Assembly Tolerances Research Articles

Design of a 360-deg panoramic capture system based on a smart phone

A panoramic imaging system has been developed using two afocal lenses and a smart phone that consists of cameras on both sides. An individual afocal lens has been developed with a large field of view (FOV) and a large exit pupil, which can enlarge the FOV of a smart phone camera to above 180 deg. Some issues with the smart phone-based 360-deg panoramic system, such as relative illuminance and assembly tolerance, were analyzed in detail and taken into consideration during the design procedure. A prototype has been developed with a low fabrication cost, yet producing impressive panoramic image quality.

Accuracy improvement with checkerboards in SLAM-integrated kinematic calibration (SKCLAM) for industrial manipulators

Today, offline programing is available on industrial manipulators and used in many factories. However, the absolute accuracy of robots is insufficient due to manufacturing and assembly tolerances, thus it is necessary to perform kinematic calibration in advance. Most of existing calibration methods require a large amount of measurements just to calibrate a robot. In addition, when programing the robot offline, it is also important to perform motion planning for safe and efficient operations. Appropriate motion planning enables the robot to move along the optimal route taking obstacle avoidance and cycle time reduction into account. For this purpose, the accurate measurement of the environment around the robot is required, but existing methods require a lot of work and time. Therefore, in order to reduce the time and effort required for kinematic calibration and environmental mapping, we developed a SKCLAM (Simultaneous Kinematic Calibration, Localization And Mapping) method, in which kinematic calibration and environmental mapping are performed simultaneously for a manipulator with an RGB-D sensor attached to its hand. In this study, in order to improve the accuracy of the SKCLAM method, we introduced checkerboard patterns. We verified the SKCLAM method with checkerboard patterns in both a virtual environment and a real environment. The results showed that the effectiveness and some limitations of our current implementation.

An Automated Method for Assembly Tolerance Analysis

Abstract This paper proposes an automated method for assembly tolerance analysis. The input of the method is an assembly model, the assembly information is stored in the assembly model, and the tolerance annotation is marked in the solid part model. The output of the method is the probability statistical results of the analyzed objective and the lists of the sensitivity and contribution of the tolerance factors. The variation in the geometric features is simulated by the control point variation model, the location of the analyzed objective is calculated based on the contact conditions of the actual geometry of the assembly model, and the analysis results are obtained based on the Monte Carlo method. To structuralize the calculation procedure of the location of the geometric features, first, the error propagation graph of the assembly model is established according to the assembly information and tolerance annotation. Subsequently, the hierarchy of the coordinate system of the geometric features is established, and the homogeneous transformation matrices between the coordinate systems are obtained. In this manner, the process to calculate the location of the geometric features can be automated. The prototype software of an automated assembly tolerance analysis is introduced, and the application of the prototype software is demonstrated.

Tolerance analysis of slider-crank mechanism for assembly functionality check

The purpose of functionality check is to analyse the stack-up of geometric deviation of part/feature whether it meets geometrical requirement and is it in the range of assembly tolerance. However, usual tolerance analysis model does not include assembly clearance. Aiming at this problem, we have done some research. Firstly, a nominal geometrical transfer model and a stackup model are established based on small displacement torsor (SDT) and homogeneous transformation matrix (HTM). Secondly, HTM expression of tolerance loop is constructed. Next, assembly tolerance matrix model is established and a new tolerance analysis method for assembling feasibility check is put forward. At last, taking a slider-crank mechanism as example, the contrastive study of tolerance analysis for functionality check is done. The results show that it is prone to lead to misjudge when analysing only dimension tolerance. And, it is more restrictively when considering dimension tolerance, geometric tolerance and assembly clearance.

Fast Assembly Tolerance Inspection Method Using Feature-Based Adaptive Scale Reduction in Automatic Assembly Line

Enormous computation and long data processing time of the online tolerance inspection procedure has been a bottleneck in reducing the production cycle time of automatic assembly line. To reduce time consumption while maintaining accuracy, a fast assembly tolerance inspection method is proposed in this paper using scale-reduced models. First, the general part surface, input by a laser-scanned dense point cloud, is segmented through feature-based clustering. Shape variation estimation are designed to determine reduction ratios between clusters adaptively. Then, assembly simulation method is further advanced to utilize coarse point models with imbalanced density. Finally, numerical experiments are designed to estimate both static and dynamic assembly tolerances as results of tolerance inspection. A case study on a motion component of a rail material transporter shows that the proposed method could reduce 81% of the data processing time compared to traditional practice. The precision loss has minor influence on the inspection results because spatial positioning error is no more than 6% of tolerance interval and 18% of scanning resolution. Moreover, the proposed method has a comprehensive advantage of time and accuracy than two conventional point cloud simplification techniques based on iterative and clustering methods.

Tolerance analysis of slider-crank mechanism for assembly functionality check

The purpose of functionality check is to analyse the stack-up of geometric deviation of part/feature whether it meets geometrical requirement and is it in the range of assembly tolerance. However, usual tolerance analysis model does not include assembly clearance. Aiming at this problem, we have done some research. Firstly, a nominal geometrical transfer model and a stackup model are established based on small displacement torsor (SDT) and homogeneous transformation matrix (HTM). Secondly, HTM expression of tolerance loop is constructed. Next, assembly tolerance matrix model is established and a new tolerance analysis method for assembling feasibility check is put forward. At last, taking a slider-crank mechanism as example, the contrastive study of tolerance analysis for functionality check is done. The results show that it is prone to lead to misjudge when analysing only dimension tolerance. And, it is more restrictively when considering dimension tolerance, geometric tolerance and assembly clearance.

Feeling machine for material-specific machining

In the machining of material compounds, materials with differing properties must be identified during the process and process parameters must be controlled accordingly. Structure integrated strain gauges in feeling machines are a promising approach for providing signals for monitoring and control tasks. This paper presents the first investigation and implementation of this technology for a turning machine turret. Firstly, the simulation based positioning of the sensors is discussed. Secondly, disturbance variables such as cooling temperature and assembly tolerances of machine components, which affect the strain measurement, are investigated. Finally, the successful material-specific machining based on the feeling machine is presented.

Field Measurements of a Cryogenic Permanent Magnet Undulator at the TPS

A PrFeB-based cryogenic permanent-magnet undulator (CPMU) with a period length of 15 mm (CU15) is being constructed to provide high brilliant X-rays for the Taiwan Photon Source (TPS) nano-probe beamline. Field measurements of this undulator will be performed with a Hall probe in a vacuum environment. The in-situ Hall probe measurement system (Yang et al. , 2014) was improved (Yang et al. , 2016) to allow measurement and tuning of the CU15 magnetic field. A field strength and temperature dependent calibration of the Hall probe was done to obtain realistic field distributions. By tuning the differential adjusters and spring modules, we can correct magnetic field errors caused by assembly tolerances and temperature gradients along the magnetic arrays, thus lowering phase errors to reach our design goals. This paper describes details of improvements in the measurement system, field tuning methods, and measurement results at cryogenic temperatures.

Package-in-Dielectric Liquid Patch Antenna Based on Liquid Metal Alloy

A fully dielectric packaged liquid patch antenna based on liquid metal alloy is presented. In this letter, there are two hollow cavities embedded in a dielectric box, including a rectangular cavity placed at the upper portion acting as the radiating element, and a nonplanar cavity with a central groove under the radiating element serving as the ground plane. The antenna is realized by a three-dimensional printing technique, alleviating assembly tolerance, and uncertainties from a printed-circuit-board approach, which would degrade an antenna performance. The radiating element and the ground plane are fully metallized by filling liquid metal alloy. Unlike traditional liquid antennas, the liquid packaging antenna is completely metallized by conductive liquids, which does not contain any solid metals. The proposed antenna is designed to operate at 5.2 GHz. Results show that the proposed liquid patch antenna produces a satisfactory impedance matching, and a good agreement between simulation and measurement in terms of radiation characteristics is achieved at the desired frequency.

A Statistical Investigation into Assembly Tolerances of Gradient Field Magnetic Angle Sensors with Hall Plates

Magnetic field-based sensors are used for reliable applications in automotive and aerospace industry because of their robustness. The electrification of powertrains and propulsion requires gradiometric sensing principles, because they suppress ubiquitous electromagnetic disturbances very efficiently. A prominent solution for the mass market uses a small permanent magnet attached to the end of a rotatable shaft and a small sensor chip with four Hall plates placed on the rotation axis and ahead of the magnet. Small misplacements of chip and magnet lead to errors in the detected angle of the shaft. The lateral position errors and tilts of the magnet and the chip give eight degrees of freedom (DoF). This large number of DoF and the nonlinearity of the system obscure the view on how to optimize such angle sensor systems. Therefore, this work presents a statistical description of angle errors caused by assembly tolerances. Probability distributions of angle errors are given and marked differences to Gaussian distributions are shown. The influence of spacing between sensor and magnet and the dominant influence of the shape of the magnet are clarified. The results obtained by numerical computations are in excellent agreement to recently published analytical theories. This work gives evident conclusions for statistical optimizations of such angle sensor systems.

Straight Path Handling Anomalies of Passenger Cars Induced by Suspension Component and Assembly Tolerances

The effects on handling due to suspension component and assembly tolerances are analysed focusing on three anomalies affecting passenger cars travelling on straight paths, namely ‘pull to side’, ‘steering wheel misalignment’ and ‘drift leeward’. These anomalies do not constitute safety problems but represent a cost factor in the automotive industry since they occur in small but not negligible percentage of the overall car production. The present contribution is therefore focused on understanding which are their causes, and on reducing their extent, in the specific case of vehicles with front Double wishbone suspension and rear Five arms suspension. To this purpose, the vehicle assembly process is analysed in terms of errors and tolerances for identify the most influential parameters on handling irregularities. Sensitivity analysis by multibody virtual modelling, and subsequent correlation with experimental data from pre-setting and wheel aligner benches, have provide sufficient information for setting tolerance thresholds, able to keep the handling anomalies under study within acceptable bounds. As a result, ‘pull to side’ and ‘steering wheel misalignment’ has been found to be mainly related to the set up phase of wheel angles (front camber angles influencing pull to side, front and rear toe angles influencing steering wheel misalignment), while the main cause of ‘drift leeward’ has been identified with (rear) ride steer. Application of the procedure to a production line led to a consistent reduction (from 3% down to about 1% of the overall production) of anomalous vehicles.

A knowledge-based online fault detection method of the assembly process considering the relative poses of components

The real-time process fault detection in the multi-station assembly process is always a challenging problem for auto body manufactures. Traditionally, the fault diagnosis approaches for variation source identification are divided into two categories, i.e. the pattern matching methods and model-based estimation ones based on the collected data set. The measurements provide effective process monitoring, but the real-time process fault diagnosis in the assembly process is still difficult with the traditional diagnosis techniques, and always depends on the engineering experience in practice. Based on the assembly process knowledge, including multi-station assembly hierarchy, fixture scheme, measurement characteristics and tolerances etc. in the multi-station, a knowledge-based diagnostic methodology and procedures are proposed with the measurements of each body in white for part/component defections and faulty assembly station identification. For the station involved with defective parts/components, the sub-coordinate system of the part/component is established reflecting its position and pose in the space, and then the relative pose matrix to the “normally build” pose is calculated based on the deviations of sub-coordinates of the parts in this station. Finally, the assembly process malfunctions are determined by a proposed rule-based strategy with the relative pose matrix in real time. A simple 3 stations assembly process with 5 sheet metal parts was analyzed and compared with the traditional diagnostic method to verify the effectiveness and stability of the proposed method.

Tolerance–reliability analysis of mechanical assemblies for quality control based on Bayesian modeling

PurposeThe purpose of this paper is to present a new efficient method for the tolerance–reliability analysis and quality control of complex nonlinear assemblies where explicit assembly functions are difficult or impossible to extract based on Bayesian modeling.Design/methodology/approachIn the proposed method, first, tolerances are modelled as the random uncertain variables. Then, based on the assembly data, the explicit assembly function can be expressed by the Bayesian model in terms of manufacturing and assembly tolerances. According to the obtained assembly tolerance, reliability of the mechanical assembly to meet the assembly requirement can be estimated by a proper first-order reliability method.FindingsThe Bayesian modeling leads to an appropriate assembly function for the tolerance and reliability analysis of mechanical assemblies for assessment of the assembly quality, by evaluation of the assembly requirement(s) at the key characteristics in the assembly process. The efficiency of the proposed method by considering a case study has been illustrated and validated by comparison to Monte Carlo simulations.Practical implicationsThe method is practically easy to be automated for use within CAD/CAM software for the assembly quality control in industrial applications.Originality/valueBayesian modeling for tolerance–reliability analysis of mechanical assemblies, which has not been previously considered in the literature, is a potentially interesting concept that can be extended to other corresponding fields of the tolerance design and the quality control.

Vibrating Powders: Electrochemical Quartz Crystal Microbalance Measurement of Potential Dependent IrO2 and Pt/C Mass Changes for Reversal Tolerant PEMFC Anodes

Oxygen evolution reaction (OER) catalysts are used to protect carbon components of polymer electrolyte membrane fuel cell (PEMFC) anodes during transient fuel starvation conditions such as start-up/shut-down [1]. OER catalysts such as IrO2 or RuO2 promote the oxidation of water instead of the corrosion of carbon components [1, 2]. However, the conditions in a PEMFC during normal operation (ca. 0 V and low pH) can induce instability in these metal oxides. IrO2 in particular can form soluble Ir3+ species [3] that migrate across the membrane electrode assembly and deposit on the cathode causing poisoning of the oxygen reduction reaction (ORR) catalyst (typically Pt/C). Currently, OER catalysts for reversal tolerant anodes (RTAs) are investigated using prototype MEA single unit cell testing which is time consuming and expensive to perform [4]. Previously, our group investigated the dissolution of different IrO2 based powder catalysts using a potential stepping stress test. The dissolution of Ir3+ from this test was compared with reversal tolerance of a membrane electrode assembly fabricated using the same IrO2 catalyst [5]. To further investigate the potential dependent mass changes of IrO2 powder layers, we have devised a series of experiments (with potential cycling between 0.05 to 1.2, 1.4 and 1.6 V vs. RHE, 30 times each at 100 mV s-1 and 298 K) using the electrochemical quartz crystal microbalance (EQCM) technique. The EQCM uses a vibrating quartz crystal and measures its frequency (inversely proportional to crystal mass) as a function of potential. Our method was used to investigate a commercially available IrO2 powder (Alfa Aesar) heat treated in air at 350, 450 and 550 °C. This heat treatment improves durability while reducing OER activity [6]. The powders were deposited (24 μg cm-2) onto a gold EQCM crystal to investigate the dissolution behavior as a function of particle size, crystallinity and electrode potential. We observed that the frequency of the untreated IrO2 increased by ca. 80 Hz (-570 ng cm-2) during the initial polarization from 1.15 V to 0.05 V vs. RHE (Figure a). The electrolyte was tested for dissolved Ir by inductively coupled plasma mass spectrometry (ICP-MS) but it was below the detection limit. This suggests that the first cycle frequency increase is caused by decreased rigidity of the IrO2 particle aggregates. During subsequent cycles, the untreated IrO2 frequency profile was consistent with previous reports. Birss et al. reported the formation of an iridium oxo-hydroxide at low potentials which causes a mass decrease (frequency increase) when polarizing to from 0 to 1.0 V vs. RHE [7]. Conversely, the frequency of heat treated layers first decreases by ca. 70 Hz (500 ng cm-2) before increasing again when polarizing to from 0.05 to 1.6 V vs. RHE (Figure b). Over the course of 90 CV cycles, there was an increase in film mass from the formation of iridium oxo-hydroxide species; confirmed by XPS. A platinum on carbon catalyst (Pt/C) was added to the IrO2 powders and the same experiment was performed (Figure c and d). This produced a dramatic increase in frequency which corresponded to a mass increase larger than the total deposited mass. Therefore, this mass decrease cannot be caused by dissolution of Pt or carbon corrosion alone and is instead attributed to loss of adhesion and changes in the viscoelasticity of the Pt/C aggregates. [8] The main challenge to using EQCM for powder catalyst investigation is producing layers with consistent and repeatable frequency behavior. In this work, the IrO2 and Pt/C deposition conditions were tightly controlled and each experiment was repeated to ensure the consistency of the results. It can also be difficult to interpret results and various analytical techniques should be used to supplement the EQCM technique. Despite these drawbacks, EQCM is a rapid and powerful tool to learn about potential dependent reactions using a myriad of powder catalysts. Ralph TR, Hudson S, Wilkinson DP (2006) ECS Trans 1:67–84.Patterson TW, Darling RM (2006) Electrochem Solid-State Lett 9:A183–A185.Danilovic N, Subbaraman R, Chang K-C, et al (2014) J Phys Chem Lett 5:2474–2478.Makharia R, Kocha S, Yu P, et al (2006) ECS Trans 1:3–18.Moore CE, Eastcott J, Cimenti M, Kremliakova N, Gyenge EL (2019) J Power Sources 417:53-60da Silva GC, Perini N, Ticianelli EA (2017) App Cat B: Env 218 287–297.Birss VI, Elzanowska H, Gottesfeld S (1991) Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 318:327–333.Lu S, Chung DDL (2013) Carbon 60:346–355. Figure 1

Analysis Line Approach for Assembly Tolerance Analysis

This work presents the analysis line approach for assembly tolerance analysis. Firstly, the product functional requirements and geometric variations of part positioning features can be converted into small displacements of a series of analysis points along the specified analysis directions. The small displacement torsor (SDT) theory is employed to establish the mathematical relations between the displacements of these analysis points. And then, the variation transfer relations and tolerance accumulation calculations of various orthogonal joints between different parts are studied to determine the maximum displacement of the analysis points on the functional surface. The final displacement accumulation results of the functional surface are compared with the geometric functional requirements of the product, so as to judge whether the product functional requirements are met. Finally, an example is given to demonstrate the effectiveness of the proposed analysis line approach.

Assembly Tolerance Design Based on Skin Model Shapes Considering Processing Feature Degradation

To increase the reliability and accuracy of tolerance design, more and more research works are considering not only orientation and position deviations; they are also forming errors in tolerance modeling. As a direct cause of form errors in industrial mass production, the processing features of the machining system degrade over time. Under the Industry 4.0 paradigm, an assembly tolerance design method based on Skin Model Shape is proposed to take the effect of degrading processing features into consideration. A continuous-time multi-dimensional Markov process is trained through maximum likelihood estimation based on the nodal sampling point set on the machined surface. Degradation of the machined surface is modeled based on the joint probability distribution of nodal displacements. Assembly force constraints and assembly entity constraints are applied to spatial assembly simulations. Tolerance synthesis takes the manufacturing cost and assembling probability as design objectives. A design example of the rotary feed component in a five-axis machine tool is proposed for explanation and verification.

New interlocking inter-module connection for modular steel buildings: Experimental and numerical studies

To improve the constructability and performance of modular buildings, a number of inter-module connections have been developed, each with their own associated advantages and disadvantages. Interlocking inter-module connections have emerged as a promising type of improvement; however, it is not clear how to provide the required installation tolerance without allowing slip. At the same time, the existing model for the shear force-slip behaviour is known to be inadequate. This study introduces a novel interlocking inter-module connection which combines structural bolts with interlocking elements to improve the constructability and shear force-slip behaviour. An experimental study was conducted to investigate the shear force-slip behaviour of the proposed connection. The effects of the interlocking elements, bolt preload, hole tolerance, and fabrication and assembly tolerance on the shear behaviour are evaluated and discussed. Numerical simulations were carried out to support the experimental program, following which the distinguishing features of the force-slip behaviour were examined, and an empirical model was proposed.

Effects of misalignments on the static and dynamic behaviour of a multiple overconstrained compliant 4-bar mechanism

The use of overconstrained mechanisms is often avoided in precision mechanics. Misalignments in the mechanism can cause deteriorated system behaviour, such as buckling. Overconstrained designs do have several advantages, such as higher load bearing capacity and higher natural frequencies. However, these advantages are only present if the mechanism is aligned within certain tolerances. In this paper a method is introduced to identify the limits of these alignment tolerances. The method allows the calculation of the forces in the mechanism due to misalignment. The internal forces are compared to the buckling loads of the mechanism yielding the critical misalignments; the method is corroborated using a multibody simulations. Subsequently, both analyses are compared to an experimental setup; this setup measures the first three modal frequencies and identifies the buckling modes. The proposed method and multibody simulation match with each other and the experiment. However, the critical misalignments are about 20% larger in the experiment; this is mainly attributed to hardware imperfections. Due to misalignment and flatness limitations of the flexures, the undeflected stiffness in the experiment is lower than modelled. The deterioration of the support stiffness is smaller in the experiment. In the most serious case, it retains 80% of the modal frequency in the support directions. The proposed method can be used as a guideline to estimate the manufacturing and assembly tolerances of an overconstrained flexure-based mechanism.

High Assembly Tolerance and Cost-Effective 100-Gb/s TOSA With Silica-PLC AWG Multiplexer

A low-cost hybrid-integrated transmitter optical sub-assembly (TOSA) for a 100-Gb/s coarse wavelength division multiplexing (CWDM) transceiver with high assembly tolerance has been demonstrated. We have proposed a novel two-lens configuration for the coupling between distributed feedback laser diodes and a silica-based planar lightwave circuit arrayed waveguide grating to relax the lenses assembly requirement. For this TOSA, the 1-dB assembly tolerances of all lenses are over ±15 μ m. Furthermore, we use a flexible printed circuit to connect the interior and exterior of the TOSA for radiofrequency signal transmission instead of the conventional ceramic feed-through box. Finally, a TOSA was packaged with a size of 22 mm × 10.7 mm × 4.5 mm. Error-free transmission over a 10-km single-mode fiber was successfully achieved when all four lanes were driven simultaneously with a total bit rate of 4 × 25.78125 Gb/s at an operating temperature of 25 °C.

Broadband Partially Reflecting Superstrate-Based Antenna for 60 GHz Applications

In this communication, a broadband low-profile partially reflecting superstrate (PRS)-based antenna is presented for 60 GHz applications. The PRS with an asymmetric pattern of circular metallic patches printed on one side of a thin dielectric slab improves the feed antenna gain from 6.5 to 18.5 dBi. A prototype antenna exhibits a peak gain of 18.8 dBi with a 3 dB gain bandwidth of 16.7%. Simulated and measured radiation patterns of the proposed antenna are highly directive toward broadside over a large operating bandwidth. The prototype antenna is well matched with a measured voltage standing wave ratio (VSWR) below 2 over a frequency range from 55.6 to 69.6 GHz, corresponding to a matching bandwidth of 22.4%. Fabrication limitations and assembly tolerances are also discussed. Overall, the prototype validates the high gain and wideband performance of the proposed antenna. The total area of the PRS is 5.2λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the overall height of the antenna is only 0.66λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> at the lowest operating frequency of 55.6 GHz.