Models to evaluate the performance of high-mix low-volume manual or semi-automatic assembly lines

To address mass customisation demand trends, assembly line flexibility and productivity are critical. Industry 4.0 technologies could support assembly operations to this end. However, clear implementation methodologies are still lacking. This article presents two models for evaluating the most relevant Key Performance Indicators (KPIs) of manual or semi-automatic assembly lines, allowing to maximise the return of investment of any digital technology addition. MATLAB® was used to implement a parametric model, and FlexSim® was employed to build a discrete event simulation model. The models were validated using data of two industrial study cases from a global white goods manufacturer

Study of Augmented Reality based manufacturing for further integration of quality control 4.0: a systematic literature review

Augmented Reality (AR) has gradually become a mainstream technology enabling Industry 4.0 and its maturity has also grown over time. AR has been applied to support different processes on the shop-floor level, such as assembly, maintenance, etc. As various processes in manufacturing require high quality and near-zero error rates to ensure the demands and safety of end-users, AR can also equip operators with immersive interfaces to enhance productivity, accuracy and autonomy in the quality sector. However, there is currently no systematic review paper about AR technology enhancing the quality sector. The purpose of this paper is to conduct a systematic literature review (SLR) to conclude about the emerging interest in using AR as an assisting technology for the quality sector in an industry 4.0 context. Five research questions (RQs), with a set of selection criteria, are predefined to support the objectives of this SLR. In addition, different research databases are used for the paper identification phase following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) methodology to find the answers for the predefined RQs. It is found that, in spite of staying behind the assembly and maintenance sector in terms of AR-based solutions, there is a tendency towards interest in developing and implementing AR-assisted quality applications. There are three main categories of current AR-based solutions for quality sector, which are AR-based apps as a virtual Lean tool, AR-assisted metrology and AR-based solutions for in-line quality control. In this SLR, an AR architecture layer framework has been improved to classify articles into different layers which are finally integrated into a systematic design and development methodology for the development of long-term AR-based solutions for the quality sector in the future

Experimental approach for the uncertainty assessment of 3D complex geometry dimensional measurements using computed tomography at the mm and sub-mm scales

The dimensional verification of miniaturized components with 3D complex geometries is particularly challenging. Computed Tomography (CT) can represent a suitable alternative solution to micro metrology tools based on optical and tactile techniques. However, the establishment of CT systems’ traceability when measuring 3D complex geometries is still an open issue. In this work, an alternative method for the measurement uncertainty assessment of 3D complex geometries by using CT is presented. The method is based on the micro-CT system Maximum Permissible Error (MPE) estimation, determined experimentally by using several calibrated reference artefacts. The main advantage of the presented method is that a previous calibration of the component by a more accurate Coordinate Measuring System (CMS) is not needed. In fact, such CMS would still hold all the typical limitations of optical and tactile techniques, particularly when measuring miniaturized components with complex 3D geometries and their inability to measure inner parts. To validate the presented method, the most accepted standard currently available for CT sensors, the Verein Deutscher Ingenieure/Verband Deutscher Elektrotechniker (VDI/VDE) guideline 2630-2.1 is applied. Considering the high number of influence factors in CT and their impact on the measuring result, two different techniques for surface extraction are also considered to obtain a realistic determination of the influence of data processing on uncertainty. The uncertainty assessment of a workpiece used for micro mechanical material testing is firstly used to confirm the method, due to its feasible calibration by an optical CMS. Secondly, the measurement of a miniaturized dental file with 3D complex geometry is carried out. The estimated uncertainties are eventually compared with the component’s calibration and the micro manufacturing tolerances to demonstrate the suitability of the presented CT calibration procedure. The 2U/T ratios resulting from the validation workpiece are, respectively, 0.27 (VDI) and 0.35 (MPE), by assuring tolerances in the range of +- 20–30 micro-m. For the dental file, the EN < 1 value analysis is favorable in the majority of the cases (70.4%) and 2U/T is equal to 0.31 for sub-mm measurands (L < 1 mm and tolerance intervals of +- 40–80 micro-m)

Traceable on-machine tool coordinate measurement through the integration of a virtual metrology frame in large machine tools

Metrological traceability and micrometre-level measurement uncertainty are the main research challenges towards traceable coordinate measurement on large machine tools. The impact of time- and space-varying thermal conditions on the machine tool structure is the major uncertainty contributor to the uncertainty budget. Aiming to minimise this influencing factor, this research proposes the use of integrated multilateration as a virtual metrology frame in combination with the machine tool controller information to characterise the position and orientation of every coordinate measurement performed by the machine tool. Experimental results demonstrate that measurement uncertainty is within an 18-micrometre range and assess the required metrological traceability

Uncertainty assessment for on-machine tool measurement: An alternative approach to the ISO 15530-3 technical specification

Touch probes are commonly employed in new machine tools (MTs), and enable machining and measuring processes to occur on the same MT. They offer the potential to measure components, either during or after the machining process, providing traceability of the quality inspection on the MT. Nevertheless, there are several factors that affect measurement accuracy on shop-floor conditions, such as MT geometric errors, temperature variation, probing system, vibrations and dirt. Thus, the traceability of a measurement process on an MT is not guaranteed and measurement results are therefore not sufficiently reliable for self-adapting manufacturing processes. The current state-of-the-art approaches employ a physically calibrated workpiece to realise traceable on-MT measurement according to the ISO 15530-3 technical specification, but it has a significant limitation in that it depends on a physical workpiece to understand the performance of the systematic error contributor (u b ). To this end, the aim of this paper is to propose an alternative methodology for on-MT uncertainty assessment without using a calibrated workpiece. The proposed approach is based on a volumetric error mapping of the MT prior to the measurement process, which provides an understanding of how the systematic error contributor(u b)performs

Comparison of surface extraction techniques performance in computed tomography for 3D complex micro-geometry dimensional measurements

The number of industrial applications of computed tomography (CT) for dimensional metrology in 100–103 mm range has been continuously increasing, especially in the last years. Due to its specific characteristics, CT has the potential to be employed as a viable solution for measuring 3D complex micro-geometries as well (i.e., in the sub-mm dimensional range). However, there are different factors that may influence the CT process performance, being one of them the surface extraction technique used. In this paper, two different extraction techniques are applied to measure a complex miniaturized dental file by CT in order to analyze its contribution to the final measurement uncertainty in complex geometries at the mm to sub-mm scales. The first method is based on a similarity analysis: the threshold determination; while the second one is based on a gradient or discontinuity analysis: the 3D Canny algorithm. This algorithm has proven to provide accurate results in parts with simple geometries, but its suitability for 3D complex geometries has not been proven so far. To verify the measurement results and compare both techniques, reference measurements are performed on an optical coordinate measuring machine (OCMM). The systematic errors and uncertainty results obtained show that the 3D Canny adapted method slightly lower systematic deviations and a more robust edge definition than the local threshold method for 3D complex micro-geometry dimensional measurements

Trajectory definition with high relative accuracy (HRA) by parametric representation of curves in nano-positioning systems

Nanotechnology applications demand high accuracy positioning systems. Therefore, in order to achieve sub-micrometer accuracy, positioning uncertainty contributions must be minimized by implementing precision positioning control strategies. The positioning control system accuracy must be analyzed and optimized, especially when the system is required to follow a predefined trajectory. In this line of research, this work studies the contribution of the trajectory definition errors to the final positioning uncertainty of a large-range 2D nanopositioning stage. The curve trajectory is defined by curve fitting using two methods: traditional CAD/CAM systems and novel algorithms for accurate curve fitting. This novel method has an interest in computer-aided geometric design and approximation theory, and allows high relative accuracy (HRA) in the computation of the representations of parametric curves while minimizing the numerical errors. It is verified that the HRA method offers better positioning accuracy than commonly used CAD/CAM methods when defining a trajectory by curve fitting: When fitting a curve by interpolation with the HRA method, fewer data points are required to achieve the precision requirements. Similarly, when fitting a curve by a least-squares approximation, for the same set of given data points, the HRA method is capable of obtaining an accurate approximation curve with fewer control points

Additive manufacturing with vat polymerization method for precision polymer micro components production

The direct fabrication of miniaturized polymer components by Additive Manufacturing (AM) processes is a remarkable method at the micro dimensional scale. However, the measurement of complex micro products and the evaluation of the related uncertainty are still particularly challenging and necessary in the micro AM field. In the DTU, a proprietary Vat Photopolymerization machine able to produce micro features has been designed, built and validated. This study evaluates the capability of the machine in terms of printed dimensions and the corresponding uncertainty assessment. For this purpose, two test parts with micro features of different geometries and dimensions have been designed and five samples of each test part have been printed. The dimensions of the micro features have been evaluated for quality control capability assessment and to stablish procedures for verification of AM machines

Advances in Sustainable and Digitalized Factories: Manufacturing, Measuring Technologies and Systems

The evolution from current to future factories is supported by research contributions in many fields of technology [...