is limited, or faster adaptation is required.

Quantitative Assessment of Clinician Assistance During Dynamic Rehabilitation Using Force Sensitive Resistors

Background: Neuromodulation using epidural electrical stimulation (EES) has shown functional restoration in humans with chronic spinal cord injury (SCI). EES during body weight supported treadmill training (BWSTT) enhanced stepping performance in clinical trial participants with paraplegia. Unfortunately, tools are lacking in availability to quantify clinician assistance during BWSTT with and without EES. Force sensitive resistors (FSRs) have previously quantified clinician assistance during static standing; however, dynamic tasks have not been addressed.Objective: To determine the validity of FSRs in measurements of force and duration to quantify clinician assistance and participant progression during BWSTT with EES in participants with SCI.Design: A feasibility study to determine the effectiveness of EES to restore function in individuals with SCI.Methods: Two male participants with chronic SCI were enrolled in a pilot phase clinical trial. Following implantation of an EES system in the lumbosacral spinal cord, both participants underwent 12 months of BWSTT with EES. At monthly intervals, FSRs were positioned on participants' knees to quantity forces applied by clinicians to achieve appropriate mechanics of stepping during BWSTT. The FSRs were validated on the benchtop using a leg model instrumented with a multiaxial load cell as the gold standard. The outcomes included clinician-applied force duration measured by FSR sensors and changes in applied forces indicating progression over the course of rehabilitation.Results: The force sensitive resistors validation revealed a proportional bias in their output. Loading required for maximal assist training exceeded the active range of the FSRs but were capable of capturing changes in clinician assist levels. The FSRs were also temporally responsive which increased utility for accurately assessing training contact time. The FSRs readings were able to capture independent stance for both participants by study end. There was minimal to no applied force bilaterally for participant 1 and unilaterally for participant 2.Conclusions: Clinician assistance applied at the knees as measured through FSRs during dynamic rehabilitation and EES (both on and off) effectively detected point of contact and duration of forces; however, it lacks accuracy of magnitude assessment. The reduced contact time measured through FSRs related to increased stance duration, which objectively identified independence in stepping during EES-enabled BWSTT following SCI.

RESULTS OF STATIC TESTS OF PROTECTIVE STRUCTURES OF AGRICULTURAL TRACTORS CABINS

The purpose of research is determination of cabin deformation indicators using standardized methods and developed technical means. Research methods. The tests were performed according to the methods described in [DSTU ISO 5700, 2019] using a loading bench, pressure and displacement sensors, digital measuring amplifier Spider 8 and laptop Panasonic CF-19 Touchbook, model: CF-19KHR88PE. Research results. The protective structure AI.209.45.011.00 of the cab of tractors type C25 "Slobozhanets" was provided for testing. Before the tests, the dimensions of the cab structure were measured and recorded. During the first longitudinal loading from front to right, the load was applied to the upper transverse element of the protective structure. The point of application of the load was at a distance of 260 mm from the outer corner of the edge of the protective structure. An even load distribution in the direction perpendicular to the direction of action and along the loading beam was ensured using a sealing element. The value of the energy absorbed by the protective structure was 13100 J (required energy - 12586 J) with a maximum applied force of 82 kN and a displacement of 340 mm. During the first and second compression tests, the structure was loaded vertically with a force of 180 kN along the front and rear upper transverse elements of the protective structure with a holding of the specified force for 5 s. The side load was applied horizontally to the upper right longitudinal element of the protective structure at a distance of 85 mm forward from the control point of the driver's seat. The length of the loading beam was 600 mm. The value of the energy absorbed by the protective structure of 17000 J (required energy - 15732 J) at a maximum applied force of 80 kN and a displacement of 290 mm was achieved. After all test stages, the frontmost point of the protective structure was 70 mm and the front left point was 35 mm. The rear end points were also shifted backwards by 45 mm - right and 30 mm - left. In the lateral direction, the front right extreme point moved forward by 15 mm. After the tests, the free space area was not violated. Conclusions. The methods and technical means used during the tests allow determine the magnitude of the applied forces and deformation with the necessary accuracy and reliability. During the compression tests, the values of the test force (180 kN) were achieved, and during the application of horizontal loads - the energy absorbed by the protective structure (13100 J - longitudinal load and 17000 J - lateral load). The greatest final deformation was suffered by the protective structure at the front extreme point - 70 mm, while the violation of the zone of free space of the driver by the elements of the protective structure is not observed. Therefore, the protective structure AI.209.45.011.00 cab of tractors type C25 "Slobozhanets" withstood static tests for compliance with DSTU ISO 5700.

Aspects of Force and Acceleration in Special Relativity

In relativistic dynamics, the direction of acceleration is not generally parallel to the direction of force. Both the magnitude and direction of an object’s three-acceleration can alter even when the magnitude of the applied three-force is constant. Graphs of the variation in acceleration and the angles between an object’s velocity, acceleration, and the applied force vectors are presented in order to illustrate the behavior at close to the speed of light.

Intra- and inter-rater reliability of compressed breast thickness, applied force, and pressure distribution in screening mammography

Background Ensuring equivalent and reproducible breast compression between mammographic screening rounds is important for the diagnostic performance of mammography, yet the extent to which screening mammography positioning and compression is reproducible for the individual woman is unknown. Purpose To investigate the intra- and inter-rater reliability of breast compression in screening mammography. Materials and Methods Eleven breast-healthy women participated in the study. Two experienced radiographers independently positioned and compressed the breasts of each participant in two projections—right craniocaudal and left mediolateral oblique—and at two time points. The spatial pressure distribution on the compressed breast was measured using a pressure sensor matrix. Applied force, compressed breast thickness, force in field of view, contact area, mean pressure, and center of mass (anterio-posterior and mediolateral axes) were measured. The reliabilities of the measures between the time points for each radiographer (intra-rater reliability) and between the radiographers (inter-rater reliability) were analyzed using the intraclass correlation coefficient (ICC). Results Intra- and inter-rater reliabilities from both projections demonstrated good to excellent ICCs (≥0.82) for compressed breast thickness, contact area, and anterio-posterior center of mass. The other measures produced ICCs that varied from poor (≤0.42) to excellent (≥0.93) between time points and between radiographers. Conclusion Intra- and inter-rater reliability of breast compression was consistently high for compressed breast thickness, contact area, and anterio-posterior center of mass but low for mediolateral center of mass and applied force. Further research is needed to establish objective and clinically useful parameters for the standardization of breast compression.

Motor memories of object dynamics are categorically organized

The ability to predict the dynamics of objects, linking applied force to motion, underlies our capacity to perform many of the tasks we carry out on a daily basis. Thus, a fundamental question is how the dynamics of the myriad objects we interact with are organized in memory. Using a custom-built three-dimensional robotic interface that allowed us to simulate objects of varying appearance and weight, we examined how participants learned the weights of sets of objects that they repeatedly lifted. We find strong support for the novel hypothesis that motor memories of object dynamics are organized categorically, in terms of families, based on covariation in their visual and mechanical properties. A striking prediction of this hypothesis, supported by our findings and not predicted by standard associative map models, is that outlier objects with weights that deviate from the family-predicted weight will never be learned despite causing repeated lifting errors.

Characterization of variable-sensitivity force sensor using stiffness change of shape-memory polymer based on temperature

In the present study, we propose a variable-sensitivity force sensor using a shape-memory polymer (SMP), the stiffness of which varies according to the temperature. Since the measurement range and sensitivity can be changed, it is not necessary to replace the force sensor to match the measurement target. Shape-memory polymers are often described as two-phase structures comprising a lower-temperature “glassy” hard phase and a higher-temperature “rubbery” soft phase. The relationship between the applied force and the deformation of the SMP changes depending on the temperature. The proposed sensor consists of strain gauges bonded to an SMP bending beam and senses the applied force by measuring the strain. Therefore, the force measurement range and the sensitivity can be changed according to the temperature. In our previous study, we found that a sensor with one strain gauge and a steel plate had a small error and a large sensitivity range. Therefore, in the present study, we miniaturize this type of sensor. Moreover, in order to describe the viscoelastic behavior more accurately, we propose a transfer function using a generalized Maxwell model. We verify the proposed model experimentally and estimated the parameters by system identification. In addition, we realize miniaturization of the sensor and achieve the same performance as in our previous study. It is shown that the proposed transfer function can capture the viscoelastic behavior of the proposed SMP sensor quite well.

The influence of uncertain loading on topology-optimized designs

The design of structures using topology optimization can improve the structural performance and save material, in turn reducing costs. Using a framework of large-scale, three-dimensional topology optimization implemented by the authors in an open-source multiphysical software, we investigate the influence of uncertain loading on the optimized design. Direct differentiation is used to reveal the relationship between displacements and applied force, giving an efficient and effective tool to postprocess optimized topologies. The developed methodology for the assessment of the sensitivity with respect to applied forces is explored using two three-dimensional examples: the classic MBB cantilever and a cableway pylon. The advantages and limitations of this method are discussed.