Search

SUMMARY: Rendering of rigid objects with high stiffness while guaranteeing system stability remains a major and challenging issue in haptics. Being a part of the haptic system, the behavior of human operators, represented as the mechanical impedance of arm, has an inevitable influence on system performance. This paper first verified that the human arm impedance can unconsciously be modified through imposing background forces and resist unstable motions arising from external disturbance forces. Then, a reliable impedance tuning (IT) method for improving the stability and performance of haptic systems is proposed, which tunes human arm impedance by superimposing a position-based background force over the traditional haptic workspace. Moreover, an adaptive IT algorithm, adjusting the maximum background force based on the velocity of the human arm, is proposed to achieve a reasonable trade-off between system stability and transparency. Based on a three-degrees-of-freedom haptic device, maximum achievable stiffness and transparency grading experiments are carried out with 12 subjects, which verify the efficacy and advantage of the proposed method. [ABSTRACT FROM AUTHOR]

Plasma sprayed coatings were fabricated from nanostructured yttria-stabilized zirconia powders (n-YSZ) with different crystalline grain sizes, prepared via sintering of nano ZrO 2 -4 mol% Y 2 O 3 powders at different temperatures. The hot corrosion behaviour of both n-YSZ powders and their corresponding coatings with sodium metavanadate (NaVO 3 ) were investigated at 700 °C. During hot corrosion, NaVO 3 reacts with Y 2 O 3 in YSZ to form YVO 4 , leading to a tetragonal to monoclinic destructive phase transformation of YSZ. The crystalline grain size of n-YSZ powders did not affect the hot corrosion mechanisms of both the n-YSZ powders and their corresponding coatings. However, compared with n-YSZ powders, the coatings were more easily corroded, and the coatings formed from starting powders with crystalline grain sizes <30 nm featured better degradation resistance to hot corrosion. [ABSTRACT FROM AUTHOR]

The wear resistance of chromium oxide (Cr 2 O 3 ) coatings could be improved by doping modification and changing the structural scale, etc. In this study, micrometric Cr 2 O 3 coatings were doped with different additives, CeO 2 and Nb 2 O 5 . Moreover, Cr 2 O 3 coatings were deposited from nanostructured feedstock by the combination process of plasma spraying and dry-ice blasting. The correlation between the microstructure, chemical components and tribological properties of plasma-sprayed Cr 2 O 3 -based coatings was discussed based on the investigation of their porosity, hardness and friction behaviors. The results showed that the composite coatings doped with additives exhibited a higher microhardness, corresponding to a lower porosity than pure Cr 2 O 3 coating under the identical plasma-spray condition. CeO 2 constituent was found to improve the wear resistance of Cr 2 O 3 coating while Nb 2 O 5 incorporation corresponds to a steep rise in the friction coefficient. The mismatch of coefficient of thermal expansion (CTE) between Cr 2 O 3 and Nb 2 O 5 lamellae facilitated the origin of fatigue cracks and the formation of microfracture pits. Although the combination process promotes a porosity reduction, the nanostructured Cr 2 O 3 (n-Cr 2 O 3 ) coatings present a lower microhardness than micrometric coatings, due to their loosen microstructure from insufficient plasma power compared to microscaled coatings. The wear mechanisms of both the micro- and nanometric Cr 2 O 3 coatings are fatigue cracks and material transfer. [ABSTRACT FROM AUTHOR]