Early chatter identification based on optimized VMD with multi-band information fusion and compression method in robotic milling process

Undesirable self-excited chatter has always been a typical issue restricting the improvement of robotic milling quality and efficiency.Sensitive chatter identification based on processing signals can prompt operators to adjust the machining process and prevent chatter damage.Compared with the traditional machine tool,the uncertain multiple chatter frequency bands and the band-moving of the chatter frequency in robotic milling process make it more challenging to extract chatter information.This paper proposes a novel method of chatter identification using optimized variational mode decomposition(OVMD)with multi-band information fusion and compression technology(MT).During the robotic milling process,the number of decomposed modes k and the penalty coefficient a are optimized based on the dominant component of frequency scope partition and fitness of the mode center frequency.Moreover,the mayfly optimization algorithm(MA)is employed to obtain the global optimal parameter selection.In order to conquer information collection about the uncertain multiple chatter frequency bands and the band-moving of the chatter frequency in robotic milling process,MT is presented to reduce computation and extract signal characteristics.Finally,the cross entropy of the image(CEI)is proposed as the final chatter indicator to identify the chatter occurrence.The robotic milling experiments are carried out to verify the proposed method,and the results show that it can distinguish the robotic milling condition by extracting the uncertain multiple chatter frequency bands and overcome the band-moving of the chatter frequency in robotic milling process.

Interface construction of NiCo LDH/NiCoS based on the 2D ultrathin nanosheet towards oxygen evolution reaction

Carbon-free hydrogen as a promising clean energy source can be produced with electrocatalysts via water electrolysis.Oxygen evolution reaction(OER)as anodic reaction determines the overall efficiency of water electrolysis due to sluggish OER kinetics.Thus,it’s much desirable to explore the efficient and earth-abundant transition-metal-based OER electrocatalysts with high current density and superior stability for industrial alkaline electrolyzers.Herein,we demonstrate a significant enhancement of OER kinetics with the hybrid electrocatalyst arrays in alkaline via judiciously combining earth-abundant and ultrathin NiCo-based layered double hydroxide(NiCo LDH)nanosheets with nickel cobalt sulfides(NiCoS)with a facile metal-organic framework(MOF)-template-involved surface sulfidation process.The obtained NiCo LDH/NiCoS hybrid arrays exhibits an extremely low OER overpotential of 308 mV at 100 mA·cm^(−2),378 mV at 200 mA·cm^(−2)and 472 mV at 400 mA·cm^(−2)in 1 M KOH solution,respectively.A much low Tafel slope of 48 mV·dec^(−1)can be achieved.Meanwhile,with the current density from 50 to 250 mA·cm^(−2),the NiCo-LDH/NiCoS hybrid arrays can run for 25 h without any degradation.Our results demonstrate that the construction of hybrid arrays with abundant interfaces of NiCo LDH/NiCoS can facilitate OER kinetics via possible modulation of binding energy of O-containing intermediates in alkaline media.The present work would pave the way for the development of lowcost and efficient OER catalysts and industrial application of water alkaline electrolyzers.

Synthesis of Iron-Carbide Nanoparticles:Identification of the Active Phase and Mechanism of Fe-Based Fischer-Tropsch Synthesis

Despite the extensive study of the Fe-based Fischer-Tropsch synthesis(FTS)over the past 90 years,its active phases and reaction mechanisms are still unclear due to the coexistence of metals,oxides,and carbide phases presented under realistic FTS reaction conditions and the complex reaction network involving CO activation,C-C coupling,and methane formation.To address these issues,we successfully synthesized a range of pure-phase iron and iron-carbide nanoparticles(Fe,Fe_(5)C_(2),Fe_(3)C,and Fe_(7)C_(3))for the first time.By using them as the ideal model catalysts on high-pressure transient experiments,we identified unambiguously that all the iron carbides are catalytically active in the FTS reaction while Fe_(5)C_(2) is the most active yet stable carbide phase,consistent with density functional theory(DFT)calculation results.The reaction mechanism and kinetics of Fe-based FTS were further explored on the basis of those model catalysts by means of transient high-pressure stepwise temperature-programmed surface reaction(STPSR)experiments and DFT calculations.Our work provides new insights into the active phase of iron carbides and corresponding FTS reaction mechanism,which is essential for better iron-based catalyst design for FTS reactions.

Adjacent Pt Nanoparticles and Sub-nanometer WO_(x)Clusters Determine Catalytic Isomerization of C_(7)H_(16)

Processes for the isomerization of light alkanes have been commercialized;however,the isomerization of paraffins(C_(n)H_(2n+2),n≥7)remains a challenge.On mesoporous tungsten-zirconia catalyst supported Pt catalysts(Pt/WZrOx),initial isomerization productivity of 5249 moli-C7/molPt/h was obtained for n-heptane reforming at 275°C and 5 bar of hydrogen.