S.N.A.K.E.: A Dynamically Reconfigurable Artificial Sensate Skin ...

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(a) Prototype boards used to calibrate sensors (b) A node covered with QTC material. Each node has four channels of pressure sensing as shown Figure 3-17: QTC pressure sensors nothing more than a non-inverting amplifier biased at mid-range by the voltage divider created by the sensor selected by the multiplexer and a resistor. Whenever the pressure sensor is not pressed, it has a resistance in the order of mega ohms. As pressure is applied to the sensor however, the resistance decreases, and the voltage divider voltage changes, which causes the output voltage to swing. One advantage of this circuit is that the sensitivity range of the pressure sensor can be adjusted by changing just one resistor, in this case the pull-down resistor used in the voltage divider. Finally, there are some mechanical design aspects to consider. Gluing the QTC films onto the substrate only by the edges causes the material to warp and bubble when the substrate is bent. There are work-arounds to avoid this: the first one would be to selectively apply an adhesive around the metal electrodes so that only the parts with no metal stick to the coated side of the sensitive material. A second option would be to encase the entire skin into a silicone rubber; this has the added advantage of evenly distributing the pressure among the four corners of the node, so gradients are better observed. 68
(a) Mini-sense cantilever with whiskers glued to end mass Proximity/Motion Sensing Figure 3-18: QTC pressure sensors (b) Kyocera’s PSAC piezo shock sensor Proximity sensing or mechanoreception (motion sensing) was added to the nodes to copy the ability that our skin has to perceive close activity through hair. As with any other sensing modality, there are several different ways to convert the whisker vibrations into electrical signals that can be then sampled by the microcontroller. Two different options based on piezoelectric cantilevers were tested. The first option was based on the design presented by Lifton in [41]. Taking advantage of piezoelectric film’s ability to turn bending strain into high voltages, nylon fibers were glued to the end of a Measurement Specialties MSP6915-ND Mini-Sense piezo cantilever to make up a vibration/mechanoreception sensor. This sensor has a mass attached to the end of the cantilever which also gives significant sensitivity to inertial forces. This design is shown on Figure 3-18. The second option was based on the same principle of the first one, however instead of using a large piezo cantilever, two different Kyocera PZT vibration sensors, the PSAC380A and PSLC382S, were tested. The only difference between these two sensors is the axis of maximum sensitivity. These sensors have the advantage of being surface mountable, and are very small and sensitive. The only minor drawback is that the sensitive part is located inside of the small package and the whisker can’t be directly glued onto it. Fortunately though, these sensors are sensitive enough that they are able to pick up vibrations if the 69
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Author S.N.A.K.E.: A Dynamically Re
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S.N.A.K.E.: A Dynamically Reconfigu
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Table of Contents Abstract 3 Acknow
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List of Figures 2-1 Created by MIT
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E-1 OpenGL Control Header File . .
Page 17 and 18: Chapter 1 Introduction “Imaginati
Page 19 and 20: The current project, named S.N.A.K.
Page 21: Hardware Each Skin Patch is compose
Page 24 and 25: living tissue. Particularly in the
Page 26 and 27: Figure 2-2: Leonardo’s Hand great
Page 28 and 29: Artificial Sensate Skins elsewhere
Page 30 and 31: 2.1.2 Ultra-dense Sensor Arrays Thi
Page 32 and 33: 2.2 Flexible Circuits Although, not
Page 34 and 35: 2.2.2 Other Technologies Figure 2-6
Page 36 and 37: human skin. The following design pr
Page 38 and 39: (a) Skin Patches as data extraction
Page 40 and 41: Figure 3-3: I 2 C Routing pattern T
Page 42 and 43: 3.2.2 Peer to Peer As we already me
Page 44 and 45: 5. Audio: by adding a MEMS micropho
Page 46 and 47: Table 3.1: Material thicknesses and
Page 48 and 49: (a) Node Front (b) Node Back Figure
Page 50 and 51: Figure 3-9: Skin Patch mechanical t
Page 52 and 53: used, which only further complicate
Page 54 and 55: 8. Teardrops and filleting were add
Page 56 and 57: (a) 7.4V, 2.2mAh Li-ion Battery (b)
Page 58 and 59: in more detail in the Results Chapt
Page 60 and 61: has a 30mA forward current with a f
Page 62 and 63: Figure 3-14: Strain gage layer prot
Page 64 and 65: an unbalanced Wheatstone bridge, fr
Page 66 and 67: Figure 3-16: QTC response curve for
Page 70 and 71: whisker is epoxied to the package o
Page 72 and 73: Sound The only sensing modality add
Page 74 and 75: Figure 3-20: Brain regular PCB fabr
Page 76 and 77: 3.4.3 Communications unit The Commu
Page 79 and 80: Chapter 4 Software “A Scientist d
Page 81 and 82: Networks. Why is this relevant? Mai
Page 83 and 84: Figure 4-1: Bootloader memory map C
Page 85 and 86: Bit Flag Name Description 0x01 FILE
Page 87 and 88: Figure 4-3: Sampling timing example
Page 89 and 90: We also mentioned before that there
Page 91 and 92: Code Instruction Description 0xA0 R
Page 93 and 94: Component Description 1 Indicates t
Page 95 and 96: last chapter. Figure 4-5: Automatic
Page 97 and 98: An important point to stress is tha
Page 99 and 100: (a) Rotation control (b) Zooming co
Page 101 and 102: 4.3 Communications Software The las
Page 103 and 104: 4.3.2 Peer to Peer Peer to peer com
Page 105 and 106: Chapter 5 Analysis of Results and E
Page 107 and 108: Figure 5-1: Stress concentration po
Page 109 and 110: of the assembled skin patch don’t
Page 111 and 112: Node SG1 SG2 R(X) R(Y) Δ(X) Δ(Y)
Page 113 and 114: Or, ∆R = R3 R3 R3 + RC (5.2) Howe
Page 115 and 116: R3 Microstrain 162Ω −99.7337969
Page 117 and 118: Figure 5-3: Strain Gage electronic
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(a) Data from both strain gages (b)
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(a) Pressure data being extracted f
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many of these did not work as expec
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Data plots were also extracted for
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(a) Temperature sensor data plots (
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Figure 5-12: Raw microphone data wi
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(a) Activity sensor data (b) Whiske
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5.3 Performance Metrics We have pre
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(a) I 2 C data when a 1500Ωs resi
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Component # per node Current consum
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Finally, since power is readily ava
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Chapter 6 Conclusions and Future Wo
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surface can be used to sense pressu
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Implement P2P Communications: curre
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Appendix A Abbreviations and Symbol
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Appendix B Bill of Materials 149
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Appendix C Schematics and PCB Layou
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1 1 2 2 3 3 4 4 D D C C B B A A Tit
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Amp1 P0Amp101 P0Amp102 P0Amp103 P0A
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P0Cin02 P0East06 P0North06 P0South0
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Cain P0C ain01 P0Cain02 L1 P0L101 P
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Figure C-10: Node Bottom Overlay 16
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4 3 2 1 A A Brain Communications Ac
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C3v P0C3v01 P0C3v02 Cavcc P0Cavcc01
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Appendix D Firmware 167
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C:\Documents and Settings\Gerardo\M
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Appendix E PC Code 183
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1 c:\Documents and Settings\Gerardo
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12 c:\Documents and Settings\Gerard
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Bibliography [1] John C. Ansel. Ski
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[33] Joseph Jacobson, B Comiskey, C
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[68] Vilis Tutis. The physiology of
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