Loose Tolerances Research Articles

Improving performance of defect detection by setting skewed tolerance and joint tolerances in crimp force monitor

AbstractA Crimp Force Monitor (CFM) detects defects by whether the crimp force curve of the force sensor exceeds the set tolerance, with the goal of low defect miss rate and false alarm rate. In this study, typical defects made by hand are crimped with an automatic crimping machine together with good products to obtain continuous data of the crimping force curves and to process the data. For the peak and area deviations of the crimp force curve, the good products show skew‐normal distribution, and the defective samples show outliers and different deviation intensities in the positive and negative directions. Furthermore, by manually intervening in the batch production of multiple groups of defects and comparing the defect miss rate and false alarm rate of CFM with different tolerance settings, the peak skewed tolerance, joint loose tolerance and joint skewed tolerance tree settings can meet a low defect miss rate and low false alarm rate at the same time. The group test results verify the skew‐normal distribution of crimping force curve deviation rate and the characteristics of deviation intensities, providing reference for the tolerance setting of CFM in automated terminal crimping production.

Ultra-wide angle panoramic imaging system based on a multiplexed reflective surface.

We propose an ultra-wide angle panoramic imaging system based on a multiplexed reflective surface, which consists of a panoramic head unit (PHU) and the relay lens group. The multiplexed reflective surface is applied in the PHU to reflect light from glass and air for imaging, obtaining the front and rear view channels, respectively. With a field of view (FoV) of 360∘×(35∘-120∘) and an f-number of four, this system has good image quality and relative illumination in the FoV. In addition, it has loose tolerance requirements and a diameter ratio of 7.2, reducing the difficulty of manufacturing and assembly. This optical system architecture provides a promising solution for panoramic perception over a wider FoV.

Cophasing detection of the segmented diffractive optical elements with the phase diversity method

The diffractive optical elements (DOEs) have the advantages of lightweight, low-cost, loose surface-figure tolerances and convenient folding, which provides a direction for next-generation large (>20 m) space telescopes. However, the cophasing of the DOEs limits its application in telescopes and decreases the optical system performance. The phase diversity method is studied and introduced to solve the cophasing detection of the two segmented DOEs. An improved experimental system is set up using the phase diversity method, and the experiment results show that the piston error and tilt error of the two mirrors are 0.03λ and 0.05 μrad, respectively, which meet the actual needs of the cophasing errors.

Compact and lightweight panoramic annular lens for computer vision tasks.

We propose a focal power distribution theory for the design of a compact panoramic annular lens (PAL) system based on Petzval sum correction. The system has a large field of view (FoV) of 360° ×(25°-100°). Its total length is 29.2 mm and weight is only 20 g. The proposed compact PAL system achieves large FoV and loose tolerances while maintaining small volume and low cost. It solves the shortcomings of traditional PAL systems that cannot be mounted on miniaturized portable devices due to their large volume and weight. We equip the compact PAL system with a novel and customized image enhancement model: PAL-Restormer to achieve better imaging quality. The produced images are further evaluated in various panoramic environment perception tasks. Extensive experiments show the promising potential of our proposed compact PAL system for the applications in wearable devices and mobile robots.

Modular cost model for Tolerance allocation, Process selection and Inspection planning

The need for highly reliable and precise products has forced industries to study potential uncertainties during designing needed parts. The reliability and acceptance of the product rely on several factors and tolerancing activity plays an important role to assure that the manufactured product meets the requirements. The importance of tolerancing activity can be noticed once designers prefer tight tolerances to ensure product performance and in contrast manufacturers want loose tolerances to reduce manufacturing and assembly complexity and then cost, to decrease the non-conformance rate. Therefore, tolerance allocation and inspection-planning design can be formalized as an optimization problem which the objective function represents the cost impacted by several aspects of the quality management: cost of failure, cost of the inspection. This paper details a modular cost model which includes four components: the manufacturing cost, the inspection cost, the scrap cost (internal failure), and the cost of external failure. Moreover, to improve the efficiency of the cost model, it integrates several factors such as frequencies of the monitoring and inspection activities, probability of conformed product, probability of non-detection of non-conformity, and probability of non-detection of confirmed. The applications of this model are illustrated and demonstrated through an industrial case study.

Optimized Runge-Kutta Methods with Automatic Step Size Control for Compressible Computational Fluid Dynamics

We develop error-control based time integration algorithms for compressible fluid dynamics (CFD) applications and show that they are efficient and robust in both the accuracy-limited and stability-limited regime. Focusing on discontinuous spectral element semidiscretizations, we design new controllers for existing methods and for some new embedded Runge-Kutta pairs. We demonstrate the importance of choosing adequate controller parameters and provide a means to obtain these in practice. We compare a wide range of error-control-based methods, along with the common approach in which step size control is based on the Courant-Friedrichs-Lewy (CFL) number. The optimized methods give improved performance and naturally adopt a step size close to the maximum stable CFL number at loose tolerances, while additionally providing control of the temporal error at tighter tolerances. The numerical examples include challenging industrial CFD applications.

On Sharing Part Dimensions Information and Its Impact on Design Tolerances In Fixed‐Bin Selective Assembly

Fixed‐bin selective assembly (FBSA) is a method for producing high‐tolerance specification assembly from lower precision components. This study investigates the design tolerance implications of an external supplier sharing dimensional information about shipped parts to be used for FBSA. An approach for reducing surplus components in FBSA is to predictively adjust the assembler's manufacturing process so that components produced internally better match those of incoming parts. However, it is unclear how the assembler's use of timely dimensions information—that is fully shared or is shared for a limited period, about the mean, variance, or both—of an externally sourced mating part would influence procedures for setting tolerances in an FBSA context. We develop and evaluate a Bayesian prediction‐based model with estimated parameters from a US assembler of bearings. Our results indicate that adjustments made using predictions from solely historical data produced comparable assembly efficiency to those made with shared information about only the dimensional variance of incoming parts. Prediction‐based adjustments, when only information about the dimensional mean was shared, yielded comparable matchable degrees to that when the mean and variance were both known. Furthermore, contrary to convention, looser tolerances were required to increase selective assembly efficiency. The shared information had a larger effect on the matchable degree than the modification of design tolerances in the absence of such information sharing. The insights have implications for coordinated component design and quality control.

A Flexible Global GCRO-DR Method for Shifted Linear Systems and General Coupled Matrix Equations

In this paper, we mainly focus on the development and study of a new global GCRO-DR method that allows both the flexible preconditioning and the subspace recycling for sequences of shifted linear systems. The novel method presented here has two main advantages: firstly, it does not require the right-hand sides to be related, and, secondly, it can also be compatible with the general preconditioning. Meanwhile, we apply the new algorithm to solve the general coupled matrix equations. Moreover, by performing an error analysis, we deduce that a much looser tolerance can be applied to save computation by limiting the flexible preconditioned work without sacrificing the closeness of the computed and the true residuals. Finally, numerical experiments demonstrate that the proposed method illustrated can be more competitive than some other global GMRES-type methods.

Tolerance allocation under behavioural simulation uncertainty of a multiphysical system

The tolerancing process impacts the product quality, the production cost and scrap rate. Tight tolerances allow to assure product performance; loose tolerances to reduce production cost. The tolerance allocation of a complex system is performed under uncertainty. In fact, the accuracy of the behaviour simulation of the system significantly affects the tolerance analysis result, and thus the tolerance allocation result. Therefore, a method is proposed to perform tolerance allocation based on the Dempster Shafer theory, Monte-Carlo simulation and genetic algorithm. The application of the proposed framework is demonstrated through a complex case study.

Probabilistic Visual Place Recognition for Hierarchical Localization

Visual localization techniques often comprise a hierarchical localization pipeline, with a visual place recognition module used as a coarse localizer to initialize a pose refinement stage. While improving the pose refinement step has been the focus of much recent research, most work on the coarse localization stage has focused on improvements like increased invariance to appearance change, without improving what can be loose error tolerances. In this letter, we propose two methods which adapt image retrieval techniques used for visual place recognition to the Bayesian state estimation formulation for localization. We demonstrate significant improvements to the localization accuracy of the coarse localization stage using our methods, whilst retaining state-of-the-art performance under severe appearance change. Using extensive experimentation on the Oxford RobotCar dataset, results show that our approach outperforms comparable state-of-the-art methods in terms of precision-recall performance for localizing image sequences. In addition, our proposed methods provides the flexibility to contextually scale localization latency in order to achieve these improvements. The improved initial localization estimate opens up the possibility of both improved overall localization performance and modified pose refinement techniques that leverage this improved spatial prior.

Tolerance analysis of multiple-element linear retrodirective cross-eye jamming

Tolerance sensitivity limits the practical application of the cross-eye jammer. Previous literature has demonstrated that retrodirective cross-eye jamming with multiple antenna elements possesses the advantage of loose tolerance requirements compared to traditional cross-eye jamming. However, the previous analysis was limited, because there are still some factors affecting the parameter tolerance of the multiple-element retrodirective cross-eye jamming (MRCJ) system and they have not been investigated completely, such as the loop difference, the baseline ratio and the jammer-to-signal ratio. This paper performs a comprehensive tolerance analysis of the MRCJ system with a nonuniform-spacing linear array. Simulation results demonstrate the tolerance effects of the above influence factors and give reasonable advice for easing tolerance sensitivity.

Development of space-based diffractive telescopes

Membrane diffractive optical elements formed by fabricating microstructures on the substrates have two important characteristics, ultra-light mass (surface mass density < 0.1 kg/m2) and loose surface shape tolerances (surface accuracy requirements are on the order of magnitude of centimeter). Large-aperture telescopes using a membrane diffractive optical element as the primary lens have super large aperture, light weight, and low cost at launch. In this paper, the research and development on space-based diffractive telescopes are classified and summarized. First, the imaging theory and the configuration of diffractive-optics telescopes are discussed. Then, the developments in diffractive telescopes are introduced. Finally, the development prospects for this technology used as a high-resolution space reconnaissance system in the future are summarized, and the critical and relevant work that China should carry out is put forward.

Simplified unobscured optics design for a diffractive telescope.

An unobscured optical system provides a good solution for a high-performance diffractive telescope. However, the unobscured diffractive telescope, such as an off-axis three-mirror diffractive telescope (OTDT), suffers from the complex calculation of initial parameters, strict tolerance, and fabrication of aspheric mirror diffractive optical elements (DOE). In this paper, a simplified unobscured design method, which is effective in achieving compact and loose tolerance, is proposed. Combining the deflection of an optical path and Schupmann achromatic theory, a novel unobscured diffractive telescope is rapidly converted from a coaxial transmissive system. Not only is the loose tolerance obtained, but the fabrication of an aspheric mirror DOE is avoided. The designed system, with a focal length of 400 mm, $f$f-number of 5, and working waveband of 612.8-652.8 nm, is analyzed. The results show that the imaging quality approached the diffraction limit within a field of view of ${0.04}^\circ \times {0.02}^\circ $0.04∘×0.02∘. Compared with the OTDT, the designed system has great advantages in design step, DOE fabricating, and system alignment. It also provides a reference for unobscured diffractive telescope development.

Optical design of compact unobscured ground-based diffractive telescope

To realize unobscured, compact structure and maintain loose tolerance, a novel method based on flat-field relay mirror for designing the ground-based diffractive telescope is proposed. Based on this mthod, we perform two different studies devised to design and reduce the manufacturing difficulty of compact unobscured ground-based diffractive telescope. Firstly, the formula of flat-field relay mirror structure based on aberration theory is deduced. Combining the Schupmann achromatic theory, a compact unobscured diffractive telescope with loose tolerance is designed. The designed focal length is 400 mm, F number is 5, the working waveband is 612.8-652.8 nm. After optimization by optical design software ZEMAX, the size of system is 720 mm × 435 mm, the total track distance is only 1/12 of transmissive diffractive telescope. The modulation transfer function (MTF) is greater than 0.73 at 50 lp/mm within 0.30°×0.07° field of view (FOV), and the imaging quality is approached the diffraction limit. Secondly, to further reduce the difficulty, the fabricating parameters of diffractive optical elements (DOE) and the alignment tolerance of system are designed and fully analyzed. The analysis results show that the DOE can be fabricated by existing binary lithography, the designed system meet the requirement of alignment. The designed system provides a good solution for ground-based diffractive telescope.

Stochastic Lanczos estimation of genomic variance components for linear mixed-effects models

BackgroundLinear mixed-effects models (LMM) are a leading method in conducting genome-wide association studies (GWAS) but require residual maximum likelihood (REML) estimation of variance components, which is computationally demanding. Previous work has reduced the computational burden of variance component estimation by replacing direct matrix operations with iterative and stochastic methods and by employing loose tolerances to limit the number of iterations in the REML optimization procedure. Here, we introduce two novel algorithms, stochastic Lanczos derivative-free REML (SLDF_REML) and Lanczos first-order Monte Carlo REML (L_FOMC_REML), that exploit problem structure via the principle of Krylov subspace shift-invariance to speed computation beyond existing methods. Both novel algorithms only require a single round of computation involving iterative matrix operations, after which their respective objectives can be repeatedly evaluated using vector operations. Further, in contrast to existing stochastic methods, SLDF_REML can exploit precomputed genomic relatedness matrices (GRMs), when available, to further speed computation.ResultsResults of numerical experiments are congruent with theory and demonstrate that interpreted-language implementations of both algorithms match or exceed existing compiled-language software packages in speed, accuracy, and flexibility.ConclusionsBoth the SLDF_REML and L_FOMC_REML algorithms outperform existing methods for REML estimation of variance components for LMM and are suitable for incorporation into existing GWAS LMM software implementations.

轻小型大视场自由曲面离轴光学系统设计

With the increasing development of space technology, space optical system with the characteristics of high-performance, miniaturization has become a new hotspot research in space optical fields. Off-axis three-mirror optical system has the advantage of high quality image, large field of view and high level of lightweight etc., which can better suit the application of miniaturized and low-cost space optical system and has broad application prospects. Based on the Gaussian optics and three-mirror aberration theory, the off-axis three-mirror with freeform surface of tertiary mirror was designed. The focal length was 1 550 mm, field of view was 3.60.45, relative aperture was 1:6.2, degrees of freedom and image quality were increased efficiently by the introduction of freeform surface. The design results show that system has a better performance in effective field of view, modulation transfer function value is above 0.43@111 lp/mm, wave-front error maximum value is 0.049 (=632.8 nm), RMS wave-front error value is 0.034 , maximum grid distortion value is 0.9%, and the imaging quality is complete symmetrical about the tangential plane. The total length of the optical system is less than f'/3.1, the height is less than f'/4.1, and is easily implemented because of the relatively loose tolerance about processing and assembling. The obtained results have a certain reference value for miniaturized space optical system.

Efficient Suspended Coupler With Loss Less Than −1.4 dB Between Si-Photonic Waveguide and Cleaved Single Mode Fiber

Benefiting from the 193-nm lithography, we have used one of the MPW platforms to realize narrow tip of width 100 nm with great repeatability and uniformity. Based on the new patterning technique, we optimized the suspended spot size converter (SSC) accordingly and the design result showed coupling loss less than −1 dB given with proper matching oil. We fabricated the device together with other photonic circuits and maintained the tip width around 105 nm across the wafers. First, we tested various matching oils, which are commercial product used for optical package but with unknown refractive index at C band, with one of them the SSC realized the state-of-the-art coupling loss less than −1.3 dB/facet with cleaved single mode fiber (SMF) for both TE and TM polarization state with a remarkable polarization-dependent loss less than 0.5 dB. Subsequently, we tried customized matching oils, which are not suitable for massive production but with known refractive index, to further confirm the effect of the refractive index of the matching oil. A similar trend with simulation result was verified. We also tested many chips randomly selected from different wafers to check the statistics and uniformity of the device, the measurement result showed variation within 0.4 dB across wafers, which is the best performance to the best of our knowledge realized in the available silicon photonics platforms worldwide. Finally, to test the feasibility of the design for package, we studied the alignment tolerance and conducted a simple packaging using ultraviolet (UV) curing to fix the fiber and the silicon chip. The 1-dB extra loss corresponded to 2-μm misalignment in cross section, similar to the tolerance between two cleaved SMF and the variation after UV curing was just 0.5 dB attributed to the loose alignment tolerance.

Scene understanding for adaptive manipulation in robotized construction work

Abstract Unlike manufacturing robots, whose kinematics are pre-programmed based on robust metrology, tight tolerances, and rigid workpieces, construction robots operate under conditions of imperfect metrology, loose tolerances, and large workpiece uncertainties. Despite having access to a designed Building Information Model (BIM), construction robots must sense and model their actual environment, and adapt their kinematic plan to compensate for deviations from the expected. This research investigates methods to enable the autonomous sensing and modeling of construction objects so construction robots can ultimately adapt to unexpected circumstances and perform quality work. To that end, two construction component model fitting techniques are presented, namely the Clustering and Iterative Closest Point (CICP) construction component model fitting technique and the Generalized Resolution Correlative Scan Matching (GRCSM) construction component model fitting technique. The GRCSM construction component model fitting technique employs the presented GRCSM search algorithm, which is a modified version of the existing Multi-Resolution Correlative Scan Matching (MRCSM) search algorithm. Three experiments are presented to evaluate the ability of the CICP and GRCSM construction component model fitting techniques to model construction features. It was found that the CICP and GRCSM construction component model fitting techniques are capable of estimating the pose and geometry of arbitrarily shaped objects and construction joints, but are susceptible to modeling error. Despite their limitations, the CICP and GRCSM construction component model fitting techniques appear to be promising tools for the geometric estimation of construction features, especially for situations involving full automation, detailed construction work, incomplete sensor data, and complex object geometry.

STUDY ON HIGH RESOLUTION MEMBRANE-BASED DIFFRACTIVE OPTICAL IMAGING ON GEOSTATIONARY ORBIT

Abstract. Diffractive optical imaging technology provides a new way to realize high resolution earth observation on geostationary orbit. There are a lot of benefits to use the membrane-based diffractive optical element in ultra-large aperture optical imaging system, including loose tolerance, light weight, easy folding and unfolding, which make it easy to realize high resolution earth observation on geostationary orbit. The implementation of this technology also faces some challenges, including the configuration of the diffractive primary lens, the development of high diffraction efficiency membrane-based diffractive optical elements, and the correction of the chromatic aberration of the diffractive optical elements. Aiming at the configuration of the diffractive primary lens, the “6+1” petal-type unfold scheme is proposed, which consider the compression ratio, the blocking rate and the development complexity. For high diffraction efficiency membrane-based diffractive optical element, a self-collimating method is proposed. The diffraction efficiency is more than 90 % of the theoretical value. For the chromatic aberration correction problem, an optimization method based on schupmann is proposed to make the imaging spectral bandwidth in visible light band reach 100 nm. The above conclusions have reference significance for the development of ultra-large aperture diffractive optical imaging system.

Cost engineering for variation management during the product and process development

Variation Management during the Product & Process Development can profoundly impact the quality, the cost of the product and the number of scraps in mass production... Designers want tight tolerances to ensure product performance; manufacturers prefer loose tolerances to reduce manufacturing and assembly cost. To analyse compromise solutions, the primary aim is to establish an objective function. This paper presents a model for the key indicators assessment to the relevance of variation management: cost, and investigates which model used in decision analysis is the most appropriate to prioritize and aggregate the predetermined performance measures. The applications of this model are demonstrated through an industrial case study where tolerance allocation, product development, problem is firstly addressed. Once optimized tolerances are attained, inspection planning, process development, problem is approached to ensure the optimized awaited quality level for the least cost.