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Industrial robots are important components in the production and manufacturing industry. As a core component of the industrial robot, the industrial robot reducer plays a crucial role in the performance of the entire industrial robot. The error analysis and accuracy traceability of the industrial robot reducer testing instrument are of great significance in improving the quality of the precision reducer. Therefore, it is essential to calibrate the dynamic torsional moment measurement error of the instrument. The features of the dynamic torsional moment measurement error are analyzed in this paper. Based on these features, a new dynamic torsional moment measurement error calibration method is proposed based on the Bisquare curve fitting-improved Bayes particle swarm optimization-nonlinear echo state network (BCF-IBPSO-NESN) algorithm. The proposed method focuses on calibrating the dynamic torsional moment measurement error of the industrial robot reducers in real time. The experimental results show that the dynamic torsional moment measurement error of the input side torsional moment measurement module and the output side torsional moment measurement module can be reduced to ±0.05 Nm and ±1 Nm, respectively. The contribution of this paper is that the method calibrates the dynamic torsional moment measurement error. It supplies a guideline for calibrating the dynamic torsional moment measurement error of the instrument under any load.

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The analytical results of normal contact stiffness for mechanical joint surfaces are quite different from the experimental data. So, this paper proposes an analytical model based on parabolic cylindrical asperity that considers the micro-topography of machined surfaces and how they were made. First, the topography of a machined surface was considered. Then, the parabolic cylindrical asperity and Gaussian distribution were used to create a hypothetical surface that better matches the real topography. Second, based on the hypothetical surface, the relationship between indentation depth and contact force in the elastic, elastoplastic, and plastic deformation intervals of the asperity was recalculated, and the theoretical analytical model of normal contact stiffness was obtained. Finally, an experimental test platform was then constructed, and the numerical simulation results were compared with the experimental results. At the same time, the numerical simulation results of the proposed model, the J. A. Greenwood and J. B. P. Williamson (GW) model, the W. R. Chang, I. Etsion, and D. B. Bogy (CEB) model, and the L. Kogut and I. Etsion (KE) model were compared with the experimental results. The results show that when roughness is Sa 1.6 µm, the maximum relative errors are 2.56%, 157.9%, 134%, and 90.3%, respectively. When roughness is Sa 3.2 µm, the maximum relative errors are 2.92%, 152.4%, 108.4%, and 75.1%, respectively. When roughness is Sa 4.5 µm, the maximum relative errors are 2.89%, 158.07%, 68.4%, and 46.13%, respectively. When roughness is Sa 5.8 µm, the maximum relative errors are 2.89%, 201.57%, 110.26%, and 73.18%, respectively. The comparison results demonstrate that the suggested model is accurate. This new method for examining the contact characteristics of mechanical joint surfaces uses the proposed model in conjunction with a micro-topography examination of an actual machined surface.

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A novel simulation method of microtopography for grinding surface was proposed in this paper. Based on the theory of wavelet analysis, multiscale decomposition of the measured topography was conducted. The topography was divided into high frequency band (HFB), theoretical frequency band (TFB), and low frequency band (LFB) by wavelet energy method. The high-frequency and the low-frequency topography were extracted to obtain the digital combination model. Combined with the digital combination model and the theoretical topography obtained by geometric simulation method, the simulation topography of grinding surface can be generated. Moreover, the roughness parameters of the measured topography and the simulation topography under different machining parameters were compared. The maximum relative error of Sa, Sq, Ssk and Sku were 1.79%, 2.24%, 4.69% and 4.73%, respectively, which verifies the feasibility and accuracy of the presented method.

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Lithium-ion capacitors (LICs) have been widely explored for energy storage. Nevertheless, achieving good energy density, satisfactory power density, and stable cycle life is still challenging. For this study, we fabricated a novel LIC with a NiO-rGO composite as a negative material and commercial activated carbon (AC) as a positive material for energy storage. The NiO-rGO//AC system utilizes NiO nanoparticles uniformly distributed in rGO to achieve a high specific capacity (with a current density of 0.5 A g-1 and a charge capacity of 945.8 mA h g-1) and uses AC to provide a large specific surface area and adjustable pore structure, thereby achieving excellent electrochemical performance. In detail, the NiO-rGO//AC system (with a mass ratio of 1:3) can achieve a high energy density (98.15 W h kg-1), a high power density (10.94 kW kg-1), and a long cycle life (with 72.1% capacity retention after 10,000 cycles). This study outlines a new option for the manufacture of LIC devices that feature both high energy and high power densities.

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Contact stiffness is an important parameter for describing the contact behavior of rough surfaces. In this study, to more accurately describe the contact stiffness between grinding surfaces of steel materials, a novel microcontact stiffness model is proposed. In this model, the novel cosine curve-shaped asperity and the conventional Gauss distribution are used to develop a simulated rough surface. Based on this simulated rough surface, the analytical expression of the microcontact stiffness model is obtained using contact mechanics theory and statistical theory. Finally, an experimental study of the contact stiffness of rough surfaces was conducted on different steel materials of various levels of roughness. The comparison results reveal that the prediction results of the present model show the same trend as that of the experimental results; the contact stiffness increases with increasing contact pressure. Under the same contact pressure, the present model is closer to the experimental results than the already existing elastic-plastic contact (CEB) and finite-element microcontact stiffness (KE) models, whose hypothesis of a single asperity is hemispherical. In addition, under the same contact pressure, the contact stiffness of the same steel material decreases with increasing roughness, whereas the contact stiffness values of different steel materials under the same roughness show only small differences. The correctness and accuracy of the present model can be demonstrated by analyzing the measured asperity geometry of steel materials and experimental results.

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The aims of this study were to predict and explain the patterns of ligament forces in the stump of a left trans-tibial amputee during walking, and to study the effects of the prosthetic alignment. Musculoskeletal modeling and computer simulation were combined to calculate ligament forces. The prosthesis was aligned to be in optimal position for the subject and then changed by +/-6 degrees in the sagittal plane. The results showed most ligaments bearing the maximum tension forces around both heel-strike and toe-off. The PT force was the biggest in all of the ligaments which were studied. The load patterns of ACL and PCL were opposite in the gait cycle, but the load patterns of MCL and LCL appeared similar. The above results showed that the ligament forces increased at the incorrect alignment, because the incorrect alignment could break the relative translation of the femur and tibia, and that would generate the extra ligament strains. As a result, the ligament forces increased, and the long-duration fatigue occurred more easily. This finding suggests that the proper prosthetic alignment is very important for the normal activities of the stump ligaments.

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PURPOSE: To assess the mechanical behaviour at interface for unilateral transtibial amputees during walking when the prosthesis is misaligned, since studies examining interface pressure between residual limb and prosthetic socket have been restricted to unsupported stance and natural gait. METHOD: One male subject with transtibial amputation volunteers for the study. Interface pressures over five sites are measured under three sagittal alignment settings. MP (mean peak interface pressure), TP(90+) (time in which pressure exceeded 90% of peak pressure) and TPI(90+) (time-pressure integral at the period of sustained sub-maximal load) are discussed for each alignment setting. RESULTS: Compared with optimal alignment, the trend of interface pressure, the mean peak pressure do not change much,but the duration of sub-maximal pressure changes remarkably, except that at the patellar tendon, and finally the TPI(90+) changes considerably with different alignment settings. CONCLUSIONS: The results offer the clinician and paramedical staff further insight in residual limb/socket interface mechanics in the transtibial amputation patients and provide potentially useful information for socket design and prosthesis fitting.

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BACKGROUND: Studies examining the stump/socket interface stresses have been restricted to unsupported stance and natural gait, i.e. walking at a comfortable speed on flat and straight walkway. However, the pressure behaviour as to the interface in unilateral transtibial amputees during walking on stairs, slope and non-flat road is unclear. METHODS: Pressure distribution changes at multiple points, expressed as mean peak stump/socket interface pressure, mean pressure level over 90% of peak pressure, time in which pressure exceeded 90% of peak pressure and time-pressure integral at the period of sustained sub-maximal load, were measured during natural ambulating and walking on stairs, slope and non-flat road. FINDINGS: Compared with natural gait, the mean peak pressure and sustained sub-maximal load increase notably over the patellar tendon during walking on stairs and non-flat road, and however decrease or change insignificantly at the patellar tendon on slope and over other measured areas in all conditions; moreover the time period of sustained sub-maximal load changes remarkably, except over the patellar tendon during walking up slope and over the popliteal area on non-flat road; finally, the time-pressure integral in the time period of sustained sub-maximal load changes considerably, except at the patellar tendon during walking up slope. INTERPRETATION: The pressure characteristics during natural ambulating seem not to be highly predictive of what occurs in the conditions of walking on stairs, slope and non-flat road, which leads to significant increase in amplitude domain of tissue loading only at the patellar tendon, and however to remarkable changes in temporal sequences of tissue (un-)loading almost in all measured regions.

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