Assembly Tolerances Research Articles

Exploring the Landscape of the PP7 Virus-like Particle for Peptide Display.

Self-assembling virus-like particles (VLPs) can tolerate a wide degree of genetic and chemical manipulation to their capsid protein to display a foreign molecule polyvalently. We previously reported the successful incorporation of foreign peptide sequences in the junction loop and onto the C-terminus of PP7 dimer VLPs, as these regions are accessible for surface display on assembled capsids. Here, we report the implementation of a library-based approach to test the assembly tolerance of PP7 dimer capsid proteins to insertions or terminal extensions of randomized 15-mer peptide sequences. By performing two iterative rounds of assembly-based selection, we evaluated the degree of favorability of all 20 amino acids at each of the 15 randomized positions. Deep sequencing analysis revealed a distinct preference for the inclusion of hydrophilic peptides and negatively charged amino acids (Asp and Glu) and the exclusion of positively charged peptides and bulky and hydrophobic amino acid residues (Trp, Phe, Tyr, and Cys). Within the libraries tested here, we identified 4000 to 22,000 unique 15-mer peptide sequences that can successfully be displayed on the surface of the PP7 dimer capsid. Overall, the use of small initial libraries consisting of no more than a few million members yielded a significantly larger number of unique and assembly-competent VLP sequences than have been previously characterized for this class of nucleoprotein particle.

Optimization Method of Assembly Tolerance Types Based on Degree of Freedom

The automatic generation of tolerance specifications is an important aspect of achieving digital product design. An obvious feature of the current automatic generation of tolerance based on rule reasoning is that all tolerance types will be inferred for the same assembly feature. However, when labelling part tolerance information, designers need to further screen based on the geometric function of the assembly, which may result in prioritizing tolerance types that do not meet the geometric requirements of the assembly. This paper presents an assembly tolerance type optimization method based on the degree of freedom (DOF) of tolerance zone for the optimization and screening problem after reasoning all possible tolerance types. Firstly, we define the DOF of tolerance zones and their representations, while also define the control parameter degrees of freedom (CPDF) of assemblies, and analyze the CPDF of typical geometric functional tolerances of assemblies; Secondly, the Boolean operation relationship between sets is used to construct a Boolean operation preference method for the CPDF. Then, an algorithm for the optimal selection of the shape and position tolerance items of the assembly is established based on the DOFs of tolerance zone. Finally, the proposed method is verified by an engineering example, and the result shows that the method can optimize and screen the geometric tolerance types of assemblies.

A posture alignment-based methodology for gap optimization of aircraft composite panel assembly

The widespread use of composite materials in the aviation industry result in the control of the assembly gaps between components a key topic. In this work, a gap optimization method based on component posture alignment is presented to assist in the intelligent assembly of aircraft composite panels. To quantify the assembly gap, a static and posture-dependent dynamic model is developed with the idea of discretization, and then a mathematical evaluation method for the assembly quality is proposed based on two new concepts: gap distribution coefficient and gap distribution factor. Moreover, with a multi-objective optimization method, the assembly gap is minimized and the gap distribution is optimized under the constraints of DOF and assembly tolerances, which provides new ideas for intelligent assembly of big composite panels. Finally, the proposed method is studied by numerical simulations of an assembly work in point cloud, as well as hardware experiments of a composite panel assembly work. These studies, taken together, demonstrate the effectiveness of the proposed method.

Numerical Simulations of Flow-Induced Deflections in MITR LEU Fuel Plate Due to Channel Size Disparity

The hydromechanical stability of the fuel plates in parallel coolant channels of a Materials Testing Reactor (MTR) fuel element design is of great importance to the safety of research and test reactors. Previous analytical, experimental, and numerical efforts focused on parallel channels with the same or similar size; also, in the prior numerical simulations, the fuel plate was often assumed to be perfectly flat. This work presents the results of a fluid-structure interaction simulation performed to evaluate the flow-induced deflections of the fuel plates in the low-enriched uranium (LEU, <20 wt% 235U) fuel element design for the conversion (from highly enriched uranium) of the Massachusetts Institute of Technology Reactor (MITR-II, also referred to as MITR). Various manufacturing and assembly tolerances of the MITR LEU elements are considered in the analysis, and the effects of channel size disparity, nonideal plate shape, and flow rate uncertainty are investigated. Results show that, for all cases analyzed, the deflection occurs toward the larger channel, and the change in any channel stripe remains small (less than 0.021 mm) compared to fabrication tolerances. In addition to simulation work, a hydraulic performance test of the MITR LEU fuel element is currently planned to support conversion to the use of LEU fuel.

Precision Denavit–Hartenberg Parameter Calibration for Industrial Robots Using a Laser Tracker System and Intelligent Optimization Approaches

Precision object handling and manipulation require the accurate positioning of industrial robots. A common practice for performing end effector positioning is to read joint angles and use industrial robot forward kinematics (FKs). However, industrial robot FKs rely on the robot Denavit–Hartenberg (DH) parameter values, which include uncertainties. Sources of uncertainty associated with industrial robot FKs include mechanical wear, manufacturing and assembly tolerances, and robot calibration errors. It is therefore necessary to increase the accuracy of DH parameter values to reduce the impact of uncertainties on industrial robot FKs. In this paper, we use differential evolution, particle swarm optimization, an artificial bee colony, and a gravitational search algorithm to calibrate industrial robot DH parameters. A laser tracker system, Leica AT960-MR, is utilized to register accurate positional measurements. The nominal accuracy of this non-contact metrology equipment is less than 3 μm/m. Metaheuristic optimization approaches such as differential evolution, particle swarm optimization, an artificial bee colony and a gravitational search algorithm are used as optimization methods to perform the calibration using laser tracker position data. It is observed that, using the proposed approach with an artificial bee colony optimization algorithm, the accuracy of industrial robot FKs in terms of mean absolute errors of static and near-static motion over all three dimensions for the test data decreases from its measured value of 75.4 μm to 60.1 μm (a 20.3% improvement).

Density-Based Prioritization Algorithm for Minimizing Surplus Parts in Selective Assembly

Selective assembly is a manufacturing method that matches and assembles pairs of parts in a manner that offsets the machining errors of these parts. In the production of products requiring high precision and efficient mass production, flow production and search-based selective assembly must be combined for market competitiveness; however, this method increases computational costs and generates many surplus parts. Therefore, research should aim to minimize surplus parts in search-based selective assembly at a low computational cost to suit flow production systems. In this paper, we propose the density-based prioritization (DBP) algorithm, which minimizes surplus parts in the search-based selective assembly of flow production systems. In addition, a method of varying the assembly tolerance is developed and incorporated into DBP to increase its process capability. The proposed algorithm requires an assembly facility to prepare parts with as many different sizes as possible. This paper confirms that DBP reduces computational costs and surplus parts while enhancing process capability.

A study of tolerance allocation and stack-up analysis to improve the assembly precision of an injection mold

ABSTRACT Tolerance designing is a critical job for the assemblies to ensure their precision and functions. Tolerance design must consider manufacturing capability for ensuring the feasibility of the designs in the following processing. This paper presents the available methods of determining tolerance sizes and tolerance analysis to improve assembly precision. An injection mold consisting of hundreds of parts is used as an example to depict the methods of tolerance designing. The precision grades and the corresponding tolerance ranges applied in engineering fits are introduced for giving reasonable tolerances in designing. The defect rates of the designed tolerances to the machining precisions are investigated for observing the effects of manufacturing capabilities. An approach based on block assembly is proposed for eliminating tolerance stack-up, as well as improving assembly precision. The assembly tolerances can be reduced from 0.071 to 0.032 mm by using the proposed method, and the defect rates in manufacturing can be improved from 9.05% to 0.02%. It means that a larger range of tolerances can be designed to meet the specifications, as well as reduce the manufacturing costs.

Assembly Error Modeling and Tolerance Dynamic Allocation of Large-Scale Space Deployable Mechanism toward Service Performance

As a satellite’s critical load-bearing structure, the large-scale space deployable mechanism (LSDM) is currently assembled using ground precision constraints, which ignores the difference between the ground and space environments. This has resulted in considerable service performance uncertainties in space. To improve satellite service performance, an assembly error model considering the space environment and a tolerance dynamic allocation method based on as-built data are proposed in this paper. Firstly, the factors influencing the service performance during ground assembly were analyzed. Secondly, an assembly error model was constructed, which considers the influence factors of the ground and space environment. Thirdly, on the basis of the assembly error model, the tolerance dynamic allocation method based on as-built data was proposed, which can effectively reduce the assembly difficulty and cost on the premise of ensuring service performance. Finally, the proposed method was validated in an assembly site, and the results show that the pointing accuracy, which is the core indicator of the satellite service performance, was improved from 0.068° to 0.045° and that the assembly cost was reduced by about 13.5%.

Robust Design of Aero Engine Structures: Using the Weighted Product Method

Total loss of quality in products or processes Reduction is the objective of robust design. Strong Design is an effective approach that aims to simultaneously decrease product costs and enhance quality while also significantly reducing development time. Strength is defined as a skill Raw material, operating conditions, process equipment, environmental conditions, and human Expected variation in factors Tolerant manufacturing process. Robust design is the design of products, devices, and manufacturing equipment so that their performance and functionality are insensitive to multiple variations, such as manufacturing and assembly tolerances, ambient use conditions, or degradation over time. Therefore, there is not strong design sensitivity – meaning that variation in the product will have minimal influence. In essence, robust design means minimizing the impact of variation on a product. One or more due to unforeseen circumstances Input variables or assumptions are rigorous although modified, their output and predictions are accurate A model is considered robust if. The alternatives being considered are related to specific aircraft features: the aerodynamic characteristic (C1), maximum takeoff weight (C2), armament (C3), and avionics (C4). The evaluation options are Ao, F-16, Su-35, and Mig-35. Based on the evaluation results, Ao obtained the top rank, while Mig-35 received the lowest rank.The value of the dataset for Robust Design of Aero Engine in Weighted product method shows that it results in Ao and top ranking

Estimation of the error field due to winding manufacturing and assembly tolerances of the DTT SC magnet system

The Divertor Tokamak Test facility (DTT) currently under construction in Frascati, Italy, is an experimental fusion reactor part of the EUROfusion roadmap to fusion energy. Due to their non-ideal winding distribution and assembly and manufacturing tolerances, real magnets are responsible for what is referred to as Error Fields (EFs). In some cases, EFs above a certain level can be unacceptable for achieving the sought performance of the fusion reaction and the implementation of dedicated in-vessel correction coils may become a necessary requirement. This work describes an approach to verify the magnet winding disposition by computing the EFs caused by the non-ideal shape of the DTT superconducting (SC) magnets. The results here presented are a contribution to the other activities aimed at deriving and verifying the requirements for the in-vessel correction coils.

Robust Design of Aero Engine Structures Using the Weighted Product Method

Total loss of quality in products or processes Reduction is the objective of robust design. Strong Design is to reduce product cost and quality to improve, the development time at the same time it is also a very powerful method of reduction. Strength is defined as a skill Raw materials, operating conditions, process equipment, environmental conditions, and human Expected variation in factors Tolerant manufacturing process. Research significance: Robust design is the design of products, devices, and manufacturing equipment so that their performance and functionality are insensitive to multiple variations, such as manufacturing and assembly tolerances, ambient use conditions, or degradation over time. Therefore, there is not strong design sensitivity – meaning that variation in the product will have minimal influence. In essence, robust design means minimizing the impact of variation on a product. One or more due to unforeseen circumstances Input variables or assumptions are rigorous although modified, their output and predictions are accurate A model is considered robust if Methology: Alternative: “The aerodynamic characteristic (C1), the maximum takeoff weight (C2), Armament (C3), Avionics (C4).” Evaluation Option: Ao, F-16, Su-35, Mig-35. Result: “from the result it is seen that Ao and is got the first rank whereas is the Mig-35 got is having the lowest rank”. Conclusion: The value of the dataset for Robust Design of Aero Engine in Weighted product method shows that it results in Ao and top ranking

Asymmetry of keyhole and weld pool geometry in PLBW of tailor-welded steel sheets with edge misalignment: Numerical modeling and experimental validation

Edge misalignment in butt welded joints is difficult to avoid due to factors such as poor processing accuracy, the presence of assembly tolerances, and welding distortion. It reduces the performance of the joints, which is inextricably associated with molten pool behaviors during the welding process. The purpose of this paper was to investigate the effects of the edge misalignment on weld pool dynamic behaviors by developing a multi-phase CFD model to reproduce the pulsed laser beam welding (PLBW) on a couple of low-carbon steel plates with a thickness of 1.8 mm, which had been verified with experimental weld pool profiles. Both experiments and numerical simulations took into account different scales of edge misalignment. The results demonstrated that the keyhole quickly penetrated the workpiece and remained quasi-steady with the continuous emission before shutting down when the laser intensity was dropped. The flow patterns within the weld pool were characterized by a vertical downward flow near the keyhole, Marangoni flows on both the top and root surfaces, together with a flow from the higher-assembled side to the lower. Those were driven by recoil pressure, surface tension gradient, and gravity, respectively. Moreover, both the weld pool and the keyhole showed a clear inclination toward the assembled lower side, as measured by positive slopes with values ranging from 5 to 25. When the sheet edges became more misaligned, the size of the weld pool shrunk because less laser energy reached the surface of the workpiece. At the termination of the third pulse cycle, the maximum weld width at the top surface (TW) and root surface (RW), as well as the penetration depth, were reduced by 5.281 %, 25.495 %, and 2.303 %, respectively. A larger scale of weld misalignment contributed to a more inclined weld pool, marked by lower slope values.

Gapwaveguide Automotive Imaging Radar Antenna With Launcher in Package Technology

A 77 GHz gapwaveguide radar antenna system with launcher-in-package (LiP) technology is presented in this paper for automotive imaging applications. Firstly, state-of-the-art LiP technology integrated with radar transceivers is proposed. The transceivers are equipped with waveguide interfaces for RF connection, enabling direct integration with waveguide antennas. Robust interconnects for coupling transceivers to waveguide antennas with non-galvanic contacts are proposed using gapwaveguide packaging technology. A simultaneous multi-mode imaging radar system using 4 cascaded aforementioned transceivers is introduced. Designated antenna elements of the system are realized by slot arrays with center-fed ridge gapwaveguides. Ultimately, the imaging radar antenna has a top radiating slot layer, a middle distribution layer and a bottom interconnect layer capable of accommodating 4 LiP radar transceivers with considerable assembly tolerance which is really one of the key aspects for commercial automotive radar applications. Input matching and radiation patterns of the antenna are verified by measurement. The results indicate that the proposed gapwaveguide imaging radar antenna in conjunction with the novel LiP packaging is able to serve the radar system properly. To the best of the authors’ knowledge, the proposed gapwaveguide antenna system is the first imaging radar antenna system ever developed for LiP components. This work provides a compact, high-efficiency and cost-effective solution for the integration of complex radar systems with waveguide antennas.

Analysis of Deformation of Thermoplastics by Using Thermomechanical Process

Nano fluidics has been a major field of research for application in areas like single molecule detection. Most of the research efforts have been concentrated in developing novel nano channel fabrication techniques. Most of these fabrication techniques developed are either expensive or time consuming.NA novel, low-cost fabrication technique to generate sub-micrometer wide channels in thermoplastic chips with potential application in single molecule detection is demonstrated. A custom, mechanical rig was designed, fabricated and optimized to produce a predefined thermo-mechanical deformation in thermo-plastic micro channel chips. Rectangular micro channels with different shapes and sizes were deformed using this rig to optimize the initial microchannel dimensions. Low aspect ratio (height: width) channels with smaller initial dimensions exhibit more potential to reach sub-micrometer widths. However, the nano channel fabrication consistency was adversely affected by manufacturing and assembly tolerances.

Numerical simulation of erosion of misaligned W/Cu monoblocks caused by ITER-like type-Iedge localized modes

The thermal performance of the divertor W/Cu monoblock tiles under the ITER-like transient events has been one of the main concerns for ITER plasma facing components. Owing to the assembly tolerances during installation, the leading edge caused by misalignment between toroidal neighboring tiles will receive the extremely high cumulative heat flux and be damaged. In this work, we develop a two-dimensional heat conductivity model, including evaporation, radiation, melting process, and coupling cooling water condition, to investigate the thermal erosion of two shapes of tiles of W/Cu monoblock (unshaped and beveled tiles) with misalignment in a range from 0 to 0.3 mm, within the allowable maximum misalignment for ITER. To reflect the geometrical effects of castellated divertor tiles on the properties of its adjacent plasma, the energy flux density distribution arriving at the castellated divertor tile surface is evaluated first by using a two-dimension-in-space and three-dimension-in-velocity particle-in-cell plus Monte Carlo collisions code, and the obtained energy flux distribution is then used as input for the heat conduction model. The simulation results show that the maximum temperature of the unshaped tile with no misalignment is lower than that of the beveled tile under the steady-state inter-ELM heat flux, which increases more quickly than that of the beveled tile with misalignment increasing and will be larger than that of the beveled tile when misalignment is not less than 0.105 mm. Two shapes of the divertor tiles would melt and vaporize under typical heat flux density of a transient event of type-I edge localized modes (ELMs) for ITER, deposition energy of 1 MJ·m&lt;sup&gt;–2&lt;/sup&gt; in a duration of 600 μs. The highest temperature, the maximum melting thickness, the maximum vaporization thickness of the unshaped tile with no misalignment are higher than those of the beveled tile except the melting volume ratio. The thermal erosion of the unshaped tile increases more remarkably than that of the beveled tile with misalignment increasing, and the melting volume ratio of the unshaped tile will exceed that of the beveled tile at a misalignment of 0.17 mm. In comparison with the unshaped tile, the beveled tile is more resistant to such a high heat flux of an ELM and misalignment.

Identification of Surrogate Models for the Prediction of Degrees of Freedom within a Tolerance Chain

The computation of assembly tolerance information is necessary to fulfill robust design requirements. This assembly is computationally costly, with current calculations taking several hours. We aim to identify surrogate models for predicting degrees of freedom within a tolerance chain based on point connections between assembly components. Thus, replacing part of the current computation workflow and consequently reduce computation time. We use manufacturing tolerances set by norms and industrial standards to identifly these surrogate models, which define all relevant features and resulting output variables. We use black-box modeling methods (artificial neural networks and gradient boosted trees), as well as white-box modeling (symbolic regression by genetic programming). We see that these three models can reliably predict the degrees of freedom of a tolerance chain with high accuracy (R2 > 0.99).

Tolerance-budgeting for ultra-stable KB systems

The emergence of new-generation light sources has driven experimental stations and optomechanical instrumentation to increasingly ambitious designs: precision engineering, optics design, and experimental techniques are being pushed to the limit of what is achievable, targeting the best spatial, spectral, and temporal resolution for their measurements. The extreme brilliance making diffraction-limited focusing feasible, also sets new sensitivity baselines for vibrations, clamping and thermal deformations, demanding stiffer mechanics and tighter tolerances for fabrication, metrology, assembly, and alignment, as well as creative commissioning and experiment control strategies. Such interdisciplinary design often requires cross-checking between mechanical, optical, and experimental specifications, where shared variables such as mirror dimensions, incidence angle, and optical magnification factor might induce conflicting behaviour, especially when tightly bounded to pioneering design targets on focus size and divergence, working distance, and flux density to name a few, stressing specifications and tolerances throughout every design step. In this manner, an analytical model integrating the main mirror tolerances could act as a more assertive starting point to broader, model-based assessments, pruning the decision space for subsequent finite-element analysis targeting globally optimal designs. This contribution suggests a tolerance budgeting approach for designing ultra-stable KB mirror systems, which in turn authorized an exactly-constrained realization [5], providing the high stability needed for ambitious nanoprobe designs, as the example of recently commissioned tarumã station, from Sirius/lnls carnaúba beamline [8], and underway designs such as mogno and sapoti stations also at Sirius.

Research on size coupling and sensitivity analysis of SAR antenna truss rod

To eliminate the influence of the size coupling of SAR antenna truss rod on assembly accuracy, this paper defines the assembly sequence, part datum, tolerance, assembly operation, and measurement operation of the model by establishing the tolerance analysis model of the assembly dimension chain and measurement target. The assembly simulation process of the deployment mechanism is simulated, the plane deviation of the antenna panel of the deployment mechanism is analyzed, and the contribution and sensitivity data of each component ring size to the closed ring size are obtained. The simulation results show that the in-plane angle error of the antenna panel is mainly affected by the length of the component ring rod. By focusing on controlling the dimensional tolerance of the truss rods with high sensitivity, the assembly accuracy of the antenna deployment system can be guaranteed. Sensitivity is the magnification of assembly deviation by the transmission of deviation source, which reflects the influence of the change of composition tolerance on the change of functional requirements. According to the sensitivity analysis, the key dimensions that affect assembly accuracy can be obtained. The assembly requirements of high-quality and low-cost products can be achieved by strictly controlling the dimensional tolerance of key components and relaxing the tolerance of non-key components.

Analysis of assembly tolerance compensation in microscope objectives with a free-form element at the aperture stop.

We analyze the feasibility of using refractive free-form phase plates at the aperture stop of microscope objectives as an alternative to active alignment to compensate for assembly tolerances. The method involves the determination of misalignment-induced aberrations at the exit pupil, and transferring them to the aperture stop while taking pupil aberrations into consideration. We demonstrate that despite being able to correct only for field-independent aberrations, this method can restore near-diffraction-limited imaging performance of passively aligned systems with practical tolerances, given that the as-designed system is highly corrected. We confirm the results via numerical simulations for two different commercial objective designs.

A policy iteration method for improving robot assembly trajectory efficiency

Bolt assembly by robots is a vital and difficult task for replacing astronauts in extra-vehicular activities (EVA), but the trajectory efficiency still needs to be improved during the wrench insertion into hex hole of bolt. In this paper, a policy iteration method based on reinforcement learning (RL) is proposed, by which the problem of trajectory efficiency improvement is constructed as an issue of RL-based objective optimization. Firstly, the projection relation between raw data and state-action space is established, and then a policy iteration initialization method is designed based on the projection to provide the initialization policy for iteration. Policy iteration based on the protective policy is applied to continuously evaluating and optimizing the action-value function of all state-action pairs till the convergence is obtained. To verify the feasibility and effectiveness of the proposed method, a noncontact demonstration experiment with human supervision is performed. Experimental results show that the initialization policy and the generated policy can be obtained by the policy iteration method in a limited number of demonstrations. A comparison between the experiments with two different assembly tolerances shows that the convergent generated policy possesses higher trajectory efficiency than the conservative one. In addition, this method can ensure safety during the training process and improve utilization efficiency of demonstration data.