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Despite the widespread use of electronic devices and consumer products integrating flexible electronics, in industrial practice, the assembly process of film-based coverlays is still performed manually, and this, in turn, affects process accuracy in first place. Additionally, the related manual tasks can be troublesome for workers, causing stress and fatigue. As a result, such a process can represent a bottleneck in the fabrication of Flexible Printed Circuit Boards (FPCBs). In the present paper, the architecture of a gripper is proposed as the core device of a completely automated film-coverlay assembly process. The architecture of the gripper is vacuum-based and exploits the action of several independent valves, enabling the grip configuration according to the geometry of the component. The gripper operation is shown by implementing specific solutions related to the removal of the coverlay protective film and partial coverlay thermal bonding, thus providing also a detailed description of the phases concerning a feasible automated assembly process. The results of the tests concerning the evaluation of both solutions are reported and discussed in the paper. Finally, a simplified gripper version is prototyped to perform some of the tests, and it is also used to preliminarily assess the performance of the gripping strategy, with good results.

In fused deposition modeling (FDM) process, several uncertainty sources contribute to low accuracy and bad surface finishing. Besides intrinsic uncertainties, other factors, related to the machine structure and actuation, participate to increase complexity and reduce the controllability of the process. On-board vision systems can be successfully exploited to monitor the deposition process and to acquire quantitative information on geometry and transients. This information can be used to calibrate the process parameters where a compensation strategy is implemented. In this paper, a low-cost vision system capable of microscopic acquisitions is integrated into an FDM machine and image-processing techniques are exploited to define calibration procedures to improve the process accuracy, thus extending the use of this equipment to micromanufacturing applications. The effectiveness of the integration is evaluated through the fabrication of a microfluidic device.

A new type of vacuum microgripper is considered. An automatic release device inserted in the gripper body allows to overcome adhesion forces that can prevent detachment of the object to be handled. A CFD analysis of a simplified model of the device is presented. The goal is to evaluate the lifting force on the release device as a function of geometric parameters, an important information for design of this class of microgrippers. A reference geometry has been firstly investigated using a highfidelity approach, i.e. a Large Eddy Simulation. The results have been used to validate a cheaper CFD approach based on the RANS solution. Then through steady RANS computations a dataset has been obtained varying geometric parameters of the device. Trends of the lifting force in terms of geometry modification are presented and discussed. All calculations have been performed with OpenFOAM®.

Full optical backplanes can be seen as a promising technology for high bandwidth ICT (Information and Communication Technology) apparatuses and high performance computing systems. According to a recent frame-based solution, the backplane mounts a number of independent optical interconnect circuits mainly consisting of a set of optical fiber ribbons of different lengths arranged to fulfill a specific planar ribbon routing. A non-negligible problem is related to the development of suitable techniques for the efficient and cost-effective assembly of such sub-circuits. New systems are required that combine ultimate hardware and software capabilities and derive from a synergic implementation of digital and advanced manufacturing technologies. The successful assembly of the optical interconnection circuits lies in the development of cyber-physical production systems within the framework of Industry 4.0. In this context, this work will present and discuss how different innovative technologies and consolidated technologies applied in a novel context were exploited to demonstrate the feasibility of the automated backplane assembly. The achieved results are discussed in terms of design of the work-cell layout and related equipment, simulation tests, tool path planning, and final task execution.

The miniaturization of an increasing number of complex hybrid micro-products is currently leading the development of several micro-components to be manipulated and assembled, meeting various specifications related to the objects properties and the planned task. However, at the micro-scale, further challenges derive from the effects of surface forces between the object and the micro-gripper that have to be overcome to provide for an effective and successful manipulation. When contact micro-grippers are used, specific solutions to support the release phase are needed. In particular, further developments and novel tools should be developed for vacuum micro-grippers to actively release the components reliably and precisely. In this context, this paper presents a vacuum micro-gripper with an automatic releasing system able to overcome the adhesive forces simply and effectively. The paper reports the results of a preliminary computational fluid dynamics analysis and the development a numerical model able to represent the main gripper characteristics then to derive a first procedure for its design.

In manipulating and assembly tasks, the gripper plays a fundamental role. Tasks at the microscale are particularly challenging due to the possible effect of unwanted stiction. Many different grasping tools (generally called microgrippers) have been developed and are described in literature. The differences rely on size, shape, exchanged forces with the manipulated parts and working principle depending on the application field. Despite the large number of research and industrial cases, each author has developed different and not comparable procedures and indices to assess the device grasping and releasing performance. Therefore, the paper proposes a formalization of methods and indices for the evaluation of the performance of a generic contact microgripper in terms of precision in grasping and releasing and successful rate. This review could be helpful to support the design or the choice of the most suitable gripper according to the properties of the components to be manipulated, the task requirements and the system constraints (i.e., according to the application requirements). The validity of the proposed methodologies and indices is confirmed by theory and experimental data analysis.

The miniaturization of an increasing number of complex hybrid micro-products is currently leading the development of several micro-components to manipulate and assemble, meeting various specifications related to the objects properties and the planned task. However, at the micro-scale, further challenges derive from the effects of surface forces between object and micro-gripper that have to be overcome for an effective and successful manipulation. When contact micro-grippers are used, specific solutions to support the release phase are needed. Further developments and novel tools should be developed for vacuum micro-grippers to actively release the components reliably and precisely. In this context, this paper presents a vacuum micro-gripper with an automatic releasing system able to overcome the adhesive forces simply and effectively. The paper reports the results of a preliminary computational fluid dynamics analysis and the development of a numerical model able to represent the main gripper characteristics and derive a first design procedure.

The current innovation of the mechatronic products has led to the use of miniaturized devices that combine components with different material, shape, reduced mass, and extremely small size, in order to increase the functionalities and the efficiency of the products. This trend involves new issues related to the manufacturing and automated assembly of these products. Even in constantly developing non-industrial sectors such as biomedicine, the need for automated equipment for preparing and manipulating biological samples represents a current challenge. In particular, the sorting and feeding systems cover an essential role since they can affect the task strategy, the operation scheduling, and the overall system performance. Moreover, they should cope with the adhesion issues related to micro-scale manipulation, as all the devices that handle sub-millimetric components. In this context, this paper presents two methods and the related tools for the automated sorting and manipulation of micro-spheres: the former exploits a micro-gripping tool and implements a pick-and-place (P&P) approach, while the latter is based on newly conceived devices implementing a "store-and-place" (S&P) strategy. The two methods were studied considering two application examples. They were firstly exploited to perform the automated reballing of a BGA (Ball Grid Array) package to be mounted on a Printed Circuit Board; the implemented tasks will be described and discussed to underline their characteristics and applicability. Furthermore, a second application of the methods to the sorting and placement of fertilized Zebrafish eggs is envisaged.

The aim of the present study is the assessment of the integration of a low cost optical measurement device into a high-precision machine tool for micro manufacturing applications. The measurement system can be effectively integrated into the working volume of different types of machines allowing both tool and workpiece measurements and avoiding its disassembly from the machine stage for off-line measurements and, consequently, reference losses. The fast measurements of tool and workpiece during the machining contribute to increase the accuracy and reduce the overall machining-measurement iterations. The assessment is achieved by a test case where a low cost USB microscope is applied to a micro-EDM machine. The low cost device has been applied for tool electrode measurements and tool wear evaluation after an accuracy enhanced calibration procedure and high performance image processing algorithms, which effectively reduce the lack of the hardware performance. The measurement performance gives a feedback on the deviations of the machined features from nominal geometry and allows their compensations by an adequate machining strategy.

The current miniaturization of several products requires manufacturing systems and methods able to meet the demanding specifications in terms of precision, efficiency, flexibility and reconfigurability. In particular, the manipulation and assembly of micro-components to obtain such products represent a crucial and challenging phase. For this reason, gripping tools have an essential role. At the micro-scale, the effects of adhesion forces can negatively affect the success and the precision of the manipulation operations, causing unexpected gripping or preventing the release of the components. Therefore, new micro-grippers and suitable release strategies have to be designed and developed to ensure high performance, overcoming the issues typical of the micro-scale. Among the different types of micro-grippers, vacuum micro-grippers represent a suitable tool to manipulate fragile and small components. In this context, this paper discusses different designs of an innovative vacuum micro-gripper integrating a simple and effective release system. The basic working principle is discussed and the related prototype is shown. Finally, a new design enhancement is also introduced to extend its applicability and release capability.

The trend toward miniaturisation of the last decade has caused a real revolution in the manufacturing of many products and systems in several fields, trying to reduce volume and weight, and integrate more functions in a smaller space. Besides the various manufacturing techniques presented in the previous chapters of the book, growing interest has been gained by the manipulation and the assembly of different micro-components for the production of such complex systems, specifically of hybrid micro-products. In this context, this chapter aims to get an overview on different micro-assembly aspects, including: methods, robots for micro-assembly with related examples, micro-manipulation strategies and tools, vision and force sensing for micro-assembly, consideration of environmental conditioning, and an example of a robotized micro-assembly work-cell developed at the authors' laboratory.

The wide investigation of the last decades on a variety of electronic products in order to increase their performance while miniaturizing them, has raised new issues related to their manufacturing, remanufacturing and reuse at their end-of-life. This scenario introduces further challenges, related to demanding specifications, to be addressed with enhanced or new (re-) manufacturing processes, innovative systems, and advanced strategies. In this context, this paper discusses some challenging applications exploiting novel automatic solutions on different complexity levels of the process, from the component to the whole system, including devices, tools and robotized work-cells developed by the authors.

Le industrie manifatturiere avanzate, utilizzando tecniche di lavorazione di precisione, come il diamond turning (tornitura con utensili in diamante), lo stampaggio a iniezione, la micro-fresatura e la micro-lavorazione per elettroerosione, sono in grado di produrre componenti in miniatura complessi, ad alta precisione. Accanto alle tecnologie di micro-lavorazione è necessario, però, possedere una serie di competenze per la misura di strutture di piccole dimensioni con tolleranze in scala micro [1]. La metrologia è essenziale per la riduzione delle tolleranze dimensionali, che permette la produzione di macchine più efficienti e il miglioramento della loro longevità, riducendo i giochi o l'usura. Un esempio sono gli ugelli di iniezione più piccoli e più efficienti nelle macchine a combustione, la cui produzione è strettamente legata al miglioramento delle capacità di misura dimensionale. Altri esempi sono la radiofrequenza o i componenti dei connettori di fibre ottiche, in cui le dimensioni caratteristiche e le tolleranze richiedono un'incertezza di misura a livello di 0,1 ?m, oppure le piccole lenti asferiche/freeform delle fotocamere digitali o dei telefoni cellulari [2]. Un settore emergente è quello dei prodotti medicali ad alta tecnologia, che molto spesso dipendono notevolmente da piccoli componenti; tra questi vi sono, ad esempio, le pompe per insulina, gli stimolatori cardiaci, i sensori per la diagnostica in vivo o i sistemi di visione endoscopici. In questo capitolo vengono descritte le tecniche a contatto e non a contatto che possono essere utilizzate per misurare feature 3D in scala micrometrica.

Recently, the remanufacturing of electronic products has become of great interest for both the industrial and research fields, for the several benefits deriving from the recovery of high added value elements at their end of life. In particular, the reballing of BGA (Ball Grid Array) packages is an important process in the rework of PCBs (Printed Circuit Boards). In this context, this paper presents two methods for the automated reballing and the corresponding tools able to operate different solder spheres. The tasks implemented for the reballing of a target BGA matrix will be described and discussed to underline their characteristics and applicability.

Oltre alle varie tecniche di lavorazione presentate nei capitoli precedenti, un interesse crescente è stato rivolto alla manipolazione e assemblaggio di diversi micro-componenti per la produzione di sistemi complessi. In questo contesto, questo capitolo mira a fornire una panoramica su diversi aspetti del microassemblaggio. Innanzitutto, nella Sezione 9.2 sono introdotti i micro-prodotti ibridi ed è evidenziata la necessità del micro-assemblaggio. In seguito, nelle Sezioni 9.3-9.4, sono classificati e descritti i metodi di micro-assemblaggio. I robot di microassemblaggio e relativi esempi sono presentati nella Sezione 9.5. Nella Sezione 9.6, dopo un'introduzione alle problematiche del manipolare micro-componenti, sono discusse le strategie e i dispositivi di micro-manipolazione e viene fornita una panoramica dei possibili metodi di rilascio. L'importanza della visione e della misura della forza per il micro-assemblaggio è discussa nella Sezione 9.7, unitamente ad alcune considerazioni sul condizionamento ambientale. Infine, nella Sezione 9.8, è presentato un esempio di cella di lavoro robotizzata per microassemblaggio sviluppata presso il laboratorio degli autori.

The paper presents the design and development of a new robotized assembly system of optical backplanes in high-capacity ICT (Information and Communication Technology) apparatus, mainly used for switching stations and distribution networks. The optical backplane solution consists of several optical fiber ribbons positioned on a planar backplane according to an innovative and optimized full-mesh layout where the overall optical interconnection is partialized into a plurality of different independent sub-circuits. Each optical interconnection sub-circuit consists of optical fiber ribbons with standardized optical and mechanical interfaces and customized components that have to be carefully and precisely assembled in order to achieve connections with low optical power losses. The paper describes the method and the main devices and tools conceived for the automatic assembly of optical interconnection sub-circuits, highlighting the critical aspects and the proposed solutions towards the automatized assembly of the whole optical backplane.Copyright © 2015 by ASME

Il documento rappresenta il contributo dell'Unità Operativa ITIA-CNR al Rapporto Tecnico sugli Stati d'Avanzamento Intermedi del Progetto (SAL) 7 del progetto BACKOP che riporta le attività relative allo Sviluppo dell'automazione dell'assemblaggio di circuiti di interconnessione ottica da integrare su backplane svolte dall'unità dal 01/10/2014 al 31/03/2015.

The paper describes a new laser device conceived for surface scanning and more specifically for mini robot calibrations. The system is based on a laser triangulation sensor which is moved by an extremely accurate device to collect a set of 3D points lying on surfaces. If the surfaces belong to the gripper of a robot that must be calibrated and a sufficient number of points of this gripper are collected, the pose of the robot can be measured. If the robot is moved to several different configurations and the gripper poses are measured for each of them, it is possible to reconstruct the kinematics of the robot and calibrate it. The paper presents the theory and describes the design, tests and calibration of the laser instrumentation with a focus on the first experimental results. These results are obtained in a working cell including a vision system, a 4-dof (xyz,θ) mini robot and a 2-dof rotating platform.Copyright © 2015 by ASME

Rapporto tecnico commissionato dal Polo Tecnologico di Pordenone per conto dell'azienda Ferramenta Livenza per conoscere lo stato dell'arte sui sistemi di alimentazione e sorting di componenti meccanici e il trend verso il quale la tecnologia si muove. Tale report è inquadrato come "Attività 1" della fornitura.

Report tecnico finale del progetto di ricerca PON BACKOP. Il report, inoltre, illustra le attività finali di validazione e test delle soluzioni e dei dimostratori prototipali e riassume tutte le attività di ricerca svolte. Nel dettaglio, ITIA-CNR nel periodo di riferimento Marzo 2015 - Giugno 2015 ha svolto le prove di test meccanici sui circuiti di interconnessione di backplane ed ha ulteriormente messo a punto la cella di assemblaggio automatizzata del circuito. Durante lo stesso periodo tutti i team di ricerca del progetto hanno svolto attività di dissemination dei risultati della ricerca partecipando a conferenze nazionali ed internazionali con paper scientifici sviluppati nel progetto.

Il documento illustra le attività di ricerca e consulenza svolte all'interno del progetto EDOC@Work nel task 14.2 da CNR-ITIA. In particolare le attività hanno previsto, lo sviluppo di un impianto pilota reale per l'assemblaggio di micro-componenti personalizzati, implementando così il paradigma della teaching/learning factory.

In high-bandwidth ICT apparatus (data centers, servers, switching stations, etc.) and high-performance computing systems, high-effectiveness optical connections are requested. [2] These high-capacity ICT apparatus are based on optical backplanes where switching cards are connected each other with optical interconnection circuits. These optical interconnection circuits on the backplane allow signal transmission between cards. They should answer to several technical requirements as low optical power losses, low disturbance and interference in transmission, low size, standardized optical and mechanical interfaces, easy maintenance and, finally, low system costs. For these reasons, in the last years several solutions have been proposed for optical backplane interconnection circuits. The paper presents the design and development of a new optical backplane interconnection circuit for high-capacity ICT apparatus, mainly used for switching stations and distribution networks. It has several innovative aspects [1] and it solves drawbacks of prior art. The paper also shows circuit optical performances and describes the innovative assembly method conceived for the automatic assembly of optical backplane circuits.

Il documento rappresenta la relazione scientifica finale del Work Package 3 del Progetto FIDEAS e riporta i risultati ottenuti nel Work Package, le relative attività di disseminazione e il contributo raggiunto dal progetto nel migliorare la dotazione tecnologica territoriale.

This paper investigates the actuation of untethered microrobots with a focused magnetic field generated by a permanent magnet wand. The microrobots are chrome-steel spheres or Neodynium cubes with a size of 250 μm, which perform desired planar motions directed by the movement of the wand. We propose and evaluate novel methods to enhance the focused magnetic field of the wand by sharpening its tip, increase microrobot velocities via novel mechanical amplifiers, and reduce environmental forces via inexpensive anti-friction coatings. We document results of automated operation and teleoperated control of the microrobot during competition at the Mobile Microrobotics Challenge (MMC) held in 2013. Experimental results from the mobility and microassembly challenge indicate an excellent degree of precision motion control over the robot, at a price of a slightly lower maximum speed when compared to conventional electromagnetic actuation.

Il rapporto tecnico intermedio illustra i risultati dell'attività di ricerca svolte dagli autori nel periodo Aprile 2014 - Settembre 2014 (6° SAL) del progetto PON R&C Backop, titolo del progetto: "Backplane ottici per apparati di telecomunicazioni ad elevata capacità". Le attività di ricerca hanno riguardato: -Analisi delle tecnologie di produzione per i componenti del circuito ottico; -Analisi dei costi dettagliata per l'approvvigionamento delle fibre ottiche a ribbon; -Progettazione di dettaglio e realizzazione del banco di assemblaggio dei circuiti; -Progettazione e realizzazione dell'automazione del banco di assemblaggio; -Analisi dei componenti del circuito ottico di interconnessione; -Prototipazione di N°2 circuiti ottici da sottoporre a test funzionali; -Sviluppo della cella robotizzata di assemblaggio dei circuiti ottici (robot, sistema di visione, gripper multiplo, ecc.).

Purpose – The purpose of this paper was the design, development, and test of a flexible and reconfigurable experimental setup for the automatic manipulation of microcomponents, enhanced by an accurately developed vision-based control. Design/methodology/approach – To achieve a flexible and reconfigurable system, an experimental setup based on 4 degrees of freedom robot and a two-camera vision system was designed. Vision-based strategies were adopted to suitably support the motion system in easily performing precise manipulation operations. A portable and flexible program, incorporating the machine vision module and the control module of the task operation, was developed. Non-conventional calibration strategies were also conceived for the complete calibration of the work-cell. The developed setup was tested and exploited in the execution of repetitive tests of the grasping and releasing of microcomponents, testing also different grasping and releasing strategies. Findings – The system showed its ability in automatically manipulating microcomponents with two different types of vacuum grippers. The performed tests evaluated the success and precision of the part grasping and release, which is a crucial aspect of micromanipulation. The results confirm reliability in grasping and that the release is precluded by adhesive effects. Thus, different strategies were adopted to improve the efficiency in the release of stuck components without negatively affecting the accuracy nor the repeatability of the positioning. Originality/value – This work provided a flexible and reconfigurable architecture devoted to the automatic manipulation of microcomponents, methodologies for the characterization of different vacuum microgrippers, and quantitative information about their performance, to date missing in literature.

In precise manipulation and assembly of components with sub-millimetric dimensions, the role of the gripping tools is fundamental. In the literature, many different types of the so-called microgrippers have been presented, based on different working principles, to cope with the issues related to the gripping, the handling and the release of different micro-components. Depending on the component properties, the task requirements and the system constraints, a microgripper could be more suitable than another and allow the achievement of higher performance. However, the performance assessment of the microgrippers lacks of a standardized and quantitative methodology. Many authors declare the good capabilities of their tools in a qualitative way or according to the results obtained executing specific and different tasks. For this reason, it is often difficult to compare different microgrippers and estimate the actual results that can be obtained e.g. in the gripping or the release of a component. In this context, after a preliminary survey of the adopted approaches in literature and of their meaning, this paper investigates the conception and formalization of methods and procedures to evaluate the performance of a generic microgripper and the definition of standard performance indices to support the presentation of the microgripper characteristics.

Il rapporto tecnico intermedio illustra i risultati dell'attività di ricerca svolte dagli autori nel periodo Ottobre 2013 - Marzo 2014 (5° SAL) del progetto PON R&C Backop, titolo del progetto: "Backplane ottici per apparati di telecomunicazioni ad elevata capacità". Le attività di ricerca hanno riguardato: -Definizione delle specifiche di dettaglio del circuito ottico di interconnessione per l'integrazione con il connettore di scheda. -Standardizzazione delle interfaccie ottico-meccaniche -Sviluppo di dettaglio del circuito ottico di interconnessione; -Prototipazione della soluzione finale; - Progettazione preliminare del banco di assemblaggio di ribbon di fibre ottiche su telaio; - Realizzazione del prototipo non attuato del banco di assemblaggio dei circuiti; -Definizione del progetto costruttivo del backplane -Integrazione di sistema -Definizione delle specifiche preliminari del sistema robotizzato di assemblaggio -Definizione della procedura di assemblaggio -Analisi delle tecnologie di produzione dei componenti il circuito e relativi costi

In the micro-manipulation field, the adoption of vision-based strategies can suitably support the motion system in easily performing precise manipulation operations. In this context, the cooperation between the robot and the vision system is fundamental to achieve high performance. The paper introduces and critically discusses the main issues related to the design and implementation of vision-based control for a micro-manipulation work-cell. The core issues of the developed software architecture, such as the work-cell calibration and the task execution module, are described and its main characteristics highlighted. The application of this program within a micro-assembly work-cell set-up allowed the execution of various manipulation operations, thus representing a test bench for its capabilities evaluation. The actual execution of a pick&place task is finally discussed.Copyright © 2013 by ASME

The paper describes the design and development of a miniaturised workcell devoted to the robotized micro manipulation and assembly of extremely small components, jointly carried out by the University of Brescia, University of Bergamo, University of Ancona and the Institute of Industrial Technologies and Automation of the Italian National Research Council in the framework of the project PRIN2009 MM&A, funded by MIUR. Besides analyzing theoretical and practical aspects related to the design of the work cell components (positioning and orienting devices, grippers, vision and control systems), an automated test bed for the assembly of micro pieces whose typical dimension belongs to the submillimeter scale range has been implemented. The perspective is to contribute to the realization of general automatic production systems at the moment absent for objects of these dimensions.

Over the years, industrial robot applications have been broadening, including complex, fast and high-precision operations, in several industrial and non-industrial fields. These new tasks require an increase in performance in terms of velocity, accuracy, trajectory design, sensor integration, control strategy and flexible programming, that can be achieved by advanced hardware and software solutions. However, achievement of high performance and actual exploitation of enhanced systems are currently almost research issues. This book addresses the development of techniques to improve the performance of industrial robots and robotic work-cells for advanced applications, highlighting the role of clever design and calibration strategies. Two innovative fields are investigated: applications requiring an intelligent and controlled interaction between the robot and the environment, and micro-manipulation, that is the handling of components with sub-millimetric size. The comprehensive analysis of theoretical aspects and experimental results aims to reduce the current gap between research and industry, making this book a tool useful to both researchers and manufacturers.

Il documento rappresenta il Deliverable 2.1 del Work Package 2 del progetto REMS e riporta lo stato dell'arte dei microdispositivi di presa e di assemblaggio e ridefinizione degli obbiettivi del Progetto

The paper introduces an experimental setup for the automatic manipulation of microcomponents, based on a 4 dof robot with Shoenflies motion and a two-camera vision system. The general architecture of the work-cell is presented. The work-cell functionality was tested via repeatability experiments using a set of vacuum grippers. Due to their intrinsic simplicity, vacuum grippers are very cheap and appear a promising solution for micromanipulation. An innovative nozzle for a vacuum gripper was designed, fabricated and tested, comparing its performance with traditional needles. The design was conceived to reduce the frequency of occlusions of the gripper and handle a wide range of particles. The performed tests evaluate the success and precision of the part release. Indeed, this is a crucial aspect of micromanipulation because microparts tend to stick to the gripper preventing the successful performance of manipulation tasks. The results confirm that adhesive effects prevent the release of components. For this reason different strategies were adopted in order to improve the efficiency in the release of stuck components. This solution increases the percentage of release and, setting appropriately the intensity of the pressure, it does not affect negatively the accuracy nor the repeatability of the positioning. © 2012 IFIP International Federation for Information Processing.