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Anticipatory muscle activations to coordinate balance and movement during motor transitions: A narrative review
No full textBackground: Maintaining balance while moving isvital forday-to-day activities. Akeychallenge inthe comprehension ofhuman movement istodetermine howmuscles contribute tobalance-movement coordination. Motor transitions, defined asmovements executed between twosteady balance states, areparticularly interesting phases tostudy balance-movement coordination because alarge, discrete change inwhole-body momentum may disturb balance. During voluntarily-initiated motor transitions, anticipatory muscle patterns provide the biomechanical conditions thatarefavourable toboth maintaining balance andexecuting themovement. Research question: What arethemechanical consequences ofanticipatory muscle activations forbalancemovement coordination during voluntarily-initiated motor transitions? Methods: Wereview thebiomechanical contributions oftheanticipatory muscle activations identified inthe literature during four types ofvoluntarily-initiated motor transitions, through theprism ofthree balance mechanisms (‘moving thecentre ofpressure (CoP)’,‘counter-rotating segments’,and‘applying new external force(s)’).Inparticular, weinvestigate howanticipatory muscle activations modulate whole-body centre ofmass acceleration. Results: Weshow thatthemechanical consequences ofanticipatory muscle activations have been extensively described, butmainly using the‘moving theCoP ’ mechanism. Unlike their roleduring steady balance states, both ‘moving theCoP ’ and‘applying new external force(s)’ mechanisms create arequired mechanical instability during theanticipatory phase ofmotor transitions. The‘counter-rotating ’ mechanism may actasastabiliser during motor transitions, butadditional research isneeded toclarify thisassumption. Significance: Thisreview establishes thatmuscle activation processes have different mechanical consequences for balance-movement coordination during theanticipatory phases ofmotor transitions, compared tosteady balance states. Because themechanical instability thatiscreated canleadtofalls, abetter understanding ofthemechanisms underlying motor transitions isneeded toenable thedesign ofmore effective fallprevention programs and/or devices forpopulation with balance deficits
Geometric error compensation through position feedback modification and comparison of correction strategies in 3- axis machine-tool
Full text linkIn machine-tools, geometrical defects are unavoidable. They can greatly affect the dimensional accuracy of the final workpiece if not corrected. Software compensation strategies are less expensive than mechanical adjustments and they provide great improvement in volumetric accuracy. In this study, different compensation methods are compared in a 3-axis milling applications: Numerical Controller (NC) internal compensation tables, modification of the programmed tool-path (G code) and modification of position feedback signals. The latter is the main purpose of this work, because it shows great potential and is not linked to one particular type of NC. It communicates with a custom software application that processes the position data and generates corrected signals according to a geometric model based on the rigid body assumption. The NC is then induced to perform volumetric error correction based on its default programming. The compensation methods are compared based on their ability to bring out or correct imposed geometric errors. The highlighted solution shows performances comparable to the G-code modification by correcting more than 96% of the imposed geometric errors without affecting the numerical chain from the program generation to its execution on the machine. It is also independent of the NC or the motors control cards
On the dependency of the extent of multiple solution zone around stability lobes on cutting law nonlinearity
No full textIn machining vibrations analyses, regenerative chatter stability boundaries aka stability lobes are known to be often accompanied by a multiple solution zone in process parameters space. In that zone the stable steady response coexists with a finite-amplitude oscillatory solution preceding cut interruption. Exploration of the oscillatory behavior requires accounting for finite nominal cut thickness and the condition of the tool exit from cut. In the present work we explore these conditions via a harmonic balancing framework, bringing forward the dependency of the extent of the unstable post-critical chatter domain on the cutting law nonlinearity
Ex vivo mechanical properties of human thoracolumbar fascia and erector spinae aponeurosis under traction loading and shear wave elastography
Full text linkThe thoracolumbar fascia (TLF) and the erector spinae aponeurosis (ESA) play an important role in the biomechanics of the spine and could be a source of low back pain. Although the TLF and ESA are key structures in several musculoskeletal dysfunctions and in tissue engineering, there is still a lack of evidence in the literature to prove that they have different mechanical properties and roles when considered as a single tissue. Furthermore, no methods are currently available to study these structures in vivo. The objective of this study was to analyze the ex-vivo tensile properties TLF and ESA, and to test the potential of ultrasound shearwave elastography (SWE) to characterize these tissues. Hundred samples from N = 10 fresh-frozen human donors were studied. Shear wave speed (SWS) was measured in all samples with SWE, and their tensile properties were measured with mechanical testing. Results show that TLF is anisotropic, and more compliant than ESA. SWS was not significantly correlated to tensile moduli.
These findings could potentially aid surgeons in their daily practices, assist engineers with in silico simulations, and support physiotherapists in musculoskeletal rehabilitation by enabling them to customize medical interventions for each specific patient and clinical condition. However, further research is necessary to further investigate the behavior in terms of time-dependent response and link between the tissue anisotropy and microstructural organization
A knowledge mapping of the state-of-the-art on DED-WAAM deposition trajectory evaluation
Full text linkThis article aims at mapping the current knowledge related to DED-WAAM in order to assess and control the deposition trajectory and associated manufacturing strategy, especially the toolpath, for building weld beads with DED-WAAM technology. To do so, a thorough state of knowledge study from a group of experts and a targeted list of scientific articles points out several issues identified as critical parameters or handles due to their influence onto the deposition trajectory throughout the WAAM manufacturing process, and therefore onto the final part quality. For instance, the studied elements in this work are namely the trajectory generation variables (e.g. deposition rate, fixtures or substrate geometry), the heating parameters (e.g. arc power or heating devices), the manufacturing time management, the weld bead shape defects, the workpiece geometry, or the final part quality indicators. Thanks to a global research methodology, the resulting maps represent the interrelations between the WAAM parameters as well as the multi-physical phenomena at stake before, during and after building a weld beadand encompasses various scientific challenges, whether geometrical, mechanical or thermal. Therefore, they contribute to understanding the main performance criteria for assessing a deposition trajectory, guiding WAAM practitioners' decisions before building a complete part with this additive technology
Femtosecond laser polishing of pure copper surfaces with perpendicular incidence
Full text linkOver the past few years, femtosecond (fs) laser processing has drawn a growing interest in a wide range of applications as it offers the possibility to process the surface morphologies of metals and semiconductors. In contrast to other polishing techniques, laser polishing offers a flexible and non-contact solution, thereby avoiding potential external contamination, while enabling a precise selection of processing areas. We investigated the influence of fs laser parameters on surface roughness of pure copper and ablation thickness, focusing on highlighting the importance of fluence and scanning overlap. With a two-step processing strategy, composed of coarse and fine polishing steps, surfaces with Sa < 400 nm were achieved, representing a 98% reduction from the high roughness of 15 μm on initial surfaces. This research demonstrated the possibility of directly polishing rough parts using a fs laser with a perpendicular incidence. © 202
Dynamic Behaviors of Couple Stress Quadrilateral Thick Microplates within a Refined DQFE Framework
No full textThis study proposes a novel refined differential quadrature finite element (DQFE) framework for the size-dependent dynamic analysis of thick quadrilateral microplates, incorporating couple-stress effect and two kinematic variables. The proposed methodology addresses inter-element compatibility through fifth-order differential quadrature geometric mapping while achieving geometric adaptability via global-local coordinate transformation. Detailed procedures for assembling element matrices and imposing boundary conditions are provided. Validation through representative quadrilateral plate configurations confirms the efficacy of the proposed framework, with particular success in modeling asymmetric trapezoidal plates through experimental correlation. The enhanced DQFE framework further elucidates fundamental mechanisms governing cyclic quadrilateral microplate dynamics by systematically investigating three critical factors: material length scale parameters (MLSP), thickness-to-length ratios, and boundary constraint configurations. Mode localization characteristics are quantitatively assessed using the mode assurance criterion. The principal conclusions reveal: (1) Superior convergence characteristics of the fifty-degree-of-freedom DQFE formulation compared to conventional lower-order implementations; (2) Emergence of mode-transition phenomena driven by central angle variations; (3) Differential sensitivity of critical mode-transition angles to MLSP variations under contrasting boundary constraint intensities; (4) Characteristic modification of vibration mode contours induced by size-dependent effects
Thermohydraulic assessment of mixing behaviors and entropy generation using pseudoplastic fluids in short microfluidic devices
No full textThermal mixing fluids in chaotic microdevices have significant importance in many potential applications and have enormous utility in thermal engineering processes. In microfluidic devices, The Two-Layer with Crossing Channels Micromixer (TLCCM) emphasized its efficiency in thermally homogenizing Newtonian fluids, which inspired us to investigate its performance using pseudoplastic fluids. A numerical comparative investigation has been carried out to evaluate the thermal mixing performances of pseudoplastic fluids in laminar steady flows using four chaotic microdevices: TLCCM, L, OH and OX. Quantitative validation of pseudoplastic fluids within a complex geometry, subject to constant heat flux, has been done. Navier-Stokes, the mass conservation, energy and species transport equations have been solved numerically employing CFD code. The pseudoplastic fluids consist of carboxymethyl cellulose solutions, which are characterized using the power-law model, the flow behavior index ranging from 0.75 to 1 and the generalized Reynolds number ranging from 0.2 to 70. To quantify the thermal mixing efficiency, the effects of the fluid behavior index, the generalized Reynolds number, on the thermal mixing degree for the proposed micromixers are presented, where high thermal mixing degrees have been obtained which evolve between 0.9 and 0.99. The entropy generation due to heat transfers and fluid pressure drops has been introduced versus the generalized Reynolds numbers for different fluid behavior indexes. The Bejan number values evolve close to 1. The probability density function PDF (%) at the TLCCM micromixer exit is localized in a narrow range that refers to the ideal temperature value for mixing, which is 315 Kelvin, whatever the fluid behavior index value
Multi-part kinematic constraint prediction for automatic generation of CAD model assemblies using graph convolutional networks
No full textThis paper presents a machine learning-based approach to predict kinematic constraints between CAD models
that have potentially never been assembled together before. During the learning phase, the algorithm is
trained to predict the next-possible-constraints between a set of parts candidate to the assembly. Assemblies
are represented in a new graph-based formalism that is capable of capturing features associated with parts,
interfaces between parts and constraints between them. Using such a multi-level feature extraction strategy
coupled to a state-by-state graph decomposition, the approach does not need to be trained on a large
database. This formalism is used to model both the network input and output where the next-possibleconstraints
appear after evaluation. The core of the approach relies on a series of networks based on a
link-prediction encoder–decoder architecture, integrating the capabilities of several convolutional networks
trained in an end-to-end manner. A decision-making algorithm is added to post-process the output and drive
the prediction process in finding one among the set of next-possible-constraints. This process is repeated until
no more constraints can be added. The experimental results show that the proposed approach outperforms
state-of-the-art methods on such assembly tasks. Although the state-by-state assembly algorithm is iterative, it
still takes into account the whole set of parts as well as the whole set of constraints already predicted, and this
makes it possible to handle constraint cycles, which is generally not possible when not considering multiple
parts as input
Knowledge Graph as Digital Twins Enhancer for Real Case Data-Driven Smart Building
No full textThe integration of data capture, analysis, monitoring, and control technologies is rapidly becoming the cornerstone of next-generation smart buildings. However, developing digital twins that dynamically interact with these buildings presents a significant challenge. In this paper, we study the most appropriate data models for leveraging a digital twin from data-driven smart buildings. We propose a framework that exploits a knowledge graph to directly address the challenges encountered in real-world building management systems, ensuring that the information is comprehensible as a preliminary step to intelligent decision-making. Furthermore, we validate this proposal for improving building performance and sustainability through a real-world use case. The experimental results, utilizing dynamic data streams from the Internet of Things (IoT), demonstrate promising outcomes. This research paves the way for using graph-based models and algorithms as digital twin enhancers for managing data-driven smart buildings