In high competitive markets, such as the automotive industry, the better quality of products, reduction of manufacturing costs and the fulfilment of all delivery deadlines can only be achieved through continuous improvement of production capabilities. One current strategy is to develop and create smarter and adaptive assembly tools.
Automation is a relevant area of development in the current industrial world and the baseline of the fourth industrial revolution (Industry 4.0). Namely, it is very important to use sensing components on jigs for assembly parts in the production line. The arrangement of sensing components on the assembly tools is very dependent of the product, making the project more complex and less flexible. This issue can penalise the productivity heavily, especially if a wide range of products and changeover operations are usual.
The use of Additive Manufacturing (AM) is growing in the industry and offers a high potential for research and development in the present stage. The AM is advantageous in many areas, especially in the rapid construction of complex tools (RP). This paper presents a new optical sensing concept based on the 3D printing of internal circuits in the assembly tools. This solution can bring many advantages and increase tools flexibility.Programa Operacional de Competividade e Internacionalização - COMPETE 2020, Projeto nº 002814; Ref. POCI-01-0247-FEDER-002814, entre a Univ. Minho e a Bosc

Alves, Tiago

Brito, A. M.

Freitas, Luís Miguel Capela Pereira Leite

Lima,  Ricardo

Noversa, João Tiago Gomes

Nunes, J. P.

Pimentel, Anthony Michael Fernandes

Sousa, Reinaldo

English

Universidade do Minho: RepositoriUM

1 INTRODUCTION 1.1 Background The discovery of new technologies and solutions has accompanied the industrial development, through early adoption of new mechanical systems to support the production process. The high level of automation present in current days in production lines aims the rapid response and adaptation to the market require-ments, which are constantly changing. Under the In-dustry 4.0 concept, astounding growth in the ad-vancement and adoption of information technology and social media networks has increasingly influ-enced consumer’s perception on product innovation, quality, variety and speed of delivery (Lee et al., 2014).  Assembly devices (jigs) are commonly used to assemble electronic components in manufacturing industries. These, guarantee the product positioning in a unique, accurate and repeatable way and allow automation assembly tasks to be performed in a de-fined sequence and with specified control parame-ters. There have also been significant efforts in finding solutions to provide a rapid response to the market, namely, focused on solutions for quick construction and changeover of assembly tools. In this context, the concept of Rapid Tooling (RT) was born, con-sisting in applying Rapid Prototyping principles in the production of tools (Levy et al., 2014). Product and process quality are the final outcome of the manufacturing process. In a repetitive process, such as on an assembly line, operator mistakes are likely to occur, which may compromise product quality. Thus, it is necessary to guaranty the correct positioning and presence of all components that con-stitute the product. The positioning mistakes are many times resolved using error-proof design sys-tems like Poka-Yoke (Shingo, 1986). Other types of error are detected with the use of sensors that pro-vides information and validate each step through multiple checks along the assembly process. There-fore, the sensing elements play a paramount role in both assembly line and device.  As it is represented in Figure 1, a sensor acquires a physical parameter and converts it into a signal suitable for processing, which can be transmitted to a controller.  SensorInput Signal Output Signal Figure 1.  Basic representation of a sensor. Presentation and validation of a new optical sensing concept based in a 3d-printing solution  Anthony Pimentel, Tiago Noversa, Luis Capela, João Pedro Nunes & António Brito U. Minho, Guimarães, Portugal Tiago Alves, Reinaldo Sousa & Ricardo Lima Bosch Car Multimedia Portugal, Braga, Portugal        ABSTRACT: In high competitive markets, such as the automotive industry, the better quality of products, reduction of manufacturing costs and the fulfilment of all delivery deadlines can only be achieved through continuous improvement of production capabilities. One current strategy is to develop and create smarter and adaptive assembly tools. Automation is a relevant area of development in the current industrial world and the baseline of the fourth industrial revolution (Industry 4.0). Namely, it is very important to use sensing components on jigs for assem-bly parts in the production line. The arrangement of sensing components on the assembly tools is very de-pendent of the product, making the project more complex and less flexible. This issue can penalise the productivity heavily, especially if a wide range of products and changeover operations are usual. The use of Additive Manufacturing (AM) is growing in the industry and offers a high potential for research and development in the present stage. The AM is advantageous in many areas, especially in the rapid con-struction of complex tools (RP). This paper presents a new optical sensing concept based on the 3D printing of internal circuits in the assembly tools. This solution can bring many advantages and increase tools flexibil-ity.   1.2 Sensing Solutions There are many sensing solutions for application on assembly devices. The main functions of the type of sensors mounted on a jig are presented in Table 1.  Table 1.  Main functions of different types of sensors Components Functions Inductive sensors -Metal parts detection; -Mask open/closed; -Pneumatic cylinder end of travel; Optical sensors  -Parts detection; Laser sensors -Parts detection; -Distance control;  -Part correct placement; -Laser barriers; Optical fiber sensors  -Parts detection; -Part correct placement; -Transparent parts detection; Vision Systems -Parts detection;  -Parts correct assembly;  -Parts connection verification; -Pattern analysis (glue, thermal past, etc);   Vision systems are increasingly used because of its great flexibility. However, the image data acquisi-tion, processing, storage and display of these systems require powerful industrial cameras with a specific hardware and software which make this solution very expensive. Therefore, significant efforts have been made to develop more cost-efficient solutions. 1.3 About Fiber Optic Sensors Fiber optic sensors consist on a fiber optical cable (fiber unit) connected to a remote sensor or amplifi-er. The sensor emits, receives and converts a light energy into an electrical signal. These sensors are ex-tremely sensitive, immune to electromagnetic inter-ference and resistant to weather and shocks (Gholamzadeh & Nabovati, 2008).  The fiber optic cable consists of a glass or poly-meric core surrounded by a cladding layer. The dif-ference between the refraction index of the core and cladding allows the conduction of light without loss-es. The light beam travels through core with succes-sive reflections on cladding surface. The light having passed through the fiber unit is dispersed at an angle of approximately 60° [Figure 2] (Keyence, 2014).   Figure 2.  Fiber optic configuration.   The fiber units can be divided in two categories: through-beam and reflective. The through-beam type consists in a separate transmitter and reflector. Al-ternatively, the reflective type comprises only one unit that emits and receive [Figure 3] (Keyence, 2015).     (A) (B) Figure 3. Different types of fiber units ((A) – Through-beam type; (B) – Reflective type). 1.4 Additive Manufacturing One recent application of additive manufacturing is the construction of assembly devices (jigs) (Stra-taSYS, 2016). In an electronic components industry, it is necessary ensure that the materials used in the assembly devices have ESD (Electronic Static Dis-charge) properties in order to protect the product against electrostatic (Rahman & Aziz, 2010). These electrostatic charges can damage electronic compo-nents, resulting in economic losses  In terms of Additive Manufacturing techniques, the FDM (Fused Deposition Molding) brings great advantages since it allows the construction of both solid and spare parts. The construction of spare parts reduces the mass of parts, their production time, ma-terial used and consequently the final price of the part (Wong & Hernadez, 2012). In an assembly de-vice, mass reduction facilitates the transport and handing of tools mainly in changeover operations. Therefore, FDM technique using ABS ESD 7 mate-rial is a good solution for construction of assembly devices for an electronic components industry. 1.5 Motivation The challenge of this study is to design a new sens-ing solution based on the concept of rapid construc-tion and change of assembly tools. Sometimes sen-sor components increase the time of changeover and construction of tools because they are embedded in the tool, which increases its complexity. Rapid construction of tools through additive manufacturing technologies allows the inclusion cir-cuits which, in turn enables the application of the metrological principle to strategic points of monitor-ing in the design phase. In this way, additive manu-facturing provides the ability of printing circuits into the tool during its construction. These circuits allow independence between the sensing components and tools, increasing the system flexibility and facilitat-ing changeover operations.  2 EXPRIMENTAL TESTS 2.1 Introduction The use of experimental tests allows for increased knowledge and control over particular aspects of a process, through measurement of quantifiable re-sults. So, in order to test the sensing concept and val-idate feasible circuits, an experimental methodology using different AM parts was adopted to study the behavior of the light beam in straight and curved cir-cuits. 2.2 Experimental parts  Two parts in ABS- ESD7 were designed and pro-duced using FDM technology for testing the behav-ior of the light beam in straight circuits and curved circuits. These parts are respectively presented in the Figure 4 and Figure 5.    Figure 4.  Part design for testing straight circuits.   Figure 5.  Part design for testing curved circuits.  The geometric parameters of the circuits present in-side the parts are presented in the tables 2 and 3. In the straight circuits, the controlled parameters in the experimental tests were the diameter and the total distance of the circuit. The geometric parame-ters of the circuits present inside the part are present-ed in the table 2.   Table 2.  Control parameters of the straight circuits. Parameter Total distance of light path (mm) Circuit diameter (mm) Circuit 1 50 3 2 50 6 3 50 10 4 100 3 5 100 6 6 100 10 7 150 3 8 150 6 9 150 10  In the case of the curved circuits the controlled pa-rameters were the total diameter, the distance of the circuit and the angle (β) between the input and out-put channels. The parameter β must be considered in the design phase.  Table 3.  Control parameters of the curved circuits. Parameter Total distance (mm) Circuit diameter (mm) Angle β (°) Circuit 1 50 3 90 2 50 6 115 3 50 10 135 4 100 3 115 5 100 6 135 6 100 10 90 7 150 3 135 8 150 6 90 9 150 10 115 2.3 Methodology The following methodology was used in the experi-mental tests made: 1- The sensor was connected to a Rohde & Schwarz HMP4040 programmable power supply. A voltage of 12V and a maximum current of 50 mA was assigned [Figure 6];  Figure 6.  Programmable power supply.  2- For the experimental tests, an OMRON E3X-DA51-S fiber optic amplifier and a fiber unit with 3 mm diameter were used. The sensor was coupled to each circuit test (straight and curved); 3- The signal provided by the sensor without iden-tification part (without target) was recorded; 4- An identification was given to the part (with target); 5- The new signal provided by the sensor after in-sertion of the identification part was recorded; 6- A set of 5 measurements were made; 7- The data obtained was processed.   All the components used in the experimental tests are presented in Figure 7.  Figure 7.  Components used to perform the experimental tests. 3 EXPERIMENTAL RESULTS  After data processing, results obtained in straight circuits are presented in Table 4.  Table 4.  Sensor outputs for straight circuits. Circuit w/o Target* w/ Target* ∆* 1 824 ± 2.0 925 ± 6.0 101 ± 5.0 2 397± 0.0 645 ± 5.0 248 ± 5.0 3 112 ± 0.0 515± 12.0 403± 12.0 4 822 ± 2.0 838 ± 2.0 16 ± 1.0 5 334 ± 1.0 380 ± 3.0 46 ± 3.0 6 124 ± 0.0 210 ± 2.0 86 ± 2.0 7 854 ± 0.0 860 ± 1.0 6 ± 1.0 8 397 ± 0.0 415 ± 2.0 18 ± 2.0 9 126 ± 0.0 159 ± 2.0 33 ± 2.0  The difference ∆ between values with (w/) and without (w/o) target is the most important parameter since it allows part detection. * The presented results are dimensionless and refer to the saturation of the sensor relative to received light. The absolute uncer-tainty of measurement is presented in the results. The value of total sensor saturation is 4000.  The higher the ∆ value the easier the part detection. From the results presented in Table 4, a graph that relates the diameter and the length of the circuit with ∆ can be plotted. Such graph is presented in Figure 8.    Figure 8.  Graphic that expresses the obtained results.  Table 5 shows the results obtained for curved cir-cuits.  Table 5.  Sensor outputs for curved circuits. Circuit  w/o Target* w/ target* ∆* 1 520 ± 0.0 520 ± 0.0 0 ± 0.0 2 442± 0.0 442± 0.0 0 ± 0.0 3 84 ± 0.0 84 ± 0.0 0 ± 0.0 4 489 ± 0.0 489 ± 0.0 0 ± 0.0 5 490 ± 0.0 490 ± 0.0 0 ± 0.0 6 33 ± 0.0 33 ± 0.0 0 ± 0.0 7 423 ± 0.0 423 ± 0.0 0 ± 0.0 8 428 ± 0.0 428 ± 0.0 0 ± 0.0 9 141 ± 0.0 141 ± 0.0 0 ± 0.0  As seen in Table 5, ∆ values equal to zero were al-ways obtained for the curved circuits, which means that is not possible to identify parts in these cases. Also, the geometric characteristics of the printed cir-cuits (diameter, length and curvature) cannot be re-lated with the ∆ value. Overall, the experimental results obtained show that:  Larger circuit diameters achieve better re-sults;  Shorter circuit length present better out-comes;  It’s not possible to identify parts in curved circuits, because the ∆ value obtained is al-ways null.  In order to increase the light conductivity inside the circuits without reducing the sensing systems flexibility, fiber optic filaments were implemented, i.e., the circuits were fit with fiber-optic filament to improve the conduction of beam light. The diameters of the applied filaments are 2 mm, 2.2 mm and 5 mm. Thus, the light beam emitted by the fiber op-tic amplifier travels through the fiber optic filament, instead of just the printed channel, until it reaches the target point.  The fiber optic filaments present good flexibility and can be applied to all curvatures, as long as the bend radius is higher than 2mm. The same experimental methodology was applied for the fiber optic filaments inside the circuits. The results obtained to the straight circuits are presented in Table 6.   Table 6. Sensor outputs for straight circuits with fiber filaments Circuit w/o Target* w/ target* ∆* 1 1497 ± 2.0 4000 ± 0.0 2503 ± 2.0 2 1502 ± 3.0 4000 ± 0.0 2498 ± 3.0 3 1480 ± 1.0 4000 ± 0.0 2520 ± 1.0 4 1517 ± 2.0 4000 ± 0.0 2483 ± 2.0 5 1509 ± 2.0 4000 ± 0.0 2491 ± 2.0 6 1526 ± 2.0 4000 ± 0.0 2447 ± 2.0 7 1545 ± 2.0 4000 ± 0.0 2455 ± 2.0 8 1493 ± 2.0 4000 ± 0.0 2507 ± 2.0 9 1482 ± 2.0 4000 ± 0.0 2518 ± 2.0  The graph expressing the parameter ∆ as a function of the geometric characteristics, diameter and length, of the straight circuits is presented in Figure 9.   Figure 9.  Graphic that expresses the obtained results with fiber optic filaments for straight circuits.  As shown in Figure 9 the results are roughly the same, which suggest that the parameter ∆ is inde-pendent of the geometric characteristics.  For curved circuits the obtained results are shown in Table 7.  Table 7. Sensor outputs for curved circuits with fiber filaments Circuit  w/o Target* w/ target* ∆* 1 1567 ± 2.0 4000 ± 0.0 2433 ± 2.0 2 1602 ± 3.0 4000 ± 0.0 2398 ± 3.0 3 1574 ± 3.0 4000 ± 0.0 2426 ± 3.0 4 1631 ± 3.0 4000 ± 0.0 2368 ± 3.0 5 1620 ± 4.0 4000 ± 0.0 2380 ± 4.0 6 1536 ± 2.0 4000 ± 0.0 2464 ± 2.0 7 1604 ± 4.0 4000 ± 0.0 2396 ± 4.0 8 1589 ± 2.0 4000 ± 0.0 2411 ± 2.0 9 1581 ± 3.0 4000 ± 0.0 2418 ± 3.0  The graph expressing the parameter ∆ as a function of the geometric characteristics of the straight cir-cuits is presented in Figure 10.   Figure 10.  Graphic that expresses the obtained results with fi-ber optic filament for curved circuits.  As shown in Figure 10, the results follow the same trend of the straight curved circuits where the pa-rameter ∆ is independent of the geometric character-istics. 4 DISCUSSION OF RESULTS The experimental results show that is possible detect the presence of a product using a light beam which goes through the printed channels of additive manu-factured tools. Regarding the straight circuits design, the signal emission and reception efficiency of the optic fiber system is closely related with the geometric charac-teristics of the printed channels. Short circuit lengths and large diameters present better results. Depending on the type and color of the material and the manu-facturing quality of the process, a significant part of the light beam may be absorbed. As it is shown in Table 4, the measured values are very low when compared with total sensor saturation value, which suggest that ABS ESD-7 parts produced by FDM process absorbs a lot of signal and, therefore, are not well-suited to this kind of applications. This be-comes more evident with a look at the curved cir-cuits results shown in Table 5. In this case, no signal is received by the optic sensor, which means that the light beam was completely absorbed by the circuit walls.  Consequently, the part detection is no longer possible. A simple, practical and cheap solution to improve significantly the results, in both straight and curved circuits, is to use optic fiber filaments inside the cir-cuits. It is not possible to introduce an optical fiber filament inside circuits that have a bend radius less than 2 mm, which means that all circuits must be de-signed considering this limitation. In this work sev-eral bend radii were considered in the curved circuits and it is possible to conclude that, when optic fiber filaments are used, the radius of curvature along the circuits do not influence the feedback signal of the system.  5 CONCLUSION This study presented a new optical sensing concept based in a 3D printing solution. The concept is based on the introduction of internal circuits in the assem-bly tools for transmission and routing of optical sig-nals. The excellent results obtained in the experi-mental tests demonstrated that is possible to apply this concept on assembly tools by using optic fiber filaments. The solution brings more flexibility to the sensing arrangement with clear industrial advantages. It also opens new possibilities for sensing standardization, simplify the electronic implementation and making maintenance and change-over operations much easi-er. In addition, this inexpensive solution exploits the potential of the additive manufacture to support the design of new assembly devices which can fulfill the requirements and expectations of the industry 4.0.  6. ACKNOWLEDGEMENTS This work is supported by: European Structural and Investment Funds in the FEDER component, through the Operational Competitiveness and Inter-nationalization Programme (COMPETE 2020) Pro-ject nº 002814; Funding Reference: POCI-01-0247-FEDER-002814” between Minho University and Bosch Braga, Portugal. 7. REFERENCES  Gholamzadeh, B., & Nabovati, H. (2008). Fiber Optic Sensors. International Journal of Electron-ics and Communication Engineering. 6 (2), 1107-1117.  Instrument Society of America. (1975). Electrical Transducer Nomenclature and Terminolo-gy.ANSI Standard MC6.1. Research Triangle Park, North Carolina: Instrument Society of America.  KEYENCE. (2014). Fibreoptic sensor – Selection examples and Countermeasures to avoid prob-lems.   KEYENCE. (2015). 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Presentation and validation of a new optical sensing concept based in a 3d-printing solution

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Presentation and validation of a new optical sensing concept based in a 3d-printing solution

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