Operator-centred Lean 4.0 framework for flexible assembly lines

This article provides a starting point for developing a methodology to successfully implement Industry 4.0 technology for assembly operations. It presents a novel multi-layer human-centred conceptual model in line with Lean philosophy which identifies the assembly operator functions and relates them to other production departments, identifying how they would be affected by incorporating new digital technologies. The model shows that assembly operators would only be directly supported by hardware digital technologies, while the production support departments would mainly employ Industry 4.0 software technologies. The work presented here paves the way for developing a methodology for implementing Lean Assembly 4.0

Lean manual assembly 4.0: A systematic review

In a demand context of mass customization, shifting towards the mass personalization of products, assembly operations face the trade-off between highly productive automated systems and flexible manual operators. Novel digital technologies—conceptualized as Industry 4.0—suggest the possibility of simultaneously achieving superior productivity and flexibility. This article aims to address how Industry 4.0 technologies could improve the productivity, flexibility and quality of assembly operations. A systematic literature review was carried out, including 234 peer-reviewed articles from 2010–2020. As a result, the analysis was structured addressing four sets of research questions regarding (1) assembly for mass customization; (2) Industry 4.0 and performance evaluation; (3) Lean production as a starting point for smart factories, and (4) the implications of Industry 4.0 for people in assembly operations. It was found that mass customization brings great complexity that needs to be addressed at different levels from a holistic point of view; that Industry 4.0 offers powerful tools to achieve superior productivity and flexibility in assembly; that Lean is a great starting point for implementing such changes; and that people need to be considered central to Assembly 4.0. Developing methodologies for implementing Industry 4.0 to achieve specific business goals remains an open research topic

Implementation of the control strategy for a 2D nanopositioning long range stage

A 2D-platform stage able to obtain an effective metrological positioning with nanometer resolution and long working range (50 x 50 mm2) is on development at the University of Zaragoza. The 2D stage has already been designed, manufactured and assembled. The movement of the platform is performed by four custom-made linear motors, and mirror laser interferometers work as positioning sensors in XYRz degrees of freedom. The work here presented focuses on the hardware implementation of the motor control, for one actuator on a 1D linear stage. The developed control strategy acts on three-phase PWM (Pulse-Width Modulation) signals and a feedback is provided by measuring the phase currents. As a preliminary solution, a sensorless algorithm substitutes the positioning sensor before implementing the laser interferometers

A surface extraction analysis in a multi-material test part for computed tomography in metrology applications

The main advantage of Computed Tomography is the capability of making measurements of non-accessible internal features in a test piece. One of the cases that can usually be found in this sense is the contact zone between two elements that are forming a common surface boundary, where the main complexity is to determine which surface belongs to which piece. Nowadays, this kind of surfaces are measurable only by utilizing Computed Tomography, taking into account that the characteristics of the Tomography can significantly vary depending on the material of the elements that are in contact. In this article a piece that has two different interfaces is analyzed: a Piece in contact with Air, and Material A in contact with Material B. Three different surface extraction algorithms are analyzed for multi-material parts, Threshold, Canny and Deriche, and the results and conclusions obtained are presented

Product development methodology "scalability"

In industrial manufacturing environments, where production requires a detailed product development, delivery times to customer are highly affected by the time required for development. Usually, product development takes long before arriving to the final solution Therefore, an improvement of the product development process can imply a very high potential in reducing the product delivery time to customer. This paper outlines a new product development methodology, based on the foundations of collaborative design and lean and agile methodologies. For that, we analyze and optimize the value stream of the product engineering process flow in a company of the sector of design, manufacturing, and commercialization of equipment in retail, through lean tools, to implement the “product scalability” concept. The case study shows a reduction of the product development lead time around 10-20%, regarding the present process, in the pilot tests conducted. Consequently, product development methodology “scalability” could have an enormous potential in reducing lead time and product development cost, in sectors with similar characteristics in terms of number of product variants and life cycles than the development of furniture and equipment for retail sector

Self-calibration technique for on-machine spindle-mounted vision systems

On-machine measuring (OMM) systems are being more and more applied in machine tools in order to measure workpieces on the machine itself. Many of these systems are directly mounted in the machine spindle, so the measuring uncertainty is affected by clamping positioning and orientation variations, especially when integrating optical systems based on machine vision. This paper presents a self-calibration technique for vision systems by using redundant information of on machine measurements, avoiding extra mechanical anchoring or calibration means. It has been applied to a vision system with the angular placement uncertainty of a tool holder coupling being the main uncertainty contributor. A milling machine pilot case has been selected for demonstration, showing an effective self-calibration capability both in laboratory and industrial conditions

Analysis of surface extraction methods based on gradient operators for computed tomography in metrology applications

Among the multiple factors influencing the accuracy of Computed Tomography measurements, the surface extraction process is a significant contributor. The location of the surface for metrological applications is generally based on the definition of a gray value as a characteristic of similarity to define the regions of interest. A different approach is to perform the detection or location of the surface based on the discontinuity or gradient. In this paper, an adapted 3D Deriche algorithm based on gradient information is presented and compared with a previously developed adapted Canny algorithm for different surface types. Both algorithms have been applied to nine calibrated workpieces with different geometries and materials. Both the systematic error and measurement uncertainty have been determined. The results show a significant reduction of the deviations obtained with the Deriche-based algorithm in the dimensions defined by flat surfaces

3D measurement simulation and relative pointing error verification of the telescope mount assembly subsystem for the large synoptic survey telescope

An engineering validation of a large optical telescope consists of executing major performing tests at the subsystem level to verify the overall engineering performance of the observatory. Thus, the relative pointing error verification of the telescope mount assembly subsystem is of special interest to guarantee the absolute pointing performance of the large synoptic survey telescope. This paper presents a new verification method for the relative pointing error assessment of the telescope mount assembly, based on laser tracker technology and several fiducial points fixed to the floor. Monte-Carlo-based simulation results show that the presented methodology is fit for purpose, even if floor movement occurs due to temperature variation during the measurement acquisition process. A further research about laser tracker technology integration into the telescope structure may suggest that such laser tracker technology could be permanently installed in the telescope in order to provide an active alignment system that aims to detect and correct possible misalignment between mirrors or to provide the required mirror positioning verification accuracy after maintenance activities. The obtained results show that two on-board laser tracker systems combined with eight measurement targets could result in measurement uncertainties that are better than 1 arcsec, which would provide a reliable built-in metrology tool for large telescopes

Uncertainty budget of a large-range nanopositioning platform based on Monte Carlo simulation

The objective of precision systems design is to obtain machines with very high and totally predictable work-zone accuracies. In already functional systems, where the errors can be measured, this is achieved by error correction and compensation. The aim of this work is to propose an uncertainty budget methodology to obtain the final measuring uncertainty of precise measuring systems, after error compensation. The case study is a nanopositioning platform, referred as NanoPla, with a confocal sensor integrated as measuring instrument. The NanoPla performs precise positioning in a large range of 50 mm × 50 mm, and its target is surface topography characterization, at a submicrometre scale. After performing the uncertainty budget of the NanoPla, Monte Carlo method is used to obtain the final measuring uncertainty along the whole NanoPla working range, considering all the casuistry. By studying the results, the authors are able to propose solutions to minimize the final measuring uncertainty

Geometrical characterisation of a 2D laser system and calibration of a cross-grid encoder by means of a self-calibration methodology

This article presents a self-calibration procedure and the experimental results for the geometrical characterisation of a 2D laser system operating along a large working range (50 mm × 50 mm) with submicrometre uncertainty. Its purpose is to correct the geometric errors of the 2D laser system setup generated when positioning the two laser heads and the plane mirrors used as reflectors. The non-calibrated artefact used in this procedure is a commercial grid encoder that is also a measuring instrument. Therefore, the self-calibration procedure also allows the determination of the geometrical errors of the grid encoder, including its squareness error. The precision of the proposed algorithm is tested using virtual data. Actual measurements are subsequently registered, and the algorithm is applied. Once the laser system is characterised, the error of the grid encoder is calculated along the working range, resulting in an expanded submicrometre calibration uncertainty (k = 2) for the X and Y axes. The results of the grid encoder calibration are comparable to the errors provided by the calibration certificate for its main central axes. It is, therefore, possible to confirm the suitability of the self-calibration methodology proposed in this article