Design and development of an electromechanical test bench for the study of optic sensors

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Figure 2.1 - Basic geometry of fiber optic [2] ... 16

Figure 2.2 - Scheme of a fiber with the distinctive angles of the acceptance and propagation of the light [3] ... 17

Figure 2.3 - Scheme of Bragg grating with the movements of the light [5] ... 19

Figure 2.4 - Scheme of the behaviour of the light which strikes the FBG [5] ... 19

Figure 2.5 - Schematic illustration of the dual-beam holographic technique .... 21

Figure 2.6 - - Schematic illustration of the phase mask technique ... 21

Figure 3.1 - Overview of the test bench assembled ... 23

Figure 3.2 - The cleaver... 24

Figure 3.3 - The splicer ... 25

Figure 3.4 - The screen of the monitor of the splicer. In the first figure it is possible to see the profiles of two fibers to be bonded. In the second you can see the signal loss of the junction reported by the displacer ... 25

Figure 3.5 - Section of the sample ... 26

Figure 3.6 - In the picture there is an example of sample with two fibers, and each fiber has two Bragg Gratings ... 26

Figure 3.7 - The properties of the composite material are defined by a lot of variables about the coupling of the fibers and the matrix ... 27

Figure 3.8 - Sample in composite ... 27

Figure 3.9 - Mixer and applicator of the adhesive ... 28

Figure 3.10 - First layer: it is a big and heavy table with dampers ... 28

Figure 3.11 - Second layer, the smaller breadboard where samples and tools will be fixed ... 29

Figure 3.12 - Micromotor Faulhaber ... 29

Figure 3.13 - Functional block diagram ... 30

Figure 3.14 - Picture with electronic of the motion controller and the supply power ... 31

Figure 3.15 - Micropositioner ... 31

Figure 3.16 - The cad projects of our supports of sample, Faulhaber micromotor and micropositioner in order of time-of-day ... 32

Figure 3.17 - Iron support ... 32

Figure 3.18 - Interrogator ... 33

Figure 3.19 - SmartScan system diagram [6] ... 33

Figure 3.20 - Schematic representation of the use of a circulator to interrogate a sensor working in reflection [7] ... 35

Figure 3.21 - Strain Gauge Aihasd 5PCS BF350 ... 35

Figure 3.22 - Example of operation of the strain gauge [8] ... 37

Figure 3.23 - Static balanced bridge circuit, with Rs that is the resistance of strain gauge ... 37

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Figure 4.1 - Main screen of SmartSoftSSI. In this example there are two fibers with two Bragg Gratings for each fiber, Fiber #1 is the white curve and Fiber #2 is the red curve... 39 Figure 4.2 - The screen for the basic acquisition. It the same example with two fibers and two Bragg grantings ... 40 Figure 4.3 - An example of the output file of the SmartSoftSSI. This output presents the analyse of two fibers and each fiber has two Bragg Gratings (Ch = channel, Br = Bragg grating) ... 40 Figure 4.4 - Example of values in output from the software ... 41 Figure 4.5 - Processing of the values of wavelength and extraction of the mean of the step ... 42 Figure 4.6 - Scheme on Patran of our sample with 20mm of deformation at the tip ... 43 Figure 4.7 - Strains shown visually on the monitor ... 43 Figure 5.1 - 2F_2B sample and gluing control ... 44 Figure 5.2 - In the two graphs above there are the signals of the FBGs original, from Bragg#1 the first and from Bragg#2 the second. Then there are also their filtered values ... 45 Figure 5.3 - In the two graphs above there are the filtered signals of the FBGs with the areas of interest. These values are highlighted in green in the graphs 46 Figure 5.4 - Progress of microstrain, in the Bragg Gratings #1, of the two fibers, by the FBGs of 2F_2B, made on the 14^th January 2019. The red line is the expected value of microstrains in output from Nastran - Patran. Instead, the zone between the green lines, is the range of plausible values, it depends on the thickness of the glue used... 48 Figure 5.5 - Progress of micro strain, in the Bragg Gratings #2, of the two fibers, by the FBGs of 2F_2B, made on the 14^th January 2019. The red line is the

expected value of microstrains in output from Nastran - Patran. Instead, the zone between the green lines, is the range of plausible values, it depends on the thickness of the glue used... 49 Figure 5.6 - The second sample, 1F_1B, and the graph of the gluing test ... 51 Figure 5.7 - Graphs with original signal from the FBG, the filtered signal and the areas of interest, like in the previous test. This test has been made on the 20^th February 2019, on the 1F_1B sample ... 52 Figure 5.8 - Progress of microstrain, in the Bragg Gratings of the test of 1F_1B sample, made on the 20^th February 2019. The red line is the expected value of microstrain in output from Nastran - Patran. Instead, the zone between the green lines, is the range of values plausible, it depends on the thickness of the glue used ... 54 Figure 5.9 - In the graph it is possible to see the strains measured by the strain gauge, the blue line, and the measure of the free strain gauge, with the green line; this will use to do the thermal offset ... 55

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Figure 5.10 - In this picture it is possible to see the measure filtered of the strain gauge in black and the point of interest with the green point. There are also the averages of the steps of the FBG output in the red lines, they are of the test made on the 27^th February 2019 ... 55 Figure 5.11 - The sample 1F_3B ... 57 Figure 5.12 - The main screen of the interrogator, it is possible to see the signal of Bragg #1, but the Bragg #2 and #3 are too much low ... 57 Figure 5.13 - The sample in composite; it is possible to see where the sample is fixed and where the sensors are ... 58 Figure 5.14 - Detail of the sample with the three strain gauges on it. The stain gauges 1 and 2 are for the strain in direction of the principal axis of the sample, and the strain gauge 3 is for the strain in the perpendicular direction ... 58 Figure 5.15 - In the graph it is possible to see the strains measured by the strain gauges, the blue line and the black line, and the measure of the free strain gauge; this will use to do the thermal offset ... 59 Figure 5.16 - In this picture it is possible to see the measure filtered of the average of the strain gauges, in black, the point of interest with the green point and the averages of the steps of the FBG output in the red lines ... 59 Figure 5.17 - In the picture it is possible to the that the strain gauge 2 is not well aligned with the FBG ... 60 Figure 6.1 - Section of the group sample and fiber glued together ... 63 Figure 6.2 - Detail of a graph of the comparison between FBG and Patran- Nastran outputs ... 63 Figure 6.3 - Scheme of frontal section of the group sample and glue, with the possible positions, upper and downer, of the fiber ... 64 Figure 6.4 - Fiber 1F_3B with a damage between Br1 and Br2 ... 64 Figure 6.5 - Wavelengths of the fiber test 2F_2B ... 65 Figure 6.7 - Frontal section of fiber glued, in two cases: the first if you have put a very low layer of glue, and the second if you have put too much glue ... 66 Figure 6.8 - Scheme of the elements and their application to make the new typology of gluing ... 67 Figure 6.9 - Sample with FBG (in line with the piece of white paper), a layer of glue and the film in PE over all ... 67 Figure 0.1 - Progress of microstrain, in the Bragg Gratings #1 and in the Bragg Gratings #2, of the two fibers of the 2F_2B sample, made on the 08^th February 2019. The red line is the expected value of microstrain in output from Nastran - Patran. Instead, the zone between the green lines, is the range of values

plausible, it depends on the thickness of the glue used ... 70 Figure 0.2 - Progress of microstrain, in the Bragg Gratings #1 and in the Bragg Gratings #2, of the two fibers of the 2F_2B sample, made on the 08^th February 2019. The red line is the expected value of microstrain in output from Nastran - Patran. Instead, the zone between the green lines, is the range of values

plausible, it depends on the thickness of the glue used ... 72

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Figure 0.3 - Progress of microstrain, in the Bragg Gratings #1 and in the Bragg Gratings #2, of the two fibers of the 2F_2B sample, made on the 15^th February 2019. The red line is the expected value of microstrain in output from Nastran - Patran. Instead, the zone between the green lines, is the range of values

plausible, it depends on the thickness of the glue used ... 74 Figure 0.4 - Progress of microstrain, in the Bragg Gratings of the 1F_1B sample, made on the 22^nd February 2019. The red line is the expected value of

microstrain in output from Nastran - Patran. Instead, the zone between the green lines, is the range of values plausible, it depends on the thickness of the glue used ... 75 Figure 0.5 - Progress of microstrain, in the Bragg Gratings of the 1F_1B sample, made on the 22^nd February 2019. The red line is the expected value of

microstrain in output from Nastran - Patran. Instead, the zone between the green lines, is the range of values plausible, it depends on the thickness of the glue used ... 76 Figure 0.6 - Progress of microstrain, in the Bragg Gratings of the 1F_1B sample, made on the 4^th March 2019. The red line is the expected value of microstrain in output from Nastran - Patran. Instead, the zone between the green lines, is the range of values plausible, it depends on the thickness of the glue used ... 77 Figure 0.1 - Mechanical strain ... 78

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Table 1 - Main features of the Faulhaber micromotor ... 29

Table 2 - Main features of the planetary gearhead ... 30

Table 3 - Main features of the power supply ... 30

Table 4 - Main features of the micropositioner ... 31

Table 5 - Datasheet of interrogator [6] ... 34

Table 6 - Main features of the strain gauge ... 38

Table 7 - Mean and Confidence interval of the steps of the F2_B2, made on the 14^th January 2019 ... 47

Table 8 - Microstrains recorded by the FBGs of 2F_2B, made on the 14^th January 2019 ... 48

Table 9 - Percentage error of the Bragg 1 respect the values from Nastran - Patran of the sample 2F_2B, made on the 14^th January 2019 ... 49

Table 10 - Percentage error of the Bragg 2 respect the values from Nastran - Patran of the sample 2F_2B, made on the 14^th January 2019 ... 50

Table 11 - Mean and Confidence interval of the steps of the F1_B1, made on the 20^th February 2019 ... 53

Table 12 - Microstrains recorded by the FBG of the 1F_1B sample made on the 20^th February 2019 ... 53

Table 13 - Percentage error of the Bragg respect the values from Nastran - Patran of the test of the 1F_1B sample, made on the 20^th February 2019 ... 54

Table 14 - The percentage of error of the FBG confronted with the tests done with strain gauge ... 56

Table 15 - The microstrains of the FBG and of the strain gauges with thermal offset and the percentage of error of the FBG confronted with the test done with the average of the strain gauge ... 60

Table 16 - Here it is possible to see the percentage of error between the FBG measure and the SG #1, more reliable than SG#2 ... 61

Table 17 - Microstrain recorded by the FBGs of the 2F_2B sample, made on the 08^th February 2019 ... 69

Table 18 - Percentage error of the Bragg 1 and Bragg 2 respect the values from Nastran - Patran of the 2F_2B sample, made on the 08^th February 2019 ... 69

Table 19 - Microstrain recorded by the FBGs of the 2F_2B sample, made on the 12^th February 2019 ... 71

Table 20 - Percentage error of the Bragg 1 and Bragg 2 of the 2F_2B sample, made on the 08^th February 2019, respect the values from Nastran - Patran .... 71

Table 21 - Microstrains recorded by the FBG of the 2F_2B sample, made on the 15^th February 2019 ... 73

Table 22 - Percentage error of the Bragg 1 and Bragg 2 of the 2F_2B sample, made on the 15^th February 2019, respect the values from Nastran - Patran .... 73

Table 23 - Microstrains recorded by the FBG of the 1F_1B sample, made on the 22^nd February 2019 ... 75

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Table 24 - Microstrains recorded by the FBG of the 1F_1B sample, made on the 27^th February 2019 ... 76 Table 25 - Microstrain recorded by the FBG of the 1F_1B sample, made on the 4^th March 2019 ... 77

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F1 - B1 F1 - B2 F2 - B1 F2 - B2

Steps

[mm] Mean [nm]

Confidence interval at 95% [nm]

Mean [nm]

Confidence interval at

95% [nm]

Mean [nm]

0 1546,85552 1546,85551

1530,76553 1530,76552

1546,80436 1546,80434

1530,77440 1530,77439

1546,85554 1530,76555 1546,80438 1530,77441

2 1546,86602 1546,86600

1530,78808 1530,78806

1546,81447 1546,81444

1530,79724 1530,79722

1546,86604 1530,78810 1546,81450 1530,79725

4 1546,87715 1546,87711

1530,80913 1530,80908

1546,82524 1546,82519

1530,81939 1530,81937

1546,87719 1530,80917 1546,82529 1530,81942

6 1546,88849 1546,88848

1530,83083 1530,83082

1546,83560 1546,83558

1530,84197 1530,84196

1546,88851 1530,83084 1546,83562 1530,84198

8 1546,89967 1546,89964

1530,85457 1530,85453

1546,84952 1546,84947

1530,86370 1530,86367

1546,89969 1530,85461 1546,84957 1530,86372

10 1546,91117 1546,91116

1530,87621 1530,87619

1546,85942 1546,85940

1530,88728 1530,88726

1546,91119 1530,87622 1546,85944 1530,88730

12 1546,92203 1546,92202

1530,89925 1530,89924

1546,86955 1546,86953

1530,90859 1530,90856

1546,92204 1530,89926 1546,86956 1530,90861

14 1546,93758 1546,93758

1530,92010 1530,92008

1546,87970 1546,87969

1530,93152 1530,93151

1546,93759 1530,92011 1546,87971 1530,93153

16 1546,94844 1546,94843

1530,94410 1530,94407

1546,88936 1546,88934

1530,95176 1530,95173

1546,94845 1530,94413 1546,88939 1530,95179

18 1546,95907 1546,95906

1530,96454 1530,96453

1546,89903 1546,89901

1530,97538 1530,97536

1546,95908 1530,96455 1546,89905 1530,97539

20 1546,97068 1546,97067

1530,98816 1530,98815

1546,90940 1546,90939

1530,99705 1530,99703

1546,97069 1530,98817 1546,90941 1530,99706

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Displace- ment im- posed to the

tip

Strain recorded by the FBG [ ]

F1 - B1 F1 - B2 F2 - B1 F2 - B2

2 mm 8,696 18,882 8,383 19,127

4 mm 17,921 36,509 17,31 37,68

6 mm 27,326 54,69 25,896 56,591

8 mm 36,586 74,569 37,434 74,786

10 mm 46,123 92,69 45,64 94,541

12 mm 55,12 111,989 54,029 112,384

14 mm 68,009 129,45 62,446 131,587

16 mm 77,008 149,551 70,454 148,541

18 mm 85,82 166,673 78,465 168,32

20 mm 95,442 186,455 87,061 186,47

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Error of the Bragg gratings respect values made by Nastran - Patran #1 [%]

Fiber 1 Fiber 2 -0,62 -4,19

2,41 -1,09

4,10 -1,35

4,09 6,50

5,67 4,56

4,49 2,42

10,58 1,54

9,78 0,43

8,63 -0,68

8,64 -0,90

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Error of the Bragg gratings respect values made by Nastran - Patran #2 [%]

Fiber 1 Fiber 2 -1,91 -0,64 -5,17 -2,13 -5,71 -2,43 -3,66 -3,38 -3,95 -2,03 -3,33 -2,99 -4,11 -2,53 -3,14 -3,79 -4,21 -3,26 -3,39 -3,38

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F1 - B1

Steps

[mm] Mean [nm] Confidence inter- val at 95% [nm]

2 1533,04396 1533,04394

1533,04398

4 1533,06502 1533,06496

1533,06508

6 1533,08581 1533,08578

1533,08584

8 1533,10659 1533,10656

1533,10663

10 1533,12634 1533,12632

1533,12636

12 1533,14588 1533,14586

1533,14589

14 1533,16621 1533,16620

1533,16622

16 1533,18676 1533,18675

1533,18677

18 1533,20741 1533,20737

1533,20745

20 1533,22818 1533,22816

1533,22821

Displacement im- posed to the tip

Strain recorded by the FBG [ ]

F1 - B1

2 mm 17,610

4 mm 34,999

6 mm 52,376

8 mm 68,892

10 mm 85,230

12 mm 102,235

14 mm 119,419

16 mm 136,685

18 mm 154,060

20 mm 171,373

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Error of the Bragg gratings respect val- ues made by Nastran

- Patran [%]

Fiber 1F-1B 3,59 2,94 3,71 2,06 0,86 0,72 1,03 1,25 1,36 1,40

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Displacement imposed to

the tip

Error [%]

Six tests effected

2 mm 3,43 1,64 -2,05 2,10 0,90 -6,50

4 mm -6,19 -8,62 -10,17 -7,61 -8,53 -13,03 6 mm -3,45 -5,66 -6,69 -5,06 -5,30 -8,31 8 mm -2,67 -4,35 -5,33 -4,14 -4,63 -6,80 10 mm -2,27 -3,51 -4,19 -3,38 -3,90 -5,98 12 mm -3,18 -4,01 -4,40 -3,81 -4,70 -6,24 14 mm -3,81 -3,88 -4,32 -3,62 -4,62 -5,89 16 mm -3,98 -3,37 -3,91 -3,20 -4,06 -5,06 18 mm -3,96 -3,01 -3,40 -2,81 -3,59 -4,69 20 mm -4,40 -3,27 -3,69 -3,08 -3,97 -4,82

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tip

Strain recorded [ ]

Error [%]

F1 - B1 SG #1 SG #2

2 mm 15,536 17,841 16,890 10,53

4 mm 34,023 35,547 33,436 1,36

6 mm 53,581 52,382 49,245 -5,45

8 mm 73,085 69,986 65,609 -7,80

10 mm 90,733 86,983 81,389 -7,78

12 mm 110,412 103,053 96,789 -10,50

14 mm 130,764 119,754 112,507 -12,60

16 mm 150,706 136,910 128,506 -13,56

18 mm 169,954 152,978 143,443 -14,67

20 mm 186,973 168,586 158,382 -14,37

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Displacement imposed to

the tip

Error [%]

2 mm 12,92

4 mm 4,29

6 mm -2,29

8 mm -4,43

10 mm -4,31

12 mm -7,14

14 mm -9,19

16 mm -10,08

18 mm -11,10

20 mm -10,91

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tip

F1 - B1 F1 - B2 F2 - B1 F2 - B2

2 mm 13,46 21,043 9,177 19,759

4 mm 23,696 39,752 18,46 39,42

6 mm 33,141 57,475 27,171 57,954

8 mm 42,933 76,763 36,148 77,553

10 mm 53,285 96,588 45,905 96,021

12 mm 62,643 115,267 57,045 116,012

14 mm 73,094 135,261 66,798 135,522

16 mm 82,545 153,656 75,512 154,555

18 mm 92,146 175,259 83,986 173,615

20 mm 105,134 194,516 93,073 193,542

Error of the Bragg gratings respect values made by Nastran - Patran

#1 [%]

#2 [%]

Fiber 1 Fiber 2 Fiber 1 Fiber 2

53,83 4,88 9,31 2,64

35,41 5,49 3,25 2,39

26,25 3,51 -0,91 -0,08

22,14 2,84 -0,82 0,20

22,07 5,17 0,09 -0,50

18,75 8,14 -0,50 0,14

18,85 8,61 0,19 0,39

17,67 7,64 -0,48 0,10

16,64 6,31 0,72 -0,22

19,67 5,95 0,79 0,28

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tip

F1 - B1 F1 - B2 F2 - B1 F2 - B2

2 mm 8,946 18,082 8,203 17,532

4 mm 20,287 36,973 15,675 36,929

6 mm 29,716 54,556 24,020 54,651

8 mm 38,599 73,388 32,147 73,937

10 mm 47,998 90,949 40,757 91,622

12 mm 57,025 110,997 49,247 110,710

14 mm 66,548 129,300 57,858 129,431

16 mm 75,636 148,423 69,280 149,050

18 mm 85,703 167,650 77,893 167,498

20 mm 95,095 188,567 86,343 186,744

#1 [%]

#2 [%]

2,24 -6,25 -6,07 -8,92

15,93 -10,43 -3,97 -4,08

13,20 -8,50 -5,94 -5,77

9,81 -8,54 -5,18 -4,47

9,96 -6,63 -5,75 -5,05

8,10 -6,64 -4,19 -4,44

8,21 -5,92 -4,22 -4,13

7,82 -1,24 -3,87 -3,47

8,48 -1,40 -3,65 -3,74

8,25 -1,72 -2,30 -3,24

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tip

F1 - B1 F1 - B2 F2 - B1 F2 - B2

2 mm 6,807 15,519 6,270 17,013

4 mm 15,982 33,671 14,399 35,560

6 mm 24,368 51,374 22,107 53,522

8 mm 34,308 68,854 31,200 71,305

10 mm 42,907 88,697 39,177 89,590

12 mm 52,601 106,407 48,886 108,586

14 mm 62,304 126,602 59,528 128,613

16 mm 70,763 144,474 67,180 146,586

18 mm 79,531 165,433 75,099 165,670

20 mm 91,930 183,891 83,802 184,828

#1 [%]

#2 [%]

-22,21 -28,34 -19,38 -11,62

-8,67 -17,72 -12,54 -7,64

-7,17 -15,78 -11,42 -7,72

-2,40 -11,24 -11,04 -7,87

-1,70 -10,25 -8,09 -7,16

-0,28 -7,33 -8,15 -6,27

1,31 -3,21 -6,22 -4,73

0,87 -4,23 -6,43 -5,06

0,67 -4,94 -4,92 -4,79

4,64 -4,61 -4,72 -4,23

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Error of the Bragg gratings respect values made by Nastran - Patran

[%]

F1 - B1

2 mm 15,816 -6,96

4 mm 31,458 -7,48

6 mm 48,285 -4,39

8 mm 64,652 -4,22

10 mm 81,078 -4,05

12 mm 96,302 -5,12

14 mm 112,94 -4,45

16 mm 128,461 -4,84

18 mm 144,949 -4,64

20 mm 161,311 -4,55

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[%]

F1 - B1

2 mm 16,919 -0,48

4 mm 36,145 6,31

6 mm 52,509 3,98

8 mm 68,945 2,14

10 mm 84,98 0,57

12 mm 102,053 0,54

14 mm 118,325 0,11

16 mm 134,276 -0,54

18 mm 149,854 -1,41

20 mm 166,174 -1,67

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[%]

F1 - B1

2 mm 15,931 -6,29

4 mm 30,983 -8,87

6 mm 46,617 -7,69

8 mm 62,353 -7,63

10 mm 78,292 -7,35

12 mm 94,628 -6,77

14 mm 110,755 -6,3

16 mm 128,56 -4,77

18 mm 145,545 -4,25

20 mm 162,54 -3,82

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