Assembly Configurations Research Articles

A Control Method of Space Manipulator for Peg-in-Hole Assembly Task Considering Equivalent Stiffness Optimization

To meet the control requirements of high precision and high robustness for peg-in-hole assembly tasks, an optimized control method for a peg-in-hole assembly task of a space manipulator is proposed to reduce the system disturbance caused by the change contact status during the assembly process. The first step is to build an equivalent stiffness model, which considers the structure and control characteristics of the space manipulator. Flexibility indices along the assembly direction are then created. On completion of the flexibility indices, the assembly configuration of the manipulator is optimized with the gain of the joint controller. After that, based on the sliding mode impedance control law, the disturbance of contact force is compensated using a zero-sum optimal control compensation strategy. Finally, the correctness and effectiveness of the control method are verified through simulation experiments. The results of the simulation experiments show that the contact force of the space manipulator can be precisely controlled by the method proposed in this paper. Compared with existing methods, the sudden change of contact force and the disturbing force of the base are reduced by 90% and 54%, respectively. A control method of the space manipulator for a peg-in-hole assembly task considering the equivalent stiffness optimization is proposed, which effectively reduces the influence of disturbance caused by contact collision and improves the control robustness of peg-in-hole assembly tasks.

Numerical and experimental evaluation of the general performance in a modular electrochemical reactor and its feasibility for electro-chlorination purposes: Effect of the different electrode assembly configurations

Evaluation of electrochemical reactors consisting of different electrode assemblies, stacks, or modular units, by the employing of computational techniques and its comparison with experimental data is desirable for its applications and scaling up for electrochemical processes like the mediated electro-chlorination. This work aimed to evaluate the effect of three different electrode configurations (flat, interspersed, and C-stack assemblies) on the general performance of a homemade modular reactor, based on former ElectroSyn design with an improved inlet-outlet system, through studies of hydrodynamics, electrical characteristics, and mass transfer. Additionally, a secondary potential-current distribution study was carried out to evaluate the feasibility of different electrode configurations tested for the electro-chlorination process, that can be applied mainly for environmental purposes like mediated oxidation of organic pollutants and disinfection by the production of active chlorine species.From the hydrodynamic study, velocity profiles and RTD curves obtained in all electrode configurations tested, suggest that the flat electrode configuration exposes a low fluid dispersion and resistance than the other configurations, because of the diminishing of the high-velocity zones and by its higher cross-sectional area, which was confirmed by the pressure drop measurements. On the other hand, calculation of primary and secondary current distribution suggests that the presence and modification of edge effect in the different configurations tested generate strong non-uniformities in the electrode corners and the reactor walls, which could affect the distribution of reaction rate during the mass transport evaluations. Also, the secondary potential-current distribution study indicates that the flat and C-stack configurations are the more electrical feasible configurations (since the effect of the flow field and mass transfer was not taken into account) to be applied in the electro-chlorination process.

Dissipative particle dynamics simulations of H-shaped diblock copolymer self-assembly in solvent

We examine the self-assembly of H-shaped block-copolymers as the function of the middle block to branch length ratio and interaction between the middle and branch blocks differing in their solvophobicity. The work shows that the examined H-shaped polymers readily transition from uniform mixing of the polymer species to domain formation and a variety of advanced assembly configurations including vesicles, onion-like, and multicompartment aggregates. We identify the polymer conformational and packing changes involved to extract governing interactions and molecule features giving rise to the different assembly structures. The findings are discussed in terms of the H-shaped polymer architecture and polymer assemblies. We conclude that the assembly structure is governed by the molecular level local curvature induced by the varying conformations of the polymers. The findings highlight that for H-shaped polymers the degree of polymerization and polymer chemistries in terms of solvation and mixing characteristics of the blocks are keys to controlling the assembling structures.

In Situ Investigation of the Motion Behavior of Graphene on Liquid Copper.

The in situ investigation of the dynamic growth process and novel assembly phenomena of graphene on liquid copper (Cu) is of great significance to deeply understand the special behavior of graphene and self‐assembly mechanism. Here, the direct observation of the graphene growth and motion behavior on liquid Cu via in situ imaging is reported. Evidence of graphene movement on liquid Cu is offered and it is demonstrated that the translation and rotation behaviors of graphene are affected by the surface condition of liquid Cu. The self‐assembly process of graphene array is also revealed by capturing the dynamic changes of graphene in real‐time. Further analysis highlights the importance of surface energy of liquid Cu and the interaction between graphene building blocks during the self‐assembling process. The growth parameters are also investigated to flexibly control the assembly configuration of graphene arrays. This work provides an insight into the mechanism of graphene motion and assembly behavior that can be used to guide the controllable manipulation of 2D materials and on‐demand fabrication assembly structures with desired properties.

Good practices for designing and experimental testing of dynamically excited jointed structures: The Orion beam

This paper proposes a new lap-joint configuration, the so-called Orion beam. The new setup is composed of two thin beams connected by three bolted joints with contact patches on each connecting bolt. The Orion beam suggests an assembly configuration, in which there are bolts dedicated to “static” functions to guarantee structural integrity and those that perform “damping” functions to increase energy dissipation due to frictional contact. In particular, this paper analyzes the influence of the Orion beam’s design in the repeatability of experimental measurements and the impact of the tightening torque and excitation amplitudes on the system’s response. A feedback controller is proposed to control the excitation amplitudes during step-sine tests in the vicinity of resonance frequencies to measure the frequency response curves used to perform such analysis. Additionally, a single-degree-of-freedom Duffing–Van der Pol oscillator is proposed to evaluate, through its calibrated parameters, the impact of several tightening torque conditions and multiple excitation amplitudes on the structural stiffness and damping considering the vibration mode that promotes pronounced deformation around the lap-joint. Due to the presence of contact patches, the results show that the structure maintained impressive repeatability after several experimental measurements. Besides, it is possible to increase the damping for amplitude attenuation without significant losses in the contact stiffness.

A novel reconfigurable spherical joint based on linear independence of screws and its resultant metamorphic mechanisms

This paper presents a novel reconfigurable spherical (rS) joint resulting from the line dependence of screws and their embodiment geometry. Subsequently, the structure and phase change of the rS joint are elaborated. With this new invention, two novel metamorphic mechanisms, that are, the Schatz-derived metamorphic mechanism and the R(rS)R-R(rS)R metamorphic mechanism, are obtained by inserting the rS joint. The mechanisms entail a reconfiguration process that occurs in two manners: the phase change of the rS joint and the bifurcation of the mechanism. The Schatz-derived metamorphic mechanism entails reconfiguration by phase change of the rS joint and the bifurcation, the R(rS)R-R(rS)R metamorphic mechanism reconfigures the configuration based on phase change of the two rS joints. Remarkably, the former realizes the switch between two assembly configurations without resorting to disassembly and reassembly, and maintains the characteristics of the original Schatz mechanism while the rS joint situates in phase R. The latter changes the mobility and bridges gap between a spatial single-loop mechanism and a structure. With this new reconfigurable joint, various reconfigurable mechanisms could be generated by inserting the reconfigurable joint into the classical ones.

Micromechanical modeling of nacre-mimetic Ti3C2-MXene nanocomposites with viscoelastic polymer matrix

A new two-dimensional nanomaterial—Titanium Carbide MXene (Ti3C2-MXene)—was reported in 2011. In this work, the microscale models of Ti3C2-MXene nanomaterial are considered with polymer matrix. The nanocomposites are modeled using nacre-mimetic brick-and-mortar assembly configurations due to enhanced mechanical properties and interlocking mechanism between the Ti3C2-MXene (brick) and polymer matrices (mortar). The polymer matrix material (Epoxy-resin) is modeled with elastic and viscoelastic behavior (Kelvin–Voigt Model). The Finite Element Method is used for numerical analysis of the microscale models with the multi-point constraint method to include Ti3C2-MXene fillers in the polymer matrix. Ti3C2-MXenes are considered as thick plate elements with transverse shear effects. The response of elastic and viscoelastic models of polymer matrix are studied. Finally, a tensile and compressive load is applied at the microscale and the effective load transfer due to nacre-mimetic configuration is discussed. This paper provides nacre-mimetic models to pre-design the nanocomposite for optimal performance with damage resistance and enhanced strength.

A facile and rapid route to self-digitization of samples into a high density microwell array for digital bioassays

Digital bioassays are powerful methods to detect rare analytes from complex mixtures and study the temporal processes of individual entities within biological systems. In digital bioassays, a crucial first step is the discretization of samples into a large number of identical independent partitions. Here, we developed a rapid and facile sample partitioning method for versatile digital bioassays. This method is based on a detachable self-digitization (DSD) chip which couples a reversible assembly configuration and a predegassing-based self-pumping mechanism to achieve an easy, fast, and large-scale sample partitioning. The DSD chip consists of a channel layer used for loading the sample and a microwell layer used for holding the sample partitions. Benefitting from its detachability, the chip avoids a lengthy oil flushing process used to remove the excess sample in loading channels and can compartmentalize a sample into more than 100,000 wells of picoliter volume with densities up to 14,000 wells/cm2 in less than 30 s. We also demonstrated the utility of the proposed method by applying it to digital PCR and digital microbial assays.

An amphipathic Bax core dimer forms part of the apoptotic pore wall in the mitochondrial␣membrane

Bax proteins form pores in the mitochondrial outer membrane to initiate apoptosis. This might involve their embedding in the cytosolic leaflet of the lipid bilayer, thus generating tension to induce a lipid pore with radially arranged lipids forming the wall. Alternatively, Bax proteins might comprise part of the pore wall. However, there is no unambiguous structural evidence for either hypothesis. Using NMR, we determined a high‐resolution structure of the Bax core region, revealing a dimer with the nonpolar surface covering the lipid bilayer edge and the polar surface exposed to water. The dimer tilts from the bilayer normal, not only maximizing nonpolar interactions with lipid tails but also creating polar interactions between charged residues and lipid heads. Structure‐guided mutations demonstrate the importance of both types of protein–lipid interactions in Bax pore assembly and core dimer configuration. Therefore, the Bax core dimer forms part of the proteolipid pore wall to permeabilize mitochondria.

MOF-enzyme hybrid nanosystem decorated 3D hollow fiber membranes for in-situ blood separation and biosensing array

Modified metal–organic frameworks (MOFs) doping with enzymes exhibit high enzyme stability and catalytic performance, which is a research hotspot in the field of enzyme-based sensing. Although the MOF-enzyme constitutes a 3D structure in the nanoscale, the macroscopic assembly configuration still stays in 1D or 2D structures, limiting sensing applications towards complex biological targets. Herein, the MOF-enzyme hybrid nanosystem was assembled into 3D porous conductive supports via a controllable physical embedding method, displaying high enzymatic loading, stability and cascade catalytic performance. The modified MOFs combing with enzymes served as a sensing reaction system, and the conductive hollow fiber membranes (HFMs) served as a functional platform. The multifunctional device integrates pumpless hydrodynamic transport, interconnected conductive polymer, and blood separation modules, showing fast capillary fluid flow, trace sampling (3 μL), high selectivity and accuracy. The linear sensing range was in 2–24 mM glucose, 0.05–6 mM lactic acid, and 0.1–10 mM cholesterol, respectively, with sensitivities of 24.2, 150, 73.6 nA mM−1. Furthermore, this strategy of modular assembly of biosensing array can easily implement multiplex metabolites detection simultaneously.

Numerical Impact Analysis of Folding-Induced Tubular Thin-walled Energy-dissipating Elements

This paper deals with the numerical impact analysis of tubular thin-walled steel-made elements with induced folding for energy dissipation application. The excellent deceleration of the impacting mass of axial collapsing structures favors their use in energy dissipation applications, such as impact resistance and rockfall protection. Dynamic Finite Element analyses have been carried out to evaluate the performance of vertical assemblies of cold-formed steel cell-shaped elements welded on each other to form collapsible tubular elements. In turn, these have been gathered in groups and restrained by galvanized steel wires to create modules. The axial collapse, which is the most effective energy absorption mechanism, has been triggered by shaping the elements' edge as serpentine. In the analysis, several assembly configurations have been subjected to a freefall rhombicuboctahedron-shaped rigid block impact; Falling height, impact angle, and block mass have been varied to investigate their effect on the performance. The numerical results show a good agreement when compared to those obtained through a real-scale experiment.

Hygrothermal performance, energy use and embodied emissions in straw bale buildings

Straw bale is a low embodied energy and technically acceptable thermal insulation material. As per today, there is a lack of standardized technical data on utilizing straw bale in building construction, while the existing research studies rather focus on limited specific experimental or computational scenarios without summarizing in an organized way the behaviour of straw bale construction under different climate conditions and assembly configurations. This comparative study presents systematically the hygrothermal and energy performance of straw bale buildings with different exterior cladding and finishing mortar or sheathing board, exposed in various representative climates. The findings provide an insight into the optimal selection of materials and furthermore highlight the importance of climate adaptation of straw bale wall constructions. Overall, straw bale buildings show robust hygrothermal performance, when properly designed, and achieve very low energy use at a minimum of embodied emissions.

Volatile aldehyde emissions from “sub-ohm” vaping devices

“Sub-ohm” atomizers with reduced resistance can deliver more power than conventional electronic cigarettes. Typical battery outputs are 100 W or more. These devices are particularly popular among young users, and can be a significant source of volatile carbonyls in the indoor environment. Emissions from next-generation sub-ohm vaping products were characterized by determining e-liquid consumption and volatile aldehydes emissions for several combinations of popular high-power configurations. Tests explored the effect of dilution air flow (air vent opening), puffing volume, and coil assembly configuration. The mass of liquid consumed per puff increased as the puff volume increased from 50 to 100 mL, then remained relatively constant for larger puff volumes up to 500 mL. This is likely due to mass transfer limitations at the wick and coil assembly, which reduced the vaporization rate at higher puff volumes. Carbonyl emission rates were systematically evaluated using a 0.15 Ω dual coil atomizer as a function of the puffing volume and dilution air flow, adjusted by setting the air vents to either 100% (fully open), 50%, 25%, or 0% (closed). The highest formaldehyde emissions were observed for the lowest puff volume (50 mL) when the vents were closed (48 ng mg−1), opened at 25% (39 ng mg−1) and at 50% (32 ng mg−1). By contrast, 50-mL puffs with 100% open vents, and puff volumes >100 mL for any vent aperture, generated formaldehyde yields of 20 ng mg−1 or lower, suggesting that a significant cooling effect resulted in limited carbonyl formation. Considering the effect of the coil resistance when operated at a voltage of 3.8 V, the amount of liquid evaporated per puff decreased as the resistance increased, in the order of 0.15 Ω > 0.25 Ω > 0.6 Ω, consistent with decreasing aerosol temperatures measured at the mouthpiece. Three different configurations of 0.15 Ω coils (dual, quadruple and octuple) were evaluated, observing significant variability. No clear trend was found between carbonyl emission rates and coil resistance or configuration, with highest emissions corresponding to a 0.25 Ω dual coil atomizer. Carbonyl emission rates were compared with those determined using the same methodology for conventional e-cigarettes (lower power tank systems), observing overall lower yields for the sub-ohm devices.

Fire performance of non‐load‐bearing double‐stud light steel frame walls: Experimental tests, numerical simulation, and simplified method

SummaryDouble‐stud light steel frame (LSF) walls provide an enhanced insulation performance when exposed to fire conditions. However, the behavior of different configurations of such assemblies under fire is not well understood. Thus, this study aimed to assess the fire resistance of non‐load‐bearing double‐stud LSF walls subjected to ISO834 standard fire. The walls were lined with one or two type F gypsum plasterboards on each side, using cavity uninsulated or insulated with ceramic fiber. The experimental tests revealed that a wider cavity slows the heat transfer through the cross‐section, delaying the temperature rise on the unexposed surfaces. The use of ceramic fiber insulation substantially increases the fire resistance of the wall and when the cavity is partially filled with this material, if the blanket is placed towards the exposed side, enhanced insulation fire resistance is achieved. Based on the finite element method, a numerical validation was conducted using a special hybrid approach that used experimental temperature values inside the cavities or insulation blankets. This approximation was essential to improve the numerical results. Also, the employment of an air layer, located at specific regions of the models, helped to improve the numerical results, introducing an extra thermal resistance. A new simplified approach was proposed based on the improved design model available in the literature, and the results obtained are consistent with the experimental results. The predicted insulation fire resistance of the numerical and simplified methods agreed well with the experimental results and useful information is supplied to support further numerical and experimental studies.

Variational nodal method for three-dimensional multigroup neutron diffusion equation based on arbitrary triangular prism

With the development of nuclear technology, new concepts of reactor core have been continuously proposed, and new types of geometric assembly and reactor core configuration would be adopted to achieve better characteristics. Traditional nodal method based on rectangle or hexagonal nodal is no longer applicable for complex geometry modeling. Given that triangles have the advantage of constructing arbitrarily complex geometry, in this study, variational nodal method of three-dimensional multigroup neutron diffusion theory based on arbitrary triangular prism was developed. ANSYS code is used to divide calculation region into arbitrary triangle mesh, which is then transformed into regular triangle mesh by coordinate transformation, and a set of orthogonal polynomial basis function is built. Variables such as nodal neutron scalar flux and neutron current on nodal surface are expanded based on those polynomial basis functions. The response relationship between neutron partial neutron current and neutron flux can be obtained by variational principle, and traditional power method is employed to solve those response matrix system. Based on above, TriVNM code was developed, and 4 types of typical benchmarks including rectangle, hexagonal assembly reactor and reactor with curved boundary were employed to verify TriVNM. Both power distributions and keff calculated by TriVNM code agree well with reference results, and the maximum relative error of all the benchmarks’ power doesn’t exceed 1% and error of keff doesn’t exceed 50 pcm. TriVNM code achieves the same or higher level of calculation accuracy compared with other diffusion codes. Mesh sensitivity analysis shows that for large mesh size TriVNM code still has good accuracy.

On passive damping in machine tool hybrid structural parts

Hybrid materials combining steel or cast iron with fibre or particle composites have a good potential for lightweight machine tool structural design with high damping ratio. These materials are analyzed in the paper with a focus on damping improvement of structural components and machine tool assemblies. Fibre composites and particle composites were selected as the lightweight elements for the hybrid machine tool structure. The fibre composites were designed as low-density, high stiffness-oriented reinforcements, which were bonded to build metal structural parts conventionally. The particle composites were applied as filler materials into the hollows of the metal structural parts. Both composite structures presented a possibility to reduce the mass of the component due to the reduction of wall thickness (fibre composite) or removal of heavy ribbing (particle composites) and to influence the parts’ static and dynamic stiffness. Hybrid structures, combining the light-weight elements with cast iron or welded steel, were designed and tested in case studies using experimental modal analysis methods. Experimental modal analysis was used as the main approach for identification of the damping ratio on a basic coupon level, followed by testing of structural parts in a stand-alone configuration and ending with a structural part assemblies testing. Both particle composites and fibre composites were successful in improving the damping ratio of single structural parts. However, the damping ratio of the hybrid component mounted into an assembly configuration shows only less significant improvement. The presented results demonstrate importance of the damping caused in the connecting interfaces.

Experimental study on interior precast concrete beam-column connections with UHPC core shells

High-performance materials are increasingly being used in precast connections to improve their mechanical performance and simplify the construction process. In this study, a novel precast beam-column connection with an ultrahigh-performance concrete (UHPC) core shell is proposed, which works as the permanent joint formwork in the precast stage and the strengthening overlay during normal service. To investigate the seismic performance of the proposed connection, a total of three precast specimens and one reference monolithic specimen were tested through the quasi-static method. The main variables in this study were the thickness of the UHPC shell and the layout and ratio of stirrups in the joint zone. The test results indicated that the UHPC core shells effectively limited the shear behavior, delayed cracking in the joint zone, and provided plump hysteretic performance. With the assembly configuration, the proposed connection had good ductility and an efficient energy dissipation capacity. The UHPC shell configurations with variable stirrup layouts and ratios led to different crack patterns in the joint core zone. In addition, strengthened by the UHPC shells, the joint cores could be reinforced with fewer stirrups than demanded by code.

Structural and functional applications of 3D-printed graphene-based architectures

Based on the huge potential of graphene-based composites in electrical, thermal and mechanical applications, which have been widely used in electronics, energy storage and conversion, sensors and structural composites, the assembly and three-dimensional (3D) configuration of graphene nanosheets is an important routine to realize and even optimize its excellent properties. Considering the anisotropy of two-dimensional (2D) graphene and the accuracy of 3D architecture, 3D printing technology stands out in the preparation of periodic and diversified 3D graphene due to its efficient and controllable construction process. Moreover, the interconnected graphene conductive network and lightweight structural regulation can realize the integration of structure and function from low-dimensional to multidimensional. In these circumstances, the structural design and related functional applications of the printed graphene-based architecture are reviewed, and it is important to understand the inks properties, macro-microstructural regulation and corresponding application prospects. Besides, a summary and outlook is prepared in the last part, which points out the application difficulties and future development of 3D-printed graphene-based architecture.

Elucidation of durability of carbon-supported PdIr alloy catalyst by experimental and theoretical approaches in polymer electrolyte membrane fuel cell

PdIr nanoparticles supported on carbon support are synthesized and their oxygen reduction reaction (ORR) activity and durability in a half cell or membrane-electrode assembly (MEA) configuration for polymer electrolyte membrane fuel cell are examined. A synergistic effect of the combination of Pd possessing the effective ORR catalytic activity and Ir as one of the most stable elements in acidic media leads to a decrease in particle size, a higher particle dispersion, and a better ORR activity than Pd monometallic catalysts. It is expected that PdIr alloys would form phase-separated nanoalloys that have Pd-rich surface owing to the higher surface energy of Ir. The addition of Ir to Pd in PdIr/C increases the metallic Pd portion. Meanwhile, the Pd5Ir/C is the most durable compared to Pd/C and Pt/C over 3000h of MEA operation. The ORR activity of PdIr alloy is expected to increase by reducing the oxygen binding energy of Pd in the presence of Ir from the first-principle calculation, and each contribution of compressive strain and ligand effects is quantified. The cohesive energy and the kinetic segregation energy are also calculated to support the improved stability of PdIr compared to Pd and Pt in the ORR condition.

Commissioning of an MRI test facility for CFD-grade flow experiments in replicas of nuclear fuel assemblies and other reactor components

A new test facility is presented, enabling single-phase isothermal fluid mechanics experiments to support nuclear reactor safety studies. The applied measurement technique Magnetic Resonance Velocimetry (MRV) is based on the medical imaging modality Magnetic Resonance Imaging (MRI). The experiments in this laboratory aim at providing the mean velocity field in models of nuclear fuel assemblies using isothermal water. Additionally, turbulence statistics in terms of the Reynolds stress tensor can be acquired. Since MRV is a non-optical measurement technique, there are no requirements on optical properties, and the investigated models can be quickly built with additive manufacturing techniques. Even though MRV offers a relatively low temporal and spatial resolution compared to laser-optical techniques and has some limitations regarding the test section materials, e.g., no metals, the main gain is that MRV provides a full three-dimensional representation of the flow field in short times. Both the model preparation and the measurement time are significantly faster than with laser-optical measurement techniques. The full-field experimental data obtained with MRV is often referred to as 'CFD grade data' as it enables a full-field validation of numerical solutions obtained with Computational Fluid Dynamics (CFD). As a commissioning experiment, measurements inside a 5x5 fuel element model of a pressurized water reactor (PWR) are conducted and compared with CFD results. The measured mean velocity field inside the PWR replica comprised of 2.9 Million velocity vectors was acquired in 79 min. In addition, turbulence measurements in a periodic hill channel demonstrate how MRV can be used to obtain all components of the Reynolds stress tensor. Although the measurements in this proof-of-concept study suffer from some measurement errors, all major error contributions are well known, and validated methods exist to overcome these shortcomings. In conclusion, this study shows how the velocity field in a specific fuel assembly configuration can be obtained highly efficiently using a specialized MRI laboratory.