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Mechanical and Chemical Properties at High Temperature of {M-25Cr}-based Alloys Containing Hafnium Carbides (M=Co, Ni or Fe): Creep Behavior and Oxidation at 1200°C
Full text linkThis study concerns three alloys based on cobalt, nickel or iron, all containing chromium (25 wt.%), carbon and hafnium. The contents in the two last elements were chosen high enough to promote the formation of HfC carbides. All alloys were elaborated by casting and their microstructures preliminarily characterized. They were selected to be tested in three-points flexural creep at 1200°C under 20 MPa in inert atmosphere. All alloys contain hafnium carbides, together with chromium carbides in some cases. The HfC carbides are generally of two types: script-like eutectic and blocky pre-eutectic. The creep deformation is fast for the nickel-based and iron-based alloys, especially for the later one. In contrast the HfC-containing cobalt-based alloy behaves much better. It displays a creep resistance at 1200°C significantly higher than another cobalt-based alloy strengthened by chromium carbides added to the study for comparison. All alloys were also briefly tested in oxidation by air at 1200°C. The creep behaviors of the cobalt-based and iron-based alloys are not good and significantly worse than the nickel-based alloy’s one. The oxidation resistance of the HfC-strengthened cobalt-based alloy must be improved to take benefit of its superior creep strength
Optimizing the Updating Stopping Condition for a Predictive Maintenance Policy
Full text linkThe updating stopping condition (USC) has great impact on the effectiveness of a predictive maintenance (PdM) policy, but did not receive enough attention. This paper reviews the common USCs, proposes a residual life based USC, and evaluates the influence of the USCs on the effectiveness of a PdM policy. The commonly used USCs are concretely defined in a PdM policy based on the stochastic linear degradation model. An extensive numerical investigation compares the performances of the PdM policy using different USCs. The investigation results verify the importance of optimizing the USC for a PdM policy
A Modified Optimal Control Strategy for a Five-Finger Robotic
Full text linkThis paper addresses a modified optimal control strategy for a 14-degrees-of-freedom, five-finger robotic hand to improve accuracy and reduce convergence time by modifying the performance index embedded with an exponential term. First, the trajectory planning of the joints of each finger is designed by using cubic polynomial. Then the kinematic and dynamic equations of the robotic hand and feedback linearization technique are employed. Next, the original and modified optimal control methods are applied to the robotic hand. Finally, simulations show that the proposed modified optimal control technique provides much faster response with high accuracy compared to a hybrid genetic algorithm-tuned PID control
Weight Reduction: A Typical Issue in the Mechanical Design of Robotic Systems
Full text linkThis paper illustrates the importance of weight reduction in the mechanical design of robotic systems. Safety and power consumption are the important aspects that deal with the reduction of robot weight for practical applications in the human being environment. A novel approach has been assumed in order to avoid these problems keeping the lightweight of the structure. The weight reduction of the mechanical structure helps to obtain final solutions with feasible characteristics of compactness, robustness and stiffness. These ideas will be explained via several examples. The design process of a new arm has been reported from the study of the mechanical details of a built prototype that presents unsuitable weight. Toques of actuating joints have been checked, at the end of the design process, by developing dynamic simulations of robot operations in order to validate the proposed approach
Fault Diagnosis of Linear Control Systems Based on the Discrete Wavelet Transform and an ART2 Neural Network
Full text linkFault detection and isolation of systems continues to be important problems to be addressed due to the increased complexities of more advanced systems. Early detection and isolation of faults can assist in avoidance of major system breakdowns. Many methods require some model of the plant in order to perform the fault diagnosis. In this paper we present a fault diagnosis method for dynamic systems based on discrete wavelet transform (DWT) and an adaptive resonance theory 2 neural network (ART2 NN). In the proposed method a fault is detected when an error between the system output and the nominal system output cross a predetermined threshold. Once a fault in the system is detected the ART2 NN based fault classifier isolates the fault. The algorithm contains three main steps: fault detection through the threshold test, data preprocessing via DWT, and fault isolation using the fault classifier. The simulation results demonstrate the effectiveness of the proposed DWT and ART2 NN based fault diagnosis method
A Survey on Recent Development of Large-Stroke Compliant Micropositioning Stage
Full text linkCompliant micropositioning mechanism plays an important role in precise positioning and alignment applications. Unlike conventional guiding mechanism, compliant mechanism delivers motion through the deformation of flexible components. As a result, the movement of flexible mechanism is continuous and the structure is more compact, which makes it a hot research topic in the field of precision machine design. As the increase of demands for micropositioning stage providing large motion range and high precision, this paper conducts a state-of-the-art survey on recent development on large-stoke compliant microopsitioning stages. First, a basic introduction of the compliant micropositioning stage is presented. The type synthesis and mechanism structure design of the flexible component are reported, which are the decisive factors determining the stage performance. Then, the design method of flexure hinge is introduced. Afterwards, the development of large-stroke compliant mechanism in recent years is reviewed, and a comparison study of several typical large-stroke compliant micropositioning stage is carried out. The existing issues and future work on the large-stroke compliant micropositioning stage are summarized
In-Situ AlN Induced Valence State Variation of V in Vanadium Oxide Films Investigated by XPS
Full text linkVanadium oxide (VOx) thin films with and without in situ AlN layer were grown on single crystal sapphire substrates by pulsed laser deposition (PLD) with V2O5 target. The significant structure and morphology transforms resulted from the insertion of in-situ AlN layer were observed by X-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM). To interpret the mechanism behind these phenomena, the valence state variation of vanadium (V) in VOx films induced by in-situ AlN layer was investigated by X-ray photoelectron spectroscopy (XPS) analyses. The results indicated that the valence state of V become more complicated and VOx films with the mixed V valence state of V5+,V4+and V3+ were obtained due to the introduction of AlN interfacial stress layer. Our achievements will be helpful for understanding the physical mechanism behind the exotic characteristics of VOx films induced by stress layer